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1
Woodd-Walker, Rachel S., Jonathan L. Watkins e Andrew S. Brierley. "Identification of Southern Ocean acoustic targets using aggregation backscatter and shape characteristics". ICES Journal of Marine Science 60, n. 3 (1 gennaio 2003): 641–49. http://dx.doi.org/10.1016/s1054-3139(03)00062-6.
Testo completoAbstract (sommario):
Abstract Acoustic surveys for biomass estimation require accurate identification of echoes from the target species. In one objective technique for identifying Antarctic krill, the difference between mean volume-backscattering strength at two frequencies is used, but can misclassify small krill and other plankton. Here, we investigate ways to improve target identification by including characteristics of backscattering energy and morphology of aggregations. To do this, multi-frequency acoustic data were collected concurrently with target fishing of Antarctic krill and other euphausiid and salp aggregations. Parameter sets for these known aggregations were collated and used to develop empirical classifications. Both linear discriminant-function analysis (DFA) and the artificial neural network technique were employed. In both cases, acoustic-backscattering energy parameters were most important for discriminating between Antarctic krill and other zooplankton. However, swarm morphology and other parameters improved the discrimination, particularly between krill and salps. Our study suggests that for krill-biomass estimates, a simple DFA based on acoustic-energy parameters is a substantial improvement over current dB-difference acoustic methods; but studies requiring the discrimination of zooplankton other than krill must still be supported by target fishing.
2
Trull, Thomas W., Abraham Passmore, Diana M. Davies, Tim Smit, Kate Berry e Bronte Tilbrook. "Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment". Biogeosciences 15, n. 1 (3 gennaio 2018): 31–49. http://dx.doi.org/10.5194/bg-15-31-2018.
Testo completoAbstract (sommario):
Abstract. The Southern Ocean provides a vital service by absorbing about one-sixth of humankind's annual emissions of CO2. This comes with a cost – an increase in ocean acidity that is expected to have negative impacts on ocean ecosystems. The reduced ability of phytoplankton and zooplankton to precipitate carbonate shells is a clearly identified risk. The impact depends on the significance of these organisms in Southern Ocean ecosystems, but there is very little information on their abundance or distribution. To quantify their presence, we used coulometric measurement of particulate inorganic carbonate (PIC) on particles filtered from surface seawater into two size fractions: 50–1000 µm to capture foraminifera (the most important biogenic carbonate-forming zooplankton) and 1–50 µm to capture coccolithophores (the most important biogenic carbonate-forming phytoplankton). Ancillary measurements of biogenic silica (BSi) and particulate organic carbon (POC) provided context, as estimates of the biomass of diatoms (the highest biomass phytoplankton in polar waters) and total microbial biomass, respectively. Results for nine transects from Australia to Antarctica in 2008–2015 showed low levels of PIC compared to Northern Hemisphere polar waters. Coccolithophores slightly exceeded the biomass of diatoms in subantarctic waters, but their abundance decreased more than 30-fold poleward, while diatom abundances increased, so that on a molar basis PIC was only 1 % of BSi in Antarctic waters. This limited importance of coccolithophores in the Southern Ocean is further emphasized in terms of their associated POC, representing less than 1 % of total POC in Antarctic waters and less than 10 % in subantarctic waters. NASA satellite ocean-colour-based PIC estimates were in reasonable agreement with the shipboard results in subantarctic waters but greatly overestimated PIC in Antarctic waters. Contrastingly, the NASA Ocean Biogeochemical Model (NOBM) shows coccolithophores as overly restricted to subtropical and northern subantarctic waters. The cause of the strong southward decrease in PIC abundance in the Southern Ocean is not yet clear. The poleward decrease in pH is small, and while calcite saturation decreases strongly southward, it remains well above saturation ( > 2). Nitrate and phosphate variations would predict a poleward increase. Temperature and competition with diatoms for limiting iron appear likely to be important. While the future trajectory of coccolithophore distributions remains uncertain, their current low abundances suggest small impacts on overall Southern Ocean pelagic ecology.
3
Hempel, Gotthilf. "Life in the Antarctic sea ice zone". Polar Record 27, n. 162 (luglio 1991): 249–53. http://dx.doi.org/10.1017/s0032247400012663.
Testo completoAbstract (sommario):
AbstractSeasonal ice of the Southern Ocean, occupying some 15 x 106 km2, supports a distinctive biota based on algae that live on, within and immediately beneath the ice floes. How this annually-forming habitat recruits its biota, and the fate of the biota after the ice thaws in late summer, are little-known. Studies in the Weddell Sea in 1984–88 have shown that the seasonal ice is important as the wintering substrate of krill Euphausia superba which, together with other zooplankton and fish, supports a large breeding population of seals and penguins. Clearly a key habitat in the economy of the Southern Ocean, this seasonal ice is likely to be vulnerable to small climatic changes.
4
Pakhomov, Evgeny A., Leonid K. Pshenichnov, Anatoly Krot, Valery Paramonov, Ilia Slypko e Pavel Zabroda. "Zooplankton Distribution and Community Structure in the Pacific and Atlantic Sectors of the Southern Ocean during Austral Summer 2017–18: A Pilot Study Conducted from Ukrainian Long-Liners". Journal of Marine Science and Engineering 8, n. 7 (2 luglio 2020): 488. http://dx.doi.org/10.3390/jmse8070488.
Testo completoAbstract (sommario):
Preliminary results of the pilot study of the zooplankton in the region between the Ross and Scotia Seas from November 2017 to April 2018 are presented. In total, 53 zooplankton samples were collected in the top 100 m water layer using vertical tows of a 0.1 m2 Juday net from four Ukrainian longliners operating during the Antarctic toothfish fishery. Total zooplankton abundance ranged from 3 to 2836 ind m−3 with a global mean of 360 ± 550 (±1 SD) ind m−3. The highest abundances were recorded at the northeastern Ross Sea. At those stations, small copepods (mainly Oithona spp., Oncaea spp., Ctenocalanus spp. and copepod nauplii) numerically dominated the samples. Total biomass ranged from 0.3 to 85 mg DW m−3 with a mean of 10.9 ± 14.5 mg DW m−3. The highest biomasses were recorded at the eastern Ross Sea, where pelagic tunicates Salpa thompsoni, siphonophores and ctenophora Callianira sp. accounted for >90% of total zooplankton biomass. At other stations, zooplankton biomass generally ranged from 5 to 20 mg DW m−3 with no clear pattern in distribution. The community composition was driven by the sampling latitude and/or season rather than longitudinally. This pilot study emphasized the unique opportunity to investigate zooplankton dynamics in the regions traditionally not sampled during the oceanographic surveys. It also created unprecedented opportunities to increase the seasonal and geographical zooplankton sampling coverage using ships of opportunity at a fraction of a dedicated oceanographic survey costs. The potential of such surveys are enormous in both providing invaluable information, contributing to existing long-term databases and enhancing an international collaboration in the Southern Ocean, particularly in light of recent modeling initiatives of the whole Antarctic system undertaken by the Commission for the Conservation of Antarctic Marine Living Resources.
5
Cropp, Roger, Georgina Kerr, Susan Bengtson-Nash e Darryl Hawker. "A dynamic biophysical fugacity model of the movement of a persistent organic pollutant in Antarctic marine food webs". Environmental Chemistry 8, n. 3 (2011): 263. http://dx.doi.org/10.1071/en10108.
Testo completoAbstract (sommario):
Environmental contextPersistent organic pollutants (POPs) are potentially toxic chemicals capable of long distance transport and are often found far from their source. Little is known of their behaviour in Antarctica, where the marine plankton food web is driven by strong seasonal variations in solar radiation. Here the first dynamic coupled ecosystem–fugacity model to describe how POPs distribute through the Antarctic environment is presented. The model is used to identify the important processes that govern the presence of hexachlorobenzene in Antarctic plankton. AbstractPolar regions can be repositories for many persistent organic pollutants (POPs). However, comparatively little is known of the movement and behaviour of POPs in Antarctic ecosystems. These systems are characterised by strong seasonal effects of light on plankton dynamics. This work describes a mass-conserving, fugacity-based dynamic model to describe the movement of POPs in the Antarctic physical and plankton systems. The model includes dynamic corrections for changes in the population volumes and the temperature dependence of the fugacity capacities, and was developed by coupling a dynamic Nutrient–Phytoplankton–Zooplankton–Detritus (NPZD) ecosystem model to fugacity models of the chemistry and biology of the Southern Ocean. The model is applied to the movement of hexachlorobenzene, a POP found in the Antarctic environment. The model predicts that the burden of HCB in the plankton varies with the seasonal cycle in Antarctic waters, and induces a seasonal variation in the biomagnification factor of zooplankton. This suggests that time series of POP concentrations in Antarctic biotic and abiotic systems should be measured over complete seasonal cycles. Furthermore, detritus is shown to be a key contributor to the movement of POPs in polar environments, linking physical and biological components of the model.
6
HONJO, SUSUMU. "Particle export and the biological pump in the Southern Ocean". Antarctic Science 16, n. 4 (30 novembre 2004): 501–16. http://dx.doi.org/10.1017/s0954102004002287.
Testo completoAbstract (sommario):
The organic carbon particle export to the interior layers in the Southern Ocean in the New Zealand–Tasmania Sector was approximately 170 mmolC m−2 yr−1. The export of particulate inorganic carbon in CaCO3 was 110 mmolC m−2 yr−1 and was contributed mostly by pteropods shells in the Antarctic Zones. The Si flux from biogenic opal at the sub-Antarctic Zone was 67 mmolSi m−2 yr−1 and rapidly increased to the south up to nearly 1 molSi m−2 yr−1 in the Antarctic Zone. The Antarctic Polar Front clearly demarcated the area where the biological pump was driven by CaCO3 to the north and biogenic SiO2 particle export to the south. Summer stratification caused by the sub-zero winter water layer in the Seasonal Ice Zone (SIZ) curtails the zooplankton community and hinders the replenishment of Fe. This hypothesis explains the large organic carbon export with large f- and export ratios at the SIZ and extremely large opal production at the Antarctic Circumpolar Zone. Estimated regeneration rate of CO2 from the export production and settling particulate fluxes of organic carbon in the water column between 100 m to 1 km was about 13 mmolC m−2 d−1 in the Antarctic Zone and Polar Frontal Zone.
7
Joiris, Claude R., e William Overloop. "PCBs and organochlorine pesticides in phytoplankton and zooplankton in the Indian sector of the Southern Ocean". Antarctic Science 3, n. 4 (dicembre 1991): 371–77. http://dx.doi.org/10.1017/s0954102091000470.
Testo completoAbstract (sommario):
Samples of phyto- and zooplankton were collected in the Indian sector of the Southern Ocean (38–67°S, 18–84°E) and analysed for organochlorine residues (PCBs and pesticides). The PCB concentration in particulate matter (mainly phytoplankton) appeared to be high and similar to that of temperate zones: 0.7 μg g−1 dry weight. Contamination levels were more constant expressed per water volume than per dry weight, and seven times lower (1.2 μg m−3) than in northern temperate zones (8.8 μm−3 in the North Sea). The Antarctic ecosystems are thus less contaminated than temperate ones — as expected — but the very low phytoplankton biomass present cause high PCB levels per unit of biomass. These results confirm the necessity of using different systems of units in order to correctly express the contamination levels and to identify the main mechanisms responsible for the accumulation of stable pollutants. PCB levels in netplankton samples (mainly zooplankton) were comparable with phytoplankton on a dry weight basis (0.7 μm−3), lower on a lipid weight basis (5.8 μg g−1 lw for netplankton, 16.3 for particulate matter) and were much higher per seawater volume (27.2 μg m−3 for netplankton, 1.2 for particulate matter). Netplankton contamination is comparable in the Antarctic (0.35 μg g−1 dw) and the North Sea (0.70) since zooplankton feeding on phytoplankton has similar levels of contamination in both ecosystems. Lindane, heptachlor epoxide, dieldrin, DDE and DDT were observed in various samples at trace levels. The high DDE/DDT ratio reflects the more recent origin of Antarctic organochlorines.
8
Kasamatsu, Nobue, So Kawaguchi, Shuichi Watanabe, Tsuneo Odate e Mitsuo Fukuchi. "Possible impacts of zooplankton grazing on dimethylsulfide production in the Antarctic Ocean". Canadian Journal of Fisheries and Aquatic Sciences 61, n. 5 (1 maggio 2004): 736–43. http://dx.doi.org/10.1139/f04-072.
Testo completoAbstract (sommario):
The role of zooplankton grazing on dimethylsulfide (DMS) and dissolved dimethylsulfoniopropionate (DMSPd) production was investigated in the Antarctic Ocean in January and February 2002. Dominant herbivorous macrozooplankton of this region, the Antarctic krill Euphausia superba and the tunicate Salpa thompsoni, were used in shipboard incubation experiments. The concentration of DMSPd + DMS increased in the water during incubation with krill. The production rate was 2.96 ± 2.78 nmol DMSPd + DMS·krill1·h1 (mean ± SD). In addition, the DMSPd + DMS production rate was linearly related to the ingestion rate of krill (r2 = 0.664, p ≤ 0.01). Addition of salps to natural surface water, however, did not change the DMSPd + DMS concentrations. During the experiments, both animals fed on phytoplankton cells. The fecal pellets of krill contained broken phytoplankton cells, whereas those of salps contained unbroken cells. These results suggest that sloppy feeding by krill is a more likely mechanism for producing DMS and DMSPd than the direct ingestion of phytoplankton cells by salps. The decrease of DMS concentrations in the upper 200 m of the water column from January to February may be explained, in part, by changes in the composition of the macrozooplankton community.
9
Venkataramana, V., N. Anilkumar, K. Swadling, R. K. Mishra, S. C. Tripathy, A. Sarkar, Soares Melena Augusta, P. Sabu e Honey U. K. Pillai. "Distribution of zooplankton in the Indian sector of the Southern Ocean". Antarctic Science 32, n. 3 (12 febbraio 2020): 168–79. http://dx.doi.org/10.1017/s0954102019000579.
Testo completoAbstract (sommario):
AbstractThe community composition of zooplankton with an emphasis on copepods was assessed in the frontal zones of the Indian sector of the Southern Ocean (SO) during summer 2013. Copepods were the dominant group in both the bongo net and multiple plankton sampler across the entire region. High zooplankton abundance was recorded along each transect in the Polar Front (PF). Community structure in this front was dominated by common taxa, including Ctenocalanus citer, Clausocalanus spp., Calanoides acutus, Calanus propinquus, Calanus australis and Rhincalanus gigas, which together accounted for > 62% of the total abundance. Calocalanus spp., Neocalanus tonsus and C. propinquus were indicator species in the Sub-Tropical Front (STF), Sub-Antarctic Front and PF, respectively. A strong contrast in population structure and biovolume was observed between then PF and the STF. The community structure of smaller copepods was associated with the high-temperature region, whereas communities of larger copepods were associated with the low-temperature region. Thus, it seems probable that physical and biological characteristics of the SO frontal regions are controlling the abundance and distribution of zooplankton community structure by restricting some species to the warmer stratified zones and some species to the well-mixed zone.
10
BARRERA-ORO, ESTEBAN. "The role of fish in the Antarctic marine food web: differences between inshore and offshore waters in the southern Scotia Arc and west Antarctic Peninsula". Antarctic Science 14, n. 4 (dicembre 2002): 293–309. http://dx.doi.org/10.1017/s0954102002000111.
Testo completoAbstract (sommario):
The role of fish in the Antarctic food web in inshore and offshore waters is analysed, taking as an example the coastal marine communities of the southern Scotia Arc (South Orkney Islands and South Shetland Islands) and the west Antarctic Peninsula. Inshore, the ecological role of demersal fish is more important than that of krill. There, demersal fish are major consumers of benthos and also feed on zooplankton (mainly krill in summer). They are links between lower and upper levels of the food web and are common prey of other fish, birds and seals. Offshore, demersal fish depend less on benthos and feed more on zooplankton (mainly krill) and nekton, and are less accessible as prey of birds and seals. There, pelagic fish (especially lantern fish) are more abundant than inshore and play an important role in the energy flow from macrozooplankton to higher trophic levels (seabirds and seals). Through the higher fish predators, energy is transferred to land in the form of fish remains, pellets (birds), regurgitation and faeces (birds and seals). However, in the general context of the Antarctic marine ecosystem, krill (Euphausia superba) plays the central role in the food web because it is the main food source in terms of biomass for most of the high level predators from demersal fish up to whales. This has no obvious equivalent in other marine ecosystems. In Antarctic offshore coastal and oceanic waters the greatest proportion of energy from the ecosystem is transferred to land directly through krill consumers, such as flying birds, penguins, and seals. Beside krill, the populations of fish in the Antarctic Ocean are the second most important element for higher predators, in particular the energy-rich pelagic Myctophidae in open waters and the pelagic Antarctic silver fish (Pleuragramma antarcticum) in the high Antarctic zone. Although the occurrence of these pelagic fish inshore has been poorly documented, their abundance in neritic waters could be higher than previously believed.
11
Lehette, Pascal, e Santiago Hernández-León. "Zooplankton biomass estimation from digitized images: a comparison between subtropical and Antarctic organisms". Limnology and Oceanography: Methods 7, n. 4 (aprile 2009): 304–8. http://dx.doi.org/10.4319/lom.2009.7.304.
Testo completo
12
Ingole, B. S., e A. H. Parulekar. "Zooplankton biomass and abundance of Antarctic krillEuphausia superba DANA in Indian ocean sector of the southern ocean". Journal of Biosciences 18, n. 1 (marzo 1993): 141–48. http://dx.doi.org/10.1007/bf02703045.
Testo completo
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McBride, Margaret M., Padmini Dalpadado, Kenneth F. Drinkwater, Olav Rune Godø, Alistair J. Hobday, Anne B. Hollowed, Trond Kristiansen et al. "Krill, climate, and contrasting future scenarios for Arctic and Antarctic fisheries". ICES Journal of Marine Science 71, n. 7 (28 marzo 2014): 1934–55. http://dx.doi.org/10.1093/icesjms/fsu002.
Testo completoAbstract (sommario):
Abstract Arctic and Antarctic marine systems have in common high latitudes, large seasonal changes in light levels, cold air and sea temperatures, and sea ice. In other ways, however, they are strikingly different, including their: age, extent, geological structure, ice stability, and foodweb structure. Both regions contain very rapidly warming areas and climate impacts have been reported, as have dramatic future projections. However, the combined effects of a changing climate on oceanographic processes and foodweb dynamics are likely to influence their future fisheries in very different ways. Differences in the life-history strategies of the key zooplankton species (Antarctic krill in the Southern Ocean and Calanus copepods in the Arctic) will likely affect future productivity of fishery species and fisheries. To explore future scenarios for each region, this paper: (i) considers differing characteristics (including geographic, physical, and biological) that define polar marine ecosystems and reviews known and projected impacts of climate change on key zooplankton species that may impact fished species; (ii) summarizes existing fishery resources; (iii) synthesizes this information to generate future scenarios for fisheries; and (iv) considers the implications for future fisheries management. Published studies suggest that if an increase in open water during summer in Arctic and Subarctic seas results in increased primary and secondary production, biomass may increase for some important commercial fish stocks and new mixes of species may become targeted. In contrast, published studies suggest that in the Southern Ocean the potential for existing species to adapt is mixed and that the potential for the invasion of large and highly productive pelagic finfish species appears low. Thus, future Southern Ocean fisheries may largely be dependent on existing species. It is clear from this review that new management approaches will be needed that account for the changing dynamics in these regions under climate change.
14
Menze, Sebastian, Daniel P. Zitterbart, Ilse van Opzeeland e Olaf Boebel. "The influence of sea ice, wind speed and marine mammals on Southern Ocean ambient sound". Royal Society Open Science 4, n. 1 (gennaio 2017): 160370. http://dx.doi.org/10.1098/rsos.160370.
Testo completoAbstract (sommario):
This paper describes the natural variability of ambient sound in the Southern Ocean, an acoustically pristine marine mammal habitat. Over a 3-year period, two autonomous recorders were moored along the Greenwich meridian to collect underwater passive acoustic data. Ambient sound levels were strongly affected by the annual variation of the sea-ice cover, which decouples local wind speed and sound levels during austral winter. With increasing sea-ice concentration, area and thickness, sound levels decreased while the contribution of distant sources increased. Marine mammal sounds formed a substantial part of the overall acoustic environment, comprising calls produced by Antarctic blue whales ( Balaenoptera musculus intermedia ), fin whales ( Balaenoptera physalus ), Antarctic minke whales ( Balaenoptera bonaerensis ) and leopard seals ( Hydrurga leptonyx ). The combined sound energy of a group or population vocalizing during extended periods contributed species-specific peaks to the ambient sound spectra. The temporal and spatial variation in the contribution of marine mammals to ambient sound suggests annual patterns in migration and behaviour. The Antarctic blue and fin whale contributions were loudest in austral autumn, whereas the Antarctic minke whale contribution was loudest during austral winter and repeatedly showed a diel pattern that coincided with the diel vertical migration of zooplankton.
15
Tanimura, A., S. Kawaguchi, N. Oka, J. Nishikawa, S. Toczko, K. T. Takahashi, M. Terazaki, T. Odate, M. Fukuchi e G. Hosie. "Abundance and grazing impacts of krill, salps and copepods along the 140°E meridian in the Southern Ocean during summer". Antarctic Science 20, n. 4 (18 marzo 2008): 365–79. http://dx.doi.org/10.1017/s0954102008000928.
Testo completoAbstract (sommario):
AbstractAbundance and grazing impacts of krill, salps and herbivorous copepods were investigated in Antarctic waters along the 140°E meridian, south of Australia, during the summers of 2002 and 2003. North of the Southern Boundary of the Antarctic Circumpolar Current (SB-ACC), macrozooplankton comprised species of Salpa thompsoni and large herbivorous copepods, while the area south of the SB-ACC was numerically dominated by Euphausia superba or E. crystallorophias. North of the SB-ACC, the estimate of grazing impact revealed that krill, salps and copepods, Calanoides acutus, Calanus propinquus, Rhincalanus gigas and Metridia gerlachei, are able to remove a maximum of 37% of the total phytoplankton standing stock in early to midsummer, but grazing is negligible in late summer. The high grazing impact is attributed to the relatively high zooplankton abundance and low phytoplankton abundance. South of the SB-ACC, overall daily grazing impact of the three zooplankton groups was low and did not exceed 6% of the total phytoplankton standing stock throughout the investigation period. Present results indicate that the contribution of krill, salps and copepods varies seasonally as well as regionally across the SB-ACC. It seems that the carbon transport from surface to deep water by macro- and mesozooplankton in summer in this area is relatively large north of the SB-ACC but small south of the SB-ACC.
16
Angel, Martin V. "Southern Ocean pelagic ecosystems". Archives of Natural History 32, n. 2 (ottobre 2005): 281–300. http://dx.doi.org/10.3366/anh.2005.32.2.281.
Testo completoAbstract (sommario):
In 1902 the Discovery sailed into an ocean that was almost totally unknown biologically. Even so, its living resources of seals had been extensively hunted almost to the point of extinction. Exploitation of the whales was about to begin. The expedition resulted in the discovery of 23 new zooplankton species; 5% of the presently known mesozooplankton fauna. The results were worked up within six years, and paved the way for the next century of research. The ultimate target was to provide the scientific basis for the sustainable management of the Southern Ocean especially the whale stocks. This paper summarizes the knowledge base at the start of the expedition and how the various strands of research became woven into our understanding of the biological oceanography of the Southern Ocean. The science has been both technology driven and technology limited. It failed to convince decision-makers in time to prevent the gross overexploitation of the whales, but the Antarctic Treaty now provides a framework of protection. However, within the last two decades we have come to realize that it is not just whales that are at risk, and that the remoteness of the Southern Ocean is proving no protection against the pervasiveness of anthropogenic influences.
17
Priddle, Julian, David B. Nedwell, Michael J. Whitehouse, David S. Reay, Graham Savidge, Linda C. Gilpin, Eugene J. Murphy e J. Cynan Ellis-Evans. "Re-examining the Antarctic Paradox: speculation on the Southern Ocean as a nutrient-limited system". Annals of Glaciology 27 (1998): 661–68. http://dx.doi.org/10.3189/1998aog27-1-661-668.
Testo completoAbstract (sommario):
The Southern Ocean is the largest of the high-nutrient, low-chlorophyll (HNLC) regions of the world ocean. Phytoplankton production fails to utilise completely the pool of inorganic nutrients in the euphotic zone, giving rise to low phytoplankton bio-mass and leaving relatively high summer nutrient concentrations. This enigma is of considerable significance for our understanding of the role of the oceans in the global carbon cycle. Various limiting factors have been considered: low light, low temperature, absence of necessary trace elements, grazing pressure and other means of biomass removal. The dynamics of nitrogen uptake by phytoplankton are of particular importance. Classically, nitrate mixed into the surface layer during winter provides the nitrogen pool for growth in the spring bloom. Some organic material is exported to depth, whilst the remainder is recycled, providing ammonium and other reduced species as nitrogenous substrates for growth during the remainder of the season. The oxidation state of the inorganic nitrogen supply thus identifies new and recycled carbon fixation. Whilst this is convenient “shorthand” for the nitrogen nutrition of carbon export in much of the ocean, it is an inappropriate model for the Southern Ocean. Here, nitrate and ammonium use are simultaneous, and nitrate is never exhausted by the annual phytoplankton production. We speculate that a range of environmental factors combine to make the large pool of nitrate partially inaccessible to phytoplankton. in addition to the documented effects of low iron availability and high ammonium concentrations, the low temperatures characteristic of the Southern Ocean may decrease nitrate availability because of the increased energetic overheads in its uptake and reduction. This in turn makes ammonium an important nitrogenous substrate, and its production by zooplankton and heterotrophic microorganisms is an important component of the plankton nitrogen cycle. There is some evidence that ammonium production by large grazing animals may stimulate phytoplankton growth. Microbial removal of nitrogen from sedimenting phytoplankton cells may result in local decoupling between the carbon and nitrogen cycles, allowing some reduced nitrogen to remain in the euphotic zone whilst carbon is exported to depth.
18
Chu, D., e P. H. Wiebe. "Measurements of sound-speed and density contrasts of zooplankton in Antarctic waters". ICES Journal of Marine Science 62, n. 4 (1 gennaio 2005): 818–31. http://dx.doi.org/10.1016/j.icesjms.2004.12.020.
Testo completoAbstract (sommario):
Abstract Sound-speed and density contrasts (h and g, respectively), two important acoustic material properties, of live zooplankton were measured off the western Antarctic Peninsula during a Southern Ocean GLOBEC cruise conducted from 9 April to 21 May 2002. The work included in situ sound-speed contrast and shipboard density-contrast measurements. The temperature and pressure (depth) dependence of the sound-speed contrast of Euphausia superba and E. crystallorophias as well as that of some other zooplankton species were investigated. The size range of E. superba used in the measurements varied from about 20 mm to 57 mm, with mean length of 36.7 mm and standard deviation of 9.8 mm, which covered life stages from juvenile to adult. For E. superba, there was no statistically significant depth dependence, but there was a moderate dependence of sound-speed and density contrasts on the size of the animals. The measured sound-speed contrast varied between 1.018 and 1.044, with mean value 1.0279 and standard deviation 0.0084, while the measured density contrast varied between 1.007 and 1.036, with mean value 1.0241 and standard deviation 0.0082. For E. crystallorophias and Calanus there was a measurable depth dependence in sound-speed contrast. The in situ sound-speed contrasts for E. crystallorophias were 1.025 ± 0.004 to 1.029 ± 0.009. For Calanus, they were variable, with one set giving a value of 0.949 ± 0.001 and the other giving 1.013 ± 0.002. Shipboard measurements of other taxa/species also showed substantial variation in g and h. In general, values of g ranged from 0.9402 to 1.051 and h ranged from 0.949 to 1.096. The variation of the material properties is related to species, type, size, stage, and in some cases depth of occurrence. The uncertainty of the estimates of zooplankton biomass attributable to these variations in g and h can be quite large (more than 100 fold). Improvements in making biological inferences from acoustic data depend strongly on increased information about the material properties of zooplankton and the biological causes for their variation, as well as a knowledge of the species composition and abundance.
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Loeb, Valerie J., Eileen E. Hofmann, John M. Klinck, Osmund Holm-Hansen e Warren B. White. "ENSO and variability of the Antarctic Peninsula pelagic marine ecosystem". Antarctic Science 21, n. 2 (19 novembre 2008): 135–48. http://dx.doi.org/10.1017/s0954102008001636.
Testo completoAbstract (sommario):
AbstractThe West Antarctic Peninsula region is an important source of Antarctic krill (Euphausia superba) in the Southern Ocean. From 1980–2004 abundance and concentration of phytoplankton and zooplankton, krill reproductive and recruitment success and seasonal sea ice extent here were significantly correlated with the atmospheric Southern Oscillation Index and exhibited three- to five-year frequencies characteristic of El Niño–Southern Oscillation (ENSO) variability. This linkage was associated with movements of the Southern Antarctic Circumpolar Current Front and Boundary, a changing influence of Antarctic Circumpolar Current and Weddell Sea waters, and eastward versus westward flow and mixing processes that are consistent with forcing by the Antarctic Dipole high-latitude climate mode. Identification of hydrographic processes underlying ecosystem variability presented here were derived primarily from multi-disciplinary data collected during 1990–2004, a period with relatively stable year-to-year sea ice conditions. These results differ from the overwhelming importance of seasonal sea ice development previously established using 1980–1996 data, a period marked by a major decrease in sea ice from the Antarctic Peninsula region in the late 1980s. These newer results reveal the more subtle consequences of ENSO variability on biological responses. They highlight the necessity of internally consistent long-term multidisciplinary datasets for understanding ecosystem variability and ultimately for establishing well-founded ecosystem management. Furthermore, natural environmental variability associated with interannual- and decadal-scale changes in ENSO forcing must be considered when assessing impacts of climate warming in the Antarctic Peninsula–Weddell Sea region.
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Laufkötter, C., M. Vogt e N. Gruber. "Long-term trends in ocean plankton production and particle export between 1960–2006". Biogeosciences Discussions 10, n. 3 (27 marzo 2013): 5923–75. http://dx.doi.org/10.5194/bgd-10-5923-2013.
Testo completoAbstract (sommario):
Abstract. We analyse long-term trends in marine primary and particle export production and their link to marine phytoplankton community composition over the period 1950–2006 using a hindcast simulation of the ocean component of the Community Climate System Model to which the Biogeochemical Elemental Cycling Model had been coupled. In our simulation, global primary and export production decreased by 6% and 7%, respectively over the last 50 yr. These changes go along with a 8% decrease in small phytoplankton biomass and 5% decrease in zooplankton biomass. Diatom biomass decreases by 3% with strong temporal and spatial variability. Strongest decreases in primary and export production occured in the Western Pacific, where increased stratification leads to a decrease in total phytoplankton and a decrease in diatom fraction. This causes decreases in zooplankton biomass and a lower export efficiency. Strong phytoplankton composition changes occur in the Southern Ocean and North Atlantic, where increased wind stress leads to stronger mixing, which reduces the biomass of small phytoplankton, while diatoms profit from higher nutrient inputs and lower grazing pressure. The relative fraction of diatoms correlates positively with the export efficiency (r = 0.8) in most areas except the Northern Pacific and Antarctic Circumpolar Current, where the correlation is negative (r = −0.5). However, long-term trends in global export efficiency are ultimately driven by decreases in small phytoplankton and consequent decreases in coccolithophore biomass.
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Spinelli, Mariela L., Andrea Malits, Virginia A. García Alonso, Jacobo Martín e Fabiana L. Capitanio. "Spatial gradients of spring zooplankton assemblages at the open ocean sub-Antarctic Namuncurá Marine Protected Area/Burdwood Bank, SW Atlantic Ocean". Journal of Marine Systems 210 (ottobre 2020): 103398. http://dx.doi.org/10.1016/j.jmarsys.2020.103398.
Testo completo
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Cornils, Astrid, Rainer Sieger, Elke Mizdalski, Stefanie Schumacher, Hannes Grobe e Sigrid B. Schnack-Schiel. "Copepod species abundance from the Southern Ocean and other regions (1980–2005) – a legacy". Earth System Science Data 10, n. 3 (16 agosto 2018): 1457–71. http://dx.doi.org/10.5194/essd-10-1457-2018.
Testo completoAbstract (sommario):
Abstract. This data collection originates from the efforts of Sigrid Schnack-Schiel (1946–2016), a zooplankton ecologist with great expertise in life cycle strategies of Antarctic calanoid copepods, who also investigated zooplankton communities in tropical and subtropical marine environments. Here, we present 33 data sets with abundances of planktonic copepods from 20 expeditions to the Southern Ocean (Weddell Sea, Scotia Sea, Amundsen Sea, Bellingshausen Sea, Antarctic Peninsula), one expedition to the Magellan region, one latitudinal transect in the eastern Atlantic Ocean, one expedition to the Great Meteor Bank, and one expedition to the northern Red Sea and Gulf of Aqaba as part of her scientific legacy. A total of 349 stations from 1980 to 2005 were archived. During most expeditions depth-stratified samples were taken with a Hydrobios multinet with five or nine nets, thus allowing inter-comparability between the different expeditions. A Nansen or a Bongo net was deployed only during four cruises. Maximum sampling depth varied greatly among stations due to different bottom depths. However, during 11 cruises to the Southern Ocean the maximum sampling depth was restricted to 1000 m, even at locations with greater bottom depths. In the eastern Atlantic Ocean (PS63) sampling depth was restricted to the upper 300 m. All data are now freely available at PANGAEA via the persistent identifier https://doi.org/10.1594/PANGAEA.884619.Abundance and distribution data for 284 calanoid copepod species and 28 taxa of other copepod orders are provided. For selected species the abundance distribution at all stations was explored, revealing for example that species within a genus may have contrasting distribution patterns (Ctenocalanus, Stephos). In combination with the corresponding metadata (sampling data and time, latitude, longitude, bottom depth, sampling depth interval) the analysis of the data sets may add to a better understanding how the environment (currents, temperature, depths, season) interacts with copepod abundance, distribution and diversity. For each calanoid copepod species, females, males and copepodites were counted separately, providing a unique resource for biodiversity and modelling studies. For selected species the five copepodite stages were also counted separately, thus also allowing the data to be used to study life cycle strategies of abundant or key species.
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Laufkötter, C., M. Vogt e N. Gruber. "Long-term trends in ocean plankton production and particle export between 1960–2006". Biogeosciences 10, n. 11 (18 novembre 2013): 7373–93. http://dx.doi.org/10.5194/bg-10-7373-2013.
Testo completoAbstract (sommario):
Abstract. We analyse long-term trends in marine primary and particle export production and their link to marine phytoplankton community composition for the period 1960–2006 using a hindcast simulation of the Biogeochemical Elemental Cycling Model coupled to the ocean component of the Community Climate System Model. In our simulation, global primary and export production decrease significantly over the last 50 yr, by 6.5% and 8% respectively. These changes are associated with an 8.5% decrease in small phytoplankton biomass and 5% decrease in zooplankton biomass. Diatom biomass decreases globally by 3%, but with strong temporal and spatial variability. The strongest decreases in primary and export production occur in the western Pacific, where enhanced stratification leads to stronger nutrient limitation and a decrease in total phytoplankton. The concurrent decrease in diatom fraction and in zooplankton biomass causes a lower export efficiency in this region. Substantial phytoplankton composition changes also occur in the Southern Ocean and North Atlantic, although these are masked in part by a high degree of interannual variability. In these regions, stronger wind stress enhances mixing, reducing the biomass of small phytoplankton, while diatoms profit from higher nutrient inputs and lower grazing pressure. The relative fraction of diatoms correlates positively with the export efficiency (r = 0.8, p < 0.05) in most areas except for the North Pacific and Antarctic Circumpolar Current, where the correlation is negative (r = –0.5, p < 0.05). However, the long-term trends in global export efficiency are ultimately driven by the reduction in small phytoplankton and particularly decreases in coccolithophore biomass. The diagnosed trends point toward a substantial sensitivity of marine primary production and export to climatic variations and trends.
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Teschke, Katharina, Hendrik Pehlke, Volker Siegel, Horst Bornemann, Rainer Knust e Thomas Brey. "An integrated compilation of data sources for the development of a marine protected area in the Weddell Sea". Earth System Science Data 12, n. 2 (4 maggio 2020): 1003–23. http://dx.doi.org/10.5194/essd-12-1003-2020.
Testo completoAbstract (sommario):
Abstract. The Southern Ocean may contribute a considerable amount to the proposed global network of marine protected areas (MPAs) that should cover about 10 % of the world's oceans in 2020. In the Antarctic, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is responsible for this task, and currently Germany leads a corresponding scientific evaluation of the wider Weddell Sea region. Compared to other marine regions within the Southern Ocean, the Weddell Sea is exceptionally well investigated. A tremendous amount of data and information has been produced over the last 4 decades. Here, we give a systematic overview of all data sources collected in the context of the Weddell Sea MPA planning process. The compilation of data sources is comprised of data produced by scientists and institutions from more than 20 countries that were either available within our institutes, downloaded via data portals or transcribed from the literature. It is the first compilation for this area that includes abiotic data, such as bathymetry and sea ice, and ecological data from zooplankton, zoobenthos, fish, birds and marine mammals. All data layer products based on this huge compilation of environmental and ecological data are available from the data publisher PANGAEA via the six persistent identifiers at https://doi.org/10.1594/PANGAEA.899595 (Pehlke and Teschke, 2019), https://doi.org/10.1594/PANGAEA.899667 (Teschke et al., 2019a), https://doi.org/10.1594/PANGAEA.899645 (Teschke et al., 2019b), https://doi.org/10.1594/PANGAEA.899591 (Teschke et al., 2019c), https://doi.org/10.1594/PANGAEA.899520 (Pehlke et al., 2019a) and https://doi.org/10.1594/PANGAEA.899619 (Pehlke et al., 2019b). This compilation of data sources including the final data layer products will serve future research and monitoring well beyond the current MPA development process.
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Ducklow, Hugh W., Karen Baker, Douglas G. Martinson, Langdon B. Quetin, Robin M. Ross, Raymond C. Smith, Sharon E. Stammerjohn, Maria Vernet e William Fraser. "Marine pelagic ecosystems: the West Antarctic Peninsula". Philosophical Transactions of the Royal Society B: Biological Sciences 362, n. 1477 (30 novembre 2006): 67–94. http://dx.doi.org/10.1098/rstb.2006.1955.
Testo completoAbstract (sommario):
The marine ecosystem of the West Antarctic Peninsula (WAP) extends from the Bellingshausen Sea to the northern tip of the peninsula and from the mostly glaciated coast across the continental shelf to the shelf break in the west. The glacially sculpted coastline along the peninsula is highly convoluted and characterized by deep embayments that are often interconnected by channels that facilitate transport of heat and nutrients into the shelf domain. The ecosystem is divided into three subregions, the continental slope, shelf and coastal regions, each with unique ocean dynamics, water mass and biological distributions. The WAP shelf lies within the Antarctic Sea Ice Zone (SIZ) and like other SIZs, the WAP system is very productive, supporting large stocks of marine mammals, birds and the Antarctic krill, Euphausia superba . Ecosystem dynamics is dominated by the seasonal and interannual variation in sea ice extent and retreat. The Antarctic Peninsula is one among the most rapidly warming regions on Earth, having experienced a 2°C increase in the annual mean temperature and a 6°C rise in the mean winter temperature since 1950. Delivery of heat from the Antarctic Circumpolar Current has increased significantly in the past decade, sufficient to drive to a 0.6°C warming of the upper 300 m of shelf water. In the past 50 years and continuing in the twenty-first century, the warm, moist maritime climate of the northern WAP has been migrating south, displacing the once dominant cold, dry continental Antarctic climate and causing multi-level responses in the marine ecosystem. Ecosystem responses to the regional warming include increased heat transport, decreased sea ice extent and duration, local declines in ice-dependent Adélie penguins, increase in ice-tolerant gentoo and chinstrap penguins, alterations in phytoplankton and zooplankton community composition and changes in krill recruitment, abundance and availability to predators. The climate/ecological gradients extending along the WAP and the presence of monitoring systems, field stations and long-term research programmes make the region an invaluable observatory of climate change and marine ecosystem response.
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Schlosser, Christian, Katrin Schmidt, Alfred Aquilina, William B. Homoky, Maxi Castrillejo, Rachel A. Mills, Matthew D. Patey, Sophie Fielding, Angus Atkinson e Eric P. Achterberg. "Mechanisms of dissolved and labile particulate iron supply to shelf waters and phytoplankton blooms off South Georgia, Southern Ocean". Biogeosciences 15, n. 16 (22 agosto 2018): 4973–93. http://dx.doi.org/10.5194/bg-15-4973-2018.
Testo completoAbstract (sommario):
Abstract. The island of South Georgia is situated in the iron (Fe)-depleted Antarctic Circumpolar Current of the Southern Ocean. Iron emanating from its shelf system fuels large phytoplankton blooms downstream of the island, but the actual supply mechanisms are unclear. To address this, we present an inventory of Fe, manganese (Mn), and aluminium (Al) in shelf sediments, pore waters, and the water column in the vicinity of South Georgia, alongside data on zooplankton-mediated Fe cycling processes, and provide estimates of the relative dissolved Fe (DFe) fluxes from these sources. Seafloor sediments, modified by authigenic Fe precipitation, were the main particulate Fe source to shelf bottom waters as indicated by the similar Fe ∕ Mn and Fe ∕ Al ratios for shelf sediments and suspended particles in the water column. Less than 1 % of the total particulate Fe pool was leachable surface-adsorbed (labile) Fe and therefore potentially available to organisms. Pore waters formed the primary DFe source to shelf bottom waters, supplying 0.1–44 µmol DFe m−2 d−1. However, we estimate that only 0.41±0.26 µmol DFe m−2 d−1 was transferred to the surface mixed layer by vertical diffusive and advective mixing. Other trace metal sources to surface waters included glacial flour released by melting glaciers and via zooplankton egestion and excretion processes. On average 6.5±8.2 µmol m−2 d−1 of labile particulate Fe was supplied to the surface mixed layer via faecal pellets formed by Antarctic krill (Euphausia superba), with a further 1.1±2.2 µmol DFe m−2 d−1 released directly by the krill. The faecal pellets released by krill included seafloor-derived lithogenic and authigenic material and settled algal debris, in addition to freshly ingested suspended phytoplankton cells. The Fe requirement of the phytoplankton blooms ∼ 1250 km downstream of South Georgia was estimated as 0.33±0.11 µmol m−2 d−1, with the DFe supply by horizontal/vertical mixing, deep winter mixing, and aeolian dust estimated as ∼0.12 µmol m−2 d−1. We hypothesize that a substantial contribution of DFe was provided through recycling of biogenically stored Fe following luxury Fe uptake by phytoplankton on the Fe-rich shelf. This process would allow Fe to be retained in the surface mixed layer of waters downstream of South Georgia through continuous recycling and biological uptake, supplying the large downstream phytoplankton blooms.
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Gruzinov, V. M. "ON PHYSICAL AND DYNAMICAL FRONTS IN THE OCEAN". Journal of Oceanological Research 47, n. 2 (30 giugno 2019): 100–107. http://dx.doi.org/10.29006/1564-2291.jor-2019.47(2).7.
Testo completoAbstract (sommario):
A review of the works of Yu. Ivanov devoted to the study of the front zones of the world ocean is made. He, in fact, made the transition from the study of mean stationary processes to quasi-periodic and non-stationary. Yu. Ivanov developed a constructive formula to compute the speed of Ekman swap on the field purely zonal wind, which allowed us to track seasonal movements of Antarctic zones of divergence and convergence. Ivanov first introduced the concept of dynamic front as a region of divergence or convergence of the flow, in contrast to the physical front, as the region of maximum horizontal gradients characteristics. Analyzing the equation of vertical diffusion, he shows that the physical fronts are on the periphery of the dynamic fronts. The general map of the location of the main front zones in the Southern ocean was obtained by processing the large-scale observations on the 86 meridian sections. In addition, he compared the position of the selected fronts, with the results of previous studies, in particular,with the works of Deacon and Mackintosh together with B. A. Tareev. Based on the developed method of calculations and the type of atmospheric pressure he developed a simple calculation scheme,which allowed to estimate the speed of vertical flows depending on the distance to the center of the cyclone. Based on typical pressure maps, it is possible to determine the zones in which favorable dynamic conditions for zooplankton accumulations are created. This is also one of the practical applications developed by the method of calculation of the position of the front zones in the ocean.
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Hunt, Brian P. V., e Graham W. Hosie. "The seasonal succession of zooplankton in the Southern Ocean south of Australia, part II: The Sub-Antarctic to Polar Frontal Zones". Deep Sea Research Part I: Oceanographic Research Papers 53, n. 7 (luglio 2006): 1203–23. http://dx.doi.org/10.1016/j.dsr.2006.05.002.
Testo completo
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Wakefield, Ewan D., Richard A. Phillips e Mark Belchier. "Foraging black-browed albatrosses target waters overlaying moraine banks - a consequence of upward benthic-pelagic coupling?" Antarctic Science 24, n. 3 (6 marzo 2012): 269–80. http://dx.doi.org/10.1017/s0954102012000132.
Testo completoAbstract (sommario):
AbstractWide-ranging, surface-feeding pelagic seabirds are the most numerous functional group of birds in the Southern Ocean. The mesoscale habitat use of these birds is increasingly being quantified by relating their movements to remotely sensed, near surface properties of the ocean. However, prey availability at the sea surface may also be determined by habitat characteristics not measurable from space. For instance, benthic-pelagic coupling, which occurs when seabed processes affect productivity in the epipelagic zone, can link benthic habitat type to availability of surface prey. We combined acoustically derived maps of the substrate of the South Georgia shelf with GPS tracking to quantify the sub-mesoscale habitat use of breeding black-browed albatrosses. We show that albatrosses preferentially used waters overlaying glacial moraine banks near the shelf edge and that this was unrelated to the presence of trawlers targeting mackerel icefish, which are also associated with these features. Stomach temperature profiles suggest that albatrosses primarily caught krill and fish over the banks. We hypothesize that black-browed albatrosses target waters overlaying moraine banks due to upward benthic-pelagic coupling, mediated by an increase in abundance of zooplankton such as Antarctic krill. Our findings suggest that the potential effects of such processes on pelagic seabird distribution warrant wider investigation.
30
Phleger, Charles F., Matthew M. Nelson, Ben D. Mooney e Peter D. Nichols. "Wax esters versus triacylglycerols in myctophid fishes from the Southern Ocean". Antarctic Science 11, n. 4 (dicembre 1999): 436–44. http://dx.doi.org/10.1017/s0954102099000565.
Testo completoAbstract (sommario):
Five species of myctophid fishes were collected by trawl from the Elephant Island region of the Antarctic Peninsula between 60°30′–62°S and 55°–61°30′W. Two species, Gymnoscopelus braueri and Krefftichthyes anderssoni were lipid-rich (406–456 mg g−1 dry weight whole fish) with wax esters (WE) the major lipid class. In three species, G. opisthopterus, G. nicholsi, and Electrona carlsbergii, triacylglycerols (TAG) were the major lipid. All fish had oily bones, with values up to 471 mg g−1 dry weight in the vertebral centra of K. anderssoni. The principal fatty acids of the TAG-rich myctophids included the monoenes 18:1(n-9) and 20:1. There were lower levels of 16:0 and 18:0 saturated fatty acids. Polyunsaturated fatty acids (PUFA) were present at higher abundance in the TAG-rich E. carlsbergii and G. opisthopterus, with lower levels in G. nicholsi. In comparison, the WE-dominated species contained lower levels of PUFA than in the TAG-rich species. The principal fatty acids of the WE-rich myctophids included the monoenes 18:1(n-9), 16:1(n-7), and 18:1(n-7), with lower levels of the saturated acids 16:0 and 18:0. Fatty alcohols were dominated by 16:0 and 14:0 and the monounsaturated 18:1(n-9) with 16:1(n-7), 18:1(n-7), and 20:1(n-9). Based on the fatty acid profiles, the diet of G. opishtopterus and G. nicholsi, previously thought to be mainly Euphausia superba, is suggested to include copepods and other zooplankton with only a minor krill component, possibly consisting of other species than E. superba.
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Reiss, Christian S., Anthony M. Cossio, Valerie Loeb e David A. Demer. "Variations in the biomass of Antarctic krill (Euphausia superba) around the South Shetland Islands, 1996–2006". ICES Journal of Marine Science 65, n. 4 (18 marzo 2008): 497–508. http://dx.doi.org/10.1093/icesjms/fsn033.
Testo completoAbstract (sommario):
Abstract Reiss, C. S., Cossio, A. M., Loeb, V., and Demer, D. A. 2008. Variations in the biomass of Antarctic krill (Euphausia superba) around the South Shetland Islands, 1996–2006. – ICES Journal of Marine Science, 65: 497–508. The time-series of acoustically surveyed Antarctic krill (Euphausia superba) biomass near the South Shetland Islands (SSI) between 1996 and 2006 is re-estimated using a validated physics-based model of target strength (TS), and a species-discrimination algorithm based on the length-range of krill in plankton samples to identify krill acoustically, derived from TS-model predictions. The SSI area is surveyed each austral summer by the US Antarctic Marine Living Resources Program, and the acoustic data are used to examine trends in krill biomass and to assess the potential impact of fishing to the reproductive success of land-based predators (seals and penguins). The time-series of recomputed biomass densities varies greatly from that computed using an empirical log-linear TS-model and fixed-ranges of differences in volume–backscattering strengths (ΔSv), conventionally used to identify krill acoustically. The new acoustic estimates of biomass are significantly correlated with both proportional recruitment and krill abundance estimated from zooplankton samples. Two distinct peaks in biomass (1996 and 2003) are in accord with recruitment events shown by net-based krill time-series. The foundation for the new TS-model and the associated krill-discrimination algorithm, coupled with the agreement between acoustic- and net-survey results, provides strong support for the use of the new analytical technique. Variable biases in the re-estimated krill biomass have been greatly reduced. However, survey variability increased as a result of the increased rejection of acoustic backscatter previously attributed to krill. Management of Southern Ocean krill stocks based on a precautionary approach may therefore result in decreased allocations of krill, given its dependence on the variability of survey estimates.
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Pieńkowski, Anna J., Fabienne Marret, James D. Scourse e David N. Thomas. "Organic-walled microfossils from the north-west Weddell Sea, Antarctica: records from surface sediments after the collapse of the Larsen-A and Prince Gustav Channel ice shelves". Antarctic Science 25, n. 4 (21 gennaio 2013): 565–74. http://dx.doi.org/10.1017/s0954102012001186.
Testo completoAbstract (sommario):
AbstractSurface sediments from six box cores along the north-eastern Antarctic Peninsula document the dinoflagellate cyst (= dinocyst) and other non-pollen palynomorph (NPP) content soon after overlying ice shelves collapsed. Prince Gustav Channel (PGC) and Larsen-A (LA) areas exhibited markedly different dinocyst abundances, concentrations being low in LA (0–20 cysts g-1) and high in PGC (2600–9100 cysts g-1, average: c. 3800 cysts g-1). Since similar water masses impact both areas, differences may be due to low biological productivity, limited sediment accumulation, and/or restricted fine-grain deposition at Larsen-A. Islandinium minutum (Harland & Reid in Harland et al.) Head et al. dominated dinocyst assemblages, occurring as both excysted and encysted forms (lesser abundance). Other taxa (Echinidinium cf. transparantum Zonneveld, Impagidinium pallidum Bujak, Bitectatodinium tepikiense Wilson, Operculodinium centrocarpum Wall & Dale, Brigantedinium spp., Selenopemphix antarctica Marret & de Vernal, Polykrikos? sp. A, and Polykrikos schwartzii Bütschli) were rare. Such assemblage composition is unusual compared to previously published Southern Ocean data, but may be specific to ice shelf and/or recently ice-free environments. Alternatively, it may be attributable to excessive production facilitated by environmental factors and/or abundant food, or similar cyst morphologies produced by different dinoflagellates. Accompanying NPPs included zooplankton remains, acritarchs, and freshwater algae. Tintinnid loricae were most abundant (max. 800 g-1), followed by foraminiferal linings (max. 320 g-1), and the acritarch Palaeostomocystis fritilla (Bujak) Roncaglia (max. 150 g-1). Collectively, NPPs were more abundant in PGC compared to LA samples.
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Navas-Pereira, Denise, e Marta Vannucci. "The hydromedusae and water masses of the Indian Ocean". Boletim do Instituto Oceanográfico 39, n. 1 (1991): 25–60. http://dx.doi.org/10.1590/s0373-55241991000100003.
Testo completoAbstract (sommario):
This analysis of distribution and abundance of species of Hydromedusae completes a report (Vannucci & Navas, 1973b) on the ecology of Indian Ocean Hydromedusae based on the zooplankton collected during the International Indian Ocean Expedition (IIOE). Distribution and abundance are taken here to be the ecological expression of variability of species in space and time. The aim was to identify the biological signature of below surface water masses that cannot be identified by remote sensing techniques. Selected species were taken as biological units, the oceanic water masses as defined by their T-S and T-O2 diagrammes were taken as the non biological units. Taken together they define different ecosystems of the Indian Ocean. About 45,000 specimens of hydromedusae taken at 480 stations were sorted from 900 plankton samples and all specimens were determined and counted. Several hauls, mostly stratified, were taken with closing nets, but not all contained hydromedusae. The distribution of each species was studied in relation to water salinity, temperature and dissolved oxygen; the limits of ecological tolerance and preference were defined by the environmental characteristics of the layers sampled by the nets and are given for each species. These can be grouped as follows: 1. Deep water species, cold tolerant, often eurytopic; 2. Antarctic species, cold loving, usually stenothermal with preference for low salinity; 3. Indian Ocean Central Water species, with preference for temperature lower than 19ºC and salinity not much higher than 35%o, usually found at sub-surface or intermediate depths, they may spread into the Arabian Sea and Bay of Bengal in surface layers; 4. Indian Ocean Equatorial System species, warm tolerant, usually prefer comparatively low salinity, high temperature and high oxygen content; 5. Bay of Bengal Surface Water species, found in surface layers of the Bay, with preference for low salinity, high temperature and high oxygen content; 6. Arabian Sea Surface Water species prefer very high salinity and high temperature; 7. Rare species. Some immigrants from the Mediterranean Sea are described and many species were found to be tolerant of dissolved oxygen content as low as 0.2 ml/1. Numerous individuals of many species were found to agglomerate at boundary layers.
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Bonecker, Ana C. T., Cristina De O. Dias, Marcia S. De Castro, Pedro F. De Carvalho, Adriana V. Araujo, Rodolfo Paranhos, Anderson S. Cabral e Sergio L. C. Bonecker. "Vertical distribution of mesozooplankton and ichthyoplankton communities in the South-western Atlantic Ocean (23°14′1″S 40°42′19″W)". Journal of the Marine Biological Association of the United Kingdom 99, n. 1 (9 gennaio 2018): 51–65. http://dx.doi.org/10.1017/s0025315417001989.
Testo completoAbstract (sommario):
A study was conducted over eight consecutive days in February 2010 in which daily variations in the vertical distributions of heterotrophic bacteria, mesozooplankton and ichthyoplankton at 1–1200 m in the South-western Atlantic Ocean were investigated. Diurnal and nocturnal samples were collected at an oceanographic station at four regional depths: Tropical Water (TW) (1 m), South Atlantic Central Water (SACW) (250 m), Antarctic Intermediate Water (AAIW) (800 m) and Upper Circumpolar Deep Water (UCDW) (1200 m). Bacterial, mesozooplankton and larval fish densities significantly differed between sample depths but not between sampling tow times. In total, 154 zooplankton species and 18 larval fish species were identified. The highest number of taxa was obtained from the night-time TW trawls. This depth zone had the highest densities of mesozooplankton, larval fish and bacterioplankton (auto and heterotrophic), associated with the highest temperature and salinity and the lowest inorganic nutrient concentrations. Two sample groups were identified based on their mesozooplankton and larval fish compositions: night-time TW and other water masses (daytime TW, SACW, AAIW and UCDW). Thirty-two indicator species were detected in night-time TW. The copepod Nullosetigera impar was, to the best of our knowledge, identified for the first time on the Brazilian coast. Our results showed significant variability in the abundance and vertical distribution of mesozooplankton, bacterioplankton and larval fish along the water column in an oceanic area. We have provided new data and insights on the composition and vertical distribution of mesozooplankton, larval fish and bacterioplankton in deep waters in the South-western Atlantic Ocean.
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Vereshchaka, Alexander, Eteri Musaeva e Anastasiia Lunina. "Biogeography of the Southern Ocean: environmental factors driving mesoplankton distribution South of Africa". PeerJ 9 (10 maggio 2021): e11411. http://dx.doi.org/10.7717/peerj.11411.
Testo completoAbstract (sommario):
Spatial distribution of zooplankton communities depends on numerous factors, especially temperature and salinity conditions (hydrological factor), sampled depth, chlorophyll concentration, and diel cycle. We analyzed and compared the impact of these factors on mesoplankton abundance, biodiversity, quantitative structure based on proportion of taxa and qualitative structure based on presence/absence of taxa in the Southern Ocean. Samples (43 stations, three vertical strata sampled at each station, 163 taxa identified) were collected with a Juday net along the SR02 transect in December 2009. Mesoplankton abundance in discrete vertical layers ranged from 0.2 to 13,743.6 ind. m−3, i.e., five orders of magnitude, maximal and minimal values were recorded in the upper mixed and in the deepest layer, respectively. Within the combined 300-m layer, abundances ranged from 16.0 to 1,455.0 ind. m−3, i.e., two orders of magnitude suggesting that integral samples provide little information about actual variations of mesoplankton abundances. A set of analyses showed that depth was the major driver of mesoplankton distribution (abundance, biodiversity, quantitative structure), hydrological factors influenced two of them (quantitative and qualitative structure), chlorophyll concentration strongly affected only quantitative structure, and diel cycle had an insignificant effect on mesoplankton distribution. Using our current knowledge of the fine structure of the Antarctic Circumpolar Current, we compared effects of four hydrological fronts, i.e., boundaries between different water-masses with distinct environmental characteristics, and eight dynamic jets (narrow yet very intense currents) on mesoplankton distribution. Subtropical, Polar, and Subantarctic Fronts drove quantitative and qualitative structure of mesoplankton assemblages (decreasing in order of influence), while the Southern Boundary affected only qualitative structure. Effects of dynamic jets were insignificant. We suggest that mesoplankton composition is driven by hydrological parameters and further maintained through compartmentalization by fronts. Impact of local eddies and meanders on biodiversity, abundance, qualitative and quantitative structure of mesoplankton is comparable to that of hydrological fronts. Qualitative structure of mesoplankton assemblages mirrors hydrological structure of the Southern Ocean better than quantitative structure and may be recommended for biogeographic analyses of the Southern Ocean. Comparisons with previous reports from the same area retrieved no significant changes in mesoplankton distribution during the period 1992–2009.
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Guihen, Damien, Sophie Fielding, Eugene J. Murphy, Karen J. Heywood e Gwyn Griffiths. "An assessment of the use of ocean gliders to undertake acoustic measurements of zooplankton: the distribution and density of Antarctic krill (Euphausia superba) in the Weddell Sea." Limnology and Oceanography: Methods 12, n. 6 (giugno 2014): 373–89. http://dx.doi.org/10.4319/lom.2014.12.373.
Testo completo
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Labat, J. Ph, P. Mayzaud, S. Dallot, A. Errhif, S. Razouls e S. Sabini. "Mesoscale distribution of zooplankton in the Sub-Antarctic Frontal system in the Indian part of the Southern Ocean: a comparison between optical plankton counter and net sampling". Deep Sea Research Part I: Oceanographic Research Papers 49, n. 4 (aprile 2002): 735–49. http://dx.doi.org/10.1016/s0967-0637(01)00076-0.
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Mayzaud, P., S. Razouls, A. Errhif, V. Tirelli e J. P. Labat. "Feeding, respiration and egg production rates of copepods during austral spring in the Indian sector of the Antarctic Ocean: role of the zooplankton community in carbon transformation". Deep Sea Research Part I: Oceanographic Research Papers 49, n. 6 (giugno 2002): 1027–48. http://dx.doi.org/10.1016/s0967-0637(02)00012-2.
Testo completo
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Gómez-Gutiérrez, Jaime, e So Kawaguchi. "Pseudocollinia HISTOPHAGOUS CILIATES INFECT KRILL IN THE PACIFIC AND ATLANTIC OCEANS AND POSSIBLY WORLDWIDE". CICIMAR Oceánides 32, n. 2 (24 novembre 2017): 15. http://dx.doi.org/10.37543/oceanides.v32i2.204.
Testo completoAbstract (sommario):
The genus Pseudocollinia (Apostomatida, Pseudocolliniidae) currently includes four species (P. beringensis, P. oregonensis, P. brintoni, and P. similis) that infect adults of seven numerically dominant krill species (Order Euphausiacea) in the northeastern Pacific (Bering Sea-to-Gulf of California). In this review, we found four reports in other parts of the world of misidentified or unidentified protists infecting krill. Based on their morphology, cell size and infection of the hemocoel’s host, we infer they are histophagous Pseudocollinia ciliates. We thus conclude that previous reports of protists (identified as microsporidians) infecting Thysanoessa inermis in the northwestern Atlantic Ocean (Bay of Fundy) and unidentified endoparasite ciliates infecting the Euphausia superba in the Southern Ocean (Admiralty Bay, King George Island), Euphausia pacifica in Sanriku, Japan and Euphausia similis var. armata in Tasmania, Australia are actually Pseudocollinia parasitoid ciliates that await to be morphologically and genetically described. This review provides strong evidence that apostome Pseudocollinia ciliates are widespread distributed in the Pacific and Atlantic Oceans, infecting at least nine krill species from Arctic–to–Antarctic zoogeographic regions, having perhaps worldwide distribution as several of their krill hosts. Future studies should focus on discovering parasitoid ciliates in other krill species, as well as in other phytoplankton and zooplankton taxonomic groups.Ciliados histiófagos Pseudocollinia que infectan krill en los oceános Pacífico y Atlántico y posiblemente en el resto del mundoEl género Pseudocollinia (Apostomatida, Pseudocolliniidae) actualmente incluye cuatro especies (P. beringensis, P. oregonensis, P. brintoni y P. similis) que han sido descubiertas infectando especímenes adultos de siete especies de krill (Orden Euphausiacea) numéricamente dominantes en el Pacífico nororiental (del Mar de Bering al Golfo de California). En esta revisión encontramos cuatro publicaciones que indican que estos ciliados se encuentran en otras partes del mundo pero que estos protistas han sido identificados erróneamente o no fueron identificados taxonómicamente. En la presente revisión se infiere que estos protistas son ciliados del género Pseudocollinia debido a que infectan krill, su morfología y tamaño celular, así como su localización de infección en el hemocele del huésped. Por lo tanto, concluimos que los reportes previos de protistas (identificados como microsporidios) descubiertos infectando a Thysanoessa inermis en el Océano Atlántico noroccidental (Bahía de Fundy) y los ciliados endoparásitos no identificados que infectan al krill Antárctico Euphausia superba en el Océano Austral (Bahía Almiralty, Isla King George), Euphausia pacifica en Sanriku, Japón y Euphausia similis var. armata en Tasmania, Australia también son ciliados parasitoides del género Pseudocollinia, pero que esperan ser descritos morfológicamente y genéticamente en el futuro. Esta revisión proporciona evidencia de que los ciliados Pseudocollinia están ampliamente distribuidos en los océanos Pacífico y Atlántico, infectando al menos nueve de las especies de hospederos de krill de regiones zoogeográficas Árticas a Antárticas teniendo una distribución probablemente mundial; como ocurre en varias especies de krill. Estudios futuros deben centrarse en descubrir los ciliados de parasitoides en otras especies de krill y en otros grupos taxonómicos de fitoplancton y zooplancton.
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Gómez-Gutiérrez, Jaime, e So Kawaguchi. "Pseudocollinia HISTOPHAGOUS CILIATES INFECT KRILL IN THE PACIFIC AND ATLANTIC OCEANS AND POSSIBLY WORLDWIDE". CICIMAR Oceánides 32, n. 2 (24 novembre 2017): 15. http://dx.doi.org/10.37543/oceanides.v32i2.204.
Testo completoAbstract (sommario):
The genus Pseudocollinia (Apostomatida, Pseudocolliniidae) currently includes four species (P. beringensis, P. oregonensis, P. brintoni, and P. similis) that infect adults of seven numerically dominant krill species (Order Euphausiacea) in the northeastern Pacific (Bering Sea-to-Gulf of California). In this review, we found four reports in other parts of the world of misidentified or unidentified protists infecting krill. Based on their morphology, cell size and infection of the hemocoel’s host, we infer they are histophagous Pseudocollinia ciliates. We thus conclude that previous reports of protists (identified as microsporidians) infecting Thysanoessa inermis in the northwestern Atlantic Ocean (Bay of Fundy) and unidentified endoparasite ciliates infecting the Euphausia superba in the Southern Ocean (Admiralty Bay, King George Island), Euphausia pacifica in Sanriku, Japan and Euphausia similis var. armata in Tasmania, Australia are actually Pseudocollinia parasitoid ciliates that await to be morphologically and genetically described. This review provides strong evidence that apostome Pseudocollinia ciliates are widespread distributed in the Pacific and Atlantic Oceans, infecting at least nine krill species from Arctic–to–Antarctic zoogeographic regions, having perhaps worldwide distribution as several of their krill hosts. Future studies should focus on discovering parasitoid ciliates in other krill species, as well as in other phytoplankton and zooplankton taxonomic groups.Ciliados histiófagos Pseudocollinia que infectan krill en los oceános Pacífico y Atlántico y posiblemente en el resto del mundoEl género Pseudocollinia (Apostomatida, Pseudocolliniidae) actualmente incluye cuatro especies (P. beringensis, P. oregonensis, P. brintoni y P. similis) que han sido descubiertas infectando especímenes adultos de siete especies de krill (Orden Euphausiacea) numéricamente dominantes en el Pacífico nororiental (del Mar de Bering al Golfo de California). En esta revisión encontramos cuatro publicaciones que indican que estos ciliados se encuentran en otras partes del mundo pero que estos protistas han sido identificados erróneamente o no fueron identificados taxonómicamente. En la presente revisión se infiere que estos protistas son ciliados del género Pseudocollinia debido a que infectan krill, su morfología y tamaño celular, así como su localización de infección en el hemocele del huésped. Por lo tanto, concluimos que los reportes previos de protistas (identificados como microsporidios) descubiertos infectando a Thysanoessa inermis en el Océano Atlántico noroccidental (Bahía de Fundy) y los ciliados endoparásitos no identificados que infectan al krill Antárctico Euphausia superba en el Océano Austral (Bahía Almiralty, Isla King George), Euphausia pacifica en Sanriku, Japón y Euphausia similis var. armata en Tasmania, Australia también son ciliados parasitoides del género Pseudocollinia, pero que esperan ser descritos morfológicamente y genéticamente en el futuro. Esta revisión proporciona evidencia de que los ciliados Pseudocollinia están ampliamente distribuidos en los océanos Pacífico y Atlántico, infectando al menos nueve de las especies de hospederos de krill de regiones zoogeográficas Árticas a Antárticas teniendo una distribución probablemente mundial; como ocurre en varias especies de krill. Estudios futuros deben centrarse en descubrir los ciliados de parasitoides en otras especies de krill y en otros grupos taxonómicos de fitoplancton y zooplancton.
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Hong, G. H., Y. I. Kim, S. H. Lee, L. W. Cooper, S. M. Choe, A. V. Tkalin, T. Lee, S. H. Kim, C. S. Chung e K. Hirose. "Pu and Cs concentrations for zooplankton and nekton in the Northwest Pacific and Antarctic Oceans (1993–1996)". Marine Pollution Bulletin 44, n. 7 (luglio 2002): 660–65. http://dx.doi.org/10.1016/s0025-326x(01)00322-8.
Testo completo
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Quillfeldt, Petra. "Variation in breeding success in Wilson's storm petrels: influence of environmental factors". Antarctic Science 13, n. 4 (dicembre 2001): 400–409. http://dx.doi.org/10.1017/s0954102001000566.
Testo completoAbstract (sommario):
The climatic and sea ice conditions of the Southern Ocean are highly variable within and between years, and a better understanding of the influence of climatic conditions on the various parts of the marine food chain is needed. This paper summarizes data on breeding success of a krill-dependent predator, the Wilson's storm petrel Oceanites oceanicus, in a colony on King George Island, South Shetland Islands, Antarctica, over four breeding seasons from 1995/1996 to 1999/2000. The seasons differed greatly in environmental conditions and in the resulting food availability which was reflected in inter- and intra-annual variations in feeding frequency. The breeding success was consequently variable. Starvation, the main cause of chick mortality in three out of four breeding seasons was associated with reduced sea ice cover in winter, which is known to depress food availability in the following breeding season. Food delivery rates also depended on the prevailing winds, which drive the transport of zooplankton-rich water masses. Snowstorms caused additional chick mortality in two out of four seasons when nest burrows became blocked. Implications for the use of Wilson's storm petrels for monitoring of krill are considered.
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Rembauville, M., S. Blain, L. Armand, B. Quéguiner e I. Salter. "Export fluxes in a naturally iron-fertilized area of the Southern Ocean – Part 2: Importance of diatom resting spores and faecal pellets for export". Biogeosciences 12, n. 11 (2 giugno 2015): 3171–95. http://dx.doi.org/10.5194/bg-12-3171-2015.
Testo completoAbstract (sommario):
Abstract. The biological composition of the material exported to a moored sediment trap located under the winter mixed layer of the naturally fertilized Kerguelen Plateau in the Southern Ocean was studied over an annual cycle. Despite iron availability in spring, the annual particulate organic carbon (POC) export (98.2 mmol m−2) at 289 m was low, but annual biogenic silica export was significant (114 mmol m−2). This feature was related to the abundance of empty diatom cells and the ratio of full to empty cells exerted a first-order control in BSi : POC export stoichiometry of the biological pump. Chaetoceros Hyalochaete spp. and Thalassiosira antarctica resting spores were responsible for more than 60% of the annual POC flux that occurred during two very short export events of < 14 days in spring–summer. Relatively low diatom fluxes were observed over the remainder of the year. Faecal pellet contribution to annual carbon flux was lower (34%) and reached its seasonal maximum in autumn and winter (> 80%). The seasonal progression of faecal pellet types revealed a clear transition from small spherical shapes (small copepods) in spring, to larger cylindrical and ellipsoid shapes in summer (euphausiids and large copepods) and finally to large tabular shapes (salps) in autumn and winter. We propose in this high-biomass, low-export (HBLE) environment that small but highly silicified and fast-sinking resting spores are able to bypass the intense grazing pressure and efficient carbon transfer to higher trophic levels that are responsible for the low fluxes observed the during the remainder of the year. More generally our study also provides a statistical framework linking the ecological succession of diatom and zooplankton communities to the seasonality of carbon and silicon export within an iron-fertilized bloom region in the Southern Ocean.
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Rembauville, M., S. Blain, L. Armand, B. Quéguiner e I. Salter. "Export fluxes in a naturally fertilized area of the Southern Ocean, the Kerguelen Plateau: ecological vectors of carbon and biogenic silica to depth (Part 2)". Biogeosciences Discussions 11, n. 12 (10 dicembre 2014): 17089–150. http://dx.doi.org/10.5194/bgd-11-17089-2014.
Testo completoAbstract (sommario):
Abstract. The chemical (particulate organic carbon and nitrogen, biogenic silica) and biological (diatoms and faecal pellets) composition of the material exported to a moored sediment trap located under the winter mixed layer of the naturally-fertilized Kerguelen Plateau in the Southern Ocean was studied over an annual cycle. Despite iron availability in spring, the annual particulate organic carbon (POC) export (98.2 mmol m−2) at 289 m was low but annual biogenic silica export was significant (114 mmol m−2). This feature was related to the abundance of empty diatom frustules and the ratio of full : empty cell exerted a first order control in BSi : POC export stoichiometry of biological pump. Chaetoceros Hyalochaete spp. and Thalassiosira antarctica resting spores were found to be responsible for more than 60% of the annual POC that occurred during two very short export events (<14 days in spring-summer) representing the majority of captured export. Low diatom fluxes were observed over the remainder of the year. Faecal pellet contribution to annual carbon flux was low (34%) and reached it's seasonal maximum in autumn and winter (>80%). The seasonal progression of faecal pellet types revealed a clear transition from small spherical shapes (small copepods) in spring, larger cylindrical and ellipsoid shapes in summer (euphausiids and large copepods) and finally large tabular shapes (salps) in autumn and winter. We propose that in this High Biomass, Low Export (HBLE) environment, small, highly silicified, fast-sinking resting spores are able to bypass the high grazing pressure and efficient carbon transfer to higher trophic levels that are responsible for the low fluxes observed the during the remainder of the year. Our study also provides a statistical framework linking the ecological succession of diatom and zooplankton communities to the seasonality of carbon and silicon export within an iron-fertilized bloom region in the Southern Ocean.
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Hartman, Julian D., Peter K. Bijl e Francesca Sangiorgi. "A review of the ecological affinities of marine organic microfossils from a Holocene record offshore of Adélie Land (East Antarctica)". Journal of Micropalaeontology 37, n. 2 (11 ottobre 2018): 445–97. http://dx.doi.org/10.5194/jm-37-445-2018.
Testo completoAbstract (sommario):
Abstract. Integrated Ocean Drilling Program (IODP) Expedition 318 recovered a ∼ 170 m long Holocene organic-rich sedimentary sequence at Site U1357. Located within the narrow but deep Adélie Basin close to the Antarctic margin, the site accumulated sediments at exceptionally high sedimentation rates, which resulted in extraordinary preservation of the organic sedimentary component. Here, we present an overview of 74 different mainly marine microfossil taxa and/or types found within the organic component of the sediment, which include the remains of unicellular and higher organisms from three eukaryotic kingdoms (Chromista, Plantae, and Animalia). These remains include phytoplanktonic (phototrophic dinoflagellates and prasinophytes) and very diverse zooplanktonic (heterotrophic dinoflagellates, tintinnids, copepods) organisms. We illustrate each marine microfossil taxon or type identified by providing morphological details and photographic images, which will help with their identification in future studies. We also review their ecological preferences to aid future (palaeo)ecological and (palaeo)environmental studies. The planktonic assemblage shows a high degree of endemism related to the strong influence of the sea-ice system over Site U1357. In addition, we found the remains of various species of detritus feeders and bottom-dwelling scavengers (benthic foraminifers and annelid worms) indicative of high export productivity at Site U1357. This study shows the potential of organic microfossil remains for reconstructing past environmental conditions, such as sea-ice cover and (export) productivity.
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Walsh, Jennifer, e Christian Reiss. "Lipid content and stable isotopes of zooplankton during five winters around the northern Antarctic Peninsula". Scientific Data 7, n. 1 (11 novembre 2020). http://dx.doi.org/10.1038/s41597-020-00722-9.
Testo completoAbstract (sommario):
Abstract The Southern Ocean zooplankton community is diverse, yet most species are understudied, especially with respect to their overwinter feeding ecologies. Here we present body condition and trophic biomarker data (lipid content and stable isotopes of carbon and nitrogen) from 19 zooplankton species collected over five consecutive winters (August and September 2012–2016) around the northern Antarctic Peninsula. We report environmental data (percent sea-ice cover, sea-ice type, water temperature, salinity, and integrated chl-a) as well as species abundance data at each sampling location to provide additional context for interpreting the lipid and stable isotope data. For most species, these are the first winter measurements or time series of body condition, trophic position, and abundance in relation to environmental variables. These data are critical for evaluating changes in ecosystem structure and predator-prey relationships in a region of Antarctica that is warming faster than most other areas on Earth as a result of climate change.
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Mekkes, Lisette, Guadalupe Sepúlveda-Rodríguez, Gintarė Bielkinaitė, Deborah Wall-Palmer, Geert-Jan A. Brummer, Linda K. Dämmer, Jef Huisman, Emiel van Loon, Willem Renema e Katja T. C. A. Peijnenburg. "Effects of Ocean Acidification on Calcification of the Sub-Antarctic Pteropod Limacina retroversa". Frontiers in Marine Science 8 (2 marzo 2021). http://dx.doi.org/10.3389/fmars.2021.581432.
Testo completoAbstract (sommario):
Ocean acidification is expected to impact the high latitude oceans first, as CO2 dissolves more easily in colder waters. At the current rate of anthropogenic CO2 emissions, the sub-Antarctic Zone will start to experience undersaturated conditions with respect to aragonite within the next few decades, which will affect marine calcifying organisms. Shelled pteropods, a group of calcifying zooplankton, are considered to be especially sensitive to changes in carbonate chemistry because of their thin aragonite shells. Limacina retroversa is the most abundant pteropod in sub-Antarctic waters, and plays an important role in the carbonate pump. However, not much is known about its response to ocean acidification. In this study, we investigated differences in calcification between L. retroversa individuals exposed to ocean carbonate chemistry conditions of the past (pH 8.19; mid-1880s), present (pH 8.06), and near-future (pH 7.93; predicted for 2050) in the sub-Antarctic. After 3 days of exposure, calcification responses were quantified by calcein staining, shell weighing, and Micro-CT scanning. In pteropods exposed to past conditions, calcification occurred over the entire shell and the leading edge of the last whorl, whilst individuals incubated under present and near-future conditions mostly invested in extending their shells, rather than calcifying over their entire shell. Moreover, individuals exposed to past conditions formed larger shell volumes compared to present and future conditions, suggesting that calcification is already decreased in today’s sub-Antarctic waters. Shells of individuals incubated under near-future conditions did not increase in shell weight during the incubation, and had a lower density compared to past and present conditions, suggesting that calcification will be further compromised in the future. This demonstrates the high sensitivity of L. retroversa to relatively small and short-term changes in carbonate chemistry. A reduction in calcification of L. retroversa in the rapidly acidifying waters of the sub-Antarctic will have a major impact on aragonite-CaCO3 export from oceanic surface waters to the deep sea.
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"Antarctic marine primary production, biogeochemical carbon cycles and climatic change". Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 338, n. 1285 (30 novembre 1992): 289–97. http://dx.doi.org/10.1098/rstb.1992.0149.
Testo completoAbstract (sommario):
In the Southern Ocean, inorganic macronutrients are very rarely depleted by phytoplankton growth. This has led to speculation on possible additional CO 2 drawdown in this region. However, the effects of climate change can only be predicted once the role of environmental and biotic factors limiting phytoplankton carbon fixation are understood. It is clear that the Southern Ocean is heterogeneous, and no single factor controls prim ary production overall. Ice cover and vertical mixing influence algal growth rates by m odulating radiance flux. Micronutrients, especially iron, may limit growth in some areas. Primary production is also suppressed by high removal rates of algal biomass. Grazing by zooplankton is the major factor determining magnitude and quality of vertical particle flux. Several of the physical controls on phytoplankton production are sensitive to climate change. Although it is impossible to make numerical predictions of future change on the basis of our present knowledge, qualitative assessments can be put forward on the basis of model predictions of climate change and known factors controlling prim ary production. Changes in water temperature and in windinduced mixing are likely to be slight and have little effect. Model predictions of changes in sea-ice cover vary widely, making prediction of biogeochemical effects impossible. Even if climatic change induces increased nutrient uptake, there are several reasons to suspect that carbon sequestration will be ineffective in comparison with continuing anthropogenic CO 2 emission.
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Reiss, Christian S., Anthony M. Cossio, Jennifer Walsh, George R. Cutter e George M. Watters. "Glider-Based Estimates of Meso-Zooplankton Biomass Density: A Fisheries Case Study on Antarctic Krill (Euphausia superba) Around the Northern Antarctic Peninsula". Frontiers in Marine Science 8 (25 marzo 2021). http://dx.doi.org/10.3389/fmars.2021.604043.
Testo completoAbstract (sommario):
We compare estimates of krill density derived from gliders to those from contemporaneous and previous ship-based surveys. Our comparisons cover several temporal and spatial scales within two strata around the northern Antarctic Peninsula (off Cape Shirreff on the north side of Livingston Island and in the Bransfield Strait). Our objective is to explore the feasibility of using gliders to supplement or replace vessel-based surveys of fishery resources. We deployed two long-duration Slocum G3 gliders manufactured by Teledyne Webb Research (TWR), each equipped with a suite of oceanographic sensors and a three-frequency (38, 67.5, and 125 kHz, each single-beam) Acoustic Zooplankton Fish Profiler. We used the acoustic data collected by these gliders to estimate biomass densities (g⋅m–2) of Antarctic krill (Euphausia superba). The two gliders were, respectively, deployed for 82 and 88 days from mid-December 2018 through mid-March 2019. Off Cape Shirreff, glider-based densities estimated from two repeat small-scale surveys during mid-December and January were 110.6 and 55.7 g⋅m–2, respectively. In Bransfield Strait, the glider-based estimate of biomass density was 106.7 g⋅m–2 during December–January. Contemporaneous ship-based estimates of biomass density, from a multi-ship broad-scale krill survey (Macaulay et al., 2019) restricted to the areas sampled by the gliders, were 84.6 g⋅m–2 off Cape Shirreff and 79.7 g⋅m–2 in Bransfield Strait during January. We compared two alternative krill-delineation algorithms (dB differencing and SHAPES); differences between biomass densities estimated by applying these algorithms were small and ranged between 4 and 7%. Alternative methods of sampling krill length-frequency distributions (LFDs) (nets or predator diets), which are required to convert acoustic energy to biomass density, also influenced the glider-based results. In Bransfield Strait, net-based estimates of biomass density were 6% less than those based on predator diets. Off Cape Shirreff the biomass density of krill estimated from a net-based LFD was 20% greater than that based on predator diets. Development of a variance estimator for glider-based biomass surveys is ongoing, but our results demonstrate that fisheries surveys using acoustically-equipped gliders are feasible, can provide density estimates to inform management, and may be conducted at lower cost than ship surveys in some cases.
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Verhaegen, Gerlien, Emiliano Cimoli e Dhugal Lindsay. "Life beneath the ice: jellyfish and ctenophores from the Ross Sea, Antarctica, with an image-based training set for machine learning". Biodiversity Data Journal 9 (13 agosto 2021). http://dx.doi.org/10.3897/bdj.9.e69374.
Testo completoAbstract (sommario):
Southern Ocean ecosystems are currently experiencing increased environmental changes and anthropogenic pressures, urging scientists to report on their biodiversity and biogeography. Two major taxonomically diverse and trophically important gelatinous zooplankton groups that have, however, stayed largely understudied until now are the cnidarian jellyfish and ctenophores. This data scarcity is predominantly due to many of these fragile, soft-bodied organisms being easily fragmented and/or destroyed with traditional net sampling methods. Progress in alternative survey methods including, for instance, optics-based methods is slowly starting to overcome these obstacles. As video annotation by human observers is both time-consuming and financially costly, machine-learning techniques should be developed for the analysis of in situ /in aqua image-based datasets. This requires taxonomically accurate training sets for correct species identification and the present paper is the first to provide such data. In this study, we twice conducted three week-long in situ optics-based surveys of jellyfish and ctenophores found under the ice in the McMurdo Sound, Antarctica. Our study constitutes the first optics-based survey of gelatinous zooplankton in the Ross Sea and the first study to use in situ / in aqua observations to describe taxonomic and some trophic and behavioural characteristics of gelatinous zooplankton from the Southern Ocean. Despite the small geographic and temporal scales of our study, we provided new undescribed morphological traits for all observed gelatinous zooplankton species (eight cnidarian and four ctenophore species). Three ctenophores and one leptomedusa likely represent undescribed species. Furthermore, along with the photography and videography, we prepared a Common Objects in Context (COCO) dataset, so that this study is the first to provide a taxonomist-ratified image training set for future machine-learning algorithm development concerning Southern Ocean gelatinous zooplankton species.