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1
Bringedal, Carina, Tor Eldevik, Øystein Skagseth, Michael A. Spall, and Svein Østerhus. "Structure and Forcing of Observed Exchanges across the Greenland–Scotland Ridge." Journal of Climate 31, no. 24 (December 2018): 9881–901. http://dx.doi.org/10.1175/jcli-d-17-0889.1.
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The Atlantic meridional overturning circulation and associated poleward heat transport are balanced by northern heat loss to the atmosphere and corresponding water-mass transformation. The circulation of northward-flowing Atlantic Water at the surface and returning overflow water at depth is particularly manifested—and observed—at the Greenland–Scotland Ridge where the water masses are guided through narrow straits. There is, however, a rich variability in the exchange of water masses across the ridge on all time scales. Focusing on seasonal and interannual time scales, and particularly the gateways of the Denmark Strait and between the Faroe Islands and Shetland, we specifically assess to what extent the exchanges of water masses across the Greenland–Scotland Ridge relate to wind forcing. On seasonal time scales, the variance explained of the observed exchanges can largely be related to large-scale wind patterns, and a conceptual model shows how this wind forcing can manifest via a barotropic, cyclonic circulation. On interannual time scales, the wind stress impact is less direct as baroclinic mechanisms gain importance and observations indicate a shift in the overflows from being more barotropically to more baroclinically forced during the observation period. Overall, the observed Greenland–Scotland Ridge exchanges reflect a horizontal (cyclonic) circulation on seasonal time scales, while the interannual variability more represents an overturning circulation.
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Beaird, Nicholas, Ilker Fer, Peter Rhines, and Charles Eriksen. "Dissipation of Turbulent Kinetic Energy Inferred from Seagliders: An Application to the Eastern Nordic Seas Overflows." Journal of Physical Oceanography 42, no. 12 (December 1, 2012): 2268–82. http://dx.doi.org/10.1175/jpo-d-12-094.1.
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Abstract Turbulent mixing is an important process controlling the descent rate, water mass modification, and volume transport augmentation due to entrainment in the dense overflows across the Greenland–Scotland Ridge. These overflows, along with entrained Atlantic waters, form a major portion of the North Atlantic Deep Water, which pervades the abyssal ocean. Three years of Seaglider observations of the overflows across the eastern Greenland–Scotland Ridge are leveraged to map the distribution of dissipation of turbulent kinetic energy on the Iceland–Faroe Ridge. A method has been applied using the finescale vertical velocity and density measurements from the glider to infer dissipation. The method, termed the large-eddy method (LEM), is compared with a microstructure survey of the Faroe Bank Channel (FBC). The LEM reproduces the patterns of dissipation observed in the microstructure survey, which vary over several orders of magnitude. Agreement between the inferred LEM and more direct microstructure measurements is within a factor of 2. Application to the 9432 dives that encountered overflow waters on the Iceland–Faroe Ridge reveals three regions of enhanced dissipation: one downstream of the primary FBC sill, another downstream of the secondary FBC sill, and a final region in a narrow jet of overflow along the Iceland shelf break.
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Uenzelmann-Neben, Gabriele, and Jens Gruetzner. "Chronology of Greenland Scotland Ridge overflow: What do we really know?" Marine Geology 406 (December 2018): 109–18. http://dx.doi.org/10.1016/j.margeo.2018.09.008.
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Biastoch, Arne, Rolf H. Käse, and Detlef B. Stammer. "The Sensitivity of the Greenland–Scotland Ridge Overflow to Forcing Changes." Journal of Physical Oceanography 33, no. 11 (November 2003): 2307–19. http://dx.doi.org/10.1175/1520-0485(2003)033<2307:tsotgr>2.0.co;2.
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Olsen, Steffen M., Bogi Hansen, Detlef Quadfasel, and Svein Østerhus. "Observed and modelled stability of overflow across the Greenland–Scotland ridge." Nature 455, no. 7212 (September 2008): 519–22. http://dx.doi.org/10.1038/nature07302.
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Rheinlænder, Jonathan W., David Ferreira, and Kerim H. Nisancioglu. "Topological Constraints by the Greenland–Scotland Ridge on AMOC and Climate." Journal of Climate 33, no. 13 (July 1, 2020): 5393–411. http://dx.doi.org/10.1175/jcli-d-19-0726.1.
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AbstractChanges in the geometry of ocean basins have been influential in driving climate change throughout Earth’s history. Here, we focus on the emergence of the Greenland–Scotland Ridge (GSR) and its influence on the ocean state, including large-scale circulation, heat transport, water mass properties, and global climate. Using a coupled atmosphere–ocean–sea ice model, we consider the impact of introducing the GSR in an idealized Earth-like geometry, comprising a narrow Atlantic-like basin and a wide Pacific-like basin. Without the GSR, deep-water formation occurs near the North Pole in the Atlantic basin, associated with a deep meridional overturning circulation (MOC). By introducing the GSR, the volume transport across the sill decreases by 64% and deep convection shifts south of the GSR, dramatically altering the structure of the high-latitude MOC. Due to compensation by the subpolar gyre, the northward ocean heat transport across the GSR only decreases by ~30%. As in the modern Atlantic Ocean, a bidirectional circulation regime is established with warm Atlantic water inflow and a cold dense overflow across the GSR. In sharp contrast to the large changes north of the GSR, the strength of the Atlantic MOC south of the GSR is unaffected. Outside the high latitudes of the Atlantic basin, the surface climate response is surprisingly small, suggesting that the GSR has little impact on global climate. Our results suggest that caution is required when interpreting paleoproxy and ocean records, which may record large local changes, as indicators of basin-scale changes in the overturning circulation and global climate.
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Olsen, Steffen Malskcer, B. Hansen, D. Quadfasel, and S. Østerhus. "Stability of the overflow across the Greenland-Scotland Ridge since 1948." IOP Conference Series: Earth and Environmental Science 6, no. 3 (January 1, 2009): 032017. http://dx.doi.org/10.1088/1755-1307/6/3/032017.
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Poore, H. R., R. Samworth, N. J. White, S. M. Jones, and I. N. McCave. "Neogene overflow of Northern Component Water at the Greenland-Scotland Ridge." Geochemistry, Geophysics, Geosystems 7, no. 6 (June 2006): n/a. http://dx.doi.org/10.1029/2005gc001085.
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Jensen, Mari F., Kerim H. Nisancioglu, and Michael A. Spall. "Large Changes in Sea Ice Triggered by Small Changes in Atlantic Water Temperature." Journal of Climate 31, no. 12 (June 2018): 4847–63. http://dx.doi.org/10.1175/jcli-d-17-0802.1.
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The sensitivity of sea ice to the temperature of inflowing Atlantic water across the Greenland–Scotland Ridge is investigated using an eddy-resolving configuration of the Massachusetts Institute of Technology General Circulation Model with idealized topography. During the last glacial period, when climate on Greenland is known to have been extremely unstable, sea ice is thought to have covered the Nordic seas. The dramatic excursions in climate during this period, seen as large abrupt warming events on Greenland and known as Dansgaard–Oeschger (DO) events, are proposed to have been caused by a rapid retreat of Nordic seas sea ice. Here, we show that a full sea ice cover and Arctic-like stratification can exist in the Nordic seas given a sufficiently cold Atlantic inflow and corresponding low transport of heat across the Greenland–Scotland Ridge. Once sea ice is established, continued sea ice formation and melt efficiently freshens the surface ocean and makes the deeper layers more saline. This creates a strong salinity stratification in the Nordic seas, similar to today’s Arctic Ocean, with a cold fresh surface layer protecting the overlying sea ice from the warm Atlantic water below. There is a nonlinear response in Nordic seas sea ice to Atlantic water temperature with simulated large abrupt changes in sea ice given small changes in inflowing temperature. This suggests that the DO events were more likely to have occurred during periods of reduced warm Atlantic water inflow to the Nordic seas.
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Wright, James D., and Kenneth G. Miller. "Control of North Atlantic Deep Water Circulation by the Greenland-Scotland Ridge." Paleoceanography 11, no. 2 (April 1996): 157–70. http://dx.doi.org/10.1029/95pa03696.
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Geoffroy, L., F. Bergerat, and J. Angelier. "Tectonic evolution of the Greenland-Scotland ridge during the Paleogene: New constraints." Geology 22, no. 7 (1994): 653. http://dx.doi.org/10.1130/0091-7613(1994)022<0653:teotgs>2.3.co;2.
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Kearey, P. "Structure and development of the Greenland-Scotland Ridge, new methods and concepts." Palaeogeography, Palaeoclimatology, Palaeoecology 52, no. 1-2 (November 1985): 174–75. http://dx.doi.org/10.1016/0031-0182(85)90046-x.
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Currie, K. L. "Structure and development of the Greenland—Scotland Ridge — New methods and concepts." Marine Geology 65, no. 3-4 (June 1985): 357–58. http://dx.doi.org/10.1016/0025-3227(85)90069-6.
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Cook, F. A. "Structure and development of the Greenland-Scotland Ridge, new methods and concepts." Earth-Science Reviews 22, no. 3 (November 1985): 239–40. http://dx.doi.org/10.1016/0012-8252(85)90061-3.
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Mu, Lin, Jun Song, LinHao Zhong, LanNing Wang, Huan Li, and Yan Li. "Mechanism of the Greenland-Scotland Ridge overflow variation under different atmospheric CO2 scenarios." Chinese Science Bulletin 56, no. 24 (August 2011): 2635–43. http://dx.doi.org/10.1007/s11434-011-4601-1.
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Thorpe, R. B., R. A. Wood, and J. F. B. Mitchell. "Sensitivity of the modelled thermohaline circulation to the parameterisation of mixing across the Greenland–Scotland ridge." Ocean Modelling 7, no. 3-4 (January 2004): 259–68. http://dx.doi.org/10.1016/s1463-5003(03)00043-x.
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Rossby, T., C. Flagg, Leon Chafik, Ben Harden, and Henrik Søiland. "A Direct Estimate of Volume, Heat, and Freshwater Exchange Across the Greenland‐Iceland‐Faroe‐Scotland Ridge." Journal of Geophysical Research: Oceans 123, no. 10 (October 2018): 7139–53. http://dx.doi.org/10.1029/2018jc014250.
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Baldreel, L. O., and M. S. Andersen. "Tertiary development of the Faeroe-Rockall Plateau based on reflection seismic data." Bulletin of the Geological Society of Denmark 41 (November 30, 1994): 162–80. http://dx.doi.org/10.37570/bgsd-1995-41-15.
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The Faeroe-Rockall Plateau is located in the NE Atlantic Ocean between Iceland and Scotland and is characterized by a late Paleocene-early Eocene basalt cover, which was extruded in association with the incipient opening of the NE Atlantic. The Faeroe-Rockall Plateau is separated from the NW European continental shelf by the Rockall Trough and the FaeroeShetland Channel, whose nature and age is still debated. Reflector configuration within the basalt allows volcanic seismic facies inteipretation to be carried out. The thickness of the basalt cover is estimated from reflection seismic data. Subbasalt geological structures are identified below subaerially extruded basalt on recently acquired as well as reprocessed seismic profiles. Overlying the basalt are early Eocene and younger Sediments. The distribution of these sedi- . ments is largely controlled by 1) the topography after the cessation of the volcanism, 2) the post volcanic subsidence of the area which is estimated from the depth to the breakpoints located on prim¥)' volcanic escaipments, 3) the Eocene-Miocene compressional tectonics which formed ridge& and minor basins, and 4) bottom currents of Norwegian Sea Deep Water (NSDW) which in the Neogene flowed into the North Atlantic south of the Greenland-Iceland-Faeroe-Scotland Ridg,e. A considerable part of the NSDW flows east and south of th
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Hansen, Bogi, Karin Margretha Húsgarð Larsen, Hjálmar Hátún, and Svein Østerhus. "A stable Faroe Bank Channel overflow 1995–2015." Ocean Science 12, no. 6 (November 17, 2016): 1205–20. http://dx.doi.org/10.5194/os-12-1205-2016.
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Abstract. The Faroe Bank Channel (FBC) is the deepest passage across the Greenland–Scotland Ridge (GSR) and there is a continuous deep flow of cold and dense water passing through it from the Arctic Mediterranean into the North Atlantic and further to the rest of the world ocean. This FBC overflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which has recently been suggested to have weakened. From November 1995 to May 2015, the FBC overflow has been monitored by a continuous ADCP (acoustic Doppler current profiler) mooring, which has been deployed in the middle of this narrow channel. Combined with regular hydrography cruises and several short-term mooring experiments, this allowed us to construct time series of volume transport and to follow changes in the hydrographic properties and density of the FBC overflow. The mean kinematic overflow, derived solely from the velocity field, was found to be (2.2 ± 0.2) Sv (1 Sv = 106 m3 s−1) with a slight, but not statistically significant, positive trend. The coldest part, and probably the bulk, of the FBC overflow warmed by a bit more than 0.1 °C, especially after 2002, increasing the transport of heat into the deep ocean. This warming was, however, accompanied by increasing salinities, which seem to have compensated for the temperature-induced density decrease. Thus, the FBC overflow has remained stable in volume transport as well as density during the 2 decades from 1995 to 2015. After crossing the GSR, the overflow is modified by mixing and entrainment, but the associated change in volume (and heat) transport is still not well known. Whatever effect this has on the AMOC and the global energy balance, our observed stability of the FBC overflow is consistent with reported observations from the other main overflow branch, the Denmark Strait overflow, and the three Atlantic inflow branches to the Arctic Mediterranean that feed the overflows. If the AMOC has weakened during the last 2 decades, it is not likely to have been due to its northernmost extension – the exchanges across the Greenland–Scotland Ridge.
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Zhang, Jinlun, Michael Steele, D. Andrew Rothrock, and Ronald W. Lindsay. "Increasing exchanges at Greenland-Scotland Ridge and their links with the North Atlantic Oscillation and Arctic Sea Ice." Geophysical Research Letters 31, no. 9 (May 6, 2004): n/a. http://dx.doi.org/10.1029/2003gl019304.
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Köhl, Armin, and Detlef Stammer. "Optimal Observations for Variational Data Assimilation." Journal of Physical Oceanography 34, no. 3 (March 1, 2004): 529–42. http://dx.doi.org/10.1175/2513.1.
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Abstract An important part of ocean state estimation is the design of an observing system that allows for the efficient study of climate related questions in the ocean. A solution to the design problem is presented here in terms of optimal observations that emerge as singular vectors of the modified data resolution matrix. The actual computation is feasible only for scalar quantities and in the limit of large observational errors. Identical twin experiments performed in the framework of a 1° North Atlantic primitive equation model demonstrate that such optimal observations, when applied to determining the heat transport across the Greenland–Scotland ridge, perform significantly better than traditional section data. On seasonal to interannual time scales, optimal observations are located primarily along the continental shelf and information about heat transport, wind stress, and stratification is being communicated through boundary waves and advective processes. On time scales of about 1 month, sea surface height observations appear to be more efficient in reconstructing the cross-ridge heat transport than hydrographic observations. Optimal observations also provide a tool for understanding changes of ocean state associated with anomalies of integral quantities such as meridional heat transport.
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Mauritzen, Cecilie. "Production of dense overflow waters feeding the North Atlantic across the Greenland-Scotland Ridge. Part 2: An inverse model." Deep Sea Research Part I: Oceanographic Research Papers 43, no. 6 (June 1996): 807–35. http://dx.doi.org/10.1016/0967-0637(96)00038-6.
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Lundrigan, S., and E. Demirov. "Mean and Eddy‐Driven Heat Advection in the Ocean Region Adjacent to the Greenland‐Scotland Ridge Derived From Satellite Altimetry." Journal of Geophysical Research: Oceans 124, no. 3 (March 2019): 2239–60. http://dx.doi.org/10.1029/2018jc014854.
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Schnurr, Sarah, and Marina V. Malyutina. "Two New Species of The Genus Eurycope (Isopoda, Munnopsidae) from Icelandic Waters." Polish Polar Research 35, no. 2 (July 29, 2014): 361–88. http://dx.doi.org/10.2478/popore-2014-0013.
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AbstractCollections of munnopsid isopods of the BIOICE (Benthic Invertebrates of Icelandic Waters; 1991–2004) and the IceAGE1 (Icelandic Marine Animals: Genetics and Ecology; since 2011) expeditions included ten species of the genusEurycopeG.O. Sars, 1864, thereof are two species new to science. Thus, the descriptions of the two new species are presented herein.Eurycope elianaesp. n. is distinguished from the other species of the genus mainly by two long, slightly robust, simple setae on the tip of the rostrum in combination with the size and shape of the rostrum itself.E elianaesp. n. shares the presence of two long, slightly robust, simple seta on the tip of the rostrum withE. tumidicarpus. The shape of the rostrum itself is more similar toE. inermisand species of theE. complanatacomplex.E. aculeatasp. n. is characterized by possessing dorsomedial acute projections on pereo-nites 5–7, which is unusual for the genus.E. aculeatasp. n. is most similar toE. cornuta. Both new species are, so far, known only from localities south of the Greenland-Scotland Ridge.
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Hansen, B., H. Hátún, R. Kristiansen, S. M. Olsen, and S. Østerhus. "Stability and forcing of the Iceland-Faroe inflow of water, heat, and salt to the Arctic." Ocean Science Discussions 7, no. 4 (July 9, 2010): 1245–87. http://dx.doi.org/10.5194/osd-7-1245-2010.
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Abstract. The flow of Atlantic water across the Greenland-Scotland Ridge (Atlantic inflow) is critical for conditions in the Nordic Seas and Arctic Ocean by importing heat and salt. Here, we present a decade-long series of measurements from the Iceland-Faroe inflow branch (IF-inflow), which carries almost half the total Atlantic inflow. The observations show no significant trend in volume transport of Atlantic water, but temperature and salinity increased during the observational period. On shorter time scales, the observations show considerable variations but no statistically significant seasonal variation is observed and even weekly averaged transport values were consistently uni-directional from the Atlantic into the Nordic Seas. Combining transport time-series with sea level height from satellite altimetry and wind stress reveals that the force driving the IF-inflow across the topographic barrier of the Ridge is mainly generated by a pressure gradient that is due to a continuously maintained low sea level in the Southern Nordic Seas. This links the IF-inflow to the estuarine and thermohaline processes that generate outflow from the Nordic Seas and lower its sea level. The IF-inflow is an important component of the system coupling the Arctic region to the North Atlantic through the thermohaline circulation, which has been predicted to weaken in the 21st century. Our observations show no indication of weakening, as yet.
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Darelius, Elin, Ilker Fer, and Detlef Quadfasel. "Faroe Bank Channel Overflow: Mesoscale Variability*." Journal of Physical Oceanography 41, no. 11 (November 1, 2011): 2137–54. http://dx.doi.org/10.1175/jpo-d-11-035.1.
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Abstract The Faroe Bank Channel is the deepest connection through the Greenland–Scotland Ridge, where dense water formed north of the ridge flows southward over the sill crest, contributing to the formation of North Atlantic Deep Water. The overflow region is characterized by high mesoscale variability and energetic oscillations, accompanied by a high degree of sea surface level variability. Here, 2-month-long time series of velocity and temperature from 12 moorings deployed in May 2008 are analyzed to describe the oscillations and explore their generation and propagation. The observed 2.5–5-day oscillations in velocity and temperature are highly coherent both horizontally and vertically, and they are associated with 100–200-m-thick boluses of cold plume water flowing along the slope. A positive correlation between temperature and relative vorticity and the distribution of clockwise/counterclockwise rotation across the slope suggest a train of alternating warm cyclonic and cold anticyclonic eddies, where the maximum plume thickness is located downslope of the eddy center. The along-slope phase velocity is found to be 25–60 cm s−1, corresponding to a wavelength of 75–180 km, while the vertical phase propagation is downward. The oscillations are present already in the sill region. The observations do not match predictions for eddies generated either by vortex stretching or baroclinic instability but agree broadly with properties of topographic Rossby waves.
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Østerhus, Svein, Rebecca Woodgate, Héðinn Valdimarsson, Bill Turrell, Laura de Steur, Detlef Quadfasel, Steffen M. Olsen, et al. "Arctic Mediterranean exchanges: a consistent volume budget and trends in transports from two decades of observations." Ocean Science 15, no. 2 (April 12, 2019): 379–99. http://dx.doi.org/10.5194/os-15-379-2019.
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Abstract. The Arctic Mediterranean (AM) is the collective name for the Arctic Ocean, the Nordic Seas, and their adjacent shelf seas. Water enters into this region through the Bering Strait (Pacific inflow) and through the passages across the Greenland–Scotland Ridge (Atlantic inflow) and is modified within the AM. The modified waters leave the AM in several flow branches which are grouped into two different categories: (1) overflow of dense water through the deep passages across the Greenland–Scotland Ridge, and (2) outflow of light water – here termed surface outflow – on both sides of Greenland. These exchanges transport heat and salt into and out of the AM and are important for conditions in the AM. They are also part of the global ocean circulation and climate system. Attempts to quantify the transports by various methods have been made for many years, but only recently the observational coverage has become sufficiently complete to allow an integrated assessment of the AM exchanges based solely on observations. In this study, we focus on the transport of water and have collected data on volume transport for as many AM-exchange branches as possible between 1993 and 2015. The total AM import (oceanic inflows plus freshwater) is found to be 9.1 Sv (sverdrup, 1 Sv =106 m3 s−1) with an estimated uncertainty of 0.7 Sv and has the amplitude of the seasonal variation close to 1 Sv and maximum import in October. Roughly one-third of the imported water leaves the AM as surface outflow with the remaining two-thirds leaving as overflow. The overflow water is mainly produced from modified Atlantic inflow and around 70 % of the total Atlantic inflow is converted into overflow, indicating a strong coupling between these two exchanges. The surface outflow is fed from the Pacific inflow and freshwater (runoff and precipitation), but is still approximately two-thirds of modified Atlantic water. For the inflow branches and the two main overflow branches (Denmark Strait and Faroe Bank Channel), systematic monitoring of volume transport has been established since the mid-1990s, and this enables us to estimate trends for the AM exchanges as a whole. At the 95 % confidence level, only the inflow of Pacific water through the Bering Strait showed a statistically significant trend, which was positive. Both the total AM inflow and the combined transport of the two main overflow branches also showed trends consistent with strengthening, but they were not statistically significant. They do suggest, however, that any significant weakening of these flows during the last two decades is unlikely and the overall message is that the AM exchanges remained remarkably stable in the period from the mid-1990s to the mid-2010s. The overflows are the densest source water for the deep limb of the North Atlantic part of the meridional overturning circulation (AMOC), and this conclusion argues that the reported weakening of the AMOC was not due to overflow weakening or reduced overturning in the AM. Although the combined data set has made it possible to establish a consistent budget for the AM exchanges, the observational coverage for some of the branches is limited, which introduces considerable uncertainty. This lack of coverage is especially extreme for the surface outflow through the Denmark Strait, the overflow across the Iceland–Faroe Ridge, and the inflow over the Scottish shelf. We recommend that more effort is put into observing these flows as well as maintaining the monitoring systems established for the other exchange branches.
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Prange, M. "The low-resolution CCSM2 revisited: new adjustments and a present-day control run." Ocean Science Discussions 3, no. 4 (August 18, 2006): 1293–348. http://dx.doi.org/10.5194/osd-3-1293-2006.
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Abstract. The low-resolution (T31) version of the Community Climate System Model CCSM2.0.1 is revisited and adjusted by deepening the Greenland-Scotland ridge, changing oceanic mixing parameters, and applying a regional freshwater flux adjustment at high northern latitudes. The main purpose of these adjustments is to maintain a robust Atlantic meridional overturning circulation which collapses in the original model release. The paper describes the present-day control run of the adjusted model which is brought into climatic equilibrium by applying a deep-ocean acceleration technique. The accelerated integration is extended by a 100-year synchronous phase. The simulated meridional overturning circulation has a maximum of 14×106 m3 s−1 in the North Atlantic. Most shortcomings found in the control run are identified as "typical problems" in global climate modelling. Given its good simulation skills and its relatively low resource demands, the adjusted low-resolution version of CCSM2.0.1 appears to be a reasonable alternative to the latest low-resolution Community Climate System Model release (CCSM3.0) if runtime is a critical factor.
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Maze, G., H. Mercier, V. Thierry, L. Memery, P. Morin, and F. F. Perez. "Mass, nutrients and oxygen budgets for the North Eastern Atlantic Ocean." Biogeosciences Discussions 9, no. 4 (April 12, 2012): 4323–60. http://dx.doi.org/10.5194/bgd-9-4323-2012.
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Abstract. A surface to bottom North-East Atlantic Ocean budget for mass, nutrients (nitrate and phosphate) and oxygen is determined using an optimization method based on climatological data from the World Ocean Atlas 2009 and three surveys of the OVIDE transect (from Greenland to Portugal). Budgets are derived for two communicating boxes representing the North Eastern European Basin (NEEB) and the Irminger Sea. For the NEEB (Irminger) box, it is found that 30% of the mass import (export) across the OVIDE section reach (originate from) the Nordic Seas while 70% is redistributed between both boxes through the Reykjanes Ridge (9.3±0.7×109 kg s−1). Net biological source/sink terms of nitrate point to both the Irminger and NEEB boxes as net organic matter production sites (consumming nitrate at a rate of −7.8±6.5 kmol s−1 and −8.4±6.6 kmol s−1 respectively). Using a standard Redfield ratio of C:N =106:16, nitrate consumption rates indicate that about 40 TgC yr−1 of carbon is fixed by organic matter production between the OVIDE transect and the Greenland-Scotland Ridge. Nutrients fluxes also induce a net biological production of oxygen of 73±60 kmol s−1 and 79±62 kmol s−1 in the Irminger and NEEB boxes which points to the region as being autotrophic. Air-sea oxygen fluxes show an oceanic oxygen uptake in the two regions (264±66 kmol s−1 in the north and 443±70 kmol s−1 in the south), dominated by the abiotic component. The abiotic flux is partitionned into a mixing and a thermal components. It is found that the Irminger Sea oceanic oxygen uptake is driven by an air-sea heat flux cooling increasing the ocean surface oxygen solubility. Over the North Eastern European Basin the mixing component is about half the thermal flux, presumably because of the oxygen minimum in the subtropical thermocline.
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Maze, G., H. Mercier, V. Thierry, L. Memery, P. Morin, and F. F. Perez. "Mass, nutrient and oxygen budgets for the northeastern Atlantic Ocean." Biogeosciences 9, no. 10 (October 24, 2012): 4099–113. http://dx.doi.org/10.5194/bg-9-4099-2012.
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Abstract. The northeast Atlantic is a key horizontal and vertical crossroads region for the meridional overturning circulation, but basic nutrient and oxygen fluxes are still poorly constrained by observations in the region. A surface to bottom northeast Atlantic Ocean budget for mass, nutrients (nitrate and phosphate) and oxygen is determined using an optimization method based on three surveys of the OVIDE transect (from Greenland to Portugal) completed with the World Ocean Atlas 2009. Budgets are derived for two communicating boxes representing the northeastern European basin (NEEB) and the Irminger Sea. For the NEEB (Irminger) box, it is found that 30% of the mass import (export) across the OVIDE section reach (originate from) the Nordic Seas, while 70% are redistributed between both boxes through the Reykjanes Ridge (9.3 ± 0.7 × 109 kg s−1). Net biological source/sink terms of nitrate point to both the Irminger and NEEB boxes as net organic matter production sites (consuming nitrate at a rate of –7.8 ± 6.5 kmol s−1 and –8.4 ± 6.6 kmol s−1, respectively). Using a standard Redfield ratio of C : N = 106 : 16, nitrate consumption rates indicate that about 40 TgC yr−1 of carbon is fixed by organic matter production between the OVIDE transect and the Greenland–Scotland Ridge. Nutrient fluxes also induce a net biological production of oxygen of 73 ± 60 kmol s−1 and 79 ± 62 kmol s−1 in the Irminger and NEEB boxes, which points to the region as being autotrophic. The abiotic air–sea oxygen flux leads to an oceanic oxygen uptake in the two regions (264 ± 66 kmol s−1 in the north and 443 ± 70 kmol s−1 in the south). The abiotic flux is partitioned into a mixing and a thermal component. It is found that the Irminger Sea oceanic oxygen uptake is driven by an air–sea heat flux cooling increasing the ocean surface oxygen solubility. Over the northeastern European basin the mixing component is about half the thermal flux, presumably because of the oxygen minimum in the subtropical thermocline.
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Hansen, B., H. Hátún, R. Kristiansen, S. M. Olsen, and S. Østerhus. "Stability and forcing of the Iceland-Faroe inflow of water, heat, and salt to the Arctic." Ocean Science 6, no. 4 (December 13, 2010): 1013–26. http://dx.doi.org/10.5194/os-6-1013-2010.
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Abstract. The flow of Atlantic water across the Greenland-Scotland Ridge (Atlantic inflow) is critical for conditions in the Nordic Seas and Arctic Ocean by importing heat and salt. Here, we present a decade-long series of measurements from the Iceland-Faroe inflow branch (IF-inflow), which carries almost half the total Atlantic inflow. The observations show no significant trend in volume transport of Atlantic water, but temperature and salinity increased during the observational period. On shorter time scales, the observations show considerable variations but no statistically significant seasonal variation is observed and even weekly averaged transport values were consistently uni-directional from the Atlantic into the Nordic Seas. Combining transport time-series with sea level height from satellite altimetry and wind stress reveals that the force driving the IF-inflow across the topographic barrier of the Ridge is mainly generated by a pressure gradient that is due to a continuously maintained low sea level in the Southern Nordic Seas. This implies that the relative stability of the IF-inflow derives from the processes that lower the sea level by generating outflow from the Nordic Seas, especially the thermohaline processes that generate overflow. The IF-inflow is an important component of the system coupling the Arctic region to the North Atlantic through the thermohaline circulation, which has been predicted to weaken in the 21st century. Our observations show no indication of weakening.
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Mauritzen, Cecilie. "Production of dense overflow waters feeding the North Atlantic across the Greenland-Scotland Ridge. Part 1: Evidence for a revised circulation scheme." Deep Sea Research Part I: Oceanographic Research Papers 43, no. 6 (June 1996): 769–806. http://dx.doi.org/10.1016/0967-0637(96)00037-4.
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Prange, M. "The low-resolution CCSM2 revisited: new adjustments and a present-day control run." Ocean Science 4, no. 2 (May 26, 2008): 151–81. http://dx.doi.org/10.5194/os-4-151-2008.
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Abstract. The low-resolution (T31) version of the Community Climate System Model CCSM2.0.1 is revisited and adjusted by deepening the Greenland-Scotland ridge, changing oceanic mixing parameters, and applying a regional freshwater flux adjustment at high northern latitudes. The main purpose of these adjustments is to maintain a robust Atlantic meridional overturning circulation which collapses in the original model release. The paper describes the present-day control run of the adjusted model (referred to as "CCSM2/T31x3a") which is brought into climatic equilibrium by applying a deep-ocean acceleration technique. The accelerated integration is extended by a 100-year synchronous phase. The simulated meridional overturning circulation has a maximum of 14×106 m3 s−1 in the North Atlantic. The CCSM2/T31x3a control run is evaluated against observations and simulations with other climate models. Most shortcomings found in the CCSM2/T31x3a control run are identified as "typical problems" in global climate modelling. Finally, examples (simulation of North Atlantic hydrography, West African monsoon) are shown in which CCSM2/T31x3a has a better simulation skill than the latest low-resolution Community Climate System Model release, CCSM3/T31.
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Dowsett, H. J., M. M. Robinson, and K. M. Foley. "Pliocene three-dimensional global ocean temperature reconstruction." Climate of the Past Discussions 5, no. 4 (July 15, 2009): 1901–28. http://dx.doi.org/10.5194/cpd-5-1901-2009.
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Abstract. A snapshot of the thermal structure of the mid-Piacenzian ocean is obtained by combining the Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM3) multiproxy sea-surface temperature (SST) reconstruction with bottom water temperature estimates produced using Mg/Ca paleothermometry. This reconstruction assumes a Pliocene water mass framework similar to that which exists today, with several important modifications. The area of formation of present day North Atlantic Deep Water (NADW) was expanded and extended further north toward the Arctic Ocean during the mid-Piacenzian relative to today. This, combined with a deeper Greenland-Scotland Ridge, allowed a greater volume of warmer NADW to enter the Atlantic Ocean. In the Southern Ocean, the Polar Front Zone was expanded relative to present day, but shifted closer to the Antarctic continent. This, combined with at least seasonal reduction in sea ice extent, resulted in decreased Antarctic Bottom Water (AABW) production (relative to present day) as well as possible changes in the depth of intermediate waters. The reconstructed mid-Piacenzian three-dimensional ocean was warmer overall than today, and the hypothesized aerial extent of water masses appears to fit the limited stable isotopic data available for this time period.
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Larsen, Karin Margretha H., Hjálmar Hátún, Bogi Hansen, and Regin Kristiansen. "Atlantic water in the Faroe area: sources and variability." ICES Journal of Marine Science 69, no. 5 (February 26, 2012): 802–8. http://dx.doi.org/10.1093/icesjms/fss028.
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Abstract Larsen, K. M. H., Hátún, H., Hansen, B., and Kristiansen, R. 2012. Atlantic water in the Faroe area: sources and variability. – ICES Journal of Marine Science, 69: 802–808. The inflow of Atlantic water (AW) across the Greenland–Scotland Ridge and into the Nordic Seas controls both physical and biological conditions in the northeastern Atlantic through its transport of heat, salt, and other properties. The two main branches of this flow pass through the Iceland–Faroe Gap and the Faroe–Shetland Channel, respectively. Regular monitoring along four standard sections crossing these flows provides time-series of the AW temperature and salinity variability since the late 1980s. The analysis of these series presented shows a persistent increasing trend in both temperature and salinity, modulated by smaller subdecadal oscillations. Using supplementary data sources, the previously established link between the large-scale circulation in the North Atlantic and Atlantic inflow properties is supported. Salinity is also impacted by large changes in the Bay of Biscay source waters, and upstream air–sea heat fluxes modulate temperature. Relationships between changes in transport and associated residence time, and the modifying strength of the air–sea interaction and mixing, are also discussed.
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Köhl, Armin, Rolf H. Käse, Detlef Stammer, and Nuno Serra. "Causes of Changes in the Denmark Strait Overflow." Journal of Physical Oceanography 37, no. 6 (June 1, 2007): 1678–96. http://dx.doi.org/10.1175/jpo3080.1.
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Abstract The warming Nordic seas potentially tend to decrease the overflow across the Greenland–Iceland–Scotland Ridge (GISR) system. Recent observations by Macrander et al. document a significant drop in the intensity of outflowing Denmark Strait Overflow Water of more than 20% over 3 yr and a simultaneous increase in the temperature of the bottom layers of more than 0.4°C. A simulation of the exchange across the GISR with a regional ocean circulation model is used here to identify possible mechanisms that control changes in the Denmark Strait overflow and its relations to changed forcing condition. On seasonal and longer time scales, the authors establish links of the overflow anomalies to a decreasing capacity of the dense water reservoir caused by a change of circulation pattern north of the sill. On annual and shorter time scales, the wind stress curl around Iceland determines the barotropic circulation around the island and thus the barotropic flow through Denmark Strait. For the overlapping time scales, the barotropic and overflow component interactively determine transport variations. Last, a relation between sea surface height and reservoir height changes upstream of the sill is used to predict the overflow variability from altimeter data. Estimated changes are in agreement with other recent transport estimates based on current-meter arrays.
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Nydal, Reidar, and Jorunn S. Gislefoss. "Further Application of Bomb 14C as a Tracer in the Atmosphere and Ocean." Radiocarbon 38, no. 3 (1996): 389–406. http://dx.doi.org/10.1017/s0033822200030046.
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Bomb 14C from nuclear tests in the atmosphere has proved to be a particularly useful tool in the study of the carbon cycle. We provide here a ca. 30-yr time series of 14C concentrations in the atmosphere between 28°N and 71°N and in the ocean surface between 45°S and 45°N. More recently (since 1990), a north-south profile also has been obtained for 14C in the surface waters of the Atlantic Ocean. The measurements were performed using the conventional technique of beta counting or large samples (4 to 5 liter CO2) in CO2 proportional counters. These data show that the 14C concentration in the atmosphere is leveling off with a time constant of 0.055 yr-1, and is now approaching that of the ocean surface at lower latitudes.Additional tracer studies have been concerned especially with the penetration of bomb 14C into the deep ocean. The Norwegian and Greenland seas are of interest as a sink for atmospheric CO2 and also a source of water for the deep Atlantic Ocean. During the last five years, several 14C depth profiles have been measured from the Fram Strait (79°N) to south of Iceland (62°N), using the AMS technique available at the University of Arizona AMS Facility. We considered it important to repeat and compare a few of the profiles with those produced by the GEOSECS expedition in 1972 and the TTO expedition in 1981. The profiles show that water descending to the deep Atlantic Ocean is originating mainly from intermediate and surface depths in the Nordic Seas. However, the ventilation rate of the Norwegian Sea deepwater is too slow to be an important component in the transfer of water over the Greenland-Scotland Ridge.
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Olsen, S. M., B. Hansen, S. Østerhus, D. Quadfasel, and H. Valdimarsson. "Biased thermohaline exchanges with the Arctic across the Iceland–Faroe Ridge in ocean climate models." Ocean Science 12, no. 2 (April 13, 2016): 545–60. http://dx.doi.org/10.5194/os-12-545-2016.
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Abstract. The northern limb of the Atlantic thermohaline circulation and its transport of heat and salt towards the Arctic strongly modulate the climate of the Northern Hemisphere. The presence of warm surface waters prevents ice formation in parts of the Arctic Mediterranean, and ocean heat is directly available for sea-ice melt, while salt transport may be critical for the stability of the exchanges. Through these mechanisms, ocean heat and salt transports play a disproportionally strong role in the climate system, and realistic simulation is a requisite for reliable climate projections. Across the Greenland–Scotland Ridge (GSR) this occurs in three well-defined branches where anomalies in the warm and saline Atlantic inflow across the shallow Iceland–Faroe Ridge (IFR) have been shown to be particularly difficult to simulate in global ocean models. This branch (IF-inflow) carries about 40 % of the total ocean heat transport into the Arctic Mediterranean and is well constrained by observation during the last 2 decades but associated with significant inter-annual fluctuations. The inconsistency between model results and observational data is here explained by the inability of coarse-resolution models to simulate the overflow across the IFR (IF-overflow), which feeds back onto the simulated IF-inflow. In effect, this is reduced in the model to reflect only the net exchange across the IFR. Observational evidence is presented for a substantial and persistent IF-overflow and mechanisms that qualitatively control its intensity. Through this, we explain the main discrepancies between observed and simulated exchange. Our findings rebuild confidence in modelled net exchange across the IFR, but reveal that compensation of model deficiencies here through other exchange branches is not effective. This implies that simulated ocean heat transport to the Arctic is biased low by more than 10 % and associated with a reduced level of variability, while the quality of the simulated salt transport becomes critically dependent on the link between IF-inflow and IF-overflow. These features likely affect sensitivity and stability of climate models to climate change and limit the predictive skill.
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Olsen, S. M., B. Hansen, S. Østerhus, D. Quadfasel, and H. Valdimarsson. "Biased thermohaline exchanges with the arctic across the Iceland-Faroe Ridge in ocean climate models." Ocean Science Discussions 12, no. 4 (July 14, 2015): 1471–510. http://dx.doi.org/10.5194/osd-12-1471-2015.
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Abstract. The northern limb of the Atlantic thermohaline circulation and its transport of heat and salt towards the Arctic strongly modulates the climate of the Northern Hemisphere. Presence of warm surface waters prevents ice formation in parts of the Arctic Mediterranean and ocean heat is in critical regions directly available for sea-ice melt, while salt transport may be critical for the stability of the exchanges. Hereby, ocean heat and salt transports play a disproportionally strong role in the climate system and realistic simulation is a requisite for reliable climate projections. Across the Greenland-Scotland Ridge (GSR) this occurs in three well defined branches where anomalies in the warm and saline Atlantic inflow across the shallow Iceland-Faroe Ridge (IFR) have shown particularly difficult to simulate in global ocean models. This branch (IF-inflow) carries about 40 % of the total ocean heat transport into the Arctic Mediterranean and is well constrained by observation during the last two decades but is associated with significant inter-annual fluctuations. The inconsistency between model results and observational data is here explained by the inability of coarse resolution models to simulate the overflow across the IFR (IF-overflow), which feeds back on the simulated IF-inflow. In effect, this is reduced in the model to reflect only the net exchange across the IFR. Observational evidence is presented for a substantial and persistent IF-overflow and mechanisms that qualitatively control its intensity. Through this, we explain the main discrepancies between observed and simulated exchange. Our findings rebuild confidence in modeled net exchange across the IFR, but reveal that compensation of model deficiencies here through other exchange branches is not effective. This implies that simulated ocean heat transport to the Arctic is biased low by more than 10 % and associated with a reduced level of variability while the quality of the simulated salt transport becomes critically dependent on the link between IF-inflow and IF-overflow. These features likely affect sensitivity and stability of climate models to climate change and limit the predictive skill.
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Tang, Yong Ming, and Malcolm J. Roberts. "The Impact of a Bottom Boundary Layer Scheme on the North Atlantic Ocean in a Global Coupled Climate Model." Journal of Physical Oceanography 35, no. 2 (February 1, 2005): 202–17. http://dx.doi.org/10.1175/jpo-2671.1.
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Abstract Although the overflow and descent of cold, dense water across the Greenland–Iceland–Scotland ridge is the principal means for the maintenance of the thermohaline circulation in the North Atlantic Ocean, this feature is not adequately treated in global ocean numerical models. In this paper, a bottom boundary layer scheme is introduced into the HadCM3 coupled atmosphere–ocean–sea ice general circulation climate model, in order to give an improved representation of cold water formation in the North Atlantic Ocean. The scheme uses a simple terrain-following bottom boundary layer incorporated into the ocean general circulation model; only the tracer tendencies are evaluated in the bottom boundary layer, with the velocities taken from the near-bottom interior values. It is found that with the bottom boundary layer scheme, there are several significant effects on the deep water formation and flow. The overflow of dense water from the Nordic Seas into the North Atlantic Seas is improved with the introduction of the authors’ bottom boundary layer scheme. Further, the thermohaline circulation is reduced in strength, but is also deeper, when compared with simulations without any bottom boundary layer scheme. There is also a stronger flow along the northwestern boundary, a more southerly location of the North Atlantic Current, and a stronger and larger subpolar gyre. Overall, these effects are an improvement when compared with climatology, although some differences remain.
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Zou, Sijia, and M. Susan Lozier. "Breaking the Linkage Between Labrador Sea Water Production and Its Advective Export to the Subtropical Gyre." Journal of Physical Oceanography 46, no. 7 (July 2016): 2169–82. http://dx.doi.org/10.1175/jpo-d-15-0210.1.
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AbstractDeep water formation in the northern North Atlantic has been of long-standing interest because the resultant water masses, along with those that flow over the Greenland–Scotland Ridge, constitute the lower limb of the Atlantic meridional overturning circulation (AMOC), which carries these cold, deep waters southward to the subtropical region and beyond. It has long been assumed that an increase in deep water formation would result in a larger southward export of newly formed deep water masses. However, recent observations of Lagrangian floats have raised questions about this linkage. Motivated by these observations, the relationship between convective activity in the Labrador Sea and the export of newly formed Labrador Sea Water (LSW), the shallowest component of the deep AMOC, to the subtropics is explored. This study uses simulated Lagrangian pathways of synthetic floats produced with output from a global ocean–sea ice model. It is shown that substantial recirculation of newly formed LSW in the subpolar gyre leads to a relatively small fraction of this water exported to the subtropical gyre: 40 years after release, only 46% of the floats are able to reach the subtropics. Furthermore, waters produced from any one particular convection event are not collectively and contemporaneously exported to the subtropical gyre, such that the waters that are exported to the subtropical gyre have a wide distribution in age.
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Dowsett, H. J., M. M. Robinson, and K. M. Foley. "Pliocene three-dimensional global ocean temperature reconstruction." Climate of the Past 5, no. 4 (December 3, 2009): 769–83. http://dx.doi.org/10.5194/cp-5-769-2009.
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Abstract. The thermal structure of the mid-Piacenzian ocean is obtained by combining the Pliocene Research, Interpretation and Synoptic Mapping Project (PRISM3) multiproxy sea-surface temperature (SST) reconstruction with bottom water temperature estimates from 27 locations produced using Mg/Ca paleothermometry based upon the ostracod genus Krithe. Deep water temperature estimates are skewed toward the Atlantic Basin (63% of the locations) and represent depths from 1000 m to 4500 m. This reconstruction, meant to serve as a validation data set as well as an initialization for coupled numerical climate models, assumes a Pliocene water mass framework similar to that which exists today, with several important modifications. The area of formation of present day North Atlantic Deep Water (NADW) was expanded and extended further north toward the Arctic Ocean during the mid-Piacenzian relative to today. This, combined with a deeper Greenland-Scotland Ridge, allowed a greater volume of warmer NADW to enter the Atlantic Ocean. In the Southern Ocean, the Polar Front Zone was expanded relative to present day, but shifted closer to the Antarctic continent. This, combined with at least seasonal reduction in sea ice extent, resulted in decreased Antarctic Bottom Water (AABW) production (relative to present day) as well as possible changes in the depth of intermediate waters. The reconstructed mid-Piacenzian three-dimensional ocean was warmer overall than today, and the hypothesized aerial extent of water masses appears to fit the limited stable isotopic data available for this time period.
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Kenigson, J. S., and M. L. Timmermans. "Nordic Seas Hydrography in the Context of Arctic and North Atlantic Ocean Dynamics." Journal of Physical Oceanography 51, no. 1 (January 2021): 101–14. http://dx.doi.org/10.1175/jpo-d-20-0071.1.
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AbstractThe hydrography of the Nordic seas, a critical site for deep convective mixing, is controlled by various processes. On one hand, Arctic Ocean exports are thought to freshen the North Atlantic Ocean and the Nordic seas, as in the Great Salinity Anomalies (GSAs) of the 1970s–1990s. On the other hand, the salinity of the Nordic seas covaries with that of the Atlantic inflow across the Greenland–Scotland Ridge, leaving an uncertain role for Arctic Ocean exports. In this study, multidecadal time series (1950–2018) of the Nordic seas hydrography, Subarctic Front (SAF) in the North Atlantic Ocean [separating the water masses of the relatively cool, fresh Subpolar Gyre (SPG) from the warm, saline Subtropical Gyre (STG)], and atmospheric forcing are examined and suggest a unified view. The Nordic seas freshwater content is shown to covary on decadal time scales with the position of the SAF. When the SPG is strong, the SAF shifts eastward of its mean position, increasing the contribution of subpolar relative to subtropical source water to the Atlantic inflow, and vice versa. This suggests that Arctic Ocean fluxes primarily influence the hydrography of the Nordic seas via indirect means (i.e., by freshening the SPG). Case studies of two years with anomalous NAO conditions illustrate how North Atlantic Ocean dynamics relate to the position of the SAF (as indicated by hydrographic properties and stratification changes in the upper water column), and therefore to the properties of the Atlantic inflow and Nordic seas.
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Yang, Jiayan, and Lawrence J. Pratt. "On the Effective Capacity of the Dense-Water Reservoir for the Nordic Seas Overflow: Some Effects of Topography and Wind Stress." Journal of Physical Oceanography 43, no. 2 (February 1, 2013): 418–31. http://dx.doi.org/10.1175/jpo-d-12-087.1.
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Abstract The overflow of the dense water mass across the Greenland–Scotland Ridge (GSR) from the Nordic Seas drives the Atlantic meridional overturning circulation (AMOC). The Nordic Seas is a large basin with an enormous reservoir capacity. The volume of the dense water above the GSR sill depth in the Nordic Seas, according to previous estimates, is sufficient to supply decades of overflow transport. This large capacity buffers overflow’s responses to atmospheric variations and prevents an abrupt shutdown of the AMOC. In this study, the authors use a numerical and an analytical model to show that the effective reservoir capacity of the Nordic Seas is actually much smaller than what was estimated previously. Basin-scale oceanic circulation is nearly geostrophic and its streamlines are basically the same as the isobaths. The vast majority of the dense water is stored inside closed geostrophic contours in the deep basin and thus is not freely available to the overflow. The positive wind stress curl in the Nordic Seas forces a convergence of the dense water toward the deep basin and makes the interior water even more removed from the overflow-feeding boundary current. Eddies generated by the baroclinic instability help transport the interior water mass to the boundary current. But in absence of a robust renewal of deep water, the boundary current weakens rapidly and the eddy-generating mechanism becomes less effective. This study indicates that the Nordic Seas has a relatively small capacity as a dense water reservoir and thus the overflow transport is sensitive to climate changes.
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Logemann, K., J. Ólafsson, Á. Snorrason, H. Valdimarsson, and G. Marteinsdóttir. "The circulation of Icelandic waters – a modelling study." Ocean Science 9, no. 5 (October 30, 2013): 931–55. http://dx.doi.org/10.5194/os-9-931-2013.
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Abstract. The three-dimensional flow, temperature and salinity fields of the North Atlantic, including the Arctic Ocean, covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The simulation reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC) and the path of the Atlantic Water south-east of Iceland. The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts, which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a hitherto unnamed current over the southern and south-eastern shelf, which is simulated to be an upstream precursor of the Faroe Current (FC). Both currents are driven by barotropic pressure gradients induced by a sea level slope across the Greenland–Scotland Ridge. The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85% during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27%. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.
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Pierrot, D., P. Brown, S. Van Heuven, T. Tanhua, U. Schuster, R. Wanninkhof, and R. M. Key. "CARINA TCO<sub>2</sub> data in the Atlantic Ocean." Earth System Science Data Discussions 3, no. 1 (January 11, 2010): 1–26. http://dx.doi.org/10.5194/essdd-3-1-2010.
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Abstract. Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 cruises in the Arctic, Atlantic and Southern Ocean have been retrieved and merged in a new data base: the CARINA (CARbon IN the Atlantic) Project. These data have gone through rigorous quality control (QC) procedures to assure the highest possible quality and consistency. Secondary quality control, which involved objective study of data in order to quantify systematic differences in the reported values, was performed for the pertinent parameters in the CARINA data base. Systematic biases in the data have been corrected in the data products. The products are three merged data files with measured, adjusted and interpolated data of all cruises for each of the three CARINA regions (Arctic, Atlantic and Southern Ocean). Ninety-eight cruises were conducted in the "Atlantic" defined as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we report the details of the secondary QC which was done on the total dissolved inorganic carbon (TCO2) data and the adjustments that were applied to yield the final data product in the Atlantic. Procedures of quality control – including crossover analysis between stations and inversion analysis of all crossover data – are briefly described. Adjustments were applied to TCO2 measurements for 17 of the cruises in the Atlantic Ocean region. With these adjustments, the CARINA data base is consistent both internally as well as with GLODAP data, an oceanographic data set based on the WOCE Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, regional oceanic carbon inventories, uptake rates and model validation.
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Tanhua, T., R. Steinfeldt, R. M. Key, P. Brown, N. Gruber, R. Wanninkhof, F. Perez, et al. "Atlantic Ocean CARINA data: overview and salinity adjustments." Earth System Science Data Discussions 2, no. 1 (August 20, 2009): 241–80. http://dx.doi.org/10.5194/essdd-2-241-2009.
Full textAbstract:
Abstract. Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic). The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the data products, i.e. three merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. Arctic, Atlantic and Southern Ocean. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report details of the secondary QC for salinity for this data set. Procedures of quality control – including crossover analysis between stations and inversion analysis of all crossover data – are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal accuracy of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s (Key et al., 2004), and is now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation.
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Pierrot, D., P. Brown, S. Van Heuven, T. Tanhua, U. Schuster, R. Wanninkhof, and R. M. Key. "CARINA TCO<sub>2</sub> data in the Atlantic Ocean." Earth System Science Data 2, no. 2 (July 12, 2010): 177–87. http://dx.doi.org/10.5194/essd-2-177-2010.
Full textAbstract:
Abstract. Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 cruises in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged in a new data base: the CARINA (CARbon IN the Atlantic) Project. These data have gone through rigorous quality control (QC) procedures so as to improve the quality and consistency of the data as much as possible. Secondary quality control, which involved objective study of data in order to quantify systematic differences in the reported values, was performed for the pertinent parameters in the CARINA data base. Systematic biases in the data have been tentatively corrected in the data products. The products are three merged data files with measured, adjusted and interpolated data of all cruises for each of the three CARINA regions (Arctic Mediterranean Seas, Atlantic and Southern Ocean). Ninety-eight cruises were conducted in the "Atlantic" defined as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we report the details of the secondary QC which was done on the total dissolved inorganic carbon (TCO2) data and the adjustments that were applied to yield the final data product in the Atlantic. Procedures of quality control – including crossover analysis between stations and inversion analysis of all crossover data – are briefly described. Adjustments were applied to TCO2 measurements for 17 of the cruises in the Atlantic Ocean region. With these adjustments, the CARINA data base is consistent both internally as well as with GLODAP data, an oceanographic data set based on the WOCE Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, regional oceanic carbon inventories, uptake rates and model validation.
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Tett, Simon F. B., Toby J. Sherwin, Amrita Shravat, and Oliver Browne. "How Much Has the North Atlantic Ocean Overturning Circulation Changed in the Last 50 Years?" Journal of Climate 27, no. 16 (August 7, 2014): 6325–42. http://dx.doi.org/10.1175/jcli-d-12-00095.1.
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Abstract Volume transports from six ocean reanalyses are compared with four sets of in situ observations: across the Greenland–Scotland ridge (GSR), in the Labrador Sea boundary current, in the deep western boundary current at 43°N, and in the Atlantic meridional overturning circulation (AMOC) at 26°N in the North Atlantic. The higher-resolution reanalyses (on the order of ¼° × ¼°) are better at reproducing the circulation pattern in the subpolar gyre than those with lower resolution (on the order of 1°). Simple Ocean Data Assimilation (SODA) and Estimating the Circulation and Climate of the Ocean (ECCO)–Jet Propulsion Laboratory (JPL) produce transports at 26°N that are close to those observed [17 Sv (1 Sv ≡ 106 m3 s−1)]. ECCO, version 2, and SODA produce northward transports across the GSR (observed transport of 8.2 Sv) that are 22% and 29% too big, respectively. By contrast, the low-resolution reanalyses have transports that are either too small [by 31% for ECCO-JPL and 49% for Ocean Reanalysis, system 3 (ORA-S3)] or much too large [Decadal Prediction System (DePreSys)]. SODA had the best simulations of mixed layer depth and with two coarse grid long-term reanalyses (DePreSys and ORA-S3) is used to examine changes in North Atlantic circulation from 1960 to 2008. Its results suggest that the AMOC increased by about 20% at 26°N while transport across the GSR hardly altered. The other (less reliable) long-term reanalyses also had small changes across the GSR but changes of +10% and −20%, respectively, at 26°N. Thus, it appears that changes in the overturning circulation at 26°N are decoupled from the flow across the GSR. It is recommended that transport observations should not be assimilated in ocean reanalyses but used for validation instead.
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Wolff, Torben. "The First Danish Deep-Sea Expedition on the Ingolf: 1895 and 1896." Earth Sciences History 27, no. 2 (November 3, 2008): 164–87. http://dx.doi.org/10.17704/eshi.27.2.201558682104577l.
Full textAbstract:
The Danish Ingolf Expedition took place in the summer months of 1895 and 1896, with C. F. Wandel as captain, a man with long experience in hydrographical work in the Arctic. The other scientific participants were the zoologists H. Jungersen, W. Lundbeck and H. J. Hansen during the 1895 cruise; C. Wesenberg-Lund replaced Hansen during the 1896 cruise. C. H. Ostenfeld was the botanist and M. Knudsen the hydrographer. The Ingolf (see Figure 1) was a naval cruiser. In both years the voyages were hindered by ice that had moved much further south than normal, even closing most of the Denmark Strait. In 1895, the best results were obtained south of Iceland and in the Davis Strait; in 1896 south and east of Iceland and as far north as Jan Mayen Island. A total of 144 stations were completed, all with soundings, trawlings and (for the first time) continuous hydrographical work associated with the deep-sea trawling (bottom measurements of temperature, salinity, chlorine contents and specific gravity). Eighty of the stations were deeper than 1,000 m. There were more than 800 hydrographical measurements, with about 3,300 registrations recordings added on the basis of the measurements. 138 gas analyses were performed on board with samples from the surface and the sea bottom. The main result of the expedition was the final demonstration of probably the most important threshold boundaries in the world: the Wyville Thompson Ridge from East Greenland to Scotland with maximum depths of 600 m, separating the fauna in the Norwegian and Polar Sea to the north, always with negative below-zero temperatures except close to the Norwegian coast, from the fundamentally different general Atlantic deep-sea fauna to the south of the ridge with positive temperatures. The results are published in the Ingolf Report, with fifteen volumes containing forty-three papers by nineteen Danish authors and fourteen papers by six foreign authors. The sieving technique was excellent—due to an apparatus designed by H. J. Hansen that kept the animals under water until preservation and using the finest silk for sieving. In this way, the expedition collected more smaller animals than had been acquired by previous deep-sea expeditions. Hansen's studies of the peracarid crustaceans and parasitic copepods and Lundbeck's report on the sponges were particularly noteworthy. The 130 photographs taken on board and on land by the ship's doctor William Thulstrup represent a cultural/historical treasure.