Thermohaline Fingerprints of the Greenland-Scotland Ridge and Fram Strait Subsidence Histories

Changes in ocean gateway configuration are known to induce basin-scale rearrangements in ocean characteristics throughout the Cenozoic. However, there is large uncertainty in the relative timing of the subsidence histories of ocean gateways in the northern high latitudes. By using a fully coupled General Circulation Model we investigate the salinity and temperature changes in response to the subsidence of two key ocean gateways in the northern high latitudes during early to middle Miocene. Deepening of the Greenland-Scotland Ridge causes a salinity increase and warming in the Nordic Seas and the Arctic Ocean. While warming this realm, deep water formation takes place at lower temperatures due to a shift of the convection sites to north off Iceland. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface causes a cooling in the southern high latitudes. These characteristic impacts in response to the Greenland-Scotland Ridge deepening are independent of the Fram Strait state. Subsidence of the Fram Strait for a deep Greenland-Scotland Ridge causes less pronounced warming and salinity increase in the Nordic Seas. A stronger salinity increase is detected in the Arctic while temperatures remain unaltered, which further increases the density of the North Atlantic Deep Water. This causes an enhanced contribution of North Atlantic Deep Water to the abyssal ocean and on the expense of the colder southern source water component. These relative changes largely counteract each other and cause little warming in the upwelling regions of the Southern Ocean.

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North Atlantic deep water formation and AMOC in CMIP5 models

Ocean Science ◽

10.5194/os-13-609-2017 ◽

2017 ◽

Vol 13 (4) ◽

pp. 609-622 ◽

Cited By ~ 26

Author(s):

Céline Heuzé

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

North Atlantic ◽

Deep Water ◽

Deep Convection ◽

The Arctic ◽

Subpolar Gyre ◽

Deep Water Formation ◽

Nordic Seas ◽

Water Formation

Abstract. Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turn, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecasting Arctic oceanic warming and its consequences for the global ocean circulation, cryosphere and marine life.

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Sea ice volume variability and water temperature in the Greenland Sea

The Cryosphere ◽

10.5194/tc-14-477-2020 ◽

2020 ◽

Vol 14 (2) ◽

pp. 477-495 ◽

Cited By ~ 2

Author(s):

Valeria Selyuzhenok ◽

Igor Bashmachnikov ◽

Robert Ricker ◽

Anna Vesman ◽

Leonid Bobylev

Keyword(s):

Sea Ice ◽

North Atlantic ◽

Heat Content ◽

The Arctic ◽

Fram Strait ◽

Greenland Sea ◽

Nordic Seas ◽

Ice Volume ◽

Long Term Variations

Abstract. This study explores a link between the long-term variations in the integral sea ice volume (SIV) in the Greenland Sea and oceanic processes. Using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS, 1979–2016), we show that the increasing sea ice volume flux through Fram Strait goes in parallel with a decrease in SIV in the Greenland Sea. The overall SIV loss in the Greenland Sea is 113 km3 per decade, while the total SIV import through Fram Strait increases by 115 km3 per decade. An analysis of the ocean temperature and the mixed-layer depth (MLD) over the climatic mean area of the winter marginal sea ice zone (MIZ) revealed a doubling of the amount of the upper-ocean heat content available for the sea ice melt from 1993 to 2016. This increase alone can explain the SIV loss in the Greenland Sea over the 24-year study period, even when accounting for the increasing SIV flux from the Arctic. The increase in the oceanic heat content is found to be linked to an increase in temperature of the Atlantic Water along the main currents of the Nordic Seas, following an increase in the oceanic heat flux from the subtropical North Atlantic. We argue that the predominantly positive winter North Atlantic Oscillation (NAO) index during the 4 most recent decades, together with an intensification of the deep convection in the Greenland Sea, is responsible for the intensification of the cyclonic circulation pattern in the Nordic Seas, which results in the observed long-term variations in the SIV.

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The Role of Southern Ocean Surface Forcings and Mixing in the Global Conveyor

Journal of Physical Oceanography ◽

10.1175/2008jpo3519.1 ◽

2008 ◽

Vol 38 (7) ◽

pp. 1377-1400 ◽

Cited By ~ 45

Author(s):

Daniele Iudicone ◽

Gurvan Madec ◽

Bruno Blanke ◽

Sabrina Speich

Keyword(s):

Southern Ocean ◽

North Atlantic ◽

Deep Water ◽

Thermohaline Circulation ◽

North Atlantic Deep Water ◽

Surface Fluxes ◽

Weddell Sea ◽

Mode Water ◽

Circumpolar Deep Water ◽

Subantarctic Mode Water

Abstract Despite the renewed interest in the Southern Ocean, there are yet many unknowns because of the scarcity of measurements and the complexity of the thermohaline circulation. Hence the authors present here the analysis of the thermohaline circulation of the Southern Ocean of a steady-state simulation of a coupled ice–ocean model. The study aims to clarify the roles of surface fluxes and internal mixing, with focus on the mechanisms of the upper branch of the overturning. A quantitative dynamical analysis of the water-mass transformation has been performed using a new method. Surface fluxes, including the effect of the penetrative solar radiation, produce almost 40 Sv (1 Sv ≡ 106 m3 s−1) of Subantarctic Mode Water while about 5 Sv of the densest water masses (γ > 28.2) are formed by brine rejection on the shelves of Antarctica and in the Weddell Sea. Mixing transforms one-half of the Subantarctic Mode Water into intermediate water and Upper Circumpolar Deep Water while bottom water is produced by Lower Circumpolar Deep Water and North Atlantic Deep Water mixing with shelf water. The upwelling of part of the North Atlantic Deep Water inflow is due to internal processes, mainly downward propagation of the surface freshwater excess via vertical mixing at the base of the mixed layer. A complementary Lagrangian analysis of the thermohaline circulation will be presented in a companion paper.

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North Atlantic Deep Water export to the Southern Ocean over the past 14 Myr: Evidence from Nd and Pb isotopes in ferromanganese crusts

Paleoceanography ◽

10.1029/2000pa000606 ◽

2002 ◽

Vol 17 (2) ◽

pp. 12-1-12-9 ◽

Cited By ~ 104

Author(s):

Martin Frank ◽

Nicholas Whiteley ◽

Sabine Kasten ◽

James R. Hein ◽

Keith O'Nions

Keyword(s):

Southern Ocean ◽

North Atlantic ◽

Deep Water ◽

North Atlantic Deep Water ◽

Pb Isotopes ◽

Ferromanganese Crusts ◽

The Past

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Evidence from Southern Ocean sediments for the effect of North Atlantic deep-water flux on climate

Nature ◽

10.1038/355416a0 ◽

1992 ◽

Vol 355 (6359) ◽

pp. 416-419 ◽

Cited By ~ 225

Author(s):

Christopher D. Charles ◽

Richard G. Fairbanks

Keyword(s):

Southern Ocean ◽

North Atlantic ◽

Deep Water ◽

Water Flux ◽

North Atlantic Deep Water

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North Atlantic deep water collapse triggered by a Southern Ocean meltwater pulse in a glacial climate state

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1307/6/3/032018 ◽

2009 ◽

Vol 6 (3) ◽

pp. 032018

Author(s):

Jessica Trevena ◽

W P Sijp ◽

M H Engl

Keyword(s):

Southern Ocean ◽

North Atlantic ◽

Deep Water ◽

North Atlantic Deep Water ◽

Glacial Climate

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Water-mass formation and distribution in the Nordic Seas during the 1990s

ICES Journal of Marine Science ◽

10.1016/j.icesjms.2004.05.003 ◽

2004 ◽

Vol 61 (5) ◽

pp. 846-863 ◽

Cited By ~ 54

Author(s):

Johan Blindheim ◽

Francisco Rey

Keyword(s):

Arctic Ocean ◽

Oxygen Content ◽

Deep Water ◽

The Arctic ◽

Central Basin ◽

Greenland Sea ◽

Nordic Seas ◽

Norwegian Sea ◽

Deep Waters ◽

Salinity Increase

Abstract Hydrographic, oxygen and nutrient data collected in the Nordic Seas during the 1990s are presented. During the decade, deep waters originating from the Arctic Ocean, identified by salinities in excess of 34.9, spread into the Greenland Basin. In 1991, these waters extended westward from the mid-ocean ridge to about 2°E. This process continued over time and by 1993 there was a layer with salinities above 34.9 along the entire section, between 7.6°W and the Barents Sea Slope, and probably across the whole basin. In 2000 the basin had these high salinities at depths greater than 1400 m. At 1500 m in the central basin the salinity increase during the decade was 0.012 units, decreasing to 0.006 at 3000 m, and associated temperatures increased by 0.28 and 0.09°C, respectively. This warming more than compensated for the salinity increase so that the density of the deep water decreased during the decade, σ3 decreasing by 0.027 kg m−3 at 1500 m and by 0.006 kg m−3 at 3000 m. Decreasing oxygen content and increasing concentrations of silicate further indicated the increasing influence of Arctic Ocean Deep Water. Interaction with the atmosphere is decisive for the conditions in the area. In the central Greenland Sea there is close correlation between wind forcing and upper-layer salinity. Significant deep-water formation occurs only during cold winters, or rather, in periods with several succeeding cold winters and the 1960s were the first period in which these conditions occurred since 1920. This is shown by meteorological observations at Jan Mayen since 1921, and at Stykkisholmur, Iceland, since 1823. Relatively high salinities were observed near the bottom over the Iceland Plateau. These waters seem to be derived from Arctic Ocean deep waters that have been diverted from the East Greenland Current, into the East Icelandic Current. While flowing through the Iceland Sea their nutrient concentration increases considerably. This water flows into the Norwegian Basin where it forms a slight salinity maximum around 1500 m, which is associated with a minimum in oxygen content. At greater depths the water masses are from the Greenland Sea. The salinity decreases and the oxygen increases toward approximately 2500 m, from where the trends are reversed toward a slight salinity maximum around 3000 m, where there also is a minimum in oxygen as well as in CFC-11. These characteristics seem to derive from Arctic Ocean Deep Water, floating above waters more characterized by Greenland Sea Bottom water nearest to the bottom as suggested by decreasing salinity and an increase in both oxygen and CFC-11 concentration. This shows that even the very homogeneous Norwegian Sea Deep Water is stratified. There are also slight differences between the deep waters of the basins in the Norwegian Sea. In the Norwegian Basin the deep water has slightly higher salinity, lower dissolved oxygen and higher silicates than the deep water in the Lofoten Basin, and even more so compared with the area west of Bear Island. This shows that the Lofoten Basin and the northern Norwegian Sea are more directly influenced by waters from the Greenland Sea than the Norwegian Basin.

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Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

Climate of the Past ◽

10.5194/cp-9-1505-2013 ◽

2013 ◽

Vol 9 (4) ◽

pp. 1505-1518 ◽

Cited By ~ 29

Author(s):

C. V. Dylmer ◽

J. Giraudeau ◽

F. Eynaud ◽

K. Husum ◽

A. De Vernal

Keyword(s):

Surface Water ◽

North Atlantic ◽

Barents Sea ◽

Water Masses ◽

Ice Age ◽

The Arctic ◽

Fram Strait ◽

Nordic Seas ◽

The North ◽

The North Atlantic

Abstract. Three marine sediment cores distributed along the Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC), and Svalbard (HH11-134-BC) continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic waters (AW) and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar/Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the strength of the North Atlantic Current. The entire investigated area, from 66 to 77° N, was affected by an overall increase in AW flow from 3000 cal yr BP (before present) to the present. The long-term modulation of westerlies' strength and location, which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic front between the area off western Norway and the western Barents Sea–eastern Fram Strait region. The Little Ice Age (LIA) was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea ice conditions and a strongly reduced AW strength. A sudden short pulse of resumed high WSC (West Spitsbergen Current) flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess flow of AW which stands as unprecedented over the last 3000 yr.

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North Atlantic deep water formation and AMOC in CMIP5 models

10.5194/os-2017-2 ◽

2017 ◽

Cited By ~ 2

Author(s):

Céline Heuzé

Keyword(s):

Sea Ice ◽

Ocean Circulation ◽

North Atlantic ◽

Deep Water ◽

Deep Convection ◽

The Arctic ◽

Subpolar Gyre ◽

Deep Water Formation ◽

Nordic Seas ◽

Water Formation

Abstract. Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often, and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turns, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecast Arctic oceanic warming and its consequences on the global ocean circulation, cryosphere and marine life.

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