Sea Ice Meltwater and Circumpolar Deep Water Drive Contrasting Productivity in Three Antarctic Polynyas

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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Thermohaline suppression of Upper Circumpolar Deep Water eddies in the Ross Gyre

Geophysical Research Letters ◽

10.1029/2021gl094476 ◽

2021 ◽

Author(s):

Yana Bebieva ◽

Kevin Speer

Keyword(s):

Deep Water ◽

Circumpolar Deep Water

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Upper ocean salinity variabilities in the Southern Ocean responding to the recent surface salting in perspective of climate changes

10.5194/egusphere-egu21-4727 ◽

2021 ◽

Author(s):

Ling Du ◽

Xubin Ni

Keyword(s):

Southern Ocean ◽

Deep Water ◽

Water Mass ◽

Water Cycle ◽

Upper Ocean ◽

Tropical Ocean ◽

Circumpolar Deep Water ◽

Salinity Changes ◽

Ocean Salinity ◽

The Antarctic

<p>Water cycle have prevailed on upper ocean salinity acting as the climate change fingerprint in the numerous observation and simulation works. Water mass in the Southern Ocean accounted for the increasing importance associated with the heat and salt exchanges between Subantarctic basins and tropical oceans. The circumpolar deep water (CDW), the most extensive water mass in the Southern Ocean, plays an indispensable role in the formation of Antarctic Bottom Water. In our study, the observed CTDs and reanalysis datasets are examined to figure out the recent salinity changes in the three basins around the Antarctica. Significant surface salinity anomalies occurred in the South Indian/Pacific sectors south of 60&#186;S since 2008, which are connected with the enhanced CDW incursion onto the Antarctic continental shelf. Saltier shelf water was found to expand northward from the Antarctica coast. Meanwhile, the freshening of Upper Circumpolar Deep Water(UCDW), salting and submergence of Subantarctic Mode Water(SAMW) were also clearly observed. The modified vertical salinity structures contributed to the deepen mixed layer and enhanced intermediate stratification between SAMW and UCDW. Their transport of salinity flux attributed to the upper ocean processes responding to the recent atmospheric circulation anomalies, such as the Antarctic Oscillation and Indian Ocean Dipole. The phenomena of SAMW and UCDW salinity anomalies illustrated the contemporaneous changes of the subtropical and polar oceans, which reflected the meridional circulation fluctuation. Salinity changes in upper southern ocean (< 2000m) revealed the influence of global water cycle changes, from the Antarctic to the tropical ocean, by delivering anomalies from high- and middle-latitudes to low-latitudes oceans.</p>

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Influence of Nordic Seas dynamics on the Atlantic Water propagation and its impacts on sea ice concentration.

10.5194/egusphere-egu21-14798 ◽

2021 ◽

Author(s):

Sourav Chatterjee ◽

Roshin P Raj ◽

Laurent Bertino ◽

Nuncio Murukesh

Keyword(s):

Sea Ice ◽

Deep Water ◽

Atlantic Water ◽

The Arctic ◽

Deep Water Formation ◽

Sea Ice Concentration ◽

Nordic Seas ◽

Ice Concentration ◽

Water Formation

<p>Enhanced intrusion of warm and saline Atlantic Water (AW) to the Arctic Ocean (AO) in recent years has drawn wide interest of the scientific community owing to its potential role in &#8216;Arctic Amplification&#8217;. Not only the AW has warmed over the last few decades , but its transfer efficiency have also undergone significant modifications due to changes in atmosphere and ocean dynamics at regional to large scales. The Nordic Seas (NS), in this regard, play a vital role as the major exchange of polar and sub-polar waters takes place in this region. Further, the AW and its significant modification on its way to AO via the Nordic Seas has large scale implications on e.g., deep water formation, air-sea heat fluxes. Previous studies have suggested that a change in the sub-polar gyre dynamics in the North Atlantic controls the AW anomalies that enter the NS and eventually end up in the AO. However, the role of NS dynamics in resulting in the modifications of these AW anomalies are not well studied. Here in this study, we show that the Nordic Seas are not only a passive conduit of AW anomalies but the ocean circulations in the Nordic Seas, particularly the Greenland Sea Gyre (GSG) circulation can significantly change the AW characteristics between the entry and exit point of AW in the NS. Further, it is shown that the change in GSG circulation can modify the AW heat distribution in the Nordic Seas and can potentially influence the sea ice concentration therein. Projected enhanced atmospheric forcing in the NS in a warming Arctic scenario and the warming trend of the AW can amplify the role of NS circulation in AW propagation and its impact on sea ice, freshwater budget and deep water formation.</p>

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Antarctic Sea Ice Control on the Depth of North Atlantic Deep Water

Journal of Climate ◽

10.1175/jcli-d-18-0519.1 ◽

2019 ◽

Vol 32 (9) ◽

pp. 2537-2551 ◽

Cited By ~ 6

Author(s):

Louis-Philippe Nadeau ◽

Raffaele Ferrari ◽

Malte F. Jansen

Keyword(s):

Sea Ice ◽

Deep Water ◽

Formation Rate ◽

Deep Ocean ◽

Meridional Overturning Circulation ◽

Ice Formation ◽

Overturning Circulation ◽

Antarctic Sea Ice ◽

Meridional Overturning

Abstract Changes in deep-ocean circulation and stratification have been argued to contribute to climatic shifts between glacial and interglacial climates by affecting the atmospheric carbon dioxide concentrations. It has been recently proposed that such changes are associated with variations in Antarctic sea ice through two possible mechanisms: an increased latitudinal extent of Antarctic sea ice and an increased rate of Antarctic sea ice formation. Both mechanisms lead to an upward shift of the Atlantic meridional overturning circulation (AMOC) above depths where diapycnal mixing is strong (above 2000 m), thus decoupling the AMOC from the abyssal overturning circulation. Here, these two hypotheses are tested using a series of idealized two-basin ocean simulations. To investigate independently the effect of an increased latitudinal ice extent from the effect of an increased ice formation rate, sea ice is parameterized as a latitude strip over which the buoyancy flux is negative. The results suggest that both mechanisms can effectively decouple the two cells of the meridional overturning circulation (MOC), and that their effects are additive. To illustrate the role of Antarctic sea ice in decoupling the AMOC and the abyssal overturning cell, the age of deep-water masses is estimated. An increase in both the sea ice extent and its formation rate yields a dramatic “aging” of deep-water masses if the sea ice is thick and acts as a lid, suppressing air–sea fluxes. The key role of vertical mixing is highlighted by comparing results using different profiles of vertical diffusivity. The implications of an increase in water mass ages for storing carbon in the deep ocean are discussed.

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Circulation of Circumpolar Deep Water and marine environment traced by 127I and 129I speciation in the Amundsen Sea Polynya, Antarctica

Journal of Environmental Radioactivity ◽

10.1016/j.jenvrad.2020.106424 ◽

2020 ◽

Vol 225 ◽

pp. 106424

Author(s):

Shan Xing ◽

Xiaolin Hou ◽

Keliang Shi ◽

Ala Aldahan ◽

Goran Possnert

Keyword(s):

Marine Environment ◽

Deep Water ◽

Amundsen Sea ◽

Circumpolar Deep Water

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Circulation of modified Circumpolar Deep Water and basal melt beneath the Amery Ice Shelf, East Antarctica

Journal of Geophysical Research Oceans ◽

10.1002/2015jc010697 ◽

2015 ◽

Vol 120 (4) ◽

pp. 3098-3112 ◽

Cited By ~ 23

Author(s):

Laura Herraiz-Borreguero ◽

Richard Coleman ◽

Ian Allison ◽

Stephen R. Rintoul ◽

Mike Craven ◽

...

Keyword(s):

Deep Water ◽

East Antarctica ◽

Ice Shelf ◽

Circumpolar Deep Water ◽

Amery Ice Shelf

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Eddy-Resolving Model Estimate of the Cabbeling Effect on the Water Mass Transformation in the Southern Ocean

Journal of Physical Oceanography ◽

10.1175/jpo-d-11-0173.1 ◽

2012 ◽

Vol 42 (8) ◽

pp. 1288-1302 ◽

Cited By ~ 20

Author(s):

L. Shogo Urakawa ◽

Hiroyasu Hasumi

Keyword(s):

Southern Ocean ◽

Deep Water ◽

Water Mass ◽

Formation Rate ◽

Ocean Model ◽

Intermediate Water ◽

Mode Water ◽

Model Estimate ◽

Circumpolar Deep Water ◽

Water Mass Transformation

Abstract Cabbeling effect on the water mass transformation in the Southern Ocean is investigated with the use of an eddy-resolving Southern Ocean model. A significant amount of water is densified by cabbeling: water mass transformation rates are about 4 Sv (1 Sv ≡ 106 m3 s−1) for transformation from surface/thermocline water to Subantarctic Mode Water (SAMW), about 7 Sv for transformation from SAMW to Antarctic Intermediate Water (AAIW), and about 5 Sv for transformation from AAIW to Upper Circumpolar Deep Water. These diapycnal volume transports occur around the Antarctic Circumpolar Current (ACC), where mesoscale eddies are active. The water mass transformation by cabbeling in this study is also characterized by a large amount of densification of Lower Circumpolar Deep Water (LCDW) into Antarctic Bottom Water (AABW) (about 9 Sv). Large diapycnal velocity is found not only along the ACC but also along the coast of Antarctica at the boundary between LCDW and AABW. It is found that about 3 Sv of LCDW is densified into AABW by cabbeling on the continental slopes of Antarctica in this study. This densification is not small compared with observational and numerical estimates on the AABW formation rate, which ranges from 10 to 20 Sv.

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