Role of Weddell Sea ice in South Atlantic atmospheric variability

The results of underwater observations and sampling of krill (Euphausia superba) in the western Weddell Sea during the joint Russian-USA Ice Station Weddell-1 Expedition (11 February–9 June 1992) are presented. Krill was sampled from the same large ice floe composed of both 1- and 2-year ice as it drifted northward for a distance of c. 700 km. Abundance estimates for krill under this floe were in the range 0.1–6.25 ind m−2. Krill aggregate in areas where rafting of ice floes and formation of new ice occur, or around a protected diving hole. The krill sampled consisted mainly of furcilia 6 and post-larvae which did not belong to the 0+ group originating in this (1991–92) year, but presumably hatched in the summer season of 1990–91 and developed very slowly so that at the end of the following summer season, larval stages were still present in the population. No increase of the mean krill size was observed during 2.5 months of observation. The role of larval advection for the maintenance of krill population in the Weddell Sea is discussed.

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Internal Ocean Dynamics Control the Long-Term Evolution of Weddell Sea Polynya Activity

Frontiers in Climate ◽

10.3389/fclim.2021.718016 ◽

2021 ◽

Vol 3 ◽

Author(s):

Jonathan W. Rheinlænder ◽

Lars H. Smedsrud ◽

Kerim H. Nisanciouglu

Keyword(s):

Sea Ice ◽

Deep Convection ◽

Vertical Mixing ◽

Open Ocean ◽

Weddell Sea ◽

Ocean Dynamics ◽

Heat Reservoir ◽

Ice Dynamics

Open-ocean polynyas effectively couple the ocean and atmosphere through large ice-free areas within the sea-ice cover, release vast quantities of oceanic heat, and impact deep ocean ventilation. Changes in polynya activity, particularly in the Weddell Sea, may be key to longer time-scale climate fluctuations, feedbacks and abrupt change. While changes in the occurrence of Weddell Sea polynyas are generally attributed to changes in the atmospheric surface forcing, the role of internal ocean dynamics for polynya variability is not well-resolved. In this study we employ a global coupled ocean-sea ice model with a repeating annual atmospheric cycle to explore changes in Weddell Sea water mass properties, stratification and ocean circulation driven by open-ocean polynyas. During the 1300-year long simulation, two large polynyas occur in the central Weddell Sea. Our results suggest that Weddell polynyas may be triggered without inter-annual changes in the atmospheric forcing. This highlights the role of ocean processes in preconditioning and triggering open-ocean polynyas on multi-centennial time-scales. The simulated polynyas form due to internal ocean-sea ice dynamics associated with a slow build-up and subsequent release of subsurface heat. A strong stratification and weak vertical mixing is necessary for building the subsurface heat reservoir. Once the water column turns unstable, enhanced vertical mixing of warm and saline waters into the surface layer causes efficient sea ice melt and the polynya appears. Subsequent, vigorous deep convection is maintained through upwelling of warm deep water leading to enhanced bottom water formation. We find a cessation of simulated deep convection and polynya activity due to long-term cooling and freshening of the subsurface heat reservoir. As subsurface waters in the Southern Ocean are now becoming warmer and saltier, we speculate that larger and more persistent Weddell polynyas could become more frequent in the future.

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Trends in Arctic sea ice and the role of atmospheric circulation

Atmospheric Science Letters ◽

10.1002/asl2.423 ◽

2013 ◽

Vol 14 (2) ◽

pp. 97-101 ◽

Cited By ~ 27

Author(s):

Masayo Ogi ◽

Ignatius G. Rigor

Keyword(s):

Sea Ice ◽

Atmospheric Circulation ◽

Arctic Sea Ice ◽

Arctic Sea

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Salinity effects on cultured Neogloboquadrina pachyderma (sinistral) from high latitudes: new paleoenvironmental insights

Geo-Marine Letters ◽

10.1007/s00367-020-00677-1 ◽

2021 ◽

Vol 41 (1) ◽

Author(s):

Jacqueline Bertlich ◽

Nikolaus Gussone ◽

Jasper Berndt ◽

Heinrich F. Arlinghaus ◽

Gerhard S. Dieckmann

Keyword(s):

Sea Ice ◽

Cold Water ◽

Weddell Sea ◽

Wall Thickening ◽

High Latitudes ◽

Neogloboquadrina Pachyderma ◽

Antarctic Sea Ice ◽

The Antarctic ◽

Water Species ◽

Cold Water Species

AbstractThis study presents culture experiments of the cold water species Neogloboquadrina pachyderma (sinistral) and provides new insights into the incorporation of elements in foraminiferal calcite of common and newly established proxies for paleoenvironmental applications (shell Mg/Ca, Sr/Ca and Na/Ca). Specimens were collected from sea ice during the austral winter in the Antarctic Weddell Sea and subsequently cultured at different salinities and a constant temperature. Incorporation of the fluorescent dye calcein showed new chamber formation in the culture at salinities of 30, 31, and 69. Cultured foraminifers at salinities of 46 to 83 only revealed chamber wall thickening, indicated by the fluorescence of the whole shell. Signs of reproduction and the associated gametogenic calcite were not observed in any of the culture experiments. Trace element analyses were performed using an electron microprobe, which revealed increased shell Mg/Ca, Sr/Ca, and Na/Ca values at higher salinities, with Mg/Ca showing the lowest sensitivity to salinity changes. This study enhances the knowledge about unusually high element concentrations in foraminifera shells from high latitudes. Neogloboquadrina pachyderma appears to be able to calcify in the Antarctic sea ice within brine channels, which have low temperatures and exceptionally high salinities due to ongoing sea ice formation.

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Variation in phytoplankton standing stock, chemical composition and physiology during sea-ice formation in the southeastern Weddell Sea, Antarctica

Journal of Experimental Marine Biology and Ecology ◽

10.1016/0022-0981(93)90054-r ◽

1993 ◽

Vol 173 (2) ◽

pp. 211-230 ◽

Cited By ~ 43

Author(s):

Markus Gleitz ◽

David N. Thomas

Keyword(s):

Chemical Composition ◽

Sea Ice ◽

Standing Stock ◽

Weddell Sea ◽

Ice Formation

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The Role of Oceanic Heat Advection in the Evolution of Tropical North and South Atlantic SST Anomalies*

Journal of Climate ◽

10.1175/jcli3961.1 ◽

2006 ◽

Vol 19 (23) ◽

pp. 6122-6138 ◽

Cited By ~ 30

Author(s):

Gregory R. Foltz ◽

Michael J. McPhaden

Keyword(s):

Surface Flux ◽

South Atlantic ◽

Shortwave Radiation ◽

Heat Advection ◽

Horizontal Advection ◽

Latent Heat Loss ◽

North And South ◽

Sst Gradient ◽

Sst Anomalies

Abstract The role of horizontal oceanic heat advection in the generation of tropical North and South Atlantic sea surface temperature (SST) anomalies is investigated through an analysis of the oceanic mixed layer heat balance. It is found that SST anomalies poleward of 10° are driven primarily by a combination of wind-induced latent heat loss and shortwave radiation. Away from the eastern boundary, horizontal advection damps surface flux–forced SST anomalies due to a combination of mean meridional Ekman currents acting on anomalous meridional SST gradients, and anomalous meridional currents acting on the mean meridional SST gradient. Horizontal advection is likely to have the most significant effect on the interhemispheric SST gradient mode through its impact in the 10°–20° latitude bands of each hemisphere, where the variability in advection is strongest and its negative correlation with the surface heat flux is highest. In addition to the damping effect of horizontal advection in these latitude bands, evidence for coupled wind–SST feedbacks is found, with anomalous equatorward (poleward) SST gradients contributing to enhanced (reduced) westward surface winds and an equatorward propagation of SST anomalies.

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