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The heat transported onto the continental shelf by Circumpolar Deep Water (CDW) is the main driver of ice shelf basal melting in the Amundsen Sea. Here, we investigate the slope current system and the variability of the heat transported through the Pine Island- Thwaites central and eastern troughs using data from 5 moorings deployed in the region between 05 March 2012 and 07 February 2016. Substantial variability on intermonthly time scales (3–4 months) is observed in the onshore heat flux, driven primarily by zonal wind stress north of the shelf break. Heat content, onshore flow and heat flux are highly correlated between central and eastern troughs, which are most likely dynamically linked by the zonal wind stress forcing. This is the first time this dynamic link between troughs is observed. In the eastern the Amundsen Sea, during the El Niño of 2015/2016, strong eastward winds led to lower temperatures over the continental shelf while the onshore heat flux is intensified. We hypothesize that this anti-correlation between heat content and heat flux results from a strengthened eastward undercurrent leading to upwelling of a colder and deeper CDW variety. These results highlight the complex and heterogeneous response of this region to environmental and the importance of velocity data for understanding the dynamics in this region. It also suggests that the hypothesized link between large scale atmospheric forcing (e.g. El El Niño-Southern Oscillation) and ice-shelf melt is not produced via changes in heat content, but instead via changes in onshore heat flux.

The Bellingshausen Sea hosts heat transport onto the continental shelf, potentially enhancing ice shelf basal melt. Here, we use the GLORYS12V1 1993-2018 reanalysis to identify physical processes that set seasonal and interannual variability of water mass properties in the Eltanin and Latady Bays on the southern Bellingshausen Sea continental shelf. Annual means of potential temperature from 300 m to the seabed reveal interannual variability and allow separation into warm and cold regimes. The Amundsen Sea Low (ASL) is more intense and extends further east during the warm regime than the cold regime. In the warm regime, a wind-induced reduction of sea ice concentration near the coast increases surface heat loss, convection, and formation of cold dense water in winter, associated with a decrease in heat content of the southern Bellingshausen Sea over time and a net northward heat transport. In contrast, in the cold regime, increased sea ice concentration reduces surface heat loss and thus formation of cold, dense water. Combined with an increase in heat content over time and a net southward heat transport, this results in a warming of the southern Bellingshausen Sea. This suggests that variability in the deep water temperature in the southern Bellingshausen Sea is primarily due to local surface heat fluxes above the shelf. The variability of surface heat fluxes is related to the variability of the ASL and its influence on sea ice extent and local formation of cold, dense water in winter.

Icebergs affect local biological production around Antarctica. We used an ocean glider to observe the effects of a large iceberg that was advected by the Antarctic Slope Current along the continental slope in the northwestern Weddell Sea in early 2012. The high-resolution glider data reveal a pronounced effect of the iceberg on ocean properties, with oxygen concentrations of (13 ± 4) μmol kg^(−1) higher than levels in surrounding waters, which are most likely due to positive net community production. This response was confined to three areas of water in the direct vicinity of the iceberg track, each no larger than 2 km^2. Our findings suggest that icebergs have an impact on Antarctic production presumably through local micronutrient injections, on a scale smaller than typical satellite observations of biological production in the Southern Ocean.

Monitoring the sources and fate of freshwater in the East Greenland Current (EGC) is important, as this water has the potential to suppress deep convection in the Nordic and Labrador Seas if the outflow of freshwater from the Arctic Ocean increases in response to climate change. Here, hydrographic, oxygen isotope ratio and dissolved barium concentration sections across Denmark Strait collected in 1998 and 1999 are used to determine the freshwater composition of the EGC at these times. Comparison of meltwater fluxes at Denmark Strait and Fram Strait indicates a net melting of sea ice into the EGC between these two locations, with a significant proportion of sea ice drifting into the Nordic Seas or on to the East Greenland Shelf. We conclude that the phase of freshwater exiting the Arctic Ocean through Fram Strait is important in determining its possible impact on deep water formation in the Nordic and Labrador Seas.

12 páginas, 12 figuras., In 1987, conductivity-temperature-depth and current data were collected in two oceanographic surveys carried out around the Indian Ocean coral atolls of Aldabra (46° 20′ E, 9° 25′ S) and Cosmoledo (47° 30′ E, 9° 45′ S) between April and July. During the surveys, significant changes were observed in the temperature and salinity of the upper layers. From temperature-salinity analysis, the dominant water masses in the upper layers (0–400 m) were categorized and their origin determined. During the first cruise, TS characteristics changed only slightly. Low salinity waters (S = 34.5–34.6 and T = 28°–30°C), brought from the east by the South Equatorial Current, were dominant in the surface layers. During the second cruise, the surface waters were saltier and cooler (S = 35.1 and T = 25°–26°C) and more homogeneous in the upper 200 m as a result of a greater admixture of a southern water mass. Seasonal cooling at this time was responsible for a deeper surface mixed layer. Near the end of the cruise, TS conditions changed suddenly due to an invasion of southern subtropical water masses in the layers above 200 m. Current meter records were dominated by the regional 50-day oscillation and higher-frequency variability and did not show the expected increase in strength of the South Equatorial Current to indicate onset of the southwest monsoon. The water mass changes were not correlated with changes in the local currents and were probably caused by advection of patches by the large-scale flow., The cruises were funded by NERC grant GR3/5549. The first author acknowledges the studentship and support given by the British Council and Instituto de Investigaciones Eléctricas, México.