Spatial variability of water masses on the Amundsen Sea shelf

Hydrographic data collected during two US-Swedish collaborative cruises in the December 2007 and December 2008 are analyzed to reveal water mass distributions on the continental shelf of the Amundsen Sea. The stratification of water column is distinctly different in the eastern (100°-112°W) and central (112°-120°W) Amundsen Sea shelf, particularly below the permanent pycnocline. In the eastern Amundsen Shelf, warm and salty modified Circumpolar Deep Water (mCDW) dominates the water column from the main thermocline to sea floor. In the central Amundsen Shelf, on average the water column at depth is about 0.7°C colder and 0.15psu fresher than in the eastern basin. The subsurface ridge extended from the Bear Peninsula prevents the lateral mixing between these two basins, resulting such different stratifications. The temperature and salinity distributions on the isosurface of neutral density 28 kg/m3 reveal that such basin scale differences extend from the ice shelf front to the continental shelf break. In addition, the depth of this isosurface near the ice shelf front reaches 900m in the central continental shelf region, about 300m deeper than in the east. Because of the extensive mCDW flooding the east basin and delivering tremendous heat to the ice shelf, the meltwater mixture rises and produces warm intrusion in the thermocline and winter water. In the central Amundsen shelf, the water column is relatively colder and fresher at depth but still about 2°C warmer than in-situ freezing point. The meltwater does not rise much due to the lower ambient density and is exported offshore along the trough in the central continental shelf region below the permanent pycnocline. The results suggest that meltwater is exported at different depths in these two basins.