1398 / 2019-08-10 10:05:28

Basal melt-induced freshening and cooling along the Amery Ice Shelf calving front, East Antarctica

15、冰冻圈科学 > 专题6：海-冰-气相互作用的物理过程和机制

While strong warming and salinification of subsurface coastal waters has been observed in the West Antarctic over recent decades, there has been relatively little change observed in the East Antarctic (EA). And yet ocean-based estimates of basal melt rates in the EA are much higher than satellite-based glaciological estimates, suggesting EA shelf waters and ice shelves are more sensitive to Southern Ocean change. Here we analyze repeat sections of oceanographic observations from eight cruises for 2001-2015 along the calving front of the Amery Ice Shelf (AIS), the largest ice shelf in the EA, showing that waters at intermediate and bottom depths on the shelf have freshened (0.020±0.024 per decade) and cooled (0.036±0.039 °C per decade) substantially. This freshening and cooling tendency is attributed to an enhanced fraction of glacial meltwater from AIS basal melt, driven by warm modified Circumpolar Deep Water (mCDW) intrusions. A warming signal on the shelf due to mCDW intrusions from March-July is strongly correlated, at a ~60 days lag, with zonal wind changes, offshore from the shelf break, with a ~60 days lag. This suggests that the autumnal-early winter mCDW intrusions are determinedwere driven by offshore wind changes in January-May when a southward displacement of the westerly wind pattern occurs. Though the Southern Annular Mode index shows a stabilization since 2001, the wind stress curl during the austral summer and autumn across 2000-2015 displays an overall strengthening trend. This promotes warm water intrusions onto the shelf through stronger upwelling of mCDW and increases oceanic heat supply to the AIS cavity. These findings are the first to showcase the strong sensitivity of AIS basal melt to long-term recent intra-decadal changes in the Southern Ocean, confirming the current hypothesis that increasing basal melt rate of the AIS will reduce both the formation rate and the density of the Antarctic Bottom Water produced in the EA.