Linking the recent decrease in Weddell Sea dense shelf water formation to shifts in the Interdecadal Pacific Oscillation

Antarctic Bottom Water (AABW) is formed in select locations around the Antarctic margin, filling the bottom 40% of the world’s ocean and circulating heat, carbon and nutrients throughout all basins. Recent observations suggest that almost half of AABW is formed in the western Weddell Sea and that since 1992, its formation has decreased by around 40%. A combination of anthropogenic warming, through the addition of freshwater from melting glaciers and ice shelves, and natural climate variability, is thought to have led to this drastic decrease. The Interdecadal Pacific Oscillation (IPO), known to exhibit teleconnections to the Weddell Sea, has been proposed as responsible for some of this decrease. However, it remains unclear to what extent recent shifts in the IPO have influenced AABW formation because limited observations include the impact of all natural and anthropogenic climate drivers and not just the IPO. Here we use the 1/10° global ocean-sea ice model ACCESS-OM2 to simulate the isolated impact of the IPO on Weddell Sea dense shelf and bottom water formation. We find indications that southward wind anomalies associated with a negative IPO phase push sea ice towards the coastline, prevent polynyas from opening and have reduce dense shelf and bottom water formation. In the Ross Sea we see the opposite, with more dense shelf water formation during negative IPO phases compared to positive phases, especially for the highest density ranges. This indicates that during IPO phase shifts, Weddell Sea AABW changes might be compensated by changes in the Ross Sea. These findings have implications for interpreting decadal-scale variability in dense shelf and AABW production and its impacts on the global ocean circulation under a rapidly warming climate.