[M-IS03] The Southern Ocean and the Antarctic Ice Sheet dynamics in past, present and future

[MIS03-P06] Nonlinear response of Antarctic ice-shelf basal melting in a warming climate

*草原 和弥¹、建部 洋晶¹、羽島 知洋¹、齋藤 冬樹¹、河宮 未知生¹ (1.海洋研究開発機構)

Changes in the Antarctic ice sheet play a critical role in the Southern Ocean and global climates. Although many studies have pointed out that enhanced ocean heat delivery onto the Antarctic continental shelf regions can cause large changes in Antarctic ice-shelf basal melting, the associated physical mechanisms require further research. Here, we perform numerical experiments using an ocean-sea ice model with an ice-shelf component to simulate future projections in Antarctic ice-shelf basal melting in a warming climate, focusing on the driving mechanism and the physical linkages with Antarctic sea-ice fields and coastal water masses. The model projects a distinct nonlinear response of ice-shelf basal melting to future atmospheric warming. Detailed examinations of sea ice and water masses demonstrate that in an extreme warming scenario, a combination of enhanced intrusions of warm deep water and warm summertime surface water can cause the nonlinear response of Antarctic ice-shelf basal melting. A large reduction in Antarctic coastal sea ice and the associated freshening effects of increased sea-ice melting in summer and reduced sea-ice production in winter on the coastal water masses provide favorable conditions for summertime warm surface water formation and warm deep water intrusions across the shelf break onto some continental shelves. Our model results demonstrate that disappearing summertime sea ice along the Antarctic coastal margins in a warming climate heralds the nonlinear increase in Antarctic ice-shelf basal melting, possibly contributing to the negative mass balance of the Antarctic ice sheet.