여름철 동남극 테라노바 만의 순환 변동과 난센 빙붕 기저 용융의 특성

Abstract

Ice shelf basal melting, caused by seawater intrusion and a consequence of ocean-ice shelf interaction, is a significant process that occupies over half of Antarctic ice mass loss. However, It is difficult to evaluate the properties of the ocean in the ice shelf cavity due to restrictive spatiotemporal observation beneath the ice shelf. Terra Nova Bay (TNB) in western Ross Sea, where high-salinity shelf water (HSSW) is formed by polynya activity, has seasonal water mass variations. Nansen Ice Shelf (NIS) near the TNB is a cold-cavity ice shelf with seasonal variations of basal melting influenced by water mass. Previous studies suggested that eddies are vital in heat transport and would support enhanced basal melting in summertime by pushing seawater into the cavity. This study presents the relationship between summertime fluctuations about local circulation and basal melting using 3- dimensional high resolution numerical model with considering ocean-ice interaction. Simulated sea conditions and eddies are analogous to hydrographic data from the same period. The result implies that mesoscale perturbations in TNB dominate regional circulation and lead to NIS basal melting variability by shifting the warm surface water inflow direction. Empirical orthogonal function (EOF) analysis for sea surface height presents mesoscale eddies and the intensity of seasonal mean current. High basal melt arises partially at the western NIS front when cyclonic (clockwise) eddy exists forward the NIS. On the other hand, high basal melt arises at the eastern NIS front when anticyclonic (anticlockwise) eddy exists. Eddies in front of the NIS play a role in adjusting the direction of warm surface water into the cavity. The surface mean current is shifted southward (northward) by cyclonic (anticyclonic) eddy; thus, higher basal melt rates are present intensively at the western (eastern) NIS front. Moreover, vertical distribution of heat advection shows that warm surface water intrudes deeper into the cavity in presence of eddies. This study suggests that the variability of seasonal mean current induced by mesoscale eddies affects surface inflows into the cavity, enhancing local basal melting. Furthermore, spatial variation for NIS melt rates implies the possibility for NIS calving event transpired in April 2016.