Increased Rotational Coupling Between Antarctic Sea Ice and the Atmosphere Over the Last 30 Years

Abstract

Antarctic sea ice has been characterized by high temporal and spatial variability since the inception of reliable satellite records. The complex oceanic and atmospheric mechanisms driving this variability present ongoing challenges in determining their respective contributions. We examine the cyclonic and anticyclonic rotation dynamics within the sea ice and overlying atmosphere at daily timescales from 1991 to 2020 using a new generation remote-sensing product for sea-ice drift. A two-dimensional pattern similarity comparison between the ice and atmospheric vorticity fields demonstrated a noteworthy increase in pattern similarity over the past 3 decades, despite the absence of any discernible trends in the mean intensity of either field. This escalating coupling suggests an increasing responsiveness of sea ice to atmospheric forcing, a phenomenon observed across all regions of the Southern Ocean. Notably, sea ice in the Weddell Sea experienced a sharp decline in the intensity of its clockwise and anticlockwise components from 2002 onwards. The increased coupling of sea-ice drift at the synoptic scale with no discernible trends in the atmospheric forcing points to a plausible role of the ocean in modifying the rheology of pack-ice. Analysis of the southern annular mode (SAM) reveals its winter correlation with sea-ice vorticity but not to the observed strengthening of the coupling trend since the winter SAM trend is negligible. Our findings reiterate the predominant role of the atmosphere in driving rotation within Antarctic sea ice, while highlighting a knowledge gap on the possibly increasing influence of the under-ice ocean on drift dynamics.