Spatial/temporal patterns in Weddell gyre characteristics and their relationship to global climate

Abstract

We examine the spatiotemporal variability of the upper ocean sea ice system of the Atlantic sector of the Southern Ocean subpolar seas (Weddell gyre) and the nature of its covariability with extrapolar climate. To systematically evaluate the sporadic and sparse distribution of subpolar data, we employed an optimal analysis involving empirical orthogonal functions (EOFs). The EOFs reveal that the pattern of spatial covariability of Weddell gyre characteristics is dominated by high interannual variability near the northern (circumpolar) rim of the gyre and lesser variability (10–20% of the variance) in the gyre's central core region. We find considerable, statistically significant teleconnections between subpolar and extrapolar climate. The dominant link is with El Niño–Southern Oscillation. Our analysis of the gyre characteristics suggest that during El Niño, the Atlantic subpolar (Weddell) gyre spins up while the eastern Pacific subpolar gyre spins down; the opposite occurs for La Niña. This regional subpolar response is consistent with recent GCM modeling analyses. These show that equatorial warm anomalies drive changes in the meridional and zonal atmospheric circulation cells. This results in opposite shifts of the subpolar jets in the Pacific and Atlantic oceans that lead to a change in the interaction (especially in cyclones) between the subtropical and polar front jets in those basins, and ultimately in the cyclonic forcing of the subpolar gyres. We also find that the Weddell gyre interior upper ocean characteristics covary positively with sea ice extent in the Atlantic region and negatively with the sea ice extent in the Amundsen/Bellingshausen regions, reflecting a strong Antarctic dipole.