Spatially Coherent Intraseasonal Velocity Fluctuations on the Western Antarctic Peninsula Shelf

Abstract

AbstractWe analyze several year‐long moored current meter records collected on the midshelf and shelf break of the western Antarctic Peninsula in order to describe the major features of the intraseasonal circulation. An empirical orthogonal function (EOF) analysis of all current meter records in any given year reveals that over 49% of the circulation variance follows a spatially coherent, nearly depth‐invariant anticyclonic cell in the downstream vicinity of Marguerite Trough, qualitatively consistent with flow‐topography interaction with the canyon. An analysis of kinetic energy spectra supports the interpretation that the shelf break current is diverted shoreward at the location of the canyon and generates substantial counterclockwise energy at periods shorter than ~10 days as the flow is compressed by a downstream bank. The circulation is well correlated with the long‐shore wind stress both local and remote. Composite velocity profiles under upwelling and downwelling winds show that the change in the barotropic current under different wind states is comparable to or larger than the shear of the mean profile in all years. The barotropic velocity fluctuations are generally not coherent with subpycnocline heat content.