Meteorology and oceanography of the Northern Gulf of Alaska

Abstract

The Gulf of Alaska shelf is dominated by the Alaska Coastal current (ACC), which is forced by along-shore winds and large freshwater runoff. Strong cyclonic winds dominate from fall through spring, and substantial runoff occurs from late spring through fall with annual distributed freshwater discharge greater than that of the Mississippi River. We examine the ACC from Icy Bay to Unimak Pass, a distance of over 1500 km. Over this distance, the ACC is a nearly continuous feature with a marked freshwater core. The annual mean transport, as measured from current meters, is approximately 1.0×10 6 m 3 s −1 along the Kenai Peninsula, with transport decreasing as the ACC travels westward. Even though the coastal GOA is a predominately downwelling system, it supports a productive ecosystem. Macro nutrients from the basin are provided to the coastal system through a number of processes including topographic steering, eddies, upwelling in response to horizontal shear in the barrier jets, and during winter the on-shelf flux in the surface Ekman layer. Micronutrients (e.g., iron) are supplied from mechanisms such as resuspension of shelf sediments and river discharge. While strong seasonal cycles and interannual variability are dominant scales in atmospheric forcing and the oceanic response, there is also forcing on ENSO and decadal time scales.