Date of Award
Doctor of Philosophy (PhD)
Thomas C. Royer
Larry P. Atkinson
The Northeast Pacific GLOBEC (GLOBal ocean Ecosystems dynamics) program (October 1997 to December 2004) collected hydrographic data along the Seward Line that stretches from the inner shelf (GAM 59.8°N, 149.5°W) and extends over 200 km beyond the continental slope (GAK13 58.1°N, 147.8°W). The complexity of the interannual hydrographic variability in this area stems from the interacting influences of local forcing such as winds, coastal freshwater discharge, eddies, fronts and remote forcing like El Niño-Southern Oscillation. Until now, the influence of winds on the system has been calculated using coarse resolution upwelling index data or spatially sparse buoy data. The coarse resolution wind measurements cannot describe the cross shelf spatial variations of the winds which are expected to be significant due to the influence of the high coastal mountain chain on atmospheric motion. A new source of high resolution wind velocity data is from satellite scatterometers. Scatterometer wind data have spatial resolutions fine enough to calculate velocity shears across the shelf. On average the wind shears produce positive wind stress curls which promote upwelling due to Ekman pumping. Calculations show that the transport due to this upwelling is 25% - 50% of the transport due to Ekman transport. On average Ekman transport produces downwelling while the transport due to Ekman pumping produces upwelling. The effect of the downwelling due to Ekman transport is apparent near the coast (0 - 20 km from the coast) at depths between 50 - 250 m. In this area there is a significant positive correlation between the anomalies of salinity with the anomalies of Ekman transport. The effect of the upwelling due to Ekman pumping is seen in the mid-shelf area (40 - 80 km from the coast) at depths between 100 - 200 m. Here the anomalies of salinity are positively correlated with the anomalies of vertical velocities. The covariance between the temperature and salinity across the Seward Line suggests that offshore surface spreading of the Alaska Coastal Current and entrainment generates a deep onshore flow of high saline, warm water onto the shelf. The onshore flow of water is expected to be high in nutrients which can then be brought up to the euphotic zone by the upwelling produced by Ekman pumping. The upwelling could be an important mechanism to supply nutrients to the surface layer.
"Annual and Interannual Variability in the Wind Field and the Hydrography Along the Seward Line in the Northern Gulf of Alaska"
(2007). Doctor of Philosophy (PhD), dissertation, Ocean/Earth/Atmos Sciences, Old Dominion University, DOI: 10.25777/91vw-rq18