Investigations of biophysical origins for continental shelf productivity
Terry Whitledge, Ph.D.,
University of Alaska Fairbanks
Wednesday, May 26, 2004
Pacific Forum – 3:00 p.m.
The relatively high productivity of the Gulf of Alaska shelf is enigmatic because it is located in a region that is predominately downwelling. A series of Long Term Observation Program (LTOP) cruises for the GOA GLOBEC project has identified the major physical processes that are responsible to shelf enrichment of nutrients. However, temporal and spatial variabilities are quite large so traditional CTD/rosette profiles are inadequate to provide detailed understanding. Moored in situ NAS-2EN nitrate sensors have provided a new understanding of the temporal dynamics of nutrient drawdown and towed SeaSoar/ISUS sensors have provided many new details of finescale and mesoscale spatial variability.A long term biophysical mooring at site M2 has been maintained on the SE Bering Sea shelf for more than 10 years. The observations of changing of physical conditions and productivity responses during several seasonal and annual cycles has greatly improved our understanding of how productivity is related to physical processes and has lead to a new Oscillating Control Hypothesis. In situ nitrate sensors (NAS and ISUS) have been deployed for three years with some success at five locations (M2, M3, M4, NBering and A3 in Bering Strait). Recent Eulerian nitrate measurements show the fall and winter enrichments processes that occur at the 70m isobath. Additional sites are being planned to provide a line of moorings along the 70m isobath for the entire eastern Bering Sea shelf.