Varela, D. E. University of British Columbia, varela@unixg.ubc.ca
Harrison, P. J. University of British Columbia, pharrisn@unixg.ubc.ca
Shipe, R. F. University of California, shipe@lifesci.ucsb.edu
Brzezinski, M. A. University of California, brzezins@lifesci.ucsb.edu
Harris, S. L. University of British Columbia, shharris@unixg.ubc.ca

 
NEW AND REGENERATED NITROGEN PRODUCTION BY PHYTOPLANKTON ASSEMBLAGES FROM A COASTAL UPWELLING REGIME IN THE NORTHEASTERN PACIFIC: COMPARISON TO BIOGENIC SILICA PRODUCTION
 
Uptake rates of nitrate, ammonium and urea were studied along inshore-offshore transects on the west coast of Vancouver Island (Canada) during the upwelling periods (spring to fall) of 1997 and 1998. Nitrate was the dominant nitrogen source for phytoplankton and f-ratios were > 0.5. Nitrogen uptake rates, mainly nitrate, increased towards the north where the continental shelf is very narrow, and upwelling is more intense. In contrast, studies done along a transect in the oceanic NE subarctic Pacific, extending from the continental slope off the southwest coast of Vancouver Island to Station Papa, showed that phytoplankton utilised mainly regenerated nitrogen forms year round, despite the availability of nitrate, and f-ratios were on average 0.2. Therefore, there seems to be a transition between a continental shelf system which relies primarily on new nitrogen, to a system relying on regenerated nitrogen in the oceanic NE Pacific. In addition to nitrogen uptake, silicon uptake rate experiments were also conducted along the west coast of Vancouver Island during May 1998. The ratios of silicon to nitrogen production will be discussed. These simultaneous measurements provide a unique data set that allows the comparison of estimates of export fluxes of nitrogen and silicon.
 
Day: Friday, Feb. 5
Time: 04:45 - 05:00pm
Location: Sweeney Center
 
Code: SS13FR0445S