Dr. Walker Smith
Virginia Institute of Marine Science
Monday, September 26, 2005
3:30 PM
Room 109, Crittenton Hall
Abstract
The Ross Sea, the site of one of the Antarctic’s largest continental shelves
and its most productive and predictable phytoplankton bloom, has been undergoing
substantial changes in physical forcing. In contrast to the West Antarctic
Peninsula/Bellingshausen Sea region (which has experienced dramatic atmospheric
warming and reductions in ice cover, along with attendant biological changes), the
Ross Sea has been experiencing significant increases in ice cover. Limited biological
impacts have been observed, but this may be due to the paucity of time series data for
the region. Shorter-term variations in ice cover that are related to the appearance of
large icebergs have also been observed. We derived an objectively generated chemical
and biological climatology for the Ross Sea using data collected from 22 cruises to the
Ross Sea. The climatology (nitrate, silicic acid, and chlorophyll) clearly showed the
spring phytoplankton bloom, as well as the uncoupling between nitrate and silicic acid
that results from phytoplankton assemblage composition and iron limitation. Decreases
in chlorophyll also are demonstrated. Data from recent field efforts is compared to the
climatology to assess the interannual variations in chemical and biological distributions
and processes. We have found that phytoplankton assemblages seem to be dominated by diatoms
to a much greater extent than in the years that were used to generate the climatology,
and that the variability in assemblage composition (and associated biogeochemical
processes) is significant. In one year (2003-2004) we found a dramatic secondary
bloom of diatoms after a large bloom of Phaeocystis antarctica in spring. We
suggest that this secondary bloom was the result of an input of iron into the surface
layer and speculate it may result from intrusions of Modified Circumpolar Deep Water
from off the continental shelf. If correct, these variations, especially when coupled
to the interannual variations in ice cover, may introduce substantial variability in
phytoplankton distribution and production on a variety of time scales.
Biography
Dr. Smith received a B.S. degree from the University of Rochester and a Ph.D. degree
from Duke University. He is currently a Professor of Marine Science at VIMS. His
research interests center on the controls of phytoplankton growth and the factors
that control the fate of the photosynthetic material in the surface layer of the ocean.
His current research is focused on understanding phytoplankton, nutrient cycling and
organic material cycling processes in the Ross Sea, Antarctica. He is currently
involved in two field projects, IVARS and CORSACS, that are investigating phytoplankton
productivity growth and controls in the Ross Sea.
Reception before seminar at 3:00 PM
Crittenton Hall
Old Dominion University
Norfolk, VA 23529
757-683-5548
Last updated 9/19/2005.
This page is maintained by
Gabriel Franke
Copyright Info: Old Dominion University 2005
