TITLE:     Temporal dynamics of coastal Antarctic phytoplankton:
           physical/chemical/biological linkages through a summer diatom bloom
AUTHOR:    MA Moline, BB Prezelin, O. Schofield, RC Smith
PAGE:      189 of SCAR SIXTH BIOLOGY SYMPOSIUM, Antarctic Communities: Species,
           Structure and Survival 
ABSTRACT:  Within the Palmer Long Term Ecological Research Program (LTER), a
suite of biological, chemical, optical and hydrographic datasets were
collected in the vicinity of the Palmer Station, Antarctica, throughout the
1991-1992 austral summer.  The temporal variation in data parameters, derived
from intensive vertical profiling of one nearshore station (Station B), are
presented here as part of an assessment of the driving forces influencing
phytoplankton community structure within the LTER grid.  Seasonal transitions
and episodic events in the physical regime led to significant temporal changes
in distribution and abundance of phytoplankton, as measured via chemotaxonomic
marker pigments.  Sea ice coverage and fresh water inputs combined with mixed
layer fluctuations, due to wind and advective forces, were determinates for
community composition.  Grazing pressure, measured by chlorophyll degradation
products, were low throughout the summer season.  Changes in phytoplankton
community structure impacted macronutrient abundance and general optical
properties of the water column.  These changes were particularly evident
during a major diatom-dominated bloom (>30 mg Chl-a/m3) that was preceded by a
shallowing of the mixed layer and apparently dissipated by advective
processes.  During the bloom, depletion of dissolved macro nutrients to below
detection limits (NO3->0.5 uM, PO43-<0.1 uM) and a significant shift in the
ratio of these nutrients were observed.  Attenuation of light by the high
biomass caused light limitation below 10m.   Shifts in phytoplankton community
structure over the summer season are discussed in context of dynamic physical
and chemical environments.