TITLE:     Temporal Dynamics of Coastal Antarctic Phytoplankton: 
           Environmental Driving Forces and Impact of a 1991-1992 
	   Summer Diatom Bloom on the Nutrient and Light Regimes

AUTHORS:   Mark A Moline, Barbara B Prezelin, Oscar Schofield, 
	   and Raymond C Smith

MEETING:   SCAR symposium volume "Antarctic Communities"
           Palmer LTER Contribution No. 47 


ABSTRACT:  Within the Palmer Long Term Ecological Research Program (PAL-LTER) 
at Palmer Station, Antarctica, a suite of environmental data sets were
collected at a nearshore station throughout the 1991-1992 austral summer. 
Seasonal changes are presented in the context of phytoplankton community
ecology.  Subseasonal fluctations in sea ice coverage, fresh water inputs,
as well as wind driven and advective processes disrupting stratified
surface waters, appeared the major driving forces affecting the timing,
duration and demise of local phytoplankton blooms.  Grazing pressure
appeared low throughout the season.  Resulting successional events and
bloom dynamics within phytoplankton communities altered macronutrient
distribution and underwater spectral light fields.  Such impacts were most
evident during a diatom-dominated bloom (>30 mg chl-a m-3) when
macronutrients were depleted below detection limits (NO3- < 0.5 mM, PO43- <
0.1 mM) and significant shifts in nutrient ratios were observed. The strong
attenuation of blue and green light within the water column during the
bloom events may have easily induced photadaptive responses in the largely
light-limited populations that might have led to even greater spectral
attenuation of in situ irradiances had the bloom not been physically
disrupted and apparently removed from the region by strong advective
processes.