TITLE:    Palmer Long-Term Ecological Research Program: Spatial and Temporal 
          Variability in the Chlorophyll a Distribution

AUTHORS:  Maria Vernet, Raymond C. Smith, Karen S. Baker

MEETING:  Carbon Fluxes and Dynamic Processes in the Southern Ocean:
	  Present and Past

DATES:    28-31 August 1995

PLACE:    Brest, France


ABSTRACT:The central hypothesis of the Palmer LTER program states that the 
annual advance and retreat of the pack ice is a major physical determinant of 
spatial and temporal changes in the structure and function of antarctic marine 
communities.  The  program established in 1991 includes two principal sampling 
modes: a temporal coverage during the growth season (October/November to 
March/April) in the area adjacent to Palmer Station (64deg 46.77S, 
64deg 04.36W) and annual cruises to the continental shelf of the 
Bellinghausen Sea during January/February.  This study analyzes the spatial 
and temporal variability of the phytoplankton biomass, estimated as 
chlorophyll a concentration, in the shelf and in Palmer Station and the 
correlation between the two areas.  
     The average chlorophyll a concentration in the top 30 m of the water 
 column showed strong seasonal and interannual variability in the Palmer area.  
Biomass accumulation started during mid November and was maximum at the end of 
December.  The 91/92 and 94/95 seasons had higher overall chlorophyll a
concentration (from 0.5 mg chla m-3 to 8 and 16 mg m-3, respectively) 
than 92/93 and 93/94.  Years of high chlorophyll a concentrations also showed a 
prolonged bloom, extending into January.  
     Similar interannual variability was observed on the shelf. Average 
chlorophyll a concentration in the top 30 m for 5 transects was 0.91, 1.24 
and 1.85 mg m-3 for January of 93, 94 and 95 respectively.  Spatial 
variability indicated north-south and east-west (onshore-offshore) gradients.  
The average chlorophyll a in the northern transect (LTER 600 grid line, 
64deg 56S, 64deg 24W; 63deg 57.94S, 66deg 51.35W) was twice as high 
as the southern line (LTER 200 grid line, 67deg 30.66S, 70deg 37.38W; 
66deg 26.65S, 73deg 01.97W) with concentrations of 1.20 and 0.68 mg 
chla m-3 respectively.  In addition, inshore chlorophyll concentrations 
(stations .040) had 3 times more chlorophyll biomass than offshore (.200) 
stations (1.35 and 0.47 mg chla m-3 respectively).  
    The onshore-offshore gradient in phytoplankton biomass showed a continuum 
between waters next to Palmer Station and shelf waters: the chlorophyll a 
concentration at the Palmer area was 1.74 times higher than on the shelf at
the same latitude (LTER 600 grid line).  This difference is similar to the 
onshore-offshore gradient in the transect itself, where the station closest 
to shore (600.040) had 2.3 times more clorophyll a than the offshore 
station (600.200).  These results suggest that the dynamics in chlorophyll a
accumulation at Palmer Station are similar to the ones at the shelf waters 
and that the seasonal variability at Palmer Station can be used to estimate 
annual chlorophyll a biomass within the surrounding region.