Chlorophyll time series in response to irradiance in Antarctic coastal waters

VERNET, 'M.; DIAZ, S.; BAKER, K.; KOZLOWSKI, W.

Buenos Aires

Congreso; SCAR Open Science Conference, Agosto 3-6 2010, Buenos Aires – Argentina; 2010

Scientific Committee on Antarctic Research (SCAR)

The annual cycle in phytoplankton abundance between 1995 and 2007 at Arthur Harbor, Anvers Island, Antarctica (64.5 S, 64.5 W) was estimated from weekly samples obtained within the summer mixed layer at 6 m depth. The seasonal cycle is characterized by a maximum at the end of January (3.14 mg chl m-3) and a minimum in July (0.08 mg chla m-3). There is a seasonal asymmetry with slower increase from July to January and a faster, more pronounced decrease in the fall.  The frequency of summers with high phytoplankton accumulation is ~40% (5 out of 13), as indicated by the monthly anomalies. The 1995-2000 period had positive anomalies in the winter and negative in the summer. In contrast, the period after 2000 has more positive anomalies in the summer, i.e, increased biomass. Thus interannual variability is high, expected to correlate with El Ninio/La Nina conditions and Southern Annular Mode. The seasonal cycle also has high variability. Positive anomalies in the spring (or 1-2 months of anomalous chl concentration) correlate with irradiance 2-3 weeks before.  There is a lag between irradiance and chla accumulation at this time of the year that could correspond to either inhibition at the time irradiance (UVB/UVA) is high or to a slow phytoplankton response to irradiance.