Fg. Figueiras et al., LIGHT AND PRODUCTIVITY OF ANTARCTIC PHYTOPLANKTON DURING AUSTRAL SUMMER IN AN ICE-EDGE REGION IN THE WEDDELL-SCOTIA SEA, Journal of plankton research, 16(3), 1994, pp. 233-253
The photosynthesis-irradiance relationships (P-I curves) of natural pl
ankton samples were studied in the Weddell Sea ice-edge zone, between
Elephant Island and South Orkney Islands, during the austral summer of
1988-89. Three water bodies were distinguished in the region: Belling
shausen Sea waters modified after flowing through Drake Passage and Br
ansfield Strait, Weddell Sea waters and Weddell Sea waters modified by
melting. The stations situated in modified Bellingshausen waters show
ed a net phytoplankton composition which was different from that of th
e other two water bodies. Weddell Sea waters and Weddell Sea waters mo
dified by melting of sea ice had the same net phytoplankton compositio
n. In the area of modified Weddell Sea waters, there was an accumulati
on of phytoplankton in the upper 40 m (>4 mg Chl m-3). (P(B)s and alph
a were independent of depth, but varied between stations. The P-1 para
meters exhibited an east-west gradient with the maximum values in the
Elephant Island region, where large diatoms were absent. The light-sat
uration parameter I(k) averaged 35 +/- 13 mumol m-2 s-1. The mean irra
diance of the upper mixed layer was 34 +/- 13 mumol m-2 s-1, thus virt
ually equal to I(k). These results are discussed in the context of cri
tical depth (Z(c)), net compensation irradiance (I(n)) and depth of th
e upper mixed layer (Z(uml)). We suggest that the phytoplankton in the
region is adapted to maximize its carbon uptake and growth rate at th
e mean irradiance of the upper mixed layer (I(uml)) in well-mixed zone
s. We also suggest that the light-saturation parameter (I(k)) could be
the irradiance at which photosynthesis approximately compensates the
total losses of the community (I(n)).