The distribution and metabolic actlvity of bactenoplankton were examined in relabon to b~ologlcal, chemical and physlcal factors in the marginal ice zone south of the confluence of the Weddell-Scotia Sea during austral spring 1983 Melt water produced by the seasonal retreat of the Ice edge resulted in regions of water wlth reduced salinity and increased vertical strabf~catlon, w h~c h in turn increased average irradiance levels for phototrophic growth The enhanced stability of the water column apparently influenced &stributions of blomass and physiological activlt~es of both autotrophs and heterotrophs Elevated biomass and productivity of phytoplankton and bactenoplankton coincided spatially with maxlma occurring from 100 to 250 km seaward of the ice edge Bacterial abundance and biomass in ice-covered and open water regions averaged 0 7 X 10" cells m-3 and 1 8 mg C m-3 and 1 6 X 10" cells m-3 and 3 7 mg C m-3 respectively Bactenal biomass represented only about 3 % of the total particulate organlc carbon but bacterial productlon integrated over the euphotic zone averaged about 11 % of pnmary production Our results suggest that bacteiloplankton productlon In the marginal ice zone of the Weddell-Scotia Sea contnbutes signlf~cantly to the enhanced biological actlvlty of the region

Sinhng rates of phytoplankton assemblages from the Weddell Sea marginal ice zone were measured during a cruise in November-December 1983. A homogeneous sample method (SET-COL) was used to measure sinking rates which permitted rates of various parameters of particulate matter to be determined simultaneously. Parameters assayed in this study included chlorophyll a. phaeophytin, biogenic silica, particulate carbon, particulate nitrogen, and for certain stations, numbers of diatoms. Sinking rates varied within each measurement but exhibited the following trends:Sinking rates as determined by chlorophyll a ranged from 0 to 2.73 m d-' (Y = 0.89), i.e. are similar to those reported for temperate and subpolar regions of the ocean. Phytoplankton assemblages from pycnoclines generally sank slower than those from the surface; differences in seawater density and viscosity between the 2 depths could account for no more than 5 '10 of the observed differences. Samples placed in the dark tended to sink faster than those placed in surface light. The reported rates represent the setthng of suspended microparticulates within the upper water column in the absence of turbulence and should not be extrapolated to estimate the vertical flux of particulates from the euphotic zone.

Results from photosynthesis-irradiance (P-I) experiments were used to examine photosynthetic adaptations of phytoplankton populations from the Bransfield Strait region in Antarctica during austral winter. Chlorophyll a concentrations during this period were low, ranging from 0.04 to 0.33 pg I-' in the mixed layer. Average photosynthetic efficiency (a) for surface populations was 0.021, andmean maximum photosynthetic rates (P:) were 1.19mg C (mg ch1)-' h-' ( 2 0 . 6 ) No apparent differences were found between photosynthetic parameters for open ocean regions or within the Bransfield Strait, and there was little evidence for adaptation within the water column. Integrated production within the euphotic zone was low, 1 to 7 mg C m-2 d-l, when estimated either from in situ measurements or from P-I relationships. These low primary productivity values support the belief that the waters within the Antarctic remain a region of extremely low productivity during the winter, despite conditions such as water column stratification and saturating surface irradiance levels which could potentially support phytoplankton growth.

We assessed the distribution of biota (autotrophs and heterotrophs) and associated carbonate chemistry variables in Arctic sea ice at latitudes >82°N during late summer and early autumn 2018. The sampled sea ice was relatively thick (average 1.4 m) with variable snow cover (mean 7 cm) and low bulk salinities throughout. Most measured variables, including carbonate chemistry parameters, were low in the upper half of the ice cores, but increased with depth. Measurements of particulate organic carbon (POC), chlorophyll a (chl a), bacterial abundance, and particulate extracellular polysaccharide (pEPS) in the cores strongly suggested that detrital carbon was the major particulate organic pool. Near the ice-water interface, autotrophic material comprised ca. 50% of the total POC, whereas pEPS and bacterial carbon accounted for ca. 8 and 1% of the total POC, respectively. Under-ice water was nutrient poor, providing only a small input of nutrients to support autotrophic growth, at least during the time of our sampling. While the Arctic Ocean has substantial interannual variability in sea-ice concentration and thickness, these measurements enrich the available database and suggest that during years when autumn sea ice is >1 m thick, sea-ice biota are limited in activity and biomass.