No abstract

No abstract

No abstract

[1] Total dimethylsulphoniopropionate (DMSPt), chlorophyll a (Chl a), and algal marker pigments were measured in 12 fast ice cores collected from Prydz Bay, eastern Antarctica (68°-69°S, 77°-79°E) in October 1997 and November 1998. Patterns of DMSPt distribution through the ice were similar on spatial scales of meters to tens of kilometers within ice sheets grouped according to growth history. This reflects the association of DMSP in fast ice with autotrophic biomass distribution, which is intrinsically linked with ice growth and differed between the ice sheets. The 12 fast ice cores were divided into three groups on the basis of ice thickness and year. Concentrations of DMSPt ranged widely from 9 to 1478 nM with marked peaks occurring within each core. Mean DMSPt concentrations were higher (200 nM) in the medium first-year ice (0.7-1.2 m) than in the thick (>1.2 m) first-year ice (90 nM), mainly because of a local surface algal assemblage that may be atypical. The fast ice algal assemblages in surface, interior, and bottom ice were dominated by diatoms (Fucoxanthin:Chl a concentrations >80%). Dinoflagellates and haptophytes were generally small and variable components of the assemblages (Peridinin:Chl a 2-11% and 19 0 -hexanoyloxyfucoxanthin:Chl a 2-4%, respectively). Our data support the important contribution of diatoms to DMSP production in sea ice. Nutrient (nitrate, silicate, phosphate) concentrations were measured for one group of cores. Silicate and Chl a concentrations were significantly correlated (r = 0.30, P < 0.02, Pearson), implying that silicate availability may have regulated algal growth. The Si:P:N ratio in interior ice (27:1:10) was different to that in surface and bottom ice (46:1:23). We have summarized DMSP data reported from six Antarctic sea ice studies to investigate whether comparisons within the growing database need to consider differences in sea ice type, thickness, location, or season. Although concentrations from individual samples ranged over 4 orders of magnitude (<1 to >1000 nM, n = 410), the mean DMSP concentrations during spring/summer were within the range of 107-322 nM, with an overall mean of 178 nM. Mean DMSP concentrations in Antarctic sea ice appear to be comparable between studies and across the Antarctic sea ice zone. We estimate that the Antarctic sea ice zone may contain up to 9 Mmole sulphur as DMSP.

Abstract. Antarctic near-shore waters are amongst the most sensitive in the world to ocean acidification. Microbes occupying these waters are critical drivers of ecosystem productivity, elemental cycling and ocean biogeochemistry, yet little is known about their sensitivity to ocean acidification. A six-level, dose–response experiment was conducted using 650 L incubation tanks (minicosms) adjusted to a gradient in fugacity of carbon dioxide (fCO2) from 343 to 1641 µatm. The six minicosms were filled with near-shore water from Prydz Bay, East Antarctica, and the protistan composition and abundance was determined by microscopy during 18 days of incubation. No CO2-related change in the protistan community composition was observed during the initial 8 day acclimation period under low light. Thereafter, the response of both autotrophic and heterotrophic protists to fCO2 was species-specific. The response of diatoms was mainly cell size related; microplanktonic diatoms (> 20 µm) increased in abundance with low to moderate fCO2 (343–634 µatm) but decreased at fCO2 ≥ 953 µatm. Similarly, the abundance of Phaeocystis antarctica increased with increasing fCO2 peaking at 634 µatm. Above this threshold the abundance of micro-sized diatoms and P. antarctica fell dramatically, and nanoplanktonic diatoms (≤ 20 µm) dominated, therefore culminating in a significant change in the protistan community composition. Comparisons of these results with previous experiments conducted at this site show that the fCO2 thresholds are similar, despite seasonal and interannual differences in the physical and biotic environment. This suggests that near-shore microbial communities are likely to change significantly near the end of this century if anthropogenic CO2 release continues unabated, with profound ramifications for near-shore Antarctic ecosystem food webs and biogeochemical cycling.

No abstract

No abstract

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Antarctic near-shore waters are amongst of the most vulnerable in the world to ocean acidification. Microbes occupying these waters are critical drivers of ecosystem productivity, elemental cycling and ocean biogeochemistry, yet little is known about their sensitivity to ocean acidification. An unreplicated, six-level dose-response experiment was conducted using 650&amp;#8201;L incubation tanks (minicosms) adjusted to fugacity of carbon dioxide (&amp;#402;CO&lt;sub&gt;2&lt;/sub&gt;) from 343 to 11&amp;#8201;641&amp;#8201;&amp;#956;atm. The minicosms were filled with near-shore water from Prydz Bay, East Antarctica and the protistan composition and abundance was determined by microscopy analysis of samples collected during the 18 day incubation. No CO&lt;sub&gt;2&lt;/sub&gt;-related change in the protistan community composition was observed during the initial 8 day acclimation period under low light. Thereafter, the response of protists to &amp;#402;CO&lt;sub&gt;2&lt;/sub&gt; were species-specific for both heterotrophic and autotrophic protists. The response by diatoms was related to cell size, large cells increasing in abundance with low to moderate &amp;#402;CO&lt;sub&gt;2&lt;/sub&gt; (634&amp;#8211;953&amp;#8201;&amp;#956;atm). Similarly, the abundance of Phaeocystis antarctica increased with increasing &amp;#402;CO&lt;sub&gt;2&lt;/sub&gt; peaking at a &amp;#402;CO&lt;sub&gt;2&lt;/sub&gt; of 634&amp;#8201;&amp;#956;atm. Above this threshold the abundances of large diatoms and Phaeocystis antarctica fell dramatically, and small diatoms dominated, therefore culminating in a significant shift in the composition of the protistan community. The threshold CO&lt;sub&gt;2&lt;/sub&gt; level at which the composition changed agreed with that previously measured at this location, indicating it remains consistent among seasons. This suggests that near-shore microbial communities are likely to change significantly near the end of this century if anthropogenic CO&lt;sub&gt;2&lt;/sub&gt; release continues unabated, with profound ramifications for near-shore Antarctic ecosystems.&lt;/p&gt;