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[1] The relationship between the production of dimethylsulfide (DMS) in the upper ocean and atmospheric sulfate aerosols has been confirmed through local shipboard measurements, and global modeling studies alike. In order to examine whether such a connection may be recoverable in the satellite record, we have analyzed the correlation between mean surface chlorophyll (CHL) and aerosol optical depth (AOD) in the Southern Ocean, where the marine atmosphere is relatively remote from anthropogenic and continental influences. We carried out the analysis in 5-degree zonal bands between 50°S and 70°S, for the period (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004), and in smaller meridional sectors in the Eastern Antarctic, Ross and Weddell seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study regions. Coherence in the CHL and AOD time series is strong in the band between 50°S and 60°S, however this synchrony is absent in the sea-ice zone (SIZ) south of 60°S. Marked interannual variability in CHL occurs south of 60°S, presumably related to variability in sea-ice production during the previous winter. We find a clear latitudinal difference in the cross correlation between CHL and AOD, with the AOD peak preceding the CHL bloom by up to 6 weeks in the SIZ. This suggests that substantial trace gas emissions (aerosol precursors) are being produced over the SIZ in spring (October-December) as sea ice melts. This hypothesis is supported by field data that record extremely high levels of sulfur species in sea ice, surface seawater, and the overlying atmosphere during ice melt.Citation: Gabric, A. J., J. M. Shephard, J. M. Knight, G. Jones, and A. J. Trevena (2005), Correlations between the satellite-derived seasonal cycles of phytoplankton biomass and aerosol optical depth in the Southern Ocean: Evidence for the influence of sea ice, Global Biogeochem. Cycles, 19, GB4018,

Marked regional differences in dissolved dimethylsulphide (DMS), atmospheric DMS and DMS flux were recorded during July 1997 through the northern Great Barrier Reef, Coral Sea, Gulf of Papua, Solomon and Bismarck Seas. Highest concentrations of dissolved DMS occurred in the Coral Sea, Gulf of Papua and Bismarck Sea, with lower concentrations in the Great Barrier Reef and Solomon Sea. Elevated levels of atmospheric DMS often occurred in south-easterly to southerly trade winds sampled in the region 18°32′–8°12′S to 145°–151°E, where the highest biomass of coral reefs occurred. Atmospheric DMS often increased in the day after low tides and was positively correlated with tidal height in the northern Great Barrier Reef (r = 0.91, P < 0.05). For tides less than 1.6 m, atmospheric DMS increased on the rising tide for the northern GBR and NW Coral Sea (r = 0.66; P < 0.05) and for the whole voyage (r = 0.25; P < 0.05). As coral reefs have been identified as significant sources of DMS, it is suggested that the daytime increase in atmospheric DMS over much of the study area was mainly a result of high winds and extremely low tides in July, which exposed the reefs during the day.

[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.

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