Dimethylsulfide and its precursors and derivatives constitute a major sulfate aerosol source. This dataset incorporates the potential for increased UV radiation effects due to stratospheric ozone depletion over spring and summer in Antarctica, using large-scale incubation systems and 13-14 day incubation periods. Surface seawater (200 micron filtered) from the Davis coastal embayment was incubated during four experiments over the 2002-03 Antarctic Summer. The data incorporates seawater measurements of DMS, DMSP and DMSO over a temporal progression during each incubation experiment. Six polyethylene tanks of varying PAR and UV irradiances were incubated. Water was collected stored and analysed by gas chromatography according to a specific sampling protocol, employed by all investigators associated with the project. The data are organised according to analysis day, with each days calibration data displayed at the top of each sheet. The sample code is followed by GC run number and then the raw count data from the GC. This is calculated to nanomoles DMS, DMSP or DMSO. Sample Codes: Codes for temporal data follow format X.XXXX 1st X gives experiment number, 1 to 4. 2nd X gives sampling day, 0, 0.5, 1, 2, 4, 7, 14 (will result in digit code for day no. less than 10 3rd X gives tank number relating to irradiance level(one to six) 4th and 5th X is replicate number, (01, 02, 03, DMS), (04, 05,06, DMSP total), (07, 08, 09, DMSP dissolved), (10, 11, 12, DMSO total). The fields in this dataset are: Sample Code Run Number from the GC Counts - GC generated raw data Log Counts - logarithmic conversion of the count data Log -c - logarithmic conversion minus the y-intercept determined by calibration of the GC. (log -c)/m - log -c divided by m, determined by calibration of the GC. ngS anti log - nanograms of Sulfur NaOH - NaOH adjustment ngS/L - adjustment per litre nM-DMSP/L - nanoMol's DMSP per litre nm-DMS/L - nanoMol's DMS per litre September 2013 Update: DMSO was analysed in these experiments according to an adaptation of the sodium borohydride (NaBH4) reduction method of Andreae (1980). The method has since been superseded and the data here probably displays inaccuracies as a result of the analytical method used. This DMSO data should be treated with caution.

This project used computer-based modelling and existing field data to analyse the production and cycling of dimethylsulphide (DMS) and predicted its role in climate regulation in the Antarctic Southern Ocean. From the Final Report: Aims (i) To calibrate an existing dimethylsulphide (DMS) production model in a section of the Antarctic Southern Ocean. (ii) To use the calibrated model to investigate the effect of GCM-predicted climate change on the production and sea-to-air flux of DMS under current and enhanced greenhouse climatic conditions. (iii) To provide regional assessments of the sign and strength of the DMS-climate feedback in the Southern Ocean. Characteristics of Study Region: Our study region extends from 60-65 degrees S, 123-145 degrees E in the Antarctic Southern Ocean, and was the site of a major biological study in the austral summer of 1996 (Wright and van den Enden, 2000). Field observations show that a short-lived spring-summer bloom event is typical of these waters (El-Sayed, 1988, Skerratt et al. 1995); however there can be high interannual variability in the timing and magnitude of the bloom (Marchant and Murphy, 1994). The phytoplankton community structure has been described by Wright and van den Enden (2000), who report maximum chlorophyll (Chl) concentrations during January-March in the range (1.0-3.4) microgL-1. During this survey, macronutrients did not limit phytoplankton growth. Thermal stratification of the mixed layer was strongly correlated with high algal densities, with strong subsurface Chl maxima (at the pycnocline) observed. The mixed layer depth determined both phytoplankton community composition and maximum algal biomass. Coccolithophorids (noted DMS producers) were favoured by deep mixed layers, with diatoms dominating the more strongly stratified waters. Pycnocline depth varied from 20-50 m in open water. Algal abundance appeared to be controlled by salp and krill grazing. Field data support the existence of seasonal DMS production in the Antarctic region. However, a large range in DMS concentrations has been reported in the open ocean , reflecting both seasonal and spatial variability (Gibson et al., 1990, Berresheim, 1987; Fogelqvist, 1991). Blooms of the coccolithophores, and prymnesiophytes such as Phaeocystis, form a significant fraction (~23%) of the algal biomass (Waters et al 2000). Concentrations of DMS in sea ice are reported to be very high (Turner et al. 1995) and may be responsible for elevated water concentrations during release from melt water (Inomata et al. 1997). Field measurements of dissolved DMS made in the study region have been summarised by Curran et al. (1998). DMS concentrations were variable in the open ocean during spring and summer (range: 0-22 nM), with the higher values recorded in the seasonal ice zone and close to the Antarctic continent. Zonal average monthly mean DMS in the study region have been estimated by Kettle et al. (1999). (See downloadable full report for reference list). A copy of the referenced publication is also available for download by AAD staff. It contains the modelling information.

Zooplankton grazing experiments using the dilution method have been conducted for 2 months at Davis station and on a weekly basis in order to investigate the relationship between zooplankton grazing rates and DMS production in surface water during the blooming season. Regular water sampling in conjunction with these experiments has been conducted to quantify pigments and phytoplankton populations in the same waters. This work was completed as part of ASAC project 2100 (ASAC_2100). The dataset also includes methods used to obtain the data. The fields in this dataset are: chlorophyll DMS DMSP Pigment Dilution

Data Acquisition: Sampling was performed on seawater collected from CTDs and minicosm experiments. Sampling involved the collection of 250 mL of seawater from each Niskin bottle and minicosm sampled. 100 mL of this was fixed with 1 mL of concentrated hydrochloric acid (HCl). A second 100 mL sample was filtered through a 0.45 micron filter and then fixed with HCl. The remaining water was filtered and purged, with the volatile gases eluted being trapped on gold wool enclosed in glass tubes. Data Analysis: Analysis of the gold wool tubes involved heating the tubes to separate the dimethylsulphide (DMS) and then purge and trap followed by gas chromatography (GC) to give the DMS concentration of the seawater sample. The fixed water samples and filtered fixed water samples were basified and then the DMS formed during this process was purged, trapped and analysed by GC to determine the dissolved and particulate dimethylsulphoniopropionate (DMSP) concentrations. Analysis is expected to take approximately one year to complete. Dataset Format: The data for the CTD sampling is in the following format - CTD Number; Niskin Bottle; DMS Concentration (nM); DMSP particulate concentration (nM); DMSP dissolved concentration (nM) The data for the minicosm sampling is in the following format: Minicosm Number; Minicosm Day; Hour; Tank Number; DMS Concentration (nM); DMSP particulate concentration (nM); DMSP dissolved concentration (nM) Acronyms Used: CTD - conductivity, temperature, pressure DMS - dimethylsulphide DMSP - dimethylsulphoniopropionate DMSO - dimethylsulphoxide GC - gas chromatography This work was completed as part of ASAC projects 2655 and 2679 (ASAC_2655, ASAC_2679).

---- Public Summary from Project ---- Understanding the strength of possible biological feedbacks is crucial to the science of climate change. This project aims to improve our understanding of one such feedback, the biogenic production of dimethylsulphide (DMS) and its impact on atmospheric aerosols. The Antarctic ocean is potentially a major source of DMS-derived aerosols. The project will investigate the coupling between satellite-derived aerosol optical depth, phytoplankton biomass and DMS production in the Antarctic Southern Ocean. From the abstract of the attached paper: We analysed the correlation between zonal mean satellite data on surface chlorophyll (CHL) and aerosol optical depth (AOD), in the Southern Ocean (in 5-degree bands between 50-70 degrees south) for the period 1997-2004), and in sectors of the Eastern Antarctic, Ross and Weddell Seas. Seasonality is moderate to strong in both CHL and AOD signatures throughout the study region. Coherence in the CHL and AOD time series is strong between 50-60 degrees south, however this synchrony is absent south of 60 degrees south. Marked interannual variability in CHL occurs south of 60 degrees south. 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 six weeks in the sea ice zone (SIZ). This is consistent with the ventilation of dimethysulphide (DMS) from sea-ice during melting, and supports field data that records high levels of sulfur species in sea-ice and surface seawater during ice-melt. The fields in this dataset are: Timeseries Worksheet: Date Mean Chlorophyll (mg CHL/cubic metre) Mean Aerosol Optical Depth (no units) 5 Day mean chlorophyll averages 5 day mean aerosol optical depth averages Correlation Worksheet: n - number lag r - correlation coefficient t - student t statistic Global Worksheet Column A = SeaWiFS filename Counter+1 is a counter to indicate the image number in series Date Mean Chlorophyll (mg CHL/cubic metre) Mean Aerosol Optical Depth (no units) Chlorophyll Standard Deviation Mean Aerosol Optical Depth Standard Deviation Chlorophyll Standard Error Mean Aerosol Optical Depth Standard Error Chlorophyll Count (the number of data 'pixels' in the image - the basic pixel size is 9x9km2) Mean Aerosol Optical Depth (the number of data 'pixels' in the image - the basic pixel size is 9x9km2)

From 1991 to 2000 14 voyages have been completed in the Southern Ocean. Measurements of DMS (Dimethylsulfide) and DMSP (Dimethylsulfoniopropionate) have been carried out on surface and subsurface waters together with physical and biological measurements, with a view to understanding the main processes that affect DMS in the Southern Ocean. The first flux measurements have been carried out for DMS (see Curran and Jones 2000) in the last 3 years a concerted study has been carried out in the seasonal ice zone this study aims to identify the major phytoplankton assemblages responsible for DMS and DMSP production in the sea ice zone. It is thought that the sea ice zone also contributes to DMS in the atmosphere. This is being quantified. The fields in this dataset are: Site Date Time (local) Latitude Longitude Snow Cover (metres) Core Length (metres) DMSPt (nano Mols) Chlorophyl a (micrograms per litre) Sea Ice depth (metres) Pigments Fucoxanthin (micrograms per litre) Peridinin (micrograms per litre) 19' hexanoyloxyfucoxanthin (micrograms per litre) Salinity (ppt) Nitrate (micro Mols) Nitrite (micro Mols) Silicate (micro Mols) Phosphate (micro Mols)