Investigating the relation between aerosol optical depth, dimethylsulphide production and phytoplankton dynamics in the Antarctic Southern Ocean
CHL (mg per cubic metre) and AOD were obtained from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) archive for the period Sept 1997 - Feb 2004. Level 3 (9x9 square kilometre) 8-day binned data representing 46 products per year were processed into standard mapped image (SMI) format. The AOD is p...
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Australian Ocean Data Network
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| Online Access: | https://researchdata.ands.org.au/investigating-relation-aerosol-southern-ocean/686479 https://data.aad.gov.au/metadata/records/ASAC_2319 http://data.aad.gov.au/aadc/portal/download_file.cfm?file_id=1788 http://oceancolor.gsfc.nasa.gov/SeaWiFS/ https://secure3.aad.gov.au/proms/public/projects/report_project_public.cfm?project_no=2319 http://nsidc.org/ http://data.aad.gov.au/aadc/metadata/citation.cfm?entry_id=ASAC_2319 |
| Summary: | CHL (mg per cubic metre) and AOD were obtained from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) archive for the period Sept 1997 - Feb 2004. Level 3 (9x9 square kilometre) 8-day binned data representing 46 products per year were processed into standard mapped image (SMI) format. The AOD is proportional to aerosol particle concentration from the ocean surface to the top of the atmosphere and can be retrieved with an accuracy of 10%. This resulted in 323 images layered into composite files for each of CHL and AOD. Sea ice data were obtained from the 'Nimbus-7 SMMR, DMSP SSM/I Passive Microwave Data, Daily and Monthly Polar Gridded Sea Ice Concentration' data administered by the National Snow and Ice Data Centre (NSIDC). The wind speed climatology was obtained from the NCAR data repository (Scientific Computing Division Data Support Section, Boulder, CO). The time series were analysed in four global latitude bands: 50-55 S, 55-60 S, 60-65 S and 65-70 S. Five-period moving averages were used to analyse temporal trends between mean CHL and AOD using data from each octad. Cross-correlation was then used to determine the relationship between parameters within each global band with a plus or minus 7 period lag. A lag of L periods referred to the correlation of CHL(t) with AOD(t=t+L). In the (60-70 S) band, data were only available from Sept-April due to the Antarctic winter. To retain valid sample sizes, bi-yearly data-sets were lagged and then appended to create a single multi-year data set (1997-2004) within each latitude band. The relationship between CHL and AOD was also explored in the longitudinal sectors: a) the Eastern Antarctic (110-140 E, 60-70 S), b) the Ross Sea (160-135 W, 60-80 S) and c) the Weddell Sea (65-0 W, 55-80 S). To explore the contribution of the SIZ to algal productivity and aerosol loads we compared the temporal cycles in CHL, AOD and sea ice cover. Mean monthly ice cover was calculated for the period Jan 1997 - Dec 2003 for 2 degree global latitude bands between 60-71 S. Effectively, this provided data up to the eastern Antarctic coastline. To ensure valid data for regions above 70 S, the analysis was repeated to cover the Ross and Weddell Sea sectors that extend further south. --- 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) |
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