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  • Metadata record for data from ASAC Project 133 See the link below for public details on this project. Surface carbon dioxide (CO2) observations are integral to understanding the role of the Southern Ocean in the global carbon cycle, and to developing reliable predictions of biogeochemical responses to altered climatic conditions. Carbon dioxide (CO2) observations made in surface waters of the Australian sector of the Southern Ocean between the years 1991 and 2002 were used to estimate the seasonal variability in the fugacity of CO2 (fCO2) and net air-sea carbon fluxes. The results showed a net annual uptake of CO2 by the surface ocean over the entire region. The greatest seasonal uptake and lowest fCO2 values were observed in Spring/Summer in the sub-Antarctic zone (SAZ: 44 degrees S-50 degrees S) and in the Seasonal Sea-ice Zone (SIZ: south of 62 degrees S). The seasonal maximum in uptake for these regions is consistent with increased phytoplankton biomass and shoaling mixed layers over the Spring/Summer period. The High Nutrient Low Chlorophyll waters between 50 degrees S and 62 degrees S, also had maximum uptake in summer, but less compared to the SAZ and SIZ regions. Winter surface waters were close to or slightly above equilibrium, with respect to atmospheric CO2. The reduced uptake in winter appeared due to deeper mixing, lower biomass, and air-sea CO2 exchange. The highest fCO2 values in Winter were observed under or near the seasonal sea-ice where entrainment of deeper CO2-rich waters and ice cover would maintain high surface fCO2 values. The smallest seasonal amplitude in the surface fCO2 and net air-sea fluxes was found from 51 degrees S to 54 degrees S, a region on the southern edge of the SAZ and between the North sub-Antarctic Front and North Polar Front. The uptake estimates derived from the data were in good agreement with the CO2 flux climatology of Takahashi (2002), except in the SAZ and SIZ where we observed greater and less uptake, respectively. Data for this project are available for download - the dataset consists of a data files, and some excel files, which provide further information about each data file (cruise, dates, etc). Furthermore, the column headings used in the data files are as follows: Cruise - name of the cruise which collected the data Date - UTC Time - in UTC Latitude - decimal Longitude - decimal Sst - Sea Surface Temperature in degrees C Teq - Temperature of surface water at which the CO2 measurement is made. Sal - Salinity Patm - atmospheric pressure in hectopascals Shipspd - ship speed in knots Windspd - wind speed in knots Winddir - wind direction in degrees xCO2 - Mole fraction of CO2 in air (dry) equilibrated with surface water and at equilibrator water temperature xCO2air - Mole fraction of CO2 in atmosphere, dry pCO2 - partial pressure of carbon dioxide in surface water

  • Data are "phytoplankton counts" for each phytoplankton taxon observed, from the CPR samples collected by the Southern Ocean CPR Survey projects 472 and 4107 (Hosie et al. 2003). The SAHFOS on-silk phytoplankton count method is used (Batten et al. 2003). Phytoplankton are identified to the best taxonomic level possible, ideally to species or at least genus, in 20 fields of view (295 plus or minus 10 microns) per sample (section of silk). See Figure 2 of Batten et al. (2003). Each sample usually represents 5 nautical miles for SO-CPR. The "phytoplankton count" is the number of fields of view where a phytoplankton species/ taxon was observed, recorded for each taxon for each sample. It is effectively a frequency of occurrence score. The CPR is a device towed at normal ship speed, approximately 100 m behind the ship at a depth of 8-10 m. Plankton enter a small aperture 12.7 x 12.7 mm which then expands into a tunnel 100 x 50 mm reducing the speed by about 1/30. Plankton are then sandwiched between two sheets of 270 micron silk gauze, before rolling into a preservation tank of formaldehyde. Each tow is approximately 450 nautical miles. Regardless of ship speed the silk advances at a fixed rate of about 1 cm per nautical mile. Silks are cut into 5 nautical mile equivalent lengths and both phyto- an zooplankton are counted. Each sample is coded with time and date (GMT) and latitude and Longitude, plus averaged environmental data over the 5 nautical miles, e.g. water temperature, salinity, fluorescence, light. Zooplankton data and methods are described in Metadata record AADC-00099. Abbreviations CPR, Continuous Plankton Recorder SAHFOS, Sir Alister Hardy Foundation for Ocean Science SO-CPR , Southern Ocean CPR Survey

  • ---- Public Summary from Project ---- The Southern Ocean is one the most significant regions on earth for regulating the build up of anthropogenic CO2 in the atmosphere, and the capacity for carbon uptake in the region could be altered by climate change. The project aims to establish a time series of anthropogenic carbon accumulation. The work will be used to identify processes regulating the CO2 uptake and to test models that predict future uptake. 2001-2002 Season: Data collection for this project was solely carried out on voyage three of the 2001/2002 season. Total dissolved inorganic carbon (TCO2) and titration alkalinity (TA) measurements were made on the CLIVAR SR3 section between Hobart and Antarctica. The carbon samples were taken from a 24 bottle rosette and have an approximate horizontal resolution of 60nm with closer spacing in regions where horizontal gradients were large. Many of the stations sampled for carbon had multiple casts to improve vertical resolution. The CRM analyses were used to calibrate the titration cell volume. Preliminary analysis of Certified Reference Material (CRM) Seawater from Scripps Institution of Oceanography show data quality was generally good. For TCO2 the measurements on Batch 52 CRM's the average concentration was 2005.65 +/- 1.36 micromol/kg (n=65; 1 s.d.). For TA the average CRM values were 2224.76 +/- 1.17 micromol/kg (n=45, 1 s.d.). The certified values for Batch 52 was 2005.57 +/- 0.39 and 2224.72 +/- 0.81 micromol/kg for TCO2 and TA, respectively. The fields in this dataset follow standard WOCE naming practices. See the url given below for further details. The fields in this dataset are: EXPOCODE SECT_ID STNNBR CASTNO SAMPNO BTLNBR BTLNBR_FLAG_W DATE TIME LATITUDE LONGITUDE DEPTH CTDPRS CTDTMP CTDSAL CTDSAL_FLAG_W SALNTY SALNTY_FLAG_W CTDOXY CTDOXY_FLAG_W OXYGEN OXYGEN_FLAG_W SILCAT SILCAT_FLAG_W NITRAT NITRAT_FLAG_W PHSPHT PHSPHT_FLAG_W CFC-11 CFC-11_FLAG_W CFC-12 CFC-12_FLAG_W CFC113 CFC113_FLAG_W CCL4 CCL4_FLAG_W TCARBN TCARBN_FLAG_W ALKALI ALKALI_FLAG_W 2008-2009 Season: The Southern Ocean is a critical region on earth for taking up anthropogenic carbon dioxide (CO2) from the atmosphere. Over the past year, underway equipment has been used on a number of Aurora Australis voyages to estimate the air-sea exchange of CO2 and to characterise the variability in the exchange. The information is part of a large long term international effort to determine how much CO2 is being taken up by the ocean and to improve predictions of how the uptake and CO2 storage will change in future. An underway CO2 system was run on a number of voyages on Aurora Australis.