Data

Your access to IMOS Biogeochemical Sensors data discovery and exploration is through the Australian Ocean Data Network (AODN) Portal. Users of these data are asked to acknowledge IMOS and the project PI.

The Biogeochemical  Sensors sub-facility data are collected, quality controlled, and formatted to internationally agreed standards (http://www.socat.info/ and Pierrot et al., 2009).

Data are contributed to the Surface Ocean CO2 Atlas (SOCAT), which is a major global data product for surface CO2 to  facilitate the use of these data by researchers in tracking ocean carbon uptake and trends, and in linking the IMOS data coverage to the rest of the global ocean. Satellite data products for chlorophyll in the Southern Ocean derived from improved algorithms that relied on data collected by the SOOP Biogeochemical  project are available to the research community through the AODN portal. Work is also in progress to develop data products on ocean acidification around Australia.

SOCAT decadal 1x1 gridded (v3) around Australia

Quality control and data reduction

The parameters logged by the CO2 system and ship sensors are quality controlled after each voyage (delayed mode data).  Data with missing parameters or obvious outliers based on expected ranges, are marked as missing and removed from the calculations. Parameter values are flagged as good (flag=2), questionable (flag=3), or bad (flag=4).  

The data set parameters are then examined in more detail, including checks for excessive warming of the seawater between the flowing to the equilibrator.

The relative wind speed and direction recorded by the ship meteorological sensors are used to evaluate if anomalous atmospheric measurements could be due to stack gas contamination. This contamination is often observed when relative wind speeds are below about 5 knots and \relative wind directions are less than ±60 degrees over the ship bow. The data with likely stack gas contamination are flagged as bad (flag = 4) and not included in the calculations outlined below.

After completion of the quality control checks, the dry mole fractions are corrected to final values using measurements of the four CO2-in-air standards analysed about every three hours (Table 1). The offsets between the measured and certified values of each standard are linearly interpolated to the times of measurement of each air and equilibrator sample. A linear regression of values versus certified standard values is used at each measurement time to calculate an offset to apply to the air and equilibrator values. The corrections are typically about 1 to 2 ppm and account for drift of the gas analyser response over time. The corrected mole fractions for the equilibrator and air samples are then used to calculate the fugacity of CO2 for saturated air at sea surface temperature and salinity (Pierrot et al., 2009)  Only data flagged as good or questionable are included in the final data set.

References

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Pierrot, D., C. Neill, K. Sullivan, R. Castle, R. Wanninkhof, H. Lüger, T. Johannessen, A. Olsen, R. A. Feely, C. E. Cosca (2009) Recommendations for Autonomous Underway pCO2 Measuring Systems and Data Reduction Routines, Deep-Sea Research II, 56, 512-522, doi:10.1016/j.dsr2.2008.12.005

Shadwick, E, B. Tilbrook and N. Cassar, T. W. Trull and S.R. Rintoul (2015) Summertime physical and biological controls on O2 and CO2 in the Australian Sector of the Southern Ocean, Journal of Marine Systems, 147, 21-28, doi:10.1016/j.jmarsys.2013.12.008

Shadwick, E., T. W. Trull, B. Tilbrook, A. J. Sutton, E. Shulz, C. L. Sabine (2015) Seasonality of biological and physical controls on surface ocean CO2 from hourly observations at the Southern Ocean Time Series site south of Australia. Global Biogeochemical Cycles, 29(2), 223-238. doi: 10.1002/2014GB004906