Dissolved and Particulate Calcium Concentration in the Southern Ocean

Description

Introduction: This study aims to elucidate the role of dissolved calcium (Ca) and potential alkalinity (PA) as tracers for calcium carbonate (CaCO3) cycling in the Southern Ocean. Understanding the dynamics of these key chemical components contributes to a broader comprehension of oceanic carbon cycling and its potential implications for marine ecosystems. Sampling Sites: Samples were collected in the Australian sector of the Southern Ocean during R/V Investigator voyage IN2020_V08, conducted between 4 December 2020 and 15 January 2021. Samples were collected at three primary sites: the Southern Ocean Time Series (SOTS) site (47°S, 141°E), and two southern sites (SS1 and SS2) located within a polar bloom at approximately 55°S, 138°E, and 58°S, 141°E, respectively. Sampling Methodology: Samples were collected using CTD rosettes at various depths to capture vertical profiles of Ca and PA. The choice of depth range is crucial for understanding the vertical distribution of these tracers. Particulate Ca (pCa) samples were obtained using McLane pumps, focusing on subsurface waters to estimate the standing stock of calcifying species. Data Analysis: Both dissolved and particulate Ca samples were diluted in 2% HNO3 and measured on the ICP-OES for Ca concentrations. The results were normalised to a salinity of 35. Uncertainty in Ca measurements was assessed based on the average one standard deviation of triplicate measurements across the dataset. Nutrient concentrations were measured on board and details can be found in the report at https://www.cmar.csiro.au/data/reporting/get_file.cfm?eov_pub_id=1553. Total alkalinity (TA) was measured at CSIRO, Hobart. PA calculation: PA calculation involves correcting measured TA concentrations for the presence of nitrate (NO3-), nitrite (NO2-), phosphate (PO4(3-)), sulphate (SO4(2-)) and ammonium (NH4+) and normalised for a salinity of 35. The concentration of sulphate is assumed to be 20% of the nitrate contribution. PA=(TA+NO3-+NO2-+PO4(3-)+SO4(2-)-NH4+)∙35/S

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