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Abstract:
Sea surface fugacity/partial pressure of carbon dioxide (fCO2ssw/pCO2ssw) was measured in autumn, 26 February-10 April 2019, from Punta Arenas, Chile, across the Weddell gyre and the eastern sector in the Atlantic sector of the Southern Ocean, coast off the Dronning Maud Land, Kong Håkon VII Hav, Antarctica, to Cape Town, South Africa. The study transect was passing through the ice-covered Astrid Ridge region near the Antarctic coast at 68˚S and in the Maud Rise region south of 66˚S in the Weddell Sea. CO2 data coverage during autumn is sparse and this dataset contributes with new surface water xCO2, pCO2 and fCO2 data with focus on the coast off the Dronning Maud Land, Antarctica, to Cape Town, South Africa ( lat 69.007S to 33.9865S long -52.7716E to 18.2651E) . This dataset highlights the importance of increasing seasonal CO2 observations especially during autumn/winter to improving the coverage of surface CO2 data and flux estimates in the seasonal sea ice-covered regions of the Southern Ocean.
CO2 data from the Southern Ocean, Dronning Maud Land cruise with the Norwegian RV Kronprins Haakon, in autumn 2019. The authors wish to be contacted (agneta.fransson@npolar.no) and offered co-authorship, if used in publication.
Quality
Sea surface CO2 molar fractions (xCO2) were measured by an autonomous underway partial pressure of CO2 (pCO2) observation system (General Oceanics® inc, model 8050) which consists of a gas-water equilibrating chamber and an infrared analyzer (LICOR®, Model, 7000). The seawater was pumped from a side intake at 4 m below the sea surface, sprayed through the equilibration chamber; to equilibrate the CO2 in the seawater with the air in the headspace of the chamber, and measured by the infrared analyzer, with an accuracy of ±0.2 ppm. The analyzer was calibrated using three standard gases in synthetic air with CO2 molar fractions of 230, 400, and 550 ppm. The accuracy of the measurements by the General Oceanics system was estimated using secondary standards calibrated towards NOAA gases (traceable to WMO-x93 scale). The sea surface water fugacity of CO2 (fCO2ssw ) were computed from the xCO2 through pCO2 corrected for non-ideal behaviour using SST and SSS following the methods of Pierrot et al., (2009) for fCO2ssw. For an uncertainty in the measured standards of less than 1 ppm (reflecting the standard deviation of the difference between measured standards and certified values), with an accuracy in the equilibrator temperature of 0.01 °C, (0.009 °C at 0 °C water temperature) and at the intake temperature of 0.001 °C, the determined fCO2 will be within 2 µatm as previously stated by Pierrot et al., (2009). This assumes that the pressure is determined within 0.2hPa.4 standard gases for calibration (0, 250, 350, 450 ppm CO2), salinity and temperature, resulting in mole fraction xCO2 (dry air), fCO2 (wet air), quality controlled against discrete samples from surface water intake. Metadata for CO2 data from the Southern Ocean, Dronning Maud Land cruise with the Norwegian RV Kronprins Haakon expocode:58US20190228 Ship: Kronprins Haakon PI: Agneta Fransson, Norwegian Polar Institute, email: agneta.fransson@npolar.no KPH continuous surface water fCO2 dataset. General Oceanics 8050 continuous pCO2 measurements setup. fCO2 of surface seawater is calculated from xCO2 closely following the methods of Pierrot et al. 2009 (P09). The STD gases 2 to 4 were used for calibration. xCO2 is the “bone-dry” mole fraction: the measurement of nearly-dry air corrected for residual water vapour. Beginning/end of dataset: 2019/Feb/28 - 2019/April/10 Lat/lon bounds of dataset: lat 69.007S to 33.9865S long -52.7716E to 18.2651E Processing performed at 2020-11-23-11-22-47 using:
- scripts modified from the reductions scripts created by Steven van Heuven (Groningen University) and
- scripts written by Ylva Ericson (Norwegian Polar Institute). Quality flags: 1=Good; 0=Bad or Missing. Questions? ylva.ericson@npolar.no abs_equ_pres is the absolute equilibrator pressure calculated as the measured differential equilibrator pressure plus Licor pressure.