Observed amplification of the seasonal CO2 cycle at the Southern Ocean Time Series

• Published in: Frontiers in Marine Science 2023-10, Vol.10
• Main Authors: Shadwick, Elizabeth H., Wynn-Edwards, Cathryn A., Matear, Richard J., Jansen, Peter, Schulz, Eric, Sutton, Adrienne J.
• Format: Article
• Language: English
• Subjects: Acidification; air-sea CO2 flux; Alkalinity; Anthropogenic factors; Atmospheric forcing; Carbon; Carbon cycle; Carbon dioxide; CO2 partial pressure (pCO2); Deep sea moorings; Fronts; Hydrography; Mixed layer; Mixed layer depth; ocean acidification; Oceanic analysis; pCO2 seasonality; Salinity; Seasonal variation; Seasonal variations; Seasonality; Seawater; Sensors; Southern Ocean Time Series (SOTS); Thermocline; Time series; Trends; Upper ocean; Ventilation
• ISSN: 2296-7745; 2296-7745
• DOI: 10.3389/fmars.2023.1281854

The Subantarctic Zone, the circumpolar region of the Southern Ocean between the Subtropical and Subantarctic fronts, plays an important role in air-sea CO 2 exchange, the storage of anthropogenic CO 2 , and the ventilation of the lower thermocline. Here we use a time series from moored platforms deployed between 2011 and 2021 as part of the Southern Ocean Time Series (SOTS) observatory to investigate the seasonality and interannual variability of upper ocean hydrography and seawater CO 2 partial pressure (pCO 2 ). The region is a net sink for atmospheric CO 2 over the nearly 10-year record, with trends revealing that the ocean pCO 2 may be increasing slightly faster than the atmosphere, suggesting that oceanic as well as anthropogenic atmospheric forcing contributes to the decadal change, which includes a decline in pH on the order of 0.003 yr −1 . The observations also show an amplification of the seasonal cycle in pCO 2 , potentially linked to changes in mixed layer depth and biological productivity.