Understanding the interannual variability of pCO2 in the sea-ice impacted Southern Ocean

Jojo, Bongiwe

Understanding the interannual variability of pCO2 in the sea-ice impacted Southern Ocean

Thesis / Dissertation

2024

Publisher

University of Cape Town

Department

Department of Oceanography

Faculty

Faculty of Science

Abstract

Sea-ice is permeable and plays an active role in the marine carbon cycle via biological and physio-chemical processes. The carbon cycle in seasonally sea-ice-covered waters needs to be better understood due to a lack of observational data and the system's complexity. To characterize the interannual variability of oceanic pCO2 in the sea-ice-impacted Southern Ocean and identify their potential primary drivers, this thesis combines in situ observations with remotely sensed data and reanalysis models during the austral summer months. The region of focus is divided into three sections: the Southern Ocean, three ocean basins, and the Goodhope line transect. Averaged over the Southern Ocean, the range of year-to-year variability of pCO2 between 2000 to 2018 was between 290 atm (2004) and 355 atm (2003). It is also noted that the interannual variability in pCO2 does not correspond to that of the Southern Annular Mode (SAM) index; however, there are some indications that the SAM may be an essential driver on longer time scales. Noticeably, the year 2016 stands out as one of the warmest and has the smallest Antarctic sea-ice extent (SIE) recorded since 1979 in the Southern Hemisphere. This SIE reduction has been attributed to positive sea surface temperature anomalies, the zonal wave pattern 3, and a SAM negative phase. pCO2 decreased in response to this ice loss event highlighting its sensitivity to rapid changes in sea ice. Overall, salinity obtains the highest correlation to the annually averaged pCO2 in the Southern Ocean and various basins. Along the Goodhope Line, variability of pCO2 indicated a higher magnitude and interannual variability of pCO2 during early summer than late summer. Non-thermal drivers primarily explain the variability of pCO2. These results suggest that the leading causes of the interannual variability of pCO2 in the sea ice-impacted Southern Ocean are those associated with non-thermal drivers of pCO2.

Keywords

oceanography

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