Investigating outgassing of CO2 from the Southern Ocean over the last 65 kyr using boron isotopes in the planktic foraminifera Globigerina bulloides

• Main Author: Shuttleworth, Rachael
• Format: Thesis
• Language: English
• Published: University of Southampton 2020
• Subjects: Antarctic; Southern Ocean; The Antarctic; Antarc*; ice core; Sea ice
• Online Access: https://eprints.soton.ac.uk/445503/; https://eprints.soton.ac.uk/445503/1/RShuttleworth_PhDThesis_Nov2020.pdf

Over the last 2.5 million years the Earth has regularly cycled between cold glacial and warm interglacial periods. Ice core records demonstrate that changes in atmosphericCO2 concentrations are a major climate forcing, which results in these changes in global climate. Although the scale and speed of atmospheric CO2 changes point to the vast deep ocean carbon reservoir as playing a crucial role, the mechanisms of CO2 supply and sequestration between the deep ocean and atmospheric carbon reservoirs remain an ongoing debate in the palaeoclimate community. The Southern Ocean is a major region of modern ocean-atmosphere CO2 exchange and has long been considered to play a key role in controlling glacial to interglacial atmospheric CO2 variability. Two mechanisms have been proposed to drive these changes in the global carbon cycle: 1) Enhanced stratification and sea-ice cover in the Antarctic Zone, and 2) Enhanced biological sequestration of carbon in response to alleviated micronutrient limitation in the Sub-Antarctic Zone. Despite the critical role the Southern Ocean is hypothesised to play, there are relatively few palaeo-records from around the region documenting the nature and character of thisCO2 exchange through time. In this thesis, boron isotopes measured in the planktic foraminifera Globigerina bulloides are used to reconstruct surface ocean pH of the Southern Ocean over the last 65 kyr, which in turn is used to infer past seawater dissolved CO2 (expressed as partial pressure;pCO2sw) and ocean-atmosphere CO2 disequilibrium (∆pCO2). The current application of the boron isotope pH proxy in planktic foraminifera is often focussed on lower latitude species, such as Globigerinoides ruber, which are absent from high latitude core sites. Therefore, this thesis initially focuses on overcoming the challenges associated with the application of the boron isotope pH-proxy in G. bulloides which has lower concentrations of boron but is dominant in Sub-Antarctic foraminifera assemblages (Chapters 2 & 3).An updated ...