The role of carbonate system dynamics in Southern Ocean CO2 uptake

• Main Author: Legge, Oliver
• Format: Thesis
• Language: English
• Published: 2017
• Subjects: Antarctic; Antarctic Peninsula; Drake Passage; Indian; Pacific; Ryder; Ryder Bay; Scotia Sea; Southern Ocean; The Antarctic; Weddell; Weddell Sea; Antarc*; North Atlantic Deep Water; North Atlantic; Sea ice
• Online Access: https://ueaeprints.uea.ac.uk/id/eprint/66840/; https://ueaeprints.uea.ac.uk/id/eprint/66840/1/O.Legge_thesis_20171220.pdf

Three years of carbonate system measurements from Ryder Bay on the West Antarctic Peninsula are presented. The strong, asymmetric seasonal cycle of surface water Dissolved Inorganic Carbon (DIC) is quantitatively attributed to four processes:mixing of water masses, air-sea CO2 flux, calcium carbonate precipitation/dissolution and photosynthesis/respiration. In summer, reduced mixing with deeper water, net photosynthesis, and melting glacial ice and sea ice reduce DIC. In winter, mixing with deeper water and net heterotrophy increase DIC, resulting in aragonite saturation states close to 1. Ryder Bay is a net annual sink of atmospheric CO2 of 0.90-1.39 mol C m-2 yr-1. The observed variability demonstrates that future climatic changes may significantly affect carbon cycling in this dynamic environment. Carbonate system measurements from the Drake Passage and A23 sections are compared. Lower Circumpolar Deep Water (LCDW) becomes colder and fresher from Drake Passage to A23 due to mixing in the Scotia Sea. The coincident decrease in Total Alkalinity (TA) increases the fugacity of CO2, potentially reducing CO2 uptake in the Weddell Sea through the influence of upwelling LCDW on surface waters. Ventilation of Upper Circumpolar Deep Water (UCDW) in the south of Drake Passage suggests that this region is an important source of CO2 to the atmosphere. The zonal variability of the carbonate system in deep water masses around the Antarctic Circumpolar Current is assessed. Zonal variability, caused by the inflow of North Atlantic Deep Water in the Atlantic sector and UCDW in the Indian and Pacific sectors, has implications for regional air-sea CO2 flux in the high-latitude Southern Ocean. Temporal variability in Sub-Antarctic ModeWater is investigated. Most of the observed DIC increase is attributed to rising atmospheric CO2. There is also weak evidence for increasing remineralised organic carbon, possibly relatedto changes in the strength and location of ventilation.