Simulation of air-sea CO2 flux in an ocean model: understanding processes and using data assimilation

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Background: The Southern Ocean plays a key role in the global carbon system, with many studies indicating that it may account for 40% of anthropogenic carbon dioxide (CO2) ocean uptake, and thus significantly slowing the rate of climate change due to fossil fuel use. Despite it's significance, the Southern Ocean remains one of the most poorly sampled and understood areas of the global ocean, with winter-time measurements of carbon uptake almost non-existent. As a result, large uncertainties remain in quantifying how carbon fluxes may vary both spatially and temporally in the Southern Ocean. For example, recent findings from the US Southern Ocean Carbon and Climate Observations and Modeling program (SOCCOM: https://soccom.princeton.edu/), which has deployed a network of specially equipped floats able to capture winter-time CO2 fluxes, suggest that the Southern Ocean is a net source of CO2 to the atmosphere. The implication of the SOCCOM results is that our understanding of the global carbon system may need some radical revision. This PhD project will tackle the important need for better quantification and understanding of the spatial and temporal patterns of Southern Ocean CO2 flux measurements through both cutting-edge autonomous instrumentation and satellite observations.MethodologyThe student will investigate CO2 flux estimates in the recent Met Office ocean model. Results will be compared with the Surface Ocean Carbon Atlas (SOCAT: www.socat.info) and SOCCOM measurements and possible the MIT GCM.The student will derive CO2 flux estimates from satellite observations of the Southern Ocean e.g. by exploiting salinity-alkalinity relationships (Land et al., 2015) using the ESA's SMOS satellite, launched in 2009. A recent study, led by the University of Exeter, is the first to demonstrate such techniques. Estimated CO2 flux patterns will be used to better understand the physical processes that modulate carbon uptake by the Southern Ocean e.g. upwelling regions, eddy variability, storms, fronts, mixed layer depth, the Southern Annular Mode and potentially the implications for global meridional overturning circulation patterns. This work will complement both the US SOCCOM initiative and current NERC funded UK programs: CaPASOS and the Role of the Southern Ocean in the Earth System (RoSES).The student will also work in collaboration with the recently funded NERC project Calibrated pCO2 in Air and Surface Ocean Sensor (CaPASOS), to aid the development of a novel carbon-flux instrument that can be mounted on unmanned surface vehicles. The student will be immediately integrated into the project (with trials starting in winter 2019/20), for which NEXUSS training will be highly relevant.Project is partly funded by the NEXUSS CDT and the student will have access to NEXUSS training evens: There will be extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial / government / policy partners