ON THE MAGNITUDE AND SEASONAL VARIABILITY OF PCO2 AND AIR-SEA CO2 FLUXES IN THE NORTHWEST ATLANTIC OCEAN

Abstract

Oceanic uptake of atmospheric CO 2 plays a major role in regulating climate and mitigating the impact of its increasing concentration on global temperature. This thesis is focused on observations of surface-ocean partial pressure of CO2 (pCO2) and air-sea CO2 fluxes, particularly on the Northwest Atlantic Ocean. First, an overview of the marine carbon cycle and air-sea CO 2 fluxes is presented (Chapter 1). Then, a study analysing how new sensor-based pCO2 systems compare with more conventional but complex measuring systems is presented (Chapter 2). This comparison showed promise for a technological change that could be crucial for expanding our observational/monitoring network on ships of opportunity, research vessels, and using new platforms for ocean observation. The next study presented is a compilation of all pCO 2 observations available for the Central Labrador Sea (Chapter 3), where a base-line reference climatology was created for this region and compared against an ensemble of global products, showing large discrepancies between these products and the observational climatology produced here. The last study (Chapter 4) presents a gap-filling reconstruction of pCO2 maps for the Northwest Atlantic, using a neural network approach. These reconstructions were done with new observations and different spatial resolutions, and the effects of additional data and finer resolution on pCO2 and air-sea CO2 fluxes estimates is discussed. Both Chapters 3 and 4 emphasize the problem of poor data coverage, specially in high latitudes regions of the North Atlantic, pin-pointing where and when additional observations are necessary for improving constraints of air-sea CO2 fluxes. Therefore, this thesis contributes to improving potential for future data-coverage by validating a new simpler pCO2 measuring system (DAL-SOOP). The thesis also provides a compilation of pCO2 observations, producing a baseline seasonal climatology for the Central Labrador Sea. Comparison of this reference against other observational-based global products revealed systematic differences in the representation of the seasonal cycle of pCO2 and uncertainties in the magnitude of air-sea CO2 fluxes. Finally, the reconstruction of pCO2 maps in the Northwestern Atlantic Ocean contributes to new estimates of air-sea CO2 fluxes for regions that are poorly sampled. This study highlights the need to increase observation capability, specially in data-poor locations and in regions with high variability of pCO2 and intense CO2 fluxes.