Climate Modulations of Air-Sea Oxygen, Carbon, and Heat Exchange
The exchanges of oxygen (O2), carbon dioxide (CO2), and heat across the air-sea interface have broad and profound implications for climate and marine ecosystems. In this thesis, I use observations and models to improve our process understanding of how natural climate variability modulates these exchanges. In chapter 2, I investigate the impacts of El Niño Southern Oscillation (ENSO) on air-sea O2 exchange. I use atmospheric inversions of global, continuous timeseries of atmospheric O2 and CO2 and ocean models to evaluate links between ENSO and air-sea O2 exchange and explore driving mechanisms using ocean and atmospheric models. I find that El Niño events lead to anomalous outgassing of oceanic O2, a response that is driven primarily by changes in the source and intensity of upwelling in the equatorial Pacific. In Chapter 3, I examine the impacts of tropical volcanic eruptions on air-sea exchanges of O2, CO2 and heat using coupled model simulations and observations. Here, I find that volcanic events lead to substantial oceanic heat loss that is accompanied by large oceanic uptakes of oxygen and carbon. An El Niño-like pattern emerges following tropical eruptions and plays a major role in modulating the oceanic response to volcanic forcing. In Chapter 4, I explore the use of global continuous atmospheric measurements of O2 and CO2 to evaluate claims that enhanced ocean heat uptake caused the recent global surface warming hiatus, based on a potential negative relationship between air-sea heat and gas exchange. Here, I find that the relationship between air-sea oxygen, carbon and heat fluxes due to natural variability is complex; air-sea heat and O2 exchange are positively coupled in the tropical Pacific, but are negatively coupled at higher latitudes. This spatially distinct relationship complicates the attribution of observed decadal trends in atmospheric O2 and CO2 to changes in ocean heat uptake, but may present an opporunitity to develop regional constraints. Collectively, the results of this thesis contribute to a quantitative and mechanistic framework enabling interpretation of O2 and CO2 trends in the context of ongoing ocean warming and deoxygenation.