The variable circulation and carbonate chemistry of ocean upwelling systems

Ocean upwelling is a process in which winds drive deep waters to the surface ocean. The biogeochemical state of these waters causes upwelling regions to have some of the strongest air-sea fluxes of carbon dioxide (CO2) and most productive fisheries in the global oceans. In this dissertation, I use Earth System models to investigate the variability and projected impacts of climate change on upwelling systems. I first use the Community Earth System Model Large Ensemble (CESM-LE) to project the impacts of climate change on upwelling in the California Current. The CESM-LE provides an ensemble of potential trajectories of the climate system that differ due to internal climate variability. I find that upwelling is expected to weaken over the next century in the summer and intensify poleward in the spring due to anthropogenic climate change. Next, I use the CESM-LE to highlight the role of internal climate variability in modulating air-sea CO2 fluxes in the major Eastern Boundary Upwelling Systems (EBUS). I identify the major mode of internal variability that influences air-sea CO2 flux in each EBUS. I then quantify how the given mode of variability modifies local conditions, which in turn leads to the anomalous air-sea CO2 fluxes. Following this, I use a version of the CESM-LE that is configured for climate prediction to examine predictability of ocean acidification in the California Current. I find that our system makes skillful forecasts of surface pH out to fourteen months relative to observations and has a potential ceiling of skillful prediction out to five years in some regions. Finally, I use the Model for Prediction Across Scales Ocean (MPAS-O) to investigate the pathways over which carbon upwells in the Southern Ocean. I seed a high-resolution version of MPAS-O with 1,000,000 Lagrangian floats and find that regions with complex ocean topography have a disproportionate influence on bringing carbon-rich waters from the deep Southern Ocean to the surface. The results of this dissertation highlight the value of using ensemble methods and the Lagrangian perspective in Earth System models to better understand the dynamic and variable biogeochemistry in ocean upwelling systems.

Brandy R. X., 2021. The variable circulation and carbonate chemistry of ocean upwelling systems. PhD thesis, University of Colorado, 24 p. Thesis (restricted access).

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