Book Description

Our understanding of the ocean historically has moved forward in parallel with our ability to make observations. In the thesis, high-resolution observations of the California Current System made by Spray underwater gliders are used to discuss extreme events, eddy across-shore transport, and the annual cycle of dissolved oxygen in the upper ocean. The time scales covered in the thesis include annual to interannual changes while the spatial scales are mesoscale and larger. The availability of high-resolution ocean glider data for over 13 years provides the backbone to conduct analyses over these time and spatial scales. The thesis starts by examining temperature and salinity extremes from 2014-2019 in the California Current System and its source waters. The 2014-2019 period was anomalously warm. In addition, a salinity anomaly from 2017-2019 in the California Current System was found to have formed in the North Pacific Subtropical Gyre in 2015 and subsequently advected into the source waters of the California Current. Next, the thesis examines the offshore propagation of subthermocline eddies from the coast. Subthermocline eddies are observed to propagate at near the local first baroclinic Rossby wave speed. It is estimated that the subthermocline eddies are important to the salt budget in the California Current System and are difficult to track with surface observations alone. The thesis next discusses dissolved oxygen observations collected from 2017 to 2020. First, the thesis considers the procedure to correct for drift in the optical sensors used to make dissolved oxygen observations. A model is fit to changes in the gain correction coefficient over time and predicts the drift for 5 years after sensor calibration. Second, the thesis describes the annual cycle of dissolved oxygen in the upper 500 m of the central and southern California Current System. A subsurface dissolved oxygen maximum is described in the oligotrophic region on the offshore edge of the California Current System. During seasonal coastal upwelling, heave of isopycnals is the primary mechanism that deoxygenates the water column, while mixing and biological sources and sinks also cause changes. Evidence of ventilation is found along sloping isopycnals which oxygenates the ocean above 300 m. The collection of work in the thesis is relevant to extreme climate events and climate change in the oceans, including impacts to the biological environment. The thesis also touches on basic research questions related to geostrophic turbulence. The discoveries in the thesis are made possible by the high-resolution ocean data collected by autonomous Spray gliders used together in a network to create sustained observations of a regional ocean.