Document Type

Honors Thesis

Publication Date

Spring 5-2018

Abstract

The overall goal of this study is to quantify interannual trends in oxygen concentrations and their spatial variability in the coastal Pacific Ocean off the southern coast of California, and to examine their relationship to concurrent hydrographic properties. The study focuses on trends within the upper 500 meters of the water column to indicate changes in seasonally upwelled waters over time. The analysis uses the publicly-available CalCOFI bottle cast data gathered and distributed by Scripps Institute. At each station, data include oxygen concentration and hydrographic information, such as potential density, depth, temperature, and salinity. This study utilizes data from 30.35° N and 34.21° N. Using MATLAB, data were bin-averaged and interpolated into quarterly time series at 24 stations and at standard depths. Figures were constructed to visualize latitudinal variability and cross-shelf variability of seasonal and interannual oxygen concentrations throughout the water column. Overall trends of oxygen at both standard depths and fixed density surfaces were approximated by a non-parametric linear fit. Observed multi-year trends in oxygen concentration are quantified and compared to those evident in hydrographic data under identical methods. Declining oxygen concentrations occur across the entire study region, peaking in the range of the California undercurrent. Deoxygenation rates maximize at equivalent magnitudes when viewed by both depth and density, reinforcing prior assertions that increasing advection of low oxygen Pacific Equatorial waters into the system is a strong driver of deoxygenation. On isopycnals, oxygen concentrations trends track best with salinity, suggesting salinity trends may be usable to predict oxygen trends.

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