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UBC Theses and Dissertations

The inorganic carbonate chemistry of the southern Strait of Georgia Moore-Maley, Benjamin Lee


A one-dimensional, biophysical, mixing layer model was modified to hindcast pH and aragonite saturation state (OmegaA) in the southern Strait of Georgia. The model skill in predicting spring phytoplankton bloom timing in previous studies was a key factor in its selection. Dissolved inorganic carbon (DIC) and total alkalinity (TA) were added as state variables, coupled to the existing nitrogen-based biological equations. Additional processes determined to be important to the system such as air-sea gas exchange and nutrient-limited excess carbon uptake were also implemented. pH and OmegaA could then be calculated from DIC and TA. Modeled DIC, TA, pH, and OmegaA were evaluated against data collected between 2003 and 2012. Modeled and observed quantities agreed except in some summers, with surface disagreement driven primarily by plume variability and subsurface disagreement driven primarily by model overproductivity. Model outputs demonstrated a near-surface seasonal cycle characterized by low pH and OmegaA in winter and high pH and OmegaA in summer. In order to evaluate the sensitivity of model pH and OmegaA to local forcing quantities, the model was run in one year increments over the period from 2001 through 2012. For each year, each of three forcing records (wind speed, freshwater flux, cloud fraction) was shifted across all possible years during the same period for a total of 432 experimental runs. When regressed against spring wind speed, model surface pH demonstrated a clear, negative correlation. Model spring OmegaA demonstrated a negative correlation to cloud fraction. Summer pH and OmegaA were most sensitive to freshwater flux, both showing negative correlations. Model pH and OmegaA sensitivity to freshwater TA and pH were also evaluated over the same period using a set of realisitic freshwater chemistry scenarios determined from observations in the Fraser River. Model pH and OmegaA demonstrated opposite correlations to freshwater TA with sensitivities at opposite extremes of freshwater pH. The sensitivity results identify important links between local processes and the carbonate chemistry in the southern Strait of Georgia, and perhaps provide some simple forecasting tools to be tested in the future.

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