Modelling oxygen dynamics in a Canadian archipelago (Discovery Islands, BC)

The Discovery Islands region is a network of deep fjords and narrow channels north of the Strait of Georgia. The complex interaction of fresh water inputs, bathymetry, and marine and atmospheric forcing leads to rich marine ecosystems, which sustain wild salmon during their migration as well as orcas and other species, and make the region suitable for finfish aquaculture. Previous modelling studies in this area have focused on the circulation and were aimed as tools for the aquaculture industry and its management (e.g., to assist in farm siting decisions, assess the connectivity between farms, evaluate the risk of spread of disease onto wild fish populations, etc.). Now, we are building a coupled physical-biogeochemical model in order to understand the distribution of nutrients and oxygen. For instance, variations in oxygen concentrations due to natural physical processes (e.g., stratification and mixing) can affect aquaculture, especially in times of climate change and ocean deoxygenation (e.g., if waters with less oxygen than usual inundate areas with farms). Furthermore, some of the deep fjords, which have shallow sills at their entrances, have been showing decreasing oxygen concentrations at depth in the recent years; this decline could be due to the lack of recent water renewal events or to the decrease in oxygen concentrations in the source waters. In addition, finfish farms can decrease oxygen in their vicinity both directly by the respiration of the fish and indirectly when organic matter (such as fish feces) gets decomposed by oxygen-consuming bacteria. For our model, we use the Finite Volume Community Ocean Model (FVCOM) coupled to the biogeochemical module FVCOM-ICM. Our goal is to understand the dominant mechanisms that determine the distribution of dissolved oxygen in the region and how they may change along with climate. In this presentation, we discuss our latest results and future plans.