Dominant Drivers and Effects of Anthropogenically Modified Carbonate Chemistry in a Temperate Fjord System

Recent observations have shown large spatial and temporal variations of pH and Aragonite Saturation (AS) in the Salish Sea and in other estuarine and coastal systems. These changes are significantly larger than the global anthropogenic change, which raises questions concerning potential effects on regional biogeochemistry, ecosystem health, and regional stakeholders such as shellfish farmers. In addition, to predict future changes to the global carbon cycle, it is critical to understand the role that anthropogenic carbon plays in a highly naturally variable coastal regions. Here, we use the SalishSeaCast biogeochemical model to investigate dominant features of this spatiotemporal variation in a temperate, naturally carbon-rich estuary on an annual timescale. The model resolves dissolved inorganic carbon, total alkalinity, pH, and AS at hourly and daily resolution. We examine the influence of previously-identified drivers, including riverine input, biological activity, and open-ocean exchange, on this natural cycle. Finally, we use the model to investigate the fate of the atmospheric and open-ocean anthropogenic carbon signal in this system, and its effects on biologically-relevant metrics such as aragonite saturation horizon and pH shifts.