Future Physical and Biogeochemical Ocean Conditions under Climate Change along the British Columbia Continental Margin

Abstract

Climate change impacts coastal ecosystems through large scale changes in temperature, stratification, circulation and ocean acidification. Here, the potential response of the British Columbia continental margin to climate change is investigated using a regional ocean circulation-biogeochemical model to downscale climate change projections from the Canadian regional and global climate models (CanRCM4/CanESM2) under two Intergovernmental Panel on Climate Change emission scenarios (RCP 4.5 and RCP 8.5). Projections of future physical and biogeochemical conditions for the 2041–2070 period are compared to the recent past (1981–2010). We found an overall annual average warming of >1.6°C in sea surface temperature, increase in stratification in the upper layer, and decrease in surface pH of as much as 0.21. Increasing stratification and changing winds have a limited impact on nitrate availability, phytoplankton biomass and primary production, whilst ocean warming increases primary production by up to 30% in most of the model domain. Increased atmospheric CO2 contributes to acidification over the model domain with a decrease in pH and aragonite saturation (Ωarag) at all depths resulting in an increase of 20 to 32% of the volume of Ωarag ≤1 in the upper 100 m of the continental shelf depending on the climate scenario. Our projected results, therefore, show that future climate change may alter the amount of food available for higher trophic levels and the habitat of benthic species, since bottom waters on the shelf will be undersaturated with respect to aragonite for 2–3 months in mid-summer. Both climate change scenarios results in a similar pattern of changes but projected changes were stronger and more extensive under RCP 8.5 showing the benefit of mitigation efforts in reducing the effect of climate change on marine ecosystem stressors.