The future influences of climate change and river regulation on high-latitude circulation as determined by ocean modelling

Abstract

The Hudson Bay Complex (HBC), encompassing Foxe Basin (FB), Hudson Strait (HS), Ungava Bay (UB), Hudson Bay (HB), and James Bay (JB), experiences notable shifts in freshwater sources. Despite being smaller than the Arctic Ocean, the HBC annually receives around 900 km3 of river discharge, constituting about 25% of the Arctic Ocean's inflow. The HBC receives freshwater primarily from river runoff and ice freeze-thaw processes, both impacted by human activities (e.g., diversions, dams, and reservoirs) and climate change. Using the NEMO ocean-sea ice model with the Arctic and Northern Hemisphere Atlantic (ANHA) configuration, we investigated how river regulation and climate change affect HBC's freshwater dynamics. We applied an ensemble of five climate simulations, which were from the Coupled Model Inter-comparison Project 5 (CMIP5) model experiments. They were initialized between 1980 and 2005, forced with naturalized and regulated river runoff, and driven by different representative concentrations of greenhouse gases (RCP4.5 and RCP8.5) over the 2006-2070 period. The results showed a general increase in freshwater content, along with a sharp decrease in ice thickness and concentration in the future. The mixed layer depth can reach up to 230 m near the north side of HS. With increased freshwater from rivers and ice thawing, future mixed layers are projected to be slightly shallower compared to the historical period. Finally, we examined atmospheric forcing changes to understand ocean-sea ice-atmosphere interactions in a changing climate. Our results reveal significant impacts of distinct ensemble members on salinity and freshwater content variations, reflecting hydrological cycle evolution in climate models. Differences in content between naturalized and regulated regimes are linked to factors including freshwater residence time and discharge timing.