Understanding the Physical Forcings Behind the Biogeochemical Productivity of the Hudson Bay Complex

• Published in: Journal of geophysical research. Biogeosciences 2023-06, Vol.128 (6), p.n/a
• Main Authors: Deschepper, Inge, Myers, Paul G., Lavoie, Diane, Papakyriakou, Tim, Maps, Fréderic
• Format: Article
• Language: English
• Subjects: biogeochemical modeling; Biogeochemistry; Biological models (mathematics); Blooms; Brackishwater environment; Chlorophyll; Chlorophyll a; chlorophyll a concentration; Climate change; Distribution; Distribution patterns; Dynamics; Empirical analysis; Estuaries; Hudson Bay Complex; Ice cover; Ice melting; Inland seas; Intercomparison; Light levels; Magnetic resonance imaging; Marine environment; Marine systems; Mathematical analysis; Mixed layer; Mixed layer depth; Nutrient cycles; Nutrient dynamics; Orthogonal functions; Phytoplankton; Plankton; Primary production; Productivity; Radiative forcing; River discharge; River flow; River regulations; Rivers; Runoff; Satellite imagery; Satellite observation; Sea ice; Simulation; Statistical analysis; Statistical methods; Water depth
• ISSN: 2169-8953; 2169-8961
• DOI: 10.1029/2022JG007294

Multiple factors influence the spatial and temporal chlorophyll‐a concentration of marine systems. The Hudson Bay Complex has historically been seen as a large, low‐production inland sea situated in the north of Canada. However, recent field campaigns, for the BaySys project, have provided new data on primary production in the bay. Due to the Hudson Bay complex's positioning, it experiences seasonal sea‐ice cover and has many rivers draining into it, resulting in a unique estuarine‐like environment. We use the biogeochemical model BLINGv0 + DIC, coupled to the online regional physical oceanographic and sea‐ice models, NEMOv3.6 and LIM2, respectively, forced with two bias‐corrected Coupled Model Intercomparison Project 5 climate forcings (MIROC5 and MRI) to simulate the base of the ecosystem. The simulations were evaluated with chlorophyll‐a satellite imagery and observations collected in 2018 and analyzed with Empirical Orthogonal Functions to understand the underlying physical forcings and key areas of chlorophyll‐a concentration distribution. The evaluation showed that both simulations successfully reproduced the sea‐ice melt, from west to east and formation, from north to south and correlated well with spatial bloom patterns. The main drivers of phytoplankton growth are the seasonal light and nutrient levels (48% and 54%), the mixed layer depth dynamics (18% and 14%), nutrient supply from rivers (13% and 8%), and sea ice production (7%) for the MIROC5 and MRI simulations, respectively. The sea‐ice dynamics and river runoff played a significant role in the system's productivity. Therefore, with future climate change and increased river regulation projects, up to 20% of overall chlorophyll‐a may be negatively impacted. Plain Language Summary The Hudson Bay Complex (HBC) is an inland sub‐Arctic sea that is covered by sea ice from December to June. Many rivers drain into the bay, making it a relatively fresh marine environment. Due to its size, difficulty to access, and seasonal ice cover, it is a challenging environment to sample. A recent Hudson Bay system study, BaySys, has allowed us to understand that the HBC is more productive than previously thought. Using regional numerical ocean, sea ice, and biological models, we can simulate the biological productivity in this area with two different climate forcings. Comparing the simulations with satellite and in situ observations from 2018, we can see that our models simulate sea‐ice production and the spatial