Air-Sea CO₂ Cycling in Arctic Coastal Seas: Case Studies in the Canadian Arctic Archipelago and Hudson Bay

• Main Author: Ahmed, Mohamed M. M.
• Other Authors: Else, Brent, Papakyriakou, Tim, Belanger, Simon, Yackel, John, Dunfield, Peter, Hales, Burke
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Graduate Studies 2020
• Subjects: marine carbon cycle; Arctic shelves; air-sea CO₂ exchange; Hudson Bay; Canadian Arctic Archipelago; biogeochemical modeling; sea-ice; CO₂ flux; freshwater stratification; Biogeochemistry; Environmental Sciences; Earth Sciences; Arctic; Hudson; Arctic Archipelago; Climate change; Sea ice
• Online Access: http://hdl.handle.net/1880/113494; https://doi.org/10.11575/PRISM/38922

In contrast to the open ocean, the sources and sinks for atmospheric carbon dioxide (CO₂) in the coastal ocean are source of large uncertainties when budgeting the global ocean carbon sink. This is mainly because of the different characteristics of coastal seas, and strong spatial and temporal heterogeneity. Furthermore, the coastal ocean has been substantially impacted by human activities (e.g., hydroelectric damming, overfishing, shipping, etc.) and is now considered one of the most sensitive parts of the marine environment to climate change. As a result, it is vital to study the carbon cycle and quantify the air-sea CO₂ fluxes in these regions to predict and understand how they may change in response to future climate change. In this thesis, I address this knowledge gap in two Arctic coastal seas by studying the spatial and temporal variability of surface water CO₂ partial pressure (pCO₂) and by quantifying air-sea CO₂ fluxes. Using continuous underway ship measurements of pCO₂, salinity, sea surface temperature, and chlorophyll a (Chl a) concentrations, we quantified the multi-annual variability of air-sea CO₂ exchange in the Canadian Arctic Archipelago and provided a baseline estimate of CO₂ sources and sinks in Hudson Bay during the spring and early summer seasons. Both study regions acted as a net oceanic sink with an average air-sea CO₂ flux of -7.7 and -7.2 TgC yr⁻¹ in the Canadian Arctic Archipelago and Hudson Bay, respectively. In the Canadian Arctic Archipelago, we estimated an increase in the atmospheric CO₂ uptake in the last four decades due to an increase in sea ice loss and higher wind speeds. In Hudson Bay, we observed a distinct spatial pattern in pCO₂ related to proximity from freshwater sources, with supersaturated pCO₂ (relative to the atmosphere) measured near river mouths, and undersaturated pCO₂ in offshore and ice-melt influenced waters. This thesis budgeted the CO₂ sources and sinks in a third of the Arctic shelf seas area (about 36%) and shows the importance of accounting for the ...