Simulated Arctic Ocean Response to Doubling of Riverine Carbon and Nutrient Delivery

• Published in: Global biogeochemical cycles 2019-08, Vol.33 (8), p.1048-1070
• Main Authors: Terhaar, J., Orr, J. C., Ethé, C., Regnier, P., Bopp, L.
• Format: Article
• Language: English
• Subjects: Acidification; Alkalinity; Arctic Ocean; Atmosphere; Biogeochemistry; Carbon; Carbon dioxide; Carbon dioxide flux; Carbon sources; Climate change; Computer simulation; Continental interfaces, environment; Dissolved inorganic carbon; Dissolved organic carbon; Fluxes; Ice; Mineral nutrients; Nutrients; Ocean circulation; Ocean currents; Ocean models; Ocean, Atmosphere; Oceans; Organic carbon; Outgassing; Permafrost; Permafrost thaws; Primary production; riverine delivery; Runoff; Runoff increase; Sciences of the Universe; Sensitivity; Shelf seas; Thaws; Water circulation
• ISSN: 0886-6236; 1944-9224; 1944-8224
• DOI: 10.1029/2019GB006200

The Arctic Ocean, more than any other ocean, is influenced by riverine input of carbon and nutrients. That riverine delivery is likely to change with climate change as runoff increases, permafrost thaws, and tree lines advance. But it is unknown to what extent these changes in riverine delivery will affect Arctic Ocean primary production, air‐to‐sea CO2 fluxes, and acidification. To test their sensitivity to changing riverine delivery, we made sensitivity tests using an ocean circulation model coupled to an ocean biogeochemical model. In separate idealized simulations, riverine inputs of dissolved inorganic carbon (CT), dissolved organic carbon (DOC), and nutrients were increased by 1%/year until doubling. Doubling riverine nutrient delivery increased primary production by 11% on average across the Arctic basin and by up to 34–35% locally. Doubling riverine DOC delivery resulted in 90% of that added carbon being lost to the atmosphere, partly because it was imposed that once delivered to the ocean, the riverine DOC is instantaneously remineralized to CT. That additional outgassing, when considered alone, reduced the net ingassing of natural CO2 into the Arctic Ocean by 25% while converting the Siberian shelf seas and the Beaufort Sea from net sinks to net sources of carbon to the atmosphere. The remaining 10% of DOC remained in the Arctic Ocean, but having been converted to CT, it enhanced acidification. Conversely, doubling riverine CT increased the Arctic Ocean's average surface pH by 0.02 because riverine total alkalinity delivery increased at the same rate as riverine CT delivery. Key Points Model sensitivity tests were used to quantify the response of Arctic Ocean biogeochemistry to changing river fluxes of carbon and nutrients Doubling riverine nutrient fluxes increase net primary production by 11% basinwide, 34–35% regionally, and 100% close to river mouths Ocean acidification is worsened by enhanced river fluxes of dissolved organic carbon but reduced by fluxes of inorganic carbon and alkalinity