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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 4
Biogeosciences, 15, 1011-1027, 2018
https://doi.org/10.5194/bg-15-1011-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Biogeosciences, 15, 1011-1027, 2018
https://doi.org/10.5194/bg-15-1011-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Feb 2018

Research article | 20 Feb 2018

Inorganic carbon fluxes on the Mackenzie Shelf of the Beaufort Sea

Jacoba Mol1, Helmuth Thomas1, Paul G. Myers2, Xianmin Hu2, and Alfonso Mucci3 Jacoba Mol et al.
  • 1Department of Oceanography, Dalhousie University, Halifax B3H 4R2, Canada
  • 2Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton T6G 2E3, Canada
  • 3Department of Earth and Planetary Sciences, McGill University, Montréal H3A 0E8, Canada

Abstract. The Mackenzie Shelf in the southeastern Beaufort Sea is a region that has experienced large changes in the past several decades as warming, sea-ice loss, and increased river discharge have altered carbon cycling. Upwelling and downwelling events are common on the shelf, caused by strong, fluctuating along-shore winds, resulting in cross-shelf Ekman transport, and an alternating estuarine and anti-estuarine circulation. Downwelling carries dissolved inorganic carbon (DIC) and other remineralization products off the shelf and into the deep basin for possible long-term storage in the world's oceans. Upwelling carries DIC and nutrient-rich waters from the Pacific-origin upper halocline layer (UHL) onto the shelf. Profiles of DIC and total alkalinity (TA) taken in August and September of 2014 are used to investigate the cycling of carbon on the Mackenzie Shelf. The along-shore transport of water and the cross-shelf transport of DIC are quantified using velocity field output from a simulation of the Arctic and Northern Hemisphere Atlantic (ANHA4) configuration of the Nucleus of European Modelling of the Ocean (NEMO) framework. A strong upwelling event prior to sampling on the Mackenzie Shelf took place, bringing CO2-rich (elevated pCO2) water from the UHL onto the shelf bottom. The maximum on-shelf DIC flux was estimated at 16.9×103molCd−1m−2 during the event. The maximum on-shelf transport of DIC through the upwelling event was found to be 65±15×10−3TgCd−1. TA and the oxygen isotope ratio of water (δ18O-H2O) are used to examine water-mass distributions in the study area and to investigate the influence of Pacific Water, Mackenzie River freshwater, and sea-ice melt on carbon dynamics and air–sea fluxes of carbon dioxide (CO2) in the surface mixed layer. Understanding carbon transfer in this seasonally dynamic environment is key to quantify the importance of Arctic shelf regions to the global carbon cycle and provide a basis for understanding how it will respond to the aforementioned climate-induced changes.

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In the fall of 2014, the upwelling of water from the deep Canada Basin brought water onto the shallower Mackenzie Shelf in the Beaufort Sea. This increased the concentration of CO2 in water on the shelf, which alters pH and changes the transfer of CO2 between the ocean and atmosphere. These findings were a combined result of water sampling for CO2 parameters and the use of a computer model that simulates water movement in the ocean.
In the fall of 2014, the upwelling of water from the deep Canada Basin brought water onto the...
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