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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-313
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-313
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  27 Aug 2020

27 Aug 2020

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This preprint is currently under review for the journal BG.

Enhancement of the North Atlantic CO2 sink by Arctic Waters

Jon Olafsson1, Solveig R. Olafsdottir2, Taro Takahashi3,, Magnus Danielsen2, and Thorarinn S. Arnarson4, Jon Olafsson et al.
  • 1Institute of Earth Sciences, Sturlugata 7 Askja, University of Iceland, IS 101 Reykjavik, Iceland
  • 2Marine and Freshwater Research Institute, Fornubúðir 5, IS 220 Hafnafjörður, Iceland
  • 3Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY 10964, USA
  • 4National Energy Authority, Grensásvegur 9, IS 108Reykjavík, Iceland
  • deceased

Abstract. The North Atlantic north of 50° N is one of the most intense ocean sink areas for atmospheric CO2 considering the flux per unit area, 0.27 Pg-C yr−1, equivalent to −2.5 mol C m−2 yr−1. The Northwest Atlantic Ocean is a region with high anthropogenic carbon inventories. This is on account of processes which sustain CO2 air-sea fluxes, in particular strong seasonal winds, ocean heat loss, deep convective mixing and CO2 drawdown by primary production. The region is in the northern limb of the Global Thermohaline Circulation, a path for the long term deep sea sequestration of carbon dioxide. The surface water masses in the North Atlantic are of contrasting origins and character, on the one hand the northward flowing North Atlantic Drift, a Gulf Stream offspring, on the other hand southward moving cold low salinity Polar and Arctic Waters with signatures from Arctic freshwater sources. We have studied by observations, the CO2 air-sea flux of the relevant water masses in the vicinity of Iceland in all seasons and in different years. Here we show that the highest ocean CO2 influx is to the Arctic and Polar waters, respectively, −3.8 mol C m−2 yr−1 and −4.4 mol C m−2 yr−1. These waters are CO2 undersaturated in all seasons. The Atlantic Water is a weak or neutral sink, near CO2 saturation, after poleward drift from subtropical latitudes. These characteristics of the three water masses are confirmed by data from observations covering 30 years. We relate the Polar and Arctic Water persistent undersaturation and CO2 influx to the excess alkalinity derived from Arctic sources, particularly the Arctic rivers. Carbonate chemistry equilibrium calculations indicate clearly that the excess alkalinity may support a significant portion of the North Atlantic CO2 sink. The Arctic contribution to the North Atlantic CO2 sink which we reveal is previously unrecognized. However, we point out that there are gaps and conflicts in the knowledge about the Arctic alkalinity budget and that future trends in the North Atlantic CO2 sink are connected to developments in the rapidly warming Arctic. The results we present need to be taken into consideration for the question: Will the North Atlantic continue to absorb CO2 in the future as it has in the past?

Jon Olafsson et al.

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Jon Olafsson et al.

Jon Olafsson et al.

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Short summary
The Atlantic north of 50° N is an intense ocean sink area for atmospheric CO2. Observations in the vicinity of Iceland reveal a previously unrecognized Arctic contribution to the North Atlantic CO2 sink. Sustained CO2 influx to waters flowing from the Arctic Ocean is linked to their excess alkalinity derived from sources in the changing Arctic. The results relate to the question: Will the North Atlantic continue to absorb CO2 in the future as it has in the past?
The Atlantic north of 50° N is an intense ocean sink area for atmospheric CO2. Observations in...
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