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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 1 | Copyright
Biogeosciences, 15, 51-72, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Jan 2018

Research article | 03 Jan 2018

Inorganic carbon and water masses in the Irminger Sea since 1991

Friederike Fröb1,2, Are Olsen1,2, Fiz F. Pérez3, Maribel I. García-Ibáñez4, Emil Jeansson4, Abdirahman Omar4, and Siv K. Lauvset4 Friederike Fröb et al.
  • 1Geophysical Institute, University of Bergen, 5007 Bergen, Norway
  • 2Bjerknes Centre for Climate Research, 5007 Bergen, Norway
  • 3Instituto de Investigaciones Marinas (IIM-CSIC), 36208 Vigo, Spain
  • 4Uni Research Climate, Bjerknes Centre for Climate Research, 5008 Bergen, Norway

Abstract. The subpolar region in the North Atlantic is a major sink for anthropogenic carbon. While the storage rates show large interannual variability related to atmospheric forcing, less is known about variability in the natural dissolved inorganic carbon (DIC) and the combined impact of variations in the two components on the total DIC inventories. Here, data from 15 cruises in the Irminger Sea covering the 24-year period between 1991 and 2015 were used to determine changes in total DIC and its natural and anthropogenic components. Based on the results of an extended optimum multiparameter analysis (eOMP), the inventory changes are discussed in relation to the distribution and evolution of the main water masses. The inventory of DIC increased by 1.43±0.17molm−2yr−1 over the period, mainly driven by the increase in anthropogenic carbon (1.84±0.16molm−2yr−1) but partially offset by a loss of natural DIC (−0.57±0.22molm−2yr−1). Changes in the carbon storage rate can be driven by concentration changes in the water column, for example due to the ageing of water masses, or by changes in the distribution of water masses with different concentrations either by local formation or advection. A decomposition of the trends into their main drivers showed that variations in natural DIC inventories are mainly driven by changes in the layer thickness of the main water masses, while anthropogenic carbon is most affected by concentration changes. The storage rates of anthropogenic carbon are sensitive to data selection, while changes in DIC inventory show a robust signal on short timescales associated with the strength of convection.

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Short summary
On long timescales, the inventory of total dissolved inorganic carbon in the ocean is mainly driven by the increase in anthropogenic CO2 emitted to the atmosphere due to human activities. On short timescales, however, the anthropogenic signal can be masked by the variability in natural inorganic carbon, shown in this study based on Irminger Sea cruise data from 1991 to 2015. In order to estimate oceanic carbon budgets, we suggest jointly assessing natural, anthropogenic and total carbon.
On long timescales, the inventory of total dissolved inorganic carbon in the ocean is mainly...