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Volume 12, issue 1 | Copyright
Ocean Sci., 12, 319-333, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 25 Feb 2016

Research article | 25 Feb 2016

Transient tracer distributions in the Fram Strait in 2012 and inferred anthropogenic carbon content and transport

Tim Stöven1, Toste Tanhua1, Mario Hoppema2, and Wilken-Jon von Appen2 Tim Stöven et al.
  • 1Helmholtz Centre for Ocean Research Kiel, GEOMAR, Kiel, Germany
  • 2Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany

Abstract. The storage of anthropogenic carbon in the ocean's interior is an important process which modulates the increasing carbon dioxide concentrations in the atmosphere. The polar regions are expected to be net sinks for anthropogenic carbon. Transport estimates of dissolved inorganic carbon and the anthropogenic offset can thus provide information about the magnitude of the corresponding storage processes.

Here we present a transient tracer, dissolved inorganic carbon (DIC) and total alkalinity (TA) data set along 78°50′N sampled in the Fram Strait in 2012. A theory on tracer relationships is introduced, which allows for an application of the inverse-Gaussian–transit-time distribution (IG-TTD) at high latitudes and the estimation of anthropogenic carbon concentrations. Mean current velocity measurements along the same section from 2002–2010 were used to estimate the net flux of DIC and anthropogenic carbon by the boundary currents above 840m through the Fram Strait.

The new theory explains the differences between the theoretical (IG-TTD-based) tracer age relationship and the specific tracer age relationship of the field data, by saturation effects during water mass formation and/or the deliberate release experiment of SF6 in the Greenland Sea in 1996, rather than by different mixing or ventilation processes. Based on this assumption, a maximum SF6 excess of 0.5–0.8fmolkg−1 was determined in the Fram Strait at intermediate depths (500–1600m). The anthropogenic carbon concentrations are 50–55µmolkg−1 in the Atlantic Water/Recirculating Atlantic Water, 40–45µmolkg−1 in the Polar Surface Water/warm Polar Surface Water and between 10 and 35µmolkg−1 in the deeper water layers, with lowest concentrations in the bottom layer. The net fluxes through the Fram Strait indicate a net outflow of  ∼ 0.4 DIC and  ∼ 0.01PgCyr−1 anthropogenic carbon from the Arctic Ocean into the North Atlantic, albeit with high uncertainties.

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Short summary
The article describes transient tracer distributions of CFC-12 and SF6 in the Fram Strait in 2012. The SF6 excess and the anthropogenic carbon content in this area was estimated assuming a standard parameterization of the inverse-Gaussian–transit-time distribution. Hydrographic data were obtained along a mooring array at 78°50’N and a mean velocity field was used for flux estimates.
The article describes transient tracer distributions of CFC-12 and SF6 in the Fram Strait in...