Ventilation of the Arctic Ocean: Mean ages and inventories of anthropogenic CO₂ and CFC‐11

Abstract

[1] The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed because of logistical difficulties, although the importance of the Arctic Ocean for global circulation and climate is widely recognized. For instance, the concentration and inventory of anthropogenic CO 2 (C ant ) in the Arctic Ocean are not properly known despite its relatively large volume of well-ventilated waters. In this work, we have synthesized available transient tracer measurements (e.g., CFCs and SF 6 ) made during more than two decades by the authors. The tracer data are used to estimate the ventilation of the Arctic Ocean, to infer deep-water pathways, and to estimate the Arctic Ocean inventory of C ant . For these calculations, we used the transit time distribution (TTD) concept that makes tracer measurements collected over several decades comparable with each other. The bottom water in the Arctic Ocean has CFC values close to the detection limit, with somewhat higher values in the Eurasian Basin. The ventilation time for the intermediate water column is shorter in the Eurasian Basin ($200 years) than in the Canadian Basin ($300 years). We calculate the Arctic Ocean C ant inventory range to be 2.5 to 3.3 Pg-C, normalized to 2005, i.e., $2% of the global ocean C ant inventory despite being composed of only $1% of the global ocean volume. In a similar fashion, we use the TTD field to calculate the Arctic Ocean inventory of CFC-11 to be 26.2 ± 2.6 Â 10 6 moles for year 1994, which is $5% of the global ocean CFC-11 inventory.

Nordic seas transit time distributions and anthropogenic CO2

“…While this number is not large in absolute terms, it reflects the overall high DIC ant concentrations of an area which comprises ∼0.3% of the global ocean volume. Combined with the estimate of Tanhua et al [2009] we get a combined Nordic seas and Arctic Ocean anthropogenic CO 2 inventory for the year of 2005 of 4.3 Gt C, ∼3-4% of the global ocean inventory.…”

“…For the North Atlantic, for instance, constrained D/G to 0.75 or larger using this approach. Assuming a D/G of unity has since then become more or less a routine [Waugh et al, 2006;Tanhua et al, 2009].…”

“…[23] The Nordic seas DIC ant inventory was determined by using the approach described for the Arctic Ocean by Tanhua et al [2009] which interpolates each DIC ant profile onto 50 m depth intervals using a piecewise cubic Hermite, and then use the topography following mapping scheme described by Davis [1998] and Rhein et al [2002] to map the interpolated data onto a regular grid. The upper 250 m were not included in our calculations (section 2.1) so we assumed that these were saturated with DIC ant .…”

Reconstruction of the history of anthropogenic CO2 concentrations in the ocean

“…The total inventory in that year was ,140 6 25 Pg C. This estimate excludes the Arctic Ocean and marginal seas not covered by the GLODAP database. Using a recent estimate based on CFC-11 for the former 15 , and an area scaling approach for the latter 2 , would increase our estimate of the global inventory by ,11 Pg C. We have also partitioned this inventory according to where at the surface the anthropogenic CO 2 penetrated the ocean. As is evident from Fig.…”

Model constraints on the anthropogenic carbon budget of the Arctic Ocean

“…Although no uncertainty is provided with that data-based air-sea flux estimate, it too must be at least ±18 Tg C yr -1 given that it is calculated 10 as the difference between the data-based storage estimate (Tanhua et al, 2009) and Olsen et al's data-based net lateral flux.…”