Ventilation of the Arctic Ocean estimated by a plume entrainment model constrained by CFCs

Intermediate and deep water formation rates in the Arctic Ocean are estimat ed using a plume entrainment model based on shelf-slope processes and const rained by tracer distributions within the deep basin. Each plume is initiat ed by a fraction, r(j), leaving the shelf break at 200 m, followed by an en trainment of r(j) for every 150 m depth the plume descends. The model is tu ned by varying rj to achieve the transient tracer (CFC-12 and carbon tetrac hloride) distribution as measured in the Nansen, Amundsen and Makarov Basin s during the Oden 1991 expedition, and the concentrations in the source wat ers are calculated assuming a water in 100% equilibrium with the atmosphere . The formation of water entering below 500 m is computed to be 1.5 and 1.9 Sv when constrained by CFC-12 and CCl4, respectively, with a total uncerta inty of +/-0.45 Sv. Sensitivities of the model settings to the entrainment rate, degree of saturation of the transient tracer in the source waters, an d age of the Atlantic Layer water are investigated. Processes in the Arctic Ocean contribute around 1/3 of the approximately 5.6 Sv that flows over th e Scotland-Greenland Ridge, with the rest likely attributed processes in th e Greenland and Iceland Seas. We thus conclude that the Arctic Ocean has to be included in the discussion of the sensitivity of the Greenland-Scotland overflow to a climate change.