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

Abstract

Intermediate and deep water formation rates in the Arctic Ocean are estimated using a plume entrainment model based on shelf-slope processes and constrained by tracer distributions within the deep basin. Each plume is initiated by a fraction, rj, leaving the shelf break at 200 m, followed by an entrainment of rj for every 150 m depth the plume descends. The model is tuned by varying rj to achieve the transient tracer (CFC-12 and carbon tetrachloride) distribution as measured in the Nansen, Amundsen and Makarov Basins during the Oden 1991 expedition, and the concentrations in the source waters 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 uncertainty of ±0.45 Sv. Sensitivities of the model settings to the entrainment rate, degree of saturation of the transient tracer in the source waters, and 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 the Scotland-Greenland Ridge, with the rest likely attributed processes in the 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. Copyright 1999 by the American Geophysical Union.