Decrease in 230Th in the Amundsen Basin since 2007: far-field effect of increased scavenging on the shelf?

Valk, Ole; Rutgers van der Loeff, Michiel M.; Geibert, Walter; Gdaniec, Sandra; Moran, S. Bradley; Lepore, Kate; Edwards, Robert Lawrence; Lu, Yanbin; Puigcorbé, Viena; Casacuberta, Nuria; Paffrath, Ronja; Smethie, William; Roy-Barman, Matthieu

This study provides dissolved and particulate inline-formula230Th and inline-formula232Th results as well as particulate inline-formula234Th data collected during expeditions to the central Arctic Ocean (GEOTRACES, an international project to identify processes and quantify fluxes that control the distributions of trace elements; sections GN04 and GIPY11). Constructing a time series of dissolved inline-formula230Th from 1991 to 2015 enables the identification of processes that control the temporal development of inline-formula230Th distributions in the Amundsen Basin. After 2007, inline-formula230Th concentrations decreased significantly over the entire water column, particularly between 300 and 1500 m. This decrease is accompanied by a circulation change, evidenced by a concomitant increase in salinity. A potentially increased inflow of water of Atlantic origin with low dissolved inline-formula230Th concentrations leads to the observed depletion in dissolved inline-formula230Th in the central Arctic. Because atmospherically derived tracers (chlorofluorocarbon (CFC), sulfur hexafluoride (SFinline-formula6)) do not reveal an increase in ventilation rate, it is suggested that these interior waters have undergone enhanced scavenging of Th during transit from Fram Strait and the Barents Sea to the central Amundsen Basin. The inline-formula230Th depletion propagates downward in the water column by settling particles and reversible scavenging.

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Valk, Ole / Rutgers van der Loeff, Michiel M. / Geibert, Walter / et al: Decrease in 230Th in the Amundsen Basin since 2007: far-field effect of increased scavenging on the shelf?. 2020. Copernicus Publications.

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