Abstract
Abstract. This study provides dissolved and particulate 230Th and 232Th results as well as particulate 234Th 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 230Th from 1991 to 2015 enables the identification of processes that control the temporal development of 230Th distributions in the Amundsen Basin. After 2007, 230Th 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 230Th concentrations leads to the observed depletion in dissolved 230Th in the central Arctic. Because atmospherically derived tracers (chlorofluorocarbon (CFC), sulfur hexafluoride (SF6)) 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 230Th depletion propagates downward in the water column by settling particles and reversible scavenging.
Highlights
The Arctic Ocean is one of the most rapidly changing parts of the Earth’s ocean–atmosphere system as a result of climate change
Excess corrections were done following Hayes et al (2015). 230Th concentrations are corrected for a proportion of 230Th released by the dissolution of lithogenic particles
There is no indication of increased scavenging removal of 230Th due to increased particle flux within the Amundsen Basin
Summary
The Arctic Ocean is one of the most rapidly changing parts of the Earth’s ocean–atmosphere system as a result of climate change. Underlying the potential anthropogenic changes is a large natural variability in the Arctic. Due to the limited observations in this extreme environment, establishing datasets that allow an assessment of its variability is important. Chemical and biological processes provide an integrated description of the changing state of the system. O. Valk et al.: Decrease of dissolved 230Th in the Amundsen Basin monitor environmental changes and provide an observational baseline against which models can be tested
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