Circulation changes in the Amundsen Basin from 1991 to 2015 revealed from distributions of dissolved 230Th

• Main Authors: 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
• Format: Text
• Language: English
• Published: 2019
• Subjects: Amundsen Basin; Arctic; Arctic Ocean; Barents Sea; amundsen basin; Fram Strait
• Online Access: https://doi.org/10.5194/os-2019-49; https://www.ocean-sci-discuss.net/os-2019-49/

This study provides dissolved and particulate 230 Th and 232 Th results as well as particulate 234 Th data collected during expeditions to the central Arctic Ocean on ARK-XXIX/3 (2015) and ARK-XXII/2 (2007) (GEOTRACES sections GN04 and GIPY11, respectively). Constructing a time-series of dissolved 230 Th from 1991 to 2015 enables the identification of processes that control the temporal development of 230 Th distributions in the Amundsen Basin. After 2007, 230 Th concentrations decreased significantly over the entire water column, particularly between 300 m and 1500 m. This decrease is accompanied by a circulation change, evidenced by a concomitant increase in salinity. Potentially increased inflow of water of Atlantic origin with low dissolved 230 Th concentrations leads to the observed depletion in dissolved 230 Th in the central Arctic. Because atmospherically derived tracers (CFC, 3 He/ 3 H) do not reveal an increase in ventilation rate, it is suggested that these interior waters have undergone enhanced scavenging of Th during transit from the Fram Strait and the Barents Sea to the central Amundsen Basin. The 230 Th depletion propagates downward in the water column by settling particles and reversible scavenging. Taken together, the temporal evolution of Th distributions point to significant changes in the large-scale circulation of the Amundsen Basin.