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Discussion papers
https://doi.org/10.5194/os-2019-49
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/os-2019-49
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Jun 2019

Research article | 14 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Ocean Science (OS).

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

Ole Valk1, Michiel M. Rutgers van der Loeff1, Walter Geibert1, Sandra Gdaniec2, S. Bradley Moran3, Kate Lepore4, Robert Lawrence Edwards5, Yanbin Lu6, Viena Puigcorbé7, Nuria Casacuberta8,9, Ronja Paffrath10, William Smethie11, and Matthieu Roy-Barman12 Ole Valk et al.
  • 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 27570 Bremerhaven, Germany
  • 2Stockholm University, Department of Geological Sciences, 106 91, Stockholm, Sweden
  • 3College of Fisheries and Ocean Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775, USA
  • 4Mount Holyoke College, South Hadley, MA 01075, USA
  • 5University of Minnesota, Minneapolis, MN 55455, USA
  • 6Nanyang Technological University, 639798, Singapore
  • 7Center for Marine Ecosystem Research, School of Science, Edith Cowan University, Joondalup, WA 6027, Australia
  • 8Laboratory of Ion Beam Physics, ETH Zurich, 8093 Zurich, Switzerland
  • 9Institute of Biogeochemistry and Pollutant Dynamics, Environmental Physics, ETH Zurich, 8092 Zurich, Switzerland
  • 10Max Planck Research Group for Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, 26129, Oldenburg, Germany
  • 11Lamont-Doherty Earth Observatory, Palisades, NY 10964-8000, USA
  • 12Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA – CNRS – UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France

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 on ARK-XXIX/3 (2015) and ARK-XXII/2 (2007) (GEOTRACES sections GN04 and GIPY11, respectively). 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 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 230Th concentrations leads to the observed depletion in dissolved 230Th in the central Arctic. Because atmospherically derived tracers (CFC, 3He/3H) 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 230Th 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.

Ole Valk et al.
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Short summary
After 2007 230Th decreased significantly in the central Amundsen Basin, this decrease is accompanied by a circulation change, indicated by changes in salinity. Ventilation of waters is most likely not the reason for the observed depletion in 230Th, atmospherically derived tracers 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.
After 2007 230Th decreased significantly in the central Amundsen Basin, this decrease is...
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