Decrease in <sup>230</sup>Th in the Amundsen Basin since 2007: far-field effect of increased scavenging on the shelf?
O. Valk,
M. M. Rutgers van der Loeff,
W. Geibert,
S. Gdaniec,
S. B. Moran,
K. Lepore,
R. L. Edwards,
Y. Lu,
V. Puigcorbé,
N. Casacuberta,
N. Casacuberta,
R. Paffrath,
W. Smethie,
M. Roy-Barman
Affiliations
O. Valk
Alfred Wegener Institute Helmholtz Centre for Polar and Marine
Research, 27570 Bremerhaven, Germany
M. M. Rutgers van der Loeff
Alfred Wegener Institute Helmholtz Centre for Polar and Marine
Research, 27570 Bremerhaven, Germany
W. Geibert
Alfred Wegener Institute Helmholtz Centre for Polar and Marine
Research, 27570 Bremerhaven, Germany
S. Gdaniec
Department of Geological Sciences, Stockholm University, 106 91,
Stockholm, Sweden
S. B. Moran
College of Fisheries and Ocean Sciences, University of Alaska
Fairbanks, Fairbanks, AK 99775, USA
K. Lepore
Department of Astronomy, Mount Holyoke College, South Hadley, MA 01075, USA
R. L. Edwards
Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA
Y. Lu
Earth Observatory of Singapore, Nanyang Technological University, Singapore 639798, Singapore
V. Puigcorbé
Center for Marine Ecosystem Research, School of Science, Edith Cowan University, Joondalup, WA 6027, Australia
N. Casacuberta
Laboratory of Ion Beam Physics, ETH Zurich, 8093 Zurich, Switzerland
N. Casacuberta
Institute of Biogeochemistry and Pollutant Dynamics, Environmental
Physics, ETH Zurich, 8092 Zurich, Switzerland
R. Paffrath
Max Planck Research Group for Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment, University of
Oldenburg, 26129 Oldenburg, Germany
W. Smethie
Lamont-Doherty Earth Observatory, Palisades, NY 10964-8000, USA
M. Roy-Barman
Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA – CNRS – UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
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.
