Song, Tengfei; Hillaire-Marcel, Claude; Liu, Yanguang; Ghaleb, Bassam et de Vernal, Anne
(2023).
« Cycling and behavior of 230Th in the Arctic Ocean: Insights from
sedimentary archives ».
Earth-Science Reviews, 244.
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Résumé
Some studies have used excesses of 230Th (230Thxs) in marine cores from low sedimentation rate sites for the setting of a late Pleistocene stratigraphy, but the temporal and spatial variability of 230Thxs fluxes in the Arctic Ocean remains poorly understood. In this paper, we review all available 230Th data from the Arctic Ocean to document the regional 230Thxs behavior within the geological time frame of the latest glacial/interglacial cycle. We evaluate the potential roles of bathymetry, sedimentological regimes, and geochemical properties of the sediment
in relation to 230Thxs fluxes. The 230Thxs inventories in the sediment accumulated since the Last Glacial Maximum suggest that 230Thxs fluxes are linked to the sea-ice regime, brine production rate and sinking, organic carbon fluxes, ice-rafting pathways, seawater exchange between Arctic and Atlantic and Pacific oceans, nepheloid transportation, and possibly other unidentified factors. During “warm” intervals, the development of “ice factories” over shelves and enhanced detrital and organic matter fluxes related to high sea levels and high summer insolation conditions constitute major parameters governing 230Thxs-records. During glacials, under a perennial ice cover or ice shelf, 230Thxs was partly exported through Fram Strait into the Nordic Seas, possibly partly built up in the water column, depending on the ventilation rate of the deep-water masses. At the sea floor over slopes and ridges, the winnowing of fine fractions and brines-related compounds by deep currents leads to post-sedimentary
redistributions of 230Thxs. These features do not invalidate chronostratigraphic inferences made using 230Thxs-records in sediments but shed light on their use and limitations. Sedimentary profiles of 230Thxs allow the identification of interglacial-interstadial and glacial stages. This remains valid for sediments encompassing from recent to Marine Isotope Stage 11 (MIS 11), with some reservations depending on the site considered. The 230Thxs records have been initially proposed for the setting of an “extinction age” assigned to the final decay of the excess within the one-sigma uncertainty of its estimate. We show here that this extinction ages may vary between ~200 to ~420 kyr, mostly depending on the site-specific relationship between 230Th deposition and sedimentary regime, and on any potential post-depositional effects, which may include redox-driven U mobility and 230Thxs losses linked to fine sediment fractions winnowing.
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