Distribution of Th-230 and Pa-231 in the water column in relation to the ventilation of the deep Arctic basins

Distribution of Th-230 and Pa-231 in the water column was measured in the Eurasian basins of the Arctic Ocean, i.e. the Makarov, Amundsen and Nansen basins. The profiles obtained were compared to one previously published from the Alpha Ridge (Bacon et al., Earth and Planetary Science Letters, 95 (1989) 15-22. The Amundsen and Nansen basins are similar in their Th-230 and Pa-231 distribution, whereas in the Makarov Basin and at the Alpha Ridge these radionuclides are comparatively enriched in the deep basin. This may be due to low particle flux in conjunction with low water mass renewal rates. The Th-230 concentration in water depth < 1000 m in the Makarov Basin is relatively low compared with the Alpha Ridge, which may be caused by an exchange of water masses between the Amundsen and Makarov basins. In the Eurasian Basin Deep Water, Th-230 profiles can be explained both by a scavenging model and by a mixing-scavenging model. Enhanced particle load caused by resuspension may explain the increased scavenging in the Eurasian Basin Bottom Water. The differences in scavenging between the Norwegian-Greenland Sea and the Eurasian basins at present are not large enough to cause significant fractionation between Th-230 and Pa-231.