HIGH-PRECISION TH-230 AND TH-232 IN THE NORWEGIAN SEA AND DENMARK BY THERMAL IONIZATION MASS-SPECTROMETRY

Seawater samples (1-2 liters) were collected from the Norwegian Sea an d Denmark Strait and analyzed for Th-230 and Th-232 using highly sensi tive thermal ionization mass spectrometry (TIMS). Depth profiles of di ssolved Th-230 and Th-232 are characterized by surface water minima (< 1 fg/kg, <5 pg/kg), subsurface maxima (12 fg/kg, 134 pg/kg), end inter mediate concentrations that progressively decrease toward the bottom ( similar to 5 fg/kg, similar to 17 pg/kg), respectively. The lack of an increase in Th-230 with depth is suggested to result from the short v entilation age of Norwegian Sea Deep Water combined with enhanced scav enging near the basin margins. The Th-230 maximum is attributed to adv ection of high Th-230 in the Arctic Intermediate Water, whereas the Th -232 maximum may be related to a particulate source. The low dissolved Th-230 and Th-232 concentrations observed in the NADW formation regio ns implies a minor advective export of these long-lived Th tracers to the North Atlantic.