High precision ²³⁰Th and ²³²Th in the Norwegian Sea and Denmark by thermal ionization mass spectrometry

Seawater samples (1–2 liters) were collected from the Norwegian Sea and Denmark Strait and analyzed for ²³⁰Th and ²³²Th using highly sensitive thermal ionization mass spectrometry (TIMS). Depth profiles of dissolved ²³⁰Th and ²³²Th are characterized by surface water minima (<1 fg/kg, <5 pg/kg), subsurface maxima (12 fg/kg, 134 pg/kg), and intermediate concentrations that progressively decrease toward the bottom (∼5 fg/kg, ∼17 pg/kg), respectively. The lack of an increase in ²³⁰Th with depth is suggested to result from the short ventilation age of Norwegian Sea Deep Water combined with enhanced scavenging near the basin margins. The ²³⁰Th maximum is attributed to advection of high ²³⁰Th in the Arctic Intermediate Water, whereas the ²³²Th maximum may be related to a particulate source. The low dissolved ²³⁰Th and ²³²Th concentrations observed in the NADW formation regions implies a minor advective export of these long‐lived Th tracers to the North Atlantic.