231Pa and 230Th in the Barents Sea and the Nansen Basin: Implications for Shelf-Basin Interactions and Changes in Particle Flux

• Main Authors: Gdaniec, Sandra, Roy-Barman, Matthieu, Levier, Martin, Missiaen, Lise, Dapoigny, Arnaud, Valk, Ole, Rutgers v. d. Loeff, Michiel, Andersson, Per S.
• Format: Conference Object
• Language: unknown
• Published: 2017
• Subjects: Arctic Ocean; Barents Sea; Nansen Basin
• Online Access: https://epic.awi.de/id/eprint/47619/; https://hdl.handle.net/10013/epic.24c17b7a-d28d-4c21-8bde-678708eec733

In seawater, particle reactive 231Pa and 230Th are uniformly produced by decay of soluble 235U and 234U. Due to differences in particle reactivity, 230Th tends to be removed to the sediment close to its production site, while 231Pa is more prone to lateral transport and is removed to the sediments in areas of high particle flux (i.e. boundary scavenging). Due to a combination of perennial ice cover, large shelf areas and river runoff, boundary scavenging in the Arctic Ocean strongly impacts the distribution of 231Pa and 230Th in the water column. Here, 231Pa and 230Th were analyzed in seawater and particles from the Arctic GEOTRACES section GN04 along the Barents shelf and in the Nansen basin. Key observations include lower concentrations of dissolved 231Pa and 230Th on the Barents shelf compared to the Nansen basin, indicating enhanced removal of 231Pa and 230Th near the margin. The particulate nuclide/total nuclide ratio increases from the surface (0.2% for 231Paxs and 0.7% for 230Thxs) to the seafloor (11% for 231Paxs and 71% for 230Thxs), highlighting the role of deep scavenging. The fractionation factor between 231Pa and 230Th (FTh/Pa) ranges from ~3 to 25 and generally increases with depth. Comparison between suspended particles and sediments will be provided. Further, dissolved 231Paxs and 230Thxs concentrations in the Nansen basin are lower compared to concentrations measured 20 years ago1 . This might reflect changes in particle flux and/or changes in circulation patterns. 1 Scholten, J., Rutgers van der Loeff, M., 1995. Distribution of 230Th and 231Pa in the water column in relation to the ventilation of the deep Arctic basins. Deep. Res. Part II 42, 1519–1531.