Radium in the Arctic Ocean - the 2015 GEOTRACES missions

• Main Authors: Rutgers v. d. Loeff, Michiel, Kipp, Lauren, Bauch, Dorothea, Charkin, Alexander N.
• Format: Conference Object
• Language: unknown
• Published: 2017
• Subjects: Arctic; Arctic Ocean; Barents Sea; Bering Strait
• Online Access: https://epic.awi.de/id/eprint/45353/; https://hdl.handle.net/10013/epic.51632

The Arctic Ocean is a small ocean basin surrounded by wide and shallow shelves receiving large river inputs. The radium quartet are four tracers of contact with sediments that give information on transport processes ranging in time scale from days to hundreds of years. 228Ra (5.8 y halflife) is a good tracer for surface water circulation. New 2015 GEOTRACES (sections GN01+GN04) 228Ra data show the first full Barents Sea to Bering Strait transect with maximum activities in the Transpolar Drift. We compare the 2015 section in the central Arctic with earlier Polarstern sections in 1987/1991, 2007 and 2011 and discuss reasons for increases in maximum 228Ra activities (Kipp et al., 2017). The penetration of 228Ra and its daughter 228Th to waters of intermediate depths (up to about 1500m) shows the exchange of these waters with shelf and slope sediments on the time scale of 228Ra decay. Input from the seafloor causes an enrichment of 228Ra and 226Ra in bottom waters. In deep waters (>2000m) of the Eurasian and Makarov basins 226Ra (1600 y halflife) accumulates to values around 16 dpm/100L or about twice the surface water concentration. It has been argued that export production increases with decreasing ice cover in the Arctic (Arrigo et al., 2008). Natural radionuclides can help to quantify export production rates, but the fluxes found may depend on the time scale of the tracer used. The most commonly used tracer 234Th/238U (24 d halflife) has a memory much shorter than a season. The 210Po/210Pb (138 d; Roca-Martí et al., 2016) and 228Th/228Ra ratios (1.9 y) are alternatives on a full seasonal time scale. Arrigo, K.R. et al., 2008. Geophys. Res. Lett. 35, L19603 Kipp, L. et al., 2017. ASLO 2017 OSM abstracts Roca-Martí, M. et al., 2016. Journal of Geophysical Research: Oceans 121, 5030-5049