230Th and 231Pa are produced in sea water by radioactive
decay of Uranium isotopes (234U, 235U). Both are particle
reactive and are scavenged onto settling particles. As 230Th is
more particle reactive than 231Pa, their distribution in the
water column and activity ratio give information about
particle fluxes and circulation patterns and –intensities.
Both particle fluxes and deep water circulation may respond
to climatic changes in the Arctic Ocean. This study discusses
temporal changes in radionuclide concentration in the context
of climate change. We compare results from 1991  2007
and 2015. We present results of dissolved 231Pa and 230Th
activities of samples collected in the Nansen-, Amundsenand
Makarov Basins during GEOTRACES sections GIPY11
(2007, 4 stations), GN04 (2015, 10 stations) aboard RV
Polarstern. Our discussion of factors controlling the 230Th and 231Pa distribution is supported by, dissolved CFC, dissolved
iron and particulate 230Th and 231Pa (3 stations) collected
during GEOTRACES section GN04.
We find that distributions and concentrations of dissolved 231Pa and 230Th in the central Arctic Ocean have changed
significantly since 1991. Dissolved 231Pa concentrations in the
Makarov basin decreased by half within less than 20 years.
These changes are discussed in the context of environmental
changes, such as declining sea ice cover and related increase
of particle fluxes or changing deep water circulation.
 Scholten, J. C., et al. (1995). Deep-Sea Research II 42: 1519-
EPIC Alfred Wegener Institut