Quantitative Considerations of Dissolved Barium as a Tracer in the Arctic Ocean

Dissolved barium (Ba) was measured along transects across Fram Strait and near Denmark Strait from August to October 1998 as part of the ARKTIS XIV/2 Polarstern Expedition. The results were combined with salinity, δ¹⁸O, nitrate, and phosphate data to develop a water mass composition analysis at the Fram Strait measurement sites. Each measurement sample with sufficient data was decomposed into five source components: Atlantic water, Pacific water, ice melt (or extraction), North American river runoff and Eurasian river runoff. The two-step analysis assumed conservation of salinity, Ba, and δ¹⁸O from the source to the measurement location, and then used the observed nitrate to phosphate ratio to detect Bering Strait Pacific water and Fram Strait Atlantic water. Inclusion of Ba in the analysis allowed the freshwater signal to be decomposed into contributions from the Eurasian and North American shelves. A combination of Pacific water and Eurasian river runoff dominated the western end of the Fram Strait section over the Greenland Shelf, contributing > 80% and > 10% of the total mass respectively, while the eastern side of the section was dominated by water from the North Atlantic. Based on much smaller contributions of Pacific water along a Fram St. section in 1980, this component appears to be quite variable in time. It is also noted that a North American river water signature does not necessarily accompany Pacific water. A budget conserving mass, heat, salt and Ba for the Arctic was estimated from the Fram St. results and existing flux estimates at other Arctic gateways. The least squares calculation used to adjust the estimates to a steady state produced a full set of correlations between each flux source. The good fit of the inverse solution to the steady state assumption for Ba should simplify its application as a tracer in models of Arctic Ocean circulation.