To the North Pole and Back: A Pan-Arctic Barium Synthesis

Barium has previously been used as a proxy for productivity within, and for freshwater discharge into, the Arctic Ocean. These applications require that Ba exhibits largely conservative behavior, an assumption that may require re-evaluation given rapid ongoing changes in this basin. Utilizing data from several cruises, mainly associated with the 2015 GEOTRACES campaigns in the Arctic Ocean, we quantify the non-conservative sources and sinks of Ba using multiple approaches. By comparing the observed dissolved Ba to an estimate of conservative Ba, we determined in the western Arctic basins there must be an additional source of Ba (i.e., observed Ba > conservative Ba), such as a shelf source, at depths typically associated with Pacific-derived waters. Surface waters tended to have a deficit (i.e., obs. Ba < cons. Ba), which is consistent with removal of Ba via biological scavenging. Furthermore, a basin-wide mass balance approach indicates that 45 - 56% of the dissolved Ba budget requires an additional net source of Ba to be balanced with outputs. We ascribe this to non-conservative components such as shelf inputs, sea ice influences, or particle formation/dissolution. Utilizing published shelf 228Ra flux estimates and the shelf Ba:Ra ratio, we determine that the inputs of Ba from the shelf account for roughly 40% of the outputs. With shelf flux considered, the budget is effectively closed – within the uncertainty of our approach.