Climate Change Impacts to the Arctic Ocean Revealed From High Resolution GEOTRACES 210Po-210Pb-226Ra Disequilibria Studies

Climate change is transforming the Arctic Ocean in unprecedented ways which can be most directly observed in the systematic decline in seasonal ice coverage. From the collection and analysis of particulate and dissolved activities of Po-210 and Pb-210 from four deepwater superstations, as a part of the US Arctic GEOTRACES cruise during 2015, and in conjunction with previously published data, the temporal and spatial variations in their activities, inventories and residence times are evaluated. The results show that the partitioning of particulate and dissolved phases has changed significantly in the 8 years between 2007 and 2015, while the total Po-210 and Pb-210 activities have remained relatively unchanged. Observed total Po-210/Pb-210 activity ratio was less than unity in all deepwater stations, implying disequilibria in the entire water column. From the distribution of total Po-210 and Pb-210 in the upper 500 m of all major Arctic Basins, the derived scavenging efficiencies decrease as per the following sequence: Makarov Basin > Gakkel Bridge > Canada Basin Nansen Basin similar to Amundsen Basin > Alpha Ridge, which is the reverse order of the calculated residence times of Po-210(T). The scavenging intensities differ between the fully ice-covered, partially ice-covered, and no ice-covered stations, as observed from the differences in the average activities of Po-210 and Pb-210. The average settling velocity of particulate matter based on the Pb-210 activity is similar to the published values based on Th-230, indicating removal mechanism(s) of Th and Pb is (are) similar.

Automated summary

Climate change is leading to unprecedented transformations in the Arctic Ocean, particularly in the decline of seasonal ice coverage. This study investigates the changes in particulate and dissolved activities of Po-210 and Pb-210 in the water column over the years. The results show significant changes in the partitioning of these radionuclides between 2007 and 2015, while the total activities remained relatively stable. The study also reveals imbalances in the water column and variations in scavenging efficiencies and intensities based on ice coverage.