Temporal changes in iodine-129 and radiocesium in the Canada Basin in the Arctic Ocean between 1993 and 2020

The Arctic Ocean plays an important role in global climate and global warming through freshwater and heat exchange with subarctic waters. A better understanding of circulation time scales in the Arctic Ocean is essential to predict changes in climate and biogeochemical cycling in the Arctic Ocean. I-129 and Cs-137, which have been discharged from the nuclear fuel-reprocessing facilities, have been employed to determine the time scale of the circulation in the Arctic Ocean. However, its temporal change has not been understood well. In 2017, 2019, and 2020, we measured I-129 and Cs-137 in the Canada Basin in the Arctic Ocean. Using our new and historical data, we discuss temporal changes in the circulation in the basin between 1993 and 2020. The tracer ages derived from the I-129/Cs-137 ratio indicate that the transport of the Atlantic water into the Canada Basin was accelerated in 2020. This is consistent with results of recent studies that indicated the intensified inflow of the Atlantic water into the eastern Arctic Ocean in the late 2010s, which is termed "atlantification". Our results confirmed the "atlantification" in the Canada Basin by temporal changes in the transient tracers for the first time.