"This is the first study to show precise and continuous tracking of Atlantic water flowing northward into the Arctic Ocean off Norway, circulating around the Arctic basins and returning to the Nordic seas in what we call the ‘Arctic loop’, and then flowing southward down the continental slope of North America to Bermuda at depths below 3000 m," said John N Smith of Bedford Institute of Oceanography in Canada, in a press release.

The iodine-129 isotope has a half-life of 15.7 million years. It takes about 20 years to travel the 15,000 km to Bermuda, where it’s possible to detect it at extremely low concentrations using accelerator mass spectrometry.

The team has measured the isotope as far south as Puerto Rico. It’s likely it will continue to flow into the South Atlantic and eventually spread throughout the global ocean.

The research is part of the GEOTRACES project, which is using geochemical markers to estimate transit times and mixing rates in the North Atlantic and Arctic Oceans.

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