New Hydrographic Measurements of the Upper Arctic Western Eurasian Basin in 2017 Reveal Fresher Mixed Layer and Shallower Warm Layer Than 2005-2012 Climatology

In 2017, Ice Atmosphere Ocean Observing System autonomous drifting platforms provided extensive physical and biogeochemical data in the upper 350m of the western Eurasian Basin through their 8-month drift across the Amundsen Basin, the Gakkel Ridge, the Nansen Basin and western Fram Strait. Comparison with WOA13 climatology indicates a fresher surface layer and shallower warm layer in 2017 than in 2005-2012. The Ice Atmosphere Ocean Observing System 2017 data feature two halocline eddies in the Amundsen Basin and two Atlantic Water (AW) mesoscale structures in the Nansen Basin. Analysis of the global (1/12)degrees Mercator Ocean operational system suggests that the halocline eddies resulted from instabilities in the frontal zone between fresher Makarov waters and saltier Eurasian waters. This frontal region appears to have shifted further southeast in 2017 (near 88 degrees N, 10 degrees E) compared to 2005-2012. The operational system depicts the large AW structure in the Nansen Basin (140km crossed as far as 83.7 degrees N, 34.5 degrees E) as an AW meander from the Arctic Circumpolar Boundary Current, which turned into an anticyclonic eddy about a month after the platforms drifted away. The AW structure at 82.8 degrees N, 3 degrees W, northwest of the Yermak Plateau, corresponds to an AW recirculating branch detaching from the Yermak Plateau slope back toward Fram Strait. Plain Language Summary In 2017, IAOOS (Ice Atmosphere Ocean Observing System) autonomous drifting platforms provided extensive physical and biogeochemical data in the upper 350 m of the Western Eurasian Basin through their 8-month drift. The surface layer is fresher and the warm layer shallower in 2017 than in 2005-2012. The IAOOS 2017 measurements document several medium scale ocean structures. Simulations from a high resolution ((1/12)degrees) model (Mercator Ocean operational model) provide insights on the nature and origin of these observed structures.