Reduced ice thickness in Arctic Transpolar Drift favors rapid ice retreat

Helicopter‐borne electromagnetic sea ice thickness measurements were performed over the Transpolar Drift in late summers of 2001, 2004, and 2007, continuing ground‐based measurements since 1991. These show an ongoing reduction of modal and mean ice thicknesses in the region of the North Pole of up to 53 and 44%, respectively, since 2001. A buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi‐ and second‐year ice in earlier years to first‐year ice in 2007, which had modal and mean summer thicknesses of 0.9 and 1.27 m. Measurements of second‐year ice which still persisted at the North Pole in April 2007 indicate a reduction of late‐summer second‐year modal and mean ice thicknesses since 2001 of 20 and 25% to 1.65 and 1.81 m, respectively. The regime shift to younger and thinner ice could soon result in an ice free North Pole during summer.