A warming climate results in sea ice loss and impacts to the Arctic water cycle. The water isotope
parameter deuterium excess, a moisture source proxy, can serve as a tracer to help understand hydrological
changes due to sea ice loss. However, unlocking the sea ice change signal of isotopes from ice cores requires
understanding how sea ice changes impact deuterium excess, which is unknown. Here we present the first
isotope data linking a gradient of sea ice extents to oceanic water vapor deuterium excess values. Initial loss of
sea ice extent leads to lower deuterium excess moisture sources, and then values progressively increase
with further ice loss. Our new process-based interpretation suggests that past rapid (1–3 years) Greenland ice
core changes in deuterium excess during warming might not be the result of abrupt atmospheric circulation
shifts, but rather gradual loss of sea ice extent at northern latitude moisture sources.

Above photo: Jeffrey Welker & Gandalf