A seasonal deuterium excess signal at Law Dome, coastal eastern Antarctica: A southern ocean signature

The snow isotopic composition (δ 18 O and δD) of two shallow cores from the high accumulation summit region of Law Dome, east Antarctica, was measured at monthly resolution over the 1980–1992 period. While the δ 18 O or δD signals clearly reflect the local temperature cycle, the deuterium excess ( d = δD ‐ 8δ 18 O) is shifted with respect to δ 18 O cycle by a 4 months lag. Interpretation of this phase lag is investigated using both an Atmospheric General Circulation Model (AGCM), which includes the water isotopic cycles, and a simple isotopic model, which better describes the microphysical processes within the cloud. Using this dual approach, we show that the seasonality of δ 18 O and d at Law Dome summit results from a combination of the southern ocean temperature cycle (shifted by 2–3 months with respect to the local insolation) and seasonal moisture origin changes due to a strong contribution of the local ocean when ice free. Both approaches are consistent with a dominant temperate to subtropical moisture origin. We thus demonstrate from our present‐day subseasonal study that the record of d in the Dome Summit South (DSS) deep ice core represents a potential tool for identifying changes in Southern Ocean temperatures and/or sea ice cover at the scale of the past thousand years.