Rapid response of Helheim Glacier in Greenland to climate variability over the past century

Abstract

During the early 2000s the Greenland Ice Sheet experienced the largest ice-mass loss of the instrumental record 1 , largely as a result of the acceleration, thinning and retreat of large outlet glaciers in West and southeast Greenland 2‐5 . The quasi-simultaneous change in the glaciers suggests a common climate forcing. Increasing air 6 and ocean 7,8 temperatures have been indicated as potential triggers. Here, we present a record of calving activity of Helheim Glacier, East Greenland, that extends back to about AD 1890, based on an analysis of sedimentary deposits from Sermilik Fjord, where Helheim Glacier terminates. Specifically, we use the annual deposition of sand grains as a proxy for iceberg discharge. Our record reveals large fluctuations in calving rates, but the present high rate was reproduced only in the 1930s. A comparison with climate indices indicates that high calving activity coincides with a relatively strong influence of Atlantic water and a lower influence of polar water on the shelf off Greenland, as well as with warm summers and the negative phase of the North Atlantic Oscillation. Our analysis provides evidence that Helheim Glacier responds to short-term fluctuations of large-scale oceanic and atmospheric conditions, on timescales of 3‐10 years. The forcings behind the rapid increase in mass loss from the Greenland Ice Sheet in the early 2000s (ref. 1) are still debated. It is unclear whether the mass loss will continue in the near future and,ifso,atwhatrate.Theseuncertaintiesareaconsequenceofour limited understanding of mechanisms regulating ice-sheet variability and the response of fast-flowing outlet glaciers to climate variability. In southeast Greenland, Helheim Glacier, one of the regions largestglaciers,thinned,acceleratedandretreatedduringtheperiod 20032005