LETTERS PUBLISHED ONLINE: 11 DECEMBER 2011 | DOI: 10.1038/NGEO1349 Rapid response of Helheim Glacier in Greenland to climate variability over the past century Camilla S. Andresen 1 * , Fiammetta Straneo 2 , Mads Hvid Ribergaard 3 , Anders A. Bjørk 4 , Thorbjørn J. Andersen 5 , Antoon Kuijpers 1 , Niels Nørgaard-Pedersen 1 , Kurt H. Kjær 4 , Frands Schjøth 6 , Kaarina Weckström 1 and Andreas P. Ahlstrøm 1 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, if so, at what rate. These uncertainties are a consequence of our limited understanding of mechanisms regulating ice-sheet variabil- ity and the response of fast-flowing outlet glaciers to climate vari- ability. In southeast Greenland, Helheim Glacier, one of the regions largest glaciers, thinned, accelerated and retreated during the period 2003–2005 (ref. 4) and although it has since slowed down and re- advanced 9 , it has still not returned to its pre-acceleration flow rates. It has been suggested that warming 8,10 and/or inflow variability 11,12 of the nearby subsurface ocean currents triggered the acceleration, but to establish a causal relationship between glacier and climate variability, long-term records are needed. Here we present three high-resolution (1–3 years per sample) sedi- mentary records from Sermilik Fjord (Fig. 1 and Supplementary Information) that capture the 2001–2005 episode of mass loss, and use them to reconstruct the calving variability of Helheim Glacier over the past 120 years. Next, this record is compared with records of climate indices. 1 Geological Survey of Denmark and Greenland, Department of Marine Geology and Glaciology, Øster Voldgade 10, 1350 Copenhagen K, Denmark, 2 Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA, 3 Danish Meterological Institute, Centre for Ocean and Ice, Lyngbyvej 100, 2100 Copenhagen Ø, Denmark, 4 Centre for GeoGenetics, Natural History Museum, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark, 5 Institute for Geology and Geography, Øster Voldgade 10, Univ. of Copenhagen, 1350 Copenhagen K, Denmark, 6 Geological Survey of Denmark and Greenland, Geological Data Centre, Øster Voldgade 10, 1350 Copenhagen K, Denmark. *e-mail:csa@geus.dk. Helheim Glacier discharges in the deep (600–900 m) Sermilik Fjord, which is connected with two deep troughs (500–700 m) that transect the shallow shelf (100–200 m) allowing exchange with shelf waters. The fjord is characterized by an upper 100–150-m-thick layer of polar water from the East Greenland Current and a deeper layer (500 m thick) of warm (3.5–4 ◦ C) and saline Atlantic water from the North Atlantic Current 11 , with the latter primarily driving submarine melting 12 . At the northern end, the fjord branches into three smaller fjords, each containing calving glaciers. Of these, Helheim Glacier is one of the most prolific iceberg exporters in Greenland 1 , whereas the two northern glaciers, Midgaard and Fenris glaciers, are smaller and far less discharging 13 . The fjord is mostly sea-ice covered from January to June and a large ice mélange extends year-round in front of Helheim Glacier. Three sediment cores were collected (Fig. 1) and age models for the past 120 years were established on the basis of 210 Pb geochronology (Supplementary Fig. S2). The massive diamicton facies in the cores is produced by delivery of heterogeneous debris from drifting icebergs, commonly referred to as ice-rafted debris (IRD; clay, silt, sand and pebbles), and the down-fjord diminishing input of fine mud (clay and silt) suspended in the turbid meltwater plume extending from the base of Helheim Glacier. This lithofacies interpretation is in accordance with the findings from other East Greenland fjords with marine-terminating glaciers 14,15 . To reconstruct a record of calving activity of Helheim Glacier, it is assumed that changes in IRD deposition rate are directly related to changes in calving activity through iceberg rafting. This is supported by a study from the nearby Kangerdlugssuaq Fjord showing that the mean annual calving rate dominates the IRD deposition rates, whereas the influence of temperature on melting of icebergs is far less important 16 . The sand fraction is used as a proxy for IRD because sand grains are too large (63–1,000 μm) to be carried in suspension by the meltwater plume and thus allow differentiation between the plume and icebergs. Accordingly, we propose that increased sand deposition reflects increased iceberg calving from Helheim Glacier and to a far lesser extent also from the Midgaard and Fenris glaciers (Supplementary Information). Iceberg residence time in the mélange is less than a year (K. Scharrer, personal communication, 2011), implying that variations in IRD entrainment over time do not significantly affect the variability in sand deposition rates down-fjord over the investigated time span (Supplementary Information). NATURE GEOSCIENCE | ADVANCE ONLINE PUBLICATION | www.nature.com/naturegeoscience 1 © 2011 Macmillan Publishers Limited. All rights reserved.