Iceberg calving rates at Helheim Glacier, Greenland, have reached present levels only once since about ad1890, suggests a study published online this week in Nature Geoscience. The findings suggest that despite large fluctuations in ice-release rates through iceberg calving, the currently observed activity is unusually high. Camilla Andresen and colleagues reconstructed iceberg calving rates from Helheim Glacier into Sermilik Fjord using sediment cores from the fjord. They find strong variability in the annual deposition of sand grains, indicative of large fluctuations in iceberg calving. Nevertheless, the present high rates stand out in the record, with similar activity reached only once before, during the 1930s. The researchers suggest that calving activity is high when the water masses on the shelf off Greenland are influenced more by Atlantic and less by polar waters, and when summers in the region are warm.