Climate-driven fluctuations in freshwater flux to Sermilik Fjord, East Greenland, during the last 4000 years

The freshwater runoff from the glaciated and snow-covered Sermilik Fjord catchment, SE Greenland, was estimated at annual resolution for the period 1900–2008 and at decadal resolution for the past four millennia. Our simulations were forced with available meteorological station data (1900–2008) and Greenland ice core estimated temperature data (1899 bc–ad 1980) from Dye3 and GISP2. Time series of estimated ice discharge (2000–2009) for the three major outlet glaciers Helheim, Fenris, and Midgård indicate that 53–74% of the ice discharge variations could be explained by variations in areally averaged glacier terminus surface (supraglacial) runoff. Based on these data and together with calculated subglacial geothermal and frictional melting as well as net precipitation for the fjord area, the Sermilik Fjord freshwater flux was deduced for the period 1900–2008. Our simulations indicated that during the last century surface freshwater runoff has equaled 13% of the Sermilik Fjord average freshwater flux of 33.0±5.7×109 m3/yr, covering a periodic runoff variation of 20 years. Ice discharge has accounted for 81%, with 63% of the freshwater flux originated from the Helheim glacier. This indicates that the Helheim outlet glacier plays a dominant role as a freshwater source to both Sermilik Fjord and ultimately the Irminger Sea. For the palaeorecords of the last 4000 years, simulated surface runoff has averaged 4.4±0.2×109 m3/yr. A very weak decreasing trend in runoff over the last 4 k years (1899 bc–ad 1980) is presumably associated with the general insolation-generated Northern Hemisphere cooling since the Holocene Thermal Maximum. Our simulations furthermore indicated centennial- to submillennial-scale variations in surface runoff concurrent with the well-known climate episodes such as the ‘Roman Warm Period’, the ‘Dark Ages Cold Period’, the ‘Medieval Climate Anomaly’, and the ‘Little Ice Age’. During the ‘Little Ice Age’, e.g., the average surface runoff was about 0.7×109 m3/yr lower than today, while the increase in runoff for the Modern Warming, since the late 1800s, was the second strongest and fastest for the last 4 k years.