Climate variability and glacial processes in eastern Iceland during the past 700 years based on varved lake sediments

Properties of varved sediments from Lake Logurinn in eastern Iceland and their link to climate and glacial processes of Eyjabakkajokull, an outlet glacier of the Vatnajokull icecap, were examined. A varve chronology, which covers the period AD 1262-2005, was constructed from visual observations, high-resolution images, X-ray density and geochemical properties determined from X-radiography and X-ray fluorescence scanning. Independent dating provided by 137Cs analysis and eight historical tephras verify the varve chronology. The thickness of dark-coloured seasonal laminae, formed mainly of coarser suspended matter from the non-glacial river Grimsa, is positively correlated (r=0.70) with winter precipitation, and our 743-year-long varve series indicates that precipitation was higher and more varied during the later part of the Little Ice Age. Light-coloured laminae thickness, controlled mainly by the amount of finer suspended matter from the glacial river Jokulsa i Fljotsdal, increased significantly during the AD 1972 surge of Eyjabakkajokull. As a consequence of the surge, the ice-dammed Lake Haoldulon formed and recurrently drained and delivered significant amounts of rock flour to Lake Logurinn. Based on these observations, and the recurring cyclic pattern of periods of thicker light-coloured laminae in the sediment record, we suggest that Eyjabakkajokull has surged repeatedly during the past 743 years, but with an increased frequency during the later part of the Little Ice Age.