Search

The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available. The only previous estimates of change during the twentieth century are based on empirical modelling and energy balance modelling. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900-1983 (75.1 ± 29.4 gigatonnes per year), 1983-2003 (73.8 ± 40.5 gigatonnes per year), and 2003-2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to predict global sea level rise.

Abstract: Continental dust impurities in Antarctic ice provide information on climate changes in the dust source areas and on past atmospheric circulation. We investigated records of dust species from the last 45 ka in the East Antarctic EPICA DomeC (EDC) ice core with special emphasis on the lithium (Li) content of dust. We obtained two complementary Li-records using a new Ion Chromatography (IC) technique in line with Inductively Coupled Plasma-Sector Field Mass Spectroscopy (ICP-SFMS). Concentrations of soluble Li (Li+) were obtained using IC, while total concentrations of Li (Li T ) were obtained using ICP-SFMS, providing an ideal opportunity to investigate the soluble and insoluble chemistry of Li in East Antarctic dust over the last glacial–interglacial transition. The records show that changes in the solubility of Li are associated with climatic changes. For the late glacial period and the Antarctic Cold Reversal (ACR) a large fraction, up to 75%, of the Li T content is present as insoluble minerals whereas for the Holocene period it seems that Li is present mainly as soluble salts (Li+). We compared the concentrations of Li+ with the concentrations of Ca2+ and the mass and size characteristics of the dust, which were obtained using Coulter Counting (CC). Furthermore we compared the concentrations of Li T with the concentrations of Ba T . Our analysis suggests that the changes in solubility of Li along the EDC ice core are related to changes in compositions of the dust minerals. During the late glacial period, changes in the dust composition is characteristic of variations in the strength of the atmospheric circulation, while changes over the last glacial–interglacial transition are indicative of a change in the major dust source areas. The dust characteristics for the glacial and the Holocene periods indicate two different dust types. The glacial dust type partly disappeared after the ACR, while the Holocene dust type appeared significantly after around 16 ka BP and became dominant after the ACR. The relative increase in the Holocene dust type at the glacial–interglacial transition could be due to changed conditions in the potential source area or to changed patterns of atmospheric circulation, resulting in enhanced transport from a source area that was different from the glacial source areas. [Copyright &y& Elsevier]