An 800-year record of changes in atmospheric composition and circulation in the central Himalayas

초록

In September 2002, two firn/ice cores drilled to bedrock (108.8 m [ER-a] and 95.8 m [ER-b] long, respectively) were recovered from the East Rongbuk (ER) glacier located on the northern slope of Mt. Everest (28°03′ N, 86°96′ E, 6518 m asl). Trace elements (Cu, Zn, As, Mo, Pb, Cd, Sn and Sb), Pb isotopic composition (206Pb/207Pb and 208Pb/207Pb) and deuterium excess (d) have been determined in 143 depth intervals, covering an 800-year time period from 1205 to 2002 AD. Significant variations in the Pb enrichment factors and 206Pb/207Pb isotope ratios from the 1970s onwards characterize unambiguous atmospheric Pb pollution and the time-dependent evolution of industrial Pb inputs as a result of industrial development in South Asia. The other elements also show pronounced increases of both concentrations and crustal enrichment factors since the 1970s, supporting that human activities in South Asia have affected the natural atmospheric cycles of these elements during the recent decades. Finally, continuous measurements for both δD and δ18O provide the first high-resolution record of deuterium excess in the central Himalayas, showing the abnormally high d value during the period 1960-64 which is linked to the strengthening of the winter westerlies.