Dust provenanace in NEEM deep ice core from Greenland over the past 30,000 years using Pb and Sr isotopic composition

초록

Pb and Sr isotopic compositions and Pb and Ba concentrations are reported in 71 sections of the 2,54-0m-long deep ice core drilled at the NEEM (North Greenland Eemian Ice Drilling) site, Greenland (77.45 N, 51.06 W, surface elevation 2,450 m). The depth of the section ranged from 1,215 m to 1,671 m, corresponding to the period of ~8,000 yr BP (Holocene) to ~30,800 yr BP (Marine Isotopic Stage 2.2). Samples were decontaminated and analyzed using a thermal ionization mass spectrometry (TIMS) (TRITON, Thermo Scientific) under class 10 clean conditions. Concentrations of Pb and Pb/ Pb ratios are observed to have strongly varied with changing climate. Pb concentrations were low (<20 pg/g) during warm climatic phases (δ18O > .40‰) and much higher up to 250 pg/g during cold climatic phases (δ18O < .40‰). Pronounced variation in206Pb/207Pb ratios is observed during warm climatic phases, while a relatively small variation in 206Pb/207Pb ratios is observed during cold climatic phases. The variation in 206Pb/207Pb isotopic ratios (also 87Sr/86Sr) linked to climatic conditions reflects changes in the source areas of dust deposited in Greenland. The combination of Pb and Sr isotopic ratios suggest that Asia (the Northern Chinese and Gobi deserts) is identified as the primary contributor to the Greenland dust during the period from ~30,000 yr BP to ~20,000 yr BP. Interestingly, our data represent that the Saharan desert was an important source of dust in Greenland between ~21,000 yr BP and ~16,000 yr BP, probably due to an increase in northward Saharan dust transport during this period of intensified atmospheric circulation in high northern latitudes. After the last deglaciation, a wide range of the isotopic compositions is observed, suggesting the exposure of other potential source areas in the high latitudes of the Northern Hemisphere such as Canada and Spitsbergen.