Mineral dust originating from the various source regions significantly impacts on the energy balance of the Earth system through the absorption and scattering of radiation in the atmosphere and the modifications of the optical properties of clouds and snow/ice surfaces. Dust collected in polar ice is known to have been introduced from the source areas by long-range transport. It is known that the averaged atmospheric dust loading of the last glacial maximum is 2.5 times higher than that of Holocene and 20 times higher at high latitudes. Changes in atmospheric residence time of mineral dust also can play an important role, suggesting the need for size and rapidity of change of source region and high wind speed in the source area. The origin of dust is also directly related to the atmospheric circulation pattern involved in long-range transport.
Isotope tracking is suitable for past dust provenance. Dust provenance studies have been performed in polar ice cores using Pb, Sr, and Nd isotopes. For the Greenland, some studies have found that the majority of Greenland dust originates from East Asian deserts during the glacial period while dust originates from various regions during interglacial. Because the large volumes of a sample were needed to obtain a reliable result and to minimize artificial contamination, previous researchers could not carry out on a high-resolution study using the fixed-diameter ice core samples. To overcome this problem, a new decontamination method has been improved to obtain an inner core by removing only a very thin layer. The experimental method was also confirmed by the analysis of recently collected at East Antarctic snow pit samples. High-resolution Pb and Sr isotopic compositions were obtained in the NEEM ice core, the most recently drilled ice core in Greenland, from the late last glacial stage (~31 kyr ago) to the early Holocene (~8 kyr ago). The Antarctic deep ice core study for Sr and Nd isotope was performed using only on glacial dust samples. In addition, the Pb isotopic approach of Antarctic ice core was carried out only during the period after mid-Brunhes event (MBE, ~430 kyr), and there is no study of dust provenance during the before MBE. In this research, Pb isotopes are presented for the EPICA Dome C ice core during the before MBE covering a period from 570 to 800 kyr BP.
Pb, Ba, and Sr concentrations recorded in the NEEM ice core are found to have significantly varied with high concentration during the cold period and lower concentration during warmer periods. It means that the concentration of the elements is changed by the amount of dust flux in Greenland. The Pb and Sr isotope data confirm that NW Greenland dust originated from the different source of Summit region. High-resolution data and advanced PSA field data allowed that East Asian deserts, particularly the Taklimakan and the Gobi have been suggested as the dominant source of NW Greenland dust during Greenland Stadials 3-5.1 (~30.8 to 23.0 kyr ago). Subsequently, the Saharan isotopic signals clearly emerge during Greenland Stadials 2.1 (~22.6 to 14.7 kyr ago) and intermittent period during the late Bølling-Allerød to the Younger Dryas (~13.6 to 12.2 kyr ago), indicating the Sahara as an additional source of Greenland dust. It can be seen that the Sahara desert was not ruled out as a significant Greenland dust source region. Our findings provide new insights into climate-related dust provenance changes and essentially paleoclimatic constraints on dust-related climate feedbacks in northern high latitudes.
The changes of the Pb isotopic composition in EPICA Dome C is inconsistent with the δD, for paleo-temperature proxy, before the MBE, while the changes in the Pb isotopic composition after the MBE is consistent with δD. The maximum value of 206Pb/207Pb before 570 ky BP is lower than after 220 kyr BP, which reduces the impact of the volcanic source or increases the impact of mineral dust. Decreased Pb/dust ratios in more recent glacial cycles indicate that the portion of dust Pb was increased, while increased Pb/dust ratios in older glacial cycles indicate an additional input of Pb from volcanic sources. New Pb isotopic data suggest that the Patagonia of southern South America is the primary dust source to the East Antarctic Plateau during glacial before the MBE. In the interglacial, Pb isotopic ratios are not increased even though the non-crustal Pb increases because of no influence of more-radiogenic Pb from Antarctic interior volcanoes. Here we confirmed that less radiogenic non-crustal Pb influenced Pb in EDC ice during the period before the MBE. This suggests that the radiogenic Antarctic interior volcanoes were not active during the period before the MBE. This increased non-crustal Pb before 570 kyr is consistent with nssSO42- flux and In concentrations. Our data also suggest that the source of less radiogenic non-crustal Pb is oceanic island including New Zealand.
Based on the results of this study, identifying the origin of the Greenland and Antarctic dust could help to understand the correlation between environmental change and climate change signals.