Dust in ice cores
Large deserts and arid areas on the continents act as natural dust sources for the atmosphere. Micrometer-sized dust particles from these areas are lifted to high altitudes and can be transported over thousands of kilometres by the wind. Dust from the otherwise clean Greenland ice sheet can be analysed, and the composition of the dust shows that the dust originates almost entirely from deserts and dry areas in eastern Asia, such as the Gobi desert (see more below). In contrast, very little or no dust comes from North America or the Saharan desert that is today's largest atmospheric dust source.
During glacial times the amount of dust that reached Greenland was 10-100 times greater than in the present interglacial, but the composition of the glacial dust is basically the same as that of today's dust. This tells us that the Greenland dust sources have largely been constant over the last glacial cycle, but that the winds were stronger and that particle wash-out in the atmosphere was much less efficient during glacial times. So the glacial period was not only a lot colder than today, it was also a lot more windy and dustier at high latitudes.
Identifying the dust sources
The potential sources of the dust found in the ice cores are determined from measurements of the Nd and Sr isotopes of the dust.
The figure shows a comparison of the isotopic composition of dust from Greenland ice cores with that of deserts and dust source areas in the Northern Hemisphere. The present-day most significant dust source areas are North America, North Africa/Middle East, and Eastern Asia (Mongolia/China). Due to their different geological histories, the dust source areas have different isotopic fingerprints in the elements of Strontium (Sr) and Neodymium (Nd). A fraction of volcanic ash in the ice core samples will drag their isotopic signature in the direction of the 'Circum Pacific Volcanic Rocks'. The ice core dust samples that have been extracted from Greenland ice core ice up to 45.000 years old (blue dots) are seen to have an isotopic composition most similar to a mixing of dust from the Asian source areas. Asia is, therefore, seen as the most important dust source area for Greenland during this period. The conclusion is supported by the mineralogical composition of the ice core dust, which is distinct from that of the African and North American dust.
Read about how the dust impurities are measured using Continuous Flow Analysis
Ice Core Drilling Projects
For more information on the topic please contact Anders Svensson