Dust in ice cores – University of Copenhagen

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Centre for Ice and Climate > Research > Reconstructing past atmospheres > Ice core impurities > Dust in ice cores

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.

 

       
source area

The main source area for continental dust transported to Greenland is Eastern Asia. The dust is lifted by storms in China and Mongolia and is transported by the westerlies all the way to Greenland (green arrow) where it can be identified in ice cores. Almost no dust arrives from the huge deserts in North Africa or North America.

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.

concentration of calcium ions

Concentration of Calcium ions ([Ca2+], essentially a measure of the dust content) and the δ18O values of three Greenland ice cores in the time interval from 32 to 12 thousand years before now (“ka b2k” means thousand years before AD 2000). Note that the [Ca2+] scale is logarithmic and upside-down. The δ18O curve below reflects temperatures in Greenland, and it can be seen that [Ca2+] is 3-500 ppb in the cold periods (Greenland stadials, denoted GS) and much lower in the mild interstadials (denoted GI) and as low as 10 ppb at the onset of the current interglacial, about 11.7 ka b2k (far left). In general there is very good agreement between δ18O and [Ca2+], but around 23-26 ka b2k, [Ca2+] reaches about 1000 ppb during two periods of about 1000 years. These are the so-called GS-3 dust peaks. Figure modified from Rasmussen et al., QSR 27, p. 18–28, 2008 (opens in new window).

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.

dust source

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