Recent seasonal changes of metal composition and size distribution of mineral particles in snow at EGRIP, Greenland

Seasonal changes of meteorological and ground surface conditions can cause seasonal changes of source area of mineral particles supplied to the Greenland ice sheet. Difference in metal composition and size distribution of them reflects their source area difference. To clarify seasonal changes in the source area of mineral particles, we examined the metal composition and size distribution of them in snow pit samples obtained from EGRIP (East Greenland Ice Core Project).

In summer 2017, we dug a 2.01 m snow pit at EGRIP camp. Snow samples were collected at 0.03 m intervals. The snow samples were melted, then fractions of them were analyzed for the particle size distribution (0.52-12μm) with a Coulter counter (Beckman Coulter: Multisizer 4). Other fractions of the samples were treated with a microwave acid digestion method to decompose particulates. Total concentrations of Al, Ca and Na in samples were measured by inductively coupled plasma mass spectrometry.

Total concentrations of Al (t-Al) and concentrations of non-sea-salt Ca (nssCa) showed peak values in winter to spring layers. In those layers, nssCa/t-Al ratios and volume fractions of fine particles (<4 μm) tended to be relatively high. In some of those layers, the nssCa/t-Al ratios were 2-3 times higher than the crustal average of Ca/Al ratio. This result suggests that fine Ca-rich mineral particles originated from remote desert areas were supplied to EGRIP in those seasons. In contrast, in summer to autumn layers, the nssCa/t-Al ratios and volume fractions tended to be relatively low. This result can be explained by supplies of coarse (≥ 4 μm) Ca-poor mineral particles originated from soil areas near Greenland in those seasons.