Geographical variations in Sr and Nd isotopic ratios of cryoconite on Asian glaciers

Abstract

Cryoconite is a dark-coloured surface dust deposited on glaciers that consists of wind-blown mineral particles, as well as organic matter derived from microbes living on glaciers. In this paper, we analyse the Sr and Nd isotopic ratios of four mineral fractions (i.e., the saline, carbonate, phosphate, and silicate mineral fractions), as well as the organic fraction, of cryoconite samples obtained from six Asian glaciers (the Altai, Pamir, Tien Shan, Qillian Shan, and Himalayan regions), and discuss their geographical variations in terms of the geological origins of the mineral particles and the biogeochemical processes on the glaciers. The silicate mineral fraction showed lower Sr and higher Nd ratios for the glaciers located to the north (Altai, 87 Sr/ 86 Sr: 0.713 490-0.715 284, εNd(0): −6.4 to −5.6), while higher Sr and lower Nd ratios for the glaciers located to the south (Himalayas, 87 Sr/ 86 Sr: 0.740 121-0.742 088, εNd(0): −16.4 to −15.7); the ratios were similar to those of desert sand, loess, and river sediments in the respective regions of the glaciers. This result suggests that the silicate minerals within the cryoconites were derived from different sources depending on the geographical locations of the glaciers. The isotopic ratios of the saline, carbonate, and phosphate mineral fractions were distinct from those of the silicate fraction, and were similar to those of evaporites and apatite deposits from the Asian deserts, but also varied geographically, indicating that they are likely to reflect their geological origin. The Sr isotopic ratios of the organic fraction were similar to those of the saline and carbonate fractions from glaciers in the central area (Tien Shan and Qillian Shan), but were higher than those of the saline and carbonate fractions, and lower than the phosphate mineral fraction, in the northern and southern areas. The ratios of organic fraction may be determined from the mixing ratio of calcium sources incorporated by microbes on the glaciers.

Provenance of cryoconite deposited on the glaciers of the Tibetan Plateau: New insights from Nd‐Sr isotopic composition and size distribution

“…Figure shows the comparison of Nd‐Sr isotopic ratios of cryoconite on the Tibetan Plateau with previous cryoconite data from central Asia (see Figure , compared with the data of Nagatsuka et al []). The colored triangles in the figure show the ratios of loess, sand, and stream sediments from Asia, including the values of North China and Junggar [ Honda et al , ; Nakano et al , ], the Taklimakan desert, southern Gobi desert and the Loess Plateau [ Chen et al , ; Honda et al , ; Nakano et al , ; Yang et al , ], and the Himalaya [ Najman , ; Xu et al , ] and the northwest Indian arid areas [ Tripathi et al , ].…”

Variations in Sr and Nd Isotopic Ratios of Mineral Particles in Cryoconite in Western Greenland

“…The isotopic ratios showed no significant variation between the sites, suggesting that the mineral dust was derived from a single source and deposited uniformly across the ice surface. Nagatsuka et al (2014b) also showed geographical variation in the isotopic ratios of cryoconites on Asian glaciers, which revealed that the sources of minerals differ among the northern, central, and southern regions in Asia. Therefore, the Sr and Nd isotopic ratios of the minerals in cryoconite could reveal geographical, regional, and altitudinal variation in the mineral sources on the Greenland Ice Sheet.…”

Cryospheric ecosystems: a synthesis of snowpack and glacial research

“…The sediment size effect suggests that a greater understanding of sediment provenance and transport history should be sought. For example, Nagatsuka et al (2014) showed how the long-range transport of fine aeolian particles may be established using their rare earth element composition and then used to understand bioflocculation into Asian cryoconite. Future work should therefore integrate the techniques described above to understand better the linkages between sediment provenance and microbial diversity.…”