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

Abstract

In order to better understand the source of minerals on the dark-colored ice, located in the Greenland ice sheet ablation zone, we analyzed the Sr and Nd isotopic ratios of minerals in cryoconite, which were collected from glaciers in northwest and southwest Greenland. We focused on the following: (i) comparison of the isotopes of minerals in cyroconite with those in sediments from local and distant areas, (ii) regional variations in western Greenland, and (iii) spatial variations across an individual a glacier. The mineral components of the cryoconite showed variable Sr and Nd isotopic ratios ( 87 Sr/ 86 Sr: 0.711335 to 0.742406, εNd (0): −33.1 to −22.9), which corresponded to those of the englacial dust and moraine on and around the glaciers but were significantly different from those of the distant deserts that have been considered to be primary sources of mineral dust on the Greenland Ice Sheet. This suggests that the minerals within the cryoconites were mainly derived from local sediments, rather than from distant areas. The Sr ratios in the northwestern region were significantly higher than those in the southwestern region. This is probably due to geological differences in the source areas, such as the surrounding glaciers in each region. The isotopic ratios further varied spatially within a glacier (Qaanaaq and Kangerlussuaq areas), indicating that the silicate minerals on the glaciers were derived not from a single source but from multiple sources, such as englacial dust and wind-blown minerals from the moraine surrounding the glaciers.

Albedo reduction of ice caused by dust and black carbon accumulation: a model applied to the K-transect, West Greenland

“…S7 in the supplements). Therefore, meltout is the main source of dust on the ice surface, which is also supported by a study of the isotopic composition (Nagatsuka and others, 2016).…”

Observations and modelling of algal growth on a snowpack in north-western Greenland

“…Previous studies reported that mineral dust on glaciers in northwestern and south-western Greenland is mainly supplied from local ground surfaces (e.g. moraine near the glacier) rather than the distant areas (Nagatsuka et al, , 2016. Therefore, the algal spores, which were washed out from the glacier and stayed on the ground, may be supplied with dust around the glacier by wind.…”

Bacterial community changes with cryoconite granule size and their susceptibility to exogenous nutrients on 10 glaciers in northwestern Greenland

“…On all of the study glaciers, filamentous cyanobacteria genus Phormidesmis (mostly P. priestleyi) was abundant in all size fractions of granules. P. priestleyi has been isolated from Antarctic lake originally (Taton et al 2010), and has also been reported from many of Arctic glaciers (Chrismas et al 2016, Gokul et al 2016, Uetake et al 2016, Anesio et al 2017, Cameron et al 2017. Relative abundance and SIMPER similarity of this genus largely increased in larger than size 250, which Uetake et al (2016) pointed out as the distinct boundary of carbon ratio and species diversity in cryoconite granules (SI Table 3 Despite of the high abundance of this genus, 16S rRNA gene network analysis showed that abundance of P. priestleyi are poorly connected to other bacteria (Gokul et al 2016).…”

“…On the glacier surface, the size of cryoconite granules usually varied from μ m to mm in diameter, because filamentous cyanobacteria interweave their cells to make a granule and granule size is changed by degree of microbial growth. 16S rRNA gene amplicon sequencing of bacterial community in different granule size on a Greenland glacier revealed that the communities were distinctive among the size (diameter) of the granules and their diversity largely differed between granules of larger and smaller than 250 μm in diameter (Uetake et al 2016). However, this study was done on a single glacier and it is difficult to presume spatial variation of microbial communities with granule size changes, because microbial communities are quite different even in adjacent glaciers (Edward et al 2011, Lutz et al 2016.…”

“…Therefore, at first, in order to know spatial difference of bacterial changes with granule growth across glaciers, we focused on bacterial community based on 16S rRNA gene sequencing in 4 different sizes (30-249 μm, 250-750 μm, 750-1599 μm, more than 1600 μm) of cryoconite granules collected from cryoconite holes on 10 different neighborhood glaciers of previous study site in Uetake et al (2016). Secondary, differences of microbial communities with granule size would change susceptibility to environmental factors, because firm aggregated granule is more stable and nutrients are potentially supply from in situ nutrient cycle such as nitrogen fixation ) and nitrification and denitrification processes (Segawa et al 2014).…”