Ge/Si and Ge Isotope Fractionation During Glacial and Non-glacial Weathering: Field and Experimental Data From West Greenland

Type Article
Date 2021-03
Language English
Author(s) Baronas J. Jotautas1, 2, Hammond Douglas E.1, Bennett Mia M.3, 4, Rouxel OlivierORCID5, Pitcher Lincoln H.3, Smith Laurence C.3
Affiliation(s) 1 : Department of Earth Sciences, University of Southern California, Los Angeles, CA, United States
2 : Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom
3 : Department of Geography, University of California Los Angeles, Los Angeles, CA, United States
4 : Department of Geography, The University of Hong Kong, Hong Kong, China
5 : IFREMER, Centre De Brest, Unité Géosciences Marines, Plouzané, France
Source Frontiers in Earth Science (2296-6463) (Frontiers Media SA), 2021-03 , Vol. 9 , P. 551900 (19p.)
DOI 10.3389/feart.2021.551900
Keyword(s) glacial weathering, germanium, isotope fractionation, Amorphous silica, experimental dissolution
Abstract

Glacial environments offer the opportunity to study the incipient stages of chemical weathering due to the high availability of finely ground sediments, low water temperatures, and typically short rock-water interaction times. In this study we focused on the geochemical behavior of germanium (Ge) in west Greenland, both during subglacial weathering by investigating glacier-fed streams, as well as during a batch reactor experiment by allowing water-sediment interaction for up to 2 years in the laboratory. Sampled in late August 2014, glacial stream Ge and Si concentrations were low, ranging between 12–55 pmol/L and 7–33 µmol/L, respectively (Ge/Si = 0.9–2.2 µmol/mol, similar to parent rock). As reported previously, the dissolved stable Ge isotope ratio (δ74Ge) of the Watson River was 0.86 ± 0.24‰, the lowest among global rivers and streams measured to date. This value was only slightly heavier than the suspended load (0.48 ± 0.23‰), which is likely representative of the bulk parent rock composition. Despite limited Ge/Si and δ74GeGe fractionation, both Ge and Si appear depleted relative to Na during subglacial weathering, which we interpret as the relatively congruent uptake of both phases by amorphous silica (aSi). Continued sediment-water interaction over 470–785 days in the lab produced a large increase in dissolved Si concentrations (up to 130–230 µmol/L), a much smaller increase in dissolved Ge (up to ∼70 pmol/L), resulting in a Ge/Si decrease (to 0.4–0.5 µmol/mol) and a significant increase in δ74Ge (to 1.9–2.2‰). We argue that during the experiment, both Si and Ge are released by the dissolution of previously subglacially formed aSi, and Ge is then incorporated into secondary phases (likely adsorbed to Fe oxyhydroxides), with an associated Δ74Gesecondary−dissolved fractionation factor of −2.15 ± 0.46‰. In summary, we directly demonstrate Ge isotope fractionation during the dissolution-precipitation weathering reactions of natural sediments in the absence of biological Ge and Si uptake, and highlight the significant differences in Ge behavior during subglacial and non-glacial weathering.

Full Text
File Pages Size Access
Publisher's official version 19 2 MB Open access
Table 1 25 KB Open access
Data Sheet 8 KB Open access
Top of the page

How to cite 

Baronas J. Jotautas, Hammond Douglas E., Bennett Mia M., Rouxel Olivier, Pitcher Lincoln H., Smith Laurence C. (2021). Ge/Si and Ge Isotope Fractionation During Glacial and Non-glacial Weathering: Field and Experimental Data From West Greenland. Frontiers in Earth Science, 9, 551900 (19p.). Publisher's official version : https://doi.org/10.3389/feart.2021.551900 , Open Access version : https://archimer.ifremer.fr/doc/00684/79577/