Soil chemistry effect on GDGT abundances and their proxies in soils of the Okavango Delta

Lattaud, Julie; Gondwe, Mangaliso J.; Griepentrog, Marco; Helfter, Carole ORCID: https://orcid.org/0000-0001-5773-4652; De Jonge, Cindy. 2024 Soil chemistry effect on GDGT abundances and their proxies in soils of the Okavango Delta. Organic Geochemistry, 195, 104847. 12, pp. 10.1016/j.orggeochem.2024.104847

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Official URL: http://dx.doi.org/10.1016/j.orggeochem.2024.104847

Abstract/Summary

Branched and isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs, and isoGDGTs) are two families of membrane lipids commonly used to reconstruct paleo-environmental parameters. Their use as a quantitative proxy for past temperatures has been hindered by the discovery of other environmental controls on their distribution in soils, such as changes in bacterial community composition, chemistry and aridity. To test for the impact of aridity-driven soil chemistry changes, GDGT concentrations and derived proxies were measured in 43 soils along a chemical gradient in the Okavango Delta. All brGDGT concentrations increase with decreasing pH. Alkalinity-promoted (6-methyl and cyclopentane-containing) brGDGTs show a secondary concentration increase in arid soils, characterized by a high pH>8 and cation exchange capacity (CEC>30 cmolc kg−1). The concentration of 5-methyl brGDGTs increases faster that of 6-methyl brGDGTs in arid compared with non-arid soils. Although limited variability in temperature is present (∼2 °C), significant variation in MBT′5ME values is observed (0.63–0.96) likely driven by the variation in CEC. IsoGDGTs are present in lower concentrations than brGDGTs, and Ri/b values, a potential proxy for paleohydrological reconstruction, correlating with soil water content (r = 0.45, p < 0.01). TEX86 values (0.57–0.97) correlate with pH across the aridity transect. In this region, where accurate proxies and quantitative paleostudies are scarce, the impact of aridity-driven chemistry changes on GDGT-proxies is shown, i.e., MBT′5ME is overall controlled by CEC, but correlates negatively with pH in non-arid soils and with IR6ME in arid alkaline soils. Furthermore, we propose GDGT-based proxies for concentration in exchangeable calcium, past hydrological changes and soil pH.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/j.orggeochem.2024.104847
UKCEH and CEH Sections/Science Areas:	Atmospheric Chemistry and Effects (Science Area 2017-)
ISSN:	0146-6380
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	Botswana, paleoenvironment, brGDGTs, isoGDGTs, MBT′5ME, TEX86, Ri/b, wetlands
NORA Subject Terms:	Agriculture and Soil Science Atmospheric Sciences
Related URLs:	Dataset
Date made live:	07 Aug 2024 12:36 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537815

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.orggeochem.2024.104847

UKCEH and CEH Sections/Science Areas:

Atmospheric Chemistry and Effects (Science Area 2017-)

ISSN:

0146-6380

Additional Information. Not used in RCUK Gateway to Research.:

Open Access paper - full text available via Official URL link.

Additional Keywords:

Botswana, paleoenvironment, brGDGTs, isoGDGTs, MBT′5ME, TEX86, Ri/b, wetlands