Assessment of branched glycerol monoalkyl glycerol tetraether (brGMGT)-based paleothermometry in the 250,000-year sediment record of Lake Chala, equatorial East Africa

A. J. Baxter; F. Peterse; D. Verschuren; J.S. Sinninghe Damsté

doi:10.1016/j.orggeochem.2024.104812

Assessment of branched glycerol monoalkyl glycerol tetraether (brGMGT)-based paleothermometry in the 250,000-year sediment record of Lake Chala, equatorial East Africa

A. J. Baxter, F. Peterse^*, D. Verschuren, J.S. Sinninghe Damsté

^*Corresponding author for this work

Research output: Contribution to journal › Article › Academic › peer-review

Abstract

Branched glycerol monoalkyl glycerol tetraethers (brGMGTs), a relatively understudied group of bacterial membrane lipids structurally similar to branched glycerol dialkyl glycerol tetraethers (brGDGTs), appear to be strongly influenced by temperature in terrestrial settings. In surficial bottom sediments of East African lakes, the abundance of brGMGTs relative to the sum of brGMGTs and brGDGTs (%brGMGT) and brGMGT distribution are strongly related to local mean annual air temperature (MAAT), stimulating development of new paleothermometers. However, applications of these methods to lake-sediment records are currently lacking. Here we investigate brGMGT concentrations and distributions in 916 samples throughout the 250,000-year (250-kyr) sediment sequence from Lake Chala, a presently fresh and permanently stratified (meromictic) tropical crater lake. All seven previously identified brGMGTs occur abundantly, reflected in a relatively high average %brGMGT of 19%. BrGMGTs and brGDGTs concentrations throughout the sequence are strongly correlated (R = 0.83, p < 0.001), suggesting that their producers and/or associated ecological niches substantially overlap. Clear distinction can be made between brGMGTs produced predominantly in the bottom sediments (H1034a and H1034c) versus the anoxic lower water column (H1020a-c and H1034b). Although a 17-month monitoring study of Lake Chala suggested brGMGTs are primarily produced in the sediments, down-core data assign greater importance to aquatic production than previously estimated. Instead of reflecting temperature, %brGMGT variations showed greatest similarity to GDGT proxies reflecting lake depth and/or mixing regime. BrGMGT-based temperature models produce ambiguous reconstructions, showing little similarity to known global temperature trends or the brGDGT-based mean summer temperature (MST) reconstruction from the same sediments.

Original language	English
Article number	104812
Journal	Organic Geochemistry
Volume	195
DOIs	https://doi.org/10.1016/j.orggeochem.2024.104812
Publication status	Published - Sept 2024

Bibliographical note

Publisher Copyright:
© 2024 The Authors

Funding

This research was mainly co-financed by NESSC Gravitation Grant 024.002.001 from the Dutch Ministry of Education, Culture and Science (OCW) to JSSD; and by Hercules infrastructure grant AUGE/15/14-G0H2916N from the Research Foundation of Flanders and a Francqui research professor mandate to DV. Recovery of the Lake Chala sediment record was accomplished with support of ICDP through the Deep-CHALLA project (https:// www.icdp-online.org/projects/world/africa/lake-challa/) , and facilitated by the government of Kenya through permit P/16/7890/10400 from the National Commission for Science, Technology and Innovation (NACOSTI) and license EIA/PSL/3851 from the National Environmental Management Authority (NEMA) ; and by the government of Tanzania through permits NA-2016-67 (270-285) and NA-2016-201 (277-292) from the Tanzania Commission for Science and Technology (COSTECH) and permit EIA/10/0143/V.I/04 from the National Environmental Management Council. The authors wish to thank DeepCHALLA partners and their institutions in Kenya and Tanzania for project facilitation; Caxton M. Oluseno and the Kamba and Taveta communities of Lake Chala area for field assistance; and the National Lacustrine Core Facility (LacCore) at the University of Min-nesota (USA) for organizing the splitting, logging and initial processing of core samples. We are further grateful to J. Riekenberg and A. Mets for analysis of samples. We kindly thank the associate editor, I. Castaneda, and reviewers Z. Zeng and D. Naafs whose feedback has improved this manuscript.

Funders	Funder number
University of Minnesota
National Lacustrine Core Facility
National Environmental Management Council
Fonds Wetenschappelijk Onderzoek
National Environmental Management Authority	NA-2016-67, 270-285, NA-2016–201 (277–292, 277-292, NA-2016-201
National Commission for Science, Technology and Innovation	EIA/PSL/3851
ICDP	P/16/7890/10400
Netherlands Earth System Science Centre	024.002.001
Tanzania Commission for Science and Technology	EIA/10/0143/V.I/04
Ministerie van onderwijs, cultuur en wetenschap	AUGE/15/14-G0H2916N

Keywords

brGDGTs
brGMGTs
DeepCHALLA
East Africa
H-shaped GDGTs
ICDP
Lake Chala
Lake sediments
Paleoclimate

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title = "Assessment of branched glycerol monoalkyl glycerol tetraether (brGMGT)-based paleothermometry in the 250,000-year sediment record of Lake Chala, equatorial East Africa",

abstract = "Branched glycerol monoalkyl glycerol tetraethers (brGMGTs), a relatively understudied group of bacterial membrane lipids structurally similar to branched glycerol dialkyl glycerol tetraethers (brGDGTs), appear to be strongly influenced by temperature in terrestrial settings. In surficial bottom sediments of East African lakes, the abundance of brGMGTs relative to the sum of brGMGTs and brGDGTs (%brGMGT) and brGMGT distribution are strongly related to local mean annual air temperature (MAAT), stimulating development of new paleothermometers. However, applications of these methods to lake-sediment records are currently lacking. Here we investigate brGMGT concentrations and distributions in 916 samples throughout the 250,000-year (250-kyr) sediment sequence from Lake Chala, a presently fresh and permanently stratified (meromictic) tropical crater lake. All seven previously identified brGMGTs occur abundantly, reflected in a relatively high average %brGMGT of 19%. BrGMGTs and brGDGTs concentrations throughout the sequence are strongly correlated (R = 0.83, p < 0.001), suggesting that their producers and/or associated ecological niches substantially overlap. Clear distinction can be made between brGMGTs produced predominantly in the bottom sediments (H1034a and H1034c) versus the anoxic lower water column (H1020a-c and H1034b). Although a 17-month monitoring study of Lake Chala suggested brGMGTs are primarily produced in the sediments, down-core data assign greater importance to aquatic production than previously estimated. Instead of reflecting temperature, %brGMGT variations showed greatest similarity to GDGT proxies reflecting lake depth and/or mixing regime. BrGMGT-based temperature models produce ambiguous reconstructions, showing little similarity to known global temperature trends or the brGDGT-based mean summer temperature (MST) reconstruction from the same sediments.",

keywords = "brGDGTs, brGMGTs, DeepCHALLA, East Africa, H-shaped GDGTs, ICDP, Lake Chala, Lake sediments, Paleoclimate",

author = "Baxter, {A. J.} and F. Peterse and D. Verschuren and {Sinninghe Damst{\'e}}, J.S.",

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language = "English",

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AB - Branched glycerol monoalkyl glycerol tetraethers (brGMGTs), a relatively understudied group of bacterial membrane lipids structurally similar to branched glycerol dialkyl glycerol tetraethers (brGDGTs), appear to be strongly influenced by temperature in terrestrial settings. In surficial bottom sediments of East African lakes, the abundance of brGMGTs relative to the sum of brGMGTs and brGDGTs (%brGMGT) and brGMGT distribution are strongly related to local mean annual air temperature (MAAT), stimulating development of new paleothermometers. However, applications of these methods to lake-sediment records are currently lacking. Here we investigate brGMGT concentrations and distributions in 916 samples throughout the 250,000-year (250-kyr) sediment sequence from Lake Chala, a presently fresh and permanently stratified (meromictic) tropical crater lake. All seven previously identified brGMGTs occur abundantly, reflected in a relatively high average %brGMGT of 19%. BrGMGTs and brGDGTs concentrations throughout the sequence are strongly correlated (R = 0.83, p < 0.001), suggesting that their producers and/or associated ecological niches substantially overlap. Clear distinction can be made between brGMGTs produced predominantly in the bottom sediments (H1034a and H1034c) versus the anoxic lower water column (H1020a-c and H1034b). Although a 17-month monitoring study of Lake Chala suggested brGMGTs are primarily produced in the sediments, down-core data assign greater importance to aquatic production than previously estimated. Instead of reflecting temperature, %brGMGT variations showed greatest similarity to GDGT proxies reflecting lake depth and/or mixing regime. BrGMGT-based temperature models produce ambiguous reconstructions, showing little similarity to known global temperature trends or the brGDGT-based mean summer temperature (MST) reconstruction from the same sediments.

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KW - Paleoclimate

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M3 - Article

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ER -

Assessment of branched glycerol monoalkyl glycerol tetraether (brGMGT)-based paleothermometry in the 250,000-year sediment record of Lake Chala, equatorial East Africa

Abstract

Bibliographical note

Funding

Keywords

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