Journal articles: 'Branched GDGTs'

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Weijers, J. W. H., G. L. B. Wiesenberg, R. Bol, E. C. Hopmans, and R. D. Pancost. "Carbon isotopic composition of branched tetraether membrane lipids in soils suggest a rapid turnover and a heterotrophic life style of their source organism(s)." Biogeosciences Discussions 7, no. 3 (May 21, 2010): 3691–734. http://dx.doi.org/10.5194/bgd-7-3691-2010.

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Abstract. Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has been determined in various soils, i.e. peat, forest, grassland and cropland, covered by various vegetation types, i.e., C3- vs. C4-plant type. These δ13C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ13C values of −28‰, branched GDGTs in C3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰ enriched relative to plant wax-derived long-chain n-alkanes (nC29–nC33). In an Australian soil covered with C4 type vegetation, the branched GDGTs have a δ13C value of −18‰, clearly higher than observed in soils with C3 type vegetation. As with C3 vegetated soils, branched GDGT δ13C values are slightly depleted (1‰) relative to bulk organic carbon and enriched (ca. 5‰) relative to n-alkanes in this soil. The δ13C values of branched GDGT lipids being similar to bulk organic carbon and their co-variation with those of bulk organic carbon and plant waxes, suggest a heterotrophic life style and assimilation of relatively heavy and likely labile substrates for the as yet unknown soil bacteria that synthesise the branched GDGT lipids. However, a chemoautotrophic lifestyle, i.e. consuming respired CO2, could not be fully excluded based on these data alone. Based on a natural labelling experiment of a C3/C4 crop change introduced on one of the soils 23 years before sampling and based on a free air CO2 enrichment experiment with labelled CO2 on another soil, a turnover time of ca. 17 years has been estimated for branched GDGTs in these arable soils.

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Weijers, J. W. H., G. L. B. Wiesenberg, R. Bol, E. C. Hopmans, and R. D. Pancost. "Carbon isotopic composition of branched tetraether membrane lipids in soils suggest a rapid turnover and a heterotrophic life style of their source organism(s)." Biogeosciences 7, no. 9 (September 28, 2010): 2959–73. http://dx.doi.org/10.5194/bg-7-2959-2010.

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Abstract. Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has been determined in a peat and various soils, i.e. forest, grassland and cropland, covered by various vegetation types, i.e., C3- vs. C4-plant type. These δ13C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ13C values of −28‰, branched GDGTs in C3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰ enriched relative to plant wax-derived long-chain n-alkanes ( nC29–nC33). In an Australian soil dominantly covered with C4 type vegetation, the branched GDGTs have a δ13C value of −18‰, clearly higher than observed in soils with C3 type vegetation. As with C3 vegetated soils, branched GDGT δ13C values are slightly depleted (1‰) relative to bulk organic carbon and enriched (ca. 5‰) relative to n-alkanes in this soil. The δ13C values of branched GDGT lipids being similar to bulk organic carbon and their co-variation with those of bulk organic carbon and plant waxes, suggest a heterotrophic life style and assimilation of relatively heavy and likely labile substrates for the as yet unknown soil bacteria that synthesise the branched GDGT lipids. However, a chemoautotrophic lifestyle, i.e. consuming respired CO2, could not be fully excluded based on these data alone. Based on a natural labelling experiment of a C3/C4 crop change introduced on one of the soils 23 years before sampling and based on a free-air CO2 enrichment experiment with labelled CO2 on another soil, a turnover time of ca. 18 years has been estimated for branched GDGTs in these arable soils.

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Tierney, Jessica E. "GDGT Thermometry: Lipid Tools for Reconstructing Paleotemperatures." Paleontological Society Papers 18 (November 2012): 115–32. http://dx.doi.org/10.1017/s1089332600002588.

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Microbial communities adjust the chemical structure of their cell membranes in response to environmental temperature. This enables the development of lipid-based paleothermometers such as the glycerol dialkyl glycerol tetraether (GDGT) proxies described here. Surface-sediment calibrations establish a strong empirical relationship between the relative distribution of GDGTs and temperature. GDGT proxies can be used in marine, lacustrine, and paleosol sequences as long as the organic material is not thermally mature. Thus far, GDGT proxies have been applied to sediments dating back to the middle Jurassic. Many of the key uncertainties of these proxies are related to our emerging understanding of archaeal (and for the branched GDGTs, bacterial) ecology.

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Chen, Yongxin, Xilong Zhang, Wen Qi, Gaoqing Zhang, Yu Pei, Xuan Fang, Yanqing Xia, and Shengyin Zhang. "Distribution of Glycerol Dialkyl Glycerol Tetraethers (GDGTs) in Carbonate-Type and Sulfate-Type Lacustrine Sediments: Insight into the Influence of Ionic Composition on GDGTs." Minerals 12, no. 10 (September 28, 2022): 1233. http://dx.doi.org/10.3390/min12101233.

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The distribution of glycerol dialkyl glycerol tetraethers (GDGTs) in carbonate-type and sulfate-type saline lacustrine sediments from the Ordos Plateau in China is investigated to explore the influence of ionic composition on GDGTs. In general, they are relatively small (1.2–6.0 km2 surface area) and shallow ponds (0.05–0.2 m water depth) and even seasonally dry lakes. The results reveal that the concentration of GDGTs has a good positive correlation with the (nCO32− + nHCO3−)/total ions, and the concentration of GDGTs in carbonate-type lake sediments is significantly higher than that in sulfate-type lake sediments. Most GDGT-based indices show no significant differences, and the distributions of GDGTs are similar in the two types of saline lake sediments. The lack of a positive correlation between the content of clay minerals and the concentration of GDGTs may imply that the ability of clay minerals to carry terrigenous organic matter is very limited in arid climates. The branched GDGTS (brGDGTs) in the two saline lake sediments may mainly come from in situ biological production and have low terrestrial inputs. The different weathering level of feldspar minerals in the two types of saline lakes results in the difference in organic matter content, which ultimately affects the concentration of GDGTs.

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Mueller-Niggemann, C., S. R. Utami, A. Marxen, K. Mangelsdorf, T. Bauersachs, and L. Schwark. "Distribution of tetraether lipids in agricultural soils – differentiation between paddy and upland management." Biogeosciences Discussions 12, no. 20 (October 19, 2015): 16709–54. http://dx.doi.org/10.5194/bgd-12-16709-2015.

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Abstract. Insufficient knowledge of the composition and variation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) in agricultural soils exists, despite of the potential effect of different management types (e.g. soil/water and redox conditions, cultivated plants) on GDGT distribution. Here, we determined the influence of different soil management types on the GDGT composition in paddy (flooded) and adjacent upland (non-flooded) soils, and if available also forest, bushland and marsh soils. To compare the local effects on GDGT distribution patterns, we collected comparable soil samples in various locations from tropical (Indonesia, Vietnam and Philippines) and subtropical (China and Italy) sites. We found that differences in the distribution of isoprenoid GDGTs (iGDGTs) as well as of branched GDGTs (brGDGTs) are predominantly controlled by management type and only secondarily by climatic exposition. In general upland soil had higher crenarchaeol contents than paddy soil, which on the contrary was more enriched in GDGT-0. The GDGT-0 / crenarchaeol ratio was 3–27 times higher in paddy soil and indicates the enhanced presence of methanogenic archaea, which were additionally linked to the number of rice cultivation cycles per year (higher number of cycles was coupled with an increase in the ratio). The TEX86 values were 1.3 times higher in upland, bushland and forest soils than in paddy soils. In all soils brGDGT predominated over iGDGTs, with the relative abundance of brGDGTs increasing from subtropical to tropical soils. Higher BIT values in paddy soils compared to upland soils together with higher BIT values in soil from subtropical climates indicate effects on the amounts of brGDGT through differences in management as well as climatic zones. In acidic soil CBT values correlated well with soil pH. In neutral to alkaline soils, however, no apparent correlation but an offset between paddy and upland managed soils was detected, which may suggest that soil moisture may exert an additional control on the CBT in these soils. Lower MBT' values and calculated temperatures (TMC) in paddy soils compared to upland soils may indicate a management (e.g. enhanced soil moisture through flooding practises) induced effect on mean annual soil temperature (MST).

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Bai, Yan, Chihao Chen, Qiang Xu, and Xiaomin Fang. "Paleoaltimetry Potentiality of Branched GDGTs From Southern Tibet." Geochemistry, Geophysics, Geosystems 19, no. 2 (February 2018): 551–64. http://dx.doi.org/10.1002/2017gc007122.

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Mueller-Niggemann, Cornelia, Sri Rahayu Utami, Anika Marxen, Kai Mangelsdorf, Thorsten Bauersachs, and Lorenz Schwark. "Distribution of tetraether lipids in agricultural soils – differentiation between paddy and upland management." Biogeosciences 13, no. 5 (March 17, 2016): 1647–66. http://dx.doi.org/10.5194/bg-13-1647-2016.

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Abstract. Rice paddies constitute almost a fifth of global cropland and provide more than half of the world's population with staple food. At the same time, they are a major source of methane and therewith significantly contribute to the current warming of Earth's atmosphere. Despite their apparent importance in the cycling of carbon and other elements, however, the microorganisms thriving in rice paddies are insufficiently characterized with respect to their biomolecules. Hardly any information exists on human-induced alteration of biomolecules from natural microbial communities in paddy soils through varying management types (affecting, e.g., soil or water redox conditions, cultivated plants). Here, we determined the influence of different land use types on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs), which serve as molecular indicators for microbial community structures, in rice paddy (periodically flooded) and adjacent upland (non-flooded) soils and, for further comparison, forest, bushland and marsh soils. To differentiate local effects on GDGT distribution patterns, we collected soil samples in locations from tropical (Indonesia, Vietnam and Philippines) and subtropical (China and Italy) sites. We found that differences in the distribution of isoprenoid GDGTs (iGDGTs) as well as of branched GDGTs (brGDGTs) are predominantly controlled by management type and only secondarily by climatic exposition. In general, upland soil had higher crenarchaeol contents than paddy soil, which by contrast was more enriched in GDGT-0. The GDGT-0 ∕ crenarchaeol ratio, indicating the enhanced presence of methanogenic archaea, was 3–27 times higher in paddy soils compared to other soils and increased with the number of rice cultivation cycles per year. The index of tetraethers consisting of 86 carbons (TEX86) values were 1.3 times higher in upland, bushland and forest soils than in paddy soils, potentially due to differences in soil temperature. In all soils brGDGT predominated over iGDGTs with the relative abundance of brGDGTs increasing from subtropical to tropical soils. Higher branched vs. isoprenoid tetraether (BIT) values in paddy soils compared to upland soils together with higher BIT values in soils from subtropical climates indicated effects on the amounts of brGDGT induced by differences in management as well as climate. In acidic soils cyclization ratio of branched tetraethers (CBT) values correlated well with soil pH. In neutral to alkaline soils, however, no correlation but an offset in CBT between paddy and upland managed soils was detected. This is interpreted as indicating soil moisture exerting an additional control on the CBT in these soils. Lower modified methylation index of branched tetraether (MBT′) values and temperatures calculated from this (TMC) in paddy soils compared to upland soils are attributed to a management-induced (e.g. enhanced soil moisture via flooding) effect on mean annual soil temperature (MST).

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Sinninghe Damsté, Jaap S., W. Irene C. Rijpstra, Ellen C. Hopmans, Johan W. H. Weijers, Bärbel U. Foesel, Jörg Overmann, and Svetlana N. Dedysh. "13,16-Dimethyl Octacosanedioic Acid (iso-Diabolic Acid), a Common Membrane-Spanning Lipid of Acidobacteria Subdivisions 1 and 3." Applied and Environmental Microbiology 77, no. 12 (April 22, 2011): 4147–54. http://dx.doi.org/10.1128/aem.00466-11.

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ABSTRACTThe distribution of membrane lipids of 17 different strains representing 13 species of subdivisions 1 and 3 of the phylumAcidobacteria, a highly diverse phylum of theBacteria, were examined by hydrolysis and gas chromatography-mass spectrometry (MS) and by high-performance liquid chromatography-MS of intact polar lipids. Upon both acid and base hydrolyses of total cell material, the uncommon membrane-spanning lipid 13,16-dimethyl octacosanedioic acid (iso-diabolic acid) was released in substantial amounts (22 to 43% of the total fatty acids) from all of the acidobacteria studied. This lipid has previously been encountered only in thermophilicThermoanaerobacterspecies but bears a structural resemblance to the alkyl chains of bacterial glycerol dialkyl glycerol tetraethers (GDGTs) that occur ubiquitously in peat and soil and are suspected to be produced by acidobacteria. As reported previously, most species also containediso-C15and C16:1ω7Cas major fatty acids but the presence ofiso-diabolic acid was unnoticed in previous studies, most probably because the complex lipid that contained this moiety was not extractable from the cells; it could only be released by hydrolysis. Direct analysis of intact polar lipids in the Bligh-Dyer extract of three acidobacterial strains, indeed, did not reveal any membrane-spanning lipids containingiso-diabolic acid. In 3 of the 17 strains, ether-boundiso-diabolic acid was detected after hydrolysis of the cells, including one branched GDGT containingiso-diabolic acid-derived alkyl chains. Since the GDGT distribution in soils is much more complex, branched GDGTs in soil likely also originate from other (acido)bacteria capable of biosynthesizing these components.

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Schouten, Stefan, Marcel T. J. van der Meer, Ellen C. Hopmans, W. Irene C. Rijpstra, Anna-Louise Reysenbach, David M. Ward, and Jaap S. Sinninghe Damsté. "Archaeal and Bacterial Glycerol Dialkyl Glycerol Tetraether Lipids in Hot Springs of Yellowstone National Park." Applied and Environmental Microbiology 73, no. 19 (August 10, 2007): 6181–91. http://dx.doi.org/10.1128/aem.00630-07.

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ABSTRACTGlycerol dialkyl glycerol tetraethers (GDGTs) are core membrane lipids originally thought to be produced mainly by (hyper)thermophilic archaea. Environmental screening of low-temperature environments showed, however, the abundant presence of structurally diverse GDGTs from both bacterial and archaeal sources. In this study, we examined the occurrences and distribution of GDGTs in hot spring environments in Yellowstone National Park with high temperatures (47 to 83°C) and mostly neutral to alkaline pHs. GDGTs with 0 to 4 cyclopentane moieties were dominant in all samples and are likely derived from both (hyper)thermophilicCrenarchaeotaandEuryarchaeota. GDGTs with 4 to 8 cyclopentane moieties, likely derived from the crenarchaeotal orderSulfolobalesand the euryarchaeotal orderThermoplasmatales, are usually present in much lower abundance, consistent with the relatively high pH values of the hot springs. The relative abundances of cyclopentane-containing GDGTs did not correlate with in situ temperature and pH, suggesting that other environmental and possibly genetic factors play a role as well. Crenarchaeol, a biomarker thought to be specific for nonthermophilic group ICrenarchaeota, was also found in most hot springs, though in relatively low concentrations, i.e., <5% of total GDGTs. Its abundance did not correlate with temperature, as has been reported previously. Instead, the cooccurrence of relatively abundant nonisoprenoid GDGTs thought to be derived from soil bacteria suggests a predominantly allochthonous source for crenarchaeol in these hot spring environments. Finally, the distribution of bacterial branched GDGTs suggests that they may be derived from the geothermally heated soils surrounding the hot springs.

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Ding, S., Y. Xu, Y. Wang, Y. He, J. Hou, L. Chen, and J. S. He. "Distributions of glycerol dialkyl glycerol tetraethers in surface soils of Qinghai–Tibetan Plateau: implications of GDGT-based proxies in cold and dry regions." Biogeosciences Discussions 12, no. 1 (January 9, 2015): 481–513. http://dx.doi.org/10.5194/bgd-12-481-2015.

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Abstract. The methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT) based on the distribution of bacteria-derived branched glycerol dialkyl glycerol tetraethers (bGDGTs) are useful proxies for the reconstruction of continental paleotemperature and soil pH. Several calibrations of the MBT-CBT index have been proposed based on global and regional soils and lake sediments. However, little is known about the distribution and applicability of GDGTs proxies in the Qinghai–Tibet Plateau (QTP), a critical region of the global climate system. Here, we investigated 33 surface soils covering a large area of the QTP. Redundancy analysis showed that soil pH was the most important factor affecting GDGT distributions, followed by mean annual precipitation (MAP) and mean annual air temperature (MAT). The branched-isoprenoid tetraether (BIT) index, an indicator for estimation of soil organic matter in aquatic environments, varied from 0.48 to 1 and negatively correlated with soil pH (r2 = 0.38), suggesting that the BIT index should be used with caution in the QTP. A transfer function of the CBT index-soil pH was established to estimate paleo-soil pH in the QTP: pH = 8.33–1.43 × CBT (r2 = 0.80, RMSE = 0.27 pH unit). The local calibration of MBT-CBT index presented a weak, still significant correlation with MAT (r2 = 0.36) mainly owing to the additional influence of MAP (r2 = 0.50). Combining our data with previously reported GDGTs for Chinese soils resulted in a new calibration of MBT/CBT-MAT: MAT = 2.68+26.14 × MBT–3.37 × CBT (r2 = 0.73; RMSE = 4.2 °C, n = 164). The correlation coefficient and residual error of this new transfer function is comparable with global calibrations, suggesting that MBT-CBT paleotemperature proxy is still valid in the QTP.

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Lopes dos Santos, Raquel A., and Christopher H. Vane. "Tracking natural organic carbon in the River Clyde, UK, using glycerol dialkyl glycerol tetraethers." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 108, no. 2-3 (June 2017): 289–98. http://dx.doi.org/10.1017/s175569101800035x.

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ABSTRACTSurface sediments from a 100-km stretch of the River Clyde, UK, and its estuary were analysed for glycerol dialkyl glycerol tetraethers (GDGTs) to track the downstream changes in the source of organic matter (OM) and to evaluate the impact of urbanisation. Bacterial membrane lipids, named branched GDGTs (brGDGTs), produced in soils and rivers ranged from 1.6 to 58μgg−1 organic carbon (OC) and the isoprenoid GDGT crenarchaeol, mainly from marine archaea, ranged from 0.01 to 42μgg−1 OC. The highest brGDGT concentrations were in the upper river, in Glasgow city and in the outer estuary, suggesting higher soil-derived OM input. By contrast, crenarchaeol concentrations gradually increased from the tidal weir in Glasgow towards the sea. This spatial distribution of the tetraethers was reflected in the branched and isoprenoid tetraether (BIT) index, a proxy for soil versus marine carbon. The highest BIT values (1.0) occurred upstream, estuarine values ranged from 0.9 to 0.6 and the lowest values (0.4) were found in the outer estuary. An independent proxy for soil-derived OM, stable carbon isotope (δ13C) values, showed a comparable decrease in terrigenous OM contribution towards the sea, but was more variable compared to the BIT. Conversely, carbon/nitrogen (C/N) showed a constant trend, suggesting that it is not a reliable indicator of OM source in the Clyde. Neither BIT, δ13C nor C/N were able to reflect the input of urban effluents from Glasgow.

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Gies, Hannah, Frank Hagedorn, Maarten Lupker, Daniel Montluçon, Negar Haghipour, Tessa Sophia van der Voort, and Timothy Ian Eglinton. "Millennial-age glycerol dialkyl glycerol tetraethers (GDGTs) in forested mineral soils: <sup>14</sup>C-based evidence for stabilization of microbial necromass." Biogeosciences 18, no. 1 (January 12, 2021): 189–205. http://dx.doi.org/10.5194/bg-18-189-2021.

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Abstract. Understanding controls on the persistence of soil organic matter (SOM) is essential to constrain its role in the carbon cycle and inform climate–carbon cycle model predictions. Emerging concepts regarding the formation and turnover of SOM imply that it is mainly comprised of mineral-stabilized microbial products and residues; however, direct evidence in support of this concept remains limited. Here, we introduce and test a method for the isolation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) – diagnostic membrane lipids of archaea and bacteria, respectively – for subsequent natural abundance radiocarbon analysis. The method is applied to depth profiles from two Swiss pre-Alpine forested soils. We find that the Δ14C values of these microbial markers markedly decrease with increasing soil depth, indicating turnover times of millennia in mineral subsoils. The contrasting metabolisms of the GDGT-producing microorganisms indicates it is unlikely that the low Δ14C values of these membrane lipids reflect heterotrophic acquisition of 14C-depleted carbon. We therefore attribute the 14C-depleted signatures of GDGTs to their physical protection through association with mineral surfaces. These findings thus provide strong evidence for the presence of stabilized microbial necromass in forested mineral soils.

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Shanahan, Timothy M., Konrad A. Hughen, and Benjamin A. S. Van Mooy. "Temperature sensitivity of branched and isoprenoid GDGTs in Arctic lakes." Organic Geochemistry 64 (November 2013): 119–28. http://dx.doi.org/10.1016/j.orggeochem.2013.09.010.

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Niemann, H., A. Stadnitskaia, S. B. Wirth, A. Gilli, F. S. Anselmetti, J. S. Sinninghe Damsté, S. Schouten, E. C. Hopmans, and M. F. Lehmann. "Bacterial GDGTs in Holocene sediments and catchment soils of a high Alpine lake: application of the MBT/CBT-paleothermometer." Climate of the Past 8, no. 3 (May 7, 2012): 889–906. http://dx.doi.org/10.5194/cp-8-889-2012.

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Abstract. A novel proxy for continental mean annual air temperature (MAAT) and soil pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a high Alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the past 11 000 yr. The distribution of bacterial GDGTs in the catchment soils is very similar to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record seems undisturbed, probably without any significant alteration of their distribution through in situ production in the lake itself or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT estimates match in timing and magnitude other proxy-based T reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (MWP, ~9th to 14th century). Together, our observations indicate the quantitative applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. In addition to the MWP, our lacustrine paleo T record indicates Holocene warm phases at about 3, 5, 7 and 11 kyr before present, which agrees in timing with other records from both the Alps and the sub-polar North-East Atlantic Ocean. The good temporal match of the warm periods determined for the central Alpine region with north-west European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European T variations during the Holocene.

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Niemann, H., A. Stadnitskaia, S. B. Wirth, A. Gilli, F. S. Anselmetti, J. S. Sinninghe Damsté, S. Schouten, E. C. Hopmans, and M. F. Lehmann. "Bacterial GDGTs in Holocene sediments and catchment soils of a high-alpine lake: application of the MBT/CBT-paleothermometer." Climate of the Past Discussions 7, no. 5 (October 19, 2011): 3449–88. http://dx.doi.org/10.5194/cpd-7-3449-2011.

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Abstract. A novel proxy for continental mean annual air temperature (MAAT) and soil-pH, the MBT/CBT-paleothermometer, is based on the temperature (T) and pH-dependent distribution of specific bacterial membrane lipids (branched glycerol dialkyl glycerol tetraethers – GDGTs) in soil organic matter. Here, we tested the applicability of the MBT/CBT-paleothermometer to sediments from Lake Cadagno, a small high-alpine lake in southern Switzerland with a small catchment of 2.4 km2. We analysed the distribution of bacterial GDGTs in catchment soils and in a radiocarbon-dated sediment core from the centre of the lake, covering the entire Holocene. The composition of bacterial GDGTs in soils are almost identical to that in the lake's surface sediments, indicating a common origin of the lipids. Consequently, their transfer from the soils into the sediment record is undisturbed, apparently without any significant alteration of their distribution through in situ production or early diagenesis of branched GDGTs. The MBT/CBT-inferred MAAT-estimates from soils and surface sediments are in good agreement with instrumental values for the Lake Cadagno region (~0.5 °C). Moreover, downcore MBT/CBT-derived MAAT-estimates match in timing and magnitude other proxy-based T-reconstructions from nearby locations for the last two millennia. Major climate anomalies recorded by the MBT/CBT-paleothermometer are, for instance, the Little Ice Age (~14th to 19th century) and the Medieval Warm Period (~10th to 14th century). Together, our observations confirm the applicability of the MBT/CBT-paleothermometer to Lake Cadagno sediments. Consistent with other T-records from both the Alps and from the subpolar NE-Atlantic, our lacustrine paleotemperature record indicates Holocene MAAT-variations with an apparent cyclicity of ~2 kyr. The good temporal match of the warm periods determined for the S-Alpine region with NW-European winter precipitation strength implies a strong and far-reaching influence of the North Atlantic Oscillation on continental European Holocene T-variations.

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Harning, David J., Brooke Holman, Lineke Woelders, Anne E. Jennings, and Julio Sepúlveda. "Biomarker characterization of the North Water Polynya, Baffin Bay: implications for local sea ice and temperature proxies." Biogeosciences 20, no. 1 (January 16, 2023): 229–49. http://dx.doi.org/10.5194/bg-20-229-2023.

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Abstract. The North Water Polynya (NOW, Inuktitut: Sarvarjuaq; Kalaallisut: Pikialasorsuaq), Baffin Bay, is the largest polynya and one of the most productive regions in the Arctic. This area of thin to absent sea ice is a critical moisture source for local ice sheet sustenance and, coupled with the inflow of nutrient-rich Arctic Surface Water, supports a diverse community of Arctic fauna and indigenous people. Although paleoceanographic records provide important insight into the NOW's past behavior, it is critical that we better understand the modern functionality of paleoceanographic proxies. In this study, we analyzed lipid biomarkers, including algal highly branched isoprenoids and sterols for sea ice extent and pelagic productivity and archaeal glycerol dibiphytanyl glycerol tetraethers (GDGTs) for ocean temperature, in a set of modern surface sediment samples from within and around the NOW. In conjunction with previously published datasets, our results show that all highly branched isoprenoids exhibit strong correlations with each other and not with sterols, which suggests a spring or autumn sea ice diatom source for all highly branched isoprenoids (HBIs) rather than a combination of sea ice and open-water diatoms as seen elsewhere in the Arctic. Sterols are also highly concentrated in the NOW and exhibit statistically higher concentrations here compared to sites south of the NOW, consistent with the order of magnitude higher primary productivity observed within the NOW relative to surrounding waters in spring and summer months. Finally, our local temperature calibrations for GDGTs and OH-GDGTs reduce the uncertainty present in global temperature calibrations but also identify some additional variables that may be important in controlling their local distribution, such as nitrate availability and dissolved oxygen. Collectively, our analyses provide new insight into the utility of these lipid biomarker proxies in high-latitude settings and will help provide a refined perspective on the past development of the NOW with their application in downcore reconstructions.

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Peterse, F., C. M. Moy, and T. I. Eglinton. "A laboratory experiment on the behaviour of soil-derived core and intact polar GDGTs in aquatic environments." Biogeosciences 12, no. 4 (February 16, 2015): 933–43. http://dx.doi.org/10.5194/bg-12-933-2015.

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Abstract. We have performed incubation experiments in order to examine the behaviour of soil-derived branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids upon entering an aquatic environment and to evaluate the processes that potentially take place during their fluvial transport from land to sea. We incubated a soil from the Rakaia River catchment on the South Island of New Zealand using Rakaia River water and ocean water collected near the river mouth as inocula for a period of up to 152 days. The concentrations, as well as the relative distribution of brGDGTs derived from intact polar ("living"; IPL) lipids and core ("fossil"; CL) lipids remained unaltered over the course of the experiment. Although the stability of the brGDGTs may be a consequence of the higher than natural soil : water ratio used in the laboratory experiment, the substantial increase (27–72%) in the total pool of isoprenoid GDGTs (isoGDGTs) in all incubation setups, including the control using distilled water, indicates that entering an aquatic environment does influence the behaviour of soil-derived GDGTs. However, the availability of water appears to be more important than its properties. As a consequence of increasing isoGDGT concentrations, a decrease in Branched and Isoprenoid Tetraether (BIT) index values – a proxy for the relative input of fluvially discharged soil material into a marine system – became evident after an incubation period of 30 days, with a maximum final decrease of 0.88 to 0.74 in the experiment with river water. The relative distribution within the isoGDGT pool shows changes with time, suggesting that isoGDGT producers may either have different rates of membrane adaptation or production/degradation, or that preferential release from the soil matrix or a shift in source organism(s) may take place. While the apparent stability of soil brGDGTs during this incubation experiment reinforces their potential as tracers for land–sea transport of soil organic carbon and their use in paleoclimate reconstructions, the distributional differences between GDGTs in river water and nearby soil, as well as in river and ocean water, indicate that further research is needed to pinpoint the sources of GDGTs that are ultimately discharged to the oceans and are subsequently archived in continental margin sediments.

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Peterse, F., C. M. Moy, and T. I. Eglinton. "Probing the fate of soil-derived core and intact polar GDGTs in aquatic environments." Biogeosciences Discussions 11, no. 7 (July 29, 2014): 11569–96. http://dx.doi.org/10.5194/bgd-11-11569-2014.

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Abstract. We have performed incubation experiments in order to examine the fate of branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids upon entering an aquatic environment and to asses the suitability of brGDGTs as tracers for fluvial land-sea transport of soil organic carbon. We incubated a soil from the Rakaia River catchment on the South Island of New Zealand using Rakaia River water and ocean water collected near the river mouth as inocula for a period of up to 152 days. The concentrations of brGDGTs derived from intact polar ("living"; IPL) lipids and core ("fossil"; CL) lipids remained stable over the course of the experiment, suggesting an absence of significant brGDGT production or degradation. Moreover, the lack of change in brGDGT distribution during the experiment implies that the initial soil signature remains unaltered during transport through the aquatic environment, at least over the time frame of the experiment. In contrast, the total pool of isoprenoid GDGTs (isoGDGTs), currently attributed to soil Thaumachaeota, increased substantially (27–72%) in all incubation setups by the end of the experiment. As a consequence, a decrease in Branched and Isoprenoid Tetraether (BIT) index values – a proxy for the relative input of fluvially discharged soil material into a marine system – became evident after an incubation period of 30 days, with a maximum final decrease of 0.88 to 0.74 in the experiment with river water. The relative distribution within the isoGDGT pool shows changes with time, suggesting different membrane adaptation rates to the aquatic environment, or a shift in source organism(s). While the stability of soil brGDGTs in aquatic environments reinforces their potential as tracers for land-sea transport of soil organic carbon and their use in paleoclimate reconstructions, the distributional differences between GDGTs in river water and nearby soil indicate that further research is needed to pinpoint the sources of GDGTs that are ultimately discharged to the oceans and are subsequently archived in continental margin sediments.

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Menges, J., C. Huguet, J. M. Alcañiz, S. Fietz, D. Sachse, and A. Rosell-Melé. "Water availability determines branched glycerol dialkyl glycerol tetraether distributions in soils of the Iberian Peninsula." Biogeosciences Discussions 10, no. 6 (June 3, 2013): 9043–68. http://dx.doi.org/10.5194/bgd-10-9043-2013.

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Abstract. The MBT/CBT has recently gained significant attention as a novel paleotemperature proxy. It is based on the distribution of branched glycerol dialkyl glycerol tetraethers (GDGTs) in soils. The CBT quantifies the degree of cyclisation and relates to soil pH. The MBT' quantifies the degree of methylation and relates to mean annual temperature and soil pH. Combining these two indices allows estimation of mean annual temperature (MAT). However other factors such as soil water availability or moisture conditions have been suggested to influence the MBT'. To assess the effect of moisture conditions on the MBT'/CBT a set of 23 Iberian Peninsula soil samples covering a temperature range from 10–18 °C and a wide range of soil moisture regimes (405 mm to 1455 mm mean annual precipitation per year), was analyzed. We find that CBT is significantly correlated to soil pH confirming it as a robust proxy. In contrast the MBT' index was not correlated to MAT and was weakly correlated to annual mean precipitation (MAP). Instead we found a significant correlation between MBT' and the Aridity Index (AI), a parameter related to water availability in soils. The AI can explain 70% of the residuals of MAT estimation and 50% of the actual variation of the MBT'. This suggests that in dry environments or under moisture shortage the degree of methylation of branched GDGTs is not controlled by temperature but rather by the degree of water available. Our results suggest that the MBT/CBT index is not applicable as a paleotemperature proxy in dry subhumid to hyperarid environments.

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Woltering, Martijn, Pia Atahan, Kliti Grice, Henk Heijnis, Kathryn Taffs, and John Dodson. "Glacial and Holocene terrestrial temperature variability in subtropical east Australia as inferred from branched GDGT distributions in a sediment core from Lake McKenzie." Quaternary Research 82, no. 1 (July 2014): 132–45. http://dx.doi.org/10.1016/j.yqres.2014.02.005.

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AbstractBranched glycerol dialkyl glycerol tetraether (GDGT) distributions observed in a sediment core from Lake McKenzie were utilized to quantitatively reconstruct the pattern of mean annual air temperature (MAAT) from coastal subtropical eastern Australia between 37 and 18.3 cal ka BP and 14.0 cal ka BP to present. Both the reconstructed trend and amplitude of MAAT changes from the top of the sediment core were nearly identical to a local instrumental MAAT record from Fraser Island, providing confidence that in this sediment core branched GDGTs could be used to produce a quantitative record of past MAAT. The reconstructed trend of MAAT during 37 to 18.3 cal ka BP and timing of the Last Glacial Maximum (LGM) in the Lake McKenzie record were in agreement with previously published nearby marine climate records. The amplitude of lower-than-present MAAT during the LGM potentially provides information on the latitude of separation of the Tasman Front from the East Australian current in the subtropical western Pacific. The Lake McKenzie record shows an earlier onset of near modern day warm temperatures in the early Holocene compared to marine records and the presence of a warmer than present day period during the mid-Holocene.

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21

Véquaud, Pierre, Alexandre Thibault, Sylvie Derenne, Christelle Anquetil, Sylvie Collin, Sergio Contreras, Andrew T. Nottingham, Pierre Sabatier, Josef P. Werne, and Arnaud Huguet. "FROG: A global machine-learning temperature calibration for branched GDGTs in soils and peats." Geochimica et Cosmochimica Acta 318 (February 2022): 468–94. http://dx.doi.org/10.1016/j.gca.2021.12.007.

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22

Zhao, Jiaju, Yongsong Huang, Yuan Yao, Zhisheng An, Yizhi Zhu, Hongxuan Lu, and Zheng Wang. "Calibrating branched GDGTs in bones to temperature and precipitation: Application to Alaska chronological sequences." Quaternary Science Reviews 240 (July 2020): 106371. http://dx.doi.org/10.1016/j.quascirev.2020.106371.

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23

Buckles, L. K., J. W. H. Weijers, X. M. Tran, S. Waldron, and J. S. Sinninghe Damsté. "Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for glycerol dialkyl glycerol tetraether (GDGT)-based palaeothermometry." Biogeosciences 11, no. 19 (October 9, 2014): 5539–63. http://dx.doi.org/10.5194/bg-11-5539-2014.

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Abstract. The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the branched vs. isoprenoidal tetratether (BIT) index, TEX86 and the MBT–CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments. Loch Lomond consists of two basins bisected by the Highland Boundary Fault, resulting in a mesotrophic to oligotrophic gradient from south to north. The north basin is fjord-like, while the south basin is shallow with a lowland catchment. Besides abundant influxes of allochthonous soil- and peat-derived (CL) brGDGTs, brGDGTs are produced in a variety of settings in Loch Lomond. Rather than integrating a scattered soil signal, there is some evidence that small rivers may contribute to the brGDGT pool through addition of brGDGTs produced in situ in these streams. Three hundred days of settling particles and water column profiles of suspended particulate matter (SPM; March and September 2011) reveal brGDGT production throughout the water column, with (IPL and CL) brGDGT distributions varying by basin. In lake sediments, in situ brGDGT production affects the distributions of sedimentary brGDGTs despite high soil- and peat-derived organic matter influxes from the catchment. MBT–CBT-derived mean annual air temperature (MAAT) estimates from soil, river and lake sediments vary widely. A strong bias towards higher MAATs in the south and lower MAATs in the north basin further complicates the application of the proxy. These results emphasise that caution must be exercised when applying the MBT–CBT palaeothermometer to individual lakes in which the use of the proxy has not been validated and therefore the factors affecting its application are not well understood. Despite elevated BIT indices, (partly) due to in situ brGDGT production, reliable TEX86 lake surface temperature (LST) estimates were obtained from SPM with BIT indices up to 0.9. Lower north basin sediments yielded accurate LST estimates but require further evaluation to properly constrain the application of the TEX86 proxy.

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Fietz, Susanne, Carme Huguet, James Bendle, Marina Escala, Christopher Gallacher, Lydie Herfort, Robert Jamieson, et al. "Co-variation of crenarchaeol and branched GDGTs in globally-distributed marine and freshwater sedimentary archives." Global and Planetary Change 92-93 (July 2012): 275–85. http://dx.doi.org/10.1016/j.gloplacha.2012.05.020.

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25

Bischoff, Juliane, Robert B. Sparkes, Ayça Doğrul Selver, Robert G. M. Spencer, Örjan Gustafsson, Igor P. Semiletov, Oleg V. Dudarev, et al. "Source, transport and fate of soil organic matter inferred from microbial biomarker lipids on the East Siberian Arctic Shelf." Biogeosciences 13, no. 17 (September 6, 2016): 4899–914. http://dx.doi.org/10.5194/bg-13-4899-2016.

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Abstract. The Siberian Arctic contains a globally significant pool of organic carbon (OC) vulnerable to enhanced warming and subsequent release by both fluvial and coastal erosion processes. However, the rate of release, its behaviour in the Arctic Ocean and vulnerability to remineralisation is poorly understood. Here we combine new measurements of microbial biohopanoids including adenosylhopane, a lipid associated with soil microbial communities, with published glycerol dialkyl glycerol tetraethers (GDGTs) and bulk δ13C measurements to improve knowledge of the fate of OC transported to the East Siberian Arctic Shelf (ESAS). The microbial hopanoid-based soil OC proxy R′soil ranges from 0.0 to 0.8 across the ESAS, with highest values nearshore and decreases offshore. Across the shelf R′soil displays a negative linear correlation with bulk δ13C measurements (r2 = −0.73, p = < 0.001). When compared to the GDGT-based OC proxy, the branched and isoprenoid tetraether (BIT) index, a decoupled (non-linear) behaviour on the shelf was observed, particularly in the Buor-Khaya Bay, where the R′soil shows limited variation, whereas the BIT index shows a rapid decline moving away from the Lena River outflow channels. This reflects a balance between delivery and removal of OC from different sources. The good correlation between the hopanoid and bulk terrestrial signal suggests a broad range of hopanoid sources, both fluvial and via coastal erosion, whilst GDGTs appear to be primarily sourced via fluvial transport. Analysis of ice complex deposits (ICDs) revealed an average R′soil of 0.5 for the Lena Delta, equivalent to that of the Buor-Khaya Bay sediments, whilst ICDs from further east showed higher values (0.6–0.85). Although R′soil correlates more closely with bulk OC than the BIT, our understanding of the endmembers of this system is clearly still incomplete, with variations between the different East Siberian Arctic regions potentially reflecting differences in environmental conditions (e.g. temperature, pH), but other physiological controls on microbial bacteriohopanepolyol (BHP) production under psychrophilic conditions are as yet unknown.

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Kirkels, Frédérique M. S. A., Huub M. Zwart, Muhammed O. Usman, Suning Hou, Camilo Ponton, Liviu Giosan, Timothy I. Eglinton, and Francien Peterse. "From soil to sea: sources and transport of organic carbon traced by tetraether lipids in the monsoonal Godavari River, India." Biogeosciences 19, no. 17 (September 1, 2022): 3979–4010. http://dx.doi.org/10.5194/bg-19-3979-2022.

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Abstract. Monsoonal rivers play an important role in the land-to-sea transport of soil-derived organic carbon (OC). However, spatial and temporal variation in the concentration, composition, and fate of this OC in these rivers remains poorly understood. We investigate soil-to-sea transport of soil OC by the Godavari River in India using glycerol dialkyl glycerol tetraether (GDGT) lipids in soils, river suspended particulate matter (SPM), and riverbed sediments, as well as in a marine sediment core from the Bay of Bengal. The abundance and composition of GDGTs in SPM and sediments in the Godavari River differs between the dry and wet season. In the dry season, SPM and riverbed sediments from the whole basin contain more 6-methyl branched GDGTs (brGDGTs) than the soils. In the upper basin, where mobilisation and transport of soils is limited due to deficient rainfall and damming, contributions of 6-methyl brGDGTs in SPM and riverbed sediments are relatively high year-round, suggesting that they have an aquatic source. Aquatic brGDGT production coincides with elevated values of the isoprenoid GDGT-0 / crenarchaeol ratio in SPM and riverbed sediments from the upper basin, indicating low-oxygen conditions. In the wet season, brGDGT distributions in SPM from the lower basin closely resemble those in soils, mostly from the north and east tributaries, corresponding to precipitation patterns. The brGDGT composition in SPM and sediments from the delta suggests that soil OC is only effectively transported to the Bay of Bengal in the wet season, when the river plume extends beyond the river mouth. The sediment geochemistry indicates that also the mineral particles exported by the Godavari River primarily originate from the lower basin, similar to the brGDGTs, suggesting that they are transported together. However, river depth profiles in the downstream Godavari reveal no hydrodynamic sorting effect on brGDGTs in either season, indicating that brGDGTs are not closely associated with mineral particles. The similarity of brGDGT distributions in bulk and fine-grained sediments (≤ 63 µm) further confirms the absence of selective transport mechanisms. Nevertheless, the composition of brGDGTs in a Holocene, marine sediment core near the river mouth appears substantially different from that in the modern Godavari basin, suggesting that terrestrial-derived brGDGTs are rapidly lost upon discharge into the Bay of Bengal and/or overprinted by marine in situ production. The large change in brGDGT distributions at the river–sea transition implies that this zone is key in the transfer of soil OC, as well as that of the environmental signal carried by brGDGTs from the river basin.

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Sparkes, R. B., A. Doğrul Selver, J. Bischoff, H. M. Talbot, Ö. Gustafsson, I. P. Semiletov, O. V. Dudarev, and B. E. van Dongen. "GDGT distributions on the East Siberian Arctic Shelf: implications for organic carbon export, burial and degradation." Biogeosciences 12, no. 12 (June 18, 2015): 3753–68. http://dx.doi.org/10.5194/bg-12-3753-2015.

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Abstract. Siberian permafrost contains a globally significant pool of organic carbon (OC) that is vulnerable to enhanced warming and subsequent release into the contemporary carbon cycle. OC release by both fluvial and coastal erosion has been reported in the region, but the behaviour of this material in the Arctic Ocean is insufficiently understood. The balance between OC deposition and degradation on the East Siberian Arctic Shelf (ESAS) influences the climate–carbon cycle feedback in this area. In this study we couple measurements of glycerol dialkyl glycerol tetraethers (GDGTs) with bulk geochemical observations to improve knowledge of the sources of OC to the ESAS, the behaviour of specific biomarkers on the shelf and the balance between delivery and removal of different carbon pools. Branched GDGT (brGDGT) concentrations were highest close to river mouths, yet low in "ice complex" permafrost deposits, supporting recent observations that brGDGTs are mostly delivered by fluvial erosion, and may be a tracer for this in complex sedimentary environments. BrGDGT concentrations and the branched and isoprenoidal tetraether (BIT) index reduced quickly offshore, demonstrating a rapid reduction in river influence. Stable carbon isotope ratios changed at a different rate to the BIT index, suggesting not only that OC on the shelf is sourced from fluvial erosion but also that erosion of coastal sediments delivers substantial quantities of OC to the Arctic Ocean. A model of OC export from fluvial, coastal and marine sources is able to recreate the biomarker and bulk observations and provide estimates for the influence of fluvial and coastal OC across the whole shelf. The model shows that coastal erosion delivers 43 % of the OC and 87 % of the mineral sediment to the ESAS, but that rivers deliver 72 % of brGDGTs, indicating that brGDGTs can be used as a proxy for river-derived sediment.

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28

Sparkes, R. B., A. Doğrul Selver, J. Bischoff, H. M. Talbot, Ö. Gustafsson, I. P. Semiletov, O. V. Dudarev, and B. E. van Dongen. "GDGT distributions in the East Siberian Sea: implications for organic carbon export, burial and degradation." Biogeosciences Discussions 12, no. 1 (January 12, 2015): 637–74. http://dx.doi.org/10.5194/bgd-12-637-2015.

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Abstract. Siberian permafrost contains a globally-significant pool of organic carbon (OC) that is vulnerable to enhanced warming and subsequent release into the contemporary carbon cycle. OC release by both fluvial and coastal erosion has been reported in the region, but the behaviour of this material in the Arctic Ocean is insufficiently understood. The balance between OC deposition and degradation on the East Siberian Arctic Shelf (ESAS) influences the climate-carbon cycle feedback in this area. In this study we couple measurements of glycerol dialkyl glycerol tetraethers (GDGTs) with bulk geochemical observations to improve knowledge of the sources of OC to the ESAS, the behaviour of specific biomarkers on the shelf and the balance between delivery and removal of different carbon pools. Branched GDGT (brGDGT) concentrations were highest close to river mouths, yet low in "Yedoma" permafrost deposits, supporting recent observations that brGDGTs are mostly delivered by fluvial erosion, and may be a tracer for this in complex sedimentary environments. BrGDGT concentrations and the Branched and Isoprenoidal Tetraether (BIT) index reduced quickly offshore, demonstrating a rapid reduction in river influence. Stable carbon isotope ratios changed at a different rate to the BIT index, suggesting that OC on the shelf is not only sourced from fluvial erosion, but that erosion of coastal sediments delivers substantial quantities of OC to the Arctic Ocean. A model of OC export from fluvial, coastal and marine sources is able to recreate the biomarker and bulk observations and provide estimates for the influence of fluvial and coastal OC across the whole shelf. The model shows that coastal erosion delivers 43% of the OC and 87% of the mineral sediment to the ESAS, but that rivers deliver 72% of brGDGTs, indicating that brGDGTs can be used as a proxy for river-derived sediment.

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Zeng, Fangming, and Huan Yang. "Temperature changes reconstructed from branched GDGTs on the central Loess Plateau during the past 130–5 ka." Quaternary International 503 (February 2019): 3–9. http://dx.doi.org/10.1016/j.quaint.2018.04.045.

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Loomis, Shannon E., James M. Russell, and Jaap S. Sinninghe Damsté. "Distributions of branched GDGTs in soils and lake sediments from western Uganda: Implications for a lacustrine paleothermometer." Organic Geochemistry 42, no. 7 (August 2011): 739–51. http://dx.doi.org/10.1016/j.orggeochem.2011.06.004.

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Colcord, Devon E., Sarah B. Cadieux, Simon C. Brassell, Isla S. Castañeda, Lisa M. Pratt, and Jeffrey R. White. "Assessment of branched GDGTs as temperature proxies in sedimentary records from several small lakes in southwestern Greenland." Organic Geochemistry 82 (May 2015): 33–41. http://dx.doi.org/10.1016/j.orggeochem.2015.02.005.

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Smith, Richard W., Thomas S. Bianchi, and Xinxin Li. "A re-evaluation of the use of branched GDGTs as terrestrial biomarkers: Implications for the BIT Index." Geochimica et Cosmochimica Acta 80 (March 2012): 14–29. http://dx.doi.org/10.1016/j.gca.2011.11.025.

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33

Coffinet, Sarah, Arnaud Huguet, Nikolai Pedentchouk, Laurent Bergonzini, Christine Omuombo, David Williamson, Christelle Anquetil, et al. "Evaluation of branched GDGTs and leaf wax n-alkane δ2H as (paleo) environmental proxies in East Africa." Geochimica et Cosmochimica Acta 198 (February 2017): 182–93. http://dx.doi.org/10.1016/j.gca.2016.11.020.

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34

Bijl, Peter K., Joost Frieling, Margot J. Cramwinckel, Christine Boschman, Appy Sluijs, and Francien Peterse. "Maastrichtian–Rupelian paleoclimates in the southwest Pacific – a critical re-evaluation of biomarker paleothermometry and dinoflagellate cyst paleoecology at Ocean Drilling Program Site 1172." Climate of the Past 17, no. 6 (November 25, 2021): 2393–425. http://dx.doi.org/10.5194/cp-17-2393-2021.

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Abstract. Sea surface temperature (SST) reconstructions based on isoprenoid glycerol dialkyl glycerol tetraether (isoGDGT) distributions from the Eocene southwest (SW) Pacific Ocean are unequivocally warmer than can be reconciled with state-of-the-art fully coupled climate models. However, the SST signal preserved in sedimentary archives can be affected by contributions of additional isoGDGT sources. Methods now exist to identify and possibly correct for overprinting effects on the isoGDGT distribution in marine sediments. Here, we use the current proxy insights to (re-)assess the reliability of the isoGDGT-based SST signal in 69 newly analyzed and 242 reanalyzed sediments at Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau, Australia) following state-of-the-art chromatographic techniques. We compare our results with paleoenvironmental and paleoclimatologic reconstructions based on dinoflagellate cysts. The resulting ∼ 130 kyr resolution Maastrichtian–Oligocene SST record based on the TetraEther indeX of tetraethers with 86 carbon atoms (TEX86) confirms previous conclusions of anomalous warmth in the early Eocene SW Pacific and remarkably cool conditions during the mid-Paleocene. Dinocyst diversity and assemblages show a strong response to the local SST evolution, supporting the robustness of the TEX86 record. Soil-derived branched GDGTs stored in the same sediments are used to reconstruct mean annual air temperature (MAAT) of the nearby land using the Methylation index of Branched Tetraethers with 5-methyl bonds (MBT'5me) proxy. MAAT is consistently lower than SST during the early Eocene, independent of the calibration chosen. General trends in SST and MAAT are similar, except for (1) an enigmatic absence of MAAT rise during the Paleocene–Eocene Thermal Maximum and Middle Eocene Climatic Optimum, and (2) a subdued middle–late Eocene MAAT cooling relative to SST. Both dinocysts and GDGT signals suggest a mid-shelf depositional environment with strong river runoff during the Paleocene–early Eocene progressively becoming more marine thereafter. This trend reflects gradual subsidence and more pronounced wet/dry seasons in the northward-drifting Australian hinterland, which may also explain the subdued middle Eocene MAAT cooling relative to that of SST. The overall correlation between dinocyst assemblages, marine biodiversity and SST changes suggests that temperature exerted a strong influence on the surface-water ecosystem. Finally, we find support for a potential temperature control on compositional changes of branched glycerol monoalkyl glycerol tetraethers (brGMGTs) in marine sediments. It is encouraging that a critical evaluation of the GDGT signals confirms that most of the generated data are reliable. However, this also implies that the high TEX86-based SSTs for the Eocene SW Pacific and the systematic offset between absolute TEX86-based SST and MBT'5me-based MAAT estimates remain without definitive explanation.

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Halamka, T. A., J. M. McFarlin, A. D. Younkin, J. Depoy, N. Dildar, and S. H. Kopf. "Corrigendum to “Oxygen limitation can trigger the production of branched GDGTs in culture” by Halamka et al., 2021." Geochemical Perspectives Letters 22 (August 2022): 49. http://dx.doi.org/10.7185/geochemlet.2132cor.

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36

Tierney, Jessica E., and James M. Russell. "Distributions of branched GDGTs in a tropical lake system: Implications for lacustrine application of the MBT/CBT paleoproxy." Organic Geochemistry 40, no. 9 (September 2009): 1032–36. http://dx.doi.org/10.1016/j.orggeochem.2009.04.014.

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37

Buckles, L. K., J. W. H. Weijers, X. M. Tran, S. Waldron, and J. S. Sinninghe Damsté. "Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for GDGT-based palaeothermometry." Biogeosciences Discussions 11, no. 3 (March 17, 2014): 4187–250. http://dx.doi.org/10.5194/bgd-11-4187-2014.

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Abstract. The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the BIT index, TEX86 and the MBT/CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments. Loch Lomond consists of two basins bisected by the Highland Boundary Fault, resulting in a mesotrophic to oligotrophic gradient from south to north. The north basin is fjord-like, while the south basin is shallow with a lowland catchment. Besides abundant influxes of allochthonous soil and peat-derived (CL) brGDGTs, brGDGTs are produced in a variety of settings in Loch Lomond. Rather than integrating a scattered soil signal, there is some evidence that small rivers may contribute to the brGDGT pool through addition of brGDGTs produced in situ in these streams. 300 days of settling particles and water column profiles of suspended particulate matter (SPM; March and September 2011) reveal brGDGT production throughout the water column, with (IPL and CL) brGDGT distributions varying by basin. In lake sediments, in situ brGDGT production affects the distributions of sedimentary brGDGTs despite high soil and peat-derived organic matter influxes from the catchment. MBT/CBT-derived mean annual air temperature (MAAT) estimates from soil, river and lake sediments vary widely. A strong bias towards higher MAATs in the south and lower MAATs in the north basin further complicates the application of the proxy. These results emphasise that caution must be exercised when applying the MBT/CBT palaeothermometer to individual lakes in which the use of the proxy has not been validated and therefore the factors affecting its application are not well understood. Despite elevated BIT indices, (partly) due to in situ brGDGT production, reliable TEX86 lake surface temperature (LST) estimates were obtained from SPM with BIT indices up to 0.9 but containing abundant crenarchaeol. Lower north basin sediments yielded accurate LST estimates but require further evaluation to properly constrain the application of the TEX86 proxy.

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Hu, Jianfang, Haoda Zhou, Ping'an Peng, Xiaoqiang Yang, Baruch Spiro, Guodong Jia, Gangjian Wei, and Tingping Ouyang. "Reconstruction of a paleotemperature record from 0.3–3.7ka for subtropical South China using lacustrine branched GDGTs from Huguangyan Maar." Palaeogeography, Palaeoclimatology, Palaeoecology 435 (October 2015): 167–76. http://dx.doi.org/10.1016/j.palaeo.2015.06.014.

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LOWE, ALEXANDER J., AARON F. DIEFENDORF, KRISTEN M. SCHLANSER, JAMES SUPER, CHRISTOPHER K. WEST, and DAVID R. GREENWOOD. "DYNAMICS OF DEPOSITION AND FOSSIL PRESERVATION AT THE EARLY EOCENE OKANAGAN HIGHLANDS OF BRITISH COLUMBIA, CANADA: INSIGHTS FROM ORGANIC GEOCHEMISTRY." PALAIOS 37, no. 5 (May 31, 2022): 185–200. http://dx.doi.org/10.2110/palo.2021.007.

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ABSTRACT The early Eocene Okanagan Highland fossil sites of Washington (USA) and British Columbia (Canada) contain exquisitely preserved plant and insect fossils that showcase a critical time and place in the evolution of the Northern Hemisphere temperate deciduous biome. A comprehensive understanding of the dynamics of fossil deposition and preservation at these sites is not fully resolved but is critical for reliable reconstructions of these ancient forests. To expand on previous interpretations (e.g., deep, stratified, anoxic lake bottoms) and address uncertainties about the environment of deposition (e.g., distance to shore, influence of diatoms), we analyzed sediment samples from three Okanagan Highland fossil sites—McAbee, Falkland, and Driftwood Canyon—for organic biomarkers, their stable carbon isotopic compositions, and glycerol dialkyl glycerol tetraethers (GDGTs; at McAbee only). Terpenoids suggest relative trends in gymnosperm abundance between sites that agree with prior macrofossil evidence, though absolute values may overestimate local gymnosperm abundance. A combination of biomarker evidence indicates a predominantly autochthonous aquatic source (e.g., diatoms) for organic matter in shale and mudstone samples, even contributing to long chain n-alkanes and likely to branched GDGTs, which are often assumed to be terrestrially sourced. In combination with biomarker evidence for anoxia and stratification, fossiliferous shales are interpreted to have been deposited offshore in deep and mesotrophic lakes that were thermally stratified with an anoxic hypolimnion, away from in-flowing tributaries, while a coal horizon at Driftwood Canyon was deposited in a shallower, eutrophic, anoxic wetland. Anoxic conditions likely minimized some degradation-based biases and promoted high quality fossil preservation. Deposition of sediment and fossil remains offshore and away from inflowing tributaries suggest fossil plants were locally sourced but highlights the need for careful consideration of transport-induced biases.

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Peterse, Francien, Graeme W. Nicol, Stefan Schouten, and Jaap S. Sinninghe Damsté. "Influence of soil pH on the abundance and distribution of core and intact polar lipid-derived branched GDGTs in soil." Organic Geochemistry 41, no. 10 (October 2010): 1171–75. http://dx.doi.org/10.1016/j.orggeochem.2010.07.004.

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Huguet, Arnaud, Céline Fosse, Fatima Laggoun-Défarge, Frédéric Delarue, and Sylvie Derenne. "Effects of a short-term experimental microclimate warming on the abundance and distribution of branched GDGTs in a French peatland." Geochimica et Cosmochimica Acta 105 (March 2013): 294–315. http://dx.doi.org/10.1016/j.gca.2012.11.037.

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D'Anjou, R. M., J. H. Wei, I. S. Castañeda, J. Brigham-Grette, S. T. Petsch, and D. B. Finkelstein. "High-latitude environmental change during MIS 9 and 11: biogeochemical evidence from Lake El'gygytgyn, Far East Russia." Climate of the Past 9, no. 2 (March 8, 2013): 567–81. http://dx.doi.org/10.5194/cp-9-567-2013.

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Abstract. Marine isotope stages (MIS) 11 has been proposed as an analog for the present interglacial; however, terrestrial records of this time period are rare. Sediments from Lake El'gygytgyn (67°30' N, 172°5' E) in Far East Russia contain a 3.56 Ma record of climate variability from the Arctic. Here, we present the first terrestrial Arctic reconstruction of environmental and climatic changes from MIS 8 through 12 (289 to 464 ka) using organic geochemical proxies. Terrestrial vegetation changes, as revealed by plant leaf wax (n-alkane) indices and concentrations of arborinol (a biomarker for trees), show increased tree cover around the lake during interglacial periods, with higher concentrations observed during MIS 11 as compared to MIS 9. A similar pattern is also observed in records of aquatic productivity revealed by molecular indicators from dinoflagellates (dinosterol), eustigmatophyte algae (long-chain (C28–C32) 1, 15 n-alkyl diols) in addition to short-chain n-alkanes, where aquatic productivity is highest during MIS 11. Changes recorded in these molecular proxies show a similar structure to relative temperature variability as recorded by the MBT/CBT (Methylation of Branched Tetraether/Cyclization of Branched Tetraether) paleothermometer, based on branched glycerol dialkyl glycerol tetraethers (GDGTs). Additionally, relative MBT/CBT temperature changes generally track pollen and diatom δ18O temperature estimates, compiled by other studies, which suggest glacial-interglacial temperature changes of ~ 9 to 12 °C. These records of environmental and climatic change indicate Arctic sensitivity to external forcings such as orbital variability and atmospheric greenhouse gas concentrations. Overall, this study indicates that organic geochemical analyses of the Lake El'gygytgyn sediment archive can provide critical insight into the response of lake ecosystems and their sensitivity in high latitude regions.

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Xiao, Wenjie, Yinghui Wang, Shangzhe Zhou, Limin Hu, Huan Yang, and Yunping Xu. "Ubiquitous production of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in global marine environments: a new source indicator for brGDGTs." Biogeosciences 13, no. 20 (October 28, 2016): 5883–94. http://dx.doi.org/10.5194/bg-13-5883-2016.

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Abstract. Presumed source specificity of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from bacteria thriving in soil/peat and isoprenoid GDGTs (iGDGTs) from aquatic organisms led to the development of several biomarker proxies for biogeochemical cycle and paleoenvironmental reconstructions. However, recent studies reveal that brGDGTs are also produced in aquatic environments besides soils and peat. Here we examined three cores from the Bohai Sea, and found distinct difference in brGDGT compositions varying with the distance from the Yellow River mouth. We thus propose an abundance ratio of hexamethylated to pentamethylated brGDGT (IIIa ∕ IIa) to evaluate brGDGT sources. The compilation of globally distributed 1354 marine sediments and 589 soils shows that the IIIa ∕ IIa ratio is generally < 0.59 in soils and 0.59–0.92 and > 0.92 in marine sediments with and without significant terrestrial inputs, respectively. Such disparity confirms the existence of two sources for brGDGTs, a terrestrial origin with lower IIIa ∕ IIa and a marine origin with higher IIIa ∕ IIa, which is likely attributed to a generally higher pH and the production of brGDGTs in cold deep water in marine waters. The application of the IIIa ∕ IIa ratio to the East Siberian Arctic Shelf proves it to be a sensitive source indicator for brGDGTs, which is helpful for accurate estimation of organic carbon source and paleoclimates in marine settings.

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Kim, Jung-Hyun, Helen M. Talbot, Barbara Zarzycka, Thorsten Bauersachs, and Thomas Wagner. "Occurrence and abundance of soil-specific bacterial membrane lipid markers in the Têt watershed (southern France): Soil-specific BHPs and branched GDGTs." Geochemistry, Geophysics, Geosystems 12, no. 2 (February 2011): n/a. http://dx.doi.org/10.1029/2010gc003364.

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Dong, Liang, Qianyu Li, Li Li, and Chuanlun L. Zhang. "Glacial–interglacial contrast in MBT/CBT proxies in the South China Sea: Implications for marine production of branched GDGTs and continental teleconnection." Organic Geochemistry 79 (February 2015): 74–82. http://dx.doi.org/10.1016/j.orggeochem.2014.12.008.

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Yao, Yuan, Jiaju Zhao, Richard S. Vachula, Josef P. Werne, Jing Wu, Xueshu Song, and Yongsong Huang. "Correlation between the ratio of 5-methyl hexamethylated to pentamethylated branched GDGTs (HP5) and water depth reflects redox variations in stratified lakes." Organic Geochemistry 147 (September 2020): 104076. http://dx.doi.org/10.1016/j.orggeochem.2020.104076.

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Hanna, Andrea J. M., Timothy M. Shanahan, and Mead A. Allison. "Distribution of branched GDGTs in surface sediments from the Colville River, Alaska: Implications for the MBT′/CBT paleothermometer in Arctic marine sediments." Journal of Geophysical Research: Biogeosciences 121, no. 7 (July 2016): 1762–80. http://dx.doi.org/10.1002/2015jg003266.

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Schoon, Petra L., Anna de Kluijver, Jack J. Middelburg, John A. Downing, Jaap S. Sinninghe Damsté, and Stefan Schouten. "Influence of lake water pH and alkalinity on the distribution of core and intact polar branched glycerol dialkyl glycerol tetraethers (GDGTs) in lakes." Organic Geochemistry 60 (July 2013): 72–82. http://dx.doi.org/10.1016/j.orggeochem.2013.04.015.

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Guo, Jingjing, Miriam Glendell, Jeroen Meersmans, Frédérique Kirkels, Jack J. Middelburg, and Francien Peterse. "Assessing branched tetraether lipids as tracers of soil organic carbon transport through the Carminowe Creek catchment (southwest England)." Biogeosciences 17, no. 12 (June 24, 2020): 3183–201. http://dx.doi.org/10.5194/bg-17-3183-2020.

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Abstract. Soils represent the largest reservoir of organic carbon (OC) on land. Upon mobilization, this OC is either returned to the atmosphere as carbon dioxide (CO2) or transported and ultimately locked into (marine) sediments, where it will act as a long-term sink of atmospheric CO2. These fluxes of soil OC are, however, difficult to evaluate, mostly due to the lack of a soil-specific tracer. In this study, a suite of branched glycerol dialkyl glycerol tetraethers (brGDGTs), which are membrane lipids of soil bacteria, is tested as specific tracers for soil OC from source (soils under arable land, ley, grassland, and woodland) to sink (Loe Pool sediments) in a small catchment located in southwest England (i.e. Carminowe Creek draining into Loe Pool). The analysis of brGDGTs in catchment soils reveals that their distribution is not significantly different across different land use types (p>0.05) and thus does not allow land-use-specific soil contributions to Loe Pool sediments to be traced. Furthermore, the significantly higher contribution of 6-methyl brGDGT isomers in creek sediments (isomerization ratio (IR) = 0.48±0.10, mean ± standard deviation (SD); p<0.05) compared to that in catchment soils (IR = 0.28±0.11) indicates that the initial soil signal is substantially altered by brGDGT produced in situ. Similarly, the riverine brGDGT signal appears to be overwritten by lacustrine brGDGTs in the lake sedimentary record, indicated by remarkably lower methylation of branched tetraethers (MBT5ME′=0.46±0.02 in creek bed sediments and 0.38±0.01 in lake core sediments; p<0.05) and a higher degree of cyclization (DC = 0.23±0.02 in creek bed sediments and 0.32±0.08 in lake core sediments). Thus, in this small catchment, brGDGTs do not allow us to trace soil OC transport. Nevertheless, the downcore changes in the degree of cyclization and the abundance of isoprenoid GDGTs produced by methanogens in the Loe Pool sediment do reflect local environmental conditions over the past 100 years and have recorded the eutrophication history of the lake.

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Coffinet, Sarah, Arnaud Huguet, Nikolai Pedentchouk, Laurent Bergonzini, Christine Omuombo, David Williamson, Christelle Anquetil, et al. "Corrigendum to “Evaluation of branched GDGTs and leaf wax n-alkane δ2H as (paleo) environmental proxies in East Africa” [Geochim. Cosmochim. Acta 198 (2017) 182–193]." Geochimica et Cosmochimica Acta 271 (February 2020): 289–91. http://dx.doi.org/10.1016/j.gca.2019.10.043.

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Journal articles on the topic 'Branched GDGTs'

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