The coupled evolution of mid- to late Holocene temperature and moisture in the southeast Qaidam Basin

Sun, Wei; Zhao, Siyuan; Pei, Hongye; Yang, Huan

doi:10.1016/j.chemgeo.2019.119282

Cited by 19 publications

(10 citation statements)

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“…The biotic values (pollen and GDGTs) were also compared to abiotic parameters (climate, elevation, location and soil features) by the way of a redundancy analysis (RDA). The regression models were run with the p value < 0.05 (model relevance), the R 2 (correlation level between the variables), the root mean square deviation (RMSE, error on parameter reconstruction) and Akaike's information criterion (AIC, effect of over-parameterization on multiple regression models; Arnold, 2010;Symonds and Moussalli, 2011). A cross-validation test was performed for all the brGDGT calibrations (from this study and from the literature) using an independent set of six lacustrine samples from the lake MMNT5C12 top-core.…”

Section: Statistical Analysesmentioning

confidence: 99%

Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Baikal area: calibrations and applicability to extremely cold–dry environments over the Late Holocene

et al. 2021

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Abstract. Our understanding of climate and vegetation changes throughout the Holocene is hampered by representativeness in sedimentary archives. Potential biases such as production and preservation of the markers are identified by comparing these proxies with modern environments. It is important to conduct multi-proxy studies and robust calibrations on each terrestrial biome. These calibrations use large databases dominated by forest samples. Therefore, including data from steppe and desert–steppe sites becomes necessary to better calibrate arid environments. The Mongolian Plateau, ranging from the Baikal area to the Gobi desert, is especially characterized by low annual precipitation and continental annual air temperature. The characterization of the climate system of this area is crucial for the understanding of Holocene monsoon oscillations. This study focuses on the calibration of proxy–climate relationships for pollen and glycerol dialkyl glycerol tetraethers (GDGTs) by comparing large Eurasian calibrations with a set of 49 new surface samples (moss polster, soil and mud from temporary dry ponds). These calibrations are then cross-validated by an independent dataset of top-core samples and applied to four Late Holocene paleosequences (two brGDGT and two pollen records) surrounding the Mongolian Plateau: in the Altai mountains, the Baikal area and the Qaidam basin, to test the accuracy of local and global calibrations. We show that (1) preserved pollen assemblages are clearly imprinted on the extremities of the ecosystem range but mitigated and unclear on the ecotones; (2) for both proxies, inferred relationships depend on the geographical range covered by the calibration database as well as on the nature of samples; (3) even if local calibrations suffer from reduced amplitude of climatic parameters due to local homogeneity, they better reflect actual climate than the global ones by reducing the limits for saturation impact; (4) a bias in climatic reconstructions is induced by the over-parameterization of the models by the addition of artificial correlation; and (5) paleoclimate values reconstructed here are consistent with Mongolia–China Late Holocene climate trends and validate the application of local calibrations for both pollen and GDGTs (closest fit to actual values and realistic paleoclimate amplitude). We encourage the application of this surface calibration method to reconstruct paleoclimate and especially consolidate our understanding of the Holocene climate and environment variations in arid central Asia.

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Section: Statistical Analysesmentioning

confidence: 99%

Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Baikal area: calibrations and applicability to extremely cold–dry environments over the Late Holocene

et al. 2021

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“…To test the reliability of our modern calibrations, we have finally selected two paleosequences close to the Mongolian plateau used as test-benches of the calibrations. For the pollen analysis, the core D3L6 from Unkelbach et al (2019) and located in the Mongolian Altai range is compared to the Xiangride section (XRD) used for brGDGT sequence from Sun et al (2019), sampled in the Chinese Qaidam Basin (Fig. 2).…”

Section: Coring Sampling Area and Sample Typesmentioning

confidence: 99%

“…ACA climate reconstruction for the 5000 year BP. (A): climate-pollen inferred for the Lake D3L6 (Unkelbach et al, 2019) comparing two transfer function methods (WAPLS and MAT) and the 4 databases (EAPDB, COSTDB, MDB and NMSDB) ; (B) climate-brGDGT inferred from the XRD section (Sun et al, 2019) comparing local (NMSDB) and global calibrations (De Jonge et al, 2014a;Naafs et al, 2017a, b). The climate periods correspond to Little Ice Age (LIA), Warm Medieval Period (WMP), Dark Ages Cold Period (DACP),…”

Section: Test-bench Of the Local Calibrations On Two Paleosequencesmentioning

confidence: 99%

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Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Siberia: calibrations and applicability to extremely cold-dry environments over the Late Holocene

Dugerdil¹,

Joannin²,

Peyron³

et al. 2020

Preprint

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Abstract. Our understanding of climate and vegetation changes throughout the Holocene is hampered by representativeness in sedimentary archives. Potential biases such as production and preservation of the markers are identified by comparing these proxies with modern environments. It is important to conduct multi-proxy studies and robust calibrations on each terrestrial biome. These calibrations use large data base dominated by forest samples. Therefore, including data from taiga and steppe sites becomes mandatory to better calibrate arid environments. The Mongolian plateau, ranging from the Baikal basin to the Gobi desert, is especially characterized by low annual precipitation and continental annual air temperature. The characterization of the climate system of this area is crucial for the understanding of Holocene Monsoon Oscillations. This study focuses on the calibration of proxy-climate relationships for pollen and glycerol dialkyl glycerol tetraethers (GDGTs) by comparing large published Eurasian calibrations with a set of 49 new surface samples (moss polster, soil and mud from temporary dry pond). These calibrations are then cross-validated by an independent dataset of top-core samples and applied to two Late Holocene paleosequences in the Altai mountains and the Qaidam basin. We show that: (1) preserved pollen assemblages are clearly imprinted on the extremities of the ecosystem range but mitigated and unclear on the ecotones; (2) for both proxies, inferred relationships depend on the geographical range covered by the calibration database as well as on the nature of samples; (3) even if local calibrations suffer from reduced amplitude of climatic parameter due to local homogeneity, they better reflect actual climate than the global ones by reducing the limits for saturation impact, (4) a bias in climatic reconstructions is induced by the over-parameterization of the models by addition of artificial correlation and (5) paleoclimate values reconstructed here are consistent with Mongolia-China Late Holocene climate trends, and validate the application of local calibrations for both pollen and GDGTs (closest fit to actual values and realistic paleoclimate amplitude). We encourage the application of this surface calibration method to reconstruct palaeoclimate and especially consolidate our understanding of the Holocene climate and environment variations in Arid Central Asia.

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“…With the development of improved liquid chromatography separation methods, a series of 6‐methyl brGDGT isomers (i.e., IIa′, IIb′, IIc′, IIIa′, IIIb′, and IIIc′ with structures illustrated in Figure S1) have been identified that coeluted with 5‐methyl brGDGTs under earlier chromatographic methods and differ only in the carbon position of the methyl branches (C6 vs. C5 position) (De Jonge et al, 2013; De Jonge, Hopmans, et al, 2014; Hopmans et al, 2016; Yang et al, 2015). Their fractional abundances were observed to be correlated strongly with soil pH in worldwide distributed soils, thus leading to the development of new brGDGT‐based soil pH indicators (e.g., CBT′) (De Jonge, Hopmans, et al, 2014; Ding et al, 2015; Xiao et al, 2015), allowing for soil pH reconstructions in loess‐paleosol sequences (Duan et al, 2019; Sun et al, 2019). The newly defined methylation index based on only 5‐methyl brGDGTs (MBT′ 5ME ) shows a better correlation with MAAT compared to traditional MBT (MBT′)/CBT proxies both in China and globally (De Jonge, Hopmans, et al, 2014; Ding et al, 2015; Yang et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Soil pH Dominates the Distributions of Both 5‐ and 6‐Methyl Branched Tetraethers in Arid Regions

et al. 2020

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Branched glycerol dialkyl glycerol tetraether (brGDGT)-based indices are increasingly used for quantitative mean annual air temperature (MAAT) and soil pH reconstructions. However, large scatter in the relationship between the methylation index of 5-methyl brGDGTs (MBT′ 5ME) and MAAT still exists in arid and/or cold regions, and specific reasons for that offset remain unclear. Here, we present the brGDGT distributions from 18 soil samples along an altitudinal transect spanning a large gradient in MAAT at Mount (Mt.) Tienshan in arid central Asia, which we compare with previously published data from 256 globally distributed soils. Our results indicate that a dramatic increase of brGDGT concentrations occurs at 2,500 m above sea level for the soils from Mt. Tienshan, and a different pattern of brGDGT distributions in response to environmental changes appears below and above this elevation. Soil pH is observed to control the distributions of both 5-and 6-methyl brGDGTs in the soils from Mt. Tienshan and other arid regions. Importantly, we find that the fractional abundances of the 5-methyl isomers of pentamethylated and hexamethylated brGDGTs (IIa, IIIa) show a distinct negative correlation with soil pH, and the noncyclopentane-containing tetra-methylated brGDGT (Ia) is not related to MAAT in arid soils, which can explain the remaining temperature offset of reconstructed MAAT based on the MBT′ 5ME index in arid regions. In addition, our data suggest that either the brGDGT-producing community differs or brGDGT-producers respond differently to temperature in arid relative to moist soils.

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The coupled evolution of mid- to late Holocene temperature and moisture in the southeast Qaidam Basin

Cited by 19 publications

References 73 publications

Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Baikal area: calibrations and applicability to extremely cold–dry environments over the Late Holocene

Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Baikal area: calibrations and applicability to extremely cold–dry environments over the Late Holocene

Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Siberia: calibrations and applicability to extremely cold-dry environments over the Late Holocene

Soil pH Dominates the Distributions of Both 5‐ and 6‐Methyl Branched Tetraethers in Arid Regions

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