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1.
Bacterially produced branched glycerol dialkyl glycerol tetraethers (GDGTs) are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures. In lakes, however, it is still unclear if these compounds are derived from eroded soils or if they are produced in situ. To better understand environmental controls on the distributions of these compounds and the sources of branched GDGTs to lake sediments, we compare branched GDGT distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western Uganda. Reconstructed mean annual air temperature (MAAT), determined from the degree of methylation (MBT) and cyclisation (CBT) of branched GDGTs in soils, decreases with increasing altitude, as is expected from the air temperature gradient in our transect. However, we observe significant offsets between observed and reconstructed temperatures in soils from wet, high elevation soils but not in most dry, low elevation soils. Branched GDGT distributions differ significantly between lake sediments and soils at all elevations, with greater differences at low elevations than at high elevations. These data support previous hypotheses that branched GDGTs are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched GDGTs. While branched GDGTs in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes, we urge caution in utilizing this proxy in lacustrine systems with high soil loadings, especially if there is evidence of changing clastic fluxes through time.  相似文献   

2.
Peatlands are widespread and important natural archives of environmental change. Here we explore the potential of the recently introduced MBT-CBT proxy (methylation index and cyclisation ratio of branched tetraethers) to estimate past annual mean air temperature (MAT) based on the distribution of bacterially-derived branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in peat and coal. To this end, branched GDGTs in an ombrotrophic peat bog from Switzerland and three coal deposits of increasing maturity were analysed.For the surface of the bog, reconstructed annual MAT is higher than both measured annual MAT and measured in situ pore water temperature. Changes in the CBT ratio, considered a proxy for pH, with depth in the bog do not match with present day in situ pore water pH, but coincide with a peat stratigraphic boundary. This indicates that GDGTs down the bog profile are predominantly fossil and not derived from extant biomass. The MBT-CBT derived annual MAT record also shows a large drop at this stratigraphic boundary, which likely relates to past change in trophic status of the bog. Branched GDGTs are abundant in an immature lignite (vitrinite reflectance, Ro 0.25%), but occur in low amount in a slightly more mature coal (Ro 0.32%). Annual MAT could be reconstructed for the lignite alone and is higher than other proxy-based estimates from approximately the same time and location.Our results indicate potential for the application of the MBT-CBT proxy in peat and immature coals, but improved constraints on the effects of different types of peat on branched GDGT distributions as well as improved calibration of MAT estimates are needed before the method can be confidently applied.  相似文献   

3.
The distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether (GDGT) lipids was studied in material from various sources in and around Lake Challa, a crater lake on the southeastern slope of Mt. Kilimanjaro (Tanzania), to examine the provenance of GDGTs in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies. The study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle, particles suspended in the stratified water column, profundal surface sediments, and soils surrounding the lake. The sediment trap time series revealed that crenarchaeol and related isoprenoid GDGTs were predominantly produced in January and February, following the locally prominent short rain season (November-December). The TEX86-inferred temperature derived from sedimenting particles corresponded well with lake surface-water temperature at this time of largest crenarchaeol flux. Molecular ecological analysis showed that Group 1.1a and 1.1b crenarchaeota are the most likely source organisms of these GDGTs. GDGT-0 in the lake sediments does not only originate from lake surface-dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper, anoxic part of the water column. The main flux of branched GDGTs to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run-off. However, a contribution from in-situ production of branched GDGTs in the lake sediment or water, or in groundwater cannot be fully excluded. We conclude that palaeoclimatic reconstruction based on branched GDGT distributions in lake sediments should only be performed when the origin of those branched GDGTs is well constrained.  相似文献   

4.
In ocean margin sediments both marine and terrestrial organic matter (OM) are buried but the factors governing their relative preservation and degradation are not well understood. In this study, we analysed the degree of preservation of marine isoprenoidal and soil-derived branched glycerol dialkyl glycerol tetraethers (GDGTs) upon long-term oxygen exposure in OM-rich turbidites from the Madeira Abyssal Plain by analyzing GDGT concentrations across oxidation fronts. Relative to the anoxic part of the turbidites ca. 7-20% of the soil-derived branched GDGTs were preserved in the oxidized part while only 0.2-3% of the marine isoprenoid GDGT crenarchaeol was preserved. Due to these different preservation factors the Branched Isoprenoid Tetraether (BIT) index, a ratio between crenarchaeol and the major branched GDGTs that is used as a tracer for soil-derived organic matter, substantially increases from 0.02 to 0.4. Split Flow Thin Cell (SPLITT) separation of turbidite sediments showed that the enhanced preservation of soil-derived carbon was a general phenomenon across the fine particle size ranges (<38 μm). Calculations reveal that, despite their relatively similar chemical structures, degradation rates of crenarchaeol are 2-fold higher than those of soil-derived branched GDGTs, suggesting preferential soil OM preservation possibly due to matrix protection.  相似文献   

5.
The relative abundances and distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in marine and lacustrine sediments have been recently used as paleo-environmental proxies for the input of soil organic matter and past continental temperatures, respectively. The putative main source of brGDGTs is soil bacteria. Therefore, these biomarkers are also part of the soil organic matter stock that accumulates in the terrigenous environment. Here we present a method for isolating and purifying these compounds from lake sediments, soils and peat for radiocarbon (14C) measurement using a combination of normal and reversed phase high performance liquid chromatography, allowing complete separation of co-eluting compounds. Radiocarbon analysis was performed on an accelerator mass spectrometer system equipped with a gas ion source. We assessed the accuracy and the necessary corrections with modern and radiocarbon-dead procedural blanks. Blank assessment revealed that the reverse phase step introduced significant amounts of extraneous carbon, while the normal phase step did not. We show that with our method and instrumentation it is possible to obtain accurate and precise 14C analyses of brGDGTs with sample amounts as small as 10 μg C. Finally we demonstrate the application of the measurement of 14C concentrations of several brGDGTs isolated from lake sediments and peat soils.  相似文献   

6.
Branched 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.  相似文献   

7.
Absence of seasonal patterns in MBT-CBT indices in mid-latitude soils   总被引：1，自引：0，他引：1  
The degree of methylation and cyclization of bacteria-derived branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in soils depends on temperature and soil pH. Expressed in the methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT), these relationships are used to reconstruct past annual mean air temperature (MAT) based on the distribution of branched GDGTs in ancient sediments; the MBT-CBT proxy. Although it was shown that the best correlation of this proxy is with annual MAT, it remains unknown whether a seasonal bias in temperature reconstructions could occur, such as towards a seasonal period of ‘optimal growth’ of the, as yet, unidentified soil bacteria which produce branched GDGTs. To investigate this possibility, soils were sampled from eight different plots in the USA (Minnesota and Ohio), The Netherlands (Texel) and the UK (Devon) in time series over 1 year and analyzed for their branched GDGT content. Further analyses of the branched GDGTs present as core lipids (CLs; the presumed fossil pool) and intact polar lipids (IPLs; the presumed extant pool) were undertaken for two of the investigated soil plots. The amount of IPL-derived branched GDGTs is low relative to the branched GDGT CLs, i.e. only 6-9% of the total branched GDGT pool. In all soils, no clear change was apparent in the distribution of branched GDGT lipids (either core or IPL-derived) with seasonal temperature change; the MBT-CBT temperature proxy gave similar temperature estimates year-round, which generally matched the mean annual soil temperature. In addition to a lack of coherent changes in relative distributions, concentrations of the branched GDGTs did not show clear changes over the seasons. For IPL-derived GDGTs these results suggest that their turnover time in soils is in the order of 1 year or more. Thus, our study does not provide evidence for seasonal effects on the distribution of branched GDGTs in soils, at least at mid-latitudes, and therefore, no direct evidence for a bias of MBT-CBT reconstructed temperatures towards a certain season of optimal growth of the source bacteria. If, however, there is a slight seasonal preference of branched GDGT production, which can easily be obscured by natural variability due to the heterogeneity of soils, then a seasonal bias may potentially still develop over time due to the long turnover time of branched GDGTs.  相似文献   

8.
The BIT index represents the relative abundances of branched glycerol dialkyl glycerol tetraethers (bGDGTs) and the isoprenoid GDGT, crenarchaeol. While bGDGTs are produced mainly by soil (anaerobic) bacteria, crenarchaeol is known to be a biomarker for aerobic ammonia oxidation by chemolithoautotrophic Thaumarchaeota, particularly in the open ocean or lakes. Thus, the index in marine and lacustrine settings has been widely used as a proxy for soil input. Here, we have investigated GDGT distribution along two transects extending from the lake shore marsh to upland soils on the NE Qinghai-Tibetan plateau. The results show that soil water content (SWC) correlates positively with concentration of bGDGTs and negatively with concentration of crenarchaeol; consequently, there is a significant positive correlation between SWC and the BIT index. Our study highlights a new potential application of BIT as a humidity proxy in loess/soil and peat deposits.  相似文献   

9.
Bacterial and archaeal lipids, such as glycerol dialkyl glycerol tetraethers (GDGTs) and dialkyl glycerol diethers, are increasingly used as proxies for specific environmental parameters, such as air temperature and soil pH in lacustrine environments. Little is known, however, about the distribution and applicability of bacterial and archaeal lipids on the Tibetan Plateau. We investigated nine different watersheds across the plateau by way of sediments from lakes and rivers, as well as the surrounding soils. Our transect study included a salinity gradient and focused on saline lakes, which are rarely examined. We analyzed archaeal isoprenoid (i) and bacterial branched (b) GDGTs, as well as archaeol to trace their sources and environmental factors, influencing their distributions. We could show that iGDGTs were produced in situ and bGDGTs were primarily soil-derived although we could not exclude in situ production of bGDGTs in the lakes. The most important environmental variables correlating with GDGT distributions were temperature and salinity. Bacterial GDGT distributions correlated mainly with salinity, while archaeal lipid distributions correlated with temperature. Based on the correlation of methylation (MBT′) and cyclisation (CBT) indices of bGDGTs with pH and mean annual air temperature (MAAT), we established local calibrations for the Tibetan lakes. TEX86 could also be applied to reconstruct temperature, which was strongly biased towards measured summer lake water temperature, indicating enhanced production of iGDGTs in the summer months. Existing proxies show, therefore, potential for palaeoclimate reconstruction on the Tibetan Plateau if local calibrations are applied.  相似文献   

10.
Isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) are archaeal and bacterial polar lipids increasingly used as environmental biomarkers, and are studied in a wide range of settings: lacustrine and oceanic sediments, water column particulate organic matter, soils, peats, sedimentary rocks and extracts from archaeal and bacterial cultures. In paleoclimatology, for example, typical work on a sediment core of several tens of m consists of several hundreds to more than a thousand HPLC–MS (high performance liquid chromatography–mass spectrometry) analyses. The measurements therefore require purification steps from total lipid extracts. We propose an automated procedure for obtaining the GDGT core lipid fraction. We first evaluate both the yield and efficiency of the separation using different cartridges. We then compare the results from automated and “classical manual” procedures for a soil and a marine sediment, as well as for a sedimentary paleosequence.  相似文献   

11.
Over the last years a novel group of branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids has been discovered in peat bogs and soils. They consist of components with 4-6 methyl groups attached to the n-alkyl chains and 0 to 2 cyclopentyl moieties in the alkyl chain. These branched membrane lipids are produced by an as yet unknown group of anaerobic soil bacteria. In this study we analysed the branched membrane lipid content of 134 soil samples from 90 globally distributed locations to study the environmental factors controlling the relative distribution of the different branched GDGT isomers. Our results show that the relative amount of cyclopentyl moieties, expressed in the cyclisation ratio of branched tetraethers (CBT), is primarily related to the pH of the soil (R2 = 0.70) and not to temperature (R2 = 0.03). The relative amount of methyl branches, expressed in the methylation index of branched tetraethers (MBT), is positively correlated with the annual mean air temperature (MAT) (R2 = 0.62) and, to a lesser extent, negatively correlated with the pH of the soil (R2 = 0.37). If both parameters are combined, however, it appears that the variation in the MBT is largely explained by both MAT and pH (R2 = 0.82). These results suggest that the relative distribution of soil-derived GDGT membrane lipids can be used in palaeoenvironmental studies to estimate past annual MAT and soil pH.  相似文献   

12.
Branched glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of unknown bacteria that are ubiquitous in soil and peat. Two indices based on the distribution of these lipids in soils, the Cyclization of Branched Tetraethers (CBT) and the Methylation of Branched Tetraethers (MBT) indices have been shown to correlate with soil pH, and mean annual air temperature (MAT) and soil pH, respectively, and can be used to reconstruct MAT in palaeoenvironments. To verify the extent to which branched GDGTs in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a MAT of <0 °C, we compared the branched GDGT distribution in Svalbard soils and nearby fjord sediments. Although branched GDGT concentrations in the soil are relatively low (0.02–0.95 μg/g dry weight (dw)) because of the cold climate and the short growing season, reconstructed MATs based on the MBT/CBT proxy are ca. ?4 °C, close to the measured MAT (ca. ?6 °C). Concentrations of branched GDGTs (0.01–0.20 μg/g dw) in fjord sediments increased towards the open ocean and the distribution was strikingly different from that in soil, i.e. dominated by GDGTs with one cyclopentane moiety. This resulted in MBT/CBT-reconstructed MAT values of 11–19 °C, well above measured MAT. The results suggest that at least part of the branched GDGTs in marine sediments in settings with a low soil organic matter (OM) input may be produced in situ. In these cases, the application of the MBT/CBT palaeothermometer will generate unrealistic MAT reconstructions. The MBT/CBT proxy should therefore only be used at sites with a substantial input of soil OM relative to the amount of marine OM, i.e. at sites close to the mouth of rivers with a catchment area where sufficient soil formation takes place and the soil thus contains substantial amounts of branched GDGTs.  相似文献   

13.
Branched glycerol dialkyl glycerol tetraether lipids (GDGTs) are membrane lipids of soil bacteria that occur ubiquitously in soil, but their occurrence as intact polar lipids (IPLs) has not been well studied. Here, we report the identification and distribution of IPL-branched GDGTs throughout a depth profile of a Swedish peat bog. In addition to two reported glycosidic IPL branched GDGTs, we identified IPL branched GDGTs with a hexose-glycuronic acid, phospho-hexose, or hexose-phosphoglycerol head group, based on mass spectrometry. A selected reaction monitoring (SRM) assay was developed to monitor changes in head group distribution with depth. The abundance of the IPL branched GDGTs increased below the water table, suggesting that they were primarily produced in this part of the peat. This was supported by the concentrations of core lipid and IPL-derived branched GDGTs, which also substantially increased below the water table. However, individual IPL trends differed, which may be due to changes in the microbial community composition with depth or to different degradation rates for the different IPL branched GDGTs. The SRM method was also applied to two different soil types, which showed that similar IPL branched GDGTs as those in peat were present, albeit with different distributions.  相似文献   

14.
We evaluate the application of the branched glycerol dialkyl glycerol tetraether (br GDGT) based palaeotemperature and palaeoenvironmental proxy to a hyper-eutrophic, polluted and shallow oxic lake. Lake Zeekoevlei is the largest freshwater lake in South Africa, located close to Cape Town. We use published lake-based and soil-based calibration equations, and compare the reconstructed mean annual air temperature (MAT) with regional (South African) and local (Cape Town) instrumental temperature records. The distribution of br GDGTs in the lake sediments is influenced by air temperature. The lake-based calibration equation, which uses the methylation index of branched tetraethers/cyclisation ratio of branched tetraethers (MBT/CBT), formulated for African lakes (Tierney et al., 2010), fits well with the instrumental temperature records. Moreover, the CBT-derived pH likely reflects historic socioeconomic changes in catchment. Our results suggest that a polluted/hyper-eutrophic status and shallow water urban setting do not preclude application of the MBT/CBT-MAT proxy. However, further research is necessary to understand the behaviour of br GDGT–producing bacteria in polluted and highly productive lakes.  相似文献   

15.
Quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability, test predictive climate models, and provide a proper context for changes that may arise in response to anthropogenically-induced climate change. The recently developed biomarker-based methylation index of branched tetraethers/cyclization ratio of branched tetraethers (MBT/CBT) proxy shows potential as a new method for continental temperature reconstruction, but thus far it has only been applied successfully in ocean margin sediments. To assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems, we investigated the distribution of branched glycerol dialkyl glycerol tetraethers (GDGTs) in recently deposited sediments from 46 lakes in tropical East Africa. These lakes span a substantial range in surface elevation (770-4500 m above sea level), and thus also a wide gradient of mean annual temperature. We find that, saline lakes excepted, branched GDGTs are universally abundant in the lakes investigated and can be used to predict mean annual air temperature (MAAT) with a high degree of accuracy. However, the existing global MBT/CBT calibration for MAAT based on soils predicts inaccurate temperatures when applied to our African lake dataset. This observation, together with the fact that surface water pH, and to lesser extent, lake depth appear to influence the distribution of branched GDGTs among sites, leads us to conclude that in situ production of branched GDGTs in lakes is likely. The robust relationship between branched GDGT distribution and the temperature and pH of African freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction, however we urge caution in using branched GDGTs in lake sediments to infer past temperatures, unless their exact origin can be determined.  相似文献   

16.
Four representatives of methanogenic Euryarchaeota (Methanosarcina mazei strain Gö1, Methanosphaera stadtmanae, Methanobrevibacter smithii and Methanosaeta thermophila), the hyperthermophilic euryarchaeon Thermococcus kodakarensis and the halophilic euryarchaeon Haloferax volcanii were studied for their glycerol ether lipid composition. The predominant core membrane lipid in all of them was archaeol, which was accompanied by variable quantities of sn-2-hydroxyarchaeol in the methanogens M. mazei (Methanosarcinales) and M. stadtmanae (Methanobacteriales). All methanogenic and hyperthermophilic Euryarchaeota also contained comparatively high abundances of the glycerol dialkyl glycerol tetraether without a cyclopentane moiety (GDGT-0). The methanoarchaeon M. stadtmanae, in addition to GDGT-0, contained GDGT core lipid structures with 1–4 cyclopentane moieties (GDGTs 1–4). We also found minor amounts of a glycerol trialkyl glycerol tetraether (GTGT) and a glycerol dialkanol diether (GDD), both of which did not contain cyclopentane moieties, as well as methylated and dimethylated GDGT-0 in all the archaea with the exception of H. volcanii. Like its GDGT distribution, M. stadtmanae showed an extended range of GDD structures with up to two cyclopentane ring systems. Our results thus indicate that both methanogenic and hyperthermophilic Euryarchaeota may represent source organisms of GTGT-0, GDDs and methylated-GDGTs in natural environments. All the latter components have recently been reported to be ubiquitously distributed in marine sediments but their biological origin is largely unknown. Moreover, a suite of unsaturated GDGTs without a cyclopentane moiety and up to four double bonds in the hyperthermophile T. kodakarensis was tentatively assigned.  相似文献   

17.
微生物细胞膜脂甘油二烷基甘油四醚（GDGTs）样品在实验室冰箱储存过程中可能会遭受降解，进而对GDGTs各指标应用的准确性产生影响.了解GDGTs各类化合物抗降解能力的差异能够为指标的准确应用提供重要的判别手段.2017年，通过对2012年的石笋样品提取物（GDGTs）进行二次测试，发现GDGTs化合物绝对含量明显减少且各化合物的相对含量变化明显:细菌brGDGTs含量相对于古菌isoGDGTs含量变化较小，对应的干旱化指标Ri/b值略有减小，陆源输入指数BIT值增大，故细菌brGDGTs化合物在保存过程中更稳定；古菌isoGDGTs含环少的化合物变化较小，环化指数CBT值增加，表明少环的化合物在降解过程中更稳定；基于古菌isoGDGTs建立的古温度指标TEX86值显著降低；基于细菌brGDGTs建立的甲基化指数MBT值增加，表明甲基越多的化合物越易降解.   相似文献   

18.
Branched glycerol dialkyl glycerol tetraether (GDGT) lipids are abundant and ubiquitous in lake sediments, potentially allowing for a paleolimnological application of the so-called MBT/CBT proxy (methylation index of branched tetraethers/cyclization ratio of branched tetraethers). To investigate the origin and characteristics of these compounds in lacustrine environments, we examined the distributions of GDGTs in soils, river sediments and lake sediments from Lake Towuti on the island of Sulawesi, Indonesia. We found significant differences in the degree of methylation and cyclization (expressed by way of the MBT and CBT indices) between the soil samples and the aquatic samples, suggesting that there may be in situ production of GDGTs in the aquatic environment. Based on these findings, we urge caution in the application of the MBT/CBT paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments.  相似文献   

19.
Distribution of intact and core GDGTs in marine sediments   总被引：1，自引：0，他引：1  
We conducted a survey of archaeal GDGT (glycerol dibiphytanyl glycerol tetraether) distributions in marine sediments deposited in a range of depositional settings. The focus was comparison of two pools presumed to have distinct geobiological significance, i.e. intact polar GDGTs (IP GDGTs) and core GDGTs (C GDGTs). The former pool has been suggested to be related to living communities of benthic archaea in marine sediments, while the latter is commonly interpreted to consist of molecular fossils from past planktonic archaeal communities that inhabited the surface ocean. Understanding the link between these two pools is important for assessment of the validity of current molecular proxies for sedimentary archaeal biomass and past sea surface temperatures. The relative distributions of GDGTs in the two pools in a core at a CH4 rich site in the Black Sea provide evidence for in situ production of glycosidic IP GDGTs and their subsequent degradation to corresponding C GDGTs on timescales that are short in geological terms. In addition, we monitored the relationship between the IP GDGT and C GDGT pools in a sample set from various ocean basins with subseafloor depth from a few cm to 320 m and 0 to 4 Myr in age. Notable differences between the two pools can be summarized as follows: the GDGT with acyclic biphytanes, GDGT-0, and its analogues with two and three cyclopentane moieties (GDGT-2 and -3) are generally more abundant in the pool of IP GDGTs, while crenarchaeol tends to be more abundant in the C GDGT pool. Consequently, the ring index is generally higher for the C GDGTs while TEX86, a molecular proxy ratio not considering the two major GDGTs, tends to be higher in the IP GDGT pool. These differences in the proportion of individual GDGTs in the two pools are probably due to in situ production of IP GDGTs with distributions differing from those of C GDGTs. Despite these differences, we observed significant correlation of these two ratios between the two pools. Specifically, in both pools TEX86 is high in sediments from warm oceanic regimes and low in cold regimes. We discuss these relationships and suggest that recycling of core GDGTs by benthic archaea is an important mechanism linking both molecular pools.  相似文献   

20.
Liquid chromatography–mass spectrometry (LC–MS) analysis of glycerol dialkyl glycerol tetraethers (GDGTs) from sediment and soil samples has become a widely adopted approach for reconstructing past ocean and continental climate variables such as temperature and pH. The LC–MS data used for constructing these GDGT climate proxies are taken directly from the peak area values of individual GDGT [M+H]+ ions, often determined from manual peak integration due to unreliable computer integrators in commercial software, particularly in cases of complex baselines, asymmetric peak shapes and peak coelution. Manual integration is not only time consuming, but also prone to user induced inconsistency when individuals utilize different criteria for peak/baseline definition. To overcome these problems, we have developed a user friendly, graphical user interface (GUI) programmed in the MATLAB environment, allowing users to efficiently and reproducibly perform batch processing and peak integration of LC–MS data. The program, “TEXPRESS” v1.0 (“tetraether index express”), incorporates modern chemometric based techniques for baseline definition and deconvolution of complex chromatographic peaks and we show that LC–MS data processed using the TEXPRESS toolbox are in strong agreement with results obtained from manual peak integration. We provide a general overview of the concepts and architecture of the TEXPRESS toolbox and discuss the advantages of chemometric based peak integration methods for processing branched and isoprenoid GDGT LC–MS data.  相似文献   

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