Distribution of bacterial and archaeal ether lipids in soils and surface sediments of Tibetan lakes: Implications for GDGT-based proxies in saline high mountain lakes

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.     

Distribution of glycerol dialkyl glycerol tetraethers in surface sediments of Lake Qinghai and surrounding soil

Glycerol dialkyl glycerol tetraethers (GDGTs) are increasingly used as proxies for paleoclimate studies of marine and lacustrine environments. While GDGT-based proxies have been applied to a number of lake environments globally, little is known about the distribution of GDGTs on the Qinghai-Tibet Plateau. We have investigated the isoprenoid GDGTs (iGDGTs) and branched GDGTs (bGDGTs) in Lake Qinghai sediments and the surrounding surface soil in order to examine their potential use as paleoclimate proxies on the Qinghai-Tibet Plateau. The results show that (i) the values of the iGDGT/bGDGT ratio for surrounding soil were at the higher end among globally distributed soils and consequently BIT values (avg. 0.71) at the lower end, (ii) the TEX₈₆ values decreased while the MBT and CBT values increased along an onshore soil–nearshore sediment–offshore sediment transect, (iii) the TEX₈₆ values for the offshore sediments were almost identical and their inferred temperatures were close to mean summer surface water temperature and (iv) the bGDGT-inferred mean annual air temperature (MAAT) and pH for soil were consistent with measured MAAT and pH. However, the CBT-inferred pH for offshore sediments seemed inconsistent with the pH of lake water or sediment. Our results suggest that (i) the higher pH may be an important factor leading to the higher iGDGT/bGDGT values (and lower BIT values) in surrounding surface soil, (ii) both iGDGTs and bGDGTs may originate from terrestrial input and in situ production for this saline lake, especially for nearshore sediments. However, for offshore sediments, terrestrial iGDGT input seems minor, and TEX₈₆ may be useful for paleoclimate studies of Lake Qinghai.     

Separation of core and intact polar archaeal tetraether lipids using silica columns: Insights into living and fossil biomass contributions

Intact polar lipids (IPLs) are frequently used as biomarkers for living microbial cells and can be separated from core lipids (i.e. lipids without polar headgroups), which are mainly derived from fossil (i.e. dead) cell material, using column chromatography. We have compared the effect of various silica column conditions on the separation and recovery of archaeal glycerol dialkyl glycerol tetraether (GDGT) core lipids, glycolipids and phosphoglycolipids using authentic standards and direct analysis with various high performance liquid chromatography-mass spectrometry (HPLC-MS) techniques. The commonly used procedure to separate these compound classes using dichloromethane, acetone and methanol as eluents, respectively, did not separate core GDGTs from glyco- and phosphoglyco-GDGTs. In contrast, a recently described procedure using hexane:ethyl acetate (3:1, v:v), ethyl acetate and methanol achieved both high recovery and successful separation of core GDGTs from the other IPLs. Application of the method to a geothermally heated soil and suspended particulate matter from the North Sea showed that it separates most of the core GDGTs from the other IPLS and that considerable qualitative and quantitative differences can occur between core and IPL-GDGTs. We conclude that the method is therefore appropriate for the separation of intact archaeal IPLs and their fossil analogues.     

An automated purification method for archaeal and bacterial tetraethers in soils and sediments

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.     

Distribution of branched tetraether lipids in geothermally heated soils: Implications for the MBT/CBT temperature proxy

Branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids occur in soils and peat bogs and are assumed to be produced by anaerobic bacteria. Two indices based on the distribution of these lipids in soils, the Cyclisation of Branched Tetraethers (CBT) and the Methylation of Branched Tetraethers (MBT) index have been shown to linearly relate to pH, and to mean annual air temperature (MAT) and pH, respectively. To directly evaluate the impact of changes in soil temperature on the MBT/CBT proxy, we determined these indices in soils sampled from a transect away from two hot springs in California, which provided a set of soils similar in composition but with different temperatures (12–41 °C). The CBT values of these geothermally heated soils show a good relation with pH (R² 0.76), similar to that of a global MBT/CBT calibration set. Also, the relationship between MBT, soil pH and temperature for the geothermally heated soils is similar to that of a global soil calibration set, although the intercept for the geothermally heated soils is significantly lower, likely because our data set is based on in situ soil temperatures rather than MAT. The results confirm the dependence of the MBT index on soil temperature and pH and support the applicability of the MBT/CBT indices as a proxy for continental palaeotemperatures and past soil pH.     

Structural diversity and fate of intact polar lipids in marine sediments

Marine sediments harbor an enormous quantity of microorganisms, including a multitude of novel species. The habitable zone of the marine sediment column begins at the sediment-water interface and probably extends to depths of several thousands of meters. Studies of the microbial diversity in this ecosystem have mostly relied on molecular biological techniques. We used a complementary method - analysis of intact polar membrane lipids - to characterize the in-situ microbial community in sediments covering a wide range of environmental conditions from Peru Margin, Equatorial Pacific, Hydrate Ridge, and Juan de Fuca Ridge. Bacterial and eukaryotic phospholipids were only detected in surface sediments from the Peru Margin. In contrast, deeply buried sediments, independent of their geographic location, were dominated by archaeal diether and tetraether lipids with various polar head groups and core lipids. We compared ring distributions of archaeal tetraether lipids derived from polar glycosidic precursors with those that are present as core lipids. The distributions of these related compound pools were distinct, suggestive of different archaeal sources, i.e., the polar compounds derive from sedimentary communities and the core lipids are fossil remnants from planktonic communities with possible admixtures of decayed sedimentary archaea. This in-situ production of distinct archaeal lipid populations potentially affects applications of the TEX86 paleotemperature proxy as demonstrated by offsets in reconstructed temperatures between both pools. We evaluated how varying cell and lipid stabilities will influence the sedimentary pool by using a box-model. The results are consistent with (i) a requirement of continuous inputs of freshly synthesized lipids in subsurface sediments for explaining the observed distribution of intact polar lipids, and (ii) decreasing lipid inputs with increasing burial depth.     

Identification and distribution of intact polar branched tetraether lipids in peat and soil

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.     

Distribution of glycerol dialkyl glycerol tetraether lipids along an altitudinal transect on Mt. Xiangpi,NE Qinghai-Tibetan Plateau,China

The distribution of glycerol dialkyl glycerol tetraethers (GDGTs) can reflect continental environmental changes. Recently, the distribution of branched GDGTs (bGDGTs) has been proposed as a novel tool for paleoelevation reconstructions. Here we report the variation in TEX₈₆ (tetraether index of 86 carbon atoms) of isoprenoidal GDGTs (iGDGTs) and MBT (methylation of branched tetraether index) of bGDGTs along an altitudinal transect on Mt. Xiangpi, NE Qinghai-Tibetan Plateau. Both TEX₈₆ and MBT values of surface soils showed significant linear decreases with altitude (TEX₈₆: R² = 0.65; n = 50; MBT: R² = 0.69; n = 24). We suggest that the apparent relationships between the two indices and altitude may be related to temperature. Our preliminary investigation suggests that the TEX₈₆ index can potentially be applied as a paleoelevation indicator in addition to the MBT index on the Qinghai-Tibetan Plateau.     

承德地区两温泉中古细菌基因型多样性分析

通过构建16S rDNA克隆文库,对承德地区两个不同温度的温泉中古细菌的基因型多样性进行了分子生态学研究。结果表明:山湾子温泉(A12)74.5℃热水中的古细菌主要分属泉古菌门(Crenarchaeota)和广古菌门(Euryarchaeota)两个门;七家温泉(A14)61.4℃热水中的古细菌则只属于泉古菌门,没有广古菌门微生物的分布。样品A12中的古细菌序列只可分为3种基因型,而A14中的古细菌序列可分为10种基因型。古细菌多样性的差异表明,温度是影响温泉中古细菌多样性水平的重要因素。样品A12中古细菌群落具有厌氧发酵乙酸产甲烷的生理功能,而A14中大多数古细菌均与氨氧化古菌有密切的亲缘关系,其主要生理功能为好氧氨氧化。     

Branched and isoprenoid tetraether (BIT) index traces water content along two marsh-soil transects surrounding Lake Qinghai: Implications for paleo-humidity variation

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.     

Archaeal polar lipids in subseafloor sediments from the Nankai Trough: Implications for the distribution of methanogens in the deep marine subsurface

Although the methane in marine methane hydrates is mainly of microbial origin, information about the distribution of methanogens in subseafloor sediments is limited. To address this issue, we analyzed sediment core samples from two sites in the Nankai Trough, off the Pacific coast of central Japan, including those bearing methane hydrates from depths > 100 m below the seafloor (mbsf), for isopranyl ether-linked polar lipids (i.e. with polar head groups of phosphate, sugar, or both) as biomarkers of archaea, including methanogens. In most samples, including the deepest (381 mbsf), archaeol, and sn-2- and sn-3-hydroxyarchaeols were detected as their hydrolyzed derivatives. Concentrations of these three archaeal lipids correlated strongly with each other, suggesting a common biological source. The δ¹³C values of phytane derived from the phytanyl groups in the archaeal lipids were distinctly higher than those of methane, indicating that methanogens rather than anaerobic methanotrophic archaea were the major biological source. Depth profiles of polar sn-2-hydroxyarchaeol concentration were consistent with those of the potential methane production activity previously estimated from incubation of core sediments from the same sites. This observation, together with results of previous studies showing the presence of sn-2-hydroxyarchaeol mainly in shallow young sediments, strongly suggests that this polar lipid is a valid biomarker for in situ methanogens in sediments. There was a strong correlation between the concentration of polar sn-2-hydroxyarchaeol and that of total organic carbon, suggesting that bulk organic matter concentration is a primary control on the distribution of methanogens in sediments.     

Comprehensive glycerol ether lipid fingerprints through a novel reversed phase liquid chromatography–mass spectrometry protocol

Glycerol ether lipid distributions have been developed as proxies for reconstructing past environmental change or, in their intact polar form, for fingerprinting the viable microbial community composition. However, due to their structural complexity, full characterization of glycerol ether lipids requires separate protocols for the analysis of the polar head groups and the alkyl chain moieties in core ether lipids. As a consequence, the valuable relationship between core ether lipid composition and specific polar head groups is often lost; this limits understanding of the diversity of ether lipids and their utility as biogeochemical proxies. Here, we report a novel reversed phase liquid chromatography–electrospray ionization-mass spectrometry (RP-ESI-MS) protocol that enables the simultaneous analysis of polar head groups (e.g. phosphocholine, phosphoglycerol, phosphoinositol, hexose and dihexose) and alkyl moieties (e.g. alkyl moieties modified with different numbers of cycloalkyl moieties, hydroxyl and alkyl groups and double bonds) in crude lipid extracts without further preparation. The protocol greatly enhances detection of archaeal intact polar lipids (IPLs) and core lipids (CLs) with double bond- and hydroxyl group-bearing alkyl moieties. With these improvements, widely used ratios that describe relative distributions of the core lipids, such as TEX₈₆ and ring index, can now be directly determined in specific intact polar lipids (IPL-specific TEX₈₆ and ring index). Since IPLs are the putative precursors of the environmentally persistent core lipids, their detailed examination using this protocol can potentially provide new insights into diagenetic and biological mechanisms inherent to these proxies. In a series of 12 samples from diverse settings, core and IPL-specific TEX₈₆ values followed the order: 2G-GDGTs > core GDGTs > 1G-GDGTs > 1G-GDGT-PI and the ring indices followed: 1G-GDGTs ≈ core GDGTs > 2G-GDGTs > 1G-GDGT-P1G > 2G-OH-GDGTs ≈ 1G-OH-GDGTs (1G, monoglycosyl; 2G, diglycosyl; P1G, phosphomonoglycosyl; GDGT, glycerol dialkyl glycerol tetraether).     

Absence of seasonal patterns in MBT-CBT indices in mid-latitude soils

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.     

滇西潞西盆地温泉水文地球化学特征及其成因

云南大理至瑞丽铁路西段的潞西盆地含水层结构复杂、温泉甚多。选择该盆地的典型温泉——法帕温泉和芒留温泉,针对该区温泉成因分析中存在的疑点问题开展了地质、水文地质和水文地球化学调查工作。在分析该区温泉的水文地球化学特征,并与不同条件的温泉作类比研究的基础上,进一步剖析了温泉的成因。研究结果表明,法帕温泉和芒留温泉为典型的断裂型温泉,接受大气降水补给,下渗后被断层中的高温内生流体加热并在断层中储集和运移,储热层均为灰岩、白云质灰岩及泥灰岩,热储深度为2000m左右,温度可达160℃左右。     

西沙地区碳酸盐台地发育过程与海平面变化:基于西科1井BIT指标分析数据

为了探讨南海碳酸盐台地的发育过程及控制因素, 采用有机分子化合物指标方法对其进行了研究.有机分子化合物指标BIT(branched isoprenoid tetraether)是沉积物中源自陆源的细菌膜脂支链甘油双烷基链甘油四醚(branched glycerol dialkyl glycerol tetraethers,简称bGDGTs)与主要来自海洋泉古菌中的类异戊二烯GDGTs(isoprenoid GDGTs,简称iGDGTs)的含量之比,在古环境研究中,用来区分沉积物有机质的来源、判断沉积环境.通过对西科1井的数据研究发现,西科1井BIT指数随深度呈现三段式规律性变化,从下到上呈现高-低-高的变化,反映了中中新世以来南海海平面变化及碳酸盐台地生长发育的过程:在中中新世晚期,受全球及区域海平面变化下降影响,西沙地区碳酸盐台地形成礁-滩交互的沉积地层,由于大气淡水的影响,造成BIT指数呈现高值;到晚中新世至上新世,全球及区域海平面出现持续上升,有利于西沙碳酸盐台地的生长发育,使该井沉积环境以礁内泻湖相为主,造成BIT指数呈现低值;在第四纪冰期,全球及区域海平面出现总体下降趋势,西沙碳酸盐台地又频繁暴露于地表,造成BIT指数又呈现高值.研究表明,西沙地区碳酸盐台地受区域相对海平面变化影响更大,说明南海海平面变化既受全球海平面变化的影响,也受南海区域构造沉降的控制.      

腾冲新生代火山区温泉CO2气体排放通量研究

近期研究表明,不仅火山喷发期会向当时的大气圈输送大量的温室气体,火山间歇期同样会释放大量的温室气体。在火山活动间歇期,火山区主要以喷气孔、温(热)泉以及土壤微渗漏等形式向大气圈释放温室气体。腾冲是我国重要的新生代火山区,同时也是重要的水热活动区,那里出露大量的温泉,然而目前未见腾冲火山区温泉气体排放通量的研究报道。本文利用数字皂膜通量仪测量了腾冲新生代火山区温泉中CO₂的排放通量。研究结果表明,腾冲新生代火山区温泉向当今大气圈输送的CO₂通量达3.58×10³ t·a^-1,相当于意大利锡耶纳Bassoleto地热区温泉中CO₂的排放规模。腾冲火山区温泉的CO₂释放通量主要受深部岩浆囊、断裂分布、地下水循环、围岩成分等多方面因素的影响。本文根据温泉中CO₂的排放特征,将腾冲温泉分为南北两区,南区温泉CO₂通量远高于北区的温泉,热海地热区的通量为腾冲CO₂通量的最大值。在北温泉区,CO₂通量主要受控于断裂的分布;而在南温泉区,除受到断裂控制外,热海地热区底部的岩浆囊及其与围岩的相互作用成为CO₂气体的重要物质来源,同时高温的岩浆囊为温泉及CO₂的形成提供了重要热源。     

Influence of lake water pH and alkalinity on the distribution of core and intact polar branched glycerol dialkyl glycerol tetraethers (GDGTs) in lakes

Branched glycerol dialkyl glycerol tetraethers (GDGTs) are bacterial membrane lipids, ubiquitously present in soils and peat bogs, as well as in rivers, lakes and lake sediments. Their distribution in soil is controlled mainly by pH and mean annual air temperature, but the controls on their distribution in lake sediments are less well understood. Several studies have found a relationship between the distribution of branched GDGTs in lake sediments and average lake water pH, suggesting an aquatic source for them, besides that for soil transported to the lake via erosion. We sampled the surface water suspended particulate matter (SPM) from 23 lakes in Minnesota and Iowa (USA), that vary widely in pH, alkalinity and trophic state. The SPM was analyzed for the concentration and distributions of core lipid (presumed fossil origin) and intact polar lipid (IPL, presumed to derive from living cells) branched GDGTs. The presence of substantial amounts (18–48%) of IPL-derived branched GDGTs suggests that branched GDGTs are likely of autochthonous origin. Temperature estimates based on their distribution using lake-specific calibrations agree reasonably with water temperature at time of sampling and average air temperature of the season of sampling. Importantly, a strong correlation between the distribution of branched GDGTs and lake water pH was found (r² 0.72), in agreement with a predominant in situ production. An stronger correlation was found with lake water alkalinity (r² 0.83), although the underlying mechanism that controls the relationship is not understood. Our results raise the potential for reconstructing pH/alkalinity of past lake environments, which could provide important knowledge on past developments in lake water chemistry.     

http://www.sciencedirect.com/science/article/pii/S1674987111001319

The microbial diversity in Wuli Area,Qinghai-Tibetan Plateau was investigated using 16S rRNA gene phylogenetic analyses.A total of 117 bacterial and 66 archaeal 16S rRNA gene clones were obtained from the Wuli cold springs.The bacterial clones could be classified into Pwteobacteria,Acidobacteria, Deinococci,Sphingobacteria,Flavobacteria.Nitrospirae,Actinobacteria,Gemmatimonadetes, and unclassified-bacteria;and the archaeal clones could be classified into Crenarchaeota and Thaumarchaeota.Among the major groups,Pwteobacteria and Crenarchaeota were dominant in the bacterial and archaeal 16S rRNA gene clone libraries,respectively.The clone sequences obtained in Wuli cold springs were closely related to those from cold habitats,such as snow/ice/soils on high mountains or at high latitude.Especially,the microbial community composition of Wuli Area was more similar to that in Tibetan glaciers than cold environments of other locations.The data presented in this study have implications for a better understanding of microbial diversity in cold springs on the Qinghai-Tibetan Plateau.     

Assessing the ratio of archaeol to caldarchaeol as a salinity proxy in highland lakes on the northeastern Qinghai–Tibetan Plateau

The ratio of archaeol to caldarchaeol (the ACE index) has been proposed recently as an index for paleosalinity reconstruction and is based principally on archaeal core lipids (CLs) from coastal salt pans (Turich, C., Freeman, K.H., 2011. Archaeal lipids record paleosalinity in hypersaline systems. Organic Geochemistry 42, 1147–1157). We have examined possible relationships between salinity and ACE in both CLs and intact polar lipids (IPLs) from suspended particulate matter (SPM) and surface sediments of lakes and surrounding soils on the northeastern Qinghai–Tibetan Plateau. Our results showed that ACE values were positively correlated with salinity in all samples; however, CL ACE values were systematically higher than IPL ACE values, probably due to different degradation kinetics of intact polar (IP) archaeol and IP caldarchaeol. On the other hand, surface sediment ACE values from both CLs and IPLs were lower than SPM ACE values, probably due to enhanced production of caldarchaeol relative to archaeol in the sediment. Our results demonstrate that the ACE proxy reflects changes in salinity in diverse environments on the Qinghai–Tibetan Plateau, which is promising for paleosalinity reconstruction; however, caution should be used when applying the salinity proxy before we have a better understanding of degradation kinetics of archaeal IPLs and in situ production of caldarchaeol and archaeol in sediments.     

水温突降-缓升型的响应机理之冷水下渗学说的研究——以重庆北温泉水Fe3+、Mn2+对汶川地震的响应为例

深井水温观测在中国已经开展了20多年,但目前对于水温响应机理的研究还不充分.而且利用温泉水对水温响应机理研究甚少.本文在2008年5月12日汶川8.0级地震前后,即2008年5月1日至7月4日,对重庆北温泉水(距震中约400 km)进行采样监测,发现泉水水温水量发生较大变化:震后水温下降了1℃:海拔相对较高的BWQ-2、BWQ-3、BWQ-4相继断流,监测点BWQ-1的水量增加了15 L/s;与此同时.各泉点Fe~(3+)、Mn~(2+)浓度于地震当日成倍增长,随后逐渐减小,7月4日时浓度与5月1日相当.重庆北温泉位于四川盆地东部边缘地带,受汶川地震强烈影响导致冷水下渗作用,海拔相对较高而温度较低的温泉水改道,并有其他来自裂隙或者地表的低温水汇入温泉含水层,Fe~(3+)、Mn~(2+)浓度的变化从水化学上印证了冷水下渗学说.