Branched glycerol dialkyl glycerol tetraethers （bGDGTs） are ubiquitous and abundant in soils, but their sources remain elusive. Recent studies demonstrate that the distributions of bGDGTs are sensitive to various en...Branched glycerol dialkyl glycerol tetraethers （bGDGTs） are ubiquitous and abundant in soils, but their sources remain elusive. Recent studies demonstrate that the distributions of bGDGTs are sensitive to various environmental factors. In an effort to understand how and to what extent soil moisture （expressed as soil water content （SWC） or mean annual precipita- tion （MAP）, pH and temperature may impact the distribution of bGDGTs, and to shed more light on the biological sources of bGDGTs in cold and arid regions, we investigated the distribution of bGDGTs as well as bacterial 16S rRNA gene and func- tional genes involved in the N cycle （including amoA, nirS and nirK） in 41 surface soil samples from around Lake Qinghai and east of Qaidam Basin on the Northeastern Qinghai-Tibetan Plateau. We found that lower soil moisture reduced the fractional concentrations of cyclic bGDGTs and thus the cyclisation ratio of branched tetraethers （CBT） index correlated negatively with SWC and MAP, suggesting that soil moisture is an important factor controlling bGDGT distributions in soils in this add and semi-add region. Two subgroups of bGDGTs were assigned on the basis of cluster analysis, and bGDGT indices behaved dif- ferently in the two groups, hinting at different biosynthetic mechanisms for bGDGTs under different environmental conditions. Real time PCR results showed that nirS and nirK genes correlated significantly with the concentration of bGDGTs, suggesting that the nirS- or nirK-encoding bacteria involved in denitrification might potentially be an additional biological source for soil bGDGTs （besides Acidobacteria）. Moreover, our results also support the application of new indices based on 5-methyl bGDGTs and 6-methyl bGDGTs in reconstructing past temperature and pH variations in this region.展开更多
Considerable efforts have been made to extend temperature records beyond the instrumental period through proxy reconstructions,in order to further understand the mechanisms of past climate variability.Yet,the global c...Considerable efforts have been made to extend temperature records beyond the instrumental period through proxy reconstructions,in order to further understand the mechanisms of past climate variability.Yet,the global coverage of existing temperature records is still limited,especially for some key regions like the Tibetan Plateau and for earlier times including the Medieval Warm Period(MWP).Here we present decadally-resolved,alkenone-based,temperature records from two lakes on the northern Tibetan Plateau.Characterized by marked temperature variability,our records provide evidence that temperatures during the MWP were slightly higher than the modern period in this region.Further,our temperature reconstructions,within age uncertainty,can be well correlated with solar irradiance changes,suggesting a possible link between solar forcing and natural climate variability,at least on the northern Tibetan Plateau.展开更多
Branched and Isoprenoid Tetraether(BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers(b GDGTs) are ...Branched and Isoprenoid Tetraether(BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers(b GDGTs) are mainly derived from terrestrial soils. However, mounting evidences have showed that the in situ production of b GDGTs is widespread in lakes, challenging BIT as a reliable terrestrial input proxy. Recently, BIT has been proven to be a reliable proxy for paleohydrology in a small crater lake(Lake Challa) in accordance with a different mechanism. However, the response of BIT to paleohydrology variation may differ for different lakes. In this study, we investigate the variations in the BIT index and the concentrations of its related GDGTs in a 12-ka sediment core from Lake Qinghai, in combination with our previous results for surface sediments. We find that variations in BIT strongly depend on the concentration of crenarchaeol in both surface and ancient sediments of this lake, whereas b GDGT concentration varies much less remarkably. Considering that crenarchaeol production is positively correlated with water depth in Lake Qinghai, water depth may exert negative control on the BIT index in this lake. This case is inconsistent with the positive relationship between BIT and lake levels or rainfall intensity reported for Lake Challa, suggesting that the response of BIT to local paleohydrology is site specific in lacustrine systems. Hence, the application of sedimentary BIT as a paleohydrological proxy in a specific lake requires caution before confirming the environmental controls on BIT in that lake.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 41373072, 40873011 &41030211)the Shanghai Bureau of Science and Technology (Grant No. 13JC1405200)the Thousand Talents Program through the State Key Laboratory of Marine Geology at Tongji University (C. L. Zhang)
文摘Branched glycerol dialkyl glycerol tetraethers （bGDGTs） are ubiquitous and abundant in soils, but their sources remain elusive. Recent studies demonstrate that the distributions of bGDGTs are sensitive to various environmental factors. In an effort to understand how and to what extent soil moisture （expressed as soil water content （SWC） or mean annual precipita- tion （MAP）, pH and temperature may impact the distribution of bGDGTs, and to shed more light on the biological sources of bGDGTs in cold and arid regions, we investigated the distribution of bGDGTs as well as bacterial 16S rRNA gene and func- tional genes involved in the N cycle （including amoA, nirS and nirK） in 41 surface soil samples from around Lake Qinghai and east of Qaidam Basin on the Northeastern Qinghai-Tibetan Plateau. We found that lower soil moisture reduced the fractional concentrations of cyclic bGDGTs and thus the cyclisation ratio of branched tetraethers （CBT） index correlated negatively with SWC and MAP, suggesting that soil moisture is an important factor controlling bGDGT distributions in soils in this add and semi-add region. Two subgroups of bGDGTs were assigned on the basis of cluster analysis, and bGDGT indices behaved dif- ferently in the two groups, hinting at different biosynthetic mechanisms for bGDGTs under different environmental conditions. Real time PCR results showed that nirS and nirK genes correlated significantly with the concentration of bGDGTs, suggesting that the nirS- or nirK-encoding bacteria involved in denitrification might potentially be an additional biological source for soil bGDGTs （besides Acidobacteria）. Moreover, our results also support the application of new indices based on 5-methyl bGDGTs and 6-methyl bGDGTs in reconstructing past temperature and pH variations in this region.
基金supported by the National Basic Research Program of China(2010CB833406, 2010CB428902)Hong Kong Rearch Grants Council(HKU 703809P)+1 种基金supported by the Special Equipment Grant from the University Grants Committee of the Hong Kong Special Administrative Region,China(SEG_HKU01)the CAS/SAFEA International Partnership Program for Creative Research Teams(KZZD-EW-TZ03)
文摘Considerable efforts have been made to extend temperature records beyond the instrumental period through proxy reconstructions,in order to further understand the mechanisms of past climate variability.Yet,the global coverage of existing temperature records is still limited,especially for some key regions like the Tibetan Plateau and for earlier times including the Medieval Warm Period(MWP).Here we present decadally-resolved,alkenone-based,temperature records from two lakes on the northern Tibetan Plateau.Characterized by marked temperature variability,our records provide evidence that temperatures during the MWP were slightly higher than the modern period in this region.Further,our temperature reconstructions,within age uncertainty,can be well correlated with solar irradiance changes,suggesting a possible link between solar forcing and natural climate variability,at least on the northern Tibetan Plateau.
基金supported by the Major State Basic Research Development Program of China(Grant No.2013CB955900)the National Natural Science Foundation of China(Grant Nos.41373022,41573005)
文摘Branched and Isoprenoid Tetraether(BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers(b GDGTs) are mainly derived from terrestrial soils. However, mounting evidences have showed that the in situ production of b GDGTs is widespread in lakes, challenging BIT as a reliable terrestrial input proxy. Recently, BIT has been proven to be a reliable proxy for paleohydrology in a small crater lake(Lake Challa) in accordance with a different mechanism. However, the response of BIT to paleohydrology variation may differ for different lakes. In this study, we investigate the variations in the BIT index and the concentrations of its related GDGTs in a 12-ka sediment core from Lake Qinghai, in combination with our previous results for surface sediments. We find that variations in BIT strongly depend on the concentration of crenarchaeol in both surface and ancient sediments of this lake, whereas b GDGT concentration varies much less remarkably. Considering that crenarchaeol production is positively correlated with water depth in Lake Qinghai, water depth may exert negative control on the BIT index in this lake. This case is inconsistent with the positive relationship between BIT and lake levels or rainfall intensity reported for Lake Challa, suggesting that the response of BIT to local paleohydrology is site specific in lacustrine systems. Hence, the application of sedimentary BIT as a paleohydrological proxy in a specific lake requires caution before confirming the environmental controls on BIT in that lake.
