Distribution Of Tetraether Lipids Research Articles

Planktonic Archaeal Ether Lipid Origins in Surface Waters of the North Pacific Subtropical Gyre.

Thaumarchaeota and Thermoplasmatota are the most abundant planktonic archaea in the sea. Thaumarchaeota contain tetraether lipids as their major membrane lipids, but the lipid composition of uncultured planktonic Thermoplasmatota representatives remains unknown. To address this knowledge gap, we quantified archaeal cells and ether lipids in open ocean depth profiles (0–200 m) of the North Pacific Subtropical Gyre. Planktonic archaeal community structure and ether lipid composition in the water column partitioned into two separate clusters: one above the deep chlorophyll maximum, the other within and below it. In surface waters, Thermoplasmatota densities ranged from 2.11 × 106 to 6.02 × 106 cells/L, while Thaumarchaeota were undetectable. As previously reported for Thaumarchaeota, potential homologs of archaeal tetraether ring synthases were present in planktonic Thermoplasmatota metagenomes. Despite the absence of Thaumarchaeota in surface waters, measurable amounts of intact polar ether lipids were found there. Based on cell abundance estimates, these surface water archaeal ether lipids contributed only 1.21 × 10–9 ng lipid/Thermoplasmatota cell, about three orders of magnitude less than that reported for Thaumarchaeota cells. While these data indicate that even if some tetraether and diether lipids may be derived from Thermoplasmatota, they would only comprise a small fraction of Thermoplasmatota total biomass. Therefore, while both MGI Thaumarchaeota and MGII/III Thermoplasmatota are potential biological sources of archaeal GDGTs, the Thaumarchaeota appear to be the major contributors of archaeal tetraether lipids in planktonic marine habitats. These results extend and confirm previous reports of planktonic archaeal lipid sources, and further emphasize the need for Thermoplasmatota cultivation, to better characterize the membrane lipid constituents of marine planktonic Thermoplasmatota, and more precisely define the sources and patterns of archaeal tetraether lipid distributions in marine plankton.

The effect of methane seeps on the bacterial tetraether lipid distributions at the Okinawa Trough

The branched glycerol dialkyl glycerol tetraethers (brGDGTs) can be produced in situ under methanotrophic/hypoxic conditions in lakes. However, the effect of dynamic methanotrophic activities in the widely-distributed seafloor methane seeps on brGDGTs distributions in global continent margins remains enigmatic. In this study, we firstly report the occurrence of in situ produced brGDGTs in cold seep environments, based on the analysis of tetraether lipid distributions in the authigenic carbonates collected from the northern section of the Okinawa Trough (OT). The abundance ratio of isoGDGTs to brGDGTs (Ri/b) was much lower in the authigenic carbonates (0.94 to 2.25) than in the adjacent normal marine sediments (>10) and suspended particulate matter (>60) in the East China Sea (ECS). Such significant higher bacterial branched GDGTs ratios in the authigenic carbonates indicate its additional sources besides terrestrial and/or water column inputs. Specifically, the brGDGT (Ia), brGDGT (IIa) and brGDGT (IIa’) appear to form in situ in cold seeps, and are influenced by the methane flux significantly as indicated by the fractional abundances of GDGTs along the transect of pipes, network analysis, and correlations between Methane Index (MI) and brGDGTs. Our study highlights that the distributions of seafloor methane seeps could impact the bacterial tetraether lipid distributions in ocean, which would hamper the universal application of brGDGT-based proxies for terrigenous organic carbon tracing and paleoclimate reconstruction in marine environments.

Distribution of tetraether lipids in sulfide chimneys at the Deyin hydrothermal field, southern Mid-Atlantic Ridge: Implication to chimney growing stage

This study presents analysis of four chimney samples in terms of glycerol dialkyl glycerol tetraether lipids (GDGTs), representing different growing stages of sulfide chimneys at the Deyin hydrothermal field, the southern mid-Atlantic ridge. The modified Bligh-Dyer method was used for lipid extraction and purification. GDGTs were analyzed with an Agilent 1200 series liquid chromatograph and 6460A triple quadrupole mass spectrometer. Our results showed that the intact polar GDGTs were more abundant than the core GDGTs in the 4 samples. The intact polar isoprenoidal GDGT-0 was the dominant composition (>70% of isoprenoidal GDGTs), indicating input of thermophilic Euryarchaeota. Most branched GDGTs were likely originated from the in situ thermophilic bacteria. However, the intact polar GDGTs in the sample at the late growing stage was similar to that in normal marine sediments, suggesting that the archaea mainly came from the planktonic Thaumarchaeota input. Our results suggested that the ratio of H-GDGTs to iGDGTs could be considered as a proxy to differentiated growing stages of a chimney. This study shed light on how to assess hydrothermal venting and sulfide chimneys in deep marine environments with a biomarker method in terms of different groups of GDGTs.

Sources and distribution of tetraether lipids in sediments from the Zhejiang–Fujian coastal mud area, China, over the past 160 years: Implications for paleoclimate change

Proxies based on glycerol dialkyl glycerol tetraether (GDGT) lipids in surface sediments have been successfully used to reconstruct sea surface temperature (SST), mean annual air temperature (MAAT), and soil pH in the East China Sea and its adjacent ocean margins. In this study, two cores from the Zhejiang–Fujian coastal mud area (ZFCMA) were studied in detail to investigate temporal changes in the source and distribution of tetraether lipids in the area, and the implications of such data for paleoclimate change. The results indicate that isoprenoid GDGTs (isoGDGTs) in the ZFCMA were derived mainly from Thaumarchaeota, with a minor contribution from in situ and allochthonous methanogenic archaea in upwelling areas, whereas branched GDGTs (brGDGTs) originated mainly from terrigenous bacteria and in situ organisms. However, the minor methanogen-derived and allochthonous isoGDGTs were considered to have had no effect on inferred SSTs in this study. The presence of brGDGTs produced in situ might corrupt the relationship between the methylation index of branched tetraethers or the cyclization index of branched tetraethers (MBT/CBT) and MAAT or pH, particularly in hypoxic areas. However, #ringtetra data, used here as an index to evaluate the sources of the brGDGTs, indicated that the brGDGTs buried in the sediments are predominantly derived from soil erosion. Furthermore, temporal changes in the GDGT-based proxy records indicate that climate changes and events (e.g., relating to the East Asian Monsoon, Pacific Decadal Oscillation (PDO)/Kuroshio Current (KC) intensity, and flood events), as well as anthropogenic influences (e.g., dam construction, soil conservation, fertilizer usage, and discharge of industrial waste water and domestic sewage) affect the signal in the core sediments. SSTs fluctuated over the past 160 years in the ZFCMA, with higher values in the 20th century than in the 19th century. In addition, the humidity, as inferred from the relationship between precipitation/soil water content and pH, and continental temperature in the mid–lower Yangtze River basin switched between dry–hot/dry–cool and wet–hot/wet–cool over the last 160 years. The results also indicate that PDO/KC intensity plays a key role in temperature changes and has a larger impact on terrestrial ecosystems than on ocean ecosystems in the ZFCMA and the adjacent continent.

Distribution of tetraether lipids in agricultural soils – differentiation between paddy and upland management

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).

Sources and proxy potential of long chain alkyl diols in lacustrine environments

Long chain 1,13- and 1,15-alkyl diols form the base of a number of recently proposed proxies used for climate reconstruction. However, the sources of these lipids and environmental controls on their distribution are still poorly constrained. We have analyzed the long chain alkyl diol (LCD) composition of cultures of ten eustigmatophyte species, with three species from different families grown at various temperatures, to identify the effect of species composition and growth temperature on the LCD distribution. The results were compared with the LCD distribution of sixty-two lake surface sediments, and with previously reported LCD distributions from marine environments. The different families within the Eustigmatophyceae show distinct LCD patterns, with the freshwater family Eustigmataceae most closely resembling LCD distributions in both marine and lake environments. Unlike the other two eustigmatophyte families analyzed (Monodopsidaceae and Goniochloridaceae), C28 and C30 1,13-alkyl diols and C30 and C32 1,15-alkyl diols are all relatively abundant in the family Eustigmataceae, while the mono-unsaturated C32 1,15-alkyl diol was below detection limit. In contrast to the marine environment, LCD distributions in lakes did not show a clear relationship with temperature. The Long chain Diol Index (LDI), a proxy previously proposed for sea surface temperature reconstruction, showed a relatively weak correlation (R2=0.33) with mean annual air temperature used as an approximation for annual mean surface temperature of the lakes. A much-improved correlation (R2=0.74, p-value <0.001) was observed applying a multiple linear regression analysis between LCD distributions and lake temperatures reconstructed using branched tetraether lipid distributions. The obtained regression model provides good estimates of temperatures for cultures of the family Eustigmataceae, suggesting that algae belonging to this family have an important role as a source for LCDs in lacustrine environments, or, alternatively, that the main sources of LCDs are similarly affected by temperature as the Eustigmataceae. The results suggest that LCDs may have the potential to be applicable as a palaeotemperature proxy for lacustrine environments, although further calibration work is still required.

Distribution of tetraether lipids in surface sediments of the northern South China Sea: Implications for TEX86 proxies

Archaea have unique glycerol dialkyl glycerol tetraether (GDGT) lipids that can be used to develop paleotemperature proxies such as TEX86. This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea (SCS). Samples were collected from core-top sediments (0–5 cm) in the northern SCS. Total lipids were extracted to obtain core GDGTs, which were identified and quantified using liquid chromatography-mass spectrometry (LC-MS). The abundance of isoprenoidal GDGTs (iGDGTs) ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment, whereas the branched GDGTs (bGDGTs), supposedly derived from terrestrial sources, ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment. The TEX86-derived sea surface temperatures ranged from 20.9 °C in the coast (water depth < 160 m) to 27.9 °C offshore (water depth > 1000 m). TEX86-derived temperatures near shore (<160 m water depth) averaged 23.1 ± 2.5 °C (n = 4), which were close to the satellite-derived winter mean sea surface temperature (average 22.6 ± 1.0 °C, n = 4); whereas the TEX86-derived temperatures offshore averaged 27.4 ± 0.3 °C (n = 7) and were consistent with the satellite mean annual sea surface temperature (average 26.8 ± 0.4 °C, n = 7). These results suggest that TEX86 may record the sea surface mean annual temperature in the open ocean, while it likely records winter sea surface temperature in the shallower water.

Distribution of tetraether lipids in the 25-ka sedimentary record of Lake Challa: extracting reliable TEX86 and MBT/CBT palaeotemperatures from an equatorial African lake

The distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether (GDGT) lipids was studied in the sedimentary record of Lake Challa, a permanently stratified, partly anoxic crater lake on the southeastern slope of Mt. Kilimanjaro (Kenya/Tanzania), to examine if the GDGTs could be used to reconstruct past variation in regional temperature. The study material comprised 230 samples from a continuous sediment sequence spanning the last 25 ka with excellent age control based on high-resolution AMS 14C dating. The distribution of GDGTs showed large variation through time. In some time intervals (i.e., from 20.4 to 15.9 ka BP and during the Younger Dryas, 12.9–11.7 ka BP) crenarchaeol was the most abundant GDGT, whereas at other times (i.e., during the Early Holocene) branched GDGTs and GDGT-0 were the major GDGT constituents. In some intervals of the sequence the relative abundance of GDGT-0 and GDGT-2 was too high to be derived exclusively from lacustrine Thaumarchaeota, suggesting a sizable contribution from methanogens and other archaea. This severely complicated application of TEX86 palaeothermometry in this lake, and limited reliable reconstruction of lake water temperature to the time interval 25–13 ka BP, i.e. the Last Glacial Maximum and the period of post-glacial warming. The TEX86-inferred timing of this warming is similar to that recorded previously in two of the large African rift lakes, while its magnitude is slightly or much higher than that recorded at these other sites, depending on which lake-based TEX86 calibration is used. Application of calibration models based on distributions of branched GDGTs developed for lakes inferred temperatures of 15–18 °C for the Last Glacial Maximum and 19–22 °C for the Holocene. However, the MBT/CBT palaeothermometer reconstructs temperatures as low as 12 °C for a Lateglacial period centred on 15 ka BP. Variation in down-core values of the BIT index are mainly determined by the varying production rate of crenarchaeol relative to in-situ produced branched GDGTs. The apparent relationship of the BIT index with climatic moisture balance can be explained either by the direct influence of lake level and wind strength on nutrient recycling, or by influx of soil nutrients promoting aquatic productivity and nitrification. This study shows that GDGTs can aid in obtaining climatic information from lake records but that the obtained data should be interpreted with care.

Biogeochemical controls on glycerol dialkyl glycerol tetraether lipid distributions in sediments characterized by diffusive methane flux

The TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) is a proxy for sea surface temperature (SST) based on the distribution of isoprenoidal glycerol dialkyl glycerol tetraether (GDGT) membrane lipids synthesized by marine pelagic Thaumarchaeota. One of the caveats of this proxy is the production of additional GDGTs by sedimentary Euryarchaeota involved in anaerobic oxidation of methane (AOM) that occurs at deep-sea methane seeps but is also widespread in many continental shelf settings. Here, GDGT distributions are investigated through the sulfate-methane transition zone (SMTZ) in Aarhus Bay, Denmark, to examine the extent the TEX86 proxy is compromised in such a continental shelf setting where AOM is characterized by a diffusive rather than rapid advective methane flux. Both free extractable and non-extractable lipid fractions were analyzed as it was expected that pelagic-derived and sediment-derived GDGTs could become incorporated into the molecular and sedimentary matrix to a different extent. The results show a large change of TEX86 values mainly due to the relative high amounts of GDGT-2 produced by AOM-related Archaea, both in the free and non-extractable lipid fractions. This additional GDGT input renders calculation of SSTs based on TEX86 inappropriate at the SMTZ. The AOM-related GDGT signature, however, did not persist into deeper sediments, perhaps reflecting rapid remineralization of the GDGTs at the SMTZ. Although the process of AOM at Aarhus Bay might not be representative for all continental margin settings, it illustrates that AOM in a variety of settings, not just cold seeps, can influence sedimentary GDGT distributions.

The major lipid cores of the archaeon Ignisphaera aggregans: implications for the phylogeny and biosynthesis of glycerol monoalkyl glycerol tetraether isoprenoid lipids

The lipid cores from Ignisphaera aggregans, a hyperthermophilic Crenarchaeon recently isolated from New Zealand hot springs, have been profiled by liquid chromatography-tandem mass spectrometry. The distribution revealed includes relatively high proportions of monoalkyl (also known as H-shaped) tetraether cores which have previously been implicated as kingdom-specific biomarkers for the Euryarchaeota. Such high expression of monoalkyl tetraether lipids is unusual in the archaeal domain and may indicate that formation of these components is an adaptive mechanism that allows I. aggregans to regulate membrane behaviour at high temperatures. The observed dialkyl tetraether and monoalkyl tetraether lipid distributions are similar but not fully concordant, showing differences in the average number of incorporated rings. The similarity supports a biosynthetic route to the ring-containing dialkyl and monoalkyl tetraether lipids via a dialkyl tetraether core containing zero rings, or a closely related structural relative, as an intermediate. Currently, however, the precise nature of the biosynthetic route to these lipids cannot be deduced.

Environmental controls on branched tetraether lipid distributions in tropical East African lake sediments

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.

Fluxes and distribution of tetraether lipids in an equatorial African lake: Constraints on the application of the TEX 86 palaeothermometer and BIT index in lacustrine settings

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 TEX 86-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.