Spatial heterogeneity of sources of branched tetraethers in shelf systems: The geochemistry of tetraethers in the Berau River delta (Kalimantan, Indonesia)

The bulk organic matter composition (total organic carbon (TOC) content and d13CTOC) and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGT) in surface sediments from 43 stations in the Berau River delta (east Kalimantan, Indonesia), including two coast-shelf transects and stations within the river mouth, were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system. The high-resolution study showed that, despite the extensive transport of eroded soil material by the river to the sea, terrestrial organic matter and brGDGTs are only deposited on a relatively small part of the shelf. The concentrations of brGDGTs are highest (up to 120 µg g-1 TOC) in sediments deposited in and close to the mouth of the Berau River and their distribution indicates that they represent a mixture of soil-derived and river in-situ produced brGDGTs. Crenarchaeol concentrations reach 700 µg g-1 TOC in sediments deposited on the outer shelf due to Thaumarchaeotal production in shelf waters. This results in a strong gradient (0.93–0.03) in the BIT index, with high values in the river mouth and low values on the shelf. The decline in the BIT index is caused by both decreasing concentrations of the brGDGTs and increasing concentrations of crenarchaeol. The BIT index shows a highly significant but non-linear relationship with d13CTOC. On the shelf, in the area not under the direct influence of the Berau River, cyclic brGDGTs become relatively dominant, most probably due to in-situ production in the alkaline pore waters of the surface sediments. The spatial heterogeneity of sources of brGDGTs on the Berau shelf complicates the use of brGDGTs as temperature proxies. Application of the global soil calibration to sedimentary mixtures of brGDGTs in the river-influenced area of the shelf results in a severe underestimation of mean annual air temperature (MAT) by 6 °C. This is due to the mixed origin of the brGDGTs, which are not only derived from soil erosion but, likely, also from riverine production, as has been observed for other river systems.Comparison of the Berau shelf other shelf systems indicates that in-situ production of brGDGTs in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca. 50–300 m. It is hypothesized that this is so because benthic in-situ production of heterotrophic brGDGT-producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf. For palaeoclimatic studies of marine shelf sediments the application of brGDGTs as proxies is severely complicated by the heterogeneity of sources of brGDGTs. Comparison of the brGDGT composition of soils with those of shelf sediments may assist in deciding if sedimentary brGDGTs are predominantly derived from soil erosion. Several methods to do so are discussed

Depth-related distribution of a key gene of the tetraether lipid biosynthetic pathway in marine Thaumarchaeota

The distribution of isoprenoid glycerol dialkyl glycerol tetraethers (GDGT) lipids synthesized by Thaumarchaeota has been shown to be temperature-dependent in world oceans. Depth-related differences in the ammonia monooxygenase (amoA) of Thaumarchaeota have led to the classification of ‘shallow’ and ‘deep water’ clusters, potentially affecting GDGT distributions. Here, we investigate if this classification is also reflected in a key gene of the thaumarchaeotal lipid biosynthetic pathway coding for geranylgeranylglyceryl phosphate (GGGP) synthase. We investigated metagenomic databases, suspended particulate matter and surface sediment of the Arabian Sea oxygen minimum zone. These revealed significant differences in amoA and GGGP synthase between ‘shallow’ and ‘deep water’ Thaumarchaeota. Intriguingly, amoA and GGGP synthase sequences of benthic Thaumarchaeota clustered with the ‘shallow water’ rather than with ‘deep water’ Thaumarchaeota. This suggests that pressure and temperature are unlikely factors that drive the differentiation, and suggests an important role of ammonia concentration that is higher in benthic and ‘shallow water’ niches. Analysis of the relative abundance of GDGTs in the Arabian Sea and in globally distributed surface sediments showed differences in GDGT distributions from subsurface to deep waters that may be explained by differences in the GGGP synthase, suggesting a genetic control on GDGT distributions

Sustainable Habitat Restoration: Fish, Farms, and Ecosystem Services

Biomass burning impacts biogeochemical cycling, vegetation dynamics and climate. However, interactions between fire, climate and vegetation are not well understood and therefore studies have attempted to reconstruct fire and vegetation history under different climatic conditions using sedimentary archives. Here we focus on levoglucosan, a thermal by-product of cellulose generated during biomass burning, and, therefore, a potential fire biomarker in the marine sedimentary archive. However, before levoglucosan can be applied as a biomass burning proxy in marine sediments, there is a need for studies on how levoglucosan is transported to the marine environment, how it is reflecting biomass burning on continents, as well as the fate of levoglucosan in the marine water column and during deposition in marine sediments. Here we present analyses of levoglucosan, using an improved Ultra High Pressure Liquid Chromatography-Electro Spray Ionization/High Resolution Mass Spectrometry (UHPLC-ESI/HRMS) method, in atmospheric particles, in particulate matter settling through the water column and in marine surface sediments on a longitudinal transect crossing the tropical North Atlantic Ocean at 12°N. Levoglucosan was detected in the atmosphere, although in low concentration, possibly due to the sampled particle size, the source area of the aerosols, or the short time interval of sampling by which large burning events may have been missed. In sinking particles in the tropical North Atlantic Ocean we find that levoglucosan deposition is influenced by a mineral ballast effect associated with marine biogenic particles, and that levoglucosan is not transported in association with mineral dust particles. Highest levoglucosan concentrations and seasonal differences in sinking particles were found close to continents and low concentrations and seasonal differences were found in the open ocean. Close to Africa, levoglucosan concentration is higher during winter, reflecting seasonal burning in northwestern Africa. However, close to South America levoglucosan concentrations appear to be affected by riverine transport from the Amazon River. In surface sediments close to South America, levoglucosan concentration is higher than in the middle of the Atlantic Ocean, implying that here the influence from the South American continent is important and perennial. Our study provides evidence that degradation of levoglucosan during settling in the marine water column is not substantial, but is substantial at the sediment–water interface. Nevertheless, levoglucosan was detected in all surface sediments throughout the tropical North Atlantic, indicating its presence in the marine sedimentary record, which reveals the potential for levoglucosan as a biomass burning proxy in marine sediments

A TEX₈₆ lake record suggests simultaneous shifts in temperature in Central Europe and Greenland during the last deglaciation

High-resolution quantitative temperature records from continents covering glacial to interglacial transitions are scarce but important for understanding the climate system. We present the first decadal resolution record of continental temperatures in Central Europe during the last deglaciation (similar to 14,60010,600cal. yrB.P.) based on the organic geochemical palaeothermometer TEX86. The TEX86-inferred temperature record from Lake Lucerne (Vierwaldstattersee, Switzerland) reveals typical oscillations during the Late Glacial Interstadial, followed by an abrupt cooling of 2 degrees C at the onset of Younger Dryas and a rapid warming of 4 degrees C at the onset of the Holocene, within less than 350years. The remarkable resemblance with the Greenland and regional stable oxygen isotope records suggests that temperature changes in continental Europe were dominated by large-scale reorganizations in the northern hemispheric climate system

数値地図データセットからの情報抽出および汎用地図ツールへの転用

We followed the abundance and distribution of ammonia-oxidizing Archaea (AOA) in the North Sea from April 2003 to February 2005 and from October 2007 to March 2008 by quantification of archaeal genes and core glycerol dibiphytanyl glycerol tetraether (GDGT) membrane lipids in suspended particulate matter, to determine whether their abundance in the North Sea is seasonal. GDGT and gene abundance increased during winters and was low during the summer. Crenarchaeol-a GDGT specific to AOA-was a major fraction of the GDGTs and varied in concert with AOA gene abundance, indicating that AOA are the predominant source of crenarchaeol. The presence of crenarchaeol-based intact polar lipids (IPLs) confirmed that the GDGTs recovered were derived from living AOA, as IPLs are rapidly degraded upon cell senescence and thus their occurrence represents living biomass more robustly than their fossil (i.e., core GDGT) counterparts. Dark incubations of North Sea water sampled during the 2007-2008 seasonal cycle with C-13-labeled bicarbonate revealed incorporation of inorganic carbon into IPL-derived GDGTs, directly showing autotrophic production of Thaumarchaeota biomass during the winter. Inhibition of C-13 uptake by nitrification inhibitors confirmed that ammonia oxidation was the main source of energy for carbon fixation. Winter blooms of planktonic AOA in the North Sea were recurrent and predictable, occurring annually between November and February, emphasizing the potential importance of AOA in nitrogen cycling in the North Sea

Nitrification and growth of autotrophic nitrifying bacteria and Thaumarchaeota in the coastal North Sea

Nitrification and the associated growth of autotrophic nitrifiers, as well as the contributions of bacteria and Thaumarchaeota to total autotrophic C-fixation by nitrifiers were investigated in the Dutch coastal North Sea from October 2007 to March 2008. Rates of nitrification were determined by incubation of water samples with ¹⁵N-ammonium and growth of autotrophic nitrifiers was measured by incubation with ¹³C-DIC (dissolved inorganic carbon) in the presence and absence of nitrification inhibitors (nitrapyrin and chlorate) in combination with compound-specific stable isotope (¹³C) analysis of bacterial and Thaumarchaeotal lipid biomarkers. Net nitrification during the sampling period was evident from the concentration dynamics of ammonium, nitrite and nitrate. Measured nitrification rates were high (41–221 nmol N L^-1 h^-1). Ammonium assimilation was always substantially lower than nitrification – with nitrification on average contributing 89% (range 73–97%) to total ammonium consumption.¹³C-DIC fixation into bacterial and Thaumarchaeotal lipids was strongly reduced by the nitrification inhibitors (27–95 %). The inhibitor-sensitive ¹³C-PLFA (phospholipid-derived fatty acid) pool was dominated by the common PLFAs 16:0, 16:1?7c and 18:1?7c throughout the whole sampling period and occasionally also included the polyunsaturated fatty acids 18:2?6c and18:3?3. ¹³C-DIC fixation activity of the nitrifying bacteria was much higher than that of the nitrifying Thaumarchaeota throughout the whole sampling period, even during the peak in Thaumarchaeotal abundance and activity. This suggests that the contribution of autotrophic Thaumarchaeota to nitrification during winter in the coastal North Sea may have been smaller than expected from their gene abundance (16S rRNA and <i>amoA</i> (ammonia monooxygenase)). These results emphasize the importance of direct measurements of the actual activity of bacteria and Thaumarchaeota, rather than abundance measurements only, in order to elucidate their biogeochemical importance. The ratio between rates of nitrification versus DIC fixation by bacterial nitrifiers was higher or even much higher than typical values for autotrophic nitrifiers, indicating that little DIC was fixed relative to the amount of energy that was generated by nitrification

Compound-specific stable isotope analysis of nitrogen-containing intact polar lipids

RATIONALE: Compound-specific isotope analysis (CSIA) of nitrogen in amino acids has proven a valuable tool in manyfields (e.g. ecology). Several intact polar lipids (IPLs) also contain nitrogen, and their nitrogen isotope ratios have thepotential to elucidate food-web interactions or metabolic pathways. Here we have developed novel methodology forthe determination of d15N values of nitrogen-containing headgroups of IPLs using gas chromatography coupled withisotope-ratio mass spectrometry. METHODS: Intact polar lipids with nitrogen-containing headgroups were hydrolyzed and the resulting compoundswere derivatized by (1) acetylation with pivaloyl chloride for compounds with amine and hydroxyl groups or(2) esterification using acidified 2-propanol followed by acetylation with pivaloyl chloride for compounds withboth carboxyl and amine groups. The d15N values of the derivatives were subsequently determined using gaschromatography/combustion/isotope-ratio mass spectrometry. RESULTS: Intact polar lipids with ethanolamine and amino acid headgroups, such as phosphatidylethanolamine andphosphatidylserine, were successfully released from the IPLs and derivatized. Using commercially available purecompounds it was established that d15N values of ethanolamine and glycine were not statistically different from theoffline-determined values. Application of the technique to microbial cultures and a microbial mat showed that themethod works well for the release and derivatization of the headgroup of phosphatidylethanolamine, a common IPLin bacteria. CONCLUSIONS: A method to enable CSIA of nitrogen of selected IPLs has been developed. The method is suitable formeasuring natural stable nitrogen isotope ratios in microbial lipids, in particular phosphatidylethanolamine, and will beespecially useful for tracing the fate of nitrogen in deliberate tracer experiments. Copyright © 2015 JohnWiley & Sons, Ltd

Occurrence and distribution of ladderane oxidation products in different oceanic regimes

Ladderane fatty acids are commonly used as biomarkers for bacteria involved in anaerobic ammonium oxidation (anammox). These lipids have been experimentally shown to undergo aerobic microbial degradation to form short chain ladderane fatty acids. However, nothing is known of the production or the distribution of these oxic biodegradation products in the natural environment. In this study, we analysed marine water column particulate matter and sediment from three different oceanic regimes for the presence of ladderane oxidation products (C-14 ladderane fatty acids) and of original ladderane fatty acids (C-18 and C-20 ladderane fatty acids). We found that ladderane oxidation products, i.e. C-14 ladderane fatty acids, are already produced within the water column of the Arabian Sea oxygen minimum zone (OMZ) and thus only low amounts of oxygen (< 3 mu M) are needed for the beta-oxidation of original ladderane fatty acids to proceed. However, no short chain ladderane fatty acids were detected in the Cariaco Basin water column, where oxygen concentrations were below detection limit, suggesting that the beta-oxidation pathway is inhibited by the absence of molecular oxygen, or that the microbes performing the degradation are not proliferating under these conditions. Comparison of distributions of ladderane fatty acids indicates that short chain ladderane fatty acids are mostly produced in the water column and at the sediment surface, before being preserved deeper in the sediments. Short chain ladderane fatty acids were abundant in Arabian Sea and Peru Margin sediments (ODP Leg 201), often in higher concentrations than the original ladderane fatty acids. In a sediment core taken from within the Arabian Sea OMZ, short chain ladderanes made up more than 90% of the total ladderanes at depths greater than 5 cm below sea floor. We also found short chain ladderanes in higher concentrations in hydrolysed sediment residues compared to those freely occurring in lipid extracts, suggesting that they had become bound to the sediment matrix. Furthermore, these matrix-bound short chain ladderanes were found at greater sediment depths than short chain ladderanes in the lipid extract, suggesting that binding to the sediment matrix aids the preservation of these lipids. Though sedimentary degradation of short chain ladderane fatty acids did occur, it appeared to be at a slower rate than that of the original ladderane fatty acids, and short chain ladderane fatty acids were found in sediments from the Late Pleistocene (similar to 100 kyr). Together these results suggest that the oxic degradation products of ladderane fatty acids may be suitable biomarkers for past anammox activity in OMZs

Tracing tetraether lipids from source to sink in the Rhône River system (NW Mediterranean)

In this study, we investigated soils and river suspended particulate matter (SPM) collected in the Rhône and its tributary basins as well as marine surface sediments taken in the Rhône prodelta (Gulf of Lions, NW Mediterranean). Thereby, we traced the signal of branched glycerol dialkyl glycerol tetraethers (brGDGTs) from the source to sink via the Rhône River and its tributaries and identified sources of brGDGTs in rivers and marine sediments. Soil pH rather than the mean annual air temperature (MAAT) explains most of the observed variances of the brGDGT distribution in our soil dataset. The observed changes in the distribution of brGDGTs in the river SPM indicate that brGDGTs brought by the river to the sea are primarily derived from the lower Rhône and its tributary soils, even though in situ production in the river itself cannot be excluded. In marine surface sediments, it appears that the input of riverine brGDGTs is the primary source of brGDGTs in the Rhône prodelta, although the brGDGT composition may be further modified by the in situ production in the marine environment. More work is required to assess fully whether brGDGTs can be used to reconstruct the terrestrial paleoenvironmental changes using marine sediment cores taken in the Rhône prodelta close to the river mouth

Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for glycerol dialkyl glycerol tetraether (GDGT)-based palaeothermometry

The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the branched vs. isoprenoidal tetratether (BIT) index, TEX86 and the MBT–CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments