Biomarker Proxies Research Articles

Neutral monosaccharides as biomarker proxies for bog-forming plants for application to palaeovegetation reconstruction in ombrotrophic peat deposits

The application of molecular approaches to palaeovegetation reconstruction in peat is still relatively rare, with molecular level studies of carbohydrate organic geochemistry being generally uncommon. In this report, neutral monosaccharides derived via acid hydrolysis were investigated in modern bog-forming plants in order to assess their potential application as biomarkers in peat palaeovegetation reconstruction. The concentrations of major neutral monosaccharides, i.e. glucose (Glu), xylose (Xyl), arabinose (Ara), galactose (Gal), mannose (Man), rhamnose (Rha) and fucose (Fuc), were determined using gas chromatography (GC) for 7 lichens, 10 Sphagnum species and 7 vascular plants collected from three ombrotrophic mires across northern Europe. Based on factor analysis of the modern plant monosaccharide compositions, two carbohydrate proxies: [(Man + Gal):(Ara + Xyl)] and % contributions of Rha and Fuc in total Glu-free monosaccharides [%(Rha + Fuc)], were selected as biomarkers for bog-forming plants. The three plant groups could be separated by [(Man + Gal):(Ara + Xyl)], which showed decreasing values following the order: lichens > Sphagna > vascular plants. The high [%(Rha + Fuc)] in Sphagna allowed their separation from lichens and vascular plants. These two factors were applied as plant group-specific indices to investigate vegetation change in a peat core from Kontolanrahka Bog, Finland. Our findings show strong correspondence with fossil plant abundances from the same core, thereby confirming the potential of carbohydrate compositional parameters as proxies for palaeovegetation reconstruction in peat bogs.

Biosynthesis of 2-methylbacteriohopanepolyols by an anoxygenic phototroph

Sedimentary 2-methyhopanes have been used as biomarker proxies for cyanobacteria, the only known bacterial clade capable of oxygenic photosynthesis and the only group of organisms found thus far to produce abundant 2-methylbacteriohopanepolyols (2-MeBHPs). Here, we report the identification of significant quantities of 2-MeBHP in two strains of the anoxygenic phototroph Rhodopseudomonas palustris. Biosynthesis of 2-MeBHP can occur in the absence of O(2), deriving the C-2 methyl group from methionine. The relative abundance of 2-MeBHP varies considerably with culture conditions, ranging from 13.3% of total bacteriohopanepolyol (BHP) to trace levels of methylation. Analysis of intact BHPs reveals the presence of methylated bacteriohopane-32,33,34,35-tetrol but no detectable methylation of 35-aminobacteriohopane-32,33,34-triol. Our results demonstrate that an anoxygenic photoautotroph is capable of generating 2-MeBHPs and show that the potential origins of sedimentary 2-methylhopanoids are more diverse than previously thought.

Lipid biomarkers in suspended particles from a subtropical estuary: Assessment of seasonal changes in sources and transport of organic matter

Temporal and spatial variations in the composition of particulate organic matter (POM) from Florida Bay, USA were examined. The predominance of short-chain homologues for n-alkanes, n-alcohols and n-fatty acids as well as relatively high abundance of C(27) and C(28) sterols suggested that an autochthonous/marine source of OM was dominant bay-wide. Several biomarker proxies such as P(aq) [(C(23)+C(25))/(C(23)+C(25)+C(29)+C(31)) n-alkanes], short/long chain n-alkanes, (C(29)+C(31)) n-alkanes and taraxerol indicated a spatial shift in OM sources, where terrestrial OM rapidly decreased while seagrass and microbial OM markedly increased along a northeastern to southwestern transect. Regarding seasonal variations, POM collected during the dry season was enriched in terrestrial constituents relative to the wet season, likely as a result of reduced primary productivity of planktonic species and seagrasses during the dry season. Principal component analysis (PCA) classified the sample set into sub-groups based on PC1 which seemed to be spatially controlled by OM origin (terrestrial-mangrove vs. marine-planktonic/seagrass). The PC2 seemed to be more seasonally controlled suggesting that hydrological fluctuations and seasonal primary productivity are the drivers controlling the POM composition in Florida Bay.

Caesarean derivation and fostering of rat pups in a pre- and post-natal study with a long-acting non-steroidal anti-inflammatory agent

Following a period of unusually strong winds and high seas in the spring of 2014, a blanket peat bog formerly covered by a beach comprised of fine sand and large rocks was uncovered at a coastal site in Spiddal, Co. Galway, Ireland. The surface of the bog was littered with standing tree stumps, the remnants of a Holocene forest that had succumbed to a relatively sudden drowning. A combination of inorganic and organic geochemical techniques was applied to determine the cause of this rapid submersion and to glean palaeoclimatic information from the preserved record within the peat. The study represents the first use of a multiproxy lipid biomarker approach to investigate palaeoclimate conditions from a peat bog in Ireland. The results provide evidence of climatic variation throughout a ca. 3400 yr timeframe during the mid-Holocene. Biomarker proxies displaying the relative contribution of Sphagnum spp. vs. higher plants were used to show changes in precipitation and temperature during peat formation. The data correlate with described events, including the 4.2 ka event and the Subboreal-Subatlantic transition and show the benefit of a lipid biomarker method for investigating Ireland’s peatland resources. In particular, the indication of colder/wetter conditions coinciding with the 4.2 ka event implies the possibility that its effects were felt in Ireland, contrary to some reports. The results suggest that a combination of warm and dry conditions followed by a rapid rise in sea level led to the growth and subsequent drowning of the ancient forest landscape.

Radionuclide and biomarker proxies of past ocean circulation and productivity in the Arabian Sea

We present new excess 231Pa/230Th activity ratios and lipid biomarker results from northeastern Arabian Sea sediments (core 93KL) spanning the past 50 ka in an effort to constrain further the relationship between climate at low and high latitudes. 231Pa/230Th activity ratios are maintained at values significantly higher than the water‐column production ratio of 0.093. Average 231Pa/230Th activity ratios are lower during the last glacial period than during the Holocene. The lowest 231Pa/230Th activity ratios coincide with the timing of Heinrich Events 1–5. Profiles of lipid biomarker fluxes and 231Pa/230Th activity ratios from 32 to 12 ka show similar patterns, suggesting that 231Pa is more efficiently scavenged relative to 230Th at times when diatoms make up a proportionally larger part of the primary biomass signal. In the Holocene, high 231Pa/230Th activity ratios may indicate enhanced 231Pa export from the southern to the northern Indian Ocean via intensified thermohaline circulation.

Molecular biomarker record of sea surface temperature and climatic change in the South China Sea during the last 140,000 years

The δ 18O and δ 18C isotopic composition of Globigerinoides ruber, the concentration of C 37 alkenones, n-nonacosane and n-hexacosan-1-ol and the populations of coccolith species in core 17961-2 have been used to characterize the climatic changes which occurred in the South China Sea (SCS) during the last climatic cycle. The relative composition of di- and triunsaturated C 37 alkenones, the U 37 K index, has been used to estimate the variation in sea surface temperatures. The concentrations of the terrigenous markers n-nonacosane and n-hexacosan-1-ol have allowed to infer changes in continental water dynamics during the glacial and interglacial times. The stratigraphic record of these compounds has shown that the influence of continental waters (i.e., the Molengraaff River) and restricted water circulation in SCS gave rise to a marginal system of higher but slower response to climatic change. Both in terminations I and II, the change from glacial to interglacial conditions involves a considerable reduction of continental water input into this semi-enclosed system. The high resolution study of the biomarker proxies in Termination I has shown that the SST increase lagged about 2.3 ky the δ 18O isotopic decrease of Cibicidoides wuellerstorfi. Probably, the SST increase corresponds to the period of the Sunda Shelf inundation onset.

97/04496 DTA and TG studies of Paleocene bituminous rocks from EI lusr oil deposit—Egypt: Markova, K. et al. J. Therm. Anal., 1997, 48, (2), 331–341

The Sylhet Basin of Bangladesh is a sub-basin of the Bengal Basin. It contains a very thick (up to 22 km) Tertiary stratigraphic succession consisting mainly of sandstones and mudstones. The Sylhet succession is divided into the Jaintia (Paleocene–late Eocene), Barail (late Eocene–early Miocene), Surma (middle–late Miocene), Tipam (late Miocene–Pliocene) and Dupitila Groups (Pliocene–Pleistocene), in ascending order. The origin of the organic matter (OM) and paleoenvironment of deposition have been evaluated on the basis of C, N, S elemental analysis, Rock-Eval pyrolysis and gas chromatography–mass spectrometry (GC–MS) analysis of 60 mudstone samples collected from drill core and surface outcrops. Total organic carbon (TOC) content ranges from 0.11% to 1.56%. Sulfur content is low in most samples. TOC content in the Sylhet succession varies systematically with sedimentation rate, with low TOC caused by clastic dilution produced by high sedimentation rates arising from rapid uplift and erosion of the Himalaya.The OM in the succession is characterized by systematic variations in pristane/phytane (Pr/Ph), oleanane/C30 hopane, n-C29/n-C19 alkane, Tm/Ts [17α(H)-22,29,30-trisnorhopane/18α(H)-22,29,30-trisnorhopane] and sterane C29/(C27 + C28 + C29) ratios during the middle Eocene to Pleistocene. Based on biomarker proxies, the depositional environment of the Sylhet succession can be divided into three phases. In the first (middle Eocene to early Miocene), deposition occurred completely in seawater-dominated oxic conditions, with abundant input of terrestrial higher plants, including angiosperms. The second phase (middle to late Miocene) consisted of mainly freshwater anoxic conditions along with a small seawater influence according to eustasic sea level change, with diluted OM derived from phytoplankton and a lesser influence from terrestrial higher plants. Oxygen-poor freshwater conditions prevailed in the third phase (post-late Miocene). Planktonic OM was relatively abundant in this stage, while a high angiosperm influx prevailed at times. Tmax values of ca. 450 °C, vitrinite reflectance (Ro) of ca. 0.66% and methylphenanthrene index (MPI 3) of ca. 1 indicate the OM to be mature. The lower part (middle Eocene to early Miocene) of the succession with moderate TOC content and predominantly terrestrial OM could have generated some condensates and oils in and around the study area.

Faunal and alkenone reconstructions of subtropical North Atlantic surface hydrography and paleotemperature over the last 28 kyr

Two techniques for estimating past variations in sea surface temperature (SST) have been used to investigate climatic change in Biogeochemical Oceanic Flux Study (BOFS) core 31K (19°N, 20°W) from the eastern subtropical Atlantic. High‐resolution SST records for the last 28 kyr have been produced using planktonic foraminiferal assemblages, based on the Imbrie‐Kipp transfer function technique, and the UK′37 index derived from abundances of C37 alkenones biosynthesized by prymnesiophyte algae. Modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean: the UK′37 index corresponds to the temperature at the time of maximum coccolith productivity, typically late spring‐early summer in the study area today, whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures. In general, the faunal and biomarker paleotemperature records display comparable SST variations during the last glacial and deglacial, but although the overall trends are similar, differences exist in the magnitude and timing of these temperature changes. Most notably, the faunal Twarm and UK′37 SST estimates diverge by 3°C between 8 ka and 6 ka, and this offset persists through the late Holocene. This difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels. We therefore propose that the deviation in SST estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring‐early summer in the modern ocean. Our results suggest that a dual approach to SST estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late Quaternary.