Bulk δ13C Values Research Articles

Carbon isotopic ratios of modern C3–C4 plants from the Gangetic Plain, India and its implications to paleovegetational reconstruction

For the first time, carbon isotope ratios (δ13C) of plants and occluded carbon in phytoliths were analyzed from three locations of the middle (26.5°N, 80.3°E) and lower (22.3°N, 87.3°E and 22.9°N, 88.5°E) Gangetic Plain, India. The bulk δ13C values of C3 plants range from −32.6 to −19.2‰ with an average of −29.6±1.9‰ (n=76, 1σ) and for C4 plants values range from −16.6 to −10.4‰, averaging at −12.7±1.4‰ (n=45, 1σ). The measured average δ13C value of C3 plants is lower than globally reported dataset. Comparison of average δ13C values of C3 plants with mean annual precipitation (MAP) of the three locations show that lowering in δ13C value with increase in MAP. However, for C4 plants, increase in MAP resulted in higher δ13C values. These observations are similar with the earlier findings that the δ13C values in C3 plants are controlled by stomatal conductance and for C4 plants leakiness of carbon from bundle sheath cell played important role. The average δ13C value of C3 plants from the modern Gangetic Plain is lower compared to the observed δ13C value (~−26‰) of bulk soil organic matter (SOM) derived from contemporary C3 plants in the lower and middle Siwalik (ancestral Gangeitc plain). The enriched value in Siwalik SOM likely indicates contribution from C4 plants. This implies early appearance (at 11Ma) of C4 plants compared to previously reported timing. The δ13C values of occluded carbon in C3-derived phytoliths range from −33.9 to −24.5‰ with an average of −29.0±2.6‰ (n=26, 1σ) and that for C4-derived phytoliths range from −30.7 to −21.4‰, averaging at −26.1±2.6‰ (n=12, 1σ). Organic carbon (OC) concentrations in C3-phytoliths vary from 0.1 to 6.1%, averaging at 1.1±1.3% (n=26, 1σ) and in C4-phytoliths 0.1 to 3.8% with an average value of 1.1±1.4% (n=12, 1σ). Being protected from degradation, selective plantation with high OC in phytoliths will enhance terrestrial carbon sequestration.

Inferring Phytoplankton, Terrestrial Plant and Bacteria Bulk δ¹³C Values from Compound Specific Analyses of Lipids and Fatty Acids.

Stable isotope mixing models in aquatic ecology require δ13C values for food web end members such as phytoplankton and bacteria, however it is rarely possible to measure these directly. Hence there is a critical need for improved methods for estimating the δ13C ratios of phytoplankton, bacteria and terrestrial detritus from within mixed seston. We determined the δ13C values of lipids, phospholipids and biomarker fatty acids and used these to calculate isotopic differences compared to the whole-cell δ13C values for eight phytoplankton classes, five bacterial taxa, and three types of terrestrial organic matter (two trees and one grass). The lipid content was higher amongst the phytoplankton (9.5±4.0%) than bacteria (7.3±0.8%) or terrestrial matter (3.9±1.7%). Our measurements revealed that the δ13C values of lipids followed phylogenetic classification among phytoplankton (78.2% of variance was explained by class), bacteria and terrestrial matter, and there was a strong correlation between the δ13C values of total lipids, phospholipids and individual fatty acids. Amongst the phytoplankton, the isotopic difference between biomarker fatty acids and bulk biomass averaged -10.7±1.1‰ for Chlorophyceae and Cyanophyceae, and -6.1±1.7‰ for Cryptophyceae, Chrysophyceae and Diatomophyceae. For heterotrophic bacteria and for type I and type II methane-oxidizing bacteria our results showed a -1.3±1.3‰, -8.0±4.4‰, and -3.4±1.4‰ δ13C difference, respectively, between biomarker fatty acids and bulk biomass. For terrestrial matter the isotopic difference averaged -6.6±1.2‰. Based on these results, the δ13C values of total lipids and biomarker fatty acids can be used to determine the δ13C values of bulk phytoplankton, bacteria or terrestrial matter with ± 1.4‰ uncertainty (i.e., the pooled SD of the isotopic difference for all samples). We conclude that when compound-specific stable isotope analyses become more widely available, the determination of δ13C values for selected biomarker fatty acids coupled with established isotopic differences, offers a promising way to determine taxa-specific bulk δ13C values for the phytoplankton, bacteria, and terrestrial detritus embedded within mixed seston.

Application of sulfur and carbon isotopes to oil–source rock correlation: A case study from the Tazhong area, Tarim Basin, China

Up until now, it has been assumed that oil in the Palaeozoic reservoirs of the Tazhong Uplift was derived from Upper Ordovician source rocks. Oils recently produced from the Middle and Lower Cambrian in wells ZS1 and ZS5 provide clues concerning the source rocks of the oils in the Tazhong Uplift, Tarim Basin, China. For this study, molecular composition, bulk and individual n-alkane δ13C and individual alkyl-dibenzothiophene δ34S values were determined for the potential source rocks and for oils from Cambrian and Ordovician reservoirs to determine the sources of the oils and to address whether δ13C and δ34S values can be used effectively for oil–source rock correlation purposes. The ZS1 and ZS5 Cambrian oils, and six other oils from Ordovician reservoirs, were not significantly altered by TSR. The ZS1 oils and most of the other oils, have a “V” shape in the distribution of C27–C29 steranes, bulk and individual n-alkane δ13C values predominantly between −31‰ to −35‰ VPDB, and bulk and individual alkyldibenzothiophene δ34S values between 15‰ to 23‰ VCDT. These characteristics are similar to those for some Cambrian source rocks with kerogen δ13C values between −34.1‰ and −35.3‰ and δ34S values between 10.4‰ and 21.6‰. The oil produced from the Lower Ordovician in well YM2 has similar features to the ZS1 Cambrian oils. These new lines of evidence indicate that most of the oils in the Tazhong Uplift, contrary to previous interpretations, were probably derived from the Cambrian source rocks, and not from the Upper Ordovician. Conversely, the δ13C and δ34S values of ZS1C Cambrian oils have been shown to shift to more positive values due to thermochemical sulfate reduction (TSR). Thus, δ13C and δ34S values can be used as effective tools to demonstrate oil–source rock correlation, but only because there has been little or no TSR in this part of the section.

Sources of organic matter in the sediments of Baoxiang river reservoir, Dianchi watershed

Baoxiang river reservoir, a semi-natural water body, is characteristised by eutrophication, which is significantly harmful to regional human health and sustainable development. The sediments are sources and sinks of nutrients. In addition to providing important habitats for aquatic organisms, sediments play a significant role in determining the overall environmental quality of a watershed. Organic carbon in sediments plays an important role in release and transformation of aquatic pollutants, which is one of the main causes of eutrophication. In this study,profiles of TOC, C/N ratio, δ13C and grain sizes in the sediments of Baoxiang river reservoir, Dianchi watershed were used to demonstrate the sources and change of sedimentary organic matter and explore reservoir eutrophication sensitivity to human activities.Considering the characteristics of topography and human activities of the study area, with the help of GPS(Global Positioning System), two reservoir bottom sediments(A and B) profiles were collected during dry period. Our results showed that the sources of sedimentary organic matter were different in the different sampling locations. C/N ratios in the sediment A varied from 2.93 to 11.73, with bulk δ13C(‰) values ranging from-23.66‰ to-21.78‰. This indicated that organic matters mainly from aquatic organisms and terrestrial input contributed little to the sedimentary organic matters. The concentrations of organic matters were influenced significantly by the grain sizes. The concentrations of sedimentary organic matters and total nitrogen in the sediment B varied from 14.62 to 24.93 g ·kg-1, and 2.11 to 3.3 g·kg1, respectively,higher than that of the sediment A, and with bulk δ13C(‰) values of-28.36‰ to-26.36‰.The grain sizes were mainly composed of clay and silt. This demonstrated that organic matters in the sediment B came mainly from terrestrial input, which is an indication of the main effect of human activities, not the sediment grain size.Based on the volume percentage of sediment in each size fraction, we found that grain size in the sediment A is classified as thick, indicating poor sorting and strong water movement. The sediment B is characteristized with fine particles, with clay and fine sand as the main components and low water flow. Correlation analysis between sediment grain size and organic carbon contents showed that they were highly correlated in the sediment A. Synchronous change was found in mean sediment grain size and precipitation.

Seasonal dynamics of zooplankton resource use revealed by carbon amino acid stable isotope values

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 531:143-154 (2015) - DOI: https://doi.org/10.3354/meps11319 Seasonal dynamics of zooplankton resource use revealed by carbon amino acid stable isotope values Jens M. Nielsen*, Monika Winder Department of Ecology, Environment and Plant Sciences, Stockholm University, 106 91 Stockholm, Sweden *Corresponding author: jens.nielsen@su.se ABSTRACT: Reliable tracer techniques are fundamental to retrieving accurate information on consumer dietary resource use in dynamic ecosystems. Analysis of δ13C values in essential amino acids has shown great promise in effectively capturing consumer food sources, since essential amino acids are not synthesized by heterotrophic organisms but instead routed directly from dietary sources to consumers, resulting in negligible 13C trophic discrimination. We assessed seasonal feeding patterns of a widespread key copepod species (Acartia spp.) in the northern Baltic proper using complementary approaches: bulk δ13C and δ15N values, δ13C values of essential amino acids, and quantitative phytoplankton taxonomic data. Our results showed distinct differences between Acartia and seston δ13C essential amino acid values measured at weekly to monthly sampling intervals, which indicated that Acartia preferentially utilized specific dietary resources that comprised only parts of the total phytoplankton composition (varying from 19.7% to 81.4% during the season). Results also indicated that care should be taken when inferring trophic position from bulk stable isotopes when consumers are highly selective, since isotope values of seston may not accurately reflect consumer specific diet resource uptake. Analysis of δ13C values in essential amino acids was shown to be a promising tool to accurately trace consumer resource use in complex natural systems. KEY WORDS: Stable isotopes · Amino acids · Acartia · Zooplankton · Phytoplankton · Food webs Full text in pdf format PreviousNextCite this article as: Nielsen JM, Winder M (2015) Seasonal dynamics of zooplankton resource use revealed by carbon amino acid stable isotope values. Mar Ecol Prog Ser 531:143-154. https://doi.org/10.3354/meps11319 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 531. Online publication date: July 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Reconstructing δ13C isoscapes of phytoplankton production in a coastal upwelling system with amino acid isotope values of littoral mussels

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 504:59-72 (2014) - DOI: https://doi.org/10.3354/meps10746 Reconstructing δ13C isoscapes of phytoplankton production in a coastal upwelling system with amino acid isotope values of littoral mussels Natasha L. Vokhshoori1,*, Thomas Larsen2, Matthew D. McCarthy1,* 1University of California, Santa Cruz, Ocean Sciences Department, 1156 High Street, Santa Cruz, California 95060, USA 2Christian-Albrechts University of Kiel, Leibniz-Laboratory for Radiometric Dating and Stable Isotope Research, Max-Eyth-Str. 11-13, 24118 Kiel, Germany *Corresponding authors: nvokhsho@ucsc.edu;mdmccar@ucsc.edu ABSTRACT: Compound-specific isotope analysis of amino acids (CSI-AA) is increasingly used to decouple trophic isotopic effects from isotopic composition at the base of food webs. The δ13C values of essential amino acids (EAAs) are particularly useful as recorders of primary production, because animals cannot synthesize EAAs de novo, so diagnostic biosynthetic δ13CEAA patterns remain unchanged up food chains. To test the potential for δ13CAA values to identify C source and resource flow in complex littoral ecosystems, we measured bulk and δ13CAA values of Mytilus californianus adductor muscle tissue in samples spanning >1700 km of coastline from San Diego, California, to southern Oregon, USA. The average bulk δ13C value for the entire region clustered around a relatively constant value (-15.7 ± 0.9‰), with no latitudinal trend (R2 = 0.022). δ13CAA patterns were highly consistent in all mussels, and δ13CEAA patterns closely matched expectations for marine phytoplankton, supporting the hypothesis that consumer EAA isotope values are unchanged from primary production. While bulk δ13C values were ambiguous in terms of source, application of a multivariate δ13CEAA ‘fingerprinting’ approach clearly indicated microalgae as the major source for all mussel EAAs. We hypothesize that integrated δ13C values of coastal phytoplankton production can therefore be directly derived from δ13CEAA of filter feeders in coastal regions. A correction derived from literature data for phytoplankton δ13CEAA values yielded reasonable δ13C values for coastal production, supporting this idea. Together, our results suggest δ13CEAA as a new approach for constructing baseline δ13C isoscapes and may have important implications for ecosystem studies in both modern and paleo-environments. KEY WORDS: Mytilus californianus · Carbon isotopes · Compound-specific isotope analysis · California · Isoscape Full text in pdf format Supplementary material PreviousNextCite this article as: Vokhshoori NL, Larsen T, McCarthy MD (2014) Reconstructing δ13C isoscapes of phytoplankton production in a coastal upwelling system with amino acid isotope values of littoral mussels. Mar Ecol Prog Ser 504:59-72. https://doi.org/10.3354/meps10746 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 504. Online publication date: May 14, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Spatial segregation and similar trophic-level diet among eastern Canadian Arctic/north-west Atlantic killer whales inferred from bulk and compound specific isotopic analysis

Killer whales in the Eastern Canadian Arctic (ECA) prey on narwhal, beluga, bowhead whales and seals, while further south in the north-west Atlantic (NWA), killer whales off the coast of Newfoundland and Labrador prey on both marine mammals and fish. Bulk and amino acid (AA) specific isotopic composition of dentinal collagen in teeth of 13 ECA/NWA killer whales were analysed to assess the degree, if any, of dietary specialization of killer whales across the region. Dentine was sampled from within annual growth layer groups (GLGs) to construct chronological profiles of stable nitrogen (δ15N) and carbon (δ13C) isotopic compositions for individual whales spanning 3–25 years. Interannual isotopic variation across GLGs was less than that among individuals, and median bulk δ15N values differed by up to 5‰ among individuals. Significant correlation between bulk δ15N values and baseline (source AA) δ15N values indicates much of the observed isotopic variation among individuals reflects foraging within isotopically distinct food webs, rather than diet differences. This interpretation is supported by consistent differences in bulk δ13C values between the two individuals with lowest source AA δ15N values and the remaining whales. After accounting for baseline isotopic variation, comparable δ15N values among individuals indicates similar trophic-level diet, although uncertainties in relative trophic15N enrichment of individual AAs currently limits trophic position estimates for top consumers. Further research is required to clarify seasonal movement patterns and possible diet shifts of ECA/NWA killer whales to better define their role in marine ecosystems across the region.

Tracing carbon sources through aquatic and terrestrial food webs using amino acid stable isotope fingerprinting.

Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring δ13C patterns among amino acids (δ13CAA) could distinguish between multiple aquatic and terrestrial primary production sources. We found that δ13CAA patterns in contrast to bulk δ13C values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their δ13CAA patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk δ13C values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer δ13C patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs.

Evaluation of the rhenium–osmium geochronometer in the Phosphoria petroleum system, Bighorn Basin of Wyoming and Montana, USA

Rhenium–osmium (Re–Os) geochronometry is applied to crude oils derived from the Permian Phosphoria Formation of the Bighorn Basin in Wyoming and Montana to determine whether the radiogenic age reflects the timing of petroleum generation, timing of migration, age of the source rock, or the timing of thermochemical sulfate reduction (TSR). The oils selected for this study are interpreted to be derived from the Meade Peak Phosphatic Shale and Retort Phosphatic Shale Members of the Phosphoria Formation based on oil–oil and oil–source rock correlations utilizing bulk properties, elemental composition, δ13C and δ34S values, and biomarker distributions. The δ34S values of the oils range from −6.2‰ to +5.7‰, with oils heavier than −2‰ interpreted to be indicative of TSR. The Re and Os isotope data of the Phosphoria oils plot in two general trends: (1) the main trend (n=15 oils) yielding a Triassic age (239±43Ma) with an initial 187Os/188Os value of 0.85±0.42 and a mean square weighted deviation (MSWD) of 1596, and (2) the Torchlight trend (n=4 oils) yielding a Miocene age (9.24±0.39Ma) with an initial 187Os/188Os value of 1.88±0.01 and a MSWD of 0.05. The scatter (high MSWD) in the main-trend regression is due, in part, to TSR in reservoirs along the eastern margin of the basin. Excluding oils that have experienced TSR, the regression is significantly improved, yielding an age of 211±21Ma with a MSWD of 148. This revised age is consistent with some studies that have proposed Late Triassic as the beginning of Phosphoria oil generation and migration, and does not seem to reflect the source rock age (Permian) or the timing of re-migration (Late Cretaceous to Eocene) associated with the Laramide orogeny. The low precision of the revised regression (±21Ma) is not unexpected for this oil family given the long duration of generation from a large geographic area of mature Phosphoria source rock, and the possible range in the initial 187Os/188Os values of the Meade Peak and Retort source units. Effects of re-migration may have contributed to the scatter, but thermal cracking and biodegradation likely have had minimal or no effect on the main-trend regression. The four Phosphoria-sourced oils from Torchlight and Lamb fields yield a precise Miocene age Re–Os isochron that may reflect the end of TSR in the reservoir due to cooling below a threshold temperature in the last 10m.y. from uplift and erosion of overlying rocks.The mechanism for the formation of a Re–Os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process. Bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer, and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187Re/188Os values from an oil family.

Stable isotopes of organics and inorganics, clay mineralogy and chemical environment of an Aptian lacustrine succession in northeastern Brazil

Abstract The studied Aptian lacustrine succession of the continental Jatobá Rift Basin varies mainly between pure carbonates (predominantly laminated limestones), marls and shales, with some intercalations of presumably deltaic sandstone complexes. In accordance with geochemical data, the occurrence of dolomite indicates intensive microbial activity in a stratified water column with slightly enhanced salinity. Petrographic data prove mild weathering conditions. Aggregates of authigenic smectite observed in sandstones, probably representing transformed volcanogenic glass particles, strongly indicate explosive volcanic activity. Occasionally occurring dolomite seems to have been formed due to intensive microbial activity under moderately increased salinity conditions. Potential hydrocarbon source rocks containing Type I organic matter (OM) were deposited during various phases of the Aptian. Enhanced biological productivity is indicated by bulk organic geochemical data (C org , hydrogen index, extraction yield) and δ 13 C values of carbonates within peletoidal and laminated limestone layers. Carbon-isotope ratios of carbonates argue for OM cycling and remineralization. High δ 18 O values of carbonates are attributed to periods of lower lake levels. A major contribution of aquatic organisms (green algae, microalgae, zooplankton) and minor input from macrophytes and land plants to OM accumulation is indicated by n -alkane distributions, steroid composition and δ 13 C values of individual biomarkers. Microbial communities included heterotrophic bacteria and cyanobacteria, as well as purple and green sulphur bacteria. The sediments were deposited in an alkaline palaeolake. Highly reducing (saline) bottom water conditions and a stratified water column existed during OM accumulation of the Crato Formation. This is indicated by low pristane/phytane, gammacerane index, and the presence of β-carotane and aryl isoprenoids. Differences in OM composition and stable isotope data reflect the evolution of the basin from a stratified saline lake to a freshwater environment with limited potential for OM preservation.

Pottery wall thinning as a consequence of increased maize processing: a case study from central New York

The histories of maize in northeastern North America are not well understood at the subregional level. The complexity of formation processes for various lines of evidence for maize use requires the application of many analytical methods and techniques to produce data on subregional maize histories. The present analysis uses bulk δ13C values on directly dated charred encrusted cooking residues to provide the first direct correlation of water-based maize cooking to trends in pottery wall thinning. The results add to the growing body of evidence for the history of maize use in central New York.

Can amino acid carbon isotope ratios distinguish primary producers in a mangrove ecosystem?

The relative contribution of carbon from terrestrial vs. marine primary producers to mangrove-based food webs can be challenging to resolve with bulk carbon isotope ratios (δ(13)C). In this study we explore whether patterns of δ(13)C values among amino acids (AAs) can provide an additional tool for resolving terrestrial and marine origins of carbon. Amino acid carbon isotope ratios (δ(13)C(AA)) were measured for several terrestrial and marine primary producers in a mangrove ecosystem at Spanish Lookout Caye (SLC), Belize, using gas chromatography-combustion-isotope ratio mass spectrometry. The δ(13)C values of essential amino acids (δ(13)C(EAA)) were measured to determine whether they could be used to differentiate terrestrial and marine producers using linear discriminant analysis. Marine and terrestrial producers had distinct patterns of δ(13)C(EAA) values in addition to their differences in bulk δ(13)C values. Microbial mat samples and consumers (Crassostrea rhizophorae, Aratus pisonii, Littoraria sp., Lutjanus griseus) were most similar to marine producers. Patterns of δ(13)C(EAA) values for terrestrial producers were very similar to those described for other terrestrial plants. The findings suggest that δ(13)C(EAA) values may provide another tool for estimating the contribution of terrestrial and marine sources to detrital foodwebs. Preliminary analyses of consumers indicate significant use of aquatic resources, consistent with other studies of mangrove foodwebs.

Signature of organic matter exported from naturally Fe-fertilised oceanic waters

Biomarker distributions and organic carbon and nitrogen isotopic signatures of organic matter (OM) produced in surface waters around the Crozet Plateau (Southern Ocean) are significantly different between a Fe-fertilised region (north) and a high nutrient low chlorophyll region (HNLC, south). If these OM signatures are exported to and preserved in surface sediments, they could potentially be used as palaeo-proxies for identifying Fe-fertilisation events in the past. Here, we assess the alteration of the OM signature through the water column and at the sediment–water interface by comparing organic signatures in surface waters, sediment traps and surface sediments. Our results suggest that there is significant degradation of OM during transport to the sea floor, which causes reduced fluxes of biomarkers to sediments north and east of the Crozet Plateau. Sterols, alkenones and C27 and C29 12-hydroxymethyl alkanoates, and C28 1,14-diols appear to be less labile than total organic carbon (TOC), except to the north, where alkenones and sterols are more rapidly degraded than TOC. Sedimentary bulk and compound specific δ13C values also reflect surface water productivity patterns, with elevated values occurring in sediments underlying the Fe-fertilised waters. In contrast, δ15N values appear to be strongly biased by degradation and grazing during export and burial. Thus, only some of the differences observed in surface waters between the Fe- fertilised and HNLC areas are exported to deep waters and preserved in the sedimentary record, suggesting that caution is required in the application of these proxies to studies of ocean palaeoproductivity.

Zooplankton, lipids and stable isotopes: importance of seasonal, latitudinal, and taxonomic differences

We found considerable seasonal, latitudinal, and taxonomic differences in zooplankton lipid content and concurrent δ13C values of zooplankton. We collected cladoceran as well as cyclopoid and calanoid copepod zooplankton from boreal and subarctic lakes throughout a year, allowing us to study zooplankton likely subjected to different isotopic fractionation processes and with highly variable lipid contents. Considerable seasonal variation was observed in the difference between bulk and lipid-extracted zooplankton δ13C values, indicating that seasonally changing lipid content introduced notable variation in zooplankton δ13C values. The difference between bulk and lipid-extracted material was most amplified in lipid-rich subarctic zooplankton in winter, δ13C difference being >5 units. Significant differences were also observed among zooplankton taxa, with copepods showing a greater lipid impact on δ13C than cladocerans. Published lipid correction models failed to produce satisfying fits to our data, and considerable variation was left even after recalibrating the model parameters. This was likely due to taxonomic differences in lipid effects on δ13C values. We therefore produced separate mass balance-based lipid correction models for cladocerans and also cyclopoid and calanoid copepods. We conclude that arithmetic lipid correction models perform well with zooplankton samples, but taxonomic differences need to be considered.

Last glacial climate variations on the tropical Leizhou Peninsula, South China

Two cores were recovered from raised peat bogs on the tropical northern Leizhou Peninsula, south China. Multiple sediment variables including organic matter (OM) content, the stable carbon isotope signature of OM, low-frequency magnetic susceptibility and degree of humification, indicate that the regional paleoclimate played an important role in determining the nature of peat that accumulated. Based on comparison with other climate proxies, the bulk peat δ13C record was interpreted as an indicator of variation in the East Asian (EA) summer monsoon, and to a lesser extent, the Indian summer monsoon, during the last glacial period between ~49 and 10 cal ka BP. More negative bulk δ13C values reflect wetter and warmer conditions, and thus a strong EA summer monsoon. More positive values indicate drier and cooler conditions. A warm and wet period occurred between ~46 and 28 cal ka BP, implying a strengthening of the EA summer monsoon. A climate shift occurred at ~22 cal ka BP and the driest and coldest period appeared between ~19 and 16 cal ka BP, suggesting weakening of the EA summer monsoon. After ~12 cal ka BP, climate shifted towards wetter and warmer conditions again. It has been suggested that variations in orbitally induced solar insolation played a role in the last glacial climate of the study region. Several millennial—scale arid and cold phases characterized by C4 plants, or by more positive δ13C values during periods when C3 plants dominated, show agreement with the Greenland GISP2 ice core and the Chinese stalagmite records. Interactions between high northern latitude cold air advection and summer moisture transported across the tropical ocean, and the migration of the mean position of the Intertropical Convergence Zone (ITCZ) would have favored these millennial–scale phases. Additionally, changes in heat transport to the North Atlantic would also have influenced climate in the region.

Nitrogen and carbon isotope values of individual amino acids: a tool to study foraging ecology of penguins in the Southern Ocean

We determined the δ15N and δ13C values of individual amino acids (AAs) isolated from chick blood of four penguin species that forage in different oceanic regions (from the subtropics of the Indian Ocean to Antarctica) to test if (1) the δ15N values of phenylalanine (δ15Nphe) revealed different foraging areas among the species, (2) the difference between glutamic acid and phenylalanine δ15N values (Δδ15Nglu-phe) accurately predicted trophic levels (TL), and (3) the δ13C value of AAs could resolve species foraging locations, as bulk δ13C values did. The δ13C values of all AAs decreased with latitude, were positively correlated with bulk δ13C data, and therefore, tracked the isotopic baseline. However, we were not able to discern additional ecological information from these δ13C values. In contrast, the δ15N analysis of individual AAs in blood distinguished the isotopic value of the nitrogen at the base of the food web from the trophic level of the consumer, providing new insight for the study of the trophic ecology of seabirds. The difference in the bulk δ15N values of northern and southern rockhopper penguins was due to both a difference in their foraging location (≠δ15Nphe) and their trophic levels (≠Δδ15Nglu-phe). The δ15Nphe values of king and Adelie penguins were higher than those from rockhoppers and we hypothesize that this difference reflects foraging on mesopelagic prey and in the highly productive Antarctic shelf waters respectively. The Δδ15Nglu-phe accurately reflected relative penguin's TL but further work is required to determine the trophic enrichment factors for compound-specific isotope analysis.

Sequestration and turnover of bacterial‐ and fungal‐derived carbon in a temperate grassland soil under long‐term elevated atmospheric pCO2

AbstractTemperate grasslands contribute about 20% to the global C budget. Elevation of atmospheric CO2 concentration (pCO2) could lead to additional C sequestration into these ecosystems. Microbial‐derived C in the soil comprising about 1–5% of total soil organic carbon may be an important ‘pool’ for long‐term storage of C under future increased atmospheric CO2 concentrations. In our study, the impact of elevated pCO2 on bacterial‐ and fungal‐derived C in the soil of Lolium perenne pastures was investigated under free air carbon dioxide enrichment (FACE) conditions. For 7 years, L. perenne swards were exposed to ambient and elevated pCO2 (36 and 60 Pa pCO2, respectively). The additional CO2 in the FACE plots was depleted in 13C compared with ambient plots, so that ‘new’ (<7 years) C inputs in the form of microbial‐derived residues could be determined by means of stable C isotope analysis. Amino sugars in soil are reliable organic biomarkers for indicating the presence of microbial‐derived residues, with particular amino sugars indicative of either bacterial or fungal origin. It is assumed that amino sugars are stabilized to a significant extent in soil, and so may play an important role in long‐term C storage. In our study, we were also able to discriminate between ‘old’ (> 7 years) and ‘new’ microbial‐derived C using compound‐specific δ13C analysis of individual amino sugars. This new tool was very useful in investigating the potential for C storage in microbial‐derived residues and the turnover of this C in soil under increased atmospheric pCO2.The 13C signature of individual amino sugars varied between −17.4‰ and −39.6‰, and was up to 11.5% depleted in 13C in the FACE plots when compared with the bulk δ13C value of the native C3 L. perenne soil. New amino sugars in the bulk soil contributed up to 16% to the overall amino sugar pool after the first year and between 62% and 125% after 7 years of exposure to elevated pCO2. Amounts of new glucosamine increased by the greatest amount (16–125%) during the experiment, followed by mannosamine (−9% to 107%), muramic acid (−11% to 97%), and galactosamine (15–62%). Proportions of new amino sugars in particle size fractions varied between 38% for muramic acid in the clay fraction and 100% for glucosamine and galactosamine in the coarse sand fraction.Summarizing, during the 7‐year period, amino sugars constituted only between 0.9% and 1.6% of the total SOC content. Therefore, their absolute significance for long‐term C sequestration is limited. Additionally new amino sugars were only sequestered in the silt fraction upon elevated pCO2 exposure while amino sugar concentrations in the clay fraction decreased. Overall, amino sugar concentrations in bulk soil did not change significantly upon exposure to elevated pCO2. The calculated mean residence time of amino sugars was surprisingly low varying between 6 and 90 years in the bulk soil, and between 3 and 30 years in the particle size fractions, representing soil organic matter pools with different but relatively low turnover times. Therefore, compound‐specific δ13C analysis of individual amino sugars clearly revealed a high amino sugar turnover despite more or less constant amino sugar concentrations over a 7 years period of exposure to elevated pCO2.

Carbon stable isotope composition of DNA isolated from an incipient paleosol

Research Article| May 01, 2006 Carbon stable isotope composition of DNA isolated from an incipient paleosol A. Hope Jahren; A. Hope Jahren 1Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA Search for other works by this author on: GSW Google Scholar Kellie Kelm; Kellie Kelm 2Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA Search for other works by this author on: GSW Google Scholar Beverly Wendland; Beverly Wendland 2Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA Search for other works by this author on: GSW Google Scholar Gitte Petersen; Gitte Petersen 3Botanical Institute, Department of Evolutionary Botany, University of Copenhagen, Gothersgade 140,DK-1123 Copenhagen K, Denmark Search for other works by this author on: GSW Google Scholar Ole Seberg Ole Seberg 3Botanical Institute, Department of Evolutionary Botany, University of Copenhagen, Gothersgade 140,DK-1123 Copenhagen K, Denmark Search for other works by this author on: GSW Google Scholar Author and Article Information A. Hope Jahren 1Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA Kellie Kelm 2Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA Beverly Wendland 2Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA Gitte Petersen 3Botanical Institute, Department of Evolutionary Botany, University of Copenhagen, Gothersgade 140,DK-1123 Copenhagen K, Denmark Ole Seberg 3Botanical Institute, Department of Evolutionary Botany, University of Copenhagen, Gothersgade 140,DK-1123 Copenhagen K, Denmark Publisher: Geological Society of America Received: 21 Nov 2005 Revision Received: 21 Dec 2005 Accepted: 22 Dec 2005 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2006) 34 (5): 381–384. https://doi.org/10.1130/G22408.1 Article history Received: 21 Nov 2005 Revision Received: 21 Dec 2005 Accepted: 22 Dec 2005 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. Hope Jahren, Kellie Kelm, Beverly Wendland, Gitte Petersen, Ole Seberg; Carbon stable isotope composition of DNA isolated from an incipient paleosol. Geology 2006;; 34 (5): 381–384. doi: https://doi.org/10.1130/G22408.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We determined the carbon isotope (δ13C) value of double-stranded DNA (dsDNA) isolated from the organic horizons of a Delaware soil that is actively being covered by an encroaching sand dune. The soil belongs to a Nymphaea odorata Ait. (water lily) wetland, and we regard its active acquisition of a thick (∼24 cm) surface mantle to embody the process of paleopedogenesis; therefore, we have termed it an “incipient paleosol.” In this study, we compared the δ13C value of paleosol dsDNA to the bulk δ13C value of N. odorata, as well as to the δ13C value of plants that had colonized the surface mantle. The isotopic offset between paleosol δ13CdsDNA and N. odorata δ13Ctissue was identical to the relationship between δ13CdsDNA and δ13Ctissue for tracheophytes, which we had previously determined. In contrast, the isotopic offset between paleosol δ13CdsDNA and the δ13Ctissue of plants colonizing the surface mantle differed from this relationship by as much as 4‰. Similarly, the δ13C value of bulk paleosol organic matter was extremely heterogeneous and varied across 6‰. All paleosol DNA polymerase chain reaction (PCR) products produced clear, sharp, 350 base-pair (bp) fragments of rbcL, a gene shared by all photosynthetic organisms. These results open the exciting possibility that stable isotope analysis of dsDNA isolated from paleosol organic matter can be used to infer the δ13C value of the plant that dominated the nucleic acid contribution. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quantification of dung carbon incorporation in a temperate grassland soil following spring application using bulk stable carbon isotope determinations

Herbivore dung constitutes a substantial input of C to temperate grassland soils, and its fate must be determined in order to fully understand nutrient cycling in this ecosystem. This experiment used changes in bulk δ13C values of the 0–1 cm and 1–5 cm soil horizons of a dung-treated temperate grassland soil to approximate percentage applied dung C incorporation over 372 days. Natural abundance 13C-labelled C4 dung (δ13C − 12.6‰) and C3 dung (δ13C − 31.3‰) were produced in a monitored diet switch from ryegrass silage (δ13C − 30.1‰) to maize silage (δ13C − 11.6‰). The dung was applied to a C3 grassland (δ13C 0–1 cm − 29.9‰, 1–5 cm − 30.6‰), and dung remains and soil cores from beneath the treatments were sampled at intervals. δ13C values were used to estimate a maximum of 12% applied dung C incorporation in the top 5 cm of the soil after 112 days, which declined to around 8% at the end of the experiment. A significant increase in percentage applied dung C was observed in the top 1 cm of soil, compared with the 1–5 cm horizon, after a substantial rain event after 30 days. However, results of forage fibre analyses of the two dung types revealed significant differences in composition which may affect subsequent calculations of percentage dung incorporation based on bulk δ13C values.

Spatial and temporal shifts in stable isotope values of the bottom-dwelling shrimp Nauticaris marionis at the sub-Antarctic archipelago

Spatial and temporal dynamics of carbon and nitrogen stable isotope signatures of the bottom-dwelling caridean shrimp Nauticaris marionis were measured during April and May between 1984 and 2000 in the vicinity of Marion Island (the Prince Edward Islands, Southern Ocean). There was one trophic-level enrichment in bulk δ15N and δ13C signatures between small ( 20 mm) specimens of N. marionis, suggesting distinct trophic differentiation among major shrimp size groups. Both δ15N and δ13C values of N. marionis increased with the depth, reflecting changes in their diet. There were no clear temporal trends in bulk δ15N signatures of N. marionis. However, compound-specific δ15N measurements of amino acids indicated that N. marionis from the inter-island realm occupied the trophic level of second order carnivores, while similarly sized shrimps in the near-shore realm were at the trophic level of first order carnivores. Compound-specific measurements also identified a change in the source of inorganic nitrogen at the base of the food web between the inter-island and near-shore realms. In contrast to the bulk δ15N values, a significant shift in bulk δ13C values of N. marionis was observed between 1984 and more recent years. This temporal change appears to be linked to changes in the overall productivity of the Prince Edward Island inter-island system, which could be linked to global climate change.