Increase In δ13C Values Research Articles

Degradation changes stable carbon isotope depth profiles in palsa peatlands

Abstract. Palsa peatlands are a significant carbon pool in the global carbon cycle and are projected to change by global warming due to accelerated permafrost thaw. Our aim was to use stable carbon isotopes as indicators of palsa degradation. Depth profiles of stable carbon isotopes generally reflect organic matter dynamics in soils with an increase of δ13C values during aerobic decomposition and stable or decreasing δ13C values with depth during anaerobic decomposition. Stable carbon isotope depth profiles of undisturbed and degraded sites of hummocks as well as hollows at three palsa peatlands in northern Sweden were used to investigate the degradation processes. The depth patterns of stable isotopes clearly differ between intact and degraded hummocks at all sites. Erosion and cryoturbation at the degraded sites significantly changes the stable carbon isotope depth profiles. At the intact hummocks the uplifting of peat material by permafrost is indicated by a turning in the δ13C depth trend, and this assessment is supported by a change in the C / N ratios. For hollows isotope patterns were less clear, but some hollows and degraded hollows in the palsa peatlands show differences in their stable carbon isotope depth profiles indicating enhanced degradation rates. We conclude that the degradation of palsa peatlands by accelerated permafrost thawing can be identified with stable carbon isotope depth profiles. At intact hummocks δ13C depth patterns display the uplifting of peat material by a change in peat decomposition processes.

Determination of δ13C and δ15N and trophic fractionation in jellyfish: implications for food web ecology

Application of stable isotope analysis (SIA) in jellyfish allows definition of trophic patterns not detectable using gut content analysis alone, but analytical protocols require standardization to avoid bias in interpreting isotopic data. We determined δ13C and δ15N in Aurelia sp. from the northern Gulf of Mexico (30°00′N, 89°00′W–30°24′N, 88°00′W) to define differences in stable isotope composition between body parts and whole body, the effect of lipid extraction on δ13C in tissues, and fractionation values from medusa to prey. The isotopic composition of bell and whole Aurelia sp. was not different. The increase in δ13C values after lipid removal suggested a correction is needed. To aid future analyses, we derived a correction equation from empirical data for jellyfish samples. Laboratory feeding experiments indicated medusae increased +4 ‰ in δ13C and +0.1 ‰ in δ15N compared to their diet. These results suggest protocols commonly applied for other species may be inaccurate to define Aurelia sp. trophic ecology. Because Aurelia spp. are commonly found in marine ecosystems, accurately defining their trophic role by use of SIA has implications for understanding marine food webs worldwide.

Large13C/12C and small15N/14N isotope fractionation in an experimental detrital foodweb (litter–fungi–collembolans)

AbstractCorrectly estimating the trophic fractionation factors (Δ15N and Δ13C) in controlled laboratory conditions is essential for the application of stable isotope analysis in studies on the trophic structure of soil communities. Laboratory experiments usually suggest large15N/14N and small13C/12C trophic fractionation, but in field studies litter‐dwelling microarthropods and other invertebrates are consistently enriched in13C relative to plant litter. In the present study, we report data from two laboratory experiments investigating both fungi–collembolans and litter–fungi–collembolans systems. In the fungi–collembolans system, Δ15N and Δ13C averaged 1.4 ± 0.1 and 1.0 ± 0.2 ‰, respectively. In microcosms with fungi‐inoculated litter, the difference in δ15N between collembolans and plant litter averaged 1.5 ± 0.2 ‰, confirming the relatively small15N/14N trophic fractionation at the basal level of detrital foodwebs reported in numerous field studies. In full agreement with field observations, the difference in δ13C between bulk litter and collembolans in laboratory microcosms averaged 3.6 ± 0.1 ‰ and only little depended on collembolan species identities or the presence of water‐soluble compounds in the litter. We conclude that increased δ13C values typical of litter‐dwelling decomposers are largely determined by an increased13C content in saprotrophic microorganisms.

Rapid Accumulation of Soil Carbon and Nitrogen in a Prairie Restoration Chronosequence

Understanding patterns of soil C and N accumulation in restored prairies is necessary to determine the sequestration potential of these systems. Estimates of C and N accumulation following prairie restoration are generally based on chronosequence studies. However, few studies have compared a chronosequence approach to direct measures of accumulation over time. Restored prairies in the Cowling Arboretum of Carleton College, Northfield, MN, were established annually from 1995 to 2007. In 2000 and 2010–2011, prairies were sampled for soil %C and %N and soil bulk density, allowing for a comparison of the effects of prairie age using a chronosequence approach to direct measures of C and N accumulation rates. Soil C and N content increased in all restorations, although there was no effect of field age across the chronosequence on C or N pools. However, rates of soil C and N accumulation decreased with restoration age, suggesting a rapid increase in the years immediately following agricultural conversion. This rapid accumulation was likely due to the turnover of annual and biennial species that dominated plant cover in the early in succession. This suggestion was supported by an observed increase in δ¹³C values with increasing prairie age. Thus, contributions from early successional species may result in rapid recovery of soil pools following restoration from agriculture. Direct measures of soil C and N accumulation may be necessary when initial variability among sites limit the ability of a chronosequence approach to detect significant changes in soil C and N content over short time periods.

Interpretation of Late Quaternary climate and landscape variability based upon buried soil macro- and micromorphology, geochemistry, and stable isotopes of soil organic matter, Owl Creek, central Texas, USA

Small-basin floodplain buried soils formed in association with low-order tributary streams are valuable archives of past climates, but have not been studied extensively in central Texas, USA. Four buried soils exposed along Owl Creek, within the larger Brazos River drainage basin, were examined using soil morphology and micromorphology, optically stimulated luminescence (OSL) dating, soil characterization, whole-soil geochemical and stable isotope analyses of soil organic matter and pedogenic carbonate. These buried soils provide a record of changes in paleoecological and paleo-alluvial conditions spanning ~14ky. Morphological and geochemical differences between buried soils reflect changes in landscape attributable to climate, with a distinct 5‰ increase in δ13C values of soil organic matter corresponding to the Holocene onset and drier conditions. Paleoecological reconstructions coupled with depth to Bk suggest possible amounts of erosion of ~1m for each of the buried soils. Compilation of the proxies presented shows evidence for a cooler and wetter late Pleistocene climate, followed by a warmer and drier climate dominating during the Holocene.

Stable isotopes of carbon dioxide in the marine atmosphere along a hemispheric course from China to Antarctica

During the 24th Chinese Antarctic Expedition, the air samples were collected at 10:00 and 22:00 (local time) along the track of ship “Xuelong” from Shanghai Harbor, China to Antarctica. Carbon dioxide (CO2) concentrations and its isotopic compositions were measured in these samples. Mean CO2 concentration at 22:00 (419.4 ± 27.1 ppmv) was higher than that at 10:00 (392.7 ± 20.0 ppmv), whereas δ13C–CO2 values at 22:00 (−8.58 ± 0.47‰) were lower than those at 10:00 (−8.23 ± 0.49‰), indicating that the 13C/12C ratio might be associated with the photosynthesis and respiration of terrestrial or marine organisms during the diurnal cycle. Overall the mean δ13C– and δ18O–CO2 were −8.39 ± 0.51‰ and 0.03 ± 1.39‰, respectively, from 30°N to 69°S, and the δ13C significantly negatively correlated with δ18O–CO2. A small but progressive increase in δ13C values with increasing latitudes southward was in good agreement with the expected trend. The enhanced CO2 concentrations occurred in the atmosphere close to Eurasia continent, Philippines, Malaysia and Indonesia, and the δ13C oscillations agreed well with anthropogenic pollution. In the range of 30°S–50°S, CO2 concentrations were generally low with relatively stable δ13C and δ18O values. In Antarctic Convergence Zone, a great difference of δ13C occurred between 10:00 and 22:00, and atmospheric CO2 was significantly depleted in 13C at 22:00. Our results indicated that the isotopic compositions of CO2 in the marine atmosphere might be a sensitive indicator for the strength of CO2 source and sink from the ocean.

Carbon cycle and sea-water palaeotemperature evolution at the Middle–Late Jurassic transition, eastern Paris Basin (France)

A very high-resolution carbon and oxygen stable isotope analysis (bulk-carbonate) of a biostratigraphically well-constrained Callovian–Oxfordian series is provided here for the first time. The homogeneity of the clayey series and the weak diagenetic alteration allow the isotopic signal variations to be considered as primary in origin. A prominent and brief negative excursion in the δ13C curve (−2‰), occurring at the start of the Middle Callovian (Jason Zone – Obductum Subzone) and correlated regionally, suggests a possible methane release. The increasing δ13C values thereafter up to the Early Oxfordian, concomitant with a warming episode, highlight the burial of carbon in organic-rich layers which, in return, may have triggered a decrease in atmospheric pCO2. At higher frequencies, observed fluctuations of the δ13C and δ18O values are orbitally driven (405-kyr and 100-kyr eccentricity cycles) and may correspond to the salinity and temperature variability recorded in sea water. The δ18O isotopic measurements from well-preserved diagenetically screened belemnites and bivalves along the series, compared to available data from Tethyan domains, agree with the scenario of a global cooling at the Middle-Late Jurassic transition. The well-dated δ18O isotopic curve suggests that the onset of this cooling event occurred at the end of the Coronatum Zone (Middle Callovian).

Atmospheric CO2 concentrations and δ13C values during 2011–2012 voyage: Mediterranean, Atlantic Ocean, southern Indian Ocean and New Zealand to Antarctica

During the 2011–2012 hemispheric voyage of the M/V Italica from Italy to the Atlantic Ocean, southern Indian Ocean, New Zealand and Antarctica, atmospheric CO2 concentrations were continuously recorded and 52 air samples collected in 4-L Pyrex flasks for the measurement of the δ13C of atmospheric CO2. In the case of CO2 concentrations, new data include the following: 1) in the Adriatic, between Ravenna and Otranto, CO2 was never measured in order to avoid the expected heavy contribution from industrial plants; the 2011 measurements fully confirm this contribution; 2) in the Atlantic, along the Moroccan coast, high values of up to 415 ppmv were recorded, apparently due to considerable industrial development in Morocco; 3) minor CO2 concentrations were also recorded along other sections of the African coast north of the Equator, whereas relatively low constant values were recorded south of the Equator; 4) in the southern Indian Ocean, CO2 concentrations were measured almost along a parallel, yielding homogeneous values not much higher than the mean values recorded at NOAA stations in nearby areas. With only one exception, the δ13C values were systematically less negative than −9‰ (VPDB), the mean values for the three oceanic sections being the following: Atlantic Ocean −8.64 ± 0.20‰; Indian Ocean −8.54 ± 0.06‰; New Zealand to Antarctica −8.49 ± 0.02‰. A small but progressive increase in δ13C values with increasing latitude was in good agreement with the expected trend. The homogeneity of such values between New Zealand and Antarctica was remarkable, as these samples had been collected in particularly rough oceanic conditions with high winds. In spite of these particular environmental conditions these values were very close to those of samples collected in the same area in 2009 and 2010 in conditions of calm sea and low wind. This similarity contrasts sharply with the theory and models of air-sea gas exchange.

Subordinate plant species enhance community resistance against drought in semi‐natural grasslands

Summary According to the insurance hypothesis, more diverse plant communities are more likely to be resistant to drought. Whilst many experiments have been carried out to determine the effects of plant diversity on plant community insurance, the results are still contradictory. Here, we conducted a drought experiment where we tested whether the presence of subordinate species increases plant community insurance. In Swiss Jura grassland, we combined a removal experiment of subordinate species with a summer drought event using rainout shelters. Plant community composition was determined after the drought and based on biomass measurements; we estimated resistance, recovery and resilience of the plant community for each combination of treatments. Moreover, to assess drought impacts on water‐use efficiency (WUE), we analysed carbon isotope ratios (δ13C values) in plant leaves of two dominants and two subordinates collected at the end of the drought period. We showed that subordinate species are more resistant to drought and increased community resistance by enhancing their above‐ground biomass production during the imposed drought. These patterns were associated with decreased competitiveness of dominant species whose biomass decreased during drought. Significant increase in δ13C values in plant tissue under drought indicated a better WUE for the measured species. Interestingly, the WUE was significantly higher in plots where subordinates were removed. Recovery and resilience were not affected by the summer drought, but the absence of subordinates reduced overall above‐ground biomass in both watered and drought plots. Synthesis. We demonstrated that, independent of plant diversity, the presence of drought‐resistant subordinate species increases plant community insurance against drought and, hence, is important for the functioning of grassland ecosystems.

Depositional facies and geochemistry of the Kangan formation in the South Pars Field, Persian Gulf (Iran)

The Kangan Formation is one of the largest carbonate reservoirs located in the South Pars Field, which is one of the major gas fields in the central basin of the Persian Gulf. Facies analyses indicate that the Kangan carbonates are formed in four microfacies belts: tidal flat, lagoon, shoal, and shallow open marine, in a platform ramp environment. The predominance of tidal flat sediments along with the oolitic shoal facies and lack of a large shoal reef indicate a homoclinal-ramp system. Major and minor elements and carbon and oxygen isotope values were used to determine the original carbonate mineralogy of the Kangan Formation. The data indicate aragonite carbonate mineralogy in a closed diagenetic system. The Kangan Formation displays a gradual upward increase in δ13C values and variation in δ18O with changing lithologies. Palaeotemperature calculation, based on the heaviest δ18O values in limestone micrites and dolomicrites, range from 36 to 44 °C, respectively. The isotopic compositions of the Kangan carbonates indicate that they were deposited in shallow tropical waters. Stratigraphic analysis indicates four major transgressive and regressive events of nearly two million years’ average duration, which controlled the development of two depositional sequences and their systems tracts.

Lipid extraction effects on stable isotope values (δ13C and δ15N) of elasmobranch muscle tissue

Given the known effect of lipid content on δ13C values and the potential effect of urea on δ15N values, examining the effects of lipid extraction, which can potentially extract both, is of particular importance for elasmobranch isotope ecology. Through analysing paired δ13C, total %C, δ15N, total %N and C:N values of non-lipid extracted (BULK) and lipid extracted (LE) muscle samples from twenty-one elasmobranch species, we assessed whether lipid extraction was required: (i) to remove lipids given reported low lipid content and, (ii) to determine if δ15N values were affected and whether this relates to the retention of isotopically light urea by elasmobranchs. The mean (±SD) δ13C values of eight out of twenty-one species significantly increased following lipid extraction with two species, the Greenland (Somniosus microcephalus) and whale (Rhincodon typus) shark, showing a marked increase (5.0±0.4‰ and 3.3‰, respectively). The mean (±SD) and maximum increase in δ13C values were 0.6±1.2‰ and 5.9‰, respectively. For δ15N data, thirteen species showed a significant increase following lipid extraction and a concomitant reduction in total percent nitrogen (%N). The C:N ratio for these species also increased from unexpectedly low values of <3.0 to ~3.0, the value expected for pure protein. The mean and maximum observed increase in δ15N values were 0.6±0.6‰ and 2.3‰, respectively. There was no effect of increasing animal size on δ13C and δ15N difference (LE–BULK) for the two species examined. Field sampled animals (sampled immediately upon capture in the marine environment) showed a greater δ15N difference than animals sampled in the laboratory (sampled several hours after capture in the marine environment) (1.0±0.5‰ and 0.4±0.4‰ respectively), while estuarine sampled animals (sampled immediately) showed the smallest difference (0.1±0.6‰). The δ13C data demonstrate that lipid extraction is required to remove lipids from elasmobranch muscle tissue given both intra- and inter- species variability. In addition, the increase in δ15N values, decrease in %N and increase in C:N ratio indicate that lipid extraction is removing soluble urea. Given lower δ15N diet-tissue discrimination factors for large marine predators, removal of urea is required to elucidate accurate trophic position estimates and relative food web position of elasmobranchs and for diet reconstruction. It is recommended that investigators undertake lipid extraction trials on elasmobranch muscle tissue to determine effects on δ13C and δ15N values on a species-by-species basis.

The Toarcian in the Subbetic basin (southern Spain): Bio-events (ammonite and calcareous nannofossils) and carbon-isotope stratigraphy

A detailed carbon-isotope stratigraphic study for the uppermost Pliensbachian‒lowermost Aalenian interval in the Median Subbetic palaeogeographic domain (External zones of the Betic Cordillera, southern Spain) has been carried out. During the Early Jurassic, the Median Subbetic, which represents a typical basin of the Hispanic Corridor connecting the Tethys and the Eastern Pacific, was located in the westernmost Tethys. The analyzed sections encompass the entire Toarcian stage as represented in the southern Iberian palaeomargin. Rocks are mainly rhythmic sequences of grey marls and marly limestones containing a rich ammonite fauna, nannofossils, and benthic foraminifers—all these provide an accurate biostratigraphic control. The lower and upper Toarcian boundaries are well represented in some of these sections and therefore represent optimal sites to link the carbon-isotope curves to ammonite zones, and to nannofossil events. δ13C values of bulk carbonates from the different localities of the Subbetic basin have similar variations from the uppermost Pliensbachian to the lowermost Aalenian, suggesting changes in the original DIC carbon isotope composition along the Hispanic corridor. The transition from Pliensbachian to Toarcian is marked by increasing δ13C values from ~1.2 to 2.0‰, interrupted in the Serpentinum Zone by a negative shift concomitant with the Toarcian oceanic anoxic event (T-OAE), with the major ammonite extinction event of the Toarcian, and an important turnover of calcareous nannoplankton. The negative shift observed in the Serpentinum Zone confirms the global perturbation of the carbon cycling documented along the Tethys and the palaeo-Pacific in organic material and in marine carbonates. However, the amplitude of the negative excursion (~ −1. 5‰) is not compatible with an isotopic homogeneous seawater DIC and/or CO2 atmospheric reservoirs. The interval from the middle to the top of the Toarcian δ13C shows relatively constant values, minor ammonite turnovers, and is associated with increasing diversity of calcareous nannoplankton.

New primary resource increases predation on a pest in a banana agroecosystem

Primary resources may affect the structure of species assemblages in upper trophic levels of food webs. These bottom‐up effects may involve important ecological processes that affect pest control. For example, population densities of natural enemies may increase when alternative preys are favoured by a new resource. Ants, particularly Solenopsis geminata Forel (Myrmicinae), are recognized as effective predators of herbivores eggs. In the present study, we tested the hypothesis that the addition of a primary resource in a banana agroecosystem will increase pest control of the banana weevil Cosmopolites sordidus Germar (Coleoptera, Curculionidae) by ants. Using stable isotope analyses, we showed that S. geminata used the new resource pathway provided by the addition of a cover crop. This change was revealed by increased δ13C values (13C/12C) in a cover crop treatment (C4 plant) compared with a banana (C3 plant) in bare soil treatment. We also showed that the abundance of S. geminata, as measured with pitfall traps, was 4.8–5.4‐fold higher in the cover crop treatment than in the bare soil treatment. Estimation of egg predation rates was in the range 7.8–70.3%, which occurred in plots with the lowest and highest S. geminata numbers, respectively. The addition of a new primary resource in this system changed the origin of the carbon consumed by predators and increased their densities. The increased ant abundance resulted in increased predation of weevil eggs, which was consistent with our hypothesis. These results will be useful for the design of cropping systems that enhance the biological regulation of pests.

Benthic resources are the key to Daphnia middendorffiana survival in a high arctic pond

Summary1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a 13C‐enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton.2. The cladoceran Daphnia middendorffiana responded to the 13C‐enrichment of benthic mats with progressively increasing δ13C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter.3. Daily net production by phytoplankton in the pond (18 mg C m−2 day−1) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C m−2 day−1), whereas benthic primary production alone (145 mg C m−2 day−1) was more than sufficient.4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient‐limited high arctic ponds.

Drought at erosion edges selects for a ‘hidden’ keystone species

Background: The presence of plants is crucial in securing steep slopes against soil erosion. Inappropriate land use in mountains often leads to vegetation loss and thus soil degradation. Aims: Here we ask if the edges of large erosion gullies select for specialist plant species that reduce or prevent the progression of soil loss. Methods: We quantified species presence and abundance across micro-transects from intact mountain pastures toward the edge of erosion gullies at ca. 1900 m elevation in the Central Caucasus, Georgia. Results: Out of a large species pool, one particular species, Festuca valesiaca, was the dominant species at the very edge of erosion gullies. Increased δ13C values in Festuca valesiaca leaves by 1.1‰ towards the edge confirmed that this species copes best with the dry conditions at the edge. Conclusion: Our findings illustrate the insurance effect of a highly diverse vegetation. The importance of a single species out of this diverse species suite to sustain key ecosystem functions becomes apparent only under extreme environmental conditions; in this case, at edges of erosion gullies.

Late Holocene paleoceanography and climate variability over the Mackenzie Slope (Beaufort Sea, Canadian Arctic)

Late Holocene paleoceanography and climate variability of the Southeastern Beaufort Sea (Canadian Arctic) have been investigated on the basis of sedimentary cores collected over the Mackenzie Slope. Piston, trigger and box cores were sampled at station 803 in 2004 aboard the CCGS Amundsen at 218m water depth. The chronology of the piston core is constrained by 4 AMS-14C dates, as the sedimentation rate in the box core is assessed from 210Pb data. We obtain a continuous composite sequence covering the last 4600years, with a sedimentation rate of ~140cm.kyr−1. Transfer functions (modern analogue technique) based on dinoflagellate cyst (dinocyst) assemblages were used to reconstruct the evolution of sea-surface conditions over the time period covered by the cores.Palynological data reveal that dinocyst assemblages are dominated by Operculodinium centrocarpum sensu lato (mean of 43.3%) throughout the core, with the accompanying taxa Brigantedinium spp. (19.6%), Islandinium minutum (15.6%) and cysts of Pentapharsodinium dalei (13.7%). Four zones have been established on the basis of dinocyst relative abundances. Dinocyst assemblage zone 1 (D1), from 4600 to 2700cal years BP, is dominated by O. centrocarpum (mean of 49.0%). In zone D2 (2700–1500cal years BP), the relative abundances of O. centrocarpum decrease (34.4%) in favour of the opportunistic, heterotrophic taxa Brigantedinium spp. (28.8%) and cysts of Polykrikos sp. var. arctic/quadratus (2.8%). Dinocyst zone D3 (1500–30cal years BP or 450–1920AD) is characterised by the high relative abundance of the peridinioid taxa I. minutum (19.9%). The last zone (D4), spanning from 1920 to 2004AD, is again dominated by O. centrocarpum (44.5%), and shows low relative abundances of Brigantedinium spp. and cf. Echinidinium karaense.Quantitative reconstructions of past sea-surface parameters (August sea-surface temperature: SST, August sea-surface salinity: SSS, and duration of sea-ice cover) indicate relatively stable conditions over the last 4.6kyr, with episodic cooling events (SST of ~1.5°C below the modern value of 6°C) that took place between 700 and 1820AD. We associate the last and the longest of these cooling events (1560–1820AD) with the Little Ice Age. Reconstructed SSS shows decadal oscillations since 1920AD that we tentatively associate with the accumulation of freshwater by the Beaufort Gyre and the subsequent Great Salinity Anomalies. Our data suggest that similar salinity anomalies could have occurred ca. 1860 and 1790AD.Stable isotopic data show a slight increase in δ13C values (from ~−27.1‰ at the base to ~−25.8‰ at the top) over the last 4.6kyr that we associate with the gradual increase in atmospheric CO2 concentration as recorded by Antarctic ice cores. Variations in the δ15N profile suggest variations in Pacific water influence from 4600 to ~1300cal years BP, associated with centennial scale shifts of the Arctic Oscillation phases.

Isotopic fractionation between seawater and the shell of Scrobicularia plana (Bivalvia) and its application for age validation

This study analyzed the isotopic profiles of four aragonitic shells of Scrobicularia plana in conjunction with measured seawater temperatures and salinities. Comparison of δ18OSHELL with expected values revealed fractionation of δ18O in near equilibrium with the ambient environment. Growth cessation occurred between November and March. Carbonate deposition stopped when temperatures were <12°C. Analysis of δ13CSHELL values suggested that carbon in the shell does not reflect the DIC in ambient water, likely due to the incorporation of metabolic carbon. An ontogenetic trend of increasing δ13C values over time was observed, likely related to changes in metabolic activity. Annual growth patterns were inferred from δ18OSHELL profiles and compared with internal and external growth lines. Estimations of age based on external lines were unreliable, resulting in overestimation of age and underestimation of growth rates, likely due to the disturbance lines being wrongly identified as annual. Analysis of internal lines may lead to over- or underestimation of age and was more reliable in recent portions of the shell.

Nitrogen and Water Uptake on Sloping Lands of Thailand

Cultivation in the tropical mountainous regions by using hedgerow systems as erosion control measures is recommended due to its effectiveness in reducing soil erosion and in supplying N. However, competition for nutrients and water between crops and hedges reduces crop performance and yield response. 13C stable isotope signature in combination with data on N and water availability and uptake in soil and plants framework was used to assess whether N or water function as a main driving force for spatial variability of crop yield along the alleys. The leaf δ13C values of maize were significantly (p&lt;0.05) less depleted close to the hedges, suggesting that water stress was not the main driving force for spatial variability along the alleys. In the opposite, significant (p&lt;0.05) N concentration depleted in maize leaf of plot with L. Leucocephala hedges, in particular at the row closed to hedgerow, in combination with significant (p&lt;0.05) increase in δ13C values of leaf of the corresponding plot indicating the influence of N stress on poor maize performance and yield decrease. In addition, the significant (p&lt;0.05) negative correlation between leaf δ13C values of maize, leaf N concentration and yield confirmed that N plays as a major role in crop decline towards hedgerows. Therefore, increasing amount of N fertilization to cropped area close to the hedgerows should be recommended for farmers, in order to encourage the acceptance of hedges system in tropical mountainous regions.

Stable carbon isotopic compositions of total carbon, dicarboxylic acids and glyoxylic acid in the tropical Indian aerosols: Implications for sources and photochemical processing of organic aerosols

[1] The tropical Indian aerosols (PM10) collected on day- and nighttime bases in winter and summer, 2007 from Chennai (13.04°N; 80.17°E) were studied for stable carbon isotopic compositions (δ13C) of total carbon (TC), individual dicarboxylic acids (C2-C9) and glyoxylic acid (ωC2). δ13C values of TC ranged from −23.9‰ to −25.9‰ (−25.0 ± 0.6‰; n = 49). Oxalic (C2) (−17.1 ± 2.5‰), malonic (C3) (−20.8 ± 1.8‰), succinic (C4) (−22.5 ± 1.5‰) and adipic (C6) (−20.6 ± 4.1‰) acids and ωC2 acid (−22.4 ± 5.5‰) were found to be more enriched with 13C compared to TC. In contrast, suberic (C8) (−29.4 ± 1.8‰), phthalic (Ph) (−30.1 ± 3.5‰) and azelaic (C9) (−28.4 ± 5.8‰) acids showed smaller δ13C values than TC. Based on comparisons of δ13C values of TC in Chennai aerosols to those (−24.7 ± 2.2‰) found in unburned cow-dung samples collected from Chennai and isotopic signatures of the particles emitted from point sources, we found that biofuel/biomass burning are the major sources of carbonaceous aerosols in South and Southeast Asia. The decrease in δ13C values of C9 diacid by about 5‰ from winter to summer suggests that tropical plant emissions also significantly contribute to organic aerosol in this region. Significant increase in δ13C values from C4 to C2 diacids in Chennai aerosols could be attributed for their photochemical processing in the tropical atmosphere during long-range transport from source regions.

DYNAMICS OF A PALEOECOSYSTEM REEF ASSOCIATED WITH OCEANIC CHANGE IN CARBONATE SEDIMENTARY REGIME AND CARBON CYCLING (OXFORDIAN, SWISS JURA)

Abstract Herein we report an analysis of an Oxfordian (Upper Jurassic) paleoreef located in the Swiss Jura Mountains. The paleoreef is located in a Middle Oxfordian transitional interval in which sedimentation switched from marl-dominated to carbonate-dominated deposits. The paleoecosystem is composed of four successive fossil communities characterized by microsolenid corals and organisms that specialized in suspension feeding. Carbon isotopes measured from echinoid spine carbonates exhibit a positive trend from ∼1.0‰ to 2.5‰ in δ13C values from the base to the top of the paleoreef. Comparison of δ13C curves with organic matter and belemnites shows different patterns not compatible with a global variation of the carbon cycle. Similar fossil assemblages and stratigraphic sequences identical in age are found along the continental margin of the Tethys–Atlantic Ocean. This biolithostratigraphic succession corresponds to increasing δ13C values of marine and biogenic carbonates, to the transition from marl-domi...