Improving accuracy and precision of ice core δD(CH4) analyses using methane pre-pyrolysis and hydrogen post-pyrolysis trapping and subsequent chromatographic separation

Firn and polar ice cores offer the only direct palaeoatmospheric archive. Analyses of past greenhouse gas concentrations and their isotopic compositions in air bubbles in the ice can help to constrain changes in global biogeochemical cycles in the past. For the analysis of the hydrogen isotopic composition of methane (δD(CH4) or δ2H(CH4)) 0.5 to 1.5 kg of ice was hitherto used. Here we present a method to improve precision and reduce the sample amount for δD(CH4) measurements in (ice core) air. Pre-concentrated methane is focused in front of a high temperature oven (pre-pyrolysis trapping), and molecular hydrogen formed by pyrolysis is trapped afterwards (post-pyrolysis trapping), both on a carbon-PLOT capillary at −196 °C. Argon, oxygen, nitrogen, carbon monoxide, unpyrolysed methane and krypton are trapped together with H2 and must be separated using a second short, cooled chromatographic column to ensure accurate results. Pre- and post-pyrolysis trapping largely removes the isotopic fractionation induced during chromatographic separation and results in a narrow peak in the mass spectrometer. Air standards can be measured with a precision better than 1‰. For polar ice samples from glacial periods, we estimate a precision of 2.3‰ for 350 g of ice (or roughly 30 mL – at standard temperature and pressure (STP) – of air) with 350 ppb of methane. This corresponds to recent tropospheric air samples (about 1900 ppb CH4) of about 6 mL (STP) or about 500 pmol of pure CH4.

Climate change impacts on tree species, forest properties, and ecosystem services

– Swiss forests experience strong impacts under the CH2011 scenarios, partly even for the low greenhouse gas scenario RCP3PD. Negative impacts prevail in low-elevation forests, whereas mostly positive impacts are expected in high-elevation forests. – Major changes in the distribution of the two most important tree species, Norway spruce and European beech, are expected. Growth conditions for spruce improve in a broad range of scenarios at presently cool high-elevation sites with plentiful precipitation, but in the case of strong warming (A1B and A2) spruce and beech are at risk in large parts of the Swiss Plateau. – High elevation forests that are temperature-limited will show little change in species composition but an increase in biomass. In contrast, forests at low elevations in warm-dry inner-Alpine valleys are sensitive to even moderate warming and may no longer sustain current biomass and species. – Timber production potential, carbon storage, and protection from avalanches and rockfall react differently to climate change, with an overall tendency to deteriorate at low elevations, and improve at high elevations. – Climate change will affect forests also indirectly, e.g., by increasing the risk of infestation by spruce bark beetles, which will profit from an extended flight period and will produce more generations per year.

Biogeochemical indicators of peatland degradation – a case study of a temperate bog in Northern Germany

Organic soils in peatlands store a great proportion of the global soil carbon pool and can lose carbon via the atmosphere due to degradation. In Germany, most of the greenhouse gas (GHG) emissions from organic soils are attributed to sites managed as grassland. Here, we investigated a land use gradient from near-natural wetland (NW) to an extensively managed (GE) to an intensively managed grassland site (GI), all formed in the same bog complex in northern Germany. Vertical depth profiles of δ13C, δ15N, ash content, C / N ratio and bulk density as well as radiocarbon ages were studied to identify peat degradation and to calculate carbon loss. At all sites, including the near-natural site, δ13C depth profiles indicate aerobic decomposition in the upper horizons. Depth profiles of δ15N differed significantly between sites with increasing δ15N values in the top soil layers paralleling an increase in land use intensity owing to differences in peat decomposition and fertilizer application. At both grassland sites, the ash content peaked within the first centimetres. In the near-natural site, ash contents were highest in 10–60 cm depth. The ash profiles, not only at the managed grassland sites, but also at the near-natural site indicate that all sites were influenced by anthropogenic activities either currently or in the past, most likely due to drainage. Based on the enrichment of ash content and changes in bulk density, we calculated the total carbon loss from the sites since the peatland was influenced by anthropogenic activities. Carbon loss at the sites increased in the following order: NW < GE < GI. Radiocarbon ages of peat in the topsoil of GE and GI were hundreds of years, indicating the loss of younger peat material. In contrast, peat in the first centimetres of the NW was only a few decades old, indicating recent peat growth. It is likely that the NW site accumulates carbon today but was perturbed by anthropogenic activities in the past. Together, all biogeochemical parameters indicate a degradation of peat due to (i) conversion to grassland with historical drainage and (ii) land use intensification.

Time-lapse pressure tomography for characterizing CO2 plume evolution in a deep saline aquifer

A time-lapse pressure tomography inversion approach is applied to characterize the CO2 plume development in a virtual deep saline aquifer. Deep CO2 injection leads to flow properties of the mixed-phase, which vary depending on the CO2 saturation. Analogous to the crossed ray paths of a seismic tomographic experiment, pressure tomography creates streamline patterns by injecting brine prior to CO2 injection or by injecting small amounts of CO2 into the two-phase (brine and CO2) system at different depths. In a first step, the introduced pressure responses at observation locations are utilized for a computationally rapid and efficient eikonal equation based inversion to reconstruct the heterogeneity of the subsurface with diffusivity (D) tomograms. Information about the plume shape can be derived by comparing D-tomograms of the aquifer at different times. In a second step, the aquifer is subdivided into two zones of constant values of hydraulic conductivity (K) and specific storage (Ss) through a clustering approach. For the CO2 plume, mixed-phase K and Ss values are estimated by minimizing the difference between calculated and “true” pressure responses using a single-phase flow simulator to reduce the computing complexity. Finally, the estimated flow property is converted to gas saturation by a single-phase proxy, which represents an integrated value of the plume. This novel approach is tested first with a doublet well configuration, and it reveals a great potential of pressure tomography based concepts for characterizing and monitoring deep aquifers, as well as the evolution of a CO2 plume. Still, field-testing will be required for better assessing the applicability of this approach.

Psychological predictors of eco-driving: A longitudinal study

Eco-driving has well-known positive effects on fuel economy and greenhouse-gas emissions. Moreover, eco-driving reduces road-traffic noise, which is a serious threat to the health and well-being of many people. We investigated the psychological predictors of the adoption of eco-driving from the perspective of road-traffic noise abatement. The data came from 890 car drivers who participated in a longitudinal survey over four months. Specifically, we tested the effects of the intention to prevent road-traffic noise, variables derived from the theory of planned behavior (social norm, perceived behavioral control, and attitude), and variables derived from the health action process approach (implementation intention, maintenance self-efficacy, and action control) on the intention to practice eco-driving and on eco-driving behavior. The intention to prevent road-traffic noise was not linked to the intention to practice eco-driving. The strongest predictors of the intention to practice eco-driving were attitude and perceived behavioral control. The strongest predictor of eco-driving behavior was action control. The link between behavioral intention and behavior was weak, indicating that drivers have difficulties putting their intention to practice eco-driving into action. Therefore, intervention efforts should directly address and support the transition from intention to behavior. This could be accomplished by providing reminders, which help to maintain behavioral intention, and by providing behavior feedback, which helps car drivers to monitor their behavior.

An inter-regional assessment of concentrations and δ13C values of methane and dissolved inorganic carbon in small European lakes

Methane (CH4) and carbon dioxide emissions from lakes are relevant for assessing the greenhouse gas output of wetlands. However, only few standardized datasets describe concentrations of these gases in lakes across different geographical regions. We studied concentrations and stable carbon isotopic composition (δ13C) of CH4 and dissolved inorganic carbon (DIC) in 32 small lakes from Finland, Sweden, Germany, the Netherlands, and Switzerland in late summer. Higher concentrations and δ13C values of DIC were observed in calcareous lakes than in lakes on non-calcareous areas. In stratified lakes, δ13C values of DIC were generally lower in the hypolimnion due to the degradation of organic matter (OM). Unexpectedly, increased δ13C values of DIC were registered above the sediment in several lakes. This may reflect carbonate dissolution in calcareous lakes or methanogenesis in deepwater layers or in the sediments. Surface water CH4 concentrations were generally higher in western and central European lakes than in Fennoscandian lakes, possibly due to higher CH4 production in the littoral sediments and lateral transport, whereas CH4 concentrations in the hypolimnion did not differ significantly between the regions. The δ13C values of CH4 in the sediment suggest that δ13C values of biogenic CH4 are not necessarily linked to δ13C values of sedimentary OM but may be strongly influenced by OM quality and methanogenic pathway. Our study suggests that CH4 and DIC cycling in small lakes differ between geographical regions and that this should be taken into account when regional studies on greenhouse gas emissions are upscaled to inter-regional scales.

Hand in hand: public endorsement of climate change mitigation and adaptation

This research investigated how an individual’s endorsements of mitigation and adaptation relate to each other, and how well each of these can be accounted for by relevant social psychological factors. Based on survey data from two European convenience samples (N = 616 / 309) we found that public endorsements of mitigation and adaptation are strongly associated: Someone who is willing to reduce greenhouse gas emissions (mitigation) is also willing to prepare for climate change impacts (adaptation). Moreover, people endorsed the two response strategies for similar reasons: People who believe that climate change is real and dangerous, who have positive attitudes about protecting the environment and the climate, and who perceive climate change as a risk, are willing to respond to climate change. Furthermore, distinguishing between (spatially) proximal and distant risk perceptions suggested that the idea of portraying climate change as a proximal (i.e., local) threat might indeed be effective in promoting personal actions. However, to gain endorsement of broader societal initiatives such as policy support, it seems advisable to turn to the distant risks of climate change. The notion that “localising” climate change might not be the panacea for engaging people in this domain is discussed in regard to previous theory and research.

Antarctic temperature changes during the last millennium: evaluation of simulations and reconstructions

Temperature changes in Antarctica over the last millennium are investigated using proxy records, a set of simulations driven by natural and anthropogenic forcings and one simulation with data assimilation. Over Antarctica, a long term cooling trend in annual mean is simulated during the period 1000–1850. The main contributor to this cooling trend is the volcanic forcing, astronomical forcing playing a dominant role at seasonal timescale. Since 1850, all the models produce an Antarctic warming in response to the increase in greenhouse gas concentrations. We present a composite of Antarctic temperature, calculated by averaging seven temperature records derived from isotope measurements in ice cores. This simple approach is supported by the coherency displayed between model results at these data grid points and Antarctic mean temperature. The composite shows a weak multi-centennial cooling trend during the pre-industrial period and a warming after 1850 that is broadly consistent with model results. In both data and simulations, large regional variations are superimposed on this common signal, at decadal to centennial timescales. The model results appear spatially more consistent than ice core records. We conclude that more records are needed to resolve the complex spatial distribution of Antarctic temperature variations during the last millennium.

Production of Ethanol from Hardwood

Diminishing crude oil and natural gas supplies, along with concern about greenhouse gas are major driving forces in the search for efficient renewable energy sources. The conversion of lignocellulosic biomass to energy and useful chemicals is a component of the solution. Ethanol is most commonly produced by enzymatic hydrolysis of complex carbohydrates to simple sugars followed by fermentation using yeast. C6Hl0O5 + H2O −Enxymes→ C6H12O6 −Yeast→ 2CH3CH2OH + 2C02 In the U.S. corn is the primary starting raw material for commercial ethanol production. However, there is insufficient corn available to meet the future demand for ethanol as a gasoline additive. Consequently a variety of processes are being developed for producing ethanol from biomass; among which is the NREL process for the production of ethanol from white hardwood. The objective of the thesis reported here was to perform a technical economic analysis of the hardwood to ethanol process. In this analysis a Greenfield plant was compared to co-locating the ethanol plant adjacent to a Kraft pulp mill. The advantage of the latter case is that facilities can be shared jointly for ethanol production and for the production of pulp. Preliminary process designs were performed for three cases; a base case size of 2205 dry tons/day of hardwood (52 million gallons of ethanol per year) as well as the two cases of half and double this size. The thermal efficiency of the NREL process was estimated to be approximately 36%; that is about 36% of the thermal energy in the wood is retained in the product ethanol and by-product electrical energy. The discounted cash flow rate of return on investment and the net present value methods of evaluating process alternatives were used to evaluate the economic feasibility of the NREL process. The minimum acceptable discounted cash flow rate of return after taxes was assumed to be 10%. In all of the process alternatives investigated, the dominant cost factors are the capital recovery charges and the cost of wood. The Greenfield NREL process is not economically viable with the cost of producing ethanol varying from $2.58 to $2.08/gallon for the half capacity and double capacity cases respectively. The co-location cases appear more promising due to reductions in capital costs. The most profitable co-location case resulted in a discounted cash flow rate of return improving from 8.5% for the half capacity case to 20.3% for the double capacity case. Due to economy of scale, the investments become more and more profitable as the size of the plant increases. This concept is limited by the amount of wood that can be delivered to the plant on a sustainable basis as well as the demand for ethanol within a reasonable distance of the plant.

Tab. 1 Mole % CO2 and 13C values of CO2 at baseline and at the final monitoring event for the eight observation wells

During CO2 storage operations in mature oilfields or saline aquifers it is desirable to trace the movement of injected CO2 for verification and safety purposes. We demonstrate the successful use of carbon isotope abundance ratios for tracing the movement of CO2 injected at the Cardium CO2 Storage Monitoring project in Alberta between 2005 and 2007. Injected CO2 had a d13C value of -4.6±1.1 per mil that was more than 10 per mil higher than the carbon isotope ratios of casing gas CO2 prior to CO2 injection with average d13C values ranging from -15.9 to -23.5 per mil. After commencement of CO2 injection, d13C values of casing gas CO2 increased in all observation wells towards those of the injected CO2 consistent with a two-source end-member mixing model. At four wells located in a NE-SW trend with respect to the injection wells, breakthrough of injected CO2 was registered chemically (>50 mol % CO2) and isotopically 1-6 months after commencement of CO2 injection resulting in cumulative CO2 fluxes exceeding 100000 m**3 during the observation period. At four other wells, casing gas CO2 contents remained below 5 mol % resulting in low cumulative CO2 fluxes (<2000 m**3) throughout the entire observation period, but carbon isotope ratios indicated contributions between <30 and 80% of injected CO2. Therefore, we conclude that monitoring the movement of CO2 in the injection reservoir with geochemical and isotopic techniques is an effective approach to determine plume expansion and to identify potential preferential flow paths provided that the isotopic composition of injected CO2 is constant and distinct from that of baseline CO2.

Physical properties of 39 sediment cores from the Bengal Fan and northeast Indian Ocean

We obtained sediment physical properties and geochemical data from 47 piston and gravity cores located in the Bay of Bengal, to study the complex history of the Late Pleistocene run-off from the Ganges and Brahmaputra rivers and its imprint on the Bengal Fan. Grain-size parameters were predicted from core logs of density and velocity to infer sediment transport energy and to distinguish different environments along the 3000-km-long transport path from the delta platform to the lower fan. On the shelf, 27 cores indicate rapidly prograding delta foresets today that contain primarily mud, whereas outer shelf sediment has 25% higher silt contents, indicative of stronger and more stable transport regime, which prevent deposition and expose a Late Pleistocene relic surface. Deposition is currently directed towards the shelf canyon 'Swatch of No Ground', where turbidites are released to the only channel-levee system that is active on the fan during the Holocene. Active growth of the channel-levee system occurred throughout sea-level rise and highstand with a distinct growth phase at the end of the Younger Dryas. Coarse-grained material bypasses the upper fan and upper parts of the middle fan, where particle flow is enhanced as a result of flow-restriction in well-defined channels. Sandier material is deposited mainly as sheet-flow deposits on turbidite-dominated plains at the lower fan. The currently most active part of the fan with 10-40 cm thick turbidites is documented for the central channel including inner levees (e.g., site 40). Site 47 from the lower fan far to the east of the active channel-levee system indicates the end of turbidite sedimentation at 300 ka for that location. That time corresponds to the sea-level lowering during late isotopic stage 9 when sediment supply to the fan increased and led to channel avulsion farther upstream, probably indicating a close relation of climate variability and fan activity. Pelagic deep-sea sites 22 and 28 contain a 630-kyear record of climate response to orbital forcing with dominant 21- and 41-kyear cycles for carbonate and magnetic susceptibility, respectively, pointing to teleconnections of low-latitude monsoonal forcing on the precession band to high-latitude obliquity forcing. Upper slope sites 115, 124, and 126 contain a record of the response to high-frequency climate change in the Dansgaard-Oeschger bands during the last glacial cycle with shared frequencies between 0.75 and 2.5 kyear. Correlation of highs in Bengal Fan physical properties to lows in the d18O record of the GISP2 ice-core suggests that times of greater sediment transport energy in the Bay of Bengal are associated with cooler air temperatures over Greenland. Teleconnections were probably established through moisture and other greenhouse-gas forcing that could have been initiated by instabilities in the methane hydrate reservoir in the oceans.

Planktonic foraminiferal oxygen isotopes of ODP Site 143-865 samples

Cool tropical sea surface temperatures (SSTs) are reported for warm Paleogene greenhouse climates based on the d18O of planktonic foraminiferal tests. These results are difficult to reconcile with models of greenhouse gas-forced climate. It has been suggested that this "cool tropics paradox" arises from postdepositional alteration of foraminiferal calcite, yielding erroneously high d18O values. Recrystallization of foraminiferal tests is cryptic and difficult to quantify, and the compilation of robust d18O records from moderately altered material remains challenging. Scanning electron microscopy of planktonic foraminiferal chamber-wall cross sections reveals that the basal area of muricae, pustular outgrowths on the chamber walls of species belonging to the genus Morozovella, contain no mural pores and may be less susceptible to postdepositional alteration. We analyzed the d18O in muricae bases of morozovellids from the central Pacific (Ocean Drilling Program Site 865) by ion microprobe using 10 ?m pits with an analytical reproducibility of ±0.34 per mil (2 standard deviations). In situ measurements of d18O in these domains yield consistently lower values than those published for conventional multispecimen analyses. Assuming that the original d18O is largely preserved in the basal areas of muricae, this new d18O record indicates Early Paleogene (~49-56 Ma) tropical SSTs in the central Pacific were 4°-8°C higher than inferred from the previously published d18O record and that SSTs reached at least ~33°C during the Paleocene-Eocene thermal maximum. This study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep-sea sediments.

Planktonic foraminifera, nannofossils and stable isotope record across tghe Paleocene-Eocene thermal maximum of ODP Hole 113-690B

The carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the Paleocene-Eocene thermal maximum (PETM) (circa 55 Ma). The rapid release of large quantities of carbon into the ocean-atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion (CIE). The brevity (120-220 kyr) of the PETM reflects the rapid enhancement of negative feedback mechanisms within Earth's exogenic carbon cycle that served the dual function of buffering ocean pH and reducing atmospheric greenhouse gas levels. Detailed study of the PETM stratigraphy from Ocean Drilling Program Site 690 (Weddell Sea) reveals that the CIE recovery period, which postdates the CIE onset by ~80 kyr, is represented by an expanded (~2.5 m thick) interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate. Collectively, the micropaleontological and sedimentological changes preserved within the CIE recovery interval reflect a transient state when ocean-atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths. A prominent peak in the abundance of the clay mineral kaolinite is associated with the CIE recovery interval, indicating that continental weathering/runoff intensified at this time as well (Robert and Kennett, 1994). Such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering/runoff and carbonate precipitation helped sequester carbon during the PETM recovery period (e.g., Dickens et al., 1997, doi:10.1130/0091-7613(1997)025<0259:ABOGIT>2.3.CO;2 ; Zachos et al., 2005, doi:10.1126/science.1109004).

Sea surface temperatures during Marine Isotope Stage (MIS) 11

The Marine Isotope Stage (MIS) 11 (424-374 ka) was characterized by a protracted deglaciation and an unusually long climatic optimum. It remains unclear to what degree the climate development during this interglacial reflects the unusually weak orbital forcing or greenhouse gas trends. Previously, arguments about the duration and timing of the MIS11 climatic optimum and about the pace of the deglacial warming were based on a small number of key records, which appear to show regional differences. In order to obtain a global signal of climate evolution during MIS11, we compiled a database of 78 sea surface temperature (SST) records from 57 sites spanning MIS11, aligned these individually on the basis of benthic (N = 28) or planktonic (N = 31) stable oxygen isotope curves to a common time frame and subjected 48 of them to an empirical orthogonal function (EOF) analysis. The analysis revealed a high commonality among all records, with the principal SST trend explaining almost 49% of the variability. This trend indicates that on the global scale, the surface ocean underwent rapid deglacial warming during Termination V, in pace with carbon dioxide rise, followed by a broad SST optimum centered at ~410 kyr. The second EOF, which explained ~18% of the variability, revealed the existence of a different SST trend, characterized by a delayed onset of the temperature optimum during MIS11 at ~398 kyr, followed by a prolonged warm period lasting beyond 380 kyr. This trend is most consistently manifested in the mid-latitude North Atlantic and Mediterranean Sea and is here attributed to the strength of the Atlantic meridional overturning circulation. A sensitivity analysis indicates that these results are robust to record selection and to age-model uncertainties of up to 3-6 kyr, but more sensitive to SST seasonal attribution and SST uncertainties >1 °C. In order to validate the CCSM3 (Community Climate System Model, version 3) predictive potential, the annual and seasonal SST anomalies recorded in a total of 74 proxy records were compared with runs for three time slices representing orbital configuration extremes during the peak interglacial of MIS11. The modeled SST anomalies are characterized by a significantly lower variance compared to the reconstructions. Nevertheless, significant correlations between proxy and model data are found in comparisons on the seasonal basis, indicating that the model captures part of the long-term variability induced by astronomical forcing, which appears to have left a detectable signature in SST trends.

Pore water and sediment geochemistry of the Bothian Sea

Methane is a powerful greenhouse gas and its biological conversion in marine sediments, largely controlled by anaerobic oxidation of methane (AOM), is a crucial part of the global carbon cycle. However, little is known about the role of iron oxides as an oxidant for AOM. Here we provide the first field evidence for iron-dependent AOM in brackish coastal surface sediments and show that methane produced in Bothnian Sea sediments is oxidized in distinct zones of iron- and sulfate-dependent AOM. At our study site, anthropogenic eutrophication over recent decades has led to an upward migration of the sulfate/methane transition zone in the sediment. Abundant iron oxides and high dissolved ferrous iron indicate iron reduction in the methanogenic sediments below the newly established sulfate/methane transition. Laboratory incubation studies of these sediments strongly suggest that the in situ microbial community is capable of linking methane oxidation to iron oxide reduction. Eutrophication of coastal environments may therefore create geochemical conditions favorable for iron-mediated AOM and thus increase the relevance of iron-dependent methane oxidation in the future. Besides its role in mitigating methane emissions, iron-dependent AOM strongly impacts sedimentary iron cycling and related biogeochemical processes through the reduction of large quantities of iron oxides.