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824 Ergebnisse:

Pliocene-Pleistocene evolution of sea surface and intermediate water temperatures from the Southwest Pacific
Paleoceanography (2016)
Erin L. McClymont, Aurora C. Elmore, Sev Kender, Melanie J. Leng, Mervyn Greaves, Henry Elderfield

Over the last 5 million years, the global climate system has evolved toward a colder mean state, marked by large amplitude oscillations in continental ice volume. Equatorward expansion of polar waters and strengthening temperature gradients have been detected. However, the response of the mid- and high-latitudes of the southern hemisphere is not well documented, despite the potential importance for climate feedbacks including sea ice distribution and low-high latitude heat transport. Here, we reconstruct the PliocenePleistocene history of both sea surface and Antarctic Intermediate Water (AAIW) temperatures on orbital timescales from DSDP Site 593 in the Tasman Sea, Southwest Pacific. We confirm overall Pliocene-Pleistocene cooling trends in both the surface ocean and AAIW, although the patterns are complex. The Pliocene is warmer than modern, but our data suggest an equatorward displacement of the subtropical front relative to present, and a poleward displacement of the subantarctic front of the Antarctic Circumpolar Current (ACC). Two main intervals of cooling, from c.3 Ma and c.1.5 Ma, are coeval with cooling and icesheet expansion noted elsewhere, and suggest that equatorward expansion of polar water masses also characterised the Southwest Pacific through the Pliocene-Pleistocene. However, the observed trends in SST and AAIW temperature are not identical despite an underlying link to the ACC, and intervals of unusual surface ocean warmth (c.2 Ma) and large amplitude variability in AAIW temperatures (from c.1 Ma) highlight complex interactions between equatorward displacements of fronts associated with the ACC and/or varying poleward heat transport from the subtropics.
Schlagworte: carbon , oxygen , ocea , clim , mulitcarb

Mangrove degradation and response to anthropogenic disturbance in Maowei Sea (SW China) since 1926 AD: Mangrove-derived OM and pollen
Organic Geochemistry (2016)
Xianwei Meng, Peng Xia, Zhen Li, Dezhen Meng

Mangrove forests, located at the interface between land and sea, have been impacted by an increase in intensive anthropogenic disturbance in developing countries or regions. In order to study the impact of human activity on mangrove forests, mangrove development was reconstructed over the last 130 yr, using the contribution of mangrove-derived organic matter (OM) and mangrove pollen as proxies, from two sediment cores from the Maowei Sea (SW China). It is a semi-enclosed bay that receives a large amount of terrestrial material from the Qinjiang and Maoling rivers, with average sedimentation rate of 0.63–0.64 cm/yr. The material accumulates mainly in the coast and its adjacent region, owing to weak water exchange through the channel. Sediment samples had C:N and δ13Corg values intermediate between mangrove leaves and flood plain sediments, indicating that OM sources could be apportioned as a mixture from only these two sources. Based on k-mean cluster analysis, mangrove development was divided into three stages since 1880 AD: (i) a flourishing period (1880–1926 AD), (ii) a phase of slow degradation (1926–1980 AD) and (iii) a time of rapid degradation (1980 AD to the present). The study indicates that anthropogenic activity, including reclamation of mangrove swamps for farmland and shrimp ponds, is the primary reason for mangrove degradation since 1926 AD, rather than climate change (temperature and precipitation).
Schlagworte: carbon , soil , ocea , poll , elem

Reclamation and Land Consolidation Effects on Organic Matter Sedimentation in Lake Kiba-Gata, Japan
Geomorphology and Society (2016)
Seiya Nagao, Hong Tuoi Bui, Yuriko Kawano, Tomoyo Suzuki, Shinya Ochiai, Koyo Yonebayashi, Masanori Okazaki, Akiko Goto, Takashi Hasegawa, Masayoshi Yamamoto

The effects of reclamation and land consolidation on organic matter sedimentation were studied in a small lagoon, Kiba-gata, which is one of the three Kaga lagoons (Shibayama-gata, Imae-gata, and Kiba-gata) located in central Japan. Reclamation work was conducted during 1954–1969 to increase the paddy field area and to improve the drainage system. Lake Kiba-gata was affected by changes in the drainage system and land consolidation around the lagoon. A sediment core was obtained in the central part of Lake Kiba-gata in June 2012. The organic matter flux recorded in the sediment core increased from 1.1 to 2.3 and from 3.9 to 7.5 g cm−2 year−1, respectively, during 1903–1974 and 1989–2012, although it was similar to the flux recorded for 1974–1989 following reclamation. The C/N ratio, δ13C, and δ15N values also changed during these time intervals. These results indicate that the primary productivity in the lagoon is increasing with time and that the recent contribution of phytoplankton to productivity has exceeded the level of past contributions because of changes in drainage and increase in human activity around the lake due to the reclamation and land consolidation
Schlagworte: nitrogen , soil , geol , elem

Discrimination between Slovenian cow, goat and sheep milk and cheese according to geographical origin using a combination of elemental content and stable isotope data
Journal of Food Composition and Analysis (2016)
Marijan Nečemer, Doris Potočnik, Nives Ogrinc

The presented work uses stable isotope ratios of major bioelements (13C/12C, 15N/14N, 18O/16O, 34S/32S) and elemental composition to determine the regional provenance of 124 Slovenian milk and 30 cheese samples collected during May, June and July in 2012 and 2013. The ability to discriminate between cow milk based on geographical origin was only possible in summer 2012, where discriminant analysis identified Cl, Zn, P, Ca and K as the most significant parameters. Both sheep milk and cheese could be distinguished according to their geographical origin based on P, S, K, Cl, Ca, Zn content and δ13C and δ15N values in casein and to refuse possible imitations with a correct classification in 97% of cases. Furthermore, stable isotopes of light elements in combination with elemental composition can distinguish sheep and goat milk and cheese from that produced from cow milk with a prediction ability of 95.2%. Such methodology can effectively contribute towards supporting the existence of the Protected Designated Origin of Bovški and Kraški sheep cheese and Tolminc cow cheese and could be incorporated into a traceability system.
Schlagworte: carbon , nitrogen , oxygen , sulfur , food , elem , gashead

Chemodenitrification in the cryoecosystem of Lake Vida, Victoria Valley, Antarctica
Geobiology (2016)
N. E. Ostrom, H. Gandhi, G. Trubl, A. E. Murray

Lake Vida, in the Victoria Valley of East Antarctica, is frozen, yet harbors liquid brine (~20% salt, >6 times seawater) intercalated in the ice below 16 m. The brine has been isolated from the surface for several thousand years. The brine conditions (permanently dark, −13.4 °C, lack of O2, and pH of 6.2) and geochemistry are highly unusual. For example, nitrous oxide (N2O) is present at a concentration among the highest reported for an aquatic environment. Only a minor 17O anomaly was observed in N2O, indicating that this gas was predominantly formed in the lake. In contrast, the 17O anomaly in nitrate (inline image) in Lake Vida brine indicates that approximately half or more of the inline image present is derived from atmospheric deposition. Lake Vida brine was incubated in the presence of 15N-enriched substrates for 40 days. We did not detect microbial nitrification, dissimilatory reduction of inline image to ammonium (inline image), anaerobic ammonium oxidation, or denitrification of N2O under the conditions tested. In the presence of 15N-enriched nitrite (inline image), both N2 and N2O exhibited substantial 15N enrichments; however, isotopic enrichment declined with time, which is unexpected. Additions of 15N–inline image alone and in the presence of HgCl2 and ZnCl2 to aged brine at −13 °C resulted in linear increases in the δ15N of N2O with time. As HgCl2 and ZnCl2 are effective biocides, we interpret N2O production in the aged brine to be the result of chemodenitrification. With this understanding, we interpret our results from the field incubations as the result of chemodenitrification stimulated by the addition of 15N-enriched inline image and ZnCl2 and determined rates of N2O and N2 production of 4.11–41.18 and 0.55–1.75 nmol L−1 day−1, respectively. If these rates are representative of natural production, the current concentration of N2O in Lake Vida could have been reached between 6 and 465 years. Thus, chemodenitrification alone is sufficient to explain the high levels of N2O present in Lake Vida.
Schlagworte: nitrogen , oxygen , clim , gashead

Aerobic gammaproteobacterial methanotrophs mitigate methane emissions from oxic and anoxic lake waters
Limnology and Oceanography (2016)
Kirsten Oswald, Jana Milucka, Andreas Brand, Philipp Hach, Sten Littmann, Bernhard Wehrli, Marcel M.M. Kuypers, Carsten J. Schubert

Freshwater lakes represent a substantial natural source of methane to the atmosphere and thus contribute to global climate change. Microbial methane oxidation is an important control on methane release from these systems, where oxygen appears to be the most essential electron acceptor for this process. However, there is extensive geochemical evidence that methane is also oxidized under anoxic conditions in lakes, though the details about the exact mechanism have still not been resolved. Here, we investigated the fate of methane in the water column of meromictic Lake Zug. We provide evidence for ongoing methane oxidation at the oxic/anoxic boundary and also in the anoxic hypolimnion, both apparently mediated by aerobic methane-oxidizing bacteria. Gammaproteobacterial methanotrophs (gamma-MOB) dominated the indigenous methanotrophic community and were active under all investigated conditions—oxic, sub-oxic and anoxic. Methane oxidation was stimulated by the additions of oxygen or iron and manganese oxides under anoxic conditions. In the latter case, trace amounts of oxygen may have still been required for methane activation, yet these findings indicate that gamma-MOB in Lake Zug might be able to respire electron acceptors other than oxygen. We propose that gamma-MOB are actively removing methane also in anoxic lake waters, thus contributing to methane mitigation from these habitats.
Schlagworte: carbon , ocea , gashead

Fossil fuel combustion-related emissions dominate atmospheric ammonia sources during severe haze episodes: Evidence from 15N-stable isotope in size-resolved aerosol ammonium
(2016)
Yuepeng Pan, Shili Tian, Dongwei Liu, Yunting Fang, Xiaying Zhu, Qiang Zhang, Bo Zheng, Greg Michalski, Yuesi Wang

The reduction of ammonia (NH3) emissions is urgently needed due to its role in aerosol nucleation and growth causing haze formation during its conversion into ammonium (NH4+). However, the relative contributions of individual NH3 sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric NH3 in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of 15N (expressed using δ15N values) of NH4+ in fine particles varies with the development of haze episodes, ranging from -37.1‰ to -21.7‰ during clean/dusty days (relative humidity: ~40%), to -13.1‰ to +5.8‰ during hazy days (relative humidity: 70-90%). After accounting for the isotope exchange between NH3 gas and aerosol NH4+, the δ15N value of the initial NH3 during hazy days is found to be -14.5‰ to -1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH3 during hazy days in urban Beijin...
Schlagworte: nitrogen , poll , gashead

Fossil Fuel Combustion-Related Emissions Dominate Atmospheric Ammonia Sources during Severe Haze Episodes: Evidence from 15 N-Stable Isotope in Size-Resolved Aerosol Ammonium
Environmental Science & Technology (2016)
Yuepeng Pan, Shili Tian, Dongwei Liu, Yunting Fang, Xiaying Zhu, Qiang Zhang, Bo Zheng, Greg Michalski, Yuesi Wang

The reduction of ammonia (NH3) emissions is urgently needed due to its role in aerosol nucleation and growth causing haze formation during its conversion into ammonium (NH4+). However, the relative contributions of individual NH3 sources are unclear, and debate remains over whether agricultural emissions dominate atmospheric NH3 in urban areas. Based on the chemical and isotopic measurements of size-resolved aerosols in urban Beijing, China, we find that the natural abundance of 15N (expressed using δ15N values) of NH4+ in fine particles varies with the development of haze episodes, ranging from −37.1‰ to −21.7‰ during clean/dusty days (relative humidity: ∼ 40%), to −13.1‰ to +5.8‰ during hazy days (relative humidity: 70–90%). After accounting for the isotope exchange between NH3 gas and aerosol NH4+, the δ15N value of the initial NH3 during hazy days is found to be −14.5‰ to −1.6‰, which indicates fossil fuel-based emissions. These emissions contribute 90% of the total NH3 during hazy days in urban Beiji...
Schlagworte: nitrogen , poll , gashead

Fatty acid composition and δ13C isotopic ratio characterisation of pumpkin seed oil
Journal of Food Composition and Analysis (2016)
Tanja Potočnik, Nives Ogrinc, Doris Potočnik, Iztok Jože Košir

This study aimed to verify the authenticity and geographical origin of pumpkin seed oil using chemical analysis by gas chromatography (GC) and isotopic characterisation by gas chromatography combustion stable isotope ratio mass spectrometry (GC/C/IRMS) combined with chemometric analysis. Thirty-eight pumpkin seed samples from various parts of the world were collected and authentic oils were prepared. Pumpkin seed oils are highly unsaturated, oleic acid varies from 26.8 to 43.6% and the content of linoleic acid is between 37.2 and 54.9%. The average δ13C values of the main fatty acids are −29.2±1.2‰, −30.3±1.6‰, −27.9±1.7‰ and −28.1±1.7‰ for C16:0, C18:0, C18:1, C18:2, respectively. To determine adulteration, rapeseed, sunflower and soybean oil, were added to pumpkin seed oil in varying percentages (1–10%). A 100% correct classification of both geographical and botanical origin was achieved based on the composition and δ13C values of fatty acids. Principal component analysis (PCA) and regularised discriminant analysis (RDA) analysis gave comparable results.

Carbon Inputs from Miscanthus Displace Older Soil Organic Carbon Without Inducing Priming Soil Carbon Sequestration Below Miscanthus
BioEnergy Research (2016)
Andy D. Robertson, Christian A. Davies, Pete Smith, Andy W. Stott, Emily L. Clark, Niall P. McNamara

The carbon (C) dynamics of a bioenergy system are key to correctly defining its viability as a sustainable alternative to conventional fossil fuel energy sources. Recent studies have quantified the greenhouse gas mitigation potential of these bioenergy crops, often concluding that C sequestration in soils plays a primary role in offsetting emissions through energy generation. Miscanthus is a particularly promising bioenergy crop and research has shown that soil C stocks can increase by more than 2 t C ha−1 yr−1. In this study, we use a stable isotope (13C) technique to trace the inputs and outputs from soils below a commercial Miscanthus plantation in Lincolnshire, UK, over the first 7 years of growth after conversion from a conventional arable crop. Results suggest that an unchanging total topsoil (0–30 cm) C stock is caused by Miscanthus additions displacing older soil organic matter. Further, using a comparison between bare soil plots (no new Miscanthus inputs) and undisturbed Miscanthus controls, soil respiration was seen to be unaffected through priming by fresh inputs or rhizosphere. The temperature sensitivity of old soil C was also seen to be very similar with and without the presence of live root biomass. Total soil respiration from control plots was dominated by Miscanthus-derived emissions with autotrophic respiration alone accounting for ∼50 % of CO2. Although total soil C stocks did not change significantly over time, the Miscanthus-derived soil C accumulated at a rate of 860 kg C ha−1 yr−1 over the top 30 cm. Ultimately, the results from this study indicate that soil C stocks below Miscanthus plantations do not necessarily increase during the first 7 years.
Schlagworte: carbon , soil , gashead