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101.
Magnesium Isotope Compositions of Natural Reference Materials 总被引:1,自引:0,他引:1
Emile B. Bolou-Bi Nathalie Vigier Agnès Brenot Anne Poszwa 《Geostandards and Geoanalytical Research》2009,33(1):95-109
This study presents a chemical protocol for the separation of Mg that is particularly adapted to alkali‐rich samples (granite, soil, plants). This protocol was based on a combination of two pre‐existing methods: transition metals were first removed from the sample using an AG‐MP1 anion‐exchange resin, followed by the separation of alkalis (Na, K) and bivalent cations (Ca2+, Mn2+ and Sr2+) using a AG50W‐X12 cation‐exchange resin. This procedure allowed Mg recovery of ~ 10 0 ± 8%. The [Σcations]/[Mg] molar ratios in all of the final Mg fractions were lower than 0.05. The Mg isotope ratios of eleven reference materials were analysed using two different MC‐ICP‐MS instruments (Isoprobe and Nu Plasma). The long‐term reproducibility, assessed by repeated measurements of Mg standard solutions and natural reference materials, was 0.14‰. The basalt (BE‐N), limestone (Cal‐S) and seawater (BCR‐403) reference materials analysed in this study yielded δ26Mg mean values of ?0.28 ± 0.08‰, ?4.37 ± 0.11‰ and ?0.89 ± 0.10‰ respectively, in agreement with published data. The two continental rocks analysed, diorite (DR‐N) and granite (GA), yielded δ26Mg mean values of ?0.50 ± 0.08‰ and ?0.75 ± 0.14‰, respectively. The weathering products, soil (TILL‐1) and river water (NIST SRM 1640), gave δ26Mg values of ?0.40 ± 0.07‰ and ?1.27 ± 0.14‰, respectively. We also present, for the first time, the Mg isotope composition of bulk plant and organic matter. Rye flour (BCR‐381), sea lettuce (Ulva lactuva) (BCR‐279), natural hairgrass (Deschampsia flexuosa) and lichen (BCR‐482) reference materials gave δ26Mg values of ?1.10 ± 0.14‰, ?0.90 ± 0.19‰, ?0.50 ± 0.22‰ and ?1.15 ± 0.27‰ respectively. Plant δ26Mg values fell within the range defined by published data for chlorophylls. 相似文献
102.
Nathalie Dubois Markus Kienast Stephanie Kienast Claire Normandeau Stephen E. Calvert Timothy D. Herbert Alan Mix 《Quaternary Science Reviews》2011,30(1-2):210-223
In this study, we use records of nitrogen isotope ratios (δ15N), UK’37 temperature estimates, organic carbon and opal percentages from high-resolution sediment cores located in the eastern equatorial Pacific (EEP) to explore the mechanisms linking millennial-scale changes in low-latitude sea surface temperature, water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100,000 yr. Our results support a hypothesis that the Southern Hemisphere, and its connection to the low latitudes via shallow subsurface ocean circulation, has a primary influence on the biogeochemistry of the EEP. In addition, our results suggest that, during the last glacial stage, denitrification rates fluctuated on millennial timescales in response to water-column ventilation rather than upstream oxidant demand in intermediate-depth waters.However, due to the poor age constraints available for Marine Isotopic Stage (MIS) 3, the EEP sedimentary data presented here could support two conflicting mechanisms, one driven by enhanced intermediate overturning circulation in the Southern Ocean during Heinrich Events/Antarctic Warm Events, implying that subsurface flow rates control thermocline ventilation, and a second one consistent with more sluggish intermediate circulation during Antarctic Warm Events and giving a central role to the temperature control on oxygen solubility in Southern Ocean surface waters. 相似文献
103.
Studying the large-scale relationships between climate and agriculture raises two different issues: the impact of climate on crops, and the potential feedbacks to climate from croplands. A relevant and consistent framework to address this twofold issue is to extend existing Dynamic Global Vegetation Models, which can be coupled to climate models, in order to explicitly account for croplands. Here we present the first results of such a strategy applied to tropical croplands over West Africa. We introduce into the terrestrial biosphere model ORCHIDEE (IPSL) adequate processes and parameterisations taken from the crop model SARRAH (CIRAD), which is calibrated for millet over this region. The resulting model, ORCH-mil, realistically simulates the growth and yield of millet when tested on an experimental station in Senegal. The model is then applied over West Africa using a 36-year climate reanalysis dataset. First the model is tested in terms of yield simulation, against national millet yields from the FAO database. The ability of the model to reproduce the spatial and temporal variability of millet yields is assessed. Then, the effects on land surface fluxes of explicitly accounting for croplands are examined: significant differences between ORCH-mil and ORCHIDEE appear, through changes in sensible and latent heat fluxes, surface albedo, and water resources. These differences encompass a potential impact on the monsoon system, mainly during the retreat of monsoon rains. 相似文献
104.
Maladaptive trajectories of change in Makira, Solomon Islands 总被引:2,自引:0,他引:2
Ioan Fazey Nathalie Pettorelli Jasper Kenter Daniel Wagatora Daniel Schuett 《Global Environmental Change》2011,21(4):1275-1289
Trajectories of change are dynamic processes of individual, group and/or societal responses to change which create further change and responses, with outcomes that reflect the cumulative properties of those processes. Understanding trajectories of change is an important initial step for designing appropriate adaptation strategies because even though responses may enable people to cope with change in the short term, the accumulated responses of individuals can generate undesirable maladaptive outcomes over longer periods of time. This paper examines trajectories of change in Kahua, Solomon Islands, where people have traditionally relied on subsistence activities and have in the past been subsistence affluent. Participatory methods, including 76 focus group discussions in 38 communities with 821 individuals, were used to determine changes in the region and its drivers. A conceptual model was developed of the underlying feedback processes within the Kahua social–ecological system. The results show that communities are facing rapid and extensive changes. Most changes, however, are being driven by the two key drivers of population growth and a strong desire for monetary prosperity that act synergistically to generate stress in communities. People are generally responding by focusing on income generation, which is reinforcing stress in communities and resulting in maladaptive trajectories of change. The results suggest development policy in the Solomon Islands needs to: (1) take the challenges of population growth much more seriously; (2) place greater effort on development activities that reduce per capita impact on the environment; (3) improve management of the high expectations for monetary prosperity; (4) increase emphasis on wellbeing aspects of development rather than income generation per se, and (5) better align development with existing adaptation strategies to ensure that vulnerability to future global change does not increase. 相似文献
105.
Cohu S Thibaut T Mangialajo L Labat JP Passafiume O Blanfuné A Simon N Cottalorda JM Lemée R 《Marine pollution bulletin》2011,62(12):2681-2691
To study environment characteristics favoring the toxic benthic dinoflagellate Ostreopsis cf. ovata, a survey was conducted in Monaco (NW Mediterranean Sea), in summers 2007 and 2008. Epiphytic and planktonic blooms occurred almost simultaneously and a high variation of abundances at low spatial scales was observed. An early and very marked bloom occurred in 2007, compared to a later and less abundant development in 2008. These distinct patterns in bloom timing corresponded with very different hydroclimatic scenarios in 2007 (hot spring and relatively cold summer) and 2008 (standard year compared to the median year profile estimated with data from 1995 to 2008). No clear impacts of summer seawater temperature, rainfall or nutrient concentrations were evident. Strong wind may favor the dispersal of benthic and planktonic cells. Our study suggests that further investigations are needed to examine the potential role of Ostreopsis nutritional mode (i.e. autotrophy vs. mixotrophy). 相似文献
106.
Peggy Vincent Nathalie Bardet Xabier Pereda Suberbiola Badi Bouya Mbarek Amaghzaz Saïd Meslouh 《Gondwana Research》2011,19(4):1062-1073
Though the Maastrichtian Phosphates of Morocco have yielded very rich marine vertebrate assemblages, plesiosaurs remain very scarce in these strata. The only hitherto recognized taxon was Plesiosaurus mauritanicus Arambourg, 1952, regarded here as a nomem dubium. Here we describe a new genus and species of elasmosaurid plesiosaur, Zarafasaura oceanis, which represents the first valid elasmosaurid plesiosaur described from the latest Cretaceous of Africa, and the second one from this continent. A phylogenetic analysis of plesiosauroids indicates that Zarafasaura oceanis has close affinities with elasmosaurids from the Late Cretaceous of North America and Japan. Among its distinctive suite of characters, the general shape and organisation of its squamosal and palate are unique among elasmosaurids. This new taxon completes our understanding of Late Cretaceous plesiosaur palaeobiodiversity and palaeobiogeography, and shows that Maastrichtian plesiosaurs were characterized by a quite high degree of endemism. They were also highly diversified and distributed worldwide, which supports the hypothesis of a catastrophic extinction of plesiosaurs at the K/T boundary. 相似文献
107.
Lakes on Mars were formed under periglacial to glacial climates. Extreme conditions prevailed including freezing temperatures, low atmospheric pressure, high evaporation/sublimation rates, and liquid water reservoirs locked in aquifers below a thick cryosphere. Although many of the Martian paleolakes display evidence of a short period of activity consistent with these conditions, others display clear evidence of lifetimes ranging from 104 to 105 years. The discovery of young seeping processes in impact craters and pole-facing valley slopes along with young volcanic activity raise questions about the conditions and limitations of liquid water flow and potential lacustrine activity today on Mars. Current climate models show that in today's conditions there exist regions on Mars of sols above the triple point and below boiling point of water that could provide hydrogeological conditions comparable to these of the Antarctic Dry Valley lakes (with the exception of the atmosphere pressure). The locations of the most recent Martian paleolakes are correlated with these regions. Throughout the history of Mars, lakes generated diversified environments, which could have provided potential habitats for life. The recent discovery of young energy sources from volcanism and the potential for liquid water reinforces the possibility of extant life on Mars, and suggests recent ponds and ancient paleolakes as primary targets for rover and sample return missions. 相似文献
108.
Sea level rise leads to coastal transgression, and the survival of ecosystems depends on their ability to migrate inland faster than they erode and submerge. We compared marsh extent between nineteenth-century maps and modern aerial photographs across the Chesapeake Bay, the largest estuary in North America, and found that Chesapeake marshes have maintained their spatial extent despite relative sea level rise rates that are among the fastest in the world. In the mapped region (i.e., 25% of modern Chesapeake Bay marshland), 94 km2 of marsh was lost primarily to shoreline erosion, whereas 101 km2 of marsh was created by upland drowning. Simple projections over the entire Chesapeake region suggest that approximately 100,000 acres (400 km2) of uplands have converted to wetlands and that about a third of all present-day marsh was created by drowning of upland ecosystems since the late nineteenth century. Marsh migration rates were weakly correlated with topographic slope and the amount of development of adjacent uplands, suggesting that additional processes may also be important. Nevertheless, our results emphasize that the location of coastal ecosystems changes rapidly on century timescales and that sea level rise does not necessarily lead to overall habitat loss. 相似文献
109.
Potential Orthopyroxene,Clinopyroxene and Olivine Reference Materials for In Situ Lithium Isotope Determination 总被引:1,自引:0,他引:1 下载免费PDF全文
Ben‐Xun Su Xiao‐Yan Gu Etienne Deloule Hong‐Fu Zhang Qiu‐Li Li Xian‐Hua Li Nathalie Vigier Yan‐Jie Tang Guo‐Qiang Tang Yu Liu Kwan‐Nang Pang Aaron Brewer Qian Mao Yu‐Guang Ma 《Geostandards and Geoanalytical Research》2015,39(3):357-369
Over 1400 electron probe and 700 ion probe microanalyses were performed on eleven mineral separates to evaluate their potential as reference materials for in situ Li isotopic determination. Our results suggest the homogenous distributions of major elements, Li and its isotopes for each sample. Hence, these samples are suitable to be used as reference materials for in situ measurements of Li abundance and Li isotopes by secondary ion mass spectrometry (SIMS) or laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). These samples have the advantage of mitigating probable matrix effects during calibration owing to the wide range of compositions. The effect of composition on the δ7Li of olivine measured by SIMS is a linear function of composition, with δ7Li increasing by 1.0‰ for each mole per cent decrease in forsterite component. 相似文献
110.
Ian Kraucunas Leon Clarke James Dirks John Hathaway Mohamad Hejazi Kathy Hibbard Maoyi Huang Chunlian Jin Michael Kintner-Meyer Kerstin Kleese van Dam Ruby Leung Hong-Yi Li Richard Moss Marty Peterson Jennie Rice Michael Scott Allison Thomson Nathalie Voisin Tristram West 《Climatic change》2015,129(3-4):573-588