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141.
Timme H. Donders Hugo Jan de Boer Walter Finsinger Eric C. Grimm Stefan C. Dekker Gert Jan Reichart Friederike Wagner-Cremer 《Climate Dynamics》2011,36(1-2):109-118
Recurrent phases of increased pine at Lake Tulane, Florida have previously been related to strong stadials terminated by so-called Heinrich events. The climatic significance of these pine phases has been interpreted in different ways. Using a pollen?Cclimate inference model, we quantified the climate changes and consistently found that mean summer precipitation (P JJA) increased (0.5?C0.9?mm/day) and mean November temperature increased (2.0?C3.0°C) during pine phases coeval with Heinrich events and the Younger Dryas. Marine sea surface temperature records indicate that potential sources for these moisture and heat anomalies are in the Gulf of Mexico and the western tropical Atlantic. We explain this low latitude warming by an increased Loop Current facilitated by persistence of the Atlantic Warm Pool during summer. This hypothesis is supported by a climate model sensitivity analysis. A positive heat anomaly in the Gulf of Mexico and equatorial Atlantic best approximates the pollen-inferred climate reconstructions from Lake Tulane during the (stadials around) Heinrich events and the Younger Dryas. 相似文献
142.
F. Hugo Lambert Glen R. Harris Matthew Collins James M. Murphy David M. H. Sexton Ben B. B. Booth 《Climate Dynamics》2013,41(11-12):3055-3072
We examine the global mean surface temperature and carbon cycle responses to the A1B emissions scenario for a new 57 member perturbed-parameter ensemble of simulations generated using the fully coupled atmosphere-ocean-carbon cycle climate model HadCM3C. The model variants feature simultaneous perturbation to parameters that control atmosphere, ocean, land carbon cycle and sulphur cycle processes in this Earth system model, and is the first experiment of its kind. The experimental design, based on four earlier ensembles with parameters varied within each individual Earth system component, allows the effects of interactions between uncertainties in the different components to be explored. A large spread in response is obtained, with atmospheric CO2 at the end of the twenty-first century ranging from 615 to 1,100 ppm. On average though, the mean effect of the parameter perturbations is to significantly reduce the amount of atmospheric CO2 compared to that seen in the standard HadCM3C model. Global temperature change for 2090–2099 relative to the pre-industrial period ranges from 2.2 to 7.5 °C, with large temperature responses occurring when atmospheric model versions with high climate sensitivities are combined with carbon cycle components that emit large amounts of CO2 to the atmosphere under warming. A simple climate model, tuned to reproduce the responses of the separate Earth system component ensembles, is used to demonstrate that interactions between uncertainties in the different components play a significant role in determining the spread of responses in global mean surface temperature. This ensemble explores a wide range of interactions and response, and therefore provides a useful resource for the provision of regional climate projections and associated uncertainties. 相似文献
143.
Estefan��a Llave Hugo Matias F. Javier Hern��ndez-Molina Gemma Ercilla Dorrik A. V. Stow Teresa Medialdea 《Geo-Marine Letters》2011,31(5-6):377-390
This study reports novel findings on the Pliocene?CQuaternary history of the northern Gulf of Cadiz margin and the spatiotemporal evolution of the associated contourite depositional system. Four major seismic units (P1, P2, QI and QII) were identified in the Pliocene?CQuaternary sedimentary record based on multichannel seismic profiles. These are bounded by five major discontinuities which, from older to younger, are the M (Messinian), LPR (lower Pliocene revolution), BQD (base Quaternary discontinuity), MPR (mid-Pleistocene revolution) and the actual seafloor. Unit P1 represents pre-contourite hemipelagic/pelagic deposition along the northern Gulf of Cadiz margin. Unit P2 reflects a significant change in margin sedimentation when contourite deposition started after the Early Pliocene. Mounded elongated and separated drifts were generated during unit QI deposition, accompanied by a general upslope progradation of drifts and the migration of main depocentres towards the north and northwest during both the Pliocene and Quaternary. This progradation became particularly marked during QII deposition after the mid-Pleistocene (MPR). Based on the spatial distribution of the main contourite depocentres and their thickness, three structural zones have been identified: (1) an eastern zone, where NE?CSW diapiric ridges have controlled the development of two internal sedimentary basins; (2) a central zone, which shows important direct control by the Guadalquivir Bank in the south and an E?CW Miocene palaeorelief structure in the north, both of which have significantly conditioned the basin-infill geometry; and (3) a western zone, affected in the north by the Miocene palaeorelief which favours deposition in the southern part of the basin. Pliocene tectonic activity has been an important factor in controlling slope morphology and, hence, influencing Mediterranean Outflow Water pathways. Since the mid-Pleistocene (MPR), the sedimentary stacking pattern of contourite drifts has been less affected by tectonics and more directly by climatic and sea-level changes. 相似文献
144.
Multi-method assessment of connectivity between surface water and shallow groundwater: the case of Limarí River basin,north-central Chile 总被引:2,自引:1,他引:1
Ricardo Oyarzún Felisa Barrera Pamela Salazar Hugo Maturana Jorge Oyarzún Evelyn Aguirre Pablo Alvarez Hervé Jourde Nicole Kretschmer 《Hydrogeology Journal》2014,22(8):1857-1873
A study that tests the applicability and consistency of independent but complementary approaches in the assessment of interactions between surface water and shallow groundwater within a water-stressed basin is described. The mostly agricultural Limarí basin in arid north-central Chile was chosen as a suitable case study. The analyses involved: (1) a connectivity index method, (2) hydrochemistry, and (3) water isotopic geochemistry. Chemical and isotopic data were obtained from two sampling campaigns conducted in April (fall) and December (summer) of 2011 in 22 sampling locations, which included surface water and groundwater. The results obtained by each of the methodologies were mutually consistent and indicate high connectivity conditions. Additionally, the relative contribution by different sources was assessed through end-member mixing analysis, and for reaches of the river that showed gaining conditions, the contribution of groundwater inflow to stream discharge was estimated. It is suggested that this multi-method approach is useful for the characterization of surface-water–groundwater interactions, since it at least represents a suitable starting point for obtaining basic information on these relationships. Thus, it may become the base for further studies in arid and semi-arid basins facing water management challenges. 相似文献
145.
Lithologic controls on mineralization at the Lagunas Norte high-sulfidation epithermal gold deposit, northern Peru 总被引:1,自引:0,他引:1
Luis M. Cerpa Thomas Bissig Kurt Kyser Craig McEwan Arturo Macassi Hugo W. Rios 《Mineralium Deposita》2013,48(5):653-673
The 13.1-Moz high-sulfidation epithermal gold deposit of Lagunas Norte, Alto Chicama District, northern Peru, is hosted in weakly metamorphosed quartzites of the Upper Jurassic to Lower Cretaceous Chimú Formation and in overlying Miocene volcanic rocks of dacitic to rhyolitic composition. The Dafne and Josefa diatremes crosscut the quartzites and are interpreted to be sources of the pyroclastic volcanic rocks. Hydrothermal activity was centered on the diatremes and four hydrothermal stages have been defined, three of which introduced Au ± Ag mineralization. The first hydrothermal stage is restricted to the quartzites of the Chimú Formation and is characterized by silice parda, a tan-colored aggregate of quartz-auriferous pyrite–rutile ± digenite infilling fractures and faults, partially replacing silty beds and forming cement of small hydraulic breccia bodies. The δ34S values for pyrite (1.7–2.2?‰) and digenite (2.1?‰) indicate a magmatic source for the sulfur. The second hydrothermal stage resulted in the emplacement of diatremes and the related volcanic rocks. The Dafne diatreme features a relatively impermeable core dominated by milled slate from the Chicama Formation, whereas the Josefa diatreme only contains Chimú Formation quartzite clasts. The third hydrothermal stage introduced the bulk of the mineralization and affected the volcanic rocks, the diatremes, and the Chimú Formation. In the volcanic rocks, classic high-sulfidation epithermal alteration zonation exhibiting vuggy quartz surrounded by a quartz–alunite and a quartz–alunite–kaolinite zone is observed. Company data suggest that gold is present in solid solution or micro inclusions in pyrite. In the quartzite, the alteration is subtle and is manifested by the presence of pyrophyllite or kaolinite in the silty beds, the former resulting from relatively high silica activities in the fluid. In the quartzite, gold mineralization is hosted in a fracture network filled with coarse alunite, auriferous pyrite, and enargite. Alteration and mineralization in the breccias were controlled by permeability, which depends on the type and composition of the matrix, cement, and clast abundance. Coarse alunite from the main mineralization stage in textural equilibrium with pyrite and enargite has δ34S values of 24.8–29.4?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of 6.8–13.9?‰, consistent with H2S as the dominant sulfur species in the mostly magmatic fluid and constraining the fluid composition to low pH (0–2) and logfO2 of ?28 to ?30. Alunite–pyrite sulfur isotope thermometry records temperatures of 190–260 °C; the highest temperatures corresponding to samples from near the diatremes. Alunite of the third hydrothermal stage has been dated by 40Ar/39Ar at 17.0?±?0.22 Ma. The fourth hydrothermal stage introduced only modest amounts of gold and is characterized by the presence of massive alunite–pyrite in fractures, whereas barite, drusy quartz, and native sulfur were deposited in the volcanic rocks. The $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ values of stage IV alunite vary between 11.5 and 11.7?‰ and indicate that the fluid was magmatic, an interpretation also supported by the isotopic composition of barite (δ34S?=?27.1 to 33.8?‰ and $ {\delta^{18 }}{{\mathrm{O}}_{{\mathrm{S}{{\mathrm{O}}_4}}}} $ ?=?8.1 to 12.7?‰). The Δ34Spy–alu isotope thermometry records temperatures of 210 to 280 °C with the highest values concentrated around the Josefa diatreme. The Lagunas Norte deposit was oxidized to a depth of about 80 m below the current surface making exploitation by heap leach methods viable. 相似文献
146.
Kristin L. Mercer Hugo R. Perales Joel D. Wainwright 《Global Environmental Change》2012,22(2):495-504
Climate change will affect agricultural production by subsistence farms in crop centers of origin, where landraces are conserved in situ. Various strategies for adaptation to climate change have been proposed. In this paper we examine the prospects of what we call the ‘transgenic adaptation strategy’, i.e. the appeal to use transgenic seeds to adapt to climate change, through the lens of smallholder maize farming in Mexico. Landraces are the bedrock of maize production in Mexico. We consider how maize farmers may respond to climate change and the effects of those responses on crop diversity. In this paper, we argue that the promotion of the transgenic adaptation strategy is problematic for biological and social reasons. Smallholder livelihoods in southern Mexico could suffer a disproportionate negative impact if transgenic technology is privileged as a response to climate change. Agroecological and evolutionary approaches to addressing the effects of climate change on smallholder agriculture provides an alternative adaptive strategy. 相似文献
147.
Christoph Mayr Andreas Lücke Nora I. Maidana Michael Wille Torsten Haberzettl Hugo Corbella Christian Ohlendorf Frank Schäbitz Michael Fey Stephanie Janssen Bernd Zolitschka 《Journal of Paleolimnology》2009,42(1):81-102
A combination of carbon-to-nitrogen ratios (TOC/TN), Rock Eval-analyses, and stable isotope values of bulk nitrogen (δ15N) and organic carbon (δ13Corg) was used to characterize bulk organic matter (OM) of a piston core from the Patagonian maar lake Laguna Potrok Aike (Argentina)
for the purpose of palaeoenvironmental reconstruction. Sedimentary data were compared with geochemical signatures of potential
OM sources from Laguna Potrok Aike and its catchment area to identify the sources of sedimentary OM. Correlation patterns
between isotopic data and TOC/TN ratios allowed differentiation of five distinct phases with different OM composition. Before
8470 calibrated 14C years before present (cal. yrs BP) and after 7400 cal. yrs BP, isotopic and organo-geochemical fingerprints indicate that
the sediments of Laguna Potrok Aike consist predominantly of soil and diatom OM with varying admixtures of cyanobacterial
and aquatic macrophyte OM. For a short phase of the early Holocene (ca. 8470–7400 cal. yrs BP), however, extremely high input
of soil OM is implied by isotopic fingerprints. Previous seismic and geochronological results indicate a severe lake-level
drop of 33 m below present-day shortly before 6590 cal. yrs BP. It is suggested that this lake level drop was accompanied
by increased erosion of shore banks and channel incision enhancing soil OM deposition in the lake basin. Thus, isotopic data
can be linked to hydrological variations at Laguna Potrok Aike and allow a more precise dating of this extremely low lake
level. An isotopic mixing model was used including four different sources (soil, cyanobacteria, diatom and aquatic macrophyte
OM) to model OM variations and the model results were compared with quantitative microfossil data. 相似文献
148.
The main goal of this paper is to compare the relative importance of destruction by tides vs. destruction by mergers, in order to assess if tidal destruction of galaxies in clusters is a viable scenario for explaining
the origin of intracluster stars. We have designed a simple algorithm for simulating the evolution of isolated clusters. The
distribution of galaxies in the cluster is evolved using a direct gravitational N-body algorithm combined with a subgrid treatment of physical processes such as mergers, tidal disruption, and galaxy harassment.
Using this algorithm, we have performed a total of 148 simulations. Our main results are:
相似文献
– | destruction of dwarf galaxies by mergers dominates over destruction by tides, and |
– | the destruction of galaxies by tides is sufficient to explain the observed intracluster light in clusters. |
149.
A step-response approach for predicting and understanding non-linear precipitation changes 总被引:1,自引:1,他引:0
Peter Good William Ingram F. Hugo Lambert Jason A. Lowe Jonathan M. Gregory Mark J. Webb Mark A. Ringer Peili Wu 《Climate Dynamics》2012,39(12):2789-2803
Future changes in precipitation represent one of the most important and uncertain possible effects of future climate change. We demonstrate a new approach based on idealised CO2 step-change general circulation model (GCM) experiments, and test it using the HadCM3 GCM. The approach has two purposes: to help understand GCM projections, and to build and test a fast simple model for precipitation projections under a wide range of forcing scenarios. Overall, we find that the CO2 step experiments contain much information that is relevant to transient projections, but that is more easily extracted due to the idealised experimental design. We find that the temporary acceleration of global-mean precipitation in this GCM following CO2 ramp-down cannot be fully explained simply using linear responses to CO2 and temperature. A more complete explanation can be achieved with an additional term representing interaction between CO2 and temperature effects. Energy budget analysis of this term is dominated by clear-sky outgoing long-wave radiation (CSOLR) and sensible heating, but cloud and short-wave terms also contribute. The dominant CSOLR interaction is attributable to increased CO2 raising the mean emission level to colder altitudes, which reduces the rate of increase of OLR with warming. This behaviour can be reproduced by our simple model. On regional scales, we compare our approach with linear ‘pattern-scaling’ (scaling regional responses by global-mean temperature change). In regions where our model predicts linear change, pattern-scaling works equally well. In some regions, however, substantial deviations from linear scaling with global-mean temperature are found, and our simple model provides more accurate projections. The idealised experiments reveal a complex pattern of non-linear behaviour. There are likely to be a range of controlling physical mechanisms, different from those dominating the global-mean response, requiring focussed investigation for individual regions, and in other GCMs. 相似文献
150.
Andrzej Kaim Alexander Nützel Hugo Bucher Thomas Brühwiler Nicolas Goudemand 《Swiss Journal of Geoscience》2010,103(1):121-128
An Early Triassic (Griesbachian) gastropod fauna is reported from South China (Shanggan, Guangxi) and consists of four species:
Bellerophon abrekensis, Wannerispira
shangganensis Kaim & Nützel sp. nov., Naticopsis sp., and Palaeonarica
guangxinensis Kaim & Nützel sp. nov. The taxon Wannerispira Kaim & Nützel nom. nov. replaces Pagodina Wanner non Van Beneden. This is the first report of Bellerophon abrekensis from China. Previously, it was only known from its type locality in Far East Russia. Wannerispira
shangganensis sp. is the first certain Triassic report of the Permian subfamily Neilsoniinae and represents a holdover taxon. The neritimorph
Palaeonarica is reported for the first time from the Early Triassic and this is the oldest occurrence of this genus. Compared with other
Griesbachian gastropods, the present material is relatively well preserved so that the taxonomy rests on rather firm ground.
Very few nominal taxa have been reported from the Griesbachian and therefore the present report presents substantial additional
information about gastropods from the aftermath of the end-Permian mass extinction event. The gastropod association from Shanggan
shares one species with Primorye, Far East Russia (B. abrekensis). Two species, W. shangganensis and P. guangxinensis, closely resemble specimens reported from the Griesbachian of Oman. This could suggest that Griesbachian gastropod faunas
of the Tethys were rather homogenous although the data are still scarce. 相似文献