Delayed carbon sequestration and rising carbon prices     

Alejandro Caparrós 《Climatic change》2009,96(3):421-441

We set out a dynamic model to investigate optimal time paths of emissions, carbon stocks and carbon sequestration by land conversion, allowing for non-instantaneous carbon sequestration. Previous research in a dynamic general equilibrium framework, assuming instantaneous carbon sequestration, has shown that land conversion should take place as soon as possible. On the contrary, previous research within a partial equilibrium framework has shown that, with increasing carbon prices, it is optimal to delay carbon sequestration through land conversion. We show that land use change alternatives, e.g. reforestation, have to be used as soon as possible before the singular path is reached, i.e. the unique trajectory that brings the system to the steady-state. We also show that faster increasing carbon prices can induce a reduction in the rate of reforestation, and that this may take place after an initial phase of increased reforestations or even immediately, depending upon the shape of the increase in carbon prices. Finally, we show that the type of species used is relevant and that the land conversion rate gets smaller the longer it takes the trees to grow. We analyze four different carbon accounting methods, describing the conditions that make them efficient and discussing the comparative advantages of each of them.  相似文献   

Bright spectroscopic binaries: III. Binary systems with orbital periods of P > 500 days     

Dennis Jack  Missael Alejandro Hernández Huerta  Faiber Danilo Rosas-Portilla  Klaus-Peter Schröder 《Astronomische Nachrichten》2024,345(1):e230123

  相似文献   

Aftershocks of the San Marcos earthquake of April 25, 1989 (M S =6.9) and some implications for the Acapulco-San Marcos,Mexico, seismic potential     

F. R. Zúñiga  C. Gutiérrez  E. Nava  J. Lermo  M. Rodríguez  R. Coyoli 《Pure and Applied Geophysics》1993,140(2):287-300

Aftershock activity following the April 25, 1989 (M _S =6.9) earthquake near San Marcos, Guerrero, Mexico, was monitored by a temporary network installed twelve hours after the mainshock and remaining in operation for one week. Of the 350 events recorded by this temporary array, 103 were selected for further analysis in order to determine spatial characteristics of the aftershock activity. An aftershock area of approximately 780 km² is delimited by the best quality locations. The area of highest aftershock density lies inside an area delimited by the aftershocks of the latest large event in the region in 1957 (M _S =7.5) and it partially overlaps the zone of maximum intensity of the earlier 1907 (M _S =7.7) shock. Aftershocks also appear to cluster close to the mainshock hypocenter. This clustering agrees with the zone of maximum slip during the mainshock, as previously determined from strong motion records. A low angle Benioff zone is defined by the aftershock hypocenters with a slight tendency for the slab to follow a subhorizontal trajectory after a 110 km distance from the trench axis, a feature which has been observed in the neighboring Guerrero Gap. A composite focal mechanism for events close to the mainshock which also coincides with the zone of largest aftershock density, indicates a thrust fault similar to the mainshock fault plane solution.The San Marcos event took place in an area which could be considered as a mature seismic gap. Due to the manner in which strain release has been observed to previously occur, the occurrence of a major event, overlapping both the neighboring Guerrero Gap and the San Marcos Gap segments of the Mexican thrust, cannot be overlooked.  相似文献   

Major,minor and trace element abundances in samples from the Apollo 17 station 7 boulder: Implications for the origin of early lunar crustal rocks     

Stephen R. Winzer  David F. Nava  Shuford Schuhmann  Charles W. Kouns  R.K.L. Lum  John A. Philpotts 《Earth and Planetary Science Letters》1974,23(3):439-444

Apollo 17 station 7 boulder consortia samples were analyzed for major and minor elements by a combined semimicro atomic absorption spectrophotometric and colorimetric procedure. Lithophile trace element abundances were determined by stable isotope dilution mass spectrometry. Three matrix types samples (77135, 77115, and 77075) were found to be KREEP-rich fragment-laden melts with analogues throughout the Apollo 17 landing site. Of the five clasts analyzed, at least one (77115,19, troctolite) is thought to be a cumulate; 77135, 77115, and 77075 are thought to have originated by impact fusion of material with similar composition. This original material may represent a partial melt of a parent material of the composition of an included, shocked norite breccia (77215).  相似文献   

Estimates of Reynolds stress in a highly energetic shelf sea     

Alejandro Jose Souza  Michael John Howarth 《Ocean Dynamics》2005,55(5-6):490-498

In recent years the use of Acoustic Doppler Current Profilers (ADCPs) to estimate Reynolds stresses, using the so-called variance method, has become popular; and although there was great effort in studying the uncertainties on this technique, there were no reports in the main literature of its validity using independent measurements. This work reports on the comparison of ADCP and Acoustic Current Velocimeter (ADV) estimates of Reynolds stresses. The comparison of the ADCP and ADV is encouraging during periods when no strong waves were present with both the explained variance of 0.8 and the slope of the regression being 0.97. Nevertheless, when strong waves are present the method breaks down and the comparison between ADCP and ADV is very poor with R² =0.04.  相似文献   

Rock magnetic and geochemical proxies for iron mineral diagenesis in a tropical lake: Lago Verde, Los Tuxtlas, East–Central Mexico     

Beatriz Ortega  Margarita Caballero  Socorro Lozano  Gloria Vilaclara  Alejandro Rodríguez 《Earth and Planetary Science Letters》2006,250(3-4):444-458

Magnetic and non-magnetic mineral analyses were conducted on a lacustrine sequence from Lago Verde in the tropical coast along the Gulf of Mexico that covers the last 2000 years. The site witnessed the transformation of the environment since the early Olmec societies until forest clearance in the last century. Through these analyses we investigated the processes that affected the magnetic mineralogy in order to construct a model of past environmental changes, and compare this model with the archeological record and inferred climatic changes in the northern hemisphere of tropical America. Volcanic activity has played a major influence on sediment magnetic properties, as a purveyor of Ti-magnetites/Ti-maghemites, and as a factor of instability in the environment. Anoxic reductive conditions are evident in most of Lago Verde's sedimentary record.

Direct observations of magnetic minerals and ratios of geochemical (Fe, Ti), and ferrimagnetic (χf) and paramagnetic (χp) susceptibility (χ) data, are used as parameters for magnetite dissolution (χp/χ, Fe/χf), and precipitation (χf/Ti) of magnetic minerals. Intense volcanic activity and anoxia are recorded before A.D. 20, leading to the formation of framboidal pyrite. Increased erosion, higher evaporation rates, lower lake levels, anoxia and reductive diagenesis in non-sulphidic conditions are inferred for laminated sediments between A.D. 20–850. This deposit matches the period of historical crisis and multiyear droughts that contributed to the collapse of the Maya civilization. Dissolution of magnetite, a high organic content and framboidal pyrite point to anoxic, sulphidic conditions and higher lake levels after A.D. 850. Higher lake levels in Lago Verde broadly coincide with the increased precipitation documented during the Medieval Warm Period (A.D. 950–1350) in the northern tropical and subtropical regions of the American continent. For the Little Ice Age (A.D. 1400–1800), the relatively moist conditions inferred are in concordance with the glacial advances recorded in central Mexico. Higher erosion rates reflect destruction of the rainforest over the last 40 years.  相似文献   

Characterisation of a Pleistocene debris-avalanche deposit in the Tenteniguada Basin,Gran Canaria Island,Spain     

Alejandro Lomoschitz  Javier Hervás  Jorge Yepes  Joaquín Meco 《Landslides》2008,5(2):227-234

We studied a large debris-avalanche deposit of Pleistocene age in the Tenteniguada Basin, Gran Canaria Island, Spain. This deposit, which is well preserved because it is mostly covered by basanite lava flows, has distinctive matrix and block facies, hummocky topography and internal structures typical of debris avalanches. However, neither syneruptive lavas nor some characteristic features of volcanic debris-avalanche deposits, such as a stratovolcano edifice or a horseshoe-shaped crater, are present. The occurrence of internal features characteristic of volcanic avalanche deposits could be attributed to the volcanic materials involved in the movement rather than to the triggering of the avalanche during a volcanic eruption. The conditioning factors are shown to be associated with specific structural and hydrological conditions, such as the presence of old volcanic domes, strength reduction of the rocks, effective stress decrease, active gully erosion and water table rise during Pleistocene humid episodes. We finally suggest that the possible triggering factor of the avalanche was a neighbouring volcanic or tectonic earthquake.  相似文献   

Plant macrofossil assemblages from surface sediment represent contemporary species and growth forms of aquatic vegetation in a shallow Mediterranean lake     

Jorge García-Girón  Camino Fernández-Aláez  Alejandro Nistal-García  Margarita Fernández-Aláez 《Journal of Paleolimnology》2018,60(4):495-509

Macrofossils are known as a useful tool in reconstructing their original plant communities. However, most studies have been focused on comparing the composition and distribution of living plant communities and their remains in temperate lakes. Mediterranean shallow lakes have been historically far less studied and little is known about the relationships between Mediterranean macrophyte communities and their remains. The aim of our study is to assess how contemporary aquatic macrophyte communities are represented by their sedimentary remains in terms of composition, distribution and concordance between the contemporary and the subfossil assemblages in a procrustean superimposition space, and to determine which surface sediment cores, collected along a depth gradient, may represent best the whole-lake macrofossil assemblage. These analyses were carried out for both species and macrophyte growth forms (submerged hydrophytes, floating-leaved hydrophytes, helophytes and charophytes) in order to check which of the two (species and growth forms) were represented best by their macro-remains. The most abundant present-day species (Myriophyllum alterniflorum DC. and Potamogeton trichoides L.) were under-represented while Characeae and some floating-leaved hydrophytes (Polygonum amphibium L. and Ranunculus peltatus Schrank) were over-represented in sedimentary samples. Additionally, macro-remains of submerged hydrophytes and helophytes were generally found in the central areas and in close proximity to contemporary vegetation, whereas floating-leaved hydrophytes distributed close to the near-shore. Notwithstanding some disparities between contemporary vegetation and their macrofossil assemblages, we found a good agreement between present-day and sedimentary datasets for both species and macrophyte growth forms. Furthermore, our study suggests that sediment cores from deep areas are more likely to represent best the whole-lake macrofossil assemblage because of their high diversity, equitability and heterogeneity. We conclude that aquatic macrophyte subfossils from the central areas of the basin can be a very useful tool in tracking the species composition and structure of the original macrophyte communities in shallow Mediterranean lakes. Additionally, when considering the use of macro-remains to reconstruct the composition and structure of macrophyte growth forms, we recommend a multicore approach that uses transects running from the shore to the lake center.  相似文献   

Gamma ray burst studies with THESEUS     

Ghirlanda  G.  Salvaterra  R.  Toffano  M.  Ronchini  S.  Guidorzi  C.  Oganesyan  G.  Ascenzi  S.  Bernardini  M. G.  Camisasca  A. E.  Mereghetti  S.  Nava  L.  Ravasio  M. E.  Branchesi  M.  Castro-Tirado  A.  Amati  L.  Blain  A.  Bozzo  E.  O’Brien  P.  Götz  D.  Le Floch  E.  Osborne  J. P.  Rosati  P.  Stratta  G.  Tanvir  N.  Bogomazov  A. I.  D’Avanzo  P.  Hafizi  M.  Mandhai  S.  Melandri  A.  Peer  A.  Topinka  M.  Vergani  S. D.  Zane  S. 《Experimental Astronomy》2021,52(3):277-308

Gamma-ray Bursts (GRBs) are the most powerful transients in the Universe, over–shining for a few seconds all other γ-ray sky sources. Their emission is produced within narrowly collimated relativistic jets launched after the core–collapse of massive stars or the merger of compact binaries. THESEUS will open a new window for the use of GRBs as cosmological tools by securing a statistically significant sample of high-z GRBs, as well as by providing a large number of GRBs at low–intermediate redshifts extending the current samples to low luminosities. The wide energy band and unprecedented sensitivity of the Soft X-ray Imager (SXI) and X-Gamma rays Imaging Spectrometer (XGIS) instruments provide us a new route to unveil the nature of the prompt emission. For the first time, a full characterisation of the prompt emission spectrum from 0.3 keV to 10 MeV with unprecedented large count statistics will be possible revealing the signatures of synchrotron emission. SXI spectra, extending down to 0.3 keV, will constrain the local metal absorption and, for the brightest events, the progenitors’ ejecta composition. Investigation of the nature of the internal energy dissipation mechanisms will be obtained through the systematic study with XGIS of the sub-second variability unexplored so far over such a wide energy range. THESEUS will follow the spectral evolution of the prompt emission down to the soft X–ray band during the early steep decay and through the plateau phase with the unique ability of extending above 10 keV the spectral study of these early afterglow emission phases.

  相似文献   

Effect of spatial resolution of satellite images on estimating the greenness and evapotranspiration of urban green spaces     

Hamideh Nouri  Pamela Nagler  Sattar Chavoshi Borujeni  Armando Barreto Munez  Sina Alaghmand  Behnaz Noori  Alejandro Galindo  Kamel Didan 《水文研究》2020,34(15):3183-3199

Urban green spaces (UGS), like most managed land covers, are getting progressively affected by water scarcity and drought. Preserving, restoring and expanding UGS require sustainable management of green and blue water resources to fulfil evapotranspiration (ET) demand for green plant cover. The heterogeneity of UGS with high variation in their microclimates and irrigation practices builds up the complexity of ET estimation. In oversized UGS, areas too large to be measured with in situ ET methods, remote sensing (RS) approaches of ET measurement have the potential to estimate the actual ET. Often in situ approaches are not feasible or too expensive. We studied the effects of spatial resolution using different satellite images, with high-, medium- and coarse-spatial resolutions, on the greenness and ET of UGS using Vegetation Indices (VIs) and VI-based ET, over a 780-ha urban park in Adelaide, Australia. We validated ET with the ground-based ET method of Soil Water Balance. Three sets of imagery from WorldView2, Landsat and MODIS, and three VIs including the Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and Enhanced Vegetation Index 2 (EVI2), were used to assess long-term changes of VIs and ET calculated from the different imagery acquired for this study (2011–2018). We found high correspondence between ET-MODIS and ET-Landsat (R² > 0.99 for all VIs). Landsat-VIs captured the seasonal changes of greenness better than MODIS-VIs. We used artificial neural network (ANN) to relate the RS-ET and ground data, and ET-MODIS (EVI2) showed the highest correlation (R² = 0.95 and MSE =0.01 for validation). We found a strong relationship between RS-ET and in situ measurements, even though it was not explicable by simple regressions; black box models helped us to explore their correlation. The methodology used in this research makes a strong case for the value of remote sensing in estimating and managing ET of green spaces in water-limited cities.  相似文献