Carbon losses in soils previously exposed to elevated atmospheric CO₂ in a chaparral ecosystem: Potential implications for a sustained biospheric C sink     

Rebecca J. Trueman  Lina Taneva  Miquel A. Gonzalez-Meler  Walter C. Oechel  Hormoz BassiriRad 《Journal of Geochemical Exploration》2009,102(3):142

Between 1996 and 2001 an experimental set up in a chaparral community near San Diego, CA, examined various plant and ecosystem responses to CO₂ concentrations ranging from 250 to 750 μl l^− 1. These experiments indicated a significant increase in soil C sequestration as CO₂ rose above the ambient levels. In 2003, two years after the cessation of the CO₂ treatments, we returned to this site to examine soil C dynamics with a particular emphasis on stability of specific pools of C. We found that in as little as two years, C content in the surface soils (0–15 cm) of previously CO₂ enriched plots had dropped to levels below those of the ambient and pretreatment soils. In contrast, C retained in response to CO₂ enrichment was more durable in the deeper soil layers (> 25 cm deep) where both organic and inorganic C were on average 26% and 55% greater, respectively, than C content of ambient plots. Using stable isotope tracers, we found that treatment C represented 25% of total soil C and contributed to 55% of soil CO₂ efflux, suggesting that most of treatment C is readily accessible to decomposers. We also found that, C present before CO₂ fumigation was decomposed at a faster rate in the plots that were exposed to elevated CO₂ than in those exposed to ambient CO₂ levels. To our knowledge, this is the first report that allows for a detail accounting of soil C after ceasing CO₂ treatments. Our study provides a unique insight to how stable the accrued soil C is as CO₂ increases in the atmosphere.  相似文献   

Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability     

Miquel Ribot  Daniel von Schiller  Francesc Sabater  Eugènia Martí 《Aquatic Sciences - Research Across Boundaries》2015,77(4):695-707

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Cold-water coral banks and submarine landslides: a review   总被引：1，自引：0，他引：1  

Ben De Mol  Veerle Huvenne  Miquel Canals 《International Journal of Earth Sciences》2009,98(4):885-899

This paper aims to review the relation between cold-water coral bank development and submarine landslides. Both are common features on continental margins, but so far it has not been reviewed which effect—if at all—they may have upon each other. Indirect and direct relations between coral banks and landslides are evaluated here, based on four case studies: the Magellan Mound Province in the Porcupine Seabight, where fossil coral banks appear partly on top of a buried slide deposit; the Sula Ridge Reef Complex and the Storegga landslide both off mid-Norway; and the Mauritania coral bank province, associated with the Mauritanian Slide Complex. For each of these locations, positive and negative relationships between both features are discussed, based on available datasets. Locally submarine landslides might directly favour coral bank development by creating substratum where corals can settle on, enhancing turbulence due to abrupt seabed morphological variations and, in some cases, causing fluid seepage. In turn, some of these processes may contribute to increased food availability and lower sedimentation rates. Landslides can also affect coral bank development by direct erosion of the coral banks, and by the instantaneous increase of turbidity, which may smother the corals. On the other hand, coral banks might have a stabilising function and delay or stop the headwall retrogradation of submarine landslides. Although local relationships can be deduced from these case studies, no general and direct relationship exists between submarine landslides and cold-water coral banks.  相似文献   

Dynamical Behavior of Asteroids Near Resonance: the 4:1 gap and the 7:2 Group     

Miquel Grau  Guillermo González-Casado 《Celestial Mechanics and Dynamical Astronomy》1998,72(3):169-186

A comparative study of the evolution of the Sun–Jupiter–Asteroid system near the 4:1 and 7:2 resonances is performed by means of two techniques that proceed differently from the Hamiltonian corresponding to the planar restricted elliptic three-body problem. One technique is based on the classical Schubart averaging while the other is based on a mapping method in which the perturbing part of the Hamiltonian is expanded and the resulting terms are ordered according to a weight function that depends on the powers of eccentricities and the coefficients of the terms. For the mapping method the effect of Saturn on the asteroidal evolution is introduced and the degree of chaos is estimated by means of the Lyapunov time. Both methods are shown to lead to similar results and can be considered a suitable tool for describing the evolution of asteroids in the Kirkwood gap and the group corresponding to the 4:1 and 7:2 Jovian resonances, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Managing coastal zone fisheries: A Mediterranean case study     

Beatriz Morales-Nin  Antoni M. Grau  Miquel Palmer 《Ocean & Coastal Management》2010,53(3):99-106

Coastal fisheries are complex ecological and social systems, evolving in time with a shift from commercial towards recreational effort. We describe the coastal fisheries of Mallorca (W Mediterranean) and the management policies implemented to show the challenges faced at regional level to handle the different management tools used to conserve biodiversity and the social fabric in the coastal zone. Our example provides evidence of the complexity of fishing rights and how they can be adapted into practical fisheries management by combining fishing rights, open access recreational fishery, community-based management and biodiversity conservation.  相似文献   

Time-series measurements of Th in water column and sediment trap samples from the northwestern Mediterranean Sea     

J. Kirk Cochran  Juan Carlos Miquel  Robert Armstrong  Scott W. Fowler  Pere Masqu  Beat Gasser  David Hirschberg  Jennifer Szlosek  Alessia M. Rodriguez y Baena  Elisabet Verdeny  Gillian M. Stewart 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1487-1501

Disequilibrium between ²³⁴Th and ²³⁸U in water column profiles has been used to estimate the settling flux of Th (and, by proxy, of particulate organic carbon); yet potentially major non-steady-state influences on ²³⁴Th profiles are often not able to be considered in estimations of flux. We have compared temporal series of ²³⁴Th distributions in the upper water column at both coastal and deep-water sites in the northwestern Mediterranean Sea to coeval sediment trap records at the same sites. We have used sediment trap records of ²³⁴Th fluxes to predict temporal changes in water column ²³⁴Th deficits and have compared the predicted deficits to those measured to determine whether the time-evolution of the two coincide. At the coastal site (327 m water depth), trends in the two estimates of water column ²³⁴Th deficits are in fairly close agreement over the 1-month deployment during the spring bloom in 1999. In contrast, the pattern of water column ²³⁴Th deficits is poorly predicted by sediment trap records at the deep-water site (DYFAMED, 2300 m water depth) in both 2003 and 2005. In particular, the transition from a mesotrophic to an oligotrophic system, clearly seen in trap fluxes, is not evident in water column ²³⁴Th profiles, which show high-frequency variability. Allowing trapping efficiencies to vary from 100% does not reconcile the differences between trap and water column deficit observations; we conclude that substantial lateral and vertical advective influences must be invoked to account for the differences.Advective influences are potentially greater on ²³⁴Th fluxes derived from water column deficits relative to those obtained from traps because the calculation of deficits in open-ocean settings is dominated by the magnitude of the “dissolved” ²³⁴Th fraction. For observed current velocities of 5–20 cm s⁻¹, in one radioactive mean-life of ²³⁴Th, the water column at the DYFAMED site can reflect ²³⁴Th scavenging produced tens to hundreds of kilometers away. In contrast, most of the ²³⁴Th flux collected in shallow sediment traps at the DFYFAMED site was in the fraction settling >200 m d⁻¹; in effect the sediment trap can integrate the ²³⁴Th flux over distances 40-fold less than water column ²³⁴Th distributions. In some sense, sediment trap and water column sampling for ²³⁴Th provide complementary pictures of ²³⁴Th export. However, because the two methods can be dominated by different processes and are subject to different biases, their comparison must be treated with caution.  相似文献   

Further investigations on why POC concentrations differ in samples collected by Niskin bottle and in situ pump     

Zhanfei Liu  J. Kirk Cochran  Cindy Lee  Beat Gasser  Juan Carlos Miquel  Stuart G. Wakeham 《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(18):1558-1567

Particulate organic carbon (POC) concentrations measured in bottles are often higher than those measured by in situ pumps when samples are taken concurrently. In previous work, we suggested that differential collection of zooplankton might explain this systematic discrepancy in POC between these small volume (bottle) and large volume (in situ pump) techniques. We have now further quantified the carbon contributed by zooplankton collected in the >70-μm particulate fractions from both bottles and pumps at sites in the Mediterranean Sea and Long Island Sound. Our results show that zooplankton abundance and lipid concentrations from zooplankton are one order of magnitude higher in the bottles than in the pumps, supporting the idea that part of the pump–bottle difference is due to collection of more zooplankton by the bottles. Particle washout off the 70-μm mesh used in the in situ pump may cause loss of some particles as well. However, zooplankton in the >70-μm fraction from the bottles contributed only about 1–2 μM POC, which cannot explain the up to 20 μM POC differences observed in this study. Thus, the mechanisms leading to such a large POC difference are still unclear and need to be further investigated. POC concentrations measured using microquartz filters were similar to those using glass fiber filters, suggesting that filter types cannot explain the higher POC observed in bottles, where glass fiber filters are normally used. Furthermore, we investigated several different pump inlet designs to determine how these might affect the ability of pumps to collect and retain large (>70 μm) particles, including zooplankton. The comparison among different pump inlets suggests that inlet design affects the efficiency and retention of large particles and that a sealed filter holder with a narrow right-angle tubular opening is the most efficient at catching/retaining zooplankton.  相似文献   

Reducing zero-point systematics in dark energy supernova experiments     

L. Faccioli  A.G. Kim  R. Miquel  G. Bernstein  A. Bonissent  M. Brown  W. Carithers  J. Christiansen  N. Connolly  S. Deustua  D. Gerdes  L. Gladney  G. Kushner  E.V. Linder  S. McKee  N. Mostek  H. Shukla  A. Stebbins  C. Stoughton  D. Tucker 《Astroparticle Physics》2011,34(12):847-857

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New constraints on the Messinian sealevel drawdown from 3D seismic data of the Ebro Margin,western Mediterranean     

Roger Urgeles  Angelo Camerlenghi  Daniel Garcia‐Castellanos  Ben De Mol  Miquel Garcés  Jaume Vergés  Ian Haslam  Martin Hardman 《Basin Research》2011,23(2):123-145

We present new 3D seismic and well data from the Ebro Margin, NW Mediterranean Sea, to shed new light on the processes that formed the Messinian Erosion Surfaces (MES) of the Valencia Trough (Mediterranean Sea). We combine these data with backstripping techniques to provide a minimum estimate of the Messinian sea level fall in the EBRO Margin, as well as coupled isostasy and river incision and transport modeling to offer new constraints on the evolution of the adjacent subaerial Ebro Basin. Four major seismic units are identified on the Cenozoic Ebro Margin, based on the seismic data, including two major prograding megasequences that are separated by a major unconfirmity: the MES. The 3D seismic data provide an unprecedented view of the MES and display characteristic features of subaerial incision, including a drainage network with tributaries of at least five different orders, terraces and meandering rivers. The Messinian landscape presents a characteristic stepped‐like profile that allows the margin to be subdivided in three different regions roughly parallel to the coastline. No major tectonic control exists on the boundaries between these regions. The boundary between the two most distal regions marks the location of a relatively stable base level, and this is used in backstripping analysis to estimate the magnitude of sea level drop associated with the Messinian Salinity Crisis on the Ebro Margin. The MES on the Ebro Margin is dominated by a major fluvial system, that we identify here as the Messinian Ebro River. The 3D seismic data, onshore geology and modeling results indicate that the Ebro River drained the Ebro Basin well in advance of the Messinian.  相似文献   

Impact of faulting in depocentres development,facies assemblages,drainage patterns,and provenance in continental half-graben basins: An example from the Fanja Basin of Oman     

Camilla L. Würtzen  Alvar Braathen  Miquel Poyatos-Moré  Mark J. Mulrooney  Lina H. Line  Ivar Midtkandal 《Basin Research》2023,35(2):705-743

Fault throw gradients create transverse folding, and this can influence accommodation creation and sedimentary routing and infill patterns in extensional half-graben basin. The Fanja half-graben basin (Oman) offers an excellent outcrop of an alluvial fan succession displaying cyclical stacking and basin-scale growth-fold patterns. These unique conditions allow for an investigation of fault-timing and accommodation development related to fault-transverse folding. Our study combines geological mapping, structural analysis, sedimentary logging and correlation, and bulk mineralogical compositions. Mapping reveals that the basin is bounded by a regional-scale fault, with local depocentres changing position in response to transverse syncline and anticline development ascribed to fault-displacement gradients. The alluvial Qahlah Formation (Late Cretaceous) is unconformably overlying the Semail Ophiolite, and is in turn overlain by the marine Jafnayn Formation (Late Palaeocene). Facies and stratigraphic analysis allows for subdivision of the Qahlah Formation into four informal units, from base to top: (i) laterite in topographic depressions of the ophiolite, (ii) greenish pebbly sandstones, deriving from axially draining braided streams deposited in the low-relief half-graben basin. This green Qahlah grades vertically into the red Qahlah, formed by alluvial fanglomerates and floodplain mudstones, with drainage patterns changing from fault-transverse to fault-parallel with increasing distance to the main fault. The red Qahlah can be divided into (iii) the Wadi al Theepa member, found in a western basin depocentre, with higher immaturity and sand: mud ratio, suggesting a more proximal source, and (iv) the Al Batah member, located in the eastern part of the basin. The latter shows better sorting, a lower sand: mud ratio, and more prominent graded sub-units. It also shows eastward expansion from an orthogonal monocline, ascribed to accommodation developed in a relay ramp. Changes in sedimentary facies and depositional patterns are consistent with differential mineralogical composition. The Green Qahlah is composed of quartz and lithic mafic rock fragments, sourced from the ophiolite and schists of the metamorphic basement. The Red Qahlah is composed of chert and kaolinite sourced from the Hawasina Nappe succession in the footwall of the master fault. These changes in source area are linked to unroofing of fault-footwalls and domal structures during the extensional collapse of the Semail Ophiolite. The novelty of this study resides in linking sedimentology and fault-displacement events controlling fault-perpendicular folding, and its influence on depocentre generation and stratigraphic architecture. This is an approach seldom considered in seismic analysis, and rarely analysed in outcrop studies, thus placing the results from this study among the key outcrop-based contributions to the field.  相似文献