Leaf wax δ2H and varve-thickness climate proxies from proglacial lake sediments, Baffin Island, Arctic Canada     

Elizabeth K. Thomas  Sean McGrane  Jason P. Briner  Yongsong Huang 《Journal of Paleolimnology》2012,48(1):193-207

We present a multiproxy paleoclimate record using leaf wax hydrogen isotopes (??²H_wax) and varve thickness from Arctic proglacial lake sediments. We also provide one of the first evaluations of the utility of ??²H_wax as a paleoclimate proxy in Arctic proglacial lakes. We compare varve thickness and ??²H_wax at sub-decadal resolution from 1948 to 2004 AD, and at sub-centennial resolution from 1450 to 2004 AD. Varve thickness and ??²H_wax both contain large interannual variability and are anti-correlated during the late twentieth century, suggesting that both proxies respond rapidly, but by different mechanisms, to catchment-scale forcings. At longer time scales, varve thickness exhibits a strong response to Little Ice Age cooling (1661?C1827 AD in this record) but does not show evidence for twentieth century warming recorded throughout the Arctic. ??²H_wax does record regional-scale temperature changes, with more ²H-depleted values during the Little Ice Age and an abrupt change to more ²H-enriched values in the twentieth century. This corresponds well with a recent Arctic-wide temperature reconstruction in which the seventeenth century is the coldest interval, and the twentieth century is the warmest interval. Our results suggest that ??²H_wax is a promising proxy that can be applied at high resolution in proglacial Arctic lakes.  相似文献   

Rapid climate change in the Upper Palaeolithic: the record of charcoal conifer rings from the Gravettian site of Dolní Vĕstonice,Czech Republic     

David Beresford-Jones  Sean Taylor  Clea Paine  Alexander Pryor  Jiří Svoboda  Martin Jones 《Quaternary Science Reviews》2011,30(15-16):1948-1964

Precisely how Upper Palaeolithic human ecology was shaped by changing climate during the Pleniglacial remains a matter of debate, for while this generally cold period is now understood to include complex and often rapid flux in climate, there are still considerable difficulties in resolving climatic variations at particular times and places — derived from various lines of proxy evidence — with the high-resolution proxy record of temperature changes from oxygen isotope analysis of the Greenland ice-cores.In this paper we apply the methodology of large-scale flotation to newly excavated contexts from the Upper Palaeolithic (Gravettian) site of Dolní V?stonice II, Czech Republic, to explore the potential of charcoal — as a natural archive of environmental information — to offer information on environmental change towards the end of the middle pleniglacial during Oxygen Isotope Stage 3, between c. 32,500 and 31,200 Cal yr BP. The results of an analysis of ring widths and other anatomical features — interpreted alongside micromorphological data — indicate that this charcoal may capture a higher-resolution record of the changing climatic conditions during which humans were first expanding into these hitherto marginal ecologies and, consequently, shed new light upon the complexity of the lifeways that enabled them to do so.  相似文献   

The invasive Asian copepodPseudodiaptomus inopinus in Oregon,Washington, and British Columbia estuaries     

Jeffery R. Cordell  Sean M. Morrison 《Estuaries and Coasts》1996,19(3):629-638

At least six species of Asian copepods have been recently introduced to the west coast of North America. Among them isPseudodiaptomus inopinus, which became established and abundant in the Columbia River estuary between 1980 and 1990. Subsequently, the tidal regions of 18 smaller rivers in the Pacific Northwest were sampled using near-bottom pumps and vertical plankton net hauls. These samples indicate thatP. inopinus has not only invaded at least seven other estuaries in this region, but that it is sometimes the dominant zooplankter in these systems.P. inopinus occurred in estuaries of both large and small rivers and in rivers with and without international shipping. Two factors may be important in the establishment of this copepod: temperature and extent of salinity intrusion. In our samples, average autumn temperature of rivers with establishedP. inopinus populations was 19.3°C, whereas those withoutP. inopinus had an average temperature of 12.4°C. Rivers withP. inopinus had salinity intrusion zones of more than 1 km length and those withoutP. inopinus usually had intrusion zones of less than 1 km.  相似文献   

Internal constitution and evolution of the moon     

Sean C. Solomon  M. Nafi Toksöz 《Physics of the Earth and Planetary Interiors》1973,7(1):15-38

The composition, structure and evolution of the moon's interior are narrowly constrained by a large assortment of physical and chemical data. Models of the thermal evolution of the moon that fit the chronology of igneous activity on the lunar surface, the stress history of the lunar lithosphere implied by the presence of mascons, and the surface concentrations of radioactive elements, involve extensive differentiation early in lunar history. This differentiation may be the result of rapid accretion and large-scale melting or of primary chemical layering during accretion; differences in present-day temperatures for these two possibilities are significant only in the inner 1000 km of the moon and may not be resolvable. If the Apollo 15 heat-flow result is representative of the moon, the average uranium concentration in the moon is 0.05–0.08 p.p.m.Density models for the moon, including the effects of temperature and pressure, can be made to satisfy the mass and moment of inertia of the moon and the presence of a low-density crust inferred from seismic refraction studies only if the lunar mantle is chemically or mineralogically inhomogeneous. The upper mantle must exceed the density of the lower mantle at similar conditions by at least 5%. The average mantle density is that of a pyroxenite or olivine pyroxenite, though the density of the upper mantle may exceed 3.5 g/cm³. The density of the lower mantle is less than that of the combined crust and upper mantle at similar temperature and pressure, thus reinforcing arguments for early moon-wide differentiation of both major and minor elements. The suggested density inversion is gravitationally unstable and implies stresses in the mantle 2–5 times those associated with the lunar gravitational field, a difficulty that can be explained or avoided by: (1) adopting lower values for the moment of inertia and/or crustal thickness, or (2) postulating that the strength of the lower mantle increases with depth or with time, either of which is possible for certain combinations of composition and thermal evolution.A small iron-rich core in the moon cannot be excluded by the moon's mass and moment of inertia. If such a core were molten at the time lunar surface rocks acquired remanent magnetization, then thermal-history models with initially cold interiors strongly depleted in radioactive heat sources as a primary accretional feature must be excluded. Further, the presence of ～||pre|40 K in a FeFeS core could significantly alter the thermal evolution and estimated present-day temperatures of the deep lunar interior.  相似文献   

Variations in the velocities of the major plates since the late cretaceous     

Daniel M. Davis  Sean C. Solomon 《Tectonophysics》1981,74(1-2)

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Atmospheric Disturbances that Generate Intermittent Turbulence in Nocturnal Boundary Layers     

Jielun Sun  Donald H. Lenschow  Sean P. Burns  Robert M. Banta  Rob K. Newsom  Richard Coulter  Stephen Frasier  Turker Ince  Carmen Nappo  Ben B. Balsley  Michael Jensen  Larry Mahrt  David Miller  Brian Skelly 《Boundary-Layer Meteorology》2004,110(2):255-279

Using the unprecedented observational facilities deployed duringthe 1999 Cooperative Atmosphere-Surface Exchange Study (CASES-99),we found three distinct turbulent events on the night of 18October 1999. These events resulted from a density current,solitary wave, and internal gravity wave, respectively. Our studyfocuses on the turbulence intermittency generated by the solitarywave and internal gravity wave, and intermittent turbulenceepisodes associated with pressure change and wind direction shiftsadjacent to the ground. Both the solitary and internal gravitywaves propagated horizontally and downward. During the passage ofboth the solitary and internal gravity waves, local thermal andshear instabilities were generated as cold air was pushed abovewarm air and wind gusts reached to the ground. These thermal andshear instabilities triggered turbulent mixing events. Inaddition, strong vertical acceleration associated with thesolitary wave led to large non-hydrostatic pressure perturbationsthat were positively correlated with temperature. The directionaldifference between the propagation of the internal gravity waveand the ambient flow led to lateral rolls. These episodic studiesdemonstrate that non-local disturbances are responsible for localthermal and shear instabilities, leading to intermittentturbulence in nocturnal boundary layers. The origin of thesenon-local disturbances needs to be understood to improve mesoscalenumerical model performance.  相似文献   

Geostatistical interpolation of object counts collected from multiple strip transects: Ordinary kriging versus finite domain kriging   总被引：2，自引：0，他引：2  

Hirotaka Saito  Sean A. McKenna  D. A. Zimmerman  Timothy C. Coburn 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(1):71-85

Data collected along transects are becoming more common in environmental studies as indirect measurement devices, such as geophysical sensors, that can be attached to mobile platforms become more prevalent. Because exhaustive sampling is not always possible under constraints of time and costs, geostatistical interpolation techniques are used to estimate unknown values at unsampled locations from transect data. It is known that outlying observations can receive significantly greater ordinary kriging weights than centrally located observations when the data are contiguously aligned along a transect within a finite search window. Deutsch (1994) proposed a kriging algorithm, finite domain kriging, that uses a redundancy measure in place of the covariance function in the data-to-data kriging matrix to address the problem of overweighting the outlying observations. This paper compares the performances of two kriging techniques, ordinary kriging (OK) and finite domain kriging (FDK), on examining unexploded ordnance (UXO) densities by comparing prediction errors at unsampled locations. The impact of sampling design on object count prediction is also investigated using data collected from transects and at random locations. The Poisson process is used to model the spatial distribution of UXO for three 5000 × 5000 m fields; one of which does not have any ordnance target (homogeneous field), while the other two sites have an ordnance target in the center of the site (isotropic and anisotropic fields). In general, for a given sampling transects width, the differences between OK and FDK in terms of the mean error and the mean square error are not significant regardless of the sampled area and the choice of the field. When 20% or more of the site is sampled, the estimation of object counts is unbiased on average for all three fields regardless of the choice of the transect width and the choice of the kriging algorithm. However, for non-homogeneous fields (isotropic and anisotropic fields), the mean error fluctuates considerably when a small number of transects are sampled. The difference between the transect sampling and the random sampling in terms of prediction errors becomes almost negligible if more than 20% of the site is sampled. Overall, FDK is no better than OK in terms of the prediction performances when the transect sampling procedure is used.  相似文献   

Specific Storage Volumes: A Useful Tool for CO2 Storage Capacity Assessment   总被引：1，自引：0，他引：1  

Sean T. Brennan  Robert C. Burruss 《Natural Resources Research》2006,15(3):165-182

Subsurface geologic strata have the potential to store billions of tons of anthropogenic CO₂; therefore, geologic carbon sequestration can be an effective mitigation tool used to slow the rate at which levels of atmospheric CO₂ are increasing. Oil and gas reservoirs, coal beds, and saline reservoirs can be used for CO₂ storage; however, it is difficult to assess and compare the relative storage capacities of these different settings. Typically, CO₂ emissions are reported in units of mass, which are not directly applicable to comparing the CO₂ storage capacities of the various storage targets. However, if the emission values are recalculated to volumes per unit mass (specific volume) then the volumes of geologic reservoirs necessary to store CO₂ emissions from large point sources can be estimated. The factors necessary to convert the mass of CO₂ emissions to geologic storage volume (referred to here as Specific Storage Volume or ‘SSV’) can be reported in units of cubic meters, cubic feet, and petroleum barrels. The SSVs can be used to estimate the reservoir volume needed to store CO₂ produced over the lifetime of an individual point source, and to identify CO₂ storage targets of sufficient size to meet the demand from that given point source. These storage volumes also can then be projected onto the land surface to outline a representative “footprint,” which marks the areal extent of storage. This footprint can be compared with the terrestrial carbon sequestration capacity of the same land area. The overall utility of this application is that the total storage capacity of any given parcel of land (from surface to basement) can be determined, and may assist in making land management decisions.  相似文献   

Nucleosynthesis and early chemical evolution in galaxies     

Stelios A Tsangarides  Enrico Arnone  Sean G Ryan 《Astronomy& Geophysics》2003,44(2):2.28-2.29

Nucleosynthesis and galactic chemical evolution are inter-linked topics that merge various fields in astronomy and physics. Speakers at the RAS discussion meeting of January 2003 combined theory and observation in understanding these fields. Stelios A Tsangarides, Enrico Arnone and Sean G Ryan report.  相似文献   

Mercury: the enigmatic innermost planet     

Sean C Solomon ^{Author Vitae} 《Earth and Planetary Science Letters》2003,216(4):441-455

The planet Mercury, a difficult object for study by astronomical observation and spacecraft exploration alike, poses multiple challenges to our general understanding of the inner planets. Mercury’s anomalously high uncompressed density implies a metal fraction of 60% or more by mass, an extreme outcome of planetary formational processes common to the inner solar system. Whether that outcome was the result of chemical gradients in the early solar nebula or removal by impact or vaporization of most of the silicate shell from a differentiated protoplanet can potentially be distinguished on the basis of the chemical composition of the present crust. Our understanding of the geological evolution of Mercury and how it fits within the known histories of the other terrestrial planets is restricted by the limited coverage and resolution of imaging by the only spacecraft to have visited the planet. The role of volcanism in Mercury’s geological history remains uncertain, and the dominant tectonic structures are lobate scarps interpreted as recording an extended episode of planetary contraction, issues that require global imaging to be fully examined. That Mercury has retained a global magnetic field when larger terrestrial planets have not stretches the limits of standard hydromagnetic dynamo theory and has led to proposals for a fossil field or for exotic dynamo scenarios. Hypotheses for field generation can be distinguished on the basis of the geometry of Mercury’s internal field, and the existence and size of a fluid outer core on Mercury can be ascertained from measurements of the planet’s spin axis orientation and gravity field and the amplitude of Mercury’s forced librations. The nature of Mercury’s polar deposits, suggested to consist of volatile material cold-trapped on the permanently shadowed floors of high-latitude impact craters, can be tested by remote sensing of the composition of Mercury’s surface and polar atmosphere. The extremely dynamic exosphere, which includes a number of species derived from Mercury’s surface, offers a novel laboratory for exploring the nature of the complex and changing interactions among the solar wind, a small magnetosphere, and a solid planet. Recent ground-based astronomical measurements and several new theoretical developments set the stage for the in-depth exploration of Mercury by two spacecraft missions within the coming decade.  相似文献