Large-scale biomass for energy, with considerations and cautions: an editorial comment     

Gregg Marland  Michael Obersteiner 《Climatic change》2008,87(3-4):335-342

  相似文献   

Transient impacts of Little Ice Age glacier expansion on sedimentation processes at glacier-dammed Iceberg Lake, southcentral Alaska     

Katie E. Diedrich  Michael Gregg Loso 《Journal of Paleolimnology》2012,48(1):115-132

Iceberg Lake, a glacier-dammed proglacial lake in southern Alaska, contains a 1,500+ year varve record complicated by a history of episodic lake-level changes associated with fluctuations in ice-dam thickness and position. To better understand the basinwide glaciolacustrine response to late Holocene climate variability, we collected five cores from two areas in the lake, including a previously unexamined deepwater area distal from inlet streams. Based on eight AMS ¹⁴C dates, and correlations among our cores and previously documented outcrops, we describe ~1,000?years of stratigraphy from each area. Deposition at both areas was dominated by fine-grained varves, but cores from the distal area uniquely contain coarser deposits, including rhythmites and graded sand beds, that we attribute to deposition of a subaqueous outwash fan-delta between ~1250 and 1650 AD. We attribute this event to thickening of the impounding glacier and consequent incursion of the glacier margin, and an associated lateral moraine, into the lake. This result suggests an early onset of the Little Ice Age (LIA) glacial advance in this region. Changes in basinwide circulation and sedimentation associated with this event probably caused minor thickening of varves used previously to reconstruct summer temperatures, reducing sensitivity of that record to early LIA cooling. The basinwide impact of this event illustrates the potentially significant spatial and temporal variability of lacustrine sedimentary processes in dynamic glacial landscapes.  相似文献   

Kinematics, substructure and luminosity-weighted dynamics of six nearby galaxy groups     

P. Firth  E. A. Evstigneeva  J. B. Jones  M. J. Drinkwater  S. Phillipps  M. D. Gregg 《Monthly notices of the Royal Astronomical Society》2006,372(4):1856-1868

  相似文献   

Lower Carboniferous peritidal carbonates and associated evaporites adjacent to the Leinster Massif,southeast Irish Midlands     

Zsolt R. Nagy  Ian D. Somerville  Jay M. Gregg  Stephen P. Becker  Kevin L. Shelton 《Geological Journal》2005,40(2):173-192

Analysis of a 275 m‐thick section in the Milford Borehole, GSI‐91‐25, from County Carlow, Ireland, has revealed an unusual sequence of shallow subtidal, peritidal and sabkha facies in rocks of mid?‐late Chadian to late Holkerian (Viséan, Lower Carboniferous) age. Sedimentation occurred on an inner ramp setting, adjacent to the Leinster Massif. The lower part of the sequence (late Chadian age) above the basal subtidal bioclastic unit is dominated by oolite sand facies associations. These include a lower regressive dolomitized, oolitic peloidal mobile shoal, and an upper, probably transgressive, backshoal oolite sand. A 68 m‐thick, well‐developed peritidal sequence is present between the oolitic intervals. These rocks consist of alternating stromatolitic fenestral mudstone, dolomite and organic shale, with evaporite pseudomorphs and subaerial exposure horizons containing pedogenic features. In the succeeding Arundian–Holkerian strata, transgressive–regressive carbonate units are recognized. These comprise high‐energy, backshoal subtidal cycles of argillaceous skeletal packstones, bioclastic grainstones with minor oolites and algal wackestones to grainstones and infrequent algal stromatolite horizons. The study recognizes for the first time the peritidal and sabkha deposits in Chadian rocks adjacent to the Leinster Massif in the eastern Irish Midlands. These strata appear to be coeval with similar evaporite‐bearing rocks in County Wexford that are developed on the southern margin of this landmass, and similar depositional facies exist further to the east in the South Wales Platform, south of St. George's Land, and in Belgium, south of the Brabant Massif. The presence of evaporites in the peritidal facies suggests that dense brines may have formed adjacent to the Leinster Massif. These fluids may have been involved in regional dolomitization of Chadian and possibly underlying Courceyan strata. They may also have been a source of high salinity fluids associated with nearby base‐metal sulphide deposits. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

A laboratory investigation into the effects of slope on lava flow morphology     

Tracy K. P. Gregg  Jonathan H. Fink 《Journal of Volcanology and Geothermal Research》2000,96(3-4)

In an attempt to model the effect of slope on the dynamics of lava flow emplacement, four distinct morphologies were repeatedly produced in a series of laboratory simulations where polyethylene glycol (PEG) was extruded at a constant rate beneath cold sucrose solution onto a uniform slope which could be varied from 1° through 60°. The lowest extrusion rates and slopes, and highest cooling rates, produced flows that rapidly crusted over and advanced through bulbous toes, or pillows (similar to subaerial “toey” pahoehoe flows and to submarine pillowed flows). As extrusion rate and slope increased, and cooling rate decreased, pillowed flows gave way to rifted flows (linear zones of liquid wax separated by plates of solid crust, similar to what is observed on the surface of convecting lava lakes), then to folded flows with surface crusts buckled transversely to the flow direction, and, at the highest extrusion rates and slopes, and lowest cooling rates, to leveed flows, which solidified only at their margins. A dimensionless parameter, Ψ, primarily controlled by effusion rate, cooling rate and flow viscosity, quantifies these flow types. Increasing the underlying slope up to 30° allows the liquid wax to advance further before solidifying, with an effect similar to that of increasing the effusion rate. For example, conditions that produce rifted flows on a 10° slope result in folded flows on a 30° slope. For underlying slopes of 40°, however, this trend reverses, slightly owing to increased gravitational forces relative to the strength of the solid wax. Because of its significant influence on heat advection and the disruption of a solid crust, slope must be incorporated into any quantitative attempt to correlate eruption parameters and lava flow morphologies. These experiments and subsequent scaling incorporate key physical parameters of both an extrusion and its environment, allowing their results to be used to interpret lava flow morphologies on land, on the sea floor, and on other planets.  相似文献   

The evolution and star formation of dwarf galaxies in the Fornax Cluster     

M.J. Drinkwater  M.D. Gregg  B.A. Holman  M.J.I. Brown 《Monthly notices of the Royal Astronomical Society》2001,326(3):1076-1094

  相似文献   

Development of a small in-situ conductivity instrument     

Pederson  A. Gregg  M. 《Oceanic Engineering, IEEE Journal of》1979,4(3):69-75

The initial development and testing of a small in-situ conductivity instrument was reported at OCEAN '73 [1]. Since then, extensive operational experience has been obtained with a number of these instruments on moorings and on free and tethered platforms that move vertically and horizontally. This experience is reported here; as well as design improvements, and calibration and maintenance procedures. Also discussed are cell-flushing characteristics and the problems of matching conductivity measurements spatially and temporally to temperature measurements.  相似文献   

Evidence that excess 210Pb flux varies with sediment accumulation rate and implications for dating recent sediments     

José-María Abril  Gregg J. Brunskill 《Journal of Paleolimnology》2014,52(3):121-137

Most ²¹⁰Pb dating models assume that atmospheric flux of excess ²¹⁰Pb (²¹⁰Pb_exc) to the sediment–water interface remains constant over time. We revisited this assumption using statistical analysis of a database of laminated sediments and evaluated the implications for radiometric dating of recent deposits. A bibliographic survey enabled us to create a database with 10 annually laminated sediment cores from a variety of aquatic systems. The database has records of ²¹⁰Pb_exc flux, initial ²¹⁰Pb_exc activity, and sediment accumulation rate (SAR). ²¹⁰Pb_exc flux to sediments varied with time, and 1/3 of the data had relative deviations from the mean value >25 %. There was no statistically significant correlation between activities at the core top and SAR, whereas a statistically significant (p < 0.01) linear regression between ²¹⁰Pb_exc flux and SAR was found for nine of the ten cores. Thus, in most of the studied aquatic systems, ²¹⁰Pb_exc flux to the sediment was governed primarily by flux of matter, rather than by direct atmospheric ²¹⁰Pb_exc deposition. Errors in chronology and SAR, attributable to varying ²¹⁰Pb_exc flux and estimated by the constant rate of supply (CRS) model, were evaluated from its analytical solutions, and tested against SAR values from this database that were derived independently from varves. We identified several constraints for general application of the CRS model, which must be taken into account to avoid its misuse.  相似文献   

A nonlinear solar cycle model with potential for forecasting on a decadal time scale     

D. P. Gregg 《Solar physics》1984,90(1):185-194

This paper describes a novel non-linear oscillator model of the sunspot cycle which accurately reproduces several of the observed qualitative and quantitative characteristics of the real cycle including the long term amplitude modulation pattern. The model accounts for 96% of cycle peak height variance over the period 1859 to 1980. The aim of this work is to assess the potential of such models for forecasting solar activity on decadal and possibly longer time scales. Longer term forecasts may have practical economic significance because of the growing evidence for relationships between solar cycle variations and terrestrial weather and climatic variations (Bandeen and Moran, 1975; Currie, 1980; Williams, 1981). The model predicts that cycle 22 will have an annual mean peak amplitude in the range 25 to 45, the lowest peak activity for 260 yr.  相似文献   

Nature of sediment dispersal off the Sepik River, Papua New Guinea: preliminary sediment budget and implications for margin processes     

Steven A. Kuehl  Gregg J. Brunskill  Kathy Burns  David Fugate  Tara Kniskern  Linda Meneghini 《Continental Shelf Research》2004,24(19):2417-2429

A sediment budget is constructed for the slope and narrow continental shelf off the Sepik River in order to estimate the relative importance of turbid plumes versus bottom gravity transport through a near-shore submarine canyon in the dispersal of sediment across this collision margin. ²¹⁰Pb geochronology and inventories of Kasten cores are consistent with the northwestward dispersal of sediment from the river mouth via hypopycnal and possible isopycnal plumes. Sediment accumulation rates are 5 cm yr⁻¹ on the upper slope just off of the Sepik mouth, decreasing gradually to 1 cm yr⁻¹ toward the northwest, and decreasing abruptly offshore (<0.2 cm yr⁻¹ at 1200 m water depth). A sediment budget indicates that only about 7–15% of the Sepik River sediment discharge accumulates on the adjacent open shelf and slope. The remainder presumably escapes offshore via gravity flows through a submarine canyon, the head of which extends into the river mouth. The divergent sediment pathways observed off the Sepik River (i.e., surface and subsurface plumes versus sediment gravity flows through a canyon) may be common along high-yield collision margins of the Indo–Pacific archipelago, and perhaps are analogous to most margins during Late Quaternary low sea-level conditions.  相似文献