Observed climate change constrains the likelihood of extreme future global warming     

PETER A. STOTT  CHRIS HUNTINGFORD  CHRIS D. JONES  JAMIE A. KETTLEBOROUGH 《Tellus. Series B, Chemical and physical meteorology》2008,60(1):76-81

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Assessment of dispersive pressure as a beach placer mechanism     

MATT R. TOMKINS  PETER NIELSEN  TOM E. BALDOCK 《Sedimentology》2010,57(2):408-417

The concept of sediment sorting extending from the Bagnold constitutive relationship for sediment under shear is examined in the context of beach placer formation. The traditional interpretation of shear sorting is found to be inconsistent with data from new granular flow experiments. A binary mixture satisfying the shear equivalence relationship displayed pronounced segregation during shear. This observation is contrary to shear sorting as applied in the literature where no such segregation for this pairing of mineral species is expected. Further experiments minimizing the potential of grain percolation of smaller grains or kinetic sieving also demonstrated sorting patterns inconsistent with the existing shear sorting interpretation. Consequently, the shear sorting process, as currently formulated, may not be an appropriate means to describe beach placer formation. Kinetic sieving appears to be a more likely mechanism in this context, enhanced by the shearing and dilation of the granular‐fluid flow.  相似文献   

Desert dust aerosol air mass mapping in the western Sahara, using particle properties derived from space-based multi-angle imaging     

By RALPH KAHN  REAS PETZOLD  MANFRED WENDISCH  EIKE BIERWIRTH  TILMAN DINTER  MICHAEL ESSELBORN  MARCUS FIEBIG  BIRGIT HEESE  PETER KNIPPERTZ  DETLEF MÜLLER  ALEXANDER SCHLADITZ  WOLFGANG VON HOYNINGEN-HUENE 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):239-251

Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite's larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05–0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR's ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.  相似文献   

Early Holocene loessic colluviation in northwest England: new evidence for the 8.2 ka event in the terrestrial record?     

PETER J. VINCENT  TOM C. LORD  MATT W. TELFER  PETER WILSON 《Boreas: An International Journal of Quaternary Research》2011,40(1):105-115

Vincent, P. J., Lord, T. C., Telfer, M. W. & Wilson, P. 2010: Early Holocene loessic colluviation in northwest England: new evidence for the 8.2 ka event in the terrestrial record? Boreas, 10.1111/j.1502‐3885.2010.00172.x. ISSN 0300‐9483. Twelve new samples of loessic silts from widely spaced locations on the karst uplands of northwest England have yielded Optically Stimulated Luminescence (OSL) dates that fall within or overlap with (within uncertainties) the early to mid‐Holocene period (11.7–6.0 ka), and support three already‐published Holocene ages from similar sediment from this region. Nine of the 15 dates are coincident with the hypothesized climatic deterioration at 8.5–8.0 ka in the North Atlantic region and eight are coincident with the 8.2 ka event. These dates demonstrate that the silts are not primary air‐fall loesses of deglacial/Lateglacial age (c. 18.0–11.7 ka) but have been reworked and now consist of loess‐derived colluvial deposits; we consider the ages to be reliable as there is no compelling evidence to indicate that the samples are partially bleached. There is no substantive archaeological or palynological evidence for Late Mesolithic hunter‐gatherers having had a major impact on the landscape, and it is considered highly unlikely that these people triggered colluviation. We estimate that during the 8.2 ka event there was a reduction in mean annual air temperature at these upland locations of ～2.6–4.6 °C, and proxy evidence from other sites indicates a shift to wetter conditions. It is inferred that there was greater snow accumulation in winter, that the snowpack survived for longer periods, and that there was an increase in the magnitude and frequency of frost‐related processes and meltwater flooding. Together, these changes in climate and their associated (sub)surface processes were responsible for the reworking of the loess. The OSL dates indicate climatically induced landscape dynamism in Great Britain during the latter half of the ninth millennium.  相似文献   

Multi‐proxy evidence for early to mid‐Holocene environmental and climatic changes in northeastern Poland     

STEFAN LAUTERBACH  ACHIM BRAUER  NILS ANDERSEN  DAN L. DANIELOPOL  PETER DULSKI  MATTHIAS HÜLS  KRYSTYNA MILECKA  TADEUSZ NAMIOTKO  BIRGIT PLESSEN  ULRICH VON GRAFENSTEIN  DECLAKES PARTICIPANTS 《Boreas: An International Journal of Quaternary Research》2011,40(1):57-72

Lauterbach, S., Brauer, A., Andersen, N., Danielopol, D. L., Dulski, P., Hüls, M., Milecka, K., Namiotko, T., Plessen, B., von Grafenstein, U. & DecLakes participants 2010: Multi‐proxy evidence for early to mid‐Holocene environmental and climatic changes in northeastern Poland. Boreas, 10.1111/j.1502‐3885.2010.00159.x. ISSN 0300‐9483. We investigated the sedimentary record of Lake Hańcza (northeastern Poland) using a multi‐proxy approach, focusing on early to mid‐Holocene climatic and environmental changes. AMS ¹⁴C dating of terrestrial macrofossils and sedimentation rate estimates from occasional varve thickness measurements were used to establish a chronology. The onset of the Holocene at c. 11 600 cal. a BP is marked by the decline of Lateglacial shrub vegetation and a shift from clastic‐detrital deposition to an autochthonous sedimentation dominated by biochemical calcite precipitation. Between 10 000 and 9000 cal. a BP, a further environmental and climatic improvement is indicated by the spread of deciduous forests, an increase in lake organic matter and a 1.7‰ rise in the oxygen isotope ratios of both endogenic calcite and ostracod valves. Rising δ¹⁸O values were probably caused by a combination of hydrological and climatic factors. The persistence of relatively cold and dry climate conditions in northeastern Poland during the first one and a half millennia of the Holocene could be related to a regional eastern European atmospheric circulation pattern. Prevailing anticyclonic circulation linked to a high‐pressure cell above the retreating Scandinavian Ice Sheet might have blocked the influence of warm and moist Westerlies and attenuated the early Holocene climatic amelioration in the Lake Hańcza region until the final decay of the ice sheet.  相似文献   

Sea-ice roughness and drag coefficients in a dynamic–thermodynamic sea-ice model for the Arctic     

NADJA STEINER  MARKUS HARDER  PETER LEMKE 《地球，A辑:动力气象学与海洋学》1999,51(5):964-978

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Regional Saharan dust modelling during the SAMUM 2006 campaign     

By BERND HEINOLD  INA TEGEN  MICHAEL ESSELBORN  KONRAD KANDLER  PETER KNIPPERTZ  DETLEF MÜLLER  ALEXANDER SCHLADITZ  MATTHIAS TESCHE  BERNADETT WEINZIERL  ALBERT ANSMANN  DIETRICH ALTHAUSEN  BENOIT LAURENT  REAS MASSLING  THOMAS MÜLLER  REAS PETZOLD  KERSTIN SCHEPANSKI  ALFRED WIEDENSOHLER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):307-324

The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006 SAMUM field campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry synoptic-scale dynamics, they are often misrepresented when dust emissions are caused by moist convection or influenced by small-scale topography that is not resolved by the model. In contrast to long-range dust transport, in the vicinity of source regions the model performance strongly depends on the correct prediction of the exact location of sources. Insufficiently resolved vertical grid spacing causes the absence of inversions in the model vertical profiles and likely explains the absence of the observed sharply defined dust layers.  相似文献   

The Ethics of Place and Environmental Change: Some Examples from the South Pacific     

PETER RAINE 《New Zealand geographer》2001,57(2):41-47

This paper concerns place and ‘placelessness’, and suggests links between those two and types of environmental ethic. An historical analysis of place based ethics and environmental degradation draws on examples from the Pacific basin. Finally, relationships between environmental ethics and traditional patterns of resource exploitation are proposed for several island societies.  相似文献   

Recent status of bowhead whales, Balaena mysticetus, in the wintering grounds off West Greenland     

RANDALL R. REEVES  MADS PETER HEIDE-JØRGENSEN 《Polar research》1996,15(2):115-125

Bowhead whales, Balaena mysticetus, belonging to the Davis Strait/Baffin Bay stock, have historically in Baffin Bay and Davis Strait, including waters along the west coast of Greenland in and near the entrance of Disko Bay. Aerial surveys of the Disko Bay region during late winter (1981, 1982, 1990,1991, 1993 and 1994) showed that it was still visited regularly by a few tens of whales. Commercial whaling on bowheads in Baffin Bay and Davis Strait ended in about 1915, but occasional killing continued until as recently as the 1970s. The low numbers of bowheads observed off West Greenland in recent years are consistent with the results of surveys of the summering grounds in the eastern Canadian Arctic, indicating that any recovery has been exceedingly slow. The only conclusion supported by the data is that the current stock size is a small fraction of what it was prior to commercial whaling.  相似文献   

Stratigraphy of a Neoglacial end moraine in Norway     

MICHAEL J. ALEXANDER  PETER WORSLEY 《Boreas: An International Journal of Quaternary Research》1973,2(3):117-142

There exposures in an outer end moraine ridge at Autre Okstindbredal, north Norway, are described and interpreted. The presence of perennially frozen ground is attributed to the present or very recent climate of the area and suggest the occurence of true sporadic permafrost. Several buried soil horizons including podzols are recognised within the moraine ridge sections. These are considered to be derived. It is thought that their occurance as imbricate stress is best explained by a basal freeze-in mechanism associated with marginal thrusting when the local glacier possessed a sub-polar thermal régime. This freeze-in phase is of late Neoglacial age but not necessarily associated with the widespread eighteenth century advance in Scandinavia. The soils in part date from the postglacial climatic optimum.  相似文献