Ice‐free conditions in eastern Fennoscandia during early Marine Isotope Stage 3: lacustrine records     

KARIN F. HELMENS  STEFAN ENGELS 《Boreas: An International Journal of Quaternary Research》2010,39(2):399-409

Helmens, K. F. & Engels, S. 2010: Ice‐free conditions in eastern Fennoscandia during early Marine Isotope Stage 3: lacustrine records. Boreas, 10.1111/j.1502‐3885.2010.00142.x. ISSN 0300‐9483. The traditional notion that Fennoscandia was glaciated throughout Marine Isotope Stages (MIS) 4–2, from c. 70 kyr BP to the deglaciation 15–10 kyr BP ago, has been challenged during the last decade. Recent studies have shown that climate and environmental settings during MIS 3 were more dynamic than previously assumed, and lacustrine sediment bodies indicate open‐water conditions for several sites in eastern Fennoscandia. In this study, three sediment sequences from western, eastern and northeast Finland are compared in detail with respect to their chronology, vegetation reconstruction and climatic inferences. OSL‐dating places the sediments in early MIS 3. Pollen evidence suggests the presence of isolated birch trees and open birch forest close to the retreating ice margin, in contrast to vegetation reconstructions from central Europe, which indicate tree‐less vegetation. Furthermore, reconstructions of climate using transfer functions have yielded surprising results, indicating present‐day summer temperatures in northeast Finland. The combined results suggest ice‐free and warm conditions in major parts of eastern Fennoscandia in early MIS 3, possibly during Greenland Interstadial (GIS) 14 around 53 kyr BP ago.  相似文献   

Building bridges to 2020 and beyond: the road from Bali     

HARALD WINKLER  SHAUN VORSTER 《Climate Policy》2013,13(3):240-254

What would the shape of a realistic, yet ambitious, package for the climate regime after 2012 look like? How do we obtain a package deal starting in Bali but building bridges to a post-2020 climate regime? A fair, effective, flexible and inclusive package deal has to strike a core balance between development and climate imperatives (mitigation, adaptation, dealing with the impacts of response measures, technology transfer, investment and finance) to create bargaining space and establish a conceptual contract zone. Within a continuum of possible packages, two packages in the contract zone are identified: ‘multi-stage’ and ‘ambitious transitional’. The latter is ambitious, combining domestic cap-and-trade for the USA, deeper cuts for Annex B countries, and quantifiable mitigation actions by developing countries. It is transitional as a possible bridge to a more inclusive regime beyond 2020. Multi-stage is defined around mechanisms by which countries move through increasingly stringent levels of participation, and must be based upon agreed triggers. Our assessment of political dynamics is that multi-stage is not yet in the political contract zone. Key to this is the absence of a ‘trigger from the North’, in that the largest historical emitter must act earlier and most decisively. But progress will also depend on continued leadership from Annex B countries, as well as more proactive, incentivized leadership in the South. Agreeing on the transitional stage is the critical next step in the evolution of the climate regime. Negotiating any package will require an institutional space for bargaining, political leadership and trust, and a clear time-frame.  相似文献   

Seismic evidence of up to 200 m lake‐level change in Southern Patagonia since Marine Isotope Stage 4     

ANDREA CATALINA GEBHARDT  CHRISTIAN OHLENDORF  FRANK NIESSEN  MARC DE BATIST  FLAVIO S. ANSELMETTI  DANIEL ARIZTEGUI  PIERRE KLIEM  STEFAN WASTEGÅRD  BERND ZOLITSCHKA 《Sedimentology》2012,59(3):1087-1100

Maar lake Laguna Potrok Aike is located north of the Strait of Magellan (south‐eastern Patagonia). Seismic reflection profiles revealed a highly dynamic palaeoclimate history. Dunes were identified in the eastern part of the lake at approximately 30 to 80 m below the lake floor, overlying older lacustrine strata, and suggest that the region experienced dry conditions probably combined with strong westerly winds. It is quite likely that this can be linked to a major dust event recorded in the Antarctic ice cores during Marine Isotope Stage 4. The dunes are overlain by a series of palaeo‐shorelines indicating a stepwise water‐level evolution of a new lake established after this dry period, and thus a change towards wetter conditions. After the initial, rapid and stepwise lake‐level rise, the basin became deeper and wider, and sediments deposited on the lake shoulder at approximately 33 m below present‐day lake level point towards a long period of lake‐level highstand between roughly 53·5 ka cal. bp and 30 ka cal. bp with a maximum lake level some 200 m higher than the desiccation horizon. This highstand was then followed by a regressional phase of uncertain age, although it must have happened some time between approximately 30 ka cal. bp and 6750 yrs cal. bp . Dryer conditions during the Mid‐Holocene are evidenced by a dropping lake level, resulting in a basin‐wide erosional unconformity on the lake shoulder. A second stepwise transgression between ca 5·8 to 5·4 ka cal. bp and ca 4·7 to 4 ka cal. bp with palaeo‐shorelines deposited on the lake shoulder unconformity again indicates a change towards wetter conditions.  相似文献   

LATE QUATERNARY MORAINES ALONG THE SEKHOKONG RANGE, EASTERN LESOTHO: CONTRASTING THE GEOMORPHIC HISTORY OF NORTH- AND SOUTH-FACING SLOPES     

BY STEPHANIE C. MILLS  STEFAN W. GRAB  SIMON J. CARR 《Geografiska Annaler: Series A, Physical Geography》2009,91(2):121-140

Considerable Quaternary environmental reconstruction for the high Drakensberg is based on geomorphological and sedimentological work undertaken along the northern aspects of the Sekhokong mountain range of eastern Lesotho. Given that no previous investigations have focused on the southern aspects, this paper documents the observed geomorphology and provides a more complete palaeo-environmental picture for this range. Data on the morphology, sedimentology and micromorphology for two linear debris ridges are presented. It is demonstrated that the two ridges are most likely moraines originating from a small niche glacier. The combined use of macro- and micro-scale sedimentology is proven to be an essential tool in ascribing a glacial process origin for the landforms, given the complex depositional history they have undergone. AMS ages obtained from the deposits (14 700 cal. yrs bp and 19 350 cal. yrs bp ) places these in the time-scale of the Last Glacial Maximum. The study demonstrates rather contrasting aspect-controlled palaegeomorphological environments along the Sekhokong range, which is also reflected in the dissimilar contemporary biophysical micro-environments. It is suggested that the south-facing slopes were dominated by glacial processes during the Last Glacial Maximum (LGM), as is evident from the moraines, while the proposition for previously described north-facing glacial cirques is rejected based on the absence of erosional/depositional evidence and greater insolation received on these warmerequator-facing slopes. Rather, we propose that the observed north-facing hollows are a product of a multitude of geomorphic processes spanning several tens to hundreds of thousands of years.  相似文献   

Latitudinally different responses of Tethyan shoal‐water carbonate systems to the Early Aptian oceanic anoxic event (OAE 1a)     

STEFAN HUCK  NIELS RAMEIL  TVRTKO KORBAR  ULRICH HEIMHOFER  THOMAS D. WIECZOREK  ADRIAN IMMENHAUSER 《Sedimentology》2010,57(7):1585-1614

Ocean‐wide anoxic events represent intensively investigated anomalies in the global carbon cycle. Most previous research has focussed on hemipelagic and pelagic settings and on the relationship between black‐shale deposition and carbon‐isotope excursions. The study of ocean‐wide anoxic events and coeval shallow‐water settings is now increasingly seen as an interesting complementary approach, but one that is not without problems. Whereas platform drowning characterizes the Early Aptian of the northern Tethyan margin, Lithocodium–Bacinella‐rich facies and ongoing shoal‐water sedimentation at the southern Tethyan margin (Oman) bears important information on potential causes of carbon‐cycle perturbations. The present paper seeks to test the supra‐regional relevance of the Oman data by investigating coeval central Tethyan limestones. Three Lower Aptian shoal‐water sections in Istria (Croatia), deposited on the isolated Adriatic Carbonate Platform, are investigated applying chemostratigraphy (carbon and strontium) and detailed sedimentological analysis. The focus is on peritidal to lagoonal facies characterized by mass occurrences of Lithocodium–Bacinella, an enigmatic microencruster community. Lithocodium–Bacinella facies occurs predominantly in layers ranging from one to several centimetres in stratigraphic thickness, with several layers merging to metre‐thick packages. Growth fabrics within the layers include oncoidal morphotypes, lumps, interconnected patches and columns, layers and rare nodular to massive bindstone facies. These growth patterns show a remarkable regional extent and consistency over study sites distributed several kilometres apart. This widespread distribution suggests that specific Lithocodium–Bacinella morphotypes might serve as regional stratigraphic markers. The high‐resolution carbon‐isotope chemostratigraphy presented here is based on pristine rudist shells and matrix micrite samples and calibrated against strontium‐isotope data obtained from screened rudist low‐Mg calcite. The chemostratigraphic data are consistent with existing biostratigraphic data and place the studied strata at the onset of Early Aptian oceanic anoxic event 1a. Moreover, results indicate the near‐coeval nature of Lithocodium–Bacinella bloom facies in Istria and Oman. The outcomes of this study point to latitudinally different responses of Tethyan shoal‐water carbonate systems (platform drowning versus Lithocodium–Bacinella blooms) to the ocean‐wide anoxic event 1a.  相似文献   

Relay ramps as pathways for turbidity currents: a study combining analogue sandbox experiments and numerical flow simulations     

WIEBKE ATHMER  REMCO M. GROENENBERG  STEFAN M. LUTHI  MARINUS E. DONSELAAR  DIMITRIOS SOKOUTIS  ERNST WILLINGSHOFER 《Sedimentology》2010,57(3):806-823

Unlike for subaerial settings, the impact of subaqueous relay ramps on sediment dispersal is still poorly understood. A combination of analogue laboratory experiments in a sandbox with numerical flow calculations is used to simulate relay ramp topographies on rifting continental margins and to analyse the resulting turbidity current pathways and their deposits. Various scenarios are investigated, including inflow perpendicular and oblique to the relay ramp axis as well as flow constrained by an incised channel on the ramp and by a landward‐directed tilt of the ramp. Without channelling, most sedimentation takes place on the basin floor because the bulk of the flow follows the steepest gradient down the fault and into the rift basin. With a channel along the relay ramp, significant flow occurs initially down the ramp axis, but channel spillover and basinward ramp tilting combine to redirect much of the sediment down the fault slope into the basin. When the relay ramp has a landward‐oriented tilt, most of the current flows down the ramp and deposits its sediment load there and at the foot of the ramp. However, also here a considerable amount of the flow is shed over the hanging wall fault and into the basin, forming a secondary depocentre, while ponding redistributes thin deposits over a wider area of the basin. The quantitative dependence of these results on the specific ramp geometries remains to be investigated further but may bear great importance for refined sedimentary models in subaqueous rifted settings as well as for hydrocarbon exploration therein.  相似文献   

New discoveries of the Vedde Ash in southern Sweden and Scotland     

STEFAN WASTEGÅRD  CHRIS S. M. TURNEY  J. JOHN LOWE  STEPHEN J. ROBERTS 《Boreas: An International Journal of Quaternary Research》2000,29(1):72-78

The Vedde Ash (c. 10 300 ¹⁴ C BP) provides a key time-parallel marker horizon within the Younger Dryas chronozone or GS-1 event of the GRIP stratigraphy. Until recently, the known distribution of wind-blown Vedde Ash outside Iceland was restricted to the west coast of Norway, off-shore sequences close to the Outer Hebrides and the Greenland summit GRIP ice core. The first discoveries of the Vedde Ash in Scotland were reported in 1997, following the development of a new technique for extracting rhyolitic micro-tephra particles from minerogenic deposits. Here we report on the discovery of the Vedde Ash at additional sites in Scotland and at sites in southern Sweden. The concentration of tephra particles in sediments is highest in sites in western Norway, but is also relatively high in sites in southwestern Sweden, suggesting that the main ash cloud travelled eastwards from its volcanic source of Katla, in southern Iceland. Electron microprobe analyses do not indicate any clear geochemical evolution within the samples reported here.  相似文献   

Late Weichselian ostracod assemblages from the southern Kattegat, Scandinavia: a palaeoenvironmental study     

STEFAN MAJORAN  KJELL NORDBERG 《Boreas: An International Journal of Quaternary Research》1997,26(3):181-200

The ostracods in three vibro cores (representing the time between c . 13000 and 12000 BP) from southern Kattegat were studied to further elucidate palaeoenvironmental conditjons in an area interpreted to be influenced by a Late Weichselian drainage of the Baltic Ice Lake via the Öresund Strait. This time represents an extremely important phase of the deglaciation of the northern hemisphere. It is characterized by rapid climatic change and enormous amounts of meltwater that are drained into the ocean. The ostracod assemblages identified are characterized by a peculiar mixture of marine (arctic and temperate) and freshwater species believed to characterize environments ranging from the tidal zone of an outer estuary (or delta) to fully marine sublittoral conditions in a subarctic climate. Dominant species display autochthonous population structures typical of in situ elements of such environments. Indications of very shallow conditions are, however, difficult to reconcile with palaeobathymetrical inferences from earlier studies of shore-level displacements. It is, therefore, possible that the present assemblages are mainly death assemblages deposited offshore by postmortem meltwater discharge. Rare pre-Quaternary ostracods similar to Mesozoic species previously reported from the Öresund Strait (drill holes) and the Swedish west coast may have been redeposited by outflowing meltwater.  相似文献   

Prediction uncertainty of conceptual rainfall-runoff models caused by problems in identifying model parameters and structure     

STEFAN UHLENBROOK  JAN SEIBERT  CHRISTIAN LEIBUNDGUT  ALLAN RODHE 《水文科学杂志》2013,58(5):779-797

Abstract

The uncertainties arising from the problem of identifying a representative model structure and model parameters in a conceptual rainfall-runoff model were investigated. A conceptual model, the HBV model, was applied to the mountainous Brugga basin (39.9 km”) in the Black Forest, southwestern Germany. In a first step, a Monte Carlo procedure with randomly generated parameter sets was used for calibration. For a ten-year calibration period, different parameter sets resulted in an equally good correspondence between observed and simulated runoff. A few parameters were well defined (i.e. best parameter values were within small ranges), but for most parameters good simulations were found with values varying over wide ranges. In a second step, model variants with different numbers of elevation and landuse zones and various runoff generation conceptualizations were tested. In some cases, representation of more spatial variability gave better simulations in terms of discharge. However, good results could be obtained with different and even unrealistic concepts. The computation of design floods and low flow predictions illustrated that the parameter uncertainty and the uncertainty of identifying a unique best model variant have implications for model predictions. The flow predictions varied considerably. The peak discharge of a flood with a probability of 0.01 year^?1, for instance, varied from 40 to almost 60 mm day^?1. It was concluded that model predictions, particularly in applied studies, should be given as ranges rather than as single values.  相似文献   

The Po Valley Fog Experiment 1989   总被引：13，自引：0，他引：13  

S. FUZZI  M. C. FACCHINI  G. ORSI  J. A. LIND  W. WOBROCK  M. KESSEL  R. MASER  W. JAESCHKE  K. H. ENDERLE  B. G. ARENDS  A. BERNER  I. SOLLY  C. KRUISZ  G. REISCHL  S. PAHL  U. KAMINSKI  P. WINKLER  J. A. OGREN^  K. J. NOONE•  A. HALLBERG  H. FIERLINGER-OBERLINNINGER  H. PUXBAUM  A. MARZORATI  H.-C. HANSSON  A. WIEDENSOHLER  I. B. SVENNINGSSON  B. G. MARTINSSON  D. SCHELL  H. W. GEORGII 《Tellus. Series B, Chemical and physical meteorology》1992,44(5):448-468

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