a record of post glacial moraine deposition and tephra stratigraphy from otokomi lake rose basin glacier national park montana the sedimentary record of otokomi lake glacier national park montana was studied to determine the age of an adjacent crowfoot moraine the presence of mt st helens jy ash near the bottom of the longest percussion core limits drainage basin deglaciation to before 11 400 14c years before present bp although 14 100 bp is the estimated basal age of the core correlative shifts in loss on ignition coarse 1 mm grain size magnetic susceptibility and x ray gray scale data at a depth of 185 cm are interpreted to be related to a sedimentary change in otokomi lake brought about by the deposition of the adjacent crowfoot moraine the estimated age of the moraine is 10 590 bp which is within the younger dryas interval this information supports the hypothesis that crowfoot moraines represent a regional western north american response to younger dryas cooling

younger dryas a data to model comparison to constrain the strength of the overturning circulation 1 the university of victoria earth system climate model uvic escm is used to compare simulated time series of radiocarbon during the younger dryas yd with paleoceanographic records i find that only a complete shut down and recovery of the atlantic meridional overturning circulation amoc can simulate both the rise in atmospheric co2 concentrations seen in ice core records and the peak and subsequent decrease in atmospheric 14c comparable to the peak recorded in the varved sediments of the cariaco basin simulated radiocarbon profiles in the western north atlantic match well with data from deep sea corals at the beginning of the yd whereas planktonic benthic foraminifera records match best with a transient state during the rapid recovery of the amoc the steepness of the increase in atmospheric 14c at 12 9 ka cal could not be simulated with oceanic circulation changes only because the response time of the climate system is too slow

late quaternary pollen record from the central california continental margin abstract a pollen record obtained from a deep sea core from the continental margin off central california contains evidence of the terrestrial floral adaptation to changing climatic conditions over the last ca 20 000 cal bp the pollen record is divided into three pollen zones two of which are late pleistocene in age glacial and transitional and the third is holocene interglacial the glacial pollen zone ca 20 000 17 000 cal bp is characterized by pinus and abies pollen reflecting environmental conditions during the last glacial maximum overlying this ca 17 000 11 600 cal bp is the transitional pollen zone containing a pollen assemblage indicative of a transitional climatic regime with species that reflect more arid environmental conditions pinus and artemisia decreasing in abundance and those reflecting moister conditions sequoia and alnus rising in abundance pediastrum and dinoflagellates are common and are attributable to increased nutrient rich coastal runoff the bolling allerod 295 256 cm ca 14 600 12 900 bp and younger dryas 256 243 cm ca 12 900 11 600 bp events occur within the transitional pollen zone as well the interglacial pollen zone ca 11 600 cal bp to present is characterized by decreasing pinus and increasing sequoia quercus and asteraceae reflecting changes in vegetation during the climatic warming of the holocene two brief dry periods are represented in this pollen zone one from 150 to 125 cm ca 8000 6400 cal bp and the other at 22 20 cm ca 800 700 cal bp they are correlated with the middle holocene dry period and the medieval climate anomaly respectively

the impact of glacial lake runoff on the goldthwait and champlain seas the relationship between glacial lake agassiz runoff and the younger dryas abstract the freshwater flux to the north atlantic ocean during the last deglaciation included runoff meltwater plus precipitation from glacial lake st lawrence ca 11 6 ka bp from glacial lake agassiz 10 9 9 9 and 9 5 8 0 ka bp and from glacial lake barlow ojibway 9 5 8 0 ka bp runoff from the glacial lakes does not appear to have mixed with the deep water of the goldthwait sea in the gulf of st lawrence and was part of the surface outflow to the north atlantic ocean radiocarbon dated invertebrate faunal assemblages show that the major impact of lake agassiz runoff to the north atlantic ocean during the 10 9 to 9 9 ka bp interval occurred after 10 5 ka bp resulting in the freshening of the champlain sea the younger dryas cold episode on the other hand began about 11 0 ka bp the discordance between the major impact of lake agassiz runoff on the champlain sea and the beginning of the cold episode indicates that lake agassiz runoff did not trigger the younger dryas cooling however the runoff from glacial lake agassiz may have sustained the cold climate during the latter part of the younger dryas cold episode

physical simulation of ground fissures triggered by underground fault activity abstract numerical modeling and physical simulation experiment are two important steps to investigate the stress and strain fields of overlying strata but sometimes it is very difficult to do the test of the physical experiment on a large scale soil sample due to the financial consideration and the available test site to investigate the features of the ground fissures prevailing in xi an city we undertook in this study a series of physical simulation tests on the large scale soil sample to analyze the stress and displacement fields caused by the underlying normal fault activity comparing with the fracturing modes of the ground fissures and the failure patterns of construction building it is evident that the experiment results coincide with the failure patterns of the building but not with the fracturing modes of the ground fissures which indicate that the ground fissures in xi an may be an old fracture surface having already spread to superficial layer covered by a very thin layer of loose soils and the groundwater over pumping is just a factor to make them exposed on the ground surface

latest pleistocene and holocene behaviour of franklin glacier mt waddington area british columbia coast mountains canada franklin glacier is an 18 km long valley glacier that originates in a broad icefield below the west face of mt waddington in the central british columbia coast mountains canada radiocarbon dated

evaluation of proposed early holocene advances of alpine glaciers in the north cascade range washington state usa constraints provided by palaeoenvironmental reconstructions many palaeoenvironmental reconstructions from across western north america indicate that the early to mid holocene was warmer and drier than present the wide distribution of these records suggests that relatively mild and arid conditions were regionally ubiquitous during the early holocene in contrast two recently proposed advances of alpine glaciers in the cascade range of washington state corresponding to equilibrium line altitude depressions of 350 to 450 m are placed in the early holocene the juxtaposition of the proposed major expansion of early holocene alpine glaciers with the constraint provided by a number of palaeoenvironmental reconstructions from directly adjacent areas results in palaeoclimatic gradients that are untenable the apparent diachronous behaviour of adjacent palaeoenvironmental records may be an artifact of dating errors

postglacial vegetation and climate dynamics in the seymour belize inlet complex central coastal british columbia canada palynological evidence from tiny lake a pollen based study from tiny lake in the seymour belize inlet complex of central coastal british columbia canada permits an evaluation of the dynamic response of coastal temperate rainforests to postglacial climate change open pinus parklands grew at the site during the early lateglacial when the climate was cool and dry but more humid conditions in the later phases of the lateglacial permitted mesophytic conifers to colonise the region early holocene conditions were warmer than present and a successional mosaic oftsugaheterophylla andalnus occurred at tiny lake climate cooling and moistening at 8740 70 14 c a bp initiated the development of closed late successional t heterophylla cupressaceae forests which achieved modern character after 6860 50 14 c a bp when a temperate and very wet climate became established the onset of early holocene climate cooling and moistening at tiny lake may have preceded change at more southern locations including within the seymour belize inlet complex on a meso to synoptic scale this would suggest that an early holocene intensification of the aleutian low pressure system was an important influence on forest dynamics in the seymour belize inlet complex and that the study region was located near the southern extent of immediate influence of this semi permanent air mass copyright 2008 john wiley sons ltd

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

two step deglaciation at the oxygen isotope stage 6 5e transition the zeifen kattegat climate oscillation comparison of marine lacustrine and terrestrial records from twenty four sites suggests the existence of a younger dryas type climate oscillation just prior to the oxygen isotope stage 6 5e boundary these records include results from biostratigraphic pedostratigraphic and speleothem studies as well as analyses of stable isotope compositions of marine records and ice cores the climate oscillation is named after the warm zeifen interstadial and the cold kattegat stadial the zeifen interstadial may be related to a major meltwater pulse in the baffin bay labrador sea norwegian sea region the climate oscillation is presumably in part a result of a variation in ocean circulation especially in the strength of the north atlantic drift but changes in the atmospheric circulation also played an important role the geographically widespread distribution of the oscillation suggests that the two step deglaciation influenced both the northern and southern hemispheres c 1996 elsevier science ltd

characteristics and genesis mechanism of ground fissures in taiyuan basin northern china abstract since the 1980s ground fissures in the taiyuan basin have experienced blowouts resulting in a significant but hidden danger to cities in the basin this paper describes the plane and damage characteristics of the ground fissures based on the findings of field investigations and mapping most ground fissures in the basin were determined as linear with pinch out reappearances on the surface they were characterized by both horizontal tension with maximum widths and vertical offsets of up to 40 and 15 cm respectively the ground fissure strikes in the basin were observed to be consistent with those of nearby active faults and the long axis direction of the groundwater depression funnel the roads and houses that lie across the fissures were determined to be the most affected by ground fissure disasters in the basin the primary damage modes for the roads were vertical offset and surface collapse whereas buildings experienced foundation failure and tensile damage profiles obtained through geological drilling and trench exploration further revealed obvious tension and synsedimentary characteristics of the ground fissures correlated with existing faults correlation analysis shows that the formation of ground fissures in taiyuan basin is mainly related to faults and excessive groundwater extraction theoretical analysis revealed that the size and activity of ground fissures in the basin were positively correlated with four factors the dip of faults in an area regional tensile stress difference between the thicknesses of aquifers on either side of a fault and groundwater exploitation the significant increase in ground fissure activity since the 1980s mainly reflects uncontrolled groundwater discharge hence prevention of excessive groundwater exploitation in the basin would mitigate the destructive effects of the ground fissures

a high resolution late glacial and early holocene diatom record from baffin island eastern canadian arctic an interval of late glacial to early holocene sedimentation spanning the period 12 9 8 4 ka bp 14c dated by accelerator mass spectrometry is contained within 15 cm of gyttja in a core from a small lake on southwestern cumberland peninsula baffin island this sediment was subsampled in continuous 2 5 mm increments for diatom analysis extremely low sediment accumulation rates 1 8 cm ka 1 are characteristic of the initial phase of organic sedimentation but they increase rapidly to 14 2 cm ka 1 after 9 ka bp the first 0 5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments thereafter and throughout the late glacial and earliest holocene diatom floras were dominated by alkaliphilous and circumneutral species of fragilaria around 9 ka bp shifts to acidophilous floras dominated by brachysira brebissonii and later eunotia rhomboidea and frustulia rhomboides vars saxonica and crassinervia suggest a period of natural lake acidification high dia

evidence for a younger dryas like cooling event on the british columbia coast two independent paleoclimatic records from the pacific coast of canada indicate that a late glacial warming trend was interrupted by a return to colder conditions between about 11 000 and 10 200 radiocarbon yr b p correlative with the classical younger dryas chronozone of the north atlantic region fossil benthic foramnifera from three cores from the continental shelf dated by accelerator mass spectrometry show peak abundances of the cold water indicator species cassidulina reniforme at this time fossil pollen spectra from two sites on the queen charlotte islands record a shift from forest to open herb rich vegetation after 11 100 yr b p probably in response to colder and wetter conditions identified by pollen climate transfer functions these preliminary data for a cold oscillation between ca 11000 and 10000 yr ago in the northeast pacific argue that this deglacial phenomenon was not restricted to the north atlantic but was a hemispheric and possibly global event

land subsidence and ground failure associated to groundwater exploitation in the aguascalientes valley mexico ground failure associated with land subsidence due to groundwater withdrawal is the main geotechnical hazard in the aguascalientes valley causing enormous economic loss by damage to public and private properties including urban infrastructures the aguascalientes valley forms a tectonic graben flanked by north to south trending normal faults where the hydrologic hydrogeologic and anthropogenic conditions are favorable for ground deformation the intensive withdrawal of groundwater has produced a critical decline in potentiometric levels particularly beneath the aguascalientes city where most of the ground failures have occurred most of the ground failures observed in this valley are directly linked to irregularities of the bedrock and buried paleo channels currently the damage caused by ground failures is variable and considerable even though local government is aware of this problem and has undertaken actions in order to mitigate the ground failure related damages for instance mapping the location of ground failures in the entire valley carrying out resistivity surveys aimed at detecting incipient ground failures and buried cracks and carrying out gravimetric surveys for detecting zones in the subsoil with the geologic conditions for the potential development of ground failures

vegetation history of pleasant island southeastern alaska since 13 000 yr b p abstract a 13 000 year history of late quaternary vegetational and climatic change has been derived from lacustrine sediments from pleasant island in the glacier bay region of southeastern alaska early arrival of lodgepole pine and mountain hemlock indicated by the presence of pollen and conifer stomata suggests expansion from refugia in the alexander archipelago a short term climatic reversal possibly correlated with the european younger dryas is inferred from the expansion of tundra elements and deposition of inorganic sediments between 10 600 and 9900 14 c yr b p two peat cores from the lake catchment verify holocene vegetation changes and aid in the separation of biogenic from climatic forces affecting vegetation history differences in pollen representation among the three cores illustrate the variation among pollen collecting substrates as well as the spatial heterogeneity of peatland development and its dependence on local hydrology initial peat accumulation and soil paludification occasioned by increases in temperature and precipitation in the early holocene allowed western and mountain hemlock to replace sitka spruce 8500 8000 yr b p open muskeg became widespread about 7000 yr b p and allowed lodgepole pine to reinvade the region after a 2000 yr absence the extensive replacement of fen elements by bog taxa at 3400 yr b p suggests increased paludification due to changing hydrologic conditions its correlation with the upland expansion of tsuga heterophylla suggests the onset of a cooler wetter neoglacial climate in southeastern alaska

ice rafted debris in the north pacific and correlation to north atlantic climatic events a high resolution record of the flux of ice rafted debris in deep sea cores from the northeast pacific indicates that the major interstadials that punctuated the last glaciation are concurrent between the north pacific and the north atlantic in the north atlantic these major interstadials immediately followed episodes of massive iceberg discharge thought to result from extensive collapse of the laurentide icesheet a mechanistic scenario is presented to explain how collapse of the laurentide icesheet could cause concurrent interstadials between the two oceans

the chronology of the last termination a review of radiocarbon dated high resolution terrestrial stratigraphies abstract the last termination is traditionally subdivided into the oldest dryas bolling older dryas allerod younger dryas and preboreal chronozones this paper briefly summarizes the history of the late weichselian chronostratigraphic system and gives an overview of recent developments in radiocarbon dating terrestrial records between 15 000 and 10 000 14 c years bp problems inherent in the traditional chronostratigraphy are discussed in the light of new and more advanced dating possibilities including accelerator mass spectrometry ams measurements on terrestrial macrofossils new results obtained using ams 14 c dated varve sequences are compared with each other and with the marine u th coral record in addition the importance of time synchronous marker horizons as a tool for long distance correlation between different archives is illustrated

a high resolution speleothem record of climatic variability at the allerod younger dryas transition in missouri central united states stable isotopic analysis and 234 u 230 th mass spectrometry dating of a single calcite stalagmite from onondaga cave east central missouri reveal climatic variability between 13 200 and 12 400 yr bp coincident with the aller d younger dryas transition in the gisp2 greenland ice cores n 18 o values of speleothem calcite mark decreasing temperatures between 13 200 and 13 000 yr bp while more rapidly decreasing n 13 c values record a sharp shift toward c3 vegetation at approximately 13 100 yr bp because of uncertainties in the chronological control of both this speleothem and the gisp2 record and the brevity of this speleothem record v800 years direct comparison of the two sequences is difficult the interval preserved by this speleothem may span the inter aller d cold period iacp alone both the iacp and the start of the younger dryas or only the first half of the younger dryas in any case these data demonstrate that the climate of the north american interior deteriorated significantly and rapidly during the interval associated with the aller d younger dryas transition fl 2001 elsevier science b v all rights reserved

late glacial vegetation dynamics of the queen charlotte islands and adjacent continental shelf british columbia canada abstract ams radiocarbon dates and paleoecological analyses of sediments from the continental shelf between the queen charlotte islands and the british columbia mainland confirm that portions of the shelf were subaerially exposed and ice free between at least 14 330 and 12 860 14c years bp 17 370 14 570 cal years bp pollen analysis suggests that cyperaceae likely formed the dominant plant cover on the exposed shelf at dogfish bank and fossil pediastrum algae confirm the presence of freshwater pollen accumulation rates suggest low plant density on the exposed shelf although this is uncertain due to over and under representation of some pollen types in relation to vegetation abundance on the landscape paleoecological analyses of late glacial sediments at west side pond on the southern queen charlotte islands demonstrate succession from herb tundra dominated by cyperaceae at 13 750 14c years bp 16 830 cal years bp to dwarf shrub tundra with salix and empetrum nigrum after 13 500 14c years bp 16 400 cal years bp pteridophytes increased in abundance during the transition to pinus contorta woodland ca 13 000 14c years bp 15 600 cal years bp fossil conifer stomata suggest that p contorta grew locally as early as 13 040 305 14c years bp alnus crispa was co dominant by 11 500 14c years bp 13 500 cal years bp and picea sitchensis or its hybrids were present as early as 11 400 14c years bp 13 400 cal years bp in the south moresby area

climate and vegetation in northeastern alaska 18 000 yr b p present changing abundances of taxa in the pollen record of northeastern alaska contain a climate signal and may be compared with gcm simulations of paleoclimates cold dry conditions indicated by full glacial pollen spectra are in broad agreement with model simulations successive expansion of betula and salix and later populus during the deglacial period 14 000 11 000 yr b p are likely correlated with the crossing of temperature thresholds determined largely by the size and position of the laurentide ice a degree of asynchroneity between sites probably reflects differential site responses to regional effects plus inaccuracies of radiocarbon dating the early holocene was probably the warmest period of the present interglacial as summer climate was influenced by a strong positive insolation anomaly picea glauca expanded in majorr river valleys ca 9000 yr ago and slightly later at upland sites in the brooks and alaska ranges at some sites a juniperus subzone which suggests particularly warm and dry conditions occurs between ca 10 000 and 8000 yr b p early mid holocene expansions of alnus 8500 7000 yr b p and picea mariana 7500 5000 yr b p suggest the subsequent development of moister conditions which have continued to the present temporal patterns in picea treeline position during the holocene are different in northern alaska northwestern canada and central canada in alaska the treeline is currently at its furthest holocene extent in northwestern canada the treeline has retreated since the mid holocene and in central canada a mid holocene advance and retreat occurred such differences between regions suggest a complex response of this taxon to climatic controls and underscore the need to interpret vegetation changes in relation to regional scale climate phenomena if the pollen chronology is calibrated with reference to u th dates the relationship of vegetational events to the insolation maximum at ca 10 000 yr b p is significantly altered the changed chronology also affects the interpretation of pollen records in relation to gcm simulations which are partly keyed to calendar years

distribution and mechanism of the ground fissures in wei river basin the origin of the silk road wei river basin wrb is the origin of the ancient and new silk road and it is located in southern fen wei graben system china since 1950s hundreds of ground fissures have formed in this affluent basin and these ground fissures have become the main geohazard in wrb this paper used a series of geological investigations such as site investigation trench excavation geological drilling and geophysical survey to understand the distribution and mechanism of formation of the ground fissures in wrb the results are 1 212 ground fissures in wrb were located in xi an xianyang weinan city and they have clear orientations mainly distributed from nee to sww nw to se and e to w moreover the ground fissures are accompanied by active faults along the same directions 2 ground fissures in wrb can be divided into two types some ground fissures display obvious horizontal and vertical separations on the earth surface whereas others only display obvious horizontal separations on the earth surface 3 ground fissures in wrb are triggered by four factors viz basin structure active fault human activities and loess erosion 4 the mechanism for the formation of ground fissures has also been proposed tectonic faulting is the fundamental cause of ground fissures in the wei river basin and imbalances in the man land caused by human actives accelerated the ground fissures activities 5 many effective measures have also been proposed to mitigate the hazards of ground fissures in wrb such as planning engineering measures controlling the exploitation of groundwater and monitoring this research will be helpful in safeguarding the sustainable development of the silk road economic belt

postglacial climates inferred from a lake at treeline southwest yukon territory canada abstract pollen chironomid and ostracode records from a lake located at alpine treeline provide regional paleoclimate reconstructions from the southwest yukon territory canada the pollen spectra indicate herbaceous tundra existed on the landscape from 13 6 11 ka followed by birch shrub tundra until 10 ka although picea pollen dominated the assemblages after 10 ka low pollen accumulation rates and picea percentages indicate minimal treeline movement through the holocene chironomid accumulation rates provide evidence of millennial scale climate variability and the chironomid community responded to rapid climate changes ostracodes were found in the late glacial and early holocene but disappeared due to chemical changes of the lake associated with changes in vegetation on the landscape inferred mean july air temperature total annual precipitation and water depth indicate a long term cooling with increasing moisture from the late glacial through the holocene during the younger dryas 12 9 11 2 ka cold and dry conditions prevailed the early and mid holocene were warm and dry with cool wet conditions after 4 ka and warm dry conditions since the end of the little ice age

exceptionally steep north south gradients in lake temperatures during the last deglaciation during the transition from the last glacial to the present interglacial climate late glacial period high summer insolation1 combined with the presence of the laurentide ice sheet is thought to have promoted the development of strong summer thermal gradients in north america south of the ice margin2 here we use palaeoecological methods to obtain quantitative evidence for the existence of these gradients our palaeoclimate reconstructions are based on water temperatures inferred from fossil assemblages of aquatic midge larvae in five lakes along a 240 km transect extending from central new brunswick canada to southeastern maine usa we show that the temperature gradient shifted during the killarney oscillation ko and younger dryas yd cooling events and that water temperature differences of 9 and 11 c existed over distances of 55 and 240 km respectively during parts of the late glacial period these gradients are much stronger than the current north south trends of lake summer surface water temperatures for these five lakes and for lakes across the northern tree line the rapid motion of such steep temperature gradients may have affected the progressive development of aquatic and terrestrial ecosystems in the region

oxygen isotope record of sea level and climate variations in the sulu sea over the past 150 000 years the sulu sea is located in the warm pool of the western pacific ocean where mean annual temperatures are the highest of anywhere on earth because this large heat source supplies the atmosphere with a significant portion of its water vapour and latent heat understanding the climate history of the region is important for reconstructing global palaeoclimate and for predicting future climate change changes in the oxygen isotope composition of planktonic foraminifera from sulu sea sediments have previously been shown to reflect changes in the planetary ice volume at glacial interglacial and millenial timeseales and such records have been obtained for the late pleistocene epoch and the last deglaciation1 3 here i present results that extend the millenial time resolution record back to 150 000 years before present on timescales of around 10 000 years the sulu sea oxygen isotope record matches changes in sea level deduced from coral terraces on the huon peninsula4 this is particularly the case during isotope stage 3 an interglacial period 23 000 to 58 000 years ago where the sulu sea oxygen isotope record deviates from the specmap deep ocean oxygen isotope record5 thus these results support the idea4 6 that there were higher sea levels and less continental ice during stage 3 than the specmap record implies and that sea level during this interglacial was just 40 50 metres below present levels the subsequent rate of increase in continental ice volume during the return to full glacial conditions was correspondingly faster than previously thought

timing and extent of allerod and younger dryas age ca 12 500 10 000 14c yr b p oscillations of the cordilleran ice sheet in the fraser lowland western north america the use of shaded digital topographic models to visualizes suites of topographic features stratigraphy and field mapping reveals newly recognized multiple moraines associated with oscillations of the remnants of the cordilleran ice sheet in the fraser lowland along the western washington british columbia border morphologic features show the extent of ice represented by sumas drift ca 11 600 10 000 14c yr b p following ca 3000 yr of retreat from the glacial maximum fraser glaciation positions 80 km south of seattle and in the strait of juan de fuca the paleogeography of the ice margin and timing of ice retreat during the sumas stade is reconstructed and bracketed by 70 radiocarbon dates 24 on marine shells 46 on wood and peat which are secured by morphologic and stratigraphic evidence four topographically distinct phases of the sumas deglaciation model are suggested phase si 11 600 11 400 14c yr b p outermost drift scattered remnants of ice contact deposits phase sii 11 600 11 400 14c yr b p glacier readvance building prominent moraine followed by glacier retreat phase siii 10 980 10 250 14c yr b p glacier readvance building of multiple moraines followed by glacier retreat phase siv 10 250 10 000 14c yr b p glacier readvance building of inner moraine followed by glacier retreat

overview of some geological hazards in the saudi arabia the saudi arabia has harsh environmental conditions which enhance some geomorphologic geological processes more than in other areas these processes create different geological hazards the general physiography of the saudi arabia is characterized by the red sea coastal plains and the escarpment foothills called tihama followed by the arabian shield mountains the arabian shelf plateau and finally the arabian gulf coastal plains these types of geological hazards can be categorized into sand accumulations earth subsidence and fissures flash floods problematic soils slope stability problems and karst problems the current study gives an overview of all these hazards with examples as well as develops a geo hazard map for the saudi arabia our findings indicate that the desert environment needs much concern and care national and international agencies have to join together with other people to keep the system balanced and to reduce the resulting geological hazards also remedial measures should be proposed to avoid and reduce these natural hazards

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

organic carbon accumulation over the last 16 kyr off vancouver island canada evidence for increased marine productivity during the deglacial abstract the organic carbon content of marine sediments is commonly used as a proxy for export production however in continental margin sediments a large fraction of the organic matter may be of terrestrial origin and it is necessary to correct the total organic carbon data accordingly radiocarbon dating of bulk organic carbon organic geochemistry and isotope data 13c and 15n are used here to characterize the type of organic matter present in core jt96 09 collected at a water depth of 920 m on the slope off western canada the quantities of marine and terrestrial organic carbon are then estimated using the 13c data the 16 kyr record obtained from core jt96 09 suggests that accumulation of total organic carbon was highest during the late glacial and deglacial but geochemical data indicate that as much as 70 of this carbon is terrestrial in origin when the palaeo record is corrected for this terrigenous input it is observed that accumulation of marine organic matter and presumably marine export production increased at the end of the last glacial contemporaneous with the bolling and that it peaked during the allerod data from other palaeoproductivity proxies i e bio barium opal and alkenones also indicate relatively high productivity during the deglacial these results indicate a return to modern upwelling conditions and high marine export production at 14 3 calendar kyr bp and a period of enhanced upwelling relative to the present during the allerod

younger dryas environments and archaeology on the northwest coast of north america abstract this paper reviews the current archaeological and palaeo environmental evidence from the younger dryas period on the northwest coast of north america sea level histories are region specific ranging from 100 m lower to 150 m higher than modern at ca 12 200 cal bp the mid point of the younger dryas palaeo environmental evidence shows temperature decrease across the study area but in some regions this is accompanied by greater precipitation and glacial advance whereas in other conditions were drier terrestrial vegetation reflects this variability with northern areas in particular showing evidence for expansion of herb and shrub tundra and southern areas marked by increased mountain hemlock and other species marine intertidal and terrestrial fauna indicate productive ecosystems with some sub regional changes such as extirpation of deer and bison perhaps associated with the younger dryas onset stable isotope analysis of bear remains show these species which are a good ecological analogue for humans exploited both marine and terrestrial resources despite patchy and dynamic marine and terrestrial environments these results suggest a challenging yet viable environment for humans archaeological evidence for younger dryas human occupation is currently limited to six sites of which four are associated with karst caves the earliest of these are in haida gwaii where bear hunting is dated to at least 12 650 cal bp during the heart of the younger dryas interval other sites in southeast alaska and in the fraser river lowlands date to around 12 100 cal bp in puget sound the presence of ca 13 000 cal bp clovis surface collections and the emerging data from the pre clovis ayer pond bison butchery site suggest pre younger dryas occupation the northwest coast was open to population movement from both the north and south in the poorly known interval before the younger dryas when conditions may have been more moderate and stable the sub regional variation and the scale of environmental change in the younger dryas especially sea level fluctuation makes discovery of pleistocene archaeological sites challenging the younger dryas may therefore be seen as something of a worst case scenario for both the human occupation and the archaeological investigation of the northwest coast

characteristics of land subsidence earth fissures and related disaster chain effects with respect to urban hazards in xi an china the ancient capital of xi an is a typical city in china with a shortage of water resources with an urban population of 7 million its domestic and industrial use of water depends almost entirely on groundwater large scale long term extraction of groundwater has caused severe land subsidence and triggered the reactivation of active normal faults in the quaternary under consolidated sediments underlying the city this has further led to ground ruptures that have gradually evolved into earth fissure zones during this process there has been a close spatiotemporal relationship between land subsidence and the formation of earth fissures from field monitoring data the subsidence bowls are typically located in loess depressions between earth fissure zones within structural blocks of sediment cut by active quaternary faults and preexisting fault planes the subsidence bowls are generally elliptical in shape with the long axes consistent with the preferred orientation of the earth fissures the underlying quaternary active faults and preexisting fault planes predispose the intervening sediment blocks to formation of earth fissures and intense groundwater extraction has led to accelerated subsidence and earth fissuring during the past 50 years mining groundwater land subsidence and earth fissures occur in a sequence and constitute a disaster chain with respect to urban hazards in xi an thus it is important to understand the relationships between these events this paper summarizes the characteristics of land subsidence and earth fissures in xi an and discusses the chain of relationships that connects them

sea surface temperature of the western equatorial pacific ocean during the younger dryas high resolution 200 yr sample spacing records of sea surface temperature for the past 15 000 yr have been inferred from planktonic foraminiferal assemblages in a sediment core from the south china sea although the assemblages imply a large glacial to interglacial temperature change 7 c for winter temperatures they give no indication of a cooling during younger dryas time this suggests that the younger dryas increase in 18o observed in cores from the western equatorial pacific is not due to a climatic cooling but rather to a change in the isotopic composition of the oceans

a 14 000 year vegetation history of a hypermaritime island on the outer pacific coast of canada based on fossil pollen spores and conifer stomata abstract pollen and conifer stomata analyses of lake sediments from hippa island on the north coast of british columbia were used to reconstruct the vegetation history of this small hypermaritime island between 14 000 and 13 230 cal yr bp the island supported diverse herb shrub communities dominated by cyperaceae artemisia and salix pinus contorta and picea sitchensis stomata indicate that these conifers were present among the herb shrub communities likely as scattered individuals transition to open p contorta woodland by 13 000 cal yr bp was followed by increases in alnus viridis alnus rubra and p sitchensis after 12 000 cal yr bp pinus dominated communities were replaced by dense p sitchensis and tsuga heterophylla forest with lysichiton americanus and fern understory thuja plicata stomata indicate that this species was present by 8700 cal yr bp but the pollen record suggests that its populations did not expand to dominate regional rainforests along with tsuga and picea until after 6600 cal yr bp conifer stomata indicate that species may be locally present for hundreds to thousands of years before pollen exceed thresholds routinely used to infer local species arrival when combined pollen and conifer stomata can provide a more accurate record of paleovegetation than either when used alone

paleoecology of late glacial terrestrial deposits with in situ conifers from the submerged continental shelf of western canada extensive portions of the continental shelf off the coast of british columbia were subaerially exposed during late wisconsinan deglaciation due to lowering of relative sea level by as much as 150 m paleoecological analyses were conducted at two sites on the emergent continental shelf where terrestrial surfaces with in situ conifers are preserved the woody plant remains confirm that during the latest period of subaerial exposure terrestrial vegetation was established on the continental shelf microscopic identification of fossil wood and analyses of pollen and plant macrofossils from the associated paleosols and overlying shallow pond sediments indicate that productive pinus contorta dominated communities with abundant alnus crispa and ferns grew on the shelf adjacent to and on the queen charlotte islands around 12 200 14c yr b p dwarf shrubs including salix and empetrum and herbaceous plants such as heracleum lanatum and hippuris vulgaris were also important components of the shelf vegetation near northern vancouver island mixed coniferous forests dominated by pinus contorta with picea tsuga spp alnus spp and ferns occupied the shelf at 10 500 14c yr b p

characteristics and mechanisms for origin of earth fissures in fenwei basin china abstract the most serious earth fissure disasters in china occur in the fenwei basin since the late 1950s earth fissure disasters have widely occurred in the weihe yuncheng linfen taiyuan and datong sub basins in the fenwei basin and such disaster has increased progressively in recent years the current paper summarizes the characteristics of earth fissures in the fenwei basin earth fissures usually occur in an extensional faulted basin along an active fault zone and within an area of land subsidence earth fissures often have a similar trend with many branches that intermittently appear along their strike the main and secondary earth fissures at a shallow depth form rupture belts of different widths but they merge into a single shear belt and stay connected with the underlying active fault the throw of two blocks increases with depth along a sedimentary fault earth fissures usually show the characteristic of three dimensional movement vertical dislocation is the primary aspect of earth fissure movement the horizontal tension is smaller and the horizontal twist is the smallest which is consistent with the movement pattern of underlying active faults earth fissures have exhibited activity three or four times since the late pleistocene in the past half century earth fissures formed during four or five periods of peak activity were influenced strongly by groundwater fluctuation our research also indicates that cluster formation of earth fissures is polygenetic and results from a combination of tectonic and human activities earth fissures are driven by deep tectonic motions beneath the basin and are controlled by the local tectonic stress of the local fault zones one of the most important factors contributing to earth fissure formation is groundwater overexploitation this paper provides a scientific basis for proposed administrative means mitigation measures and engineering solutions in the field of engineering geology

land subsidence and ground fissures in xi an china 2005 2012 revealed by multi band insar time series analysis abstract xi an china has been undergoing significant land subsidence along with ground fissure development these geohazards have brought about severe damages to buildings bridges and other facilities in order to warn of and mitigate disasters it is urgently necessary to obtain the latest rate extent and temporal evolution of land subsidence in xi an with multiple sar datasets as well as leveling gps and ground water level of aquifers we study and map the spatial and temporal evolution of land subsidence and ground fissures over xi an first 62 synthetic aperture radar sar images acquired by envisat alos and terrsar x during 2005 2012 are used to form three independent interferometric stacks to unveil the spatial and temporal variations of land subsidence and ground fissures by using the time series interferometric synthetic aperture radar insar technique gps and leveling measurements are applied to calibrate the insar results precision of our insar annual subsidence results is less than 9 mm we derive the east west and vertical components of the observed land deformation in 2009 using descending and ascending insar observations finding out that the horizontal component of land deformation cannot be ignored if the deformation is large or ground fissures are active second four main land subsidence zones are detected in xi an with an average subsidence rate of 50 mm a during 2005 2012 time series insar results indicate that land subsidence rates in xi an increased by 200 from 2005 2007 to 2008 2010 extending existing ground fissures third insar derived land subsidence correlates with the change in ground water level and seasonal variations in subsidence correlate with changes in ground water pumping last the consistency on the spatial temporal distribution variation between ground fissures and land subsidence could be drawn from the time series results and profile analysis shapes of subsiding zones follow the general trends of mapped ground fissures and main faults in an ene direction changes in the subsidence gradient are also observed over most of the ground fissures and faults subsidence triggered fissures can cause localized surface displacements aggravate localized subsidence discontinue the integrity of ground water flow and limit the horizontal spread of subsidence funnels with continuing mass construction projects in xi an monitoring ground deformation with satellite insar therefore can provide efficient means to image land subsidence movements of fissures and faults and the associated geohazards

paleoceanographic changes on the farallon escarpment off central california during the last 16 000 years abstract new benthic and planktic foraminiferal assemblage census data and benthic foraminiferal oxygen index bfoi values previously published marine climate proxy data stable isotopes and ca cd and unpublished results of total carbon organic carbon and calcium carbonate analyses of sediments recovered off central california on the farallon escarpment 1605 m water depth 37 13 4 n 123 14 6 w core f 8 90 g21 document paleoceanographic changes during the latest quaternary which reflect the intensity and source of north pacific intermediate water npiw and surface productivity accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age depth model for the last 16 000 years covering the latest glacial bolling allerod younger dryas and early middle and late holocene intervals a q mode cluster analysis separated the benthic fauna into three clusters one pleistocene and two holocene whereas the planktic fauna was divided only into pleistocene and holocene clusters stable oxygen isotope values show an increase in water temperature of 1 c from the late glacial to late holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well a general trend of decreasing dissolved oxygen concentration from the pleistocene high oxic 3 0 6 0 ml l o2 to the holocene low oxic 1 5 3 0 ml l o2 suggested by the bfoi and cd ca data reflect decreased ventilation as the source of the npiw shifted from the sea of okhotsk to the tropical east pacific at 11 000 cal bp the middle holocene cooling reported in other central and northern california margin studies is not apparent in f 8 90 g21 which compares more favorably with studies from southern california and british columbia total carbon and organic carbon values are highest in the bolling allerod early holocene and late holocene similarly calcium carbonate values are high in the bolling allerod and peak in the early holocene but decrease significantly in the latest middle and late holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60 cm 70000 0 cal bp of the core and poor preservation of the benthic foraminiferal fauna at 40 cm 3000 cal bp decoupling is evident between the planktic and benthic faunal response to changing climatic conditions with the surface dwelling assemblage often leading the bottom dwelling assemblage by several millennia

implications of a late glacial pollen record for the glacial and climatic history of the fraser lowland british columbia abstract late glacial sediments at mike lake in the fraser lowland of southwestern british columbia shed light on the timing and significance of the younger dryas and sumas events on the west coast of canada five pollen zones span the period from about 11 700 to 9700 radiocarbon years before present yr bp or 13 700 to 11 200 calibrated calendar years before present cal bp climate during this interval is inferred to have ranged from cool continental to warm and dry changes in pollen assemblages lithology and loss on ignition in mike lake sediments deposited prior to 11 000 yr bp 13 000 cal bp may signal the sumas glacial advance which has been dated elsewhere in the fraser lowland to this time palynologic and sedimentological data indicate that there was much climatic and ecological variability in southwestern british columbia during the younger dryas chronozone detrended correspondence analysis of modern pollen from lake sediment surface samples collected throughout british columbia is used to compare mike lake fossil pollen assemblages to modern vegetation zones the inferred vegetation assemblage during most of the younger dryas chronozone indicates a progressively warming climate with a cool interval between 10 400 and 10 000 yr bp the pollen assemblage in this interval is similar to that of present subalpine forests on the west coast of canada the cooling coincides with the later part of the younger dryas chronozone and occurred too late to be the driving mechanism for the final sumas advance which peaked around 11 300 14c yr bp 13 200 cal bp

a deep sea coral record of north atlantic radiocarbon through the younger dryas evidence for intermediate water deepwater reorganization requires the existence of large mobile gradients of d 14 c in the ocean during the younger dryas the d 14 c water column profile from keigwin 2004 provides direct evidence for the presence of one such gradient at the beginning of the younger dryas 12 9 ka with a 100 offset between shallow 2400 m and deep water our early younger dryas data are consistent with this profile and also show a d 14 c inversion with 35 more enriched water at 2400 m than at 1700 m this feature is probably the result of mixing between relatively well 14 c ventilated northern source water and more poorly 14 c ventilated southern source intermediate water which is slightly shallower over the rest of the younger dryas our intermediate water deepwater coral d 14 c data gradually increase while the atmosphere d 14 c drops for a very brief interval at 12 0 ka and at the end of the younger dryas 11 5 ka intermediate water d 14 c 1200 m approached atmospheric d 14 c these enriched d 14 c results suggest an enhanced initial d 14 c content of the water and demonstrate the presence of large lateral d 14 c gradients in the intermediate deep ocean in addition to the sharp vertical shift at 2500 m the transient d 14 c enrichment at 12 0 ka occurred in the middle of the younger dryas and demonstrates that there is at least one time when the intermediate deep ocean underwent dramatic change but with much smaller effects in other paleoclimatic records

paleoceanography of the gulf of alaska during the past 15 000 years results from diatoms silicoflagellates and geochemistry article i nfo abruptly during the bolling allerod bo al warm interval 14 7 12 9 cal ka declined during the younger dryas yd cold interval 12 9 to 11 7 cal kyr bp and rose again during the earliest holocene at this site the record after 11 cal kyr bp is dominated by oceanic diatoms and silicoflagellates with geochemical proxies displaying more subtle variation cores ew0408 66jc in the yakobi sea valley near cross sound and ew0408 11jc in the gulf of esquibel contain an expanded composite record along the southeast alaskan margin core 66jc contains a detailed record of the bo al and yd diatoms and silicoflagellates indicate that coastal upwelling and biosiliceous productivity were strong during the bo al but declined during the yd sea ice related diatoms increased in abundance during the yd indicating cooler but less productive waters

late pleistocene post vashon alpine glaciation of the nooksack drainage north cascades washington during the maximum late wisconsin glaciation ca 15 000 14c yr b p the cordilleran ice sheet overwhelmed the nooksack drainage of the northwestern cascades leaving only peaks higher than 2000 m above the ice surface ice sheet flow over the nooksack drainage and the adjacent puget lowland was essentially north south rapid deglaciation between 14 500 and 12 500 14c yr b p resulted in dropping of the ice sheet surface below ridge crests in the nooksack drainage and glacial activity thereafter became topographically controlled long valley glaciers in the upper nooksack valley were no longer connected to the cordilleran ice sheet and the source area changed from the main ice sheet to mount baker mount shuksan and the twin sisters range at that time the margin of the remnants of the cordilleran ice sheet was 30 km to the northwest separated from the nooksack valley glaciers by several ridges 1200 m higher than the surface of the ice sheet moraines were built in all three forks of the nooksack drainage 25 45 km downvalley from their sources the middle fork glacier stagnated 12 300 14c yr b p and deposited ice contact drift that was later overridden when ice readvanced over ice contact drift and deposited a prominent 2 km long lateral moraine logs in a lateral moraine in the upper middle fork were dated at 10 680 70 and 10 500 70 14c yr b p the north fork glacier which originated at a large cirque on mount shuksan and was fed by glaciers from mount baker extended to kendall where two moraines were deposited outwash from the younger moraine in the north fork valley overlies glaciomarine drift dated as 11 910 80 14c yr b p and contains charcoal layers dated at 10 603 69 and 10 788 77 14c yr b p the south fork glacier at its maximum was joined by ice from the middle fork and extended downvalley to lake whatcom and to cranberry lake it retreated from its terminal position slightly before ca 12 700 14c yr b p

evidence for cirque glaciation in the colorado front range during the younger dryas chronozone abstract late pleistocene glacial chronologies developed for the front range mountains of colorado include two or more cirque glacier advances locally known as the satanta peak advances sediment cores were recovered from sky pond an alpine lake 3320 m located less than 100 m downvalley from a moraine that exhibits late pleistocene to early holocene relative age features and appears to correlate to the satanta peak deposits one of the cores penetrated 0 5 m of basal diamict and recovered 3 3 m of overlying sediments that are predominantly gyttja an accelerator mass spectrometry ams age of 12 040 60 yr14c b p was obtained from directly above the basal diamict and is similar to other reported ages for cirque deglaciation in the front range mountains the lower portion of the gyttja contains an interval of clastic sediments that show characteristics consistent with glacial activity in alpine catchments radiocarbon ages obtained from below and near the upper contact of this clastic interval are 11 070 50 and 9970 8014c yr b p respectively an additional ams age of 10 410 9014c yr b p was obtained from within the clastic interval in a second core the most likely source for this interval of clastic sediments is a moraine situated directly upvalley from sky pond and consequently it appears that the deposition of this moraine was coeval with the european younger dryas event 11 000 10 00014c yr b p similarities in soil development weathering features and altitude between this moraine and the type satanta peak moraines suggest that the moraines are correlative these findings are in agreement with a growing body of evidence that suggests a relatively minor advance of alpine glaciers occurred in the north american rockies during the younger dryas chron

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

differential response of vegetation to postglacial climate in the lower salmon river canyon idaho late pleistocene to holocene terrestrial climate and vegetation records in the lower salmon river canyon of idaho are interpreted from the stable isotopic composition of soil carbonates and from aeolian sedimentation frequencies carbonate and sediment samples from six sections were processed and analyzed with the resulting isotopic and grainsize data organized in relation to a normalized time series developed from an associated radiocarbon chronology this record is interpreted in regards to changes in aridity temperature and wind speed during the late quaternary and is further compared with regional paleoenvironmental records lowered n 18 o and n 13 c concentrations before 20 000 yr bp are interpreted as reflecting late wisconsinan cold conditions after 18 000 yr bp climatic conditions show warmer periods punctuated by sharp returns to colder temperatures and increased c3 flora by 12 000 yr bp higher resolution data show very unstable climatic conditions across the pleistocene holocene boundary reflected in wide variations in n 18 o and n 13 c and aeolian sand deposition during the period between 12 000 and 9000 yr bp the lower salmon river canyon is thought to have experienced marked seasonality with summers and winters respectively warmer and colder than today this climatic scenario was accompanied by an initial instability in canyon vegetation following the establishment of a low energy floodplain in the canyon after 10 000 yr bp a pattern of c3 dominant riparian flora appears during the middle holocene climatic and vegetative variability is much reduced from the preceding period after 4000 yr bp soil carbonate isotopes reflect a trend toward cooler climate conditions and more mesic vegetation populations 2002 elsevier science b v all rights reserved

glacier readvance during the late glacial younger dryas in the ahklun mountains southwestern alaska an expansion of alpine glaciers during the latest pleistocene produced an extraordinarily well defined end moraine system in the ahklun mountains southwestern alaska these moraines deposited during the mount waskey advance are several kilometers beyond modern glacier termini and 80 km upvalley of the late wisconsin ahklun mountains ice cap terminal moraine eleven cosmogenic 10 be and 26 al exposure ages on moraine boulders combined with radiocarbon ages from a lake core upvalley of a moraine deposited during the mount waskey advance suggest that the advance culminated between 12 4 and 11 0 ka sometime during or shortly following the younger dryas event ca 12 9 11 6 ka we believe that the mount waskey advance was a consequence of cooling during the younger dryas these data further strengthen emerging evidence for younger dryas age cooling of the north pacific region

ground cracks in ethiopian rift valley facts and uncertainties abstract no accurate relationship has been obtained in this study between ground cracks in ethiopian rift valley and the most common causes of earth fissures such as aquifer system compaction and increased horizontal seepage stresses this is due to the fact that the level of groundwater withdrawal responsible for these processes is still negligible in ethiopia if aquifer system compaction and increased horizontal seepage stresses have a certain role then it should be through the long term effect of groundwater flow from basins to neighboring lakes the ground cracks appeared also not to have a direct link with active faulting or distant earthquakes structurally the ethiopian rift valley is dominated by ne sw trending tensional faults but no evidence is obtained in this study to associate the process of surface cracking with major tectonics however an aseismic elastic strain which originates at depth and propagates upward through sediments without the formation of bedrock faults could result in conditions conducive to the development of cracks then fissures might ultimately be created after heavy rainfalls by near surface processes such as piping and hydrocompaction along water line sources

humptulips revisited a revised interpretation of quaternary vegetation and climate of western washington usa abstract new pollen data from a 770 cm core of a mire at humptulips on the southwestern olympic peninsula 47 17 00 n 123 54 40 w and from a nearby deposit regarded as interglacial in age on the west fork of the humptulips river provide evidence for a reinterpretation of previous accounts of the quaternary vegetation and climate using a new age model the highly variable record at humptulips is here correlated with marine oxygen isotope stages ois 1 5a vegetation during ois 5a was pine dominated mixed woodland and tundra in ois 4 3 and 2 oscillations in pollen assemblages imply repeated intervals of mountain hemlock parkland and tundra pine as an indicator of openness is also abundant in these stages interstadial fluctuations in ois 3 reflect episodes of lowland western hemlock communities the earliest of the episodes is of infinite radiocarbon age and the latest dates to approximately 30 000 14 c yr b p parkland in ois 2 occurring after 24 600 until at least 18 440 14 c yr b p was replaced by transitional pine alder in ois 1 holocene which unlike any of the earlier stages conveys the development of modern lowland forest dominated by western hemlock pollen assemblages over the length of record imply that temperature and humidity at no time were as high as at present only in ois 3 do conditions approach those occurring in ois 1 during ois 2 3 and 4 when tree line apparently stood at the location of the site climate was colder and drier temperatures were depressed an estimated 5 c with precipitation close to 1000 mm compared with 2000 3000 mm at present atmospheric circulation during ois 2 appears to have been much controlled by the location of the laurentide ice sheet in the continental interior whereas under the current climatic regime beginning in the early holocene westerly air flow has dominated regulated by interplay between the north pacific high in summer and the wintertime aleutian low

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

advance of alpine glaciers during final retreat of the cordilleran ice sheet in the finlay river area northern british columbia canada abstract sharp crested moraines up to 120 m high and 9 km beyond little ice age glacier limits record a late pleistocene advance of alpine glaciers in the finlay river area in northern british columbia the moraines are regional in extent and record climatic deterioration near the end of the last glaciation several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern cordilleran ice sheet other lateral moraines merge with ice stagnation deposits in trunk valleys these relationships confirm the interaction of advancing alpine glaciers with the regionally decaying cordilleran ice sheet and verify a late glacial age for the moraines sediment cores were collected from eight lakes dammed by the moraines two tephras occur in basal sediments of five lakes demonstrating that the moraines are the same age plant macrofossils from sediment cores provide a minimum limiting age of 10 550 10 250 cal yr bp 9230 50 14c yr bp for abandonment of the moraines the advance that left the moraines may date to the younger dryas period the finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late glacial glacier advances

new dates on late pleistocene dacitic tephra from the mount edgecumbe volcanic field southeastern alaska new radiocarbon dates on charcoal incorporated in proximal airfall deposits indicate the largest late pleistocene eruption from the mt edgecumbe volcanic field in southeast alaska occurred ca 11 250 5014c yr b p the more precise dating of the principal edgecumbe tephra layer greatly improves its utility as a tephrochronologic marker horizon in southeastern alaska

evidence for younger dryas age cooling on the north pacific coast of america abstract a review of the palynological evidence from the olympic peninsula of washington state north to the alaska panhandle strongly supports the existence of a climatic oscillation similar in timing and effect to the younger dryas cooling 11 10 ka bp of europe and eastern north america the evidence includes many late glacial pollen peaks of mountain hemlock tsuga mertensiana an indicator of cool and moist climate reversals from forest to non arboreal vegetation and paleoclimate analysis using pollen climate transfer functions on the queen charlotte islands evidence of cooler ocean waters based on fossil foraminifera in cores from the continental shelf also supports an interpretation of a younger dryas age climatic reversal on the other hand geological evidence of glacier readvances during the younger dryas chronozone is weak and poorly dated although more and better constrained ams dates are needed to confirm the timing of the pacific northwest cold oscillation results so far point to maximum cooling and increased moisture between ca 10 7 10 ka bp followed by rapid warming in the early holocene additional late glacial sites need to be investigated in detail to confirm the geographical pattern of vegetation and climate change during this interval which is best expressed in hypermaritime and maritime climate regions similar to the younger dryas event around the north atlantic these results suggest that the search for causal mechanisms to drive the younger dryas cooling cannot be limited to events in the north atlantic region but should focus on possible hemispheric or global processes

correlation of marine and coastal terrestrial records of central california response to paleoceanographic and paleoclimatic change during the past 19 000 years new benthic foraminiferal census data combined with previously published planktic foraminiferal and pollen data from the continental margin off central california provide a unique opportunity to document concurrent paleoceanographic and paleoclimatic changes in the region during the late quaternary all three datasets were evaluated in gravity core s3 15g collected at a depth of 3491 on the western levy of the monterey fan 36 23 53 n 123 20 52 w accelerator mass spectrometry radiocarbon dates and the ratio of the planktic foraminiferal species neogloboquardrina pachyderma ehrenberg to neogloboquadrina incompta cifelli provide a good age depth model for the last 19 000 years covering the last glacial bolling allerod younger dryas and holocene intervals separate q mode cluster analyses of the hemipelagic as well as mixed combined hemipelagic and turbiditic mud samples grouped the benthic foraminiferal fauna into two clusters reflecting faunal adaptation to changing climatic conditions during the pleistocene and holocene r mode cluster analysis also differentiated glacial uvigerina senticosa and globobulimina auriculata and interglacial melonis pompilioides and gyroidina planulata faunas a general trend of slightly increasing oxygen in the deep sea is suggested from the pleistocene to holocene based on the reduction in abundance of g auriculata and increased frequency of m pompilioides q mode cluster analysis of the planktic foraminifera illustrates a change in the surface water from a glacial subpolar fauna in the pleistocene to a transitional fauna in the holocene whereas the pollen record separated into three clusters two of pleistocene age glacial and transitional and one in the holocene interglacial reflecting the terrestrial floral adaptation in the california coast ranges of central california to the warmer climate in the holocene decoupling is evident between the benthic and planktic foraminiferal and terrestrial floral responses to changing oceanographic and climatic conditions the floral response leads the surface dwelling fauna by several millennia and is followed by the deep dwelling benthic foraminiferal fauna a millennium later

a lateglacial climatic reversion in hokkaido northeast asia inferred from the larix pollen record abstract at present larix gmelini is a main component of taiga developed in north sakhalin northeast china and east siberia during the interval from 11 8 to 12 4 ka bp pollen assemblages from north hokkaido japan are dominated by larix pollen assemblages of this lateglacial climatic reversal known as the kenbuchi stadial are similar to pollen assemblages from the last glacial maximum in north hokkaido vegetation of hokkaido inferred from these pollen assemblages open taiga composed of larix gmelini pinus pumila and picea jezoensis and or picea glehnii may have been like that of north sakhalin today comparison of these fossil pollen assemblages from hokkaido with pollen assemblages from modern surface samples in sakhalin suggests that 11 8 to 12 4 ka bp temperatures relative to today were at least 9 c lower in january and 7 c lower in august and that annual precipitation was at least 735 mm lower than present

a study of the symbiotic relationship between tectonic fissures and faults in the fenwei graben system china the fenwei graben system is an important extensional fault depression zone which is the tectonic boundary between the ordos block and the south china block and the north china block the graben system presents an s shape with a total length of 1200 km and a width of 30 60 km and an overall strike of nne due to complex tectonic background and active faults nearly 612 ground fissures develop in these basins and more than 90 of these ground fissures are tectonic fissures which are closely associated with fault activities to reveal the plane symbiotic phenomena profile symbiotic modes and symbiotic mechanism between tectonic fissures and faults in the fenwei graben system the developmental characteristics were investigated in detail by surveying mapping trenching and drilling in the study area the main conclusions are as follows 1 the tectonic fissures of the fenwei graben system are mainly distributed along the margin faults of basins the boundary faults between blocks and the hidden faults within blocks causing serious damages to farmlands houses and roads the symbiosis between these fissures and faults is obvious on the surface 2 the profile symbiotic morphology includes vertical extension type syncline and anticline y type and stepped type 3 the symbiotic mechanisms include vertical growth lateral rupture and clustery derivation 4 the activities of underlying faults give impetus to the formation and expansion of tectonic fissures the exposure of the fissures makes underlying faults continue to develop in the form of surface fractures

late quaternary vegetation and climate history near little lake central coast range oregon pollen and plant macrofossils recovered from little lake oregon provide the first record of late quaternary climate and vegetation changes in oregon9s central coast range the pollen data suggest that the period from ca 42 000 to 24 770 yr b p featured an open forest of western white pine western hemlock and fir the inferred climate was cooler and wetter than today the full glacial period was characterized by a parkland of spruce lodgepole pine and mountain hemlock which suggests that the climate was colder and possibly drier than today the oregon coast range was not a glacial refugium for temperate conifers as has been proposed by 16 000 yr b p the pollen and plant macrofossil data suggest the development of a montane forest composed of pine fir western hemlock and mountain hemlock temperate taxa were present in the vegetation at 13 500 yr b p during a period of climatic amelioration a reversal in this warming trend may have occurred between 11 000 and 10 500 yr b p when pine western and mountain hemlock and spruce were slightly more abundant early holocene forests featured douglas fir red alder and bracken fern implying more severe summer drought and more frequent fires after 5600 yr b p douglas fir western hemlock and western red cedar dominated the record marking the introduction of the present day cool moist climate however during the past 2800 yr increased douglas fir and decreased cedar suggest the possibility of reduced effective moisture at little lake

a glacial readvance during retreat of the cordilleran ice sheet british columbia central coast descriptions of the cordilleran ice sheet retreat after the last glacial maximum have included short lived readvances occurring during the older and younger dryas stadial periods and into the holocene but identification of these events has been largely limited to southwest and central british columbia and northwest washington state we present evidence of a late pleistocene readvance of cordilleran ice occurring on the central coast of british columbia on calvert island between northern vancouver island and haida gwaii evidence is provided by sedimentological and paleoecological information contained in a sedimentary sequence combined with geomorphic mapping of glacial features in the region results indicate that a cold climate existed between 15 1 and 14 3 cal ka bp and that ice advanced to and then retreated from the western edge of the island between 14 2 and 13 8 cal ka bp these data provide the first evidence of a major fluctuation in the retreating ice sheet margin in this region and suggest that a cold climate was a major factor in ice readvance these data contribute to the understanding of past temperature ice loading and crustal response the nature of ice margin retreat and the paleoenvironment of an understudied area of the pacific northwest

rapid response of alpine timberline vegetation to the younger dryas climate oscillation in the colorado rocky mountains usa paleobotanical records from two high altitude 3 300 m sites in colorado show a clear and immediate response to the younger dryas climate oscillation the black mountain lake and sky pond records indicate that alpine timberline migrated upslope to near modern elevations during the late bolling allerod 13 6 12 9 ka subsequent declines in arboreal pollen percentages and accumulation rates during the younger dryas interval 12 9 11 7 ka reflect a downslope displacement of the alpine timberline ecotone of 60 120 m in elevation this change translates to a cooling of summer temperature by approximately 0 4 0 9 c and is consistent with proposed younger dryas advances of alpine glaciers in the rocky mountains to positions close to little ice age maxima alpine timberline readvanced upslope to elevations above both sites between 11 7 and 11 4 ka the concomitant response of temperature sensitive alpine timberline vegetation in colorado and late glacial changes in north atlantic thermohaline circulating implicates a rapid widespread atmospheric transmission of the younger dryas climate oscillation

postglacial vegetation and climate change in the northern bristol bay region southwestern alaska pollen analysis of sediment cores from grandfather and ongivinuk lakes reveals a record of postglacial vegetation and climate change in the northern bristol bay region the chronology is based on six conventional 14c dates of bulk organic matter from the grandfather core a mesic herb tundra dominated the landscape 13 000 9800 yr b p betula shrubs probably first appeared in the region 11 300 yr b p but were restricted to favorable microhabitats until 9800 yr b p the later establishment of betula shrubs and relatively low betula pollen abundance in these records compared to other areas of eastern beringia suggest that postglacial warming in southwestern alaska was dampened by regional climatic controls possibly low sea surface temperatures of the north pacific ocean between 10 800 and 9800 yr b p diminished betula shrub cover along with decreased aquatic productivity as recorded by pediastrum cell nets and biogenic silica suggest a brief reversion to colder and drier climatic conditions possibly associated with the younger dryas event around 9800 yr b p betula shrub tundra and meadow communities expanded probably in response to increased temperature and precipitation alnus arrived and formed extensive thickets within the region ca 7400 yr b p the establishment of the modern boreal forest tundra ecotone is marked by the arrival of picea glauca at grandfather lake ca 4000 yr b p and the subsequent increase to present population densities ca 2000 yr b p the unique features of these pollen records emphasize the spatial complexity of late quaternary vegetation and climate history in eastern beringia

a re evaluation and spatial analysis of evidence for a younger dryas climatic reversal in beringia abstract an objective classification of paleoclimatic proxies from 75 lake and peat records is used to re evaluate data quality and inferred climatic patterns in beringia during the younger dryas mapped data reveal coherent but spatially complex regional patterns suggesting the younger dryas was characterized by 1 cooling in southern alaska eastern siberia and portions of northeastern siberia and 2 uniform to warmer than present conditions through most of central alaska northeastern siberia and possibly the russian far east and northern alaska the beringian patterns correspond to distinctive large scale climatic forcings although in some locations further modified by more local influences such as topography general circulation models and modern synoptic climatology provide a conceptual framework for exploring possible mechanisms responsible for the observed changes forcings and associated climatic responses consistent with the proxy data include 1 lowered sea surface temperatures in the north atlantic and pacific reducing temperature and precipitation in eastern siberia 2 intensified aleutian low and lowered sea surface temperatures causing cooler summers and higher winter precipitation in southern alaska 3 stronger pacific subtropical high and an eastward shift of the east asian trough reducing summer temperatures in southern alaska and causing relative warmth in northeastern siberia and 4 strong high pressure system producing warm dry conditions in interior alaska

late quaternary dynamics of forest vegetation on northern vancouver island british columbia canada abstract pollen analysis of radiocarbon dated lake sediment from northern vancouver island southwest british columbia reveals regional changes in forest vegetation over the last 12 200 14c yr 14 900 cal yr between at least 12 200 and 11 700 14c yr bp 14 900 13 930 cal yr bp open woodlands were dominated by pinus contorta alnus crispa and various ferns as p contorta decreased in abundance alnus rubra and more shade tolerant conifers i e picea and tsuga mertensiana increased increases in t mertensiana p contorta and a crispa pollen accumulation rates pars between 10 600 and 10 400 14c yr bp 11 660 11 480 cal yr bp reflect a cool and moist climate during the younger dryas chronozone orbitally induced warming around 10 000 14c yr bp 11 090 cal yr bp allowed the northward extension of pseudotsuga menziesii although picea tsuga heterophylla and a rubra dominated early holocene forests by 7500 14c yr bp 8215 cal yr bp shade tolerant t heterophylla was the dominant forest tree cupressaceae thuja plicata and chamaecyparis nootkatensis was present by 7500 14c yr bp but reached its maximum after 3500 14c yr bp 3600 cal yr bp when a cooler and wetter regional climate facilitated the development of temperate rainforest the highest rates of vegetation change are associated with lateglacial climate change and species with rapid growth rates and short life spans

midges and palaeotemperature reconstruction the north american experience abstract the development of midge based palaeoclimatology in north america is reviewed with a focus on lateglacial and holocene climatic change although relatively few sites have been studied midge inferred palaeotemperatures reveal detailed records of lateglacial climate oscillations and more subtle holocene temperature changes holocene climate changes are often at or near the detection limit using current palaeotemperature inference models interference from other environmental variables including water depth and oxygen concentration changes are discussed as well as the challenges inherent to developing better models the isotopic signature of chitin preserved in midge head capsules has opened new avenues for midge palaeotemperature inference through coordinated research efforts national and international collaborations will provide opportunities to reconstruct holocene palaeoclimate at continental and hemispheric scales

timing and significance of late glacial and holocene cirque glaciation in the sierra nevada california mapping and radiocarbon dates of cirque moraines in the sierra nevada demonstrate that the last significant pre little ice age glacier advance in the range the recess peak resulted from snowline lowering roughly twice that of the matthes little ice age advance and that the recess peak advance is late pleistocene in age we mapped recess peak and matthes deposits in 64 cirques along a profile of the main sierran crest that spans the north south limits of neoglacial deposits in the range equilibrium line altitudes for the reconstructed recess peak glaciers vary greatly but coherently with those of the matthes advance the variability of both sets of deposits reflects strong topographic influences on snow accumulation and ablation patterns in their deep cirques tephrochronology and radiocarbon dates from lake sediment cores provide limits on the timing of the two advances previous work documenting the absence of a young regionally extensive tephra on matthes moraines in the central sierra demonstrates that they formed after 700 14c years bp 650 cal years bp the age of the recess peak advance has been less certain we therefore collected and dated sediment cores from lakes dammed behind terminal moraines correlating to the recess peak advance in four widely separated drainages along the sierran crest north to south south fork american river lee vining creek middle fork san joaquin river and bishop creek twenty three high precision ams radiocarbon dates on gyttja peat and macrofossils from the cores are internally consistent and demonstrate that the recess peak advance previously thought to be of late holocene age 2500 years bp ended before 11 190 70 14c years bp 13 100 85 cal years bp recess peak is therefore late pleistocene in age and probably predates the north atlantic younger dryas climatic reversal the absence of any glacial deposits on the bedrock between the recess peak and matthes deposits indicates that 1 any advance related to the younger dryas event in central california was smaller than the matthes advance 2 the matthes advance was the most extensive and possibly the only neoglacial event in the range and 3 climate in the sierra between 13 000 cal years bp and 650 cal years bp was apparently too warm and or dry to support glaciers larger than those of the little ice age other mapping indicates that the recess peak is the first significant glacier advance after retreat of tioga local late wisconsin maximum glaciers these results suggest a regionally variable climate in western north america during the younger dryas event because glaciers appear to have expanded in the canadian rockies at that time the new recess peak age limits combined with other dated lake cores indicate that the sierra was essentially deglaciated by 14 000 15 000 cal years bp 12 000 13 000 14c years bp substantially earlier than previously estimated this finding indicates that current production rates of some in situ cosmogenic nuclides calibrated on an assumed deglaciation of the range at 11 000 cal years bp 10 000 14c years bp may be systematically too high by as much as 20

cordilleran ice sheet mass loss preceded climate reversals near the pleistocene termination the cordilleran ice sheet cis once covered an area comparable to that of greenland previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost canada as late as 12 5 thousand years ago ka new data indicate that substantial areas throughout westernmost canada were ice free prior to 12 5 ka and some as early as 14 0 ka with implications for climate dynamics and the timing of meltwater discharge to the pacific and arctic oceans early bolling allerod warmth halved the mass of the cis in as little as 500 years causing 2 5 to 3 0 meters of sea level rise dozens of cirque and valley glaciers along with the southern margin of the cis advanced into recently deglaciated regions during the bolling allerod and younger dryas

holocene intracontinental deformation of the northern north china plain evidence of tectonic ground fissures abstract following the collecting and analyzing of field data on the geometry and kinematics characteristics of ground fissures in the northern north china plain nncp this paper shows that en echelon ground fissures or tectonic ground fissures with a length of several meters to tens of kilometers extending along active faults are possibly controlled by underlying active faults there are two groups of tectonic ground fissures developed in the nncp one group consists of ene trending right stepping ground fissures some of which have a component of sinistral motion the other group is nne trending left stepping ground fissures with dextral motion a large amount of data from trenches boreholes and seismic exploration reflect that they are active faulting related the nnw trending regional extensional stress field and the reactivation of pre existing faults are the major factors controlling ground fissures data from the quaternary sedimentary records deep incised valleys the distribution of earthquakes and ground fissures and our field work show that the holocene intracontinental deformation of the nncp is characterized by intense faulting and northwestward tilting which may be related to a nnw sse oriented tensional stress field in the shallow crust and asthenospheric upwelling in the mantle

origin of ground fissures in the shanxi graben system northern china abstract since the 1950s hundreds of ground fissures have occurred in the shanxi graben system in northern china the fissures and related subsidence and differential settlement have caused and are causing substantial damage to homes agricultural land roads canals and other infrastructure although generally similar in appearance the fissures have different origins 1 some fissures coincide with northeast trending faults trenching shows that the fissures extend into the near surface faults increasing vertical offset clay beds and other stratigraphic markers at depth and therefore are probably the surface expression of fault movements 2 some fissures are demonstrably related to accelerated groundwater withdrawal this is particularly apparent in xi an city where groundwater levels have declined by about 15 m within 4 years 3 other fissures owe their origin to the well known process of soil collapse this is particularly common in the silty loessial sediments that occur within most of the valleys that comprise the shanxi graben system

millennial scale rhythms in peatlands in the western interior of canada and in the global carbon cycle abstract anatural 1450 yr global holocene climate periodicity underlies a portion of the present global warming trend calibrated basal radiocarbon dates from 71 paludified peatlands across the western interior of canada demonstrate that this periodicity regulated western canadian peatland initiation peatlands the largest terrestrial carbon pool and their carbon budgets are sensitive to hydrological fluctuations the global atmospheric carbon budget experienced corresponding fluctuations as recorded in the holocene atmospheric co 2 record from taylor dome antarctica while the climate changes following this 1450 yr periodicity were sufficient to affect the global carbon budget the resultant atmospheric co 2 fluctuations did not cause a runaway climate co 2 feedback loop this demonstrates that global carbon budgets are sensitive to small climatic fluctuations thus international agreements on greenhouse gasses need to take into account the natural carbon budget imbalance of regions with large climatically sensitive carbon pools