fungal proliferation at the cretaceous tertiary boundary we have found that a fungal spike occurs between the diverse late cretaceous palynoflora and the low diversity fern dominated early paleocene assemblages in a new zealand section the fungal layer is coincident with the ir anomaly marking the extinction event

the use of gis based 3d geological tools to improve hydrogeological models of sedimentary media in an urban environment a software platform was developed to facilitate the development of 3d geological models of sedimentary media for hydrogeological modelling especially for urban environments it is composed by a geospatial database and a set of tools that enable the user to perform an accurate stratigraphic analysis the geospatial database is used for the management of a large amount of different data types coming from different sources geophysical logs borehole logs hydraulic tests etc its structure allows us to store accurate and very detailed geological borehole log description that can be straightforwardly generalized and further upscaled the set of stratigraphic analysis instruments working within a geographical information system gis environment has been set up to facilitate the geological data interpretation detailed stratigraphic columns of the selected boreholes can be generated using customized queries creating automatically a geological profile is further possible by displaying the boreholes lithological columns and the geophysical and geotechnical field tests results together with the defined stratigraphic units based on an interactive analysis environment is created where the user is able to analyze and to define the possible existing correlation surfaces units and faults the obtained information represented by the geological units subunits can be then converted within a 3d environment the resulted 3d features could be used within the same gis environment or by external software packages for further stochastic analysis or to build up 3d geological and hydrogeological models starting from an accurate and very detailed geological description the software allows us to represent in three dimensions 3d the heterogeneity of the sedimentary media and their spatial distribution thus it shows how connectivity implemented into hydrogeological models among the different sedimentary bodies plays an important role results are shown consisting in a case study located in the besos river delta in the metropolitan area of barcelona on the mediterranean coast in ne spain

thermokarst lake basin sediments tuktoyaktuk coastlands western arctic canada three stages of deposition are distinguished in thermokarst lake basin sequences in ice rich permafrost of the tuktoyaktuk coastlands western arctic canada 1 widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes forming a distinctive basal unit of impure sand and or diamicton 2 a reduction or cessation of slumping because of the pinching out of adjacent ground ice slump stabilization or climatic cooling that reduces the input of clastic sediment permitting reworking of sediment around lake margins and suspension settling principally in basin centres 3 lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand radiocarbon dating of detrital peat and wood from a progradational sequence basal unit defines a lateral younging trend in the direction of progradation a progradation rate is calculated to be 4 cm yr 1 consistent with rapid deposition during stage 1 above the nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents in comparison with thermokarst lake basin sequences previously described in alaska canada and siberia the middle unit of those in the tuktoyaktuk coastlands is similar whereas the basal unit is generally thicker and by contrast often contains diamicton these differences are attributed respectively to larger scale resedimentation of upland sediments by retrogressive thaw slumping and debris flow deposition in thermokarst lakes in the tuktoyaktuk coastlands compared with the sediments within supraglacial lakes in areas of moderate to high relief the middle unit of thermokarst lake basin sequences in the tuktoyaktuk coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable these differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the tuktoyaktuk coastlands it may be impossible to distinguish glacial and periglacial thermokarst lake basin sediments in permafrost areas of incomplete deglaciation not only is it often difficult to distinguish intrasedimental and buried glacier ice but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

temporal changes of a delta example from the holocene yahagi delta central japan abstract the depositional history of a delta was investigated by using radiocarbon dated borehole cores from the yahagi delta nishimikawa plain central japan in particular historical changes in the gradient thickness and grain size distribution of the delta front and sediment discharge of the yahagi river are discussed the latest pleistocene to holocene sequence in the yahagi delta is interpreted as an incised valley fill system formed after the last glacial and subdivided into five sedimentary facies facies a fluvial facies b estuary facies c prodelta facies d delta front and facies e gravelly tidal flat in the main axis of the incised valley facies a facies b facies c facies d and facies a are deposited in ascending order in the western area of the valley facies e adjoins facies d the delta front was formed by river floods without reworking by wave or tide the succession was interpreted as a transgressive systems tract and highstand systems tract formed under sea level rise until ca 7 cal kyr bp and the subsequent highstand after the formation of the delta in ca 7 cal kyr bp characteristic features of the delta front changed twice as the delta prograded first during 4 5 cal kyr bp the delta front became thicker and steeper this change was induced by differences in water depth between the middle incised valley and the outer incised valley which resulted from a buried clinoform second in ca 3 cal kyr bp the grain size distribution of the delta front became coarser and the sorting became poorer the sediment discharge of the yahagi river also increased abruptly this change was induced by the increase of erosional capacity in the hinterland increasing human activities such as deforestation and poor soil conservation might have induced this change

anthropogenic contribution to the geological and geomorphological record a case study from great yarmouth norfolk uk abstract reconstruction of artificial or anthropogenic topographies sediment thicknesses and volumes provides a mechanism for quantifying anthropogenic changes to sedimentary systems in the context of the proposed anthropocene epoch we present a methodology for determining the volumetric contribution of anthropogenic deposits to the geological and geomorphological record and apply it to the great yarmouth area of norfolk uk 115 boreholes drilled to a maximum depth of 6 m below ground level were used to determine the thickness and distribution of seven geo archaeological units comprising natural and anthropogenic deposits in the central great yarmouth area this was supplemented by additional depth information derived from 467 existing ground investigation boreholes and published 1 50 000 scale geological maps the top and base of each geo archaeological unit were modelled from elevations recorded in the borehole data grids were produced using a natural neighbour analysis with a 25 m cell size using mapinfo 8 0 vertical mapper 3 1 to produce palaeotopographical surfaces maximum minimum and average elevations for each geo archaeological unit generally increase with decreasing age with the exception of the early medieval palaeotopographical surface which locally occurs at higher elevations than that of the younger late medieval unit the total sediment volume for the combined modern post medieval late medieval and early medieval geo archaeological units is 10 91 10 5 m 3 the total sediment volume for the aeolian river terrace and marine geo archaeological units combined is 65 58 10 5 m 3 anthropogenic sedimentation rates were calculated to increase from 590 m 3 yr during the early medieval period 1500 m 3 yr during the post medieval period and 2300 m 3 yr during the modern period it is estimated that the combined anthropogenic geo archaeological units contribute approximately 15 of the total volume of sediments that would have been traditionally considered natural holocene deposits in the great yarmouth area the results indicate that an approach combining geological and archaeological deposit modelling can be used to quantify anthropogenic landscape impact and its associated sediment flux

stratigraphy of the anthropocene the anthropocene an informal term used to signal the impact of collective human activity on biological physical and chemical processes on the earth system is assessed using stratigraphic criteria it is complex in time space and process and may be considered in terms of the scale relative timing duration and novelty of its various phenomena the lithostratigraphic signal includes both direct components such as urban constructions and man made deposits and indirect ones such as sediment flux changes already widespread these are producing a significant event layer locally with considerable long term preservation potential chemostratigraphic signals include new organic compounds but are likely to be dominated by the effects of co2 release particularly via acidification in the marine realm and man made radionuclides the sequence stratigraphic signal is negligible to date but may become geologically significant over centennial millennial time scales the rapidly growing biostratigraphic signal includes geologically novel aspects the scale of globally transferred species and geologically will have permanent effects

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

chicxulub impact predates k t boundary new evidence from brazos texas abstract multidisciplinary studies including stratigraphy sedimentology mineralogy and geochemistry of the new core mullinax 1 and outcrops along the brazos river and cottonmouth creek falls county texas reveal the complex history of the chicxulub impact the event deposit and the k t boundary event the k t boundary as identified by the negative 13c shift first occurrence of danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core mullinax 1 the underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest maastrichtian as indicated by high stress microfossil assemblages small shells and burrows infilled with framboidal pyrite the underlying event deposit commonly interpreted as k t impact tsunami consists of a basal conglomerate with clasts containing chicxulub impact spherules repeated upward fining units of spherule rich sands followed by hummocky cross bedded and laminated sands which are burrowed by thalassinoides planolites and ophiomorpha and truncated by erosion this suggests a series of temporally separated storm events with re colonization of the ocean floor by invertebrates between storms rather than a series of waning tsunami generated waves the lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the chicxulub impact ejecta layer predates the event deposit but was eroded and re deposited during the latest maastrichtian sea level lowstand the original chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late maastrichtian clay and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone cf1 which spans the last 300 kyr of the maastrichtian the yellow clay consists of cheto smectite derived from alteration of impact glass as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and chicxulub impact spherules from ne mexico and haiti the brazos sections thus provide strong evidence that the chicxulub impact predates the k t boundary by about 300 kyr consistent with earlier observations in ne mexico and the chicxulub crater core yaxcopoil 1

river discharge influences on particulate organic carbon age structure in the mississippi atchafalaya river system 1 applying ramped pyrolysis radiocarbon analysis to suspended river sediments we generate radiocarbon 14c age spectra for particulate organic carbon poc from the lower mississippi atchafalaya river system mars to better understand a major river system s role in carbon transport ramped pyrolysis 14c analysis generates age distributions of bulk carbon based on thermochemical stability of different organic components our results indicate higher proportions of older material in the poc during higher discharge ages increase throughout the high discharge age spectra indicating that no single component of the poc is responsible for the overall age increases observed instead older material is contributed across the poc age spectrum and unrelated to increased bedload suspension in this comparison of 2 spring discharges less than half of the poc transported during higher discharge is less than 1000 14c years in age constraining of the role of the mars as a flux of atmospheric co2 toward longer term sedimentary sinks in the mississippi delta and the gulf of mexico the results suggest that delta building processes benefit disproportionately from high discharge events carrying larger amounts of sediment because these events involve both a higher proportion of millennially aged carbon from floodplain exchange of poc and a potentially higher proportion of petrogenic carbon 30 530 increase overall an internally consistent picture of po14c age distributions from a major river system emerges as differences in space and time are small compared to the range of ages of poc sources in such a large basin

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

permafrost response to last interglacial warming field evidence from non glaciated yukon and alaska abstract we present stratigraphic observations from three sites in eastern beringia ch ijee s bluff in northern yukon and nearby exposures on the old crow river the palisades on the yukon river in alaska and placer mining exposures at thistle creek in west central yukon which provide insight into the response of permafrost to regional warming during the last interglaciation chronology is based on the presence of old crow tephra an important regional stratigraphic marker that dates to late marine isotope stage 6 supplemented by paleoecology and non finite 14c ages on wood rich organic silts old crow tephra overlies several relict ice wedges at the palisades and thistle creek indicating that permafrost at these sites did not thaw completely during the last interglaciation prominent deposits of last interglacial wood rich organic silt are present at multiple sites in eastern beringia and probably represent accumulations of reworked forest vegetation due to thaw slumping or deposition into thermokarst ponds or depressions consistent stratigraphic relations between these deposits old crow tephra and ice wedge pseudomorphs at our three study sites and at least six other sites in eastern beringia suggest that thaw of shallow permafrost was widespread during the last interglaciation limited stratigraphic evidence suggests that thaw was probably on the order of meters rather than 10s of meters the ubiquity of shallow permafrost degradation during the last interglaciation suggests that current ground warming may foreshadow widespread near surface thaw under even modest future warming scenarios however the persistence of relict pre last interglacial ice wedges highlights the potential for the regional antiquity of discontinuous permafrost and provides compelling field evidence for the long term resilience of deep permafrost during sustained periods of warmer than present climate

carbon storage in a holocene deltaic sequence an example from the nobi plain central japan abstract we estimated the rate of accumulation and total amount of organic carbon oc stored in holocene sediments of the nobi plain of central japan by analyzing 2701 existing borehole sections and 218 14c ages reconstructing the three dimensional stratigraphic architecture of the delta system calculating the volume of sediments in the delta and using oc contents measured from sediments from eight boreholes on the plain we calculated that a total of 167 tg of oc was stored in deltaic deposits on the plain during the past 6000 years a dramatic increase in the amount of stored oc since 1000 cal bp is probably a combined result of increases in sediment supply to the delta in response to human activities in the drainage basin and expansion of the area of subaerial delta as a result of progradation oc accumulation rates for the nobi plain during the past 6000 years ranged from 15 3 to 37 5 g m 2 y 1 which are comparable to rates obtained from other holocene delta and to rates from floodplain and lake systems with higher oc contents in their sediments the higher sedimentation rates of the deltaic deposits compensates for their lower oc contents

cryostratigraphy of late pleistocene syngenetic permafrost yedoma in northern alaska itkillik river exposure abstract extremely ice rich syngenetic permafrost or yedoma developed extensively under the cold climate of the pleistocene in unglaciated regions of eurasia and north america in alaska yedoma occurs in the arctic foothills the northern part of the seward peninsula and in interior alaska a remarkable 33 m high exposure along the lower itkillik river in northern alaska opened an opportunity to study the unmodified yedoma including stratigraphy particle size distribution soil carbon contents morphology and quantity of segregated wedge and thermokarst cave ice the exposed permafrost sequence comprised seven cryostratigraphic units which formed over a period from 48 000 to 5 000 14c yr bp including 1 active layer 2 intermediate layer of the upper permafrost 3 4 two yedoma silt units with different thicknesses of syngenetic ice wedges 5 buried peat layer 6 buried intermediate layer beneath the peat and 7 silt layer with short ice wedges this exposure is comparable to the well known mus khaya and duvanny yar yedoma exposures in russia based on our field observations literature sources and interpretation of satellite images and aerial photography we have developed a preliminary map of yedoma distribution in alaska

dinosaurs on the north slope alaska high latitude latest cretaceous environments abundant skeletal remains demonstrate that lambeosaurine hadrosaurid tyrannosaurid and troodontid dinosaurs lived on the alaskan north slope during late campanian early maestrichtian time about 66 to 76 million years ago in a deltaic environment dominated by herbaceous vegetation the high ground terrestrial plant community was a mild to cold temperate forest composed of coniferous and broad leaf trees the high paleolatitude about 70 to 85 north implies extreme seasonal variation in solar insolation temperature and herbivore food supply great distances of migration to contemporaneous evergreen floras and the presence of both juvenile and adult hadrosaurs suggest that they remained at high latitudes year round this challenges the hypothesis that short term periods of darkness and temperature decrease resulting from a bolide impact caused dinosaurian extinction

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

a centennial record of fluvial organic matter input from the discontinuous permafrost catchment of lake tornetrask 1 high latitude regions are underlain by the most organic carbon oc rich soils on earth and currently subject to intense climate warming potentially increasing remobilization and mineralization of soil oc sub arctic scandinavia is located on the 0 c mean annual isotherm and is therefore particularly vulnerable to climate change this study aimed to establish a baseline for soil oc release over the past century into lake tornetrask the largest lake in sub arctic scandinavia through bulk geochemical and molecular radiocarbon analyses in chronologically constrained sediment cores our results suggest a dominance of peat derived terrestrial oc inflow we show that the annual terrestrial oc inflow to the lake is 12 times higher than the in lake produced particulate oc and consists for a large part ca 60 of old oc from deep reservoirs in the catchment the sedimentary record shows signs of increasing inflow of more degraded terrestrial matter since 1975 as indicated by increasing toc concentrations a lower 13c value and lower toc tn ratios based on simultaneous changes in local climate and reported signs of permafrost degradation e g active layer deepening mire peat erosion the observed changes in the sedimentary record of scandinavia s largest mountain lake likely reflect a climate warming induced change in terrestrial oc inflow

holocene summer temperature reconstruction from sedimentary chlorophyll content with treatment of age uncertainties kurupa lake arctic alaska quantitative records of pre industrial temperature changes are fundamental for understanding long term natural climate variability we used visible reflectance spectroscopy to measure chlorophyll c

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

human caused avulsion in the rhine meuse delta before historic embankment the netherlands although the shifting of deltaic river branches avulsion is a natural process that has become increasingly influenced by humans the impact of early human activities as a driver of avulsion success has remained poorly explored this study demonstrates how two important avulsions in the downstream part of the rhine meuse delta the netherlands were stimulated by human activities in the first millennium ce before historic embankment constrained the river courses peatland reclamation induced land subsidence in the lower delta this effect together with a human induced increase in suspended fluvial sediments and tidal backwater effects allowed for a gradual ingression of tidal creek channels and progradation of fluvial crevasse channels into human occupied and drained peatlands where they eventually connected we reconstructed the initial situation and identified the feedback loops among overbank sedimentation tidal incursion and land drainage subsidence that led to avulsion success the processes and feedbacks resulting from human activities are generic and hence relevant to many other deltas today where humaninduced subsidence results in tidal ingression potentially connecting to rivers and causing unexpected avulsions 2018 geological society of america

can humans force a return to a cretaceous climate abstract the modern pole to equator sea level temperature difference is about 50 c that of the mid cretaceous ranged from 30 c to as little as 24 c implying a much more equable climate this may have been caused by 1 reduction of the ice forced albedo of the polar regions 2 more efficient meridional energy transport by the atmosphere and ocean and 3 increased atmospheric greenhouse gas concentrations earth s icy polar regions stabilize its present inequable climate through the ice albedo feedback effect the polar ice results in permanent atmospheric highs that stabilize earth s wind systems in turn the stable winds drive the ocean currents and determine the location of the frontal systems that separate the low and high latitude oceanic gyre systems and bound the region where water sinks into the ocean interior as thermocline and intermediate water masses increased ocean heat transport can assist in making a more equable climate but unrealistic volume transports would be required to warm the polar regions to cretaceous levels the major factor forcing the equable climate of the cretaceous is now thought to be increased greenhouse gas concentrations dominated by co2 the modern rate of change in atmospheric concentration is greater than 200 ppmv per century and increasing this compares with 1 ppmv per century during the last deglaciation at current rates of fossil fuel burning atmospheric co2 levels will reach cretaceous levels of 2 times the pre industrial level about 2070 and 8 times the pre industrial level shortly after 2300 it is likely that cretaceous atmospheric co2 concentrations will last for many thousands to tens of thousands of years in addition to increased atmospheric greenhouse gas concentrations a return to climatic conditions resembling those of the cretaceous would require ice free poles and large changes in atmospheric and oceanic circulation arctic sea ice is melting much more rapidly than had been expected and the arctic ocean will soon be free of sea ice in summer the greenland ice sheet is melting more rapidly than expected because of greenhouse warming surface meltwater forms lakes and then flows down through crevasses and holes in the ice to lubricate the base allowing ice steams to flow much more rapidly the lifetime of the greenland ice sheet may be only a few hundred years the west antarctic ice sheet is inherently unstable being grounded on rock well below sea level the ice shelves blocking ice streams off west antarctica have begun to melt from beneath and break up as the southern ocean warms the east antarctic ice sheet has been regarded as highly stable but discovery of lakes beneath the ice and fast flowing ice streams raises questions about whether the ice sheet will ultimately succumb to global warming and disintegrate i conclude that a return to climatic conditions resembling those of the mid cretaceous is not only possible but also likely unless humanity can organize an effective campaign to stop co2 emissions to the atmosphere and remove some of the excess co2 already introduced

new evidence concerning the age and biotic effects of the chicxulub impact in ne mexico abstract in the 1990s the chicxulub impact was linked to the k t boundary by impact spherules at the base of a sandstone complex that was interpreted as an impact generated tsunami deposit since that time a preponderance of evidence has failed to support this interpretation revealing long term deposition of the sandstone complex the k t boundary above it and the primary impact spherule ejecta interbedded in late maastrichtian marls below based on evidence from mexico and texas we suggested that the chicxulub impact predates the k t boundary impact tsunami proponents have challenged this evidence largely on the basis that the stratigraphically lower spherule layer in mexico represents slumps and widespread tectonic disturbance although no such evidence has been presented the decades old controversy over the cause of the k t mass extinction will never achieve consensus but careful documentation of results that are reproducible and verifiable will uncover what really happened at the end of the crectaceous this study takes an important step in that direction by showing 1 that the stratigraphically older spherule layer from el penon ne mexico represents the primary chicxulub impact spherule ejecta in tectonically undisturbed sediments and 2 that this impact caused no species extinctions

sediment and carbon storages in the yahagi river delta during the holocene central japan abstract we estimated stored sediment and carbon during the holocene for each layer of the yahagi river delta central japan and discussed the provenance of stored carbon to estimate the bulk density and the carbon content of each layer we collected two 30 m deep undisturbed cores the volume of each layer was calculated using arcview 3d analyst although the volume ratio of each layer to the total volume was calculated to be 9 5 for the top mud layer 34 9 for the upper sand layer 32 8 for the middle mud layer and 22 9 for the lower sand layer the mass ratio of each layer to the total mass was calculated to be 8 5 40 9 25 2 and 25 4 respectively and the stored carbon ratio in each layer to the total stored carbon was 20 4 4 7 55 9 and 18 9 respectively these results suggest that the top mud and middle mud layers have a significant role as a place for carbon sequestration during postglacial time total stored carbon in the study area of only 92 1 km 2 was estimated at 26 tg c which is equivalent to 0 003 of atmospheric carbon this suggests that deltas on the globe have accumulated a massive amount of carbon during the evolution the inorganic carbon ratio to total carbon reached more than 45 around the boundary between the middle mud and lower sand layers the increasing trend in the c org n total ratio accompanied with a decrease in 13 c from the bottom to the top horizon in the middle mud layer indicates a gradual increase in terrestrial organic matter contribution the relative proportion of terrestrially derived materials decreases with increasing distance seaward

high resolution climate signals in the bolling allerod interstadial greenland interstadial 1 as reflected in european tree ring chronologies compared to marine varves and ice core records abstract lateglacial and holocene tree ring chronologies are unique archives which provide various information on past environments on a true annual time scale changes in ring width can be related to past climate anomalies and dendrodated wood provides an ideal source for radiocarbon calibration we present a 1051 year tree ring chronology from the late glacial built from subfossil scots pines pinus sylvestris that grew in different regions of central and southern europe through a series of high precision radiocarbon measurements we obtained a floating radiocarbon chronology which allowed accurate wiggle matching to the intcal98 calibration curve the trees show a coherent pattern in ring width variations throughout central europe and extending into the mediterranean which indicates a strong external climatic factor most probably temperature during the growing season we identified major growth events which appear synchronous with events seen in isotopic and tracer signals in the greenland ice cores and with changes in the strength of upwelling in the cariaco basin

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

sedimentary facies and holocene progradation rates of the changjiang yangtze delta china abstract the changjiang yangtze river one of the largest rivers in the world has formed a broad tide dominated delta at its mouth during the holocene sea level highstand three boreholes cm97 js98 and hq98 were obtained from the changjiang delta plain in 1997 1998 to clarify the characteristics of tide dominated delta sediments and architecture based on sediment composition and texture and faunal content core sediments were divided into six depositional units in ascending order they were interpreted as tidal sand ridge prodelta delta front subtidal to lower intertidal flat upper intertidal flat and surface soil deposits the deltaic sequence from the prodelta deposits to the delta front deposits showed an upward coarsening succession overlain by an upward fining succession from the uppermost part of the delta front deposits to the surface soil thinly interlaminated to thinly interbedded sand and mud sand mud couplets and bidirectional cross laminations in these deposits show that tide is the key factor affecting the formation of changjiang deltaic facies sediment facies and their succession combined with ams 14c dating revealed that isochron lines cross unit boundaries clearly and delta progradation has occurred since about 6000 to 7000 years bp when the rising sea level neared or reached its present position the average progradation rate of the delta front was approximately 50 km kyear over the last 5000 years the progradation rate however increased abruptly ca 2000 years bp going from 38 to 80 km kyear the possible causes for this active progradation could have been an increase in sediment production in the drainage basin due to widespread human interference and or decrease in deposition in the middle reaches related to the channel stability caused by human activity and climatic cooling after the mid holocene

floodplains permafrost cottonwood trees and peat what happened the last time climate warmed suddenly in arctic alaska abstract we use the stratigraphy of floodplains on alaska s north slope to describe how tundra watersheds responded to climate changes over the last 15 000 calibrated years bp 15 cal ka bp two episodes of extremely rapid floodplain alluviation occurred during the pleistocene holocene transition one between 14 and 12 8 cal ka bp and the other between 11 5 and 9 5 cal ka bp these aggradation episodes coincided with periods of warming in summer when cottonwood populus balsamifera l expanded its range peatlands became established and widespread thermokarst occurred the two aggradation episodes were separated by a period of floodplain incision during the younger dryas under cooler and possibly drier conditions at times of increasing summer warmth melting permafrost and enhanced precipitation probably triggered widespread mass wasting on hillslopes that overwhelmed the capacity of streams to transport sediment downstream and rapid floodplain aggradation resulted after peatlands became widespread in the early holocene rivers slowly incised their valley fills because major pulses of sediment input were limited to times of rapid thaw and increasing moisture many floodplains on the north slope have been effectively decoupled from upstream hillslopes for much of the past 15 000 years our findings a confirm the sensitivity of arctic watersheds to rapid warming in summer b emphasize the importance of hillslope mass wasting in landscape scale responses to climate change and c suggest that the presence of peatland on this arctic landscape today has raised its geomorphic response threshold to climate warming compared to what it was 14 000 years ago

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

holocene climatic change in the alaskan arctic as inferred from oxygen isotope and lake sediment analyses at wahoo lake despite recent progress in understanding high latitude climate variability paleoclimate records are scarce from the alaskan arctic we conducted isotopic and sediment analyses at wahoo lake to infer holocene climate variability in northeastern alaska water 18o and d values from the lake and its inlet outlet streams suggest that winter precipitation dominates modern water inputs and that evaporation has limited influence on the lake s hydrological budget the isotopic composition of pisidium exhibits marked variations during the past 11 500 years with 18o ranging between 18 7 and 16 2 and 13c between 7 1 and 2 3 vienna pee dee belemnite vpdb elevated 18o and sediment composition from 11 5 to 8 9 kcal bp suggest evaporative 18o enrichment and arid conditions rising lake levels are evidenced by the disappearance of pisidium and a transition to low carbonate gyttja ca 6 3 kcal bp and by the onset of sediment deposition on an adjacent shelf by 5 3 kcal bp these changes coincided with

10be ages of late pleistocene deglaciation and neoglaciation in the north central brooks range arctic alaska we present a chronology of late pleistocene deglaciation and neoglaciation for two valleys in the north central brooks range alaska using cosmogenic 10be exposure dating the two valleys show evidence of ice retreat from the northern range front before 16 15 ka and into individual cirques by 14 ka there is no evidence for a standstill or re advance during the lateglacial period indicating that a glacier advance during the younger dryas if any was less extensive than during the neoglaciation the maximum glacier expansion during the neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4 6 0 5 and 2 7 0 2 cal ka bp both moraine ages agree with previously published lichen inferred ages and confirm that glaciers in the brooks range experienced multiple advances of similar magnitude throughout the late holocene the similar extent of glaciers during the middle holocene and the little ice age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as neoglaciation progressed copyright 2012 john wiley sons ltd

evidence for permafrost thaw and transport from an alaskan north slope watershed burial of organic carbon oc in marine sediments is one of the most important linkages between the short term biologic carbon cycle and the long term geologic carbon cycle yet much is still unknown about the fate of terrigenous oc in marine coastal margins here the delivery of particulate oc poc to the colville river deltaic region in the alaskan beaufort sea by particulates of varying densities is studied through the use of ramped temperature pyrolysis and radiocarbon analyses the colville river is the largest river in north america whose watershed is underlain completely by high arctic permafrost tundra a variety of sources of poc are considered including terrestrial soils pleistocene aged yedoma like sediments coastal peat erosion and marine poc we provide the first evidence that riverine poc from the colville river contains old pleistocene sourced oc suggesting ongoing thaw and mobilization of yedoma like permafrost oc from this northern alaskan watershed additionally much of this oc appears to be fairly labile and therefore could be readily oxidized and returned to the atmosphere

quaternary glacial lacustrine and fluvial interactions in the western noatak basin northwest alaska abstract the 130 km long noatak basin is surrounded by mountains of the western brooks range middle and late pleistocene glaciers flowing southeast into the basin dammed a succession of proglacial lakes defined by shorelines outlet channels and upper limits of wave erosion more than 60 bluffs along the noatak river and its principal tributaries expose glacial and glaciolacustrine sediments that exhibit cut and fill relationships with interglacial and interstadial river channel and floodplain deposits this report focuses on the western noatak basin where high bluffs created by deep postglacial erosion record four major glacial advances during the cutler advance a floating ice tongue terminated in a large proglacial lake that filled the noatak basin the retreating glacier abandoned a trough along the valley center that subsequently filled with about 40 m of sediment during several younger glaciations and probably two major interglacial episodes alluvium that formed near the beginning of the younger interglaciation contains the 140 000 yr old old crow tephra the subsequent closely spaced okak and makpik advances are clearly younger than the maximum of the last interglaciation but they preceded a middle wisconsin 36 30 ka nonglacial interval in the noatak basin the okak advance terminated in an extensive lake whereas glaciers of the makpik and the subsequent anisak advances flowed into much narrower lakes that filled only the basin center the anisak advance bracketed by radiocarbon ages of about 35 and 13 6 ka represents the last glacial maximum lgm in the western noatak basin correlations with the oldest and youngest glacial deposits of the central brooks range are clear but relationships to events of intermediate age are more tenuous early pleistocene and older glacial advances from the central brooks range must have filled the noatak basin and overflowed northward through howard pass a younger glacial advance of inferred middle pleistocene sagavanirktok river age extended down the noatak valley into the basin center but its deposits are deeply buried beneath the basin floor and must be older than the cutler moraine the cutler advance may have been synchronous with the older of two advances of itkillik i age in the atongarak creek area but other evidence indicates that the okak makpik moraine succession more likely was synchronous with the two atongarak creek moraines radiocarbon ages surface morphology soil and weathering profiles and lake level history all support correlation of the last anisak major glacial advance in the western basin with the douglas creek moraine farther east and with itkillik ii late wisconsin glaciation of the central brooks range

terrain controls on the occurrence of coastal retrogressive thaw slumps along the yukon coast canada retrogressive thaw slumps rtss are among the most active landforms in the arctic their number has increased significantly over the past decades while processes initiating discrete rtss are well identified the major terrain controls on the development of coastal rtss at a regional scale are not yet defined our research reveals the main geomorphic factors that determine the development of rtss along a 238 km segment of the yukon coast canada we 1 show the current extent of rtss 2 ascertain the factors controlling their activity and initiation and 3 explain the spatial differences in the density and areal coverage of rtss we mapped and classified 287 rtss using high resolution satellite images acquired in 2011 we highlighted the main terrain controls over their development using univariate regression trees model coastal geomorphology influenced both the activity and initiation of rtss active rtss and rtss initiated after 1972 occurred primarily on terrains with slope angles greater than 3 9 and 5 9 respectively the density and areal coverage of rtss were constrained by the volume and thickness of massive ice bodies differences in rates of coastal change along the coast did not affect the model we infer that rates of coastal change averaged over a 39 year period are unable to reflect the complex relationship between rtss and coastline dynamics we emphasize the need for large scale studies of rtss to evaluate their impact on the ecosystem and to measure their contribution to the global carbon budget

sediment flux and the anthropocene data and computer simulations are reviewed to help better define the timing and magnitude of human influence on sediment flux the anthropocene epoch impacts on the earth surface processes are not spatially or temporally homogeneous human influences on this sediment flux have a secondary effect on floodplain and delta plain functions and sediment dispersal into the coastal ocean human impact on sediment production began 3000 years ago but accelerated more widely 1000 years ago by the sixteenth century societies were already engineering their environment early twentieth century mechanization has led to global signals of increased sediment flux in most large rivers by the 1950s this sediment disturbance signal reversed for many rivers owing to the proliferation of dams and sediment load reduction below pristine conditions is the dominant signal today a delta subsidence signal began in the 1930s and is now a dominant signal in terms of sea level for many coastal environments overwhelming even the global warming imprint on sea level humans have engineered how most water and sediment are discharged into the coastal ocean hyperpycnal flow events have become more common for some rivers and less common for other rivers bottom trawling is now widespread suggesting that even continental shelves have received a significant but as yet quantified anthropocene impact the anthropocene attains the level of a geological climate event such as that seen in the transition between the pleistocene and the holocene

dated wood from alaska and the yukon implications for forest refugia in beringia abstract postulations on the existence of forest refugia in parts of beringia during the last glacial have been in large part based on ambiguous evidence existing data on radiocarbon dated and identified fossil wood and macrofossils from alaska and northwest canada are synthesized here and are augmented by results of palynological studies in an effort to show the persistence of some and total extinction of other tree and large shrub species possible dispersal routes taken by species that reinvaded beringia in postglacial times are also reconstructed from the fossil record macrofossil and pollen evidence when combined with climatic factors makes cottonwood a good candidate for survival during the last glacial larch and aspen are also candidates though the evidence for them is less positive pollen and macrofossils of alder are very scarce in deposits of the last glacial age and if it survived at all it was probably in very isolated vegetatively reproducing clones shrub birch may have been present in beringia but tree birch probably was reintroduced during the holocene spruce also appears to have been absent in alaska from about 30 000 to 11 500 yr ago and probably reinvaded beringia from a refugium south of the laurentide ice sheet

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

holocene climate inferred from oxygen isotope ratios in lake sediments central brooks range alaska analyses of sediment cores from two lakes in the central brooks range provide temperature and moisture balance information for the past 8500 cal yr at century scale resolution two methods of oxygen isotope analysis are used to reconstruct past changes in the effective moisture precipitation minus evaporation and temperature effective moisture is inferred from oxygen isotope ratios in sediment cellulose from meli lake area 0 13 km 2 depth 19 4 m the lake has a low watershed to lake area ratio 7 and significant evaporation relative to input summer temperature shifts are based on oxygen isotope analyses of endogenic calcite from tangled up lake area 0 25 km 2 depth 3 5 m this basin has a larger watershed to lake area ratio 91 and less evaporation relative to input sediment oxygen isotope analyses from the two sites indicate generally more arid conditions than present prior to 6000 cal yr b p subsequently the region became increasingly wet temperature variability is recorded minimally at centennial scale resolution with values that are generally cool for the past 6700 cal yr the timing and direction of climate variability indicated by the oxygen isotope time series from meli and tangled up lakes are consistent with previously established late holocene glacier advances at 5000 cal yr b p in the central brooks range and high lake levels at birch lake since 5500 cal yr b p this unique use of oxygen isotopes reveals both moisture balance and temperature histories at previously undetected high resolution temporal scales for northern alaska during the middle to late holocene c 2001 university of washington

antarctic sediment chronology by programmed temperature pyrolysis methodology and data treatment 1 we report a detailed programmed temperature pyrolysis combustion methodology for radiocarbon 14c dating of antarctic sub ice shelf sediments the method targets the autochthonous organic component in sediments that contain a distribution of acid insoluble organic components from several sources of different ages the approach has improved sediment chronology in organic rich sediments proximal to antarctic ice shelves by yielding maximum age constraints significantly younger than bulk radiocarbon dates from the same sediment horizons the method proves adequate in determining isotope ratios of the pre aged carbon end member however the isotopic compositions of the low temperature measurements indicate that no samples completely avoided mixing with some proportion of pre aged organic material dating the unresolved but desired young end member must rely on indirect methods but a simple mixing model cannot be developed without knowledge of the sedimentation rate or comparable constraints a mathematical approach allowing for multiple mixing components yields a maximum likelihood age a first order approximation of the relative proportion of the autochthonous component and the temperature at which allochthonous carbon begins to volatilize and mix with the autochthonous component it is likely that our estimation of the cutoff temperature will be improved with knowledge of the pyrolysis kinetics of the major components chronology is improved relative to bulk acid insoluble organic material ages from nine temperature interval dates down to two but incorporation of inherently more pre aged carbon in the first division becomes more apparent with fewer and larger temperature intervals

selective preservation of old organic carbon fluvially released from sub arctic soils amplified climate warming in the arctic may cause thaw remobilization of its large soil organic carbon soc pool here we assess the remobilization and preservation of old soc by the watershed integrated radiocarbon signature of molecular soc markers released from northernmost scandinavia the radiocarbon analyses revealed a remarkable fractionation for identical vascular plant markers 420 or 6000 14c years upon settling from surface water to the underlying sediments from this we infer fluvial export of two soc pools a young surface peat component and an old deep mineral soil component the young pool exists as an easily degradable humic suspension while the old pool is matrix protected from degradation and ballasted for preferential settling the two soil types with highest oc in arctic permafrost evidently exhibit different susceptibilities to degradation hence a significant part of the thaw released oc may simply be fluvially relocated to sediments instead of being emitted to the atmosphere

dinosaur demise in light of their alleged perennial polar residency the end cretaceous biological crisis is represented by the demise of the non avian dinosaurs however most crucial biologically was the elimination of the photosynthesizing marine phyto and zooplankton forming the base of the marine food chain their abrupt demise attests to sunlight screening darkening the atmosphere for a few years alvarez et al science 208 1095 1108 1980 doi 10 1126 science 208 44 noticed in deep marine end cretaceous sediments an anomalous rise in the chemical element iridium ir which is rare on planet earth and thus suggests an extraterrestrial origin through an impact of a large asteroid this impact would have ejected enormous quantities of particles and aerosols shading the solar illumination as attested to by the elimination of the marine photosynthesizing plankton such a dark period must have affected life on land the apparent cold blooded non avian dinosaurs which were used to living in open terrains to absorb the solar illumination became inactive during the dark period and were incapable of withstanding predators this was in contrast to cold blooded crocodilians turtles and lizards that could hide in refuge sites on land and in the water dinosaur relics discovered in cretaceous polar regions were attributed to perennial residents surviving the nearly half year long dark winter despite their ability to leave the polar concentrations of disarticulated dinosaur bones were suggested as having resulted from a catastrophic burial of a population by floods however this should have fossilized complete skeletons alternatively herds of dinosaurs living in high latitudes might have been sexually driven to spend the half year of continuously illuminated polar summer for mating rather than for nourishment in which the lower latitudes provided as well the aggressive mating competitions would have left victims among the rivals and of young ones incidentally trampled over all being consumed and their skeletons disarticulated accordingly the alleged polar dinosaurs do not challenge the logical conclusion that the non avian dinosaurs were cold blooded as a result of which they became inactive and subjected to predation during the end cretaceous dark period

an oxygen isotope record of holocene climate change in the south central brooks range alaska abstract understanding the ecological and socio economic impacts of climatic warming requires knowledge of associated changes in moisture balance reconstructions of holocene moisture balance variation offer indispensible baseline information against which recent changes can be evaluated we analyzed chara stem encrustations in the sediments of takahula lake located in the south central brooks range of alaska for oxygen and carbon isotope composition to infer climatic change over the past 8000 years to help constrain climatic interpretations of the sediment 18 o record we also analyzed water samples from takahula and other lakes in the region for oxygen and hydrogen isotope composition results show that winter precipitation dominates the water balance of these lakes and that post input evaporation is a key control of lake water isotope composition of takahula lake stratigraphic patterns in chara 18 o supplemented by those in 13 c and sediment lithology reveal distinct changes in effective moisture precipitation minus evaporation over the past 8000 years effective moisture was relatively high from 8000 to 5000 cal bp with marked fluctuations between 6800 and 5000 cal bp it then decreased to reach a minimum around 4000 cal bp and increased with fluctuations from 4000 to 2500 cal bp followed by a decreasing trend toward the present that was interrupted by a wet little ice age centered at 400 cal bp aridity during the 20th century was among the highest of the entire 8000 year record at the millennial timescale the temporal patterns of moisture balance shifts at takahula lake are broadly coherent with those inferred from previous paleoclimate records from the region the chara 18 o values around 5600 cal bp and during the little ice age are up to 5 lower than at present and 3 6 lower than that of the modern input water to the lake these exceptionally low values suggest that factors other than effective moisture must have contributed to the pronounced variations in the takahula lake 18 o record increased winter precipitation associated with a westerly aleutian low position may account for 1 of the 18 o decrease other factors leading to the 18 o depletion during these periods probably include decreased temperatures as well as increased lake ice cover and associated reductions in evaporation

multiple thermo erosional episodes during the past six millennia implications for the response of arctic permafrost to climate change anthropogenic warming may promote rapid permafrost thaw in the arctic and alter the global carbon cycle although several studies suggest increased thermo erosion as a result of recent warming a long term context is necessary to assess the linkages of thermokarst processes with climate variability we analyzed sediment cores from two lakes on the alaskan north slope usa one with lake ne14 and one without perch lake watershed thermo erosion distinct geochemical and lithological characteristics provide evidence for sedimentary input from carbonate rich permafrost soils associated with past retrogressive thaw slumping at lake ne14 but not at perch lake these characteristics include increases in ca sr ca k carbonate feldspar clay minerals percent caco3 and 13c and decreases in 87sr 86sr at least ten episodes of thermo erosion occurred over the past 6000 yr at lake ne14 most of these episodes coincided with periods of elevated summer temperatures but moisture variation and geomorphic factors likely played a role in driving their occurrence our results suggest that positive feedbacks facilitate reactivation of thermo erosion in ice rich terrain adding to the growing body of evidence that these arctic landscapes are unstable in a changing climate

holocene glaciation of alaska and adjoining yukon territory canada abstract holocene glacial fluctuations between arctic central interior and southern maritime alaska are broadly synchronous this synchrony is evident from a review of work in 11 study areas with varying numbers of glaciers 3 100 glacier types subpolar cirque temperate valley tidewater surging and dating methodologies the pattern is temporally and spatially consistent with vegetation data and generally with climatic deteriorations culminating in the little ice age early holocene glacial advances are confirmed for 7 6 5 8 lichen ka bp at 4 of 97 glaciers in the brooks range advances also occurred by 5 85 and 5 7 ka bp at separate glacier tongues in the northern alaska range at least by 6 5 ka bp in lituya bay and possibly also in the malaspina and aleutian islands areas a sharp increase in glacier activity began by 4 4 ka bp in the arctic and glacier bay areas and by about 3 ka bp major glacier advances probably were initiated or well underway throughout alaska during holocene glacial maxima ice filled glacier and lituya bays as well as fjords of prince william sound and massive moraines buried forests in the northeastern st elias mountains area minor recession is recorded directly or implied in most of alaska about 2 ka bp or locally through the following millennium subsequently distinct but locally weak advances occurred by about 1 2 ka bp in most areas again followed by intervals of glacier recession most pervasive and ubiquitous were the little ice age advances initiated about 700 bp these generally culminated in two major advances between about 400 and 50 bp in the arctic those of a d 1600 dominated those of the late 1800s in the gulf of alaska those of the middle 1700s or late 1800s dominated large scale asynchronous advances and retreats of calving tidewater glaciers have been recorded during the twentieth century but most such movements are only indirectly related to climate

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

temperature and precipitation history of the arctic as the planet cooled from peak warmth in the early cenozoic extensive northern hemisphere ice sheets developed by 2 6 ma ago leading to changes in the circulation of both the atmosphere and oceans from not vert similar2 6 to not vert similar1 0 ma ago ice sheets came and went about every 41 ka in pace with cycles in the tilt of earth s axis but for the past 700 ka glacial cycles have been longer lasting not vert similar100 ka separated by brief warm interglaciations when sea level and ice volumes were close to present the cause of the shift from 41 ka to 100 ka glacial cycles is still debated during the penultimate interglaciation not vert similar130 to not vert similar120 ka ago solar energy in summer in the arctic was greater than at any time subsequently as a consequence arctic summers were not vert similar5 c warmer than at present and almost all glaciers melted completely except for the greenland ice sheet and even it was reduced in size substantially from its present extent with the loss of land ice sea level was about 5 m higher than present with the extra melt coming from both greenland and antarctica as well as small glaciers the last glacial maximum lgm peaked not vert similar21 ka ago when mean annual temperatures over parts of the arctic were as much as 20 c lower than at present ice recession was well underway 16 ka ago and most of the northern hemisphere ice sheets had melted by 6 ka ago solar energy reached a summer maximum 9 higher than at present not vert similar11 ka ago and has been decreasing since then primarily in response to the precession of the equinoxes the extra energy elevated early holocene summer temperatures throughout the arctic 1 3 c above 20th century averages enough to completely melt many small glaciers throughout the arctic although the greenland ice sheet was only slightly smaller than at present early holocene summer sea ice limits were substantially smaller than their 20th century average and the flow of atlantic water into the arctic ocean was substantially greater as summer solar energy decreased in the second half of the holocene glaciers re established or advanced sea ice expanded and the flow of warm atlantic water into the arctic ocean diminished late holocene cooling reached its nadir during the little ice age about 1250 1850 ad when sun blocking volcanic eruptions and perhaps other causes added to the orbital cooling allowing most arctic glaciers to reach their maximum holocene extent during the warming of the past century glaciers have receded throughout the arctic terrestrial ecosystems have advanced northward and perennial arctic ocean sea ice has diminished here we review the proxies that allow reconstruction of quaternary climates and the feedbacks that amplify climate change across the arctic we provide an overview of the evolution of climate from the hot house of the early cenozoic through its transition to the ice house of the quaternary with special emphasis on the anomalous warmth of the middle pliocene early quaternary warm times the mid pleistocene transition warm interglaciations of marine isotope stages 11 5e and 1 the stage 3 interstadial and the peak cold of the last glacial maximum

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

herd structure in late cretaceous polar dinosaurs a remarkable new dinosaur tracksite denali national park alaska usa the discovery of a new tracksite of mostly hadrosaurid dinosaur footprints made by a herd living in an ancient high latitude continental ecosystem provides insight into the herd structure and behavior of northern polar dinosaurs and perspective on populations of large bodied herbivores in an arctic greenhouse world this tracksite occurs in the upper cretaceous cantwell formation in the alaska range denali national park alaska united states and it is the largest tracksite known from this far north preservation of the tracksite is exceptional most tracks regardless of size contain skin impressions and they co occur with well preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects statistical analyses of the tracks show that individuals of four different age classes of hadrosaurids lived together in a large social group our research results independently corroborate the growth curve for hadrosaurids proposed by paleohistologists that suggests that these dinosaurs experienced a period of rapid growth early in their life history

dinosaurs nesting on tidal flats abstract the discovery of a dinosaur clutch in upper cretaceous tidal flat deposits in the tremp formation in biscarri isona lleida spain provides insight into the mode of life of some dinosaurs the clutch occurs in grey marls that were originally waterlogged muddy sediments the seven elongated eggs are parallel to each other and with their long axis almost vertically oriented a mound nest is inferred in contrast to hole nest described so far for similar eggshell types the permeability of the eggshell oospecies megaloolithus siruguei was highly enhanced by a braided network of multicanaliculate pore canals the nest style eggshell porosity and tidal flat environment point to a periaquatic habitat for these dinosaurs a modern analogue occurs in crocodiles alligators and some birds living in periaquatic environments with nesting on plant mounds above waterlogged soils or even on floating vegetation

radiocarbon age offsets in an arctic lake reveal the long term response of permafrost carbon to climate change continued warming of the arctic may cause permafrost to thaw and speed the decomposition of large stores of soil organic carbon oc thereby accentuating global warming however it is unclear if recent warming has raised the current rates of permafrost oc release to anomalous levels or to what extent soil carbon release is sensitive to climate forcing here we use a time series of radiocarbon age offsets 14c between the bulk lake sediment and plant macrofossils deposited in an arctic lake as an archive for soil and permafrost oc release over the last 14 500 years the lake traps and archives oc imported from the watershed and allows us to test whether prior warming events stimulated old carbon release and heightened age offsets today the age offset 2 ka thousand of calibrated years before a d 1950 and the depositional rate of ancient oc from the watershed into the lake are relatively low and similar to those during the younger dryas cold interval occurring 12 9 11 7 ka in contrast age offsets were higher 3 0 5 0 ka when summer air temperatures were warmer than present during the holocene thermal maximum 11 7 9 0 ka and bolling allerod periods 14 5 12 9 ka during these warm times permafrost thaw contributed to ancient oc depositional rates that were 10 times greater than today although permafrost oc was vulnerable to climate warming in the past we suggest surface soil organic horizons and peat are presently limiting summer thaw and carbon release as a result the temperature threshold to trigger widespread permafrost oc release is higher than during previous warming events

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

late weichselian and holocene palaeogeography of the rhine meuse delta the netherlands abstract a large number of lithological borehole descriptions 14c dates archaeological artefacts and gradients of palaeochannels were used to reconstruct the holocene development of the rhine meuse delta data were stored in a geographical information system database that enables generation of palaeogeographical maps for any time during the holocene the time resolution of the palaeogeographic reconstruction is about 200 years during the holocene avulsion was an important process resulting in frequent shifts of areas of clastic sedimentation palaeogeographic evolution of the rhine meuse delta is mainly governed by complex interactions among several factors these are 1 location and shape of the late weichselian palaeovalley 2 sea level rise which resulted in back filling of the palaeovalley 3 peat formation which was most extensive in the western part of the back barrier area especially between 4000 and 3000 14c yr bp this more or less fixed the river pattern at that time and resulted in few avulsions 4 neotectonics differential tectonic movements of the peel horst and roer valley graben seem to have influenced river behaviour formation of an asymmetrical meander belt location of avulsion nodes especially from 4500 to 2800 14c yr bp when the rate of sea level rise had decreased after 2800 14c yr bp the sea level rise further decreased and the tectonic influence still may have influenced avulsions but from then on other factors became dominant 5 increased discharge sediment load and or within channel sedimentation after 2800 14c yr bp river meanders of rhine distributaries as well as the single channel of the meuse show remarkable increases in wavelength interpreted as a result of increased bankfull discharge and sediment load increased discharge may initially have been caused by a higher precipitation after 2000 14c yr bp both discharge and sediment load seem to have increased as a result of human influence alternatively decreasing gradients as a result of sea level rise may have caused an increased within channel sedimentation and channel widening which would also lead to increased meander wavelengths 6 composition of the river banks meandering river channels tend to adhere to the sandy margins of the late weichselian palaeovalley and a high channel sinuosity is found in areas where river banks consist of sand 7 marine ingressions e g the ad 1421 st elizabeth s flood caused large scale erosion in the southwestern part of the fluvial deltaic plain 8 human influence since about ad 1100 human influence dominated the palaeogeographic evolution rivers were embanked and dredged meanders were cut off and for the meuse a new distributary canal the bergsche maas was dug in ad 1904 discharge distribution over the various channels is strictly controlled nowadays an unusual feature of the delta is the prolonged existence of the oude rijn channel belt

timing of retrogressive thaw slump initiation in the noatak basin northwest alaska usa in the north american low arctic increased retrogressive thaw slump frequency and headwall retreat rates have been linked with climate warming trends since the midtwentieth century but specific weather drivers of slump initiation timing are less clear we examined relationships among retrogressive thaw slump initiation and annual air temperature precipitation and snow cover using time series of satellite imagery and weather station data in northwest alaska synthetic aperture radar and optical imagery were used to examine retrogressive thaw slump initiation between 1997 and 2010 over 80 of the slump features examined in this study first appear within a 13 month span from late june 2004 to july 2005 remote weather station data show that 2004 and 2005 are among several years exhibiting above average thawing indices and average summer temperatures between 1992 and 2011 however 2004 is distinct from the rest of the record with unusually warm temperatures primarily occurring early in the thaw season between april and early june and including two intense precipitation events in may regional weather reported by the noaa national weather service also reflects these local findings snowmelt timing in 2004 corresponded with warmer air temperatures and precipitation between april and may exposing the ground surface more than 2 weeks earlier than average for 2001 2012 within the noatak basin future rates of thaw slump initiation may be linked with changing trends in the timing of weather in addition to general climate warming

quantitative analysis of land transformation in a holocene delta an example from the tama river lowland central japan abstract human activities such as the expansion of agricultural and urban land use on subaerial deltas and landfilling of subaqueous deltas have large impacts on holocene deltas here we quantified the volume of the holocene deltaic deposits in the tama river lowland located in the tokyo metropolitan area by analyzing 3872 existing borehole sections using gis and evaluated artificial land transformation the total volume of deltaic deposits accumulated during the past 9000 years was estimated to be 3925 106 m3 of which artificially deformed near surface material ad 676 106 m3 occupies approximately 17 this ratio is much larger than that in the nobi plain 4 6 in the nagoya metropolitan area suggesting that the impact of anthropogenic disturbance on the delta has been greater in tokyo than in the nagoya metropolitan area approximately 71 of ad is distributed in the seaward area where landfills were created mainly after the taisho period 1912 1926 the source of the ad is considered to be dredged soil construction waste soil and mountain sand the remaining 29 of ad occurred in the landward area floodplain and delta plain and likely originates from the in situ disturbed sediments of the delta plain and floodplain in addition to earth fill the seaward ad deposits including redeposition by dredging within the delta accumulated at a rate of 4 79 106 m3 year which is much higher than that of the accumulation of natural deltaic deposits during the holocene 0 36 106 m3 year this clearly shows that anthropogenic forcing has become a strong influence on geomorphological and sedimentological processes within the delta

identification of unrecognized tundra fire events on the north slope of alaska 1 characteristics of the natural fire regime are poorly resolved in the arctic even though fire may play an important role cycling carbon stored in tundra vegetation and soils to the atmosphere in the course of studying vegetation and permafrost terrain characteristics along a chronosequence of tundra burn sites from ad 1977 1993 and 2007 on the north slope of alaska we discovered two large previously unrecognized tundra fires the meade river fire burned an estimated 500 km2 and the ketik river fire burned an estimated 1200 km2 based on radiocarbon dating of charred twigs analysis of historic aerial photography and regional climate proxy data these fires likely occurred between ad 1880 and 1920 together these events double the estimated burn area on the north slope of alaska over the last 100 to 130 years assessment of vegetation succession along the century scale chronosequence of tundra fire disturbances demonstrates for the first time on the north slope of alaska that tundra fires can facilitate the invasion of tundra by shrubs degradation of ice rich permafrost was also evident at the fire sites and likely aided in the presumed changes of the tundra vegetation postfire other previously unrecognized tundra fire events likely exist in alaska and other arctic regions and identification of these sites is important for better understanding disturbance regimes and carbon cycling in arctic tundra

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

climate driven thaw of permafrost preserved glacial landscapes northwestern canada ice marginal glaciated landscapes demarcate former boundaries of the continental ice sheets throughout circumpolar regions permafrost has preserved relict ground ice and glacigenic sediments delaying the sequence of postglacial landscape change that transformed temperate environments millennia earlier here we show that within 7 10 6 km 2 of glaciated permafrost terrain extensive landscapes remain poised for major climate driven change across northwestern canada 60 100 km wide concentric swaths of thaw slump affected terrain delineate the maximum and recessional positions of the laurentide ice sheet these landscapes comprise 17 of continuous permafrost terrain in a 1 27 10 6 km 2 study area indicating widespread preservation of late pleistocene ground ice these thaw slump relict ground ice and glacigenic terrain associations are also evident at the circumpolar scale recent intensification of thaw slumping across northwestern canada has mobilized primary glacial sediments triggering a cascade of fluvial lacustrine and coastal effects these geologically significant processes highlighted by the spatial distribution of thaw slumps and patterns of fluvial sediment mobilization signal the climate driven renewal of deglaciation and postglacial permafrost landscape evolution

holocene evolution of the song hong red river delta system northern vietnam abstract the song hong red river delta located on the western coast of the gulf of bac bo tonkin in the south china sea formed as a result of the song hong sediment discharge throughout the holocene the river s sedimentary basin upstream from the delta plain is not large the delta plain comprises emerged tidal mangrove flats formed during the sea level highstand at 2 3 m 6 4 cal kyr bp and a beach ridge strandplain with straight to lobate beach ridges on the landward and seaward sides of the delta plain respectively the delta affords us the opportunity to examine river mouth morphodynamics comprehensively in relation to sediment discharge and sea level changes in this paper we describe the holocene evolution of the song hong delta system and the river mouth morphodynamics on the basis of seven sediment cores each 30 70 m long taken from the delta plain during 1999 2001 and 101 radiocarbon dates obtained from the core sediments sediments from the seven cores consisting of incised valley fills since the last glacial maximum can be divided in ascending order into fluvial sediments composed of gravelly sand and mottled clay tide influenced estuarine sediments containing shell and wood fragments and deltaic sediments composed of tide influenced sand and mud deposits in which the contents of sand and wood fragments increase upward by applying sequence stratigraphic concepts a transgressive surface can be identified at the gravelly sand mottled clay boundary and the maximum flooding surface can be identified at the estuarine deltaic sediments boundary the lowstand systems tract transgressive systems tract and highstand systems tract record 15 15 9 and 9 0 cal kyr bp respectively during the past 9 kyr the majority of the sediment discharged by the song hong accumulated in the incised valley and enhanced progradation at the river mouth the river mouth prograded from the bay head toward the gulf and its morphology changed from funnel shaped 9 6 cal kyr bp to straight 6 2 cal kyr bp and finally to lobate 2 0 cal kyr bp the morphological change from a funnel shaped to straight coast is interpreted to have been closely related to a hydrologic regime shift from a tide dominated bay head setting to a wave influenced open coast setting the cessation of the sea level rise at 6 cal kyr bp may have played only a small role in the change of river mouth morphology because the progradation rate decelerated from 22 to 4 m yr instead of accelerating at that time the river mouth morphodynamic change from straight to lobate was largely caused by an increase in the song hong sediment discharge from 17 27 9 2 cal kyr bp to 49 million t yr 2 0 cal kyr bp as a result of anthropogenic deforestation along the upper reaches of the song hong

the chicxulub impact event and its environmental consequences at the cretaceous tertiary boundary abstract an impact mass extinction hypothesis for the cretaceous tertiary k t boundary transition has been confirmed with multiple lines of evidence beginning with the discovery of impact derived ir in k t boundary sediments and culminating in the discovery of the chicxulub impact crater likewise a link between the chicxulub impact crater and k t boundary sediments has been confirmed with multiple lines of evidence including stratigraphic petrological geochemical and isotopic data the environmental effects of the chicxulub impact event were global in their extent largely because of the interaction of ejected impact debris with the atmosphere the environmental consequences of the chicxulub impact event and their association with the k t boundary mass extinction event indicate that impact cratering processes can affect both the geologic and biologic evolution of our planet