flux and provenance of ice rafted debris in the earliest pleistocene sub polar north atlantic ocean comparable to the last glacial maximum relatively little is known in detail about the locations of the early pleistocene ice sheets responsible for ice rafted debris ird inputs to the sub polar north atlantic ocean during intensification of northern hemisphere glaciation inhg to shed new light on this problem we present the first combined in depth analysis of ird flux and geochemical provenance of individual sand sized ird deposited in the sub polar north atlantic ocean during the earliest large amplitude pleistocene glacial marine isotope stage mis 100 2 52 ma arguably the key glacial during inhg ird provenance is assessed using laser ablation lead pb isotope analyses of single feldspar grains we find that the pb isotope composition 206pb 204pb 207pb 204pb and 208pb 204pb of individual ice rafted 150 m feldspars deposited at dsdp site 611a odp site 981 and iodp site u1308 during mis 100 records a shift from predominantly archaean aged circum north atlantic ocean continental sources during early glacial ice rafting events to dominantly palaeozoic and proterozoic aged sources during full glacial conditions the distribution of feldspars in pb pb space for full glacial mis 100 more closely resembles that documented for feldspars deposited at the centre of the last glacial ird belt at iodp dsdp site u1308 609 during ambient non heinrich event ice rafting episodes of mis 2 23 8 ka than that documented for mis 5d 106 ka comparison of our early pleistocene and last glacial cycle datasets suggests that mis 100 was characterised by abundant iceberg calving from large ice sheets on multiple continents in the high northern latitudes not just on greenland

intensification of northern hemisphere glaciations in the circum atlantic region 3 5 2 4 ma ice rafted detritus evidence abstract records of ice rafted detritus ird from ocean drilling program sites 644 and 907 in the nordic seas and deep sea drilling program sites 610 and 607 in the north atlantic ocean are used to determine the growth and history of northern hemisphere glaciations spanning the interval from 3 6 to 2 4 ma the records document that the initiation of large scale glaciation in the circum atlantic region occurred stepwise between 3 5 and 2 4 ma with greenland leading the other areas the first major pulse of ird occurs at 3 3 ma suggesting a distinct expansion of the greenland ice sheet progressive increases in ird occur from 3 0 ma with a synchronous ice sheet development between the greenland scandinavian and north american regions starting around 2 72 2 75 ma the regional records of ird correspond to major trends in the oxygen isotope record suggesting a tight connection between the record of global ice volume and evidence for expanding glaciers in the northern hemisphere it appears as if widespread ird distribution occurs when the global ice volume surpasses certain thresholds similar to the late quaternary situation

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

plio pleistocene megacycles record of climate and tectonics abstract paleoclimatic records from the deep sea floor show that in the last 3 m y more than 100 oscillations of mild and cool global climate took place with a larger amplitude than any experienced during the holocene variations of dry and wet climates in the chinese loess plateau and in the loess belt of central europe have similar frequency it has been convincingly proved that the periodicity of the past gross climate changes agrees with that of the earth s orbital perturbations however while the amplitude of the orbital cycles and of the oceanic oxygen isotope variations is relatively uniform several of the cold climate episodes recorded on land appear more severe than the remainder they correspond to chinese loess units l1 l2 l5 l6 and l9 correlating with central european loess of cycles b c f h and j these units correspond to oxygen isotope stages 2 6 12 16 and 22 and to the weichselian saalian and elsterian ice advances in addition chinese loess layers l13 l15 wl1 wl2 wl3 and wl4 appear to represent exceptionally dry and cold episodes apparently correlative with the inter bavelian cooling and with menapian eburonian and praetiglian glacials of the rhine delta based on this observation we propose to distinguish within the last 2 5 m y ten megacycles describe them in the chinese loess sequences and name them in the order of increasing age mc1 mc10 each megacycle starts with an unusually thick loess unit interpreted as a deposit of an exceptionally severe glaciation and terminates with a cluster of well developed soils indicative of warm humid climates interrupted by relatively mild glacials the megacycles of the last 2 5 m y lasted between 200 and 340 millennia each with an average duration of 255 thousand years when correlated with the stratigraphic record of the chinese loess plateau the wurm terrace as well as the saale glacier advances the eem marine transgression the weichsel ice advance and the holocene correspond to a still incomplete megacycle mc1 the riss terrace the elster ice advance holstein transgression and subsequent mild and cool intervals ending with the schoningen interglacial sensu urban 1992 belong to the megacycle mc2 recognition of four megacycles within brunhes resolves the long standing discrepancy between the limited number of classical continental glacial and interglacial units and the frequent climate oscillations recorded in the deep sea sediments and the loess sequences only in the holsteinian and eemian interglacials was the crustal rebound delayed enough to permit oceanic transgressions reaching deep inland there is no apparent astronomic reason for the exceptional intensity and deep southward penetration of continental ice sheets during only some of the cold intervals since the differences are much more pronounced on land than in the ocean and since the major ice advances are closely linked with terraces it seems that the megacycles were preconditioned by tectonic movements intermittent pulses of rapid uplift of mountain ranges could have impacted climate worldwide by deflecting atmospheric circulation in the sense of ruddiman and raymo 1988 it is also probable that the tectonically changing shape of the sea floor sills reoriented the oceanic circulation which then could have affected plio pleistocene climates world wide the loess covered terraces in the lanzhou area demonstrate that the tectonic movements in the northern part of the tibet plateau correlate closely with the advances of continental ice in europe suggesting that the uplift of the tibet plateau significantly contributed to the gradual climate deterioration of the last million years

genesis and evolution of hco3 rich and so4 rich groundwaters of quaternary sediments pinawa canada abstract groundwaters collected from sediments at aecl research whiteshell laboratories include ca mg na hco3 na mg ca hco3 and ca mg na so4 hco3 water types the type produced is determined by the reactive phases encountered during migration through the enclosing sediments these include calcite gypsum and a clay substrate on which cation exchange occurs co2 charged soil waters undergo cation exchange reactions with solids of the enclosing sediments and dissolve calcite to saturation yielding ca mg hco3 groundwaters containing up to 700 mg l 1 total dissolved solids tds more saline sulphate rich groundwaters 1100 3000 mg l 1 tds are produced through combined reaction with gypsum calcite and a mg rich exchange substrate the type of groundwater produced is critically dependent upon the proportions of exchangeable cations on the bulk exchange substrate dissolution of gypsum increases so4 of the solutions but much of the released ca is taken onto the exchange substrate displacing na k first then mg continued gypsum dissolution causes precipitation of calcite and a decrease in solution ph the resulting saline waters are enriched in mg and na relative to ca compared with most groundwaters and are enriched in so4 relative to hco3 many sulphate rich groundwaters common to the northern north american prairies may have similar origins three solid phases exchange substrate calcite and gypsum are needed to model successfully these waters but interactions among them are complex calcite for example dissolves initially but is subsequently precipitated during evolution of sulphate rich waters consequently changes to major dissolved constituents and carbon isotopic ratios are difficult to predict without a comprehensive understanding of the geochemical evolution of these waters

strengthening of north american dust sources during the late pliocene 2 7 ma here we present orbitally resolved records of terrestrial higher plant leaf wax input to the north atlantic over the last 3 5 ma based on the accumulation of long chain n alkanes and n alkanl 1 ols at iodp site u1313 these lipids are a major component of dust even in remote ocean areas and have a predominantly aeolian origin in distal marine sediments our results demonstrate that around 2 7 million years ago ma coinciding with the intensification of the northern hemisphere glaciation nhg the aeolian input of terrestrial material to the north atlantic increased drastically since then during every glacial the aeolian input of higher plant material was up to 30 times higher than during interglacials the close correspondence between aeolian input to the north atlantic and other dust records indicates a globally uniform response of dust sources to quaternary climate variability although the amplitude of variation differs among areas we argue that the increased aeolian input at site u1313 during glacials is predominantly related to the episodic appearance of continental ice sheets in north america and the associated strengthening of glaciogenic dust sources evolutional spectral analyses of the n alkane records were therefore used to determine the dominant astronomical forcing in north american ice sheet advances these results demonstrate that during the early pleistocene north american ice sheet dynamics responded predominantly to variations in obliquity 41 ka which argues against previous suggestions of precession related variations in northern hemisphere ice sheets during the early pleistocene

impact processes permafrost dynamics and climate and environmental variability in the terrestrial arctic as inferred from the unique 3 6 myr record of lake el gygytgyn far east russia a review lake el gygytgyn in far east russia is a 3 6 myr old impact crater lake located in an area that has never been affected by cenozoic glaciations nor desiccation the unique sediment record of the l

preliminary paleoenvironmental analysis of permafrost deposits at batagaika megaslump yana uplands northeast siberia a megaslump at batagaika in northern yakutia exposes a remarkable stratigraphic sequence of permafrost deposits 50 80 m thick to determine their potential for answering key questions about quaternary environmental and climatic change in northeast siberia we carried out a reconnaissance study of their cryostratigraphy and paleoecology supported by four rangefinder 14c ages the sequence includes two ice complexes separated by a unit of fine sand containing narrow syngenetic ice wedges and multiple palaeosols overall the sequence developed as permafrost grew syngenetically through an eolian sand sheet aggrading on a hillslope wood remains occur in two forest beds each associated with a reddened weathering horizon the lower bed contains high amounts of larix pollen 20 plus small amounts of picea and pinus pumila and is attributed to interglacial conditions pollen from the overlying sequence is dominated by herbaceous taxa 70 80 attributed to an open tundra landscape during interstadial climatic conditions of three hypothetical age schemes considered we tentatively attribute much of the batagaika sequence to marine isotope stage mis 3 the upper and lower forest beds may represent a mid mis 3 optimum and mis 5 respectively although we cannot discount alternative attributions to mis 5 and 7

past gateways palaeo arctic spatial and temporal gateways introduction and overview this special issue relates to the second international conference of the past gateways palaeo arctic spatial and temporal gateways network which was held in trieste italy in 2014 twenty five papers are included and they address topics under four main themes 1 the growth and decay of arctic ice sheets 2 arctic sea ice and palaeoceanography 3 terrestrial arctic environments and permafrost change and 4 holocene arctic environmental change geographically the focus is circum arctic the special issue includes detailed regional studies from greenland scandinavia russia and arctic north america and the adjoining seas as well as a series of synthesis type review papers on fennoscandian ice sheet deglaciation and holocene arctic palaeo climate change the methodologies employed are diverse and include marine sediment core and geophysical investigations terrestrial glacial geology and geomorphology isotopic analysis of ground ice palaeo ecological analysis of lacustrine and terrestrial sedimentary archives geochronology and numerical ice sheet modeling

glacial induced closure of the panamanian gateway during marine isotope stages mis 95 100 2 5 ma the final phase of the closure of the panamanian gateway and the intensification of northern hemisphere glaciation nhg both occurred during the late pliocene glacial interglacial g ig variations in sea level might therefore have had a significant impact on the remaining connections between the east pacific and the caribbean here we present combined foraminiferal mg ca and 18o measurements from ocean drilling program odp site 1241 from the east pacific and odp site 999 from the caribbean the studied time interval covers the first three major g ig marine isotope stages mis 95 100 2 5 ma 2 5 ma after the intensification of nhg analyses were performed on the planktonic foraminifera neogloboquadrina dutertrei and globigerinoides sacculifer representing water mass properties in the thermocline and the mixed layer respectively changes in sea water temperature relative salinity and water column stratification strongly suggest that the panamanian gateway temporarily closed during glacial mis 98 and 100 as a result of changes in ice volume equivalent to a drop in sea level of 60 90 m reconstructed sea surface temperatures sst from g sacculifer show a glacial decrease of 2 5 c at site 1241 but increases of up to 3 c at site 999 during glacial mis 98 and 100 suggesting that the panamanian gateway closed during these glacial periods the mg ca temperatures of n dutertrei remain relatively stable in the east pacific but do show a 3 c warming in the caribbean at the onset of these glacial periods suggesting that the closing of the gateway also changed the water column stratification we infer that the glacial closure of the gateway allowed the western atlantic warm pool to extend into the southern caribbean increasing sst g sacculifer and deepening the thermocline n dutertrei additionally ice volume appears to have become large enough during mis 100 to survive the relatively short lasting interglacial mis 99 so that the gateway remained closed towards the end of mis 98 during mis 97 and into mis 96 temperatures on both sides are mostly similar suggesting water masses exchanged again additionally caribbean variations in sst and 18owater follow a precession like cyclicity rather than the obliquity controlled variations characteristic of the east pacific and many other tropical areas suggesting that regional atmospheric processes related to the trade winds and the intertropical convergence zone itcz had a dominant impact in the caribbean

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

enhanced stratification and seasonality in the subarctic pacific upon northern hemisphere glaciation new evidence from diatom bound nitrogen isotopes alkenones and archaeal tetraethers abstract coincident with the intensification of northern hemisphere glaciation nhg around 2 73 million years ma ago sediment cores from both the open subarctic north pacific and the antarctic indicate a rapid decline in diatom opal accumulation flux to the seabed representing one of the most abrupt and dramatic changes in the marine sediment record associated with the development of pleistocene glacial cycles in the north pacific bulk sediment nitrogen isotope data and alkenone derived sea surface temperature sst estimates suggest that the productivity decline was driven by reduced exchange between surface and deep water due to weaker wind driven upwelling and or a strengthening of the halocline i e stratification in this study of the 2 73 ma transition at ocean drilling program odp site 882 in the western subarctic north pacific diatom bound nitrogen isotopes 15 n db alkenone mass accumulation rate and alkenone and archaeal tetraether based sst reconstructions support the stratification hypothesis indicating perennially lower export production generally higher nitrate consumption and greater inter seasonal variation in sst after the 2 73 ma transition in addition the 15 n db of large and small size fractions of coscinodiscus spp suggest that these diatoms grew mostly during the spring bloom during the late pliocene switching to their current fall to winter growth period at the 2 73 ma transition this view is consistent with their decline in dominance and provides further evidence for increased stratification reduced vertical exchange in the north pacific after 2 73 ma the 15 n db data indicate that over the 100 kyr period after the 2 73 ma transition studied here nitrate consumption did not reach late pleistocene ice age levels and that nitrate consumption in post 2 73 ma warm stages was similar to that before the transition even though productivity was greatly reduced we tentatively attribute this to relatively weak dust borne iron inputs in the early post 2 73 ma period

late pliocene vegetation and climate of the lake baikal region southern east siberia reconstructed from palynological data abstract palynomorphs from a palaeomagnetically dated late pliocene sediment core 3 6 2 35 ma reflect highly variable climatic conditions and repeated expansion of steppe and boreo alpine vegetation mixed coniferous forests picea tsuga pinus with associated broadleaved taxa quercus corylus ulmus tilia were affected by dry and cold intervals already between 3 48 and 3 39 ma peak records of non arboreal pollen types and spores including subarctic boreo alpine selaginella selaginoides evidence advances of open vegetation which can be correlated to glacial marine oxygen isotope stages a cooling trend occurred from 3 15 ma to 2 5 ma documented by cold dry intervals and increased fluctuations of picea and pinus around 3 2 9 ma the palaeoclimate variation pattern shifted towards cold dry and warm moist oscillations cooling strengthened after 2 89 ma and severely restricted tsuga development cool and oligotrophic limnic conditions are documented by abundant gonyaulax dinoflagellate cysts in the interval 2 65 2 57 ma due to decreasing precipitation extensive areas with open steppe and rock steppe vegetation became permanently established after 2 62 ma dry conditions became a dominant environmental factor in the baikal region coeval in time with the red clay loess shift in northern china this climatic transition can be explained as a consequence of major intensification of northern hemisphere glaciation around 2 75 ma evidenced by marine records of ice rafted debris

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

vegetation succession and climate change during the early pleistocene 2 2 1 8 ma in the nihewan basin northern china abstract the nihewan formation northern china is ideal for studying environmental changes during the early pleistocene in conjunction with palaeomagnetic measurements pollen and grain size analyses were conducted on 120 samples from a 24 m long section 2 2 1 8 ma of core nha from the nihewan basin in order to reconstruct past vegetation and climatic changes the pollen assemblages were dominated by pinus indicating that the vegetation was primarily pine forest and that the climate was relatively warm and wet from 2 15 1 92 ma deciduous broad leaved tree pollen significantly increased to 10 of the total showing that more broad leaved trees grew in the study area during the warmest and wettest period in the study section from 1 92 1 78 ma coeval with the olduvai event pinus and broad leaved tree pollen types decreased the percentages of picea 20 artemisia and chenopodiaceae increased indicating that spruce forests expanded the openness of the forested areas increased and the climate became cold and dry the vegetation changes reconstructed during the olduvai period indicates that the climate in the nihewan basin was cold and dry relating to global cooling facilitated by the uplift of the tibetan plateau and the strengthening of the winter monsoon

iron fertilisation and biogeochemical cycles in the sub arctic northwest pacific during the late pliocene intensification of northern hemisphere glaciation abstract increases in the low field mass specific magnetic susceptibility dropstones and the terrigenous sediment component from ocean drilling program odp site 882 45 n have been interpreted to indicate a major onset of ice rafting to the sub arctic northwest pacific ocean during marine isotope stage mis g6 from 2 75 ma in contrast studies of the terrigenous content of sediments cored downwind of odp site 882 indicate that dust and disseminated volcanic ash deposition in the sub arctic pacific increased markedly during mis g6 to investigate the relative contribution of dust volcanic ash and ice rafting to the pliocene increase we present new high resolution environmental magnetic and ice rafted debris records from odp sites 882 and 885 our results demonstrate that the increase at both sites across mis g6 is predominantly controlled by a previously overlooked mixture of aeolian dust and volcanic ash our findings call into question the reliability of as a proxy for ice rafting to the north pacific they also highlight a previously undocumented link between iron fertilisation and biogeochemical cycling in the north pacific at a key stage during intensification of late pliocene northern hemisphere glaciation

the onset of extensive loess deposition around the g m boundary in china and its palaeoclimatic implications abstract in northern china the red clay loess contact is palaeomagnetically defined at about the gauss matuyama boundary the red clay formation has recently been proposed as mostly of wind blown origin and can be interpreted as having been formed under climatic conditions of continuous warmth punctuated by small amplitude oscillations the shift from red clay development to extensive loess deposition exhibits a 3 fold abrupt increase in aeolian dust deposition rate and marks the beginning of frequent and chaotic climatic fluctuations this event implies a large scale reorganization of the atmospheric circulation over east asia in particular the northward shift and intensification of the siberian high which may have resulted from a dramatic uplift of the tibetan plateau compared to another climatic shift recorded by the chinese loess deposits which occurred at about the upper boundary of the olduvai subchron the red clay loess shift is much more pronounced and recognizable in the field it appears that in regional stratigraphic studies the g m magnetic reversal has a better correlation potential than the upper olduvai

an extensive late cenozoic terrestrial record of multiple glaciations preserved in the tintina trench of west central yukon stratigraphy paleomagnetism paleosols and pollenthis is a companion paper to barendregt et al also in this issue geological survey of canada contribution 20100035 the tintina trench in west central yukon is a late miocene graben formed along the antecedent early tertiary tintina fault since its formation the trench has served as a sediment trap for alluvial and glacial deposits an extensive record of preglacial glacial and interglacial sediments spanning the late pliocene to late pleistocene has been preserved and is exposed today in modern landslide scars this sedimentary record comprises multiple sequences of tills outwash mudflows loess and paleosols the glacial sediments are the product of both local montane and regional cordilleran ice advances that channeled into the trench while loess and well developed paleosols brunisols and luvisols reflect nonglacial and interglacial conditions respectively the tintina trench exposures provide the most complete record of glaciations for the region paleomagnetism paleosols and palynology provide age constraints for the geological events a formal stratigraphic nomenclature is proposed for this region

late pliocene and early pleistocene environmental evolution from the sporopollen record of core pl02 from the yinchuan basin northwest china abstract to investigate the change of climate during the pliocene pleistocene transition in the asian interior sporopollen records from the 567 3 m 247 9 m depths ca 2 87 1 52 ma of the core pl02 in the yinchuan basin were studied which could be regarded as an excellent archive of vegetation and climate changes the results indicated that the climate of the yinchuan basin was relatively warm and humid with a desert steppe environment before 2 6 ma at the beginning of the early pleistocene the pollen content of xerophytic plants nitraria and chenopodiaceae increased sharply the climate became drier than that of the late pliocene and the environment obviously worsened however from 1 99 ma to 1 73 ma xerophytic plants in the pollen content decreased for a short time and the climate became more humid after 1 73 ma the pollen content of herbaceous plants continually increased and the vegetation type shifted from desert steppe to desert which reflects a cold and dry climate in the study region the vegetation change suggested an aridification trend in central asia inland since the late pliocene which might be related to global cooling and the uplift of the tibetan plateau

millennial scale vegetation changes in the north eastern russian arctic during the pliocene pleistocene transition 2 7 2 5 ma inferred from the pollen record of lake el gygytgyn abstract the sediment record of lake el gygytgyn 67 30 n 172 05 e spans the past 3 6 ma and provides unique opportunities for qualitative and quantitative reconstructions of the regional paleoenvironmental history of the terrestrial arctic millennial scale pollen studies of the sediments that accumulated during the late pliocene and early pleistocene ca 2 7 to 2 5 ma demonstrate orbitally driven vegetation and climate changes during this transitional interval pollen spectra show a significant vegetation shift at the pliocene pleistocene boundary that is however delayed by a few thousand years compared to lacustrine response about 2 70 2 68 ma the vegetation at lake el gygytgyn currently a tundra area was mostly dominated by larch forests with some shrub pine shrub alder and dwarf birch in understory during the marine isotope stages g3 and g1 ca 2 665 2 647 and 2 625 2 617 ma some spruce trees grew in the local larch pine forests pointing to relatively warm climate conditions at the beginning of the pleistocene around 2 588 ma a prominent climatic deterioration led to a change from larch dominated forests to predominantly treeless steppe and tundra like habitats between ca 2 56 2 53 ma some climate amelioration is reflected by the higher presence of coniferous taxa mostly pine and larch but probably also spruce in the area after 2 53 ma a relatively cold and dry climate became dominant again leading to open steppe like and shrubby environments followed by climate amelioration between ca 2 510 and 2 495 ma when pollen assemblages show that larch forests with dwarf birch and shrub alder still grew in the lake s vicinity increased contents of green algae colonies botryococcus remains and zygnema cysts around 2 691 2 689 2 679 2 677 2 601 2 594 2 564 2 545 and 2 532 2 510 ma suggest a spread of shallow water environments most likely due to a lake level lowering these events occurred simultaneously with dry climate conditions inferred from broad distribution of steppe habitats with artemisia and other herbs

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

a latest pliocene age for the earliest and most extensive cordilleran ice sheet in northwestern canada abstract the klondike gravel is a widespread glaciofluvial gravel marking the earliest and most extensive cordilleran ice sheet cis in nw north america new terrestrial cosmogenic nuclide tcn burial ages indicate this gravel was emplaced 2 64 0 20 0 18 ma 1 coupled with previously interpreted paleomagnetic stratigraphy this numerical age constrains the timing of the earliest cis to the late gauss chron and provides a minimum age for the upper white channel gravel a significant placer gold source in the yukon this implies the first cis glacial maximum pre dates the maximum extent of the laurentide ice sheet indicating that during the initial stages of northern hemisphere glaciation the most extensive glaciers were present in the relatively cold and high elevation northern cordillera our results verify the cis as a likely source of persistent coeval ice rafted debris in the northern pacific and suggest that the first cis formed as a response to the establishment of the northern pacific halocline and emergence of the 41 ka obliquity cycle during the plio pliocene transition

climate change and arctic ecosystems 1 vegetation changes north of 55 n between the last glacial maximum mid holocene and present a unified scheme to assign pollen samples to vegetation types was used to reconstruct vegetation patterns north of 55 n at the last glacial maximum lgm and mid holocene 6000 years b p the pollen data set assembled for this purpose represents a comprehensive compilation based on the work of many projects and research groups five tundra types cushion forb tundra graminoid and forb tundra prostrate dwarf shrub tundra erect dwarf shrub tundra and low and high shrub tundra were distinguished and mapped on the basis of modern pollen surface samples the tundra forest boundary and the distributions of boreal and temperate forest types today were realistically reconstructed during the mid holocene the tundra forest boundary was north of its present position in some regions but the pattern of this shift was strongly asymmetrical around the pole with the largest northward shift in central siberia 200 km little change in beringia and a southward shift in keewatin and labrador 200 km low and high shrub tundra extended farther north than today at the lgm forests were absent from high latitudes graminoid and forb tundra abutted on temperate steppe in northwestern eurasia while prostrate dwarf shrub erect dwarf shrub and graminoid and forb tundra formed a mosaic in beringia graminoid and forb tundra is restricted today and does not form a large continuous biome but the pollen data show that it was far more extensive at the lgm while low and high shrub tundra were greatly reduced illustrating the potential for climate change to dramatically alter the relative areas occupied by different vegetation types

progress in esr dating of pleistocene corals a new approach for de determination abstract esr dating has been widely applied for dating of corals of the age up to 500 000 to 600 000 years ago many studies have yielded promising results but the accurate determination of the equivalent dose d e remains a major limitation inflexion points in the dose response curve are shown to hinder correct fitting and limit the reliability of d e values here we present a new approach to obtain more reliable d e values

pliocene palaeoceanography of the arctic ocean and subarctic seas the pliocene is important in the geological evolution of the high northern latitudes it marks the transition from restricted local to extensive regional scale glaciations on the circum arctic continents between 3 6 and 2 4 ma since the arctic ocean is an almost land locked basin tectonic activity and sea level fluctuations controlled the geometry of ocean gateways and continental drainage systems and exerted a major influence on the formation of continental ice sheets the distribution of river run off and the circulation and water mass characteristics in the arctic ocean the effect of a water mass exchange restricted to the bering and fram straits on the oceanography is unknown but modelling experiments suggest that this must have influenced the atlantic meridional overturning circulation cold conditions associated with perennial sea ice cover might have prevailed in the central arctic ocean throughout the pliocene whereas colder periods alternated with warmer seasonally ice free periods in the marginal areas the most pronounced oceanographic change occurred in the mid pliocene when the circulation through the bering strait reversed and low salinity waters increasingly flowed from the north pacific into the arctic ocean the excess freshwater supply might have facilitated sea ice formation and contributed to a decrease in the atlantic overturning circulation

palynological evidence for a southward shift of the north atlantic current at 2 6 ma during the intensification of late cenozoic northern hemisphere glaciation the position of the north atlantic current nac during the intensification of northern hemisphere glaciation inhg has been evaluated using dinoflagellate cyst assemblages and foraminiferal geochemistry from a 260 kyr interval straddling the base of the quaternary system from two sites eastern north atlantic deep sea drilling project site 610 in the path of the present nac and central north atlantic integrated ocean drilling program site u1313 in the subtropical gyre stable isotope and foraminiferal mg ca analyses confirm cooling near the marine isotope stage mis g7 g6 transition 2 74 ma however a continued dominance of the dinoflagellate cyst operculodinium centrocarpum sensu wall and dale 1966 indicates an active nac in the eastern north atlantic for a further 140 kyr at mis 104 2 60 ma a profound dinoflagellate cyst assemblage turnover indicates nac shutdown in the eastern north atlantic implying elevated atmospheric pressure over the arctic and a resulting shift in the westerlies that would have driven the nac these findings challenge recent suggestions that there was no significant southward shift of the nac or the arctic front during inhg and reveal a fundamental climatic reorganization near the base of the quaternary

pliocene warmth polar amplification and stepped pleistocene cooling recorded in ne arctic russia understanding the evolution of arctic polar climate from the protracted warmth of the middle pliocene into the earliest glacial cycles in the northern hemisphere has been hindered by the lack of co

quantitative reconstruction of the last interglacial vegetation and climate based on the pollen record from lake baikal russia changes in mean temperature of the coldest t c and warmest month t w annual precipitation p ann and moisture index were reconstructed from a continuous pollen record from lake baikal russia the pollen sequence con01 603 2 53 57 n 108 54 e was recovered from a 386 m water depth in the continent ridge and dated to ca 130 114 8 ky bp this time interval covers the complete last interglacial li corresponding to mis 5e results of pollen analysis and pollen based quantitative biome reconstruction show pronounced changes in the regional vegetation throughout the record shrubby tundra covered the area at the beginning of mis 5e ca 130 128 ky consistent with the end of the middle pleistocene glaciation the late glacial climate was characterised by low winter and summer temperatures t c 38 to 35 c and t w 11 13 c and low annual precipitation p ann 300 mm however the wide spread of tundra vegetation suggests rather moist environments associated with low temperatures and evaporation reconstructed 1 tundra was replaced by boreal conifer forest taiga by ca 128 ky bp suggesting a transition to the interglacial taiga dominant phase lasted until ca 117 4 ky bp e g about 10 ky the most favourable climate conditions occurred during the first half of the li p ann reached 500 mm soon after 128 ky bp however temperature changed more gradually maximum values of t c 20 c and t w 16 17 c are reconstructed from about 126 ky bp conditions became gradually colder after ca 121 ky bp t c dropped to 27 c and t w to 15 c by 119 5 ky bp the reconstructed increase in continentality was accompanied by a decrease in p ann to 400 420 mm however the climate was still humid enough 0 9 to support growth of boreal evergreen conifers a sharp turn towards a dry climate is reconstructed after ca 118 ky bp causing retreat of forest and spread of cool grass shrub communities cool steppe dominated the vegetation in the area between ca 117 5 ky and 114 8 ky bp suggesting the end of the interglacial and transition to the last glacial mis 5d shift to the new glaciation was characterised by cool and very dry conditions with t c 28 to 30 c t w 14 15 c p ann 250 mm and 0 5

pliocene pleistocene climatic change recorded in fluviolacustrine sediments in central china abstract a 250 m thick section located in the guanzhong basin central china consisting of a loess paleosol sequence in the upper part and fluviolacustrine sequence in the lower was selected for this study which involves documenting the climate transition around the global glacial initiation about 2 5 ma and focuses on the climatic information recorded in the fluviolacustrine sediments paleomagnetic study indicates that the entire shijiawan section developed during the past 3 08 ma and the fluviolacustrine sequence spans the time interval of 3 08 1 9 ma sedimentary analysis shows that alluvial facies dominates the so called fluviolacustrine sequence with strong cyclicity pollen study combined with stable carbon isotope analysis of organic matter displays profound changes of the paleovegetation in response to climate forcing during the period of 3 0 2 7 ma persistent steppe vegetation and elephant fossil fauna suggest long lasting dry and warm climate conditions with little change from 2 7 to 2 5 ma sparse steppe flora manifests a striking climatic deterioration the first thick loess like layer in the fluviolacustrine sequence consistent with the commencement of the loess deposition in the loess plateau marks a rapid and great intensification of the siberian cold high pressure regime at 2 6 ma afterwards the regional vegetation fluctuated between dry steppe and forest grasslands in agreement with loess paleosol alternations corresponding to the climatic oscillations between cold dry and warm wet such secular climate variation patterns demonstrate the predominant influence of global glacial and interglacial forcing on the regional climate system of the east asian monsoon the late pliocene climate warm and dry is distinct from the harmony of temperature with precipitation i e cold with dry and warm with wet which is fully exhibited throughout the past 2 6 ma thus the time of the first global glaciation must have involved a rapid reorganization of the regional climate regime and the onset of the modern east asian monsoon

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

late quaternary paleoenvironments and modern pollen data from wrangel island northern chukotka abstract new lacustrine records from central and southern wrangel island are analyzed for their pollen content in an attempt to clarify possible linkages between paleoenvironmental shifts and the dwarfing and or extinction of the island s mammoth population a younger dryas aged peat is also examined to provide better understanding of the regional climatic history samples of surficial lake sediments from wrangel island and chukotka aid in interpreting the lacustrine records the modern spectra differentiate the herb dominated tundra of wrangel island from the shrub tundras of the mainland and are unique when compared to other arctic assemblages analysis of the fossil data indicates that a herb dominated tundra has been present on southern and central wrangel island since at least 11 ka bp comparison to modern palynological data implies little change in vegetation during the holocene the lacustrine interpretations contrast to those based on paleobotanical study of peats and alluvium which suggest modern vegetation was not present until ca 4 3 ka bp pre holocene assemblages have high percentages of cyperaceae pollen perhaps indicating more moderate conditions summer climate is inferred to be warmer and moister than present during the latest pleistocene and early holocene the pattern of postglacial warming on wrangel island is more like that from eastern beringia than from other areas of western beringia modern synoptic anomaly maps indicate that such a climatic pattern is reasonable and related to the presence of negative anomalies over western beringia and a region of weaker positive 500 mb pressure centered over the beaufort sea

late pliocene and early pleistocene vegetation and climate change revealed by a pollen record from nihewan basin north china abstract the nihewan formation is an important early quaternary sedimentary formation in north china we conducted pollen analyses of 183 samples and 1611 modern surface samples to characterize the processes of vegetation succession and climate change during the pliocene pleistocene transition 2 89 2 34 ma in the nihewan basin the results show that pollen assemblages are dominated by arboreal pollen indicating that the vegetation in the study area was forest dominated and that the climate was more humid than today however the temperature varied substantially the most substantial vegetation and climate changes occurred at 2 8 ma when the pollen representation of warm and humid tolerant taxa such as evergreen quercus and carya disappeared and also broadleaved deciduous types such as ulmus deciduous quercus and betula decreased obviously on the contrary the pollen representation of cold and drought tolerant taxa increased substantially e g picea from generally less than 20 to more than 30 and chenopodiaceae from generally less than 10 to more than 20 the quantitative reconstructed results indicating that tann decreased by about 2 3 c and pann decreased by 150 mm compared to before 2 8 ma with a maximum decrease of 9 c for tann and 450 mm for pann another important vegetation and climate changes occurred at 2 6 ma which was the coldest and driest of the studied interval when the vegetation was substantially simplified with spruce generally above 80 as the dominated types