the roles of co2 and orbital forcing in driving southern hemispheric temperature variations during the last 21 000 yr abstract transient climate model simulations covering the last 21 000 yr reveal that orbitally driven insolation changes in the southern hemisphere combined with a rise in atmospheric pco2 were sufficient to jump start the deglacial warming around antarctica without direct northern hemispheric triggers analyses of sensitivity experiments forced with only one external forcing component greenhouse gases ice sheet forcing or orbital forcing demonstrate that austral spring insolation changes triggered an early retreat of southern ocean sea ice starting around 19 18 ka bp the associated sea ice albedo feedback and the subsequent increase of atmospheric co2 concentrations helped to further accelerate the deglacial warming in the southern hemisphere implications for the interpretation of southern hemispheric paleoproxy records are discussed

reconstructed tree fern alethopteris zeilleri carboniferous medullosales abstract from a smaller open pit area in the roof shale of the basal cantabrian coal seam in sydney coalfield cape breton island nova scotia canada large amounts of the pteridosperm foliage alethopteris zeilleri ragot were found this foliage is associated with abundant naked medullosalean axes and dichotomies of varying sizes up to 0 80 m long cauline structures 0 90 m and 1 3 m long detached ovules assigned to pachytesta incrassata brongniart rare male pollen organs of the type dolerotheca halle rooted tree ferns in life position and one specimen each of a juvenile medullosalean frond and root mantle the fossils are compression impression preserved and the foliage yielded thickly cutinized cuticles with unoriented cells 57 103 by 27 57 m in intercostal fields ultimate rachises and abaxial surfaces excluding costal fields show a mixture of simple and complexly branched trichomes and two different structural bases these together with fractal dimensionality of curvatures of anticlinal walls in intercostal fields have taxonomic potential for alethopterids the finds suggest reconstructing a zeilleri ragot as a tree 5 7 m high that bore both p incrassata brongniart and dolerotheca type fructifications its habitat was low land coastal plains in the pennsylvanian coal swamps of ancestral sydney coalfield

on the hemispheric origins of meltwater pulse 1a abstract during the glacial interglacial transition that began subsequent to the last glacial maximum approximately 21 000 calendar years ago globally averaged eustatic sea level rose by approximately 120 m as climate warmed to its current holocene state this rise of relative sea level rsl did not occur smoothly however but was characterized by the occurrence of one or more episodes of extremely rapid increase the most extreme of these events has come to be referred to as meltwater pulse 1a and was initially identified in the coral based record of rsl history from the island of barbados in the caribbean sea although it has usually been assumed that this episode of rapid rsl rise was derivative of a partial collapse of the northern hemisphere ice sheets it has recently been suggested that this pulse could have originated in a dramatic melt back of the antarctic ice sheet in this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this alternative scenario based upon the analyses presented it is concluded that the evidence previously provided in support of the southern hemisphere scenario is in fact unable to rule out an entirely northern hemisphere source for the meltwater pulse 1a since explicit evidence does exist that both the laurentide and fennoscandian ice sheets contributed to this event and that antarctic ice sheet melting occurred significantly later the southern hemisphere appears not to have been a prime mover of northern hemisphere events

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

palaeoecology of macroneuropteris scheuchzeri and its implications for resolving the paradox of xeromorphic plants in pennsylvanian wetlands abstract the medullosan pteridosperm macroneuropteris scheuchzeri hoffmann cleal shute zodrow was widespread and abundant in the middle to late pennsylvanian forests of tropical pangaea on the basis of its thick cuticles few adaxial stomata sunken stomata and dense trichomes it has been inferred to be a xeromorphic plant here we test that hypothesis by analyzing its facies distribution especially in relation to coals at 273 site collections from 45 stratigraphic horizons accessioned in the smithsonian national museum of natural history washington d c u s a the collections represent mostly par autochthonous assemblages and cover the taxon s complete known temporal range west of the appalachians in west central pangaea chi square analysis of facies occurrence data indicates that m scheuchzeri had a strong preference for mineral enriched wetlands that immediately preceded and followed the development of peat swamps and mires coals particularly during the late middle pennsylvanian late moscovian times coincident with a period of reduced polar ice volume in the late pennsylvanian following an interval of global warming and tropical wetland reorganization palaeoequatorial climate shifted to an overall drier mode this was accompanied by the disappearance of m scheuchzeri from europe and its limitation west of the appalachians to the wettest available habitats on the landscape thus our data falsify the hypothesis that m scheuchzeri was a conventional xerophyte but highlight the paradox of a plant with apparent xeromorphic features confined to a wetland habitat we consider several possible explanations for this association 1 response to nutrient deficiency 2 response to substrate salinity due to growth in coastal mangrove habitats 3 response to the composition of the palaeozoic atmosphere 4 return on investment long leaf lifespan and 5 phylogenetic constraint reflecting ancestral conditions our findings have broader implications for interpreting a wide variety of other pennsylvanian wetland plants which similarly show xermorphic features

marine derived 14c calibration and activity record for the past 50 000 years updated from the cariaco basin abstract an expanded cariaco basin 14c chronology is tied to 230th dated hulu cave speleothem records in order to provide detailed marine based 14c calibration for the past 50 000 years the revised high resolution cariaco 14c calibration record agrees well with data from 230th dated fossil corals back to 33 ka with continued agreement despite increased scatter back to 50 ka suggesting that the record provides accurate calibration back to the limits of radiocarbon dating the calibration data document highly elevated 14c during the glacial period carbon cycle box model simulations show that the majority of observed 14c change can be explained by increased 14c production however from 45 to 15 ka 14c remains anomalously high indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today additional observations of the magnitude spatial extent and timing of deep ocean 14c shifts are critical for a complete understanding of observed glacial 14c variability

millennial scale variations in western sierra nevada precipitation during the last glacial cycle mis 4 3 transition abstract dansgaard oeschger d o cycles had far reaching effects on northern hemisphere and tropical climate systems during the last glacial period yet the climatic response to d o cycles in western north america is controversial especially prior to 55 ka we document changes in precipitation along the western slope of the central sierra nevada during early marine oxygen isotope stages mis 3 and 4 55 67 ka from a u series dated speleothem record from mclean s cave the timing of our multi proxy geochemical dataset is coeval with d o interstadials 15 18 and stadials including heinrich event 6 the mclean s cave stalagmite indicates warmer and drier conditions during greenland interstadials giss 15 18 signified by elevated 18o 13c reflectance and trace element concentrations and less radiogenic 87sr 86sr our record extends evidence of a strong linkage between high latitude warming and reduced precipitation in western north america to early mis 3 and mis 4 this record shows that the linkage persists in diverse global climate states and documents the nature of the climatic response in central california to heinrich event 6

late pleistocene and early holocene climate and limnological changes in the sierra nevada california usa inferred from midges insecta diptera chironomidae chironomid and stratigraphic analyses of a lake sediment core recovered from a high elevation lake in the central sierra nevada california usa was undertaken to assess chironomid community development during the pleistocene holocene transition and to quantitatively reconstruct the thermal regime that existed during this interval between 14 800 cal yr bp and 13 700 cal yr bp the chironomid community consisted almost exclusively of heterotrissocladius suggesting this period was characterized by extremely cold climatic conditions evidence of post glacial climatic amelioration as manifested by increases in thermophilous chironomid taxa head capsule concentrations and taxon richness and diversity commenced at approximately 13 300 cal yr bp in order to quantify the magnitude of the water temperature changes associated with post glacial climatic amelioration a recently developed chironomid based inference model for surface water temperature was applied to the subfossil chironomid assemblages the one component weighted averaging partial least squares wa pls model has an r2jack 0 72 rmsepjack 1 1 c and a maximum bias of 1 24 c the reconstructed surface water temperatures suggest a minimum warming of approximately 4 7 c occurred during the pleistocene holocene transition however warming during this interval may not have been monotonic evidence of the younger dryas has been previously discovered in the study area and adjacent regions our research indicates that changes in chironomid community composition and an inferred short term cooling event occurred between 12 000 cal yr bp and 11 500 cal yr bp which may represent a local manifestation of the younger dryas chironomid community development during the pleistocene holocene transition appears to primarily reflect the influence of changing climate conditions

the cause of carbon isotope minimum events on glacial terminations the occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the indo pacific sub antarctic and south atlantic we use the 13 c record of a thermocline dwelling foraminifera neogloboquadrina dutertrei and surface temperature estimates from the eastern equatorial pacific to demonstrate that the onset of 13 c minimum events and the initiation of southern ocean warming occurred simultaneously timing agreement between the marine record and the 13 c minimum in an antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification renewed circumpolar deep water upwelling and advection of low 13 c waters to the convergence zone at the sub antarctic front on the basis of age agreement between the absolute 13 c minimum in surface records and the shift from low to high 13 c in the deep south atlantic we suggest that the 13 c rise that marks the end of the carbon isotope minima was due to the resumption of north atlantic deep water influence in the southern ocean

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

palynological evidence for early holocene aridity in the southern sierra nevada california sediments of balsam meadow have produced a 11 000 yr pollen record from the southern sierra nevada of california the balsam meadow diagram is divided into three zones 1 the artemisia zone 11 000 7000 yr b p is characterized by percentages of sagebrush artemisia and other nonarboreal pollen higher than can be found in the modern local vegetation vegetation during this interval was probably similar to the modern vegetation on the east slope of the sierra nevada and the climate was drier than that of today 2 pinus pollen exceeded 80 from 7000 to 3000 yr b p in the pinus zone the climate was moister than during the artemisia zone 3 fir abies cupressaceae and oak quercus percentages increased after 3000 yr b p in the abies zone as the modern vegetation at the site developed and the present cool moist climatic regime was established decreased fire frequency after 1200 yr b p is reflected in decreased abundance of macroscopic charcoal and increased concentration of abies magnifica and pinus murrayana needles

mid depth circulation in the northwest pacific during the last deglaciation evidence from foraminiferal radiocarbon ages 1 sediment cores mr01 k03 pc4 pc5 1366 m water depth collected from off northern japan were studied using coexisting planktonic and benthic foraminiferal radiocarbon measurements to reconstruct the history of mid depth circulation in the northwest pacific reconstructed ventilation ages indicate that consistent with data from a previous radiocarbon study at a shallower site there was significant variation in mid depth circulation during the last deglaciation especially in the bolling allerod 13 15 ka and younger dryas 11 5 13 ka intervals our record indicates that the ventilation changes in the north pacific were antiphase to those of the north atlantic suggesting that atmospheric moisture transport associated with the asian monsoon might have played a great role in millennium scale ventilation changes in the north pacific during the last deglaciation

late quaternary zonation of vegetation in the eastern grand canyon fossil assemblages from 53 packrat middens indicate which plant species were dominant during the last 24 000 years in the eastern grand canyon past vegetational patterns show associations that cannot be attributed to simple elevational displacement of the modern zones a model emphasizing a latitudinal shift of climatic values is proposed

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

antarctic sea ice and the control of pleistocene climate instability a hypothesis is presented for the origin of pleistocene climate instability based on expansion of antarctic sea ice and associated changes in the oceans salinity structure the hypothesis assumes that thermohaline overturning is dominated by the reconfigured conveyor of toggweiler and samuels 1993b in which deepwater upwelling is restricted to high southern latitudes the reconfigured conveyor is shown to be potentially stabilized in an on mode by precipitation at high southern latitudes and potentially destabilized into on and off modes by the counteracting influence of antarctic sea ice the mechanism is clarified by the use of a hydraulic analogue we hypothesize that this mechanism accounts for dominant patterns of thermohaline overturning and climate instability between pleistocene warm and cold periods the hypothesis is shown to be consistent with a range of paleoceanographic evidence and to potentially account for details of observed rapid climate changes during glacial and interglacial periods including aspects of interhemispheric timing

packrat midden evidence of late quaternary vegetation change in the white mountains california nevada packrat neotoma spp middens from the white mountains indicate climatic and plant community conditions for the last 19 000 yr during full glacial times ca 19 000 yr b p and at the pleistocene holocene boundary juniper woodlands were 600 m lower in elevation than at present midden assemblages and stable isotope data suggest lower temperatures and increased precipitation relative to the present into the early holocene two early holocene middens ca 8000 yr b p from lower elevations of the white mountains contain fragments of pinyon pine and indicate that both pinyon and juniper grew at a site that today supports only a pinyon woodland two middle holocene middens ca 5000 yr b p indicate that there was an upward migration of pinyon juniper woodlands along a high elevation ecotone but little change in the middle of the pinyon juniper woodland middens from the late holocene indicate that present day plant communities were in place by ca 2000 yr b p or before

assessing ams 14c ages of detrital organics from holocene and late pleistocene moraines east central sierra nevada california usa obtaining age estimates of moraines which have insufficient carbon for conventional 14 c dating may be possible by ams 14 c dating of detrital organic material in the till matrix sufficient detrital carbon was available in the till matrix of holocene and late pleistocene moraines of upper laurel creek canyon east central sierra nevada california for ams 14 c measurements radiocarbon analysis of till matrix organics from the moraine closest to the headwall ml reveals an age of 2875 60 bp eth 13550 the next oldest moraine m2 yields 4450 60 bp eth 12810 m3 the oldest moraine in the bloody mountain cirque yielded organics with a radiocarbon age of 13 600 120 bp eth 12812 while results are preliminary these ages are among the first on till matrix in the sierra nevada and are consistent with geomorphic context other palaeoecologic records in the sierra nevada and palaeolake records in the western united states

effect of global ocean temperature change on deep ocean ventilation 1 a growing number of paleoceanographic observations suggest that the ocean s deep ventilation is stronger in warm climates than in cold climates here we use a general ocean circulation model to test the hypothesis that this relation is due to the reduced sensitivity of seawater density to temperature at low mean temperature that is at lower temperatures the surface cooling is not as effective at densifying fresh polar waters and initiating convection in order to isolate this factor from other climate related feedbacks we change the model ocean temperature only where it is used to calculate the density to which we refer below as dynamic temperature change we find that a dynamically cold ocean is globally less ventilated than a dynamically warm ocean with dynamic cooling convection decreases markedly in regions that have strong haloclines i e the southern ocean and the north pacific while overturning increases in the north atlantic where the positive salinity buoyancy is smallest among the polar regions we propose that this opposite behavior of the north atlantic to the southern ocean and north pacific is the result of an energy constrained overturning

late carboniferous cyclothems and alluvial paleovalleys in the sydney basin nova scotia cyclothems are documented for the first time in alluvial to coastal plain strata west phalian d to stephanian of the sydney basin nova scotia well developed cyclothems commence with an extensive carbonaceous lime stone or shale with a restricted marine biota that indicates maximal flooding succeeding gray detrital bay and lake fills with distributary channel deposits are overlain by stacked channel deposits paleovalley fills that mark an abrupt basinward facies shift and a profound change in alluvial style channel fills and red vertisols were deposited on an alluvial plain above the filled valleys and the paleovalley is equated with thick vertisols in adjacent inter fluve areas the cyclothems are capped by gray coastal deposits with economic coals agglutinated foraminifera are present in seat earths beneath the coals which formed as a result of a brief stillstand during transgression red mudstones pass laterally into gray detrital bay fills in regions of greater subsidence associated with faulted basement blocks poorly developed cyclothems are bounded by extensive but split coals and autogenic effects partially obscure allogenic patterns mean cyclothem duration approximates 200 ka

el nino southern oscillation like variability during glacial terminations and interlatitudinal teleconnections interannual decadal variability in the equatorial pacific el nino southern oscillation enso induces climate changes at global scale but its potential influence during past global climate change is not yet well constrained new high resolution eastern equatorial pacific proxy records of thermocline conditions present new evidence of strong orbital control in enso like variability over the last 275 000 years recurrent intervals of saltier thermocline waters are associated with the dominance of la nina like conditions during glacial terminations coinciding with periods of low precession and high obliquity the parallel dominance of 13c depleted waters supports the advection of antarctic origin waters toward the tropical thermocline this oceanic tunneling is proposed to have reinforced orbitally induced changes in enso like variability composing a complex high and low latitude feedback during glacial terminations

the taylor dome antarctic 18o record and globally synchronous changes in climate abstract the 18 o 16 o profile of a 554 m long ice core through taylor dome antarctica shows the climate variability of the last glacial interglacial cycle in detail and extends at least another full cycle taylor dome shares the main features of the vostok record including the early climatic optimum with later cool phase of the last interglacial period in antarctica taylor dome 18 o fluctuations are more abrupt and larger than those at vostok and byrd station although still less pronounced than those of the greenland gisp2 and grip records the influence of the atlantic thermohaline circulation on regional ocean heat transport explains the partly north atlantic character of this antarctic record under full glacial climate marine isotope stage 4 late stage 3 and stage 2 this marine influence diminished and taylor dome became more like vostok varying degrees of marine influence produce climate heterogeneity within antarctica which may account for conflicting evidence regarding the relative phasing of northern and southern hemisphere climate change

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

origin of the 100 000 year timescale in antarctic temperatures and atmospheric co2 1 a new mechanism is proposed to explain the 100 000 year timescale for variations in antarctic temperatures and atmospheric co2 over the last 650 000 years it starts with fluctuations in the oceanic overturning around antarctica that release co2 up to the atmosphere or trap it in the deep ocean every 50 000 years one of these fluctuations coincides with a changeover in the burial of caco3 in the deep ocean the changeover alters the atmospheric pco2 in a way that augments the tendency of the overturning the augmented overturning then enhances the tendency of the caco3 burial which augments the overturning etc in this way an individual random fluctuation becomes one of the big transitions seen in the antarctic ice cores alternating transitions toward the warm and cold states every 50 000 years produce the 100 000 year timescale the 50 000 year time interval is set by the turnover time for co3 ions in the ocean with respect to the co2 induced weathering of silicate rocks and the burial of caco3 on the seafloor

late pleistocene vegetation of kings canyon sierra nevada california seven packrat midden samples make possible a comparison between the modern and late pleistocene vegetation in kings canyon on the western side of the southern sierra nevada one modern sample contains macrofossils and pollen derived from the present day oak chaparral vegetation macrofossils from the six late pleistocene samples record a mixed coniferous forest dominated by the xerophytic conifers juniperus occidentalis pinus cf ponderosa and p monophylla the pollen spectra of these pleistocene middens are dominated by pinus sp taxodiaceae cupressaceae taxaceae tct and artemisia sp mesophytic conifers are represented by low macrofossil concentrations sequoiadendron giganteum is represented by a few pollen grains in the full glacial edaphic control and snow dispersal are the most likely causes of these mixed assemblages the dominant macrofossils record a more xeric plant community than those that now occur on similar substrates at higher elevations or latitudes in the sierra nevada these assemblages suggest that late wisconsin climates were cold with mean annual precipitation not necessarily greater than modern values this conclusion supports a model of low summer ablation allowing for the persistence of the glaciers at higher elevations during the late wisconsin the records in these middens also suggest that s giganteum grew at lower elevations along the western side of the range and that p monophylla was more widely distributed in cismontane california during the pleistocene

pluvial climatic episodes in north america and north africa types and correlation with global climate abstract differences in late quaternary pluvial chronologies among the world s deserts can be related to fundamental differences in the climatology of those pluvial episodes paleoenvironmental records and climate model simulations for two northern hemisphere desert regions are used to illustrate two types of pluvial climatic regime in the higher latitude deserts of the american southwest pluvial conditions during the last glacial maximum were caused by the southward displacement of the westerly jet stream in turn caused by the blocking effect of laurentide ice sheet and a steepened arctic equator pressure gradient winter seasonality of precipitation and substantially lower mean annual temperatures are reflected in the paleoenvironmental record and simulated by models of 18 000 yr b p climate a second pluvial climate type which strongly influences the lower latitude deserts of north africa is characterized by enhanced summer monsoons and occurs during interglacials and perhaps interstadials the primary forcing mechanism of the last pluvial episode in the sahara and libyan deserts appears to have been increased solar radiation milankovitch forcing causing thermally enhanced ocean land pressure gradients and increased flow of maritime tropical air into the interior of the continent poleward displacement of the summer monsoon is consistent with floristic evidence for summer seasonality of precipitation and replicated by model simulations of 9000 and 6000 yr b p climate chronologies from some deserts such as the southern portion of the american southwest suggest the consecutive occurrence of both types of pluvial climatic regime pluvial conditions during the last glacial maximum were brought about by the equatorward displacement of the prevailing westerlies a subsequent more subdued pluvial period occurred later between 12 500 and 8000 yr b p caused by the poleward displacement of summer monsoons characterization of the climatology of pluvial episodes generates explanations for their temporal distribution and therefore this approach may be useful in assessing the quaternary chronology of pluvial episodes in other desert regions

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

radiocarbon age anomaly at intermediate water depth in the pacific ocean during the last deglaciation 1 benthic and planktonic 14c ages are presented for the last glacial termination from marine sediment core vm21 30 from 617 m in the eastern equatorial pacific the benthic planktonic 14c age differences in the core increased to more than 6000 years between heinrich 1 time and the end of the younger dryas period several replicated 14c ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation scanning electron microscopy reveals no evidence of calcite alteration or contamination the oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old glacial age values and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane it appears therefore that the benthic 14c excursion in this core is not an artifact of diagenesis bioturbation or a pulse of methane a benthic 14c stratigraphy reconstructed from the 14c ages from the deglacial section of vm21 30 appears to match that of baja margin core mv99 mc19 gc31 pc08 705 m but the magnitude of the low 14c excursion is much larger in the vm21 30 record this would seem to imply that the vm21 30 core was closer to the source of 14c depleted waters during the deglaciation but the source of this co2 remains elusive

the paleoecology and stratigraphy of nichols meadow sierra national forest california usa sediment stratigraphy and pollen plant macrofossil and charcoal analyses along with nine radiocarbon dates from nichols meadow provides the most intensive investigation of sierra nevada montane meadow development and paleoecology during pollen zone nm i ca 18 500 12 500 yr b p the nichols meadow area contained a stream during the tioga glacial stage the presence of high artemisia and gramineae pollen percentages along with a very low pollen influx rate reflects a cold dry steppe woodland environment pollen zone nm ii ca 12 500 8800 yr b p documents the development of a lower montane forest and giant sequoia sequoiadendron giganteum community which existed around a small meadow the higher sediment accumulation rates suggest that fallen trees contributed to the aggregation of meadow sediments arly holocene aridity is recorded in pollen zone nm iii ca 8800 6000 yr b p by poorly preserved pollen we infer that the forest trees closed in on the meadow and occupied the meadow floor the reduction in available moisture caused giant sequoia to become locally extinct in the nichols meadow area probably moving into their current distribution within the nelder grove pollen zone nm iv 6000 yr b p present reflects the development of the modern nichols meadow less sand in the meadow sediments due to stable vegetation surrounding nichols meadow allowed the increased retention of ground water this along with the neoglacial cooling trend at ca 3000 yr b p caused ground water to rise and saturate the meadow these events excluded the conifers from the meadow surface and allowed herbaceous vegetation associated with wet meadows to dominate overgrazing and channeling of the meadow s outflowing stream caused the water table to drop resulting in the incision of the meadow

rock glaciers and related periglacial landforms in the sierra nevada ca usa inventory distribution and climatic relationships abstract rock glaciers and related periglacial rock ice features rifs are abundant yet overlooked landforms in the sierra nevada california where they occur in diverse forms we mapped 421 rifs from field surveys and grouped these into six classes based on morphology and location these categories comprise a greater range of frozen ground features than are commonly described in rock glacier surveys mapped features extended from 2225 to 3932 m modern mean 3333 m occurred mostly on nnw to nne aspects and ranged in apparent age from modern to relict late pleistocene many of the smaller features mapped here are not readily discernible with remote e g air photo observation field surveys remain the best approach for their detection we interpreted the presence of outlet springs basal lakes suspended silt in outlet streams and fringing phreatophytic vegetation in addition to morphologic indications of current rock movement as evidence for interstitial ice either persistent or seasonal the six classes were distinct in their geographic settings and morphologic conditions indicating process level differences to assess modern climate we intersected mapped locations with the 30 arcsec prism climate model discriminant analysis indicated significant differences among the climate means of the classes with the first three canonical vectors describing 94 of the differences among classes mean annual air temperatures maat for modern features ranged from 0 3 to 2 2 c mean precipitation ranged from 1346 to 1513 mm we calculated differences between modern and pleistocene temperatures in two ways one based on elevation differences of modern and relict rifs 662 m and standard lapse rate the other using prism estimates for the first we estimate the difference in maat as 3 9 c range 2 2 to 7 9 c from prism the difference was 3 3 c range 1 0 to 6 1 c in that persistent snowfields and glaciers are retreating in the sierra nevada under warming climates rifs will likely become increasingly important in prolonging water storage during the warm season and providing small but distributed water reserves for biodiversity and runoff their presence and water contributions would benefit by further hydrologic study

geomagnetic field intensity during the last 60 000 years based on 10be and 36cl from the summit ice cores and 14c abstract based on 10 be 36 cl and 14 c records we reconstruct past changes in the geomagnetic field intensity under the assumption that radionuclide records are mainly influenced by changes in their production rates subsequent comparison of these records with independent geomagnetic field reconstructions allows us to assess the reliability of our approach and to identify periods where our method or the geomagnetic field reconstructions might be problematic the geomagnetic field derived from the 10 be flux to summit in central greenland agrees well with independent geomagnetic field intensity reconstructions however compared to independent palaeomagnetic data the radionuclide record suggests increased geomagnetic field intensities especially for the period from 20 000 to 30 000 years bp 36 cl from the grip ice core agrees well with the 10 be record for the last ice age and hence also the reconstructed geomagnetic field based on the tree ring radiocarbon record it is possible to reconstruct geomagnetic field intensity changes during the holocene a comparison of radiocarbon based and independent geomagnetic field reconstructions indicates that changes in the carbon cycle significantly influenced the atmospheric radiocarbon concentration before 10 000 years bp

paleonutrient and productivity records from the subarctic north pacific for pleistocene glacial terminations i to v our study addresses fundamental questions of the mode and timing of orbital and millennial scale changes in the meridional overturning circulation moc of the subarctic north pacific particular concerns are the vertical mixing the present and past abundance of nutrients in surface waters despite strong stratification and the north pacific north atlantic seesaw of oscillations in sea surface temperature sst we do this by generating and interpreting multiple records for glacial terminations i v down two long piston cores one each from the western and eastern subarctic pacific chlorins and biogenic opal are proxies for surface water productivity delta 13 c of epibenthic foraminifera is a record of deepwater ventilation and the delta 13 c of n pachyderma sin is a tracer of nutrients in subsurface waters that extend up to the sea surface during times of vertical mixing the degree of mixing is traced by pairing sst and delta 18 o records of planktic surface and subsurface pycnocline dwellers tight age control is deduced from a suite of age calibrated 14 c plateau boundaries for termination i and benthic delta 18 o and geomagnetic events for the last 800 ka carbon 14 paleoreservoir ages record the ages of surface and deep waters to uncover short term changes in moc over termination i we have defined a standard sequence of short term productivity events for termination i also evident during terminations ii to v and subsequent interglacials over the last 450 ka the peak glacial regime of stable stratification and low productivity terminated together with the end of ice rafting and melting near 17 ka similar to 2000 years after the onset of termination i pulses of vertical mixing and incursion of warm surface waters from the subtropics followed convected young water masses finally penetrated down to 3600 m water depth at 17 0 to less than 14 5 ka significantly improving bottom water ventilation through the late deglacial and earliest interglacial mixing with upwelled nutrients from the pycnocline induced short term maxima in algal production of chlorins and biogenic opal near 17 15 and 15 12 ka respectively deglacial meltwater incursions in the aleutian current and silica input from north american rivers also promoted east pacific productivity after 15 5 ka productivity decreased during the late deglacial and early interglacial coeval with an exceptional peak in caco 3 preservation caused by both low organic flux and well ventilated deepwater subsequently low salinity and cool surface waters and in turn stratification were gradually restored a second opal dominated productivity maximum marked the ends of interglacials the deglacial pulses of vertical mixing around 17 11 ka imply an important contribution of the north pacific to the coeval release of oceanic co 2 into the atmosphere and support the east west seesaw model of climate change

extremely large variations of atmospheric 14c concentration during the last glacial period a long record of atmospheric 14c concentration from 45 to 11 thousand years ago ka was obtained from a stalagmite with thermal ionization mass spectrometric 230th and accelerator mass spectrometric 14c measurements this record reveals highly elevated 14c between 45 and 33 ka portions of which may correlate with peaks in cosmogenic 36cl and10be isotopes observed in polar ice cores superimposed on this broad peak of 14c are several rapid excursions the largest of which occurs between 44 3 and 43 3 ka between 26 and 11 ka atmospheric 14c decreased from 700 to 100 per mil modulated by numerous minor excursions carbon cycle models suggest that the major features of this record cannot be produced with solar or terrestrial magnetic field modulation alone but also require substantial fluctuations in the carbon cycle

medullosalean fusain trunk from the roof rocks of a coal seam insight from ftir and nmr pennsylvanian sydney coalfield canada abstract reported for the first time from the sydney coalfield canada is a fragmentary fusain r o 2 51 specimen 41 cm long of a medullosalean trunk or massive petiole that originated from the roof rocks of the banded bituminous hub seam r o 0 65 megascopic characteristics of the flat preserved specimen include an irregular cracked fusain surface with secretinite rodlet structures and sclerenchymatous strands some of which still embedded in the shaly matrix and locally preserved vitrain r o 0 69 co occurrence with a compression flora composed virtually of only the seed fern taxon macroneuropteris scheuchzeri hoffmann is noted the goal of this study is to provide a framework for the phytophysicochemical taphonomic history which includes the perspective on vitrinite fusinite relationship formation of fusinite and on the significance the only fusinized identifiable plant fossil specimen in the sydney coalfield we use state of the art solid state ftir 13 c 1 h nmr cp mas techniques and standard reflected light microscopy and sem methods as investigative tools results indicate that the fusinite is characterized by long and narrow xylem fibers without fungal signals and cell structures infilled with pyrite and carbonate ftir spectra of the fusinite and secretinite are similar particularly in respect to high absorbance of aromatic and low absorbance of aliphatic compounds and absorbance of si o functionalities relating to kaolinite 13 c nmr experiments with direct carbon excitation quantify the aromatic to aliphatic ratio as being 20 3 1 as part of the taphonomic history the evidence favors a hot 400 c directional surface fueled flame palaeofire of local extent that charred trunks of growing arborescent seed ferns on only one side and that these trunks were transported to comprise part of the roof rocks of the hub seam

chemotaxonomy for naturally macerated tree fern cuticles medullosales and marattiales carboniferous sydney and mabou sub basins nova scotia canada abstract naturally macerated cuticles nmc and one synangium representing medullosalean and marattialean tree fern species from two carboniferous coalfields in nova scotia canada are investigated the samples were analyzed by infrared spectroscopy ftir and by pyrolysis gas chromatograph mass spectrometry py gc ms techniques in search for chemical signatures that would help in developing a chemotaxonomic classification of carboniferous fern species assuming genetically dependent make up of cuticles ftir derived ch 2 ch 3 ratios in conjunction with contributions from carboxyl groups demonstrated a better potential for discriminating between medullosalean genera and species than molecular signatures obtained by py gc ms however the latter provided better data for differentiating medullosalean from marattialean tree ferns as a group changes in the chemical make up of naturally macerated cuticles due to sample preparation are discussed

late wisconsin paleoecologic record from swamp lake yosemite national park california a 7 86 m sediment core from swamp lake in yosemite national park california provides a continuous record of environmental change over the last ca 16 000 yr as inferred from pollen macrofossil and microscopic charcoal analyses the core stratigraphy documents late wisconsin tioga stage deglaciation between 16 000 and 13 700 yr b p approximately 6000 3500 yr earlier than higher elevation sierra nevada records the core includes five volcanic ash layers chemically identified as four mono craters ashes and the tsoyawata ash mt mazama oregon the fossil record shows that herbs and sagebrush dominated the glacial environment at swamp lake by 12 000 yr b p a mixed conifer forest composed of high and mid elevation conifers grew around the lake suggesting a cool wet late glacial environment the modern sierra montane forest did not become established until ca 10 400 yr b p when maximum charcoal concentrations and minimum fir pollen percentages indicate an early holocene xeric period the record suggests that a cooling trend began ca 6500 yr b p and persisted until ca 3700 yr b p when the modern climatic regime was established

phytochemistry of the fossilized cuticle frond macroneuropteris macrophylla pennsylvanian seed fern canada abstract in canada s sydney coalfield specimens of the extinct carboniferous seed fern macroneuropteris macrophylla brongniart invariably show preservation stages intermediate between compression and fossilized cuticle even concerning a single pinnule in this interdisciplinary approach we study a ca 300 to 350 mm long fossilized cuticle preserved frond section of m macrophylla brongniart that represents about one third of the length of a frond that was originally 1 m long size and preservation allow us to study the phytochemistry of the cuticle biomacropolymers over the length of the frond to assess what impact if any results would have on carboniferous palaeophytochemotaxonomy for comparison the phytochemistry of compressions with their extracted cuticles from the same species and the same sample locality is also investigated we use solid and liquid state semi quantitative fourier transform infrared spectroscopy ftir for the chemical characterization of the frond based on our results we infer an essentially uniform phytochemistry over the fossilized cuticle frond suggesting that only a single pinnule needs to be analyzed to get an overall phytochemical picture of the frond which has been our long time working hypothesis we distinguish between phytochemistry and cutinization the latter is much less pronounced above than below the frond dichotomy and we suggest a palaeoecological cause rather than differing pathways of organic matter transformation moreover cuticles below and above the frond dichotomy have essentially the same epidermal pattern but those from below have features that may have been an adaptation to prevent stomatal flooding during the tropical rainy season this study suggests that chemically the fossilized cuticle is more similar to the compression than to the cuticle obtained from that compression of the same species which invites reevaluation of the classical compression concept

modeling speleothem δ13c variability in a central sierra nevada cave using 14c and 87sr 86sr abstract carbon isotopes in speleothems can vary in response to a number of complex processes active in cave systems that are both directly and indirectly related to climate progressing downward from the soil zone overlying the cave these processes include soil respiration fluid rock interaction in the host limestone degassing of co2 and precipitation of calcite upflow from the speleothem drip site and calcite precipitation at the drip site here we develop a new approach to independently constrain the roles of water rock interaction and soil processes in controlling stalagmite 13c this approach uses the dead carbon proportion dcp estimated from coupled 14c and 230th u measurements in conjunction with sr isotope analyses on stalagmite calcite from a central sierra nevada foothills cave in california a region characterized by a highly seasonal mediterranean type climate to determine the roles of water rock interaction and soil processes in determining stalagmite 13c increases in stalagmite dcp between 16 5 and 8 8 ka are coincident with decreased 13c indicating a varying yet substantial contribution from the soil organic matter som reservoir likely due to significantly increased average age of som in the soil veneer above the cave during wet climatic intervals we use geochemical and isotope mixing models to estimate the host carbonate contribution throughout the 13c time series and determine the degree of degassing and calcite precipitation that occurred prior to precipitation of stalagmite calcite the degree of degassing and prior calcite precipitation we calculate varies systematically with other climate indicators with less degassing and prior calcite precipitation occurring during wetter climatic intervals and more during drier intervals modeled 13c values and degassing calculations suggest that some degree of prior calcite precipitation is necessary at all time intervals to explain measured stalagmite 13c values even during relatively wet intervals these results illustrate the importance of constraining degassing and prior calcite precipitation in the interpretation of speleothem 13c records particularly those from caves that formed in seasonal semi arid to arid environments

late holocene forest dynamics volcanism and climate change at whitewing mountain and san joaquin ridge mono county sierra nevada ca usa deadwood tree stems scattered above treeline on tephra covered slopes of whitewing mtn 3051 m and san joaquin ridge 3122 m show evidence of being killed in an eruption from adjacent glass creek vent inyo craters using tree ring methods we dated deadwood to ad 815 1350 and infer from death dates that the eruption occurred in late summer ad 1350 based on wood anatomy we identified deadwood species as pinus albicaulis p monticola p lambertiana p contorta p jeffreyi and tsuga mertensiana only p albicaulis grows at these elevations currently p lambertiana is not locally native using contemporary distributions of the species we modeled paleoclimate during the time of sympatry to be significantly warmer 3 2 c annual minimum temperature and slightly drier 24 mm annual precipitation than present resembling values projected for california in the next 70 100 yr

late holocene vegetation changes in greenwater valley mojave desert california abstract small scale late holocene vegetation changes were determined from a series of 13 modern and fossil packrat middens collected from a site in the greenwater valley northern mojave desert california although the site is above the modern lower limit of coleogyne ramosissima black brush macrofossils of this shrub are only present in samples younger than 270 yr b p in order to measure changes more subtle than presence vs absence macrofossil concentrations were quantified and principal components and factor analyses were used to distinguish midden plant assemblages both the presence absence data and the statistical analyses suggest a downward shift of 50 to 100 m for coleogyne blackbrush communities between 1435 and 1795 a d

carbon isotope evidence for changes in antarctic intermediate water circulation and ocean ventilation in the southwest pacific during the last deglaciation 1 deep sea sediment core fr1 97 gc 12 is located 990 mbsl in the northern tasman sea southwest pacific where antarctic intermediate water aaiw presently impinges the continental slope of the southern great barrier reef analysis of carbon 13c and oxygen 18o isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr during the last glacial maximum there was a large 13c offset 1 1 between the surface dwelling planktonic foraminifera and benthic species living within the aaiw in contrast during the last deglaciation termination 1 the 13cplanktonic benthic offset reduced to 0 4 prior to an intermediate offset 0 7 during the holocene we suggest that variations in the dominance and direction of aaiw circulation in the tasman sea and increased oceanic ventilation can account for the rapid change in the water column 13cplanktonic benthic offset during the glacial interglacial transition our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics in this case climatic variations in the southern hemisphere may have led to the rapid ventilation of deep water and aaiw during termination 1 which contributed to the postglacial rise in atmospheric co2

tropical air sea interactions accelerate the recovery of the atlantic meridional overturning circulation after a major shutdown abstract using a coupled ocean sea ice atmosphere model of intermediate complexity the authors study the influence of air sea interactions on the stability of the atlantic meridional overturning circulation amoc mimicking glacial heinrich events a complete shutdown of the amoc is triggered by the delivery of anomalous freshwater forcing to the northern north atlantic analysis of fully and partially coupled freshwater perturbation experiments under glacial conditions shows that associated changes of the heat transport in the north atlantic lead to a cooling north of the thermal equator and an associated strengthening of the northeasterly trade winds because of advection of cold air and an intensification of the trade winds the intertropical convergence zone itcz is shifted southward changes of the accumulated precipitation lead to the generation of a positive salinity anomaly in the northern tropical atlantic and a negative anomaly in the southern tropical atlantic during the shutdown phase of

compression cuticle relationship of seed ferns insights from liquid solid states ftir late palaeozoic early mesozoic canada spain argentina abstract cuticles have been macerated from suitably preserved compressed fossil foliage by schulze s process for the past 150 years whereas the physical biochemical relationship between the coalified layer with preserved cuticle as a unit has hardly been investigated although they provide complementary information this relationship is conceptualized by an analogue model of the anatomy of an extant leaf vitrinite mesophyll cuticle biomacropolymer compression alkaline solutions from schulze s process as a proxy for the vitrinite are studied by means of liquid solid states fourier transform infrared spectroscopy ftir in addition cuticle free coalified layers and fossilized cuticles of seed ferns mainly from canada spain and argentina of late pennsylvanian late triassic age are included in the study sample infrared data of cuticle and alkaline solutions differ which is primarily contingent on the mesophyll biomacropolymer characteristics the compression records two pathways of organic matter transformation one is the vitrinized component that reflects the diagenetic post diagenetic coalification history parallel with the evolution of the associated coal seam the other is the cuticle that reflects the sum total of evolutionary pathway of the biomacropolymer its monomeric or polymeric fragmentation though factors promoting preservation include entombing clay minerals and lower ph conditions caution is advised when interpreting liquid state based ftir data as some ir signals may have resulted from the interaction of schulze s process with the cuticular biochemistry a biochemical study course for taphonomy is suggested as fossilized cuticles cuticle free coalified layers and compressions are responses to shared physicogeochemical factors

vegetation heterogeneity on a late pennsylvanian braided river plain draining the variscan mountains la magdalena coalfield northwestern spain article the spatial heterogeneity and community ecology is reconstructed for late pennsylvanian stephanian b sensu lato vegetation preserved in la magdalena coalfield northwestern spain the 1500 m thick basin fill accumulated rapidly along the margin of the variscan mountains and the principal sedimentary facies comprise the deposits of large braided streams that dissected extensive wetlands containing large lakes quadrat analysis of 93 mostly par autochthonous megafloral assemblages indicates that pteridosperms and ferns dominated communities with three taxa pecopteris spp callipteridium pteridium and neuropteris ovata accounting for 58 of all plant remains sphenopsids and lycopsids were less common but widespread and cordaitaleans were rare at the local scale laterally exposed bedding planes reveal that communities comprised a complex and heterogeneous mosaic of species at the landscape scale ecological gradients are evident from multivariate analyses of quadrats in a facies context pteridosperms dominated marginal wetlands adjacent to steep basin margins a greater proportion of ferns occurred in or adjacent to

stalagmite records of hydroclimate in central california during termination 1 abstract the last deglaciation is marked by large and abrupt hydroclimatic changes in the great basin and the american southwest however comparatively little is known about how hydroclimate varied on the western side of the sierra nevada we present new evidence for abrupt changes in precipitation amount in the central sierra nevada during the last deglaciation our new record from mclean s cave overlaps with a previously published record from nearby moaning cave oster et al 2009 and extends the record of hydroclimatic change in the region through heinrich stadial 1 mclean s cave speleothem 18o 13c mg ca and sr ca indicate a shift to drier conditions at the beginning of heinrich stadial 1 from 16 1 to 17 5 ka followed by wetter conditions at the end of heinrich stadial 1 when the majority of great basin lakes reached their deglacial highstands during the last deglaciation coincident shifts in the moaning and mclean s cave proxy records indicate drier conditions in the western sierra nevada during millennial scale intervals of warming at high latitudes such as the bolling and allerod and wetter conditions during cooler intervals such as the older and younger dryas thus the sierra nevada speleothem records are consistent with other regional records that document increased winter rainfall during millennial scale cold periods of the last deglaciation however regional differences exist in the hydroclimatic response to the younger dryas with central californian and interior southwestern sites indicating an increase in winter storms that is not apparent in southern california dynamic simulations of atmospheric circulation indicate that wetter conditions during the younger dryas relative to the bolling at mclean s cave may have resulted from a stronger storm track in the north pacific at the latitude of northern california

50 000 years of vegetation and climate history on the colorado plateau utah and arizona usa sixty packrat middens were collected in canyonlands and grand canyon national parks and these series include sites north of areas that produced previous detailed series from the colorado plateau the exceptionally long time series obtained from each of three sites n48 000 14 cy r bp to present include some of the oldest middens yet discovered most middens contain a typical late wisconsinan glaciation mixture of mesic and xeric taxa evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference the oldest middens from canyonlands np however differ in containing strictly xeric assemblages including middens incorporating needles of arizona single leaf pinyon far north of its current distribution similar aged middens from the eastern end of grand canyon np contain plants more typical of glacial climates but also contain fossils of one seed juniper near its current northern limit in arizona holocene middens reveal the development of modern vegetation assemblages on the colorado plateau recording departures of mesic taxa from low elevation sites and the arrival of modern dominant components much later published by university of washington

late pleistocene california droughts during deglaciation and arctic warming abstract recent studies document the synchronous nature of shifts in north atlantic regional climate the intensity of the east asian monsoon and productivity and precipitation in the cariaco basin during the last glacial and deglacial period yet questions remain as to what climate mechanisms influenced continental regions far removed from the north atlantic and beyond the direct influence of the inter tropical convergence zone here we present u series calibrated stable isotopic and trace element time series for a speleothem from moaning cave on the western slope of the central sierra nevada california that documents changes in precipitation that are approximately coeval with greenland temperature changes for the period 16 5 to 8 8 ka from 16 5 to 10 6 ka the moaning cave stalagmite proxies record drier and possibly warmer conditions signified by elevated 18 o 13 c mg sr and ba and more radiogenic 87 sr 86 sr during northern hemisphere warm periods bolling early and late allerod and wetter and possibly colder conditions during northern hemisphere cool periods older dryas inter allerod cold period and younger dryas moaning cave stable isotope records indicate that wet conditions persisted in this area well beyond 11 5 ka suggesting the effects of the younger dryas event may have been longer lived in the western sierra nevada than in greenland however a shifting drip center and corresponding change in seepage water routing may have influenced the trace element records between 10 6 and 9 6 ka linkages between northern high latitude climate and precipitation in the sierra nevada suggested here could indicate that under conditions of continued global warming this drought prone region may experience a reduction in pacific sourced moisture

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

comment on anomalous radiocarbon ages for foraminifera shells by w broecker et al a correction to the western tropical pacific md9821 81 record 1 the effort to obtain high resolution paleoceanographic data often leads to continental margin settings where the flux of clastic sediments produces higher sediment accumulation rates however on continental margins the possibility for down slope transport of reworked sediment is a concern this is particularly true in tectonically active settings such as the western pacific which includes the maritime islands of the philippines and the adjacent archipelago the continental margins of the western tropical pacific are strategically located within the pacific warm pool and detailed paleoceanographic information from this region is a valuable asset in efforts to improve our understanding of what factors contribute to large and sometimes abrupt changes in global climate the acquisition of data sets such as sea surface temperatures from the tropical pacific warm pool through the last glacial cycle has indeed added measurably to a growing array of data from lowlatitude locations certainly there is much left to be learned from the high deposition rate records located in continental margin settings however over the past 2 years there have been concerns that one of the high deposition rate sequences in the western tropical pacific r v marion dufresne core md98 2181 is composed of down slope transport of reworked material or slumping broecker et al 2006 because this site has provided one of the highest resolution data sets of sea surface temperature and salinity information for the pacific warm water pool through the last glacial cycle stott et al 2002 2004 it is important to assess the stratigraphic integrity of the sequence and to identify where there may be problems with the record 2 the md98 2181 core was collected from a depth of 2114 m on the continental slope south of mindanao island during the last glacial and holocene sediments accumulated at this site at rates of between 50 and 80 cm kyr making this an ideal location to collect high resolution paleoceanographic information from the pacific warm pool stott et al 2004 we have worked on the md98 2181 core for the past eight years conducting stable isotope and mg ca measurements on planktonic and benthic foraminifers in an effort to document the timing and the magnitude of sea surface temperature and salinity changes in the western tropical pacific warm pool through the last glacial cycle stott et al 2002 2004 in doing so we have obtained c ages for 42 planktonic foraminifer samples from the holocene and late glacial portions of the core table 1 and figure 1 the majority of our md98 2181 samples were taken from u channel subcores these subcores were sectioned continuously at 2 cm increments in stott s laboratory and the samples were washed in buffered di water over a 63 mm sieve to remove fine clays the planktonic globigeriniodes ruber used for stable isotope and mg ca measurements and also for c determinations was picked from the 150 mm fraction whereas globigerinoides sacculifer was picked from the 250 mm fraction in some instances other more robust planktonic species have also been c dated including pulleniatina obliquiloculata and neogloboquadrina dutertrei which were picked from the 250 mm fractions m rincon who has been stott s laboratory manager for the past 15 years picked each sample used in these studies the g ruber do stratigraphy for md98 2181 is shown in figure 2 3 the late glacial to recent do stratigraphy from this core matches other high resolution sequences from this region with the exception of a 20 cm interval between 941 and 961 cm the samples from the 941 961 cm interval exhibit do values that are clearly higher than adjacent intervals immediately above and below figure 2 the interval centered at 950 cm would have been deposited during the last deglaciation and the apparent timing of the anomalously high do values would put it close to the time of the younger dryas for this reason it was not initially clear whether these values represented the presence of reworked glacial age material or if the values were indicative of a brief return to glacial like conditions during the deglaciation the intervals directly below 961 cm do not exhibit such high do values as those at 950 cm and the isotope stratigraphy appears to closely match that of other high resolution records from the western tropical pacific region stott et al 2004 4 in 2003 w broecker approached stott about a collaboration that involved c dating of planktonic and paleoceanography vol 22 pa1211 doi 10 1029 2006pa001379 2007 click here for full article

analysis of the atmospheric 14c record spanning the past 50 000 years derived from high precision 230th 234u 238u 231pa 235u and 14c dates on fossil corals abstract changes in the geomagnetic field intensity solar variability and the internal changes of the carbon cycle are believed to be the three controlling factors of past atmospheric radiocarbon 14 c concentrations denoted as 14 c of these three it is believed that the field intensity is the dominant factor we analyze an atmospheric 14 c record spanning the past 50 000 years based on previously published 230 th 234 u 238 u and 14 c dates of fossil corals from kiritimati barbados araki and santo islands and identify the role of the laschamp geomagnetic field excursion on the long term trend of the 14 c record there is a general consistency between the coral 14 c record and the 14 c output from carbon cycle models based on the global 14 c production estimates high precision high accuracy 230 th 234 u 238 u dates and redundant 231 pa 235 u dates anchor the timing of this 14 c record we propose that a significant fraction of the long term 14 c trend may be due to inaccuracies in the generally accepted 14 c decay constant the uncertainty in estimating the shape of 14 c beta spectrum below 20 kev leads to one of the greatest errors in decay constant estimates once the 14 c half life is validated via redundant techniques 14 c records will provide a better opportunity to examine the roles of carbon cycle and 14 c production influences

chemometric study of functional groups in pennsylvanian gymnosperm plant organs sydney coalfield canada implications for chemotaxonomy and assessment of kerogen formation abstract the samples comprise the foliage of four pteridosperm medullosalean plant fossil species of differing preservation states and one of a cordaitean species from two canadian maritime sub basins of carboniferous age 300 ma sydney and stellarton coalfields nova scotia respectively included in the sample set were some coal samples from sydney coalfield along with published data for coal macerals for comparison by applying schulze s maceration process to the fossil foliage to obtain the cuticles five sample forms evolved viz compressions cuticles and fossilized cuticles and acidic and alkaline solutions from schulze s process to which was added the sydney coal samples as the sixth form area integration of the absorbance spectra from solid and liquid state fourier transform infrared ftir spectroscopy produced functional chemical parameters which were organized into a data matrix of eight variables and 62 samples 8 62 matrix since we were interested in grouping the sample forms as a function of phytochemistry functional groups to assess primarily the palaeophytotaxonomic potential as a general approach to carboniferous taxonomy principal components were extracted from the matrix and a subset of 4 33 samples in order to refine the grouping results from the initial component analysis in each case a two component model resulted accounting for least 80 of the cumulative variance overall the results are encouraging in offering increasing support for fossil leaf chemotaxonomy but bearing in mind the limited sampling number 56 and restricted sampling of genera 5 apart from this general conclusion which supports our previous ftir work vis a vis chemotaxonomy we noted functional group similarities in our ftir data with types of kerogen and coal macerals on this basis we hypothesize that in combination with the different preservation states of our fossil specimens these factors have a bearing on kerogen genesis from plant material i e the oil and gas prone types i and ii

a 190 drop in atmosphere s δ14c during the mystery interval 17 5 to 14 5 kyr reconstructions of atmospheric 14c for the deglacial period reveal a 190 10 drop between 17 5 and 14 5 kyr before present during the mystery interval while it appears that the major contributor must be the mixing between an isolated low radiocarbon abyssal reservoir and the remainder of the ocean a combination of 14c measurements on coexisting benthic and planktic foraminifera shells and 13c 12c measurements on benthic foraminifera make it difficult to identify a sufficiently large volume for this reservoir an alternative scenario based on higher 14c production rates between about 38 and 18 kyr ago would escape the need for a large isolated reservoir prior to the mystery interval but instead would call for a better ventilated ocean afterwards the addition of 14c deficient sedimentary carbon appears not to be an important contributor while the unlikely explanation that the half life of 14c is 15 greater than the accepted value 5730 yr would eliminate the steady decrease in the 14c c over the last 40 kyr it would not explain the steep drop which occurred between 17 5 and 14 5 kyr

phyto and chronostratigraphical correlations between the late pennsylvanian morien group sydney nova scotia and the silesian pennant measures south wales three macrofloral interval zones lobatopteris vestita l micromiltoni and linopteris bunburii recognized in the westphalian d and the cantabrica biozone in the stephanian of europe are also present in the morien group pictou group of sydney coalfield nova scotia these zones allow a more refined correlation to be made between sequences of the same age in the sydney and south wales coalfields and thus between western europe and north america in general

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

ventilation of the glacial deep pacific ocean measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial pacific deep sea cores suggest that during peak glacial time the radiocarbon age of water at 2 kilometers depth was no greater than that of today these results make unlikely suggestions that a slowdown in deep ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon 14 14c to carbon in the atmosphere and surface ocean during glacial time comparison of 14c ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14c to c ratio difference was not substantially different from today s

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles