direct correlation of millennial scale changes in western north american vegetation and climate with changes in the california current system over the past 60 kyr terrestrial pollen and marine climate proxies from seven sediment cores taken on the continental margin of western north america between 32 and 43 n show systematically related short term changes superposed on milankovitch scale oscillations of the past 60 kyr during oxygen isotope stage 3 brief warming events in california and oregon appear correlative with interstadial events in waters offshore as do the rapid climate oscillations of the last glacial transition 14 10 ka estimated temperature depression of the coastal lowlands ranges from 10 c in southern california to 5 c in oregon during the last glacial the absence of long distance migration of pacific coastal plant assemblages concurs with marine evidence that southward movement of the polar front during the last glacial maximum was limited correlative changes in terrestrial and marine ecosystems imply that broad reorganizations of circulation in the northeast pacific ocean were synchronous with reorganizations of atmospheric circulation over western north america

climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

late pleistocene time series of atmospheric and oceanic variables recorded in sediments from the subarctic pacific time series analyses of atmospheric and oceanic variables in a late pleistocene record from the northwest pacific show the complex relationship of the response of various segments of the climate system to changes in the earth s orbit most variance spectra of time series from this subarctic record contain frequency peaks with periods corresponding to at least one of the major orbital components of eccentricity obliquity or precession although the radiolarian faunal water mass assemblages have prominent spectral peaks with 41 000 year periods which are coherent with obliquity at this frequency only the transitional faunal assemblage contains variance focused at a frequency corresponding to the 100 000 year period of eccentricity three of these faunal time series also show variance concentrated at a frequency with a 20 000 year period these three time series are not coherent at a 20 000 year frequency with either of the dominant spectral peaks of precession they are coherent however with variations in the second harmonic of the obliquity cycle changes in obliquity apparently affect siliceous faunal abundances in the northwest pacific region of this high latitude site more than variations in eccentricity or precession maxima in the time series of quartz abundance occur during low values of eccentricity and high glacial ice volume because atmospheric winds serve as the major source of supply of quartz to the sediments at this site these high quartz values reflect increased aridity at the source region except for short periods during interglacials the characteristics of the surface waters in this region of the subarctic pacific during much of the last 460 000 years were similar to those which exist today in the sea of okhotsk the spectrum of winter sea surface temperature estimates derived from siliceous microfaunal abundances contains dominant frequency peaks at periods of 100 000 41 000 and 23 000 years which are coherent with eccentricity obliquity and precession respectively based upon the relationship of the subarctic front with the dominance of specific faunal asemblages the front was positioned south of its present day location throughout much of the late pleistocene

aeolian silt contribution to soils on mountain slopes mt śleza southwest poland this paper evaluates the possible contribution of aeolian silt to soils of mt leza southwest poland silt loam textures are common across lower silesia and are often confused with silt clay loam especially at the outer boundaries with thin loess deposits eight study sites with different thicknesses of silt loam mantles that are covered and or mixed with underlying sediments were examined in the field to test our hypothesis we analyzed the particle size and geochemistry of representative horizons concentrations of major and trace elements as well as their cross ratios confirmed the aeolian origin of silt loam materials and clearly distinguished them from basal sediments there is a clear relationship between the presence and depth of aeolian mantles and mixing zones with the type of underlying material furthermore the incorporation of aeolian silt to regoliths soils was a main agent initiating and stimulating clay translocation leading to the formation of an argic horizon below the silt mantles mixing aeolian silt with acid granite regoliths and further illuviation resulted in the formation of alisols while silt contributions to serpentine sediments resulted in development of skeletic luvisols soils receiving very weak input of aeolian silts remain as leptosols cambisols

sea level records at 80 ka from tectonically stable platforms florida and bermuda studies from tectonically active coasts on new guinea and barbados have suggested that sea level at 80 ka was significantly lower than present whereas data from the atlantic and pacific coasts of north america indicate an 80 ka sea level close to that of the present we determined ages of corals from a shallow submerged reef off the florida keys and an emergent marine deposit on bermuda both localities are on tectonically stable platforms distant from plate boundaries uranium series ages show that corals at both localities grew during the 80 ka sea level highstand and geologic data show that sea level at that time was no lower than 7 9 m below present florida and may have been 1 2 m above present bermuda the ice volume discrepancy of the 80 ka sea level estimates is greater than the volume of the greenland or west antarctic ice sheets comparison of our ages with high latitude insolation values indicates that the sea level stand near the present at 80 ka could have been orbitally forced

the influence of changing orbital parameters and surface boundary conditions on climate simulations for the past 18 000 years abstract general circulation model experiments at 3000 year intervals for the past 18 000 years were made to estimate the magnitude timing and pattern of the climatic response to prescribed changes of orbital parameters date of perihelion axial tilt eccentricity and glacial age lower boundary conditions ice sheets land albedo sea ice and sea surface temperature the experiments used the community climate model ccm of the national center for atmospheric research ncar the response of monsoon circulations and tropical precipitation to the orbitally produced solar radiation changes was much larger than the response to changes of glacial age boundary conditions the continental interior of eurasia was 2 4 k warmer in summer and summer monsoon precipitation of north africa south asia was increased by 10 20 between 12 000 and 6000 yr bp before present when perihelion occurred during northern summer rather than in winter as now and the earth s axial tilt was larger than now southern hemisphe

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

climate records covering the last deglaciation the oxygen 18 oxygen 16 ratio of molecular oxygen trapped in ice cores provides a time stratigraphic marker for transferring the absolute chronology for the greenland ice sheet project gisp ii ice core to the vostok and byrd ice cores in antarctica comparison of the climate records from these cores suggests that near the beginning of the last deglaciation warming in antarctica began approximately 3000 years before the onset of the warm bolling period in greenland atmospheric carbon dioxide and methane concentrations began to rise 2000 to 3000 years before the warming began in greenland and must have contributed to deglaciation and warming of temperate and boreal regions in the northern hemisphere

patterns and causes of millennial scale climate change in the pacific northwest during marine isotope stages 2 and 3 abstract a high resolution pollen record from fargher lake washington shows a series of millennial scale changes in vegetation and climate during marine isotope stages mis 3 and 2 a comparison of fargher lake with pollen records from little lake oregon and carp lake washington reveals regional patterns of change during the early part of mis 3 ca 60 000 45 000 cal yr bp fargher and carp lakes indicate transitions between open and closed vegetation and cold dry and warm wet conditions between 45 000 and 27 500 cal yr bp all three records show shifts between low and high elevation taxa that indicate a series of temperature changes these temperature changes are similar to those in the santa barbara basin and may be explained by changes in the strength of the aleutian low during mis 2 27 500 14 000 cal yr bp shifts between wet and dry adapted taxa were most prominent at little lake there is also evidence for two minor warmings mis 2 climate variations do not correlate well with those in the santa barbara basin however precipitation changes in the pacific northwest during mis 2 correlate with evidence of ice sheet surges into the north atlantic and were probably related to variations in the strength and position of the glacial anticyclone and the jet stream

late glacial to holocene changes in winds upwelling and seasonal production of the northern california current system abstract a core 120 km off the coast of southern oregon was examined for changes in lithology diatoms and pollen over the past 30 000 yr primary production during the late pleistocene was about half that of the holocene evidence from diatoms and pollen indicates that summer upwelling was much weaker implying an absence of strong northerly winds early pliocene diatoms found throughout the late pleistocene section were probably derived from diatomites east of the cascades and provide evidence for strong easterly winds over a dry continental interior the findings verify predictions of a climate model based on glacial maximum conditions there is no compelling evidence for a climatic reversal corresponding to the european younger dryas chron during the early holocene 9000 7000 yr b p there may have been years when winds were insufficiently strong to support upwelling so that warm stratified waters lay closer to the coast

late glacial vegetation and climate at the manis mastodon site olympic peninsula washington abstract as the late wisconsin cordilleran ice sheet retreated sediment accumulated in shallow depressions at the manis mastodon archaeological site on the olympic peninsula near sequim washington pollen plant macrofossils and bones of mastodon caribou and bison occur within the lower 47 cm of these deposits the fossil pollen and seed assemblages indicate persistence for 1000 yr 11 000 12 000 yr b p of an herb and shrub dominated landscape at a time when forest species appear elsewhere in washington and in adjacent british columbia at present sequim is near the northern coastal limits of both cactaceae and ceratophyllum mean annual precipitation is 42 7 cm and summer temperatures average 15 16 c in july the absence of coniferous trees and the presence of cactus and ceratophyllum in late glacial sediments are explained by a regional climate that was drier and at least as warm as today these conditions persisted in the rain shadow of the olympic mountains until at least 11 000 yr b p

age and correlation of a paleomagnetic episode in the western united states by 40ar 39ar dating and tephrochronology the jamaica blake or a new polarity episode high resolution paleomagnetic records from two sites near pringle falls oregon are compared with similar records from summer lake oregon 170 km to the southeast paoha island in mono lake 660 km to the southeast and benton crossing in long valley approximately 700 km to the southeast in east central california the sequences at pringle falls contain a distinctive coarse pumice lapilli tephra layer which we have dated as 218 10 ka by 40ar 39ar step heating of plagioclase feldspar stratigraphically this tephra is closely associated with a suite of several other tephra layers that bracket the interval studied paleomagnetically each tephra layer is distinguished by the unique chemical composition of its volcanic glass shards the pumice layer dated at pringle falls is correlated with layers at three of the other localities using all the tephra layers we can correlate the lake stratigraphic sequences and associated paleomagnetic records among the four distant localities additional age control is obtained from a fifth locality at tulelake in northern california where the stratigraphic interval of interest is bracketed between 171 43 and approximately 140 ka characteristics of the paleomagnetic records indicate virtually identical paleofield variation particularly the geometry of a normal to normal n n geomagnetic polarity episode the observed paleofield behavior resembles the blake geomagnetic polarity episode but is significantly older than the generally accepted age of the blake episode either the age of the blake episode is significantly underestimated or the polarity episode documented here is older perhaps the jamaica episode or is an as yet unreported episode a corollary of the latter option is that paleomagnetic polarity episodes of different ages may have similar transition polar paths a conclusion implying that a common mechanism is involved

evolution of eureka flat a dust producing engine of the palouse loess usa sedimentologic stratigraphic and pedologic evidence demonstrates that eureka flat ef a narrow 80 km long deflation plain in south central washington usa is the source for the thick and widespread loess of the palouse region located in the southern columbia plateau ef has been a depocenter for abundant clay to sand sized sediment derived from repeated glacial outburst floods that swept through the area during the pleistocene prevailing sw winds that were funneled across ef remobilized flood sediment into sand dunes sand sheets and loess an eolian sand sheet buried beneath 1 8 m of loess at the downwind end of ef attests to bioclimatically driven changes in the style of eolian deposition the depositional transition from sand sheet to loess is characterized by a change from wind rippled strata to structureless bimodal sand and silt with insect burrows and rhizoliths to unimodal sandy loess soil moisture and density of dust trapping vegetation control where sand dunes and loess accumulate up to 4 5 m of post lgm loess mantles the landscape adjacent to and downwind from ef some of the thickest loess deposits owe their origins to the sequestering of eolian sand particles by topographic traps such as the touchet river and its tributary valleys the removal of saltating sand from the eolian system promotes thick accumulation of loess downwind of topographic traps patterns of loess accumulation across the columbia plateau are identified on isopach maps of major pre and post lgm loess units and show that ef has been the major engine for the production of atmospheric dust and loess during both times

magnetostratigraphy and tephrochronology of an upper pliocene to holocene record in lake sediments at tulelake northern california combined paleomagnetic and tephra chronologies of one of the most complete middle pliocene through holocene stratigraphic records yet recovered in western north america provide a reference section for much of northwestern north america and adjacent pacific ocean five long drill cores of lacustrine sediments at tulelake northern california recovered a nearly continuous 331 m thick record spanning the past 3 m y the brunhes normal polarity matuyama reversed polarity and gauss normal polarity chronozones are recognized within these the jaramillo olduvai reunion and kaena subchronozones are present six short stratigraphic intervals exhibit anomalous remanent inclinations that may record excursions and brief subchrons within the brunhes and matuyama chronozones age estimates suggest correlation of five of the anomalous intervals with 1 one of the biwa excursions at about 18 000 yr b p 2 the mono lake excursion at about 27 000 yr b p 3 the blake reversed polarity subchron at about 114 000 yr b p 4 the kamikatsura normal polarity subchron at about 850 000 yr b p and 5 the cobb mountain normal polarity subchron at about 1 10 ma age of the sixth interval of anomalous inclination is broadly constrained between 117 000 and 180 000 yr b p sixty three individual tephra layers were characterized by electron microprobe and x ray fluorescence analyses of volcanic glass shards identified tephra of relatively well known age include 1 the basal airfall pumice at llao rock 7015 yr b p 2 the trego hot springs bed 23 400 yr b p 3 the olema ash bed between 55 000 and 75 000 yr b p 4 the airfall pumice at cloudcap road pumice castle like tephra 2 about 120 000 yr b p 5 the rockland ash bed about 410 000 yr b p 6 the lava creek b ash bed 620 000 yr b p 7 the rio dell ash bed about 1 45 ma and 8 the bear gulch ash bed about 1 9 ma a sedimentation rate curve based on independently dated tephra and polarity reversals is used to infer age estimates of undated or previously unidentified ash beds some of these ash beds are found over large areas of the western united states and eastern pacific ocean basin and provide widespread horizons for correlation most of the tephra at tulelake records eruptions from the nearby southern and central cascade range of oregon and northern california and the medicine lake highland of northern california deposition took place during most of the past 3 m y within the tulelake basin notable periods of slow or sporadic accumulation or erosion occurred between about 620 000 and 200 000 yr b p and between about 2 5 and 2 1 ma rapid deposition occurred during marine oxygen isotope stage 6 between about 170 and 125 ka regional volcanism during the past 3 m y was markedly episodic with notable volcanic activity from about 2 1 to 1 9 ma and from 0 4 ma to the present

case for periodic colossal jokulhlaups from pleistocene glacial lake missoula two classes of field evidence firmly establish that late wisconsin glacial lake missoula drained periodically as scores of colossal jokulhlaups glacier outburst floods 1 more than 40 successive flood laid sand to silt graded rhythmites accumulated in back flooded valleys in southern washington hiatuses are indicated between flood laid rhythmites by loess and volcanic ash beds disconformities and nonflood sediment between rhythmites are generally scant because precipitation was modest slopes gentle and time between floods short 2 in several newly analyzed deposits of pleistocene glacial lakes in northern idaho and washington lake beds comprising 20 to 55 varves average 30 40 overlie each successive bed of missoula flood sediment these and many other lines of evidence are hostile to the notion that any two successive major rhythmites were deposited by one flood they dispel the notion that the prodigious floods numbered only a few the only outlet of the 2 500 km 3 glacial lake missoula was through its great ice dam and so the dam became incipiently buoyant before the lake could rise enough to spill over or around it like grimsvotn iceland lake missoula remained sealed as long as any segment of the glacial dam remained grounded when the lake rose to a critical level 600 m in depth the glacier bed at the seal became buoyant initiating underflow from the lake subglacial tunnels then grew exponentially leading to catastrophic discharge calculations of the water budget for the lake basin including input from the cordilleran ice sheet suggest that the lakes filled every three to seven decades the hydrostatic prerequisites for a jokulhlaup were thus re established scores of times during the 2 000 to 2 500 yr episode of last glacial damming j harlen bretz9s spokane flood outraged geologists six decades ago partly because it seemed to flaunt catastrophism the concept that lake missoula discharged regularly as jokulhlaups now accords bretz9s catastrophe with uniformitarian principles

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

record of pre late wisconsin giant floods in the channeled scabland interpreted from loess deposits loess deposits adjacent to flood coulees on the columbia plateau in eastern washington state record multiple episodes of pre late wisconsin cataclysmic floods evidence in the loess consists of flood cut unconformities upward fining in individual loess strata and flood deposits that consist of basaltic gravel fragments of calcified paleosols and slackwater sediment at least six episodes of floods during the pleistocene are indicated by paleomagnetic measurements tephra correlations and the stratigraphic position of flood indicators one episode of the six occurred prior to 790 ka the most recent episode before the last glacial floods occurred at 36 ka at the latest

weichselian palynological records from southern europe correlation and chronology abstract the high resolution independently dated palynostratigraphic record from lago grande di monticchio spanning the last 101 530 calendar years provides a basis for re evaluating the correlations between palaeoenvironmental events in europe during the last glacial as well as a means to determine their chronology the interstadial events recorded from various localities throughout europe are combined into a single scheme of correlations and a chronological framework is suggested this provides a basis for assessing the evolution of the vegetation and environmental patterns across europe during the last glacial revealing a general tendency for the latitudinal climatic gradient to have been steeper than it has been during the holocene the vegetation has also generally been subject to greater moisture deficiency either because of prevailing climatic conditions or as a reflection of the lower atmospheric concentration of co 2 the scheme of correlations is shown to be capable of being extended beyond europe not only to marine and ice core records from the north atlantic region but also to a palynological record from north west north america

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

late quaternary vegetation near battle ground lake southern puget trough washington pollen and plant macrofossil records from battle ground lake along with published data are used to reconstruct the late quaternary vegetation history of the nonglaciated southern puget trough coinciding with the end of the evans creek stade circa 20 000 17 000 yr b p of fraser glaciation gramineae artemisia herbs and picea cf engelmannii grew in a parkland tundra around battle ground this assemblage recorded throughout the southern puget trough implies cold relatively dry conditions similar to subalpine environments east of the cascade range the presence of pseudotsuga picea sitchensis and alnus rubra as macrofossils suggests a slight interstadial warming between 17 000 and 15 000 yr b p cool humid conditions prevailed during the vashon stade when south of the cordilleran ice sheet open forest or parkland featured mesophytic subalpine taxa at battle ground lake temperate conifers were part of forest communities circa 11 200 yr b p but elsewhere they were present as early as 12 500 yr b p from 10 000 to 4500 yr b p pseudotsuga quercus savannah spread into the battle ground area offering evidence for summer drought more severe than today pseudotsuga and thuja forest was established in the late holocene with the introduction of the modern humid climate consideration of all the pollen data from the southern puget trough and the available radiometric chronology suggests that postglacial migration of most lowland conifers into the puget trough was rapid and not necessarily from southern refugia

isotopic evidence for temporal variation in proportion of seasonal precipitation since the last glacial time in the inland pacific northwest of the usa abstract large scale atmospheric circulation patterns determine the quantity and seasonality of precipitation the major source of water in most terrestrial ecosystems oxygen isotope 18o dynamics of the present day hydrologic system in the palouse region of the northwestern u s a indicate a seasonal correlation between the 18o values of precipitation and temperature but no seasonal trends of 18o records in soil water and shallow groundwater their isotope values are close to those of winter precipitation because the palouse receives 75 of its precipitation during winter palouse loess deposits contain late pleistocene pedogenic carbonate having ca 2 to 3 higher 18o values and up to 5 higher carbon isotope 13c values than holocene and modern carbonates the late pleistocene 18o values are best explained by a decrease in isotopically light winter precipitation relative to the modern winter dominated infiltration the 13c values are attributed to a proportional increase of atmospheric co2 in soil co2 due to a decrease in soil respiration rate and 13c discrimination in plants under much drier paleoclimate conditions than today the regional climate difference was likely related to anticyclonic circulation over the pleistocene laurentide and ice sheet

repeating waveform initiated by a 180 190 ka geomagnetic excursion in western north america implications for field behavior during polarity transitions and subsequent secular variation new paleomagnetic lithologic and stratigraphic data are presented from the sediments of lake chewaucan in the summer lake basin oregon the new data place better age constraints on the sediments and improve the accuracy of the previously published paleomagnetic record from this locality a complex yet distinct waveform is observed in all three components of the paleomagnetic vector the waveform begins as the 180 190 ka pringle falls long valley summer lake ii geomagnetic excursion and continues for two cycles after the excursion until the record is interrupted by an unconformity that we correlate to the oxygen isotope stage 6 5e boundary the waveform s directional morphology in virtual geomagnetic pole vgp space is defined by two clockwise loops followed by a distinctive counterclockwise clockwise counterclockwise looping sequence the vgp paths of the two cycles after the excursion are rotated 180 about earth s spin axis with respect to the vgp paths of the excursion cycle the waveform also consists of a relative paleointensity variation which repeats during the two cycles after the excursion the average paleointensity of the postexcursion waveform repetitions is high relative to the extremely low values that occur during the excursion this observation indicates that excursion initiated secular variations can occur after the field fully recovers from the low intensities which commonly typify excursions because of the similarities noted previously between this excursion and full polarity transitions trie et al 1991 our new observations constrain models for a wide range of field behavior including polarity transitions excursions and secular variation

the effects of fire and tephra deposition on forest vegetation in the central cascades oregon high resolution charcoal and pollen analyses were used to reconstruct a 12 000 yr long fire and vegetation history of the tumalo lake watershed and to examine the short term effects that tephra deposition have on forest composition and fire regime the record suggests that from 12 000 to 9200 cal yr bp the watershed was dominated by an open pinus forest with artemisia as a common understory species fire episodes occurred on average every 115 yr beginning around 9200 cal yr bp and continuing to the present abies became more common while artemisia declined suggesting the development of a closed forest structure and a decrease in the frequency of fire episodes occurring on average every 160 yr high resolution pollen analyses before and after the emplacement of three distinct tephra deposits in the watershed suggest that nonarboreal species were most affected by tephra events and that recovery of the vegetation community to previous conditions took between 40 and 100 yr changes in forest composition were not associated with tephra depositional events or changes in fire episode frequency implying that the regional climate is the more important control on long term forest composition and structure of the vegetation in the cascade range

a framework for interpreting paleoclimatic variations in eastern beringia abstract paleoclimatic variations in a particular region can be viewed as the outcome of the superimposition of the effects of a number of large scale controls a framework for understanding paleoclimatic variations in a region can be established by considering the long term history of those controls jointly with climatic modeling results that illustrate how regional climates respond to changes of individual controls the relevant controls of late quaternary paleoclimatic variations in eastern beringia include 1 the size of the ice sheet which influences both atmospheric circulation and temperature 2 insolation which influences mainly temperature and seasonality 3 carbon dioxide concentration in the atmosphere which influences temperature and 4 feedbacks involving sea ice sea surface temperatures and snow cover which reinforce the insolation effects we review the results of a number of paleoclimatic experiments with general circulation models to illustrate the potential response of eastern beringia to the variations of these controls we then present a framework for understanding paleoclimatic variations in eastern beringia by describing the likely responses of the climate of this region to the known variations in the controls in addition we discuss key times during the quaternary when particular combinations of the controls give rise to natural experiments which lend themselves to the testing of particular hypotheses our understanding of the nature of climatic variations at high latitudes should increase through examination of paleoclimatic evidence that documents the response of the region at those key times

high elevation paleoenvironmental change during mis 6 4 in the central rockies of colorado as determined from pollen analysis abstract paleoecological studies from rocky mountain usa high elevations encompassing the previous interglacial mis 5e are rare the 10 m composite profile from the ziegler reservoir fossil site 2705 m asl of central colorado allows us to determine paleoenvironments from marine oxygen isotope stages mis 6 4 using pollen zones that are approximately equivalent to marine oxygen isotope stages during pollen zone pz 6 time pollen assemblages dominated by artemisia sagebrush suggest that alpine tundra or steppe occurred nearby the transition to pz 5e was characterized by a rapid increase in tree pollen initially picea spruce and pinus pine but also quercus oak and pseudotsuga menziesii douglas fir non arboreal pollen nap types increased during pz 5d while abies fir and juniperus juniper increased during pz 5c pollen evidence suggests that temperatures during pz 5b were as cold as during pz 6 with the site again surrounded by alpine tundra picea dominated during pz 5a before the onset of cooler conditions during pz 4 the mis 6 mis 5e transition here was similar to the mis 2 mis 1 transition at other rocky mountain sites however the ziegler reservoir pollen record contains evidence suggesting unexpected climatic trends at this site including a warmer than expected mis 5d and cooler than expected mis 5b

late glacial vegetation and climate change in western oregon abstract pollen records from two sites in western oregon provide information on late glacial variations in vegetation and climate and on the extent and character of younger dryas cooling in the pacific northwest a subalpine forest was present at little lake central coast range between 15 700 and 14 850 cal yr b p a warm period between 14 850 and 14 500 cal yr b p is suggested by an increase inpseudotsugapollen and charcoal the recurrence of subalpine forest at 14 500 cal yr b p implies a return to cool conditions another warming trend is evidenced by the reestablishment ofpseudotsugaforest at 14 250 cal yr b p increased haploxylonpinuspollen between 12 400 and 11 000 cal yr b p indicates cooler winters than before after 11 000 cal yr b p warm dry conditions are implied by the expansion ofpseudotsuga a subalpine parkland occupied gordon lake western cascade range until 14 500 cal yr b p when it was replaced during a warming trend by a montane forest a rise inpinuspollen from 12 800 to 11 000 cal yr b p suggests increased summer aridity pseudotsugadominated the vegetation after 11 000 cal yr b p other records from the pacific northwest show an expansion ofpinusfrom ca 13 000 to 11 000 cal yr b p this expansion may be a response either to submillennial climate changes of younger dryas age or to millennial scale climatic variations

methane and hydrogen sulfide seepage in the northwest peloponnesus petroliferous basin greece origin and geohazard gas seepages along the ionian coast of the northwestern peloponnesus greece at killini katakolo and kaiafas reflect deep hydrocarbon generation processes and represent a real hazard for humans and buildings methane microseepage gas concentration in offshore and onshore vents and gas dissolved in water springs including the isotopic analysis of methane have shown that the seeps are caused by thermogenic methane that had accumulated in mesozoic limestone and had migrated upward through faults or zones of weakness induced by salt diapirism a link between local seismicity and salt tectonics is suggested by the analyses of hypocenter distribution methane acts as a carrier gas for hydrogen sulfide produced by thermal sulfate reduction and or thermal decomposition of sulfur compounds in kerogen or oil methane seeps in potentially explosive amounts and hydrogen sulfide is over the levels necessary to induce toxicological diseases and lethal effects

mid holocene glacier peak and mount st helens we tephra layers detected in lake sediments from southern british columbia using high resolution techniques abstract a glacier peak tephra has been found in the mid holocene sediment records of two subalpine lakes frozen lake in the southern coast mountains and mount barr cirque lake in the north cascade mountains of british columbia canada the age depth relationship for each lake suggests an age of 5000 5080 14 c yr b p 5500 5900 cal yr b p for the eruption which closely approximates the estimated age 5100 5500 14 c yr b p of the dusty creek tephra assemblage found near glacier peak the tephra layer which has not been reported previously from distal sites and was not readily visible in the sediments was located using contiguous sampling magnetic susceptibility measurements wet sieving and light microscopy the composition of the glass in pumice fragments was determined by electron microprobe analysis and used to confirm the probable source of this mid holocene tephra layer using the same methods the a d 1481 1482 mount st helens we tephra layer was identified in sediments from dog lake in southeastern british columbia suggesting the plume drifted further north than previously thought this high resolution method for identifying tephra layers in lake sediments which has worldwide application in tephrachronologic paleoenvironmental studies has furthered our knowledge of the timing and airfall distribution of holocene tephras from two important cascade volcanoes

late quaternary vegetation in the southwestern columbia basin washington abstract a 33 000 yr pollen record from carp lake provides information on the vegetation history of the forest steppe border in the southwestern columbia basin the site is located in the pinus ponderosa zone but through much of late quaternary time the area was probably treeless pollen assemblages in sediments dating from 33 000 to 23 500 yr b p suggest a period of temperate climate and steppe coinciding with the end of the olympia interglaciation the fraser glaciation ca 25 000 10 000 yr b p was a period of periglacial steppe or tundra vegetation and conditions too dry and cold to support forests at low altitudes aridity is also inferred from the low level of the lake between 21 000 and 8500 yr b p and especially after about 13 500 yr b p about 10 000 yr b p chenopodiineae and other temperate taxa spread locally providing palynological evidence for a shift from cold dry to warm dry conditions pine woodland developed at the site with the onset of humid conditions at 8500 yr b p further cooling is suggested at 4000 yr b p when pseudotsuga and abies were established locally

determining the post glacial evolution of a northeast pacific coastal fjord using a multiproxy geochemical approachthis article is one of a series of papers published in this special issue on the theme polar climate stability network a 40 32 m piston core recovered from effingham inlet on the west coast of vancouver island provides the basis for a high resolution geochemical study of the last deglaciation and the holocene glacial retreat basin isolation sea level rise and productivity variations are determined using proxies for sediment composition k al fe al mg al grain size ti al zr al sedimentary redox conditions mo al u al and productivity wt organic carbon wt opal as local ice retreated and marine waters inundated the basin coarse grained glacimarine sediments were replaced by finer grained laminated opal rich sediments during meltwater pulse 1a the dominance of local crustal rise over eustatic sea level rise resulted in the progressive restriction of ocean circulation in effingham inlet and the formation of a temporary freshwater lake the transition into stable holocene conditions was initiated at 12 700 bp which corresponds to the onset of the younger dryas as identified by the greenland ice

environmental history and tephrostratigraphy at carp lake southwestern columbia basin washington usa sediment cores from carp lake provide a pollen record of the last ca 125 000 years that helps disclose vegetational and climatic conditions from the present day to the previous interglaciation 120 133 ka the core also contained 15 tephra layers which were characterised by electron microprobe analysis of volcanic glass shards identified tephra include mount st helens ye 3 69 ka mazama ash bed 7 54 ka mount st helens layer c 35 50 ka an unnamed mount st helens tephra 75 150 ka the tephra equivalent of layer e at pringle falls oregon 218 ka and an andesitic tephra layer similar to that at tulelake california 174 ka ten calibrated radiocarbon ages and the ages of mount st helens ye mazama ash and the unnamed mount st helens tephra were used to develop an age depth model this model was refined by also incorporating the age of marine oxygen isotope stage is boundary 4 5 73 9 ka and the age of is 5e 125 ka the justification for this age model is based on an analysis of the pollen record and lithologic data the pollen record is divided into 11 assemblage zones that describe alternations between periods of montane conifer forest pine forest and steppe the previous interglacial period is 5e supported temperate xerothermic forests of pine and oak and a northward and westward expansion of steppe and juniper woodland compared to their present occurrence the period from 83 to 117 ka contains intervals of pine forest and parkland alternating with pine spruce forest suggesting shifts from cold humid to cool temperate conditions between 73 and 83 ka a forest of oak hemlock douglas fir and fir was present that has no modern analogue it suggests warm wet summers and cool wet winters cool humid conditions during the mid wisconsin interval supported mixed conifer forest with douglas fir and spruce the glacial interval featured cold dry steppe with an expansion of spruce in the late glacial xerothermic communities prevailed in the early holocene when temperate steppe was widespread and the lake dried intermittently the middle holocene was characterised by ponderosa pine forest and the modern vegetation was established in the last 3900 yr when ponderosa pine douglas fir fir and oak were part of the local vegetation 2000 elsevier science b v all rights reserved

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

quaternary highstands in bear lake valley utah and idaho surficial deposits in bear lake valley utah and idaho demonstrate that bear lake and its surrounding wetlands expanded and contracted several times during the quaternary period deposits in 40 outcrops and the geomorphology of the valley were studied to reconstruct the water level history temporal control was provided by amino acid geochronology on 29 samples of aquatic mollusks calibrated by 14 c dating and tephrochronology samples of three molluscan genera were heated and analyzed to determine intergeneric differences in aspartic asp and glutamic glu acid racemization the covariance of asp and glu racemization in these genera was used to identify aberrant amino acid analyses the rate of glu racemization was calibrated by using a parabolic model that was used to estimate sample ages although the paucity of exposures uncertainty of the depositional setting and postdepositional uplift of deposits hamper an accurate reconstruction of water level in bear lake valley several conclusions can be drawn during the middle pleistocene lacustrine or wetland environments in northern bear lake valley may have extended up to 1830 masl meters above sea level 6000 ft twice between ca 1000 100 ka bear hollow phase during the late pleistocene the shoreline of bear lake transgressed at least three times 1 to 1817 masl 5960 ft at 47 39 cal calendar year corrected ka jensen spring phase 2 to 1814 masl 5950 ft at ca 16 15 cal ka raspberry square phase and 3 to 1814 masl at ca 9 cal ka willis ranch phase bear river currently bypasses bear lake but flowed into the lake during highstands and allowed the water level to rise to the valley threshold at nounan narrows water levels have lowered to 1806 masl 5923 ft since the middle pleistocene likely because of downcutting by bear river at nounan narrows because downcutting at nounan narrows controls the maximum attainable water level in bear lake valley effects of climate change on lake level are limited and bear lake may actually have been smaller than today when lake bonneville transgressed to its maximum shoreline during the last glacial maximum

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

quaternary history of the thatcher basin idaho reconstructed from the 87sr 86sr and amino acid composition of lacustrine fossils implications for the diversion of the bear river into the bonneville basin abstract the bear river the largest river in the great basin was diverted from its former course to the pacific ocean into the bonneville basin by quaternary basalt flows that form the northern rim of thatcher basin idaho reconstructing the history of the river s diversion is important to understanding the aquatic biogeography of the bonneville basin and the climatological implications of its lake level fluctuations this study employs strontium sr isotopes in lacustrine mollusc fossils as a tracer of bear river water that entered lake thatcher a small lake into which the redirected river flowed en route to the bonneville basin the 87sr 86sr composition and sr concentration of modern rivers were measured to construct a mixing model for lake thatcher water the low 87sr 86sr ratio of the bear river and its large discharge assures that the presence or absence of its flow into lake thatcher is readily detectable temporal control is provided by amino acid geochronology on lacustrine molluscs and calibrated using tephrochronology and 14c dating 87sr 86sr ratios of six fossil molluscs from the oldest exposed quaternary deposits in thatcher basin lower main canyon formation mcf indicate that during the early quaternary 620 ka the basin was occupied by shallow locally fed lakes a single shell from the base of the upper mcf together with sedimentological evidence suggests that the bear river may have been diverted into thatcher basin by 140 ka 87sr 86sr ratios in eight younger shells from the upper mcf indicate that the bear river was not present in the basin between 140 and 80 ka by 50 10 ka however it was tributary to lake thatcher a simple hydrologic model shows that if not for drainage through oneida narrows thatcher basin would fill to its highest shoreline under present climate even without the input of the bear river it is not clear when the lava flows that form the northern divide had been built high enough to allow lake thatcher to spill over its former southern divide into the bonneville basin but it was probably by 100 ka at that time headward incision of oneida narrows was underway by 20 ka the incision of the narrows was complete and lake bonneville had backed up into thatcher basin

the use of glass for dating volcanic ash by thermoluminescence the development of a new physical dating method for late pleistocene tephrochronometry is described here tests of laboratory procedures applied to glass from independently dated samples show that the thermoluminescence tl additive dose dating method can yield accurate ages for both proximal and distal tephra from a few hundred years to at least 400 ka the technique involves purification of 4 to 11 m glass by heavy liquid centrifugation pre tl readout heating at 50 75 c for 8 days and careful regression analysis of tl growth curves several unknown age tephra are dated directly by this method for the first time these include five ash beds from summer lake oregon 67 200 ka a sheep creek valley ash from alaska 81 9 ka an ash from nevada 200 50 ka correlated to the wadsworth tephra an unknown ash 210 30 ka from rye patch dam in nevada previously correlated to the 400 to 600 ka dibekulewe tephra and ash 9m from washtucna in eastern washington 250 30 ka

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

correlation of distal tephra layers in loess in the channeled scabland and palouse of washington state abstract thirty two distal tephra layers that are interbedded in quaternary loess at 13 sites in the channeled scabland and palouse were sampled as part of a regional study of the stratigraphy and chronology of dominantly windblown sediments on the columbia plateau an electron microprobe was used to determine the elemental composition of volcanic glass in all of the samples and also to determine the composition of ilmenite in 14 of them two of the distal tephra layers correlate with glacier peak eruptions 11 200 yr b p five with mount st helens tephra set s 13 000 yr b p and nine with mount st helens tephra set c ca 36 000 yr b p based on analysis of glass and ilmenite in reference pumices from glacier peak mount st helens mount mazama mount rainier and mount jefferson on the calculation of similarity coefficients for comparisons of both glass and ilmenite reference compositions with those of distal tephras and on considerations of stratigraphic position the composition of glass and ilmenite and the stratigraphic position of one distal tephra layer in the loess suggests that it is from an eruption of mount st helens at least several thousand years older than the set c eruptions glass composition and stratigraphic position of a distal tephra at another site in loess suggested a possible correlation with some layers of the pumice castle eruptive sequence at mount mazama ca 70 000 yr b p but similarity coefficients on ilmenite of only 45 and 48 fail to support the correlation and show why multiple correlation methods should be used similarity coefficients higher than 96 for both glass and ilmenite establish a correlation with mount st helens layer cw for distal layers in two widely separated sites these layers are in sedimentary successions that are closely associated with giant floods in the channeled scabland the 36 000 yr b p radiocarbon age of the mount st helens set c establishes a minimum limiting date for an episode of flooding that predates the widespread late wisconsin floods a correlation of distal tephra layers at two other sites in the scabland and palouse establishes a chronostratigraphic link to a still older episode of flooding within the brunhes normal polarity chron six distal tephra layers in pre late quaternary loess that are not correlated with known or dated eruptions have compositions and distinctive stratigraphic positions relative to magnetic reversal boundaries that make them key markers for future work

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

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

thermoluminescence dating of late pleistocene loess and tephra from eastern washington and southern oregon and implications for the eruptive history of mount st helens the first numeric dating of late pleistocene loess from the palouse region of eastern washington is reported this loess is interbedded with thin distal tephra layers some identified as mount st helens products both the interbedded tephra layers and thick paleosols that have developed in the loess have previously been correlated across the region a thicker correlative of one of these tephra layers mount st helens set c was collected from summer lake oregon for direct dating by thermoluminescence tl polymineral fine grain tl ages for loess from three chosen sections in washington range from 17 to 83 ka these imply ages for some tephra beds that are significantly older than implied by earlier radiocarbon 14c dating for example tl ages of 17 21 ka for loess bracketing a tephra layer correlated to mount st helens set s suggests a somewhat older age for this ash than the previously accepted 14c age of 15 5 0 5 ka cal yr corrected to calendar years tl ages of 46 6 1 ka and 57 7 ka for loess above and of 53 7 ka and 75 6 ka below a tephra bed correlated to a mount st helens set cw layer along with a tl age of 46 5 ka for fine silt sized glass from a mount st helens set cy bed in oregon revise upward from 38 ka cal yr 14c age is 36 ka b p to 50 ka the age of this regionally important marker ash set several tl ages taken together imply a much longer eruptive history for mount st helens than previously thought a tl age of 83 8 ka just below a previously undated tephra layer from mount st helens emsh ash suggests that the eruptive history of the mountain extends back to at least 80 ka furthermore age depth extrapolation through our sections to an ash wa 5c probably correlated to mount st helens suggests an eruptive history of at least 120 ka

geomagnetic field control of 14c production over the last 80 ky implications for the radiocarbon time scale we have used a recent estimate of the geomagnetic dipole field strength over the last 80 ky to examine the extent to which changes in geomagnetic field intensity have affected the radiocarbon time scale the magnetic record was converted into a 14c production signal which was then used to produce a synthetic atmospheric 14c record using a two box model for the carbon cycle this calibration suggests that the geomagnetic field has been the main factor governing the production of cosmogenic 14c atoms over the period of time considered and that 14c changes due to other causes such as climatic changes have been of lesser importance the results indicate that the radiocarbon ages are 2 to 3 ky younger than true age in the interval 18 40 ky b p in good agreement with recent u th and 14c age comparisons moreover the results predict that a negligible difference between true and 14c ages should be observed around 45 50 ky

last interglacial plant macrofossils and climates from ziegler reservoir snowmass village colorado usa abstract ninety plant macrofossil taxa from the ziegler reservoir fossil site near snowmass village colorado record environmental changes at high elevation 2705 m asl in the rocky mountains during the last interglacial period present day vegetation is aspen forest populus tremuloides intermixed with species of higher picea abies and lower artemisia quercus elevations stratigraphic units 4 13 contain montane forest taxa found near the site today and several species that today generally live at lower elevations within abies concolor lycopus americanus and outside colorado najas flexilis these data suggest near modern climatic conditions with slightly warmer summer and winter temperatures this montane forest period was succeeded by a shorter treeless interval unit 14 representing colder and or drier conditions in units 15 16 conifer trees reoccur but deciduous and herb taxa are lacking suggesting a return to warmer conditions although cooler than during the earlier forest period comparison of these inferred paleoclimatic changes with the site s geochronologic framework indicates that the lower interval of sustained warmth correlates with late mis 6 early 5b 138 94 ka the cold interval with mis 5b 94 87 ka and the uppermost cool assemblages with mis 5a 87 77 ka

geology and paleoecology of a mid wisconsin peat from the queen charlotte islands british columbia canada abstract a peat bed on east central graham island of the queen charlotte islands occurs within a nonglacial fluvial succession that is both overlain and underlain by glacial deposits radiocarbon dates of 27 500 400 and 45 700 970 yr b p at the top and base of the peat respectively indicate that it was deposited during the mid wisconsin nonglacial interval the peat is the first documented mid wisconsin organic deposit in northern coastal areas of british columbia three local pollen zones are represented the lowest zone pm 1 is restricted to sandy silt directly underlying the dated peat very high cyperaceae and moderate poaceae pollen percentages characterize zone pm 1 and a variety of other herbs are common suggesting an open landscape rather than a forested one the middle zone pm 2 is characterized by abundant pollen of picea tsuga mertensiana and cyperaceae and also contains pollen of abies a genus now absent from the queen charlotte islands graham island probably had extensive forests at this time but abundant pollen and macrofossils of cyperaceae and emergent aquatics such as hippuris vulgaris veronica scutellata potentilla palustris and menyanthes trifoliata indicate that there also were open wetland areas zone pm 3 also contains abundant arboreal pollen large amounts of sphagnum spores and selaginella selaginoides megaspores indicate succession of the wetland area at the sample site to a peat bog paleoecological analysis of the data suggests that subalpine vegetation elements were depressed by at least 400 m probably due to a cooler climate probable modern analogs in southeastern alaska and the presence of abies probably a amabilis indicate that precipitation was higher on eastern graham island during the mid wisconsin than at present

palynology and paleotemperature analysis of the whidbey formation puget lowland washington a series of pollen assemblages and the environments of deposition are shown by samples from 143 levels of interbedded sand silt clay and peaty and woody sediments in sections from the pleistocene whidbey formation at useless bay the type locality west beach point wilson and foulweather bluff deposition of the formation is interpreted to have taken place over a broad floodplain under fluvial conditions where drainage shifted between and into tracts of paludified ground of the four sections studied only useless bay and point wilson contain assemblages with analogs found in the modern pollen rain on the floodplains of the nisqually skokomish and chehalis rivers in western washington q mode factor analysis of pollen percentages in the whidbey samples extracted douglas fir pine alder grass and sedge as the principals for 93 of the data stepwise regression relating modern pollen rain and temperature resulted in a transfer function that when applied to the principals for the whidbey produced mean july temperatures for the intervals represented by the sections temperature curves for useless bay and point wilson show maxima comparable with the modern average of 15 8 c maximum values at west beach and foulweather bluff are approximately 2 lower these curves when compared with curves from late quaternary deposits and the interglacial puyallup and alderton formations indicate that sediments belonging to the whidbey are largely from an interglacial age comparable to the holocene or present interglaciation but also from cooler episodes similar to the late fraser glaciation

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr