glacial outburst floods and loess sedimentation documented during oxygen isotope stage 4 on the columbia plateau washington state abstract stratigraphy and age control of late pleistocene loess associated glacial outburst flood deposits and flood cut unconformities in the channeled scabland washington state united states indicate a significant cordilleran ice sheet advance during marine oxygen isotope stage 4 glacial outburst flood deposits from stage 2 classic bretz flood deposits ca 21 to 13 ka and related features in the channeled scabland overlie a widespread layer of loess that contains buried soils and the mount st helens set c tephra ca 46 ka this loess in turn overlies deposits of the penultimate episode of giant outburst floods and an unconformity cut by those floods regional trends in the thickness texture and overall composition of the older loess are strikingly similar to those from the youngest loess known to be derived from stage 2 flood deposits we conclude that the older loess also is derived from fine grained flood deposits luminescence ages tephrochronology and soil development rates indicate that the bulk of deposition of the older loess occurred during stage 3 following glacial outburst flooding marked by a regional flood cut unconformity the apparent cyclical pattern of cold climate buried soils flood deposits and thick loess accumulations demonstrate that sediment supply renewed by flood episodes is a major control on accumulation of loess on glacial timescales

millennial scale climate variability of the northeast pacific ocean and northwest north america based on radiolaria and pollen abstract radiolaria and pollen abundances in marine sediment cores from the northeast pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle 0 150 kyr these data allow direct comparison of the climate response of continental and oceanic systems detailed 18 o and ams 14 c measurements provide a link into global stratigraphic frameworks canonical correlation analysis extracts two modes of variation common to both the radiolaria and pollen records the first mode of variation correlates an assemblage of radiolaria associated with coastal upwelling with increased redwood western hemlock and alder pollen this association is consistent with the modern relationship between coastal upwelling coastal fog and redwood forests a second canonical mode relates an oceanic fauna now found in highest abundance in the far north pacific with reduced pine and western hemlock pollen abundance comparison of these records to an ice core 18 o record suggests that at wavelengths 3000 years warm events in greenland are correlated to intervals of increased coastal upwelling off oregon decreases in importance of very cold north pacific fauna suggesting warming and increases in pollen associated with wetter coastal environments radiolarian based sea surface temperature estimates suggest that the variability of the northeast pacific on this time scale is about 2 c warming in the coastal regions reflects reduced advection of the california current but is moderated by increases in cool coastal upwelling we infer that the response of the northeast pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid to high latitudes preliminary analysis suggests that oceanic variability off oregon at wavelengths 18 o records this variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements this finding suggests that unlike longer period millennial scale events the propagation of the shorter wavelength events to the northeast pacific is through subtropical or tropical teleconnections

age model for a continuous ca 250 ka quaternary lacustrine record from bear lake utah idaho abstract the quaternary sediments sampled by continuous 120 m long drill cores from bear lake utah idaho comprise one of the longest lacustrine sequences recovered from an extant lake the cores serve as a good case study for the construction of an age model for sequences that extend beyond the range of radiocarbon dating from a variety of potential age indicators we selected a combination of radiocarbon ages one magnetic excursion correlated to a standard sequence and a single uranium series age to develop an initial data set the reliability of the excursion and u series data require consideration of their position with respect to sediments of inferred interglacial character but not direct correlation with other paleoclimate records data omitted from the age model include amino acid age estimates which have a large amount of scatter and tephrochronology correlations which have relatively large uncertainties because the initial data set was restricted to the upper half of the bl00 1 core we inferred additional ages by direct correlation to the independently dated paleoclimate record from devils hole we developed an age model for the entire core using statistical methods that consider both the uncertainties of the original data and that of the curve fitting process with a combination of our initial data set and the climate correlations as control points this age model represents our best estimate of the chronology of deposition in bear lake because the age model contains assumptions about the correlation of bear lake to other climate records the model cannot be used to address some paleoclimate questions such as phase relationships with other areas

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

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

variations in fire frequency and climate over the past 17 000 yr in central yellowstone national park a 17000 yr fire history from yellowstone national park demonstrates a strong link between changes in climate and variations in fire frequency on millennial time scales the fire history reconstruction is based on a detailed charcoal stratigraphy from cygnet lake in the rhyolite plateau region macroscopic charcoal particles were tallied from contiguous 1 cm samples of a 6 69 m long core and the data were converted to charcoal accumulation rates at evenly spaced time intervals intervals of high charcoal accumulation rates were interpreted as local fire events on the basis of information obtained from modern charcoal calibration studies in the yellowstone region the record indicates that fire frequency was moderate 4 fires 1000 yr during the late glacial period reached highest values in the early holocene 10 fires 1000 yr and decreased after 7000 calendar yr b p the present fire regime 2 3 fires 1000 yr was established in the past 2000 yr the charcoal stratigraphy correlates well with variations in july insolation through time which suggests that regional climate changes are responsible for the long term variations in fire frequency in the early holocene summer insolation was near its maximum which resulted in warmer effectively drier conditions throughout the northwestern united states at this time the fire frequency near cygnet lake was at its highest after 7000 calendar yr b p summer insolation decreased to present values the regional climate became cooler and wetter and fires were less frequent the cygnet lake record suggests that long term fire frequencies have varied continuously with climate change even when the vegetation has remained constant

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

geomorphology of the burnt river eastern oregon usa topographic adjustments to tectonic and dynamic deformation abstract eastern oregon contains the deepest gorge in north america where the snake river cuts vertically down 2300 m this deep gorge is known as hells canyon a landscape containing such a topographic feature is likely undergoing relatively recent deformation study of the burnt river a tributary to the snake river at the upstream end of hells canyon yields data on active river incision in eastern oregon indicating that quaternary faults are a first order control on regional landscape development through 1 24 000 scale geologic mapping a 500 000 year record of fluvial incision along the burnt river was constructed and is chronologically anchored by optically stimulated luminescence dating and tephrochronology analyses a conceptual model of fluvial terrace formation was developed using these ages and likely applies to other non glaciated catchments in eastern oregon mapped terraces inferred to have formed during glacial interglacial cycles provide constraints on rates of incision of the burnt river incision through these terraces indicates that the burnt river is down cutting at 0 15 to 0 57 m kyr 1 this incision appears to reflect a combination of local base level adjustments tied to movement along the newly mapped durkee fault and regional base level control imposed by the downcutting of the snake river deformation of terraces as young as 38 7 5 1 ka indicates quaternary activity along the durkee fault and when combined with topographic metrics slope relief hypsometry and stream steepness reveals a landscape in disequilibrium longer wavelength lithospheric dynamics delamination and crustal foundering that initiated in the miocene may also be responsible for continued regional deformation of the earth s surface

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

orbital and millennial scale vegetation and climate changes of the past 225 ka from bear lake utah idaho usa continuous high resolution pollen data for the past 225 ka from sediments in bear lake utah idaho reflect changes in vegetation and climate that correlate well with variations in summer insolation and global ice volume during mis 1 through 7 spectral analysis of the pollen data identified peaks at 21 22 and 100 ka corresponding to periodicities in earth s precession and eccentricity orbital cycles suborbital climatic fluctuations recorded in the pollen data denoted by 6 and 5 ka cyclicities are similar to greenland atmospheric temperatures and north atlantic ice rafting heinrich events our results show that millennial scale climate variability is also evident during mis 5 6 and 7 including the occurrence of heinrich like events in mis 6 showing the long term feature of such climate variability this study provides clear evidence of a highly interconnected ocean atmosphere system during the last two glacial interglacial cycles that extended its influence as far as continental western north america our study also contributes to a greater understanding of the impact of long term climate change on vegetation of western north america such high resolution studies are particularly important in efforts of the scientific community to predict the consequences of future climate change r 2007 elsevier ltd all rights reserved

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

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

the use of paleoceanographic proxies in carbonate periplatform settings opportunities and pitfalls in a sediment core from the leeward side of the great bahama bank ocean drilling program odp leg 166 1006a 24h early pliocene several paleoceanographic proxies were compared with carbonate mineralogy the proxies measured on the planktonic foraminifera species globigerinoides sacculifer are mg ca and sr ca elemental ratios and 18o values these proxies are widely used in pelagic sediments to derive parameters of water masses such as paleo temperature and salinity to produce quantitative estimates it is necessary to verify that the primary shell mineralogy of the foraminifera was not altered diagenetically diagenetic alteration can be rapid in periplatform settings relative to pelagic deep sea sediments since the meta stable carbonate phases provide an additional driving force for recrystallisation we show that the sr ca ratio of foraminiferal calcite can be used to assess the degree of diagenetic alteration of their shell chemistry using this method we demonstrate that the primary signal in the oxygen isotope ratios is preserved in the studied core in the mg ca record the relative change of foraminiferal mg ca ratios seems to be preserved but absolute values are influenced by diagenesis the second set of proxies comprises 13c and c n ratios of organic carbon these are used in pelagic sediments in order to assess the origin of organic carbon terrestrial or marine phytoplankton it is demonstrated here that a simple two end mixing model cannot explain the observed co occurrence of relatively high 13corg and c n values as the 13corg values co vary with the aragonite content we attribute this signature to varying contribution of organic carbon from benthic algae which are also the major aragonite producers on the platform top

holocene fire and vegetation along environmental gradients in the northern rocky mountains abstract holocene records of fire vegetation and climate were reconstructed from four sites in the bitterroot range region of the northern rocky mountains in order to examine the vegetation and fire histories and evaluate the hypothesis proposed by whitlock and bartlein 1993 regarding the effects of increased summer insolation on precipitation patterns vegetation history in the series of sites was broadly similar in the late glacial period the pollen data suggest open parkland dominated by picea or alpine meadow which reflect conditions cooler and drier than present these open forests were replaced in the early to middle holocene by forests composed mainly of pinus and pseudotsuga which suggest conditions warmer than present modern forest compositions were in place by ca 3000 cal yr bp and small variations in the timing of the vegetation shifts reflect local differences among sites the long term trends in fire occurrence support the hypothesis proposed by whitlock and bartlein 1993 that precipitation regimes were sharpened during the early holocene summer insolation maximum but their location has remained unchanged as a result of topographic constraints sites located in areas currently summer dry were drier than present during the early holocene and fires were more frequent conversely sites located in the areas that are summer wet at present were wetter than present in the early holocene and fires were less frequent on millennial time scales it appears that the climate boundary is controlled by topography and does not shift

late quaternary vegetation and climatic history of the long valley area west central idaho u s a abstract paleoenvironmental data including pollen and sediment analyses radiocarbon ages and tephra identifications of a core recovered from a fen provide a ca 16 500 14c yr b p record of late quaternary vegetation and climate change in the long valley area of west central idaho the fen was deglaciated prior to ca 16 500 14c yr b p after which the pollen rain was dominated by artemisia suggesting that a cold dry climate prevailed until ca 12 200 14c yr b p from ca 12 200 to 9750 14c yr b p temperatures gradually increased and a cool moist climate similar to the present prevailed during this period a closed spruce pine forest surrounded the fen this cool moist climate was briefly interrupted by a dry and or cold interval between ca 10 800 and 10 400 14c yr b p that may be related to the younger dryas climatic oscillation from ca 9750 to 3200 14c yr b p the regional climate was significantly warmer and drier than at present and an open pine forest dominated the area around the fen maximum aridity occurred after the deposition of the mazama tephra ca 6730 14c yr b p after 3200 14c yr b p regional cooling brought cool moist conditions to the area the establishment of the modern montane forest around the fen and present day cool and moist climate began at ca 2000 14c yr b p

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

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

a 180 000 year pollen record from owens lake ca terrestrial vegetation change on orbital scales abstract pollen from the upper 90 m of core ol 92 from owens lake is a climatically sensitive record of vegetation change that indicates shifts in the plant associations representing warm and cold desertscrub pinyon juniper woodland and pine fir forest during the past 180 000 years these changes are synchronized with glacial interglacial cycles during glacial and stadial climates juniper woodland expanded downslope and replaced warm desert shrubs while upper montane and subalpine forests in the arid inyo mountains also expanded and those in the sierra nevada were displaced by the ice cap and periglacial conditions conversely during interglacial and interstadial climates warm desert plants expanded their range in the lowlands juniper and sagebrush retreated upslope and montane and subalpine forests expanded in the sierra nevada the reconstructed vegetation history demonstrates a regional climatic response and the congruence of the pollen sequence with marine and ice cap oxygen isotope stratigraphies suggests a link between regional vegetation and global climate change at orbital scales

a 7600 yr vegetation and fire history from anthony lake northeastern oregon usa with linkages to modern synoptic climate patterns we used pollen and high resolution charcoal analysis of lake sediment to reconstruct a 7600 yr vegetation and fire history from anthony lake located in the blue mountains of northeastern oregon from 7300 to 6300 cal yr bp the forest was composed primarily of populus and fire was common indicating warm dry conditions from 6300 to 3000 cal yr bp populus declined as pinus and picea increased in abundance and fire became less frequent suggesting a shift to cooler wetter conditions from 3000 cal yr bp to present modern day forests composed of pinus and abies developed and from 1650 cal yr bp to present fires increased we utilized the modern climate analogue approach to explain the potential synoptic climatological processes associated with regional fire the results indicate that years with high fire occurrence experience positive 500 mb height anomalies centered over the great basin with anomalous southerly component of flow delivering dry air into the region and with associated sinking motions to further suppress precipitation it is possible that such conditions became more common over the last 1650 cal yr bp supporting an increase in fire despite the shift to more mesic conditions

vegetation responses to quaternary volcanic and hydrothermal disturbances in the northern rocky mountains and greater yellowstone ecosystem usa abstract volcanic and hydrothermal processes produce disturbances by diverse mechanisms and ecological responses are varied new and published pollen records from the northern rocky mountains and greater yellowstone ecosystem document the response of vegetation to three different types of volcanic and hydrothermal disturbances 1 pleistocene rhyolite lava flows in the central greater yellowstone ecosystem created infertile landscapes that have shaped vegetation since rhyolite emplacement nutrient poor well drained soils that developed on these flows supported low diversity grassland during late glacial time and pinus contorta forests in interglacial periods 2 ash layers from eruptions of pacific northwest stratovolcanoes are commonly preserved in lake sediment records in the northern rocky mountains and associated pollen records show enhancement of steppe vegetation for years to decades 3 local hydrothermal explosions have resulted in vegetation changes in hydrothermal areas that indicate tree mortality following deposition of explosion debris followed by recovery in years thus the type and duration of the vegetation response to volcanic and hydrothermal disturbances are highly contextual and governed by the antecedent plant communities and the magnitude and mechanism of the volcanic or hydrothermal disturbance vegetation resilience varied between disturbances ranging from enduring ecosystem parameter changes to short lived state changes in resilient plant communities

a full holocene tephrochronology for the kamchatsky peninsula region applications from kamchatka to north america abstract geochemically fingerprinted widespread tephra layers serve as excellent marker horizons which can directly link and synchronize disparate sedimentary archives and be used for dating various deposits related to climate shifts faulting events tsunami and human occupation in addition tephras represent records of explosive volcanic activity and permit assessment of regional ashfall hazard in this paper we report a detailed holocene tephrochronological model developed for the kamchatsky peninsula region of eastern kamchatka nw pacific based on 2800 new electron microprobe analyses of single glass shards from tephra samples collected in the area as well as on previously published data tephra ages are modeled based on a compilation of 223 14c dates including published dates for shiveluch proximal tephra sequence and regional marker tephras new ams 14c dates and modeled calibrated ages from the krutoberegovo key site the main source volcanoes for tephra in the region are shiveluch and kliuchevskoi located 60 100 km to the west in addition local tephra sequences contain two tephras from the plosky volcanic massif and three regional marker tephras from ksudach and avachinsky volcanoes located in the eastern volcanic front of kamchatka this tephrochronological framework contributes to the combined history of environmental change tectonic events and volcanic impact in the study area and farther afield this study is another step in the construction of the kamchatka wide holocene tephrochronological framework under the same methodological umbrella our dataset provides a research reference for tephra and cryptotephra studies in the northwest pacific the bering sea and north america

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

interglacial theme and variations 500 k y of orbital forcing and associated responses from the terrestrial and marine biosphere u s pacific northwest sediments collected off northern california by ocean drilling program leg 167 contain time series that show strong orbitally driven insolation forcing of surface oceanographic conditions orbital forcing caused a strong response in the distribution of major terrestrial vegetation but a less predictable response for primary productivity offshore terrestrial vegetation responded primarily to regional sea surface temperature sst coastal ocean productivity appears highest when sst is moderately high not during peak interglacial conditions nor during insolation maxima when individual interglacial intervals are examined closely each has a different signature two of six interglacials mis marine isotope stage 5 and mis 11 have higher sst than modern conditions but each elicits a different response from the terrestrial and marine communities the type of vegetation and the strength of upwelling vary between interglacials depending on the relative strength of factors that drive the warming including insolation ice cap size and level of greenhouse gases

evidence for millennial scale climate change during marine isotope stages 2 and 3 at little lake western oregon u s a pollen and geochemical data from little lake western oregon suggest several patterns of millennial scale environmental change during marine isotope stage mis 2 14 100 27 600 cal yr b p and the latter part of mis 3 27 600 42 500 cal yr b p during mis 3 a series of transitions between warm and cold adapted taxa indicate that temperatures oscillated by ca 2 4 c every 1000 3000 yr highs and lows in summer insolation during mis 3 are generally associated with the warmest and coldest intervals warm periods at little lake correlate with warm sea surface temperatures in the santa barbara basin changes in the strength of the subtropical high and the jet stream may account for synchronous changes at the two sites during mis 2 shifts between mesic and xeric subalpine forests suggest changes in precipitation every 1000 3000 yr increases in tsuga heterophylla pollen at 25 000 and 22 000 cal yr b p imply brief warmings minimum summer insolation and maximum global ice volumes during mis 2 correspond to cold and dry conditions fluctuations in precipitation at little lake do not correlate with changes in the santa barbara basin and may be explained by variations in the strength of the glacial anticyclone and the position of the jet stream c 2001 university of washington

climate and vegetation since the last interglacial mis 5e in a putative glacial refugium northern idaho usa abstract there are very few terrestrial sediment records from north america that contain a nearly continuous sequence spanning from the last interglacial period to the present we present stratigraphic records of pollen and several other proxies from a carex dominated wetland star meadows located 140 km south of the maximum extent of the cordilleran ice sheet and near the current southern extent of interior mesic forests in northern idaho many species in this region are disjunct by 160 km of arid steppe and dry forest from their more extensive distribution along the pacific northwest coast and may have survived in an interior refugium the chronology for the upper 251 cm was determined by six radiocarbon dates and one tephra deposit and the age of the remainder of the core 251 809 cm was estimated by correlation with specmap 18 o fluctuating water levels were inferred from alternating peat biogenic silica and aquatic pollen types during mis 5e the region was warmer and drier than today and was dominated by pinus likely pinus contorta mixed conifer forest surrounding a carex meadow a cool moist climate mis 5b 5d soon developed and the site was inundated with deep water pollen indicated wetland vegetation betula glandulosa typhaceae and salix developed around a lake with a pseudotsuga larix and picea forest on the surrounding slopes during mis 5a a warmer climate supported a pseudotsuga larix abies and picea forest on the surrounding hillsides and a carex dominated environment within a dry meadow from mis 4 to mis 3 a cool and wet pinus and picea forest predominated water levels rose enabling nuphar to persist within a perennial lake while a sedge fen established along the lake margin as climate transitioned into mis 2 a cooler and drier climate supported a pinus and picea subalpine parkland though water levels remained high enough to support nuphar during the last glacial maximum the sediment was mainly silt and clay with high artemisia and very poor pollen preservation glaciers descended to 500 m elevation above star meadows in adjacent drainages suggesting a periglacial environment occurred at the site lake level decreased through the pleistocene holocene transition ca 11 7 ka and the site returned to a sedge peatland surrounded by an open pinus forest the most striking vegetation change occurred in the middle to late holocene with the first occurrence and then later dominance of cupressaceae pollen most likely thuja plicata which is a dominant species in modern interior mesic forests the late holocene vegetation was uniquely mesic in the context of the last 120 000 years casting doubt on this region serving as a glacial refugium

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

prehistoric human responses to volcanic tephra fall events in the ust kamchatsk region kamchatka peninsula kamchatsky krai russian federation during the middle to late holocene 6000 500 cal bp abstract prehistoric peoples in kamchatka coped with recurrent volcanic tephra fall events during the middle to late holocene recent data collected by the international collaborative circumpolar archaeological project icaap between 2009 and 2011 explores the long term relationships between drastic landscape change and concomitant human response a combination of new archaeological paleoenvironmental and tephrochronological data demonstrate how the major ksudach 1750 cal bp ks1 eruption accelerated settlement relocation from the interior to the paleo coastline

fire and vegetation history during the last 3800 years in northwestern montana abstract foy lake in northwestern montana provides a record of annual to decadal scale landscape change sedimentary charcoal and pollen analyses were used to document fire and vegetation changes over the last 3800 years which were then compared to similar records from ad 1880 to 2000 the long term record at foy lake suggests shifts between forest and steppe as well as changes in fire regime that are likely the result of climate change fire activity inferred from the frequency of charcoal peaks averaged 18 fire episodes 1000 years from 3800 to 2125 cal year bp and increased from 16 fire episodes 1000 years at 2125 cal year bp to 22 episodes 1000 years at 750 cal year bp a period when the pollen data suggest that steppe vegetation yielded to increasing patches of forest cover between 2125 and 750 cal year bp increased forest cover produced more background charcoal than before and after this period when vegetation was dominated by steppe between 750 and 75 cal year bp steppe has expanded and fire episode frequency averaged 33 episodes 1000 years increasing to a maximum of 40 episodes 1000 years at ca 300 cal year bp and then decreasing to present levels since ad 1880 the pollen record indicates an increase in shrubs and grasses from ad 1895 to 1960 as a result of vegetation changes associated with timber harvesting and livestock grazing no fires have been documented in the foy lake watershed since ad 1880 charcoal from the extralocal fires of ad 1910 burning over 4 111 249 ha in idaho montana and wyoming however is present in foy lake between ad 1970 and 2000 increased arboreal pollen in the record is consistent with observations that the forest has become more closed the activities of euro americans have led to a decline in forest cover between ad 1880 and 1970 followed by a recent increase as trees are now growing in areas previously occupied by steppe euro americans are likely the cause of a reduction in fire activity in watershed since ad 1880

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

glacial cycles and astronomical forcing narrow spectral features in ocean sediment records offer strong evidence that the cycles of glaciation were driven by astronomical forces two million years ago the cycles match the 41 000 year period of earth s obliquity this supports the croll milankovitch theory which attributes the cycles to variations in insolation but for the past million years the spectrum is dominated by a single 100 000 year feature and is a poor match to the predictions of insolation models the spectrum can be accounted for by a theory that derives the cycles of glaciation from variations in the inclination of earth s orbital plane

evidence for an additional heinrich event between h5 and h6 in the labrador sea 1 an additional heinrich ice rafting event is identified between heinrich events 5 and 6 in eight cores from the labrador sea and the northwest atlantic ocean it is characterized by sediment rich in detrital carbonate 40 caco3 with high concentration of floating dropstones high coarse fraction 150 m content and has a sharp contact with the underlying but grades into the overlying hemipelagic sediment it also shows lighter 18onpl values indicating freshening due to iceberg rafting and or meltwater discharge this event is correlated with dansgaard oeschger event 14 and interpreted as an additional heinrich event h5a the thickness of h5a in the labrador sea reaches up to 220 cm this additional heinrich event has also been reported in cores ps2644 and so82 5 from the northern north atlantic with the recognition of h5a the temporal spacing between heinrich events 1 to 6 becomes more uniform 7 ka

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

postglacial fire vegetation and climate history in the clearwater range northern idaho usa the environmental history of the northern rocky mountains was reconstructed using lake sediments from burnt knob lake idaho and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large scale climate changes during the holocene vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold dry conditions from 14 000 to 12 000 cal yr b p abundant pinus pollen suggests warmer moister conditions than the previous period most sites record the development of a forest with pseudotsuga ca 9500 cal yr b p indicating warm dry climate coincident with the summer insolation maximum as the amplification of the seasonal cycle of insolation waned during the middle holocene pseudotsugawas replaced by pinus and abies suggesting cool moist conditions the fire reconstructions show less synchroneity in general the sites west of the continental divide display a fire frequency maximum around 12 000 8000 cal yr b p which coincides with the interval of high summer insolation and stronger than present subtropical high the sites on the east side of the continental divide have the highest fire frequency ca 6000 3500 cal yr b p and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late holocene this study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher than present fire frequency occurred in the past

130 000 yr continuous pollen record from clear lake lake county california pollen analysis of a 115 m sediment core from clear lake lake county california provides a climatic record that is continuous for the past 130 000 yr the pollen record reflects migrations of the tree species of the california coast ranges in response to the climatic changes of the last glacial cycle during interglacials the clear lake pollen rain was dominated by quercus oak pollen during cooler periods oak pollen was replaced by pollen of coniferous species the curve for quercus pollen strongly resembles and is used to correlate with both deep sea oxygen isotope curves and the climatic record from certain european pollen studies

the impact of mt mazama tephra deposition on forest vegetation in the central cascades oregon usa the eruption of mt mazama c 7630 yr bp was the largest north american volcanic event during the holocene high resolution pollen and charcoal analyses were used to examine the impact of mt mazama tephra on forest vegetation and possible synergistic interactions with fire activity in the central oregon cascade range we selected four small watersheds on a longitudinal transect north of mt mazama and recovered lake sediment that spanned the period of tephra deposition our sediment records had between 14 and 50 cm of tephra deposited and we analyzed the sediment at centimeter resolution before and after the deposition horizon in each sediment record our analysis shows that nonarboreal pollen percentages and accumulation rates were depressed after mazama tephra deposition recovery to pre tephra deposition rates occurred after approximately 50 100 years arboreal pollen percentage and accumulation rates were less severely impacted suggesting that the mazama tephra deposition disrupted understory communities more significantly than overstory species and that forest communities returned to their pre tephra deposition conditions after approximately 50 100 years fire events in conjunction with the mazama tephra occurred in two of the four sites suggesting that tephra deposition did not create conditions that precipitated a fire event in a consistent way this research reinforces the notion that disturbance events may have cumulative effects on forest vegetation but that the impacts of disturbance events need to be felt by similar constituents of the forest ecosystem to be truly additive

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event