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

u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

pollen and lignin records of late quaternary vegetation lake washington analyses of lignin oxidation products and pollen for an 11 meter core from lake washington provide independent but similar reconstructions of the late quaternary vegetation in the puget lowland an exception is in sediments of the late pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region this dissimilarity appears to result from different major provenances eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the lake washington drainage basin

the uplift history of the haiyuan liupan shan region northeast of the present tibetan plateau integrated constraint from stratigraphy and thermochronology abstractthe haiyuan liupan shan delimits the northeastern margin of the tibetan plateau we present the integrated results of new stratigraphic investigations apatite fission track analyses and related thermal history modeling tied to the structural fabric of this region these constraints provide insight into the timing of northward propagation of the plateau with 1 local relief creation and enhanced erosion in the latest jurassic to earliest cretaceous representing the local element of a complex regional far field deformation response to the lhasa qiangtang collision with the south asian margin 2 evidence for likely late cretaceous exhumation but this is uncertain given the regional sedimentary gap that exists across this interval 3 eocene relief generation as a first likely response to far field effects of the india asia collision and related to wider regional events recognized in this part of northwestern china and 4 the latest deformation episode propagating strongly into the haiyuan

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

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

postglacial vegetation and fire history eastern klamath mountains california usa pollen and high resolution charcoal data from bluff lake and crater lake california indicate simi lar changes in climate vegetation and fire history during the last 15 500 years pollen data at bluff lake suggest that the vegetation between c 15 500 and 13 100 cal bp consisted of subalpine parkland with scattered pinus and abies after 13 100 cal bp a relatively closed forest of p monticola p contorta and abies developed and fire event frequency was low the inferred climate then was cooler and wetter than present pinus and quercus vaccinifoliadominated at both sites during the early holocene when conditions were warm and dry as climate became wetter and cooler in the late holocene abies spp at both sites and tsuga mertensi ana at crater lake increased in importance displacing pinus and quercus the two lake records have similar trends in fire history with high event frequencies at c 8400 4000 and 1000 cal bp and low values at c 4800 cal bp the fire and vegetation history at both sites suggests a similar response to large scale changes in climate during the holocene

characteristic patterns of the circulation in the santa barbara channel the subtidal near surface circulation in the santa barbara channel sbc and on the shelf north of point conception is described based on observations obtained during the 3 year period from 1993 to 1995 near surface currents in the channel are a superposition of a larger than sbc scale flow and a cyclonic circulation of variable intensity located inside the channel on seasonal timescales the larger than sbc scale flow near the surface is equatorward in spring and poleward from summer through winter the increase in equatorward flow in spring occurs concurrently with the increase in equatorward wind stress and the decrease in near surface temperatures and synthetic subsurface pressures ssps the flow reverses in late spring simultaneously with the increase in the along channel ssp difference and months before wind stress has reached its peak the period during which the cyclonic circulation within the sbc is strongest coincides with the period of strongest poleward flow through the eastern entrance a synoptic description of the circulation in the sbc is presented in terms of six characteristic patterns labeled upwelling relaxation cyclonic propagating cyclones flood east and flood west an analysis of the 5 and 45 m currents into empirical orthogonal functions eofs isolates 50 53 of the 5 m 45 m low frequency current variance into three two modes combining these modes with the mean current fields the modes have spatial patterns that correspond to the characteristic flow patterns subjectively deduced from inspection of daily averages of the near surface currents from late spring through fall the two largest 5 m current modes produce a repeating pattern of circulation in which the sequence of four states namely upwelling cyclonic relaxation and quiescent is traversed roughly every 16 days in addition to the large scale cyclonicity in the central sbc smaller cyclonic eddies form frequently in the eastern channel and travel toward the west with an average speed of 0 06 m s 1 the patterns described here develop in response to the wind stress and the along channel ssp gradient

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

varied climatic and topographic influences on late pleistocene mountain glaciation in the western united states the timing of late pleistocene mountain glacier fluctuations varied widely across the western united states glaciers in the maritime olympic mountains reached local maxima 125 60 ka and 34 31 ka and were far less extensive during the global last glacial maximum lgm glaciers in the cascade mountains showed a similar general pattern but with contrasts in detailed timing most mountain glacier systems further inland exhibited maximum ice extent during marine isotope stage mis 2 in the wallowa wind river and possibly the sawtooth mountains maximum ice extent occurred ca 20 23 ka mountain glacier systems of the cordilleran ice sheet puget lobe greater yellowstone region and uinta mountains reached maximum extent ca 19 16 ka and those in the wallowa sawtooth and wind river ranges were at near maximum positions ca 17 ka the variable timing of maximum and near maximum ice advances appears to be related to climatic setting and glacier mass balance characteristics mountain glacier systems under the strongest maritime influences reached maximum extent at times of strong westerly atmospheric flow olympic and cascades glaciers appear to have been negatively influenced by weakened westerly flow at the time of the global lgm perhaps associated with ice sheet induced anticyclonic flow glacier systems with maximum advances correlative with the global lgm appear to have responded more strongly to depressed temperature the ca 17 ka ice advances of several glacier systems are broadly correlative with heinrich event 1 in the north atlantic region and imply a cooling event and reinvigoration of moisture transport into the region post lgm advances of uinta mountain glaciers appear to have arisen from moisture influences of pluvial lake bonneville copyright 2008 john wiley sons ltd

enhanced marine productivity off western north america during warm climate intervals of the past 52 k y studies of the santa barbara basin off the coast of california have linked changes in its bottom water oxygen content to millennial scale climate changes as recorded by the oxygen isotope composition of greenland ice through the use of detailed records from a sediment core collected off the magdalena margin of baja california mexico we demonstrate that this teleconnection predominantly arose from changes in marine productivity rather than changes in ventilation of the north pacific as was originally proposed

deglacial climatic oscillations in the gulf of california a high resolution accelerator radiocarbon dated climate record of the interval 8 000 18 000 years b p from deep sea drilling project site 480 guaymas basin gulf of california shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation nonlaminated sediments are associated with cooler climatic conditions during the late glacial up to 13 000 years b p and from 10 300 to 10 800 years b p equivalent to the younger dryas event of the north atlantic region we propose that the changes from laminated varved to nonlaminated sediments resulted from increased oxygen content in pacific intermediate waters during the glacial and the younger dryas episodes and that the forcing for the latter event was global in scope prominent events of low 18o are recorded in benthic foraminifera from 8 000 to 10 000 and at 12 000 years b p evidence for an earlier event between 13 500 and 15 000 years b p is weaker maximum 18o is found to have occurred 10 500 13 500 and 15 000 years ago and beyond oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of pacific waters of intermediate depth during deglaciation or environmental changes within the gulf of california region several lines of evidence suggest that during deglaciation the climate of the american southwest was marked by increased precipitation that could have lowered salinity in the gulf of california recent modelling studies show that cooling of the gulf of mexico due to glacial meltwater injection which is believed to have occurred at least twice during deglaciation would have resulted in increased precipitation with respect to evaporation in the american southwest during summertime the timing of deglacial events in the gulf of mexico and the gulf of california supports such an atmospheric teleconnection

the california current system in the southern california bight and the santa barbara channel recent observations in the santa barbara channel and over the california cooperative oceanic fisheries investigations calcofi southern california grid are used to examine seasonal circulation patterns in and near the southern california bight defined as the region east of the santa rosa ridge and including the santa barbara channel poleward flow relative to 500 m is found throughout the bight in all seasons except for spring and all subregions except the western part of the santa barbara channel in spring there is equatorward flow throughout the bight at all depths to 500 m though it tends to be surface or midcolumn intensified equatorward flow offshore of the bight present in all seasons narrows and accelerates into a jet like feature and simultaneously moves close to the santa rosa ridge in summer current meter data from the eastern entrance to the santa barbara channel are consistent with the seasonal results from the calcofi data and further show an upward propagation of phase at annual period with a phase speed of 1 to 2 m d 1 comparison with the calcofi ship winds suggests that poleward flow in the bight may be the result of positive wind stress curl through a sverdrup balance though the observed transport is only about 75 of that expected from the curl amplitude equatorward flow in the bight may be the result of coastal upwelling though the transport is larger than expected from the relatively weak winds in the bight and the offshore extent of the equatorward flow is about 10 rossby radii farther than might be expected for linearized coastal upwelling equatorward flow outside the bight cannot be explained as a sverdrup flow because the wind stress curl is positive throughout most of the region upward propagation of phase and downward propagation of energy may be indicative of forcing by remote wind equatorward of the bight given the complexity of possible forcing mechanisms for circulation in and near the bight a model that includes effects of remote wind forcing ekman pumping and topography is needed to explain the observations in a satisfactory way

holocene earthquake records from the cascadia subduction zone and northern san andreas fault based on precise dating of offshore turbidites abstract we present preliminary evidence for a 10 000 year earthquake record from two major fault systems based on sediment cores collected along the continental margins of western north america new stratigraphic evidence from cascadia demonstrates that 13 earthquakes ruptured the entire margin from vancouver island to at least the california border since the eruption of the mazama ash 7700 years ago the 13 events above this prominent stratigraphic marker have an average repeat time of 600 years and the youngest event 300 years ago coincides with the coastal record we also extend the record of past earthquakes to the base of the holocene at least 9800 years ago during which 18 events correlate along the same region the sequence of holocene events in cascadia appears to contain a repeating pattern of events a tantalizing first look at what may be the long term behavior of a major fault system the northern california margin cores show a cyclic record of turbidite beds that may represent holoce

deglacial sea level record from tahiti corals and the timing of global meltwater discharge the timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets1 and their effects on the earth s surface2 3 moreover the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans which probably disturbed the ocean s thermohaline circulation and hence global climate4 7 sea level increases bear witness to the melting of continental ice sheets but only two such records from barbados8 9 and new guinea10 11 corals have been accurately dated but these corals overlie active subduction zones where tectonic movements are large and often discontinuous especially in new guinea so the apparent sea level records may be contaminated by a complex tectonic component here we date fossil corals from tahiti which is far from plate boundaries and thus is likely to be tectonically relatively stable and remote from the locations of large former ice sheets the resulting record indicates a large sea level jump shortly before 13 800 calendar years bp which corresponds to meltwater pulse 1a in the barbados coral records8 9 the timing of this event is more accurately constrained in the tahiti record revealing that the meltwater pulse coincides with a short and intense climate cooling event12 15 that followed the initiation of the bolling allerod warm period12 16 but preceded the younger dryas cold event by about 1 000 years

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

millennial climate oscillations in ne pacific surface waters over the last 82 kyr new evidence from alkenones 1 a climate instability in the last glacial corresponding to dansgaard oeschger d o events has been already recognized in the california margin in northeast pacific detailed sea surface temperature sst changes in this region however have not been so far well elucidated here we report estimates of alkenone derived ssts with the do time scale from odp hole 1017e off point conception over the last 80 kyr our results show that alkenone ssts clearly record d o and heinrich events we also found that alkenone ssts during 82 58 ka and 18 15 ka were considerably higher and those in 15 12 ka were lower than those derived from 18o of planktonic foraminifera these results appear to reflect fluctuations of water masses

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

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

geometry and kinematic evolution of the hotan tiklik segment of the western kunlun thrust belt constrained by structural analyses and apatite fission track thermochronology abstractthe western kunlun thrust belt defines the boundary between the stable tarim basin in the north and the intensely deformed cenozoic tibetan plateau in the south because of its important tectonic position understanding its tectonic evolution should have important implications for propagation of deformation from tibet to its neighboring cratonal regions during india eurasia convergence we here present new structural analyses based on field investigations and seismic reflection profiles across the hotan tiklik segment of the western kunlun thrust belt the results indicate that the structural section crosses two major thrust zones the tiklik zone in the hinterland to the south and the hotan zone in the foreland to the north within these the hotan thrust zone is thin skinned with its deformation characterized by fault bend folding and fault slipping along detachment layers whereas the tiklik thrust zone involves basement with its deformation driven by the currently steeply dipping tiklik faul

late holocene sea level record in a core from the puget lowland washington abstract diatoms and lithological facies of an 8 45 m core collected from shine swamp 47 52 20 n lat 122 41 45 w long about 2 m above the mean tide level in the northern puget lowland reveal a rise in relative sea level during the past 6000 yr a layer of fresh water peat at a depth of 6 6 6 3 m ca 7000 5000 yr b p indicates a low stand of the sea in early and middle holocene time about 5000 yr ago the rise in relative sea level resulted in accumulation of subtidal or lower intertidal clayey gyttja and gyttja which contain mainly marine and brackish water diatoms 80 95 by about 3500 yr b p the basin had shoaled to upper intertidal levels and peat began to accumulate again while the sea continued its relative rise during the period of this continuous peat growth several alterations in fresh water and marine brackish water diatom assemblages took place indicating slight differences in the contemporaneous sea level rise and vertical peat growth

high resolution paleoceanography of the guaymas basin gulf of california during the past 15 000 years abstract deep sea drilling project site 480 27 54 10 n 111 39 34 w 655 m water depth contains a high resolution record of paleoceanographic change of the past 15 000 years for the guaymas basin a region of very high diatom productivity within the central gulf of california analyses of diatoms and silicoflagellates were completed on samples spaced every 40 50 yr whereas icp aes geochemical analyses were completed on alternate samples sample spacing 80 100 yr the bolling allerod interval 14 6 12 9 ka note ka refers to 1000 calendar years bp throughout this report is characterized by an increase in biogenic silica and a decline in calcium carbonate relative to surrounding intervals suggesting conditions somewhat similar to those of today the younger dryas event 12 9 11 6 ka is marked by a major drop in biogenic silica and an increase in calcium carbonate increasing relative percentage contributions of azpeitia nodulifera and dictyocha perlaevis a tropical diatom and silicoflagellate respectively and reduced numbers of the silicoflagellate octactis pulchra are supportive of reduced upwelling of nutrient rich waters between 10 6 and 10 0 ka calcium carbonate and a nodulifera abruptly decline at dsdp 480 while roperia tesselata a diatom indicative of winter upwelling in the modern day gulf increases sharply in numbers a nearly coincident increase in the silicoflagellate dictyocha stapedia suggests that waters above dsdp 480 were more similar to the cooler and slightly more saline waters of the northern gulf during much of the early and middle parts of the holocene 10 to 3 2 ka at about 6 2 ka a stepwise increase in biogenic silica and the reappearance of the tropical diatom a nodulifera marks a major change in oceanographic conditions in the gulf a winter shift to more northwesterly winds may have occurred at this time along with the onset of periodic northward excursions el nino driven of the north equatorial countercurrent during the summer beginning between 2 8 and 2 4 ka the amplitude of biogenic silica and wt fe al and ti proxies of terrigenous input increase possibly reflecting intensification of enso cycles and the establishment of modern oceanographic conditions in the gulf increased numbers of o pulchra after 2 8 ka suggest enhanced spring upwelling

intermittent existence of a southern californian upwelling cell during submillennial climate change of the last 60 kyr 1 application of a high resolution multiproxy approach to a sedimentary section drilled at ocean drilling program site 1017 located under a highly active upwelling cell off point conception california provides clear evidence for surface ocean productivity shifts on submillennial timescales during the last 60 kyr the proxies include bulk sediment major and minor elements organic carbon and carbonate concentrations 15n and planktonic foraminiferal species assemblage and carbon isotope determinations the collective results demonstrate that marine productivity in this area was not simply linearly related to cold and warm cycles except during the millennial scale climate oscillations of marine isotope stage mis 3 during that interval the upwelling cell and resulting high productivity were active during warm interstadial events and were largely inactive during cool stadial events however the last glacial maximum was also relatively productive productivity increased dramatically during the bolling warm interval while the allerod and younger dryas were much less productive high coccolithophorid abundance commenced during the earliest holocene after 10 ka the complexity of the productivity response was probably related to interplay between local winds as well as california undercurrent strength

paleoproductivity ventilation and organic carbon burial in the santa barbara basin odp site 893 off california since the last glacial biogenic burial rates and coccolith assemblage data were generated for the past 16 ka at odp site 893 in the santa barbara basin off california to determine if dysoxic events in the basin were related to changes in marine productivity coccolith abundance data show that changes in surface water conditions did indeed change in concert with oxygen levels at the sea floor however organic carbon burial rates varied independently indicating that oxygenation of the water column is related mainly to intermediate water ventilation a strong correlation of organic carbon burial rates with lithogenic and to a lesser extent with carbonate and opal accumulation rates confirms recent conclusions that the export of organic carbon from the sea surface is largely controlled by the presence of ballast minerals

apparent synchroneity of submillennial scale climate events between greenland and santa barbara basin california from 30 10 ka abstract evidence is presented from odp hole 893a santa barbara basin for possible synchroneity between greenland and california margin submillennial climate change records during termination 1 and the last glacial maximum lgm planktonic foraminiferal isotope and faunal records are compared to the gisp2 18o records greenland for the interval between 30 and 10 ka using a new chronology based on 38 planktonic 14c dates apparent synchronous climatic events include interstadial is events 2 3 and 4 a broad warming trend between 21 and 19 ka and a broad cooling trend between 19 and 17 ka bolling and allerod warm episodes separated by the cooler older dryas event younger dryas cool episode and the preboreal the resulting tight correlation supports an intimate teleconnection between santa barbara basin surface waters and greenland air temperatures differences between greenland and santa barbara basin suggest that some regional variations were superimposed on the global pattern of climate change e g the pre bolling warming

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

paleoceanographic history of the guaymas basin gulf of california during the past 15 000 years based on diatoms silicoflagellates and biogenic sediments high resolution records of calcium carbonate biogenic opal diatoms and silicoflagellates from western guaymas basin gravity core ggc55 and piston core jpc56 and eastern guaymas basin dsdp site 480 reveal a complex paleoceanographic history of the central gulf of california during the past 15 000 years prior to 6 2 ka the eastern and western guaymas basin proxy records were remarkably similar after conditions similar to those of today during the bolling allerod the younger dryas yd saw a major drop in diatom production coincident with increased calcium carbonate and tropical microfossils suggestive of el nino like conditions biosiliceous productivity began increasing during the latter part of the yd but it was only during the earliest holocene 11 6 to 11 0 ka that conditions similar to those of the bolling allerod returned to the central gulf between around 11 0 and 6 2 ka tropical diatoms and silicoflagellates were virtually absent from the central gulf as relatively cooler and fresher surface waters resembling those of the modern northern gulf were present in the central gulf beginning at about 6 2 ka tropical diatoms and silicoflagellates began increasing in the central gulf and coccoliths returned to western gulf sediments the onset of modern day monsoon conditions in the american southwest required the presence of warm ssts in the northern gulf which probably did not occur until after about 5 4 ka when tropical diatoms and silicoflagellates became relatively common in the central gulf modern east west contrasts which arise from late winter early spring coastal upwelling on the mainland side and lower diatom productivity on the western side of the gulf commenced between 6 2 and 5 4 ka possibly due to a shift in the direction of late winter early spring winds more towards the southeast or down the axis of the gulf this proposed wind shift might have ultimately been due to a late holocene strengthening of enso like conditions in the eastern equatorial pacific published by elsevier b v

on the preservation of laminated sediments along the western margin of north america 1 piston gravity and multicores as well as hydrographic data were collected along the pacific margin of baja california to reconstruct past variations in the intensity of the oxygen minimum zone omz gravity cores collected from within the omz north of 24 n did not contain laminated surface sediments even though bottom water oxygen bwo concentrations were close to 5 mol kg however many of the cores collected south of 24 n did contain millimeter to centimeter scale brown to black laminations in holocene and older sediments but not in sediments deposited during the last glacial maximum in addition to the dark laminations holocene sediments in soledad basin silled at 290 m also contain white coccolith laminae that probably represent individual blooms two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated holocene sediment occurring at 12 9 and 11 5 ka respectively the transition is delayed and more gradual 11 3 10 0 ka in another dated core from soledad basin the observations indicate that bottom water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors with the caveat that laminated sections should therefore not be correlated without independent age control the pattern of older sequences of laminations along the north american western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr

late glacial and early holocene sea level fluctuations in the central puget lowland washington inferred from lake sediments abstract analyses of sediments diatoms and pollen in a 12 65 m long sediment core taken from lake carpenter in the central puget lowland washington provide detailed information regarding the history of deglaciation and late glacial early holocene sea level changes the lake outlet now 8 2 m above sea level has been lowered 1 1 5 m by postglacial erosion the lithology and pollen record suggest that no lengthy hiatuses in sedimentation have occurred the basal sediments are glacialmarine and contain shell fragments and brackish marine diatoms freshwater sediments above the basal section are interrupted only by a short section containing few fossils most of which are brackish to marine indicators and by the mazama tephra at 9 5 m the pollen record in the basal 4 m reveals a pinus zone ca 13 850 11 000 yr b p with a brief peak of picea at ca 13 700 yr b p and an alnus pseudotsuga zone ca 11 000 6500 yr b p the chronology is based on nine radiocarbon ages a relative lowering of sea level below the 9 5 m threshold is recorded in the core at 12 41 m and dates 13 850 to 13 700 yr b p a marine episode occurred about 13 600 yr b p implying that relative sea level temporarily rose above 9 5 m no subsequent transgressions above the 9 5 m level have been recorded comparison of six radiocarbon dates 13 600 yr b p suggest that the marine reservoir correction of 760 yr currently used for this area may be too high for this time period

wildfire and abrupt ecosystem disruption on california s northern channel islands at the allerod younger dryas boundary 13 0 12 9 ka abstract sedimentary records from california s northern channel islands and the adjacent santa barbara basin sbb indicate intense regional biomass burning wildfire at the allerod younger dryas boundary 13 0 12 9 ka all age ranges in this paper are expressed in thousands of calendar years before present ka radiocarbon ages will be identified and clearly marked 14c years multiproxy records in sbb ocean drilling project odp site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats abrupt ecosystem disruption is evident on the northern channel islands at the allerod younger dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape these wildfires coincide with the extinction of mammuthus exilis pygmy mammoth the earliest evidence for human presence on these islands at 13 1 12 9 ka 11 000 10 900 14c years is followed by an apparent 600 800 year gap in the archaeological record which is followed by indications of a larger scale colonization after 12 2 ka although a number of processes could have contributed to a post 18 ka decline in m exilis populations e g reduction of habitat due to sea level rise and human exploitation of limited insular populations we argue that the ultimate demise of m exilis was more likely a result of continental scale ecosystem disruption that registered across north america at the onset of the younger dryas cooling episode contemporaneous with the extinction of other megafaunal taxa evidence for ecosystem disruption at 13 12 9 ka on these offshore islands is consistent with the younger dryas boundary cosmic impact hypothesis firestone r b west a kennett j p becker l bunch t e revay z s schultz p h belgya t kennett d j erlandson j m dickenson o j goodyear a a harris r s howard g a kloosterman j b lechler p mayewski p a montgomery j poreda r darrah t que hee s s smith a r stich a topping w wittke j h wolbach w s 2007 evidence for an extraterrestrial impact 12 900 years ago that contributed to the megafaunal extinctions and younger dryas cooling proceedings of the national academy of sciences 104 16016 16021

postglacial vegetation and climate of the cascade range central oregon abstract pollen data from two sites provide information on the postglacial vegetation and climate history of the cascade range indian prairie in the western cascade range was colonized by subalpine forests of pinus picea and tsuga and open meadows prior to ca 12 400 14 c yr b p the treeline lay 500 to 1000 m below its modern elevation and conditions were cooler than at present from ca 12 400 to ca 9950 14 c yr b p abies became important and the forest resembled that presently found at middle elevations in the western cascade range the pollen record implies a rise in treeline and warmer conditions than before from ca 10 000 to 4000 4500 14 c yr b p conditions that were warmer and effectively drier than today led to the establishment of a closed forest composed of pseudotsuga abies and at lower elevations quercus and corylus during this period gold lake bog in the high cascades was surrounded by closed forest of pinus and abies the early holocene pollen assemblages at both indian prairie and gold lake bog lack modern analogues and it is likely that greater than present summer radiation fostered unique climatic conditions and vegetation associations at middle and high elevations in the late holocene beginning ca 4000 4500 14 c yr b p cooler and more humid conditions prevailed and the modern vegetation was established a comparison of these sites with others in the pacific northwest suggests that major patterns of vegetational change at individual sites were a response to large scale changes in the climate system that affected the entire region

the changes in north american atmospheric circulation patterns indicated by wood cellulose general circulation model simulations suggest that during the last glacial maximum the northern circumpolar vortex intensifi ed and enlarged a glacial anticyclone developed over the laurentide ice sheet and the position of the jet stream was shifted southward however observations directly related to shifts in wind patterns across the north american continent have not yet been reported we examined tree ring cellulose from the holocene and the last glacial period for 1 covariation between precipitation 18 o and d and relative humidity and 2 variation of cellulose 18 o and d with longitude holocene isotopic features are consistent with modern moisture trajectories the isotopic features during the last glaciation are dissimilar to those in the holocene and constitute direct evidence for an expansion of the polar easterlies to latitudes as low as 40 n this is the fi rst time that moisture transport patterns have been inferred from covariation between isotopic composition in precipitation and relative humidity a technique that holds much promise for future studies of atmospheric circulation

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

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

equilibrium structure and dynamics of the california current system this paper addresses the structure and dynamical mechanisms of regional and mesoscale physical variability in the subtropical northeast pacific ocean using the regional oceanic modeling system roms the model is configured with a u s west coast domain that spans the california current system ccs with a mesoscale horizontal resolution up to as fine as 3 5 km its mean seasonal forcing is by momentum heat and water fluxes at the surface and adaptive nudging to gyre scale fields at the open water boundaries its equilibrium solutions show realistic mean and seasonal states and vigorous mesoscale eddies fronts and filaments the level of eddy kinetic energy eke in the model is comparable to drifter and altimeter estimates in the solutions with sufficiently fine resolution because the model lacks nonseasonal transient forcing the authors conclude that the dominant mesoscale variability in the ccs is intrinsic rather than transiently forced the primary eddy generation mechanism is the baroclinic instability of upwelling alongshore currents there is progressive movement of meanseasonal currents and eddy energy offshore and downward into the oceanic interior in an annually recurrent cycle the associated offshore eddy heat fluxes provide the principal balance against nearshore cooling by mean ekman transport and upwelling the currents are highly nonuniform along the coast with important influences by capes and ridges in both maintaining mean standing eddies and launching transient filaments and fronts

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

refuting the evidence for an earlier birth of the taklimakan desert in a recent issue of pnas zheng et al 1 report a late oligocene early miocene age of the taklimakan desert in northwest china their age was based on 40ar 39ar dating of biotites and u pb dating of zircons from layers within the xiyu formation which they interpreted as volcanic ash this chronology effectively extends the formation of the taklimakan desert from 5 ma as recently reported from outcrop 2 and high resolution borehole data 3 to 27 ma 1

early holocene juniper woodland and chaparral taxa in the central baja california peninsula mexico abstract a packrat midden located in the sierra san francisco baja california sur mexico dating to ca 10 200 14c yr b p contains remains of california juniper juniperus californica and other taxa now associated with southern california chaparral california juniper does not occur in the sierra san francisco today although relict populations of a few chaparral taxa still occur at higher elevations this midden record documents the early holocene occurrence of baja california coniferous woodland and chaparral vegetation far south of its present distribution or its previously known extent from other fossil records based on modern climatic tolerances of california juniper and other taxa central baja california experienced a mild mediterranean type climate at least 5 6 c cooler than the climate of today with at least twice the winter precipitation the region now receives

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

from asia to the americas by boat paleogeography paleoecology and stemmed points of the northwest pacific abstract rising postglacial seas have flooded the world s continental shelves limiting our ability to reconstruct human migrations the history of settlement along pleistocene coastlines and the antiquity of coastal shell middens this includes the southern coast of beringia where dramatic landscape changes make it difficult to test the coastal migration theory which proposes that upper paleolithic peoples followed pacific shorelines from northeast asia to the americas to help overcome such problems this paper discusses the paleogeography and paleoecology of late pleistocene north pacific coastlines then examines pacific rim technologies for possible evidence of a coastal migration by 16 000 1000 cal bp the pacific rim was a plausible migration route entirely at sea level with rich and diverse resources from both marine and terrestrial ecosystems within this vast region scattered late pleistocene technological assemblages that include leaf shaped bifaces and stemmed projectile points found in coastal or peri coastal sites from japan and kamchatka to western north america and much of south america may support the idea that a coastal migration contributed to the peopling of the americas

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

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

extensive early and middle wisconsin glaciation on the western olympic peninsula washington and the variability of pacific moisture delivery to the northwestern united states abstract large glaciers descended western valleys of the olympic mountains six times during the last wisconsin glaciation terminating in the pacific coastal lowlands the glaciers constructed extensive landforms and thick stratigraphic sequences which commonly contain wood and other organic detritus the organic material coupled with stratigraphic data provides a detailed radiocarbon chronology of late pleistocene ice margin fluctuations the early wisconsin lyman rapids advance which terminated prior to ca 54 000 14c yr b p represented the most extensive ice cover subsequent glacier expansions included the hoh oxbow 1 advance which commenced between ca 42 000 and 35 000 14c yr b p the hoh oxbow 2 advance ca 30 800 to 26 300 14c yr b p the hoh oxbow 3 advance ca 22 000 19 300 14c yr b p the twin creeks 1 advance 19 100 18 300 14c yr b p and the subsequent undated twin creeks 2 advance the hoh oxbow 2 advance represents the greatest ice extent of the last 50 000 yr with the glacier extending 22 km further downvalley than during the twin creeks 1 advance which is correlative with the global last glacial maximum local pollen data indicate intensified summer cooling during successive stadial events because ice extent was diminished during colder stadial events precipitation not summer temperature influenced the magnitude of glaciation most strongly regional aridity independently documented by extensive pollen evidence limited ice extent during the last glacial maximum the timing of glacier advances suggests causal links with north atlantic bond cycles and heinrich events

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

postglacial vegetation fire and climate history of the siskiyou mountains oregon usa the forests of the siskiyou mountains are among the most diverse in north america yet the long term relationship among climate diversity and natural disturbance is not well known pollen plant macrofossils and high resolution charcoal data from bolan lake oregon were analyzed to reconstruct a 17 000 yr long environmental history of high elevation forests in the region in the late glacial period the presence of a subalpine parkland of artemisia poaceae pinus and tsuga with infrequent fires suggests cool dry conditions after 14 500 cal yr b p a closed forest of abies pseudotsuga tsuga and alnus rubra with more frequent fires developed which indicates more mesic conditions than before an open woodland of pinus quercus and cupressaceae with higher fire activity than before characterized the early holocene and implies warmer and drier conditions than at present in the late holocene abies and picea were more prevalent in the forest suggesting a return to cool wet conditions although fire episode frequency remained relatively high the modern forest of abies and pseudotsuga and the present day fire regime developed ca 2100 cal yr b p and indicates that conditions had become slightly drier than before sub millennial scale fluctuations in vegetation and fire activity suggest climatic variations during the younger dryas interval and within the early holocene period the timing of vegetation changes in the bolan lake record is similar to that of other sites in the pacific northwest and klamath region and indicates that local vegetation communities were responding to regional scale climate changes the record implies that climate driven millennial to centennial scale vegetation and fire change should be considered when explaining the high floristic diversity observed at present in the siskiyou mountains d 2005 university of washington all rights reserved

radiocarbon age constraints on rates of advance and retreat of the puget lobe of the cordilleran ice sheet during the last glaciation abstract calibrated radiocarbon dates of organic matter below and above till of the last fraser glaciation provide limiting ages that constrain the chronology and duration of the last advance retreat cycle of the puget lobe in the central and southeastern puget lowland seven dates for wood near the top of a thick proglacial delta have a weighted mean age of 17 420 90 cal yr b p which is the closest limiting age for arrival of the glacier near the latitude of seattle a time distance curve constructed along a flowline extending south from southwestern british columbia to the central puget lowland implies an average glacier advance rate of ca 135 m yr the glacier terminus reached its southernmost limit ca 16 950 yr ago and likely remained there for ca 100 yr in the vicinity of seattle where the glacier reached a maximum thickness of 1000 m ice covered the landscape for ca 1020 yr postglacial dates constraining the timing of ice retreat in the central lowland are as old as 16 420 cal yr b p and show that the terminus had retreated to the northern limit of the lowland within three to four centuries after the glacial maximum the average rate of retreat was about twice the rate of advance and was enhanced by rapid calving recession along flowline sectors where the glacier front crossed deep proglacial lakes

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

a speleothem record of younger dryas cooling klamath mountains oregon usa awell dated d 18 o record in a stalagmite from a cave in the klamath mountains oregon with a sampling interval of 50 yr indicates that the climate of this region cooled essentially synchronously with younger dryas climate change elsewhere in the northern hemisphere the d 18 o record also indicates significant century scale temperature variability during the early holocene the d 13 c record suggests increasing biomass over the cave through the last deglaciation with century scale variability but with little detectable response of vegetation to younger dryas cooling d 2005 university of washington all rights reserved

younger dryas environments and human adaptations on the west coast of the united states and baja california on the pacific coast of the united states and baja california the younger dryas was one component of dynamic late pleistocene and holocene environmental changes changing climate sea level rise and shifting shorelines created ecological challenges for ancient coastal peoples and daunting challenges for archaeologists searching for early coastal sites this paper reviews the evidence for ecological change in this west coast region including shoreline changes that may have submerged or destroyed archaeological sites from this time period examining the regional record of human occupation dating to the younger dryas well dated coastal sites are limited to california s northern channel islands and isla cedros off baja california a small number of fluted points found in coastal areas may also date to the younger dryas but their context and chronology is not well defined review of the implications of these two data sets considers whether the early but discontinuous younger dryas archaeological record from the west coast might result from a migration of maritime peoples from northeast asia into the americas

sea surface temperature changes in the northeastern pacific ocean during the past 20 000 years and their relationship to climate change in northwestern north america abstract modern ocean atmosphere interactions in the northeastern pacific ocean have a significant effect on the climate of the west coast of north america we present radiolarian microfossil based temperature reconstructions for the eastern north pacific spanning the past 20 000 yr to examine possible correlations and linkages between continental climate change and changes in sea surface temperature sst in the northeastern pacific ocean on millennial time scales the reconstructions indicate that the regional pattern of ocean circulation off the west coast of north america was further south 15 000 cal yr b p than it is today and reached its present location 13 000 cal yr b p the north pacific drift and transition zone were further south as a result of a more southerly north pacific high pressure cell prior to 13 000 cal yr b p while two continental paleoclimate records from northwestern north america show regional differences they also can be correlated to the sst changes a coastal site at 48 n shows similar patterns in summer temperatures as observed in offshore marine records of ssts however an inland continental record seems to reflect more regional scale changes in sea surface conditions showing a thermal maximum centered at 10 000 cal yr b p which is observed in the marine transect south of 42 n we conclude based on the pattern of oceanographic change as reflected in radiolarian assemblages that changes in the past latitudinal position of the north pacific drift played a significant role in controlling continental climate immediately to its east as it does in the present environment we also conclude that during the past 20 000 yr much of the evolution of oceanographic change is related to the migration of the atmospheric pressure cells the north pacific high and aleutian low of the northeastern pacific

late quaternary climate change record from two long sediment cores from guaymas basin gulf of california modern guaymas basin gulf of california mexico is a region of high diatom productivity where exceptional preservation factors maintain biannually alternating sediment deposition as annual varves new sediment cores from guaymas basin md02 2512 and md02 2515 present the opportunity to construct climate records from below the last glacial period a low resolution age model has been constructed from oxygen isotope analysis correlation with other dated short piston cores from guaymas basin and an estimate of sedimentation rate md02 2512 from eastern guaymas basin has an age range from the holocene to late marine isotope stage 6 mis 6 md02 2515 from western guaymas basin has an age range from 8000 to 40 000 yr shipboard analyses of colour reflectance magnetic susceptibility and sediment density are combined with continuous x ray fluorescence scans to reconstruct a picture of glacial climate in the gulf of california eastern guaymas basin is affected by glacial sea level fall which results in a drastic change in productivity rates and sediment type the laminated record of mis 5 allows comparison with the holocene showing a similarity of sedimentation patterns during deglaciation and a series of very rapid variations just prior to the last glaciation in western guaymas basin there are a series of younger dryas like events during the glacial typified by low productivity and high terrigenous input long term climate and productivity changes appear to be caused by the southward displacement of the subtropical high pressure zone copyright 2005 john wiley sons ltd

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

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

terrigenous input response to glacial interglacial climatic variations over southern baja california a rock magnetic approach abstract the sediments deposited off south western baja california have recorded millennial scale fluctuations in biogenic compounds and trace metals accumulation during the last glacial period ortiz j d o connell s b delviscio j dean w e carriquiry j d marchitto t zheng y van geen a 2004 enhanced marine productivity off western north america during warm climate intervals of the past 52 ky geology 32 521 524 dean w e zheng y ortiz j d van geen a 2006 sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 ka paleoceanography 21 pa4209 since the variations in trace metals concentration appear to result from dilution with nonbiogenic matter the variability of the terrigenous sedimentation needs to be addressed therefore we performed rock magnetic and geochemical analysis on a 38 m long sediment core collected from the slope off baja california the temporal framework provided by 14c dating and identification of palaeoclimatic transitions allows assigning the sequence to the last glacial interglacial cycle last 120 ka the comparison of magnetic and geochemical properties led to retain the hypothesis of a primary modulation of iron oxides quantity and quality by terrigenous input variations with a secondary diagenetic amplification two magnetic mineral input regimes are distinguished i magnetic susceptibility variations reveal changes in titano magnetite concentration related to fluvial transport of the terrigenous fraction ii coercivity changes allow detecting variations of hematite or goethite concentrations minerals generally issued from aeolian deflation of weathered rock surfaces these two regimes are paced by two distinct climatic forcing the millennial scale changes in titano magnetite input are related to the northern hemisphere climatic variability whilst the record of wind blown magnetic mineral input contains its major power in the precessional frequency band with higher input during low insolation periods and conversely this record highlights the great sensibility of this region to high and low latitudes climatic regimes

sedimentology and magnetostratigraphy of the tierekesazi cenozoic section in the foreland region of south west tian shan in western china abstract the geology of tian shan provides an excellent example for understanding the intracontinental orogeny in the context of indian eurasian convergence previous studies leave much space in basinfill deposition process to be assessed in the regions west to the talas fergana fault tff we improve the understanding by conducting new investigations on sedimentology and magnetostratigraphy in the tierekesazi section of the foreland region of south west tian shan four lithofacies have been identified i marine lithofacies from the aertashi to bashibulake formations ii lacustrine to fluvial plain lithofacies from the keziluoyi to the middle pakabulake formations iii alluvial sand gravel sheet lithofacies in the upper pakabulake formation and iv conglomerate lithofacies from the atushi to xiyu formations magnetostratigraphic analysis accompanied with biostratigraphic correlation indicates that four lithofacies cover age intervals of ca 65 ma to 34 ma ca 22 1 ma to 12 ma 12 ma to 5 2 ma and 5 2 ma to approximately present with the sediment accumulation rates increasing from ca 2 4 3 3 3 5 compacted decompacted cm ka in the lithofacies i to 12 3 16 17 cm ka in the lithofacies ii to 16 3 19 5 20 6 cm ka in the lithofacies iii and finally to 22 8 22 8 cm ka in the lithofacies iv these results suggest three episodes of sedimentary events combined with previous results these episodes of sedimentary events are attributed to tectonic activities that are widespread along south tian shan we speculate that the oligo miocene boundary event more directly and likely marks the initial underthrusting of the tarim block beneath the south tian shan the mid miocene and mio pliocene boundary events although approximately synchronous between the regions east and west to the tff have different structural expressions in the two regions such difference is proposed to cause the dextral slipping of the tff and more fundamentally likely be driven by the northward indentation of the pamir at this time

a record of late quaternary vegetation from davis lake southern puget lowland washington abstract pollen and macrofossil analyses of a core spanning 26 000 yr from davis lake reveal late pleistocene and holocene vegetational patterns in the puget lowland the core ranges lithologically from a basal inorganic clay to a detritus gyttja to an upper fibrous peat and includes eight tephra units the late pleistocene pollen sequence records two intervals of tundra parkland vegetation the earlier of these has high percentages of picea gramineae and artemisia pollen and represents the vegetation during the evans creek stade fraser glaciation ca 25 000 17 000 yr b p the later parkland interval is dominated by picea tsuga mertensiana and gramineae it corresponds to the maximum ice advance in the puget lowland during the vashon stade fraser glaciation ca 14 000 yr b p an increase in pinus ontorta pollen between the two tundra parkland intervals suggests a temporary rise in treeline during an unnamed interstade after 13 500 yr b p a mixed woodland of subalpine and lowland conifers grew at davis lake during a period of rapid climatic amelioration in the early holocene the prolonged expansion of pseudotsuga and alnus woodland suggests dry temperate conditions similar to those of present rainshadow sites in the puget lowland more mesic forests of tsuga eterophylla thuja plicata and pseudotsuga similar to present lowland vegetation appeared in the late holocene ca 5500 yr b p

the california current of the last glacial maximum reconstruction at 42 n based on multiple proxies multiple paleoceanographic proxies in a zonal transect across the california current near 42 n record modern and last glacial maximum lgm thermal and nutrient gradients the offshore thermal gradient derived from foraminiferal species assemblages and oxygen isotope data was similar at the lgm to that at present warmer offshore but average temperatures were 3 3 1 5 c colder observed gradients require that the sites remained under the southward flow of the california current and thus that the polar front remained north of 42 n during the lgm carbon isotopic and foraminiferal flux data suggests enhanced nutrients and productivity of foraminfera in the northern california current up to 650 km offshore in contrast marine organic carbon and coastal diatom burial rates decreased during the lgm these seemingly contradictory results are reconciled by model simulations of the lgm wind field which suggest that wind stress curl at 42 n and thus open ocean upwelling increased while offshore ekman transport and thus coastal upwelling decreased during the last ice age the ecosystem of the northern california current during the lgm approximated that of the modern gulf of alaska cooling and production in this region was thus driven by stronger open ocean upwelling and or southward flow of high latitude water masses rather than by coastal upwelling

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

millennial pulsing of environmental change in southern california from the past 24 k y a record of indo pacific enso events century long variations in coastal california vegetation inferred from polliniferous sediments deposited in the santa barbara basin record a succession of brief 14 c yr b p ka these millennial scale pulses many of which correspond with western great basin hydrological fluctuations are also linked to events of southwest monsoon intensification in southern asia we suggest that these correlative high frequency variations in the asian summer and northeast pacific winter climates may reflect submillennial scale el nino southern oscillation enso type forcing involving water vapor transport over the indian and pacific oceans

a 14 300 year long record of fire vegetation climate linkages at battle ground lake southwestern washington high resolution macroscopic charcoal analysis was used to reconstruct a 14 300 year long fire history record from the lower columbia river valley in southwestern washington which was compared to a previous vegetation reconstruction for the site in the late glacial period ca 14 300 13 100 cal yr bp pinus picea dominated parkland supported little to no fire activity from the late glacial to the early holocene ca 13 100 10 800 cal yr bp pseudotsuga abies dominated forest featured more frequent fire episodes that burned mostly woody vegetation in the early to middle holocene ca 10 800 5200 cal yr bp quercus dominated savanna was associated with frequent fire episodes of low to moderate severity with an increased herbaceous i e grass charcoal content from the middle to late holocene ca 5200 cal yr bp to present forest dominated by pseudotsuga thuja type and tsuga heterophylla supported less frequent but mostly large or high severity fire episodes fire episodes were least frequent but were largest or most severe after ca 2500 cal yr bp the fire history at battle ground lake was apparently driven by climate directly through the length and severity of the fire season and indirectly through climate driven vegetation shifts which affected available fuel biomass

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

fire and vegetation history on santa rosa island channel islands and long term environmental change in southern california the long term history of vegetation and fire was investigated at two locations soledad pond 275 m from ca 12 000 cal a bp and abalone rocks marsh 0 m from ca 7000 cal a bp on santa rosa island situated off the coast of southern california a coastal conifer forest covered highlands of santa rosa during the last glacial but by ca 11 800 cal a bp pinus stands coastal sage scrub and grassland replaced the forest as the climate warmed the early holocene became increasingly drier particularly after ca 9150 cal a bp as the pond dried frequently and coastal sage scrub covered the nearby hillslopes by ca 6900 cal a bp grasslands recovered at both sites pollen of wetland plants became prominent at soledad pond after ca 4500 cal a bp and at abalone rocks marsh after ca 3465 cal a bp diatoms suggest freshening of the abalone rocks marsh somewhat later probably by additional runoff from the highlands introduction of non native species by ranchers occurred subsequent to ad 1850 charcoal influx is high early in the record but declines during the early holocene when minimal biomass suggests extended drought a general increase occurs after ca 7000 cal a bp and especially after ca 4500 cal a bp the holocene pattern closely resembles population levels constructed from the archaeological record and suggests a potential influence by humans on the fire regime of the islands particularly during the late holocene copyright 2009 john wiley sons ltd

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

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

nitrogen isotopic variations in the gulf of california since the last deglaciation response to global climate change high resolution records of the nitrogen isotopic composition of organic matter 15norg opal content and opal accumulation rates from the central gulf of california reveal large and abrupt variations during deglaciation and gradual holocene changes coincident with climatic changes recorded in the north atlantic homogenous sediments with relatively low 15norg values and low opal content were deposited at the end of the last glacial period during the younger dryas event and during the middle to late holocene in contrast laminated sediments deposited in the two deglacial stages are characterized by very high 15norg values 14 and opal accumulation rates 29 41 mg cm 2 yr 1 abrupt shifts in 15norg were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling vertical mixing and or the latitudinal position of the intertropical convergence zone

palynologic and geomorphic evidence for environmental change during the pleistocene holocene transition at point reyes peninsula central coastal california abstract three sites on the point reyes peninsula california provide evidence of major environmental change during the pleistocene holocene transition a 12 300 yr long pollen record from coast trail pond reveals a change from closed canopy pseudotsuga abies forest to coastal scrub and grassland about 10 000 yr b p the same change is also evident in pollen records from two sea cliff exposures that contain a series of buried soils interstratified with fluvial and debris flow deposits eight radiocarbon dates from these exposures indicate that aggradation at both sites began ca 12 000 yr b p and that the change from forest to scrub and grassland occurred between 10 300 and 9400 yr b p high percentages of alder pollen and bracken fern spores reflect repeated geomorphic disturbance at ca 10 400 yr b p the occurrence of major aggradation accompanied by recurrent debris flows between ca 12 000 and 10 000 yr b p suggests that this was a period of more frequent high intensity storms