the oxygen isotopic compositions of silica phytoliths and plant water in grasses implications for the study of paleoclimate abstract information about climatic conditions during plant growth is preserved by the oxygen isotope composition of biogenic silica phytoliths deposited in grasses the oxygen isotope composition of phytolith silica is dependent on soil water 18 o values relative humidity and evapotranspiration and temperature during plant growth phytolith and plant water 18 o values for c3 a breviligulata and c4 c longifolia grasses from natural and greenhouse sites in southwestern ontario were used to compare the isotopic fractionation between biogenic silica and water in various parts of these living plants for non or weakly transpiring tissues rhizomes stems sheaths in both grass species the 18 o silica plant water remained constant at 34 and the 18 o and d values of plant water collected from pre dawn and mid day samplings showed little variation these plant waters were only slightly enriched in 18 o and d relative to water provided to the grasses isotopic temperatures calculated from the silica and plant water isotopic data matched measured growing temperatures for the region by comparison the upper leaf water was extremely enriched in oxygen 18 and deuterium at maximum rates of transpiration relative to water from non transpiring tissues as were the calculated steady state values for leaf water 18 o and d silica produced in the transpiring tissues leaf inflorescence has higher 18 o values than silica from non transpiring tissues but the enrichment is modest compared to upper leaf water under mid day conditions leaf phytoliths have formed from plant water typical of average conditions in the lower leaf where the extreme 18 o enrichment is not encountered c longifolia was also collected from alberta and nebraska where growing conditions are different from southwestern ontario phytoliths at all three sites have a similar pattern of 18 o values within the plants but the isotopic separation between leaf and stem silica increases from 4 to 8 as average relative humidity decreases the difference between actual growing temperature and that calculated using measured 18 o values for stem silica and local meteoric water became progressively larger as relative humidity decreased likely because of evaporative 18 o enrichment of soil water such effects are most pronounced in arid environments and pertinent in grasslands where much of the active rooting zone can be situated at the shallower depths most affected by the 18 o enrichment of soil water

phytoliths indicators of grassland dynamics during the late holocene in intertropical africa abstract the reconstruction of african tropical grassland history during the late holocene can be carried out using phytolith analysis fossil phytolith assemblages from lake guiers in the sahelian region of senegal and from lake sinnda in the guineo congolian region of congo were investigated the results are interpreted on the basis of modern phytolith assemblages from the same regions and compared to pollen data previously obtained tall or short grass associations are discriminated by their phytolith index iph saddle cross dumbel saddle while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytoliths the phytolith data emphasize that in the guineo congolian region around lake sinnda the driest phase of the late holocene occurred between 4000 and 1200 yr b p commencing with the opening of the dense forest and its replacement by a short grass savanna from ca 1000 yr b p wetter climatic conditions developed as represented by the setting up of a tall grass savanna woodland the modern shrub and tall grass savanna was developed ca 700 yr b p in the sahelian region around lake guiers the driest phase occurred after about 2000 yr b p and has not been followed by moister conditions a tall grass savanna woodland was gradually replaced by a shrub and short grass savanna which still occurs a short period of development of swampy vegetation which can be related to a lake level change interrupted the semi arid adaptation of the vegetation between about 2000 yr b p and the present

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

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

millennial scale deep water oscillations reflections of the north atlantic in the deep pacific from 10 to 60 ka northeast pacific benthic foraminiferal 18o and 13 reveal repeated millennial scale events of strong deep sea ventilation associated with nutrient depletion and or high gas exchange during stadial cool high ice volume episodes from 10 to 60 ka opposite the pattern in the deep north atlantic two climate mechanisms may explain this pattern north pacific surface waters chilled by atmospheric transmission from a cold north atlantic and made saltier by reduced freshwater vapor transports could have ventilated the deep pacific from above alternatively faster turnover of pacific bottom and mid depth waters driven by southern ocean winds may have compensated for suppressed north atlantic deep water production during stadial intervals during the younger dryas event 11 6 13 0 cal ka ventilation of the deep ne pacific 2700 m lagged that in the santa barbara basin 450 m by 500 years suggesting that the ne pacific was first ventilated at intermediate depth from above and then at greater depth from below this apparent lag may reflect the adjustment time of global thermohaline circulation

latest quaternary north pacific surface water responses imply atmosphere driven climate instability a full sequence of brief interstadials dansgaard oeschger d o cycles are recorded from 60 to 25 ka in santa barbara basin california ocean drilling program hole 893a by planktonic foraminiferal isotopic and assemblage changes at unparalleled high resolution for the oceans synchronous climatic response between north pacific surface waters and the greenland ice sheet during d o cycling is strongly indicated by remarkable similarities in speed magnitude and character of rapid oceanic and atmospheric reorganizations inferred sea surface temperature warmings of as much as 5 c within a few decades and brief warming overshoots of as much as 3 c suggest involvement of an atmospheric amplification top down in situ atmospheric warming of the ocean is implied by differential responses partial decoupling in the changes recorded in surface and thermoclinal waters

phytolith analysis from the archaeological site of kush ras al khaimah united arab emirates despite the wealth of archaeological sites and excellent conditions for preservation few phytolith investigations have been undertaken from the arabian gulf region the results from the sasanian and islamic archaeological tell of kush ras al khaimah united arab emirates are presented kush is situated just inside the gulf on an important trade route the occupation sequence dates from the 4th century a d until the 13th century a d recording the development of the site in the sasanian period followed by the arrival of islam in the 7th century a d and the final abandonment of the site in the late 13th century when the nearby site of al mataf julfar began to develop closer to the present day coastline all the samples analyzed contained abundant phytoliths short cells elongated cells and groups of elongated cells of various types they included date palm phoenix dactylifera papillae possibly from barley hordeum and hair cells possibly from species of canary grass phalaris spp some researchers have suggested that groups of elongated cells may indicate the presence of irrigation in semiarid environments the present results for this class of phytoliths appeared to imply that intensive irrigation was unlikely to have taken place around kush

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

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

icing the north atlantic there is debate over the causes of the large and abrupt climate changes that the north atlantic region has experienced in the past and may do in the future the driving forces of such changes might originate in the north atlantic itself or could be transmitted to the region from elsewhere new evidence on the extent and movement of the british ice sheet around the end of the last ice age supports the first contention and in particular implicates the advance and retreat of the laurentide ice sheet in causing some of the big climate jumps of the past

paleofire severity and vegetation change in the cascade range oregon usa paleoecological research has expanded our knowledge of the relationships between climate fire and vegetation fire can be a significant driver of forest composition and structure change but identifying and quantifying fire regimes has been elusive using high resolution charcoal analysis and pollen analysis we reconstructed a 13 200 year old fire and vegetation history from breitenbush lake oregon located in the central cascade range usa our objective was to examine if fire occurrence and severity may have been a driver of holocene forest composition change the data from this study suggests that while fire can create opportunities for successional process to occur fire events were not significant catalysts for forest change instead most major transitions at breitenbush lake occurred during prolonged fire free intervals our results reinforce the view that climate is the major control of vegetation composition change in the cascade range

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

sensitivity of northern hemisphere air temperatures and snow expansion to north pacific sea surface temperatures in the goddard institute for space studies general circulation model circum pacific marine and terrestrial records indicate a series of temperature inferred oscillations during the late glacial while many previous studies have probed the role of the north atlantic in these oscillations we test the sensitivity of the northern hemisphere air temperatures to north pacific sea surface temperature sst oscillation in the goddard institute for space studies general circulation model the effect of a colder north pacific is to cool air temperatures over north america as well as parts of europe and asia the colder ssts result in a large hemispheric response due to the loss of water vapor as a greenhouse gas the large sensitivity of the northern hemisphere to a north pacific sst change has implications for the ice age climate as well as the late glacial interval the results of this experiment provide a rapid mechanism for widespread cooling which has not been previously addressed

the paleoenvironment of the olympia beds based on fossil beetles from discovery park seattle washington u s a abstract two fossil insect assemblages with ages of 17 959 and 19 786 cal bp are reported from cross laminated silts and sands within the olympia beds at magnolia bluff discovery park seattle washington n 47 39 w 122 25 the silts accumulated during mis 2 at a time when the puget lobe of the cordilleran ice sheet was advancing southward eventually the olympia beds were buried sequentially by lacustrine beds outwash sands and gravels and finally till the depositional environment based on paleoecology and sedimentary facies was a floodplain of a large braided river the fossils are disarticulated skeletal parts representing a diverse fauna of 132 beetle species all extant the habitats represented by fossils include sparsely vegetated sand and gravel bars opisthius richardsoni open muddy areas elaphrus californicus and vegetation shaded banks elaphrus clairvillei and elaphrus purpurans outside of the floodplain the habitat was grassland carabus taedatus with occasional stands of coniferous trees indicated by scolytids bark beetles large mammals probably used the river as a watering hole based on the abundance of dung feeding aphodiinae scarabs and staphylinid beetles tachinus most of the beetle species have modern geographic ranges which include northern washington state notably however species characteristic of the temperate rainforest of the pacific northwest are absent for the older of the two fossil assemblages mean summer temperature is estimated to be 17 c or similar to seattle today the climate was more continental and winters would have been colder than at seattle today the occurrence of the northern species pelophila borealis and olophrum boreale in the younger of the two assemblages indicates a colder climate estimated to represent a lowering of mean summer temperature by 1 2 c the climatic cooling is possibly associated with the advance of the puget lobe both pollen and fossil beetle evidence are in agreement that there was less available moisture possibly one half of today s precipitation palynologists have referred to the mis 2 vegetation as tundra cold steppe or subarctic parkland none of the discovery park fossils are obligate tundra species and because the majority of taxa have ranges which overlap in northern washington state today we prefer to use the term prairie for the temperate to cold temperate mis 2 grassland

correlation of late pleistocene glaciation in the western united states with north atlantic heinrich events a survey of the chronology of late pleistocene glaciers in the western united states indicates a record of glacier advances during the last glaciation which is more variable than that predicted by orbital forcing numerical dating of late pleistocene deposits from the puget lobe of the cordilleran ice sheet and alpine glaciers and ice caps in the rocky mountains and cascade range suggests that advances and retreats of these glaciers were in phase with episodes of growth and collapse of the laurentide ice sheet associated with the north atlantic heinrich events specifically the existing chronologies indicate that these glaciers were advancing to their terminal areas up to several thousand years before a heinrich event and retreated shortly thereafter because midlatitude glaciers respond relatively rapidly to climate change this complex record of glacial fluctuations suggests mechanisms of climate forcing in western north america that are in some way tied to heinrich events one possible mechanism involves southerly and northerly displacement of the jet stream across the western united states in response to growth and collapse of the laurentide ice sheet

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

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

late quaternary climatic controls on erosion rates and geomorphic processes in western oregon usa climate regulation of erosion in unglaciated landscapes remains difficult to decipher while climate may disrupt process feedbacks that would otherwise steer landscapes toward steady erosion sediment transport processes tend to erase past climate landforms and thus bias landscape evolution interpretations here we couple a 50 k y paleoenvironmental record with 24 10be derived paleo erosion rates from a 63 m thick sediment archive in the unglaciated soil mantled oregon coast range our results span the forested marine oxygen isotope stage mis 3 50 29 ka the subalpine mis 2 29 14 ka and the forested mis 1 14 ka to present from 46 ka through 28 5 ka erosion rates increased from 0 06 mm yr 1 to 0 23 mm yr 1 coincident with declining temperatures mean mis 2 erosion rates remained at 0 21 mm yr 1 and declined with increasing mis 1 temperatures to the modern mean rate of 0 08 mm yr 1 paleoclimate reconstructions and a frost weathering model suggest periglacial processes were vigorous between 35 and 17 ka while steady erosion is often assumed our results suggest that climate strongly modulates soil production and transport on glacial interglacial time scales by applying a cosmogenic paleo erosion model to evaluate 10be concentrations in our sedimentary archive we demonstrate that the depth of soil mixing which is climate dependent controls the lag time required for cosmogenic erosion rates to track actual values our results challenge the widely held assumption that climate has minimal impact on erosion rates in unglaciated midlatitude terrain which invites reconsideration of the extent to which past climate regimes manifest in modern landscapes

subsistence practices in an arid environment a geoarchaeological investigation in an iron age site the negev highlands israel the negev highlands southern israel is an arid zone characterized by settlement oscillations one settlement peak occurred in the early iron age iia late 10th and early 9th centuries bc the most conspicuous structure in many sites of this period is an oval compound comprised of an internal courtyard surrounded by rooms two hypotheses for the function of these oval compounds are that they served as israelite fortresses which guarded the southern border and routes of the solomonic kingdom or that they represent local agro pastoral groups in order to gather more information regarding the subsistence practices conducted in these oval compounds we carried out a small scale excavation at the site of atar haroa we focused on sediment sampling and used several geoarchaeological as well as isotopic techniques in order to identify macroscopic and microscopic remains related to animal husbandry and crop agriculture the remains identified from the archaeological sediments were compared with modern reference materials collected from abandoned bedouin camps the excavation included two half rooms and several test pits in the courtyard of the oval compound featuring one iron age occupation level composed of gray sediments and relatively small amounts of pottery bones and macro botanical charred remains micromorphological mineralogical dung spherulite and isotopic analyses carried out on the gray occupational sediments from the rooms show that they originate from wood ash and dung both used as fuel similar analyses of the gray sediments in the courtyard show that they originate only from degraded livestock dung phytolith analyses show that the gray anthropogenic sediments have similar concentrations of phytoliths as in control yellowish sediments and in the dung of winter free grazing desert livestock and lichen grazing black dwarf bedouin goats phytoliths indicative of cereal crops are completely absent in the archaeological dung remains indicating that cereal crops were not processed by the site inhabitants based on ethnographic and archaeological parallels and on the presence of grinding stones and absence of sickle blades in the excavated rooms we infer that the inhabitants at the oval compound at atar haroa subsisted on livestock herding and bought or exchanged cereal grains our results support the hypothesis that the inhabitants at the oval compound at atar haroa were desert adapted pastoralists rather than garrisoned soldiers

vegetational history of a site in the central amazon basin derived from phytolith and charcoal records from natural soils abstract analysis of phytoliths and macroscopic charcoal from natural soils near manaus brazil shows that the central amazonian terra firme forest has not been stable during the holocene phytolith taxonomic composition and radiocarbon ages indicate that a closed forest has continuously existed in the area since at least 4600 yr b p but that forest composition and species abundance changed significantly sometime during the holocene epoch there is no evidence that the vegetation experienced swidden cultivation the distribution and dates of the charcoal in the soils indicate that forest fires between 1795 and 550 yr b p burned an area of about 200 hectares vegetational changes and fires appear to be a result of climatic drying that may have affected large areas of the amazon basin over the past 5000 to 7000 years soil phytolith analysis is a promising tool for the study of environmental history in the humid tropics and may reduce the previous dependence on lake and swamp sediments at least for the holocene epoch

soil erosion and sedimentation indicated by caesium 137 jackmoor brook catchment devon england summary the tracer caesium 137 was used to study the status of soil erosion and sedimentation in the jackmoor brook catchment devon u k it was postulated that 1 sites at the top of a cultivated slope should be most depleted of caesium 137 2 sites at the base of a slope should contain greater amounts of caesium 137 and have a distinctive depth profile 3 hillslope erosion indicated by caesium 137 levels should be related to slope length and angle and 4 caesium 137 levels should discriminate between the chief source of sediment transferred to the stream cultivated soils and uncultivated soils under pasture orchards and woodland these hypotheses were tested in two contrasting physiographic areas of the basin depletion of caesium 137 levels at the top of slopes indicated soil erosion and deeper than plough depth caesium 137 profiles at the base of slopes indicated sedimentation these characteristics were most marked in the steeper upper jackmoor portion of the catchment slope length effects on soil movement were more difficult to ascertain from the caesium 137 levels but soil sampling of contrasting land uses showed that cultivated soils had significantly less caesium 137 probably as a result of soil erosion in general the hypotheses were supported and the utility of the caesium 137 technique was confirmed

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

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

reconstruction of last glacial to early holocene monsoon variability from relict lake sediments of the higher central himalaya uttrakhand india abstract proglacial lake sediments at goting in the higher central himalaya were analyzed to reconstruct the summer monsoon variability during the last glacial to early holocene sedimentary structures high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions optically stimulated luminescence osl dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka during this period goting basin witnessed moderate to strengthened monsoon conditions around 25 ka 23 5 ka 22 5 ka 22 ka 18 ka 17 ka 16 5 ka and after14 5 13 ka the last glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of holocene condition additionally centennial scale fluctuations between 16 5 ka and 12 7 ka in the magnetic and geochemical data are seen a close correspondence at the millennial scale between our data and that of continental and marine records from the indian sub continent suggests that goting basin responded to periods of strengthened monsoon during the last glacial to early holocene we attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes however centennial scale abrupt changes are attributed to the result of albedo changes on the himalaya and tibetan plateau

modelling teleconnections between the north atlantic and north pacific during the younger dryas evidence for a cooling event synchronous with the younger dryas 12 000 calendar years before present has been found in the north pacific ocean north of 30 n in records of surface1 5 and subsurface water properties6 7 these changes may be related to a temporary shut down of north atlantic deep water formation and associated surface cooling over the north atlantic it has remained unclear however whether this north atlantic cooling was communicated to the north pacific ocean through the atmosphere or the ocean here we report results of a sensitivity experiment with a coupled ocean atmosphere general circulation model that support a primarily atmospheric forcing of north pacific climate variations changes in wind strongly affect coastal upwelling at the north american west coast and surface cooling by the atmosphere causes better ventilation of the thermocline waters of the northeast pacific this effect is amplified by oceanic progagation to the pacific of the signal arising from collapse of north atlantic deep water formation these teleconnections may also explain earlier north pacific and western north american millenial scale cooling events of a similar nature8 12

phytolith and carbon isotope evidence for late quaternary vegetation and climate change in the southern black hills south dakota abstract analyses of phytoliths and carbon isotopes document change in late quaternary grasslands in the red valley of the southern black hills late pleistocene grassland composition was equivalent to the c3grass parklands of modern central alberta the rise of mixed grassland occurred rapidly between 11 000 and 9000 yr b p early holocene mixed grasslands included both short and tall c4grasses a mid holocene erosional unconformity ca 8000 to 4500 yr b p precludes phytolith or isotope analysis but suggests lack of vegetation and landscape denudation caused by a drier climatic basin wide stability and soil development followed the erosional episode ca 4500 to 3600 yr b p mesic adapted c4panicoid grasses increased during this period of soil development low magnitude fluctuation in the c4 dominated mixed grassland occurred throughout the late holocene 3600 yr b p to present rise in 13c values during the last 1000 yr without corresponding change in phytoliths may indicate a decrease in woodlands caused by increased fire frequency

geoarchaeology in an urban context the uses of space in a phoenician monumental building at tel dor israel abstract interpretation of past urban societies in the near east whose settlements are known mostly as tell sites is largely based on macro stratigraphy and on the association of architecture with macroscopic artifacts analyses of sediments common in prehistoric sites are rare in tell sites here we show the results of a detailed geoarchaeological study of the micro stratigraphy of a sedimentary sequence associated with early iron age phoenician monumental architecture the study involves mineralogical micromorphological and phytolith analyses and provides new insights into the stratigraphic sequence and the use of architectural spaces the sedimentary sequence examined comprises alternating layers of gray fill deposits and white floors we show that floors made from local calcareous sandstone in the lower part of the sedimentary sequence were heated and are thus in effect plaster floors a concentration of micro laminated trampled fish remains above the most elaborate of these plaster floors indicates activities related to fish processing fine white layers in the upper part of the sedimentary sequence that were considered as plaster based on macroscopic examination are in fact composed almost entirely of opaline grass phytoliths the phytoliths appear in an undulating micro laminated structure and are associated with dung spherulites and phosphate nodules thus probably reflecting livestock penning the formation of phytolith floors involves extensive volume reduction due to the degradation of the organic material and this may result in floor subsidence a phenomenon that is often observed in archaeological sites most fill deposits include macroscopic and microscopic remains of wood ash bones phytoliths charcoal ceramics plaster and mollusk shells reflecting the debris produced from household activities this study shows how a combination of macro stratigraphy with microscopic and mineralogical analyses of the sediments within architectural spaces can provide information on the varying ways in which the space was used through time and also contributes to solving macro stratigraphic problems

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

using phytolith assemblages to reconstruct the origin and spread of grass dominated habitats in the great plains of north america during the late eocene to early miocene abstract this paper outlines a general approach for analyzing siliceous microfossils from plants phytoliths in geologic sediments and uses this method to reconstruct the evolution of grasslands in the central great plains during the late tertiary phytolith assemblage analysis is widely employed for reconstructing vegetation types in pleistocene holocene paleoecology and archaeology but no standardized methodology is currently available published phytolith studies are often system specific and tailored after specific modern analogues as a result they vary in extraction technique classification scheme and method of inference for ancient phytolith assemblages whose modern analogues are not well understood a more general analytic approach is necessary this analytic approach includes studying all size fractions 2 250 mm using a classification scheme based on the available literature and a comprehensive modern phytolith reference collection and comparing relative frequencies through time of all diagnostic phytoliths to interpret changes in habitat structure this general method was applied to late eocene to early miocene sediment samples from northwestern nebraska to deduce vegetation history and the results were compared to those obtained using a more specific technique stromberg paleogeogr paleoclimatol paleoecol 177 2002 59 in both studies phytoliths were extracted by means of heavy liquid separation from the following lithostratigraphic units 1 the late eocene chadron formation and the early oligocene brule formation white river group 2 the late oligocene early miocene monroe creek formation the early miocene harrison formation and anderson ranch formation arikaree group and 3 the early miocene runningwater formation and box butte formation ogallala group the two techniques general vs specific produced results that differ markedly data from the general approach indicate the presence of relatively closed habitats in late eocene to early oligocene typified by the presence of phytoliths from bambusoid grasses woody and herbaceous dicotyledons and palms the introduction and spread of modern open habitat grasses such as pooids arundinoids and panicoids occurred between the late oligocene and early miocene this resulted in a savanna or woodland type habitat by the early miocene in contrast analysis using the specific method suggested the presence of open habitats in northwestern nebraska from the late eocene onward the difference in interpretation based on the two approaches is principally due to inclusion of phytoliths 50 mm and the use of an expanded reference collection in the current study general analytic approach these results point to the importance of methodological choices in phytolith analysis and emphasize the usefulness of phytoliths as paleoecological indicators in the fossil record

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

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

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

forest or no forest implications of the vegetation record for climatic stability in western beringia during oxygen isotope stage 3 abstract two conflicting stratigraphic schemes describe the siberian karginskii interstade oxygen isotope stage 3 equivalent as having 1 relatively stable climate with environments more similar to the full glaciation or 2 variable climate with landscapes that more closely approximate contemporary ones new data from continuous lake cores and a nearly continuous section from western beringia wb suggest that both schemes are valid herb dominated communities possibly with isolated populations of larix characterized northern wb with only a slight shift from relatively warm to cool summers during the mid interstade in contrast herb and shrub tundra steppe forest tundra and modern larix forest occurred at various times in areas of southern wb suggesting greater climatic instability a thermal optimum is evident in the south during the mid interstade with modern vegetation in southeastern wb and larix forest tundra in the southwest variations in pinus pumila pollen indicate summer warm winter dry and summer warm winter wet conditions in southeastern wb these fluctuations contrast to other areas of wb where summers and probably winters were consistently arid although the interstade presents a unique interval within the late pleistocene paleodata and paleoclimatic models suggest that changes in marine conditions including sea level were likely key drivers in the regional climate history

olympia interstadial vegetation landscape history and paleoclimatic implications of a mid wisconsinan mis3 nonglacial sequence from southwest british columbia canada lithostratigraphic 14c and palynologic analyses of peat and silty peat at three nearby sites reveal a 25 000 year vegetation and climate history of the olympia interstade for the fraser lowland british columbia 300 km within the southern limit of the cordilleran ice sheet at lynn valley polypodiaceae fern spores and nonarboreal pollen dominate 47 8 14c ka bp reflecting unstable and cold landscapes a pinus poaceae zone follows representing pine parkland and cool dry climate fluctuating values of picea and tsuga mertensiana pollen at lynn and seymour valleys and port moody characterize most of the olympia interstade during local peat deposition in cyperaceae and myrica wetlands until about 26 7 14c ka bp under a cool and moist climate a brief pinus tsuga heterophylla zone at lynn valley 44 39 14c ka bp suggests a climatic optimum a poaceae artemisia assemblage and deposition of silty sand after 26 7 14c ka bp reflect cooling and drying after which a unique lycopodium assemblage at lynn valley

the relative utility of foraminifera and diatoms for reconstructing late holocene sea level change in north carolina usa abstract foraminifera and diatoms preserved in salt marsh sediments have been used to produce high resolution records of holocene relative sea level rsl change to determine which of these microfossil groups is most appropriate for this purpose we investigated their relative utility from salt marshes in north carolina usa regional scale transfer functions were developed using foraminifera diatoms and a combination of both multi proxy from three salt marshes oregon inlet currituck barrier island and pea island we evaluated each approach on the basis of transfer function performance foraminifera diatoms and multi proxy based transfer functions all demonstrated a strong relationship between observed and predicted elevations r 2 jack 0 74 and rmsep 210 pb and 14 c based chronology and we were able to reconcile this with tide gauge records

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

domestic activities and spatial distribution in ain abū nukhayla wadi rum southern jordan the use of phytoliths and spherulites studies abstract the pre pottery neolithic b site of ayn ab nukhayla wadi rum jordan contains structural installations loci composed of inter connected oval rock walled pithouses questions that arose from their study centered on how to identify possible herding and agricultural activities and to assess any differences in how the loci were used the combined study of phytoliths and spherulites identified from different loci are presented here the results of quantitative morphologic and morphometric analyses of phytoliths and spherulites identified in the different loci are discussed cereal processing is evident in some loci by the concentration of the inflorescent parts of festucoid grass phytoliths associated with the presence of handstones and querns these loci appear to have encompassed specific areas in which domestic activities including the grinding of cereals and the preparation of other plant resources were undertaken in contrast other loci such as locus 20 seem to have been used as pens for herd animals sheep goats as indicated by very high densities of spherulites the results of this study provide new insights on plant uses herding practices and the economic diversity of early neolithic communities in the levant

late quaternary climatic and oceanographic changes in the northeast pacific as recorded by dinoflagellate cysts from guaymas basin gulf of california mexico a high resolution record of organic walled dinoflagellate cyst production in guaymas basin gulf of california mexico reveals a complex paleoceanographic history over the last 40 ka guaymas basin is an excellent location to perform high resolution studies of changes in late quaternary climate and paleo productivity because it is characterized by high primary productivity high sedimentation rates and low oxygen bottom waters these factors contribute to the deposition and preservation of laminated sediments throughout large portions of the core md02 2515 in this study we document dinoflagellate cyst production at a centennial to millennial scale throughout the late quaternary based on the cyst assemblages three dinoflagellate cyst zones were established and roughly correspond to marine isotope stages miss 1 to 3 miss 1 and 3 are dominated by cysts of heterotrophic dinoflagellates whereas mis 2 is characterized by enhanced variability and a greater proportion of cysts produced by autotrophic taxa the most dominant dinoflagellate cyst taxa found throughout the core were brigantedinium spp and operculodinium centrocarpum dansgaard oeschger event 8 is observed in the dinoflagellate cyst record where it is characterized by an increase in warm taxa such as spiniferites pachydermus other intervals of interest are the younger dryas where warmer conditions are recorded and the holocene which is characterized by the consistent presence of tropical species stelladinium reidii tuberculodinidum vancampoae bitectatodinium spongium and an increase in quinquecuspis concreta changes in cyst assemblages concentrations and species diversity along with geochemical data reflect major orbital to millennial scale climatic and oceanographic changes reference price a m k n mertens v pospelova t f pedersen and r s ganeshram 2013 late quaternary climatic and oceanographic changes in the northeast pacific as recorded by dinoflagellate cysts from guaymas basin gulf of california mexico paleoceanography 28 doi 10 1002 palo 20019

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

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

evidence for large amplitude biome and climate changes in atlantic canada during the last interglacial and mid wisconsinan periods abstract last interglacial and mid wisconsinan pollen data from sedimentary sequences of cape breton island in atlantic canada were analyzed to reconstruct biome and climate conditions our results show warm and humid climate with mean annual temperature 6 7 c higher than today up to 15 20 more sunshine and significantly longer growing season that fostered growth of temperate trees during the optimum of the last interglacial the northern limit of the deciduous forest biome was then about 500 km north of its modern limit towards the end of the interglacial the deciduous forest was replaced by conifer hardwood forest and boreal forest climate was then similar to modern the transition from interglacial to glacial was marked by a change towards coniferous forest related to colder and dryer conditions during the mid wisconsinan the development of forest tundra to boreal forest reflects migration of the arctic front and significant cooling with mean annual temperature anomalies of 8 to 12 c the overall time series reflect large amplitude climate changes that point to high sensitivity of the southeastern canadian margins likely as a response to latitudinal shifts of the gulf stream and variable strength of the labrador current together with changes in large scale atmospheric circulation pattern

assessing bioturbation in archaeological sediments using soil morphology and phytolith analysis abstract analysis of ditch infill at an early modern burial complex dating from the 16th century ad in upland northwestern thailand was undertaken to assess the role of bioturbation in interpreting palaeolandscapes evidence for bioturbation and water percolation is contrasted with ams radiocarbon determinations and a phytolith sequence while more than 50 of the sediment column was disturbed by insect activity the dates and phytolith data suggest soil mixing was localized by understanding the processes of bioturbation a distinctive pattern of swidden agriculture over the last 400 years can be distinguished we conclude that for environments conventionally considered to be prone to bioturbation the combination of soil morphology and phytolith analysis provides a new and effective measure of the extent of vertical movement in a sediment column

millennial scale climate instability during the early pleistocene epoch climate proxy records of the past 100 000 years show that the earth s climate has varied significantly and continuously on timescales as short as a few thousand years 1 7 similar variability has also recently been observed for the interval 340 500 thousand years ago8 these dramatic climate shifts expressed most strongly in the north atlantic region may be linked to and possibly amplified by alterations in the mode of ocean thermohaline circulation4 5 6 7 8 9 here we use sediment records of past iceberg discharge and deep water chemistry to show that such millennial scale oscillations in climate occurred over one million years ago this was a time of significantly different climate boundary conditions not only was the early pleistocene epoch generally warmer but global climate variations were governed largely by changes in earth s orbital obliguity our results suggest that such millennial scale climate instability may be a pervasive and long term characteristic of earth s climate rather than just a feature of the strong glacial interglacial cycles of the past 800 000 years

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

a reassessment of u th and14c ages for late glacial high frequency hydrological events at searles lake california u th isochron ages of tufas formed on shorelines suggest that the last pluvial event in lake lahontan and searles lake was synchronous at about 16 500 cal yr b p equivalent to a radiocarbon age of between 14 000 and 13 500 yr b p whereas the timing of this pluvial event determined by radiocarbon dating is on the order of 1000 yr younger the timing of seven distinct periods of near desiccation in searles lake during late glacial time has been reinvestigated for u th age determination by mass spectrometry u th dating of evaporite layers in the interbedded mud and salt unit called the lower salt in searles lake was hampered by the uncertainty in assessing the initial230th 232th of the samples the resulting ages corrected by a conservative range of initial230th 232th ratios suggest close correlation of the abrupt changes recorded in greenland ice cores dansgaard oeschger events and wet dry conditions in searles lake between 35 000 and 24 000 cal yr b p

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

phytoliths and microcharcoal at jinluojia archeological site in middle reaches of yangtze river indicative of paleoclimate and human activity during the last 3000 years a variety of phytoliths together with prolific microcharcoal particles sponge spicules and diatoms were extracted and identified in four cultural layers from an archeological site at jinluojia macheng hubei province central china the warmth iw and aridity iph indices calculated from grass phytoliths reveal warm and wet periods during the west zhou early east zhou tang and song dynasties whilst cool and dry periods occurred during the late east zhou ming and qing dynasties the paleoclimate conditions reconstructed on the basis of grass phytoliths extracted from archeological sediments are in agreement with those from natural sediments in the middle yangtze region in contrast the woody phytoliths show a positive correlation with microcharcoal particles suggesting an anthropogenic contribution to the woody phytoliths from the use of woody plants for fuel during cooking and heating two episodes of the enhanced abundance of woody phytoliths and microcharcoal particles were found to occur at east zhou dynasty and from ming and qing dynasties to the present proposed to be a consequence of the population expansion and or the frequent wars

a 560 year record of santa ana fires reconstructed from charcoal deposited in the santa barbara basin california microscopic charcoal from varved santa barbara basin sediments was used to reconstruct a 560 yr record a d 1425 to 1985 of santa ana fires comparison of large 3750 m2 charcoal with documented fire records in the santa barbara ranger district shows that high accumulations correspond to large fires 20 000 ha that occurred during santa ana conditions the charcoal record reconstructed a minimum of 20 large fires in the santa barbara region during the study period the average time between fires shows no distinct change across three different land use periods the chumash period apparently characterized by frequent burning the spanish early american period with nominal fire control and the 20th century with active fire suppression pollen data support the conclusion that the fire regime has not dramatically changed during the last 500 yr comparison of large charcoal particle accumulation rates and precipitation reconstructed from tree rings show a strong relationship between climate and fire history with large fires consistently occurring at the end of wet periods and the beginning of droughts