a multiproxy approach to reconstructing sea surface conditions using coral skeleton geochemistry 1 we use elemental ratio mg ca sr ca u ca and ba ca and oxygen isotope data from a porites lutea coral head collected from offshore amedee island new caledonia 22 29 s 166 28 e to assess the degree to which changes in these geochemical variables reflect variations in sea surface conditions we have assessed the robustness of each geochemical proxy by comparing 25 years 1992 1968 of monthly geochemical variations with a local record of sea surface temperature sst and with the appropriate 1 by 1 grid box from a global gridded sst data set we conclude from our comparison that the most consistent proxies of monthly sst variations at this site are 18o r2 0 84 p 0001 and sr ca r2 0 84 p 0001 the fidelity of the coral based sr ca sst proxy was assessed via calibration verification exercises at new caledonia and rarotonga the paleoclimate accuracy of the coral sr ca sst technique is judged to be robust and the precision of the technique is estimated to be 0 3 0 5 2 based on the calibration verification exercise in contrast monthly variations in mg ca and u ca ratios are only moderately correlated with monthly sst variations r2 0 55 p 0001 for mg ca and r2 0 47 p 0001 the strength of the correlation between sst and mg ca and u ca varies as a function of time suggesting that variations in these ratios are not a simple function of sst variations this variability in goodness of fit between u ca sst and mg ca sst may ultimately limit the use of these ratios as coral paleothermometers averaging or stacking individual proxy sst records sr ca mg ca and u ca to generate a composite proxy sst record does not necessarily improve the proxy record if the signal to noise ratio in each proxy is highly variable for example stacking of sr ca mg ca u ca records at new caledonia produces a proxy sst time series that has greater standard error than the individual sr ca sst time series cf ordinary least squares standard error of 1 16 c versus 0 86 c ba ca variations have little correlation with sst sr ca mg ca or u ca variations at new caledonia in conclusion variations in oxygen isotopic composition of seawater calculated by removing the sr ca based temperature component of the 18o signal agree reasonably well with observed variations in sea surface salinity especially at the interannual timescale

influence of late quaternary climatic changes on geomorphic and pedogenic processes on a desert piedmont eastern mojave desert california radiocarbon dating of late quaternary deposits and shorelines of lake mojave and cation ratio numerical age dating of stone pavements dorn 1984 on the adjacent soda mountains piedmont provide age constraints for alluvial and eolian deposits these deposits are associated with climatically controlled stands of lake mojave during the past 15 000 yr six alluvial fan units and three eolian stratigraphic units were assigned ages based on field relations with dated shorelines and piedmont surfaces as well as on soil geomorphic data all but one of these stratigraphic units were deposited in response to time transgressive climatic changes beginning approximately 10 000 yr ago increased eolian flux rates occurred in response to the lowering of lake mojave and a consequent increase in fine sediment availability increased rates of deposition of eolian fines and associated salts influenced pedogenesis stone pavement development and runoff infiltration relations by 1 enhancing mechanical weathering of fan surfaces and hillslopes and 2 forming clay and silt rich surface horizons which decrease infiltration changes in alluvial fan source areas from hillslopes to piedmonts during the holocene reflect runoff reduction on hillslopes caused by colluvial mantle development and runoff enhancement on piedmonts caused by the development of less permeable soils inferred increased in early to middle holocene monsoonal activity resulted in high magnitude paleo sheetflood events on older fan pavements this runoff triggered piedmont dissection which in turn caused increased sediment availability along channel walls thus runoff infiltration changes during the late quaternary have occurred in response to eolian deposition of fines pedogenesis increased sheetflood activity in the holocene and vegetational changes which are related to many complicated linkages among climatic change lake fluctuations and eolian hillslope and alluvial fan processes

the use of hornblende etching clast weathering and soils to date alpine glacial and periglacial deposits a study from southwestern montana many techniques for relative dating of surficial deposits suffer from 1 the need to make judgments and 2 poor reproducibility of data furthermore many of the techniques generate data that do not permit the use of statistical analysis in contrast assessing the etching of hornblende grains yields objectively obtained reproducible data that can be subjected to statistical analysis in a study of the deposits of the bear gulch basin tobacco root range southwestern montana the hornblende etching data proved superior to the clast weathering data and the soil profile data in making interpretations of age relationships the mean etching of hornblende grains decreases as a logarithmic function of depth hornblende grains from older deposits are more etched especially near the surfaces of the profiles the collective evidence supports a record of four first order glacial and periglacial events which have been correlated with 1 the youngest pre bull lake glaciation about 280 000 yr b p 2 the bull lake glaciation about 140 000 yr b p 3 the pinedale glaciation consisting of two second order advances the first and most extensive between 26 000 and 20 000 yr b p and the second about 12 000 yr b p and 4 a mid neoglacial episode of periglacial activity in addition a major landslide blocked the valley in pre bull lake time and an episode of flood erosion along the valley floor is believed to have truncated the late pinedale terminal moraine about 1500 yr b p in a study area for which numerical ages of the deposits are available hornblende etching can be expressed mathematically as a function of the time since deposition with the resulting relationship used to date deposits wherein ages are unknown

simulation and inversion of borehole temperature profiles in surrogate climates spatial distribution and surface coupling a heat conduction forward model driven by ground surface temperature from three 1000 year climate simulations with the state of the art echo g model has been used to simulate underground temperature perturbation profiles an inversion approach has been applied to reconstruct ground surface temperature histories from the simulated profiles and to compare them with the climate model temperatures results support the skill of borehole inversion methods to retrieve long term temperature trends and the robustness of using the present day borehole network for reconstructing sat variations

neotectonic note the ruby east humboldt range northeastern nevada the northwest flank of the ruby east humboldt range is bounded by a 73 km long normal fault that is composed of three distinct sections each separated by a 3 to 5 km wide left step in fault trace stratigraphic structural and soil relations observed in a trench across the northern section of the fault at reed creek indicate the last surface rupture occurred between 4800 and 7600 cal yr b p preceded by tens of thousands of years of tectonic quiescence on the fault morphologic analyses of single event scarp profiles suggest that the length of the range front ruptured during a relatively short period of time in the holocene and allow that the last rupture was synchronous along the entire range front offset of a late pleistocene glacial moraine along the central section of the fault places a maximum bound on the vertical separation rate of the fault at between 0 06 and 0 2 mm yr

strontium calcium ratios in modern porites corals from the great barrier reef as a proxy for sea surface temperature calibration of the thermometer and monitoring of enso high precision sr ca ratios are reported for porites corals from davies reef at 19 s on the midshelf of the great barrier reef australia skeletal growth parameters were also determined from coral slabs using x ray photographs and densitometry measurements a calibration of the sr ca thermometer has been obtained using in situ measured sea surface temperatures which gives sr ca 10 10 48 0 01 0 0615 0 0004 t wheret is in c this calibration applies to different species of porites and a large range of annual extension and calcification rates provided sampling follows a major growth axis biases of 1 2 c have been observed in the low density margins where growth is hampered by interfering fans of corallites the analytical and the long term reproducibility of sr ca derived temperatures are both better than 0 3 c 2 coral growth parameters such as the extension rate or density generally appear to respond to environmental changes such as rainfall but do not affect the sr ca partitioning between coralline aragonite and seawater no correlation has been found between calcification rate and sr ca variations consistent with sr ca being mainly controlled by temperature in the great barrier reef the interannual variability in sst is primarily related to the el nino southern oscillation phenomenon and is typically marked by a cold anomaly during the winter preceding the mature warm phase instrumental records show that the surface waters of the coral sea around 19 s have experienced a significant cooling associated with the el ninos of 1965 1972 and 1982 1983 which the porites corals record faithfully the coral derived temperatures for the period from 1965 to 1993 show an increase of 1 3 c which has occurred mainly since 1979 this warming is larger in magnitude but consistent with the trend for the southern hemisphere land and marine temperature records which shows an increase of around 0 4 c

some geological implications of average quaternary glacial conditions analyses of quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages but for most of quaternary time environments were intermediate in character average quaternary glacial conditions based on assessment of the marine isotope record approximated those near the stage 2 stage 1 transition and during substages 5b and 5d isotope stages 3 and 4 and substages 5a d lie within one standard deviation of the mean value under average glacial conditions ice sheets lying over northern north america and europe were much more contracted than their full glacial counterparts and the distribution of mountain glaciers reflected a snowline depression of some 500 m geomorphic processes operating under average quaternary conditions contributed importantly to landscape evolution examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the pacific northwest the fjords and strandflat of western norway and atolls of the tropical oceans by examining the geologic record from the perspective of average conditions rather than those of climatic extremes added insight can be gained regarding the evolution of quaternary landscapes

canadian arctic permafrost observatories detecting contemporary climate change through inversion of subsurface temperature time series 1 we describe long term permafrost temperature and climate change observatories established in the northeastern canadian high arctic 77 82 5 n two sites have deep temperature logs 165 and 800 m and thermistor cables and automatic loggers have been installed in the upper 65 m the third site has multiple temperature logs at three 61 m boreholes with thermistor cables frozen into the permafrost a fourth deep site 750 m is included for regional completeness geothermal spectrum inversion is used to determine ground surface temperature histories the little ice age is resolved from the mid 1700s to mid 1800s with surface temperatures 1 k below the long term mean a subsequent recovery yields late 20th century surface temperatures 3 k higher these results correlate with similar reconstructions reported for greenland ice cap holes grip and dye 3 to the southeast the canadian and greenland surface temperatures show a weak inverse correlation with the north atlantic oscillation suggesting recent climate change as a common causal source simultaneous inversions of multiple logs over 22 years at the 61 m holes resolve two to three major cycles in ground surface temperature variation over the latter half of the 20th century here permafrost ground temperatures increase 0 3 0 5 c decade compared to 0 6 c decade for air temperatures annual total snow increases 22 cm decade and may insulate permafrost from the larger transient trends in air temperatures finally atmospheric temperature inversions prevalent in arctic winters may contribute to anomalously high ground surface temperatures observed at two locations

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

climate change on the yucatan peninsula during the little ice age we studied a 5 1 m sediment core from aguada x caamal 20 36 6 n 89 42 9 w a small sinkhole lake in northwest yucatan mexico between 1400 and 1500 a d oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2 2 and the benthic foraminifer ammonia beccarii parkinsoniana appeared in the sediment profile indicating a hydrologic change that included increased lake water salinity pollen from a core in nearby cenote san jose chulchaca showed a decrease in mesic forest taxa during the same period oxygen isotopes of shell carbonate in sediment cores from lakes chichancanab 19 53 0 n 88 46 0 w and salpeten 16 58 6 n 89 40 5 w to the south also increased in the mid 15th century but less so than in aguada x caamal climate change in the 15th century is also supported by historical accounts of cold and famine described in maya and aztec chronicles we conclude that climate became drier on the yucatan peninsula in the 15th century a d near the onset of the little ice age lia comparison of results from the yucatan peninsula with other circum caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the lia at that time sea surface temperatures cooled and aridity in the circum caribbean region increased

stable isotope air temperature relationships in ice cores from dolleman island and the palmer land plateau antarctic peninsula whilst stable isotope analysis of ice cores yields the best quantitative evidence for past climate there remains considerable uncertainty about the detailed relationship between the isotopic composition and air temperature analysis of two ice cores from the antarctic peninsula a 47 2 m core from the palmer land plateau 74 oi s 70 38 w and a 32 m core from dolleman island 70035 2 s 60055 5 w has shown that an oxygen isotope temperature relationship exists at a resolution of inter annual variations during the period 1938 86 all the major regional temperature anomalies known from climatic records at several stations are visible in the isotope profiles including the overall temperature increase between 1960 and 1980 an isotope temperature gradient of 0 5 o 6 c is indicated for the climatic interpretation of isotopic fluctu

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

rates of soil development from four soil chronosequences in the southern great basin abstract four soil chronosequences in the southern great basin were examined in order to study and quantify soil development during the quaternary soils of all four areas are developed in gravelly alluvial fans in semiarid climates with 8 to 40 cm mean annual precipitation lithologies of alluvium are granite gneiss at silver lake granite and basalt at cima volcanic field limestone at kyle canyon and siliceous volcanic rocks at fortymile wash ages of the soils are approximated from several radiometric and experimental techniques and rates are assessed using a conservative mathematical approach average rates for holocene soils at silver lake are about 10 times higher than for pleistocene soils at kyle canyon and fortymile wash based on limited age control holocene soils in all four areas appear to develop at similar rates and pleistocene soils at kyle canyon and fortymile wash may differ by only a factor of 2 to 4 over time spans of several millennia a preferred model for the age curves is not linear but may be exponential or parabolic in which rates decrease with increasing age these preliminary results imply that the geographical variation in rates within the southern great basin mojave region may be much less significant than temporal variation in rates of soil development the reasons for temporal variation in rates and processes of soil development are complexly linked to climatic change and related changes in water and dust erosional history and internally driven chemical and physical processes

nao signal recorded in the stable isotopes of greenland ice cores 1 the winter 18o signal is extracted from 7 greenland ice cores covering the past 700 years to filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data a comparison between the time series of the first principal component pc1 with 67 years of winter december to march temperature measurements from 3 southern greenland synoptic stations shows highly significant correlations southern greenland winter temperatures are known to be greatly influenced by the north atlantic oscillation nao a good proxy for southern greenland temperatures is therefore expected to reveal at least parts of the nao signal it is shown that the pc1 time series indeed is significantly correlated to the nao during the winter months the inclusion of ice core winter season 18o time series in future multiproxy nao reconstructions is therefore recommended

soil forming intervals caused by eolian sediment pulses in the lahontan basin northwestern nevada we have studied a series of toyeh post isotope stage 2 eolian dust fall was the source of fines and salts in these soils apparently this influx was concentrated during two brief intervals or pulses one during the holocene and one during the previous isotope stage 5 interpluvial leaching during the sehoo pluvial removed salts from churchill soils carbonate and soluble salts now observed in the churchill soils represent a toyeh overprint on the churchill profile these pulses of fine sediment and accompanying salts are tantamount to the soil forming intervals that morrison described in the lahontan area episodic eolian dustfall provides fine particles of silicates calcite and soluble salts that infiltrate into the clast supported alluvial piedmont sediments several hundred playas exist in the basin and range each providing directional dust contributions that influence local and regional soil development we counsel caution in assuming constant gradual development of soil properties without due consideration of paleoenvironmental influences on soil forming factors

a 900 year stable isotope record of interdecadal and centennial change from the california current this paper describes the development of a high resolution record of interdecadal and centennial variability of ocean climate of the california current from continuous 5 year sampling intervals based on varve counts from santa barbara basin sediments we show the importance of the choice of species and size fraction as well as the practice of making multiple measurements per interval to obtain a clear environmental signal capable of resolving interdecadal change changes in temperature and salinity from oceanographic surveys of the past 50 years indicate that thermal variability dominates the 18o signal a 18o record from neogloboquadrina dutertrei spanning 1030 1905 a d contains interdecadal thermal fluctuations within the upper thermocline that are centered around periods of roughly 55 70 and 90 years the interdecadal changes comprise the major share of total variability compared to a low amplitude mode of underlying multicentennial variability corresponding to the medieval warm period and the little ice age

summer temperature patterns over europe a reconstruction from 1750 a d based on maximum latewood density indices of conifers abstract temperature variations over europe are reconstructed for a 6 month summer season from april to september for the period 1750 1850 using a network of maximum latewood density chronologies of coniferous trees around 44 of the variance of the whole temperature grid was explained in calibration independent verification indicates that over the reconstruction period the explained variance averaged over the whole grid should lie in the range 30 to 35 the reconstructions are better in the north of the region about 50 explained temperature variance based on comparison with independent climate data than in the south below 20 the temperature recontructions indicate cooler summers over europe from 1812 to 1816 and during the 1830s the summers of the 1820s were the warmest reconstructed decadal variations occur on a regional scale but no similar periods of anomalously cooler or warmer summers occurred between 1750 and 1810 throughout europe

last millennium summer temperature variations in western europe based on proxy data we present a method of multiproxy reconstruction of the climate of europe during the last millennium the proxies used comprise long tree ring width series grape harvest dates greenland ice oxygen isotope series and temperature indices based on historical documents the proxies are calibrated using gridded april to september mean temperatures for western europe i e between 10 degrees w and 20 degrees e and between 35 degrees n and 55 degrees n they are calibrated also using the long instrumental summer temperature series of the marseilles observatory of longchamp which begins in the mid eighteenth century the method is a combination of an analogue technique which is able to deal with missing data an artificial neural network technique for an optimal non linear calibration and a bootstrap technique for calculating error bars on the reconstruction about 70 of the temperature variance is reconstructed the amplitude of the past temperature variations is particularly well reconstructed which is important when considering whether the recent temperature trend is or is not within the natural variability it appears that the temperature of the last decade of the twentieth century was reached only 14 times during the last millennium the reconstruction is discussed with respect to other multiproxy and borehole temperature reconstructions we conclude that a reconstruction such ours with a specific regional focus as opposed to the larger northern hemisphere is more reliable and is in better agreement with borehole results even allowing for the fact that only a part of the long term variance is reconstructed little ice age c ad 1560 1930 summers were 0 2 0 5 degrees c cooler than the 1961 1990 period borehole temperatures indicate a cooling of 0 4 degrees c which falls in the 95 confidence interval of our reconstructions

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

glacial chronology of the ruby mountains east humboldt range nevada abstract the ruby mountains east humboldt range one of the interior mountain groups of the basin and range province lies about midway between the wasatch mountains and the sierra nevada after blackwelder s description in his review of glaciation in the western mountains sharp mapped and named the deposits of the lamoille and angel lake glaciations and correlated them with early and late wisconsin deposits of the great lakes area the refinement of relative dating rd methods the availability of airphotos and modern topographic maps and new road cuts have aided the restudy of these alpine glacial deposits and the basis for their correlation lamoille moraines are smooth ridges and show little detail of constructional topography valleys glaciated only by lamoille ice still show the characteristics of a glaciated trough but they have been greatly modified by weathering and erosion granite boulders on lamoille moraines are pitted and pegmatites have grotesque shapes with 30 cm deep pits cuts through lamoille end moraines and alluvial talus cones expose a thick soil profile with a well developed blocky structure in a reddish brown argillic b horizon subsurface granitic boulders in the b horizon of lamoille tills show much greater weathering than do those in angel lake tills in contrast angel lake moraines are irregular and rugged contain closed depressions and have been little altered since deposition surfaces scoured by angel lake ice are fresh and unweathered granites of angel lake moraines have weathered surfaces but show little pitting pegmatites have pits up to 10 cm deep the thin soil profiles on angel lake tills and alluvial talus cones display brown colors minor clay accumulation and no b horizon structure these weathering and morphological differences suggest that the lamoille deposits have been exposed to weathering and erosion for a period of time as much as an order of magnitude longer than the angel lake deposits thus only the angel lake is wisconsinan in age and the lamoille drift is more reasonably correlated with the illinoian stage of the great lakes region

sst artifacts in coral proxy records produced by early marine diagenesis in a modern coral from rabaul papua new guinea 1 we investigated the effects of early marine diagenesis on the skeletal geochemistry of a porites coral collected live offshore of rabaul papua new guinea the lowermost 14 cm of the 1 9 m coral core contains physical evidence of alteration which is clearly visible in x radiograph sem and petrography images abrupt and significant increases in coral 18o and sr ca and decreases in coral mg ca occur at the transition from unaltered to altered skeleton all of which imply significant sst cooling if the altered nature of the coral skeleton went unrecognized screening for the effects of early marine diagenesis should become a standard procedure in coral climate studies

polygenetic history of paleosols in middle upper pennsylvanian cyclothems of the illinois basin u s a part i characterization of paleosol types and interpretation of pedogenic processes abstract the morphology mineralogy and stratigraphic and lateral distribution of paleosols in pennsylvanian moscovian gzhelian atokan virgilian mixed marine and terrestrial coal bearing strata i e cyclothems in the illinois basin ib are presented in order to determine the dominant pedogenic processes within a cyclic sedimentary depositional framework paleosol morphologies range from weakly developed horizons with evidence of rooting and little to no pedogenic structure to horizons with well developed pedogenic slickensides angular blocky structure and carbonate nodules and tubules the majority of paleosols in strata from the basin interior preserve 1 low chroma gley colors 2 identifiable fossil plant organic matter that increases in abundance upward in the profiles toward the interpreted paleo surface and 3 calcite sphaerosiderite and pyrite cements and nodules in contrast paleosols in strata from the northern margin of the basin display high chroma colors and calcite cements and less fossil organic matter sphaerosiderite and pyrite cements these observations indicate that paleosols from the basin interior underwent a multi phase pedogenic and shallow burial history characterized by an initial better drained oxygenated stage under seasonal precipitation followed by a poorly drained reducing stage while paleosols from the northern margin of the basin experienced overall more oxygenated conditions throughout their pedogenic development x ray diffraction analysis of the 2 m size fraction of paleosol matrix in ib paleosols indicates a mineralogical composition dominated by kaolinite randomly interstratified r0 and ordered r1 illite smectite i s and subordinate amounts of chlorite these combined observational and mineralogical datasets indicate that significant changes in paleohydrology were largely responsible for the development of pennsylvanian soil profiles in the ib

dynamic winter climate response to large tropical volcanic eruptions since 1600 1 we have analyzed the mean climate response pattern following large tropical volcanic eruptions back to the beginning of the 17th century using a combination of proxy based reconstructions and modern instrumental records of cold season surface air temperature warm anomalies occur throughout northern eurasia while cool anomalies cover northern africa and the middle east extending all the way to china in north america the northern portion of the continent cools with the anomalies extending out over the labrador sea and southern greenland the analyses confirm that for two years following eruptions the anomalies strongly resemble the arctic oscillation northern annular mode ao nam or the north atlantic oscillation nao in the atlantic eurasian sector with our four century record the mean response is statistically significant at the 95 confidence level over much of the northern hemisphere land area however the standard deviation of the response is larger than the mean signal nearly everywhere indicating that the anomaly following a single eruption is unlikely to be representative of the mean both the mean response and the variability can be successfully reproduced in general circulation model simulations driven by the solar heating induced by the stratospheric aerosols these models produce enhanced westerlies from the lower stratosphere down to the surface the climate response to volcanic eruptions thus strongly suggests that stratospheric temperature and wind anomalies can affect surface climate by forcing a shift in the ao nam or nao

evaluating the use of the massive coral diploastrea heliopora for paleoclimate reconstruction 1 to date coral based paleoclimate research in the pacific has primarily utilized core samples from the genus porites and has been most successful reconstructing past variability on interannual timescales particularly the el nino southern oscillation enso the indo pacific coral genus diploastrea however owing to its slower extension rate denser structure and longer lifespan can potentially preserve geochemical proxy records 2 3 times longer than porites cores of the same length before its potential can be realized diploastrea must first be calibrated and its climate signal assessed we present oxygen isotope 18o and sr ca results from two diploastrea cores collected in fiji 16 49 s 179 14 e that allow for simultaneous evaluation of this coral s paleoclimatic utility and the reproducibility of each tracer at this site comparison to a porites record from the same location allows for further evaluation of diploastrea as a paleoclimatic archive we demonstrate that diploastrea s septal and columellar material yield similar 18o sst relationships and that despite some sacrifice of the seasonal 18o amplitude bulk sampling of either region is satisfactory for resolving interannual and lower frequency modes of climatic variability therefore paleoclimate reconstructions employing either a septal or columellar sampling regime of this genus may be useful at filling in spatial and temporal sampling gaps which currently hinder the reconstruction of long term changes in major climate fields in the western pacific

optimal sites for coral based reconstruction of global sea surface temperature we determine the structure of a network of sites from which coral based proxy measurements of sea surface temperature sst variability minimize the error in a reconstruction of the large scale features of the global sst field for a wide range of coral derived sst observational error and several minimization criteria sites in the equatorial oceans especially the central and eastern equatorial pacific best minimize the error in the reconstruction if the observational error is sufficiently low additional optimal sites are in selected subtropical locations if the observational error is high the error is minimized by resampling the most important equatorial sites the marginal return on additional sites diminishes rapidly and is not sensitive to the size of the observational error two sites reduce the analysis error by half as much as 10 sites while the first 6 7 sites achieve half the error reduction of all 65 sites in the analysis domain in the extratropics the reduction of reconstruction error is small and gradual while error in the tropical pacific is sharply reduced by 2 3 sites and gradually thereafter these results suggest that a limited set of redundantly sampled sites with uncorrelated and low observational error 0 3 0 6 c will provide the best approach to reconstruction of large scale features of the sst field from coral data for the preinstrumental period

reconstruction of sea level pressure fields over the eastern north atlantic and europe back to 1500 spatially and temporally high resolution estimates of past natural climate variability are important to assess recent significant climate trends the mid latitude atmospheric circulation is the dominant factor for regional changes in temperature rainfall and other climatic variables here we present reconstructions of gridded monthly sea level pressure slp fields back to 1659 and seasonal reconstructions from 1500 1658 for the eastern north atlantic european region 30 w to 40 e 30 n to 70 n these were developed using principal component regression analysis based on the combination of early instrumental station series pressure temperature and precipitation and documentary proxy data from eurasian sites the relationships were derived over the 1901 1960 calibration period and verified over 1961 1990 under the assumption of stationarity in the statistical relationships a transfer function derived over the 1901 1990 period was used to reconstruct the 500 year large scale slp fields systematic quality testing indicated reliable winter reconstructions throughout the entire period lower skill was obtained for the other seasons although meaningful monthly reconstructions were available from around 1700 onwards when station pressure series became available the quality and the reconstructed slp fields for two exceptionally cold years 1573 1740 are discussed and climatologically interpreted an eof analysis of the 1500 1999 winter slp revealed firstly a zonal flow pattern with pronounced decadal to centenial time scale variations secondly a monopole pattern over northwest europe and thirdly a pattern modulating the meridional flow component over europe these 500 year slp reconstructions should be useful for modelling studies particulary for analyses of low frequency atmospheric variability and for circulation dynamics

climate since ad 1510 on dyer plateau antarctic peninsula evidence for recent climate change a 480 year record of the oxygen isotope ratios dust content chemical species and net accumulation from ice cores drilled in 1989 90 on dyer plateau in the antarctic peninsula is presented the continuous analyses of small sub annual samples reveal well preserved annual variations in both sulfate content and 18o thus allowing an excellent time scale to be established this history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries furthermore unlike in east antarctica on dyer plateau conditions appear to have been fairly normal from ad 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930 reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present this intuitive conflict between increasing net accumulation and depleted 18o cooler climate in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources air temperatures and snow accumulation the complex meteorological regime in the antarctic peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high frequency processes upon the larger scale climate picture

a new method of fracture analysis azimuth versus traverse distance plots traditional fracture analysis emphasizes the statistics of fracture orientations at individual stations a new method the azimuth versus traverse distance plot avtd is proposed whereby map patterns and fracture domain boundaries receive much greater emphasis the method can be applied to any area where outcrop is nearly continuous and map data can be represented by strike alone ideal features for the method are nearly vertical joint sets which can be plotted on the proposed avtd diagrams and contoured with concentration factor statistics somewhat analogous to those used for equal area plots examples of avtd plots are given for jointing in the southern beartooth mountains wyoming illustrating ways in which generally overlooked joint set patterns may be identified and ways in which joint domain boundaries may be integrated in geologic mapping using the plots the examples show the utility of the method in assigning relative ages to fracture domains in relating the domain distributions to other structures and in testing for tectonic heredity of older fractures by upward propagation through an unconformity

resolving seasonality in tropical trees multi decade high resolution oxygen and carbon isotope records from indonesia and thailand abstract dendrochronological techniques have found limited applications in the tropics because of invisible or indistinct banding in wood the seasonal cycles of rainfall and relative humidity in these regions while not sufficient to produce distinct visible rings may still generate seasonal signals in the oxygen isotopic composition of tree cellulose which can be used for climate reconstruction and chronology we explore this approach using trees from indonesia and thailand from three different families multi decade 18o records from javanese cross dated teak rings and bomb radiocarbon dated suar wood lacking visible rings demonstrate the reproducibility of the signal between trees grown at the same locality as well as from wider geographical regions these results confirm predictions that the trees oxygen isotopic signatures reflect an external climatic forcing high resolution 18o records reveal large seasonal cycles up to 4 for javanese suar samples and up to 18 for a thai podocarpus sample we show that the six 18o and 13c cycles measured on a podocarpus match the number of growth years for the period spanning the time of wounding and cutting of the wedge section this result demonstrates that the isotopic cycles found in this tree with indistinct annual rings are indeed seasonal and could be used for chronology we present evidence that stable isotope chronologies of tropical trees also contain insights in tropical tree physiology and growth dynamics

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

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

five hundred years of gridded high resolution precipitation reconstructions over europe and the connection to large scale circulation we present seasonal precipitation reconstructions for european land areas 30 w to 40 e 30 71 n given on a 0 5 0 5 resolved grid covering the period 1500 1900 together with gridded reanalysis from 1901 to 2000 mitchell and jones 2005 principal component regression techniques were applied to develop this dataset a large variety of long instrumental precipitation series precipitation indices based on documentary evidence and natural proxies tree ring chronologies ice cores corals and a speleothem that are sensitive to precipitation signals were used as predictors transfer functions were derived over the 1901 1983 calibration period and applied to 1500 1900 in order to reconstruct the large scale precipitation fields over europe the performance quality estimation based on unresolved variance within the calibration period of the reconstructions varies over centuries seasons and space highest reconstructive skill was found for winter over central europe and the iberian peninsula precipitation variability over the last half millennium reveals both large interannual and decadal fluctuations applying running correlations we found major non stationarities in the relation between large scale circulation and regional precipitation for several periods during the last 500 years we identified key atmospheric modes for southern spain northern morocco and central europe as representations of two precipitation regimes using scaled composite analysis we show that precipitation extremes over central europe and southern spain are linked to distinct pressure patterns due to its high spatial and temporal resolution this dataset allows detailed studies of regional precipitation variability for all seasons impact studies on different time and space scales comparisons with high resolution climate models as well as analysis of connections with regional temperature reconstructions

a 700 year record of atmospheric circulation developed from the law dome ice core east antarctica 1 a 700 year high resolution multivariate ice core record from dome summit south dss 66 46 s 112 48 e 1370 m law dome is used to investigate sea level pressure slp variability in the region of east antarctica empirical orthogonal function eof analysis reveals that the first eof ldeof1 of the combined glaciochemical oxygen isotope ratio and accumulation rate record from dss represents most of the variability in sea salt seen in the record ldeof1 is positively correlated at least 95 confidence level to instrumental june mean slp across most of east antarctica over the last 700 years ldeof1 levels at law dome were the highest during the nineteenth century suggesting an increase in intensification of winter circulation during this period the law dome dss oxygen isotope ratio series also indicates that the nineteenth century had the coldest winters of any century in the record in contrast ldeof1 levels were the lowest at law dome during the eighteenth century suggesting a significant shift in the patterns and or intensity of east antarctic atmospheric circulation between the eighteenth and the nineteenth centuries the ldeof1 sea salt record is characterized by significant decadal scale variability with a strong 25 year periodic structure

gulf stream density structure and transport during the past millennium the gulf stream transports approximately 31 sv 1 sv 10 6 m 3 s 1 of water and 1 3 10 15 w of heat into the north atlantic ocean the possibility of abrupt changes in gulf stream heat transport is one of the key uncertainties in predictions of climate change for the coming centuries given the limited length of the instrumental record our knowledge of gulf stream behaviour on long timescales must rely heavily on information from geologic archives here we use foraminifera from a suite of high resolution sediment cores in the florida straits to show that the cross current density gradient and vertical current shear of the gulf stream were systematically lower during the little ice age ad 1200 to 1850 we also estimate that little ice age volume transport was ten per cent weaker than today s the timing of reduced flow is consistent with temperature minima in several palaeoclimate records implying that diminished oceanic heat transport may have contributed to little ice age cooling in the north atlantic the interval of low flow also coincides with anomalously high gulf stream surface salinity suggesting a tight linkage between the atlantic ocean circulation and hydrologic cycle during the past millennium

late miocene climate and life on land in oregon within a context of neogene global change abstract clarendonian 12 ma fossil soils plants molluscs fish and mammals of eastern oregon allow reconstruction of late miocene paleogeography paleoclimate and paleoecology on land between the global thermal maximum of the middle miocene 16 ma and global cooling and drying of the late miocene 7 ma six different pedotypes of paleosols recognized near unity and juntura allow reinterpretation of local mammalian paleoecology fossil beavers dominated gleyed entisols of riparian forest abundant camels and common hipparionine horses dominated alfisols of wooded grassland and grassy woodland diatomites overlying mammal bearing beds have bullhead catfish ictalurus ameiurus vespertinus as well as fossil leaves dominated by live oak quercus pollardiana fossil plants and soils of unity and juntura are most like those of grassy live oak woodland and savanna on the western slopes of the sierra nevada in northern california today fossil plants and soils indicate mean annual temperature of 12 9 7 7 17 7 c and mean annual precipitation of 879 604 1098 mm miocene paleoclimatic changes in eastern oregon show no relationship to changes in oxygen isotopic composition of marine foraminifera usually taken as an index of global paleoclimatic change mismatch between land and sea paleoclimatic records is most likely an artefact of global ice volume perturbation of oxygen isotopic values instead miocene paleoclimatic change in eastern oregon parallels changes in carbon isotopic composition of marine foraminifera presumably through fluctuations in greenhouse gases

soil polygenesis as a function of quaternary climate change northern great basin usa abstract the quaternary environmental history of the northern great basin is characterized by a combination of lower temperature and higher moisture than present using water balance analysis of soils sampled along a climatic gradient we demonstrate that long term average effective moisture was about 2 4 cm yr 1 greater than present although this long term average represents most of quaternary time there are important short term excursions from these values during full glacial and interglacial times full glacial conditions are characterized by effective moisture about 7 9 cm yr 1 greater than present interglacial times similar to present conditions are characterized by dry lake basins that provide major increases in eolian activity these climatic extremes drive pedogenic processes that leave polygenetic imprints on soils of pleistocene age soils that are now dominated by opaline silica carbonate and smectite contain evidence of earlier more acidic chemical environments conducive to dissolution of primary carbonate and formation of kaolinite during interglacial time more eolian activity and less effective moisture combine to decrease the depth of leaching increase base cations and modify the soil chemical environment in relict paleosols in a soil of bull lake age 150 ky bp desert loess accumulation created a 25 increase in water holding capacity and decreased the depth of water penetration by 65 cm climatic drying at the end of the pleistocene decreased leaching depth by about 150 cm

intercomparison of coral oxygen isotope data and historical sea surface temperature sst potential for coral based sst field reconstructions we examine the extent to which the large scale features of the sea surface temperature sst anomaly field are represented by a sparse observational network of coral oxygen isotope 18o time series regression of annually averaged 18o data against gridded estimates of local sst anomaly within the period 1856 1990 confirm the literature regression of 18o anomaly on sst anomaly for indo pacific corals however while interannual sst variability is generally well represented by individual coral time series observed decadal and secular variability does not always display a linear relationship to local sst anomaly instead many records appear to better recover nonlocal large scale phenomena which in turn are related to either the coral local sst or sst covariant changes in seawater 18o we employ empirical orthogonal function eof analysis to identify common patterns of variability in the coral data we find two significant patterns which are interpretable as the oceanographic signature of the el nino southern oscillation enso and as a near global warming in which the eastern equatorial pacific cools a third pattern weakly resembles the pacific decadal oscillation these modes are seen more clearly in a singular vector decomposition svd of the covariance between the coral data and the dominant patterns of large scale historical sst variability the results are consistent with those found in eof and svd analyses of sst data from the coral locations as additional coral based proxy estimates become available they will improve the resolution of the patterns recovered these results suggest that a sparse network of coral data may be used to reconstruct interannual secular and decadal sst variability for preinstrumental periods albeit with large uncertainty

distribution of calcium carbonate in desert soils a model a model that describes the distribution of calcium carbonate in desert soils as a function of dust flux time climate and other soil forming factors shows which factors most strongly influence the accumulation of carbonate and can be used to evaluate carbonate based soil age estimates or paleoclimatic reconstructions models for late holocene soils have produced carbonate distributions that are very similar to those of well dated soils in new mexico and southern california these results suggest that 1 present climate is a fair representation of late holocene climate 2 carbonate dust flux can be approximated by its holocene rate and 3 changes in climate and or dust flux at the end of the pleistocene effected profound and complex changes in soil carbonate distributions both higher carbonate dust flux and greater effective precipitation are required during the latest pleistocene early holocene to explain carbonate distributions in latest pleistocene soils 21 refs 4 figs 1 tab

a comparison of evidence for late holocene summer temperature variations in the northern hemisphere data on glacier tree line tree ring pollen and ice core variations in north america greenland and europe during the last 2000 yr up to a d 1800 are compared in detail on the century time scale only data that may be indicative of summer temperature changes are included since these comprise most of the available paleoclimatic information although some variations especially of glaciers may have been in response to precipitation changes instead radiocarbon dates and 14c dated records are converted to calendar dendrochronological years using the calibration of m stuiver 1982 radiocarbon 24 1 26 despite the basic uncertainties in dating interpretation response times and noise level of proxy climatic data there is at times good agreement among different kinds of evidence from within a region to suggest an episode of generally warmer or cooler summers three previously identified episodes find expression in records from all of the regions considered the little ice age of the last few centuries a medieval warm period around the 12th century a d and an earlier cold period some time between the 8th and 10th centuries however the timing of minima and maxima within these episodes seems to have varied from region to region although the evidence is consistent within regions in the 15th century summers were warm in the eastern canadian arctic and southern greenland while there was a cold episode in europe and western north america

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

recording of el nino in ice core δ18o records from nevado huascaran peru the 68 year monthly resolved time series of 18 o from ice cores retrieved from the glaciated col of nevado huascaran peru 9 s 77 w 6050 m reflects climate variability over amazonia and the western tropical atlantic over the 25 year period 1968 1993 of midtroposphere observations the interannual variations in huascaran 18 o relate closely with the zonal wind variations over tropical south america at the 500 hpa level additionally there is some evidence that the spatial distribution of temperature anomalies in the western tropical atlantic has influence on the 500 hpa circulation and hence the isotopic fractionation of moisture advected across amazonia during el nino warming the moisture convergence axis over the atlantic ocean is commonly diverted northward leading to unusual warm and dry conditions over northeast brazil and 18 o enriched snowfall at huascaran this enrichment phase is enhanced when the peak pacific warming occurs during the first half of the calendar year coincident with the wet season over amazonia approximately 12 months later the el nino demise is affiliated with a reprisal of strong trade wind circulation and the resultant cool pluvial environment over amazonia triggers a reversal to strongly depleted isotope anomalies

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

evaluation of sampling resolution in coral stable isotope records a case study using records from new caledonia and tarawa we have generated a 40 year long monthly stable isotope record from a porites lutea coral collected offshore of amedee new caledonia 22 s 167 e to investigate the relation between sampling resolution in coral isotope studies and retrieval of sea surface environmental information we interpret the high correlation between our oxygen isotope record and a twenty year long sea surface temperature record at the monthly timescale r 0 88 to indicate that our coral isotope record is an accurate monitor of environmental conditions offshore of amedee the character of the signal and the percent variance explained in the record at the annual band at the quasi biennial oscillation band qbo 2 0 2 4 years and at the el nino southern oscillation band enso 3 8 years changes little in response to a reduction in sampling density from monthly to bimonthly to quarterly similar results have been obtained in a reanalysis of a coral isotope record from tarawa kiribati our results indicate that a significant amount of the information obtained from high density sampling can also be retrieved from lower density sampling in particular bimonthly sampling yields virtually no drop off in variance explained and quarterly sampling is satisfactory for resolving interannual and decadal scale trends in time series the proposed sampling approach may enable a more rapid filling in of numerous spatial holes in coral sampling sites needed for reconstruction of long term decadal scale variations in climate

rates of hornblende etching in soils in glacial deposits of the northern rocky mountains wyoming montana u s a influence of climate and characteristics of the parent material abstract hornblende grains in the soil matrix of glacial deposits in the northern rocky mountains etch at rates that depend primarily upon the influences on soil moisture of the climate and the texture of the parent materials etching is a logarithmic function of age of the parent material and etching rates decline rapidly after a period of initial high rates over the first 10 15 ka after deposition in this study a comparison of etching rates was made among four chronosequences in the wind river range of western wyoming and the tobacco root range of southwestern montana which have differences in mean annual precipitation map and texture of the till parent materials using rates calculated for the first 12 ka after deposition etching is slowest 0 02 m ka 1 in coarse textured granitic parent materials where the map is 25 40 cm in contrast etching is faster by an order of magnitude 0 21 m ka 1 where the map is 110 150 cm and the parent material is finer textured because 15 sedimentary rock material has been mixed with the granitic component within individual chronosequences deposits at higher elevations have accelerated etching rates due to higher orographic precipitation or the influence of late lying snow

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

evaluating u series tools for weathering rate and duration on a soil sequence of known ages four soil profiles of known age 40 250 600 and 3000 ka from the merced soil chronosequence in california were analysed for u and th isotopes and for major and trace element compositions to test the assumption that leaching of u series isotopes is a first order process with an invariant rate constant as frequently assumed when applying this isotopic tool to determine weathering duration and sediment residence time average 230 th 238 u values for each profile decrease from a high of 1 28 in the youngest soil 40 ka to 1 09 0 99 and 0 98 in the 250 ka 600 ka and 3000 ka soils respectively 234 u 238 u values also show variation across the 4 soils the simultaneous variation in 230 th 238 u and 234 u 238 u cannot be explained by a first order kinetic model with invariant rate constants and instead requires that leaching coefficients for the u series isotopes change with time the observed data is consistent with a two stage model that reflects an initial period of fast leaching of u and th from a readily weathered soil pool such as grain boundaries or defects followed by slow leaching from a more resistant soil pool application of such a two stage model may lead to significantly shorter calculated timescales of weathering than those obtained by the widely applied single stage model of u series weathering which assumes no change in leaching coefficients over time the results of this study have wide implications for published and future use of u series tools in weathering studies

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

climate variability in west antarctica derived from annual accumulation rate records from itase firn ice cores thirteen annually resolved accumulation rate records covering the last 200 years from the pine island thwaites and ross drainage systems and the south pole are used to examine climate variability over west antarctica accumulation is controlled spatially by the topography of the ice sheet and temporally by changes in moisture transport and cyclonic activity a comparison of mean accumulation since 1970 at each site to the long term mean indicates an increase in accumulation for sites located in the western sector of the pine island thwaites drainage system accumulation is negatively associated with the southern oscillation index soi for sites near the ice divide and periods of sustained negative soi 1940 42 1991 95 correspond to above mean accumulation at most sites correlations of the accumulation rate records with sea level pressure slp and the soi suggest that accumulation near the ice divide and in the ross drainage system may be associated with the mid latitudes the post 1970 increase in accumulation coupled with strong slp accumulation rate correlations near the coast suggests recent intensification of cyclonic activity in the pine island thwaites drainage system

soil landscape response to mid and late quaternary climate fluctuations based on numerical simulations abstract we use a numerical dynamic soil landscape model to study one aspect of the spatio temporal soil landscape evolution process the effect of climatic fluctuations on soil grading distribution in space and time in response to the interplay between physical weathering and surface erosion soil mineralogical fluxes we simulate a synthetic soil landscape system over the middle and late quaternary last 400 ka the results show that 1 soil landscape response to climate change is non linear and highly spatially variable even at hillslope scale and 2 soil landscape adjustment to climate change can lag tens of thousands of years and is both spatially and temporally variable we propose that the legacy of past climatic condition i e last glacial maximum in modern soil landscape systems vary considerably in space this implies that the spatiotemporal uniformity in which soil is typically described in earth system modeling and analysis e g carbon cycle grossly underestimates their actual complexity

an 8 century tropical atlantic sst record from the cariaco basin baseline variability twentieth century warming and atlantic hurricane frequency 1 we present the first direct comparison and calibration of a downcore foraminiferal mg ca record to historical instrumental sea surface temperature sst mg ca measured on the planktic foraminifer globigerina bulloides from a cariaco basin sediment core strongly correlate with spring march may instrumental ssts between a d 1870 and 1990 a mg ca sst equation is derived and a paleo sst record is presented spanning the last 8 centuries an interval that includes the end of the medieval warm period and the little ice age the long term record displays a surprising amount of variability the temperature swings are not necessarily related to local upwelling variability but instead represent wider conditions in the caribbean and western tropical atlantic the mg ca sst record also captures the decadal and multidecadal variability observed in records of global land and sea surface temperature anomalies and atlantic tropical storm and hurricane frequency over the late nineteenth and twentieth centuries a divergence between the sst proxy record and atlantic storm frequency around 1970 appears to reflect a fundamental change in atlantic hurricane behavior noted in historical data on average twentieth century temperatures are not the warmest in the entire record but they do show the largest increase in magnitude and fastest rate of sst change over the last 800 a

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

the real color of climate change reconstructions of past temperatures often use a combination of climate proxies such as ice cores and tree rings and the instrumental temperature record how accurate are these reconstructions over time scales of decades to centuries in their perspective osborn and briffa 1 highlight the report of von storch et al 2 who have simulated the errors associated with climate proxies over these longer time scales because of systematic errors that are not taken into account in such reconstructions the amplitude of the northern hemisphere temperature fluctuations over the last millennium may have been underestimated 1 http www sciencemag org cgi content full 306 5696 621 2 http www sciencemag org cgi content short 306 5696 679

use of soil catena field data for estimating relative ages of moraines soils at the crests of moraines are commonly used to estimate the relative ages of moraines however for various pedologic and geomorphic reasons soil development at crest sites may not truly reflect the time since moraine formation for example some crest soils on moraines of greatly different age are similar in morphology and development soil catena data for soils at several sites aligned downslope from the crest can greatly improve on the usefulness of soil data for estimating moraine ages for this purpose the authors use the weighted mean catena profile development index which condenses field data for all of the soils in each catena into a single value

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

late quaternary environments and biogeography in the great basin abstract plant and animal remains found in packrat neotoma spp middens and cave fill from the eastern and southern great basin region reveal the presence of subalpine conifers and boreal mammals at relatively low elevations during the late wisconsin limber pine pinus flexilis and bristlecone pine p longaeva were important in the late pleistocene plant communities throughout this region spruce picea cf engelmannii and common juniper juniperus communis were present in some of the more northerly localities and douglas fir pseudotsuga menziesii and white fir abies concolor were present in southern and eastern localities single needle pinyon pine pinus monophylla common across this region today was apparently not present north of the sheep range of southern nevada during the late wisconsin pikas ochotona cf princeps small boreal mammals present in only a few great basin mountain ranges today were common throughout the region heather voles phenacomys cf intermedius have been found in two cave fill deposits in nevada though they are unknown in the great basin today limber and bristlecone pines are generally restricted to rocky substrates in modern subalpine habitats in the great basin and this may also have been the case when these plants grew at lower elevations during the late wisconsin subalpine conifers were present on the rock outcrops sampled by the packrat middens but shrub communities perhaps dominated by sagebrush artemisia spp may have been present on alluvial valley bottom substrates forested habitats would thus have been isolated habitat islands as they are today boreal small mammals including pikas and heather voles were able to colonize the great basin mountain ranges during the late pleistocene we suggest that these mammals were able to survive in the intervening valley bottoms under a cool summer climatic regime and that continuous forest or woodland corridors were not necessary for migration

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

changes in the content and composition of pedogenic iron oxyhydroxides in a chronosequence of soils in southern california abstract studies of the pedogenic iron oxyhydroxides in suites of latest holocene to middle pleistocene soils formed on fluvial deposits of the transverse ranges southern california indicate that the content and composition of iron oxyhydroxide change in a systematic manner analysis of total secondary free iron oxides dithionite extractable fe 2 o 3 d and ferrihydrite oxalate extractable fe 2 o 3 o shows that 1 a single logarithmic model y a b log x or double logarithmic model log y a b log x where y is the total mass of pedogenic fe oxides g cm 2 soil column and x is soil age describes the rate of increase in fe 2 o 3 d with time 2 the fe 2 o 3 d content correlates linearly with soil reddening and clay content 3 the fe 2 o 3 o fe 2 o 3 d ratio which indicates the degree of fe oxide crystallinity is moderately high to very high 0 22 0 58 in middle holocene to latest pleistocene soils and progressively decreases to less than 0 10 in older soils 4 the value of the fe 2 o 3 o fe 2 o 3 d ratio also appears to be infuenced by climate and 5 temporal changes in fe oxide content and mineralogy are accompanied by related systematic changes in clay mineralogy and organic matter content these relationships are attributed to a soil environment that must initially favor ferrihydrite precipitation and or organic matter fe complexation subsequent transformation to hematite causes increasingly intense reddening and a concomitant decrease in the fe 2 o 3 o fe 2 o 3 d ratio the results demonstrate that iron oxide analysis is useful for numerical age studies of noncalcic soils and shows potential as an indicator of paleoclimates

climatic implications of alternating clay and carbonate formation in semiarid soils of south central montana abstract evidence for climatic change is found in petrographic thin sections from soils formed on glaciofluvial deposits of rock creek and the lower clarks fork montana these soils presently in a semiarid climate range from late pliocene to holocene in age and have undergone periodic fluctuations in soil moisture caused by climatic changes in the lower parts of soil b horizons accretion of illuvial layers of clay argillans occurs mainly during wet glacial climatic periods whereas carbonate precipitates mainly during dry interglacial climatic periods thin section studies of the argillan and carbonate layers show that 1 post pinedale soils that have formed only in the present interglacial climate contain areas of secondary carbonate unrelated to argillans 2 soils formed on outwash of successively older glaciations contain proportionately more alternating layers of argillans and carbonate and 3 the maximum number and sequence of layers in a soil correspond to the number of local cycles of glacial outwash deposition and subsequent stream incision that followed the beginning of soil formation these cycles are inferred to correspond to local glacial interglacial fluctuations the correspondence between the microscopic record and the glacial outwash record for rock creek suggests that some of the climatic changes seen in the marine oxygen isotope record did not strongly affect the study area

increased seasonality in middle east temperatures during the last interglacial period the last interglacial period about 125 000 years ago is thought to have been at least as warm as the present climate owing to changes in the earth s orbit around the sun it is thought that insolation in the northern hemisphere varied more strongly than today on seasonal timescales which would have led to corresponding changes in the seasonal temperature cycle here we present seasonally resolved proxy records using corals from the northernmost red sea which record climate during the last interglacial period the late holocene epoch and the present we find an increased seasonality in the temperature recorded in the last interglacial coral today climate in the northern red sea is sensitive to the north atlantic oscillation a climate oscillation that strongly influences winter temperatures and precipitation in the north atlantic region from our coral records and simulations with a coupled atmosphere ocean circulation model we conclude that a tendency towards the high index state of the north atlantic oscillation during the last interglacial period which is consistent with european proxy records contributed to the larger amplitude of the seasonal cycle in the middle east

sources of strontium and calcium in desert soil and calcrete the carbon cycle significance of soil carbonate fluxes is subject to large uncertainties because it is not clear precisely how much calcium is derived from atmospheric sources compared with that from the chemical weathering of silicate minerals in the petrocalcic horizon calcrete of a pleistocene soil from the usda scs desert project area near las cruces nm approximately 1 5 g ca cm 3 has been added with an associated expansion of the profile of200 strontium isotope values for the labile cations and carbonate from the a b and k soil horizons have 87 sr 86 sr values that range from 0 7087 to 0 7093 similar to the values for easily soluble local dust and rain the parent material non calcareous camp rice alluvial sediment has a 87 sr 86 sr ratio of0 7165 mixing calculations indicate a minimum atmospheric contribution to soil carbonate calcium of 94 the more likely scenarios indicate at least 98 of the ca originated from atmospheric input the variations in 87 sr 86 sr ratios of soil silicate 0 7131 to 0 7173 are consistent with weathering of volcanogenic sediments and neoformation of clay minerals in the petrocalcic horizon moreover the sr isotope data suggest that 50 70 of silicate in the uppermost 25 cm of the profile could be atmosphere derived the isotopic composition of labile strontium in the a horizon and the mass distribution of silicon and calcium indicate that the uppermost portion of the profile is the present zone for the release of cations due to silicate weathering steady state models of the whole profile yield a sr weathering flux ranging from200 to 400 m gc m 2 ma 1 the results indicate that both the present day and long term contribution of calcium from silicate weathering is less than 2 of that supplied from the atmosphere and confirm that desert soil formation is not a significant sink for atmospheric carbon 1999 elsevier science b v all rights reserved

borehole versus isotope temperatures on greenland seasonality does matter new simulation results obtained with the hamburg atmosphere general circulation model echam 4 under maximum glacial boundary lgm conditions confirm the paleotemperatures on greenland determined by borehole thermometry the disagreement between 18o isotope based temperatures and the borehole temperatures of the lgm is not only reproduced by the model but the simulation results provide a plausible explanation paleotemperatures inferred from 18o measurements in ice cores are biased by a substantially increased seasonality of precipitation over greenland during the lgm during the glacial winter a much more zonal circulation prevents the effective transport of moisture to the greenland ice sheet and therefore reduces the contribution of isotopically strongly depleted winter snow to the annual mean isotope signal

soil development on stable landforms and implications for landscape studies abstract soil development parameters include a wide variety of morphological chemical and mineralogical parameters but some of the best indicators of time and surface stability are derived from field morphology over long time spans the most common time function for soil development is exponential or logarithmic in which rates decrease with increasing age over shorter time spans in semi arid and moister climates holocene and pleistocene soil development functions appear as linear segments with holocene rates about 10 to 50 times those of pleistocene rates in contrast to significant temporal variation in rates geographical variation in rates within a the southern great basin and b the east central valley of california is on the order of 2 or 3 times when comparing soil development indices of the semi arid great basin to those of moister central california holocene rates are similar but pleistocene rates are more than 10 times slower in the great basin in a range of climatic settings the reasons for declining rates over time are several and are complexly related to erosional history fluxes in water and dust related to climatic changes rates of primary mineral dissolution and intrinsic soil processes

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

on the temperature correlation of δ18o in modern precipitation reevaluation of modern precipitation temperature and isotope data permits reconciliation of previous disparate values for the correlation between 18o of modern precipitation and surface temperature past analysis has used the mean surface temperature over the time interval of sample collection e g mean weekly monthly or annual temperature to calculate temperature coefficients and different approaches at mid latitudes yield different temperature coefficients 18o t spatial correlations among geographically distinct sites yield 0 55 k seasonal variations at single sites yield 0 2 0 4 k and 12 month running averages yield 0 5 1 k however there are systematic differences in temperature during precipitation events vs time averaged surface temperature means correction for this bias using hourly weather and monthly isotope data from u s sites yields a single value of 0 55 k for all three approaches revised temperature coefficients based on surface observations are also commensurate with coefficients obtained using cloud base temperatures and with theoretical distillation models 0 5 0 7 k these coefficients provide a consistent basis for validation of general circulation models that incorporate stable isotopes of precipitation and for comparison to independent estimators of the isotopic response to climate change

late oligocene bunch grassland and early miocene sod grassland paleosols from central oregon usa abstract fossil soils burrows and mammals of the upper john day formation in central oregon are evidence of bunch grasses and open semiarid vegetation as old as late oligocene earliest arikareean 30 ma root traces in these paleosols include both stout tapering tubes like roots of trees as well as sinuous filamentous tubes similar to roots of grasses paleosol structure is fine subangular blocky with patchy distribution of grass like roots as in wooded grassland and sagebrush steppe with bunch grasses cursoriality in horses mesohippus miohippus and hypsodonty in rhinos diceratherium is also evidence for open grassy vegetation trace fossils of pallichnus dung beetle boli and edaphichnium earthworm chimneys are characteristic of wooded grassland paleosols whereas taenidium cicada burrows dominates desert shrubland paleosols as has also been found in quaternary paleosols and soils of eastern washington in both oligocene and quaternary paleosol sequences arid shrubland and semiarid grassland paleosols alternate on milankovitch frequencies 23 41 100 ka the oldest known paleosols in oregon with crumb structure and abundant fine fossil root traces characteristic of sod grasslands are dated by mammalian biostratigraphy as hemingfordian early miocene ca 19 ma wooded grassland habitats are indicated by scattered chalcedony calcite rhizoconcretions from large woody plants and by fossil chalicotheres moropus camels gentilicamelus paratylopus and horses parahippus silty texture and silcrete horizons are evidence of semiarid to arid paleoclimate and are in striking contrast to highly calcareous and clayey underlying paleosols of the john day formation these silcrete paleosols may represent the miocene onset of summer dry mediterranean seasonality as opposed to a summer wet monsoonal pattern of seasonality found in this region during the oligocene oregon s early rangelands can be compared with those in the north american great plains granular structured calcareous paleosols of the brule formation of south dakota are evidence of dry bunch grasslands as old as 33 ma early orellan early oligocene and crumb structured paleosols of the anderson ranch formation of nebraska are evidence of sod grasslands as old as 19 ma late arikareean early miocene although grasses were a conspicuous part of dry rangelands well back into the oligocene early and middle miocene sod grasslands in north america were restricted to regions estimated to have had less than 400 mm mean annual precipitation

influence of climate and eolian dust on the major element chemistry and clay mineralogy of soils in the northern bighorn basin u s a abstract soil chronosequences in the northern bighorn basin permit the study of chronologic changes in the major element chemistry and clay mineralogy of soils formed in different climates two chronosequences along rock creek in south central montana formed on granitic alluvium in humid and semiarid climates over the past two million years a chronosequence at the kane fans in north central wyoming formed on calcareous alluvium in an arid climate over the past 600 000 years detailed analyses of elemental chemistry indicate that the soils in all three areas gradually incorporated eolian dust that contained less zirconium considered to be chemically immobile during weathering than did the alluvium b and c horizons of soils in the wettest of the chronosequences developed mainly at logarithmic rates suggesting that leaching initially rapid but decelerating dominated the dust additions in contrast soils in the most arid of the chronosequences developed at linear rates that reflect progressive dust additions that were little affected by leaching both weathering and erosion may cause changes with time to appear logarithmic in a horizons of soils under the moist and semiarid climatic regimes clay minerals form with time in the basal b and c horizons and reflect climatic differences in the three areas vermiculite mixed layer illite smectite and smectite form in the soils of the moist climate chronosequence smectite forms in the semiarid climate chronosequence and smectite and palygorskite form in the arid climate chronosequence

temperature history and accumulation timing for the snowpack at gisp2 central greenland previous research has documented a close association between high resolution snow pit profiles of hydrogen and oxygen stable isotope ratios and multi year special sensor microwave imager ssm i 37 ghz brightness temperature data in central greenland comparison of the ssm i data to profiles obtained during the 1989 91 field seasons indicated that d and 18 o data from the near surface snow at the greenland summit are a reliable high resolution temperature proxy to test this new technique further additional stable isotope data were obtained from a 2 m snow pit constructed during late june 1995 near the gisp2 site this new profile supported by pit stratigraphy and chemistry data confirms the utility ofcomparing stable isotope records with ssm i brightness temperatures the sub annual variation of the d record at the gisp2 site was determined using 15 match points from approximately december 1991 through june 1995 and was guided in part by time constrained hoar layers the close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year this is also independently confirmed by analysis of h 2 o 2 data the slope of the multi year t vs 6 correlation was evaluated along with the sub annual variation in the amount rate and timing of accumulation these new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub annual resolution this encourages confident interpretation of the paleoclimatic signal variations in the gisp2 and grip deep cores

rapid 20th century increase in coastal upwelling off northwest africa near shore waters along the northwest african margin are characterized by coastal upwelling and represent one of the world9s major upwelling regions sea surface temperature sst records from moroccan sediment cores extending back 2500 years reveal anomalous and unprecedented cooling during the 20th century which is consistent with increased upwelling upwelling driven ssts also vary out of phase with millennial scale changes in northern hemisphere temperature anomalies nhtas and show relatively warm conditions during the little ice age and relatively cool conditions during the medieval warm period together these results suggest that coastal upwelling varies with nhtas and that upwelling off northwest africa may continue to intensify as global warming and atmospheric co 2 levels increase

a quantitative reconstruction of a loess paleosol sequence focused on paleosol genesis an example from a section at chaoyang china abstract a typical loess paleosol sequence at chaoyang in china deposited continuously since 423 ka bp was examined to quantitatively reconstruct a loess paleosol sequence first particle size distribution was evaluated based on clay free fractions where the sum of sand silt 100 and fine earth fractions and used to characterize the parent material uniformity as well as field morphology geochemical features and micro morphology characteristics second mass balance mb and soil reconstruction sr approaches were employed to examine the linkage between pedogenesis and loess deposition the results indicated a uniform loess deposit below 228 cm depth and the presence of four reddish stratigraphic layers interbedded with four yellowish stratigraphic layers all derived mostly from silt eolian deposits the main soil pedogenic processes following silt deposition were clay eluviation illuviation silification and ferrallitization the strongest pedogenesis occurred for the s3 deposit layer during 225 243 ka bp and was associated with the greatest mass loss of non clay 7 6 na2o 42 cao 21 mgo 28 sio2 10 and at the same time with the greatest gains in clay 42 fe2o3 8 and al2o3 4 together with mass loss changes mc of 620 g 100 cm2 the greatest mass gain changes 234 g 100 cm2 occurred in the l4 deposit layer during 243 311 ka bp and were associated with gains in na2o 18 and p2o5 4 5 indicating the fastest deposition rate during the long period of sedimentation 423 ka bp loess deposition was predominant during dry cold periods whereas paleosol formation from pedogenic processes was predominant during wet warm periods thus the formation of paleosols and loess deposition were dependent on the relative rate of pedogenesis and deposition as controlled by climate change under an east asian summer monsoon eas paleosol formation dominated whereas loess deposition dominated under an east asian winter monsoon eaw quantification of the degree of loess development paleosols or loess deposits aids reconstructing soil genesis and understanding the loess paleosol formation sequence and its linkage to climate change

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

summer temperature variations in the european alps a d 755 2004 abstract annually resolved summer temperatures for the european alps are described the reconstruction covers the a d 755 2004 period and is based on 180 recent and historic larch larix decidua mill density series the regional curve standardization method was applied to preserve interannual to multicentennial variations in this high elevation proxy dataset instrumental measurements from high low elevation grid boxes back to 1818 1760 reveal strongest growth response to current year june september mean temperatures the reconstruction correlates at 0 7 with high elevation temperatures back to 1818 with a greater signal in the higher frequency domain r 0 8 low elevation instrumental data back to 1760 agree with the reconstruction s interannual variation although a decoupling between warmer instrumental and cooler proxy data before 1840 is noted this offset is larger than during any period of overlap with more recent high elevation instrumental data even though the proxy time series

late miocene advent of tall grassland paleosols in oregon abstract paleosols in the late miocene rattlesnake formation reveal three successive paleoclimatic regimens that can be dated using cumulative paleosol development prior to the radiometrically dated rattlesnake ash flow tuff 7 05 ma the basal rattlesnake formation ca 7 5 7 3 ma has a suite of weakly calcareous paleosols indicating subhumid paleoclimate 800 1000 mm mean annual precipitation or map and seasonal waterlogging a shift at ca 7 3 ma to semi arid paleoclimate map 500 850 is indicated by paleosols with calcic horizons at depths of 105 85 cm a second shift at ca 7 2 ma ushered in an assemblage of soils with shallow 36 53 cm calcic horizons indicating semi arid conditions map 200 600 mm not much different from today along with the climatic shifts documented by the paleosols there also are substantial changes in alluvial architecture and paleotopography the lower rattlesnake formation ca 7 5 7 2 ma was deposited by a stream flowing northeast in an ancestral john day valley the upper part of the formation ca 7 2 7 1 ma was deposited within large alluvial fans shed from the growing anticline of picture gorge basalt to the north stepwise changes in former vegetation can also be interpreted from paleosols the basal rattlesnake formation 7 5 7 3 ma has a suite of paleosols with root traces clay skins and manganese nodules like those of riparian woodland and seasonally waterlogged riparian meadow the succeeding paleoclimatic sequence 7 3 7 2 ma includes the earliest known mollic paleosols with deep 50 cm calcareous nodules interpreted as former soils of tall grassland also found are manganese stained paleosols of seasonally waterlogged meadows and weakly developed paleosols of early successional riparian vegetation a later paleoclimatic sequence 7 2 7 1 ma includes desert shrubland paleosols as well as paleosols of early successional riparian vegetation fossil bones and teeth found in many paleosols indicate coeval changes in mammalian faunas the major shift from woodland to grassland at ca 7 3 ma introduced into this area tall grassland ecosystems including large cursorial horses and pronghorns aridification continued with the shift to shrubland ca 7 2 ma early hemphillian which corresponds to continent wide mass extinction of most remaining browsing mammals from the clarendonian chronofauna

clay illuviation and calcium carbonate accumulation along a precipitation gradient in kansas one of the significant features of loess derived soils in kansas is the occurrence of clay rich subsurface horizons above a layer enriched with pedogenic carbonates in order to examine the extent of clay increase and pedogenic carbonate enrichment in a precipitation gradient ten soil profiles from three different precipitation regions were studied using micromorphological and mineralogical techniques the precipitation gradient was divided into three groups 400 550 mm 550 750 mm and 750 1100 mm regions the objectives were to 1 understand the cause of clay orientation in clay rich horizons 2 investigate the reasons for the clay increase and 3 observe the interaction of clay and pedogenic carbonate accumulation features along a precipitation gradient in kansas although clay films were identified in the field for soils in the 400 550 mm regions illuvial clay films were not observed in thin section analysis the clay accumulations mostly occurred as grain coatings the rest of the clay accumulations observed were very thin striated and mostly associated with voids the argillic horizons had a granostriated b fabric which indicates stress orientation of micromass caused by high shrink swell activity thick and continuous illuvial coatings were observed in the buried horizons of paleosols in the other two regions where precipitation exceeds 550 mm illuvial clay coatings with strong orientation were observed along with thin and striated stress oriented clay both types of clay orientations exceeded 1 of the cross sectional area for the thin section although illuvial clay features and pedogenic carbonates were observed in all soils at approximately the same depth complete obliteration of clay coatings was not observed in these horizons in situ weathering of biotite was one of the reasons for the clay increase in all soil profiles in all soils studied the clay increase and cause of clay orientation cannot be attributed to a single genetic process or event both illuviation and shrink swell activity were involved in the orientation of clay although orientation of clay and pedogenic carbonates were observed in all soils at approximately the same depth the decomposition of clay coatings was not observed in these horizons

atmospheric circulation variability associated with shallow core seasonal isotopic extremes near summit greenland seasonal back diffused 18o time series reconstructed for nine shallow firn cores from the greenland summit for 1959 1987 are evaluated in terms of 1 their spatial and temporal variability and 2 their association to the atmospheric circulation rotated principal component analysis evaluates spatial and temporal patterns of organization in the back diffused 18o ice core time series mean sea level pressure and 500 hpa height fields are obtained for winter and summer seasons that fall in the isotopically warmest and coldest thirds of the seasonal data the winter back diffused 18o data indicate that some degree of longitudinal separation takes place between isotopic records from western and eastern greenland in agreement with coastal station climatic data temporal variability is linked with statistical significance to the variability of the atmospheric circulation over the denmark strait as well as over the norwegian and barents seas the north atlantic oscillation nao and the mean icelandic low in the denmark strait affect isotopic variability over the cores west of the ice divide just as they have been shown to prominently affect west coast air temperature records isotopic variability at some ice cores east of the divide is influenced by pressure variability over the norwegian and barents seas although statistical significance is lower the nao appears insignificant in summer isotopic variability as the circulation in that season is very much localized and dominated by either ridging warm cases or troughs cold cases over eastern greenland and the arctic ocean results suggest that long term winter 18o variability can potentially be linked to climate variation over europe especially from the mediterranean basin northward to about 55 n and as far east as central siberia