sea surface temperature variability in the norwegian sea during the late pliocene linked to subpolar gyre strength and radiative forcing the mid piacenzian warm period 3 264 3 025 ma of the pliocene epoch has been proposed as a possible reference for future warm climate states however there is significant disagreement over the magnitude of high latitude warming between data and models for this period of time raising questions about the driving mechanisms and responsible feedbacks we have developed a new set of orbital resolution alkenone based sea surface temperature sst and ice rafted debris ird records from the norwegian sea spanning 3 264 3 14 ma the ssts in the norwegian sea were 2 3 c warmer than the holocene average likely caused by the radiative effect of higher atmospheric co2 concentrations there is notable obliquity driven sst variability with a range of 4 c shown by evolutive spectra the correlation of sst variability with the presence of ird suggests a common climate forcing acting across the nordic seas region changes of the sst gradient between the norwegian sea and north atlantic sites suggest that the subpolar gyre was at least as strong as during the holocene and that the northward heat transport by the north atlantic current was comparable

isotopic and geochemical evidence of palaeoclimate changes in salton basin california during the past 20 kyr 1 δ18o and δ13c records in lake tufa deposits abstract investigation of 18 o and salt content of surface waters in the salton basin california shows that there is a strongly positive correlation between 18 o values and salt contents and that the 18 o of salton sea is much heavier than that of its input waters due to strong evaporation using a steady state 18 o model we have discussed the 18 o of lake cahuilla an ancient lake in the basin under through flowed closed and overflowed situations an ams 14 c dated stable isotope record of a 60 cm lake tufa slice lc 1 from the ancient shoreline of lake cahuilla indicates that the lake experienced closed and or overflowed conditions between 1 300 and 20 500 yr bp the variations in 18 o and 13 c values of lc 1 ranging from 8 52 to 2 50 pdb and from 0 8 to 3 76 respectively reflect changes in the relative humidity in salton basin and variations in the colorado river inflow and hence climatic conditions in the colorado river drainage basin the tufa record exhibits palaeoclimates of salton basin as follows 1 relatively dry climate between 20 and 18 kyr bp was followed by a wet climate between 18 and 17 kyr bp 2 decreasing effective moisture precipitation evaporation from 17 to 16 kyr bp corresponded to heinrich 1 event whereas effective moisture increased at ca 15 5 kyr bp during the trans us wet period contrasting patterns between the lc 1 record and the greenland ice core and chinese speleothem records during the bolling allerod interstadial from 15 2 to 11 7 kyr bp may be caused by age uncertainty of the lc 1 record further study of this interval is needed 3 wet warm early holocene corresponding to the maximum effective moisture period perhaps brought about by the strengthening of north american monsoon 4 toward 2 kyr bp the climate became dryer apparently resulting from weakening of the monsoons especially around 6 2 and 2 5 kyr bp 5 a wet regime occurred in the basin during the medieval warm period

mutvei s solution an ideal agent for resolving microgrowth structures of biogenic carbonates accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits variable growth rates function as environmental and physiological proxies and growth increments as calendars recognition of growth structures is thus a prime necessity for sclerochronological studies here we present a new handy easy to use and time efficient technique that resolves annual and sub annual growth structures in skeletons of a wide range of different organisms mutvei s solution simultaneously etches biogenic carbonates and calcium phosphates fixates the soluble and insoluble organic matrices and fibers and stains mucopolysaccharides it produces a filigreed three dimensional relief of etch resistant ridges growth lines and etched depressions growth increments and stains skeletal growth structures in shadings of blue growth lines stand out as crisp darker blue stained lines reflected optical light microscopy axial and oblique illumination and scanning electron microscopy can be used to analyze the microgrowth structures we demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves a coral a sclerosponge a barnacle gastropods a cephalopod a fish otolith and a whale s ear bone this technique may be of interest for paleoclimatologists geochemists and biologists it can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars

a 22 000 year record of vegetation change in the north central sonoran desert abstract plant macrofossils from eleven packrat neotoma sp middens provide a history of vegetation change over the last 22 140 years at eagle eye mountain near the northern border of the sonoran desert in arizona this site is located in the arizona upland subdivision departures and arrivals of various perennial plant species during the holocene were similar to other records from more southerly sites and support earlier generalizations of van devender van devender t r 1990 late quaternary vegetation and climate of the sonoran desert united states and mexico in betancourt j l van devender t r martin p s eds packrat middens the last 40 000 years of biotic change university of arizona press tucson pp 134 165 regarding the tempo and mode of late quaternary changes in the arizona upland evergreen woodland containing pinus monophylla singleleaf pinyon juniperus osteosperma utah juniper and quercus turbinella shrub live oak occupied the site during full glacial times the latter two species but not p monophylla persisted into the early holocene and were joined by a limited number of desertscrub species including acacia greggii catclaw carnegiea gigantea saguaro and several other succulents with the arrival of many other species during the middle holocene a desertscrub community that differed considerably from the modern vegetation developed acacia greggii and cercidium floridum blue paloverde were the principal large woody species on exposed hillslopes assemblages similar in composition to the modern desertscrub did not appear until approximately 4000 years ago when the more xerophytic cercidium microphyllum foothills paloverde arrived and c floridum disappeared from hillslopes the delayed arrival of c microphyllum in comparison to other sonoran desertscrub species with similar climatic tolerances is attributed to the limited dispersal distance of its seeds by seed eating heteromyid rodents at 4540 and 6425 yr b p the cold intolerant shrub encelia farinosa was present on northeasterly aspect exposures where it is absent today suggesting slightly warmer winter conditions during the middle holocene the presence of the tree cercidium floridum and the perennial c 4 grass setaria leucopila on exposed slopes during the middle holocene indicates substantially moister conditions during that time than in the late holocene or today at sites on the xeric limits of the modern distributions of both species average annual precipitation is from 50 to 100 greater than that presently received at eagle eye mountain in particular the responses of s leucopila and cacti during the middle holocene indicate substantial increases in warm season precipitation

paleoclimatic implications of holocene plant remains from the sierra bacha sonora mexico abstract a total of 93 plant taxa were identified from 11 packrat neotoma sp midden samples from the sierra bacha on the coast of the gulf of california near puerto libertad sonora mexico nine indurated samples have radiocarbon dates ranging from 9970 to 320 yr b p sonoran desertscrub was present on rocky slopes throughout the holocene early holocene assemblages dominated by fouquieria columnaris boojum tree reflect vegetation and climate more like modern baja california with greater winter rainfall and cooler summers middle holocene vegetation was essentially modern with modest indications of greater monsoonal rainfall even though cold water upwelling locally inhibits summer precipitation the results are similar to all previous midden reconstructions of early and middle holocene climates in the sonoran desert but contradict general atmospheric circulation model simulations

isotope palaeotemperatures from the tjornes beds in iceland evidence of pliocene cooling abstract the mid pliocene warming episode is well established along the margins of the north atlantic and probably affected areas as far north as iceland rich marine mollusc faunas have been described from the 500 m of pliocene siliciclastic deposits on the tjornes peninsula in northeast iceland the faunal compositions indicate a development from warm water to arcto boreal conditions we have analysed the oxygen isotope composition of 96 well preserved specimens of the bivalves arctica islandica and pygocardia rustica and interpreted the data as palaeotemperatures after corrections for the isotopic composition of pliocene seawater the temperatures are in accordance with other palaeotemperature proxies we interpret our data as reflecting a gradual change from warm water conditions summer temperatures between 10 and 15 c during the deposition of the lower part of the tjornes beds tapes zone and lower part of mactra zone to cold water conditions summer temperatures between 5 and 10 c at the top top of mactra zone and serripes zone the coldest interval is found in the middle of the serripes zone where summer temperatures 5 8 c are comparable to those of the present environment off northern iceland the arrival to tjornes of cold water molluscs of pacific origin postdates the cooling of the seas around iceland we suggest that the cold interval in the serripes zone represents a cooling event prior to the final warm period ca 3 3 3 0 ma dowsett et al 1999 middle pliocene paleoenvironmental reconstruction prism2 us geol survey open file rep 99 53 of the mid pliocene warming

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

late holocene lacustrine chronology and archaeology of ancient lake cahuilla california freshwater lakes existed intermittently in the salton trough of southern california during the late holocene the lakes formed north of the subaerial colorado river delta whenever the colorado river flowed west into the trough instead of south to the gulf of california water filled the trough to a maximum altitude of 12 m stratigraphy radiocarbon dates and supplementary evidence document four lacustral intervals of lake cahuilla between a d 700 and 1580 archaeological sites are associated with the 12 m shoreline and their occupation correlates with these lacustral intervals

formal ratification of the quaternary system period and the pleistocene series epoch with a base at 2 58 ma in june 2009 the executive committee of the international union of geological sciences iugs formally ratified a proposal by the international commission on stratigraphy to lower the base of the quaternary system period to the global stratotype section and point gssp of the gelasian stage age at monte san nicola sicily italy the gelasian until then had been the uppermost stage of the pliocene series epoch the base of the gelasian corresponds to marine isotope stage 103 and has an astronomically tuned age of 2 58 ma a proposal that the base of the pleistocene series epoch be lowered to coincide with that of the quaternary the gelasian gssp was also accepted by the iugs executive committee the gssp at vrica calabria italy which had hitherto defined the basal boundary of both the quaternary and the pleistocene remains available as the base of the calabrian stage age now the second stage of the revised pleistocene in ratifying these proposals the iugs has acknowledged the distinctive qualities of the quaternary by reaffirming it as a full system period correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the pleistocene to that of the quaternary and fully respected the historical and widespread current usage of both the terms quaternary and pleistocene copyright 2009 john wiley sons ltd

gisp2 oxygen isotope ratios the gisp2 oxygen isotope record with its high resolution detail yields crucial information on past climate change the glacial 18o oscillations of the gisp2 core with their very fast onsets are templates of a prototype oscillation of variable duration with an amplitude of 3 9 the halfway mark of the cold warm transition is reached in 2 years the top is reached in 50 years the 18o time gradient of the leading front is about 7 8 per 100 yr after reaching the top 18o slowly declines by 0 14 per 100 yr the duration of 18o decline varies from a couple of centuries for fast oscillations to about 4000 yr for slower ones the subsequent 18o downturn during the warm cold transition has a 18o time gradient of 3 2 per 100 yr and lasts about 80 yr

new 230th u and 14c ages from lake lahontan carbonates nevada usa and a discussion of the origin of initial thorium five sets of coeval lacustrine carbonate samples from pleistocene lake lahontan in western nevada were dated by both the ams 14c and 230th u isochron methods all five groups of samples were analyzed for u th isotopes by alpha spectrometry and one of the groups was additionally measured by thermal and secondary ionization mass spectrometry tims and sims for comparison the 14c ages were corrected to calendar years using the calibration curve recommended by bard et al 1992 without local reservoir correction on the 14c ages mean 230th u isochron ages of some sets are apparently older than their calendar corrected 14c ages by up to 2300 years modern carbon contamination of these carbonate samples through recrystallization or deposition of secondary calcite is likely to be responsible for part of the age discrepancies we explored additional biases associated with the isochron ages maybe produced by the presence of initial th coprecipitated from the lake water it can be shown that if dissolved hydrogenous th is directly incorporated into the pure carbonates then the three component mixing among 1 detrital th 2 hydrogenous th adsorbed on detritus and 3 hydrogenous th incorporated by the carbonate can introduce a positive age bias we have developed an approach to estimate the magnitude of this bias of the lake lahontan carbonates the preliminary estimates suggest a positive age bias of 1000 to 2000 years for two sets of the samples

marine climate and hydrography of the coralline crag early pliocene uk isotopic evidence from 16 benthic invertebrate taxa abstract the taxonomic composition of the biota of the coralline crag formation early pliocene eastern england provides conflicting evidence of seawater temperature during deposition some taxa indicating cool temperate conditions by analogy with modern representatives or relatives others warm temperate to subtropical tropical conditions previous isotopic 18 o evidence of seasonal seafloor temperatures from serial ontogenetic sampling of bivalve mollusk shells indicated cool temperate winter 18 o the shell 18 o data either strongly indicate or are at least consistent with cool temperate seafloor conditions the subtropical tropical conditions suggested by the presence of the bryozoan metrarabdotos did not exist microgrowth increment and 13 c evidence indicate summer water column stratification during deposition of the ramsholt member unlike in the adjacent southern north sea at present well mixed due to shallow depth and strong tidal currents summer maximum surface temperature was probably about 5 c above seafloor temperature and thus often slightly higher than now 17 19 c rather than 16 17 c but only sometimes in the warm temperate range winter minimum surface temperature was below 10 c and possibly the same as at present 6 7 c an expanded surface temperature range compared to now may reflect withdrawal of oceanic heat supply in conjunction with higher global temperature

a global synthesis of the marine and terrestrial evidence for glaciation during the pliocene epoch abstract the pliocene climate is globally warm and characterised by high atmospheric carbon dioxide concentrations yet the terrestrial and marine scientific communities have gathered considerable evidence for substantial glaciation events in both the northern and southern hemisphere prior to the quaternary evidence on land is fragmentary but marine records of glaciation present a more complete history of pliocene glaciation here we present a global compilation of the terrestrial and marine glacial evidence for the pliocene and demonstrate four glaciation events that can be identified in the southern and or northern hemisphere prior to the latest pliocene intensification of northern hemisphere glaciation there are two globally recognisable glacial events in the early pliocene c 4 9 4 8 ma and c 4 0 ma one event around the early late pliocene transition c 3 6 ma and one event during marine isotope stage m2 c 3 3 ma long term climate cooling decreasing carbon dioxide concentrations in the atmosphere and high climate sensitivity in the pliocene probably facilitated each glaciation event however the mechanisms behind the early pliocene glacial events are unclear the global glaciation at c 3 3 ma may be caused by changes in ocean gateways whereas the decline in carbon dioxide concentrations is important for the latest pliocene intensification of northern hemisphere glaciation

comparative sclerochronology of modern and mid pliocene c 3 5 ma aequipecten opercularis mollusca bivalvia an insight into past and future climate change in the north east atlantic region records of environment contained within the accretionarily deposited tissues of fossil organisms afford a means of detailed reconstruction of past climates and hence of rigorous testing of numerical climate models we identify the environmental factors controlling oxygen and carbon stable isotopic composition and microgrowth increment size in the shell of modern examples of the queen scallop aequipecten opercularis this understanding is then applied in interpretation of data from mid pliocene a opercularis from eastern england on the basis of oxygen isotope evidence we conclude that winter minimum seafloor temperature was similar to present values typically 6 7 c in the adjacent southern north sea and that summer maximum seafloor temperature was a few degrees lower than present values typically 16 17 c this contrasts with evidence from other proxies that winter and summer temperatures were higher than present the pattern of seasonal variation in microgrowth increment size suggests the existence of intense thermal stratification in summer we therefore conclude that summer surface temperatures were much higher maxima well over 20 c than those recorded isotopically on the seafloor and that the annual range of surface temperature probably over 14 c was greater than now at the times in the mid pliocene when the investigated a opercularis were alive taken in conjunction with other proxy evidence of warmer winters as well as summers the data point to substantial fluctuation up to 10 c in winter minimum temperatures during the mid pliocene in the north east atlantic region this fluctuation may be attributable to variation in the strength of the gulf stream north atlantic drift since the pliocene has been widely used as a test bed for numerical models of a greenhouse earth the results have implications for prediction of future climate in the north east atlantic region under the influence of anthropogenic global warming

unionid shells hyriopsis cumingii record manganese cycling at the sediment water interface in a shallow eutrophic lake in china lake taihu abstract aquatic eutrophication is becoming a serious environmental problem throughout the world the utility of bivalves as bio filters to improve water quality and reduce algal blooms has been widely acknowledged but the potential usefulness of bivalve shells as retrospective monitors of eutrophication induced environmental change has received little attention here we present the first multi year high resolution mn ca shell records of the freshwater mussel hyriopsis cumingii lea 1852 from a shallow eutrophic lake lake taihu china mn ca shell time series of the two studied shells exhibit a high degree of synchrony after being placed in a precise temporal context by means of growth pattern analysis there is a large inter annual variability of mn ca shell records during 2011 2015 with the highest value occurring in 2013 mn ca shell also displays a pronounced intra annual variability with maxima consistently occurring during late spring early summer the high reproducibility of mn ca shell time series among contemporaneous specimens highlights the existence of strong environmental rather than biological control on the incorporation of mn into the shells in particular the striking feature of late spring early summertime mn ca shell maxima is synchronous with the occurrence of reducing conditions beneath the sediment water interface swi the latter results in substantial increases of biologically available mn 2 in the sediment pore water and organic particles the element being rapidly taken up from these sources by the mussels with subsequent incorporation of mn into their shells therefore mn ca shell can potentially serve as a high resolution proxy of the mobility of mn at the swi as demonstrated by the present study documenting and understanding geochemical properties of bivalve shells can help to retrospectively monitor eutrophication induced environmental change in aquatic ecosystems

pliocene dinoflagellate cyst stratigraphy palaeoecology and sequence stratigraphy of the tunnel canal dock belgium dinoflagellate cysts and sequence stratigraphy are used to date accurately the tunnel canal dock section which contains the most complete record of marine pliocene deposits in the antwerp harbour area the zanclean kattendijk formation was deposited between 5 0 and 4 4 ma during warm temperate conditions on a shelf influenced by open marine waters the overlying lillo formation is divided into four members the lowest is the luchtbal sands member estimated to have been deposited between 3 71 and 3 21 ma under cooler conditions but with an open water influence the oorderen sands kruisschans sands and merksem sands members of the lillo formation are considered a single depositional sequence and biostratigraphically dated between 3 71 and c 2 6 ma with the oorderen sands member no younger than 2 72 2 74 ma warm temperate conditions had returned but a cooling event is noted within the oorderen sands member shoaling of the depositional environment is also evidenced with the transgressive oorderen sands member passing upwards into near coastal high stand deposits of the kruisschans sands and merksem sands members as accommodation space decreased applying sequence stratigraphy to our section implies that the kattendijk lillo formation boundary corresponds to the sequence boundary sb za2 4 04 ma the luchtbal oorderen sands boundary to sb pia1 3 21 ma and the top of the merksem sands to sb pia2 2 76 ma finally the belgian deposits are compared with marine pliocene deposits of eastern england

seasonal temperature salinity changes and thermocline development in the mid atlantic bight as recorded by the isotopic composition of bivalves stable isotope records across annual growth increments in specimens of the surf clam spisula solidissima from the mid atlantic bight shelf from 10 m and 45 m depths reflect the changes in temperature and nutrient concentrations on the shelf over the year the 18 o and 13 c records from clams at the two depths record well mixed conditions in the water column during the winter months and the development of a thermocline during the summer spring high productivity and a transient salinity excursion in surface waters are also recorded reconstructing the paleoceanography of late cenozoic temperate continental shelves may be possible using stable isotope records from fossil spisula solidissima and other bivalves

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

late quaternary lacustrine history and paleoclimatic significance of pluvial lake cochise southeastern arizona abstract during the latest quaternary freshwater pluvial lakes intermittently formed in the topographically closed willcox basin arizona a lacustrine sequence of six separate high stands of lake cochise is documented by stratigraphic studies 19 radiocarbon ages and supplementary evidence two stands of pluvial lake cochise older than 14 000 yr b p reached elevations above 1290 m the prominent 1274 m shoreline of lake cochise which circumscribes the basin was largely created during a high stand between 13 750 and 13 400 yr b p during the holocene water filled the willcox basin three times to an elevation slightly below the crest of the 1274 m shoreline this occurred once during the early holocene around or before 8900 yr b p and twice during the later part of the middle holocene since the middle holocene only shallow ephemeral lakes have occupied the deflated central portion of ancient lake cochise a depression known as the willcox playa the lacustrine sequence of lake cochise provides an independent evaluation of late quaternary paleoclimatic reconstructions for southern arizona and the american southwest

stable isotope studies on mono lake california 1 d18 in lake sediments as proxy for climatic change during the last 15 years mono lake is a hypersaline alkaline lake in the mono basin located at the eastern base of the californian sierra nevada its lake level history since 1912 has been recorded instrumentally showing the decline of lake surface elevations initiated by the 1941 artificial diversion of stream inflow we have made high resolution oxygen isotopic measurements on the total carbonate fraction of lake sediments and shown that the s o record parallels the lakelevel fluctuations rather well the measurements were carried out on sediments that had been leached with deionized water to isolate the isotopic signals of the calcium carbonate from those of pore water and water soluble carbonate salts in the sediment extending the s o record back in time we found that lake level changed markedly during the past 150 yr reflecting climatic variations and resultant runoff fluctuiitions lake levels were high around 1845 1880 and 19 15 and low around 1860 1900 and 1933 this study demonstrates that closed basin lake sediment s180 provides an effective means of probing past precipitation variations in arid to semiarid regions such as the great basin in the western united states numerous attempts have been made to reconstruct paleolake levels on the basis of geological and stable isotopic evidence from which paleohydrological conditions have been inferred studies on closed basin lakes in semiarid and tropical zones have contributed greatly to paleoclimatic research particularly for the late pleistocene and the holocene e g street perrott and harrison 1985 chivas et al 1986 gasse et al 1991 water entering closed basin lakes via rain and runoff leaves by evaporation hence fluctuations in lake level and volume should serve to indicate changes in the moisture budget associated with climatic change mono lake located in eastern california about 480 km north of los angeles fig l is the only terminal lake in the mono basin its present ratio of surface area 150 km2 to catchment area 2 072 km2 is 7 100 in contrast to the ratio of 33 100 for lake russell during the last glacial period russell 1889 lajoie 1968 mono lake committee 1981 since 1912 the levels of mono lake have been measured by the u s geological survey usgs and the los angeles department of water and power ladwp blevins et al 1987 since its historic high in 1915 the water level within the lake has fallen as a result of climatic changes the lake level fall has been exacerbated by the diversion of inflow to the lake by ladwp since 1941 and has caused a further increase in salinity and alkalinity dur

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

pliocene climate and seasonality in north atlantic shelf seas this paper reviews north atlantic shelf seas palaeoclimate during the interval 4 3 ma prior to and incorporating the mid pliocene warm period ca 3 29 2 97 ma fossil assemblages and stable isotope data demonstrate northwards extension of subtropical faunas along the coast of the carolinas virginia yorktown and duplin formations relative to the present day suggesting a more vigorous florida current with reduced seasonality and warm water extending north of cape hatteras reconstructed annual range for virginia 12 30 c this interpretation supports conceptual models of increased meridional heat transport for the pliocene sea temperatures for florida lower pinecrest beds were similar to or slightly cooler than summers 25 27 c today and were probably influenced by seasonal upwelling of cold deep water reduced seasonality is also apparent in the coralline crag formation of the southern north sea with ostracods suggesting winter sea temperatures of 10 c modern 4 c however estimates from pliocene bivalves 3 6 16 6 c are similar to or cooler than the present day this mixed signal is problematic given warmer seas in the carolinas virginia and climate model and oceanographic data that show warmer seas in the mid pliocene eastern north atlantic this may be because the coralline crag formation was deposited prior to peak mid pliocene warmth

a holocene climatic record for the sonoran desert from pollen analysis of montezuma well arizona usa abstract pollen and macrofossil analyses of a radiocarbon dated core 1125 cm long from montezuma well elev 1125 m yavapai county arizona provide a record of summer precipitation similar to that of other monsoonal regions of the world precipitation was least from 4000 to 5000 yr b p and generally was greater than today before 8400 yr b p during the early holocene moist period oak and grass pollen are abundant and the best modern analogs are within the arizona monsoon boundary so increased summer precipitation is indicated climatic parameters are estimated with the technique of best modern analogs for fossil samples temperature was highest ca 3400 and 5700 yr b p and generally was cooler than today before 6800 yr b p brief cold intervals in the holocene match periods of global cooling and of positive 14 c and 10 be anomalies

continuous holocene record of diatom stratigraphy paleohydrology and anthropogenic activity in a spring mound in southwestern united states abstract this study presents the first continuous record of fossil diatoms taken from an open spring mound in southwestern united states diatoms were analyzed from a radiocarbon dated core taken from montezuma well a near thermally constant spring in northcentral arizona fluctuations in total diatom density oscillations in the relative abundance of anomoeoneis sphaerophora and intermittent deposition of calcite suggest that water levels in montezuma well underwent dramatic fluctuations to the degree of being intermittently dry or at least very shallow during the middle holocene 8000 5000 yr b p the fluctuations in water level probably correspond to oscillations in regional temperature and precipitation which regulate hydrologic input and evaporation rates the dramatic fluctuations in water level during the middle holocene suggest that the endemic biota of montezuma well underwent relatively rapid speciation within the past 5000 yr the appearance of endemic species gomphonema montezumense and cyclotella pseudostelligera f parva at 5000 3000 yr b p supports this hypothesis diatom indicators for organic enrichment aulacoseira granulata and a islandica closely coincide with the prehistoric native occupation of montezuma well

isotopic evidence of cool winter conditions in the mid piacenzian pliocene of the southern north sea basin oxygen isotope thermometry of aequipecten opercularis and atrina fragilis bivalves which demonstrate all year growth provides quantitative evidence of cool temperate winter conditions below 10 c during deposition of the mid piacenzian oorderen sands and time equivalent strata in the southern north sea basin snsb isotopic summer temperatures seafloor are within or only marginally above the cool temperate range upper limit 20 c the occurrence of warm temperate dinoflagellate cysts alongside and presumably contemporaneous with the bivalves indicates the development of a correspondingly warm surface layer in summer encystment allowing the dinoflagellates to survive cool winter conditions this evidence of greater surface seasonality than now is consistent with greater global warmth and a reduction in the vigour of the gulf stream north atlantic drift gs nad leading to a reduced supply of winter heat this reduction in gs nad strength may be linked to breaching of the emerging isthmus of panama

climate and hydrology of the last interglaciation mis 5 in owens basin california isotopic and geochemical evidence from core ol 92 abstract 18 o 13 c total organic carbon total inorganic carbon and acid leachable li mg and sr concentrations on 443 samples from 32 to 83 m depth in owens lake core ol 92 were analyzed to study the climatic and hydrological conditions between 60 and 155 ka with a resolution of 200 a the multi proxy data show that owens lake overflowed during wet cold conditions of marine isotope stages mis 4 5b and 6 and was closed during the dry warm conditions of mis 5a c and e the lake partially overflowed during mis 5d our age model places the mis 4 5 boundary at ca 72 5 ka and the mis 5 6 boundary termination ii at ca 140 ka agreeing with the devils hole chronology the diametrical precipitation intensities between the great basin cold wet and eastern china cold dry on milankovitch time scales imply a climatic teleconnection across the pacific it also probably reflects the effect of high latitude ice sheets on the southward shifts of both the summer monsoon frontal zone in eastern asia and the polar jet stream in western north america during glacial periods

the shell of the queen scallop aequipecten opercularis l as a promising tool for palaeoenvironmental reconstruction evidence and reasons for equilibrium stable isotope incorporation abstract the queen scallop aequipecten opercularis has been an important part of the marine fauna of the northeast atlantic region since the miocene and is a suitable candidate for palaeoenvironmental studies using stable isotopes modern shells were investigated to determine if carbonate is precipitated in isotopic equilibrium in this species and to confirm that growth continues through the year specimens of a opercularis were cultured under monitored semi natural conditions over an autumn winter period and the analyses of these specimens were supplemented with isotope data from preserved indigenous north sea specimens the results indicated that the cultured specimens grew in relatively low temperatures that oxygen isotopes of shell exterior carbonate were precipitated in isotopic equilibrium and that a large proportion of the ambient temperature range was recorded in shell carbonate the indigenous north sea specimens exhibited a good correspondence to predicted oxygen isotope values for summer the isotopic record related to winter was however somewhat truncated due to growth decelerations in the specimens carbon isotopes of shell exterior carbonate were calculated as being derived primarily from external sources and showed comparatively little influence from metabolically derived carbon this suggests that carbon isotopes were at least close to equilibrium with ambient waters the limited incorporation of metabolic products suggests that a opercularis would be a good monitor of changing carbon isotope ratios in seawater dissolved inorganic carbon the occurrence of equilibrium shell precipitation is explained using a pteriomorph shell calcification model which proposes that transport of ions through the periostracum caused the composition of the extrapallial fluid to be effectively the same as seawater carbonate secretion is therefore not influenced significantly by biological vital effects

temperate meteoric diagenesis of pliocene skeletal carbonates from eastern england the crags of eastern england include marine skeletal carbonates which were deposited and lithified under temperate conditions the coralline crag pliocene in particular exhibits a variety of carbonate cement types which indicate exposure to meteoric groundwaters during a regressive episode the coralline crag has been divided into an upper division of dominantly well sorted skeletal calcarenites and calcirudites and a lower poorly sorted silty calcarenite division dogtooth spardcement and rudimentary syntaxial cement overgrowths on echinoderm fragments are characteristic of the sediments of the upper division which has undergone extensive aragonite dissolution this division is consequently relatively evenly cemented in the underlying sediments aragonite dissolution has not occurred and the sediments have remained largely uncemented with cement restricted to irregular patches where growth of intra and inter particle equant spar has effectively eliminated porosity in contrast with the upper leached sediments syntaxial echinoderm overgrowths show a greater development but only where interference from surrounding sediment and sparry cement was absent the elongate shape of the coralline crag outcrop may be the result of preferential cementation of the upper coarser well sorted calcarenites originally deposited as an elongate sediment body possibly as an offshore sandbank

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

early holocene vegetation record from the salton basin california abstract plant and vertebrate macrofossils in an early holocene fossil packrat neotoma sp midden with a radiocarbon age of 8640 100 14 c yr b p are reported from the chocolate mountains near the salton sea riverside county california an inventory of the midden has permitted a comparison of the modern flora and fauna of the site with that extant during the early holocene whereas the biota had assumed most aspects of its modern sonoran desert aspect by this date statistically significant evidence of differences is attributed to an increased flow of surface water in salt creek a high standing low salinity lake leconte and the late arrival of some characteristic sonoran desert plants these observations are consistent with models of significant fall winter precipitation in the sonoran desert although we cannot exclude alternative explanations

carbonate microbialites and hardgrounds from manito lake an alkaline hypersaline lake in the northern great plains of canada abstract manito lake is a large perennial na so 4 dominated saline to hypersaline lake located in the northern great plains of western canada significant water level decrease over the past several decades has led to reduction in volume and surface area as well as an increase in salinity the salinity has increased from 10 ppt to about 50 ppt tds this decrease in water level has exposed large areas of nearshore microbialites these organogenic structures range in size from several cm to over a meter and often form large bioherms several meters high they have various external morphologies vary in mineralogical composition and show a variety of internal fabrics from finely laminated to massive in addition to microbiolities and bioherms the littoral zone of manito lake contains a variety of carbonate hardgrounds pavements and cemented clastic sediments dolomite and aragonite are the most common minerals found in these shoreline structures however calcite after ikaite monohydrocalcite magnesian calcite and hydromagnesite are also present the dolomite is nonstoichiometric and calcium rich the magnesian calcite has about 17 mol mgco 3 ams radiocarbon dating of paired organic matter and endogenic carbonate material confirms little or no reservoir affect although there is abundant evidence for modern carbonate mineral precipitation and microbialite formation most of the larger microbialites formed between about 2300 and 1000 cal bp whereas the hardgrounds cements and laminated crusts formed about 1000 500 cal bp

response of the north american monsoon to regional changes in ocean surface temperature 1 the north american monsoon nam an onshore wind shift occurring between july and september has evolved in character during the holocene largely due to changes in northern hemisphere insolation published paleoproxy and modeling studies suggest that prior to 8000 cal years bp the nam affected a broader region than today extending westward into the mojave desert of california holocene proxy sst records from the gulf of california goc and the adjacent pacific provide constraints for this changing nam climatology prior to 8000 cal years bp lower goc ssts would not have fueled northward surges of tropical moisture up the goc which presently contribute most of the monsoon precipitation to the western nam region during the early holocene the north pacific high was further north and ssts in the california current off baja california were warmer allowing monsoonal moisture flow from the subtropical pacific to take a more direct northwesterly trajectory into an expanded area of the southwestern u s west of 114 w a new upwelling record off southwest baja california reveals that enhanced upwelling in the california current beginning at 7500 cal year bp may have triggered a change in nam climatology focusing the geographic expression of nam in the southwest usa into its modern core region east of 114 w in arizona and new mexico holocene proxy precipitation records from the southwestern u s and northwestern mexico including lakes vegetation pollen and caves are reviewed and found to be largely supportive of this hypothesis of changing holocene nam climatology

scanning micro x ray fluorescence elemental mapping a new tool for the study of laminated sediment records 1 the utility of elemental mapping by scanning x ray fluorescence xrf in the study of annual laminated sedimentary records was investigated on eight annually laminated sediment types the examples were chosen to illustrate the potential of this approach in environments dominated by terrigenous biological and chemical deposition individual laminae were identifiable in elemental maps of all sediment types and were enhanced through the use of data reduction techniques e g principal components transformation laminae were least apparent in clastic dominated systems with no seasonal changes in sediment sources in biologically dominated systems element maps provided insights into the composition of the varve subcomponents related to alternating terrigenous and biologically dominated seasonal periods of deposition chemically precipitated structures were more prevalent than expected from visual investigations alone and may provide an underutilized paleoenvironmental signature of changing limnological conditions elemental mapping offers a valuable tool for the study of laminated records that complements existing techniques e g sem digital image analysis

a new age model for the pliocene pleistocene tjornes section on iceland its implication for the timing of north atlantic pacific palaeoceanographic pathways abstract the plio pleistocene outcrops of the tjornes peninsula in northern iceland present a unique section in which near shore and terrestrial deposits alternate with lava flows this section plays an important role in the correlation of climate signals from around the north atlantic but a solid age model has not been available for the entire sequence due to problematic k ar dating and incompletely recorded palaeomagnetic signal a palynological analysis with dinoflagellate cysts of 68 samples from the tjornes beds and twenty samples from the younger breidavik group was carried out in order to establish an age model for the tjornes section independent of the available k ar ages the dinoflagellate cyst record of the tjornes beds consists mainly of pliocene taxa and indicates most probably a post miocene age for the tapes and mactra zones of the tjornes beds both operculodinium tegillatum and batiacasphaera minuta which have a highest occurrence near the top of the zanclean at c 3 8 ma were present in the section up to the middle of the serripes zone reticulatosphaera actinocoronata with a highest occurrence around 4 4 ma was recorded in situ at the base of the serripes zone this suggests that the entire serripes zone was deposited between c 4 0 and 4 5 ma further the normal polarities below and above the skeifa lavas in the serripes zone were consequently linked to the nunivak and cochiti subchron respectively the entire tjornes beds were likely deposited in the early pliocene before c 4 0 ma the breidavik group is deposited much later in the quaternary from just before the olduvai subchron at c 2 2 ma the gilbert gauss transition is located between the tjornes beds and the hoskuldsvik lavas and the gauss matuyama transition between the furuvik and horgi formations the exact position of both reversals is not preserved because two appreciable hiatuses of c 600 kyr up to maximally 900 kyr occur at these locations according to the new age model the major invasion of pacific molluscs at the base of the serripes zone took place before 3 8 ma in combination with the palaeopolarity data this event can be placed in the nunivak subchron at c 4 5 ma the invasion is likely a result of the northward flow of pacific waters through the bering strait to the north atlantic which may have been caused by the shoaling of the central american seaway between 4 7 and 4 2 ma sarnthein et al 2009

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

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

the lower colorado river valley a pleistocene desert abstract a chronological sequence of plant macrofossil assemblages from twenty five pack rat middens provides a record of desert scrub vegetation for most of the last 13 380 yr b p from a hyperarid portion of the lower colorado river valley at the end of the late wisconsin and probably during much of the quaternary the picacho peak area imperial county california supported a typical mohave desert association of larrea divaricata creosote bush coleogyne ramosissima blackbrush yucca brevifolia joshua tree and y whipplei whipple yucca recent arrivals of sonoran desert plants such as olneya tesota ironwood and fouquieria splendens ocotillo suggest that the area supported relatively modern sonoran desert scrub species for relatively short periods during interglaciations

the molluscan fauna of the coralline crag pliocene zanclean at raydon hall suffolk uk palaeoecological significance reassessed abstract this study assesses the environmental implications of a quantitative study of the unusually well preserved molluscan fauna of over 200 species about 47 extinct from six samples from both the ramsholt and sudbourne members of the coralline crag formation at a british geological survey borehole at raydon hall near orford suffolk uk it reveals a shallow shelf fauna locally transported from a variety of habitats dominated by infaunal species spisula turritella abra amyclina from relatively fine sediments plus epifauna especially heteranomia possibly in part originating from nearby bryozoan communities as well as dead bivalve shells there was a small but consistent component of deeper water elements such as limopsis and a lack of strictly littoral species overall a water depth of about 50 m is suggested with bottom temperatures at times perhaps warmer than the present southern north sea but not as high as the modern mediterranean and a more oceanic setting this is in contrast to inferences from previous nineteenth century studies of coralline crag molluscs which viewed it as largely mediterranean in character but understated the regular presence of boreal forms such as arctica current interpretations still have to account for the coexistence of some lusitanian or mediterranean molluscan taxa alongside the cooler water elements

meltwater pulse recorded in last interglacial mollusk shells from bermuda the warm climate of bermuda today is modulated by the nearby presence of the gulf stream current however iceberg scours in the florida strait and the presence of ice rafted debris in bermuda rise sediments indicate that during the last deglaciation icebergs discharged from the laurentide ice sheet traveled as far south as subtropical latitudes we present evidence that an event of similar magnitude affected the subtropics during the last interglacial potentially due to melting of the greenland ice sheet using the clumped isotope paleothermometer we found temperatures 10 c colder and seawater 18o values 2 lower than modern in last interglacial cittarium pica shells from grape bay bermuda in contrast last interglacial shells from rocky bay bermuda record temperatures only slightly colder and seawater 18o values similar to modern likely representing more typical last interglacial conditions in bermuda outside of a meltwater event the significantly colder ocean temperatures observed in grape bay samples illustrate the extreme sensitivity of bermudian climate to broad scale ocean circulation changes they indicate routine meltwater transport in the north atlantic to near equatorial latitudes which would likely have resulted in disruption of the atlantic meridional overturning circulation these data demonstrate that future melting of the greenland ice sheet a potential source of the last interglacial meltwater event could have dramatic climate effects outside of the high latitudes

a 35 000 year vegetation and climate history from potato lake mogollon rim arizona abstract a new record from potato lake central arizona details vegetation and climate changes since the mid wisconsin for the southern colorado plateau recovery of a longer record discrimination of pine pollen to species groups and identification of macrofossil remains extend whiteside s 1965 original study during the mid wisconsin ca 35 000 21 000 yr b p a mixed forest of engelmann spruce picea engelmannii and other conifers grew at the site suggesting a minimum elevational vegetation depression of ca 460 m summer temperatures were as much as 5 c cooler than today during the late wisconsin ca 21 000 10 400 yr b p even cooler temperatures 7 c colder than today ca 800 m depression allowed engelmann spruce alone to predominate warming by ca 10 400 yr b p led to the establishment of the modern ponderosa pine pinus ponderosa forest thus the mid wisconsin was not warm enough to support ponderosa pine forests in regions where the species predominates today climatic estimates presented here are consistent with other lines of evidence suggesting a cool and or wet mid wisconsin and a cold and or wet late wisconsin climate for much of the southwest potato lake was almost completely dry during the mid holocene but lake levels increased to near modern conditions by ca 3000 yr b p

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

late glacial and holocene vegetation history and paleoclimate of the kaibab plateau arizona sediment cores spanning the last 13 500 calendar years cal yr were obtained from two lakes fracas lake 2518 m bear lake 2778 m on the kaibab plateau in northern arizona pollen and plant macrofossil records indicate that before 12 900 cal yr b p high elevation landscapes of the kaibab plateau near bear lake were covered by alpine tundra while lower elevations near fracas lake were occupied by picea woodland at12 900 cal yr b p picea engelmannii and abies lasiocarpa forest expanded upward to occupy the top of the plateau pinus ponderosa arrived near fracas lake 11 000 cal yr b p replacing picea forests since then pinus ponderosa forest has dominated the fracas lake area pinus ponderosa did not appear at bear lake until9730 cal yr b p mixed forests of picea mainly picea pungens abies lasiocarpa pinus ponderosa a ndpseudotsuga after8000 cal yr b p grew near bear lake for the remainder of the holocene picea engelmannii populations reexpanded near bear lake after 4000 cal yr b p charcoal records indicate that fire probably helpedpinus ponderosa to become established near bear lake climate changes on the kaibab plateau since the late glacial were inferred from lake levels and vegetation patterns the late glacial 11 000 cal yr b p was cold and probably wet the early holocene 11 000 to8000 cal yr b p was cooler than today and may have been the wettest period fracas lake and bear lake were probably deepest then during this period a strengthened summer monsoon brought in more moisture from the eastern pacific ocean and the gulf of mexico during the dry and warm mid holocene fracas lake and bear lake experienced water level declines the late holocene was relatively wet and cool again and aquatic plants were abundant in the two lakes increasing effective moisture in the late holocene was related to decreasing summer insolation 1999 elsevier science b v all rights reserved

mid to late wisconsin pollen record of san felipe basin baja california abstract a lacustrine sequence from laguna seca san felipe baja california in the southwestern sonoran desert provides the first record of mid to late wisconsin vegetation in one of the driest regions of north america pollen analysis was performed in the intermediate part of the sequence from ca 44 000 to ca 13 000 14 c yr b p according to six 14 c radiocarbon dates sedimentation of eolian sands prior to 44 000 14 c yr b p indicates dry conditions high pollen concentration of montane and chaparral species in the pollen assemblages contrast with the modern desert vegetation sixty four pollen types were identified the source of mid to late wisconsin sedimentation must have been the plant communities in the surrounding highlands of the basin mid wisconsin pollen assemblages dominated by pines junipers and artemisia reflect humid conditions in the area by late wisconsin time a significant increment in junipers indicates a lowering in the altitudinal ranges of woodlands chaparral pollen from wind pollinated species is abundant while desert plants specifically animal or insect pollinated species are poorly represented the san felipe record does not identify the last glacial maximum as the time of greatest effective moisture as suggested by pluvial lake levels and other paleoclimatic evidence in the soutwestern united states

the eastern mediterranean paleoclimate as a reflection of regional events soreq cave israel the climate of the eastern mediterranean region of the last 60 ky was determined by a high resolution study of the oxygen and carbon isotopic composition 1500 measurement pairs of speleothems from the soreq cave israel with chronology provided by 53 precise 230 th 234 u tims ages the high precision of the speleothem tims ages permits us to determine the timing of regional climatic events in the eastern mediterranean region and to see if they correlate with global events during the period from 60 to 17 ky the 18 o and 13 c values were generally 2 2 5 higher than during the period from 17 ky to present this is consistent with the climatic transition from glacial to interglacial within the 60 to 17 ky period the soreq cave stable isotope profile includes four cold peaks at 46 35 25 and 19 ky and 2 warm peaks at 54 and 36 ky in addition the period 17 ky has two more cold peaks at 16 5 and from 13 2 to 11 4 ky the ages of four of the six cold peaks correlate well with the ages of three heinrich events h1 h2 h5 and with the age of the younger dryas however the other two heinrich events are not reflected in the soreq cave record several other isotope peaks which appear during the last 7 ky are contemporaneous with regional climatic events in the middle east and north africa in addition to the drop in 18 o and 13 c observed between the last glacial and the holocene sharp simultaneous drops in 234 u 238 u 0 ratios sr concentrations and in 87 sr 86 sr are also observed suggesting that the latter are climate related these variations are interpreted in terms of major changes in the temperature the mean annual rainfall and its isotopic composition the isotopic composition of the mediterranean vapor source the soil moisture conditions and in the mixing proportions of sources with different 87 sr 86 sr ratios sea spray dust particles and dolomitic host rock

climate variability in east central california during the past 1000 years reflected by high resolution geochemical and isotopic records from owens lake sediments abstract core ol 97a retrieved from the depocenter of owens lake represents a depositional history spanning the past 1000 yr among the 17 elements analyzed in the acid leachable fractions of 315 salt free samples at 3 yr sample mg and li which come chiefly from authigenic mg hydroxy silicates were found to have concentration variations reflecting lake salinity and climatic changes during the past a total of 231 isotopic measurements on carbonates from the same samples in the upper 181 cm show that 18 o and 13 c values range from 5 66 to 0 12 pdb and 1 38 to 4 28 pdb respectively the rate of change with time in 18 o records the rate of change in lake s volume due to climate fluctuations whereas variations in 13 c reflect mainly variations in biological productivity nutrient supply and dissolved carbonate in the lake results indicate an effectively dry climate between a d 950 and 1220 corresponding to the medieval climatic anomaly a warm period in northern europe during which owens lake approached playa conditions wet climates prevailed during a d 1220 1480 producing relatively large and deep lakes beginning about a d 1550 the regional climate turned colder but had frequently oscillating precipitation six wet dry cycles with 50 yr duration occurred between a d 1480 and 1760 during the later half of which owens lake became a playa since a d 1880 the lake level has steadily dropped from its historic high stand under strong impact of human activity

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

structural analysis and paleoenvironmental potential of dog cockle shells glycymeris glycymeris in brittany northwest france to compensate for the lack of high resolution data on variation in environmental parameters before the establishment of monitoring networks we evaluated dog cockle shells glycymeris glycymeris mollusca bivalvia as archives for temperature and climate perturbations such as the north atlantic oscillation nao over the last 50 years oxygen isotope compositions were measured from annual increments of shells collected from the bay of brest and the chausey islands in northwestern france simultaneously sclerochronological analyses were performed on the same shells oxygen isotopic ratios measured in shells collected from the bay of brest were compared to in situ temperature and salinity data from monitoring stations and buoys in order to build a specific paleotemperature equation r2 0 87 p 0 001 for the dog cockle the specific equation was used to estimate sea surface temperatures around the chausey islands between 1966 and 1994 standardized growth indices sgi calculated through sclerochronological methods were strongly correlated to oxygen isotope derived temperatures the sgi however did not capture the area s predominant climate pattern the nao this study demonstrates that dog cockle shells can be used for long term high resolution reconstructions of past sea surface temperatures

using tetraether lipids archived in north sea basin sediments to extract north western european pliocene continental air temperatures the pliocene is often regarded as a suitable analogue for future climate due to an overall warmer climate 2 3 c coupled with atmospheric co2concentrations largely similar to present values 400 ppmv numerous pliocene sea surface temperature sst records are available however little is known about climate in the terrestrial realm here we generated a pliocene continental temperature record for northwestern europe based on branched glycerol dialkyl glycerol tetraether brgdgt membrane lipids stored in a marine sedimentary record from the western netherlands the total organic carbon toc content of the sediments and its stable carbon isotopic composition 13corg indicate a strong transition from primarily marine derived organic matter om during the pliocene to predominantly terrestrially derived om after the transition into the pleistocene this trend is supported by the ratio of branched and isoprenoid tetraethers bit index the marine terrestrial transition indicates a likely change in brgdgt sources in the core which may complicate the applicability of the brgdgt paleotemperature proxy in this setting currently the application of the brgdgt based paleothermometer on coastal marine sediments has been hampered by a marine overprint here we propose a method to disentangle terrestrial and marine sources based on the degree of cyclizationof tetramethylated brgdgts rings using a linear mixing model based on the global soil calibration set and a newly developed coastal marine temperature transfer function application of this method on our brgdgt record resulted in a corrected terrestrial temperature record matterr this latter record indicates that continental temperature were 12 14 c during the early pilocene and 10 5 12 c during the mid pilocene pollen based terrestrial temperatures estimate from nortern and central europe furthermore two colder 5 7 c periods in the pilocene maytterr record show that the influence of pilocene glacials reached well into nw europe

δ13c δ18o and deposition rate of tufa in xiangshui river sw china implications for land cover change caused by climate and human impact during the late holocene

a holocene paleoclimatic and environmental record from stoneman lake arizona abstract stoneman lake coconino county arizona occupies a 600 000 yr old caldera on the southern edge of the colorado plateau changes in fossil diatom floras pollen profiles macrofossil remains and geological characteristics of a sediment core show changing aquatic and terrestrial environments over the past 9000 yr cool temperatures and greater effective precipitation than at present are indicated during the early holocene prior to 8500 yr b p a warmer and drier period followed 8000 and 2000 yr b p during which time a marsh like environment developed within the caldera and xeric pleat communities were established along the southern colorado plateau modern plant communities have existed in this region for the past 6000 yr although lake conditions have fluctuated

pliocene palaeotemperature reconstruction for the southern north sea based on ostracoda abstract the development of a large northeastern atlantic shelf ostracod database has confirmed that an intrinsic relationship exists between watermass temperature and the spatial latitudinal distribution of benthonic shelf ostracoda a second pliocene ostracod database using assemblages from four boreholes in the netherlands and a number of localities from the east anglian neogene succession has also been constructed a quantitative method of modern analogues and the squared chord distance dissimilarity coefficient has been employed as a means of calculating the level of similarity between recent and neogene assemblages and therefore to aid in the reconstruction of palaeotemperatures in the southern north sea basin during the pliocene the results in the form of contoured dissimilarity values indicate the presence of at least seven palaeoceanographical climatic phases between ca 5 2 and 1 6 ma bp an early pliocene cooling phase ecozone a in which the fauna is dominated by the cryophilic species palmenella limicola norman elofsonella concinna jones robertsonites tuberculatus sars neomonoceratina tsurugasakensis tabuki and acanthocythereis dunelmensis norman supervenes a period of stable subtropical conditions in the miocene a mid pliocene warming phase ecozone b which has been documented throughout the north atlantic can be recognized in the faunal composition of the sublittoral ostracod assemblages of both the netherlands and east anglia a hiatus between the coralline and waltonian crags is thought to be associated with a deterioration in climatic conditions recent analogues to the netherlands faunas of ecozone c first phase late pliocene cooling ca 2 9 ma bp indicate a decrease of approximately 5 6 c in mean summer surface temperatures a return to elevated temperatures of a mauritanian aspect can be seen in the fauna of the fa2 zone and waltonian crag this amelioration of climate occurred prior to the praetiglian cold phase second phase late pliocene cooling ca 2 4 ma bp which again saw the reintroduction of cryophilic species including baffinicythere howei hazel fimarchinella logani brady crosskey and robertson and hemicythere emarginata sars into the southern north sea during the newbournian and butleyan stages the final phase of the latest pliocene third phase late pliocene cooling is only documented in the ostracod fauna of the norwich crag evidence in the covariance of loxoconchidae and norwegian provincial cryophilic species indicates that the polar front may have been as much as 2000 km further south during the deposition of the chillesford sand member norwich crag fm ca 2 0 1 6 ma bp

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

spatial variability of late quaternary paleoclimates in the western united states abstract paleoclimatic interpretation of proxy data is complicated sometimes by the appearance of heterogeneous patterns of climatic responses across networks of sites modern climate analogues for the western united states similar to those patterns of atmospheric circulation of 18 000 and 9000 yr b p were examined in order to explain such patterns of spatial heterogeneity modern analogues were defined by comparing modern atmospheric circulation patterns with those simulated by general circulation models maps of temperature and precipitation anomalies of the modern analogues reveal patterns of spatial heterogeneity which resemble the patterns of effective moisture compiled from paleoclimatic data january 1957 was found to be a reasonable 18 000 yr b p analogue and it features isolated areas of increased wetness in the northern great basin and increased dryness in the northwest interior analogues for 9000 yr b p from a composite of 11 augusts display patterns of spatial heterogeneity of effective moisture over most of the mountainous areas the analogues suggest that spatial heterogeneity of climate is the rule rather than the exception over much of the western united states with the climatic anomalies at any particular time representing the outcome of the mediation of large scale atmospheric circulation controls by smaller scale topographic features

gulf of maine shells reveal changes in seawater temperature seasonality during the medieval climate anomaly and the little ice age article i nfo in this study we use subannually resolved oxygen isotope values of fossil dead collected and modern live caught bivalve shells arctica islandica l from the northwestern atlantic gulf of maine usa to reconstruct past seasonal changes in seawater temperature our results indicate decreased seasonal temperature amplitude of about 1 6 c or 21 during medieval times ca ad 1033 1062 compared to shells from the early little ice age ca ad 1321 1391 and during the late 19th century ad 1864 1886 additionally seasonal oxygen isotope data suggest that summers were cooler and winters were warmer in the gulf of maine during the 11th century compared to summers and winters in the 14th century and the late 19th century the inferred decreased seasonality during medieval times likely resulted from increased stratification of the coastal waters due to warmer seawater temperatures as seawater cooled during the little ice age we suggest that increased vertical mixing of the coastal surface waters was a major driving factor for the observed increase in the amplitude of the seasonal seawater temperature cycle