late pleistocene pinon pines in the chihuahuan desert abstract examination of late pleistocene packrat middens from the northern and central chihuahuan desert disclosed macrofossils of colorado pinon pinus edulis and texas pinon p remota radiocarbon dating indicates that texas pinon was widespread in trans pecos texas and northeastern mexico between 30 000 and 11 000 yr b p today it is found in small refugia east of its former range in the late pleistocene colorado pinon occurred at lower elevations on the northern edge of the chihuahuan desert both species occurred in the hueco mountains near el paso texas no clear evidence was found of the presence of mexican pinon p cembroides though today it is abundant in the davis and chisos mountains a paleoclimate is postulated that had the following characteristics increased winter precipitation from pacific frontal sources reduced summer temperatures and precipitation and milder winter temperatures due to a reduced frequency of arctic airmass incursion winter precipitation appears to have decreased from north to south while winter temperatures and possibly summer precipitation increased from north to south during the late pleistocene the northern chihuahuan desert was dominated by woodlands of pinon pines junipers and oaks the desert scrub communities that characterize the area today are a holocene phenomenon

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

biogeography of pleistocene conifer species from the ziegler reservoir fossil site snowmass village colorado article i nfo article history received 7 november 2013 available online xxxx pleistocene biogeography of conifer species is poorly known in much of western north america we conducted morphological studies on 201 conifer cones and cone fragments recovered from pleistocene sediments at the ziegler reservoir fossil site 2705 m near snowmass village colorado the basin formed 155 130 ka contains fossil bearing lacustrine palustrine and colluvial sediments spanning approximately 85 ka using a suite of mor phological characters particularlycone scale bracts we differentiated species of abies picea a ndpseudotsuga all fossil abies specimens were assignable based on bract morphology to abies concolor which is currently absent from central colorado nearest populations are 160 km southwest of the site a concolor occurs only in sedi ments of mis 5d and 5c pseudotsuga menziesii and picea engelmanniicones occurred in sediments corresponding to mis 5e 5d 5c and 5a a fourth conifer species occurring in sediments of mis 5e 5d 5c and 5a is difficult to assign to any extant species bract morphology is similar to picea pungens which grows near the site today but scale morphology is unlike p pungens these fossils may represent ancestral p pungens an extinct variant or an extinct sister species

isotopic evidence of holocene climatic change in the san juan mountains colorado abstract the d of cellulose from 14c dated wood collected in the san juan mountains of southwestern colorado decreased by about 45 from 9600 to 3100 yr b p and an additional 25 to the present the wood samples are from trees that grew above present day tree line and reflect a time of warmer average summer temperatures these changes in d are interpreted to indicate a major change during the holocene in the sources of moisture in the seasonality of precipitation or in both

reply to the comment of talwani et al 2017 on the sibuet et al 2016 paper entitled thinned continental crust intruded by volcanics beneath the northern bay of bengal the northern bay of bengal velocity depth profiles do not follow the velocity depth curve for the north atlantic volcanic margins and only partially the kerguelen plume velocity depth curves compared with the south china sea northern margin proxy we still suggest that the bay of bengal crust is thinned continental crust intruded by post rifting volcanics as also shown by the interpretation of the numerous high quality deep multichannel seismic profiles we collected there what was supposed to be underplating might be sills intruded through the lower thinned continental crust

a 16 000 14c yr b p packrat midden series from the usa mexico borderlands abstract a new packrat midden chronology from playas valley southwestern new mexico is the first installment of an ongoing effort to reconstruct paleovegetation and paleoclimate in the u s a mexico borderlands playas valley and neighboring basins supported pluvial lakes during full and or late glacial times plant macrofossil and pollen assemblages from nine middens in the playas valley allow comparisons of two time intervals 16 000 10 000 and 4000 0 14c yr b p vegetation along pluvial lake margins consisted of open pinyon juniper communities dominated by pinus edulis juniperus scopulorum juniperus cf coahuilensis and a rich understory of c4 annuals and grasses this summer flowering understory is also characteristic of modern desert grassland in the borderlands and indicates at least moderate summer precipitation p edulis and j scopulorum disappeared or were rare in the midden record by 10 670 14c yr b p the late holocene is marked by the arrival of chihuahuan desert scrub elements and few departures as the vegetation gradually became modern in character larrea tridentata appears as late as 2190 14c yr b p based on macrofossils but may have been present as early as 4095 14c yr b p based on pollen fouquieria splendens one of the dominant desert species present at the site today makes its first appearance only in the last millennium the midden pollen assemblages are difficult to interpret they lack modern analogs in surface pollen assemblages from stock tanks at different elevations in the borderlands

late quaternary paleohydrological conditions in the drylands of northern mexico a summer precipitation proxy record of the last 80 cal ka bp abstract we present a late quaternary multi proxy record from the paleolake babicora in order to understand the influence of north american monsoon nam and westerly winter storms on the paleohydrological budget of the drylands of northern mexico stratigraphy 14 c chronology mineral magnetism and geochemistry of the 976 cm long sediment core were used to reconstruct the hydrological conditions over the last 80 cal ka bp the inverse relationship between the proxy records of runoff into babicora and winter precipitation in southwestern usa indicate the minimal influence of westerly winter storms at 29 n during the last glacial period westerly winds transported minimally chemically altered sediments from the dry watershed during the cold stadials and the basin received more than average runoff as a result of a stronger nam during the warm interstadials the highest pluvial discharge occurred prior to 58 cal ka bp and terrestrial plants became the major contributor to organic matter deposited between 71 and 53 cal ka bp over the last 40 cal ka bp the high amplitude fluctuations in runoff and lake water salinity mirrored an unstable summer rainfall regime

evidence for prolonged el nino like conditions in the pacific during the late pleistocene a 43 ka noble gas record from california groundwaters abstract information on the ocean atmosphere state over the period spanning the last glacial maximum from the late pleistocene to the holocene provides crucial constraints on the relationship between orbital forcing and global climate change the pacific ocean is particularly important in this respect because of its dominant role in exporting heat and moisture from the tropics to higher latitudes through targeting groundwaters in the mojave desert california we show that noble gas derived temperatures in california averaged 4 2 1 1 c cooler in the late pleistocene from 43 to 12 ka compared to the holocene from 10 to 5 ka furthermore the older groundwaters contain higher concentrations of excess air entrained air bubbles and have elevated oxygen 18 oxygen 16 ratios 18o indicators of vigorous aquifer recharge and greater rainfall amounts and or more intense precipitation events respectively together these paleoclimate indicators reveal that cooler and wetter conditions prevailed in the mojave desert from 43 to 12 ka we suggest that during the late pleistocene the pacific ocean atmosphere state was similar to present day el nino like patterns and was characterized by prolonged periods of weak trade winds weak upwelling along the eastern pacific margin and increased precipitation in the southwestern u s

timberline fluctuations and late quaternary paleoclimates in the southern rocky mountains colorado pollen and plant macrofossils from eight sedimentary basins on the west slope of the colorado rocky mountains document fluctuations in upper and lower timberline since the latest pleistocene by tracking climatically sensitive forest boundaries the moisture controlled lower timberline and the temperature controlled upper timberline paleoclimatic estimates can be derived from modern temperature and precipitation lapse rates pollen data suggest that prior to 11 000 yr b p a subalpine forest dominated by picea spruce and pinus pine grew 300 700 m below its modern limit the inferred climate was 2 5 c cooler and had 7 16 cm greater precipitation than today abies fir increased in abundance in the subalpine forest around 11 000 yr b p probably in response to cooler conditions with increased winter snow pollen and plant macrofossil data demonstrate that from 9000 to 4000 yr b p the subalpine forest occupied a greater elevational range than it does today upper timberline was 270 m above its modern limit suggesting that mean annual and mean july temperatures were 1 2 c warmer than today intensification of the summer monsoon coupled with increased summer radiation between 9000 and 6000 yr b p raised mean annual precipitation by 8 11 cm and allowed the lower limit of the subalpine and montane forests to descend to lower elevations the lower forest border began to retreat upslope between 6000 and 4000 yr b p in response to drier conditions and the upper timberline descended after 4000 yr b p when temperatures cooled to about 1 c warmer than today the modern climatic regime was established about 2000 yr b p when the summer precipitation maxima of the early and middle holocene were balanced by increased winter precipitation

climatic backdrop to the terminal pleistocene extinction of north american mammals north american terminal pleistocene mammal extinctions are the subject of a long running scientifi c debate although the role of climate has fi gured centrally we lack clear knowledge of the timing and nature of terminal pleistocene climate variability herein we document lengthy terminal pleistocene drought in the southwestern united states usa using 13 c and 234 u effective moisture proxy data in speleothem calcite stalagmite fs2 from fort stanton cave new mexico supplemented with age data from pool basin shelfstone speleothems from the big room in carlsbad cavern this terminal pleistocene drought defi ned by a sharp rise in both 13 c and 234 u values began just before 14 5 k y ago and lasted at least until 12 9 k y ago when it was briefl y and only mildly interrupted by the younger dryas the timing and length of this drought 1500 yr match the northern hemisphere bolling allerod oscillation preserved in greenland ice cores and exhibited in the 18 o record of stalagmite fs2 rapid transition from cool moist late glacial to warm dry holocenelike climatic conditions was likely unfavorable to many species of pleistocene mammals in the southwestern usa a climate induced extinction implies that this last glacial cycle and its termination were more extreme than previous glacial cycles and or glacial terminations

the occurence and paleolimnologic significance of cutthroat trout oncorhynchus clarki in pluvial lakes of the estancia valley central new mexico cutthroat trout oncorhynchus clarki fossils in the quaternary age lacustrine sediment of the estancia valley provide insight into the paleolimnologic history of the valley the presence of fish is evidence that a pluvial system overflowed into the pecos river watershed most likely the overflow occurred during the expansion of early lake estancia an illinoian or pre illinoian pluvial lake known only in subcrop once established in the estancia watershed trout occupied headwater streams and only intermittently migrated and resided in developing lake systems the headwater streams served as refugia through the sangamon and early and middle wisconsin time when a fresh water lake did not exist in the valley with the advent of full pluvial conditions during the late wisconsin trout migrated from headwater streams into the first of three fresh water phases of late lake estancia on two occasions climate shifted to warmer and drier conditions causing significant lake level drawdown salinity increased and trout were eliminated from the lake only to be reintroduced during the next fresh water phase near the close of the late wisconsin late lake estancia waned and desiccated but headwater streams remained as fish refugia following the interpluvial episode the basin again filled culminating in lake willard considered to be of latest wisconsin age with evolution into a fresh water body trout migrated into a lake environment for the last time ensuing hot dry conditions brought about the desiccation of lake willard and severely impacted the headwater streams this factor in possible combination with human fishing activity led to the elimination of fish from the estancia valley after a continuous occupation of at least 130 000 yr

is methane driven deglaciation consistent with the ice core record the rapid climate changes at the terminations marking the end of the last glaciation are poorly understood this study uses the cambridge two dimensional atmospheric model to investigate the impact of a large marine sediment slump or permafrost rupture releasing 4000 tg of ch 4 into the high latitudes of the northern hemisphere with particular emphasis on the evolution of atmospheric ch 4 concentrations which may have led to an associated direct radiative effect of the order of 1 w m 2 persisting for a few decades because of enhanced levels of atmospheric ch4 the model generated ch 4 concentrations were converted into synthetic ice core signals for 66 n and 85 s representing arctic and antarctic cores respectively a range of possible averaging times was considered the results show that irrespective of the site or enclosure time chosen with the current sampling interval of 300 years it is not possible to discount completely the existence of a spike as a result of the instantaneous release of 4000 tg of ch 4 detection or refutation of a ch 4 spike would however be probable if the sampling interval were reduced to around 50 100 years

late quaternary alluvial stratigraphy of whitewater draw arizona implications for regional correlation of fluvial deposits in the american southwest the alluvial history of whitewater draw an arroyo in the sulphur springs valley southeastern arizona is characterized by numerous degradational and aggradational events shifts in climate appear to be responsible for the major changes in depositional environments recognized in whitewater draw over the past 15 000 yr however the degradation and aggradation documented during apparently stable climatic periods were primarily controlled by geomorphic parameters comparison between the alluvial records of arroyos in the adjacent upper san pedro valley and whitewater draw shows that periods of degradation and aggradation were out of phase in number character and timing these differences indicate that the fluvial systems in the sulphur springs valley and the san pedro valley responded differently to external climate shifts and that both systems were influenced by local geomorphic parameters this demonstrates that regional correlation of late quaternary deposits from one valley to the next should not be attempted without absolute temporal control and that intervalley correlations must take into consideration the complexity of fluvial processes

late quaternary vegetation history of rough canyon south central new mexico usa abstract south central new mexico usa at the junction of the rocky mountains high plains and chihuahuan desert is one of the better known regions in the late quaternary of north america plant macrofossils and pollen from a packrat midden series in rough canyon new mexico allows refinement of plant distributions and paleoclimates in this transitional area since full glacial times from 17 000 to 12 000 14c yr bp pinus edulis juniperus scopulorum woodlands dominated limestone substrates between 1800 and 1490 m with pseudotsuga menziesii and other mixed conifer species restricted to shady north facing slopes juniperus deppeana the dominant juniper today above 2000 m in southern new mexico is conspicuously absent from glacial middens and must have been displaced south of the us mexico border the minimum climatic conditions for p edulis j scopulorum woodlands are ca 20 wetter and 3 5 5 c cooler july mean maximum temperatures than the modern climate at rough canyon holocene warming drying may have started as early as 12 000 14c yr bp with the extirpation of j scopulorum from rough canyon and was completed by at least 10 54014c yr bp the record for arrivals of some desert species is confounded by traces of pollen and macrofossils in some of the glacial middens which could signify either earliest occurrence or temporal mixing contamination of assemblages ams 14c dating can discriminate between early arrival and contamination in midden macrofossils but not in pollen ams dates show that choisya dumosa presently near its northern cold limits at rough canyon endured late glacial winters possibly as clonal populations some larrea tridentata leaves and pollen occur in middens dominated by conifers and oaks no longer at the site an ams date of 3205 14c yr bp on larrea leaves from one midden indicates contamination evidence for some macrofossil contamination however does not rule out the possibility that pollen of desert elements e g larrea prosopis in late glacial early holocene middens indicates their presence in the tularosa basin well ahead of their local appearance in rough canyon finally the increasing dominance of desert elements after 5000 14c yr bp in the rough canyon series and elsewhere in the northern chihuahuan desert could reflect slow postglacial migration from the south and or progressive encroachment with gradual stripping of soils formed during the last glacial period

heterogeneous seawater 187os 188os during the late pleistocene glaciations abstract we report high temporal resolution osmium isotopes records of bulk sediment and sediment leachates from dsdp site 480 gulf of california over the last 30 ka from odp site 849 eastern equatorial pacific from the last 200 ka and from odp site 1002c cariaco basin across the 9 17 ka time interval in order to critically evaluate claims of a global 10 shift in the 187 os 188 os of seawater from glacial to interglacial intervals we use organic rich continental margin sites and carbonate rich pelagic sites to isolate the temporal variations of the osmium seawater isotopic composition our results reveal that variations in 187 os 188 os fail to correlate with global changes in temperature across glacials interglacials cycles as previously claimed instead these results indicate differences of a few percent in the measured 187 os 188 os between each oceanic basin we argue that these differences strongly suggest that seawater is not well homogenized with respect to its os isotope composition

a middle holocene vegetation record from the mojave desert of north america and its paleoclimatic significance abstract packrat middens from the mccullough range in the southeastern mojave desert of nevada record vegetation conditions during the periods 6800 to 5060 yr b p and 1250 yr b p to present their age and location are ideal to test for middle holocene aridity the period between 6800 and 5060 yr b p does appear to have been more arid than during the late holocene period of record this agrees with other evidence for middle holocene aridity from the southwest arguments for strengthened middle holocene monsoons in the region are based chiefly on packrat midden samples older than 7500 yr b p or on samples that are younger than 5500 yr b p simulations of 6000 yr b p climate that fail to show strong subtropical flow into the southwest are therefore supported by evidence for enhanced aridity in that region

eolian landscape evolution and soil formation in the chaco dune field southern colorado plateau new mexico abstract eolian deposits of the chaco dune field cover a broad expanse of the southeastern colorado plateau in new mexico and comprise a large part of the late quaternary sedimentary record in this region the primary eolian landforms include sand sheets parabolic and modified parabolic dunes barchan barchanoid dune complexes and ridge dunes many of the eolian landforms in the chaco dune field have remained stable over a sufficiently long time to permit soil development weakly to moderately developed calcic soils which formed in eolian deposits of mid holocene and latest pleistocene age possess clay enriched weak argillic b horizons these soils have been buried progressively by younger eolian sediments forming regionally correlative bounding surfaces over the chaco dune field and recording relict latest pleistocene and middle holocene eolian landscapes soil geomorphic relations and radiocarbon dated material within the eolian deposits have been useful in 1 delineating three regionally correlative soil stratigraphic units and their associated landforms and 2 studying the types and rates of landscape evolution and climatic changes within this portion of the colorado plateau the most significant period of eolian landform construction is inferred to have occurred during the latest pleistocene glacial to interglacial climatic change forming widespread sand sheets and modified parabolic dunes eolian deposition during the middle and late holocene were dramatically influenced by the presence of previously developed latest pleistocene to early holocene buried soils which may have enhanced sand sheet and parabolic dune development due to the binding effect of the soils middle holocene eolian deposition may be related primarily to neoglacial climatic changes which enhanced ground surface moisture and promoted sand sheet and parabolic dune formation the youngest period of wolian deposition occurred after 1 5 ka and resulted in the formation of the most diverse suite of eolian landforms and deposition of volumetrically more eolian sediments than the mid holocene event in contrast to earlier interpretations the classic mid holocene or altithermal event apparently did not play a major role in the formation of eolian landscapes in the chaco dune field

late pleistocene c4plant dominance and summer rainfall in the southwestern united states from isotopic study of herbivore teeth abstract patterns of climate and c4plant abundance in the southwestern united states during the last glaciation were evaluated from isotopic study of herbivore tooth enamel enamel 13c values revealed a substantial eastward increase in c4plant consumption formammuthusspp bisonspp equusspp andcamelopsspp the 13c values were greatest inbisonspp 6 9 to 1 7 andmammuthusspp 9 0 to 0 3 and in some locales indicated c4 dominated grazing the 13c values of antilocaprids were lowest among taxa 12 5 to 7 9 and indicated c3feeding at all sites on the basis of modern correlations between climate and c4grass abundance the enamel data imply significant summer rain in parts of southern arizona and new mexico throughout the last glaciation enamel 18o values range from 19 0 to 31 0 and generally increase to the east this pattern could point to a tropical or subtropical source of summer rainfall at a synoptic scale the isotope data indicate that interactions of seasonal moisture temperature and lowered atmospheric pco2determined glacial age c4abundance patterns

evidence from western north america for rapid shifts in climate during the last glacial maximum the estancia basin in southwestern united states contains evidence for strong and rapid pulsations in the supply of moisture brought into the region during the last ice age the pulses were recorded during episodes of stream discharge that spread plumes of fresh water laden with quartz sand over the saline lake the largest pulses in stream discharge lasted only a few decades were organized into cycles that were spaced approximately 200 to 250 and 2000 years apart and were of sufficient magnitude to freshen and maintain the lake at its maximum recorded elevation

wetter and cooler late holocene climate in the southwestern united states from mites preserved in stalagmites the presence of at least 12 species of well preserved mites in two late holocene stalagmites from hidden cave guadalupe mountains new mexico depicts changing climate over the past 3200 yr growth of both stalagmites determined by uranium series dating occurred from at least 3171 48 yr ago and ceased by 819 82 yr ago some of the 12 subfossil genera and species in the stalagmites are like those currently found in wetter and cooler climates northern like and distinctly different from those known in the cave n 16 and on the surface immediately around the cave n 32 the mismatch of genera and species in the stalagmites cave and surface near the cave argues for a wetter and cooler late holocene climate in the southwestern united states from ca 3200 to 800 yr ago

the breakup of east gondwana assimilating constraints from cretaceous ocean basins around india into a best fit tectonic model published models for the cretaceous sea oor spreading history of east gondwana result in unlikely tectonic scenarios for at least one of the plate boundaries involved and or violate particular constraints from at least one of the associated ocean basins we link east gondwana spreading corridors by integrating magnetic and gravity anomaly data from the enderby basin off east antarctica within a regional plate kinematic framework to identify a conjugate series of east west trending magnetic anomalies m4 to m0 126 7 120 4 ma the mid ocean ridge that separated greater india from australia antarctica propagated from north to south starting at 136ma northwest of australia and reached the southern tip of india at 126 ma sea oor spreading in the enderby basin was abandoned at 115 ma when a ridge jump transferred the elan bank and south kerguelen plateau to the antarctic plate our revised plate kinematic model helps resolve the problem of successive two way strike slip motion between madagascar and india seen in many previously published reconstructions and also suggests that sea oor spreading between them progressed from south to north from 94 to 84 ma this timing is essential for tectonic ow lines to match the curved fracture zones of the wharton and enderby basins as greater india gradually began to unzip from madagascar from 100 ma in our model the 85 east ridge and kerguelen fracture zone formed as conjugate anks of a leaky transform fault following the 100ma spreading reorganization our model also identi es the afanasy nikitin seamounts as products of the conrad rise hotspot

stable carbon and oxygen isotopes in quaternary soil carbonates as indicators of ecogeomorphic changes in the northern chihuahuan desert usa stable carbon and oxygen isotopes in soil carbonates provide an additional technique for investigating quaternary ecogeomorphic changes in arid and semiarid regions this study presents 13c and 18o values in surface and buried soils in a basin and range region of southern new mexico and west texas three landform categories were investigated for their isotopic content 1 middle piedmont slopes 2 a lower piedmont slope and adjacent playa depressions and 3 an intermontane basin floor soils of the middle piedmont slopes had greatest 13c variability ranging from 0 6 in buried soils to 11 1 pdb in surface soils soils of the basin floor had greatest variability in 18o values ranging from 0 6 to 7 6 pdb fossil pollen patterns roughly paralleled 13c shifts with cheno am pollen exhibiting greatest changes both isotope and pollen data across stratigraphic discontinuities suggest that a conversion from c4 grasses to c3 desert shrubs accompanied holocene erosion

timing and extent of late quaternary paleolakes in the trans pecos closed basin west texas and south central new mexico abstract the trans pecos closed basin is a hydrographically closed region covering 20 000 km 2 centered on salt basin 160 km east of el paso texas geomorphic and limnetic evidence have been used to identify four major highstands for lake king during the last glacial maximum lgm additional geomorphic features from a second recently identified paleolake lake sacramento have been found in the beargrass subbasin a nested subbasin approximately 75 km northwest of salt basin radiocarbon ages of the organic material in lake king sediments date four abrupt climate changes and rapid lacustrine transgressions during the lgm with a quasi periodicity of 2000 yr geomorphic evidence in the beargrass subbasin identifies lake cycles contemporaneous with those in lake king the dates for these transgressions correlate with the dates of freshening events identified by researchers in paleolake basins elsewhere in new mexico the quasi periodicity of the events approximates that of dansgaard oeschger events identified from greenland ice cores the contemporaneity of the trans pecos transgressions with transgressive events in other basins in the region suggests that paleolakes in the region were in phase with respect to abrupt climate changes during the latter stages of the lgm

caves as sources of biotic remains in arid western north america caves have been a valuable source of paleoenvironmental information since the eighteenth century in arid portions of western north america caves have replaced small lakes as the primary source of biotic remains of quaternary age packrat middens dung of extinct animals pollen and archeological artifacts are excellently preserved aridity of the sediment which is influenced by the cave s topographic position internal morphology and the regional climate is the primary cause of good preservation for stratigraphic pollen analysis the best sites are those without internal moisture sources and without extensive bioturbation pollen samples should be taken near the center of the chamber where eolian deposition is most rapid pollen concentrations in cave sediment are lower 2000 355 000 grains g 1 than in lake sediment and pollen percentages in cave sediment differ from those in packrat middens due to additional transport mechanisms on plant tissue and on the packrats themselves for middens pollen diagrams for bechan cave utah and organ pipe cactus national monument arizona are presented as examples of cave sediment and packrat midden analysis

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

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

fossil packrat middens and the tandem accelerator mass spectrometer analyses of well preserved plant remains from ancient packrat neotoma middens have yielded much information on the history of vegetation fauna and climate from the more arid portions of north america over the past 40 000 years1 2 in most of the modern deserts woodland or forest communities were present during the last glacial age the wisconsin radiocarbon dating of packrat midden assemblages from a single cave or from several nearby sites in a homogeneous local area can yield a detailed local vegetation chronology for many thousands of years from within 30 50 m on the rocky slopes in front of the dry rock shelters3 4 the development of radiocarbon dating using the tandem accelerator mass spectrometer tams allows direct dating of very small samples here we present 20 examples of tams radiocarbon dates on packrat midden materials to illustrate their usefulness in testing anomalous mixtures of species in ice age communities understanding the details of plant migrations and refining wisconsin and holocene time boundaries based on range changes of important plant species table 1 fig 1

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

evidence for younger dryas global climate oscillation and human response in the american southwest whether or not abrupt younger dryas climate change affected regional paleoenvironments and late pleistocene hunter gatherer populations is an important topic in the archaeology of the american southwest this paper reviews multiple age resolved proxy evidence to gauge the magnitude and direction of younger dryas chronozone ydc environmental changes in different settings and systems there is no record of ydc pluvial lake highstands in arizona or new mexico but there are impressive records of vegetation faunal stable isotope and geomorphological change coincident with the ydc these correlate with important adaptive changes in human hunting and land use as revealed in the analysis of the spatiotemporal distribution of late pleistocene hunting technologies clovis and folsom projectile point distributions do not support extant models of paleoenvironmental conditions in these interpretations significant cultural changes that coincide with the ydc include the clovis to folsom transition the demise of mammoth hunting and the development of a highly successful emphasis on bison increased regionalization and the abandonment of the northwestern chihuahuan and the sonoran deserts by mobile big game hunters

middle holocene drought on the southern high plains abstract the climate of the southern high plains during the middle holocene is indicated by data from a variety of sources stratigraphic geomorphic and pedologic research at six localities in draws several dune sites and one playa lake basin show that widespread eolian erosion and sedimentation began in some areas by 9000 yr b p and culminated 6000 4500 yr b p probably because of warmer drier conditions that reduced the vegetative cover archaeological investigations at three sites provide evidence for the excavation of wells at this time apparently because of a declining water table studies of a few vertebrate and invertebrate faunas also indicate warming and drying in the middle holocene climate models and very limited isotopic data from bison bone suggest that summers in the middle holocene were warmer than present with reduced effective precipitation all lines of evidence indicate that the southern high plains was subjected to prolonged drought in the middle holocene with a maximum between 6500 and 4500 yr b p conforming climatically and chronologically to the altithermal

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

paleoindians paleolakes and paleoplayas landscape geoarchaeology of the tularosa basin new mexico abstract karl butzer was one of the first prehistorians to think about and write about people ancient and modern on the landscape moreover as a geomorphologist he knew that past landscapes were as dynamic and varied as they are today not static entities that formed the backdrop for human activity that viewpoint is critical in understanding the physical environment faced by humans during the early peopling of the americas 13 500 to 10 000 cal ybp north america was undergoing rapid environmental changes as the continent was coming out of the last ice age in the southwestern part of the continent large paleolake levels were falling and smaller playa basins were aggrading as the area was occupied by paleoindian groups such as clovis folsom and later first americans the paleolakes would have provided some resources but modern gypsum deposits indicate that lake waters were unpotable numerous small depressions playas scattered around the floor of the tularosa basin contain muddy fills that span the holocene and terminal pleistocene indicative of fresher water at least seasonally paleoindian sites tend to be clustered around these small basins and along drainages off of the mountains that flank the basin as well as settings with good viewsheds rather than the main paleolake margins paleolakes were dramatic components of the late pleistocene landscape in the southwest but likely were not the primary attractions to the first americans

geoarchaeological and paleohydrological evidence for a clovis age drought in north america and its bearing on extinction abstract at the murray springs clovis site in southeastern arizona stratigraphic and geomorphic evidence indicates that an abnormally low water table 10 900 yr b p was followed soon thereafter by a water table rise accompanied by the deposition of an algal mat the black mat that buried mammoth tracks clovis artifacts and a well this water table fluctuation correlates with pluvial lake fluctuations in the great basin during and immediately following clovis occupation of that region many elements of pleistocene megafauna in north america became extinct during the dry period oxygen isotope records show a marked decrease in 18o correlated with the younger dryas cold dry event of northern europe which ended 10 750 yr b p essentially the same time as the water table began to rise in southeastern arizona clovis hunters may have found large game animals easier prey when concentrated at water holes and under stress if so both climate and human predation contributed to pleistocene extinction in america

development of the mixed conifer forest in northern new mexico and its relationship to holocene environmental change chihuahuenos bog 2925 m in the jemez mountains of northern new mexico contains one of the few records of late glacial and postglacial development of the mixed conifer forest in southwestern north america the chihuahuenos bog record extends to over 15 000 cal yr bp an artemisia steppe then an open picea woodland grew around a small pond until ca 11 700 cal yr bp when pinus ponderosa became established c n ratios 13c and 15n values indicate both terrestrial and aquatic organic matter was incorporated into the sediment higher percentages of aquatic algae and elevated c n ratios indicate higher lake levels at the opening of the holocene but a wetland developed subsequently as climate warmed from ca 8500 to 6400 cal yr bp the pond desiccated in what must have been the driest period of the holocene there c n ratios declined to their lowest holocene levels indicating intense decomposition in the sediment wetter conditions returned after 6400 cal yr bp with conversion of the site to a sedge bog as groundwater levels rose higher charcoal influx rates after 6400 cal yr bp probably result from greater biomass production rates only minor shifts in the overstory species occurred during the holocene suggesting that mixed conifer forest dominated throughout the record

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

san agustin plains new mexico age and paleoenvironmental potential reassessed paleomagnetic analysis of samples from the original 600 m long core from the san agustin plains new mexico showed an unquestionable reversal stratigraphy dating the record back to at least 1 6 my analysis of pollen ostracodes and algae of a duplicate sample section in the vicinity of the original coring site and spanning the last 18 000 yr b p shows a much higher resolution than the earlier results

biogeographic implications of a packrat midden sequence from the sacramento mountains south central new mexico abstract thirteen packrat neotoma spp and two porcupine erethizon dorsatum middens from 1555 to 1690 m elevation from the sacramento mountains new mexico provide an 18 000 yr vegetation record in the northern chiuahuan desert the vegetation sequence is a mesic wisconsin fullglacial 18 000 16 000 yr b p pinyon juniper oak woodland a xeric early holocene ca 11 000 8000 yr b p juniper oak woodland a middle holocene ca 8000 4000 yr b p desert grassland and a late holocene ca 4000 yr b p to present chihuahuan desertscrub the frequency of spring freezes and summer droughts in the late wisconsin probably set the northern limits of pinus edulis and juniperus monosperma at about 34 n or 6 south of today s limit rising summer tempratures in the early holocene eliminated pinyon and other mesic woodland plants from the desert lowlands and allowed the woodland to move upslope at this time pinyon juniper woodland and pine forest dominated by pinus ponderosa probably began their spectacular holocene expansions to the north continued warming in the middle holocene led to very warm summers with strong monsoons relatively dry cold winters and widespread desert grasslands desertscrub communities in the northern chihuahuan desert did not develop until the late holocene when the biseasonal rainfall shifted slightly back toward the winter catastrophic winter freezes decreased and droughts in all seasons increased the creosote bush desertscrub corridor across the continental divide between the chihuahuan and sonoran deserts was probably connected for the first time since the last interglaciation

late glacial and holocene record of climatic change in the southern rocky mountains from sediments in san luis lake colorado usa abstract large rapid climate changes occurred over the last glacial cycle in the southwestern united states and elsewhere in many regions of the world some of these changes were attributed to alternations between stadial and interstadial conditions in the north atlantic but intense debate exists on how climate anomalies in the north atlantic transmit to the southwest here we report a sediment record from san luis lake in southern colorado through analyses of grain size magnetic susceptibility mg ca total inorganic carbon 18 o and 13 c to indicate climatic and environmental changes in the southern rocky mountains over the last 16 5 ka we found that san luis lake remained hydrologically closed most of the time but overflowed during the second half of the mystery interval the big wet 15 7 14 9 ka and the latter part of the mid holocene the neopluvial 4 3 ka over the course of the last deglaciation san luis lake underwent a series of large millennial scale hydroclimatic changes such as the big dry 16 5 15 7 ka the big wet the bolling allerod dry 14 9 12 7 ka and the younger dryas wet 12 8 11 6 ka corresponding to warm cold phases in the high latitude northern hemisphere the north american monsoon waxed during the pre boreal interval 11 6 10 5 ka and waned through the holocene in phase with northward and southward displacement of the intertropical convergence zone itcz the san luis lake basin was relatively dry in the early holocene 10 5 6 7 ka wet and fluctuating in the mid holocene 6 7 2 6 ka and dry and less variable in the late holocene 2 6 0 ka we found evidence that extreme pluvial episodes of the southern rocky mountains and elsewhere in the american southwest were coeval with cold phases of the north pacific our results highlight the role of the north pacific in modulating atmospheric circulations over the region on millennial timescales

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

50 000 years of vegetation and climate history on the colorado plateau utah and arizona usa sixty packrat middens were collected in canyonlands and grand canyon national parks and these series include sites north of areas that produced previous detailed series from the colorado plateau the exceptionally long time series obtained from each of three sites n48 000 14 cy r bp to present include some of the oldest middens yet discovered most middens contain a typical late wisconsinan glaciation mixture of mesic and xeric taxa evidence that plant species responded to climate change by range adjustments of elevational distribution based on individual criteria differences in elevational range from today for trees and shrubs ranged from no apparent change to as much as 1200 m difference the oldest middens from canyonlands np however differ in containing strictly xeric assemblages including middens incorporating needles of arizona single leaf pinyon far north of its current distribution similar aged middens from the eastern end of grand canyon np contain plants more typical of glacial climates but also contain fossils of one seed juniper near its current northern limit in arizona holocene middens reveal the development of modern vegetation assemblages on the colorado plateau recording departures of mesic taxa from low elevation sites and the arrival of modern dominant components much later published by university of washington

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

representation of flora and vegetation in quaternary fossil assemblages known and unknown knowns and unknowns paleoecological inference rests on a foundation of processes and relationships that lie between the target variables of interest and the proxy data extracted from the fossil record inattention to these processes can lead to overconfidence reification of proxies and ignorance creep a process by which assumptions become taken for granted and ultimately hidden or forgotten paleoecological inference can be strengthened and its uncertainties identified and quantified by developing forward conceptual models that incorporate the processes and relationships known to lie between target variables and proxy data these may fall into four general categories source vector diagenesis and analysis the uncertainties within each of these categories are somewhat unique although interactions often arise among processes in different categories i use inference of regional species occurrence from macrofossil assemblages in woodrat neotoma middens to illustrate the effects of various processes and interactions on strength of inference and origin of uncertainties and to identify how uncertainties can be characterized reduced or quantified the kinds of issues discussed in the woodrat midden example are pervasive in paleoenvironmental and paleoecological inference and should be examined thoroughly for all proxies and archives on a regular basis

calibration of radiocarbon ages and the interpretation of paleoenvironmental records abstract calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls the differences between calendar ages and radiocarbon ages that arise from variations in 14c production through time can distort the chronologies of individual records and the interpretations based on them misleading impressions of synchrony or diachrony of events among multiple records can result and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased displays of the temporal patterns of migration or extinction may also be affected spurious correlations may arise between records with radiocarbon controlled chronologies and time series of potential controls that are expressed on a calendar time scale support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not this situation is illustrated using the eastern beringian populus subzone as an example when the radiocarbon ages that control the timing of the populus subzone are calibrated the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone

wetter or colder during the last glacial maximum revisiting the pluvial lake question in southwestern north america abstract well preserved shorelines in estancia basin and a relatively simple hydrologic setting have prompted several inquiries into the basin s hydrologic balance for the purpose of estimating regional precipitation during the late pleistocene estimates have ranged from 86 to 150 of modern the disparity largely the result of assumptions about past temperatures in this study we use an array of models for surface water runoff groundwater flow and lake energy balance to examine previously proposed scenarios for late pleistocene climate constraints imposed by geologic evidence of past lake levels indicate that precipitation for the last glacial maximum lgm may have doubled relative to modern values during brief episodes of colder and wetter climate and that annual runoff was as much as 15 of annual precipitation during these episodes

holocene alluvial geology and geoarchaeology of the san xavier reach of the santa cruz river arizona the 15 km segment of the santa cruz river traversing the san xavier indian reservation near tucson arizona has undergone major environmental changes during the past 8 000 yr the holocene alluvial sequence for this segment called the san xavier reach of the santa cruz river shows three major episodes aggradation until 8000 yr b p by a braided stream channel erosion from 8000 to 5500 yr b p and subsequent vertical aggradation of the flood plain punctuated by short periods of arroyo cutting the major changes in the fluvial regime were probably the result of climatic changes but cycles of arroyo cutting and filling during the past 2 500 yr were probably the result of unstable internal geomorphic conditions flooding and human impacts on the flood plain the alluvial history of the san xavier reach had a pronounced effect on the preservation of archaeological remains environmental changes on the flood plain including arroyo cutting and filling cienega formation and destruction and sand dune development led to the disruption and reorganization of hohokam settlement and subsistence patterns between 1150 and 500 yr b p

high resolution migration history of the subtropical high trade wind system of the northeastern pacific during the last 55 years implications for glacial atmospheric reorganization 1 guaymas basin gulf of california is a restricted basin located under the present day wet dry subtropical divide 27 n and is ideally circumstanced for detecting variations in the north pacific subtropical high npsh trade wind system controlled by climate cell boundary displacement npsh midwinter location was the primary influence on timing and intensity of upwelling seasons in guaymas basin analysis of high resolution x ray fluoresence data and sediment fabric log from 75 laminated core md02 2517 2515 western guaymas basin reveals systematic changes in npsh behavior over the last 55 kyr bp southward displacement of the wet dry subtropical divide controlled upwelling related diatom productivity while sea level and regional rainfall controlled terrigenous supply the basin was oxic during the glacial and preservation was ensured by high burial rate due to the increased deposition of terrigenous sediment sediment fabric style number and or thickness of laminae plus color banding and homogeneous intervals changes systematically through the core and gives insights into the number of seasons occurring in guaymas basin and the occurrence and intensity of the upwelling season five millennial scale low flux events with close timing to heinrich events and ten decadal centennial scale low biogenic silica events occurring in the interval 33 16 5000 years before present kyr bp are interpreted as times of extreme aridity at 16 5 kyr bp a regime shift from terrigenous dominated oxic to evenly balanced biogenic terrigenous dysoxic conditions occurred although there was a further extreme arid event at 11 5 kyr bp 16 5 kyr bp was essentially the beginning of the interglacial

a 36 000 yr vegetation history from the peloncillo mountains southeastern arizona usa a 36 200 cal yr b p vegetation history was developed from macrofossils and pollen from 55 packrat middens from 1287 to 1442 m elevation in the peloncillo mountains of southeasternmost arizona usa today these elevations are dominated by semidesert grassland with a mixture of chihuahuan and sonoran desert shrubs including an eastern disjunct population of jojoba simmondsia chinensis from 36 200 to 15 410 cal yr b p rocky areas just above large pluvial lakes that occupied what are now dry playas supported pinus edulis juniperus osteosperma juniperus cf coahuilensis quercus cf turbinella and a rich understory of summer flowering c4 annuals and grasses indicating abundant summer rains and mild winters after 15 410 cal yr b p p edulis declined in abundance and disappeared briefly at 13 925 cal yr b p coincident with expansion of more xeric species and paleohydrological evidence for regional aridity during the bolling allerod warm interval p edulis rebounded briefly during the younger dryas at 12 405 cal yr b p before disappearing along with other mesic woodland species sometime after 12 100 cal yr b p the few middens dating from the early to middle holocene 10 000 4000 yr b p indicate wetter conditions than today at 7790 cal yr b p followed by a general drying trend the 35 middens from the late holocene detail the sequential arrival of desertscrub species as vegetation became more modern in character

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

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

holocene vegetation history from fossil rodent middens near arequipa peru rodent abrocoma lagidium phyllotis middens collected from 2350 to 2750 m elevation near arequipa peru 16 s provide an 9600 yr vegetation history of the northern atacama desert based on identification of 50 species of plant macrofossils these midden floras show considerable stability throughout the holocene with slightly more mesophytic plant assemblages in the middle holocene unlike the southwestern united states rodent middens of mid holocene age are common in the arequipa area the midden record does not reflect any effects of a mid holocene mega drought proposed from the extreme lowstand 100 m below modern levels 6000 to 3500 yr b p of lake titicaca only 200 km east of arequipa this is perhaps not surprising given other evidence for wetter summers on the pacific slope of the andes during the middle holocene as well as the poor correlation of summer rainfall among modern weather stations in the central andes atacama desert the apparent difference in paleoclimatic reconstructions suggests that it is premature to relate changes observed during the holocene to changes in el nino southern oscillation modes

a 164 ka record of environmental change in the american southwest from a carlsbad cavern speleothem abstract a horizontal core 2 8 m in length drilled from the georgia giant column in carlsbad cavern provides climate information for the last 164 ka forty six alpha spectrometric u series ages determined at intervals of 7 6 cm along the core indicate five periods of deposition and five hiatuses the longest from 136 to 110 ka variations in growth rate 0 to 70 mm ka in the abundance of aragonite chalcedony and fe bearing phases and in 13c indicate that glacial intervals of the last 164 ka ois 6 4 and 2 were much wetter than today as were the colder substages 5d and 5b of ois 5 by contrast during the two warmest periods of the past 164 ka namely ois 5e and 1 there was no deposition on either side of the speleothem suggesting conditions as dry or drier than today the record from carlsbad parallels data from many other sites in the southwestern usa and northern mexico and data from marine sediments and ice cores demonstrating the extent to which ice sheet fluctuations influenced conditions in southern new mexico detailed correlation of 13c values in the georgia giant which range from 6 6 to 0 9 relative to pdb with distant speleothem records and with data from ice cores further documents the linkage of southwestern climate with global scale extent of glaciation values of 18o in the georgia giant core range from 9 7 to 4 7 relative to pdb and average 6 6 18o depleted carbonate in the georgia giant during ois 6 at a time when the world s oceans were enriched in 18o suggests that precipitation during cold intervals was brought largely by pacific air masses in fall winter and spring as a result of the southward displacement of the polar jet stream by the growth of the laurentide ice sheet termination ii marking the end of the penultimate glaciation is well defined in the core s 18o data analytical uncertainties in the radiometric ages do not preclude a start of termination ii as late as 128 ka as suggested by specmap data however data from the georgia giant core are more compatible with an earlier start like that obtained from devils hole and vostok data raising the possibility that early warming was widespread in the u s southwest region by 145 ka