precipitation driven decadal scale decline and recovery of wetlands of lake pannon during the tortonian high resolution pollen and dinoflagellate analyses were performed on a continuous 98 cm long core from tortonian deposits of lake pannon in the styrian basin in austria the sample distance of 1 cm corresponds to a resolution of roughly one decade allowing insights into environmental and climatic changes over a millennium of late miocene time shifts in lake level surface water productivity on a decadal to centennial scale can be explained by variations of rainfall during the tortonian climatic optimum related to negative fine scale shifts of mean annual precipitation shoreline vegetation belts reacted in an immediate replacement of poaceae by cyperaceae as dominant grasses in the marshes fringing the lake in contrast to such near synchronous ecosystem responses to precipitation a delayed lake level rise of 4 6 decades is evident in the hydrological budget of lake pannon this transgression caused by a precipitation increase up to 1200 mm yr resulted in a complete dieback of marshes simultaneously open water dinoflagellates such as impagidinium took over in the brackish lagoon and fresh water dinoflagellates disappeared as soon as the rainfall switched back to moderate levels of 1100 1200 mm yr the rise of the lake level slowed down the marsh plants could keep up again and the former vegetation belts became re established thus mean annual precipitation more than temperature was the main driving force for high frequency fluctuations in the tortonian wetlands and surface water conditions of lake pannon such high resolution studies focusing on tortonian decadal to centennial climate change will be crucial to test climate models which try to compare the tortonian models with predictions for future climate change

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

october field the latest giant under development in egypt s gulf of suez october field the third largest oil field in egypt produced 378 mmbo from its discovery in 1977 until january 1990 it is the northernmost giant oil field in the gulf of suez rift basin twenty wells from five platforms in approximately 190 ft 58 m of water currently drain over 3 238 ha recent successful field extensions demonstrate the viability of continuing exploration in this oil rich area this structurally trapped field is a complex of rotated fault blocks typical of rift basins worldwide a northwest trending normal fault with an approximate throw of 1 220 m has trapped an 335 m oil column on the upthrown eastern side on the upthrown side the carboniferous through oligocene prerift section dips gently to the northeast and is unconformably overlain by generally flat miocene to holocene clastics carbonates and evaporites severe multiple problems result from thick miocene evaporites hampering seismic definition of the highly productive prerift section these same evaporites serve as the ultimate seal in october field and throughout the gulf of suez although four layers are productive approximately 95 of field reserves are within carboniferous to lower cretaceous massive nubia sandstones the remaining reserves are in more stratified upper cretaceous sandstones basal miocene rift fill nukhulmore formation clastics and a lower miocene clastic in the upper rudeis formation several distinct reservoir accumulations exist with the deepest and most significant original oil water contact at minus 10 670 ft subsea october field oil gravities range from 14 to 34 degree api with an initial solution gor of 134 to 474 scf stb the hydrocarbon source for all october field oil as well as most gulf of suez oil is believed to be the campanian brown limestone member of the sudr formation average reservoir parameters for the nubia formation are 16 porosity 236 md permeability 137 m net pay thickness and 5 506 psi original reservoir pressure less

widespread evidence of 1500 yr climate variability in north america during the past 14 000 yr there is debate concerning the spatial extent and magnitude of the recently identified 1500 yr climate oscillation existing evidence is largely restricted to the north atlantic and adjacent landmasses the spatial extent magnitude and effects of these climate variations within the terrestrial environment during the holocene have not been established we show that millennial scale climate variability caused changes in vegetation communities across all of north america with a periodicity of 1650 500 yr during the past 14 000 calendar years cal yr times of major transitions identified in pollen records occurred at 600 1650 2850 4030 6700 8100 10 190 12 900 and 13 800 cal yr b p consistent with ice and marine records we suggest that north atlantic millennial scale climate variability is associated with rearrangements of the atmospheric circulation with far reaching influences on the climate

early holocene climate oscillations recorded in three greenland ice cores a new ice core chronology for the greenland dye 3 grip and ngrip ice cores has been constructed making it possible to compare the 18 o and accumulation signals recorded in the three cores on an almost annual scale throughout the holocene we here introduce the new time scale and investigate 18 o and accumulation anoma lies that are common to the three cores in the early holocene 7 9 11 7 ka before present three time periods with significant and synchronous anomalies in the 18 o and accumulation signals stand out the well known 8 2 ka event an event of shorter duration but of almost similar amplitude around 9 3 ka before present and the preboreal oscillation during the first centuries of the holocene for each of these sections we present a 18 o anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the greenland ice cap

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

lower timberline in central colorado during the past 15 000 yr a 15 000 yr paleoenvironmental record at the elevation of lower timberline in central colorado suggests two major paleoclimatic changes during that interval 1 at 10 000 yr b p from cool moist conditions to warm moist conditions and 2 at 4 000 yr b p to warm dry conditions this sequence can be interpreted as a shift from precipitation predominantly originating from pacific winter storms before 10 000 yr b p to a predominantly monsoonal type regime lasting until 4 000 yr b p to the present pattern contemporaneity of higher upper timberline and lower lower timberline during the 10 000 to 4 000 yr b p interval is not contradictory but a result of changes in those circulation patterns

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

late quaternary temperature record from buried soils of the north american great plains we present the first comprehensive late quaternary record of north american great plains temperature by assessing the behavior of the stable isotopic composition 13 c of buried soils after examining the relationship between the 13 c of topsoil organic matter and july temperature from 61 native prairies within a latitudinal range of 46 38 n we applied the resulting regression equation to 64 published 13 c values from buried soils of the same region to construct a temperature curve for the past 12 k y estimated temperatures from 12 to 10 ka 1 k y 1000 14 c yr b p fluctuated with a periodicity of 1 k y with two cool excursions between 4 5 and 3 5 c and two warmer excursions between 1 and 0 c relative to modern early holocene temperatures from ca 10 7 5 ka were 1 0 to 2 0 c before rising to 1 0 c in the middle holocene between 6 0 and 4 5 ka after a cool interlude from 4 2 to 2 6 ka when temperatures dropped to slightly below modern another warm interval ensued from 2 6 to 1 ka as temperatures increased to 0 5 c a final decline in temperature to below modern occurred beginning ca 0 5 ka cooler than present temperatures in the great plains indicate telecommunications with cool water episodes in the gulf of mexico and north atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance

el nino variability off peru during the last 20 000 years here we present a high resolution marine sediment record from the el nino region off the coast of peru spanning the last 20 000 years sea surface temperature photosynthetic pigments and a lithic proxy for el nino flood events on the continent are used as paleo el nino southern oscillation proxy data the onset of stronger el nino activity in peru started around 17 000 calibrated years before the present which is later than modeling experiments show but contemporaneous with the heinrich event 1 maximum el nino activity occurred during the early and late holocene especially during the second and third millennium b p the recurrence period of very strong el nino events is 60 80 years el nino events were weak before and during the beginning of the younger dryas during the middle of the holocene and during medieval times the strength of el nino flood events during the last millennium has positive and negative relationships to global and northern hemisphere temperature reconstructions

contributions of la nina and el nino to middle holocene drought and late holocene moisture in the american southwest eolian landforms in estancia basin central new mexico record two episodes of extreme drought and low groundwater levels during the middle holocene 7000 5400 1 4 c yr b p followed by a rise in the water table throughthe late holocene blowouts and associated lunettes formed when water levels fell below the desiccated floor of pluvial lake estancia allowing widespread deflation elevation of the water table in the basin is regulated by a balance between evaporation from playas that occupy the blowouts and recharge of aquifers in the adjacent manzano mountains isotopic analyses of modern precipitation and groundwater reveal that recharge originates primarily as winter moisture which is amplified during el ninos and diminished during la ninas thus changes in the elevation of a reconstructed holocene water table may reflect systematic changes in el nino southern oscillation enso circulation

glacial isostatic adjustment of the british isles new constraints from gps measurements of crustal motion summary we compared estimates of crustal velocities within great britain based on continuous global positioning system cgps measurements to predictions from a model of glacial isostatic adjustment gia the observed and predicted values for vertical motion are highly correlated indicating that gia is the dominant geodynamic process contributing to this field in contrast motion of the eurasian plate dominates the horizontal motion component a model of plate motion was adopted to remove this signal in order to estimate intraplate horizontal motion associated with gia however a coherent pattern of horizontal motion was not evident in the resulting velocity field we adopted a recently published model of the british irish ice sheet to predict vertical crustal motion for a large number of spherically symmetric earth viscosity models our results show that the adopted ice model is capable of producing a high quality fit to the observations the cgps derived estimates of vertical motion provide a useful constraint on the average value of viscosity within the upper mantle values of model lithospheric thickness and lower mantle viscosity are less well resolved however a suite of predictions based on an alternative ice model indicates that the vertical motion data are relatively insensitive to uncertainties in the ice loading history and so the constraints on upper mantle viscosity are robust

15 k y paleoclimatic and glacial record from northern new mexico the southern sangre de cristo mountains new mexico contain evidence of glacial activity from the late pleistocene to late holocene sediment cores recovered from an alpine bog 3100 m trapped behind a pinedale age moraine 2 km downvalley from a high elevation cirque reached glacial age debris and recovered 6 m of lake clays overlain by gyttja accelerator mass spectrometry dating sedimentology variations in magnetic properties and organic carbon data reveal six distinct periods of glacial and or periglacial activity these include a late pleistocene pinedale glacial termination just before 12120 1 4 c yr b p a younger dryas chron cirque glaciation an early neoglacial periglacial event ca 4900 1 4 c yr b p a late holocene cirque glaciation 3700 1 4 c yr b p as well as late holocene periglacial events at 2800 1 4 c yr b p and the little ice age ca 120 1 4 c yr b p cold events in the middle to late holocene correlate with subtle ice rafting events in the north atlantic and records of cold events in north america and europe and were probably hemispheric in extent

evidence for pacific modulated precipitation variability during the late holocene from the southwestern usa 1 the mechanisms driving late holocene drought cycles in the western united states are not well known due to the general scarcity of long term high resolution absolutely dateable proxies for precipitation in continental interiors here we show that late holocene precipitation variability in the southwestern united states has been caused by changes in the pacific ocean we present a stalagmite based annually resolved moisture record that indicates large shifts from pluvial to drought conditions alternating with periods of dampened near average precipitation over the last 3000 years significant spectral peaks at decadal scale 20 50 70 80 year frequencies likely correspond to modern frequencies of the pacific decadal oscillation or a low frequency component of the el nino southern oscillation and are dominant during episodes of large precipitation shifts overall pluvial conditions punctuated by severe droughts may have challenged the adaptive capacities of emerging agrarian communities of ancestral americans

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

orbital and millennial scale vegetation and climate changes of the past 225 ka from bear lake utah idaho usa continuous high resolution pollen data for the past 225 ka from sediments in bear lake utah idaho reflect changes in vegetation and climate that correlate well with variations in summer insolation and global ice volume during mis 1 through 7 spectral analysis of the pollen data identified peaks at 21 22 and 100 ka corresponding to periodicities in earth s precession and eccentricity orbital cycles suborbital climatic fluctuations recorded in the pollen data denoted by 6 and 5 ka cyclicities are similar to greenland atmospheric temperatures and north atlantic ice rafting heinrich events our results show that millennial scale climate variability is also evident during mis 5 6 and 7 including the occurrence of heinrich like events in mis 6 showing the long term feature of such climate variability this study provides clear evidence of a highly interconnected ocean atmosphere system during the last two glacial interglacial cycles that extended its influence as far as continental western north america our study also contributes to a greater understanding of the impact of long term climate change on vegetation of western north america such high resolution studies are particularly important in efforts of the scientific community to predict the consequences of future climate change r 2007 elsevier ltd all rights reserved

paleoclimatic interpretations of meadow sediment and pollen stratigraphies from california a comparison of sediment stratigraphies from nine meadow cores in the sierra nevada california with fossil pollen reconstructions of paleoclimates shows excellent correlation between these parameters and confirms the results of recent paleoclimatic models colluvium and alluvium dominate early holocene sedimentary deposits and undoubtedly originated from greater erosion on dry basin side slopes fossil pollen suggests that species characteristic of dry microclimates flourished the transition to peats after 4 5 ka is concurrent with increases in pollen of plants that require abundant soil moisture during the dry summer these results confirm the importance of analysis of the physical stratigraphy of holocene deposits in pollen based reconstructions

oxygen isotope and palaeotemperature records from six greenland ice core stations camp century dye 3 grip gisp2 renland and northgrip oxygen isotope variations spanning the last glacial cycle and the holocene derived from ice core records for six sites in greenland camp century dye 3 grip gisp2 renland and northgrip show strong similarities this suggests that the dominant influence on oxygen isotope variations reflected in the ice sheet records was regional climatic change differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios palaeotemperature estimates have been obtained from the records using three approaches i inferences based on the measured relationship between mean annual 18o of snow and of mean annual surface temperature over greenland ii modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile or iii by using monte carlo simulation techniques the third of these approaches was adopted to reconstruct holocene temperature variations for the dye 3 and grip temperature profiles which yields remarkably compatible results a new record of holocene isotope variations obtained from the northgrip ice core matches the grip short term isotope record and also shows similar long term trends to the dye 3 and grip inverted temperature data the northgrip isotope record reflects i a generally stronger isotopic signal than is found in the grip record ii several short lived temperature fluctuations during the first 1500 yr of the holocene iii a marked cold event at ca 8 2 ka the 8 2 ka event iv optimum temperatures for the holocene between ca 8 6 and 4 3 ka a signal that is 0 6 stronger than for the grip profile v a clear signal for the little ice age and vi a clear signal of climate warming during the last century these data suggest that the northgrip stable isotope record responded in a sensitive manner to temperature fluctuations during the holocene copyright 2001 john wiley sons ltd

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

radwany formation a new formation name for the early middle eocene carbonate sediments of the offshore october oil field gulf of suez contribution to the eocene sediments in egypt abstract the eocene sediments plays critical role in the evolution and development of the petroleum system in the gulf of suez region where it is representing a self source rock or self reservoir or combination in some areas within the basin microfacies analysis and paleontological studies have not been conducted on these eocene sediments in the area of the october oil field which is mandatory for the formation characteristics assessment therefore sidewall core and ditch cuttings samples that was obtained from october eocene carbonate sediments so far ascribed to the thebes formation was studied in terms of sedimentology paleontology and depositional environment a total of 64 thin sections were analyzed petrographically and three microfacies types recognized both calcareous nanoplankton and foraminifers were examined the study of the eocene carbonate facies in the october field revealed that the succession is composed of pelagic foraminiferal limestone of varied color containing abundant planktonic foraminifers and minor traces of chert three microfacies are distinguished including wackestone of smaller planktonic foraminifera 50 wackestone packstone of planktonic foraminifera 40 and packstone of planktonic foraminifera 10 nannoplankton and foraminifers indicate that the studied succession is of early eocene to middle eocene age microfacies and fossil assemblage of the studied section indicate a pelagic environment and deposition in deep basin at water depths of a few hundred meters finally the current results were compared with data from previous publications on eocene sediments in the region it is revealed that the studied succession provides new data and contribution for the evolution of carbonate platform in the ypresian lutetian age and differs from the typical thebes formation and other eocene formations concerning facies lithology fossil content age and depositional environment therefore we suggest to abandon the term thebes formation for this eocene carbonate succession in the october field and a new lithostratigraphic unit named radwany formation is formally introduced

solar forcing of holocene climate new insights from a speleothem record southwestern united states holocene climate change has likely had a profound infl uence on ecosystems and culture a link between solar forcing and holocene climate such as the asian monsoon has been shown for some regions although no mechanism for this relationship has been suggested here we present the fi rst high resolution complete holocene climate record for the north american monsoon region of the southwestern united states southwest in order to address the nature and causes of holocene climate change we show that periods of increased solar radiation correlate with decreased rainfall the opposite to that observed in the asian monsoon and suggest that a solar link to holocene climate is through changes in the walker circulation and the pacifi c decadal oscillation and el nino southern oscillation systems of the tropical pacifi c ocean given the link between increased warming and aridity in the southwest additional warming due to greenhouse forcing could potentially lead to persistent hyperarid conditions similar to those seen in our record during periods of high solar activity

the magnitudes of millennial and orbital scale climatic change in eastern north america during the late quaternary abstract temporal differences among fossil pollen samples from eastern north america provide a measure of the amount of climatic change that occurred on a broad spatial scale since the last glacial maximum 21 000 cal yr bp square chord distances scds quantify the difference between pollen samples and thus represent the potential magnitude of climatic change underlying the pollen record the magnitude varied significantly among time scales with small changes common at centennial to millennial scales and large changes common at multi millennial i e orbital scales scds measured across 3000 yr intervals averaged 0 20 and often exceeded the maximum difference expected from samples collected within the same biome 0 15 scds across individual millennia were smaller and averaged 0 08 scds across the millennia at the beginning 13 000 12 000 cal yr bp and end 12 000 11 000 cal yr bp of the younger dryas chronozone 12 900 11 600 cal yr bp however averaged 0 20 and 0 18 respectively these rapid step changes large at sub millennial scales equal about 5 25 of the total glacial interglacial transition large magnitude progressive changes in insolation ice sheet extent and atmospheric composition parallel the dominant trends in the scd data which show that progressive change comprises the first order climatic pattern of the holocene rather than stable or oscillatory patterns

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

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

a 2000 year tree ring record of annual temperatures in the sierra nevada mountains tree ring data have been used to reconstruct the mean late season june through january temperature at a timberline site in the sierra nevada california for each of the past 2000 years long term trends in the temperature reconstruction are indicative of a 125 year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records the results indicate that both the warm intervals during the medieval warm epoch a d 800 to 1200 and the cold intervals during the little ice age a d 1200 to 1900 are closely associated with the 125 year period significant changes in the phase of the 125 year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior

high elevation paleoenvironmental change during mis 6 4 in the central rockies of colorado as determined from pollen analysis abstract paleoecological studies from rocky mountain usa high elevations encompassing the previous interglacial mis 5e are rare the 10 m composite profile from the ziegler reservoir fossil site 2705 m asl of central colorado allows us to determine paleoenvironments from marine oxygen isotope stages mis 6 4 using pollen zones that are approximately equivalent to marine oxygen isotope stages during pollen zone pz 6 time pollen assemblages dominated by artemisia sagebrush suggest that alpine tundra or steppe occurred nearby the transition to pz 5e was characterized by a rapid increase in tree pollen initially picea spruce and pinus pine but also quercus oak and pseudotsuga menziesii douglas fir non arboreal pollen nap types increased during pz 5d while abies fir and juniperus juniper increased during pz 5c pollen evidence suggests that temperatures during pz 5b were as cold as during pz 6 with the site again surrounded by alpine tundra picea dominated during pz 5a before the onset of cooler conditions during pz 4 the mis 6 mis 5e transition here was similar to the mis 2 mis 1 transition at other rocky mountain sites however the ziegler reservoir pollen record contains evidence suggesting unexpected climatic trends at this site including a warmer than expected mis 5d and cooler than expected mis 5b

cyclic variation and solar forcing of holocene climate in the alaskan subarctic high resolution analyses of lake sediment from southwestern alaska reveal cyclic variations in climate and ecosystems during the holocene these variations occurred with periodicities similar to those of solar activity and appear to be coherent with time series of the cosmogenic nuclides 14c and 10be as well as north atlantic drift ice our results imply that small variations in solar irradiance induced pronounced cyclic changes in northern high latitude environments they also provide evidence that centennial scale shifts in the holocene climate were similar between the subpolar regions of the north atlantic and north pacific possibly because of sun ocean climate linkages

environmental change during the penultimate glacial cycle a high resolution pollen record from odp site 1144 south china sea abstract in order to study environmental change within the penultimate glacial cycle mis 6 5 a total of 385 pollen samples with an average time resolution of 530 years were analyzed from odp site 1144 20 3 18 n 1170 25 14 e northeastern south china sea a characteristic feature of pollen diagram is the alternating peaks of pine and herbs generally corresponding to the glacial cycle pine dominates in the interglacial herb pollen dominates in the glacial a detailed comparison shows that the pollen assemblages changed earlier at the glacial interglacial transition between mis 6 and 5 termination ii than the ice volume indicated by the oxygen isotope record implying that mid low latitude climate warming preceded high latitude ice sheet retreat responses of pollen assemblages to orbital and suborbital cyclicities and to monsoon variations are also discussed

internal structure and deformation of an accommodation zone in the northern part of the suez rift abstract detailed structural study of the eastern onshore part of the gharandal accommodation zone that separates the northern sw dipping and central ne dipping half grabens of the suez rift helped decipher the internal structure and deformation of accommodation zones of continental rifts this 60 km wide zone is affected by pure normal faulting the ne dipping faults of the northern half graben extend southward into the accommodation zone where they interfinger with sw dipping faults extending from the central half graben these two sets of rift parallel faults form several horsts and grabens in the accommodation zone areas dipping parallel to the northern or southern half grabens form several intermixing dip domains in the accommodation zone smaller scale accommodation of dip between these dip domains proceeds by the development of rift parallel folds twist zones in contrast to the southern accommodation zone of the suez rift the internal structure of the gharandal accommodation zone is believed to be representative of accommodation zones in regions a unaffected by prerift structures lying at high angles to the rift and b experiencing relatively small extension accommodation zones in areas having pre rift structures lying at high angle to the rift have relatively narrow width and are characterized by transverse strike slip faults strike slip movement on these faults is related to the torsional strain resulting from the opposite tilt directions and transport of fault blocks of adjacent half grabens

a postglacial palaeoecological record from the san juan mountains of colorado usa fire climate and vegetation history continuous sediment charcoal and pollen records were developed from a 4 5 m sediment core from little molas lake lml 3370 m elevation san juan county co lml formed by 11 200 cal bp subsequent to glacial retreat turbated clay and gyttja was derived from in lake productivity and outwash sediments from the drainage basin from 1 1 200 cal bp until 10 200 cal bp cessation of glacial input and replacement of tundra with picea forest correlates with the termination of the younger dryas and indicates warming an increase in diploxylon pollen cf p ponderosa probably from lower elevations reflects the influence of the southwestern monsoon c 10 160 cal bp pollen ratios indicate that picea and other conifers persisted near the lake for the remainer of the holocene the driest holocene period occurs c 6200 to 5900 cal bp when lake levels were the lowest as indicated by all the proxy records wetter conditions during the last c 2600 cal bp favoured the expansion of p edulis and p ponderosa lat

vegetation fire climate and human disturbance history in the southwestern mediterranean area during the late holocene detailed pollen charcoal isotope and magnetic susceptibility data from an alpine lake sediment core from sierra nevada southern spain record changes in vegetation fire history and lake sedimentation since ca 4100 cal yr bp the proxies studied record an arid period from ca 3800 to 3100 cal yr bp characterized by more xerophytic vegetation and lower lake levels a humid period is recorded between ca 3100 and 1850 cal yr bp which occurred in two steps 1 an increase in evergreen quercus between 3100 and 2500 cal yr bp indicating milder conditions than previously and 2 an increase in deciduous quercus and higher lake levels between ca 2500 and 1850 cal yr bp indicating a further increase in humidity and reduction in seasonal contrast humid maxima occurred during the roman humid period previously identified in other studies in the mediterranean region intensified fire activity at this time could be related to an increase in fuel load and or in human disturbance an arid period subsequently occurred between 1850 and 650 cal yr bp though a decrease in quercus and an increase in xerophytes the alternation of persistent north atlantic oscillation modes probably played an important role in controlling these humid arid cycles

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

centennial scale vegetation and north atlantic oscillation changes during the late holocene in the southern iberia high reso ce to lution pollen analysis charcoal non pollen palynomorphs and magnetic susceptibility have been analyzed in the sediment record of a peat bog in sierra nevada in southern iberia the study of these proxies provided the reconstruction of vegetation climate fire and human activity of the last 4500 cal yr bp a progressive trend towards aridification during the late holocene is observed in this record this trend is interrupted by millennial and centennial scale variability of relatively more humid and arid periods arid conditions are recorded between 4000 and 3100 cal yr bp being characterized by a decline in arboreal pollen and with a spike in magnetic susceptibility this is followed by a relatively humid period from 3100 to 1600 cal yr bp coinciding partially with the iberian roman humid period and is indicated by the increase of pinus and the decrease in xerophytic taxa the last 1500 cal yr bp are characterized by several centennial scale climatic oscillations generally arid conditions from 450 to 1300 ce depicted by a decrease in pinus and an increase in artemisia comprise the dark ages and the medieval climate anomaly since 1300 to 1850 ce pronounced oscillations occur between relatively humid and arid conditions four periods depicted by relatively higher pinus coinciding with the beginning and end of the little ice age are interrupted by three arid events characterized by an increase in artemisia these alternating arid and humid shifts could be explained by centennial scale changes in the north atlantic oscillation and solar activity

deglaciation and postglacial timberline in the san juan mountains colorado abstract lake emma which no longer exists because of a mining accident was a tarn in a south facing cirque near the headwaters of the animas river in the san juan mountains of southwestern colorado during the pinedale glaciation this area was covered by a large transection glacier centered over the lake emma region three radiocarbon dates on basal organic sediment from lake emma indicate that by ca 15 000 yr b p this glacier one of the largest in the southern rocky mountains no longer existed twenty two radiocarbon dates on picea and abies krummholz fragments in the lake emma deposits indicate that from ca 9600 to 7800 yr b p from 6700 to 5600 yr b p and at 3100 yr b p the krummholz limit was at least 70 m higher than present these data in conjunction with picea pinus pollen ratios from both the lake emma site and the hurricane basin site of j t andrews p e carrara f b king and r struckenrath 1975 quaternary research 5 173 197 suggest than from ca 9600 to 3000 yr b p timberline in the san juan mountains was higher than present cooling apparently began ca 3000 yr b p as indicated by decreases in both the percentage of picea pollen and picea pinus pollen ratios at the hurricane basin site andrews et al 1975 cooling is also suggested by the lack of picea or abies fragments younger than 3000 yr b p at either the lake emma or the hurricane basin site

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

sea level changes during the last 41 000 years in the outer shelf of the southern tyrrhenian sea evidence from benthic foraminifera and seismostratigraphic analysis abstract an integrated high resolution study based both on a seismostratigraphic approach and on a sedimentary core vib 10 collected in the outer shelf 127 m depth from the southern tyrrhenian sea gulf of termini sicily provides new data about climatic eustatic and paleoenvironmental changes during the last 41 000 years the results based on the interpretation of a seismic profile on benthic foraminifera assemblages and on 18o records allowed recognition of two drastic sea level falls during the last glacial maximum lgm and the younger dryas yd the short deglacial event between lgm and yd known as bolling allerod played an important role in the sea level rise that produced changes in benthic foraminiferal assemblages favoring the proliferation of shallow water species of the inner shelf after the younger dryas warmer climatic conditions were rapidly established climatic optimum as indicated by the decrease of 18o values the rapid sea level rise due to the input of fresh water from ice caps melting following the increase of earth s mean temperature is also indicated by the aggradational geometries of sedimentary layers observed in the seismic profile and by the increase of benthic foraminiferal species typical of the outer shelf

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

enhancement of enso variability by a weakened atlantic thermohaline circulation in a coupled gcm abstract a coupled ocean atmosphere general circulation model is used to investigate the modulation of el nino southern oscillation enso variability due to a weakened atlantic thermohaline circulation thc the thc weakening is induced by freshwater perturbations in the north atlantic and leads to a well known sea surface temperature dipole and a southward shift of the intertropical convergence zone itcz in the tropical atlantic through atmospheric teleconnections and local coupled air sea feedbacks a meridionally asymmetric mean state change is generated in the eastern equatorial pacific corresponding to a weakened annual cycle and westerly anomalies develop over the central pacific the westerly anomalies are associated with anomalous warming of sst causing an eastward extension of the west pacific warm pool particularly in august february and enhanced precipitation these and other changes in the mean state lead in turn to an eastward shift of the zonal wind anomalies associated with el nin

large holocene lakes and climate change in the chihuahuan desert lake level variations preserved as beach ridges in the laguna el fresnal and laguna santa maria subbasins northern mexico record millennially spaced episodes of increased precipitation during the holocene epoch we find that the early middle and late holocene were punctuated by periods wet enough to establish large pluvial lakes in currently dry basins in the chihuahuan desert the largest dated pluvial lake covered 5650 km2 during the early holocene constructional beach ridges in these subbasins are 221 33 14c yr b p little ice age equivalent 3815 52 to 4251 59 14c yr b p early neoglacial 6110 80 to 6721 68 14c yr b p mid holocene and 8269 64 to 8456 97 14c yr b p early holocene dates that correlate with other millennially spaced wet or cold events in the northern hemisphere we attribute these wet episodes to increased precipitation cooler temperatures and reduced evaporation following southward shifts in winter storm tracks which are related to long term el nino southern oscillation variability during the holocene

rapid response of alpine timberline vegetation to the younger dryas climate oscillation in the colorado rocky mountains usa paleobotanical records from two high altitude 3 300 m sites in colorado show a clear and immediate response to the younger dryas climate oscillation the black mountain lake and sky pond records indicate that alpine timberline migrated upslope to near modern elevations during the late bolling allerod 13 6 12 9 ka subsequent declines in arboreal pollen percentages and accumulation rates during the younger dryas interval 12 9 11 7 ka reflect a downslope displacement of the alpine timberline ecotone of 60 120 m in elevation this change translates to a cooling of summer temperature by approximately 0 4 0 9 c and is consistent with proposed younger dryas advances of alpine glaciers in the rocky mountains to positions close to little ice age maxima alpine timberline readvanced upslope to elevations above both sites between 11 7 and 11 4 ka the concomitant response of temperature sensitive alpine timberline vegetation in colorado and late glacial changes in north atlantic thermohaline circulating implicates a rapid widespread atmospheric transmission of the younger dryas climate oscillation

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

a high resolution late quaternary upwelling record from the anoxic cariaco basin venezuela results are presented of a high resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the cariaco basin in the southern caribbean sea the cariaco basin is a small anoxic marine basin on the northern continental margin of venezuela in an area today characterized by both seasonal trade wind induced upwelling and pronounced dry and wet seasons our data indicate that large changes in the intensity of upwelling and hence trade wind strength occurred in this region during the last glacial interglacial transition and throughout the holocene during the last glacial lowstand of sea level the cariaco basin was effectively isolated from the open caribbean along its northern margin by the then largely emergent tortuga bank oxic conditions existed in the deep cariaco basin at this time and surface productivity was low about 12 600 years ago the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the laurentide ice sheet into the gulf of mexico strong upwelling between 12 600 and about 10 000 years ago may be related to intensified trade winds resulting in part from cooler sea surface temperatures in the caribbean and gulf of mexico after about 10 000 years ago upwelling intensity was reduced though highly variable a preliminary frequency domain analysis of the holocene portion of the cariaco basin time series suggests that solar forcing may explain a significant component of the century scale variability observed in the record of upwelling and trade wind strength

a 15 000 year record of vegetation and climate change from a treeline lake in the rocky mountains wyoming usa future climate projections predict warming at high elevations that will impact treeline species but complex topographic relief in mountains complicates ecologic response and we have a limited number of long term studies examining vegetation change related to climate in this study pollen and conifer stomata were analyzed from a 2 3 m sediment core extending to 15 330 cal yr bp recovered from a treeline lake in the rocky mountains of wyoming both pollen and stomata record a sequence of vegetation and climate change similar in most respects to other regional studies with sagebrush steppe and lowered treeline during the late pleistocene rapid upward movement of treeline beginning about 11 500 cal yr bp treeline above modern between 9000 and 6000 cal yr bp and then moving downslope 5000 cal yr bp reaching modern limits by 3000 cal yr bp between 6000 and 5000 cal yr bp sediments become increasingly organic and sedimentation rates increase we interpret this as evidence for lower lake levels

millennial and centennial scale vegetation and climate changes during the late pleistocene and holocene from northern new mexico usa abstract high resolution pollen and magnetic susceptibility ms data from a sediment core from an alpine bog 3100 m in the sangre de cristo mountains new mexico record variations in treeline elevation and in sedimentation for the last 14 ka cal yr bp strong correspondence between the paleovegetation and the ms profile suggests that both records can be used to reconstruct past climatic conditions the coldest conditions in this area occurred at the end of the late pleistocene during the pinedale glaciation and the younger dryas chron a general warming trend took place during the early holocene lasting until 5 6 ka when the warmest conditions occurred a progressive climate cooling is then observed until today millennial and centennial scale changes are also observed throughout the vegetation and ms records the higher amplitude millennial scale cold events appear to correlate with the timing and duration of episodes of enhanced sea ice drift in the north atlantic and the lower amplitude centennial scale cold events may correlate with periods of lower solar activity a solar climate connection is suggested from these records by a prominent ca 200 yr cycle in tree pollen abundance which may correlate with the 208 yr suess solar cycle this study shows an immediate response of the vegetation treeline to climate change at millennial and centennial scales probably related to variations in summer insolation and solar activity during the late pleistocene and holocene such high resolution studies are very important in order to predict future climate change and particularly in very arid areas where human activity and economies are strongly influenced by climate