rainfall response to orbital and millennial forcing in northern peru over the last 18 ka we present a high resolution marine record of sediment input from the guayas river ecuador that reflects changes in precipitation along western equatorial south america during the last 18ka we use log ti ca derived from x ray fluorescence xrf to document terrigenous input from riverine runoff that integrates rainfall from the guayas river catchment we find that rainfall induced riverine runoff has increased during the holocene and decreased during the last deglaciation superimposed on those long term trends we find that rainfall was probably slightly increased during the younger dryas while the heinrich event 1 was marked by an extreme load of terrigenous input probably reflecting one of the wettest period over the time interval studied when we compare our results to other deglacial to holocene rainfall records located across the tropical south american continent different modes of variability become apparent the records of rainfall variability imply that changes in the hydrological cycle at orbital and sub orbital timescales were different from western to eastern south america orbital forcing caused an antiphase behavior in rainfall trends between eastern and western equatorial south america in contrast millennial scale rainfall changes remotely connected to the north atlantic climate variability led to homogenously wetter conditions over eastern and western equatorial south america during north atlantic cold spells these results may provide helpful diagnostics for testing the regional rainfall sensitivity in climate models and help to refine rainfall projections in south america for the next century

seasonal variation in the flux of planktonic foraminifera time series sediment trap results from the panama basin abstract a mooring array with three automated sediment traps capable of collecting time series samples was deployed in the panama basin for one year beginning in december 1979 a series of six consecutive two month long samples was collected at each of three depths 890 2590 and 3560 m in order to examine seasonal variation in the flux of planktonic foraminifera and evaluate the contribution of foraminifera to the total carbonate flux the flux of the larger planktonic foraminifera 250 500 m and 500 1000 m is greatest during february march when upwelling is most intense in the panama basin in contrast the maximum flux of the smaller foraminifera 125 250 m is associated with a phytoplankton bloom during the summer months june through september this size dependent flux pattern appears to be a species specific effect the flux of the larger foraminifera is dominated by non spinose forms i e neogloboquadrina dutertrei and globorotalia theyeri while the flux of the smaller foraminifera consists predominantly of spinose species i e globigerinoides ruber g sacculifer and g conglobatus although the magnitude of the flux varied throughout the year the average weight of individual foraminiferal tests in different size fractions showed no seasonal variability with the exception of the june july period when there was a major coccolith bloom planktonic foraminifera greater than 125 m account for between 28 and 34 of the total carbonate flux at this location during the coccolith bloom planktonic foraminifera accounted for less than 2 of the total carbonate flux planktonic foraminifera in the 250 500 m size range are the most significant contributors to the overall particulate flux accounting for roughly 70 80 of the total foraminiferal fluxes measured at the three trap depths

proxy dependence of the temporal pattern of deglacial warming in the tropical south china sea toward resolving seasonality abstract sea surface temperatures ssts reconstructed from two globigerinoides ruber white morphotypes g ruber sensu stricto s s g ruber sensu lato s l mg ca and alkenones uk 37 from core md01 2390 from the tropical south china sea scs during the last deglaciation reveal a proxy dependent discrepancy in the temporal pattern of the deglacial warming alkenone data suggest that the deglacial warming is punctuated by a decrease in temperature between 17 and 15 ka bp corroborating previously published alkenone uk 37 sst records from the southern scs within dating uncertainties this cooling is coeval with the heinrich event 1 h1 time interval in the north atlantic region underscoring the imprints of northern hemisphere forcing on tropical scs ocean temperatures the deglacial uk 37 sst minimum is also paralleled by a maximum in g ruber morphotype specific 18o g ruber mg ca sst estimates suggest a morphotype specific record of ssts during the time interval of h1 whereas g ruber s s imply a continuous warming starting around 18 ka bp without any marked response to h1 g ruber s l based mg ca sst estimates reveal a cooling around 17 15 ka bp similar to the h1 interval cooling seen in the alkenone sst record similar proxy dependent differences in deglacial surface water warming have been recorded in the eastern equatorial pacific implying a common pattern on both sides of the tropical pacific ocean we submit that this discrepancy could be due to differences in seasonality of planktonic foraminifera g ruber morphotypes and alkenone producing algae

el nino evolution during the holocene revealed by a biomarker rain gauge in the galapagos islands abstract the el nino southern oscillation enso represents the largest perturbation to the climate system on an inter annual time scale but its evolution since the end of the last ice age remains debated due to the lack of unambiguous enso records lasting longer than a few centuries changes in the concentration and hydrogen isotope ratio of lipids produced by the green alga botryococcus braunii which blooms during el nino rains in the galapagos islands indicate that the early holocene 9200 5600 yr bp was characterized by alternating extremes in the intensity and or frequency of el nino events that lasted a century or more our data from the core of the enso region thus calls into question earlier studies that reported a lack of el nino activity in the early holocene in agreement with other proxy evidence from the tropical pacific the mid holocene 5600 3500 yr bp was a time of consistently weak el nino activity as were the early middle ages 1000 1500 yr bp el nino activity was moderate to high during the remainder of the last 3500 years periods of strong or frequent el nino tended to occur during peaks in solar activity and during extended droughts in the united states great plains linked to la nina these changing modes of enso activity at millennial and multi centennial timescales may have been caused by variations in the seasonal receipts of solar radiation associated with the precession of the equinoxes and or changes in solar activity respectively

a 130 ka reconstruction of rainfall on the bolivian altiplano new efforts to link climate reconstructions from shoreline deposits and sediment cores yield an improved and more detailed lake history from the bolivian altiplano on the southern altiplano 10 lake oscillations have been identified from this new unified chronology each coincident with north atlantic cold events such as heinrich events h5 h2 h1 and the younger dryas by coupling this new lake history to a hydrologic budget model we are able to evaluate precipitation variability on the southern bolivian altiplano over the last 130 ka these modeling efforts underscore the relative aridity of the altiplano during the rare and small lake cycles occurring between 80 and 20 ka when colder temperatures combined with little or no change in rainfall produced smaller paleolakes relative aridity between 80 and 20 ka contrasts with the immense tauca lake cycle 18 1 14 1 ka which was six times larger than modern lake titicaca and coincided with heinrich event 1 this improved paleolake record from the southern altiplano reveals a strong link between central andean climate and atlantic sea surface temperature gradients during the late pleistocene even though today rainfall variability is driven mostly by pacific sea surface temperature anomalies associated with el nino southern oscillation however not all heinrich events appear to result in lake expansions most conspicuously during the global cold interval between 80 and 20 ka when the altiplano and amazon basin were relatively arid

meridional reorganizations of marine and terrestrial productivity during heinrich events 1 to study the response of the global carbon cycle to a weakening of the atlantic meridional overturning circulation amoc a series of freshwater perturbation experiments is conducted both under preindustrial and glacial conditions using the earth system model of intermediate complexity loveclim a shutdown of the amoc leads to substantial cooling of the north atlantic a weak warming of the southern hemisphere intensification of the northeasterly trade winds and a southward shift of the intertropical convergence zone itcz trade wind anomalies change upwelling in the tropical oceans and hence marine productivity furthermore hydrological changes associated with a southward displacement of the itcz lead to a reduction of terrestrial carbon stocks mainly in northern africa and northern south america in agreement with paleoproxy data in the freshwater perturbation experiments the ocean acts as a sink of co2 primarily through increased solubility the net atmospheric co2 anomaly induced by a shutdown of the amoc amounts to about 15 ppmv and 10 ppmv for preindustrial and glacial conditions respectively this background state dependence can be explained by the fact that the glacial climate is drier and the terrestrial vegetation therefore releases a smaller amount of carbon to the atmosphere this study demonstrates that the net co2 response to large scale ocean circulation changes has significant contributions both from the terrestrial and marine carbon cycle

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

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

inferring moisture transport across central america can modern analogs of climate variability help reconcile paleosalinity records abstract the interpretation of sea surface paleosalinity reconstructions from the eastern tropical pacific in terms of atlantic to pacific moisture transport is revisited it is argued that the use of modern analogs of interannual climate variability may help to reconcile seemingly contradictory results from paleosalinity reconstructions at different locations in the east pacific for the last glacial maximum the pattern of tropical east pacific paleosalinity suggests that the atlantic to pacific moisture export was similar to today s while the wind field was probably biased towards el nino like conditions in that region a la nina analog for heinrich stadial 1 leads to the conclusion that the atlantic to pacific vapor transport was reduced during times of thermohaline circulation slowdown it is further argued that the modern seasonal cycle is not a useful analog for longer term hydroclimatic variability in the tropical pacific atlantic region

diagenesis provenance and reservoir quality of triassic tagi sandstones from ourhoud field berkine ghadames basin algeria the triassic tagi trias argilo greseux inferieur fluvial sandstones are the main oil reservoirs in the berkine basin algeria nonetheless their provenance and diagenesis and their impact on reservoir quality are virtually unknown samples from the ourhoud field representing the lower middle and upper tagi subunits were studied using a combination of petrographic mineralogical and geochemical techniques the lower tagi sandstones have an average framework composition of q98 3f0 6r1 1 and 95 of the quartz grains are monocrystalline by contrast the middle upper tagi sandstones have an average framework composition of q88 3f9 8r1 9 and 79 7 of the quartz grains are monocrystalline the lower tagi quartz arenites derived from paleozoic siliciclastic rocks whereas the middle upper tagi subarkoses originated mainly from metamorphic terrains this change in provenance is a potential criterion for correlation within the tagi also this change has contributed to the significantly different diagenetic paths followed by the lower tagi quartz arenites and the middle upper tagi subarkoses grain coating illitic clays are abundant in the lower tagi where they exert a critical control on reservoir quality these clays are interpreted as pedogenic and or infiltrated in origin and to have had in part smectitic precursors shallow burial fe dolomite cementation was favored in the downthrown block of the field bounding fault where it contributed to the poor reservoir quality magnesite siderite cements are multiphase the earliest generation is composed of fe rich magnesite that precipitated during shallow burial from hypersaline fluids with high mg ca ratios probably refluxed residual brines associated with the liassic evaporites later magnesite siderite generations precipitated during deeper burial from waters with progressively higher fe mg ratios authigenic vermicular kaolin largely consists of dickite that replaced previously formed kaolinite dickitization was followed by late stage illitization related to the dissolution of detrital and authigenic k feldspar quartz the most abundant cement was mainly sourced by the pressure or clay induced dissolution of detrital quartz and is a critical factor controlling the reservoir quality overall quartz cement is more abundant in the lower tagi than in the middle upper tagi and this increase correlates with a decrease in average porosity within the lower tagi quartz cement abundance is stratigraphically very variable which is in part related to facies controlled variations in grain coating clay resulting in major vertical variations in reservoir quality anhydrite and barite cements postdate quartz overgrowth the sulfate necessary for their formation was likely sourced by deep subsurface dissolution of late triassic liassic evaporites

constraining past seawater δ18o and temperature records developed from foraminiferal geochemistry paired measurements of magnesium to calcium ratios mg ca and the stable oxygen isotopic composition 18o in foraminifera have significantly advanced our knowledge of the climate system by providing information on past temperature and seawater 18o 18osw a proxy for salinity and ice volume however multiple sources of uncertainty exist in transferring these downcore geochemical data into quantitative paleoclimate reconstructions here we develop a computational toolkit entitled paleo seawater uncertainty solver psu solver that performs bootstrap monte carlo simulations to constrain these various sources of uncertainty psu solver calculates temperature and 18osw and their respective confidence intervals using an iterative approach with user defined errors calibrations and sea level curves our probabilistic approach yields reduced uncertainty constraints compared to theoretical considerations and commonly used propagation exercises we demonstrate the applicability of psu solver for published records covering three timescales the late holocene the last deglaciation and the last glacial period we show that the influence of salinity on mg ca can considerably alter the structure and amplitude of change in the resulting reconstruction and can impact the interpretation of paleoceanographic time series we also highlight the sensitivity of the records to various inputs of sea level curves transfer functions and uncertainty constraints psu solver offers an expeditious yet rigorous approach to test the robustness of past climate variability inferred from paired mg ca 18o measurements

climatic evolution of the central equatorial pacific since the last glacial maximum this paper investigates paleoceanographic changes at a central equatorial pacific site 6 40 n 177 28 w since the last glacial maximum using planktic foraminifera assemblages together with the oxygen isotope 18o and mg ca compositions of three species globigerinoides sacculifer pulleniatina obliquiloculata and globorotalia tumida that dwell in the mixed layer upper thermocline and lower thermocline respectively while the mg ca derived temperatures of the mixed layer and lower thermocline varied within a narrow range from 18 ka onward the upper thermocline temperature increased by as much as 3 c during the last deglaciation 18 12 ka with a simultaneous decrease of 18o these changes are best explained by an enhanced mixing of the upper ocean and a reduced habitat depth separation between p obliquiloculata and g sacculifer during the 18 12 ka interval the planktic foraminifera assemblage during the same period resembles modern composition at subtropical central pacific sites that are strongly influenced by the northeasterly trades and north equatorial current nec we suggest that the study site presently under the control of the intertropical convergence zone itcz north equatorial countercurrent had been influenced by the northeasterly trades and nec during the 18 12 ka interval this interpretation is consistent with previous documentation of a more southerly location of the itcz during two northern hemisphere cooling events the heinrich stadial 1 and the younger dryas and implies that the mean annual position of the itcz was located south of the study site by at least 2 of latitude

paleoceanographic implications of the difference in deep sea sediment mixing between large and fine particles more and more paleoceanographic studies are performed on different size fractions of deep sea sediments although it has been a controversial issue for some time the bioturbation process depends on the particle size and can in principle decouple paleoceanographic records obtained in the same core this problem is studied by using a simple mixing model which allows the derivation of analytical equations for both the expected phase shift and relative attenuation of signals carried by different size fractions depending on several parameters the time shift and relative attenuation can be on the order of a few millenia and 50 respectively however high sedimentation rates 10 20 cm kyr minimize these potential complications allowing us to study millenium scale events in well chosen sedimentary environments

rapid precipitation changes in the tropical west pacific linked to north atlantic climate forcing during the last deglaciation abstract the cause of rapid hydrological changes in the tropical west pacific during the last deglaciation remains controversial in order to test whether these changes were triggered by abrupt climate change events in the north atlantic ocean variations in precipitation during the last deglaciation 18 10 ka were extracted from proxy records of chemical weathering and terrigenous input in the western philippine sea wps the evolution of chemical weathering and terrigenous input since 27 ka was reconstructed using the chemical index of alteration cia elemental ratios k al toc tn and ti ca 13corg terrigenous fraction abundance and flux data from international marine global change study program images core md06 3054 collected on the upper continental slope of eastern luzon northern philippines sediment deposited during the last glacial maximum lgm shows weathering equal to or slightly greater than holocene sediment in the wps this unusual state of chemical weathering which is inconsistent with lower air temperatures and decreased precipitation in luzon during the lgm may be due to reworking of poorly consolidated sediments on the eastern luzon continental shelf during the lgm sea level lowstand rapid changes in chemical weathering characterized by higher intensity during the heinrich event 1 h1 and younger dryas yd and lower intensity during the bolling allerod b a were linked to rapid variations in precipitation in the wps during the last deglaciation the higher terrigenous inputs during the lgm relative to those of the holocene were controlled by sea level changes rather than precipitation the terrigenous inputs show a long term decline during the last deglaciation punctuated by brief spikes during the h1 and yd related to sea level rises and rapid precipitation changes in the wps respectively the proxy records of chemical weathering and terrigenous input from eastern luzon suggest high rainfall during the h1 and yd events consistent with inferred rainfall patterns based on fe ca records from offshore mindanao rapid precipitation changes in the wps did not coincide with migrations of the intertropical convergence zone itcz but rather were related to state shifts of the el nino southern oscillation enso during the last deglaciation based on proxy records and modeling results we argue that the atlantic meridional overturning circulation amoc controlled rapid precipitation changes in the tropical west pacific through zonal shifts of enso or meridional migration of the itcz during the last deglaciation our findings highlight the dominant role of the north atlantic ocean in the tropical hydrologic cycle during the last deglaciation

four thousand years of environmental change and human activity in the cochabamba basin bolivia the cochabamba basin bolivia is on the ancient road network connecting andean and lowland areas little is known about the longevity of this trade route or how people responded to past environmental changes the eastern end of the cochabamba valley system constricts at the vacas lake district constraining the road network and providing an ideal location in which to examine past human environmental interactions multi proxy analysis of sediment from lake challacaba has allowed a c 4000 year environmental history to be reconstructed fluctuations in drought tolerant pollen taxa and calcium carbonate indicate two periods of reduced moisture availability c 4000 3370 and c 2190 1020 cal yr bp compared to adjacent wetter episodes c 3370 2190 and c 1020 cal yr bp present the moisture fluctuations broadly correlate to el nino southern oscillation variations reported elsewhere high charcoal abundance from c 4000 to 2000 yr ago indicates continuous use of the ancient road network a decline in charcoal and an increase in dung fungus sporormiella c 1340 1210 cal yr bp suggests that cultural changes were a major factor in shaping the modern landscape despite undisputable impacts of human populations on the polylepis woodlands today we see no evidence of woodland clearance in the challacaba record

sea surface temperature records of termination 1 in the gulf of california challenges for seasonal and interannual analogues of tropical pacific climate change 1 centennial scale records of sea surface temperature and opal composition spanning the last glacial maximum and termination 1 circa 25 6 ka are presented here from guaymas basin in the gulf of california through the application of two organic geochemistry proxies the u37k index and the tex86h index we present evidence for rapid stepped changes in temperatures during deglaciation these occur in both temperature proxies at 13 ka 3 c increase in 270 years 10 0 ka 2 c decrease over 250 years and at 8 2 ka 3 c increase in 200 years an additional rapid warming step is also observed in tex86h at 11 5 ka in comparing the two temperature proxies and opal content we consider the potential for upwelling intensity to be recorded and link this millennial scale variability to shifting intertropical convergence zone position and variations in the strength of the subtropical high the onset of the deglacial warming from 17 to 18 ka is comparable to a southern hemisphere signal although the opal record mimics the ice rafting events of the north atlantic heinrich events neither the modern seasonal cycle nor el nino southern oscillation patterns provide valid analogues for the trends we observe in comparison with other regional records fully coupled climate model simulations confirm this result and in combination we question whether the seasonal or interannual climate variations of the modern climate are valid analogues for the glacial and deglacial tropical pacific

deglacial δ18o and hydrologic variability in the tropical pacific and indian oceans abstract evidence from geologic archives suggests that there were large changes in the tropical hydrologic cycle associated with the two prominent northern hemisphere deglacial cooling events heinrich stadial 1 hs1 19 to 15 kyr bp kyr bp 1000 yr before present and the younger dryas 12 9 to 11 7 kyr bp these hydrologic shifts have been alternatively attributed to high and low latitude origin here we present a new record of hydrologic variability based on planktic foraminifera derived 18o of seawater 18osw estimates from a sediment core from the tropical eastern indian ocean and using 12 additional 18osw records construct a single record of the dominant mode of tropical eastern equatorial pacific and indo pacific warm pool ipwp hydrologic variability we show that deglacial hydrologic shifts parallel variations in the reconstructed interhemispheric temperature gradient suggesting a strong response to variations in the atlantic meridional overturning circulation and the attendant heat redistribution a transient model simulation of the last deglaciation suggests that hydrologic changes including a southward shift in the intertropical convergence zone itcz which likely occurred during these northern hemisphere cold events coupled with oceanic advection and mixing resulted in increased salinity in the indonesian region of the ipwp and the eastern tropical pacific which is recorded by the 18osw proxy based on our observations and modeling results we suggest the interhemispheric temperature gradient directly controls the tropical hydrologic cycle on these time scales which in turn mediates poleward atmospheric heat transport

eastern tropical pacific hydrologic changes during the past 27 000 years from d h ratios in alkenones 1 the tropical pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation quantifying the role of the tropics in late pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period here we present records of hydrogen isotope ratios dd of alkenones from the panama basin off the colombian coast that document hydrologic changes in equatorial south america and the eastern tropical pacific over the past 27 000 years a and the past 3 centuries in detail comparison of alkenone dd values with instrumental records of precipitation over the past 100 a suggests that dd can be used as a hydrologic proxy on long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the intertropical convergence zone and an associated reduction of pacific moisture transport into colombia precipitation increases at 17 ka in concert with sea surface temperature sst cooling in the north atlantic and the eastern tropical pacific a regional coupled model forced by negative sst anomalies in the caribbean simulates an intensification of northeasterly trade winds across central america increased evaporative cooling and a band of increased rainfall in the northeastern tropical pacific these results are consistent with the alkenone sst and dd reconstructions that suggest increasing precipitation and sst cooling at the time of heinrich event 1

strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation the climate of the last glacial period was extremely variable characterized by abrupt warming events in the northern hemisphere accompanied by slower temperature changes in antarctica and variations of global sea level it is generally accepted that this millennial scale climate variability was caused by abrupt changes in the ocean thermohaline circulation here we use a coupled ocean atmosphere sea ice model to show that freshwater discharge into the north atlantic ocean in addition to a reduction of the thermohaline circulation has a direct effect on southern ocean temperature the related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical north atlantic caused by a fast wave adjustment process we present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of greenland and antarctic temperature changes the slow changes in antarctic temperature and its similarity to sea level as well as a possible time lag of sea level with respect to antarctic temperature during marine isotope stage 3

grip deuterium excess reveals rapid and orbital scale changes in greenland moisture origin the northern hemisphere hydrological cycle is a key factor coupling ice sheets ocean circulation and polar amplification of climate change here we present a northern hemisphere deuterium excess profile covering one climatic cycle constructed with the use of 18 o and d greenland ice core project grip records past changes in greenland source and site temperatures are quantified with precipitation seasonality taken into account the imprint of obliquity is evidenced in the site to source temperature gradient at orbital scale at the millennial time scale grip source temperature changes reflect southward shifts of the geographical locations of moisture sources during cold events and these rapid shifts are associated with large scale changes in atmospheric circulation

seasonal changes in the isotopic composition of planktonic foraminifera collected in panama basin sediment traps abstract isotopic analyses have been made on five species of planktonic foraminifera collected in two deployments of parflux mark ii time series sediment traps in the panama basin the automated sampling system on the traps provided 4 one month samples from 29 july to 16 november 1979 and 6 two month samples from december 1979 to november 1980 the 18o values of globigerinoides ruber and globigerinoides sacculifer in this region are primarily affected by a low salinity surface layer that forms during the early winter these species each show a 1 total range in 18o the 18o values of the colder water species globorotalia menardii neogloboquadrina dutertrei and globorotalia theyeri show smaller seasonal changes in 18o the 13c values of g ruber and g sacculifer exhibit small seasonal changes 0 35 and 0 4 respectively despite large seasonal changes in surface water productivity the colder water species exhibit only slightly larger changes in 13c up to 0 55 throughout the year all colder water species exhibit minimum or near minimum 13c values during february and march which is the period of maximum upwelling and primary productivity seasonal variations in the flux of foraminifera in the water column at this location will have only a small effect on the isotopic composition of the sediment assemblage extreme values of 18o and 13c do not occur during the periods which are associated with the high flux of foraminiferal tests

vegetation climate and fire in the eastern andes bolivia during the last 18 000years a c 18 ka cal bp long sediment record from laguna khomer kocha upper 4153 m asl bolivia shows that fire regime governed by climatic variation has long been a transformative agent in the eastern andes before c 14 5 ka cal bp warming and relatively moist conditions free from fire facilitated the expansion of high andean polylepis woodland fire onset at c 14 5 ka cal bp quickly transformed the local vegetation and the woodlands became restricted to areas protected from fire a major increase in burning c 10 1 6 4 ka cal bp removed polylepis woodland locally and this coincided with a region wide holocene dry event hde which caused falling lake levels and allowed fire intensification a decline in burning at c 6 4 ka cal bp and an increase in marsh woodland alnus marked the termination of the hde and a return to wetter conditions as well as recording the environmental history of local vegetation dynamics long distance pollen transport provides evidence of changes in the yungas montane forests highlighting their sensitivity to climate and burning regimes simultaneous adjustments in both andean and yungas montane taxa suggest that vegetation dynamics in the two environments are linked to a common climatic driver there is no evidence to indicate that human activity had any impact on the local landscape

holocene variability in the intensity of wind gap upwelling in the tropical eastern pacific wind driven upwelling in pacific panama is a significant source of oceanographic variability in the tropical eastern pacific this upwelling system provides a critical teleconnection between the atlantic and tropical pacific that may impact climate variability on a global scale despite its importance to oceanographic circulation ecology and climate little is known about the long term stability of the panamanian upwelling system or its interaction with climatic forcing on millennial time scales using a combination of radiocarbon and u series dating of fossil corals collected in cores from five sites across pacific panama we reconstructed the local radiocarbon reservoir correction r from 6750 cal b p to present because the r of shallow water environments is elevated by upwelling our data set represents a millennial scale record of spatial and temporal variability of the panamanian upwelling system the general oceanographic gradient from relatively strong upwelling in the gulf of panama to weak to absent upwelling in the gulf of chiriqui was present throughout our record however the intensity of upwelling in the gulf of panama varied significantly through time our reconstructions suggest that upwelling in the gulf of panama is weak at present however the middle holocene was characterized by periods of enhanced upwelling with the most intense upwelling occurring just after of a regional shutdown in the development of reefs at 4100 cal b p comparisons with regional climate proxies suggest that whereas the intertropical convergence zone is the primary control on modern upwelling in pacific panama the el nino southern oscillation drove the millennial scale variability of upwelling during the holocene

wet phases in tropical southern africa during the last glacial period 1 a 45 000 year high resolution sedimentary record from lake masoko in tanzania shows the climate in this part of east africa to have been characterized by a short and less severe dry season during the last glacial maximum moisture and lake level proxies pollen assemblages and magnetic susceptibility indicate that rainfall in the masoko area was strongly controlled by low latitude insolation i e precessional forcing such observations contrast with the climatic patterns previously reconstructed in east africa for the last glacial indeed widespread dry conditions are generally observed and are attributed to the predominant control of high latitude glacial forcing over insolation forcing on the tropical hydrology however during the younger dryas cold event out of phase with regional insolation behaviour wetter conditions prevailed in this area suggesting that the rainfall belt over africa was probably shifted to the south bringing moisture to the southernmost tropics

millennial scale precipitation changes in southern brazil over the past 90 000 years 1 a u th dated 90 000 year long speleothem oxygen isotope record from southern brazil anti correlates remarkably with the cave calcite records from eastern china but positively correlates with the speleothem record from northeastern brazil suggesting an interhemispheric anti phasing of rainfall on both millennial and orbital timescales likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in hadley circulation the phase relationships among these records are consistent with the hypothesis that abrupt climate events during the last glacial period are triggered by oceanic circulation changes in the high latitudes and enhanced by tropical feedbacks

earthquakes casting stress shadows earthquakes may trigger or retard quakes on nearby faults but such relationships are difficult to verify observations showing that the landers earthquake in california shut down aftershocks from a preceding event validate such relationships

a bi polar signal recorded in the western tropical pacific northern and southern hemisphere climate records from the pacific warm pool during the last ice age abstract western tropical pacific sea surface temperatures and pacific deep water temperatures during marine isotope stage 3 have been reconstructed from the 18o and mg ca of planktonic and benthic foraminifera from marion dufresne core md98 2181 this 36 m marine core was collected at 6 3 n from a water depth of 2114 m with sediment accumulation rates of up to 80 cm ky it provides a decadally resolved history of ocean variability during the last glacial period surface temperatures and salinities at this site varied in close association with millennial scale atmospheric temperature swings at high northern latitudes as reflected in the gisp2 ice core at times of colder atmospheric temperatures over greenland the western pacific was more saline and summer season ssts were 2 c colder these millennial scale changes within the tropics are attributed to a southward displacement of the summer season itcz in response to steeper meridional temperature gradients within the pacific the benthic 18o record from md98 2181 documents upper pacific deep water temperature and salinity variability benthic 18o variations of 0 3 0 5 during mis 3 indicate deep waters within the pacific were varying by 1 1 5 c with the possibility that some of the variability was due to changing salinity and minor glacial eustatic changes the observed deep water variability correlates to changes in antarctic surface temperatures and thus reflects changes in southern ocean temperatures at the site of pacific deep water formation the combined planktonic and benthic records from md98 2181 thus provide a northern and southern hemispheric climate record of anti phased variability during mis 3 as has been inferred previously from ice core records furthermore the deep sea temperature excursions appear to have led millennial variations in atmospheric co2 as recorded in the edml ice core by 1 kyr

erratum millennial scale trends in west pacific warm pool hydrology since the last glacial maximum nature 2007 449 452 455

progress in paleosalinity overview and presentation of a new approach this paper concerns the use of stable oxygen isotope ratios 18o and stable hydrogen isotope ratios 2h or d to derive paleosalinity first i evaluate the potential and limitations of existing methods based on 18o and d separately next i propose a new theoretical framework for the combined use of 18o and d to constrain the impact of the hydrological cycle on the surface waters and to thus characterize changes in surface water salinity this new method is accompanied by an error propagation exercise to demonstrate its limitations and areas of potential improvement a feasible strategy is outlined for achieving reconstructions of paleosalinity change with an uncertainty of 1 practical salinity unit or less with the newly proposed method especially in regions with high deuterium excess values

simulation of glacial interglacial cycles by simple relaxation models consistency with observational results the model of paillard and parrenin earth planet sci lett 227 263 271 2004 was modified to obtain a closer fit to 18o and co2 time series for the last 800 kyr the model performance can be improved if its co2 sensitivity to i65 insolation is eliminated and if different response times are assumed for ablation accumulation of ice correlations between simulated and experimental time series for co2 and ice volume v increase from 0 59 and 0 63 to 0 79 and 0 88 respectively according to these models terminations are produced by i65 amplification through co2 t and t co2 feedbacks in synergy with an extra co2 contribution from the deep ocean this contribution is strongly dependent on ice sheet extent and ice volume or alternatively co2 concentration which is a good proxy of antarctic temperature but is insensitive to southern ocean so insolation on 21 february i60 change of deep so state may be the order parameter for nonlinear deglacial changes according to these models 100 kyr periodicity of glacial cycles arises from the characteristic time of antarctic ice sheet advance to the continental slope

contribution of organic matter molecular proxies to interpretation of the last 55ka of the lynch s crater record ne australia the lynch s crater ne australia deposit is a key information source on late quaternary palaeoenvironmental change including human induced deforestation since the arrival of aboriginals megaherbivore extinction and southern hemisphere tropical climate dynamics this study adds to the important dataset available for the site by assessing the molecular composition of organic matter in the record using pyrolysis gc ms to elucidate ecological and hydrological conditions since 55 ka bp pyrolysates were dominated by methylene chain compounds mccs and lignin products methoxyphenols concomitant increases in mccs and aquatic source indicators biogenic opaline silica si al ratio sem visible debris of sponges and diatoms and aquatic pollen taxa which roughly coincide with abrupt climate events in gisp2 18o heinrich event h3 h1 8 2ka and oscillations at 33 36ka bp reflect transitions from peat dominated by lignin from terrestrial plants to lacustrine mccs from aquatic plants conditions the evidence points towards wet conditions causing the accumulation of layers rich in inorganic sediment during h events favouring the hypothesis of a southward itcz shift rather than an enso induced northward shift as the underlying mechanism this contradicts previous studies using the degree of peat humification index dph we measured dph and the extracts and residues by py gc ms to better understand the validity of this surface moisture proxy paradoxically high dph corresponds to the relatively young 15ka ombrotrophic peat environment as dph relies on the proportion of extractable carbohydrates concentrated in this part of the core while deeper and unarguably more evolved layers are comprised of alkali inextricable lignin and mccs therefore dph does not accurately reflect humidity controlled degradation preservation dynamics and its use for studying climate change in complex records such as lynch s crater is cautioned finally the decoupling of humidity conditions from changes in regional arboreal vegetation supports the hypothesis of an anthropogenic rather than climate driven shift towards sclerophyllous vegetation since 45ka but the hydroseral complexity of the system demands caution on this matter

new views of tropical paleoclimates from corals abstract corals offer a rich archive of past climate variability in tropical ocean regions where instrumental data are limited and where our knowledge of multi decadal climate sensitivity is incomplete in the eastern equatorial pacific coral isotopic records track variations in enso related changes in sea surface temperature further west corals record variability in sea surface temperature and rainfall that accompanies zonal displacement of the indonesian low during enso events these multi century records reveal previously unrecognised enso variability on time scales of decades to centuries outside the enso sensitive equatorial pacific long term trends towards recent warmer wetter conditions suggest the tropics respond to global forcings new coral paleothermometers indicate that surface ocean temperatures in the tropical southwestern pacific were depressed by 4 6 c during the younger dryas climatic event and rose episodically during the next 4000 yr high temporal resolution measurements of sr ca and 18 o in corals provide information about the surface ocean hydrologic balance and can resolve the seasonal balance between precipitation and evaporation radiocarbon measurements in corals coupled with ocean circulation models may be used to reconstruct near surface ocean circulation past mixing rates and the distribution of fossil fuel co2 in the upper ocean most recently seasonal to interannual variations in the radiocarbon of corals from the equatorial pacific have been linked to the redistribution of surface waters associated with the enso

holocene laminated sediments from the southern gulf of california geochemical mineral magnetic and microfossil study geochemical magnetic mineral analyses and microfossils radiolarians are used to characterise a holocene laminated sequence from the alfonso basin northern bay of la paz southern gulf of california in most cases dark and light laminae show similar bulk chemical compositions and magnetic mineral properties however dark laminae contain relatively more terrigenous elements al si fe k and mg supporting a pluvial origin related to the volcanic siliceous tuffs around the bay of la paz in light laminae calcium content is higher representing biogenic input the magnetic signal is dominated by low coercivity fine grained low titanium titanomagnetites and magnetite hysteresis ratio parameters in domain state plots show that samples fall in the pseudo single domain field indicating mixtures of single and multi domain particles variations in hysteresis saturation magne tisation parameters for dark and light laminae reflect changes in relative mineral concentration results indicate a dominant volcanic source for magnetic minerals into the basin associated with variable pluvial and or aeolian transport low radiolarian abundance in dark laminae seems to be associated with larger penetration and longer residence time of oligotrophic subtropical waters into the bay that occurred during el nino southern oscillation enso events light laminae are the result of episodic pulses of high productivity we suggest that dark light laminae result from oceanographic and climatic cyclic processes with main terrigenous input variation possibly associated with enso forcing of pluvial influx and or latitudinal migration of the intertropical convergence zone the laminated sequence of the alfonso basin formed a non annual depositional system in contrast to the varved sediments characteristic of the central gulf of california basins copyright 2010 john wiley sons ltd

155 000 years of west african monsoon and ocean thermal evolution a detailed reconstruction of west african monsoon hydrology over the past 155 000 years suggests a close linkage to northern high latitude climate oscillations ba ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the gulf of guinea in the eastern equatorial atlantic eea reveal centennial scale variations of riverine freshwater input that are synchronous with northern high latitude stadials and interstadials of the penultimate interglacial and the last deglaciation eea mg ca based sea surface temperatures ssts were decoupled from northern high latitude millennial scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low latitude solar insolation the onset of enhanced monsoon precipitation lags behind the changes in eea ssts by up to 7000 years during glacial interglacial transitions this study demonstrates that the stadial interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the west african monsoon dynamics through an atmospheric linkage

holocene changes in eastern equatorial atlantic salinity as estimated by water isotopologues the isotopic composition of surface seawater is widely used to infer past changes in sea surface salinity using paired foraminiferal mg ca and 18o from marine sediments at low latitudes paleosalinity reconstructions using this method have largely been used to document changes in the hydrological cycle this method usually assumes that the modern seawater 18o 18osw salinity relationship remained constant through time modelling studies have shown that such assumptions may not be valid because large scale atmospheric circulation patterns linked to global climate changes can alter the seawater 18osw salinity relationship locally such processes have not been evidenced by paleo data so far because there is presently no way to reconstruct past changes in the seawater 18osw salinity relationship we have addressed this issue by applying a multi proxy salinity reconstruction from a marine sediment core collected in the gulf of guinea we measured hydrogen isotopes in c37 2 alkenones da to estimate changes in seawater d we find a smooth long term increase of 10 in da between 10 and 3 kyr bp followed by a rapid decrease of 10 in da between 3 kyr bp and core top to values slightly lighter than during the early holocene those features are inconsistent with published salinity estimations based on 18osw and foraminiferal ba ca as well as nearby continental rainfall history derived from pollen analysis we combined da and 18osw values to reconstruct a holocene record of salinity and compared it to a ba ca derived salinity record from the same sedimentary sequence this combined method provides salinity trends that are in better agreement with both the ba ca derived salinity and the regional precipitation changes as inferred from pollen records our results illustrate that changes in atmospheric circulation can trigger changes in precipitation isotopes in a counter intuitive manner that ultimately impacts surface salinity estimates based on seawater isotopic values our data suggest that the trends in holocene rainfall isotopic values at low latitudes may not uniquely result from changes in local precipitation associated with the amount effect

holocene land sea climatic links on the equatorial pacific coast bay of guayaquil ecuador we analyzed the pollen content of a marine core located near the bay of guayaquil in ecuador to document the link between sea surface temperatures ssts and changes in rainfall regimes on the adjacent continent during the holocene based on the expansion regression of five vegetation types we observe three successive climatic patterns in the first phase between 11 700 and 7700 cal yr bp the presence of a cloud andean forest in the mid altitudes and mangroves in the estuary of the guayas basin were associated with a maximum in boreal summer insolation a northernmost position of the intertropical convergence zone itcz a land sea thermal contrast cloud dripping and dry edaphic conditions between 7700 and 2850 cal yr bp the expansion of the coastal vegetation and the regression of the mangrove indicate a drier climate with weak itcz and low el nino southern oscillation enso variability while austral summer insolation gradually increased the interval between 4200 and 2850 cal yr bp was marked by the coolest and driest climatic conditions of the holocene because of the weak influence of the itcz and a strengthening of the humboldt current after 2850 cal yr bp high variability and amplitude of the andean forest changes occurred when enso frequency and amplitude increased indicating high variability in land sea connections the itcz reached the latitude of guayaquil only after 2500 cal yr bp inducing the bimodal precipitation regime we observe today our study shows that besides insolation the itcz position and enso frequency changes in eastern equatorial pacific ssts play a major role in determining the composition of the ecosystems and the hydrological cycle of the ecuadorian pacific coast and the western cordillera in ecuador

global patterns of enso induced precipitation although there have been many analyses of el nino southern oscillation enso induced precipitation anomalies global patterns from these analyses remain incomplete here we combine recent satellite estimates of oceanic precipitation and historical rain gauge records to derive a global climatology of enso induced precipitation anomalies using empirical orthogonal function eof analyses the patterns suggest that the re arrangement of convection centers of the walker circulation during enso events induces large precipitation anomalies in the tropics while associated changes in the monsoon systems through the hadley cell over the pacific indian and atlantic oceans and their interactions with midlatitude westerlies generate coherent anomaly patterns over the extratropics our results can be used to evaluate climate models and forecast enso induced precipitation anomalies

modes of eastern equatorial pacific thermocline variability implications for enso dynamics over the last glacial period 1 changes in el nino southern oscillation enso variability are difficult to extract from paleoceanographic reconstructions because they are superimposed on changes in seasonal variability that modulate the first order climate signal here we address this problem by reconstructing thermocline structure from a marine sediment core retrieved from the eastern equatorial pacific at the core location changes in hydrologic parameters within the thermocline are linked to enso activity with a reduced influence of seasonal variability compared to surface waters we performed repeated isotopic analyses 18o on single specimens of the thermocline dwelling planktonic foraminifera neogloboquadrina dutertrei at several targeted time periods over the last 50 ka to extract the total thermocline variance a parameter supposed to reveal changes in enso no fundamental changes in amplitude and frequency of the events were detected despite differences in climatic background however our data suggest that long term variations in the thermocline variability occurred over the last 50 ka with the highest and lowest enso activities occurring during the last glacial period and the last glacial maximum respectively

a multiproxy assessment of the western equatorial pacific hydrography during the last 30 kyr foraminiferal species assemblages and uk37 0 1 2 c these estimates are consistent with estimates from other wpwp cores thereby suggesting that the discrepancy is due to proxy compatibility rather than differences in cores qualitity postdepositional dissolution above the lysocline might have altered the mg ca based temperature estimates in our site but this effect is insufficient to resolve discrepancies between mg ca in g ruber and the other proxies we suggest that the lower estimates obtained from mg ca in g sacculifer faunal transfer functions and uk37 0 might reflect subsurface temperature changes rather than strict surface estimates accounting for potential artefacts including dissolution and bioturbation we suggest that the glacial wpwp sst was about 2 5 0 7 c cooler than during the holocene whereas the subsurface upper thermocline temperature change was only about 1 8 0 7 c interpreting variations in d 18 osw in terms of salinity changes suggests a possibly slight decrease in surface salinity at the site of md97 2138 during the lgm though lgm freshening in md97 2138 is not robust to postdeposition dissolution effects this inferred freshening appears to be a general feature of the western equatorial pacific

the california current system as a transmitter of millennial scale climate change on the northeastern pacific margin from 10 to 50 ka a high resolution record of 18o and mg ca based temperatures spanning 10 50 ka has been reconstructed from the vancouver margin of the northeastern pacific ocean md02 2496 from two planktonic foraminiferal species neogloboquadrina pachyderma s and globigerina bulloides while 18ocalcite appears synchronous with dansgaard oeschger interstadials dois throughout the record millennial scale variability in sea surface temperatures ssts and reconstructed 18oseawater are frequently out of phase with greenland climate changes in water mass characteristics such as 18ocalcite and enriched 15n events apparently responded to millennial scale climate change during marine isotope stage 3 mis 3 such that negative 18ocalcite excursions coincided with heavier 15n these water mass characteristic shifts are suggestive of the presence of surface water advected from the eastern tropical north pacific etnp by relative strengthening of the california undercurrent cuc bringing warm salty tropical waters poleward the linkage between the strength of the cuc on the ne pacific margin and millennial scale climate change may be related to increased sea surface heights off central america as the intertropical convergence zone itcz shifted northward in response to changes in north atlantic ocean circulation poor correlations between proxies exist through late mis 3 into mis 2 ice sheet growth could have disrupted the linkage between cuc and the ne pacific margin as the laurentide ice sheet disrupted atmospheric circulation and the cordilleran ice sheet increasingly influenced regional paleoceanography

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

oxygen isotopes upper ocean salinity and precipitation sources in the eastern tropical pacific westward transport of freshwater across the panama isthmus helps to maintain the salinity s contrast between the atlantic and pacific oceans important in global thermohaline circulation and climate relatively low sea surface salinities in the panama bight reflect high net precipitation we infer sources of this freshwater input to the region based on oxygen isotopes 18o of precipitation p and seawater sw the primary trend of the surface water sw s relationship implies a freshwater endmember 18o of 8 5 0 3 significantly lower than the mean p of rainwater we measured in the region 4 8 1 8 mixing with waters upwelled from the subsurface s 34 9 35 1 psu sw 0 3 0 4 based on limited isotope and salinity data these upwelling waters are a mixture of 60 tropical waters and 40 subtropical mode waters three secondary trends in the surface water sw s distribution point to similar freshwater sources with 18o of 2 5 1 2 4 7 0 5 and 4 8 0 6 consistent with local precipitation sources accounting for the primary surface water trend intermittent cross isthmus transport of moist air masses from the caribbean may introduce relatively 18o depleted rainfall due to a combination of recycling and orographic distillation in addition relatively infrequent but large tropical storms which may contain freshwater of both pacific and caribbean origin deliver rainfall with p of 10 to 14 the primary trend of regional surface seawater data which integrates the different sources over time suggests that about half of the total precipitation reflects local sources and half reflects a combination of cross isthmus transport and large storms the regional sw s distribution is sensitive to the relative contributions of these freshwater sources which may change under different climate regimes

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

variations in the western pacific warm pool across the mid pleistocene evidence from oxygen isotopes and coccoliths in the west philippine sea abstract we present planktonic foraminifera oxygen isotope and florisphaera profunda abundance data from the international marine global change study program images core md06 3050 which was collected in the west philippine sea on the margin of the western pacific warm pool wpwp our records reveal marked changes in the upper water structure in the kuroshio source region as early as 1 5 ma continuing through the mid pleistocene climate transition mpt these changes are evidenced by reconstructions of the thermocline based on planktonic foraminiferal oxygen isotope differences and the nutricline based on the relative abundance of the coccolithophore species florisphaera profunda in the kuroshio source region the evolution of the thermocline nutricline featured three prominent phases 1 phase i 1 5 1 1 ma which was characterized by low amplitude variations in a shallow thermocline 2 phase ii 1 1 0 8 ma which was characterized by high amplitude variations in a relatively shallow thermocline nutricline and 3 phase iii 0 8 0 5 ma which was characterized by low amplitude variations in a deep thermocline nutricline combined with the zonal sea surface temperature gradient in the tropical pacific the evolution of the upper water structure can be linked to tropical climatic changes across the mpt including the intensification of atmospheric circulation and a gradual cessation of the long term el nino like state the upper water structure of the wpwp was asymmetric before 0 8 ma with a shallow thermocline nutricline along the northern margin and a deep thermocline nutricline in the center of the wpwp and south china sea scs the modern wpwp was established by approximately 0 8 ma and the upper water structure has changed synchronously as a whole since that time a comparison of the 18 o values derived from globigerinoides ruber tests from the md06 3050 core with those from other cores in the western pacific suggests that the lower glacial interglacial g ruber 18 o values in md06 3050 before 0 8 ma could be related to the enhancement of the wpwp and to changes in atmospheric circulation patterns

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

east asian monsoon forcing of suborbital variability in the sulu sea during marine isotope stage 3 link to northern hemisphere climate 1 we have generated a new high resolution record of variations in planktonic foraminiferal oxygen isotopes 18o and mg ca from a sediment core images 97 2141 in the sulu sea located in the philippine archipelago of western tropical pacific this record reveals distinct suborbital scale 18o changes most notably during marine isotope stage 3 mis3 30 000 to 60 000 years b p the amplitudes of these 18o fluctuations 0 4 to 0 7 exceed that which can be attributed to sea level changes and must be due to changes in sea surface conditions in the same interval variations in planktonic foraminifera mg ca suggest that suborbital surface ocean temperature variations of 1 to 1 5 c in the sulu sea were not in phase with 18o combined this evidence indicates that the mis3 millennial 18o events in the sulu sea were primarily the result of changes in surface water salinity which today is directly related to the east asian monsoon eam and its influence on the balance between surface water contributions from the south china sea and western pacific warm pool wpwp within dating uncertainties the mis3 sulu sea 18o suborbital variability indicates that times of fresher surface conditions in the sulu sea coincide with similar conditions in the wpwp stott et al 2002 and also with intensifications of the summer eam as recorded in the u th dated chinese hulu cave speleothem 18o record wang et al 2001 and thus by inference with interstadials in the greenland ice core records combined these results indicate that pronounced suborbital variability in the summer eam and intertropical convergence zone itcz during mis3 was tightly coupled with climate conditions in the northern high latitudes

persistent millennial scale climate variability in the eastern tropical north pacific over the last two glacial cycles high resolution sediment records from the eastern tropical north pacific etnp spanning the last 240 ka b p were studied to document the nature of millennial scale climatic events in the tropical pacific and to investigate teleconnection mechanisms we present organic carbon oc and diffuse spectral reflectivity records as indicative of upwelling and productivity changes off nw mexico over the middle to late pleistocene the new productivity records document the persistence of abrupt millennial scale changes over the last two glacial cycles detailed spectral and wavelet time series analyses show the predominance of longer climatic cycles 2 6 ka during the last and the penultimate glacial periods the persistence of millennial variability during the penultimate glacial in absence of large ice rafted debris events in the north atlantic suggests that freshwater input through ice sheet dynamics is not essential for millennial scale climate variability given the worldwide emerging picture of remarkable similar millennial scale records over long time periods we suggest that the pacing of this climate variability may represent a natural resonance in the climate system amplified by a tightly coupled oceanic and atmospheric teleconnection processes we present a schematic scenario of millennial scale climate change depicting the role of the tropical pacific in this global teleconnection system by linking productivity and upwelling changes in the etnp with shifts in the position of the intertropical convergence zone and the strength of the subtropical north pacific high

variations in sea surface hydrology in the southern makassar strait over the past 26 kyr we present centennial scale records of sea surface temperature and oxygen isotopes in a sediment core from mandar bay offshore sulawesi in the southern makassar strait which provide new insights into the variability of indonesian climate over the past 26 kyr the age model for the core is constrained by 17 ams radiocarbon ages with a surface ocean reservoir age correction based on paired wood and foraminiferal samples small holocene reservoir ages of 105 180 years point to intense surface ocean atmosphere interchange linked to increased monsoonal precipitation whereas last glacial maximum and deglacial reservoir ages are significantly higher mg ca derived sea surface temperature reconstructions based on globigerinoides ruber s s white exhibit an extended plateau during the antarctic cold reversal suggesting an atmospheric connection to high latitude southern hemisphere climate and a seasonal bias on g ruber this is in agreement with southern hemisphere sites along the track of the indonesian throughflow and in contrast to northern hemisphere records from the south china sea sulu sea and western pacific off mindanao which exhibit warming during the bolling allerod ice volume corrected delta o 18 seawater delta o 18 sw increased during heinrich stadial 1 and the younger dryas whereas the bolling allerod is characterized by low delta o 18 sw we attribute delta o 18 sw variability in the southern makassar strait during the last glacial maximum and glacial termination to changes in provenance and seasonality of precipitation rather than to variability in the amount of local precipitation and runoff c 2016 elsevier ltd all rights reserved

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

the amplitude and phasing of climate change during the last deglaciation in the sulu sea western equatorial pacific 1 variations in tropical sea surface temperature patterns and the phasing relative to climate change in higher latitudes provide insight into the mechanisms of climate change on both orbital and shorter time scales here we present well dated high resolution records of planktonic foraminiferal 18o and mg ca based sst spanning the last deglaciation from the sulu sea located in the western equatorial pacific the results indicate that the last glacial maximum was 2 3 0 5 c cooler than present in the sulu sea with a concomitant decrease in sea surface salinity the similarity between variations in surface salinity in the sulu sea the western and eastern equatorial pacific and the greenland ice core record suggests that the observed changes in salinity reflect large scale rearrangement of atmospheric patterns which were coherent and synchronous throughout the northern hemisphere the results suggest that the glacial equatorial pacific climate was strongly influenced by both tropical and extra tropical forcing although it is not clear whether interannual enso variability is a good analogue of glacial interglacial climate change

itcz rather than enso signature for abrupt climate changes across the tropical pacific latitudinal movements of the intertropical convergence zone itcz analogous to its present day seasonal shifts and el nino southern oscillation enso type variability both potentially impacted rainfall changes at the millennial timescale during the last glacial period in this study we compare tropical pacific sedimentary records of paleoprecipitation to decipher which climate mechanism was responsible for the past rainfall changes we find that latitudinal movements of the itcz are consistent with the observed rainfall patterns challenging the enso hypothesis for explaining the rapid rainfall changes at low latitudes the itcz related mechanism appears to reflect large scale atmospheric rearrangements over the tropical belt with a pronounced heinrich dansgaard oeschger signature this observation is coherent with the simulated tropical rainfall anomalies induced by a weakening of the atlantic thermohaline circulation in modeling experiments c 2009 university of washington published by elsevier inc all rights reserved

hemispherically asymmetric trade wind changes as signatures of past itcz shifts abstract the atmospheric hadley cells which meet at the intertropical convergence zone itcz play critical roles in transporting heat driving ocean circulation and supplying precipitation to the most heavily populated regions of the globe paleo reconstructions can provide concrete evidence of how these major features of the atmospheric circulation can change in response to climate perturbations while most such reconstructions have focused on itcz related rainfall here we show that trade wind proxies can document dynamical aspects of meridional itcz shifts theoretical expectations based on angular momentum constraints and results from freshwater hosing simulations with two different climate models predict that itcz shifts due to anomalous cooling of one hemisphere would be accompanied by a strengthening of the hadley cell and trade winds in the colder hemisphere with an opposite response in the warmer hemisphere this expectation of hemispherically asymmetric trade wind changes is confirmed by proxy data of coastal upwelling and windblown dust from the atlantic basin during heinrich stadials showing trade wind strengthening in the northern hemisphere and weakening in the southern hemisphere subtropics in concert with southward itcz shifts data from other basins show broadly similar patterns though improved constraints on past trade wind changes are needed outside the atlantic basin the asymmetric trade wind changes identified here suggest that itcz shifts are also marked by intensification of the ocean s wind driven subtropical cells in the cooler hemisphere and a weakening in the warmer hemisphere which induces cross equatorial oceanic heat transport into the colder hemisphere this response would be expected to prevent extreme meridional itcz shifts in response to asymmetric heating or cooling understanding trade wind changes and their coupling to cross equatorial ocean cells is key to better constraining itcz shifts and ocean and atmosphere dynamical changes in the past especially for regions and time periods for which few paleodata exist and also improves our understanding of what changes may occur in the future

late quaternary moisture export across central america and to greenland evidence for tropical rainfall variability from costa rican stalagmites abstract we present a high resolution terrestrial archive of central american rainfall over the period 100 24 and 8 1 6 5 ka based on 18o time series from u series dated stalagmites collected from a cave on the pacific coast of costa rica our results indicate substantial 18o variability on millennial to orbital time scales that is interpreted to reflect rainfall variations over the cave site correlations with other paleoclimate proxy records suggest that the rainfall variations are forced by sea surface temperatures sst in the atlantic and pacific oceans in a fashion analogous to the modern climate cycle higher rainfall is associated with periods of a warm tropical north atlantic ocean and large sst gradients between the atlantic and pacific oceans rainfall variability is likely linked to the intensity and or latitudinal position of the intertropical convergence zone itcz periods of higher rainfall in costa rica are also associated with an enhanced sea surface salinity gradient on either side of the isthmus suggesting greater freshwater export from the atlantic basin when the itcz is stronger and or in a more northerly position further wet periods in central america coincide with high deuterium excess values in greenland ice suggesting a direct link between low latitude ssts tropical rainfall and moisture delivery to greenland our results indicate that a stronger tropical hydrological cycle during warm periods and large inter ocean sst gradients enhanced the delivery of low latitude moisture to greenland

moisture transport across central america as a positive feedback on abrupt climatic changes reconstruction of sea surface salinities in the eastern equatorial pacific ocean over the past 90 000 years detected strong millennial scale fluctuations that are associated with the migration of the tropical atlantic intertropical convergence zone thus millennial scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes modulating the north atlantic freshwater budget and hence north atlantic ocean circulation moisture transport from the atlantic to the pacific ocean across central america leads to relatively high salinities in the north atlantic ocean1 and contributes to the formation of north atlantic deep water2 this deep water formation varied strongly between dansgaard oeschger interstadials and heinrich events millennial scale abrupt warm and cold events respectively during the last glacial period3 increases in the moisture transport across central america have been proposed to coincide with northerly shifts of the intertropical convergence zone and with dansgaard oeschger interstadials with opposite changes for heinrich events4 here we reconstruct sea surface salinities in the eastern equatorial pacific ocean over the past 90 000 years by comparing palaeotemperature estimates from alkenones and mg ca ratios with foraminiferal oxygen isotope ratios that vary with both temperature and salinity we detect millennial scale fluctuations of sea surface salinities in the eastern equatorial pacific ocean of up to two to four practical salinity units high salinities are associated with the southward migration of the tropical atlantic intertropical convergence zone coinciding with heinrich events and with greenland stadials5 the amplitudes of these salinity variations are significantly larger on the pacific side of the panama isthmus as inferred from a comparison of our data with a palaeoclimate record from the caribbean basin6 we conclude that millennial scale fluctuations of moisture transport constitute an important feedback mechanism for abrupt climate changes modulating the north atlantic freshwater budget and hence north atlantic deep water formation

eastern pacific warm pool paleosalinity and climate variability 0 30 kyr multiproxy geologic records of 18o and mg ca in fossil foraminifera from sediments under the eastern pacific warm pool epwp region west of central america document variations in upper ocean temperature pycnocline strength and salinity i e net precipitation over the past 30 kyr although evident in the paleotemperature record there is no glacial interglacial difference in paleosalinity suggesting that tropical hydrologic changes do not respond passively to high latitude ice sheets and oceans millennial variations in paleosalinity with amplitudes as high as 4 practical salinity units occur with a dominant period of 3 5 ky during the glacial deglacial interval and 1 0 1 5 ky during the holocene the amplitude of the epwp paleosalinity changes greatly exceeds that of published caribbean and western tropical pacific paleosalinity records epwp paleosalinity changes correspond to millennial scale climate changes in the surface and deep atlantic and the high northern latitudes with generally higher lower paleosalinity during cold warm events in addition to intertropical convergence zone itcz dynamics which play an important role in tropical hydrologic variability changes in atlantic pacific moisture transport which is closely linked to itcz dynamics may also contribute to hydrologic variations in the epwp calculations of interbasin salinity average and interbasin salinity contrast between the epwp and the caribbean help differentiate long term changes in mean itcz position and atlantic pacific moisture transport respectively

mechanisms for millennial scale global synchronization during the last glacial period global climate during the last glacial period was punctuated by abrupt warmings and occasional pulses of freshwater into the north atlantic that disrupted deepwater production these massive freshwater pulses known as heinrich events arose in part from instabilities within the laurentide ice sheet paleoevidence from the north atlantic suggests that these events altered the production of deep water and changed downstream climate throughout the northern hemisphere in the tropical western pacific sea surface temperatures and salinity varied together with ocean and climate changes at high latitudes here we present results from coupled modeling experiments that shed light on a possible dynamical link between the north atlantic ocean and the western tropical pacific this link involves a global oceanic standing wave pattern brought about by millennial scale glacial density variations in the north atlantic atmospheric teleconnections triggered by meridional sea surface temperature gradients and local air sea interactions furthermore our modeling results are compared with hydrological records from the cariaco basin the indian ocean the sulu sea and northern australia

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

millennial variability and long term changes of the diatom production in the eastern equatorial pacific during the last glacial cycle 1 the modern eastern equatorial pacific eep is a major natural source for atmospheric carbon dioxide and is thought to be connected to high latitude ocean dynamics by oceanic teleconnections on glacial interglacial timescales a wealth of sedimentary records aiming at reconstructing last quaternary changes in primary productivity and nutrient utilization have been devoted to understanding those linkages between the eep and other distant oceanic areas most of these records are however clustered in the pelagic eep cold tongue with comparatively little attention devoted to coastal areas here we present downcore measurements of the composition and concentration of the diatom assemblage together with opal biogenic silica concentration at site md02 2529 recovered in the coastal panama basin piston core md02 2529 collected in an area affected by a multitude of processes provides evidence for strong variations in diatom production at the millennial timescale during the last glacial cycle the maxima in total diatom concentration occurred during the early marine isotopic stage mis 4 as well as during the mis 4 3 transition and mis 3 rapid changes in diatom concentrations during the mis 3 mimics bond cycles as independently recorded by the sea surface salinity estimation derived from planktonic foraminifera from the same core such patterns indicate a clear linkage between diatom production in the coastal eep and rapid climate changes in the high latitude north atlantic in parallel the long term succession of the diatom community from coastal diatoms predominantly thriving during mis 5 and 4 toward pelagic diatoms dominant during mis 3 and 2 points to a long term change in the surface hydrology during heinrich events diatoms strongly reduced their production probably because of enhanced stratification in the upper water column after the last glacial maximum diatom production and valve preservation strongly decreased in response to the advection of nutrient depleted h2sio4 warmer water masses our high resolution record highlights how regional climatic processes can modulate rapid changes in siliceous primary production as triggered by wind induced local upwelling indicating that millennial climatic variability can overtake other prominent hydrological processes such as those related to silicic acid leakage

warm pool hydrological and terrestrial variability near southern papua new guinea over the past 50k here we presenta 50k archiveof u37 seasurface temperature sst planktic foraminifera oxygen isotopes and terrestrial input indicators including branched and isoprenoid tetraether bit biomarkers 232 th activity and non biogenic sediment components recorded in core md052928 from the wpwp near southern papua new guinea png the planktic foraminifer oxygen isotopes in the core show millennial scale changes indicating fresher seawater during the nh cold periods i e heinrich events hes and suggesting hydrological changes that are most likely linked to the strength of the boreal winter asian australian monsoon aam our observations are corroborated by evidence from the same core that indicates increased terrestrial input caused by higher precipitation on land and more river runoff from southern png during the cold periods consistent with other nearby hydrological records from land our study indicates persistent millennial scale hydrological changes within the past 50k in the western tropical pacific and southeast asia the timing of the millennial scale changes appears to have been determined by the latitudinal displacement of the intertropical convergencezone itcz thatreflectsahistoryofheattrans

mechanical compaction and ultrasonic velocity of sands with different texture and mineralogical composition this study presents the results of experimental compaction while measuring ultrasonic velocities of sands with different grain size shape sorting and mineralogy uniaxial mechanical compaction tests up to a maximum of 50 mpa effective stress were performed on 29 dry sand aggregates derived from eight different sands to measure the rock properties a good agreement was found between the gassmann saturated bulk moduli of dry and brine saturated tests of selected sands sand samples with poor sorting showed low initial porosity while sands with high grain angularity had high initial porosity the sand compaction tests showed that at a given stress well sorted coarse grained sands were more compressible and had higher velocities vp and vs than fine grained sands when the mineralogy was similar this can be attributed to grain crushing where coarser grains lead to high compressibility and large grain to grain contact areas result in high velocities at medium to high stresses the angular coarse to medium grained sands both sorted sands and un sorted whole sands showed high compaction and velocities vp and vs the small grain to grain contact areas promote higher deformation at grain contacts more crushing and increased porosity loss resulting in high velocities compaction and velocities vp and vs increased with decreasing sorting in sands however at the same porosity the velocities in whole sands were slightly lower than in the well sorted sands indicating the presence of loose smaller grains in between the framework grains quartz poor sands containing less than 55 quartz showed higher velocities vp and vs compared to that of quartz rich sands this could be the result of sintering and enlargement of grain contacts of ductile mineral grains in the quartz poor sands increasing the effective bulk and shear stiffness tests both from wet measurements and gassmann brine substitution showed a decreasing vp vs ratio with increasing effective stress the quartz rich sands separated out towards the higher side of the vp vs range the gassmann brine substituted vp and vs plotted against effective stress provide a measure of the expected velocity range to be found in these and similar sands during mechanical compaction deviations of actual well log data from experimental data may indicate uplift the presence of hydrocarbon overpressure and or cementation data from this study may help to model velocity depth trends and to improve the characterization of reservoir sands from well log data in a low temperature 80 100o c zone where compaction of sands is mostly mechanical

hydrological changes and paleoproductivity in the gulf of california during middle and late holocene and their relationship with itcz and north american monsoon variability abstract this study investigates changes in precipitation patterns and variations in paleoproductivity in the tropical pacific region associated with the north american monsoon intertropical convergence zone itcz latitudinal migration and changes in insolation during the middle and late holocene major and trace element records al ba c k si and ti and zr al and ba al ratios in a core from alfonso basin southern gulf of california are used as proxies of terrigenous input and bio productivity records reveal an increase in precipitation and low bio productivity ca 6200 to 2400 cal yr bp associated with the strengthening of monsoonal precipitation and northward shift of the itcz mean position in the eastern tropical pacific a multi centennial drought from ca 2400 to 1900 cal yr bp and a dry and cold interval ca 700 and 500 cal yr bp are characterized by strong aeolian input and enhanced productivity associated with diminution of the summer monsoonal precipitation and reduced insolation in the northern hemisphere and more southerly itcz position correlation of alfonso basin records with other records in the gulf of california and the pigmy and cariaco basins in the gulf of mexico and central atlantic provides constraints on nam itcz migration and insolation driven changes

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

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

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

palaeoclimate analogue complexity the last deglaciation was punctuated by several millennial scale climate changes in the gulf of california the cold stages were marked by decreased upwelling opposite to the changes expected if these shifts were analogous to modern seasonal variability

environmental processes in rano aroi easter island peat geochemistry forced by climate variability during the last 70kyr abstract we analyze the geochemistry of rano aroi mire record easter island using bulk peat composition c n s and stable isotopes 13c 15n 34s and major minor and trace elemental compositions obtained by icp aes al ti zr sc v y fe mn th ba ca mg and sr peat geochemistry and the pollen record are used to reconstruct the environmental changes during the last 70 kyr bp principal component analysis on icp aes data revealed that three main components account for the chemical signatures of the peat the first component characterized by lithogenic elements combined signal of v al sc y cr cd ti zr and cu evidences long term changes in the basal fluxes of mineral material into the mire this component in combination with stable isotopes and pollen data suggests a link between soil erosion and vegetation cover changes in the rano aroi watershed the second component is identified by the signal of fe mn th ba zr and ti and is indicative of strong runoff events during enhanced precipitation periods the third component tied mainly to ca sr and mg reflects a strong peat oxidation event that occurred during an arid period with more frequent droughts sometime between 39 and 31 kyr bp correlation coefficients and a multiple regression model pcr analysis between peat organic chemistry and the principal components of icp aes analysis were calculated isotope chemistry of the peat organic matter further contributes to define rano aroi environmental history 13c data corroborates a vegetation shift documented by the palynological record from c4 to c3 between 55 and 45 cal kyr bp the 15n record identifies periods of changes in mire productivity and denitrification processes while the 34s peat signature indicates a marine origin of s and significant diagenetic cycling the geochemical and environmental evolution of rano aroi mire is coherent with the regional climatic variability and suggests that climate was the main forcing in mire evolution during the last 70 kyr bp the coupling of geochemical and biological proxies improves our ability to decipher depositional processes in tropical and subtropical peatlands and to use these sequences for paleoenvironmental and paleoclimate reconstructions

directly dated mis 3 lake level record from lake manix mojave desert california usa abstract an outcrop based lake level curve constrained by 70 calibrated 14 c ages on anodonta shells indicates at least 8 highstands between 45 and 25 cal ka bp within 10 m of the 543 m upper threshold of lake manix in the mojave desert of southern california correlations of manix highstands with ice marine and speleothem records suggest that at least the youngest three highstands coincide with dansgaard oeschger d o stadials and heinrich events 3 and 4 the lake level record is consistent with results from speleothem studies in the southwest that indicate cool wet conditions during d o stadials notably highstands between 43 and 25 ka apparently occurred at times of generally low levels of pluvial lakes farther north as interpreted from core based proxies mojave lakes may have been supported by tropical moisture sources during oxygen isotope stage 3 perhaps controlled by southerly deflection of pacific storm tracks due to weakening of the sea surface temperature gradient in response to north atlantic climate perturbations

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

hydrological variability in the western tropical pacific over the past 700 kyr and its linkage to northern hemisphere climatic change abstract el nino southern oscillation enso events and latitudinal shifts of the intertropical convergence zone itcz cause large scale hydrologic changes in the western tropical pacific wtp however there is still a debate on the role of enso and itcz shifts on the hydroclimate in the wtp and their linkage to northern hemisphere climate change on glacial interglacial timescales for that reason we present ice volume corrected seawater 18o 18osw ice a proxy for salinity and sea surface temperature sst records from images core md06 3047b recovered from the northern wtp to investigate the hydroclimate in the wtp during the last 700 kyr planktic foraminifera globigerinoides ruber based mg ca sst and 18osw ice records reveal distinct glacial interglacial variations the 18osw ice record shows that our study site is characterized by fresher conditions and thus higher precipitation during glacials than during interglacials our results are in good agreement with numerical model simulations which also suggest a glacial freshening in the northern wtp a glacial freshening of the wtp is most likely related to a substantial weakening of the atlantic meridional overturning circulation amoc and or exposure of the maritime continent due to sea level changes which resulted in an enhanced pacific walker circulation and or southward shift of the itcz in addition sst records from the wtp and the eastern tropical pacific etp suggest an enhanced tropical pacific zonal sst gradient and thus la nina like conditions which may have contributed to fresher conditions in the wtp during glacial periods besides our rainfall record is in antiphase to the chinese speleothem 18o records supporting the idea of an opposing trend in precipitation changes between the wtp and east asia on orbital timescales

synchronous tropical south china sea sst change and greenland warming during deglaciation the tropical ocean plays a major role in global climate it is therefore crucial to establish the precise phase between tropical and high latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change here we present alkenone sea surface temperature sst records from the tropical south china sea that show an abrupt temperature increase of at least 1 c at the end of the last glacial period within the recognized dating uncertainties this sst increase is synchronous with the bolling warming observed at 14 6 thousand years ago in the greenland ice sheet project 2 ice core

possible evidence for wet heinrich phases in tropical ne australia the lynch s crater deposit unarguably one of the most significant paleoclimatological discoveries of the last two decades has been that of abrupt climate events dansgaard oeschger cycles and heinrich events most evidence for these events has originated from the high latitude northern hemisphere with few records documenting the response of the low latitude southern hemisphere here we present new data from lynch s crater a unique terrestrial record from ne australia that may show evidence for southward propagations of the intertropical convergence zone itcz during abrupt climate perturbations as a result of alteration of the low latitude air masses proxies for precipitation wetness indicate enhanced rainfall in the region during heinrich events h events 1 3 and the 8 2 ka northern hemisphere cold event a fully coupled atmosphere ocean climate model simulating a 1 sv freshwater influx to the north atlantic ocean produces a scenario which agrees with the climate changes shown by the lynch s crater record the model shows precipitation anomalies that include a southward migration of the itcz and a zonal shift in mid latitude storm tracks over the southern hemisphere equatorial region these data indicate large scale shifts of the austral summer itcz position that is known to control monsoonal precipitation in ne australia this terrestrial record from australia may demonstrate the involvement of the tropical western pacific ocean in itcz migrations during abrupt climate events of the last glacial period defining such past migrations offers insight into the importance and role of the equatorial region in global climate dynamics

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

seawater isotope constraints on tropical hydrology during the holocene 1 paleoceanographic data from the low latitude pacific ocean provides evidence of changes in the freshwater budget and redistribution of freshwater within the basin during the holocene reconstructed holocene seawater 18o changes compare favorably to differences predicted between climate simulations for the middle holocene mh and for the pre industrial late holocene lh the model simulations demonstrate that changes in the tropical hydrologic cycle affect the relationship between 18osw and surface salinity and allow for the first time quantitative estimates of western pacific salinity change during the holocene the simulations suggest that during the mh the mean salinity of the pacific was higher because less water vapor was transported from the atlantic ocean and more was transported to the indian ocean the salinity of the western pacific was enhanced further due both to the greater advection of salt to the region by ocean currents and to an increase in continental precipitation at the expense of maritime precipitation the latter a consequence of the stronger asian summer monsoon

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

diagenetic constraints on heterogeneous reservoir quality assessment a triassic outcrop analog of meandering fluvial reservoirs reliable modeling of meandering fluvial reservoirs is challenging because of the heterogeneity in magnitude and pattern of porosity and permeability related to depositional and diagenetic features early mechanical and chemical alterations proceed along different pathways directly related to depositionally governed differences in textural and compositional parameters in a well constrained sedimentological framework and with relatively homogeneous conditions of detrital composition this study aims to determine the effect of depositional fabric on early diagenetic processes and their collective effect on petrophysical properties pore size distribution open porosity and permeability a high resolution qualitative and quantitative petrographic analysis is conducted on 22 fine to very fine grained sandstones from the main meandering fluvial facies of the channel center and margin point bar lower middle and upper scroll bar and chute channel of a triassic outcrop analog the occurrence of small scale internal heterogeneity associated with detrital matrix and suspension settling laminae favors the compaction process and hinders early pore filling cement precipitation that helps the preservation of primary porosity multivariate statistical treatment of data demonstrates that large 1 m and well connected primary intergranular pores are the main contributors to permeability in the more heterogeneous samples the distribution of the finer grained sediment fraction is strongly facies related as a result of hydraulic sorting better understanding of linkages between depositionally predictable features and diagenetically induced heterogeneity may lead to realistic reservoir models and enhanced effectiveness of exploitation and bypassed oil recovery strategies