an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

solar forcing of florida straits surface salinity during the early holocene 1 previous studies showed that sea surface salinity sss in the florida straits as well as florida current transport covaried with changes in north atlantic climate over the past two millennia however little is known about earlier holocene hydrographic variability in the florida straits here we combine mg ca paleothermometry and stable oxygen isotope measurements on the planktonic foraminifera globigerinoides ruber white variety from florida straits sediment core knr166 2 jpc 51 24 24 70 n 83 13 14 w 198 m deep to reconstruct a high resolution 25 yr sample early to mid holocene record of sea surface temperature and d 18 osw a proxy for sss variability after removing the influence of global d 18 osw change due to continental ice volume variability we find that early holocene sss enrichments are associated with increased evaporation precipitation ratios in the florida straits during periods of reduced solar forcing increased ice rafted debris in the north atlantic and the development of more permanent el nino like conditions in the eastern equatorial pacific when considered with previous high resolution reconstructions of holocene tropical atmospheric circulation changes our results provide evidence that variations in solar forcing over the early holocene had a significant impact on the global tropical hydrologic cycle

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

last interglacial climates the last interglacial commonly understood as an interval with climate as warm or warmer than today is represented by marine isotope stage mis 5e which is a proxy record of low global ice volume and high sea level it is arbitrarily dated to begin at approximately 130 000 yr b p and end at 116 000 yr b p with the onset of the early glacial unit mis 5d the age of the stage is determined by correlation to uranium thorium dates of raised coral reefs the most detailed proxy record of interglacial climate is found in the vostok ice core where the temperature reached current levels 132 000 yr ago and continued rising for another two millennia approximately 127 000 yr ago the eemian mixed forests were established in europe they developed through a characteristic succession of tree species probably surviving well into the early glacial stage in southern parts of europe after ca 115 000 yr ago open vegetation replaced forests in northwestern europe and the proportion of conifers increased significantly farther south air temperature at vostok dropped sharply pulses of cold water affected the northern north atlantic already in late mis 5e but the central north atlantic remained warm throughout most of mis 5d model results show that the sea surface in the eastern tropical pacific warmed when the ice grew and sea level dropped the essentially interglacial conditions in southwestern europe remained unaffected by ice buildup until late mis 5d when the forests disappeared abruptly and cold water invaded the central north atlantic ca 107 000 yr ago

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

did glacials start with global warming abstract correlation of paleoclimatic evidence with orbital changes shows that the build up of polar ice accelerated when low obliquity coincided with perihelion in northern hemisphere winter under low obliquity the insolation was channeled to the tropics at the expense of both polar caps as perihelion moved from winter solstice toward spring equinox the solar beam in astronomic winter and spring became stronger than in summer and autumn this orbital configuration under climate conditions like today would lead to warming of tropical oceans but cooling of the polar regions the areally weighted global mean surface temperature which is dominated by the low latitudes would increase consequently during the first millennia the early glacial ice build up was most likely accompanied by global warming it was the associated increase of meridional insolation and temperature gradients which were instrumental in the transition to a glacial a significant part of the current global warming is due to the gradual temperature increase of the tropical oceans as the changing orbital configuration today resembles that of the last interglacial glacial transition the warming is likely to have a natural component

el nino like climate teleconnections in new england during the late pleistocene a glacial varve chronology from new england spanning the 4000 year period from 17 500 to 13 500 calendar years before the present was analyzed for evidence of climate variability during the late pleistocene the chronology shows a distinct interannual 3 to 5 years band of enhanced variability suggestive of el nino southern oscillation enso teleconnections into north america during the late pleistocene when the laurentide ice sheet was near its maximum extent and climatic boundary conditions were different than those of today this interannual variability largely disappears by the young end of the 4000 year chronology with only the highest frequency components roughly 3 year period persisting this record provides evidence of enso like climate variability during near peak glacial conditions

glacial surface temperatures of the southeast atlantic ocean a detailed record of sea surface temperature from sediments of the cape basin in the subtropical south atlantic indicates a previously undocumented progression of marine climate change between 41 and 18 thousand years before the present ky b p during the last glacial period whereas marine records typically indicate a long term cooling into the last glacial maximum around 21 ky b p consistent with gradually increasing global ice volume the cape basin record documents an interval of substantial temperate ocean warming from 41 to 25 ky b p the pattern is similar to that expected in response to changes in insolation owing to variations in earth s tilt

late caradoc graptolitic faunal gradients across the iapetus ocean late caradoc graptolite assemblages across the iapetus ocean in wales and scotland became progressively more disparate despite the narrowing of the ocean we compare faunal distributions in continuous sections from opposite sides of iapetus at whitland in south wales and hartfell score in the southern uplands of scotland a comprehensive graptolite range chart is given for each the graptolite assemblages from the clingani biozone are subdivided into a lower ensigraptus caudatus subzone and upper dicellograptus morrisi subzone at both localities though the faunas differ in detail higher in the sequence the distinctive scottish linearis biozone fauna is not recognizable at whitland its presumed equivalent being a fauna dominated by variable morphotypes of the genus normalograptus this suggests that environmental gradients depth and or temperature were changing more rapidly than the geography significantly the subsequent inception of limestone deposition at whitland was approximately contemporaneous with widespread replacement of black mudstones by oxic bioturbated sediments elsewhere in the welsh basin and in scotland this was possibly a response to an early phase of cooling prior to the end ordovician glaciation in wales the claimed hiatus at the caradoc ashgill boundary may rather reflect biofacies variation

timing and significance of maximum and minimum equatorial insolation variations in summer insolation at high northern latitudes on a timescale of 100 ka are very small thus a common belief is that the pronounced 100 ka glacial cycles are not directly linked to the very weak 100 ka insolation periodicity here we show analytically and numerically that the annual maximum and minimum of daily equatorial insolation has pronounced eccentricity periodicities with timescales of 400 ka and 100 ka as well as a pronounced half precession periodicity with timescale of 11 ka the timing of the maximum and minimum annual equatorial insolation may change around the equinoxes solstices alternating between the vernal and autumnal equinoxes summer and winter solstices where the time of the maximum minimum equatorial insolation may occur up to more than 1 month from the equinoxes solstices we also show that when considering the mean insolation of periods larger than 1 d the 11 ka periodicity becomes less dominant and it vanishes when the averaging period is half a year for the later case the maximum minimum may occur for any day in the annual cycle the maximum equatorial insolation may alter the timing and amplitude of the maximum surface temperature of the summer hemisphere and in this way may drastically affect the hadley circulation changes in hadley circulation affect the heat and moisture transport from low to high latitudes affecting the buildup of the high latitude northern hemisphere ice sheets

meridional shifts in the marine itcz and the tropical hydrologic cycle over the last three glacial cycles 1 paleoproxy studies show a strong correlation between tropical climate and high latitude temperature variability recorded in the greenland ice cores over the last glacial cycle in particular abrupt cooling events in the greenland ice sheet project ii 18o ice record appear synchronous with a southward migration of the intertropical convergence zone itcz in the atlantic a weakening of the indian and east asian monsoon systems and a strengthening of the south american monsoon system because this high to low latitude climate teleconnection significantly alters the tropical hydrologic cycle around the globe it plays a critical role in regulating global climate on glacial interglacial time scales we compare 18oseawater reconstructions a salinity proxy generated from previously published mg ca and oxygen isotope data on globigerinoides ruber white var obtained from western caribbean core odp 999a and western equatorial pacific core 806b across the last three glacial cycles to show that systematic variations in surface salinity at these sites suggest the tropical hadley cell hydrologic system undergoes systematic reorganizations that differ dramatically between warm interglacial and cold glacial periods furthermore cross spectral and phase angle analyses of the ice volume corrected caribbean and western pacific 18osw records reveal a 100 kyr frequency in both records that is almost 180 out of phase and a 23 kyr frequency that is nearly in phase this results in the development of a very large 18osw gradient between the caribbean and the western equatorial pacific on glacial interglacial time scales that is best explained by a southward shift in both the atlantic and pacific itcz during north atlantic cold phases

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

last interglacial and early glacial enso although the link between insolation and climate is commonly thought to be in the high northern latitudes in summer our results show that the start of the last glaciation in marine isotope stage mis 5d was associated with a change of insolation during the transitional seasons in the low latitudes a simplified coupled ocean atmosphere model shows that changes in the seasonal cycle of insolation could have altered el nino southern oscillation enso variability so that there were almost twice as many warm enso events in the early glacial than in the last interglacial this indicates that ice buildup in the cooled high latitudes could have been accelerated by a warmed tropical pacific

western caribbean sea surface temperatures during the late quaternary 1 mg ca ratios in the planktonic foraminifera globigerinoides ruber from colombian basin core odp 999a suggest that caribbean sea surface temperatures ssts were from 2 1 to 2 7 c colder than the present during the last three glacial maximums in comparison faunal derived ssts simmax method show that august ssts in the caribbean varied 2 c over the past 360 kyr whereas february ssts varied between 21 0 c and 26 5 c changes in the mg ca sst record contain a strong 23 kyr periodicity suggesting the mg ca sst record reflects a warm season weighted sst average rather than an annual mean sst combining several dissolution indices we identify brief periods of decreased carbonate preservation in our record and show that mis 11 stands out as the most intensive dissolution cycle in the caribbean over the last 460 kyr comparison of caribbean sst change with a similar estimate of tropical sst variability in the western pacific over the past 360 kyr reveals shifts in the east west tropical sst gradient that are coeval with glacial interglacial climate change and consistent both with a southward migration of the glacial itcz and with a glacial el nino like mode of tropical circulation

geoarchaeological evidence from peru for a 5000 years b p onset of el nino for the tropical west coast of south america where el nino southern oscillation enso is most pronounced archaeological and associated paleontological deposits in northern peru revealed a major climate change at about 5000 years before the present yr b p the data implied the presence of stable warm tropical water as far south as 10 s during the early mid holocene about 8000 to 5000 yr b p these data suggest that enso did not occur for some millennia preceding 5000 yr b p when global and regional climate was warmer than today

late pleistocene climatic events reflected in the caspian sea geological history based on drilling data abstract the analysis of seismic acoustic profiles and drilling data from the northern caspian showed the climatic events are quite distinguishable in the upper pleistocene sedimentary sequence the climatic events of the first half of late pleistocene mis 5 resulted in the onset of two warm water transgressive basins late khazarian and hyrcanian ones though cooler than at the late khazarian transgression the climate during the hyrcanian time was attributable to interglacial one as the glacial stage mis 4 approached its maximum under conditions of a dry and cold climate the hyrcanian sea basin regressed the atelian regression of the caspian sea corresponded to mis 4 stage and to the initial phases of the mis 3 interstadial warming the development of the global interstadial warming led to a considerable increase in the surface runoff from the catchment and resulted in the rising of the atelian lake level and the onset of the first phase of the khvalynian transgression the sea level rising was interrupted at the time of maximum cooling and aridization at mis 2 and resumed when the ice sheet was decaying the conspicuous climatic events known as warm phases of bolling and allerod promoted the ice sheet melting along with thawing of permafrost the latter having been widespread in the volga drainage basin all the above contributed to the khvalynian transgression the chocolate clays were accumulated in the volga estuary as well as in depressions of the pre khvalynian topography phases of a noticeable cooling known as the oldest older and younger dryas marked by a decrease in the runoff volume from the caspian drainage basin are correlated with regressive stages in the khvalynian basin history the khvalynian came to its end at the time of the first sharp warming that resulted in the rise of the caspian level and is generally taken as marking the pleistocene holocene boundary the mangyshlakian regression is dated to the holocene and was essentially a response of the caspian sea to the increase in the climate continentality during the boreal period

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

low latitude hydrological cycle and rapid climate changes during the last deglaciation sea surface temperature and oxygen isotopic records from two well dated indian ocean cores covering the last deglaciation show the occurrence of two periods of increased salinity along the route of warm surface water transport from the indian to the atlantic ocean one between 18 and 14 5 ka and the other during the younger dryas our results imply that during these periods salt accumulated in the tropical atlantic creating favorable conditions for an abrupt resumption of the thermohaline circulation and abrupt northern hemisphere warming furthermore we suggest that the observed pattern of millennial climate variability during the last glacial and deglaciation resulted from the interaction between the relatively slow rhythm of expansion and decay of the northern hemisphere ice sheets and el nino southern oscillation variability through changes in the position of the intertropical convergence zone this interaction generated an oscillator with millennial time response that operated at times of sufficient northern hemisphere ice sheets extent

a fossil coral perspective on western tropical pacific climate 350 ka 1 the nature of tropical climate variability 350 ka is addressed using 18o and sr ca records from a modern and a fossil coral from vanuatu southwestern tropical pacific ocean modern el nino events at vanuatu produce positive coral 18o and sr ca anomalies similar anomalies observed in the fossil coral records suggest that el nino was operative 350 kyr ago seasonal variations in coral sr ca a sea surface temperature sst proxy have the same amplitude in both corals whereas seasonal 18o variations are smaller in the fossil coral than in the modern coral this is consistent with displacement of the south pacific convergence zone toward the southwest during the boreal summer 350 ka mathematical modeling results preclude warmer sst and higher sss at vanuatu during this time but permit the surface ocean to be 2 c cooler and 0 2 psu fresher than today assessing the potential of variations in late quaternary seawater sr ca remains the largest obstacle to accurately reconstructing tropical sst using pristine fossil corals

an oceanic cold reversal during the last deglaciation a detailed deuterium excess profile measured along the dome c epica european project for ice coring in antarctica core reveals the timing and strength of the sea surface temperature changes at the source regions for dome c precipitation we infer that an oceanic cold reversal took place in the southern indian ocean 800 years after the antarctic cold reversal the temperature gradient between the oceanic moisture source and antarctica is similar to the dome c sodium profile during the deglaciation illustrating the strong link between this gradient and the strength of the atmospheric circulation

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

western caribbean intraplate deformation defining a continuous and active microplate boundary along the san andres rift and hess escarpment fault zone colombian caribbean sea the san andres rift sar located on the lower nicaraguan rise is a previously poorly studied active 015 trending bathymetric and structural rift basin that is 11 27 km 7 17 mi wide and extends for 346 km 215 mi across the western flank of the caribbean plate in this study we integrate bathymetric maps potential field data and high resolution two dimensional 2 d seismic lines to understand the crustal structure tectonic history and tectonic origin of the sar which is one of the active areas within the otherwise stable caribbean plate we compiled regional gravity and magnetic data that revealed a negative gravity anomaly and positive magnetic anomaly that we interpret as a result of crustal thinning and an elevated moho along the main rift axis of the sar forward models of gravity data show four possible interpretations for the origin of the crust underlying and surrounding the sar interpretations of 2 d seismic reflection data show structural features within the upper crust and sedimentary sections typical of other active rift systems including a sar parallel north south alignment of earthquakes with the larger events showing normal and strike slip focal mechanisms sequential kinematic restorations based on 2 d seismic profiles reveal three major phases of sar opening 1 the initial early eocene rifting stage 2 middle eocene extension and 3 a rapid middle miocene to early pliocene extension accompanied by emergence of the san andres island as a rift shoulder we propose slab rollback and intraplate extension as main tectonic mechanisms to explain all rift phases and neogene volcanism found in the western caribbean region

long term variations of monthly insolation as related to climatic changes qualitative multivariate models which combine past insolations of selected months at selected latitudes explains 55 to 67 of the variance in the 135 millenia long oxygen isotope record of pleistocene climates

saalian supercycle mindel riss interglacial and milankovitch s dating abstract there are five pleistocene glacial interglacial cycles recorded in deep sea sediments from the last half million years but only two classic interglacials are recognized on land the dilemma stems from the different understanding and identification of glacials and interglacials in the geologic records on land and in the ocean only those intervals of warm climate that followed a major southward ice sheet advance and were accompanied by a deep penetrating oceanic transgression were recognized in their type areas of northern europe as true interglacials only those ice advances which left moraines farther south than younger ones were recognized as glacials in contrast all intervals reflecting exceptionally low global ice volume high sea level and warm sea surface are taken as interglacials in the deep sea record classic subdivisions are aligned with the glacial interglacial cycles of marine isotope stage stratigraphies by proposed higher order units called supercycles sc bracketed by superterminations st the saalian supercycle sc2 includes glacial cycles c d and e composed of marine isotope stages mis 6 7 8 9 10 and 11 the units mis 7 to mis 11 correspond to the great gross interglacial estimated from the early geologic considerations to be about 240 millennia long penck and bruckner 1909 die alpen im eiszeitalter vols 1 3 christian herman tauchnitz leipzig and determined from astronomic computations to last 235 millennia milankovitch 1941 kanon der erdbestrahlung und seine anwendung auf das eiszeitenproblem academie royale serbe editions speciales section des sciences mathematiques et naturelles tome cxxxiii stamparija mihaila curcica beograd 633pp the current high precision radiometric dating fully confirms the accuracy of milankovitch s determination and the pivotal role of orbital mechanisms in pleistocene climate change

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr