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

sea surface and subsurface circulation dynamics off equatorial peru during the last 17 kyr the complex deglacial to holocene oceanographic development in the gulf of guayaquil eastern equatorial pacific is reconstructed for sea surface and subsurface ocean levels from isotope geochemical proxies based on marine sediment cores at sea surface southern sourced cold coastal water and tropical equatorial surface water tropical surface water are intimately related in particular since 10 ka independent sea surface temperature proxies capturing different seasons emphasize the growing seasonal contrast in the gulf of guayaquil which is in contrast to ocean areas further offshore cold coastal water became rapidly present in the gulf of guayaquil during the austral winter season in line with the strengthening of the southeast trades while coastal upwelling off peru gradually intensified and expanded northward in response to a seasonally changing atmospheric circulation pattern affecting the core locations intensively since 4 ka bp equatorial surface water instead was displaced and tropical surface water moved northward together with the equatorial front at subsurface the presence of equatorial under current sourced equatorial subsurface water was continuously growing prominently since 10 8 ka b p during heinrich stadial 1 and large parts of the bolling allerod and similarly during short holocene time intervals at 5 1 4 ka b p and 1 5 0 5 ka b p the admixture of equatorial subsurface water was reduced in response to both short term weakening of equatorial under current strength from the northwest and emplacement by tropical equatorial surface water considerably warming the uppermost ocean layers

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

northern timing of deglaciation in the eastern equatorial pacific from alkenone paleothermometry 1 the equatorial cold tongue ect of the eastern pacific is the most dynamic ocean region in the world s tropics and sets the tempo for global climate anomalies arising from el nino southern oscillation enso events this region s deglaciation history and relationship with north and south polar climates remains poorly understood impeding integration of tropical pacific ocean atmosphere dynamics and enso variability in our understanding of glacial cycles here we present alkenone reconstructions of sea surface temperature sst across the last glacial termination from five ect cores east of the galapagos islands a composite index of sst based on these demonstrates strong temporal affinity with the two step deglaciation of the northern hemisphere composed of two distinct warming steps at the beginning of the bolling and the end of the younger dryas intervals within dating uncertainty warming in the ect began in phase with the bolling excursion was followed by a 2 3 ka plateau and resumed with a second pulse at the end of the younger dryas on the basis of our reconstructions about two thirds of the warming materialized at or after the end of the younger dryas implying a marked delay in the region s response to deglaciation the results challenge the prevailing paradigm that ect deglacial history conforms to an antarctic timing commonly attributed to advection from the southern ocean through an interior oceanic link or to synchronous response of both regions to co2 forcing our results emphasize instead the role of dynamical adjustments linked to northern hemisphere processes most likely transmitted through the atmosphere

luminescence dating of the rissian type section in southern germany as a base for correlation abstract the exact timing of the rissian has been under discussion since being established by penck and bruckner 1909 at the beginning of the 20th century difficulties in correlating and especially dating the sediments associated with the rissian have led to different nomenclatures in the different regions of the northern alpine foreland naf various dating approaches have led so far to often unsatisfying results in this study we successfully dated the high terrace gravels of the rissian type section using single grain feldspar luminescence we were able to evade the problems of incomplete bleaching in fluvioglacial sediments using the post infrared irsl protocol at 225 c we were able to show that the feldspar in the research area only shows low rates of anomalous fading we were able to show that these low fading rates have an influence on the age determination this is remarkable because many of the signals were close to saturation the conclusive age range of 149 15 179 17 ka corresponds to marine isotope stage 6 defining an age for the rissian is a first step to consolidate the heterogeneous nomenclature and to reconstruct the chronology of past major alpine glaciations

oceanic conditions in the eastern equatorial pacific during the onset of enso in the holocene abstract records from south america show that modern enso el nino southern oscillation did not exist 7000 cal yr b p and has developed progressively since then there has been little information available on oceanic conditions in the eastern equatorial pacific eep to constrain explanations for enso onset we report quantitative observations on thermocline and mixed layer conditions in the eep during enso start up we found important changes in both the thermocline and the mixed layer indicating increased upwelling of cooler waters since 7000 cal yr b p this resulted from change in the source and or properties of waters supplying the equatorial undercurrent which feeds upwelling along the equator and the peru margin modeling shows that enso is sensitive to subsurface conditions in the eastern equatorial pacific and that the changes in the thermocline we observed were driven by extratropical processes giving these a role in conditioning the development of enso this is in contrast to models that call for control of equatorial pacific oceanography by tropical processes only these infer stronger upwelling and cooler surface waters for the eep during the mid holocene which is not supported by our results

seismic evidence of partial melt within a possibly ubiquitous low velocity layer at the base of the mantle three source regions show evidence of a low velocity layer that is less than 15 kilometers thick on top of the core mantle boundary and require about a 3 1 ratio of shear to compressional velocity reduction which is consistent with partial melt layer thickness is correlated with travel time residuals of the seismic phases that are most sensitive to the lowermost mantle velocity these observations suggest that the layer is thinned beneath downwellings but is present everywhere along the core mantle boundary low viscosity accompanying partial melt can localize the upwelling of warmed mantle making the low velocity layer a plausible source of mantle plumes

taking the temperature of past ocean surfaces accurate reconstructions of past climatic conditions on earth are important for modeling future climate change researchers use climate proxies from deep sea sediments corals or ice cores to reconstruct these past climatic conditions but as nurnberg explains in this perspective different techniques often give different answers a relatively new technique mg ca paleothermometry is a particularly promising tool especially in conjunction with oxygen isotope measurements on the same planktonic foraminiferal specimens the power of this method is exemplified by the study by lea et al

the physical environment of the peruvian upwelling system abstract knowledge of the characteristics of the physical environment of the peru coastal upwelling zone has increased greatly during the past decade observations made during 1976 and 1977 many made as part of the coastal upwelling ecosystem analysis joint ii expedition provide the basis for an interpretative description of the physical processes and phenomena occurring in peru coastal waters four important phenomena are discussed wind driven upwelling the poleward undercurrent surface mixed layer deepening and low frequency coastal trapped waves the coastal winds were invariably favorable for coastal upwelling even during the 1976 el nino the agreement between the offshore transport in the relatively shallow 30 m surface layer and the ekman transport deduced from the local wind was good for both the mean and variable state the agreement with the deeper onshore transport was less good consistent with the marked three dimensionally and spatial variability of the upwelling the poleward undercurrent was apparently continuous from 5 s to at least 15 s flowing just below the surface layer over the continental shelf and slope and supplying the upwelling water the variability in the alongshore velocity field was dominated by baroclinic free coastal trapped waves with periods of 5 20 days although there is appreciable temporal and spatial variability in the peru coastal upwelling system the upwelling the undercurrent and the low frequency coastal trapped waves were ubiquitous

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

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

the termination of the equatorial undercurrent in the eastern pacific abstract the termination of the equatorial undercurrent euc in the eastern tropical pacific has been studied through analysis of the historical hydrographic station data in the region bounded by 5 n 10 s 80 w and 100 w three distinctive hydrographic features associated with the euc are used along with dynamic topography to trace the mean path of the euc and to investigate aspects of its seasonal variation these features are 1 the 13 c thermostad 2 the high salinity core and 3 the high dissolved oxygen concentration tongue the thermostad is thickest just south of the equator to the west of the galapagos islands with a decreasing maximum extending southeast to the coast of south america near 7 s the thermostad is poorly developed in the mean near the equator east of the galapagos islands this pattern appears to be produced by convergence of eastward flow in the euc and in the southern subsurface countercurrent as the euc flows southeastward from the galapagos this interpretation is supported by the geostrophic flow calculated from the mean dynamic topography the isolated high salinity core is found to the south of the equator and is traced all the way to the coast of south america the high oxygen tongue associated with the euc splits at the galapagos with the southward projecting branch disappearing rapidly as an identifiable feature the other branch of the tongue continues around the islands to the north and along the equator to the coast of ecuador some evidence of recirculation of euc water in the south equatorial current is seen to the northwest of the galapagos a strong seasonal pulsation of the euc affects these features in a consistent way with the pulse occurring first west of the galapagos and later along the coast the thermostad first reaches maximum development and then a pronounced downwelling of the thermocline occurs rapidly leading to minimum thermostad extent associated wtih this downwelling is an eastward protruding high salinity tongue near the equator which is later seen as an isolated core along the coast at 4 s and 6 s pressure gradients along the equator and the coast inferred from dynamic topography suggest that this pulse is associated with an increase in the flow of the euc and ultimately the peru chile undercurrent the pressure gradient reversal along the equator occurs prior to the annual wind reversal suggesting that remote forcing plays a role in the seasonal pulse of the euc in the eastern pacific

water masses in the humboldt current system properties distribution and the nitrate deficit as a chemical water mass tracer for equatorial subsurface water off chile abstract three sections are used to analyze the physical and chemical characteristics of the water masses in the eastern south pacific and their distributions oceanographic data were taken from the scorpio may june 1967 piquero may june 1969 and krill june 1974 cruises vertical sections of temperature salinity dissolved oxygen nitrate nitrite phosphate and silicate were used to analyze the water column structure five water masses were identified in the zone through t s diagrams subantarctic water subtropical water equatorial subsurface water antarctic intermediate water and pacific deep water their proportions in the sea water mixture are calculated using the mixing triangle method vertical sections were used to describe the geographical distributions of the water mass cores in the upper 1500 m several characteristic oceanographic features in the study area were analyzed the shallow salinity minimum displacement towards the equator the equatorial subsurface salinity maximum associated with a dissolved oxygen minimum zone and a high nutrient content displacement towards the south and the equatorward intermediate antarctic salinity minimum associated with a dissolved oxygen maximum the nitrate deficit generated in the denitrification area off peru and northern chile is proposed as a conservative chemical tracer for the equatorial subsurface waters off the coast of chile south of 25 s

oceanographic considerations for the application of the alkenone based paleotemperature u37k index in the gulf of california abstract alkenone concentrations were determined in sediment trap samples and surficial sediments collected from guaymas basin gulf of california to investigate the factors that control the relationship between the u37k index and sst the results from the sediment trap study reveal a positive correlation r2 0 5 between alkenone fluxes and satellite avhrr sea surface temperature sst and a strong correlation r2 0 9 between u37k and sst over an annual temperature range of 20 c although sst and u37k are tightly coupled throughout two upwelling seasons the relationship deviates from the expression developed by prahl et al 1988 at temperatures higher than 26 c the possible reasons for this deviation are varied but include the observed changes in the coccolithophore species assemblage and the evolution of the thermocline during periods of high sst the seasonal pattern of alkenone fluxes higher fluxes during warm periods observed throughout the 1996 to 1997 study period causes a bias in the annually averaged u37k record resulting in temperature estimates that are 1 c higher than the annual avhrr sst average furthermore the u37k ratios obtained from core top sediments indicate an additional 2 c warm bias in the sedimentary record that may be related to the lateral inputs of alkenones from other regions of the gulf these results highlight the importance of oceanographic processes in determining the alkenone temperature signal that is preserved in sediments after accounting for such effects u37k ratios from a box core were used to reconstruct a sst record extending back to the 18th century for the guaymas basin these results indicate a steady 2 c warming of the surface waters of the gulf from early 1700s to the 1950s followed by a rapid apparent 1 c cooling between the 1950s and the 1980s

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

el nino southern oscillation like variability during glacial terminations and interlatitudinal teleconnections interannual decadal variability in the equatorial pacific el nino southern oscillation enso induces climate changes at global scale but its potential influence during past global climate change is not yet well constrained new high resolution eastern equatorial pacific proxy records of thermocline conditions present new evidence of strong orbital control in enso like variability over the last 275 000 years recurrent intervals of saltier thermocline waters are associated with the dominance of la nina like conditions during glacial terminations coinciding with periods of low precession and high obliquity the parallel dominance of 13c depleted waters supports the advection of antarctic origin waters toward the tropical thermocline this oceanic tunneling is proposed to have reinforced orbitally induced changes in enso like variability composing a complex high and low latitude feedback during glacial terminations

sedimentary opal records in the eastern equatorial pacific it is not all about leakage 1 the clear predictions of the silicic acid leakage hypothesis salh resulted in a number of studies of downcore opal records from the tropical pacific the original salh predicts that unused silicic acid due to fe driven changes in si versus n limitation escaped from the glacial southern ocean to equatorial upwelling regimes where it enhanced diatom productivity thereby decreasing coccolith growth and lowering atmospheric co2 in contrast to salh predictions however sedimentary records from the eastern equatorial pacific eep do not show enhanced opal burial during the last glacial maximum lgm but higher rates of opal burial during the deglaciation and marine isotopic stage 3 mis3 the peak in opal productivity during the deglaciation has been attributed to increased supply of nutrient rich waters driven by stronger upwelling of deep water in the southern ocean at the end of last glacial period the large peak in opal burial observed in a number of eep cores during mis3 was interpreted as evidence for si leakage when southern ocean diatom productivity was limited by both low dust flux and extended sea ice on the other hand the paradoxical lgm decline in opal accumulation in the eep was explained by enhanced dust input that lowered the diatom si c uptake ratio here we use a combination of molecular fingerprints of algal productivity and radioisotope tracers of sedimentation to revisit opal burial in the eep in particular during the mis3 opal peak an increase in algal productivity is not supported by the sedimentary concentration of brassicasterol an organic molecule commonly found in diatoms or by the ratio of 231pa 230th xs 0 a proxy for opal export production we therefore conclude that the large peak in opal burial during mis3 reflects enhanced preservation of diatoms building on mechanisms invoked in previous studies we hypothesize that opal burial in the eep is controlled both by the physiological response of diatoms to low latitude fe inputs and by the high latitude processes leading to silicic acid leakage

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

stable isotopes of planktonic foraminifera from tropical atlantic caribbean core tops implications for reconstructing upper ocean stratification abstract 18o values of nine tropical subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core top samples along an east west transect across the tropical atlantic caribbean were used to test the applicability of interspecific 18o gradients for reconstructions of tropical upper ocean stratification in general the 18o difference 18o between intermediate and shallow dwelling species decreases and 18o between deep and intermediate dwellers increases with increasing thermocline depth towards the west the statistical significance of regional differences in 18o highlights 18o between the intermediate dwellers in particular globorotalia scitula and globorotalia tumida and the shallow dweller globigerinoides ruber pink as well as 18o between the deep dwellers globorotalia crassaformis or globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical atlantic thermocline depth based on the observed regional variations in interspecific 18o we propose a multispecies stratification index stratrop 18ointermediate 18oshallow 18odeep 18oshallow for the tropical ocean statistically significant differences in stratrop values between the e atlantic and the caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

holocene and eemian sea surface temperature trends as revealed by alkenone and mg ca paleothermometry in this study we review a global set of alkenone and foraminiferal mg ca derived sea surface temperatures sst records from the holocene and compare them with a suite of published eemian sst records based on the same approach for the holocene the alkenone sst records belong to the actualized ghost database kim j h schneider r r 2004 ghost global database for alkenone derived holocene sea surface temperature records available from http www pangaea de projects ghost while the mg ca derived sst database represents a new compilation the actualized ghost database not only confirms the sst changes previously described but also documents the holocene temperature evolution in new oceanic regions such as the northwestern atlantic the eastern equatorial pacific and the southern ocean a comparison of holocene sst records stemming front the two commonly applied paleothermometry methods reveals contrasting sometimes divergent sst evolution particularly at low latitudes where sst records are abundant enough to infer systematic discrepancies at a regional scale opposite sst trends at particular locations could be explained by out of phase trends in seasonal insolation during the holocene this hypothesis assumes that a strong contrast in the ecological responses of coccolithophores and planktonic foraminifera to winter and summer oceanographic conditions is the ultimate reason for seasonal differences in the origin of the temperature signal provided by these organisms as a simple test for this hypothesis eemian sst records are considered because the holocene and eemian time periods experienced comparable changes in orbital configurations but had a higher magnitude in insolation variance during the eemian for several regions sst changes during both interglacials were of a similar sign but with higher magnitudes during the eemian as compared to the holocene this observation suggests that the ecological mechanism shaping sst trends during the holocene was comparable during the penultimate interglacial period although this ecology hypothesis fails to explain all of the available results we argue that any other mechanism would fail to satisfactorily explain the observed sst discrepancies among proxies c 2010 elsevier ltd all rights reserved

near coastal circulation in the northern humboldt current system from shipboard adcp data the near coastal circulation of the northern humboldt current system is described analyzing 8700 velocity profiles acquired by a shipboard acoustic doppler current profiler sadcp during 21 surveys realized between 2008 and 2012 along the peruvian coast this data set permits observation of i part of the peru coastal current and the peru oceanic current that flow equatorward in near surface layers close to the coast and farther than 150 km from the coast respectively ii the peru chile undercurrent pcuc flowing poleward in subsurface layers along the outer continental shelf and inner slope iii the near surfacing equatorial undercurrent renamed as ecuador peru coastal current that feeds the pcuc and iv a deep equatorward current referred to as the chile peru deep coastal current flowing below the pcuc a focus in the pcuc core layer shows that this current exhibits typical velocities of 5 10 cm s 1 the pcuc deepens with an increasing thickness poleward consistent with the alongshore conservation of potential vorticity the pcuc mass transport increases from 1 8 sv at 5 s to a maximum value of 5 2 sv at 15 s partly explained by the sverdrup balance the pcuc experiences relatively weak seasonal variability and the confluence of eddy like structures and coastal currents strongly complicates the circulation the pcuc intensity is also affected by the southward propagation of coastally trapped waves as revealed by a strong pcuc intensification in march 2010 coincident with the passage of a downwelling coastal wave associated with a weak el nino event

sea surface temperature anomalies associated with the 1997 1998 el nino recorded in the oxygen isotope composition of planktonic foraminifera anomalously warm sea surface temperatures and associated high rainfall propagated northward from the eastern equatorial pacific along the western margin of north america during the 1997 1998 el nino we present data from the guaymas basin gulf of california and the santa barbara basin southern california borderlands that clearly demonstrate that the oxygen isotope composition of planktonic foraminifera accurately records the local sea surface temperature changes related to the el nino phenomenon on the basis of this observation the varved sediments accumulating in these basins should contain a detailed history of both the occurrence and intensity of past el nino events

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

barbados based estimate of ice volume at last glacial maximum affected by subducted plate coral records from the barbados have been used to infer that due to ice expansion sea level was 120 m lower than today during the last glacial maximum a 3d simulation of the mantle in this region suggests these estimates were biased by the presence of a subducted slab and indicates the sea level difference was closer to 130 m

interacting loop current variability and mississippi river discharge over the past 400 kyr the loop current mediating the oceanic heat and salt flux from the caribbean sea into the atlantic ocean and its interference with the mississippi river discharge are critical for both the regional climate in the gulf of mexico area and the water vapor transport towards high northern latitudes we present a 400 kyr record of sea surface temperature and local surface salinity from the northeastern gulf of mexico images core md02 2575 approximated from combined planktonic foraminiferal 18o and mg ca which reflects the temporal dynamics of the loop current and its relationship to both varying mississippi discharge and evolution of the western hemisphere warm pool the reconstructed sea surface temperature and salinity reveal glacial interglacial amplitudes that are significantly larger than in the western hemisphere warm pool sea surface freshening is observed during the extreme cool periods of marine isotope stages 2 8 and 10 caused by the strengthened mississippi discharge which spread widely across the gulf favored by the less established loop current interglacial and interstadial sea surface conditions instead point to a strengthened northward flowing loop current in line with the northward position of the intertropical convergence zone allowing northeastern gulf of mexico surface hydrographic conditions to approach those of the caribbean at these times the mississippi discharge was low and deflected westward promoted by the extended loop current previously described deglacial megadischarge events further to the west did not affect the northeastern gulf of mexico hydrography implying that meltwater routing from the laurentide ice sheet via the mississippi river is unlikely to have affected atlantic meridional overturning circulation

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

more humid interglacials in ecuador during the past 500 kyr linked to latitudinal shifts of the equatorial front and the intertropical convergence zone in the eastern tropical pacific 1 studying past changes in the eastern equatorial pacific ocean dynamics and their impact on precipitation on land gives us insight into how the intertropical convergence zone itcz movements and the el nino southern oscillation modulate regional and global climate in this study we present a multiproxy record of terrigenous input from marine sediments collected off the ecuadorian coast spanning the last 500 kyr in parallel we estimate sea surface temperatures sst derived from alkenone paleothermometry for the sediments off the ecuadorian coast and complement them with alkenone based sst data from the panama basin to the north in order to investigate sst gradients across the equatorial front near the equator today s river runoff is tightly linked to sst reaching its maximum either during the austral summer when the itcz migrates southward or during el nino events our multiproxy reconstruction of riverine runoff indicates that interglacial periods experienced more humid conditions than the glacial periods the north south sst gradient is systematically steeper during glacial times suggesting a mean background climatic state with a vigorous oceanic cold tongue resembling modern la nina conditions this enhanced north south sst gradient would also imply a glacial northward shift of the intertropical convergence zone at least in vicinity of the cold tongue a pattern that has not yet been reproduced in climate models

average circulation seasonal cycle and mesoscale dynamics of the peru current system a modeling approach h isolines the pccc appears to be directly forced by the cyclonic wind stress curl the model is able to produce the upwelling front the cold water tongue which extends toward the equator and the equatorial front as described in the literature model seasonal changes in sst and ssh are compared to measurements for the central pcs model eke is 10 to 30 lower than the observations the model eddy diameters follow a strong equatorward increase the injection length scales derived from the energy spectra strongly correlate to the rossby radius of deformation confirming the predominant role of baroclinic instability at 3 s the model solution appears to switch from a turbulent oceanic regime to an equatorial regime dominated by zonal currents