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

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

southward intertropical convergence zone shifts and implications for an atmospheric bipolar seesaw abstractin this study southward intertropical convergence zone itcz shifts are investigated in three different scenarios northern hemispheric cooling southern hemispheric warming and a bipolar seesaw like forcing that combines the latter two the experiments demonstrate the mutual effects that northern and southern high latitude forcings exert on tropical precipitation suggesting a time scale dependent dominance of northern versus southern forcings in accordance with this two phase tropical precipitation shifts are suggested involving a fast component dominated by the high northern latitude forcing and a slower component due to the southern high latitude forcing the results may thus be useful for the future understanding and interpretation of high resolution tropical paleoprecipitation proxies and their relation to high latitude records e g ice core data the experiments also show that southern ocean warming has a global impact affecting both the tropics and northern extratropics as seen

the cause of carbon isotope minimum events on glacial terminations the occurrence of carbon isotope minima at the beginning of glacial terminations is a common feature of planktic foraminifera carbon isotopic records from the indo pacific sub antarctic and south atlantic we use the 13 c record of a thermocline dwelling foraminifera neogloboquadrina dutertrei and surface temperature estimates from the eastern equatorial pacific to demonstrate that the onset of 13 c minimum events and the initiation of southern ocean warming occurred simultaneously timing agreement between the marine record and the 13 c minimum in an antarctic atmospheric record suggests that the deglacial events were a response to the breakdown of surface water stratification renewed circumpolar deep water upwelling and advection of low 13 c waters to the convergence zone at the sub antarctic front on the basis of age agreement between the absolute 13 c minimum in surface records and the shift from low to high 13 c in the deep south atlantic we suggest that the 13 c rise that marks the end of the carbon isotope minima was due to the resumption of north atlantic deep water influence in the southern ocean

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

spatial and temporal sea surface temperatures in the eastern equatorial pacific over the past 150 kyr 1 we present the new alkenone based sea surface temperature sst records from the eastern equatorial pacific over the past 150 kyr core hy04 4 n at the north equatorial countercurrent necc registered the invariant ssts 25 8 27 2 c whereas core hy06 0 n registered cyclic glacial interglacial sst variations 22 4 26 1 c although hy06 alkenone based sst evolution was almost consistent with the previously published sst records from around the equator at site hy04 alkenone and foraminiferal mg ca based ssts showed a large difference in the magnitude of lgm sst cooling we hypothesize that alkenone based ssts might not fully express the true magnitude of glacial sst cooling in the necc as suggested by the coincidence of higher glacial productivity and unchanged glacial ssts at site hy04 however further sst data in the necc are needed before this can be accepted with any degree of confidence

oxygen minimum zone variations in the tropical pacific during the holocene we performed simulations with a global model of ocean biogeochemistry forced with orbitally driven anomalies of oceanic conditions for the mid holocene known as holocene climate optimum to investigate natural variability in the eastern equatorial pacific oxygen minimum zone eep omz while the global mean temperature during the mid holocene was likely slightly higher than the 1961 1990 mean the sea surface temperature in the eep was slightly lower mid holocene oxygen concentrations in the eep omz are generally increased locally by up to 50 and the eep omz volume was depending on definition of the omz threshold at least 6 lower these higher oxygen levels are the combined result of competing physical and biogeochemical processes our results imply that mechanisms for past changes in the eep omz intensity and extension can differ from the global warming driven decline in oxygen levels observed for the recent decades and predicted for the future

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

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

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

millennial scale variations in hydrography and biogeochemistry in the eastern equatorial pacific over the last 100 kyr abstract in this study we use records of nitrogen isotope ratios 15n uk 37 temperature estimates organic carbon and opal percentages from high resolution sediment cores located in the eastern equatorial pacific eep to explore the mechanisms linking millennial scale changes in low latitude sea surface temperature water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100 000 yr our results support a hypothesis that the southern hemisphere and its connection to the low latitudes via shallow subsurface ocean circulation has a primary influence on the biogeochemistry of the eep in addition our results suggest that during the last glacial stage denitrification rates fluctuated on millennial timescales in response to water column ventilation rather than upstream oxidant demand in intermediate depth waters however due to the poor age constraints available for marine isotopic stage mis 3 the eep sedimentary data presented here could support two conflicting mechanisms one driven by enhanced intermediate overturning circulation in the southern ocean during heinrich events antarctic warm events implying that subsurface flow rates control thermocline ventilation and a second one consistent with more sluggish intermediate circulation during antarctic warm events and giving a central role to the temperature control on oxygen solubility in southern ocean surface waters

adjustment of the coupled ocean atmosphere system to a sudden change in the thermohaline circulation 1 the adjustment of the coupled ocean atmosphere system to a fresh water anomaly in the north atlantic ocean is investigated using a coupled gcm in response to the anomaly the atlantic thermohaline circulation thc collapses and the associated reduction in northward heat transport causes sea surface temperatures sst to fall over the north atlantic and to increase over the tropical south atlantic atmospheric feedbacks are excited as soon as the sst anomalies reach sufficient magnitude a key stage in the adjustment process occurs 4 6 years after the perturbation is introduced when a significant sst dipole develops in the tropical atlantic this dipole causes a southward shift of the itcz and leads in year 7 to the triggering of an el nino event it is concluded that atmospheric feedbacks could spread globally the influence of a sudden change in the thc much more quickly and efficiently than could ocean processes alone

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

southern ocean sea ice and frontal changes during the late quaternary and their linkages to asian summer monsoon abstract the present study documents the interactions between southern hemisphere high latitude antarctica southern ocean southern indian ocean subtropics agulhas leakage and asian summer monsoon the study uses sst and sea ice reconstructions along with diatom absolute abundances and diatom biometry from two sediment cores located at the subantarctic front saf and antarctic polar front apf in the southwest indian sector of the southern ocean sea ice records suggest the presence of the mean winter sea ice limit at around the modern apf location during mis 2 and mis 4 and episodic and unconsolidated winter sea ice far north as 43 s during lgm when the ssts were lowest higher diatom productivity and larger mean sizes of f kerguelensis and t lentiginosa recorded at the northern core site during the glacial stages suggest a northward shift of the apf a decrease in diatom productivity and sizes at the southern core site highlights stratified permanent open ocean zone pooz surface waters in response to longer sea ice presence during the glacial stages the comparative study between the records of southern hemisphere high latitude and asian summer monsoon climate variability revealed that the asian summer monsoon variability could have been more likely forced by low latitude insolation gradient changes and supported by antarctic climate changes via meridional shifts of the fronts and sea ice the past changes in the intensity of asian summer monsoon along with the southern ocean frontal variation might have influenced the southern indian ocean surface circulation by changing the agulhas leakage intensity

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

reconstruction of indian summer monsoon winds and precipitation over the past 10 000 years using equatorial pacific sst proxy records using a multiproxy reduced dimension methodology we reconstruct fields of arabian sea summer wind stress curl and indian monsoon rainfall anomalies since early holocene using sea surface temperature sst proxies mg ca and alkenones from 27 locations scattered across the equatorial pacific reconstructions of summer wind stress curl reveal positive anomalies of 30 greater than present day off the coastlines of oman and yemen at 10 ka suggesting enhanced ocean upwelling and an enhanced monsoon jet during this time positive wind stress curl anomalies in these regions continued but weakened to 12 greater than present day at 6 ka wind stress curl anomalies increased by about 8 from 6 to 4 ka but declined again until 2 ka positive anomalies in wind stress curl during the early to middle holocene are consistent with greater early holocene abundances of the upwelling indicator globigerina bulloides in the western arabian sea which accumulates most rapidly in present climates during periods of marked upwelling spatial rainfall reconstructions reveal the greatest difference in precipitation at 10 ka over the core monsoon region 20 60 greater than present day and concurrently the greatest deficit in rainfall in north east india and on the eastern side of the western ghats 10 30 less than present day specifically reconstructions for 10 ka reveal 40 60 greater rainfall than present day over northwest india these findings advance the hypothesis that teleconnections from the equatorial pacific contributed to if not accounted for greater early to middle holocene wetness over india as recorded by various e g cave lacustrine and discharge paleoclimate proxies throughout the monsoon region

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

deglacial to holocene ocean temperatures in the humboldt current system as indicated by alkenone paleothermometry the response of the humboldt current system to future global warming is uncertain here we reconstruct alkenone derived near surface temperatures from multiple cores along the peruvian coast to infer the driving mechanisms of upwelling changes for the last 20 kyr our records show a deglacial warming consistent with antarctic ice core temperatures and a mid holocene cooling which in combination with other paleoceanographic records suggest a strengthening of upwelling conditions this cooling during the globally warm mid holocene is consistent with an intensification of the walker circulation and the south eastern pacific subtropical anticyclone indicative of la nina like conditions in the tropical pacific surprisingly oxygen contents in the subsurface increased and productivity was low during the mid holocene which are at odds with la nina like conditions this suggests that the humboldt current system reacts in multiple ways to a warmer world and may even include a reversal in the present day subsurface deoxygenation

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

a deeper respired carbon pool in the glacial equatorial pacific ocean article i nfo atmospheric pco2 was approximately 80 ppm lower during the last glacial period than during pre industrial times identifying the fate of that carbon has been one of the great challenges in paleoceanography we present evidence from ten equatorial pacific ocean sediment cores to show that the deep pacific ocean likely stored more carbon during the last glacial period than the holocene the concentration of the redox sensitive metal uranium u in sediments was systematically greater during the last glacial period than during the holocene indicating more reducing conditions in glacial age sediments reconstructions of biogenic opal flux indicate that changes in u distribution were not the result of changes in biological productivity and the ensuing rain of organic carbon to the sea floor which also affects the redox conditions of the sediments together these results lead to the interpretation that bottom water in the equatorial pacific during the glacial period had significantly lower oxygen concentration than during the holocene and a correspondingly greater level of respired co2 this conclusion is supported by evidence for greater preservation of brassicasterol a biomarker produced by diatoms in glacial age sediments of the eastern equatorial pacific the presence of additional respired co2 in the glacial deep ocean would have lowered atmospheric pco2 by 1 increasing the total storage of co2 in the glacial ocean and 2 increasing ocean alkalinity following a transient carbonate dissolution event our results are consistent with recently published data from the north pacific ocean this suggests that increased carbon storage in the glacial deep pacific ocean was a basin wide phenomenon consistent with a large scale transfer of carbon to the deep ocean during glacial periods

using silicon isotopes to understand the role of the southern ocean in modern and ancient biogeochemistry and climate abstract the growth of siliceous phytoplankton mainly diatoms in the southern ocean influences the preformed nutrient inventory in the ocean on a global scale silicic acid use by diatoms and deep circulation combine to trap dissolved si in the southern ocean resulting in high levels of silica production and expansive diatom oozes in southern ocean sediments the analysis of the silicon isotope composition of biogenic silica or opal and dissolved silicic acid provide insight into the operation of the global marine silicon cycle and the role played by the southern ocean in nutrient supply and carbon drawdown both in the modern and in the past silicon isotope studies of diatoms have provided insight into the history of silica production in surface waters while the analysis of spicules from deep sea sponges has defined both the spatial and the temporal variability of silicic acid concentrations in the water column together these and other proxies reveal variations in the northward flow of southern ocean intermediate and mode waters and how changes in southern ocean productivity altered their preformed nutrient content we present a new hypothesis the silicic acid ventilation hypothesis savh to explain the geographical variation of opal based proxy records in particular the contrasting patterns of opal burial change found in the low and high latitudes by understanding the silicon isotope systematics of opal and silicic acid in the modern we will be able to use opal based proxies to reconstruct past changes in the southern ocean and so investigate its role in global carbon cycling and climate

carbon 13 in pacific deep and intermediate waters 0 370 ka implications for ocean circulation and pleistocene co2 stable isotopes in benthic foraminifera from pacific sediments are used to assess hypotheses of systematic shifts in the depth distribution of oceanic nutrients and carbon during the ice ages the carbon isotope differences between 1400 and 3200 m depth in the eastern pacific are consistently greater in glacial than interglacial maxima over the last 370 kyr this phenomenon of bottom heavy glacial nutrient distributions which boyle proposed as a cause of pleistocene co2 change occurs primarily in the 1 100 and 1 41 kyr 1 milankovitch orbital frequency bands but appears to lack a coherent 1 23 kyr 1 band related to orbital precession averaged over oxygen isotope stages glacial 13c gradients from 1400 to 3200 m depth are 0 1 greater than interglacial gradients the range of extreme shifts is somewhat larger 0 2 to 0 5 in both cases these changes in pacific 13c distributions are much smaller than observed in shorter records from the north atlantic this may be too small to be a dominant cause of atmospheric pco2 change unless current models underestimate the sensitivity of pco2 to nutrient redistributions this dampening of pacific relative to atlantic 13c depth gradient favors a north atlantic origin of the phenomenon although local variations of pacific intermediate water masses can not be excluded at present

antarctic climate signature in the greenland ice core record a numerical algorithm is applied to the greenland ice sheet project 2 gisp2 dust record from greenland to remove the abrupt changes in dust flux associated with the dansgaard oeschger d o oscillations of the last glacial period the procedure is based on the assumption that the rapid changes in dust are associated with large scale changes in atmospheric transport and implies that d o oscillations in terms of their atmospheric imprint are more symmetric in form than can be inferred from greenland temperature records after removal of the abrupt shifts the residual dejumped dust record is found to match antarctic climate variability with a temporal lag of several hundred years it is argued that such variability may reflect changes in the source region of greenland dust thought to be the deserts of eastern asia other records from this region and more globally also reveal antarctic style variability and suggest that this signal is globally pervasive this provides the potential basis for suggesting a more important role for gradual changes in triggering more abrupt transitions in the climate system

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

links between eastern equatorial pacific stratification and atmospheric co2 rise during the last deglaciation it is difficult to untangle the mixed influences of high and low latitude climate forcing in the eastern equatorial pacific eep here we test the hypothesis that the southern ocean drove change in the eep via subsurface intermediate waters during the last deglaciation we use the 18o signature of benthic foraminifera to reconstruct water density changes during the last 25 kyr at three intermediate water depths 370 m 600 m and 1000 m in the eep carbonate 18o records a combined signature of temperature and salinity and is therefore more closely related to density than temperature or salinity alone we find that benthic foraminiferal 18o values decreased first in the subsurface simultaneously with rising temperatures over antarctica and propagated up to the surface within 3 kyr the early subsurface response initiated a rapid decrease in density stratification over the upper water column as indicated by reduced 18o gradients between surface and intermediate depths stratification of the upper water column remained low through the termination with stratification minima reached during heinrich stadial 1 and the younger dryas yd synchronous with the two part deglacial rise in atmospheric co2 centennial scale shifts toward heavier 18o signatures at 370 and 600 m during the yd indicate short lived shifts in the subantarctic mode water antarctic intermediate water boundary to shallower intermediate depths we suggest that decreased density gradients during the deglaciation accelerated vertical mixing across the eep and potentially the entire south pacific subtropical gyre which enhanced co2 delivery from depth to the surface ocean and atmosphere

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

reconstructing past upwelling intensity and the seasonal dynamics of primary productivity along the peruvian coastline from mollusk shell stable isotopes 1 we present here a potential new method to evaluate past variations of the mean intensity of peruvian coastal upwelling and of the seasonal timing of phytoplankton blooms this method uses a combination of the monthly carbon and oxygen isotopic signals preserved in fossil mollusk shells and a series of corrections to extract the variations of the dissolved inorganic carbon dic 13c based on the analysis of five shell samples 85 shells in total from the southern peruvian coast we suggest that the mean coastal upwelling intensity can be determined from a linear relationship between average values of corrected shell 13c and 18o this new potential proxy would bring additional independent information valuable to interpret paleoproductivity changes reconstructed from marine sediment of the nearby continental shelf results obtained on fossil samples from the middle holocene show an increase in upwelling intensity during this period associated to a spatial reorganization of upwelling centers along the south peruvian coast at the seasonal scale corrected shell 13c enrichment indicates a phytoplankton bloom seasonal timing of phytoplankton blooms can be estimated by the lag with the annual temperature cycle reproduced by shell 18o monthly variations the results obtained with two modern shell samples indicate phytoplankton blooms occurring during summer and fall consistently with in situ productivity observations our method relies on revisited assumptions about the influence of temperature and metabolism in mollusk shell 13c we further discussed the validity of these assumptions and the potential implications for the interpretation of similar data sets

influence of growth faults on coastal fluvial systems examples from the late miocene to recent mississippi river delta abstract the details of how fluvial systems respond to spatial changes in land surface subsidence produced by active faulting remain incompletely understood here we examine the degree to which the positioning of individual channels and channel belts is affected by local maxima in subsidence associated with the hanging walls of growth faults the channel forms and faults are imaged using a seismic volume covering 1400 km2 of breton sound and barataria bay in southern louisiana usa we look at the consequences of interactions between channels channel belts and faults in late miocene to recent strata more than fifty individual channels that crossed the traces of active growth faults were examined of these channels only three appear to have been redirected by the faults there also appeared to be no systematic change in the cross sectional geometries of channels or channel belts associated with crossing a fault though the orientation of the channel belts appears to be more influenced by faulting than the orientation of individual channels seven out of ten mapped channel belts appear to have been steered by growth faults we propose that channel belts are more likely to be influenced by faults than individual channels because channel belts are longer lived features unlikely to shift their overall position before experiencing a discrete faulting event in addition the style of influence in the few cases where an individual channel is affected by a fault is different from that of larger systems while downstream of a fault channel belts generally become oriented perpendicular to fault strike the individual channels are directed along the hanging wall of the fault running parallel to the fault trace we relate this to the ratio of the length scale of fault rollover relative to the channel or channel belt width fluvial fault interactions with higher values for this ratio are more likely to be carried parallel to the fault trace than systems with lower ratio values

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

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

temperature correlations between the eastern equatorial pacific and antarctica over the past 230 000 years abstract tropical sea surface temperatures ssts warmed and cooled in step with the pleistocene ice age cycles but the mechanisms are not known it is assumed that the answer must involve radiative forcing by co2 but sst reconstructions have been too sparse for a conclusive test here i present a 230 000 yr tropical sst stack from the eastern equatorial pacific eep using two new mg ca reconstructions combined with three earlier ones the eep stack shows persistent covariation with antarctic temperature on orbital and millennial timescales indicating tight coupling between the two regions this coupling however cannot be explained solely by co2 forcing because in at least one important case the marine isotope stage mis 5e 5d glacial inception both regions cooled 5 6 5 thousand years before co2 decreased more likely their covariation was due to advection of antarctic climate signals to the eep by the ocean to explain the mis 5e 5d event and glacial inception in general the hypothesis is advanced that the cooling signal spreads globally from the northern hemisphere with an active ocean circulation first from the north atlantic to the southern ocean with a colder north atlantic deep water and then to the indian and pacific oceans with cooler antarctic deep and intermediate waters

precession forcing of productivity in the eastern equatorial pacific during the last glacial cycle abstract we present a new multi proxy reconstruction of sea surface properties spanning the last 140 ka in the images core md02 2529 located in the eastern tropical pacific ocean off costa rica spectral analysis of the records allowed us to examine the ecological imprints of orbital changes on planktic foraminiferal and coccolithophore assemblages and on the pattern of primary production in the eastern equatorial pacific north of the equatorial upwelling independent productivity reconstructions based on phyto and zooplankton assemblages show a coherent pattern dominated by orbital precession which appears to have control productivity changes recorded in the studied core over the last glacial interglacial cycle the proposed mechanism of this control invokes an atmospheric forcing associated with equatorial insolation maxima in spring and fall with a period of 20 ka faunal evidence for a stronger upper ocean mixing with enhanced nutrient supply to the euphotic zone suggests a more vigorous local atmospheric circulation and associated enlargement of the costa rica dome that influenced the core site at times of may insolation maxima the last two terminations in the studied record are associated with conspicuous changes in planktic assemblages which require additional nutrient delivery mechanisms to amplify the precession forcing our faunal and stable isotope data are in favour of the previously postulated nutrient advection via the southern ocean tunnelling operating during deglaciations

evidence for tropical south pacific climate change during the younger dryas and the bolling allerod from geochemical records of fossil tahiti corals abstract we present monthly resolved records of strontium calcium sr ca and oxygen isotope 18o ratios from well preserved fossil corals drilled during the integrated ocean drilling program iodp expedition 310 tahiti sea level and reconstruct sea surface conditions in the central tropical south pacific ocean during two time windows of the last deglaciation the two tahiti corals examined here are uranium thorium u th dated at 12 4 and 14 2 ka which correspond to the younger dryas yd cold reversal and the bolling allerod b a warming of the northern hemisphere respectively the coral sr ca records indicate that annual average sea surface temperature sst was 2 6 3 1 c lower at 12 4 ka and 1 0 1 6 c lower at 14 2 ka relative to the present with no significant changes in the amplitude of the seasonal sst cycle these cooler conditions were accompanied by seawater 18o 18osw values higher by 0 8 and 0 6 relative to the present at 12 4 and 14 2 ka respectively implying more saline conditions in the surface waters along with previously published coral sr ca records from the island cohen and hart 2004 deglacial sea surface temperatures of the western tropical pacific a new look at old coral paleoceanography 19 pa4031 doi 10 1029 2004pa001084 our new tahiti coral records suggest that a shift toward lower sst by 1 5 c occurred from 13 1 to 12 4 ka which was probably associated with a shift toward higher 18osw by 0 2 along with a previously published coral sr ca record from vanuatu correge et al 2004 interdecadal variation in the extent of south pacific tropical waters during the younger dyras event nature 428 927 929 the tahiti coral records provide new evidence for a pronounced cooling of the western to central tropical south pacific during the northern hemisphere yd event

does the trigger for abrupt climate change reside in the ocean or in the atmosphere two hypotheses have been put forward to explain the large and abrupt climate changes that punctuated glacial time one attributes such changes to reorganizations of the ocean s thermohaline circulation and the other to changes in tropical atmosphere ocean dynamics in an attempt to distinguish between these hypotheses two lines of evidence are examined the first involves the timing of the freshwater injections to the northern atlantic that have been suggested as triggers for the global impacts associated with the younger dryas and heinrich events the second has to do with evidence for precursory events associated with the heinrich ice rafted debris layers in the northern atlantic and with the abrupt dansgaard oeschger warmings recorded in the santa barbara basin

alkenone paleothermometry biological lessons from marine sediment records off western south america an empirical global core top calibration that relates the alkenone unsaturation index u k 0 37 to mean annual sst masst is statistically the same as that defined for a subarctic pacific strain of emiliania huxleyi ccmp1742 grown exponentially in batch culture under isothermal conditions although both equations have been applied widely for paleosst reconstruction uncertainty still stems from two key ecological factors variability in the details of biosynthesis among genetically distinct alkenone producing strains and impacts of nonthermal physiological growth factors on u k 0 37 new batch culture experiments with ccmp1742 here reveal that u k 0 37 diverge systematically from the core top calibration in response to nutrient depletion and light deprivation two physiological stresses experienced by phytoplankton populations in the real ocean other aspects of alkenone alkenoate composition also respond to these stresses and may serve as signatures of such effects providing an opportunity to detect understand and potentially correct for such impacts on the geologic record a test case documents that sediments from the southeast pacific display the alkenone alkenoate compositional signature characteristic of cells physiologically stressed by light deprivation such an observation could be explained if marine snow provided a major vector of sedimentation for these biomarkers late pleistocene u k 0 37 records in the southeast pacific yield plausible paleotemperature histories of ice age cooling but ice age alkenone alkenoate signatures fall outside the range of modern calibration samples of similar u k 0 37 they better match core top samples deposited beneath waters characterized by much cooler masst suggesting key features of ice age ecology for alkenone producing haptophytes were different from today and that the u k 0 37 index taken alone may misgauge the total range of ice age cooling at these locations analysis of the full spectrum of alkenone alkenoate compositions preserved in sediments opens up a new opportunity that may improve the accuracy of paleotemperature estimates based on simple u k 0

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

improving mixing length scale for stable boundary layers we intend to improve the z less mixing length scale for parametrization of turbulence in the stable atmospheric boundary layers sabl since the sabl structures are far from being fully understood today their parametrizations or explicit treatment are still usually very sketchy in most mesoscale and climate models typically an over diffusion through the sabl occurs in most numerical models with the z less mixing length scale proposed here the over diffusion is absent in particular the mesoscale model used gave results similar to those from an improved calibrated prandtl model i e katabatic flow occupying the lower and more active part of the sabl developed in both models the corresponding low level jet that is embedded in the strong near surface inversion appears similar in both models certain details vary simply because of the very different nature of the models deployed the results that should be also valid for other types of sabl flows could be used in different types of numerical modelling parametrizations of the sabl further development of analytical models and data interpretation copyright 2008 royal meteorological society

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

northern and southern hemisphere controls on seasonal sea surface temperatures in the indian ocean during the last deglaciation 37 are consistently warmer than those derived from mg ca by 2 3 c except for the heinrich event 1 in addition the initial timing for the deglacial warming of alkenone sst started at 15 6 ka which lags behind that of mg ca temperatures by 2 5 kyr we argue that the discrepancy between the two sst proxies reflects seasonal differences between summer and winter rather than postdepositional processes or sedimentary biases the u k 37 sst record clearly mimics the deglacial sst trend recorded in the north atlantic region for the earlier part of the termination indicating that the early deglacial warming trend attributed to local summer temperatures was likely mediated by changes in the atlantic meridional overturning circulation at the onset of the deglaciation in contrast the glacial to interglacialsstpatternrecordedbyg rubermg ca probably reflectscoldseasonssts this indicates that the cold season ssts was likely mediated by climate changes in the southern hemisphere as it closely tracks the antarctic timing of deglaciation therefore our study reveals that the tropical southwestern indian ocean seasonal sst was closely linked to climate changes occurring in both hemispheres the austral summer and winter recorded by each proxy is further supported with seasonal sst trends modeled by atmosphere ocean general circulation models for our core site our interpretation that the alkenone and mg ca ssts are seasonally biased may also explain similar proxy mismatches observed in other tropical regions at the onset of the last termination

global temperature calibration of the alkenone unsaturation index uk 37 in surface waters and comparison with surface sediments in this paper we compile the current surface seawater c37 alkenone unsaturation uk 37 measurements n 629 1 to 30 c temperature range to derive a global field based calibration of uk 37 with alkenone production temperature a single nonlinear global surface water calibration of uk 37 accurately predicts alkenone production temperatures over the diversity of modern day oceanic environments and alkenone synthesizing populations t 0 957 54 293 uk 37 52 894 uk 37 2 28 321 uk 37 3 r2 0 97 n 567 the mean standard error of estimation is 1 2 c with insignificant bias in estimated production temperature among the different ocean regions sampled an exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients e g the brazil malvinas confluence in contrast to the surface water data the calibration of uk 37 in surface sediments with overlying annual mean sea surface temperature anno is best fit by a linear model anno 29 876 uk 37 1 334 r2 0 97 n 592 the standard error of estimation 1 1 c is similar to that of the surface water production calibration but a higher degree of bias is observed among the regional data sets the sediment calibration differs significantly from the surface water calibration uk 37 in surface sediments is consistently higher than that predicted from anno and the surface water production temperature calibration and the magnitude of the offset increases as the surface water anno decreases we apply the global production temperature calibration to the coretop uk 37 data to estimate the coretop alkenone integrated production temperature coretop ipt and compare this with the overlying annual mean sea surface temperature anno we use simple models to explore the possible causes of the deviation observed between the coretop temperature signal as estimated by uk 37 and anno our results indicate that the deviation can best be explained if seasonality in production and or thermocline production as well as differential degradation of 37 3 and 37 2 alkenones both affect the sedimentary alkenone signal

oxygen 18 16 variability in greenland snow and ice with 10 3 to 105 year time resolution the 3 km long greenland ice sheet project 2 gisp2 ice core presents a 100 000 year detailed oxygen isotope profile covering almost a full glacial interglacial cycle measuranents of isotopic fluctuations in snow frost and atmospheric water vapor samples collected during summer field seasons up to 20 0 are compatible with the large and abrupt 80 160 changes observed in accumulated tim snow pit 15 80 profiles from the gisp2 summit area however show rapid smoothing of the 180 160 signal near the surface beyond about 2 m depth the smoothedi5180 signal is fairly well preserved and can be interpreted in terms of average local weather conditions and climate the longer climate fluctuations also have regional and often global significance in the older part of the record corresponding to marine isotope stages mis 5a to 5d the effect of orbital climate forcing via the 19 and 23 kyr precession cycles and the 41 kyr obliquity cycle is obvious from the end ofmis 5a at about 75 000 years b p till the end of the glacial at the younger dryas preboreal transition at 11 650 years b p the o180 160 record shows frequent rapid switches between intermediate interstadial and low stadial values fourier spectra of the oscillations that are superimposed on the orbitally induced changes contain a strong periodicity at 1 5 kyr a broad peak at 4 0 kyr and additional shorter periods detailed comparison of the gisp2 180 160 record with the vostok antarctica 15d record pacific ocean foraminiferal 180 160 grande pile france tree pollen and insolation indicates that a counterpart to many of the rapid 180 160 fluctuations of gisp2 can be found in the other records and that the gisp2 isotopic changes clearly are the local expression of climate changes of worldwide extent correlation of events on the independent gisp2 and specmap time scales for the interval 10 000 50 000 years b p shows excellent chronometric agreement except possibly for the event labeled 3 1 the glacial to interglacial transition evidently started simultaneously in the arctic and the antarctic but its development and its expression in greenland isotopes was later suppressed by the influence of meltwater especially from the barents sea ice sheet on deep water formation and ocean circulation meltwaters from different ice sheets bordering the north atlantic also influenced ocean circulation during the bolling allerod interstadial complex and the younger dryas and led to a distinct development of european climate and greenland 180 160 values the holocene interval with long term stable mean isotopic values contains several fluauations with periods from years to millennia dominant is a 6 3 year oscillation with amplitude up to 3 to 4 0 periodicities of 11 and 210 years also found in the solar modulated records of the cosmogenic isotopes 1obe and 14c suggest solar processes as the cause of these cycles depression of180 160 values cooling by volcanic eruptions is observed in stacked gisp215 80 records but the effect is small and not likely to trigger major climate changes

southern ocean contributions to the eastern equatorial pacific heat content during the holocene abstract temperature reconstructions from a shallow core 375 m from the peru margin are used to test the influence of subantarctic mode water samw on the eastern equatorial pacific eep thermostad and thus the effect of southern high latitude climate on interior ocean heat content ohc temperature estimates based on mg ca measurements of planktonic and benthic foraminifera neogloboquadrina dutertrei and uvigerina spp respectively show higher temperatures in the early holocene a cooling of 2 by 8 kyr b p and after relatively stable temperatures to the present the temperature signal is similar in direction and timing to a rather robust holocene climate signal from the southern high latitudes suggesting it originated there and was advected to the core site in the eep based on the n dutertrei and uvigerina mg ca temperature and 13c records we conclude that samw acted as a conduit transporting the southern high latitude climate to the interior of the equatorial pacific we propose that the early holocene warmth is related to a southward migration of the subtropical front which enhanced the influence of warm subtropical water in the region of samw formation and was then transported to the eep thermostad the early holocene warmth recorded in the eep thermostad has a muted sea surface temperature expression indicating this mechanism is important for sequestering heat in the ocean interior

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

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

high latitude influence on the eastern equatorial pacific climate in the early pleistocene epoch many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr orbital precession and 100 kyr during the past 0 5 myr refs 1 5 whereas high latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr ref 6 little is known however about tropical climate variability before the mid pleistocene transition about 900 kyr ago which marks the change from a climate dominated by 41 kyr cycles7 when ice age cycles and high latitude sea surface temperature variations were dictated by changes in the earth s obliquity8 9 to the more recent 100 kyr cycles of ice ages here we analyse alkenones from marine sediments in the eastern equatorial pacific ocean to reconstruct sea surface temperatures and marine productivity over the past 1 8 myr we find that both records are dominated by the 41 kyr obliquity cycles between 1 8 and 1 2 myr ago with a relatively small contribution from orbital precession and that early pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial pacific ocean we conclude that during the early pleistocene epoch climate variability at our study site must have been determined by high latitude processes that were driven by orbital obliquity forcing

reduced dimension reconstruction of the equatorial pacific sst and zonal wind fields over the past 10 000 years using mg ca and alkenone records we develop a multiproxy reduced dimension methodology to blend magnesium calcium mg ca and alkenone u 37k paleo sea surface temperature sst records from the eastern and western equatorial pacific to recreate snapshots of full field ssts and zonal winds from 10 to 2 ka b p in 2000 year increments single proxy reconstructions mg ca only versus u 37k only reveal differences in the timing and duration of maximum cooling across the east central equatorial pacific the largest zonal temperature differences average west pacific sst minus average east pacific sst occur at 6 ka b p for the mg ca only reconstruction 0 61 c and at 10 and 4 ka for the u 37k only reconstruction 0 55 c and 0 47 c respectively disagreements between sst trends suggested by each proxy call for methods that can resolve the common patterns between each and have motivated the work presented in this study in combining inferences from these proxies we treat both mg ca and u 37k reconstructions of sst as annual average values but we recognize that they may be sensitive to different seasons in the multiproxy reconstruction the zonal sst difference is largest at 10 ka 0 26 c with coldest sst anomalies of 0 9 c in the eastern equatorial pacific and concurrent easterly maximum zonal wind anomalies of 7 m s 1 throughout the central pacific from 10 to 2 ka the entire equatorial pacific warms but at a faster rate in the east than the west and the average central pacific easterly winds weaken gradually to approximately 2 m s 1 these patterns are broadly consistent with previous inferences of reduced el nino southern oscillation variability associated with a la nina like state during the early to middle holocene

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

a record of atmospheric co2 during the last 40 000 years from the siple dome antarctica ice core 1 we have measured the co2 concentration of air occluded during the last 40 000 years in the deep siple dome a hereafter siple dome ice core antarctica the general trend of co2 concentration from siple dome ice follows the temperature inferred from the isotopic composition of the ice and is mostly in agreement with other antarctic ice core co2 records co2 rose initially at 17 5 kyr b p thousand years before 1950 decreased slowly during the antarctic cold reversal rose during the younger dryas fell to a local minimum at around 8 kyr b p and rose continuously since then the co2 concentration never reached steady state during the holocene as also found in the taylor dome and epica dome c hereafter dome c records during the last glacial termination a lag of co2 versus siple dome isotopic temperature is probable the siple dome co2 concentrations during the last glacial termination and in the holocene are at certain times greater than in other antarctic ice cores by up to 20 ppm mol co2 mol air while in situ production of co2 is one possible cause of the sporadic elevated levels the mechanism leading to the enrichment is not yet clear

sediment focusing in the panama basin eastern equatorial pacific ocean abstract age model derived sediment mass accumulation rates mars are consistently higher than 230th normalized mars in the equatorial pacific ocean during the past 25 ka the offset being highest in the panama basin suggests a significant role for deep sea sediment redistribution i e sediment focusing in this region here we test the hypothesis that downslope transport of sediments from topographically high regions that surround the panama basin is the cause of higher than expected xs230th inventories over the past 25 ka in the deeper parts of the basin we find little difference in xs230th inventories between the highest and lowest reaches of the basin furthermore there is no correlation between xs230th derived sediment focusing factors and water depth which suggests that the topographic highs do not serve as a source of xs230th a spatial analysis suggests that there may be an enhanced scavenging effect on xs230th concentrations in sediment closest to the equator where productivity is the highest although further data is necessary to corroborate this at the equator xs230th derived focusing factors are high and range from about 1 to 5 during the holocene and about 1 to 11 during the last glacial in contrast non equatorial cores show a smaller range in variability from about 0 7 to 2 8 during the holocene and from 0 7 to 3 6 during the last glacial based on 232th flux measurements we hypothesize that the location at which eolian detrital fluxes surpass the riverine detrital fluxes is approximately 300 km from the margin while riverine fluxes from coastal margins were higher during the holocene eolian fluxes were higher during the last glacial

enso suppression due to weakening of the north atlantic thermohaline circulation changes of the north atlantic thermohaline circulation thc excite wave patterns that readjust the thermocline globally this paper examines the impact of a freshwater induced thc shutdown on the depth of the pacific thermocline and its subsequent modification of the el nino southern oscillation enso variability using an intermediate complexity global coupled atmosphere ocean sea ice model and an intermediate enso model respectively it is shown by performing a numerical eigenanalysis and transient simulations that a thc shutdown in the north atlantic goes along with reduced enso variability because of a deepening of the zonal mean tropical pacific thermocline a transient simulation also exhibits abrupt changes of enso behavior depending on the rate of thc change the global oceanic wave adjustment mechanism is shown to play a key role also on multidecadal time scales simulated multidecadal global sea surface temperature sst patterns show a large degree of similarity with previous climate reconstructions suggesting that the observed pan oceanic variability on these time scales is brought about by oceanic waves and by atmospheric teleconnections

timing of millennial scale climate change in antarctica and greenland during the last glacial period a precise relative chronology for greenland and west antarctic paleotemperature is extended to 90 000 years ago based on correlation of atmospheric methane records from the greenland ice sheet project 2 and byrd ice cores over this period the onset of seven major millennial scale warmings in antarctica preceded the onset of greenland warmings by 1500 to 3000 years in general antarctic temperatures increased gradually while greenland temperatures were decreasing or constant and the termination of antarctic warming was apparently coincident with the onset of rapid warming in greenland this pattern provides further evidence for the operation of a bipolar see saw in air temperatures and an oceanic teleconnection between the hemispheres on millennial time scales

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

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

assessing divergent sst behavior during the last 21 ka derived from alkenones and g ruber mg ca in the equatorial pacific equatorial pacific sst reconstructions derived from mg ca ratios in planktonic foraminifera globigerinoides ruber and from alkenone producing coccolithophorids record different trends throughout the holocene and the last deglaciation we set forth the hypothesis that their diverging behavior may be related to different seasonal sensitivities which result from the annually varying production rates of alkenone producing coccolithophorids and of g ruber using a series of transient paleoclimate model simulations forced with the time varying forcing history over the last 21 ka a good qualitative agreement is found between simulated boreal winter temperatures and alkenone sst reconstructions as well as between simulated boreal summer temperatures and reconstructed mg ca based sst variations pronounced features in the reconstructions that can be readily explained by the conjectured seasonal biases include the mismatch in middle to late holocene temperature trends and the different onsets of deglacial climate change in the eastern equatorial pacific the analysis presented here further suggests that through combinations of mg ca and alkenone sst reconstructions information can be gained on annual mean temperature changes and the amplitude of the seasonal cycle in sst our study concludes by discussing potential weaknesses of the proposed model derived seasonal bias interpretation of tropical pacific sst proxies in terms of present day core top data sediment trap studies and satellite based observations of chlorophyll

linking holocene drying trends from lonar lake in monsoonal central india to north atlantic cooling events abstract we present the results of biogeochemical and mineralogical analyses on a sediment core that covers the holocene sedimentation history of the climatically sensitive closed saline and alkaline lonar lake in the core monsoon zone in central india we compare our results of c n ratios stable carbon and nitrogen isotopes grain size as well as amino acid derived degradation proxies with climatically sensitive proxies of other records from south asia and the north atlantic region the comparison reveals some more or less contemporaneous climate shifts at lonar lake a general long term climate transition from wet conditions during the early holocene to drier conditions during the late holocene delineating the insolation curve can be reconstructed in addition to the previously identified periods of prolonged drought during 4 6 3 9 and 2 0 0 6 cal ka that have been attributed to temperature changes in the indo pacific warm pool several additional phases of shorter term climate alteration superimposed upon the general climate trend can be identified these correlate with cold phases in the north atlantic region the most pronounced climate deteriorations indicated by our data occurred during 6 2 5 2 4 6 3 9 and 2 0 0 6 cal ka bp the strong dry phase between 4 6 and 3 9 cal ka bp at lonar lake corroborates the hypothesis that severe climate deterioration contributed to the decline of the indus civilisation about 3 9 ka bp

subtropical north atlantic temperatures 60 000 to 30 000 years ago a reconstruction of sea surface temperature based on alkenone unsaturation ratios in sediments of the bermuda rise provides a detailed record of subtropical climate from 60 000 to 30 000 years ago northern sargasso sea temperatures changed repeatedly by 2 to 5 c covarying with high latitude temperatures that were previously inferred from greenland ice cores the largest temperature increases were comparable in magnitude to the full glacial holocene warming at the site abrupt cold reversals of 3 to 5 c lasting less than 250 years occurred during the onset of two such events greenland interstadials 8 and 12 suggesting that the largest most rapid warmings were especially unstable