the evolution of oceanic and atmospheric anomalies in the northeast pacific during the el nino and la nina events of 1995 2001 abstract from late 1995 through early 2001 three major interannual climate events occurred in the tropical pacific the 1995 97 la nina ln 1997 98 el nino en and 1998 2001 ln we analyze atmospheric and upper oceanic anomalies in the northeast pacific nep during these events and compare them to anomalies both elsewhere in the north and tropical pacific and to typical en and ln anomaly patterns the atmospheric and oceanic anomalies varied strongly on intraseasonal and interannual scales during the 1995 97 ln and 1997 98 en the northeast pacific was dominated by negative slp and cyclonic wind anomalies and by upper ocean temperature and sea surface height ssh anomalies the latter were positive along the north american west coast and in the nep thermal anomaly pool between hawaii vancouver island and baja california and negative in the central north pacific this atmospheric oceanic anomaly pattern is typical of en an eastward shift in the atmospheric teleconnection from east asia created en like anomalies in the nep during the 1995 97 ln well before the 1997 98 en had begun the persistence of negative sea level pressure slp and cyclonic wind anomalies in the nep during the 1997 98 en intensified pre existing upper oceanic anomalies atmospheric anomalies were shifted eastward during late 1996 early 1998 leading to a similar onshore shift of oceanic anomalies this produced exceptionally strong positive upper ocean temperature and ssh anomalies along the west coast during the 1997 98 en and explains the unusual coastal occurrences of several species of large pelagic warm water fishes the growth and eastward shift of these pre existing anomalies does not appear to have been linked to tropical pacific en anomalies until late 1997 when a clear atmospheric teleconnection between the two regions developed prior to this remote atmospheric impacts on the nep were primarily from east asia as the 1998 2001 ln developed nep anomalies began reversing toward the typical ln pattern this led to predominantly negative slp and cyclonic wind anomalies in the nep and upper ocean temperature and ssh anomalies that were mainly negative along the west coast and positive in the central north pacific the persistence of these anomalies into mid 2001 and a number of concurrent biological changes in the nep suggest that a decadal climate shift may have occurred in late 1998 during 1995 2001 nep oceanic anomalies tracked the overlying atmospheric anomalies as indicated by the maintenance of a characteristic spatial relationship between these anomalies in particular wind stress curl and ssh anomalies in the nep maintained an inverse relationship that strengthened and shifted eastward toward the west coast during late 1996 early 1998 this consistent relationship indicates that anomalous ekman transport driven by regional atmospheric forcing was an important contributor to temperature and ssh anomalies in the nep and ccs during the 1997 98 en other studies have shown that coastal propagations originating from the tropical pacific also may have contributed to coastal nep anomalies during this en our results indicate that at least some of this coastal anomaly signal may have been generated by regional atmospheric forcing within the nep

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

mid holocene el nino southern oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments holocene reconstructions of the el nino southern oscillation enso provide valuable perspective on its recent evolution and can be important for assessing its future optimal assessment of past enso variability requires observations from its center of action in the eastern equatorial pacific but these are limited due to paucity of high resolution paleoceanographic archives e g corals here we use a new approach to quantify past enso variance based on the oxygen isotopic composition 18 o of individual foraminifera globigerinoides ruber from deep sea sediments in the enso source region individual g ruber foraminifera behave as monthly recorders of sea surface conditions including enso extremes circumventing the lack of annual resolution in the sediments intrapopulation 18 o distributions derived with this method from a core near the galapagos islands reveal mid holocene reductions in variance of 50 requiring drastic attenuation of the enso amplitude furthermore mg ca thermometry indicates that mid holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward displaced intertropical convergence zone itcz the results suggest that the position of the itcz is an important factor in the low frequency modulation of enso and could influence its future evolution

1 500 year cycle in the arctic oscillation identified in holocene arctic sea ice drift decadal to centennial scale variability has been identified in the arctic oscillation but less is known about variations on the millennial scale a record of sea ice drift from off the alaskan coast shows a 1 500 year cycle in the phase of the arctic oscillation

the control of the tropical north atlantic on holocene millennial climate oscillations changes in ocean dynamics in the northern north atlantic affect the thermohaline circulation that controls global climate during glacial and deglaciation periods these dynamics are enhanced due to large variations in the surface ocean density caused by changes in glacier volumes during full interglacial conditions the dominant role of the northern north atlantic on global climate is limited due to the reduced discharge of freshwater to the ocean causing other regional dynamics to gain importance here we present a speleothem 18 o record from the iberian peninsula that supports that the northern north atlantic and tropical north atlantic were both source regions of millennial climate oscillations during the holocene the speleothem 18 o signal records millennial time scale changes in the hydrological cycle as a result of persistent anomalies of the gulf stream north atlantic current dynamics in addition the speleothem 18 o record shows synchronous variability with records from the eastern pacific region though the entire holocene whereas records from western pacific region have limited or no correlation beyond periods of major instability of the northern north atlantic the discontinuous climate connection among the studied records is the result of different mechanisms affecting the climate system that originated in distant regions we suggest that two regions the tropical north atlantic and northern north atlantic alternate their dominance as source regions causing millennial climate anomalies in large planetary regions the duration of these persistent climate changes and the extension of the regions affected depend on the region triggering the anomaly because different mechanisms affecting the climate system are involved

assessing the impact of mid holocene insolation on the atmosphere ocean system a sequence of numerical simulations was performed in order to assess the role of early to mid holocene orbital forcing on the coupled atmosphere ocean system results from both an atmosphere only general circulation model gcm forced by specified sea surface temperatures and a coupled atmosphere ocean gcm consistently suggest a stronger south asian monsoon and a strengthened pacific walker circulation the latter feature interacts dynamically with the equatorial ocean in the coupled model to produce enhanced pacific upwelling a more pronounced cold tongue and an even stronger monsoon results suggest that the climate of the equatorial pacific was more similar to the la nina phase of the modern southern oscillation rather than the el niiio phase

response of diatom and silicoflagellate assemblages in the central gulf of california to regional climate change during the past 55 kyrs abstract high resolution studies of diatoms and silicoflagellates of the past 55 kyrs in cores md02 2517 2515 from the central gulf of california goc reveal profound changes in goc surface waters roperia tesselata a diatom proxy for late winter early spring upwelling and dictyocha stapedia a subtropical silicoflagellate indicative of goc sea surface temperatures ssts 24 c are common during the holocene but rare during marine isotope stage mis 2 and most of mis 3 a relationship that likely reflects a more northerly position of the north pacific high nph during the holocene in contrast during most of mis 2 27 15 ka the persistent presence of distephanus speculum a silicoflagellate associated with ssts during mis 3 55 27 ka increased dominance of azpeitia nodulifera diatom implies that stratified tropical waters were present year round whereas silicoflagellate assemblages suggest that stratified tropical conditions alternated with more productive upwelling conditions on millennial timescales reduced biosiliceous productivity during heinrich events likely reflected a reduction in both surface water nutrient levels and in the strength of northwest winds due to a weakened and more southerly nph conversely enhanced biosiliceous productivity during mis 3 interstadials was probably linked to heightened nutrient levels and a strengthened nph abrupt relative abundance increases of the silicoflagellate dictyocha aculeata approximate the termination of mis3 heinrich events and may signal times when nutrient rich deep waters associated with the resumption of enhanced atlantic meridional overturning circulation penetrated into the central gulf

ocean atmosphere forcing of centennial hydroclimate variability in the pacific northwest reconstructing centennial timescale hydroclimate variability during the late holocene is critically important for understanding large scale patterns of drought and their relationship with climate dynamics we present sediment oxygen isotope records spanning the last two millennia from 10 lakes as well as climate model simulations indicating that the little ice age was dry relative to the medieval climate anomaly in much of the pacific northwest of north america this pattern is consistent with observed associations between the el nino southern oscillation enso the northern annular mode and drought as well as with proxy based reconstructions of pacific and atlantic ocean atmosphere variations over the past 1000 years the large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer term shifts in enso like dynamics and that an improved understanding of the centennial timescale relationship between external forcing and drought is necessary for projecting future hydroclimatic conditions in western north america

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

a review of holocene solar linked climatic variation on centennial to millennial timescales physical processes interpretative frameworks and a new multiple cross wavelet transform algorithm article i nfo wereportontheexistenceandnature of holocene solar andclimaticvariationson centennialto millennial time scales we introduce a new solar activity proxy based on nitrate no3 concentration from the talos dome ice core east antarctica we also use a new algorithm for computing multiple cross wavelet spectra in time fre quency space that is generalized for multiple time series beyond two our results provide a new interpretive framework for relating holocene solaractivity variations on centennial to millennial timescales to co varying cli mate proxies drawn from a widespread area around the globe climatic proxies used represent variation in the north atlantic ocean western pacific warm pool southern ocean and the east asian monsoon regions our wavelet analysis identifies fundamental solar modes at 2300 yr hallstattzeit 1000 yr eddy and 500 yr unnamed periodicities leaves open the possibility that the 1500 1800 yr cycle may either be fundamental or derived and identifies intermediary derived cycles at 700 yr and 300 yr that may mark rectified responses of the atlantic thermohaline circulation to external solar modulation and pacing dating uncertainties suggest that the 1500 yr and 1800 yr cycles described in the literature may represent either the same or two separate cycles but in either case and irrespective too of whether it is a fundamental or derived mode in the sense of dima and lohmann 2009 the 1500 1800 yr periodicity is widely represented in a large number of paleoclimate proxy records it is obviously premature to reject possible links between changing solar activity at these multiple scales and the variations that are commonly observed in paleoclimatic records

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

dynamical response of the tropical pacific ocean to solar forcing during the early holocene we present a high resolution magnesium calcium proxy record of holocene sea surface temperature sst from off the west coast of baja california sur mexico a region where interannual sst variability is dominated today by the influence of the el nino southern oscillation enso temperatures were lowest during the early to middle holocene consistent with documented eastern equatorial pacific cooling and numerical model simulations of orbital forcing into a la nina like state at that time the early holocene ssts were also characterized by millennial scale fluctuations that correlate with cosmogenic nuclide proxies of solar variability with inferred solar minima corresponding to el nino like warm conditions in apparent agreement with the theoretical ocean dynamical thermostat response of enso to exogenous radiative forcing

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

large variations in holocene solar activity constraints from 10be in the greenland ice core project ice core 1 cosmogenic radionuclides extracted from ice cores hold a unique potential for reconstructing past solar activity changes beyond the direct instrumental period taking the geomagnetic modulation into account the solar activity in terms of the heliospheric modulation function can quantitatively be reconstructed in high resolution throughout the holocene for this period our results reveal changes in heliospheric modulation of galactic cosmic rays significantly larger than the variations reconstructed on the basis of neutron monitor measurements of galactic cosmic rays for the last 50 years moreover the 10be data from the greenland ice core project ice core as well as 14c support a high current solar activity however although the reconstruction of solar activity on long timescales is difficult our result suggests that the modern activity state of the sun is not that exceptional regarding the entire holocene this extended solar activity record provides the basis for further detailed investigations on solar and cosmic ray physics as well as on solar forcing of the earth s climate whose importance is suggested by increasing paleoclimatic evidences

changes in el nino southern oscillation enso conditions during the greenland stadial 1 gs 1 chronozone revealed by new zealand tree rings the warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in greenland greenland stadial 1 or gs 1 and europe younger dryas stadial or yd this reversal to glacial like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain whilst the wider atlantic region has a network of high resolution proxy records spanning gs 1 the pacific ocean suffers from a scarcity of sub decadally resolved sequences here we report the results from an investigation into a tree ring chronology from northern new zealand aimed at addressing the paucity of data the conifer tree species kauri agathis australis is known from contemporary studies to be sensitive to regional climate changes an analysis of a historic 452 year kauri chronology confirms a tropical pacific teleconnection via the el nino southern oscillation enso we then focus our study on a 1010 year sub fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring width downturn between 12 500 and 12 380 cal bp within gs 1 wavelet analysis shows a marked increase in enso like periodicities occurring after the downturn event comparison to low and mid latitude pacific records suggests a coherency with enso and southern hemisphere atmospheric circulation change during this period the driver s for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and or increased expression of enso across the mid latitudes of the pacific seemingly independent of the atlantic and polar regions

seasonal variability in the δ18o and δ13c of planktonic foraminifera from an upwelling environment sediment trap results from the san pedro basin southern california bight stable isotopic analyses 18o and 13crpar on four species of planktonic foraminifera collected from high resolution time series sediment trap sampling indicate that rapid and significant seasonal variability occurred in response to rapid changes in both the hydrographic environment and the isotopic composition of ambient seawater specimens were collected at a depth of 500 m for 28 consecutive 1 week periods in the san pedro basin within the southern california bight a region seasonally influenced by upwelling hydrographic monitoring of the study area revealed a 6 week period late april to mid june during which pulses of upwelling occurred causing significant increases in the oxygen isotopic composition of surrounding waters while decreasing the carbon isotopic composition analyses of globigerina bulloides orbulina universa neogloboquadrina dutertrei and neogloboquadrina pachyderma right coiling indicate that during the upwelling period these species live respectively at the surface in the surface mixed layer within the thermocline and below the thermocline globigerina bulloides ascends from well below the thermocline to the surface at the onset of upwelling and increases production to its maximum simultaneously as its morphology changes to less calcified open forms both n dutertrei and n pachyderma follow isothermal ranges migrating to shallower waters during upwelling and subsequently descending after upwelling ceases neogloboquadrina dutertrei appears to inhabit the region associated with both the thermocline base and chlorophyll maximum when it is most abundant following upwelling orbulina universa increases its depth habitat as solar irradiance increases but this species decreases in abundance during upwelling the 18o signal of o universa appears to be a useful indicator of seasonal temperature variations above the thermocline whereas the 18o of g bulloides documents near surface temperatures during upwelling the 13c signal of both n dutertrei and n pachyderma appears to record the 13c of equilibrium calcite for the regions of the thermocline and just below the thermocline respectively due to the relative preservation potentials of the four species analyzed only n dutertrei and n pachyderma are likely to be preserved in the sedimentary record in regions of oxygenated bottom waters thus an actual record of hydrographic conditions during upwelling as would be found in tests of g bulloides is not preserved instead conditions before n pachyderma and just after n dutertrei are more likely recorded

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

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

millennial to centennial scale climate periodicities and forcing mechanisms in the westernmost mediterranean for the past 20 000 yr abstract cyclostratigraphic analysis conducted on a continuous high resolution marine record from the western most mediterranean reveals well identified paleoclimate cycles for the last 20 000 yr the detrital proxies used si al ti al zr al mg al k al rb al are related to different sediment transport mechanisms including eolian dust and fluvial runoff which involve fluctuations in the atmosphere hydrosphere systems these fluctuations are accompanied by changes in marine productivity supported by ba al and bottom water redox conditions cu al v al zn al fe al mn al u th spectral analysis conducted using the lomb scargle periodogram and the achieved significance level implemented with the permutation test allowed us to establish major periodicities at 1300 1515 2000 and 5000 yr and secondary peaks at 650 1087 and 3000 yr some of these cycles also agree with those previously described in the north atlantic ocean and circum mediterranean records the periodicities obtained at 2000 and 5000 yr support a global connection with records distributed at high mid and low latitudes associated with solar activity monsoonal regime and orbital forcing the 1300 and 1515 yr cycles appear to be linked with north atlantic climate variability and the african monsoon system thus the analyzed record provides evidence of climate cycles and plausible forcing mechanisms coupled with ocean atmosphere fluctuations

early holocene multi centennial moisture change reconstructed from lithology grain size and chemical composition data in the eastern mu us desert and potential driving forces abstract the sequence of paleo aeolian sands and sandy paleosols from the shenmu section in the eastern mu us desert was used to reconstruct the history of moisture change during the early holocene analyses of lithologies grain size distributions and elemental compositions revealed that the early holocene climate in the eastern mu us desert experienced at least seven multi centennial oscillations between humid and arid episodes four humid episodes occurred at 10 800 to 10 200 cal calendar yr bp 9800 to 9400 cal yr bp 8900 to 8300 cal yr bp and 8000 to 7700 cal yr bp three arid episodes occurred at 10 200 to 9800 cal yr bp 9400 to 8900 cal yr bp and 8300 to 8000 cal yr bp these humid arid oscillations were representative of multi centennial fluctuations in the history of waxing and waning of the east asian summer monsoon easm and the east asian winter monsoon eawm in the eastern margin of the mu us desert comparisons with other climate records based on pollen based annual precipitation pann reconstructed from gonghai lake and the stalagmite 18 o records from dongge cave southern china supported certain influences of the indian summer monsoon on moisture variations in the eastern margin of the mu us desert our results also revealed a possible climatic connection between the variability of the east asian winter monsoons and air temperature changes at high latitudes in the northern hemisphere and north atlantic thermohaline circulation during the early holocene the similarity between early holocene climate evolution in the eastern mu us desert and several proxies 14 c residuals sunspot numbers spectral analysis of grain size and elemental compositions supports the hypothesis that variations in solar insolation are a major external force responsible for east asian monsoon variations at the multi centennial scale during the early holocene

provenance study of the holocene sediments in the changjiang yangtze river estuary and inner shelf of the east china sea abstract the source to sink process of terrigenous sediment from east asia continent to the marginal seas is crucial for the understanding of land ocean interaction and marine sedimentary process in the west pacific continental margin this paper presents element geochemical and sr nd isotopic records of core cm97 in the changjiang yangtze river estuary and core md06 3040 on the inner shelf of east china sea aiming to reconstruct the changjiang sediment source to sink transport process and its major controlling mechanism during the holocene driven by the asynchronous evolution of the indian and east asian summer monsoon the provenance of sediments accumulated in the changjiang estuary gradually changed from the upper catchment during the late glacial period to the mid lower valley in the early mid holocene with the intensive agricultural cultivation and urbanization development in the catchment during the late holocene the major source of changjiang sediment into the sea shifted back to the upper catchment again the high frequency enso activity may superimpose the effect of human disturbances on sediment source to sink process in the late holocene therefore the holocene provenance evolution of changjiang sediments in the east china sea witnessed the changes of governing sediment erosion process within a large catchment from monsoon climate dominated to anthropogenic driving our study also suggests the strong effect of hydrodynamics in coastal and shelf environments on sedimentary geochemical compositions which deserves more attention in further sediment provenance study

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

solar forcing of centennial scale east asian winter monsoon variability in the mid to late holocene abstract centennial scale variability of the east asian winter monsoon during the holocene is poorly understood because suitable archives and proxies are lacking here we present a high resolution 30 yr spacing planktonic foraminiferal o 18 record of neogloboquadrina incompta dextral form which reflects sea surface temperature during the winter season for the last 6000 yrs from marine sediments in the western north pacific stronger winter monsoons indicated by cooler winter ssts correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial scale variability the variability also shows good correlation with o 18 records in lake sediments and ice cores from the yukon territory canada spanning the last 4500 yrs suggesting east west climate coupling across the north pacific furthermore the climate changes across the north pacific co vary over widespread regions such as the eastern tropical pacific and the northern red sea and the reconstructed solar activity the cross spectral and wavelet analyses show that the east asian winter monsoon shares some cyclicity with the solar variability our results suggest that the solar activity is a fundamental forcing producing the centennial scale eawm variability mediated by the large scale climate linkages

evolution of oceanographic conditions off baja california 1997 1999 abstract this paper examines the oceanic response off baja california mexico to the 1997 1998 el nino and the transition to la nina conditions the data presented were gathered during seven cruises over a grid based on the calcofi station plan from lines 100 130 out to station 80 t s diagrams with data obtained during the peak phase of el nino demonstrate that warmer and saltier spicier than normal conditions prevailed in the upper 600 m over this region temperature and salinity anomalies calculated for calcofi line 120 revealed waters near the coast at 50 m depth to be up to 8 7 c warmer and s 0 8 saltier than the climatology during october 1997 these large anomalies persisted through january 1998 with some slight diminution in the magnitudes near the surface this study suggests that anomalously warm and salty waters were fed from a source of spicy water to the southwest identified as subtropical surface water stsw and that low salinity tropical surface waters tsw were blocked to the southeast in the vicinity of the tip of the peninsula subsurface waters associated with the california undercurrent cu fed from the eastern tropical pacific etp were also warmer and saltier than normal and indicate a significant expansion in volume of the cu presumably a result of intensification of poleward flow at depth we postulate that the well defined near surface and deep poleward flows in the study area reflect anomalous large scale cyclonic circulation affecting the flow in the southeastern region of the north pacific subtropical gyre east of 125 w following the el nino event warm and salty upper waters retreated to latitudes south of punta eugenia with the return to normal and cooler conditions equatorward flow over the sampling grid predominated with an increased meandering and mesoscale activity transition to la nina conditions would have been associated with re establishment of normal anticyclonic flow in the southeastern quadrant of the pacific subtropical gyre

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

a tibetan lake sediment record of holocene indian summer monsoon variability article history sedimentological data and hydrogen isotopic measurements of leaf wax long chain n alkanes dwax from an alpine lake sediment archive on the southeastern tibetan plateau paru co provide a holocene perspective of indian summer monsoon ism activity the sedimentological data reflect variations in lake level and erosion related to local ism rainfall over the paru co catchment whereas dwax reflects integrated synoptic scale ism dynamics our results indicate that maximum ism rainfall occurred between 10 1 and 5 2 ka during which time there were five century scale high and low lake stands after 5 2 ka the ism trended toward drier conditions to the present with the exception of a pluvial event centered at 0 9 ka the paru co results share similarities with paleoclimate records from across the tibetan plateau suggesting millennial scale ism dynamics were expressed coherently these millennial variations largely track gradual decreases in orbital insolation the southward migration of the intertropical convergence zone itcz decreasing zonal pacific sea surface temperature sst gradients and cooling surface air temperatures on the tibetan plateau centennial ism and lake level variability at paru co closely track reconstructed surface air temperatures on the tibetan plateau but may also reflect indian ocean dipole events particularly during the early holocene when enso variability was attenuated variations in the latitude of the itcz during the early and late holocene also appear to have exerted an influence on centennial ism rainfall 2014 elsevier b v all rights reserved

on the preservation of laminated sediments along the western margin of north america 1 piston gravity and multicores as well as hydrographic data were collected along the pacific margin of baja california to reconstruct past variations in the intensity of the oxygen minimum zone omz gravity cores collected from within the omz north of 24 n did not contain laminated surface sediments even though bottom water oxygen bwo concentrations were close to 5 mol kg however many of the cores collected south of 24 n did contain millimeter to centimeter scale brown to black laminations in holocene and older sediments but not in sediments deposited during the last glacial maximum in addition to the dark laminations holocene sediments in soledad basin silled at 290 m also contain white coccolith laminae that probably represent individual blooms two open margin cores from 430 and 700 m depth that were selected for detailed radiocarbon dating show distinct transitions from bioturbated glacial sediment to laminated holocene sediment occurring at 12 9 and 11 5 ka respectively the transition is delayed and more gradual 11 3 10 0 ka in another dated core from soledad basin the observations indicate that bottom water oxygen concentrations dropped below a threshold for the preservation of laminations at different times or that a synchronous hydrographic change left an asynchronous sedimentary imprint due to local factors with the caveat that laminated sections should therefore not be correlated without independent age control the pattern of older sequences of laminations along the north american western margin reported by this and previous studies suggests that multiple patterns of regional productivity and ventilation prevailed over the past 60 kyr

solar forcing induced spatial synchronisation of the east asian summer monsoon on centennial timescales abstract spatial patterns in centennial scale variations of the east asian summer monsoon easm during the holocene are poorly constrained due to the lack of high resolution records with detailed chronologies especially in southern china here we present high resolution 35 yr proxy records spanning the last 7500 years from a well dated sediment core yj core from the northern inner shelf of the south china sea al ti and fe variations were employed as indicators of terrigenous influx and k al ratios were used as a tracer of chemical weathering to document variations in the intensity of the easm the results show a series of centennial scale weak easm events which are generally synchronous with those inferred from other geologic archives from monsoonal regions in the eastern and southern china moreover these events are synchronous with periods of weak solar activity and the spectral analysis demonstrates that the easm and solar activity share some general cyclicity patterns we therefore suggest that solar activity is a fundamental driving force for the spatial synchronisation of the easm on centennial timescales across the monsoon region

link between east asian summer monsoon and sedimentation in river mouth sandbars since the early holocene preserved in the yangtze river subaqueous delta front this paper presents geochemical and grain size records since the early holocene in core ecs0702 with a fine chronology frame obtained from the yangtze river subaqueous delta front since 9500 cal yr bp the proxy records of chemical weathering from the yangtze river basin generally exhibit a holocene optimum in the early holocene a weak east asian summer monsoon easm period during the middle holocene and a relatively strong easm period in the late holocene the 8 2 and 4 4 cal ka bp cooling events are recorded in core ecs0702 the flooding events reconstructed by the grain size parameters since the early holocene suggest that the floods mainly occurred during strong easm periods and the yangtze river mouth sandbar caused by the floods mainly formed in the early and late holocene the yangtze river mouth sandbars since the early holocene shifted from north to south affected by tidal currents and the coriolis force and more importantly controlled by the easm our results are of great significance for enriching both the record of holocene climate change in the yangtze river basin and knowledge about the formation and evolution progress of the deltas located in monsoon regions

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

paleotemperature variability in central china during the last 13 ka recorded by a novel microbial lipid proxy in the dajiuhu peat deposit the asian summer monsoon is a very important climatic component affecting the land ecosystem on the eastern asian continent here we assess microbe derived lipid biomarker evidence from a well date

modeling climate shift of el nino variability in the holocene a coupled ocean atmosphere general circulation model is used to investigate climatic shift of el nino in the holocene the model simulates a reduced enso intensity in the early and mid holocene in agreement with paleoclimate record the enso reduction is proposed to be caused by both an intensified asian summer monsoon and a warm water subduction from the south pacific into the equatorial thermocline

high resolution sea surface reconstructions off cape hatteras over the last 10 ka 1 this study presents high resolution foraminiferal based sea surface temperature sea surface salinity and upper water column stratification reconstructions off cape hatteras a region sensitive to atmospheric and thermohaline circulation changes associated with the gulf stream we focus on the last 10 000 years 10 ka to study the surface hydrology changes under our current climate conditions and discuss the centennial to millennial time scale variability we observed opposite evolutions between the conditions off cape hatteras and those south of iceland known today for the north atlantic oscillation pattern we interpret the temperature and salinity changes in both regions as co variation of activities of the subtropical and subpolar gyres around 8 3 ka and 5 2 3 5 ka positive salinity anomalies are reconstructed off cape hatteras we demonstrate for the 5 2 3 5 ka period that the salinity increase was caused by the cessation of the low salinity surface flow coming from the north a northward displacement of the gulf stream blocking the southbound low salinity flow concomitant to a reduced meridional overturning circulation is the most likely scenario finally wavelet transform analysis revealed a 1000 year period pacing the 18o signal over the early holocene this 1000 year frequency band is significantly coherent with the 1000 year frequency band of total solar irradiance tsi between 9 5 ka and 7 ka and both signals are in phase over the rest of the studied period

rapid sea level rise abstract several global and regional factors contribute to observed sea level change along any particular coast global processes include changes in ocean mass glacio eustasy from ice melt ocean volume steric effects viscoelastic land movements glacioisostatic adjustment gia and changes in terrestrial water storage regional processes often connected to steric and glacial changes include changes in ocean circulation meridional overturning circulation moc glacial melting local gia regional subsidence and others paleoclimate instrumental and modeling studies show that combinations of these factors can cause relatively rapid rates of sea level rise exceeding 3 mm yr 1 over various timescales along particular coasts this paper discusses patterns and causes of sea level rise with emphasis on paleoclimatological records it then addresses the hypothesis of late holocene pre 20th century sea level stability in light of paleoclimatic evidence notably from reconstructions of sea surface temperature and glacial activity for significant climate and sea level variability during this time the practical difficulties of assessing regional sea level sl patterns at submillennial timescales will be discussed using an example from the eastern united states

holocene cyclic climatic variations and the role of the pacific ocean as recorded in varved sediments from northeastern china we present an n alkane and compound specific carbon isotope record of the past 9 ka from the annually laminated sedimentary sequence of lake xiaolongwan northeastern china the n alkane distribution suggests that lake xiaolongwan has undergone a shift from an oligotrophic state with low algal production and little emergent submerged macrophytes in the early holocene to a eutrophic state with high algal production and abundant emergent submerged macrophytes since the middle holocene the pattern of variation observed in the biomarker proxies acl the n alkane average chain length paq aquatic macrophyte versus aquatic macrophyte and terrestrial plant ratio and lptp lake productivity terrigenous organic production is throughout the record similar to that of the total organic carbon the variation of compound specific carbon isotopic values in the middle and short chain alkanes was mainly regulated by lake productivity and the accumulating organic pool through time in this forested region where the vegetation is dominated by c 3 plants the long chain n alkanes c27ec31 are predominantly derived from leaf wax lipids the compound specific d 13 c27e31 value is sensitive to effective precipitation and therefore represents a useful indicator of regional monsoonal precipitation spectral analysis on the d 13 c27e31 time series reveals significant periodicities of 87e89 205e212 1020e1050 and 1750e2041 years on the centennial timescale the quasi periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall the millennial monsoon cycle in northeastern china is associated with sea surface temperature sst variations in two active centers of the summer monsoon the western pacific subtropical high wpsh and the okhotsk high increasing sst in the subtropical sea may cause a northwards shift of the wpsh which extends the monsoon rain band meiyu to northeastern china and thus increasing rainfall in that region meanwhile decreasing sst in the okhotsk sea may strengthen the okhotsk high bringing more moisture into northeastern china we suggest that the pacific ocean is a main regulator for summer monsoon rainfall in northeastern china at present and at different time scales during the holocene

a synthesis of abrupt changes in the asian summer monsoon since the last deglaciation we have compiled 36 previously published palaeoclimate records to determine the timing and spatial pattern of century scale abrupt changes in asian monsoon precipitation since the last deglaciation we identify abrupt events from 1 the interpretations of the authors of these records and 2 the more objective moving t test calculation our results indicate that abrupt climatic changes occurred at 11 5 cal ka 4 5 5 0 cal ka and ad 1300 at the start of the holocene 11 5 cal ka asian monsoon precipitation increased dramatically this climatic change is synchronous with an abrupt warming in the north atlantic during the middle holocene there was a time of preferred and widespread weakening in monsoon strength 4 5 5 0 cal ka this result contradicts previous notions of either a gradual trend towards drier conditions or a series of abrupt events that occurred in an unorganized fashion across space and time the middle holocene abrupt event could have been synchronous with an abrupt cooling event in the north atlantic as well as a warming and intensie cation of internannual variability in the tropical pacie c in contrast to previous periods precipitation changes at ad 1300 have a heterogeneous spatial pattern we e nd no conclusive evidence for a change in the asian monsoon at 8 2 cal ka as suggested by several previous studies more high resolution data may be needed to observe this short lived event overall our results attest to the potential for rapid and major shifts in asian monsoon precipitation that may be triggered by variations in other components of the climatic system

mid to late holocene organic carbon export variability at the southern boundary of the california current an approach based on diffuse spectral reflectance of marine sediment cores here we present the results obtained from diffuse spectral reflectance dsr on the visible wave spectra on a 4 5 m long calypso kasten core md02 2506 c2 collected from the san lazaro basin slb with the aim of reconstructing the mid to late holocene variability in export production in the california current system ccs we applied an r mode maximum likelihood factor analysis on the first derivative of the diffuse spectral reflectance we then compared the factor scores obtained with this method and the organic carbon oc content of the core in order to establish a statistical transfer function between both variables we eliminated high frequency noise with the aid of singular spectral analysis ssa from both records increasing the correlation between both variables r 0 71 p 0 001 these results indicated that dsr can be used as a reliable proxy of the oc content in high resolution slb sediments which we used to reconstruct past ccs organic carbon export variability our findings suggest changes in organic carbon production and export from the mid to late holocene most likely resulting from changing influences on the slb due to the interaction of the pacific decadal oscillation pdo and el nino

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

helium and methane measurements in hydrothermal fluids from the mid atlantic ridge the snake pit site at 23 n methane and helium isotopes concentrations have been measured in hydrothermal fluids of black smoker vents at the snake pit area mar 23 n as part of the hydrosnake cruise with the submersible nautile the samples contain large quantities of helium and methane with endmember values of 4 6 10 5 cm3 stp g for helium and 1 38 10 3 cm3 stp g for methane the helium isotopic ratio 3he 4he is 8 4 times the atmospheric ratio these values are strikingly similar to those already obtained on the east pacific rise the ch4 3he ratio is also quite similar ch4 3he 2 6 106 suggesting a non biogenic origin of this gas in the fluids assuming that the range of variation of the 3he concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid ocean ridges the global mass flow involved in the hydrothermal circulation at the ridge s axis is estimated between 1000 and 3000 m3 of water sec leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years this estimate implies that in addition to the individual vents smokers there is an extensive diffuse circulation of hydrothermal fluids along the ridges in agreement with recent observations concerning heat budgets at hydrothermal sites in the eastern pacific

abrupt variations in south american monsoon rainfall during the holocene based on a speleothem record from central eastern brazil well dated high resolution oxygen isotope records of speleothems in central eastern brazil spanning from 1 3 to 10 2 kyr b p reveal that the occurrence of abrupt variations in monsoon precipitation is not random they show a striking match with bond events and a significant pacing at 800 yr a dominant periodicity present in sea surface temperature records from both the north atlantic and equatorial pacific oceans that is possibly related to periods of low solar activity high 14 c based on the atmospheric 14 c record the precipitation variations over central eastern brazil are broadly antiphased with the asian and indian monsoons during bond events and show marked differences in duration and structure between the early and late holocene our results suggest that these abrupt multicentennial precipitation events are primarily linked to changes in the north atlantic meridional overturning circulation amoc anomalous cross equatorial flow induced by negative amoc phases may have modulated not only the monsoon in south america but also affected el nino like conditions in the tropical pacific during the holocene

itcz and enso like pacing of nile delta hydro geomorphology during the holocene abstract the nile valley accommodates the world s longest river and shaped the development of numerous complex societies providing a reliable source of water for farming and linking populations to sub saharan africa and the mediterranean sea its fertile delta lay at the heart of ancient egyptian civilization however little is known of its morpho sedimentary response to basin wide changes in holocene hydrology here we present two well resolved records from the nile delta based on 320 radiocarbon dates to reconstruct the timing and rhythm of catchment scale modifications during the past 8000 years on the orbital timescale we demonstrate that nilotic hydrology and sedimentation have responded to low latitude insolation forcing while on sub millennial timescales many of the major phases of deltaic modification were mediated by climate events linked to el nino southern oscillation type enso variability

response of the north american monsoon to regional changes in ocean surface temperature 1 the north american monsoon nam an onshore wind shift occurring between july and september has evolved in character during the holocene largely due to changes in northern hemisphere insolation published paleoproxy and modeling studies suggest that prior to 8000 cal years bp the nam affected a broader region than today extending westward into the mojave desert of california holocene proxy sst records from the gulf of california goc and the adjacent pacific provide constraints for this changing nam climatology prior to 8000 cal years bp lower goc ssts would not have fueled northward surges of tropical moisture up the goc which presently contribute most of the monsoon precipitation to the western nam region during the early holocene the north pacific high was further north and ssts in the california current off baja california were warmer allowing monsoonal moisture flow from the subtropical pacific to take a more direct northwesterly trajectory into an expanded area of the southwestern u s west of 114 w a new upwelling record off southwest baja california reveals that enhanced upwelling in the california current beginning at 7500 cal year bp may have triggered a change in nam climatology focusing the geographic expression of nam in the southwest usa into its modern core region east of 114 w in arizona and new mexico holocene proxy precipitation records from the southwestern u s and northwestern mexico including lakes vegetation pollen and caves are reviewed and found to be largely supportive of this hypothesis of changing holocene nam climatology

reconciling discrepancies between uk37 and mg ca reconstructions of holocene marine temperature variability significant discrepancies exist between the detrended variability of late holocene marine temperatures inferred from mg ca and uk37 proxies with the former showing substantially more centennial scale variation than the latter discrepancies exceed that attributable to differences in location and persist across various calibrations indicating that they are intrinsic to the proxy measurement we demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation sampling and measurement noise and aliasing of seasonal variability the smaller number of individual samples incorporated into mg ca measurements relative to uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability an inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions the correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high resolution records applying this inverse method to the actual mg ca and uk37 data results in estimates of the spectrum of temperature variance that are consistent this approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records

reconstruction of past climate variability and enso like fluctuations in the southern gulf of california alfonso basin since the last glacial maximum abstract nannofossil assemblages from core md02 2510 provide a 22 ka record of past oceanographic variability in alfonso basin gulf of california east subtropical pacific in this area environmental conditions depend on a monsoonal system heavily influenced by changes in the location of the itcz and nearby atmospheric pressure centers to reconstruct nutricline depth and enso like variability two ecological indexes were calculated based on the relative abundance of the three dominant coccolith species the late glacial period is characterized by intensified wind driven upwelling high primary productivity and la nina like conditions an environmental shift occurs during the glacial interglacial transition el nino like conditions intensify nutricline deepens and surface productivity declines the late holocene is characterized by a persistent increase in nutricline depth and dominance of el nino like conditions the fluctuations in the composition of the coccolith assemblages can be related to orbital scale fluctuations in the average position of the itcz however while the enso like signal that overprints the record varies in response to orbital forcing on suborbital time scales the relation between enso like conditions and the average position of the itcz and the north pacific high changes suggesting that the development of persistent el nino like conditions is strongly dependent on the specific climatic background

holocene climatic variations in the western cordillera of colombia a multiproxy high resolution record unravels the dual influence of enso and itcz abstract the paramo de frontino 3460 m elevation in colombia is located approximately halfway between the pacific and atlantic oceans it contains a 17 kyr long stratigraphically continuous sedimentary sequence dated by 30 ams 14c ages our study covers the last 11 500 cal yr and focuses on the biotic pollen and abiotic microfluorescence x or xrf components of this high mountain ecosystem the pollen record provides a proxy for temperature and humidity with a resolution of 20 35 yr and xrf of ti and fe is a proxy for rainfall with a sub annual ca 6 month resolution temperature and humidity display rapid and significant changes over the holocene the rapid transition from a cold mean annual temperature mat 3 5 c lower than today and wet younger dryas to a warm and dry early holocene is dated at 11 410 cal yr bp during the holocene mat varied from ca 2 5 c below to 3 5 above present day temperature warm periods 11 410 10 700 9700 6900 4000 2400 cal yr bp were separated by colder intervals the last 2 4 kyr of the record is affected by human impact the holocene remained dry until 7500 cal yr bp then precipitations increased to reach a maximum between 5000 and 4500 cal yr bp a rapid decrease occurred until 3500 cal yr bp and the late holocene was dry spectral analysis of xrf data show rainfall cyclicity at millennial scale throughout the holocene and at centennial down to enso scale in more specific time intervals the highest rainfall intervals correlate with the highest activity of enso variability in solar output is possibly the main cause for this millennial to decadal cyclicity we interpret enso and itcz as the main climate change driving mechanisms in frontino comparison with high resolution xrf data from the caribbean cariaco basin a proxy for rainfall in the coastal venezuelian cordilleras demonstrates that climate in frontino was pacific driven enso dominated during the yd and early holocene whereas it was atlantic driven in cariaco itcz dominated from ca 8000 cal yr bp climate in both areas was under the dual influence of enso and itcz thereby showing existing teleconnections between the tropical pacific and atlantic oceans the frontino record is to date the highest resolution holocene study in nw colombia an implication of these results is that new records should be analyzed with multiproxy tools in particular those providing high resolution time series such as xrf

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

mid holocene emergence of a low frequency millennial oscillation in western mediterranean climate implications for past dynamics of the north atlantic atmospheric westerlies the nature and tempo of holocene climate variability is examined in the record of forest vegetation from western mediterranean marine core md95 2043 episodes of forest decline occurred at 10 1 9 2 8 3 7 4 5 4 4 5 and 3 7 2 9 cal ka bp and between 1 9 cal ka bp and the top of the record 1 3 cal ka bp wavelet analysis confirms a 900 yr periodicity prior to and during the early holocene and the dominance of a 1750 yr periodicity after 6 cal ka bp the 900 yr periodicity has counterparts in numerous north atlantic and northern hemisphere palaeoclimate records and in solar irradiance proxies 14c and 10be and may relate to a sun climate connection during the early holocene comparisons between the md95 2043 forest record and strategically located records from morocco iceland norway and israel suggest that the 1750 yr mid to late holocene oscillation reflects shifts between a prevailing strong and weak state of the zonal flow with impacts similar to the positive and negative modes of th

development of the california current during the past 12 000 yr based on diatoms and silicoflagellates detailed diatom and silicoflagellates records in three cores from the offshore region of southern oregon to central california reveal the evolution of the northern part of the california current during the past 12 000 yr the early holocene prior to 9 ka was characterizedbyrelativelywarmseasurfacetemperatures sst owingtoenhancednortherlyflowofthesubtropicalwaterscomparable tothemoderndavidsoncurrent progressivestrengtheningof thenorthpacifichighleadtointensificationofthesouthwardflowofthe california current at 8 ka resulting in increased coastal upwelling and relatively cooler sst which persisted until 5 ka reduced southward flow of the california current between 4 8 ka and 3 6 ka may have been responsible for a period of decreased upwelling modern seasonal oceanographic cycles as evidenced by increased spring early summer coastal upwelling and warming of early fall sst evolved between 3 5 and 3 2 ka widespread occurrence of paleoceanographic and paleoclimatic change between 3 5 3 0 ka along the eastern margins of the north pacific was likely a response to increasing enso variability in the tropical pacific published by elsevier b v

the holocene environmental changes in southern indonesia reconstructed from highland caldera lake sediment in bali island diatom pollen geomagnetic and geochemical analyses were carried out on a 3 6 m long sediment core taken from lake buyan a highland caldera lake in central bali island to reconstruct the holocene climate changes in equatorial southern indonesia the core represents 8 thousand years sedimentation of organic diatomaceous lake mud constant inclusion of benthic diatom fossils as main components indicated that suspension and inflow of littoral materials were the main sedimentary process the core contained laminated sediments in two distinct intervals at 6 5 5 0 and 3 6 3 1 cal ky bp and multi proxy records showed generally drier climate in these sections especially at 3 6 3 1 cal ky bp lake bottom waters were more reducing condition in these laminated periods probably due to increased lake productivity by prolonged dry season and wind mixing laminae structures were made up of a layer composed of benthic diatoms and amorphous organic materials and a layer made by only planktonic diatom fossils each of which may represent rainy and dry period deposits although southern indonesia shows clear australian monsoon rainfall seasonality at present counting of layer numbers showed interannual cycles of laminae formation prolonged dry seasons could obscured the rainfall seasonality in these periods but precise depositional patterns were elusive unlaminated sections showed homogeneous sediment mixture of benthic planktonic diatoms and more volume of terrigenous materials indicating wetter climate and seasonality similar to the present time this was supported by the higher share of marsh environment pollens reflecting more stable lake level trends the dry climate from 6 5 cal ky bp was in line with the general perception of stronger enso dynamics from the mid holocene due to weaker than before boreal summer insolation but the sporadic appearances of dry periods imply the influence of regional climate forcings such as temporal migrations of inter tropical convergence zone itcz it was however possible that temporal shifts of large climate mode occurred in equatorial pacific and indian oceans wettest climate was inferred from 3 1 cal ky bp to the present and this might reflect increased importance of austral hemisphere atmospheric convection and subsequent southerly position of itcz in austral summer time

modeling el nino and its tropical teleconnections during the last glacial interglacial cycle 1 simulations with the ncar climate system model csm a global coupled ocean atmosphere sea ice model for the last glacial interglacial cycle reproduce recent estimates based on alkenones and mg ca ratios of sea surface temperature sst changes and gradients in the tropical pacific and predict weaker el ninos la ninas compared to present for the holocene and stronger el ninos la ninas for the last glacial maximum lgm changes for the lgm holocene are traced to a weakening strengthening of the tropical pacific zonal sst gradient wind stresses and upwelling and a sharpening weakening of the tropical thermocline results suggest that proxy evidence of weaker precipitation variability in new guinea and ecuador are explained not only by changes in el nino la nina but also changes in the atmospheric circulation and hydrologic cycle index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4522 oceanography physical el nino 3337 meteorology and atmospheric dynamics numerical modeling and data assimilation 9604 information related to geologic time cenozoic citation otto bliesner b l e c brady s i shin z liu and c shields modeling el nino and its tropical teleconnections during the last glacial interglacial cycle geophys res lett 30 23 2198 doi 10 1029 2003gl018553 2003

an assessment of the mean annual precipitation needed to sustain lake sambhar in rajasthan india during mid holocene time an application of a simple hydrological model to likely climatic conditions of lake sambhar provides tighter bounds on the range of increased precipitation seen during the early to mid holocene than those inferred from paleoclimatic proxies to examine past lake levels we developed a simple lake model based on hydrological principles of a watershed balance between precipitation evaporation and runoff from the watershed to calculate daily depth and volume calculations reveal that early to mid holocene rainfall was most likely in a range of 40 65 greater than present levels resulting in lake depths of 6 8 m this estimate incorporates all major sources of uncertainty into the lake model but it is likely that the value of mid holocene precipitation lies in the lower part of the 40 65 range additionally a 40 65 greater precipitation could have led to greater interannual variability in lake levels which may account for the lack of clear shorelines we find however that it is unlikely that lak

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

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

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

oxygen isotope records of holocene climate variability in the pacific northwest abstract oxygen isotope 18o measurements of authigenic carbonate from cleland lake southeastern british columbia paradise lake central british columbia and lime lake eastern washington provide a 9000 year holocene record of precipitation evaporation balance variations in the pacific northwest both cleland lake and paradise lake are small surficially closed basin systems with no active inflows or outflows lime lake is surficially open with a seasonally active overflow water isotope values from cleland and paradise plot along the local evaporation line indicating that precipitation evaporation balance is a strong influence on lake hydrology in contrast lime lake water isotope values plot on the local meteoric water line signifying minimal influence by evaporation to infer past hydrologic balance variations at a high temporal resolution we sampled the cleland paradise and lime lake sediment cores at 1 60 mm intervals 3 33 years per sample on average and measured the isotopic composition of fine grained

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

lake sediment records of holocene hydroclimate and impacts of the mount mazama eruption north central washington usa abstract multi proxy sediment records from castor lake and scanlon lake north central washington provide a late quaternary perspective on lake catchment hydrologic and ecosystem responses to climate change and the mazama volcanic ashfall event analyses of authigenic carbonate mineral oxygen and carbon isotope values organic carbon and nitrogen content and sedimentological facies were conducted on sediment from castor lake in order to reconstruct lake catchment hydrologic balance the source and abundance of organic matter and variations in lake level sedimentary facies characterization was conducted on the scanlon lake sediment in order to provide supporting evidence for the lake level shifts inferred from the castor lake data marked changes in castor lake proxy values occur from 12 860 to 11 440 calendar years before present yr bp suggesting lake catchment responses to the younger dryas cold reversal including higher lake levels substantial variability in productivity and increased catchment erosion high 18o values at 9630 yr bp indicate that lake levels were lower than at present and that the early holocene was dry sedimentological analyses and 18o data demonstrate that subsequent to the mazama climactic eruption 7600 yr bp a transition to the lowest lake levels of the holocene occurred over several centuries with maximum 18o values at 7290 90 uncertainty range 7020 7500 yr bp and low lake levels persisting until 6190 5960 6410 yr bp lithological changes in the scanlon lake record support these inferences the lowest 18o values of the holocene occur in sediment from 5000 yr bp indicating high lake levels at this time after which a secular trend toward higher 18o values and lower lake levels occurred the prolonged lowstand in the centuries following the mazama eruption suggests that catchment hydrologic characteristics were strongly impacted by the ashfall through effects on soil water retention capacity that similar responses may have occurred in comparable settings within the mazama ashfall zone and that such volcanic events have the potential confound the climate signal in lake sediment records were a similar event to happen in the future catchment hydrology stream river discharge and lake catchment ecosystem dynamics could be affected for centuries

1500 year cycle dominated holocene dynamics of the yellow river delta china the world s mega deltas are extremely important from a human perspective and attract considerable effort to reveal their evolution growth related driving forces and human impacts here we report a case study on the holocene deltaic evolution of the yellow river through development of a conceptual model which is compared with paleo proxy to analyze the forcing acting on the delta the main conclusion is that superlobe switching was modulated by the 1500 year cycle cooling in mongolia in response to strong bond ird events which is coincident with warming in eastern china due to a strong kuroshio current enhances the meridional temperature gradient which then increases cyclone frequency and activates dust storms and terrestrial erosion throughout the catchment enhanced erosion supplies great amounts of material to the yellow river and causes channel evulsion and superlobe development expressed as dominant 1500 year cycle at the same time summer monsoon and solar forcing are uncorrected with deltaic evolution on these timescales therefore we conclude that holocene dynamics of the delta on a millennial timescale was dominated by winter cyclone activity across northern china and mongolia

a geochemical record of the link between chemical weathering and the east asian summer monsoon during the late holocene preserved in lacustrine sediments from poyang lake central china abstract this paper presents relatively high resolution geochemical records spanning the past 4000 cal yr bp obtained from the lacustrine sediments of poyang lake in central china the variations in the intensity of the east asian summer monsoon easm are traced using the k na ti na al k kaolinite illite and clay feldspar ratios together with the chemical index of alteration cia as indicators of chemical weathering during the last 4000 years the proxy records of chemical weathering from poyang lake exhibit an overall enhanced trend consistent with regional hydrological changes in previous independent records further comparisons and analyses demonstrate that regional moisture variations in central china is inversely correlated with the easm intensity with weak easm generating high precipitation in central china our data reveal three intervals of dramatically dry climatic conditions i e ca 4000 3200 cal yr bp ca 2800 2400 cal yr bp and ca 500 200 cal yr bp a period of weak chemical weathering related to cold and dry climatic conditions occurred during the little ice age lia whereas more intense chemical weathering reflecting warm and humid climatic conditions was recorded during the medieval warm period mwp besides an intensification of chemical weathering in poyang lake during the late holocene agrees well with strong enso activity suggesting that moisture variations in central china may be predominantly driven by enso variability

hydrographic changes in the tropical and extratropical pacific during the last deglaciation fine scale paired mg ca 18o profiles globigerinoides ruber white sensu lato from the san lazaro basin slb at 25 n in the northeast pacific reveal a transition from a predominant presence of tropical subtropical waters during the last glacial termination t1 to an increasing influence of fresh and cold california current waters toward the holocene changing atmospheric circulation patterns over the northeast pacific in step with the demise of the northern hemisphere ice sheets and or with a shift from el nino to la nina like conditions toward the holocene are prime candidates to explain this water mass change 18osw ivc increases of 0 5 0 7 during the younger dryas yd and heinrich stadial 1 hs1 at the slb are observed in a number of 18osw ivc records from the tropical pacific more directly influenced by changes in the position of the intertropical convergence zone itcz conditioning by itcz migration of the tropical pacific ocean towards salinity increase during yd and hs1 and the subsequent advection of those water masses as far north as 25 n likely accounted for the reconstructed hydrographical changes at the slb a larger influence of tropical water masses as far north as 25 n plausibly contributed to changes in the atmospheric moisture transports to western north america and affected the regional hydrological cycle across t1 finally the fine scale resolution of our 18osw ivc record allows pinpointing a shift from relative salty to fresh surface conditions at 16 2 ka signaling that the two phase structure of hs1 is plausibly a ubiquitous feature of the northern tropical to extratropical ocean atmosphere dynamics