a high resolution speleothem record of western equatorial pacific rainfall implications for holocene enso evolution abstract the el nino southern oscillation enso is the primary driver of interannual climate variability in the tropics and subtropics despite substantial progress in understanding ocean atmosphere feedbacks that drive enso today relatively little is known about its behavior on centennial and longer timescales paleoclimate records from lakes corals molluscs and deep sea sediments generally suggest that enso variability was weaker during the mid holocene 4 6 kyr bp than the late holocene 0 4 kyr bp however discrepancies amongst the records preclude a clear timeline of holocene enso evolution and therefore the attribution of enso variability to specific climate forcing mechanisms here we present 18 o results from a u th dated speleothem in malaysian borneo sampled at sub annual resolution the 18 o of borneo rainfall is a robust proxy of regional convective intensity and precipitation amount both of which are directly influenced by enso activity our estimates of stalagmite 18 o variance at enso periods 2 7 yr show a significant reduction in interannual variability during the mid holocene 3240 3380 and 5160 5230 yr bp relative to both the late holocene 2390 2590 yr bp and early holocene 6590 6730 yr bp the borneo results are therefore inconsistent with lacustrine records of enso from the eastern equatorial pacific that show little or no enso variance during the early holocene instead our results support coral mollusc and foraminiferal records from the central and eastern equatorial pacific that show a mid holocene minimum in enso variance reduced mid holocene interannual 18 o variability in borneo coincides with an overall minimum in mean 18 o from 3 5 to 5 5 kyr bp persistent warm pool convection would tend to enhance the walker circulation during the mid holocene which likely contributed to reduced enso variance during this period this finding implies that both convective intensity and interannual variability in borneo are driven by coupled air sea dynamics that are sensitive to precessional insolation forcing isolating the exact mechanisms that drive long term enso evolution will require additional high resolution paleoclimatic reconstructions and further investigation of holocene tropical climate evolution using coupled climate models

enso variability and teleconnections during glacial climates abstract understanding the origin of sub milankovitch and millennial scale abrupt climate change still poses a major challenge an important role of communicating the orbital scale forcing into abrupt climate change on millennial and centennial timescales has been hypothesized for the tropics in earlier studies based on the assumption of stationary teleconnections this paper presents a modelling study for the last glacial maximum and marine isotope stage 3 using the comprehensive climate model ccsm3 glacial boundary conditions and freshwater hosing at high latitudes of the north atlantic are imposed to mimic a heinrich stadial and dansgaard oeschger stadials and interstadials it is shown that glacial enso variability is strongly enhanced by a substantial slowdown of the atlantic meridional overturning circulation the simulations also suggest that glacial boundary conditions induce major modifications to enso teleconnections and that the blueprint of modern enso teleconnections should only be applied with caution to glacial climate periods

multi model changes in el nino teleconnections over north america in a future warmer climate previous studies with single models have suggested that el nino teleconnections over north america could be different in a future warmer climate due to factors involving changes of el nino event amplitude and or changes in the midlatitude base state circulation here we analyze a six member multi model ensemble three models with increasing future el nino amplitude and three models with decreasing future el nino amplitude to determine characteristics and possible changes to el nino teleconnections during northern winter over the north pacific and north america in a future warmer climate compared to observed el nino events all the models qualitatively produce general features of the observed teleconnection pattern over the north pacific and north america with an anomalously deepened aleutian low a ridge over western north america and anomalous low pressure over the southeastern united states however associated with systematic errors in the location of sea surface temperature and convective heating anomalies in the central and western equatorial pacific the models anomaly patterns are shifted to the west the anomalous low pressure center in the north pacific is weaker and shifted somewhat south compared to the observations for future el nino events two different stabilization experiments are analyzed one with co2 held constant at year 2100 concentrations in the sres a1b scenario roughly doubled present day co2 and another with co2 concentrations held constant at 4xco2 consistent with the earlier single model results the future el nino teleconnections are changed in the models with a weakened as well as an eastward and northward shifted anomalous low in the north pacific this is associated with weakened anomalous warming over northern north america strengthened cooling over southern north america and precipitation increases in the pacific northwest in future events compared to present day el nino event teleconnections these changes are consistent with the altered base state upper tropospheric circulation with a wave 5 pattern noted in previous studies that is shown here to be consistent across all the models whether there are projected future increases or decreases in el nino amplitude the future teleconnection changes are most consistent with this anomalous wave 5 pattern in the models with future increases of el nino amplitude but less so for the models with future decreases of el nino amplitude

interdecadal change of the structure of the enso mode and its impact on the enso frequency in the late 1970s the enso cycle exhibited frequency change the oscillation period increased from 2 4 yr high frequency during 1962 75 to 4 6 yr low frequency during 1980 93 observations suggest that this frequency change was accompanied by a significant change in the structure of the coupled enso mode in comparison with the high frequency regime the structure of the coupled mode in the low frequency regime shows three distinctive features during the warm phase of enso the eastward shift of the westerly anomalies the meridional expansion of the westerly anomalies and the weaker intensity of the easterly anomalies in the eastern pacific to test the robustness of the relationship between the oscillation period and the structure of the coupled mode the authors designed empirical atmospheric models based on observations and coupled them with the ocean model of zebiak and cane numerical experiments demonstrate that the enso period is sensitive to changes in the wind anomaly pattern in a way much like the observed enso frequency structure relation the increase of the enso period after 1980 is mainly due to the eastward shift of the zonal wind stress with respect to the sst anomalies physical explanations of the dependence of enso frequency on the structure of the coupled mode are provided by diagnosing the relative contributions of the thermocline feedback and zonal advection feedback on enso evolution

the weakening and eastward movement of enso impacts during the last glacial maximum abstractthe assumption of a stationary global signal linked to el nino southern oscillation enso events is often used in paleo enso proxy data interpretation this paper attempts to investigate w

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

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

growth of heterostegina depressa under natural and laboratory conditions the use of micro computed tomography ct provides a unique opportunity to look inside the shells of larger benthic foraminifera to investigate their structure by measuring linear and volumetric parameters for this study gamonts schizonts and agamonts of the species heterostegina depressa d orbigny were examined by ct each single chamber s volume was digitally measured this approach enables cell growth to be recognised in terms of chamber volume sequence which progressively increases until reproduction occurs this sequence represents the ontogeny of the foraminiferal cell and has been used here to investigate controlling factors potentially affecting the process of chamber formation this is manifested as instantaneous or periodic deviations of the realised chamber volumes derived from modelled growth functions the results obtained on naturally grown specimens show oscillations in chamber volumes which can be modelled by sums of sinusoidal functions a set of functions with similar periods in all investigated specimens points to lunar and tidal cycles to determine whether such cyclic signals are genuine and not the effects of a theoretical model the same analysis was conducted on specimens held in a closed laboratory facility as they should not be affected by natural environmental effects surprisingly similar cyclicities were observed in such samples however a solely genetic origin of these cycles couldn t be verified either therefore detailed analysis on the phase equality of these growth oscillations have been done this approach is pivotal for proving that the oscillatory patterns discovered in lbf are indeed genuine signals and on how chamber growth might be influenced by tidal currents or lunar months

effects of temperature on mg ca in neogloboquadrinid shells determined by live culturing 1 new culturing protocols allowed the development of a mg ca temperature calibration equation for neogloboquadrina pachyderma d when cultured between 9 c and 19 2 c mg ca in n pachyderma d shell calcite exhibits a clear dependence on temperature shell calcite mg ca increased exponentially with temperature mg ca 0 51 0 15 0 23 exp 0 10 0 02 t limited data suggest n dutertrei exhibit similar elemental temperature relationships to n pachyderma d we applied the temperature relationship established by culturing to mg ca in neogloboquadrinid shells collected using plankton tows compared to measured sst the calculated temperatures were within 2 c for mg ca 95 ci multiple samples from single tows generally had calculated temperatures that ranged from near surface values to temperatures consistent with calcification depths down to 70 m our work indicates that mg ca temperature calibration equations for temperate and polar foraminiferal species have a similar exponential constant but a higher pre exponential constant than those for surface dwelling tropical species therefore accurate paleotemperature reconstructions from temperate and polar species require the use of an equation distinct from those used for tropical species

salinity bias on the foraminifera mg ca thermometry correction procedure and implications for past ocean hydrographic reconstructions 1 mg ca in foraminiferal calcite has recently been extensively used to estimate past oceanic temperatures here we show however that the mg ca temperature relationship of the planktonic species globigerinoides ruber is significantly affected by seawater salinity with a 1 psu change in salinity resulting in a 1 6 c bias in mg ca temperature calculations if not accounted for such a bias could lead for instance to systematic overestimations of mg ca temperatures during glacial periods when global ocean salinity had significantly increased compared to today we present here a correction procedure to derive unbiased sea surface temperatures sst and 18osw from g ruber tmg ca and 18of measurements this correction procedure was applied to a sedimentary record to reconstruct hydrographic changes since the last glacial maximum lgm in the western pacific warm pool while uncorrected tmg ca data indicate a 3 c warming of the western pacific warm pool since the lgm the salinity corrected sst result in a stronger warming of 4 c

barotropic models of the extratropical response to el nino abstract a series of linear and nonlinear barotropic models are used to interpret the extratropical response to el niflo equatorial surface temperatures as simulated by an atmospheric general circulation model gcm the divergence time mean vorticity tendency due to transients and the zonal mean tlow are specified from the gcm and the deviation of the streamfunction from its zonal mean at an upper tropospheric level is predicted nonlinearsteady state models suggest that the extratropical wave train is primarily forced from the central rather than the western pacific and that subtropical divergence anomalies are of more importance than tropical anomalies these nonlinear solutions can be reproduced with little loss in accuracy by linearizing about the zonally asymmetric climatological flow if one linearizes about the zonally symmetric flow the part of the solution forced from thewestern pacific deteriorates significantly the solution in the tropics and subtropics also deteriorates if advection of v

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

mg ca and sr ca ratios in planktonic foraminifera proxies for upper water column temperature reconstruction reliable temperature estimates from both surface and subsurface ocean waters are needed to reconstructpast upper water column temperature gradients and past oceanic heat content this work examines therelationships between trace element ratios in fossil shells and seawater temperature for surface dwellingforaminifera species globigerinoides ruber white and globigerina bulloides and deep dwelling species globorotalia inflata globorotalia truncatulinoides dextral and sinistral and pulleniatina obliquiloculata mg ca and sr ca ratios in shells picked in 29 modern core tops from the north atlantic ocean are calibratedusing calculated isotopic temperatures mg ca ratios on g ruber and g bulloides agree with published dataand relationships for deep dwelling species mg ca calibration follows the equation mg ca 0 78 0 04 exp 0 051 0 003 t with a significant correlation coefficient of r

what have we learnt from palaeoclimate simulations there has been a gradual evolution in the way that palaeoclimate modelling and palaeoenvironmental data are used together to understand how the earth system works from an initial and largely descriptive phase through explicit hypothesis testing to diagnosis of underlying mechanisms analyses of past climate states are now regarded as integral to the evaluation of climate models and have become part of the toolkit used to assess the likely realism of future projections palaeoclimate assessment has demonstrated that changes in large scale features of climate that are governed by the energy and water balance show consistent responses to changes in forcing in different climate states and these consistent responses are reproduced by climate models however state of the art models are still largely unable to reproduce observed changes in climate at a regional scale reliably while palaeoclimate analyses of state of the art climate models suggest an urgent need for model improvement much work is also needed on extending and improving palaeoclimate reconstructions and quantifying and reducing both numerical and interpretative uncertainties

the response of the walker circulation to last glacial maximum forcing implications for detection in proxies 1 the response of the walker circulation to last glacial maximum lgm forcing is analyzed using an ensemble of six coordinated coupled climate model experiments the tropical atmospheric overturning circulation strengthens in all models in a manner that is dictated by the response of the hydrological cycle to tropical cooling this response arises from the same mechanism that has been found to explain the weakening of the tropical circulation in response to anthropogenic global warming but with opposite sign analysis of the model differences shows that the ascending branch of the walker circulation strengthens via this mechanism but vertical motion also weakens over areas of the maritime continent exposed due to lower sea level each model exhibits a different balance between these two mechanisms and the result is a pacific walker circulation response that is not robust further even those models that simulate a stronger walker circulation during the lgm do not simulate clear patterns of surface cooling such as la nina like cooling or enhanced equatorial cooling as proposed by previous studies in contrast the changes in the walker circulation have a robust and distinctive signature on the tilt of the equatorial thermocline as expected from zonal momentum balance the changes in the walker circulation also have a clear signature on the spatial pattern of the precipitation changes a reduction of the east west salinity contrast in the indian ocean is related to the precipitation changes resulting from a weakening of the indian walker circulation these results indicate that proxies of thermocline depth and sea surface salinity can be used to detect actual lgm changes in the pacific and indian walker circulations respectively and help to constrain the sensitivity of the walker circulation to tropical cooling

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

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

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

feasibility of borehole ambient noise interferometry for permanent reservoir monitoring the analysis of seismic ambient noise acquired during temporary or permanent microseismic monitoring campaigns e g improved enhanced oil recovery monitoring surveillance of induced seismicity is potentially well suited for time lapse studies based on seismic interferometry no additional data acquisition required ambient noise processing can be automatized to a high degree and seismic interferometry is very sensitive to small medium changes thus there is an opportunity for detection and monitoring of velocity variations in a reservoir at negligible additional cost and effort data and results are presented from an ambient noise interferometry study applied to two wells in a producing oil field in romania borehole microseismic monitoring on three component geophones was performed for four weeks concurrent with a water flooding phase for improved oil recovery from a reservoir in ca 1 km depth both low frequency 2 hz 50 hz p and s waves propagating through the vertical borehole arrays were reconstructed from ambient noise by the virtual source method the obtained interferograms clearly indicate an origin of the ambient seismic energy from above the arrays thus suggesting surface activities as sources it is shown that ambient noise from time periods as short as 30 seconds is sufficient to obtain robust interferograms sonic log data confirm that the vertical and horizontal components comprise first arrivals of p wave and s waves respectively the consistency and high quality of the interferograms throughout the entire observation period further indicate that the high frequency part up to 100 hz represents the scattered wave field the temporal variation of apparent velocities based on first arrival times partly correlates with the water injection rate and occurrence of microseismic events it is concluded that borehole ambient noise interferometry in production settings is a potentially useful method for permanent reservoir monitoring due to its high sensitivity and robustness

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

the effect of sea level on glacial indo pacific climate the indo pacific warm pool is the largest source of heat and moisture vapour to the atmosphere proxy reconstructions and model simulations suggest that during the last glacial maximum the exposure of the sunda shelf of southeast asia weakened deep convection over the warm pool

reduced el nino southern oscillation during the last glacial maximum el nino southern oscillation enso is a major source of global interannual variability but its response to climate change is uncertain paleoclimate records from the last glacial maximum lgm provide insight into enso behavior when global boundary conditions ice sheet extent atmospheric partial pressure of co2 were different from those today in this work we reconstruct lgm temperature variability at equatorial pacific sites using measurements of individual planktonic foraminifera shells a deep equatorial thermocline altered the dynamics in the eastern equatorial cold tongue resulting in reduced enso variability during the lgm compared to the late holocene these results suggest that enso was not tied directly to the east west temperature gradient as previously suggested rather the thermocline of the eastern equatorial pacific played a decisive role in the enso response to lgm climate

decadal changes of enso persistence barrier in sst and ocean heat content indices 1958 2001 decadal changes of el nino southern oscillation enso persistence barriers in various indices of sea surface temperature sst and ocean heat content ohc are examined in this study using observations and ocean data assimilation products for the period 1958 2001 it is found that the sst indices in the eastern and central equatorial pacific exhibit very different decadal barrier variability the variability is large for the eastern pacific sst indices nino1 2 and nino3 whose persistence barriers shifted abruptly in 1976 1977 and 1989 1990 in contrast the central pacific sst indices nino3 4 and nino4 experienced little decadal barrier variability and have had their persistence barriers fixed in spring in the past four decades the zonal mean ohc index averaged over the equatorial pacific shows decadal barrier changes similar to those in the eastern pacific sst indices and always leads the nino3 sst barrier by about one season it is noticed that the sst persistence barrier appeared first in the eastern pacific before 1976 1977 first in the central pacific between 1976 1977 and 1989 1990 and almost simultaneous in both the eastern and central pacific after 1989 1990 these timings coincide with the westward propagating eastward propagating and standing pattern of enso sst anomalies observed in these three periods these results suggest that enso sst anomalies in the equatorial pacific can be considered to consist of two different processes a central pacific process whose phase transition such as onset and barrier always happen in spring and an eastern pacific process whose phase transition and barrier change from decade to decade and are influenced by changes in the mean thermocline depth along the equatorial pacific

linkages between 200 mb tropical and extratropical circulation anomalies during the 1986 1989 enso cycle abstract nmc operational wind analyses have been used to document the 200 mb circulation anomalies during the solstice seasons of the 1987 1989 enso cycle using the one level vorticity balance diagnostic approach the 200 mb rossby wave anomalous source distribution was derived as departures from a three year mean for the single warm phase season january march 1987 the effective rossby wave anomaly sources were found to be generally quite small within 15 of the equator poleward of about 15 the anomalous 200 mb divergence through the planetary vorticity divergence anomaly stretching term is the dominant factor in determining the anomalous 200 mb vorticity source distribution its jfm standard deviation around 30 35 n was an order of magnitude larger than that found in the deep tropics the january march and june august 200 mb circulation differences between the warm and cold phase of the 1987 1989 enso cycle are described the enso cycle linkages between the equatorial pacific convection anomali

the eastward shift of the walker circulation in response to global warming and its relationship to enso variability this study investigates the global warming response of the walker circulation and the other zonal circulation cells represented by the zonal stream function in cmip3 and cmip5 climate models the changes in the mean state are presented as well as the changes in the modes of variability the mean zonal circulation weakens in the multi model ensembles nearly everywhere along the equator under both the rcp4 5 and sres a1b scenarios over the pacific the walker circulation also shows a significant eastward shift these changes in the mean circulation are very similar to the leading mode of interannual variability in the tropical zonal circulation cells which is dominated by el nino southern oscillation variability during an el nino event the circulation weakens and the rising branch over the maritime continent shifts to the east in comparison to neutral conditions vice versa for a la nina event two thirds of the global warming forced trend of the walker circulation can be explained by a long term trend in this interannual variability pattern i e a shift towards more el nino like conditions in the multi model mean under global warming further interannual variability in the zonal circulation exhibits an asymmetry between el nino and la nina events el nino anomalies are located more to the east compared with la nina anomalies consistent with this asymmetry we find a shift to the east of the dominant mode of variability of zonal stream function under global warming all these results vary among the individual models but the multi model ensembles of cmip3 and cmip5 show in nearly all aspects very similar results which underline the robustness of these results the observed data era interim reanalysis from 1979 to 2012 shows a westward shift and strengthening of the walker circulation this is opposite to what the results in the cmip models reveal however 75 of the trend of the walker circulation can again be explained by a shift of the dominant mode of variability but here towards more la nina like conditions thus in both climate change projections and observations the long term trends of the walker circulation seem to follow to a large part the pre existing dominant mode of internal variability

mg and sr uptake in benthic foraminifera ammonia aomoriensis based on culture and field studies abstract trace elements incorporated in foraminiferal test are commonly used as paleoproxies however the incorporation of trace elements is controlled by more than one environmental parameter we conducted one year sampling from june 2014 to may 2015 in the qingdao intertidal flat the yellow sea and retrieved surface samples in the jiaozhou bay 3 9 6 8 m water depth the yellow sea in february 2015 as well as performed a laboratory culture experiment under temperature 6 24 c and salinity 24 33 psu by combining 18oc values of field a aomoriensis parameters controlling mg ca and sr ca ratios of ammonia aomoriensis were investigated under constant seawater chemistry temperature dominates the magnesium incorporation into a aomoriensis test by an exponential increase of 5 1 per c mg ca 1 0980 0 2073 e0 0510 0 0097 t mg ca 0 5565 0 3897 0 1279 0 0242 t 2 4 24 c including field samples whereas temperature has no significant effect on strontium uptake calcite sr ca of a aomoriensis is primarily explained by mg ca value 3 per mmol mol salinity variations are of subordinate importance for both mg and sr content in the test of a aomoriensis mg ca raises linearly with approximately 2 per salinity unit and sr ca increases 1 per salinity unit importantly biological mechanism might be an inestimable factor perturbing mg and sr response to environmental parameters in natural waters complicating the paleoclimate reconstruction

the pacific south american modes and tropical convection during the southern hemisphere winter abstract atmospheric circulation features and convection patterns associated with two leading low frequency modes in the southern hemisphere sh are examined in multiyear global reanalyses produced by ncep ncar and nasa dao the two leading modes referred to as the pacific south american psa modes are represented by the first two eof patterns the two patterns are in quadrature with each other and are dominated by wavenumber 3 in midlatitudes with large amplitudes in the pacific south american sector in the pacific anomalies in the subtropics and in the midlatitudes are opposite in phase taken together the two psa modes represent the intraseasonal oscillation in the sh with periods of roughly 40 days the evolution of the psa modes shows a coherent eastward propagation a composite analysis was conducted to study the evolution of tropical convection and the corresponding circulation changes associated with the psa modes outgoing longwave radiation olr anomaly composites during the mature phase

temperature and carbonate ion effects on mg ca and sr ca ratios in benthic foraminifera aragonitic species hoeglundina elegans received 16 march 2005 revised 20 june 2005 accepted 3 november 2005 published 21 february 2006 1 core top samples from atlantic little bahama banks lbb and pacific hawaii and indonesia depth transects have been analyzed in order to assess the influence of bottom water temperature bwt and aragonite saturation levels on mg ca and sr ca ratios in the aragonitic benthic foraminifer hoeglundina elegans both the mg ca and sr ca ratios in h elegans tests show a general decrease with increasing water depth although at each site the decreasing trends are consistent with the in situ temperature profile mg ca and sr ca ratios in lbb are substantially higher than in indonesia and hawaii at comparable water depths with a greater difference observed with increasing water depth because we find no significant difference between results obtained on live and dead specimens we propose that these differences are due to primary effects on the metal uptake during test formation evaluation of the water column properties at each site suggests that in situ co3 ion concentrations play an important role in determining the h elegans mg ca and sr ca ratios the co3 ion effect is limited however only to aragonite saturation levels dco3 aragonite below 15 mmol kg 1 above this level temperature exerts a dominant effect accordingly we propose that mg ca and sr ca in h elegans tests can be used to reconstruct thermocline temperatures only in waters oversaturated with respect to the mineral aragonite using the following relationships mg ca 0 034 0 002 bwt 0 96 0 03 and sr ca 0 060 0 002 bwt 1 53 0 03 for dco3 aragonite 1 5mmol kg 1 the standard error associated with these equations is about 1 1 c reconstruction of deeper water temperatures is complicated because in undersaturated waters changes in mg ca and sr ca ratios reflect a combination of changes in co3 and bwt overall we find that sr ca rather than mg ca in h elegans may be a more accurate proxy for reconstructing paleotemperatures

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

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

a secondary ionization mass spectrometry calibration of cibicidoides pachyderma mg ca with temperature an evaluation of c pachyderma mg ca using a new suite of warm water multicores from the florida straits shows that the slope of mg ca with temperature is shallower than previously thought using secondary ionization mass spectrometry we have documented that the distribution of magnesium within the polished walls of foraminiferal tests is gaussian suggesting that the mg ca in these samples is not affected by the addition of a secondary high magnesium calcite in the walls the mg ca within a typical c pachyderma test varies by about 20 1 100 and the variability increases slightly in tests with higher mg ca the regression of c pachyderma mg ca with temperature has a slope of 0 13 0 05 mmol mol 1 per c indistinguishable from the slope observed in inductively coupled plasma mass spectrometry measurements from a different subset of the same multicores but about one half the slope of previously published calibrations the largest differences between the calibrations comes at the warm water end of the regression where previously published c pachyderma mg ca values from little bahama bank are at least 3 mmol mol 1 higher than observed in these new cores the reasons for this difference are not fully known but are most likely related to diagenesis at little bahama bank

annually resolved ice core records of tropical climate variability over the past 1800 years ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics but they are difficult to recover and few exist here we report annually resolved ice core records from the quelccaya ice cap 5670 meters above sea level in peru that extend back 1800 years and provide a high resolution record of climate variability there oxygen isotopic ratios 18 o are linked to sea surface temperatures in the tropical eastern pacific whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the intertropical convergence zone in the region of the tropical andes quelccaya continues to retreat and thin radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia