extratropical influence on itcz shifts in slab ocean simulations of global warming abstractrecent studies with climate models have demonstrated the power of extratropical forcing in causing the intertropical convergence zone itcz to shift northward or southward and paleoclimate data support the notion that there have been large shifts in the itcz over time it is shown that similar notions apply to slab ocean simulations of global warming nine slab ocean model simulations from different modeling centers show a wide range of itcz shifts in response to doubling carbon dioxide concentrations which are experienced in a rather zonally symmetric way in the tropics using an attribution strategy based on fundamental energetic constraints it is shown that responses of clouds and ice in the extratropics explain much of the range of itcz responses there are also some positive feedbacks within the tropics due to increasing water vapor content and high clouds in the new itcz location which amplify the changes driven from the extratropics this study shows the clear importance of simulating

precipitation changes in the western tropical pacific over the past millennium modern seasonal and inter annual precipitation variability in palau is linked to both meridional movement of the intertropical convergence zone itcz and changes in the pacific walker circulation pwc associated with the el nino southern oscillation thus palau s hydroclimate should be sensitive to mean shifts in the itcz and pwc on decadal to centennial time scales using compound specific hydrogen isotope ratios 2h of dinosterol in lake sediments we generated a decadal resolution proxy record of hydroclimatic variability in palau spanning the past 800 yr results indicate a drying trend during the little ice age in palau consistent with a southward displacement of the itcz in addition to the secular drying trend there are persistent large 20 multi decadal to centennial oscillations in the 2h record the most recent of which indicates an abrupt shift to drier conditions in the mid 1970s that coincides with a decadal scale negative shift in the southern oscillation index

hydrogen isotopes in dinosterol from the chesapeake bay estuary abstract the hydrogen isotope ratio of the dinoflagellate sterol dinosterol 4 23 24 trimethyl 5 cholest 22e en 3 ol was measured in suspended particles and surface sediments from the chesapeake bay estuary in order to evaluate the influence of salinity on hydrogen isotope fractionation d h fractionation was found to decrease by 0 99 0 23 per unit increase in salinity over the salinity range 10 29 psu a similar decrease to that observed in a variety of lipids from hypersaline ponds on christmas island kiribati we hypothesize that the hydrogen isotopic response to salinity may result from diminished exchange of water between algal cells and their environment lower growth rates and or increased production of osmolytes at high salinities regardless of the mechanism the consistent sign and magnitude of dinosterol d response to changing salinity should permit qualitative to semi quantitative reconstructions of past salinities from sedimentary dinosterol d values

compound specific d h ratios of the marine lakes of palau as proxies for west pacific warm pool hydrologic variability abstract we tested the use of hydrogen isotopic ratios d of lipids in marine lake sediments from the micronesian republic of palau against the instrumental record of the last century to assess their capacity to record past hydrological changes of the western pacific warm pool d values of the algal lipid biomarker dinosterol d dino and the more generic palmitic acid d pa were found to be sensitive indicators of the intensity of regional precipitation as recorded by the southern oscillation index soi the observed sensitivity is caused by the combined effect of 1 the amount effect in tropical precipitation 2 dilution of the isotopically heavy saline surface waters with light precipitation 3 a salinity effect on the biosynthetic d h fractionation between lipid and lake water both lake water d d lake and d dino could be expressed as a quadratic function of either precipitation or lake water salinity d dino values were used to reconstruct past hydrological changes of the region long term variations in the strength and sign of the el nino southern oscillation enso since the little ice age lia 1450 1850 a d and during the early holocene 7 9 kyr bp appeared to dominate decadal variability and indicate very dry conditions during the lia early holocene d dino values were on average 10 higher than those of recent centuries which we interpret as a result of millennial scale hydrologic and water mass changes on a global level the similar 35 range of d changes during the early holocene and last several centuries imply a similar range of decadal centennial hydrologic variability during those two climate regimes our results indicate that a correlation exists between solar irradiance levels and tropical pacific climate

el nino evolution during the holocene revealed by a biomarker rain gauge in the galapagos islands abstract the el nino southern oscillation enso represents the largest perturbation to the climate system on an inter annual time scale but its evolution since the end of the last ice age remains debated due to the lack of unambiguous enso records lasting longer than a few centuries changes in the concentration and hydrogen isotope ratio of lipids produced by the green alga botryococcus braunii which blooms during el nino rains in the galapagos islands indicate that the early holocene 9200 5600 yr bp was characterized by alternating extremes in the intensity and or frequency of el nino events that lasted a century or more our data from the core of the enso region thus calls into question earlier studies that reported a lack of el nino activity in the early holocene in agreement with other proxy evidence from the tropical pacific the mid holocene 5600 3500 yr bp was a time of consistently weak el nino activity as were the early middle ages 1000 1500 yr bp el nino activity was moderate to high during the remainder of the last 3500 years periods of strong or frequent el nino tended to occur during peaks in solar activity and during extended droughts in the united states great plains linked to la nina these changing modes of enso activity at millennial and multi centennial timescales may have been caused by variations in the seasonal receipts of solar radiation associated with the precession of the equinoxes and or changes in solar activity respectively

dynamics and thermodynamics of a warming event in a coupled tropical atmosphere ocean model abstract a simple coupled ocean atmosphere model similar to that of zebiak and cane is used to examine the dynamic and thermodynamic processes associated with el nino southern oscillation enso the model is run for 300 years the interannual variability which results is regular with a period of either 3 or 4 years quantized by the annual cycle the amplitude 1 5 m s 1 wind and 2 c sst anomalies period and structure of the interannual variability compare well with observations the model warm event is initiated in the spring prior to the event peak and is well described as an instability of the coupled system during instability growth the sea surface temperature sst anomaly is primarily generated by vertical upwelling processes the sst anomaly can be approximately described by the expression t t kth t where t is the sst anomaly t time h the upper layer thickness pycnocline perturbation and an effective damping time which includes heat loss to the atmosphere kt parameterizes

a closer look at the central pacific el nino and warm pool migration events from 1982 to 2011 national science foundation nsf 11 582 nasa physical oceanography program epscor noaa sea grant

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

eastern tropical pacific hydrologic changes during the past 27 000 years from d h ratios in alkenones 1 the tropical pacific plays a central role in the climate system by providing large diabatic heating that drives the global atmospheric circulation quantifying the role of the tropics in late pleistocene climate change has been hampered by the paucity of paleoclimate records from this region and the lack of realistic transient climate model simulations covering this period here we present records of hydrogen isotope ratios dd of alkenones from the panama basin off the colombian coast that document hydrologic changes in equatorial south america and the eastern tropical pacific over the past 27 000 years a and the past 3 centuries in detail comparison of alkenone dd values with instrumental records of precipitation over the past 100 a suggests that dd can be used as a hydrologic proxy on long timescales our records indicate reduced rainfall during the last glacial period that can be explained by a southward shift of the mean position of the intertropical convergence zone and an associated reduction of pacific moisture transport into colombia precipitation increases at 17 ka in concert with sea surface temperature sst cooling in the north atlantic and the eastern tropical pacific a regional coupled model forced by negative sst anomalies in the caribbean simulates an intensification of northeasterly trade winds across central america increased evaporative cooling and a band of increased rainfall in the northeastern tropical pacific these results are consistent with the alkenone sst and dd reconstructions that suggest increasing precipitation and sst cooling at the time of heinrich event 1

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

a rotated eigenanalysis of the correlation between 700 mb heights and sea surface temperatures in the pacific and atlantic abstract associations between pacific and atlantic sea surface temperature sst and the 700 mb circulation were studied using 30 years 1949 78 of gridded monthly data the monthly data were grouped into four nonstandard seasons for the analysis the linear correlation between the two fields sst and 700 mb heights was analyzed by finding the eigenvalue solution of the mean product matrix of the cross correlations this technique introduced by prohaska was modified through the use of a varimax rotation the result is a set of pairs of patterns one pattern for each medium which explains part of the linear correlation between the two fields the number of significant modes pairs was determined by a monte carlo simulation one well known atmospheric teleconnections pattern referred to as the pacific north american pna pattern by wallace and gutzler was found in all seasons however seasonal differences were noted during the warm season the pna pattern manifests itself as the great plains g

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

separating itcz and enso related rainfall changes in the galapagos over the last 3 kyr using d h ratios of multiple lipid biomarkers abstract we present a 3000 yr rainfall reconstruction from the galapagos islands that is based on paired biomarker records from the sediment of el junco lake located in the eastern equatorial pacific the climate of the galapagos islands is governed by movements of the intertropical convergence zone itcz and the el nino southern oscillation enso we use a novel method for reconstructing past enso and itcz related rainfall changes through analysis of molecular and isotopic biomarker records representing several types of plants and algae that grow under differing climatic conditions we propose that d values of dinosterol a sterol produced by dinoflagellates record changes in mean rainfall in el junco lake while d values of c34 botryococcene a hydrocarbon unique to the green alga botryococcus braunii record changes in rainfall associated with moderate to strong el nino events we use these proxies to infer changes in mean rainfall and el nino related rainfall over the past 3000 yr during periods in which the inferred change in el nino related rainfall opposed the change in mean rainfall we infer changes in the amount of itcz related rainfall simulations with an idealized isotope hydrology model of el junco lake help illustrate the interpretation of these proxy reconstructions opposing changes in el nino and itcz related rainfall appear to account for several of the largest inferred hydrologic changes in el junco lake we propose that these reconstructions can be used to infer changes in frequency and or intensity of el nino events and changes in the position of the itcz in the eastern equatorial pacific over the past 3000 yr comparison with el junco lake sediment grain size records indicates general agreement of inferred rainfall changes over the late holocene

rainfall variations in central indo pacific over the past 2 700 y tropical rainfall variability is closely linked to meridional shifts of the intertropical convergence zone itcz and zonal movements of the walker circulation the characteristics and mechanisms of tropical rainfall variations on centennial to decadal scales are however still unclear here we reconstruct a replicated stalagmite based 2 700 y long continuous record of rainfall for the deeply convective northern central indo pacific ncip region our record reveals decreasing rainfall in the ncip over the past 2 700 y similar to other records from the northern tropics notable centennial to decadal scale dry climate episodes occurred in both the ncip and the southern central indo pacific scip during the 20th century current warm period cwp and the medieval warm period mwp resembling enhanced el nino like conditions further we developed a 2 000 y long itcz shift index record that supports an overall southward itcz shift in the central indo pacific and indicates southward mean itcz positions during the early mwp and the cwp as a result the drying trend since the 20th century in the northern tropics is similar to that observed during the past warm period suggesting that a possible anthropogenic forcing of rainfall remains indistinguishable from natural variability

preservation of lipid hydrogen isotope ratios in miocene lacustrine sediments and plant fossils at clarkia northern idaho usa abstract we measured d h ratios of individual lipids isolated from plant fossils and water lain sediments from the miocene clarkia lacustrine deposit 15 20 ma in northern idaho usa in order to assess the preservation potential of lipid hydrogen isotope ratios distinct n alkyl lipid profiles in plant fossils platanus quercus salix and the sedimentary matrix demonstrate the high degree of lipid preservation as previously reported our data suggest that original hydrogen isotope ratios of carbon bound hydrogen in lipids may have been preserved after 15 20 million years of burial in the water lain lacustrine sediment because d values of individual lipids show large variations between different fossil genera and between fossils and sediments and hydrogen isotope values of fossil lipids differ by more than 123 from the associated sediment water these data are consistent with minimal isotopic exchange between carbon bound hydrogen in lipids and sediment water hydrogen our results validate the use of lipid hydrogen isotope ratios for paleoecological studies over an extended geological time period

observed influence of north pacific sst anomalies on the atmospheric circulation abstract a lagged maximum covariance analysis mca of monthly anomaly data from the ncep ncar reanalysis shows significant relations between the large scale atmospheric circulation in two seasons and prior north pacific sea surface temperature sst anomalies independent from the teleconnections associated with the enso phenomenon regression analysis based on the sst anomaly centers of action confirms these findings in late summer a hemispheric atmospheric signal that is primarily equivalent barotropic except over the western subtropical pacific is significantly correlated with an sst anomaly mode up to at least 5 months earlier although the relation is most significant in the upper troposphere significant temperature anomalies are found in the lower troposphere over north america the north atlantic europe and asia the sst anomaly is largest in the kuroshio extension region and along the subtropical frontal zone resembling the main mode of north pacific sst anomaly variability in late winter

the demise of the alga botryococcus braunii from a norwegian fjord was due to early eutrophication in the sedimentary record of the permanently anoxic drammensfjord a suite of lipid biomarkers that are derived from the alga botryococcus braunii kiutzing botryococcenes is present in varying amounts but absent in sediments deposited after ad 1850 the disappearance is concurrent with the industrialization of sawmills and the introduction of paper and pulp mills along the river drammen and upstream water bodies and the related increase of anthropogenic eutrophication because of the sensitivity of this alga for environmental change a direct correlation between these two events is inferred this implies that the disappearance of the botryococcenes can serve as a palaeoenvironmental indicator for early eutrophication or environmental change in general this may be a useful tool in the ongoing research to unravel the response of natural systems to climatic geophysical or anthropogenic changes

molecular isotopic and dinoflagellate evidence for late holocene freshening of the black sea abstract the black sea is the world s largest anoxic basin with oxygen free conditions below water depths of approximately 100 m resulting from strong density stratification the salinity of its surface water likely varied substantially over time due to variations in freshwater input from large rivers and in the saline bottom water of mediterranean origin coming across the shallow sill of the bosporus however long term reconstructions of surface water salinities are lacking the invasion of the coccolithophorid emiliania huxleyi in the black sea at approximately 2720 a responsible for a marked change in sediment composition lithology has been commonly attributed to salinity levels rising above 11 we analyzed the d values of long chain alkenones produced by haptophyte algae mainly e huxleyi in a core from the eastern basin of the black sea to reconstruct past variations in sea surface salinities and combined this with relative salinity changes generated from organic walled dinoflagellate cyst dinocyst distributions from the same core combined results indicate a substantial freshening of black sea surface waters in the last 3000 years suggesting that sea surface salinity was substantially higher than the present day salinity of approximately 18 at the time e huxleyi invaded the black sea

spring arctic oscillation east asian summer monsoon connection through circulation changes over the western north pacific in the present study the links between spring arctic oscillation ao and east asian summer monsoon easm was investigated with focus on the importance of the north pacific atmospheric circulation and sea surface temperature sst to reduce the statistical uncertainty we analyzed high pass filtered data with the inter annual time scales and excluded the el nino southern oscillation signals in the climate fields using a linear fitting method the significant relationship between spring ao and easm are supported by the changes of multi monsoon components including monsoon indices precipitation and three dimensional atmospheric circulations following a stronger positive spring ao an anomalous cyclonic circulation at 850 hpa appears in southeastern asia and the western north pacific in summer with the easterly anomalies spanning from the pacific to asian continent along 25 n 30 n and the westerly anomalies south of 15 n at the same time the summer western north pacific subtropical high becomes weaker consistently the positive precipitation anomalies are developed over a broad region south of 30 n stretching from southern china to the western pacific and the negative precipitation anomalies appear in the lower valley of the yangtze river and southern japan the anomalous cyclone in the western north pacific persisting from spring to summer plays a key role in modulating easm and monsoon precipitation by a positive air sea feedback mechanism during spring the ao associated atmospheric circulation change produces warmer ssts between 150 e 180 near the equator the anomalous sensible and latent heating in turn intensifies the cyclone through a gill type response of the atmosphere through this positive feedback the tropical atmosphere and sst patterns sustain their strength from spring to summer that consequently modifies the monsoon trough and the western north pacific subtropical high and eventually the easm precipitation moreover the sst response to ao circulation is supported by the numerical simulations of an ocean model and the anomalous atmospheric circulation over the western north pacific is also reproduced by the dedicated numerical simulations using the coupled atmosphere ocean model the observation evidence and numerical simulations suggest the spring ao can impact the easm via triggering tropical air sea feedback over the western north pacific

franciscan complex limestone deposited at 24 n limestone and diabase from 11 sites in the permanente quarry the largest outcrop of calera limestone in the franciscan terranes have been studied by paleomagnetic and biostratigraphic methods observation of the upper albian uppennost albian boundary at one outcrop provides age and polarity control we propose a primary origin for a magnetic component identified in this unit another unit has been remagnetized by the diabase sill however predeformational inclinations are in agreement suggesting that remagnetization occurred shortly after deposition inclinations from these sites and another farther north at royce quarry successfully pass a megaconglomerate test and suggest a depositional paleolatitude of 24 n 4 this agrees with a plate model in which the calera limestone was deposited on the farallon plate at about 100 ma and was accreted to north america at about 70 ma

relationship between the tibetan plateau heating and east asian summer monsoon rainfall 1 this study reveals the close correspondence between the interannual variability of the dominant east asian summer rainfall pattern and the diabatic heating over the tibetan plateau in both spring and summer the heating fluctuation over the tibetan plateau is associated with two wave like circulation patterns which bear the characteristics of forced rossby wave emanating away from the deep heating the wave like pattern in turn affects the east asian summer rainfall because of the persistent heating over the tibetan plateau from spring to summer and its possible effect on the surrounding areas the heating index defined in this study can be used as a good predictor for the jja heating and precipitation distributions evidences shown suggest that external conditions other than the sst anomaly must be considered to understand the interannual variability of the east asian summer rainfall

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

interannual variability of the north pacific mixed layer associated with the spring tibetan plateau thermal forcing abstractby using multisourced data and two sets of sensitivity runs from the coupled general circulation model cesm1 2 0 we investigated the effects of the spring march april and may mam sur

biomarker evidence for the co occurrence of three races a b and l of botryococcus braunii in el junco lake galapagos in spite of the fact that individual races of botryococcus braunii are widely distributed in lakes reports of the co exis tence of different chemical races are rare here we report biomarker evidence for the co occurrence of three different races of b braunii a b and l in the water column and sediments of el junco lake a freshwater crater lake at 700 m elevation on san cristobal island galapagos we also show the existence of lycopadienes and lycopatrienes in suspended particles and sediments biomarker indicators of the three races were cis and trans c25 c31 n alkadienes and a c29 triene for race a a series of c34h58 botryococcenes for race b and a c40h78 hydrocarbon trans trans lycopadiene accompanied by minor amounts of isomers for race l epoxides derived from n alkadienes and trans trans lycopadiene specific to races a and l respectively were also detected several previously unreported lycopadienes and lycopatrienes were identified in both the water column and sediment and are believed to represent by products and intermediates respectively of trans trans lycopadiene synthesis botryococcene and lycopadiene concentrations reached 16 7 and 0 8 mg g dry sediment in near surface sediments and varied over more than three orders of magnitude while n alkadienes were present in trace quantities pyrolysates from the kerogen fraction of sediment contained lycopadiene and alkadiene related lipids along with chemically resistant polymers of b braunii cell walls apparently n alkadienes botryococcenes and lycopadienes and trienes can survive in oxic sedi ments for several decades and the down core variation in these lipids likely reflects changes in lake hydrology alternately favoring the bloom or near extinction of b braunii race b 2007 elsevier ltd all rights reserved

interhemispheric propagation of stationary rossby waves in a horizontally nonuniform background flow abstractsignificant interhemispheric teleconnections are identified that span the tropical easterlies in the boreal summer 300 hpa streamfunction such as the north africa antarctic naa and the north pacific south america npsa patterns these patterns are not supported by traditional wave theory since stationary waves in a basic state without meridional wind would be trapped in the easterlies to describe the interhemispheric responses more realistically two dimensional spherical rossby wave theory in a horizontally nonuniform basic state is considered conditions sufficient for the existence of one propagating wave are obtained and the meridional group velocity of the wave is shown to have the same direction as the meridional basic wind at the traditional critical latitude it is concluded that stationary waves with a specific wavelength can propagate across the easterlies from south north to north south via southerly northerly flows hence energy transport by stationary waves on a horizont

dynamics of an interhemispheric teleconnection across the critical latitude through a southerly duct during boreal winter abstractin this study an interhemispheric teleconnection pattern across the critical latitude from southern africa through south asia to the north pacific was revealed in boreal winter monthly averaged 250 hpa streamfunction fields obtained from both the 40 yr ecmwf re analysis era 40 and the ncep ncar reanalysis data from 1957 58 to 2001 02 classical rossby wave theory for zonally varying flow in which the effects of the basic state meridional wind are ignored predicts that stationary rossby waves cannot propagate across easterlies to elucidate the underlying mechanisms responsible for this interhemispheric teleconnection the theoretical basis for stationary wave propagation across the critical latitude is considered taking into account meridional ambient flow the theoretical results suggest that the southerly flow over east africa the western indian ocean and south asia creates a path for the northward propagation of stationary waves across the critical latitude stationary wavenumber and grou