variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

effect of wind scouring on climatic records from ice core oxygen isotope profiles removal of winter snow by wind explains why the annual mean oxygen isotope ratio at an ice divide is 2 5 less negative than it is 1 2 km downslope cores from two sites on an ice cap ellesmere island canada show past variations in the difference depending on where the ice originated relative to the scoured zone some ice core climatic records may need correction for scouring

abrupt mid holocene onset of centennial scale climate variability on the peru chile margin 1 understanding the natural climate variations in the eastern tropical pacific etp is crucial for predicting the evolution of the el nino southern oscillation enso here we present the first continuous decadal resolution holocene climate record from the peru chile margin near the epicenter of the modern enso system geochemical proxies allow us to reconstruct sea surface temperature phytoplankton productivity and thermocline ventilation variables that are tightly correlated to enso events today despite the observation that the mean state of all three variables did not change over the past 10 000 years our data reveal a dramatic increase in climate variability near 5 ka represented by prolonged periods 50 200 yrs of climate extremes which are absent in the early holocene these centennial scale oscillations do not show typical el nino la nina correlations between proxies we therefore posit that a significant fraction of super enso variance may originate outside the tropics through processes that ventilate the etp subsurface waters

holocene rainfall variability in southern chile a marine record of latitudinal shifts of the southern westerlies geochemical and clay mineral parameters of a high accumulation marine sediment core from the chilean continental slope 41 s provide a 7700 yr record of rainfall variability in southern chile related to the position of the southern westerlies we especially use the iron content measured with a time resolution of ca 10 yr on average of 14 caccelerator mass spectrometry dated marine sediments as a proxy for the relative input of iron poor coastal range and iron rich andean source rocks variations in this input are most likely induced by rainfall changes in the continental hinterland of the core position based on these interpretations we find a pronounced rainfall variability on multicentennial to millennial time scales superimposed on generally more arid conditions during the middle holocene 7700 to 4000 cal yr b p compared to the late holocene 4000 to present this variability and thus changes in the position of the southern westerlies are first compared to regional terrestrial paleoclimate data sets from central and southern chile in order to derive possible wider implications and forcing mechanisms of the holocene latitudinal shifts of the southern westerlies we then compare our data to ice core records from both tropical south america and coastal antarctica these records show similar bands of variability centered at ca 900 and 1500 yr comparisons of band pass filters suggest a close connection of shifts of the southern westerlies to changes within the tropical climate system the correlation to climate conditions in coastal antarctica shows a more complicated picture with a phase shift at the beginning of the late holocene coinciding with the onset of the modern state of el nin o southern oscillation system the presented data provide further evidence that the well known millennial scale climate variability during the last glacial continued throughout the holocene fl 2001 elsevier science b v all rights reserved

the use of borehole video in investigating the hydrology of a temperate glacier a geovision micro colour video camera was used to investigate the internal structure of 11 boreholes at haut glacier d arolla switzerland the boreholes were distributed across a half section of the glacier with closest spacing towards the glacier margin the boreholes were used to investigate the hydrology of the glacier through automatic monitoring of borehole water level and electrical conductivity ec at the glacier bed ec profiling was undertaken in several boreholes to determine the existence of water quality stratification temporal variations in ec stratification were used to infer borehole water sources and patterns of water circulation borehole video was used to confirm the conclusions made from these indirect sources of evidence and to provide an independent source of information on the structure and hydrology of this temperate valley glacier the video showed variations in water turbidity englacial channels and voids conditions at the glacier bed and down borehole changes in ice structure based on the video observations englacial channels accounted for approximately 0 1 of the vertical ice thickness and englacial voids for approximately 0 4 overall the video images provided useful qualitative and semi quantitative data that reinforce interpretations of a range of physical and chemical parameters measured in boreholes 1997 by john wiley sons ltd

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

tropical cooling at the last glacial maximum and extratropical ocean ventilation1 1 the ncar csm is used to simulate the climate at last glacial maximum the csm simulates a tropical sst cooling of 2 1 c it is shown that about half of this tropical cooling is associated with the upper ocean circulation especially the ventilation of thermocline and intermediate waters from the mid high latitude south pacific

antarctic intermediate water circulation and variability in a coupled climate model the variability of antarctic intermediate water aaiw in a long term natural integration of a coupled climate model is examined the mean state of the climate model includes a realistic representation of aaiw which appears centered on the su 5 27 2 kg m23 density surface hereinafter s 27 2 both in observations and the model an assessment of ventilation rates on the s 27 2 surface suggests that this particular climate model forms aaiw in a mostly circumpolar fashion with a significant contribution from antarctic surface water this motivates the assessment of oceanic variability along this core aaiw isopycnal surface complex empirical orthogonal function analyses decompose the variability into three dominant modes showing circumpolar patterns of zonal wavenumber 1 2 and 3 on the s 27 2 density surface the modes contain eastward propagating signals at interannual to centennial time scales mechanisms forcing this variability are investigated using heat and salt budget analyses at the wintertime outcrop of the s 27 2 surface such an approach ignores the mechanism of aaiw variability sourced by subantarctic mode water variations which has been examined previously and is for the most part beyond the present study variability in meltwater rates and atmospheric heat and freshwater fluxes are found to dominate the intermediate water variability at the outcrop region in contrast northward ekman transport of heat and salt plays a significant but localized role in aaiw temperature salinity variability there is also an important contribution from the antarctic circumpolar current to the variability at the outcrop region via zonal transport of heat and salt while the magnitude of aaiw natural variability can be large near the outcrop of the salinity minimum layer recent observations of cooling and freshening at depth are suggested to be beyond that of the unperturbed system

subdecadally resolved paleoceanography of the peru margin during the last two millennia 1 using multiproxy sediment core data from the el nino southern oscillation enso sensitive peru margin subdecadally resolved down to 0 6 year surface productivity and subsurface denitrification are reconstructed for the last 2300 years scanning xrf generated major elemental data ti fe si correlate well with discrete inductively coupled plasma atomic emission spectometry icp aes analyses and together with x radiography core density are used as productivity indices as surface productivity in this marine region is strongly impacted by enso higher lower periods of surface productivity are inferred to represent a persistent normal la nina el nino like state surface productivity and subsurface denitrification appear to have remained intimately coupled during this period due to direct stimulation of requisite subsurface suboxia and or hydrographic restructuring the late holocene peru margin is characterized by persistent moderate productivity and subsurface denitrification punctuated at centennial scale by shorter duration periods of high production and intense denitrification these centennial scale events are likely analogous to modern observations of decadal scale regime shifts but of higher amplitude and provide a background history for future natural changes to this system solar irradiance variability is suggested to have influenced peru productivity as evidenced in numerous high resolution paleorecords from the northern hemisphere

climate and antarctic intermediate water coupling during the late holocene little is known about the scale of natural variability of the southern hemisphere upper ocean on decadal to centennial time scales despite its potential importance for influencing regions as distant as the tropical pacific el nino southern oscillation enso or even the north atlantic overturning circulation here we present the first subdecadally sampled reconstruction of variability in the southeast pacific upper intermediate ocean from ca a d 0 1300 using foraminiferal oxygen and carbon isotope records our results reveal large variability in surface ocean physical properties on both decadal and centennial time scales in the southeast pacific as much as 3 c or more in as little as 50 yr on centennial time scales changes in antarctic intermediate water physical properties benthic foraminiferal 18 o covary with those in the surface and are associated with shifts in tropical temperatures thermocline nutrient dynamics and enso suggesting that they are part of a common pacific wide phenomenon our results reveal that natural variability in upper ocean properties is greater than previously appreciated and coherent with changes in the tropical thermocline supporting both theories and models postulating the importance of extratropical tropical teleconnections and the oceanic tunnel in interdecadal to centennial climate variability

multidecadal and multicentennial variability of the meridional overturning circulation the variability of the meridional overturning circulation moc simulated in a multimillenial control integration of the kiel climate model kcm displays enhanced variability relative to the red background at decadal and centennial timescales the multidecadal variability is the model s version of the atlantic multidecadal variability amv often referred to as atlantic multidecadal oscillation amo while multidecadal variability originates in the north atlantic multicentennial variability is driven in the southern ocean both multidecadal and multicentennial variability are associated with considerable changes in sea ice extent this may be important to understand the different evolution of sea ice cover in the northern and southern hemisphere during the most recent decades with a strong decline observed in the north and almost no trend in the south

strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation the climate of the last glacial period was extremely variable characterized by abrupt warming events in the northern hemisphere accompanied by slower temperature changes in antarctica and variations of global sea level it is generally accepted that this millennial scale climate variability was caused by abrupt changes in the ocean thermohaline circulation here we use a coupled ocean atmosphere sea ice model to show that freshwater discharge into the north atlantic ocean in addition to a reduction of the thermohaline circulation has a direct effect on southern ocean temperature the related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical north atlantic caused by a fast wave adjustment process we present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of greenland and antarctic temperature changes the slow changes in antarctic temperature and its similarity to sea level as well as a possible time lag of sea level with respect to antarctic temperature during marine isotope stage 3

wobbly ocean conveyor circulation during the holocene abstract compared to the last glacial period the climate of the holocene has been quite stable however the record does suggest that at high latitudes in the north temperatures have cooled at least since the middle holocene and that this cooling has been modulated by millennial duration fluctuations that culminated in the medieval warm little ice age oscillation in this paper we explore the possibility that these variations were associated with concurrent changes in the strength of the atlantic s conveyor circulation three lines of evidence are considered one involves records that relate directly to ocean operation a second involves the tie between sea ice extent in the northern atlantic and the extent of mountain glaciers in the european alps and in the cordillera of western north america and a third involves evidence for a bipolarity in climate changes in the northern and southern polar regions in addition we look into clues provided by the atlantic multidecadal oscillation amo although at this point no firm conclusion can be drawn the case for ocean involvement is sufficiently strong to merit further attention

the 11 december 1995 earthquake mw 6 4 implications for the present day relative motion on the rivera cocos plate boundary the 11 december 1995 earthquake is the largest and best constrained instrumentally recorded event which has occurred on the rivera cocos plate boundary the reported focal mechanism for this event indicates almost pure strike slip faulting with nodal planes oriented north south and east west a visual inspection shows that the seismograms recorded world wide strongly suggest a directivity effect indicative of a rupture propagating eastward from the epicenter this observation is confirmed by a directivity analysis which shows a sharp reduction in the difference between observed and synthetic seismograms when the rupture direction is at an azimuth of approximately 90 these results indicate that the east west trending nodal plane of the earthquake of 11 december 1995 is the actual fault plane considering that this is the largest instrumentally recorded earthquake in the region it strongly suggests that the relative motion of the rivera plate with respect to the cocos plate takes place along east west oriented faults and that the sense of motion is right lateral strike slip

cooling of the southern high latitudes during the medieval period and its effect on enso abstract a high resolution multiproxy study performed on a marine record from se pacific off southern south america was used to reconstruct past regional environmental changes and their relation to global climate particularly to el nino southern oscillation enso phenomenon during the last 2200 years our results suggest a sustained northward shift in the position of the zonal systems i e the southern westerly wind belt and the antarctic circumpolar current which occurred between 1300 and 750 yr bp the synchrony of the latitudinal shift with cooling in antarctica and reduced enso activity observed in several marine and terrestrial archives across south america suggests a causal link between enso and the proposed displacement of the zonal systems this shift might have acted as a positive feedback to more la nina like conditions between 1300 and 750 yr bp by steepening the hemispheric and tropical pacific zonal sea surface temperature gradient this scenario further suggests different boundary conditions for enso before 1300 and after 750 yr bp

unprecedented recent warming of surface temperatures in the eastern tropical pacific ocean climate variability in the tropical pacific ocean influences climate across much of the planet a diatom based record of sea surface temperatures from el junco lake galapagos reveals that the most recent half century is the warmest 50 year period in the past 1 200 years through its intimate connection with the el nino southern oscillation system climate variability in the tropical pacific ocean influences climate across much of the planet but the history of temperature change in the tropical pacific ocean during recent millennia is poorly known the available annually resolved records1 2 are discontinuous and rarely span more than a few centuries longer records at coarser temporal resolution suggest that significant oceanographic changes observed at multi year to multi century resolution have had important effects on global climate3 4 5 here we use a diatom record from el junco lake galapagos to produce a calibrated continuous record of sea surface temperature in the eastern tropical pacific ocean at subdecadal resolution spanning the past 1 200 years our reconstruction reveals that the most recent 50 years are the warmest 50 year period within the record because our diatom based sea surface temperature index resembles northern hemisphere temperature reconstructions we suggest that with continued anthropogenic warming the eastern tropical pacific ocean may continue to warm

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

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

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

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

simulated changes in the extratropical southern hemisphere winds and currents 1 the results from 12 global climate models show a remarkably consistent strengthening and poleward shifting of the zonal wind stress through the 20th and 21st centuries at extratropical southern hemisphere latitudes changes in the zonal circulation of the ocean in the region are broadly consistent with the changes in zonal wind stress in particular the climate models simulate a strengthening and a poleward shift of the antarctic circumpolar current the strengthening of the zonal wind stress also results in intensifying northward ekman transport across the antarctic circumpolar current which in the unblocked latitudes of drake passage implies increasing southward geostrophic transport in the ocean below about 2000 m zonal wind stress changes such as these may be expected to enhance the mesoscale eddy activity in the southern ocean

tv video observations of bed and basal sliding on storglaciaren sweden four boreholes in storglaciaren a small valley glacier in northernsweden were inspected with a video camera in two of the boreholes the apparentglacier bed was filmed in one borehole the bed was found to be composed of softsediment but in the other it consisted of bedrock in the latter the camera moved5 6 mm relative to the bed during an 80 min period the recorded camera movementshowed a background motion which is in the expected range of basal sliding superimposed on the background motion a jerky motion of a high speed spike wasfound the jerky motion is interpreted as a stress release induced by local topographyat the ice bed interface

warming and circulation change in the eastern south pacific ocean deep ocean temperature salinity and dissolved oxygen observations in the eastern south pacific ocean collected during the late austral fall in 1995 are compared with observations made there 28 years earlier during the same season and similar el nino southern oscillation phase warming observed above 800 m at 43 s reflects the production of warmer subantarctic mode water in recent decades warming observed above 1600 m at 28 s is due to downward isotherm displacement and southward movement of water masses by 100 200 km as revealed by joint analysis of temperature and oxygen data such changes would be expected for a weaker subtropical gyre in the south pacific an observed oxygen decrease between about 1800 m and 2900 m at 28 s may indicate enhanced southward boundary current flow at mid depths off chile

antarctic timing of surface water changes off chile and patagonian ice sheet response marine sediments from the chilean continental margin are used to infer millennial scale changes in southeast pacific surface ocean water properties and patagonian ice sheet extent since the last glacial period our data show a clear antarctic timing of sea surface temperature changes which appear systematically linked to meridional displacements in sea ice westerly winds and the circumpolar current system proxy data for ice sheet changes show a similar pattern as oceanographic variations offshore but reveal a variable glacier response time of up to 1000 years which may explain some of the current discrepancies among terrestrial records in southern south america

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

regional cooling in a warming world recent temperature trends in the southeast pacific and along the west coast of subtropical south america 1979 2006 1 while it is widely accepted that the global mean atmospheric temperature has increased in recent decades the spatial distribution of global warming has been complex in this study we comprehensively characterize the spatial pattern including vertical structure of temperature trends along the subtropical west coast of south america continental chile for the period 1979 2006 and examine their consistency with expectations based on the cmip 3 ensemble of coupled ocean atmosphere simulations for the late 20th century in central and northern chile 17 37 s the most notable feature is a strong contrast between surface cooling at coastal stations 0 2 c decade and warming in the andes 0 25 c decade only 100 200 km further inland coastal radiosonde data imply that the coast andes variation is largely due to strong vertical stratification of temperature trends in the atmosphere west of the andes the coastal cooling appears to form part of a larger scale la nina like pattern and may extend below the ocean mixed layer to depths of at least 500 m over continental chile the cmip 3 gcm ensemble predicts temperature trends similar to those observed in the andes the cooling along the chilean coast is not reproduced by the models but the mean sst warming is weaker there than any other part of the world except the southern ocean it is proposed that the intensification of the south pacific anticyclone during recent decades which is also a simulated consequence of global warming is likely to play a major role in maintaining cooler temperatures off the coast of chile

regional differences in quaternary subantarctic nutrient cycling link to intermediate and deep water ventilation several fundamental issues regarding carbon cycling in the glacial oceans rest on the development of reliable descriptions of high southern latitude surface waters here we compare new subantarctic planktonic foraminiferal 13c records with previously published records to demonstrate two distinct regional patterns over glacial cycles 1 a low amplitude signal 0 7 previously observed in the indian primarily in globigerina bulloides that also dominates the pacific and 2 a higher amplitude signal previously observed in neogloboquadrina pachyderma that is confined to the atlantic and western indian sectors the new observations from the southeast pacific a primary region of antarctic intermediate water aaiw formation strengthen the suggestion that intermediate water acted as a conduit for transferring 13c variability to low latitudes because the timing and amplitude of the indo pacific low amplitude 13c changes are similar to those observed in planktonic records from the tropical pacific and atlantic a new benthic foraminiferal 13c record from intermediate depths in the south atlantic is also similar to the southeast pacific surface water records further demonstrating that this link between high and low latitude surface waters might be maintained the widespread indo pacific subantarctic surface water signal is obscured in records from the atlantic sector by the large glacial interglacial 13c signal 1 0 that is most likely the result of nutrient changes related to variable north atlantic deep water nadw production we find that the large change found uniformly in atlantic n pachyderma 13c records is not matched in a new g bulloides 13c record the confined regional extent of the high amplitude signal and the discrepancy between the two species suggest that most of the excess nutrients in the glacial atlantic inferred from 13c may be removed seasonally by increased production in the subantarctic

wisconsinan and pre wisconsinan ice thicknesses on ellesmere island canada inferences from ice cores study of two cores through an ice cap on northern ellesmere island suggests 1 during the wisconsin glaciation the ice near the crest was never more than about 200 m thicker than at present 2 in a preceding glaciation the ice was thicker than this and the local ice divide near the boreholes was eliminated 3 early in the sangamon interglacial basal melting occurred in a deep bedrock valley south of the borehole site and 4 the change in 18o at the wisconsinan holocene transition is 11 of which at least 8 results from climatic warming

debris from the basal ice of the agassiz ice cap ellesmere island arctic canada this article describes the characteristics of debris obtained from the basal ice in a borehole in the agassiz ice cap ellesmere island northwest territories by the canadian polar continental shelf project in 1979 the debris appears to have been incorporated by basal freezing at a time when the base of the glacier upstream was near the pressure melting point and some 19 c warmer than at the present site such an occurrence may be explained by a different flow regime by a thicker ice sheet by the influence of irregular bedrock topography on basal ice conditions at some stage in the past or by a combination of these factors

the effect of subtropical cooling on the amplitude of enso a numerical study the effect of an enhanced subtropical surface cooling on el nino southern oscillation enso through the ocean tunnel is investigated using a coupled model here the term ocean tunnel refers to the water pathway that connects the equatorial upwelling water to the subtropical extratropical surface water the subtropical cooling is introduced through a reduction of the radiative convective equilibrium sst sstp in that region the sstp for the equatorial region is kept fixed it is found that an enhanced cooling in the subtropics results in a regime with stronger enso this is because an enhanced subtropical cooling reduces the temperature of the water feeding the equatorial undercurrent through the ocean tunnel the resulting larger difference between the warm pool sst and the temperature of the equatorial thermocline water the source water for the equatorial upwelling tends to increase the equatorial zonal sst contrast between the western and the eastern pacific in response to this destabilizing forcing to the coupled equatorial ocean atmosphere a stronger enso develops enso is found to regulate the time mean difference between the warm pool sst and the temperature of the equatorial undercurrent the findings provide further support for the heat pump hypothesis for enso which states that enso is an instability driven by the meridional differential heating over the pacific ocean and that enso regulates the long term stability of the coupled equatorial pacific climate the results also substantiate the notion that surface variability from higher latitudes may influence equatorial sst variability through the ocean tunnel

the freshening of surface waters in high latitudes effects on the thermohaline and wind driven circulations abstract the impacts of a freshening of surface waters in high latitudes on the deep slow thermohaline circulation have received enormous attention especially the possibility of a shutdown in the meridional overturning that involves sinking of surface waters in the northern atlantic ocean a recent study by fedorov et al has drawn attention to the effects of a freshening on the other main component of the oceanic circulation the swift shallow wind driven circulation that varies on decadal time scales and is closely associated with the ventilated thermocline that circulation too involves meridional overturning but its variations and critical transitions affect mainly the tropics a surface freshening in mid to high latitudes can deepen the equatorial thermocline to such a degree that temperatures along the equator become as warm in the eastern part of the basin as they are in the west the tropical zonal sea surface temperature gradient virtually disappears and permanently warm conditions prevail

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

linear trends in salinity for the world ocean 1955 1998 1 quality controlled oceanographic profile salinity measurements from the world ocean database 2001 wod01 were used to calculate linear trends of zonally averaged salinity anomalies for running five year periods from 1955 1959 through 1994 1998 for the world ocean and the atlantic pacific and indian ocean basins from the surface to 3000 meters depth each basin exhibits large scale coherent trends most of the pacific is freshening with the exception of the subtropical south pacific the atlantic exhibits a deep freshening in the subpolar gyre and a shallower more intense increase in salinity in the tropics and subtropics the indian ocean is becoming more saline at all latitudes in the upper 150 meter layer with a subsurface freshening between 40 s and the equator in the 250 1000 meter layer there is freshening in both the weddell and ross seas