a review of the intracontinental porphyry deposits in the middle lower yangtze river valley metallogenic belt eastern china abstract the middle lower yangtze river valley metallogenic belt mlyb is one of the most important metallogenic belts in eastern china and contains many important porphyry deposits these deposits include the tongshankou cu mo jiguanzui cu au chengmengshan cu mo wushan cu mo fengshandong cu au dingjiashan cu yangjishan au shaxi cu au dongguashan cu au shujiadian cu and anjishan cu deposits etc in this review we summarize the geological characteristics including the stratigraphy structure ore bearing porphyry types vein characteristics and wall rock alteration metallogenic ages and petro geochemistry of representative porphyry deposits in the mlyb we conclude that porphyritic magmatism and metallogeny have occurred in three stages the early ca 149 135 ma and late ca 123 105 ma stages comprise mainly porphyry skarn mineralization whereas the middle ca 133 125 ma stage comprises porphyry mineralization ore bearing porphyries in the mlyb are the high k calc alkaline to calc alkaline series with the majority possess adakitic geochemical signature the ore bearing porphyries with adakitic signature may have originated from magma mixing produced by the delamination of enriched lithospheric mantle and partial melting of the thickened lower crust the enriched mantle derived mafic melts component are very important for generating fertile magma and the 34s and 18o values suggest that ore forming materials were magma derived compared with porphyry deposits in typical magmatic arc settings porphyry deposits in the mlyb do not contain advanced argillic lithocaps or high to intermediate sulfidation systems and the magmatic and ore forming material sources are also very different

the equatorial undercurrent in the central atlantic and its relation to tropical atlantic variability seasonal to interannual variations of the equatorial undercurrent euc in the central atlantic at 23 w are studied using shipboard observation taken during the period 1999 2011 as well as moored velocity time series covering the period may 2005 june 2011 the seasonal variations are dominated by an annual harmonic of the euc transport and the euc core depth both at maximum during september and a semiannual harmonic of the euc core velocity maximum during april and september substantial interannual variability during the period of moored observation included anomalous cold warm equatorial atlantic cold tongue events during 2005 2008 the easterly winds in the western equatorial atlantic during boreal spring that represent the preconditioning of cold warm events were strong weak during 2005 2008 and associated with strong weak boreal summer euc transport the anomalous year 2009 was instead associated with weak preconditioning and smallest euc transport on record from january to july but during august coldest sst anomalies in the eastern equatorial atlantic were observed the interannual variations of the euc are discussed with respect to recently described variability of the tropical atlantic ocean

distribution of chemical tracers in the eastern equatorial pacific during and after the 1982 1983 el nino southern oscillation event during april 1983 and march april 1984 two cruises were conducted in the central equatorial pacific to determine the effects of the el nino southern oscillation enso event on the sea air exchange of co2 measurements of total carbon dioxide pco2 total alkalinity freon 11 salinity temperature oxygen nutrients and wind and current velocities were made along three meridional transects 158 w april 1983 150 w march 1984 170 w april 1984 the cessation of upwelling during the enso event caused pco2 concentrations in surface waters to decrease to near saturation levels along the equator the calculated net flux of co2 across the sea air interface was essentially negligible in the eastern equatorial pacific during this period however when normal trade winds and consequent upwelling returned in late 1983 and early 1984 the equatorial region returned to a pco2 condition of highly supersaturated surface waters in the region between 8 n and 8 s along the 150 and 170 w transects the calculated post enso sea air flux of co2 exceeded 6 0 mmol co2 m 2d 1 the mean annual co2 flux in the equatorial pacific was estimated to be 0 02 gt of carbon during the 1982 1983 enso event as compared with 0 6 gt during 1984

near equatorial ctd observations at 85 w in october 1982 ctd data collected about the equator along 85 w between october 8 and 12 1982 are used to investigate stratification changes in the upper 1 km associated with the 1982 83 el nino with respect to the thermal field observed in november 1981 virtually the entire section exhibited downward displacements in the upper kilometer of the water column observed displacements at the depth of the mean thermocline were large 150 m and relatively symmetric about the equator displacements around 1 km depth were near zero this stratification change appears to have been produced by a zonal convergence of mass at temperatures above 15 c with divergence below least square modal decompositions of the vertical displaced profiles revealed significant contributions from modes 1 and 2 with meridional structure consistent with kelvin waves the observations thus support current theories that relate el nino onset in the eastern pacific to anomalous wind forcing in the west

subsurface equatorial zonal current in the eastern indian ocean 1 variations of subsurface zonal current in the eastern equatorial indian ocean are investigated by examining 6 year data december 2000 november 2006 from acoustic doppler current profiler adcp mooring at 0 s 90 e the analysis indicates the presence of an eastward equatorial subsurface current between 90 and 170 m depths during both boreal winter and summer during boreal winter the generation of eastward pressure gradient which drives an eastward flow in the thermocline is caused primarily by upwelling equatorial kelvin waves excited by prevailing easterly winds on the other hand the downwelling rossby waves generated by the reflection of the spring downwelling kelvin waves in the eastern boundary as well as the upwelling equatorial kelvin waves triggered by easterlies create an oceanic state that favors the generation of the eastward pressure gradient during boreal summer the subsurface current reveals a distinct seasonal asymmetry the maximum eastward speed of 63 cm s 1 is observed in april and secondary maximum of 49 cm s 1 is seen in october the zonal transport per unit width within depth of the subsurface current exhibits similar variations reaching maximum eastward transport of 35 m2 s 1 in april and secondary maximum of 29 m2 s 1 in october moreover the subsurface current during boreal summer undergoes significant interannual variations it was absent in 2003 but it was anomalously strong during 2006

observations of annual and el nino thermal and flow variations at 0 110 w and 0 95 w during 1980 1985 moored measurements of the surface wind and of the current and temperature fields within the uppermost 250 m were recorded from march 1980 to september 1985 at 0 110 w and from july 1981 to november 1983 at 0 95 w at these sites the annual mean thicknesses of the equatorial undercurrent euc and of the surface portion of the south equatorial current sec were about 200 m and 20 m respectively the annual mean euc core speed was 0 9 m s 1 annual cycles of temperature and zonal current at 110 w were most distinctive near the surface at nominal depths of 15 m and 47 5 m the average annual amplitudes were 1 5 c and 0 5 m s 1 at about 100 m the annual amplitudes were about 0 5 c and 0 10 m s 1 at 15 m the annual mean zonal current was 0 05 m s 1 which was not representative of the monthly mean zonal current in april the monthly mean direction was eastward and in october it was westward with speeds of about 0 5 m s 1 in both months warmer water occurred in april and colder water in october the direction of the zonal wind component was westward throughout the year and the annual amplitude of the zonal wind was only about 2 5 times larger than that of the zonal current the average amplitude of the annual cycle of the meridional current component was less than 0 05 m s 1 and not distinguishable from year to year monthly mean variations monthly mean anomalous or el nino currents at 110 w were defined as the difference between the observations and the annual cycle during the august december 1982 onset phase of el nino the strength of the normally westward flowing near surface sec was greatly reduced to near zero speed by an el nino eastward flowing zonal current of about 0 3 m s 1 the largest vertically averaged 15 250 m zonal current anomaly 0 5 m s 1 occurred in january and february 1983 and represented a substantial decrease in the eastward transport of the euc causing a disappearance of the undercurrent the duration of the euc disappearance was longer at 95 w than at 110 w a surface intensified eastward jet with a maximum daily speed of 1 75 m s 1 at 15 m occurred in may 1983 at 110 w but not at 95 w a massive redistribution of heat throughout the mixed layer and thermocline was associated with the 1982 1983 el nino beginning in august 1982 the thermocline at 110 w and 95 w sank 100 m reaching its maximum depth in december 1982 temperatures at 100 m and 150 m which normally were about 15 c and 14 c reached 27 5 c and 22 5 c the time rate of change of the 15 to 200 m heat content was 500 w m 2 during the august december 1982 warming phase and 460 w m 2 during the january february 1983 subsurface cooling phase the euc disappeared during the subsurface cooling phase a second less intensive mixed layer deepening occurred in may 1983 at 95 w but not at 110 w

upper equatorial atlantic variability during 2002 and 2005 associated with equatorial kelvin waves on the basis of moored 35 degrees w 0 degrees and 23 degrees w 0 degrees and satellite observations we contrast the upper equatorial atlantic variability during 2002 with those during 2005 inspection of the interannual boreal summer cold tongue variability revealed a warm cold event in 2002 2005 with relaxed intensified winds in the west and the equatorial undercurrent euc embedded in a shallower deeper thermocline at 23 degrees w during both years 2002 and 2005 equatorial kelvin waves are present in moored observations as 20 degrees c isotherm depth anomalies and dynamic height anomalies basin wide sea surface height anomalies are used to derive an equatorial kelvin wave mode the time evolution of this mode represents the basis for a regression analysis to investigate related oceanic variability compared to the exceptionally strong wave activity in 2002 equatorial kelvin waves were generally weaker during 2005 the main effect of equatorial kelvin waves on zonal velocity anomalies at 23 degrees w 0 degrees is evident well below the euc core their direct influence on cold tongue sea surface temperature is small but they are found to affect the equatorial thermocline slope prior to the cold tongue onset in 2002 2005 the presence of equatorial kelvin waves is associated with a flattened steeper thermocline slope that is crucial for the shallowing deepening of the euc core at 23 degrees w and that might precondition the development of the warm cold event

temporal variability of current driven upwelling at jarvis island 1 the temporal variability of upwelling on the western side of jarvis island caused by the island blocking of free stream currents is investigated using in situ and shipboard observations variations in upwelling are related to changes in the strength and depth of the equatorial undercurrent euc caused by wind forcing at different timescales seasonally the strongest upwelling at jarvis occurs in boreal spring when a weakening of the trade winds in the eastern and central pacific coincides with a locally shallow thermocline and shallow and strong euc year to year differences in springtime upwelling are associated with the strength of the trade winds in the western pacific intensified trade winds associated with la nina conditions favor the shoaling of the thermocline and the euc at jarvis on intraseasonal timescales upwelling events at jarvis are linked to local trade wind bursts which cause a regional upwelling that also enhances euc driven upwelling strong 1 00 m s 1 near surface eastward currents measured at jarvis associated with trade wind relaxations in the central pacific are downwelling favorable during periods of euc driven upwelling interactions of the semidiurnal tide with jarvis result in abrupt cold spikes 1 4 c that tend to occur at 12 hour period tidal currents and temperature fluctuate 180 out of phase such that minimum temperatures coincide with maximum eastward current the high frequency upwelling appears to be most consistent with the presence of internal tides

paleoceanography of the tropical eastern pacific ocean the east pacific barrier epb is the most effective marine barrier to dispersal of tropical shallow water fauna in the world today the fossil record of corals in the eastern pacific suggests this has been true throughout the cenozoic in the cretaceous the epb was apparently less effective in limiting dispersal equatorial circulation in the pacific then appears to have been primarily east to west and the existence of oceanic atolls now drowned guyots in the eastern pacific probably aided dispersal similarly in the middle and early mesozoic and late paleozoic terranes in the central tropical pacific likely served as stepping stones to dispersal of tropical shelf faunas reducing the isolating effect of an otherwise wider pacific ocean panthalassa

fresh equatorial jets abstract a vertically sheared eastward jet in the equatorial pacific in late 1991 and early 1992 carried relatively fresh water from the western pacific overriding the saltier surface layer of the central region salinity anomalies of about 1 0 psu were observed over a period of several months in a surface layer 50 m thick near the equator below this fresh layer them was a steep halocline having very little temperature stratification so that the density changes were dominated by salinity in december 1991 eastward surface velocities in the fresh jet at 170 w were 100 cm s 1 with a shear of about 40 cm s 1 in the top 100 m the core of the jet was about 200 km in width centered at 1 5 s the jet decayed and vanished over the next few months though the surface halocline remained a simple extension of the familiar 1 layer model can account for the initial development of the sheared eastward jet the surface pressure gradient in this initial value problem tending to accelerate the fluid eastward dim

shallow equatorial jets when zonal velocity profiles from the central equatorial pacific are expanded into sums of vertical normal modes the peak amplitudes occur consistently near modes 1 5 12 and 18 the first two of these peaks sum to a recognizable equatorial undercurrent profile the two higher mode peaks blunt and thicken the equatorial undercurrent euc and add a westward extremum near 340 m during the 1982 1983 el nino the low mode component of the flow modes 1 10 was more variable than the residual component which was dominated by the modes near 12 and 18 the residuals below 120 m persisted as alternating westward and eastward current bands the shallow jets through the disappearance of the euc in the second half of 1982 and its reappearance in 1983 the shallow jets were nearly constant in depth until late 1982 and then gradually rose through the end of the time series in june 1983 differences in temporal behavior among the mode amplitude peaks indicate that these peaks are describing dynamically separate components of the flow which are not tightly coupled on time scales shorter than a few months

equatorial undercurrent disappears during 1982 1983 el nino the equatorial undercurrent at 159 w decayed during august 1982 partially reversed during september and rapidly reappeared in january 1983 the virtual disappearance is consistent with the basin wide adjustment of sea surface slope to the strong westerly winds in the western and central pacific that caused the 1982 1983 el nino event

the north equatorial countercurrent and heat storage in the western pacific ocean during 1982 83 a sequence of extreme climate anomalies known as an el nino southern oscillation episode was observed in the tropical pacific ocean during 1982 831 2 models suggest that oceanic circulation has an important role in the formation of such anomalies1 3 4 by altering the pattern of sea surface temperature through advection the baroclinic structure of the upper 500 m of the ocean has been monitored routinely in the western pacific since 1979 providing indirect current measurements by the geostrophic method these observations reported here show large changes in the near equatorial currents during 1982 83 which are consistent with currents observed in the central and eastern pacific5 6 in particular the north equatorial countercurrent necc flowed with 25 50 increased strength during the early phase then weakened almost to zero flow the west pacific heat pool cooled by more than 1 c observed changes in circulation were large enough to alter surface heat storage by advection although other potentially important processes may not be negligible

comparison of equatorial pacific sea surface temperature variability and trends with sr ca records from multiple corals coral sr ca is widely used to reconstruct past ocean temperatures however some studies report different sr ca temperature relationships for conspecifics on the same reef with profound implications for interpretation of reconstructed temperatures we assess whether these differences are attributable to small scale oceanographic variability or vital effects associated with coral calcification and quantify the effect of intercolony differences on temperature estimates and uncertainties sr ca records from four massive porites colonies growing on the east and west sides of jarvis island central equatorial pacific were compared with in situ logger temperatures spanning 2002 2012 in general sr ca captured the occurrence of interannual sea surface temperature events but their amplitude was not consistently recorded by any of the corals no long term trend was identified in the instrumental data yet sr ca of one coral implied a statistically significant cooling trend while that of its neighbor implied a warming trend slopes of sr ca temperature regressions from the four different colonies were within error but offsets in mean sr ca rendered the regressions statistically distinct assuming that these relationships represent the full range of sr ca temperature calibrations in jarvis porites we assessed how well sr ca of a nonliving coral with an unknown sr ca temperature relationship can constrain past temperatures our results indicate that standard error of prediction methods underestimate the actual error as we could not reliably reconstruct the amplitude or frequency of el nino southern oscillation events as large as 2 c our results underscore the importance of characterizing the full range of temperature sr ca relationships at each study site to estimate true error

the vertical structure of the zonal pressure gradient in the eastern equatorial pacific ctd data from the epocs and norpax experiments were used to construct a mean zonal pressure gradient profile between 110 w and 150 w for the 1979 to 1981 pre el nino time period the mean zonal pressure gradient referenced to 100 dbar had a value of 4 5 10 7 m s 2 at the surface and decreased to within two standard errors of zero at 200 dbar below this depth the mean was not significantly different from zero deviations from this mean were not related to fluctuations of the zonally averaged zonal wind stress between 150 w and 110 w rather the largest deviations in the boreal springs of 1979 and 1980 appeared to be associated first with vertical mode kelvin wave pulses propagating eastward along the equator the 1979 81 mean profile was also used as a reference to examine variations in zonal pressure gradient during the 1982 83 enso event the sea surface was more sharply sloped upward from the east to west in april and september 1982 before arid near the beginning of the event the surface slope was below normal in april and october 1983 vertical profiles of the zonal pressure gradient deviations showed large high vertical mode contributions during the vent than in the prevent samples

a linear stratified ocean model of the equatorial undercurrent a linear stratified ocean model is used to study the wind driven response of the equatorial ocean the model is an extension of the lighthill 1969 model that allows the diffusion of heat and momentum into the deeper ocean and so can develop non trivial steady solutions to retain the ability to expand solutions into sums of vertical normal modes mixing coefficients must be inversely proportional to the square of the back ground vaisala frequency the model is also similar to the earlier homogeneous ocean model of stommel i960 he extended ekman dynamics to the equator by allowing his model to generate a barotropic pressure field the present model differs in that the presence of stratification allows the generation of a baroclinic pressure field as well the most important result of this paper is that linear theory can produce a realistic equatorial current structure the model undercurrent has a reasonable width and depth scale there is westward flow both above and below the undercurrent the meridional circulation conforms to the classical picture suggested by cromwell 1953 unlike the stommel solution the response here is less sensitive to variations of parameters ocean boundaries are not necessary for the existence of the undercurrent but are necessary for the existence of the deeper equatorial intermediate current the radiation of equatorially trapped rossby and kelvin waves is essential to the development of a realistic undercurrent because the system supports the existence of these waves low order vertical modes can very nearly adjust to sverdrup balance defined below which in a bounded ocean and for winds without curl is a state of rest as a result higher order vertical modes are much more visible in the total solution this property accounts for the surface trapping and narrow width scale of the equatorial currents the high order modes tend to be in yoshida balance defined below and generate the characteristic meridional circulation pattern associated with equatorial ekman pumping

upper equatorial pacific ocean current and salinity variability during the 1996 1998 el nino la nina cycle the recent el nino la nina cycle exhibited striking patterns of current and salinity variability in the upper equatorial pacific ocean this evolution is described from mid 1996 through 1998 using a remarkable data set of 35 meridional conductivity temperature depth ctd acoustic doppler current profiler adcp sections along with buoy data the sections nominally from 8 s to 8 n between 165 e and 95 w were occupied over the course of 27 months a wide range of current variability was sampled with currents that appeared or disappeared some time during the cycle including an equatorially trapped eastward surface current the equatorial undercurrent the northern branch of the south equatorial current and the north equatorial countercurrent basin wide interannual changes in upper ocean and pycnocline zonal transports were as large as 64 32 106 m3 s 1 changes in the salinity structure included a deep and fresh mixed layer in the central equatorial pacific that built up during the el nino and was then disrupted by upwelled salty water with the onset of la nina a very fresh mixed layer observed in the eastern equatorial pacific late in the el nino and a reduction in the strength of the meridional equatorial salinity gradient within the pycnocline to one third of the usual value during the el nino finally the zonal transports above the thermocline from 5 s to 5 n were well correlated with the rate of change of warm water volume west of the individual ctd adcp sections

a simulation of the 1982 1983 el nino a general circulation model of the equatorial pacific ocean was used to simulate the 1982 1983 el nino event the wind data set used to force the model is that of florida state university fsu the results are presented here and compared with those from other simulations the model results show that the simulation is successful in reproducing the major features of the 1982 1983 el nino such as the disappearance of the equatorial undercurrent the pattern and magnitude of the sea surface temperature anomaly and the variations of the thermocline however there is a delay of about 2 3 months in these events in the model compared with those observed this is attributed to the wind stress forcing during 1982 in the eastern equatorial pacific which is more intense in the fsu wind data set than in the national meteorological center data set along the south american coast the model results show a persistent cooling before a slight warming in april 1983 during the event which is not understood

interannual modality of upper ocean temperature 4d structure revealed by argo data abstractusing the newly available decade long argo data for the period 2004 13 a detailed study is carried out on deriving four dimensional 4d modality of sea temperature in the upper ocean with emphasis on its interannual variability in terms of amplitude phase and periodicity three principal modes with central periodicities at 19 2 33 8 and 50 3 months have been identified and their relationship with el nino southern oscillation enso is investigated yielding a number of useful results and conclusions 1 a striking tick shaped pipe like feature of interannual variability maxima which is named the nino pipe in this paper has been revealed within the 10 s 10 n upper pacific ocean 2 the pipe core extends downward from 50 m at 130 e to 250 m near the date line before tilting upward to the sea surface at about 275 e coinciding nicely with the pathway of the pacific equatorial undercurrent euc 3 the double peak zonal modality pattern of the nino pipe in the upper pacific is echoed in

observed relationships between oceanic kelvin waves and atmospheric forcing abstract the madden julian oscillation mjo has been implicated as a major source of the wind stress variability that generates basin scale kelvin waves in the equatorial pacific one source of debate concerning this relationship is the apparent difference in the frequencies of the two processes this work utilizes data from the tropical atmosphere ocean tao array of moored buoys along with outgoing longwave radiation data to show by means of a multiple linear regression model and case studies that the frequency discrepancy is due to a systematic decrease in the phase speeds of the kelvin waves and an increase in the period of the waves toward the east as conditions adjust toward el nino among the potential contributing factors to this phase speed decrease is an apparent air sea interaction that enhances the wind forcing of some of the kelvin waves allowing them to continue to amplify because the propagating wind stress anomaly decelerates to the speed of the developing kelvin wave instead of the sig

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

observing the galapagos euc interaction insights and challenges although sustained observations yield a description of the mean equatorial current system from the western pacific to the eastern terminus of the tropical atmosphere ocean tao array a comprehensive observational dataset suitable for describing the structure and pathways of the equatorial undercurrent euc east of 958w does not exist and therefore climate models are unconstrained in a region that plays acriticalroleinocean atmospherecoupling furthermore oceanmodelssuggestthattheinteractionbetween

long term observations of tropical instability waves abstract reynolds sea surface temperature sst data showing tropical instability waves tiws in the tropical pacific are analyzed along with current measurements from the tropical atmosphere ocean tao buoy array and wind speeds from the european remote sensing satellite ers 1 and 2 scatterometers tiws are visible as undulations in the sst cold fronts that delineate the northern and southern boundaries of the cold tongue in the equatorial pacific the sst pattern results from advection of the sst front by instabilities in the near surface equatorial currents although the waves are seen on both sides of the pacific cold tongue and north of the equator in the atlantic they are most intense and thereby most observable in the north equatorial pacific the combination of data used in this analysis provides information about these waves the factors controlling them and their coupling to the atmosphere on annual and interannual timescales on annual timescales the tiws generally establish a strong

the hawaii to tahiti shuttle experiment the shuttle experiment conducted between hawaii and tahiti from january 1979 to june 1980 was designed to observe the changing equatorial ocean structure and circulation to study the variations and interactions of the four major equatorial ocean currents and to develop a scientific basis for their monitoring by simple observations of thermal structure and sea level preliminary analyses of the results show that the equatorial thermal structure remains intact during a normal year and that only the positions and intensities of the currents are subject to change the water transport of the equatorial undercurrent varied from 25 x 106 cubic meters per second in january to 51 x 106 cubic meters per second in july but also exhibited strong short term pulsations the equatorial surface flow responded strongly to the winds at periods of 1 month and longer an array of drifter buoys in the equatoral countercurrent was subject to very little dispersion while traveling over 4500 kilometers in 4 months low frequency fluctuations in the north equatorial countercurrent can be monitored by means of the difference in sea level between fanning and majuro

strong sea surface cooling in the eastern equatorial pacific and implications for galapagos penguin conservation the galapagos is a flourishing yet fragile ecosystem whose health is particularly sensitive to regional and global climate variations the distribution of several species including the galapagos penguin is intimately tied to upwelling of cold nutrient rich water along the western shores of the archipelago here we show using reliable high resolution sea surface temperature observations that the galapagos cold pool has been intensifying and expanding northward since 1982 the linear cooling trend of 0 8 c per 33 years is likely the result of long term changes in equatorial ocean circulation previously identified moreover the northward expansion of the cold pool is dynamically consistent with a slackening of the cross equatorial component of the regional trade winds leading to an equatorward shift of the mean position of the equatorial undercurrent the implied change in strength and distribution of upwelling has important implications for ongoing and future conservation measures in the galapagos

variability in the eastern equatorial pacific ocean during 1986 1988 we examine variability in the eastern equatorial pacific during 1986 1988 using conductivity temperature depth data velocity and temperature data from equatorial moorings between 110 w and 140 w and wind data from a basin scale zonal array of islands and moorings between 110 w and 165 e the period studied coincides with the el nino southern oscillation enso event of 1986 1987 and a subsequent cold event in 1988 weak warm sea surface temperature anomalies first appeared in the eastern equatorial pacific in mid 1986 and increased to 1 c in september november 1986 in association with a 30 cm s 1 weakening of the south equatorial current and a 20 to 40 m depression of the thermocline these warm anomalies lasted until early 1988 after which a large scale shoaling of the thermocline led to sea surface temperatures more than 3 c colder than climatology year to year fluctuations in the eastern pacific were related primarily to zonal wind variations in the central and western pacific westerly wind stress anomalies of 0 02 0 05 n m 2 were observed between 140 w and 165 e from the latter half of 1986 until the end of 1987 these were replaced by easterly wind anomalies of similar magnitude between 157 w and 165 e in 1988 energetic intraseasonal fluctuations with periods of 2 3 months were also prominent in zonal current temperature and dynamic height time series these fluctuations propagate eastward at approximately first baroclinic mode kelvin wave phase speeds and are forced west of the date line by episodes of westerly winds extrema in several oceanic variables occurred in association with these waves though their precise dynamical link to the enso cycle is unclear from our data sea surface temperature and thermocline depth anomalies at 0 110 w were less pronounced during the 1986 87 enso than during the 1982 1983 enso the equatorial undercurrent though weaker than normal in early 1987 did not disappear as it did in early 1983

annual reversal of the equatorial intermediate current in the pacific observations and model diagnostics abstract a large reversal of zonal transport below the thermocline was observed over a period of 6 months in the western pacific ocean between 2 s and the equator from 26 2 sv 1 sv 106 m3 s 1 eastward in october 1999 to 28 6 sv westward in april 2000 to document this reversal and assess its origin an unprecedented collection of adcp observations of zonal currents 2004 06 together with a realistic ogcm simulation of the tropical pacific was analyzed the results of this study indicate that this reversal is the signature of intense annual variability in the subsurface zonal circulation at the equator at the level of the equatorial intermediate current eic and the lower equatorial intermediate current l eic in this study the eic and the l eic are both shown to reverse seasonally to eastward currents in boreal spring and winter for the l eic over a large depth range extending from 300 m to at least 1200 m the peak to peak amplitude of the annual cycle of subthermocline zonal currents at

sea level fluctuations in the pacific during the 1982 83 el nino sea level records are used to describe and discuss the response of the sea surface topography of the equatorial pacific ocean during the 1982 83 el nino event during the second half of 1982 westerly winds over the western pacific caused a draining of warm water from the area north of the equator and a first peak of sea level at the galapagos islands in december during the first half of 1983 westerly winds to the south of the equator caused draining of warm water from the area between the solomon islands and the marquesas islands and a second peak of sea level at the galapagos islands in may at the end of el nino in october 1983 sea level over the entire equatorial pacific was below normal indicating a loss of warm water from the equatorial pacific

equatorial currents in the pacific ocean 1992 1997 a medium resolution ocean general circulation model of the tropical pacific ocean is used to explore current structure and variability on the equator for the period from 1992 to 1997 the model assimilates surface and subsurface temperature data from expendable bathythermographs and the tropical ocean global atmosphere tropical atmosphere ocean toga tao moorings and altimetry data from the topex poseidon satellite currents from the model are compared with current observations from the toga tao moorings at 110 w 140 w and 165 e since current data are not assimilated these data provide an independent verification of the model results the comparison shows that the model produces accurate currents over a wide range of spatial and temporal scales in particular the model correctly resolves temporal variability from instability waves with periods of less than a month to interannual changes with periods of several years the model results are used to explore zonal velocity changes associated with the onset of the 1997 1998 el nino southern oscillation enso event the event began with a series of equatorial kelvin waves which were excited by westerly wind bursts in the western pacific and propagated to the eastern pacific the passage of these waves is associated with an initial strengthening of the equatorial undercurrent euc followed by a rapid shutdown of the euc the weakening of the undercurrent during enso is consistent with previous descriptions and results from the collapse of the easterly trade winds in the western pacific

uranium series dating of sediments from searles lake differences between continental and marine climate records one of the major unresolved questions in pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial 18 o marine record searles lake in california now a dry salt pan is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 x 10 6 years uraniumseries dates on the salt beds range from 35 x 10 3 to 231x 10 3 years this range of dates allows identification of lake sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3 4 boundary back to the 8 9 boundary the 5 6 boundary coincided with a deepening of the lake but the analogous 1 2 boundary coincided with desiccation the 3 4 4 5 6 7 7 8 and 8 9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate these hydrologic results demonstrate that the continental paleoclimate record at this mid latitude site does not mimic the marine record

the slope of sea level along the equator during the 1982 1983 el nino observed deviations of monthly mean sea level at seven island stations along the equator in the pacific have been superimposed on the mean dynamic topography to determine the variations of the east west slope of sea surface topography during the 1982 1983 el nino the normal east west slope is eliminated in january 1983 when the bulk of warm water flowing eastward has reached the coast of south america the sea surface remains essentially flat from january to june 1983 although zonal winds are very weak until april only the slope requires several months to be reestablished and in october and november sea level along the entire equator is 10 cm or more below normal indicating a net loss of warm water from the equatorial pacific