western pacific interannual variability associated with the el nino southern oscillation observations of sea surface temperature sst sea level pressure slp surface wind and outgoing longwave radiation olr show that the el nino southern oscillation enso displays western pacific anomaly patterns in addition to eastern pacific anomaly patterns during the warm phase of enso warm sst and low slp anomalies in the equatorial eastern pacific and low olr anomalies in the equatorial central pacific are accompanied by cold sst and high slp anomalies in the off equatorial western pacific and high olr anomalies in the off equatorial far western pacific also while the zonal wind anomalies over the equatorial central pacific are westerly those over the equatorial far western pacific are easterly the nearly out of phase behavior between the eastern and western tropical pacific is also observed during the cold phase of enso but with anomalies of opposite sign these western pacific interannual anomaly patterns are robust features of enso independent of data sets it is argued that equatorial easterly westerly wind anomalies over the far western pacific during the warm cold phase of enso are initiated by off equatorial western pacific cold warm sst anomalies and that these winds are important for the evolution of enso an atmosphere model is employed to demonstrate that small off equatorial western pacific cold warm sst anomalies compared to those in the east are sufficient to produce equatorial easterly westerly wind anomalies as observed over the far western pacific the coupled ocean atmosphere model of zebiak and cane is then modified to investigate the evolution of the western pacific interannual anomaly patterns in a coupled ocean atmosphere system by including a meridional structure to the subsurface temperature parameterization in the western pacific the modified model produces both western and eastern pacific interannual anomaly patterns

the initial response of a stratified lake to a surface shear stress laboratory experiments are used to study the initial response of a stratified fluid to the action of a wind stress the experiments are described in the context of a parameterization scheme that quantifies the strength of the applied stress relative to the bulk stability of the fluid and also the duration of the wind stress relative to the periods of the waves generated by the stress this study concentrates on the first fundamental internal wave period in experiments where the fluid is considered to have upwelled i e the stratified region of the fluid reaches the surface at the upwind endwall the majority of the experiments use three layer initial density profiles as an approximation to a continuously stratified water column a linear model using normal modes proved successful prior to the commencement of upwelling and this enabled an estimate to be made of the time at which upwelling occurred at this point the wave development ceased and the flows developed via entrainment mechanisms consideration of the energy budget showed that little of the input energy was stored in the system the initial mixing efficiency defined as the ratio of the mean potential energy gained to the energy imparted by the belt never exceeded 30 peak efficiency occurred when the surface stress was just sufficient to bring the interfacial region to the surface

oxygen isotopic composition of multiple species of planktonic foraminifera recorders of the modern photic zone temperature gradient abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected as expected from previous work in the tropics all dominant tropical species occur in greatest abundance within the photic zone many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration while a few algal symbiont bearing species occur in greatest abundance in the mixed layer the 18o measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by ravelo et al 1990 comparison between the measured 18o values of planktonic foraminifera with the predicted 18o profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be found within the photic zone of the overlying water column sometime during the year species which calcify below the photic zone have only trace relative abundances finally it appears that the total range of 18o values of the dominant species approximates the predicted annual 18o of calcite range in the upper 80 m of the water column

ice volume forcing of winter monsoon climate in the south china sea high resolution studies of a planktonic foraminifer core record from the south china sea scs 31kl 18 45 4 n 115 52 4 e water depth 3360 m reveal changes driven by ice volume forcings in the climate of the east asian monsoon in the western pacific marginal sea during the late quaternary the analyses of planktonic foraminifer faunal abundance data from the core indicate significant variations in the relative abundances of the dominant taxa over the past 100 000 years since the isotope stage 5 the transfer function estimates of faunal sea surface temperatures sst correlate well with a long term 104 105 years trend of global glaciation about 65 000 years ago there was an observable change in the mode of sst variability as many low latitude records have shown these findings suggest that the scs surface circulation and the east asian winter monsoon systems are mainly driven by variations in global glaciation levels the association of surface ocean cooling in the scs with global climatic events suggests that fluctuations in the strength of the east asian winter monsoon may be linked to shifts in the latitudinal position of the westerly winds and the siberian high pressure system

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

thermocline dynamics in the northwestern tropical pacific over the past 700 kyr abstract variations in thermoclinal conditions play an important role in the evolution of the western pacific warm pool wpwp and in connecting the tropical and extratropical regions of the pacific ocean however secular thermoclinal changes in the northwestern part of the wpwp and their forcing mechanisms are not yet well understood particularly on orbital timescales in this study we report thermoclinal variation at site md06 3047 b in the western philippine sea over the last 700 kyr our data show that variations in thermocline temperature and salinity in the study area were correlated with changes in earth s obliquity with warmer and saltier colder and fresher thermocline waters corresponding to high low earth axial obliquity at high obliquity increases in thermocline temperature and salinity may have been linked to advection of warm north pacific tropical water in the study area a lower higher vertical temperature gradient in the upper water column suggests a deeper shallower thermocline during glacials interglacials the main factor leading to thermoclinal deepening during glacials was strengthening of the east asian winter monsoon eawm and more la nina like conditions may have contributed to concurrent subsurface warming and thus thermoclinal deepening in phase thermoclinal deepening in the northern and peri equatorial southern wpwp during glacial stages may have been triggered by changes in glacial boundary conditions such as increased ice sheet thickness through intensification of the eawm and strengthening of the tropical trade winds

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

western equatorial pacific planktic foraminiferal fluxes and assemblages during a la nina year 1999 abstract a correlation between foraminiferal community dynamics and environmental conditions may provide a basis for establishing paleoclimatic proxies we studied planktic foraminiferal shell fluxes and assemblages in samples collected in three time series sediment trap deployments in the western equatorial pacific under la nina conditions from january to november 1999 eleven species contributed about 90 of the total flux in all traps two sites mt1 mt3 in the western pacific warm pool region wpwp were characterized by common occurrences of the species globigerinoides ruber globigerinoides sacculifer globigerinoides tenellus and neogloboquadrina dutertrei site mt5 farther to the east in the equatorial upwelling region had common occurrences of globigerina bulloides globigerinita glutinata and pulleniatina obliquiloculata very high abundances of g bulloides and g glutinata at mt5 indicate that equatorial upwelling eu occurred during the 1999 la nina the two western sites have similar assemblage compositions but mt1 135 e has the highest fluxes up to 3800 tests m 2 day 1 whereas mt3 145 e has fluxes below 2200 tests m 2 day 1 relatively high fluxes up to 3000 tests m 2 day 1 occur at site mt5 176 e where upwelling occurred the differences in faunal composition in the wpwp and eu might be attributable to differences in the way in which nutrients are supplied to the phytoplankton large amounts of suspended material are supplied to the wpwp by advection of waters passing through the coastal region of an archipelago whereas upwelling of nutrient rich waters enhances primary production in the eu at the westernmost site in the wpwp a peak in the g bulloides flux coincided with southward flow of the new guinea coastal current ngcc in late february but the highest g ruber flux coincided with northward flow of this current in late may thus the differences in species dominance at this location may be caused by monsoon driven variability in the flow direction of the nggc

tropical pacific response to continental ice sheet topography the last glacial maximum was marked by maximum land ice extent and lowest greenhouse gases concentration during the last ice age we explore the impact of glacial continental ice sheet topography on the large scale tropical ocean atmosphere climate in particular the tropical pacific in an intermediate complexity coupled model increasing the thickness of continental ice sheets causes a southward displaced pacific intertropical convergence zone itcz and a strengthening weakening of northern southern hemisphere winter hadley cell the equatorial zonal sea surface temperature gradient weakened with an increased continental ice sheets thickness the reduction being caused by cooling in the western equatorial pacific and warming in the eastern equatorial pacific the evolution of the tropical climate with changing ice thickness has distinct quasi linear and nonlinear parts while the linear part is a direct response to the ice topographic changes the nonlinear part was a result of the tropical thermocline adjustment our analysis of a fully coupled transient deglacial simulation strongly indicates the dominant role of ice sheet topography in determining the deglacial evolution of the simulated pacific climate the thickness of continental ice sheet separate from ice albedo effect has significant impact on the tropical ocean atmosphere climate in particular with the meridional displacement in the pacific itcz the altered circulation states seen in the model may aid understanding of the relationship between tropical and high latitude climate records in glacial interglacial cycles

shoaling of the western equatorial pacific thermocline during the last glacial maximum inferred from multispecies temperature reconstruction of planktonic foraminifera abstract glacial interglacial scale climate variability in the tropical pacific is often discussed with reference to modern el nino southern oscillation enso however proxy records show diverse results and result in inconsistent interpretations to investigate changes in the thermocline depth of the western pacific warm pool wpwp which is strongly related to the strength of the walker circulation this study conducted 18 o and mg ca analyses of multispecies planktonic foraminifera for the last 25 000 years habitat depths and calcification temperatures of seven foraminiferal species were estimated by comparing measured 18 o values with the predicted values by assuming isotopic equilibrium reconstructed mg ca based temperatures calculated with a newly calibrated multispecies equation showed 1 2 c larger cooling at the thermocline depth than that at the surface during the last glacial maximum lgm suggesting shoaling of the thermocline furthermore fresher surface water in the wpwp which is attributed to the suppressed evaporation by low sea surface temperature suggests the weakened deep atmospheric convection these results suggest that the walker circulation during the lgm was weaker than that during the late holocene

decadal characterization of indo pacific ocean subsurface temperature modes in soda reanalysis abstractstudies of decadal to multidecadal ocean subsurface temperature variability are fundamental to improving the understanding of low frequency climate signals the present study uses the simple ocean data assimilation soda version 2 2 4 product for the period 1950 2007 to identify decadal modes of variability that characterize the upper indo pacific ocean temperature structure 5 466 m depth an empirical orthogonal function eof analysis of the 10 yr low pass filtered temperature field applied across four depths shows that the dominant mode is characterized by a long term temperature trend with warming at the surface and cooling at the thermocline depth connecting the tropical western pacific with the southern indian ocean via the indonesian seas eof analysis of the detrended 10 yr filtered temperature data and correlation analyses of the eof time series with established large scale climate indices identified the interdecadal pacific oscillation as eof1 the north pacific gyre oscillation as e

corroborating ecological depth preferences of planktonic foraminifera in the tropical atlantic with the stable oxygen isotope ratios of core top specimens 1 past variability in upper ocean thermocline depth is commonly estimated from the abundance of different species of planktonic organisms or the difference in oxygen isotopic composition between two species of planktonic foraminifera one that lives in the mixed layer and one that lives in or near the thermocline to test the latter relationships we measured the oxygen isotopic composition of eight species of planktonic foraminifera pink and white varieties of globigerinoides ruber globigerinoides sacculifer without the final chamber orbulina universa pulleniatina obliquiloculata globorotalia menardii neogloborotalia dutertrei and globorotalia tumida in surface sediment samples from 31 tropical atlantic deep sea sediment cores bayesian analysis was used to compare measured oxygen isotopic compositions with their predictions based on modern data sets of annual temperatures and oxygen isotopic composition of ocean water in the upper 500 m at the core sites posterior probability densities for predictive model parameters were computed probability distributions of calcification depth for analyzed species corroborated their ecological preferences inferred from net tow and sediment trap data robustness of the habitat signals in core top specimens suggests that reconstructions of the entire upper ocean temperature profiles not just their thermocline depth or temperature might be possible

ice volume forcing of east asian winter monsoon variations in the past 800 000 years particle size measurements of some typical loess soil samples taken in different localities of the chinese loess plateau demonstrate that the grain size ratio of 10 m can be used as an indicator of variations in intensity of the east asian winter monsoon winds grain size curves of the baoji and weinan sections show that this proxy indicator is very sensitive to loess soil alterations analytical results also suggest that during soil forming periods eolian dust accumulation was still substantial and hence loess deposition can be regarded as a nearly continuous process during the quaternary period in this study we compared the baoji grain size time series with the specmap marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation both records show good agreement at both time and frequency domains in particular the winter monsoon variations are also dominated by a 100 000 yr period over the past 800 000 yr it is thus inferred that direct local insolation forcing could be less important in driving the east asian winter monsoon variability and alternatively variations in glacial age boundary conditions may have played a key role in modulating and pacing its strength and timing

reconstructing the southern south china sea upper water column structure since the last glacial maximum implications for the east asian winter monsoon development difference in the stable oxygen isotopes dd 18 o and mg ca based temperatures dt of surface dwelling g ruber and thermocline dwelling p obliquiloculata planktonic foraminifera and the temperature difference between alkenone and p obliquiloculata mg ca based temperatures to estimate the upper ocean thermal gradient at international marine past global change study images core md01 2390 estimates of the upper ocean thermal gradient were used to reconstruct mixed layer dynamics we find that our dd 18 o estimates are biased by changes in salinity and thus do not display a true upper ocean thermal gradient the d to fg ruber and p obliquiloculata as well as the alkenone and p obliquiloculata suggest increased surface water mixing during the late glacial likely due to enhanced eawm winds surface water mixing was weaker during the late holocene indicating a weaker influence of winter monsoon winds the weakest winter monsoon activity occurred between 6 5 ka and 2 5 ka inferred eawm changes since the last glacial maximum coincide with eawm changes as recorded in chinese loess sediments we find that the intensity of the eawm and the east asian summer monsoon show an inverse behavior during the last glacial and deglaciation but covaried during the middle to late holocene

boundary mixing in the thermocline of a large lake 1 high resolution measurements of near bottom temperature stratification and current velocity were performed on the sloping boundary of a large lake at the depth of the seasonal thermocline the measurements cover nearly the entire stratified period and reveal the periodic occurrence of strong temperature and current velocity fluctuations which can be attributed to shoaling high frequency internal waves with periods between 5 and 20 min two different techniques are applied to obtain a long term record of dissipation rates of turbulent kinetic energy from the current velocity measurements shoaling of high frequency internal waves is associated with a strong and rapid increase of turbulent dissipation rates of up to four orders of magnitude since the occurrence of high frequency internal waves on the slope is correlated with the passage of the dominant basin scale internal kelvin wave with a period of four days energy dissipation rates on the slope vary with the same period diapycnal diffusivities estimated by combining the dissipation estimates with simultaneously measured density stratification follow a similar dynamics and a comparison with a basin scale diffusivity estimate based on tracer measurements reveal the importance of boundary mixing which at this particular site is mainly driven by the interaction of high frequency internal waves with the sloping boundary

tropical pacific ocean thermocline depth reconstructions for the last glacial maximum we evaluate the relationship between ten surface ocean 0 300 m hydrographic parameters and the spatial distribution of factor analyzed core top planktonic foraminiferal abundances in the tropical pacific ocean 24 n 24 s for core tops 3800 m the spatial distribution of the first three faunal factor loadings 88 of the variance are most highly correlated to subsurface variability mixed layer depth thermocline depth and resistant species percent rsp however rsp is not related to dissolution but is related to thermocline depth factor i mixed layer species g glutinata g ruber and factor iii g ruber can be distinguished from each other by low abundances of g glutinata in factor iii both assemblages spatially comprise the deep mixed layer region of the western tropical and equatorial pacific ocean but are associated with distinct water mass properties a combination of factor i and iii loadings shows a higher correlation to thermocline depth r 0 70 factor ii loadings dominated by thermocline dwelling species n dutertrei are most significantly correlated with the thermocline depth r 0 73 most factors show only marginally significant correlation to sea surface temperatures ssts indicating that sst is not the primary forcing factor on the planktonic foraminiferal species distributions in the tropical pacific a new transfer function was calculated to predict tropical pacific thermocline depth from planktonic foraminifera abundances using the imbrie kipp method ikm standard deviation of residuals 22 m 1 an additional 5 m error is attributed to low species counts in the core top database the modern analog technique mat was also used to predict thermocline depth standard deviation of residuals 21 m while last glacial maximum lgm thermocline depth changes by ikm and mat were generally within error estimated changes were geographically uniform suggesting an oceanographic response to climate forcing we estimate that the thermocline depth of the lgm was shallower than present by 20 m south of 8 s possibly due to a shift in the south pacific anticyclone to the northeast both the ikm and mat estimate a steeper east west thermocline slope along the equator suggesting that zonal wind stress walker circulation was intensified during the lgm collectively the thermocline estimates for the lgm suggest an equatorward compression of the climate zones in both hemispheres

deep dwelling foraminifera as thermocline temperature recorders we measured the oxygen isotopic composition of the deep dwelling foraminiferal species g inflata g truncatulinoides dextral and sinistral and p obliquiloculata in 29 modern core tops raised from the north atlantic ocean we compared calculated isotopic temperatures with atlas temperatures and defined ecological models for each species g inflata and g truncatulinoides live preferentially at the base of the seasonal thermocline under temperature stress i e when the base of the seasonal thermocline is warmer than 16 c g inflata and g truncatulinoides live deeper in the main thermocline p obliquiloculata inhabits the seasonal thermocline in warm regions we tested our model using 10 cores along the mauritanian upwelling and show that the comparison of o variations registered by the surficial species g ruber and g bulloides and the deep dwelling species g inflata evidences significant glacial interglacial shifts of the mauritanian upwelling cells

decoupled holocene variability in surface and thermocline water temperatures of the indo pacific warm pool 1 the holocene variability in sea surface and thermocline water temperatures sst and twt in the indo pacific warm pool ipwp has been reconstructed by planktonic foraminiferal mg ca from sediments of the western tropical philippine sea afterward the younger dryas interval yd sst warmed gradually till 10 ka and remained approximately constant afterwards but twt rose more rapidly to a peak between 12 and 10 ka and then declined by 1 5 c through the holocene the trend of twt closely followed the boreal summer insolation and could be correlated to tropical climate changes represented by southward movement of the inter tropical convergence zone itcz and related changes in east asian monsoons

inside story an x ray computed tomography method for assessing dissolution in the tests of planktonic foraminifera x ray computed tomography ct provides an insight into the progression of dissolution in the tests of planktonic foraminifera four species of foraminifera g ruber white g sacculifer n dutertrei and p obliquiloculata from pacific atlantic and indian ocean core top samples were examined by ct and sem inner chamber walls began to dissolve at co32 values of 12 14 mol kg close to the calcite saturation horizon dissolution and precipitation of calcite may occur simultaneously inner calcite of g sacculifer n dutertrei and p obliquiloculata from such sites appeared altered or replaced whereas outer crust calcite was dense with no pores unlike the other species there was no distinction between inner and outer calcite in ct scans of g ruber empty calcite crusts of n dutertrei and p obliquiloculata were most resistant to dissolution and were present in samples where co32 20 mol kg five stages of preservation were identified in ct scans and an empirical dissolution index xdx was established xdx appears to be insensitive to initial test mass mass loss in response to dissolution was similar between species and sites at 0 4 g mol kg we provide calibrations to estimate co32 and initial test mass from xdx

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

progress in paleosalinity overview and presentation of a new approach this paper concerns the use of stable oxygen isotope ratios 18o and stable hydrogen isotope ratios 2h or d to derive paleosalinity first i evaluate the potential and limitations of existing methods based on 18o and d separately next i propose a new theoretical framework for the combined use of 18o and d to constrain the impact of the hydrological cycle on the surface waters and to thus characterize changes in surface water salinity this new method is accompanied by an error propagation exercise to demonstrate its limitations and areas of potential improvement a feasible strategy is outlined for achieving reconstructions of paleosalinity change with an uncertainty of 1 practical salinity unit or less with the newly proposed method especially in regions with high deuterium excess values

seasonal thermocline in the china seas and northwestern pacific ocean climatological seasonal variations of the thermocline in the china seas and northwestern pacific ocean were studied using historical data from 1930 through 2001 707 624 profiles the quantitative roles of surface thermal buoyancy b q haline buoyancy flux b p and total buoyancy flux b against the wind induced mixing tau in different seasons and regions were also explored using the buoyancy ratio r b q b p and the monin obukhov depth ratio delta respectively the thermocline has obvious seasonal variations in the study area north of 20 degrees n there is no thermocline along the west coast of the bohai sea bs yellow sea ys and northern east china sea from december to march resulting from surface cooling and wind mixing the significantly different variation of the thermocline strength on and off the chinese shelf is mainly caused by the fact that the thermal stratification is enhanced by bottom tidal mixing on the shelf the delta indicates that the thermocline depth on the chinese shelf is mainly dominated by b in summer while it is dominated by tau in winter it reveals an opposite feature in the kuroshio region the dominating factor is b in winter associated with the large heat buoyancy loss there south of 20 degrees n the dominating factor is similar to that on the shelf with the more obvious b dominant characteristic during the monsoon transition periods the r demonstrates that b is mainly controlled by b q all year round with some sporadically b p dominated regions in the tropical area in winter and in the bs and eastern ys in september

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

late quaternary upwelling intensity and east asian monsoon forcing in the south china sea foraminifera from two cores off eastern vietnam and the northwestern philippines where modern summer and winter monsoon driven upwelling occurs in the south china sea respectively were analyzed to evaluate the changes in paleoproductivity and upper water structure over the last 220 000 yr we observed enhanced organic carbon flux and a shoaled thermocline when upwelling intensified off eastern vietnam during interglacial ages and off the northwestern philippines during glacial ages this indicates that the east asian summer monsoon increased while the winter monsoon decreased during interglacial ages particularly the upwelling reached a maximum off eastern vietnam during late marine isotopic stage mis 5 and off the northwestern philippines during mis 2 implying that the summer monsoon decreased gradually since mis 5 while the winter monsoon displayed an opposite trend the variations in upwelling proxies exhibit a distinct cyclicity with frequencies near 41 000 yr and 23 000 yr off eastern vietnam in contrast to a strong frequency peak near 100 000 yr off the northwestern philippines we suggest that the east asian summer monsoon has been forced by changes in solar insolation associated with precession and obliquity while ice volume forcing is probably a primary factor in determining the strength and timing of the east asian winter monsoon but with less important insolation forcing

western caribbean sea surface temperatures during the late quaternary 1 mg ca ratios in the planktonic foraminifera globigerinoides ruber from colombian basin core odp 999a suggest that caribbean sea surface temperatures ssts were from 2 1 to 2 7 c colder than the present during the last three glacial maximums in comparison faunal derived ssts simmax method show that august ssts in the caribbean varied 2 c over the past 360 kyr whereas february ssts varied between 21 0 c and 26 5 c changes in the mg ca sst record contain a strong 23 kyr periodicity suggesting the mg ca sst record reflects a warm season weighted sst average rather than an annual mean sst combining several dissolution indices we identify brief periods of decreased carbonate preservation in our record and show that mis 11 stands out as the most intensive dissolution cycle in the caribbean over the last 460 kyr comparison of caribbean sst change with a similar estimate of tropical sst variability in the western pacific over the past 360 kyr reveals shifts in the east west tropical sst gradient that are coeval with glacial interglacial climate change and consistent both with a southward migration of the glacial itcz and with a glacial el nino like mode of tropical circulation

on the dynamics of interdecadal thermocline depth and sea surface temperature variability in the low to mid latitude pacific ocean the role of upper ocean dynamics in generating interdecadal sea surface temperature sst variations is investigated with the help of the australian bureau of meteorology research centre coupled general circulation model cgcm and a first baroclinic mode shallow water ocean model swm an empirical orthogonal function analysis is performed on the lowpass filtered sst and vertically averaged temperature in the upper 300 m anomaly data output from a 100 year cgcm simulation the dominant mode sst spatial pattern and time variability is consistent with the interdecadal pacific oscillation the swm is forced by wind stresses from the cgcm 100 year simulation to investigate the role of oceanic rossby and kelvin wave propagation on thermocline depth variations the swm produces variability similar to the cgcm interdecadal variability we conclude that large scale wind forced upper ocean dynamics play a dominant role in generating interdecadal upper ocean temperature variations on decadal and longer timescales

dynamics of mixed bottom boundary layers and its implications for diapycnal transport in a stratified natural water basin here we report on two field experiments from lake alpnach surface area 4 8 km 2 maximum depth 34 m that were designed to study the process of boundary mixing and to estimate its efficiency the ratio between the turbulent kinetic energy converted into potential energy and dissipated into heat for diapycnal tracer transport lake alpnach is particularly suited for this purpose because it is known from earlier experiments that 1 its currents follow a regular oscillatory pattern associated with basin wide standing internal waves seiches period similar to 0 5 days and 1 day respectively and 2 diapycnal tracer transport is mainly caused by boundary mixing during one of the experiments reported here strong seiches were excited regularly and damped on a timescale of the order of 3 days during the other experiment seiching motion was comparably weak if seiching is excited regularly we find a persistent well mixed bottom layer of 4 5 m height at the deepest part of the lake in the absence of regular seiching the layer disappears within 10 20 days on the sloping bottom boundaries the well mixed layers 1 are of much more transient nature 2 exhibit different thermal structure and 3 decrease in thickness toward shallower depth inversely proportionally to the stability at the same depth in the lake interior their reduced thickness is possibly the result of repeatedly occurring intrusions of boundary mixed water masses that are observed to extend horizontally similar to 100 200 m into the lake interior as a consequence of repeated generation of intrusions mixing on the sloping boundaries is expected to be considerably more efficient compared to mixing over flat bottom boundaries the observed mixing efficiency the ratio of the rate of change of potential energy below depth z caused by turbulence to the energy loss by bottom friction below depth z increases indeed from 0 01 0 01 in the deepest well mixed layers to 0 15 0 04 in the upper pycnocline

origin and evolution of the west philippine basin a new interpretation abstract combined analyses of the magnetic lineations and seafloor structures of the west philippine basin show that it was formed by spreading from the central basin spreading center in two distinctly different spreading phases before and after subduction was initiated along the palau kyushu trend at 45 ma b p these episodes are recognized by differences in the strike of the magnetic lineations spreading rates density and strike of fracture zones and basement relief from 60 45 ma b p spreading was ne sw relative to present orientations at a half rate of 44 mm a at about 45 ma b p the spreading direction changed to a more n s direction with a reconfiguration of the central basin spreading center into numerous short e w segments offset by closely spaced n s transform faults spreading slowed to a half rate of 18 mm a and ceased at 35 ma b p thus the west philippine basin originated at 45 ma b p by the trapping of normal ocean crust west of the initial subduction along the palau kyushu trend the 45 35 ma b p period represents the dying phase of spreading on the central basin spreading center following isolation of the west philippine basin from the plate driving forces of the pacific

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

seasonal change in foraminiferal production in the western equatorial pacific warm pool evidence from sediment trap experiments seasonal changes in the flux of individual planktonic foraminifera in the deep ocean have been studied in the western equatorial pacific warm pool using material collected by sediment traps over a period of 1 yr 1991 1992 mean total foraminiferal fluxes tffs were 171 and 97 shells m 2 day 1 at sites n1 2 59 8 n 135 01 5 e and n2 4 07 5 n 136 16 6 e respectively the seasonal change in tffs was much higher than for organic matter om and carbonate fluxes the major species of planktonic foraminifera were pulleniatina obliquiloculata neogloboquadrina dutertrei globigerinoides sacculifer globigerinella aequilateralis and globigerinoides ruber symbiont bearing species and n dutertrei were predominant in the western equatorial pacific warm pool comparison between the warm pool and upwelling deep sea research ii 43 1996 1257 mar micropaleontology 33 1998 157 indicates that the foraminiferal assemblage trapped at the western equatorial pacific warm pool was comparable with the south equatorial and subtropical assemblages during a plankton tow study conducted at 140 w in 1992 it suggests that fairly oligotrophic conditions prevailed in the western equatorial pacific warm pool in association with terrestrial nutrient inputs or temporary mixing by wind bursts the om flux was more positively correlated with the 63 m carbonate fraction mainly composed of coccoliths r 0 87 and biogenic opal which suggests that om fluxes were more affected by phytoplankton productivity although food availability is generally important for foraminiferal production tffs were poorly correlated with om fluxes at sites n1 and n2 which is partly attributed to the significant influence of symbiont photosynthesis the 18o values of p obliquiloculata and n dutertrei showed maxima in association with high om fluxes during period 2 from august to october and period 4 from late december to april at site n1 reflecting thickening of the mixed layer following wind bursts g sacculifer showed a lunar reproduction cycle when between july and october carbonate production was more predominant than biogenic opal production a similar profile was evident for g ruber orbulina universa and g aequilateralis these four species are generally predominant at low latitudes therefore the lunar reproduction cycle may significantly affect the fluctuation in carbonate production in the equatorial ocean

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

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

dissipation and mixing during the onset of stratification in a temperate lake windermere acoustic doppler current profilers and chains of temperature sensors were used to observe the spring transition to stable stratification over a 55 d period in a temperate lake observations of the flow structure were complemented by measurements of dissipation based on the structure function method near the lake bed and in the upper part of the water column during complete vertical mixing wind driven motions had horizontally isotropic velocities with roughly equal barotropic and baroclinic kinetic energy dissipation was closely correlated with the wind speed cubed indicating law of the wall scaling and had peak values of 1 10 5 5 w kg 1 at ten meters depth during maximum wind forcing w 15 m s 1 as stratification developed the flow evolved into a predominantly baroclinic regime dominated by the first mode internal seiche with root mean square axial flow speeds of 2 3 cm 1 2 5 times the transverse component at 2 8 m above the bed most of the dissipation occurred in a number of strong maxima coinciding with peaks of near bed flow in the pycnocline dissipation was low most of the time but with pronounced maxima reaching 1 10 5 w kg 1 closely related to the local velocity shear the downward diffusive heat flux across the pycnocline over 27 5 d accounted for 70 of the temperature rise in the water column below total lake kinetic energy increased by a factor of three between mixed and stratified regimes in spite of reduced wind forcing indicating less efficient damping in stable conditions

assessing influence of diagenetic carbonate dissolution on planktonic foraminiferal mg ca in the southeastern arabian sea over the past 450 ka comparison between globigerinoides ruber and globigerinoides sacculifer 1 the influence of supralysoclinal calcite dissolution on the mg ca thermometer over the last 450 ka is assessed using globigerinoides ruber and globigerinoides sacculifer from a core site in the eastern arabian sea the studied site is characterized by precession cycled paleoproductivity changes that have induced calcite dissolution in the sediments although the core still contains 40 80 caco3 during high productivity periods the narrow sized test weights of both foraminiferal species tend to decrease with increasing mn ca ratio indicating corrosive pore water conditions scanning electron microscope observations show that g sacculifer maintains a better preserved test ultrastructure than g ruber microprobe mapping reveals that mg rich bands in g ruber chamber walls are preserved despite reduced ca content assuming that the low test weight and offset in mg ca temperature between g sacculifer and g ruber are exclusively produced by calcite dissolution the bias in mg ca temperature determination can be estimated at around 1 c comparable to uncertainty of this thermometry despite the evidence for test dissolution foraminiferal mg ca seems to preserve initial temperature signals under the studied conditions

mindanao dome variability over the last 160 kyr episodic glacial cooling of the west pacific warm pool we present sea surface upper thermocline and benthic delta 18 o data as well as temperature and paleoproductivity proxy data from the international marine global change study program images core md06 3067 6 degrees 31 n 126 degrees 30 e 1575 m water depth located in the western equatorial pacific ocean within the flow path of the mindanao current our records reveal considerable glacial interglacial and suborbital variability in the mindanao dome upwelling over the last 160 kyr dome activity generally intensified during glacial intervals resulting in cooler thermocline waters whereas it substantially declined during interglacials in particular in the early holocene and early marine oxygen isotope stage mis 5e when upwelling waters did not reach the thermocline during mis 3 and mis 2 enhanced surface productivity together with remarkably low sst and low upper ocean thermal contrast provide evidence for episodic glacial upwelling to the surface whereas transient surface warming marks periodic collapses of the mindanao dome upwelling during heinrich events we attribute the high variability during mis 3 and mis 2 to changes in the el nino southern oscillation state that affected boreal winter monsoonal winds and upper ocean circulation glacial upwelling intensified when a strong cyclonic gyre became established whereas el nino like conditions during heinrich events tended to suppress the cyclonic circulation reducing ekman transport thus our findings demonstrate that variations in the mindanao dome upwelling are closely linked to the position and intensity of the tropical convection and also reflect far field influences from the high latitudes

history of asian eolian input to the west philippine sea over the last one million years the eolian component in pacific ocean sediments has been recognized as providing a direct link between the continental loess and marine delta o 18 climate records over orbital timescales since 500 ka here we extend this eolian record over the past one million years we constructed high resolution clay mineral stratigraphies based on delta o 18 chronology in sediments from the international marine past global change images core md06 3050 from the west philippine sea in order to trace the sources of clay minerals and reconstruct proxy records of past changes in the asian eolian input to the basin since 1 0 ma the clay mineral assemblage in core md06 3050 mainly consists of smectite similar to 65 and illite similar to 25 with minor kaolinite similar to 5 and chlorite similar to 5 provenance analysis suggests that smectite was derived mainly from the weathering of volcanic rocks on luzon island whereas illite chlorite and kaolinite were mainly transported as eolian dust by the east asian winter monsoon from central asia illite smectite values in core md06 3050 are generally higher and more variable during glacial periods and lower during interglacials suggesting that higher eolian input to the west philippine sea generally co varied with east asian winter monsoon intensity and more aridity in continental asia since 1 0 ma spectral analysis further reveals the close link between the extent of high latitude glaciation east asian winter monsoon intensity and eolian input to the west philippine sea at eccentricity 100 ka obliquity 41 ka and precession 23 ka bands since 1 0 ma c 2012 elsevier b v all rights reserved

internal seiche modes and bottom boundary layer dissipation in a temperate lake from acoustic measurements measurements with acoustic doppler current profilers adcps and a thermistor string were used to investigate the seasonal variation of internal seiches in a 5 km long temperate lake and the dissipation induced by the seiches in the bottom boundary layer velocity data from a bottom mounted 1 2 mhz adcp were analyzed by cross spectral analysis to determine the seiche modes the first vertical mode was generally dominant but the second mode made a significant contribution at times and was present throughout the summer season the modal periods which were consistent with normal mode analysis exhibited a marked seasonal change that correlated closely with the evolution of stratification measurements in the bottom boundary layer by another adcp in pulse pulse coherent mode sampling at 4 hz allowed determination of the rate of turbulent kinetic energy dissipation via the structure function method episodes of energy dissipation 1027 wk g21 occurred during peak flow 0 05 m s21 in the seiche motion period 10 h and coincided with times of significant reynolds stress between these episodes dissipation fell below the noise level 5 3 1029 wk g21 the ratio of internal wave energy to the boundary layer dissipation rate implies a decay time of 75 h which is similar to that for energy decay in strong seiches indicating that boundary layer dissipation makes a substantial contribution to energy loss from seiche motions a major mixing event in august caused by near resonant wind forcing brought metalimnion water to the surface and induced substantial mixing the internal motions of stratified lakes have long been observed by measuring the vertical displacement of isotherms it was through such measurements in loch ness by watson 1904 that he and wedderburn 1907 first demonstrated the importance in lakes of internal standing wave seiche motions forced by wind set up subsequent studies notably by mortimer 1974 have investigated the details of the modal structure of the internal seiches in lakes

stratification and mixing on sloping boundaries 1 in lakes as well as in the ocean vertical transport is to a large extent controlled by localized mixing along the boundaries of the respective basin direct measurements of turbulent mixing and density stratification in the bottom boundary layer of a large and deep lake reveal the importance of cross slope advection near sloping boundaries for local and basin scale vertical transport the periodic internal wave driven occurrence of up and downslope directed currents results in periodic heating and cooling of the boundary layer cooling of the boundary layer during periods of up slope flow is associated with unstable stratification and turbulent diffusivities exceed those observed during periods of down slope flow by almost one order of magnitude the periodic replacement of water in this layer with water from the interior of the basin maintains vertical density gradients and thus enhances the overall efficiency of the boundary mixing

reconstructing paleosalinity from δ18o coupled model simulations of the last glacial maximum last interglacial and late holocene reconstructions of salinity are used to diagnose changes in the hydrological cycle and ocean circulation a widely used method of determining past salinity uses oxygen isotope ow residuals after the extraction of the global ice volume and temperature components this method relies on a constant relationship between ow and salinity throughout time here we use the isotope enabled fully coupled general circulation model gcm hadcm3 to test the application of spatially and time independent relationships in the reconstruction of past ocean salinity simulations of the late holocene lh last glacial maximum lgm and last interglacial lig climates are performed and benchmarked against existing compilations of stable oxygen isotopes in carbonates oc which primarily reflect ow and temperature we find that hadcm3 produces an accurate representation of the surface ocean oc distribution for the lh and lgm our simulations show considerable variability in spatial and temporal ow salinity relationships spatial gradients are generally shallower but within 50 of the actual simulated lh to lgm and lh to lig temporal gradients and temporal gradients calculated from multi decadal variability are generally shallower than both spatial and actual simulated gradients the largest sources of uncertainty in salinity reconstructions are found to be caused by changes in regional freshwater budgets ocean circulation and sea ice regimes these can cause errors in salinity estimates exceeding 4 psu our results suggest that paleosalinity reconstructions in the south atlantic indian and tropical pacific oceans should be most robust since these regions exhibit relatively constant ow salinity relationships across spatial and temporal scales largest uncertainties will affect north atlantic and high latitude paleosalinity reconstructions finally the results show that it is difficult to generate reliable salinity estimates for regions of dynamic oceanography such as the north atlantic without additional constraints

evolution of east asian monsoon clay mineral evidence in the western philippine sea over the past 700 kyr clay mineral assemblage of the core md06 3047 in the western philippine sea has been used to trace sediment provenance and transport process and thus to constrain the east asian monsoon evolution as well as its forcing mechanism over the past 700 kyr clay minerals mainly consist of smectite 61 and illite 23 with minor chlorite 10 and kaolinite 6 provenance analyses suggest that the smectite originates predominantly from the alteration of nearby luzon volcanic rocks illite is primarily derived from the asian continent with eolian origin illite contents show strong glacial interglacial cyclicity as constrained by oxygen isotope stratigraphy variations of illite contents are ultimately controlled by the east asian monsoon evolution characterized by higher illite values during glacials with relatively stronger east asian winter monsoon but weaker east asian summer monsoon during interglacials enhanced east asian summer monsoon and rainfall could produce more smectite with poor crystallinity from luzon to the study core spectral analyses of illite content and smectite crystallinity display a strong periodicity at 100 kyr for the east asian winter monsoon and 100 kyr 30 kyr and 23 kyr periodicities for the east asian summer monsoon respectively suggesting the unique forcing processes of the east asian winter monsoon from high latitudes i e ice volume and the east asian summer monsoon from both high latitudes and low latitudes i e tropical pacific c 2012 elsevier ltd all rights reserved

seasonal evolution of the basin scale internal wave field in a large stratified lake the response of the water column to varying conditions of stratification and wind forcing was investigated in lake kinneret israel using data collected from thermistor chains and acoustic doppler current profilers during 1997 and 1998 the strong daily sea breeze was found to generate a vertical mode 1 internal kelvin wave and basin scale internal poincarewaves of vertical modes 1 2 and 3 the kelvin wave the dominant component of the internal wave field was responsible for alongshore velocities in the nearshore regions in the upwind nearshore regions velocities were dominated by the forced response to the wind and were cross shore in nature in the lake interior the kelvin wave effect on the horizontal velocity field was minor compared to the higher vertical mode poincarewaves the kelvin wave is shown to exist in resonant and nonforced states with the wind whereas the vertical mode 1 poincarewave energy remained relatively constant despite large variability in the forcing condi tions the energy in the higher mode poincarewaves varied greatly both on daily and seasonal timescales the results demonstrate that the wind energy forces multiple basin scale internal wave modes and that prior motion in the water column must be considered when determining the subsequent internal wave response in periodically forced systems lake kinneret israel has long been an important regional resource providing a substantial supply of drinking water as well as supporting a commercial fishery the monomictic lake is forced daily during the summer by a powerful sea breeze with stratification and wind patterns showing little variation from year to year these factors along with a fa vorable bathymetric pattern combine to make lake kinneret an ideal place for the field investigation of large scale inter nal waves and related phenomena such as the benthic bound ary layer horizontal transport and vertical mixing processes in addition to providing substantial insight into the local pro cesses and hence influencing local management study of the lake also provides fundamental knowledge of the dynam ics of enclosed basins on a geophysical scale during summer the internal rossby radius in lake kin neret is typically one half the basin width hence large scale motion in the lake will be affected by the earth s rotation and basin scale internal waves may be of topographic ross by kelvin or poincareform topographic rossby waves are sub inertial frequency oscillations that exist only in rotating fluids with variable bathymetry mysak et al 1985 stocker and hutter 1987 and these waves result from changes in depth affecting the relative vorticity of fluid elements in the absence of vertical boundaries wavelike solutions to the lin ear inviscid equations of motion for a flat bottomed region of homogeneous fluid with a constant rate of rotation are 1

tropical pacific climate response to obliquity forcing in the pleistocene 1 marine proxy records of pleistocene seawater temperature and productivity in the tropical pacific ocean vary over a 41 000 year period that has been attributed to earth s obliquity cycle the proxy records are paradoxical both because obliquity has a small effect on low latitude insolation and because tropical seawater temperature and productivity were anticorrelated with obliquity insolation forcing in this study we investigate the response of the tropical pacific climate to obliquity forcing using a coupled ocean atmosphere model to reconcile the proxy records with climate theory two glacial and two modern simulations were completed with extreme high and low axial tilts of 24 5 and 22 2 in response to an increase in axial tilt tropical sea surface temperatures decrease by as much as 0 8 c because of the local reduction in insolation subsurface water temperatures in the eastern and central equatorial pacific increase by nearly 1 c anomalous heating through high obliquity forcing also generates dynamical responses that weaken mean annual midlatitude westerlies and subtropical trade winds contributing to a 20 reduction in the subtropical gyre circulation analyses using a lagrangian transport model indicate that low latitude subsurface warming is due to a reduction in heat export from the tropics and the advection and ventilation of anomalously warm south pacific extratropical waters through the thermocline circulation the model s response to obliquity is consistent with pleistocene proxy data that indicate the tropical walker circulation and thermocline slope were not strongly influenced by changes in axial tilt the model results also support the hypothesis that earth s obliquity influences climate through its control on meridional insolation gradients

gold bearing fluvial and associated tidal marine sediments of proterozoic age in the mporokoso basin northern zambia abstract the structurally defined mporokoso basin contains up to 5000 m of continental and marine clastic sediments and minor silicic volcanics which together form the mporokoso group these rocks overlie unconformably a basement of silicic intermediate igneous rocks and accumulated within the interval 1830 1130 ma this sedimentological study was restricted to the eastern end of the basin and was part of an assessment of the potential for palaeoplacer gold in the mporokoso group at the base of the mporokoso group the mbala formation consists of 1000 1500 m of purple sandstones and conglomerates deposited in a braided stream system overlain by 500 1000 m of mature quartz arenites deposited in a tidal marine setting a general coarsening upward trend exists within the fluvial sediments sandy distal braided stream facies passes upwards into more proximal conglomeratic facies in proximal sections poorly sorted conglomerates form the top of the coarsening up sequence which is 500 700 m thick the overlying fluvial sediments fine upwards the tidal marine sandstones at the top of the mbala formation resulted from reworking of fluvial sediments during a marine transgression well exposed sections with fluvial conglomerates were studied in detail individual conglomerate bodies form sheets extending for hundreds of metres downstream and at least one hundred metres across stream with little sign of deep scouring or channelling they are generally matrix supported the whole fluvial sequence is characterised by a paucity of mud or silt these conglomerates were deposited by large velocity sheet flows of water which transported a bed load of pebbles and sand most fine material settling out from suspension was eroded by the next flow the great lateral and vertical extent and the uniformity of the fluvial sediments suggest that the sediments accumulated over an unconfined alluvial plain and that the tectonic evolution of the source area was relatively continuous and not episodic these features are characteristic of other proterozoic fluvial sequences there are no distinctly channelised fluvial conglomerates nor angular unconformities within the fluvial sequence both of which would have been potential sites for economic gold concentrations reworking of the fluvial sands during the marine transgression may have concentrated gold locally within the marine sandstones

deglacial δ18o and hydrologic variability in the tropical pacific and indian oceans abstract evidence from geologic archives suggests that there were large changes in the tropical hydrologic cycle associated with the two prominent northern hemisphere deglacial cooling events heinrich stadial 1 hs1 19 to 15 kyr bp kyr bp 1000 yr before present and the younger dryas 12 9 to 11 7 kyr bp these hydrologic shifts have been alternatively attributed to high and low latitude origin here we present a new record of hydrologic variability based on planktic foraminifera derived 18o of seawater 18osw estimates from a sediment core from the tropical eastern indian ocean and using 12 additional 18osw records construct a single record of the dominant mode of tropical eastern equatorial pacific and indo pacific warm pool ipwp hydrologic variability we show that deglacial hydrologic shifts parallel variations in the reconstructed interhemispheric temperature gradient suggesting a strong response to variations in the atlantic meridional overturning circulation and the attendant heat redistribution a transient model simulation of the last deglaciation suggests that hydrologic changes including a southward shift in the intertropical convergence zone itcz which likely occurred during these northern hemisphere cold events coupled with oceanic advection and mixing resulted in increased salinity in the indonesian region of the ipwp and the eastern tropical pacific which is recorded by the 18osw proxy based on our observations and modeling results we suggest the interhemispheric temperature gradient directly controls the tropical hydrologic cycle on these time scales which in turn mediates poleward atmospheric heat transport

an airborne expendable bathythermograph survey of the south china sea may 1995 an extensive airborne expendable bathythermograph survey of the south china sea scs conducted in may 1995 and historical data are used to analyze and infer the upper layer 300 m synoptic structure and general circulation the primary thermal feature observed was a central scs warm pool surrounded by several cool pools the size of the warm pool decreased with depth from approximately 200 000 km2 at 50 m depth to about 70 000 km2 at 300 m depth the maximum temperature of the warm pool was 30 c appearing near the surface at the depth of 50 m the temperature of the central scs warm pool was 29 c and the temperature of the five surrounding cool pools ranged from 26 c to 22 c a three dimensional estimate of the absolute velocity field was obtained from the observed temperature field and a climatological salinity field using the spiral method striking circulation features were the existence of dual anticyclonic eddies in the central scs warm pool and the existence of cyclonic eddies associated with the cool pools in the upper layer the tangential velocity of the dual central scs anticyclonic warm core eddies is around 30 40 cm s and that of the five cyclonic cool core eddies varies from 10 cm s to 40 cm s the tangential velocity of all the eddies decreased with depth at 300 m depth it became less than 5 cm s for all the eddies

western pacific thermocline structure and the pacific marine intertropical convergence zone during the last glacial maximum paleoclimate proxy evidence suggests a southward shift of the intertropical convergence zone itcz during times of northern hemisphere cooling including the last glacial maximum 19 23 ka before present however evidence for movement over the pacific has mainly been limited to precipitation reconstructions near the continents and the position of the pacific marine itcz is less well constrained in this study we address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field we reconstruct changes in the upper ocean density structure during the lgm using oxygen isotope measurements on the planktonic foraminifera g ruber and g tumida in a transect of sediment cores from the western tropical pacific the data suggests a ridge in the thermocline just north of the present day itcz persists for at least part of the lgm and a structure in the southern hemisphere that differs from today the reconstructed structure is consistent with that produced in a general circulation model with both a northern and southern hemisphere itcz