late quaternary benthic foraminifera and deep water paleoceanography in the south china sea abstract recent and late quaternary deep sea benthic foraminifera in the south china sea scs have been quantitatively studied in order to approach some disputable questions about the glacial deep circulation of the pacific from the paleoceanographic records of a marginal sea for example whether or not there existed the north pacific deep water npdw during glacials based on the quantitative data of deep sea benthic foraminiferal faunas from sixty six surface sediment samples of the scs a q mode factor analysis indicates that the globocassidulina subglobosa assemblage the astrononion novozealandicum and bulimina aculeata assemblages and the eggerella bradyi assemblage are associated with the intermediate water mass iwm deep water mass dwm and the deep water below ccd in the scs respectively the factor assemblages resulted from surface sample data were then applied to the quantitative analysis of late quaternary deep sea benthic foraminifera in eight cores from the scs and western pacific the results show a generally increased contribution of the dwm assemblage relative to that of the iwm assemblage during glacials which implies that the influence of the dwm increased and that of the iwm decreased in the scs and western pacific however there were two major deep water paleoceanographic changes during the late quaternary 1 the deep sea carbonate dissolution of the scs and western pacific was intensified during 18 0 stages 4 5 evidenced by the higher arenaceous calcareous ratios of benthic foraminifera and relative abundance of eggerella bradyi 2 the influence of the pacific dwm above 2500 m greatly increased during the last glacial maximum lgm inferred from the increased abundances of the pacific dwm benthic foraminiferal assemblage as compared to those of the pacific iwm and pacific bottom water mass assemblages in the western pacific particularly the water in which favocassidulina favus was distributed could not enter the scs since the lgm meanwhile the great changes had taken place in the dwm of the scs during the lgm reflected in the occurrence of a clearly cooled and ventilated dwm and the replacement of a novozealandicum and b aculeata assemblages by b aculeata melonis barleeanum assemblage at water depths of 1000 2500 m these significant changes during the lgm may be related to the formation of the npdw

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

recent changes in the pacific subtropical cells inferred from an eddy resolving ocean circulation model abstract in this study the subtropical cells stc in the pacific ocean are analyzed using an eddy resolving ocean general circulation model driven by atmospheric forcing for the years 1992 2003 in particular the authors seek to identify decadal changes in the stcs in the model and to compare them with observations in order to understand the consequences of such changes for the equatorial ocean heat and mass budgets the simulation shows a trend toward increasing pycnocline volume transport at 9 n and 9 s across the basin from 1992 to 2003 this increase 4 9 1 0 sv sv 106 m3 s 1 is in qualitative agreement with observations and is attributed primarily to changes in the interior ocean transport which are partially compensated by opposing western boundary transports the subtropical meridional volume transport convergence anomalies in the model pycnocline are found to be consistent with anomalous volume transports in both the observed and modeled equatorial undercurrent as well as with the magni

the mean and the time variability of the shallow meridional overturning circulation in the tropical south pacific ocean the meridional transport in the pacific ocean subtropical cell is studied for the period from 2004 to 2011 using gridded argo temperature and salinity profiles and atmospheric reanalysis surface winds the poleward ekman and equatorward geostrophic branches of the subtropical cell exhibit an el ni no southern oscillation signature with strong meridional transport occurring during la ni and weak meridional transport during el ni no at 7 58s mean basinwide geostrophictransportabove 1000 dbar is 48 56 2 5 sv sv 10 6 m 3 s 21 of which 30 3 38 4 sv return to the subtropics in the surface ekman layer whereas 10 2 18 3 sv flow northward feeding the indonesian throughflow geostrophic transport within the subtropical cell is stronger in the ocean interiorandweakerinthewesternboundaryduringlani theinteriordominatingbasinwide transport using atmospheric reanalyses only half of the mean heat gain by the pacific north of 7 58 si s compensated by oceanicheat transport outof theregion thenationaloceanography centreat southampton air sea flux climatology is more consistent for closing the oceanic heat budget in summary the use of argo data for studying the pacific subtropical cell provides an improved estimate of basinwide mean geostrophic transport includes both interior and western boundary contributions quantifies el ni ni transport variability and illustrates how the meridional overturning cell dominates ocean heat transport at 7 58s

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

pacific thermocline bridge revisited abstract the coupling on decadal time scales of the mid latitude and tropical pacific via an oceanic bridge in the thermocline is investigated using ocean general circulation model hindcasts and a coupled ocean atmosphere model results indicate that in the tropics decadal anomalies of isopycnal depth are forced by ekman pumping and are largely independent of the arrival of subducted anomalies in the thermocline that originate in the mid latitudes of either hemisphere in the coupled model temperature anomalies on isopycnals show little coupling from the tropics to the northern hemisphere but are lag correlated between southern hemisphere mid and low latitudes however anomaly magnitudes on the equator are small these results suggest that the oceanic bridge to the northern hemisphere explains only a small part of the observed decadal variance in the equatorial pacific coupling to the southern mid latitudes via temperature anomalies on isopycnals remains an intriguing possibility

long term el nino southern oscillation enso like variation with special emphasis on the south pacific mechanisms for el nino southern oscillation enso like decadal 7 35 years variability are analyzed using observational data when a decadal positive temperature anomaly occurs in the eastern tropical pacific the atmospheric response excites negative wind stress curl in the western tropical south pacific which causes the thermocline to shoal and induce a negative temperature anomaly there the cold anomaly moves northwestward to the western and central equatorial region and then turns eastward along the equator to reverse the original temperature anomaly in the east the eastward propagation of the oceanic signal along the equatorial thermocline correlates with a zonal wind anomaly the cold anomaly in the east grows through tropical air sea interaction and induces a positive wind stress curl in the western tropical south pacific associated with the atmospheric teleconnection in the southern hemisphere subsequent evolution of the negative phase is similar to that of the positive phase the complete scenario for this enso like decadal variability due to the air sea interaction processes within the tropics has a period of 14 years we also discuss enso like variation on the interdecadal 35 years timescale with possible relationship to the 1976 1977 climate regime shift

depth profiles of δ13c in bottom water and core top c wuellerstorfi on the ontong java plateau and emperor seamounts we have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the ontong java plateau western equatorial pacific and on the northern emperor seamounts northwest pacific each of these locations is several hundred miles from the nearest geochemical ocean sections study geosecs stations and the observed 13c values at each site differ substantially from regionally averaged geosecs 13c profiles we discuss the possible causes of these differences including horizontal variability near bottom effects and problems with the pacific geosecs 13c data we also measured the isotopic composition c and o of core top c wuellerstorfi from a depth transect of cores at each location the 18o data are used to verify that our samples are holocene comparison of foraminiferal and bottom water 13c values shows that this species faithfully records bottom water 13c at both sites and demonstrates that there is no depth related artifact in the dissolved inorganic carbon c wuellerstorfi 13c relationship at these sites

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

orbitally paced paleoproductivity variations in the timor sea and indonesian throughflow variability during the last 460 kyr 1 a high resolution 1 2 kyr multiproxy record from the timor sea in the easternmost indian ocean international marine global change images program core md01 2378 latitude 13 04 95 s longitude 121 47 27 e 1783 m water depth closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the indonesian throughflow spectral analysis of five different flux based productivity proxies indicates spectral power concentrated in the 100 kyr glacial interglacial and the 23 kyr and 19 kyr precessional periods paleoproductivity maxima lead ice volume benthic 18o maxima by 20 to 40 1300 to 2600 years at the precession band the spectral differences in tropical paleoproductivity records from the pacific and indian oceans suggest that local processes wind and circulation patterns driven by insolation are dominant in driving productivity rather than large scale tropical features in the timor sea productivity fluctuations over the last 460 kyr were strongly influenced by monsoonal wind patterns offshore nw australia 23 and 19 kyr and were also modulated by sea level related variations in the intensity of the indonesian throughflow 100 kyr

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

a decadal spiciness mode in the tropics analysis of a complex climate model suggests the existence of a mode of coupled ocean atmosphere variability in the tropical pacific with the following dynamics anomalous strong pacific trade winds accelerate the north equatorial current and countercurrent at 10 to 15 n in the central pacific thermocline this causes anomalous advection across mean gradients of temperature and salinity on isopycnal surfaces and generates cool fresh spiciness anomalies of the order of 0 3 k these are advected by the mean circulation via the western boundary region to the equatorial pacific in approximately five years at the equatorial outcrops of the isopycnals the cool fresh anomalies affect the surface heat budget and are hypothesized to initiate a relaxation of the trade winds that is reinforced by positive feedbacks with the slope of the thermocline and with air sea fluxes of heat and freshwater at 5 to 10 s the decrease of the trades generates by anomalous advection cool fresh spiciness anomalies that migrate to the equator in one to two years and provide a positive feedback at 10 to 15 n the decrease of the trades decelerates north equatorial current and countercurrent and causes warm salty anomalies on isopycnals that arrive at the equator five years later and close the cycle

pleistocene δ18o records from ontong java plateau effects of winnowing and dissolution abstract sedimentation processes on ontong java plateau in the western equatorial pacific are reflected in oxygen isotope grain size and carbonate records processes recorded are dissolution of carbonate particles winnowing of fines and to some degree the gradient of productivity away from the equator carbonate dissolution begins to affect sediments significantly at about 3 km water depth winnowing is important on the top of the plateau and down the flanks to about 2 5 km water depth winnowing appears to have been greatly intensified during the ice age intervals

north south asymmetry of warm water volume transport related with el nino variability 1 a better understanding of variability in the volume of warm water in the equatorial pacific pycnocline warm water volume or wwv is critical to understanding el nino southern oscillation enso variability we have investigated the meridional wwv transport in the northern nh and southern hemispheres sh using a high resolution general circulation model the transport in the western boundary region compensates the interior transport in the sh where sverdrup balance holds approximately in contrast such compensation does not hold in the nh because the boundary transport lags interior transport by about 7 months hence the wwv exchange in the nh has more impact on the recharge discharge of the equatorial wwv the north south asymmetry of the wwv transport which is interpreted based on the linear rossby theory is related with the southward migration of westerly wind and the negative wind curl over the northwestern off equatorial region after the mature stage of enso

late pleistocene carbonate stratigraphy on ontong java plateau in the western equatorial pacific abstract late pleistocene carbonate cycles on ontong java plateau are characterized by maxima during deglaciations deglacial preservation spikes and by minima during transitions from interglacial to glacial conditions ice growth dissolution spikes superimposed on these short period fluctuations there is a long term oscillation of carbonate contents with a period of nearly 400 ky the brunhes dissolution cycle dissolution related sand fraction profiles 63 m indicate that the lysocline was at a water depth of about 3 6 km during deglacial transitions and that it rose up to 2 6 km during the stages of ice growth a fluctuation of the lysocline by 1 km can account for more than half of the total amplitude of the observed carbonate cycles assuming a linear increase in carbonate dissolution rates with increasing water depth below the lysocline and a constant ccd a shoaling of the lysocline during ice buildup may result from downward transfer of metabolic co 2 from intermediate waters to greater depths in the water column enhanced carbonate dissolution below 2 6 km increases alkalinity in deep waters predisposing the system toward reducing atmospheric co 2 partial pressure during a subsequent period

productivity control of fine particle transport to equatorial pacific sediment accumulation rates of 3he from cosmic dust 230th produced in the water column barite produced in the water column during decay of organic matter and fe and ti arriving with wind borne dust all are positively correlated in an equatorial pacific core tt013 pc72 01 1 n 139 4 w water depth 4298 m these accumulation rates are also positively correlated with the accumulation rates of noncarbonate material they are not significantly correlated to the mass accumulation rate of carbonate which makes up the bulk of the sediment the fluctuations in accumulation rates of these various components from different sources thus must result from variations in some process within the oceans and not from variations in their original sources sediment focusing by oceanic bottom currents has been proposed as this process marcantonio et al 1996 we argue that the variations in the accumulation rates of all these components are dominantly linked to changes in productivity and particle scavenging 3he 230th fe ti by fresh phytoplankton detritus which delivers ba upon its decay in the equatorial pacific upwelling region we speculate that as equatorial pacific productivity is a major component of global oceanic productivity its variations over time might be reflected in variations in atmospheric levels of methanesulfonic acid an atmospheric reaction product of dimethyl sulfide which is produced by oceanic phytoplankton and recorded in antarctic ice cores

seasonal eddy kinetic energy modulations along the north equatorial countercurrent in the western pacific seasonal eddy kinetic energy eke variability and its associated eddy energy conversion processes in the western tropical pacific are investigated using satellite altimeter observations and a global eddy resolving ocean general circulation model ogcm both the altimeter observed sea surface height anomalies and the ogcm simulation show an area with enhanced eke east of the mindanao island centered around 133 e and 5 n this enhanced eke area corresponds to the location of the quasi stationary meander of the north equatorial countercurrent necc and is bordered to the south by the halmahera eddy the mesoscale eke in this area exhibits a clear seasonality strong in summer july august and weak in winter november january and much of this seasonality is confined to the upper 200 m layer an investigation into the upper ocean eddy energetics based on the ogcm simulation reveals that the areal barotropic eddy energy conversion rate has an annual cycle similar to the eke variations while the areal baroclinic eddy energy conversion is found to be much smaller that the barotropic conversion rate and exhibits no clear seasonal changes this indicates that the eke variations are largely controlled by barotropic conversion of the seasonally varying regional circulation by examining the seasonal background circulation changes we find that the amplification of the barotropic eddy energy conversion rate in july august is related to the seasonal evolution of the mindanao current and the new guinea coastal current that amplifies the curvature and amplitude of the quasi stationary meander of the necc and results in an elevated eke level through increased regional barotropic conversion

dust impact on marine biota and atmospheric co2 during glacial periods 1 we assess the impact of high dust deposition rates on marine biota and atmospheric co2 using a state of the art ocean biogeochemistry model and observations our model includes an explicit representation of two groups of phytoplankton and colimitation by iron silicate and phosphate when high dust deposition rates from the last glacial maximum lgm are used as input our model shows an increase in the relative abundance of diatoms in today s iron limited regions causing a global increase in export production by 6 and an atmospheric co2 drawdown of 15 ppm when the combined effects of changes in dust temperature ice cover and circulation are included the model reproduces roughly our reconstruction of regional changes in export production during the lgm based on several paleoceanographic indicators in particular the model reproduces the latitudinal dipole in the southern ocean driven in our simulations by the conjunction of dust sea ice and circulation changes in the north pacific the limited open ocean data suggest that we correctly simulate the east west gradient in the open ocean but more data are needed to confirm this result from our model data comparison and from the timing of the dust record at vostok we argue that our model estimate of the role of dust is realistic and that the maximum impact of high dust deposition on atmospheric co2 must be 30 ppm

deep sea benthic foraminifera and biogenic opal glacial to postglacial productivity changes in the western equatorial pacific the accumulation rate of benthic foraminifera in deep sea sediments is strongly correlated with the productivity of the surface ocean core tops from diverse deep sea settings straddling different export production levels are used in this study for the calibration between the organic carbon flux to the seafloor jsf flux and the benthic foraminifera accumulation rate bfar the correlation can be used to reconstruct organic carbon flux to the seafloor in the past and hence the productivity of past oceans these results are compared with the accumulation rates of carbonate and biogenic opal in the sediments it is found that biogenic opal is more sensitive to productivity changes in the modern ocean than is carbonate the appropriate equations are derived for the equatorial pacific using core material fromeurydice erdc indomed inmd andpleiades plds expeditions these equations are then applied to two selected time horizons in sediments from the ontong java plateau a western equatorial pacific pelagic depth transect the last transition lt and the last glacial lg it is found that productivity was higher during the last glacial relative to the late holocene by a factor between 1 6 and 2 during the last transition productivity was intermediate between glacial and recent values we do not see any corresponding increase in the rates of accumulation of carbonate or biogenic opal during the last glacial this observation questions the importance of ocean productivity as the main controlling factor of carbonate and biogenic opal accumulation rates back through geological time

observations of warm water volume changes in the equatorial pacific and their relationship to el nino and la nina abstract this paper describes observed changes in surface winds sea surface temperature sst and the volume of water warmer than 20 c wwv in the equatorial pacific ocean for the period 1980 99 the purpose is to test recent hypotheses about the relationship between variations in wwv and the el nino southern oscillation enso cycle the results confirm inferences based on theory models and previous empirical analyses using proxy data namely sea level that enso involves a recharge and discharge of wwv along the equator and that the cyclic nature of enso results from a disequilibrium between zonal winds and zonal mean thermocline depth the authors also find that the magnitude of enso sst anomalies is directly related to the magnitude of zonal mean wwv anomalies furthermore for a given change in equatorial wwv the corresponding warm el nino sst anomalies are larger than the corresponding cold la nina anomalies this asymmetry between the warm and cold phases of the enso cycle implies differences

a 400 kyr record of combustion oxygen demand in the western equatorial pacific evidence for a precessionally forced climate response we have developed a combustion analysis technique for sediments which measures the amount of o2 consumed by the reduced species we have measured this quantity which we call combustion oxygen demand cod on a carbonate rich sediment core from the ontong java plateau in the western equatorial pacific back to marine oxygen isotope stage 11 the precision of the cod technique is 6 3 mol o2 g 1 which corresponds to 0 0076 wt corg assuming oxidation of organic carbon dominates the signal the cod time series is characterized by values which are about twice as high during glacials as during interglacials the largest shift occurring from 401 mol o2 g 1 in midstage 6 to 144 mol o2 g 1 at 5e and is coherent with the oxygen isotope curve of globigerinoides sacculifer in the same core at the milankovitch frequencies of 100 and 41 kyr pronounced variations in the 19 23 kyr band suggest that the climate of the western equatorial pacific is sensitive to precessional forcing a response not apparent from other records obtained in this region

southern hemisphere origins of the 1976 climate shift 1 observations from the tropical pacific ocean identify an abrupt climate shift in 1976 with surface temperatures changing from cooler than normal to warmer than normal in the span of about 1 year model results show that this climate shift originates with subsurface temperature anomalies in the south tropical pacific ocean which propagate first to the western boundary then northward to the equator and finally eastward along the equator to 140 w where they rise to the surface the results suggest that changes in the north pacific respond to changes in the tropical pacific

biogenic sediments in the west caroline basin the western equatorial pacific during the last 330 000 years abstract primary productivity as well as new production have played an important role in the global carbon cycle during the late quaternary the mean organic carbon nitrogen atomic ratio was 8 3 from the c4402 sediments in the west caroline basin which indicates a limited contribution of terrigenous organic carbon to the organic matter in the sediments the fluctuation of carbonate preservation shows that the accumulation rate of organic carbon has reflected primary productivity the results from sediment trap experiments which were carried out at site c4402 indicate that plankton bloom was characterized by a large influx of siliceous plankton when organic carbon was effectively removed palaeoproductivity estimates calculated by using the formula of sarnthein et al 1988 would be plausible because the fluctuation pattern of such estimates correlates closely with changes in the accumulation rate of biogenic opal in the sediments the primary productivity in the west caroline basin increased during stage 2 stage 3 late stage 6 stage 6 7 boundary and stage 8 at a glance the results are similar to other studies that have reported higher glacial productivity in low latitude regions however some leads and lags are found between the west caroline basin and other areas of the equatorial pacific and atlantic the spectral analysis of mar organic indicates that the western equatorial pacific reaches a maximum in mar organic approximately 7000 years before the maxima in the eastern pacific a regional variation of the response of mar organic to the orbital forcing climatic condition suggests that the efficiency of the organic carbon pump may vary with longitude in the equatorial pacific

precessional forcing of nutricline dynamics in the equatorial atlantic climate control of nutricline depth in the equatorial atlantic can be monitored by variations in the abundance of the phytoplankton species florisphaera profunda a conceptual model based on in situ evidence associates high abundances of f profunda with a deep nutricline and low abundances with a shallow nutricline a 200 000 year record of f profunda relative abundances obtained from a deep sea core sited beneath the region of maximum equatorial divergence at 10 w has 52 percent of its variance centered on the 23 000 year precessional band cross spectral analysis between the signals of f profunda and sea surface temperature independently derived from zooplankton species shows their 23 000 year cycles to be coherent and nearly in phase abundance minima of f profunda coincide with times of december perihelion whereas abundance maxima coincide with june perihelion these relations indicate that nutricline dynamics in the divergence region of the equatorial atlantic are controlled by variations in the tropical easterlies forced by the precessional component of orbital insolation on time scales greater than 10 000 years

modes of interannual and interdecadal variability of pacific sst abstract the multichannel singular spectrum analysis has been used to characterize the spatio temporal structures of interdecadal and interannual variability of sst over the pacific ocean from 20 s to 58 n using the comprehensive ocean atmosphere data set from 1950 to 1993 three modes with distinctive spatio temporal structures were found they are an interdecadal mode a quasi quadrennial qq oscillation with a period of 51 months and a quasi biennial qb oscillation with a period of 26 months the interdecadal mode is a standing mode with opposite signs of sst anomalies in the north pacific and in the tropical pacific the amplitude of this mode is larger in the central north pacific than in the tropical pacific this mode contributes 11 4 to the total variance it is associated with cooling in the central north pacific and warming in the equatorial pacific since around 1976 77 the qq oscillation exhibits propagation of sst anomalies northeastward from the philippine sea and then eastward along 4

do tropical cells ventilate the indo pacific equatorial thermocline source waters of the indo pacific equatorial thermocline are studied with a high resolution ocean model in the annual mean fields tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively tropical cells are common in ocean models but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters the tropical cells are much weaker when the overturning is considered in density coordinates when high frequency mass fluxes are included tropical cells are compensated by an eddy induced overturning seasonal variations and tropical instability waves are responsible for the compensation it follows that only subtropical cells transfer surface water to the equatorial thermocline strong tropical cells are shown to be an artefact

alkaline rocks from continental brazil abstract the present literature review on brazilian alkaline rocks stresses mainly the petrographic and geologic aspects at least eight different rock associations are represented agewise four groups are found among southern brazilian outcrops an older one about 240 m y only that is still poorly known the massifs clustered around jacupiranga about 130 m y old a few occurrences 100 110 m y old tunas itapirapua and the youngest and most important one with an age spread from about 80 m y to about 53 m y recent research shows a clear tectonic control both on local and on regional scales of alkaline occurrences in southern brazil alkaline magmatism was set off by pre drift and drift activity and is at its onset geologically related to basaltic activity emplacement of many massifs is also locally controlled by old lineaments e g in the minas gerais goias belt as is emphasized by geophysical data on a petrographic and chronologic basis several alkaline provinces are distinguished in southern brazil preliminary data on the cambrian precambrian rocks from southern bahia state a province with undersaturated syenites and litchfieldites and from cratonic areas in northern brazil are also presented

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

decadal variations in the subtropical cells and equatorial pacific sst 1 a mechanism for generating decadal sea surface temperature sst variability in the equatorial pacific is investigated using an ocean general circulation model forced by observed wind stress equatorial sst variability is governed by different ocean dynamics on interannual and decadal time scales at interannual time scales equatorial sst anomalies are mainly driven by equatorial winds at decadal time scales on the other hand they are forced both by equatorial winds and by off equatorial winds in the tropics while the contribution from midlatitude winds poleward of 25 is negligible trade wind variations in the off equatorial tropics force equatorial sst variability by spinning up and down the subtropical cells that transport cold water into the equatorial upwelling zone equatorial sst anomalies induced by this mechanism lag behind the response to local equatorial winds by about two years

enso like forcing on oceanic primary production during the late pleistocene late pleistocene changes in oceanic primary productivity along the equator in the indian and pacific oceans are revealed by quantitative changes in nanoplankton communities preserved in nine deep sea cores we show that variations in equatorial productivity are primarily caused by glacial interglacial variability and by precession controlled changes in the east west thermocline slope of the indo pacific the precession controlled variations in productivity are linked to processes similar to the southern oscillation phenomenon and they precede changes in the oxygen isotopic ratio which indicates that they are not the result of ice sheet fluctuations the 30 000 year spectral peak in the tropical indo pacific ocean productivity records is also present in the antarctica atmospheric co2 record suggesting an important role for equatorial biological productivity in modifying atmospheric co2

globally increased pelagic carbonate production during the mid brunhes dissolution interval and the co2 paradox of mis 11 the mid brunhes dissolution interval mbdi represents a period of global carbonate dissolution lasting several hundred thousand years centred around marine isotope stage mis 11 here we report the effects of dissolution in odp core 982 taken from 1134 m in the north atlantic paradoxically records of atmospheric co2 from antarctic ice cores reveal no long term trend over the last 400 kyr and suggest that co2 during mis 11 was no higher than during the present interglacial we suggest that a global increase in pelagic carbonate production during this period possibly related to the proliferation of the gephyrocapsa coccolithophore could have altered marine carbonate chemistry in such a way as to drive increased dissolution under the constraints of steady state an increase in the production of carbonate in surface waters would cause a drawdown of global carbonate saturation and increase dissolution at the seafloor in order to reconcile the record of atmospheric co2 variability we suggest that an increase in the flux of organic matter from the surface to deep ocean associated with either a net increase in primary production or the enhanced ballasting effect provided by an increased flux of caco3 could have countered the effect of increased calcification on co2

interannual to decadal variations of tropical subtropical exchange in the pacific ocean boundary versus interior pycnocline transports abstract interannual to decadal variations of tropical subtropical mass exchange in the pacific ocean are investigated using a near global ocean general circulation model along with satellite observations of sea level and wind and a data assimilation product the analysis focuses on the variability of pycnocline transports through the western boundary and interior near 10 n and 10 s in contrast to time mean exchange where boundary and interior pycnocline transports are both equatorward the variations of boundary and interior pycnocline transports are found to be generally anticorrelated to each other moreover the variation of the boundary pycnocline transport is smaller than that of the interior again different from time mean exchange where the boundary transport at 10 n is substantially larger than that through the interior interannual variations of the boundary and interior transports are consistent with near surface geostrophic flow inferred from sea level data interior pycnocline flow into th

temporal variability in living deep sea benthic foraminifera a review the deep ocean environment is disturbed by various processes many of which involve episodic inputs of organic matter some inputs e g phytodetritus at mid high latitudes in the north atlantic and northeast pacific are seasonally pulsed others e g falls of whale carcasses are irregular and unpredictable but together they evoke a variety of responses from the benthic biota in the case of deep sea foraminifera only those responses arising from seasonal food pulses have been fairly well documented the population dynamics of deep sea benthic foraminifera total live populations and individual species appear to be controlled largely by two inversely related parameters the flux of organic matter to the seafloor and concentrations of oxygen in the sediment porewater organic matter food inputs are most intense along bathyal continental margins and their oxidation often leads to the depletion of oxygen in surface sediments under these conditions foraminiferal faunas are dominated by low oxygen tolerant infaunal species the abundance of which fluctuate in response to seasonally varying amounts of food and oxygen at some sites e g sagami bay off japan species migrate up and down in the sediments tracking critical oxygen concentrations where oxygen concentrations are consistently low less than about 0 5 ml l 1 as in parts of the california borderland foraminifera may undergo population increases solely in response to food pulses in the abyssal north atlantic and in some continental margin areas of this ocean organic matter inputs are weaker and do not lead to oxygen depletion within surface sediments these systems are food limited and seasonal population fluctuations reflect the availability of food phytodetritus rather than oxygen here the species which respond to phytodetritus are mainly epifaunal or shallow infaunal opportunists which represent a small proportion of highly diverse communities 2 or 3 out of 120 species per core of 25 5 cm2 surface area seasonal phytodetrital pulses to the deep seafloor and hence foraminiferal population dynamics are not entirely predictable being dependent on climatic and upper ocean processes they vary in intensity from year to year and occasionally e g at the porcupine abyssal plain pap in 1997 fail to materialise foraminiferal responses to irregular non seasonal organic matter inputs are poorly known however there is some evidence that whale falls turbidite deposits hydrothermal vents and seeps are exploited by species typical of organically enriched low oxygen environments rather than by a specialised fauna fossil foraminiferal assemblages from bathyal and abyssal environments may provide evidence for an increase or decrease in the seasonality of surface production as well as for longer term changes in palaeoproductivity however the accurate interpretation of this record depends on filling the many gaps which remain in our understanding of relations between benthic foraminiferal ecology and seasonal phenomena in the deep ocean

symmetric and antisymmetric mass exchanges between the equatorial and off equatorial pacific associated with enso 1 mass exchanges in the upper ocean between the equatorial and off equatorial pacific ocean associated with the el nino southern oscillation enso are investigated using the national centers for environmental prediction ncep ocean assimilation data the data show that enso related meridional mass transport in the northern hemisphere nh is larger than that in the southern hemisphere sh we found that the antisymmetric characteristics are mainly due to a southward shift of themaximum zonal wind stress anomaly during the enso mature phase the ekman and geostrophic transports associated with enso are separated into symmetric and antisymmetric components for the symmetric part the mass divergence over the equatorial pacific by the geostrophic transport is generally larger than the convergence by the ekman transport during the el nino mature phase therefore mass is transported from the equator to off the equator at this time as for the antisymmetric part the ekman transport due to antisymmetric wind stress dominates the geostrophic transport so that the mass is transported from the sh to the nh during the el nino mature phase the net mass transport in the nh is larger than that in the sh a theoretical interpretation and intermediate model experiments support these arguments index terms 4522 oceanography physical el nino 4572 oceanography physical upper ocean processes 4512 oceanography physical currents 4504 oceanography physical air sea interactions 0312 4215 oceanography general climate and interannual variability 3309 keywords enso mass exchange wind stress antisymmetry

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

pacific caco3 preservation and δ18o since 4 ma paleoceanic and paleoclimatic implications the pliocene pleistocene history of caco3 preservation in the central equatorial pacific is reconstructed from a suite of deep sea cores and is compared to fluctuations in global ice volume inferred from 18o records the results are highlighted by 1 a strong covariation between caco3 preservation and ice volume over 104 to 106 year time scales 2 a long term increase in ice volume and caco3 preservation since 3 9 ma demonstrated by a deepening of the lysocline and the carbonate critical depth 3 a dramatic shift to greater caco3 preservation at 2 9 ma 4 distinctive ice volume growth and caco3 preservation events at 2 4 ma which are associated with the significant intensification of northern hemisphere glaciation 5 a mid pleistocene transition to 100 kyr cyclicity in both caco3 preservation and ice volume and 6 a 600 kyr brunhes dissolution cycle superimposed on the late pleistocene glacial interglacial 100 kyr cycles caco3 preservation primarily reflects the carbonate chemistry of abyssal waters and is controlled by long term 106 year and short term 104 to 105 year biogeochemical cycling and by distinct paleoclimatic events we attribute the long term increase in caco3 preservation primarily to a fractionation of caco3 deposition from continental shelf to ocean basin and secondarily to a gradual rise in the riverine and glaciofluvial flux of ca on shorter time scales the fluctuations in caco3 preservation slightly lag ice volume fluctuations and are attributed to climatically induced changes in the circulation and chemistry of pacific deep water

decadal phase change in large scale sea level and winds in the indo pacific region at the end of the 20th century 1 satellite observations of sea surface height ssh and wind stress for the period of 1993 2006 reveal a near coherent large scale decadal variability in much of the indo pacific region with a phase change at the turn of the 20th century trade wind variations in the tropical pacific and south indian ocean are anti correlated with each other as are ssh differences across these two basins implying anti correlated variation of the subtropical cells in the two oceans decadal changes in large scale ssh in the extra tropics are mostly associated with well defined patterns of wind stress curl indicating a near coherent decadal variation in the strength of subtropical and subpolar gyres together these variations reflect a linkage in the circulation of the pacific and indian oceans via atmospheric and oceanic bridges the phase change in the tropical pacific tends to occur earlier than elsewhere suggesting a potential role of the tropical pacific in regulating decadal variability of the entire region

benthic foraminiferal paleoceanography of the south china sea over the last 40 000 years benthic foraminifera in gravity and piston cores from two sites of the northern and southern slopes of the south china sea scs were analyzed to evaluate changes in surface productivity and deep water mass characteristics over the last 40 000 years our observations suggest that changes in organic carbon flux that is food supply and chemical and or physical properties of the ambient water mass may be the two primary and intercorrelated factors controlling the distribution patterns of benthic foraminifera when organic carbon flux increased above 3 5 g c m 2 yr 1 in the southern scs during the last glacial maximum and in the northern scs during the first part of the holocene around 10 ka b p a group of detritus feeders including bulimina aculeata and uvigerina peregrina dominated the benthic foraminiferal assemblage as shown by relative abundance and accumulation rates this may reflect episodes of increased surface productivity possibly induced by increased input of nutrients from nearby river runoff suspension feeders such as cibicidoides wuellerstorfiand a group of opportunistic species including oridorsalis umbonatus melonis barleeanum and chilostomella ovoidea gradually became more abundant than detritus feeders as soon as the organic carbon flux decreased to 2 5 3 5 g c m 2 yr 1 similar glacial to interglacial changes in relative abundance and accumulation rates were observed in both cores for a number of species including eggerella bradyi globocassidulina subglobosa astrononion novozealandicum sphaeroidina bulloidesand cibicidoides robertsonianus these changes were not correlated to the distribution patterns of organic carbon in both cores and may have been related to yet unspecified changes in chemical and or physical properties of the ambient water mass independent of changes in organic carbon flux 1999 elsevier science b v all rights reserved

biomass burning and oceanic primary production estimates in the sulu sea area over the last 380 kyr and the east asian monsoon dynamics abstract coccolithophorid assemblages and micro charcoal content were analysed in giant piston core md97 2141 recovered in the sulu sea philippines these proxies help to reconstruct respectively the dynamics of the oceanic primary production pp and biomass burning in that area pp in the sulu sea intensifies during the east asian winter monsoon eawm and therefore pp constitutes a proxy for eawm dynamics most of the precipitation in the sulu sea region occurs during the east asian summer monsoon easm because the intensity of biomass burning is related to dryness of the surrounding area the sedimentary micro charcoal content can be used as an inverse proxy for easm intensity our results show that the eawm intensifies during glacial times in agreement with previous studies precessional forcing appears to act directly on eawn because of the early response of pp in that frequency band the micro charcoal record exhibits complex dynamics which we attribute to the competing influence of the long term el nino southern oscillation enso like forcing and the glacial interglacial cycle on easm these influences create an unusual frequency spectrum with power around 30 kyr and 19 kyr attributed to the non linear response to the 100 kyr cycle glacial and the 23 kyr enso cycle a factor of two increase in the amplitude of the micro charcoal variability between 51 and 10 ka bp could correspond to homo sapiens biomass burning in the style of the fire stick farming of the australian aborigines we also find on precession cycles an opposite phase between easm and eawm records and an advance of 18 o and 18 o respectively by 2000 yr

quantitative composition of benthic foraminiferal assemblages as a proxy indicator for organic carbon flux rates in the south china sea abstract the organic carbon flux signal embedded in the distribution data of benthic foraminifera from 43 box core surface samples from the south china sea scs is compared to data from two gravity cores on the northern core 17940 2 and southern core 17964 3 slope of the scs surface sampling stations cover almost the entire area of the south china sea including areas with preferential summer monsoonal upwelling or winter monsoonal upwelling as well as a wide range of water depths 300 4000 m we use correspondence analysis afc to examine the relation between the quantitative composition of benthic foraminiferal assemblages water depth and organic carbon flux rates we find a clear correlation between benthic foraminiferal assemblage composition factor 1 of the afc and organic carbon flux rates in the surface samples and use the same model to calculate paleo flux rates for the two cores significantly increased carbon flux rates are observed in the southern scs sunda shelf margin during the last glacial maximum lgm whereas the organic carbon flux rates along the northern slope of the scs seem to be highest during the early holocene

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

chronology of earth s glacial and tectonic record the glacial record yields a pattern of ice ages that shows distinctive characters for different periods however ages of deposits generally provide constraints on the time sequence which because of uncertainties are still too wide to be used critically for or against any regular or cyclic history it seems better to assume no periodicity until such can be argued models for cyclic mechanisms with a longer period than the milankovitch cycle that have been proposed include major chancge in tilt of earth s spin axis galactic year and tectonic cycles evolutionary tectonic changes or changes in atmospheric co 2 are more likely to have been contributing factors but the late proterozoic vendian varangian ice ages with at least equatorial glaciation remain enigmatic

enso driven interhemispheric pacific mass transports previous studies have shown that enso s anomalous equatorial winds including the observed southward shift of zonal winds that occurs around the event peak can be reconstructed with the first two empirical orthogonal functions eofs of equatorial region wind stresses using a high resolution ocean general circulation model we investigate the effect of these two eofs on changes in warm water volume wwv interhemispheric mass transports and indonesian throughflow itf wind stress anomalies associated with the first eof produce changes in wwv that are dynamically consistent with the conceptual recharge oscillator paradigm the itf is found to heavily damp these wwv changes reducing their variance by half wind stress anomalies associated with the second eof which depicts the southward wind shift are responsible for wwv changes that are of comparable magnitude to those driven by the first mode the southward wind shift is also responsible for the majority of the observed interhemispheric upper ocean mass exchanges these winds transfer mass between the northern and the southern hemisphere during el nino events whilst water is transferred in the opposite direction during la nina events the magnitude of this exchange is roughly half of that seen during el nino events thus the discharging of wwv during el nino events is meridionally asymmetric while the wwv recharging during a la nina event is largely symmetric the inclusion of the southward wind shift is also shown to allow enso to exchange mass with much higher latitudes than that allowed by the first eof alone

observed equatorial rossby waves and enso related warm water volume changes in the equatorial pacific ocean 1 modifications of the volume of warm water above the thermocline in the equatorial pacific are thought to be critical for enso el nino southern oscillation preconditioning development and prediction in this paper changes in this warm water volume wwv are first reviewed from the literature and then analyzed within 5 n 5 s in using 1992 2006 altimeter derived sea level anomalies sla and in situ observations we conclude that the 1992 2006 wwv changes in the equatorial band are a residual from the opposite effects of zonally integrated meridional ekman and geostrophic transports of warm water the latter being estimated from sla and validated against in situ observations for the first time with observations we evidence first baroclinic first meridional mode equatorial rossby waves to be responsible for the anomalous meridional geostrophic transports of warm water in changing the basin scale zonal pressure gradient these transports appear in phase opposition and proportional to the anomalous sea surface temperature sst in the region nino3 4 170 w 120 w 5 n 5 s the links between our observational results and the recharge discharge oscillator theory the differences in wwv between enso events and the hint for possible recent changes in the relation between wwv and nino3 4 sst are discussed

stable carbon cycle climate relationship during the late pleistocene a record of atmospheric carbon dioxide co2 concentrations measured on the epica european project for ice coring in antarctica dome concordia ice core extends the vostok co2 record back to 650 000 years before the present yr b p before 430 000 yr b p partial pressure of atmospheric co2 lies within the range of 260 and 180 parts per million by volume this range is almost 30 smaller than that of the last four glacial cycles however the apparent sensitivity between deuterium and co2 remains stable throughout the six glacial cycles suggesting that the relationship between co2 and antarctic climate remained rather constant over this interval

foraminiferal responses to major pleistocene paleoceanographic changes in the southern south china sea a detailed age model for core 17957 2 of the southern south china sea was developed based on delta 18 o coarse fraction magnetostratigraphy and biostratigraphy for the last 1500 kyr the delta 18 o record has clear similar to 100 kyr cycles after the mid pleistocene revolution mpr at the entrance of marine isotopic stage mis 22 planktonic foraminifera responded to the mpr immediately showing the increased sea surface temperature sst and dissolution after the mpr benthic foraminifera did not respond to it until the brunhes matuyama boundary since the mpr the depth of thermocline gradually became shallower until miss 6 5 this major change within miss 6 5 was also reflected in the decreased ssts and increased productivity and deep water mass thus two major pleistocene paleoceanographic changes were found one was around the mpr the other occurred within miss 6 5 which speculatively might be ascribed to the reorganization of surface and deep circulation possibly induced by tectonic forces

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

mass extinctions the view of a sceptic the concept of periodic mass extinctions by extraterrestrial impacts has contributed very strongly to the current revival of interest in the problem of mass extinctions in this context several radical claims have been made asserting that the newly emerging picture of mass extinctions as a separate class of biological phenomena caused by a separate class of processes demands a far reaching revision of the the neodarwinian paradigm of evolution and implies a vindication of the cuvierian perspective on earth9s history the validity of these claims however is questionable at all levels from the interpretation of particular events to the concept of mass extinctions as a special class of phenomena to their proposed causation by impacts and to their alleged historical pedigree and implications for current evolutionary theory mass extinctions may actually be clusters of more or less accidentally aggregated in time but causally distinct extinction episodes

an interhemispheric tropical sea level seesaw due to el nino taimasa abstractduring strong el nino events sea level drops around some tropical western pacific islands by up to 20 30 cm such events referred to as taimasa in samoa expose shallow reefs thereby causing severe damage to associated coral ecosystems and contributing to the formation of microatolls during the termination of strong el nino events a southward movement of weak trade winds and the development of an anomalous anticyclone in the philippine sea are shown to force an interhemispheric sea level seesaw in the tropical pacific that enhances and prolongs extreme low sea levels in the southwestern pacific spectral features in addition to wind forced linear shallow water ocean model experiments identify a nonlinear interaction between el nino and the annual cycle as the main cause of these sea level anomalies

late pleistocene paleoclimatology of the central equatorial pacific sea surface response to the southeast trade winds proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late pleistocene all indicators fluctuate at higher frequencies than the 100 000 year glacial interglacial cycle display reduced amplitude variations since 300 000 years ago exhibit a change in the record character at about 300 000 years ago the mid brunhes climatic event and have higher amplitude variations in sediments 300 000 850 000 years old time series analyses were conducted to determine the spectral character of each record 18o of planktonic foraminifer sea surface temperature values equatorial divergence indicators and wind intensity indicators and to quantify interrecord coherence and phase relationships the record was divided at the 300 000 year clear change in climatic variability nonstationarity the 18o based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402 000 774 000 years the 18o spectra show 100 000 and 41 000 year power in the younger portion 0 300 000 years and 100 000 41 000 and 23 000 year power in the older interval all highly coherent and in phase with the specmap average stacked isotope record unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31 000 years this period is also important in the sea surface temperature signal where the dominant spectral peak is 100 000 years the 31 000 year spectral component is coherent and in phase between the eolian and divergence records confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record since the 31 000 year power appears in independent data sets within this core and also appears in other equatorial records j imbrie personal communication 1987 we assume it to be real and representative of both a nonlinear response to orbital forcing possibly a combination of orbital tilt and eccentricity and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component the mid brunhes climatic event is an important aspect of these records but its cause remains unknown

linkage between the pacific decadal oscillation and the low frequency variability of the pacific subtropical cell the decadal variability of pacific subtropical cell stc and its linkages with the pacific decadal oscillation pdo are investigated in the present study based on a simple ocean data assimilation soda 2 2 4 it is found that on decadal time scales the western boundary and interior pycnocline transports are anticorrelated and the variation of the interior component is more significant which is consistent with previous studies the decadal variability of stc in the northern hemisphere is found to be strongly associated with pdo associated with a positive negative phase of pdo the relaxation acceleration of the northeast trades slows down spins up the stc within a few years through baroclinic adjustment in conjunction with the subduction of the cold warm mixed layer anomalies in the extratropics the cold warm water is then injected into the thermocline and advected further southwestward to the tropics along the isopycnal surfaces leading to the slowdown spin up of stc due to zonal pressure gradient change at low latitude along with the stc weakening strengthening a significant warming cold anomaly appears in the tropics and it is advected to the midlatitude by the kuroshio and north pacific currents thus feeding back to the atmosphere over the north pacific in contrast to the northern hemisphere it is found the stc in the south only passively responds to the pdo the mechanism found here highlights the role of the stc advection of extratropical anomalies to the tropics and horizontal gyre advection of the tropical anomalies to the extratropics in decadal variability of the stc and pdo

a stability analysis of tropical ocean atmosphere interactions bridging measurements and theory for el nino abstract interactions between the tropical oceans and atmosphere permit a spectrum of natural modes of oscillation whose properties period intensity spatial structure and direction of propagation depend on the background climatic state i e the mean state this mean state can be described by parameters that include the following the time averaged intensity of the pacific trade winds the mean depth h of the thermocline and the temperature difference across the thermocline t a stability analysis by means of a simple coupled ocean atmosphere model indicates two distinct families of unstable modes one has long periods of several years involves sea surface temperature variations determined by vertical movements of the thermocline that are part of the adjustment of the ocean basin to the fluctuating winds requires a relatively deep thermocline and corresponds to the delayed oscillator the other family requires a shallow thermocline has short periods of a year or two has sea surface tempe

rapid subsurface warming and circulation changes of antarctic coastal waters by poleward shifting winds the southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s this wind trend is projected to persist under continued anthropogenic forcing but the impact of the changing winds on antarctic coastal heat distribution remains poorly understood here we show that a poleward wind shift at the latitudes of the antarctic peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 c at 200 700 m depth the model simulated warming results from a rapid advective heat flux induced by weakened near shore ekman pumping and is associated with weakened coastal currents this analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around antarctica with potentially significant ramifications for global sea level rise

a benthic foraminiferal proxy of pulsed organic matter paleofluxes in the temperate open ocean of the modern northeast atlantic the spring bloom of phytoplankton leads to a seasonal pulse of detrital organic material phytodetritus to the ocean floor opportunistic benthic foraminifera rapidly colonise this food resource producing large numbers of individuals whose tests are ultimately added to the sediment one of these taxa epistominella exigua shows periodic peaks in abundance in the fossil record at many open ocean sites previously such peaks have been commonly interpreted to result from changes in physicochemical properties of bottom water mass and thus deep sea circulation the main purpose of this paper is to propose thate exigua may be used as a proxy of pulsed organic matter inputs to the deep ocean and therefore as an indicator of relative changes in productivity

past hydrographic and climatic changes in the subantarctic zone of the south atlantic the pleistocene record from odp site 1090 abstract pleistocene summer sea surface temperatures ssst have been reconstructed on a composite core section recovered in the subantarctic zone of the southern ocean from planktonic foraminifers applying the modern analog technique the composite consists of core ps2489 2 and the sections recovered at odp site 1090 and documents the last 1 83 ma three distinct climatic periods can be identified that mirror the pleistocene development of the southern ocean hydrography cold climatic conditions prevailed at 43 s during glacial as well as during interglacial periods during the early pleistocene 1 83 0 87 ma indicating a northward shift of isotherms that characterize the present day polar front zone by about 7 of latitude evidence shows a strong linkage between southern ocean and low latitude climate during that interval time between the mid pleistocene revolution ca 0 9 ma and the mid brunhes event ca 0 4 ma we observe higher amplitude fluctuations in the ssst between glacial and interglacial periods corresponding to the temperature range between the present polar front and subantarctic front these climatic variations have been related to changes in the northern hemisphere ice sheets the past 0 4 ma are characterized by strong ssst variations of up to 8 c between glacials and interglacials only during the climatic optima stages 11 3 9 3 7 5 7 1 5 5 and the early holocene ssst exceeded present ssst at the core locality 10 2 c although the carbonate dissolution record exhibits high variability during the pleistocene it can be shown that ssst estimates were not significantly biased the mid brunhes dissolution cycle as well as the mid pleistocene enhanced carbonate preservation appear to belong to a global long term variability in carbonate preservation

pacific ocean circulation rebounds 1 recent observations indicate that the shallow meridional overturning circulation in the tropical pacific ocean has rebounded since 1998 following 25 years of significantly weaker flow convergence of cold interior ocean pycnocline water towards the equator increased to 24 1 1 8 106 m3 s 1 during 1998 2003 from a low of 13 4 1 6 106 m3 s 1 during 1992 98 intensified circulation led to the development of anomalously cool tropical pacific sea surface temperatures which may have affected pacific marine ecosystems and global climate the abruptness of the rebound also obscures presumed anthropogenic warming trends in the instrumental temperature record of the tropical pacific

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

gliders measure western boundary current transport from the south pacific to the equator abstract spray gliders most launched from small boats near shore have established a sustainable time series of equatorward transport through the solomon sea the first 3 5 years mid 2007 through 2010 are analyzed coast to coast equatorward transport through the solomon sea fluctuates around a value of 15 sv 1 sv 106 m3 s 1 with variations approaching 15 sv transport variability is well correlated with el nino indices like nino 3 4 with strong equatorward flow during one el nino and weak flow during two la ninas mean transport is centered in an undercurrent focused in the western boundary current variability has a two layer structure with layers separated near 250 m near the core of the undercurrent that fluctuate independently the largest variations are in midbasin confined to the upper layer and are well correlated with enso analysis of velocity and salinity on isopycnals shows that the western boundary current within the solomon sea consists of a deep core coming from the coral sea

tropical pacific decadal variability and the subtropical tropical cells abstract the decadal scale variability in the tropical pacific has been analyzed herein by means of observations and numerical model simulations the two leading modes of the sea surface temperature sst variability in the central western pacific are a decadal mode with a period of about 10 yr and the enso mode with a dominant period of about 4 yr the sst anomaly pattern of the decadal mode is enso like the decadal mode however explains most variance in the western equatorial pacific and off the equator a simulation with an ocean general circulation model ogcm forced by reanalysis data is used to explore the origin of the decadal mode it is found that the variability of the shallow subtropical tropical overturning cells is an important factor in driving the decadal mode this is supported by results from a multicentury integration with a coupled ocean atmosphere general circulation model cgcm that realistically simulates tropical pacific decadal variability finally the sensitivity of the shal

rate of production dissolution and accumulation of biogenic solids in the ocean the equatorial current system by its response to global circulation changes provides a unique recording mechanism for long range climatic oscillations a permanent record of the changes in rate of upwelling and organic production is generated in the equatorial deep sea sediments particularly by such biogenic components which are unaffected by secondary dissolution in order to determine the rates of accumulation of various sedimentary components a reliable differential measurement of age of the strata must be obtained various approaches to this problem are reviewed and sources of error discussed secondary dissolution of calcium carbonate introduces a substantial and variable difference between the dissolution modified and hence a priori unknown rate of deposition on one hand and the rate of accumulation derivable from the observed concentration on the other the cause and magnitude of these variations are of importance particularly since some current dating schemes are based on assumed constancy in the rate of accumulation of this and in some cases also all other sedimentary components the concepts used in rate evaluation are discussed with emphasis on the difference between the state of dissolution an observable property of the sediment and the rate of dissolution a parameter that requires deduction of the carbonate fraction dissolved and of the time differential as a most likely cause of the enhanced state of dissolution of the interglacial carbonate sediments is proposed the lowered rates of biogenic production and deposition which cause longer exposure of the carbonate microfossils to corrosion in the bioturbated surface layer of the sediment historical perspective is included in the discussion in view of the dedication of the symposium to hans pettersson the leader of the swedish deep sea expedition 1947 1948 an undertaking that opened a new era in deep sea research and planetary dynamics

decadal upper ocean temperature variability in the tropical pacific decadal variability in upper ocean temperature in the pacific is studied by using observations and results from model experiments especially propagation of upper ocean thermal anomalies from the midlatitudes to the tropics is studied as a possible source for decadal equatorial thermocline variability in the observations propagation along the subtropical gyre of the north pacific is clear however no propagation into the equatorial region is found model experiments with an ocean model forced with observed monthly wind and wind stress anomalies are performed to study the apparent propagation distinct propagation of thermal anomalies in the subtropics is found in the model although the amplitude of the anomalies is small the anomalies clearly propagate into the tropics but they do not reach the equatorial region the small response at the equator to extratropical variability consists of a change in the mean depth of the thermocline it appears that most variability in the subtropics and tropics is generated by local wind stress anomalies the results are discussed by using results from a linear shallow water model in which similar features are found

major pleistocene stages in a carbon perspective the south china sea record and its global comparison 1 carbon isotope sequences at ocean drilling program site 1143 south china sea reveal a long term cyclicity of 500 kyr that is superimposed on the glacial cycles and is present in long 13c sequences from all oceans the quaternary 13c record is punctuated by four 13c maximum events 13cmax i which began in marine isotope stage mis 3 around 50 60 kyr ago 13cmax ii mis 13 0 47 0 53 ma 13cmax iii mis 27 29 0 97 1 04 ma and 13cmax vi mis 53 57 1 55 1 65 ma as the same cyclicity is also found in carbonate curves the 13cmax events must denote major reorganization in the carbon reservoir of the global ocean they also are associated with major changes in glacial cyclicity such as the mid brunhes event following 13cmax ii and the mid pleistocene revolution following 13cmax iii which in turn were associated with expansion of the ice sheets from a carbon perspective therefore the quaternary period has passed through three major stages and each appears to represent a further step in ice cap development

coupled atmosphere mixed layer ocean response to ocean heat flux convergence along the kuroshio current extension the winter response of the coupled atmosphere ocean mixed layer system to anomalous geostrophic ocean heat flux convergence in the kuroshio extension is investigated by means of experiments with an atmospheric general circulation model coupled to an entraining ocean mixed layer model in the extra tropics the direct response consists of positive sst anomalies along the kuroshio extension and a baroclinic low level trough and upper level ridge circulation anomaly over the north pacific the low level component of this atmospheric circulation response is weaker in the case without coupling to an extratropical ocean mixed layer especially in late winter the inclusion of an interactive mixed layer in the tropics modifies the direct coupled atmospheric response due to a northward displacement of the pacific inter tropical convergence zone which drives an equivalent barotropic anomalous ridge over the north pacific although the tropically driven component of the north pacific atmospheric circulation response is comparable to the direct response in terms of sea level pressure amplitude it is less important in terms of wind stress curl amplitude due to the mitigating effect of the relatively broad spatial scale of the tropically forced atmospheric teleconnection

western equatorial pacific productivity and carbonate dissolution over the last 550 kyr foraminiferal and nannofossil evidence from odp hole 807a we analyzed foraminiferal and nannofossil assemblages and stable isotopes in samples from odp hole 807a on the ontong java plateau in order to evaluate productivity and carbonate dissolution cycles over the last 550 kyr kilo year in the western equatorial pacific our results indicate that productivity was generally higher in glacials than during interglacials and gradually increased since mis 13 carbonate dissolution was weak in deglacial intervals but often reached a maximum during interglacial to glacial transitions carbonate cycles in the western equatorial pacific were mainly influenced by changes of deep water properties rather than by local primary productivity fluctuations of the estimated thermocline depth were not related to glacial to interglacial alternations but changed distinctly at similar to 280 kyr before that time the thermocline was relatively shallow and its depth fluctuated at a comparatively high amplitude and low frequency after 280 kyr the thermocline was deeper and its fluctuations were at lower amplitude and higher frequency these different patterns in productivity and thermocline variability suggest that thermocline dynamics probably were not a controlling factor of biological productivity in the western equatorial pacific ocean in this region upwelling the influx of cool nutrient rich waters from the eastern equatorial pacific or of fresh waters from rivers have probably never been important and their influence on productivity has been negligible over the studied period variations in the inferred productivity in general are well correlated with fluctuations in the eolian flux as recorded in the northwestern pacific a proxy for the late quaternary history of the central east asian dust flux into the pacific therefore we suggest that the dust flux from the central east asian continent may have been an important driver of productivity in the western pacific c 2007 elsevier b v all rights reserved

late pleistocene paleoclimatology of the central equatorial pacific a quantitative record of eolian and carbonate deposition detailed records of vso 6i3c percentage and mass accumulation rate of caco and eolian percentage mass accumulation rate and grainsize generated for core rcl l 210 from the equatorial pacific reveal the timing of paleoclimatic events over the past 950 000 yr the caco percentage record shows the standard pacific correlation of high caco content with glacial periods but displays a marked change of character about 490 000 yr ago with older stages showing much less variability the carbonate mass flux record however does not show such a noticeable change sedimentation rates vary from about 0 5 to 3 0 cm l000 yr and during the past 490 000 yr sections with enhanced sedimentation rates correspond to periods of high caco percentage eolian mass accumulation rates an indication of the aridity of the source region are usually higher during glacial times eolian grainsize an indication of the intensity of atmospheric circulation generally fluctuates at a higher frequency than the loo ooo yr glacial cycle the mid brunhes climatic event centered at 300 000 yr ago appears as a 50 000 yr interval of low intensity and reduced variability of atmospheric circulation furthermore the nature of this entire record changes then with the younger portion indicating less variation in wind intensity than the older part of the record the late matuyama increase in amplitude of paleoclimatic signals begins 875 000 yr ago in the eolian record 25 000 yr before the 6i80 and caco percentage amplitude increases about

on the pathways of the equatorial subsurface currents in the eastern equatorial pacific and their contributions to the peru chile undercurrent 1 theconnections between theequatorial currentsystem andtheperu currentsystem in the eastern tropical pacific etp are examined with a primitive equations eddy resolving regional model the quasi equilibrium solutions reproduce three eastward equatorial subsurface currents of interest the equatorial undercurrent euc located between 1 n and 1 s the primary southern subsurface countercurrent psscc between 3 and 4 s and farther south the secondary southern subsurface countercurrent ssscc between 7 and 8 s using a lagrangian tracking procedure the fate of these currents in the etp and their contribution to the peru chile undercurrent pcuc are studied lagrangian diagnostics show that for the most part the euc water contributes to westward flows including the south equatorial current and deeper flows below it and strikingly only a very little fraction feeds the pcuc while a significant part of both ssccs contribute substantially mesoscale eddies are shown to exert an effect on these connections in addition about 30 of the pcuc is fed by the three subsurface equatorial flows euc psscc ssscc the remaining part of the pcuc comes from an alongshore recirculation associated with flows below it and from the southern part of the domain south of 9 s