planktonic foraminiferal mg ca as a proxy for past oceanic temperatures a methodological overview and data compilation for the last glacial maximum as part of the multi proxy approach for the reconstruction of the glacial ocean margo incentive published and unpublished temperature reconstructions for the last glacial maximum lgm based on planktonic foraminiferal mg ca ratios have been synthesised and made available in an online database development and applications of mg ca thermometry are described in order to illustrate the current state of the method various attempts to calibrate foraminiferal mg ca ratios with temperature including culture trap and core top approaches have given very consistent results although differences in methodological techniques can produce offsets between laboratories which need to be assessed and accounted for where possible dissolution of foraminiferal calcite at the sea floor generally causes a lowering of mg ca ratios this effect requires further study in order to account and potentially correct for it if dissolution has occurred mg ca thermometry has advantages over other paleotemperature proxies including its use to investigate changes in the oxygen isotopic composition of seawater and the ability to reconstruct changes in the thermal structure of the water column by use of multiple species from different depth and or seasonal habitats presently available data are somewhat limited to low latitudes where they give fairly consistent values for the temperature difference between late holocene and the lgm 2 3 5 c data from higher latitudes are more sparse and suggest there may be complicating factors when comparing between multi proxy reconstructions

phosphorus cycling in sediments of the bohai and yellow seas using a box sampler surface and core sediment samples were collected from the bohai and yellow seas in 1998 1999 the sediments were sequentially extracted to determine six phosphorus fractions and non sequentially extracted for total p tp and inorganic p ip where the difference between tp and ip was assumed to be organic p op it was found that more than 70 of the total p is inorganic p the concentrations of phosphorus were high near the river mouth reflecting the influence from the huanghe and changjiang sediment loads the phosphorus levels in the bohai sea are higher than those in the yellow sea which is related to the sediment sources and distribution of chlorophyll a in these areas concentrations of tp in the bohai and yellow seas are comparable to the other worldwide coastal areas among the six forms of phosphorus phosphorus distribution ranges were 0 8 2 for loosely sorbed p 3 10 for iron bound inorganic p 4 19 for leachable organic p 3 15 for authigenic apatite 35 66 for detrital apatite and 14 36 for refractory organic p potentially bioavailable phosphorus accounts for a small amount of tp while phosphorus load associated with eroded soil may be larger than the anthropogenic load the regeneration of dissolved p from sediments is a slow process which could play a role in maintaining low phosphate levels in the seas most of the phosphorus was regenerated in a water column and almost all of the remaining phosphorus was buried in the sediments after its accumulation the high values of p burial efficiencies in the study areas were related to low benthic phosphate flux which is due to the high percent of detrital apatite that is not bioavailable and the high sediment accumulation rate

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

ecological controls on the shell geochemistry of pink and white globigerinoides ruber in the northern gulf of mexico implications for paleoceanographic reconstruction abstract we evaluate the relationship between foraminiferal test size and shell geochemistry 13c 18o and mg ca for two of the most commonly used planktonic foraminifers for paleoceanographic reconstruction in the subtropical atlantic ocean the pink and white varieties of globigerinoides ruber geochemical analyses were performed on foraminifera from modern core top samples of high accumulation rate basins in the northern gulf of mexico mg ca analysis indicates a positive relationship with test size increasing by 1 1 mmol mol 2 5 c from the smallest 150 212 m to largest 500 m size fractions of g ruber pink but with no significant relationship in g ruber white in comparison oxygen isotope data indicate a negative relationship with test size decreasing by 0 6 across the size range of both pink and white g ruber the observed increase in mg ca and decrease in 18o are consistent with an increase in calcification temperature of 0 7 c per 100 m increase in test size suggesting differences in the seasonal and or depth distribution among size fractions overall these results stress the necessity for using a consistent size fraction in downcore paleoceanographic studies in addition we compare downcore records of 18o and mg ca from pink and white g ruber in a decadal resolution 1000 year sedimentary record from the pigmy basin based on this comparison we conclude that pink g ruber is calcifying in warmer waters than co occurring white g ruber suggesting differences in the relative seasonal distribution and depth habitat of the two varieties

upper water mass variability in the anegada jungfern passage ne caribbean during the last 11 100 cal yr using qualitative and quantitative analyses of planktonic foraminifera assemblages 18o measurements mg ca temperature relationship globigerinoides ruber pink sensu stricto data and sea surface temperatures ssts derived from artificial neural network ann transfer functions a reconstruction was made of upper water mass variability in the anegada jungfern passage ajp northeastern caribbean sea over the last c 11 100 years our record is based on the study of two marine sediment cores and reveals three main circulation stages during the holocene in the early holocene 11 100 6300 cal yr bp ann based sst estimations indicate moderately cooler than present winter condition in the ne caribbean with ssts of 25 5 c these conditions presumably reflect advection of well mixed upper water masses from the guyana upwelling area associated with a strong atlantic meridional overturning circulation amoc and enhanced trade wind activity linked to a more northerly location of the inter tropical convergence zone itcz between 6300 and 3700 cal yr bp a relative warming of winter ssts 26 5 c was probably related to a weaker circulation and upper water mass mixing because of less intense trade wind activity as the itcz moved southwards from 3700 cal yr bp to the present the region was characterised by small seasonal sst variations and generally stable winter and summer ssts the data suggest a minor shift in the sub surface inflow pattern during the last 2000 years possibly related to changes in northern hemisphere large scale atmospheric circulation also observed at higher latitude the ann based temperature pattern is supported by fluctuations in the mg ca derived temperature record although temperature maxima derived from the mg ca ratio appear anomalously high on a holocene timescale we conclude that the northeastern caribbean sst and circulation regime have been mainly dependent on the position of the itcz which in turn is controlled by changes in hemispheric solar insolation

a possible local anomaly in the 670 km discontinuity beneath kerguelen abstract the mapping of the 670 km discontinuity in regions of ascending or descending flows is of major interest for a better understanding of the nature of this discontinuity in this paper an attempt is made to investigate the properties of deep mantle discontinuities beneath the kerguelen hot spot anomalous p to s converted waves are observed for some earthquakes recorded at the kerguelen long period geoscope station the characteristics of these phases are specified owing to a three dimensional polarization analysis of the signals a tilted discontinuity is able to explain the data this discontinuity dips toward the northeast with at 20 the depth at which the conversion takes place is 880 km assuming standard velocities in the upper mantle beneath kerguelen or 810 km if a hot upper mantle with a poisson s ratio of 0 30 0 31 is present however the constraints given by the data are not strong enough to specify unambiguously this depth a conversion at 600 km or 550 km assuming a hot upper mantle may alternatively be proposed a strong velocity increase at the discontinuity is in each case necessary to explain the amplitude of the converted waves geophysical arguments show that this tilted discontinuity must be a local feature possible other mechanisms such as wave focusing due to undulations of the discontinuity may also be proposed

short period s p conversion in the mantle at a depth near 700 km summary data from 16 deep earthquakes originating in the tonga subduction zone and recorded at the warramunga seismic array wra in central australia show the presence of a distinct later arrival in the coda of p this phase which is not predicted by smooth velocity depth models of the earth has been called x in the paper slownesses and arrival azimuths of x are similar to those of the p wave it is unlikely that x was radiated as the result of multiple focal activity because a corresponding phase was not observed neither in the coda of scp nor on seismograms of seismic stations located at close epicentral distances relative to p the variation in arrival times with focal depth of the earthquakes indicates that x is produced by s p conversion below the source at a depth near 700 km most of the observed x phases have approximately the same signal duration as the p waves thus suggesting a transition zone near 700 km which is only a few kilometres thick synthetic seismograms calculated for a model with a first order seismic discontinuity at a depth of 700 km show reasonable agreement with the observations as demonstrated by the synthetic seismogram modelling the amplitude of x depends on the radiation pattern of the earthquake source variations in the radiation pattern offer a plausible explanation that first x is only intermittently detected at wra and secondly that x has most frequently been observed from the southern part of the tonga subduction zone

millennial scale climate variability during the last 12 5 ka recorded in a caribbean speleothem abstract we present a speleothem stable oxygen isotope record for the last 12 5 ka based on two stalagmites from western cuba the 18o signal is interpreted to represent past precipitation variability both stalagmites show a pronounced transition from higher 18o values indicating drier conditions to more negative 18o values suggesting wetter conditions between 10 and 6 ka this transition is also visible in a planktonic 18o record off haiti on orbital timescales the 18o value of caribbean precipitation thus strongly resembles the oxygen isotope composition of caribbean surface water on millenial timescales the speleothem 18o record shows a high correlation to a north atlantic sea surface temperature sst record off west africa as well as a similarity with the bond events periods of lower north atlantic sst correspond to less precipitation in the caribbean and vice versa the potential teleconnection to the caribbean may reflect the position of the intertropical convergence zone because a further southward position of the itcz leads to reduced precipitation in the northern caribbean

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

impact of abrupt deglacial climate change on tropical atlantic subsurface temperatures both instrumental data analyses and coupled ocean atmosphere models indicate that atlantic meridional overturning circulation amoc variability is tightly linked to abrupt tropical north atlantic tna climate change through both atmospheric and oceanic processes although a slowdown of amoc results in an atmospheric induced surface cooling in the entire tna the subsurface experiences an even larger warming because of rapid reorganizations of ocean circulation patterns at intermediate water depths here we reconstruct high resolution temperature records using oxygen isotope values and mg ca ratios in both surface and subthermocline dwelling planktonic foraminifera from a sediment core located in the tna over the last 22 ky our results show significant changes in the vertical thermal gradient of the upper water column with the warmest subsurface temperatures of the last deglacial transition corresponding to the onset of the younger dryas furthermore we present new analyses of a climate model simulation forced with freshwater discharge into the north atlantic under last glacial maximum forcings and boundary conditions that reveal a maximum subsurface warming in the vicinity of the core site and a vertical thermal gradient change at the onset of amoc weakening consistent with the reconstructed record together our proxy reconstructions and modeling results provide convincing evidence for a subsurface oceanic teleconnection linking high latitude north atlantic climate to the tropical atlantic during periods of reduced amoc across the last deglacial transition

high resolution sea surface reconstructions off cape hatteras over the last 10 ka 1 this study presents high resolution foraminiferal based sea surface temperature sea surface salinity and upper water column stratification reconstructions off cape hatteras a region sensitive to atmospheric and thermohaline circulation changes associated with the gulf stream we focus on the last 10 000 years 10 ka to study the surface hydrology changes under our current climate conditions and discuss the centennial to millennial time scale variability we observed opposite evolutions between the conditions off cape hatteras and those south of iceland known today for the north atlantic oscillation pattern we interpret the temperature and salinity changes in both regions as co variation of activities of the subtropical and subpolar gyres around 8 3 ka and 5 2 3 5 ka positive salinity anomalies are reconstructed off cape hatteras we demonstrate for the 5 2 3 5 ka period that the salinity increase was caused by the cessation of the low salinity surface flow coming from the north a northward displacement of the gulf stream blocking the southbound low salinity flow concomitant to a reduced meridional overturning circulation is the most likely scenario finally wavelet transform analysis revealed a 1000 year period pacing the 18o signal over the early holocene this 1000 year frequency band is significantly coherent with the 1000 year frequency band of total solar irradiance tsi between 9 5 ka and 7 ka and both signals are in phase over the rest of the studied period

variability of the north atlantic oscillation over the past 5 200 years the north atlantic oscillation influences climate in the arctic region and northern europe reconstructions of circulation patterns associated with the north atlantic oscillation from a 5 200 year long lake sediment record suggest that the atmospheric circulation responded to significant transitions in northern hemisphere climate

hotspots in the southern oceans an absolute frame of reference for motion of the gondwana continents abstract the geometry and geochronology of aseismic ridges and oceanic islands in the southern oceans provide a good test of the proposition that hotspots remain fixed over long periods of time that is motion of an order of magnitude less than the relative motion between plate pairs in most cases it is concluded that inter hotspot movement cannot be discerned for the period 100 m y to present and that widely distributed hotspots in the atlantic and indian oceans provide a frame of reference for plate motions following the disintegration of gondwanaland which is independent of paleomagnetism this frame of reference is absolute in that it gives the motion of the lithosphere with respect to the mantle hotspots the absolute motion model indicates that africa and antarctica are now moving only very slowly that there has been significant relative movement between east and west antarctica since the cretaceous and prescribes the relative motion between the somali and african plates

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

phosphorus in sediments of the amazon river and estuary implications for the global flux of phosphorus to the sea abstract the distribution of various forms of p in suspended and depositional bank sediments of the amazon river and bottom sediments of the mixing and freshwater portions of the amazon estuary and shelf have been determined using a modified sequential extraction method forms of p distinguished are p associated with ferric oxides hydroxides fe p organic p org p p extracted with acetate buffer at ph 4 acet p and detrital apatite detr p results indicate that there is a distinct drop in fe p org p and total p after deposition of suspended sediment on the banks of the river similar results are found for sediment deposited on the freshwater portion river channel bottom of the continental shelf sediment deposited on estuarine portions of the shelf also shows a significant drop in total p due mostly to a drop in org p no appreciable change in acet p was found between river suspended sediments and those of either the river banks or of the estuarine shelf an inverse correlation is found for all sediments between concentrations of fe p and detr p because of the association of detrital apatite with the coarser fractions of the sediments and fe p with the finer fractions these results suggest that considerable amounts of p are added to the oceans by the bacterial decomposition of river transported organic matter and by the desorption of p from iron oxides hydroxides some desorption from al silicates may also occur the organic p is released to interstitial solution during early diagenesis and this p may be adsorbed by fe oxides in the sediment during frequent resuspension events the fe oxides are carried to the overlying water where the p is desorbed and thereby released to solution based on our amazon results the total global p flux to the oceans by rivers may be more than three times that carried only in solution by the rivers further work is needed on other river systems to check these preliminary results

measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy 3 inversion lateral heterogeneity in the earth s upper mantle is investigated by inverting dispersion curves of long period surface waves 100 330 s models for seven different tectonic regions are derived by inversion of regionalized great circle phase velocity measurements from our previous studies we also obtain a representation of upper mantle heterogeneities with no a priori regionalization from the inversion of the degree 6 spherical harmonic expansion of phase and group velocities the data are from the observation of about 200 paths for love waves and 250 paths for rayleigh waves for both the regionalized and the spherical harmonic inversions corrections are applied to take into account lateral variations in crustal thickness and other shallow parameters these corrections are found to be important especially at low spherical harmonic order the trench region and fast velocities down to 250 km under shields below 200 km under the oceans both s velocity and s anisotropy support a model of small scale convection in which cold blobs detach from the bottom of the lithosphere when its age is large enough the spherical harmonic models clearly demonstrate a posteriori the relation between surface tectonics and s velocity heterogeneities in the first 250 km all shields are fast most ridges are slow below 300 km a belt of fast mantle follows the pacific subduction zones however at greater depths large scale heterogeneities that seem to bear no relationship to surface tectonics are observed the most prominent feature at 450 km is a fast velocity region under the south atlantic ocean smaller scale heterogeneities that are not related to surface tectonics are also mapped at shallower depths an anomalously slow region centered in the south central pacific is possibly linked to intense hot spot activity a very fast region southeast of south america may be related to subduction of old pacific plate between 200 and 400 km a belt of sv sh anisotropy follows part of the ridge and subduction systems indicating vertical mantle flow in these regions the spherical harmonic results open new horizons for the understanding of convection in the mantle perspectives for the improvement of the models presented are discussed

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

speciation bioavailability and preservation of phosphorus in surface sediments of the changjiang estuary and adjacent east china sea inner shelf abstract the speciation potential bioavailability and preservation of phosphorus p in surface sediments of the changjiang yangtze river estuary and adjacent east china sea ecs inner shelf were investigated through the analyses of p fractions and sediment bulk properties a sequential extraction method sedex was used to separate and quantify the following six sedimentary p reservoirs exchangeable p ex p authigenic p au p detrital p de p organic p or p refractory p re p and fe bound p fe p total p tp in surface sediments ranged from 15 0 to 21 4 mol g 1 and was highest near the changjiang river mouth the average contribution of each form of p to tp was 55 6 de p 17 8 re p 16 1 or p 5 5 au p 2 5 ex p and 2 5 fe p respectively de p showed relatively higher concentrations in the river mouth and the ecs shelf region off the changjiang estuary high concentrations of or p were found mainly in mud areas showing a similar distribution pattern with silt sediment surface area ssa and total organic carbon toc re p was mainly distributed near the estuarine area and the zhe min coast bioavailable p bap accounted for 9 5 32 0 of tp with a mean of 21 2 and showed a similar distribution pattern to that of or p de p ssa and toc ssa loadings both decreased with increasing of ssa while or p ssa loadings varied little with ssa indicating that or p may have reached an adsorption desorption equilibrium on mineral surfaces toc to total organic p top sum of re p and or p ratios less than the redfield ratio 84 in average may have indicated efficient remineralization of organic matter in mobile muds of the changjiang estuary and adjacent ecs inner shelf furthermore the relatively high toc or p ratios 72 422 with a mean of 188 likely suggest a higher degree of preferential regeneration of labile or p over toc in sediments

persistent summer expansion of the atlantic warm pool during glacial abrupt cold events palaeoclimate records and numerical model simulations indicate that changes in tropical and subtropical sea surface temperatures and in the annual average position of the intertropical convergence zone are linked to high latitude climate changes on millennial to glacial interglacial timescales it has recently been suggested that cooling in the high latitudes associated with abrupt climate change events is evident primarily during the northern hemisphere winter implying increased seasonality at these times8 however it is unclear whether such a seasonal bias also exists for the low latitudes here we analyse the mg ca ratios of surface dwelling foraminifera to reconstruct sea surface temperatures in the northeastern gulf of mexico for the past 300 000 years we suggest that sea surface temperatures are controlled by the migration of the northern boundary of the atlantic warm pool and hence the position of the intertropical convergence zone during boreal summer and are relatively insensitive to winter conditions our results suggest that summer atlantic warm pool expansion is primarily affected by glacial interglacial variability and low latitude summer insolation because a clear signature of rapid climate change events such as the younger dryas cold event is lacking in our record we conclude that high latitude events seem to influence only the winter caribbean climate conditions consistent with the hypothesis of extreme northern hemisphere seasonality during abrupt cooling events

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

s to p scattering at the 650 km discontinuity summary a search of seismograms recorded at the warramunga seismic array wra from events occurring below the izu bonin islands shows an arrival on some but not all of the records with an onset at 25 30 s after p which is not predicted by the standard travel time tables the slowness and azimuth of the phase show that it is generated almost in line with p and the variation of arrival time with the hypocentral depth of the earthquake indicates that its origin lies on the receiver side of the source it appears in fact to be an s to p conversion at a depth of 650 700 km which is seen only when the receiver is close to a node of the p radiation pattern and an antinode for s so that its amplitude compared with that of p is at a maximum finally the duration of the phase indicates that it is not simply a refracted wave but that it has a coda of scattered arrivals from lateral heterogeneity in the neighbourhood of 650 km below the izu bonin islands

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

combined records from a stalagmite from barbados and from lake sediments in haiti reveal variable seasonality in the caribbean between 6 7 and 3 ka bp abstract the growth of a well dated stalagmite from barbados records high infiltration rates into the karst aquifer and hence increased rainfall intensity between 6 7 and 3 ka bp in agreement with records from lake miragoane haiti hodell et al 1991 reconstruction of the caribbean climate change over the past 10 500 years nature 352 790 793 mainly reflecting the insolation maximum of the northern hemisphere both the lake record and the stable isotope record of the stalagmite reveal additional centennial variability of recharge high oxygen isotope values in stalagmite calcite corresponding to reduced recharge are synchronous with periods of lower stable isotope values recorded in lake miragoane ostracods previously attributed to enhanced precipitation accordingly periods of increased recharge in barbados correspond to 18o enriched isotope values of ostracods which were attributed to higher evaporation precipitation ratios in the lakes we ascribe this apparent discrepancy to changes in seasonality i e winter periods of reduced temperature and relative humidity following summer months of increased precipitation at present such climate conditions occur during periods of enhanced northern atlantic oscillation nao if enhanced seasonality is a consequence of a nao situation the apparent discrepancy of high isotope values in lakes previously attributed to droughts can be reconciled with lower winter temperatures in the lakes further the correlation of solar intensity derived from 14c and 10be with the isotopic signals recorded in the lacustrine sediments suggests a solar forcing of the nao during the mid holocene

orbital insolation ice volume and greenhouse gases abstract the specmap models of orbital scale climate change imbrie et al paleoceanography 7 1992 701 paleoceanography 8 1993 699 are the most comprehensive to date all major climatic observations were analyzed within the framework of the three orbital signals subsequently tuning of signals in vostok ice to insolation forcing has fixed the timing of greenhouse gas changes closely enough to permit an assessment of their orbital scale climatic role in addition evidence from several sources has suggested changes in the specmap 18 o time scale this new information indicates that the timing of co 2 changes at the periods of precession and obliquity does not fit the 1992 specmap model of a train of responses initiated in the north propagated to the south and later returning north to force the ice sheets in addition analysis of the effects of rectification on 100 000 year climatic signals reveals that all have a phase on or near that of eccentricity this close clustering of phases rules out the long time constants for 100 000 year ice sheets required by the 1993 specmap model a new hypotheses presented here revives elements of an earlier climap view hays et al science 194 1976a 1121 but adds a new assessment of the role of greenhouse gases as proposed by milankovitch summer mid july insolation forces northern hemisphere ice sheets at the obliquity and precession periods with an ice time constant derived here of 10 000 years changes in ice volume at 41 000 years drive ice proximal signals sst nadw dust that produce a strong positive co 2 feedback and further amplify ice volume changes at the precession period july insolation forces ice sheets but it also drives fast and early responses in ch 4 through changes in tropical monsoons and boreal wetlands and variations in co 2 through southern hemisphere processes these ch 4 and co 2 responses enhance insolation forcing of ice volume climatic responses at 100 000 years result from eccentricity pacing of forced processes embedded in obliquity and precession cycles increased modulation of precession by eccentricity every 100 000 years produces 23 000 year co 2 and ch 4 maxima that enhance ablation caused by summer insolation and drive climate deeper into an interglacial state when eccentricity modulation decreases at the 100 000 year cycle ice sheets grow larger in response to obliquity forcing and activate a 41 000 year co 2 feedback that drives climate deeper into a glacial state alternation of these forced processes because of eccentricity pacing produces the 100 000 year cycle the 100 000 year cycle began 0 9 myr ago because gradual global cooling allowed ice sheets to survive during weak precession insolation maxima and grow large enough during 41 000 year ice volume maxima to generate strong positive co 2 feedback the natural orbital scale timing of these processes indicates that ice sheets should have appeared 6000 3500 years ago and that co 2 and ch 4 concentrations should have fallen steadily from 11 000 years ago until now but new ice did not appear and co 2 and ch 4 began anomalous increases at 8000 and 5000 years ago respectively human generation of co 2 and ch 4 is implicated in these anomalous trends and in the failure of ice sheets to appear in canada

a 10 300 14c yr record of climate and vegetation change from haiti abstract pleistocene and holocene vegetation dynamics in the american tropics are inferred largely from pollen in continental lake sediments maritime influences may have moderated climate and vegetation changes on caribbean islands stable isotope 18 o study of a 7 6 m core from lake miragoane haiti provided a high resolution record of changing evaporation precipitation e p since 10 300 14 c yr b p the miragoane pollen record documents climate influences and human impacts on vegetation in hispaniola the 18 o and pollen data near the base of the core indicate cool dry conditions before 10 000 14 c yr b p lake miragoane filled with water in the early holocene as e p declined and the freshwater aquifer rose despite increasing early holocene moisture shrubby xeric vegetation persisted forest expanded 7000 14 c yr b p in response to greater effective moisture and warming the middle holocene 7000 3200 14 c yr b p was characterized by high lake levels and greatest relative abundance of pollen from moist forest taxa climatic drying that began 3200 14 c yr b p may have driven some mesophilic animal species to extinction the pollen record of the last millennium reflects pre columbian taino and european deforestation long term holocene vegetation trends in southern haiti are comparable to trends from continental lowland circum caribbean sites suggesting a common response to regional climate change

stable isotopes of planktonic foraminifera from tropical atlantic caribbean core tops implications for reconstructing upper ocean stratification abstract 18o values of nine tropical subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core top samples along an east west transect across the tropical atlantic caribbean were used to test the applicability of interspecific 18o gradients for reconstructions of tropical upper ocean stratification in general the 18o difference 18o between intermediate and shallow dwelling species decreases and 18o between deep and intermediate dwellers increases with increasing thermocline depth towards the west the statistical significance of regional differences in 18o highlights 18o between the intermediate dwellers in particular globorotalia scitula and globorotalia tumida and the shallow dweller globigerinoides ruber pink as well as 18o between the deep dwellers globorotalia crassaformis or globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical atlantic thermocline depth based on the observed regional variations in interspecific 18o we propose a multispecies stratification index stratrop 18ointermediate 18oshallow 18odeep 18oshallow for the tropical ocean statistically significant differences in stratrop values between the e atlantic and the caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record

a centennial scale variability of tropical north atlantic surface hydrography during the late holocene abstract sea surface temperature sst and sea surface salinity sss fluctuations in the northeastern caribbean have been reconstructed through the last 2000 yr using an artificial neural network and 18 o analyses of planktonic foraminifera a warmer period prevailed in the ne caribbean from ad 700 950 which may reflect the occurrence of stronger and or more frequent el nino events a 2 c cooling of winter ssts from ad 1400 to 1550 coincides with the occurrence of reduced solar output the sporer event episodes of lower ssss with marked minima at the onsets of the dark ages in europe ad 500 600 and little ice age ad 1400 are cyclically recurrent at intervals of 200 400 yr and coincide with drier periods in mexico this may indicate that the tropical atlantic evaporation precipitation budget and ssss are affected by a centennial scale modulation involving the freshwater export import from into the atlantic ocean coeval changes recorded in the deep north atlantic circulation indicate that low latitude sss anomalies may be advected polewards by the north atlantic current system thus affecting deep ocean convection and strength of the thermohaline circulation

holocene water mass changes in the labrador current the labrador current is part of the anticlockwise subpolar gyre and plays a major role in the formation of north atlantic deep water it is influenced by the west greenland and baffin currents supp

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

first analyses of broadband records on the geoscope network potential for detailed studies of mantle discontinuities examples of the first analyses of broadband geoscope data at station ssb france show that these data will make possible a detailed study of the deep mantle discontinuities analysis of the p coda of earthquakes using specific methods suggests the existence of p to s conversions at 670 km depth beneath ssb for earthquakes with northern to eastern azimuths a comparison with results from the nars and grafenberg arrays indicate that the 670 km discontinuity beneath western europe is highly heterogeneous or horizontally discontinuous a frequency analysis reveals that the relevant discontinuity is not very sharp 20 to 70 km thick besides a sharp 5 km thick discontinuity at 900 km depth is observed beneath the mid atlantic ridge from p reflections giving pp precursors for the strong march 1985 chilean earthquake but no 670 km discontinuity seems to be present beneath the ridge

a seismic refraction survey in the kerguelen isles southern indian ocean summary two 65 km long on land refraction lines with shot detonated at sea were implemented in the courbet peninsula eastern region of the kerguelen archipelago terres australes et antarctiques francaises southern indian ocean the first profile pi oriented ne sw runs from cap ratmanoff toward mont ross and the second one p2 from pointe suzanne se of the courbet peninsula through the val studer data from both profiles were supplemented by using the bouguer gravity anomaly map not previously studied the data combined standard travel time interpretation wide angle reflected wave study synthetic seismograms and s wave analysis the velocity depth behaviour shows that the mean crustal thickness ranges from 14 to kerguelen resembles those observed beneath aseismic ridges i e the crozet rise and the madagascar ridge average velocity of 5 5 km s on both lines is in the range of those determined for oceanic layer 2 which is there 8 9 km thick average velocity of 6 6 km s is in the range of velocities within oceanic layer 3 the transition to mantle velocity 7 95 km s is best modelled by a positive velocity gradient within the crust this feature is similar to that observed on structures generated near spreading centres these new data com bined with geological and geochemical investigations in the archipelago support an oceanic origin for the kerguelen heard ridge and also broken ridge both structures were joined 40myr ago as shown by the magnetic anomaly pattern refraction studies invalidate the assumption that isostatic compensation is achieved by a 23 km deep crustal root but substantiate the i 17km only varying with the locality the structure of the crust beneath

upper mantle converted waves beneath the nars array several registrations of teleseismic events on the nars array show a phase which can be identified as a p to s conversion at the 670 km discontinuity beneath western europe variations in the amplitude and arrival time of the so called ps phase are observed for different azimuths a single station multiple event stacking technique was applied to the data to determine the consistency of the phase the results are indicative of amplitude arrival time and slowness variations of the converted phase on a local scale these observations are most logically explained by a model with depth variations of the 670 km discontinuity of the order of 20 km over a distance of 200 km

ocean atmosphere climate shift during the mid to late holocene transition article history climate records of the mid to late holocene transition between 3 4 thousand years before present ka often exhibit a rapid change in response to the gradual change in orbital insolation here we investigate north atlantic central water circulation as a possible mechanism regulating the latitudinal temperature gradient ltg which in turn amplifies climate sensitivity to small changes in solar irradiance through this mechanism sharp climate events and transitions are the result of a positive feedback process that propagates and amplifies climate events in the north atlantic region we explore these linkages using an intermediate water temperature record reconstructed from mg ca measurements of benthic foraminifera hyalinea balthica f rom as ediment core off nw africa 889 md epth between 0t o 5 5 ka our results show that eastern north atlantic central waters enacw cooled by 1 0 7 ca nd densities decreased by 0 4 0 2b etween 3 3 and 2 6 ka this shift in enacw hydrography illustrates at ransition towards enhanced mid latitude atmospheric circulation after 2 7 ka in particular during cold events of the late holocene the presented records demonstrate the important role of enacw circulation in propagating the climate signatures of the ltg by reducing the meridional heat transfer from high to low latitudes during the transition from the holocene thermal maximum to the late holocene in addition the dynamic response of enacw circulation to the gradual climate forcing of ltgs provides a prime example of an amplifying climate feedback mechanism published by elsevier b v

interlaboratory comparison study of calibration standards for foraminiferal mg ca thermometry an interlaboratory study of mg ca and sr ca ratios in three commercially available carbonate reference materials bam rs3 cmsi 1767 and ecrm 752 1 was performed with the participation of 25 laboratories that determine foraminiferal mg ca ratios worldwide these reference materials containing mg ca in the range of foraminiferal calcite 0 8 mmol mol to 6 mmol mol were circulated with a dissolution protocol for analysis participants were asked to make replicate dissolutions of the powdered samples and to analyze them using the instruments and calibration standards routinely used in their laboratories statistical analysis was performed in accordance with the international standardization organization standard 5725 which is based on the analysis of variance anova technique repeatability rsdr an indicator of intralaboratory precision for mg ca determinations in solutions after centrifuging increased with decreasing mg ca ranging from 0 78 at mg ca 5 56 mmol mol to 1 15 at mg ca 0 79 mmol mol reproducibility rsdr an indicator of the interlaboratory method precision for mg ca determinations in centrifuged solutions was noticeably worse than repeatability ranging from 4 5 at mg ca 5 56 mmol mol to 8 7 at mg ca 0 79 mmol mol results of this study show that interlaboratory variability is dominated by inconsistencies among instrument calibrations and highlight the need to improve interlaboratory compatibility additionally the study confirmed the suitability of these solid standards as reference materials for foraminiferal mg ca and sr ca determinations provided that appropriate procedures are adopted to minimize and to monitor possible contamination from silicate mineral phases

planktonic foraminifera stable isotopes and water column structure disentangling ecological signals differential carbon and oxygen stable isotope 13c and 18o fractionation between planktonic foraminifera test calcite and sea water related to ecology and life stage confound the potential for reconstructing palaeo water column temperature and carbon gradients multi species analysis and strict selection of test sizes are useful methods for identifying these fractionation processes also known as vital effects in fossil taxa however there are a limited number of species with adequate size controlled data sets needed for ground truthing the approach in the modern here we report 13c and 18o measurements made on twelve species of modern planktonic foraminifera across a range of fourteen tightly constrained size windows from a tropical indian ocean core top sample this data set includes more test size windows per species especially from the smallest identifiable test size classes and a wider range of species than previously attempted we use the size controlled 18o calcite trajectories to infer depth habitats and calculate species specific calcification temperatures the temperatures are then used to constrain species specific calcification depths along the modern vertical temperature profile in the western tropical indian ocean by overlaying the per species 13c calcite trajectories on local water column 13cdic profiles we estimate if and when i e at which test sizes the planktonic foraminifera species investigated approach ambient 13cdic values the profiling shows significant size controlled 13c deviation from seawater values in all species at some life growth stage which we attribute to i metabolic fractionation in tests 300 m of mixed layer photosymbiotic taxa for most species there is a size window where these effects appear to be at a minimum and or in balance exceptions are globigerinita glutinata a small 200 m surface living species globigerina bulloides which is highly opportunistic and deep living globorotalia tumida and globorotaloides hexagonus the latter two species being affected by various unexplained 13c vital effects use of our refined guidelines for test size selection should improve the potential for making realistic reconstructions of water column 13cdic in a modern tropical stratified setting and potentially in the distant geological past when there are no living analogues present

interdecadal changes in the enso teleconnection to the caribbean region and the north atlantic oscillation abstract the el nino southern oscillation enso phenomenon and variability in the subtropical north atlantic high sea level pressure slp are known to affect rainfall in the caribbean region an el nino event is associated with drier than average conditions during the boreal summer of year 0 and wetter than average conditions during the spring of year 1 dry conditions during the summer of year 0 of an el nino are associated with the locally divergent surface circulation engendered by the eastward shift of deep convection in the pacific ocean wet conditions during the spring of year 1 of an el nino are associated with the lagged warming of the tropical north atlantic ocean variability in the strength of the north atlantic high is governed mainly by the north atlantic oscillation nao with a positive nao phase implying a stronger than normal high and vice versa the nao is negatively correlated with caribbean rainfall indirectly via anomalous sea surface temperatures sst associated with a

florida straits density structure and transport over the last 8000 years 1 the density structure across the florida straits is reconstructed for the last 8000 years from oxygen isotope measurements on foraminifera in sediment cores the oxygen isotope measurements suggest that the density contrast across the florida current increased over this time period the magnitude of this change corresponds to an increase in the geostrophic transport referenced to 800 m water depth of 4 sverdrups sv over the last 8000 years the spatial and seasonal distribution of incoming solar radiation due to changes in the earth s orbit has caused systematic changes in the atmospheric circulation including a southward migration of the intertropical convergence zone over the last 8000 years these changes in atmospheric circulation and the associated wind driven currents of the upper ocean could readily account for a 4 sv increase in the strength of the florida current we see no evidence in our data for dramatic changes in the strength of the atlantic meridional overturning circulation over this time period

a simple evaluation of cleaning procedures on fossil benthic foraminiferal mg ca 1 recent studies suggest that benthic foraminiferal mg ca may be useful in reconstructing deep water temperature changes during the quaternary and on longer timescales rosenthal et al 1997 lear et al 2000 martin et al 2002 because changes in deep water temperature may be small sample preparation could play an important role in reconstructing accurate temperatures from shell mg ca a simple examination of changes in measured shell chemistry of benthic foraminifera from two intervals subjected to increasingly rigorous cleaning reveals that fossil benthic foraminiferal samples cleaned by oxidation yield lower mg ca values than samples only rinsed and weak acid leached reductive cleaning further lowered the shell mg ca of one of the two benthic species examined lower mg ca values following oxidation and reduction appear to reflect removal of contaminant mg associated with remnant organic matter and adsorbed phases

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

planktic foraminifers and hydrography of the eastern and northern caribbean sea the distribution of living planktic foraminifers and their relation to the hydrography of the caribbean sea was investigated in plankton net tows and surface sediment samples taken along the antilles island arc during april may 1996 the planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of orinoco river water into the southeastern caribbean sea and inflowing sargasso sea water in the north along the antilles island arc globigerinoides ruber was the dominant species in the surface waters throughout in the southeastern caribbean sea where orinoco river outflow influences the planktic community standing stocks of planktic foraminifers 100 m between 4 and 50 specimens m 3 were medium to low the southeastern faunas between tobago and guadeloupe were characterized by increased proportions of neogloboquadrina dutertrei highest standing stocks of 159 specimens m 3 in the upper 20 m of the water column were recorded in the northeastern caribbean sea and the assemblages were characterized by high proportions of globigerinita glutinata associated with cyclonic eddies in the anegada passage where sargasso sea water flows into the caribbean sea low standing stocks of 18 specimens m 3 indicate oligotrophic conditions together with the oligotrophic surface waters the subtropical underwater enters the caribbean sea through the anegada passage in water depths between 100 and 300 m these waters are characterized by higher concentrations of globorotalia truncatulinoides relative to the adjacent water masses comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species in the vicinity of islands globigerinoides ruber reaches higher relative frequencies than in the open ocean pointing towards a higher tolerance of this species towards neritic conditions than in other species

particulate element inventory of the huanghe yellow river a large high turbidity river abstract suspended sediments from the river mouth to the upper portions of the huanghe yellow river were collected and analysed to determine their chemical composition comparison with other large world rivers indicates that trace element levels are relatively low in this high turbidity river natural weathering and erosion are of primary importance in controlling particulate element concentrations although the impact from anthropogenic activities is also visible finally input of particulate elements to the china sea is assessed from the river sediment load and compositions

caribbean hydrological variability during the holocene as reconstructed from crater lakes on the island of grenada contemporary precipitation patterns in the caribbean region are spatially variable and the small number of holocene paleoclimatic records may not adequately capture patterns of variation in the past the hydrological history of grenada was inferred from paleolimnological analyses of sediment cores from two crater lakes on the island the basins were formed by volcanic activity some time during the last termination but were dry between ca 13 000 and ca 7200 cal a bp after filling the lakes were initially very shallow and sedimentation was interrupted by a hiatus ca 6300 5500 cal a bp followed by deposition of a thick tephra in both sites after 5500 cal a bp lake level shows considerable multi centennial variability superimposed upon a long term trend of generally higher lake level after 3200 cal a bp the pattern of lake level variation in grenada shows some similarity with other caribbean paleoclimatic records in terms of the timing of transitions but differs from several classic studies in the sign of inferred precipitation change the differences among records may reflect spatially variable precipitation patterns in the past in response to the position of the intertropical convergence zone and to sea surface temperature influences on the trade winds and caribbean low level jet copyright c 2011 john wiley sons ltd less

assessing the effect of dissolution on planktonic foraminiferal mg ca ratios evidence from caribbean core tops in order to assess the dissolution effect on foraminiferal mg ca ratios we analyzed mg ca of seven planktonic foraminiferal species and four of their varieties from caribbean core tops from 900 4700 m water depth depending on the foraminiferal species and variety mg ca start to decline linearly below co32 levels of 18 26 mol kg by 0 04 0 11 mmol mol per 1 mol kg co32 similar to decreases of 0 5 0 8 mmol mol per kilometer below 2500 3000 m water depth above these species specific critical levels mg ca remains stable with higher intraspecific mg ca variability than below we developed routines to correct mg ca from below these critical thresholds for dissolution effects which reduce the overall intraspecific variability by 24 64 and provide dissolution corrected mg ca appropriate to calculate holocene paleotemperatures when taking into account only dissolution unaffected mg ca from 2000 m the systematic succession of foraminiferal species according to their mg ca reflects expected calcification depths

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

glacial interglacial surface water variations in the caribbean sea during the last 300 ky based on calcareous nannofossil analysis abstract quantitative and qualitative analyses of nannofossil assemblages from odp site 999 in the caribbean sea were performed to reveal changes in upper seawater structures and implications for climatic changes during the last 300 000 years overall there is an inverse relationship in stratigraphic fluctuations between the absolute abundance aa of a lower photic taxon florisphaera profunda and 18 o this fluctuation pattern is considered to represent climatic changes in the subtropical under water suw in the caribbean cross spectral analysis demonstrates that the suw was characterized by nutrient rich water during interglacials changes in orbitally driven gyre circulation system strongly affected fluctuations in the suw in the caribbean conversely the surface water was enriched in nutrients during glacials as the result of increased terrigenous materials and shallowing of the thermocline based on changes of the n ratio abundance of reticulofenestrids relative to f profunda and results of cross spectral analysis between them and 18 o the relationship between the thermocline variation and the ice volume fluctuation suggests that changes in the subtropical gyre circulation system in the north atlantic have had stronger influences on the caribbean thermocline variations and there may be a little contribution of climatic fluctuations that originated in the southern ocean to the caribbean sea a large floral turnover in nannofossil assemblages between oxygen isotope stages 6 and 5 was observed in hole 999a which corresponds to termination ii on the basis of floral compositions photosynthetic primary productions had been more active than today before termination ii

comparison of statistical and artificial neural network techniques for estimating past sea surface temperatures from planktonic foraminifer census data we present the first detailed and rigorous comparison of six different computational techniques used to reconstruct sea surface temperatures sst from planktonic foraminifer census data these include the imbrie kipp transfer functions iktf the modern analog technique mat the modern analog technique with similarity index simmax the revised analog method ram and for the first time a set of back propagation artificial neural networks ann trained on a large faunal data set including a modification where geographical information was added among the input variables annd by training the techniques on an identical database we were able to explore the differences in sst reconstructions resulting solely from the use of different mathematical methods the comparison indicates that while the iktf technique consistently shows the worst performance ann and ram perform slightly better than mat and that the inclusion of the geographical information into the training database simmax and annd further improves the accuracy of modern sst estimates however when applied to an independent validation data set and an additional fossil data set the results did not conform to this ranking the largest differences in the reconstructed sst values occurred between groups of techniques with different approaches to sst reconstruction that is ann and annd produced sst reconstructions significantly different from those produced by ram simmax and mat the application of the various techniques to the validation data set which allowed comparison of sst reconstructions with instrumental records suggests that artificial neural networks might provide better paleo sst estimates than the other techniques

planktonic foraminifera as recorders of past surface water stratification the 18 o difference between shallow and deep living planktonic foraminifera is a proxy for the stratification of surface waters in holocene sediments from the atlantic this difference increases from about 0 in subpolar regions to 3 in the tropics the 18 o values of the shallow dwellers globigerinoides sacculifer and neogloboquadrina pachyderma mainly reflect surface water conditions the calcification depth of the deep living species globorotalia truncatulinoides right coiling is affected by the stratification of the water column in the subtropics shell formation of g truncatulinoides right coiling begins in weakly stratified surface waters in the tropics the initial shell is secreted below the mixed layer this hydrographically induced difference in calcification depth allows the use of the isotopic difference between g truncatulinoides and the shallow species as a proxy for the stratification of surface waters the 18 o between g truncatulinoides and g sacculifer from tropical gravity core geob 1523 1 was significantly lower during isotope stage 2 this suggests that the glacial temperature stratification of western equatorial atlantic surface waters was significantly reduced relative to the holocene

the dynamical and thermal structure of deep mantle plumes abstract if the interpretation of the d layer at the base of the mantle as a thermal boundary layer with a temperature increment in the order of 800 k is correct then the formation of deep mantle plumes to vent material from it appears inevitable we demonstrate quantitatively that the strong temperature dependence of viscosity guides the upward flow into long lived chimneys that are 20 km in diameter near the base of the mantle and decrease in width with progressive upward softening and partial melting of plume material the speed of flow up the axis of the plume is correspondingly fast 1 6 m y 1 at the base and 4 8 m y 1 at 670 km depth thermal diffusive spreading of a heated plume is compensated by a slow horizontal convergence of mantle material toward the chimney in response to the lower pressure there this convergence which contributes only a small increment to the flux of material up the plume also serves to throttle the flow in the chimney the global plume mass flux necessary to transport 1 6 10 12 w of core heat upward through the mantle is 1 8 10 6 kg s 1 at its base plume material is probably still significantly below its solidus or eutectic temperature but substantial partial melting is very likely as it rises we speculate that a small fraction of this fluid component eventually emerges at the surface in hot spots with the fate of the remainder being unknown the behaviour and properties of d and of plumes are closely coupled not only are plumes a necessary consequence of a thermal boundary layer but their existence is impossible without that layer

sr ca ratios and oxygen isotopes from sclerosponges temperature history of the caribbean mixed layer and thermocline during the little ice age we investigate aragonitic skeletons of the caribbean sclerosponge ceratoporella nicholsoni from jamaica 20 m below sea level mbsl and pedro bank 125 mbsl we use d18o and sr ca ratios as temperature proxies to reconstruct the caribbean mixed layer and thermocline temperature history since 1400 a d with a decadal time resolution our age models are based on u th dating and locating of the radiocarbon bomb spike the modern temperature difference between the two sites is used to tentatively calibrate the c nicholsoni sr ca thermometer the resulting calibration points to a temperature sensitivity of sr ca in c nicholsoni aragonite of about 0 1 mmol mol k our sr ca records reveal a pronounced warming from the early 19th to the late 20th century both at 20 and 125 mbsl two temperature minima in the shallow water record during the late 17th and early 19th century correspond to the maunder and dalton sunspot minima respectively another major cooling occurred in the late 16th century and is not correlatable with a sunspot minimum the temperature contrast between the two sites decreased from the 14th century to a minimum in the late 17th century and subsequently increased to modern values in the early 19th century this is interpreted as a long term deepening and subsequent shoaling of the caribbean thermocline the major trends of the sr ca records are reproduced in both specimens but hardly reflected in the d18o records

reconstruction of sea surface temperatures from assemblages of planktonic foraminifera multi technique approach based on geographically constrained calibration data sets and its application to glacial atlantic and pacific oceans abstract we present a conceptual framework for a new approach to environmental calibration of planktonic foraminifer census counts this approach is based on simultaneous application of a variety of transfer function techniques which are trained on geographically constrained calibration data sets it serves to minimise bias associated with the presence of cryptic species of planktonic foraminifera and provides an objective tool for assessing reliability of environmental estimates in fossil samples allowing identification of adverse effects of no analog faunas and technique specific bias we have compiled new calibration data sets for the north n 862 and south n 321 atlantic and the pacific ocean n 1111 we show evidence that these data sets offer adequate coverage of the sea surface temperature sst and faunal variation range and that they are not affected by the presence of pre holocene samples and or calcite dissolution we have applied four transfer function techniques including artificial neural networks revised analog method and simmax with and without distance weighting on faunal counts in a last glacial maximum lgm data set for the atlantic ocean 748 samples in 167 cores based on the glamap 2000 compilation and a new data set for the pacific ocean 265 samples in 82 cores and show that three of these techniques provide adequate degree of independence for the advantage of a multi technique approach to be realised the application of our new approach to the glacial pacific lends support to the contraction and perhaps even a cooling of the western pacific warm pool and a substantial 3 c cooling of the eastern equatorial pacific and the eastern boundary currents our results do not provide conclusive evidence for lgm warming anywhere in the pacific the atlantic reconstruction shows a number of robust patterns including substantial cooling of eastern boundary currents with considerable advection of subpolar waters into the benguela current a cooling of the equatorial atlantic by 5 c and steep sst gradients in the mid latitude north atlantic the transfer function techniques generally agree that subtropical gyre areas in both hemispheres did not change significantly since the lgm although the ann technique produced glacial sst in the southern gyre 1 2 c warmer than today we have revisited the issue of sea ice occurrence in the nordic seas and using the distribution of subpolar species of planktonic foraminifera in glacial samples we conclude that the norwegian sea must have been ice free during the summer

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

water masses and circulation in the surface layers of the caribbean at 66 w a meridional hydrographic section was made in august september 1997 at 66 w from the coast of venezuela to woods hole aboard the r v knorr in this report we concentrate on near surface measurements in the caribbean the data show two distinct water masses with different origins from approximately 14 n to puerto rico caribbean surface water and subtropical under water with their source in the north atlantic are found as previously observed from venezuela to approximately 13 n a less saline water mass with its source in the tropics and south atlantic is found within the southern portion of the section two different velocity patterns are observed namely an eastward flow with a subsurface maximum near the coast of venezuela and a surface intensified westward jet with velocities of 130 cm s 1 in midbasin

reflection properties of phase transition and compositional change models of the 670 km discontinuity seismic observations of the amplitude ratio amplitude p 670p amplitude p p suggest a reflection coefficient r 7 13 for reflections from the underside of the 670 km discontinuity this can be compared with calculated reflection coefficients to constrain the nature of the mantle transition region velocity and density profiles through the transition region were calculated for olivine pyroxene garnet and olivine garnet model mineral assemblages for models with identical upper and lower mantle compositions the computed reflection coefficients from the phase transitions pertinent to the 670 km discontinuity are less than 0 5 these phase transitions produce their maximum r if they are effectively discontinuous which gives r 2 3 except for the garnet to perovskite transformation which gives r 8 in general given realistic impedance contrasts across a phase transition the change in material properties must occur over a region less than 3 km thick for r to be of the order of 5 a discontinuous change in chemical composition at 670 km depth coupled with a change in phase can also produce a reflection coefficient of the observed magnitude r 2 3 for a first order change in phase at 670 km with different iron concentrations on each side of the discontinuity and r 4 6 for cases with a discontinuous increase in silica content based on our analysis the thermal and chemical boundary layers which would occur across such a chemical discontinuity would probably have negligible effects on the reflection coefficient thus although limited by considerable uncertainties the mineralogical and seismic data suggest a two layered model of the mantle with a discontinuous change in both phase and composition at 670 km

broadband observations of ps conversions from the upper mantle in eurasia summary the delay and sum method by vinnik 1977 to detect weak ps conversions in the p coda is applied to german czechoslovakian and chinese broadband data clear phases a factor 4 5 above the noise level are observed in the 3 11 s period band from the 670 and 400 km discontinuities after summing several hundred traces the decisive step to obtain such a good signal to noise ratio was the summation of records from stations in different regions the summation of a large number many hundreds of traces of a single station does not result in similar improvements because of coherent signal generated noise due to scattering below the station there are weak indications of a 520 km discontinuity in our data the delay times relative to p of the converted phases are stable within 1 s between central europe and china

exotic pollen as an indicator of variable atmospheric circulation over the labrador sea region during the mid to late holocene variability in the abundance of exotic non native pollen in sediment cores has long been considered as a potential proxy for changing atmospheric circulation but the difficulty of gaining sufficient total exotic pollen and the incomplete under standing of atmospheric pollen transport patterns has hindered its application in light of recent advances in the study of pollen transport we present an exotic pollen record from two fjord sediment cores taken from the west placentia bay newfoundland and east narsaq sund greenland labrador sea as a basis for studying variations in regional atmospheric circulation the two cores cover the last ca 5500 years and indicate a shift in dominant spring summer air masses at ca 2000 southern greenland and 3000 cal a bp newfoundland transporting reduced concentrations of pollen from southerly and south westerly vegetation zones this may suggest a shift away from more dominantly zonal atmospheric circulation a feature of positive north atlantic oscillation years to more frequent meridional circulation these results support sea ice sea surface temperature proxy reconstructions from newfoundland investigated as part of the same project which also suggest increased winter atmospheric circulation during the early part of the time period studied in this region more positive north atlantic oscillation years and therefore more zonal atmospheric circulation are associated with increased atmospheric circulation in both the winter and the summer seasons copyright 2011 john wiley sons ltd

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas

mg ca ratios of single planktonic foraminifer shells and the potential to reconstruct the thermal seasonality of the water column mg ca ratios of surface and subsurface dwelling foraminifera provide valuable information about the past temperature of the water column planktonic foraminifera calcify over a period of weeks to months therefore the range of mg ca temperatures obtained from single specimens potentially records seasonal temperature changes we present solution derived mg ca ratios for single specimens of the planktonic foraminifera species globigerinoides ruber pink globigerinoides ruber white and globorotalia inflata from a sediment trap off northwest africa 20 45 6 n 18 41 9 w cleaning of single specimens was achieved using a flow through system in order to prevent sample loss mg ca ratios of surface dwelling g ruber pink show strong seasonality linked to sea surface temperature mg ca ratios of g ruber white do not show such seasonality subsurface dwelling g inflata flux is largest during the main upwelling season but mg ca ratios reflect annual temperatures at intermediate water depths the sediment trap time series suggests that changes in the range of mg ca ratios exhibited by single specimens of g ruber pink and g inflata from the sedimentary record should provide information on the past temperature range under which these species calcified statistical analysis suggests detectable changes in the mg ca range are 0 80 mmol mol g ruber pink and 0 34 mmol mol g inflata for g ruber pink such changes would indicate changes in the seasonal sea surface temperature range 4 c or a shift in the main calcification and reproductive period for g inflata such changes would indicate 1 7 c changes in the thermocline temperature or a change in the depth habitat

seismic reflections from the upper mantle discontinuities beneath the mid atlantic ridge observed by a seismic array in hokkaido region japan following a recent big deep event mb 6 8 in the fiji islands region a seismic array in hokkaido region japan recorded clear impulsive precursors to the p p phases p is another symbol for pkp and p p is the surface reflection of p in the epicentral distance range of 70 72 4 reflection points of the phases are located 1 5 3 5 west of the mid atlantic ridge 13 s 15 w the precursors were also recorded at two wwssn stations in japan travel times and slowness measured by the array are best explained as the precursors being underside reflections from a depth of 660 km the amplitude ratios of p 660p p p are about 0 1 a value similar to previous observations the observation suggests that there exists a sharp discontinuity at a depth of 660 km beneath the area close to the mid atlantic ridge

drainage basin weathering and major element transport of two large chinese rivers huanghe and changjiang long term records show high concentrations of dissolved major elements in the changjiang yangtze river and the huanghe yellow river the huanghe drainage basin is characterized by intense weathering and erosion of carbonates and evaporites while weathering and erosion of carbonates and silicates over the drainage basin is the main source of major elements in the changjiang the rock soil composition and tectonics of the drainage basin are more important than atmospheric precipitation in affecting major element composition of these two rivers compared with other large rivers of the world the high suspended sediment and major element loads of the changjiang and huanghe reveal intense physical and chemical erosion over the chinese continent

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

phosphorus speciation and availability in intertidal sediments of the yangtze estuary china abstract in order to better understand p cycling and bioavailability in the intertidal system of the yangtze estuary both surface 0 5 cm and core 30 cm long sediments were collected and sequentially extracted to analyze the solid phase reservoirs of sedimentary p loosely sorbed p fe bound p authigenic p detrital p and organic p the total sedimentary p in surface and core sediments ranged from 14 58 36 81 mol g 1 and 17 11 24 55 mol g 1 respectively and was dominated by inorganic p the average percentage of each fraction of p in surface sediments followed the sequence detrital p 54 9 fe bound p 23 7 organic p 14 3 authigenic p 6 3 loosely sorbed p 0 8 whereas in core sediments it followed the sequence detrital p 61 7 fe bound p 17 0 authigenic p 13 1 organic p 7 5 loosely sorbed p 0 7 post depositional reorganization of p was observed in both surface and core sediments converting organic p and fe bound p to authigenic p the accumulation rates and burial efficiencies of the total p in the intertidal area ranged from 118 70 904 98 mol cm 2 a 1 and 80 29 88 11 respectively high burial efficiency of the total p is likely related to the high percentage of detrital p and the high sediment accumulation rate in addition the bioavailable p represented a significant proportion of the sedimentary p pool which on average accounted for 37 4 and 25 1 of the total p in surface and core sediments respectively this result indicates that the tidal sediment is a potential internal source of p for this p limiting estuarine ecosystem

calibrating mg ca ratios of multiple planktonic foraminiferal species with δ 18 o calcification temperatures paleothermometry for the upper water column in order to consistently approximate the thermal vertical structure of past upper water columns mg ca ratios of eight planktonic foraminiferal species with different preferential calcification depths selected from 76 tropical atlantic and caribbean sediment surface samples were calibrated with 18o derived calcification temperatures with an overall range of 8 28 c extending the broad number of species specific calibrations which agree well especially with our shallow dweller calibrations this study presents new bulk calcite mg ca vs calcification temperature relationships for shallow dwelling globigerinoides ruber pink thermocline dwelling globorotalia menardii and deep dwelling globorotalia truncatulinoides dextral and globorotalia crassaformis not separately calibrated before the species specific temperature sensitivities are relatively similar 7 11 increase in mg ca per 1 c yet y axis intercepts vary from 0 23 0 65 for the shallow and thermocline dwellers to 0 83 1 32 for the deep dwellers based on these differences we established a warm water calibration for temperatures 19 c mg ca 0 29 exp 0 101 t r 0 90 shallow and thermocline dwellers and a cold water calibration for temperatures 15 c mg ca 0 84 exp 0 083 t r 0 85 deep dwellers these calibrations are offset by 8 c this may be significant for paleotemperature reconstructions which are afflicted with the problem that similar mg ca offsets are probably characteristic of extinct species used to calculate past temperatures

reconstructing 7000 years of north atlantic hurricane variability using deep sea sediment cores from the western great bahama bank q1 enso show abrupt changes around 6000 yrs b p but most coastal sedimentary records do not span this time period establishing longer records is essential for understanding mid holocene patterns of storminess and their climatic drivers which will lead to better forecasting of how climate change over the next century may affect tropical cyclone frequency and intensity storms are thought to be an important mechanism for transporting coarse sediment from shallow carbonate platforms to the deep sea and bank edge sediments may offer an unexplored archive of long term hurricane activity here we develop this new approach reconstructing more than 7000 years of north atlantic hurricane variability using coarse grained deposits in sediment cores from the leeward margin of the great bahama bank high energy event layers within the resulting archive are 1 broadly correlated throughout an offbank transect of multi cores 2 closely matched with historic hurricane events and 3 synchronous with previous intervals of heightened north atlantic hurricane activity in overwash reconstructions from puerto rico and elsewhere in the bahamas lower storm frequency prior to 4400 yrs b p in our records suggests that precession and increased nh summer insolation may have greatly limited hurricane potential intensity outweighing weakened enso and a stronger west african monsoon factors thought to be favorable for hurricane development

time variations of phosphorus and sources of sediments beneath the chang jiang yangtze river abstract depth dependent changes of different forms of sediment phosphorus in a 98 m drill core from near the mouth of the chang jiang yangtze river have been determined using a modified chemical extraction method results indicate that the dominant portion of the phosphorus is in inorganic form and that there is an upward increase in detrital apatite the concentration of phosphorus associated with hydrous ferric oxides fe p exhibits an excellent positive correlation with the fine size fraction of the sediments indicating the close association between ferric oxides and high surface area mineral grains most notable is a yellow clayey silt layer of low sand content at 39 5 m depth which is very rich in fe p four possibilities are presented to explain the possible source of the yellow layer one possibility is that the yellow layer may represent loess rich huang he yellow river sediment transported far to the south due to a large former shift of the huang he mouth the visual characteristics and chemical observations for the above core combined with some geological clues are in agreement with this hypothesis besides these geological observations chinese historical documents provide additional evidence for large former shifts of the mouth of the huang he

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

a 2000 year record of caribbean and tropical north atlantic hydrographic variability 1 here we present near annually resolved oxygen isotope records from two species of planktic foraminifera from the cariaco basin that reflect sea surface temperature sst and intertropical convergence zone itcz precipitation related salinity variations over the caribbean and tropical north atlantic spanning the last 2000 years a strong broad spatial pattern of correlation exists between foraminiferal 18o and ssts over the period of instrumental overlap but the correlations weaken as they are extended back in time and instrumental sst records become discontinuous a long term trend in the globigerinoides ruber 18o record can be explained by two different but equally plausible scenarios first the increase in 18o may indicate that tropical summer fall ssts have cooled by as much as 2 c over the last 2000 years possibly as a result of a long term increase in upwelling intensity alternately comparisons to other studies of itcz and regional evaporation precipitation variability suggest that much of the 18o record is influenced by decadal to centennial scale variations in the mean annual position of the itcz and associated rainfall patterns similarities between the g bulloides 18o record and the 11 year sunspot cycle support prior studies that suggest solar variability plays a role in influencing the hydrologic balance of the circum caribbean

century scale movement of the atlantic intertropical convergence zone linked to solar variability 1 the abundance of the planktic foraminifer globigerinoides sacculifer in gulf of mexico gom sediments is a proxy for the influx of caribbean surface waters the loop current into the gom penetration of the loop current into the gom is related to the position of the intertropical convergence zone itcz northward migration of the itcz results in increased incursion of the loop current into the gom southward migration of the itcz results in decreased penetration of the loop current into the gom abundance variations of g sacculifer in a sediment core from the pigmy basin in the gom show distinct century scale cyclicity over the last 5 000 years the periodicity of these abundance variations is similar to the century scale periodicity observed in proxy records of solar variability which suggests that the average position of the itcz and thus holocene century scale variability in the caribbean gom region is linked to solar variability

global relationship between oceanic geoid and topography in order to compare model predictions of upper mantle convection with surface observations we have computed global residual depth and geoid anomalies on a 5 5 grid over all oceans after removal of lithospheric cooling effects and long wavelength geoid components 4000 km related to lower mantle sources we have derived the transfer function admittance of geoid over topography as a function of wavelength in the range 1000 4000 km the observed admittance is positive at all and presents a maximum of 2 5 3 5 m km at 2750 km comparing this result with the theoretical admittance computed for the lithospheric cooling plate model we ascribe most of the admittance peak at 2750 km to errors in the depth age and geoid age correction this suggests that a standard age correction applied to all seafloor is not valid at shorter wavelengths the admittance remains roughly constant on the order of 1 5 m km and can be explained in terms of sediment loading and crustal thickening effects comparing spatially the residual geoid and depth anomaly maps we note a positive correlation over a few areas coinciding with hot spot swells volcanic plateaus or seafloor deeps the geoid versus depth ratio amounts then to 6 8 m km in agreement with the values predicted above upwellings and downwellings by models of constant viscosity convection however the global admittance analysis leads to much lower values at all wavelengths suggesting that these areas are too limited in number and in extent to produce any significant signal

phosphorus speciation and its bioavailability in sediments of the jiaozhou bay abstract phosphorus p is an important macronutrient that can limit primary productivity in coastal marine ecosystems in this study four sediment cores were collected in the jiaozhou bay to study the phosphorus forms and their bioavailability including exchangeable or loosely sorbed p ex p iron bound p fe p authigenic p ca p detrital p de p and organic p op which were separated and quantified using a sequential extraction method sedex the results showed that the concentration of total p tp in core sediments ranged from 6 23 to 10 46 mol g and inorganic p ip was the dominated p form fe p and de p were the main chemical forms of ip in core sediments the profile variation of op presented the most significant among the phosphorus forms whereas the concentrations of ex p fe p and ca p varied slightly with depth indicating that the transformation of ex p fe p ca p and op could occur during sedimentary p burial moreover the distribution of p species was influenced by many factors including terrigenous input biological processes organic matter degradation and increasing human activities high total organic carbon toc op ratio occurred in the jiaozhou bay ranging from 73 to 472 average 180 81 in core sediments which was caused by the increasing terrestrial organic matter the ratio of toc p reactive ranged from 24 to 101 average 46 15 in core sediments lower than the redfield ratio implying a surplus of sedimentary reactive p compared with toc potential bioavailable p bap accounted for about 28 2 60 8 average 47 1 7 4 of tp in core sediments and presented an increasing trend since 1980s which might be responsible for the shift of phytoplankton community composition during these decades

interacting loop current variability and mississippi river discharge over the past 400 kyr the loop current mediating the oceanic heat and salt flux from the caribbean sea into the atlantic ocean and its interference with the mississippi river discharge are critical for both the regional climate in the gulf of mexico area and the water vapor transport towards high northern latitudes we present a 400 kyr record of sea surface temperature and local surface salinity from the northeastern gulf of mexico images core md02 2575 approximated from combined planktonic foraminiferal 18o and mg ca which reflects the temporal dynamics of the loop current and its relationship to both varying mississippi discharge and evolution of the western hemisphere warm pool the reconstructed sea surface temperature and salinity reveal glacial interglacial amplitudes that are significantly larger than in the western hemisphere warm pool sea surface freshening is observed during the extreme cool periods of marine isotope stages 2 8 and 10 caused by the strengthened mississippi discharge which spread widely across the gulf favored by the less established loop current interglacial and interstadial sea surface conditions instead point to a strengthened northward flowing loop current in line with the northward position of the intertropical convergence zone allowing northeastern gulf of mexico surface hydrographic conditions to approach those of the caribbean at these times the mississippi discharge was low and deflected westward promoted by the extended loop current previously described deglacial megadischarge events further to the west did not affect the northeastern gulf of mexico hydrography implying that meltwater routing from the laurentide ice sheet via the mississippi river is unlikely to have affected atlantic meridional overturning circulation

comments on reflection properties of phase transition and compositional change models of the 670 km discontinuity by alison c lees m s t bukowinski and raymond jeanloz

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

meridional shifts of the atlantic intertropical convergence zone since the last glacial maximum the position of the intertropical convergence zone is thought to be linked to changes in the earth s climate state analyses of marine sediment show that over the past 25 000 years the intertropical convergence zone over the atlantic ocean migrated in response to climate changes

variable north atlantic climate seesaw patterns documented by a late holocene marine record from disko bugt west greenland abstract the reconstruction of past sea surface conditions in the labrador sea is essential for understanding climate fluctuations in the north atlantic region we here study late holocene sea surface conditions off west greenland in order to elucidate the possible relationship between a north atlantic seesaw and centennial to millennial scale climate fluctuations in the labrador sea region for that purpose we have studied the particulate organic matter especially dinoflagellate cysts and acritarchs from two marine sediment cores from disko bugt central west greenland our data show significant variations in sea surface temperature and sea ice cover during the last ca 3200 years after a cooling at ca 2 9 ka cal bp presumably related to the neoglacial cooling seen in large parts of the northern hemisphere the area was subjected to significant variability both in the entrainment of atlantic water west greenland current water and in atmospheric temperatures from 2 0 1 5 ka cal bp corresponding to the later part of the roman warm period the area experienced a return to a stronger influx of atlantic water and an increased fresh water influx from land probably related to increased precipitation or to melt water outflow from the nearby inland ice the dark ages 1 5 1 3 ka cal bp were characterised by an only minor cooling of the surface waters however as seen in other records from the labrador sea region the beginning of the medieval warm period 1 3 0 9 ka cal bp signified a severe cooling presumably due to a significant reduction in atlantic water entrainment the cold conditions continued through the little ice age after 0 9 ka cal bp although the area seems to have experienced a minor decrease in sea ice cover until 0 5 ka cal b p after which sea ice cover may again have increased the period of modern warming is not represented in our data our study shows that a north atlantic oscillation type pattern played a significant role in the late holocene centennial to millennial scale climate fluctuations in the labrador sea region however this cannot explain the full complexity of the climate signal the fact that a simple pattern of cold versus warm climate scenario does not exist demonstrates that it will hardly be feasible to select the correct baseline data set when modelling future climate development

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

hydrological variability in florida straits during marine isotope stage 5 cold events modeling and proxy studies indicate that a reduction of atlantic meridional overturning circulation amoc strength profoundly impacts temperatures and salinities in the sub tropical atlantic especially on subsurface levels while previous studies focused on prominent periods of amoc reduction during the last deglaciation we aim to test whether similar reconfigurations of the subtropical hydrography occurred during the moderate climatic alterations punctuating the last interglacial marine isotope stage mis 5 here we present temperature and salinity records from a florida straits core by combining d18o and mg ca analyses on surface globigerinoides ruber white and deep dwelling globorotalia crassaformis foraminifera covering mis 5 in high resolution the data reveal increasing salinities at intermediate depths during interglacial cooling episodes decoupled from relatively stable surface conditions this probably indicates the spatial expansion of saline subtropical gyre waters due to enhanced ekman downwelling and might also point to a changed density structure and altered geostrophic balance in florida straits notably these oceanographic alterations are not consistently occurring during periods of amoc reduction the data suggest that the expansion of gyre waters into florida straits was impeded by the increasing influence of antarctic intermediate water aaiw from mis 5 5 to 107 kyr bp afterward increasingly positive benthic d13c values imply a recession of aaiw allowing the temporary expansion of gyre waters into florida straits we argue that the inferred transient subtropical salt accumulation and warm pool expansion might have played a pivotal role in reinvigorating meridional overturning and dampen the severity of interglacial cold phases

phosphorus forms related to sediment grain size and geochemical characteristics in french coastal areas abstract phosphorus forms with respect to sediment characteristics such as grain size and major chemical elements were studied in french coastal marine areas the bay of seine and the loire and gironde estuaries in the three areas fe al bound phosphate fe al p and exchangeable phosphate exch p were significantly related to the proportion of fine fraction calcium bound phosphate ca p was found in all grain size classes with comparable concentrations in the bay of seine where there was no correlation between ca p and ca this corresponded to the calcium s marine origin shells in the bay of seine in contrast the correlation of ca p with ca and the fine fraction of the sediment in the loire and gironde estuaries was characteristic of the predominant metamorphic origin of ca p in these areas useful information for interpretation of p forms can be obtained from major sediment characteristics thus for areas where specific relationships have previously been established good estimates of p forms could be predicted from sediment properties