geochemistry of a piston core from ontong java plateau western equatorial pacific evidence for sediment redistribution and changes in paleoproductivity we discuss geochemical proxies reflecting processes of primary productivity caco3 dissolution and sediment redistribution in a piston core rndb 74p from the ontong java plateau due to the shallow water depth biogenic carbonate is well preserved and a very good 18o stratigraphy is available down to isotopic stage 11 230thex gives evidence that the sediment accumulation pattern is driven mainly by processes of sediment focusing or winnowing due to the constant production of230th in the water column the bulk sediment accumulation rates could be corrected for the particle rain deriving from the water column above the230thex 0 caco3 ratio reflects the well known pacific caco3 preservation pattern with ice growth dissolution spikes and deglacial preservation spikes the record of the grain size fraction 63 m supports these results the downcore concentrations and accumulation rates of barium ba are on a higher level during interglacials and show several peaks normalization of ba with230thex 0 delivers a more uniform level of the ba accumulation rates throughout the core this pattern suggests a constantly higher biological productivity nearly tenfold in this area throughout the past 200 kyr compared with an open ocean environment barium peaks observed at the climatic transitions 2 1 and 6 5 and in stage 5 are in contrast to a predicted reduction of interglacial productivity at this location a possible explanation might be the onset of the modern circulation pattern the transition from ba enriched deep water to lower contents in the atlantic might have resulted in an enhanced deposition of ba in the pacific

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

precessionally forced productivity variations across the equatorial pacific 1 measurements of combustion oxygen demand cod in two sediment cores provide a record of paleoproductivity driven by surface ocean dynamics in the equatorial eastern and western pacific for the past 400 000 years the cod time series are well correlated with each other over this time span and show pronounced precessionally forced peaks of higher productivity during globally colder periods the phase of this signal in the two cores is identical to within chronological uncertainties suggesting a common insolation forcing mechanism for the upper ocean across the equatorial pacific cod is also in phase with the precessionally forced component of global ice volume as indicated by oxygen isotopes and with atmospheric methane in the vostok ice core these relationships imply that the cod relative paleoproductivity index provides an important diagnostic measure of the mechanisms of tropical ocean dynamics and climate change

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

biogenic silica dissolution in sediments of the southern ocean i solubility abstract a stirred flow through reactor technique was used to determine silica solubilities in sediments collected with a multicorer in the indian sector of the southern ocean antares i cruise the results show that the apparent silica solubility in the cores may decrease increase or remain constant with depth the silica solubility profiles are best explained by the early diagenetic interactions between biogenic silica and soluble aluminum derived from detrital material by combining the solubility data with measured dissolved silica profiles it is shown that the variable asymptotic pore water silica levels in the cores cannot be explained solely by differences in silica solubility in sediments that experience a significant detrital input the simultaneous reprecipitation of dissolved aluminum and dissolved silica prevents water silicic acid from reaching saturation with the dissolving biogenic silica the principal oceanographic control on pore water silica build up in the cores studied is the ratio of the deposition fluxes of biogenic silica and detrital material solubility differences inherited from the biomineralization process in the surface waters do not appear to have a significant effect on the observed pore water silica levels

boundary scavenging in the pacific ocean a comparison of 10be and 231pa concentrations of u th 231pa and 10be were measured in holocene sediments from two cores collected off the west coast of south america two cores from the east pacific rise two from the equatorial pacific and one from the south pacific central gyre our results together with data from 5 cores reported in the literature show that boundary scavenging plays a major role in the removal of 10be from the pacific ocean deposition rates of 10be at three margin sites are more than an order of magnitude greater than at sites of red clay accumulation in the deep central pacific deposition of 231pa is 4 to 5 fold greater at the margin sites the residence time of 10be with respect to chemical scavenging defined as its inventory in the water column divided by its rate of removal to the sediments varies regionally from 1000 years at the red clay sites in the deep central pacific to 100 years at the margin sites different factors control boundary scavenging of pa and be for example scavenging of 231pa is enhanced by metal oxide coatings of particles whereas this seems to have little influence on the scavenging of 10be 1990

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

rapid bioturbation in equatorial pacific sediments evidence from excess 234th measurements in order to evaluate bioturbation in equatorial pacific sediments profiles of excess 234th were measured in cores collected during november and december 1992 at six abyssal sites along the jgofs equatorial pacific 140 w transect from 5 s to 9 n excess 234th half life 24 1 days was detected at all sites mean inventories ranged from a low of 0 25 dpm cm 2 at 9 n to a high of 2 6 dpm cm 2 at 2 n eddy diffusive models of the excess 234th profiles suggest that on 100 day timescales particle mixing is slow at 5 s and 2 s eddy diffusion coefficient db 0 4 cm2 year 1 faster at 0 and 2 n db 0 34 4 8 cm2 year 1 and fastest at 5 n db 4 7 11 cm2 year 1 at 9 n 234th is found almost entirely in the upper 5 mm of the seabed and db values are 0 1 cm2 year 1 db values generally increase as poc flux increases although the linear relationship r2 0 334 p 0 365 displays considerable scatter however if the only sites included in the regression are those where 234th profiles were measured in at least two core sets i e 0 2 n 5 n and 9 n the linear regression improves substantially r2 0 754 p 0 0012 these results suggest that measurements on a single core may not fully characterize the sediment mixing regime in a particular region and highlight the need for multiple samples from an individual site thorium 234 db values at 5 s 2 s and 9 n are in rough agreement with published db values calculated from the profiles of intermediate half life radioisotopes such as 210pb and 137cs in open ocean abyssal sediments however at 0 2 n and 5 n 234th db values are as much as an order of magnitude greater than published 210pb db values this phenomenon has been observed in other marine environments and may result from age dependent mixing non steady state mixing or a combination of the two processes particle mixing in cores collected at 5 s and 5 n appears to be best described as a largely eddy diffusive process however in cores collected at 2 s 0 2 n and 9 n non local mixing processes appear to affect 15 30 of the excess 234th inventory at these sites non local mixing appears to transport recently deposited material at least 3 4 cm below the sediment water interface within 100 days of its arrival at the seafloor the combination of rapid biodiffusive mixing and non local transport allows recently deposited reactive biogenic debris to be rapidly mixed into the seabed this may affect a wide range of diagenetic processes including oxygen consumption dissolution of biogenic debris and organic carbon remineralization models of early diagenesis in deep sea sediments may need to incorporate both non diffusive transport terms and rapid biodiffusive mixing of recently deposited particles

biogenic sedimentation beneath the california current system for the past 30 kyr and its paleoceanographic significance a north south transect of 17 cores was constructed along the eastern boundary of the california current system from 33 to 42 n to investigate the changes in biogenic sedimentation over the past 30 kyr percentages and mass accumulation rates of caco3 corg and biogenic opal were assembled at 500 to 1000 years sample to provide relatively high resolution time space maps reveal a complex pattern of changes that do not follow a simple glacial interglacial two mode model biogenic sedimentation shows responses that are sometimes time transgressive and sometimes coeval and most of the responses show more consistency within a limited geographic area than any temporal consistency reconstructed conditions during late oxygen isotope stage 3 were more like early holocene conditions than any other time during the last 30 kyr coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central california margin but were weak along the northern california margin precipitation increased during the last glacial interval in the central california region and the waters of the southern california margin had relatively low productivity productivity on the southern oregon margin was relatively low at the beginning of the last glacial interval but by about 20 ka productivity in this area significantly increased this change suggests that the center of the divergence of the west wind drift shifted south at this time the end of the last glacial interval was characterized by increased productivity in the southern california margin and increased upwelling along the central california margin but upwelling remained weak along the northern california margin a sudden 300 years decrease in caco3 corg and biogenic opal occurred at 13 ka the changes suggest a major reorientation of the atmospheric circulation in the north pacific and western north america and the establishment of a strong seasonality in the central california region a carbonate preservation event occurred at 10 ka that appears to reflect the uptake of co2 by the terrestrial biosphere as the northern latitudes were reforested following retreat of the glaciers the holocene has been a period of relatively high productivity in the southern california margin relatively strong coastal upwelling along the central california margin relatively weak upwelling along the northern california margin and the northward migration of the divergence zone of the west wind drift

sediment size fractionation and focusing in the equatorial pacific effect on 230th normalization and paleoflux measurements we use flux dissolution and excess 230th data from the joint global ocean flux study and manganese nodule project equatorial pacific study site c to assess the extent of sediment focusing in the equatorial pacific measured mass accumulation rates mar from sediment cores were compared to reconstructed mar by multiplying the particulate rain caught in sediment traps by the 230th focusing factor and subtracting measured dissolution caco3 mar is severely overestimated when the 230th focusing factor correction is large but is estimated correctly when the focusing factor is small in contrast al fluxes in the sediment fine fraction are well matched when the focusing correction is used since caco3 is primarily a coarse sediment component we propose that there is significant sorting of fine and coarse sediments during lateral sediment transport by weak currents because caco3 does not move with 230th normalization typically overcorrects the caco3 mar and because caco3 is 80 of the total sediment 230th normalization overestimates lateral sediment flux fluxes of 230th in particulate rain caught in sediment traps agree with the water column production sorption model except within 500 m of the bottom near the bottom 230th flux measurements are as much as 3 times higher than model predictions there is also evidence for lateral near bottom 230th transport in the bottom nepheloid layer since 230th fluxes caught by near bottom sediment traps are higher than predicted by resuspension of surface sediments alone resuspension and nepheloid layer transport under weak currents need to be better understood in order to use 230th within a quantitative model of lateral sediment transport

biogenic carbonate and ice rafted debris heinrich layer accumulation in deep sea sediments from a northeast atlantic piston core abstract biogenic carbonate mass accumulation rates show distinct quaternary glacial interglacial changes in a mid latitude northeast atlantic deep sea core during the last 208 kyr these were generally higher during interglacials averaging 2 2 g cm 2 kyr than during glacial periods with a maximum average of 1 2 g cm 2 kyr intervals containing high ice rafted debris have very low biogenic carbonate accumulation rates paleo primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gc m 2 yr than during glacials which average 49 gc m 2 yr maximum estimate short intervals with possibly reduced primary productivity correspond to heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the north atlantic we identified thirteen heinrich layers in isotopic stages 7 to 2 they have calendar ages of about 201 189 182 183 164 167 146 149 142 128 131 64 67 52 54 40 43 29 31 21 and 15 kyr these heinrich layers contain large amounts of ice rafted debris including detrital carbonate low amounts of coccoliths and planktic foraminifera mainly neogloboquadrina pachyderma sinistral the upper five heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera the virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs considering the limited use of other proxies such as organic carbon diatom and benthic foraminifera due to their very low content abundance in the sediments biogenic carbonate mass accumulation rates offer a workable paleo primary productivity proxy in open ocean sediments of the carbonate dominated northeast atlantic

models of depth dependent bioturbation at manop site h in the eastern equatorial pacific the vertical distribution of excess 226ra sorbed to manganese rich sediments from a box core taken at manop site h 6 34 n 92 48 w in the eastern equatorial pacific can be modeled only if the rate of bioturbation decreases rapidly downward from the seafloor within the upper few centimeters of sediment independent bioturbation rates estimated by balancing dissolved and particulate diagenetic mn fluxes are compatible with the values obtained from the radium model such results are consistent with 210pb and 230th measurements reported here and with manop lander and porewater observations that rapid organic carbon degradation in these sediments consumes oxygen within a few centimeters of the sediment seawater interface the modeled decrease in bioturbation expressed as a biodiffusion coefficient is consistent with values of more than 25 cm2 kyr at the surface falling to less than 0 4 cm2 kyr at a depth of 14 cm

tephrochronology of marine tephra adjacent to central america geochemical analyses performed on volcanic ash layers from the 3 ocean basins surrounding central america revealed 11 distinct tephra horizons during the past 300 000 yr and the distribution of each tephra was delineated the los chocoyos ash 84 000 yr old and worzel layer l ash 230 000 yr old are the 2 most widespread tephra in the region two tephra y 6 75 000 yr old and w 1 136 000 yr old are restricted to the western gulf of mexico the remaining tephra b 36 000 yr old j 1 135 000 yr old g 190 000 yr old i 212 000 yr old k 270 000 yr old i 2 270 000 yr old and i 6 300 000 yr old are primarily restricted to the eastern equatorial pacific ocean immediately adjacent to central america the age of each layer was determined by correlation to oxygen isotope and calcium carbonate stratigraphy in marine cores or by interpolation or extrapolation of ages from that stratigraphy of the marine tephra two were correlated to terrestrial exposures of silicic volcanic rocks the layer d tephra had been correlated to the los chocoyos ash from the lake atitlan caldera in guatemala the layer i 2 tephra is correlated with the t fall ash from lake amatitlan caldera in guatemala the age of the terrestrial volcanic units was determined by identifying the stratigraphic age of the marine tephra the los chocoyos ash and t fall deposit are dated at 84 000 and 270 000 yr b p respectively geochemical correlation of the marine tephra to other terrestrial sources will facilitate dating of explosive volcanic eruptions in southern mexico central america and northern south america

glacial enrichments of authigenic cd and u in subantarctic sediments a climatic control on the elements oceanic budget we examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic cd inventory thereby decoupling cd from po4 we suggest that the precipitation of cd sulfide in suboxic sediments is the single largest sink in the oceanic cd budget and that the accumulation of authigenic cd and u is tightly coupled to the organic carbon flux into the seafloor sediments from the subantarctic ocean and the cape basin south atlantic where oxic conditions currently prevail show high accumulation rates of authigenic cd and u during glacial intervals associated with increased accumulation of organic carbon these elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon a third core overlain by circumpolar deep water cpdw as are the other two cores but located south of the antarctic polar front shows an approximately inverse pattern to the subantarctic record the contrasting patterns to the north and south of the antarctic polar front suggest that higher accumulation rates of cd and u in subantarctic sediments were driven primarily by increased productivity this proposal is consistent with the hypothesis of glacial stage northward migration of the antarctic polar front and its associated belt of high siliceous productivity however the increase in authigenic cd and u glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts suggesting greater partitioning of organic carbon into the sediments during glacial intervals lower oxygen content of cpdw and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes higher glacial productivity in the cape basin record very likely reflects enhanced coastal up welling in response to increased wind speeds we suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum however our calculations suggest low sensitivity of seawater cd concentrations to glacial doubling of the extent of reducing sediments the model suggests that during the last 250 kyr seawater cd concentrations fluctuated only slightly between high levels about 0 66 nmol kg 1 on glacial initiations and reaching lowest values about 0 57 nmol kg 1 during glacial maxima the estimated 5 lower cd content at the last glacial maximum relative to modern levels 0 60 nmol kg 1 cannot explain the discordance between cd and 13c such as observed in the southern ocean this low sensitivity is consistent with foraminiferal data suggesting minimal change in the glacial cd mean oceanic content

paired carbon isotope and cadmium data from benthic foraminifera implications for changes in oceanic phosphorus oceanic circulation and atmospheric carbon dioxide abstract the carbon isotope and cadmium content of foraminiferal shells from oceanic sediments provides information on past chemical distributions in the ocean starting from reasonable assumptions it can be shown that paired data on both tracers provides more information than does either separately the slope of paired isochronous 13c and cd ca data from fossil benthic foraminifera depends on oceanic p cd and gd 13c p ratios the zero cd ca intercept of this line depends on mean oceanic 13c p and the 13c p ratio given data sufficient to define oceanic mean 13c and cd contents it is possible to place quantitative constraints on the product of the c p redfield ratio and mean oceanic phosphorus and to estimate a circulation parameter which is independent of changes in ocean chemical inventories with the limited available data no significant changes in oceanic p cd can be detected between the holocene and most recent glacial maximum if this data is taken to be representative of the whole ocean then the p and cd contents of the ocean were about 17 higher during the last glacial maximum than at present ocean box models indicate that this change in oceanic p and a 2 c deep ocean cooling during glacials would cause a 47 ppmv reduction in atmospheric pco2 during glacial intervals

transport and release of transition elements during early diagenesis sequential leaching of sediments from manop sites m and h part i ph 5 acetic acid leach sediments from manop sites m and h in the eastern tropical pacific ocean can be partitioned into operationally defined phases by means of a sequential leach procedure this paper reports the results of the first leach in the sequence an acetic acid solution buffered as p h 5 with sodium acetate this leach is designed to remove carbonate bound and sorbed cations the only cation bound in a consistent ratio to calcium in the carbonate is strontium the molar ratio is 2 10 3 in contrast transition metals are sorbed onto the surfaces of other sedimentary particles the proportions sorbed range from 2 to 10 of the total manganese about 10 of the total nickel and copper and less than 1 of the total iron the pool of sorbed metals in surface sediments is sufficiently large and the rate of biological stirring is sufficiently rapid for this metal reservoir potentially to dominate the porewater reservoir in supplying metals to ferromanganese nodules a simple model for nodule growth based upon transfer of metals through this reservoir suggests that only 1 of the sedimentary sorbed metals within a radius of 2 to 9 cm is required to support typical nodule growth rates

climatically forced organic carbon burial in equatorial atlantic and pacific oceans over the past ten years sedimentary geochemists have noted that climate changes associated with pleistocene glaciations have had a pronounced effect on the rate of organic carbon burial found in the tropical oceans1 4 in particular two to five times higher organic carbon accumulation rates have been observed for the 18 kyr bp glacial maximum than for the holocene in several short sediment cores from both oceans see fig 1 here i present 300 kyr time series for organic carbon mass accumulation rate from four sediment cores two each from the equatorial pacific and atlantic and show that orbital forcing of global climate has strongly affected the rate of organic carbon burial in the equatorial oceans

quaternary history of calcium carbonate fluctuations in the western equatorial indian ocean somali basin abstract a study of the quaternary history of calcium carbonate fluctuations in the equatorial indian ocean based on the swedish deep sea expedition core 154 demonstrates that the calcite compensation depth ccd was shallower during interglacial periods than during glacials higher percentages of calcium carbonate lower percentages of dissolution resistant planktonic foraminifera and lower values of the berger dissolution index suggesting better calcium carbonate preservation are recorded during glacial periods and or at glacial interglacial transitions in contrast interglacial periods are marked by stronger calcium carbonate dissolution the data indicate that dissolution is the main controlling factor of calcium carbonate in the western equatorial indian ocean higher dissolution during interglacial periods and enriched 13 c are due to higher noncarbonate productivity and enhanced antarctic bottom water aabw ventilation in the equatorial indian ocean

biogenic sediment regimes in the neogene equatorial pacific iodp site u1338 burial production and diatom community abstract the equatorial pacific experienced significant changes in productivity and microfossil assemblage since 16 million years ago ma we compiled a record of those changes from iodp site u1338 using a reconnaissance of diatom assemblages and high resolution xrf scan chemical profiles 1 2 kyr spacing productivity and caco3 dissolution intervals are defined by sediment component ratios in particular opal clay opal baso4 and caco3 baso4 or caco3 clay there are large abrupt changes in export production in the miocene especially compared to the pleistocene and pliocene and average levels of export production are higher throughout the miocene compared to the pliocene and pleistocene using diatom assemblages and bulk sediment composition the u1338 sediment record is divided into several distinct deposition regimes 1 a middle miocene regime 13 2 ma marked by low diatom numbers and a few short lived productivity intervals 2 a carbonate crash regime distinguished by an older substage 13 2 10 2 ma with relatively high abundances of productivity related diatoms and common productivity related depositional intervals interspersed with caco3 dissolution intervals and a younger carbonate crash substage 10 2 8 0 ma with weaker brief productivity intervals high caco3 dissolution and moderately high numbers of upwelling diatom species 3 the biogenic bloom regime 8 0 4 5 ma marked by extended periods of high opal and caco3 deposition with a maximum between 7 0 and 6 4 ma and 4 a pliocene modern regime 4 5 0 ma with lower productivity and high cyclic caco3 dissolution changes in production and dissolution result from reorganizations of nutrient supply to the equatorial pacific not by higher wind driven upwelling we propose that nutrients were more accessible in the miocene because of a combination of factors including higher organic matter degradation in the upper water column and deep intermediate nutrient pathways that efficiently recycled nutrients to upwelling zones closure of the central american seaway was likely a prime cause of the biogenic bloom

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

photosynthetic fractionation of 13c and concentrations of dissolved co2 in the central equatorial pacific during the last 255 000 years carbon isotopically based estimates of co2 levels have been generated from a record of the photosynthetic fractionation of 13c is equivalent to epsilon p in a central equatorial pacific sediment core that spans the last approximately 255 ka contents of 13c in phytoplanktonic biomass were determined by analysis of c37 alkadienones these compounds are exclusive products of prymnesiophyte algae which at present grow most abundantly at depths of 70 90 m in the central equatorial pacific a record of the isotopic composition of dissolved co2 was constructed from isotopic analyses of the planktonic foraminifera neogloboquadrina dutertrei which calcifies at 70 90 m in the same region values of epsilon p derived by comparison of the organic and inorganic delta values were transformed to yield concentrations of dissolved co2 is equivalent to c e based on a new site specific calibration of the relationship between epsilon p and c e the calibration was based on reassessment of existing epsilon p versus c e data which support a physiologically based model in which epsilon p is inversely related to c e values of pco2 the partial pressure of co2 that would be in equilibrium with the estimated concentrations of dissolved co2 were calculated using henry s law and the temperature determined from the alkenone unsaturation index u k 37 uncertainties in these values arise mainly from uncertainties about the appropriateness particularly over time of the site specific relationship between epsilon p and 1 c e these are discussed in detail and it is concluded that the observed record of epsilon p most probably reflects significant variations in delta pco2 the ocean atmosphere disequilibrium which appears to have ranged from approximately 110 microatmospheres during glacial intervals ocean atmosphere to approximately 60 microatmospheres during interglacials fluxes of co2 to the atmosphere would thus have been significantly larger during glacial intervals if this were characteristic of large areas of the equatorial pacific then greater glacial sinks for the equatorially evaded co2 must have existed elsewhere statistical analysis of air sea pco2 differences and other parameters revealed significant p 0 01 inverse correlations of delta pco2 with sea surface temperature and with the mass accumulation rate of opal the former suggests response to the strength of upwelling the latter may indicate either drawdown of co2 by siliceous phytoplankton or variation of co2 si oh 4 ratios in upwelling waters

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

a comparative study of the northwest africa and eastern equatorial pacific upwelling zones as sources of co2 during glacial periods based on boron isotope paleo ph estimation paleo ph reconstructions based on boron isotopic composition of foraminifera have been used to estimate glacial interglacial changes in surface ocean pco2 of the northwest african upwelling zone on comparison with a similar study for the eastern equatorial pacific upwelling zone it can be concluded that the two major upwelling zones acted quite differently during the glacial periods as compared to today while the ph of the surface ocean off northwest africa was 0 2 0 07 units higher during the glacial period compared to that during holocene there was no significant glacial interglacial change in the surface ocean ph in the eastern equatorial pacific carbonate chemistry reconstructions based on the estimated ph changes suggest that the ocean atmosphere pco2 gradient off northwest africa was lower by at least 70 40 atm during glacial periods compared to during the holocene in contrast the ocean atmosphere pco2 gradient in the eastern equatorial pacific was higher by at least 80 40 atm during glacial periods as compared to during the holocene hence the eastern equatorial pacific upwelling system was a significantly larger source of co2 to the atmosphere while the one off northwest africa was a significantly smaller source of co2 during the last glacial period the pco2 reconstructions further indicate that in spite of higher glacial productivity compared to during the holocene neither of the two areas became a sink of co2

new temporal constraints on the rotation of the peruvian central andes obtained from paleomagnetism new paleomagnetic data from middle eocene to middle miocene volcanic and plutonic formations of the western cordillera of central peru document a counterclockwise rotation of 11 7 4 this rotation similar to previous results reported for the northern peruvian margin is post middle miocene in age it is thus coeval with the acceleration of the andean uplift and supports isacks model

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

reconstruction of oceanic circulation patterns in the tropical pacific across the early middle miocene boundary as inferred from radiolarian assemblages abstract although there have been attempts to infer neogene oceanic circulation patterns in the tropical pacific on the basis of multiple marine proxies oceanic circulation patterns across the early middle miocene boundary are still poorly understood despite paleoclimate having significantly changed during this interval in this study we reconstruct the changes in tropical oceanic circulation patterns in the pacific across the early middle miocene boundary based on radiolarian assemblages obtained at integrated ocean drilling program site u1335 in the eastern tropical pacific the radiolarian upwelling taxa increased during four intervals 18 4 18 1 ma 16 9 15 7 ma 15 2 14 6 ma 14 2 13 4 ma radiolarian temperature index rti was calculated using the relative abundances of the warm water cluster b1 and cool water taxa cluster b2 in order to evaluate relative temperature fluctuations of the surface water the sea surface temperature index was relatively high from 16 8 to 16 0 ma and gradually decreased from 16 0 to 14 6 ma subsequently the temperature index decreased stepwise at 13 9 and 13 4 ma and became relatively low from 13 4 to 12 7 ma comparison of the rti record in the eastern tropical pacific to the climatic index based on the benthic foraminiferal 18o record shows that variability in the two records follows a roughly similar trend from the early to the middle miocene however the sea surface temperature record does not indicate a sharp increase in warmth in the eastern tropical pacific during the mid miocene climatic optimum 1 mmco 1 as suggested by the benthic isotopic record this is likely because of increased upwelling of cool nutrient rich water at this time beginning in the latest early miocene 17 ma radiolarian assemblages were dominated by different taxa in the eastern and western tropical pacific this pattern is interpreted as indicating a shallower thermocline in the east and a deeper thermocline in the west based on the relative abundance of the upwelling taxa there is an overall increasing trend in this difference since the latest early miocene we tie these events to the effective closure of the indo pacific seaway and the development of a substantial western pacific warm pool along with the development of a strong equatorial undercurrent

decoupling of carbonate preservation carbonate concentration and biogenic accumulation a 400 kyr record from the central equatorial pacific ocean in order to investigate the paleoceanographic record of dissolution of calcium carbonate caco3 in the central equatorial pacific ocean we have studied the relationship between three indices of foraminiferal dissolution and the concentration and accumulation of caco3 opal and corg in core wec8803b gc51 1 3 n 133 6 w 4410 m this core spans the past 413 kyr of deposition and moved in and out of the lysoclinal transition zone during glacial interglacial cycles of caco3 production and dissolution the record of dissolution intensity provided by foraminiferal fragmentation the proportion of benthic foraminifera and the foraminiferal dissolution index consistently indicates that the past corrosion of pelagic caco3 in the central equatorial pacific does not vary with the observed sedimentary concentration of caco3 although there is a weak low frequency variation 100 kyr in dissolution intensity it is unrelated to sedimentary caco3 concentration there are many shorter lived episodes where high caco3 concentration is coincident with poor foraminiferal preservation and where conversely low caco3 concentration is coincident with superb foraminiferal preservation spectral analyses indicate that dissolution maxima consistently lagged glacial maxima manifest by the specmap 18o stack in the 100 kyr orbital band additionally there is no relationship between dissolution and the accumulation of biogenic opal or corg or between dissolution and the burial ratio of corg cinorg calculated from corg and caco3 because previous studies of this core strongly suggest that surface water productivity varied closely with caco3 accumulation both the mechanistic decoupling of carbonate dissolution from caco3 concentration and from biogenic accumulation and the substantial phase shift between dissolution and global glacial periodicity effectively obscure any simple link between export production caco3 concentration and dissolution of sedimentary caco3

more reducing bottom water redox conditions during the last glacial maximum in the southern challenger deep mariana trench western pacific driven by enhanced productivity abstract the modern southern mariana trench is characterized by oligotrophic surface waters resulting in low primary productivity and well oxygenated bottom waters this study investigates changes in the redox conditions of bottom waters in the southern mariana trench during the last glacial maximum lgm and their potential causes we measured major trace and rare earth elements ree in three gravity cores gc03 gc04 and gc05 and one box core bc11 retrieved from the southern challenger deep at water depths from 5289 to 7118 m the upper sediment layers of both gc05 and bc11 are dominated by valve fragments of the giant diatom ethmodiscus rex forming laminated diatom mats ldms 14c ams dates of bulk organic matter show that the ldms accumulated between 18 4 and 21 8 kyr b p corresponding to the lgm modest enrichments of u and mo along with weak or absent ce anomalies in the ldm point to suboxic conditions during the lgm in contrast non ldm samples exhibit little to no enrichment of redox sensitive elements as well as negative ce anomalies indicating deposition under oxic bottom water conditions the ce anomalies are considered valid proxies for bottom water redox conditions because ree signatures were acquired in the early diagenetic environment as indicated by strong p ree correlations and middle ree enrichment associated with early diagenetic cycling of fe mn oxyhydroxides in the sediment column followed by capture of the ree signal by biogenic and or authigenic apatite we postulate that the more reducing bottom water conditions during the lgm were linked to increased primary productivity induced by enhanced asian dust input as shown in earlier studies the increased primary productivity associated with ethmodiscus rex blooms in the eastern philippine sea played a significant role in capturing atmospheric co2 during the lgm consequently the magnitude of atmospheric co2 sequestration by giant diatom blooms during the lgm may have been greater than previously envisaged

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

revised ages for laminated sediment and a holocene marker diatom from the northern california continental slope abstract conventional and accelerator mass spectrometry 14 c ages indicate that laminated sediment in three cores from the northern california continental slope near 38 n and 39 n were deposited between 42 000 and 25 000 yr b p this revises and refines our previous estimates that laminated sediment accumulated during the late pleistocene to early holocene j v gardner and e hemphill haley 1986 geology 14 691 694 preservation of laminated sediment on the upper slope in this area suggests a period of intense coastal upwelling high primary productivity and resultant depletion of oxygen in bottomwaters preceding the onset of global glacial conditions the transition from pleistocene to holocene conditions and the establishment of a modern climatic regime driven by the california current included the incursion of the subtropical diatom pseudoeunotia doliola p doliola is common in sediment younger than about 10 000 yr and thus is a reliable marker species for identifying holocene deposits off northern california

biogenic sedimentation and surface productivity changes in the southern california borderlands during the last glacial interglacial cycle abstract a variety of geochemical evidence suggests that surface productivity in the california borderlands region was 1 5 2 times higher during the last glacial relative to the holocene high accumulation rates of opaline silica and organic carbon suggest increased glacial productivity while carbonate accumulation records and c org c co 3 ratios point toward a dominantly siliceous plankton community at that time the observed productivity changes are attributed to a southerly migration of the north pacific high pressure cell which resulted in an intensification of the california current and enhanced upwelling south of 40 n during the last glacial

links between iron input and opal deposition in the pleistocene equatorial pacific ocean iron is often a limiting nutrient in ocean regions that have a constant supply of other macro nutrients and changes in iron supply over time have been linked to fluctuations in primary productivity marine sediments from the equatorial pacific ocean show that over the past million years iron input was linked to the export and burial of biogenic silica

fecal pellet flux to modern bottom sediment of santa barbara basin california based on sediment trapping fecal pellets constituted more than 60 of the material collected during 45 days of deployment of a suitcase type sediment trap in santa barbara basin the flux was 660 g m 2 yr 1 of which 22 g m 2 yr 1 was carbon flux pellet transport can account for about one half of the sediment flux to the central basin floor including the supply of terrigenous matter the clearing activities of pellet producing plankton have important implications for sedimentation and fertility in the coastal ocean

late quaternary paleoproductivity changes off the congo deduced from stable carbon isotopes of planktonic foraminifera a detailed record 2 kyr intervals of the difference in stable carbon isotopes 13c between globigerina bulloides and globigerinoides ruber pink is used to reconstruct changes in upwelling intensity off the congo river for the last 190 000 yr comparisons of the oxygen and carbon isotope data from this core with records from the niger fan and from pelagic cores in the eastern equatorial south atlantic indicate that the congo fan isotope records do not contain a strong freshwater signal as is described off other major rivers the temporal pattern of the 13c signal correlates with the marine organic carbon record from the congo fan thus the planktonic 13c record reflecting past changes in upwelling intensity and nutrient content corroborates the signal provided by sedimentary organic carbon which is presumed to indicate changes in the amount of biological productivity and export flux to the seafloor the planktonic 13c signal is characterized by a dominant 23 kyr periodicity which provides evidence for a strong response of upwelling fluctuations off the congo to precessional forcing minima in the 13c record are aligned with periods of minimum boreal summer insolation over central africa reflecting an increase of upwelling and biological productivity off the congo at periods of enhanced zonal intensity of southeast trades and corresponding weak southeast monsoon over the eastern south atlantic a strong response to changes in river discharge probably did not occur indicating that fertilization by river derived nutrients has played only a minor role with respect to late quaternary changes in the total amount of primary productivity off the congo

planktonic foraminiferal flux to the deep ocean sediment trap results from the tropical atlantic and the central pacific abstract the flux of planktonic foraminifera between 100 m and 1 mm to the seafloor has been estimated for the central pacific abyssal plain east of hawaii and the tropical atlantic demerara abyssal plain based on sediment trap samples collected from various water depths the faunas in each region are quite similar with 4 to 5 species generally accounting for 70 80 of the total assemblage at both study sites the total foraminiferal flux and the carbonate flux tend to decrease with depth in addition the flux of individual species of planktonic foraminifera varies significantly with depth with the number of small solution susceptible species decreasing with increasing water depth these results suggest that there is significant dissolution of small m foraminifera as they settle through the water column material collected from the sediment water interface directly below the pacific sediment trap array contains no planktonic foraminifera suggesting that the residence time of an individual on the seafloor before it dissolves is extremely short

high resolution stratigraphic correlation of benthic oxygen isotopic records spanning the last 300 000 years abstract in order to compare the response of different oceanographic regions to global climate change very detailed stratigraphic techniques are required the global signal of ice volume changes recorded in the oxygen isotopic composition of foraminifera can provide the tool for developing the necessary high resolution stratigraphy in order to evaluate the resolution of a stratigraphy based on detailed isotopic records two techniques are used to correlate a set of benthic oxygen isotope records from seven piston cores taken in the north and south atlantic the indian and the equatorial and north pacific oceans the first technique was modified from the graphic correlation procedure of shaw 1964 this procedure requires the identification of isotopic events that are correlated from core to core detailed correlations for intervals of the cores between events are provided by a series of straight line segments connecting all common events the second technique developed by martinson et al 1982 uses inverse procedures to define a continuous non linear mapping function that correlates the isotopic records the mapping function maximizes the correlation coefficient between data sets being compared the techniques are independent in that they rely on different criteria for correlating the data series stratigraphic correlations obtained by these procedures are in excellent agreement the mean difference between the correlations is on the order of the sampling intervals of each core and when corrected for sedimentation rates suggests that benthic isotope records from the suite of seven cores can be correlated to a resolution of 2000 to 4000 yrs

productivity patterns in the equatorial pacific over the last 30 000 years the equatorial pacific traverses a number of productivity regimes from the highly productive coastal upwelling along peru to the near gyre like productivity lows along the international dateline making it an ideal target for investigating how biogeochemical systems respond to changing oceanographic conditions over time however conflicting reconstructions of productivity during periods of rapid climate change like the last deglaciation render the spatiotemporal response of equatorial pacific productivity ambiguous in this study surface productivity since the last glacial period 30 000 years ago is reconstructed from seven cores near the line islands central equatorial pacific and integrated with productivity records from across the equatorial pacific three coherent deglacial patterns in productivity are identified 1 a monotonic glacial holocene increase in productivity primarily along the equator associated with increasing nutrient concentrations over time 2 a deglacial peak in productivity 15 000 years ago due to transient entrainment of nutrient rich southern sourced deep waters and 3 possible precessional cycles in productivity in the eastern equatorial pacific that may be related to intertropical convergence zone migration and potential interactions with el nino southern oscillation dynamics these findings suggest that productivity was generally lower during the glacial period a trend observed zonally across the equatorial pacific while deglacial peaks in productivity may be prominent only in the east

stable carbon isotopes in marine porewaters abstract we present centimeter scale porewater 13 c profiles from four sites in the central equatorial pacific ocean which reveal steep porewater 13 c gradients up to 1 0 cm 1 at the deep sea sediment water interface we describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep sea benthic carbon cycle our measured 13 c profiles are then used to estimate carbon rain rates at two of these sites manop sites c and s the 13 c data yield organic carbon rain rates of 10 mol c cm 2 yr 1 at site c and 3 mol c cm 2 yr 1 at site s these carbon rain rates agree with recent carbon rain estimates based on sediment trap data and porewater nitrate profiles but are a factor of 2 lower than estimates based on millimeter scale porewater oxygen profiles our model results indicate that changes of the same magnitude in organic carbon rain rate and bottom water composition o 2 co 2 and 13 c have comparable effects on the carbon isotopic composition of surficial porewaters this suggests the need to consider the effects of benthic carbon cycling on the stable carbon isotope record preserved in deep sea benthic foraminifera tests

changes in ph in the eastern equatorial pacific across stage 5 6 boundary based on boron isotopes in foraminifera estimates of paleo ph for the eastern equatorial pacific ocean across the oxygen isotopic stage 5 6 boundary have been made based on the boron isotopic composition of planktonic orbulina universa and benthic mixed species foraminifera from core v19 28 the estimated deep ocean ph during the penultimate glacial period was about 0 3 0 1 ph units higher compared to the modern deep ocean this is consistent with previously estimated deep ocean ph changes across the stage l 2 boundary in the western equatorial pacific and tropical atlantic thus arguing against the possibility that the benthic foraminifera analyzed to estimate deep ocean ph changes have been significantly affected by anomalous local environment and or diagenesis the estimated changes in the deep ocean carbonate chemistry require a decoupling of several kilometers between the saturation horizon and the lysocline during the glacial periods though such a decoupling could be achieved by enhanced respiration co2 driven calcite dissolution in sediments during glacial periods it lacks support from the calcite sedimentary records the boron isotopic compositions of planktonic foraminifera on the other hand indicate no significant ph change in the eastern equatorial pacific surface ocean during the glacial interglacial transition this is inconsistent with an expected higher surface ocean ph during the glacial period due to lower atmospheric pco2 and is also in contrast with the previously estimated boron isotope based glacial interglacial ph change of 0 2 0 1 ph units in the western equatorial pacific and tropical atlantic the lack of change in eastern equatorial pacific surface ocean ph between glacial interglacial periods could be attributed to less nutrient utilization efficiency and or enhanced calcite production during glacial periods such a decrease in nutrient utilization efficiency and or increase in calcite production would lead to a greater disequilibrium between the pco2 of eastern equatorial pacific surface ocean and that of the atmosphere making this part of the ocean a greater source of co2 to the atmosphere during glacial periods compared to today

export production fluctuations in the eastern equatorial pacific during the pliocene pleistocene reconstruction using barite accumulation rates export production is an important component of the carbon cycle modulating the climate system by transferring co2 from the atmosphere to the deep ocean via the biological pump here we use barite accumulation rates to reconstruct export production in the eastern equatorial pacific over the past 4 3 ma we find that export production fluctuated considerably on multiple time scales export production was on average higher 51 g c m 2 yr 1 during the pliocene than the pleistocene 40 g c m 2 yr 1 decreasing between 3 and 1 ma from more than 60 to 20 g c m 2 yr 1 followed by an increase over the last million years these trends likely reflect basin scale changes in nutrient inventory and ocean circulation our record reveals decoupling between export production and temperatures on these long million years time scale on orbital time scales export production was generally higher during cold periods glacial maxima between 4 3 and 1 1 ma this could be due to stronger wind stress and higher upwelling rates during glacial periods a shift in the timing of maximum export production to deglaciations is seen in the last 1 1 million years results from this study suggest that in the eastern equatorial pacific mechanisms that affect nutrient supply and or ecosystem structure and in turn carbon export on orbital time scales differ from those operating on longer time scales and that processes linking export production and climate modulated oceanic conditions changed about 1 1 million years ago these observations should be accounted for in climate models to ensure better predictions of future climate change

can sediment geochemistry record changes in coastal upwelling palaeoproductivity evidence from northwest africa and the arabian sea abstract the causes and consequences of organic carbon c org burial in sediments underlying regions of coastal upwelling are of profound importance to studies of palaeoceanography and palaeoclimatology alike the primary control on coastal upwelling wind stress and resulting ekman transport is linked intimately to variation in the earth s insolation record via a variety of feedback mechanisms in comparison the nutrients required to sustain productivity and the factors affecting the c org content of the sediment are related to variation in global glacial boundary conditions using a variety of geochemical indicators it is apparent that the record of upwelling off northwest africa driven by the northeast trade winds is characterized by arid glacial conditions and high wind stress sustaining elevated euphotic zone productivity the resulting c org accumulation record reflects higher palaeoproductivity during glacial episodes in contrast the arabian sea upwelling is seasonal faunal and geochemical ba al u th ratios indicators suggest strong interglacial 23 ka cyclicity in the southwest monsoon the c org record is spatially and temporally consistent but in disagreement with other palaeoproductivity indicators these results point to the decoupling of surface ocean productivity in areas of coastal upwelling from deep ocean circulation and nutrient supply this result has important consequences for driving atmospheric p co 2 changes on timescales less than that of oceanic mixing further applications of geochemical tracers to areas of coastal upwelling such as northwest africa and peru are needed urgently

middle miocene climate cooling linked to intensification of eastern equatorial pacific upwelling during the middle miocene earth s climate transitioned from a relatively warm phase miocene climatic optimum to a colder mode with reestablishment of permanent ice sheets on antarctica thus marking a fundamental step in cenozoic cooling carbon sequestration and atmospheric co2 drawdown through increased terrestrial and or marine productivity have been proposed as the main drivers of this fundamental transition we integrate high resolution 1 3 k y benthic stable isotope data with x ray fluorescence scanner derived biogenic silica and carbonate accumulation estimates in an exceptionally well preserved sedimentary archive recovered at integrated ocean drilling program site u1338 to reconstruct eastern equatorial pacific productivity variations and to investigate temporal links between high and low latitude climate change over the interval 16 13 ma our records show that the climatic optimum 16 8 14 7 ma was characterized by high amplitude climate variations marked by intense perturbations of the carbon cycle episodes of peak warmth at southern hemisphere insolation maxima coincided with transient shoaling of the carbonate compensation depth and enhanced carbonate dissolution in the deep ocean a switch to obliquity paced climate variability after 14 7 ma concurred with a general improvement in carbonate preservation and the onset of step wise global cooling culminating with extensive ice growth over antarctica ca 13 8 ma we find that two massive increases in opal accumulation ca 14 0 and ca 13 8 ma occurred just before and during the final and most prominent cooling step supporting the hypothesis that enhanced siliceous productivity in the eastern equatorial pacific contributed to co2 drawdown

late pleistocene paleoclimatology of the central equatorial pacific flux patterns of biogenic sediments high resolution records of the concentration and mass accumulation rate mar or flux of biogenic sediments from core rc11 210 in the central equatorial pacific are compared for the entire late pleistocene the fluxes of calcium carbonate and organic carbon correlate well the opal flux pattern shows no direct correlation with the other two rather opal flux maxima correlate with slopes of i e both precede and follow the organic carbon and carbonate mar peaks organic carbon and calcite therefore may both be better indicators of past productivity than opal which is an indicator of transition at this location we interpret the sequence low biogenic fluxes high opal fluxes high carbonate carbon and opal fluxes as representing the transition from low to high sea surface biological productivity the phase relationships for eccentricity of the biogenic sedimentation records were compared to those of other climatic indications including the oxygen isotope record of ice volume the ice core co2 record the pacific 13c record the deep nutrient cd ca record and the eolian grain size record of wind intensity we find that starting from maximum ice volume phase angle of 0 the phase relationships of the 100 000 year periodicity show in the first quadrant maximum wind intensity 30 and maximum calcite and carbon flux 45 occurring first followed by maximum opal flux 75 and then maximum deep nutrients 95 minimum pacific 13c occurs at a phase angle of 155 the maximum co2 in the vostok record and minimum ice volume is at 180 thus in the eccentricity climate cycle glacial conditions lead to stronger wind driven circulation which enhances productivity which in turn results in enhanced oceanic and atmospheric carbon dioxide and minimum ice volume

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr