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

late pliocene climatic change and the onset of northern hemisphere glaciation as recorded in the northeast atlantic ocean the relative abundances of planktonic foraminifera oxygen isotope values of benthic foraminifera and the sedimentology of 156 samples from deep sea drilling project international phase of ocean drilling site 548 in the northeast atlantic ocean have been analyzed for the time span from about 3 5 to 2 0 m y b p the planktonic assemblage at site 548 in the late pliocene consisted mainly of subpolar to temperate species warm water species were rare the planktonic record shows that waters in the northeast atlantic were warm temperate before 3 4 m y ago and gradually changed to subpolar through a series of steps by 2 0 m y b p an initial cooling event occurred between about 3 4 and 3 1 m y b p the beginning of this cooling event preceded the global benthic isotopic shift at 3 2 to 3 1 m y b p but the isotopic shift correlates to a marked change in the planktonic assemblage suggesting that the cause of the shift also affected northeast atlantic surface circulation following the 3 4 to 3 1 m y b p cooling event the assemblages at site 548 indicate a return of temperate waters at this time however the assemblages also became quite variable with a clear cyclicity from about 2 6 m y b p onward there is a progressive cooling recorded at site 548 leading to marked glaciations beginning at about 2 4 m y b p about 2 0 m y b p the planktonic assemblages were dominated by cold water species and became quite stable contrasting markedly with the immediately preceding interval of glaciation and extreme variability the cyclicity seen in the faunal data after about 3 1 m y b p is principally of one period with a cycle length closest to that of the earth9s obliquity and its influence on global insolation the effect of obliquity on the earth9s insolation is most strongly felt at high latitudes and so the cyclicity at site 548 indicates that conditions in the arctic have exerted an influence on the northeast atlantic since at least 3 m y ago calculation of global insolation fluctuations for the late pliocene shows that the major changes in the planktonic record at site 548 cannot be explained by insolation variation except for the period of stability at 2 0 m y b p which corresponds to a time of stable insolation the planktonic data however do contain cyclicity that can be related to the periodicity of the earth9s orbital elements

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

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

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

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

carbonate dissolution in recent sediments of the eastern equatorial indian ocean preservation patterns and carbonate loss above the lysocline abstract multiple dissolution indices from 45 sediment samples show that the foraminiferal lysocline is near 3800 m in the eastern equatorial indian ocean close to the saturation horizon with respect to calcite in the water column below the lysocline the increase in foraminiferal fragmentation decrease in absolute abundance and progressive modification of planktic foraminiferal assemblages with depth is accompanied by an increasing rate of loss of carbonate from the sediments above the lysocline some dissolution must occur in order to produce the dramatic reduction in foraminiferal numbers up to 60 and the pattern of increased fragmentation with depth however the amount of carbonate actually lost from supralysoclinal sediments reaches at most 20 30 of the total at the depth of the lysocline the principal driving force behind supralysoclinal dissolution is most likely the oxidation of organic matter incorporated into the sediments dissolution above the lysocline has a greater apparent impact on relative preservation in the coarse 150 m fraction than it does on total carbonate loss because of redistribution of carbonate to the finer size fractions as fragments though the effects of dissolution on foraminiferal preservation are clearly visible at all depths the lysocline itself does appear to mark the local onset of large scale loss of dissolved carbonate from the sediments such an interpretation is broadly consistent with models regarding the saturation state of the overlying waters as the principal driving force behind the preservation or dissolution of recent carbonate sediments on the sea floor

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

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

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

the influence of organic matter diagenesis on caco3 dissolution at the deep sea floor abstract in situ benthic flux chamber measurements were performed at seafloor locations in the atlantic and pacific oceans where the bottomwaters were supersaturated approximately saturated and undersaturated with respect to calcite there was no evidence of significant dissolution at or above the saturation horizon below the saturation horizon however significant benthic fluxes of titration alkalinity and calcium out of the sediments were observed indicating appreciable dissolution where observed the rate of dissolution is consistent with a rate expression of reaction order 4 5 and a rate constant in the range of 0 05 to 0 5 per day a numerical simulation was constructed to represent organic matter and caco3 diagenesis at the seafloor at the supersaturated and near saturation sites the model over predicts the influence of metabolically produced co2 on the extent of caco3 dissolution it is possible that these results can be reconciled by a better understanding and parameterization of organic matter mineralization and porewater transport processes in surface sediments the primary factors to be considered include 1 the oxidation state of the carbon being oxidized 2 the vertical distribution of oxidation rates including the role of doc in sediment remineralization 3 the influence of nondiffusive transport of near surface porewaters and 4 the influence of episodic depositional events on organic and inorganic carbon cycling

a new paleomagnetic pole for the neoproterozoic uinta mountain supergroup central rocky mountain states usa abstract hematite cemented strata of the neoproterozoic age 800 750 ma uinta mountain group umg provide a new well defined mid neoproterozoic paleomagnetic pole for laurentia thermal demagnetization results and rock magnetic experiments reveal the presence of two discrete magnetizations in umg rocks both magnetizations are carried by hematite the dominant characteristic remanent magnetization chrm is an east directed or antipode shallow positive to negative inclination magnetization that is typically unblocked over a narrow range of high laboratory temperatures between 660 and 680 c the second magnetization exclusively of normal polarity is north to northeast directed and has a moderate to steep positive inclination and probably represents a recent or modern day viscous remanent magnetization the response of umg samples to thermal and chemical demagnetization comparison with previously obtained data from umg rocks in the area results from rock magnetic experiments and the inferred low latitude of laurentia during umg deposition in the neoproterozoic are all consistent with the interpretation that the west or east directed shallow magnetization is a near primary remanence the presence of dual polarities of the chrm with the west directed remanence inferred to be of normal polarity and the east directed of reverse polarity suggests that magnetization acquisition in the umg rocks took place over a sufficient amount of time to average secular variation of the geomagnetic field the mean paleomagnetic pole derived from the inferred primary magnetizations from umg strata 0 8 n 161 3 e 95 4 6 n 9 sampling localities consisting of 79 sites is fully consistent with recently reported results from rocks of mid neoproterozoic age for southwest laurentia which define a tight counterclockwise loop located in the south pacific in the apparent polar wander path for laurentia during the neoproterozoic

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

calcium carbonate preservation patterns in the central north atlantic during the last 150 000 years abstract the dissolution record of the canary and eastern north american basins was examined in 15 cores spanning the last 150 000 years stratigraphic control was based on fluctuations in percent carbonate and 18 0 16 0 dissolution changes were determined based on variations in percent planktonic foraminiferal fragments and benthonic foraminifera results indicate three main dissolution events coincident with 18 0 stages 2 4 and 6 the lysocline apparently shallowed about 300 m in the canary basin at these times there is no simple linear relationship between dissolution intensity and ice volume dissolution was more intense during stage 4 than during stage 2 even though 18 0 records indicate the reverse is true for ice volume also carbonate preservation during the lower part of stage 3 is comparable to stages 1 and 5e a comparison of atlantic pacific carbonate dissolution patterns indicates a tendency for out of phase preservation patterns in 18 0 stages 1 and 2 and an in phase dissolution event during stage 4 the out of phase pattern may partially reflect variations in the production rate of north atlantic deep water the in phase dissolution peak correlates with a major cooling regression transport of organic carbon from transient shallow reservoirs into the deep sea could have contributed to formation of such a pattern however additional evidence from longer atlantic pacific records is needed before the shelf basin model can be more fully evaluated

pliocene pleistocene oxygen isotope record site 586 ontong java plateau abstract oceanographic changes in the western equatorial pacific during the past 6 ma are inferred from oxygen isotopic analyses of planktic and benthic foraminifera from ontong java plateau dsdp site 586 the taxa areglobigerinoides sacculifer pulleniatina cibicidoides wuellerstorfi andoridorsalis umbonatus cooling and ice buildup are indicated by an18o enrichment of 0 3 in the planktic species near 3 4 ma this shift apparently is compensated in the benthic data by a warming of the deep waters by between 1 and 2 c we suggest that the dominant source of upper deep water supply to the pacific changed from antarctic to north atlantic at that time the north atlantic derived water being warmer near 2 8 ma approximately the planktic foraminifera again record an enrichment in18o 18o 0 25 we suggest ice buildup in the northern hemisphere as the cause because of subsequent sharp increase in fluctuations of the 18o signal that is instability the enrichment is magnified in the benthic foraminifera 18o 0 5 by a cooling of the deep water by 1 5 at the time presumably signalling a glacial type reduction of north atlantic deep water nadw production episodic divergence between the signals ofg sacculifer andpulleniatina in the pleistocene apparently reflects periods of increased upwelling in the western equatorial pacific the amplitude of ice volume fluctuations cannot be reconstructed from 18o data alone unless there are constraints on temperature variations the increase in amplitude of fluctuation of the benthic and planktic signals during the pleistocene may be attributed either to an increase in maximum ice volume or to an increase in the fractionation of continental ice or a combination of both causes

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

closure of the central american isthmus and its effect on deep water formation in the north atlantic modern ocean thermohaline driven circulation influences global climate by transporting heat to high latitudes1 2 and by affecting the exchange of co2 between ocean and atmosphere3 north atlantic deep water nadw plays a key role in this circulation and quaternary climate cycles have been linked to changes in nadw flow4 general circulation model simulations indicate that before closure some 3 4 million years ago of the central american isthmus the narrow strip of land linking north and south america the direct flow of low salinity water from the pacific to the atlantic ocean would have led to a smaller nadw flow5 6 sedimentation patterns7 and nutrient proxies8 11 support these model results by indicating an increase in nadw flow around the time of isthmus closure but these records do not allow changes in different nadw sources to be distinguished and the overall effect of closure on global ocean circulation is poorly known here we present nd pb and sr isotope records preserved by a hydrogenous ferromanganese crust from the nadw flow path in the western north atlantic ocean these records indicate that the isotopic signal associated with nadw strengthened around 3 4 million years ago showing that deep water that formed in the labrador sea made a gradually increasing contribution to nadw flow these data taken together with those from the central pacific ocean12 indicate an increased nadw flow since isthmus closure and suggest that the closure established today s general pattern of ocean circulation

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

pleistocene dissolution fluctuations from apparent depth of deposition in core erdc 127p west equatorial pacific partial dissolution of deep sea carbonates changes grain size distributions as sand size particles break up and debris accumulates in the fine fractions these patterns can be used to describe quantitatively the preservation state of the sediment the state at any one horizon in the sediment column is determined by the original conditions at the time of deposition and by subsequent diagenesis detection of the diagenesis effect is possible using observations on shell preservation in a resistant species of planktonic foraminifera pulleniatina obliquiloculata to predict the grain size distributions which could be expected in non diagenetic conditions expected and observed grain size distributions deviate from each other in the sediments older than 470 000 years this is taken as an indication of recrystallization the original preservation state as far as recoverable is expressed as apparent depth of deposition add which allows direct comparison of preservation records between different sites and different studies in the case of ontong java plateau the add is typically seen to vary over an interval of 900 m or more with the present add being near the minimum of the range signifying maximum dissolution the fluctuations of the add through the last 700 000 years follow those in the 18o record indicating climatic control interglacials correspond to deeper add levels and glacials to shallower ones i e the sediments appear as if they were deposited in shallower depths during glacials this parallels the familiar carbonate cycles of the equatorial pacific which show greater carbonate accumulation during the cold stages

a narrowly spaced double seismic zone in the subducting nazca plate 1 high precision relocations of intermediate depth earthquakes 80 130 km below the central andes reveal a fine scale double layered wadati benioff zone wbz upper and lower band of seismicity are separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle respectively analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events earthquakes in the oceanic crust occur on pre existing normal faults due to hydraulic embrittlement from metamorphic dehydration and on subvertical faults that connect the two layers in a narrow depth range extensional faulting predominates in both layers indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the nazca plate

carbonate preservation history in the peru basin paleoceanographic implications we studied preservation dissolution cycles and paleoproductivity in eight sediment cores from the peru basin south of the highly productive surface waters of the eastern equatorial pacific stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy sediment cores which span the last 8 m y were retrieved during cruise 79 with rv sonne close to the carbonate compensation depth ccd in general sediments show pacific type carbonate cycles we interpret a pronounced carbonate peak between 6 and 7 ma as the result of a western and northern extension of the highly productive peru current decreased carbonate contents from the late miocene to the late pliocene might be associated with a slow contraction of the latitudinal extent of the high productivity belt north of the study areas during the pliocene carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets which should have been associated with pulsations of the antarctic ice cap an abrupt collapse of the carbonate system occurred at 2 4 ma higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation during the quaternary carbonate fluxes are high during glacials and low during interglacials large amplitude variations with long broad minima and maxima associated with small migrations of the lysocline and the ccd 200 m are indicative of the preservation dissolution history in the peru basin during the early pleistocene climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record during the last 800 kyr variability in the carbonate record was dominated by the 100 kyr eccentricity cycle fluxes of biogenic material calcium carbonate organic carbon opal and barium were greatest during glacials which imply higher productivity and export production of the peru current during cold climatic periods dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate after the mid brunhes event 400 ka we observe a plateaulike shift to enhanced dissolution and to intensified productivity

pliocene calcium carbonate sedimentation patterns of the ontong java plateau odp sites 804 and 806 abstract two deep sea cores from the northeastern slope of the ontong java plateau ocean drilling program site 806 2520 mbsl and site 804 3861 mbsl has been studied with the purpose of investigating pliocene site 806 2 4 3 8 ma site 804 1 8 4 4 ma sub and supralysoclinal changes in calcium carbonate accumulation based on caco3 coarse fraction and faunal data at the shallower site site 806 there is a slight decrease in carbonate content and a distinct long term trend in decreasing accumulation rate throughout the studied interval small scale changes in density hence accumulation rate are related to grain size changes due to winnowing at this site but the overall pattern of decreasing carbonate accumulation seems to be the result of both winnowing and a decrease in productivity the deeper site site 804 exhibits a general increase in carbonate content after about 3 15 ma as well as a long term increase in mass accumulation rate throughout the pliocene interval studied detailed comparison of the records of density and carbonate content emphasizes the strong relationship between carbonate content and accumulation rate at this site the observed pattern of decreasing accumulation rate at shallow depth parallel to enhanced preservation at greater depths may be explained by a decrease in the production of north atlantic deep water nadw a reduction of the volume of nadw pumped into the pacific would reduce the supply of nutrients and deep water co2 this could account for both the decrease in accumulation rate at the shallower site due to decreased productivity and the enhanced preservation at the deeper site due to a decrease in the corrosiveness of deep waters

isotopic paleoceanography of the caribbean and east pacific role of panama uplift in late neogene time comparisons of carbon isotopic data on benthic foraminifera from deep sea drilling project sites 502 western caribbean and 503 eastern pacific indicate that the difference between the atlantic and the pacific in the per mil enrichment in carbon 13 of total dissolved carbon dioxide increased about 6 million years ago and again 3 million years ago when the difference reached the modern level 1 per mil comparisons of planktonic foraminiferal oxygen isotopic data for the caribbean and the pacific suggest that the salinity of caribbean surface waters began increasing 4 million years ago possibly in response to shoaling of the panama isthmus these results suggest that modern circulation patterns in the caribbean and eastern pacific developed by 3 million years ago in concert with changing tectonic climatic and biogeographic patterns

neogene carbonate stratigraphy of ontong java plateau western equatorial pacific three unexpected findings the neogene carbonate stratigraphy of five sites drilled on ontong java plateau during leg 130 reveals a number of patterns which are unexpected and which we refer to as loss paradox equatorial insensitivity and climate paradox they denote the following unresolved questions 1 the loss of carbonate at depth as derived from differences in accumulation rates is much greater than suggested by the change in carbonate percentages calculated under the assumption that carbonate dissolution is the cause of loss this indicates an important role for redeposition processes such as winnowing bottom currents sifting resuspension and catabatic flow and episodic sloughing or solifluction presumably stimulated by earthquakes 2 accumulation rates are not markedly increased at the time a site crosses the equator there are several possible reasons equatorial upwelling may be unimportant in controlling sedimentation rates this far in the western pacific or its output may be spread over a considerable distance from the equator alternatively increased supply below the equator is compensated for by increased removal e g from resuspension by bioturbation combined with catabatic flow it is conceivable that errors in the timescale could also produce the effect seen 3 there is an overall tendency for agreement between the stratigraphic patterns of carbonate content and of accumulation rates but neither pattern is readily explained by reference to changes in climate represented by benthic 18o or in sea level as derived from sequence stratigraphy

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

late quaternary caco3 production and preservation in the southern ocean implications for oceanic and atmospheric carbon cycling recent geochemical models invoke ocean alkalinity changes particularly in the surface southern ocean to explain glacial age pco2 reduction in such models alkalinity increases in glacial periods are driven by reductions in north atlantic deep water nadw supply which lead to increases in deep water nutrients and dissolution of carbonate sediments and to increased alkalinity of circumpolar deep water upwelling in the surface southern ocean we use cores from the southeast indian ridge and from the deep cape basin in the south atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by circumpolar deep water this suggests that deep southern ocean carbonate ion concentrations were lower in glacial stages than in interglacials rather than higher as suggested by the polar alkalinity model broecker and peng 1989 our observations show that changes in southern ocean caco3 preservation are coherent with changes in the relative flux of nadw suggesting that southern ocean carbonate chemistry is closely linked to changes in deepwater circulation the pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient depleted water nadw to the southern ocean and with an increase of nutrients in deep water masses carbonate mass accumulation rates on the southeast indian ridge 3200 3800 m and in relatively shallow cores 3000 m from the kerguelen plateau and the south pacific were significantly reduced during glacial stages by about 50 the reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in caco3 corg flux ratios acting as another mechanism which would raise the alkalinity of southern ocean surface waters the polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant even if overall productivity in the southern ocean were held constant a decrease in the caco3 corg ratio would result in increased alkalinity and reduced pco2 in southern ocean surface waters during glacials this ecologically driven surface alkalinity change may enhance deepwater mediated changes in alkalinity and amplify rapid changes in pco2

calcite dissolution and the modification of planktonic foraminiferal assemblages abstract the results of an in situ experiment in the panama basin allow us to determine the way in which planktonic foraminiferal assemblages are modified by calcite dissolution pre weighed planktonic foraminiferal samples of known species composition were attached to a deep sea mooring at various water depths between 665 m and 3791 m for a period of 123 days weight loss due to dissolution during this period ranged from less than 5 for the shallowest samples to slightly over 30 for the deepest samples in terms of change in foraminiferal number this is equivalent to decreases of between 1 and 26 only in the samples placed at the two deepest levels 3769 m and 3791 m was there a significant loss in the total number of foraminifera the magnitude of change in the abundance of individual species in early related to their different susceptibilities to dissolution species such as hastigerina pelagica globigerinella aequilateralis and candeina nitida which are very susceptible to dissolution exhibited the largest decreases in frequency percentage while the more resistent species sphaeroidinella dehiscens pulleniatina obliquiloculata and globorotalia truncatulinoides had minimal changes from these results a solution susceptibility ranking for planktonic foraminifera is established that is quite similar to those derived from previous laboratory experiments and sea floor studies

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