geochemical reconstruction of pacific decadal variability from the eastern north pacific during the holocene determining climate variations over the holocene requires high resolution records with well developed age models a 40 m long marine sediment core raised from effingham inlet an anoxic fjord on the west coast of vancouver island british columbia canada yields such a record forty six 14c accelerator mass spectrometry ams dates determined from terrestrial plant material form the age model downcore sampling at both 5 cm 20 year and 1 5 cm 7 year resolution indicates that high frequency oceanographic variability has prevailed at this site over the last 10 000 years spectral analysis of wt opal a proxy for diatom productivity in the basin reveals the bidecadal and pentadecadal periods of the pacific decadal oscillation pdo north pacific index npi that are related to changes in the strength of the aleutian low coherence analysis between the effingham inlet data and 18o records from jellybean lake a high elevation site in southwest yukon indicates regional coherence at periods of 45 7

a 300 kyr high resolution aridity record of the north african continent new oxygen isotope data and a high resolution carbonate record of a core from the northwest african margin are presented in combination with geochemical zr rb ratio al ba organic carbon and biogenic opal fluxes and sedimentological median grain size parameters to show variations in african continental aridity wind strength and upwelling productivity the carbonate record is diluted by the supply of aeolian dust from the arid saharan region of north africa and is seen to vary with a characteristic sawtooth pattern indicating rapid increases in dust flux followed by gradual declines spectral analysis of the carbonate profile and comparison with specmap stacked oxygen isotope and etp solar radiation profiles shows that the precessional 23 kyr insolation induced african climate system is decoupled from global ice volume climate changes operating on a 100 kyr frequency detailed studies of glacial terminations i ii and iii confirm the presence of rapid short timescale climatic variations in aridity

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

controls on the distribution of deep sea sediments deep sea sediments represent the largest geological deposit on earth and provide a record of our planet s response to conditions at the sea surface from where the bulk of material originates we use a machine learning method to analyze how the distribution of 14 400 deep sea sediment sample lithologies is connected to bathymetry and surface oceanographic parameters our probabilistic gaussian process classifier shows that the geographic occurrence of five major lithologies in the world s ocean can be predicted using just three parameters sea surface salinity and temperature provide a major control for the growth and composition of plankton and specific ranges are also associated with the influx of non aerosol terrigenous material into the ocean while bathymetry is an important parameter for discriminating the occurrence of calcareous sediment clay and coarse lithogenous sediment from each other we find that calcareous and siliceous oozes are not linked to high surface productivity diatom and radiolarian oozes are associated with low salinities at the surface but with discrete ranges of temperatures reflecting the diversity of planktonic species in different climatic zones biosiliceous sediments cannot be used to infer paleodepth but are good indicators of paleotemperature and paleosalinity our analysis provides a new framework for constraining paleosurface ocean environments from the geological record of deep sea sediments it shows that small shifts in salinity and temperature significantly affect the lithology of seafloor sediment as deep sea sediments represent the largest carbon sink on earth these shifts need to be considered in the context of global ocean warming

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

pre quaternary landforms in the low latitude context the example of australia abstract direct effects of quaternary glaciation and periglacial activity affected only comparatively small areas of southeastern australia certainly volcanicity continued in a few districts extensive new planation surfaces were formed dunefields were widely developed and there were important developments at the coastline and offshore during this period but many pre quaternary terrains persist in the contemporary landscape tertiary volcanic plains and plateaux are widespread in the eastern uplands and duricrusted ferruginised silicified remnants some of them folded are characteristic of many parts of the central and western sectors of the continent drainage systems of similar age are also increasingly recognised older gondwanan elements also feature prominently but especially in the eastern uplands and on the craton some of these ancient elements are exhumed but others are epigene and etched though the so called epigene surfaces are mostly of etch type the survival of the ancient epigene and etch forms is attributed to resistance of bedrock through drainage unequal activity and reinforcement mechanisms

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

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

clinoptilolite as a new proxy of enhanced biogenic silica productivity in lower miocene carbonate sediments of the bahamas platform isotopic and thermodynamic evidence abstract massive clinoptilolite authigenesis was observed at about 1105 meters below sea floor mbsf in lower miocene well compacted carbonate periplatform sediments from the great bahama bank ocean drilling program odp leg 166 site 1007 the diagenetic assemblage comprises abundant zeolite crystallized within foraminifer tests and sedimentary matrix as well as mg smectites in carbonate rich deposits the formation of the zeolite requires a supply of silica thus the objective of the study is to determine the origin of the silica supply its diagenetic evolution and consequently the related implications on interpretation of the sedimentary record in terms of local or global paleoceanographic change for lack of evidence for any volcaniclastic input or traces of si enriched deep fluids circulation an in situ biogenic source of silica is validated by isotopic data and chemical modeling for the formation of such secondary minerals in shallow water carbonate sequences geochemical and strontium isotopic data clearly establish the marine signature of the diagenetic zeolite as well as its contemporaneous formation with the carbonate deposition sr model ages of 19 6 23 2 ma the test of saturation for the pore fluids specifies the equilibrium state of the present mineralogical assemblage seawater rock modeling specifies that clinoptilolite precipitates from the dissolution of biogenic silica which reacts with clay minerals the amount of silica opal a involved in the reaction has to be significant enough at least 10 wt to account for the observed content of clinoptilolite occurring at the most zeolite rich level modeling also shows that the observed amount of clinoptilolite 19 reflects an in situ and short term reaction due to the high reactivity of primary biogenic silica opal a until its complete depletion the episodic occurrence of these well lithified zeolite rich levels is consistent with the occurrence of seismic reflectors particularly the p2 seismic sequence boundary located at 1115 mbsf depth and dated as 23 2 ma the age range of most zeolitic sedimentary levels biostratigraphic ages of 21 5 22 ma correlates well with that of the early miocene glaciation mi 1 and mi 1a global events thus the clinoptilolite occurrence in the shallow carbonate platform environment far from volcanogenic supply or in other sensitive marine areas is potentially a significant new proxy for paleoproductivity and oceanic global events such as the miocene events which are usually recognized in deep sea pelagic sediments and high latitude deposits

organic carbon accumulation over the last 16 kyr off vancouver island canada evidence for increased marine productivity during the deglacial abstract the organic carbon content of marine sediments is commonly used as a proxy for export production however in continental margin sediments a large fraction of the organic matter may be of terrestrial origin and it is necessary to correct the total organic carbon data accordingly radiocarbon dating of bulk organic carbon organic geochemistry and isotope data 13c and 15n are used here to characterize the type of organic matter present in core jt96 09 collected at a water depth of 920 m on the slope off western canada the quantities of marine and terrestrial organic carbon are then estimated using the 13c data the 16 kyr record obtained from core jt96 09 suggests that accumulation of total organic carbon was highest during the late glacial and deglacial but geochemical data indicate that as much as 70 of this carbon is terrestrial in origin when the palaeo record is corrected for this terrigenous input it is observed that accumulation of marine organic matter and presumably marine export production increased at the end of the last glacial contemporaneous with the bolling and that it peaked during the allerod data from other palaeoproductivity proxies i e bio barium opal and alkenones also indicate relatively high productivity during the deglacial these results indicate a return to modern upwelling conditions and high marine export production at 14 3 calendar kyr bp and a period of enhanced upwelling relative to the present during the allerod

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

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

variation of baseflows in the headstreams of the tarim river basin during 1960 2007 summary the tarim river is the largest inland river of china and a major water resource to the vast arid region in northwest china for its four major headstreams which contribute 98 of the tarim river s streamflow we investigated the dynamics of baseflow in the past 50 years the digital filtering method was used to separate baseflow from surface flow after which the baseflow index bfi was calculated and analyzed the major findings of this study include 1 baseflows of the four headstreams have increased considerably over the past 50 years the large baseflow index bfi usually occurred in the wet years but the change rate was irregular because of the increasing recharge from snow and glacial meltwater 2 the annual baseflow variation of the four headstreams appeared to have cycles of 3 5 years 10 14 years and 25 years 3 the baseflow and bfi showed obvious seasonal variation the lowest baseflow and bfi typically occurred in december and january and both increased gradually until the maximums reached in august or july 4 the responses of runoff and baseflow to climatic factors were different precipitation possessed a great impact on runoff whereas temperature possessed a great impact on baseflow baseflow is an important source to the tarim river and is affected by the increasing snow and glaciers melt as a result of temperature rise for the four headstreams we identified temperature thresholds in the time series of bfi and calculated regression relationships between temperature and bfi in the past 50 years the thresholds and the regression relationships would help to assess and predict the impact of climate change on headwater inflow to the tarim river

alternative modes of quaternary pelagic biosiliceous and carbonate sedimentation a perspective from the east sea japan sea abstract six piston cores 95pc 1 mb97pc 19 ty99 pc18 95pc 3 95pc 4 and 96ebp 4 from the east sea japan sea were examined to assess the fluctuations in carbonate and biogenic silica sedimentation data from four of these cores 95pc 1 mb97pc 19 ty99 pc18 and 96ebp 4 collected from depths above the present carbonate compensation depth ccd clearly show that carbonate content increased during glacial periods and decreased during interglacial periods whereas biogenic silica content shows the opposite pattern the two cores collected below the ccd also show glacial interglacial variations in carbonate and biogenic opal contents with patterns similar to the cores collected above the ccd this study provides strong evidence for cyclic variations of biogenic components corresponding to interglacial glacial cycles even though variations in carbonate and opal contents seem to be affected by dissolution and dilution the inverse correlation between carbonate and biogenic silica contents suggests that two mutually exclusive oceanic modes affected the biogenic sedimentation these modes may have resulted from sea level changes that led to water column stratification during glacial low stands and breakdown of water column stratification and consequent active vertical mixing during interglacial high stands

what controls opal preservation in tropical deep sea sediments measurements of opal preservation in deep sea sediment cores have been presented in three ways the opal concentration as a fraction of total dry weight opaltot the opal concentration normalized to calcite free dry weight opalcalcite free and me opal accumulation rate opal mar it is tempting to interpret changes in these indices as indicators of rates of biological production in past oceans based on theoretical constraints we argue that in typical tropical and subtropical sediments both opalcalcite free and opal mar reflect a significant artifact of dilution by other phases thus the band of high opalcalcite free in the equatorial pacific appears to be caused in large part by the high calcite in that region rather than by high opal productivity the best candidate for a reliable paleoproductivity proxy appears to be opaltot unfortunately present day opaltot data from tropical and subtropical regions show little or no systematic trend with the rain rate of opal pore water silica concentration data reveal that the apparent pore water opal solubility is not constant but correlates regionally with the rain rate of opal to the seafloor a model that treats opal as a single homogeneous phase with a single well defined solubility product predicts a strong dependence of opal concentration on rain rate in stark contrast to the data and a constant asymptotic pore water si two models representing opal as multiple heterogeneous phases with different solubilities are able to reproduce the observed asymptotic pore water si rain rate relationship but not the lack of rain rate trend in the opal concentration data only by assuming a systematic trend in the quality of opal i e the solubility as a function of opal production can we reproduce the observed pattern of opal preservation the implication of this study is that changes in opal preservation in the geologic record cannot simply be interpreted in terms of changes in surface ocean productivity until our understanding of opal diagenesis can be improved

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

asymptotic forms and solutions of the model for silica opal diagenesis in bioturbated sediments early diagenesis of the coupled dissolved silica opal system in bioturbated sediments may be explained by one of three possible models of increasing mathematical complexity i e the simple but unused constant opal model abbreviated c o the schink et al 1975 model abbreviated sg f for which wong and grosch 1978 have supplied an analytical solution designated as w g and the improved but much more sophisticated model proposed by schink and guinasso 1980 that must be solved numerically s g scaling analysis and computational comparisons show that the c o model and the sg f model as calculated via the w g solution are asymptotically valid forms of more complete s g model for the limits of large and small opal concentrations respectively specifically the c o model is found to provide an excellent approximation to the vastly more complicated s g model if the amount of opal preserved at depth in the sediment b satisfies the inequality b 0 1 1 db ds cs cw 1 b 1 1 where is the porosity db is the mixing coefficient ds is the tortuosity corrected molecular diffusivity of silica cs is the solubility of opal cw is the silica concentration in the overlying waters b is the intrinsic density of opal and is a unit conversion constant if b and c are in different units schink and guinasso 1980 have criticized wong and grosch 1978 for utilizing their solution of the earlier sg f model to describe opal accumulation a situation for which they believed the sg f model was invalid this study has found however that for conditions characteristic of the deep sea the sg f model and so the w g solution remain reasonably accurate even if small amounts of opal escape dissolution and collect but that radical divergence from the s g model can be expected if the flux of silica is sufficient to create a siliceous ooze this reflects the minor role played by the divergence of the advective flux in the balance of terms in the diagenetic conservation equations when little opal is preserved these findings should resolve any uncertainty and controversy over the use of the w g solution opal diagenesis in bioturbated shelf like sediments appears to be adequately described by the c o model alone the c o model coupled where necessary to the w g solution constitutes an attractive alternative to the s g model because relatively simple analytical methods of solution may be employed rather than advanced numerical techniques

early oligocene glaciation and productivity in the eastern equatorial pacific insights into global carbon cycling the onset of sustained antarctic glaciation across the eocene oligocene transition eot marks a pivotal change in earth s climate but our understanding of this event particularly the role of the

dissolved aluminium in interstitial waters of recent terrigenous marine sediments from the north atlantic ocean the vertical distribution of dissolved al in interstitial waters of recent marine sediments has been determined using a fluorimetric analytical method adapted for interstitial water analysis the results suggest that diagenetic reactions occur in the sediment soon after deposition a narrow depth zone acting as a source of dissolved al is found in each core outside this zone al appears to be removed from solution and its concentration decreases to values of 1 5 gal l or less comparable to those of open ocean waters dissolved al and sio2 concentrations in interstitial waters close to the sediment seawater interface are linearly correlated in most cases suggesting that the geochemistry of al may be related to the behaviour of biogenic silica in marine sediments

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

neogene palaeoceanography of chatham rise southwest pacific based on sediment geochemistry approximately one thousand sediment samples from odp site 1123 on the chatham rise east of new zealand have been examined for inorganic elemental concentrations odp 1123 provides a record of sediment drift deposition under the deep western boundary current the main inflow of deep water to the pacific ocean since the early oligocene though a major hiatus spans the late early oligocene to the early miocene normalisation of the elemental concentrations by aluminium was used to allow for the effects of variable carbonate dilution the elemental ratios were used as proxies for sediment composition and as palaeoceanographic indices the samples were collected at a resolution designed to sample adequately any variation in elemental ratios at the scale of the milankovitch orbital cycles the sampled intervals span the early oligocene early miocene mid miocene and late pleistocene to recent anomalous si al k al ti al values in the upper pleistocene section often associated with horizons of low carbonate are attributed to tephras derived from north island not all of the tephras detected geochemically had been detected visually in the cores a total of 37 tephra events between 1 17 ma bp and the present are recognised based on this and the shipboard investigations the tephra events cluster at intervals of approximately 326 000 years 326 ka perhaps due to variations in eruption frequency on north island and or to variations in the regional palaeowind intensity and direction in the late pleistocene to recent p al inferred nutrient availability percent calcium carbonate caco3 and ba al inferred productivity varied regularly at a period of 40 000 years with these factors lagging minimum global ice volumes interglacials during the mid miocene caco3 ba al p al and si al all gradually increased with caco3 and p al showing regular 138 000 yr cyclicity and ba al showing 44 ka cyclicity inferred productivity ba al may have been rising in association with increasing nutrient availability p al at the same time as increased vigour of the deep western boundary current that was connected to a period of rapid ice sheet growth in antarctica in the early miocene p al and si al were much higher than subsequently and both caco3 and p al exhibited 131 000 yr cycles by far the highest nutrient levels and inferred productivity at this site apparently occurred during the early oligocene as revealed by long term changes in p al and si al a progressive rise in k al but stable ti al from the early oligocene to the recent probably indicates increased proportions of illite in the clay mineral fraction of the drift sediments caused by increased flux of debris from the southern alps

dissolution and preservation of antarctic diatoms and the effect on sediment thanatocoenoses abstract comparison of southern ocean diatom populations from i surface ocean production ii underlying antarctic sediments and iii laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in southern ocean sediments increasing dissolution causes relative depletions in n kerguelensis k enrichments in t lentiginosa l and slight enrichments in e antarctica a this reflects the relative susceptibility to dissolution of the three species that dominate antarctic sediments we have devised a preservation index for the southern ocean based on the ratio k k l to estimate relative extents of dissolution and applied it to natural assemblages holocene southern ocean sediments display increasing opal preservation toward higher latitudes but south of the antarctic polar front preservation decreases in the order well preserved se indian s atlantic sw indian se pacific poorly preserved dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum lgm sediments of the indian and pacific sectors but in the atlantic increased e antarctica abundances at lgm must have resulted from an increase in surface ocean production of this species holocene and lgm diatoms in atlantic and pacific sector sediments are equally well preserved but in the indian sectors holocene sediments are better preserved than those of lgm age paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution

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