an effect of dissolved nutrient concentrations on alkenone based temperature estimates the ratio of 37 carbon diunsaturated to diunsaturated and triunsaturated alkenones uk 37 produced by some haptophytes is widely used as a proxy for past sea surface temperatures however our isothermal culturing experiments with emiliania huxleyi clone ccmp372 show uk 37 values to also vary with nutrient availability and cell division rate these results provide a reasonable explanation for large isothermal variation in uk 37 values of single coccolithophorid strains grown in culture they also suggest that alkenone based estimates of past sea surface temperatures may have been influenced by dissolved nutrient concentrations as well as by temperature

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

a monte carlo study of parameters affecting computer simulations of crater saturation density computer models of cratered surfaces often use inputs of uncertain nature and importance this work evaluates the sensitivity of the resulting crater saturation estimates to the input parameters principally applicable to the study of craters upward from 8 km diameter in order of decreasing importance crater saturation simulations are found to be sensitive to 1 the dynamic range of crater diameters used 2 the effectiveness of ejecta blanket obliteration assumed and 3 the number of points taken to describe the crater rim the size of the largest crater in proportion to the size of the simulated surface has no effect on the results when the edges of the simulated surface are correctly treated and craters are not counted simply by integers craters should be counted by their fractions lying within the simulated area a similar procedure is recommended when gathering crater size density data from images

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

review of alkenone calibrations culture water column and sediments 1 i review the status of alkenone unsaturation parameters as proxies for growth temperature and the potential for pco2 estimates using the carbon isotopic composition of alkenones culture studies allow investigators to manipulate parameters that could influence the relative proportions of c37 and c38 ketones in producing organisms and to assess the possible influence of genetic variability on the calibration of unsaturation to growth temperature culture studies suggest large variability in the relation of unsaturation indices to growth temperature and hint that growth rate may play a role along with temperature in controlling unsaturation water column studies match the unsaturation index measured in particulate matter to ambient temperature providing a snapshot of unsaturation temperature relationship in comparison to culture work assemblages of regional water column data sets give more consistent relations of the unsaturation index to temperature although the argument can be made for regional rather than basin wide or global calibrations a much simpler picture emerges from analyzing a global array of core top sediments regressions show that the sedimentary unsaturation indices follow a linear trend that is best correlated to mean annual temperature in the upper 10 m of the overlying water column the regression is indistinguishable from the original prahl et al 1988 culture calibration of the u37k index to growth temperature exceptions occur at high latitudes where the effects of highly seasonal production and the possible influence of salinity may affect the unsaturation index in sediments core top analyses also fail to reveal the variability of other alkenone parameters for example the ratio of c37 to c38 ketones which have been found in culture studies much of the variance that appears in culture and water column calibrations is thus apparently removed in sediments perhaps by temporal averaging the promising paleo pco2 approach based on the isotopic composition of alkenones awaits the arrival of a significant number of core top and stratigraphic studies that will determine the extent to which physiological factors compromise the alkenone paleobarometer

primary production in the arabian sea during the last 135 000 years abstract variations in primary productivity pp have been reconstructed in eutrophic mesotrophic and oligotrophic parts of the arabian sea over the past 135 000 years applying principal component analysis and transfer function to planktic foraminiferal assemblages temporal variation in paleoproductivity is most pronounced in the mesotrophic northern nast site and oligotrophic eastern east site arabian sea and comparatively weak in the western eutrophic geob 3011 1 site in the upwelling area off oman higher pp during interglacials 250 320 g c m 2 year 1 than during cold stages 210 270 g c m 2 year 1 at geob 3011 1 could have been caused by a strengthened upwelling during intensified summer monsoons and increased wind velocities at nast during interglacials pp is estimated to exceed 250 g c m 2 year 1 and during glacials to be as low as 140 180 g c m 2 year 1 these fluctuations may result from a 1 varying impact of filaments that are associated to the oman coastal upwelling and 2 from open ocean upwelling associated to the findlater jet at east highest productivity of about 380 g c m 2 year 1 is documented for the transition from isotope stage 5 to 4 we suggest that during isotope stages 2 4 5 2 the transition 5 4 and the end of stage 6 deep mixing of surface waters was caused by moderate to strong winter monsoons and induced an injection of nutrients into the euphotic layer leading to enhanced primary production the deepening of the mixed layer during these intervals is confirmed by an increased concentration of deep dwelling planktic foraminiferal species a high productivity event in stage 3 displayed by estimated pp values and by planktic foraminifera and radiolaria flux and accumulation rate likely resulted from a combination of intensified sw monsoons with moderate to strong ne monsoons differential response of globigerina bulloides globigerinita glutinata and mixed layer species to the availability of food is suited to subdivide productivity regimes on a temporal and spatial scale

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

identification of dissolution patterns in nannofossil assemblages a high resolution comparison of synchronous records from ceara rise odp leg 154 1 fossil nannoplankton assemblages are controlled by both initial plankton production and dissolution throughout the water column and on the seafloor it is usually assumed that dissolution can be identified by subjective visual assessment of preservation state we have tested this by a quantitative comparison of mid pliocene nannofossil assemblages in two closely located odp sites ceara rise sites 926 and 929 both with apparently good preservation but located respectively above and below the lysocline we demonstrate that despite an absence of obvious qualitative preservation differences dissolution has removed perhaps 80 of the assemblage in the sub lysocline site 929 this has produced consistent distortions in the assemblages and artificially enhanced abundance variations patterns of individual species the results provide strong cautions for palaeoceanographic interpretation of nannofossil data and allow us to uniquely extract a dissolution variation record and provide a detailed ranking of dissolution susceptibility of pliocene nannofossils

el nino controls holocene rabbit and hare populations in baja california abstract the el nino southern oscillation enso is a major source of climatic variation worldwide with significant impacts on modern human and animal populations however few detailed records exist on the long term effects of enso on prehistoric vertebrate populations here we examine how lagomorph rabbit and hare deposition rate population age structure and taxonomic composition from abrigo de los escorpiones a well dated trans holocene vertebrate fauna from northern baja california mexico vary as a function of the frequency of wet el nino events and eastern pacific sea surface temperatures ssts derived from eastern pacific geological records faunal indices vary significantly in response to el nino based precipitation and sst with substantial moisture driven variability in the middle and late holocene the late holocene moisture pulse is coincident with previously documented changes in the population dynamics of other vertebrates including humans as the frequency and intensity of enso is anticipated to vary in the future these results have important implications for change in future vertebrate populations

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

the violent collisional history of asteroid 4 vesta vesta is a large differentiated rocky body in the main asteroid belt that accreted within the first few million years after the formation of the earliest solar system solids the dawn spacecraft extensively imaged vesta s surface revealing a collision dominated history results show that vesta s cratering record has a strong north south dichotomy vesta s northern heavily cratered terrains retain much of their earliest history the southern hemisphere was reset however by two major collisions in more recent times we estimate that the youngest of these impact structures about 500 kilometers across formed about 1 billion years ago in agreement with estimates of vesta asteroid family age based on dynamical and collisional constraints supporting the notion that the vesta asteroid family was formed during this event

phytoplankton mineralization in the tropical and subtropical atlantic ocean organic carbon fluxes to the deep ocean may be enhanced by association with ballast mineral material such as calcite and opal we made simultaneous measurements of the upper ocean production of calcite calcification opal silicification and organic carbon photosynthesis at 14 stations between 42 s and 49 n in the atlantic ocean these measurements confirm the light dependency of calcification and photosynthesis and the substrate dependency of silicification we estimate that mineralizing phytoplankton represent 5 20 of organic carbon fixation with similar contributions from both coccolithophores and diatoms estimates of average turnover times for calcite and phytoplankton carbon are 3 days indicative of their relatively labile nature by comparison average turnover times for opal and particulate organic carbon are 10 days rapid turnover of calcite suggests an important role for the plankton community in removing calcite from the upper ocean comparison of our surface production rates to sediment trap data confirms that 70 of calcite is dissolved in the upper 2 3 km and only a small proportion of total organic carbon 2 reaches the deep ocean

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

postdepositional oxic degradation of alkenones implications for the measurement of palaeo sea surface temperatures free and bound long chain alkenones c37 2 and c37 3 in oxidized and unoxidized sections of four organic matter rich pliocene and miocene madeira abyssal plain turbidites one from ocean drilling program site 951b and three from site 952a were analyzed to determine the effect of severe post depositional oxidation on the value of u37k the profiles of both alkenones across the redox boundary show a preferential degradation of the c37 3 compared to the c37 2 compound because of the high initial u37k values and the way of calculating the u37k this degradation hardly influences the u37k profiles however for lower u37k values measured selective degradation would increase u37k up to 0 17 units equivalent to 5 c for most of the u37k band width much smaller degradation already increases u37k beyond the analytical error 0 017 units consequently for interpreting the u37k record in terms of past sea surface temperatures selective degradation needs serious consideration

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

mapping of the topography of continental ice by inversion of satellite altimeter data satellite altimeter data over ice sheets provide the best tool for mapping their topography and its possible climatic variations however these data are affected by measurement errors orbit errors and slope errors we develop here a three step inversion technique which accommodates the a priori information on the expected topography and correctly handles and propagates the data errors it estimates first a large scale reference surface then maps the residuals related to undulations and finally iteratively corrects the slope error the method is tested on overlapping small fragments of the antarctic ice sheet using a sub set of seasat data finally a topographic map of terre adelie is produced over areas of small slopes the a posteriori error should be of the order of 0 4 m using ers i data it is therefore expected that climatic variations in the ice sheet topography since the introduction of seasat will be observable

long chain alkenones and alkyl alkenoates and the fossil coccolith record of marine sediments long chain n c37 c39 alkenones and alkyl alkenoates are biological markers for sediment inputs of algae from the class prymnesiophyceae which includes the coccolithophorids these compounds have been recognized in many recent and ancient marine sediments but in only a few living algal species notably the ubiquitous coccolithophorid emiliania huxleyi the proven value of long chain alkenones in palaeotemperature assessment prompts an evaluation of their sedimentary record especially their correspondence with coccolithophorid fossils in ancient marine sediments synthesis of available micropalaeontological and molecular data suggests that morphologically related species of the genera crenalithus dictyococcites emiliania gephyrocapsa pseudoemiliania and reticulofenestra all belonging to the family gephyrocapsaceae were potential biological sources of alkenones and alkyl alkenoates in marine sediments deposited since the eocene 45 ma the occurrence of alkenones in cenomanian and albian sediments devoid of nannofossils may be presumed to reflect contributions from ancestors of the gephyrocapsaceae although an investigation of cretaceous samples containing both coccoliths and alkenones would provide further evidence of this proposed correspondence the combination of palaeontological and molecular chemotaxonomic information offers a novel approach to the evaluation of the phylogenetic lineages that link living and extinct algae

the equilibrium size frequency distribution of small craters reveals the effects of distal ejecta on lunar landscape morphology abstract small craters of the lunar maria are observed to be in a state of equilibrium in which the rate of production of new craters is on average equal to the rate of destruction of old craters crater counts of multiple lunar terrains over decades consistently show that the equilibrium cumulative size frequency distribution sfd per unit area of small craters of radius r is proportional r 2 and that the total crater density is a few percent of so called geometric saturation which is the maximum theoretical packing density of circular features while it has long been known that the primary crater destruction mechanism for these small craters is steady diffusive degradation there are few quantitative constraints on the processes that determine the degradation rate of meter to kilometer scale lunar surface features here we combine analytical modeling with a monte carlo landscape evolution code known as the cratered terrain evolution model to place constraints on which processes control the observed equilibrium size frequency distribution for small craters we find that the impacts by small distal ejecta fragments distributed in spatially heterogeneous rays is the largest contributor to the diffusive degradation which controls the equilibrium sfd of small craters other degradation or crater removal mechanisms such cookie cutting ejecta burial seismic shaking and micrometeoroid bombardment likely contribute very little to the diffusive topographic degradation of the lunar maria at the meter scale and larger

glacial interglacial productivity changes recorded by alkenones and microfossils in late pliocene eastern equatorial pacific and atlantic upwelling zones oceanic upwelling regions are highly productive systems that dominate global ocean new production with important implications for cycling of nitrogen and carbon as well as for climate many proxy methods have been proposed to reconstruct past changes in ocean productivity but uncertainties are associated with the interpretation of each here we report new records of calcareous nannofossil assemblages and siliceous fragment abundance from the late pliocene eastern equatorial pacific and atlantic oceans and compare them with records of total c37 alkenone content from the same sediment samples our data show prominent coherent glacial interglacial timescale variability among all three of these time series with remarkable inter correlation lending support to their interpretation as records of climate coupled changes in productivity we infer that prior to the dominance of the relatively well understood modern alkenone synthesising coccolithophores reticulofenestra spp were the principal calcifying alkenone synthesisers during the late pliocene our records suggest that in upwelling areas on orbital timescales total c37 alkenone concentration tracks productivity not only of the alkenone synthesising coccolithophores but also of the wider phytoplankton community including siliceous diatoms these results lend new significance to pre pleistocene records of total c37 alkenone concentration from upwelling regions particularly those from the eastern equatorial pacific today this region accounts for the majority of global ocean to atmosphere co2 efflux and through biological pump invigoration has the capacity to have contributed significantly to oceanic opal burial and drawdown of atmospheric carbon dioxide the strong correlations that we demonstrate between c37 alkenone concentration and other palaeoproductivity proxies suggest that alkenone accumulation may represent a useful means of inferring pre pleistocene carbon cycle changes

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

ocean surface water response to short term climate changes revealed by coccolithophores from the gulf of cadiz ne atlantic and alboran sea w mediterranean the response of coccolithophore assemblages to short term millennial and centennial climatic changes over the last 50 kyr is studied in core m39029 7 from the gulf of cadiz atlantic ocean and core md95 2043 from the alboran sea western mediterranean sea the nannoplankton data are compared with oxygen isotopes u37k sst and other biogeochemical and sedimentological proxies to obtain a new perspective of the paleoceanography and paleoecology of the area during these short term climatic changes coccolithophores indicate that heinrich events he were characterised by the presence of cold low salinity and turbid water masses on both sides of the strait of gibraltar high abundances of the lower photic zone lpz species florisphaera profunda in the gulf of cadiz synchronous with he are interpreted as being an evidence of upper water column stratification on the atlantic side these episodes coincided with input of terrigenous material especially during h2 surface waters during dansgaard oeschger do stadials were also cold and turbid while most of do interstadials were characterised by warm water flora the increase in small placoliths small gephyrocapsa and emiliania huxleyi 4 m which is considered here as a cold water indicator the sharp decrease in large specimens of e huxleyi related to the warming trend in the last deglaciation can be used as a biostratigraphic reference level that marks at least approximately the deglaciation and the beginning of the holocene peaks of f profunda are observed during termination 1 t1 in the alboran sea they are isochronous with the organic rich layer 1 recognised in the western mediterranean in this interval the water column of the region was stratified as a consequence of the global increase in the sea level following the deglaciation quantitative analyses of the coccolithophore assemblage allow us to interpret that coccolithophore production has been higher in the alboran sea than in the gulf of cadiz during the holocene

late quaternary insolation forcing on total organic carbon and c37 alkenone variations in the arabian sea we here present records of total organic carbon toc and c37 alkenones used as indicators for past primary productivity from the western was and eastern arabian sea eas new data from an open ocean site of the was upwelling area are compared with similar records from ocean drilling program odp site 723 from the continental margin off oman and md 900963 from the eas these records together with other proxies used to reconstruct upwelling intensity indicate periods of high productivity in tune with precessional forcing on the basis of their phase relationship to boreal summer insolation they can be divided into three groups in the was differences between monsoonal proxies 1 and productivity 2 document a combined signal of moderate sw monsoon winds and of strengthened and prolonged ne monsoon winds whereas in the eas phasing indicates maximum productivity 3 at times of stronger ne monsoon winds associated with precession related maxima in ice volume

on the reconstruction of upwelling history namibia upwelling in context abstract eastern boundary upwelling is an important aspect of the modern ocean despite the relatively small area involved consequences of increased upwelling during the neogene as a result of intensifying trade winds include increased heat transport by the ocean increased mixing increased fractionation of phosphate from silicate and opportunities for evolution of new species coastal upwelling has been studied since the first decade of the 20th century the processes involved are complex and differ depending on geographic setting off namibia upwelling history has been studied by a number of drilling expeditions the last of these was odp leg 175 which occupied seven sites on the continental slope between walvis ridge and cape town during september and october of 1997 productivity proxies all along southwestern africa suggest the presence of increased upwelling and organic matter supply to the sea floor during glacial periods at the same time there is a decrease in the supply of diatoms and other siliceous plankton remains this is the walvis opal paradox established through the contrasting results of studies by diester haass 1985 and oberhansli 1991 we propose that the walvis opal paradox is fundamental to the understanding of glacial interglacial productivity fluctuations on a global scale furthermore a central feature of the history of late neogene upwelling off namibia is the matuyama opal maximum centered between gauss and olduvai magnetic chrons wefer et al proc odp 175 1998 it is due to the fact that diatom supply first increases during the gauss when the planet cools and then decreases again during additional cooling on entering the quaternary on a 400 000 year scale peak productions are coincident with or slightly lag maximum seasonal contrast potential in the high latitude insolation curve we suggest that this is further evidence that the nutrient content of thermocline waters was diminished during glacial periods the reasons why this should be so remain to be discovered

the onset of the lunar cataclysm as recorded in its ancient crater populations abstract the earliest bombardment history of the moon potentially provides powerful constraints for solar system evolution models a major uncertainty however is how much of this history is actually recorded in lunar craters for example some argue that most ancient lunar craters and basins were produced by a declining bombardment of leftover planetesimals produced by terrestrial planet formation processes others believe that most lunar craters and large basins were formed in a narrow time interval between 3 8 and 4 0 ga the so called lunar cataclysm in the light of recent improvements in our understanding of early solar system evolution it is possible that the contributions from both scenarios could be represented in the lunar crater record if so when did the declining bombardment end and the lunar cataclysm begin here we show using new counts of 15 150 km diameter craters on the most ancient lunar terrains that the craters found on or near nectaris basin appear to have been created by projectiles hitting twice as fast as those that made the oldest craters on various pre nectarian era terrains this dramatic velocity increase is consistent with the existence of a lunar cataclysm and potentially with a late reconfiguration of giant planet orbits which may have strongly modified the source of lunar impactors this work also suggests that the lunar cataclysm may have started near the formation time of nectaris basin this possibility implies that south pole aitken basin spa the largest lunar basin and one of the oldest by superposition was not created during the cataclysm this view is strengthened by our interpretation that a substantial fraction of ancient craters on spa were made by low velocity impactors finally we believe these results shed new light on the impact history of the primordial earth

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

oceanographic considerations for the application of the alkenone based paleotemperature u37k index in the gulf of california abstract alkenone concentrations were determined in sediment trap samples and surficial sediments collected from guaymas basin gulf of california to investigate the factors that control the relationship between the u37k index and sst the results from the sediment trap study reveal a positive correlation r2 0 5 between alkenone fluxes and satellite avhrr sea surface temperature sst and a strong correlation r2 0 9 between u37k and sst over an annual temperature range of 20 c although sst and u37k are tightly coupled throughout two upwelling seasons the relationship deviates from the expression developed by prahl et al 1988 at temperatures higher than 26 c the possible reasons for this deviation are varied but include the observed changes in the coccolithophore species assemblage and the evolution of the thermocline during periods of high sst the seasonal pattern of alkenone fluxes higher fluxes during warm periods observed throughout the 1996 to 1997 study period causes a bias in the annually averaged u37k record resulting in temperature estimates that are 1 c higher than the annual avhrr sst average furthermore the u37k ratios obtained from core top sediments indicate an additional 2 c warm bias in the sedimentary record that may be related to the lateral inputs of alkenones from other regions of the gulf these results highlight the importance of oceanographic processes in determining the alkenone temperature signal that is preserved in sediments after accounting for such effects u37k ratios from a box core were used to reconstruct a sst record extending back to the 18th century for the guaymas basin these results indicate a steady 2 c warming of the surface waters of the gulf from early 1700s to the 1950s followed by a rapid apparent 1 c cooling between the 1950s and the 1980s

modern coccolithophore and carbonate sedimentation along a productivity gradient in the canary islands region seasonal export production and surface accumulation rates abstract coccolithophores one of the main primary and carbonate producers in the surface waters of the canary islands region were investigated to quantify coccolith and coccolith carbonate export fluxes and to determine possible trends in species composition related to different productivity conditions present day fluxes were compared to the long term records of coccolith and carbonate accumulation in holocene sediments underneath the mooring locations coccolithophore flux variations in sediment traps at three stations along an e w transect at approximately 29 n from the upwelling influenced north west african shelf region to the open ocean were recorded from january to september 1997 total coccolith fluxes along the studied transect were highly seasonal with pronounced sedimentation events occurring in february upper traps and march deep traps related to the winter phytoplankton bloom in surface waters while total coccolith flux rates and fluxes of different species at the two oceanic sites lp and estoc were comparable mean 6 4 and 5 4 10 8 coccoliths m 2 d 1 fluxes increased significantly towards the shallower site ebc mean 13 7 10 8 coccoliths m 2 d 1 this gradient points to increased productivity in surface waters at the near shore station probably associated with nutrient rich upwelling filaments detaching from the coast and or the easternmost islands additionally a strong influence of laterally advected coccolith rich material was demonstrated for the deeper sediment traps at the two offshore sites resulting in an increase of mean daily coccolith fluxes by a factor 3 lp and by a factor 2 estoc respectively estimated coccolith carbonate fluxes along the transect were 2 8 g m 2 ebc and 1 2 1 3 g m 2 estoc lp in the upper traps representing 31 33 of the total annual carbonate flux the coccolith carbonate supply was higher in the deeper traps with 63 at lp and 44 at estoc respectively average holocene coccolith and coccolith carbonate accumulation rates derived from surface samples at the mooring locations generally confirm the sediment trap results discrepancies mainly result from near bottom and down slope particle transfer processes which especially influence the site closer to the shelf dissolution processes are likely to affect primarily the deep sediments at the oligotrophic site lp the diverse subtropical coccolithophore assemblages were quite similar in all sediment trap samples from the three mooring sites with three species emiliania huxleyi florisphaera profunda gephyrocapsa ericsonii contributing significantly to the assemblage despite the good correspondence between the assemblage compositions along the transect some trends towards the upwelling influenced site ebc could be observed whereas all gephyrocapsa species mainly g ericsonii respond positively to higher productivity conditions at the near shore station calcidiscus leptoporus and the deep photic zone species f profunda increased in mean relative abundances towards the two offshore sites pointing to a preference for the more stable oligotrophic conditions of the subtropical gyre

physiological impacts on alkenone paleothermometry we conducted isothermal 15 c batch culture experiments with the coccolithophorid emiliania huxleyi strain nepcc 55a to evaluate the extent to which nutrient and light stress contribute to variability in the alkenone unsaturation index u37k alkenone content and composition were constant throughout exponential growth in both experiments when nutrients nitrate and orthophosphate were replete stationary phase nutrient starved cells continued to produce alkenones amassing concentrations alk 3 times higher than those dividing exponentially 1 5 2 pg cell 1 and the u37k of excess alkenone dropped by 0 11 units in contrast 5 days of continuous darkness resulted in a 75 decrease in cellular alk and a significant u37k increase 0 11 units given an established 0 034 unit c response for exponentially growing cells of this strain the observed range of u37k variability at 15 c corresponds to an uncertainty of 3 2 c in predicted growth temperature this level of variability matches that of the global u37k annual mean sea surface temperature calibration for surface marine sediments begging the question what is the physiological condition of alkenone producing cells exported to marine sediments comparison of our laboratory results for a strain of e huxleyi isolated from the subarctic pacific ocean with depth profiles for alkenones in surface waters from two contrasting sites in the northeast pacific ocean suggests that the answer to this question depends on the ocean regime considered a possibility with significant bearing on how stratigraphic u37k records in marine sediments are to be interpreted paleoceanographically

a quantitative assessment of diatom dissolution and late quaternary primary productivity in the eastern equatorial pacific the eastern equatorial pacific eep is an important area for ocean atmosphere carbon exchange and yields different opal accumulation records for sites influenced by equatorial divergence and peru upwelling the divergence zone is characterized by a lower opal accumulation rate during the last glacial compared with the holocene but the reverse is true for the peru upwelling zone as a gauge of opal production versus preservation in the eep differential diatom preservation was investigated via a quantitative four stage preservation index using the vellum of the ubiquitous tropical centric diatom azpeitia nodulifer we find similar dissolution records at both sites from the last glacial maximum lgm through the holocene despite differing accumulation rates implying that production not preservation controlled the accumulation rates thus the increased silica accumulation in the peru upwelling region is related to increased production suggesting higher availability of silica in the photic zone in accord with the silica leakage hypothesis described by matsumoto et al 2002 silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric co global biogeochemical cycles 5 doi 10 1029 2001gb001442 and discussed by richaud et al 2007 furthermore we suggest an ecological control on opal preservation due to silica recycling by diatoms in the water column most likely in the photic zone increased production causes rapid silica recycling and thinner walled frustules resulting in enhanced water column dissolution in this setting diatom dissolution is independent of the rate of accumulation of silica or sediment high opal productivity does not necessarily lead to high preservation as proposed for southern ocean sediments sayles f martin w chase z anderson r 2001 benthic remineralization and burial of biogenic sio2 caco3 organic carbon and detrital material in the southern ocean along a transect at 170 west deep sea research ii 48 4323 4383 our observations are compatible with a production increase in the late deglacial and early holocene as reported by loubere 2001 nutrient and oceanographic changes in the eastern equatorial pacific from the last full glacial to the present global and planetary change 29 77 98 and inferred by spero h and lea d 2002 the cause of carbon isotope maximum events on glacial terminations science 296 522 525 and rickaby r and osborne a 2006 oceanic redistribution of phosphate during the last deglaciation in preparation

alkenone and coccolithophorid species changes in late quaternary sediments from the walvis ridge implications for the alkenone paleotemperature method abstract sea surface temperatures ssts derived from the alkenone u37 record of quaternary sediments may be subject to bias if algae with different temperature sensitivities have contributed to the sedimentary alkenone record the alkenone derived sst records are usually based on a u37 temperature relationship which was measured in culture experiments using the coccolithophorid emiliania huxleyi f g prahl l a muehlhausen and d l zahnle 1988 further evaluation of long chain alkenones as indicators of paleoceanographic conditions geochim cosmochim acta 52 2303 2310 to assess possible effects of past species changes on the u37 temperature signal we have analysed long chain alkenones and coccolithophorids in a late quaternary sediment core from the walvis ridge and compared the results to sst estimates extracted from the 18o record of the planktonic foraminifer globigerinoides ruber alkenones and isotopes were determined over the entire 400 kyr core record while the coccolithophorid study was confined to the last 200 kyr when the most pronounced changes in alkenone content occurred throughout oxygen isotope stages 6 and 5 species of the genus gephyrocapsa were the predominating coccolithophorids e huxleyi began to increase systematically in relative abundance since the stage 5 4 transition became dominant over gephyrocapsa spp during stage 3 and reached the highest abundances in the holocene carbon normalized alkenone concentrations are inversely related to the relative abundances of e huxleyi and directly related to that of gephyrocapsa spp suggesting that species of this genus were the principal alkenone contributors to the sediments nevertheless sst values obtained from the u37 temperature relationship for e huxleyi compare favourably to the isotope derived temperatures the recently reported u37 temperature relationship for a single strain of gephyrocapsa oceanica j k volkman s m barrett s i blackburn and e l sikes 1995 alkenones in gephyrocapsa oceanica implications for studies of paleoclimate geochim cosmochim acta 59 513 520 produces unrealistically high sst values indicating that the temperature response of the examined strain is not typical for the genus gephyrocapsa this is supported by the c37 c38 alkenone ratios of the sediments which are comparable to average ratios reported for e huxleyi but significantly higher than for the g oceanica strain most notably the general accordance of the alkenone characteristics between sediments and e huxleyi persists through stages 8 to 5 and even in times that predate the first appearance of this species 268 ka h r thierstein k r geitzenauer and b molfino 1977 global synchroneity of late quaternary coccolith datum levels validation by oxygen isotopes geology 5 400 404 our results suggest that u37 temperature relationships based on e huxleyi produce reasonable paleo sst estimates even for late quaternary periods when this species was scarce or absent because other alkenone synthesizing algae e g of the genus gephyrocapsa responded similarly to temperature changes

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

crater ejecta scaling laws fundamental forms based on dimensional analysis a model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events general relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation the so called gravity and strength regimes in the gravity regime ejecta velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity this relation implies geometric similarity of ejecta blankets that is the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii in the strength regime ejecta velocities are independent of crater size consequently ejecta blankets are not geometrically similar in this regime for points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws the exponents in these power laws are functions of an exponent that appears in crater radius scaling relations thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta predicted ejection velocities and ejecta blanket profiles based on measured values of are compared to existing measurements of velocities and debris profiles

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

proceedings of a workshop on alkenone based paleoceanographic indicators 1 the papers in this theme derive from a workshop on alkenone based paleoceanographic indicators held at the j erik jonsson center of the national academy of sciences in woods hole massachusetts october 3 6 1999 the papers fall into two groups position papers prepared in advance of the workshop by the leaders of six different working groups and reports prepared during and after the workshop by rapporteurs and members of the working groups their publication here is intended to provide a record of the discussions and thus to serve to the paleoceanographic community an overview of the conference and its participants is also provided

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

the relationship between sedimentary organic carbon isotopic composition and organic biomarker compound concentration abstract a study of organic biomarker compounds which could serve as tracers of terrigenous and marine sedimentary organic matter sources was performed on samples from a 208 7 m hydraulic piston core hole dsdp hole 619 from the hemipelagic pigmy basin in the northern gulf of mexico organic carbon normalized concentrations of total long chain c37 c39 alkenones and some individual c27 c29 desmethyl sterols were determined to be useful proportional indicators tracers of preserved marine and terrigenous organic carbon respectively the alkenones whose only known source is marine phytoplankton of the class prymnesiophyceae generally occurred in higher concentrations in interglacial isotope stages 1 and 5a b than in the intervening glacial stages sterols c27 c29 apparently of a dominantly terrigenous origin occurred in lower concentrations during interglacial stages than in glacial stages tracers of both terrigenous and marine organic matter appear to be affected by the differential diagenetic alteration of the biomarker corg ratios as indicated by a simple first order kinetic model the lack of any desmethylor 4a methylsterol which is linearly related to the proportion of marine sedimentary organic matter as scaled by 13corg indicates that either 1 1 sedimentary diagenesis has obscured the biomarker corg vs 13corg record 2 2 phytoplanktonic assemblage changes caused variations in the biomarker corg ratio of the primary input preferential preservation of terrigenous sterols may result in a biased sedimentary record of sterol input which could be misinterpreted as indicating solely terrigenous sterol sources a simple model which characterizes the effects of sedimentary diagenesis on the relationship between corg normalized biomarker ratios and 13corg demonstrates the potential problems of long term differential diagenetic skewing on those tracer records

high amplitude variations in north atlantic sea surface temperature during the early pliocene warm period 1 we provide the first continuous orbital resolution sea surface temperature sst record from the high latitude north atlantic a region critical to understanding the origin of the plio pleistocene ice ages and proximal to regions that became frequently glaciated after 2 7 ma we analyzed sediments from ocean drilling program site 982 over the last 4 ma for their alkenone unsaturation index and compared this surface water signal to a benthic 18o record obtained from the same section we find that while ocean surface temperatures were significantly warmer 6 c than modern temperatures during the early pliocene they were also as variable as those during the late pleistocene a surprising result in light of the subdued variance of oxygen isotopic time series during the interval of 3 5 ma we propose two possible explanations for the high orbital scale sst variability observed either that a strong high latitude feedback mechanism not involving large continental ice sheets alternately cooled and warmed a broad region of the northern high latitudes or that by virtue of its location near the northern margin of the north atlantic drift the site was unusually sensitive to obliquity driven climate shifts on supraorbital time scales a strong sustained cooling of north atlantic ssts 4 5 c occurred from 3 5 to 2 5 ma and was followed by an interval of more modest cooling an additional 1 5 c from 2 5 ma to the present evolutionary orbital scale phase relationships between north atlantic sst and benthic 18o show that sst began to lead 18o significantly coincident with the onset of strong cooling at site 982 3 5 ma we speculate that these changes were related to the growth and subsequent persistence of a greenland ice sheet of approximately modern size through interglacial states

coccolithophores in the equatorial atlantic ocean response to seasonal and late quaternary surface water variability abstract the present study was initiated to ascertain the significance of coccolithophores as a proxy for paleoceanographic and paleoproductivity studies in the equatorial atlantic data from a range of different samples from the plankton surface sediments as well as sediment cores are shown and compared with each other in general the living coccolithophores in the surface and subsurface waters show considerable variation in cell numbers and distribution patterns cell densities reached a maximum of up to 300 103 coccospheres l in the upwelling area of the equatorial atlantic here emiliania huxleyi is the dominant species with relatively high cell numbers whereas umbellosphaera irregularis and umbellosphaera tenuis are characteristic for oligotrophic surface waters although they are observed in high relative abundances these species only occur in low absolute numbers the lower photic zone is dominated by high abundances and considerable cell numbers of florisphaera profunda the geographical distribution pattern of coccoliths in surface sediments reflects the conditions of the overlying surface water masses however abundances of the oligotrophic species umbellosphaera irregularis and umbellosphaera tenuis are strongly diminished causing an increase in relative abundance of the lower photic zone taxa florisphaera profunda and gladiolithus flabellatus during the past 140 000 years the surface water circulation of the equatorial atlantic has changed drastically as can be seen from changes in the coccolithophore species composition absolute coccolith numbers as well as coccolith accumulation rates significant increases in coccolith numbers and accumulation rates is observed in the southern equatorial atlantic during the last glacial interval oxygen isotope stages 2 4 which we attribute to enhanced upwelling intensities and advection of cool nutrient rich waters at this site in the western equatorial atlantic we observe an opposite trend with decreasing numbers of coccoliths during glacial periods which probably is caused by a deepening of the thermocline

a biomarker approach to the organic matter deposited in the north atlantic during the last climatic cycle abstract the study of the composition of total organic carbon toc c37 alkenones and c23 c33 n alkanes in the north atlantic ocean cores su90 08 and su90 39 has allowed the development of a model for the differentiation of marine and terrigenous toc this model gives rise to results in good agreement with inorganic markers such as magnetic susceptibility ms and non carbonate content according to this model the terrigenous toc accounts for most of the organic matter in the glacial sediments thus the higher toc of the glacial periods 0 1 0 45 vs 0 05 0 15 in the interglacials is due to the increase in terrigenous toc the changes in marine toc those associated to sea surface productivity are independent of the glacial interglacial evolution the terrigenous toc is more important at higher latitudes probably due to higher terrigenous detrital inputs associated with iceberg transport in this respect the correlation between n alkanes and ms strongly suggests that the main source of these hydrocarbons are ice rafted materials and that aeolian inputs only represent minor contributions the four peaks of reworked n alkanes in the su90 08 core that are coincident with the heinrich layers h1 h2 h4 and 115 are in agreement with this hypothesis on the other hand the abrupt marine toc peaks of su90 08 show a 23 ka periodicity indicating that the marine productivity at 43 n in the north atlantic ocean was precessionally driven the productivity maxima in this core correlate with low latitude oceanographic processes such as periods of enhanced trade wind intensity and equatorial upwelling which are also tuned to precession and independent of the global glacial interglacial evolution

combined coccolith foraminiferal and biomarker reconstruction of paleoceanographic conditions over the past 120 kyr in the northern north atlantic 59 n 23 w we present data for north atlantic core biogeochemical ocean flux study bofs 16k 59 n 23 w water depth 2370 m including coccolith flora 18o planktonic foraminiferal sea surface temperatures ssts by fa20 and simmax methods and alkenone based u37k and u37k ssts a good correlation exists between the abundances of cold water coccolith species and foraminifera and a broad correlation exists between coccolith and alkenone abundances except in the holocene reworked cretaceous coccoliths at the last glacial maximum are coincident with warm deviations of the u37k signal assessment of various calibrations of u37k and u37k with paleotemperature shows the inappropriateness of a global correlation we have produced a north atlantic u37k calibration on the basis of north atlantic data alone u37k 0 026t 0 186 which produces sst data for summer season at 0 m water depth comparable to the warm season foraminiferal ssts except during the intervals 26 36 58 65 and 100 120 ka when the alkenones indicate somewhat cooler surface waters

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

constraints on early events in martian history as derived from the cratering record the shapes and densities of crater size frequency distribution curves are used to constrain two major events early in martian history termination of high obliteration rates and viability of the multiple impact origin of the crustal dichotomy distribution curves of fresh craters superposed on uplands intercrater plains and ridged plains display shapes and densities indicative of formation prior to the end of heavy bombardment this observation correlates with other geologic evidence suggesting a major change in the erosional regime following the last major basin size impact i e argrye in addition the multisloped nature of the curves supports the idea that the downturn in the crater size frequency distribution curves reflects the size frequency distribution of the impactors rather than being the result of erosion the crustal dichotomy formed prior to the heavy bombardment intermediate epoch based on distribution curves of knobby terrain if the dichotomy resulted from a single gigantic impact this observation places constraints on when this event happened an alternate theory for dichotomy formation the multiple impact basin idea is questioned since distribution curves of large basins as well as heavy bombardment era units are not represented by a 3 differential power law function this study finds fewer basins missing on mars compare to the moon and mercury than previously reported the area covered by these missing basins is less than that covered the northern plains

pliocene pleistocene variability of upwelling activity productivity and nutrient cycling in the benguela region in this study we present combined high resolution records of sea surface temperature sst phytoplankton productivity and nutrient cycling in the benguela upwelling system bus for the past 3 5 ma the sst record provided evidence that upwelling activity off namibia mainly intensified ca 2 4 2 0 ma ago in response to the cooling of the southern ocean and the resultant strengthening of trade winds as revealed by productivity related proxies bus intensification led to a major transition in regional biological productivity when considering the termination of the matuyama diatom maximum a diatom high production event major oceanic reorganization in the benguela was accompanied by nutrient source changes as indicated by a new nitrogen isotopic delta n 15 record that revealed a stepwise increase at ca 2 4 and ca 1 5 ma ago the change in source region likely resulted from significant changes in intermediate water formation tied to the reorganization of oceanic conditions in the southern ocean which may have in turn mainly controlled the global ocean n cycle and therefore the n isotopic composition of nutrients since 3 5 ma ago

the variability of crater identification among expert and community crater analysts abstract the identification of impact craters on planetary surfaces provides important information about their geological history most studies have relied on individual analysts who map and identify craters and interpret crater statistics however little work has been done to determine how the counts vary as a function of technique terrain or between researchers furthermore several novel internet based projects ask volunteers with little to no training to identify craters and it was unclear how their results compare against the typical professional researcher to better understand the variation among experts and to compare with volunteers eight professional researchers have identified impact features in two separate regions of the moon small craters diameters ranging from 10 m to 500 m were measured on a lunar mare region and larger craters 100s m to a few km in diameter were measured on both lunar highlands and maria volunteer data were collected for the small craters on the mare our comparison shows that the level of agreement among experts depends on crater diameter number of craters per diameter bin and terrain type with differences of up to 45 we also found artifacts near the minimum crater diameter that was studied these results indicate that caution must be used in most cases when interpreting small variations in crater size frequency distributions and for craters 10 pixels across because of the natural variability found projects that emphasize many people identifying craters on the same area and using a consensus result are likely to yield the most consistent and robust information

floral and solution patterns of coccoliths in surface sediments of the north pacific coccolith assemblages from core top samples of the north pacific seafloor follow the distribution of surface water masses gephyrocapsa caribbeanica umbellosphaera tenuis and coccolithus pelagicus are the most important identifiers of surface water mass different multivariate statistical techniques group shallow samples in somewhat different spatial patterns factor analysis condenses the information contained in sixteen ies percentages to four new variables that can be interpreted as species assemblages by canonical correlation analysis these assemblages can in turn be related to the environment the first canonical correlation indicates that factor 2 the g caribbeanica assemblage is represented in samples underlying cooler surface water a second possible correlation describes a direct relationship between factor 3 the umbilicosphaera sibogae assemblage and the remaining environmental variable surface water salinity factor 1 the g oceanica assemblage and factor 4 the emiliania huxleyi assemblage are not as closely related to the selected environmental measures of temperature salinity dissolved oxygen and inorganic phosphate phosphorus as are factor 2 and factor 3 because samples were coded according to their overlying water mass group separations produced by discriminant analysis are easily interpreted in terms of the environment overlap of group assignments occurs for samples from the south china sea and extreme western pacific even partially dissolved samples retain the signature of surface water mass group assignment for those samples is generally reliable with the exception of samples from the central water mass where almost half of the shallow and half of the deep samples show strongest affinities with one of the other three water masses selective solution therefore only partially obscures the record of floral provinciality partial dissolution of coccolith assemblages does not proceed according to one systematic rank order the sequence of species removal is variable from region to region the more abundant species tend to consistently appear at an extreme of the ranking for example umbilicosphaera sibogae is among the least resistant and c leptoporus and g oceanica are among the most resistant species maximum depths of coccolith lysocline and compensation depth occur generally in the central part of the basin and shoal towards its margins as previously observed for planktonic foraminifera

coccolithophore export production in guaymas basin gulf of california response to climate forcing abstract the flux and taxonomic composition of coccolithophores has been determined for sediment trap samples collected over a two year period from guaymas basin central gulf of california the gulf of california is a subtropical marginal sea with exceptionally high rates of primary productivity the annual biogenic sediment fluxes are largely dominated by silica with diatoms as the major contributor to the opal flux for the july 1990 through november 1992 study period the total coccolithophore export production in guaymas varied in response to the strength of el nino southern oscillation enso coccolithophore production follows the general surface primary productivity pattern with relatively high fluxes from late fall to late winter and low production in the summer when the water column is highly stratified and nutrient depleted high fluxes of up to 10 9 coccoliths m 2 day 1 and 3 10 6 coccospheres m 2 day 1 indicate that coccolithophores are an important component of the phytoplankton population in guaymas basin the intensification of enso conditions during 1992 altered the typical hydrography of the gulf of california by increasing sst and reducing the strength of spring upwelling this is reflected in reduced opal and diatom fluxes during this period conversely these more oligotrophic conditions resulted in higher total coccolithophore fluxes during spring and summer 1992 gephyrocapsa oceanica is present in the gulf throughout the study period but is dominant during weak or non enso times emiliania huxleyi and to a lesser degree florisphaera profunda are abundant during strong enso periods two major coccolithophore signals are indicative of strong enso conditions and could be used as paleo enso indicators in the gulf of california a the switch in dominance between g oceanica and e huxleyi and b high abundances of the deep dwelling species f profunda the abundance of this latter species shows a strong inverse relationship with opal fluxes a comparison of the annual coccolith flux with coccolith accumulation rates in the surface sediments indicates that only about 10 20 of the coccolith export production is preserved in the anoxic sediments of guaymas basin this very low level of preservation is probably due to bacterial processes on the sea floor which cause acidification of the bottom waters at the sediment water interface coccolith accumulation rates are higher in surface sediments from the western coast of the central gulf suggesting both higher coccolithophore production and better preservation in this region probably associated with lower diatom production tintinnids which agglutinate coccoliths are strongly selective for both coccolith size and species

a comparison of multiple proxies for export production in the equatorial pacific 1 several commonly used paleoproductivity proxies were compared to evaluate the validity of assumptions and limitations associated with each proxy export production fluxes cexport over glacial interglacial timescales were calculated from previously developed proxy specific algorithms at ttn013 pc72 and ttn013 pc114 both located in the equatorial pacific comparison of data from the same core intervals yields conflicting results despite calibrations based on the same core top samples the periodicity of marine barite excess ba and excess al based cexport records is similar the relative magnitude of cexport when calculated using excess ba and algorithms based on sediment trap data is significantly different than records based on core top calibrations particularly during glacial intervals at both sites bulk sedimentary al ti and ba ti ratios covary however these ratios do not correspond with the downcore records of their respective excess concentrations and their accumulation rates or with contemporaneous records based on marine barite excess ba and excess al accumulation although downcore records based on sediment mass accumulation rates may be compromised by sediment focusing this process cannot explain all the differences observed among the various data sets presented here this implies that some or all of these proxies do not exclusively respond to changes in export production the contradictions among these data highlight the importance of addressing inconsistencies among paleoproxies and re examining assumptions imbedded in proxy fundamentals prior to applying paleoproductivity proxies and interpreting paleoceanographic records

coccolithophore response to oceanographic changes in the equatorial atlantic during the last 200 000 years a deep sea core from the eastern equatorial atlantic meteor core 16772 1 21 s 11 58 w revealed strong primary productivity variations 70 230 gc m2 year based on the relative abundance of the deep living coccolithophore florisphaera profunda with productivity maxima following temperature minima during the last 200 000 years the response of the coccolithophore flora was investigated by relative and absolute abundance records of coccoliths the wind strength and the resulting equatorial upwelling intensity are thought to comprise the most important control of coccolith abundance and species composition which reflects the different abundance of coccolithophores living in the upper or lower photic zone relative abundances of the different species varies widely throughout the core although a wide range of species were present in the different samples three different taxa dominated the assemblage the lower photic zone species f profunda was the most abundant with a mean relative abundance of 49 4 throughout the core the upper photic zone flora were divided into three groups emiliania huxleyi together with small gephyrocapsa 3 m was the second most abundant species group mean 20 8 gephyrocapsa oceanica was the third most important species in the core and had a mean relative abundance of 16 8 all other species together represented a mean of 13 highest absolute abundance of coccoliths number gram sediment occurs in sediments deposited during periods of high sst mainly in warm isotope stages 1 and 5 the accumulation rates of coccoliths number cm2 ky show peaks in isotope stages 1 and 5 but also in some parts of cool isotope stages 4 and 6 high relative and absolute abundance of f profunda were found in warm isotope stages which suggests that a deep nutricline existed and that primary productivity was low absolute and relative abundance records of e huxleyi and small gephyrocapsa 3 m mainly showed higher values in sediments from warm periods the other upper photic zone coccolith species were generally more abundant during periods of low sst particularly in isotope stages 2 4 and 6 which were times of high primary productivity and a shallow nutricline this suggest that e huxleyi and small gephyrocapsa probably were able to live deeper in the water column than most other species during periods of low nutrient supply to the upper photic zone in summary the composition of the coccolith flora can be explained by the nutricline depth level with three different assemblages being recognized a deep photic zone assemblage consisting of f profunda a middle upper photic zone assemblage of e huxleyi and small gephyrocapsa and an upper photic zone assemblage consisting of all other species

characteristics of alkenone distributions in suspended and sinking particles in the northwestern north pacific abstract we investigated alkenones recorded in suspended particles and a settling particle time series collected at three stations 40n 40 n 165 e knot 44 n 155 e and 50n 50 n 165 e in the northwestern north pacific from december 1997 to may 1999 emiliania huxleyi the most abundant alkenone producer in this area is present in surface to subsurface to 50 m depth waters the alkenone concentrations recorded in the suspended particles indicated that the seasonal alkenone particle distribution differed significantly interannually alkenone export fluxes at the three sediment trap stations ranged from 0 16 to 49 3 g m 2 day 1 and the maximum export flux which occurred in summer to fall july november was associated with a high organic carbon export flux the amount of alkenone produced during the maximum export season accounted for 60 80 of the total annual amount of alkenone and the alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer autumn season alkenone derived temperatures recorded in suspended particles corresponded to the in situ temperature within 2 c although alkenone derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high export season large differences were observed during the low export winter spring period for example the alkenone derived temperatures observed at stations knot and 50n were much higher than the in situ subsurface temperatures reported in the world ocean atlas 2001 relatively large differences between alkenone derived temperatures and in situ temperatures in the subarctic might be due to 1 a low light limitation or 2 contributions of allochthonous alkenones in particulate material transported from subtropical areas within a warm core ring