winter cyclone frequencies in thirteen models participating in the atmospheric model intercomparison project amip1 various aspects of the simulated behaviour of cyclones in thirteen models participating in the amip1 exercise are presented in the simulation of the winter climatological mean sea level pressure field for the northern hemisphere the models produce reasonable simulations of the semi permanent features of the climatology the greatest departures from the observed climatology occur near the exit regions of the oceanic storm tracks i e over northwestern north america over and to the west of the british isles and in the mediterranean the departures in the three geographical areas are very systematic in that at least eleven of the models exhibit similar departures from observations in the southern hemisphere the intensity of the circumpolar trough is generally well simulated but positioned slightly too far north most models exhibit errors south of africa new zealand and south america the simulations of the cyclone events show that the models are reasonably successful in reproducing the large scale aspects of observed cyclone events but deficiencies in the details of the simulations are apparent the paucity of simulated events to the south of the alps and to the east of the rockies suggests that the models have difficulty simulating lee cyclogenesis over much of north america the models have difficulty simulating the correct level of synoptic activity as demonstrated by the low numbers of both cyclone events and anticyclone events the models have difficulty simulating the distribution of cyclone events as a function of central pressure the most common problem is that the models exhibit an ever increasing deficit of events with decreasing central pressure this problem is more apparent in the southern hemisphere than in the northern hemisphere and does not appear to be resolution dependent there is an apparent enso signal in the observed northern hemisphere interannual variability of intense winter cyclone events with the exception of ecmwf the models fail to reproduce this phenomenon there is some evidence that the models do indeed respond to the interannual variability in the ssts but the response tends to be negatively correlated with that of the real atmosphere in the southern hemisphere there does not appear to be enso induced interannual variability in the observed numbers of cyclone events consequently it could be argued that the models have been reasonably successful in the southern hemisphere since they like the observations do not exhibit any enso induced interannual variability

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

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

carbon isotopes in continental weathering environments and variations in ancient atmospheric co2 pressure abstract abundance and carbon isotope data from an fe co3 oh component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric co2 pressures a test of the validity of these estimates might be comparisons of the carbon isotope compositions of fe co3 oh in oolitic goethites with time equivalent pedogenic calcites temporal trends of the oolitic goethite and pedogenic calcite 13c values are generally similar but time equivalent samples from each of these two groups are not common in the existing data to facilitate discussion of the concept comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical in four out of the five comparisons fe co3 oh abundance and 13c data were combined with pedogenic calcite 13c data to calculate physically reasonable soil co2 concentrations for the ancient calcitic soids this suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon i e atmospheric co2 atmospheric pco2 as determined from the goethites in these four well behaved cases ranged from values indistinguishable from modern within analytical uncertainty to values up to approximately 16 time modern modern atmospheric pco2 was taken to be 10 3 5 atm one interpretation of the fifth anomalous comparison is that atmospheric co2 levels increased from about 3 times modern to about 18 times modern from the triassic into the early jurassic this inferred value for the pco2 of the early jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated however even considerably lower early jurassic atmospheric pco2 values of 6 to 9 times modern i e 1 3 to 1 2 of the estimated value of 18 times modern would still indicate significant differences between the global carbon cycles then and now these results highlight the need for more research on the behavior of the atmosphere during and after the triassic jurassic transition

geochemical evidence for variations in delivery and deposition of sediment in pleistocene light dark color cycles under the benguela current upwelling system abstract distinctive light dark color cycles in sediment beneath the benguela current upwelling system indicate repetitive alternations in sediment delivery and deposition geochemical proxies for paleoproductivity and for depositional conditions were employed to investigate the paleoceanographic processes involved in creating these cycles in three mid pleistocene intervals from odp sites 1082 and 1084 concentrations of total organic carbon toc vary between 3 5 and 17 1 concentrations of caco3 vary inversely to toc and al which suggests that both carbonate dissolution and terrigenous dilution contribute to the light dark cycles opal concentrations are independent of both toc and caco3 therefore eliminating diatom production and lateral transport of shelf material as causes of the light dark cycles 13corg and 15ntot values do not vary across light dark sediment intervals implying that the extent of relative nutrient utilization did not change the stable 15ntot values represent a balanced change in nitrate supply and export production and therefore indicate that productivity was elevated during deposition of the toc rich layers parallel changes in concentrations of indicator trace elements and toc imply that changes in organic matter delivery influenced geochemical processes on the seafloor by controlling consumption of pore water oxygen cu ni and zn are enriched in the darker sediment as a consequence of greater organic matter delivery redox sensitive metals vary due to loss mn and ba or enrichment mo under reducing conditions created by toc oxidation organic matter delivery impacts subsequent geochemical changes such as carbonate dissolution sulfate reduction and the concentration of metals thus export production is considered ultimately responsible for the generation of the color cycles

quantifying the role of geographic change in cenozoic ocean heat transport using uncoupled atmosphere and ocean models abstract a series of five cenozoic atmospheric general circulation model agcm experiments has been performed using a new set of paleogeographic reconstructions for 55 40 33 20 and 14 ma the five continental reconstructions incorporate the tectonic evolution of early eocene to middle miocene continental positions and topography with all other model boundary conditions and forcings held constant the series of agcm experiments captures a

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

a multiple proxy and model study of cretaceous upper ocean temperatures and atmospheric co2 concentrations foraminiferal d 18 o and mg ca suggests that the ratio of magnesium to calcium in the turonian coniacian ocean may have been lower than in the albian cenomanian ocean perhaps coincident with an ocean 87 sr 86 sr minimum the carbon isotopic compositions of distinct marine algal biomarkers were measured in the same sediment samples the d 13 c values of phytane combined with foraminiferal d 13 c and inferred temperatures were used to estimate atmospheric carbon dioxide concentrations through this interval estimates of atmospheric co2 concentrations range between 600 and 2400 ppmv within the uncertainty in the various proxies there is only a weak overall correspondence between higher lower tropical temperatures and more less atmospheric co2 the genesis climate model underpredicts tropical atlantic temperatures inferred from odp leg 207 foraminiferal d 18 o and mg ca when we specify approximate co2 concentrations estimated from the biomarker isotopes in the same samples possible errors in the temperature and co2 estimates and possible deficiencies in the model are discussed the potential for and effects of substantially higher atmospheric methane during cretaceous anoxic events perhaps derived from high fluxes from the oxygen minimum zone are considered in light of recent work that shows a quadratic relation between increased methane flux and atmospheric ch4 concentrations with 50 ppm ch4 genesis sea surface temperatures approximate the minimum upper ocean temperatures inferred from proxy data when co2 concentrations specified to the model are near those inferred using the phytane d 13 c proxy however atmospheric co2 concentrations of 3500 ppm or more are still required in the model in order to reproduce inferred maximum temperatures

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

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

controls on the carbon isotopic composition of southern ocean phytoplankton carbon isotopic compositions of suspended organic matter and biomarker compounds were determined for 59 samples filtered from southern ocean surface waters in january 1994 along two north south transects woce sr3 from tasmania to antarctica and across the princess elizabeth trough pet east of prydz bay antarctica along the sr3 line bulk organic matter show generally decreasing 13c contents southward which are well correlated with increasing dissolved molecular carbon dioxide concentrations co2 aq this relationship does not hold along the pet transect using concentrations and isotopic compositions of molecular compounds we evaluate the relative roles of several factors affecting the 13c of southern ocean suspended particulate organic matter along the woce sr3 transect the concentration of co2 aq plays an important role it is well described by a supply versus demand model for the extent of cellular co2 utilization and its associated linear dependence of isotopic fractionation ep on the reciprocal of co2 aq an equally important factor appears to be changes in algal assemblages along the sr3 transect with their contribution to isotopic fractionation also well described by the supply and demand model when formulated to include the cell surface volume control of supply changes in microalgal growth rates appear to have a minor effect on ep along the pet transect algal assemblage changes and possibly changes in microalgal growth rates appear to strongly affect the carbon isotopic variations of suspended organic matter these results can be used to improve the formulation of modern carbon cycle models that include phytoplankton carbon isotopic fractionation

origins and accumulation of organic matter in expanded albian to santonian black shale sequences on the demerara rise south american margin ocean drilling program leg 207 recovered thick sequences of albian to santonian organic carbon rich claystones at five drill sites on the demerara rise in the western equatorial atlantic ocean dark colored finely laminated cenomanian santonian black shale sequences contain between 2 and 15 organic carbon and encompass oceanic anoxic events 2 and 3 high rock eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin however d 13 corg values lie mostly between 30 and 27 and toc tn ratios range from 15 to 42 which both mimic the source signatures of modern c3 land plants the contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations the low d 13 corg values which are actually common in mid cretaceous marine organic matter are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle the elevated c n ratios which are also typical of black shales indicate depressed organic matter degradation associated with low oxygen conditions in the water column that favored preservation of carbon rich forms of marine organic matter over nitrogen rich components underlying the laminated cenomanian santonian sequences are homogeneous dark colored lower to middle albian siltstones that contain between 0 2 and 9 organic carbon the organic matter in these rocks is mostly marine in origin but it occasionally

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

high resolution stable isotope records from the upper cretaceous rocks of italy and spain glacial episodes in a greenhouse planet high resolution 13c and 18o records from upper albian to lower santonian pelagic carbonates of the contessa quarry section in italy exhibit large positive oxygen isotopic excursions of 1 in the lower cenomanian and upper turonian coniacian strata within the uncertainties of biostratigraphic correlation these positive excursions appear to correspond to times of large sea level regressions in global sequence stratigraphic sea level curves several lines of evidence suggest that the major 18o excursions in contessa reflect episodes of global cooling and not differential diagenesis numerical models of oxygen isotope exchange during diagenesis show that a high contrast in the degree of alteration would be required to produce these signals as artifacts of diagenesis and lithological data provide no evidence for such large contrasts in the degree of alteration furthermore although precise correlation with a section in the south of spain is hampered by stratigraphic complexities the general sequence of major positive 18o excursions is reproduced it is unlikely that differential diagenesis would produce similar artifacts in multiple sites one explanation for the link between episodes of global cooling and sea level falls is that global cooling events led to polar ice sheet accumulation lowering sea level although ice free conditions have been inferred from evidence for a much warmer climate in late cretaceous time our results suggest that the relationship between continental high latitude ice sheets and overall climatic warmth warrants further examination

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

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

high temperatures in the late cretaceous arctic ocean to understand the climate dynamics of the warm equable greenhouse world of the late cretaceous period it is important to determine polar palaeotemperatures the early palaeoceanographic history of the arctic ocean has however remained largely unknown because the sea floor and underlying deposits are usually inaccessible beneath a cover of floating ice a shallow piston core taken from a drifting ice island in 1970 fortuitously retrieved unconsolidated upper cretaceous organic rich sediment from alpha ridge a submarine elevated feature of probable oceanic origin a lack of carbonate in the sediments from this core has prevented the use of traditional oxygen isotope palaeothermometry here we determine arctic palaeotemperatures from these upper cretaceous deposits using tex86 a new palaeothermometer that is based on the composition of membrane lipids derived from a ubiquitous component of marine plankton crenarchaeota from these analyses we infer an average sea surface temperature of approximately 15 degrees c for the arctic ocean about 70 million years ago this calibration point implies an equator to pole gradient in sea surface temperatures of approximately 15 degrees c during this interval and by extrapolation we suggest that polar waters were generally warmer than 20 degrees c during the middle cretaceous approximately 90 million years ago

factors controlling 13c contents of sedimentary organic compounds principles and evidence the carbon isotopic composition of any naturally synthesized organic compound depends on 1 the carbon source utilized 2 isotope effects associated with assimilation of carbon by the producing organism 3 isotope effects associated with metabolism and biosynthesis and 4 cellular carbon budgets these factors are reviewed and quantitative considerations summarized particularly with regard to active and passive modes of carbon assimilation by phytoplankton and the existence of discernible regularities in isotope effects associated with lipid biosynthesis it is concluded that n alkyl lipids are in general depleted in 13c by about 1 5 relative to polyisoprenoid lipids produced by the same organism the effects of biological reworking on isotopic compositions of organic carbon are examined and it is suggested that enrichment of 13c in sedimentary organic carbon may result from loss of ch4 from zooplanktonic gut communities isotopic methods for estimation of ancient co2 levels are considered and a hyperbolic form favored for the relationship between concentrations of dissolved co2 and isotopic fractionation

fault zone weakening and character of slip along low angle normal faults insights from the zuccale fault elba italy a seismically active low angle normal fault is recognized at depth in the northern apennines italy where recent exhumation has also exposed ancient examples at the surface notably the zuccale fault on elba field based and microstructural studies of the zuccale fault reveal that an initial phase of pervasive cataclasis increased fault zone permeability promoting influx of co 2 rich hydrous fluids this triggered low grade alteration and the onset of stress induced dissolution precipitation processes e g pressure solution as the dominant grain scale deformation process in the pre existing cataclasites leading to shear localization and the formation of a narrow foliated fault core dominated by fine grained hydrous mineral phases these rocks exhibit ductile deformation textures very similar to those formed during pressure solution accommodated frictional viscous creep in experimental fault rock analogues the presence of multiple hydrofracture sets also points to the local attainment of fluid overpressures following development of the foliated fault core which significantly enhanced the sealing capacity of the fault zone a slip model for low angle normal faults in the apennines is proposed in which aseismic frictional viscous creep occurs on a weak slow moving slip rate 1 fault interspersed with small seismic ruptures caused by cyclic hydrofracturing events our findings are potentially applicable to other examples of low angle normal faults in many tectonic settings

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

sequence stratigraphy structure and tectonic history of the southwestern ontong java plateau adjacent to the north solomon trench and solomon islands arc the ontong java plateau ojp is the largest and thickest oceanic plateau on earth and one of the few oceanic plateaus actively converging on an island arc we present velocity determinations and geologic interpretation of 2000 km of two dimensional multi channel seismic data from the southwestern ontong java plateau north solomon trench and northern solomon islands we recognize three megasequences ranging in age from early cretaceous to quaternary on the basis of distinct interval velocities and seismic stratigraphic facies megasequence oj1 is early cretaceous upper igneous crust of the ojp and correlates with basalt outcrops dated at 122 125 ma on the island of malaita the top of the overlying megasequence oj2 a late cretaceous mudstone unit had been identified by previous workers as the top of igneous basement seismic facies and correlation to distant deep sea drilling project ocean drilling program sites indicate that oj2 was deposited in a moderately low energy marine environment near a fluctuating carbonate compensation depth that resulted in multiple periods of dissolution oj2 thins south of the stewart arch onto the solomon islands where it is correlated with the kwaraae mudstone formation megasequence oj3 is late cretaceous through quaternary pelagic cover which caps the ontong java plateau it thickens into the north solomon trench and seismic facies suggest that oj3 was deposited in a low energy marine environment we use seismic facies analysis sediment thickness structural observations and quantitative plate reconstructions of the position of the ojp and solomon islands to propose a tectonic magmatic and sedimentary history of the southwestern ontong java plateau prior to 125 ma late jurassic and early cretaceous oceanic crust formed from 125 to 122 ma the first mantle plume formed igneous crust oj1 between 122 and 92 ma marine mudstone oj2 and kwaraae mudstone of malaita solomon islands was deposited on ontong java plateau at 92 ma a second mantle plume caused widespread volcanism on the plateau from 92 to 15 ma pelagic carbonate sediment oj3 was deposited at 15 ma the southern ontong java plateau was deformed by normal faults during its approach toward the north solomon trench finally from 4 to 0 ma the malaita accretionary prism formed during collision between a substantially thicker portion of the ontong java plateau and the solomon islands arc flexure of the ontong java plateau near the trench caused coeval normal faulting

extreme polar warmth during the cretaceous greenhouse paradox of the late turonian δ18o record at deep sea drilling project site 511 1 oxygen isotope data for upper turonian planktonic foraminifera at deep sea drilling project site 511 falkland plateau 60 s paleolatitude exhibit an 2 excursion to values as low as 4 66 vienna peedee belemnite standard pdb coincident with the warmest tropical temperature estimates yet obtained for the open ocean the lowest planktonic foraminifer 1 8 o values suggest that the upper ocean was as warm as 30 32 c this is an extraordinary temperature for 60 s latitude but is consistent with temperatures estimated from apparently coeval mollusc 1 8 o from nearby james ross island 65 s paleolatitude glassy textural preservation a well defined depth distribution in site 511 planktonics low sediment burial temperature 32 c and lack of evidence of highly depleted pore waters argue against diagenesis even solid state diffusion as the cause of the very depleted planktonic values the lack of change in benthic foraminifer 1 8 o suggests brackish water capping as the mechanism for the low planktonic 1 8 o values however mixing ratio calculations show that the amount of freshwater required to produce a 2 shift in ambient water would drive a 7 psu decrease in salinity the abundance and diversity of planktonic foraminifera and nannofossils high planktonic benthic ratios and the appearance of keeled foraminifera argue against lower than normal marine salinities isotope calculations and climate models indicate that we cannot call upon more depleted freshwater 1 8 o to explain this record without more late turonian data especially from outside the south atlantic basin we can currently only speculate on possible causes of this paradoxical record from the core of the cretaceous greenhouse

mid cretaceous pco2 based on stomata of the extinct conifer pseudofrenelopsis cheirolepidiaceae stomatal characteristics of an extinct cretaceous conifer pseudofrenelopsis parceramosa fontaine watson are used to reconstruct atmospheric carbon dioxide p co 2 over a time previously inferred to exhibit major fluctuations in this greenhouse gas samples are from nonmarine to marine strata of the wealden and lower greensand groups of england and the potomac group of the eastern united states of hauterivian to albian age 136 100 ma atmospheric p co 2 is estimated from the ratios between stomatal indices of fossil cuticles and those from four modern analogs nearest living equivalent plants using this approach and two calibration methods to explore ranges results show relatively low and only slightly varying p co 2 over the hauterivian albian interval a low of 560 960 ppm in the early barremian and a high of 620 1200 ppm in the albian data from the barremian wealden group yield p co 2 values indistinguishable from a soil carbonate based estimate from the same beds the new p co 2 estimates are compatible with sedimentological and oxygen isotope evidence for relatively cool mid cretaceous climates

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

effects of sources and diagenesis on the isotopic and chemical composition of carbon and sulfur in cretaceous shales abstract the cretaceous lea park formation of south central saskatchewan contains organic matter from marine and terrestrial sources in proportions that vary as a result of deposition during the campanian claggett transgressive regressive cycle in the western interior seaway of north america the relative proportions of organic matter from these sources were determined using a terrestrial index ti that compares n alkanes considered to be of terrestrial origin n c25 to n c59 to those considered to be of marine origin n c15 to n c22 the c isotopic composition of cretaceous marine organic matter is found to be near 32 o while terrestrial organic matter is near 24 the lower 13c values of marine organic matter from the lea park formation as compared with those of recent marine organic matter are similar to the relation observed in other cretaceous rocks 13c values of terrestrial organic matter however are similar to those of the present during the miocene 13c values of marine organic matter became similar to recent values and this change in isotopic composition may be related to the development of deep cold water associated with the formation of antarctic ice sheets consequences of the formation of deep cold water may include improved exchange of co2 between atmosphere and oceans reduced pco2 levels and co2 concentrations in the photic zone of the oceans and environmental changes sufficient to produce an alternate metabolic pathway in phytoplankton all of these processes potentially result in higher 13c values in marine organic matter pyrite formation in the lea park mudstones was limited by the availability of metabolizable organic matter with the greatest amount of pyrite typically associated with organic matter having the lowest ti values 34spy values range nearly 30 and vary directly with the composition of associated organic matter variations in the supply of metabolizable organic matter were more important than differences in sedimentation rate in producing the range of 34spy values a34s values 534sseawater 34spyrite vary with the composition of organic matter and become larger when associated with more metabolizable organic matter

application of secondary ion mass spectrometry to the determination of mg ca in rare delicate or altered planktonic foraminifera examples from the holocene paleogene and cretaceous 1 secondary ion mass spectrometry sims is useful for measuring mg ca in both primary calcite and diagenetic minerals in planktonic foraminifera the excellent spatial resolution 10 m and small amount of material removed 2 ng makes it easy to avoid targets that include obvious embedding material and encrusting or infilling minerals such as secondary calcite and authigenic clays in diagenetically altered samples because analyses can be performed on individuals sims is also a viable technique for generating mg ca values from sediment samples in which foraminifera are rare or have low mass for clean primary calcite samples mg ca ratios from sims compare well to those obtained using inductively coupled plasma mass spectrometry icp ms while maintaining information regarding the true variability of elemental ratios within individual tests for samples with secondary calcite or stubbornly adhering clays sims enables us to accurately measure primary calcite compositions and to assess and reconcile contamination problems in bulk samples analyzed by solution based icp ms we have observed that sims is an invaluable and reliable tool for the identification and avoidance of problems of diagenesis and the analysis of rare or delicate planktonic foraminifera however because of operator time required to properly target delicate thin walled or contaminated planktonic foraminifera sims may not be feasible for mg ca studies where large numbers hundreds of samples must be processed and bulk measurements on multiple individuals will suffice

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

high concentrations of greenhouse gases and polar stratospheric clouds a possible solution to high latitude faunal migration at the latest paleocene thermal maximum high latitude faunal migrations have been documented during a rapid warming event near the paleocene eocene boundary the latest paleocene thermal maximum lptm the migrations are difficult to explain from a climate perspective climate along these routes is at present too harsh to support the migrations and no mechanism has yet proved adequate to explain the past high latitude warmth required by such migrations a large negative excursion in the 13c record at the lptm suggests that a large quantity of ch4 was released into the atmosphere at this time high concentrations of atmospheric ch4 have been linked to the formation of polar stratospheric clouds we used an atmospheric general circulation model to explore early cenozoic climate response to the combined effects of high atmospheric ch4 levels and polar stratospheric clouds a unique combination of forcing factors in paleoclimate modeling studies our interests are in understanding if the climate response to this forcing may explain the high latitude faunal migrations model results indicate that high latitude winter warming with high methane levels and polar stratospheric clouds is sufficient to facilitate the high latitude migrations temperatures along high latitude migration routes remained above freezing year round and thus permitted exchanges of fauna between asia north america and europe on the basis of our results we suggest that other paleogene migrations may be correlated with lptm like events with high concentrations of greenhouse gases and polar stratospheric clouds

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape

an explanation of the effect of seawater carbonate concentration on foraminiferal oxygen isotopes abstract stable oxygen isotope ratios of foraminiferal calcite are widely used in paleoceanography to provide a chronology of temperature changes during ocean history it was recently demonstrated that the stable oxygen isotope ratios in planktonic foraminifera are affected by changes of the seawater chemistry carbonate system the 18 o of the foraminiferal calcite decreases with increasing co 3 2 concentration or p h this paper provides a simple explanation for seawater chemistry dependent stable oxygen isotope variations in the planktonic foraminifera orbulina universa which is derived from oxygen isotope partitioning during inorganic precipitation the oxygen isotope fractionation between water and the dissolved carbonate species s h 2 co 3 hco 3 co 3 2 decreases with increasing p h provided that calcium carbonate is formed from a mixture of the carbonate species in proportion to their relative contribution to s the oxygen isotopic composition of caco 3 also decreases with increasing p h the slope of shell 18 o vs co 3 2 of orbulina universa observed in culture experiments is 0 0022 mol kg 1 1 spero et al 1997 whereas the slope derived from inorganic precipitation is 0 0024 mol kg 1 the theory also provides an explanation of the nonequilibrium fractionation effects in synthetic carbonates described by kim and o neil 1997 which can be understood in terms of equilibrium fractionation at different p h the results presented here emphasize that the oxygen isotope fractionation between calcium carbonate and water does not only depend on the temperature but also on the p h of the solution from which it is formed