high resolution i ca ratios of benthic foraminifera from the peruvian oxygen minimum zone a sims derived assessment of a potential redox proxy oceanic oxygen decline due to anthropogenic climate change is a matter of growing concern tropical oxygen minimum zones omzs are the most important areas of oxygen depletion in the modern oceans a quantitative oxygen proxy in omzs is highly desirable in order to identify and monitor recent dynamics as well as to reconstruct pre anthropocene changes in amplitude and extension of oxygen depletion a previous study revealed that there are significant correlations between i ca ratios of foraminiferal bulk samples for different benthic foraminiferal species from the peruvian omz nevertheless species for which less specimens were available showed a higher variability between i ca ratios in different badges to test if this might be related to intra or inter shell heterogeneity we focused on microanalyses of i ca ratios within these species in our present study we developed a method for measuring benthic foraminiferal i ca ratios a potential proxy for the reconstruction of marine oxygen concentrations we applied 92 spot analyses in individual foraminiferal specimens from the peruvian omz using secondary ion mass spectrometry sims the i ca ratios on 8 of 11 cleaned uvigerina striata and planulina limbata specimens determined with sims showed no significant difference to previous icp ms measurements on bulk samples from the same species this indicates that both techniques are suited to the analysis and that the applied cleaning protocols efficiently removed the strong iodine contaminations nevertheless despite the highly significant correlation between bulk icp ms i ca ratios and bottom water oxygen concentrations for u striata no significant correlation was observed for the sims derived individual i ca ratios this indicates that icp ms bulk analyses on pooled bulk samples might be more suitable for reliable oxygen reconstructions using i ca ratios on the contrary the strong intra test e g shell variations could be induced by the oxygen variability in the habitats of foraminifera therefore the high resolution findings provide the perspective for tracking relative short term oxygen fluctuations by measuring ontogenetic changes in i ca ratios within individual foraminiferal tests measurements on cross sections of uncleaned u striata specimens revealed a strong contaminant iodine phase within the massive centre of the foraminiferal test walls which usually would be considered to be free of contamination the contaminant iodine is probably associated to organic matter and located inside a microporous framework within the foraminiferal calcite this might be related to microtubular structures which have been revealed in previous studies during early dissolution states of foraminiferal test walls

tropical sea surface temperature reconstruction for the early paleogene using mg ca ratios of planktonic foraminifera 1 to understand the climate dynamics of hypothesized past greenhouse intervals it is essential to constrain tropical sea surface temperatures sst yet existing proxy records give conflicting results here we present the first mg ca based study of pre quaternary sst and investigate early paleogene late paleocene through late middle eocene 58 6 39 8 ma tropical temperatures using planktonic foraminifera belonging to the genus morozovella from ocean drilling program site 865 on allison guyot western central equatorial pacific ocean calcification temperatures similar to or warmer than modern tropical sst are calculated using a range of assumptions regarding diagenesis temperature calibration and seawater mg ca long term warming is observed into the early eocene 54 8 49 0 ma with peak sst between 51 and 48 ma and rapid cooling of 4 c beginning at 48 ma these findings are inconsistent with the 18o based sst previously estimated for this site

understanding the effects of dissolution on the mg ca paleothermometer in planktic foraminifera evidence from a novel individual foraminifera method

are granitic intrusions scale invariant published length l and thickness t data on 135 laccolith and 21 granite intrusions define power law relationships of the form l kt a typical of systems exhibiting scale invariant fractal behaviour both data sets are characterised by an exponent a 1 0 88 0 1 for laccoliths and 0 80 0 20 for plutons that reflects an inherent preference for scale invariant tabular sheet geometries these power law size relationships can be explained in mechanical terms by the need for an incoming magma sheet to travel laterally some distance before vertical thickening can occur sheet thickness is a function of available magma pressure which for an intrusion fed by a feeder dyke is proportional to the vertical magma transport distance

mutvei s solution an ideal agent for resolving microgrowth structures of biogenic carbonates accretionary hard parts of many organisms provide excellent archives of past climate and environmental conditions or life history traits variable growth rates function as environmental and physiological proxies and growth increments as calendars recognition of growth structures is thus a prime necessity for sclerochronological studies here we present a new handy easy to use and time efficient technique that resolves annual and sub annual growth structures in skeletons of a wide range of different organisms mutvei s solution simultaneously etches biogenic carbonates and calcium phosphates fixates the soluble and insoluble organic matrices and fibers and stains mucopolysaccharides it produces a filigreed three dimensional relief of etch resistant ridges growth lines and etched depressions growth increments and stains skeletal growth structures in shadings of blue growth lines stand out as crisp darker blue stained lines reflected optical light microscopy axial and oblique illumination and scanning electron microscopy can be used to analyze the microgrowth structures we demonstrate the use of the technique on hard tissues of various marine and freshwater bivalves a coral a sclerosponge a barnacle gastropods a cephalopod a fish otolith and a whale s ear bone this technique may be of interest for paleoclimatologists geochemists and biologists it can significantly expand the use of biogenic hard parts as environmental and physiological indicators because it reveals microgrowth structures of biogenic skeletons that potentially form on a periodic basis and thus function as calendars

patterns and processes of shell fragmentation in modern and ancient marine environments shell fragments are important components of many recent and fossil marine benthic ecosystems and can provide crucial information on past and present environmental conditions interpreting such fragments requires integrated knowledge in various fields and the information potential is therefore rarely optimally utilized this paper uses the definition of a fragment as being a piece of shell having less than 90 of its original form it then outlines the potential characteristics pathways and fates that shells and their fragments can have fragmentation is a key factor shaping the shelly part of death assemblages but it is difficult to interpret because it can be broadly caused by ecological biostratinomic or diagenetic processes and also depends on shell strength strength in turn reflects multifunctionality during ontogeny and depends on a complex set of skeletal and taphonomic factors therefore no particular shell parameter clearly determines strength but thickness microstructure type and degree of organic matrix have the strongest influence on pre and post mortality strength size measurements are usually less important for shell strength than thickness although ecologically complex size refuges from predation do exist similarly shell shape sculptural features and specific aperture types in gastropods provide various defence strategies rather than increasing strength per se key ecological factors of fragmentation include predation due to crushing peeling along with mistaken predation selfinflicted damage during predation and burrowing and more physical aspects such as impacts by stones modern studies must consider damage by benthic commercial fisheries or dredging by scientific vessels key biostratinomic factors include transportinduced abrasion littoral zone of surf washed beaches bioerosion and dissolution mainly sublittoral environments diagenetically fragmentation during compaction mainly occurs when shells are in direct contact with one another or with coarser grains taphonomic features e g drillholes have only minor influence a key step in interpreting fragments is to categorize breakage into repaired versus unrepaired diagnostic versus nondiagnostic and severe versus localized damage quantifying the above categories can then provide useful information on breakage patterns and underlying processes understanding the many characteristics of shells and their fragments is a significant interpretive tool in maximizing the information gain in palaeoecological and taphofacies analyses d 2003 elsevier science b v all rights reserved

evolution of the slave craton greenstone belts in the slave craton represent the episodic accumulation of volcanic and sedimentary rocks over as much as 200 m y in the western craton volcanic and sedimentary rocks were deposited between 2 81 and 2 60 ga on 2 9 3 1 ga sialic basement not tectonically juxtaposed with it deposition of 2 6 ga turbidite and conglomerate sequences across the entire slave craton was synchronous with or followed by the main phase of regional deformation and metamorphism at 2 6 2 58 ga and final stabilization of the craton

effects of diagenesis on the isotopic record of late paleogene tropical sea surface temperatures abstract oxygen isotope records of planktonic foraminifera indicate that late eocene and oligocene tropical sea surface temperatures were as much as 8 c lower than present at a time when high latitude sea surface temperatures were higher than present using a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate the effects of diagenesis on bulk carbonate 18 o records for the cenozoic are quantified for four tropical sites most of the observed variations in measured 18 o values at all sites can be accounted for by diagenetic effects there are no systematic trends that support substantial variations in tropical sea surface temperatures beyond diagenetic effects with the possible exception of the early eocene for which the data are consistent with slightly higher sea surface temperatures reconstructions based on oxygen isotope records of planktonic foraminifera which indicate cooler tropical sea surface temperatures for the eocene and oligocene may be artifacts of diagenetic recrystallization as such records are particularly sensitive to diagenetic effects

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

response of calcareous nannofossils to the paleocene eocene thermal maximum from a shelf section in jordan abstract the paleocene eocene thermal maximum petm is known as an approximately 200 kyr long lasting interval of extreme global warming accompanied by major alterations in the ocean atmosphere system these include a negative carbon isotope excursion intense carbonate dissolution and biotic changes of marine floras and faunas the current study reports the response of calcareous nannofossils across the paleocene eocene boundary in a paleoshelf setting in jordan core os 28 clearly marked by a negative 13 c org excursion and the occurrence of characteristic excursion taxa e g discoaster araneus rhomboaster spp coccolithus bownii while this section suffers from intense dissolution at the onset of the event and the peak of the isotopic excursion it retains well preserved diverse nannofossil assemblages from the pre petm petm recovery and post petm intervals these assemblages are dominated by two taxa of inferred mesotrophic affinities coccolithus pelagicus toweius spp and show only low abundances of oligotrophic taxa discoaster spp fasciculithus spp sphenolithus spp overall there appear to be only relatively low level changes in the general assemblage composition across the petm during the post petm however there was a gradual decrease in relative abundance of c pelagicus and toweius spp this decline co coccured with a relative increase of coccolithus bownii and coccolithus foraminis and in its later phase was accompanied by an increase in the relative abundance of sphenolithus spp these changes indicate a possible shift towards less fertile conditions following the hyperthermal event the relatively muted signal of biotic change associated with the petm interval at this site was partly a consequence of poor preservation within the key sequence of the studied core on the other hand the low signal may also be indicative for local environment processes such as variations in riverine sourced nutrients salinity turbidity operating on a regional scale these local factors overrode the direct and indirect temperature signals that are the dominant control on nannofossil communities across the petm in open ocean sites finally the assemblages from the jordan section highlight further the overall spatial heterogeneity in reported responses of shelf area communities to the petm interval these heterogeneities have been observed in shelf assemblages from tanzania new jersey and the tethyan margins which again points to the strong influence of regional controls like river input in more marginal settings

assessing the impact of diagenesis on δ11b δ13c δ18o sr ca and b ca values in fossil planktic foraminiferal calcite the geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo climatic oceanographic and ecological changes however dissolution of biogenic calcite and precipitation of inorganic calcite overgrowth and recrystallization at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test biasing any resulting paleoenvironmental reconstruction the 11b of planktic foraminiferal calcite is a promising ocean ph proxy but the effect of diagenesis is still poorly known here we present new 11b 13c 18o sr ca and b ca data from multiple species of planktic foraminifera from time equivalent samples for two low latitude sites clay rich tanzanian drilling project tdp site 18 from the indian ocean containing well preserved glassy foraminifera and carbonate rich ocean drilling program odp site 865 from the central pacific ocean hosting recrystallized frosty foraminifera our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis planktic foraminiferal 18o and 13c records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration sr ca and b ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa in contrast 11b values indicate no large differences between well preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the 11b of biogenic calcite appears robust potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing caco3 our finding may remove one potential source of uncertainty in 11b based ph reconstructions and provide us with greater confidence in our ability to reconstruct ph in the ancient oceans from at least some recrystallized foraminiferal calcite however further investigations should extend this approach to test the robustness of our findings across a range of taphonomies ages and burial settings

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

fracture control of late archean pluton emplacement in the northern slave province canada the structural and geophysical characteristics of 2590 2580 ma leucogranites in the northern slave province have been studied to determine the role and conditions of late archean regional deformation during their emplacement the irregularly shaped straight sided c 10 km long ulu pluton is located in the southern part of the high lake greenstone belt northern slave province fabrics in the pluton and its wall rocks indicate that it was emplaced at mid to upper crustal levels during regional e w late archean compression a gravity survey and resulting three dimensional gravity model of the pluton show that it has several linear deep 6 km root zones which feed a relatively thin 2 km tabular body the orientations of the major root zone along the pluton s western side and three subsidiary roots correspond to those of the pluton contacts to within 5 landsat tm data reveal several sets of lineaments interpreted to represent fractures formed during the early assembly of the slave province which cut both the greenstone belt and the younger plutons analysis of these lineaments defines several maxima whose orientations correspond with those of both the feeder zones and the contacts of the ulu pluton the pluton therefore appears to have been emplaced via an intersecting set of vertical fractures magma was arrested by and spread along an unknown horizontal structure subsequent inflation of the pluton was also facilitated by vertical translation on pre existing fractures

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

rapid and sustained surface ocean acidification during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been associated with the release of several thousands of petagrams of carbon pg c as methane and or carbon dioxide into the ocean atmosphere system within 10 kyr on the basis of the co occurrence of a carbon isotope excursion cie widespread dissolution of deep sea carbonates and global warming in theory this rapid carbon release should have severely acidified the surface ocean though no geochemical evidence has yet been presented using boron based proxies for surface ocean carbonate chemistry we present the first observational evidence for a drop in the ph of surface and thermocline seawater during the petm planktic foraminifers from a drill site in the north pacific ocean drilling program site 1209 show a 0 8 decrease in boron isotopic composition 11b at the onset of the event along with a 30 40 reduction in shell b ca similar trends in 11b are present in two lower resolution records from the south atlantic and equatorial pacific these observations are consistent with significant global acidification of the surface ocean lasting at least 70 kyr and requiring sustained carbon release the anomalies in the b records are consistent with an initial surface ph drop of 0 3 units at the upper range of model based estimates of acidification

microstructural preservation and the effects of diagenesis on the carbon and oxygen isotope composition of late cretaceous aragonitic mollusks from the gulf coastal plain and the western interior seaway the carbon and oxygen isotope compositions of calcium carbonate shells are widely accepted and applied proxies for tracking changes in paleoenvironmental conditions such as temperature salinity and productivity in order to accurately interpret isotopic measurements diagenetic alteration must first be assessed the occurrence of aragonitic shells is often taken as a first order sign of unaltered material because aragonite at the earth9s surface is metastable and converts to calcite however even specimens that retain an aragonitic composition and are macroscopically well preserved often exhibit subtle to considerable signs of alteration when shell microstructure is examined using scanning electron microscopy sem to determine the textural and isotopic effects of progressive alteration on differing types of shell microstructure we undertook a comparative study of aragonitic shells from two regions frequently used in paleoenvironmental reconstructions and diagenetic studies the upper cretaceous of the gulf coastal plain gcp and the western interior seaway wis because the gcp is within a passive margin setting and the wis has experienced tectonic processes we also evaluate how diagenetic history affects isotopic composition visually well preserved ammonite bivalve and gastropod shells were collected from one locality in the gcp and examined using sem to evaluate microstructural preservation we used a previously published scale based on wis specimens for nacreous shell material and a complementary scale we developed for crossed lamellar microstructure the stable carbon and oxygen isotope compositions of specimens across the preservational scale from both regions were analyzed isotopic composition does not change systematically with degrading preservation in the gcp specimens a result that contrasts strongly with patterns in wis specimens where isotopic composition systematically decreases with decreasing microstructural preservation dissimilar tectonic regimes that led to unique post depositional conditions for each region are invoked to explain this difference the wis was a foreland basin subjected to significant meteoritic groundwater flow driven by active uplift while the gcp was a passive margin that has remained close to sea level with low hydraulic potential since the time of deposition thus during diagenesis the wis shells were exposed to fluids that differed greatly from the seawater in which the organisms grew whereas diagenetic fluids in gcp settings likely were similar to marine waters as expected shells with the best preserved microstructure provide the most consistently reliable isotopic data for paleoenvironmental reconstructions but our comparisons show that similar degrees of microstructural alteration can express very different diagenetic shifts in isotopic values

minimal influence of recrystallization on middle miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial pacific stable carbon and oxygen isotopes 13c and 18o of foraminiferal tests are amongst the most important tools in paleoceanography but the extent to which recrystallization can alter the isotopic composition of the tests is not well known here we compare three middle miocene 16 13 ma benthic foraminiferal stable isotope records from eastern equatorial pacific sites with different diagenetic histories to investigate the effect of recrystallization to test an extreme case we analyzed stable isotope compositions of benthic foraminifera from integrated ocean drilling program site u1336 for which the geochemistry of bulk carbonates and associated pore waters indicates continued diagenetic alteration in sediments 14 7 ma despite this diagenetic overprinting the amplitudes and absolute values of the analyzed u1336 stable isotopes agree well with high resolution records from better preserved sites u1337 and u1338 nearby our results suggest that although benthic foraminiferal tests of all three sites show some degree of textural changes due to recrystallization they have retained their original stable isotope signatures the good agreement of the benthic foraminiferal stable isotope records demonstrates that recrystallization occurred extremely rapidly 100 kyr after deposition this is confirmed by the preservation of orbital cyclicities in u1336 stable isotope data and 18o values being different to inorganic calcite that would precipitate from u1336 pore waters during late recrystallization the close similarity of the benthic foraminiferal stable isotope records between the sites allows the well resolved paleomagnetic results of site u1336 to be transferred to sites u1337 and u1338 improving the global geological timescale

spatiotemporal patterns of carbonate sedimentation in the south atlantic implications for carbon cycling during the paleocene eocene thermal maximum abstract rapid carbon input into the ocean atmosphere system caused a dramatic shoaling of the lysocline during the paleocene eocene thermal maximum petm a transient 170 kyr global warming event that occurred roughly 55 ma carbon cycle models invoking an accelerated carbonate silicate feedback mechanism to neutralize ocean acidification predict that the lysocline would subsequently deepen to depths below its original position as the marine carbonate system recovered from such a perturbation to test this hypothesis records of carbonate sedimentation and preservation for petm sections in the weddell sea odp site 690 and along the walvis ridge depth transect odp sites 1262 1263 and 1266 were assembled within the context of a unified chronostratigraphy the meridional gradient of undersaturation delimited by these records shows that dissolution was more severe in the subtropical south atlantic than in the weddell sea during the petm a spatiotemporal pattern inconsistent with the view that atlantic overturning circulation underwent a transient reversal deepening of the lysocline following its initial ascent is signaled by increases in caco3 and coarse fraction content at all sites carbonate preservation during the recovery period is appreciably better than that seen prior to carbon input with carbonate sedimentation becoming remarkably uniform over a broad spectrum of geographic and bathymetric settings these congruent patterns of carbonate sedimentation confirm that the lysocline was suppressed below the depth it occupied prior to carbon input and are consistent with the view that an accelerated carbonate silicate geochemical cycle played an important role in arresting petm conditions

stable warm tropical climate through the eocene epoch earth s climate cooled from a period of extreme warmth in the early eocene epoch ca 50 ma to the early oligocene ca 33 ma when a large ice cap first appeared on antarctica evidence from the planktonic foraminifer oxygen isotope record in deep sea cores has suggested that tropical sea surface temperatures declined by 5 10 degrees over this interval eventually becoming much cooler than modern temperatures here we present paleotemperature estimates from foraminifer isotopes and the membrane lipids of marine crenarcheota from new drill cores in tanzania that indicate a warm and generally stable tropical climate over this period we reinterpret the previously published isotope records in the light of comparative textural analysis of the deep sea foraminifer shells which shows that in contrast to the tanzanian material they have been diagenetically recrystallized we suggest that increasingly severe alteration of the deep sea plankton shells through the eocene produced a diagenetic overprint on their oxygen isotope ratios that imparts the false appearance of a tropical sea surface cooling trend this implies that the long term eocene climatic cooling trend occurred mainly at the poles and had little effect at lower latitudes

a blast of gas in the latest paleocene simulating first order effects of massive dissociation of oceanic methane hydrate carbonate and organic matter deposited during the latest paleocene thermal maximum is characterized by a remarkable 2 5 excursion in delta 13c that occurred over approximately 10 4 yr and returned to near initial values in an exponential pattern over approximately 2 x 10 5 yr it has been hypothesized that this excursion signifies transfer of 1 4 to 2 8 x 10 18 g of ch4 from oceanic hydrates to the combined ocean atmosphere inorganic carbon reservoir a scenario with 1 12 x 10 18 g of ch4 is numerically simulated here within the framework of the present day global carbon cycle to test the plausibility of the hypothesis we find that 1 the delta 13c of the deep ocean shallow ocean and atmosphere decreases by 2 3 over 10 4 yr and returns to initial values in an exponential pattern over approximately 2 x 10 5 yr 2 the depth of the lysocline shoals by up to 400 m over 10 4 yr and this rise is most pronounced in one ocean region and 3 global surface temperature increases by approximately 2 degrees c over 10 4 yr and returns to initial values over approximately 2 x 10 6 yr the first effect is quantitatively consistent with the geologic record the latter two effects are qualitatively consistent with observations thus significant ch4 release from oceanic hydrates is a plausible explanation for observed carbon cycle perturbations during the thermal maximum this conclusion is of broad interest because the flux of ch4 invoked during the maximum is of similar magnitude to that released to the atmosphere from present day anthropogenic ch4 sources

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

oxygen isotope exchange in a two layer model of oceanic crust abstract a numerical model is presented for the transport and exchange of oxygen isotopes in an idealized two layer oceanic crust basalt carbonate that is saturated with a non advecting pore fluid open to the overlying ocean the model allows for time varying sedimentation rate porosity chemical diffusivity and temperature dependent 18o fractionation factors reaction is modeled as solution precipitation of calcite in the carbonate sediment and as modified solution precipitation basalt dissolves smectite precipitates in the basalt layer generic models using input parameters that are typical of those measured in dsdp odp cores and constant sedimentation rates illustrate the behavior of the system sufficiently well to allow first order effects to be discerned that have important implications for paleotemperature and ocean floor weathering studies the solution precipitation reactions allow oxygen to be exchanged between the low 18o basalt layer and the high 18o carbonate sediment through the medium of the pore fluids this results in 18o increasing upwards in the basalt and decreasing downwards in the sediment pore fluid 18o values decrease with depth from zero to values of 1 to 3 at the basalt sediment interface and to values of 7 to 15 within the basalt because reaction rates are slow relative to diffusion in the pore fluid high frequency 18o variations in the solid are preserved indefinitely but the amplitude of the variations decreases as e rt where r is the reaction rate fraction reacted per unit time the results suggest that the diagenetic shifts of the 18o values of benthic and high latitude planktonic foraminifera samples younger than oligocene age are typically negligible for samples older than 50 ma diagenetic effects are typically significant and generally cause estimates of bottom and high latitude surface ocean temperatures in the cretaceous and early tertiary to be too high on the other hand the model suggests that diagenesis will shift the 18o values of low latitude planktonic foraminifera to higher values and that paleotemperature estimates of low latitude surface waters particularly in the eocene and oligocene may be too low using a synthetic 18o record for dsdp site 167 we demonstrate how numerical models can be used to correct specific measured records for diagenesis this approach could provide a means of extracting paleotemperature information from heavily altered late cretaceous and older samples and for quantifying the subtle effects of diagenesis on the 18o record at all sites

evolutionary consequences of the latest paleocene thermal maximum for tropical planktonic foraminifera study of planktonic foraminiferal assemblages preserved in the central equatorial pacific odp site 865 reveal that genera which inhabited the near surface mixed layer diversified during the latest paleocene thermal maximum lptm this transient diversification gave rise to a suite of short lived 50 to several 100 ka distinctive morphotypes morozovella allisonensis sp nov m africana and acarinina sibaiyaensis that are restricted to the lptm interval parallel morphometric and stable isotopic data have been recorded from individual shells of members of the m velascoensis m allisonensis and a soldadoensis a sibaiyaensis lineages the single specimen isotope data confirm that m allisonensis and a sibaiyaensis are indeed stratigraphically restricted to the lptm carbon isotope excursion all specimens recorded anomalously low 13c values a stratigraphic succession of single specimen isotope data from within the 13c excursion interval was used to reconstruct the complex population dynamics which mediated the rapid 10 ka evolution of the lptm taxa these data reveal that local populations of ancestral m velascoensis temporarily collapsed with the descendant m allisonensis suddenly originating from a peripherally isolated population this pattern is most consistent with peripatric speciation overall the evolutionary transition from acarinina soldadoensis to a sibaiyaensis is most consistent with sympatric speciation although certain elements of this transition are suggestive of a parapatric mechanism we postulate that the rapid evolution of the lptm taxa a sibaiyaensis and m allisonensis was fostered by a deepening of the nutrient depleted mixed layer alternatively the lptm morphotypes m allisonensis and a sibaiyaensis may have been extreme ecophenotypic variants arrayed along an intensified ecological gradient support for this latter interpretation is derived from the morphometric data which clearly show the morphological intergradation of the lptm taxa with their respective ancestors thus the morphologic diversification seen during the lptm may represent failed speciations both scenarios invoke a temporary steepening of clinal gradients in response to intensified oligotrophy the strong size dependencies displayed by the 18o and 13c signatures of m allisonensis and a sibaiyaensis suggest that photosymbiosis facilitated the evolutionary success of the morozovellids and acarininids during the lptm

low frequency pliocene climate variability in the eastern nordic seas the pliocene 5 3 2 6 ma is often described as a relatively stable climatic period with warm temperatures characterizing high latitudes new suborbital resolved stable isotope records from ocean drilling program hole 642b in the eastern nordic seas document that the pliocene was not a stable period characterized by one climate rather seven distinct climate phases each lasting between 150 000 and 400 000 years are identified and characterized in the time interval 5 1 3 1 ma four of the transitions between the defined climate phases occurred close to an eccentricity minimum and a minimum in amplitude of change for northern hemisphere summer insolation while two occurred around an eccentricity maximum and a maximum in amplitude in insolation change hence a low frequency response of the nordic seas to insolation forcing is indicated in addition paleogeographic and related paleoceanographic changes expansion of the arctic sea ice cover and onset of northern hemisphere glaciation were important factors behind the evolving pliocene low frequency variability in the eastern nordic seas it is likely that the identified climate phases and transitions are important beyond the nordic seas due to their association with changes to both insolation and paleogeography however a strong and variable degree of diagenetic calcite overgrowth is documented for the planktic foraminifera especially influencing the planktic 18o results the absolute values and amplitude of change cannot be taken at face value

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

late paleocene middle eocene benthic foraminifera on a pacific seamount allison guyot odp site 865 greenhouse climate and superimposed hyperthermal events we investigated the response of late paleocene middle eocene 60 37 5 ma benthic foraminiferal assemblages to long term climate change and hyperthermal events including the paleocene eocene thermal maximum petm at ocean drilling program odp site 865 on allison guyot a seamount in the mid pacific mountains seamounts are isolated deep sea environments where enhanced current systems interrupt bentho pelagic coupling and fossil assemblages from such settings have been little evaluated assemblages at site 865 are diverse and dominated by cylindrical calcareous taxa with complex apertures an extinct group which probably lived infaunally dominance of an infaunal morphogroup is unexpected in a highly oligotrophic setting but these forms may have been shallow infaunal suspension feeders which were ecologically successful on the current swept seamount the magnitude of the petm extinction at site 865 was similar to other sites globally but lower diversity postextinction faunas at this location were affected by ocean acidification as well as changes in current regime which might have led to increased nutrient supply through trophic focusing a minor hyperthermal saw less severe effects of changes in current regime with no evidence for carbonate dissolution although the relative abundance of infaunal benthic foraminifera has been used as a proxy for surface productivity through bentho pelagic coupling we argue that this proxy can be used only in the absence of changes in carbonate saturation and current driven biophysical linking

deep time foraminifera mg ca paleothermometry nonlinear correction for secular change in seawater mg ca 1 the mg ca ratio of foraminifera tests is increasingly being utilized as a paleotemperature proxy deep time pre pleistocene mg ca paleothermometry is complicated by the fact that the mg ca ratio of seawater mg casw has undergone considerable secular variation over the cenozoic previous studies have corrected for this by assuming an invariant mg distribution coefficient dmg with mg casw more recent laboratory culturing has shown that this is not the case demonstrating that a power relationship best describes the variation in test mg ca mg catest with mg casw therefore previous corrections are likely to have led to inaccurate temperature reconstructions here we show how the systematics of such a correction should be applied and demonstrate why this provides good evidence that the mg ca ratio of paleogene seawater was lower than previously implied by foraminiferal constraints in agreement with the majority of the proxy mg casw evidence we also demonstrate how it is indirectly possible to constrain the value of h the power component of a mg catest mg casw calibration potentially enabling the appropriate correction of results derived from species where this relationship has not been calibrated however this technique should not be treated as a substitute for culturing the previous erroneous assumptions regarding both 1 the relationship between mg catest and mg caswand 2 the mg ca ratio of seawater at a given time in the past may counteract each other to differing extents as a result previous absolute pre pleistocene paleotemperature estimates derived from mg ca ratios in foraminifera should be treated with caution although relative temperature changes over short 1 ma timescales are likely to be reliable

paired analyses of oxygen isotope and elemental ratios within individual shells of benthic foraminifera genus uvigerina abstract we compare different methodologies in situ and bulk for obtaining oxygen isotope 18o and elemental ratios in the benthic foraminifera genus uvigerina from odp site 1015 california margin to assess what new information can be obtained with high resolution in situ techniques specimens were prepared in epoxy mounts and exposed in cross section such that multiple high resolution analyses could be completed on the same shells using both secondary ionization mass spectrometry sims and laser ablation inductively coupled mass spectrometry la icp ms we also measured elemental ratio data using la icp ms depth profile measurements on whole uncast foraminifera and elemental ratio and 18o with standard bulk techniques using the same species of benthic foraminifera from the same sediment sub samples comparison of the data collected by the different methodologies indicates that there is a consistent offset of 0 9 0 1 between sims and bulk analysis of 18o in these samples the in situ laser data studied in epoxy mount is correlated with the foraminifera bulk measurements for both mg and sr whereas the in situ depth profile laser measurements of mg and sr from whole foraminifera are less correlated with the bulk measurements we also observe that the intra shell variability for each of the proxies is larger than the analytical error and does not follow chamber number we propose that the 18o mg and sr variability within and between single specimens at this site is linked to some combination of measurement bias vital effects and variable environmental conditions in the pore water where the tests were precipitated this information can in turn be related to the regional setting of the site

sea level rise due to polar ice sheet mass loss during past warm periods background although thermal expansion of seawater and melting of mountain glaciers have dominated global mean sea level gmsl rise over the last century mass loss from the greenland and antarctic ice sheets is expected to exceed other contributions to gmsl rise under future warming to better constrain polarice sheetresponse to warmer temperatures we draw on evidence from in terglacial periods in the geologic record that ex perienced warmer polar temperatures and higher gmsls than present coastal records of sea level from these previous warm periods dem onstrate geographic variability because of the influence of several geophysical processes that operate across a range of magnitudes and time scales inferring gmsl and ice volume changes from these reconstructions is nontrivial and generally requires the use of geophysical models advances interdisciplinary studies of geo logic archives have ushered in a new era of deciphering magnitudes rates and sources of sea level rise advances in our understanding of polar ice sheet response to warmer climates have been made through an increase in the number and geographic distribution of sea level reconstructions better ice sheet constraints and the recognition that several geophysical processes cause spatially complex patterns in sea level in particular accounting for glacial isostatic processes helps to decipher spatial variability in coastal sea level records and has reconciled a number of site specific sea level reconstructions for warm periods that have oc curred within the past several hundred thou sand years this enables us to infer that during recent interglacial periods small increases in

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

evidence for a composite organic inorganic fabric of belemnite rostra implications for palaeoceanography and palaeoecology carbonate skeletons of fossil marine organisms are widely used to reconstruct palaeoceanographic parameters specifically the geochemistry of jurassic and cretaceous belemnite rostra is traditionally interpreted to represent near sea surface seawater properties more recently an increasing number of workers have reported significant scatter in geochemical data e g 18o 13c element ca ratio when comparing rostra from the same stratigraphic level or within a single belemnite rostrum this scatter is not explained by differential diagenetic overprint alone here we report petrographic evidence on the primary ultrastructure of rostra of megateuthis middle jurassic and belemnitella and gonioteuthis late cretaceous the biogenic ultrastructure consists of a filigree framework of triaxial branches and tetrahedrons of variable size forming a honeycomb like network data presented here suggest that these rostra yielded as much as 50 to 90 primary pore space on the level of a working hypothesis and in analogy with modern cephalopods we propose that the pore space was formerly filled with body fluid and or organic compounds during the life time of these organisms intra rostral porosity was post mortem occluded by earliest diagenetic isopachous calcite cements of a non biogenic origin these may have been precipitated due to increased alkalinity related to the decay of organic matter if this holds true then the resulting fabric represents a composite biogenic abiogenic structure in order to optically separate the two calcite phases forming a single calcite fibre we employed a wide range of state of the art analytical tools to thin sections and ultra thin sections of well preserved specimens pending a verification of these well supported ultrastructural data by means of high resolution geochemical analyses from biogenic and abiogenic phases we suggest that these findings have significance for those using belemnite rostra as archives of their palaeoenvironment

ba ra th and u in marine mollusc shells and the potential of 226ra ba dating of holocene marine carbonate shells the geochemistry of ba ra th and u and the potential of using 226 ra ba ratios as an alternative dating method are explored in modern and holocene marine mollusc shells five modern shells of the antarctic scallop adamussium colbecki collected from the present day beach and six radiocarbon dated specimens from holocene beach terraces of the ross sea region antarctic between 700 and 6100 calibrated yr bp old have been analysed by mass spectrometry in clean shells 226 ra concentrations and 226 ra ba ratios show a clear decrease with increasing age suggesting the possibility of 226 ra dating limiting factors for such dating are ba and 226 ra present in surface contaminants and ingrowth of 226 ra from u present within the shell surface contamination is difficult to clean off entirely but moderate levels of residual contamination can be corrected using 232 th sub samples from the same shell with different proportions of contamination form a mixing line in a 226 ra ba 232 th ba graph and the 226 ra ba of the pure shell can be derived from the intercept on the 226 ra ba axis contaminant corrected 226 ra ba ratios of late holocene 14 c dated samples fall close to that expected from simple 226 ra excess decay from seawater 226 ra ba values 226 ra ingrowth from u incorporated into the shell during the lifetime of the mollusc can be corrected for however the unknown timing of post mortem u uptake into the shell makes a correction for 226 ra ingrowth from secondary u difficult to achieve in the a colbecki shells 226 ra ingrowth from such secondary u becomes significant only when ages exceed 2500 yr in younger shells 226 ra ba ratios corrected for surface contamination provide chronological information if evidence for a constant oceanic relationship between 226 ra and ba in the ocean can be confirmed for that time scale the 226 ra ba chronometer may enable the reconstruction of variability in sea surface 14 c reservoir ages from mollusc shells and allow its use as a paleoceanographic

trace metal mg ca and sr ca analyses of single coccoliths by secondary ion mass spectrometry here we present the first multi species comparison of modern and fossil coccolith trace metal data obtained from single liths we present both trace metal analyses sr ca mg and al and distribution maps of individual paleogene fossil coccoliths obtained by secondary ion mass spectrometry sims we use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite the analysis of coccoliths from deep ocean sediments spanning the eocene oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments instead where present diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite diagenetic overgrowths on coccoliths are easily distinguished in sims analyses on the basis of relatively higher mg and lower sr concentrations than co occurring primary coccolith calcite this interpretation is confirmed by the comparable sims analyses of modern cultured coccoliths of coccolithus braarudii further with diagenetic calcite overgrowth being the principle source of bias in coccolith based geochemical records we infer that lithologies with lower carbonate content deposited below the palaeo lysocline are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate rich sediments where overgrowth is ubiquitous the preservation of primary coccolith carbonate in low carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism

magma traps and driving pressure consequences for pluton shape and emplacement in an extensional regime abstract the level of emplacement and final form of felsic and mafic igneous rocks of the wichita mountains igneous province southwestern oklahoma u s a are discussed in light of magma driving pressure lithostatic load and crustal magma traps deposition of voluminous a type rhyolites upon an eroded gabbroic substrate formed a subhorizontal strength anisotropy that acted as a crustal magma trap for subsequent rising felsic and mafic magma intruded along this crustal magma trap are the a type sheet granites length thickness 100 1 of the wichita granite group of which the mount scott granite sheet is typical and smaller plutons of biotite bearing roosevelt gabbro in marked contrast to the subhorizontal granite sheets the gabbro plutons form more equant stocks with flat roofs and steep side walls late diabase dikes cross cut all other units but accompanying basaltic flows are extremely rare in the volcanic pile based on magmastatic calculations we draw the following conclusions concerning the level of emplacement and the shape of these intrusions 1 magma can rise to a depth at which the magma driving pressure becomes negligible magma that maintains a positive driving pressure at the surface has the potential to erupt 2 magma ascent may be arrested at a deeper level in the crust by a subhorizontal strength anisotropy i e crustal magma trap if the magma driving pressure is greater than or equal to the lithostatic load at the depth of the subhorizontal strength anisotropy 3 subhorizontal sheet intrusions form along crustal magma traps when the magma driving pressure greatly exceeds the lithostatic load under such conditions the magma driving pressure is sufficent to lift the overburden to create the necessary space for the intrusion 4 thicker steep sided stocks or batholiths with flat roofs form at crustal magma traps when the magma driving pressure approximates that of the lithostatic load under these conditions the necessary space for the intrusion must be created by other mechanisms e g stoping 5 subvertical sheets i e dikes form when the magma driving pressure is less than the lithostatic load at the level of emplacement

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

an evaluation of inoceramid single prism sclerochronology abstract inoceramid prisms are among the most common microfossils that can be found in late cretaceous strata since these biomineral units were formed by sequential accretion in the outer shell layer of the bivalves they potentially serve as archives of short term circa annual paleowater temperature fluctuations in the present study we tested to what extent intra prismatic stable isotope variations of individual inoceramid prisms reflect sub annual 13c and the 18o patterns we obtained multiple carbonate samples from prisms recovered from the sediment and from a cross sectioned inoceramid shell fragment and compared data from these samples to data from classical sclerochronological sampling i e sequential drilling the analyzed shell material belonged to the species platyceramus platinus from the smoky hill chalk member niobrara formation kansas usa scanning electron microscopy sem was used to evaluate the diagenetic alteration of the studied prisms and allowed to identify suitable material for stable isotope analyses the 18o values of drilled carbonate samples 18odrill and of prisms 18oip compare very well to each other when temporally aligned r2 0 98 the stable carbon isotope values 13cdrill 13cip however show less agreement r2 0 28 which is likely attributable to different time averaging of the samples we discuss how to identify the most suitable prisms for sub annual paleotemperature reconstructions from disarticulated material using microgrowth patterns and geometrical features of the prisms as proxies for changing growth rates finally we apply the novel sampling strategy to naturally occurring disarticulated prisms from the sediment and compare their intra prismatic isotope values 13cips and 18oips to those of bulk analyzed prism fragments from the sediment 13cbps and 18obps sclerochronological analysis of the prisms from the sediment yields 18oips fluctuations of 1 89 virtually identical to the 18oip chronologies of the prisms extracted from the shell cross section 1 90 the overall ranges of the 18oip and 18oips values are identical 2 60 and capture very well the expected seasonal stable oxygen isotope oscillation derived from the 18odrill values 2 61 the range of the 18oips data is two fold larger than that of the 18obps values 1 19 suggesting a strong effect of time averaging on the stable oxygen isotope data of the bulk analyzed prisms fragments according to our novel statistical model the resolution of 18obps data can be increased by preferentially analyzing short ca 300 m individual prisms fragments at least n 20

organic matrix taphonomy in some molluscan shell microstructures abstract the organic matrix of selected specimens of cephalopods and bivalves was observed by scanning electron microscopy upon shell sections etched and preserved by critical point drying for specimens ranging in age from pennsylvanian to recent it was noted that physical preservation of the organic matrix was not strongly dependent on age matrices were also found to have degraded at different rates in different shell microstructures even in the same shell the type of degradation had also varied even for the same kind of microstructures the occurrence of preserved organic matrix may be more widespread among molluscan fossils than commonly thought

late turonian climate variability in the bohemian cretaceous basin a sclerochronological study of inoceramus hercules shells from the upohlavy quarry czech republic abstract the 18o record of well preserved shells of the inoceramid inoceramus hercules from the upohlavy working quarry czech republic provides an insight into the climate variability in the late turonian benthic environment of the bohemian cretaceous basin similar to modern bivalves this inoceramid species built its shell near equilibrium with the oxygen isotope value of the ambient water due to the nearly year round shell growth sequentially sampled 18o values allowed to estimate the narrowest sub annual temperatures fluctuations that prevailed during lifetime of the organisms in accordance with previous studies reconstructed temperatures suggest colder water conditions 19 0 0 9 c during the earliest late turonian coinciding with the hyphantoceras event also known as hitch wood event than during the later part of the substage 20 9 1 1 c climate warming however did not affect the sub annual temperature fluctuations evenly but predominantly affected the warmest part of the year at least 4 0 c on the contrary the coldest recorded temperatures remained more or less invariant varying not much more than 1 0 c across the studied time interval the observed changes in the benthic temperature estimates likely reflect shifts in seasonal sea surface temperature amplitudes in response to climate forcing given the widespread distribution of i hercules in the upper turonian lower coniacian hemipelagic strata of europe the present study sets the basis for future continent wide sub annually resolved climate reconstructions

subtropical sea surface warming and increased salinity during eocene thermal maximum 2 eocene thermal maximum 2 etm 2 ca 54 2 ma represents the second largest of the major eocene hyperthermals yet comparatively little is known about the scale and rate of climatic change for key regions here we provide the first detailed records of subtropical sea surface warming and salinization for etm 2 at two subtropical locations ocean drilling program sites 1209 north pacific and 1265 south atlantic coupled planktic foraminiferal mg ca and 18o indicate 2 4 c of rapid warming and local salinization of 1 2 ppt at both sites the increase in sea surface temperature is equivalent to anomalies reported from higher latitude sites and is consistent with theory on the expected pattern of spatial temperature response to greenhouse gas forcing in an ice free world i e no ice albedo feedback similarly the observed salinization is consistent with the hypothesis of enhanced meridional vapor transport and increased subtropical aridity in a warmer world

in situ δ18o and mg ca analyses of diagenetic and planktic foraminiferal calcite preserved in a deep sea record of the paleocene eocene thermal maximum we report 18o and minor element mg ca sr ca data acquired by high resolution in situ secondary ion mass spectrometry sims from planktic foraminiferal shells and 100 500 m sized diagenetic crystallites recovered from a deep sea record odp site 865 of the paleocene eocene thermal maximum petm the 18o of crystallites 1 2 pee dee belemnite pdb is 4 8 higher than that of planktic foraminiferal calcite 3 6 pdb while crystallite mg ca and sr ca ratios are slightly higher and substantially lower than in planktic foraminiferal calcite respectively the focused stratigraphic distribution of the crystallites signals an association with petm conditions hence we attribute their formation to early diagenesis initially sourced by seafloor dissolution burndown ensued by reprecipitation at higher carbonate saturation the mg ca ratios of the crystallites are an order of magnitude lower than those predicted by inorganic precipitation experiments which may reflect a degree of inheritance from donor phases of biogenic calcite that underwent solution in the sediment column in addition sims 18o and electron microprobe mg ca analyses that were taken within a planktic foraminiferal shell yield parallel increases along traverses that coincide with muricae blades on the chamber wall the parallel 18o and mg ca increases indicate a diagenetic origin for the blades but their 18o value 0 5 pdb is lower than that of crystallites suggesting that these two phases of diagenetic carbonate formed at different times finally we posit that elevated levels of early diagenesis acted in concert with sediment mixing and carbonate dissolution to attenuate the 18o decrease signaling petm warming in whole shell records published for site 865

the a type mount scott granite sheet importance of crystal magma traps the presence of rapakivi feldspar and of distinctive porphyritic texture of mount scott granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile final crystallization conditions are interpreted to have been 50 mpa at depths 1 4 km based on stratigraphic constraints however geobarometry based on the al content of amphibole phenocrysts and comparison of granite compositions with phase relations in the sio2 naalsi3o8 kalsi3o8 ternary system both yield pressure estimates of 200 mpa these pressure estimates are interpreted as plumbing the depth of a temporary storage chamber at 7 8 km this depth coincides in this case both with the probable proterozoic basement cover contact and with the calculated brittle ductile transition at time of ascent of mount scott magma although rising magma that fed the preceeding voluminous carlton rhyolite apparently rose unimpeded past these horizontal anisotropies rising magma that formed mount scott granite temporarily paused at this depth based on magmastatic calculations we suggest that horizontal anisotropies e g brittle ductile transition become crustal magma traps where the magma driving pressure exceeds the lithostatic load when the anisotropy is encountered during rifting initial large influxes of magma may proceed passed crustal anisotropies but have the effect of increasing the relative magma driving pressure through reducing horizontal stress thus magma driving pressure may eventually exceed the lithostatic load at the depth of the brittle ductile transition thereby activating this crustal magma trap ponding of magma at the brittle ductile transition chokes the eruption such a pause in magma supply rate may permit a return to initial stress conditions and deactivate the crustal magma trap once again magma will rise to the surface initiating a new magmatic cycle

no place to retreat heavy extinction and delayed recovery on a pacific guyot during the paleocene eocene thermal maximum modern global change threatens alpine ecosystems by forcing species to migrate to higher elevations and potentially eliminating alpine habitat altogether here we show that an analogous restriction of suitable habitat operates on submarine mountains during the paleocene eocene thermal maximum petm ca 55 96 ma ostracodes underwent local extinction on the crest of allison guyot in the central pacific ocean which lost 64 of its ostracode species richness 14 species reduced to three species and as much as 94 of ostracode abundance for 1 1 m y before recolonization rebuilt biodiversity and abundance over the next 200 k y biotic changes may reflect an increase in current speeds acidification and a decrease in food supply owing to a temperature driven increase in metabolic rates notably continental margin ostracodes also underwent extinction during the petm 25 38 loss but unlike allison guyot faunas could quickly repopulate the continental slope the absence of refugia for isolated seamounts prolonged the reduction in biodiversity initiated by the petm a pattern that may be expected for modern seamount faunas in an era of future global change

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

revisiting diagenesis on the ontong java plateau evidence for authigenic crust precipitation in globorotalia tumida the calcite tests of foraminifera lie in marine sediments for thousands to millions of years before being analysed to generate trace element and isotope palaeoproxy records these sediments constitute a distinct physio chemical environment from the conditions in which the tests formed storage in sediments can modify the trace element and isotopic content of foraminiferal calcite through diagenetic alteration which has the potential to confound their palaeoceanographic interpretation a previous study of g tumida from the ontong java plateau western equatorial pacific found that preferential dissolution of higher mg chamber calcite and the preservation of a low mg crust on the tests significantly reduced whole test mg ca and sr ca brown and elderfield 1996 here we revisit these specimens with a combination of synchrotron x ray computed tomography sxct and electron probe micro analyses epma to re evaluate the nature of their diagenetic alteration the dissolution of higher mg calcite with depth was directly observed in the sxct data confirming the inference of the previous study the sxct data further reveal a thickening of the chemically and structurally distinct calcite crust with depth we propose that these crusts have a diagenetic origin driven by the simultaneous dissolution of high mg chamber calcite and precipitation of low mg crust from the resulting modified pore water solution while the breadth of the study is limited by the nature of the techniques the observation of both dissolution and re precipitation of foraminiferal calcite serves to demonstrate the action of two simultaneous diagenetic alteration processes with significant impacts on the resulting palaeoproxy signals

late cretaceous oceans and the cool tropic paradox oxygen isotopic proxies of paleo sea surface temperatures ssts suggest that maastrichtian about 66 million years ago tropical ssts were lower than those of today they also demonstrate that maastrichtian latitudinal sst gradients were much lower than those of the present the low maastrichtian sst gradients indicate that meridional heat transport was much greater or latitudinal differences in the balance of radiation to and from the sea surface were much less extreme during the latest cretaceous than they are today or that both conditions were true these findings challenge traditional interpretations of greenhouse late cretaceous climates

impact of dissolution on the sedimentary record of the paleocene eocene thermal maximum the input of massive amounts of carbon to the atmosphere and ocean at the paleocene eocene thermal maximum petm 55 53 ma resulted in pervasive carbonate dissolution at the seafloor at many sites this dissolution also penetrated into the underlying sediment column the magnitude of dissolution at and below the seafloor a process known as chemical erosion and its effect on the stratigraphy of the petm are notoriously difficult to constrain here we illuminate the impact of dissolution by analyzing the complete spectrum of sedimentological grain sizes across the petm at three deep sea sites characterized by a range of bottom water dissolution intensity we show that the grain size spectrum provides a measure of the sediment fraction lost during dissolution we compare these data with dissolution and other proxy records electron micrograph observations of samples and lithology the complete data set indicates that the two sites with slower carbonate accumulation and less active bioturbation are characterized by significant chemical erosion at the third site higher carbonate accumulation rates more active bioturbation and possibly winnowing have limited the impacts of dissolution however grain size data suggest that bioturbation and winnowing were not sufficiently intense to diminish the fidelity of isotopic and microfossil assemblage records

comparison of δ18o analyses on individual planktic foraminifer orbulina universa shells by sims and gas source mass spectrometry author s wycech jb kelly dc kozdon r orland ij spero hj valley jw abstract 2018 elsevier b v the oxygen isotope 18o compositions of final chamber fragments of individual shells of the planktic foraminifer orbulina universa were measured in situ via secondary ion mass spectrometry sims and by traditional gas source mass spectrometry gsms entailing acid digestion of sampled calcite the paired sims gsms analyses were performed on final chamber fragments of fossil shells taken from the top of a sediment core holocene as well as shells grown in laboratory culture multiple iterations of sims gsms analyses were conducted on final chamber fragments treated with a variety of cleaning protocols the series of paired analyses yielded an average sims gsms 18o offset 18osims gsms of 0 9 0 1 2 se the volume of material analyzed in 10 m sims spots is 105 times smaller than that analyzed by gsms hence the extent to which these 18osims gsms values represent real differences in analyte vs instrumental factors remains unclear possible contributing factors to the sims gsms 18o difference include sample standard mismatch by sims differences in standardization of sims and gsms and non calcite contaminants in samples although the two datasets are consistently offset sims values reproduce inter shell 18o variability delineated by shell fragment gsms values this strong positive covariance proved useful for bringing the two datasets into agreement i e 18osims gsms 0 and confirms that sims based foraminifer 18o values record changes in calcification temperature and or 18o of seawater whether shells of foraminifer taxa with differing microcrystalline structures chemical composition and or preservation histories register a similar 18osims gsms value is a subject of ongoing testing

coupled evolution of temperature and carbonate chemistry during the paleocene eocene new trace element records from the low latitude indian ocean abstract the early paleogene represents the most recent interval in earth s history characterized by global greenhouse warmth on multi million year timescales yet our understanding of long term climate and carbon cycle evolution in the low latitudes and in particular the indian ocean remains very poorly constrained here we present the first long term sub eccentricity resolution stable isotope 13 c and 18 o and trace element mg ca and b ca records spanning the late paleocene early eocene 58 53 ma across a surface deep hydrographic reconstruction of the northern indian ocean resolving late paleocene 405 kyr paced cyclicity and a portion of the petm recovery our new records reveal a long term warming of 4 5 c at all depths in the water column with absolute surface ocean temperatures and magnitudes of warming comparable to the low latitude pacific as a result of warming we observe a long term increase in 18 o sw of the mixed layer implying an increase in net evaporation we also observe a collapse in the temperature gradient between mixed layer and thermocline dwelling species from 57 54 ma potentially due to either the development of a more homogeneous water column with a thicker mixed layer or depth migration of the morozovella in response to warming synchronous warming at both low and high latitudes along with decreasing b ca ratios in planktic foraminifera indicating a decrease in ocean ph and or increasing dissolved inorganic carbon suggest that global climate was forced by rising atmospheric co2 concentrations during this time

exploding xenoliths and the absence of elephants graveyards in granite batholiths abstract biotite monzogranite near the eastern margin of the late devonian south mountain batholith at portuguese cove nova scotia surrounds a large 20 m 25 m anisotropic decimetre scale interbedded psammite and semipelite xenolith of the metamorphic regional greenschist thermal cordierite hornfels country rocks of the cambro ordovician meguma group the xenolith has two distinct types of surfaces against the monzogranite i one rounded diffuse and apparently old surface that had prolonged contact with the granite magma and ii two straight sharp and apparently new surfaces that had more recently come into contact with the granite magma more than 375 thin sheets width n 224 0 1 0 5 cm n 66 0 5 1 0 cm n 51 1 0 5 0 cm n 30 5 0 10 0 cm n 3 10 cm n 2 ranging in composition from monzogranite to pegmatite to coarse quartz sericite cut the xenolith parallel to bedding producing a cumulative volume expansion of 14 in the xenolith aspect ratios in some of the thin sheets exceed 1000 1 several sheets cut the xenolith perpendicular to bedding producing a volume expansion of

low temperature stable mineral recrystallization of foraminiferal tests and implications for the fidelity of geochemical proxies abstract fossilized foraminiferal tests are widely used as proxies to constrain paleoenvironments including past sea surface and bottom water temperatures and the chemical composition of ancient seawater however relatively little is known about the extent to which calcareous foraminiferal tests exchange with seawater prior to burial in this study we used a 45ca radiotracer approach to quantify the extent and rate of foraminiferal calcite fluid exchange over a three month period modern foraminiferal tests exhibited faster exchange with a 45ca spiked solution 2 6 10 4 to 2 0 10 5 mol m2 d than fossil foraminiferal tests 7 6 10 5 to 5 3 10 6 mol m2 d from odp site 807 the impact of dissolved si on the exchange rate of modern foraminifera was minimal 2 6 10 4 to 9 2 10 6 mol m2 d unlike foraminiferal calcite inorganic calcite exchanged at remarkably slow rates 6 6 10 6 to 5 9 10 7 mol m2 d suggesting that biogenic calcite is more reactive than inorganic calcite increased ca2 mg2 and sr2 concentrations in fluids from parallel tracer free reactors indicated preferential dissolution of tests though there was no overt change in test morphology during experiments as imaged by scanning electron microscopy and micro ct scanning time dependent box model simulations of 45ca as well as aqueous elemental chemistry support the hypothesis that calcite fluid exchange occurred via dissolution reprecipitation of foraminiferal tests that was induced by intra test chemical heterogeneity the short term exchange reactions investigated in this study are comparable to the reactions that can occur in the seawater column and at the sediment seawater interface this work suggests that dissolution reprecipitation in such settings has the potential to overprint the chemistry of foraminiferal tests without overt physical alteration which can lead to a potential bias in paleoenvironmental reconstructions model based estimates suggest a maximum of 2 3 c alteration of mg ca based temperatures over experimental time scales model efforts also suggest that the diagenetic trajectories in mg ca 18 o space for instance are impacted by the partition coefficient of mg in calcite mg as well as by the mechanism of alteration this is demonstrated for i the ratio of exchange to dissolution and ii the relative rate of high mg calcite to low mg calcite reaction we have illustrated that the mechanism of alteration in addition to water rock ratios determine diagenetic trajectories finally surface reaction has implications for our ability to constrain fractionation factors in experimental and natural systems the experimental observations suggest that exchange between tests and solution is nominal over 100 days experiments aimed at deducing fractionation factors rely on the equilibration of bulk solid and fluid since these are the readily analyzed reservoirs we quantify the fraction of carbonate 5 that must react so that surface reaction does not impact the interpretation of ca isotopic fractionation factors and discuss the implications for more fluid dominated elements such as mg and o

a new form of needle fiber calcite produced by physical weathering of shells needle fiber calcite is a common crystal form in soils and sediments from diverse environmental settings and it has been used as evidence of a specific soil development either past or present however it can have either a physicochemical or a biological origin and its ubiquity prevents straightforward use as an environmental proxy in this paper we present a new form of needle fiber calcite derived neither from biologically mediated mineralization in the soil nor from physicochemical precipitation this needle fiber calcite is monocrystalline and prismatic and is associated with the physical weathering of mytilus edulis linnaeus bivalve shells found in soils from anthropic shell middens located on the northern coast of the beagle channel argentina the effects of freeze thaw cycles can be observed in the local soils and would be responsible for the release of the calcite crystals that make up the outer layer of the shell in this respect the new form of needle fiber calcite would be specific for this process in anthropogenic soils in cold climates and could provide information on past climatic conditions

was the ediacaran shuram excursion a globally synchronized early diagenetic event insights from methane derived authigenic carbonates in the uppermost doushantuo formation south china abstract the ediacaran period is characterized by the most profound negative carbon isotope 13c excursion in earth history the shuram excursion various hypotheses including the massive oxidation of dissolved organic carbon doc in the oceans the weathering of terrestrial organic carbon or the release and oxidation of methane hydrates and or expelled petroleum from the subsurface have been proposed as sources of the 13c depleted carbon more recently it has been suggested that global scale precipitation of early authigenic carbonates driven by anaerobic microbial metabolism in unconsolidated sediments may have caused the shuram excursion but empirical evidence is lacking here we present a comprehensive analysis of a shuram associated interval from the uppermost doushantuo formation in south china our study reveals petrographic evidence of methane derived authigenic calcite formed as early diagenetic cements and nodules that are remarkably depleted in 13c suggesting a buildup of alkalinity in pore fluids through the anaerobic oxidation of methane aom and systematically depleted in 18o relative to co occurring dolomite early authigenesis of these minerals is likely to be driven by increased microbial sulfate reduction triggered by enhanced continental weathering in the context of a marked rise in atmospheric oxygen levels in light of the finding of methane derived authigenic carbonates at zhongling and based on our basin scale stratigraphic correlation we hypothesize that the marked 13c and 18o depletion including their co variation noted worldwide in the shuram excursion may reflect an episode of authigenesis occurring within a sulfate methane transition zone smtz if true the shuram excursion was then a global biogeochemical response to enhanced seawater sulfate concentration in the ediacaran ocean driven by the neoproterozoic oxidation of surface environments this paleo oceanographic transition may have therefore paved the way for subsequent evolution and diversification of animals our study highlights the significance of an integrated approach that combines petrography mineralogy and texture specific micro drilling geochemistry in chemostratigraphic studies

the paleocene eocene thermal maximum how much carbon is enough the paleocene eocene thermal maximum petm 55 53 million years before present was an abrupt warming event that involved profound changes in the carbon cycle and led to major perturbations of marine and terrestrial ecosystems the petm was triggered by the release of a massive amount of carbon and thus the event provides an analog for future climate and environmental changes given the current anthropogenic co2 emissions previous attempts to constrain the amount of carbon released have produced widely diverging results between 2000 and 10 000 gigatons carbon gtc here we use the uvic earth system climate model in conjunction with a recently published compilation of petm temperatures to constrain the initial atmospheric co2 concentration as well as the total mass of carbon released during the event thirty six simulations were initialized with varying ocean alkalinity river runoff and ocean sediment cover simulating various combinations of pre petm co2 levels 840 1680 and 2520 ppm and total carbon releases 3000 4500 7000 and 10 000 gtc we find that both the 840 ppm plus 7000 gtc and 1680 ppm plus 7000 10 000 gtc scenarios agree best with temperature reconstructions bottom waters outside the arctic and north atlantic oceans remain well oxygenated in all of our simulations while the recovery time and rates are highly dependent on ocean alkalinity and sediment cover the maximum temperature anomaly used here to constrain the amount of carbon released is less dependent on this slow acting feedback

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

effects of sample pretreatment and external contamination on bivalve shell and carrara marble δ 18 o and δ 13 c signatures abstract stable isotope signatures of bivalve shells serve as important paleoclimate proxies however such data can be biased as a consequence of physical and chemical sample pretreatment and contamination during sampling as yet the potential isotope error induced by paleontological preservation techniques and specific methods used in bivalve sclerochronology have not been systematically assessed to address these issues homogenized powder of a well preserved aragonitic fossil shell glycymeris obovata ca 30 ma old as well as carrara marble powder calcite were exposed to ultrasound a set of different staining solutions and cleaning agents in addition these reference materials were artificially contaminated with increasing proportions of powder prepared from periostracum alcian blue and cured adhesives whereas some treatments rinsing with milli q water immersion in alizarin red s solution and possibly mutvei s solution did not affect the isotope values of the carbonate samples severe isotope shifts were observed after immersing shell powder in feigl s solution 18 o 0 62 and mixing carrara marble powder with gluetec metal epoxy a contamination level of 41 7 wt shifted 18 o and 13 c values by 2 12 and 1 74 respectively increasing levels of metal epoxy in the sample resulted in a sharp non linear decrease of the isotope values the majority of tested treatments conducted with the carbonate powders and contaminants added to them caused minor to moderate mainly statistically significant isotope offsets bleaching with naocl and h 2 o 2 exposure to ethyl alcohol and rewoquat w 3690 pg a surfactant ultrasonic cleaning contamination with powder of alcian blue cured superglue several different polyepoxies methacrylates and polyvinyl butyral resins as well as periostracum in conclusion pretreatment of bivalve shells with an intended use for isotope analysis should be kept at an absolute minimum and contamination with adhesives etc should be avoided specimens from museum collections that underwent special conservation methods may be of limited value for isotope studies unless the history of sample treatment is known although only a few of the tested substances and methods strongly biased the isotope signatures even small changes can accumulate to levels that are inacceptable for high resolution paleoclimatology

i ca evidence for upper ocean deoxygenation during the petm anthropogenic global warming affects marine ecosystems in complex ways and declining ocean oxygenation is a growing concern forecasting the geographical and bathymetric extent rate and intensity of future deoxygenation and its effects on oceanic biota however remains highly challenging because of the complex feedbacks in the earth ocean biota system information on past global warming events such as the paleocene eocene thermal maximum petm 55 5 ma a potential analog for present and future global warming may help in such forecasting documenting past ocean deoxygenation however is hampered by the lack of sensitive proxies for past oceanic oxygen levels throughout the water column as yet no evidence has been presented for pervasive deoxygenation in the upper water column through expansion of oxygen minimum zones omzs we apply a novel proxy for paleoredox conditions the iodine to calcium ratio i ca in bulk coarse fraction sediment and planktonic foraminiferal tests from pelagic sites in different oceans and compared our reconstruction with modeled oxygen levels the reconstructed iodate gradients indicate that deoxygenation occurred in the upper water column in the atlantic indian oceans and possibly the pacific ocean as well during the petm due to vertical and potentially lateral expansion of omzs

foraminifer test preservation and diagenesis comparison of high latitude eocene sites foraminifer tests are prone to diagenetic recrystallization on a micron scale that can affect their geochemical composition hence it is important to identify fossil material that is well preserved here we illustrate the textures of tests from several high latitude eocene sites using a combination of reflected light microscopy and high resolution scanning electron microscopy the sites are ocean drilling program odp site 647 in the labrador sea 53 n odp site 689 at maud rise in the weddell sea 64 s odp site 1135 kerguelen plateau c 59 s and outcrop samples from hampden beach new zealand palaeolatitude c 55 s the foraminifera studied from site 647 and hampden beach have glassy transparent tests that show only minor signs of diagenetic alteration whereas the foraminifera from sites 690 and 1135 are opaque and recrystallized we associate the better state of foraminifer preservation at the former sites with the high clay content of the sediments our observations suggest that site 647 and hampden beach may be useful for the establishment of high latitude sea surface temperatures and hence global temperature gradients in the eocene

diagenetic mg rich calcite in mediterranean sediments quantification and impact on foraminiferal mg ca thermometry abstract mg ca ratios in planktonic foraminifera have been developed into a powerful tool in paleoceanography to reconstruct past sea surface temperatures sst however additional factors that might have an influence on mg ca like dissolution salinity diagenesis and carbonate ion effects have come into focus in this paper the occurrence of diagenetic calcification and its potential effects on mg ca have been studied using 20 well preserved core tops recovered from the mediterranean sea analyses were performed on two planktonic foraminifer species globigerinoides ruber and globigerina bulloides using icp aes mg ca measurements sem observations and x ray diffractometry analyses foraminiferal mg ca values are higher than those obtained in the open sea the highest values were found in the eastern mediterranean basin these anomalies cannot be simply explained by a salinity effect because mg ca ratios when corrected for temperature influence do not display any significant correlation with salinity our results seem to indicate that diagenesis can account for anomalously high mg ca values indeed sem observations show aggregates of rhombohedral crystals that could be interpreted as secondary calcite overgrowths we note also the occurrence of numerous coccoliths trapped in foraminifer walls and covered with a secondary mineral phase x ray diffraction diagrams of numerous foraminiferal samples exhibit peak of mg rich calcite 10 12 associated with the usual foraminifer calcite peak it has been demonstrated that this calcite highly rich in mg is compatible with an inorganic calcite precipitated directly from seawater the deconvolution of the main xrd peak 104 shows that the percentage of mg rich calcite can reach up to 21 of the total foraminiferal calcite in the eastern basin whereas in the western mediterranean sea proportions do not exceed 5 in addition we demonstrate that the diagenetic process is very heterogeneous even at the sample scale and is not simply a reflection of co 3 at the sea bottom thus the high mg ca ratios measured from mediterranean sea planktonic foraminifera does not appear to be caused by increased mg uptake in a high salinity setting but instead result chiefly from the presence of mg rich calcite 10 12 deposited during early diagenetic processes

the accuracy of mid pliocene δ 18 o based ice volume and sea level reconstructions abstract understanding the sensitivity of the polar ice caps to a modest global warming 2 3 c above preindustrial is of paramount importance if we are to accurately predict future sea level change knowledge that will inform both social and economic policy in the coming years however decades of study of the pliocene 2 6 5 3 ma an epoch in recent earth history characterized by atmospheric co2 levels similar to today have so far failed to provide definitive sea level and ice volume estimates for that time here we review the sources of uncertainty in the paired mg ca 18o methodology used to estimate past sea level ice volume and ocean temperature as well as discuss common assumptions that may bias our interpretation of ocean geochemical records including the lr04 benthic 18o stack a global compilation of 57 oxygen isotope records that forms the standard template of climate change history for the last 5 3 million years

the micropaleontological record of marine early eocene oil shales from jordan abstract core os 28 located in central jordan offers an expanded record of calcareous nannofossils and benthic foraminifera for the early eocene of the southern tethys the oil shale succession of the studied interval covers calcareous nannofossil biozones np10 np11 np12 and np13 microfossils document the biotic response of calcareous nannofossils and benthic foraminifera to short and long term warming trends of the early eocene following the paleocene eocene thermal maximum petm on a global scale two early eocene short term shifts to higher atmospheric co 2 concentration are recorded by negative 13 c excursions these are known as eocene thermal maximum 2 and 3 etm2 etm3 stable isotope records 13 c org 13 c carb 18 o carb from the study area do not show these negative excursions which elsewhere can be correlated with the two hyperthermal events known from early eocene successions the absence of negative 13 c signals otherwise typical for etm2 and etm3 is explained by a diagenetic alteration of the isotope signal after deposition high abundances of the nannofossil taxon sphenolithus spp in biozone np10 indicate less fertile conditions for this interval than for the overlying biozone np11 throughout biozones np11 to np13 coccolithus pelagicus and toweius spp are the dominant taxa of the assemblages suggesting a mesotrophic environment surface waters experienced a temperature change from warm to moderate warm the benthic foraminifera in calcareous nannofossils biozone np10 and in the lower part of np11 reflect oligo mesotrophic and moderate to well oxygenated bottom water conditions throughout the upper part of biozones np11 np12 and np13 the benthic foraminifera are characterized by an increasing abundance of anomalinoides zitteli lenticulina spp and valvulineria scrobiculata this coincides with enriched total organic matter content toc indicating a shift to mesotrophic conditions and a moderate oxygen supply of the bottom waters based on the micropaleontological observations made in core os 28 the early eocene is first characterized by an increase and subsequently by a decrease of nutrients and oxygen the composition of both benthic and planktic communities was rather controlled by variations of regional environmental parameters than by global ones these include strong runoff climatic variability and the architecture of the basin

low latitude sea surface temperatures for the mid cretaceous and the evolution of planktic foraminifera isotopic data from exceptionally well preserved foraminifera show that the subtropical north atlantic had sea surface temperatures ssts between 30 and 31 c during the late albian and early cenomanian these temperatures were warmer than average modern temperatures in the tropical western atlantic and support previous inferences based on diagenetically suspect material of albian tropical ssts of 30 c this finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle cretaceous greenhouse however our data do not support the concept of a super tethyan region of hypersaline waters in the western north atlantic during late albian and early cenomanian time because seawater salinities substantially higher than modern ones would require significantly higher ssts than those reported here isotopic analysis of mid cretaceous planktic foraminifera shows that planomalina ticinella and biticinella grew in surface waters and provide isotopic proxies for sst whereas deeper growing species include hedbergella rotalipora and praeglobotruncana none of these taxa display isotopic indications of photosymbiosis suggesting that this ecology did not evolve in planktic foraminifera before the late cretaceous contrary to previous hypotheses none of these species increased their depth habitat during their life cycles unlike many extant planktic foraminifera the rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles

influence of temperature on the composition of magnesian calcite overgrowths precipitated from seawater a constant disequilibrium technique was used to determine the composition of magnesian calcite overgrowths precipitated on pure calcite seeds from artificial seawater at 5 25 and 40 c the amount of magnesium incorporated in the overgrowths at a given temperature is independent of the precipitation rate over a wide range of saturation states and is believed to correspond to a composition in true equilibrium with seawater the distribution coefficient of magnesium dmg2 c in the magnesian calcite overgrowths increases almost linearly with temperature being 0 0121 0 0013 at 5 c 0 0172 0 0022 at 25 c and 0 0271 0 0013 at 40 c these values apply only to magnesian calcites precipitated from standard composition seawater since a previous study has shown dmg2 c to be a function of the mg2 ca2 ratio in the parent solution results of this study are compared with values reported previously by other workers and with the compositional distribution of naturally occurring magnesian calcite cements and ooids found in seawater it appears that variations in temperature are not sufficient to account for the compositional variability of naturally occurring inorganic marine magnesian calcite cements

rapid diversification of planktonic foraminifera in the tropical pacific odp site 865 during the late paleocene thermal maximum the planktonic foraminiferal generamorozovellaandacarininarapidly in 10 k y diversified during the late paleocene thermal maximum lptm giving rise to such morphotypes asm allisonensis new species m africana anda sibaiyaensis single specimen isotopicanalysisconfirmsthatm allisonensisanda sibaiyaensisarerestrictedtothelptm carbon isotope excursion recorded at ocean drilling program site 865 equatorial pacific ocean the short lived 50 to several 100 k y excursion taxa attest to the ephemeral effectsofthelptmonthecalcareousplankton single specimenoxygenisotopedatashow that evolution of m allisonensis and a sibaiyaensis was accompanied by migration to deeper water depths ancestralm velascoensisanda soldadoensiswere extremely rare or absent during the early stages of the lptm but immigrated back into the study area to coexist with their descendants in later lptm horizons photosymbiosis may have facilitatedthemorozovellidandacarininiddiversificationsduringtheoligotrophicconditionsof the lptm

planktonic foraminiferal oxygen isotope analysis by ion microprobe technique suggests warm tropical sea surface temperatures during the early paleogene 1 cool tropical sea surface temperatures ssts are reported for warm paleogene greenhouse climates based on the 18o of planktonic foraminiferal tests these results are difficult to reconcile with models of greenhouse gas forced climate it has been suggested that this cool tropics paradox arises from postdepositional alteration of foraminiferal calcite yielding erroneously high 18o values recrystallization of foraminiferal tests is cryptic and difficult to quantify and the compilation of robust 18o records from moderately altered material remains challenging scanning electron microscopy of planktonic foraminiferal chamber wall cross sections reveals that the basal area of muricae pustular outgrowths on the chamber walls of species belonging to the genus morozovella contain no mural pores and may be less susceptible to postdepositional alteration we analyzed the 18o in muricae bases of morozovellids from the central pacific ocean drilling program site 865 by ion microprobe using 10 m pits with an analytical reproducibility of 0 34 2 standard deviations in situ measurements of 18o in these domains yield consistently lower values than those published for conventional multispecimen analyses assuming that the original 18o is largely preserved in the basal areas of muricae this new 18o record indicates early paleogene 49 56 ma tropical ssts in the central pacific were 4 8 c higher than inferred from the previously published 18o record and that ssts reached at least 33 c during the paleocene eocene thermal maximum this study demonstrates the utility of ion microprobe analysis for generating more reliable paleoclimate records from moderately altered foraminiferal tests preserved in deep sea sediments

changes in the depth habitat of the oligocene planktic foraminifera dentoglobigerina venezuelana induced by thermocline deepening in the eastern equatorial pacific understanding planktic foraminiferal depth habitat along with consistent taxonomic concepts is key to accurate reconstruction of paleoceanographic records the oligocene pliocene long ranging and widely distributed species dentoglobigerina venezuelana lived in the mixed layer shallower during the early oligocene whereas the same species calcified at thermocline or subthermocline depths deeper during the late oligocene and miocene the exact timing of the species depth habitat change and its possible relationships with oligocene climate dynamics remain unknown here we reveal isotopic records of d venezuelana along with the paragloborotalia siakensis group a mixed layer dweller by using sediments at integrated ocean drilling program site u1334 in the eastern equatorial pacific throughout the oligocene a two step depth habitat change of d venezuelana is apparent 1 from upper to lower mixed layer 27 4 ma and 2 from lower mixed layer to thermocline depth 26 3 ma in addition the planktic foraminiferal faunal assemblage experienced a marked change from dominantly thermocline deeper species to abundant mixed layer shallower species suggesting that depth habitat shifts of d venezuelana were clearly related to thermocline deepening in the eastern equatorial pacific comparison of the first isotopic shift 27 4 ma at multiple sites u1334 u1333 and 1218 revealed a southward depth habitat change of d venezuelana within 200 kyr implying overall thermocline deepening with reduced steepness in the eastern equatorial pacific we consider that global warming conditions during the late oligocene likely caused thermocline deepening with upwelling decrease in the eastern equatorial pacific guiding d venezuelana to adapt to greater depths in the water column

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity

vertical thermal gradient history in the eastern equatorial pacific during the early to middle miocene implications for the equatorial thermocline development knowledge of the equatorial thermocline is essential for understanding climate changes in the tropical pacific multispecies planktic foraminiferal analyses provide a way to examine temperature distributions and thus the structure of the thermocline although the secular thermocline development has been documented back to the late miocene the early to middle miocene interval has rarely been examined in addition relationships with the dynamic antarctic ice sheets remain unclear here we investigate the vertical thermal gradient in the upper water column at integrated ocean drilling program site u1337 in the eastern equatorial pacific eep throughout the early to middle miocene 23 1 to 11 7 ma the gradient increased over the miocene climatic optimum whereas it decreased during the east antarctic ice sheet expansion eaie comparison of the eep record with its western equatorial pacific wep counterpart suggests that sea surface temperature was more stable in the wep than in the eep we further estimated equatorial thermocline from two diagonal gradients between the eep and the wep thermocline shoaled from 16 7 to 15 7 ma and tilt weakened between 16 5 and 13 8 ma the onset of the monterey excursion and the reduced antarctic ice sheet volume would have affected thermocline depth and tilt respectively thermocline depth was likely much deeper compared to pliocene to modern conditions furthermore a 4 point based distribution of isotherms 4di index was used as a metric of the evenness or unevenness of the isotherm distributions the 4di index considerably reduced at around the eaie and other mi events reflecting the evenly distributed isotherms under a more glaciated antarctica

micron scale intrashell oxygen isotope variation in cultured planktic foraminifers abstract in this study we show that the rate of shell precipitation in the extant planktic foraminifer orbulina universa is sufficiently rapid that 12 h calcification periods in 18 o labeled seawater can be resolved and accurately measured using secondary ion mass spectrometry sims for in situ 18 o analyses calcifying o universa held at constant temperature 22 c were transferred every 12 h between ambient seawater 18 o w 0 4 vsmow and seawater with enriched barium and 18 o w 18 6 vsmow to produce geochemically distinct layers of calcite separated by calcite precipitated with an ambient geochemical signature we quantify the position of the ba labeled calcite in the shell wall of o universa via laser ablation icp ms depth profiling of trace element ratios and then measure intrashell 18 o calcite in the same shells using sims with a 3 m spot and an average precision of 0 6 2 sd measured 18 o calcite values in o universa shell layers are within 1 1 of predicted 18 o calcite values elemental and oxygen isotope data show that la icp ms and sims measurements can be cross correlated within the spatial resolution of the two analytical techniques and that 18 o calcite and elemental tracers appear to be precipitated synchronously with no measurable spatial offsets these results demonstrate the capability of sims to resolve daily growth increments in foraminifer shells and highlight its potential for paleoceanographic and biomineralization applications on microfossils

fracture controlled magma conduits in an obliquely convergent continental magmatic arc magnetic fabric patterns of two mid cretaceous nested plutons 102 1 and 96 3 ma in the central sierra nevada batholith provide evidence that felsic magma emplacement and ascent occurred via north trending steeply dipping planar fracture conduits oriented obliquely to the arc u pb geochronology data indicate that emplacement of the plutons was separated by 2 to 10 m y and that they were emplaced in part via the same conduit magnetic fabrics in the younger pluton are related to its final emplacement which was strongly influenced by a system of host rock joints formation of the north trending conduits at 100 ma can be related to a small arc parallel dextral shear component that produced tension fractures and that was associated with high angle oblique convergence by 90 ma convergence had become sufficiently oblique for the development of nearly arc parallel structures which were then favored as magma conduits