the stratigraphic and sedimentological significance of late devensian ice sheet surging in holderness yorkshire u k amino acid analyses of marine mollusc valves show that the basement till of holderness yorkshire is of late devensian age ca 20 000 bp and not pre ipswichian 125 000 bp as is traditionally supposed together with the overlying skipsea and withernsea tills the basement till is argued to be a deformation till resulting from the repeated onshore surging of late devensian ice over a muddy sea floor and the subglacial transport attenuation and mixing of marine sediment silts on the surface of the basement till yielding 14c dates of 18 500 and 18 240 bp have been regarded as minimum ages for late devensian glaciation in eastern england e g the dimlington stadial of rose 1985 1989 the amino acid data presented here indicates that the maximum of the late devensian glaciation in eastern england occurred earlier sedimentological interpretation of the late devensian tills of holderness as glacially reworked marine sediments supports previous glaciological models of the british ice sheet involving surging of ice lobes along the coast of eastern england the basement skipsea and withernsea tills are separated by shallow marine sediments and may be representative of deformable bed till facies deposited below pleistocene ice sheets moving over soft fine grained sediments

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

the last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

variations in seawater sr ca recorded in deep sea bamboo corals 1 a depth transect of deep sea bamboo corals along the california margin provides evidence that coral strontium to calcium ratios sr cacoral record seawater sr ca ratios sr casw a calibration was constructed utilizing sr cacoral ratios and previously published pacific sr casw data r2 0 53 n 12 p 0 01 sr cacoral mmol mol 4 62 sr casw mmol mol 36 64 sr casw is ultimately governed by the remineralization of sr containing shells of surface water derived marine organisms e g acantharia at intermediate water depths california margin sr cacoral records from 792 and 1295 m document fluctuations in sr casw that appear decadal scale these results suggest that sr casw may not be as stable as previously assumed and may be influenced by surface productivity on short timescales

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

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

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

factors controlling the fluoride content of planktonic foraminifera an evaluation of its paleoceanographic applicability abstract this work is an assessment of the effects of seawater salinity and temperature on the incorporation of fluoride into calcitic shells of planktonic foraminifera and of the subsequent modification of shell chemistry by postdepositional dissolution a strong correlation between the fluoride content of most planktonic species and their calcification depth was observed deeper calcifying foraminifera have lower fluoride content and heavier 18o composition perhaps suggesting a temperature control on the partition coefficient however species deviations from this general trend and the absence of correlation between fluoride and sea surface temperature within an individual species suggest that the coprecipitation of fluoride in foraminiferal calcite is more strongly controlled by biological processes rather than by simple chemical relationships foraminiferal fluoride shows weak or no correlation with sea surface salinity core top planktonic foraminifera from the eastern equatorial atlantic sierra leone rise show a substantial decrease of fluoride and to a lesser extent mg content with increasing water depth 2931 5104 m these decreasing trends with depth are attributed to selective dissolution i e removal of the more dissolution susceptible fraction with a different chemical composition than the residual a process which previously has been suggested to account for variations in the isotopic composition of planktonic foraminifera these findings indicate that foraminiferal fluoride cannot serve as a reliable tracer of oceanic paleo temperature or salinity it is possible however that fluoride may be useful for the study of dissolution in deep sea sediments

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

improving temperature estimates derived from mg ca of planktonic foraminifera using x ray computed tomography based dissolution index xdx 1 temperatures derived from mg ca ratios of the calcite tests of planktonic foraminifera are distorted when samples are partially dissolved and methods are required to quantify this source of inaccuracy here we compare a dissolution index xdx based on x ray computed tomography scans to mg ca of four species of foraminifera g ruber white g sacculifer without sac n dutertrei and p obliquiloculata from core top sediments from the tropical pacific atlantic and western indian ocean deepwater calcite saturation values co32 at the sites ranged from 55 to 23 mol kg an estimate of mg ca reduction in mg ca due to dissolution was made for each sample mg ca decreased linearly from deepwater co32 values of between 10 4 and 15 5 mol kg these values are minimum estimates of the threshold below which mg ca is affected by dissolution as they are limited by assumptions made in calculating mg ca sensitivity of mg ca to co32 was greatest for g ruber where mg ca decreased by 0 102 0 036 mmol mol per mol kg sensitivity was similar for g sacculifer 0 047 0 015 mmol mol per mol kg n dutertrei 0 037 0 010 mmol mol per mol kg and p obliquiloculata 0 040 0 008 mmol mol per mol kg sensitivity was similar at all sites for each species excepting an apparently greater response for n dutertrei from the caribbean compared to other sites calibrations between xdx and mg ca provide a means to estimate dissolution bias on mg ca poor correlation between xdx and 18o suggests that for the small sample size typical for analysis variability in initial 18o overwhelms dissolution effects

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

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

biomineralization in perforate foraminifera in this paper we review the current understanding of biomineralization in perforate foraminifera ideas on the mechanisms responsible for the flux of ca2 and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera from the 1980s onward tracer experiments fluorescent microscopy and high resolution test geochemical analysis have added to existing calcification models despite recent insights no general consensus on the physiological basis of foraminiferal biomineralization exists current models include seawater vacuolization transmembrane ion transport involvement of organic matrices and or ph regulation although the magnitude of these controls remain to be quantified disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and or lack of a more systematic approach to study dis similarities between taxa in order to understand foraminiferal controls on element incorporation and isotope fractionation and thereby improve the value of foraminifera as paleoceanographic proxies it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research

origin of an esker like ridge erosion or channel fill sedimentology of the monington esker in southwest wales abstract a ridge of stratified gravel and sand near cardigan in southwest wales has previously been interpreted as an esker its sedimentology is exposed in sand pits and consists of cross bedded gravel and sand incised into a complex of climbing ripple cross laminated sand interbedded with silt and clay the succession records the progradation of fluvial channels across a former lake floor there is no clear sedimentological evidence that the sediments were deposited in an ice contact setting and therefore the feature should not be called an esker the interpretation favoured here is that the ridge is an erosional remnant either of a formerly more extensive outwash plain or of a kame terrace deposited when the adjacent valley was filled with dead ice recognition of an esker needs to be based on sedimentology and regional setting as well as on geomorphology

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

exploring the dissolution effect on the intrashell mg ca variability of the planktic foraminifer globigerinoides ruber the mg ca ratio of the planktic foraminifer globigerinoides ruber is widely used for reconstructing past sea surface temperatures the shell mg ca ratio is also lowered by dissolution which results in lower sea surface temperature estimates in partially dissolved shells here we use an electron microprobe image mapping technique to map the intrashell variability of the mg ca ratio in g ruber white sensu stricto shells to explore changes in the intrashell mg ca ratio associated with dissolution we examine shells from shallow and deep cores ceara rise western tropical atlantic from the holocene and last glacial maximum that represent a preservational gradient image map results show that the mg ca ratio is highly variable both within a single shell and among samples obtained from the same sediment interval our results show that intrashell mg ca variability is retained in samples that have undergone dissolution quantitative analysis of the data from mg ca mapping suggests that preferential loss of high mg ca calcite alone cannot account for the difference in intrashell mg ca variability of shells from shallow and deep cores in both time periods rather the data imply that in g ruber analyzed in this study there is a loss of high mg ca ratios accompanied by a more uniform lowering of mg ca over the range of intershell mg ca variability of shells subjected to dissolution at the 1 m resolution of the microprobe analysis in this study

numerical models for diagenesis and the neogene sr isotopic evolution of seawater from dsdp site 590b abstract a numerical model for the diagenetic exchange of sr between carbonates and their pore fluids during sedimentation and compaction has been developed the model has been applied to data from dsdp site 590b in order to assess the accuracy with which the sr isotope record in the carbonate sediment reflects that of seawater the most important process affecting the sr in the solid carbonate is exchange with the pore fluid due to solution reprecipitation but the concentration or isotopic composition of sr in the solid itself gives little or no information as to the magnitude of this exchange the key to determining the rate of exchange is the pore fluid where the variations of sr2 and87sr 86sr with depth are very sensitive indicators the logical structure of applying the model to data from dsdp 590b is to find by successive iteration an ocean history i e the initial87sr 86sr and sr concentration of each increment of carbonate deposited and a rate of sr exchange between pore water and solid carbonate such that the model matches the present sr concentration and87sr 86sr of both pore water and solid carbonate once all the data are matched the model provides an estimate of the rate of sr exchange due to solution reprecipitation and the evolution of87sr 86sr in seawater over the past 20 million years for dsdp 590b we find that solution reprecipitation decreases rapidly with depth from a near surface value of about 10 per million years to about 1 per million years below 200 m this rate of exchange of sr results in the carbonates of dsdp 590b preserving an accurate record of the sr isotopic evolution of the ocean over the past 5 million years but for ages greater than 5 million years the87sr 86sr ratio of the carbonate is systematically displaced from that of the seawater in which it was deposited the maximum difference is of order 5 10 5

inside story an x ray computed tomography method for assessing dissolution in the tests of planktonic foraminifera x ray computed tomography ct provides an insight into the progression of dissolution in the tests of planktonic foraminifera four species of foraminifera g ruber white g sacculifer n dutertrei and p obliquiloculata from pacific atlantic and indian ocean core top samples were examined by ct and sem inner chamber walls began to dissolve at co32 values of 12 14 mol kg close to the calcite saturation horizon dissolution and precipitation of calcite may occur simultaneously inner calcite of g sacculifer n dutertrei and p obliquiloculata from such sites appeared altered or replaced whereas outer crust calcite was dense with no pores unlike the other species there was no distinction between inner and outer calcite in ct scans of g ruber empty calcite crusts of n dutertrei and p obliquiloculata were most resistant to dissolution and were present in samples where co32 20 mol kg five stages of preservation were identified in ct scans and an empirical dissolution index xdx was established xdx appears to be insensitive to initial test mass mass loss in response to dissolution was similar between species and sites at 0 4 g mol kg we provide calibrations to estimate co32 and initial test mass from xdx

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

assessing the effect of dissolution on planktonic foraminiferal mg ca ratios evidence from caribbean core tops in order to assess the dissolution effect on foraminiferal mg ca ratios we analyzed mg ca of seven planktonic foraminiferal species and four of their varieties from caribbean core tops from 900 4700 m water depth depending on the foraminiferal species and variety mg ca start to decline linearly below co32 levels of 18 26 mol kg by 0 04 0 11 mmol mol per 1 mol kg co32 similar to decreases of 0 5 0 8 mmol mol per kilometer below 2500 3000 m water depth above these species specific critical levels mg ca remains stable with higher intraspecific mg ca variability than below we developed routines to correct mg ca from below these critical thresholds for dissolution effects which reduce the overall intraspecific variability by 24 64 and provide dissolution corrected mg ca appropriate to calculate holocene paleotemperatures when taking into account only dissolution unaffected mg ca from 2000 m the systematic succession of foraminiferal species according to their mg ca reflects expected calcification depths

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

relationships between temperature ph and crusting on mg ca ratios in laboratory grown neogloboquadrina foraminifera author s davis cv fehrenbacher js hill tm russell ad spero hj abstract 2017 american geophysical union all rights reserved mg ca ratio paleothermometry in foraminifera is an important tool for the reconstruction and interpretation of past environments however existing mg ca temperature relationships for planktic species inhabiting middle and high latitude environments are limited by a lack of information about the development and impact of low mg ca ratio crusts and the influence of the carbonate system on mg ca ratios in these groups to address this we cultured individual specimens of neogloboquadrina incompta and neogloboquadrina pachyderma in seawater across a range of temperature 6 12 c and ph 7 4 8 2 we found by laser ablation inductively couple mass spectrometry analyses of shells that culture grown crust calcite in n incompta had a lower mg ca ratio than ontogenetic calcite formed at the same temperature suggesting that temperature is not responsible for the low mg ca ratio of neogloboquadrinid crusts the mg ca temperature relationship for ontogenetic calcite in n incompta was consistent with the previously published culture based relationship and no significant relationship was found between mg ca ratios and ph in this species however the mg ca ratio in laboratory cultured n pachyderma was much higher than that reported in previous core top and sediment trap samples due to lack of crust formation in culture application of our ontogenetic calcite specific mg ca temperature relationships to fossil n pachyderma and n incompta from five intervals in cores from the santa barbara basin and the bering sea shows that excluding crust calcite in fossil specimens may improve mg ca based temperature estimates

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

ice proximal glaciomarine sedimentation and sea level change in the inverness area scotland a review of the deglaciation of a major ice stream of the british late devensian ice sheet abstract evidence of both rising and falling relative sea levels and glacitectonic movements is preserved in two formations of raised glaciomarine deposits that were laid down in front of an oscillating grounded tidewater glacier in the inverness firth these changes occurred during the latter stages of the disintegration of the moray firth ice stream one of the major ice streams that drained the british main late devensian ice sheet most of the glaciomarine deposits antedate a sequence of glacio isostatically tilted late devensian marine shorelines and associated littoral and estuarine deposits the shorelines began forming at about 13 000 bp and record a progressive fall in relative sea level a new model for the deglaciation of the moray firth region is proposed after a critical appraisal of published accounts of both onshore and offshore quaternary sequences the disintegration of the moray firth ice stream involved several rapid phases of retreat to pinning points caused by iceberg calving and triggered by rising global sea level each retreat was followed by minor readvances or stillstands possibly caused by short lived accelerated periods of glacio isostatic rebound and concomitant temporary falls in relative sea level two such events occurred in the inverness firth the ardersier oscillation and the alturlie stillstand substantial differences lower relative sea levels later deglaciation are apparent between the pattern of ice retreat in the moray firth region and published accounts of the deglaciation of the irish sea basin these differences require a reassessment of some current hypotheses concerning the disintegration of major ice streams associated with high relative sea levels furthermore geological and geomorphological evidence suggesting both rising and falling sea levels in the inverness area prior to ca 13 500 bp is not fully compatible with recently published computer simulations of the dissolution of the british main late devensian ice sheet

geological survey of canada s contributions to understanding the composition of glacial sediments drift compositional studies were initiated at the geological survey of canada gsc in the mid 1960 s in projects that drew heavily on the technology and approaches developed in fennoscandia over the previous century as this research progressed and expanded in the 1970 s its fennoscandian character diminished and like the geochemical exploration research program that it closely paralleled drift prospecting began to acquire a distinctly canadian character imposed by the geographical and logistical constraints of climate and asymmetric population distribution gsc research has increasingly focused on understanding and explaining the geochemical expression of the mineralogical composition of glacial sediments that are unaltered or only slightly altered by postdepositional weathering because glacial sediments are generated largely by crushing and abrasion their various mineral and lithological components attain characteristic size modes based on physical properties such as cleavage and hardness this s

ice flow evolution of the labrador sector of the laurentide ice sheet a review with new evidence from northern quebec abstract outcrops bearing stained striated facets indicative of north northeastward moving ice truncated by unstained striated facets indicative of various younger flows occur in the caniapiscau area of north central quebec this is the first report of differential staining of striated facets in the region we propose that the staining occurred in an ice free interval of probable interglacial age this early ice flow probably occurred during ice retreat toward the quebec highlands ice flow and glacial transport data from the southern hudson bay and james bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an early wisconsinan glacier in the quebec highlands the northern part of this flow was diverted northwestward through hudson bay and the southern part southwestward across james bay following a progressive counterclockwise rotation of flow a zone of intersection zi of two major glacier bedform systems often referred to as the horseshoe shaped labrador ice divide represents the head of a large northward convergent ice flow system that extended to ungava bay and beyond the ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of caniaspiscau reservoir we propose that this capture event correlates with the gold cove advance in ungava bay and on baffin island at about 9900 14c yr bp it is the largest advance of quebec labrador ice yet proposed for the region this correlation is based on the relative ice flow chronology accommodation of glacial lakes naskaupi and mclean in the deglaciation sequence the constraints placed on last glacial maximum lgm ice configuration by the postglacial uplift pattern and events in the deep sea record therefore the ungava ice flow pattern is not a relict pre wisconsinan glacial landscape as recently proposed

global dissolution effects on planktonic foraminiferal mg ca ratios controlled by the calcite saturation state of bottom waters mg ca ratios of planktonic foraminiferal tests are important tools for reconstructing past ocean temperatures at different levels of the upper water column yet numerous studies suggest a significant influence of calcite dissolution on mg ca ratios lowering their initial signal recorded within a planktonic foraminiferal habitat to determine the effect of dissolution this study presents mg ca ratios of eight planktonic foraminiferal species from the south china sea sediment surface continuously decreasing with increasing water depth the mg ca ratios also decrease with calcite saturation states close to and below saturation bottom water delta co32 40 mu mol kg 1 this preservation pattern compares well with examples of mg ca dissolution from the tropical atlantic ocean and is independent of the foraminiferal species merging a global data set by separate normalization of 79 mg ca data sets from the pacific atlantic and indian oceans which removes thermal differences between the ocean regions and foraminiferal species enabled us to quantify a global decrease in planktonic foraminiferal mg ca ratios of 0 054 0 019 mu mol mol 1 per mol kg 1 below a critical threshold for dissolution of 21 3 6 6 mu mol kg 1 the absolute decline in mg ca ratios which is similar for all species affects temperature estimates from sub thermocline species more strongly than those from shallow dwellers the water depth of this critical threshold in the global oceans shoals from 3 5 km in the north atlantic to 0 5 km in the north pacific based on calculations of the global calcite saturation state from 6321 hydrographic stations above this critical threshold mg ca ratios are well preserved and paleotemperature estimates are broadly unaffected by dissolution

determination of intratest variability of trace elements in foraminifera by laser ablation inductively coupled plasma mass spectrometry 1 we have developed a technique to determine the variability of trace elements including li b na mg mn cu zn sr and ba within foraminifera tests using laser ablation inductively coupled plasma mass spectrometry la icp ms this technique has a high spatial resolution width 40 80 m depth 0 5 m is reproducible 8 external reproducibility and has low detection limits generally 0 05 g g 1 we demonstrate that normalization of data to a calcite standard usually gives results that are more consistent with solution icp ms data than normalization to nist 612 rastering into the wall of the final chamber of globigerinoides sacculifer shows that the outermost 1 5 m of the test is enriched in trace elements including mn relative to the interior indicating the presence of a contaminant surface phase pustule calcite close to the aperture of globorotalia tumida has different sr ca and ba ca compared to other parts of the test sr ca and ba ca partition coefficients suggest that the pustule calcite is diagenetic and or formed in a more open system multiple analyses of orbulina universa tests recovered from a latitudinal transect in the north atlantic give a relationship between mg ca and sea surface temperature similar to that reported elsewhere in the literature these initial data demonstrate the validity of this technique and show that it is potentially an extremely powerful microanalytical tool for palaeoceanographic and palaeontological studies

valley asymmetry evidence for periglacial activity in the central north sea present day open valleys with distinct asymmetric profiles have been studied from the central north sea the bulk of the valleys exhibit steep north facing and shallow south facing slopes this asymmetry is ascribed to preferential slumping of the south facing slope under periglacial climatic conditions exceptions to the regional asymmetric trend are probably the result of more localized factors such as fluvial and microclimatic processes and the effects of local geology the recognition of this type of within valley asymmetry associated with slumping in buried valleys within the quaternary sequence may be indicative of former periglacial activity

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

ice marginal depositional responses to readvance episodes in the late devensian deglaciation of the isle of man abstract remapping of the quaternary geology of the isle of man and consequent revision of the stratigraphic succession identifies three glacigenic formations each separated by a major unconformity the oldest formation the shellag represents an extensive ice advance beyond the island limits to the last glacial maximum lgm the overlying formation the orrisdale represents a major readvance episode during retreat from the lgm and is associated with the construction of the bride moraine and the deposition of extensive proglacial subaqeous sediment examination of the sedimentology and micropalaeontology of these sediments indicates that the water body was most likely lacustrine and not marine application of sequence stratigraphy to the overlying jurby formation identifies evidence for three further phases of readvance each off lapping one another into the margin of the lake basin via a complex system of ice contact subaqueous fans and outwash fan deltas the jurby formation is dated by organic sediments overlying it as older than 18 5 14 4 kyr bp and provides an ice marginal correlative for heinrich event 1 readvance limits identified 50 km to the west in eastern ireland

respiration dissolution and the lysocline 1 here i synthesize the results of several types of measurements of organic carbon respiration and calcium carbonate dissolution rates in pelagic seafloor sediments measurements of pore water oxygen demonstrate that most of the respiration takes place very near the sediment water interface with a scale depth of a few millimeters the remainder of the oxic respiration occurs much deeper in the sediments with a scale depth of several centimeters all measures of respiration from locations as disparate as the tropical pacific and atlantic and the subtropical north atlantic agree that pelagic seafloor rates of oxic respiration of organic carbon are relatively independent of depth and location with the exception of sediments beneath the pacific eastern equatorial upwelling zone calcite dissolution in seafloor sediments requires forcing by respiration produced co2 and rates are consistent with a first order dependence on pore water undersaturation solubility as determined by mucci 1983 at atmospheric pressure and locally variable mass specific dissolution rate constants respiration driven calcite dissolution fluxes predicted by this combination of respiration and dissolution rate expressions are significantly lower than many previous estimates comparison of dissolution fluxes in the oligotrophic open ocean measured by other researchers with benthic chamber incubation techniques with those predicted by this combination of rate expressions is within stated uncertainties in agreement in all but one case questioning the need for complicated mechanisms such as surface buffering or authigenic precipitation to explain seafloor calcite diagenesis applying these kinetics to a simple one dimensional steady state model of the bulk calcite content and sediment accumulation rates of the sediment mixed layer yields results consistent with observations of the seafloor lysocline the region of transition from high calcite to low calcite sediments on the ceara rise in the western tropical north atlantic and the ontong java plateau in the western equatorial pacific scenarios ignoring dissolution driven by respiration produced co2 in pore waters and using the high order dependence on undersaturation and very large dissolution rate constants implied by some earlier laboratory studies do not simulate these observations while the scheme represented here does in fact imply a strong shift in the locus of carbonate dissolution toward the sediment water interface as bottom water saturation decreases as implied by the observations of martin et al 2000 no simple combination of sediment transport coefficients and reaction kinetics can reproduce the observation of increasing 14c age as dissolution progresses these results emphasize the importance of accurate knowledge of the kinetics of respiration and dissolution to interpretation of either the present day or paleolysocline

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

effects of seafloor and laboratory dissolution on the mg ca composition of globigerinoides sacculifer and orbulina universa tests a laser ablation icpms microanalysis perspective article i nfo partial or selective dissolution of planktonic foraminiferal tests on the seafloor has been shown to alter original test mg ca compositions and thus may limit the accuracy of mg ca based thermometry for reconstructions of past sea surface temperatures we have employed laser ablation icpms to determine the extent of dissolution caused changes in mg ca distribution across individual chamber walls of the planktonic foraminifera globigerinoides sacculifer and orbulina universa g sacculifer samples collected from a core top depth transect in the ne indian ocean and laboratory dissolution experiments show little if any evidence of preferential removal of mg rich calcite layers by progressive dissolution of the tests we attribute the absence of selective dissolution to the banded distribution of mg across the chamber walls of these foraminiferal species and to the minimal presence of calcite crusts with relatively low mg composition on the outer surfaces of tests mg ca microanalyses of g sacculifer from core top samples further indicate that for samples collected above the calcite lysocline the effect of postdepositional dissolution on mg ca sample mean values is minimal and within the uncertainty of mg ca thermometry i e 0 4 mmol mol 0 8 c at 28 c comparison with previously published results for g sacculifer supports these observations simple modelling of g sacculifer test dissolution indicates that selective removal of calcite with high mg ca values from within the final chamber of g sacculifer test appears insufficient to cause the 10 decrease in mg ca values observed above calcite lysocline these changes in test composition might be related to development removal as a function of co3 2 of a thin diagenetic surface coating which has a relatively high mg ca

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

sedimentology and micropalaeontology of glacimarine sediments from the central and southwestern celtic sea thin discontinuous glacigenic sediments occur at or close to the sea bed as far south as 49 n in the celtic sea the northern samples facies a are clast rich overconsolidated lodgement tills or proximal glacimarine sediments containing sparse reworked microfaunas the southern samples facies b are distal glacimarine plastic silty clays containing abundant cold water microfaunas both these facies are correlated with the late devensian scilly till enabling a quantitative reconstruction of ice thicknesses grounding line sea level and shoreline elevations in the celtic sea at 19 000 years bp the ice advance terminated in marine waters towards the shelf edge break and is likely to have constituted a thin lobate surge over deformable marine sediments 1990 the geological society

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

reconstruction of palaeo ice sheets the use of geomorphological data the article discusses the nature of the glacial inversion problem which is defined as the extraction of time slice ice sheet flow patterns from the patchy and partly overprinted landform record present in former ice sheet areas a coherent inversion model for derivation of flow patterns and interior ice sheet configuration from geomorphological data is presented glacial landscapes are classified according to the three criteria of internal age gradients presence or absence of meltwater traces aligned to flow traces and basal condition frozen bed thawed bed inferred from morphology the inversion model uses landscapes classified accordingly spatially delineated into fans as input data relative chronologies at fan intersections are used to sort fans in a relative age stack that can be linked to stratigraphic dating information

the rate and consequences of sr diagenesis in deep sea carbonates we have used a diffusion advection reaction model for sr exchange during deep sea carbonate diagenesis to determine the rate and consequences of sr exchange between porewaters and bulk carbonate at six dsdp sites 590b 575 593 516 305 and 289 where the required sr concentration and isotopic composition data for the interstitial waters are available from the literature the model can reproduce both the sr2 and 87sr 86sr profiles in the porewaters at each of the sites by adjusting the rate of sr exchange due to solution reprecipitation as a function of sediment age we find that the rate of solution reprecipitation at all of the sites is highest for the youngest sediment 1 10 m y and decreases by about an order of magnitude over the first 10 m y of sediment age the effect of this exchange on the properties of the bulk carbonate is to reduce the sr content by 5 25 depending primarily on the sedimentation rate and shift the 87sr 86sr by as much as 0 00004 from the value the sediment had when first deposited isotopic shifts of this magnitude are large compared to present analytical uncertainties and therefore should be corrected for when using bulk carbonate 87sr 86sr for stratigraphic correlation the average sr loss in the carbonate sections studied is about 15 from which we conclude that the sr flux from carbonate sediments to the overlying ocean is of the order of 15 of the riverine sr flux we also show that the isotopic composition of the diagenetic sr flux is at all times quite close to the contemporaneous seawater value and therefore this flux plays a very minor role in the overall sr budget that determines the sr isotopic composition of seawater the range of sr losses from bulk carbonate due to diagenesis that we calculate is too small to account for the typical decrease in sr content seen in pelagic carbonates as a function of age about 70 over the first 100 m y we conclude that this decrease is not the result of diagenesis and must involve some changing property of the ocean itself

diagenesis and sr isotopic evolution of seawater using data from dsdp 590b and 575 new sr isotopic and concentration analyses of bulk carbonate and porewaters from a carbonate rich miocene section sampled at dsdp site 575 are reported and used along with our earlier data from a section of similar age at dsdp site 590b in a numerical model to determine for each site the rate of sr exchange during diagenesis and the degree to which this amount of exchange has shifted the87sr86sr of the bulk carbonate from the ratio each increment of sediment had when first deposited despite the fact that the two sites have very different water depth 4536 m at 575 vs 1299 m at 590b different sedimentation rate 10 m my at 575 vs 40 m my at 590b and significantly different porewater sr2 gradients we find that the rate of sr exchange as a function of sediment age is almost indistinguishable between the two sites the rate of sr exchange determined at the two sites is such that the resulting shift in bulk carbonate87sr86sr due to diagenesis is small compared to the total range of87sr86sr values measured but large compared to the analytical uncertainty of the individual isotopic ratio measurements by taking this shift into account we reconstruct the original87sr86sr of each increment of carbonate sampled which when plotted as a function of age becomes our best estimate of the sr isotopic evolution of seawater because sr is very well mixed in the ocean at any given time there is a single worldwide value of seawater87sr86sr therefore if we are quantitatively accounting for the effect sr exchange we should find the same seawater evolution curve regardless of what dsdp site is used when we compare the observed bulk carbonate87sr86sr vs age at the two sites they are seen to differ by amounts that are sometimes large compared to the analytical uncertainties of the measurements however when these data are corrected for the post depositional sr isotopic shifts predicted by our diagenetic model we find almost perfect agreement this agreement suggests that we have made a realistic determination of the rate of sr exchange and its consequences in terms of shifting the87sr86sr of the bulk carbonate and more importantly that sr isotopes can be used to correlate marine sediments with an accuracy comparable to the very small analytical uncertainties of modern isotopic measurements

mechanism of leached layer formation during chemical weathering of silicate minerals the dissolution of most common multicomponent silicate minerals and glasses is typically incongruent as shown by the nonstoichiometric release of the solid phase components this results in the formation of so called surface leached layers due to the important effects these leached layers may have on mineral dissolution rates and secondary mineral formation they have attracted a great deal of research however the mechanism of leached layer formation is a matter of vigorous debate here we report on an in situ atomic force microscopy afm study of the dissolution of wollastonite casio 3 as an example of leached layer formation during dissolution our in situ afm results provide for the first time clear direct experimental evidence that leached layers are formed in a tight interface coupled two step process stoichiometric dissolution of the pristine mineral surfaces and subsequent precipitation of a secondary phase most likely amorphous silica from a supersaturated boundary layer of fluid in contact with the mineral surface this occurs despite the fact that the bulk solution is undersaturated with respect to the secondary phase our results differ significantly from the concept of preferential leaching of cations as postulated by most currently accepted incongruent dissolution models this interface coupled dissolution precipitation model has important implications in understanding and evaluating dissolution kinetics of major rock forming minerals

a late devensian ice free area and possible interglacial site on the isle of lewis scotland at the time of the last glacial maximum the last scottish ice sheet has been considered by some1 2 to have extended to the continental shelf edge fig 1a whilst others3 4 have suggested that there were ice free areas in northern scotland no radiocarbon dated strati graphical evidence has been published to support either interpretation we present here data from the isle of lewis establishing that the shelly deposits from the north of that island are of late devensian age but which also show that a late devensian ice margin lay across northern lewis leaving part of the island ice free a peat possibly of interglacial status has been found in the ice free area the last scottish ice sheet therefore did not pass beyond the outer hebrides and may not even have reached the north of the island chain this evidence is also of interest to the debate on the relative expansions of the northern and southern margins of the laurentide and scandinavian ice sheets at the last glacial maximum5 6 for it suggests a restricted glacial expansion of the northern margin of the last british ice sheet at the time of its greatest southerly extent

amino acid evidence for devensian ice west gower south wales complete inundation of south wales by ice during the penultimate wolstonian glaciation has been widely suggested1 3 although it is generally agreed that the last glaciation was less extensive than the preceding one4 6 there has been controversy concerning its limits stemming mainly from the lack of clear geomorphological evidence and the dearth of datable material7 9 14c dates from the shelly till in pembrokeshire were first thought to indicate an extension of last glaciation ice into the area10 but serious doubts were subsequently raised about the reliability of finite dates on shells of this age range11 12 we present here results of amino acid analysis of shells from recently exposed till and from underlying raised beach remnants at broughton bay west gower total d allo l iso ratios from the raised beach are consistent with analyses on shells from comparative beach remnants elsewhere in south west britain7 13 15 shells of 21 identifiable littoral species extracted from the till suggest inshore marine conditions similar to those at present amino acid ratios from littorina spp provide firm evidence for the encroachment of devensian ice on to gower approximately to the limit suggested by bowen7 fig 1a

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

calibrations for benthic foraminiferal mg ca paleothermometry and the carbonate ion hypothesis benthic foraminiferal magnesium calcium ratios were determined on one hundred and forty core top samples from the atlantic ocean the norwegian sea the indian ocean the arabian sea and the pacific ocean mostly at sites with bottom water temperatures below 5 c mg ca ratios are consistently lower by not vert similar 0 2 mmol mol in samples cleaned using oxidative and reductive steps than using oxidative cleaning differences between cibicidoides species have been identified mg ca of cibicidoides robertsonianus cibicidoides kullenbergi cibicidoides wuellerstorfi comparison with bottom water temperatures support observations of lowered mg ca of c wuellerstorfi at temperature below not vert similar 3 c compared with values predicted by published calibrations and from other cibicidoides species hydrographic data shows that carbonate ion saturation co32 decreases rapidly below this temperature an empirical sensitivity of co32 on mg ca has been established for c wuellerstorfi of 0 0086 0 0006 mmol mol mol kg a novel application using modern temperatures and last glacial maximum temperatures derived via pore fluid modelling supports a carbonate ion saturation state effect on mg incorporation this may significantly affect calculated 18oseawater obtained from foraminiferal 18o and mg ca temperature

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

defining uncertainty and error in planktic foraminiferal oxygen isotope measurements foraminifera are the backbone of paleoceanography planktic foraminifera are one of the leading tools for reconstructing water column structure however there are unconstrained variables when dealing with uncertainty in the reproducibility of oxygen isotope measurements this study presents the first results from a simple model of foraminiferal calcification foraminiferal isotope reproducibility model firm designed to estimate uncertainty in oxygen isotope measurements firm uses parameters including location depth habitat season number of individuals included in measurement diagenesis misidentification size variation and vital effects to produce synthetic isotope data in a manner reflecting natural processes reproducibility is then tested using monte carlo simulations importantly this is not an attempt to fully model the entire complicated process of foraminiferal calcification instead we are trying to include only enough parameters to estimate the uncertainty in foraminiferal 18o records two well constrained empirical datasets are simulated successfully demonstrating the validity of our model the results from a series of experiments with the model show that reproducibility is largely controlled by the number of individuals in each measurement but also strongly a function of local oceanography if the number of individuals is held constant parameters like diagenesis or misidentification have an impact on both the precision and the accuracy of the data firm is a tool to estimate isotopic uncertainty values and to explore the impact of myriad factors on the fidelity of paleoceanographic records particularly for the holocene

the dissolution kinetics of major sedimentary carbonate minerals abstract among the most important set of chemical reactions occurring under near earth surface conditions are those involved in the dissolution of sedimentary carbonate minerals these minerals comprise about 20 of phanerozoic sedimentary rocks calcite and to a significantly lesser extent dolomite are the major carbonate minerals in sedimentary rocks in modern sediments aragonite and high magnesian calcites dominate in shallow water environments however calcite is by far the most abundant carbonate mineral in deep sea sediments an understanding of the factors that control their dissolution rates is important for modeling of geochemical cycles and the impact of fossil fuel co 2 on climate diagenesis of sediments and sedimentary rocks it also has practical application for areas such as the behavior of carbonates in petroleum and natural gas reservoirs and the preservation of buildings and monuments constructed from limestone and marble in this paper we summarize important findings from the hundreds of papers constituting the large literature on this topic that has steadily evolved over the last half century our primary focus is the chemical kinetics controlling the rates of reaction between sedimentary carbonate minerals and solutions we will not attempt to address the many applications of these results to such topics as mass transport of carbonate components in the subsurface or the accumulation of calcium carbonate in deep sea sediments such complex topics are clearly worthy of review papers on their own merits calcite has been by far the most studied mineral over a wide range of conditions and solution compositions in recent years there has been a substantial shift in emphasis from measuring changes in solution composition to determine batch reaction rates to the direct observation of processes occurring on mineral surfaces using techniques such as atomic force microscopy afm however there remain major challenges in integrating these two very different approaches a general theory of surface dissolution mechanisms currently lacking although see lasaga and luttge science 291 2001 2400 is required to satisfactorily relate observations of mineral surfaces and the concentration of dissolved components studies of aragonite high magnesian calcites magnesite and dolomite dissolution kinetics are much more limited in number and scope than those for calcite and provide at best a rather rudimentary understanding of how these minerals are likely to behave in natural systems although the influences of a limited number of reaction inhibitors have been studied probably the greatest weakness in application of experimental results to natural systems is understanding the often profound influences of foreign ions and organic matter on the near equilibrium dissolution kinetics of carbonate minerals

characterization of mg ca distributions in planktonic foraminifera species by electron microprobe mapping 1 the distribution of mg ca within the tests of eight modern planktonic foraminifer species has been characterized using electron microprobe mapping species include several that are commonly used for estimation of past seawater temperatures globigerinoides ruber g sacculifer neogloboquadrina incompta synonym of n pachyderma dex n dutertrei and g truncatulinoides each of the investigated species displays large variations in mg ca composition within individual tests however the pattern of mg ca variation is notably different between symbiont bearing and symbiont free species in symbiotic species cyclic mg ca compositional banding occurs that is characterized by narrow 1 3 m high mg ca typically 8 11 mmol mol bands intercalated between broader low mg ca typically 1 5 mmol mol bands this factor of 2 3 difference equates to an apparent calcification temperature change of 10 c or more such temperature changes are considered highly improbable and suggest vital effects significantly modify the incorporation of mg ca into the tests of symbiont bearing species these vital effects remain poorly understood and demand further careful evaluation as they may need to be accounted for when making reliable reconstructions of past oceanic temperatures symbiont free species typically have fewer and broader compositional bands that may reflect more closely changes in calcification temperature as these species migrate within a water column