paleoceanography of surface waters in the gulf of mexico during the late quaternary abstract late quaternary paleotemperatures and paleosalinities of surface waters of the gulf of mexico were estimated using a multivariate statistical analysis of census data of planktonic foraminifera two climatic extremes were selected for detailed basinwide study the climatic optimum 125 000 yr ago and the glacial maximum 18 000 yr ago in addition patterns of climatic change were examined in seven piston cores from 127 000 yr ago to the present day during the climatic optimum 125 000 yr ago temperature distributions in surface waters were similar to those of the present the 22 c winter isotherm trended northeastward across the central basin and paleotemperatures decreased northward summer distributions were nearly homogeneous and ranged between 28 and 29 c winter salinities were 1 fresher than present values in the northmost gulf and 0 4 fresher in the central basin summer salinities were similar during both times in contrast during the last glacial maximum temperatures were 1 to 2 c cooler in winter and 1 c cooler in summer and isotherms formed a circular pattern in the gulf during both seasons salinity was 0 3 fresher in winter than at present but 0 6 saltier in summer conditions deteriorated from the climatic optimum to the glacial maximum in the mexico basin winter temperatures were 2 c cooler from 75 000 to 45 000 yr ago y6 to y3 subzones summer temperatures reached a minimum 3 c cooler 32 000 yr ago y2 y3 boundary and seasonality reached minimal values 5 c from 45 000 to 15 000 yr ago all three parameters became similar in value to those in the straits of florida from 45 000 to 15 000 yr ago suggesting that the exchange of surface waters was enhanced at this time between the two regions summer salinities remained similar to present conditions in the mexico basin whereas winter salinities increased 2 by 32 000 yr ago and then fell 0 5 until the glacial maximum ended the westerlies may have migrated southward over the mexico basin in winter from 32 000 to 15 000 yr ago

the central paratethys during oligocene as an ancient counterpart of the present day black sea unique records from the coccolith limestones abstract four isochronous oligocene coccolith limestone horizons from the carpathians were examined in order to reconstruct paleoceanographic conditions in the central paratethys the dominance of small and size uniform pyrite framboids the occurrence of low diversity dinoflagellate cysts and coccolithophorids and the presence of biomarker molecule 28 30 dinorhopane indicate that the water column was stratified with the upper water column being relatively well oxygenated but the bottom water being anoxic the latter is confirmed by the fine and consistent horizontal laminations in various parts of the basin scarcity of benthic organisms and their trace fossils the limestones exhibit typical marine 13c values but are significantly depleted in 18o and enriched in 87sr relative to contemporaneous ocean water these isotopic compositions result from a decreased salinity of the surface waters caused by an increased riverine input this is confirmed by the lack or impoverishment of planktonic foraminifers presence to abundance of goniodomid dinoflagellate cysts and massive occurrence of low diversity nannoplankton assemblages which indicates decreased salinities as low as 17 and high productivity in the upper water column these observations indicate that the limestones were formed during periods when connection of the central paratethys with the global ocean was limited which impeded water exchange causing the development of low salinity conditions of surface water and bottom water anoxia during the deposition of the oldest tylawa horizon primary productivity was enhanced and chemocline was positioned exceptionally high in the water column moreover decreased 13c values in both carbonates and organic matter of this horizon suggest that widespread methane venting took place in the basin during np23 all these data show that during the oligocene the central paratethys experienced similar conditions to those of the current black sea which can be used as a modern analogue especially for the tylawa horizon therefore the tylawa horizon can be perceived as a potential effect of future post depositional processes of coccolith marls analogous to those having been deposited in the black sea for 2 7 kyr

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

relationships between anoxia glacial meltwater and microfossil preservation in the orca basin gulf of mexico abstract the isotopic and microfossil records from piston core en32 pc6 from the orca basin gulf of mexico reveal that various factors have moderated the sediment composition of the basin during the last 29 000 yrs 29 ka b p coincident with the introduction of isotopically depleted glacial meltwater into the gulf approximately 16 ka b p anoxic conditions commenced within the intraslope basin as evidenced by sedimentary laminations and improved microfossil pteropod planktonic foraminifera and radiolaria preservation the increased delivery of terrigenous organic matter with the glacial meltwater may have been responsible for inducing the anoxia also at this time the water of the orca basin was most likely somewhat stratified due to elevated salinities and the increased supply of organic matter onto the continental slope from the continent would have depleted the oxygen supply of the orca basin by oxidative consumption about 13 ka b p oxygenated conditions resumed and microfossil abundance preservation decreased when meltwater input diminished at 8 5 ka b p the orca basin again became anoxic due to the development of the orca basin brine

ba ca in neogloboquadrina pachyderma as an indicator of deglacial meltwater discharge into the western arctic ocean 1 down core samples of the planktonic foraminifer neogloboquadrina pachyderma sinistral from the mendeleyev ridge in the western arctic ocean have been analyzed for ba ca and 18o the apparent distribution coefficient for n pachyderma sin is estimated at dba 0 22 0 02 a meltwater event is identified at around 11 8 14c kyr bp and is coincident with elevated ba ca ratios the barium enrichment is believed to be the result of enhanced weathering and erosion following glaciation additionally barium may have desorbed from shelf sediments as sea level rose changes in ba ca correlate with the retreat of the laurentide ice sheet and the evolution of the mackenzie river drainage basin therefore maximum ba ca in arctic surface waters at 11 8 ka may be indicative of an increase in the export of freshwater from the arctic to the north atlantic potentially contributing to the onset of the younger dryas this work suggests that ba ca in planktonic foraminifera may be a useful indicator of the timing and processes associated with deglaciation

glacial meltwater cooling of the gulf of mexico gcm implications for holocene and present day climates an atmospheric general circulation model the ncar ccm has been used to investigate the possible effects that reduced gulf of mexico sea surface temperatures sst could have on regional and hemispheric climates 18o records and terrestrial evidence indicate at least two major glacial meltwater discharges into the gulf of mexico subsequent to the last glacial maximum it is probable that these discharges reduced gulf of mexico sst we have conducted three numerical experiments with imposed gulf wide sst coolings of 3 c 6 c and 12 c and find in all three experiments significant reductions in the north atlantic storm track intensity along with a strong decrease in transient eddy water vapor transport out of the gulf of mexico surface pressures are higher over the north atlantic indicating a reduction of the climatological icelandic low the region is generally cooler and drier with a reduction in precipitation that agrees well with evidence from greenland ice cores other statistically significant changes occur across the northern hemisphere but vary between the three experiments in particular warmer wetter conditions are found over europe for both the 6 c and 12 c sst reductions but cooler conditions are found for the 3 c reduction this indicates a dependence in both the sign and magnitude of the model response on the magnitude of the imposed sst anomaly the results suggest that the present day north atlantic storm track is dependent on warm gulf of mexico sst for much of its intensity they also suggest that meltwater induced coolings may help account in part for some of the climatic oscillations that occurred during the last glacial interglacial transition

α β phase transition in quartz monitored using acoustic emissions summary it is usually suggested that thermal cracking in a quartz bearing rock results from the anomalously high volumetric expansion coefficients of quartz e g simmons cooper 1978 it has also been recognized that thermal expansion mismatch and mineral anisotropy contribute to thermal cracking in materials that consist of a polycrystalline aggregate composed of several anisotropic minerals even in the absence of a temperature gradient friedrich wong 1986 experiments investigating thermal cracking in rocks commonly involve imaging and quantitative stereology of crack populations induced in rocks treated to various peak temperatures e g friedrich johnson 1978 homand etienne troalan 1984 atkinson mcdonald meredith 1984 meredith atkinson 1985 here we report on acoustic emission experiments that monitor the process of thermal cracking as it occurs during heating supported by measurements of crack surface area pore fluid permeability porosity and surface conductivity carried out on rock samples treated to various peak temperatures the acoustic emission measurements show a strong peak of microcracking at the phase transition temperature for quartz 573 c superimposed upon a background of microcracking due to thermal expansion there is also a clear peak of microcracking at higher temperatures 800 c that can be attributed to oxidation dehydroxylation reactions of hornblende and chlorite measurements of fluid permeability pore surface area porosity and electrical conductivity made on samples that have been heat treated to various maximum temperatures show increases associated with a major episode of cracking in the 500 600 c temperature range indicating that the new cracks form a well interconnected network this has been confirmed by sem and optical microscopy these results have implications for the electrical conductivity of the continental crust providing a mechanism enabling the high pore fluid connectivity needed to explain zones of high electrical conductivity at depth providing that cracks opened in this way remain open at the high pressures existing at depth it should be recognized however that th se measurements are limited in their direct application since they were obtained under initially dry conditions at laboratory pressures

evidence of the younger dryas in central america abstract three sites provide records that address whether the younger dryas was manifest in central america marine records from barbados and the cariaco basin are discussed as well as possible climatic forcing mechanisms sequences from montane la chonta bog costa rica and lowland lake quexil guatemala record a temperature decline of 1 5 2 5 c dated between 11 070 10 400 14c years bp and ca 12 000 10 300 14c years bp respectively the record from lake la yeguada panama does not include cooling although significant reorganization of local communities occurred during the younger dryas chronozone colder tropical ssts throughout deglaciation contributed to sub regional climatic variation more intense monsoonal activity and cooler air temperatures however the temperature reversals are not associated with the coldest tropical ssts which occurred during meltwater pulses the temperature reversals appear to be a response to extra tropical conditions presumably in the north atlantic which suggests that younger dryas cooling extended as far south as costa rica in panama monsoonal conditions may have blocked cooler temperatures precipitation continued to increase throughout deglaciation due to strong forcing by seasonal solar insolation in central america while desiccation events occurred to the north and south

a reevaluation of the evidence for a younger dryas climatic reversal in the tropical andes abstract a review of the evidence for a younger dryas equivalent climatic reversal in the tropical andes shows that a number of hypotheses need to be reassessed assumptions of the el abra cold and humid phase in colombia are compromised by insufficient dating control periods of glacier advance in peru and bolivia lack sufficient dating control to be correlated with the european younger dryas only glaciers on the quelccaya ice cap in peru may have advanced shortly before the onset of the european climatic reversal but even there a correlation is questionable a late glacial advance in the chimborazo area in ecuador is considerably older than previously suggested the same glacier advance has been dated to earlier than 12 000 bp in other areas of ecuador the emerging picture suggests two phases of glacier advances in the tropical andes 13 000 12 000 bp and 9000 10 000 bp both may have been caused by increasing precipitation unequivocal evidence for a cold younger dryas event in the tropical andes has yet to emerge

coincident high resolution optical sar image analysis for surface albedo estimation of first year sea ice during summer melt abstract the parameterization of sea ice albedo during summer when fluctuations in the fractional coverage of melt ponds change on a variety of spatial and temporal scales represents a significant challenge for both the modelling and remote sensing communities ubiquitous cloud cover in summer inhibits the use of optical sensors for providing large scale estimates of sea ice surface albedo c band 5 3 ghz synthetic aperture radar sar data from envisat asar is compared to coincident surface climatological albedo estimates derived from high resolution quickbird vis nir imagery in order to demonstrate the utility of high resolution dual polarized vv hh sar for detecting variations in of melt pond covered landfast first year sea ice fyi adjacent to hudson bay variations in ice are detected from sar imagery using the co polarization ratio shown to be significantly correlated 0 81 with when melt ponds are in liquid form results show the use of represents a substantial increase in correlation to when compared to conventional like polarized sar backscattering coefficients a regression model demonstrates that can be used as an estimator for landfast fyi to within 5 2 provided 1 the sar images at a shallow enough incidence angle to induce separation between like polarized channels and 2 the conditions of bragg surface scattering characteristic of relatively shallow fyi melt ponds is met

evidence for seasonal low salinity surface waters in the gulf of mexico over the last 16 000 years oxygen isotopic analyses of individual orbulina universa from orca basin core en32 pc6 document the presence of low salinity surface waters in the northern gulf of mexico over the past 16 kyr isotopic data from an interval immediately following the younger dryas event indicate the rapid decrease in 18o values at the conclusion of the younger dryas was due to a year round return of meltwater to the gulf of mexico data indicate periodic or seasonal low salinity waters existed over the region of the orca basin prior to the initiation of the meltwater spike estimates suggest o universa grew its shell in salinities at least 4 5 below ambient since o universa may have calcified deep in the mixed layer during periods of low salinity surface salinities could have been even lower comparison of the average of individual o universa oxygen isotopic values with data from multiple shell samples of white gs ruber from the same core samples demonstrates that the two species record similar values during the late holocene in contrast o universa records lower oxygen isotopic values during the late glacial deglacial intervals possibly due to differences in seasonal distribution or shell ontogeny between the two species

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

sedimentary evidence of deglacial megafloods in the northern gulf of mexico pigmy basin abstract cored sediments from the pigmy basin northern gulf of mexico were analyzed in order to better constrain late deglacial and early holocene paleoenvironmental and sedimentary changes in response to north american climate evolution mineralogical and geochemical proxies indicate the succession of two sedimentary regimes dominantly detrital during the deglaciation 15 12 9 cal ka bp whereas biogenic contribution relatively increased later on during the younger dryas and early holocene 12 9 and 10 cal ka bp geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the mississippi river rather than modifications of redox conditions in the basin specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode meltwater spike described or modeled in previous marine or continental studies during this episode most parameters display stair step like pattern variations highlighting three successive steps within the main meltwater flow variations in grain size and clay mineral assemblage recorded in the pigmy basin indicate that the erosional regime was very strong on land during the first part of the meltwater spike and then milder inducing more subtle modifications in the sedimentary regime in this part of the gulf specific geochemical and mineralogical signatures notably clay minerals and trace metal geochemistry pinpoint a dominant origin from nw north america for detrital particles reflecting meltwater outflow from the south western laurentide ice sheet lis margin during the most intense freshwater discharge the observed decrease of the sedimentation rate from about 200 to 25 cm ka at ca 12 9 ka evidenced a drastic decrease of erosional processes during late phase of discharge consistently with the hypotheses of major reduction of meltwater flow the major modification at 12 9 cal ka bp is interpreted to result from both modifications of the main mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the younger dryas and the increase of sea surface temperature linked to insolation finally slight grain size modifications suggest that some freshwater discharges may have episodically reached the gulf of mexico after the younger dryas reflecting possible small adjustments of the postglacial hydrological regime

structure and timing of the last deglaciation oxygen isotope evidence foraminiferal oxygen isotope data from 24 tropical atlantic sediment cores constrained by 77 14c dates are stacked to form a composite record of isotopic termination 1 this record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka bp and 6 ka bp minor isotopic expression of deglaciation is permitted as early as 16 ka bp but the most rapid rate of change occurred between 14 ka bp and 12 ka bp three steps of maximum change are present although they are close to the statistical limits of detection in the composite record the clear presence of the steps in individual records suggests that they are real we estimate their timing at 14 12 ka bp termination 1 a 10 9 ka bp termination 1 b and 8 6 ka bp termination 1 c centering of the termination near 11 ka bp is consistent with the milankovitch hypothesis that high summer insolation caused deglaciation in detail however maximum rates of change prior to the 11 ka bp insolation extreme and the inferred steps require additional mechanisms controlling the tempo of glacial interglacial climate change steps equivalent to those in 18o have not been detected in ice margin retreat data steps in the isotopic transition if real may record thinning of the ice sheets not accompanied by loss of area alternation between near equilibrium and near stagnant ice sheet profiles during deglaciation is hypothesized perhaps due to calving and unstable down draw of the ice sheets followed by partial re equilibration significant problems remain the effects of temperature on the isotope record are only partially constrained presently available data allow only semi quantitative intercalibration of ice volume sea level and isotopic estimates of glaciation

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

wood s metal dynamic wettability on quartz granite and limestone wood s metal wettability was experimentally studied as a function of both liquid and solid parameters the influence of solid liquid relative velocity wood s metal temperature and surface roughness on the unit work of wetting cos was analysed through tests on various specimens made of quartz synthetic single crystal la peyratte granite fine grained and coarse grained and soultz micrite sub micronic limestone a few tests with mercury were performed for comparison a slight temperature dependency is found on both quartz and rocks the largest effect being observed on quartz the most significant dependency observed on quartz la peyratte granite and soultz micrite is controlled by roughness rough specimens always show larger values of unit work of wetting cos when compared to polished ones a range of cos values is determined for each mineral and rocks which implies the determination of break through radii using laplace s equation within ranges of 7 10

opening the carbon isotope vital effect black box 1 seasonal temperatures in the euphotic zone recent laboratory experiments with orbulina universa show that the carbon and oxygen isotope signals from this symbiont bearing planktonic foraminifera record distinct environmental parameters irradiance and temperature since light levels are correlated with depth in the marine environment the carbon isotopic composition of o universa can be utilized to differentiate individuals from different depth habitats by combining 18o and 13c data from individuals in an assemblage estimates of seasonal temperature ranges are possible for the upper and lower euphotic zone of the ocean reconstruction of seasonal temperatures using individual holocene o universa from western equatorial pacific ocean boxcore erdc 83 yields ranges of 23 5 to 29 9 c and 20 1 to 24 5 c for the shallow and deep euphotic zone respectively these values are in excellent agreement with recent temperature measurements from this region analyses of individual late glacial 12 000 13 000 years b p o universa from this site suggest the seasonal upper euphotic zone temperature range was approximately 2 5 c lower than it is today a function of cooler summers

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

interacting loop current variability and mississippi river discharge over the past 400 kyr the loop current mediating the oceanic heat and salt flux from the caribbean sea into the atlantic ocean and its interference with the mississippi river discharge are critical for both the regional climate in the gulf of mexico area and the water vapor transport towards high northern latitudes we present a 400 kyr record of sea surface temperature and local surface salinity from the northeastern gulf of mexico images core md02 2575 approximated from combined planktonic foraminiferal 18o and mg ca which reflects the temporal dynamics of the loop current and its relationship to both varying mississippi discharge and evolution of the western hemisphere warm pool the reconstructed sea surface temperature and salinity reveal glacial interglacial amplitudes that are significantly larger than in the western hemisphere warm pool sea surface freshening is observed during the extreme cool periods of marine isotope stages 2 8 and 10 caused by the strengthened mississippi discharge which spread widely across the gulf favored by the less established loop current interglacial and interstadial sea surface conditions instead point to a strengthened northward flowing loop current in line with the northward position of the intertropical convergence zone allowing northeastern gulf of mexico surface hydrographic conditions to approach those of the caribbean at these times the mississippi discharge was low and deflected westward promoted by the extended loop current previously described deglacial megadischarge events further to the west did not affect the northeastern gulf of mexico hydrography implying that meltwater routing from the laurentide ice sheet via the mississippi river is unlikely to have affected atlantic meridional overturning circulation

climate change in the circum north atlantic region during the last deglaciation a survey of new and published palaeoclimate data indicates that both the high and low latitude north atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial to interglacial transi tion climate model results suggest that changes in the melting history of the laurentide ice sheet may explain much of this nonlinear response of the climate system to astronomical milankovitch forcing

physical properties and brittle strength of thermally cracked granite under confinement 1 effects of thermal crack damage on the rupture processes of a fine grained granite were investigated under triaxial stress under water wet and argon gas dry saturated conditions and at room temperature thermal cracking was introduced by slowly heating and cooling two samples of la peyratte granite up to 700 c which were compared to two intact specimens for each rock sample a hydrostatic test was first carried up to 90 mpa effective pressure 5 mpa constant pore pressure the samples were then deformed to failure at a constant strain rate of 2 10 6s 1 at 30 mpa effective pressure our results show that 1 permeability of heat treated specimens was 4 5 orders of magnitude larger than that of intact specimens at low effective mean pressure 2 nevertheless at our experimental conditions 2 10 6 s 1 thermal cracking had no significant influence on the brittle strength 3 similarly no obvious water weakening effect was observed 4 however with increasing stress elastic anisotropy appeared at lower differential stress in heat treated specimens than in intact ones but close to failure the magnitude of p wave anisotropy was approximately the same for both types of specimens 5 acoustic emission hypocenter locations and p wave velocity anisotropy in the basal plane demonstrate that strain localization started right at the onset of dilatancy for heat treated specimens later in the intact specimens and 6 inverting wave velocities for crack density we show that failure was reached for vertical crack densities of 0 35 for dry specimens and possibly 0 5 for water saturated specimens

stratigraphy of the younger dryas chronozone and paleoenvironmental implications central and southern great plains abstract the great plains of the united states was the setting for some of the earliest research in north america into patterns and changes in the character of late pleistocene environments and their effects on contemporary human populations many localities in the region have well stratified records of terminal pleistocene and early holocene human paleoindian activity and past environments these have proven important in debates over the character of the younger dryas chronozone ydc 11 000 10 000 14c bp 12 900 11 700 cal bp in the continental interior this paper reviews the lithostratigraphic record of the ydc on the central and southern great plains and summarizes paleobiological records largely isotopic the goal is to determine if there is any uniformity in the timing character direction and or magnitude of changes in depositional environments or broader geomorphic systems before during or after the ydc in order to address the question of the character of environments through this time the stratigraphic records of the late pleistocene to early holocene transition and in particular the stratigraphic records of the ydc vary through time and space the data clearly show that a host of geomorphic processes produced the terminal pleistocene and early holocene stratigraphic records of the great plains moreover the ydc is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils the various geomorphic systems of the great plains did not behave synchronously in response to any common climate driver these stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid latitude climates in the terminal pleistocene and early holocene

statistical constraints on el nino southern oscillation reconstructions using individual foraminifera a sensitivity analysis recent investigations of submillennial paleoceanographic variability have attempted to resolve high frequency climate signals such as the el nino southern oscillation enso using the population statistics of individual planktic foraminiferal 18o analyses this approach is complicated by the relatively short lifespan of individual foraminifers 2 4 weeks compared to the time represented by a typical marine sediment sample decades to millennia here we investigate the uncertainty associated with individual foraminiferal analyses ifa through simulations on forward modeled 18ocarbonate first focusing on the nino3 4 region of the tropical pacific ocean a bootstrap monte carlo algorithm is developed to constrain the uncertainty on ifa statistics subsequently to test the sensitivity of ifa to changes in seasonal cycle amplitude enso amplitude and enso frequency synthetic time series of 18ocarbonate with differing variability are constructed and tested with our algorithm the probabilities of the ifa technique in detecting changes in enso amplitude and seasonal cycle amplitude or a combination of both for the surface ocean and thermocline at different locations in the tropical pacific are quantified we find that the uncertainty in the standard deviation is smaller than the range that the ifa signal is insensitive to enso frequency and at certain locations the seasonal cycle may dominate enso ifa sensitivity towards enso is highest at the central equatorial pacific surface ocean and the eastern equatorial pacific eep thermocline whereas sensitivity towards the seasonal cycle is highest at the eep surface ocean our results suggest that rigorous uncertainty quantification should become standard practice for accurately interpreting ifa data

the younger dryas cool episode in the gulf of mexico data are presented from orca basin piston core en32 pc4 in the gulf of mexico that confirm the existence of surface water cooling during the younger dry as chronozone 11 10 ka late glacial planktonic foraminiferal species made a reappearance between 11 4 and 9 8 ka an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer globigerinoides ruber the presence of the younger dryas event in the gulf at 27 n demonstrates that surface water cooling extended to mid latitude regions in the north atlantic the cool surface water interval is bracketed by rapid shifts in 18o related to changes in the influx of meltwater to the gulf of mexico a chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a 500 year period and ended in less than 200 years these results are among the first deep sea sediment data documenting the climatic transitions bracketing the younger dryas with a rapidity observed in ice core records a rapid decrease in 18o values measured in the white form of gs ruber at 10 2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures surprisingly a similar decrease is not observed in the pink form of gs ruber a summer surface water dweller in the gulf this discrepancy may be explained by continued meltwater influx throughout the younger dryas during the summers only such that there was no change in the 18o of the pink form at the end of the episode an additional possibility is that warming at the end of the younger dryas raised year average temperatures and summer temperatures remained constant the coincidence of rapid shifts in 18o with the younger dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the younger dryas cooling based on changes in the routing of laurentide glacial meltwater

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

a global compilation of late holocene planktonic foraminiferal δ18o relationship between surface water temperature and δ18o we review the different sources of uncertainty affecting the oxygen isotopic composition of planktonic foraminifera and present a global planktonic foraminifera oxygen isotope data set that has been assembled within the margo project for the late holocene time slice the data set consists of over 2100 data from recent sediment with thorough age control that have been checked for internal consistency we further examine how the oxygen isotopic composition of fossil foraminifera is related to hydrological conditions based on published results on living foraminifera from plankton tows and cultures oxygen isotopic values 18o of margo recent fossil foraminifera are 0 2 0 8 higher than those of living foraminifera our results show that this discrepancy is related to the stratification of the upper water mass and generally increases at low latitudes therefore as stratification of surface waters and seasonality depends on climatic conditions the relationship between temperature and 18o established on fossil foraminifera from recent sediment must be used with caution in paleoceanographic studies before models predicting seasonal flux abundance and 18o composition of a foraminiferal population in the sediment are available we recommend studying relative changes in isotopic composition of fossil planktonic foraminifera these changes primarily record variations in temperature and oxygen isotopic composition of sea water although part of the changes might reflect modifications of planktonic foraminifera seasonality or depth habitat

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

implications of pore space characteristics on diffusive transport in basalts and granites a detailed characterization of the pore space is crucial for understanding of transport and element transfer in rocks here the effect of differences in texture and content of secondary minerals on transport in pore systems was determined for two rocks of widespread occurrence mid ocean ridge basalts morb and granites pore space characteristics were analyzed by hg porosimetry intrusion of a molten alloy and synchrotron based x ray tomographic microscopy for evaluating the role of pore space characteristics for the prediction of diffusive transport data on porosity and the effective diffusion coefficient deff were compared extended connective pore systems due to cracks and mineral dissolution are present in samples of both rocks indicating high internal specific surface area uneven pore size distributions in altered morb samples can be assigned to secondary minerals pore spaces determined by x ray tomography used to determine main direction of pores in the 3 d orthogonal system suggest a slight anisotropy in log log plots both rocks show roughly a linear dependence of deff for h2o and compounds with comparable diffusivities d2o monovalent cations and anions on porosity but at same porosity deff is clearly higher in granitic than in basaltic samples this difference is increasing with decreasing porosity indicating that at low porosities the efficiency of element transport in basaltic samples is diminished mainly inherited by the presence of small pores slowing down diffusion the fact that diffusive transport in basaltic rocks is stronger dependent on porosity than in granitic rocks shows that also other rock characteristics such as pore size distribution and tortuosity of the pore network highly affected by the alteration degree can markedly affect transport and reactivity of pore solution