climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

paleoceanographic evolution of north pacific surface water off japan during the past 150 000years abstract hydrographic variability in the mixed water region of the northwest pacific ocean at latitudes 35 40 n between the kuroshio extension and oyashio front causes complex upwelling leading to large primary productivity and thus great fishery resources we reconstructed the periodicity of the variability in north pacific intermediate water upwelling and surface ocean hydrography based on the high resolution analysis of diatom assemblages in seven cores representing the last 150 000 years we derived annual sea surface temperatures ssts through a diatom based proxy td the td derived annual ssts c are controlled by orbital forcing and show a reversed saw tooth in southern cores in contrast to a normal saw tooth pattern in the northern cores oceanic diatom abundances along the northern margin of the mixed water region are twice times as high as beneath the axis of the kuroshio extension and fluctuated in a revised saw tooth pattern with higher overall abundances interglacials after the last deglaciation annual ssts declined markedly during heinrich and bond events in the northern north atlantic when ice rafted detritus transported by icebergs was abundant wavelet analyses of the record of oceanic diatom abundances show significant variability at 2 0 kyr 2 to 5 6 kyr and 3 2 to 9 6 kyr periods wavelet analyses of the annual sst records show significant periodicity at 1 4 to 2 6 kyr 3 3 to 4 0 kyr 7 2 to 12 8 kyr cycles

ice streams as the arteries of an ice sheet their mechanics stability and significance ice streams are corridors of fast ice flow ca 0 8 km year within an ice sheet and are responsible for discharging the majority of the ice and sediment within them consequently like the arteries in our body their behaviour and stability is essential to the well being of an ice sheet ice streams may either be constrained by topography topographic ice streams or by areas of slow moving ice pure ice streams the latter show spatial and temporal patterns of variability that may indicate a potential for instability and are therefore of particular interest today pure ice streams are largely restricted to the siple coast of antarctica and these ice streams have been extensively investigated over the last 20 years this paper provides an introduction to this substantial body of research and describes the morphology dynamics and temporal behaviour of these contemporary ice streams before exploring the basal conditions that exist beneath them and the mechanisms that drive the fast flow within them the paper concludes by reviewing the potential of ice streams as unstable elements within ice sheets that may impact on the earth s dynamic system d 2002 elsevier science b v all rights reserved

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

simulating the impact of freshwater inputs and deep draft icebergs formed during a mis 6 barents ice sheet collapse 1 an intermediate complexity climate model is used to simulate the collapse of the barents ice sheet during marine isotope stage 6 mis 6 140 ka b p with the purpose of investigating whether a mass input of freshwater from the collapse could have affected the convection and deep water formation in the north atlantic ocean further experiments used a coupled dynamic and thermodynamic iceberg model to determine the effects of deep draft icebergs rather than freshwater alone on the ocean circulation the results predict that the collapse of the barents ice sheet had a significant impact on the meridional overturning circulation in both the atlantic and pacific oceans freshwater fluxes have more of an impact on the atlantic overturning circulation during the actual release period compared to icebergs but the bergs induce effects over longer time scales even after the pulse is removed freshwater fluxes of 0 15 sverdrup sv and iceberg surges of 0 1 sv trigger significant changes in the global patterns particularly in the north pacific where there is strengthening of the overturning circulation at the expense of that in the north atlantic and associated increases in pacific sea surface temperatures these results highlight the importance of simulating not only the correct flux but also the form of the freshwater input from ice sheet collapses appropriately

response of interior north america to abrupt climate oscillations in the north atlantic region during the last deglaciation several broad scale climatic oscillations during the last deglaciation are well documented in regions around the north atlantic ocean this paper reviews empirical evidence for these deglacial climatic oscillations from non coastal north america and discusses implications for testing climatic simulations and for understanding the cause and transmittal mechanisms paleoclimatic interpretation of oxygen isotope records from several small sites in the eastern great lakes region indicates a classic deglacial climatic sequence that is comparable with records from europe and greenland the climatic events as interpreted from crawford lake oxygen isotopes include the bolling allerod boa warming at 12 700 14c bp a warm boa at 12 500 10 920 14c bp an intra allerod cold period shortly before 11 000 14c bp a cold younger dryas yd climate reversal at 10 920 10 000 14c bp the holocene warming at 10 000 14c bp a brief preboreal oscillation pb at 9650 14c bp and an early holocene cold event at 7500 14c bp 8200 cal bp some of these events were also evident from changes in upland and aquatic vegetation and sediment lithology the pronounced yd climatic reversal has been documented from pollen records along the ecotones at this time and from glacier readvances in the great lakes region along the rocky mountains from alberta to colorado the yd event is indicated by alpine glacier advance and or shift in timberline vegetation in minnesota and upper new york early holocene climatic instability is also suggested by oxygen isotope records and or varve thickness the regional variations in evidence for the yd and other events in north america suggest that climatic oscillations may have different expressions in paleo records depending on geographic location and characteristics of a particular site the extent and magnitude of these climatic oscillations across north america suggest that these oscillations are an expression of climatic change that was probably widespread rather than locally induced by a nearby glacier the location of these sites implies that climatic signals were likely carried over the northern hemisphere through the atmosphere as indicated by general circulation models we hypothesize that the lack of evidence for a cold yd in interior north america west of the great lakes region and east of the rocky mountains was caused by the trapping of cold arctic air mass north of the laurentide ice sheet and by uninterrupted northward expansion of warm caribbean air this strongly contrasted climate also produced non analogous biological assemblages

geochronologies and environmental records of quaternary fluvial sequences in the guadalope basin northeast spain based on luminescence dating

simulated variability of the atlantic meridional overturning circulation to examine the multi annual to decadal scale variability of the atlantic meridional overturning circulation amoc we conducted a four member ensemble with a daily reanalysis forced medium resolution global version of the isopycnic coordinate ocean model micom and a 300 years integration with the fully coupled bergen climate model bcm the simulations of the amoc with both model systems yield a long term mean value of 18 sv and decadal variability with an amplitude of 1 3 sv the power spectrum of the inter annual to decadal scale variability of the amoc in bcm generally follows the theoretical red noise spectrum with indications of increased power near the 20 years period comparison with observational proxy indices for the amoc e g the thickness of the labrador sea water the strength of the baroclinic gyre circulation in the north atlantic ocean and the surface temperature anomalies along the mean path of the gulf stream shows similar trends and phasing of the variability indicating that the simulated amoc variability is robust and real mixing indices have been constructed for the labrador the irminger and the greenland iceland norwegian gin seas while convective mixing in the labrador and the gin seas are in opposite phase and linked to the nao as observations suggest the convective mixing in the irminger sea is in phase with or leads the labrador sea newly formed deep water is seen as a slow anomalous cold and fresh plume flowing southward along the western continental slope of the atlantic ocean with a return flow of warm and saline water on the surface in addition fast travelling topographically trapped waves propagate southward along the continental slope towards equator where they go east and continue along the eastern rim of the atlantic for both types of experiments the northern hemisphere sea level pressure and 2 m temperature anomaly patterns computed based on the difference between climate states with strong and weak amoc yields a nao like pattern with intensified icelandic low and azores high and a warming of 0 25 0 5 c of the central north atlantic sea surface temperature sst the reanalysis forced simulations indicate a coupling between the labrador sea water production rate and an equatorial atlantic sst index in accordance with observations this coupling is not identified in the coupled simulation

the role of clay surfaces in the heterogeneous nucleation of calcite molecular dynamics simulations of cluster formation and attachment abstract in many environments calcium carbonate minerals precipitate in the presence of clay minerals and observations suggest that clays particularly smectites facilitate carbonate formation in order to understand the interactions between clay surfaces and carbonate precipitating solutions we built model aqueous solutions of various compositions containing ca2 mg2 and co32 ions between layers of clay minerals montmorillonite and kaolinite and performed extensive molecular dynamics simulations the results were compared with simulations for bulk solutions contrary to intuition ionic clusters formed preferentially in the interlayer solution instead of on the clay surface the clusters grew both by the association of individual ions and aggregation and were adsorbed to the clay surfaces with distinctly different efficiencies in the various systems montmorillonite was found to be more efficient than kaolinite in capturing clusters from solution however the efficiency of anchoring ionic clusters to the clay surfaces strongly depended on the na concentration of the solution since na appeared to strongly attach to the surface and thereby block it from clusters in the solution montmorillonite and probably other smectite clays as well may thus have an important role in certain primarily freshwater systems in the localization of ionic clusters on its surface thereby promoting the nucleation and templated growth of crystalline calcium magnesium carbonate minerals

icing the north atlantic there is debate over the causes of the large and abrupt climate changes that the north atlantic region has experienced in the past and may do in the future the driving forces of such changes might originate in the north atlantic itself or could be transmitted to the region from elsewhere new evidence on the extent and movement of the british ice sheet around the end of the last ice age supports the first contention and in particular implicates the advance and retreat of the laurentide ice sheet in causing some of the big climate jumps of the past

the flickering switch of late pleistocene climate change polar ice contains a unique record of past climate variations previous greenland ice cores have documented relatively warm interstadial periods during the last glaciation and short centuryscale returns to colder conditions during the glacial to interglacial warming see for example ref 1 these climate features have also been observed to varying degrees in ocean sediment cores2 4 and terrestrial pollen and insect records5 7 here we report electrical conductivity measurements from a new greenland ice core which confirm these previous observations and also reveal a hitherto unrecognized mode of rapid climate variation fluctuations in ice conductivity on the scales of 5 20 years reflect rapid oscillations in the dust content of the atmosphere this flickering between two preferred states would seem to require extremely rapid reorganizations in atmospheric circulation

syneresis cracks subaqueous shrinkage in argillaceous sediments caused by earthquake induced dewatering abstract syneresis cracks often confused with subaerial desiccation phenomena are traditionally ascribed to subaqueous shrinkage whereby salinity changes caused deflocculation of clay this and other previously proposed mechanisms fail to account for their occurrence in low energy typically non evaporitic facies stratigraphically sporadic distribution intrastratal formation under shallow burial depths variation in morphology degree of contraction generation of sedimentary dikelets as crack fills and deformation of dikelets and enclosing layers instead it is suggested that ground motion from strong synsedimentary earthquakes caused argillaceous sediments to dewater interbedded sands and silts to be almost simultaneously liquefied and injected into the resulting fissures and then these dikelets to be distorted comparative rarity of syneresis cracks in phanerozoic versus precambrian marine strata is considered to be primarily an evolutionary consequence of theological changes caused by increased organic binding of clay flocs in the water column greater input of organic matter into the sediment and the diversification of sediment dwelling bacteria and meiofauna in phanerozoic deposits

ice sheet variability around the north atlantic ocean during the last deglaciation millennial scale variability in the flux of ice rafted detritus to north atlantic sediments during the last glacial period has been interpreted to reflect a climate forced increase in the discharge of icebergs from ice sheet margins surrounding the northern north atlantic ocean 1 but the relationship between ice sheet variability and climate change is not clear as both the sources of ice rafted detritus and the ice marginal processes are varied and complex 2 4 terrestrial records are helpful in unravelling this complexity because they can demonstrate the scale of ice sheet oscillations and whether the ice sheet or sector was advancing or retreating with respect to climate change here we constrain the age and anatomy of a prominent readvance of the british ice sheet in the northern irish sea region at similar to 14 14 c kyr bp similar to 16 4 calendar kyr bp the analysis indicates that the british ice sheet participated in an iceberg discharge episode known as heinrich event 1 comparison with other terrestrial and marine ice sheet records suggests that the dynamic collapse of the laurentide ice sheet beginning at 14 6 15 0 c 14 kyr bp1 4 similar to 17 2 17 6 calendar kyr bp 5 initiated varied responses from other ice sheet margins around the northern north atlantic region these observations support the argument that the release of icebergs and meltwater during heinrich event 1 disrupted the north atlantic thermohaline circulation 6 8 leading to a delay or reversal of deglaciation of the northern hemisphere and at least as far south as 40 degrees s for two to three thousand years 5 9 10 suggesting a climate forcing and response similar to that of the ensuing younger dryas cold snap 11 12

coupled climate and sea level changes deduced from huon peninsula coral terraces of the last ice age abstract huon peninsula papua new guinea is a tectonically unstable uplifting shoreline ringed by emergent coral terraces the terraces were formed during episodes of rapid sea level rise when corals constructed large discrete coral platforms that were subsequently uplifted uranium series ages of four prominent huon peninsula last glacial ois 3 coral terraces coincide with the timing of major north atlantic climate reversals at intervals of 6000 7000 yr between 30 000 yr and 60 000 yr ago terrace elevations when combined with uplift indicate 10 15 m high sea level excursions at these times we attribute the growth of the terraces directly to sea level rises arising from ice calving episodes from major north atlantic ice sheets and the antarctic ice sheet that precipitated extremes of cold climate called heinrich events these periods are associated with major discharges of land based ice and enhanced concentrations of ice rafted debris in deep sea cores sea levels at this time were 60 90 m lower than present

late holocene climate variability in the adriatic sea central mediterranean planktic and benthic foraminifera assemblages from a set of sediment cores collected on the adriatic shelf and the southern adriatic deep basin provide compelling evidence of submillennial scale environmental changes during the last 6000 years repeated peaks in globigerinoides sacculifer represent warm dry intervals including the mediaeval warm period the roman age the late bronze age and the copper age the last occurrence lo of g sacculifer 550 years bp approximates the base of the little ice age lia significant turnovers in the structure of the water column reflect changes in the rate of formation and depth of flow of the north adriatic dense water naddw and the levantine intermediate water liw about 7500 years bp the benthic oxygen isotope records mark the timing when the naddw formation intensified on the slope and shifted to its modern route about 5500 years bp when sea level reached its modern high stand oxygen isotope records of intermediate planktic dwellers indicate a northward intrusion of the liw on the slope the oscillating isotope trends during the last five millennia document a discontinuous invasion of liw into the central adriatic possibly reflecting short term climate changes with weakened liw production during colder and wetter intervals

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

textures and fabrics in the grip ice core a comprehensive study of textures and fabrics has been carried out on the greenland ice core project grip ice core crystal sizes and c axis orientations have been measured on thin sections with conventional techniques yielding new information on the growth rotation and recrystallization of ice crystals in the greenland ice sheet normal grain growth is found to persist to a depth of 700 m in the core where the onset of polygonization due to increasing strain prevents a further increase in grain size in the holocene ice smaller crystals are observed in the wisconsin ice larger crystals are found in the eemian ice and the crystal size is found to vary with climatic parameters in these periods this dependence which probably results from variable impurity content in the ice persists to a depth of 2930 m coarse grained ice probably resulting from rapid growth of crystals at comparatively high temperatures is found in the lowest 100 m of the core the data on c axis orientations reveal a steady evolution of the fabric from random near the surface to a strong single maximum in the lower part of the ice sheet a significant strengthening is not observed at the holocene wisconsin transition the fabric development indicates that vertical compression at the ice divide is the main mode of deformation down to a depth of 2850 m the evolution toward a single maximum fabric hardens the ice against vertical compression but softens it against simple shear evidence of simple shear deformation is clearly observed between 2850 m and 2950 m depth stretched fabrics in coarse grained ice in the lowest 100 m could be due to tensional stresses this ice is unlikely to be undergoing any significant horizontal deformation at the present time

orbital and millennial scale vegetation and climate changes of the past 225 ka from bear lake utah idaho usa continuous high resolution pollen data for the past 225 ka from sediments in bear lake utah idaho reflect changes in vegetation and climate that correlate well with variations in summer insolation and global ice volume during mis 1 through 7 spectral analysis of the pollen data identified peaks at 21 22 and 100 ka corresponding to periodicities in earth s precession and eccentricity orbital cycles suborbital climatic fluctuations recorded in the pollen data denoted by 6 and 5 ka cyclicities are similar to greenland atmospheric temperatures and north atlantic ice rafting heinrich events our results show that millennial scale climate variability is also evident during mis 5 6 and 7 including the occurrence of heinrich like events in mis 6 showing the long term feature of such climate variability this study provides clear evidence of a highly interconnected ocean atmosphere system during the last two glacial interglacial cycles that extended its influence as far as continental western north america our study also contributes to a greater understanding of the impact of long term climate change on vegetation of western north america such high resolution studies are particularly important in efforts of the scientific community to predict the consequences of future climate change r 2007 elsevier ltd all rights reserved

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

a compositional classification for grain assemblages in fine grained sediments and sedimentary rocks reply abstract a tripartite compositional classification is proposed for sediments and sedimentary rocks that have grain assemblages with greater than 50 percent of a weight or volume of particles smaller than 62 5 m 4 phi tarl terrigenous argillaceous contains a grain assemblage dominated by more than 75 percent of particles of extrabasinal derivation including grains derived from continental weathering and also volcanogenic debris carl calcareous argillaceous contains less than 75 percent of particles of extrabasinal derivation debris and among its intrabasinal grains contains a preponderance of biogenic carbonate particles including carbonate aggregates sarl siliceous argillaceous contains less than 75 percent of particles of extrabasinal derivation and contains a preponderance of biogenic siliceous particles over carbonate grains these three classes of fine grained particulate sediments and rocks effectively separate materials that have distinct depositional settings and systematic contrasts in organic matter content and minor grain types in the subsurface the grain assemblages that define these classes follow contrasting and predictable diagenetic pathways that have significant implications for the evolution of bulk rock properties and thus assigning a fine grained rock to one of these classes is an important first step for predicting its economic and engineering qualities for purposes of description these three class names can be joined to modifier terms denoting rock texture more precise compositional divisions specific grain types of notable importance and diagenetic features

atmospheric transmission of north atlantic heinrich events this research was supported by the u s geological survey global change program and nsf under grants atm 9523584 atm 9632029 and ear 9725554

rodent paleofaunas as indicators of climatic change in europe during the last 125 000 years abstract this paper presents a quantitative reconstruction of the european late pleistocene paleoclimate based on 72 rodent assemblages of five sequences from france germany and bulgaria covering the last interglacial glacial cycle they show a pattern of severe changes in temperature with reduced precipitation during the coldest periods a tentative correlation between the isotopic and palynological records and the paleotemperature changes is shown these changes are consistent with variations in atmospheric circulation patterns in response to an expanding retracting fennoscandian ice sheet they can be attributed to the enhancement weakening of the scandinavian polar anticyclone and its associated dry winds the south north shifting of the north atlantic polar front and the varying supply of moist air from the atlantic qualitative paleoenvironmental analysis shows broadleaved deciduous forests in france and bulgaria during most of the studied period taiga and tundra appeared in eastern france during the lower wurm the german sequence indicates the presence of coniferous forests these results are broadly consistent with other paleobiological records mammalian avian and insect faunas isotopic record in dental tissue palynology the main discrepancies with the paleoclimate inferred from the palynological record are found during the coldest periods and are probably due to the interaction between vegetation climate and atmospheric co2 levels

description and esr dating of the holsteinian interglaciation abstract the classical region of the holsteinian interglacial is in the vicinity of hamburg and the lower elbe it is defined on the basis of pollen and is clearly distinguishable from the eemian interglacial hallik 1960 muller 1974 the holsteinian interglacial is represented by a sequence of sediments up to 100 m in thickness these consist of limnic fluvial and marine beds and show a transgression up to the height of present sea level twenty seven molluscs from holsteinian deposits were used for esr dating the ages show that the holsteinian may be correlated with stage 7 of the deep sea record v28 238 shackleton and opdyke 1973

the three forks playa lake depositional model implications for characterization and development of an unconventional carbonate play the upper devonian three forks formation of the williston basin is an important reservoir interval in the bakken petroleum system with estimates suggesting greater than 3 7 billion bbl of recoverable oil detailed stratigraphic analyses are sparse but current studies propose shallow marine tidal flat or coastal sabkha environments for its deposition based on stratigraphic sedimentological and petrographic analyses of 28 cores we infer that the three forks formation was deposited in a continental setting with little to no marine influence the setting was subaerial to subaqueous environments comparable to those found in playa lake systems or continental sabkhas late devonian paleography and tectonics provided the isolation and slow subsidence of the williston basin that led to the accumulation of the three forks formation in a hot and arid climate occasional floods were responsible for the deposition of the terrigenous sediments debrite like deposits reworking bedforms scouring and erosional surfaces flood waters collected in ephemeral lakes and ponds evaporated resulting in the deposition of subaqueous dolomite anhydrite and even halite the ponds and lakes progressively evaporated and contracted until they eventually dried out the drying is characterized by dewatering structures subaerially exposed and transported sediments with ripples scour surfaces evaporite cemented surfaces evaporite removal breccias halite pseudomorphs and a variety of cracks vertical successions record an upward trend of increasing proportions of subaqueous facies indicating a transition from arid to relatively less arid climatic conditions during three forks deposition this depositional system resulted in the accumulation of a complex mosaic of lithologies composed of different proportions and textures of silt sized detrital dolomite and quartz clay and evaporites in patchy to bull s eye configurations this depositional model provides a coherent understanding of the existing depositional lithofacies and their petrophysical and geomechanical properties and provides the background for the prediction of their lateral distribution from wire line logs

coherent resonant millennial scale climate oscillations triggered by massive meltwater pulses the role of mean and stochastic freshwater forcing on the generation of millennial scale climate variability in the north atlantic is studied using a low order coupled atmosphere ocean sea ice model it is shown that millennial scale oscillations can be excited stochastically when the north atlantic ocean is fresh enough this finding is used in order to interpret the aftermath of massive iceberg surges heinrich events in the glacial north atlantic which are characterized by an excitation of dansgaard oeschger events based on model results it is hypothesized that heinrich events trigger dansgaard oeschger cycles and that furthermore the occurrence of heinrich events is dependent on the accumulated climatic effect of a series of dansgaard oeschger events this scenario leads to a coupled ocean ice sheet oscillation that shares many similarities with the bond cycle further sensitivity experiments reveal that the timescale of the oscillations can be decomposed into stochastic linear and nonlinear deterministic components a schematic bifurcation diagram is used to compare theoretical results with paleoclimatic data

modelling iceberg trajectories sedimentation rates and meltwater input to the ocean from the eurasian ice sheet at the last glacial maximum we model iceberg flow paths from the eurasian ice sheet and the associated meltwater production and sedimentation rates within the norwegian greenland sea during the last glaciation results from a numerical ice sheet model an atmospheric general circulation model and an ocean general circulation model are collated and used to provide iceberg production rate wind field and surface current forcings to an iceberg trajectory model the iceberg model then determines how icebergs issuing from the eurasian ice sheet travel across the ocean and eventually melt in addition the release of iceberg sediments is also predicted the results show that iceberg trajectories are complex and that common features of iceberg movement are clustering in zones of convergence and exit into the north atlantic through the iceland faeroes channel eurasian icebergs do not penetrate into the interior of the arctic ocean the gathering of icebergs produces a complex meltwater pattern that does not follow the conceptual idea of decreasing meltwater production with distance from the ice sheet margin sedimentation results are compared with the meltwater configuration and are found to be a poor indicator of past zones of iceberg melt with zones of sedimentation extending significantly less far

diatom records in the quaternary marine sequences around the japanese islands abstract understanding the quaternary is a key to estimating what the earth s climate will be like in the future such studies demand high resolution analyses based on paleoclimatic proxy records of changing earth s orbital forcing and solar insolation that affect the climate system quaternary diatom biostratigraphy and paleoceanography have been well established based on the quaternary marine sequences obtained by piston coring and deep sea drilling around the japanese islands this paper firstly reviews the quaternary diatom datum levels that are directly tied to magnetic polarity and then the late pleistocene and holocene rhythmic fluctuations in td derived ssts c which correlate with the earth s orbital parameters and finally reveals the large and abrupt climatic changes that have occurred around the japanese islands on centennial to millennial time scales the main aim is to provide the results of td ssts c based on the late pliocene to pleistocene sequences from three holes obtained by deep sea drilling dsdp odp the main difference between td and twt is that twt gives 0 5 values to xt warm transitional taxa thalassiosira oestrupii is grouped with xt in twt but with warm water species in td differences between the twt and td ssts c curves at hole 436 are unremarkable the remarkable variations of paleo temperatures based on td ssts c show four conspicuous episodes which correspond to the double precession cycle of mis 11 in the japan sea the twt ratio remarkably decreases at 2 6 ma due to a large increase in cold water taxa and indicates the beginning of the glacial age defined as the pliocene pleistocene boundary both twt and td ssts c increase at 2 60 2 0 ma and coincide with the lithologic change from diatom bearing clay with few dark colored layers to fine grained sediments with distinct dark light colored cycles wavelet analysis of td ssts c at site 798 indicates a reversed saw tooth pattern of 48 to 24 ky periods during 1 2 0 7 ma and 24 to 12 ky periods during 0 7 0 ma resulting in a change from longer to shorter cycles these fluctuations correlate with the earth s orbital parameters and climatic changes on a millennial time scale

late quaternary bottom current activity in the south aegean sea reflecting climate driven dense water production abstract the eastern mediterranean transient emt represents a recent early 1990s to today water circulation phenomenon during which more arid climatic conditions in the mediterranean lead to the production of very dense surface water masses in the north aegean sea the produced north aegean dense water nadw sinks to seafloor flows to the south aegean sea and then spills into the eastern mediterranean sea through the cretan straits contributing to the rejuvenation of the bottom water a large dataset of vintage high resolution seismic reflection profiles indicates that the floors of the basins in the southwest aegean sea are characterised by late quaternary erosional gullies abraded surfaces and channel related sediment drifts such structures provide evidence for the presence of strong bottom currents which originate from the southward propagation of nadw masses the basins have depths of 300 m to 1000 m and are connected to each other by narrow a few km straits and sills the dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits sills between them provides evidence that the southward propagation of the nadw occurs by the filling and flooding of each basin by dense water which then spills and cascades into the next basin southward seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage mis 11 420 ka bp the coincidence of at least three erosional surfaces within the sediment drifts with interglacial mis 11 5 and 1 respectively suggests that bottom currents were mostly active during high sea level stands and sluggish during glacial low sea level stands a 90 100 m drop of the sea level below the current level would have resulted in the emergence of the eastern cyclades plateau and thus in the disconnection of the southwest aegean sea from the north aegean sea several 0 05 0 5 m thick beds of gravelly sand with algal and mollusc debris laminated to mottled sand and mottled mud are observed in the sediment cores analysed in this paper these beds can be confidently correlated from core to core and are interpreted as bottom current deposits the separation of these beds by hemipelagic sediments indicates that bottom current activity in the southwest aegean is not permanently established but episodic six episodes of intense bottom current activity are recorded in the mis 2 4 10 80 ka sediments and they appear to correlate well with the cold and dry younger dryas and heinrich 3 4 5 6 and 7 events in contrast at least three episodes of intense bottom current activity are recorded in the cores during the holocene the higher frequency of strong bottom current episodes in the southwest aegean sea during the holocene is attributed to the higher sea level stand that makes the circulation of water masses in the aegean sea more sensitive to climatic changes

climatic and oceanographic changes in the northeast atlantic reflected by magnetic properties of sediments deposited on the portuguese margin during the last 340 ka abstract rock magnetic parameters measured along two giant piston cores md95 2040 40 34 n 9 51 w and md95 2042 37 47 n 10 09 w collected off the portuguese margin related to other proxy climatic data have been used to reconstruct magnetic mineralogical changes of in relation to environmental and climatic conditions over the north atlantic western europe and northwest africa during the last three climatic cycles since isotope stage 10 thin discrete layers containing coarse grains of titano magnetite are associated with events of iceberg discharge during heinrich events 1 6 heinrich quat res 29 1988 142 that have equivalent events in isotope stages 5 8 concentrations of fine grained ti magnetite and hematite goethite varying in phase opposition are directly linked with alternations of cold and warm climatic periods spectral analyses of the rock magnetic signals reveal milankovitch periods at 100 and 41 ka confirming the relationship with long term climatic changes at high latitudes the nature ti magnetite and size range of the finest ferrimagnetic fraction as well as its variation suggest a control by deep currents carrying a colloidal clayey fraction from remote sources iceland faeroes mid atlantic ridge variation of hematite goethite contents is linked with transport by rivers and winds from the neighbouring continent a tight correlation with the d o cycles in greenland ice records confirms that north atlantic oceanic regimes and continental wind regimes were strongly influenced by millennial scale climatic changes throughout the last 350 ka

nucleation and growth of mg bearing calcite in a shallow calcareous lake both inorganic and microbial processes play important roles in carbonate mineral precipitation in freshwater lakes identifying the individual factors that determine particle size shape composition and the spatial relationships of carbonates with other constituents of the sediment are important for understanding sediment formation and nutrient cycling and for providing input for lake management planning we studied the formation of mg bearing calcite in lake balaton a large shallow mg rich calcareous lake in hungary by filtering particles from the water and analyzing them using x ray powder diffraction and electron microscopy techniques mg bearing calcite particles from lake balaton have distinct and remarkably consistent morphologies independent of seasonal and annual variations in water temperature and composition they are typically elongated parallel to the 001 crystallographic direction are about 4 to 8 m long and even though appear to be composed of many smaller units electron diffraction patterns indicate they are perfect single crystals the mg content of calcite increases from west to east reflecting a gradient in lakewater composition the calcite crystals are invariably attached to nm scale flakes of smectite suggesting that the clay mineral serves as a nucleation site the templated nucleation may direct the growth of calcite parallel to the clay flakes resulting in its elongated shape and single crystalline character while in deep oligotrophic lakes calcite typically nucleates on picoplankton cells we rarely observe this phenomenon in lake balaton because of the shallowness of the lake sediments are stirred up by even moderate winds and the movement of organisms making nm scale smectite flakes readily available for templating calcite nucleation thus while calcite precipitation is an indirect consequence of biological activity photosynthesis the physical properties of the particles are primarily determined by inorganic factors

role of the thermohaline circulation in the abrupt warming after heinrich events evidence of rapid climate oscillations during the last glacial period has been identified in climate records from greenland ice cores1 2 and ocean sediments in the north atlantic3 4 these records show that periods of gradual cooling are terminated by abrupt warming events5 with the coldest periods coinciding with the deposition of ice rafted debris so called heinrich events throughout the north atlantic heinrich events are thought to be a signature of massive iceberg discharges owing to collapse of the laurentide ice sheet bond et al 5 have proposed that the decrease in meltwater flux following collapse and retreat of the ice sheet enhanced the ocean s thermohaline circulation6 thereby increasing advection of heat from the tropics and giving rise to abrupt climate warming here we test this idea using a simple ocean model coupled to a model of a periodically surging ice sheet we find that massive discharges of icebergs first stop the thermohaline circulation because of the consequent freshwater influx cooling the north atlantic region this is followed by a rapid restart of the circulation leading to abrupt warming thus our model can reproduce the qualitative features of the climate oscillations seen in the ice core and ocean records

oceanographic variations over the last 150 000 yr in the japan sea and synchronous holocene with the northern hemisphere abstract the paleo hydrography in the japan sea called a mini ocean was reconstructed based on the high resolution analysis of diatom assemblages over the period of 150 000 yr the decrease of diatom fertilization in the japan sea when it was isolated from surrounding seas due to the drop of sea level during the glacial to stadial phase resulted in dissolution and or extremely low diatom production in the northern cores in the subarctic water masses the annual td derived paleo ssts c were controlled by the fluctuations of 2 kyr and 4 kyr periods at intervals of 20 kyr and 40 kyr over the last 160 kyr bp respectively a 23 kyr cycle is recognized during the periods from 140 ka to 100 ka according to the wavelet analysis after temperature and sea level increased both at 133 128 ka 60 53 ka and 15 10 ka oceanic warm water diatom species predominated at 127 119 ka and after 9 cal ka in the interstadial phase at 21 3 16 9 ka and 12 9 9 8 ka sea level and salinity increased as the transgression developed at 10 0 7 0 ka the oceanic association shifted from cold water species in the stadial period to warm water ones in the interstadial phase the fluctuations of td derived ssts c on century to millennial time scales during the holocene are well correlated with abrupt climatic events that different paleoclimatic proxies record in many regions of the northern hemisphere

millennial variability in an idealized ocean model predicting the amoc regime shifts abstracta salient feature of paleorecords of the last glacial interval in the north atlantic is pronounced millennial variability commonly known as dansgaard oeschger events it is believed that these events are related to variations in the atlantic meridional overturning circulation and heat transport here the authors formulate a new low order model based on the howard malkus loop representation of ocean circulation capable of reproducing millennial variability and its chaotic dynamics realistically it is shown that even in this chaotic model changes in the state of the meridional overturning circulation are predictable accordingly the authors define two predictive indices which give accurate predictions for the time the circulation should remain in the on phase and then stay in the subsequent off phase these indices depend mainly on ocean stratification and describe the linear growth of small perturbations in the system thus monitoring particular indices of the ocean state could help predict

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

related changes in biodiversity insolation and climate in the atlantic rainforest since the last interglacial abstract the long term colonia record is located in the atlantic rainforest domain in brazil 23 52 s 46 42 20 w 900 m a s l the 780 cm long core co3 provides a coverage of a complete interglacial glacial cycle for the first time in a neotropical rainforest information on the behavior of tropical climates compared to global changes in temperatures indicates specific climate responses in terms of precipitation at these latitudes winter extratropical circulation was very active during the last interglacial and most of the glacial floristic composition of the rainforest changed several times in each phase of expansion twice during the interglacial and three times during glacial episodes araucaria was well developed in the area of sao paulo until the beginning of the first dry phase of the glacial at ca 50 000 yr b p changes in insolation controlled the expansion of the rainforest and the tropical hydrological cycle as evidenced by a strong precession signal however precession had no impact on regional climatic features the two interglacials mis 5e and holocene showed completely different patterns attesting to the continuous evolution of the forest the biodiversity index shannon wiener index remained high during both the interglacial and glacial attesting to the permanence of small patches of rainforest refugia during drier phases the lowest shannon wiener indexes were recorded between 23 000 and 12 000 yr b p and 40 000 and 30 000 yr b p and characterize two marked phases of stress for the rainforest

evidence for millennial scale climate change during marine isotope stages 2 and 3 at little lake western oregon u s a pollen and geochemical data from little lake western oregon suggest several patterns of millennial scale environmental change during marine isotope stage mis 2 14 100 27 600 cal yr b p and the latter part of mis 3 27 600 42 500 cal yr b p during mis 3 a series of transitions between warm and cold adapted taxa indicate that temperatures oscillated by ca 2 4 c every 1000 3000 yr highs and lows in summer insolation during mis 3 are generally associated with the warmest and coldest intervals warm periods at little lake correlate with warm sea surface temperatures in the santa barbara basin changes in the strength of the subtropical high and the jet stream may account for synchronous changes at the two sites during mis 2 shifts between mesic and xeric subalpine forests suggest changes in precipitation every 1000 3000 yr increases in tsuga heterophylla pollen at 25 000 and 22 000 cal yr b p imply brief warmings minimum summer insolation and maximum global ice volumes during mis 2 correspond to cold and dry conditions fluctuations in precipitation at little lake do not correlate with changes in the santa barbara basin and may be explained by variations in the strength of the glacial anticyclone and the position of the jet stream c 2001 university of washington

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

isotopic evidence for dolomite formation in soils abstract dolomite formation in soils constitute a particular challenge because of 1 scant magnesium content in continental environments as opposed to the marine medium 2 the kinetic problem related to the incorporation of magnesium into the carbonate and 3 the unknown role of soil dolomites in the global carbon cycle pedogenic dolomite formed at deeper soil levels subsoil before the development of petrocalcic horizon barriers was investigated in a semiarid region of se spain guadix baza basin mineralogical characterization textural relationships and isotopic data concerning soil dolomite together with the results of a precipitation experiment provided fuller knowledge of the processes and conditions governing neoformation of dolomite in these soils in the study case dolomite enrichment occurs beyond the limit of major biological activity which coincides with the rooting depth of native perennial plants in the semiarid soils studied textural studies reveal the corrosion of inherited dolomite crystals in the upper soil horizons and the formation of dolomite in depth in relation to a clayey material composed mainly of smectites stable isotope distribution in dolomites throughout the profiles indicates a fractionation with depth this is explained by the formation of dolomites after the dissolution of the pedogenic calcite the calcite detected in the subsoil is interpreted here as a precursor of the neoformed dolomites that transport the isotopic signal associated with biological activity of soils to deeper layers dolomite formation appears to be favoured by the presence of clay minerals in the precipitation media clays retain water during evapotranspiration stages which drastically change the transport properties of the media and promote the incorporation of mg into the structure of the neoformed ca mg carbonate as confirmed by laboratory experiments diffusion controlled crystal growth processes lead to the formation a precursory protodolomite with disordered ca mg distribution from a fluid locally supersaturated in dolomite

depositional environments and diagenesis in lake parakeelya a cambrian alkaline playa from the officer basin south australia laminated and desiccated siliceous dolostones dolomitic mudstones and dolomitic sandstones in the cambrian parakeelya alkali member of the observatory hill formation accumulated in an alkaline playa four facies are recognized from lake centre to lake edge lake saline mudflat dry mudflat and sandflat facies the facies occur in cycles cycles of tens of metres thickness record the gradual expansion and contraction of the playa superimposed smaller cycles of tens of centimetres thickness record minor oscillations in the position of the strandline in a shallow lake the dominance of saline mudflat dry mudflat and sandflat facies indicates that the lake was rimmed by broad flat areas with negligible relief the high 18o values of primary and penecontemporaneous diagenetic carbonates of 24 to 28 smow indicate strong evaporation of ground and surface waters within the lake system calcite pseudomorphs of the sodium carbonate minerals trona and shortite have 18o values between 19 and 22 5 and contain fluid inclusions with variable salinites and homogenization temperatures up to around 110 c this suggests that the euhedral alkaline evaporites were dissolved by heated waters calcite pseudomorphs then precipitated from a mixed solution formed by the interaction of these incoming fluids with the relatively saline interstitial brines the sodium bicarbonate solutions formed by dissolution of the evaporites would have been dispersed by the basinal brines so that despite the closed drainage further groundwater concentration did not take place

u s geological survey 2013 assessment of undiscovered resources in the bakken and three forks formations of the u s williston basin province abstract the upper devonian three forks and upper devonian to lower mississippian bakken formations comprise a major united states continuous oil resource current exploitation of oil is from horizontal drilling and hydraulic fracturing of the middle member of the bakken and upper three forks with ongoing exploration of the lower three forks and the upper lower and pronghorn members of the bakken formation in 2008 the u s geological survey usgs estimated a mean of 3 65 billion bbl of undiscovered technically recoverable oil resource within the bakken formation the usgs recently reassessed the bakken formation which included an assessment of the underlying three forks formation the pronghorn member of the bakken formation where present was included as part of the three forks assessment due to probable fluid communication between reservoirs for the bakken formation five continuous and one conventional assessment units aus were defined these aus are modified from the 2008 au boundaries to incorporate expanded geologic and production information the three forks formation was defined with one continuous and one conventional au within the continuous aus optimal regions of hydrocarbon recovery or sweet spots were delineated and estimated ultimate recoveries were calculated for each continuous au resulting undiscovered technically recoverable resource estimates were 3 65 billion bbl for the five bakken continuous oil aus and 3 73 billion bbl for the three forks continuous oil au generating a total mean resource estimate of 7 38 billion bbl the two conventional aus are hypothetical and represent a negligible component of the total estimated resource 8 million barrels of oil

a triple sea ice state mechanism for the abrupt warming and synchronous ice sheet collapses during heinrich events 1 abrupt switch like changes in sea ice cover are proposed as a mechanism for the large amplitude abrupt warming that seemed to have occurred after each heinrich event sea ice changes are also used to explain the colder than ambient glacial conditions around the time of the glacier discharge the abrupt warming events occur in this mechanism owing to rapid sea ice melting which warmed the atmosphere via the strong sea ice albedo and insulating feedbacks such abrupt sea ice changes can also account for the warming observed during dansgaard oeschger events the sea ice changes are caused by a weak order of 5 sv response of the thermohaline circulation thc to glacier discharges the main point of this work is therefore that sea ice may be thought of as a very effective amplifier of a weak thc variability explaining the abrupt temperature changes over greenland synchronous ice sheet collapses from different ice sheets around the north atlantic indicated by some proxy records are shown to be possible via the weak coupling between the different ice sheets by the atmospheric temperature changes caused by the sea ice changes this weak coupling can lead to a nonlinear phase locking of the different ice sheets which therefore discharge synchronously it is shown that the phase locking may also lead to precursor glacier discharge events from smaller ice sheets before the laurentide ice sheet discharges the precursor events in this mechanism are the result rather than the cause of the major glacier discharges from the laurentide ice sheet

zooming in on heinrich layers theories explaining the origin of the abrupt massive discharges of ice rafted detritus ird into the glacial north atlantic the heinrich layers hls generally point to the laurentide ice sheet as the sole source of these events until it was found that the irds also originated from icelandic and european ice sheets bond and lotti 1995 snoeckx et al 1999 grousset et al 2000 this apparent contradiction must be reconciled as it raises fundamental questions about the mechanism s of hl origin we have analyzed two 12 cm thick hls in an ultrahigh resolution mode 1 2 century intervals in a mid atlantic ridge piston core the 18o record n pachyderma left coiling reveals strong excursions induced by the melting of the icebergs these excursions are associated with a strong decrease in the amount of planktic foraminafersand with a 3 c cooling of the surface waters counts of coarse detrital grains reveal that ird are deposited according to a typical sequence 1 volcanic glass 2 quartz and feldspars 3 detrital carbonate that implies a chronology in the melting of the differentpan atlantic ice sheets sr and nd isotopic composition confirm that in both heinrich layers h1 and h2 precursor ird came from first europe iceland followed then by laurentide derived ird an internal cyclicity can be identified during h1 and h2 about four to six major abrupt discharges occurred roughly on a century timescale the 13c and 15n records reveal that dominant inputs of continent derived organic matter are associated with ird within the hls hiding the plankton productivity signal

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

the recurrence time of dansgaard oeschger events and limits on the possible periodic component abstract by comparing the high resolution isotopic records from the greenland ice core project grip and the north greenland ice core project ngrip ice cores the common climate signal in the records has been approximately separated from local noise from this an objective criterion for defining dansgaard oeschger do events is achieved the analysis identifies several additional short lasting events increasing the total number of do events to 27 in the period 12 90 kyr before present bp the quasi regular occurrence of the do events could indicate a stochastic or coherent resonance mechanism governing their origin from the distribution of waiting times a statistical upper bound on the strength of a possible periodic forcing is obtained this finding indicates that the climate shifts are purely noise driven with no underlying periodicity

chemical and textural controls on the formation of sepiolite palygorskite and dolomite in volcanic soils abstract a 3 m deep soil profile from gran canaria canary islands has been studied the profile is interesting because soil development on mafic tephra produced a pattern of clay mineral and carbonate distribution carbonates precipitated abundantly increasingly towards the bottom making up 20 90 wt of the soil sepiolite and calcite are dominant at the top whereas palygorskite and dolomite are the major components at the lower part of the profile quartz is present in low amounts in most of the profile and smectite and non crystalline partially altered tephra occur in low amounts towards the bottom mineralogical chemical and textural investigations indicate that sepiolite and calcite precipitated in the space between the original tephra grains from ca mg and si dissolved in situ and transported in the runoff palygorskite and smectite precipitated within tephra grains from in situ tephra weathering as well as dolomite the distribution of the clay minerals is due to clay composition and ion mobility sepiolite consisting only of si and mg precipitated outside tephra grains where the mobile si and mg ions were abundant in the interstitial waters palygorskite and smectite contain si al fe and mg and only precipitated within the tephra grains where the immobile al and fe were available calcite precipitation in solution is kinetically favored over that of dolomite and thus calcite precipitated between the grains dolomite precipitated within altering tephra grains and spherical clay structures because tephra and clay generated a viscous medium where dolomite supersaturation increased and the kinetic barrier for precipitation was overcome these results are relevant to the dolomite problem as they illustrate how dolomite can precipitate in surface conditions and to co 2 sequestration because dolomite can immobilize higher co 2 amounts both ca and mg are involved and not only ca and in a much more stable manner dolomite is eight orders of magnitude less soluble than calcite

links between climate and sea levels for the past three million years the oscillations between glacial and interglacial climate conditions over the past three million years have been characterized by a transfer of immense amounts of water between two of its largest reservoirs on earth the ice sheets and the oceans since the latest of these oscillations the last glacial maximum between about 30 000 and 19 000 years ago approximately 50 million cubic kilometres of ice has melted from the land based ice sheets raising global sea level by approximately 130 metres such rapid changes in sea level are part of a complex pattern of interactions between the atmosphere oceans ice sheets and solid earth all of which have different response timescales the trigger for the sea level fluctuations most probably lies with changes in insolation caused by astronomical forcing but internal feedback cycles complicate the simple model of causes and effects

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr