relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

seismic stratigraphy of mcmurdo sound antarctica implications for glacially influenced early cenozoic eustatic change abstract analyses by barrett et al 1989 of the stratigraphic sequences of the ciros 1 drill core provided evidence of late paleogene and early neogene glacial advances and retreats that appear to correlate with the global eustatic curve of haq et al 1987 during leg 2 of the polar duke 90 pd90 cruise in the ross sea approximately 650 km of highresolution seismic data were collected in mcmurdo sound with the main objective of facilitating regional correlation of stratigraphic events observed in the cores of the ciros 1 dvdp 15 and mssts 1 drilling programs and therefore providing an opportunity to test hypotheses on linkages between cenozoic eustatic and antarctic ice volume fluctuations twenty unconformity bound seismic stratigraphic sequences labeled from top a to t were identified in the mcmurdo sound pd90 data base however seismic data from the shallow shelf on which ciros 1 was drilled show erosional surfaces at many levels indicating a condensed section in this area it is difficult to distinguish individual lithological units identified by barrett et al 1989 in the seismic data but seismic units o p and q correspond to the upper oligocene interval where they recognized 3 glacioeustatic events these three sequences totaling around 300 m in thickness can be traced over a distance of almost 100 km however they lack the seismic characteristics of glacial facies identified by anderson and bartek 1992 and thus the significance of waxing and waning events suggested for upper oligocene strata in ciros 1 remains equivocal the younger sequences in the mcmurdo sound data base are largely miocene e n the oldest of these forming the upper 70 m in ciros 1 these sequences can be traced 300 km north into the center of the victoria land basin where they have seismic features characteristic of glacial facies this suggests that ice sheets of continental scale and hence large enough to affect eustasy waxed and waned across the ross sea continental shelf at least 10 times during the miocene the data presented here for the oligocene do not preclude similar ice sheet behavior but are insufficient to test the hypothesis properly

paleolatitude distribution of phanerozoic marine ooids and cements opdyke b n and wilkinson b h 1990 paleolatitude distribution of phanerozoic marine ooids and cements palaeogeogr palaeoclimatol palaeoecol 78 135 148 data on 493 phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric co2 and or oceanic temperature gradient holocene ooid and cement precipitation occurs over similar latitudes with means centered around 24 and 28 respectively aragonite and calcite also display roughly comparable distributions with average occurrences between 25 and 28 surface seawater saturation values requisite for ooid cement carbonate precipitation are at least 3 8 rs for aragonite and 3 4 a s for calcite ancient ooid cement occurrences vary in space and time with depositional zones generally closer to the equator during continental emergence greatest extent correlates with periods of maximum transgression aragonite formation is favored in more equatorial localities than calcite when cement ooid distributions are narrow and continents are emergent similarity of latitude distribution of marine ooids cement and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in phanerozoic seas than biological processes related to net productivity of various carbonate platform communities continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

sedimentological and stable isotope evolution of lakes in the vestfold hills antarctica the sedimentological chemical and isotopic characteristics of sediment cores from three slightly saline to hypersaline lakes highway ace and organic lakes and two marine inlets ellis fjord and taynaya bay in the vestfold hills antarctica have been examined sections of the cores deposited in marine environments are characterized by uniform regularly laminated fine grained organic rich sediments with uniform organic 13c values 18 0 to 19 4 vs pdb and sulfur contents in contrast sediments deposited in lacustrine environments are extremely heterogeneous varying from finely laminated mat like sequences to poorly sorted clastic rich sediments authigenic monohydrocalcite and aragonite occur in some lake sediments the 13c values of organic matter in the lacustrine sediments exhibit an extremely wide range 10 5 to 25 3 that can be related to variations in physico chemical conditions in the lake waters strongly negative organic 13c values coupled with high sulfur contents are indicative of an anoxic zone in the overlying lake waters whereas less negative organic 13c values coupled with low sulfur contents are indicative of well mixed oxic conditions particularly high organic 13c values result during high levels of microbial activity in the lakes due to high rates of photosynthetic co2 fixation the large shifts in organic 13c are not necessarily accompanied by any change in macroscopic sedimentological characteristics illustrating the utility of isotopic investigations in these environments the 13c composition of authigenic carbonate in hypersaline organic lake sediments provides a record of changes in palaeoproductivity while the 18o of the carbonate provides information on rates of meltwater input and evaporation in the lake 14c dating suggests that highway lake was isolated from the sea by isostatic uplift at least 4600 yr before present b p whereas organic lake was isolated at approximately 2700 yr b p apparent emergence rates calculated from the 14c ages range from 1 0 to 2 1 mm yr 1 the reservoir effect in the lacustrine and marine environments is variable but probably does not exceed 1000 yr in any of the lakes examined

temperature limits for preservation of primary calcite clumped isotope paleotemperatures abstract solid state reordering of c o bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations metrics commonly used to gauge preservation quality to correctly interpret the paleoenvironmental significance of clumped isotope derived paleotemperatures it is necessary to understand the temperature time domain in which solid state c o bond reordering is important we address this question using a combination of laboratory and natural geological experiments on paleozoic brachiopod shells the laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13 c 18 o bond reordering the resulting arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions we develop an alternative kinetic model for reordering that accounts for non first order reaction progress observed during the initial several hundred minutes of laboratory heating experiments and show that the simplified first order approximation model passey and henkes 2012 predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins we evaluate our laboratory based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories specifically we use the laboratory derived arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million year time steps reflecting the burial and exhumation temperature paths of each basin while this exercise is limited by the relatively large uncertainties in the temperature histories of these basins we find general correspondence within error between predicted and observed clumped isotope values we present simplified temperature time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved partially reordered and fully reordered in conclusion calcite samples dwelling at 100 c or lower for 10 6 10 8 year timescales should not be affected by solid state c o bond reordering

plio pleistocene sedimentation in ferrar fiord antarctica a 166 m thick plio pleistocene sequence of glacial sediments has been cored in ferrar fiord in the southwestern corner of the ross sea antarctica the core has the following lithofacies massive diamictite 33 of the core interpreted as lodgement or waterlain till weakly stratified diamictite 25 waterlain till or proximal glaciomarine sediment well stratified diamictite 8 proximal glaciomarine or glaciolacustrine sediment sandstone 25 sand of aeolian or supraglacial origin mudstone 7 derived from subglacial debris and transported offshore in suspension and minor amounts of rhythmite and tuff the range of facies in this polar setting differs from those normally found in subpolar and temperate glacier fiord settings in the high proportion of aeolian derived sand and the low proportion of mudstone facies the core can be divided into two sequences based on composition and texture the sequence from 162 to 100 mbsf metres below the sea floor comprises alternations of diamictite dominated by basement lithologies and thin marine mudstone beds it is pliocene in age 4 9 2 0 ma and records several advances and retreats of ice through the transantarctic mountains and across the drill site from the west the sequence from 100 mbsf to the sea floor of pleistocene age consists of alternations of diamictite interpreted as lodgement and waterlain till and sandstone of aeolian origin deposited in a glaciolacustrine setting similar to ice covered lakes in the dry valleys today these sediments have a high volcanic component and hence are thought to have been derived by the grounding and advance of the ross ice shelf from the east past volcanic ross island this change in source is attributed to the rising transantarctic mountains increasingly containing east antarctic ice the pleistocene sequence above 100 mbsf clearly represents polar glacial sedimentation with alternations of till and glaciolacustrine sand mudstones from the pliocene sequence beneath include palynomorphs indicating times when the landscape was at least partially vegetated but contain no evidence of meltwater influence

relative sea level rise around east antarctica during oligocene glaciation during the middle and late eocene 48 34 myr ago the earth s climate cooled and an ice sheet built up on antarctica the stepwise expansion of ice on antarctica induced crustal deformation and gravitational perturbations around the continent close to the ice sheet sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet here we identify the crustal response to ice sheet growth by forcing a glacial hydro isostatic adjustment model with an antarctic ice sheet model we find that the shelf areas around east antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed the inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice sheet margins consequently the coasts experienced a progressive relative sea level rise our analysis of sediment cores from the vicinity of the antarctic ice sheet are in agreement with the spatial patterns of relative sea level change indicated by our simulations our results are consistent with the suggestion that near field processes such as local sea level change influence the equilibrium state obtained by an ice sheet grounding line

physicochemical characteristics of drip waters influence on mineralogy and crystal morphology of recent cave carbonate precipitates speleothems are one of the most intensively explored continental archives for palaeoclimate variability the parameters however that control speleothem petrography and its changes with time and space specifically calcite crystal morphology and carbonate mineralogy are still poorly understood in order to shed light on processes and their products precipitation experiments of recent carbonate crystals on watch glasses and glass plates were performed in seven selected caves drip water sites were analysed for their fluid mg ca molar ratio ph degree of saturation for calcite and aragonite and drip rates corresponding precipitates were analysed with respect to their mineralogy calcite crystal morphology and mg ca molar ratio of calcite the following results are found high fluid mg ca ratios are found only for caves situated in dolostone thus the hostrock lithology indirectly controls the carbonate mineralogy and calcite crystal morphology of speleothems the precipitation of aragonite in place of calcite occurred only in dolostone caves and is bound to very specific conditions these are high fluid mg ca ratios 0 5 high fluid ph 8 2 and low fluid saturation indices for calcite 0 8 these specific conditions are induced by slow drip rates of 0 2 ml min as often under more arid conditions causing the precipitation of calcite aragonite prior to reaching the stalagmite top due to this fluid chemistry is altered which in turn leads to changes in carbonate mineralogy and geochemistry on the stalagmite top calcite growth is inhibited at high fluid mg ca ratios and hence aragonite precipitation is kinetically stabilised an increase of the drip water mg ca ratio leads to an increased incorporation of mg2 into the calcite crystal lattice and thus to a change in calcite crystal morphology four distinctive changes occur with increasing mg2 incorporation i development of new forms steeper rhombohedra and base pinacoid at the edges and corners of the crystal seed ii crystal habit tend to elongate along 0 0 1 due to slower growth of faces with high mg2 densities iii reconstitution of crystal faces with low mg2 densities and iv occurrence of calcite crystals with bended faces and edges due to very high mg2 mg ca ratios of 0 009 0 051 incorporation growth rates and possibly also organic compounds however may also affect the morphology of calcite crystals based on the data shown here the relation of mg2 incorporation and the resulting changes in calcite crystal morphologies as well as the conditions of aragonite precipitation are now clearly better understood further work should aim at linking the calcite crystal morphology of watch glass precipitates with calcite crystal fabrics in speleothems in order to exploit the petrographic archive of speleothem deposits

oxygen carbon and u series isotopes of aragonites from vestfold hills antarctica clues to geochemical processes in subglacial environments aragonites occurring in situ on the gneissic bedrock at vestfold hills an ice free coastal antarctic oasis possess morphologic and petrographic characteristics typical of subglacial carbonate precipitates the sup 14 c chronology of the samples is invalidated by modern carbon contamination and a sup 14 c sup 12 c reservoir correction of unknown magnitude in contrast u and th isotope analyses suggest that the subglacial deposits can be treated as closed datable systems if allowance is made for the excess sup 230 th derived from the small and variable detrital silicate fraction coexisting with the aragonites the mean sup 230 th depositional age of 35 000 plus minus 2 000 yrs correlates with late isotope stage 3 of deep sea glacial chronology and represents the time when the vestfold hills were partially or completely buried under the advancing east antarctic ice sheet the survival of the aragonites following the ice sheet retreat during the holocene is attributed to the extreme arid climate of the area the aragonites are anomalously depleted in sup 18 o and slightly depleted in sup 13 c relative to smow and pdb standards respectively delta sup 18 o 15 7 plus minus 0 9 per thousand delta sup 13 c minus 3 6 plus minus 0 4 per thousand the melt water with which the aragonitesmore would have equilibrated at 0 degree c is about 7 to 9 per thousand more depleted in sup 18 o relative to the extant basal ice source delta sup 18 o minus 41 per thousand part of this enhanced sup 18 o deficiency i e 4 to 6 per thousand is ascribed to temporal shifts in delta sup 18 o of the antarctic ice the rest to isotope effects of the subglacial hydrology a model of subglacial aragonite precipitation is proposed on the basis of water flow between warm melting zones and cold freezing zones at the ice sheet sole less

oxygen isotope fractionation during the freezing of sea water the dependence of oxygen isotope fractionation on ice growth rate during the freezing of sea water is investigated based on laboratory experiments and field observations in mcmurdo sound antarctica the laboratory experiments were performed in a tank filled with sea water with sea ice grown under calm conditions at various room temperatures ranging from 58c to 208c in mcmurdo sound the ice growth rate was monitored using thermistor probes for first year landfast ice that grew to 2 m in thickness combining these datasets allows for the first time examination of fractionation at a wide range of growth rates from 0 8 10 7 to 9 3 10 7 ms 1 in the analysis a stagnant boundary layer model is parameterized using these two independent datasets as a result the optimum values of equilibrium pure ice fractionation factor and boundary layer thickness are estimated it is suggested that a regime shift may occur at a growth rate of 2 0 10 7 ms 1 a case study on sea ice in the sea of okhotsk where the growth rate is modeled by coupling the thermodynamic properties of the sea ice with meteorological data demonstrates the utility of the fitted models

modern aragonite formation at near freezing conditions in an alpine cave carnic alps austria abstract aragonite is a common mineral in caves hosted in dolomitic bedrock and in particular in those from warm climate regions it is much less common in cold caves such as in the alps where the vast majority of speleothems consist of low mg calcite here we report the occurrence of modern aragonite at very low temperatures the first of its kind from an alpine cave in the interior part of obstanser eishohle a high alpine cave containing perennial ice in its near entrance zone aragonite forms stalactites and flowstones which coexist with calcite and locally also hydromagnesite precipitation of aragonite occurs at saturation indices between 0 4 and 0 6 at 1 0 0 4 c modern 230th dates of the youngest aragonite deposits demonstrate that aragonite formation is an ongoing process 13c values are high and overlap with those of the host rock a comparison between 18o values of aragonite and drip water showed that modern aragonite formation does not occur at isotopic equilibrium surprisingly no radiocarbon bomb peak was detected in these speleothems despite their young age in addition these samples are characterized by extremely high reservoir ages between 8800 and 10 100 yr the highest ever reported for a speleothem worldwide these data are best reconciled with a model of karst dissolution largely decoupled from the soil zone oxidation of disseminated pyrite in the dark gray host rock gives rise to acidic solutions driving carbonate dissolution the dolomitic nature of the bedrock prior calcite precipitation and ventilation enhanced degassing leads to high mg ca ratios in the drip water favoring aragonite formation these in situ observations confirm previous findings that temperature is not the dominant control on calcite versus aragonite formation in caves they also suggest that ancient aragonite speleothems should be examined carefully and ideally be compared to coeval calcite samples prior to interpreting their stable isotope data in terms of environmental climatic changes

calcite and aragonite precipitation under controlled instantaneous supersaturation elucidating the role of caco3 saturation state and mg ca ratio on calcium carbonate polymorphism abstract for many decades researchers have attempted to clarify the factors controlling the precipitation of calcium carbonate polymorphs and the incorporation of mg into calcite precipitating in natural systems in this study a novel experimental approach delineates the role of instantaneous supersaturation and solution mg ca ratio in calcium carbonate mineralogy and composition the results of this study show that in solutions with different mg ca ratios the transition between the aragonite and the calcite aragonite precipitation fields is controlled by a combination of the saturation state of the solution with respect to caco3 and the mg ca ratio in solution the data show that for increasing solution mg ca ratios progressively higher supersaturation level is required for calcite precipitation the predominance of aragonite at high solution mg ca and low supersaturations is attributed to a relative decrease in calcite growth rates as a result of increasing incorporation of mg2 in the calcite lattice at higher solution mg ca ratios as suggested by abundant experimental work increasing solution mg ca decreases the growth rate of calcite while aragonite growth rates stay unaffected our experiments do demonstrate that despite decreased growth rate the percentage of mgco3 in calcite increases with increasing solution mg ca ratio as calcite growth rates decrease aragonite growth rates stay constant and it becomes the dominant mineral phase in solutions with high mg ca ratio and low supersaturations these findings are relevant to present day mineralogical distributions in carbonate systems and might be the key to elucidate the environmental conditions responsible for mineralogic changes through geologic time the observed dependence of calcium carbonate mineralogy on solution composition and supersaturation suggests that carbonate mineralogy is controlled by kinetics of growth

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

oxygen and carbon isotopic systematics of aragonite speleothems and water in furong cave chongqing china abstract to understand oxygen and carbon stable isotopic characteristics of aragonite stalagmites and evaluate their applicability to paleoclimate the isotopic compositions of active and fossil aragonite speleothems and water samples from an in situ multi year october 2005 july 2010 monitoring program in furong cave located in chongqing of china have been examined the observations during october 2005 june 2007 show that the meteoric water is well mixed in the overlying 300 500 m bedrock aquifer reflected by relatively constant 18o 0 11 0 14 1 of drip waters in the cave which represents the annual status of rainfall water active cave aragonite speleothems are at oxygen isotopic equilibrium with drip water and their 18o values capture the surface water oxygen isotopic signal aragonite to calcite transformation since the last glaciation is not noticeable in furong stalagmites our multi year field experiment approves that aragonite stalagmite 18o records in this cave are suitable for paleoclimate reconstruction with high u 0 5 7 2 ppm and low th 20 1270 ppt the furong aragonite stalagmites provide very precise chronology as good as 20s yrs 2 of the climatic variations since the last deglaciation the synchroneity of chinese stalagmite 18o records at the transition into the bolling allerod t ba and the younger dryas from furong hulu and dongge caves supports the fidelity of the reconstructed east asian monsoon evolution however the furong record shows that the cold older dryas od occurred at 14 0 thousand years ago agreeing with greenland ice core 18o records but 200 yrs younger than that in the hulu record the od age discrepancy between chinese caves can be attributable to different regionally climatic environmental conditions or chronological uncertainty of stalagmite proxy records which is limited by changes in growth rate and subsampling intervals in absolute dating seasonal dissolved inorganic carbon 13c variations of 2 3 in the drip water and 5 7 in the pool and spring waters are likely attributed to variable degrees of co2 degassing in winter and summer the variable 13c values of active deposits from 11 to 0 could be caused by kinetically mediated co2 degassing processes the complicated nature of pre deposition kinetic isotopic fractionation processes for carbon isotopes in speleothems at furong cave require further study before they can be interpreted in a paleoclimatic or paleoenvironmental context

experimental evidence for carbonate precipitation and co2 degassing during sea ice formation chemical and stable carbon isotopic modifications during the freezing of artificial seawater were measured in four 4 m3 tank incubations three of the four incubations were inoculated with a non axenic antarctic diatom culture the 18 days of freezing resulted in 25 to 27 cm thick ice sheets overlying the residual seawater the ice phase was characterized by a decrease in temperature from 1 9 to 2 2oc in the under ice seawater down to 6 7oc in the upper 4 cm of the ice sheet with a concurrent increase in the salinity of the under ice seawater and brine inclusions of the ice sheet as a result of physical concentration of major dissolved salts by expulsion from the solid ice matrix measurements of ph total dissolved inorganic carbon ct and its stable isotopic composition d13ct all exhibited changes which suggest minimal effect by biological activity during the experiment a systematic drop in ph and salinity normalized ct by up to 0 37 phsws units and 376 mol c kg 1 respectively at the lowest temperature and highest salinity part of the ice sheet were coupled with an equally systematic 13c enrichment of the ct calculations based on the direct ph and ct measurements indicated a steady increase in the in situ concentration of dissolved carbon dioxide co2 aq with time and increasing salinity within the ice sheet partly due to changes in the dissociation constants of carbonic acid in the low temperature high salinity range within sea ice the combined effects of temperature and salinity on the solubility of co2 over the range of conditions encountered during this study was a slight net decrease in the equilibrium co2 aq concentration as a result of the salting out overriding the increase in solubility with decreasing temperature hence the increase in the in situ co2 aq concentration lead to saturation or supersaturation of the brine inclusions in the ice sheet with respect to atmospheric pco2 3 5x10 4 atm when all physico chemical processes are considered we expect co2 degassing and carbonate mineral precipitation from the brine inclusions of the ice sheet which were saturated or highly supersaturated with respect to both the anhydrous calcite aragonite vaterite and hydrated ikaite carbonate minerals

aragonite calcite relationships in speleothems grotte de clamouse france environment fabrics and carbonate geochemistry abstract in grotte de clamouse france aragonite forms in a variety of crystal habits whose properties reflect the conditions of formation prolonged degassing and evaporation yield needle aragonite which is more enriched in 18o and 13c than aragonite ray crystals which form near isotopic equilibrium at present aragonite ray crystals form at the tops of stalagmites at very low discharge 0 00035 ml min and when fluid mg ca ratio is 1 1 temperature and evaporation do not seem to have a significant role in their formation the presence of aragonite in stalagmites should be indicative of a decrease in drip rate related to either dry climate conditions or local hydrology fossil aragonite was in part replaced by calcite in a time frame 13c signal and u content and preserved aragonite relicts up to 16 weight the isotope signal of different aragonite habits may reflect conditions of formation rather than climate parameters the real extent of aragonite to calcite transformation may be underestimated when replacement calcite inherits both textural and chemical properties of the precursor

controls on trace element sr mg compositions of carbonate cave waters implications for speleothem climatic records abstract at two caves clamouse s france and ernesto ne italy cave drip and pool waters were collected and sampled at intervals over a 2 3 year period mg ca and sr ca concentration ratios corrected for marine aerosols are compared with those of bedrocks and in some cases aqueous leachates of soils and weathered bedrocks cave waters do not lie along mixing lines between calcite and dolomite of bedrock carbonate but typically show enhanced and covarying mg ca and sr ca four factors are considered as controlling processes 1 the much faster dissolution rate of calcite than dolomite allows for the possibility of increase of mg ca if water rock contact times are increased during drier conditions a theoretical model is shown to be comparable to experimental leachates 2 prior calcite precipitation along a flow path is a powerful mechanism for generating enhanced and covarying mg ca and sr ca ratios this mechanism requires the solution to lose co 2 into pores or caverns 3 incongruent dolomite dissolution has only limited potential and is best regarded as two separate processes of dolomite dissolution and calcite precipitation 4 selective leaching of mg and sr with respect to ca is shown to be important in leachates from ernesto where it appears to be a phenomenon of calcite dissolution in general selective leaching can occur whenever ca is sequestered into precipitates due to freezing or drying of soils or if there is derivation of excess sr and mg from non carbonate species the ernesto cave has abundant water supply which in the main chamber is derived from a reservoir with year round constant p co 2 of around 10 2 4 and no evidence of calcite precipitation in the karst above the cave two distinct but overlying trends of enhanced and covarying mg ca and sr ca away from the locus of bedrock compositions are due to calcite precipitation within the cave and at a variable drip site due to enhanced selective leaching at slow drip rates mg enhancement in the first chamber is due to a more dolomitic bedrock and longer residence times the clamouse site has a less abundant water supply and presents geochemical evidence of prior calcite precipitation both in the cave and in overlying porous dolomite dedolomitized limestone bedrock initial p co 2 values as high as 10 1 are inferred experimental incubations of clamouse soils which generated enhanced p co 2 and precipitated caco 3 had compositions similar to the karst waters calcite precipitation is inferred to be enhanced in drier conditions hydrological controls on cave water chemistry imply that the trace element chemistry of speleothems may be interpretable in palaeohydrological terms drier conditions tends to promote not only longer mean residence times enhancing dolomite dissolution and hence mg ca but also enhances degassing and calcite precipitation leading to increased mg ca and sr ca

climatological distribution of aragonite saturation state in the global oceans aragonite saturation state arag in surface and subsurface waters of the global oceans was calculated from up to date through the year of 2012 ocean station dissolved inorganic carbon dic and total alkalinity ta data surface arag in the open ocean was always supersaturated 1 ranging between 1 1 and 4 2 it was above 2 0 2 0 4 2 between 40 n and 40 s but decreased toward higher latitude to below 1 5 in polar areas the influences of water temperature on the ta dic ratio combined with the temperature effects on inorganic carbon equilibrium and apparent solubility product k sp explain the latitudinal differences in surface arag vertically arag was highest in the surface mixed layer higher hydrostatic pressure lower water temperature and more co2 buildup from biological activity in the absence of air sea gas exchange helped maintain lower arag in the deep ocean below the thermocline aerobic decomposition of organic matter along the pathway of global thermohaline circulation played an important role in controlling arag distributions seasonally surface arag above 30 latitudes was about 0 06 to 0 55 higher during warmer months than during colder months in the open ocean waters of both hemispheres decadal changes of arag in the atlantic and pacific oceans showed that arag in waters shallower than 100 m depth decreased by 0 10 0 09 0 40 0 37 yr 1 on average from the decade spanning 1989 1998 to the decade spanning 1998 2010

carbonate clumped isotope bond reordering and geospeedometry carbonate clumped isotope thermometry is based on the preference of 13c and 18o to form bonds with each other at elevated temperatures such bond ordering is susceptible to resetting by diffusion of c and o through the solid mineral lattice this type of bond reordering has the potential to obscure primary paleoclimate information but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates we determined arrhenius parameters for solid state reordering of c o bonds in two different calcites through a series of laboratory heating experiments we find that the calcites have different susceptibilities to solid state reordering reaction progress follows a first order rate law in both calcites but only after an initial period of non first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature we show that the apparent equilibrium temperature equations or closure temperature equations for carbonate clumped isotope reordering are analogous dodson s equations for first order loss of daughter isotopes for each calcite the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of 5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years however because the calcites have different susceptibilities to reordering each calcite defines its own cooling rate apparent equilibrium temperature relationship the cooling rates of carrara marble inferred from carbonate clumped isotope geospeedometry are 10 6 10 3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods cooling rates for 13c depleted calcites from the late neoproterozoic doushantou cap carbonates in south china are on the order of 102 104 degrees per annum consistent with rapid cooling following formation of these calcites by a short lived hydrothermal event bristow et al 2011 nature v 474 p 68 71 most of the uncertainty in these estimates relates to uncertainty in arrhenius parameters for different calcites thus while the carbonate clumped isotope geospeedometer shows promise for recording cooling rates in settings and lithologies where other geospeedometers may not be applicable the uncertainty in cooling rate will be large without independent knowledge of the reordering kinetics of each study material thus the full potential of the method will only be realized if reordering kinetics can be accurately determined for each study material or predicted on the basis of mineral composition texture or other observable parameters

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

the role of seawater freezing in the formation of subsurface brines abstract several mechanisms evaporation water rock interaction ultra filtration have been suggested to explain the evolution of ubiquitous ca chloride subsurface brines in the present paper the freezing of seawater in polar regions and in even wider areas during glacial periods is proposed as an additional possible path of brine formation four detailed seawater freezing experiments to 14 c resulting in a concentration factor of about 5 were carried out and na k ca mg sr cl so4 and br were analysed in the residual brines and in the ice br and sr whose behavior during the freezing of seawater is reported here for the first time show a conservative behavior throughout the studied temperature range our data and earlier literature show that the high salinities which are common in subsurface brines 300 g l may be obtained by the removal of h2o as ice in the primary glacial environment the decrease in the na cl ratio is caused by the crystallization of mirabilite na2so4 10h2o supplemented by hydrohalite nacl 2h2o sulfate is removed both in mirabilite and by bacterial reduction the brine then migrates to the subsurface heats up under the local geothermal gradient and interacts with the adjacent rocks at this stage it may be diluted by meteoric waters its mg ca ratio decreases dolomitization and chloritization the so 4 cl ratio varies according to the local gypsum anhydrite equilibrium conditions and the ca so 4 hco 3 ratio increases as a result of dolomitization or chloritization the interaction with rocks in the subsurface may affect both the original 87 sr 86 sr and the 18 o 16 o ratios of the brine although several of the processes which lead to the formation of ca chloride brines are common for both the evaporative and the freezing models the na br cl relationship in a given brine can be used to discriminate between the two modes of brine evolution several subsurface brines from the canadian shield and one brine from finland are used as examples of the seawater freezing model and an explanation is proposed for the necessary mass production of brines in glacial environments

alteration of volcanic matter in deep sea sediments evidence from the chemical composition of interstitial waters from deep sea drilling cores six deep sea drilling project dsdp sites 252 285 315 317 336 386 were examined for the chemical composition of the dissolved salts in interstitial waters the oxygen isotopic composition of the interstitial waters and the major ion composition of the bulk solid sediments an examination of the concentration depth profiles of dissolved calcium magnesium potassium and h218o in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in dsdp pelagic drill sites concentration gradients in ca mg k and h218o are largely due to alteration reactions occurring in the basalts of layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column oxygen isotope mass balance calculations require substantial alteration of layer 2 up to 25 of the upper 1000 m but only minor exchange of ca mg and k occurs with the overlying ocean this implies that alteration reactions in layer 2 are almost isochemical

determining the δ47 acid fractionation in dolomites abstract this paper reports the fractionation of 47 during the digestion of dolomite in phosphoric acid between 25 c and 90 c using five different samples including three of pliocene age from the bahamas one from the jurassic in the middle east and one obtained from the national institute of standards nist 88b the composition of the dolomites analyzed varied from ca0 56mg0 44co3 to ca0 50mg0 50co3 fractionation values were also compared between the common acid bath and sealed vessel techniques at various temperatures no statistically significant differences were observed either between these two methods or as a function of the dolomite s stoichiometry these data produce a difference in fractionation of 0 153 0 011 for dolomite samples digested at 90 c compared to those reacted at 25 c a value higher and statistically different to previously published values utilization of this value in a study of dolomites from a core drilled on the island of san salvador in the bahamas yielded temperatures and 18ofluid values which agree with previous interpretations on the formation of these dolomites application of this value to other published studies produces lower estimates of temperature and 18ofluid values for the dolomitization process that are more consistent with the geologic models suggested for these studies

environmental controls on the petrology of a late holocene speleothem from botswana with annual layers of aragonite and calcite abstract a carbonate stalagmite from drotsky s cave in northwestern botswana consists of alternating layers of calcite and aragonite layer counts and radiocarbon ages indicate that the calcite aragonite pairs are annual layers representing about 1500 years of deposition the annual layering probably resulted from highly seasonal rainfall comparison of the uppermost layers of the speleothem with meteorological records shows that precipitation of caco3 in drotsky s cave was controlled by climate thickness of calcite layers correlates with rainfall suggesting that calcite precipitation was largely dependent on the quantity of water supplied to the speleothem by contrast thickness of aragonite layers correlates with temperature although variation in temperature cannot explain greater aragonite abundance on the sides of the speleothem compared to its center mg ca ratios in calcite layers increase upward to the bases of overlying aragonite layers and analyses of cave waters suggest that fluid mg ca ratios reach levels sufficient to cause aragonite precipitation increasing evaporation which caused greater ionic strength and supersaturation resultant increasing mg ca ratios in the fluid and perhaps increasing temperature probably combined to cause aragonite precipitation detailed petrographic analysis suggests that each annual cycle of caco3 precipitation began with relatively intense fluid flow sometimes sufficient to dissolve some of the underlying aragonite before precipitation of calcite calcite precipitation under a thick fluid layer allowed euhedral crystals to form at first but thinning of the fluid to a film allowed only flatly terminated calcite crystals by season s end as fluid flow diminished increasing evaporation increasing mg ca ratios in the fluid and perhaps increasing temperature combined to cause aragonite precipitation to begin particularly on the sides of the speleothem in some years fluid flow diminished to the point that dust accumulated on aragonite surfaces before the onset of the next year s precipitation p

glaciation across the oligocene miocene boundary in southern mcmurdo sound antarctica new chronology from the ciros 1 drill hole few palaeogene and neogene sediment cores from the antarctic continental margin have been dated with sufficient precision to enable establishment of direct linkages between glacial events on the antarctic continent and marked events in deep sea delta 18o records as a result much of our knowledge of the gradual but stepwise shift from greenhouse climates of the cretaceous to the ice house climates of the quaternary is inferred from well dated and more continuously deposited deep sea sediments in this study we present new magnetostratigraphic results from the ciros 1 drill core from mcmurdo sound antarctica along with a reinterpretation of a published diatom biostratigraphic zonation that is constrained by correlation to a high precision age model from the nearby crp 2 2a drill core our results suggest that most of the upper 350 m of the ciros 1 drill core represents rapid sediment accumulation during a short time interval spanning the oligocene miocene boundary chronostratigraphic control is precise enough to enable correlation of this interval of glacimarine sedimentation with the mi 1 deep sea delta 18o event which confirms that the mi 1 event was related to a major expansion of antarctic ice a major unconformity at 366 m in the ciros 1 drill core which is widely observed in regional seismic reflection studies represents 9 myr of missing time this unconformity can be traced offshore into the ross sea using seismic stratigraphy and is interpreted to indicate significant east antarctic ice sheet development during the mi 1 glaciation the stratigraphic expression of this 400 kyr glacial event is evidently multiphase and complex in the victoria land basin probably because it was punctuated by higher frequency orbitally induced glacial oscillations the presence of nothofagidites pollen throughout the ciros 1 drill core and the presence of a nothofagus southern beech leaf within the early miocene portion of the core indicate that antarctic mean summer temperatures did not decrease below 5 deg c throughout the mi 1 glaciation these temperatures are significantly warmer than present day mean summer temperatures at sea level in mcmurdo sound the persistence of a nothofagus forest in coastal southern victoria land throughout this time interval suggests that the present state of deep refrigeration was not reached until some time after the mi 1 glaciation

inorganic calcite morphology roles of fluid chemistry and fluid flow abstract evaluation of calcite crystal habits and fabric and their relation to precipitating fluids in spelean environments indicates that habit variations are controlled primarily by degree of supersaturation at less than 6 times supersaturation crystal habits are limited to those with shallow to steep rhombohedral forms i e 1011 4041 with increasing supersaturation scalenohedrons extremely steep rhombohedrons pinacoids and hexagonal prisms are developed slight elongation due to differences in crystal dimensions of these forms may arise i e scalenohedrons versus shallow rhombohedrons at extreme supersaturation 12 times curvature of crystal faces or curved surfaces appear the development of fibrous versus equant fabrics is the result of changes or modification of reactant supply rates and the number of crystallites nuclei present under rapid flow conditions growth rates are accelerated and greater numbers of nuclei are present thus compromise boundaries parallel to c axis and perpendicular to flow and substrate are rapidly attained in the absence of flow fewer crystallites are present and larger well developed crystals or branching forms dictated by saturation conditions arise in the absence of flow at low supersaturation elongate composite crystals and hence fibrous fabrics may result from migration of the fluid crystal interface as a result of changing or oscillating water levels a flow control mechanism can be applied to numerous geological conditions in which transitions from fibrous to equant crystal morphologies are observed

magnetobiostratigraphic chronology of the eocene oligocene transition in the ciros 1 core victoria land margin antarctica implications for antarctic glacial history in 1986 cores were obtained to a depth of 702 m with 98 recovery from the ciros 1 drill hole beneath the ross sea on the victoria land margin glaciogene sediments identified near the base of the hole mark the earliest known record of antarctic glaciation initial biostratigraphic analysis indicated that the lower 336 m of the core is early oligocene in age and that the upper 366 m is of late oligocene early miocene age recently the chronology of the ciros 1 core has been questioned we developed a magnetostratigraphy for the lower 400 m of the ciros 1 core to clarify the chronology our magnetobiostratigraphic results indicate that the base of the ciros 1 core is early late eocene in age corresponding to chron c16r ca 36 5 ma we identify the eocene oligocene boundary at about 410 420 m within a 20 m thick poorly stratified bioturbated sandy mudstone this makes the ciros 1 core the highest latitude site 77 1 s from which this datum event has been recognized at 366 m a 4 m y hiatus which lies immediately beneath fluvial sediments accounts for most of chrons c11 and c12 we recognize three major climatic episodes in the ciros 1 core 1 the late eocene 34 5 36 5 ma 430 702 m when relatively warm conditions dominated and there were high sedimentation rates and some glacial activity 2 the late eocene early oligocene boundary interval 28 5 34 5 ma 340 430 m which was a transition from relatively warm to cooler conditions that coincided with glacial intensification sea level fall and subaerial erosion of the shelf and 3 the late oligocene early miocene 22 28 5 ma 50 340 m when large scale glaciation dominated the region and glaciers grounded across the continental shelf from correlation with global oxygen isotope and sea level records we infer that the antarctic climate and surrounding oceans cooled after separation of australia and antarctica and development of deep water circulation between them this marked the onset of the eocene oligocene transition at ca 34 5 ma a major east antarctic ice sheet did not develop until the early late oligocene boundary toward the end of the eocene oligocene transition ca 28 5 ma outlet glaciers did not breach the transantarctic mountains and ground across the ross sea shelf until 0 5 m y later ca 28 ma

trace element variation in speleothem aragonite potential for palaeoenvironmental reconstruction trace element variation in annually laminated stalagmites has the potential to record long term high resolution palaeoclimatic data provided both 1 the relationship between trace element content in the carbonate and the climate and 2 the mechanism of stalagmite growth are understood here we report a secondary ion mass spectrometry sims study of an aragonitic speleothem t7 from cold air cave southern africa which achieves small m spatial resolution and ppm precision t7 has a series of fine visible laminae believed to be annual to subannual this article establishes 1 the usefulness of sims in analyzing speleothem aragonite at the spatial resolution and precision relevant to climatic studies 2 the distribution of trace elements in aragonite on micron scales and their relationship to models for speleothem growth and 3 the potential of aragonite speleothems to encode climatic data at subannual resolution complex reproducible oscillations in sr ca and ba ca are observed parallel to the growth direction of the speleothem however in addition to this variability we observe trace element oscillations perpendicular to the growth direction and infer that aragonite crystallites in the speleothem are laterally as well as vertically zoned stepscans parallel to the growth direction demonstrate complex zoning patterns from which simple climatic data are difficult to extract due to small scale lateral heterogeneity in the aragonite however time series analysis of the whole data set reveals regular cycles in sr ca and ba ca at a scale that matches the magnitude of the visible laminae on this basis it appears that within the complex geochemical variability there resides a regular environmental control possibly variation in water throughput hence rainfall

cryogenic origin for brine in the subsurface of southern mcmurdo sound antarctica sampling of interstitial fluids during deep coring in southern mcmurdo sound antarctica revealed the presence of seawater sourced hypersaline brine at depths 200 m below the seafloor na cl br and so 4 cl br relationships are consistent with a concentration mechanism that involves the removal of pure h 2 o as ice and precipitation of mirabilite na 2 so 4 10h 2 o during progressive freezing of seawater the brine is in neogene subglacial glacimarine and marine facies that record advance and retreat of glaciers through the ross sea embayment in this environment sea ice formation in semi isolated marine basins that occupied flexural troughs along ice sheet margins produced dense brines that sank and infiltrated the permeable subglacial sediment repeated cycles of glacial advance and retreat provided multiple opportunities for batches of seawater to be transformed into brine that now is in the subsurface of southern mcmurdo sound results demonstrate the feasibility of brine formation via seawater freezing and attest to the potential of a cryogenic origin for subsurface brines in high latitude regions of the northern hemisphere as proposed by some workers

use of clumped isotope thermometry to constrain the crystallization temperature of diagenetic calcite we describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped isotope thermometry a paleothermometer based on the 13 c 18 o bond enrichment in carbonates application of this thermometer to calcified gastropod shells and calcite cements in an early eocene limestone from the colorado plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123 c the early eocene host sediments were never deeply buried but they experienced a significant thermal pulse associated with the emplacement of a late miocene basalt flow the combination of independent constraints on thermal history with clumped isotope thermometry petrographic including cathodoluminescence observations and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources the petrography and calcite 18 o values taken alone suggest that the aragonite to calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample however addition of clumped isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94 123 c in a highly rock buffered microenvironment i e with the isotopic composition of fluid buffered by coexisting carbonate millions of years after lithification of the matrix and formation of initial low temperature 14 19 c calcite cements within shell body cavities clumped isotope temperatures in excess of reasonable earth surface conditions recorded by later formed cements demand that cement growth occurred in association with the lava emplacement our results illustrate the potential for clumped isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable isotopic and petrographic data alone and demonstrate how petrographic characterization of clumped isotope thermometry samples can benefit paleoclimate studies

reproducing early martian atmospheric carbon dioxide partial pressure by modeling the formation of mg fe ca carbonate identified in the comanche rock outcrops on mars 1 the well defined composition of the comanche rock s carbonate magnesite0 62siderite0 25calcite0 11rhodochrosite0 02 and its host rock s composition dominated by mg rich olivine enable us to reproduce the atmospheric co2partial pressure that may have triggered the formation of these carbonates hydrogeochemical one dimensional transport modeling reveals that similar aqueous rock alteration conditions including co2partial pressure may have led to the formation of mg fe ca carbonate identified in the comanche rock outcrops gusev crater and also in the ultramafic rocks exposed in the nili fossae region hydrogeochemical conditions enabling the formation of mg rich solid solution carbonate result from equilibrium species distributions involving 1 ultramafic rocks ca 32 wt olivine fo0 72fa0 28 2 pure water and 3 co2partial pressures of ca 0 5 to 2 0 bar at water to rock ratios of ca 500 molh2o mol 1rock and ca 5 c 278 k our modeled carbonate composition magnesite0 64siderite0 28calcite0 08 matches the measured composition of carbonates preserved in the comanche rocks considerably different carbonate compositions are achieved at 1 higher temperature 85 c 2 water to rock ratios considerably higher and lower than 500 mol mol 1 and 3 co2partial pressures differing from 1 0 bar in the model set up the comanche rocks hosting the carbonate may have been subjected to long lasting 104 to 105 years aqueous alteration processes triggered by atmospheric co2partial pressures of ca 1 0 bar at low temperature their outcrop may represent a fragment of the upper layers of an altered olivine rich rock column which is characterized by newly formed mg fe ca solid solution carbonate and phyllosilicate rich alteration assemblages within deeper unexposed units

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

an intercomparison of a bryan cox type ocean model and an isopycnic ocean model part i the subpolar gyre and high latitude processes abstract this paper describes a model intercomparison between a bryan cox type ocean model and an isopycnic coordinate ocean model the two models are integrated for 30 years on a domain of the north atlantic stretching from 20 s to 82 n the main purpose of this work is to illuminate aspects of the respective models that give a realistic representation of the north atlantic circulation and the physical processes that occur therein and to identify those which need to be improved to this end the same forcing fields and as many of the same parameter settings as possible were chosen so that differences between the models would be due to distinct model features rather than choice of parameters where we felt that using the same setup between the models was inappropriate or impossible we examined the possible difference this could make to the simulators in the isopycnic model the path of the north atlantic current after separation is simulated quite realistically whereas in the bryan cox model it become