did antarctic sea ice expansion cause glacial co2 decline 1 recently stephens and keeling 2000 have put forward an appealing theory for explaining the decrease in glacial atmospheric co2 they argue that a compact sea ice cover extending southward of 55 s trapped large amounts of co2 beneath the sea surface thus accounting for the lower atmospheric concentrations an atmosphere ocean box model in which sea ice area is prescribed allows them to simulate 80 of the co2 drawdown however glacial co2 levels can be attained in their model only when the fraction of ice covered area southward of the antarctic polar front rises to 99 100 we present simulations with a coupled sea ice upper ocean model indicating that ice area fractions so large might have not prevailed even under rather extreme glacial conditions the combination of our glacial ice coverage estimates with the ice area co2 relation derived by stephens and keeling suggests that co2 sequestration under sea ice could account for at most 15 50 of the total glacial co2 decline

new estimates of carbon transfer to terrestrial ecosystems between the last glacial maximum and the holocene ice core records of atmospheric co2 show an 80 ppm rise between the last glacial maximum lgm and the mid holocene during a corresponding world wide expansion of the terrestrial biomass and changes in ocean chemistry therefore the absolute amount of carbon transferred to the atmosphere probably from the oceans remains uncertain to address this issue i evaluated changes in terrestrial ecosystem carbon storage and isotopic fractionations between the lgm and the mid holocene using a process based terrestrial carbon cycle model forced with two general circulation model gcm simulations of each interval the results indicate that global carbon storage in terrestrial ecosystems vegetation and soils increased by 668 gt c during the last glacial interglacial transition a value within the range obtained from a revised global carbon isotope mass balance analysis 550 680 gt c and consistent with independent estimates from the marine isotopic record

impact of strong deep ocean stratification on the glacial carbon cycle 1 during the last glacial maximum the climate was substantially colder and the carbon cycle was clearly different from the late holocene according to proxy data deep oceanic 13c was very low and the atmospheric co2 concentration also reduced several mechanisms have been proposed to explain these changes but none can fully explain the data especially the very low deep ocean 13c values oceanic core data show that the deep ocean was very cold and salty which would lead to enhanced deep ocean stratification we show that such an enhanced stratification in the coupled climate model climber 2 helps get very low deep oceanic 13c values indeed the simulated 13c reaches values as low as 0 8 in line with proxy data evidences moreover it increases the oceanic carbon reservoir leading to a small yet robust atmospheric co2 drop of approximately 10 ppm

evidence for a reduction in the carbonate ion content of the deep sea during the course of the holocene the paleo carbonate ion proxy proposed by broecker et al 1999 is applied in a search for trends in the holocene acidity of waters in the transition zone between north atlantic deep water and antarctic bottom water aabw a clear signal emerges that the carbonate ion content of waters in this zone declined during the past 8000 years in order to determine whether this decline represents a strengthening of the northward penetrating tongue of low co3 content aabw or a global reduction of co3 ion measurements were made on a core from the ontong java plateau in the western equatorial pacific evidence for a similar decline in co3 ion over the course of the holocene was obtained lending support of the latter explanation such a drop is consistent with the recent finding by indermuhle et al 1999 that the co2 content of the atmosphere as recorded in the taylor dome antarctica ice core rose by 20 25 ppm during the past 8000 years

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

ultrahigh temperature metamorphism followed by two stage decompression of garnet orthopyroxene sillimanite granulites from ganguvarpatti madurai block southern india the mg al granulites from ganguvarpatti consist of orthopyroxene sillimanite garnet quartz as peak assemblage with a few porphyroblasts of cordierite and sapphirine these assemblages were strongly overprinted by late symplectites and coronas orthopyroxene inclusions in garnet and porphyroblast cores have the highest xmg 0 80 and al2o3 content 10 7 wt the estimated near peak metamorphic conditions 1 000 50 c and 11 kbar using garnet orthopyroxene geothermobarometry are consistent with those determined using a petrogenetic grid the proposed multi stage evolution process implies an initial decompression deduced from multi phase symplectites followed by cooling during biotite formation further late decompression is explained from the orthopyroxene rims on biotite this proposed p t path thus suggests a unique and complex evolution history for the uht granulites of southern india present results are comparable with similar adjacent terranes in the gondwana supercontinent but the lack of structural and geochronological data makes a link with any major metamorphic event uncertain

complementary constraints from carbon 13c and nitrogen 15n isotopes on the glacial ocean s soft tissue biological pump a three dimensional process based model of the ocean s carbon and nitrogen cycles including 13c and 15n isotopes is used to explore effects of idealized changes in the soft tissue biological pump results are presented from one preindustrial control run pictrl and six simulations of the last glacial maximum lgm with increasing values of the spatially constant maximum phytoplankton growth rate max which accelerates biological nutrient utilization mimicking iron fertilization the default lgm simulation without increasing max and with a shallower and weaker atlantic meridional overturning circulation and increased sea ice cover leads to 280 pg more respired organic carbon corg storage in the deep ocean with respect to pictrl dissolved oxygen concentrations in the colder glacial thermocline increase which reduces water column denitrification and with delay nitrogen fixation thus increasing the ocean s fixed nitrogen inventory and decreasing 15nno3 almost everywhere this simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well but it overestimates deep ocean 13cdic and underestimates 15nno3 at high latitudes increasing max enhances corg and lowers deep ocean 13cdic improving the agreement with sediment data in the model s antarctic and north pacific oceans modest increases in max result in higher 15nno3 due to enhanced local nutrient utilization improving the agreement with reconstructions there models with moderately increased max fit both isotope data best whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well the best fitting models reproduce major features of the glacial 13cdic 15n and oxygen reconstructions while simulating increased corg by 510 670 pg compared with the preindustrial ocean these results are consistent with the idea that the soft tissue pump was more efficient during the lgm both circulation and biological nutrient utilization could contribute however these conclusions are preliminary given our idealized experiments which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes the analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes whereas carbon isotopes are sensitive to circulation changes and indicate well the three dimensional corg distribution nitrogen isotopes are more sensitive to biological nutrient utilization

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

modeling ocean atmosphere carbon budgets during the last glacial maximum heinrich 1 meltwater event bolling transition benthic carbon isotope data indicate that the rate of north atlantic deep water nadw formation and the mode of oceanic thermohaline circulation thc varied considerably across the transition from the last glacial maximum lgm to the heinrich 1 meltwater event mwe and subsequently to the bolling warm period we simulate changes in the ocean atmosphere carbon cycle induced by and linked to these oceanic fluctuations by means of a carbon cycle box model which resolves the major oceanic basins the output from an ocean general circulation model ogcm which is forced by observed or reconstructed boundary conditions at its surface serves to constrain the physical parameters of the carbon cycle model the ogcm depicts three modes of atlantic thc an interglacial mode with vigorous nadw formation a glacial mode with active although weaker 65 nadw formation and an mwe mode characterized by the complete lack of nadw formation the carbon cycle model is forced from the lgm scenario into the mwe and finally into the bolling interstadial the glacial circulation mode accounts for approximately half i e 37 3 mu atm depending on parameterization of biological productivity of the observed glacial reduction in atmospheric co2 partial pressure pco 2 approximately 70 of this pco 2 decline is linked to changes in sea surface temperature and salinity the mwe circulation mode has only a small effect on atmospheric pco 2 1 mu atm but goes along with a massive redistribution of carbon from the indo pacific and southern oceans to the atlantic ocean which stores 85 8 gt gigatons excess carbon during the mwe the onset of nadw formation after a meltwater event has the potential to release 81 6 gt carbon from the model ocean to the atmosphere corresponding to an atmospheric pco 2 increase by 38 3 mu atm equivalent to approximately half of the modern man made pco 2 load

role of increased marine silica input on paleo pco2 levels changing the supply of silica to the ocean may alter pco2 levels the increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake the increased silica levels shifted species composition diatom populations increased and coccolith populations decreased decreasing the population of coccoliths decreased the flux of calcite to the sediments which in turn lowered pco2 levels enough to explain the glacial interglacial pco2 transition furthermore the contemporary increase in dust delivered to the ocean s mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present to set the stage this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses

climate change during the last deglaciation in antarctica greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators in this work rapid climate change events in the northern and southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores high resolution glaciochemical series covering the period 10 000 to 16 000 years ago from a central greenland ice core and a new site in east antarctica display similar variability these findings suggest that rapid climate change events occur more frequently in antarctica than previously demonstrated

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

ice age terrestrial carbon changes revisited n shackleton 1977 first proposed that changes in the marine 13 c record 13 c could be used to infer ice age changes in carbon storage on land the previously published best estimate from the marine record is equivalent to about 490 gt 0 32 13 c however adams et al 1990 utilized a pollen database to estimate a 1350 gt change in carbon storage which would cause a 13 c of about 0 90 the nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land to address the nature of this discrepancy i have reexamined the terrestrial carbon record based on a new pollen database compiled by r webb and the cooperative holocene mapping project cohmap group i estimate about 750 1050 gt glacial interglacial change in terrestrial carbon storage with the range reflecting uncertainties in carbon storage values for different biomes additional uncertainties apply to rainforest and wetland extent and presence of c4 plants which have a significantly different isotopic signature than c3 plants although some scenarios overlap a new estimate of carbon storage based on the oceanic 13 c record revised to 0 40 and 610 gt most estimates seem to fall outside the envelope of uncertainty in the marine record several possible explanations for this gap involve 1 a missing sink may be involved in land sea carbon exchange e g continental slopes 2 the geochemistry of the exchange process is not understood 3 carbon storage by biome may have changed under ice age boundary conditions or 4 the standard interpretation of whole ocean changes in the marine 13 c record requires reevaluation this latter conclusion receives some support from comparison of the 13 c records for 18 o stages 2 and 6 for the stage 6 glacial the 13 c changes are 50 60 larger than for the stage 2 glacial yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading to summarize the above analysis implies that despite the uncertainties remaining in estimates of terrestrial carbon storage changes a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine 13 c record

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

estimating the carbon transfer between the ocean atmosphere and the terrestrial biosphere since the last glacial maximum carbon dioxide records from polar ice cores and marine ocean sediments indicate that the last glacial maximum lgm atmosphere co2 content was 80 90 ppm lower than the mid holocene this represents a transfer of over 160 gtc into the atmosphere since the lgm palaeovegetation studies suggest that up to 1350 gtc was transferred from the oceans to the terrestrial biosphere at the end of the last glacial evidence from carbon isotopes in deep sea sediments however indicates a smaller shift of between 400 and 700 gtc to understand the functioning of the carbon cycle this apparent discrepancy needs to be resolved thus older data have been reassessed new data provided and the potential errors of both methods estimated new estimates of the expansion of terrestrial biomass between the lgm and mid holocene are 700 gtc 300 gtc using the ocean carbon isotope based method compared with of 1100 gtc 500 gtc using the palaeovegetation estimate if these estimates of the carbon shift to the terrestrial biosphere are equilibrated with the dissolved carbon in the oceans and the caco3 compensation of the ocean is taken into account then the glacial atmospheric co2 would have been between 50 30 ppm and 95 50 ppm higher the glacial atmosphere therefore should have had a co2 partial pressure of between 330 and 375 atm hence a rise of between 130 and 175 atm in atmospheric co2 rather than 80 atm at the end of the last glacial must be accounted for

extreme thermal metamorphism associated with gondwana assembly evidence from sapphirine bearing granulites of rajapalayam southern india

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

the calcite lysocline as a constraint on glacial interglacial low latitude production changes we investigate the response of the calcite lysocline to changes in the export production of the low latitude surface ocean the combined equatorial tropical and subtropical regions we employ different caco3 throughput schemes in a time dependent ocean carbon cycle model to separate the caco3 production lysocline balance from the other components of the model response and to estimate the effect of dissolution driven by organic matter decomposition in surface sediments with this model we carry out three experiments based on previous hypotheses for the cause of glacial interglacial atmospheric co2 variations 1 a simple increase in low latitude production 2 a decrease in its caco3 organic carbon rain ratio and 3 an increase in the depth of organic carbon regeneration none of these changes when taken alone can lower atmospheric co2 to glacial levels without violating observations of the glacial lysocline depth if a low latitude production increase were accompanied by a decrease in the caco3 organic carbon rain ratio then these simultaneous changes could lower atmospheric co2 to observed glacial levels without causing a significant change in the ocean average depth of the lysocline however even with these simultaneous changes the required increase in production is 50 or more of the modern rate of production

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

influence of a co2 aq dependent biological c isotope fractionation on glacial 13c 12c ratios in the ocean planktonic foraminiferal shells buried in deep ocean sediments record lower 13c values of surface water dissolved inorganic carbon during glacial times than during holocene in the southern ocean and at high northern latitudes a drop of between 0 3 and 0 9 is observed whereas the mean change in low and middle latitudes is only 0 15 however a stronger biological carbon pump sufficient to explain the 80 ppmv lower atmospheric pco2 values during glacial times would raise the surface ocean 13c values of dissolved inorganic carbon by about 1 0 here the results of a three dimensional ocean circulation model study are presented which demonstrate that the increase of 13c values in the sea surface due to a strengthening of the biological carbon pump is counteracted by processes which drive the 13c values in the opposite direction this was found by performing simulations employing the three dimensional hamburg model of the oceanic carbon cycle hamocc combined with a co2 aq dependent parameterization of the biological carbon isotope fractionation the difference in the biological carbon isotope fractionation between glacial and holocene is responsible for a lowering of 13c values in surface water dissolved inorganic carbon by about 0 3 the additional effects of the glacially elevated co32 concentration 0 25 0 50 combined with the 0 35 lowering of 13c values for the whole ocean due to a transfer of terrestrial organic carbon from the biosphere to the ocean atmosphere reservoir also contribute to a further 13c drop of 0 6 0 85 hence a small glacial decrease of the planktonic foraminifera 13c of the order of 0 25 instead of an increase is predicted

ocean biology could control atmospheric delta c 13 during glacial interglacial cycle 1 estimates of changes in the global carbon budget are often based on the assumption that the terrestrial biosphere controls the isotopic composition of atmospheric co2 since terrestrial plants discriminate against the 13c isotope during photosynthesis however this method disregards the influence of 13c fractionation by the marine biota here an interpretation of the glacial interglacial shifts in the atmospheric co2 concentration and 13co2 measured in the taylor dome ice core smith et al 1999 is given by accounting for possible changes in the ocean biology based on sensitivity simulations undertaken with the intermediate complexity model climber 2 with a combined scenario of enhanced biological and solubility pumps the model simulates glacial atmospheric co2 and 13co2 similar to those inferred from the ice core the simulations reveal that a strengthening of the oceanic biological carbon pump considerably affects the atmospheric 13co2

production and accumulation of calcium carbonate in the ocean budget of a nonsteady state present day production of caco3 in tne world ocean is calculated to be about 5 billion tons bt per year of which about 3 bt accumulate in sediments the other 40 is dissolved nearly half of the carbonate sediment accumulates on reefs banks and tropical shelves and consists largely of metastable aragonite and magnesian calcite deep sea carbonates predominantly calcitic coccoliths and planktonic foraminifera have orders of magnitude lower productivity and accumulation rates than shallow water carbonates but they cover orders of magnitude larger basin area twice as much calcium is removed from the oceans by present day carbonate accumulation as is estimated to be brought in by rivers and hydrothermal activity 1 6 bt suggesting that outputs have been overestimated or inputs underestimated that one or more other inputs have not been identified and or that the oceans are not presently in steady state one missing calcium source might be groundwater although its present day input is probably much smaller than that of rivers if as seems likely caco3 accumulation presently exceeds terrestial and hydrothermal input this imbalance presumably is offset by decreased accumulation and increased input during lowered sea level shallow water accumulation decreases by an order of magnitude with a 100 m drop in sea level while groundwater influx increases because of heightened piezometric head and the diagenesis of metastable aragonite and magnesian calcite from subaerially exposed shallow water carbonates

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

modeling the calcite lysocline a numerical model of calcite dissolution in contact with sediment pore water is used to predict the depth and shape of the calcite lysocline in the deep sea model results are compared with lysocline data from 13 regions in the atlantic pacific and indian oceans the model lysocline shape is sensitive to the calcite dissolution rate constant the calcite organic carbon and refractory material rain rates and the rates of oxic versus anoxic organic carbon degradation in the sediment the model is able to reproduce the observed lysocline within the constraints of the sediment trap and calcite accumulation data using a calcite dissolution rate constant of 30 100 d 1 a molar ratio of organic carbon to calcite rain rates of 0 5 1 0 and an initial caco3 fraction of 90 excluding organic carbon this rate constant is consistent with microelectrode results presented by archer et al 1989 the model predicts that 30 50 of the calcite rain to the sea floor at the saturation horizon dissolves in response to organic carbon respiration consistent with previous modeling studies the range in the best fit value of the organic inorganic carbon rain rates arises from model sensitivity to uncertainty in the rate of anoxic carbon degradation in the sediment and in the rain rate of refractory material rather than from scatter in the data lysocline data from the western equatorial atlantic are anomalous to the rest of the data this anomaly may be explained by high rates of refractory material sedimentation from the amazon river

first report of sapphirine bearing rocks from the palghat cauvery shear zone system southern india abstract silica deficient mg al granulites from paramati within the palghat cauvery shear system contain sapphirine in association with corundum spinel and sillimanite gedrite which occurs commonly in this locality coexists with cordierite corundum and sillimanite mineral assemblages and reaction textures indicate peak metamorphism at ultrahigh temperature conditions this new locality provides evidence for extreme crustal metamorphism along the archean proterozoic collision boundary in southern india

present status of the geochronology of the precambrian rocks of rajasthan abstract age determinations mostly by rb sr analyses of the precambrian rocks of rajasthan by us and by others are summarized and discussed broad periods of acid magmatism at 1 3000 2900 m y 2 2600 2500 m y 3 2000 1900 m y 4 1700 1500 m y and 5 850 750 m y were identified the oldest rocks in the area are the yet undated banded gneisses bgc east of udaipur intruded by the untala granite dated at 2950 m y and hence of mid archean age the basal status hitherto attributed to the berach granite dated at 2600 m y is no longer tenable the radiometric control on the beginning and duration of the overlying aravalli supergroup is not yet satisfactory though a lower limit at 2000 m y is indicated heron s original delhi rocks have recorded two magmatic events widely separate in space and time while the earliest granitic activity at 1600 m y is recorded only in the alwar basin in the northeast the younger activity between 850 750 m y is widespread as shown by the nearly concordant ages of erinpura type granites along the aravalli mountain range and the malani rhyolites in the western plains of the aravalli range

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

pan african granulite facies assemblages in kodaikanal anaimalai ranges tamil nadu and mt abu balaram areas of gujarat india madagascar india connection in eastern gondwana assembly

sphagnum peatland distribution in north america and eurasia during the past 21 000 years the distribution and abundance of sphagnum spores in north america and eurasia are mapped for the past 21 ka the present day distribution of abundant sphagnum spores corresponds closely to areas with peatland development with maximum sphagnum abundance between 630 and 1300 mm annual precipitation and between 2 and 6 c mean annual air temperature during the wisconsin glaciation there were apparently not large areas of peatland in north america except in alaska high sphagnum spore percentages were found in eastern north america during deglaciation major peatland development occurred in boreal north america after 9 ka and there was a southward movement of high sphagnum spore abundance after 5 ka in the western great lakes region major peatland development began after 9 ka in europe and asia on the basis of maps of the area supporting peatlands carbon accumulation in peatlands is estimated to be low prior to 11 ka increased slightly between 11 and 5 ka and greatly increased during the past 5 ka

carbon stocks and isotopic budgets of the terrestrial biosphere at mid holocene and last glacial maximum times abstract the carbon fluxes stocks and isotopic budgets of the land biosphere at mid holocene 6 ka bp and last glacial maximum 21 ka bp times are reconstructed with the carbon assimilation in the biosphere caraib model forced with two different sets of climates simulated by the european centre hamburg echam and lmd general circulation models it is found that the trends predicted on the basis of both sets of gcm climatic fields are generally consistent with each other although substantial discrepancies in the magnitude of the changes may be observed actually these discrepancies in the biospheric results associated with the use of different gcm climatic fields are usually smaller than the differences between biospheric runs performed while considering or neglecting the co2 fertilization effect which might however be overestimated by the model due to uncertainties concerning changes in nutrient availability the calculated changes with respect to the present of the biosphere carbon stock range from 132 to 92 gt c for the mid holocene and from 710 to 70 gt c for the last glacial maximum it is also shown that the relative contribution of the material synthesized by c4 plants to the total biomass of vegetation litter and soils was substantially larger at mid holocene and last glacial maximum times than today this change in the relative importance of the c3 and c4 photosynthetic pathways induced changes in the 13 c fractionation of the land biosphere these changes in the average biospheric fractionation resulting from the redistribution of c3 and c4 plants were partly compensated for by changes of opposite sign in the fractionation of c3 plants due to the modification of the intercellular co2 pressure within their leaves with respect to present times the combination of both processes reduced the 13 c discrimination i e less negative fractionation of the land biosphere by 0 03 to 0 32 during the mid holocene and by 0 30 to 1 86 at the last glacial maximum

mercury s geochronology revised by applying model production function to mariner 10 data geological implications 1 model production function mpf chronology uses dynamic models of the main belt asteroids mbas and near earth objects neos to derive the impactor flux to a target body this is converted into the crater size frequency distribution for a specific planetary surface and calibrated using the radiometric ages of different regions of the moon s surface this new approach has been applied to the crater counts on mariner 10 images of the highlands and of several large impact basins on mercury mpf estimates for the plains show younger ages than those of previous chronologies assuming a variable uppermost layering of the hermean crust the age of the caloris interior plains may be as young as 3 59 ga in agreement with messenger results that imply that long term volcanism overcame contractional tectonics the mpf chronology also suggests a variable projectile flux through time coherent with the mbas for ancient periods and then gradually comparable also to the neos

reaction textures in a suite of spinel granulites from the eastern ghats belt india evidence for polymetamorphism a partial petrogenetic grid in the system kfmash and the roles of zno and fe2o3 spinel granulites with or without sapphirine occur as lenses in garnetiferous quartzofeldspathic gneisses leptynites near gokavaram in the eastern ghats belt india spinel granulites are mineralogically heterogeneous and six mineral associations occur in closely spaced domains these are i spinel quartz cordierite ii spinel quartz cordierite garnet orthopyroxene sillimanite iii spinel cordierite orthopyroxene sillimanite iv spinel quartz sapphirine sillimanite garnet v spinel quartz sapphirine garnet and iv rhombohedral fe ti oxide cordierite orthopyroxene sillimanite common to all the associations are a porphyroblastic garnet containing an internal schistosify defined by biotite sillimanite and quartz perthite and plagioclase spinel contains variable amounts of exsolved magnetite and is distinctly zn rich in the sapphirine absent associations x mg in the coexisting phases decreases in the order cordierite biotite sapphirine orthopyroxene spinel garnet fe ti oxides textural criteria and compositional characteristics of the phases document several retrograde mineral reactions which occurred subsequent to prograde dehydration melting reactions involving biotite sillimanite quartz plagioclase and spinel the following retrograde mineral reactions are deduced 1 spinel quartz cordierite 2 spinel quartz garnet sillimanite 3 garnet quartz cordierite orthopyroxene 4 garnet quartz sillimanite cordierite 5 spinel cordierite orthopyroxene sillimanite 6 spinel sillimanite quartz sapphirine 7 spinel sapphirine quartz garnet sillimanite and 8 spinel quartz sapphirine garnet a partial petrogenetic grid for the system feo mgo al 2 o 3 sio 2 k 2 o h 2 o at high fo 2 has been constructed and the effects of zno and fe 2 o 3 on this grid have been explored combining available experimental and natural occurrence data the high fo 2 invariant points in the partial grid have been located in p t space geothermobarometric data and consideration of the deduced mineral reactions in the petrogenetic grid show that the spinel granulites evolved through an anticlockwise p t trajectory reaching peak metamorphic conditions 9 kbar and 950 c followed by near isobaric cooling dt dp 150 c kbar this was superimposed by an event of near isothermal decompression dt dp 15 c kbar the studied spinel granulites therefore preserve relic prograde mineral associations and reaction textures despite being metamorphosed at very high temperatures and bear evidence of polymetamorphism

sapphirine bearing granulites from abu balaram area gujarat state implications for india madagascar connection p t conditions of sapphirine bearing granulites from a new locality from the north eastern part of gujarat range from 8 2 8 8 kbars at t of 950 c the discovery of this uht assemblage in the north western part of the indian shield bordering the aravalli delhi fold belt provides additional evidences for india madagascar connection linking the aravalli malani sequences to similar lithologies in northern madagascar