the flank margin model for dissolution cave development in carbonate platforms the bahama islands contain many abandoned dissolution caves at elevations between two and seven metres above current sea level the development of dissolution caves in tropical carbonate islands is dependent on the position and nature of the freshwater lens lens position is controlled by sea level which in stable carbonate platforms like the bahamas is a function of glacioeustatic sea level still stands caves in the bahamas that are currently subaerial must have developed during past higher sea levels during the late quaternary sea levels higher than present have been relatively short lived and that limits the amount of time that a freshwater lens could be situated at the elevation required for the cave formation the bahama islands are low lying landforms where only aeolian ridges extend to elevations higher than six metres above current sea level past high sea level events greatly reduced the exposed land area of the bahama islands thus also limiting both the catchment for and size of freshwater lenses caves must be younger than the rock in which they are developed most subaerial bahamian caves are found in limestones that are less than 150000 years old development of large dissolution caves under these limitations of time and lens size requires a powerful dissolutional mechanism the mixing of discharging freshwater with tide pulsed incoming marine water under the flanks of emergent dune ridges may have produced the conditions necessary bahamian caves formed by this process are phreatic chambers with complex interconnections and blind tubes their presence demonstrates that significant dissolution can occur rapidly as a result of the mixing of fresh and marine waters beneath small carbonate islands

influence of late cenozoic mountain building on ocean geochemical cycles in a steady state ocean input fluxes of dissolved salts to the sea must be balanced in mass and isotopic value by output fluxes for the elements strontium calcium and carbon rivers provide the primary input whereas marine biogenic sedimentation dominates removal dissolved fluxes in rivers are related to rates of continental weathering which in turn are strongly dependent on rates of uplift the largest dissolved fluxes today arise in the himalayan and andean mountain ranges and the tibetan plateau during the past 5 m y uplift rates in these areas have increased significantly this suggests that weathering rates and river fluxes may have increased also the oceanic records of carbonate sedimentation level of the calcite compensation depth and delta sup 13 c and delta sup 87 sr in biogenic sediments are consistent with a global increase in river fluxes since the late miocene the cooling of global climate over the past few million years may be linked to a decrease in atmospheric co sub 2 driven by enhanced continental weathering in these tectonically active regions

long term changes of chemical weathering products in rivers heavily impacted from acid mine drainage insights on the impact of coal mining on regional and global carbon and sulfur budgets abstract the long term impacts of acid mine drainage amd on stream chemistry and regional carbon and sulfur budgets were explored using watersheds of pennsylvania underlain by extensive coal deposits areas of these watersheds have been mined for 200 yr yet mining activity decreased to 2 watersheds witnessed dramatic changes in ph alkalinity calcium magnesium and sulfate sulfate fluxes from these watersheds for instance were 4 12 times higher in the 1940s than they are currently fluxes of sulfate and magnesium from the susquehanna river at danville the major tributary to the chesapeake bay are currently 32 and 70 of what they were in the 1940s while alkalinity fluxes have doubled and ph has recovered 0 8 ph units the direct impact on regional carbon budgets through the degassing of co 2 from carbonates was intense during the height of amd but the long term regional impact is modest resulting in the loss of 3 1 tg of carbon to the atmosphere over the last century during the 1940s the export of amd derived sulfate to the 29 000 km 2 portion of the susquehanna river studied here was twice as large as the current input from so x deposition to the entire 71 000 km 2 susquehanna watershed this is surprising comparing the small spatial footprint of amd to the large footprint of the entire susquehanna watershed normalizing these export rates to coal production data we estimate that global sulfur releases from amd could account for 28 40 of riverine sulfate derived from pyrite oxidation and be equal to 20 of anthropogenic s from atmospheric deposition this study emphasizes the potential importance of amd to global s budgets particularly since coal mining is predicted to increase by 50 in the coming century

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

subglacial methanogenesis a potential climatic amplifier 1 subglacial environments are a previously neglected component of the earth s global carbon cycle a reflection of the view held until recently that they are dominated by abiotic and oxic conditions here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over north america and europe during glaciations were host to significant populations of anaerobic microorganisms including methanogens able to metabolize organic carbon sequestered during interglacials and overridden during quaternary glacials in doing so we review the current evidence for subglacial methane release during deglaciation estimate the size of the subglacial reservoir of organic carbon soc and assess the amount of soc available to subglacial microbes and the likely pathways and rates of carbon turnover we then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations we calculate that the soc equates to 418 610 pg c and includes carbon from terrestrial soils vegetation peatlands lake and marine sediments the soc that is potentially available for microbial conversion to methane is smaller than this estimate due to 1 glacial erosion 2 accumulation of recalcitrant organic carbon compounds over time 3 conversion to carbon dioxide by aerobic anaerobic respiration and 4 incomplete conversion of labile organic matter to methane we estimate that the total soc available for conversion to methane is 63 pg c our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates we believe however that there is a strong likelihood that subglacial microbes could convert 63 pg of soc to methane during a glacial cycle if this were the case release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations our findings suggest that it may well be important to consider subglacial environments as active components of the earth s carbon cycle conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation however awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions

heterogeneous distributions of co 2 may be more important for dissolution and karstification in coastal eogenetic limestone than mixing dissolution mixing dissolution a process whereby mixtures of two waters with different chemical compositions drive undersaturation with respect to carbonate minerals is commonly considered to form cavernous macroporosity e g flank margin caves and banana holes in eogenetic karst aquifers on small islands macroporosity commonly originates when focused dissolution forms globular chambers lacking entrances to the surface suggesting that dissolution processes are decoupled from surface hydrology mixing dissolution has been thought to be the primary dissolution process because meteoric water would equilibrate rapidly with calcium carbonate as it infiltrates through matrix porosity and because pco2 was assumed to be homogeneously distributed within the phreatic zone here we report data from two abandoned well fields in an eogenetic karst aquifer on san salvador island bahamas that demonstrate pco2 in the phreatic zone is distributed heterogeneously the pco2 varied from less than log 2 0 to more than log 1 0 atm over distances of less than 30 m generating dissolution in the subsurface where water flows from regions of low to high pco2 and cementation where water flows from regions of high to low pco2 using simple geochemical models we show dissolution caused by heterogeneously distributed pco2 can dissolve 2 5 to 10 times more calcite than the maximum amount possible by mixing of freshwater and seawater dissolution resulting from spatial variability in pco2 forms isolated globular chambers lacking initial entrances to the surface a morphology that is characteristic of flank margin caves and banana holes both of which have entrances that form by erosion or collapse after cave formation our results indicate that heterogeneous pco2 rather than mixing dissolution may be the dominant mechanism for observed spatial distribution of dissolution cementation and macroporosity generation in eogenetic karst aquifers and for landscape development in these settings copyright 2015 john wiley sons ltd

sulfuric acid speleogenesis sas close to the water table examples from southern france austria and sicily caves formed by rising sulfuric waters have been described from all over the world in a wide variety of climate settings from arid regions to mid latitude and alpine areas h2s is generally formed at depth by reduction of sulfates in the presence of hydrocarbons and is transported in solution through the deep aquifers in tectonically disturbed areas major fractures eventually allow these h2s bearing fluids to rise to the surface where oxidation processes can become active producing sulfuric acid this extremely strong acid reacts with the carbonate bedrock creating caves some of which are among the largest and most spectacular in the world production of sulfuric acid mostly occurs at or close to the water table but also in subaerial conditions in moisture films and droplets in the cave environment these caves are generated at or immediately above the water table where condensation corrosion processes are dominant creating a set of characteristic meso and micromorphologies due to their close connection to the base level these caves can also precisely record past hydrological and geomorphological settings certain authigenic cave minerals produced during the sulfuric acid speleogenesis sas phase allow determination of the exact timing of speleogenesis this paper deals with the morphological geochemical and mineralogical description of four very typical sulfuric acid water table caves in europe the grotte du chat in the southern french alps the acqua fitusa cave in sicily italy and the bad deutsch altenburg and kraushohle caves in austria

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

carbonate minerals in the global carbon cycle abstract carbonate minerals constitute earth s largest c reservoir this reservoir is considered unimportant to the global c cycle over long periods of time e g 10 6 yrs because it provides balanced sources and sinks of atmospheric co 2 as carbonate minerals precipitate and dissolve from carbonic acid respectively however carbonate mineral reactions may impact the carbon cycle at short time scales 10 2 to 10 5 yrs particularly when atmospheric pco 2 changes by several hundred ppm as exemplified by the paleocene eocene thermal maximum at transitions between glacial interglacial times and over the past century from anthropogenic inputs here i review recent literature about mechanisms in which carbonate minerals may impact the global carbon cycle carbonate mineral dissolution which increases dissolved inorganic carbon dic concentrations may represent a net atmospheric co 2 sink as primary productivity consumes dic resulting in organic c burial in fluvial systems of carbonate terrains alternatively carbonate minerals dissolved by sulfuric and nitric acids may represent an atmospheric source of co 2 with no rapid balancing atmospheric sink sulfuric acid dissolves carbonate minerals of modern carbonate platform sediments and water filled sinkholes and in the deep sea at the base of carbonate platform scarps in terrestrial landscapes sulfuric acid dissolves carbonate minerals of karst terrains hypogene caves and in comminuted glacial sediments nitric acid forms from oxidation of reactive n which has doubled in the past hundred years as humans fix atmospheric n 2 similar to some reactions involving sulfuric acid nitric acid dissolution of carbonate minerals represents a net source of atmospheric co 2 this source is concentrated in fertilized agricultural fields in carbonate terrains each of these processes represents a small flux relative to major c exchanges such as volcanic sources and silicate mineral weathering but collectively they could impact the c cycle at magnitudes similar to these major processes these impacts may increase as humans further alter elemental cycles of s and n

sulfuric acid speleogenesis of carlsbad cavern and its relationship to hydrocarbons delaware basin new mexico and texas sulfur isotope data and ph dependence of the mineral endellite support the hypothesis that carlsbad cavern and other caves in the guadalupe mountains were dissolved primarily by sulfuric acid rather than by carbonic acid floor gypsum deposits up to 10 m thick and native sulfur in the caves are significantly enriched in 32 s isotope 34 s values as low as 25 8 per mil cdt indicate that the cave sulfur and gypsum are the end products of microbial reactions associated with hydrocarbons a model for a genetic connection between hydrocarbons in the basin and caves in the guadalupe mountains is proposed as the guadalupe mountains were uplifted during the late pliocene pleistocene oil and gas moved updip in the basin the gas reacted with sulfate anions derived from dissolution of the castile anhydrite to form h 2 s co 2 and castile limestone the hydrogen sulfide rose into the capitan reef along joints forereef carbonate beds or bell canyon siliciclastic beds and there reacted with oxygenated groundwater to form sulfuric acid and carlsbad cavern a sulfuric acid mode of dissolution may be responsible for large scale porosity of some delaware basin reservoirs and for oil field karst reservoirs in other petroleum basins of the world

formation of phreatic caves in an eogenetic karst aquifer by co2 enrichment at lower water tables and subsequent flooding by sea level rise formation of extensive phreatic caves in eogenetic karst aquifers is widely believed to require mixing of fresh and saltwater extensive phreatic caves also occur however in eogenetic karst aquifers where fresh and saltwater do not mix for example in the upper floridan aquifer these caves are thought to have formed in their modern settings by dissolution from sinking streams or by convergence of groundwater flow paths on springs alternatively these caves have been hypothesized to have formed at lower water tables during sea level low stands these hypotheses have not previously been tested against one another analyzing morphological data and water chemistry from caves in the suwannee river basin in north central florida and water chemistry from wells in the central florida carbonate platform indicates that phreatic caves within the suwannee river basin most likely formed at lower water tables during lower sea levels consideration of the hydrological and geochemical constraints posed by the upper floridan aquifer leads to the conclusion that cave formation was most likely driven by dissolution of vadose co2 gas into the groundwater sea level rise and a wetter climate during the mid holocene lifted the water table above the elevation of the caves and placed the caves tens of meters below the modern water table when rising water tables reached the land surface surface streams formed incision of surface streams breached the pre existing caves to form modern springs which provide access to the phreatic caves phreatic caves in the suwannee river basin are thus relict and have no causal relationship with modern surficial drainage systems neither mixing dissolution nor sinking streams are necessary to form laterally extensive phreatic caves in eogenetic karst aquifers dissolution at water tables potentially driven by vadose co2 gas offers an underappreciated mechanism to form cavernous porosity in eogenetic carbonate rocks copyright 2012 john wiley sons ltd

the contribution of agricultural and urban activities to inorganic carbon fluxes within temperate watersheds abstract the lateral transport of bicarbonate as dissolved inorganic carbon dic to the oceans is an integral component of the global carbon budget and can represent the sequestration of co 2 from the atmosphere recently studies have implicated land use change in particular agricultural development as an accelerator of bicarbonate export however due to the co variation of land use bedrock and surficial geologies and the relationship between bicarbonate export and climate the impact of anthropogenic activities on dic export remains an important research question in order to examine the land use controls on dic export from small temperate watersheds we sampled 19 streams draining catchments of varying land uses with similar bedrock and surficial geologies in addition to an agricultural effect there was a strong correlation between the percent of watershed in urban development and dic concentrations and dic yields urban watersheds exported 7 8 times more dic than their nearby forested counterparts and 2 0 times more dic than nearby agricultural catchments isotopic data suggest that excess dic export from altered systems results from increased chemical weathering enhanced co 2 production within urban green spaces and as a result of organic matter loading from septic systems and leaky sewer lines furthermore we found that nitrogen additions e g fertilizers and manure are aiding in the dissolution of lime increasing the total export of dic from agricultural watersheds calculated anthropogenic loading rates ranged from 0 43 to 0 86 mol c m 2 yr 1 these loading rates suggest that a significant portion of global dic export might be attributable to human activities although the impacts on co 2 sequestration are difficult to determine

the ion chemistry of lakes and late holocene desiccation in the badain jaran desert inner mongolia china abstract in the markedly arid badain jaran desert one of the least studied areas in the world over a hundred permanent lakes exist among the dunes the geochemistry of water samples from nine lakes and from the groundwater in the desert and on its periphery was investigated ion chemistry of the water from these desert lakes changes considerably on a regional scale we argue that there is a positive correlation between the ages of these lakes and their totally dissolved solids tds varying between 1 2 and 398 2 g l tritium analysis of groundwater in wells gives an age generally older than four decades and younger than 100 years the lacustrine deposits freshwater fauna and shorelines indicate the existence of large water bodies with low salinities in the inter dune hollows of this desert during the early and middle holocene the precipitation in this desert during the early and middle holocene was estimated to be ca 200 mm year on average at least twice as high as at present on the basis of paleoecology tl and radiocarbon ages it was concluded that the huge enrichment of ions in the lakes and decrease of water availability originated from climatic desiccation during the last 4000 years the paleoclimate of the badain jaran desert reported here was remarkably consistent with the late quaternary climatic histories of the regions to the immediate north west east and south of the study area

hydrochemical variations during flood pulses in the south west china peak cluster karst impacts of caco3 h2o co2 interactions high resolution measurements of rainfall water level ph conductivity temperature and carbonate chemistry parameters of groundwater at two adjacent locations within the peak cluster karst of the guilin karst experimental site in guangxi province china were made with different types of multiparameter sonde the data were stored using data loggers recording with 2 min or 15 min resolution waters from a large perennial spring represent the exit for the aquifer s conduit flow and a nearby well measures water in the conduit adjacent fractured media during flood pulses the ph of the conduit flow water rises as the conductivity falls in contrast and at the same time the ph of groundwater in the fractures drops as conductivity rises as ca 2c and hco3 were the dominant 90 ions we developed linear relationships both r 2 0 91 between conductivity and those ions respectively and in turn

morphogenesis of hypogenic caves abstract hypogenic speleogenesis is the formation of solution enlarged permeability structures by waters ascending to a cave forming zone from below in leaky confined conditions where deeper groundwaters in regional or intermediate flow systems interact with shallower and more local groundwater flow systems this is in contrast to more familiar epigenic speleogenesis which is dominated by shallow groundwater systems receiving recharge from the overlying or immediately adjacent surface hypogenic caves are identified in various geological and tectonic settings formed by different dissolutional mechanisms operating in various lithologies despite these variations resultant caves demonstrate a remarkable similarity in patterns and meso morphology which strongly suggests that the hydrogeologic settings were broadly identical in their formation hypogenic caves commonly demonstrate a characteristic suite of cave morphologies resulting from rising flow across the cave forming zone with distinct buoyancy dissolution components in addition to hydrogeological criteria hydrostratigraphic position recharge discharge configuration and flow pattern viewed from the perspective of the evolution of a regional groundwater flow system morphogenetic analysis is the primary tool in identifying hypogenic caves cave patterns resulting from ascending transverse speleogenesis are strongly guided by the permeability structure in a cave formation they are also influenced by the discordance of permeability structure in the adjacent beds and by the overall hydrostratigraphic arrangement three dimensional mazes with multiple storeys or complex 3 d cave systems are most common although single isolated chambers passages or crude clusters of a few intersecting passages may occur where fracturing is scarce and laterally discontinuous large rising shafts and collapse sinkholes over large voids associated with deep hydrothermal systems are also known hypogenic caves include many of the largest by integrated length and by volume documented caves in the world more importantly hypogenic speleogenesis is much more widespread than it was previously presumed growing recognition of hypogenic speleogenesis and improved understanding of its peculiar characteristics has an immense importance to both karst science and applied fields as it promises to answer many questions about karst porosity especially as deep seated settings are concerned which remained poorly addressed within the traditional epigenetic karst paradigm

the fluvial geochemistry and denudation rate of the guayana shield in venezuela colombia and brazil abstract the guayana shield is composed of early to mid precambrian igneous and metamorphic basement rocks with a quartzitic platform cover the complete absence of limestones and evaporites allows a clear chemical expression in the stream data of the primary weathering of the basement in a humid tropical environment total erosion rates are extremely slow 10 m m y with equal contributions from the dissolved and suspended loads however the former is largely silica with ratios of si to total cation equivalents si tz ranging to in excess of three weathering is complete to kaolinite and gibbsite i e the environment is one of active laterisation with a penetration rate of the weathering front into the fresh substrate about twice the denudation rate in basins of relatively homogeneous lithology rb sr isochrons constructed from the river data agree with the whole rock ages from the drainages thus all the common refractory rb containing minerals k feldspar mica are completely dissolved the thick lateritic regolith that is accumulating as a result of this intense weathering is a common relict feature on other southern hemisphere shields in the absence of active tectonics or greatly accelerated mechanical erosion the weathering rates of these basement rocks must be quite insensitive to environmental change

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago

contribution of carbonate rock weathering to the atmospheric co2 sink to accurately predict future co2 levels in the atmosphere which is crucial in predicting global climate change the sources and sinks of the atmospheric co2 and their change over time must be determined in this paper some typical cases are examined using published and unpublished data firstly the sensitivity of carbonate rock weathering including the effects by both dissolution and reprecipitation of carbonate to the change of soil co2 and runoff will be discussed and then the net amount of co2 removed from the atmosphere in the carbonate rock areas of mainland china and the world will be determined by the hydrochem discharge and carbonate rock tablet methods to obtain an estimate of the contribution of carbonate rock weathering to the atmospheric co2 sink these contributions are about 0 018 billion metric tons of carbon a and 0 11 billion metric tons of carbon a for china and the world respectively further by the dbl diffusion boundary layer model calculation the potential co2 sink by carbonate rock dissolution is estimated to be 0 41 billion metric tons of carbon a for the world therefore the potential co2 source by carbonate reprecipitation is 0 3 billion metric tons of carbon a

dissolution in a variably confined carbonate platform effects of allogenic runoff hydraulic damming of groundwater inputs and surface groundwater exchange at the basin scale in variably confined carbonate platforms impermeable confining units collect rainfall over large areas and deliver runoff to rivers or conduits in unconfined portions of platforms runoff can increase river stage or conduit heads in unconfined portions of platforms faster than local infiltration of rainfall can increase groundwater heads causing hydraulic gradients between rivers conduits and the aquifer to reverse gradient reversals cause flood waters to flow from rivers and conduits into the aquifer where they can dissolve limestone previous work on impacts of gradient reversals on dissolution has primarily emphasized individual caves and little research has been conducted at basin scales to address this gap in knowledge we used legacy data to assess how a gradient of aquifer confinement across the suwannee river basin north central florida affected locations magnitudes and processes of dissolution during 2005 2007 a period with extreme ranges of discharge during intense rain events runoff from the confining unit increased river stage above groundwater heads in unconfined portions of the platform hydraulically damming inputs of groundwater along a 200 km reach of river hydraulic damming allowed allogenic runoff with sical 4 to fill the entire river channel and flow into the aquifer via reversing springs storage of runoff in the aquifer decreased peak river discharges downstream and contributed to dissolution within the aquifer temporary storage of allogenic runoff in karst aquifers represents hyporheic exchange at a scale that is larger than found in streams flowing over non karst aquifers because conduits in karst aquifers extend the area available for exchange beyond river beds deep into aquifers post depositional porosity in variably confined carbonate platforms should thus be enhanced along rivers that originate on confining units this distribution should be considered in models of porosity distribution used to manage water and hydrocarbon resources in carbonate rocks copyright 2013 john wiley sons ltd

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

a simple model for the caco3 saturation state of the ocean the strangelove the neritan and the cretan ocean 1 a simple model of the caco3 saturation state of the ocean is presented it can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration it should also attract researchers unfamiliar with complex biogeochemical models despite its limitations the model calculated caco3 saturation state of today s ocean agrees well with observations in general the model reveals three distinctly different modes of operation the strangelove ocean of high supersaturation which is dominated by inorganic caco3 precipitation 2 the neritan ocean of indefinite saturation dominated by biogenic shallow water caco3 precipitation and 3 the cretan ocean of low saturation dominated by biogenic pelagic caco3 precipitation in the latter mode the deep ocean co32 is remarkably stable provided that the biogenic production of caco3 exceeds the riverine flux of ca2 and co32 this explains the overall constancy of the saturation state of the ocean documented over the last 100 ma the model is then used to address diverse questions one important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

worldwide distribution of continental rock lithology implications for the atmospheric soil co2 uptake by continental weathering and alkalinity river transport to the oceans 1 the silicate rock weathering followed by the formation of carbonate rocks in the ocean transfers co2 from the atmosphere to the lithosphere this co2 uptake plays a major role in the regulation of atmospheric co2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks this leads us to develop the first world lithological map with a grid resolution of 1 1 this paper analyzes the spatial distribution of the six main rock types by latitude continents and ocean drainage basins and for 49 large river basins coupling our digital map with the gem co2 model we have also calculated the amount of atmospheric soil co2 consumed by rock weathering and alkalinity river transport to the ocean among all silicate rocks shales and basalts appear to have a significant influence on the amount of co2 uptake by chemical weathering

synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation antarctic ice core data reveal that the atmosphere experienced abrupt centennial increases in co2 concentration during the last deglaciation 18 thousand to 11 thousand years ago establishing the role of ocean circulation in these changes requires high resolution accurately dated marine records here we report radiocarbon data from uranium thorium dated deep sea corals in the equatorial atlantic and drake passage over the past 25 000 years two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric co2 rises at 14 8 thousand and 11 7 thousand years ago we interpret these radiocarbon enriched signals to represent two short lived less than 500 years overshoot events with atlantic meridional overturning stronger than that of the modern era these results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation