the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

abyssal circulation driven by near boundary mixing water mass transformations and interior stratification the emerging view of the abyssal circulation is that it is associated with bottom enhanced mixing which results in downwelling in the stratified ocean interior and upwelling in a bottom boundary layer along the insulating and sloping seafloor in the limit of slowly varying vertical stratification and topography however boundary layer theory predicts that these upslope and downslope flows largely compensate such that net water mass transformations along the slope are vanishingly small using a planetary geostrophic circulation model that resolves both the boundary layer dynamics and the large scale overturning in an idealized basin with bottom enhanced mixing along a midocean ridge we show that vertical variations in stratification become sufficiently large at equilibrium to reduce the degree of compensation along the midocean ridge flanks the resulting large net transformations are similar to estimates for the abyssal ocean and span the vertical extent of the ridge these results suggest that boundary flows generated by mixing play a crucial role in setting the global ocean stratification and overturning circulation requiring a revision of abyssal ocean theories

examining possible effects of seawater ph decline on foraminiferal stable isotopes during the paleocene eocene thermal maximum 1 a large body of paleoceanographic data for the paleocene eocene thermal maximum petm is based on foraminiferal stable carbon and oxygen isotope composition 13c and 18o however the proxy records could be biased due to a ph effect on stable isotopes during times when the ocean became more acidic as has been demonstrated for modern planktonic foraminifera in this paper we calculate the possible ranges of the ph effect on 13c and 18o during the petm based on the relative ph decline ph from the preperturbation steady state simulated by a carbon cycle model and the empirical relationships obtained from culture experiments with planktonic foraminifera the model is configured with eocene paleogeography and simulates ph for surface intermediate and deep water in the major ocean basins in response to various carbon input scenarios 2000 to 5000 pg c for an array of scenarios the modeled ph of the surface ocean ranges from 0 1 to 0 28 units this suggests that 13c of planktonic foraminifera may be increased by up to 2 1 and 18o may be increased by up to 0 7 corresponding to over 3 c error in paleotemperature estimate under conditions in which the model best simulates the global caco3 dissolution pattern we find marked differences in the deep sea ph between the atlantic 0 4 and pacific oceans 0 1 this would imply that the magnitude of the negative 13c and 18o excursions of benthic foraminifera in the atlantic ocean was dampened by up to 2 8 and 0 9 at maximum respectively relative to a constant ph scenario

coastal ocean co2 carbonic acid carbonate sediment system of the anthropocene 1 there is little doubt that human activities such as burning of fossil fuels and land use practices have changed and will continue to change the cycling of carbon in the global coastal ocean in the present study two biogeochemical box models were used to investigate the consequences of increasing atmospheric co2 and subsequent ocean acidification and increasing riverine transport of organic matter and nutrients arising from human activities on land on the global coastal ocean between the years 1700 and 2300 numerical simulations show that the net flux of co2 between coastal ocean surface water and the atmosphere is likely to change during this time from net evasion to net invasion owing to increasing atmospheric co2 increasing net ecosystem production arising from increasing nutrient loading to this region and decreasing net ecosystem calcification due to lower carbonate ion concentration and subsequent lower surface water saturation state with respect to carbonate minerals model calculations show that surface water saturation state with respect to calcite will decrease 73 by the year 2300 under a business as usual scenario which in concert with increasing temperature will cause overall biogenic calcification rate to decrease by 90 dissolution of carbonate minerals increased by 267 throughout the model simulation this increase was in part due to increased invasion of atmospheric co2 but mainly due to greater deposition and remineralization of land derived and in situ produced organic matter in the sediments producing co2 that caused pore water ph and carbonate saturation state to decrease this decrease in turn drove selective dissolution of metastable carbonate minerals as a consequence the relative carbonate composition of the sediments changed in favor of carbonate phases with lower solubility than that of an average 15 mol magnesian calcite phase model projected changes in surface water carbonate saturation state agree well with observations from the hawaiian ocean time series and the calculated air sea co2 exchange agrees well with a recent independent estimate of this flux derived from measurements from diverse coastal ecosystems scaled up to the global coastal ocean area

decadal changes in the aragonite and calcite saturation state of the pacific ocean 1 based on measurements from the woce jgofs global co2 survey the clivar co2 repeat hydrography program and the canadian line p survey we have observed an average decrease of 0 34 yr 1 in the saturation state of surface seawater in the pacific ocean with respect to aragonite and calcite the upward migrations of the aragonite and calcite saturation horizons averaging about 1 to 2 m yr 1 are the direct result of the uptake of anthropogenic co2 by the oceans and regional changes in circulation and biogeochemical processes the shoaling of the saturation horizon is regionally variable with more rapid shoaling in the south pacific where there is a larger uptake of anthropogenic co2 in some locations particularly in the north pacific subtropical gyre and in the california current the decadal changes in circulation can be the dominant factor in controlling the migration of the saturation horizon if co2 emissions continue as projected over the rest of this century the resulting changes in the marine carbonate system would mean that many coral reef systems in the pacific would no longer be able to sustain a sufficiently high rate of calcification to maintain the viability of these ecosystems as a whole and these changes perhaps could seriously impact the thousands of marine species that depend on them for survival

quantitative interpretation of atmospheric carbon records over the last glacial termination 1 the glacial interglacial rise in atmospheric pco2 is one of the best known changes in paleoclimate research yet the cause for it is still unknown forcing the coupled ocean atmosphere biosphere box model of the global carbon cycle bicycle with proxy data over the last glacial termination we are able to quantitatively reproduce transient variations in pco2 and its isotopic signatures 13c 14c observed in natural climate archives the sensitivity of the box model of the isotopic carbon cycle bicycle to high or low latitudinal changes is comparable to other multibox models or more complex ocean carbon cycle models respectively the processes considered here ranked by their contribution to the glacial interglacial rise in pco2 in decreasing order are the rise in southern ocean vertical mixing rates 30 ppmv decreases in alkalinity and carbon inventories 30 ppmv the reduction of the biological pump 20 ppmv the rise in ocean temperatures 15 20 ppmv the resumption of ocean circulation 15 20 ppmv and coral reef growth 5 ppmv the regrowth of the terrestrial biosphere sea level rise and the increase in gas exchange through reduced sea ice cover operate in the opposite direction decreasing pco2 during termination i by 30 ppmv according to our model the sequence of events during termination i might have been the following a reduction of aeolian iron fertilization in the southern ocean together with a breakdown in southern ocean stratification the latter caused by rapid sea ice retreat trigger the onset of the pco2 increase after these events the reduced north atlantic deep water nadw formation during the heinrich 1 event and the subsequent resumption of ocean circulation at the beginning of the bolling allerod warm interval are the main processes determining the atmospheric carbon records in the subsequent time period of termination i we further deduce that a complete shutdown of the nadw formation during the younger dryas was very unlikely changes in ocean temperature and the terrestrial carbon storage are the dominant processes explaining atmospheric 13c after the bolling allerod warm interval

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

the circulation of north atlantic deep water at 16 n 2000 2003 1 the circulation of north atlantic deep water nadw at 16 n is studied with chlorofluorocarbon cfc and current measurements in 2000 2002 and 2003 the transport of the deep western boundary current dwbc ranges from 25 6 to 28 9 sv in 2000 and 2002 cfc concentrations in the dwbc increased by 30 per year during that period in 2003 the dwbc was weak and the main cfc increase between 2002 and 2003 occurred offshore of the dwbc for all three repeats a major drop in the cfc concentrations of the nadw took place at 55 w this was also found in the distributions of salinity and oxygen the region west of 55 w was characterized by a predominantly southward flow the lowest cfc concentrations were found above the mid atlantic ridge where the zonal and meridional velocities were small and no preference of flow direction could be detected

the global ocean flux of particulate organic carbon areal distribution and magnitude the magnitude and distribution of the particulate organic carbon poc rain rate to the seafloor in the atlantic pacific and indian ocean basins between 61 n and 61 s has been estimated from benthic oxygen flux estimates for water depths 1000 m only the calculation utilizes the extensive data sets of sedimentary organic carbon caco3 and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically derived correlation between the seafloor oxygen flux and these parameters the poc flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap determined fluxes and water depth total oxygen utilization in the deep ocean is estimated to be 1 2 1014 mol o2 yr 1 a value that agrees well with previous estimates which were based on surface water primary productivity sediment trap and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization aou 14c relationships on the basis of the derived global ocean flux distribution it is concluded that 1 dissolved organic carbon doc inputs are not required to account for estimated deep water respiration rates 2 the majority of the poc input to the deep ocean occurs within 30 of the equator 3 the proportion of primary production that reaches the deep sea does not vary greatly with latitude 4 gyre and continental margin regions contribute roughly equally to the deep poc flux with a relatively minor contribution from the equatorial divergence region 5 of the estimated 7 2 1013 mol c yr 1 of poc that sinks below the 1000 m depth horizon 45 3 3 1013 mol c yr 1 reaches the seafloor where it is oxidized 6 when normalized to basin area average deep flux rates in the atlantic and pacific are similar while highest rates are observed in the indian ocean and 7 the results can be fully reconciled only if the benthic flux of doc is significantly less than the benthic o2 flux

dissolution of calcite in deep sea sediments ph and o2 microelectrode results abstract we present microelectrode profiles of oxygen ph and porosity measured at in situ depth across the sediment water interface from stations above and below the calcite saturation horizon in the equatorial atlantic resistivity electrode data indicate that the diffusion coefficient for solutes is attenuated by nearly a factor of two within the top centimeter of the sediment lattice oxygen and porosity data are used to estimate that the organic carbon respiration rate of the sediment is 10 15 mol cm 2 yr 1 in these locations comparison of the ph data with numerical model results reveals that sedimentary calcite dissolves in response to respiration in the top few centimeters of sediment even above the saturation horizon we calculate that the effective in situ dissolution rate constant for calcite required to explain these data is the neighborhood of 10 100 d 1 although more data are needed to confirm this result it appears to be at least an order of magnitude less than the rate observed in laboratory stirred reactor experiments

chemical accumulation variations under the peru current during the past 130 000 years the titanium to aluminum ratio in core v19 29 is correlated with aluminosilicate accumulation rates this correlation may be due to pleistocene eolian transport fluctuations which alter the mean grain size of sedimented eolian material the relation between aluminum accumulation rate and ti al established from accumulation rates integrated over 11 000 50 000 year intervals can be inverted to compute a high resolution record of aluminosilicate and calcium carbonate accumulation rates over the past 130 000 years carbonate accumulation rates are closely related to the oxygen isotope record in the core with a phase lag and damping constant that is compatible with the response time shown to be only 6000 years of calcium carbonate in the ocean carbonate sedimentation at this site responds to several processes independently correlated with climatic change the relative importance of these processes for carbonate sedimentation at this site can be constrained by the record in this core and other lines of evidence 15 of the increased carbonate deposition at this site during glacial periods may be due to diminished nadw north atlantic deep water formation 10 is due to carbonate productivity decreases in the north atlantic 25 may be due to a diminished shallow sea carbonate sink and the residual 50 must be due to a local productivity increase these assignments are consistent with observations on carbonate paleoceanography in the north atlantic aluminosilicate accumulation rate variations correlate with the record of eolian quartz deposition near northwest africa and in a general way with the climatic record but in detail the record differs substantially from the oxygen isotope record and may provide independent evidence on the nature of climate dynamics

short term dissolution response of pelagic carbonate sediments to the invasion of anthropogenic co2 a model study 1 this study addresses the potential for and the quantification of dissolution of marine calcium carbonate caco3 sediments occurring on century timescales in response to the invasion of anthropogenic co2 it presents results obtained with the global biogeochemical model pisces interactively coupled to a global sediment model the latter represents the principal reactions involved in early diagenesis of biogenic opal caco3 and organic matter the model reproduces observed distributions of core top caco3 content and bottom water carbonate chemistry e g co32 starting from the climatological state a model experiment is carried out according to the standard cmip scenario of atmospheric pco2 increasing at a rate of 1 per year from 286 to 1144 ppm over a 140 year time period the invasion of anthropogenic co2 results in a strong decrease in bottom water co32 reaching 100 m in areas of deep water formation in the north atlantic and mode and intermediate water formation in the southern hemisphere the concomitant decrease in calcite saturation state of bottom waters drives the dissolution of caco3 the absolute caco3 content averaged over the top first centimeter decreases by up to 6 while the change in advection calculated at the base of the bioturbated layer 10 cm is indicative of net erosion the predicted changes in bottom water chemistry are discussed in terms of their potential impact on benthic communities

coastal ocean and carbonate systems in the high co2 world of the anthropocene the behavior of the ocean carbon cycle has been and will continue to be modified by the increase in atmospheric co2 due to fossil fuel combustion and land use emissions of this gas the consequences of a high co2 world and increasing riverine transport of organic matter and nutrients arising from human activities were investigated by means of two biogeochemical box models model numerical simulations ranging from the year 1700 to 2300 show that the global coastal ocean changes from a net source to a net sink of atmospheric co2 over time in the 18th and 19th centuries the direction of the co2 flux was from coastal surface waters to the atmosphere whereas at present or in the near future the net co2 flux is into coastal surface waters these results agree well with recent syntheses of measurements of air sea co2 exchange fluxes from various coastal ocean environments the model calculations also show that coastal ocean surface water carbonate saturation state would decrease 46 percent by the year 2100 and 73 percent by 2300 observational evidence from the pacific and atlantic oceans shows that the carbonate saturation state of surface ocean waters has already declined during recent decades for atolls and other semi enclosed carbonate systems the rate of decline depends strongly on the residence time of the water in the system based on the experimentally observed positive relationship between saturation state and calcification rate for many calcifying organisms biogenic production of caco3 may decrease by 42 percent by the year 2100 and by 85 to 90 percent by 2300 relative to its value of about 24 1012 moles c yr in the year 2000 if the predicted change in carbonate production were to occur along with rising temperatures it would make it difficult for coral reef and other carbonate systems to exist as we know them now into future centuries because high latitude cold water carbonates presently occur in waters closer to saturation with respect to carbonate minerals than the more strongly supersaturated waters of the lower latitudes it might be anticipated that the cool water carbonate systems might feel the effects of rising atmospheric co2 and temperature before those at lower latitudes in addition modeling results show that the carbonate saturation state of coastal sediment pore water will decrease in the future owing to a decreasing pore water ph and increasing co2 concentrations attributable to greater deposition and remineralization of land derived and in situ produced organic matter in sediments the lowered carbonate saturation state drives selective dissolution of metastable carbonate minerals while a metastable equilibrium is maintained between the pore water and the most soluble carbonate phase present in the sediments in the future the average composition of carbonate sediments and cements may change as the more soluble mg calcites and aragonite are preferentially dissolved and phases of lower solubility such as calcites with lower magnesium content increase in percentage abundance in the sediments

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

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

comment on modern age buildup of co2 and its effects on seawater acidity and salinity by hugo a loaiciga a doubling of present atmospheric co2 concentrations to 760 ppm may occur by the end of this century in the absence of efforts to diminish co2 emissions from fossil fuel combustion intergovernmental panel on climate change ipcc 2001 based on inappropriate assumptions and erroneous thermodynamic calculations loa iciga 2006 mistakenly reports that atmospheric co2 concentrations of 760 ppm will lower the ph of the surface ocean by 0 28 relative to the natural mid 18th century conditions he implies that a drop of this magnitude will have minimal biological impact neglecting numerous recent experiments and observations showing that this decrease in ph would substantially affect the physiology and health of marine organisms here we focus on two fundamental flaws in the published analysis that invalidate his conclusions 1 he assumes instantaneous chemical equilibration of the ocean with carbonate minerals although this process is known to take five to ten thousand years and 2 contrary to what is implied by loa iciga many marine organisms are sensitive to a ph decrease of 0 2 units

beyond methane towards a theory for the paleocene eocene thermal maximum abstract extreme global warmth and an abrupt negative carbon isotope excursion during the paleocene eocene thermal maximum petm have been attributed to a massive release of methane hydrate from sediments on the continental slope 1 however the magnitude of the warming 5 to 6 c 2 3 and rise in the depth of the ccd 2 km 4 indicate that the size of the carbon addition was larger than can be accounted for by the methane hydrate hypothesis additional carbon sources associated with methane hydrate release e g pore water venting and turbidite oxidation are also insufficient we find that the oxidation of at least 5000 gt c of organic carbon is the most likely explanation for the observed geochemical and climatic changes during the petm for which there are several potential mechanisms production of thermogenic ch4 and co2 during contact metamorphism associated with the intrusion of a large igneous province into organic rich sediments 5 is capable of supplying large amounts of carbon but is inconsistent with the lack of extensive carbon loss in metamorphosed sediments as well as the abrupt onset and termination of carbon release during the petm a global conflagration of paleocene peatlands 6 highlights a large terrestrial carbon source but massive carbon release by fire seems unlikely as it would require that all peatlands burn at once and then for only 10 to 30 ky in addition this hypothesis requires an order of magnitude increase in the amount of carbon stored in peat the isolation of a large epicontinental seaway by tectonic uplift associated with volcanism or continental collision followed by desiccation and bacterial respiration of the aerated organic matter is another potential mechanism for the rapid release of large amounts of co2 in addition to the oxidation of the underlying marine sediments the desiccation of a major epicontinental seaway would remove a large source of moisture for the continental interior resulting in the desiccation and bacterial oxidation of adjacent terrestrial wetlands

in situ measurements of calcium carbonate dissolution rates in deep sea sediments benthic fluxes of alkalinity carbon dioxide and oxygen have been measured using an in situ incubation chamber at three sites manop sites c and s and pacflux site sc in the central equatorial north pacific at two carbonate rich sites c and sc a budget for oxygen alkalinity and tco2 fluxes indicate a net caco3 dissolution rate of approximately 0 4 mmol m 2 day 1 this rate is only 20 of previous estimates but is consistent with a dissolution rate constant predicted from laboratory experiments with deep sea sediments and derived from in situ flux measurements in sediments of the southern california borderland organic matter oxidation in the sediment column provides the acid for 60 100 of the calcium carbonate dissolution occurring at these sites with the remainder derived from undersaturated bottom water at a low carbonate site s no carbonate dissolution in the sediment or on the sea floor is apparent although sediment traps indicate a rain of caco3 through 3400 m the rates of remineralization relative to resuspension or erosion at this site must differ for organic carbon and calcium carbonate so that carbonate grains reaching the sea floor are physically removed by erosion or resuspension before they dissolve while organic carbon is largely oxidized before it can be physically removed

impact of dissolution on the sedimentary record of the paleocene eocene thermal maximum the input of massive amounts of carbon to the atmosphere and ocean at the paleocene eocene thermal maximum petm 55 53 ma resulted in pervasive carbonate dissolution at the seafloor at many sites this dissolution also penetrated into the underlying sediment column the magnitude of dissolution at and below the seafloor a process known as chemical erosion and its effect on the stratigraphy of the petm are notoriously difficult to constrain here we illuminate the impact of dissolution by analyzing the complete spectrum of sedimentological grain sizes across the petm at three deep sea sites characterized by a range of bottom water dissolution intensity we show that the grain size spectrum provides a measure of the sediment fraction lost during dissolution we compare these data with dissolution and other proxy records electron micrograph observations of samples and lithology the complete data set indicates that the two sites with slower carbonate accumulation and less active bioturbation are characterized by significant chemical erosion at the third site higher carbonate accumulation rates more active bioturbation and possibly winnowing have limited the impacts of dissolution however grain size data suggest that bioturbation and winnowing were not sufficiently intense to diminish the fidelity of isotopic and microfossil assemblage records

a data driven model of the global calcite lysocline gridded maps of sediment calcium carbonate calcite concentration and overlying water saturation state archer 1996 are combined with maps of benthic oxygen fluxes and sediment accumulation rates from jahnke 1996 and cweink 1986 to drive a diagenetic model of calcium carbonate preservation in deep sea sediments the only model input for which we cannot draw a detailed map is the rain rate of calcite to the seafloor so i use the model to calculate the calcite rain rate required to simulate the observed distribution of calcite concentration on the seafloor the predictive power of the model can be checked by searching for input parameters to which the model is sensitive and comparing the model requirements with independent data the model is sensitive to the ratio of organic carbon to calcite rain rates the rain ratio and within the constraint of pelagic sediment trap rain ratio data is unable to reproduce the calcite field without respiratory dissolution the promotion of calcium carbonate dissolution by the oxic degradation of organic carbon however relative to variability in sediment trap data the required model rain ratio is insensitive to the extent of anoxic respiration the stoichiometric ratio of o c during respiration the bioturbation rate the dissolution rate constant the effect of borate chemistry and small offsets in the saturation state for caco3 the model is sensitive to the accumulation rate of non caco3 material and predicts an atlantic pacific difference in non caco3 rain rate which is consistent with observations the model predicts that the dissolution flux of caco3 from sediments is 25 40 1012 mol yr 1 roughly half of the total deep sea caco3 dissolution rate estimated from the water column alkalinity distribution broecker and peng 1987 archer and maier reimer 1994 wollast 1994 the model also predicts that only 20 30 of the flux of caco3 to the seafloor globally escapes dissolution

oceanic calcium changes from enhanced weathering during the paleocene eocene thermal maximum no effect on calcium based proxies 1 during the paleocene eocene thermal maximum petm 55 myr ago prominent climatic and biogeochemical changes took place in the atmosphere ocean and on land for example deep sea temperatures rose by 5 c to 6 c while sea surface temperatures at high latitudes increased by up to 9 c in the sedimentary record the onset of the petm is marked by widespread dissolution of calcium carbonate on the seafloor in addition there is evidence for globally higher humidity precipitation and increased weathering during the petm both calcium carbonate dissolution and enhanced weathering probably affected the seawater calcium concentration here we investigate implications that possible changes in the ocean s calcium inventory may have had on boron calcium b ca and magnesium calcium mg ca ratios which are used as proxies for deep water carbonate chemistry and temperature respectively we also examine effects on 44ca of seawater which is used as an indicator for variations in the marine calcium cycle we focus on the magnitude of change in the ocean s calcium ion concentration as a result of the carbon perturbation which resulted in increased weathering fluxes and the dissolution of calcite on the ocean floor during the petm different ranges of carbon input scenarios and their effect on ocean chemistry were examined using the long term ocean atmosphere sediment carbon cycle reservoir loscar model we found that under the most plausible scenario the calcium ion concentration change ca2 was less than 0 7 and around 2 in the most extreme scenario our results show that b ca and mg ca proxies were not affected within analytical precision by changes in oceanic calcium due to weathering and carbonate dissolution during the petm the most extreme scenario ca2 2 would result in 4 mol kg 1 uncertainty in reconstruction of co32 the same scenario affects the temperature reconstruction by 0 2 c the effect on the ocean s calcium isotope budget was insignificant as well resulting in 44casw of less than 0 05

an atlas of the distribution of calcium carbonate in sediments of the deep sea historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater co3 concentration to reveal regional variations in the calcite lysocline the most obvious mode of variability of the calcite lysocline is the thickness of the lysocline defined here as the difference in overlying water carbonate saturation co3 between high and low calcite sediments with a thicker lysocline in the atlantic than in the pacific i attribute this variation to differences in the delivery rate of terriginous material a recent model for the lower glacial atmospheric pco2 proposed to change the relationship between the depth of the lysocline and the co3 of the water column by changing the rain rate ratio of organic carbon to calcite production the rain ratio model archer and maier reimer 1994 i search the data set for analogs to the proposed glacial world by looking for a link between the regional climate at the sea surface and the depth of the lysocline below the co3 at the carbonate compensation depth ccd in the tropics appears to be 10 20 mol kg 1 co3 more undersaturated than in high latitudes but this is smaller than the 40 mol kg 1 shift required by the model in addition the general resemblance of the glacial lysocline to the present day requires that the proposed shift in co3 at the ccd be globally uniform rather than locally variable as climate forcing would probably generate i conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time such as a change in ocean si content if it is to explain the entire pco2 decrease observed in the glacial atmosphere finally i grid the sedimentary data to estimate that the inventory caco3 which is available to neutralize fossil fuel co2 is approximately 1600 gt carbon a quantity which may be exceeded by fossil fuel release in the next several centuries

identifying ordered strata evidence methods and meaning abstract identifying order or pattern in strata on the basis of qualitative interpretation forms the basis for much current sedimentological and sequence stratigraphic analysis order can be usefully defined as some arrangement of facies or unit thickness that has a discernable trend or pattern that is unlikely to occur by chance because it requires some particular systematic process to form coarsening fining thickening or thinning upward trends and arrangement of strata into cycles are examples of order qualitative interpretations of order often demonstrate little more than an implicit assumption of order this paper defines a robust yet simple to apply quantitative method to identify order in strata and to indicate when order cannot be reliably demonstrated the method is based on two calculated metrics the markov metric m derived from analysis of a vertical facies succession and the runs metric r derived from analysis of observed thicknesses of stratal units most importantly both metrics can be compared with equivalent metrics calculated for disordered strata composed of many randomly shuffled versions of the same lithological units probability values can then be calculated from the comparison between observed and randomly shuffled cases and these p values indicate the degree of evidence present for order in the observed strata several test examples using synthetic strata show that the m and r values can define and identify different degrees and types of stratal order and that the metrics are robust for both stationary and non stationary successions with a range of different lengths and numbers of distinct facies analysis of four outcrop examples two siliciclastic and two carbonate demonstrate that ordered facies successions and thickness trends may be less common than typically assumed none of the four examples analyzed show trends in thickness and only the examples from the book cliffs which represent a bedset scale composite of observations show evidence for facies order the examples demonstrate how a quantitative analysis can lead to better understanding of strata either ordered or disordered and can provide better insight into the validity of current stratigraphic interpretations and models absence of order in many of the analyzed 1d vertical successions may also indicate that we need to focus more on longer term trends and analysis of 2d and 3d stratal geometries

relating estimates of caco3 production export and dissolution in the water column to measurements of caco3 rain into sediment traps and dissolution on the sea floor a revised global carbonate budget 1 the global caco3 budget is constrained by new estimates of standing stocks fluxes through the water column and dissolution in the water column and on the sea floor previous estimates of carbonate production and export are indistinguishable within a large range of values 0 4 1 8 gt pic yr 1 globally excess alkalinity ta and water mass tracers indicate dissolution of 1 0 gt pic yr 1 between 200 and 1500 m suggesting production and export must at least equal this amount most water column dissolution occurs at high latitudes and alkalinity fluxes from outer shelf and upper slope sediments 100 1500 m only support 5 10 of the ta inventory below 2000 m the sinking flux of pic 0 6 gt pic yr 1 is consistent with the rate of sea floor dissolution 0 4 gt pic yr 1 plus burial 0 1 gt pic yr 1 this rain rate constrains the export value to 1 6 gt pic yr 1 satellite based estimates of standing stocks of caco3 indicate a decrease equatorward which is opposite in trend to sediment trap fluxes this observation may be explained by an equatorward decrease in sinking particle dissolution systematic changes in pic residence time with latitude or satellite retrieval problems globally averaged euphotic zone standing stock 5 4 mmol m 2 and export estimates indicate pic residence times of 5 18 days

geochemical cycles in an ocean general circulation model preindustrial tracer distributions a state of the art report is given of the hamburg model of the oceanic carbon cycle the model advects geochemical tracers important to the carbon cycle by the currents of a general circulation model the geochemical cycling is driven by a michaelis menten type production kinetics the model is an extension of the bacastow and maier reimer 1990 model it is based on a more realistic current field and includes a mechanism of lysocline sediment interaction principal variables are co2 alkalinity phosphate oxygen and silicate the carbon variables are defined for 12c 13c and 14c separately in addition to these carbon isotopes 39a and 18o of dissolved oxygen are predicted the model predicts realistic global patterns of tracer distribution in the equatorial eastern pacific however the structures are exaggerated due to a strong upwelling which is a common feature of coarse resolution models of the general circulation of the ocean

patterns and magnitude of deep sea carbonate dissolution during eocene thermal maximum 2 and h2 walvis ridge southeastern atlantic ocean 1 eocene thermal maximum 2 etm2 or h1 53 7 ma represents a short lived warming episode associated with the injection of a large mass of 13c depleted carbon into the ocean atmosphere system the mass of injected carbon the extent of deep sea dissolution and the amount of warming during etm2 appear to be approximately half of those documented for the paleocene eocene thermal maximum petm 55 5 ma but the pattern of lysocline migration during etm2 has not yet been documented sufficiently to decipher potential differences in carbon sources and sequestration mechanisms we present high resolution carbonate dissolution and bulk stable isotope records across etm2 and the successive h2 event 53 6 ma on a common age model for four sites along the walvis ridge depth transect 1500 to 3600 m paleowater depth to assess lysocline evolution the onset of etm2 is characterized by multiple depth dependent transitions of carbonate dissolution up to 96 of the total flux associated with rapid depletions in bulk carbonate carbon up to 1 1 5 and oxygen up to 0 7 1 5 isotope values h2 shows a 0 7 negative carbon isotope excursion with a coeval decrease in 18o of 0 5 and 80 of carbonate dissolution during etm2 the lysocline recovered within 30 ka we attribute this rapid recovery to terrestrial caco3 neutralization through enhanced chemical weathering of carbonates in soils and rocks according to theory carbonate dissolution was lower after recovery than prior to etm2 indicating carbonate ion oversaturation and a deeper position of the lysocline spectral analysis indicates that the changes in carbonate dissolution and 13c values were precession paced implying that weathering feedbacks and short term perturbations in the carbon cycle were important in determining early eocene background and hyperthermal ocean co32 conditions

missing organic carbon in eocene marine sediments is metabolism the biological feedback that maintains end member climates 1 ocean chemistry is affected by pco2 in the atmosphere by increasing the dissolution of solid calcium carbonate and elevating the dissolved inorganic carbon concentrations in seawater positive feedbacks between the ocean and atmosphere can maintain high atmospheric pco2 and affect global climate we report evidence for changes in the oceanic carbon cycle from the first high quality organic carbon corg data set of eocene sediments beneath the equatorial pacific upwelling region leg 199 of the ocean drilling program eocene corg mass accumulation rates mars are 10 times lower than holocene rates even though expected corg mars estimated from biogenic barium mars an indicator of biological production equal or exceed modern fluxes what happened to the missing corg recent advances in ecology and biochemical kinetics show that the metabolism of nearly all animals marine and terrestrial is positively correlated by first principles to environmental temperatures the approximately 10 c abyssal temperature difference from eocene to holocene should have radically reduced pelagic corg burial as we observe we propose that higher basal metabolism and nutrient utilization recycling rates in the eocene water column and surface sediments precluded corg sediment burial in the pelagic ocean increased rates of metabolism nutrient utilization and lowered corg sedimentation caused by increased temperature may have acted as a biological feedback to maintain high atmospheric pco2 and hothouse climates conversely these same parameters would reverse sign to maintain low pco2 when temperatures decrease thereby maintaining icehouse conditions during cold climate regimes

initial responses of carbonate rich shelf sediments to rising atmospheric pco2 and ocean acidification role of high mg calcites abstract carbonate rich sediments at shoal to shelf depths 3 reservoir that can rapidly react to the decreasing saturation state of seawater with respect to carbonate minerals produced by the increasing partial pressure of atmospheric carbon dioxide p co 2 and acidification of ocean waters aragonite is usually the most abundant carbonate mineral in these sediments however the second most abundant typically 24 wt carbonate mineral is high mg calcite mg calcite whose solubility can exceed that of aragonite making it the first responder to the decreasing saturation state of seawater for the naturally occurring biogenic mg calcites dissolution experiments have been used to predict their stoichiometric solubilities as a function of mol mgco 3 the only valid relationship that one can provisionally use for the metastable stabilities for mg calcite based on composition is that for the synthetically produced phases where metastable equilibrium has been achieved from both under and over saturation biogenic mg calcites exhibit a large offset in solubility from that of abiotic mg calcite and can also exhibit a wide range of solubilities for biogenic mg calcites of similar mg content this indicates that factors other than the mg content can influence the solubility of these mineral phases thus it is necessary to turn to observations of natural sediments where changes in the saturation state of surrounding waters occur in order to determine their likely responses to the changing saturation state in upper oceanic waters brought on by increasing p co 2 in the present study we investigate the responses of mg calcites to rising p co 2 and ocean acidification by means of a simple numerical model based on the experimental range of biogenic mg calcite solubilities as a function of mg content in order to bracket the behavior of the most abundant mg calcite phases in the natural environment in addition observational data from bermuda and the great bahama bank are also presented in order to project future responses of these minerals the numerical simulations suggest that mg calcite minerals will respond to rising p co 2 by sequential dissolution according to mineral stability progressively leading to removal of the more soluble phases until the least soluble phases remain these results are confirmed by laboratory experiments and observations from bermuda as a consequence of continuous increases in atmospheric co 2 from burning of fossil fuels the average composition of contemporary carbonate sediments could change i e the average mg content in the sediments may slowly decrease furthermore evidence from the great bahama bank indicates that the amount of abiotic carbonate production is likely to decline as p co 2 continues to rise

history of seawater carbonate chemistry atmospheric co 2 and ocean acidification humans are continuing to add vast amounts of carbon dioxide co2 to the atmosphere through fossil fuel burning and other activities a large fraction of the co2 is taken up by the oceans in a process that lowers ocean ph and carbonate mineral saturation state this effect has potentially serious consequences for marine life which are however difficult to predict one approach to address the issue is to study the geologic record which may provide clues about what the future holds for ocean chemistry and marine organisms this article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras the results allow evaluation of the current anthropogenic perturbation in the context of earth s history it appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past for which sufficiently well preserved records are available