atmospheric co2 content in the last 120 000 years the phosphate extraction model broecker 1982 has proposed that during the retreat of the wisconsin ice sheets atmospheric co2 increased because of the extraction of phosphorus from the ocean as sea level rose using a time dependent box model we examine the consequences of the phosphate extraction hypothesis over the last 120 000 years assuming that 18o change in core v28 238 is analogous to sea level variation the model takes into account the total co2 and alkalinity balance in the deep sea and in an upper reservoir consisting of the surface ocean and atmosphere which are assumed to be in equilibrium dissolution of deep sea calcium carbonate sediment is assumed to respond to the supply of particulate carbonate from the upper box and to the dissolved carbonate ion concentration of the deep sea assuming 1015 mole of phosphorus and 1017 mole of carbon were extracted during deglaciation the predicted increase in pco2 is 54 ppm variation of pco2 follows the ice volume forcing function with a 1000 yr lag which is the input residence time of water in the deep sea the accumulation supply minus dissolution of caco3 and the percent preservation accumulation over supply follow the derivative of the ice volume function both are similar to the solution index and percent fragments of core v28 238 in addition unusually good preservation is predicted during deglaciation due to carbon extraction if phosphorus but not carbon is assumed to be extracted the accumulation of caco3 varies little remaining near a value equivalent to the river input

the influence of continental ice atmospheric co2 and land albedo on the climate of the last glacial maximum the contributions of expanded continental ice reduced atm9spheric co2 and changes in land albedo to the maintenance of the climate of the last glacial maximum lgm are examined a series of experiments is perform ed using an atmosphere mixed layer ocean model in which these changes in boundary conditions are incorporated either singly or in combination the model used has been shown to produce a reasonably reajistic simulation of the reduced temperature of the lgm manabe and broccoli 1985 by comparing the results from pairs of ex periments the effects of each of these envirornnental changes can be determined expanded continental ice and reduced atmospheric co2 are found to have a substantial impact on global mean temperature the ice sheet effect is confined almost ex clusively to the northern hemisphere while lowered co2 cools both hemispheres changes in land albedo over ice free areas have only a minor thermal effect on a global basis the reduction of co2 content in the atmosphere is the primary contributor to the cooling of the southern hemisphere the model sensitivity to both the ice sheet and co2 effects is characterized by a high latitude amplification and a late autumn and early winter maximum

the mid quaternary climatic transition as the free response of a three variable dynamical model abstract a simplified version of a previously described dynamical model governing global ice mass atmospheric carbon dioxide and mean ocean temperature that may also be a proxy for some other co2 controlling oceanic variable e g nutrient supply is shown to possess solutions in a realistic parameter range that can replicate the main features of the climatic variations implied by the full two million years quarternary 18o record these variations include a major transition between a low ice 18o low variance mode before roughly 900 kyr bp to a high ice near 100 kyr period variance mode after that time to the present the model contains only three free parameters in this simplified form no external earth orbital forcing is prescribed i e the model represents only internal dynamics from the previous studies it seems clear that additional variance representing such features as the rapid deglaciation and the phase of the major quaternary oscillation can be largely explained with no more

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

coupled 100 kyr cycles between 3 and 1 ma in terrestrial and marine paleoclimatic records earth s climate over the last one million years experienced several 100 kyr glacial cycles but no simple forcing mechanism has been identified numerous studies have tried to explain strong 100 kyr glacial cycles without recognizable forcing which has come to be known as the 100 kyr problem few studies have examined 100 kyr band paleoclimatic signals before 1 ma a recent study has demonstrated that benthic oxygen and carbon isotope records are phase locked and amplitude coupled at the 100 kyr band but that neither is phase locked to and amplitude coupled with the 100 kyr eccentricity signal between 3 and 1 ma this phasing and amplitude mismatch of the 100 kyr band between 3 and 1 ma between marine records and the eccentricity forcing signal has been called the late pliocene early pleistocene 100 kyr problem however it remains unknown whether terrestrial paleoclimate records are consistent with marine records at the 100 kyr band here i show that loess monsoon records from china are amplitude coupled with benthic oxygen and carbon isotope records at the 100 kyr band but not with the 100 kyr eccentricity forcing between 3 and 1 ma this observation provides further evidence in support of a free 100 kyr oscillation as the cause of the 100 kyr band amplitude variability in paleoclimatic records between 3 and 1 ma in contrast benthic oxygen isotope records and loess monsoon records at the 100 kyr band are not amplitude coupled with 100 kyr benthic carbon isotope records over the last 0 4 million years indicating that the late pleistocene 100 kyr climatic cycles may not result exclusively from a free oscillation

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

plio pleistocene time evolution of the 100 kyr cycle in marine paleoclimate records to constrain theories for the dynamic evolution of global ice mass through the late neogene it is important to determine whether major changes in the record were gradual or rapid of particular interest is the evolution of the near 100 kyr ice age cycle in the middle pleistocene we describe and apply a new technique based on multiple taper spectral analysis which allows us to model the time evolution of quasi periodic signals this technique uses both phase and amplitude information and enables us to address the question of abrupt versus gradual onset of the 100 kyr periodicity in the middle pleistocene we analyzed three long 2 6 m y time series from deep sea drilling project dsdp site 607 midlatitude atlantic and ocean drilling program odp site 677 equatorial pacific the published time scales for these sites differ significantly influencing the interpretation of the mid pleistocene climate transition when the data series are expressed on the same time scale there is evidence for a coherent 18o signal at both sites in the eccentricity and obliquity frequency bands consistent with variations in global ice volume as the causative factor if the shaddeton et al 1990 time scale for odp 677 is accepted the amplitude match between the 18o obliquity cycle and the 65 n insolation derived from the recent astronomical solution of laskar 1988 1990 is excellent for times t 2 3 ma if the ruddiman raymo time scale for dsdp 607 is accepted the 41 kyr 18o cycle has enhanced amplitude between 1 0 and 1 5 ma relative to the late pleistocene t 1 0 ma implying a nonlinear earth system response to obliquity insolation cycles we do not find compelling evidence for an abrupt change in the 100 kyr 18o signal although we cannot rule it out at this time if the shackleton et al 1990 time scale for odp 677 is accepted our three 18o records are consistent with a low amplitude 100 kyr cycle between 1 2 and 2 6 ma whose local period of oscillation alternates between the 95 and 124 kyr eccentricity periods and a gradual increase in the 100 kyr 18o signal between 0 5 amd 1 0 ma the dsdp 607 time scale is more favorable to an abrupt jump in amplitude for the 95 kyr 18o envelope but not in the 124 kyr envelope rather long period 18o fluctuations appear phase locked with the 124 kyr eccentricity cycle some 300 400 kyr prior to its growth in amplitude and phase lock with the 95 kyr eccentricity cycle in the late pleistocene

the δ13c of equatorial atlantic surface waters implications for ice age pco2 levels carbon isotopic records of nutrient depleted surface water place constraints on the past fertility of the oceans and on past atmospheric pco2 levels the best records of nutrient depleted 13c are obtained from planktonic foraminifera living in the thick mixed layers of the western equatorial and tropical atlantic ocean we have produced a composite stacked globigerinoides sacculifer 13c record from the equatorial atlantic which exhibits significant spectral power at the 100 000 and 41 000 year milankovitch periods but no power at the 23 000 year period similar to the record presented by shackleton and pisias 1985 surface deep ocean 13c produced with the g sacculifer record leads the 18o ice volume record however the glacial interglacial amplitudes of 13c differ between our record and shackleton and pisias 1985 record although large changes in 13c occur in the equatorial atlantic during early stages of the last three glacial cycles surface deep 13c at glacial maxima 18o stage 2 late stage 6 and late stage 8 was only about 0 2 greater than during the subsequent interglacial our results imply that nutrient driven pco2 changes account for about one third of the pco2 decrease observed in ice cores and consequently 13c should not be used as a proxy pco2 index enough variance in the ice core pco2 records remains to be explained that conclusions about pco2 and ice volume phase relationships should also be reexamined as much as 40 ppm pco2 change still has not been accounted for by models of past physics and chemistry of the ocean

carbon cycle instability as a cause of the late pleistocene ice age oscillations modeling the asymmetric response a dynamical model of the pleistocene ice ages incorporating many of the qualitative ideas advanced recently regarding the possible role of ocean circulation chemistry temperature and productivity in regulating long term atmospheric carbon dioxide variations has been constructed this model involves one additional term and free parameter beyond that included in a previous model b saltzman and a sutera 1987 providing the capacity for an asymmetic for example saw toothed response it is shown that many of the main features exhibited by the 18o derived ice record and the vostok core 13c derived carbon dioxide record in the late pleistocene can be deduced as a free oscillatory solution of the model including a rapid deglaciation during which a spike of high co2 and a rapid surge in north atlantic deep water production occurs it is expected that the addition of reasonable levels of external for example earth orbital forcing will enable the model to account for a significant amount of the remaining observed variance and covariance of the slow response climatic variables over the full pleistocene including the mid pleistocene transition

late pleistocene climatic trajectory in the phase space of global ice ocean state and co2 observations and theory we consider the evolution of three main slow response variables describing the state of the climate system during the late pleistocene global ice mass atmospheric carbon dioxide and the ocean state as measured respectively by the specmap 18o record the vostok co2 record and the north atlantic sea surface temperature record at 50 n core k708 1 which is coherent with other ocean state properties their coevolution is portrayed in the form of a trajectory in the phase space of the three variables and its projections on its three phase planes the oscillatory nature and phase lags of the variables are clearly illustrated suggesting a physical process scenario that can account for the observations the basic element of this scenario is a free near 100 kyr period oscillation driven by internal instability involving feedbacks between all three variables under the influence of earth orbital milankovitch forcing and long term tectonic co2 forcing it is shown that a phenomenological theory advanced by the authors emphasizing the role of co2 provides a credible account of the phase space trajectory

the late quaternary glaciations as the response of a three component feedback system to earth orbital forcing abstract a climatic feedback system previously described consisting of three prognostic nonlinear equations governing the mass of ice sheets the mass of marine and continental marginal ice and the mean ocean temperature is forced by a representation of the effects of external earth orbital variations with reasonable amplitudes for the eccentricity obliquity and precession forcing the free oscillatory solutions of major period near 100 kyr can be modified in a way that substantially agrees with the 18o derived observations of ice mass evolution in particular a proper structure variance spectrum and phase lock of the major variations are obtained over the last 400 kyr an analysis of the sensitivity of these results to variations in the model parameters and to random perturbations shows that the solution is robust for small changes in all but a few of the equation coefficients concomitant variability in the marine ice mass ocean temperature and net radiation at the top of the atmospher

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

geochemical and qualitative assessment of groundwater of the high mekerra watershed nw algeria groundwater constitutes the main source of water supply in the high mekerra watershed of northwestern algeria this resource is currently under heavy pressures to meet the growing needs of drinking water and irrigation this study assesses the geochemical characteristics of groundwater of the high mekerra watershed at 21 points distributed across the two main aquifers ras el ma and mouley slissen in the region hydrochemical facies of ras el ma groundwater are dominantly mgcl and cacl type while those of mouley slissen groundwater are of cahco3 type principal component analysis shows a strong correlation between groundwater mineralization and ca2 na cl and so4 2 ions stemming from the dissolution of carbonates gypsum and anhydrite groundwater mineralization evolves from south to north geochemical modeling shows that the high mekerra groundwater is saturated with respect to calcite and dolomite and undersaturated with respect to gypsum and anhydrite nitrate concentrations that exceed the who standard 50 mg l 1 at several points are linked to the agro pastoral activities in this region

oceanographic conditions associated with high abundances of the radiolarian cycladophora davisiana abstract the cosmopolitan radiolarian cycladophora davisiana usually comprises less than 5 of the radiolarian fauna in holocene sediments in recent sediments from the sea of okhotsk however this species frequently represents more than 20 of the radiolarian assemblage at times during the late pleistocene abundances of this species in excess of 40 are recorded in marine sediments from high latitude oceans 40 of both hemispheres the sea of okhotsk apparently represents a modern analogue of climatic and oceanographic conditions that existed throughout large portions of high latitude oceans at times during the late pleistocene the near surface water structure of the sea of okhotsk is characterized by a low salinity surface layer with a strong temperature minimum near its base the low surface salinities are responsible for maintaining near freezing subsurface temperatures as well as establishing relatively stable temperatures and salinities at depths below the temperature minimum this water structure is produced at least in part by intense freezing of sea ice in winter with subsequent summer melting the physical characteristics of the upper water column affect the abundance and activity of shallow dwelling flora and fauna while providing a stable subsurface environment for deeper dwelling fauna

deglacial co2 buildup constraints on the coral reef model abstract the coral reef hypothesis of degalcial co2 buildup in the atmosphere can account for about one half of the signal seen in ice cores assuming additional coral reef growth releases 2 atmospheric carbon masses acm the carbonate dissolution signal on the deep sea floor suggest titration of only 1 acm at least 4 acm of co2 must be made available to satisfy the requirements of pco2 increases growth of biosphere and of sedimentary carbon pool carbonate dissolution on the sea floor and saturation of newly introduced meltwater a drop in ocean fertility is called for to provide the missing co2 such a drop is evident in deep sea cores from the western equatorial pacific co2 buildup appears to occur as a step near 13 500 years b p dissolution on the deep sea floor begins near 11 000 years b p the difference of 2500 years may describe a mixing lag due to meltwater input the worthington effect

linear and nonlinear couplings between orbital forcing and the marine δ18o record during the late neocene previous investigations of the response of plio pleistocene climatic records to long term orbitally induced changes in radiation have considered a linear response of climate while the second order statistics of power spectra and cross spectra provide necessary information on linear processes insight into the nonlinear characteristics of pliocene and pleistocene climate is not provided by these statistical quantities second order statistics do not contain the phase information necessary to investigate nonlinear phase coupled processes such information is provided by higher order statistical quantities in particular bispectral analysis indicates that nonlinear couplings are present in the climatic radiative forcing at the milankovitch frequencies through a linear transfer this forcing produces similar nonlinear couplings in deep sea sedimentary oxygen isotope records odp site 677 and dsdp site 607 from 1 0 to 0 ma during the late neogene this analysis suggests that during the late pleistocene the dominance of the 100 000 year cycle in the climate record is consistent with a linear resonant response to eccentricity forcing in the period from 2 6 to 1 0 ma a change in the nature of the climatic response to orbital forcing is indicated as phase couplings present in the isotopic time series are not similar to the phase couplings present in the insolation forcing third order moments skewness and asymmetry are used to quantify the shape of the climatic response from 2 6 ma to present an increase in the asymmetry sawtoothness of the oxygen isotopic records is accompanied by a corresponding decrease in the skewness peakedness of the records this indicates an evolution in the nature of the phase coupling within the climate system these results may provide important constraints useful in development of models of paleoclimate

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

multiple instabilities and modes of glacial rhythmicity in the plio pleistocene a general theory of late cenozoic climatic change it has been noted that several distinct modes of glacial oscillation have existed during the past few million years ranging from low amplitude high frequency oscillations in the early pliocene through relatively high amplitude predominantly near 40 ky period oscillations in the late pliocene and early pleistocene to the major near 100 ky period oscillations of the late pleistocene in addition to other plausible mechanisms suggested previously to explain aspects of this multirhythmic phenomenon we now illustrate another possible contributor to this type of behavior based on the hypothesis that the slow response climatic system is bistable and that two kinds of internal instability may be operative along with externally imposed forcing due to earth orbital milankovitch radiation changes and slow tectonically induced changes in atmospheric carbon dioxide these two instabilities have been discussed previously one is due to positive feedback in the global carbon cycle leading to near 100 ky free oscillations of the ice sheets and the other is due to the potential for ice calving catastrophes associated with bedrock variations that can lead to oscillations of a period near 40 ky independent of obliquity forcing within the framework of a dynamical model containing the possibility for these two instabilities as well as for stable modes we show 1 how milankovitch radiative changes or stochastic forcing influencing ice sheets can induce aperiodic chaotic transitions between the possible stable and unstable modes and more significantly 2 how progressive long term tectonically induced changes in carbon dioxide acting in concert with earth orbital radiative variations in high northern hemisphere latitudes can force systematic transitions between the modes such systematic changes can result in an ice mass chronology for the past 5 my that is qualitatively similar to the observed record of global ice mass in essence we have constructed a minimum dynamical model of the late cenozoic climatic changes containing what are believed to be the main physical factors determining these changes ice mass bedrock depression atmospheric carbon dioxide concentration deep ocean thermohaline state milankovitch radiation forcing and slow tectonically induced carbon dioxide forcing this model forms the basis for a coherent theory for the complex climatic events of this long period

the effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the neoproterozoic johnnie formation death valley usa abstract carbonates within the rainstorm member in the terminal neoproterozoic johnnie formation of death valley california record a remarkable negative carbon isotope anomaly to a nadir of near 11 that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate 34 s values the carbonates including the laterally extensive johnnie oolite were deposited during marine flooding atop a sequence boundary best observed in cratonward sections the 12 c rich alkalinity delivered to the seawater pool was likely associated with a dramatic rise in atmospheric o 2 which resulted in 1 the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides and 2 the ventilation of the oceans similar carbon isotope anomalies are recorded in broadly equivalent successions that post date known marinoan glacial deposits and pre date the precambrian cambrian boundary in oman india china australia and namibia supporting the view that the oxygenation event was global thus the biogeochemical anomaly post dates the last widely recognized neoproterozoic ice age but is nonetheless associated with sea level drawdown that is likely to be eustatic in origin the radiation of a high diversity microbiota and the first appearance of large metazoan fossils ediacaran animals follow this carbon isotope anomaly suggesting that a critical threshold with respect to atmospheric o 2 had been crossed by this time a negative excursion of similar magnitude occurs in overlying strata at the precambrian cambrian boundary which likely reflects similar processes