geochemistry of a piston core from ontong java plateau western equatorial pacific evidence for sediment redistribution and changes in paleoproductivity we discuss geochemical proxies reflecting processes of primary productivity caco3 dissolution and sediment redistribution in a piston core rndb 74p from the ontong java plateau due to the shallow water depth biogenic carbonate is well preserved and a very good 18o stratigraphy is available down to isotopic stage 11 230thex gives evidence that the sediment accumulation pattern is driven mainly by processes of sediment focusing or winnowing due to the constant production of230th in the water column the bulk sediment accumulation rates could be corrected for the particle rain deriving from the water column above the230thex 0 caco3 ratio reflects the well known pacific caco3 preservation pattern with ice growth dissolution spikes and deglacial preservation spikes the record of the grain size fraction 63 m supports these results the downcore concentrations and accumulation rates of barium ba are on a higher level during interglacials and show several peaks normalization of ba with230thex 0 delivers a more uniform level of the ba accumulation rates throughout the core this pattern suggests a constantly higher biological productivity nearly tenfold in this area throughout the past 200 kyr compared with an open ocean environment barium peaks observed at the climatic transitions 2 1 and 6 5 and in stage 5 are in contrast to a predicted reduction of interglacial productivity at this location a possible explanation might be the onset of the modern circulation pattern the transition from ba enriched deep water to lower contents in the atlantic might have resulted in an enhanced deposition of ba in the pacific

the influence of degree 1 mantle heterogeneity on the past dynamo of mars abstract the hemispheric dichotomy in the crustal magnetic field of mars may indicate that the planet s past dynamo was influenced by a degree 1 heterogeneity on the outer boundary of its liquid metallic convecting core here we use numerical dynamos driven by purely volumetric internal heating with imposed degree 1 heat flux heterogeneities to study mantle control on the past dynamo of mars we quantify both south north and east west magnetic field dichotomies from time average properties that are calculated according to two different end member crust formation scenarios our results indicate that a moderate heat flux anomaly may have been sufficient for obtaining the observed dichotomy because of the excitation of a strong equatorial upwelling in the dynamo the efficiency of a mantle heterogeneity centered at the geographical pole in producing a south north dichotomy is much higher than that of an heterogeneity centered at the equator in producing an east west dichotomy these results argue against a significant true polar wander event with major planet re orientation after the cessation of the dynamo

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

climate change signature of small scale parasequences from lateglacial holocene transgressive deposits of the arno valley fill abstract despite recent report of short term cyclicity from lateglacial holocene deposits of several coastal plains worldwide no precise documentation of the key factors controlling cyclic facies architecture has been made available by previous work detailed sedimentological analysis of a continuously cored borehole around the town of pisa in western tuscany provides evidence for the occurrence of three high frequency transgressive regressive cycles within the post last glacial maximum lgm transgressive succession 13 8 cal kyr bp of the arno incised valley fill these cycles which are bounded by lateral equivalents of marine flooding surfaces are 8 12 m thick and correspond to small scale parasequences micropalaeontological foraminifers and ostracods investigations based upon differentiation of eight microfossil associations allow to refine the stratigraphic framework emphasizing subtle changes in palaeosalinity across parasequence boundaries diagnostic changes in vegetation patterns driven by opposite climate conditions enable precise documentation of parasequence development as a function of climate change pollen spectra invariably show expansions of broad leaved forests at parasequence boundaries suggesting that rapid shifts to warmer climate conditions accompanied episodes of rapid sea level rise in contrast stillstand phases saw the development of cold temperate communities upper parts of parasequences suggesting transition to temporary colder climate conditions reconstruction of parasequence architecture on the basis of adjacent stratigraphic data combined with palaeoclimate characterization and radiometric dating enable identification within the transgressive arno valley body of three major regressive pulsations that are tentatively correlated with the most important cooling events of the post lgm period the sedimentary response to these short term phases of climatic cooling is clearly documented by episodes of widespread coastal plain and bay head delta progradation leading to partial estuary infilling and temporary establishment of continental environments in the proximal and central sectors of the valley

spatial and temporal distribution of biogenic carbonate and opal in deep sea sediments from the eastern equatorial pacific implications for ocean history since 1 3 ma abstract high resolution records of glacial interglacial variations in biogenic carbonate opal and detritus derived from non destructive core log measurements of density p wave velocity and color r 0 9 from 15 sediment sites in the eastern equatorial sampling resolution is 1 kyr clear response to eccentricity and precession forcing for the peru basin we generate a high resolution 21 kyr increment orbitally based chronology for the last 1 3 ma spectral analysis indicates that the 100 kyr cycle became dominant at roughly 1 2 ma 200 300 kyr earlier than reported for other paleoclimatic records the response to orbital forcing is weaker since the mid brunhes dissolution event at 400 ka a west east reconstruction of biogenic sedimentation in the peru basin four cores 91 85 w distinguishes equatorial and coastal upwelling systems in the western and eastern sites respectively a north south reconstruction perpendicular to the equatorial upwelling system 11 cores 11 n 8 s shows high carbonate contents 50 between 6 n and 4 s and highly variable opal contents between 2 n and 4 s carbonate cycles b 6 b 8 b 10 b 12 b 14 m 2 and m 6 are well developed with b 10 430 ka as the most prominent cycle carbonate highs during glacials and glacial interglacial transitions extended up to 400 km north and south compared to interglacial or interglacial glacial carbonate lows our reconstruction thus favors glacial interglacial expansion and contraction of the equatorial upwelling system rather than shifting north or south elevated accumulation rates are documented near the equator from 6 n to 4 s and from 2 n to 4 s for carbonate and opal respectively accumulation rates are higher during glacials and glacial interglacial transitions in all cores whereas increased dissolution is concentrated on peru basin sediments close to the carbonate compensation depth and occurred during interglacials or interglacial glacial transitions

stable isotope anomalies in mediterranean pleistocene records oxygen and carbon isotope records of twelve mediterranean cores raised from west alboran sea to east off israel and of four atlantic cores raised from the western side of gibraltar and located respectively inside below and beyond the modern mediterranean outflow are compared to open ocean records of core 71 139c from the north atlantic and core v19 30 from the east pacific oxygen isotope stratigraphies can be established for deep mediterranean records and the major events of the last 150 ka are easily identifiable for instance the five substages of stage 5 or the 18 ka event stage 2 are identified but the 10 ka event younger dryas is only recorded by globigerina bulloides and benthic foraminifera suggesting that the cooling affected only winter sst 14c dates for the two terminations ia and ib of the last deglaciation which are recorded in sediment cores from areas with high sedimentation rates faro ridge alboran sea sicilian strait are in good agreement with the dates published for the same termination in atlantic cores an intermediate step however has been identified in some cores at 14 ka and divides termination ia into two phases oxygen isotope anomalies are recorded by the shallow water species globigerinoides ruber they correspond to 1 a higher amplitude glacial interglacial change in 18o values which exceeds that of the open ocean by 1 in the western basin and by 1 7 in the eastern basin 2 large isotopic depletions during the deposition of sapropel s1 s3 and s5 they are interpreted as the result of fresh water run off responsible for a strong dilution in the shallower layers of the east mediterranean waters the isotopic effect of this dilution averages 0 75 for sapropel s1 and 1 6 for sapropel s5 during the last glacial maximum the mediterranean still acted as a concentration basin and a gradient of 18o values similar to the modern one 0 75 existed from west to east in the deep waters apparently deep water temperatures were lower during the last glacial but the decrease did not exceed 4 c in the eastern basin major anomalies are also contained in the 13c records of g bulloides and benthic foraminifera the 13c records from surface intermediate and deep waters of the eastern basin and from intermediate and deep waters of the western basin are opposite to that of the open ocean during glacial time 13c values were higher in intermediate and deep waters of the whole mediterranean and also in surface water of the eastern basin at the same time the 13c gradient of surface to deep waters was low this gradient increased during the last deglaciation while 13c values of g bulloides and benthic foraminifera decreased this decrease interrupted at 10 ka may have been related to increased fresh water run off from the bordering contintents due to increased precipitation especially in the tropical belt the 13c depletion is clearly recorded in the levantine and deep water masses and can be traced westward in the mediterranean outflow oxygen and carbon isotope anomalies recorded simultaneously in the east mediterranean by the shallow water species globigerinoides ruber during sapropel deposition indicate that increased precipitation on the bordering continents and strong fresh water run off during the time of the last deglaciation may have caused a density stratification and deep stagnation in the eastern basin uncertainties arise from the fact that in the mixing model deglacial mediterranean waters are mixed with continental fresh waters the isotopic characteristics of which are not entirely understood although increased surface water production of biogenic material can not be excluded as a possible cause of 13c depletion it appears that the river discharge including the nile as well as black sea input are also plausible sources for the fresh water layering

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

pelagic carbonate chemostratigraphy sr mg 18o 13c abstract a synthesis of the elementary sr and mg and isotopic 18 o and 13 c geochemistry of mesozoic to recent bulk pelagic carbonates suggests that the influence of late burial diagenesis is considerably less than was previously thought and that bulk carbonate geochemistry could be important for both paleoceanography and stratigraphy numerous chemical fluctuations in sr ca mg ca and 13 c 12 c ratios have occurred in the ocean during the last 140 ma the main factors responsible are 1 variations in submarine hydrothermal activity and 2 sea level fluctuations the validity of the chemostratigraphic methodology can be demonstrated by the synchroneity and the worldwide occurrence of various geochemical shifts

martian magnetic paleopoles a geostatistical approach 1 various attempts have been made to locate magnetic paleopoles on mars by modeling individual magnetic field anomalies in this study a quite different approach based on geostatistics is taken discreet magnetic sources form magnetic doublet anomalies in the magnetic field that tend to align with the horizontal direction of magnetization a semivariogram of radial field polarities on mars indicates that magnetic field anomalies of opposite polarity tend to be separated by 14 this phenomenon is interpreted to be due to the presence of magnetic doublet anomalies in the field accordingly the autocovariances of the field polarity along longitudinal lines relative to over 1000 trial paleopole locations were examined magnetic paleopoles within about 50 of 230 e 17 n and 50 e 17 s were found to best explain the geostatistical structure of the polarity of the martian magnetic field

serpentinization of the martian crust during noachian abstract this paper proposes a model of serpentinization of the southern martian crust that may explain the topographic dichotomy the absence of an associated free air gravity anomaly and the presence of strong magnetic anomalies in the southern hemisphere the thermodynamical conditions for serpentinization were likely met in the lithosphere during the noachian period this process may have decreased the density in the southern crust and created the topographic dichotomy different reactions of serpentinization that can form magnetite have been considered assuming an intense magnetic field core dynamo we obtain chemical remanent magnetizations that are in the order of the estimates deduced from martian magnetic anomaly studies the pertinence and the implications of our model concerning the early thermal evolution of mars are discussed with emphasis on the intensity of the paleo magnetic field

carbonate dissolution fluctuations in the western equatorial pacific during the late quaternary planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial pacific erdc 93p 1619 m rc17 177 2600 m v28 238 3120 m thompson 1976 were examined for the last 500 kyr at sample intervals from 2 5 to 5 kyr to study the fluctuations of dissolution in the western equatorial pacific the age models were constructed by correlating the 18o records with the specmap stack imbrie et al 1984 results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles fragmentation varied with a greater amplitude and the carbonate ion concentration changed less in the deep than in the intermediate water dissolution has significant variance distributions and coherencies with 18o over the 100 41 and 23 kyr periods of orbital variations dissolution maxima lag ice volume minima by 6 to 20 kyr the dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric co2 concentration at the last glacial maximum broecker 1982 boyle 1988

differential dissolution modification of late pleistocene oxygen isotope records in the western equatorial pacific deep sea records of the pacific ocean show dramatic variations in the dissolution intensity of calcium carbonate through the late pleistocene extremes are characterized by much depressed dissolution intensity during deglaciation preservation spikes and much enhanced dissolution intensity during ice growth dissolution spikes increased dissolution intensity at dissolution spikes distorts 18o records by preferential removal of 16o rich shells resulting in heavier 18o values at these sections the 18o values tend to remain unaltered at deglacial preservation spikes thus the fluctuations of carbonate dissolution intensity modify the late pleistocene oxygen isotope records in such a fashion that apparent climate optima as defined by the lightest 18o values tend to shift toward preservation spikes while apparent glacial maxima characterized by the heaviest 18o values shift toward dissolution spikes

approximate paleomagnetic poles for some of the new england seamounts abstract paleomagnetic pole positions were estimated for several of the new england seamounts by a simple dipole method computer poles are in agreement with poles determined by others for several seamounts in the chain using three dimensional modeling collectively the poles plot in a swath which follows the late mesozoic polar wander path across northern siberia to the bering strait it is shown that for relatively simple seamount geometries and dipole like magnetic anomalies inclinations and declinations determined by the dipole method agree within a few degrees with those found by three dimensional methods paleopole determinations by either method may be degraded by interfering neighboring anomalies and other effects but the five poles considered best determined are consistent with the overall distribution of poles the distribution is not consistent with a model involving a hot spot origin or with geologic evidence suggesting origin during a brief time within the cretaceous normal interval statistically the poles are in much better agreement with the hypothesis that the seamounts are the same age as the sea floor underlying them

pleistocene δ18o records from ontong java plateau effects of winnowing and dissolution abstract sedimentation processes on ontong java plateau in the western equatorial pacific are reflected in oxygen isotope grain size and carbonate records processes recorded are dissolution of carbonate particles winnowing of fines and to some degree the gradient of productivity away from the equator carbonate dissolution begins to affect sediments significantly at about 3 km water depth winnowing is important on the top of the plateau and down the flanks to about 2 5 km water depth winnowing appears to have been greatly intensified during the ice age intervals

late pleistocene evolution of the ocean s carbonate system abstract we demonstrate that the carbonate record from a single site ocean drilling program site 1089 in the deep south atlantic represents a qualitative high resolution record of the temporal evolution of the carbonate saturation state of the deep sea the record is especially notable because it is free from many of the complications that limit other records low sedimentation rates blurring by chemical erosion bioturbation etc the pattern of carbonate variability is characteristic of indo pacific cores with high carbonate glacials and low carbonate interglacials wt carbonate lags changes in benthic 18 o by an average of 7 6 kyr and carbonate variations are in phase with the rate of change first derivative of benthic 18 o intense dissolution occurs at the transition from interglacial to glacial periods and increased preservation occurs during deglaciations these observations represent two fundamentally different responses of the marine carbonate system the lagged response of carbonate to 18 o reflects a steady state mass balance process whereby the lysocline adjusts to maintain alkalinity balance between riverine input and marine burial the site 1089 carbonate signal is remarkably similar to inferred changes in the sr ca of seawater for the past 250 kyr which implies that both carbonate dissolution and seawater sr ca may be controlled by sea level induced changes in the location of carbonate deposition shelf basin fractionation during glacial to interglacial cycles the transient change in preservation during the transitions into and out of glacial stages reflects a response of the carbonate system to a redistribution of alkalinity and dic in the ocean i e carbonate compensation comparison of the site 1089 carbonate and vostok p co 2 records suggests a role of deep sea co 3 2 variations for governing at least some second order features of the atmospheric p co 2 signal in order to quantify this role however measurement of indices of dissolution along a true depth transect will be required to estimate the magnitudes of changes in deep sea co 3 2

late pleistocene carbonate stratigraphy on ontong java plateau in the western equatorial pacific abstract late pleistocene carbonate cycles on ontong java plateau are characterized by maxima during deglaciations deglacial preservation spikes and by minima during transitions from interglacial to glacial conditions ice growth dissolution spikes superimposed on these short period fluctuations there is a long term oscillation of carbonate contents with a period of nearly 400 ky the brunhes dissolution cycle dissolution related sand fraction profiles 63 m indicate that the lysocline was at a water depth of about 3 6 km during deglacial transitions and that it rose up to 2 6 km during the stages of ice growth a fluctuation of the lysocline by 1 km can account for more than half of the total amplitude of the observed carbonate cycles assuming a linear increase in carbonate dissolution rates with increasing water depth below the lysocline and a constant ccd a shoaling of the lysocline during ice buildup may result from downward transfer of metabolic co 2 from intermediate waters to greater depths in the water column enhanced carbonate dissolution below 2 6 km increases alkalinity in deep waters predisposing the system toward reducing atmospheric co 2 partial pressure during a subsequent period

thickness of the magnetic crust of mars 1 to estimate the thickness of the magnetic crust of mars six observational magnetic spectra are fitted with the theoretical spectrum expected from a novel bimodal distribution of magnetic sources observational spectra differ for each comes from a different map or model of variously selected and analyzed mars global surveyor magnetometer electron reflectometer measurements of the vector magnetic field around mars the new theoretical spectrum represents fields from both compact sources and extended laterally correlated sources on a spherical shell so the estimated shell depth can now be doubled to obtain layer thickness this typical magnetic crustal thickness is put at 47 8 8 4 km the extensive sources are enormous typically 650 km across and account for over half the magnetic energy at low degrees there is some indication that these sources are relatively shallow but the typical area remains about 330 000 km2 granted such extended sources represent magnetization of mars ancient crust in a core source field dominated by a reversing areocentric paleodipole each one arguably formed during a single polarity chron how did such vast regions of magnetic crust form a survey of many eligible mechanisms suggests magnetization of cooling igneous rock at minimal rates of about 1 to 0 1 km3 a during superchrons of order 15 to 150 ma long

effects of magnetic anomalies discovered at mars on the structure of the martian ionosphere and solar wind interaction as follows from radio occultation experiments the slopes of the electron density profiles obtained by radio occultation experiments at mars revealed different variations with solar zenith angle in comparison with behavior of the electron density profiles in the magnetic field free ionosphere of venus the results obtained by the mars global surveyor mgs spacecraft show the existence of highly variable and very localized magnetic fields of crustal origin at mars addressing the difference between the ionosphere at venus and mars the scale heights of electron density profiles obtained by radio occultation methods onboard mariner 9 and viking 1 are analyzed at altitudes higher than the topside boundary of the photoequlibrium region in the magnetic field free ionosphere the local increase of the mean scale height in the altitude region 180 250 km is assumed to be either an effect of a nonhorizontal magnetic field associated with the magnetic anomalies or diffusive equilibrium in the magnetic field free ionosphere the areas where the scale height of electron density profile is increased in comparison with average one have been selected the angle between the magnetic field measured by mgs mag er at altitudes 120 250 km and local zenith direction is investigated throughout these selected areas

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

history of atmospheric co2 constraints from the deep sea record the carbon chemistry of deep ocean water is quantitatively reflected in carbonate preservation and in the 13c values of foraminifera by using benthic 13c ranges to estimate total dissolved co2 and correcting for the aging effect of deep water back aging the pco2 of the atmosphere can be reconstructed data at hand are insufficient for detailed studies but allow the calculation of an upper limit of pco2 for selected periods within the last 100 million years the limit is probably near a factor of 2 5 times present atmospheric co2 for post eocene time and below a factor of 10 for the late cretaceous

spectral effects of time depth nonlinearities in deep sea sediment records a demodulation technique for realigning time and depth scales carbon 14 dating and percent caco3 in late pleistocene sediments suggest that deepsea sedimentation rates vary cyclically and that this cyclicity is related to climate sedimentation rate variability leads to nonlinearity in the time depth mapping function this nonlinearity can have profound affects on signal spectra leading to the development of harmonics and intermodulation tones these distortion effects in the spectra give a direct indication of the degree of nonlinearity thereby providing a tool for realigning time and depth scales a tuning technique is developed which assumes a direct link between climate as measured in 18o from planktonic foraminifer tests and sedimentation rates a criterion of spectral simplicity as quantified in the varimax norm is used to demodulate the input spectrum application of this technique to an equatorial pacific piston core erdc 84 found peak glacial sedimentation rates to be 30 higher than peak interglacial rates a figure in good agreement with 14c based estimates from the same area this technique is compatible with other time scale tuning techniques such as those using orbital parameters and in combination with these other techniques provides a method for fine tuning any late pleistocene record

two step deglaciation 14c dated high resolution δ18o records from the tropical atlantic ocean abstract eight box cores from the tropical atlantic were studied in detail with regard to foraminiferal oxygen isotopes radiocarbon and globorotalia menardii abundance a standard atlantic oxygen isotope signal was reconstructed for the last 20 000 yr it is quite similar to the west equatorial pacific signal published previously deglaciation is seen to occur in two steps which are separated by a pause onset of deglaciation is after 15 000 yr b p the pause is centered between 11 000 and 12 000 yr b p but may be correlative with the younger dryas 10 500 yr b p if allowance is made for a scale shift due to mixing processes on the sea floor step 2 is centered near 10 000 yr b p and is followed by a brief excursion toward light oxygen values this excursion the m event may correlate with the gulf of mexico meltwater spike

extraterrestrial 3 he as a tracer of marine sediment transport and accumulation the deposition rate of deep sea sediments and their focused redeposition by deep sea currents can be evaluated from analyses of sedimentary 230th with a temporal resolution limited only by bioturbation6 7 10 11 230th is produced uniformly throughout the ocean by radioactive decay of dissolved 234u and is removed sufficiently fast by sorption onto sinking particles to act as a constant flux tracer of sedimentation rates but the half life of 230th 75 kyr limits its use for this purpose to the past 200 250 kyr here we explore the use of extraterrestrial 3he from interplanetary dust particles1 4 idps as a constant flux proxy that is free from this limitation a comparison of 3he with 230th in two cores from the equatorial pacific ocean indicates that the variability in the mean flux of idps over the past 200 kyr is less than 75 but in contrast to this relatively constant rate of supply of 3he to the deep sea the local burial rates of 3he and 230th have varied by a factor of five over the past 450 and 200 kyr respect ively we interpret this variability as reflecting sediment focusing with a temporal pattern that suggests regular cycles of climate driven reorganization of near bottom currents in the deep pacific ocean

abyssal ne atlantic benthic foraminifera during the last 15 kyr relation to variations in seasonality of productivity abstract benthic foraminiferal faunas 63 m and stable isotopes from the last 15 kyr were studied in bengal programme high resolution temporal and spatial study of the benthic biology and geochemistry of a north eastern atlantic abyssal locality kasten core 13078 16 from the porcupine abyssal plain ne atlantic 48 49 91 n 16 29 94 w water depth 4844 m changes occurred in the accumulation rates species composition diversity and stable isotopes during the last 15 kyr today the area is strongly influenced by seasonal inputs of phytodetritus following the spring blooms in surface water primary productivity variations in the relative abundance of the two most abundant species epistominella exigua and alabaminella weddellensis which today show significant increases in abundance with the presence of phytodetritus on the sea floor are interpreted as resulting from changes in the seasonality of productivity seasonal productivity was higher during the holocene than during the last deglaciation and younger dryas probably coinciding with the retreat of the polar front to higher latitudes this hypothesis is consistent with simultaneous decreases in the percentage of the polar planktic foraminifera neogloboquadrina pachyderma s and increases in the percentage of globigerina bulloides a warmer water planktic foraminifera indicative of phytoplankton blooms and enhanced productivity the relative abundance of the phytodetritus species e exigua and a weddellensis covary between 14 7 and 8 1 kyr but not between 7 8 and 1 2 kyr major decreases in the numbers per gram and accumulation rates of planktic and benthic foraminifera occurred at 12 8 5 kyr and at 4 kyr which correspond to decreases in the sediment coarse fraction and published data on inorganic carbon contents suggesting that dissolution may have increased at these times relationships between benthic foraminiferal faunas and benthic stable isotope records suggest no simple relationship between faunal abundances and test isotope chemistry for example the abundances of phytodetritus species do not show strong correlations with either the 13c values of e exigua or the 13c e exigua p wuellerstorfi record which have previously been suggested as indicative of seasonality of productivity

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

magnetization of the martian crust 1 this paper presents the lateral variations of the vertically averaged magnetization model of the martian crust determined from the degree 50 spherical harmonic model of the magnetic potential the model potential is derived using the mars global surveyor low altitude magnetic data acquired within elevations of 85 200 km the potential model is first verified by comparing the three orthogonal components of the corresponding vector field with the observed high altitude 380 km data using the paleopole positions calculated through modeling 10 isolated small magnetic anomalies the model potential is inverted to determine the vertically averaged magnetization of a nominal 50 km thick crust the crust is highly magnetic with a magnetization contrast peak to trough as high as 35 a m the lack of distinct magnetic signatures for the giant impact basins hellas argyre and isidis and the absence of a magnetic anomaly associated with the north south topographic dichotomy indicate that the upper parts of the crust are low magnetic and that the strong magnetic source bodies are in the lower parts

magnetic lineations in the ancient crust of mars the mars global surveyor spacecraft in a highly elliptical polar orbit obtained vector magnetic field measurements above the surface of mars altitudes 100 kilometers crustal magnetization mainly confined to the most ancient heavily cratered martian highlands is frequently organized in east west trending linear features the longest extending over 2000 kilometers crustal remanent magnetization exceeds that of terrestrial crust by more than an order of magnitude groups of quasi parallel linear features of alternating magnetic polarity were found they are reminiscent of similar magnetic features associated with sea floor spreading and crustal genesis on earth but with a much larger spatial scale they may be a relic of an era of plate tectonics on mars

dike intrusion as a possible cause of linear martian magnetic anomalies a model in which the ancient 100 200 km wide magnetic lineations in the southern hemisphere of mars are formed by repeated dike intrusion is proposed on the basis of magnetizations observed at terrestrial mid ocean ridges a likely upper bound on the martian crustal magnetization is about 15 a m 1 this upper bound gives a minimum magnetized layer thickness of 35 60 km because the magnetic material is likely to be magnetite the long term stability of the anomalies probably requires ilmenite lamellae to have exsolved from the magnetite this exsolution process provides an upper bound on the cooling time available of 102 105 yr these bounds can be satisfied if the magnetic anomalies are created by successive intrusion of dikes from 20 to 2000 m wide production of a martian crust 35 60 km thick by rifting requires either mantle potential temperatures in excess of 1430 c or stretching factors greater than 5

high resolution local magnetic field models for the martian south pole from mars global surveyor data we present two high resolution local models for the crustal magnetic field of the martian south polar region models sp130 and sp130m were derived from three component measurements made by mars global surveyor at nighttime and at low altitude 200 km the availability area for these data covers the annulus between latitudes 76 and 87 and contains a strongly magnetized region southern parts of terra sirenum adjacent to weakly magnetized terrains such as prometheus planum our localized field inversions take into account the region of data availability a finite spectral bandlimit spherical harmonic degree l 130 and the varying satellite altitude at each observation point we downward continue the local field solutions to a sphere of martian polar radius 3376 km while weakly magnetized areas in model sp130 contain inversion artifacts caused by strongly magnetized crust nearby these artifacts are largely avoided in model sp130m a mosaic of inversion results obtained by independently solving for the fields over individual subregions robust features of both models are magnetic stripes of alternating polarity in southern terra sirenum that end abruptly at the rim of prometheus planum an impact crater with a weak or undetectable magnetic field from a prominent and isolated dipole like magnetic feature close to australe montes we estimate a paleopole with a best fit location at longitude 207 and latitude 48 from the abruptly ending magnetic field stripes we estimate average magnetization values of up to 15 a m

simple models for the beattie magnetic anomaly in south africa abstract the origin of the approximately 1000 km long beattie magnetic anomaly bma in south africa remains unclear and contentious key issues include the width depth and magnetization of its source in this study we use uniformly magnetized spheres prisms and cylinders to provide the simplest possible models which predict the 1 km altitude aeromagnetic measurements along a profile across the bma the source parameters are adjusted by forward modeling in case of a sphere an inversion technique is applied to refine the parameters our results suggest that two similarly magnetized and adjacent sources with a vertical offset can explain the observed magnetic anomaly the best fitting model corresponds to two highly magnetized 5 a m 1 sheet like prisms extending from 9 to 12 km depth and from 13 to 18 km depth respectively and with a total width reaching 80 km other less preferred models show thicker and deeper magnetized volumes associated magnetizations seem to be mostly induced although a weak remanent component is required to improve the fit we also compare our results with the interpretation of independent magnetotelluric and seismic experiments along the same profile it suggests that the geological sources for the bma are mostly located in the middle crust and may be displaced by a shear zone or a fault contrary to previous models suggesting a serpentinized sliver of paleo oceanic crust within the natal namaqua mobile belt we propose that granulite facies mid crustal rocks within this belt may cause the bma

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

magsat anomaly data over the kursk region u s s r abstract a new method of reducing magsat orbits was developed to produce a map of the kursk magnetic anomaly at satellite altitude two different techniques to estimate the direction of magnetization were applied to the components of the anomaly to determine the presence of remanent magnetization we propose that there is a significant component of remanent magnetization however we are unable to determine the importance of remanence relative to induced magnetization

planktonic foraminifera differential dissolution and the quaternary stable isotope record in the west equatorial pacific differential dissolution affects the isotopic composition of different species of planktonic foraminifera in different ways in the two species studied here in cores from ontong java plateau the less resistant species globigerinoides sacculifer is more readily affected at a shallower depth than the more resistant species pulleniatina obliquiloculata 2 9 versus 3 4 km but shows a smaller and less predictable response to partial dissolution 0 2 to 0 3 per mil versus 0 6 to 0 7 per mil comparison of isotopic values from the last glacial period with those from the late holocene indicates that the apparent dissolution effect is considerably reduced during the last glacial presumably due to reduced dissolution intensity during glacial time a change in the level of the lysocline of about 400 m is suggested in the published isotope records from pacific cores v28 238 and v28 239 the dissolution generated difference in 18o noted previously by shackleton and opdyke 1976 is seen to describe a mid brunhes dissolution maximum between 300 and 500 thousand years ago this mid brunhes dissolution excursion is well known from the pacific and the indian ocean

mapping and modeling of magnetic anomalies in the northern polar region of mars vector crustal magnetic field maps of the northern polar zone 60 n to 90 n are constructed from selected mars global surveyor magnetometer data obtained during the period from may 28 to september 13 1998 two medium anomalies amplitudes 50 nt at 170 km altitude are mapped in locations consistent with earlier studies no visible surface features correlate with the anomalies suggesting that the sources lie beneath the visible veneer of polar deposits and volcanic lava flows if so then they formed prior to the immediate end of the heavy bombardment upper hesperian period modeling of anomaly vector field components combined with independent constraints on the depth to the curie isotherm yields lower limits on bulk magnetization intensities 0 4 0 9 a m that are significantly greater than those measured for martian snc meteorite samples rocks that contain substantially more titanomagnetite than snc meteorites or that contain magnetic phases in addition to titanomagnetite possibly resulting from hydrothermal alteration are therefore suggested alternatively remanence acquisition in a field of earthlike intensity 50 t rather than in the relatively weak inferred paleointensities for snc meteorites 1 10 t would also help to explain the relatively strong inferred remanent magnetizations the approximate south paleomagnetic pole positions corresponding to these two anomaly sources are located in a region between olympus mons and the present north rotational pole this region is adjacent to the approximate location predicted by melosh 1980 for the paleopole prior to the formation of the tharsis gravity anomaly

insolation cycles as a major control of equatorial indian ocean primary production analysis of a continuous sedimentary record taken in the maldives indicates that strong primary production fluctuations 70 to 390 grams of carbon per square meter per year have occurred in the equatorial indian ocean during the past 910 000 years the record of primary production is coherent and in phase with the february equatorial insolation whereas it shows diverse phase behavior with 18o depending on the orbital frequency eccentricity obliquity or precession examined these observations imply a direct control of productivity in the equatorial oceanic system by insolation in the equatorial indian ocean productivity is driven by the wind intensity of westerlies which is related to the southern oscillation therefore it is suggested that a precession forcing on the southern oscillation is responsible for the observed paleoproductivity dynamics

an altitude normalized magnetic map of mars and its interpretation techniques developed for the reduction and analysisofterrestrialsatellitemagneticelddataareusedto better understand the magnetic eld observations made by mars global surveyor a global distribution of radial br magnetic eld observations and associated uncertainties is invertedfor an equivalentsource magnetization distribution and then used to generate an altitude normalized map of br at 200 km the observations are well represented by a potential function of crustal origin consistent with a rema nent origin for the martian magnetic features the correla tion between the 40546 br observations andbr calculated from the magnetization solution at observation locations is 0 978 for a magnetization distribution connedto a 50 km layer calculatedmagnetizationsrangefrom 22to 17a m we see correlations with tectonics that were only hinted at in earlier maps magnetic features appear to be truncated against valles marineris and ganges chasma suggestive of a major change in crustal properties associated with fault ing

variation of spherical harmonic power as a function of harmonic order for earth s core and crustal magnetic field and for mars crustal field 1 the variation of power of the spherical harmonics of earth s magnetic field as a function of degree is well known at earth s surface the power decreases as a function of degree until the crustal component dominates at the core surface the spectrum is flat apart from the dipole term and each degree contributes about equally to the power however as a function of order the power tends to decrease for high harmonic orders these represent sources at low geographic latitudes and so a field in which high order power is low represents one in which low latitude sources are weaker than high latitude sources thus the explanation for the reduction in power for high order harmonics in earth s core field is that in the core low latitude sources of the nondipole field are less intense than high latitude sources earth s crustal field is represented by harmonic degrees greater than 15 and also shows the power falling off as a function of order implying that there is an increase in the intensity of magnetic anomalies from equator to poles this can be explained if the magnetizations have been produced by a dipole field aligned along the spin axis because such a field is twice as strong at the poles as at the equator for the martian field there is no central dipole source but there are strong crustal sources that were created when mars had a planetary dynamo and presumably an axial dipolar field martian harmonics show the same pattern of variation as a function of order as those on earth one explanation for this is that these crustal sources were magnetized with a dipolar field aligned along the present spin axis implying that there has not been much martian polar wander since the crust was magnetized components 8239 words 15 figures 1 table

is there a component of pleistocene co2 change associated with carbonate dissolution cycles the only processes which could have decreased atmospheric co2 during glacial climates without appreciably changing the carbon isotope distribution in the sea appear to be 1 dissolved calcium carbonate input to the ocean e g coral reef buildup and erosion 2 the ocean solubility pump due to changes in surface temperature or air sea exchange or 3 decreased biological production of calcium carbonate it is assumed here that one of these mechanisms caused part of the atmospheric co2 changes recorded in the 200 kyr long vostok ice core two residual co2 records are generated by scaling the 13c difference between planktonic and benthic foraminifera in marine sediment cores to 82 ppm co2 per 1 increase in 13c and subtracting from this the measured co2 concentration in the ice core both residual co2 records exhibit two broad maximums between about 20 50 ka and 140 200 ka indicating that during these times about 40 ppm of the co2 decrease from interglacial levels cannot be explained by the interaction of the ocean s biological and vertical mixing cycles the shape of the residual co2 curve is similar qualitatively to the variation of calcium carbonate in central equatorial pacific sediments during this time period which would imply that changes in dissolved carbonate input to the ocean contributed the added component of co2 change however recent models of atmospheric co2 change in response to changing alkaline input to the ocean exhibit about a 25 to 35 ppm decrease per 1013 mol yr 1 increase in dissolved caco3 input if compensation for the changing input is occurring mostly within an area of about 40 106 km below the lysocline in the indo pacific the change in carbonate accumulation rate corresponding to a 40 ppm co2 change would be a minimum of 3 mg cm 2 yr 1 this can be compared to glacial increases of 0 5 to 1 0 mg cm 2 yr 1 during the last 200 kyr in central equatorial pacific sediments thus the added glacial accumulation of carbonate does not seem to match quantitatively with the 40 ppm amplitude of the residual co2 signal leading one to suspect that solubility plays a greater role than expected on the basis of a 2 c cooler surface ocean

stable isotopes in benthic foraminifera from ontong java plateau box cores erdc 112 and 123 abstract detailed oxygen and carbon isotope stratigraphies for two species of benthic foraminifera planulina wuellerstorfi oridorsalis umbonatus are compared between two box cores spanning the period of deglaciation and holocene within core stratigraphies are quite well correlated between core signals less so vertical mixing and possibly horizontal redeposition processes disturb the signals nevertheless there is a strong suggestion of fluctuations in the ambient bottom water conditions fo the entire time span considered

east west trending magnetic anomalies in the southern hemisphere of mars modeling analysis and interpretation abstract maps of the vector components of the martian crustal magnetic field over the strongly magnetized terra cimmeria sirenum region are constructed using mars global surveyor magnetometer data although pronounced east west trending anomalies are present on the radial and north field component maps at the mapping altitude 360 380 km these trends are much less prominent at the lower aerobraking altitude 90 150 km comparisons with similar maps produced using artificial data at the aerobraking altitude indicate that elongated sources in this region may have maximum lengths along the martian surface of 500 km and maximum aspect ratios of 2 iterative forward modeling of several relatively isolated anomalies in the mapped region yields paleomagnetic pole positions consistent with those estimated in previous studies of other anomalies using mapping phase and science phasing orbit data on this basis it is inferred that sources in the studied region are most probably magnetized primarily in northward or southward directions using this additional constraint iterative forward modeling is then applied to determine a magnetization distribution that is consistent with data at both the aerobraking altitude and the mapping altitude the model magnetization distribution which includes 41 discrete sources again indicates no highly elongated sources an examination of surface geology in the region as well as a consideration of the global distribution of anomalies suggests that magmatic intrusions e g subsurface dike swarms cooling in the presence of water are the most likely sources of the magnetic anomalies

magnetic field and plasma observations at mars initial results of the mars global surveyor mission the magnetometer and electron reflectometer investigation mag er on the mars global surveyor spacecraft has obtained magnetic field and plasma observations throughout the near mars environment from beyond the influence of mars to just above the surface at an altitude of 100 kilometers the solar wind interaction with mars is in many ways similar to that at venus and at an active comet that is primarily an ionospheric atmospheric interaction no significant planetary magnetic field of global scale has been detected to date 2 1021 gauss cubic centimeter but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of mars is reported

questions about magnetic lineations in the ancient crust of mars connerney et al 1 1 claim to have discovered sea floor spreading type magnetic anomalies in the measurements of the martian magnetic field done by the mars global surveyor it is possible that sea floor spreading may have occurred on mars but the information that these authors use to

paleo pole positions from martian magnetic anomaly data magnetic component anomaly maps were made from five mapping cycles of the mars global surveyor s magnetometer data our goal was to find and isolate positive and negative anomaly pairs which would indicate magnetization of a single source body from these anomalies we could compute the direction of the magnetizing vector and subsequently the location of the magnetic pole existing at the time of magnetization we found nine suitable anomaly pairs and from these we computed paleo poles that were nearly equally divided between north south and mid latitudes these results suggest that during the existence of the martian main magnetic field it experienced several reversals and excursions

late quaternary upwelling off tropical nw africa new micropalaeontological evidence from odp hole 658c planktonic foraminifera and radiolaria have been analysed in a late quaternary 40 0 ka sediment sequence from ocean drilling program odp hole 658c located under a coastal upwelling system near cap blanc offshore northwest africa in order to document the palaeoceanographic history of the area temporal variations in species abundance and faunal assemblage analysis reveal a tripartite phased sequence of palaeoceanographic change through the late quaternary phase 1 spans 40 14 5 ka and is characterised by moderate upwelling but heinrich event 2 is distinguished as a brief episode of strengthened upwelling phase 2 begins with a change in a number of variables at ca 14 5 ka and extends to ca 5 5 ka this phase is characterised by a general strengthening of upwelling but may be subdivided into three minor phases including a the recognition of the younger dryas marked by a temporary reduction in upwelling strength followed by b an intensification of upwelling and c upwelling and high productivity between 8 and 5 5 ka this phase of upwelling corresponds with maximum holocene cooling possibly triggered by the collapse of the laurentide ice sheet phase 3 extends from 5 5 to 0 ka and is characterised by weak upwelling and significant calcite dissolution these phases are related to climatic events particularly the african humid period ahp which is coincident with phase 2 the ahp is characterised by increased precipitation linked to an intensification of the african monsoon that enhances north east trade wind driven coastal upwelling and is associated with the expansion of continental vegetation across north africa copyright 2006 john wiley sons ltd

productivity of the glacial ocean discussion of the iron hypothesis an increase in the productivity of the glacial age southern ocean has been postulated to explain the decrease in pc0 of the atmosphere observed in ice cores a plausible mechanism has been proposed elsewhere that productivity is limited by the availability of fe in this region and that the greater supply of eolian dust during glacial time removed this limit recently published evidence from cores from the southern ocean suggests that in fact there was no change in productivity in the assumed manner glacial age productivity was indeed greatly increased in the equatorial pacific and in the eastern boundary upwelling systems the cause presumably was the mechanical action of glacial age winds rather than a greater supply of fe however a role of increased supply of micronutrients from the continents in the increase of equatorial productivity during glacial time cannot be excluded such enhancement from increased supply of dust would have the interesting corollary of more efficient export transfer to depth possibly contributing to nutrient depletion in glacial age deep intermediate waters there is some indication as well of a general decrease in nutrient content in the tropical thermocline in the western pacific during the last several million years a depletion that may have been fostered by increasing supply of dust from emerging asian highlands alternative explanations are available the case for fe as a major modifier of productivity and biogenic sedimentation on geological time scales cannot be made in the absence of criteria diagnostic for fe supply as opposed to stirring and upwelling

understanding the causes and consequences of past marine carbon cycling variability through models abstract on geological time scales the production and degree of recycling of biogenic carbon in the marine realm and ultimately its removal to sediments exerts a dominant control on atmospheric co 2 and hence variability in climate this is a highly complex system involving a myriad of inter connected biological chemical and physical processes for this reason alone linking observations often highly abstracted in the form of proxies to the primary processes involved and ultimately to explanatory hypotheses for specific geological events and transitions is challenging the past few decades have seen a progressive improvement in theoretical and process based understanding of the various components that make up the marine carbon cycle and hand in hand with this the development of numerical model representations of the complete system models have also been designed and or adapted with paleoclimate questions in mind and applied to quantitatively explore the role of the marine carbon cycle in both perturbations and long term geologic evolutionary trends in global climate and possible feedbacks between them however we must ask whether paleoclimate models incorporate sufficiently appropriate representations of the dynamics and sensitivities of the marine carbon cycle and indeed whether in the geological context we really know what these dynamics are here we provide a comprehensive overview of how marine carbon cycling and the biological carbon pump is treated in available paleoclimate models with the aim of critically evaluating their ability to help interpret past marine carbon cycle and climate dynamics to this end we first provide an overview of commonly used paleoclimate models and some of their associated paleo applications drawing from a wide range of global carbon cycle box models and earth system models of intermediate complexity emics secondly we review and evaluate the three dominant processes involved in the cycling of organic and inorganic carbon in the marine system and how they are represented in models namely biological productivity at the ocean surface remineralisation dissolution of particulate carbon within the water column and the benthic pelagic coupling at the seafloor we generate and employ illustrative examples using the model genie to show how different parameterisations of water column and sediment processes can lead to significantly different model projections our compilation reveals the prevalence of static parameterisations of marine carbon cycling among existing paleoclimate models which are commonly empirically derived from present day observations although such approaches tend to represent carbon transfer in the modern ocean well they are potentially compromised in their ability to reflect the true degree of freedom and strength of feedbacks with respect to past climate events particularly those characterised by environmental boundary conditions that differ fundamentally from today finally we discuss the importance of using models of different complexities and how questions of model uncertainty may start to be addressed

pole wandering of mars evidence from paleomagnetic poles abstract we use the mapping phase high altitude magnetic measurements provided by mars global surveyor mgs between march 1999 and april 2003 to model nine relatively isolated magnetic anomalies of mars each anomaly is modeled with an elliptical prism each component of the observed magnetic field is modeled independently using an elliptical prism in order to assess the reliability of the results and suppress non crustal and nearby crustal source contaminations the paleomagnetic pole positions are obtained from the magnetization vectors of the model source bodies we clean the data by removing the bad tracks and then divide the entire data into two sets that are measured at different times applying covariance analysis in the fourier domain to two maps of the same magnetic component that are derived from the two sets provides a means to extract the most common features of the maps the quality of a model is evaluated and only good models are used in the final geophysical interpretation most poles that come from good models cluster in the tharsis region suggesting that mars experienced polar motion since the magnetic source bodies were magnetized

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

interpretation of mars southern highlands high amplitude magnetic field with total gradient and fractal source modeling new insights into the magnetic mystery of mars abstract using model studies the total gradient tg of the z component magnetic field is shown to be a useful quantity for delineating sources of satellite altitude magnetic anomalies this field is used to constrain the location and lateral boundaries of sources of high amplitude magnetic anomalies of southern highlands of mars the tg field suggests two parallel linear and oppositely magnetized sources of 1000 and 1800 km length separated by 1000 km of region of intervening non parallel sources the simplest interpretation of the long linear features is that they are zones of multitudinous crustal scale dikes formed in separate episodes of rifting and not features associated with the mechanism of seafloor spreading forward modeling with uniformly magnetized sources suggests that magnetizations of the order of 10 50 a m 40 km thickness over 100 km width in the case of the southern source and of 12 5 27 5 a m 40 km thickness and 200 km width for the northern source are necessary to explain the z component amplitudes and features of the tg field if the crustal magnetization on mars were to be distributed fractally as on earth magnetizations matching the largest amplitude features on mars may be spatially correlated from a 50 100 km distance range 3 to approaching nearly uniform magnetization 5 values to keep magnetization intensity as small as possible the higher end of values are preferred whereas small amplitude anomaly features could be generated from sources with 3 many of the mars anomaly features could be coalescence effects similar to the coalescence of anomaly features observed on http icarus cornell edu information keywords html earth

glacial interglacial variability of atmospheric co2 due to changing continental silicate rock weathering a model study an 11 box model of the oceanic carbon cycle including sedimentary processes is used to explore the role chemical weathering of continental silicate rocks might play in driving atmospheric co2 levels on glacial interglacial timescales histories for the consumption of co2 by silicate rock weathering processes are derived from the marine ge si record taking the major uncertainties in the knowledge of the ge and si cycles into account several histories for the evolution of the riverine dissolved silica fluxes are calculated from this record the investigation of the systematics between riverine dissolved silica and bicarbonate fluxes under different weathering regimes leads us to the tentative conclusion that although there is no correlation between dissolved silica and total bicarbonate concentrations in the major rivers there may exist a negative correlation between weathering intensity and the ratio of dissolved silica to bicarbonate derived from silicate weathering alone with this correlation as a working hypothesis it is possible to interpret the dissolved silica fluxes in terms of equivalent co2 consumption rates the calculated histories indicate that glacial rates of co2 consumption by chemical silicate rock weathering could have been twice and possibly up to 3 5 times as high as they are today when used to force the carbon cycle model they are responsible for glacial interglacial pco2 variations in the atmosphere of typically 50 60 ppm and up to 95 110 ppm these variations are superimposed to a basic oscillation of 60 ppm generated by the model mainly in response to coral reef buildup and erosion processes the total pco2 signal has an amplitude of about 80 90 ppm and up to 125 135 ppm although these large amplitudes indicate that silicate weathering processes should be taken into account when studying glacial interglacial changes of co2 in the atmosphere it also raises new problems such as too high co2 levels during the period from 110 70 kyr b p requiring further study

rate of production dissolution and accumulation of biogenic solids in the ocean the equatorial current system by its response to global circulation changes provides a unique recording mechanism for long range climatic oscillations a permanent record of the changes in rate of upwelling and organic production is generated in the equatorial deep sea sediments particularly by such biogenic components which are unaffected by secondary dissolution in order to determine the rates of accumulation of various sedimentary components a reliable differential measurement of age of the strata must be obtained various approaches to this problem are reviewed and sources of error discussed secondary dissolution of calcium carbonate introduces a substantial and variable difference between the dissolution modified and hence a priori unknown rate of deposition on one hand and the rate of accumulation derivable from the observed concentration on the other the cause and magnitude of these variations are of importance particularly since some current dating schemes are based on assumed constancy in the rate of accumulation of this and in some cases also all other sedimentary components the concepts used in rate evaluation are discussed with emphasis on the difference between the state of dissolution an observable property of the sediment and the rate of dissolution a parameter that requires deduction of the carbonate fraction dissolved and of the time differential as a most likely cause of the enhanced state of dissolution of the interglacial carbonate sediments is proposed the lowered rates of biogenic production and deposition which cause longer exposure of the carbonate microfossils to corrosion in the bioturbated surface layer of the sediment historical perspective is included in the discussion in view of the dedication of the symposium to hans pettersson the leader of the swedish deep sea expedition 1947 1948 an undertaking that opened a new era in deep sea research and planetary dynamics

oxygen and carbon isotopes of individual shells of planktonic foraminifera from ontong java plateau equatorial pacific abstract analyses of single shells of orbulina universa and two other species show ranges of 2 in 18 o and 13 c at various levels in a box core from the western equatorial pacific seasonal and inter annual variations can account for only about half of this range variations in depths of calcification and in metabolic effects must account for the rest the large range must introduce considerable noise in multi shell analysis unless the number of shells in the sample is of the order of 50 or more we did not find a change in the range downcore nor did we find any evidence for the deglacial meltwater spike

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

reconstruction of atmospheric co2 from ice core data and the deep sea record of ontong java plateau the milankovitch chron we provide a reconstruction of atmospheric co2 from deep sea sediments for the past 625000 years milankovitch chron our database consists of a milankovitch template of sea level variation in combination with a unique data set for the deep sea record for ontong java plateau in the western equatorial pacific we redate the vostok ice core data of barnola et al 1987 to make the reconstructions we employ multiple regression between deep sea data on one hand and ice core co2 data in antarctica on the other the patterns of correlation suggest that the main factors controlling atmospheric co2 can be described as a combination of sea level state and sea level change for best results squared values of state and change are used the square of sea level rule agrees with the concept that shelf processes are important modulators of atmospheric co2 e g budgets of shelf organic carbon and shelf carbonate nitrate reduction the square of change rule implies that on short timescales any major disturbance of the system results in a temporary rise in atmospheric co2

stable isotope composition of benthic foraminifera from the equatorial pacific when ranked according to deviation from isotopic equilibrium deep sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon both rank sequences are stable from east to west in the equatorial pacific fertility independent and from glacial to post glacial time independent records for the past 15 000 yr suggest marked changes in deep sea circulation during this time interval

paleomagnetic pole positions and pole reversals of mars the paleomagnetic pole positions of mars obtained by modeling 10 small size isolated magnetic anomalies show considerable clustering 7 out of 10 are within a circle of 30 degrees radius centered at 230e 25n the directions of the magnetization of some nearby source bodies differ by 180 degrees and both north and south poles are found in the cluster suggesting the magnetic pole reversals of mars