carbonate ion concentration in glacial age deep waters of the caribbean sea 1 on the basis of the whole foraminifera shell weights for g sacculifer and n dutertrei from caribbean cores it appears that the carbonate ion concentration of water at 1800 m depth in the open atlantic i e the depth of the caribbean sill was 14 mol kg greater during glacial time than during the holocene the sense of this difference is consistent with the observation that the 13c 12c ratio for benthic foraminifera from glacial age atlantic upper deep water was higher than that for their holocene equivalents it is also consistent with fragment to whole foraminifera results however as several questions regarding the assumptions involved in converting shell weights to paleocarbonate ion concentrations remain unanswered this reconstruction must be considered tentative critical in this regard are the assumptions that shell wall thicknesses were the same as today s at any given site during glacial time and that the 0 3 g per mol kg relationship between shell weight and carbonate ion concentration is applicable over the entire deep water column the records reported here reveal no evidence for an early holocene preservation event however that for core v28 122 documents a dissolution event close to the mis 5 4 boundary

shell weights from intermediate depths in the caribbean sea 1 whole foraminifera shell weights for g sacculifer and n dutertrei in caribbean sea cores covering a depth range of 680 to 3620 m show a decrease in weight of 3 6 0 4 g between glacial time and the holocene this difference likely reflects a thickening of foraminifera shells as a result of the higher carbonate ion concentration of glacial surface water the fact that the shells from the core at 680 m depth are considerably lighter than those from the core at 1030 m depth suggests either that there is an up water column increase in the offset between the pore water and the bottom water carbonate ion concentration or that factors other than surface water carbonate ion concentration influence the initial shell weight of particular interest is a strong preservation event corresponding to the deglacial interval at 680 m depth the present day core of the intermediate water mass

an evaluation of lohmann s foraminifera weight dissolution index down water column traverses of core top weights for three planktonic species confirm lohmann s 1995 relationship between foraminifera shell weight loss and bottom water carbonate ion content however they also suggest that the initial shell thickness varies with growth habitat and that the offset between bottom water and pore water carbonate ion concentration varies even on small space scales

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

reevaluation of the caco3 size index paleocarbonate ion proxy measurements of the caco3 size index broecker and clark 1999 and of whole foraminifera shell weights lohmann 1995 on glacial age sediment from a series of water depths on the ceara rise in the west equatorial atlantic clearly demonstrate that the relationship between size index and pressure normalized carbonate ion concentration established for holocene equatorial sediments does not apply to glacial sediments rather it appears that the ratio of fine to coarse caco3 raining to the seafloor was greater during glacial time than during the holocene this finding squelches our previous enthusiasm regarding the application of the size index as a paleocarbonate ion proxy

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

relationship between weights of planktonic foraminifer shell and surface water co3 concentration during the holocene and last glacial period shell weights of globigerinoides sacculifer and the elemental concentration of magnesium and calcium mg ca from globigerinoides ruber measured from an arabian sea sediment core aas9 21 exhibit an inverse relationship with each other which reveals that shell weights are mainly controlled by surface water co3 rather than calcification temperature down core shell weight variations of core aas9 21 shows an excellent correspondence with co2 concentrations in an antarctic ice core which reveals that planktic forminifera shells can trace atmospheric co2 due to the resultant change in surface water co3 hence shell weights of g sacculifer can be used as a proxy to reconstruct atmospheric co2 concentrations in the past here based on the shell weights surface water co3 change in the arabian sea is quantified and found that a co3 variation of 8 mol kg occurred during the holocene and a 36 mol kg variation occurred during the last glacial period

crustal complexity from regional waveform tomography aftershocks of the 1992 landers earthquake california we construct a two dimensional velocity section sampling the mojave crustal block in southern california by modeling shear wave sh seismograms our approach uses individual generalized rays computed from a layered model the model is divided into blocks with variable velocity perturbations such that ray responses are allowed to shift relative to each other to maximize synthetic waveform fits to data an efficient simulated annealing algorithm is employed in this search the technique is applied to a collection of 25 aftershocks landers earthquake as recorded at two stations gsc and pfo separated by 200 km which bracket the event population along the landers fault system the events are assumed to have known mechanisms and epicenters but both their depths and origin times are allowed to vary the results indicate considerable variation especially in the top layer up to 13 which mirrors surface geology best fitting models contain a low velocity zone in the lower crust if we constrain the crustal thickness 29 km from receiver function analysis reduced lower crustal velocities imply crustal weakening which appears compatible with the shallow seismogenic zone found in the northern end of this section there is also evidence for a lateral jump in velocity of several percent across the san andreas with the faster velocities on the west

progress toward a multi basin calibration for quantifying deep sea calcite preservation in the tropical subtropical world ocean article i nfo the development of a quantitative and multi basin deep sea calcite preservation proxy is important for a better understanding of the marine carbonate system both in modern sediments and in down core work we present caco3 preservation data from 89 core top samples in tropical and subtropical areas of the pacific atlantic and indian oceans we observe that the globorotalia menardii fragmentation index mfi has potential to trace deep sea caco3 dissolution quantitatively across the tropical subtropical world ocean this is evident in the robust relationship between mfi and bottom water calcite under saturation in six depth transects with markedly different bottom water co3 2 saturation states we also found a strong relationship between mfi and modeled estimates of percent caco3 dissolved at our core top locations corroboration for mfi s dissolution trend in the subtropics comes from the concurrent drop in size normalized shell weight of globorotalia truncatulinoides specimens with increasing co3 2

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

glacial age deep sea carbonate ion concentrations 1 a second stab is taken at the reconstruction of the distribution of carbonate ion concentration in the deep tropical pacific and atlantic oceans it takes into account glacial to holocene changes in size normalized initial shell weights it adopts a more rigorous relationship between measured core top shell weights and pressure normalized co3 concentrations and it employs an expanded glacial data set while the conclusion that the effective glacial co3 ion concentration decreased with water depth when greater initial shell weights for glacial age shells are adopted the conclusion is that dissolution during glacial time exceeded that during the late holocene this conclusion is seemingly at odds with previous studies of deep pacific sediments all of which suggest that more extensive dissolution occurred during periods of interglaciation than during periods of glaciation

calcite dissolution along a transect in the western tropical indian ocean a multiproxy approach three paleocarbonate ion proxies size index planktonic foraminifera shell weight and calcite crystallinity have been employed here to a set of core top samples from the western tropical indian ocean in the water depth ranges from 1086 to 4730 m all three proxies complement each other well and reveal that calcite dissolution starts to affect planktonic foraminifera from 2250 m depth onward and intense calcite dissolution begins around 3900 m depth in this sector of the tropical indian ocean three planktonic foraminifera species globigerinoides sacculifer pulleniatina obliquiloculata and neogloboquadrina dutertrei show wide variability in shell weights from core top sediments in the depth range of 3300 to 3400 m bathed by similar bottom water co3 concentrations this variability is attributed to shell calcification and shell weights are controlled by co3 concentration in the surface waters further surface water co3 concentrations override milder dissolution effects experienced by samples from shallower water depths bathed by similar bottom water co3 concentrations

what caused the atmosphere s co2 content to rise during the last 8000 years 1 we make a case that the 20 ppm rise in atmospheric co2 content over the last 8000 years was at least in part a consequence of the 500 gt c increase in terrestrial biomass early in the present interglacial rather than of a 200 gt c decrease in terrestrial biomass during the latter part of the holocene as proposed by indermuhle et al 1999 in support of this claim we present new 13c measurements from an ontong java plateau box core which do not reproduce the trend deduced from measurements on co2 from the taylor dome ice core in attempt to distinguish between scenarios put forth to accounting for the late holocene rise in atmospheric co2 content we also made foraminifera shell weight measurements on three box cores from the ontong java plateau we were surprised to find that the early holocene caco3 preservation event we sought was strongly depth dependent the largest magnitude was at 4 km where co3 ion concentrations appear to have been 30 mol kg higher than today s and hence nearly as high as those in today s north atlantic deep water

the coulon deposit quantifying alteration in volcanogenic massive sulphide systems modified by amphibolite facies metamorphism the coulon deposit is a volcanogenic massive sulphide vms system in the james bay area superior craton quebec that was metamorphosed to amphibolite facies conditions the chemistry and mineralogy of the vms related alteration halo proximal to the mineralized sulphide lenses are investigated using samples collected in the field and 5583 chemical analyses provided by osisko ltd alteration is quantified using mass balance and normative calculations and the application and performance of these methods in an exploration context are investigated in vms systems altered rocks proximal to the ore zones are characterized by multi element metasomatism which is best quantified by mass balance methods that have been successfully applied in the study area however mass balance calculations necessitate the documentation of a precursor which is not always possible in an exploration context therefore an alternative method i e alteration indices was also evaluated in most vms systems proximal alteratio

calcite saturation foraminiferal test mass and mg ca based temperatures dissolution corrected using xdx a 150 ka record from the western indian ocean a record of deep sea calcite saturation inline image derived from x ray computed tomography based foraminifer dissolution index xdx was constructed for the past 150 ka for a core from the deep 4157 m tropical western indian ocean g sacculifer and n dutertrei recorded a similar dissolution history consistent with the process of calcite compensation peaks in calcite saturation 15 mol kg higher than the present day value occurred during deglaciations and early in mis 3 dissolution maxima coincided with transitions to colder stages the mass record of g sacculifer better indicated preservation than did that of n dutertrei or g ruber dissolution corrected mg ca derived sst records like other sst records from marginal indian ocean sites showed coolest temperatures of the last 150 ka in early mis 3 when mixed layer temperatures were 4 c lower than present sst temperatures recorded by n dutertrei showed the thermocline to be 4 c colder in mis 3 compared to the holocene 8 ka b p

glacial to holocene redistribution of carbonate ion in the deep sea we have reconstructed the glacial age distribution of carbonate ion concentration in the deep waters of the equatorial ocean on the basis of differences in weight between glacial and holocene foraminifera shells picked from a series of cores spanning a range of water depth on the western atlantic s ceara rise and the western pacific s ontong java plateau the results suggest that unlike today s ocean sizable vertical gradients in the carbonate ion concentration existed in the glacial age deep ocean in the equatorial pacific the concentration increased with depth and in the atlantic it decreased with depth in addition the contrast between the carbonate ion concentration in deep waters produced in the northern atlantic and deep water in the pacific appears to have been larger than in today s ocean

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

crystallinity of foraminifera shells a proxy to reconstruct past bottom water co3 changes 1 the reconstruction of past changes in bottom water co3 is central to evaluating competing oceanic scenarios that deal with long term variations in atmospheric pco2 in search of a quantitative bottom water co3 proxy we analyzed the variations of calcite crystallinity of planktonic foraminifera globigerinoides ruber shells picked from core top samples along three depth transects ontong java plateau and the northeast margin of irian jaya in the western equatorial pacific and the sierra leone rise in the eastern tropical atlantic the strong empirical relationship between calcite crystallinity inferred from the full width at half maximum fwhm of calcite 104 x ray diffraction peak and bottom water saturation relative to calcite co3 shows that foraminifera calcite crystallinity could be a promising proxy for the reconstruction of upper pleistocene bottom water carbonate ion concentration

holocene atmospheric co2 increase as viewed from the seafloor 1 three scenarios have been proposed to explain the 20 ppm post 8000 bp rise in atmospheric co2 content indermuhle et al 1999 call on a climate induced decrease in terrestrial biomass w f ruddiman personal communication 2002 calls on an anthropogenically induced decrease in terrestrial biomass broecker et al 2001 suggest instead that this rise in co2 was a response to a caco3 preservation event induced by an early holocene increase in terrestrial biomass the biomass decline hypothesis not only rests on shaky 13c data but also requires an unreasonably large decrease in biomass 195 40 gtc while evidence for a decrease in deep sea carbonate ion concentration over the last 8000 years reconstructed from caco3 size index and foraminifera shell weight measurements appears to support the idea that the co2 rise was caused by a change in the inventory of terrestrial biomass the decrease appears to be too large to be explained solely in this way regardless the co3 decline cannot be used to distinguish between the late holocene biomass decrease and early holocene biomass increase scenarios only when a convincing 13c record for atmospheric co2 has been generated will it be possible to make this distinction

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

constructing synthetics from deep earth tomographic models recent studies of deep mantle structure indicate strong heterogeneity to conduct high resolution waveform modelling of these structures we have developed a new method to construct 2 d synthetics directly from block style tomographic models unlike the wkbj approximation which utilizes rays overshooting and undershooting receivers our method wkm approximation uses rays that arrive at the receiver first the ray paths from the 1 d layered reference model are used to localize each ray segment where the anomalous velocities are applied by overlay as in tomography next new p i t i p i ray parameter ti traveltime are computed to satisfy snell s law along with their numerical derivative p t which is used to construct a synthetic seismogram similar to the wkbj method as a demonstration of the usefulness of this method we generated wkm synthetics for the d region of high velocities beneath central america based on grand s tomography model reasonable fits to broad band data are obtained by condensing his distributed anomalies into his lowermost mantle layer such a 2 d model predicts synthetics containing a laterally varying s cd triplication similar to observations

effects of seafloor and laboratory dissolution on the mg ca composition of globigerinoides sacculifer and orbulina universa tests a laser ablation icpms microanalysis perspective article i nfo partial or selective dissolution of planktonic foraminiferal tests on the seafloor has been shown to alter original test mg ca compositions and thus may limit the accuracy of mg ca based thermometry for reconstructions of past sea surface temperatures we have employed laser ablation icpms to determine the extent of dissolution caused changes in mg ca distribution across individual chamber walls of the planktonic foraminifera globigerinoides sacculifer and orbulina universa g sacculifer samples collected from a core top depth transect in the ne indian ocean and laboratory dissolution experiments show little if any evidence of preferential removal of mg rich calcite layers by progressive dissolution of the tests we attribute the absence of selective dissolution to the banded distribution of mg across the chamber walls of these foraminiferal species and to the minimal presence of calcite crusts with relatively low mg composition on the outer surfaces of tests mg ca microanalyses of g sacculifer from core top samples further indicate that for samples collected above the calcite lysocline the effect of postdepositional dissolution on mg ca sample mean values is minimal and within the uncertainty of mg ca thermometry i e 0 4 mmol mol 0 8 c at 28 c comparison with previously published results for g sacculifer supports these observations simple modelling of g sacculifer test dissolution indicates that selective removal of calcite with high mg ca values from within the final chamber of g sacculifer test appears insufficient to cause the 10 decrease in mg ca values observed above calcite lysocline these changes in test composition might be related to development removal as a function of co3 2 of a thin diagenetic surface coating which has a relatively high mg ca

receiver structure beneath the southern mojave block california an inversion of a receiver function recorded at lawrence livermore national laboratory nevada test site network station lac reveals a range of 1 d velocity structures that are consistent the observed waveform the shear velocity structure southeast of lac is relatively simple consisting of an approximately 30 to 34 km thick crust all models contain relatively sharp crust mantle boundaries with a change in velocity from about 3 5 km sec to approximately 4 6 km sec over a depth range of 4 to 6 kilometers the range of models can be roughly divided into two groups that differ mostly in the mid to lower crust the first model of the earth structure contains a large low velocity zone in the middle and lower crust shear wave velocities as low as 2 8 km sec the second model contains nearly constant velocities approximately 3 5 km sec through the middle to lower crust in contrast with the simplicity of the southeast receiver function the receiver functions corresponding to the northwest and southwest show the influence of lateral velocity heterogeneity and can at best be discussed qualitatively

deepwater carbonate ion concentrations in the western tropical pacific since 250 ka evidence for oceanic carbon storage and global climate influence we present new size normalized weight snw co32 core top calibrations for three planktonic foraminiferal species and assess their reliability as a paleo alkalinity proxy snws of globigerina sacculifer and neogloboquadrina dutertrei can be used to reconstruct past deep pacific co32 whereas snws of pulleniatina obliquiloculata are controlled by additional environmental factors based on this methodological advance we reconstruct snw based deepwater co32 for core wp7 from the western tropical pacific since 250 ka secular variation in the snw proxy documents little change in deep pacific co32 between the last glacial maximum and the holocene further back in time deepwater co32 shows long term increases from marine isotope stage mis 5e to mis 3 and from early mis 7 to late mis 6 consistent with the coral reef hypothesis that the deep pacific ocean carbonate system responded to declining shelf carbonate production during these two intervals during deglaciations we have evidence of co32 peaks coincident with terminations 2 and 3 which suggests that a breakdown of oceanic vertical stratification drove a net transfer of co2 from the ocean to the atmosphere causing spikes in carbonate preservation i e the deglacial ventilation hypothesis during mis 4 a transient decline in snw based co32 along with other reported co32 and or dissolution records implies that increased deep ocean carbon storage resulted in a global carbonate dissolution event these findings provide new insights into the role of the deep pacific in the global carbon cycle during the late quaternary

large amplitude moho reflections sms from landers aftershocks southern california closely spaced aftershocks of the 28 june 1992 landers earthquake m w 7 3 were used to make event record sections that show the transverse components of s and sms arrivals at a distance of 70 to 170 km for the data recorded toward the north in the mojave desert large sms phases are observed with amplitudes 2 to 5 times greater than the direct s for similar distances to the south the sms arrival is comparable to or smaller than the s comparisons to synthetic seismograms indicate that the large amplitude sms phases are produced by the simple crustal structure of the mojave desert that allows a large moho reflection in contrast the more complex geologic structure to the south partitions the seismic energy into a more complicated set of seismic phases so that the moho reflection is diminished in amplitude the large sms phases observed in the mojave enhance the overall ground motions by a factor of 2 to 3 this suggests that when damaging earthquakes occur in other regions of simple crustal structures moho reflections will produce amplified strong motions at distance ranges around 100 km depending on the local structure

caco3 size distribution a paleocarbonate ion proxy lysocline reconstructions play an important role in scenarios purporting to explain the lowered atmospheric co2 content of glacial time these reconstructions are based on indicators such as the caco3 content the percent of coarse fraction the ratio of fragments to whole foraminifera shells the ratio of solution susceptible to solution resistant species and the ratio of coarse to fine caco3 all assume that changes with time in the composition of the input material do not bias the result however as the composition of the input material does depend on climate none of these indicators provides an absolute measure of the extent of dissolution in this paper we evaluate the reliability of the ratio of 63 m caco3 to total caco3 as a dissolution indicator we present here results that suggest that in today s tropics this ratio appears to be determined solely by co3 ion concentration and water depth i e the saturation state of bottom waters this finding offers the possibility that the size fraction index can be used to reconstruct co3 ion concentrations for the late quaternary ocean to an accuracy of 5 mol kg 1

caco3 dissolution in the deep sea paced by insolation cycles 1 three caco3 dissolution events have been documented in the western equatorial atlantic one associated with marine isotope stage 5d one with stage 5b and one with early stage 4 the intensity of these events appears to require a greatly expanded invasion of waters with a low carbonate ion concentration akin to that characterizing today s deep pacific and also the antarctic bottom water while evident in a core from a depth of 3 4 km these three events appear to be much less intense in the western equatorial pacific than in the western atlantic the atlantic results appear to be telling us that the density difference between southern ocean and north atlantic deep waters has been modulated by insolation changes associated with the 23 000 year precession cycle

pseudo dissolution of marine calcite abstract an enigma exists regarding observations aimed at determining the extent of calcite dissolution on the ceara rise in the western equatorial atlantic based on pore water gradients for ca alkalinity ph 13 c and 14 c a strong case can be constructed that at a depth of 3 3 km about 30 of the calcite rain dissolves martin and sayles geochim cosmochim acta 60 1996 243 263 hales and emerson geochim cosmochim acta 61 1997 501 514 martin et al geochim cosmochim acta 61 2000 1391 1404 however benthic chambers deployed at this site record no ca or alkalinity flux jahnke and jahnke geochim cosmochim acta 2002 in press further there is no evidence for shell weight loss or shell breakup between 2 8 and 4 1 km water depth on the ceara rise broecker and clark global geochem cycles 2002 in press a possible scenario which accounts for all but the 14 c observations martin et al geochim cosmochim acta 61 2000 1391 1404 is that coatings formed on the calcite are stirred downward into the respiration co 2 rich core top mixed layer and there redissolve we term this phenomenon pseudo dissolution

teleseismic body waveforms and receiver structures beneath seismic stations summary in this paper we describe a practical method for determining crustal structure by comparing observations of teleseismic body waves with synthetics constructed using generalized ray theory layered crustal structure beneath a seismic station strongly influences teleseismic body waves arriving in the 50 s or so after the initial p however the effect of crustal structure differs significantly for vertical component and radialcomponent records for any proposed crustal structure we develop an approximate theoretical formulation to predict the radial component seismogram as a function of the vertical component observations then we compare the observed and predicted radial component seismograms in the time domain and vary the proposed crustal structure using a grid search scheme until we obtain an optimum match the theoretical approximation is complete to second order in the reflection and transmission coefficients and is accurate to within a few per cent for modelling teleseismic waveforms we demonstrate the feasibility of this second order radial vertical comparison sorvec method by testing it on synthetically generated waveforms having complicated source properties and significant levels of background noise we illustrate the application to real data by determining the crustal structure beneath two seismic stations in tibet lzh and amdo beneath station lzh the crustal thickness is about 65 km beneath station amdo the crustal thickness is about 75 km and there is a low velocity layer in the lower crust

planktonic foraminiferal area density as a proxy for carbonate ion concentration a calibration study using the cariaco basin ocean time series 1 biweekly sediment trap samples and concurrent hydrographic measurements collected between march 2005 and october 2008 from the cariaco basin venezuela are used to assess the relationship between co32 and the area densities a of two species of planktonic foraminifera globigerinoides ruber pink and globigerinoides sacculifer calcification temperatures were calculated for each sample using species appropriate oxygen isotope 18o temperature equations that were then compared to monthly temperature profiles taken at the study site in order to determine calcification depth ambient co32 was determined for these calcification depths using alkalinity ph temperature salinity and nutrient concentration measurements taken during monthly hydrographic cruises the a which is representative of calcification efficiency is determined by dividing individual foraminiferal shell weights 0 43 g by their associated silhouette areas and taking the sample average the results of this study show a strong correlation between a and ambient co32 for both g ruber and g sacculifer r2 0 89 and 0 86 respectively confirming that co32 has a pronounced effect on the calcification of these species though the a for both species reveal a highly significant p 0 001 relationship with ambient co32 linear regression reveals that the extent to which co32 influences foraminiferal calcification is species specific hierarchical regression analyses indicate that other environmental parameters temperature and po43 do not confound the use of g ruber and g sacculifer a as a predictor for co32 this study suggests that g ruber and g sacculifer a can be used as reliable proxies for past surface ocean co32

past changes in biologically mediated dissolution of calcite above the chemical lysocline recorded in indian ocean sediments abstract in a deep sea sediment core recovered from a site lying well above the local lysocline several organic geochemical proxies and two different calcite dissolution indicators are compared in order to evaluate the relationship between calcite dissolution and paleoproductivity over the past three glacial interglacial cycles the degree of foraminiferal break up and the caco3 particle size distribution both point to significant periods of dissolution every 22 kyr during glacial stages and substages these dissolution events are concomitant with periods of enhanced primary productivity as indicated by the abundance of several biomarkers alkenones cholesterol brassicasterol keto ol used here to indicate changes in paleoproductivity dissolution fluctuations are highly coherent and in phase with the estimated paleoproductivity variations providing strong evidence that the observed dissolution is due to organic matter remineralization within the sediments rather than to changes in co32 concentration in the overlying water column