can the aluminum and titanium contents of ocean sediments be used to determine the paleoproductivity of the oceans in the central equatorial pacific settling particles collected with sediment traps have al ti values greater than those of a typical crustal source the al ti values of the sediment trap material are not well correlated with either the flux of organic carbon or with total particle mass suggesting that this ratio cannot be used as a simple index of paleoproductivity however the al ti values of some trap samples are more than 3 times the ratio for typical crustal materials indicating a noncrustal source of excess al numerical analysis using linear programming indicates that the excess al is associated with opal and that this biological component carries as much as 1200 ppm of al because of the low particulate fluxes of lithogenic material in the equatorial pacific and the relatively high opal content of equatorial sediment trap material opal appears to be the predominant conveyor of al to the equatorial sediments our sediment trap al ti values are similar to ratios previously measured in equatorial sediments suggesting that measurements of this element pair in ocean sediments may be an indicator of opal rain to the seafloor the particle reactive nature of al and ti means their ratios in sediments may be relatively insensitive to opal preservation or other diagenetic processes however the al ti values of raining particles are highly sensitive to the relative proportion of opal and lithogenic material where opal lithogenic ratios are less than 20 the al ti values are indistinguishable from a crustal source ratio in addition the amount of excess al associated with opal in settling particles may be a function of the concentration of al in the water column and of the processes that fractionate dissolved al and ti these issues must be evaluated before the al ti values of ocean sediments can be used as a reliable proxy of opal flux to the seafloor

biogenic silica dissolution in sediments of the southern ocean i solubility abstract a stirred flow through reactor technique was used to determine silica solubilities in sediments collected with a multicorer in the indian sector of the southern ocean antares i cruise the results show that the apparent silica solubility in the cores may decrease increase or remain constant with depth the silica solubility profiles are best explained by the early diagenetic interactions between biogenic silica and soluble aluminum derived from detrital material by combining the solubility data with measured dissolved silica profiles it is shown that the variable asymptotic pore water silica levels in the cores cannot be explained solely by differences in silica solubility in sediments that experience a significant detrital input the simultaneous reprecipitation of dissolved aluminum and dissolved silica prevents water silicic acid from reaching saturation with the dissolving biogenic silica the principal oceanographic control on pore water silica build up in the cores studied is the ratio of the deposition fluxes of biogenic silica and detrital material solubility differences inherited from the biomineralization process in the surface waters do not appear to have a significant effect on the observed pore water silica levels

gravity currents with residual trapping motivated by geological carbon dioxide co 2 storage we present a vertical equilibrium sharp interface model for the migration of immiscible gravity currents with constant residual trapping in a two dimensional confined aquifer the residual acts as a loss term that reduces the current volume continuously in the limit of a horizontal aquifer the interface shape is self similar at early and at late times the spreading of the current and the decay of its volume are governed by power laws at early times the exponent of the scaling law is independent of the residual but at late times it decreases with increasing loss owing to the self similar nature of the current the volume does not become zero and the current continues to spread in the hyperbolic limit the leading edge of the current is given by a rarefaction and the trailing edge by a shock in the presence of residual trapping the current volume is reduced to zero in finite time expressions for the up dip migration distance and the final migration time are obtained comparison with numerical results shows that the hyperbolic limit is a good approximation for currents with large mobility ratios even far from the hyperbolic limit in gently sloping aquifers the current evolution is divided into an initial near parabolic stage with power law decrease of volume and a later near hyperbolic stage characterized by a rapid decay of the plume volume our results suggest that the efficient residual trapping in dipping aquifers may allow co 2 storage in aquifers lacking structural closure if co 2 is injected far enough from the outcrop of the aquifer

process dependent residual trapping of co2 in sandstone this paper demonstrates that the nature and extent of residual co2 trapping depend on the process by which the co2 phase is introduced into the rock we compare residual trapping of co2 in berea sandstone by imbibing water into a core containing either exsolved co2 or co2 introduced by drainage x ray computed tomography measurements are used to map the spatial distribution of co2 preimbibition and postimbibition unlike during drainage where the co2 distribution is strongly influenced by the heterogeneity of the rock the distribution of exsolved co2 is comparatively uniform postimbibition the co2 distribution retained the essential features for both the exsolved and drainage cases but twice as much residual trapping is observed for exsolved co2 even with similar preimbibition gas saturations residually trapped exsolved gas also disproportionately reduced water relative permeability development of process dependent parameterization will help better manage subsurface flow processes and unlock benefits from gas exsolution

relative permeability and trapping of co2 and water in sandstone rocks at reservoir conditions 1 we report the results of an experimental investigation into the multiphase flow properties of co2 and water in four distinct sandstone rocks a berea sandstone and three reservoir rocks from formations into which co2 injection is either currently taking place or is planned drainage relative permeability and residual gas saturations were measured at 50 c and 9 mpa pore pressure using the steady state method in a horizontal core flooding apparatus with fluid distributions observed using x ray computed tomography absolute permeability capillary pressure curves and petrological studies were performed on each sample relative permeability in the four samples is consistent with general characteristics of drainage in strongly water wet rocks measurements in the berea sample are also consistent with past measurements in berea sandstones using both co2 brine and oil water fluid systems maximum observed saturations and permeabilities are limited by the capillary pressure that can be achieved in the experiment and do not represent endpoint values it is likely that maximum saturations observed in other studies are limited in the same way and there is no indication that low endpoint relative permeabilities are a characteristic of the co2 water system residual trapping in three of the rocks is consistent with trapping in strongly water wet systems and the results from the berea sample are again consistent with observations in past studies this confirms that residual trapping can play a major role in the immobilization of co2 injected into the subsurface in the mt simon sandstone a nonmonotonic relationship between initial and residual co2 saturations is indicative of a rock that is mixed or intermediate wet and further investigations should be performed to establish the wetting properties of illite rich rocks the combined results suggest that the petrophysical properties of the multiphase flow of co2 water through siliciclastic rocks is for the most part typical of a strongly water wet system and that analog fluids and conditions may be used to characterize these properties further investigation is required to identify the wetting properties of illite rich rocks during imbibition processes

dissolved al in sediments and waters of the east china sea implications for authigenic mineral formation abstract numerous previous studies indicate that several different authigenic aluminosilicates form in the oceans in this study we show using dissolved al distributions in sediments and waters from the nearshore regions of the east china sea that the process of aluminosilicate formation probably begins rapidly upon contact of detrital clays with seawater statistical analyses of dissolved al si h relations in surface sediments indicate that the minerals forming in east china sea sediments low in dissolved fe are dioctahedral chlorites with an average composition ex 0 91 mg 0 77 al 5 0 si 2 7 o 10 oh 8 where ex exchangeable 1 cation this composition is also consistent with dissolved al and si measurements as a function of salinity in turbid overlying waters results suggest a dissolution reprecipitation mechanism for clay mineral reconstitution this mechanism can help to explain why different authigenic clays are found in different areas of the oceans in the east china sea the total amount of authigenic clays present must constitute a very minor fraction of the bottom sediments thus the formation of these minerals has a relatively small impact upon dissolved si distributions clay mineral reconstitution in nearshore regions may provide a mechanism for buffering sediments and overlying waters with respect to ph as the composition of minerals formed should be a direct function of the h activity in the surrounding environment

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

significance of the sedimentary al ti ratio as an indicator for variations in the circulation patterns of the equatorial north atlantic this paper presents results of geochemical investigations conducted on three gravity cores recovered along an e w transect 3 5 n in the equatorial atlantic considering the high terrigenous content of the sediments approximately 12 74 wt al and ti concentrations are predominantly associated with the input of lithogenous phases the terrigenous fraction of western equatorial atlantic sediments is more influenced by material derived from the amazon river than by deposition of african dust particles as a possible route of transport the north equatorial countercurrent is considered fluctuations in al ti records generally reflect changes in the low latitude insolation cycle 19 23 kyr and thus indicate a close coupling to variations of the trade wind systems and continental climate changes however characteristics of the terrigenous signals in the eastern and western equatorial atlantic differ significantly while the precessional signal in the al ti record and low latitude portion in the 18o record are in phase in the eastern equatorial atlantic variations in the terrigenous fraction westward of the mid atlantic ridge precede the marine signal by 2 3 kyr which we ascribe to a shift between trade wind systems of the northern and southern hemispheres

capillary pressure and saturation relations for supercritical co2 and brine in sand high pressure pc sw controller meter measurements and capillary scaling predictions capillary pressure and saturation relations for supercritical co 2 and brine in sand high pressure p c s w controller meter measurements and capillary scaling predictions tetsu k tokunaga 1 jiamin wan 1 jong won jung 1 2 tae wook kim 1 3 yongman kim 1 and wenming dong 1 1 in geologic carbon sequestration reliable predictions of co 2 storage require understanding the capillary behavior of supercritical sc co 2 given the limited availability of measurements of the capillary pressure p c dependence on water saturation s w with scco 2 as the displacing fluid simulations of co 2 sequestration commonly rely on modifying more familiar air h 2 o and oil h 2 o p c s w relations adjusted to account for differences in interfacial tensions in order to test such capillary scaling based predictions we developed a high pressure p c s w controller meter allowing accurate p c and s w measurements drainage and imbibition processes were measured on quartz sand with scco 2 brine at pressures of 8 5 and 12 0 mpa 45 o c and air brine at 21 o c and 0 1 mpa drainage and rewetting at intermediate s w levels shifted to p c values that were from 30 to 90 lower than predicted based on interfacial tension changes augmenting interfacial tension based predictions with differences in independently measured contact angles from different sources led to more similar scaled p c s w relations but still did not converge onto universal drainage and imbibition curves equilibrium capillary trapping of the nonwetting phases was determined for p c 0 during rewetting the capillary trapped volumes for scco 2 were significantly greater than for air given that the experiments were all conducted on a system with well defined pore geometry homogeneous sand and that scco 2 brine interfacial tensions are fairly well constrained we conclude that the observed deviations from scaling predictions resulted from scco 2 induced decreased wettability wettability alteration by scco 2 makes predicting hydraulic behavior more challenging than for less reactive fluids and bachu 2008 benson and cole 2008 the depend ence of capillary pressure p c on water saturation s w under reservoir conditions is a basic constitutive relation needed to predict co 2 flow and capillary trapping during sequestration indeed with only knowledge of how rela tive permeability depends on s w neither fluid flow nor equilibrium saturation conditions are predictable at later stages of geologic carbon sequestration rewetting of reser voirs with native brine results in capillary trapping resid ual trapping of co 2 a main storage mechanism bachu et al 2007 ipcc 2005 the capillary trapping capacity of reservoir materials has complex dependence on porosity pore size distribution nonwetting phase displacement extent and the rewetting process iglauer et al 2011b tanino and blunt 2012 although capillary trapping of co 2 at its residual saturation depends on p c s w relations few investigations to date have directly measured these ba sic relations with co 2 h 2 o at reservoir pressures and tem peratures krevor et al 2011 pentland et al 2011 pini et al 2012 plug and bruining 2007 the study by plug and bruining 2007 appears to be the only one in which capillary trapped scco 2 saturation was determined while 1 introduction 2 geologic carbon sequestration may become an im portant technology for mitigating co 2 buildup in the atmosphere from fossil fuel combustion and for moderating climate change intergovernmental panel on climate change ipcc 2005 however predicting the perform ance of geologic co 2 sequestration requires reliable under standing of co 2 mobility and its saturation and pressure distribution within reservoirs bachu et al 2007 bennion earth sciences division lawrence berkeley national laboratory berkeley california usa now at civil and environmental engineering department louisiana state university baton rouge louisiana usa now at department of energy resources engineering stanford uni versity stanford california usa corresponding author t k tokunaga earth sciences division law rence berkeley national laboratory 1 cyclotron rd berkeley ca 94720 usa tktokunaga lbl gov

western mediterranean planktonic foraminifera events and millennial climatic variability during the last 70 kyr abstract detailed study of associations of planktonic foraminifera in cores md95 2043 and odp 977 located in the alboran sea mediterranean sea has allowed the identification of 29 new faunal events defined by abrupt changes in the abundances of neogloboquadrina pachyderma right and left coiling turborotalita quinqueloba globorotalia scitula globorotalia inflata globigerina bulloides and globigerinoides ruber white and pink varieties the age model for odp 977 was based on that of md95 2043 cacho et al 1999 paleoceanogr 14 698 705 on the isotopic stratigraphy and on two ams 14c measurements sea surface temperatures ssts were estimated for the last 54 kyr using the modern analog technique mat and were compared with the ssts provided by the uk 37 method the uk 37 record is very similar to the mat annual mean temperature record for the last 8 kyr however for older times alkenone derived temperatures are consistently higher than the annual mat temperatures this offset may be due to an underestimation of the sst provided by the planktonic foraminiferal method for glacial times to an overestimation of the uk 37 record or to changes in the seasonal production of alkenones most of the variability in the fauna is related to the millennial variability of heinrich and dansgaard oeschger d o events during heinrich events hes and most of the other d o stadials g bulloides t quinqueloba and g scitula increased while n pachyderma right coiling g inflata and g ruber decreased by contrast n pachyderma left coiling was only abundant in the hes the main component of the associations n pachyderma right coiling follows a general trend similar to that of sea level and 18o this species reached its highest abundance during the last glacial maximum when sea level was at a lower position the occurrence of a shallower nutricline owing to a shallowing of the interface between atlantic inflowing and mediterranean outflowing waters could have favoured the development of neogloboquadrinids in the vicinity of the strait of gibraltar

sea level changes control organic matter accumulation in the longmaxi shales of southeastern chongqing china abstract fine grained sediments in the ordovcian silurian o s longmaxi formation on the yangtze platform represent a significant shale gas source and reservoir in south china the formation of the organic rich black rock has been attributed to high primary productivity suboxic anoxic environments and or low detrital dilution however these claims remain to be debated here we investigated total organic carbon toc contents iron speciation major and trace elements of the o s longmaxi shale in the inner shelf qianqian 1 drillcore southeastern chongqing south china our results show that the longmaxi formation is composed of black shale with high toc values 4 7 0 6 in the lower member lm 0 6 m and silty shale with low toc values 1 3 0 5 in the upper member um 6 77 m the data from the lm suggests high primary productivity ferruginous conditions punctuated with episodes of intermittent euxinia and low terrigenous fluxes in contrast data for the um indicate reduced primary productivity ferruginous conditions and higher terrigenous fluxes leading to dilution of the organic matter a good coupling of local redox conditions with primary productivity and p al ratios rather than water mass restriction suggests that water column anoxia was mainly driven by high primary productivity and had a minor effect on primary productivity through marine p cycling changes in primary productivity might result from variable upwelling intensities associated with the fluctuations of sea levels variations in local redox conditions and terrigenous fluxes are mainly controlled by sea level fluctuations this study thus suggests that sea level fluctuations and related environmental effects play key roles in organic matter accumulation through primary productivity redox state and detrital dilution these findings highlight that multiple factors are responsible for organic matter accumulation at this location during the o s transition in south china

scavenged excess aluminum and its relationship to bulk titanium in biogenic sediment from the central equatorial pacific ocean we present results from chemical analyses of al and ti in surface sediment sampled along two cross equator latitudinal transects at 135w and 140w in the central equatorial pacific ocean although traditionally both al and ti are considered to reside exclusively within terrigenous phases in marine sediment these sediments present extremely high al ti ratios that are several times that of average shale and other potential crustal sources a sharp maximum in al ti is observed slightly south of the equator where sedimentary bulk accumulation rate bar is also highest reflecting elevated productivity in the overlying water caused by surface water divergence bulk al ti decreases sharply away 2 latitude to near crustal values at 4 north and south the latitudinal profiles of al ti are entirely unrelated to the concentration of the biogenic components as well as to the absolute accumulation of al and ti these results indicate the presence of a significant scavenged component of al sourced directly from seawater during particle settling the data from the two transects analytically and oceanographically confirms our earlier work that was based on the single 135w transect calculations of alexcess indicate that the highest al ti ratios correspond to 50 of the total al being unsupported by the small amount of terrigenous phases present these results are consistent with previous and ongoing studies of biogenic sediment suspended particulate matter and sediment trap material quantitative use of al as an index of terrigenous material may therefore lead to an overestimation by a factor of two of the true terrigenous load in marine sediment sedimentary rock and settling particles because bulk al ti appears to respond to sedimentary bar which in biogenic regimes is linked to surface water productivity downcore records of al ti in biogenic sediment may track productivity changes through time such al ti proxy records may be applicable in sediment of all ages unlike radionuclide tracers which are limited by radioactive decay to use over the past hundreds of kyr

capillary heterogeneity trapping of co2 in a sandstone rock at reservoir conditions 1 the storage of co2 in deep subsurface porous rocks is being developed worldwide for the mitigation of emission from large industrial sources such as power plants and steel manufacturing a main concern of this technology is in ensuring that the upwardly buoyant co2 does not migrate to the surface simulation studies suggest that substantial amounts of co2 can be trapped within permeable sections of a reservoir by capillary forces and intra reservoir heterogenities but there is little experimental observation of these phenomena we report the results of co2 core flooding experiments at high pressure and temperature performed to investigate the impact of natural capillary heterogeneity in a sandstone rock on co2 saturation buildup and trapping co2 and water were injected through a mt simon sandstone core at 9 mpa pore pressure and 50 c the core had two regions of distinct capillarity an upstream 10 cm long region of the core consisted of a relatively high permeability and homogenous sand a downstream 3 cm long region of the core consisted of a low permeability region characterized by significant cross bedding and a high capillary entry pressure for co2 during a drainage process of co2 displacing water co2 builds up upstream of the capillary barrier once in place co2 on the upstream side of the barrier cannot be displaced during 100 water flooding leading to trapped saturations that are a factor 2 5 times higher than what would be expected from residual trapping alone

high resolution elemental records from the south china sea and their paleoproductivity implications 1 the biogenic related elements ca sr ba p cd scavenged al and ti were analyzed by inductively coupled plasma mass spectrometry icp ms and inductively coupled plasma atomic emission spectrometry icp aes for core ns93 5 from the west slope of the south china sea terrestrial input as estimated from the accumulation of ti was higher during glacials than during interglacials carbonate accumulation rates are inversely related to those of terrestrial input suggesting higher production of calcareous phytoplankton during interglacials the accumulation patterns of authigenic sr ba p and cd match that of carbonate further indicating higher calcareous phytoplankton production during interglacials scavenged al and excess sio2 which is related to biogenic opal exhibit higher accumulation rates during glacials and correspond with changes in terrestrial input this indicates that terrestrial input driven is important to siliceous phytoplankton production but not for calcareous phytoplankton production as calcareous phytoplankton is the dominant component of the biogenic sediments in the south china sea particularly during interglacials previous inference of higher productivity in the south china sea during glacials based on only the biogenic opal proxy needs to be reconsidered

excess aluminum in deep sea sediments of the central indian basin abstract the aluminum concentration in the marine sediments has long been considered an indicator of terrigenous abundance the al ti values 48 5 of the central indian basin subsurface siliceous sediment are up to three times that of post archean australian shale paas the estimation of structurally unsupported al al ex from six sediment cores suggests that an average of 40 of total al is from noncrustal sources higher al ti or al ex values are often but not exclusively associated with abundant volcanic unaltered glass shards electron microprobe analysis of 60 of these glass shards reveals that they are rhyolitic in composition and of youngest toba 74 ka origin from northern sumatra these glass shards have very high al ti ratio of 175 mean al ti values are also above the paas in sediment where glass shards are absent which could be due to scavenging of dissolved al by biogenic components

capillary trapping in sandstones and carbonates dependence on pore structure 1 residual non wetting phase saturation and wetting phase permeability were measured in three limestones and four sandstones ranging in porosity from 0 13 to 0 28 and in absolute permeability from 2 10 15 to 3 10 12 m2 this paper focuses on the residual state established by waterflooding at low capillary number from minimum water saturation achieved using the porous plate technique which yields the maximum residual under strongly water wet conditions the pore coordination number and pore body throat aspect ratio of each rock were estimated using pore networks extracted from x ray microtomography images of the rocks residual saturation decreases with increasing porosity with no apparent difference in magnitude between the limestones and sandstones at a given porosity thus intraparticle intra aggregate microporosity does not significantly alter the efficiency of capillary trapping in the rocks considered presently residual saturation broadly decreases as conditions become less favorable for snap off i e with decreasing pore aspect ratio and increasing coordination number the measured residual saturations imply that capillary trapping may be an effective mechanism for storing carbon dioxide in both sandstones and carbonates provided that the systems are strongly water wet

paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom mats in the tropical west pacific paleoproductivity and paleoredox conditions were reconstructed in a sediment core in the parece vela basin of the eastern philippine sea the core consists of three units from youngest to oldest 1 laminated diatom mats ldm formed by ethmodiscus rex during the last glacial maximum similar to 18 28 kyr b p 2 diatomaceous clay dc and 3 pelagic clay pc elevated levels of export productivity during ldm deposition are indicated by high values for excess ba opal content and toc ti ratios estimated rates of organic carbon degradation ca 98 opal mass accumulation average 1322 g m 2 yr 1 and corrected organic carbon flux average 248 g m 2 yr 1 are comparable to high productivity regions of the modem ocean the ldm is also characterized by moderate enrichment of redox sensitive elements such as u mo cd and zn highly s 34 depleted pyrite sulfur isotopic compositions indicating bacterial sulfate reduction in a sulfate unlimited system and c s fe systematics reflecting limitation of pyrite formation by organic matter rather than reactive fe availability these features suggest mainly suboxic conditions in bottom waters but development of sulfidic anoxic conditions at or close to the sediment water interface association of intensified anoxia with productivity maxima indicates that export production was a more important control on bottom water redox conditions than lateral ventilation the dc and pc accumulated under oxic to suboxic conditions our observations suggest that redox environments during deposition of laminated marine sediments are more complicated and varied than previously thought and thus the use of sediment lamination as an indicator of anoxic bottom water conditions must be approached cautiously c 2012 elsevier b v all rights reserved

systematics of variations in excess al and al ti in sediments from the central equatorial pacific the proposal that the accumulation rate ar of scavenged al in central equatorial pacific sediments is controlled by bulk particle flux and therefore can be used as a paleoproduction proxy is tested by examining the relationship between al and ti using data on core wec8803b gc51 published by murray et al 1993 the downcore profile of the excess al ar follows the bulk ar consistent with the al scavenging hypothesis and is due to a relatively constant abundance of excess al down core however there have been large changes in the aluminosilicate ar to this region suggesting that changes in the al ti value do not solely trace variability in the delivery rate of scavenged al assuming that the excess al in this core is not the result of an analytical artifact we present an alternative to the al scavenging hypothesis that involves authigenic clay mineral formation or some other process causing the occurrence of excess al at a relatively constant abundance of the sediment this process may well be independent of bulk particle flux or paleoproduction

equatorial pacific calcite preservation cycles production or dissolution in the equatorial pacific ocean the depth and shape of the calcite lysocline appears to have changed significantly in response to climate forcing farrell and prell 1989 taking the farrell and prell record at face value the lysocline apparently became steeper during each of the last eight glacial stages also the accumulation rate of calcite during the last glacial maximum was 2 4 times higher than it was during the previous interglacial arrhenius 1952 1988 broecker 1971 farrell 1991 a numerical model for calcite dissolution in sediment is used to interpret these observations the model was validated by comparison with observations from the present day ocean these results are presented elsewhere if the lysocline fluctuations in the equatorial pacific are primarily a dissolution record then changes in the glacial pacific co3 of 20 40 m can be inferred here i offer the alternative explanation that cycles in equatorial production are responsible for the observations higher rates of calcite and organic carbon rain to the sediment in the equatorial region would have depressed the calcite lysocline and increased the calcite accumulation rate as observed a twofold increase in glacial production appears to be adequate to explain the observations but a precise determination is prevented by uncertainties in some of the model parameters

pore scale imaging of geological carbon dioxide storage under in situ conditions 1 while geological carbon dioxide co2 storage could contribute to reducing global emissions it must be designed such that the co2 cannot escape from the porous rock into which it is injected an important mechanism to immobilize the co2 preventing escape is capillary trapping where co2 is stranded as disconnected pore scale droplets ganglia in the rock surrounded by water we used x ray microtomography to image at a resolution of 6 4 m the pore scale arrangement and distribution of trapped co2 clusters in a limestone we applied high pressures and temperatures typical of a storage formation while maintaining chemical equilibrium between the co2 brine and rock substantial amounts of co2 were trapped with an average saturation of 0 18 the cluster sizes obeyed a power law distribution with an exponent of approximately 2 1 consistent with predictions from percolation theory this work confirms that residual trapping could aid storage security in carbonate aquifers

al to oxide and ti to organic linkages in biogenic sediment relationships to paleo export production and bulk al ti abstract to increase our understanding of the mechanisms that control the distribution of al and ti within marine sediment we performed sequential extractions targeting the chemical signatures of the loosely bound exchangeable carbonate oxide organic opal and residual fraction of sediment from a carbonate dominated regime equatorial pacific and from a mixed opal terrigenous regime west antarctic peninsula we observe a systematic partitioning of al and ti between sediment phases that is related to bulk al ti we show that where we can quantify an alexcess component the dissolved al is preferentially affiliated with the oxide fraction resulting in al ti molar ratios of 500 3000 this is interpreted as the result of surface complexation in the water column of dissolved al onto oxyhydroxides we also observe a previously undetected tiexcess with as much as 80 of the total ti in the organic fraction which is most likely a function of metal organic colloidal removal from the water column in samples where the excess metals are obscured by the detrital load the al and ti are almost exclusively found in the residual phase this argues for the paired removal of al preferentially by the oxide component and ti preferentially by the organic component from the water column by settling particulate matter this research builds upon earlier work that shows changes in the bulk ratio of al to ti in carbonate sediment from the central equatorial pacific that coincide with changes in the sedimentary bulk accumulation rate bar the ratios that are observed are as much as three times higher than typical shale values and were interpreted as the result of scavenging of dissolved al onto particles settling in the water column because this non terrigenous alexcess accounts for up to 50 of the total sedimentary al inventory and correlates best with bar the bulk al ti may be a sensitive tracer of particle flux and therefore export production because we show that the excess metals are the result of scavenging processes the bulk al ti may be considered a sensitive proxy for this region

a comparison of multiple proxies for export production in the equatorial pacific 1 several commonly used paleoproductivity proxies were compared to evaluate the validity of assumptions and limitations associated with each proxy export production fluxes cexport over glacial interglacial timescales were calculated from previously developed proxy specific algorithms at ttn013 pc72 and ttn013 pc114 both located in the equatorial pacific comparison of data from the same core intervals yields conflicting results despite calibrations based on the same core top samples the periodicity of marine barite excess ba and excess al based cexport records is similar the relative magnitude of cexport when calculated using excess ba and algorithms based on sediment trap data is significantly different than records based on core top calibrations particularly during glacial intervals at both sites bulk sedimentary al ti and ba ti ratios covary however these ratios do not correspond with the downcore records of their respective excess concentrations and their accumulation rates or with contemporaneous records based on marine barite excess ba and excess al accumulation although downcore records based on sediment mass accumulation rates may be compromised by sediment focusing this process cannot explain all the differences observed among the various data sets presented here this implies that some or all of these proxies do not exclusively respond to changes in export production the contradictions among these data highlight the importance of addressing inconsistencies among paleoproxies and re examining assumptions imbedded in proxy fundamentals prior to applying paleoproductivity proxies and interpreting paleoceanographic records