upwelling off the gulfs of panama and papagayo in the tropical pacific during march 1985 satellite measurements of sea surface temperatures sst were made in the eastern tropical pacific ocean during march 1985 unusually persistent upwelling was observed southwest of the gulf of panama and gulf of papagayo from march 7 to 22 the sst was depressed by 6 to 10 c relative to the surrounding waters the cooler waters off panama extended southwestward for over 1000 km and reached the galapagos islands the northern sst front off panama was wavelike in appearance and long waves of 600 km length moved southwestward at a phase speed of about 30 km d these waves resemble the long waves that appear each year along the northern boundaries of the equatorial sst fronts in the pacific and the atlantic oceans the sst fronts off the gulf of papagayo remained relatively stationary with a large area of colder water centered at 88 w and 10 n during these events the upwelling off the gulf of tehuantepec was relatively weak these satellite observations provide a view of an unusual oceanic response on the leeward side of mountain pass wind jets

dissolution kinetics of calcium carbonate in equatorial pacific sediments benthic chambers were deployed in the equatorial eastern pacific ocean on a transect along the equator between 103 w and 140 w and on a transect across the equator at 140 w in order to establish the rate of calcium carbonate dissolution on the seafloor dissolution was determined from the rate of alkalinity increase within an incubation chamber measured over an 80 120 hour incubation period dissolution rates were lowest at eastern pacific sites 0 2 0 4 mmol caco3 m2 d and highest at the equatorial 140 w sites 0 5 0 7 mmol m2 d both oxygen consumption rates and the degree of bottom water saturation govern dissolution rates measured dissolution and oxygen consumption rates are used with a numerical model to constrain the value of the dissolution rate constant k formulated according to the equation developed by keir 1980 dissolution rate k 1 n the observed dissolution fluxes are predicted by the model when k 5 to 100 d and n 4 5 this range of k values has important implications regarding the type of carbonate dissolving and its location within the sediment column at low values of k organic carbon rain rates to the seafloor become the dominant driving force of carbonate dissolution at higher values of k the degree of bottom water undersaturation becomes more important dissolution of carbonate within equatorial pacific sediments can be adequately described with k 20 10 d a rate constant much lower than some previously used values dissolution rates do not vary significantly over chamber boundary layer thicknesses between 200 and 800 m indicating that dissolution is not controlled by hydrodynamic conditions chambers acidified with hcl yield very large dissolution rates but for a given degree of acidification the dissolution rate was constant for sites ranging from water depths of 3300 4400 m this implies that there are not more and less easily dissolved forms of caco3 arriving on the seafloor between these depths a budget for alkalinity in the deep pacific predicted by the dissolution model and based on the assumption that all carbonate dissolution takes place in the sediments is within 85 of the input required by a published box model alkalinity budget based on the distribution of nutrients and the water mass transport rates

tectono sedimentary evolution of the bowland basin n england during the dinantian the bowland basin is a ne sw trending sedimentary basin lying between the askrigg bowland high to the n and nw and the central pennine high to the se the basin was initiated in late devonian tournaisian times sediment thickness and facies variations within the dinantian succession show marked asymmetry on both a basin wide and intra basin scale as a result of approximate nw se to n s extension across normal faults thickening of the sedimentary sequence from ne to sw over much of the basin resulted from fault controlled extension along the se margin of the basin with downthrow to the nw giving the basin a half graben character extension occurred in two distinct episodes marked by basin wide debris flow and sedimentary slide slump deposits during the late chadian early arundian the simple half graben became modified by a series of ne sw trending antithetic and nw se trending transfer faults associated with local unconformities and marked lateral thickness and facies variations this interval marks the transition from carbonate ramp to slope sedimentation and a temporary halt in carbonate supply to the basin the second episode of extension the late asbian early brigantian marks the break up of the northern basin margin ending major carbonate deposition within the basin reactivation of these structures at the end of the carboniferous created the ribblesdale fold belt as a result of nw se to n s compression transpression application of this research to areas surrounding the bowland basin has led to the recognition of additional shelf basins the orientation of which suggests control by normal and transfer fault systems discussion and

development and flow structures of sand injectites the hind sandstone member injectite complex carboniferous uk abstract the hind sandstone member of the carboniferous craven basin occurs within a thick succession of marine mudstone and is here interpreted as a sandstone injectite complex injectites take the form of i sills ii upwards emplaced dykes iii downwards emplaced dykes iv a sedimentary laccolith and v sandstone bodies remobilised in situ the remobilised and injected sand originated from small turbidite scour fills and potentially a more significant sand body such as a submarine slope gully fill the sedimentary laccolith appears to jack up the units it injects and is filled by sandstone with a chaotic fabric suggestive of brecciation of partly cemented sand the laccolith and sill dominated nature are suggestive of relatively shallow remobilisation sills are commonly laterally gradational with upwards emplaced dykes and in some cases these feed apparently downwards emplaced dykes a series of flow structures are preserved within some of the injectites and these provide clues to the emplacement history crack propagation direction is inferred from the orientation of undulating crests developed on the upper and lower surfaces of injectites peak flow is indicated by scour marks resembling flute and tool marks which are superimposed onto these undulating surfaces internal flow structures highlighted by pyrite mineralistion record the waning stage of injection the observed flow structures suggest that the apparent crack propagation direction was generally oblique to the peak flow and nearly perpendicular to the direction of late stage fluidised sediment flow crack propagation relates to the local stress field whilst injection flow may be related to the local pore pressure distribution recognition of this suite of structures may provide a useful interpretational tool for other injectites in both core and outcrop pore fluid overpressure which drove injection developed through the migration of petroleum and mineralising fluids from the underlying bowland shales and older limestones a complex brecciated fracture network within the mudstones underlying the injectites records fluid migration pathways sliced blocks and thin sections from injectites reveal flow structures defined by iron pyrite mineralisation the trigger is here related to growth of compressional structures and associated syn sedimentary slumps which occur at the same stratigraphic level as the injectites

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

origin and implications of early diagenetic quartz in the mississippian bowland shale formation craven basin uk abstract silica cementation exerts a key control on the compaction and geotechnical properties of mudstones and by extension the style of hydrocarbon and or mineral systems present in a given sedimentary basin integrated microscopic and bulk geochemical observations demonstrate that siliceous mudstones in the bowland shale formation a target for uk shale gas extraction exhibit abundant dispersed discrete m scale quartz cements and exhibit silica enrichment excess above a local detrital si al threshold of 2 5 dissolution of siliceous radiolarian tests during early diagenesis is identified as the main source of silica opal a required for quartz precipitation either via opal ct or directly to quartz and potentially generated as a product of anoxic marine weathering dissolution of reactive silicates during early diagenesis excess silica correlates with free hydrocarbons s1 normalised to total organic carbon oil saturation index osi we propose early diagenetic quartz precipitation suppressed pore collapse buttress effect retaining the pore space capacity to host oil quartz precipitation was likely catalysed for example via low porewater ph elevated al and or fe oxide content and or abundant labile organic matter juxtaposition of siliceous mudstones and mudstones lacking quartz cement indicates silica was immobile beyond the bed scale thus metre scale siliceous packages likely represent more prospective units within the bowland shale in terms of unconventional hydrocarbons on the basis of early diagenetic biogenic derived quartz cementation leading to improved hydrocarbon storage capacity coupled to enhanced brittleness these findings are relevant for shale oil and shale gas systems specifically where oil retained in pores subsequently cracks to generate gas these findings also suggest the bowland shale is a sub class of black shale defined by the potential to host a relatively large volume of early diagenetic fluids derived from anoxic bottom waters which were potentially s and or metal bearing this is potentially relevant for understanding the genesis of adjacent and related pb zn mineral deposits

coalbed methane resources and reservoir characteristics from the alberta plains canada abstract alberta has vast coal resources that may be a potential source of coalbed methane cbm exploration and research are currently underway in the province to quantify gas potential identify key geological factors that maximize cbm potential and identify the most favourable areas for cbm production potential there are four main coal zones within the plains and foothills of alberta the ardley coal zone of the plains is undergoing cbm exploration and production piloting much of this effort is within the west central pembina area horseshoe canyon formation coals of south central alberta were initially thought to have gas concentrations too low to be economic cbm producers it is these coals however that host alberta s first commercial cbm production project although similar in both geographic distribution and coal quality to horseshoe canyon coals not much is known regarding the gas potential of underlying coals of the belly river group the deeper mannville coals have some of the highest gas concentrations of alberta coals however they are also relatively deep and have lower permeability than the overlying belly river horseshoe canyon and ardley coals maximum gas in place for the plains and foothills has been estimated to be greater than 500 trillion cubic feet 1 42 10 13 m 3 although this number is very large little is known as to how much of this huge resource is actually producible a key challenge to producibility in alberta has been the generally low permeability of coals with the highest gas concentrations mannville coals and the moderate to low gas concentrations of higher permeability coals horseshoe canyon and ardley coals regionally coal distribution and average gas in place concentrations are calculated for the alberta plains identifying and explaining local areas with favourable cbm production characteristics within the regional setting is necessary to establish economic cbm plays within alberta there are currently several pilots and numerous exploration efforts underway in the province to demonstrate production potential this study integrates existing data with new data collected from key areas that show favourable cbm potential there is great opportunity for cbm development in alberta local areas have enhanced characteristics favourable to production ongoing geological investigations are needed to identify characteristics that will serve as an exploration tool for future cbm discoveries

sediment redistribution and grainsize effects on 230th normalized mass accumulation rates and focusing factors in the panama basin abstract here we examine how redistribution of differing grain sizes by sediment focusing processes in panama basin sediments affects the use of 230th as a constant flux proxy we study representative sediments of holocene and last glacial maximum lgm time slices from four sediment cores from two different localities close to the ridges that bound the panama basin each locality contains paired sites that are seismically interpreted to have undergone extremes in sediment redistribution i e focused versus winnowed sites both holocene and lgm samples from sites where winnowing has occurred contain significant amounts up to 50 of the 230th within the 63 m grain size fraction which makes up 40 70 of the bulk sediment analyzed for sites where focusing has occurred holocene and lgm samples contain the greatest amounts of 230th up to 49 in the finest grain sized fraction kretschmer et al 2010 suggest a maximum change of about 30 in 230th derived mars and focusing factors at focused sites except for our most focused site which requires an approximate 70 correction in one sample our 230th corrected 232th flux results suggest that the boundary between hemipelagically and pelagically derived sediments falls between 350 and 600 km from the continental margin

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

deglacial changes in dust flux in the eastern equatorial pacific abstract atmospheric dust levels may play important roles in feedbacks linking continental source areas tropical convection marine productivity and global climate these feedbacks appear to be particularly significant in the tropical pacific where variations in local convection and productivity have been demonstrated to have impacts on climate at higher latitudes modeling of past dust levels and related feedbacks has been limited however by a paucity of observational data in this study we present a temporal and spatial survey of dust fluxes to the eastern equatorial pacific over the past 30 kyr glacial and holocene fluxes of 232th a proxy for continental material were calculated by normalization to 230th from a north south transect of cores along 110 w between 3 s and 7 n odp sites 848 853 fluxes were 30 100 higher during the last glacial suggesting increased dustiness in both hemispheres during the glacial period in both time periods dust fluxes decrease towards the south reflecting scavenging of northern hemisphere dust by precipitation at the itcz the holocene meridional dust flux gradient between 7 n and 3 s is characterized by a steep drop in dust levels at the southern edge of the modern range of the itcz while the gradient is shallower and more nearly linear during the last glacial this change may indicate that the glacial itcz in this region was a less effective barrier to inter hemispheric dust transport most likely due to a decrease in convective intensity and precipitation during the last glacial alternatively the change in gradient may be explained by increased variability in the location of the glacial itcz our data do not appear to require a mean southerly displacement of the glacial itcz as suggested by the results of other studies

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

coalbed gas systems resources and production and a review of contrasting cases from the san juan and powder river basins coalbed gas has been produced commercially from the northern appalachian basin since the 1930s and from the san juan basin since the early 1950s however the magnitude and economic sig nificance of coalbed gas resources were realized only in the 1970s and early 1980s when the u s bureau of mines u s department of energy the gas research institute and oil and gas operators made a concerted effort to demonstrate commercial production of coalbed gas from vertical wells exploration and development ex panded in the late 1980s and early 1990s due partly to an uncon ventional fuels tax credit by 2000 coalbed gas accounted for 8 8 of the reserves 15 7 tcf 0 44 tm3 and 9 2 of the annual pro duction 1 38 tcf 40 gm3 of dry gas in the united states from 1989 through 2000 cumulative united states coalbed gas produc tion was 9 63 tcf 272 gm3 today coalbed gas development has spread to about a dozen basins in the united states and exploration is progressing worldwide coal beds are self sourcing reservoirs that can contain ther mogenic migrated thermogenic biogenic or mixed gas coalbed gas is stored primarily within micropores of the coal matrix in an adsorbed state and secondarily in micropores and fractures as free gas or solution gas in water the key parameters that control gas resources and producibility are thermal maturity maceral compo sition gas content coal thickness fracture density in situ stress permeability burial history and hydrologic setting these param eters vary greatly in the producing fields of the united states and the world in 2000 the san juan basin accounted for more than 80 of the united states coalbed gas production this basin contains a gi ant coalbed gas play the fruitland fairway which has produced more than 7 tcf 0 2 tm3 of gas the fruitland coalbed gas system and its key elements contrast with the fort union coalbed gas play in the powder river basin the fort union coalbed play is one of the fastest developing gas plays in the united states its production escalated from 14 bcf 0 4 gm3 in 1997 to 147 3 bcf 4 1 gm3 in 2000 when it accounted for 10 7 of the united states coalbed gas production by 2001 annual production was 244 7 bcf 6 9 gm3 differences between the fruitland and fort union petroleum systems make them ideal for elucidating the key elements of contrasting coalbed gas petroleum systems

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

climatic change and caco3 preservation an 800 000 year bathymetric reconstruction from the central equatorial pacific ocean sixteen deep sea cores from the central equatorial pacific are used to reconstruct a continuous 800 000 year 800 kyr record of bathymetric variations in carbonate preservation as measured by calcium carbonate caco3 content the depth of the sedimentary lysocline has fluctuated markedly in conjunction with late pleistocene climate cycles while the carbonate critical depth ccrd which is the water depth where the sediments contain 10 caco3 has remained relatively constant as a result the depth of the lysocline controls the bathymetric position and thickness of the caco3 transition zone defined as the depth from the lysocline to the ccrd modern and interglacial aged sediments show poor caco3 preservation and thick caco3 transition zones glacial aged sediments show good preservation and deep thin zones due to the deepening of the lysocline detailed comparison of the caco3 preservation and oxygen isotope records from the central equatorial pacific confirms the observation that preservation maxima and minima tend to occur during the latter half of glacial and interglacial stages and on climate transitions rather than during the middle of climatic stages during the nine major glacial stages of the last 800 kyr the lysocline deepened by at least 400 to 800 m this deepening indicates an increase in the abyssal carbonate ion concentration co3 and a depression of the calcite saturation horizon best explained by the deeper presence of a more carbonate saturated water mass the bottom of the transition zone has remained at a relatively constant depth during the brunhes chron indicating a balance between caco3 sedimentation and dissolution in the deepest waters of the central equatorial pacific

changes in opal flux and the rain ratio during the last 50 000 years in the equatorial pacific abstract changes in the orgc caco3 ratio in particles sinking from the surface to the deep ocean have the potential to alter the atmospheric pco2 over the span of a glacial interglacial cycle recent paleoceanographic and modern observational studies suggest that silica is a key factor in the global carbon biogeochemical cycle that can influence the flux ratio especially at low latitudes through silicic acid leakage brzezinski m pride c franck m sigman d sarmiento j matsumoto k gruber n rau r coale k 2002 a switch from si oh 4 to no 3 depletion in the glacial southern ocean geophysical research letters 29 5 to test this hypothesis we reconstruct biogenic fluxes of caco3 orgc and si for three equatorial pacific cores we find evidence that a floral shift from a sio2 based community to a caco3 based occurred starting in mid marine isotope stage mis 3 24 59 cal ka and declining toward mis 2 19 24 cal ka this could reflect the connection of the peru upwelling system to the subantarctic region and we postulate that excess silica was transported from the subantarctic via the deep equatorial undercurrent to the eastern equatorial pacific in the eastern equatorial pacific only we document a significant decrease in rain ratio starting mid mis 3 toward mis 2 this decrease is concomitant with a significant decrease in silica accumulation rates at the seabed this pattern is not observed in the pacific influenced by equatorial divergence and shallow upwelling where all reconstructed fluxes caco3 orgc and opal increase during mis 2 we conclude that the overall calcium carbonate pump weakened in the eep under peru upwelling influence

transpressive duplex and flower structure dent fault system nw england abstract revised mapping along the dent fault northwest england has improved the resolution of folds and faults formed during variscan late carboniferous sinistral transpression a nne trending east down monocline comprising the fell end syncline and taythes anticline was forced in carboniferous cover above a reactivated precursor to the dent fault within the lower palaeozoic basement the taythes anticline is periclinal due to interference with earlier acadian folds the steep limb of the monocline was eventually cut by the west dipping dent fault the hangingwall of the dent fault was dissected by sub vertical or east dipping faults together forming a positive flower structure in cross section and a contractional duplex in plan view the footwall to the dent fault preserves evidence of mostly dip slip displacements whereas strike slip was preferentially partitioned into the hangingwall faults this pattern of displacement partitioning may be typical of transpressive structures in general the faults of the taythes duplex formed in a restraining overlap zone between the dent fault and the rawthey fault to the west the orientations of the duplex faults were a response to kinematic boundary conditions rather than to the regional stress field directly kinematic constraints provided by the dent and neighbouring variscan faults yield a nnw sse regional shortening direction in this part of the variscan foreland

regional evaluation of the coalbed methane potential of the foothills mountains of alberta canada abstract coal is present in the alberta foothills mountains in five zones the kootenay gething gates brazeau and coalspur coal zones for coalbed methane cbm evaluation purposes they can be divided into shallow less than 1000 m depth and deep greater than 1000 m depth coal zones the potential gas content of all shallow coal zones totals about 878 10 9 m 3 31 tcf of cbm which is considered an inferred initial in place coalbed methane resource estimate based on limited data the limited amount of data on formation testing and measured gas content indicate that the inferred resource is bordering on the speculative category the gas content of all deep coal zones deeper than 1000 m totals 2 8 10 12 m 3 about 99 tcf of in place coalbed methane gas consequently the total ultimate coalbed methane resource could be 3 7 10 12 m 3 130 tcf however coalbed methane recovery from deep coals is generally not attempted because of the high cost of drilling and the low permeability that results from high overburden load and stress the only limited foothills coalbed methane production has been from the southern alberta kootenay coal zone which is very prospective for coalbed methane production the shallow gates coal zone in the central and northern foothills is also prospective but needs to be better tested the best potential for coalbed methane in the coalspur coal zone is in the edson area entrance syncline and triangle zone the kootenay and gates coal zones are not well defined in the northern part of the calgary nts 82o map sheet

millennial scale variations in hydrography and biogeochemistry in the eastern equatorial pacific over the last 100 kyr abstract in this study we use records of nitrogen isotope ratios 15n uk 37 temperature estimates organic carbon and opal percentages from high resolution sediment cores located in the eastern equatorial pacific eep to explore the mechanisms linking millennial scale changes in low latitude sea surface temperature water column denitrification and surface productivity to the timing of northern or southern polar climate during the last 100 000 yr our results support a hypothesis that the southern hemisphere and its connection to the low latitudes via shallow subsurface ocean circulation has a primary influence on the biogeochemistry of the eep in addition our results suggest that during the last glacial stage denitrification rates fluctuated on millennial timescales in response to water column ventilation rather than upstream oxidant demand in intermediate depth waters however due to the poor age constraints available for marine isotopic stage mis 3 the eep sedimentary data presented here could support two conflicting mechanisms one driven by enhanced intermediate overturning circulation in the southern ocean during heinrich events antarctic warm events implying that subsurface flow rates control thermocline ventilation and a second one consistent with more sluggish intermediate circulation during antarctic warm events and giving a central role to the temperature control on oxygen solubility in southern ocean surface waters

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

caco3 dissolution in california continental margin sediments the influence of organic matter remineralization in situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of caco3 on the continental rise adjacent to central california usa the porewater distributions and benthic fluxes of o2 no3 ta ca2 13c and tic are interpreted using a numerical simulation of organic matter remineralization and caco3 dissolution in marine sediments the processes considered in the simulation include organic matter oxidation by o2 no3 and so42 caco3 dissolution and precipitation hs and nh4 oxidation and sediment mixing and sediment accumulation calculated benthic fluxes of o2 no3 ta tic 13c and ca2 porewater concentrations of o2 no3 and nh4 and sediment distributions of organic carbon caco3 excess 210pb and 14c agree well with the measurements benthic fluxes of alkalinity and inferred caco3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation if the influence of metabolically produced co2 is included benthic fluxes are fully reconciled however this is in agreement with benthic chamber ca2 and 13c results that independently imply substantial caco3 dissolution in these sediments the above observations are in contrast to those reported by jahnke et al 1994 for the west african continental rise and the western equatorial pacific where 1 g diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers we conclude that the extent of metabolic caco3 dissolution may vary regionally numerous factors such as the depth of metabolic co2 production and caco3 dissolution kinetics are known or predicted to influence metabolic dissolution among the factors that should be considered in reconciling these observations are l the extent to which sulfate reduction and reoxidation reactions may influence acid base properties in surface sediments and 2 the total sedimentary caco3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

deep sea carbonate preservation in the western philippine sea over the past 1ma abstract in this paper we present a continuous record of calcium carbonate caco 3 content that covers the last 1 ma from core md06 3050 15 57 0943 n 124 46 7747 e water depth 2967 m which was collected in the western philippine sea wps the caco 3 content in this study core is characterized by maxima during deglaciations and minima during the onsets of glacial periods and generally shows pacific style patterns with relatively high and low values during glacial and interglacial periods respectively proxies of dissolution and primary productivity pp the caco 3 content and the oxygen isotope record from this core are compared throughout the 1 ma study interval to improve our understanding of the mechanisms that affected carbonate preservation and dissolution at this site the planktonic foraminifera shell fragmentation ratio shell fragment is used as a dissolution proxy in this study the shell fragment data from md06 3050 provide evidence of preservation maxima during most of the deglaciations whereas intense dissolution is recorded at the onsets of glacial periods within the past 1 ma the variations in shell fragments are similar to those seen in the caco 3 content which demonstrates that the bulk caco 3 content patterns were controlled by dissolution in deep seawater the primary productivity from the coccolith record shows limited similarity with the caco 3 content on glacial interglacial time scales since 1 ma which suggests that pp played a negligible role in the glacial interglacial caco 3 cycle however a bloom of the coccolithophores geophyrocapsa caribbeanica that extended from mis 9 to mis 12 likely contributed to the increased caco 3 content observed during the mid brunhes interval mbe over the glacial interglacial fluctuations therefore the caco 3 content should be used as a dissolution proxy with caution during the mbe in the tropical pacific especially for water depths that are shallower than the carbonate lysocline

oblique cleavage folds a critical discussion with examples from the canadian appalachians abstract examples of transected folds from three localities in notre dame bay north central newfoundland are described and analyzed the oblique relationship of cleavage and folds is the result of overprinting of the folds by the cleavage in two of the three localities and the result of overprinting of the cleavage by the folds in the third locality thus it is argued that transected folds need not form synchronously with the oblique cleavage an axial plane cleavage associated with the folds may be completely obliterated by the oblique cleavage or may never have existed the term oblique cleavage folds is introduced as a geometric term to describe folds with a cleavage oblique to their hinges transected fold models are generally based on the orientation of cleavage and folds with respect to the strain ellipsoids on the scale of the deforming zones or on the scale of layers of variable competence here we follow a different approach transected fold models and the geometry of oblique cleavage folds are discussed in terms of the progressive development of the folds and cleavage we assume no special relationships to strain oblique cleavage folds are most commonly reported from shear zones where the strain path is non coaxial and the deformation is progressive such zones produce overprinting relationships even where only one deformation event is involved and commonly have a long history of reactivation we suggest that the significance of this correlation is that transected folds are generally and perhaps always a product of overprinting the age of folds and cleavage however may be very similar and both may be a product of the same protracted deformation event thus in studying oblique cleavage folds the possibility that the cleavage is pre syn or post folding should be considered even where there is only one recognisable generation of both folds and cleavage

late quaternary caco3 stratigraphy of the eastern equatorial pacific four patterns of caco3 abundance occur in cores retrieved from the eastern equatorial pacific during the venture 01 expedition core locations lie along a north south transect at 110 w underneath the different currents of the equatorial current system and along an east west transect from 110 to 90 w at approximately 3 s underneath the south equatorial current the classic or central equatorial pacific pattern of caco3 abundance maxima associated with glacial stages as defined by the 18o record characterizes only a small portion of the area studied in the area where the peru current turns west to join the south equatorial current the carbonate record is characterized by a broad low centered on interglacial carbonate stage b 3 approximately stage 5 in 18o stratigraphy overlying a broad mid brunhes maximum low amplitude variations in caco3 percentages are superimposed on this pattern this pattern extends westward in a long wavelength pattern in which the b 3 carbonate low becomes decreasingly pronounced away from the equator the fourth pattern observed north of 10 n is erratic and may be only local in extent

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

230th normalization an essential tool for interpreting sedimentary fluxes during the late quaternary there is increasing evidence indicating that syndepositional redistribution of sediment on the seafloor by bottom currents is common and can significantly affect sediment mass accumulation rates notwithstanding its common incidence this process generally referred to as sediment focusing is often difficult to recognize if redistribution is near synchronous to deposition the stratigraphy of the sediment is not disturbed and sediment focusing can easily be overlooked ignoring it however can lead to serious misinterpretations of sedimentary fluxes particularly when past changes in export flux from the overlying water are inferred in many instances this problem can be resolved at least for sediments deposited during the late quaternary by normalizing to the flux of 230th scavenged from seawater which is nearly constant and equivalent to the known rate of production of 230th from the decay of dissolved 234u we review the principle advantages and limitations of this method notwithstanding its limitations it is clear that 230th normalization does provide a means of achieving more accurate interpretations of sedimentary fluxes and eliminates the risk of serious misinterpretations of sediment mass accumulation rates

do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific 1 the paleoceanographic recording fidelity of pelagic sediments is limited by chemical diagenesis and physical mixing bioturbation and horizontal sediment transport diagenesis and bioturbation are relatively well studied but the effects of physical sedimentation have been largely ignored modeling u series isotopes e g 230th can potentially quantify horizontal sediment movement but model horizontal sediment focusing often equals or exceeds the vertical particle rain we find no evidence of this level of sediment focusing in the equatorial pacific from geophysical data or sediment core comparisons the overestimate of sediment focusing by 230th is probably caused by poor model assumptions that sediment does not fractionate does not sort according to size during transport and that 230th cannot leak from slowly accumulating sediments both assumptions are weak u series methods do hold promise to quantify sediment focusing if properly calibrated with calibration the trade offs between seeking high sedimentation rates for better time resolution and the blurring by horizontal sediment focusing can be better assessed

diachronous benthic δ18o responses during late pleistocene terminations 1 benthic 18o is often used as a stratigraphic tool to place marine records on a common age model and as a proxy for the timing of ice volume sea level change however skinner and shackleton 2005 found that the timing of benthic 18o change at the last termination differed by 3900 years between one atlantic site and one pacific site these results suggest that benthic 18o change may not always accurately record the timing of deglaciation we compare benthic 18o records from 20 atlantic sites and 14 pacific sites to evaluate systematic differences in the timing of terminations in benthic 18o analysis of sedimentation rates derived from the alignment of benthic 18o suggests a statistically significant atlantic lead over pacific benthic 18o change during the last six terminations we estimate an average pacific benthic 18o lag of 1600 years for terminations 1 5 slightly larger than the delay expected from ocean mixing rates given that most glacial meltwater probably enters the north atlantic we additionally find evidence of 4000 year pacific 18o lags at approximately 128 ka and 330 ka suggesting that stratigraphic correlation of 18o has the potential to generate age model errors of several thousand years during terminations a simple model demonstrates that these lags can be generated by diachronous temperature changes and do not require slower circulation rates most importantly diachronous benthic 18o responses must be taken into account when comparing atlantic and pacific benthic 18o records or when using benthic 18o records as a proxy for the timing of ice volume change

a deeper respired carbon pool in the glacial equatorial pacific ocean article i nfo atmospheric pco2 was approximately 80 ppm lower during the last glacial period than during pre industrial times identifying the fate of that carbon has been one of the great challenges in paleoceanography we present evidence from ten equatorial pacific ocean sediment cores to show that the deep pacific ocean likely stored more carbon during the last glacial period than the holocene the concentration of the redox sensitive metal uranium u in sediments was systematically greater during the last glacial period than during the holocene indicating more reducing conditions in glacial age sediments reconstructions of biogenic opal flux indicate that changes in u distribution were not the result of changes in biological productivity and the ensuing rain of organic carbon to the sea floor which also affects the redox conditions of the sediments together these results lead to the interpretation that bottom water in the equatorial pacific during the glacial period had significantly lower oxygen concentration than during the holocene and a correspondingly greater level of respired co2 this conclusion is supported by evidence for greater preservation of brassicasterol a biomarker produced by diatoms in glacial age sediments of the eastern equatorial pacific the presence of additional respired co2 in the glacial deep ocean would have lowered atmospheric pco2 by 1 increasing the total storage of co2 in the glacial ocean and 2 increasing ocean alkalinity following a transient carbonate dissolution event our results are consistent with recently published data from the north pacific ocean this suggests that increased carbon storage in the glacial deep pacific ocean was a basin wide phenomenon consistent with a large scale transfer of carbon to the deep ocean during glacial periods

inertial wind path and sea surface temperature patterns near the gulf of tehuantepec and gulf of papagayo during the northern hemisphere winter the surface atmospheric pressure on the gulf of mexico side of central america is often higher than that on the pacific side the resultant southward pressure gradient drives strong southward winds through a gap in the sierra madre mountain range at the isthmus of tehuantepec the atmospheric jet is narrow in comparison with the relevant radius of deformation so when it leaves the coast and flows out over the gulf of tehuantepec it is an inertial jet therefore the jet is expected to be deflected into a clockwise inertial circle by the coriolis force a similar process should also occur for central american atmospheric jets through mountain range gaps near the gulf of papagayo satellite measurements of sea surface temperature together with coastal wind data for the first 41 days of 1986 were examined to see if the expected wind path influenced sea surface temperature sst near the gulf of tehuantepec and the gulf of papagayo consecutive daily satellite images when the coastal southward tehuantepec wind increased suggest that the initial development of cold surface water in a clockwise loop is due to the wind mixing the shallow thermocline surface water along its inertial path a simple 1 layer analytical ocean model suggests in agreement with observations that the wind can drive surface quasi geostrophic currents of 1 m s 1 since the wind path is circular the wind actually generates a clockwise rotating ocean eddy with the approximate scale of the wind inertial circle the satellite sea surface temperature measurements also suggest that the wind driven surface ocean current is unstable in addition stronger gradients in sst to the right of the expected wind flow are consistent with advection of sea surface temperature by ocean surface ekman flow

inversion tectonics of the variscan foreland of the british isles late westphalian inversion structures on the variscan foreland display wide variations in orientation that are the product of the underlying basement grain the orientation of the major basement lineaments in relation to the direction of maximum shortening also determined the severity of deformation of the inverted basins ne sw trending faults were oriented roughly perpendicular to the nw se to nnw sse direction of maximum shortening determined from thrust transport directions in the variscan orogen to the south as a consequence ne sw trending basins in the variscan foreland have been strongly inverted the silesian post rift fill has commonly been expelled from the basins and the syn rift sediments have been deformed by chevron folds dublin and bowland basins in contrast the n s and nw se trending faults were oriented more obliquely to the direction of maximum shortening and as a consequence display a significant component of oblique slip this oblique slip component is manifested as en echelon periclines and flower structures in general the n s and nw se trending basins were less strongly inverted and the silesian post rift fill has been retained

the structure and evolution of the northumberland trough from new seismic reflection data and its bearing on modes of continental extension an 18 km long n s seismic reflection profile has been acquired across the faulted boundary between the alston block and the northumberland trough a nw se geological cross section has been constructed across the trough by integrating this line with other data and a tricentrol seismic profile confirms the suitability of this model the trough has a markedly asymmetric form with a thickness of more than 4 2 km of dinantian strata adjacent to its faulted southern margin the present day surface faults stublick ninety fathom are related to variscan and later inversion and transpression and do not everywhere correspond precisely to the earlier syn depositional normal faults the basin is believed to have formed in response to reactivation of the iapetus suture in a dominantly n s extensional stress field basin evolution has been analysed by fault restorations and subsidence modelling the fault restorations indicate an upper crustal extension factor of 1 15 to 1 19 subsidence modelling indicates a whole crustal extension factor of 1 30 with similar sub crustal lithospheric extension it is possible that the difference between the inferred extension factors is due to non uniform increasing downwards lithospheric extension but the uncertainties inherent in both methods are such that this cannot yet be confirmed

stream and slope weathering effects on organic rich mudstone geochemistry and implications for hydrocarbon source rock assessment a bowland shale case study abstract this study contributes to the exploration and quantification of the weathering of organic rich mudstones under temperate climatic conditions bowland shales exposed by a stream and slope were sampled in order to develop a model for the effects of weathering on the mudstone geochemistry including major and trace element geochemistry rock eval pyrolysis and 13 c org four weathering grades i iv are defined using a visual classification scheme visually fresh and unaltered i chemically altered ii iii and paper shale that typifies weathered mudstone on slopes iv bedload abrasion in the stream exposes of visually fresh and geochemically unaltered mudstone natural fractures are conduits for oxidising meteoric waters that promote leaching at the millimetre scale and or precipitation of iron oxide coatings along fracture surfaces on the slope bedding parallel fractures formed and may continue to form in response to chemical and or physical weathering processes these fractures develop along planes of weakness typically along laminae comprising detrital grains and exhibit millimetre and centimetre scale leached layers and iron oxide coatings fracture surfaces are progressively exposed to physical weathering processes towards the outcrop surface and results in disintegration of the altered material along fracture surfaces grade iv paper shale mudstone is chemically unaltered but represents a biased record driven by initial heterogeneity in the sedimentary fabric chemically weathered outcrop samples exhibit lower concentrations of both free s1 up to 0 6 mghc g rock and bound s2 up to 3 2 mghc g rock hydrocarbon reduced total organic carbon content up to 0 34 wt reduced hydrogen index up to 58 mghc gtoc increased oxygen index up to 19 mgco co 2 gtoc and increased t max up to 11 c compared with unaltered samples if analysis of chemically weathered samples is unavoidable back extrapolation of rock eval parameters can assist in the estimation of pre weathering organic compositions combining cs cu with oxygen index is a proxy for identifying the weathering progression from fresh material i to paper shale iv this study demonstrates that outcrop samples in temperate climates can provide information for assessing hydrocarbon potential of organic rich mudstones

changes in the hydrological cycle ocean circulation and carbon nutrient cycling during the last interglacial and glacial transition 1 a complex earth system model has been forced by insolation changes for the last interglacial lig for which geological records evidence a climate cooling that culminated in the last glacial inception during an early warm period 127 125 ka b p the arctic north atlantic drainage basin north of 30 n receives 27 000 m3 s more fresh water mainly imported across the watershed of north america compared to a cooler period centered around 115 ka b p together with a strong surface warming by up to 2 k this results in a weaker north atlantic overturning reduced by 20 sea ice cover is reduced by 3 106 km2 in the northern hemisphere stimulating a stronger productivity in the barents and kara seas in the north pacific a lowered salinity and a surface warming of more than 3 k increase the stratification the eastern pacific becomes nutrient poorer which leads to a reduction in the export production in areas with vigorous upwelling the climate cooling in the course of the lig induces a carbon release by the terrestrial biosphere of 308 gt which is counteracted by an oceanic sedimentary uptake of 290 gt the rest remains in the atmosphere increasing the pco2 by 9 ppm the large oceanic co2 uptake corresponds to a rise of the calcite lysocline of about 300 m in the midlatitude atlantic the chemically interactive carbonate sediment pool in the atlantic is reduced by 10 for nearly the entire north atlantic our results are contradictory to the common interpretation of carbonate preservation proxies as a reliable tool for monitoring changes in deep water circulation

from marine bands to hybrid flows sedimentology of a mississippian black shale this study was funded by the natural environment research council nerc grant no ne l002493 1 within the central england training alliance centa consortium the study received case funding from the british geological survey nick riley carboniferous limited is thanked for sharing his expertise and assistance charlotte watts is thanked for providing field assistance nick marsh tom knott cheryl haidon and annika burns are thanked for offering expertise and laboratory assistance pete sadler university of california is thanked for compilation and provision of the background sediment accumulation rate dataset we thank all reviewers editor peir pufahl and elaine richardson editorial office for their valuable comments and advice which have significantly improved this manuscript

timing of late quaternary productivity pulses in the panama basin and implications for atmospheric co2 high resolution percent corg and 18oforam records obtained from panama basin core atlantis ii 54 25pc and additional data from nearby core p7 show that enhanced burial of organic carbon has characterized every major glacial period for the last 500 kyr in that area both corg concentration and mass accumulation rate profiles exhibit a sawtooth pattern with maxima occurring typically in the later stages of glacial periods comparison with dust records suggests that the carbon accumulation rate profile reflects both the upwelling history and a variable rate of iron input during the late quaternary the sawtooth character may derive from increased wind velocities and rates of upwelling during glacials which are indirectly related to ice volume sarnthein et al 1988 the rapid decline in export production at the end of glacials in the equatorial pacific may be attributed to the retreat of ice sheets thus reduced wind velocities and upwelling coupled with a coincident decline in atmospheric dust load and or delivery rate the corg accumulation rate profiles do not correlate well with atmospheric co2 records for example atmospheric co2 was already at a minimum 40 kyr ago when production in the panama basin began increasing dramatically commensurate with an increase in global dust levels using the relationship between the degree of photosynthetic fractionation and the concentration of free co2 in the surface ocean postulated by popp et al 1989 13corg measurements made on core p7 show that panama basin surface waters have been supplying co2 to the atmosphere continually for at least the last 50 kyr there is no evidence for a flux of co2 into the surface ocean in this area at any time during this period despite the higher production if the panama basin cores are representative of the eastern and central equatorial pacific then these observations weaken the influence on co2 drawdown postulated for increased glacial productivity at low latitudes

the micropaleontological character of anomalous calcareous sediments of late pliocene through early pleistocene age below the ccd in the northwestern north pacific ocean calcium carbonate was preserved more than 1 km below the modern calcite compensation depth ccd at odp site 1179 over several short intervals around 2 5 2 4 1 65 and 0 9 0 7 ma this anomalous preservation resulted from a combination of increased production of planktonic foraminiferal tests at the sea surface and increased rate of sedimentation to the sea floor the abundance of dinoflagellate cysts in calcareous sediments records intense plankton blooms and the preservation of oxidationsusceptible round brown brigantedinium cysts in foraminifer rich samples supports the theory of rapid burial the rise in seasurface productivity was driven by enhanced flux of continentally derived limiting nutrients consistent with the pollen evidence of continental aridification cooling and an increase in wind strength the abundant pollen dominated by steppe herb and montane boreal conifer taxa contrasts with lower pollen concentrations dominated by temperate subtropical deciduous tree and taxodium type pollen in non calcareous sediments d 2004 elsevier b v all rights reserved

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

invariance of the carbonate chemistry of the south china sea from the glacial period to the holocene and its implications to the pacific ocean carbonate system abstract substantial and correlated changes in marine carbonate caco3 content of oceanic sediments commonly accompany the transitions from cold glacial periods to warm interglacial periods the south china sea scs is said to be ocean dominated at depth and its caco3 records should reflect and preserve the effects of changes in the carbonate chemistry of the western pacific ocean using published and newly acquired caco3 data and a model for carbonate compensation dynamics we show that a significant change with respect to carbonate saturation is unlikely to have occurred in the scs during the last glacial interglacial transition instead the results from a carbonate deposition model argue that the saturation state of the scs was largely invariant a separate diagenetic model argues that changes in sediment caco3 content can be explained by alterations in lithogenic input in turn this could indicate that the carbonate ion concentration of the western pacific at depths shallower than the sill to the scs ca 2 400 m has not changed appreciably between the last glacial period and the present interglacial

is the core top modern observations from the eastern equatorial pacific abstract a compilation of ages from 67 core tops in the eastern equatorial pacific eep does not display an easily discernible regional pattern the ages range from 790 to over 15 000 years the youngest core tops with the highest sediment focusing factors are located in the panama basin there are weak but statistically significant inverse relationships between core top age and age model based mass accumulation rates bioturbation depth linear sedimentation rate and sediment focusing factors however we found no statistically significant relationship between core top age and calcite dissolution in sediments or 230th normalized mass accumulation rates we found evidence suggesting that greater amount of sediment focusing helps to preserve the carbonate fraction of the sediment where focusing is taking place when focusing factors are plotted against percent calcite dissolved we observe a strong inverse relationship and core tops younger than 4500 years tend to occur where focusing factors are high and percent calcite dissolved values are low using labile organic carbon fluxes to estimate bioturbation depth in the sediments results in the observation that where bioturbation depth is shallow

some reconciliation of glacial interglacial calcite flux reconstructions for the eastern equatorial pacific 1 carbonate production in the open ocean plays a significant role in fixing upper water column pco2 and carbonate flux from the surface transfers alkalinity to the deep sea a key region for this is in the eastern equatorial pacific eep reconstructions of calcite accumulation rates with traditional methods mass accumulation rate mar have been used to infer a large last glacial maximum lgm increase in fluxes for the eep the opposite result has been obtained using thorium normalization th norm of accumulation rates new 14c dating combined with detailed correlation among eep cores based on planktonic and benthic stable isotope records emphasizes the sensitivity of the mar approach to the age model and brings some reconciliation to the methodologies the new results lead to lgm mar based accumulation rates that are less than previously estimated and to lower lgm paleofluxes both the mar and thorium normalized methods show a flux maximum during the deglacial with the new age model although the signals show some convergence the magnitudes of mar accumulation rates appear to be between about 2 and 4 times those from th normalization for the lgm at the sites examined thus sediment focusing inferred from th normalization remains significant for the eep

ocean and atmosphere teleconnections modulate east tropical pacific productivity at late to middle pleistocene terminations the modern eastern equatorial pacific eep is a key oceanographic region for regulating the earth s climate system accounting for between 5 10 of global marine production whilst also representing a major source of carbon dioxide efflux to the atmosphere changes in ocean dynamics linked to the nutrient supply from the southern ocean have been suggested to have played a dominant role in regulating eep productivity over glacial interglacial timescales of the past 500 ka yet the full extent of the climate and oceanic teleconnections and the mechanisms promoting the observed increase of productivity occurring at glacial terminations remain poorly understood here we present multi proxy micropaleontological geochemical and sedimentological records from the easternmost eep to infer changes in atmospheric patterns and oceanic processes potentially influencing regional primary productivity over glacial interglacial cycles of the mid late pleistocene 0 650 ka these proxy data support a leading role for the north south migration of the intertropical convergence zone itcz in shaping past productivity variability in the eep productivity increases during glacial periods and notably peaks at major and extra glacial terminations those occurring 1 2 precession cycles after some major terminations coincident with the inferred southernmost position of the itcz the comparison of our reconstructions with proxy records of climate variability suggests the intensification of related extratropical atmospheric and oceanic teleconnections during deglaciation events these processes may have re activated the supply of southern sourced nutrients to the eep potentially contributing to enhanced productivity in the eep and thus counterbalancing the oceanic carbon dioxide outgassing at glacial terminations

export fluxes of calcite in the eastern equatorial pacific from the last glacial maximum to present 1 the eastern equatorial pacific eep is an important center of biological productivity generating significant organic carbon and calcite fluxes to the deep ocean we reconstructed paleocalcite flux for the past 30 000 years in four cores collected beneath the equatorial upwelling and the south equatorial current sec by measuring ex230th normalized calcite accumulation rates corrected for dissolution with a newly developed proxy for fraction of calcite preserved this method produced very similar results at the four sites and revealed that the export flux of calcite was 30 50 lower during the lgm compared to the holocene the internal consistency of these results supports our interpretation which is also in agreement with emerging data indicating lower glacial productivity in the eep possibly as a result of lower nutrient supply from the southern ocean via the equatorial undercurrent however these findings contradict previous interpretations based on mass accumulation rates mar of biogenic material in the sediment of the eep which have been taken as reflecting higher glacial productivity due to stronger wind driven upwelling

a mississippian black shale record of redox oscillation in the craven basin uk early diagenetic redox oscillation processes have been rarely recognised in the ancient rock record but potentially exert an important control on mineral authigenesis hydrocarbon prospectivity and supply of metals and or reduced s as part of associated mineral systems the upper unit of the mississippian bowland shale formation is a candidate record of diagenetic redox oscillation processes because it was deposited under a relatively high sediment accumulation rate linked to a large delta system and under dominantly anoxic and intermittently sulphidic bottom water conditions in order to characterise the syngenetic and early diagenetic processes sedimentological and geochemical data were integrated through the upper bowland shale at three sites in the craven basin lancashire uk organic matter om comprises a mixture of type ii ii s ii iii and iii om redox zones are defined by patterns of fe speciation and redox sensitive trace element enrichment and split into two groups sulphidic zones eux an iii an i and an it represent sediments deposited under conditions of at least intermittently active sulphate reduction in bottom waters non sulphidic zones ox rx ox f and ox represent sediments deposited under non sulphidic oxic to ferruginous anoxic bottom waters operation of a shelf to basin reactive fe fehr shuttle moderated by sea level fluctuation and delta proximity controlled the position and stability of redoxclines between zones of fe and sulphate reduction and methanogenesis early diagenetic redoxclines were capable of migration through the shallow sediment column relatively quickly in response to sea level fluctuation preservation of syngenetic and early diagenetic geochemical signals shows redoxclines between fe and sulphate reduction and the upper boundary of sulphate methane transition zone were positioned within decimetres i e 10 s cm of seabed falling sea level and increasing fehr supply is recognised as a switch from zones eux high sea level an iii and ultimately an i and an it low sea level zone an i defines the operation of redox oscillation between zones of fe and sulphate reduction in shallow porewaters associated with enhanced degradation of om and complete dissolution of primary carbonate preservation of om and carbonate in this system was a function of changing bottom and pore water redox processes redox oscillation operated in a siliciclastic prodeltaic environment associated with a relatively high sediment accumulation rate and high loadings of labile organic matter and metal oxides these findings are important for understanding late palaeozoic black shales in the context of hydrocarbon and mineral systems

patterns of caco3 deposition in the eastern tropical pacific ocean for the last 150 kyr evidence for a southeast pacific depositional spike during marine isotope stage mis 2 1 we constructed biogenic mass accumulation rate mar time series for eastern pacific core transects across the equator at 105 and 85 w and along the equator from 80 to 140 w we used empirical orthogonal function eof analysis to extract spatially coherent patterns of caco3 deposition for the last 150 kyr eof mode 1 51 variance is a caco3 mar spike centered in marine oxygen isotope stage 2 mis 2 found under the south equatorial current eof mode 2 19 of variance is high north of the equator eof mode 3 9 of variance is an east west mode centered along the north equatorial counter current the mis 2 caco3 spike is the largest event in the eastern pacific for the last 150 kyr caco3 mars are 2 3 times higher at 18 ka than elsewhere in the record including mis 6 it is caused by high caco3 production rather than minimal dissolution eof 2 while it resembles deep water flow patterns nevertheless shows coherence to corg deposition and is probably also driven by caco3 production index terms 4267 oceanography general paleoceanography 1615 global change biogeochemical processes 4805 1030 geochemistry geochemical cycles 0330 3022 marine geology and geophysics marine sediments processes and transport keywords late pleistocene paleoproductivity pacific calcite biogeochemistry carbon cycle

interpreting complex fluvial channel and barform architecture carboniferous central pennine province northern england the bashkirian lower brimham grit of north yorkshire england is a fluvio deltaic sandstone succession that crops out as a complex series of pinnacles the three dimensional arrangement of which allows high resolution architectural analysis of genetically related lithofacies assemblages combined analysis of sedimentary graphic log profiles architectural panels and palaeocurrent data have enabled three dimensional geometrical relationships to be established for a suite of architectural elements so as to develop a comprehensive depositional model small scale observations of facies have been related to larger scale architectural elements to facilitate interpretation of the palaeoenvironment of deposition to a level of detail that has rarely been attempted previously thereby allowing interpretation of formative processes detailed architectural panels form the basis of a semi quantitative technique for recording the variety and complexity of the sedimentary lithofacies present their association within recognizable architectural elements and thus the inferred spatio temporal relationship of neighbouring elements fluvial channel fill elements bounded by erosional surfaces are characterized internally by a hierarchy of sets and cosets with subtly varying compositions textures and structures simple cross bedded sets represent in channel migration of isolated mesoforms dunes cosets of both trough and planar tabular cross bedded facies represent lateral accreting and downstream accreting macroforms bars characterized by highly variable yet predictable patterns of palaeocurrent indicators relationships between sandstone dominated strata bounded by third order and fifth order surfaces which represent in channel bar deposits and incised channel bases respectively chronicle the origin of the preserved succession in response to autocyclic barform development and abandonment major episodes of incision probably influenced by episodic tectonic subsidence differential tilting and fluvial incision associated with slip on the nearby north craven fault system overall the succession represents the preserved product of an upper delta plain system that was traversed by a migratory fluvial braid belt system comprising a poorly confined network of fluvial channels developed between major sandy barforms that evolved via combined lateral accretion and downstream accretion

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

reply to comment by r francois et al on do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific further explorations of 230th normalization

palaeo stress fields in the variscan foreland during the carboniferous from microstructural analysis in the british isles abstract north of the variscan front the carboniferous series of the british isles is affected by mainly n s trending folds which are almost perpendicular to this e w oriented front flat and unconformable overlying permian strata demonstrate a variscan age for the deformation a microtectonic survey made in dinantian and to a lesser extent namurian calcareous layers has revealed two successive events according to chronological criteria the first event maximum stress e w trending led to the formation of n s folds with local reorientation in the vicinity of major pre existing faults this compression may have been active since the namurian it pre dates a second compressional event orientated n s which is related to the final emplacement of the variscan nappes

comment on do geochemical estimates of sediment focusing pass the sediment test in the equatorial pacific by m lyle et al accurately estimating the vertical flux of material reaching the seafloor from the overlying surface waters is essential for the paleoceanographic reconstruction of a wide variety of oceanic processes two approaches are currently being used one consists of estimating mass accumulation rates mar between dated horizons as the product of linear sedimentation rates sediment dry bulk densities and concentrations one pitfall with this approach is that sediments can be redistributed on the seafloor by bottom currents and their accumulation may not necessarily reflect the true vertical rain rate originating from the overlying water column to address this problem the method of 230th normalization was developed bacon 1984 this method is based on the assumption that the rapid scavenging of 230th produced in the water column by decay of dissolved uranium results in its flux to the seafloor always being close to its known rate of production to the extent that this assumption is correct scavenged 230th can be used as a reference to estimate the settling flux of other sedimentary constituents and to correct for sediment redistribution on the seafloor henderson and anderson 2003 francois et al 2004

a pacific hydrographic section at 88 w water property distribution full depth conductivity temperature depth ctd hydrographic measurements with high horizontal and vertical resolution were made in february april 1993 along a line lying at a nominal longitude of 88 w and extending from southern chile 54 s to guatemala 14 n it crossed five major deep basins southeast pacific chile peru panama and guatemala basins east of the east pacific rise vertical sections of potential temperature salinity potential density oxygen silica phosphate nitrate and nitrite are presented to illustrate the structure of the entire water column some features of interest found in the sections are described and an attempt is made to interpret them in terms of the isopycnal property distributions associated with the large scale ocean circulation these features include various near surface waters observed in the tropical and subtropical regions and the fronts that mark the boundaries of these waters the possible importance of salt fingering to the downward salt transfer from the high salinity subtropical water a shallow thermostad pycnostad developed at 16 18 5 c in the subtropical water low salinity surface water in the subantarctic zone west of southern chile large domains of extremely low oxygen in the subpycnocline layer on both sides of the equator and a secondary nitrite maximum associated with a nitrate minimum in these low oxygen domains high salinity low oxygen high nutrient subpycnocline water that is carried poleward along the eastern boundary by the peru chile undercurrent the subantarctic mode and antarctic intermediate waters middepth isopycnal property extrema observed at the crest of the sala y gomez ridge influences of the north pacific and the north atlantic upon deep waters along the section and the characteristics and sources of the bottom waters in the five deep basins along the section

carbonate preservation history in the peru basin paleoceanographic implications we studied preservation dissolution cycles and paleoproductivity in eight sediment cores from the peru basin south of the highly productive surface waters of the eastern equatorial pacific stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy sediment cores which span the last 8 m y were retrieved during cruise 79 with rv sonne close to the carbonate compensation depth ccd in general sediments show pacific type carbonate cycles we interpret a pronounced carbonate peak between 6 and 7 ma as the result of a western and northern extension of the highly productive peru current decreased carbonate contents from the late miocene to the late pliocene might be associated with a slow contraction of the latitudinal extent of the high productivity belt north of the study areas during the pliocene carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets which should have been associated with pulsations of the antarctic ice cap an abrupt collapse of the carbonate system occurred at 2 4 ma higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation during the quaternary carbonate fluxes are high during glacials and low during interglacials large amplitude variations with long broad minima and maxima associated with small migrations of the lysocline and the ccd 200 m are indicative of the preservation dissolution history in the peru basin during the early pleistocene climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record during the last 800 kyr variability in the carbonate record was dominated by the 100 kyr eccentricity cycle fluxes of biogenic material calcium carbonate organic carbon opal and barium were greatest during glacials which imply higher productivity and export production of the peru current during cold climatic periods dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate after the mid brunhes event 400 ka we observe a plateaulike shift to enhanced dissolution and to intensified productivity

paleoposition of the intertropical convergence zone in the eastern pacific inferred from glacial interglacial changes in terrigenous and biogenic magnetic mineral fractions magnetic properties are increasingly used for paleoclimatic and paleoceanographic studies utilizing recently developed proxies an environmental magnetic study was conducted on the uppermost 12 m sediments of integrated ocean drilling program site u1337 in the eastern equatorial pacific ocean this interval is above the fe redox boundary and covers the past 800 k y the site is located near the present southern boundary of the intertropical convergence zone itcz and is thus expected to be sensitive to variations of the itcz position the ratio of anhysteretic remanent magnetization susceptibility to saturation isothermal remanent magnetization k arm sirm first order reversal curve diagrams and irm acquisition curves indicate that the magnetic mineral assemblage consists of a dominant biogenic component and a minor terrigenous component two groups the biogenic soft bs and hard bh are identified for the biogenic component and probably correspond to different magnetofossil morphology the bh component probably carried by elongated magnetofossils increases in sediments of glacial periods which are probably in less oxic conditions due to increased ocean productivity this demonstrates that magnetofossil morphology which can be discriminated by the rock magnetic technique is a sensitive indicator of slight oxic suboxic environmental fluctuations in sediments temporal variations of the terrigenous component most likely transported as eolian dust were estimated from the k arm sirm ratio and s ratio ratio of a moderate field irm to sirm representing relative contribution of lower and higher coercivity magnetic minerals significant glacial interglacial variations occurred at marine isotope stage mis 10 and before but not after in addition coeval upcore increases in sedimentation rates and the bh component were observed suggesting increased productivity these observations may indicate that the position of the itcz was more southward than today ca 250 ka and before

thorium 230 normalized particle flux and sediment focusing in the panama basin region during the last 30 000 years 1 application of the 230 th normalization method to estimate sediment burial fluxes in six cores from the eastern equatorial pacific eep reveals that bulk sediment and organic carbon fluxes display a coherent regional pattern during the holocene that is consistent with modern oceanographic conditions in contrast with estimates of bulk mass accumulation rates mars derived from core chronologies two nearby sites less than 10 km apart which have different mars show nearly identical 230 th normalized bulk fluxes focusing factors derived from the 230 th data at the foot of the carnegie ridge in the panama basin are 2 in the holocene implying that lateral sediment addition is significant in this part of the basin new geochemical data and existing literature provide evidence for a hydrothermal source of sediment in the southern part of the panama basin and for downslope transport from the top of the carnegie ridge the compilation of core records suggests that sediment focusing is spatially and temporally variable in the eep during oxygen isotope stage 2 ois 2 from 13 27 ka bp focusing appears even higher compared to the holocene at most sites similar to earlier findings in the eastern and central equatorial pacific the magnitude of the glacial increase in focusing factors however is strongly dependent on the accuracy of age models we offer two possible explanations for the increase in glacial focusing compared to the holocene the first one is that the apparent increase in lateral sediment redistribution is partly or even largely an artifact of insufficient age control in the eep while the second explanation which assumes that the observed increase is real involves enhanced deep sea tidal current flow during periods of low sea level stand

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

timescales of lateral sediment transport in the panama basin as revealed by radiocarbon ages of alkenones total organic carbon and foraminifera abstract paired radiocarbon measurements on haptophyte biomarkers alkenones and on co occurring tests of planktic foraminifera neogloboquadrina dutertrei and globogerinoides sacculifer from late glacial to holocene sediments at core locations me0005 24jc y69 71p and mc16 from the south western and central panama basin indicate no significant addition of pre aged alkenones by lateral advection the strong temporal correspondence between alkenones foraminifera and total organic carbon toc also implies negligible contributions of aged terrigenous material considering controversial evidence for sediment redistribution in previous studies of these sites our data imply that the laterally supplied material cannot stem from remobilization of substantially aged sediments transport if any requires syn depositional nepheloid layer transport and redistribution of low density or fine grained components within decades of particle formation such rapid and local transport minimizes the potential for temporal decoupling of proxies residing in different grain size fractions and thus facilitates comparison of various proxies for paleoceanographic reconstructions in this study area anomalously old foraminiferal tests from a glacial depth interval of core y69 71p may result from episodic spillover of fast bottom currents across the carnegie ridge transporting foraminiferal sands towards the north

sediment sorting and focusing in the eastern equatorial pacific abstract the interpretation of sedimentary records in terms of glacial interglacial changes in particle flux in the eastern equatorial pacific eep has been controversial here we analyze disaggregated inorganic grain size digs distributions of three marine sediment cores from this region focusing on the last 21 ka to investigate evidence of sediment redistribution on the sea floor grain size sorting coefficients show that sediments in the eep are moderately to well sorted indicating sediment reworking in this region due to bottom currents furthermore a systematic correlation between focusing factors and sorting coefficients at two sites shows that more focused sediments are also better sorted we conclude that grain size based sedimentary records are consistent with the 230 th based evidence of lateral sediment redistribution on the sea floor in the eep

southern ocean control on the extent of denitrification in the southeast pacific over the last 70 ka abstract temporal changes in oceanic denitrification the bacterial reduction of nitrate under suboxic conditions highlight the potential importance of n inventory changes and the production of n 2 o on the climate system at the same time the cause of the globally observed variation in denitrification remains unclear high resolution benthic foraminiferal oxygen isotope and bulk sediment nitrogen isotope records from odp site 1234 on the chile margin record integrated denitrification changes within the peru chile upwelling system over the last 70 ka denitrification changes in the southeast pacific are coherent with antarctic climate changes recorded by the byrd ice core 18 o record and lead northern hemisphere climate events the southern hemisphere character of the chile margin 15 n record suggests that episodes of reduced denitrification in the se pacific represent times when more oxygen was supplied as the result of changes in the ventilation and preformed nutrient content of subantarctic mode water samw which forms in the subantarctic zone of the southern ocean and feeds into the low latitude thermocline

late holocene rupture of the northern san andreas fault and possible stress linkage to the cascadia subduction zone we relate the late holocene northern san andreas fault nsaf paleo seismic history developed using marine sediment cores along the northern california continental margin to a similar dataset of cores collected along the cascadia margin including channels from barclay canyon off vancouver island to just north of mon terey bay stratigraphic correlation and evidence of synchronous triggering imply earthquake origin and both temporal records are compatible with onshore paleoseis mic data in order to make comparisons between the temporal earthquake records from the nsaf and cascadia we refine correlations of southern cascadia great earth quakes including the land paleoseismic record along the nsaf during the last 2800 yr 15 turbidites including one likely from the great 1906 earthquake establish an average repeat time of 200 yr similar to the onshore value of 240 yr the combined land and marine paleoseismic record from the southern cascadia subduction zone includes a similar number of events during the same period while the average recurrence interval for full margin cascadia events is 520 yr the southern cascadia margin has a repeat time of 220 yr similar to that of the nsaf thirteen of the 15 nsaf events were preceded by cascadia events by 0 80 yr averaging 25 45 yr as compared to 80 400 yr by which cascadia events follow the nsaf based on the temporal association we model the coseismic and cumulative post seismic deformation from great cascadia megathrust events and compute related stress changes along the nsaf in order to test the possibility that cascadia earth quakes triggered the penultimate and perhaps other nsaf events the coulomb fail ure stress cfs resulting from viscous deformation related to a cascadia earthquake over 60 yr does not contribute significantly to the total cfs on the nsaf however the coseismic deformation increases cfs on the northern san andreas fault nsaf b y up to about 9 bars offshore of point delgada most likely enough to trigger that fault to fail in north to south propagating ruptures

modeling the particle flux effect on distribution of 230th in the equatorial pacific 1 the normalization of sediment accumulation rates by 230th is increasingly used to constrain particle rain rates because 230th is produced at a known rate in the water column and removed relatively quickly to the sediment several recent contributions have questioned this approach and suggested that the preferential removal of 230th in areas of high particle flux the particle flux effect introduces a systematic bias in the 230th normalization technique we use a circulation model that includes a description of particle scavenging to show that the particle flux effect cannot explain observations of high 230th accumulation in equatorial pacific sediments relative to 230th production in the water column we further consider the possible variation of particle rain rates over time we find only a minimal sensitivity in the particle flux effect due to increases in the particle rain rate at the equatorial pacific by a factor of up to 10 this situation exists because the residence time of 230th in the water column is too short to permit significant lateral transport with reasonable isopycnal mixing coefficients we conclude that the increased rates of 230th accumulation found in equatorial pacific sediments deposited during the last glacial maximum cannot have been caused by the particle flux effect

sediment focusing in the panama basin eastern equatorial pacific ocean abstract age model derived sediment mass accumulation rates mars are consistently higher than 230th normalized mars in the equatorial pacific ocean during the past 25 ka the offset being highest in the panama basin suggests a significant role for deep sea sediment redistribution i e sediment focusing in this region here we test the hypothesis that downslope transport of sediments from topographically high regions that surround the panama basin is the cause of higher than expected xs230th inventories over the past 25 ka in the deeper parts of the basin we find little difference in xs230th inventories between the highest and lowest reaches of the basin furthermore there is no correlation between xs230th derived sediment focusing factors and water depth which suggests that the topographic highs do not serve as a source of xs230th a spatial analysis suggests that there may be an enhanced scavenging effect on xs230th concentrations in sediment closest to the equator where productivity is the highest although further data is necessary to corroborate this at the equator xs230th derived focusing factors are high and range from about 1 to 5 during the holocene and about 1 to 11 during the last glacial in contrast non equatorial cores show a smaller range in variability from about 0 7 to 2 8 during the holocene and from 0 7 to 3 6 during the last glacial based on 232th flux measurements we hypothesize that the location at which eolian detrital fluxes surpass the riverine detrital fluxes is approximately 300 km from the margin while riverine fluxes from coastal margins were higher during the holocene eolian fluxes were higher during the last glacial

climatically driven changes in oceanic processes throughout the equatorial pacific 1 the mass accumulation rates of sedimentary components carbonate organic carbon opal barite reactive phosphate iron terrigenous minerals etc are used in many paleoceanographic reconstructions to learn about temporal and spatial changes in surficial earth processes including wind stress and direction oceanic circulation weathering rates marine productivity and ecosystem structure climate change and more in most studies it is assumed desired that the sediment accumulation represents the production and deposition of particles from the overlying water column since substantial horizontal transport imply homogenization of paleoceanographic proxies and little confidence in any paleoceanographic time series in this note we highlight some discrepancies between the different approaches used to reconstruct sediment mass accumulation rates and specifically discuss the consequences of these discrepancies to the reconstruction of paleoproductivity in the equatorial pacific we pose research questions and suggest possible approaches research strategies for the community to solve them

glacial deep ocean sequestration of co2 driven by the eastern equatorial pacific biologic pump abstract the potential influence of low latitude ocean primary productivity on glacial atmospheric carbon dioxide levels has proven challenging to deduce using mass accumulation rates mars of biogenic particulates in deep sea sediment cores benthic foraminiferal b ca serves as a proxy for past seawater calcite saturation state and thereby provides a fresh perspective on this outstanding paleoceanographic problem here we employ cibicidoides wuellerstorfi b ca in the panama basin region of the eastern equatorial pacific eep to investigate the nature of deep tropical pacific carbon storage over the past 50 ka bp we present evidence for persistently lower deep panama basin calcite saturation state reflecting an increase in total carbon dioxide storage during the last ice age relative to the holocene these results reflect the modification of inflowing deep waters by overlying export productivity and support the concept of an invigorated glacial eep soft tissue pump possibly driven by oceanic nutrient iron and silica redistribution benthic cibicidoides spp carbon 13 is consistent with this conclusion by exhibiting substantially lighter values during glacial time reflecting the accumulation of metabolic carbon dioxide in the deep tropical pacific counterintuitively downcore application of the globorotalia menardii calcite fragmentation index mfi reveals enhanced glacial sedimentary calcite preservation in the panama basin together these results point towards a systematic decoupling of bottom water chemistry from biogenic burial fluxes the crux of the aforementioned traditional paleoproductivity problem

deciphering latitudinal shifts in coccolith accumulation in the eastern tropical pacific ocean through the pleistocene abstract middle and late pleistocene coccolithophore assemblages from ocean drilling program odp sites 1241 and 1242 in the northeastern tropical pacific north etp were analyzed to reconstruct coccolithophore productivity and surface water conditions over the last 925 kyr stratigraphic control was provided by 18o data and geomagnetic time scales and the identification of synchronous calcareous nannofossil events formerly described in mid and low latitudes changes in sea surface coccolithophore productivity were inferred by estimates of the so called n ratio an independent proxy on conversion to accumulation rates and the total coccolith derived carbonate accumulation rate car car variations follow those of the n ratio but show larger amplitude changes fluctuations in the n ratio and total car values imply coccolithophore productivity maxima during glacial times most likely as a result of a shallower nutri thermocline defined as the boundary beneath the sea surface at which nutrient rich cool and nutrient poor warm waters are separated low interglacial values of the n ratio and car suggest lower coccolithophore productivity and a deeper nutri thermocline deep stratification of the mixed layer this result implies that coccolithophore productivity controlled cars and dissolution were driven by the ratio between caco3 production and organic matter oxidation and that effects of dissolution were enhanced when coccolith production fell the data suggest high coccolithophore productivity and a shallow nutri thermocline during mis 22 through mis 6 likely due to the reinforcement of northeastern wind driven advection of nutrient rich waters which is compatible with a la nina like state the dominance of gephyrocapsa caribbeanica during the mid brunhes event mbe is consistent with this eutrophic environment conversely data from mis 5 suggests a weakening of trade winds in the etp which would have reduced the normal upwelling of cool water and warmed sst and which is compatible with the oligotrophic setting of an el nino like state during mis 4 through mis 1 coccolithophore productivity was not significantly different from mis 5 and therefore not indicative of a prominent la nina like state as previously reported for the equatorial cold tongue ect comparison with coccolithophore data from site 1240 supports a reduction of coccolithophore productivity and nutri thermocline deepening from the ect to the costa rica margin and suggests that nutrient availability was the primary control on the distribution of the whole assemblage during the past 925 kyr

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

glacial to interglacial fluctuations in productivity in the equatorial pacific as indicated by marine barite an empirical correlation between marine barite baso4 accumulation rate in core top sediment samples from two equatorial pacific transects at 140 w and 110 w and the estimated primary productivity of the overlying water column were used to evaluate glacial to interglacial changes in productivity fluctuations in barite accumulation rates down core indicate that during glacial periods of the past 450 000 years the productivity in the central and eastern equatorial pacific was about two times that during intervening interglacial periods this result is consistent with other evidence that productivity was high in the eastern and central equatorial pacific during the last glacial

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr