sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

interannual variability of summer biochemical enhancement in relation to mesoscale eddies at the shelf break in the vicinity of the pribilof islands bering sea abstract this study examined variability of the eddy field and primary production over the bering sea s eastern shelf break area during summer using a satellite multi sensor data set the eddy field and on shelf nutrient flux below 50 m water depth were also investigated using a numerical model the satellite altimeter data analysis and numerical experiments indicated that the eddy field was induced by perturbations of the bering slope current system and or instabilities in the bering sea basin via flow through the aleutian passes the distribution of high primary production roughly coincided with the high variability area of the eddy field numerical experiments showed a 70 increase in net on shelf flux and 54 increase in net on shelf transport by the generation propagation of eddies along the shelf break at pribilof canyon towed ctd fluorometer measurements during the summer of 2003 revealed a stable water column and high fluorescence 10 g l 1 in the area between the 200 and 1000 m isobaths at a time when there was a low level of on shelf flux regardless of the eddy field conversely the eddy induced on shelf flux and stable water column can enhance primary production from spring to summer at the shelf break moreover the eddy induced on shelf nutrient flux probably contributes to the primary productivity at the western shelf of the pribilof islands where the bering sea ecosystem is very dynamic this eddy related shelf break process can be applied to not only the bering sea shelf break but also all shelf break areas in which propagating eddies are found

chamber formation leads to mg ca banding in the planktonic foraminifer neogloboquadrina pachyderma many species of planktonic foraminifera show distinct banding in the intratest distribution of mg ca this heterogeneity appears biologically controlled and thus poses a challenge to mg ca paleothermometry the cause of this banding and its relation with chamber formation are poorly constrained and most of what we know about intratest mg ca variability stems from culture studies of tropical symbiont bearing foraminifera here we present data on the non spinose symbiont barren neogloboquadrina pachyderma from the subpolar north atlantic where wintertime mixing removes vertical gradients in temperature and salinity this allows investigation of biologically controlled mg ca intratest variability under natural conditions we find that intratest mg ca varies between 0 1 and 7 mmol mol even in winter specimens high mg ca bands occur at the outer edge of the laminae indicating reduced mg removal at the end of chamber formation our data thus provide new constraints on the timing of the formation of such bands and indicate that their presence is intrinsic to the chamber formation process additionally all specimens are covered with an outer crust consisting of large euhedral crystals the composition of the crust is similar to the low mg ca bands in the laminar calcite in winter and summer specimens indicating a tight biological control on crust formation and composition nevertheless despite high intratest variability the median mg ca of summertime tests is higher than that of wintertime tests this provides support for mg ca paleothermometry but to improve the accuracy of paleotemperature estimates biological effects on mg incorporation need to be better accounted for

phase transformations in serpentine at high pressures and temperatures and implications for subducting lithosphere abstract serpentine may be regarded as a hydrous form of a 1 1 molecular mixture of olivine and pyroxene or a simplified hydrous pyrolite upper mantle composition the phase behaviour of two natural serpentines having the approximate compositions of mg0 99fe0 01 3si2o5 oh 4 and mg0 91fe0 09 3si2o5 oh 4 was investigated between 60 and 280 kbar inclusive at 700 1000 c in a diamond anvil pressure cell coupled with laser heating by incorporating earlier work the results suggest that at pressures greater than 30 kbar and temperatures in the range 600 1000 c serpentine displays the following sequence of phase transformations with increasing pressure serpentine 40 60 kb forsterite talc water 70 80 kbforsterite orthoenstatite water 100 kg forsterite clinoenstatite water 120 kb clinoenstatite phase a water 130 kb stishovite phase a brucite 180 kg stishovite phase b brucite 220 kb none of the high pressure phases expected in olivine and pyroxene such as the spinel modification of olivine the ilmenite and perovskite modifications of pyroxene was observed in serpentine up to about 280 kbar loading pressure on the basis of these results the effect of h2o on phase transformations of olivine and pyroxene at high pressures and high temperatures has been deduced it has been found that the modified spinel phase of mg2sio4 does not occur in the system having a 1 1 mixture of forsterite and enstatite and containing more than about 4 wt h2o the spinel phase of mg2sio4 does not appear at its equilibrium transition boundary modified spinel spinel in the same system containing more than about 3 wt h2o thus if more than about 4 wt h2o is present in the middle portion of a subducting lithosphere the so called 400 km seismic discontinuity observed in the normal mantle may not take place in the downgoing slabs where these transitions do occur at a low h2o content the associated change in density and accordingly the magnitude of discontinuities in the seismic wave velocities would be reduced by a factor of 2 3 if 2 wt h2o is present in the system

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

vertical turbulent iron flux sustains the green belt along the shelf break in the southeastern bering sea 1 to evaluate the impact of vertical turbulent iron flux on the summertime biological productivity in the bering sea green belt gb we conducted the concurrent observations of dissolved iron d fe and turbulence in the bering sea for the first time we show that the gb can be sustained by iron supply from iron rich subsurface thick layer distributed along the southeastern shelf break where the gb is located via strong turbulent vertical mixing the flux ratio of d fe and nitrate was within the range of the n fe uptake ratio by gb phytoplankton suggesting this flux of nutrients can sustain gb productivity we also analyzed historical hydrographic data and suggest the thick subsurface layer along the gb is formed by the mixing of relatively warm water with some iron from the aleutian passes and iron rich outer shelf cold water in which the d fe derived from seafloor sediment is suspended due to strong vertical mixing

ch 4 consuming microorganisms and the formation of carbonate crusts at cold seeps to understand the role played by microorganisms in the formation of cold seep carbonates we conducted an integrated microbial mineralogical and organic geochemical study of methane related authigenic carbonate crusts formed on eastern mediterranean mud volcanoes we show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane combined lipid biomarker analysis and 16s rrna gene surveys identified a highly diversified methane consuming archaeal community possibly comprising novel species implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation moreover pore water sulphate gradients produced by co occurring methane based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation we propose that this may be the dominant mode of carbonate crust formation at cold seeps world wide in agreement with aquatic chemistry predictions and explaining carbonate mineralogy

deep crustal reflections from a vibroseis survey in northern switzerland abstract in 1982 a vibroseis survey comprising 180 km of reflection profiles was run in northern switzerland in order to investigate the suitability of the crystalline basement for the deposition of highly radioactive waste a configuration was chosen with 144 channels 25 m of geophone spacing 20 s sweeps ranging from 11 to 61 hz and stacking of 4 or 8 sweeps of 3 simultaneous vibrators at twice the geophone spacing the listening time was generally 4 s and at 4 sites it was extended to 11s for the detection of deeper crustal reflectors this survey unravelled the complicated fault and thrust system beneath the swiss folded jura mountains the stack from 4 s to 11 s reveals clearly a strong sloping reflector between 3 0 and 3 5 s which is strong evidence for a pronounced differentiation in the upper crust a series of reflections is observed between 5 8 and 7 2 s the top of which can be correlated with the conrad discontinuity a strong layered signal between 9 0 and 9 5 s is interpreted as reflections from the m discontinuity the main features are compatible with results from nearby refraction surveys in the southern rhinegraben rift system which show a distinct velocity increase of about 0 5 km s in the lower crust at a depth ranging from 15 to 20 km followed by an inversion zone or a laminated structure before reaching the moho at about 27 km depth the correlation of the field recordings with the first 10 s of the up sweep only shows some loss of resolution in the uppermost 3 s because of the lower frequency content of the signal however the lower parts of the sections are nearly identical the fact that the deeper reflectors in the sections can consistently be traced laterally is a strong argument for using this processing technique thus high coverage vibroseis surveys utilizing up sweep can be processed for deep crustal reflections even if the recording time is restricted to the standard 4 s provided the surface static corrections are carried out with high precision

mg ca sr ca and ca isotope ratios in benthonic foraminifers related to test structure mineralogy and environmental controls we analysed mg ca sr ca and ca isotope ratios of benthonic foraminifers from sediment core tops retrieved during several research cruises in the atlantic ocean in order to improve the understanding of isotope fractionation and element partitioning resulting from biomineralisation processes and changes in ambient conditions species include foraminifers secreting tests composed of hyaline low magnesium calcite porcelaneous high magnesium calcite as well as aragonite our results demonstrate systematic isotope fractionation and element partitioning patterns specific for these foraminiferal groups calcium isotope fractionation is similar in porcelaneous and hyaline calcite tests and both groups demonstrate the previously described anomaly with enrichment of heavy isotopes around 3 4 degrees c gussone and filipsson 2010 calcium isotope ratios of the aragonitic species hoeglundina elegans on the other hand are about 0 4 parts per thousand lighter compared to the calcitic species which is in general agreement with stronger fractionation in inorganic aragonite compared to calcite however the low and strongly variable sr content suggests additional processes during test formation and we propose that transmembrane ion transport or a precursor phase to aragonite may be involved porcelaneous tests composed of high mg calcite incorporate higher amounts of sr compared to hyaline low mg calcite in agreement with inorganic calcite systematics but also porcelaneous tests with reduced mg ca show high sr ca while calcium isotopes sr ca and mg ca in benthonic foraminifers primarily appear to fractionate and partition with a dominant inorganic control delta ca 44 40 temperature and growth rate dependencies of benthonic foraminifer tests favour a dominant contribution of light ca by transmembrane transport relative to unfractionated seawater ca to the calcifying fluid thus controlling the formation of foraminiferal delta ca 44 40 and sr ca proxy signals c 2015 elsevier ltd all rights reserved less

assessing the impact of diagenesis on δ11b δ13c δ18o sr ca and b ca values in fossil planktic foraminiferal calcite the geochemical composition of foraminiferal tests is a valuable archive for the reconstruction of paleo climatic oceanographic and ecological changes however dissolution of biogenic calcite and precipitation of inorganic calcite overgrowth and recrystallization at the seafloor and in the sediment column can potentially alter the original geochemical composition of the foraminiferal test biasing any resulting paleoenvironmental reconstruction the 11b of planktic foraminiferal calcite is a promising ocean ph proxy but the effect of diagenesis is still poorly known here we present new 11b 13c 18o sr ca and b ca data from multiple species of planktic foraminifera from time equivalent samples for two low latitude sites clay rich tanzanian drilling project tdp site 18 from the indian ocean containing well preserved glassy foraminifera and carbonate rich ocean drilling program odp site 865 from the central pacific ocean hosting recrystallized frosty foraminifera our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis planktic foraminiferal 18o and 13c records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration sr ca and b ca ratios in planktic foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa in contrast 11b values indicate no large differences between well preserved and recrystallized foraminifera suggesting that despite extensive diagenetic alteration the 11b of biogenic calcite appears robust potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing caco3 our finding may remove one potential source of uncertainty in 11b based ph reconstructions and provide us with greater confidence in our ability to reconstruct ph in the ancient oceans from at least some recrystallized foraminiferal calcite however further investigations should extend this approach to test the robustness of our findings across a range of taphonomies ages and burial settings

repeated pulses of vertical methane flux recorded in glacial sediments from the southeast bering sea 1 there is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period in this study of two sediment cores from the southeast bering sea 700 m and 1467 m water depth we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor within the uncertainty of the radiocarbon age model the episodes are contemporaneous in the two cores and have similar timing and duration as dansgaard oeschger events the episodes are marked by horizons of sediment containing 13c depleted authigenic carbonate minerals 13c depleted archaeal and bacterial lipids which resemble those found in anme 1 type anaerobic methane oxidizing microbial consortia and changes in the abundance and species distribution of benthic foraminifera the similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region wide increase in the upward flux of methane bearing fluids this study is the first observation outside santa barbara basin of pervasive repeated methane flux in glacial sediments however contrary to the clathrate gun hypothesis kennett et al 2003 these coring sites are too deep for methane hydrate destabilization to be the cause implying that a much larger part of the ocean s sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales we speculate that pulses of methane in these opal rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis the release could be triggered by seismic shaking on the aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials

depth migration of deep seismic reflection profiles crustal thickness variations in alberta variations in crustal thickness provide important clues as to the formation of the crust present day isostatic equilibrium and crustal stress the map of the topography of the mohorovicic discontinuity in alberta is revised using 1900 km of reanalysed seismic reflection profiles acquired as part of the lithoprobe alberta basement transect time sections were depth migrated using a parallelized algorithm that accounts for steeply dipping structures the migration process employed a geologically consistent velocity model of the metamorphic crust derived from earlier refraction experiments and constrained by compilations of high pressure rock velocity measurements we found that knowledge of the velocities in the sedimentary column strongly influenced the quality of the migration calculations the mohorovicic discontinuity is generally distinguished in these profiles on the basis of sharp changes in reflectivity at depths of 35 48 km sharp reflections from this boundary are rare a number of geologic fe

microstructural and geochemical perspectives on planktic foraminiferal preservation glassy versus frosty in recent years it has become apparent that the cool tropic paradox of paleogene and cretaceous greenhouse climates arises because of the diagenetic alteration of tropical planktic foraminiferal calcite near the seafloor yielding artificially high 18o values because the mg ca compositions of foraminiferal and inorganic calcite are thought to be quite different mg ca measurements should be a sensitive way of monitoring diagenetic alteration here we examine the extent of diagenetic alteration of eocene planktic foraminiferal calcite using scanning electron microscope imaging of foraminiferal test microstructures and geochemical 18o and mg ca analyses we compare microstructural and geochemical characteristics between given species exhibiting two contrasting states of preservation those that appear frosty under reflected light and those that appear glassy microstructural evidence reveals extensive diagenetic alteration of frosty foraminiferal tests at the micron scale while 18o analyses document consistently higher 18o and therefore lower paleotemperatures in this material yet we find that 18o offsets between species in these frosty foraminiferal assemblages appear to be generally preserved suggesting that frosty foraminifera remain valuable for generating relatively short approximately 1 myr paleoceanographic time series that do not demand absolute estimates of paleotemperature we also find that the observed increase in mg ca for planktic foraminifera exhibiting diagenetic alteration compared to glassy taphonomies is far smaller than would be expected from the addition of inorganic calcite based on laboratory derived mg2 partition coefficients our findings imply that a much lower mg2 partition coefficient controls inorganic calcite formation in deep sea sedimentary sections in accordance with the findings of baker et al 1982

alteration of monazite and zircon and lead migration as geochemical tracers of fluid paleocirculations around the oklo okelobondo and bangombe natural nuclear reaction zones franceville basin gabon abstract large scale light rare earth element lree uranium lead and phosphorus migration has been evidenced in the fa lower proterozoic sandstones of the franceville basin gabon hosting oklo natural nuclear reaction zones rz in relation with extensive accessory mineral alteration by highly saline diagenetic brines 28 7 wt nacl eq to 30 wt cacl2 eq at about 140 c and 1 kbar monazite is the most severely altered accessory mineral in the coarse grained sandstones of the basal fa formation detrital monazite crystals are altered to th oh silicate microcrystalline phase with very low concentrations of u and lree the th la ratio increase from non altered th la 0 27 to altered sandstones th la 1 14 shows that about 76 of the lree was leached this corresponds to the leaching of 2 01 109 metric tons at the scale of the fa formation in the franceville basin similarly the th u increase from monazite th u 18 6 to the th silicate phase th u 88 7 is interpreted as a result of an alteration by oxidizing brines with leaching of u together with lree and p it corresponds to the leaching of 9 06 106 metric tons of uranium this amount of uranium largely exceeds the known uranium reserves from the franceville basin in zircon crystals the cores are generally homogeneous weakly fractured and well preserved as attested by the archean ages 2867 24 and 2865 51 ma obtained by ionic microprobe analysis on zircon of the fa formation respectively from the marginal and central parts of the basin their composition corresponds to the pure end member zr hf sio4 poor in th and u th u 1 at the contrary their rims which present several growth zones with cracks fillings are enriched in ree p th and u with higher th u ratios 5 10 both altered monazite and altered zircon contain galena as numerous inclusions in the outer growth zones and as crack fillings for example in zircon the pb of galena crystals 3 23 wt largely exceeds the amount of pb maximum 0 1 wt that would have been produced in situ by radioactive decay in this mineral nearly all the lead were introduced into altered zones of accessories dissolution of accessory minerals occurred at 2000 ma producing a porous and distorted crystal structure which has allowed a later incorporation of pb galena inclusions in altered zircons located in the vicinity of reactor zones have radiogenic lead compositions altered zircon rims and galena inclusions in altered zircon located far from reactor zones have non radiogenic pb isotopic compositions confirming the external origin of lead pb isotopic evolution models indicate a crystallization age sometime after 1000 ma both for galena located close to and far from u mineralizations and reactor zones which may be synchronous with a regional extension event contemporaneous with intrusion of dolerite dyke swarms between 1000 and 750 ma at the scale of the franceville basin the present study also illustrates the different retention capacities of accessory mineral for elements representing analogs of the radiotoxic nuclides in the relatively extreme natural conditions created by the circulation of moderately hot and chloride rich fluids during the diagenesis of a sedimentary basin

orbital scale benthic foraminiferal oxygen isotope stratigraphy at the northern bering sea slope site u1343 iodp expedition 323 and its pleistocene paleoceanographic significance abstract a continuous composite oxygen isotope 18o stratigraphy from benthic foraminifera in the bering sea was reconstructed in order to provide insight into understanding sea ice evolution in response to northern hemisphere glaciation oxygen isotope records from multiple species of benthic foraminifera at integrated ocean drilling program iodp expedition 323 site u1343 54 33 4 n 176 49 0 e water depth 1950 m yield a highly refined orbital scale age model spanning the last 1 2 ma and a refined age model between 1 2 and 2 4 ma an inter species calibration was used to define species offsets and to successfully obtain a continuous composite benthic 18o record correlated with the global composite benthic 18o stack curve lr04 to construct an orbital scale age model the consistency of the benthic 18o stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age the time difference between cyclic changes in sedimentary physical properties and glacial interglacial cycles since 0 8 ma is notable and suggests that physical properties alone cannot be used to construct an orbital scale age model amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0 9 ma indicate that the glacial sea ice edge extended beyond the bering sea slope site u1343 at this time

extraction of deep crustal reflections from shallow vibroseis data using extended correlation lower crustal seismic reflections can be extracted from shallow crustal seismic profiles through the application of extended correlation to uncorrelated vibroseis seismic data fixed bandwidth extended correlation shortens the correlation operator before crosscorrelation producing reflections over an increased correlation time range all with lowered bandwidth self truncating extended correlation preserves the full bandwidth in the original seismic reflection times but loses bandwidth in a predictable manner at the additional later arrival times correlation wavelet shape and extra correlation time are directly related and can be calculated for specific acquisition parameters pre correlation tapering is necessary to avoid undue wavelet distortion at extended correlation times seismic data collected in the basin and range province illustrate the application of the method the results are verified with conventional correlations of long sweep records and with impulsive source data

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

multi elemental composition of authigenic carbonates in benthic foraminifera from the eastern bering sea continental margin international ocean discovery program site u1343 abstract bering sea sediments represent exceptional archives offering the potential to study past climates and biogeochemistry at a high resolution however abundant hydrocarbons of microbial origin especially along the eastern bering sea continental margin can hinder the applicability of palaeoceanographic proxies based on calcareous foraminifera due to the formation of authigenic carbonates nonetheless authigenic carbonates may also bear unique opportunities to reconstruct changes in the sedimentary redox environment here we use a suite of visual and geochemical evidence from single specimens of the shallow infaunal benthic foraminiferal species elphidium batialis saidova 1961 recovered from international ocean discovery program iodp site u1343 in the eastern bering sea to investigate the influence of authigenic carbonates on the foraminiferal trace metal composition our results demonstrate that foraminiferal calcite tests act as a nucleation template for secondary carbonate precipitation altering their geochemistry where organoclastic sulphate reduction and anaerobic oxidation of methane cause the formation of low and high mg calcite respectively the authigenic carbonates can occur as encrusting on the outside and or inside of foraminiferal tests in the form of recrystallization of the test wall or as banding along natural laminations within the foraminiferal test walls in addition to mg authigenic carbonates are enriched in u ca mn ca fe ca and sr ca depending on the redox environment that they were formed in our results demonstrate that site specific u ca thresholds are a promising tool to distinguish between diagenetically altered and pristine foraminiferal samples important for palaeoceanographic reconstructions utilising the primary foraminiferal geochemistry consistent with previous studies u mn ratios of foraminifera at iodp site u1343 increase according to their degree of diagenetic alteration suggesting a potential response of authigenic u mn to the microbial activity in turn linked to the sedimentary redox environment

enhanced framboidal pyrite formation related to anaerobic oxidation of methane in the sulfate methane transition zone of the northern south china sea abstract many studies have confirmed that size distributions of framboidal pyrite can be an effective indicator of bottom water redox conditions in modern as well as ancient sedimentary environments however one environment in which production of framboidal pyrite has not been sufficiently studied to date is the sulfate methane transition zone smtz in which anaerobic oxidation of methane aom is coupled with microbial sulfate reduction msr to enhance iron sulfide mineral precipitation e g fes2 fes and fe3s4 here we document for the first time size distributions for pyrite framboids from the smtz based on data from two sites in the methane hydrate bearing region of the northern south china sea on the basis of framboid size pyrite concentration and sulfur isotope data we propose new insights into the formation process of authigenic pyrite framboids within the smtz we conclude that 1 enhanced anaerobic oxidation of methane aom not only plays a dominant role in the accumulation of 34s enriched pyrite but also is responsible for formation of highly variable and sometimes exceptionally large pyrite framboids in the smtz 2 most framboids occur in framboid clusters which commonly exhibit rod like shapes secondary overgrowths heavier 34s values and unusual size distributions e g mean size 20 m and standard deviation 3 0 m in the smtz 3 pyrite framboids formed in the smtz which have characteristics different from those formed in the sulfate reduction zone srz do not comment on redox conditions of the overlying water column and 4 framboid occurrences with similar characteristics in ancient marine deposits may be considered indicators of enhanced aom and mark the former position of the smtz in the paleo marine system in addition significant quantities of elemental sulfur were observed in the smtz possibly related to anaerobic oxidation of hydrogen sulfide and fluctuations of the smtz

foraminifera as indicators of methane rich environments a study of modern methane seeps in santa barbara channel california methane hydrates have been implicated as a possible forcing mechanism for rapid climate change during the late quaternary via the release of methane from marine reservoirs carbon isotopic excursions of foraminifera observed in high resolution sediment records from santa barbara basin odp site 893 have been interpreted as evidence of episodes of methane release during the late quaternary however the potential relationship between methane in the modern environment and its effect on the stable isotopic composition of benthic and planktonic foraminifera is not well understood short cores taken inside a 500 m diameter pockmark with active methane seeps in santa barbara channel ca usa yield information on the effect of high concentrations of environmental methane on foraminiferal assemblages and their stable isotopic composition these seeps reside at 120 m water depth in the eastern portion of the channel associated with faults and fractures in the miocene monterey formation planktonic foraminiferal assemblages and radiocarbon ages show that surface sediments are of late glacial age 25 300 calendar years this finding suggests an absence of holocene and deglacial sedimentation in the seep area likely due the formation of the pockmarks and subsequent winnowing or lack of sedimentation benthic foraminiferal assemblages are marked by high abundance of bolivina tumida a species previously observed during interstadial episodes and the early holocene in santa barbara basin interpreted to include episodes of high methane flux from the basin while oxygen isotopic values of both benthic and planktonic foraminifera appear normal for cool glacial conditions negative carbon isotopic values are seen in benthic foraminifera primarily in the near surface intervals in one interval 1 2 cm below surface both benthic and planktonic species record highly negative carbon isotopic values implying that isotopically light methane influenced the entire water column this spike is of similar or larger magnitude than several earlier observed spikes in the late quaternary record from odp site 893 single specimen isotopic analyses give an indication of the total range of carbon isotopic values recorded 0 01 to 25 23 for benthics 0 07 to 22 22 for planktonics in the spike interval since modern methane seeps are commonly associated with authigenic carbonate precipitation scanning electron microscopy was used to assess the possibility that post depositional alteration may have affected the isotopic composition of the test these experiments indicate that authigenic carbonate is absent and therefore unable to account for the highly negative carbon isotopic signatures these data improve our understanding of methane associated environments by showing that foraminiferal isotopic composition and assemblages may be used to discern the flux of methane from the oceanic reservoir in the geologic record

mg ca ratios of the benthic foraminifera oridorsalis umbonatus obtained by laser ablation from core top sediments relationship to bottom water temperature 1 a laser ablation system connected to an inductively coupled plasma mass spectrometer was used to determine mg ca ratios of the benthic foraminifera oridorsalis umbonatus a set of modern core top samples collected along a depth transect on the continental slope off namibia 320 2300 m water depth 2 9 to 10 4 c was used to calibrate the mg ca ratio against bottom water temperature the resulting mg ca bottom water temperature relationship of o umbonatus is described by the exponential equation mg ca 1 528 e0 09 bwt the temperature sensitivity of this equation is similar to previously published calibrations based on cibicidoides species suggesting that the mg ca ratio of o umbonatus is a valuable proxy for thermocline and deep water temperature

quaternary deep sea temperature histories derived from benthic foraminiferal mg ca abstract we have generated benthic foraminiferal mg ca records from eastern tropical atlantic core m16772 3 9 km and eastern tropical pacific core tr163 31p 3 2 km to assess the potential for using benthic mg paleothermometry to reconstruct quaternary bottom water temperature histories variations in mg ca records from both the atlantic and pacific show a significant correlation with climatic oscillations of the last 330 kyr shell mg ca peaks during interglacial episodes with marine isotope stage mis 5e mg ca nearly matching holocene values in both cores lower mg ca values occur during glacial intervals to estimate temperatures from downcore mg ca we have augmented the published cibicidoides sp mg ca temperature dataset rosenthal et al geochim cosmochim acta 61 1997 3633 3643 with new data to include the temperature range of deep waters applying the 10 9 change in mg ca per c defined by the expanded calibration to the deep atlantic data implies glacial interglacial shifts in deep water temperature of 2 4 c over the last 300 kyr temperature estimates are comparable to deep atlantic temperature changes proposed by labeyrie et al nature 327 1987 477 482 there is greater uncertainty in deriving temperatures from the tropical pacific core due to a limited uvigerina spp core top calibration set however glacial interglacial temperature oscillations appear to be on the order of 2 3 c in addition core tr163 31p records clear millennial scale mg ca and 18 o oscillations in mis 3 corresponding to temperature fluctuations of 0 5 c additional calibration studies are needed to address potential secondary effects on mg ca

an evaluation of benthic foraminiferal u ca and u mn proxies for deep ocean carbonate chemistry and redox conditions the deep ocean is thought to have played a crucial role in modulating atmospheric co2 changes and thus reconstructions of deep ocean conditions can place important constraints on the past global carbon cycle some previous studies suggested that foraminiferal u ca could be used to infer seawater carbonate chemistry changes but others showed complications from diagenesis and temperature a recent down core study suggested that foraminiferal u mn may be used for sedimentary redox conditions but no core top work has been done to investigate factors affecting u mn we investigate controlling factors on u ca and u mn in two benthic foraminiferal species from 120 global core tops and three atlantic sediment cores our core top data reveal no significant correlation between core top benthic u ca and carbonate system parameters the lack of an influence of deep water co32 on u ca is further supported by our down core results together our data highlight complications to use benthic u ca for deep water carbonate chemistry reconstructions although no correlation is found between core top u mn and hydrographic data high resolution u mn and u ca in core tno57 21 show similar patterns to authigenic u au and vary in tandem with atmospheric co2 on millennial timescales changes in u mn u ca and au in tno57 21 may reflect post depositional diagenesis linked to sedimentary oxygen which is controlled by subantarctic surface productivity and ventilation of deep south atlantic in the past we suggest that benthic u mn and u ca may be used as auxiliary indicators for past sedimentary redox conditions and along with other proxies could reflect deep water oxygenation this article is protected by copyright all rights reserved

coupled organic and inorganic carbon cycling in the deep subseafloor sediment of the northeastern bering sea slope iodp exp 323 abstract we studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern bering sea slope to a depth of 745 meters below seafloor mbsf sites u1343 u1344 and u1345 were drilled during integrated ocean drilling program iodp expedition 323 at water depths of 1008 to 3172 m they are situated in the high productivity green belt region with organic carbon burial rates typical of the high productivity upwelling domains on western continental margins the three sites show strong geochemical similarities the downward sequence of microbially mediated processes in the sediment encompasses 1 organoclastic sulfate reduction 2 anaerobic oxidation of methane aom coupled to sulfate reduction and 3 methanogenesis the sediment contains two distinct zones of diagenetic carbonate formation located at the sulfate methane transition zone smtz and between 300 and 400 mbsf the smtz at the three sites is located between 6 and 9 mbsf the upward methane fluxes into the smtz are similar to fluxes in smtzs underlying high productivity surface waters off chile and namibia our bering sea results show that intense organic carbon mineralization drives high ammonium and dissolved inorganic carbon dic production rates 4 2 mmol m 3 y 1 in the uppermost 10 mbsf and strongly imprints on the stable carbon isotope composition of dic driving it to a minimum value of 27 vpdb at the smtz pore water calcium and magnesium profiles demonstrate formation of diagenetic mg rich calcite in the smtz below the smtz methanogenesis results in 13c enrichment of pore water dic with a maximum value of 11 9 the imprint of methanogenesis on the dic carbon isotope composition is evident down to a depth of 150 mbsf below this depth slow or absent microbially mediated carbon mineralization leaves dic isotope composition unaffected ongoing carbonate formation between 300 and 400 mbsf strongly influences pore water dic and magnesium concentration profiles the linked succession of organic carbon mineralization and carbonate dissolution and precipitation patterns that we observe in the bering sea slope sediment may be representative of passive continental margin settings in high productivity areas of the world s ocean

seismic structure of the crust and upper mantle in the peace river arch region canada four intersecting 300 km long reversed refraction lines within northwestern alberta and northeastern british columbia have been interpreted for crustal and upper mantle seismic velocity structure in the peace river arch pra region of the western canada sedimentary basin the data have been modeled using a two dimensional ray trace forward modeling approach based on asymptotic ray theory to match travel times and amplitudes of first and coherent later arrivals in addition an inversion of first arrival travel times along a fan shot profile has been performed to constrain crustal thickness northwest of the arch in a region not sampled by the reversed profiles the major features of the structural models are 1 weak to moderate lateral variations in crustal structure with no evidence of significant layering or thick low velocity zones within the crust 2 an average sub basement rms crustal velocity of 6 6 km s average upper mantle velocity of 8 25 km s and average crustal thickness of 40 km 3 regional variations in structure which appear related to the dominant n s trending cratonic structure including crustal thickness upper crustal and upper mantle velocities and pmp character and 4 subtle variations in structure that may be associated with the e w trending devonian axis of the pra including a shallowing of high lower crustal velocities thickening of the crust and an anisotropic pmp character beneath the arch and a weak trend in the dip of intracrustal reflectors away from the center of the pra region evidence from the refraction and other geophysical data for the presence of a local crustal expression of the pra is weak but suggests a thermal as opposed to flexural origin for its anomalous vertical movements

methane induced early diagenesis of foraminiferal tests in the southwestern greenland sea abstract planktic and epibenthic foraminiferal 13c records at site ps62 015 3 southwestern greenland sea reveal a series of transient events of extreme 13c depletion down to 6 during the period 90 40 ka scanning electron microscope studies of the ultrastructures of foraminiferal tests suggest that 13c depleted specimens are affected by some 10 20 overgrowth by authigenic calcite contributing to the light 13c signal incremental leaching experiments and census counts of pristine versus overgrowth affected specimens show that the 13c depleted foraminiferal tests incorporate a primary 13c signature most likely ranging from 1 to 1 7 and a post depositional 13c signature around 17 to 19 5 extremely low values of productivity and organic carbon in late quaternary sediments along the east greenland margin preclude organic matter as potential source of the isotopically light carbon in contrast thermal instability of clathrates and subsequent aerobic oxidation of highly 12c enriched methane in pore and ocean water provide a compelling mechanism to account for the negative 13c excursions of both primary and post depositional carbonates here pore water methane may have led to a supersaturation of 13c depleted bicarbonate and precipitation of isotopically light authigenic calcite on and in foraminiferal tests a feature that may serve as a tracer to former sites of clathrate destabilization

isotopic evidence for the incorporation of methane derived carbon into foraminifera from modern methane seeps hydrate ridge northeast pacific the presence of modern methane seeps at hydrate ridge offshore oregon provide an opportunity to study the influence of methane seeps on the ecology and geochemistry of living foraminifera a series of cores were collected from the southern summit of hydrate ridge in 2002 samples were preserved and stained to determine the 13c composition of three species of live stained and dead benthic foraminifera uvigerina peregrina cibicidoides mckannai and globobulimina auriculata specimens were examined under light and scanning electron microscopy sem and exhibit no evidence of diagenesis or authigenic carbonate precipitation individual living foraminifera from seep sites recorded 13c values from 0 4 to 21 2 indicating the isotopic influence of high methane concentrations average 13c values calculated from single specimens range from 1 28 to 5 64 at seep sites and 0 81 to 0 85 at a control off seep site two distinct seep environments distinguished by the presence of microbial mats or clam fields were studied to determine environmental influences on 13c values individual foraminifera from microbial mat sites exhibited more depleted 13c values than those from clam field sites we interpret these differences as an effect of food source and or symbiotic microbes on foraminiferal carbon isotopic values acting to magnify the negative 13c values recorded via the dic pool no statistical difference was found between 13c values of live vs dead specimens this suggests that authigenic carbonate precipitation did not play a dominant role in the observed isotopic compositions however a few dead specimens with extremely negative 13c composition 12 do indicate potential evidence for an authigenic influence on the recorded 13c composition

paleo methane emissions recorded in foraminifera near the landward limit of the gas hydrate stability zone offshore western svalbard we present stable isotope and geochemical data from four sediment cores from west of prins karls forland ca 340 m water depth offshore western svalbard recovered from close to sites of active methane seepage as well as from shallower water depths where methane seepage is not presently observed our analyses provide insight into the record of methane seepage in an area where ongoing ocean warming may be fueling the destabilization of shallow methane hydrate the 13c values of benthic and planktonic foraminifera at the methane seep sites show distinct intervals with negative values as low as 27 8 that do not coincide with the present day depth of the sulfate methane transition zone smtz these intervals are interpreted to record long term fluctuations in methane release at the present day landward limit of the gas hydrate stability zone ghsz shifts in the radiocarbon ages obtained from planktonic foraminifera toward older values are related to methane derived authigenic carbonate overgrowths of the foraminiferal tests and prevent us from establishing the chronology of seepage events at shallower water depths where seepage is not presently observed no record of past methane seepage is recorded in foraminifera from sediments spanning the last 14 ka cal bp 14c ams dating 13c values of foraminiferal carbonate tests appear to be much more sensitive to methane seepage than other sediment parameters by providing nucleation sites for authigenic carbonate precipitation foraminifera thus record the position of even a transiently stable smtz which is likely to be a characteristic of temporally variable methane fluxes

manganese micronodules a possible indicator of sedimentary environments abstract manganese micronodule distribution size internal features and chemical composition as well as the composition of associated sediments have been determined in eight sediment cores taken from the siliceous ooze area of the central indian basin cib micronodule abundance expressed as the number of micronodules per gram of dried sediment 0 375 n g and size 75 1000 m show considerable variation with core depth and are directly related to each other the morphology surface texture and internal features of the micronodules are similar to those of surface macronodules from the same basin micronodules have high contents of mn 35 02 cu 1 6 ni 1 4 and zn 0 37 high mn fe ratios 5 101 and very low fe 1 8 al 2 o 3 1 3 tio 2 0 30 sio 2 2 7 and rare earth element 522 ppm contents compared to surface and buried macronodules micronodule abundance size and composition depend on the redox characteristics of the sedimentary environment and can therefore be used as indicators of the sedimentary environment

authigenic uranium in foraminiferal coatings a proxy for ocean redox chemistry the rate of uranium accumulation in oceanic sediments from seawater is controlled by bottom water oxygen concentrations and organic carbon fluxes two parameters that are linked to deep ocean storage of co2 to investigate glacial interglacial changes in what is known as authigenic u we have developed a rapid method for its determination as a simple addition to a procedure for foraminiferal trace element analysis foraminiferal calcite acts as a low u substrate u ca 15 nmol mol upon which authigenic u accumulates in reducing sediments we measured a downcore record of foraminiferal u ca from odp site 1090 in the south atlantic and found that u ca ratios increase by 70 320 nmol mol during glacial intervals there is a significant correlation between u ca records of benthic and planktonic foraminiferal species and between u ca and bulk sediment authigenic u these results indicate that elevated u ca ratios are attributable to the accumulation of authigenic u coatings in sediments foraminiferal mn ca ratios were lower during the glacial intervals suggesting that the observed u accumulation on the shells is not directly linked to u incorporation into secondary manganese phases thus foraminiferal u ca ratios may provide useful information on past changes in sediment redox conditions

characterization of contaminant phases in foraminifera carbonates by electron microprobe mapping the advent of new microanalytical techniques such as electron microprobe mapping emp and laser ablation microsamplers coupled to mass spectrometers la icp ms provides a new array of possibilities to explore in great detail the trace elements distribution in foraminiferal carbonates here we apply these techniques to characterize diagenetic phases present in foraminiferal shells from ocean drilling program site 1240 in the panama basin a region characterized by the presence of manganese rich minerals in the sediments the combined application of these techniques allows us to characterize the elemental and spatial distribution on the surface and across the foraminiferal shells results illustrate the presence of at least two different mn rich contaminant phases in the foraminiferal carbonates mn rich carbonates and ferromanganese oxides elemental maps also highlight the relevance of the foraminifera shell texture and porosity in the distribution and formation of these contaminant phases in the case of neogloboquadrina dutertrei mn phases form a continuous thin layer in the inner part of the chambers whereas for globigerinoides ruber mn phases have a rather patchy distribution and are usually found within the pores significant high magnesium concentrations are always associated with these mn rich phases these new findings support the need of removing these mn rich contaminant phases in order to measure accurately the mg ca ratios in the foraminifera shell and therefore obtain reliable mg ca paleotemperature reconstructions

biogenic opal production changes during the mid pleistocene transition in the bering sea iodp expedition 323 site u1343 abstract biogenic opal content and mass accumulation rate mar at iodp expedition 323 site u1343 were found to fluctuate consistently generally being high under warm conditions and low under cold conditions during the last 2 4 ma continuous wavelet transform analysis of the normalized biogenic opal content indicates that export production in the bering sea varied predominantly at 41 ka periodicity before 1 25 ma and shifted to 100 ka periodicity at the onset of the mid pleistocene transition mpt 1 25 0 7 ma the 100 ka cycles dominated until the holocene export production in the bering sea decreased markedly in the bering sea two times during the mpt the first occurred at the beginning of the mpt 1 25 ma and the second in the middle of the mpt 0 9 ma these decreases coincided with both increases in the relative abundance of sea ice diatoms and decreases in the warm water diatom species neodenticula seminae indicating that reductions in export production in the bering sea during the mpt were associated with climate cooling decreases in export production in the bering sea during the mpt were most likely associated with the increased influence of polar arctic domains on the high latitude north pacific

on the use of seismic reflection surveys from oil exploration in deep crustal studies abstract a very large number of seismic reflection surveys is carried out by the oil industry throughout the world some of these surveys are designed to study deep oil traps and may use field parameters which for the most part are not significantly different from those used in deep crustal reflection studies the one parameter which always varies is the record length listening time in the case of a vibratory source the record length can be increased at the processing stage by the equivalent reduction of vibration time through partial correlation we have used an oil exploration survey from a deep sedimentary basin in the coastal plain of israel and extended its record length using this technique we show that if a survey with appropriated field parameters i e a survey for a deep target is chosen deep crustal reflectors can be traced since a cocorp type deep crustal reflection study was also carried out in the same region we can compare the two sets of results we note that in this case the extended oil exploration record is at least equivalent to and probably of better quality than the cocorp type survey this result is due mostly to a better s n ratio in the oil exploration survey where input power was significantly larger than in special purpose study this result indicates the as yet untapped potential of oil exploration data in deep continental crustal studies

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

preferential dissolution of benthic foraminiferal calcite during laboratory reductive cleaning we have investigated the effect of cleaning procedures on eight element ca ratios in three widely used benthic foraminifera species from core top and down core sediments two cleaning techniques were employed 1 comparison between mg cleaning and cd cleaning methods and 2 comparison between the various constituent reagents li ca b ca and sr ca ratios remained unchanged for samples subjected to different treatments but mg ca mn ca zn ca cd ca and u ca were substantially decreased when foraminifera shells were cleaned with reagents containing citrate in contrast no significant decreases in element ca ratios were observed for samples cleaned in n2h4 without citrate indicating that the role of n2h4 was insignificant during reductive cleaning and that citrate is responsible for decreases of mg ca mn ca zn ca cd ca and u ca decreases in these ratios are most likely due to 1 removal of contaminant particles enriched in mg mn zn cd and u and or 2 preferential leaching of caco3 by the formation of stable metal complexes through chelation between citrate and metals heterogeneously distributed in foraminiferal shells due to the negligible effect of n2h4 and preferential dissolution of caco3 during reductive cleaning it is suggested that the reductive cleaning step should be omitted and the mg cleaning method barker et al 2003 could be employed to clean foraminiferal shells for trace element measurements

new spatial mg ca temperature calibrations for three arctic benthic foraminifera and reconstruction of north iceland shelf temperature for the past 4000 years 1 we have developed cold end mg ca temperature calibrations for three common arctic benthic foraminifera islandiella norcrossi helenae melonis barleeanus and cassidulina neoteretis and compare the three calibrations in a late holocene downcore record 0 4000 cal yr b p the calibration and downcore trends for the three arctic species extend the observation that mg incorporation into benthic foraminifera is species specific for the calibration we use a set of ctd casts bottom water 18oseawater measurements and surface grab samples collected from the iceland margin cruise b997 and the greenland margin cruise bs1191 water depth of sites used ranges from 165 to 656 m while spatial bottom temperature ranges from 0 to 7 c mg ca values ranged from 1 02 to 1 47 for i norcrossi helenae 0 64 to 2 21 for m barleeanus and 0 93 to 1 38 mmol mol for c neoteretis we calibrated mg ca content against isotopic calcification temperature calculated using t 16 9 4 0 18ocalcite corrected for vital effect 18oseawater exponential calibrations for the three species are as follows i norcrossi helenae mg ca 1 051 0 03 exp 0 060 0 011 t m barleeanus mg ca 0 658 0 07 exp 0 137 0 020 t and c neoteretis mg ca 0 864 0 07 exp 0 082 0 020 t on the basis of mg ca in these benthic species the downcore record from core md99 2269 is reconstructed bottom temperature values are interpreted to reflect variable inflow of atlantic and arctic water to the north iceland shelf during the last 4000 cal yr b p all three reconstructions show a decline by 0 1 c per century from circa 1500 0 cal yr b p which coincides with an increase in arctic benthic foraminifera abundances and a rise in sea ice proxies in the same core intriguingly c neoteretis diverges periodically to higher average temperature atlantic water conditions than shown by m barleeanus or i norcrossi helenae which both show arctic water temperature circa 1500 4000 cal yr b p

bering sea cyclonic and anticyclonic eddies observed during summer 2000 and 2001 abstract using satellite altimeter and ship data bering sea cyclonic and anticyclonic eddies were observed in summer 2000 and 2001 to examine their biological chemical and physical structures results from the ship transect revealed the interactions between the physical and biological conditions of bering sea eddies at the center of a cyclonic anticlockwise eddy upwelling was transporting nutrient no3 no2 rich water 25 m to the surface which resulted in relatively high chlorophyll a concentrations 1 0 mg m 3 developing under the pycnocline in contrast in the center of an anticyclonic clockwise eddy there was downwelling this downwelling of surface warm water was destroying a cold layer at about 150 m depth caused by winter convection however around the periphery of the anticyclonic eddy the isopycnals were tilted up and nutrient rich water was being transported along with them up into the euphotic zone so that high chlorophyll a concentrations were being developed above the pycnocline inside the anticyclonic eddy

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

influence of volcanic shards on foraminiferal mg ca in a core from the galapagos region 1 variability in the mg fe al mn and u to ca composition of the planktonic foraminifera g ruber in core tr163 22 an 8 8 m long piston core from just northwest of the galapagos islands reveals distinct patterns of downcore behavior mg ca data follow a general climatic trend with lower values during cold intervals i e marine isotope stages mis 2 4 and higher values during warm intervals i e mis 1 and 5 fe ca and al ca data reveal distinct intervals in which concentrations are elevated tenfold or more over baseline values with highly variable elemental ratios in these intervals the mg ca data are highly correlated with the fe ca and al ca data in these intervals with slopes of 1 13 0 03 and 0 66 0 07 mole mole respectively examination of the sediments from these intervals reveals that they are rich in volcanic debris that is likely derived from galapagos volcanic rocks the presence of small amounts of this volcanic debris can bias shell mg ca to elevated values attempts to use enhanced cleaning to remove the volcanic particles were largely unsuccessful the most successful strategy is to use the fe ca and al ca from the shell digests along with the fe to mg ratio of the volcanic debris to correct the mg ca data for al silicate contamination in which case the corrected data more clearly reveal the primary climatological patterns mn ca and u ca data are characterized by cycles of 20 200 cm length with mn ca having a distinct trend toward higher values between the core top and 200 cm these trends appear to be related to diagenetic coatings on the foraminifera shells most likely in the form of mn carbonates

geochemical composition and inferred accretion rates of sediments and managanese nodules from a submarine hill in the madeira abyssal plain eastern north atlantic abstract the porewater and sediment composition of two boxcores and of a small gravity core taken on a manganese nodule covered hill and in the madeira abyssal plain proper respectively are compared the pore water study of the two boxcores indicates that oxic conditions prevail in both cores in addition it indicates that no detectable fluxes of mn or fe occur from the porewater to the ocean bottom water variations in the geochemical composition of the sediments can be explained by fluctuations in the amount of carbonate which acts as a diluting agent a clear carbonate minimum is observed at 20 22 cm depth in the two cores this minimum is likely to be associated with the last glacial period 10 20 kyr b p this association is supported by the sediment accumulation rate of 15 mm kyr as found by extrapolation from the rate for pelagic sediments in the madeira abyssal plain the bulk composition of the manganese nodules recovered from the submarine hill is chemically almost identical to the average composition of atlantic nodules the trace metal and rare earth elements composition indicate a hydrogenous origin for the manganese nodules of this study on the basis of the chemical composition and that of nodules relative to that of the adjacent sediments an average nodule accretian rate of 2 8 3 3 mm myr has been calculated although the analyses of the entire ferromanganese nodules that have been studied seem to indicate a homogenous composition internal structures of the nodules reveal great inhomogeneity both visually and chemically these fluctuations may be related to variations in the fluxes of mn and fe which in turn could be climate related

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

mg ca temperature calibration for the benthic foraminifera melonis barleeanum and melonis pompilioides an important tool for deep sea temperature reconstruction is mg ca paleothermometry applied to benthic foraminifera foraminifera of the genus melonis appear to be promising candidates for temperature reconstructions due to their wide geographical and bathymetric distribution and their infaunal habitat which was suggested to reduce secondary effects from carbonate ion saturation co3 2 here we make substantial advances to previous calibration efforts and present new multi lab mg ca data for melonis barleeanum and melonis pompilioides from more than one hundred core top samples spanning in situ bottom temperatures from 1 to 16 c coupled with morphometric analyses of the foraminifer tests both species and their morphotypes seem to have a similar response of mg ca to growth temperature compilation of new and previously published data reveals a linear dependence of temperature on mg ca with a best fit of mg ca mmol mol 0 113 0 005 bwt c 0 792 0 036 r2 0 81 n 120 1 sd salinity bottom water co3 2 and varying morphotypes have no apparent effect on the mg ca temperature relationship but pore water co3 2 might have had an influence on some of the samples from the tropical atlantic

u ca in benthic foraminifers a proxy for the deep sea carbonate saturation the ocean plays a major role in the global carbon cycle and attempts to reconstruct past changes in the marine carbonate system are increasing the speciation of dissolved uranium is sensitive to variations in carbonate system parameters and previous studies have shown that this is recorded in the uranium to calcium ratio u ca of the calcite shells of planktonic foraminifera here we test whether u ca ratios of deep sea benthic foraminifera are equally suited as an indicator of the carbonate system we compare u ca in two common benthic foraminifer species planulina wuellerstorfi and cibicidoides mundulus from south atlantic core top samples with the calcite saturation state co32 co32 in situ co32 sat of the ambient seawater and find significant negative correlations for both species compared with planktonic foraminifera the sensitivity of u ca in benthic foraminifera to changes in co32 is about 1 order of magnitude higher although co32 exerts the dominant control on the average foraminiferal u ca the intertest and intratest variability indicates the presence of additional factors forcing u ca

origin of the deep bering sea nitrate deficit constraints from the nitrogen and oxygen isotopic composition of water column nitrate and benthic nitrate fluxes 1 on the basis of the normalization to phosphate a significant amount of nitrate is missing from the deep bering sea bs benthic denitrification has been suggested previously to be the dominant cause for the bs nitrate deficit we measured water column nitrate 15n 14n and 18o 16o as integrative tracers of microbial denitrification together with pore water derived benthic nitrate fluxes in the deep bs basin in order to gain new constraints on the mechanism of fixed nitrogen loss in the bs the lack of any nitrate isotope enrichment into the deep part of the bs supports the benthic denitrification hypothesis on the basis of the nitrate deficit in the water column with respect to the adjacent north pacific and a radiocarbon derived ventilation age of 50 years we calculate an average deep bs 2000 m water depth sedimentary denitrification rate of 230 mol n m 2 d 1 or 1 27 tg n yr 1 more than 3 times higher than high end estimates of the average global sedimentary denitrification rate for the same depth interval pore water derived estimates of benthic denitrification were variable and uncertainties in estimates were large a very high denitrification rate measured from the base of the steep northern slope of the basin suggests that the elevated average sedimentary denitrification rate of the deep bering calculated from the nitrate deficit is driven by organic matter supply to the base of the continental slope owing to a combination of high primary productivity in the surface waters along the shelf break and efficient down slope sediment focusing along the steep continental slopes that characterize the bs

comparison of near coincident crustal refraction and extended vibroseis reflection data peace river region canada a 10 km long uncorrelated vibroseis data set was processed to test the feasibility of using industry reflection data for deep crustal imaging in the peace river region and elsewhere in the western canada sedimentary basin these results were compared with a crustal refraction interpretation of a line 10 km to the north the vibroseis data were extended from a conventional 3 s to 14 s two way travel time using the self truncating sweep method the reflection section contains a prominent eastward dipping event at 9 4 s 29 km depth which corresponds to the zero offset two way travel time of an intracrustal boundary in the refraction model this may represent the riel discontinuity imaged at similar depths in southern alberta a series of near vertical incidence reflections over 1 1 5 s terminating at 13 s corresponds well with the refraction moho at 12 8 s 41 km depth this suggests that locally the crust mantle boundary is a complex possibly layered transition zone of 3 5 km thickness

multi disciplinary investigation of fluid seepage on an unstable margin the case of the central nile deep sea fan we report on a multidisciplinary study of cold seeps explored in the central nile deep sea fan of the egyptian margin our approach combines in situ seafloor observation geophysics sedimentological data measurement of bottom water methane anomalies pore water and sediment geochemistry and 230 th u dating of authigenic carbonates two areas were investigated which correspond to different sedimentary provinces the lower slope at 2100 m water depth indicates deformation of sediments by gravitational processes exhibiting slope parallel elongated ridges and seafloor depressions in contrast the middle slope at not vert 1650 m water depth exhibits a series of debris flow deposits not remobilized by post depositional gravity processes significant differences exist between fluid escape structures from the two studied areas at the lower slope methane anomalies were detected in bottom waters above the depressions whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities carbonate u th age dates 8 kyr bp pore water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past in contrast large 1 km2 carbonate paved areas were discovered in the middle slope with u th isotope evidence for ongoing carbonate precipitation during the late holocene since 5 kyr bp at least our results suggest that fluid venting is closely related to sediment deformation in the central nile margin it is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of fossil carbonate ridges whereas pervasive diffuse flow prevails at the unfailed middle slope

composition and origin of authigenic carbonates in the krishna godavari and mahanadi basins eastern continental margin of india abstract the mineralogical and stable isotopic composition of authigenic carbonates from the krishna godavari kg and mahanadi basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of india in the bay of bengal authigenic carbonate cements micro nodules bioturbation casts and tubes from 12 core locations drilled during the indian national gas hydrate program nghp expedition 01 were investigated for this study three main processes responsible for authigenic carbonate precipitation are identified organoclastic sulfate reduction anaerobic oxidation of methane and methanogenesis evidence of vigorous methane seepage is indicated in carbonates recovered at sites 7 10 12 kg basin and 19 mahanadi basin these methane derived carbonates display typical paragenetic carbonate mineralogies aragonite high mg calcite with 15 mol mgco 3 ca rich dolomite two separate horizons of methane derived carbonates are correlated between 4 drill holes up to 16 km apart the upper horizon has been dated with 14 c 40 100 51 600 a bp 1950 and clearly indicates that methane seepage has been much more vigorous in the past possibly due to the effect of lower sea level on the gas hydrate stability zone across the margin

preservation of benthic foraminifera and reliability of deep sea temperature records importance of sedimentation rates lithology and the need to examine test wall structure preservation of planktic foraminiferal calcite has received widespread attention in recent years but the taphonomy of benthic foraminiferal calcite and its influence on the deep sea palaeotemperature record have gone comparatively unreported numerical modeling indicates that the carbonate recrystallization histories of deep sea sections are dominated by events in their early burial history meaning that the degree of exchange between sediments and pore fluids during the early postburial phase holds the key to determining the palaeotemperature significance of diagenetic alteration of benthic foraminifera postburial sedimentation rate and lithology are likely to be important determinants of the paleoceanographic significance of this sediment pore fluid interaction here we report an investigation of the impact of extreme change in sedimentation rate a prolonged and widespread upper cretaceous hiatus in the north atlantic ocean on the preservation and 18o of benthic foraminifera of middle cretaceous age nannofossil zone nc10 uppermost albian lowermost cenomanian 99 ma ago from multiple drill sites at sites where this hiatus immediately overlies nc10 benthic foraminifera appear to display at least moderate preservation of the whole test however on closer inspection these tests are shown to be extremely poorly preserved internally and yield 18o values substantially higher than those from contemporaneous better preserved benthic foraminifera at sites without an immediately overlying hiatus these high 18o values are interpreted to indicate alteration close to the seafloor in cooler waters during the late cretaceous hiatus intersite differences in lithology modulate the diagenetic impact of this extreme change in sedimentation rate our results highlight the importance of thorough examination of benthic foraminiferal wall structures and lend support to the view that sedimentation rate and lithology are key factors controlling the paleoceanographic significance of diagenetic alteration of biogenic carbonates

benthic foraminiferal growth seasons implied from mg ca temperature correlations for three arctic species core top sediment samples from kongsfjorden svalbard and adjacent fjord and shelf areas were collected in order to investigate a potential relationship between mg ca ratios of arctic benthic foraminifera and the ambient bottom water temperatures bwt the area is influenced by large seasonal variation in factors such as light and temperature which is further strengthened by oceanographic shifts including inflow of relatively warm atlantic water four hydrological seasons have been defined the studied samples were collected during the years 2005 2010 and comprise data from three hydrological seasons spring summer and autumn five common species of cold water benthic foraminifera were investigated islandiella helenae norcrossi buccella frigida nonionellina labradorica elphidium clavatum and cassidulina reniforme for e clavatum and c reniforme the investigations failed for the remaining three species the mg ca temperature correlations initially appeared stochastic holding correlation coefficients between 0 01 and 0 15 however grouping the data based on seasons gave stronger mg ca temperature correlations indicating specific growing seasons for the three species the equations represent a starting point for a discussion on seasonality rather than robust ready to use equations i helenae norcrossi seem to reproduce and grow during summer july august in outer kongsfjorden for b frigida a mg ca temperature correlation is seen both in summer july august and autumn october november samples indicative of a continuous reproduction growth season lasting from july november n labradorica appears to reproduce and grow during autumn october november the results indicate that temperature reconstructions based on these benthic foraminifera reproduce seasonal temperatures rather than annual average temperatures this article is protected by copyright all rights reserved

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

diagenetic mg calcite overgrowths on foraminiferal tests in the vicinity of methane seeps methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera here we present structural geochemical and stable carbon isotope data from single foraminiferal calcite tests and authigenic mg calcite overgrowths in a sediment core recovered from an area of active methane seepage in western svalbard at ca 340 m water depth the foraminifera are from intervals in the core where conventional bulk foraminiferal 13c 13c values are as low as 11 3 mg ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain mg rich interlayers with mg ca up to 220 mmol mol transmission electron microscopy tem of the contact point between the biogenic calcite and authigenic mg calcite layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation secondary ion mass spectrometry sims analyses reveal that the mg rich layers are strongly depleted in 13c 13c 13c as low as 34 1 these very low 13c 13c values indicate that the authigenic mg calcite precipitated from pore waters containing methane derived dissolved inorganic carbon at the depth of the sulfate methane transition zone smtz as the depth of the smtz can be located several meters below the sediment seawater interface interpretation of low foraminiferal 13c 13c values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

testing the impact of diagenesis on the δ18o and δ13c of benthic foraminiferal calcite from a sediment burial depth transect in the equatorial pacific stable oxygen and carbon isotope 18o and 13c values measured in foraminiferal calcite are one of the primary tools used in paleoceanography diagenetic recrystallisation of foraminiferal calcite can act to reset primary isotopic values but its effects are typically poorly quantified here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial pacific ocean recovered during ocean drilling program odp leg 199 and integrated ocean drilling program iodp expedition 320 our selected sites form paleowater and burial depth transects with excellent stratigraphic control allowing us to confidently correlate our records we observe large inter site differences in the preservation state of benthic foraminiferal calcite implying very different recrystallisation histories but negligible inter site offsets in benthic 18o and 13c values we infer that diagenetic alteration of benthic foraminiferal calcite in sedimentary oozes must predominantly occur at shallow burial depths 100 m where offsets in both the temperature and isotopic composition of waters in which the foraminifera calcified and pore waters in which diagenesis occurs are small our results suggest that even extensive recrystallisation of benthic foraminiferal calcite results in minimal shifts from primary 18o and 13c values this finding supports the long held suspicion that diagenetic alteration of foraminiferal calcite is less problematic in benthic than in planktic foraminifera and that in deep sea sediments routinely employed for palaeoceanographic studies benthic foraminifera are robust recorders of stable isotope values in the fossil record

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

sr ca and mg ca ratios in niger delta sediments implications for authigenic carbonate genesis in cold seep environments we report on a reconnaissance analysis of the geochemical composition of authigenic carbonates and sediment samples collected from various seepage sites on the niger deep sea fan our aim has been to investigate whether evidence for the presence of authigenic carbonates and gas hydrates within sediments is discernible from solid phase sediment geochemistry we show that sedimentary sr ca and mg ca ratios can be used to infer the presence of authigenic aragonite sr rich and mg rich carbonate phases high mg calcite dolomite in cold seep settings using sr ca and mg ca ratios the proportion wt of authigenic carbonates in niger fan sediments can be calculated from a mixing model between sediment fractions of terrigenous material biogenic calcite aragonite and high mg calcite this approach was applied to high resolution geochemical profiles along sediment cores recovered from various cold seep settings mud volcano diapirs pockmarks gas hydrate bearing sediments our data reveal that authigenic carbonates occur as discrete phases in sediments from gas hydrate bearing areas suggesting that such carbonate rich sediment layers may represent paleo indicators for ancient methane seepage in marine sediments possibly associated to gas hydrate reservoirs

living benthic foraminifera of the okhotsk sea faunal composition standing stocks and microhabitats live rose bengal stained benthic foraminifera were investigated in surface sediment samples from the okhotsk sea to reveal the relationship between faunal characteristics and environmental parameters live benthic foraminifera were quantified in the size fraction 125 m in the upper 8 cm of replicate sediment cores recovered with a multicorer at five stations along the sakhalin margin and at three stations on the southwestern kamchatka slope the stations are from water depths between 625 to 1752 m located close or within the present okhotsk sea oxygen minimum zone with oxygen levels between 0 3 and 1 5 ml l 1 at the high productivity and ice free kamchatka stations live benthic foraminifera are characterized by maximal standing stocks about 1700 3700 individuals per 50 cm2 strong dominance of calcareous species up to 87 91 of total live faunas and maximal habitat depths down to 5 2 6 7 cm depth vertical distributions of total faunal abundances exhibit a clear subsurface maximum in sediments at the sakhalin stations which are seasonally ice covered and less productive live benthic foraminifera show lower standing stocks about 200 1100 individuals per 50 cm2 lower abundance of calcareous species 10 64 of total live faunas and shallower habitat depths down to 2 5 5 4 cm depth faunal vertical distributions are characterized by maximum in the uppermost surface sediments it is suggested that 1 lower and strongly seasonal organic matter flux caused by the seasonal sea ice cover and seasonal upwelling 2 lower bottom water oxygenation 0 3 1 1 ml l 1 and 3 more pronounced influence of carbonate undersaturated bottom water along the sakhalin margin are the main factors responsible for the observed faunal differences according to species downcore distributions and average living depths common calcareous species were identified as preferentially shallow intermediate and deep infaunal foraminiferal microhabitat occupation correlates with the organic matter flux and the depth of the oxygenated layer in sediments

cenozoic benthic foraminiferal mg ca and li ca records toward unlocking temperatures and saturation states the sensitivities of benthic foraminiferal mg ca and li ca to bottom water temperature and carbonate saturation state have recently been assessed here we present a new approach that uses paired mg ca and li ca records to calculate simultaneous changes in temperature and saturation state using previously published records we first use this approach to document a cooling of deep ocean waters associated with the establishment of the antarctic ice sheet at the eocene oligocene climate transition we then apply this approach to new records of the middle miocene climate transition from odp site 761 to estimate variations in bottom water temperature and the oxygen isotopic composition of seawater we estimate that the oxygen isotopic composition of seawater varied by 1 between the deglacial extreme of the miocene climatic optimum and the glacial maximum following the middle miocene climate transition indicating large amplitude variations in ice volume however the longer term change between 15 3 and 12 5 ma is marked by a 1 c cooling of deep waters and an increase in the oxygen isotopic composition of seawater of 0 6 we find that bottom water saturation state increased in the lead up to the middle miocene climate transition and decreased shortly after this supports decreasing pco2 as a driver for global cooling and ice sheet expansion in agreement with existing boron isotope and leaf stomatal index co2 records but in contrast to the published alkenone co2 records

syndepositional dissolution of calcareous foraminifera in modern shallow water sediments abstract dissolution of calcareous tests in waters undersaturated with respect to calcium carbonate causes postmortem changes to assemblages of modern benthic foraminifera comparison of the percentage of agglutinated tests in the living and dead assemblages from the same sample enables the amount of dissolution to be quantified re examination of data from the continental shelf off new york and the estuarine chezzetcook inlet canada reveals major dissolution losses which lead to dead assemblages rich in agglutinated tests it is probable that partial dissolution of the calcareous component of modern assemblages is more widespread than has been recognised

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

identification and removal of mn mg rich contaminant phases on foraminiferal tests implications for mg ca past temperature reconstructions 1 the geochemical composition of foraminifera shells from an ocean drilling program site in the panama basin has been analyzed by several analytical techniques la icp ms icp ms xrd sem edx in order to identify and evaluate the occurrence of contaminant phases which may bias paleoenvironmental reconstructions la icp ms results on uncleaned tests indicate the presence of mnmg rich contaminant phases at the inner surfaces of the foraminiferal shells which have mn ca ratios up to 400 mmol mol 1 and mg ca ratios up to 50 mmol mol 1 we have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included the analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high mn values are associated with at least two different contaminant phases of which only one is linked to high mg values xrd analysis further reveals that the mn mg rich phase is the ca mn mg carbonate kutnahorite ca mn mg co3 2 our results demonstrate that the presence of kutnahorite like minerals can bias mg ca ratios toward higher values by 7 36 and lead to significant overestimation of past seawater temperatures by 0 9 up to 6 2 c in the case of these panama basin samples components 11 867 words 13 figures 3 tables

carbon stable isotopic composition of benthic foraminifera from pliocene cold methane seeps cascadia accretionary margin abstract cold methane seep carbonates preserve the distinctive carbon stable isotope signatures of their ambient porewaters thus facilitating the identification of methane sources and fluid migration pathways this study employs an isotopic indicator from microfossils in a diffuse fossil seep for the recognition and characterization of methane seepage in the rock record benthic foraminifera from the pliocene quinault formation western washington state are plentiful and provide a temporal link between modern and more ancient seeps stable carbon isotope analyses of individual foraminiferal tests revealed a clear distinction between seep and non seep foraminifera infaunal species globobulimina pacifica and nonion basispinatum collected from seep samples exhibited 13 c values that were highly variable and often strongly depleted values ranged from 33 1 to 55 3 pdb in g pacifica and from 2 1 to 42 9 pdb in n basispinatum the epifaunal species cibicidoides mckannai though less depleted also showed considerable variability with 13 c values ranging from 1 7 to 3 1 pdb in contrast non seep specimens were much more enriched and less variable non seep specimens of n basispinatum displayed 13 c values clustering between 0 5 and 1 5 pdb while non seep specimens of c mckannai yielded a range of 1 1 to 1 8 pdb sem analyses and oxygen isotope values of foraminiferal tests indicated minimal diagenetic alteration 13 c values from authigenic blebs small nodules with wispy indistinct boundaries ranged from 8 7 to 38 4 pdb by combining these inorganic carbonate data with the foraminiferal values the association of seep specific bivalves and the present day leakage of thermogenic methane from the nearby garfield gas mound we conclude that these foraminifera precipitated their tests in the presence of methane derived carbon thus they record pore water 13 c depletion and syn depositional fluid flow pathways near the sediment water interface in a seep system active 3 4 mya and continuing onshore and offshore today the range and degree of 13 c depletion in the pliocene microfossils is due to the heterogeneity of seepage caused by different methane sources i e thermogenic and biogenic the tortuosity of fluid migration pathways reaching the seafloor sediments and mixing of seep fluids with dissolved inorganic carbon dic and marine organic carbon

calibrations for benthic foraminiferal mg ca paleothermometry and the carbonate ion hypothesis benthic foraminiferal magnesium calcium ratios were determined on one hundred and forty core top samples from the atlantic ocean the norwegian sea the indian ocean the arabian sea and the pacific ocean mostly at sites with bottom water temperatures below 5 c mg ca ratios are consistently lower by not vert similar 0 2 mmol mol in samples cleaned using oxidative and reductive steps than using oxidative cleaning differences between cibicidoides species have been identified mg ca of cibicidoides robertsonianus cibicidoides kullenbergi cibicidoides wuellerstorfi comparison with bottom water temperatures support observations of lowered mg ca of c wuellerstorfi at temperature below not vert similar 3 c compared with values predicted by published calibrations and from other cibicidoides species hydrographic data shows that carbonate ion saturation co32 decreases rapidly below this temperature an empirical sensitivity of co32 on mg ca has been established for c wuellerstorfi of 0 0086 0 0006 mmol mol mol kg a novel application using modern temperatures and last glacial maximum temperatures derived via pore fluid modelling supports a carbonate ion saturation state effect on mg incorporation this may significantly affect calculated 18oseawater obtained from foraminiferal 18o and mg ca temperature

methane derived carbonates and authigenic pyrite from the northwestern black sea abstract methane seeps in the northwestern black sea are accompanied by carbonate and pyrite precipitates sediments were sampled at locations on the romanian 120 m depth and ukrainian 180 200 m depth shelf and slope layered carbonate crusts are formed of i carbonate cemented siliciclastic sediment containing dreissenoid bivalves ii microcrystalline high mg calcite or aragonite and iii aragonitic cement the dreissena sediment is subrecent and was deposited during the freshwater phase of the black sea it has been affected by seepage of methane rich fluids which induced intergranular precipitation of authigenic carbonates the microcrystalline carbonates exhibit an intense autofluorescence high mg calcite contains 11 14 mol mgco3 the aragonitic cement 8300 9500 ppm sr forms either isopachous layers or botryoids microbial filaments about 10 20 m in diameter and up to 900 m in length are preserved within and on carbonate crusts the carbonates are depleted in 13c microcrystalline carbonate ranges from 27 to 41 pdb and botryoidal aragonite ranges from 26 to 38 pdb the 13c depletion indicates that the carbonates predominantly derive from the microbial oxidation of methane carbonate deposits do not project up into the oxic water column they are restricted to the anoxic water column and to anoxic sediments revealing the crucial role of anaerobic methane oxidation for carbonate precipitation 14c contents give apparent radiocarbon ages of 20 640 180 a bp for a sample of botryoidal aragonite and 19 110 180 a bp for a sample of microcrystalline carbonate compatible with minimum ages of carbon derived from a fossil hydrocarbon source the 18o values of methane derived carbonates show a narrow range from 1 2 to 0 2 pdb 87sr 86sr ratios of microcrystalline carbonate mean 0 70927 and aragonitic cement mean 0 70918 are indistinguishable from ambient seawater mean 0 70917 and thus indicate a shallow sr source higher 87sr 86sr ratios of the dreissena sediment mean 0 71005 are probably caused by sr derived from detrital mica carbonates are accompanied by blocks and crusts composed of pyrite the framboidal sulphide exhibits a palisade like fabric with framboids arranged to parallel pillars sulphur isotopic ratios 34s ranging from 16 8 to 19 7 cdt indicate that the sulphur derives not from the 34s depleted h2s of the water column or the uppermost sediment layers most likely pyrite formed in the lacustrine sediments after the first incursion of mediterranean seawater

rates of anaerobic oxidation of methane and authigenic carbonate mineralization in methane rich deep sea sediments inferred from models and geochemical profiles abstract pore water chemical data obtained from a 10 5 m long giant gravity core collected in methane rich sediments from 647 m water depth in the northern gulf of mexico n 28 04 00 w 89 43 15 defines sub bottom gradients in unprecedented detail this core penetrated the sulfate methane interface smi at 300 cm below the seafloor cmbsf at the smi dissolved inorganic carbon dic concentrations reach a maximum 13 5 mm and pore water 13 c dic 63 2 pdb and 13 c methane 89 5 pdb values are most negative below the smi pore water sulfate is nearly depleted methane concentrations rise sharply with simultaneous occurrence of a bubble textured sediment and fine grained methane derived authigenic carbonate nodules and cements are common the sharp peaks in dic concentration and isotope values centered at the smi indicate that dic is being produced by anaerobic oxidation of methane aom within a narrow zone centered at the smi the detailed sulfate and dic concentration profiles and dic 13 c values have enabled geochemical models to be constructed that explore the rate of dic formation by aom and its effect on pore water dic 13 c values model results closely match measured dic concentration and 13 c isotope profiles and indicate that microbiological conversion of methane carbon to dic is rapid in geologic terms and that aom is occurring at the present position of the smi isotope values for authigenic carbonate found immediately below the present day smi 13 c 60 2 0 7 pdb at 440 cmbsf are consistent with derivation of the carbonate carbon from methane via aom at the former location of a smi these observations and model results suggest that aom is occurring at rates that would generate the observed profiles and begin the precipitation of methane derived carbonate occur on time scales of centuries model results also show that the time needed to produce the resulting authigenic cements is an order of magnitude greater than that for aom to produce the observed dic profiles the metabolic rates for dic production by aom inferred from modeling the geochemical profiles compare favorably with available rate data obtained from laboratory microbial incubations and radiolabeled tracer experiments

mineralogical geochemical and isotopic characterization of authigenic carbonates from the methane bearing sediments of the bering sea continental margin iodp expedition 323 sites u1343 u1345 abstract during expedition 323 of the integrated ocean drilling program to the bering sea july 5 september 4 2009 three sites were drilled along the bering sea northeastern continental margin u1343 down to 745 meters below sea floor mbsf u1344 745 mbsf u1345 150 mbsf diagenetic carbonates are present at all sites within the clayey diatom rich oozes of the bering sea where pore waters are also characterized by extremely high methane concentrations we here present mineralogical elemental and isotopic data obtained from the authigenic carbonate rich intercalations within the clay rich pleistocene sediments deposited along the bering sea continental margin the mineralogy of the authigenic carbonates is generally represented by composite mixtures of very small crystals of magnesian calcite dolomite and iron rich carbonates with the latter phases occurring below 260 mbsf at site u1343 below 200 mbsf at site u1344 and below 130 mbsf at site u1345 element geochemistry shows that ca mg fe ba mn sr and u are enriched in the carbonate rich intercalations relative to the background sediments due to their incorporation into the carbonates and into other authigenic phases e g barite and pyrite the oxygen and carbon isotopic compositions of the authigenic carbonate minerals show that they were sequentially precipitated from pore waters at different temperatures i e different burial depths and with different isotopic compositions of dissolved inorganic carbon dic the authigenic mg calcite precipitated early during diagenesis and shallow burial from a 13 c depleted dic pool whereas dolomite and fe rich carbonates formed during later diagenesis and deeper burial from a 13 c enriched dic pool these authigenic carbonate occurrences are interpreted as resulting from microbial sulfate reduction combined with anaerobic oxidation of methane and methanogenesis that was intimately linked to the alteration of silicates especially iron rich clay minerals

determination of the mg mn ratio in foraminiferal coatings an approach to correct mg ca temperatures for mn rich contaminant phases the occurrence of manganese rich coatings on foraminifera can have a significant effect on their bulk mg ca ratios thereby biasing seawater temperature reconstructions the removal of this mn phase requires a reductive cleaning step but this has been suggested to preferentially dissolve mg rich biogenic carbonate potentially introducing an analytical bias in paleotemperature estimates in this study the geochemical composition of foraminifera tests from mn rich sediments from the antarctic southern ocean odp site 1094 was investigated using solution based and laser ablation icp ms in order to determine the amount of mg incorporated into the coatings the analysis of planktonic and benthic foraminifera revealed a nearly constant mg mn ratio in the mn coating of 0 2 mol mol consequently the coating mg mn ratio can be used to correct for the mg incorporated into the mn phase by using the down core mn ca values of samples that have not been reductively cleaned the consistency of the coating mg mn ratio obtained in this study as well as that found in samples from the panama basin suggests that spatial variation of mg mn in foraminiferal mn overgrowths may be smaller than expected from mn nodules and mn ca carbonates however a site specific assessment of the mg mn ratio in foraminiferal coatings is recommended to improve the accuracy of the correction