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

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

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

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

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

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

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

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

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

tropical cyclones in the southwest pacific spatial patterns and relationships to southern oscillation and sea surface temperature abstract an analysis of a 20 yr dataset of tropical cyclones in the southwest pacific has been made to determine the spatial patterns of cyclone occurrence and how these depend on the southern oscillation so and sea surface temperature a local measure of cyclone incidence is defined as the number of cyclones that enter into a 2 lat long square during some period eg within one season and this quantity is mapped for four southern oscillation index soi categories the maps show that the geographical distribution of cyclone incidence shifts eastward and northward during negative soi phases and vice versa the mean annual incidence for the whole region is 28 higher than average for our strongly negative so category and 16 below average for our near zero category to explore the roles of the so and local sst correlation analysis was applied to mean values of cyclone incidence for four subregions of 20 longitude width between 10 and 22 s markedly different soi sst responses were found on either s

modulation of north pacific tropical cyclone activity by three phases of enso abstract tropical pacific ocean warming has been separated into two modes based on the spatial distribution of the maximum sea surface temperature sst anomaly an east pacific warming epw and a central pacific warming cpw when combined with east pacific cooling epc these three regimes are shown to have different impacts on tropical cyclone tc activity over the north pacific by differential modulation of both local thermodynamic factors and large scale circulation patterns in epw years the genesis and the track density of tcs tend to be enhanced over the southeastern part and suppressed in the northwestern part of the western pacific by strong westerly wind shear the extension of the monsoon trough and the weak wind shear over the central pacific increases the likelihood of tc activity to the east of the climatological mean tc genesis location in cpw years the tc activity is shifted to the west and is extended through the northwestern part of the western pacific the westward shifting of c

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

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

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

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

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

distinct influences of the enso like and pmm like sst anomaly on the mean tc genesis location in the western north pacific the 2015 summer as an extreme example abstractthis study reports the different effects of tropical and subtropical sea surface temperature anomalies sstas on the mean tropical cyclone tc genesis location in the western north pacifi

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

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

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

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

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

the relationship between the southern oscillation index and tropical cyclone tracks in the eastern north pacific points of origin and downgradation of tropical cyclones in the eastern north pacific enp east of 160 w are related to the southern oscillation index soi during the hurricane season all enp tropical storms and hurricanes from 1966 through 1997 were grouped into three soi based categories those occurring during strong el nino events mean soi 0 6 or near zero periods 0 6 mean soi 0 6 during el nino storm seasons enp tropical cyclones originated approximately 5 7 617 km west and downgraded 7 5 780 km west of the long term mean longitudes for the positive soi group near zero group storms also followed more northerly tracks than the negative soi group storms however no significant differences in storm track are evident between the positive soi and near zero groups and the track length is not significantly different for any storm group

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

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

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

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

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

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

genesis of super cyclone pam 2015 modulation of low frequency large scale circulations and the madden julian oscillation by sea surface temperature anomalies abstractsuper cyclone pam 2015 formed in the central tropical pacific under conditions that included el nino modoki and the passage of a convectively enhanced phase of the madden julian oscillation mjo in the western pacific this study examines the influence that sea surface temperature anomalies sstas have on the mjo and low frequency large scale circulation and establishes how they modulated the genesis of pam two series of numerical experiments were conducted by using a nonhydrostatic global atmospheric model with observed obssst and climatological clmsst ssts the results suggested that low frequency westerly winds at 850 hpa u850 were intensified in the central tropical pacific due to the observed ssta the amplitude of the mjo simulated in obssst was larger than in clmsst in addition the experiments initialized 26 february 2 march exhibited that the phase of the mjo in obssst was ahead of that in clmsst and that the genesis location in obssst was 10 to the east of that in clmsst

clustering of eastern north pacific tropical cyclone tracks enso and mjo effects 1 a probabilistic clustering technique is used to describe tropical cyclone tracks in the eastern north pacific on the basis of their shape and location the best track data set is decomposed in terms of three clusters these clusters are analyzed in terms of genesis location trajectory landfall intensity seasonality and their relationships with the el nino southern oscillation enso and madden julian oscillation mjo longitudinal track location plays a strong discriminating role in the regression mixture model s solution with the average track orientation becoming more zonal toward the west this progression encapsulates well the relationship between tropical cyclones over the eastern tropical pacific and the mjo or enso two of the clusters describe tropical cyclones tcs with tracks that lie near the coast of mexico and central america the most frequent cluster contains tracks that trend west northwestward while the second most frequent one has genesis locations that lie slightly to the southeast of those in the most frequent cluster and tracks that run typically parallel to the central american coast this second cluster is shown to be significantly associated with the westerly phase of the mjo the third least frequent cluster contains tcs with westward trajectories over the central and eastern equatorial pacific some of these tcs have an impact on hawaii and other islands as far as the central and western north pacific regions the least frequent cluster is strongly related to enso while the others are not it occurs significantly more frequently during el nino conditions examination of the large scale patterns of atmospheric circulation and sea surface temperature associated with each of our three clusters are consistent with previous studies anomalous low level westerly zonal winds from the monsoon trough and mjo meet anomalous easterlies near the region of genesis in each cluster

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

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

tropical cyclone activity in the northwest pacific in relation to the el nino southern oscillation phenomenon abstract the interannual variations in tropical cyclone activity in the northwest pacific nwpac and their relationships with the el nino southern oscillation enso phenomenon were studied using the method of spectral analyses time series of a southern oscillation index soi defined as the sea level pressure difference between easter island and darwin and tropical cyclone activity in the entire nwpac ocean basin as well as in different regions of the nwpac were analyzed two spectral peaks are apparent in all these time series one corresponds to the generally accepted southern oscillation with a period of 3 to 3 5 years and another at the quasi biennial oscillation qbo frequency cross spectral analyses between the soi and tropical cyclone activity show significant coherence in these two spectral peaks the dominant peak is at the southern oscillation frequency with the soi leading typhoon activity by almost a year at the qbo frequency the two series are almost in phase cyclone activity in t

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

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

a teleconnection between atlantic sea surface temperature and eastern and central north pacific tropical cyclones the el nino southern oscillation enso is a major source of seasonal tropical cyclone tc predictability in both local and remote ocean basins unusually warm eastern central equatorial pacific sea surface temperature sst during el nino tends to enhance eastern and central north pacific ecnp tcs and suppress atlantic tcs here we demonstrate that atlantic sst variability likewise influences remote tc activity in the eastern central pacific through a walker circulation type response analogous to the enso atlantic tc teleconnection using observations and 27 km resolution tropical channel model tcm simulations observed and simulated ecnp tc activity is reduced during the positive atlantic meridional mode amm which is characterized by warm northern and cool southern tropical atlantic sst anomalies and vice versa during the negative amm large ensembles of tcm simulations indicate that sst variability rather than internal atmospheric variability drives extreme ecnp hurricane seasons

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

evolution of a thrust sheet top basin the tertiary barreme basin alpes de haute provence france in the french sector of the tertiary alpine mountain belt of southern europe the early stages of compression established an initial thrust front a long distance into the foreland 30 40 km rearward of the terminal thrust front an extensive region of thrust sheet top basins was established behind this initial thrust front particularly after a regional marine transgression in late eocene time priabonian these basins were initially connected but became increasingly compartmentalized as the thrust belt evolved the basins are now preserved as a series of structurally isolated synclinal remnants in the external zones of the alpine thrust belt one of these remnants known as the barreme basin has a preserved fill that is 900 m thick spans 18 m y and is exposed over 50 km 2 the tertiary basin fill comprises initial nonmarine deposits overlain by a marine succession and subsequent continental strata and includes evidence of submarine gravity slides growth structures and abrupt changes in sediment transport directions and provenance evolution of the basin fill was influenced by both far field and more localized near field deformation events the latter being dominated by the progressive growth of a steep thrust related anticline that defined the eastern margin of the basin this basin fill records several key steps in the evolution of the alpine mountain belt such as the first incursion of clasts derived from the emplacement of major thrust structures in the inner parts of the mountain belt ca 32 30 ma synsedimentary volcanic activity and the growth of an important out of sequence anticline that progressively separated the barreme basin from the gres d9annot basin to the east in addition the basin preserves the progression from an early underfilled flysch basin to a subsequent overfilled molasse basin in early oligocene time rupelian between ca 33 and 30 ma records of these events are not available from the fill of the younger foreland basin preserved beyond the final thrust front and this remnant of the thrust sheet top basin province therefore provides a unique record of the early structural and stratigraphic evolution of the alpine mountain belt

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