modeling phosphorus cycling and carbon burial during cretaceous oceanic anoxic events article i nfo in the greenhouse world of the cretaceous there were episodes of oxygen depletion in the deep ocean associated with enhanced organic carbon burial in sediments black shale formation in this study we use a box model of the oceanic phosphorus p organic carbon orgc and oxygen cycles to explore the hypothesis that variations in marine p availability control deep ocean oxygen depletion anoxia and the formation of black shales under cretaceous ocean conditions we find that for the cretaceous ocean with large continental shelves slow oceanic overturning and high sea surface temperatures oceanic anoxic events oaes can be triggered by enhanced p supply from land and that the system is particularly sensitive to oceanic mixing in our baseline scenario the deep sea becomes completely anoxic while the shelves attain only partial anoxia sedimentary burial differs between the shelves and open ocean while organic carbon burial is enhanced in both regions deep sea reactive p burial decreases dramatically under anoxia but not on the shelves where oxygen depletion is not complete furthermore our model results imply that oaes can be sustained by p recycling from sediments under low oxygen conditions ultimately however the feedbacks which result in the accumulation of atmospheric oxygen terminate the anoxic event atmospheric oxygen is modulated by land processes such as forest fires and oxidative weathering which limit the rise of atmospheric o2 our model findings are corroborated by p burial data from the geological record for oae2 approximately 94 myr bp through a sensitivity analysis we identify two necessary criteria for oaes low mixing of surface and deep waters poor ocean ventilation and enhanced sedimentary p recycling under low oxygen conditions when these criteria are met ocean anoxia is a robust result to a mild increase of continental supply of phosphorus under a wide range of environmental conditions

160 m y record of marine sedimentary phosphorus burial coupling of climate and continental weathering under greenhouse and icehouse conditions a compilation of all meaningful phosphate data published in the proceedings of the deep sea drilling project and the ocean drilling program is used here for the extraction of a 160 m y marine burial record of bulk phosphorus all sediment types 5648 measurements and a 100 m y marine burial record of biogenic phosphorus pelagic biogenic sediment types 1754 data these records serve as estimates for total and dissolved bioavailable phosphorus flux rates which in turn are highly dependent on total and chemical continental weathering rates respectively the similarity of both records indicates that in the past 100 m y changes in total weathering rates may have been tracked by changes in chemical weathering rates prior to 32 ma phosphorus burial and long term sea level change are positively correlated from 32 ma to the present this correlation is inverse this points to a fundamental change in feedback mechanisms between continental weathering phosphorus and climate which was probably linked to the onset of major glaciation

nutrients as the dominant control on the spread of anoxia and euxinia across the cenomanian turonian oceanic anoxic event oae2 model data comparison 1 the cenomanian turonian oceanic anoxic event oae2 is characterized by large perturbations in the oxygen and sulfur cycles of the ocean potentially resulting from changes in oxygen supply via oxygen solubility and ocean circulation and in marine productivity we assess the relative impact of these mechanisms comparing model experiments with a new compilation of observations for seafloor dysoxia anoxia and photic zone euxinia the model employed is an intermediate complexity earth system model which accounts for the main ocean dynamics and biogeochemistry of the cretaceous climate the impact of higher temperature and marine productivity is evaluated in the model as a result of higher atmospheric carbon dioxide and oceanic nutrient concentrations the model shows that temperature is not alone able to reproduce the observed patterns of oceanic redox changes associated with oae2 observations are reproduced in the model mainly via enhanced marine productivity due to higher nutrient content responsible for 85 of the change higher phosphate content could have been sustained by increased chemical weathering and phosphorus regeneration from anoxic sediments which in turn induced an enhanced nitrogen nutrient content of the ocean via nitrogen fixation the model also shows that the presence of seafloor anoxia as suggested by black shale deposition in the proto north atlantic ocean before the event might be the result of the silled shape and lack of deep water formation of this basin at the late cretaceous overall our model data comparison shows that oae2 anoxia was quasi global spreading from 5 of the ocean volume before the event to at least 50 during oae2

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

a numerical study on the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal winds abstract a numerical model simulation investigates the influence of the mid atlantic ridge on nonlinear first mode baroclinic rossby waves generated by seasonal wind fluctuations the north atlantic is simulated by a square box two layer quasi geostrophic qg model the bottom topography is ridge like and compromises the qg approximation and the actual shape of the ridge sponge layers protect all boundaries except the eastern one from wave reflection and eliminate the build up of the western boundary current the model is forced by a purely fluctuating wind stress curl derived from the most significant eofs of the fgge winds a flat bottom and a ridge experiment are compared in both experiments the eastern boundary is an important source of annual period baroclinic rossby waves wave trains having a wavelength of about 1060 km and a westward phase speed around 3 4 cm s 1 propagate energy westward at 3 cm s 1 in the flat bottom experiment a source of directly wind forced baroclinic waves of annual per

end cretaceous marine mass extinction not caused by productivity collapse an asteroid impact at the end of the cretaceous caused mass extinction but extinction mechanisms are not well understood the collapse of sea surface to sea floor carbon isotope gradients has been interpreted as reflecting a global collapse of primary productivity strangelove ocean or export productivity living ocean which caused mass extinction higher in the marine food chain phytoplankton dependent benthic foraminifera on the deep sea floor however did not suffer significant extinction suggesting that export productivity persisted at a level sufficient to support their populations we compare benthic foraminiferal records with benthic and bulk stable carbon isotope records from the pacific southeast atlantic and southern oceans we conclude that end cretaceous decrease in export productivity was moderate regional and insufficient to explain marine mass extinction a transient episode of surface ocean acidification may have been the main cause of extinction of calcifying plankton and ammonites and recovery of productivity may have been as fast in the oceans as on land

environmental significance of foraminiferal morphogroups in jurassic north sea deltas abstract the distribution of morphological groups of foraminifera has been analysed in toarcian and bajocian deposits of the northern north sea and the yorkshire coast the deposits are referred to prodeltaic lower delta front and interdistributary bay environments and contain mainly or entirely agglutinating assemblages of low to intermediate diversity a total of 33 agglutinating species are recognized in the studied material and these are arranged into eleven morphotypes composing seven subgroups and four morphogroups the categories are distinguished on the basis of main morphological features of the taxa combined with their life positions and micro habitats as inferred from modern analogues the prodelta deposits were formed in a normal saline and slightly stagnant depositional setting with foraminiferal faunas composed mainly of surficial and infaunal morphogroups the lower delta front and interdistributary bay sediments were deposited in shallow hyposaline waters strongly dominated by an epifaunal morphogroup with a partly phytal association a model of agglutinated morphotype distribution reveals increasing morphotype diversity and by inference ecological niche span from interdistributary bay through lower delta front to prodeltaic environments

high resolution geochemical and biotic records of the tethyan bonarelli level oae2 latest cenomanian from the calabianca guidaloca composite section northwestern sicily italy abstract high resolution micropalaeontological and chemostratigraphic records for the upper cenomanian portion of the calabianca guidaloca composite section nw sicily provide new insight into the palaeoclimatic and palaeoceanographic evolution of the tethys ocean the bonarelli level equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy and radiolarian assemblages as well as by the 13 c curve showing a marked positive excursion up to 4 7 the bonarelli level equivalent deposition is characterized by highly eutrophic conditions as testified by radiolarian proliferation black shale samples from the calabianca guidaloca composite section contain very high toc up to 26 and moderate to high amounts of caco 3 on average 20 among the planktonic foraminifera hedbergellids and globigerinelloids tolerated the environmental stress induced by the oceanic anoxic event 2 oae2 the occurrence of some benthic foraminifera testifies to dysoxic rather than completely anoxic conditions at the sea floor during the deposition of some portions of the bonarelli level equivalent based on micropalaeontological results and geochemical proxies 13 c d rb ti v ni ba si cr the bonarelli level equivalent is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle we propose that periodically increased riverine influxes triggered by enhanced humidity resulted in a sluggish circulation mode and consequent anoxic euxinic conditions favouring the preservation of organic matter at the sea floor spectral analyses performed on selected geochemical signals reveal within the main high productivity event a strong orbital climatic forcing represented by a long term eccentricity steered humidity cyclicity that amplifies a short term precession controlled productivity fluctuation

evolution in the test size of deep sea benthic foraminifera during the past 120 m y evidence is presented for stratigraphic variations in test size of the largest deep water 1500 m water depth calcareous trochospiral benthic foraminifera for eight dominant lineages composed of ten genera over the past 120 m y variations in test size show 1 a general trend of increasing test size during the past 120 m y and 2 fluctuations highlighted by six minima and six maxima that are synchronized among genera the long term increase in size corresponds to an increase in the 18o of deep water benthic foraminifera the minimum and maximum sizes correspond to minima and maxima in the 18o respectively in addition three major minima in test size correspond to distinct low dissolved oxygen events these latter synchronisms indicate that oceanic climate and dissolved oxygen or related factors likely controlled evolution in test size of deep water calcareous trochospiral benthic foraminiferal genera

decadal sea level variability in the south pacific in a global eddy resolving ocean model hindcast sea level variability and related oceanic changes in the south pacific from 1970 to 2003 are investigated using a hindcast simulation of an eddy resolving ocean general circulation model ogcm for the earth simulator ofes along with sea level data from tide gauges since 1970 and a satellite altimeter since 1992 the first empirical orthogonal function mode of sea level anomalies slas of ofes exhibits broad positive slas over the central and western south pacific the corresponding principal component indicates roughly stable high low and high slas separated by a rapid sea level fall in the late 1970s and sea level rise in the late 1990s consistent with tide gauge and satellite observations these decadal changes are accompanied by circulation changes of the subtropical gyre at 1000 m depth and changes of upper ocean zonal current and eddy activity around the tasman front in general agreement with previous related studies it is found that sea level variations in the tasman sea can be explained by propagation of long baroclinic rossby waves forced by wind stress curl anomalies if the impact of new zealand is taken into account the corresponding atmospheric variations are associated with decadal variability of el nino southern oscillation enso thus decadal sea level variability in the western and central south pacific in the past three and half decades and decadal enso variability are likely to be connected the sea level rise in the 1990s which attracted much attention in relation to the global warming is likely associated with the decadal cooling in the tropical pacific

calcareous nannofossil assemblages of oceanic anoxic event 2 in the equatorial atlantic evidence of an eutrophication event the calcareous nannofossils of the cenomanian turonian boundary interval of sites 1258 and 1260 ocean drilling program leg 207 have been studied in order to understand the depositional environment during oceanic anoxic event 2 oae2 in the equatorial atlantic nannofossil assemblages show a significant change in relative abundances during the positive 13 corg excursion interval the strong increase of the high productivity indicator zeugrhabdotus erectus and the simultaneous decrease of the oligotrophic taxa watznaueria barnesiae and watznaueria fossacincta are indicative of enhanced fertility the decrease of eprolithus floralis may be attributed to the surface water temperature increase during oae2 which is however not very significant 2 3 c as suggested by published tex86 data it seems more likely that the decrease of e floralis during oae2 was evoked by the breakdown of water column stratification indicating it as a deep dwelling species which prefers stratified waters with a deep nutricline prediscosphaera spp and retecapsa ficula which show a significant increase in relative abundances during oae2 seem to prefer eutrophic environments while amphizygus brooksii and zeugrhabdotus noeliae lower surface water fertility gartnerago segmentatum broinsonia spp watznaueria biporta and seribiscutum gaultensis decrease in abundances during oae2 it is not clear if they preferred an oligotrophic environment cooler surface waters or if they were inhabitants of the lower photic zone published geochemical data suggest that enhanced fertility and higher temperatures during oae2 may have been caused by submarine volcanic activity through the release of biolimiting micronutrients into the ocean and carbon dioxide into the atmosphere the breakdown of water column stratification may have increased further nutrient availability 2007 elsevier b v all rights reserved

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

foraminiferal response to sea level change organic flux and oxygen deficiency in the cenomanian of the tarfaya basin southern morocco the mohammed plage coastal section and well s13 in the tarfaya basin southern morocco are key sections to investigate the subsidence of the basin and the cenomanian eustatic sea level history results from a canonical correspondence analysis cca based on benthic foraminiferal assemblage counts and additional proxies percent planktic foraminifera planktic foraminifera morphogroups total organic carbon content toc show a general deepening trend for the investigated sections the most important factor identified in the ordination of species and samples is water depth the cca identifies bolivina anambra globulina lacrima lenticulina spissocostata and spiroplactammina sp as typical shallow water species praebulimina nannina gavelinella dakotensis gavelinella sp saccammina alexanderi and valvulineria lenticula as deep water species and gabonita levis gabonita obesa neobulimina albertensis lingulogavelinella asterigerinoides lenticulina gaultina haplophragmoides gigas haplophragmoides bauchensis and trochammina taylorana as unrestricted or intermediate species the temporal succession of benthic foraminiferal assemblages indicates repeated periods of shallowing within the general deepening trend in particular within the lower portion of the sections rotalipora brotzeni and r reicheli planktic foraminiferal zones restricted assemblages occurred when intensification of the oxygen minimum zone inhibited a diverse benthic community abundant high organic flux indicators at the base of the mohammed plage section indicate that an upwelling cell off northwest africa was already active during the early cenomanian c 2004 elsevier b v all rights reserved

consequences of moderate 25 000 yr lasting emission of light co 2 into the mid cretaceous ocean future warming is predicted to shift the earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming this study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not vert similar 112 myr ago our study focuses on the cretaceous oceanic anoxic event oae 1b and explores how the earth system responded to a moderate not vert similar 25 000 yr lasting climate perturbation that is modelled to be less than 1 c in global average temperature using a new chronological model for oae 1b we present high resolution elemental and bulk carbon isotope records from dsdp site 545 from mazagan plateau off nw africa and combine this information with a coupled atmosphere land ocean model the simulations suggest that a perturbation at the onset of oae 1b caused almost instantaneous warming of the atmosphere on the order of 0 3 c followed by a longer not vert similar 45 000 yr period of not vert similar 0 8 c cooling the marine records from dsdp site 545 support that these moderate swings in global climate had immediate consequences for african continental supply of mineral matter and nutrients phosphorous subsequent oxygen availability and organic carbon burial in the eastern subtropical atlantic however without turning the ocean anoxic the match between modelling results and stratigraphic isotopic data support previous studies summarized in jenkyns h c 2003 evidence for rapid climate change in the mesozoic palaeogene greenhouse world the royal society 361 1885 1916 in that methane emission from marine hydrates albeit moderate in dimension may have been the trigger for oae 1b though we can not finally rule out alternative mechanisms following the hydrate mechanism a total of 1 15 1018 g methane carbon 13c 60 equivalent to about 10 to the total modern gas hydrate inventory generated the 13ccarb profile recorded in the section modelling suggests a combination of moderate scale methane pulses supplemented by continuous methane emission at elevated levels over not vert similar 25 000 yr the proposed mechanism though difficult to finally confirm in the geological past is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously this study shows that once set off this mechanism can maintain earth s climate in a perturbed mode over geological time leading to pronounced changes in regional climate

response of middle jurassic benthic foraminiferal morphogroups to dysoxic anoxic conditions in the pieniny klippen basin polish carpathians abstract the distribution of foraminiferal morphological groups has been analyzed in upper aalenian lower bajocian black siltstones and mudstones of the pieniny klippen belt polish carpathians the deposits are assigned to middle neritic outer and upper bathyal zones represented by three succession and contain agglutinated and calcaeous foraminifera assemblages separate classifications of agglutinated and calcareous morphogroups are established and used for a palaeocological study the groups are distinguished on the basis of morphological features modes of life and feeding habits as inferred from modern analogues infaunal preferences of some foraminifera have been supported by comparison with other infaunal indicators such as trace fossil tiering and abundance of infaunal ostracods a new quantitative method to estimate dissolution of calcareous tests has been tested on the most common genus lenticulina it reveals a special survival strategy of this genus in suboxic muddy and flocculent substrate the distribution of morphogroups in comparison with other palaeoecological taphonomical and sedimentological indicators allows interpretations of organic input rate of sedimentation level of oxygenation position of the redox boundary and p h the studied deposits represent regional anoxic dysoxic event which occured within a semienclosed silled basin

storm tracks in the southern hemisphere subtropical oceans ocean storm tracks have previously been associated with the midlatitude western boundary currents wbcs and the antarctic circumpolar current acc here we identify and examine large scale baroclinically unstable waves occurring within waveguides associated with potential density gradients in the subtropical regions of the southern hemisphere sh oceans where the trade winds and westerlies meet and at depths associated with mode water formation in contrast to the northern hemisphere subtropics the sh pathways are more extensive allowing large scale coherent disturbances to communicate information westward from the midlatitudes to the subtropics south pacific ocean and from the subtropics to the tropics indian ocean particular consideration is given to the subtropical south pacific ocean as this is a region where resonant interactions between large scale rossby waves and significant topographic features have been reported to occur using an ocean general circulation model and a simple potential energy transfer diagnostic we identify the relevant nonlinearly modified structures comparing their propagation characteristics to planetary rossby waves calculated using a shallow water model although at first appearance baroclinic disturbances resemble planetary rossby waves we show they are inherently nonlinear multiscale and are amplified where topography occurs the location of the disturbances coincides with regions of high variability in sea surface height observed in satellite altimetry and their speeds closely match the large scale coherent westward propagating structures described in the observational literature our study provides evidence that in addition to the midlatitude wbcs and the acc significant ocean storm tracks are also manifest in the sh subtropics

enhanced productivity led to increased organic carbon burial in the euxinic north atlantic basin during the late cenomanian oceanic anoxic event 1 three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in 13c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

on the sea ice regime of the ross sea antarctica variations spatiotemporelles de la glace de mer determinees a partir de donnees microondes passives et meteorologiques hydrologiques

benthonic foraminiferal mass extinction and survival assemblages from the cenomanian turonian boundary event in the menoyo section northern spain

barium in sediments off northwest africa a tracer for paleoproductivity or meltwater events 1 high resolution down core analyses of the solid phase content of total barium batot and total organic carbon toc back to 25 kyr b p were performed on a gravity core from the upper continental slope off cape yubi morocco the observed discrepancy between the two potential paleoproductivity proxies batot and toc initiated supplementary examinations of the pore water the geochemistry of the clay fraction x ray diffraction analyses and the application of a sequential ba extraction method of selected samples additionally we analyzed down core samples of the planktonic foraminifera turborotalita quinqueloba and globorotalia inflata for their ba ca ratios these analyses which were performed for the first time on these species were used to reconstruct past oceanic ba concentrations we suggest that in the study area which is characterized by high accumulation rates the preserved toc content is a valuable proxy for past primary productivity whereas the solid phase batot contents appear to be affected by other mechanisms and factors peaks of total barium content in the clay fraction and of ba ca ratios in the planktonic foraminifera shells found during the younger dryas and the heinrich 1 event are likely to result from increased meltwater influx into the northern north atlantic we suggest that ba enriched meltwater was transmitted by the eastern boundary current system from higher latitudes to the region of the canary islands total barium contents of the clay fraction batot clay and ba ca in planktonic foraminifera shells seem to be reliable proxies for this discharge of meltwater

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

paleoenvironmental changes across the mid cenomanian event in the tropical atlantic ocean demerara rise odp leg 207 inferred from benthic foraminiferal assemblages abstract this study is based on cenomanian sediments of ocean drilling program odp sites 1258 and 1260 from demerara rise leg 207 western tropical atlantic off suriname 1000 and 500 m paleo water depth respectively studied sediments consist of laminated black shales with toc values between 3 and 18 and include the mid cenomanian event mce a positive carbon isotope excursion predating the well known oceanic anoxic event 2 oae 2 benthic foraminiferal assemblages of the continuously eutrophic environment at demerara rise are characterized by low diversities 9 species per sample and large fluctuations in abundances indicating oxygen depletion and varying organic matter fluxes dominant species at both sites are bolivina anambra gabonita levis gavelinella dakotensis neobulimina albertensis praebulimina prolixa and tappanina cf laciniosa benthic foraminiferal assemblages across the mce show a threefold pattern 1 stable ecological conditions below the mce interval indicated by relatively high oxygenation and fluctuating organic matter flux 2 decreasing oxygenation and or higher organic matter flux during the mce with decreasing benthic foraminiferal numbers and diversities site 1258 and a dominance of opportunistic species site 1260 and 3 anoxic to slightly dysoxic bottom water conditions above the mce as indicated by very low diversities and abundances or even the absence of benthic foraminifera slightly dysoxic conditions prevailed until oae 2 at demerara rise a comparison with other atlantic ocean and tethyan sections indicates that the mce reflects a paleoceanographic turning point towards lower bottom water oxygenation at least in the proto north atlantic ocean and in the tethyan and boreal realms this general trend towards lower oxygenation of bottom waters across the mce is accompanied by ongoing climate warming in combination with rising sea level and the development of vast shallow epicontinental seas during the middle and late cenomanian these changes are proposed to have favoured the formation of warm and saline waters that may have contributed to intermediate and deep water masses at least in the restricted proto north atlantic and tethyan ocean basins poor oxygenation of the late cenomanian sediments and the changes in benthic foraminiferal assemblages across the mce

u mo ratios and δ98 95mo as local and global redox proxies during mass extinction events abstract when used in conjunction with trace metal redox proxies the use of u mo ratios and 98 95 mo values can considerably enhance the interpretation of ocean oxygenation trends both locally and globally this is illustrated with studies from two biogenic chert dominated records of mass extinction the ordovician silurian boundary and the late permian in sections from the yangtze block in south china the latest ordovician mass extinction is well known to coincide with oxygenation episode in the hirnantian stage here revealed by trace metal proxies v v ni v cr ni co that show it sandwiched between anoxic euxinic black shales the predominantly anoxic euxinic ordovician silurian strata provide a record of seawater 98 95 mo values that are seen to gradually rise during the interval from 0 5 to 1 0 the exception to the 98 95 mo stability is the datum of the slight negatively 98 95 mo associated with decreasing of v cr and v v ni ratio suggesting the hirnantian oxygenation event the upper permian chert succession at shangsi reveals an overall better ventilated record in which the best oxygenated strata show the highest u mo values that is interpreted as relative enrichment of u in suboxic conditions at a few levels anoxic euxinic conditions show the 98 95 mo values to be 2 close to modern values implying that latest permian oceans were as well ventilated as those today the well known end permian oceanic anoxic event is therefore suggested to only develop at the end of this period

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

modeling organic carbon burial during sea level rise with reference to the cretaceous after three decades of research on the correlation between sea level and various proxies there has been very little quantification of the first order influence of sea level change on nutrient inventory marine productivity and burial of organic carbon we present a model aimed at quantifying the burial of organic carbon as a function of sea level rise the biogeochemical model explicitly considers the mean surface area distribution of the earth as a function of elevation also included is dissolved inorganic phosphate dip liberated from coastal sediments during transgression we quantify how sea level rise of magnitudes inferred for the mid cretaceous influences the phosphorus cycle and burial of organic carbon the burial efficiency is greater on the shelf therefore in the model the larger shelf area under high sea level results in more efficient burial of marine organic carbon for a given dip concentration and associated new production of organic matter np with a late cretaceous model shelf area the residence time of dip decreases by 60 relative to the present day reference thus in the final steady state dip and np in the open ocean are reduced compared to today when the biologically reactive phosphorus preac fluxes to the ocean from land are held constant the lower new production reduces the oxygen demand for respiration and results in a significant oxygenation of the global ocean finally the global organic carbon burial decreases by 30 relative to today in the model this decrease results from feedbacks between the flux of organic carbon to the seafloor and the ratio of organic carbon to preac in buried sediments in contrast during sea level rise coastal erosion may increase the preac flux to the ocean by up to 20 relative to today and cause a temporary increase in dip concentration in the ocean the resulting increase in organic carbon burial is equivalent to a carbon isotope event of 0 5 to 1 larger carbon isotope events can be triggered by sea level rise only when the ocean is sufficiently close to anoxia in the oxygen minimum zone just prior to the sea level rise

three types of south pacific subtropical mode waters their relation to the large scale circulation of the south pacific subtropical gyre and their temporal variability a detailed spatial distribution of south pacific subtropical mode water spstmw and its temporal variation were investigated using the world ocean atlas woa 2001 climatology and high resolution expendable bathythermograph hrx line data in the woa 2001 climatology spstmw can be classified into western and eastern parts a detailed examination of spatial distributions using hrx px06 line data revealed that the eastern part can be further divided into two types by the tasman front tf extension consequently spstmw can be classified into three types referred to in the present study as the west north and south types the west type situated in the recirculation region of the east australia current eac has a core layer temperature clt of about 19 1 c the north type in the region north of the tf extension has a clt of about 17 6 c and the south type in the region south of the tf extension has a clt of about 16 0 c the long term 6 yr variations in the inventories of the three types were dissimilar to each other the short term 6 yr and long term variations in the mean clt of the north and south types were greater than that of the west type winter cooling in the previous year may have influenced the short term variation in the south type clt moreover the strength of the eac may have influenced long term variation in the west type inventory and thickness and in the north type thickness and clt

periodic mid cretaceous oceanic anoxic events linked by oscillations of the phosphorus and oxygen biogeochemical cycles 1 a series of oceanic anoxic events oaes occurred in the mid cretaceous warm period 120 80 ma that have been linked with high rates of organic carbon burial warm high and low latitude temperatures and sea level changes oaes have been studied individually but a causal mechanism that connects them has been lacking we show that peaks in phosphorus accumulation in marine sediments broadly coincide with oaes 1a 1b 1d 2 and 3 and exhibit a 5 6 myr periodicity which for reactive p is prominent over 100 80 ma oxic anoxic oscillations of this frequency are also found in a model of the coupled n p c and o2 biogeochemical cycles these oscillations are maintained by positive feedbacks between phosphate concentration biological productivity and anoxia in the global ocean and counteracting but slower negative feedbacks involving changes in atmospheric oxygen an increase in phosphorus weathering rate above a critical threshold can shift the system into self sustaining oscillation this could have been caused by tectonic and volcanic forcing increasing atmospheric co2 and global warmth 120 80 ma augmented by the rise of flowering plants around 100 ma with a plausible forcing scenario we are able to reproduce the approximate timing of oaes 1a 1b 1d 2 and 3 in the model

isotopic evidence for glaciation during the cretaceous supergreenhouse the turonian 93 5 to 89 3 million years ago was one of the warmest periods of the phanerozoic eon with tropical sea surface temperatures over 35 c high amplitude sea level changes and positive 18 o excursions in marine limestones suggest that glaciation events may have punctuated this episode of extreme warmth new 18 o data from the tropical atlantic show synchronous shifts 91 2 million years ago for both the surface and deep ocean that are consistent with an approximately 200 000 year period of glaciation with ice sheets of about half the size of the modern antarctic ice cap even the prevailing supergreenhouse climate was not a barrier to the formation of large ice sheets calling into question the common assumption that the poles were always ice free during past periods of intense global warming

multiple westward propagating signals in south pacific sea level anomalies the characteristics of multiple westward propagating signals in the satellite observed south pacific sea level anomalies sla between 10 s and 50 s are analyzed using the two dimensional radon transform 2d rt we test the hypothesis that these signals are most likely to be the signature of the first few baroclinic rossby wave modes this involves a comparison of the estimated phase speeds of the 2d rt peaks against the first four baroclinic mode rossby wave speeds predicted from the extended theory the 2d rt analysis typically identified up to three propagating signals in the sla and very occasionally a fourth the first radon transform rt peak phase speeds corresponded very well with first baroclinic mode rossby wave phase speed estimates from linear theory between 15 s and 25 s and the extended theory phase speed estimates poleward of 25 s rt peak 2 speeds were less coherent but fell within the range of extended theory estimates of the first four baroclinic rossby wave modes consistent with large scale rossby wave dynamics the relationship between peaks 3 and 4 and the extended theory higher order baroclinic mode speed estimates varied markedly across the basin regional variability in the spectral characteristics of the peaks suggests that different dynamical regimes dominate north and south of 30 s in the south pacific basin the presence of secondary peaks in the middle to high latitudes suggests that higher order modes may play a role in these regions

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

terrigenous input and paleoproductivity in the southern ocean the geochemistry of several sites along the polar front zone of the southern ocean revealed significant changes in terrigenous input and productivity on glacial timescales our records indicate concentrations and fluxes of terrigenous elements i e fe al and ti are low during interglacials and increase tenfold to twentyfold during glacials phosphorus accumulation reactive p concentrations and p ti ratios exhibit similar trends as the terrigenous components suggesting increased export production during glacials in all cores elemental ratios remain relatively constant indicating terrigenous sources at each site have not likely varied over the past 250 kyr iron accumulation rates for these sites are 10 times higher during glacials than interglacials and exceed the estimated regional eolian fluxes by 50 times the source of this terrigenous material is thus likely to be hemipelagic rather than direct eolian input or ice rafting and we speculate fe upwelled from this source may have stimulated glacial productivity in the southern ocean

a linear inverse model of tropical and south pacific seasonal predictability a multivariate linear inverse model lim is developed to demonstrate the mechanisms and seasonal predictability of the dominant modes of variability from the tropical and south pacific oceans we construct a lim whose covariance matrix is a combination of principal components derived from tropical and extratropical sea surface temperature and south pacific ocean vertically averaged temperature anomalies eigen decomposition of the linear deterministic system yields stationary and or propagating eigenmodes of which the least damped modes resemble el nino southern oscillation enso and the south pacific decadal oscillation spdo we show that although the oscillatory periods of enso and spdo are distinct they have very close damping time scales indicating that the predictive skill of the surface enso and spdo is comparable the most damped noise modes occur in the midlatitude south pacific ocean reflecting atmospheric eastward propagating rossby wave train variability we argue that these ocean wave trains occur due to the high frequency atmospheric variability of the pacific south american pattern imprinting onto the surface ocean the enso spring predictability barrier is apparent in lim predictions initialized in march may mam but displays a significant correlation skill of up to 3 months for the spdo the predictability barrier tends to appear in june september jas indicating remote but delayed influences from the tropics we demonstrate that subsurface processes in the south pacific ocean are the main source of decadal variability and further that by characterizing the upper ocean temperature contribution in the lim the seasonal predictability of both enso and the spdo variability is increased

lithium isotope evidence for enhanced weathering during oceanic anoxic event 2 the ocean anoxic event 2 oae2 about 93 5 million years ago was marked by high atmospheric co2 concentration rapid global warming and marine anoxia and euxinia the event lasted for about 440 000 years and led to habitat loss and mass extinction the marine anoxia is thought to be linked to enhanced biological productivity but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery here we use lithium isotope measurements from carbonates spanning the interval including oae2 to assess the role of silicate weathering we find the lightest values of the li isotope ratio 7li during oae2 indicating high levels of weathering and therefore atmospheric co2 removal which we attribute to an enhanced hydrological cycle we use a geochemical model to simulate the evolution of 7li and the ca sr and os isotope tracers our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric co2 concentrations and rapid global warming which initiated oae2 the simulated warming was accompanied by a roughly 200 000 year pulse of accelerated weathering of mafic silicate rocks which removed co2 from the atmosphere the weathering also delivered nutrients to the oceans that stimulated primary productivity we suggest that this process together with the burial of organic carbon allowed the rapid recovery and stabilization from the greenhouse state

planktonic and benthic foraminiferal extinction events during the last 100 m y abstract five major planktonic and benthic foraminiferal extinction events occurred during the past 100 m y at the cenomanian turonian c t boundary at the cretaceous tertiary k t boundary in the latest paleocene in the late eocene and in the early middle miocene to clarify the character of the five events i estimated 1 paleo waterdepths and paleoenvironments where foraminifera were affected 2 the duration of each extinction event and 3 evaluated possible causes for each extinction event on the basis of recent literature these extinction events can be classified into three fundamentally different types 1 the mass extinction event at the k t boundary was abrupt and concentrated among surface dwelling species 2 extinctions at the c t boundary and during the latest paleocene were abrupt and mainly affected intermediate and deep water taxa over short periods 3 the late eocene and early middle miocene events affected surface and deep water species and involved stepwise or gradual extinctions over a long period 4 m y i attributed the extinction events to 1 a bolide impact for the k t event 2 a decrease in dissolved oxygen in intermediate and deep waters due to climatic warming for the c t and latest paleocene events and 3 long term global cooling for the late eocene and early middle miocene events the following relationships exist between the causes and types of extinction events 1 large extraterrestrial impacts strongly affected surface dwelling organisms in short term extinction events 2 intermediate and deep water low oxygen conditions induced by climatic warming have severely affected intermediate and deep water organisms over medium and short terms

phosphorus and the roles of productivity and nutrient recycling during oceanic anoxic event 2 four sections documenting the impact of the late cenomanian oceanic anoxic event oae 2 were studied in basins with different paleoenvironmental regimes accumulation rates of phosphorus p bound to iron organic matter and authigenic phosphate are shown to rise and arrive at a distinct maximum at the onset of oae 2 with an associated increase in 13 c values accumulation rates of p return to preexcursion values in the interval where the 13 c record reaches its fi rst maximum an offset in time between the maximum in p accumulation and peaks in organic carbon burial hydrogen indices and corg preact molar ratios is explained by the evolution of oae 2 in the following steps 1 an increase in productivity increased the fl ux of organic matter and p into the sediments the preservation of organic matter was low and its oxidation released p which was predominantly mineralized 2 enhanced productivity and oxidation of organic matter created dysoxic bottom waters the preservation potential for organic matter increased whereas the sediment retention potential for p decreased 3 the latter effect sustained high primary productivity which led to an increase in the abundance of free oxygen in the ocean and atmosphere system after the sequestration of co 2 in the form of black shales this oxygen helped push the ocean back into equilibrium terminating black shale deposition and removing bioavailable p from the water column

in search of the latest danian event in a paleobathymetric transect off kasserine island north central tunisia danian lower paleocene sequences in north central tunisia are dominantly composed of marls and shales but a conspicuous indurated glauconite bearing marker bed is associated with the p3a p3b transition this glauconite bed is considered to correlate with the latest danian event lde described from the nile basin in egypt with the top chron c27n event atlantic and pacific oceans and with the cie ds1 zumaia spain the lde is thought to reflect a short period of global warming similar to the paleocene eocene thermal maximum but of lesser magnitude the presence of a glauconitic bed at the p3a p3b transition in tunisia suggests that the sequence is condensed which is confirmed by planktic foraminifer and nannofossil biostratigraphy and by the absence of the typical lde beds found in most egyptian sections benthic foraminiferal assemblages were quantitatively analyzed in three sections in north central tunisia sidi nasseur garn halfaya elles in order to characterize the paleoenvironmental evolution during the late danian and compare this with sections in egypt the benthic foraminiferal assemblages indicate that the tunisian sections were located along a depth and a paleoenvironmental gradient on the shelf north of kasserine island the reconstructed depth range is comparable with sections in egypt and encompasses middle neritic sidi nasseur section to shallow upper bathyal depths elles section with up to 16 gavelinella beccariiformis below the p3a p3b like in egypt assemblage shifts across the p3a p3b subzonal transition indicate shallowing and a transition to a more eutrophic paleoenvironment characterized by relatively high abundances of buliminids and stainforthia sp the 13c and 18o records generated on well preserved specimens of the ostracode species bairdia failed to demonstrate the presence of the carbon isotope excursion cie associated with the lde at the base of subzone p3b a condensed section or a hiatus associated with the glauconite bed would explain why the cie is not recorded in the tunisian sections

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

contemporaneous massive subaerial volcanism and late cretaceous oceanic anoxic event 2 abstract oceanic anoxic events oaes are geological time intervals characterized by extremely high burial rates of organic carbon that led to deposition of organic rich black shales in the global ocean it has been proposed that oceanic anoxic events are ultimately caused by massive volcanism associated with formation of large igneous provinces lips because of chronological similarities but no general consensus has developed yet to investigate the possibility of lip volcanism instigating oaes we measured stable isotopic compositions of bulk organic carbon 13 c org and lead pb isotopic compositions in the silicate sediment fraction across the bonarelli black shale italy a type stratigraphic section for the end cenomanian oae oae 2 94 ma ultra high resolution 13 c org records determined every 1 5 mm capture a 3 sharp negative shift at the base of the bonarelli at the same stratigraphic level pb isotopic compositions in the silicate sediment fraction exhibit significant shifts toward characteristic values of volcanic rocks from contemporaneous lips caribbean and madagascar flood basalts these data suggest a rapid substantial increase in the relative supply of silicate minerals from the two lips massive subaerial volcanism associated with lip formation provides a simple explanation for these two isotopic geochemical signals via release of a huge amount of carbon dioxide 10 5 gt co 2 and particulate materials into the atmosphere which resulted in a rapid negative shift of 13 c in sea water and changes in pb isotopic compositions in the silicate sediment fraction respectively we interpret that massive volcanism triggered significant climatic changes inducing biotic crises and oceanic anoxia

paleoceanographic changes at the northern tethyan margin during the cenomanian turonian oceanic anoxic event oae 2 abstract the late cenomanian early turonian oceanic anoxic event oae 2 represents major paleoceanographic and faunal perturbations samples from the northern tethyan margin rehkogelgraben eastern alps were investigated in order to trace the paleoceanographic processes paleoecologic conditions were reconstructed by combining the results of assemblage counts of indicative microfossil groups foraminifera and radiolaria assemblages size distributions and abundances show a tripartite subdivision for surface and bottom waters 1 oligotrophic surface conditions and oxic bottom waters with a reasonably high food supply for the late cenomanian interval 2 an oae period with black shales characterized by very low numbers but high diversities and a lack of high productivity indicators among planktic foraminifera low abundances of small sized benthic foraminifera indicate low oxic dysoxic conditions at the seafloor 3 post oae assemblages are characterized by mesotrophic planktic species and benthic foraminifera suggest oxic bottom waters it took about 300 ky to re establish a pelagic carbonate producing regime the semi enclosed basin situation of the penninic ocean is thought to be responsible for differences between the high productivity in the world ocean during the oae 2 and the overall absence of high productivity indicators and high foraminiferal diversities at rehkogelgraben the penninic ocean may have even served as a refuge during the environmental crisis

remote forcing of tasman sea marine heatwaves recent marine heatwave mhw events in the tasman sea have had dramatic impacts on the ecosystems fisheries and aquaculture off tasmania s east coast however our understanding of the large scale drivers forcing and potential predictability of mhw events in this region off southeast australia is still in its infancy here we investigate the role of oceanic rossby waves forced in the interior south pacific on observed mhw occurrences off southeast australia from 1994 to 2016 including the extreme 2015 16 mhw event first we used an upper ocean heat budget analysis to show that 51 of these historical tasman sea mhws were primarily due to increased east australian current eac extension poleward transports through the region second we used lagged correlation analysis to empirically connect the eac extension intensification to incoming westward propagating sea surface height ssh anomalies from the interior south pacific third we dynamically analyzed these ssh anomalies using simple process based baroclinic and barotropic rossby wave models forced by wind stress curl changes across the south pacific finally we show that associated monthly ssh changes around new zealand may be a useful index of western tasman sea mhw predictability with a lead time of 2 3 years in conclusion our findings demonstrate that there is potential predictability of advection dominated mhw event likelihoods in the eac extension region up to several years in advance due to the deterministic contribution from baroclinic and barotropic rossby waves in modulating the eac extension transports

south pacific decadal climate variability and potential predictability the south pacific decadal oscillation spdo characterizes the southern hemisphere contribution to the pacific wide interdecadal pacific oscillation ipo and is analogous to the pacific decadal oscillation pdo centered in the north pacific in this study upper ocean variability and potential predictability of the spdo is examined in hadisst data and an atmosphere forced ocean general circulation model the potential predictability of the ipo related variability is investigated in terms of both the fractional contribution made by the decadal component in the south tropical and north pacific oceans and in terms of a doubly integrated first order autoregressive ar1 model despite explaining a smaller fraction of the total variance we find larger potential predictability of the spdo relative to the pdo we identify distinct local drivers in the western subtropical south pacific where nonlinear baroclinic rossby wave topographic interactions act to low pass filter decadal variability in particular we show that the kermadec ridge in the southwest pacific enhances the decadal signature more prominently than anywhere else in the pacific basin applying the doubly integrated ar1 model we demonstrate that variability associated with the pacific south american pattern is a critically important atmospheric driver of the spdo via a reddening process analogous to the relationship between the aleutian low and pdo in the north pacific albeit that the relationship in the south pacific appears to be even stronger our results point to the largely unrecognized importance of south pacific processes as a key source of decadal variability and predictability

cenomanian turonian facies and sequence stratigraphy bahloul formation tunisia abstract the cenomanian turonian bahloul formation in tunisia consists of well bedded dark grey limestones with common local intercalations of marls and argillaceous limestones in the oued bahloul section the bahloul formation 28 m in thickness directly overlies a massive bed 4 m consisting of conglomeratic sandy limestone showing an incised base in terms of sequences the oued bahloul section shows that the bahloul formation is composed of deepening upward metric cycles each comprising three units each cycle starts with a laminated dark grey limestone progressively changing to argillaceous limestone and terminates with bioturbated marls containing microfauna of the whiteinella archaeocretacea biozone this deepening upward cycle package constituting the bahloul formation is interpreted to be the expression of a transgressive interval directly overlying in the oued bahloul area a shelf margin wedge formed by the conglomeratic limestones the transgressive interval ends with a maximum flooding surface mfs included within the filaments rich facies this mfs represents the upper boundary of the bahloul formation which is directly overlain by a marly unit the annaba member of the kef formation assigned to the helvetoglobotruncana helvetica biozone indicating an early turonian age the filament event is one of four biosedimentary event horizons identified within the late cenomanian early turonian interval in the oued bahloul section from base to top these four event horizons correspond to 1 the extinction of rotalipora 2 the heterohelix shift 3 the whiteinella proliferation and 4 the filament event these events are recognized also in other areas in tunisia and abroad and we identify them here within sections preferentially located on the platform to the south in the basin to the north and especially within the transitional platform basin environments in central tunisia toward the sw in jebel bireno the bahloul formation is thinner 6 m than in oued bahloul and wholly carbonate and it was deposited in relatively shallower conditions probably in an outer platform environment in fact organic rich facies constituting the bahloul formation change to the south to open platform facies in which planktonic microfauna are associated with benthonic foraminifera and rudists however toward the north in the bazina area for example the bahloul facies changes to basinal marls rich in ammonites and planktonic foraminifera isotope analyses show that the main 13c positive excursions coincide with transgressive and maximum flooding surfaces the latter are commonly used in regional and global correlations

benthic foraminiferal morphogroups of mid to outer shelf environments of the late jurassic prebetic zone southern spain characterization of biofacies and environmental significance abstract benthic foraminiferal assemblages belonging to a mixed carbonate siliciclastic shelf succession of the oxfordian upper jurassic in the prebetic southern spain were analyzed the faunal data obtained on thin sections of strongly lithified sediments allowed the detailed differentiation of a foraminiferal morphogroups system to be applied to the interpretation of paleoenvironmental conditions eleven morphogroups were differentiated according to shell composition general morphology number of chambers and mode of coiling paleoenvironmental analysis combines these features with inferred life style epifaunal shallow infaunal and deep infaunal and feeding strategy suspension feeder deposit feeder herbivores etc of the foraminifera analogies and differences regarding previously established morphogroup systems could be outlined accordingly in the prebetic oxfordian distribution trends of foraminiferal morphogroups allow for a comparison of mid to outer shelf environments occupying the south iberian paleomargin indicating that nutrient supply was the most important factor controlling morphogroup development the mid shelf settings are dominated by epifaunal active herbivores phytodetritivores in shallow to deep substrate position of the redox boundary the outer shelf is dominated by agglutinated and infaunal detritivore bacterial scavenger morphogroups revealing a deep substrate position of the redox boundary particularly favorable trophic conditions in mid shelf environments are related with higher phytodetritus input from more proximal and shallower shelf areas

geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the burgess shale formation abstract deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the burgess shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation methods of paleo redox determination that are based upon trace fossils organic carbon content or size analysis of pyrite framboids are problematic when applied to the burgess shale fortunately patterns in redox sensitive trace elements hold great potential for determining paleo redox conditions for these greenschist facies rocks because they are independent of both age and metamorphic grade four burgess shale type bst fossil bearing sections were studied three lie within the burgess shale formation whereas one lies within the slightly younger duchesnay unit of the middle chancellor formation the geochemical proxies of seawater redox conditions that were used are mo u th v cr v v ni ni co and v sc each of these redox sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which bst preservation developed non fossiliferous beds at the base of the mt stephen trilobite beds yield three geochemical indices v v ni v sc ni co that indicate deposition under dysoxic to anoxic conditions thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft bodied taxa further contradicting the notion that bottom water anoxia is a factor in bst preservation the laminated nature of the burgess shale and evidence for subsurface anoxia coupled with evidence for oxygenated bottom waters presence of bacterial mats and surficial trace fossils suggest that the burgess shale was deposited in the exaerobic zone oxic anoxic boundary at the water sediment interface implications of this reinterpretation of the depositional environment of the burgess shale include 1 taphonomic models for bst preservation must account for the presence of oxygen in bottom waters 2 paleoecological interpretations of the burgess shale need to account for a probable autochthonous benthic component in what is a complex assemblage of fossils that includes elements derived from the platform and 3 the possibility of burgess shale communities based upon chemosynthesis and or bacteria grazing must be considered

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

cenomanian turonian transition in a shallow water sequence of the sinai egypt environmental and depositional changes across the late cenomanian oceanic anoxic event oae2 in the sinai egypt are examined based on biostratigraphy mineralogy 13c values and phosphorus analyses comparison with the pueblo colorado stratotype section reveals the whadi el ghaib section as stratigraphically complete across the late cenomanian early turonian foraminifera are dominated by high stress planktic and benthic assemblages characterized by low diversity low oxygen and low salinity tolerant species which mark shallow water oceanic dysoxic conditions during oae2 oyster biostromes suggest deposition occurred in less than 50 m depths in low oxygen brackish and nutrient rich waters their demise prior to the peak 13c excursion is likely due to a rising sea level characteristic oae2 anoxic conditions reached this coastal region only at the end of the 13c plateau in deeper waters near the end of the cenomanian increased phosphorus accumulations before and after the 13c excursion suggest higher oxic conditions and increased detrital input bulk rock and clay mineralogy indicate humid climate conditions increased continental runoff and a rising sea up to the first 13c peak above this interval a dryer and seasonally well contrasted climate with intermittently dry conditions prevailed these results reveal the globally synchronous 13c shift but delayed effects of oae2 dependent on water depth

pliocene holocene evolution of depositional conditions in the eastern mediterranean role of anoxia vs productivity at time of sapropel deposition a multiproxy geochemical study of nine sapropel layers from odp hole 964a odp leg 160 in the eastern mediterranean spanning the pliocene holocene time interval provides new insights into the evolution of sapropel deposition paleoenvironmental proxies were used for reconstruction of productivity ba derived from marine barite oxygen conditions trace metal ratios and sedimentary regime clay minerals detrital elements these proxies reveal a significant increase in river runoff relative to decreasing aeolian input during sapropel deposition over the whole time interval ba excess supports the argument that a significant increase in export productivity is the main triggering mechanism for sapropel deposition although preservation also played an important role furthermore major differences exist in depositional conditions including both oxygenation and productivity since the pliocene productivity fluctuated substantially and was higher during the pliocene and pleistocene than during the holocene at the same time decreasing oxygen availability parallels the enhanced productivity dysoxic to anoxic conditions appear to coincide with marine productivity maxima thus suggesting that oxygen depletion may be linked to greater consumption rather than restricted circulation this correspondence supports the hypothesis that productivity fluctuations resulting from climate oscillations were the main cause of enhanced organic matter contents and also a main controlling factor for reduced oxygen availability

long extratropical planetary wave propagation in the presence of slowly varying mean flow and bottom topography part ii ray propagation and comparison with observations ray theory is used to predict phase and group velocities for long planetary waves under realistic albeit slowly varying oceanic conditions the results are compared with local theory using fields smoothed to the same amount 9 latitude longitude as well as those with much less smoothing 1 the agreement is excellent showing that local theory forms a good proxy for ray theory results the predicted speeds agree well with observations of planetary waves deduced from sea surface height data the theory uses purely baroclinic mean flow the inclusion of barotropic flow has little effect except at high latitudes

palaeoceanographic and palaeoclimatic inferences from late cretaceous planktonic foraminiferal assemblages from the exmouth plateau odp sites 762 and 763 eastern indian ocean the evolution of planktonic foraminifera during the late cretaceous is marked in the santonian by the disappearance of complex morphotypes the marginotruncanids and the contemporary increasing importance and diversification of another group of complex taxa the globotruncanids upper turonian to lower campanian planktonic foraminiferal assemblages from holes 762c and 763b ocean drilling program leg 122 exmouth plateau 47 s palaeolatitude were studied in detail to evaluate the compositional variations at the genus and species level based on the assumption that in the cretaceous oceans as in the modern any faunal change was associated with changes in the characteristics and the degree of stability of the oceanic surface waters three major groups were recognised based on gross morphology and following the assumption that cretaceous planktonic foraminifera although extinct had life history strategies comparable to those of modern planktonics 1 r selected opportunists 2 k selected specialists 3 r k intermediate morphotypes which include all genera that display a range of trophic strategies in between opportunist and specialist taxa although planktonic foraminiferal assemblages are characterised by a progressive appearance of complex taxa this trend is discontinuous variation in number of species and specimens within genera has allowed recognition of five discrete intervals each of them reflecting different oceanic conditions based on fluctuations in diversity and abundance of the major morphotypes planktonic forms show cyclical fluctuations in diversity and abundance of cold r strategists and warm taxa k strategists perhaps representing alternating phases of unstable conditions suggesting a weakly stratified upper water column in a mesotrophic environment and well stratified surface and near surface waters indicating a more oligotrophic environment interval 1 middle turonian to early coniacian in age is dominated by the r k intermediate morphotypes which alternate with r strategists these cyclical alternations are used to identify three additional sub intervals interval 2 aged middle to late coniacian is characterised by the increasing number of species and relative abundance of k strategists after this maximum diversification the k strategists show a progressive decrease reaching a minimum value in interval 3 early to late santonian which corresponds to the extinction of the genus marginotruncana in the interval 4 latest santonian in age the k strategists represented mainly by the genera globotruncana increase again in diversity and abundance the last interval 5 early campanian is dominated by juvenile globotruncanids and r strategists which fluctuate in opposite phase the positive peak interval 2 related to the maximum diversification of warm taxa k strategists in the coniacian seems to correspond to a warmer episode it is followed by a marked decrease in the relative abundance of warm taxa k strategists crisis with a minimum in the late santonian interval 3 reflecting a decrease in temperature detailed analysis of faunal variations allows the santonian faunal turnover to be ascribed to a cooling event strong enough to cause the extinction of the marginotruncanids

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

processes controlling the geochemical composition of the south china sea sediments during the last climatic cycle abstract sediments of the upper 28 2 m of ocean drilling program odp site 1145 from the northern south china sea scs were analyzed for their geochemical composition most of the major and trace elements exhibit significant fluctuations at glacial interglacial scales implying a close relation with regional and global climate change al normalized elemental ratios can be subdivided into three principal components pc pc1 e g ca al ba al sr al displays significant glacial interglacial variation and is related to paleoproductivity in the northern scs pc2 e g k al mg al rb al is associated with the degree of chemical weathering in the source regions and shows little glacial interglacial variation pc3 e g ti al zr al reflects the relative contribution of coarse and fine grained materials in the terrigenous components of the scs sediments likely associated with changes in sea level and monsoon induced fluvial input spectral analyses indicate that paleoproductivity i e ba al in the south china sea lags hulu sanbao speleothem 18o record an indicator of annual average meteoric precipitation by 102 and indian summer monsoon multi proxy stack by 23 at the precession band indicating a close relationship with the indian summer monsoon however the chemical weathering degree in the source area pc2 is not sensitive to monsoon related changes at the precession band during the last climatic cycle

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

the origin and timing of fluvial activity at eberswalde crater mars the fan deposit in eberswalde crater has been interpreted as strong evidence for sustained liquid water on early mars with a paleolake formed during the noachian period 3 7 gy this location became a key region for understanding the mars paleo environment eberswalde crater is located 50 km north of the rim of the 150 km diameter crater holden stratigraphic relationships and chronology obtained using recent mars express high resolution stereo camera and mars reconnaissance orbiter context camera images show that eberswalde fluvial activity crosscuts holden ejecta and thus postdates holden crater whose formation age is estimated from crater counts as late hesperian 3 5 gy depending on models fluvial modeling shows that short term activity over several years to hundreds of years involving dense flows with sediment water ratio between 0 01 and 0 3 may be as good an explanation of the fluvial landforms as dilute flow over longer durations modeling of the thermal effect of the holden impact in the eberswalde watershed is used to evaluate its potential role in aqueous activity the relative timing of the holden impact and eberswalde s fan is a constraint for future studies about the origin of these landforms holden ejecta form a weak and porous substrate which may be easy to erode by fluvial incision in a cold climate scenario impact heating could have produced runoff by melting snow or ground ice any attempt to model fluvial activity at eberswalde should take into account that it may have formed as late as in the late hesperian after the great majority of valley network formation and aqueous mineralization on mars this suggests that hypotheses for fan formation at eberswalde by transient and or localized processes i e impact volcanism unusual orbital forcing should be considered on a par with globally warmer climate

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

long extratropical planetary wave propagation in the presence of slowly varying mean flow and bottom topography part i the local problem one of the most successful theories to date to explain why observed planetary waves propagate westward faster than linear flat bottom theory predicts has been to include the effect of background baroclinic mean flow which modifies the potential vorticity waveguide in which the waves propagate barotropic flows are almost everywhere too small to explain the observed differences that theory accounted for most but not all of the observed wave speeds a later attempt to examine the effect of the sloping bottom on these waves without the mean flow effect did not find any overall speedup this paper combines these two effects assuming long geostrophic waves and slowly varying mean flow and topography and computes group velocities at each point in the global ocean these velocities turn out to be largely independent of the orientation of the wave vector a second speedup of the waves is found over that for mean flow only almost no eastward oriented group velocities are found and so features that appear to propagate in the same sense as a subtropical gyre would have to be coupled with the atmosphere or be density compensated in some manner

age and paleoenvironment of the cenomanian turonian global stratotype section and point at pueblo colorado biostratigraphy and stable isotopes indicate that the global stratotype section and point gssp at pueblo contains an essentially complete sedimentary record across the global ocean anoxic event oae 2 and the cenomanian turonian boundary the oae 2 d 13 c shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression which at its peak was marked by an incursion of oxygen rich waters creating a benthic oxic zone that lasted about 100 ky a mid cenomanian d 13 c shift sea level transgression and faunal turnover occurred about 2 my before oae 2 d 18 o values of the planktic foraminifer hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions whereas dominance by the low oxygen tolerant heterohelix species indicates a well developed oxygen minimum zone omz for most of the middle to late cenomanian and early turonian profound faunal changes accompanied these oceanographic events including the extinction of 30 of the species assemblage and an equal gain in evolutionary diversification though the overall combined relative abundances of outgoing and incoming species were less than 2 and 4 respectively of the total assemblages the faunal turnover began with the sea level transgression and rapid increase in d 13 c values and accelerated with the influx of oxygen rich deep water increased water mass stratification and competition during the benthic oxic zone the incursion of oxygen rich deep waters at this time was also observed in morocco and may represent a global event of a still unknown source d 2003 elsevier b v all rights reserved

changes in northeast atlantic temperature and carbon flux during the cenomanian turonian paleoceanographic event the goban spur stable isotope record stable isotopes of bulk sediment and well preserved tests of planktonic and benthic foraminifera from midlatitude ne atlantic dsdp site 551 goban spur provide the first estimates of carbon isotope gradients within the water column at a lower bathyal site during the cenomanian turonian boundary interval ctbi the ctbi carbon isotope excursion is prominent up to 2parts per thousand shift in delta 13 c in the bulk coccolith signal but less pronounced approximately 0 5 parts per thousand shift in delta 13 c in planktonic and benthic foraminifera this difference indicates a very steep 13 c gradient in the upper water column and a very efficient biological pump during the ctbi carbon isotope excursion we suggest significantly increased seasonal primary production in the uppermost water column with an enhanced shallow water chlorophyll maximum as a cause for this steep carbon isotope gradient deep water and surface water temperature changes during the ctbi are estimated using benthic and planktonic foraminiferal oxygen isotopes warm deep water masses 13 16degreesc and a low temperature gradient within the water column prevailed in the late cenomanian additional warming approximately 2degreesc for both surface and deep water occurred in the latest cenomanian prior to ctbi black shale deposition this pattern of ctbi black shale deposition during a temperature maximum is also evident at two low latitude locations odp site 1050 blake nose and tarfaya southern morocco c 2003 published by elsevier b v

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

the cenomanian turonian anoxic event in europe an organic geochemical study received 14 october 1988 revised 14august 1989 accepted 31 august 1989 thirty two sediment samples mainly black shales from cenomanian turonian organic rich sequences in europe and tunisia were examined by organic geochemical techniques the results of molecular analyses indicate that all the black shales are dominated by marine derived organic matter from both algal and bacterial sources with only a minor terrestrial component oxygen deficient conditions prevailed during the deposition of the black shales although interbedded non laminated organic lean horizons indicate that oxygen deficiency was intermittent at some sites the presence of 17cx h 18c h 211 h 28 30 bisnorhopane in some black shale samples from shallow shelf areas may be evidence for severely oxygen depleted conditions possibly in association with upwelling and an oxygen minimum layer overall the organic geochemical data are in agreement with a depositional model whereby an oxygen minimum layer developed in response to high surface productivity this oxygen minimum layer may have extended over a considerable thickness of the water column 1000 m in some areas we report the first observation of an a ring methylated c29 hopane namely methyl 17e h 18 h 211 h 28 30 bisnorhopane the environmental significance of this compound cannot yet be assessed although in the sample in which it occurs the direct parallel between the carbon number distribution of the hopanes and that of the methylhopanes suggests either that they have the same biological origin or that methylation of hopanoids may have occurred possibly during diagenesis

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

surface water dynamics and phytoplankton communities during deposition of cyclic late messinian sapropel sequences in the western mediterranean abstract distinctive precession scale sapropel marl sequences of late messinian age are found in several outcrops bordering the western mediterranean to examine the roles of stratification and productivity in driving this cyclic sedimentation we performed a high resolution analysis of calcareous nannofossil assemblages through four orbital sequences composed of sapropel marl diatomite marl from the sorbas basin in southern spain this effort also involved a detailed comparison between calcareous nannofossil abundances and other micropaleontological sedimentological and geochemical proxies to further understand the behaviour of some taxa for this period fluctuations in the depth and gradient of the pycnocline and the distribution and remobilization of nutrients seem to be the main factors controlling the calcareous nannoplankton assemblages with temperature of secondary importance in the sapropels the warm oligotrophic genus sphenolithus and discoaster are abundant especially significant is the progressive increase towards the top of discoaster pentaradiatus indicator of severe oligotrophic deep pycnocline conditions at the top of the sapropels peaks in reticulofenestra rotaria are interpreted here as the result of an increase of surface water temperatures although decreasing salinity may also play a role small reticulofenestra 5 m are more frequent in diatomites even considering conditions of extreme mixing and eutrophication occurred in the basin umbilicosphaera jafari peaks just after diatomites replacing small reticulofenestra probably as a response to an increase in salinity and or nutrient limitation species such as coccolithus pelagicus and helicosphaera carteri are abundant at the top of the diatomites and in the overlying marls indicating relatively mesotrophic and cool water conditions this succession shows similar characteristics in the four studied cycles allowing us to interpret surface water dynamics in this region on orbital time scales the top of the sapropel represents a warm low salinity and well stratified episode under a situation of maximum insolation a well developed pycnocline and oligotrophic conditions moderate production of calcareous phytoplankton coinciding with anoxic conditions at the bottom enhance the preservation of organic matter and consequently generate a sapropel diatomites are deposited under a situation of unstable pycnocline that produce an increase in productivity in surface waters diatoms significantly deplete limiting nutrients and consequently calcareous nannofossils start to be dominant again in the water column as result of a progressive stabilization of the pycnocline

causes of anoxia in the world ocean we examine the hypothesis that global scale episodes of anoxia such as occurred in the cretaceous are due to

recovery of the deep sea floor after the cretaceous paleogene boundary event the benthic foraminiferal record in the basque cantabrian basin and in south eastern spain abstract a detailed analysis of the upper cretaceous and lower paleogene benthic foraminiferal assemblages 63 m from the middle bathyal loya section basque cantabrian basin southwestern france has been carried out the benthic foraminiferal and palaeoenvironmental turnover across the k pg boundary at loya has been compared to that observed in the nearby bidart section both sections exhibit mesotrophic conditions in the uppermost maastrichtian and a drastic decrease in the nutrient supply to the sea floor in coincidence with the k pg boundary moreover a faunal recovery of the assemblages is observed through the lowermost danian the pattern of faunal and palaeoenvironmental recovery in the basque cantabrian basin has been compared to that observed in the middle bathyal agost and caravaca sections south eastern spain where a similar decrease in the food supply to the sea floor is observed in coincidence with the k pg boundary however whereas low oxygen conditions have been recorded in the lowermost danian in these two sections no evidence for oxygen deficiency has been found in the basque cantabrian basin thus pointing to the regional and not global nature of low oxygen conditions following the k pg boundary event benthic foraminifera from the g cretacea biozone suggest environmental instability in the basque cantabrian basin and in southeastern spain such environmental stress has been related not only to the collapse of the food web due to the extinction of calcareous primary producers but also to a rapidly changing food supply driven by phytoplankton blooms although stabilization of the ecosystems in surface waters probably occurred towards the upper part of the g cretacea biozone data available from the ps pseudobulloides biozone at bidart and agost indicate that food supply to the benthos had not completely recovered at least 200 kyr after the k pg boundary

variability in the south pacific deep western boundary current from current meter observations and a high resolution global model observations of the south pacific deep western boundary current from the world ocean circulation experiment pacific current meter array 9 woce pcm 9 current meter array are compared with the los alamos national laboratory high resolution global ocean model a simple integration of pcm 9 velocity yields a mean northward transport of water deeper than 3000 m that is some 5 times greater than the model mean transport of 3 35 106 m3 s 1 the low modeled abyssal transport suggests a poor simulation of the mean thermohaline circulation however model and observed transport variability correlate significantly space time spectral analysis shows planetary waves are responsible for most of the variability and are resolved well in the model the details of interaction of the long waves at the western boundary are different in model and data the model reflects these waves predominantly as planetary short waves which decay over the region 600 800 km east of the kermadec ridge pcm 9 has a higher proportion of energy as topographic waves along the kermadec ridge these two classes of waves are associated with the two observed zonal scales in the boundary current the model results can be separated into vertical modes baroclinic energy is found at all timescales including those too short for free baroclinic waves the baroclinic flow correlates with the barotropic so as to enhance surface and reduce abyssal kinetic energy this is the signature of planetary wave scattering at the submerged western boundary ridge and results in enhanced baroclinic wave energy in the tasman sea

observed variability of the south pacific westward sea level anomaly signal in the presence of bottom topography this study investigates the behavior of westward propagating sea level anomalies across the south pacific ocean with a focus on the long rossby wave signal determined from filtered topex poseidon and ers satellite altimeter data an evaluation of the energy variability of the signal using a two dimensional radon transform analysis suggests that rossby waves interact with both ridges and seamounts at various locations across the basin anomalously slow rossby wave phase speeds are found over steep isolated bathymetric features in the tropical south pacific and over the plateau around new zealand interaction with ridges increases the energetic variability range of dominant propagation speeds and meridional deviations in the rossby wave signal

changing ocean circulation and hydrothermal inputs during ocean anoxic event 2 cenomanian turonian evidence from nd isotopes in the european shelf sea nd isotopes of fish debris collected from the english chalk at eastbourne sussex uk are used to reconstruct the history of ocean circulation in the nw european shelf sea during oceanic anoxic event 2 oae 2 cenomanian turonian the eastbourne end record exhibits a 1 unit negative excursion decreasing from 9 to 10 immediately followed by a 3 unit positive excursion reaching 7 the onset of the negative end excursion lags the global 13c rise characteristic of oae 2 suggesting stable patterns of ocean circulation in the nw european shelf sea at this time both negative and positive nd isotope excursions took place during a transient cooling episode within oae 2 the negative end excursion is interpreted as due to a change in ocean circulation with northerly sourced water masses becoming the dominant bottom waters at eastbourne the positive excursion is best explained by the transport of radiogenic nd derived from a volcanic source possibly the high arctic or caribbean large igneous province lip an input of volcanic nd may reconcile the eastbourne record with coeval end records on demerara rise in the western tropical atlantic the broad synchroneity of high end values 7 registered at both sites suggests a possible period with efficient oceanic mixing between the tropical atlantic and the nw european shelf sea during the cooling episode the eastbourne end record of oae 2 together with coeval temperature reconstructions provides evidence for the coincidence of changes in ocean circulation and transient climatic cooling implying a tight coupling between the two phenomena during this interval

observations in the canary basin and the azores frontal region using geosat data this paper discusses observations of the sea level in the azores frontal region and the canary basin as seen by the geosat altimeter frorn 5 to 45 w and 25 to 45 n two years of geosat exact repeat data were processed by colocating the data on a 0 06 grid then removing the mean by the along track difference method and removing the orbit error by a crossover analysis technique the data set was then interpolated by the successive correction method onto 15 day 0 5 maps to produce 47 residual height fields which were analyzed using complex empirical orthogonal functions eof and spectral analysis the results show that there is a region of high variability in the northwest corner reflecting the gulf stream extension and a region of medium variability at approximately 35 n reflecting the azores current the variability changes only slightly throughout the year with the winter season being the highest the data set also shows first mode baroclinic rossby waves between 30 and 35 n there is evidence that these rossby waves have different wavenumbers to the east and west of the mid atlantic ridge it is postulated that these waves have different generation mechanisms the mid atlantic ridge topography in the west and some other generation mechanism in the canary basin rossby waves are not apparent at 40 n

enhanced productivity rather than enhanced preservation led to increased organic carbon burial in the euxinic southern proto north atlantic ocean during the cenomanian turonian oceanic anoxic event three cenomanian turonian c t 93 5 ma black shale sections along a northeast southwest transect in the southern part of the proto north atlantic ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in c values of both bulk organic matter om and molecular fossils of algal chlorophyll and steroids all three sites show an increase in marine organic carbon oc accumulation rates during the c t oceanic anoxic event oae the occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria lack of bioturbation and high abundance of redox sensitive trace metals indicate sulfidic conditions periodically reaching up into the photic zone before as well as during the c t oae during the c t oae there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and mo al ratios the presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the c t oae however bottom water conditions did not dramatically change as indicated by more or less constant v al and zn al ratios at site 367 this suggests that the increase in oc burial rates resulted from enhanced primary productivity rather than increased anoxia which is supported by stable carbon isotopic evidence and a large increase in ba al ratios during the c t oae the occurrence of the productivity event during a period of globally enhanced organic carbon burial rates i e the c t oae points to a common cause possibly related to the formation of a deep water connection between north and south atlantic basins

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes