organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

construction of the pyreneo languedocian sedimentary ridge and associated sediment waves in the deep western gulf of lions western mediterranean migrating sediment waves have been recognized in a wide range of marine settings including turbidite levees adjacent to submarine canyons and valleys the pyreneo languedocian sedimentary ridge plsr located in the gulf of lions north western mediterranean appears similar to such a levee in an attempt to understand the construction of both the plsr and associated sediment waves several scale studies were done the data include high and medium resolution seismic reflection profiles and cores collected both on upslope and downslope sides of two successive waves at a regional scale the situation of the plsr was strongly influenced by pliocene salt tectonics movements that resulted in a basin at the mouth of the catalano languedocian canyons later salt tectonics were chiefly inactive during quaternary and waves do not result of an extensive superficial tectonic activity at the scale of the plsr the construction occurred during the quaternary and is divided in three stages recognized on the basis of waves geometry sediment supplies changes and spillover source variations common sediment wave cross sections have been identified and suggest a turbidite or a gravity flow origin sedimentological lithostratigraphical and biostratigraphical studies focus on the last sea level rise and high stand period the results support the sediment wave initiation and the occurrence of sand transfers even during the more recent period sand layers and high sedimentation rates characterize the deposits on upstream flanks lower rates of deposition correspond with downstream flanks

evaluation of palaeoenvironmental changes during the last 18 000 years in the myrtoon basin sw aegean sea abstract high resolution last glacial maximum to holocene palaeoenvironmental changes corresponding to a time interval between 200 and 500 years are examined in the myrtoon basin in the sw aegean sea using the abundance variation in foraminifera and pollen in relation to accelerator mass spectrometry 14 c dating and limited oxygen isotope data foram abundance variation shows that from 18 ka to the late glacial holocene boundary at around 10 5 to 9 5 ka the sea surface was cold during this period two intervals of relatively high and low sea surface temperature sst were observed the first high sst occurred at around 14 2 ka whereas the second high sst was centred at around 12 8 ka and appears to correspond to the termination 1a event the first low sst was centred at around 13 7 ka and the second low sst occurred between 11 8 and 10 8 ka the former event may correspond to the heinrich 1 event and the latter to the younger dryas chronozone the holocene started with a sharp warming of sea surface water reaching present day levels and probably associated with a reduction in salinity the formation of the sapropel sequence in the myrtoon basin started at about 10 ka about the same time as the sapropel formation in the other aegean basins which means that the environmental conditions became suitable for the formation of sapropels in the aegean about 800 years earlier than in the adriatic ionian and levantine basins within the sapropel sequence there are two high organic carbon corg content sublayers s 1 a 9 7 9 ka and s 1 b 7 3 6 9 ka separated by a lower corg content sublayer indicating variation in the oceanographic and climatic conditions prevailing in the area during the sapropel sequence formation the depositions of s 1 a and s 1 b coincide with an increase in sst increased temperature and enhanced fresh water inputs from the outflowing rivers in to the aegean sea which later was supplemented by the overflowing of the black sea lowered the sea surface density and reduced the vertical water masses circulation resulting in reduced bottom water ventilation the reduction of o 2 supply to the seabed in combination with increased fluxes of terrigenous and or marine organic matter were responsible for the creation of dysoxic to anoxic conditions in the seabed which led to the formation of sapropel s 1 the sapropel formation ended at 5 2 ka and about the same time the sst attained present day levels during the last glacial maximum and late glacial periods the pollen source area was providing a suitable environment for the growth and survival of arboreal taxa the source area was apparently ice free and was characterized by sufficient humidity and non lethal low temperatures probably only a few degrees colder than present day

hydrological relationship between the north atlantic ocean and the mediterranean sea during the past 15 75 kyr the mediterranean sea hydrology at the time of the heinrich formation in the north atlantic ocean was analyzed by comparing sea surface temperatures ssts and oxygen isotope composition of seawater w changes during the past 75 kyr in two marine cores these were compared to the palynological variations derived in the mediterranean sea core during the last glacial the two oceanic sst records show similar and synchronous patterns with several long term cooling periods ending by abrupt sst increases at the time of the heinrich events cold ssts and low salinity prevailed in the mediterranean sea the freshwater budget was similar to the modern one permitting the presence of a mixed forest on the mediterranean borderlands the post heinrich periods are marked by a freshwater budget decrease limiting oak and fir tree growth in the mediterranean region increase of precipitation or reduction of evaporation is observed before the heinrich episode and is associated with a well developed mixed mediterranean forest

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

seismic and mechanical properties of opalinus clay comparison between sandy and shaly facies from mont terri switzerland for the safe disposal of high level radioactive waste different host rocks are currently being considered the favorable properties of clay are low permeability some retention capacity concerning radionuclides and the ability to self seal cracks and fissures e g by swelling or time dependent compaction creep in switzerland the jurassic opalinus clay is envisaged as a potential host rock which at mont terri is subdivided into the sandy shaly and carbonate rich facies the latter being less abundant for long term safety assessments the understanding of the relations of properties e g mineralogical composition and microstructure and performance e g mechanical behavior of clays and claystones is essential in the case of the sandy opalinus clay the mechanical strength increases with increasing carbonate content because carbonates form the matrix the mineralogical investigation of a set of sandy facies samples proved a significantly larger carbonate content 20 40 mass when compared to the shaly facies 10 20 mass the carbonates of the shaly opalinus clay on the other hand are mostly localized fossils aligned parallel to the bedding acting as predetermined breaking points image analysis of sem images of polished sections proved the determined microstructural differences in addition carbonate particles of the sandy facies are mostly isometric whereas carbonate particles of the shaly facies cover a greater range of shapes the mechanical tests were accompanied by investigations of the p and s wave velocities which revealed that the anisotropy of the sandy facies is less pronounced than sedimentological analyses would suggest the mechanical strength which for the first time presents results of real triaxial tests of the sandy facies the samples of the sandy facies exhibit a failure strength of eff b approximately twice as high as was found for the shaly facies considering the deformation axis parallel to the bedding similar values were obtained when measuring perpendicularly to the bedding

environmental and biological effects on the stable isotope composition of recent deep sea benthic foraminifera from the western mediterranean sea abstract the influence of microhabitat organic matter flux and metabolism on the stable oxygen and carbon isotope composition of live rose bengal stained and dead empty tests deep sea benthic foraminifera from the gulf of lions western mediterranean sea have been studied the total range of observed foraminiferal isotope values exceeds 1 0 for 18o and 2 2 for 13c demonstrating a wide range of coexisting disequilibria relative to 18o of equilibrium calcite 18oeq and 13c of bottom water dissolved inorganic carbon 13cdic the mean 18o values reveal strongest disequilibria for the studied epifaunal to shallow infaunal species cibicidoides pachydermus uvigerina mediterranea uvigerina peregrina while values approach equilibrium in deep infaunal species globobulimina affinis globobulimina pseudospinescens the mean 13c values decrease with increasing average living depths of the different species thus reflecting a dominant microhabitat pore water signal at the axis of the lacaze duthier canyon a minimum 13cdic pore water gradient of approximately 2 1 is assessed for the upper 6 cm of the surface sediment although live individuals of u mediterranea were found in different depth intervals their mean 13c values are consistent with calcification at an average living depth around 1 cm the deep infaunal occurrence of u mediterranea specimens suggests association with macrofaunal burrows creating a microenvironment with geochemical characteristics similar to the topmost centimeter this also explains the excellent agreement between stable isotope signals of live and dead individuals the ontogenetic enrichment in both 18o and 13c values of u mediterranea suggests a slow down of metabolic rates during test growth similar to that previously observed in planktic foraminifera enhanced organic carbon fluxes and higher proportion of resuspended terrestrial organic material at the canyon axis are reflected by 13c values of u mediterranea on average 0 58 lower than those from the open slope these results demonstrate the general applicability of the 13c signal of this species for the reconstruction of past organic matter fluxes in the mediterranean sea further studies on live specimens are needed for a more quantitative paleoceanographic approach

response of global deep water circulation to earth s climatic change 135 000 107 000 years ago the response of deep ocean circulation to major climatic events of the past 135 000 years is inferred using carbon 13 analyses of benthic foraminifera from the major ocean basins the results demonstrate that the circulation of the world ocean deep water is very sensitive to climate and that it changes drastically during climatic transitions

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

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

synchroneity between marine and terrestrial responses to millennial scale climatic variability during the last glacial period in the mediterranean region land sea climatic proxies have been obtained from the last glacial section of images core md95 2043 western mediterranean sea vegetation and alkenone derived sst curves indicate rapid 150 years and synchronous terrestrial and marine climatic changes paralleling the dansgaard oeschger d o climatic variability over greenland this frequency of climate change can be related to shifts between the two modes of operation of the north atlantic oscillation nao transfer functions applied to the pollen data indicate that there was an amplification of the climatic signal during heinrich events hes in comparison with other d o stadials the development and persistence of both scandinavian and atlantic mobile polar highs over southwestern europe may explain the extreme cooling 10 c and dryness 400 mm during heinrich events 5 and 4 in the mediterranean region comparison of the results of core md95 2043 with similar climatic data from images core md95 2042 located off portugal indicates that thermal and precipitation gradients occurred between the mediterranean and the atlantic sides of iberia within hes hes 4 and 5 are associated with more humid conditions in the atlantic by 200 mm than in the mediterranean site as is the case at the present time this comparison also illustrates the different behaviour of these areas during the d o stadials in contrast with the mediterranean site the atlantic site shows similar precipitation and temperature drops for all the d o stadials including those related to the hes here we propose the operation of different mobile polar highs mph as the driving mechanism for this difference in behaviour between the atlantic and mediterranean sides of iberia hes are related to a stronger influence of the scandinavian mph forcing a severe aridification and cooling of the full iberian peninsula the atlantic mph may have been dominant during the other stadials which would preferentially affect southwestern iberia

variation of deepwater convection in the western mediterranean sea gulf of lion during the last 28 ka abstract the oxygen and carbon isotopes record from fossil foraminifera in deep sea sediments are commonly used as proxy for global thermohaline and productivity changes the last 28 ka record of oxygen and carbon isotopes are characterized by a slow transfer of isotopic signal from surface to deep mediterranean at the beginning of heinrich events h2 and h1 and during the bolling allerod these changes in deep waters properties occur some 180 years later indicating a decrease of ventilation in the beginning of these events the slowing of the thermohaline convection is more marked in the early holocene characterized by less than 500 years of lag time between the isotopic signals

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

thermohaline instability in the north atlantic during meltwater events stable isotope and ice rafted detritus records from core so75 26kl portuguese margin a benthic isotope record has been measured for core so75 26kl from the upper portuguese margin 1099 m water depth to monitor the response of thermohaline overturn in the north atlantic during heinrich events evaluating benthic 18o in ts diagrams in conjunction with equilibrium c fractionation implies that advection of mediterranean outflow water mow to the upper portuguese margin was significantly reduced during the last glacial 15 compared to 30 today the benthic isotope record along core so75 26kl therefore primarily monitors variability of glacial north atlantic conveyor circulation the 14c accelerator mass spectrometry ages of 13 54 07 and 20 46 12 ka for two ice rafted detritus ird layers in the upper core section and an interpolated age of 36 1 ka for a third ird layer deeper in the core are in the range of published 14c ages for heinrich events h1 h2 and h4 marked depletion of benthic 13c by 0 7 1 1 during the heinrich events suggests reduced thermohaline overturn in the north atlantic during these events close similarity between meltwater patterns inferred from planktonic 18o at site 609 and ventilation patterns inferred from benthic 13c in core so75 26kl implies coupling between thermohaline overturn and surface forcing as is also suggested by ocean circulation models benthic 13c starts to decrease 1 5 2 5 kyr before heinrich events hl and h4 fully increased values are reached 1 5 3 kyr after the events indicating a successive slowdown of thermohaline circulation well before the events and resumption of the conveyor s full strength well after the events benthic 13c changes in the course of the heinrich events show subtle maxima and minima suggesting oscillatory behavior of thermohaline circulation a distinct feature of thermohaline instability in numerical models inferrred gradual spin up of thermohaline circulation after hl and h4 is in contrast to abrupt wanning in the north atlantic region that is indicated by sudden increases in greenland ice core 18o and in marine faunal records from the northern north atlantic from this we infer that thermohaline circulation can explain only in part the rapid climatic oscillations seen in glacial sections of the greenland ice core record

neogene growth of the sedimentary organic carbon reservoir we develop a recycling model using 13c 12c mass balance for net growth loss of the sedimentary organic carbon corg reservoir and apply it to the neogene bulk marine carbonate 13c record the model allows for variations in photosynthetic fractionation factors carbon cycling rates and the isotopic composition of riverine carbon inputs to the oceans the sign of the net flux term is controlled by the difference between fractional corg burial and fractional corg weathering independent of any variations in carbon cycling rate these terms are in turn estimated from the carbon isotope mass balance of newly deposited and weathered sediments respectively the magnitude of the net flux is sensitive to the global carbon cycling erosion deposition rate which may be estimated by the use of the records of radiogenic isotopic variations nd sr in paleoseawater a key observation and input to the model is that photosynthetic carbon isotope fractionation by both marine algae and terrestrial plants has decreased during the cenozoic incorporating time dependent carbon isotope fractionation into the model shows that the sedimentary corg reservoir has grown throughout most of the neogene even as marine 13c values fell after 14 ma a similar result is obtained if the variation in the marine 13c record is largely caused by changes in the carbon isotopic composition of river fluxes to the oceans rather than changes in the organic inorganic ratio of output to the burial sink the growth of the sedimentary organic carbon reservoir requires that the neogene sedimentary carbon cycle was a net source of o2 and a net sink of co2 to the atmosphere at least until the plio pleistocene as a consequence neogene co2 consumption by silicate weathering cannot be balanced by oxidation of sedimentary corg placing a significant constraint on global carbon balance models a related prediction of our model is that atmospheric o2 levels rose during the neogene

calibration of stable isotopic data an enriched δ18o standard used for source gas mixing detection and correction we present empirically based calibrations of our measurements made on a finnigan mat252 equipped with a kiel device to vienna pee dee belemnite using an enriched 18o standard calibrations include corrections for biases caused by the differences in isotopic composition of carbonate standards measured on the two parallel extraction lines of the kiel device and for decreases in the isotopic difference between the reference and sample gas caused by mixing in the source after correcting for these biases the precision of 2200 nbs19 analyses 10 300 g is 0 07 for 18o and 0 03 for 13c we have shared our standard enriched in 18o with 18 laboratories engaged in paleoceanographic research producing the first large scale interlaboratory calibrations for this community using correction procedures reported here water mass reconstructions using data produced on multiple mass spectrometers may now be possible with a precision approaching the level necessary to reconstruct temperature salinity and density variability in the deep ocean

stable oxygen and carbon isotopes of live benthic foraminifera from the bay of biscay microhabitat impact and seasonal variability we determined the stable oxygen and carbon isotopic composition of live rose bengal stained benthic foraminifera n150 am size fraction of seven taxa sampled along a downslope transect between 140 to 2000 m water depth in the bay of biscay at the five stations hoeglundina elegans cibicidoides pachydermus uvigerina peregrina uvigerina mediterranea preferentially occupy shallow infaunal niches whereas melonis barleeanus and uvigerina elongatastriata occupy an intermediate infaunal microhabitat and globobulimina spp live in a deep infaunal niche close to the zero oxygen boundary when compared with d 18 o values of calcite formed in equilibrium with bottom waters u peregrina forms its test in close equilibrium with bottom water d 18 o all other foraminiferal taxa calcify with a constant offset to calculated equilibrium calcite there is no systematic relationship between the foraminiferal microhabitat depth and the dd 18 o between foraminiferal and equilibrium calcite we calculated correcting factors for the various taxa which are needed for constructing multispecies based oxygen isotope records in paleoceanographic studies of the study area the d 13 c values of foraminiferal taxa investigated in this study do neither record bottom water d 13 cdic in a 1 1 relationship nor with a constant offset but appear to be mainly controlled by microhabitat effects the increase of d 13 c values of shallow infaunal taxa with increasing water depth reflects the decrease of the exported flux of organic carbon along the bathymetric transect and early diagenetic processes in the surface sediment this is particularly the case for the shallow infaunal u peregrina the d 13 c values of deep infaunal globobulimina spp are much less dependent on the exported organic matter flux we suggest that the dd 13 c between u peregrina and globobulimina spp can shed light on the various pathways of past degradation of organic detritus in the benthic environments at a station in 550 m water depth where periodic eutrophication of sediment surface niches was demonstrated previously we performed a two year seasonal survey of the isotopic composition of foraminiferal faunas no marked seasonal changes of the stable carbon isotopic composition of shallow intermediate and deep infaunal foraminiferal taxa were observed thus the d 13 c values of foraminiferal individuals belonging to the n150 am fraction may result from rather long term calcification processes lasting for several weeks or months which limit the impact of ephemeral 12 c enrichment of shallow infaunal niches on the isotope chemistry of adult individuals during eutrophic periods only highly opportunistic taxa reproducing or calcifying during

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

palaeoceanography of the last deglaciation in the alboran sea western mediterranean stable isotopes and planktonic foraminiferal records abstract oxygen isotope changes of the foraminiferal species globigerina bulloides and uvigerina peregrina eleven radiocarbon dates on the sediment fraction above 50 m and 13 biostratigraphical events allow us to correlate and to date the sediment record of the last climatic cycle in four cores from the alboran sea nine ecozones are recognized which differ from those previously established for atlantic sediments cored immediately west of gibraltar these ecozones can be grouped into two broad phases from the last glacial maximum up to near 9 500 yr b p cold north atlantic microfaunas are the major component of the assemblages during this interval dominant species replace each other according to the varying temperature and density stratification of the water masses from 9 500 yr b p up to the present time subtropical forms from the central atlantic dominate the northern atlantic forms an abrupt increase in the percentages of g inflata occurred near 7 000 b p this event was diachronous within the mediterranean during the last glacial g inflata was endemic inside the mediterranean and its abrupt increase near the end of the deglaciation did not result from replenishment from the atlantic between 4 000 and 5 000 yr b p percentages of g bulloides also increased abruptly warming conditions associated with the onset of a seasonal thermal stratification and a contrasting winter vertical convection are strongly suggested

glacial rapid variability in deep water temperature and δ18o from the western mediterranean sea abstract deep water temperatures dwts from the western mediterranean sea are reconstructed for the last 50 ka based on the analysis of mg ca ratios in benthic foraminifera from core md95 2043 collected in the alboran sea the exceptionally high sedimentation rates of this core and the robust chronology available allow discussion of the results in the context of the dansgaard oeschger d o rapid climatic variability the applicability of mg ca thermometry in the western mediterranean deep water mass wmdw is first tested by the analysis of different benthic species in a collection of mediterranean core tops the results indicate the need of a readjustment of the existing cibicidoides spp calibrations in order to reconstruct present western mediterranean dwt values 12 7 c different physiological effects in the mg uptake between the c pachydermus living in different regions could account for this offset in the mediterranean samples consequently the obtained dwt record still has many uncertainties in absolute terms but trends provide valuable information on past changes in wmdw conditions the dwt record shows significant oscillations in relation to the d o cycles colder values occurred during the time of d o stadials and warmer ones during d o interstadials surprisingly the coldest dwts occurred during the time of heinrich event 4 he4 and not during the last glacial maximum lgm when dwts were mostly warm these and other particular features of the dwt reconstruction mimic changes in the vegetation from the eastern mediterranean indicating the control of the mediterranean climate on the dwt record paired analyses of mg ca and 18 occ calcite 18 o provide the opportunity to reconstruct deep water 18 o 18 odw and past salinities and hence changes in past wmdw density due to the large error associated with these calculations they can only be discussed in terms of relative changes between different intervals the results suggest the dominance of a heavier water end member during glacial times and a lighter one during the early holocene in relation to the 18 odw conditions present today densest wmdw were formed during most of marine isotopic stage mis 2 and during the d o stadials not associated with hes while lightest wmdw dominated during d o interstadials the 18 odw record shows a d o variability pattern likely controlled by changes in the composition and intensity of the local run off and also to changes in the 18 ow signal of the atlantic inflow changes in the residence time of the mediterranean waters governed by the global sea level are also considered to exert an important role governing mediterranean 18 ow and salinity particularly during mis 2 overall our results are consistent with the formation of dense wmdw during d o stadials and even denser during most of mis 2

evidence for enhanced mediterranean thermohaline circulation during rapid climatic coolings molecular biomarkers c37 alkenones n nonacosane and n hexacosanol and toc are used together with benthic 18o and 13c data to document the hydrographic response of the western mediterranean sea to rapid climatic variability these proxies are recorded in core md 95 2043 alboran sea affording the study of the dansgaard oeschger d o and heinrich he variability during the last glacial period the results suggest that rapid changes in the western mediterranean thermohaline circulation occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation occurred during cold intervals he and d o stadials probably driven by a strengthening of north westerly wind over the north western mediterranean sea in contrast decreased intensity of the thermohaline circulation is detected during warm intervals d o interstadials which led to low oxygenated deep water masses and better preservation of the organic matter in the sediment

abrupt climate change sea surface salinity and paleoproductivity in the western mediterranean sea gulf of lion during the last 28 kyr abstract the planktonic foraminiferal record of core md99 2346 gulf of lion shows a decrease of sea surface temperature sst at the time of heinrich event h2 24 23 5 cal kyr bp younger dryas and during the early to middle holocene these events were associated with a decrease of surface water salinity the salinity lowering events were similar and synchronous to those recorded in the north atlantic ocean during h1 h2 and the younger dryas they can be explained by a decrease in the salinity of the atlantic surface water entering the mediterranean through the strait of gibraltar this result indicates that the mediterranean sea remained a concentration basin and that its freshwater budget was not significantly different from the modern conditions at the time of these low salinity events higher abundances of the benthic foraminifer cibicidoides pachydermus at the time of heinrich events h2 and h1 may result from a seasonal and more pulsed supply of labile organic matter a high abundance of intermediate and deep infaunal taxa globobulimina spp during the warm bolling allerod period is interpreted as a result of an increased lateral advection of organic matter to the deeper environments of the gulf of lion surface water productivity as reflected by the organic flux to the benthic ecosystem reaches a maximum during the cold younger dryas period it is possible that cold conditions at the time of the younger dryas have allowed an enhanced vertical mixing and deep water cascading in the gulf of lion this may have resulted in an increase of primary and export production this putative intensification of deep water cascading would have occurred after the sustained rise of the global sea level from 16 to 12 5 cal kyr bp the deglacial sea level rise may also have played an important role in favouring the downslope movement of dense shelf water enriched in organic matter originating from the early rhone delta complex the conditions during the holocene were characterized by a low surface productivity and oligotrophic environment similar to the modern situation

mediterranean outflow strengthening during northern hemisphere coolings a salt source for the glacial atlantic abstract high resolution grain size and magnetic susceptibility records from the eastern gulf of cadiz site md99 2339 1170 m water depth reveal contourites formed by the mediterranean outflow mow during the last 47 kyr bp oscillations in the mow s intensity occurred in phase with greenland temperature variations with a stronger outflow during northern hemisphere coolings such as dansgaard oeschger stadials heinrich events and the younger dryas benthic 13c data implies the western mediterranean deep water as one of the main sources feeding the outflow current while differential changes in the properties of the mediterranean source and entrained north atlantic central water largely control the mow s strength detailed studies for heinrich events 1 4 and 5 show that the flow strength peaked only when subtropical surface waters prevailed in the eastern gulf of cadiz while incursions of icebergs and subpolar surface water were not favorable for the mow s intensification as the mow was strong when the atlantic s thermohaline circulation thc was weakened the heat and salt injected by the mow into the intermediate north atlantic waters might have preconditioned the thc to switch from the stadial to the interstadial mode

enhanced aridity and atmospheric high pressure stability over the western mediterranean during the north atlantic cold events of the past 50 k y multiproxy paleoenvironmental records pollen and planktonic isotope from ocean drilling program site 976 alboran sea document rapid ocean and climate variations during the last glacial that follow the dansgaard oeschger climate oscillations seen in the greenland ice core records thus suggesting a close link of the mediterranean climate swings with north atlantic climates continental conditions rapidly oscillated through cold arid and warm wet conditions in the course of stadial interstadial climate jumps at the time of heinrich events i e maximum meltwater flux to the north atlantic western mediterranean marine microflora and microfauna show rapid cooling correlated with increasing continental dryness enhanced aridity conceivably points to prolonged wintertime stability of atmospheric high pressure systems over the southwestern mediterranean in conjunction with cooling of the north atlantic

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

impact of iceberg melting on mediterranean thermohaline circulation during heinrich events down core samples of planktonic and benthic foraminifera were analyzed for oxygen and carbon isotopes in international marine past global changes study images core md99 2343 in order to study the interactions between climate change in the northern hemisphere and the western mediterranean thermohaline circulation at times of heinrich events he our results confirm the antiphase correlation between enhanced north atlantic deep water formation and low ventilation in the mediterranean however this study reveals that this antiphase relationship in deepwater formation between the north atlantic and mediterranean was interrupted during times of he when the injection of large volumes of water from melting icebergs reached the entrance to the mediterranean these events which lasted less than 1000 years are represented by pronounced decreases in both planktonic d18o and benthic d13c signals lower salinities of mediterranean surface water resulted in a slowdown of western mediterranean deepwater overturn even though cold sea surface temperatures and drier climate should have resulted in enhanced deepwater formation

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

links between marine and atmospheric processes oscillating on a millennial time scale a multi proxy study of the last 50 000 yr from the alboran sea western mediterranean sea abstract the large dataset obtained from the extensive study of images core md95 2043 recovered from the alboran sea western mediterranean shows the periodicities and phase relationships of oceanographic and atmospheric processes on a millennial time scale the 1470 yr cycle is the most significant with the exception of the records reflecting climatic or environmental changes on land which show statistically significant 3300 and 8000 frequency bands the investigation of these core records on a millennial scale resolution allows us to establish the evolution of oceanographic and atmospheric mechanisms that influenced the western mediterranean region in the course of the dansgaard oeschger cycles accordingly possible land sea interactions can be identified and situated in the context of the temporal succession of the different climatic processes for instance saharan dust supply from northern africa appears to lead high latitude climate changes suggesting that low latitude feedback processes were involved in forcing the millennial climatic variability in the westernmost mediterranean

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

benthic foraminiferal δ13c and accumulation rates of organic carbon uvigerina peregrina group and cibicidoides wuellerstorfi the glacial to interglacial 13c records of the benthic foraminifera cibicidoides wuellerstorfi and the uvigerina peregrina group from deep sea cores cannot be adjusted by a generally valid constant the 13c values of the u peregrina group largely correlate with the accumulation rates of organic carbon suggesting a local habitat effect those of c wuellerstorfi vary independently with respect to the carbon flux and record fluctuations in the 13c of the ambient bottom water isotopic composition

the fluvial and pyroclastic deposits of the cagayan basin northern luzon philippines an example of non marine volcaniclastic sedimentation in an interarc basin the cagayan basin of northern luzon an interarc basin 250 km long and 80 km wide contains a 900 m thick sequence of plio pleistocene fluvial and pyroclastic deposits these deposits are divided into two formations the ilagan and awidon mesa and three lithofacies associations the facies which are interpreted as meandering stream braided stream lahar and pyroclastic flow and fall deposits occur in a coarsening upward sequence meandering stream deposits interbedded with tuffs are overlain by braided stream deposits interbedded with coarser pyroclastic deposits lahars and ignimbrites the coarsening upward volcaniclastic deposits reflect the tectonic and volcanic evolution of the adjacent cordillera central volcanic arc uplift of the arc resulted in the progradation of coarser clastics further into the basin the development of an alluvial fan and migration of the basin depocentre away from the arc the coarsening of the pyroclastic deposits reflects the development of a more proximal calc alkaline volcanic belt in the maturing volcanic arc the cagayan basin sediments serve as an example of the type and sequence of non marine volcaniclastic sediments that may form in other interarc basins this is because the tectonic and volcanic processes which controlled sedimentation in the cagayan basin also affect other arc systems and will therefore control or significantly influence volcaniclastic sedimentation in other interarc basins