gravity field of the moon from the gravity recovery and interior laboratory grail mission spacecraft to spacecraft tracking observations from the gravity recovery and interior laboratory grail have been used to construct a gravitational field of the moon to spherical harmonic degree and order 420 the grail field reveals features not previously resolved including tectonic structures volcanic landforms basin rings crater central peaks and numerous simple craters from degrees 80 through 300 over 98 of the gravitational signature is associated with topography a result that reflects the preservation of crater relief in highly fractured crust the remaining 2 represents fine details of subsurface structure not previously resolved grail elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

δ18o values of coexisting brachiopods and fish temperature differences and estimates of paleo water depths to estimate vertical thermal gradients and paleo water depths to marine platforms we present a new method based on the difference between 18 o values of contemporaneous brachiopod carbonate and fish phosphate present day marine fauna of well known ecology from the surface to the sea floor record isotopic temperatures that agree with measured temperatures we predict distributions of isotopic data that result from sampling strategy basin morphology and fauna ecology and discuss limitations application of the method to the jurassic paris london basin gives vertical thermal variations of up to 14 c associated with depths varying from a few meters to 170 30 m the estimated depths are minimum values and are greater than those estimated from sedimentological criteria for this ancient epicontinental sea

middle and late jurassic radiolarian palaeoecology versus carbon isotope stratigraphy abstract jurassic radiolarians are sensitive to palaeoclimatic palaeoceanographic changes recorded by the stable carbon isotope curve carbon isotopic variations have been linked to changes in ocean structure productivity and concentrations of greenhouse gases in the atmosphere in the middle upper jurassic terminilletto section of the umbria marche sabina apennines central italy well preserved radiolarians are present in a sequence of cherty limestones interbedded with platform derived carbonates the 13 c curve in the aalenian kimmeridgian interval indicates three main positive 13 c events in the lower bajocian late bathonian lower callovian and middle oxfordian the positive 13 c shifts are correlated to increases in visible chert in the outcrop and may represent periods of increased biological productivity of surface sea water spumellaria nassellaria ratios and the fluctuations of relative abundance of selected genera tend to correlate with 13 c and chert abundance values and seem to be related to episodes of high nutrient mobilisation from the base of the bajocian the radiolarian associations show a slight tendency towards diversification coincident with increasing 13 c values in the upper part of the middle bajocian last appearances prevail over first appearances associated with the peak of the 13 c event this may indicate maximum eutrophic conditions coincident with the late bathonian early callovian positive 13 c shift the radiolarian associations record a different trend with respect to the bajocian event when the 13 c values are increasing to a maximum radiolarian associations tend to be reduced in species diversity followed by a small diversification trend when the 13 c values are decreasing we speculate that during the callovian a more stressful palaeoenvironment due to high level of eutrophication is indicated by the combination of high productivity of biogenic silica and low carbonate input although varying preservational conditions may have influenced the observed trends in the radiolarian associations the good correlation between changes of sedimentation patterns radiolarian assemblages and 13 c positive anomalies open interesting avenues for further investigations concerning the palaeoecology of mesozoic radiolarians

palaeoclimatic and biotic changes during the aalenian middle jurassic at the southern laurasian seaway basque cantabrian basin northern spain the uppermost toarcian lowermost bajocian deposits have been studied in 10 sections located in the western part of the basque cantabrian basin northern spain the studied 276 successive recorded ammonite assemblages allowed detailed biostratigraphical subdivision and the correlation of the sections at the ammonite zone and subzone scale the foraminifers were studied in 96 samples and 55 diagenetically screened belemnite rostra were analyzed for c and o isotope facies and thickness distribution of the aalenian sediments suggest that deposition took place in a nearly symmetrical sub basin included into an intraplate shallow platform developed over continental crust on which flexure was the main control responsible for subsidence and basin evolution noteworthy negative 13cbel excursions coinciding with seawater temperature changes were recorded during the bradfordensis biochron around the concavum limitatum biochron boundary and around the aalenian bajocian boundary a close relationship between the changes in seawater temperature and the biotic changes observed in the foraminiferal and in the ammonoids assemblages has been evidenced during the comptum biochron the 18obel based palaeotemperature shows a remarkable cooling interval with an average seawater temperature of 15 7 c this cooling favoured the immigration of species of foraminifers that thrived in platforms with colder seawater temperatures located north of the basque cantabrian basin as a consequence a strong increase in the diversity of the foraminiferal assemblages 28 5 of first appearances occurred this interval also coincides with the highest ammonoid abundance recorded during the aalenian a notable increase in temperature with peak values up to 24 3 c was measured during the bradfordensis biochron this warming marks the beginning of progressive loss of foraminifer diversity and the decrease in the abundance of ammonoids however the increase in the relative abundances of some foraminiferal taxa such as the genus spirillina during the warming phase is remarkable some of the foraminiferal species that had their last occurrence during this interval seem to be immigrants from nw europe that arrived during the comptum cooling interval and that did not survive to rise of the seawater temperature another drop in temperature was recorded during the late gigantea and the early concavum biochrons coinciding with this cooling interval nearly 20 of the foraminiferal species disappeared while the ammonoid abundance increased a new and significant warming episode occurred during the latest aalenian limitatum biochron extending to the earliest bajocian discites biochron biotic response to this new t of 2 5 c is remarkable marking one of the most important crises of the aalenian more than 30 of the foraminiferal species disappeared and no new appearances were recorded ammonoids show a decrease in the specimen abundance during the limitatum discites warming preceding a drastic decrease in the species abundance the remarkable biotic changes linked to the variations of seawater temperature recorded in the basque cantabrian basin during the aalenian open the possibility that some of these faunal turnovers specially marked in the benthic foraminifers were of global extent and mainly forced by climate changes

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

crustal thickness and support of topography on venus united states national aeronautics and space administration nasa planetary geology and geophysics program grant

climatic ups and downs in a disturbed jurassic world the tropical warm and equable climate of the jurassic world is regularly challenged by geoscientists especially since oxygen isotopes 18 o of fossil hardparts have been used to reconstruct the paleotemperature history of seawater by applying the innovative sizer sig nifi cant zero crossings of the derivatives statistical approach to a newly compiled 18 o data base for the jurassic we demonstrate the occurrence of major and multiscale 18 o changes mainly related to climate disturbances for the fi rst time two long term anomalies in 18 o are identifi ed during the toarcian and the late jurassic in conjunction with intensive volcanism in large igneous provinces these results support a strong infl uence of repeated volcanic pulses on the modulation of pco 2 temperatures and polar ice cap volumes over protracted periods at shorter time scales 13 relatively rapid 0 5 1 m y and signifi cant warming and cooling events are identifi ed the causes of which include transient fl uctuations in greenhouse gas con centrations related to still debated mechanisms

ice shelf water overflow and bottom water formation in the southern weddell sea 1 cold shelf waters flowing out of the filchner depression in the southern weddell sea make a significant contribution to the production of weddell sea bottom water wsbw a precursor to antarctic bottom water aabw we use all available current meter records from the region to calculate the flux of cold water 1 9 c over the sill at the northern end of the filchner depression 1 6 0 5 sv and to determine its fate the estimated fluxes and mixing rates imply a rate of wsbw formation referenced to 0 8 c of 4 3 1 4 sv we identify three pathways for the cold shelf waters to enter the deep weddell sea circulation one path involves flow constrained to follow the shelf break the other two paths are down the continental slope resulting from the cold dense water being steered northward by prominent ridges that cross the continental slope near 36 w and 37 w mooring data indicate that the deep plumes can retain their core characteristics to depths greater than 2000 m probably aided by thermobaricity the plume water at this depth can flow at a speed approaching 1 m s 1 implying that the flow is occasionally supercritical we postulate that such supercriticality acts to limit mixing between the plume and its environment the transition from supercritical to slower more uniform flow is associated with very efficient mixing probably as a result of hydraulic jumps

a numerical investigation of formation and variability of antarctic bottom water off cape darnley east antarctica abstractat several locations around antarctica dense water is formed as a result of intense sea ice formation when this dense water becomes sufficiently denser than the surrounding water it descends the continental slope and forms antarctic bottom water aabw this study presents the aabw formation off the coast of cape darnley cape darnley bottom water cdbw in east antarctica using a nonhydrostatic model the model is forced for 8 months by a temporally uniform surface salt flux because of sea ice formation estimated from advanced microwave scanning radiometer for earth observing system eos amsr e data and a heat budget calculation the authors reproduce aabw formation and associated periodic downslope flows of dense water descending pathways of dense water are largely determined by the topography most dense water flows into depressions on the continental shelf advects onto the continental slope and is steered downslope to greater depths by the canyons intense sea ice formation is the

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

early jurassic climatic trends in the south tethyan margin abstract the early jurassic period was characterized by extreme environmental changes as reflected by major global carbon isotope anomalies and abrupt changes in oxygen isotope and elemental records of marine organisms available data suggest an overall warm early jurassic climate interrupted by periods of severe cooling with a climatic optimum during the early toarcian available geochemical studies however have mainly focused on the northern margin of the tethys ocean so that the palaeogeographic extent of these environmental perturbations latitudinal palaeotemperature gradients and climate belt boundaries remain poorly constrained here we report the first stable isotope records of brachiopod shells 13c and 18o values from the upper sinemurian middle toarcian interval in the southern margin of the tethys ocean northwest algeria these data were used to better constrain the palaeoenvironmental evolution of the north gondwana margin during the early jurassic which likely played an important role on supra regional climate the diagenetic history of the analysed brachiopod shells was monitored using scanning electron microscopy and elemental manganese and strontium compositions the brachiopod 13c and 18o data show very similar trends as those reported for various tethyan regions and record negative carbon and oxygen isotope excursions near the sinemurian pliensbachian and pliensbachian toarcian transitions and during the toarcian oceanic anoxic event t oae despite these similarities the carbon and oxygen isotope records are systematically offset towards more positive 13c values average 0 5 and more negative 18o values 1 0 compared to those obtained from sites of higher palaeolatitudes in the northern tethyan margin these offsets suggest a spatial heterogeneity in the stable isotope composition of dissolved inorganic carbon in the early jurassic ocean and a marked latitudinal temperature gradient between the southern and northern margins of the tethys

duration of the early bajocian and the associated δ13c positive excursion based on cyclostratigraphy the early bajocian about 172 ma ago was a period of tectonic changes a global carbon isotope positive excursion and biological diversification of marine invertebrates e g ammonites radiolarians and coccolithophores unfortunately both the duration of the early bajocian and the associated palaeoenvironmental changes are still poorly constrained we propose here an estimate of the duration of this sub stage based on a cyclostratigraphic analysis of the carbonate content from the chaudon norante section french subalpine basin france the chaudon norante succession has been correlated with les dourbes section using greyscale variations to detect possible local hiatuses the duration estimated here for the entire early bajocian is 4 082 ma two intervals were identified in the positive 13 c excursion an increase of carbon isotope values lasting 1 36 ma and climax isotope values lasting for 2 72 ma a cooling at high latitudes and warming at low latitudes may have enhanced the earth s temperature gradient leading to an increase in humidity which in turn triggered ocean eutrophication at the origin of the 13 c positive excursion supplementary material the complete dataset presented in the paper a colour version of the figure 8 and correlation of 13 c excursions between our studied site and contemporaneous sites are available at www geolsoc org uk sup18555

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

constraints on the maximum crustal density from gravity topography modeling applications to the southern highlands of mars abstract gravimetric methods commonly used to constrain crustal parameters such as the mean crustal thickness and density are ambiguous with a noted trade off between these parameters however combining two different methods the geoid topography ratio and bouguer inversion in regions that are homogeneous with respect to lateral density variations and compensation state can help to constrain a maximum density of the crust for the martian noachian southern highlands a combination of these methods gives us a maximum crustal density of 3020 70 kg m 3 assuming a single layer crustal structure we also test various two layer crustal structures to check how they influence the results we find a possibility to fit the observed data with a crust having a dense uniformly thick lower crust but in these models the upper crustal density was also limited to 3000 kg m 3 the obtained results together with the findings on crustal densities and composition of other regions on mars are consistent with various scenarios of crustal evolution a temporal increase in the crustal density or a large scale density variation that has been already manifested in the early evolution during the formation of the crustal dichotomy

oxygen isotopes and mgco3 in brachiopod calcite and a new paleotemperature equation abstract modern brachiopods and their ambient seawater compiled from 34 localities covering shallow waters from the poles to the tropics were analyzed for their oxygen isotopic compositions and srco3 and mgco3 contents if the routine seawater 18o composition and the mgco3 effect on oxygen isotopes are considered in calculations calcification temperatures are concordant with measured ambient seawater temperatures the srco3 contents of modern brachiopods appear to be unrelated to ambient growth temperatures while their mgco3 contents exhibit some relationship with temperature and growth rate controlled in part by ambient productivity or clearance rates or local environment and by taxonomic affinity such as presence or absence of caeca linear least squares regression analysis yields a new oxygen isotope paleotemperature equation for brachiopod calcite which makes adjustment for shell mgco3 contents and covers habitats with water temperatures ranging from 2 to 32 c t c 16 192 3 468 c sw mg c n 319 r 2 0 98 the mg effect adjustment is based on the change in shell calcite 18o by 0 17 per mol mgco3 jimenez lopez et al 2004 this adjustment is critical to the determination of calcification temperatures for modern articulated brachiopods especially the ones from cold and warm water habitats and or the ones with exceptionally low or high mgco3 contents which otherwise may be offset lower or higher by as much as 7 c furthermore this adjustment may be critical for fossil brachiopods and other marine calcitic invertebrates with variable mgco3 contents and when using their 18o and 47 for determining ancient seawater 18o compositions and temperatures

calcareous nannofossil assemblage turnover in response to the early bajocian middle jurassic palaeoenvironmental changes in the subbetic basin abstract the calcareous nannofossil assemblages from three lower bajocian pelagic successions from the subbetic basin well dated by ammonites have been investigated biostratigraphically they encompass the njt9 to njt10a nannofossil tethyan zones pca factor analysis performed on percentage abundances of selected taxa suggests that the main factors controlling the early bajocian nannofossil assemblages of the subbetic basin were trophic level nutrient availability and nutricline depth a gradual eutrophication is recorded in the calcareous nannofossil assemblages through an increase in the percentage abundance of watznaueria spp especially in the taxa best adapted to unstable and more eutrophic conditions w britannica gr and w manivitiae gr this eutrophication is concomitant with a trend of increasing carbonate 13 c values over the early bajocian and a rise in biogenic silica production and deposits in the study sections and other basins of the western tethys around the middle part of the laeviuscula subzone a decrease in the absolute and relative abundance of the deep dwelling taxa especially crepidolithus crassus suggests a deterioration of the environmental conditions in the lower photic zone this has been interpreted as caused by a nutricline shallowing and or greater turbidity that could be related in turn to surface water stratification two different episodes have been differentiated in relation to nutricline dynamics 1 from the latest aalenian to earliest early bajocian a weak and or deep nutricline with nutrients rather uniformly spread throughout the photic zone and concomitant with mesotrophic conditions and increasing productivity is suggested 2 a shallowing of the nutricline and or increase in surface water turbidity concomitant with more eutrophic conditions is suggested for the latest early bajocian the observed decrease in the deep dwelling taxa supports the hypothesis of a climatically driven fertilization of the surface waters instead of fertilization by upwelling for the early bajocian eutrophication episode

topographic vorticity waves forced by antarctic dense shelf water outflows we use numerical simulations to investigate excitation of topographic vorticity waves tvws along the antarctic continental slope by outflows of dense shelf water through troughs idealized models show that wave frequency depends on the amount of stretching in the ambient fluid over the outflow and on background along slope mean flow frequency is higher for steeper bottom slope larger outflow density anomaly and stronger westward mean flow for weak stratification and weak westward along slope flows typical of the antarctic slope wave energy propagates eastward in the opposite direction from phase velocity our results are consistent with recent observations of tvws in the southern weddell sea in a realistic simulation of the ross sea tvw properties are modulated on seasonal and shorter time scales as background ocean state varies we expect these waves to affect mixing cross slope exchanges and sea ice concentration in the vicinity of sources of dense water outflows

eddy formation by dense flows on slopes in a rotating fluid properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments the dense fluid may initially flow down the slope but it turns under the influence of rotation to flow along the slope and initial geostrophic adjustment gives it an anticyclonic velocity profile some of the dense fluid drains downslope in a viscous ekman layer which may become unstable to growing waves provided that the viscous draining is not too strong cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes three processes may contribute to the formation of these eddies first initial downslope flow of the dense current may stretch columns of ambient fluid by the taylor column process which we term capture secondly the initial geostrophic adjustment implies lower layer collapse which may stretch the fluid column and thirdly viscous drainage will progressively stretch and spin up a captured water column overall this last process may be the most significant but viscous drainage has contradictory effects in that it progressively removes dense lower layer fluid which terminates the process when the layer thickness approaches that of the ekman layer the eddies produced propagate along the slope owing to the combined effects of buoyancy coriolis balance and beta gyres this removes fluid from the vicinity of the source and causes the cycle to repeat the vorticity of the upper layer cyclones increases linearly with l d where l is the rossby deformation radius the bottom slope and d the total depth reaching approximately 2 f in the experiments presented here the frequency at which the eddy dome structures are produced also increases with while the speed at which the structures propagate along the slope is reduced by viscous effects the flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed

facies and climate environmental changes recorded on a carbonate ramp a sedimentological and geochemical approach on middle jurassic carbonates paris basin france a detailed sedimentological geochemical and mineralogical study is carried out on the early bajocian to early callovian middle jurassic limestones of the paris basin objectives are to document and explain the facies changes in the context of the climate environmental evolution at the nw european scale deposits include 18 lithofacies which are stacked into 10 third order depositional sequences at a greater time scale 4 biosedimentary packages are distinguished by their allochems associations 1 an intracratonic carbonate environment with coral reefs and crinoid rich facies is typical of the early bajocian 2 a major facies change occurred at the early late bajocian transition with a shift from crinoid and coral rich facies to ooid rich facies during the late bajocian a southward dipping ooid ramp with successive progradational trends was emplaced 3 a large lagoon protected by ooid shoals developed during the bathonian in a muddy ramp setting 4 at the bathonian callovian boundary a second major change occurred with the lagoonal facies being superseded by an ooid bioclastic crinoids corals ramp associated with a waning of carbonate productivity retrogradational trend our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern a cooling from the latest early bajocian to the late bajocian and a subsequent warming from the earliest callovian to the early middle callovian transition are described using a proxy of sea surface temperatures together with 13c and mineralogical data our new 18o values suggest a palaeo climatic palaeo environmental control of facies in this shallow carbonate ramp environment

integrated stratigraphy radiolarians and calcareous nannofossils of the middle to upper jurassic alpine radiolarites lombardian basin italy constraints to their genetic interpretation abstract new biostratigraphic data obtained by integrating radiolarians and calcareous nannofossils document a depositional history for the middle to upper jurassic radiolarites of the italian southern alps characterized by strong fluctuations in the sedimentation rates associated to shifts from gravity driven to hemipelagic sedimentary process we studied the radiolarites in four sections located in different settings of the lombardian basin a rifted basin of the northern adriatic plate the sections studied were described and sampled in detail to obtain data on their lithology using facies and microfacies analysis and calcimetry and their nanno and microfossils content especially radiolarians and calpionellids an almost complete record of radiolarians was detected throughout the selcifero lombardo formation so that the radiolarian zonation uazs for the middle to upper jurassic interval partially integrated with calcareous nannofossil and calpionellid biostratigraphic data was successfully applied accordingly the lower member radiolariti correlates with the lower bathonian uaz 5 to the kimmeridgian uaz 11 interval and the upper member rosso ad aptici displays an age spanning from the kimmeridgian to the base of upper thitonian from uazs 10 11 to nannofossil njk zone we interpret the radiolarites as pelagic sediment relatively enriched in radiolarian during a long time span of basin starvation due to the near absence of periplatform exportation if we except bathonian a period of relatively higher sedimentation rates the radiolarites are characterized by very low sedimentation rates implying equally low radiolarian productivity therefore it is not necessary to claim for high tethyan water fertility during middle to late jurassic even if this latter condition likely played a role in the production exportation of the carbonate platforms

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

density and lithospheric structure at tyrrhena patera mars from gravity and topography data the tyrrhena patera highland volcano mars is associated with a relatively well localized gravity anomaly and we have carried out a localized admittance analysis in the region to constrain the density of the volcanic load the load thickness and the elastic thickness at the time of load emplacement the employed admittance model considers loading of an initially spherical surface and surface as well as subsurface loading is taken into account our results indicate that the gravity and topography data available at tyrrhena patera is consistent with the absence of subsurface loading but the presence of a small subsurface load cannot be ruled out we obtain minimum load densities of 2960 kg m 3 minimum load thicknesses of 5 km and minimum load volumes of 0 6 106 km3 photogeological evidence suggests that pyroclastic deposits make up at most 30 of this volume such that the bulk of tyrrhena patera is likely composed of competent basalt best fitting model parameters are a load density of 3343 kg m 3 a load thickness of 10 8 km and a load volume of 1 7 106 km3 these relatively large load densities indicate that lava compositions are comparable to those at other martian volcanoes and densities are comparable to those of the martian meteorites the elastic thickness in the region is constrained to be smaller than 27 5 km at the time of loading indicating surface heat flows in excess of 24 mw m 2

water mass exchange and variations in seawater temperature in the nw tethys during the early jurassic evidence from neodymium and oxygen isotopes of fish teeth and belemnites article i nfo oxygen and neodymium isotope analyses performed on biostratigraphically well dated fish remains recovered from the hettangian to toarcian of the paris basin were used to reconstruct variations of early jurassic seawater temperature and to track oceanographic changes in the nw tethys our results indicate a strong correlation between 18 o trends recorded by fish remains and belemnites confirming the paleoenvironmental origin of oxygen isotope variations interestingly temperatures recorded by pelagic fishes and nektobenthic belemnites and bottom dwelling fishes are comparable during the late pliensbachian sea level lowstand but gradually differ during the early toarcian transgressive episode recording a difference in water temperatures of 6 c during the bifrons zone this could suggest that the surface bottom water temperature difference was not large enough during regressive phases to be recorded by organisms living near the lower and upper part of the water column the globally unradiogenic nd budget of euro boreal waters through the early jurassic suggests that these waters were strongly affected by continental neodymium input from surrounding emerged areas and that exchange with more radiogenic waters from the tethys and panthalassa oceans remained limited this supports the existence of a southward directed current in the euro boreal area for most of the early jurassic the only exception is observed at the early late pliensbachian transition where a positive end excursion is recorded suggesting northward influx of low latitude tethyan or panthalassan waters which may have contributed to the warming of nw tethyan seawater recorded at this time the absence of a marked negative excursion in end concomitant with a negative 18 o shift recorded during the falciferum zone exaratum subzone argues against the influence of less radiogenic arctic water influxes with low 18 o values during this interval instead we suggest that

evidence of increasing surface water oligotrophy during the campanian maastrichtian boundary interval calcareous nannofossils from dsdp hole 390a blake nose abstract the latest cretaceous campanian maastrichtian is characterized by several global cooling and intermittent warming events these climatic changes influenced the palaeoceanography substantially including changes of the deep water sources and surface water currents one of the most prominent episodes of climatic cooling occurred during the campanian maastrichtian transition this study focuses on the palaeoclimate and palaeoceanography of the campanian maastrichtian transition by analysing the calcareous nannofossils of dsdp hole 390a 139 92 126 15 mbsf blake nose for the examination of calcareous nannofossils sixty samples were processed using the settling technique biostratigraphical index taxa broinsonia parca constricta uniplanarius trifidus and tranolithus orionatus suggest a late campanian age for the major part of the studied section the calcareous nannofossils are well preserved highly abundant 6 80 billion specimens gram sediment and diverse 80 species sample the assemblages are dominated by prediscosphaera spp 20 5 watznaueria spp 20 3 and retecapsa spp 9 8 cool water taxa ahmuellerella octoradiata gartnerago segmentatum and kamptnerius magnificus however appear less frequently and do not exceed more than 1 due to their rarity these cool water taxa do not support the existence of an intense cooling phase during the campanian maastrichtian transition at dsdp hole 390a around 133 mbsf several nannofossil taxa however show a distinctive turnover mesotrophic species like discorhabdus ignotus zeugrhabdotus bicrescenticus and zygodiscus exmouthiensis are abundant below 133 mbsf whereas oligotrophic taxa like watznaueria spp eiffellithus spp and staurolithites flavus become common above this level these changes imply a decrease in the input of nutrients perhaps caused by a reorganization of ocean currents palaeo gulf stream and reduced upwelling

aalenian carbon isotope stratigraphy calibration with ammonite radiolarian and nannofossil events in the western tethys abstract in this study a detailed carbon isotope stratigraphy of four aalenian sections well dated with ammonites from the median subbetic palaeogeographic domain external zones of the betic cordillera southern spain is presented two of these represent the most complete aalenian sections of the southern iberian palaeomargin western tethys these sections are rhythmic sequences made of marls and marly limestones containing rich ammonite fauna and nannofossils that enable an accurate biostratigraphic control at the subzone level moreover the lower and upper aalenian boundaries are well defined in these sections and therefore represent optimal sites to link the carbon isotope curves to ammonite zones and subzones and nannofossil events the uppermost toarcian lowermost bajocian 13 c values of bulk carbonates show evident fluctuations the values are low 1 in the upper toarcian mactra subzone increase slightly to 2 in lower aalenian comptum subzone fall to a relative minimum 1 1 5 in the middle aalenian bradfordensis zone reach a marked positive peak of 2 5 2 7 in the upper aalenian concavum subzone and then the values decrease again to 1 5 1 7 near the aalenian bajocian boundary marine carbonate 13 c curves in subbetic and the apennines shows similar variations but higher 13 c values in the apennines sections a slight offset is also present between the sections from the same basin this drift is interpreted by variations in carbon isotopic composition of sea water dic associated with different palaeoceanographic settings comparison of the 13 c values of bulk carbonates and biotic events ammonite diversity and nannofossil and radiolarian abundances reveals relationships between the carbon cycle and biotic evolution the latest toarcian aalenian turnovers toarcian aalenian boundary and middle late aalenian follow low 13 c values where extinct taxa are replaced by new ones radiation episodes are associated with increasing 13 c values and with sea level rise in the earliest late aalenian concomitantly with a major 13 c positive excursion and with the transgressive cycle it is noted a major increase of the eutrophic calcareous nannofossil genus biscutum and a sharp peak in radiolarian abundance although the aalenian interval seems not to be characterized by major large amplitude negative or positive excursions as observed in other phanerozoic intervals these data point to a close connection between perturbations in the global carbon cycle and the palaeoenvironmental changes that occurred which in turn had important interactions with the evolution of pelagic biota

evidence for major environmental perturbation prior to and during the toarcian early jurassic oceanic anoxic event from the lusitanian basin portugal the timing and causal relationships between the pronounced negative c isotope excursion and paleoenvironmental perturbations associated with the toarcian oceanic anoxic event early jurassic remain unclear particularly because biotic crises and carbonate production decrease appear to have been initiated earlier than the main c isotope anomaly here we present a new quantification of late pliensbachian early toarcian calcareous nannofossils abundance and size from the peniche reference section portugal together with o and c isotope records of well preserved brachiopod shells from the same section the brachiopod shell 13c curve parallels that of bulk carbonate and records two pronounced negative isotopic excursions close to the pliensbachian toarcian boundary 2 and during the toarcian oceanic anoxic event 3 5 our results indicate that both c isotope negative excursions were characteristic of benthic and shallow water environments suggesting that these two carbon cycle perturbations affected all epioceanic reservoirs coeval shifts toward lower values of brachiopod oxygen isotope compositions and closely correlated northward migrations of mediterranean ammonite fauna suggest that both events coincided with major rises in seawater temperatures probably as a result of increased co2 levels and enhanced greenhouse conditions co2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems as evidenced by synchronous drops of platform derived carbonate accumulation and drastic reductions in size 3 m of the main pelagic carbonate producer schizosphaerella we suggest that the early toarcian paleoenvironmental crisis occurred in two distinct episodes that were most likely related to two successive phases of intense volcanic degassing in the karoo ferrar province

potential vorticity dynamics of coastal outflows abstracta simple quasigeostrophic model is used to examine the outflow from a river estuary or strait into a coastal ocean as shown by johnson et al these quasigeostrophic outflows are accurately described by analytical long wave solutions this paper first uses these solutions and contour dynamics simulations to discuss the behavior of coastal outflows second it extends the model and the long wave theory to consider the effects of ambient currents tides winds or a variable source flux third consideration of the momentum flux at the source is used to understand the turning of the current showing that steady solutions conserve momentum hence resolving the momentum imbalance paradox of pichevin and nof finally a new numerical scheme to compute steady outflow boundaries is developed the model focuses on the key dynamics driven by the source velocity and the generation of vorticity as the buoyant fluid adjusts the simplicity of the model and insight given by the long wave solutions enables

climato environmental controls on clay mineralogy of the hettangian bajocian successions of the mecsek mountains hungary an evidence for extreme continental weathering during the early toarcian oceanic anoxic event abstract clay mineralogy has been successfully used in palaeoclimatic interpretation of jurassic rocks in the mecsek zone hungary the clay mineral assemblages of the hettangian sinemurian fluvial and shallow marine coal bearing siliciclastic rocks gresten facies mecsek coal and vasas marl formations comprise predominantly illite smectite i s mixed layer minerals illite ill and kaolinite kao with the presence of berthierine and or chlorite these clay mineral suites suggest a humid subtropical climate with short term climate changes of high and low rainfall and a high supply of terrigenous clastics to the basin in the pliensbachian part of the sequence studied which is composed of predominantly hemipelagic mudstones allgau facies with intercalations of redeposited sandstone and limestone bodies the hosszuheteny calcareous marl mecseknadasd sandstone and kecskehat limestone formations are predominantly made up of illite and very little kaolinite and i s mixed layer minerals kao ill 1 suggesting a humid climate and intense continental weathering possibly related to the oceanic anoxic event in contrast rocks of the bajocian komlo calcareous marl formation contain high proportions of i s mixed layer mineral and illite with sparse occurrence of kaolinite kao ill 0 or kao ill

global characteristics of porosity and density stratification within the lunar crust from grail gravity and lunar orbiter laser altimeter topography data the gravity recovery and interior laboratory grail mission is providing unprecedentedly high resolution gravity data the gravity signal in relation to topography decreases from 100 km to 30 km wavelength equivalent to a uniform crustal density of 2450 kg m3 that is 100 kg m3 smaller than the density required at 100 km to explain such frequency dependent behavior we introduce rock compaction models under lithostatic pressure that yield radially stratified porosity and thus density and examine the depth extent of porosity our modeling and analysis support the assertion that the crustal density must vary from surface to deep crust by up to 500 kg m3 we found that the surface density of megaregolith is around 2400 kg m3 with an initial porosity of 10 20 and this porosity is eliminated at 10 20 km depth due to lithostatic overburden pressure our stratified density models provide improved fits to both grail primary and extended mission data

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

middle jurassic coccolith fluxes a novel approach by automated quantification coccolithophores major pelagic carbonate producers underwent important changes during the latest aalenian early bajocian ca 170 ma middle jurassic specifically a new genus called watznaueria diversified and started dominating the coccolith assemblages while this change in the coccolith assemblages is already known the impact on coccolith absolute abundances and fluxes is still misunderstood here we tested for the first time on mesozoic deposits an automated counting method using the syraco system and then compared these results with a classic counting method two neural networks were created based on the shape birefringence and size of coccoliths the first of which contained only one class and the second of which was composed of six classes based on the morphological criteria used for the neural networks coccoliths were not identified at the species level we quantified coccolith absolute abundances and estimated fluxes for the latest aalenian early bajocian in two well dated and correlated sections cabo mondego in portugal and chaudon norante in france there is a strong linear correlation between classic and automatic counting r 0 8 supporting the latter as a reliable method for coccolith absolute abundance and flux quantification in spite of under or over estimation by automatic counting with respect to classic counting the absolute abundance stratigraphic trends are remarkably similar under or over estimation may be reduced by further technical improvements such as automatic focus at cabo mondego coccolith fluxes increased from 0 2 109 coccoliths m2 yr in the latest aalenian to 700 109 coccoliths m2 yr in the middle of the laeviuscula ammonite zone early bajocian remaining high for the rest of the early bajocian at chaudon norante a similar trend was observed this coccolith flux increase is therefore considered to be a supra regional event matching an important 13cbulk carbonate positive excursion the carbon isotopic positive excursion along with the onset of radiolarian sedimentation and coccolith fluxes is related to a gradual increase in the fertility of the oceans during the early bajocian and is likely associated with warmer and more humid climates and associated enhanced continental weathering

carbon isotope stratigraphy and pelagic biofacies of the middle upper jurassic transition in the tethys central atlantic connection abstract a bulk carbon isotope stratigraphy based on high resolution sampling of five stratigraphic ammonite dated sections from pelagic swells of the subbetic basin external zones of the betic cordillera southern spain is presented the studied sections are characterized by callovian oxfordian stratigraphic successions located in the south iberian palaeomargin a key area connecting the central atlantic to the tethys oceans the rocks are mainly nodular limestones with common extreme condensation rosso ammonitico facies discontinuities with hiatuses of variable duration submarine hardgrounds fe mn ooids limonite crusts and neptunian dykes are observed around the callovian oxfordian boundary the stratigraphic record although very time averaged allows for a consistent and accurate ammonite chronostratigraphy the carbon isotopes of marine carbonates show a marked trend towards high 13c values from lower oxfordian to the middle oxfordian 4 3 near the plicatilis transversarium boundary the isotopic values stand between 2 7 and 3 0 at the upper oxfordian bifurcatus and hypselum zones and lowermost kimmeridgian bimammatum zone afterward 13c values decrease and reach a relative minimum 2 3 2 5 in the lower kimmeridgian bimammatum planula boundary finally isotopic values increase again 2 6 2 7 in the lower kimmeridgian mid part of the planula zone comparison of carbon isotope stratigraphy between subbetic and other tethyan areas shows similar trends the replacement of thin shelled bivalves by planktonic foraminifers and radiolarians that took place in the callovian oxfordian boundary can be associated to the widening of the trans pangaean seaway this in turn triggered the global warming which increased nutrients concentration in upper water column due to intensified nutrient input by river plumes these phenomena are concomitant with the major oxfordian 13c positive excursion and with a transgressive cycle

biostratigraphy of jurassic and triassic successions in the balazuc 1 borehole gpf programme stratigraphic setting inferred from dinoflagellate cysts pollen spores and calcareous nannofossils abstract biostratigraphic studies palynology dinoflagellate cysts spores pollen and calcareous nan nofossils of core from the borehole balazuc 1 bal allowed the various formations intersected from the lower kimmeridgian upper oxfordian to the toarcian to be dated within the studied interval in balazuc 1 borehole 34 1652 m only ditch cuttings samples were available through the upper and middle jurassic section 34 554 m whereas conventional cores were studied from the lowerjurassic and triassic sections 556 1652 m the beds were dated on dinoflagellate cysts and calcareous nannofossils for the lower kimmeridgian 34 m to lower bajocian aalenian 554 m a hiatus was identified between the lower oxfordian and the upper callovian the upper levels of the liassic contain only a poor microflora providing a toarcian aalenian dating the rhaetian hettangian boundary is characterized at 1347 50 m and the triassic was identified in the gres du roubreau anisian ladinian and in the argilites sulfatees superieures anhydritiques carnian the identification of major sedimentary cycles in the borehole razin et al 1996 mar petrol geol 13 625 652 has enabled correlations between variations in sea level and the estimated abundance of both dinoflagellate cysts in the middle jurassic and organic matter in the upper jurassic the distribution of calcareous nannofossils in the balazuc 1 borehole was compared with that of sections in the ardeche region and has enabled the establishment of bioevents in particular for the mid oxfordian and upper bathonian periods

tides of the northwestern ross sea and their impact on dense outflows of antarctic bottom water abstract moored and depth profile measurements of hydrography and currents during the 2003 2005 antarctic slope anslope program on the shelf slope region near drygalski trough sill in the northwest ross sea have revealed an energetic benthic outflow of cold dense antarctic bottom water aabw produced near the shelf break this outflow couples dense water production processes on the continental shelf to ventilation of the global deep ocean we use time series of bottom pressure and currents on the anslope moorings and a high resolution three dimensional primitive equation numerical model to explore the hypothesis that the tidal currents near the shelf break have a significant impact on outflow volume transport and hydrographic properties tidal currents exceed 1 m s 1 at spring tide over the outer shelf and upper slope tidal advection at spring tide carries water parcels 20 km across slope during a half tidal cycle sufficient to advect water from northern drygalski trough across the sill to the shelf break or similarly from the shelf break 500 m water depth down to the 1600 m isobath a tidally rectified lagrangian mean flow of order 0 05 0 1 m s 1 over the outer shelf and upper slope accompanies the spring tide thickness and water mass properties of the benthic layer over the sill and upper slope exhibit pronounced tidal cycles due to advection of hydrographic gradients and to energetic mixing that can extend more than halfway up from the seabed to the ocean surface maximum parameterized diapycnal diffusivity in the benthic layer at spring tides approaches 1 m 2 s 1 the addition of tides has a profound effect on time averaged outflows of aabw primarily through an increase in benthic layer thickness during spring tide downslope volume fluxes of aabw over the slope averaged over a tidal cycle are 2 5 times larger at spring tide than at neap indicating a need to include the effect of tides in large scale ocean models attempting to represent shelf water contributions to the global ocean circulation

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

variability and mixing of the filchner overflow plume on the continental slope weddell sea abstracta large fraction of antarctic bottom water is produced in the weddell sea through mixing between the cold and dense shelf water masses and the warm and saline off shelf water we present o

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

deciphering processes controlling mid jurassic coccolith turnover the middle jurassic is characterized by major changes within the fossil coccolithophorid community with a transition from lotharingius dominated to watznaueria dominated assemblages concomitant with a significant increase in the pelagic carbonate production the mechanisms that triggered this overturn remain poorly understood here we present a compilation new and previously published data of lotharingius and watznaueria abundances through the early middle jurassic transition alongside this trends in newly acquired and literature derived carbon and oxygen isotope data were used to represent paleoceanographic indicators such as nutrient and temperature changes the nannofossil data show a rapid around 1 5 myr turnover around the aalenian bajocian transition across the aalenian bajocian boundary assemblages dominated by lotharingius spp give way to assemblages dominated by watznaueria spp coinciding with a peak in a particular morphological group of watznaueria species with a cross in the central area the proliferation of this morphogroup occurred during a time of oceanic opening and rearrangement of ocean circulation this led on to the evolution of pioneering coccolithophorid taxa but also to extinctions in several marine groups in the early bajocian the proliferation of two other morphogroups watznaueria without a central area structure and watznaueria with a bar corresponds to the major diversification of watznaueria and the beginning of its meso zoic dominance the watznaueria diversification and dominance are associated with radiation in other marine groups and these biotic changes occurred during a time of putative enhanced oceanic fertility and relatively low temperatures this study suggests that restructuring of fossil coccolithophorid communities may be favored during short turnover intervals related to major paleoceanographic change

influence of a variable thermal conductivity on the thermochemical evolution of mars 1 the influences of variations in thermal conductivity due to composition temperature and pressure in mantle and crust on the thermochemical evolution of mars have been examined with parameterized convection models we use a temperature and pressure dependent thermal conductivity in the mantle and column averaged values between 1 5 and 4 wm 1k 1 for the crust with 2 wm 1k 1 as the representative value for a basaltic crust the major characteristic of the models is a slower cooling of the upper mantle with a long existing global partial melt zone and a stronger crustal production late in the evolution compared to earlier models which assume a constant thermal conductivity of 4 wm 1k 1 to explain the observed crustal thickness and the early crustal formation on mars the formation of an enriched primordial crust is required recent volcanism can be explained by lateral temperature variations that are caused by thickness variations of the low conducting crust these melt zones which occur underneath thicker than average crust may be the source region for the observed longstanding volcanism in tharsis and elysium instead of plumes rising from the core mantle boundary the evolution of the elastic lithosphere is characterized by a transition at which the elastic strength is first provided by the crust and later also by the upper mantle this finding may explain the estimated elastic lithosphere thickness of less than 16 km in the noachian and more than 100 km in the hesperian and amazonian

carbon isotope stratigraphy and ammonite faunal turnover for the middle jurassic in the southern iberian palaeomargin variations in the stable carbon isotope ratio of marine and continental sediments can reflect changes in sink and flux modifications of the palaeocarbon cycle here we report carbon isotope compositions of middle jurassic marine carbonates from the betic cordillera southern spain which represents an ideal region to link the stable carbon isotope curves directly to ammonite zones and subzones and thereby for the first time achieve an accurate chronostratigraphic calibration the five sections studied represent basin and high swell deposits of the southern iberian palaeomargin we find a similar 13 c of carbonates between different oceanic areas suggesting a homogeneous carbon isotope oceanic reservoir through the middle jurassic the aalenian bajocian transition is a critical period in ammonite evolution hence the early jurassic fauna are replaced by new ammonite families which become dominant throughout the middle and late jurassic for this reason we compared the 13 c values of carbonates with ammonite diversity and extinction rates at different taxonomical levels in order to explore the possible relationship between the carbon cycle and ammonite evolution the carbon isotope values of carbonates are not exactly linearly correlated with the extinction rate and ammonite diversity but the main faunal turnovers follow minimum 13 c values where extinct taxa are replaced by new ones likewise radiation episodes are associated with increasing 13 c values and with transgressive sea level rise all these data support the idea that perturbations in the global carbon cycle reflect rapid palaeoenvironmental changes we made detailed analyses of these faunal turnovers using them as a proxy to identify major palaeoenvironmental crises in their ecosystems forced by modification in the carbon cycle

evidence for a low bulk crustal density for mars from gravity and topography knowledge of the average density of the crust of a planet is important in determining its interior structure the combination of high resolution gravity and topography data has yielded a low density for the moon s crust yet for other terrestrial planets the resolution of the gravity field models has hampered reasonable estimates by using well chosen constraints derived from topography during gravity field model determination using satellite tracking data we show that we can robustly and independently determine the average bulk crustal density directly from the tracking data using the admittance between topography and imperfect gravity we find a low average bulk crustal density for mars 2582 209 kg m 3 this bulk crustal density is lower than that assumed until now densities for volcanic complexes are higher consistent with earlier estimates implying large lateral variations in crustal density in addition we find indications that the crustal density increases with depth

thermal evolution of tethyan surface waters during the middle late jurassic evidence from δ18o values of marine fish teeth 1 oxygen isotope compositions of phosphate from vertebrate tooth enamel were measured to determine the evolution of tropical sea surface 0 owing to limited growth of continental ice during the early middle oxfordian the resulting sea level fall is estimated to be at least 50 m and is compatible with a global regression stage the middle oxfordian thermal minimum is followed by a new warming stage of 3 4 c from the middle to the late oxfordian

the smooth brachiopods of the mediterranean jurassic refugees or invaders the jurassic brachiopod fauna of the alpine mediterranean region is dominated by smooth rhynchonellids and spiriferinids and sulcate or perforate terebratulids in contrast to the typical coarsely ribbed brachiopods of the contemporaneous european and african epicontinental areas the best studied example of the mediterranean brachiopod province is the pliensbachian fauna of the bakony mountains hungary there the five most abundant genera are all smooth linguithyris securithyris apringia bakonyithyris pisirhynchia these smooth genera represent different morphological types sulcate axiniform uniplicate phylogenetically related forms are known from several evolutionary lineages of discontinuous record ranging from the triassic to the recent the triassic jurassic and the neogene recent parts of these evolutionary lineages are represented by several genera while in the late cretaceous paleogene interval they seemingly disappear at least they have no record the recent relatives of the above pliensbachian genera live mostly in the deep sea three are shallow bathyal 200 400 m three deep bathyal 800 1200 m and three abyssal 2000 4500 m the abyssal genera occur mainly in the east pacific the geographical distribution of the bathyal genera shows peculiar features they are more or less confined to the western sides of the great ocean basins west pacific west indian ocean caribbean region and they are thalassobathyal i e they are living on submarine plateaus seamounts or island aprons and not on the continental slopes this pattern extrapolated to the past shows good analogy with the jurassic palaeogeographical model developed for the western part of the tethys ocean it is hypothesized that smooth mainly sulcate articulate brachiopods flourished in the bathyal or even abyssal zones during the palaeozoic they were not refugees but formed well adapted communities this stable conservative fauna may have survived the crises manifested in the shelf seas and in cases of appropriate palaeogeographical situations may have implanted its descendants to the shallow bathyal or even sublittoral regions of the western margins of the ocean basins the mediterranean microcontinent system at the western part of the jurassic tethys might have been such an invaded region correlation between plate tectonic changes of ocean continent configurations the presence of ocean basins closed on the west and the occurrence of smooth articulate brachiopod groups in shallow bathyal to sublittoral settings collectively suggest that the deep water forms invaded the shallow environments of the western tethys in early mesozoic times and the w pacific and w indian oceans in the neogene they stayed in the deep sea reservoir when a circum equatorial ocean existed in the late mesozoic

carbon cycle perturbation in the middle jurassic and accompanying changes in the terrestrial paleoenvironment abstract carbon isotope analyses of fossil wood from the middle jurassic ravenscar group yorkshire ne england reveal a significant excursion toward light isotopic values 13c change of 3 to 4 at about the aalenian bajocian boundary 174 ma a positive carbon isotopic excursion is also shown for the middle bajocian 170 ma but is less clearly defined these isotopic patterns are very similar to the few published marine carbonate records available for this time in particular one based on belemnites from the hebrides basin nw scotland and others from pelagic limestones in italy the similarity of the terrestrial and marine isotope curves is an indication that the observed isotopic signal is a global phenomenon through parts of the ravenscar group the scarborough formation supplementary data from bulk organic carbon and palynofacies analysis confirm that isotopic curves based on bulk analyses may be strongly influenced by the balance of terrestrial versus marine organic matter present in th

the antarctic slope current in a changing climate the antarctic slope current asc is a coherent circulation feature that rings the antarctic continental shelf and regulates the flow of water towards the antarctic coastline the structure and variability of the asc influences key processes near the antarctic coastline that have global implications such as the melting of antarctic ice shelves and water mass formation that determines the strength of the global overturning circulation recent theoretical modeling and observational advances have revealed new dynamical properties of the asc making it timely to review earlier reviews of the asc focused largely on local classifications of water properties of the asc s primary front here we instead provide a classification of the current s frontal structure based on the dynamical mechanisms that govern both the along slope and cross slope circulation these two modes of circulation are strongly coupled similar to the antarctic circumpolar current highly variable motions such as dense overflows tides and eddies are shown to be critical components of cross slope and cross shelf exchange but understanding of how the distribution and intensity of these processes will evolve in a changing climate remains poor due to observational and modeling limitations results linking the asc to larger modes of climate variability such as el nino show that the asc is an integral part of global climate an improved dynamical understanding of the asc is still needed to accurately model and predict future antarctic sea ice extent the stability of the antarctic ice sheets and the southern ocean s contribution to the global carbon cycle

western tethys early and middle jurassic calcareous nannofossil biostratigraphy an exhaustive biostratigraphic study based on the calcareous nannofossil content from lower and middle jurassic lusitanian basin sections in portugal is here presented located at the strategic intersection of important jurassic water masses during a period of drastic environmental changes the lusitanian basin conveyed mixed phytoplanktonic communities in its surface waters approximately 800 m of exceptionally continuous lower and middle jurassic series bearing detailed ammonite biostratigraphy and two global stratotype section and point are studied vertical and lateral ubiquity of calcareous nannofossils in marine sediments and rapid evolutionary rate and radiation make this fossil group a remarkable biostratigraphic tool nearly 100 bioevents are acknowledged in 24 myr time span this work refers to bridging 11 nannofossil zones and 29 subzones a thorough revision of the existing literature referring to early and middle jurassic calcareous nannofossil biostratigraphy is presented and causes and implications for zonal marker discrepancies discussed under a palaeoceanographic and jurassic nannofossil evolution angle in order to create a solid biostratigraphic frame and to compare it with c and o stable isotopic trends brachiopod calcite shells were analysed for geochemistry this work yields for the first time a very detailed and inclusive biostratigraphic scheme for the early and middle jurassic epochs

the bajocian middle jurassic a key interval in the early mesozoic phytoplankton radiation abstract dinoflagellates and coccolithophores are two of the most important groups of phytoplankton in the modern oceans these groups originated in the triassic and radiated through the early mesozoic rising to ecological prominence within this long term radiation important short term intervals of evolutionary and ecological change can be recognised the bajocian middle jurassic 170 168 ma was characterised by an important ecological transition within the coccolithophores and the radiation of one of the principal families of cyst forming dinoflagellates the gonyaulacaceae during the early bajocian the coccolith genus watznaueria diversified and expanded ecologically to dominate coccolith floras a situation which continued for the remainder of the mesozoic this pattern was paralleled within dinoflagellate cyst floras by the ecological dominance of the genus dissiliodinium in the mid palaeolatitudes these phenomena appear to be linked to a positive carbon isotope shift and an interval of enhanced productivity driven by a shift to a more humid climate enhanced continental weathering and nutrient flux or by changes in ocean circulation and upwelling the latest early bajocian to earliest bathonian was then characterised by the rapid increase in diversity of dinoflagellate cysts within the family gonyaulacaceae through this interval the gonyaulacaceae transitioned from being a relatively minor component of dinoflagellate cyst floras to becoming one of the prominent groups of cyst forming dinoflagellates which has persisted to the holocene in europe the pattern of this radiation was strongly influenced by sea level with the increase in gonyaulacacean diversity reflecting a major second order transgression on a finer scale the main pulses of first appearances correlate with third order transgressive episodes a rise in sea level coupled with changes in the tectonic configuration of ocean gateways appears to have controlled the pattern of plankton diversification in europe these palaeoceanographic changes may have enhanced water mass transfer between europe the northwest tethys ocean and the hispanic corridor which promoted the floral interchange of dinoflagellates whilst sea level rise and associated large scale palaeoenvironmental shifts appear to have controlled the pattern of dinoflagellate cyst appearances in several regions outside europe there is no direct correlation between dinoflagellate cyst diversity and sea level rise on a global scale although the bajocian was transgressive in several regions widespread flooded continental area was also present throughout the preceding aalenian an interval of low gonyaulacacean diversity moreover although the middle jurassic was an interval of major climatic cooling there was a 5 myr gap between the onset of cooling and the radiation of gonyaulacaceans during the bajocian the bajocian was however marked by a major evolutionary radiation in the pelagic realm including ammonites giant suspension feeding fishes and planktonic foraminifera these phenomena may indicate an underlying ecological driver to the radiation of dinoflagellates during the bajocian evolutionary explosion which could represent an extension of the mesozoic marine revolution

normal modes of the world ocean part ii description of modes in the period range 8 to 80 hours abstract we have calculated normal modes with period between 8 and 80 h for a domain consisting of the arctic atlantic indian and pacific oceans in this period range the numerical model has 56 modes of which 13 are topographic vorticity waves all slower than 30 h the trapping sites for these modes are the siberian shelf the icelandic plateau the grand banks the falkland plateau and patagonian shelf the kerguelen plateau the new zealand and fiji plateaus and the hawaiian ridge predominantly planetary vorticity waves do not appear in the model at periods less than 80 h the 41 modes found between 30 and 8 h include basin modes in the north atlantic indian and equatorial pacific quarter wave resonances in the arabian sea bay of bengal and gulf of guinea and kelvin waves on the antarctic coast the pacific north american coast and the new zealand coast several vorticity and gravity modes exhibit an eastward circumglobal flow of energy that is confined to equatorial latitudes except where defl

density and lithospheric thickness of the tharsis province from mex mars and mro gravity data 1 radio science tracking of mars express mars experiment and mars reconnaissance orbiter produced high resolution martian gravity data applying localized spectral analysis on the new gravity data sets we study the surface density and lithospheric elastic thickness in the tharsis province the gravity signal is predicted with geophysical models either including bottom loading top bottom model or taking into account the loading history top top model volcanic shields are mainly composed of high density lava but their construction could have begun with lower density lava with the exception of ascraeus mons which has a top of lower density buoyant bottom loading may have been present in the form of a mantle plume under olympus mons the elastic thickness was much larger at olympus mons than at other volcanoes suggesting large spatial variations of heat flux during the hesperian alternatively small elastic thicknesses could be artifacts reflecting the presence of very localized high density crustal intrusions beneath the volcanoes thaumasia highlands were probably supported by a mantle plume at the time of formation in valles marineris top bottom models predict low densities and large elastic thicknesses in conflict with the basaltic rock composition and hesperian age of the valley dense mafic dikes underlie the western part of the valley the top top model serves to test another scenario in which the trough is formed with sedimentary infilling removed much later by erosion the elastic thickness increasing in between at the large volcanoes the relation between gravity and topography is anisotropic probably because of density variations

mesoscale variability in denmark strait the pv outflow hypothesis abstract the outflow through denmark strait shows remarkable mesoscale variability characterized by the continuous formation of intense mesoscale cyclones just south of the sill these cyclones have a diameter of about 30 km and clear signatures at the sea surface and in currents measured near the bottom they have a remnant of arctic intermediate water aiw in their core the authors hypothesis is that these cyclones are formed by stretching of the high potential vorticity pv water column that outflows through denmark strait the light upper layer of the outflow the east greenland current remains on the surface in the irminger sea while the dense overflow water descends the east greenland continental slope the midlevel waters mostly aiw could thus be stretched by more than 100 which would induce very strong cyclonic relative vorticity the main test of this new hypothesis is by way of numerical experiments carried out with an isopycnal coordinate ocean model configured to have a marginal sea

black shales and carbon isotopes in pelagic sediments from the tethyan lower jurassic detailed sampling and analysis of jurassic pelagic limestones and marls from italy hungary and switzerland have enabled construction of an isotope stratigraphy across the pliensbachian toarcian boundary with resolution to the zonal level the oxygen isotope record is unremarkable the carbon isotopes however show two positive excursions one relatively minor during the pliensbachian margaritatus zone subnodosus subzone the other more major during the toarcian early falciferum zone where a maximum 13c value of 4 52 pdb is attained these intervals are known to be favoured periods of organic rich sedimentation in diverse parts of the globe and the isotopic excursions are interpreted as a response to abnormally high rates of storage of organic carbon in the sedimentary record a comparable phenomenon has been documented from the cenomanian turonian boundary in the cretaceous where it has been referred to the influence of an oceanic anoxic event some italian sections spanning this lower jurassic interval contain organic rich shales in the falciferum zone the isotopic signatures from their included locally manganiferous carbonate betray a considerable diagenetic overprint and they cannot therefore be incorporated in a composite isotopic curve carbon isotopes from the organic carbon itself are extremely negative falling to 33 pdb and in one section examined in detail correlate with the calcium carbonate content of the shales they may reflect a partial change to a non calcified planktonic biota during deposition of this lime poor interval possibly responding to upwelling and increased fertility of near surface waters the onset of upwelling may have been as early as spinatum tenuicostatum zone time that is at the pliensbachian toarcian boundary

microfacies biofacies and depositional environments of the bajocian bathonian middle dhruma carbonates central saudi arabia three cliff forming outcrops of the dhruma formation representing the carbonate platform in the hafirat nisha district west of riyadh saudi arabia were investigated to identify and understand the microfacies variability in a carbonate ramp setting an integrated approach including detailed field investigations petrographic biofacies and micropaleontological analyses was used to construct a model of the depositional environments of the investigated outcrop sections the depositional model indicates that the identified lithofacies were predominantly deposited in outer ramp middle ramp inner ramp and lagoonal settings the presence of the benthic foraminifera redmondoides lugeoni and nautiloculina oolithica and the trace fossil thalassinoides indicates deposition in shallow water environments and the prevalence of warm climatic conditions during the middle jurassic the occurrences of calcareous and agglutinated benthic foraminiferal species pseudomarssonella maxima siphovalvulina variabilis timidonella sarda n oolithica r lugeoni praekurnubia crusei paleopfenderina salernitana haurania deserta siphovalvulina spp lenticulina sp textulariopsis sp and amijella amiji imply that our studied sections are situated within the dm 2 to dm 5 biozones bajocian to early bathonian this is also supported by the calcareous nannofossil assemblages that show a bajocian to early bathonian age the depositional sequences indicate a shift in the depositional environment from low energy lagoonal with intermittent shoal complexes in the d2 and d3 units to predominantly shoal complex and open marine settings in the d4 unit suggesting a seaward shift towards the top of the d4 unit the interpreted depositional settings are similar to those previously documented in the subsurface equivalent faridah reservoir this indicates that the investigated d2 d4 units outcrops are excellent analogues of the subsurface reservoir

western ross sea continental slope gravity currents antarctic bottom water of the world ocean is derived from dense shelf water that is carried downslope by gravity currents at specific sites along the antarctic margins data gathered by the anslope and clima programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the ross sea when high salinity shelf water exits the shelf through drygalski trough joides trough immediately to the east offers an additional escape route for less saline shelf water while the glomar challenger trough still farther east is a major pathway for export of the once supercooled low salinity ice shelf water that forms under the ross ice shelf the drygalski trough gravity currents increase in thickness from 100 to 400 m on proceeding downslope from 600 m the shelf break to 1200 m upper slope sea floor depth while turning sharply to the west in response to the coriolis force during their descent the mean current pathway trends 35 downslope from isobaths benthic layer current and thickness are correlated with the bottom water salinity which exerts the primary control over the benthic layer density a 1 year time series of bottom water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of shelf water export through drygalski trough these cold 34 75 pulses correlate with strong downslope bottom flow extreme examples occurred during austral summer fall 2003 comprising concentrated high salinity shelf water 1 9 c 34 79 and approaching 1 5 m s 1 at descent angles as large as 60 relative to the isobaths such events were most common during november may consistent with a northward shift in position of the dense shelf water during austral summer the coldest saltiest bottom water was measured from mid april to mid may 2003 the summer fall export of high salinity shelf water observed in 2004 was less than that seen in 2003 this difference if real may reflect the influence of the large iceberg c 19 over drygalski trough until its departure in mid may 2003 when there was a marked decrease in the coldest saltiest gravity current adjacent to drygalski trough northward transport of cold saline recently ventilated antarctic bottom water observed in march 2004 off cape adare was 1 7 sv including 0 4 sv of high salinity shelf water

paleotemperature variations of early jurassic seawater recorded in geochemical trends of belemnites from the basque cantabrian basin northern spain abstract here we present new o isotope mg ca and sr ca data of early jurassic belemnites from the basque cantabrian basin of northern spain a succession deposited in a periodically anoxic restricted hemipelagic basin nearly 200 pliensbachian lower toarcian belemnites were collected and examined using optical cathodoluminescence and chemical techniques to constrain the effects of potential diagenetic alteration after a precise diagenetic screening of samples 176 belemnites were selected to provide records of changes in seawater geochemistry and temperature the records show a fairly good correlation of 18o with mg ca ratios r 0 65 and a weak correlation of 18o with sr ca ratios r 0 34 the oxygen isotope data if interpreted in terms of paleotemperature have revealed a period of relatively uniform and warm seawater temperatures during the early pliensbachian followed by a sharp temperature drop during the late pliensbachian earliest toarcian the onset of this cooler period occurred within the protogrammoceras celebratum subzone and the coolest seawater temperatures were reached at the end pliensbachian pleuroceras spinatum zone this was followed by a rapid seawater warming during the harpoceras serpentinus zone of the early toarcian in addition the data set provides new information regarding paleoceanographic conditions for anoxic events in a critical region of connection between the boreal and tethys realms it is the background to relatively high 18o values that prevailed during the anoxic episodes concerning the impact of the early toarcian anoxic event in northern spain the detected 18o and mg ca excursions reached their minimum and maximum respectively during the lower h serpentinus zone while the anoxic black shale interval developed earlier during the upper dactylioceras tenuicostatum lowermost h serpentinus zones

δ18o and δ13c values of modern brachiopod shells abstract researchers have not rigorously tested the hypothesis that calcite from modern brachiopod shells is precipitated in oxygen isotope equilibrium with ambient seawater isotopic variability at the intraspecimen and intertaxon levels has not been examined without such data for modern brachiopods similar data from ancient brachiopods cannot be accurately interpreted in this study a survey is made of 18 o and 13 c values of terebratulid rhynchonellid thecideidine and craniacean brachiopods from antarctica the bay of fundy curacao japan new zealand norway puget sound palau sicily and south africa this suite of samples provides a wide range of taxonomic levels temperatures salinities and depositional environments for evaluating the degree of isotopic equilibrium attained during precipitation of brachiopod calcite new data indicate that modem brachiopod calcite is not always precipitated in oxygen and carbon isotope equilibrium with ambient seawater calcite from the primary layer and specialized shell structures hinge brachidium foramen interarea muscle scars are depleted in both 18 o and 13 c a characteristic of biological fractionation or vital effects often found in other calcerous marine organisms our findings suggest that these portions of the brachiopod shell should be avoided during sampling of ancient brachiopods secondary layer calcite the material most often analyzed in ancient brachiopods has higher 18 o and 13 c values which approach and sometimes correspond with predicted equilibrium values therefore secondary layer calcite is the most suitable portion of the brachiopod shell for use as an ancient seawater proxy although near equilibrium precipitation in secondary layer calcite is encouraging to those studying the isotopic composition of ancient oceans these data come with caveats large intraspecimen variability in the 18 o values of secondary layer calcite 1 in some samples limits the use of brachiopods as precise indicators of the 18 o value or temperature of ancient seawater the 18 o and 13 c values of secondary layer calcite deviate from predicted equilibrium values toward the lower values of the primary layer and specialized shell structures indicating a measurable vital effect in most cases measured 18 o values are lower than the calculated equilibrium values dictated by seasonal variations in the 18 o value and temperature of seawater ontogenetic variations in the 13 c values of secondary layer calcite have also been measured and must be assessed when interpreting ancient data modern brachiopods occur in a wide range of seawater salinities and temperatures therefore the relation between salinity and the 18 o value of seawater must be known to correctly calculate the temperature of calcite precipitation from secondary layer 18 o values errors of up to 15 c are found if ambient seawater is assumed to have a constant 18 o value e g 0 smow and the 18 o values of secondary layer calcite are used to calculate temperature coupled with vital effects and intraspecimen variability these errors can obscure the resolution of secular variations in the rock record

strontium isotope variations in middle jurassic late bajocian callovian seawater implications for earth s tectonic activity and marine environments abstract strontium isotope ratios of well preserved belemnite rostra and ammonite shells are presented from stratigraphically well dated upper bajocian callovian sediments of the polish jura chain in central poland nekto benthic belemnites show a narrow trend of changes of 87 sr 86 sr ratio that are interpreted to record secular variations in the strontium isotope composition of seawater a new fit of the seawater strontium isotope curve for the late bajocian callovian is presented based on current and literature data the data show a gradual decrease of seawater 87 sr 86 sr ratio throughout the late bajocian earliest middle callovian lowest 87 sr 86 sr ratios 0 706850 and the flat minimum of the curve were reached in the latest middle and the late callovian the middle jurassic decrease in seawater 87 sr 86 sr ratio is interpreted to have been a result of the increased volcanic activity of the seafloor studied nektonic ammonites are considered to have lived in surface or shallow near coastal waters of the polish jura chain basin and been affected by the freshwater influx a slight enrichment of ammonite shells in 87 sr isotope is linked to a change in strontium isotope composition of the surface or near coastal waters due to the riverine strontium input

a model study of circumpolar deep water on the west antarctic peninsula and ross sea continental shelves abstract transport of relatively warm nutrient rich circumpolar deep water cdw onto continental shelves around antarctica has important effects on physical and biological processes however the characteristics of the cdw along the shelf break as well as what happens to it once it has been advected onto the continental shelf differ spatially in the present study high resolution 4 5 km regional models of the ross sea and the west antarctic peninsula coastal ocean are used to compare differences in cdw transport the models compared very well with observations from both regions examining the fluxes not only of heat but also of a simulated dye representing cdw shows that in both cases cdw crosses the shelf break in specific locations primarily determined by the bathymetry but eventually floods much of the shelf the frequency of intrusions in marguerite trough was ca 2 3 per month similar to recent mooring observations a significant correlation between the along shelf break wind stress and the cross shelf break dye flux through marguerite trough was observed suggesting that intrusions are at least partially related to short duration wind events the primary difference between the cdw intrusions on the ross and west antarctic peninsula shelves is that there is more vigorous mixing of the cdw with the surface waters in the ross sea especially in the west where high salinity shelf water is created the models show that the cdw moving across the antarctic peninsula continental shelf towards the base of the ice shelves not only is warmer initially and travels a shorter distance than that advected towards the base of the ross ice shelf but it is also subjected to less vertical mixing with surface waters which conserves the heat available to be advected under the ice shelves this difference in vertical mixing also likely leads to differences in the supply of nutrients from the cdw into the upper water column and thus modulates the impacts on surface biogeochemical processes