the krithe problem first test of peypouquet s hypothesis with a redescription of krithe praetexta praetexta crustacea ostracoda the ostracode genus krithe is generally regarded as an index for deeper water but its known depth range is 15 4500 m further uncertainty is caused by anterior vestibule variations in otherwise identical specimens peypouquet 1977 suggested that interior vestibule size in krithe is inversely correlated with the dissolved oxygen content of the ambient seawater this hypothesis if true would enable more precise interpretations of paleodepth by means of fossil krithe assemblages we made a partial test of the hypothesis by examining living krithe praetexta praetexta collected during may 1988 at 45 m depth in the gullmar fjord on the west coast of sweden our paper includes a description of this taxon and notes some associated ecological factors in gullmar fjord we used a quantitative method to describe their vestibules based on linear measures obtained by rapid image digitization a canonical variate analysis of the measures clearly indicates four different groups one for each valve right and left and one for each sex all our specimens belonged to peypouquet s b12 morphotype the actual dissolved oxygen values in gullmar fjord during may were very close to those predicted by peypouquet for the b12 morphotype but values during june were rather less than his prediction possibly the imperfect agreement can be related to variations in food supply and other sources of ostracode shell calcium thus although the test has proved confirmatory as far as it goes we believe that further study at different depths and latitudes is required the elements of the ostracode fauna are illustrated

an integrated geophysical investigation of recent seismicity in the al hoceima region of north morocco abstract data produced by the moroccan national seismological network and marine seismic reflection profiles are used to investigate the most seismically active region in morocco located on the mediterranean coast at the intersection of the rif mountain belt and the submarine alboran ridge this region in the vicinity of the city of al hoceima marks an east west transition in the marine and land deformation styles of the distributed plate boundary between africa and iberia and was the site of an m w 6 0 earthquake on 26 may 1994 the epicenter of the al hoceima earthquake is relocated onshore refining the initial submarine location close to the alboran ridge the spatial distribution of foreshocks and aftershocks shows a ne sw trend that continues partly offshore and is subparallel to the earlier yet still prominent miocene geologic structural trend the predominantly strike slip focal mechanism for the al hoceima event is characteristic of earthquakes in the region marine seismic reflection profiles that intersect the offshore region of seismicity image active high angle faults with possible strike slip components the seismicity trend is not directly related to the submarine alboran ridge or the geomorphologically prominent nekor fault deformation appears to be occurring on a number of subsidiary strike slip faults that together compose a ne sw zone of distributed shear the distributed strike slip and documented normal faulting taking place in the eastern rif mountains although characteristic of the rif region are in contrast to the thrusting style of deformation that occurs farther to the east in the algerian tell atlas this may be related to the reported lateral variations and evolution of the convergent plate boundary in these regions during the neogene and quaternary times

palaeo water depth estimation for a 600 year record from nam co tibet using an ostracod based transfer function a modern training set of ostracods from the large slightly saline lake nam co on the southeastern tibetan plateau is presented in total 44 samples covering the largest part of the lake and water depth from 2 to 93 m were taken there are eight ostracod species in surface sediments of nam co leucocytherella sinensis leucocythere dorsotuberosa fabaeformiscandona gyirongensis candona xizangensis candona candida ilyocypris cf mongolica eucypris gyirongensis and limnocythere inopinata in order of mean dominance a morphological variant of l dorsotuberosa the forma postilirata is an indicator form of deep water below the thermocline the 36 samples comprise a sufficient number of ostracods for analysis covering water depths between 3 7 and 89 3 m two transfer function models based on weighted average binomial regression wa br and weighted average partial least square regression wa pls using the programs excel and c2 were established to estimate past water depths of nam co transfer functions were applied to ostracod data from two short cores from nam co covering approximately the past 600 years model results show a lake level minimum occurring during the little ice age lia between about 1490 and 1760 ad this minimum corresponds to results from previous stable isotope analysis and indicates a lake level which was about 5 m below the present day level the more exact transfer function model wa pls was set up using c2 and revealed a higher correlation index r o f 0 91 and a lower standard error of 6 7 m however the more selective because of using indicator taxa only wa br model using excel r 0 88 standard error 10 6 m seems to represent palaeo water depths better at least for the studied short cores

neogene tectonics in the western mediterranean may have caused the messinian salinity crisis and an associated glacial event the messinian salinity crisis msc was a catastrophic event which led to the deposition of 106 km3 of evaporite in the mediterranean between 6 5 and 5 ma b p stratigraphic investigations have previously suggested that the progressive increase of salinity in the mediterranean leading to the msc may have been caused by tectonic narrowing and closure of seaways between the mediterranean and the atlantic detailed reconstruction of the tectonic history of the arc of gibraltar and adjacent alboran basin independently suggests 1 1 that the early miocene guadalquivir and alboran seaways closed and narrowed respectively near the end of the tortonian 7 ma b p and 2 2 that the tectonic arc of gibraltar progressively emerged above the sea level during the messinian 7 5 ma b p which caused together with a eustatic glacial lowering of the sea level the isolation and subsequent dessication of the mediterranean this is in agreement with a two stage history of the msc previously postulated on the basis of stratigraphical observations 1 1 deep basin deep water and 2 2 deep basin shallow water salt deposition the closure of the seaways between the mediterranean and the atlantic and the associated drop in world wide oceanic surface salinity may even have caused the kapitean optian glacial event about 5 5 ma b p

the palaeolimnology of the aral sea a review abstract formerly the fourth largest inland water body in the world the volume and area of the aral sea have decreased dramatically over the past 30 yr largely as a result of human actions throughout its approximately 2 million year history the fate of this water body has been intimately linked with that of its two main in flowing rivers the amu darya and the syr darya we present a review of the hydrological palaeontological and sedimentological evidence for the evolution of the aral sea based largely on russian literature although the structure of the aral basin can be traced back to the late neogene the sea has only existed in its present form for the past 8 10 ka and the holocene history has been shaped by regional climatic variations the development of the associated drainage system and anthropogenic forces past hydrological changes in the aral basin have led to systematic shifts in the level of the aral sea which are reflected sedimentologically through the deposition of transgressive and regressive sedimentary units and geomorphologically through the development of terraces all the above data are integrated to produced a late quaternary history of this important water body

solar and proxy sensitivity imprints on paleohydrological records for the last millennium in west central europe this paper presents a lake level record established for the last millennium at lake saint point in the french jura mountains a comparison of this lake level record with a solar irradiance record supports the hypothesis of a solar forcing of variations in the hydrological cycle linked to climatic oscillations over the last millennium in west central europe with higher lake levels during the solar minimums of oort around ad 1060 wolf around ad 1320 sporer around ad 1450 maunder around ad 1690 and dalton around ad 1820 further comparisons of the saint point record with the fluctuations of the great aletsch glacier swiss alps and a record of rhone river floods from lake bourget french alps give evidence of possible imprints of proxy sensitivity on reconstructed paleohydrological records in particular the great aletsch record shows an increasing glacier mass from ad 1350 to 1850 suggesting a cumulative effect of the little ice age cooling and or a possible reflection of a millennial scale general cooling until the mid 19th century in the northern hemisphere in contrast the saint point and bourget records show a general trend toward a decrease in lake levels and in flood magnitude anti correlated with generally increasing solar irradiance

an important current reversal influx in the rifian corridor morocco at the tortonian messinian boundary the end of tethys ocean atlantic psychrospheric and temperate mesopelagic faunas found in the lower messinian marls in morocco indicate that a strong eastward flowing bottom current was present in the rifian corridor before the salinity crisis this influx began just before diatomite deposition in the paleo mediterranean continued during a decrease in species diversity in coral reef formation and diminished with the initial stages of brine concentration in the deep water phase of the crisis the influx is most readily studied in a condensed section of marl in the bou regreg valley near rabat the beginning of this siphon event coincides with the tortonian messinian boundary 6 4 ma subchron 6n1 it is identified by 1 a change in the planktonic foraminifera from dominance of warm tropical epipelagic globorotalia menardii with globigerinoides to the temperate mesopelagic gl miotumida plexus with conomiozea 2 the sudden appearance of an upper psychrospheric ostracode fauna with agrenocythere pliocenica and oblitacythereis ruggierii 3 a change in nannoflora and 4 beginning of the 6 3 ma global carbon shift the initial strong influx stage of the siphon lasted at least 0 7 m y decreasing after the middle of chron 5 ca 5 7 to be lost ca 5 3 ma conditions for the siphon formed when the continental climate created a deficit in the water budget of the paleo mediterranean sea the reversal took place when tectonic movement in the foredeeps of the betic rif orogene changed the thresholds of the twin straits the rifian corridor and the iberian portal inflow increased rapidly in the southern corridor to draw in waters from beneath the rising atlantic pycnocline while paleo mediterranean overflow water pmow continued out of the northern iberian portal the invasion of nappes or olistoliths first into the portal and then into the corridor led to the end of the outflow of the pmow terminating the need for the siphon and then to the isolation of the paleo mediterranean

the krithe problem a case history of the distribution of krithe and parakrithe crustacea ostracoda in the south china sea abstract the distribution of 12 species of krithe and 4 species of parakrithe through the depth range of 150 4000 m and 5 depth stratified water masses in the south china sea reveals that there is no correlation between size and shape of the anterior vestibulum and levels of dissolved oxygen nor between the length of specimens and water depth given this evidence from elsewhere it is recommended that the peypouquet hypothesis which argues for these relationships should be re evaluated and not used as a palaeoceanographical tool it is suggested that the relative abundance of krithe as a percentage of the total ostracod fauna may be an important factor in reconstructing palaeodepth in the south china sea despite its somewhat restricted nature and endemically low oxygen levels the krithidae are shown to be the dominant deep sea ostracoda

early cretaceous ostracod biostratigraphy of eastern brazil and western africa an overview petroleum exploration in the offshore basins of eastern brazil and western africa has been aided for the last fifty years by an understanding of the early cretaceous ostracod biostratigraphy of the proto south atlantic this review charts the development of the presently accepted zonation from its early development in the reconcavo tucano basin and recognition as palaeontological evidence for continental drift in the 1960s to its application over the following five decades in the brazilian sergipe alagoas araripe and campos basins and the western african congo gabon and kwanza basins the distribution of ostracod species in the lakes which formed during the early stages of the opening of the atlantic during the early cretaceous was often extensive and this has resulted in effectively south atlantic wide application for many species and certainly for the zonation as a whole indeed petroleum companies continue to exploit the predictability of the ostracods in south atlantic operations due to the fact that they are often able to provide accurate constraints on stratigraphic position for a relatively low cost however the ostracod biozonations of the pre salt section for several eastern brazilian basins such as the reconcavo tucano sergipe alagoas and campos have not been thoroughly revised since the 1980s and the taxonomy of these remains somewhat outdated furthermore ostracod biozonations for many basins on both coasts e g the brazilian espirito santo and the western african namibe basins have never been published an updated and revised taxonomy of the ostracods of the basins of eastern brazil and western africa is presented appendix i as well as a revision of the biozonation on both sides of the modern day atlantic ocean it is hoped that this paper will act as a catalyst for further work in the basins surrounding the modern day south atlantic which hold much interest for petroleum companies and micropalaeontologists alike

reduced early holocene moisture availability in the bayan har mountains northeastern tibetan plateau inferred from a multi proxy lake record abstract a late glacial and holocene lake sediment record from the northeastern tibetan plateau was investigated using ostracod and geochemical analysis after lake koucha was established about 16 cal ka bp oligohaline conditions gradually converted to mesohaline conditions about 10 cal ka bp clearly suggesting that the water body was a closed basin lake from about 10 cal ka bp the salinity of the lake rose continuously until hyperhaline levels were reached about 7 5 cal ka bp this increase in salinity was accompanied by a falling lake level extreme rainfall and flooding events in a generally dry climate hit the shallow saline lake around 8 5 cal ka bp causing a unique thin gravel containing layer within the continuous fine grained lake sediments the age control of our record does not allow us to correlate this event exactly to the widely recorded 8 2 cal ka bp event however the recovered sediments from lake koucha provide strong evidence that climate changes around 8 5 cal ka bp had significant environmental implications in northeastern tibet after about 7 3 cal ka bp the available moisture significantly increased causing a continuous salinity decline until the present day freshwater conditions of a through flow lake were established about 6 5 cal ka bp in lake koucha this major shift from a shallow saline to a deeper freshwater lake was probably accompanied by a fundamental change from a macrophyte dominated to a phytoplankton dominated lake a slight reduction in available moisture in comparison to the periods before and afterward was recorded between 4 3 and 2 0 cal ka bp in phase with numerous records from monsoonal asia the reconstructed overall change in moisture availability from dry conditions before about 7 3 cal ka bp to wetter conditions afterwards contradicts most palaeoclimate records from the tibetan plateau and its surroundings which show that wetter conditions in the early holocene were replaced by drier and probably cooler conditions in the mid and late holocene however in the semi arid region of lake koucha with a mean annual precipitation of about 500 mm the insolation driven strengthened monsoon in the early holocene may have resulted in a temperature rise and higher evaporation rates which outweighed the increase in precipitation and therefore led to significantly lower moisture availability our record provides further evidence for a regionally non uniform response of the available moisture evolution to the overall monsoonal signal in the holocene climate history of central asia

cataclastic flow and semi brittle deformation of anorthosite abstract a series of experiments on dry bushveldt anorthosite an 75 350 m grain size 5 impurities is carried out at 25 700 c 500 1500 mpa pressures and 10 5 s 1 strain rate the strength of the bushveldt anorthosite remains pressure sensitive throughout the applied p t range while weakening occurs with increased temperature at a given pressure a transition from stick slip to stable sliding occurs at 200 300 c and pressures of 1500 mpa reduction in strength at 200 300 c localized cataclastic flow and lack of microscopic evidence of crystal plastic deformation raises the possibility that the transition may be coincident with the propagation of a critical number of randomly distributed thermal cracks uniform ductile flow occurs only at temperatures of 600 and 700 c and 1000 1500 mpa pressures coincident with the development of mechanical twinning patchy and banded undulatory extinction and is likely to be due to semi brittle deformation under these conditions the deformation remains distributed to strains as high as 44

quaternary glacial and deglacial ostracoda in the thermocline of the little bahama bank nw atlantic palaeoceanographic implications abstract we determined faunal and oceanographic changes during the last glacial and deglacial in the providence channel little bahama bank lbb using modern ocean from lbb florida hatteras slope and blake plateau western north atlantic and late quaternary lbb distributions of the benthic ostracode genus krithe from the mid depth 300 1600 m subtropical north atlantic ocean nine species of krithe are limited in their bathymetric distribution by warm bottom water temperatures or a temperature related parameter in the thermocline of the modern atlantic during the last glacial interval in the northwest providence channel of the little bahama bank five species of krithe k aequabilis k dolichodeira k gr minima k reversa and k trinidadensis migrated upslope conversely during the deglaciation most krithe species migrated downslope re occupying their deeper niches these vertical species migrations are attributed to decreased glacial bottom water temperatures and perhaps increased dissolved oxygen during the last glacial and warmer water temperatures during the deglacial based upon thermal values of recent depth ranges of selected species of krithe we estimate that glacial waters cooled about 4 c shallower than 900 m and about 2 c deeper than 900 m and deglacial waters warmed about the same values in shallow and mid depth water masses comparing to modern temperatures the discovery of common halocypris a mesopelagic ostracode in little bahama bank glacial and deglacial sediments also suggests greater oxygenation relative to the late holocene

benthonic ostracods and deep watermasses a qualitative comparison of southwest pacific southern and atlantic oceans abstract the upper depth limits of the dominant cosmopolitan deep water benthonic ostracod taxa present in five localities in the southern ocean kerguelen plateau southeast australian continental slope and southwest pacific chatham rise tasman sea coral sea are compared to investigate the degree to which the position of intermediate and deep watermasses antarctic intermediate water aaiw deep water dw and antarctic bottom water aabw control the vertical faunal succession although none of the taxa studied is restricted to one watermass their upper depth limits appear to be closely related to the position of antarctic intermediate water aaiw taxa showing the most consistent pattern include krithe upper depth limit above aaiw poseidonamicus upper depth limit in lower aaiw but in underlying deep water on the kerguelen plateau and pterygocythere mucronalatum dw but in aabw on the kerguelen plateau bathyal above approximately 1000 m upper depth levels of taxa species diversity species turnover and changes in the proportion of the dominant deep sea taxa krithe and poseidonamicus match closely that of the atlantic ocean dingle and lord 1990 however the upper depth limits of the abyssal taxa poseidonamicus and dutoitella appear to be very different in the cape basin se atlantic and the sw pacific with respect to watermass characteristics for example in the atlantic poseidonamicus has its upper limit within lower north atlantic deep water nadw whereas in the sw pacific it occurs consistently within the aaiw these discrepancies in the upper depth level of abyssal taxa between the pacific and atlantic oceans suggest that different watermasses or other environmental variables control their upper range in different oceanic basins it follows that these differences must be taken into account if deep sea ostracods are to be used as a reliable means to trace modern or reconstruct ancient watermass pathways between ocean basins

seismicity of morocco for the period 1987 1994 a seismic data file of 3 740 earthquakes from january 1987 to december 1994 has been elaborated for morocco and the border regions with 10 main events registering magnitudes from 5 to 5 6 such seismicity is particularly important for morocco as the released seismic energy constitutes a considerable part of the total energy radiated during the 20th century relative seismicity maps confirm the persistence of the major features of the seismicity of morocco an important seismic activity is observed in the alboran region continental crust which absorbs the maximum deformation resulting from the convergence of the african and iberian plates however in the longitude window 3 5 6 w at depths of 25 to 50 km a seismic gap zone seems to take place an explanation of this phenomenon may be provided by the slab breakoff model even if the seismicity of morocco remains moderate heavy damage is observed when the magnitude of earthquakes exceeds 4 5 especially in the case of traditional buildings

paleoecology of limnic ostracodes a review of some major topics abstract the paleoecology of limnic ostracodes is reviewd in the context of the evolution of their environment in order to understand why there is a rich ostracode fossil record we examine data such as the quantitative and qualitative distribution of living ostracode species and ostracode assemblages ways of describing and limitations importance of biological and physico chemical factors for the local accumulation of high numbers of ostracodes and diversified assemblages is emphasized we discuss the limits of extrapolations of information from ecology to paleocology we stress how paleontological knowledge can be applied to neontological studies the possibility of using holocene ostracodes as indicators of morphometric changes of lakes temperature salinity eutrophication and as a criterion of meromictic conditions is demonstrated relationships between ostracodes and the chemical environment and particularly the morphological response of the carapace are considered e g diversity and qualitative composition of assemblages and chemical stability types of carapace mineralization and ornamentation and chemistry of bottom waters these ideas developed from studies on recent material are tested for limnic cenozoic faunas in the mesozoic the main questions arising from the study of nonmarine ostracodes deal with the possible evaluation of paleosalinities in marginal lagoonal environments purbeck wealden and with evaluation of depth and hydrochemical and paleoclimatological regime in truly lacustrine intracratonic basins some peculiarities of paleozoic nonmarine ostracode assemblages are described the paleoecological cause of changes in diversity of several ostracode groups in the carboniferous and permian is emphasized

rise and fall of the paratethys sea during the messinian salinity crisis abstract extremely thick evaporite units were deposited during the so called messinian salinity crisis msc 5 96 5 33 ma in a deep mediterranean basin that was progressively disconnected from the atlantic ocean a crucial but still poorly understood component in messinian evaporite models is the connectivity between mediterranean and paratethys i e the former black sea domain inadequate stratigraphic correlations and insufficient age control for paratethys sediments have so far hampered a thorough understanding of hydrological fluxes and paleoenvironmental changes here we present a new chronology for the eastern paratethys by integrating biostratigraphic and paleomagnetic data from mio pliocene sedimentary successions of romania and russia we show that a major flooding event from the mediterranean surged the paratethys basins at the maeotian pontian boundary 6 04 million years ago this indicates that sea level in both mediterranean and paratethys was high at the beginning of the msc we argue in favor of changes in paratethys mediterranean connectivity to initiate the msc in combination with elusive tectonic processes in the gibraltar arc a subsequent fall of paratethyan water level closely coincides to the mediterranean isolation event corresponding in age to the glacial cycles tg12 14 5 60 5 50 myr in the latest messinian a major climate change towards more humid conditions produced a positive hydrological balance and likely a transgression in the paratethys although our stratigraphic resolution cannot exclude a possible relation to the pliocene flooding of the mediterranean here

the early messinian velona basin siena central italy paleoenvironmental and paleobiogeographical reconstructions abstract a multi disciplinary study of the basal lacustrine succession of the velona basin tuscany central italy provides informations about the paleoenvironmental and paleogeographical evolution of a post collisional basin located in the mediterranean area detailed sedimentological paleontological molluscs ostracods mammals charophytes and pollen and geochemical analyses on biogenic carbonates were carried out on a 66 m thick muddy sandy succession integrating the vertical distribution of selected species of ostracods and molluscs with the range of the mammal assemblage it has been possible to correlate the basal succession of the velona basin to the early messinian pre evaporitic corresponding to the lower part of the mn 13 zone the basal portion of the velona filling deposits corresponds to an unstable shallow lacustrine marshy environment rich in aquatic vegetation surrounded by swamps dominated by taxodiaceae and uplands dominated by warm temperate deciduous forests waters were generally brackish oligo mesohaline alternating with hypohaline episodes salinity changes recorded by the faunal assemblages do not parallel with changes in the geochemical signatures in ostracod shells and charophyte gyrogonites geochemistry of biogenic carbonates points to an athalassic origin of the water salinity probably linked to the dissolution of the triassic evaporites of the basement thus the absence of connections between the velona basin and the mediterranean sea during early messinian is confirmed ostracods molluscs and mammals show a central european paleobiogeographical affinity showing that at the time of deposition of the velona filling deposit the endemic tusco sardinian paleobioprovince was already disrupted and the northwards connections were noticeable on the other hand ostracods do not show any paleobiogeographic affinity with the ostracod assemblages of the paratethyan realm suggesting that no links between mediterranean and paratethys were present at that time

an environmental tolerance index for ostracodes as indicators of physical and chemical factors in aquatic habitats abstract continental ostracode occurrences reflect salinity solute composition temperature flow conditions and other environmental properties of the water they inhabit their occurrences also reflect the variability of many of these environmental parameters environmental tolerance indices etis offer a new way to express the nature of an ostracode s environment as defined herein etis range in value from zero to one and may be calculated for continuous and binary variables for continuous variables such as salinity the eti is the ratio of the range of values of salinity tolerated by an ostracode to the total range of salinity values from a representative database in this investigation the database of continuous variables consists of information from 341 sites located throughout the united states binary etis indicate whether an environmental variable such as flowing water affects ostracode presence or absence the binary database consists of information from 784 sites primarily from illinois usa etis were developed in this investigation to interpret paleohydrological changes implied by fossil ostracode successions eti profiles may be cast in terms of a weighted average or on presence absence the profiles express ostracode tolerance of environmental parameters such as salinity or currents tolerance of a wide range of values is taken to indicate shallow water because shallow environments are conducive to thermal variability short term water residence and the development of currents from wind driven waves

the use of ostracoda to reconstruct the oxygen levels of late palaeozoic oceans abstract it has been recently demonstrated that in post palaeozoic and modern oceans filter feeding ostracods totally dominate over deposit feeders during times of dysaerobia in modern oceans the filter feeding platycopida the sole extant group with this feeding strategy in terms of abundance completely dominate the oxygen minimum zone despite occurring there in low specific diversity the percentage of filter feeders has been used previously to locate kenoxic events and to determine palaeoxygen levels in liassic cenomanian and palaeogene oceans the term kenoxic is used to denote an event when oxygen levels were reduced most so called anoxic events which for the name implies total deprivation of oxygen were in fact kenoxic a kenoxic event produces dysaerobic rather than anaerobic conditions in the present paper upper palaeozoic ostracoda are analysed and it is concluded that the palaeocopida metacopina platycopina kloedenellacea and the paraparchitacea were filter feeders filter feeders were therefore much more diverse in the palaeozoic than subsequently in the palaeopsychrosphere all ostracods even podocopids acquired peculiar adaptations to allow them to live in the oxygen minimum zone using the percentage of filter feeding ostracod species of shelf seas as a guide relative oxygen levels for the seas which deposited the carbonate platforms of northwest europe during the emsian to visean interval are calculated changes in oceanic oxygen are related to global climatic changes especially in temperature and are therefore important in any considerations of palaeoclimatology our reconstructions for both dissolved oxygen and sea water temperatures from the late early devonian to the early carboniferous based upon the percentage of filter feeding species clearly depict the late devonian events as a time of low oxygen high temperatures and high filter feeders into the frasnian there was a subsequent cooling and improved oxygenation into the famennian and a glacial maximum marked by a low percentage of filter feeders in the lower tournaisian this was followed by a slight increase in the percentage of filter feeders into the visean a signal of lower levels of oxygen but continuing in a contrasted climate a model which yields reference points giving absolute values of oxygen is proposed for late palaeozoic benthic marine environments

modern and holocene sublittoral ostracod assemblages crustacea from the caspian sea a unique brackish deep water environment abstract we present a reconnaissance study of sublittoral ostracods from a number of caspian sea core tops collected during a joint french russian scientific cruise in 1994 cores from between 13 and 875 m water depth the modern ostracods show little depth restriction and this reflects the hydrography of the caspian sea which maintains relatively constant conditions 5 c 13 salinity below 50 m throughout the year we also present the ostracod faunal record from a 10 m core of laminated sediments recovered from the central caspian basin at a water depth of 475 m which we believe shows repetitive quasi cyclic changes in bottom water conditions over approximately the last 14 15 000 years with a major change at about the late glacial to holocene transition the faunal record from this core illustrates the potential of these sediments for reconstructing environmental changes in the caspian region during the late quaternary to holocene the continuous occurrence of in situ benthic meiofauna throughout the core also indicates that the bottom water must have remained ventilated throughout this period although variability in the faunal assemblages may reflect long and short term changes in the strength of ventilation

from naples 1963 to rome 2013 a brief review of how the international research group on ostracoda irgo developed as a social communication system abstract the 1st international symposium on ostracoda iso was held in naples 1963 the philosophy behind this symposium and the logical outcome of what is now known as the international research group on ostracoda irgo are here reviewed namely ostracodology over the last 50 years is sociologically analysed three different and important historic moments for the scientific achievements of this domain are recognised the first one between about 1963 and 1983 is related to applied research for the oil industry as well as to the great interest in the better description of the marine environment by both zoologists and palaeontologists another important aspect during this period was the work by researchers dealing with palaeozoic ostracods who had their own discussion group irgpo gradually the merger of this latter group with those dealing with post palaeozoic ostracods at various meetings improved the communication between the two groups of specialists a second period was approximately delineated between 1983 and 2003 during this time slice more emphasis was addressed to environmental research with topics such as the study of global events and long term climate change ostracodologists profited also from the research politics within national and international programmes large international research teams emerged using new research methods during the third period 2003 2013 communication and collaborative research reached a global dimension amongst the topics of research we cite the reconstruction of palaeoclimate using transfer functions the building of large datasets of ostracod distributions for regional and intercontinental studies and the implementation of actions that should lead to taxonomic harmonisation projects within which molecular biological techniques are routinely used combined with sophisticated morphological information expanded now in their importance the documentation of the ostracod description improved through new techniques to visualise morphological details which stimulated also communication between ostracodologists efforts of making available ostracod information through newsletters and electronic media are evoked

environmental responses to lateglacial climatic fluctuations recorded in the sediments of pre alpine lake mondsee northeastern alps investigation of the sedimentary record of pre alpine lake mondsee upper austria focused on the environmental reaction to rapid lateglacial climatic changes results of this study reveal complex proxy responses that are variable in time and influenced by the long term evolution of the lake and its catchment a new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub annual resolution for mu xrf element scanning carbon geochemistry stable isotope measurements on ostracods pollen analyses and large scale thin sections for microfacies analysis the holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometric 14 c dating of terrestrial plant macrofossils whereas the lateglacial age model is based on delta 18 o wiggle matching with the greenland ngrip record using the gicc05 chronology microfacies analysis enables the detection of subtle salimentological changes proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing comparing periods of major warming at the onset of the lateglacial and holocene and of major cooling at the onset of the younger dryas reveals differences in proxy responses reflecting threshold effects and ecosystem inertia temperature increase vegetation recovery decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the holocene took place with only decadal leads and lags over a ca 100 a period whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the lateglacial interstadial by ca 500 750a cooling at the onset of the younger dryas is reflected by the simultaneous reaction of delta 18 o and vegetation but sedimentological changes reduction of endogenic calcite content increase in detrital flux were delayed by about 150 300 a three short term lateglacial cold intervals corresponding to greenland isotope substages gl 1d gl 1c2 and gl 1b also show complex proxy responses that vary in time copyright c 2011 john wiley sons ltd

the platycopid signal deciphered responses of ostracod taxa to environmental change during the cenomanian turonian boundary event late cretaceous in se england abstract a multi proxy investigation of the cenomanian turonian boundary event ctbe near dover in southern england previously demonstrated that coincident with a major global positive carbon stable isotope excursion during oceanic anoxic event 2 oae 2 the diversity of nanoplankton dinoflagellates planktonic and benthonic foraminifera and ostracods was severely reduced this was attributed to decreasing levels of dissolved oxygen consequent on an intensification and expansion of the oceanic oxygen minimum zone omz into shelf seas in the case of the ostracods it was noted that as podocopid taxa became locally extinct platycopids became the dominant component of the fauna subsequently the platycopid signal hypothesis psh claimed that dominance of platycopids in ostracod assemblages could be regarded as a signal of dysaerobic conditions on the sea floor based on the premise that the filter feeding platycopids able to pass more water over their respiratory surface were better equipped than other benthonic ostracods to survive in water of reduced oxygen concentration the psh has been widely accepted and applied in palaeoenvironmental reconstructions of stratigraphic intervals ranging from the palaeozoic to the quaternary however the modern biological and ecological support claimed for the platycopid signal has been challenged platycopids are occasionally dominant in modern omzs but often they are not and in any case the same can be said about some podocopids apparently precise calibration scales published by some authors are not justified by available data furthermore platycopid signal indications of dysaerobic intervals in the english chalk succession often conflict with the evidence of macrofossils and trace fossils here we review old and new data from two ctbe sites in se england dover and eastbourne and advance an alternative interpretation of the platycopid signal based on the concept of the spread of oceanic oligotrophic conditions into the european chalk sea during oae2 we propose that ostracod assemblages overwhelmingly dominated by platycopids signify oligotrophy because living platycopids appear to be adapted to filter feed on nano and picoplankton which are predominant in oligotrophic conditions

the use of ostracods from marginal marine brackish waters as bioindicators of modern and quaternary environmental change abstract ostracoda microscopic aquatic crustacea from brackish waters have a great potential for ecological monitoring and palaeoenvironmental analyses in highly variable environments this has been proven in many articles during recent decades but their potential has yet to be fully developed or utilised the analysis of ostracod assemblage composition species distributions eco phenotypic variability and the analysis of stable isotopes and trace elements in ostracod shells provide valuable information on present and past water salinity temperature and chemistry hydrodynamic conditions substrate characteristics climate sea level variations oxygen and nutrient availability this article provides an overview on the application of ostracods from brackish waters for palaeoenvironmental reconstruction in the quaternary and for environmental studies in present day environments

faunal and geochemical evidence for changes in intermediate water temperature and salinity in the western coral sea northeast australia during the late quaternary abstract ostracod assemblages and geochemical analyses of valves of specific ostracod taxa are used to reconstruct both qualitatively and quantitatively bottom water temperatures bwt for the last 100 000 years in the western coral sea the investigated core 51gc21 is situated in the lower reaches of the antarctic intermediate water at 1630 m water depth first we ran a principal coordinate analysis pcoa of 42 surface samples from the coral sea and then compared fossil assemblages with results of the pcoa in addition we selected well preserved speciments of the two genera krithe and bythocypris for mg ca analyses the mg ca is used to infer past changes in bwt for intermediate waters of the western coral sea results indicate large temperature fluctuations over the last 100 000 years of interest is the documentation that the bwt was similar to the present day temperature during part of isotope stage 3 comparison between our temperature record and the benthic foraminifer 18o record of core 51gc21 and with the 18o variations in seawater as reconstructed by labeyrie et al 1987 allowed assessment of past changes in bwt salinity and density thus we identify for the western coral sea three distinct periods on the basis of water mass density changes i e for isotope stage 1 stages 2 3 and 4 and stage 5 our temperature record also indicates a good correlation with the 60 s summer insolation calculations for the period between 25 000 yr b p and 75 000 yr b p comparison of our results from this study with other records from the western pacific the ontong java plateau in particular reveal the role of new guinea as an oceanographic barrier a wet phase recorded on continental australia coincides with our high bottom water temperature record for isotopic stage 3

benthic ostracods and deep water masses in the atlantic ocean ostracod faunas at six locations are compared and related to distributions in an atlantic ocean wide data base five widely developed vertical faunal sequences are recognised at particular levels within deep water masses henryhowella fauna lower part of antarctic intermediate water krithe fauna upper north atlantic deep water poseidonamicus bosquetina fauna upper part of lower nadw dutoitella fauna lower part of lower nadw legitimocythere fauna antarctic bottom water these faunas are correlated with previously established deep water benthic foraminiferal assemblages and their possible palaeo oceanographic use is discussed

the platycopid signal of oxygen depletion in the ocean a critical evaluation of the evidence from modern ostracod biology ecology and depth distribution abstract the use of relative abundances of filter feeding platycopid ostracods in estimating past levels of dissolved oxygen in the ocean the platycopid signal hypothesis is examined paying particular attention to evidence from faunistic biological and ecological studies the degree of support for the hypothesis has been overstated available data on ostracod depth distribution show that previous claims for platycopid dominance in the oxygen minimum zone in different oceanic regions are misleading and based on only a few studies observations and experimental studies on living platycopids are limited in scope and should be treated with caution we conclude that previously published and widely applied calibrations of platycopid abundance against dissolved oxygen levels are inadequately justified by the available data any further application of the platycopid signal technique should necessarily address these criticisms

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials

an overview of neogene brackish leptocytherids from italy and spain biochronological and palaeogeographical implications abstract an overview of the neogene euryhaline leptocytherids from italian and spanish basins is reported together with their chronological and geographical distributions eight genera or subgenera have been considered mediocytherideis s s m sylvestra chartocythere leptocythere tavanicythere amnicythere euxinocythere s s and e maeotocythere the study has shown that these leptocytherids could be a valuable biochronological tool in both marginal marine and the athalassic saline environments since even at generic level they show separate temporal distributions for example the presence of chartocythere and euxinocythere s s in the mediterranean seems to be limited to the late serravallian tavanicythere seems to have been exclusively distributed during the late miocene with different species spanning the late tortonian and early messinian m sylvestra seems to attain its maximum diversity in the same time interval the widespreading of amnicythere and e maeotocythere in the mediterranean marks the latest messinian lago mare event about 5 5 5 3 ma the important radiation of leptocythere characterises the pliocene moreover a comparative analysis between neogene mediterranean and paratethyan leptocytherids has shown that the geographical and stratigraphical distribution of the eight genera analysed matches the palaeogeographic events that affected the peri tethyan realm during neogene