late eocene to early miocene ice sheet dynamics and the global carbon cycle paired benthic foraminiferal trace metal and stable isotope records have been constructed from equatorial pacific ocean drilling program site 1218 the records include the two largest abrupt 1 myr increases in the cenozoic benthic oxygen isotope record oi 1 in the earliest oligocene 34 ma and mi 1 in the earliest miocene 23 ma the paired mg ca and oxygen isotope records are used to calculate seawater 18o w calculated w suggests that a large antarctic ice sheet formed during oi 1 and subsequently fluctuated throughout the oligocene on both short 0 5 myr and long 2 3 myr timescales between about 50 and 100 of its maximum earliest oligocene size the magnitudes of these fluctuations are consistent with estimates of sea level derived from sequence stratigraphy the transient expansion of the antarctic ice sheet at mi 1 is marked in the benthic 18o record by two positive excursions between 23 7 and 22 9 ma each with a duration of 200 300 kyr bottom water temperatures decreased by 2 c over the 150 kyr immediately prior to both rapid 18o excursions however the onset of each of these phases of ice growth is synchronous within the resolution of the records with the onset of a 2 c warming over 150 kyr we suggest that the warming during these glacial expansions reflect increased greenhouse forcing prompted by a sudden decrease in global chemical weathering rates as antarctic basement silicate rocks became blanketed by an ice sheet this represents a negative feedback process that might have operated during major abrupt growth phases of the antarctic ice sheet

on the post 25 ma geodynamic evolution of the western mediterranean during the neogene and quaternary western mediterranean geodynamics were dominated by the eastward migration of the apenninic arc and associated back arc basins the migration was controlled by retreat of the apenninic slab and was associated with boudinage of the lithosphere in the back arc area palaeo reconstruction of the kinematics of the arc suggests about 775 km of migration from the late oligocene to present along a transect from the gulf of lions to calabria a maximum of 135 km of n s converge occurred between africa and europe during the same time span the western mediterranean was thus mainly shaped by the migration of the slab related to west directed subduction it is hypothesized that minor n s convergence deformed the arc but was not the cause of its formation 1998 elsevier science b v all rights reserved

palaeoceanography of lower cretaceous alpine platform carbonates shallow water carbonate platforms evolve in an interplay of local regional and global dynamics thereby generating a detailed record of environmental conditions platform sediments constitute important archives of past environmental change and as such they are increasingly analysed for the information they contain on wider scale patterns the integration of this information with palaeoceanographic data obtained from deeper water sediments provides a powerful tool to develop a more diverse and complete image of past environmental change in this contribution the remains of the northern tethyan carbonate platform of early cretaceous age cropping out in the western swiss jura and the helvetic alps are used to illustrate the advantage of a palaeoceanographic approach in their interpretation the tools applied are biostratigraphy and chemostratigraphy carbon and strontium isotopes in order to obtain a precise age model for correlation with hemi pelagic sediments in adjacent basins sequence stratigraphy as a means to reconstruct the impact of sea level change phosphorus stratigraphy as a proxy for trophic levels facies and microfacies analyses as a gateway to gain better insight into the carbonate factory and the detailed analysis of platform drowning unconformities as an indicator of wider scale palaeoenvironmental change it is shown that changes from periods of predominantly photozoan to predominantly heterozoan carbonate production near the berriasian valanginian boundary and middle early aptian coincided with substantial increases in phosphorus burial rates and major carbon isotope excursions furthermore the majority of the platform drowning episodes occurred just prior to and during episodes of major palaeoenvironmental change and last but not least the platform itself may have influenced the chemistry of adjacent basins and the carbon isotope composition of associated carbonates by the export of periplatform ooze

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

an alternative model for positive shifts in shallow marine carbonate 13c and 18o positive shifts in global seawater d 13 cdic are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in d 18 o here an alternative model is proposed for the formation of local positive isotope shifts in shallow marine settings the model involves geochemically altered platform top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition both mechanisms are active on modern sub tropical carbonate platforms and result in low carbonate d 13 ca ndd 18 o relative to typical oceanic values during high amplitude transgressive events the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced and 13 c depleted platform top water mixes with open oceanic water masses having higher isotope values both factors are recorded as a transient increase in carbonate 13 c and 18 o relative to low background values these processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas

the monterey event within the central mediterranean area the shallow water record the middle miocene is an important time to understand modern global climate evolution and its consequences on marine systems the mid miocene climatic optimum between 17 0 ma and13 5 ma was the warmest time interval of the past 35 million years during which atmospheric co2 concentrations were lower than today in the mid miocene climatic optimum a significant carbon cycle perturbation occurred expressed as a last long term positive carbon isotope shift known in literature as the monterey carbon isotope excursion and recorded in open ocean settings in this work the lower to middle miocene carbon isotope records from three different domains of the central mediterranean are analyzed with the aim of identifying the local carbonate platform response to the major global carbon cycle perturbation of the monterey event carbon and oxygen isotope ratios have been measured on samples belonging to three different stratigraphic sections two of them representative of shallow water settings latium abruzzi and apula platforms and the latter of a hemipelagic setting umbria marche basin a well defined monterey carbon isotope excursion is recorded also in these shallow water sections despite their expected problematic stratigraphic constraints a reliable age model is provided by calcareous nannofossil biostratigraphy and strontium isotope stratigraphy in both carbonate platform successions examined the monterey carbon isotope excursion coincides with a spread of bryozoans over other carbonate producing biota the high productivity of the bryozoan dominated factory in the aphotic zone had an important control on the platform depositional profile the high rates of sediment production in the deeper aphotic and oligophotic zones produced a depositional profile of a low angle ramp this article is protected by copyright all rights reserved

unravelling the origin of a paleogene unconformity in the latium abruzzi carbonate succession a shaved platform the latium abruzzi carbonate platform constitutes the sedimentary record from the triassic to the late miocene of the southern tethyan margin outcropping in the apennines this sedimentary succession is punctuated by an important hiatus between the end of the cretaceous and the early miocene this paleogene hiatus has long been interpreted as the result of prolonged subaerial exposure however no evidence of such exposure has ever been documented on the latium abruzzi platform this is contrary to the coeval and adjacent apulia and lessini carbonate platforms where a broadly developed paleokarst system formed between the eocene and the early miocene the assumption that the miocene marine transgression deeply eroded a karstified cretaceous substrate on the latium abruzzi platform is not supported because this surface appears in the field as a perfectly flat bioeroded paraconformable surface in this work a marine origin is proposed for this unconformity from late paleocene to early miocene the latium abruzzi carbonate platform was a shaved isolated platform exposed to wave action in the middle of the proto mediterranean area bioclastic sediment accumulated during transgressive and sea level highstand phases whereas in the following falling and lowstand stages sediment was eroded as the seafloor came into the zone of wave abrasion the sediment eroded from the platform was shed into the basin where it produced coarse bioclastic intercalations in the hemipelagites of the scaglia formation at the end of the oligocene when the adjacent basin was filled a small ramp was established in the transitional zone between the platform and the basin there cross bedded carbonates accumulated in middle to outer ramp environments the inner ramp remained within the zone of wave abrasion such that sediment generated there was washed out into the middle and outer ramp environments finally in the early burdigalian the mediterranean progressively evolved into closed sea during the initial stages of the closure of indo pacific connection the reduction of the wave base depth typical of an enclosed sea created increased accommodation space allowing sediments to accumulate and form the complete inner to outer ramp facies belts of the miocene latium abruzzi ramp

downslope migrating large dunes in the chattian carbonate ramp of the majella mountains central apennines italy abstract this work is the result of detailed geological mapping and stratigraphic analysis of the lepidocyclina limestone in the northern sector of the majella mountains central apennines the lepidocyclina limestone represents an informal member of the bolognano formation chattian to messinian in age four main lithofacies have been recognized planar cross bedded grainstone fa moderate angle cross bedded grainstone to packstone fb sigmoidal cross bedded grainstone fc and bioturbated marly packstone to wackestone fd a detailed description of the recognized lithofacies and facies association of the lepidocyclina limestone is given in this work together with an interpretation of the corresponding depositional setting and a discussion of the related larger scale processes in summary the depositional profile of the lepidocyclina limestone is consistent with a carbonate ramp where most of the sediments appear to be parautochthonous in the middle ramp environment and autochthonous dominated in the outer ramp environment palaeocurrent patterns indicate a strong generally north west basin ward direction that affected the middle ramp environment and developed a wide down slope migrating dune field considering that the warm oligocene climate of the mediterranean area was favorable to tropical cyclone development both in terms of frequency and intensity it is suggested that return currents generated by strong winds or storms were common on the lepidocyclina carbonate ramp thus favoring the development of the observed dune field

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

carbon and oxygen isotope records of palaeoenvironmental and carbonate production changes in shallow marine carbonates kimmeridgian swiss jura carbon and oxygen isotope ratios are commonly used to correlate shallow and deep marine successions carbon and oxygen isotope analyses were performed on bulk carbonate samples from two kimmeridgian sections of the swiss jura platform in order to correlate them with biostratigraphically well dated coeval sections in the adjacent basin on the platform a general decrease in 13 c and 18 o values from the base to the top of the studied interval is measured whereas time equivalent pelagic hemipelagic carbonates record an increase in carbon and oxygen isotope ratios moreover the measured 13 c and 18 o values are generally lower than those indicated for the kimmeridgian open ocean and show high frequency variations superimposed on the general trend samples were screened for diagenetic alteration using optical and cathodoluminescence petrography and coupled carbon and oxygen isotope and trace element analyses some observations favour a role for diagenetic alteration but isotopic and elemental trends as well as sedimentological evidence suggest that the more negative values of 13 c and 18 o relative to kimmeridgian seawater are also due to local environmental conditions high frequency changes in 18 o and 13 c values most likely result from variations in salinity and carbonate production and accumulation rates these variations were produced by different water masses that were isolated from the open ocean and developed their own geochemical signatures repeated isolation was induced by high frequency sea level fluctuations and helped by irregular platform morphology consequently carbon and oxygen isotope records in shallow marine carbonates can be used for stratigraphic correlation only if their origin is well known

early miocene tephra in the apennine pelagic sequence an inferred sardinian provenance and implications for western mediterranean tectonics during the tertiary period the northeastern apennines of italy functioned as a quiet depositional basin for fine grained volcanic ashfalls from distant explosive volcanism accompanying the alpine apennine orogenesis these ashes have been dated by several authors with different radioisotopic methods in the past decade k ar 40ar 39ar and rb sr on biotite separates 40ar 39ar single crystal laser fusion on plagioclase and sanidine and u pb on zircon and provide the means for a precise accurate age calibration of the tertiary magnetostratigraphic and biostratigraphic timescales however the provenance of these tephras has remained uncertain to resolve this problem we have carried out detailed grain size analysis of the so called livello raffaello a feldspar bearing bentonite recognized in numerous outcrops throughout the region at the very base of the aquitanian to burdigalian bisciaro formation the raffaello stratigraphically located in the upper part of planktonic foraminiferal zone n4 and calcareous nannofossil zone nnl upper chron 6a r middle aquitanian yielded an isochron age of 21 2 0 5 ma 2 from 27 40ar 39ar dates by laser fusion on plagioclase we measured the mean grain size m of the 63 m felsic fraction i e feldspar and quartz of the raffaello in 11 representative outcrops in the region and compared the grain size against distance from two possible volcanic sources the venetian province northern provenance and the sardinian province western provenance while the venetian source shows no distinct trend of the m distribution the sardinian plot exhibits a very clear linear grain size decrease with distance after having tentatively established a sardinian source no other volcanoes of aquitanian age are known west of the apennine basin we revised the m distribution through palinspastic restoration including the post aquitanian anticlockwise rotation of the sardinian microplate and consequent orogenic shortening of the northeastern apennine fold and thrust belt for this we have used the thick skinned model of lavecchia et al 1984 which envisions a shortening for the northeastern apennines of 3 to 30 km and the thin skinned model of bally et al 1986 which assumes a variable shortening of 50 to 250 km we have also modeled the distribution of the m of felsic crystals for modern analogue stratospheric westerly winds blowing in this region from fall to spring at speeds of 10 to 30 m s and altitudes ranging from 25 km to 40 km which account for distal 400 km transport of fine tephra cornell et al 1983 in addition we have calculated the m of felsic crystals from six representative sites of the quaternary y 5 ash which was produced 38 000 years ago by an explosive volcanic event in the neapolitan area and was distributed downwind throughout the eastern mediterranean basin our results indicate that restoration by the thick skinned model yields a crystal size distribution gradient incompatible with that predicted by the computed model and overall m values much finer than those observed in the y 5 sample at a comparable distance from the source on the other hand restoration using the thin skinned structural setting yields good agreement with that of the computed model and with the observed m distribution of the y 5 ash

middle miocene isotope stratigraphy and paleoceanographic evolution of the northwest and southwest australian margins wombat plateau and great australian bight abstract the benthic stable isotope record from odp site 761 wombat plateau nw australia 2179 3 m water depth documents complete recovery of the middle miocene 13c excursion corresponding to the climatic optimum and subsequent expansion of the east antarctic ice sheet the six main 13c maxima of the monterey excursion between 16 4 and 13 6 ma and the characteristic stepped increase in 18o between 14 5 and 13 9 ma are clearly identified the sedimentary record of the shallower odp sites 1126 and 1134 great australian bight gab sw australia 783 8 and 701 m water depth respectively is truncated by several unconformities however a composite benthic stable isotope curve for these sites provides a first middle miocene bathyal record for southwest australia the 18o and 13c curves for sites 1126 and 1134 indicate a cooler better ventilated water mass at 700 m water depth in the great australian bight since approximately 16 ma this cooler and younger water mass probably originated from a close southern source cooling of the bottom water at 16 ma started much earlier than at other sites of equivalent paleodepths in the central and western parts of the indian ocean at site 761 the 18o curve shows an excellent match with the global sea level curve between 11 5 and 15 1 ma and thus closely reflects changes in global ice volume prior to 15 1 ma the mismatch between the 18o curve and the sea level curve indicates that 18o fluctuations are mainly due to changes in bottom water temperature

temperate carbonate platform drowning linked to miocene oceanographic events maiella platform margin italy carbonate platform drownings are frequent often synchronous global occurrences yet explanations for these world wide events remain unsatisfactory in the central apennines lower and middle miocene carbonate rocks deposited on a temperate ramp in the maiella platform margin record two episodes of platform drowning followed by hemipelagic sedimentation dated as latest oligocene aquitanian 26 23 ma and as burdigalian langhian 20 16 ma a high resolution stratigraphy based on strontium isotopes allows us to correlate key phases of platform evolution with events recorded in deep water ocean sediments this paper suggests that high weathering rates and nutrient input in the mediterranean during the early and middle miocene possibly linked to the uplift of the tibetan region set the preconditions for platform drowning which were ultimately caused by rapid eustatic sea level rises

a first assessment of icebridge snow and ice thickness data over arctic sea ice we present a first assessment of airborne laser and radar altimeter data over snow covered sea ice gathered during the national aeronautics and space administration operation icebridge mission we describe a new technique designed to process radar echograms from the university of kansas snow radar to estimate snow depth we combine icebridge laser altimetry with radar derived snow depths to determine sea ice thickness results are validated through comparison with direct measurements of snow and ice thickness collected in situ at the danish greenarc 2009 sea ice camp located on fast ice north of greenland the icebridge instrument suite provides accurate measurements of snow and ice thickness particularly over level ice mean icebridge snow and ice thickness agree with in situ measurements to within 0 01 and 0 05 m respectively while modal snow and ice thickness estimates agree to within 0 02 and 0 10 m respectively icebridge snow depths were correlated with in situ measurements r 0 7 for an averaging length of 55 m the uncertainty associated with the derived icebridge sea ice thickness estimates is 0 40 m the results demonstrate the retrieval of both first year and multiyear ice thickness from icebridge data the airborne data were however compromised in heavily ridged ice where snow depth and hence ice thickness could not be measured techniques developed as part of this study will be used for routine processing of icebridge retrievals over arctic sea ice the limitations of the greenarc study are discussed and recommendations for future validation of airborne measurements via field activities are provided

impact of carbonate producing biota on platform architecture insights from miocene examples of the mediterranean region abstract different types of carbonate platforms formed in the mediterranean during the miocene low angle homoclinal types of ramp distally steepened ramps flat topped platforms and reef rimmed shelves the critical differences between these platforms result from differences in the capacities of the carbonate systems to accumulate sediments above hydrodynamic base level ecologically controlled accommodation the various depositional profiles and facies belt distributions resulted from the interplay between different sediment production and redistribution processes and the internal architectures resulted from the response of each type of platform to changes in accommodation heterogeneities driven by high frequency sea level cycles are maximized in platforms ruled by shallow water euphotic framework dominated production and minimized in low angle ramps where sediment resulted from aphotic and oligophotic carbonate production in the mediterranean region there is no direct relationship between type of platform and global temperature as shown by the coeval occurrence of different platforms in similar latitudinal settings although temperature is a key limiting factor other paleoceanographic factors such as trophic resources may have also been along with biological evolution important factors influencing different types of carbonate producing biotas

stratigraphy and sedimentology of phosphate rich sediments in malta and south eastern sicily latest oligocene to early late miocene the maltese archipelago and south eastern sicily include an uppermost oligocene to upper miocene hemipelagic sedimentary succession representing the malta hyblean plateau which limits the eastern mediterranean to the west this succession hosts a unique and well exposed series of condensed and allochthonous phosphate rich beds which were formed in a sedimentary regime of erosion sediment reworking and frequent gravity flow deposition the combination of nannofossil biostratigraphy and 87sr 86sr isotope stratigraphy allows for the precise attribution of ages to the phosphate deposits and for the distinction of three periods of major phosphogenesis the first phase occurred between 24 5 and 21 ma and 25 and 18 9 ma clustering of ages between 25 and 22 5 ma on malta and sicily respectively the second and third phases of phosphogenesis are documented from the maltese islands and are dated as 17 2 to 13 1 ma and 10 9 to 9 8 ma respectively the phosphate rich beds are associated with hiatuses and phases of important condensation which for the oldest phosphogenic period envelop the time period of 23 2 to 22 ma for the fomm ir rhi bay section malta and from 19 1 to 16 3 ma for the sections of sampieri and modica sicily for the second phase of phosphogenesis on the maltese islands a consistent hiatus was found which embraces the time period of approximately 17 to 15 ma also the third phase of phosphogenesis appears to be associated with a major hiatus which probably envelops the time period between 12 5 and 10 9 ma but a better age control is needed here the correspondence in timing of the maltese sicilian phases of phosphogenesis with major phases of phosphogenesis outside the mediterranean realm to maxima in oceanic phosphorus burial rates and maxima in the 13c benthic foraminiferal record suggests that the palaeoceanographic evolution of the eastern mediterranean was well in phase with that of other ocean basins until at least the early late miocene despite its increasing isolation due to the gradual closure of the eurasian arabian strait and progressive sea level fall

mixed carbonate siliciclastic record on the north african margin malta coupling of weathering processes and mid miocene climate we investigated rock outcrops spanning the middle miocene global climate cooling step on the maltese islands in order to reconstruct continental weathering rates and terrigenous fluxes as well as to explore the coupling between these later regional climate and carbonate accumulations sedimentation at this location was dominated during the oligocene and early miocene by a transitional platform to slope carbonates but progressively switched to a clay rich carbonate slope system in the middle miocene around 13 ma an abrupt change toward clay dominated marls occurred and marl deposition persisted until the tortonian ca 12 ma when a shallow water carbonate ramp was reestablished clay mineralogy and bulk rock oxygen isotope analyses suggest that the deposition of the blue clay formation was mainly caused by global climate change and related change in the rate of continental weathering a significant negative correlation r 2 0 65 exists between the carbonate content and the 1 8 o record this combined with the variation of mass accumulation rate of terrigenous material suggests that shorter term periods of globally cooler climate mi events were associated with higher rates of accumulation in continental derived material since during the miocene malta was attached to the north african margin we propose that the observed trends were due to a regional increase in rainfall during cooler periods which consequently increased continental weathering and runoff we further suggest that this pattern was linked to the perturbation of atmospheric fronts due to an increased thermal gradient during the miocene thus regional increase in rainfall might have been linked to the northward migration of the intertropical convergence zone itcz

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

carbonate systems along nutrient and temperature gradients some sedimentological and geochemical constraints research over the past several decades has clearly demonstrated that changes in the ocean environment have had major impacts on carbonate systems changes in climate ocean circulation and seafloor spreading rates have influenced temperature and seawater chemistry including carbonate saturation state and nutrient availability and thereby have determined boundary conditions for the biota that form carbonate platforms in turn the biota determine accumulation rates and facies zonations thus controlling platform geometry and facies dynamics in the first section of this paper we examine how nutrient availability influences carbonate facies associations we first discuss the role of temperature and nutrient gradients in the modern ocean and their influence on biotic associations then we discuss how carbonate sedimentation can be characterized along nutrient gradients in the second section we review proxies currently used to reconstruct paleoproductivity in open ocean environments and discuss their applicability to neritic carbonate systems we highlight the variety of existing proxies and their limitations and suggest that multiple lines of evidence are needed for valid interpretations our short review discusses sedimentological biogenic and geochemical proxies that can be used to reconstruct past nutrient fluxes and to constrain paleoceanographic controls over the distribution of carbonate associations however it also reveals that more data and case studies are needed that integrate shallow and deep water carbonate sequences and elucidate the links between temperature vs nutrient supplies changes and facies in ancient carbonate sequences

combined airborne laser and radar altimeter measurements over the fram strait in may 2002 knowledge of sea ice thickness is critical for the prediction of future climate and for assessing the significance of changes in thickness sea ice thickness can be calculated from radar or laser satellite altimetry measurements of freeboard however a lack of knowledge of snow depth introduces significant uncertainties into these calculations this paper compares the first coincident airborne laser and radar altimetry data over sea ice collected during the laser radar altimetry lara field campaign lara was a flight of opportunity that provided valuable data to explore techniques to validate satellite measurements of ice freeboard and the possibility of combining laser and radar measurements over snow covered sea ice to calculate the snow depth two new methods were created to analyse these data sets a new radar retracker and a radar power simulator which models radar returns from the laser data we present the first quantitative analysis of data from the lara laser and radar altimeters and demonstrate the potential of combining laser and radar altimetry to estimate snow depth lara elevation estimates compare well with elevations from the radar altimeter onboard ers 2 at the sub meter level and the study provides lessons for future validation of satellite altimetry data over sea ice laser elevations are consistently higher than the radar elevations over snow covered sea ice as lara was a flight of opportunity no coincident in situ measurements were available nevertheless the difference between the reflecting surface of the laser and radar is consistent with snow depth from climatology and the analysis techniques developed in this paper will be useful for future radar and laser altimetry comparisons

large scale ice thickness distribution of first year sea ice in spring and summer north of svalbard the large scale thickness distribution of sea ice was measured during several campaigns in the european arctic north of svalbard from 2007 using an airborne electromagnetic induction device in august 2010 and april may 2011 this was complemented by extensive on ice work including measurements of snow thickness and freeboard ice thicknesses show a clear difference between the seasons with thicker ice during spring than in summer in spring 2011 negative freeboard and flooding were observed as a result of the extensive snow cover we find that the characteristics of the first year sea ice allow combining observations from different years the ice thickness in the marginal ice zone increases with increasing latitude and increasing distance to the ice edge however in the inner ice pack from 100 km from the ice edge the thickness remains almost constant modal ice thickness in spring reaches 2 4 m whereas in summer it is 1 0 1 4 m our study provides new insight into ice thickness distributions of a typical ice cover consisting of mainly first and second year ice which may become the dominant ice type in the arctic in the future

the oligocene miocene stratigraphic evolution of the majella carbonate platform central apennines italy abstract the stratigraphic architecture of the bolognano formation documents the evolution of the majella carbonate platform in response to global and local changes that affected the mediterranean area during the oligocene miocene interval the bolognano formation consists of a homoclinal ramp that developed in a warm subtropical environment five different lithofacies associations have been identified lepidocyclina calcarenites cherty marly limestones bryozon calcarenites hemipelagic marls and marly limestones and lithothamnion limestones each association corresponds to a single lithostratigraphic unit except for the lepidocyclina calcarenites that form two distinct lithostratigraphic units lepidocyclina calcarenites 1 and 2 these six units reflect alternation of shallow water carbonate production and drowning specifically two of the three stages of shallow water carbonate production regard the development of wide dune fields within the middle ramp one stage dominated by red algae and a sea grass carbonate factory whereas the two drowning phases are represented by marly cherty limestones and calcareous marls a new biostratigraphic framework for bolognano formation is presented based on high resolution analysis of calcareous nannofossil assemblages which proved to be very useful for biostratigraphic constraints also in shallow water settings using this approach we have linked the first drowning phase late chattian aquitanian p p in age to western mediterranean volcanism and the mi 1 event and the second drowning phase late burdigalian serravallian in age to the closure of the indo pacific passage and the occurrence of the global monterey event these results permit a new deciphering in terms of sequence stratigraphy of the bolognano formation that is interpreted as a 2nd order super sequence that can be subdivided into 3 transgressive regressive sequences

stepwise extinction of larger foraminifers at the cenomanian turonian boundary a shallow water perspective on nutrient fluctuations during oceanic anoxic event 2 bonarelli event a two step pattern in the extinction of larger foraminifers is recorded in the upper cenomanian shallow water carbonates of the southern apennines italy the first step eliminated the alveolinids the most extreme oligotrophs and reduced dramatically the diversity of larger foraminifers the second step wiped out the few survivors seemingly able to tolerate mesotrophic conditions leaving a disaster fauna dominated by small heterotrophs this pattern of extinction parallels the ecological succession of shallow water benthic foraminiferal assemblages along a gradient of increasing nutrient availability high resolution carbon isotope stratigraphy shows that the extinction of alveolinids was contemporaneous with the extinction of rotaliporid planktic foraminifers the drowning of certain tethyan carbonate platforms and an episode of thermal instability recorded in sea surface temperature in the open ocean ocean stratification during the first phase of oceanic anoxic event 2 would have promoted oligotrophic conditions in surface tropical waters and maximum diversity of larger foraminifers following this ocean overturning caused by surface water cooling is credited with delivering to shallow water environments the excess nutrient loads previously stored at depth triggering the environmental changes leading to stepwise extinction of larger foraminifers

strontium isotope stratigraphy in the upper cenomanian shallow water carbonates of the southern apennines short term perturbations of marine 87sr 86sr during the oceanic anoxic event 2 abstract strontium isotope stratigraphy of shallow water carbonates from the southern apennines italy indicates that the late cenomanian early turonian evolution of marine 87sr 86sr is not accurately depicted by the marine reference curve using the low mg biotic calcite of well preserved rudist shells as a study material and carbon isotope stratigraphy for correlation to the standard ammonite biozonal scheme of northern europe new 87sr 86sr values are proposed for four different stratigraphic levels the middle and uppermost part of the guerangeri zone the lower and upper part of the geslinianum zone the southern apennines data suggest that a sharp positive shift at the onset of oceanic anoxic event 2 precedes the well known sr isotope negative shift the positive shift is interpreted in terms of enhanced rates of chemical weathering driven by global warming forced by volcanogenic co2 outgassing a stratified ocean is invoked to reconcile the high gradient and the short lag time of the perturbation with estimates of present day total mass and residence time of strontium in the ocean the sharp switch to the negative shift is related to the collapse of water column density gradient driven by thermal instability during a late cenomanian cool event more active ocean circulation suddenly delivered to surface waters the signal of increased submarine volcanism that had accumulated in deep waters

correlating carbon and oxygen isotope events in early to middle miocene shallow marine carbonates in the mediterranean region using orbitally tuned chemostratigraphy and lithostratigraphy during the miocene prominent oxygen isotope events mi events reflect major changes in glaciation while carbonate isotope maxima cm events reflect changes in organic carbon burial particularly during the monterey carbon isotope excursion however despite their importance to the global climate history they have never been recorded in shallow marine carbonate successions the decontra section on the maiella platform central apennines italy however allows to resolve them for the first time in such a setting during the early to middle miocene the present study improves the stratigraphic resolution of parts of the decontra section via orbital tuning of high resolution gamma ray gr and magnetic susceptibility data to the 405 kyr eccentricity metronome the tuning allows within the established biostratigraphic sequence stratigraphic and isotope stratigraphic frameworks a precise correlation of the decontra section with pelagic records of the mediterranean region as well as the global paleoclimatic record and the global sea level curve spectral series analyses of gr data further indicate that the 405 kyr orbital cycle is particularly well preserved during the monterey event since gr is a direct proxy for authigenic uranium precipitation during increased burial of organic carbon in the decontra section it follows the same long term orbital pacing as observed in the carbon isotope records the 405 kyr gr beat is thus correlated with the carbon isotope maxima observed during the monterey event finally the mi events can now be recognized in the 18o record and coincide with plankton rich siliceous or phosphatic horizons in the lithology of the section

airborne electromagnetic footprints in 1d earths existing estimates of footprint size for airborne electromagnetic aem systems have been based largely on the inductive limit of the response we present calculations of frequency domain aem footprint sizes in infinitehorizontal thin sheet and half space models for the case of finite frequency and conductivity in a half space the original definition of the footprint is extended to be the side length of the cube with its top centered below the transmitter that contains the induced currents responsible for 90 of the secondary field measured at the receiver for a horizontal coplanar helicopter frequency domain system the in phase footprint for induction numbers less than 0 4 thin sheet or less than 0 6 half space increases from around 3 7 times the flight height at the inductive limit to more than 10 times the flight height for a vertical coaxial system the half space footprint exceeds nine times the flight height for induction numbers less than 0 09 for all models geometries and frequencies the quadrature footprint is approximately half to two thirds that of the in phase footprint these footprint estimates are supported by 3d model calculations that suggest resistive targets must be separated by the footprint dimension for their individual anomalies to be resolved completely analysis of frequency domain aem field data acquired for antarctic sea ice thickness measurements supports the existence of a smaller footprint for the quadrature component in comparison with the in phase but the effect is relatively weak in phase and quadrature footprints estimated by comparing aem to drillhole data are considerably smaller than footprints from 1d and 3d calculations however we consider the footprints estimated directly from field data unreliable since they are based on a drillhole data set that did not adequately define the true 3d sea ice thickness distribution around the aem flight line

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

high resolution chemostratigraphy of a miocene wedge top carbonate shelf san marino fm northern apennines italy the major role of the monterey global fertility event abstract the evolution of the san marino carbonate succession developed on a wedge top basin of the northern apennines during the middle miocene torriana outcrop marecchia valley was studied through a high resolution stable isotope analysis on different carbonate components a marked positive carbon isotopic excursion is identified at ca 16 ma the excellent correlation of the san marino 13c carbonates with the global 13c reference curve from zachos et al 2008 allows to link the marked positive 13c present in the san marino section with the global carbon isotope maximum of the monterey event subordinate long eccentricity driven 13c cycles 405 kyr as recorded by holbourn et al 2007 were also identified the correlation with carbon signatures of coeval successions of the mediterranean region shows that this main carbon isotopic excursion at the burdigalian langhian boundary is widely recorded and predates the crisis of these heterozoan shelves the demise of the san marino shelf resulted from a combination of global and regional factors that controlled the nutrient budget the detrital input and the subsidence of the basin the high resolution chemostratigraphy of san marino succession shows that even though the shelf evolved in the complex setting of a wedge top basin which should be largely influenced by local factors i e tectonic subsidence and detrital input it records the monterey event and its eccentricity paced rhythms with high precision this highlights the strong connection of the monterey event with the development and subsequent demise of shallow water carbonate depositional systems in the mediterranean irrespective of variable and changing local conditions

miocene phosphate rich sediments in salento southern italy abstract the upper middle to lower upper miocene serravallian to tortonian sedimentary succession in salento southern italy includes glauconite and phosphate rich deposits which are associated with pelagic micrite in baia del ciolo and marittima southern salento the succession is composed of shallow water platform carbonates of late oligocene age chattian porto badisco formation which are overlain by a 20 to 30 cm thick level of glauconite rich micrite with abundant reworked particles and fossils of the underlying porto badisco formation this interval is in turn covered by an up to 15 cm thick phosphatic crust livello ad aturia which itself is overlain either by a hemipelagic chalk like carbonate of middle to late miocene age pietra leccese marittima or directly by a micrite of late miocene age messinian novaglie formation baia del ciolo which shallows upwards into a shallow water platform carbonate a large hiatus is present in this succession which likely includes the lower and lower middle miocene in the region of lecce two discrete levels enriched in glauconite and phosphate each associated with a major discontinuity occur within the pietra leccese the strontium isotope ages derived on phosphate nodules and phosphatized and non phosphatized fossils and calcareous nannofossil ages indicate a time interval of phosphogenesis between 13 5 and 7 5 ma with two clusters at 12 and 10 5 ma the glauconite and phosphate rich sediments resulted from a current dominated regime which was characterized by low overall sedimentation rates erosion and sediment reworking and authigenesis this regime was likely related to a generally westward directed bottom current which was forced to upwell once it arrived at the western border of the eastern mediterranean basin the timing of the principal phosphogenic phases can only partly be correlated to those of other occurrences in this part of the mediterranean malta gozo southern sicily matese latium abruzzi platform the partial diachrony in phosphogenesis may express the effect of lateral switching in and or focusing of upwelling zones

phosphogenesis and organic carbon preservation in the miocene monterey formation at naples beach california the monterey hypothesis revisited the middle part of the miocene monterey formation at naples beach west of santa barbara california is predominantly composed of organic rich mudstone interstratified with phosphatic laminae minor lithologies include volcanic ash dolomite porcelanite and chert and condensed phosphatic beds sediments dated as 14 3 13 5 ma have average total organic carbon toc values around 8 5 wt and organic carbon oc accumulation rates are around 565 mg cm2 k y sediments dated as 13 5 13 ma are characterized by average toc values of 12 6 wt and oc accumulation rates of around 1130 mg cm2 k y the interval between 13 and 10 6 ma is marked by condensation average toc values are around 8 6 wt and oc accumulation rates diminished to around 55 mg cm2 k y the last interval studied is dated as 10 6 9 4 ma and average toc values are around 6 wt whereas oc accumulation rates rose again to 320 mg cm2 k y the presence of erosional surfaces angular unconformities and reworked clasts and nodules suggests that bottom current activity and gravity flow deposition have been instrumental in sediment accumulation the phosphatic laminae were precipitated at a very early stage of diagenesis during periods of nonsedimentation they formed less permeable sedimentary lids and may as such have contributed to enhanced oc preservation between 13 and 10 6 ma the thus formed phosphatic laminae were frequently subjected to subsequent sediment winnowing and reworking resulting in the formation of condensed phosphatic beds calculated p c molar ratios suggest that 1 the measured section is highly enriched in phosphorus p relative to oc 2 regeneration of organic p from organic matter decomposition was negligible and 3 the source of p was external likely upwelled bottom water rich in inorganic p in spite of good preservation conditions and correspondingly high toc contents the overall oc accumulation rates are moderate in comparison to those of actual high productivity areas which is mainly due to the episodic character of depositional processes and the intervening long periods of nondeposition and sediment reworking they preclude this section and by extrapolation the monterey formation in general from being an important oc sink during the middle miocene alternatively large oc sinks were probably created on the continent lignite deposits and in sedimentary depocenters which received increasing amounts of detrital sediments due to a combination of climate change spreading of grasslands and the increasing importance of mountain chains such as the himalaya the associated high nutrient fluxes may have been involved in the backstepping and drowning of carbonate platforms and in the generation of widespread phosphat rich deposits during the late early and early middle miocene

mesozoic climates and oceans a tribute to hugh jenkyns and helmut weissert the study of past greenhouse climate intervals in earth history such as the mesozoic is an important relevant and dynamic area of research for many sedimentary geologists geochemists palaeontologists and climate modellers the mesozoic sedimentary record provides key insights into the mechanics of how the earth system works under warmer conditions providing examples of natural climate change and perturbations to ocean chemistry including anoxia that are of societal relevance for understanding and contextualizing ongoing and future environmental problems furthermore the deposition of widespread organic carbon rich sediments black shales during the mesozoic means that this is an era of considerable economic interest in july 2015 an international group of geoscientists attended a workshop in ascona switzerland to discuss all aspects of the mesozoic world and to celebrate the four decade long contributions to our understanding of this fascinating era in earth history made by hugh jenkyns university of oxford and helmut weissert eth zurich this volume of sedimentology arose from that meeting and contains papers inspired by and co authored by hugh and helmi here a brief introduction to the volume is provided that reviews aspects of hugh and helmi s major achievements contextualizes the papers of the thematic issue and discusses some of the outstanding questions and areas for future research this article is protected by copyright all rights reserved

miocene c isotope signature from the central apennine successions italy monterey vs regional controlling factors the c isotope composition of a miocene carbonate succession from the latium abruzzi sector of the central apennines was studied to evaluate the influence of local vs global factors in changing d 13 c we propose that the oligo miocene igneous activity of the western mediterranean and the closure of the indo pacific connection influenced climate change and mediterranean sea water circulation the huge aquitanian burdigalian volcanic activity during the formation of the

aphotic zone carbonate production on a miocene ramp central apennines italy the lower miocene latium abruzzi platform was a low angle ramp that developed under tropical to subtropical conditions but was dominated by bryomol and rhodalgal sediment associations the aquitanian to serravallian sequence described here paraconformably overlies the cretaceous limestones it consists of a lowstand systems tract a transgressive systems tract and a highstand systems tract based on facies analysis and on the light dependence of biotic associations the ramp is divided into three parts an inner ramp a middle ramp and an outer ramp the inner ramp facies are represented by a few metres of coral framestone rhodolith floatstone rudstone and balanid macroids floatstone without wave related structures the middle ramp consists of structureless bioclastic grainstone to packstone floatstone and rudstone with rhodoliths and larger foraminifera the outer ramp facies proximal sector are composed of crudely stratified bryozoan dominated packstone to floatstone which extend over the whole platform the outer ramp facies intermediate sector are represented by wackestone packstone and rarely grainstone with foraminifera and echinoid fragments the final depositional profile of the ramp was strongly influenced by the main organisms producing sediment during the lowstand the resulting profile is a ramp type during the transgressive phase the rapid spreading of the outer ramp facies belt as a consequence of the enhanced productivity of the light independent biota is believed to be promoted by a change from oligotrophic to eutrophic conditions climate and or tectonics are presumed to have played an important role in continental runoff and then in the nutrients delivery during the highstand phase the system returns to rates of production uniform throughout the platform the high rates of carbonate production occurring in the aphotic zone are quite unusual in tropical settings and represent a provocative trend in apparent contrast with the common idea about the locus of the most significant carbonate production as derived from the tropical model the example described here shows that carbonate production and accumulation below the photic zone might be higher than in the shallow euphotic zone even in tropical conditions d 2003 elsevier science b v all rights reserved

evolution of the northern nicaragua rise during the oligocene miocene drowning by environmental factors abstract possible causes to explain platform drowning have been hotly debated by carbonate sedimentologists for more than a decade now in this paper we present multiple evidence to explain the drowning of a carbonate megabank that covered most of the modern northern nicaragua rise nnr during an interval spanning from late oligocene to early miocene by the interaction of several environmental factors the recovery during odp leg 165 of late oligocene to middle miocene sedimentary sequences in the sub seafloor of the modern channels and basin pedro channel and walton basin respectively that dissect the nnr site 1000 and south of the rise in the colombian basin site 999 combined with information from dredged rock samples allows us to explore in more detail the timing and possible mechanisms responsible for the drowning of the megabank and its relationship to miocene climate change the modern system of isolated banks and shelves dissected by a series of intervening seaways and basins on the nnr has evolved from a continuous shallow water carbonate megabank that extended from the honduras nicaraguan mainland to the modern island of jamaica available information suggests that this megabank broke apart and partially drowned in the late part of the late oligocene at around 27 ma and finally foundered during the late early miocene around 20 ma resulting in limited neritic coral growth in the areas where the modern isolated carbonate banks and shelves are occurring today available information also suggests that the southern and central parts of pedro channel were already a deep water area before the major episode of platform drowning and its formation predates the initiation of the caribbean current however after the partial drowning of the megabank the channel has become a major pathway for the caribbean current stratigraphic units identified in deep water carbonates sampled at odp sites 999 and 1000 help to constrain the environmental setting leading to the drowning of the banks changes in lithology and mass accumulation rates of both the carbonate and non carbonate fraction parallel stable isotope shifts and likely indicate regional changes in climate and circulation during the late oligocene middle miocene interval carbonate mass accumulation rates mars at site 999 suggest increased regional productivity during the early miocene terrigenous mars at both sites 999 and 1000 show a general increase from the burdigalian through the serravallian the temporal association among episodes of neritic platform deposition followed by increased productivity as identified by higher carbonate mars and positive excursion in carbon isotopes suggests that oceanographic changes such as local upwelling and nutrification have led to the partial drowning of the nnr megabank

sea ice thickness from airborne laser altimetry over the arctic ocean north of greenland 1 we present a new method to measure ice thickness of polar sea ice freeboard heights using airborne laser altimetry combined with a precise geoid model giving estimates of thickness of ice through isostatic equilibrium assumptions in the paper we analyze a number of flights from the polar sea off northern greenland and estimate accuracies of the estimated freeboard values to be at a 13 cm level corresponding to about 1 m in absolute thickness

eustasy and sea water sr composition application to high resolution sr isotope stratigraphy of miocene shallow water carbonates oceanic 87 sr 86 sr isotope ratios are strongly influenced by rates of silicate weathering and therefore linked not only to glaciation but also to sea level change the present study combines analysis of sequence stratigraphy and basin architecture with sr isotope stratigraphy in miocene shallow water sediments in southern portugal and crete greece the common method is to use smoothed global sea water sr isotope reference curves but here a different approach is chosen instead measured sr isotope curves are correlated with unsmoothed reference curves by identification of similar fluctuations in the order of several 100 kyr transgressive intervals are characterized by increasing sr isotope ratios interpreted as corresponding to intensified silicate weathering as a consequence of deglaciation while lowstand deposits have low sr isotope ratios comparison of sr isotope curves and sedimentary sequences in the studied basins with independent global d 18 o data and data on global sea level might suggest a general relationship supporting a connection to global climate change because of these relationships the method presented herein has a high potential for use in high resolution age dating and is also applicable in shallow water sediments

direct helicopter em sea ice thickness inversion assessed with synthetic and field data accuracy and precision of helicopter electromagnetic hem sounding are the essential parameters for hem sea ice thickness profiling for sea ice thickness research the quality of hem ice thickness estimates must be better than 10 cm to detect potential climatologic thickness changes we introduce and assess a direct 1d hem data inversion algorithm for estimating sea ice thickness for synthetic quality assessment an analytically determined hem sea ice thickness sensitivity is used to derive precision and accuracy precision is related directly to random instrumental noise although accuracy is defined by systematic bias arising from the data processing algorithm for the in phase component of the hem response sensitivity increases with frequency and coil spacing but decreases with flying height for small scale hem instruments used in sea ice thickness surveys instrumental noise must not exceed 5 ppm to reach ice thickness precision of 10 cm at 15 m nominal flying height comparable precision is y

miocene rotation of sardinia new paleomagnetic and geochronological constraints and geodynamic implications the miocene rotation of sardinia western mediterranean remains poorly constrained despite a wealth of paleomagnetic data primarily due to poor chronostratigraphic control however this rotation is contemporaneous with the opening of the liguro provencal back arc oceanic basin and its history is key to understanding the kinematics of opening of the western mediterranean we address this issue through paleomagnetic and 40ar 39ar geochronological investigations of miocene volcanic sequences in sardinia precise age control allows secular variation of the geomagnetic field to be evaluated these data provide constraints on the rotational history of this continental microplate sardinia rotated 45 counterclockwise with respect to stable europe after 20 5 ma aquitanian which is a marked increase over the estimate of 30 derived from prior paleomagnetic studies rotation was essentially complete by 15 ma about 30 of rotation occurred between 20 5 and 18 ma burdigalian corresponding to the period of maximum volcanic activity in sardinia the observed rotation validates palinspastic models derived from a morphological fit of basin margins and indicates high rates of opening up to 9 cm yr 1 in the southern part of the basin between 20 5 and 18 ma

combined observations of arctic sea ice with near coincident colocated x band c band and l band sar satellite remote sensing and helicopter borne measurements in this study we compare colocated near coincident x c and l band fully polarimetry sar satellite images with helicopter borne ice thickness measurements acquired during the norwegian young sea ice 2015 n ice2015 expedition in the region of the arctic ocean north of svalbard in april 2015 the air borne surveys provide near coincident snow plus ice thickness surface roughness data and photographs this unique data set allows us to investigate how the different frequencies can complement one another for sea ice studies but also to raise awareness of limitations x band and l band satellite scenes were shown to be a useful complement to the standard sar frequency for sea ice monitoring c band for lead ice and newly formed sea ice identification this may be in part be due to the frequency but also the high spatial resolution of these sensors we found a relatively low correlation between snow plus ice thickness and surface roughness therefore in our dataset ice thickness cannot directly be observed by sar which has important implications for operational ice charting based on automatic segmentation

interannual variability of summer sea ice thickness in the siberian and central arctic under different atmospheric circulation regimes extensive drill hole and electromagnetic induction measurements of sea ice thickness in the siberian and central arctic seas in the summers of 1993 1995 and 1996 reveal significant interannual variability in the laptev sea minimum and maximum modal first year ice thicknesses amounted to 1 25 and 1 85 m in 1995 and 1996 respectively ice thickness correlates with ice extent which reached a record minimum in august 1995 and was well above average in 1996 these differences are explained by the strength and location of a summer cyclonic atmospheric circulation pattern affecting both ice advection and surface melt from drifting buoys deployed in 1995 and satellite radar backscatter data first and second year ice regimes are delineated differences in first year ice backscatter coefficients between 1993 1995 and 1996 are explained by differences in level ice surface roughness the lagrangian evolution of ice thickness between 1995 and 1996 is studied while the shape of the thickness distribution does not change significantly the mean modal ice thickness of the ice field increases from 1 80 m 1 25 m in 1995 to 2 86 m 2 25 m in 1996 the thickness distribution of second year ice in 1996 closely agrees with that of level multiyear ice downstream in the transpolar drift obtained in 1991 in 1996 mean level ice thickness increases at 0 23 and 0 16 m deg 1 with latitude in the kara and laptev sea sectors of the arctic ocean respectively

isotopic and chemical intra shell variations in low mg calcite of rudist bivalves mollusca hippuritacea disequilibrium fractionations and late cretaceous seasonality isotopic 13c 18o and elemental mg sr mn fe compositions were analysed in sclerochronological profiles of several shells of late cretaceous rudist bivalves from greece turkey somalia and the arabian peninsula the preservation of original compositions of low mg calcite of outer shell layers is indicated by constant and high sr generally low fe and mn and the preservation of fibrous prismatic ultrastructures cyclic variations in 18o and mg are interpreted to reflect seasonal temperature salinity cycles and thus annual growth increments in shells of torreites amplitudes of correlated 13c and 18o cycles cannot be related to reasonable palaeotemperatures or salinity this isotopic pattern reflects vital fractionations of an extent which is unknown from modern bivalves in contrast almost identical ranges and amplitudes of 18o cycles are observed in 13 shells of five species from santonian campanian localities in central greece and northern turkey suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations the effect of seasonal salinity changes on 18o of the shells is evaluated and mean palaeotemperatures are constrained within the range of 30 32 5 c the annual range of temperature was estimated to be 7 c assuming a constant salinity this agrees with other isotopic proxies of late cretaceous palaeotemperatures and with global circulation models which predict higher low latitude sea surface temperatures than the present ones

early marine lithification and hardground development on a miocene ramp maiella italy key surfaces to track changes in trophic resources in nontropical carbonate settings abstract phosphatic and carbonate hardgrounds occur in a lower miocene nontropical carbonate succession in the maiella carbonate platform margin located in the central apennines multiple diagenetic events occurred at or near the sea floor before the deposition of the overlying sediment and included precipitation of inclusion rich calcite micrite iron oxides and phosphates later diagenetic features are limited to chemical compaction and precipitation of clear calcite cement we relate the development of these features to a two step model involving progressive intensification of upwelling on this carbonate margin which was triggered by regional changes in water circulation and modulated by sea level changes leading initially to precipitation of inclusion rich calcite with an increase in trophic resources related to the paleoceanographic conditions on the ramp increased flux of organic matter to the sea floor led to temporary formation of microbial biofilms these conditions were associated with extensive precipitation of micrite and phosphate microspherules in the uppermost sediment the lack of sedimentation provides the precondition to accumulate and preserve evidence for organic matter utilization in the uppermost sediment layer our study suggests that hardgrounds in nontropical carbonates might be used as indicators of circulation changes and can provide a useful link to major environmental changes in the ocean margin environment the occurrence of microbial micrite and phosphate microspherules precipitated in the absence of sedimentation near the sea floor as a response to higher nutrient supply provides a new and important criterion to differentiate nontropical carbonate facies deposited under the influence of higher nutrient supplies rather than temperature alone furthermore our study shows that local depletion in 13c at a key stratigraphic surface does not necessarily reflect meteoric exposure but may be related to microbial activity at the sea floor

mapping arctic landfast ice extent using l band synthetic aperture radar interferometry in recent years methods have been developed to extract the seaward landfast ice edge from series of remote sensing images with most of them relying on incoherent change detection in optical infrared or radar amplitude imagery while such approaches provide valuable results some still lack the required level of robustness and all lack the ability to fully automate the detection and mapping of landfast ice over large areas and long time spans this paper introduces an alternative approach to mapping landfast ice extent that is based on coherent processing of interferometric l band synthetic aperture radar sar data the approach is based on a combined interpretation of interferometric phase pattern and interferometric coherence images to extract the extent and stability of landfast ice due to the low complexity of the base imagery used for landfast ice extraction significant improvements in automation and reduction of required manual interactions by operators can be achieved a performance analysis shows that l band interferometric sar insar data enable the mapping of landfast ice with high robustness and accuracy for a wide range of environmental conditions

the 2017 reversal of the beaufort gyre can dynamic thickening of a seasonal ice cover during a reversal limit summer ice melt in the beaufort sea during winter 2017 the semi permanent beaufort high collapsed and the anticyclonic beaufort gyre reversed the reversal drove eastward ice motion through the western arctic causing sea ice to converge against banks island and halted the circulation of multiyear sea ice via the gyre preventing its replenishment in the beaufort sea prior to the reversal an anomalously thin seasonal ice cover had formed in the beaufort following ice free conditions during september 2016 with the onset of the reversal in january 2017 convergence drove uncharacteristic dynamic thickening during winter by the end of march despite seasonal ice comprising 97 of the ice cover the reversal created the thickest roughest and most voluminous regional ice cover of the cryosat 2 record within the beaufort sea previous work has shown that winter ice export can precondition the region for increased summer ice melt but that a short reversal during april 2013 contributed to a reduction in summer ice loss hence the deformed ice cover at the end of winter 2017 could be expected to limit summer melt in spite of this the beaufort ice cover fell to its fourth lowest september area as the gyre re established during april and divergent ice drift broke up the pack negating the reversal s earlier preconditioning our work highlights that dynamic winter thickening of a regional sea ice cover for instance during a gyre reversal offers the potential to limit summer ice loss but that dynamic forcing during spring dictates whether this conditioning carries through to the melt season

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

oligocene and pliocene interglacial events in the antarctic peninsula dated using strontium isotope stratigraphy strontium isotope stratigraphy is used to date two interglacial marine deposits in the antarctic peninsula region on king george island interglacial pectinid rich sediments in the low head member of the polonez cove formation give a strontium isotope stratigraphy age of 29 0 0 7 0 6 to 29 8 0 8 0 7 ma mid oligocene which in conjunction with previous k ar dating of volcanic rocks indicates a glacial episode in the antarctic peninsula between middle eocene 42 0 1 0 ma and mid oligocene time in addition an inter glacial deposit pecten conglomerate from tectonically elevated exposures on cockburn island is dated as pliocene 3 5 5 3 ma published data suggest these latter sediments were deposited under shallow marine conditions which were warmer than those of present day antarctica

monitoring ice thickness and elastic properties from the measurement of leaky guided waves a laboratory experiment the decline of arctic sea ice extent is one of the most spectacular signatures of global warming and studies converge to show that this decline has been accelerating over the last four decades with a rate that is not reproduced by climate models to improve these models relying on comprehensive and accurate field data is essential while sea ice extent and concentration are accurately monitored from microwave imagery an accurate measure of its thickness is still lacking moreover measuring observables related to the mechanical behavior of the ice such as young s modulus poisson s ratio etc could provide better insights in the understanding of sea ice decline by completing current knowledge so far acquired mostly from radar and sonar data this paper aims at demonstrating on the laboratory scale that these can all be estimated simultaneously by measuring seismic waves guided in the ice layer the experiment consisted of leaving a water tank in a cold room in order to grow an ice layer at its sur

facies analysis and sequence stratigraphy of a miocene warm temperate carbonate ramp montagna della maiella italy abstract the uppermost oligocene lower miocene to upper miocene ramp carbonates from montagna della maiella italy form a supersequence bounded by deeply incised truncation surfaces this supersequence is subdivided into four sequences each sequence is composed of skeletal limestones in its lower part and marly limestones in its upper part the lower parts of the sequences are foramol limestones which suggest deposition in the warm temperate climate zone changes in climate oceanography and relative sea level combined to control sedimentation in the four sequences in the lower parts of the two older sequences the skeletal sands built dunes suggesting high energy conditions the dominant skeletal grains in the oldest sequence are larger foraminifers and in the next sequence they are bryozoans this change reflects cooling around the time of the aquitanian burdigalian boundary in the lower parts of the two younger sequences of middle and late miocene age sediment sheets with red algal bryozoan oncoids suggest deposition under calmer conditions transgressive and highstand systems tracts are recognized in all sequences a shelf margin systems tract may be exposed in the second oldest sequence in contrast to the situation that exists when warm water carbonates are deposited sedimentation of the foramol limestones on this isolated ramp was unable to balance accommodation during sea level rise this led to hemipelagic sedimentation during sea level highstands conglomerates resulted from reworking along flooding surfaces

perennial pack ice in the southern beaufort sea was not as it appeared in the summer of 2009 1 in september 2009 we observed a much different sea icescape in the southern beaufort sea than anticipated based on remotely sensed products radarsat derived ice charts predicted 7 to 9 tenths multi year my or thick first year fy sea ice throughout most of the southern beaufort sea in the deep water of the canada basin in situ observations found heavily decayed very small remnant my and fy floes interspersed with new ice between floes in melt ponds thaw holes and growing over negative freeboard older ice this icescape contained approximately 25 open water predominantly distributed in between floes or in thaw holes connected to the ocean below although this rotten ice regime was quite different that the expected my regime in terms of ice volume and strength their near surface physical properties were found to be sufficiently alike that their radiometric and scattering characteristics were almost identical

the monterey event in the mediterranean a record from shelf sediments of malta oligo miocene carbonate platform and shelf sediments outcropping on the maltese islands provide an excellent archive of the paleoceanography of the central mediterranean a sequence of shallow water limestones than shelf limestones and marls followed again by shallow water limestones reflects drowning of a carbonate platform the establishment of a shelf environment and in the late miocene renewed progradation and aggradation of shallow water carbonates the sequence recording the deepening of the maltese platform contains several phosphorite hardgrounds and phosphorite pebble beds these phosphorites were dated with strontium isotopes major episodes of phosphogenesis occurred between 25 and 16 ma and they are coeval with those phosphorite events reported from florida and north carolina a miocene carbon isotope and oxygen isotope stratigraphy was established on planktic and benthic foraminifera and on bulk samples a major carbon isotope excursion with an amplitude of up to l between 18 and 12 5 ma can be correlated with the globally recognized monterey carbon isotope excursion this is the first record of this event both in shallow water sediments and in the mediterranean the carbon isotope excursion precedes an oxygen isotope excursion which also was recognized in deep sea records major episodes of phosphogenesis and platform drowning preceded the carbon isotope excursion by up to millions of years

nutrients sea level and tectonics constrains for the facies architecture of a miocene carbonate ramp in central italy in the western part of the central apennines lower middle miocene carbonates were deposited on a tropical subtropical carbonate ramp they record two long term cycles the first of which is illustrated in this paper between 21 and 17 5 ma miocene carbonates paraconformably overlying the cretaceous limestones record a transgressive event during a time of global 2nd order sea level lowstand it is postulated that this deviation is related to an increase in tectonic subsidence between 17 5 ma and 16 15 ma with a progressive relative sea level rise the inner middle ramp facies belt stepped back whereas the bryozoan dominated outer ramp facies belt stepped back but simultaneously prograded this bloom of suspension feeding organisms is interpreted to reflect an increased nutrient availability hence a change from oligotrophic to eutrophic conditions strontium isotope dates constrain correlation of the second phase with a eutrophic event possibly linked to the influence of the neighbouring apenninic accretionary wedge and foredeep system

arctic sea ice conditions in spring 2009 2013 prior to melt 1 measurements from nasa icebridge airborne surveys in march april 2009 2013 over the western arctic ocean are presented in the context of previous observations to assess changes in the characteristics of the sea ice cover during the last decade taking into account spatial and temporal limitations in the available data following a precipitous drop in the amount and thickness of multiyear my ice in 2007 2008 the characteristics of the ice cover have remained largely consistent through march 2013 the central arctic continues to be dominated by my ice with mean and modal thicknesses of 3 2 m and 2 4 m respectively the southern beaufort and chukchi sea region is a complex mixture of 75 first year ice and 25 my ice icebridge observations indicate that the mean thickness in the beaufort and chukchi seas may have decreased from 2 5 m to as low as 1 6 m over the 5 year period

global dominance of coralline red algal facies a response to miocene oceanographic events rhodoliths free living coralline red algae can thrive under a wide range of temperatures reduced light and increased nutrient levels and often form a distinct so called rhodalgal lithofacies that is an important component of cenozoic shallow water carbonates global distributions illustrate that from the late early to early late miocene burdigalian early tortonian rhodalgal facies reached peak abundances and commonly replaced coral reef environments accompanied by a decline in other carbonate producing phototrophs we argue that the dominance of red algae over coral reefs was triggered in the burdigalian by enhanced trophic resources associated with a global increase in productivity as evidenced by a long term shift toward higher carbon isotope values rhodalgal lithofacies expanded further in the middle miocene when strengthened thermal gradients associated with the establishment of the east antarctic ice sheet led to enhanced upwelling while climate change generated increased weathering rates introducing land derived nutrients into the oceans globally cooler temperatures following a climatic optimum in the early middle miocene contributed to sustain the dominance of red algae and prevented the recovery of coral reefs the global shift in nearshore shallow water carbonate producers to groups tolerant of higher levels of trophic resources provides further evidence for increased nutrient levels during that time interval and shows the sensitivity of shallow water carbonate facies as indicators of past oceanographic conditions

synoptic airborne thickness surveys reveal state of arctic sea ice cover 1 while summer arctic sea ice extent has decreased over the past three decades it is subject to large interannual and regional variations methodological challenges in measuring ice thickness continue to hamper our understanding of the response of the ice thickness distribution to recent change limiting the ability to forecast sea ice change over the next decade we present results from a 2400 km long pan arctic airborne electromagnetic em ice thickness survey in april 2009 the first ever large scale em thickness dataset obtained by fixed wing aircraft over key regions of old ice in the arctic ocean between svalbard and alaska the data provide detailed insight into ice thickness distributions characteristic for the different regions comparison with previous em surveys shows that modal thicknesses of old ice had changed little since 2007 and remained within the expected range of natural variability

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum september 2007 marked a record minimum in sea ice extent while there have been many studies published recently describing the minimum and its causes little is known about how the ice thickness has changed in the run up to and following the summer of 2007 using satellite radar altimetry data covering the arctic ocean up to 81 5 degrees north we show that the average winter sea ice thickness anomaly after the melt season of 2007 was 0 26 m below the 2002 2003 to 2007 2008 average more strikingly the western arctic anomaly was 0 49 m below the six year mean in the winter of 2007 2008 these results show no evidence of short term preconditioning through ice thinning between 2002 and 2007 but show that after the record minimum ice extent in 2007 the average ice thickness was reduced particularly in the western arctic citation giles k a s w laxon and a l ridout 2008 circumpolar thinning of arctic sea ice following the 2007 record ice extent minimum geophys res lett 35 l22502 doi 10 1029 2008gl035710

a younger thinner arctic ice cover increased potential for rapid extensive sea ice loss 1 satellite derived estimates of sea ice age and thickness are combined to produce a proxy ice thickness record for 1982 to the present these data show that in addition to the well documented loss of perennial ice cover as a whole the amount of oldest and thickest ice within the remaining multiyear ice pack has declined significantly the oldest ice types have essentially disappeared and 58 of the multiyear ice now consists of relatively young 2 and 3 year old ice compared to 35 in the mid 1980s ice coverage in summer 2007 reached a record minimum with ice extent declining by 42 compared to conditions in the 1980s the much reduced extent of the oldest and thickest ice in combination with other factors such as ice transport that assist the ice albedo feedback by exposing more open water help explain this large and abrupt ice loss

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

comparison of the sea ice thickness distribution in the lincoln sea and adjacent arctic ocean in 2004 and 2005 results of helicopter borne electromagnetic measurements of total ice plus snow sea ice thickness performed in may 2004 and 2005 in the lincoln sea and adjacent arctic ocean up to 868 n are presented thickness distributions south of 848 n are dominated by multi year ice with modal thicknesses of 3 9 m in 2004 and 4 2 m in 2005 mean thicknesses 4 67 and 5 18 m respectively modal and mean snow thickness on multi year ice amounted to 0 18 and 0 30 m in 2004 and 0 28 and 0 35 m in 2005 there are also considerable amounts of 0 9 2 2 m thick first year ice modal thickness mostly representing ice formed in the recurring refrozen lincoln polynya results are in good agreement with ground based electromagnetic thickness measurements and with ice types demarcated in satellite synthetic aperture radar imagery four drifting buoys deployed in 2004 between 868 n and 84 58 n show a similar pattern of a mean southward drift of the ice pack of 83 18 km between may 2004 and april 2005 towards the coast of ellesmere island and nares strait the resulting area decrease of 26 between the buoys and the coast is larger than the observed thickness increase south of 848 n this points to the importance of shear in a narrow band along the coast and of ice export through nares strait in removing ice from the study region

the nature of the δ13c of periplatform sediments implications for stratigraphy and the global carbon cycle the carbon isotopic composition y 13 c of bulk carbonates obtained from a transect of sites drilled through platform and periplatform sediments of holocene to early miocene age has been compared to ascertain whether changes in the y 13 c can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the y 13 c of the dissolved inorganic carbon in the oceans over this time period five of the sites were drilled during leg 166 of the ocean drilling project 1003 1007 in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of holocene to oligocene age that are contained in 17 depositional sequences a q two shallow water sites clino and unda were situated on a extension of the same transect on great bahama bank in a water depth of 10 15 m with the exception of unda and clino the y 13 c of the carbonates ranges from 5x in the younger sequences to 1x in the early miocene in each of the sites the y 13 c is strongly positively correlated with the percentage of aragonite as a consequence the y 13 c of sequences a through f is strongly correlated reflecting the decreasing amount of aragonite with increasing depth in the two platform sites the y 13 c is significantly lower in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the pleistocene although the y 13 c of the individual sequences can be correlated in most instances between the odp holes the changes are not related to global changes in the y 13 c of the oceans which in contrast to the y 13 c of the platform sediments become isotopically lower towards the present day instead variations in the y 13 c appear to be related to varying mixtures of y 13 c rich banktop sediments and pelagic material

oceanographic and climatic evolution of the miocene mediterranean deduced from nd sr c and o isotope compositions of marine fossils and sediments isotopic compositions of marine sediments and fossils have been investigated from northern basins of the mediterranean to help constrain local oceanographic and climatic changes adjacent to the uplifting alps stable c and o isotope compositions of benthic and planktonic foraminifera from the umbria marche region umc have an offset characteristic for their habitats and the changes in composition mimic global changes suggesting that the regional conditions of climate and the carbon cycle were controlled by global changes the radiogenic isotope composition of these fossil assemblages allows recognition of three distinct periods in the first period from 25 to 19 ma high nd values and low 87sr 86sr of sediments and fossils support intense tectonism and volcanism related to the opening of the western mediterranean in the second period from 19 to 13 ma the 87sr 86sr ratio of mediterranean umc deviate from the global ocean which is compatible with rapid uplift of the hinterland and intense influx of sr from mesozoic carbonates of the western apennines this local control on the seawater was driven by a humid and warm climate and indicates restricted exchange of water with the global ocean generally the nd values of the fossils are very similar to those of indian ocean water with brief periods of a decrease in the nd values coinciding with volcanic events and maybe sea level variation at 15 2 ma in the third period from 13 to 10 ma the fossils have 87sr 86sr similar to those of miocene seawater while their nd values change considerably with time this indicates fluctuating influence of the atlantic versus the paratethys and or locally evolved seawater in the mediterranean driven by global sea level changes other investigated localities near the alps and from the odp 900 site are compatible with this oceanographic interpretation however in the late early miocene enhanced local control reflecting erosion of old crustal silicate rocks near the alps results in higher 87sr 86sr

p t x conditions on the genesis of orogenic au as bi ag deposit in metasedimentary rocks of the buracao area arai group brasilia fold belt brazil the orogenic au as bi ag mineralization up to 31 g t of the buracao area is hosted in the metasedimentary paleo mesoproterozoic trairas formation arai group brasilia fold belt brazil in order to discuss the p t x conditions that generated this mineralization we present mineralogical geochemical and fluid inclusion data of veins gold and wall rocks coupled with previous structural data these additional data allow us to link metamorphism and deformation with fluid migration and ore genesis the integration of fluid inclusion microthermometry with mineral geothermobarometers and structures show that rocks of the study area evolved from i syn d1a metamorphic peak 400 560 c 6 kbar through to the ii development of syn d1b type i barren veins from low salinity h2o nacl fluids during syn to late metamorphic peak and to the iii development of syn d2a type ii veins with the pyritic ore precipitation from low to high salinity h2o co2 ch4 nacl hco3 fluids during post metamorphic peak 345 285 c 2 7 1 6 kbar the high fineness gold nuggets accompanied by as bi and ag within pyrite arsenopyrite bismuthinite association in the pyritic ore allows the buracao area to be classified as a gold only orogenic ore deposit fluid inclusion compounds and the enrichment of as bi pb cu te se and ag in pyrite from the pyritic ore point out to metamorphism of carbonaceous phyllites and carbonate rocks of the trairas formation as a source for ore forming fluids we suggest that sulfur and gold in these fluids were derived by metamorphism of sedimentary rocks and conversion of pyrite into pyrrhotite in a metamorphic hydrothermal system the au hs 2 bearing fluids percolated along intrabasinal d2a regional shear zones through the trairas formation towards the buracao area where they precipitated type ii ore bearing veins within local structures the ore precipitation was induced by contrasting fo2 fs2 related to the interaction between the sulfur bearing fluid and host magnetite graphite phyllites the lithological control is represented by a series of reactions such as 2feo in silicates magnetite 4au hs 2 aq 4h aq 2fes2 s 4au s 4h2s aq 2h2o l the deposits of the buracao area and other orogenic gold deposits hosted in metasedimentary rocks in the brasilia fold belt and worldwide confirm the potential of ore genesis in zones that do not show any relation with meta igneous rocks thus expanding the exploration possibilities in metasedimentary successions

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

uncertainty in modeled arctic sea ice volume 1 uncertainty in the pan arctic ice ocean modeling and assimilation system piomas arctic sea ice volume record is characterized a range of observations and approaches including in situ ice thickness measurements icesat retrieved ice thickness and model sensitivity studies yields a conservative estimate for october arctic ice volume uncertainty of 1 35 103 km3 and an uncertainty of the ice volume trend over the 1979 2010 period of 1 0 103 km3 decade 1 a conservative estimate of the trend over this period is 2 8 103 km3 decade 1 piomas ice thickness estimates agree well with icesat ice thickness retrievals 0 1 m mean difference for the area for which submarine data are available while difference outside this area are larger piomas spatial thickness patterns agree well with icesat thickness estimates with pattern correlations of above 0 8 piomas appears to overestimate thin ice thickness and underestimate thick ice yielding a smaller downward trend than apparent in reconstructions from observations piomas ice volume uncertainties and trends are examined in the context of climate change attribution and the declaration of record minima the distribution of 32 year trends in a preindustrial coupled model simulation shows no trends comparable to those seen in the piomas retrospective even when the trend uncertainty is accounted for attempts to label september minima as new record lows are sensitive to modeling error however the september 2010 ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record

global versus regional influence on the carbonate factories of oligo miocene carbonate platforms in the mediterranean area abstract the oligocene miocene is a key interval that was characterized by a cooling trend associated with a progressive decrease of atmospheric co2 concentrations that ends in the present days in the central mediterranean area during this interval three main carbonate platform domains developed in the foreland zone of the apennines the latium abruzzi campana and apulia domain in the central and south eastern sectors of the chain and the hyblea and pelagian carbonate platforms in the south and south western sectors this work analyzes the impact and interplay of global and regional factors controlling the development of different carbonate factories and facies associations over the chattian and the early messinian time interval three well studied examples of the central mediterranean will be used the chattian ramp of malta the latium abruzzi ramp and the bolognano ramp within the northern portion of the apulian carbonate platform outcropping on majella mountain the malta ramp represents the reference model for the heterozoan oligo miocene carbonate factory since it developed far from terrigenous input in persistent oligotrophic conditions and within a tropical climate in contrast the evolution of the central apennine ramps is strictly related to the geodynamic evolution of the apennines and simultaneously to global oceanographic changes the chattian apennine ramps are affected by a basin conformation that favored the development of dominant currents and related dune fields successively these ramps were exposed to strong aquitanian volcanism that induced a shift towards an aphotic dominated carbonate factory since the burdigalian the development of the apennines has affected the evolution of the investigated ramps through the eastward migration of foredeep systems and related nutrient input this influence becomes more evident between the tortonian and messinian during which reef rimmed platforms developed in the rest of the mediterranean while red algae still dominated in the apennine ramps amongst the global events the c cycle perturbation occurring between the late burdigalian and serravallian monterey event leaves a clear sign on the two apennine ramps

origin and significance of isotope shifts in pennsylvanian carbonates asturias nw spain abstract the primary variability of the composition and properties of seawater is much greater in the shallow coastal zones than in the main body of ocean water an inadequate understanding of this variability as well as different diagenetic environments severely limit the interpretation of the stable isotope record of shoalwater carbonates in order to investigate this primary and diagenetic variability along a bashkirian moscovian platform to basin transect 13c and 18o analyses have been performed on more than 1000 matrix micrite carbonate cement and brachiopod shell samples in isotope analysis these different carbonate materials tend to complement each other inasmuch as they have different advantages and shortcomings the resulting data reveal spatial trends in 13c and 18o signatures from platform top lower values to basin higher values in the case of 13c from pristine brachiopods this trend can be explained by the long residence time aging of platform top water masses in the case of brachiopod 18o this variance is interpreted to reflect temperature differences between warm surface and colder bottom water separated by a permanent thermocline at about 150 to 200 m beneath the shelf break micrite and marine cement isotopic values from the platform interior were reset lowered during pervasive early meteoric diagenesis in contrast micrite and marine cement isotopic values from the outer platform slope and basin show higher values close to the assumed pennsylvanian seawater isotopic composition this implies that isotopic data from shoalwater carbonates including pristine brachiopod shells might not necessarily reflect paleoceanographic trends of the open ocean water masses because of changes in coastal water mass isotope signature and interaction with early meteoric fluids

high resolution ice volume estimates for the early miocene evidence for a dynamic ice sheet in antarctica ice volume estimates for the early miocene 23 16 ma ats were determined by applying d 18 o to sea level calibrations to high resolution d 18 o records from odp sites 1090 and 1218 these calibrated records indicate that ice volume ranged between 50 and 125 of the present day east antarctic ice sheet eais during most of the early miocene 23 17 ma maximum icevolume occurred at each of the early miocene isotopic events i e mi events concomitant with bottom water temperatures generally between 1 and 2 8c rapid bb 1 myr and high amplitude ice volume changes also occurred intermittently during this period with some fluctuations ranging from a fully glaciated east antarctic continent to a partial collapse of the ice sheet equivalent to a 50 70 reduction in the eais these large scale ice volume changes often occurred at b100 kyr time scales suggesting an orbitally driven dynamic eais existed during the early miocene in contrast the calibrated d 18 o record from site 1090 indicates significantly less ice volume 25 70 of the present day eais was present between 17 and 16 ma these results are supported by numerical climate ice sheet modeling studies that show increased orbitally driven ice volume variability with elevated levels of atmospheric co2 the distribution of bottom water masses during the miocene was likely significantly different from today owing to variability in the production of deep water near the antarctic continent i e proto antarctic bottom water proto aabw weakening of proto aabw is suggested to have occurred during the early miocene especially during glacial minima resulting in it becoming more spatially restricted to the southern ocean and becoming entrained into a warmer deep water mass increased production of a warmer bottom water mass is also considered to have been important in the lighter isotopic values observed in the atlantic and indian oceans these changes are supported by evidence of a large dynamic eais based on strata cored on the antarctic margin and require a reevaluation of the view that antarctic ice volume was significantly reduced for most of the early miocene previous estimates have been constrained by the lack of deep water isotopic records proximal to antarctica and unduly influenced by the expansion of warmer deep water into most of the ocean basins at this time d 2005 elsevier b v all rights reserved

orbitally paced climate evolution during the middle miocene monterey carbon isotope excursion one of the most enigmatic features of cenozoic long term climate evolution is the long lasting positive carbon isotope excursion or monterey excursion which started during a period of global warmth after 16 9 ma and ended at similar to 13 5 ma approximately 400 kyr after major expansion of the antarctic ice sheet we present high resolution 1 9 kyr astronomically tuned climate proxy records in two complete sedimentary successions from the northwestern and southeastern pacific odp sites 1146 and 1237 which shed new light on the middle miocene carbon isotope excursion and associated climatic transition over the interval 17 1 12 7 ma we recog nize three distinct climate phases with different imprints of orbital variations into the climatic signals 1146 and 123 7 delta 18 o delta 13 c 1237 xrt fe fraction 63 pm 1 climate optimum prior to 14 7 ma characterized by minimum ice volume and prominent 100 and 400 kyr variability 2 long term cooling from 14 7 to 13 9 ma principally driven by obliquity and culminating with rapid cryosphere expansion and global cooling at the onset of the last and most pronounced delta 13 c increase 3 icehouse mode after 13 9 ma with distinct 100 kyr variability and improved ventilation of the deep pacific the monterey carbon isotope excursion 16 9 13 5 ma consists overall of nine 400 kyr cycles which show high coherence with the long eccentricity period superposed on these low frequency oscillations are high frequency variations 100 kyr which closely track the amplitude modulation of the short eccentricity period in contrast to delta 13 c the delta 18 o signal additionally shows significant power in the 41 kyr band and the 1 2 myr amplitude modulation of the obliquity cycle is clearly imprinted in the 1146 delta 18 o signal our results suggest that eccentricity was a prime pacemaker of middle miocene climate evolution through the modulation of long term carbon budgets and that obliquity paced changes in high latitude seasonality favored the transition into the icehouse climate c 2007 elsevier b v all rights reserved

miocene heterozoan carbonate systems from the western atlantic equatorial margin in south america the pirabas formation abstract outcrops of neogene carbonates of the north brazilian platform occur exclusively along the equatorial coast and represent some of the few existing examples of neogene carbonate systems of the atlantic coast of south america the pirabas formation early middle miocene is the northernmost part of this platform although onshore mainly consists of small and scattered outcrops it considerably extends in the subsurface keeping record of relevant geological and paleontological episodes of tropical south american history intending to improve the knowledge of south american carbonate and providing a solid basis for future comparisons between the pirabas basin and other largely subsurface cenozoic basins this research investigates the aricuru outcrops by combining a standard petrographical and paleontological approach with advanced microct analyses the aricuru area is characterized by mixed siliciclastic carbonate sand sized deposits which probably deposited after the early miocene according to the palynological assemblage the bioclastic fraction of the rock is dominated by benthic foraminifera mostly soritids amphisteginids small rotaliids and small miliolids typical of marginal marine environments bryozoans calcareous algae halimeda echinoderms and mollusks the abundant siliciclastic fraction together with the taxonomic composition of the foraminiferal echinodermal crustacean ichnofossil and fish assemblages indicates deposition in a tropical coastal environment featuring both protected and more exposed sectors the carbonate system probably developed under abundant nutrient supply which fostered heterotroph suspension feeders over hermatypic corals the demise of this system was most likely caused by a growth in siliciclastic input due to increased rainfall in the coastal area the sedimentary evolution of the pirabas formation is similar to the one of the foz do amazonas basin and fits well with the general evolutionary trend of cenozoic carbonate factories of the region indicating the potential of the pirabas subsurface record for understanding other cenozoic basins their paleoenvironmental significance and their potential as oil gas and water reservoirs

orbitally induced climate and geochemical variability across the oligocene miocene boundary to assess the influence of orbital scale variations on late oligocene to early miocene climate and ocean chemistry high resolution 5 kyr benthic foraminiferal carbon and oxygen isotope and percent coarse fraction time series were constructed for ocean drilling program site 929 on ceara rise in the western equatorial atlantic these time series exhibit pervasive low to high frequency variability across a 5 myr interval 20 5 25 4 ma the records also reveal several large scale secular variations including two positive 1 6 oxygen isotope excursions at 22 95 and 21 1 ma suggestive of large but brief glacial maxima mi 1 and mi 1a events of miller et al 1991 and a long term cyclical increase in the carbon isotopic composition of seawater shift of 1 52 that reaches a maximum coincident with peak 18o values at 22 95 ma lower resolution 25 kyr records constructed from benthic and planktonic foraminifera as well as bulk carbonate at a shallower site on ceara rise site 926 for the period 21 7 24 9 ma covary with site 929 18o values reflecting changes in antarctic ice volume likewise covariance among carbon isotopic records of bulk sediment benthic and planktonic foraminifera suggest that the low frequency cycles 400 kyr and long term increase in 13c values represent changes in the mean carbon composition of seawater co2 the time series presented here constitute the longest most continuous and highest resolution records of pre pliocene climate and oceanography to date the site 929 carbon and oxygen isotope power spectra show significant concentrations of variance at 400 100 and 41 kyr demonstrating that orbitally induced oscillations have been a normal characteristic of the global climate system since at least the oligocene including periods of equable climate and times with no apparent northern component water production

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer