oceanic cooling recorded in shells spanning the medieval climate anomaly in the subtropical eastern north atlantic ocean abstract the medieval climate anomaly mca 900 1300 ad was the most recent period of pre industrial climatic warming in the northern hemisphere and thus estimations of mca signals can illuminate possible impacts of anthropogenic climate change current high resolution mca climate signals are restricted to mid and high latitude regions which confounds inferences of how the mca impacted some global hemispheric climate mechanisms e g north atlantic oscillation nao to address this knowledge gap we estimate seasonally resolved sea surface temperatures ssts from the oxygen isotope composition 18o of serially sampled phorcus atratus shells from archaeological sites spanning the mca in the canary islands twelve archaeological and six modern p atratus shells were analyzed and archaeological shells were dated using carbonate target radiocarbon dating ssts were estimated using the published aragonite water equilibrium fractionation equation modern shells showed a mean sst of 20 0 1 5 c with a seasonal amplitude of 5 3 0 9 c archaeological shells exhibited a mean sst of 18 2 0 7 c with a mean seasonal amplitude of 5 5 1 0 c thus shells that span the mca in the canary islands recorded ssts that were significantly cooler than the modern p

oxygen and carbon isotopes in planktonic foraminifera as indicators of upwelling intensity and upwelling induced high productivity in sediments from the northwestern arabian sea

a major holocene enso anomaly during the medieval period 1 here we present a high resolution marine el nino flood record from peru a period of extreme drought without strong flooding occurred from a d 800 1250 anomalous precipitation patterns characterized the entire indo pacific enso domain with dry events in the northern arabian sea and the mid latitudes of both americas coinciding with wet periods in the atlantic cariaco basin the occurrence of contemporaneous moisture anomalies in other archives in the enso region highlights the role of el nino strength in global climate evolution during the late medieval period when temperature reconstructions show a rather heterogeneous pattern

the 13c suess effect in scleractinian corals mirror changes in the anthropogenic co2 inventory of the surface oceans 1 new 13 c data are presented from 10 coral skeletons collected from florida and elsewhere in the caribbean dominica dominican republic puerto rico and belize these corals range from 96 to 200 years in age and were collected between 1976 and 2002 the change in the 13 c of the skeletons from these corals between 1900 and 1990 has been compared with 27 other published coral records from the atlantic pacific and indian oceans the new data presented here make possible for the first time a global comparison of rates of change in the 13 c value of coral skeletons of these records 64 show a statistically significant p 0 05 decrease in 13 c towards the modem day 23 out of 37 this decrease is attributable to the addition of anthropogenically derived co 2 13 c suess effect to the atmosphere between 1900 and 1990 the average rate of change of the 13 c in all the coral skeletons living under open oceanic conditions is approximately 0 01 o yr 1 in the atlantic ocean the magnitude of the decrease since 1960 0 019 yr 1 0 015 is essentially the same as the decrease in the 13 c of atmospheric co 2 and the 13 c of the oceanic dissolved inorganic carbon 0 023 to 0 029 yr 1 while in the pacific and indian oceans the rate is more variable and significantly reduced 0 007 yr 1 0 013 these data strongly support the notion that i the 13 c of the atmosphere controls ambient 13 c of the dissolved inorganic carbon which in turn is reflected in the coral skeletons ii the rate of decline in the coral skeletons is higher in oceans with a greater anthropogenic co 2 inventory in the surface oceans iii the rate of 13 c decline is accelerating superimposed on these secular variations are controls on the 13 c in the skeleton governed by growth rate insolation and local water masses

calibration of the oxygen isotope ratios of the gastropods patella candei crenata and phorcus atratus as high resolution paleothermometers from the subtropical eastern atlantic ocean abstract the oxygen isotope composition 18o recorded in shells of the gastropods patella candei crenata and phorcus atratus from the canary islands 27 29 n potentially provide invaluable high resolution paleoclimatic data however because these two species have never been studied isotopically it is necessary to calibrate and validate this approach by using live collected specimens that can be compared to present day climate data for p candei crenata live organisms were collected at 15 day intervals for nearly one year between 2011 and 2012 from the rocky intertidal coast of se tenerife along with sea surface temperatures sst and seawater 18o values the 18o values of the last growth episode along the shell growth margin representing the conditions when organisms were collected illustrate that p candei crenata 18o values were 1 3 0 2 higher than expected values from isotopic equilibrium this finding resulted in estimated sst 5 7 0 6 c lower than observed values this offset or vital effect is uniform and predictable and therefore can be corrected by subtracting 1 3 from the measured shell 18o value adjusted temperatures from the shell coincided with observed sst in the study area therefore patella candei crenata shells are reliable repositories of sst data in agreement with other species of patella from higher latitudes for phorcus atratus a live specimen was analyzed isotopically along shell growth direction the intrashell 18o values showed the entire range of measured sst in the region without an apparent vital effect in correspondence with other phorcus species from the mediterranean both patella candei crenata and phorcus atratus are common components of archaeological and pleistocene holocene paleontological sites across the canary archipelago this study suggests that well preserved shells of these two taxa retrieved from ancient settings have the capacity to serve as excellent high resolution paleotemperature archives for the tropical subtropical eastern atlantic region

testing and parameterizing a conceptual model for solute transport in a fractured granite using multiple tracers in a forced gradient test 1 a cross hole tracer test involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients bromide and pentafluorobenzoate and a weakly sorbing solute tracer lithium ion was conducted in a fractured granite near an underground nuclear test cavity in central nevada the test was conducted to 1 test a conceptual radionuclide transport model for the site and 2 obtain transport parameter estimates for predictive modeling the differences between the responses of the two nonsorbing tracers when normalized to injection masses are consistent with a dual porosity transport system in which matrix diffusion is occurring the large concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggests that diffusion occurs primarily into matrix pores not simply into stagnant water within the fractures the relative responses of the tracers at late times suggest that the diffusion accessible matrix pore volume is possibly limited to only half the total volume of the flow system implying that the effective retardation factor due to matrix diffusion may be as small as 1 5 for nonsorbing solutes in the system the lower end of the range of possible sorption kd values deduced from the lithium response is greater than the upper 95 confidence bound of kd values measured in laboratory sorption tests using crushed granite from the site this result suggests that the practice of using laboratory sorption data in field scale transport predictions of cation exchanging radionuclides such as 137cs and 90sr should be conservative for the shoal site

sorbing tracer experiments in a crystalline rock fracture at aspo sweden 2 transport model and effective parameter estimation 1 transport and retention of sorbing tracers in a single altered crystalline rock fracture on a 5 m scale is investigated we evaluate the results of a comprehensive field study referred to as

decoupling of coral skeletal δ13c and solar irradiance over the past millennium caused by the oceanic suess effect many factors influence the seasonal changes in c levels in coral skeletons consequently the climatic and environmental significance of such changes is complicated and controversial however it is widely accepted that the secular declining trend of coral c over the past 200 years reflects the changes in the additional flux of anthropogenic co from the atmosphere into the surface oceans even so the centennial scale variations and their significance of coral c before the industrial revolution remain unclear based on an annually resolved coral c record from the northern south china sea the centennial scale variations of coral c over the past millennium were studied the coral c and total solar irradiance tsi have a significant positive pearson correlation and coupled variation during the medieval warm period and little ice age when natural forcing controlled the climate and environment this covariation suggests that tsi controls coral c by affecting the photosynthetic activity of the endosymbiotic zooxanthellae over centennial timescales however there was a decoupling of the coral skeletal c and tsi during the current warm period the period in which the climate and environment became linked to anthropogenic factors instead coral c levels have a significant pearson correlation with both the atmospheric co concentration and c levels in atmospheric co the correlation between coral c and atmospheric co suggests that the oceanic c suess effect caused by the addition of increasing amounts of anthropogenic co to the surface ocean has led to the decoupling of coral c and tsi at the centennial scale

continuous marine radiocarbon reservoir calibration and the 13c suess effect in the irish sea results from the first multi centennial shell based marine master chronology abstract the identification in various proxy records of periods of rapid decadal scale climate change over recent millennia together with the possibility that feedback mechanisms may amplify climate system responses to increasing atmospheric co2 highlights the importance of a detailed understanding at high spatial and temporal resolutions of forcings and feedbacks within the system such an understanding has hitherto been limited because the temperate marine environment has lacked an absolute timescale of the kind provided by tree rings for the terrestrial environment and by corals for the tropical marine environment here we present the first annually resolved multi centennial 489 year absolutely dated shell based marine master chronology the chronology has been constructed by detrending and averaging annual growth increment widths in the shells of multiple specimens of the very long lived bivalve mollusc arctica islandica collected from sites to the south and west of the isle of man in the irish sea the strength of the common environmental signal expressed in the chronology is fully comparable with equivalent statistics for tree ring chronologies analysis of the 14c signal in the shells shows no trend in the marine radiocarbon reservoir correction r although it may be more variable before 1750 the 13c signal shows a very significant r2 0 456 p

aminochronology and time averaging of quaternary land snail assemblages from colluvial deposits in the madeira archipelago portugal understanding the properties of time averaging age mixing in a stratigraphic layer is essential for properly interpreting the paleofauna preserved in the geologic record this work assesses the age and quantifies the scale and structure of time averaging of land snail rich colluvial sediments from the madeira archipelago portugal by dating individual shells using amino acid racemization calibrated with graphite target and carbonate target accelerator mass spectrometry radiocarbon methods gastropod shells of actinella nitidiuscula were collected from seven sites on the volcanic islands of bugio and deserta grande desertas islands where snail shells are abundant and well preserved in quaternary colluvial deposits results show that the shells ranged in age from modern to 48 cal ka bp calibrated radiocarbon age covering the last glacial and present interglacial periods snail shells retrieved from two of the colluvial sites exhibit multimillennial age mixing 6 ka which significantly exceeds the analytical error from dating methods and calibration the observed multimillennial mixing of these assemblages should be taking into consideration in upcoming paleoenvironmental and paleoecological studies in the region the extent of age mixing may also inform about the time span of colluvial deposition which can be useful in future geomorphological studies in addition this study presents the first carbonate target radiocarbon results for land snail shells and suggests that this novel rapid and more affordable dating method offers reliable age estimates for small land snail shells younger than 20 cal ka bp

testing the robustness of a precipitation proxy based north atlantic oscillation reconstruction abstract the reconstruction of past atmospheric circulation is crucial for the understanding of natural climate change and its driving factors a recent reconstruction suggests that during medieval times the european region was dominated by a persistent positive phase of the north atlantic oscillation nao followed by a shift to a more oscillatory behavior we test this hypothesis and the concept underlying the reconstruction in a pseudo proxy approach using instrumental records reanalysis data sets and millennial simulations with four different climate models while a shift from a more positive to a more negative phase of the nao seems to be likely the amplitude and persistence of the reconstructed positive phase cannot be reproduced by models the analysis further reveals that proxy locations that were used in the reconstruction are not always sufficient to describe the nao this is reflected in a failure of the reconstruction to verify against instrumental records of the nao in the 19th century by adding complementary proxies the robustness of an nao reconstruction can be improved to the degree that it would withstand the tests presented here

power law breakthrough curve tailing in a fracture the role of advection summary we offer an explanation of the strongly tailed solute breakthrough curve typically observed when a tracer test is conducted in fractured bedrock in this example we limit the model to a single planar fracture of varying aperture flow heterogeneity derives from variable fracture aperture which implies variable transmissivity t the analysis employs a physically based model well suited to strong heterogeneity and relies only upon advective transport the purely advective model is able to explain a power law trend of magnitude 2t o 3 in the breakthrough curve tail a range that has been found in field tracer experiments the principle cause of this trend is the comparatively slow transport in zones of small transmissivity tight aperture slow advection occurs when either heterogeneity variance of ln t i s strong or when the assumed heterogeneity distribution is non gaussian thus we link breakthrough tailing to the statistical parameters for the transmissivity field

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

oxygen isotopes from phorcus osilinus turbinatus shells as a proxy for sea surface temperature in the central mediterranean a case study from malta abstract the marine topshell phorcus osilinus turbinatus is a common component of many archaeological sites in the mediterranean this species has been successfully used as a palaeoclimate proxy in italy to test whether 18 o from p turbinatus shells can serve as a reliable palaeoclimate archive for other regions of the mediterranean we collected live p turbinatus from the northeast coast of malta each month for a year the 18 o shell values of the outermost growth increments of these live collected shells ranged between 0 4 and 2 4 these values correspond to growing temperatures calculated from shell edge 18 o of between 15 c and 27 c calculated shell edge sea surface temperatures are highly correlated with instrumental records of sea surface temperature recorded over the period of collection the individuals analysed for this study are smaller than p turbinatus from populations studied elsewhere in the mediterranean nonetheless 18 o shell provides a robust record of sea surface temperatures suggesting that smaller younger shells in archaeological deposits can still provide reliable palaeothermometry records this study extends the upper growth limit p turbinatus by 2 c compared with the previous studies of p turbinatus in the mediterranean and suggests that contrary to the previous studies growth shutdown does not occur in all p turbinatus when sea surface temperatures exceed 25 c this may reflect the higher sample resolution that can be obtained from smaller faster growing shells or it may reflect actual higher growth tolerances of p turbinatus populations in malta by showing that p turbinatus precipitate their shells in 18 o equilibrium with surrounding sea water this study reinforces the potential for the stable isotope chemistry of p turbinatus shells preserved in mediterranean archaeological sites to provide a window into the climate and seasonality regimes of the past

warming and cooling the medieval climate anomaly in africa and arabia the medieval climate anomaly mca is a well recognized climate perturbation in many parts of the world with a core period of 1000 1200 common era here we present a palaeotemperature synthesis for the mca in africa and arabia based on 44 published localities the data sets have been thoroughly correlated and the mca trends palaeoclimatologically mapped the vast majority of available afro arabian onshore sites suggest a warm mca with the exception of the southern levant where the mca appears to have been cold mca cooling has also been documented in many segments of the circum africa arabian upwelling systems as a result of changes in the wind systems which were leading to an intensification of cold water upwelling offshore cores from outside upwelling systems mostly show warm mca conditions the most likely key drivers of the observed medieval climate change are solar forcing and ocean cycles conspicuous cold spikes during the earliest and latest mca may help to discriminate between solar oort minimum and ocean cycle atlantic multidecadal oscillation amo influence compared to its large share of nearly one quarter of the world s landmass data from africa and arabia are significantly underrepresented in global temperature reconstructions of the past 2 000 years onshore data are still absent for most regions in africa and arabia except for regional data clusters in morocco south africa the east african rift and the levant coast in order to reconstruct land palaeotemperatures more robustly over africa and arabia a systematic research program is needed

influence of the north atlantic oscillation on the canary islands precipitation abstract the aim of this paper is to investigate the relationship between the canary island rainfall and the atlantic large scale circulation characterized by the north atlantic oscillation nao index the canary islands are located in the atlantic subtropical belt under the direct influence of the azores high and the trade winds their steep orography makes the islands very sensitive to small variations in a synoptic situation thus providing an excellent natural observatory for the north atlantic variability associated with changes in pressure patterns a significant relationship between rainfall and the nao is found for five of the seven canary islands in order to characterize the physical mechanisms involved a set of automatic objective techniques for identification and detection of disturbances is applied to the 1000 and 500 hpa geopotential from the ncep ncar reanalysis for the period from 1955 to 1998 this method allows for the identification and detection of four main synoptic systems either

interpreting tracer breakthrough tailing from different forced gradient tracer experiment configurations in fractured bedrock 1 conceptual and mathematical models are presented that explain tracer breakthrough tailing in the absence of significant matrix diffusion model predictions are compared to field results from radially convergent weak dipole and push pull tracer experiments conducted in a saturated crystalline bedrock the models are based upon the assumption that flow is highly channelized that the mass of tracer in a channel is proportional to the cube of the mean channel aperture and the mean transport time in the channel is related to the square of the mean channel aperture these models predict the consistent 2 straight line power law slope observed in breakthrough from radially convergent and weak dipole tracer experiments and the variable straight line power law slope observed in push pull tracer experiments with varying injection volumes the power law breakthrough slope is predicted in the absence of matrix diffusion a comparison of tracer experiments in which the flow field was reversed to those in which it was not indicates that the apparent dispersion in the breakthrough curve is partially reversible we hypothesize that the observed breakthrough tailing is due to a combination of local hydrodynamic dispersion which always increases in the direction of fluid velocity and heterogeneous advection which is partially reversed when the flow field is reversed in spite of our attempt to account for heterogeneous advection using a multipath approach a much smaller estimate of hydrodynamic dispersivity was obtained from push pull experiments than from radially convergent or weak dipole experiments these results suggest that although we can explain breakthrough tailing as an advective phenomenon we cannot ignore the relationship between hydrodynamic dispersion and flow field geometry at this site the design of the tracer experiment can severely impact the estimation of hydrodynamic dispersion and matrix diffusion in highly heterogeneous geologic media

on equations for the speed of sound in seawater long range acoustic transmissions made in conjunction with extensive environmental measurements and accurate mooring position determinations have been used to test the accuracy of equations used to calculate sound speed from pressure temperature and salinity the sound speed field computed using the del grosso equation v a del grosso j acoust soc am 56 1084 1091 1974 give predictions of acoustic arrival patterns which agree significantly better with the long range measurements than those computed using the chen and millero equation c chen and f j millero j acoust soc am 62 1129 1135 1977 the predicted ray travel times and travel time error have been calculated using objectively mapped sound speed fields computed from ctd and xbt data using the measured and predicted ray travel times a negligible correction to del grosso s equation of 0 05 0 05 m s at 4000 m depth is calculated small errors of about 50 m in the gps determination of mooring positions lends a depth independent error of 0 1 m s to the sound speed equation correction work supported by nsf and onr

life history of the pliocene scallop fortipecten based on oxygen and carbon isotope profiles abstract oxygen and carbon isotope profiles from the outer calcite layer of two well preserved specimens of the pliocene scallop fortipecten takahashii exhibit distinct attenuation in their annual ranges throughout the complete growth history of approximately 10 years the segments of oxygen isotope profiles corresponding to winter or summer extremes were compressed suggesting growth retardation during extreme water temperatures these profile compressions correspond well with the positions of growth rings on the outer shell surface one scallop shell which evidently grew in warmer environments based on mean oxygen isotope values developed growth rings in summer while a second shell with colder mean temperature values exhibits winter growth rings a drastic reduction in isotope fluctuation occurred at a shell age of approximately 3 years and possibly is related to the onset of the reproductive phase which may have suppressed shell growth in favor of building up reproductive tissue sexual maturity brought a change in life habit from a swimming to a reclining mode which is clearly shown by the change in shell architecture although scallop shells during the juvenile stage may record a complete seasonal cycle isotopic profiles in the adult stage contain repeated growth breaks as a result using isotope signals as paleoenvironmental proxies must be done carefully at least with scallop shells

low frequency variability in the northern hemisphere winter geographical distribution structure and time scale dependence abstract low frequency variability in wintertime 500 mb height is examined with emphasis on its structure geographical distribution and frequency dependence a 39 year record of 500 mb geopotential height fields from the nmc analyses is time filtered to partition the fluctuations into frequency bands corresponding to periods of 10 60 days 60 180 days and 180 days winter is defined as the six month period november through april variance teleconnectivity and anisotropy fields and selected loading vectors derived from orthogonal and oblique rotations of the eigenvectors of the temporal correlation matrix for each band are shown and discussed the variability in all frequency bands exhibits substantial anistropy with meridionally elongated features arranged as zonally oriented wave trains prevailing over the continents and zonally elongated features organized in the form of north south oriented dipole patterns prevailing over the oceanic sectors of the hemisphere the wave trains are most pronounc

solar modulation of north atlantic central water formation at multidecadal timescales during the late holocene article i nfo understanding natural climate variability in the north atlantic region is essential not only to assess the sensitivity of atmosphere ocean climate signal exchange and propagation but also to help distinguish between natural and anthropogenic climate change the north atlantic oscillation is one of the controlling modes in recent variability of atmosphere ocean linkages and ice freshwater fluxes between the polar and north atlantic ocean through these processes the nao influences water mass formation and the strength of the atlantic meridional overturning circulation and thereby variability in ocean heat transport however the impact of the nao as well as other forcing mechanisms on multidecadal timescales such as total solar irradiance on eastern north atlantic central water production central water circulation and climate signal propagation from high to low latitudes in the eastern subpolar and subtropical basins remains uncertain here we use a 1200 yr long benthic foraminiferal mg ca based temperature and oxygen isotope record from a 900 m deep sediment core off northwest africa to show that atmosphere ocean interactions in the eastern subpolar gyre are transferred at central water depth into the eastern boundary of the subtropical gyre further we link the variability of the nao over the past 165 yrs and solar irradiance late holocene and their control on subpolar mode water formation to the multidecadal variability observed at mid depth in the eastern subtropical gyre our results show that eastern north atlantic central waters cooled by up to 0 8 0 7 c and densities decreased by 0 3 0 2 during positive nao years and during minima in solar irradiance during the late holocene the presented records demonstrate the sensitivity of central water formation to enhanced atmospheric forcing and ice freshwater fluxes into the eastern subpolar gyre and the importance of central water circulation for cross gyre climate signal propagation during the late holocene 2011 elsevier b v all rights reserved

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

pleistocene holocene environmental change in the canary archipelago as inferred from the stable isotope composition of land snail shells abstract the isotopic composition of land snail shells was analyzed to investigate environmental changes in the eastern canary islands 28 29 n over the last 50 ka shell 13c values range from 8 9 to 3 8 at various times during the glacial interval 15 to 50 ka moving average shell 13c values were 3 higher than today suggesting a larger proportion of c4 plants at those periods shell 18o values range from 1 9 to 4 5 with moving average 18o values exhibiting a noisy but long term increase from 0 1 at 50 ka to 1 6 1 8 during the lgm 15 22 ka subsequently the moving average 18o values range from 0 0 at 12 ka to 0 9 at present calculations using a published snail flux balance model for 18o constrained by regional temperatures and ocean 18o values suggest that relative humidity at the times of snail activity fluctuated but exhibited a long term decline over the last 50 ka eventually resulting in the current semiarid conditions of the eastern canary islands consistent with the aridification process in the nearby sahara thus low latitude oceanic island land snail shells may be isotopic archives of glacial to interglacial and tropical subtropical environmental change

the transition zone of the canary current upwelling region abstract like all the major upwelling regions the canary current is characterised by intense mesoscale structure in the transition zone between the cool nutrient rich waters of the coastal upwelling regime and the warmer oligotrophic waters of the open ocean the canary island archipelago which straddles the transition introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and trade winds the combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability on the basis of historical data and a series of interdisciplinary field studies the principal features of the region are described these include a prominent upwelling filament originating near 28 n off the african coast cyclonic and anti cyclonic eddies downstream of the archipelago and warm wake regions protected from the trade winds by the high volcanic peaks of the islands the filament is shown to be a recurrent feature apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone its role in the transport and exchange of biogenic material including fish larvae is considered strong cyclonic eddies observed throughout the year drift slowly southwestward from gran canaria one sampled in late summer was characterised by large vertical isopycnal displacements apparent surface divergence and strong upwelling producing a fourfold increase in chlorophyll concentrations over background values such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen the lee region of gran canaria is shown to be a location of strong pycnocline deformation resulting from ekman pumping on the wind shear boundaries which may contribute to the eddy formation process

lee region of gran canaria the mountainous canary islancls present obstacles to the trade wincls ancl to the canary current flowing equatorwarc past them in situ observations of hydrographic properties ancl surface wincls south of gran canaria together with advancecl very high resolution racliometer ancl synthetic aperture racial images e uring 2 weeks in summer 1995 are analyzecl a cyclonic edcly shecl l rom the west of the islancl c1riftecl southwestwarcl at 5 s j while the southeast coast was approachecl by an upwelling filament originating off nw africa a wincllee region bounclecl by intense horizontal shear lines hacl a weak return islandwarcl wincl in its center the lee formee a triangulai c1iurnally varying war111 water 001 with two sea surface temperature maxima separatecl by lower temperatures below the return wincl shallow temperature stratification occurrecl behincl the islancl in contrast to the l1niform surface mixecllayer in exposecl regions upwelling ancl clownwelling of 10 20 111 were indicatecl on the cyclonic ancl anticyclonic sicles of the lee region in the sar la u lines of strong current shear along a temperature front between the cyclonic eclcly the upwelling filament were iclentifiable i iowever the racial images were clominatecl atmospheric phenomena including mountain lee wave paclcets winclrows and wincl lines estimation of the wincl field l rom the sar backscatter intensity revealed ex structure and intensification on the eclges of the warm lee

short term upwelling events at the western african coast related to synoptic atmospheric structures as derived from satellite observations satellite scatterometers provide continuously valuable surface wind speed and direction estimates over the global ocean on a regular grid both in space and time the level 3 data derived from the advanced scatterometer ascat available at 1 4 spatial resolution hereafter as25 and quick scatterometer quikscat available on 1 2 and 1 4 horizontal grids qs50 and qs25 respectively are studied at regional scales in both the benguela and canary upwelling systems they are compared to the european center for medium range weather forecast surface wind analysis with insight into their intrinsic and actual spatial resolutions in the coastal band the finest spatial patterns are found in the qs25 winds and are o 75 km this demonstrates the sensitivity of the high resolution satellite derived winds to coastal processes related to sea surface temperature sst perturbations and land sea transition next short lived upwelling episodes sues calculated from sst anomalies are defined consistently with the qs25 actual resolution these cold events refer to local short lived perturbations that add to seasonal upwelling variability we characterize concomitant atmospheric synoptic conditions for sues identified at chosen latitudes and highlight two subregions in both upwelling systems with contrasted patterns for the alongshore wind stress component and curl the complexity of the latter patterns is closely linked to local short term sst variability closer to the shore numerical sensitivity experiments show that the imbalance between ekman transport and ekman pumping has an impact on ocean dynamics wind reduction in the coastal qs25 forcing partially induced by orography tends to reduce coastal sst cooling

sclerochronology and geochemical variation in limpet shells patella vulgata a new archive to reconstruct coastal sea surface temperature 1 climate archives contained in shells of the european limpet patella vulgata accumulated in archaeological deposits can potentially provide much needed information about holocene environmental change in midlatitude coastal areas before reconstructing climate information preserved in these zooarchaeological records we studied the controls on oxygen and carbon isotope ratios 18o and 13c respectively in modern specimens we tested the hypothesis that p vulgata precipitates its shell in isotopic equilibrium with the ambient water by comparing 18oshell with predicted values predicted 18oshell was constructed using observed sea surface temperature sst records and the equilibrium fractionation equation for calcite and water we assumed a constant 18owater value of 0 10 vsmow based on published regional measurements comparison of 18oshell with predicted values revealed that 18oshell values were higher than expected by 1 01 0 21 consequently estimated sst calculated from 18oshell was 4 2 2 3 c lower than observed sst however because of the relatively uniform offset between observed and expected 18o an adjustment can be made to account for this predictable vital effect thus past climate can be reliably reconstructed using this temperature proxy once the offset is taken into account 13c values have a similar cyclicity to the 18o variation and therefore vary seasonally however 13c is slightly out of phase relative to 18o an overall negative shift in 13cshell over the lifetime of the individual indicates a vital effect associated with ontogeny further study of environmental and ecological factors that influence shell 13c is required to evaluate fully the potential of carbon isotope ratios as a useful environmental proxy

carbon isotope records from extant caribbean and south pacific sponges evolution of δ13c in surface water dic stable isotope records of demosponges from the caribbean and coral sea are described for the purpose of studying the influence of fossil fuel co2 on the carbon isotopic composition of dissolved inorganic carbon dic in surface water the slow growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in 13cdic from pre industrial times early 19th century to the present we observed similar shapes and ranges in 13c curves measured on caribbean specimens collected from water depths of 25 84 and 91 m as well as a specimen collected in shallow waters off new caledonia the records reveal a highly significant correlation with atmospheric 13cco2 13cdic values for caribbean and coral sea surface waters were calculated using the 13c sponge records while 13c of atmospheric co2 decreased by about 1 4 from the early 19th century to 1990 13cdic of caribbean and coral sea surface waters decreased by 0 9 0 2 and 0 7 0 3 respectively no isotopic equilibrium between surface water dic and atmospheric co2 was observed either during the pre industrial steady state or during the last 100 years the lower amount of depletion in the surface water 13cdic with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water dic the lower 13c decrease in the coral sea points to a stronger influence of the subsurface water source compared to the caribbean

the felsic dikes of la gomera canary islands identification of cone sheet and radial dike swarms on the northern part of la gomera there exists a great abundance of trachytic phonolitic dikes showing a broad diversity in dip and strike several methods have been applied in order to separate these dikes in different sets localise the area from where they derive and reconstruct the geometry of the swarms the oldest dikes correspond to a radial swarm dated at 8 ma the felsic activity migrated then southwestwards and a second radial swarm and a cone sheet complex were developed between 7 5 and 6 4 ma ago the cone sheet complex is 10 km in diameter and shared its centre with that of the second radial structure the cone sheets exhibit an outward decrease of dip angle whilst every individual sheet maintains a constant inclination this geometry reflects the existence of an ancient single dome shaped shallow magma chamber situated some 1650 m below present sea level the eastern radial swarm represents a felsic episode that could mark the ending of the lower old basalts the earlier subaerial activity of la gomera the two other dike swarms represent a younger episode coeval with the upper old basalts

on the radiocarbon record in banded corals exchange parameters and net transport of 14co2 between atmosphere and surface ocean we have made radiocarbon measurements of banded hermatypic corals from florida belize and the galapagos islands interpretation is presented here of these previously reported results these measurements represent the 14c 12c ratios in dissolved inorganic carbon dioc in the surface ocean waters of the gulf stream and the peru current at the time of coral ring formation a depletion in radiocarbon concentration was observed in coral rings that grew from a d 1900 1952 it was caused by dilution of existing 14c levels with dead co2 from fossil fuel burning the suess effect or se the observed depletion of radiocarbon was greater in corals from the gulf stream 11 than in corals from the peru current 6 a similar trend was observed in the distribution of bomb produced 14c in corals that had grown during the years following a d 1952 the concentration of bomb produced radiocarbon was much higher in corals from temperate regions florida belize hawaiian islands than in corals from tropical regions galapagos islands and canton island a linear relationship appears to exist between the preanthropogenic 14c values and the se values measured in the individual corals because the 14c in corals is derived from two different carbon reservoirs 1 the atmosphere and 2 the subsurface ocean a linear relationship is also observed between the preanthropogenic 14c values and the concentration of bomb produced 14c in the individual corals during a d 1973 the apparent radiocarbon ages of the surface waters in temperate and tropical oceans during the preanthropogenic period range from about 280 to 520 years b p 40 to 69 at all investigated locations it is likely that waters at subsurface depths have the same apparent radiocarbon age of about 670 years b p from the change of oceanic 14c in the surface ocean during post bomb times the approximate annual rate of net input of 14co2 to the ocean waters is calculated to be about 8 of the prevailing 14c difference between atmosphere and ocean from this input and from preanthropogenic 14c values found at each location it can be seen that vertical mixing of water in the peru current is about 3 times greater than that in the gulf stream

rapid 20th century increase in coastal upwelling off northwest africa near shore waters along the northwest african margin are characterized by coastal upwelling and represent one of the world9s major upwelling regions sea surface temperature sst records from moroccan sediment cores extending back 2500 years reveal anomalous and unprecedented cooling during the 20th century which is consistent with increased upwelling upwelling driven ssts also vary out of phase with millennial scale changes in northern hemisphere temperature anomalies nhtas and show relatively warm conditions during the little ice age and relatively cool conditions during the medieval warm period together these results suggest that coastal upwelling varies with nhtas and that upwelling off northwest africa may continue to intensify as global warming and atmospheric co 2 levels increase

shell midden sclerochronology abstract sclerochronological analysis of shell midden faunal remains offers a unique opportunity to study climate and environmental change in relation to human activity middens exist near most aquatic habitats almost worldwide for much of the late pleistocene and holocene they afford good preservation of accretionary calcium carbonate remains such as mollusk shells and fish otoliths in comparatively well dated contexts as such midden samples are a source of sequential proxy records of past climate and environmental conditions and may provide detailed pictures of human environment interaction however midden samples present several challenges to the development and application of sclerochronological proxies including unique taphonomic concerns here these challenges are outlined within descriptions of the major applications of midden sclerochronology archeological concerns including season of capture reconstructing the history of anthropogenic environmental impacts and paleoclimate environment proxy reconstructions

scale of time averaging in archaeological shell middens from the canary islands characterizing the degree of disturbance in archaeological deposits is critically important for archaeologists assessing foraging strategies environmental conditions or behavior patterns of ancie

enso related modulation of coastal upwelling in the eastern atlantic an index of enso in the pacific during early boreal winter is shown to account for a significant part of the variability of coastal sst anomalies measured a few months later within the wind driven west african coastal upwelling region from 10 n to 26 n this teleconnection is thought to result from an atmospheric bridge between the pacific and atlantic oceans leading to warm cold enso events being associated with a relaxation intensification of the atlantic trade winds and of the wind induced coastal upwelling this enso related modulation of the wind driven coastal upwelling appears to contribute to the connection observed at the basin scale between enso and sst in the north atlantic the ability to use this teleconnection to give warnings of large changes in the west african upwelling several months in advance is successfully tested using data from the 1998 and 1999 enso events

flow dependence of matrix diffusion in highly heterogeneous rock fractures diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties the flow dependence of matrix diffusion is quantified by a random variable transport resistance denoted as t l and computed from the flow field by following advection trajectories the numerical methodology for simulating fluid flow is mesh free using fup basis functions a generic statistical model is used for the transmissivity field featuring three correlation structures i highly connected non multi gaussian ii poorly connected or disconnected non multi gaussian and iii multi gaussian the moments of are shown to be linear with distance irrespective of the structure after approximately 10 integral scales of ln t percentiles of are found to be linear with the mean when considering all three structures taking advantage of this property a potentially useful relationship is presented between percentiles and the fracture mean water residence time that integrates all structures with high variability it can be used in discrete fracture network simulations where t statistical data on individual fractures are not available

the medieval climate anomaly and little ice age in chesapeake bay and the north atlantic ocean abstract a new 2400 year paleoclimate reconstruction from chesapeake bay cb eastern us was compared to other paleoclimate records in the north atlantic region to evaluate climate variability during the medieval climate anomaly mca and little ice age lia using mg ca ratios from ostracodes and oxygen isotopes from benthic foraminifera as proxies for temperature and precipitation driven estuarine hydrography results show that warmest temperatures in cb reached 16 17 c between 600 and 950 ce common era centuries before the classic european medieval warm period 950 1100 ce and peak warming in the nordic seas 1000 1400 ce a series of centennial warm cool cycles began about 1000 ce with temperature minima of 8 to 9 c about 1150 1350 and 1650 1800 ce and intervening warm periods 14 15 c centered at 1200 1400 1500 and 1600 ce precipitation variability in the eastern us included multiple dry intervals from 600 to 1200 ce which contrasts with wet medieval conditions in the caribbean the eastern us experienced a wet lia between 1650 and 1800 ce when the caribbean was relatively dry comparison of the cb record with other records shows that the mca and lia were characterized by regionally asynchronous warming and complex spatial patterns of precipitation possibly related to ocean atmosphere processes

impact of end member mixing on depth distributions of δ13c cadmium and nutrients in the n atlantic ocean abstract the po 4 13 c and cd depth distributions measured in the n atlantic ocean during recent geotraces and clivar cruises are a result of biological and circulation processes with in situ uptake and remineralization of organic matter dominating in the upper 300 m and mixing of water masses dominating in the thermocline and deep sea the observed slopes of the no 3 po 4 preindustrial 13 c po 4 and by analogy cd po 4 along isopycnals deviate significantly from that expected from redfield in the thermocline and deep sea and in each case the observed slope is similar to the slopes of the end member water masses being mixed the depth increase in the cd po 4 slope resulting from end member mixing explains the observed kink at 1 m po 4 in the cd po 4 relationship in the n atlantic the observation that the po 4 preindustrial 13 c cd relationship in the modern n atlantic is heavily influenced by end member mixing throughout most of the water column complicates the use of 13 c and cd as proxies of the paleocean s nutrient distribution because changes in the po 4 13 c cd composition of locally and remotely produced end members water masses would change the po 4 13 c and cd depth distributions in the paleo n atlantic ocean

old carbon in living organisms and young cac03 cements from abyssal brine seeps abyssal brine springs at the base of the florida escarpment in the gulf of mexico 3 280 m 26 o2 n 84 55 w are surrounded by communities of abundant heterotrophic organisms1 4 and carbonate cemented crusts5 these organisms are apparently supported by local chemosynthetic primary production because the 13c content of their tissues is lower than that found in typical photosynthetically fixed organic carbon6 and the enzymes associated with chemosynthetic metabolism are present in their tissues7 8 here we report that fossil methane is the dominant source of carbon found in living tissues and recent authigenic carbonate minerals associated with abyssal brine seeps at the base of the florida escarpment most organic carbon and authigenic carbonates adjacent to the seeps contain progressively less modern carbon as their 13c contents approach that of methane carried in the brine incorporation of fossil methane 1 3 modern carbon into living tissues and carbonate cements results in recently formed materials which are depleted in 14c therefore 14c cannot be used to indicate the age of authigenic materials produced at the pore water seepage environments that speckle the continental margins of the world

planktonic foraminiferal δ13c records from southern ocean sediment traps new estimates of the oceanic suess effect the carbon isotopic composition is measured for three species of planktonic foraminifera globigerina bulloides globorotalia inflata and neogloboquadrina pachyderma s from southern ocean sediment traps the sediment traps represent the annual flux of foraminifera in subtropical to polar frontal environments from the western pacific southern australia sector comparison between the seasonal 13c composition of the foraminifera and estimated 13c of dissolved inorganic carbon dic allows disequilibrium effects to be determined disequilibrium exhibits a latitudinal trend with greatest offsets from equilibrium at lower latitudes this effect causes a north to south increase in foraminiferal 13c while the 13cdic displays a decrease across these latitudes disequilibrium in g bulloides can be accounted for by changes in temperature the relationship between disequilibrium and temperature which we derive in this field study is consistent with the laboratory relationship of bemis et al 2000 corrected 13c for g bulloides is closely correlated to seasonal changes in nutrients at each site indicating the utility of g bulloides 13c as a nutrient tracer in southern ocean environments comparison between flux weighted sediment trap values and nearby core tops indicates a modern depletion in 13c which we attribute to the oceanic suess effect the imprint of this effect on the foraminiferal isotopes provides further evidence for the equilibration between surface waters and the atmosphere in the subantarctic zone

climate change and the collapse of the akkadian empire evidence from the deep sea the akkadian empire ruled mesopotamia from the headwaters of the tigris euphrates rivers to the persian gulf during the late third millennium b c archeological evidence has shown that this highly developed civilization collapsed abruptly near 4170 150 calendar yr b p perhaps related to a shift to more arid conditions detailed paleoclimate records to test this assertion from mesopotamia are rare but changes in regional aridity are preserved in adjacent ocean basins we document holocene changes in regional aridity using mineralogic and geochemical analyses of a marine sediment core from the gulf of oman which is directly downwind of mesopotamian dust source areas and archeological sites our results document a very abrupt increase in eolian dust and mesopotamian aridity accelerator mass spectrometer radiocarbon dated to 4025 125 calendar yr b p which persisted for 300 yr radiogenic nd and sr isotope analyses confirm that the observed increase in mineral dust was derived from mesopotamian source areas geochemical correlation of volcanic ash shards between the archeological site and marine sediment record establishes a direct temporal link between mesopotamian aridification and social collapse implicating a sudden shift to more arid conditions as a key factor contributing to the collapse of the akkadian empire

estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses cappa et al modelling pressure pulses in rock fractures estimation of fracture flow parameters through numerical analysis of hydromechanical pressure pulses frederic cappa 1 yves guglielmi 2 jonny rutqvist 3 chin fu tsang 3 and alain thoraval 4 geosciences azur university of nice sophia antipolis sophia antipolis france geologie des systemes et des reservoirs carbonates university of provence aix marseille france earth sciences division lawrence berkeley national laboratory berkeley usa ineris ecole national superieure des mines de nancy parc de saurupt nancy france corresponding author fax 33 4 92 94 26 10 e mail address cappa geoazur unice fr f cappa