quantitative textural analyses of tobi sonar imagery along the almeria canyon almeria margin alboran sea se spain hydrocarbon exploration and the ongoing assessment of potential seismic risks are the main drivers behind the high resolution mapping of continental margins the large volume of literature devoted to turbidite systems in particular shows the importance of detailed descriptions of their characteristics and overall geomorphological variability primarily through the distribution of sediment facies these descriptions rely mainly on acoustic measurements which are notoriously difficult to interpret textural analyses quantify the second order statistics of sonar imagery detecting and quantifying details invisible to the human eye we show the potential and limitations of this approach using high resolution 6m towed ocean bottom instrument tobi sidescan sonar imagery acquired in the alboran sea south of almeria spain during the high resolution imaging of tsunamigenic structures hits 2001 programme the imagery is co registered with em 12 multibeam bathymetry topographic parametric sonar topas sub bottom profiles and localized ground truthing our study focuses on the almeria canyon a meandering channel system more than 57 km long and transporting large amounts of sediments from the coast down to the alboran trough c 1700 m deep textural analyses quantify the variations of sediment processes along the slope of the almeria canyon they agree with the results of previous studies and they can be used to provide new insights into the dynamics and evolution of the canyon

statistical characterization of high frequency shallow water seafloor backscatter knowledge of the background reverberation environment is a prerequisite for the design of any target detection scheme while the problem of understanding and predicting high frequency background seafloor reverberation level or mean energy scattered per unit area of the seabed has received considerable attention studies of high frequency reverberation amplitude statistics are relatively scarce of these studies many have dealt with scattering from more or less homogeneous seafloors in terms of bottom type whereas most shallow water areas will not be homogeneous but will have patchiness in space and time which will have a strong influence on scattered amplitude statistics in this work a comparison is presented between 80 khz seafloor backscatter statistics obtained at shallow water sites around sardinia and sicily the data include measurements from several distinct bottom provinces including sites with posidonia oceanica sea grass and sites covered with live shellfish results of the analysis are cast both in terms of mean power level or backscattering coefficient as well as of the amplitude statistics the reverberation statistics did not always exhibit a rayleigh probability distribution function pdf but exhibited statistical distributions with heavier tails several more appropriate models of reverberation pdf were examined in order to better describe the measured amplitude distributions the rayleigh mixture and the k models were found to be the most robust in describing the observed data

coupled north atlantic slope water forcing on gulf of maine temperatures over the past millennium to investigate ocean variability during the last millennium in the western gulf of maine gom we collected a 142 year old living bivalve arctica islandica l in 2004 and three fossil a islandica shells calibrated 14cams 1030 78 ad 1320 45 ad 1357 40 ad for stable isotope and growth increment analysis a statistically significant relationship exists between modern gom temperature records shell isotope derived 30 m r 0 79 p 0 007 prince 5 50 m r 0 72 p 0 019 boothbay harbor sst r 0 76 p 0 011 and labrador current lc transport data from the eastern newfoundland slope during 1993 2003 in all cases as lc transport increased gom water temperatures decreased the following year decadal trends in the north atlantic oscillation nao and the atlantic multidecadal oscillation amo influence gom water temperatures in the most recent period with water temperatures decreasing during nao and amo negative modes most likely linked to lc transport and gulf stream interaction mean shell derived isotopic changes 18oc during the last 1 000 years were 0 47 and likely reflect a 1 2 c cooling from 1000 ad to present based on these results we suggest that observed cooling in the gom during the last millennium was due to increased transport and or cooling of the lc and decreased gulf stream influence on the gom

compositional signatures in acoustic backscatter over vegetated and unvegetated mixed sand gravel riverbeds multibeam acoustic backscatter has considerable utility for remote characterization of spatially heterogeneous bed sediment composition over vegetated and unvegetated riverbeds of mixed sand and gravel however the use of high frequency decimeter resolution acoustic backscatter for sediment classification in shallow water is hampered by significant topographic contamination of the signal in mixed sand gravel riverbeds changes in the abiotic composition of sediment such as homogeneous sand to homogeneous gravel tend to occur over larger spatial scales than is characteristic of small scale bedform topography ripples dunes and bars or biota such as vascular plants and periphyton a two stage method is proposed to filter out the morphological contributions to acoustic backscatter first the residual supragrain scale topographic effects in acoustic backscatter with small instantaneous insonified areas caused by ambiguity in the local beam to beam bed sonar geometry are removed then coherent scales between high resolution topography and backscatter are identified using cospectra which are used to design a frequency domain filter that decomposes backscatter into the unwanted high pass component associated with bedform topography ripples dunes and sand waves and vegetation and the desired low frequency component associated with the composition of sediment patches superimposed on the topography this process strengthens relationships between backscatter and sediment composition a probabilistic framework is presented for classifying vegetated and unvegetated substrates based on acoustic backscatter at decimeter resolution this capability is demonstrated using data collected from diverse settings within a 386 km reach of a canyon river whose bed varies among sand gravel cobbles boulders and submerged vegetation

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

the flip side of the north atlantic oscillation and modal shifts in slope water circulation patterns a large single year reversal in the phase of the north atlantic oscillation nao during 1996 led to a dramatic shift in the slope water circulation patterns of the northwest nw atlantic analyses of time series data collected from the region over the past half century show that both physical and biological responses are commonly elicited by such phase reversals in the nao here we use a model developed from time series data to predict responses of the nw atlantic slope water circulation patterns to phase reversals in the nao

controls on δ18o and δ13c profiles within the aragonite bivalve arctica islandica the geochemistry of arctica islandica shells provides an opportunity to reconstruct intra annual resolution climate records in temperate latitudes and the annual banding allows close temporal constraint stable isotope analyses of carbon and oxygen from an arctica islandica live collected at 6 m depth from irvine bay uk are presented seawater temperature ranges reconstructed from shell 18o agree within error with instrumental sea surface temperature measurements the saw tooth profile of the seasonal 18o signal compared with the sinusoidal seawater temperature indicates that shell accretion rate is not constant throughout the year modelling the expected 18o profile from water temperature salinity and shell growth rate suggest that a islandica at this site has significant variation in the shell extension rate during the year material deposited during shell damage shows a positive shift in 18o a strong ontogenetic effect is seen in 13c and damage to the shell is associated with a significa

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

sea surface water temperatures over the period 1884 1983 reconstructed from oxygen isotope ratios of a bivalve mollusk shell arctica islandica southern north sea although climate system modeling cannot be imagined without long sea surface temperature sst records observational data is spatiotemporally incomplete and inhomogeneous prior to about 1950 moreover almost no high resolution sst proxies exist from temperate and boreal marine settings here we present a temporally equidistant high resolution sst proxy record of the southern north sea during the period 1884 1983 calculated from oxygen isotope ratios 18oaragonite of arctica islandica l a bivalve mollusk shell arctica islandica produces daily growth increments which enable precise intraannual dating the growing season of specimens from about 25 m water depth upper well mixed layer of the ocean started in february and ended in september observational coads etc and 18oaragonite derived sst data during february through september compare well to each other especially after 1950 apart from similar overall sst trends we found north atlantic oscillation type cycles of 7 9 years in our proxy sst record and in various different instrumentally determined sst chronologies no vital effects exist so that 18oaragonite ratios determined across the shell i e throughout lifetime of the studied specimen reflect ambient water temperatures that occurred during shell growth results of our study demonstrate that a islandica provides long independent and high resolution sst proxy chronologies from higher latitudes such records can complement and further validate observational sst data and help improving climate system models

measuring the shallow porosity structure of sediments on the continental shelf a comparison of an electromagnetic approach with cores and acoustic backscatter we validate estimates of shallow sedimentary porosities made on the continental shelf by electromagnetic methods through a comparison with those measured directly in cores specifically we show that an electromagnetic surveying system we have used to measure sediment resistivity in a number of seafloor locations returns porosity depth profiles that are related to those measured in cores and that our data have good sensitivity to the structure within the uppermost few tens of centimeters of seafloor we then consider inferences of sediment type made by observations of acoustic backscatter in the light of our porosity measurements our results suggest that electromagnetic methods provide complementary information that can be used to improve grain type estimates at and just below the seafloor especially when combined with acoustic backscatter data because the system is pulled along the seafloor data can be quickly collected from a large area of seafloor and can be used to interpolate facies conditions between core locations

angular dependence of cal k distributed sonar data backscattered signal statistics are widely used for target detection and seafloor characterization the k distribution shows interesting properties for describing experimental backscattered intensity statistics in addition to the fact that its probability distribution function accurately fits actual sonar data it advantageously provides a physical interpretation linked to the backscattering phenomenon sonar systems usually record backscattered signals from a wide angular range across the ship s track in this context previous studies have shown that backscatter statistics strongly depend on the incidence angle in this paper we propose an extension of previous works to model the angular evolution of the k distribution shape parameter this evolution is made clear and analyzed from experimental data recorded with two sonar systems a 95 khz multibeam echosounder and a 110 khz sidescan sonar model fitting with data backscattered from six seafloor configurations shows the improvement provided by our extension as compared to two previous models

a tree ring based reconstruction of the atlantic multidecadal oscillation since 1567 a d 1 we present a tree ring based reconstruction of the atlantic multidecadal oscillation amo which demonstrates that strong low frequency 60 100 yr variability in basin wide 0 70 n sea surface temperatures ssts has been a consistent feature of north atlantic climate for the past five centuries intervention analysis of reconstructed amo indicates that 20th century modes were similar to those in the preceding 350 yr and wavelet spectra show robust multidecadal oscillations throughout the reconstruction though the exact relationships between low frequency sst modes higher frequency 7 25 yr atmospheric modes e g north atlantic oscillation arctic oscillation and terrestrial climates must still be resolved our results confirm that the amo should be considered in assessments of past and future northern hemisphere climates

the shell of the queen scallop aequipecten opercularis l as a promising tool for palaeoenvironmental reconstruction evidence and reasons for equilibrium stable isotope incorporation abstract the queen scallop aequipecten opercularis has been an important part of the marine fauna of the northeast atlantic region since the miocene and is a suitable candidate for palaeoenvironmental studies using stable isotopes modern shells were investigated to determine if carbonate is precipitated in isotopic equilibrium in this species and to confirm that growth continues through the year specimens of a opercularis were cultured under monitored semi natural conditions over an autumn winter period and the analyses of these specimens were supplemented with isotope data from preserved indigenous north sea specimens the results indicated that the cultured specimens grew in relatively low temperatures that oxygen isotopes of shell exterior carbonate were precipitated in isotopic equilibrium and that a large proportion of the ambient temperature range was recorded in shell carbonate the indigenous north sea specimens exhibited a good correspondence to predicted oxygen isotope values for summer the isotopic record related to winter was however somewhat truncated due to growth decelerations in the specimens carbon isotopes of shell exterior carbonate were calculated as being derived primarily from external sources and showed comparatively little influence from metabolically derived carbon this suggests that carbon isotopes were at least close to equilibrium with ambient waters the limited incorporation of metabolic products suggests that a opercularis would be a good monitor of changing carbon isotope ratios in seawater dissolved inorganic carbon the occurrence of equilibrium shell precipitation is explained using a pteriomorph shell calcification model which proposes that transport of ions through the periostracum caused the composition of the extrapallial fluid to be effectively the same as seawater carbonate secretion is therefore not influenced significantly by biological vital effects

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

the long lived mollusc arctica islandica a new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern north atlantic ocean the carbonate shell of the bivalve arctica islandica has been recognized for more than a decade as a potentially important marine geochemical biorecorder owing to this species great longevity 200 years and wide geographic distribution throughout the northern north atlantic ocean a region vital to global climate and ocean circulation however until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry a stable oxygen isotope record 1956 1957 and 1961 1970 has been obtained from a live captured 38 year old a islandica specimen collected near the former position of the nantucket shoals lightship 41 n 69 w the shell s 18o signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period the results show that a islandica s 18o record 1 is in phase with its growth banding confirming the annual periodicity of this species growth bands 2 is in oxygen isotopic equilibrium with the ambient seawater 3 shows a consistent shell growth shutdown temperature of 6 c which translates into an 8 month may december shell growth period at this location and 4 records the ambient bottom temperature with a precision of 1 2 c these results add important information on the life history of this commercially important shellfish species and demonstrate that a islandica shells can be used to reconstruct inter and intra annual records of the continental shelf bottom temperature

an overview of biomineralization processes and the problem of the vital effect biomineralization links soft organic tissues which are compositionally akin to the atmosphere and oceans with the hard materials of the solid earth it provides organisms with skeletons and shells while they are alive and when they die these are deposited as sediment in environments from river plains to the deep ocean floor it is also these hard resistant products of life which are mainly responsible for the earth s fossil record consequently biomineralization involves biologists chemists and geologists in interdisciplinary studies at one of the interfaces between earth and life leadbeater and riding 1986 biomineralization refers to the processes by which organisms form minerals the control exerted by many organisms over mineral formation distinguishes these processes from abiotic mineralization the latter was the primary focus of earth scientists over the last century but the emergence of biogeochemistry and the urgency of understanding the past and future evolution of the earth are moving biological mineralization to the forefront of various fields of science including the earth sciences the growth in biogeochemistry has led to a number of new exciting research areas where the distinctions between the biological chemical and earth sciences disciplines melt away of the wonderful topics that are receiving renewed attention the study of biomineral formation is perhaps the most fascinating truly at the interface of earth and life biomineralization is a discipline that is certain to see major advancements as a new generation of scientists brings cross disciplinary training and new experimental and computational methods to the most daunting problems it is however by no means a new field the first book on biomineralization was published in 1924 in german by w j schmidt schmidt 1924 and the subject has continued to intrigue a dedicated community of scientists for many years until the early 1980s the field was known as

high frequency volume and boundary acoustic backscatter fluctuations in shallow water volume and boundary acoustic backscatter envelope fluctuations are characterized from data collected by the toroidal volume search sonar tvss a 68 khz cylindrical array capable of 360 multibeam imaging in the vertical plane perpendicular to its axis the data are processed to form acoustic backscatter images of the seafloor sea surface and horizontal and vertical planes in the volume which are used to attribute nonhomogeneous spatial distributions of zooplankton fish bubbles and bubble clouds and multiple boundary interactions to the observed backscatter amplitude statistics three component rayleigh mixture probability distribution functions pdfs provided the best fit to the empirical distribution functions of seafloor acoustic backscatter sea surface and near surface volume acoustic backscatter pdfs are better described by rayleigh mixture or log normal distributions with the high density portion of the distributions arising from boundary reverberation and the tails arising from nonhomogeneously distributed scatterers such as bubbles fish and zooplankton pdf fits to the volume and near surface acoustic backscatter data are poor compared to pdf fits to the boundary backscatter suggesting that these data may be better described by mixture distributions with component densities from different parametric families for active sonar target detection the results demonstrate that threshold detectors which assume rayleigh distributed envelope fluctuations will experience significantly higher false alarm rates in shallow water environments which are influenced by near surface microbubbles aggregations of zooplankton and fish and boundary reverberation

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

annually resolved δ13cshell chronologies of long lived bivalve mollusks arctica islandica reveal oceanic carbon dynamics in the temperate north atlantic during recent centuries abstract the ability of the ocean to absorb carbon dioxide is likely to be adversely affected by recent climate change however relatively little is known about the spatiotemporal variability in the oceanic carbon cycle due to the lack of long term high resolution dissolved inorganic carbon isotope 13 c dic data especially for the temperate north atlantic which is the major oceanic sink for anthropogenic co 2 here we report shell carbon isotope values 13 c shell a potential proxy for 13 c dic of old grown specimens of the long lived bivalve mollusk arctica islandica this paper presents the first absolutely dated annually resolved 13 c shell record from surface waters of the north atlantic iceland gulf of maine covering the time interval between 1753 and 2003 according to our results the 13 c shell data were unaffected by trends related to ontogenetic age however the shell carbonate was precipitated with a constant offset from expected equilibrium by 1 54 to 2 7 0 2 corresponding to a 6 2 to 10 8 0 8 contribution of respiratory co 2 25 the offset did not appear to vary through the lifetime of individual specimens and among specimens therefore the 13 c shell data of this species can very likely be used as a measure of 13 c dic furthermore shell stable carbon isotope chronologies exhibited habitat specific differences and a significant inter annual and decadal variability related to the natural carbon cycle in addition a distinct negative 13 c shell shift was found reflecting the oceanic suess effect i e the admixture of anthropogenic co 2 however this shift only occurred after the early 1920s when a major climate regime shift led to a northward movement of the oceanic polar front in the nordic seas and a large scale reorganization of atmospheric and oceanic currents in the north atlantic this likely resulted in a reduced admixture of cold polar water onto the north icelandic shelf through the east iceland current and the gulf of maine through the labrador current with an increased volume of warmer isotopically well equilibrated atlantic waters our shell based 13 c dic proxy record provides the basis to quantitatively assess natural and anthropogenically induced patterns of carbon uptake in the north atlantic

characterizing riverbed sediment using high frequency acoustics 1 spectral properties of scattering bed sediment classification using high frequency hydroacoustic instruments is challenging when sediments are spatially heterogeneous which is often the case in rivers the use of acoustic backscatter to classify sediments is an attractive alternative to analysis of topography because it is potentially sensitive to grain scale roughness here a new method is presented which uses high frequency acoustic backscatter from multibeam sonar to classify heterogeneous riverbed sediments by type sand gravel and rock continuously in space and at small spatial resolution in this the first of a pair of papers that examine the scattering signatures from a heterogeneous riverbed methods are presented to construct spatially explicit maps of spectral properties from georeferenced point clouds of geometrically and radiometrically corrected echoes backscatter power spectra are computed to produce scale and amplitude metrics that collectively characterize the length scales of stochastic measures of riverbed scattering termed stochastic geometries backscatter aggregated over small spatial scales have spectra that obey a power law this apparently self affine behavior could instead arise from morphological scale and grain scale roughnesses over multiple overlapping scales or riverbed scattering being transitional between rayleigh and geometric regimes relationships exist between stochastic geometries of backscatter and areas of rough and smooth sediments however no one parameter can uniquely characterize a particular substrate nor definitively separate the relative contributions of roughness and acoustic impedance hardness combinations of spectral quantities do however have the potential to delineate riverbed sediment patchiness in a data driven approach comparing backscatter with bed sediment observations which is the subject of part two of this manuscript

long term stability of δ13c with respect to biological age in the aragonite shell of mature specimens of the bivalve mollusk arctica islandica the stable carbon isotope ratio in bivalve shells 13cs is an enigmatic geochemical archive whose interpretation is often frustrated by the intrusion of variable and unpredictable vital effects which can influence the mix of metabolic and dissolved inorganic carbon dic in the shell material the impacts of vital effects and rapid changes in calcification rates on the variability and value of 13cs have been described in a number of studies and in many bivalve species with typical lifespans between a few years and a few decades 13cs has been observed to change usually decreasing with biological age very long lived animals by contrast spend most of their lives in the mature slow growing phase and it might be expected that in these instances the effect of changes in calcification rates on 13cs would be less marked or even absent analysis of 13cs in mature 40years old arctica islandica reported here indicates that this is the case 13cs in shell samples with biological ages between 42 and 391 years from four distinct sites in the north atlantic shelf seas gulf of maine north icelandic shelf irish sea and north sea shows no age related trend this suggests that metabolic vital effects in mature a islandica may be reasonably stable at the population level if the drivers of isotopic disequilibrium between shell and ambient environment can be identified and quantified it may be feasible to adjust for them and use 13cs in mature a islandica to investigate long term changes in nutrient sources and as a robust proxy for 13c of environmental dic

marine climate in the irish sea analysis of a 489 year marine master chronology derived from growth increments in the shell of the clam arctica islandica abstract we demonstrate here that the growth increment variability in the shell of the long lived bivalve mollusc arctica islandica can be interpreted as an indicator of marine environmental change in the climatically important north atlantic shelf seas multi centennial up to 489 year chronologies were constructed using five detrending techniques and their characteristics compared the strength of the common environmental signal expressed in the chronologies was found to be fully comparable with equivalent statistics for tree ring chronologies the negative exponential function using truncated increment width series from which the first thirty years have been removed was chosen as the optimal detrending technique chronology indices were compared with the central england temperature record and with seawater temperature records from stations close to the study site in the irish sea statistically significant correlations were found between the chronology indices and a mean air temperature for the 14 month period beginning in the january preceding the year of growth b mean seawater temperatures for february october in the year preceding the year of growth c late summer and autumn air temperatures and sea surface temperatures for the year of growth and d the timing of the autumn decline in sst changes through time in the correlations with air and seawater temperatures and changes towards a deeper water origin for the shells in the chronology were interpreted as an indication that shell growth may respond to stratification dynamics

riverbed sediment classification using multi beam echo sounder backscatter data a method has recently been developed that employs multi beam echo sounder backscatter data to both obtain the number of sediment classes and discriminate between them by applying the bayes decision rule to multiple hypotheses simons and snellen appl acoust 70 1258 1268 2009 in deep water the number of scatter pixels within the beam footprint is large enough to ensure gaussian distributions for the backscatter strengths and to increase the discriminative power between acoustic classes in very shallow water 10 m however this number is too small this paper presents an extension of this high frequency methodology for these environments together with a demonstration of its performance using backscatter data from the river waal the netherlands the objective of this work is threefold i increasing the discriminating power of the classification method high resolution bathymetry data allow precise bottom slope corrections for obtaining the true incident angle and the high resolution backscatter data reduce the statistical fluctuations via an averaging procedure ii performing a correlation analysis the dependence of acoustic backscatter classification on sediment physical properties is verified by observing a significant correlation of 0 75 and a disattenuated correlation of 0 90 between the classification results and sediment mean grain size iii enhancing the statistical description of the backscatter intensities angular evolution of the k distribution shape parameter indicates that the riverbed is a rough surface in agreement with the results of the core analysis

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

ultra low frequency electromagnetic measurements associated with the 1998 mw 5 1 san juan bautista california earthquake and implications for mechanisms of electromagnetic earthquake precursors abstract ultra low frequency ulf 0 01 10 hz magnetic field anomalies prior to m 6 0 earthquakes have been reported in various regions of the world here we test whether smaller magnitude earthquakes have associated ulf anomalies by using continuous measurements made 9 km above and 2 km ne of the epicenter of the m w 5 1 8 12 98 san juan bautista ca earthquake half hour spectral averages of the magnetic field data in nine different ulf frequency bands show no long term days to weeks magnetic field anomaly prior to the earthquake in addition magnetic and electric field polarization shows no anomalous behavior clearly associated with seismic activity an 0 02 nt increase in activity for 2 h prior to the earthquake is close to the background noise levels precluding identification of a precursor we present scaling calculations to show if precursory ulf anomalies are related to the size of the earthquake the observed 0 02 nt increase is the approximately expected magnetic anomaly prior to the san juan bautista sbj earthquake based on the anomaly observed prior to the 1989 loma prieta lp earthquake our reexamination of previously proposed dilatant conductive and piezomagnetic mechanisms for ulf precursors shows that these effects are consistent with the observations prior to the sjb earthquake based on the observations i e lack of a strong precursor in contrast previously proposed electrokinetic and magnetohydrodynamic mhd mechanisms do not appear to be appropriate for this particular earthquake this analysis further supports the hypothesis that precursory ulf signals are related to the size of the earthquake

acoustic backscattering at low grazing angles from the ocean bottom part ii statistical characteristics of bottom backscatter at a shallow water site analyses of the statistical characteristics of bottom backscatter measured in shallow water off san diego ca t g goldsberry s p pitt and r a lamb j acoust soc am suppl 1 72 s74 1982 are presented an experimental sonar operating at 30 khz mounted on the sea bottom was used to gather data over a wide sector of the bottom within its operating range the bottom was comprised of areas of coarse and fine sand the distribution function and probability of false alarm function of the detected envelope of a widebeam and a narrowbeam signal were measured some spatial and temporal correlation functions of the signal amplitudes were measured a limited attempt was made to compare the results with existing theoretical models work supported by navsea 63r and norda code 113

seasonality in the north sea during the allerod and late medieval climate optimum using bivalve sclerochronology seasonal temperature patterns may have changed through time in response to current global warming however the temporal resolution of available proxy records is not sufficient to quantify paleotemperature seasonality prior to anthropogenic forcing of the climate in the present study we reconstructed seasonal and inter annual temperature patterns of the north sea during the last 140 years the allerod interglacial and the late medieval climate optimum using sclerochronological and 18oaragonite data from bivalve shells arctica islandica on average the climate during 1278 1353 ad was ca 1 1 c colder and seasonality was ca 60 less than today during the allerod long term temperatures remained about 3 2 c below present values and absolute summer and winter anomalies were ca 4 and 2 7 c respectively however seasonality was statistically indistinguishable from today long term average temperatures compare well with existing data for the late medieval and allerod but detailed information on seasonality during the studied time intervals has never been presented before our data also demonstrated that annual instrumental and 18oaragonite derived temperatures did not always match this difference is explained by 1 nao driven salinity changes which influence the temperature estimation from 18oaragonite and 2 food driven changes in growth rates portions of the shell that formed more rapidly are overrepresented in carbonate samples our study indicated that individual bivalve shells can open discrete near century long ultra high resolution windows into the climate past such information can be vital for testing and verifying numerical climate models

fluctuations of high frequency shallow water seafloor reverberation high frequency shallow water reverberation statistics were measured from a seafloor that was covered by a thick layer of coarse shells the reverberation statistics are presented as a function of frequency 20 180 khz grazing angle 8 8 28 and source beamwidths 1 2 16 in most cases the reverberation statistics did not follow a rayleigh fading model the model dependence of the reverberation statistics ranged from near gaussian high grazing angle to beyond log normal low grazing angle the results suggest that small scale variations in bottom scattering properties and system beamwidth will significantly change the model dependence of the reverberation statistics

accurate increment identification and the spatial extent of the common signal in five arctica islandica chronologies from the fladen ground northern north sea 1 the creation of networks of shell based chronologies which can provide regionally extensive high resolution proxies for the marine environment depends on the spatial extent of the common environmental signal preserved in the shell banding and on the reliability of the dating model here arctica islandica chronologies from five neighboring sites in the north sea are compared and the strength of the common environmental signal across distances up to 80 km is analyzed using statistical techniques derived from dendrochronology the signal is found to be coherent across these distances in a linked study chronologies based on one of the same sites but constructed by two different research teams are compared methodological differences in increment interpretation are found to lead to slippage in the dating models systematic inclusion or exclusion of intermittently occurring increments results in the two chronologies becoming misaligned by 4 years over a 70 year period comparisons with neighboring chronologies indicate that such increments can generally be regarded as genuine annual increments even if they are not visible in all shells