geoacoustic inversion with ships as sources estimation of geoacoustic parameters using acoustic data from a surface ship was performed for a shallow water region in the gulf of mexico the data were recorded from hydrophones in a bottom mounted horizontal line array hla the techniques developed to produce the geoacoustic inversion are described and an efficient method for geoacoustic inversion with broadband beam cross spectral data is demonstrated the performance of cost functions that involve coherent or incoherent sums over frequency and one or multiple time segments is discussed successful inversions for the first sediment layer sound speed and thickness and some of the parameters for the deeper layers were obtained with the surface ship at nominal ranges of 20 30 or 50 water depths the data for these inversions were beam cross spectra from four subapertures of the hla spanning a little more than two water depths the subaperture beams included ten frequencies equally spaced in the 120 200 hz band the values of the geoacoustic parameters from the inversions are validated by comparisons with geophysical observations and with the parameter values from previous inversions by other invesigators and by comparing transmission loss tl measured in the experiment with modeled tl based on the inverted geoacoustic parameters

hybrid geoacoustic inversion of broadband mediterranean sea data this paper describes an acoustic experiment prosim 97 carried out to investigate inversion for seabed properties at a site off the west coast of italy where previous acoustic and geophysical studies have been performed acoustic fields were measured at a vertical hydrophone array due to a swept frequency source towed over weakly range dependent bathymetry based on the known geology the seabed is modeled as a sediment layer overlying a semi infinite basement with unknown model parameters consisting of the sediment thickness sediment and basement sound speeds source range and depth water depth at the source and array and array tilt a hybrid inversion algorithm is applied to determine the model values that minimize the mismatch with the measured acoustic fields multiple data sets are analyzed to examine the consistency of the inversion results it is found that the low sound speed of the sediment layer together with a large uncertainty in bathymetry leads to strong correlations between the water

catastrophic early holocene sea level rise human migration and the neolithic transition in europe abstract the collapse of the laurentide ice sheet and release of freshwater 8740 8160 years ago abruptly raised global sea levels by up to 1 4 m the effect on human populations is largely unknown here we constrain the time of the main sea level rise and investigate its effect on the onset of the neolithic across europe an analysis of radiocarbon ages and palaeoshoreline reconstruction supports the hypothesis that flooding of coastal areas led to the sudden loss of land favoured by early farmers and initiated an abrupt expansion of activity across europe driven by migrating neolithic peoples

central european vegetation response to abrupt climate change at 8 2 ka oxygen isotope records show a major climatic reversal at 8 2 ka in greenland and europe annually laminated sediments from two lakes in switzerland and germany were sampled contiguously to assess the response of european vegetation to climate change ca 8 2 ka with time resolution and precision comparable to those of the greenland ice cores the pollen assemblages show pronounced and immediate responses 0 20 yr of terrestrial vegetation to the climatic change at 8 2 ka a sudden collapse of corylus avellana hazel was accompanied by the rapid expansion of pinus pine betula birch and tilia linden and by the invasion of fagus silvatica beech and abies alba fir vegetational changes suggest that climatic cooling reduced drought stress allowing more drought sensitive and taller growing species to out compete corylus avellana by forming denser forest canopies climate cooling at 8 2 ka and the immediate reorganization of terrestrial ecosystems has gone unrecognized by previous pollen studies on the basis of our data we conclude that the early holocene high abundance of c avellana in europe was climatically caused and we question the conventional opinion that postglacial expansions of f silvatica and a alba were controlled by low migration rates rather than by climate the close connection between climatic change and vegetational response at a subcontinental scale implies that forecasted global warming may trigger rapid collapses expansions and invasions of tree species

a centennial scale record of vegetation and climate variability from 312 to 240 ka marine isotope stages 9c a 8 and 7e from tenaghi philippon ne greece abstract based on a new centennial scale resolution pollen record from the terrestrial site of tenaghi philippon ne greece we report a series of high amplitude millennial scale forest expansion events during the interval from 312 to 240 ka equivalent to isotopic substages c a of marine isotope stage mis 9 mis 8 and the onset of mis 7e pollen based indices support the climatic interpretation of the forest expansion events as indicators of abrupt increases in temperature and moisture availability in the mediterranean region long term changes in vegetation cover and composition during the studied interval permit the definition of glacial substages early middle and late analogous to the glacial substages of the last climatic cycle within this framework forest expansion events occurred during the early glacial equivalent to mis 9c a and the later part of the middle glacial mid to late mis 8 but are absent from the early part of the middle glacial early mis 8 forest expansion events are also detected during the lateglacial and onset of mis 7 associated with a millennial scale climate oscillation across the glacial interglacial transition i e termination iii t iii a peak for peak match between forest expansion events and antarctic temperature maxima suggests interhemispheric coupling of millennial scale climate variability via global oceanic circulation change and synergistic variability in atmospheric circulation consistent with the bipolar see saw the resolution of our record mean 290 yr also permits the characterisation of climate evolution over the course of interstadial episodes following forest expansion events and highlights differences in the characteristics of early and middle glacial interstadials saw tooth vs plateau profile these differences point to an influence of long term boundary conditions especially global ice volume on the characteristics of millennial scale events

revisiting the y 3 tephrostratigraphic marker a new diagnostic glass geochemistry age estimate and details on its climatostratigraphical context the y 3 tephra is a crucial stratigraphic marker within the central mediterranean region that falls close to the marine isotope stage 3 2 transition and a cooling event proposed as a correlative of the north atlantic heinrich stadial 3 hs3 consequently this tephra offers great potential to assess any leads and lags in environmental responses to this abrupt climatic transition new grain specific glass analysis empa and la icp ms of the type locality y 3 tephra recorded in the ionian sea confirms its origin from campi flegrei cf but reveals that it is compositionally different from the previously suggested proximal equivalent the vra eruptive unit verdolino valley cf consequently the 40ar 39ar age of the vra should not be exported distally to the y 3 tephra instead we propose a new robust age for the y 3 tephra following its identification in the tenaghi philippon sedimentary record ne greece a bayesian based 14c age model from tenaghi philippon provides a distal age of 28 680 29 420 cal yrs bp for the y 3 tephra the identification of this tephra in ne greece markedly extends its known eastern dispersal whilst its stratigraphic position falls within the latter part of a period of low tree pollen percentages related to dry stadial conditions this new age and environmental context suggest that this marker postdates the onset of hs3 in the eastern mediterranean region by 2300 years

lateglacial and holocene vegetation dynamics in the aegean region an integrated view based on pollen data from marine and terrestrial archives to elucidate the vegetation dynamics in the aegean region during the last 20 kyr we have studied terrestrial palynomorphs in marine core geotu sl152 mount athos basin northern aegean sea at centennial scale 125 to 300 yr resolution the robust chronology of the core allows us to reliably date signals of short term vegetation change in the aegean region for the pleniglacial interval until 14 6 kyr bp our data document steppe vegetation suggesting dry climatic conditions in the borderlands of the aegean sea subaerially exposed parts of the shelf were probably colonized by pinus dominated vegetation until shelf areas were flooded during lateglacial sea level rise the final rapid decrease of pinus pollen percentages between 14 and 13 kyr bp appears to be connected to meltwater pulse mwp 1a the lateglacial interstadial complex ie meiendorf bolling and allerod is characterized by the spread of oak trees but also by the continuous presence of steppe elements indicating only slightly increas

contrasting patterns of hydrological changes in europe in response to holocene climate cooling phases the quantitative reconstruction of climatic parameters from pollen and lake level data obtained at saint jorioz lake annecy eastern france gives evidence for cooler and wetter conditions during the 8 2 ka cold event a comparison of these regional data with other hydrological records reconstructed in europe for the same period suggests as a working hypothesis that mid latitudes between ca 50 and 43 underwent wetter conditions in response to the cooling whereas northern and southern europe were marked by drier climate in the latter case leading to an interruption of the sapropel 1 formation in the mediterranean a similar hydrological tri partition of europe can be observed during other holocene cooling phases associated with north atlantic ird events data indicate that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8 2 ka event the differences in expansion of the wet mid european zone depending on holocene climate cooling phases could reflect variations in the strength of the atlantic westerly jet in relation with the thermal gradient between high and low latitudes

geoacoustic inversion of broadband data by matched beam processing this paper describes results of geoacoustic inversion using broadband signals from an experiment carried out at a site near the south florida ocean measurement centre in the florida straits m sequence coded pulse trains at different center carrier frequencies from 100to3200hz were recorded at a vertical line array at a distance around 10km geoacoustic inversion was carried out to determine the feasibility of inverting the environmental parameters from this long range propagation experiment the received signal at lower frequencies below 400hz consisted of a dominant water column signal and a secondary arrival delayed by 0 4s the secondary signal was spatially filtered by beamforming the array data and the beam data were inverted by matched beam processing in the time domain combined with an adaptive simplex simulated annealing algorithm the estimated values of compressional wave speed and density were in good agreement with ground truth values from sediment cores the inverted shear wave speed appea

pollen based continental climate reconstructions at 6 and 21 ka a global synthesis subfossil pollen and plant macrofossil data derived from 14c dated sediment profiles can provide quantitative information on glacial and interglacial climates the data allow climate variables related to growing season warmth winter cold and plant available moisture to be reconstructed continental scale reconstructions have been made for the mid holocene mh around 6 ka and last glacial maximum lgm around 21 ka allowing comparison with palaeoclimate simulations currently being carried out as part of the fifth assessment report ar5 of the intergovernmental panel on climate change the synthesis of the available mh and lgm climate reconstructions and their uncertainties obtained using modern analogue regression and model inversion techniques is presented for four temperature variables and two moisture variables reconstructions of the same variables based on surface pollen assemblages are shown to be accurate and unbiased reconstructed lgm and mh climate anomaly patterns are coherent consistent between variables and robust with respect to the choice of technique they support a conceptual model of the controls of late quaternary climate change whereby the first order effects of orbital variations and greenhouse forcing on the seasonal cycle of temperature are predictably modified by responses of the atmospheric circulation and surface energy balance

a novel approach for extraction of gaoshanhe group outcrops using landsat operational land imager oli data in the heavily loess covered baoji district western china abstract we studied the applicability of landsat operational land imager oli data for extraction of gaoshanhe group outcrops in a heavily loess covered area in the northern baoji district of china which is always a crucial but challenging issue in geological remote sensing mapping an integrated approach was employed to process the remote sensing data first the interpretation target area of interest was clipped using certain slope and elevation difference thresholds topographical analysis second band ratio b4 b2 and fractal summation algorithms were conducted in succession to extract the bedrock induced anomalies third spatial clumping and hot spot analysis were performed in order to eliminate residual false anomalies and finally we introduced high resolution worldview 2 data for visual interpretation and further spectral analysis the findings show that the rocky outcrops were somewhat spectrally indistinguishable and they were identified mainly due to their generally moderate degree of spatial clustering thirteen anomalous pixels were extracted from nearly 200 000 pixels covering the study area and our field reconnaissance verified the results this research constitutes the first useful case study on the applicability of landsat data derived lithology interpretation in china s loess plateau region

a comparison of broadband and narrow band modal inversions for bottom geoacoustic properties at a site near corpus christi texas detailed comparison between narrow band and broadband techniques used in a series of acoustic experiments are presented with emphasis on a comparisons of the pressure field versus range predicted b comparisons of the bottom compressional wave speed model generated c the variance of the bottom model estimated and d the resolution of the bottom model generated the range dependence of the bottom medium and the seasonal dependence of the near surface sediment sound speed profile are observed and discussed

cold event at 8200 yr b p recorded in annually laminated lake sediments in eastern europe a quantitative annual mean temperature reconstruction from an annually laminated lake sediment sequence in estonia eastern europe shows a distinct cold period at 8400 8080 yr b p before a d 2000 the timing is consistent with that seen in the greenland ice core data and various high resolution records from western europe during maximal cooling at 8250 8150 yr b p the annual mean temperature in estonia was 2 0 c colder than prior to and 3 0 c colder than after the cooling the pollen stratigraphic and sedimentological data suggest especially cold and snowy winter conditions the duration and amplitude of the cold event agree with the modeled impact of a sudden freshening of the north atlantic surface water and subsequent perturbation of the thermohaline circulation provided that the cold event was caused by a pulse of freshwater from the melting laurentide ice sheet to the north atlantic the results indicate a strong teleconnection between the north atlantic oceanic forcing and the east european climate at least up to long 26 e mediated probably by the changing intensity of the zonal atmospheric circulation

model data comparison for the 8 2 ka bp event confirmation of a forcing mechanism by catastrophic drainage of laurentide lakes abstract to improve our understanding of the mechanism behind the 8 2 ka bp cooling event we compare proxy evidence with climate model simulations in which the thermohaline ocean circulation is perturbed by a freshwater pulse into the labrador sea both the proxy data and model results show a cooling that is mainly concentrated in the north atlantic region ranging from more than 5 c cooling in the nordic seas to about 0 5 1 c over europe and less than 0 5 c over the subtropical north atlantic data and model also indicate a weakening of the summer monsoon and generally a drier circum north atlantic over the south atlantic ocean the model simulates a slight warming mostly less than 0 5 c which falls within the uncertainty of proxy data and thus could not be confirmed to examine in detail the structure of the 8 2 ka bp event we also compare the modeled climatological evolution at two locations with high quality records revealing a generally consistent picture the good model data agreement confirms the hypothesis that the 8 2 ka bp event was forced by a freshwater induced weakening of the thermohaline circulation other forcings are unlikely since they would result in an alternative geographical distribution and expression of the climate response

late glacial to mid holocene palaeoclimate development of southern greece inferred from the sediment sequence of lake stymphalia ne peloponnese abstract the sedimentary sequence of lake stymphalia ne peloponnese for the first time sheds light on the palaeoclimate development of southern greece from 15 to 5 ka bp new geochemical data based on high resolution x ray fluorescence scanning provide in situ and continuous analysis of predefined element suites on split core surfaces variations of elements over time were assessed constructing correlation matrices based on the calculation of pearson correlation coefficients the element suite includes al si k ca ti mn fe zn rb sr and zr a major result includes that changes in element behaviour are related to hydrological changes in the catchment precipitation lake level status and evaporation insolation solar activity and are ultimately driven by climate major trends shifts in elemental ratios correspond to the climate development in the eastern mediterranean region based on correlation of rb sr reflecting wet dry climates with foraminiferal proxies of marine core lc21 from the southern aegean sea and the stable oxygen isotope record of soreq cave israel the bolling allerod the younger dryas and the 8 2 ka cold event were identified

broadband sound propagation in shallow water and geoacoustic inversion part of an experiment to test a measurement package in a shallow water region in the gulf of mexico was designed to gather broadband acoustic data suitable for inversion to estimate seabed geoacoustic parameters continuous wave tow acoustic signals at multiple frequencies and broadband impulsive source signals were recorded on a horizontal line array in a high noise environment simulated annealing with a normal mode forward propagation model is utilized to invert for a geoacoustic representation of the seabed several inversions are made from different data samples of two light bulb implosions the measured sound speed profiles at the hla and at the positions of the light bulb deployments and for two different cost functions the different cost functions measured sound speed profiles and measured time series result in different inverted geoacoustic profiles from which transmission loss is generated for comparison with measurements on the basis of physical consistency and from the comparison of the transmission loss and time series a best estimate geoacoustic profile is selected and compared to those obtained from previously reported inversions uncertainties in the sound speed profile are shown to affect the uncertainties of the estimated seabed parameters

passive bottom reflection loss estimation using ship noise and a vertical line array an existing technique for passive bottom loss estimation from natural marine surface noise generated by waves and wind is adapted to use noise generated by ships the original approach based on beamforming of the noise field recorded by a vertical line array of hydrophones is retained however additional processing is needed in order for the field generated by a passing ship to show features that are similar to those of the natural surface noise field a necessary requisite is that the ship position relative to the array varies over as wide a range of steering angles as possible ideally passing directly over the array to ensure coverage of the steepest angles the methodology is illustrated through simulation and applied to data from a field experiment conducted offshore of san diego ca in 2009

broadband localization by matched fields in range and bearing in shallow water data from a moving source received by three horizontally separated bottomed sensors in a shallow water environment are analyzed using a broadband matched field approach to source localization the water depth was approximately 150 m and the low bottom loss in the area results in low spatial coherence of the broadband field the modeled acoustic fields are constructed via a ray model localizations are made in the x y plane in a large search area the time evolution of the ambiguity surfaces produced from the data agree fairly well with simulated surfaces ambiguity surfaces are generated successively at intervals of about 1 6 s in small search areas with a fine spatial grid to test the possibility of tracking a source results of the source tracking are presented the analysis also considers the effects of the sea floor on localization in the context of spatial coherence

proof of principle for inversion of vector sensor array data acoustic data collected from a 22 m long horizontal line array with elements comprised of omni directional hydrophone sensors co located with acceleration vector sensor triplets are analyzed for seabed geo acoustic information broadband and continuous wave tone data were recorded from the passage of a surface vessel source the r v montague in an august 2006 experiment conducted in monterey bay the water depth at the array and along the source track was approximately 85 m simultaneous inversions for source track and geo acoustic parameters were performed with 18 tones from the 62 415 hz tone data for source ranges 0 5 2 0 km the efficacy of inversions with vector sensor data is demonstrated by the fact that data from vector sensor acceleration components parallel to the array line of bearing produced inversion solutions approximately identical to the solutions obtained from the inversion of data for the same tones from the hydrophone array components in addition the source spectra derived from these inversions are in nominal agreement with the source spectra obtained from an independent measurement

modeling the effect of freshwater pulses on the early holocene climate the influence of high frequency climate variability freshwater 4 67 10 14 m 3 into the labrador sea at three different constant rates 1 5 sv 1 sv 1 10 6 m 3 s 1 i n 10 years 0 75 sv in 20 years and 0 3 sv in 50 years for each rate five ensemble experiments have been performed varying in initial conditions the freshwater pulses produce a weakening of the thermohaline circulation the perturbed state is in agreement with proxy evidence for the 8 2 ka event two types of recovery of the thermohaline circulation occurred differing in time scale 1 200 years and 2 200 years in the experiments with 10 year and 20 year pulses both types of recovery were observed this suggests that the model response is unpredictable in the range of parameters studied here it is hypothesized that the unpredictability is associated with annual to decadal climate variability our results demonstrate that several types of recovery may exist with the same kind of perturbation the interpretation of events observed in proxy data may be thus more complex than realized until now since the magnitude and duration of climatic events caused by freshwater pulses is likely to depend strongly on nonlinear dynamics inside the coupled atmosphere sea ice ocean system index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4255 oceanography general numerical modeling 4532 oceanography physical general circulation 4215 oceanography general climate and interannual variability 3309 9325 information related to geographic region atlantic ocean keywords holocene thermohaline circulation predictability meltwater coupled climate model

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

plant wax δd values record changing eastern mediterranean atmospheric circulation patterns during the 8 2 kyr b p climatic event abstract throughout the holocene the climate of the mediterranean region has been strongly influenced by variability in the atmospheric circulation of the high and low latitudes a prominent example for such holocene climate perturbations is the 8 2 kyr b p climatic event reorganization of northern hemisphere atmospheric circulation patterns resulted in variations of temperature and precipitation distribution across the mediterranean the effects of changing high and low latitude atmospheric circulation on mediterranean climate in relation to the 8 2 kyr b p climatic event are however not well understood here we present a high resolution record of stable hydrogen isotope composition of plant wax n alkanes dwax across the 8 2 kyr b p climatic event from the tenaghi philippon peat deposit ne greece in order to characterize patterns of precipitation and changes in atmospheric circulation in the eastern mediterranean region our record reveals pronounced changes in dwax that correlate closely with previously published palynological data a long term decline in dwax values characterizes the lower part of the section the 8 2 kyr b p climatic event itself is connected to two distinct positive dwax excursions a minor shift in dwax around 8 2 kyr b p and a major shift in dwax between ca 8 1 and 8 0 kyr b p the upper part of the section shows a progressive trend towards higher dwax values we link shifts in dwax to changes in mediterranean air mass trajectories supplying precipitation to ne greece caused by variations in the relative contributions of northerly derived d depleted moisture and southerly derived d enriched moisture possible control mechanisms for alternating air mass trajectories include changes in the influence of the siberian high and differences in the influence of the african and asian monsoon circulation on anticyclonic conditions in the mediterranean region as well as regional inflow of moist air masses from the aegean sea

nonlinear inversion for ocean bottom properties high resolution methods based on simulated annealing and full wave sound propagation models are developed for nonlinear inversion for ocean bottom properties simulated annealing is used to search the high dimensional parameter space of ocean bottoms for the parameter set corresponding to the best replica field the parabolic equation method is used to solve range dependent inversion problems for data taken by lynch et al from a range dependent region of the gulf of mexico j acoust soc am 89 648 665 1991 this approach achieves excellent agreement between the theoretical and measured acoustic pressures the recovered sediment parameters suggest that a sound speed boundary layer exists in the upper part of the sediment and that the depth of an interface in the sediment is range dependent for locally range independent problems inversion is performed in wave number space large efficiency gains are possible with this approach because the number of wave number samples required for inversion is mu

matched field geoacoustic inversion with a horizontal array and low level source this paper applies geoacoustic inversion to acoustic field data collected on a bottom moored horizontal line array due to a continuous wave towed source at a shallow water site in the barents sea the source transmitted tones in the frequency band of 30 160hz at levels comparable to those of a merchant ship with resulting signal to noise ratios of 9 15db bayesian inversion is applied to cross spectral density matrices formed by averaging spectra from a sequence of time series segments snapshots quantifying data errors including measurement and theory errors is an important component of bayesian inversion to date data error estimation for snapshot averaged data has assumed either that averaging reduces errors as if they were fully independent between snapshots or that averaging does not reduce errors at all this paper quantifies data errors assuming that averaging reduces measurement error dominated by ambient noise but does not reduce theory modeling error providing a physically reasonable

climate dynamics in the borderlands of the aegean sea during formation of sapropel s1 deduced from a marine pollen record abstract to unravel the climatic and environmental dynamics in the borderlands of the aegean sea during the early and middle holocene and notably for the interval of sapropel s1 s1 formation we have analysed terrestrial palynomorphs from a marine core in the northern aegean sea the qualitative results were complemented by quantitative pollen based climate reconstructions a land sea correlation was established based on pollen data and sediment lightness measurements from the same core and previously published benthic foraminifer data from a nearby core the borderlands of the aegean sea underwent a transition from an open vegetation to oak dominated woodlands between 10 4 and 9 5 ka cal bp a coeval increase in winter precipitation suggests that moisture availability was the main factor controlling holocene reforestation the 50 higher winter precipitation during s1 formation relative to pre sapropelic conditions suggests a strong contribution from the borderlands of the aegean sea to the freshwater surplus during s1 formation the humid and mild winter conditions during s1 formation were repeatedly punctuated by short term climatic events that caused a partial deforestation and a reorganisation within the broad leaved arboreal vegetation in the marine realm these events are documented by improved benthic oxygenation the strongest event represents the regional expression of the 8 2 ka cold event and led to an interruption in s1 formation except for the interval of s1 formation the pollen derived winter temperatures correlate with the smoothed gisp2 k series they support the previously published marine based concept that the intensity of the siberian high strongly controlled the winter climate in the aegean region during s1 formation in the aegean sea however climate conditions in the borderlands were more strongly affected by the monsoonally influenced climate system of the lower latitudes

small scale spatial variation of the stress field in the back arc aegean area results from the seismotectonic study of the broader area of mygdonia basin n greece abstract in the present work a detailed seismotectonic study of the broader area of the mygdonia basin n greece is performed digital data for earthquakes which occurred in the broader mygdonia basin and were recorded by the permanent telemetric network of the geophysical laboratory of the aristotle university of thessaloniki during the period 1989 1999 were collected and fault plane solutions for 50 earthquakes which occurred in the study area were calculated with a modified first motions approach which incorporates amplitude and radiation pattern information fault plane solutions for the 3 main shocks of volvi 23 05 78 m w 5 8 and 20 06 78 m w 6 5 and arnaia 04 05 95 m w 5 8 events and the 1978 aftershock sequence were additionally used moreover data from two local networks established in the mygdonia basin were also incorporated in the final dataset determination of the stress field was realized by the use of the method of gephart and forsyth gephart j w forsyth d w 1984 an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence jour geophys res v 89 no b11 p 9305 9320 for the stress tensor inversion and the results were compared with independent estimates based on the calculation of the average moment tensor papazachos c b kiratzi a a 1992 a formulation for reliable estimation of active crustal deformation and its application to central greece geophys j int 111 424 432 the obtained stress results show a relatively good agreement between the two approaches with differences in the azimuth of the dominant extension axis of the order of 10 furthermore comparison with independent information for the mean stress axes provided by the study of kinematics on neotectonic faults mountrakis d kilias a tranos m thomaidou e papazachos c karakaisis g scordilis e chatzidimitriou p papadimitriou e vargemezis g aidona e karagianni e vamvakaris d skarlatoudis a 2003 determination of the settings and the seismotectonic behavior of the main seismic active faults of northern greece area using neotectonic and seismological data earthquake planning and protection organisation oasp in greek shows a similar agreement with typical misfit of the order 10 the stress inversion method was modified in order to select one or both nodal planes of the focal mechanism which corresponds to the true fault plane of the occurred earthquakes and was able to select a single fault plane in the majority of examined cases using this approach the obtained fault plane rose diagrams are in agreement with results from various neotectonic studies moreover several secondary active fault branches were identified which are still not clearly observed in the field

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

environmental evolution of the paliouras coastal lagoon in the eastern thermaikos gulf greece during holocene the integration of lithology determination micropaleontological and molluscan analyses scanning electron microscopy magnetic susceptibility measurement and radiocarbon dating contributed to the interpretation of a sedimentary succession recovered from a 870 cm long borehole drilled at the paliouras coastal lagoon in the eastern thermaikos gulf greece in this way the reconstruction of the creation and evolution of the lagoon during the last 8000 years was accomplished four main evolutionary phases are identified 1 initially the pre holocene basement of the study area was inundated during the early holocene marine transgression 2 since 8000 7900 cal yr bp an inner lagoon had been formed in the paliouras coastal plain within a rather restricted environment characterized by a haynesina germanica cerastoderma glaucum and hydrobia sp assemblage relatively high sediment magnetic susceptibility and an intense presence of abnormal foraminiferal tests and lenticular gypsum crystals 3 during 7600 6900 cal yr bp the inner lagoon presented a transition to an open system clearly connected to the sea and characterized by an ammonia beccarii aubignyna perlucida and miliolids assemblage more diversified molluscan fauna minimum sediment magnetic susceptibility and the occurrence of lenticular gypsum aggregates and finally 4 since 5900 cal yr bp to the present time the lagoon water body appears isolated from the marine environment except of occasional seawater intrusions the proposed evolutionary scenario for the paliouras coastal lagoon is in accordance with the existing models of the sea level rise in the aegean coastal areas concerning the time span before 4000 yr bp and the mid late holocene climate events

surface and deep ocean interactions during the cold climate event 8200 years ago evidence from a north atlantic deep sea sediment core reveals that the largest climatic perturbation in our present interglacial the 8200 year event is marked by two distinct cooling events in the subpolar north atlantic at 8490 and 8290 years ago an associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the atlantic meridional overturning circulation the existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying laurentide ice sheet margin

massive perturbation in terrestrial ecosystems of the eastern mediterranean region associated with the 8 2 kyr b p climatic event the climatic perturbation at ca 8 2 kyr b p is the strongest short term climate anomaly within the holocene it is generally attributed to a meltwater induced slowdown of the thermohaline circulation in the north atlantic model simulations and available proxy data suggest that it was strongest in the high to middle latitudes around the north atlantic based on new pollen data from tenaghi philippon northeastern greece we provide evidence for a massive climate induced turnover in terrestrial ecosystems of the aegean region associated with the 8 2 kyr b p event the reconstructed winter temperature decline of 4 c is much stronger than suggested by model simulations and proxy data from more northern latitudes of europe although the latter provide a direct downstream response to a north atlantic thermohaline circulation slowdown we attribute this discrepancy to mesoclimatic effects a stronger influence of the siberian high during the 8 2 kyr b p event may have enhanced the katabatic air flow from the mountains bordering the study site via a larger longer persisting snow cover our data demonstrate that high amplitude temperature anomalies and increased seasonality connected to the 8 2 kyr b p event may also have occurred in the lower mid latitudes much farther south than previously thought the magnitudes of these anomalies appear to have been strong enough to have seriously affected neolithic settlers in the northeastern mediterranean region

climatic and human impact on the environment a question of scale abstract the environmental context of cultural transformation frames the central issue of this paper how were neolithic and chalcolithic landscapes in the aegean balkan and carpathian abc zones shaped and transformed by climatic and anthropogenic impacts the difficulties in interpreting proxy records for the middle transitional stage of the holocene aridification sequence falling between the early wet stage and the late arid stage have been created by the conjoint influence of two kinds of impact climatic and anthropogenic an unhelpful influence in this debate stems from willis and bennett s 1994 hypothesis of minimal human impact on the pre bronze age landscapes of south east europe in this paper two questions are posed 1 what were the effects of the claimed global changes in holocene climate at the regional and local scale in the abc zones and 2 can we recognise human impact in these proxy records prior to the bronze age of our study regions following a discussion of general long term climatic trends and rccs episodes of rapid climatic change i base a discussion of the so called 8200bp event and pre bronze age human impacts on a suite of 24 well dated proxy records mostly pollen sequences the principal findings are that there is little evidence for impact from the 8200bp event in these records while there is substantial evidence for pre bronze age human impacts on the landscapes of the aegean balkan and carpathian regions

late quaternary bottom current activity in the south aegean sea reflecting climate driven dense water production abstract the eastern mediterranean transient emt represents a recent early 1990s to today water circulation phenomenon during which more arid climatic conditions in the mediterranean lead to the production of very dense surface water masses in the north aegean sea the produced north aegean dense water nadw sinks to seafloor flows to the south aegean sea and then spills into the eastern mediterranean sea through the cretan straits contributing to the rejuvenation of the bottom water a large dataset of vintage high resolution seismic reflection profiles indicates that the floors of the basins in the southwest aegean sea are characterised by late quaternary erosional gullies abraded surfaces and channel related sediment drifts such structures provide evidence for the presence of strong bottom currents which originate from the southward propagation of nadw masses the basins have depths of 300 m to 1000 m and are connected to each other by narrow a few km straits and sills the dominance of abraded surfaces and erosional gullies on the northern flank of the basins and in the narrow straits sills between them provides evidence that the southward propagation of the nadw occurs by the filling and flooding of each basin by dense water which then spills and cascades into the next basin southward seismic stratigraphy suggests that the formation of the drifts started at marine isotope stage mis 11 420 ka bp the coincidence of at least three erosional surfaces within the sediment drifts with interglacial mis 11 5 and 1 respectively suggests that bottom currents were mostly active during high sea level stands and sluggish during glacial low sea level stands a 90 100 m drop of the sea level below the current level would have resulted in the emergence of the eastern cyclades plateau and thus in the disconnection of the southwest aegean sea from the north aegean sea several 0 05 0 5 m thick beds of gravelly sand with algal and mollusc debris laminated to mottled sand and mottled mud are observed in the sediment cores analysed in this paper these beds can be confidently correlated from core to core and are interpreted as bottom current deposits the separation of these beds by hemipelagic sediments indicates that bottom current activity in the southwest aegean is not permanently established but episodic six episodes of intense bottom current activity are recorded in the mis 2 4 10 80 ka sediments and they appear to correlate well with the cold and dry younger dryas and heinrich 3 4 5 6 and 7 events in contrast at least three episodes of intense bottom current activity are recorded in the cores during the holocene the higher frequency of strong bottom current episodes in the southwest aegean sea during the holocene is attributed to the higher sea level stand that makes the circulation of water masses in the aegean sea more sensitive to climatic changes

holocene atmosphere ocean interactions records from greenland and the aegean sea we compare paleoclimate proxy records from central greenland and the aegean sea to offer new insights into the causes timing and mechanisms of holocene atmosphere ocean interactions a direct atmospheric link is revealed between aegean sea surface temperature sst and high latitude climate the major holocene events in our proxies of aegean sst and winter spring intensity of the siberian high gisp2 k record follow an 2300 year spacing recognised also in the 14c record and in worldwide holocene glacier advance phases suggesting a solar modulation of climate we argue that the primary atmospheric response involved decadal centennial fluctuations in the meridional pressure gradient driving aegean sst events via changes in the strength duration and or frequency of northerly polar continental air outbreaks over the basin the observed natural variability should be accounted for in predictions of future climate change and our timeframe for the aegean climate events in addition provides an independent chronostratigraphic argument to middle eastern archaeological studies

impact of lateglacial cold events on the northern aegean region reconstructed from marine and terrestrial proxy data marine palynomorph data paired with other indicators of sea surface hydrography planktic foraminiferal assemblages and oxygen isotopes were used to decipher the impact of cold events on the northern aegean region during the last glacial to interglacial transition the data which were derived from marine sediment cores geotusl152 and geotusl148 point to a strong impact of the heinrich 1 and younger dryas cold events on surface water conditions in the northern aegean sea shifts in marine palynomorph assemblages correlate with changes in terrestrial vegetation and climate i e precipitation and temperature reconstruc tions based on pollen assemblages in the northern borderlands of the aegean sea the climate responses of the aegean region to heinrich event 1 h1 ca 17 5 to ca 15 7 cal ka bp and younger dryas ca 12 6 to ca 11 7 cal ka bp events appear similar in magnitude with mean annual temperatures between 6 and 108c and mean annual precipitation between 300 and 450 mm however the annual temperature decline during the h1 relative to the preceding already cold conditions was minor 38c the transition from the relatively warm and humid local equivalent of the allerod interstadial to the younger dryas on the other hand witnessed an annual temperature decline of 68c and an annual precipitation decrease of 300 mm the latter occurring abruptly within only ca 150 a the return to warmer conditions in the northern aegean region after the younger dryas was completed at ca 11 6 cal ka bp copyright 2011 john wiley sons ltd

inversion for geometric and geoacoustic parameters in shallow water experimental results experimental results on the estimation of both geometric and geoacoustic parameters in shallow water are presented genetic algorithms are used for estimation of the forward model parameters the estimated parameters are then used by a standard bartlett processor for source localization a stationary source at a range of 5 6 km and a moving source at ranges from 5 8 7 7 km were successfully localized in range and depth using a single frequency bartlett processor the results indicate that global estimation of the forward model parameters significantly improves source localization performance

enhanced seasonality of precipitation in the mediterranean during the early part of the last interglacial the deposition of sapropels in the eastern mediterranean sea is thought to occur during intervals of intensified african monsoon and increased precipitation in the mediterranean borderlands speleothem and pollen records however reveal conflicting evidence for a mediterranean wide precipitation increase suggesting that seasonal changes in the hydrological regime may be important using a multiproxy record we present the first independent evidence for seasonality of precipitation during the early last interglacial ca 130 119 ka from the tenaghi philippon peatland in northeast greece during the early part of the interglacial mineralogical macrofossil and pollen records from the same core show a shift from mire to lacustrine conditions simultaneous with an expansion of sclerophyllous vegetation and the presence of acicular aragonite indicating the onset of highly evaporative summer conditions this indicates enhanced seasonality of precipitation and reconciles the apparent incongruity between mediterranean pollen and speleothem records it also provides evidence for significantly increased winter precipitation coeval with the deposition of sapropel s5 one of the most prominent sapropels of the pleistocene we suggest that in addition to the summer african monsoon component increased winter precipitation from the northern mediterranean borderlands may have contributed to maintaining reduced surface water salinities in the mediterranean sea over the entire year

multiproxy analyses of lake allos reveal synchronicity and divergence in geosystem dynamics during the lateglacial holocene in the alps abstract palaeoenvironmental reconstructions of ecosystem responses to external forcing are generally limited by the difficulty of understanding the geosystem as a whole because of the complex interactions between ecological compartments therefore identifying which geosystem compartments or proxies co vary is a prerequisite in unravelling the propagation of disturbances e g climatic or anthropogenic from one compartment to another a multiproxy study of a continuous 13 500 year sedimentary profile cored in lake allos european alps 2200 m a s l was carried out on the basis of high resolution sedimentological geochemical and botanical analyses as well as determination of aquatic biotic proxies diatoms ostracods these multiproxy datasets are rare at these high altitudes major changes occurred in the course of the palaeoenvironmental history of this alpine watershed at 12 000 8600 7200 and 3000 cal bp during the holocene two main transitions were recorded in all the ecological compartments 8600 and 3000 cal bp but the period 4500 3000 cal bp stands out because of major changes that concerned only the lacustrine ecosystem the frequent switches in lake level might correspond to the 4 2 ka climatic event proximity of this alpine lake to climatically sensitive thresholds ice cover thermal stratification hydrological balance may have amplified climatic signals in the lake ecosystem this study illustrates the difficulties inherent to the use of common intra holocene stratigraphical limits given that ecological compartments are likely to have different responses to forcing factors depending on the characteristics of the watershed and its capacity to accommodate disturbances

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

tomographic inversion of geoacoustic properties in a range dependent shallow water environment this paper presents a matched field tomographic method to estimate the geoacoustic properties of the ocean bottom for a range dependent medium in shallow water the inversion method has been developed in order to interpret experimental data from the haro strait primer sea trial this experiment was carried out in june 96 and used low frequency broadband signals that were received on three vertical line arrays inversion of the data is particularly difficult because of the complex bathymetry of the haro strait experimental site for this inversion a range dependent ray code was developed to solve the forward problem allowing an arbitrarily layered bottom environment the inversion scheme is based on modeling the propagation time and the amplitude of the recorded data and a simple new cost function is proposed the signal ray paths are identified automatically using a simple process that compares calculated and measured travel times data from multiple source positions are used to invert the range dependence of the geoacoustic model the environment is separated into segments and within each segment the inversion is carried out layer by layer for a multilayer geoacoustic model starting with the topmost layer the range dependent thickness and sound speed are estimated via a monte carlo method inversion results are presented for synthetic and experimental data from the haro strait sea trial

holocene climate and cultural evolution in late prehistoric early historic west asia abstract the precipitation climatology and the underlying climate mechanisms of the eastern mediterranean west asia and the indian subcontinent are reviewed with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation holocene climate change of the region is summarized from proxy records the indian monsoon weakened during the holocene over its northernmost region the ganges and indus catchments and the western arabian sea southern regions the indian peninsula do not show a reduction but an increase of summer monsoon rain across the holocene the long term trend towards drier conditions in the eastern mediterranean can be linked to a regionally complex monsoon evolution abrupt climate change events such as the widespread droughts around 8200 5200 and 4200 cal yr bp are suggested to be the result of altered subtropical upper level flow over the eastern mediterranean and asia the abrupt climate change events of the holocene radically altered precipitation fundamental for cereal agriculture across the expanse of late prehistoric early historic cultures known from the archaeological record in these regions social adaptations to reduced agro production in both dry farming and irrigation agriculture regions are visible in the archaeological record during each abrupt climate change event in west asia chronological refinement in both the paleoclimate and archaeological records and transfer functions for both precipitation and agro production are needed to understand precisely the evident causal linkages

reconciling the greenland ice core and radiocarbon timescales through the laschamp geomagnetic excursion abstract cosmogenic radionuclides such as 10be and 14c share a common production signal with their formation in the earth s upper atmosphere modulated by changes to the geomagnetic field as well as variations in the intensity of the solar wind here we use this common production signal to compare between the radiocarbon intcal and greenland ice core gicc05 timescales utilising the most pronounced cosmogenic production peak of the last 100 000 years that associated with the laschamp geomagnetic excursion circa 41 000 years ago we present 54 new 14c measurements from a peat core tp 2005 from tenaghi philippon ne greece contiguously spanning between circa 47 300 and 39 600 cal bp demonstrating a distinctive tripartite structure in the build up to the principal laschamp production maximum that is not present in the consensus intcal13 calibration curve this is the first time that a continuous non reservoir corrected 14c dataset has been generated over such a long time span for this the oldest portion of the radiocarbon timescale this period is critical for both palaeoenvironmental and archaeological applications with the replacement of neanderthals by anatomically modern humans in europe around this time by placing our tenaghi philippon 14c dataset on to the hulu cave u series timescale of cheng et al 2018 via bayesian statistical modelling the comparison of tp 2005 14c with greenland 10be fluxes also implicitly relates the underlying u series and gicc05 timescales themselves this comparison suggests that whilst these two timescales are broadly coherent the intcal13 timescale contains erroneous structure circa 40 000 cal bp

geoacoustic inversion of short range source data using a plane wave reflection coefficient approach acoustic time series data were collected in a shallow hard bottom lake environment located in central texas using both short range 2 m implosive data obtained with the source and a single hydrophone located near mid depth in the waveguide along with longer range implosive and explosive data from a near surface source to a bottom mounted hydrophone matched field inversions using simulated annealing were performed with a ray trace plus complex plane wave reflection coefficient forward propagation model that was validated in previous work isolating bottom interacting paths to perform the inversions is shown to be essential to reduce parameter uncertainties in the hard bottom environment and enables a systematic approach to the inversions which establishes the number of layers needed to represent the lake environment measured transmission loss data from a towed source were compared through a rms error analysis to modeled transmission loss constructed with the parameters from inversions of data from several source types to further establish the validity of the inversion approach for this environment geoacoustic parameters obtained by inversions of short range low frequency impulsive data are used to predict transmission loss at longer ranges and higher frequencies the range dependence of the global minimum is discussed

early to mid holocene paleohydrology in northeast mediterranean the detrital record of aliakmon river in loudias lake greece one of the prominent features of northeast mediterranean nem holocene climate are recurrent phases of cold and aridity their impacts on the hydrological cycle remain at large unknown as few existing paleohydrological records are either restricted to lake level fluctuations or focus near the 8 2 kyr bp event here we present the detrital record of aliakmon river in lake loudias between 9500 and 3000 cal bp magnetic susceptibility ms exhibits high correlation with mean grain size r 0 7 of silt sized fractions and is used as a proxy of the distal clastic input of aliakmon river whereas organic matter om carbonate content caco3 water content wc and clay concentrations decipher sedimentological and biological processes in lake loudias periods of high hydrological activity were interrupted by short intervals of low river discharge at c 9400 8600 8200 7500 7000 6200 5300 and 4500 cal bp and during a multi century event centered at 3500 cal bp in agreement with marine and terrestrial paleoclimatic reconstructions from nem with exception of the wet period between c 8 6 and 7 9 cal bp periods of increased hydrological activity are synchronous to contraction of pinus forests and increased sea surface temperatures and silt transport in the aegean sea the long term similar to 580 years variability of ms is in phase with southeast europe pollen inferred annual temperature variations and with north atlantic ice rafted debris ird events

centennial scale climate cooling with a sudden cold event around 8 200 years ago the extent of climate variability during the current interglacial period the holocene is still debated temperature records derived from central greenland ice cores show one significant temperature anomaly between 8 200 and 8 100 years ago which is often attributed to a meltwater outflow into the north atlantic ocean and a slowdown of north atlantic deep water formation this anomaly provides an opportunity to study such processes with relevance to present day freshening of the north atlantic anomalies in climate proxy records from locations around the globe are often correlated with this sharp event in greenland but the anomalies in many of these records span 400 to 600 years start from about 8 600 years ago and form part of a repeating pattern within the holocene more sudden climate changes around 8 200 years ago appear superimposed on this longer term cooling the compounded nature of the signals implies that far field climate anomalies around 8 200 years ago cannot be used in a straightforward manner to assess the impact of a slowdown of north atlantic deep water formation and the geographical extent of the rapid cooling event 8 200 years ago remains to be determined

middle holocene rapid environmental changes and human adaptation in greece numerous researchers discuss of the collapse of civilizations in response to abrupt climate change in the mediterranean region the period between 6500 and 5000 cal yr bp is one of the least studied episodes of rapid climate change at the end of the late neolithic this period is characterized by a dramatic decline in settlement and a cultural break in the balkans high resolution paleoenvironmental proxy data obtained in the lower angitis valley enables an examination of the societal responses to rapid climatic change in greece development of a lasting fluvio lacustrine environment followed by enhanced fluvial activity is evident from 6000 cal yr bp paleoecological data show a succession of dry events at 5800 5700 5450 and 5000 4900 cal yr bp these events correspond to incursion of cold air masses to the eastern mediterranean confirming the climatic instability of the middle holocene climate transition two periods with farming and pastural activities 6300 5600 and 5100 4700 cal bp are evident the intervening period is marked by environmental changes but the continuous occurrence of anthropogenic taxa suggests the persistence of human activities despite the absence of archaeological evidence the environmental factors alone were not sufficient to trigger the observed societal changes

seabed acoustics of a sand ridge on the new jersey continental shelf acoustic measurements were made on a sand ridge on the new jersey continental shelf data collected on two l arrays separated by 20km from a single multi frequency tow suggest small horizontal environmental variability values for the sound speed structure of the seabed are extracted by first applying a geo acoustic inversion method to broadband and narrowband acoustic data from short range sources then a parabolic equation algorithm is used to properly include the bathymetry and sub bottom layering finally the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long range transmission loss data in the 50 3000hz band

mid holocene emergence of a low frequency millennial oscillation in western mediterranean climate implications for past dynamics of the north atlantic atmospheric westerlies the nature and tempo of holocene climate variability is examined in the record of forest vegetation from western mediterranean marine core md95 2043 episodes of forest decline occurred at 10 1 9 2 8 3 7 4 5 4 4 5 and 3 7 2 9 cal ka bp and between 1 9 cal ka bp and the top of the record 1 3 cal ka bp wavelet analysis confirms a 900 yr periodicity prior to and during the early holocene and the dominance of a 1750 yr periodicity after 6 cal ka bp the 900 yr periodicity has counterparts in numerous north atlantic and northern hemisphere palaeoclimate records and in solar irradiance proxies 14c and 10be and may relate to a sun climate connection during the early holocene comparisons between the md95 2043 forest record and strategically located records from morocco iceland norway and israel suggest that the 1750 yr mid to late holocene oscillation reflects shifts between a prevailing strong and weak state of the zonal flow with impacts similar to the positive and negative modes of th

bayesian geoacoustic inversion of ship noise on a horizontal array this paper applies geoacoustic inversion to low frequency narrow band acoustic data from a quiet surface ship recorded on a bottom moored horizontal line array in shallow water a bayesian matched field inversion method is employed which quantifies geoacoustic uncertainties and allows for meaningful comparison of inversion results from different data sets geoacoustic inversion results for ship noise data are compared with inversion results for multitone data from a towed controlled source collected in the same experiment and with independent geophysical measurements to increase the information content of low level ship noise data the effect of including multiple independent data segments in the inversion is investigated and shown to significantly reduce geoacoustic parameter uncertainties geoacoustic uncertainties are also shown to depend on ship range and orientation with increased uncertainties for long ranges and for the ship stern oriented away from the array

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

climate forcing due to the 8200 cal yr bp event observed at early neolithic sites in the eastern mediterranean we explore the hypothesis that the abrupt drainage of laurentide lakes and associated rapid switch of the north atlantic thermohaline circulation 8200 yr ago had a catastrophic influence on neolithic civilisation in large parts of southeastern europe anatolia cyprus and the near east the event at 8200 cal yr bp is observed in a large number of high resolution climate proxies in the northern hemisphere and in many cases corresponds to markedly cold and arid conditions we identify the relevant archaeological levels of major neolithic settlements in central anatolia cyprus greece and bulgaria and examine published stratigraphic architectural cultural and geoarchaeological studies for these sites the specific archaeological events and processes we observe at a number of these sites during the study interval 8400 8000 cal yr bp lead us to refine some previously established neolithisation models the introduction of farming to south east europe occurs in all study regions thrace macedonia thessaly bulgaria near 8200 cal yr bp we observe major disruptions of neolithic cultures in the levant north syria south east anatolia central anatolia and cyprus at the same time we conclude that the 8200 cal yr bp aridity event triggered the spread of early farmers by different routes out of west asia and the near east into greece and bulgaria

sedimentological response to holocene climate events in the istron area gulf of mirabello ne crete this paper aims to reveal the depositional environment of istron and its sedimentological response to holocene climatic events the results of a multi disciplinary geoarchaeological research undertaken in the coastal area of istron northeastern crete provided information on the depositional environment and the palaeoenvironmental evolution of the area during the holocene detailed fieldwork and sampling by drilling cores in the coastal area provided samples for further analytical studies the identification of the stratigraphy and the distinction of sedimentological units provided evidence for landscape evolution of the coastal area changes of sedimentation rates determined by optical dating and sedimentological analysis were also correlated with holocene climatic phases

offset timing of climate oscillations during the last two glacial interglacial transitions connected with large scale freshwater perturbation multidecadal to centennial planktic 18o and mg ca records were generated at ocean drilling program site 976 odp976 in the alboran sea the site is in the flow path of atlantic inflow waters entering the mediterranean and captured north atlantic signals through the surface inflow and the atmosphere the records reveal similar climatic oscillations during the last two glacial to interglacial transitions albeit with a different temporal pacing glacial termination 1 t1 was marked by heinrich event 1 h1 post h1 bolling allerod warming and younger dryas yd cooling during t2 the h11 18o anomaly was twice as high and lasted 30 longer than during h1 the post h11 warming marked the start of mis5e while the subsequent yd style cooling occurred during early mis5e the post h11 temperature increase at odp976 matched the sudden asian monsoon termination ii at 129 ka b p extending the 230th dated speleothem timescale to odp976 suggests glacial conditions in the northeast atlantic region were terminated abruptly and interglacial warmth was reached in less than a millennium the early mis5e cooling and freshening at odp976 coincided with similar changes at north atlantic sites suggesting this was a basin wide event by analogy with t1 we argue that this was a yd type event that was shifted into the early stages of the last interglacial period this scenario is consistent with evidence from northern north atlantic and nordic sea sites that the continuing disintegration of the large saalian stage mis6 ice sheet in eurasia delayed the advection of warm north atlantic waters and full strength convective overturn until later stages of mis5e

vegetation and climate changes in the south eastern mediterranean during the last glacial interglacial cycle 86 ka new marine pollen record the eastern mediterranean located at the meeting between the mediterranean vegetation of the eurasian continent and the desert vegetation of the saharan arabian desert belt is ideal for tracking changes in regional vegetation as function of climate changes reconstruction of these changes in the south eastern mediterranean during the last 86 ka is based on a palynological record from deep sea core 9509 taken by r v marion dufresne off the southern israeli coast the chronological framework is based on the correlation of d 18 o records of planktonic foraminifera with the high resolution well dated u th speleothem record from the soreq cave israel and the occurrence of sapropel layers several cycles of humid dry periods were documented during the last 86 ka the record starts with the moderate humid and warm sapropel s3 marking the end of marine isotope stage mis 5 the climate during the last glacial period 75 5e16 2 ka was cold and dry with low arboreal pollen ap levels and high values of semi desert and desert vegetation e g artemisia sagebrush the driest and coldest period during the last 86 ka corresponds to mis 2 27 1e16 2 ka characterized by the lowest tree cover along the sequence and the dominance of steppe vegetation some slightly more humid fluctuations were identified during the period of 56 3 and 43 5 ka with its peak between 56 0 and 54 4 ka the most pronounced climate change started at the beginning of the deglaciation 16 2e10 ka and continued throughout the holocene last 10 ka notwithstanding some short fluctuations high ap levels were dominated by quercus callipprinos evergreen oak suggesting that the mediterranean forest was more extensive in the area and the climate was wet sapropels s3 and s1 were clearly recognized here by the high concentrations and good state of preservation of pollen because of the development of anoxia in the bottom water that may be related to more extensive nile discharge coinciding with high insolation values at 65

geomorphologic and paleoclimatic evidence of holocene glaciation on mount olympus greece this study investigates the possibility of holocene glaciation on mount olympus greece with a respective local temperature precipitation equilibrium line altitude tp ela at c 2200m a s l based on geomorphologic and paleoclimatic evidence at present the local tp ela is situated above the mountain s summit c 2918 m a s l but permanent snowfields and ice bodies survive within megala kazania cirque between c 2400 and c 2300 m a s l because of the cirque s maritime setting that results from its close proximity c 18km to the aegean sea and of the local topographical controls the snow and ice bodies occupied a considerably larger area and attained a stabilization phase between ad 1960 and 1980 also manifested from aerial photographs a period characterized by increased winter precipitation pw with subsequent tp ela depression to c 2410m a s l mid to late 20th century pw and tp ela variations exhibit negative correlations with the winter north atlantic oscillation index naow at annual and multidecadal 30 years timescales late holocene ad 1680 1860 reconstructed summer mean temperatures were lower by ts 1 1 c in relation to the reference period between ad 1960 and 1980 and were also superimposed to negative naow phases thus bracketing this time interval as a favorable one to glacial formation and or advance millennial scale annual precipitation reconstructions at the hypothesized tp ela c 2200m a s l point the period between 8 and 4 kyr bp as another glacier friendly candidate the mid holocene rather simplistic sequence of potential glacial advance phase was disturbed by short lived cold climatic deteriorations well documented over the northern aegean region that may partly explain the multicrested shape of the highest c 2200 m a s l morainic complex of megala kazania cirque

depositional frequency of german subfossil oaks climatically and non climatically induced fluctuations in the holocene a highly resolved record of the depositional frequency of subfossil trees since 8263 bc in the valley of the river main is presented different aspects of forest dynamics are explored including depositional anomal ies phases of low or zero departures changes in forest density based on tree growth trend classes gtcs and regeneration using mean lifespan ml data this reveals a number of climatically induced environmental changes that are synchronous with events in the north atlantic region and therefore may reflect a facet of the north atlantic climate system three periods are recognized 1 pre 3500 bc when depositional frequency was dominated by climatic events with notable anomalies at 6200 and 4100 bc 2 between 3500 and 1200 bc when climatically triggered events were enhanced by forest clearances especially marked anomalies occurring around 2700 2300 and 1700 bc and 3 post 1200 bc when the climatic information is obscured by human activities

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

climatic forcing of eastern mediterranean deep water formation and benthic ecosystems during the past 22 000 years abstract lateglacial and holocene faunal and stable isotope records from benthic foraminifers in the eastern mediterranean sea ems suggest a high spatiotemporal variability of deep water oxygenation and biogeochemical processes at the sea floor during that time changes in the oxygenation and food availability of the deep sea ecosystems are closely linked to the hydrology of the ems borderlands they reflect orbital and suborbital climate variations of the high northern latitudes and the african monsoon system during the last glacial maximum cool surface waters and high evaporation resulted in maximum convection and oxic deep waters in all sub basins strong wind induced mixing fostered surface water production with seasonal phytodetritus fluxes during the glacial termination and the holocene oxygenation and food availability of deep sea benthic ecosystems were characterized by a pronounced regional differentiation local deep water formation and trophic conditions were particularly variable in the northern aegean sea as a response to changes in riverine runoff and black sea outflow during the interval of sapropel s1 formation in the early holocene average oxygen levels decreased exponentially with increasing water depth suggesting a basin wide shallowing of vertical convection superimposed by local signals in the northernmost aegean sea deep water ventilation persisted during the early period of s1 formation owing to temperature driven local convection and the absence of low salinity black sea outflow at the same time severe temporary anoxia occurred in the eastern levantine basin at water depths as shallow as 900 m this area was likely influenced by enhanced nutrient input of the nile river that resulted in high organic matter fluxes and related high oxygen consumption rates in the water column in the southern aegean and levantine seas we observe a gradual increase in deep water residence times preceding s1 formation by approximately 1 1 5 kyr once oxygen levels fell below a critical threshold the benthic ecosystems collapsed almost synchronously with the onset of s1 deposition the recovery of benthic ecosystems during the terminal phase of s1 formation is controlled by subsequently deeper convection and re ventilation over a period of approximately 1500 years after the re ventilation of the various sub basins had been completed during the middle and late holocene deep water renewal was more or less similar to recent rates during that time deep sea ecosystem variability was driven by short term changes in food quantity and quality as well as in seasonality all of which are linked to millennial scale changes in riverine runoff and associated nutrient input