potential links between surging ice sheets circulation changes and the dansgaard oeschger cycles in the irminger sea 60 18 kyr surface and deepwater paleoclimate records in irminger sea core so82 5 59on 31 ow and icelandic sea core ps2644 68on 22ow exhibit large fluctuations in thermohaline circulation thc from 60 to 18 calendar kyr b p with a dominant periodicity of 1460 years from 46 to 22 calendar kyr b p matching the dansgaard oeschger d o cycles in the greenland ice sheet project 2 gisp2 temperature record grootes and tuiver 1997 during interstadials summer sea surface temperatures sstsu in the irminger sea averaged to 8oc and sea surface salinities sss averaged to 36 5 recording a strong irminger current and atlantic thc during stadials sstsu dropped to 2o 4oc in phase with sss drops by 1 2 they reveal major meltwater injections along with the east greenland current which turned off the north atlantic deepwater convection and hence the heat advection to the north in harmony with various ocean circulation and ice models on the basis of the ird composition icebergs came from iceland east greenland and perhaps svalbard and other northern ice sheets however the southward drifting icebergs were initially jammed in the denmark strait reaching the irminger sea only with a lag of 155 195 years we also conclude that the abrupt stadial terminations the d o warming events were tied to iceberg melt via abundant seasonal sea ice and brine water formation in the meltwater covered northwestern north atlantic in the 1 1460 year frequency band benthic 15 80 brine water spikes led the temperature maxima above greenland and in the irminger sea by as little as 95 years thus abundant brine formation which was induced by seasonal freezing of large parts of the northwestern atlantic may have finally entrained a current of warm surface water from the subtropics and thereby triggered the sudden reactivation of the thc in summary the internal dynamics of the east greenland ice sheet may have formed the ultimate pacemaker of d o cycles

high spatial resolution electron probe microanalysis of tephras and melt inclusions without beam induced chemical modification wavelength dispersive analysis of tephra grains and melt inclusions by epma has been carried out using a focused beam of 3 m diameter without detected loss of sodium or potassium in standard glasses including anhydrous basalts a slightly hydrated rhyolite and a sodium rich intermediate composition the ability to make analyses without chemical modification is strongly dependent upon current density at the analysis site analysis with narrow beams requires extremely low beam currents that are normally associated with energy dispersive analysis experiments indicate that a value of 0 1 na m2 must not be exceeded at least for moderately hydrated samples if sodium loss is to be avoided high resolution analysis without beam induced analytical artefacts enables fully quantitative analysis of very distal and or highly vesicular tephras and very small melt inclusions without the need to use post analysis corrections this development has enabled high quality analyses from crypto tephra layers that were pre

tracing marine cryptotephras in the north atlantic during the last glacial period protocols for identification characterisation and evaluating depositional controls abstract tephrochronology is increasingly being utilised as a key tool for improving chronological models and correlating disparate palaeoclimatic sequences for many sedimentary environments however there is an increased recognition that a range of processes may impart a delay in deposition and or rework tephra these processes can affect the integrity of tephra deposits as time synchronous markers therefore it is crucial to assess their isochronous nature especially when cryptotephras are investigated in a dynamic marine environment a methodology for the identification and characterisation of marine cryptotephras alongside a protocol for assessing their integrity is outlined this methodology was applied to a wide network of north atlantic marine sequences covering the last glacial period a diverse range of cryptotephra deposits were identified and based on similarities in physical characteristics e g glass shard concentration profiles and geochemical homogeneity heterogeneity indicative of common modes of tephra delivery and post depositional reworking a deposit type classification scheme was defined the presence and dominance of different deposit types within each core allowed an assessment of spatial and temporal controls on tephra deposition and preservation overall isochronous horizons can be identified across a large portion of the north atlantic due to preferential atmospheric dispersal patterns however the variable influence of ice rafting processes and an interplay between the high eruptive frequency of iceland and relatively lower sedimentation rates can also create complex tephrostratigraphies in this sector sites within a wide sector to the south and east of iceland have the greatest potential to be repositories for isochronous horizons that can facilitate the synchronisation of palaeoclimatic records

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

tephrological implications of beam size sample size effects in electron microprobe analysis of glass shards this paper concerns the potential consequences of varying procedures for the determination of tephra geochemistry by electron microprobe application of electron probe microanalysis to tephrostratigraphical methods has increasingly facilitated the resolution and refinement of quaternary chronology associated with records of proxy environmental or proxy climatic change the geographical range over which tephras are recovered has expanded significantly with the identification and analysis of crypto or hidden tephras in areas far removed from tephra sources these tephras are dominated by glass shards which in many distal environments may be either small in size m or may be highly pumiceous with low glass void ratios and thin 10 m shard walls we demonstrate that reducing the size of the electron beam used to analyse shard geochemistry cannot be used reliably to permit analysis of thin glass walls this approach distorts the geochemical data creating analytical differences that may generate inappropriate tephrogeochemical fingerprints additional distortion of the geochemical fingerprint in the form of hybrid analyses may be encountered in glass fragments containing micron sized crystalline phases such as feldspar copyright 2001 john wiley sons ltd

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

a tephra lattice for greenland and a reconstruction of volcanic events spanning 25 45 ka b2k tephra layers preserved within the greenland ice cores are crucial for the independent synchronisation of these high resolution records to other palaeoclimatic archives here we present a new and detailed tephrochronological framework for the time period 25 000 45 000 a b2k that brings together results from 4 deep greenland ice cores in total 99 tephra deposits the majority of which are preserved as cryptotephra are described from the ngrip neem grip and dye 3 records the major element signatures of single glass shards within these deposits indicate that 93 are basaltic in composition all originating from iceland specifically 43 originate from grimsvotn 20 are thought to be sourced from the katla volcanic system and 17 show affinity to the kverkfjoll system robust geochemical characterisations independent ages derived from the gicc05 ice core chronology and the stratigraphic positions of these deposits relative to the dansgaard oeschger climate events represent a key framework that provides new information on the frequency and nature of volcanic events in the north atlantic region between gs 3 and gi 12 of particular importance are 19 tephra deposits that lie on the rapid climatic transitions that punctuate the last glacial period this framework of well constrained time synchronous tie lines represents an important step towards the independent synchronisation of marine terrestrial and ice core records from the north atlantic region in order to assess the phasing of rapid climatic changes during the last glacial period

ash layers from iceland in the greenland grip ice core correlated with oceanic and land sediments four previously known ash layers ash zones i and ii saksunarvatn and the settlement layer all originating in iceland have been identified in the central greenland ice core grip this correlation of the ash between the different environments is achieved by comparison of the chemical composition of glass shards from the ash this establishes and confirms detailed correlations between the different types of depositional records and the absolute dating of the younger part of the ice core by counting annual layers dates the eruptions accurately a precise connection with dates obtained by14c beyond the range of dendrochronology is established which provides an excellent confirmation of230th 234u dates from corals four additional icelandic ash layers have also been identified in the core but not yet correlated with known ash deposits

hard and soft bottom thanatofacies from the santa maria di leuca deep water coral province mediterranean thanatofacies and the skeletonized components of the living facies from which they originate have been studied from the santa maria di leuca sml deep water coral mound province faunal analysis was carried out by means of bottom sampling and underwater video observations taking into account all benthic taxonomic groups mostly corals molluscs serpulids bryozoans ostracods foraminifers and barnacles which permitted recognition of six different facies these thanatofacies are easily distinguishable and appear to be largely corresponding and overlapping with related living facies some occur in mound areas others in the intermound ones they are as follows the framework building coral facies fc characterised by colonial corals mostly madrepora oculata the coral rubble facies cr with proximal and distal aspects characterised by large to small sized and densely to loosely packed coral fragments the solitary coral facies sc dominated by different species depending on the availability and dimensions of hard exploitable surfaces the gryphus and isidella facies gi in relatively coarse grained bottoms the mollusc mud facies mm and the foraminifer mud facies fm in comparably homogeneous silty bottoms facies distribution and spatial variability are discussed in relation to hydrology and sea floor topography furthermore the sml facies are compared with living facies from the present day mediterranean and pleistocene sediments of the same area data on bioclastic assemblages can serve for comparison with other recent aphotic non tropical carbonates

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

widespread tephra dispersal and ignimbrite emplacement from a subglacial volcano torfajokull iceland the tephra dispersal mechanisms of rhyolitic glaciovolcanic eruptions are little known but can be investigated through the correlation of eruptive products across multiple depositional settings using geochemistry and geochronology we correlate a regionally important pleistocene tephra horizon the rhyolitic component of north atlantic ash zone ii ii rhy 1 and the thorsmork ignimbrite with rhyolitic tuyas at torfajokull volcano iceland the eruption breached an ice mass 400 m thick leading to the widespread dispersal of ii rhy 1 across the north atlantic and the greenland ice sheet locally pyroclastic density currents traveled across the ice surface depositing the variably welded thorsmork ignimbrite beyond the ice margin and 30 km from source the widely dispersed products of this eruption represent a valuable isochronous tie line between terrestrial marine and ice core paleoenvironmental records using the tephra horizon estimates of ice thickness and extent derived from the eruption deposits can be directly linked to the regional climate archive which records the eruption at the onset of greenland stadial 15 2

mid pleistocene silicic tephra beds in the auckland region new zealand their correlation and origins based on the trace element analyses of single glass shards abstract the trace element composition of individual glass shards from twelve distinct mid pleistocene silicic tephra beds from the auckland region new zealand has been determined by laser ablation la icp ms analysis this is the first application of such data to tephra correlation studies in new zealand these analyses support earlier major element based correlations between three surface sections oruarangi and okariha at port waikato and st kentigern s at east auckland and a long core patiki road west auckland the correlations provide a higher resolution record of taupo volcanic zone tvz activity than is preserved in more proximal deposits where burial and erosion obscure much of the volcanic record a combination of major and trace element analysis enables the correlation of three units exposed in the auckland region with their proximal equivalents ignimbrites from the tvz namely deposits associated with 1 the ongatiti ignimbrite 1 21 0 04 ma 2 an un named post ahuroa pre unit e ignimbrite sample ut1274 from the rocky hill section king country and 3 the unit e ignimbrite 1 ma combined major and trace element data show a marked evolution in magma chemistry with the large ongatiti and unit e ignimbrite eruptions occurring after a change in composition caused by replenishment reactivation of the magma chamber changes in magma chemistry between these deposits resulted from a combination of assimilation of metasedimentary country rocks and periods of fractional crystallisation of a plagioclase dominated assemblage trace element data and the wider dispersal of the silicic tephras in the auckland region suggests that they are all sourced from the mangakino volcanic centre mvc in the tvz this study illustrates for the first time in a new zealand context the potential for correlating tephra deposits using single glass shard trace element chemistry

non synchronous deposition of north atlantic ash zone ii in greenland ice cores and north atlantic and norwegian sea sediments an example of complex glacial stage tephra transport tephra provides regional chronostratigraphical marker horizons that can link different climate archives with highly needed accuracy and precision the results presented in this work exemplify however that the intermittent storage of tephra in ice sheets and during its subsequent iceberg transport especially during glacial stages constitutes a potential source of serious error for the application of tephrochronology to nordic seas and north atlantic sediment archives the peak shard concentration of the rhyolitic component of the north atlantic ash zone ii naaz ii tephra complex often used to correlate marine and ice core records in marine isotope stage mis 3 is shown to lag the eruption event by ca 100 400 years in some north atlantic and norwegian sea cores while still allowing for a correlation of archives on millennial timescales this time delay in deposition is a major obstacle when addressing the lead lag relationship on short timescales years to centuries a precise and accurate determination of lead lag relationships between archives recording different parts of the climate system is crucial in order to test hypotheses about the processes leading to abrupt climate change and to evaluate results from climate models copyright 2011 john wiley sons ltd

optimising the use of marine tephrochronology in the north atlantic a detailed investigation of the faroe marine ash zones ii iii and iv abstract tephrochronology is central to the intimate 1 goals for testing the degree of climatic synchroneity during abrupt climatic events that punctuated the last glacial period since their identification in north atlantic marine sequences the faroe marine ash zone ii fmaz ii fmaz iii and fmaz iv have received considerable attention due to their potential for high precision synchronisation with the greenland ice cores in order to optimise the use of these horizons as isochronous markers a detailed re investigation of their geochemical composition sedimentology and the processes that deposited each ash zone is presented shard concentration profiles geochemical homogeneity and micro sedimentological structures are investigated for each ash zone preserved within core jm11 19pc retrieved from the southeastern norwegian sea on the central north faroe slope this approach allows a thorough assessment of primary ash fall preservation and secondary depositional features and demonstrates its value for assessing depositional integrity in the marine environment results indicate that the fmaz ii and iv are well resolved primary deposits that can be used as isochrons for high precision correlation studies we outline key recommendations for future marine tephra studies and provide a protocol for optimising the application of tephrochronology to meet the intimate synchronisation goals

composition and origin of ash zones from marine isotope stages 3 and 2 in the north atlantic abstract the composition and distribution of four north atlantic ash zones from the faroe islands margin is presented including the widespread north atlantic ash zone ii naaz ii 52 53 ka bp and three mainly basaltic ash zones here referred to as the faroe marine ash zones fmaz i ca 15 4 14 c ka bp ii ca 23 14 c ka bp also referred to as the fugloyarbanki tephra and iii ca 33 14 c ka bp one core from the south east labrador sea was also analysed naaz ii was found in all investigated cores indicating very large eruption events in the early marine isotope stage mis 3 detailed investigations of naaz ii in high resolution cores show that two separate layers can be distinguished a lower mixed alkalic basalt and rhyolitic layer and an upper predominantly tholeiitic basalt tephra the main component of the basaltic fmaz ii was found in all cores from the faroe island margin and the labrador sea indicating that this tephra is the most widespread tephra from mis 2 in the north atlantic discovered so far we discuss the possibility to use these tephra layers for exact correlations between marine records and land sections such as the greenland ice cores and terrestrial records on the european mainland

stratigraphy and distribution of tephra layers in marine sediment cores from the faeroe islands north atlantic the stratigraphical position of eight discrete tephra layers is investigated in four marine sediment cores from north and south of the faeroe islands the tephras are correlated to the marine oxygen isotope stratigraphy and the interstadial stadial cycles dansgaard oeschger cycles of the greenland ice cores a very prominent volcanic event occurred during interstadial 23 in marine oxygen isotope stage mis 5c correlating with a cold event within this otherwise warm interval two tephra horizons in mis 5a correlate with the beginning and end of interstadial 21 respectively the most widely distributed ash is the well known ash zone 2 from the lower part of mis 3 in the two cores from north of the faeroe islands it consists of two discrete layers a lower one composed of rhyolitic and basaltic tephra and an upper layer composed exclusively of basaltic glass the two tephra falls coincide with the two warm intervals of dansgaard oeschger cycle no 15 a hitherto unknown basaltic tephra was recorded just above heinrich event h4 in the lower part of the warm interstadial 8 and dated to ca 33 14c ka bp another frequently recorded layer termed the fugloyarbanki tephra is likewise basaltic it is dated to 23 1 14c ka bp it was deposited after the peak warm phase of interstadial 3 at the mis 3 2 transition finally a tephra dated ca 15 4 14c ka bp was found in two cores from north of the ridge it was deposited at the beginning of the deglaciation between the last glacial maximum and heinrich event h1

the age and chronostratigraphical significance of north atlantic ash zone ii rhyolitic tephra with the geochemical characteristics of north atlantic ash zone naaz ii are described from the giant piston core md95 2006 from the northeast atlantic ocean shard size distribution indicates that the tephra represent a wind sorted primary air fall deposit but with a mode close to 200 m they are too coarse to be air fall deposits at the core site which lies ca 1000 km from the possible tephra source randomly sampled shards reveal a single geochemical population belonging to the icelandic transitional alkali magma series suggesting that they are unlikely to represent ice rafted debris derived from icelandic icebergs the tephra probably represent air fall deposits transported to the core site by sea ice within the northeast atlantic gyre the naaz ii peak coincides with the rapid climate transition cooling at the end of interstadial 15 which can be assigned an age of 53 260 2660 yr bp from direct correlation with the greenland ice core gisp2 record a comparison of the md95 2006 neogloboquadrina pachyderma sinistral relative abundance and gisp2 18o records relative to the naaz ii isochron suggests that this climatic event was synchronous across the north atlantic by direct correlation of interstadial maxima between the two records the gisp2 time scale is transferred to md95 2006 comparison of corrected and calibrated radiocarbon ages derived from monospecific foraminifers with the gisp2 ages at the same stratigraphical horizon suggest major age differences these probably result from large variations in atmospheric 14c concentration and highlight the significant uncertainties associated with radiocarbon calibration during marine isotope stage 3 copyright 2004 john wiley sons ltd

tephra horizons identified in the western north atlantic and nordic seas during the last glacial period extending the marine tephra framework abstract geochemically distinct volcanic ash tephra deposits are increasingly acknowledged as a key geochronological tool to synchronize independent paleoclimate archives recent advances in the detection of invisible crypto tephra have led to the ongoing establishment development and integration of regional tephra lattices these frameworks offer an overview of the spatial extent of geochemically characterized tephra from dated eruptions a valuable tool for precise correlation of paleorecords within these areas here we harness cryptotephra analysis to investigate the occurrence of two well known tephra markers from the last glacial period i e fmaz ii 1 26 7 ka b2k and naaz ii ii rhy 1 55 3 ka b2k in marine sediment cores from the nordic irminger and labrador seas in addition we assess the imprint of bioturbation on two of these tephra deposits using computed tomography ct imagery we have successfully identified fmaz ii 1 in the nordic and irminger seas the tephra deposit is a visible deposit in the nordic seas whereas it appears as a single high concentration peak within the fine grained shard size fraction i e 25 80 m in the irminger sea both horizons are primary airfall deposits and this study is the first to identify a fmaz ii 1 deposit of isochronous nature in the irminger sea region in addition we have identified a new tephra horizon in the irminger sea which is stratigraphically associated with fmaz ii 1 and geochemically similar to the known 2 jpc 192 1 population we discuss its potential to serve as a new reference tie point for correlations in the region lastly we have successfully identified naaz ii ii rhy 1 of isochronous nature in both the irminger and labrador sea the layers are interpreted to be deposited by either direct airfall or by sea ice drifting past the sites compared to the existing frameworks which previously mainly focused on sites east of iceland our findings expand the knowledge and utility of the fmaz ii 1 and naaz ii ii rhy 1 horizons

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

norwegian sea tephrostratigraphy of marine isotope stages 4 and 5 prospects and problems for tephrochronology in the north atlantic region abstract this paper presents an account of the tephrostratigraphy of south eastern norwegian sea core md99 2289 for the interval spanning marine isotope stage mis 5 and part of mis 4 from 70 000 to 130 000 years ago tephra deposits from in the order of 100 mainly basaltic volcanic eruptions in iceland and on jan mayen are described in terms of their stratigraphic context and geochemical composition representing the most comprehensive record of iceland and jan mayen volcanism over this time span the most important transport mechanism of tephra to the core site is considered to have been iceberg rafting which is thought to be responsible for a centennial to millennial scale time lag between the volcanic eruption events and the subsequent deposition of tephra in deep sea sediments while this clearly limits the use of some of the tephras as isochronous markers twelve discrete tephra deposits show stratigraphical and geochemical characteristics that suggest them to have been deposited near contemporaneously with their source volcanic events and hence suitable candidates as regional isochrones four of these accords with the geochemical signatures of tephra deposits previously described from the nordic seas region potential problems for the application of tephrochronology highlighted by this work are discussed and recommendations for strategies to overcome them are proposed

benthic habitat characterization and distribution from two representative sites of the deep water sml coral province mediterranean abstract two sites ms04 and ms06 from the santa maria di leuca sml coral province were analyzed by a video and acoustic survey during the national italian project apulian plateau bank ecosystem study aplabes site ms04 atlantis mound is characterized by a sub conical mound 500 m wide and 25 m high located at a water depth of about 650 m site ms06 yellow chain comprises several elongated reliefs nnw sse oriented up to 25 m high and 500 m in maximum lateral extent located at a depth of between 490 and 540 m at both sites two main mesohabitats mound and intermound containing several coral bearing and barren macrohabitats were observed in recorded videos and detected in side scan sonographs the coral rich macrohabitats characterized by densely packed colonies of the scleractinians madrepora oculata and secondarily lophelia pertusa m l are typically restricted to the mound areas the mud dominated ones almost devoid of m l colonies are more common within the intermound mesohabitat however on the most extensive mounds both macrohabitat typologies exist they are heterogeneously distributed on the mound surface often showing a clear differentiation along two opposite flanks of the same topographic feature m l rich macrohabitats are preferentially located on top and along the mound northeastern flank showing a typical step like distribution probably reflecting the arrangement of hard substrate outcrops along this flank fan shaped madrepora colonies and sponges are often oriented nnw sse implying together with other evidence a primary southwestern current flow the hard bottom macrohabitats of the southwestern mound flank are generally restricted to sparse exposed subvertical to overhanging scarps as well as to heterometric boulders located at the scarp base their fauna is mainly characterized by small sized organisms such as sponges and solitary scleractinians although m sized boulders may locally host very large antipatharian colonies leiopathes glaberrima the heterogeneous distribution of the observed benthic macrohabitats seems to be strictly related to the local topography the main current flow and consequently larvae food supply per unit of time and the substrate typology hard vs soft bottom

composition and origin of volcanic ash zones in late quaternary sediments from the reykjanes ridge evidence for ash fallout and ice rafting abstract seven quaternary volcanic ash zones including the well known ash zones az i and az ii have been investigated in five well dated sediment cores from the reykjanes ridge between 59 and 60 n the zones were defined on their geochemical composition morphological variation of the particles and stratigraphic position the ash zones az i and az ii show a mixture of colorless bubble wall shards and brown blocky glasses whereas ash zones vz 1 to 5 are composed of dark to light brown volcanic glasses ranging in shape and texture from blocky nonvesicular shards to highly vesicular pumiceous types the dark brown glass shards of ash zones vz 1 to 5 represent subalkalic and low k subalkalic basaltic series geochemical correlation of the ash zones with possible source areas indicates that they all derived from iceland the colorless shards in az i and az ii are of rhyolitic composition the eastern volcanic zone on iceland is the most important source with abundant volcaniclastics being produced by subaerial subglacial eruptions and secondary erosion of volcanic rocks explosive volcanism on iceland is manifested by marine ash layers az i and az ii most of the volcaniclastic zones vz 1 to 5 coincide chronologically with peak abundances of coarse ice rafted material ird indicating that most of this volcanic glass was incorporated into the icelandic ice sheet and released to the ocean by iceberg calving and subsequent melting however two layers in vz 1 and vz 5 have no correlatives in the ird record suggesting that they were probably transported by local sediment gravity flows from this we must infer that most of the ice rafting episodes bearing volcanic particles as observed in sediments from reykjanes ridge monitor glacier fluctuations on iceland

secular variation of iron isotopes in north atlantic deep water a high precision iron isotope time series for a ferromanganese crust demonstrates that the iron isotope composition in north atlantic deep water has changed substantially over the past 6 million years and that iron isotope variations in the crust are closely correlated to those of lead isotopes the close correlation between the two isotope series indicates that the observed iron isotope variations predominantly reflect those of iron input from terrigenous sources and provides no evidence for biologically induced mass fractionation within north atlantic deep water

deep sea survey for the detection of methane at the santa maria di leuca cold water coral mounds ionian sea south italy abstract the santa maria di leuca cold water coral cwc province northern ionian sea was investigated for the first time to detect eventual occurrence of methane anomalies as a possible indication of hydrocarbon seepage stimulating the coral growth most coral mounds have developed in correspondence with tectonic scarps and faults orthogonal to the southern margin and trending nw se which could be potential sites of gas escape a visual and instrumental inspection was performed by using a new deep sea probe equipped with video cameras sonar ctd methane sensors and a water sampler eight areas were explored by 10 surveys depths ranging from 380 to 1100 m for a total of more than 26 h of continuous video and instrumental recording sediments were also sampled by gravity corers and analysed in laboratory the images allowed to assess distribution abundance and geometry of the colonies most of which are developed on morphological highs often characterised by tectonic scarps all data indicate however the lack of a significant occurrence of methane both in seawater and sediments no direct or indirect expressions of gas seepage were recognised on the seabed weak methane anomalies were detected only in seawater at the base of some fault linked scarps where more reducing conditions and bacterial methanogenesis are possibly enhanced by less water circulation the faults are not fluid bearing as previously suggested by high resolution geophysical signatures the development of the coral colonies thus cannot be attributed to seeping fluids but to a favourable physiographic position with exposure to nutrient rich currents

dansgaard oeschger cycles interactions between ocean and sea ice intrinsic to the nordic seas dansgaard oeschger d o cycles are the most dramatic frequent and wide reaching abrupt climate changes in the geologic record on greenland d o cycles are characterized by an abrupt warming of 10 5 c from a cold stadial to a warm interstadial phase followed by gradual cooling before a rapid return to stadial conditions the mechanisms responsible for these millennial cycles are not fully understood but are widely thought to involve abrupt changes in atlantic meridional overturning circulation due to freshwater perturbations here we present a new high resolution multiproxy marine sediment core monitoring changes in the warm atlantic inflow to the nordic seas as well as in local sea ice cover and influx of ice rafted debris in contrast to previous studies the freshwater input is found to be coincident with warm interstadials on greenland and has a fennoscandian rather than laurentide source furthermore the data suggest a different thermohaline structure for the nordic seas during cold stadials in which relatively warm atlantic water circulates beneath a fresh surface layer and the presence of sea ice is inferred from benthic oxygen isotopes this implies a delicate balance between the warm subsurface atlantic water and fresh surface layer with the possibility of abrupt changes in sea ice cover and suggests a novel mechanism for the abrupt d o events observed in greenland ice cores

north atlantic deep sea sedimentation of late quaternary tephra from the iceland hotspot piston cores recovered from the north atlantic were used to study the sedimentation of holocene and pleistocene volcanic ash in the irminger and iceland basins ash zones 1 11 100 yr b p 2 55 000 yr b p and 3 305 000 yr b p were identified from their major element glass composition the silicic and alkalic ash zones 1 and 2 originate from the southeastern volcanic zone of iceland where they correlate with the solheimar ignimbrite from katla volcano and the thorsmork ignimbrite from tindfjallajokull volcano respectively the low alkali composition of silicic ash zone 3 indicates a source from one of the silicic centers in the active rift system ash zones 2 and 3 occur in the irminger basin as dispersed glass shards over a depth interval of several tens of centimeters their compositional and granulometric characteristics reflect an initial fallout on pack ice north of iceland followed by ice rafting sedimentation in the denmark strait prior to bioturbation 18o stratigraphy of foraminifera in the cores indicates that the ash zones were deposited during a cold interval at the time when seas north of iceland were ice covered sedimentary features indicate that turbidity currents were also involved in the dispersal of ash zones 1 and 2 south of iceland the initiation of these gravity currents from the shelf can be attributed to either glacier bursts jokulhlaups carrying tephra or the entrance of pyroclastic flows into the ocean

tephrochronology and the extended intimate integration of ice core marine and terrestrial records event stratigraphy 8 128 ka b2k the comparison of palaeoclimate records on their own independent timescales is central to the work of the intimate integrating ice core marine and terrestrial records network for the north atlantic region an event stratigraphy has been established from the high precision greenland ice core records and the integrated gicc05 chronology this stratotype provides a palaeoclimate signal to which the timing and nature of palaeoenvironmental change recorded in marine and terrestrial archives can be compared to facilitate this wider comparison without assuming synchroneity of climatic change proxy response intimate has also focussed on the development of tools to achieve this in particular the use of time parallel marker horizons e g tephra layers volcanic ash coupled with the recent temporal extension of the greenland stratotype as part of this special issue we present an updated intimate event stratigraphy highlighting key tephra horizons used for correlation across europe and the north atlantic we discuss the advantages of such an approach and the key challenges for the further integration of terrestrial palaeoenvironmental records with those from ice cores and the marine realm

stratigraphic framework of the apulian deep water coral province ionian sea abstract shallow sediment lithology and stratigraphy were investigated at selected areas off santa maria di leuca sml on the apulian margin between 350 and 1200 m water depth in order to define the sea bottom character on which coral mounds have developed according to existing geophysical data and in situ observations deep coral growth in the sml area creates patches of colonies typically settled on hard substrates on the upper flanks and or near the top of mound like structures and elongated ridges the sedimentary stratigraphy is strongly influenced by the local topography which is modeled by tectonic and geomorphological forcing large scale erosional features slope failure and sediment mass accumulation are evident from seismic investigations additionally sites of preferential sediment accumulation due to the action of bottom currents are identified as a result a complex sedimentary pattern characterizes this part of the apulian margin with strong lateral variability in sediment type and age although hemipelagic silty clay constitutes the main lithology there are sites characterized by periodic accumulation of silt and fine sand and local re deposition of coarse biogenic sand from the surrounding areas and from shallower depths excluding one site where mid pleistocene sediments are brought very close to the bottom surface due to wide scale erosion all collected sediments are late pleistocene to holocene in age and fall biostratigraphically within the emiliania huxleyi acme nannofossil zone reworking detected through nannofossil analysis is common in most cores excluding the ones taken from topographic highs and is variable in extent from site to site and within the sediment column it includes cretaceous to early pleistocene species suggesting provenance from extended successions or various stratigraphic levels outcropping on the submerged apulian margin or in adjacent land sections reworking is often associated with a high content of lithogenic particles and an increase in the coarser silt fraction coral debris was collected at many stations both at the sediment surface and within the stratigraphic sequence with varying abundance in relation to proximity to the coral colonies radiometric dating and micropaleontological analyses at some sites allow us to propose a sequence of coral colonization phases

the greenland ice core chronology 2005 15 42 ka part 2 comparison to other records a new greenland ice core chronology gicc05 based on multi parameter counting of annual layers has been obtained for the last 42 ka here we compare the glacial part of the new time scale which is based entirely on records from the northgrip ice core to existing time scales and reference horizons covering the same period these include the grip and northgrip modelled time scales the meese sowers gisp2 counted time scale the shackleton fairbanks grip time scale sfcp04 based on 14c calibration of a marine core the hulu cave record three volcanic reference horizons and the laschamp geomagnetic excursion event occurring around greenland interstadial 10 gicc05 is generally in good long term agreement with the existing greenland ice core chronologies and with the hulu cave record but on shorter time scales there are significant discrepancies around the last glacial maximum there is a more than 1 ka age difference between gicc05 and sfcp04 and a more than 0 5 ka discrepancy in the same direction between gicc05 and the age of a recently identified tephra layer in the northgrip ice core both sfcp04 and the tephra age are based on 14c dated marine cores and fixed marine reservoir ages for the laschamp event gicc05 agrees with a recent independent dating within the uncertainties

identification of cryptotephra horizons in a north east atlantic marine record spanning marine isotope stages 4 and 5a 60 000 82 000 a b2k abstract tephrochronology is one of the few techniques that offer considerable but as yet largely unrealised potential for the correlation of north atlantic palaeoclimatic archives spanning the mis 4 and 5a substage period a phase of pronounced global cooling during the initiation of the last glacial period in this investigation two previously unidentified rhyolitic tephra horizons believed to be sourced from iceland were isolated within the giant piston core md04 2822 retrieved from the rockall trough north east atlantic one horizon was deposited at the beginning of greenland stadial 19 70 150 a b2k and the other around the cooling transition at the end of greenland interstadial 20 75 320 a b2k density separation epma and la icp ms techniques were utilised for the identification of these cryptotephra within the fine fraction sediment

volcanic ash from icelandic 57 300 yr bp eruption found in gisp2 greenland ice core we have found volcanic ash in wisconsinan ice from the gisp2 ice core retrieved from the summit location in central greenland the ash consists predominantly of large rhyolitic glass shards similar to the ones found in wisconsinan dye 3 ice from southern greenland we give the results of our analysis of the ash and present evidence that correlates this ash with the z2 ash layer found in atlantic sediment cores with the dye 3 ash with ash recently found in the grip ice core from central greenland and with ash associated with the icelandic thorsmork ignimbrite the mineralogy of the ash is very similar to that of ash from the icelandic tindfjallajokull volcano that is also present in the thorsmork ignimbrite and we suggest that this is the source volcano tindfjallajokull has also been suggested as the source of the z2 ash based on the excellent dating of the gisp2 ice core we determined that the eruptions that produced the gisp2 ash occured 57 300 1 700 yr bp which agrees extremely well with the most recent dating of 57 500 1 300 yr bp of the z2 ash based on the specmap chronology this provides us with a reliable revision of the dye 3 ice core dating at a depth of 1950 m this ice was originally dated at 70 000 yr bp

tracing marine cryptotephras in the north atlantic during the last glacial period improving the north atlantic marine tephrostratigraphic framework tephrochronology is increasingly being recognised as a key tool for the correlation of disparate palaeoclimatic archives underpinning chronological models and facilitating climatically independent comparisons of climate proxies tephra frameworks integrating both distal and proximal tephra occurrences are essential to these investigations providing key details on their spatial distributions geochemical signatures eruptive sources as well as any available chronological and or stratigraphic information frameworks also help to avoid mis correlation of horizons and provide important information on volcanic history here we present a comprehensive chronostratigraphic framework of 14 tephra horizons from north atlantic marine sequences spanning 60 25 cal ka bp horizons previously discovered as visible or coarse grained deposits have been combined with 11 newly recognised volcanic deposits identified through the application of cryptotephra identification and characterisation methods to a wide network of marine sequences their isochronous integrity has been assessed using their physical characteristics all horizons originated from iceland with the vast majority having a basaltic composition sourced from the grimsvotn kverkfjoll hekla vatnafjoll and katla volcanic systems new occurrences improved stratigraphic placements and a refinement of the geochemical signature of the naaz ii are reported and the range of the fmaz iv has been extended in addition several significant geochemical populations that further investigations could show to be isochronous are reported this tephra framework provides the foundation for the correlation and synchronisation of these marine records to the greenland ice cores and european terrestrial records to investigate the phasing rate timing and mechanisms controlling rapid climate changes that characterised the last glacial period

the synchronization of palaeoclimatic events in the north atlantic region during greenland stadial 3 ca 27 5 to 23 3 kyr b2k two high resolution marine sediment cores located 83 km apart in the ne atlantic have been studied md95 2006 barra fan 57 01 82 n 10 03 48 w 2120 m water depth and md04 2822 rockall trough 56 50 54 n 11 22 96 w 2344 m water depth the records are anchored to the ngrip ice core stratigraphy and gicc05 chronology by the presence of geochemically characterized fugloyarbanki tephra and further tested by radiocarbon age control replicated sea surface temperature sst records show evidence for an abrupt and short lived warming within greenland stadial gs 3 to which we tentatively assign an age of ca 25 6 24 8 kyr gicc05 b2k based on these and another marine palaeoclimate record link17 from the faroe shetland channel we propose a new three fold event stratigraphy for gs 3 within the north east atlantic region the recognition of this warming event within gs 3 in ne atlantic sst records demonstrates that such events may not readily be identified within the coldest stadials of the greenland ice cores highlights the need for carefully constructed event stratigraphies independently tested by the use of tephra isochrones and radiocarbon and illustrates pervasive millennial scale climate variability of the north atlantic region dansgaard oeschger d o events is deeply embedded in the dynamics of atlantic meridional overturning circulation amoc

identification of the fugloyarbanki tephra in the ngrip ice core a key tie point for marine and ice core sequences during the last glacial period a visible tephra horizon in the ngrip ice core has been identified by geochemical analysis as the fugloyarbanki tephra a widespread marker horizon in marine cores from the faroe islands area and the northern north atlantic an age of 26 740 390 yr b2k 1 uncertainty is derived for this tephra according to the new greenland ice core chronology gicc05 based on multi parameter counting of annual layers detection of this tephra for the first time within the ngrip ice core provides a key tie point between marine and ice core records during the transition between mis 3 and 2 identification of this volcanic event within the greenland records demonstrates the future potential of using tephrochronology to precisely correlate palaeoarchives in widely separated localities that span the last glacial period as well as providing a potential method for examining the extent of the radiocarbon marine reservoir effect at this time copyright 2008 john wiley sons ltd

visualizing tephra deposits and sedimentary processes in the marine environment the potential of x ray microtomography localized tephra deposition in marine sequences is the product of many complex primary and secondary depositional processes these can significantly influence the potential applicability of tephra deposits as isochronous marker horizons and current techniques used in isolation may be insufficient to fully unravel these processes here we demonstrate the innovative application of x ray microtomography ct to successfully identify tephra deposits preserved within marine sediments and use these parameters to reconstruct their internal three dimensional structure three dimensional visualizations and animations of tephra dispersal in the sediment permit a more thorough assessment of postdepositional processes revealing a number of complex microsedimentological features that are not revealed by conventional methods these features include bioturbation burrows and horizontally discontinuous tephra packages which have important ramifications for the stratigraphic placement of the isochron in a sedimentary sequence our results demonstrate the potential for utilizing rigorous two and three dimensional microsedimentological analysis of the ichnofabric to enhance and support the use of tephra deposits as isochronous marker horizons and to identify the stratigraphic position that best reflects the primary fallout of ash the application also provides an exceptional insight into the style and rate of sedimentation processes and permits an assessment of the stratigraphic integrity of a tephra deposit we discuss the possibility of applying these ct methods to the identification of cryptotephras within various paleoclimatic sequences and to enhance our understanding of marine sedimentation processes

fallout tuffs of trapper creek idaho a record of miocene explosive volcanism in the snake river plain volcanic province a 900 m thick section of tuffaceous sedimentary rock vitric fallout tuff and ash flow tuff is well exposed along trapper creek in south central idaho this section provides nearly continuous exposure through the fill of the goose creek basin a major north trending miocene extensional basin located along the southern margin of the snake river plain volcanic province srpvp some 51 separate units of vitric fallout tuff are recognized in the trapper creek section petrographic and chemical characteristics of these vitric tuffs indicate that most are from srpvp sources new 40ar 39ar laser fusion dating along with prior isotopic age determinations show that the trapper creek tuffs span the period ca 13 9 8 6 ma chemical correlation indicates that fallout tuffs in the central part of the trapper creek section 12 5 10 0 ma are from sources in the bruneau jarbidge volcanic field of the srpvp centered 100 km west of trapper creek underlying fallout tuffs may have had sources in the owyhee humboldt field of the srpvp centered 200 km west of trapper creek while overlying fallout tuffs interlayered with several ash flow tuffs had a relatively proximal source possibly in the proposed twin falls volcanic field centered 60 km north of trapper creek the trapper creek tuffs provide insight into the characteristics of explosive silicic volcanism within the srpvp during middle late miocene time from ca 13 9 to ca 9 5 ma major eruptions those depositing 1 5 m of fallout tuff were frequent about one event per 200 k y their products display a trend toward the eruption of progressively less evolved higher temperature silicic magma after 12 5 ma this trend to higher temperature eruptions termed the cougar point flare up culminated in the eruption of high temperature 1000 c plagioclase rich magma during the period 10 5 9 5 ma in contrast to these eruptions later 7 0 ma major silicic eruptions within the srpvp were characterized by the lower temperature 850 c of the erupted magma and by the longer intervals about one event per 500 600 k y between eruptions variations in the character of srpvp explosive silicic eruptions may reflect changes in the structure composition or state of stress in the crust beneath the eastward propagating srpvp or perhaps changes in the yellowstone hot spot plume that may drive the srpvp volcanism

cryptotephras the revolution in correlation and precision dating from its icelandic origins in the study of visible tephra horizons tephrochronology took a remarkable step in the late 1980 s with the discovery of a ca 4300 year old microscopic ash layer in a scottish peat bog since then the search for these cryptotephra deposits in distal areas has gone from strength to strength indeed a recent discovery demonstrates how a few fine grained glass shards from an alaskan eruption have been dispersed more than 7000 km to northern europe instantaneous deposition of geochemically distinct volcanic ash over such large geographical areas gives rise to a powerful correlation tool with considerable potential for addressing a range of scientific questions a prerequisite of this work is the establishment of regional tephrochronological frameworks that include well constrained age estimates and robust geochemical signatures for each deposit with distal sites revealing a complex record of previously unknown volcanic events frameworks are regularly revised and it has become apparent that some closely timed eruptions have similar geochemical signatures the search for unique and robust geochemical fingerprints thus hinges on rigorous analysis by electron microprobe and laser ablation inductively coupled plasma mass spectrometry historical developments and significant breakthroughs are presented to chart the revolution in correlation and precision dating over the last 50 years using tephrochronology and cryptotephrochronology

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

long range transport of volcanic ash to the greenland ice sheet betzer et al 1 reported the surprising discovery of giant 75 m mineral particles transported more than 10 000 km from their source we have found volcanic ash containing glass shards as large as 300 m in a section of wisconsinian ice from the dye 3 core in greenland which is similarly unexpected and raises interesting questions concerning the long range aeolian transport of particulate matter as the volcanic ash correlates well with similar ash in deep sea sediment cores from the atlantic it also allows us to date the ice with some confidence

correlation of late quaternary tephra layers in a long pluvial sequence near summer lake oregon abstract near summer lake in southern oregon 54 tephra beds of late quaternary age are exposed in pluvial lake sediments of lake chewaucan seven of the tephra beds near the top can be correlated with tephra deposits younger than 117 000 yr at mount st helens washington at crater lake oregon and in northwestern nevada in the deposits of pluvial lake lahontan however most of the section at summer lake lies below the correlated units and contains 39 tephra beds older than 117 000 yr major element chemistry of tephra glasses was determined by electron microprobe analysis petrography supports the correlations made from chemical evidence compositions correlated range from 70 to 76 sio 2 the least silicic summer lake glass contained 57 extrapolation of depositional rate suggests that most of the sediments at summer lake are younger than about 335 000 yr but older lake beds containing tephra layers occur at one place the long lacustrine record suggests that lake chewaucan persisted through the last interpluvial stage and that the lake may have dried up at the end of the pleistocene due to diversion of the chewaucan river by relict shore features

age extent and climatic significance of the c 3400 bp aniakchak tephra western alaska usa tephra deposits at whitefish lake and cape espenberg on the northernmost seward peninsula of western alaska were derived from the aniakchak caldera on the alaska peninsula more than 1500 km to the south radiocarbon dates on the climactic caldera forming aniakchak eruption and on proximal and distal tephra indicate the aniakchak tephra was deposited about 3435 40 bp 3614 3815 cal bp and forms an isochronous marker horizon across much of western alaska the aniakchak tephra eruption and several other targe eruptions during the seventeenth century bc may have had widespread effects on climate

quaternary sedimentation and norwegian sea overflow pathways around bill bailey bank northeastern atlantic abstract using high resolution multi channel sleeve gun seismics and tobi side scan sonar and subbottom profiler acoustic data as well as sediment cores and published hydrographic measurements a study has been made of quaternary sedimentation patterns and depositional processes around bill bailey bank bbb in the northeastern atlantic from the western outlet of the faeroe bank fb channel which is the main conduit of norwegian sea overflow water nsow there is a complex pattern of nsow controlled sediment transport pathways extending to areas north of lousy bank lb the acoustic data and sediment cores reveal the existence of a contour current at water depths exceeding 1000 m flowing from the wyville thomson ridge via the southern rise of fb and bbb into the valley between bbb and lb and further northward towards the area north of bbb we conclude that this contour current is related to intermittent nsow overflow of the wyville thomson ridge the maximum bottom flow speed along this secondary nsow flow pathway is inferred to reach about 0 50 m s bedforms observed in the northeastern part of the study area north of bbb suggest a maximum bottom flow speed of locally at least 1 0 m s the maximum thickness 0 5 s twt of the pliocene quaternary seismic sequence at water depths in excess of 1000 m south of bbb is nearly twice that found north of bbb on average higher accumulation rates in the former area can be ascribed to a hydrographic setting favouring sediment accumulation which especially under glacial conditions markedly differed from conditions north of bbb this applies to both bottom and surface circulation linear bulk sedimentation rates north of bbb were largest during deglacial warming when the rates were about three times higher than the average holocene rate 4 5 cm ka increased fluxes during deglaciation reflect transport and depositional conditions associated with reactivation of the nsow current system south of bbb average linear bulk accumulation rates were persistently higher i e in the range 15 23 cm ka during various late pleistocene stages between 30 and 10 ka

hydrographic characteristics of water masses and circulation in the northern ionian sea abstract the hydrography of intermediate and deep water masses in the northern ionian sea apulian plateau was studied through four quasi synoptic multidisciplinary surveys carried out in 2004 2006 as an ancillary oceanographic activity in the frame of the aplabes project this area plays a crucial role for the entire mediterranean basin being influenced by the water outflow of adriatic origin which under severe winter conditions is a primary source of dense water for the eastern mediterranean at the end of the 1980s such outflow showed a different behavior and only in the recent years has a gradual re establishing of the former condition been detected as such the adriatic sea has regained its role as a main source of the east mediterranean deep water which was temporarily inhibited during the well known eastern mediterranean transient which progressively modified the intermediate and deep layers of the mediterranean sea the general structure of water masses was similar through the investigated period but interesting differences within the bottom layer have been detected the interaction of the different water types present in the basin is reviewed by means of property property plots vertical sections isopycnal analyses and using an optimum multiparameter analysis omp which is an objective method to measure the mixing of water masses due to the lack of any direct information about the dynamics of the water column in the area of the apulian plateau during the whole analyzed period the classical method to infer the baroclinic velocity from the mass field has been applied to hydrographic data the well known indeterminacy of this method due to the barotropic component of the velocity field has been resolved using a short time series of current velocities acquired synoptically by a mooring located in the northern part of the studied area the wavelet transform was adopted for localizing and quantifying the variability of currents simultaneously in both frequency and time domains the presence of the adriatic deep water close to the bottom was detected on all four surveys with different signature as underlined by the objectively analysis with the optimum multiparameter analysis of the thermohaline field a core of cold less saline and oxygenated water of adriatic origin coming from the otranto channel was identified this water mass moved in geostrophic balance along the isobaths at 600 1000 m depth at the isopycnal surface of 29 18 kg m 3 not being dense enough to reach the deeper layers of the ionian basin carrying 0 27 0 36 sv

shallow gas and flood deposition on the po delta abstract sediment cores acquired on the po delta northwestern adriatic sea in water depths of 10 to 25 m yielded anomalous concentrations of methane up to 41 300 ppm of the 19 unique sites analyzed 5 sites 9 cores had more than 90 ppm of ch 4 and of those 3 sites 4 cores had more than 13 800 ppm methane compositional and isotopic analyses of the gas support a bacterial origin anomalous methane concentrations were found in kasten gravity and box cores where more than one core type was acquired at a single location all cores contained anomalous methane despite the regional high productivity in the adriatic all of the highest gas concentrations were found in the region associated with the thickest accumulation of recent flood deposits off the most active channel of the po delta po di pila cores acquired in this region contain primary sedimentary structures that indicate rapid burial of thick 10 cm flood deposits and a relative lack of bioturbation down to the base of the flood layer we propose that in the po delta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried on the prodelta effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial in areas unaffected by this high flux of organic matter and rapid thick flood deposition or in between flood events our data indicate that the conditions for methanogenesis and gas accumulation have not been met we suggest that in these areas the physical and biological reworking of the surficial sediment between flood events may effectively oxidize and mineralize organic matter derived from both marine and terrestrial sources and limit bacterial methanogenesis in the subsurface

a new and less destructive laboratory procedure for the physical separation of distal glass tephra shards from sediments abstract tephrochronology a key tool in the correlation of quaternary sequences relies on the extraction of tephra shards from sediments for visual identification and high precision geochemical comparison a prerequisite for the reliable correlation of tephra layers is that the geochemical composition of glass shards remains unaltered by natural processes e g chemical exchange in the sedimentary environment and or by laboratory analytical procedures however natural glasses particularly when in the form of small shards with a high surface to volume ratio are prone to chemical alteration in both acidic and basic environments current techniques for the extraction of distal tephra from sediments involve the cleaning of samples in precisely such environments and at elevated temperatures the acid phase of the cleaning process risks alteration of the geochemical signature of the shards while the basic phase leads to considerable sample loss through dissolution of the silica network here we illustrate the degree of alteration and loss to which distal tephras may be prone and introduce a less destructive procedure for their extraction this method is based on stepped heavy liquid flotation and which results in samples of sufficient quality for analysis while preserving their geochemical integrity in trials this method out performed chemical extraction procedures in terms of the number of shards recovered and has resulted in the detection of new tephra layers with low shard concentrations the implications of this study are highly significant because i the current database of distal tephra records and their corresponding geochemical signatures may require refinement and ii the record of distal tephras may be incomplete due to sample loss induced by corrosive laboratory procedures it is therefore vital that less corrosive laboratory procedures are developed to make the detection and classification of distal glass tephra more secure

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

high resolution bathymetry and acoustic geophysical data from santa maria di leuca cold water coral province northern ionian sea apulian continental slope abstract a total of 800 km 2 of multibeam echo sounder coverage roughly 800 km of chirp sonar data and 18 km of side scan sonar profiles 100 500 khz were acquired a few km offshore santa maria di leuca south eastern italy from 200 m to 1300 m water depth the explored area belongs to the upper slope of the gently south eastward dipping apulian continental margin northern ionian sea acoustic datasets were collected by three different oceanographic expeditions where evidence of living cold water coral cwc colonies were documented by previous surveys and samples high resolution multibeam bathymetry indicated an extensive rough seafloor with an irregular faulted upper surface to the west reflecting large scale tectonic control on the margin and a highly disrupted upper slope formed by prominent downslope mass movements to the north a broad area in the east was influenced by mass transport deposition which resulted in a very complex hummocky seafloor mainly shaped by detached block like features and failure related bedforms i e low scarps downslope lineations and compressional ridges from the shallow seismic stratigraphic data failure events appeared to be multiple and recurrent and chaotic reflectors both buried and exposed at the seafloor affected most of the investigated area drift sedimentation was also recognised along a central large ridge resulting in an interplay between contour currents and downslope turbidity currents the spatial distribution of the cwc reefs was inferred from the acoustic facies interpretation based on video images and ground truthed by sediment samples it appeared that 1 within the investigated area living coral frameworks were located along large topographic highs facing the main flow of the bottom currents where hard and firm substrata and or failure related sediment bedforms occurred 2 cwc mainly settled on clustered and isolated mound like features tens to a few hundreds of metres long and no more than 25 m high and were located between 600 and 900 m water depth within the broad area affected by downslope mass transport deposits such mound like morphologies could thus be interpreted as a result of sediment accreted by coral growth with the consequent sediment trapping on small scale positive seafloor irregularities formed by different types of pleistocene exposed mass transport deposits their burial prevented by bottom currents

do norwegian deep water coral reefs rely on seeping fluids hundreds of large coral reefs up to 45 m high exist a on the continental shelf and b on morainic threshold ridges in fjords of northern mid and southwest norway they occur in water depths between 400 and 40 m and contain a large variety of megafauna the most common frame building coral is lophelia pertusa l the oldest reef found to date is 8600 calendar years old determined by radiocarbon dating of buried lophelia skeleton even though many of these reefs have been known to science for over 200 years there is as yet no viable and unifying hypothesis to explain their existence in deep cool waters other than perhaps the hydraulic theory presented by the author in 1990 it states that primary producers mainly bacteria are locally formed and concentrated at reef locations due to seepage of light hydrocarbons mainly methane on the continental shelf and nutrient rich groundwater in the fjords the hydraulic theory is supported by the following topographic reflection seismic and geochemical indicators for the continental shelf reefs a seaward dipping sedimentary permeable strata enhanced acoustic seismic reflectors adjacent pockmark craters locally elevated light hydrocarbon sediment content locally elevated seawater methane content for the fjord reefs b threshold morainic substratum rather than adjacent hardrock substratum sub surface dipping sedimentary layers h2s smell of near surface sediment samples these indicators or reef associated observations have been documented by german british and norwegian researchers over the last 10 15 years however all the listed indicators do not necessarily occur at each of the respective shelf and fjord reef locations simultaneously

a continuous 5300 yr holocene cryptotephrostratigraphic record from northern new zealand and implications for tephrochronology and volcanic hazard assessment a continuous 5280 calendar cal yr long cryptotephrostratigraphic record of a peat core from northern new zealand demonstrates that cryptotephra studies can enhance conventional tephra records by extending the known distribution of ash fall and enabling re assessment of volcanic hazards a systematic sampling strategy was used to locate peaks in glass shard concentrations and to determine loci of individual geochemical populations and a palynological method involving spiking samples with lycopodium spores was adapted to facilitate accurate counting of glass shard concentrations using glass shard major element compositions and a core chronology based on eight ams 14c ages and two visible macroscopic tephra layers taupo tephra unit y 1688 1748 cal bp and tuhua tephra 6800 7230 cal bp 2cr age ranges four cryptotephras were correlated with known eruptions whakaipo unit v 2743 2782 cal bp stent unit q 4240 4510 cal bp and unit k 4970 5290 cal bp erupted from taupo volcanic ce