temporal offsets between surface temperature ice rafting and bottom flow speed proxies in the glacial mis 3 northern north atlantic rapid climatic switches during marine isotope stage 3 29 59 ka bp are often attributed to ocean circulation changes caused by freshwater input into the north atlantic through the melting of large amounts of icebergs and sea ice however recent studies have questioned this direct coupling between factors influencing the ocean climate system by combining multiple proxies from two mid depth northern north atlantic sediment cores we assess temporal offsets and links between freshwater input and response of the near bottom flow as well as between near bottom flow and sea surface temperatures changes grain size mineralogical and magnetic proxies for ice rafting and near bottom flow speed interpreted as indicators of freshwater input and deep circulation strength consistently indicate a delay in the recovery of the deep circulation after freshwater perturbations sea surface temperature variability is inferred from foraminiferal assemblages and mg ca and 18o of neogloboquadrina pachyderma s the records show rapid switches towards higher temperatures following the ice rafting events interestingly near sea surface temperatures increased and decreased again during periods of accelerating bottom flow speed likely reflecting the sudden release of heat from deeper in the water column rather than circulation changes our data thus confirm the impact of freshwater forcing on the atlantic deep circulation but suggest that temperature variability at the surface was not directly linked to these circulation changes

clay mineral signature of the nw atlantic boundary undercurrent abstract surface sediments were sampled along 2 transects across the iceland and irminger basins and in the labrador sea clay mineral assemblages deduced from x ray analyses of the carbonate free

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

changes in north atlantic deep water formation associated with the dansgaard oeschger temperature oscillations 60 10 ka we closely comparedhigh resolution d 13 c records of benthic foraminifera cibicides wuellerstorfi a proxy for deep water ventilation with the dansgaard oeschger temperature oscillations our results reveal different perturbations of deep water formation in the north atlantic ocean associated with the millennial scale climate oscillations during the last glacial period the cooling episodes associated with the drastic heinrich events are related to large reductions of deep water formation and a northward migration of 13 c depleted southern source deep waters to 621n in the north atlantic ocean the inter heinrich events which are correlatedto the other coldstad ials are markedby significant changes of sea surface temperature aroundthe rockall plateau variations in the flux of icebergs to the north atlantic ocean but are not associated with such important reduction of deep water formation if changes in the thermohaline circulation thc are associatedwith these millennial scale climatic oscillation they affect only the deeper water masses below 2000 m of the north atlantic ocean we thus show that equivalent degree of cooling over greenland is obtained with different perturbations of deep water formation our results either question the role of the thc as the unique explanation for these millennial scale climate oscillations or call upon an amplifying mechanism not yet taken into account r 2002 elsevier science ltd all rights reserved

sortable silt cycles in svalbard slope sediments 74 0 ka the grain size of sortable silt ss 10 63 m was studied in sediment core jm04 025pc from a sediment drift on the lower part of the western svalbard slope the study aims to reconstruct the bottom current activity and intermediate water circulation in the greenland sea the ss record covers the last 74 ka and shows consistent millennial scale oscillations in grain size the youngest part of the record 25 ka is well correlated with the few available previously published reconstructions of grain size from the north atlantic ocean and the nordic seas fining of ss occurs during four well known regional cold climatic intervals the 8 2 ka cold spell the younger dryas and north atlantic heinrich events h1 and h2 as well as during a local meltwater event at 14 4 14 7 ka possibly coinciding with the older dryas also before 25 ka grain size oscillated in pace with the northern hemisphere climate with finer grain sizes during cold periods and coarser grain sizes during warm periods the fining of ss indicates reduced bottom current strength and reduced water exchange between the greenland sea and the arctic ocean during regional climate cooling events and probably also reduced deep ocean convection in the greenland sea gyre

north atlantic climate and deep ocean flow speed changes during the last 230 years variations in the near bottom flow speed of iceland scotland overflow water isow are documented in a 230 year long deep sea sediment record from the eastern flank of reykjanes ridge in the subpolar north atlantic at sub decadal time scales for recent decades the isow palaeocurrent reconstructions show similarities with observational hydrographic data furthermore recent isow flow changes fall mostly within the range of its variability of the past 230 years the record also reveals a hitherto unrecognized coupling of deep flow speeds in the subpolar north atlantic with the north atlantic oscillation nao index with more less vigorous isow flow during negative positive phases of the nao our results suggest that the changes in isow vigor are largely controlled by the transport and characteristics of labrador sea water rather than variations in the overflow itself with implications for the meridional overturning of the atlantic ocean and climate

erosional history of the himalayan and burman ranges during the last two glacial interglacial cycles abstract the results of a clay mineralogy study combined with major element geochemistry strontium neodymium and oxygen isotopes and 14c ams stratigraphy are reported for deep sea gravity cores located in the bay of bengal md77 180 and the andaman sea md77 169 end 0 and 87sr 86sr from holocene and last glacial maximum lgm sediments of fifteen other cores have also been investigated to identify sediment sources and to estimate oceanic sedimentary transport the data show the contribution of three sources 1 ganges brahmaputra rivers 2 irrawaddy river and 3 sediment derived from the western part of the indo burman ranges the dispersion of the detrital material issuing from these sources has been constrained by the geographic distribution of nd and sr isotopic ratios the lgm sediments are characterized by a significant increase of 87sr 86sr small changes in end 0 and a general decrease of smectite illite chlorite which together imply a decrease in weathering intensity the increased 87sr 86sr are attributed to a decrease in chemical weathering which should release preferentially 87sr during weathering processes in the andaman sea sediments smectite illite chlorite and kaolinite quartz ratios combined with a chemical index of alteration cia indicate that the weathering intensity of the irrawaddy river basin is mainly controlled by the summer monsoon rainfall intensity the wet summer monsoons increase vegetation cover in the plains and favor soil development by the production of pedogenic clays smectite and kaolinite

changes in the western boundary undercurrent outflow since the last glacial maximum from smectite illite ratios in deep labrador sea sediments high resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the labrador sea located at the inlet sw greenland rise and outlet labrador rise of the western boundary undercurrent wbuc gyre at the two sites smectites transported from the eastern iceland and irminger basins by the wbuc are observed clay mineral changes are used as proxies for the paleointensity reconstruction of the wbuc on the greenland rise a clay mineral index smectite illite s i ratio is defined a s i ratio of 1 characterized the last glacial maximum it increased after 17 ka and reached a maximum value of 4 during the early holocene the mineralogical changes are gradual and do not show any reversal during the younger dryas this pattern which is confirmed by first order estimations of smectite and illite fluxes suggests gradually increasing sedimentary fluxes and wbuc intensity since the last glacial maximum a peak in the velocity of the wbuc at 9 ka as recorded by clay assemblages is consistent with other regional studies based on pollen foraminifera or grain size measurements a massive dilution of smectites by illite and chlorite s i 3 occurs at 8 5 ka it corresponds to a period of rapid sediment accumulation and reflects an intensified illite rich detrital supply by meltwaters from the southern greenland ice margin on the labrador rise the smectite content varies between 20 and 60 with no obvious trend through time the mineralogical composition is strongly influenced by ice rafted deposition and by the abundance of fast deposit units cf heinrich layers in the north atlantic which contain abundant detrital carbonates spilled over from the north west atlantic mid ocean channel in such layers smectites are present but are diluted by the addition of illites chlorites and kaolinites this provides evidence for a discrete and continuous wbuc supply of fine particles from the irminger and iceland basins as far as the southeastern part of the labrador basin early deglacial smectite rich layers up to 60 are also observed at this site they indicate an increase in the outflow of the wbuc at 13 5 ka bolling allerod as previously reported from grain size or foraminiferal assemblage studies

variations of the acc cdw during mis3 traced by magnetic grain deposition in midlatitude south indian ocean cores connections with the northern hemisphere and with central antarctica we examine the magnetic mineral deposition in three cores located at midlatitude sites in the south indian ocean in an area where sediment eroded from the kerguelen crozet plateau and transported by the marine currents principally the antarctic circum current accumulates at a high sedimentation rate we focus on marine isotopic stage 3 characterized by large climatic fluctuations at northern latitudes and compare the obtained records to the climatic records at byrd antarctica and summit gisp2 greenland and to the north atlantic deep water variations in the north atlantic magnetic mineral deposition at the studied sites exhibits a profile with maxima at the time of heinrich events h4 and h5 which suggests a strong antarctic circum current when the north atlantic deep water was reduced at northern latitude during these events we show that an interhemispheric seesaw characterized by temporary surface warmings in the southern hemisphere is also marked by a strong antarctic circum current at the time of the northern heinrich events the rapid dansgaard oeschger oscillations evidenced in the northern records after interstadials is12 and is8 are not visible suggesting a limited counterpart of these events in the midlatitude southern indian ocean

synchronous changes in sediment transport and provenance at the iceland faroe ridge linked to millennial climate variability from 55 to 6 ka bp unique marine sediment cores retrieved from the southwestern slope of the iceland faroe ridge ifr close to the main axis of the iceland scotland overflow water isow revealed prominent sedimentary cycles reflecting near bottom current dynamics sediment transport and deposition coincident with dansgaard oeschger cycles and deglacial perturbations of the atlantic meridional overturning circulation the transition between greenland stadials gss and greenland interstadials gis follows a distinct recurring sedimentation pattern basaltic ti rich silts were transported from local volcanic sources by strong bottom currents and deposited during gis comparable to modern ocean circulation finer grained felsic k rich sediments were deposited during gss when iceland scotland overflow was weak possible felsic source areas include british ireland and or fennoscandian shelf areas a cyclic sawtooth pattern of bottom current strength is characterized by gradual intensification during gis followed by a sharp decline toward gss as is documented at core sites along the flank of reykjanes ridge the cores north of the faroe channel instead document the opposite pattern this suggests that the near bottom currents along the reykjanes ridge are strongly controlled by the flow cascading over the ifr heinrich like hs 1 and hs 2 are characterized by the deposition of very fine felsic sediments pointing to weakened bottom currents distinct coarse grained intervals of ice rafted debris are absent from the sediment records although pebble and gravel sized ice rafted debris is irregularly distributed throughout the fine sediment matrix near bottom currents are considered to have a major control on the lithogenic sediment deposition southwest of the ifr and further downstream

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

smectite composition as a tracer of deep circulation the case of the northern north atlantic abstract the link between smectite composition in sediments from the northern north atlantic and labrador sea and deep circulation is being further investigated through detailed studies of the x ray pattern of smectites and cation saturations this allows clear distinction of dominant terrigenous sources associated to the main components of the modern western boundary undercurrent time variations of smectite characteristics in two piston cores from the inlet and outlet of the western boundary undercurrent gyre in the labrador sea indicate 1 a more southern circulation of north east atlantic deep water during the late glacial 2 a step by step transition to the modern pattern of deep circulation during the late glacial holocene transition with intensification of north east atlantic deep water and davis strait overflow 3 an expansion of davis strait overflow and labrador sea water circulation in relation to ice surges and deposition of detrital layers 4 an intensified circulation of north east atlantic deep water during the younger dryas and 5 a very recent increased influence of denmark strait overflow water beginning between 4 4 and

chlorine 36 evidence for the mono lake event in the summit grip ice core abstract a distinct peak has been discovered in the 36 cl data from the grip ice core between the dansgaard oeschger d o events 6 and 7 at approximately 32 kyr bp this peak can be attributed to a minimum of the geomagnetic dipole field associated with the mono lake event since the 36 cl peak reflects a higher production rate of all cosmogenic radionuclides it has an impact on the 14 c dating of the last ice age furthermore it provides an additional time marker similar to a peak found earlier corresponding to the laschamp event at approximately 39 kyr bp

deep water mass source and dynamic associated with rapid climatic variations during the last glacial stage in the north atlantic a multiproxy investigation of the detrital fraction of deep sea sediments in order to investigate north atlantic deep water nadw dynamics and variability during the last glacial stage a very high resolution multiproxy analysis of the detrital fraction of sediments deposited during heinrich event 4 and dansgaard oeschger cycles 8 and 7 has been conducted on three deep sea cores these cores are distributed along the path of the north atlantic deep water from the faeroe shetland channel to the reykjanes ridge and the irminger basin the concentration in fine grained magnetites the ti content and the smectite percentage within the clay minerals show similar and coeval fluctuations at each site and are comparable from one site to the other this is the imprint of the detrital fraction originating from the northern basaltic provinces and transported to the studied sites the average grain size in the fine fraction indicates a transport by deep sea currents therefore the observed fluctuations illustrate changes in the vigor of the bottom currents associated with the nadw with weak currents during cold periods heinrich 4 and stadials and reactivation of the bottom circulation during interstadials

evaluation of rock slope stability for a touristic coastal area near kusadasi aydin turkey the study area which will be open to tourism in kusadasi aydin has steep and high cliffs on the aegean coast in turkey flysch is the main lithological unit and consists of alternating sandstone claystone marl sequences some sliding and rockfall problems have occurred in the area in the past so potential geological hazards need to be investigated to ensure the safety of tourists the aim of this study is to mitigate geological hazards by recommending engineering solutions which will ensure the continuation of the nature friendly appearance of the slopes to accomplish these tasks a geological survey was performed it involved gathering information on rock discontinuities by means of scan line surveys and collection of rock samples furthermore in situ and laboratory tests were also carried out the data collected from the field and laboratory test results were used to perform slope stability and rockfall 2 d and 3 d analyses for different slope conditions along 43 profiles based on the analyses rockfall was found to be the main slope instability problem in the study area under the light of these studies rock removal drainage greening vegetation filling of caverns protective wall building and erosion prevention are offered as remedial measures

improvements in long core measurement techniques applications in palaeomagnetism and palaeoceanography we report on new developments in the long core measurement techniques using u channels in connection with new small access cryogenic magnetometers with these new instruments u channel samples allow us to measure a wide range of magnetic parameters along entire core length with a spatial resolution and accuracy virtually equivalent to that obtained using discrete cubic samples an additional advantage is that the sediment disturbance when sampling is significantly less when using u channels we present comparisons of results from both continuous and discrete measurements and examine the effectiveness of minimal deconvolution using various techniques examples of continuous measurements of low field susceptibility nrm arm irm hrc from north atlantic deep sea cores show that it is possible to generate logs of combination of parameters related to rock magnetic characteristics of the sediments useful in palaeoceanography in particular the continuous method allows us to rapidly detect core regions with fast changing magnetic parameters useful for correlation between cores and also for understanding changes in palaeo environmental conditions the fast scan also allows us to detect regions of the core where the rock magnetic parameters are suitable or not suitable for palaeomagnetic studies related to changes in the geomagnetic field such as the relative changes in palaeointensity

physical properties of reykjanes ridge sediments and their linkage to high resolution greenland ice sheet project 2 ice core data five gravity cores taken from the reykjanes ridge have been used to establish a link between sediment physical properties and atmospheric records documented by 18o variations in greenland ice cores over the last 45 000 calendar years marine gamma ray attenuation porosity evaluator density and magnetic susceptibility variations could be linked with the ice core dansgaard oeschger and bond cycles this is supported by ice rafted detritus ird grain size the quartz feldspar ratio and carbonate isotopic and foraminiferal records the covariation of the sediment physical properties and 18o in greenland ice indicates a coupling of atmospheric temperature and paleocirculation variations gradual reduced bottom currents iceland scotland overflow water and enhanced iceberg discharges have been reconstructed for cold atmospheric periods relative to interstadial times in the study area the magnetic susceptibility signal is not related to the ice rafted detritus input but most probably reflects the variations of the iceland scotland overflow water intensity transporting titanomagnetite into the reykjanes ridge region

rapid climatic variations during marine isotopic stage 3 magnetic analysis of sediments from nordic seas and north atlantic abstract the bulk magnetic parameters of seven deep sea cores distributed from the nordic seas 67 n to the north atlantic as far south as the bermuda rise 33 n exhibit short term variations which correlate with rapid climatic changes during marine isotopic stage 3 mis3 the magnetic mineralogy is uniformly dominated by well sorted low ti content magnetites indicating that these variations are due to variations in the relative amount of magnetic minerals because the magnetic minerals predominantly originate from one common source area the nordic basaltic province these changes arise from changes in the efficiency of the transport of the magnetic particles by deep currents from the source to the site of deposition these results therefore show that the fast climatic changes are related to coeval fast changes in the strength of the deep sea circulation the latter was active reduced during the interstadials stadials and heinrich events transporting the magnetic particles from the norwegian sea into the north atlantic ocean along a path similar to the present path of the nadw it is tentatively suggested that the faeroe shetland channel and the denmark strait were the only two active paths for the overflow water during mis3 the presence of magnetic oscillations in the bermuda rise core in phase with those from the north atlantic indicates that the activity of the southern newfoundland basin gyre was linked to that of the nadw during mis3

ice sheet dynamics on the lofoten vesteralen shelf north norway from late mis 3 to heinrich stadial 1 abstract we present an account of the glacial dynamics from late marine isotope stage mis 3 to the heinrich stadial hs 1 on the lofoten vesteralen margin northern norway this account is based on an analysis of the sedimentary stratigraphy on the upper slope close to the ice sheet grounding line at the continental shelf edge and an analysis of the glacial morphology on the shelf areas our results point to a dynamic ice sheet that waxed and waned on the lofoten vesteralen continental shelf from the late mis 3 through the last glacial maximum lgm and the hs 1 glacigenic debris flows and deposition of laminated diamicts suggest that the ice sheet reached the shelf edge on several occasions these are dated to 25 5 ka bp hs3 between 21 1 and 21 7 ka bp 19 5 ka bp 15 6 ka bp and 14 4 ka bp uncorrected 14c ages a contouritic sorted sand sediment unit that formed in a relatively warm interval during late mis 3 suggests that a strong norwegian atlantic slope current also developed during glacial interstadials implying that the oceanic circulation in the eastern norwegian sea was similar as today the general pattern is that the ice sheet advanced onto the shelf during cold period with little influx of atlantic water to the norwegian sea and that it retreated toward the coast during intervals with higher temperatures and higher influx of warm atlantic water the last ice advance to the edge of the continental shelf occurred during hs 1

circulation changes in the faeroe shetland channel correlating with cold events during the last glacial period 58 10 ka a core from the margin of the faeroe shetland channel covering the last glacial period 58 10 ka reveals a very detailed record of oscillations in benthic and planktic foraminifera oxygen isotopes and ice rafted detritus the oscillations correlate almost exactly with the dansgaard oeschger cycles in the greenland ice cores including similar subdivision of the cycles into warmer interstadial and colder stadial sections the remarkably close agreement between the benthic faunas and their 18 o data and the record of the ice cores provides new empirical evidence for a close relationship between the deep ocean circulation and the abrupt climatic changes of the last glacial period

ocean circulation and iceberg discharge in the glacial north atlantic inferences from unmixing of sediment size distributions variability in iceberg discharge and deep ocean circulation in the north atlantic during the last glacial period is inferred from the grain size distribution and trace elemental composition of terrigenous sediments in a deep sea core taken on reykjanes ridge south of iceland end member modeling of the grain size distributions is used to unmix the signals of varying bottom current speed and iceberg discharge the size distribution within the silt fraction appears to be influenced by both factors based on th sc la relationship we established that during the ice rafted detritus events continental material of likely greenlandic origin increased to 87 and that bottom current derived material contains to 40 mid oceanic ridge fines probably of icelandic origin our results have important implications for the use of silt grain size as an indicator for paleocurrent speed in the glacial north atlantic we show that reconstructions of variations in bottom current speed based on the raw grain size data are opposite to inferences from the unmixed record the latter indicates that deep water convection decreased during periods of enhanced iceberg discharge which is in general agreement with paleoceanographic reconstructions of the north atlantic

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

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

the avaatech xrf core scanner technical description and applications to ne atlantic sediments abstract x ray fluorescence xrf core scanning provides rapid high resolution down to 1 mm records of chemical composition on split sediment cores the measurements are non destructive and require very limited sample preparation the new avaatech xrf core scanner operational since 2002 covers the atomic mass range from al to u instrument parameters especially tube voltage can be adjusted to provide optimum settings for selected elements or sets thereof owing to the nature of the surface of split sediment cores particularly effects resulting from sample inhomogeneity and surface roughness results are semiquantitative yet provide reliable records of the relative variability in elemental composition downcore selected case studies from diverse sedimentary settings in the ne atlantic ocean illustrate a range of applications of xrf logging data these include preliminary stratigraphic interpretations glacial interglacial cycles provenance studies of the terrigenous sediment fraction lithological characterization early diagenetic processes and distinction between carbonate phases aragonite v calcite

climatic and oceanographic changes in the northeast atlantic reflected by magnetic properties of sediments deposited on the portuguese margin during the last 340 ka abstract rock magnetic parameters measured along two giant piston cores md95 2040 40 34 n 9 51 w and md95 2042 37 47 n 10 09 w collected off the portuguese margin related to other proxy climatic data have been used to reconstruct magnetic mineralogical changes of in relation to environmental and climatic conditions over the north atlantic western europe and northwest africa during the last three climatic cycles since isotope stage 10 thin discrete layers containing coarse grains of titano magnetite are associated with events of iceberg discharge during heinrich events 1 6 heinrich quat res 29 1988 142 that have equivalent events in isotope stages 5 8 concentrations of fine grained ti magnetite and hematite goethite varying in phase opposition are directly linked with alternations of cold and warm climatic periods spectral analyses of the rock magnetic signals reveal milankovitch periods at 100 and 41 ka confirming the relationship with long term climatic changes at high latitudes the nature ti magnetite and size range of the finest ferrimagnetic fraction as well as its variation suggest a control by deep currents carrying a colloidal clayey fraction from remote sources iceland faeroes mid atlantic ridge variation of hematite goethite contents is linked with transport by rivers and winds from the neighbouring continent a tight correlation with the d o cycles in greenland ice records confirms that north atlantic oceanic regimes and continental wind regimes were strongly influenced by millennial scale climatic changes throughout the last 350 ka

magnetic characterisation of present day deep sea sediments and sources in the north atlantic the north atlantic plays a key role in global climate through formation of north atlantic deep water which drives the thermohaline circulation to understand past and future climate change it is essential to understand the processes occurring within the present day north atlantic but ocean wide studies of present day sediment distribution and sources are relatively sparse here we use magnetic measurements to characterise the surface sediments of the north atlantic and identify the major climatic and oceanographic controls on their magnetic signatures the magnetic data and subsequent cluster analysis identify distinct spatial patterns of sediment sources and transport pathways much of the sedimentary magnetic signal appears to be controlled by detrital inputs especially of windblown dust and ice rafted debris ird with a range of different sources these sediment transport pathways can be validated by making direct comparison of the sediment magnetic properties with source rocks and soils and with iceberg trajectory and observation data the spatial distributions of the ird dominated sediments substantiate those mapped previously using lithological tracers provide additional spatial information on sediment sources and pathways and suggest that deep water currents are less significant than proposed in controlling present day sediment mineralogy and distribution the data form a present day basis for comparison with glacial stage ird and dust distributions and modes of ocean circulation

geochemistry of surface sediments from the mid oceanic kolbeinsey ridge north of iceland in order to assess recent submarine volcanic contributions to the sediments from the active kolbeinsey ridge surface samples were analyzed chemically the contribution of major and trace elements studied differ within the study area a statistical analysis of the geochemical variables using factor analysis and cluster method allows to distinguish possible sample groups cluster method identifies three distinct sediment groups located in different areas of sedimentation group 1 is characterized by highest contents of fe2o3 v co ni cu and zn demonstrating the input of volcaniclastic material group 2 comprises high values of caco3 cao and sr representing biogenic carbonate group 3 is characterized by the elements k rb cs la and pb indicating the terrigenous component the absolute percentage of the volcanic biogenic and terrigenous components in the bulk sediments was calculated by using a normative sediment method the highest volcanic component 60 on a carbonate free basis is found on the ridge crest the biogenic component is highest 10 30 in the eastern part of the spar fracture zone influenced by the east iceland current samples from the western and southeastern region of the study area contain more than 90 of terrigenous component which appears to be mainly controlled by input of ice rafted debris

the deglaciation of the northern hemisphere a global perspective orbitally induced increase in northern summer insolation after growth of a large ice sheet triggered deglaciation and associated global warming ice albedo sealevel and greenhouse gas feedbacks together with tropical warming from weakening winds in response to polar amplification of warming caused regionalto global near synchronization of deglaciation effects were larger at orbital rather than millennial frequencies because ice sheets and carbon dioxide vary slowly ice sheet linked changes in freshwater delivery to the north atlantic and possibly free oscillations in the climate system forced millennial climate oscillations associated with changes in north atlantic deep water nadw flow the north atlantic typically operates in one of three modes modern glacial and heinrich deglaciation occurred from a glacial mode ocean that in comparison to modern had shallower depth of penetration of nadw formed further south causing strong northern cooling and the widespread cold dry and windy conditions associated with the glacial maximum and the cold phases of the millennial dansgaard oeschger oscillations the glacial mode was punctuated by meltwater forced heinrich conditions that caused only small additional cooling at high northern latitudes but greatly reduced the formation of nadw and triggered an oceanic seesaw that warmed some high latitude southern regions centered in the south atlantic

grain size and srnd isotopes as tracer of paleo bottom current strength northeast atlantic ocean abstract a crucial question in modern paleoceanographic research is how vigourous was the bottom current in the glacial north atlantic ocean distribution of sediment grain size can provide such information if the characteristics of the source functions are known the interest of this paper is to use the sr nd isotopic composition of lithic particles as a tracer of origin in order to determine possible changes in the source function over the last 185 kyr grain size distribution data are derived from a sediment core in the icelandic basin gardar drift the distribution pattern reveals a well sorted silt size modal size 20 m in the glacial deposits sr and nd isotopic composition measured on separate size fractions indicates a more constant local origin iceland for the silt fraction than for the fine fraction these data suggest that the increase in the silt fraction during glacial periods is related primarily to an increase in the bottom current strength rather than to changes in sediment supply i e ice rafting turbidity current the increase in vigour of the bottom current recorded during the isotopic stages 6 4 and the last post glacial periods could have been initiated by a southward shift of the zone of deep water formation in the northern part of the icelandic basin

geochemical response of the mid depth northeast atlantic ocean to freshwater input during heinrich events 1 to 4 heinrich events are intervals of rapid iceberg sourced freshwater release to the high latitude north atlantic ocean that punctuate late pleistocene glacials delivery of fresh water to the main north atlantic sites of deep water formation during heinrich events may result in major disruption to the atlantic meridional overturning circulation amoc however the simple concept of an amoc shutdown in response to each freshwater input has recently been shown to be overly simplistic here we present a new multi proxy dataset spanning the last 41 000 years that resolves four heinrich events at a classic mid depth north atlantic drill site employing four independent geochemical tracers of water mass properties boron calcium carbon and oxygen isotopes in foraminiferal calcite and neodymium isotopes in multiple substrates we also report rare earth element distributions to investigate the fidelity by which neodymium isotopes record changes in water mass distribution in the northeast north atlantic our data reveal distinct geochemical signatures for each heinrich event suggesting that the sites of fresh water delivery and or rates of input played at least as important a role as the stage of the glacial cycle in which the fresh water was released at no time during the last 41 kyr was the mid depth northeast north atlantic dominantly ventilated by southern sourced water instead we document persistent ventilation by glacial north atlantic intermediate water gnaiw albeit with variable properties signifying changes in supply from multiple contributing northern sources

saw tooth pattern of north atlantic current speed during dansgaard oeschger cycles revealed by the magnetic grain size of reykjanes ridge sediments at 59 n detailed mineral rock magnetic measurements including high resolution magnetic hysteresis loops were carried out on three sediment cores recovered from the reykjanes ridge in the north atlantic supported by physical grain size analyses titanomagnetite grain size variations form a proxy of the speed of near bottom currents and reveal a cyclic saw tooth pattern between dansgaard oeschger cycles 8 and 5 the magnetic grain size data suggest that these dansgaard oeschger cycles were characterized by gradual intensification of the near bottom current speed while other paleoceanographic proxies indicate escalating iceberg discharge and declining sea surface temperatures these observations are contrary to the frequently assumed and strictly applied positive relationship between high latitude warmth and north atlantic deep water formation within the confines of temporal control however it would appear that peaks in iceberg discharge and slow near bottom current speeds were synchronous the magnetic hysteresis data also demonstrate that magnetic concentration parameters such as magnetic susceptibility do not necessarily provide direct evidence of paleocirculation less

threshold behavior of millennial scale variability in deep water hydrography inferred from a 1 1 ma long record of sediment provenance at the southern gardar drift 1 integrated ocean drilling program iodp site u1314 of the north atlantic is a critical sedimentary archive record of subpolar deep water from the southern gardar drift for which we derived an age model of orbital resolution for the last 1 8 ma this chronology combined with high resolution cm scale x ray fluorescence core scanning measurements of major elements allows tracking changes in terrigenous provenance during the last 1 1 ma low potassium to titanium k ti ratios reflect enhanced transport of basalt derived titanomagnetites during warm climate intervals while high k ti ratios indicate a dominance of acidic sediment sources typical for glacial and stadial events changes in k ti and magnetic concentration at site 1314 are coeval with fluctuations in smectite content and grain size data from nearby piston cores suggesting that the provenance changes are mainly controlled by variable flow of the iceland scotland overflow water an important branch of north atlantic deep water furthermore k ti variations on orbital time scales show a striking similarity to the deep sea 13c record from odp site 607 pervasive features of the k ti time series during and after the mid pleistocene transition are suborbital changes similar to dansgaard oeschger and bond oscillations that appear to be strongly amplified during ice growth phases when global benthic 18o was within the range of 4 1 4 6 per mil the strong increase in variability of sediment provenance and subsequently deep hydrography at benthic 18o values below 4 1 suggests that the extent of glaciations and therefore sea level corresponding to this value constitutes an important physical threshold that was persistent at least for the last 1 1 ma

geochemistry of tertiary alterite clay phases on the iceland faeroe ridge northeast atlantic leg 38 site 336 abstract the geochemistry analyses of the clay fraction m of tertiary alterites overlying tholeiitic basalt site 336 on the iceland faeroe ridge revealed close to the parent rock the predominance of ferriferous montmorillonite 80 over kaolinite and halloysite conversely the top of alterite redbeds proved to be exclusively composed of kaolinite a comparative study of these redbeds with the present day ones derived from the same type of parent rock suggested genesis under tropical climatic conditions compared to the basaltic parent rock alterites are characterized by moderate desilication and partial elimination of ca na mg mn sr cu and sr and on the other hand by a concentration of some elements such as al fe ti k rb and zr

origin of orbital periods in the sedimentary relative paleointensity records abstract orbital cycles with 100 kyr and or 41 kyr periods detected in some sedimentary normalized remanence relative paleointensity records by power spectral analysis or wavelet analysis have been attributed either to orbital forcing of the geodynamo or to lithologic contamination in this study local wavelet power spectra lwps with significance tests have been calculated for seven relative paleointensity rpi records from different regions of the world the results indicate that orbital periods 100 kyr and or 41 kyr are significant in some rpi records during certain time intervals and are not significant in others time intervals where orbital periods are significant are not consistent among the rpi records implying that orbital periods in these rpi records may not have a common origin such as orbital forcing on the geodynamo cross wavelet power spectra xwt and squared wavelet coherence wtc between rpi records and orbital parameters further indicate that common power exists at orbital periods but is not significantly coherent and exhibits variable phase relationships implying that orbital periods in rpi records are not caused directly by orbital forcing similar analyses for rpi records and benthic oxygen isotope records from the same sites show significant coherence and constant in phase relationships during time intervals where orbital periods were significant in the rpi records indicating that orbital periods in the rpi records are most likely due to climatic contamination although common power exists at orbital periods for rpi records and their normalizers with significant coherence during certain time intervals phase relationships imply that contamination at orbital periods is not directly due to the normalizers orbital periods are also significant in the nrm intensity records and contamination in rpi records can be attributed to incomplete normalization of the nrm records further tests indicate that contamination is apparently not directly related to physical properties such as density or carbonate content or to the grain size proxy arm however wtc between rpi records and the grain size proxy arm irm implies that arm irm does reflect the contamination in some rpi records it appears that orbital periods were introduced into the nrm records and have not been normalized when calculating rpi records through magnetite grain size variations reflected in the arm irm grain size proxy the orbital power in arm irm for some north atlantic sites is probably derived from bottom current velocity variations that are orbitally modulated and are related to the vigor of thermohaline circulation and the production of north atlantic deep water nadw in the case of odp site 983 the orbital power in rpi appears to exhibit a shift from 41 kyr to 100 kyr period at the mid pleistocene climate transition 750 ka reinforcing the climatic origin of these orbital periods rpi records from the atlantic and pacific oceans and rpi records with orbital periods eliminated by band pass filters are highly comparable with each other in the time domain and are coherent and in phase in time frequency space especially at non orbital periods indicating that contamination although present at orbital periods is not debilitating to these rpi records as a global signal that is primarily of geomagnetic origin

correcting for the influence of ice rafted detritus on grain size based paleocurrent speed estimates the grain size of deep sea sediments provides an apparently simple proxy for current speed however grain size based proxies may be ambiguous when the size distribution reflects a combination of processes with current sorting only one of them in particular such sediment mixing hinders reconstruction of deep circulation changes associated with ice rafting events in the glacial north atlantic because variable ice rafted detritus ird input may falsely suggest current speed changes inverse modelling has been suggested as a way to overcome this problem however this approach requires high precision size measurements that register small changes in the size distribution here we show that such data can be obtained using electro sensing and laser diffraction techniques despite issues previously raised on the low precision of electro sensing methods and potential grain shape effects on laser diffraction down core size patterns obtained from a sediment core from the north atlantic are similar for both techniques reinforcing the conclusion that both techniques yield comparable results however ird input leads to a coarsening that spuriously suggests faster current speed we show that this ird influence can be accounted for using inverse modelling as long as wide size spectra are taken into account this yields current speed variations that are in agreement with other proxies our experiments thus show that for current speed reconstruction the choice of instrument is subordinate to a proper recognition of the various processes that determine the size distribution and that by using inverse modelling meaningful current speed reconstructions can be obtained from mixed sediments

magnetic susceptibility variations in upper pleistocene deep sea sediments of the ne atlantic implications for ice rafting and paleocirculation at the last glacial maximum magnetic susceptibility ms variations are used to intercorrelate 17 upper pleistocene sediment cores taken from the ne atlantic between 40 degrees and 60 degrees n the ms based correlation depends on regionally consistent patterns of variation in the deposition of ice rafted detritus ird in response to pleistocene glaciations and especially to high frequency ice rafting episodes referred to in recent studies as heinrich events the sedimentological and rock magnetic basis for the apparent relationship between the ms signal and ird content of ne atlantic sediments is examined by 1 comparing the ms profiles of selected cores with their records of coarse fraction 150 mu m lithic fragment abundance and neogloboquadrina pachyderma sin percentages and 2 normalizing ms by expressing it both on a carbonate free basis and as a quotient with anhysteretic remanent magnetization a parameter sensitive to magnetic mineral grain size variations these comparisons show that variations in bulk sediment ms are only partly driven by simple carbonate dilution productivity and dissolution effects changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk ms values in particular horizons rich in ird are associated with significant increases in the relative proportion of coarse grained multidomain ferrimagnetic particles in the sediment this is because ice rafting in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments has a high potential for delivering large ferrimagnetic grains as components of sand sized polycrystalline lithic fragments this fundamental linkage between the ird content and ms signal of ne atlantic sediments is used to reconstruct the patterns of variation in ird deposition and by inference surface currents of the last glacial maximum lgm similar to 18 19 ka relative to the present day ne atlantic using the time slice mapping approach developed by the climap project group our lgm holocene ms ratio map based on sample pairs from over 80 deep sea cores confirms that there was a weak cyclonic gyre north of the polar front in the lgm north atlantic the gyre comprised a sluggish warm current in the ne atlantic flowing north between latitudes 47 degrees and 62 degrees n partly fed by subtropical waters from south of the polar front and carrying large numbers of icebergs derived from several sources most of which melted between latitudes 45 degrees and 52 degrees n the warm current probably continued its flow into the iceland basin where it fed into a south flowing current which transported melting icebergs from iceland and scandinavia along the western flank of the reykjanes ridge

rapid changes in the mechanism of ocean convection during the last glacial period high amplitude rapid climate fluctuations are common features of glacial times the prominent changes in air temperature recorded in the greenland ice cores1 2 are coherent with shifts in the magnitude of the northward heat flux carried by the north atlantic surface ocean3 4 changes in the ocean s thermohaline circulation are a key component in many explanations of this climate flickering5 here we use stable isotope and other sedimentological data to reveal specific oceanic reorganizations during these rapid climate change events deep water was generated more or less continuously in the nordic seas during the latter part of the last glacial period 60 to 10 thousand years ago but by two different mechanisms the deep water formation occurred by convection in the open ocean during warmer periods interstadials but during colder phases stadials a freshening of the surface ocean reduced or stopped open ocean convection and deep water formation was instead driven by brine release during sea ice freezing these shifting magnitudes and modes nested within the overall continuity of deep water formation were probably important for the structuring and rapidity of the prevailing climate changes

late quaternary sedimentation on the mid atlantic reykjanes ridge clay mineral assemblages and depositional environment sediment samples from the mid atlantic reykjanes ridge 59 n were taken to get information about sediment genesis and to identify different sources during the late quaternary samples were investigated by x ray diffraction and grain size analyses the clay mineral assemblages in sediments of the reykjanes ridge reflect paleoceanographic changes during the late quaternary holocene sediments are characterized by high contents of smectite mainly of less developed crystallinity in the spatial distribution of clay minerals high smectite concentrations on the eastern flank and slightly decreasing concentrations on the western flank of the reykjanes ridge indicate the action of bottom water transport the smectite originates mainly from the volcanogenous icelandic shelf and reflects the influence of iceland scotland overflow water isow stratigraphic variability in the clay mineral composition reflects predominantly the influence of different sources resulting from oceanographic and glacial transport processes during glacial time sediment transport is due mainly to input by icebergs increasing amounts of illite chlorite and kaolinite characterize ice rafted sediments of the heinrich layers in these sediments smectite crystallinity is well developed in contrast several other ice rafted layers contain smectite with low crystallographic order similar to smectites of holocene age the icelandic source was proved by distinct amounts of basaltic glass in the coarse grained sediment at approximately 55 ka increasing amounts of chlorite and kaolinite suggest an enhanced influx of warm north atlantic surface waters this hypothesis is supported by a high carbonate shell production at this time relative low concentrations and the well developed crystallinity of smectite minerals characterize the last glacial maximum lgm 18 16 ka indicating a reduced supply of fine icelandic material shortly after the lgm at the beginning of termination ia a distinct increase in fine grained quartz 2 m and smectite are visible which are proposed to reflect a supply of fine grained ice rafted material at 13 ka linear increasing smectite concentrations of lower crystallographic order indicate increasing supply of fine grained material from iceland linked to reinitiation of bottom currents of the isow full reinitiation is indicated at around 10 ka where a strong increase in smectite of low crystallographic order is detected

late quaternary sedimentation between the gibbs fracture and the greenland basin mineralogical and geochemical data the geochemical study of core samples taken between the gibbs fracture zone and the south of the greenland basin leads to an understanding of the sedimentogenesis of this region since the last interglacial stage by demonstrating well defined mineralogical and chemical assemblages it is possible to suggest an origin for sediments and the direction of flow two major families of influx one of a petrographically acidic nature the other basic observed in the neighbouring basins are distinguished variations in their relative importance are linked to climate and hydrology the basic phase is represented chiefly by an inflow of volcanic detritus derived from the erosion of iceland and the faeroes iron titanium and smectite distribution patterns indicate that iceland is their probable source while nickel and copper would come from the faeroe islands in the south of the basin gibbs fracture the basic deposition reaches 10 cm103yrs the acidic phase is brought by ice rafting during the colder period and by bottom currents during the warmer period in the post glacial its contribution reaches 30 cm103yrs as far away as the gibbs fracture zone

norwegian sea warm pulses during dansgaard oeschger stadials zooming in on these anomalies over the 35 41 ka cal bp interval and their impacts on proximal european ice sheet dynamics abstract the last glacial millennial climatic events i e dansgaard oeschger and heinrich events constitute outstanding case studies of coupled atmosphere ocean cryosphere interactions here we investigate the evolution of sea surface and subsurface conditions in terms of temperature salinity and sea ice cover at very high resolution mean resolution between 55 and 155 years depending on proxies during the 35 41 ka cal bp interval covering three dansgaard oeschger cycles and including heinrich event 4 in a new unpublished marine record i e the md99 2285 core 62 69 n 3 57s e we use a large panel of complementary tools which notably includes dinocyst derived sea ice cover duration quantifications the high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean cryosphere interactions occurring during these periodic ice sheet collapse events our results evidence a paradoxical hydrological scheme where i greenland interstadials are marked by a homogeneous and cold upper water column with intensive winter sea ice formation and summer sea ice melting and ii greenland and heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation separated by a strong halocline from a less warm and saltier subsurface layer our work also suggests that this stadial surface subsurface warming started before massive iceberg release in relation with warm atlantic water advection these findings thus support the theory that upper ocean warming might have triggered european ice sheet destabilization besides previous paleoceanographic studies conducted along the atlantic inflow pathways close to the edge of european ice sheets suggest that such a feature might have occurred in this whole area nonetheless additional high resolution paleoreconstructions are required to confirm such a regional scheme

coherent patterns of ice rafted debris deposits in the nordic regions during the last glacial 10 60 ka we have synchronized records of ice rafted rock debris deposits of three sediment cores from the norwegian sea and the irminger basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties our synchronized records indicate that layers rich in ice rafted debris were deposited throughout the nordic regions at times near to synchronous with the major collapses of the laurentide ice sheet during the heinrich events there are also millennial scale coherent and near to synchronous deposits of ice rafted rock debris into the norwegian sea related to repetitive changes of the flux of icebergs from the fenno scandinavian the correlation with the cold phases of the dansgaard oeschger temperature record points to a close coupling between atmospheric temperature oscillations and variations of iceberg fluxes into the norwegian sea during the last glacial variations in atmospheric circulation patterns bringing moisture supply to high latitudes and the distribution of this moisture over the different northern hemisphere coastal ice sheets and ice shelves could be controlling both the timing of ice sheet advances and the flux of iceberg to the open ocean

source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern north atlantic magnetic properties of eight particle size ranges from nine locations in iceland and 26 locations in southern greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment these terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand fine pseudo single domain psd size magnetic grains dominate the magnetic assemblage of all icelandic fractions in contrast greenlandic samples possess greater variation in magnetic grain size only fine silt and clay are as magnetically fine as the icelandic psd grains while greenlandic silts and sands are dominated by coarser psd and multi domain grains these observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between icelandic and greenlandic sources using these results to examine magnetic grain size records from marine sediment cores collected across the northern north atlantic suggests that source not just transport controlled physical grain size has a significant impact on determining the magnetic grain size at a particular location homogeneity of magnetic grain size in icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding iceland and their ability to buffer large environmental changes

eurasian ice sheet collapse was a major source of meltwater pulse 1a 14 600 years ago rapid sea level rise caused by the collapse of large ice sheets is a threat to human societies in the last deglacial period the rate of global sea level rise peaked at more than 4 cm yr 1 during meltwater pulse 1a which coincided with the bolling warming event some 14 650 years ago however the sources of the meltwater have proven elusive and the contribution from eurasian ice sheets has been considered negligible here we present a regional carbon 14 calibration curve for the norwegian sea and recalibrate marine 14c dates linked to the eurasian ice sheet retreat we find that marine based sectors of the eurasian ice sheet collapsed at the bolling transition and lost an ice volume of 4 5 7 9 m sea level equivalents sle over 500 years during peak melting 3 3 6 7 m sle of ice was lost potentially explaining up to half of meltwater pulse 1a a mean meltwater flux of 0 2 sv over 300 years was injected into the norwegian sea and the arctic ocean at a time when proxy evidence suggests vigorous atlantic meridional overturning circulation our reconstruction shows that massive marine based ice sheets can collapse in as little as 300 500 years marine based sections of the eurasian ice sheet collapsed rapidly during a warming event 14 600 years ago and contributed to the meltwater pulse 1a event according to a recalibrated age model for sediments from the norwegian sea

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

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

surface and deep ocean variability in the northern sargasso sea during marine isotope stage 3 new geochemical proxy data from bermuda rise piston cores reveal ocean and climate conditions in the northern sargasso sea during marine isotope stage 3 using 18o on the planktonic foraminifer globigerinoides ruber we can correlate explicitly with every stadial interstadial change in greenland ice between 32 and 58 ka these data suggest repetitive changes of 4 c in the annual average sea surface temperature sst with maximum cooling comparable to or greater than sst during glacial maximum conditions the extent of sst depression is about the same for typical stadial events and for heinrich events 4 and 5 which we have identified on the bermuda rise by traces of ice rafting benthic foraminiferal 13c decreases during every stadial event consistent with reduced production of the deepest component of north atlantic deep water and shoaling of its interface with antarctic bottom water this interpretation is supported by benthic cd ca data from the climate cycle associated with interstadial 8

benthic δ18o records in the north atlantic over the last glacial period 60 10 kyr evidence for brine formation four high resolution benthic isotope records from north atlantic and south norwegian sea cores are compared for the past 60 kyr the benthic records show light 18o peaks simultaneously to or following the heinrich events the amplitude of these light peaks varies between 1 for the most northern core enam93 21 and 0 35 for the deep north atlantic cores the high 18o gradient between the north atlantic cores and the pacific core v19 30 suggests a regional influence of 18o depleted meltwater to deeper depth during periods of iceberg discharges the most likely process for transferring 18o depleted meltwater to depth is sea ice formation induced by brine formation during heinrich events 4 and 3 this mecanism was of major importance compared to open ocean convection in the southern norwegian sea and at the northern boundaries of the atlantic leading to intermediate to deep water formation other 18o excursions appearing in all the records point to the contribution of both brine formation and global changes in the 18o of seawater associated with the heinrich event periods

millennial scale propagation of atlantic deep waters to the glacial southern ocean the compilation of changes in the magnetic properties at various sites distributed along the path of the deepwater mass in north atlantic shows large amplitude short term fluctuations reflecting changes in the strength of the north atlantic deep water nadw these changes which suggest a two mode deep glacial circulation dynamic are perfectly concurrent with air temperature changes over greenland they also share a similar pattern with those reported in the nd isotope ratios from the deep cape basin during the same time period greenland interstadials were accompanied by increased flow speed of nadw and relatively more nadw reaching the southern ocean while during greenland stadials and heinrich events both the north atlantic flow speed of nadw and its presence in the south atlantic were reduced it is demonstrated that both proxies are tracing the same water mass and their reliability for monitoring changes in the deepwater circulation is therefore clearly established after using the climatically independent geomagnetic assisted stratigraphy to put the northern and southern hemisphere records on the same age scale the south atlantic record appears to lag changes in north atlantic flow speeds by approximately 860 220 years during the most prominent and best defined cycles interstadials 12 and 8 although future work is needed this significant offset provides a first observation and tentative quantification of the time needed for glacial northern component water to mix downward and to flow from the north to the south atlantic

were glacial iceberg surges in the north atlantic triggered by climatic warming high resolution physical mineralogical sedimentological and micropalaeontological studies were carried out on north atlantic cores from the reykjanes ridge at 59degreesn and from the region southwest of the faeroe islands all core sites are situated along the pathway of iceland scotland overflow water isow and the various parameters measured display similar features previously identified carbonate oscillations keigwin and jones 1994 j geophys res 99 12397 12410 in the time span back to the marine isotope stage 5 4 transition and late glacial lithic events bond and lotti 1995 science 267 1005 1010 such as the heinrich ice rafting events are all represented in the core records long term trends and higher frequency changes in isow intensity were reconstructed on the basis of various independent proxy records the long term trends in circulation match theoretical orbitally forced insolation changes our observed links between ice rafted detritus ird input variations in sea surface temperature sst and circulation at greater depth point to the need to re examine the origin of ird events we suggest that these events may have been triggered by enhanced partly sub surface heat transport to the north enhanced northward heat transport may have caused bottom melting of floating outlet glaciers and ice shelves leading to increased iceberg discharge and ice sheet destabilization this discharge resulted in lower sst s and a lower temperature over greenland thus as shown by our records this scenario implies a temporary de coupling of surface processes and circulation at greater depth a key feature is the occurrence of a saw tooth pattern in the marine data which is similar to the greenland ice core records moreover the warming theory of ird events would explain the observed out of phase relationship between the greenland and antarctic ice core records and also the rapid establishment of higher temperatures over greenland immediately after the cold phases stadials of the dansgaard oeschger cycles less

the importance of the terrigenous fraction within a cold water coral mound a case study in the nineties cold water coral mounds were discovered in the porcupine seabight ne atlantic west of ireland a decade later this discovery led to the drilling of the entire challenger cold water coral mound eastern slope porcupine seabight during iodp expedition 307 as more than 50 of the sediment within challenger mound consists of terrigenous material the terrigenous component is equally important for the build up of the mound as the framework building corals moreover the terrigenous fraction contains important information on the dynamics and the conditions of the depositional environment during mound development in this study the first in depth investigation of the terrigenous sediment fraction of a cold water coral mound is performed combining clay mineralogy sedimentology petrography and sr nd isotopic analysis on a gravity core md01 2451g collected at the top of challenger mound sr and nd isotopic fingerprinting identifies ireland as the main contributor of terrigenous material in challenger mound besides this a variable input of volcanic material from the northern volcanic provinces iceland and or the nw british isles is recognized in most of the samples this volcanic material was most likely transported to challenger mound during cold climatic stages in three samples the isotopic ratios indicate a minor contribution of sediment deriving from the old cratons on greenland scandinavia or canada the grain size distributions of glacial sediments demonstrate that ice rafted debris was deposited with little or no sorting indicating a slow bottom current regime in contrast interglacial intervals contain strongly current sorted sediments including reworked glacio marine grains the micro textures of the quartz sand grains confirm the presence of grains transported by icebergs in interglacial intervals these observations highlight the role of ice rafting as an important transport mechanism of terrigenous material towards the mound during the late quaternary furthermore elevated smectite content in the siliciclastic glaciomarine sediment intervals is linked to the deglaciation history of the british irish ice sheet biis the increase of smectite is attributed to the initial stage of chemical weathering processes which became activated following glacial retreat and the onset of warmer climatic conditions during these deglaciations a significant change in the signature of the detrital fraction and a lack of coral growth is observed therefore we postulate that the deglaciation of the biis has an important effect on mound growth it can seriously alter the hydrography nutrient supply and sedimentation processes thereby affecting both sediment input and coral growth and hence coral mound development

the use of na cl ratios to trace solute sources in a semiarid zone rainwater interaction with soils is a major source of dissolved salts in groundwater the transition zone between the humid and the arid area is characterized by a specific combination of reactions which do not exist elsewhere this combination of caco3 dissolution and base exchange reactions affects the na cl ratio which is the quantitatively most important parameter used for tracing salinity sources of groundwater the increase in the na cl ratio in the coastal plain aquifer of israel from north to south is related to local recharge of na rich water after interaction with soils of loessial origin

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

onset and demise of coral reefs relationship with regional ocean circulation on the wyville thomson ridge abstract results from a vibrocore collected on the northern edge of the scottish continental shelf at around 300 m water depth on the wyville thomson ridge enable to reconstruct the history of cold water coral cwc reef growth and demise during the holocene period we report on significant age differences between u th and 14c dates obtained on pristine well preserved cwc lophelia pertusa which may reflect an diagenetic process that standard quality tests have failed to highlight additional 14c dates derived from bivalve fragments venus sp and foraminifera cibicides refulgens samples show a gradual ageing with core depth but with significant age inversions in the lower section of the sediment core which we consider reflects sedimentary mixing we thus chose to derive an independent age model using planktonic foraminifera globigerina bulloides stable isotope profiles the vibrocore record is divided into 3 phases 1 mixed sediment deposits of glacial age corresponding to the base of the core with ages older than 13 cal ka bp 2 the end of the deglacial early holocene between 13 and 9 cal ka bp and 3 finally the holocene period from around 9 cal ka bp with abundant lophelia pertusa fossils siliciclastic grain size and clay mineralogical composition show two significant shifts at around 13 and 9 cal ka bp indicating changes in sedimentary sources and transport associated with the dynamics and flow patterns of surface currents during the deglaciation and holocene our results show that the onset of cwc reef growth on the wyville thomson ridge occurred around 9 cal ka bp and was associated with a shift in flow patterns of surface currents in this area this change of circulation patterns induced favourable sedimentological and hydrological conditions for corals to grow and is associated with large scale modifications of north atlantic circulation patterns at the end of the deglaciation