late quaternary tephrochronology of sweden a review abstract studies of late quaternary sediments in south and central sweden have yielded a detailed tephrochronology for the last glacial interglacial transition lgit ca 15 000 10 000 cal yr bp and the holocene more than ten tephra layers have been detected and geochemically characterised the most widespread tephra from the lgit is the rhyolitic phase of the vedde ash ca 12 000 cal yr bp which has been found in lacustrine sediments and marine clays south of the younger dryas moraines in south sweden other horizons from the lgit identified to date include the borrobol tephra ca 14 400 cal yr bp the hasseldalen tephra ca 11 500 cal yr bp the 10 ka askja tephra ca 11 300 cal yr bp and the hogstorpsmossen tephra ca 10 200 cal yr bp the most significant holocene isochrones are hekla 4 ca 4260 cal yr bp hekla selsund kebister ca 3750 cal yr bp hekla 3 ca 3000 cal yr bp and askja 1875 two new late holocene tephra horizons the stomyren tephra ca 2100 cal yr bp and the gullbergby tephra ca 2700 cal yr bp were identified in single sites and are so far less valuable as marker horizons but are potentially important for the future

late quaternary glacial interglacial changes in sediment composition at the east greenland continental margin and their paleoceanographic implications stable isotope records and sedimentological and organic geochemical investigations of marine sediments from the east greenland sea at 70 n provide important information about glacial interglacial variations of paleoenvironments through the last 225 kyr the oxygen isotope records established on the planktonic foraminifer n pachyderma sin show some excursions from the global climate pattern probably due to local regional overprint by meltwater supply the cold low saline east greenland current and fluctuations in sea ice covering were a crucial element controlling the carbonate production in the subsurface surface water column in the east greenland sea over the last 225 kyr the beginning of termination ia is ams 14c dated at about 15 8 kyr b p and interpreted as a greenland ice sheet meltwater signal the stage 2 3 boundary is dated at about 25 kyr b p the timing of the onset of the last deglacial meltwater event is about 800 years earlier than that of the barents shelf ice sheet meltwater signal recorded in the fram strait several major pulses of increased supply of coarse grained terrigenous material by glacio marine processes occurred during the last 225 kyr the supply of coarse grained ice rafted debris at the east greenland continental slope reached maximum values during the last glacial maximum stage 2 weichselian 15 19 kyr b p the drastic climatic change and the gradual retreat of continental ice masses glaciers during the last deglaciation termination i are clearly documented in the marine sedimentary sequences from shelf and upper slope environments this process resulted in distinctly decreased supply and deposition of ice rafted debris in the open shelf upper slope environments during termination i the sea ice cover also decreased causing an increase in surface water productivity indicated by increased organic carbon and biogenic opal deposition

multiple stage deglacial retreat of the southern greenland ice sheet linked with irminger current warm water transport 1 there is limited knowledge pertaining to the history of the greenland ice sheet gis during the last glacial interglacial transition as it retreated from the continental margins to an inland position here we use multiproxy data including ice rafted debris ird planktonic isotopes alkenone temperatures and tephra geochemistry from the northern labrador sea off southwest greenland to investigate the deglacial response of the gis and evaluate its implications for the north atlantic deglacial development the results imply that the southern gis retreated in three successive stages 1 early deglaciation of the east greenland margins by tephra rich ird that embrace heinrich event 1 2 progressive retreat during allerod culminating in major meltwater releases 18o depletion of 1 2 at the allerod younger dryas transition 12 8 13 0 kyr b p and 3 a final stage of glacial recession during the early holocene 9 11 kyr b p rather than indicating local temperatures of ambient surface water the alkenones likely were transported to the core site by the irminger current we attribute the timing of gis retreat to the incursion of warm intermediate waters along the base of grounded glaciers and below floating ice shelves on the continental margin the results lend support to the view that gis meltwater presented a forcing factor for the younger dryas cooling

inferring maximum geostrophic current velocities in the norwegian greenland sea from settling velocity measurements of sediment surface samples methods application and results abstract critical shear velocities and geostrophic current velocities were calculated from measured grain sizes and settling velocities using a shields type threshold curve of particle movement and assuming bedload transport for particles that were found to be transported by currents because this reconstruction of the current velocities is based on the coarsest transported component that could be recognized in the sediment the resulting current velocities represent a maximum flow speed that was effective during deposition of sediment the shape of the settling velocity distributions identifies the dominant type of deposition that controlled the accumulation of sediment residual well sorted or low energy depositional the resulting pattern of reconstructed maximum geostrophic current velocities in the norwegian greenland sea reflects the known features of present day thermohaline circulation which is influenced by the bathymetry at many places reconstructed current velocities are higher in areas where the cross section of meridional flows is restricted by topographic barriers the distribution of the depositional characters shows that residual and well sorted sediment types are generally associated with higher current velocities in areas of strong geostrophic currents e g fram strait and east greenland continental slope the low energy depositional sediment type is widespread in the basins of the eastern norwegian greenland sea where lower reconstructed maximum current velocities occur the high reconstructed velocities on the spitsbergen bank can be attributed to the disturbance from storm waves in shallower water depths

were rhyolitic glasses in the vedde ash and in the north atlantic s ash zone 1 produced by the same volcanic eruption abstract new evidence from north atlantic deep sea sediment cores suggests that rhyolitic glass shards in ash zone 1 and in the vedde ash may not have been produced by the same eruption as has been widely assumed our argument is based on 1 a marine ice rafted deposit approximately 1000 years older than the vedde ash contains rhyolitic shards with the same major element chemistry as the vedde ash itself and 2 coincidence of ash zone 1 with an abrupt increase in discharge of glacial icebergs into the north atlantic hence we cannot rule out the possibility that vedde like rhyolitic glasses were erupted onto icelandic glaciers before eruption of the vedde ash stored in the glacial ice then dispersed by icebergs into the north atlantic and deposited partly or entirely as ash zone 1 while not disproving that ash zone 1 and the vedde ash came from the same eruption our findings indicate that further study is needed to establish the exact relation between the two ash deposits

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

dynamics of atlantic water advection to the norwegian greenland sea a time slice record of carbonate distribution in the last 300 ky abstract short term variability in volume and configuration of atlantic water advection to the norwegian greenland sea ngs has recently been identified as a new and significant element for northern hemisphere glacial interglacial climatic fluctuations the amount of salt heat and moisture transferred by atlantic waters to the high arctic effectively influences northern hemisphere climates and is critical for the overall oceanic turnover rate in particular determining the extent and duration of atlantic water intrusions in the ngs is essential because of 1 its effect on the climate of the nordic continents and 2 its trigger function on the stability of the ice sheets with a weak inflows of atlantic water during glacials promoting an increase in ice volume by moisture supply to polar areas and b positive feed back mechanisms of atlantic water intrusions during ice sheet decay in this study the dynamics of surface water mass regimes in the ngs have been reconstructed for the past 300 ky by means of time slice compilations of calcium carbonate distribution and micropaleontologic proxies in addition carbonate preservation records are used to quantify deep water ventilation and production rates in contrast to the climap scenario but in accordance with many recent publications results of this study indicate that atlantic water advection was also a common feature during most glacial periods but varied strongly in volume and configuration significant modes recognized are 1 the full interglacial mode with a wide inflow of warm atlantic waters covering a broad area in the eastern sector of the ngs and extending far north combined with excellent carbonate preservation and very efficient deep water formation stages 1 and 5 5 1 2 the moderate interglacial mode with a rather small extension of atlantic waters along a narrow corridor in the southeastern sector of the ngs but still very efficient deep water exchange stages 9 isotopic events 7 5 7 3 7 1 5 3 and 5 1 3 pronounced cool phases during interglacials with only a very narrow inflow of atlantic waters into the southeastern ngs while the coastal areas off norway were still affected by iceberg drift substages 7 4 and 5 2 carbonate preservation records indicate ongoing deep water formation in the ngs 4 the normal glacial mode characterized by a variable but persistent inflow of cool temperate atlantic water lower stage 8 repetitively during stages 6 4 3 1 and 2 carbonate preservation records indicate ongoing deep water formation in the ngs 5 short glacial and deglacial periods characterized by episodic high inputs of ird evidenced by a wide coverage of diamicton deposition and strong carbonate dissolution e g episodically within stages 10 6 and 2 the 6 5 4 3 and 2 1 transitions some of these ngs diamicton layers correlate with heinrich layers in the north atlantic but generally ngs diamicton layers occur more frequently than heinrich layers the role of atlantic water influence during these events remains enigmatic but atlantic water influence is frequently found just above and below these sections a scenario with rapid ice sheet disintegration induced by atlantic water advection via increase of the thermal regime along the ice margin possibly triggered by small scale sea level rise might be envisaged more obviously the short term cessation of deep water formation in the ngs as evidenced by the dissolution spikes may be correlated with contemporaneous ventilation minima in the north atlantic

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

the 1732 surtseyan eruption of eggoya jan mayen north atlantic deposits distribution chemistry and chronology the island of jan mayen in the north atlantic ocean is home to the world s northernmost active subaerial volcano beerenberg of the five known historical eruptions on the island the locations of two eruptions 1732 and 1818 have not been accurately located it is known that the 1732 and 1818 eruptions occurred on the south flank of beerenberg and several eruption sites have been proposed for these events here we show that the tuff cone of eggoya on the sw flank of beerenberg was the site of the 1732 eruption based on interpretation of the deposits field relations and historical sources we further describe the deposits from the eruption and show that eggoya is the largest explosive eruption described from jan mayen emplacing at least at least 0 3 0 4 km3 vei 4 of basanitic tephra up to distances of at least 111 km from jan mayen and covering a minimum area of around 500 km2 within the 2 cm isopach we also present our eruption scenario and show that this was an emergent surtseyan eruption with activity shifting between tephra jetting continuous uprush and more magmatic phases

a variational scheme for retrieving ice cloud properties from combined radar lidar and infrared radiometer 1 a variational method is described for retrieving profiles of visible extinction coefficient ice water content and effective radius in ice clouds using the combination of ground based or spaceborne radar lidar and infrared radiometer the forward model includes effects such as non rayleigh scattering by the radar and molecular and multiple scattering by the lidar by rigorous treatment of errors and a careful choice of state variables and associated a priori estimates a seamless retrieval is possible between regions of the cloud detected by both radar and lidar and regions detected by just one of these two instruments thus when the lidar signal is unavailable for reasons such as strong attenuation the retrieval tends toward an empirical relationship using radar reflectivity factor and temperature and when the radar signal is unavailable such as in optically thin cirrus accurate retrievals are still possible from the combination of lidar and radiometer the method is tested first on simulated profiles from aircraft data and then on real observations taken in west africa it would be straightforward to expand the approach to include other measurements simply by including a forward model for them

tephrabase tephrochronology and the development of a centralised european database tephrabase was launched on the world wide web in 1995 as a tool for tephrochro nological research in order to facilitate the identification correlation and dating of tephra deposits this database may be interrogated through multiple routes including by source volcano date location and tephra chemistry datasets include stratigraphy geochemistry chronology and spatial information currently all the european data refer to late quaternary icelandic sourced tephras post 12 k yr bp the sites 62 where the tephra deposits are found include iceland the united kingdom ireland the faroe islands sweden and russia in addition there are also data on tephra layers in central mexico use of tephrabase highlights the importance of selected geochemical data but this has to be used with care as major element characteristics alone do not always produce unique definitions for single tephra deposits for the most accurate results multiple criteria must be used tephrabase can be found at http www tephrabase org copyright 2007 john wiley sons ltd

source of ash zone 1 in the north atlantic geochemical evidence shows that the silicic component of the widespread ash zone 1 in the north atlantic is derived from a major ignimbrite forming eruption which occurred at the katla caldera in southern iceland during the transition from glacial to interglacial conditions in younger dryas time both trace and major element evidence of the rhyolitic products excludes the oraefajokull volcano as a source the high ti basaltic component in the marine ash zone can also be attributed to contemporaneous eruption in the katla volcanic complex dispersal of tephra from this event is primarily attributed to the generation of co ignimbrite ash columns in the atmosphere with ash fallout on both sea ice and on the ocean floor north and east of iceland owing to the changing ocean circulation characteristics of the glacial regime including suppression of the irminger current and a stronger north atlantic current tephra was rafted on sea ice south into the central north atlantic and deposited as dispersed ash zone 1 sediments south of iceland also show evidence of the formation of ash turbidites generated either by the entrance of pyroclastic flows into the sea or during discharge of jokulhlaups or glacier bursts from this subglacial eruption

geochemistry of holocene cryptotephras from the north iceland shelf md99 2269 intercalibration with radiocarbon and palaeomagnetic chronostratigraphies tephra grain counting morphology and geochemistry in the 150 1000 m size fraction were used to identify 22 individual tephra horizons and one visible tephra layer saksunarvatn from postglacial sediment of the north iceland shelf core md99 2269 66 37 53 n 20 51 16 w water depth 365 m length 2533 cm from the reykjafjardarall basin is constrained at the base by the vedde tephra c 12 000 cal yr bp geochemical analyses and stratigraphical position of the 22 tephra horizons were used to identify the following cryptotephras kol 1372 ad 1372 hekla 1104 ad 1104 snaefellsnes 1 c 1790 cal yr bp hekla 3 c 2970 cal yr bp hekla 4 c 4230 cal yr bp tv 5 c 6860 cal yr bp and suduroy c 8070 cal yr bp a tephra of the same geochemistry as kol 1372 was found near the base of the core and is here named kol3 2269 11 000 cal yr bp eleven additional cryptotephras were geochemically typed to their respective icelandic volcanic centres of origin and their ages constrained four teph

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

evolution of iceberg melting biological productivity and the record of icelandic volcanism in the irminger basin since 630 ka abstract planktic 18 o and 13 c records and point count records of biogenic volcanic and nonvolcanic terrigenous ice rafted debris ird sediment components from hole 919a in the irminger basin northern north atlantic provide a comprehensive dataset from which a paleoceanographic reconstruction for the last 630 kyr has been developed the paleoceanographic evolution of the irminger basin during this time contains both long term patterns and significant developmental steps one long term pattern observed is the persistent deposition of hematite stained ice rafted debris this record suggests that the modern and late pleistocene discharges of icebergs from northern redbed regions to the irminger sea lie in the low end of the range observed over the last 630 kyr in addition arctic front fluctuations appear to have been the main controlling factor on the long term accumulation patterns of ird and planktic biogenic groups the hole 919a sediment record also contains a long term association between felsic volcanic ash abundances and light 18 o excursions in both interglacial and glacial stages which suggests a causal link between deglaciations and explosive icelandic eruptions a significant developmental step in the paleoceanographic reconstruction based on benthic evidence was for diminished supply of denmark strait overflow water dsow beginning at 380 ka possibly initiated by the influx of meltwater from broad scale iceberg discharges along the east greenland coast there is also planktic evidence of a two step cooling of sea surface conditions in the irminger basin first at 338 309 ka and later at 211 190 ka after which both glacials and interglacials were colder as the arctic front migrated southeast of site 919 in addition to offering these findings this reconstruction provides a longer term geologic context for the interpretation of more recent paleoceanographic events and patterns of deposition from this region

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

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

evidence for the occurrence of vedde ash in sweden radiocarbon and calendar age estimates a tephra layer of rhyolitic composition has been recorded in sediments from lake madtjarn southwestern sweden geochemical analyses have shown that the tephra is identical to the rhyolitic component of the middle younger dryas vedde ash a series of ams radiocarbon measurements places the radiocarbon age of the tephra within a 14c plateau at 10 400 10 300 14c y bp based on a linear younger dryas sedimentation rate and assumptions about the apparent synchroneity of changes in lake sediments tree rings and ice core records the calendar year age of the tephra concentrations is estimated at 12 045 11 975 yr bp which accords well with the age of the equivalent tephra in the grip core 1998 john wiley sons ltd

40ar 39ar dating of the thorsmork ignimbrite and icelandic sub glacial rhyolites abstract robust correlation of paleoclimatic archives e g marine sediments ice speleothems necessitates an increase of the number of independent and accurately dated stratigraphic markers using numerical methods icelandic rhyolitic volcanism has a strong chronological interest because these products are found as tephra in the north atlantic marine archives as well as in greenland ice cores in this study we have dated using the 40ar 39ar method subglacial rhyolites of the tindfjallajokull kerlingarfjoll and torfajokull volcanoes which are the main sources of rhyolitic tephra identified in marine and glaciological records the thorsmork ignimbrite tindfjallajokull which correlates with the rhyolitic component ii rhy 1 of the north atlantic ash zone ii naaz ii layer is dated at 55 6 2 4 ka an age that agrees with the ones given by the ice core chronologies gicc05 55 4 1 2 ka the eruptions of rau fossafjoll and fannborg are respectively dated at 77 0 3 0 ka and 149 3 3 4 ka these new ages along with the published ones confirm as already concluded by flude et al 2010 that there is no clear evidence at least at the latitude of iceland that climate warming is the main mechanism that triggered rhyolitic eruptions combining major and trace element compositions with our new age determinations it appears that the rau fossafjoll and the snaefell rhyolitic eruptions have not yet been discovered in marine sediment cores nevertheless given the accuracy and precision of our dating these rhyolitic eruptions have the potential to become chronostratigraphic markers once tephra shards corresponding to these eruptions are discovered in ice and or marine sediment records the fannborg eruption might be recorded in the marine core link 16 during mis 6 prior to the transition to mis5e

a tephra based correlation between the faroe islands and the norwegian sea raises questions about chronological relationships during the last interglacial marine ash zones from the last interglacial period have been described from cores from the north atlantic and an ash zone from the middle part of the interglacial has been observed in connection with a major cooling event here we present evidence for a coeval ash zone in a terrestrial site on the faroe islands the investigated sediments are correlated with the upper part of oxygen isotope stage 5e and the beginning of stage 5d the eemian climatic optimum is represented in the lower part of the sequence close to the first occurrence of the ash zone a tephra based correlation suggests that the climatic optimum was synchronous with the marine record from the norwegian sea but several thousand years later than in eemian sections of west central europe however many questions on the chronological relationship between the eemian and oxygen isotope stage 5e still remain to be answered

geochemistry of historical age silicic tephras in iceland the major element chemistry of nine silicic tephras of historical age from iceland is assessed as a key step in the development of the recent tephrochronology of the north atlantic region the tephras include the largest such layers produced by each of the five central volcanoes hekla o raefajokull eyjafjallajokull torfajokull and askja since the ninth century ad h 1104 o1362 e 1821 landnam tephra c 870 a 1875 and four other tephras h 1158 h 1510 h 1947 o1727 the determination of grain discrete major element chemistry of the glass fraction is a fundamental stage in the identification and correlation of tephra and allows links to be made between icelandic source areas with precise dating evidence and distal deposits elsewhere in the north atlantic region although major element data can be used to discriminate between tephra layers produced by the different central volcanoes on its own it cannot be used to identify all the holocene layers produc

north atlantic ice sheet fluctuations 10 000 70 000 yr ago as inferred from deposits on the reykjanes ridge southeast of greenland abstract marine records from the reykjanes ridge indicate ice sheet variations and abrupt climate changes one of these records ice rafted detritus ird serves as a proxy for iceberg discharges that probably indicates ice sheet fluctuations the ird records suggest that iceberg discharge 68 000 10 000 yr b p happened more frequently than the 7000 to 10 000 yr spacing of the heinrich events an ird peak 67 000 to 63 000 yr b p further suggests that the middle weichselian glaciation started about 12 000 yr earlier in the north atlantic than in the norwegian sea several later ird events in contrast correlate with norwegian sea ird rich layers and imply coeval ice sheet advances in the north atlantic and the norwegian sea coccoliths in a core from the reykjanes ridge show distinct peaks in species that record occasional inflow of warm surface water during the last glaciation as previously reported from the eastern labrador sea high abundances of coccoliths together with a decrease ofneogloboquadrina pachydermasin and relatively low 18o values imply enhanced advection of the north atlantic current 69 000 67 000 yr b p 56 000 54 000 yr b p 35 000 33 000 yr b p and 26 000 23 000 yr b p this advection provided a regional moisture source for extension of ice sheets onto the shelf in contrast most of the ird events are characterized by cold polar surface water masses indicating rapid variations in ocean surface conditions

quaternary tephrachronology on the iceland plateau north of iceland four major ash zones recorded in piston cores raised from the iceland plateau north of iceland are shown to be coincident with the last four interglacial isotopic stages their geochemical composition links the ashes to volcanic events on iceland the occurrence of these ash layers which record events orders of magnitude larger than the normal holocene volcanic eruptions can not be explained by changes in sea ice cover and atmospheric circulation alone it is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the icelandic ice cap

a north atlantic tephrostratigraphical framework for 130 60 ka b2k new tephra discoveries marine based correlations and future challenges abstract building chronological frameworks for proxy sequences spanning 130 60 ka b2k is plagued by difficulties and uncertainties recent developments in the north atlantic region however affirm the potential offered by tephrochronology and specifically the search for cryptotephra here we review the potential offered by tephrostratigraphy for sequences spanning 130 60 ka b2k we combine newly identified cryptotephra deposits from the ngrip ice core and a marine core from the iceland basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time interval forty three tephra or cryptotephra deposits are incorporated into this framework twenty three tephra deposits are found in the greenland ice cores including nine new ngrip tephras and twenty separate deposits are preserved in various north atlantic marine sequences major minor and trace element results are presented for the new ngrip horizons together with age estimates based on their position within the ice core record basaltic tephras of icelandic origin dominate the framework with only eight tephras of rhyolitic composition found new results from marine core md99 2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits tephra based correlations in the marine environment provide independent tie points for this time interval and highlight the potential of widening the application of tephrochronology further investigations however are required that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes in order to trace coeval events between the two depositional realms

hydrodynamic properties and grain size characteristics of volcaniclastics deposits on the mid atlantic ridge north of iceland kolbeinsey ridge surface sediments from a transect across the mid ocean ridge north of iceland kolbeinsey ridge have been analyzed according to their compositional textural and hydromechanical characteristics the results were used to reconstruct sediment formation and depositional processes the ridge sediments are dominated by volcaniclastic particles of hyaloclastic and pyroclastic origin these particles show a wide variety in size shape and density single grain settling velocities of the different glass types reveal the suitability of this parameter as a reflector of the particle properties of size shape and density which are also known to be relevant to grain transport observations concerning different current expositions of central ridge sediments combined with the parameters of settling velocity distribution grain size distribution and sediment particle composition were applied to distinguish between transport association with rare easily movable glass shards and poorly sorted sediments in sheltered ponds a bimodal settling velocity distribution of steep ridge flank sediments probably indicates the effect of sediment admixture from poorly sorted mass flows alternating coarse and fine grained layers characterize the transition between ridge glass sands and the ridge adjacent plain which is dominated by slow settling pelagic material

paleoceanography of the last interglacial glacial cycle in the polar north atlantic abstract using to its position close to the sites of waxing and waning of the major northern hemisphere ice sheets during the late quaternary climatic cycles the polar north atlantic plays a key role in driving global change therefore analyzing the present day sedimentation processes and reconstructing the late quaternary paleoceanography in this region has been a focus of major scientific interest through the last fifteen years this paper aims to combine the vast amount of new results about modern sediment fluxes surface sediment distribution and the paleoceanographic record and to present a comprehensive overview of the paleoceanography in the polar north atlantic through the last 200 000 years which is based on the basinwide analysis of carbonate and ice rafted detritus records during the last fifteen years the climap paleoceanographic view of the glacial polar north atlantic as an almost permanently isolated sea covered by heavy sea ice throughout the year has been shifted to a much more dynamic view of the environmental conditions a meridional current system similar to the present day conditions secured the exchange of water ice and heat between the polar north atlantic and the alantic and arctic oceans although affected by variations in strength and intensity this meridional current pattern resulted in an almost permanent presence of at least some seasonally ice free areas with all the consequences for e g marine life and deep water formation in addition the development of the continental ice sheets namely the fennoscandian and the barents sea ice sheets is closely related to this dynamic circulation pattern during the so called nordway events the pronounced inflow of temperate waters from the south provided moisture for the growth of the ice sheets the most prominent of these events stage 6 stage 4 and substage 3 1 2 ended in major glaciations reflected in the terrestrial sequences and in the deep sea ird records

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

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

chemical composition distribution and origin of silicic volcanic ash layers in the greenland iceland norwegian sea explosive volcanism from 10 to 300 ka as recorded in deep sea sediments explosive ocean island volcanism in the greenland iceland norwegian sea gin sea is indicated by marine tephra layers at 10 300 ka peaks of explosive volcanism occurred in oxygen isotope stages 8 7 5 and 1 the depositional age of the tephra was estimated using the oxygen isotope stratigraphy and dating of marine records geochemical analyses of the tephra layers show that all originate from iceland here we report the characteristics of tephra from these major icelandic events in 30 deep sea cores from the gin sea our findings provide constraints on the distribution of tephra from the eruption source for the vedde ash oxygen isotope stage 1 we estimate a minimum fallout area of 2 105 km2 stretching from central greenland in the west and southern sweden in the east to 71 n in the gin sea the magnitude of the eruption and the regional wind conditions controlled the extent and concentrations of these ash fallout events oceanic circulation and differential settling may have affected the distribution and final deposition of ash particles such as bubble wall shards

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

linking the north atlantic to central europe a high resolution holocene tephrochronological record from northern germany a high resolution holocene tephrochronology for northern germany has been established based on systematic tephrostratigraphical analysis of three peat bogs microscopic volcanic ash layers have been traced and characterised petrographically and by the chemical composition of the glass shards at least 37 ash horizons representing 16 different explosive volcanic eruptions have been identified and many can be correlated between the three sites up to 100 km apart the tephra layers can be related to icelandic volcanic sources and some correlated to the eruptions of askja 1875 hekla 3 hekla selsund hekla 4 and hekla 5 as well as to unspecified eruptions of icelandic volcanic systems e g torfajokull the source volcanoes for some tephra layers remain unidentified some tephra layers were known previously from the north atlantic region e g sluggan glen garry others have not been recorded previously in the literature e g microlite tephra this study provides the first comprehensive holocene tephrostratigraphical record for northern germany complementing the north atlantic tephrostratigraphical dating framework effectively extending it into central europe the study shows that icelandic ash layers are even more widespread than hitherto thought copyright 2002 john wiley sons ltd

variability in surface and deep water conditions in the nordic seas during the last interglacial period abstract stable isotope foraminifera and ice rafted detritus ird records covering the last interglacial the eemian from 7 sediment cores in a transect from the norwegian to the greenland sea are presented the percentages of neogloboquadrina pachyderma s and globigerina quinqueloba foraminiferal content and to some extent planktonic stable isotope records demonstrate marked regional changes in surface water conditions importantly the variability in the abundances of subpolar foraminifera and foraminiferal content are not coherent implying that these two types of proxies fluctuated independently of each other and most likely reflect changes in sea surface temperature and surface water carbonate productivity respectively paleoceanographic reconstructions demonstrate significant movements of the oceanographic fronts at the warmest periods the arctic front was located far west of the present day location at least within the iceland sea region at 126 125 ka this was most probably due to a stronger or more westerly located norwegian current within the later warm intervals higher heat flux to the western part of the basin reflects a combination of a stronger irminger current and or a weaker east greenland current during the main cold spell at 124 ka a diffuse arctic front had a more southeasterly location than today and intrusion of atlantic surface waters was probably limited to a narrow corridor in the eastern norwegian sea a general correspondence between minima in sea surface temperatures and light benthic 18o may indicate enhanced influx of freshwater to the basin within the cold events at least in the norwegian sea we find some evidence that the changes in surface water conditions are associated with changes in deep water ventilation the majority of the fluctuations may be related to occasional breakdown or reduction of the thermohaline circulation within the nordic seas in the earliest eemian this could result from meltwater forcing during the remaining part of the last interglacial the fine balance between temperature and salinity which the deep water formation is depending on may have been disturbed by periodic increases in fresh water supply or variable influx of warm atlantic surface waters

a detailed framework of marine isotope stages 4 and 5 volcanic events recorded in two greenland ice cores sulphate records from greenland ice cores indicate that marine isotope stages 4 and 5 were charactensed by a higher incidence of large volcanic eruptions than other periods during the last glacial

near surface circulation of the nordic seas as measured by lagrangian drifters in the period june 1991 to august 1993 107 argos tracked drifters drogued to 15 m depth were released in the nordic seas or greenland iceland and norwegian seas the drifter movements revealed the strong and spatially confined current systems along the surface salinity fronts of the iceland faroe frontal zone and of the norwegian coast and along the continental margins and their extensions to the barents sea and spitsbergen the norwegian atlantic current is composed of three distinct streams two continental margin and one coastal branches which join into one single swift mean current west of the lofoten and vesteralen islands where the strongest measured currents are in excess of 110 cm s 1 in addition to the general cyclonic gyre circulation in the nordic seas the drifters indicate smaller cyclonic circulation patterns in all the major subbasins i e the iceland plateau the norwegian the lofoten and the greenland basins no surface signature of the east icelandic current is disclosed by the drifters interpolated and low pass filtered position data were used to construct maps of 15 m depth ensemble mean velocity velocity variability and residence time vigorous eddy fields are dominant in the strong currents and in the lofoten basin eulerian correlations indicate that they tend to propagate to the west in contrast the iceland plateau appears quiescent both in the mean and eddy velocities single particle diffusivities are computed and are found to be in the range 1 7 107 cm2 s 1 the corresponding lagrangian timescale and space scale are 1 3 days and 10 40 km respectively these lagrangian drifter measurements compose the first basin scale accurate near surface velocity data set of the nordic seas

late quaternary calcium carbonate sedimentation and terrigenous input along the east greenland continental margin nine large box cores collected in the western greenland iceland norwegian gin sea were analyzed for calcium carbonate content and coarse fraction components stratigraphic control is based on oxygen isotope records performed on four of the cores all cores were correlated using oxygen and carbon isotope data fluctuations in calcium carbonate content coarse terrigenous particle content and volcanic ash beds glacial and interglacial cycles are documented by a number of terrigenous particle events and differentiated calcium carbonate production which can be correlated to major paleoceanographic and paleoclimatic shifts in the older core sections extensive deposition of ice rafted detritus ird persisted until about oxygen isotope stage 9 and document a relatively stable environment in this area strongly influenced by cold surface water masses the following interval was characterized by variations in the general surface water circulation pattern although high amounts of ird are still present in iceland sea sediments pronounced shifts in terrigenous input and pelagic carbonate records were identified close to the oxygen isotope stage full size image 1 k and full size image 1 k boundaries indicating massive melting of icebergs in the western gin sea these enormous inputs of debris were followed by an increase in calcium carbonate production caused by maximum intrusion of warm atlantic surface waters relatively high calcium carbonate contents also show that only little dilution by fine grained material and a minimum of ice melting occurred during these warm phases during oxygen isotope stage 5 conditions were more uniform indicating a less pronounced westward penetration of atlantic waters as compared to the holocene the last glacial stages 4 2 is characterized by the occurrence of heinrich like events although high ird contents were present throughout this interval a distinct contrast between the northernmost cores and the cores in the south is indicative of a rather strong westward penetration of atlantic water in the north and of an area dominated by cold water east of the kolbeinsey ridge during the holocene however conditions west of jan mayen seem to have remained constantly dominated by cold surface waters throughout the whole time investigated

influence of convective sedimentation on the formation of widespread tephra fall layers in the deep sea the formation of widespread volcanic ash fall layers in deep sea sediments was investigated experimentally to examine the settling behavior of tephra 20 180 m diameter as it travels from the atmosphere into water using a fallout mass flux rate that was constrained by measurements of distal fallout from the 1980 eruption of mount st helens 0 2 g cm 2 hr the experiments show that particle settling in the water column is dramatically accelerated by the formation of diffuse vertical gravity currents the currents form as a result of convective instabilities that develop in a surface boundary layer when the local particle concentration becomes large at the air water interface the settling velocity of particles drops abruptly and the concentration of particles increases because of the differential in mass flux above and below the fluid surface the implication of the experiments is that deposition of distal tephra fall layers in deep sea sediments may be dominantly controlled by diffuse vertical gravity currents as opposed to passive settling of individual particles through the water column this process greatly reduces the residence time of fine ash in the ocean and diminishes the role of ocean currents in influencing the distribution patterns of individual tephra layers support for this mechanism comes from observations of greatly accelerated tephra settling rates in the south china sea following the 1991 eruption of mount pinatubo in the philippines

history of a stable ice margin east greenland during the middle and upper pleistocene abstract the east greenland record of glaciation and environmental change is based on a combination of onshore and offshore studies glaciological work on contemporary outlet glaciers provides background for interpreting the glaciation styles of the past the scoresby sund fjord system the single largest outlet of the inland ice in east greenland and the adjacent continental shelf and slope were the main working areas the regionality of these results was tested with onshore and offshore work on sites further to the north in the east greenland fjord zone the record spans the period since isotope stage 7 ca 240 ka the most extensive glaciation phases were the lollandselv and scoresby sund glaciations isotope stages 7 and 6 the langelandselv interglaciation isotope substage 5e comprises shallow marine sediments at more than 20 sites onshore and cibicides wuellerstorfii carrying sediments on the continental slope summer temperatures were 2 3 warmer than the holocene optimum and there was vigorous advection of warm atlantic water into the fjords the warm period seems to be accompanied by a eustatic sea level rise of ca 20 m during the weichselian there were three major glacier advances the aucellaelv jyllandselv and flakkerhuk stades isotope substages 5d 5b and stages 3 2 all three advances mark a shift from one topographically determined stable position to another in each phase the glaciers occupied almost the same space in the fjord basins and had their fronts on the inner shelf but the glacial regime and duration was different the aucellaelv stade lasted ca 10 ka and the regime resembled that of present day outlet glaciers 600 km further to the north the flakkerhuk stade lasted for ca 50 ka but left only thin and sporadic till as well as glaciolacustrine sediments in ice dammed river valleys the regime was polar similar to present day glaciers in antarctica its culmination the last glacial maximum in the period between 22 and 14 ka is shown by a maximum in ird deposition on the continental slope after 12 ka and before 10 ka the outer fjord basins in the southern fjord zone had been abandoned by the glaciers and at ca 9 5 ka the last resurgence the milne land stade had ended

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

explosive silicic volcanism in iceland and the jan mayen area during the last 6 ma sources and timing of major eruptions abstract fifty three major explosive eruptions on iceland and jan mayen island were identified in 0 6 ma old sediments of the north atlantic and arctic oceans by the age and the chemical composition of silicic tephra the depositional age of the tephra was estimated using the continuous record in sediment of paleomagnetic reversals for the last 6 ma and paleoclimatic proxies 18 o ice rafted debris for the last 1 ma major element and normative compositions of glasses were used to assign the sources of the tephra to the rift and off rift volcanic zones in iceland and to the jan mayen volcanic system the tholeiitic central volcanoes along the iceland rift zones were steadily active with the longest interruption in activity recorded between 4 and 4 9 ma they were the source of at least 26 eruptions of dominant rhyolitic magma composition including the late pleistocene explosive eruption of krafla volcano of the eastern rift zone at about 201 ka the central volcanoes along the off rift volcanic zones in iceland were the source of at least 19 eruptions of dominant alkali rhyolitic composition with three distinct episodes recorded at 4 6 5 3 3 5 3 6 and 0 1 8 ma the longest and last episode recorded 11 pleistocene major events including the two explosive eruptions of tindfjallajokull volcano thorsmork ca 54 5 ka and katla volcano solheimar ca 11 9 ka of the southeastern transgressive zone eight major explosive eruptions from the jan mayen volcanic system are recorded in terms of the distinctive grain size mineralogy and chemistry of the tephra the tephra contain k rich glasses k 2 o sio 2 0 06 ranging from trachytic to alkali rhyolitic composition their normative trends ab q or and their depleted concentrations of ba eu and heavy ree reflect fractional crystallisation of k feldspar biotite and hornblende in contrast their enrichment in highly incompatible and water mobile trace elements such as rb th nb and ta most likely reflect crustal contamination one late pleistocene tephra from jan mayen was recorded in the marine sequence its age estimated between 617 and 620 ka and its composition support a common source with the borga pumice formation at sor jan in the south of the island

evidence for a steeper eemian than holocene sea surface temperature gradient between arctic and sub arctic regions sediment proxy data from the norwegian greenland and iceland seas nordic seas are presented to evaluate surface water temperature sst differences between holocene and eemian times and to deduce from these data the particular mode of surface water circulation records from planktic foraminiferal assemblages caco3 content oxygen isotopes of foraminifera and iceberg rafted debris form the main basis of interpretation all results indicate for the eemian comparatively cooler northern nordic seas than for the holocene due to a reduction in the northwardly flow of atlantic surface water towards fram strait and the arctic ocean therefore the cold polar water flow from the arctic ocean was less influencial in the southwestern nordic seas during this time as can be further deduced from the eemian data slightly higher eemian ssts are interpreted for the western iceland sea compared to the norwegian sea ca south of 70 n this eemian situation is in contrast to the holocene when the main mass of warmest atlantic surface water flows along the norwegian continental margin northwards and into the arctic ocean thus a moderate northwardly decrease in sst is observed in the eastern nordic seas for this time causing a meridional transfer in ocean heat due to this distribution in ssts the holocene is dominated by a meridional circulation pattern the interpretation of the eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in ssts

volcanic ash layers from the last glacial termination in the ngrip ice core the tephrochronological record of the 1400 1640 m depth 10 000 16 000 calendar ice core years before present of the ngrip ice core has been established by particle screening of selected samples ash was identified in 20 samples correlation with ice marine and terrestrial records from volcanic source regions in the northern hemisphere positively identifies the saksunarvatn ash and the vedde ash ash zone 1 major element chemistry of the remaining identified ash layers mainly points towards an icelandic origin this tephrochronological record provides new important marker horizons for correlating the timing of the climatic changes associated with the last glacial termination within the north atlantic region as well as outlining more details concerning the frequency and composition of volcanic eruptions occurring at this deglaciation copyright 2005 john wiley sons ltd

quaternary volcanic ash zones on the iceland plateau southern norwegian sea four quaternary volcanic ash zones in the southern norwegian sea have been investigated in core p57 7 from the iceland plateau both the geochemical composition and morphological variation of each ash layer have been studied the four volcanic ash zones appear in the light oxygen isotope stages 1 5 7 and 11 the ash zones are composed of transparent platy grains light brown transparent grains brown blocky and black blocky grains and white transparent pumice and each zone shows a distinct stratigraphic evolution the geochemical results show a mixture of basaltic and silicic grains in each ash zone and that each zone contains grains from more than one eruption the geochemical investigations strongly suggest that all the ashes are derived from iceland the youngest ash zone includes two layers which based on their geochemical composition and stratigraphic position are correlated with the 14c dated vedde ash 10 600 yr bp and saksunarvatn ash 9 100 yr bp possible sources on iceland for these layers are discussed

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

identification of a mis 6 age c 180 ka icelandic tephra within ne atlantic sediments a new potential chronostratigraphic marker the incidence of volcanic ash tephra within marine sediments serves as a useful stratigraphic marker and tool for correlation in addition where an independent age estimate exists tephra layers can provide a means of dating the sediments themselves here we present a geochemically characterized size sorted tephra layer within marine isotope stage mis 6 most likely resulting from primary air fall from an icelandic volcanic source this tephra layer is tentatively correlated to the kerlingarfjoll volcanic system using major element geochemistry the ash layer has an interpolated age of 181 6 ka based on the age model for md04 2822 we briefly review the occurrence of silicic tephra in the north atlantic region from mis 7 to mis 5e inclusive and find potential correlatives to the md04 2822 mis 6 ash layer in the norway basin and irminger sea

the eyjafjallajokull ad 2010 eruption and the preservation of medium sized eruptions in marine surface sediment offshore southern iceland the recent volcanic eruptions of eyjafjallajokull 2010 and grimsvotn 2011 demonstrated the risks that mediumsized explosive icelandic eruptions pose to the north atlantic region using the eyjafjallajokull 2010 eruption as a case study we assess how traceable such eruptions are in the marine sedimentary record at medial distances from the source and investigate which factors have affected the particle transport to the marine sedimentary archive during r v poseidon cruise 457 we recovered 13 box cores at 100 1600 m water depths and distances of 18 180 km southwest south and east of iceland volcanic glass shards from the uppermost surface sediment were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting the predominantly basaltic particles are mostly derived from the katla grimsvotn lakagigar and bar arbunga vei ivotn volcanic systems we also identified rhyolitic particles from the askja 1875 and oraefajokull 1362 eruptions only three out of almost 900 analyzed glass shards are derived from the recent eyjafjallajokull 2010 eruption suggesting that medium sized eruptions are only poorly preserved in marine sediments located at medial distances southwest to east of iceland we conclude that the frequency of past medium sized eruptions is likely higher than detectable in this archive

changes in sedimentation patterns of the nordic seas region across the mid pleistocene sediment core data from a site in the central nordic seas suggest that during the mid pleistocene revolution mpr this region has experienced a systematic change in its overall oceanographic and climatic conditions first distinct changes occur around 1 ma and reveal the beginning of a shift in climate periodicity from stronger 41 ka cycles towards a dominant 100 ka cyclicity most pronounced are the changes at the study region between about 700 and 420 ka when parallel to the evolution of large 100 ka cycles a distinct decrease in the input of magnetic particles is observed also for this interval an intensification of glacial conditions is indicated by a marked increase in the accumulation rates of ice rafted debris ird during marine isotope stages 16 and 12 the observed mid pleistocene changes were likely due to a gradual shift from a more zonal behavior of the coupled ocean atmosphere system at high northern latitudes prior to the mpr to more meridionality thereafter a shift that affected both the patterns of ocean circulation and ice drift in the nordic seas region accordingly the subsequent mpr related changes of these two climate parameters should be responsible for the decrease in the concentration of magnetic particles at the study site after 700 ka with the mid pleistocene strengthening of the nordic heat pump the mode of deep water production and the flow of bottom currents changed at high northern latitudes which led to an increased export of magnetic particles from basaltic source regions around greenland and iceland into the subpolar north atlantic consequently less magnetic material was deposited in the nordic seas than before the mpr when water mass exchange between the nordic seas and the north atlantic was more restricted in addition the large late pleistocene expansions of glacial ice caps on the eastern margin of the nordic seas led to a major change in the composition of ird material in the study area with more material originating from the scandinavian and barents sea shelf regions which ultimately caused a dilution of the magnetic signal

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

holocene explosive volcanism of the jan mayen island volcanic province north atlantic abstract the volcanic island jan mayen located in the norwegian greenland sea hosts the active stratovolcano of beerenberg the northernmost active subaerial volcano in the world at least five eruptions are known from the island following its discovery in the 17th century but its eruptive history prior to this is basically unknown in this paper two sediment cores retrieved close to jan mayen have been studied in detail to shed light on the holocene history of explosive volcanism from the jan mayen volcanic province horizons with elevated tephra concentrations were identified and tephra from these was analysed to determine major element chemistry of the tephra the tephra chemistry was used to provide a link between the two cores and the land based tephra records from jan mayen island we managed to link two well developed tephra peaks in the cores by their geochemical composition and age to jan mayen one of these peaks represents the 1732 ad eruption of eggoya while the other peak represents a previously undescribed eruption dated to around 10 3 ka bp two less prominent tephra peaks one in each core dated to approximately 2 3 and 3 0 ka bp also have a distinct geochemical character linking them to jan mayen volcanism however the most prominent tephra layer in the cores located close to jan mayen and numerous other cores along the jan mayen ridge is the 12 1 ka bp vedde ash originating from the iceland volcanic province we find that the holocene volcanism on jan mayen is much less explosive than volcanism in iceland and propose that either low amounts of explosive volcanic activity from the summit region of beerenberg or small to absent glacier cover on beerenberg is responsible for this

new radiocarbon dates for the vedde ash and the saksunarvatn ash from western norway abstract the vedde ash bed mid younger dryas and the saksunarvatn ash early holocene are important regional stratigraphic event markers in the north atlantic the norwegian sea and the adjacent land area it is thus essential to date them as precisely as possible the occurrence of the saksunarvatn ash is reported for the first time from western norway and both tephras are dated precisely by ams analyses of terrestrial plant material and lake sediment at krakenes the vedde ash has been previously dated at sites in western norway to about 10 600 yr b p it is obvious in the younger dryas sediments at krakenes and its identity is confirmed geochemically the mean of four ams dates of samples ofsalix herbacealeaves adjacent to the tephra is 10 310 50 yr b p the saksunarvatn ash is not visible in the early holocene lake sediment at krakenes after removal of organic material and diatoms the identity of the tephra particles was confirmed geochemically and their stratigraphic concentration was estimated from curve matching of a series of seven ams dates of terrestrial plant macrofossils and whole sediment the radiocarbon age of the ash is 8930 9060 yr b p corresponding to an age of 9930 10 010 cal yr b p 7980 8060 cal yr b c

sedimentary facies of glacial interglacial cycles in the norwegian sea during the last 350 ka sediment fluxes were highest in the norwegian sea during late glacial early deglacial periods i e at oxygen isotope transition 43 below transition 65 at various levels within stage 6 and below stage 9 dark diamictons deposited at these times reflect intense iceberg rafting in surface waters fed by surges along the front of the marine based parts of the continental ice sheets in the southeastern sector of the norwegian sea the high organic carbon content 0 5 1 3 in these layers reflects input from erosion of terrigenious matter rich sediments outcropping on the shelves partial oxidation of organic matter and decreased deep water renewal may explain the strong carbonate dissolution observed during these periods interglacial environments were strongly variable throughout the last 350 ka circulation patterns of stage 5e best resemble modern conditions while stage 7 and 9 sediments record a much weaker norwegian current

integrating the intimate records using tephrochronology rising to the challenge little has challenged our understanding of climate change more so than the abruptness with which large scale shifts in temperature occurred during the late quaternary the causal mechanisms driving

thermal history of the eastern margin of the gulf of suez i reconstruction from borehole temperature and organic maturity measurements abstract the gulf of suez is a tertiary continental rift associated with prominent flank uplift despite numerous studies which focused mainly on the western and central parts of the graben the thermo mechanics controlling the tectonic evolution of the gulf of suez is still enigmatic we have integrated borehole temperatures and organic maturity measurements in the eastern margin of the gulf of suez in order to study rift related paleothermometry and the present day thermal regime the data obtained suggest that the present thermal regime represents the maximum heat flow and temperatures for the sedimentary section in the basin furthermore lateral distributions of geothermal gradient and heat flow in the gulf of suez do not correlate mainly because of extensive variability in lithology and thermal conductivity rift related heat flow increases systematically and subparallel to the rift axis from about 60 mw m2 in the darag subbasin in the north to about 80 mw m2 in the ras garra area in the south both values are higher than 45 mw m2 the average heat flow assumed for the pre rift stage and the characteristic level for the present day heat flow away from the rift the north to south increase in heat flow probably reflects the southward increase of extension as well as lateral transfer of heat flow from the red sea this latter conclusion is supported by the fact that heat flow in the southern gulf of suez recorded by the paleothermometric reconstructions and borehole temperature data is somewhat higher than that estimated by model calculations for the extension derived from structural and subsidence reconstruction

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr