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

the mjauvotn tephra and other holocene tephra horizons from the faroe islands a link between the icelandic source region the nordic seas and the european continent six different tephra horizons were found in peat and lacustrine sediments on the faroe islands in the north atlantic their geochemistry showed that they were of icelandic origin three of these can be correlated with previously described tephra horizons from the faroe islands the saksunarvatn tephra c 9000 bp the hekla 4 c 3800 bp and hekla selsund c 3600 bp a previously unrecorded basaltic tephra dated to c 5700 5300 bp was found in two lacustrine successions this horizon is named the mjauvotn tephra after mjauvotn lake on the island of streymoy two further tephras were recorded the basaltic phase of the landnam tephra viia c ad 870s and the rhyolitic tjornuvk tephra these were found in sediments deposited shortly after the first phase of human settlement at tjornuvik which is ams dated to ad 675 861 calibrated age the faroe islands are an important link between the volcanic sources on iceland and the established tephrochronological frameworks on the british isles scandinavia and germany their position within a sensitive region of the northeastern branch of the north atlantic drift make the faroe islands ideal for registering climate changes during the holocene the establishment of a modern tephrochronology may provide a tool for more precisely dating and correlating regional climate events in and around the nordic seas

sediment fluxes along the northeastern european margin inferring hydrological changes between 20 and 8 kyr abstract in an attempt to delineate past hydrographic conditions on the northeastern atlantic ocean margin along a latitudinal transect 37 63 n and link the eastern north atlantic ocean with the norwegian sea we have investigated planktonic and benthic stable oxygen isotopes as well as abundances and fluxes of planktonic and benthic foraminifera calcium carbonate organic carbon and detrital grains in six sediment cores studied by the enam project in our joint approach we focused on the major climatic events of the last 20 kyr that is the last glacial maximum lgm the heinrich event 1 h1 the younger dryas yd and the holocene climatic optimum hco simmax temperature estimates suggest glacial ssts off portugal similar to holocene values contradicting the proposed polar front position of climap project members 1976 besides increased planktonic and benthic foraminiferal fluxes in the norwegian sea and the faeroe islands cores point to nordic seas partially ice free with seasonally productive polynas multiple ird spikes observed at the faeroe islands and norwegian sea sites coeval with h1 suggest multiple pulses of the fenno scandian ice sheet at the same time the presence of ird on the portuguese margin cores confirms the southward influence of icebergs the increase in foraminiferal abundances and fluxes that parallel ird spikes at all sites suggests that times of increased productivity either succeed or occur simultaneously with the iceberg surges in the open north atlantic productivity conditions similar to those observed during h1 are also registered during the yd even though planktonic foraminiferal assemblages suggest less cold conditions

application of tephrochronology to the timing and correlation of palaeoceanographic events recorded in holocene and late glacial shelf sediments off north iceland abstract the north icelandic shelf is partly distinguished by the tjornes fracture zone featuring numerous active basins in a mud dominated shelf environment late glacial and holocene high resolution sedimentary records from this area have been studied with tephrochronology as the main tool for correlation and for exact timing of palaeoceanographic events in the area data from three new piston cores from the shelf demonstrate the importance of tephra markers for the first chronological evaluation and correlation of the cores the correlation is extended with lithological logs and with magnetic susceptibility records a detailed multidisciplinary study including biostratigraphy and tephrochronology of a late holocene record of predominantly muddy sediments at the same location demonstrates that marked variations in the distribution of water masses occurred repeatedly through the last 4500 cal yr of special interest is the exact timing of a marked drop in sea surface temperature in the area indicated by ice rafting debris concentration to about 50 years before the hekla 3 eruption which occurred at 2980 cal yr bp this appears to predate most records of a general cooling event in nw europe by a couple of centuries two different possible age models one based on 14c dates combined with tephra markers and one based on tephra markers alone are discussed in context with the problem of different marine reservoir ages of the water masses in the area

towards a holocene tephrochronology for the faroe islands north atlantic abstract the faroe islands hold a key position in the north atlantic region for tephra studies due to their relative proximity to iceland several tephras have been described over the last 50 years in peat and lake sediment sequences including the type sites for the saksunarvatn and mjauvotn tephras here we present a comprehensive overview of holocene tephras found on the faroe island in total 23 tephra layers are described including visible macrotephras such as the saksunarvatn and hekla 4 tephras and several cryptotephras the importance of tephras originally described from the faroe islands is highlighted and previously unpublished results are included in addition full datasets for several sites are published here for the first time the saksunarvatn ash now considered to be the result of several eruptions rather than one major eruption can be separated into two phases on the faroe islands one early phase with two precursor eruptions with lower mgo concentrations 4 5 5 0 wt than the main eruption and a later phase with higher mgo concentrations 5 5 6 0 wt including the visible saksunarvatn ash the tjornuvik tephra previously considered to be a primary deposit is now interpreted as a reworked tephra with material from at least two middle holocene eruptions of hekla several of the tephras identified on the faroe islands provide useful isochrons for climate events during the holocene

identification and significance of a visible basalt rich vedde ash layer in a late glacial sequence on the isle of skye inner hebrides scotland this paper reports the discovery of a visible tephra horizon of late glacial age from the site of loch ashik in the isle of skye the inner hebrides scotland although the tephra shards have a bimodal geochemical composition identical to that of the vedde ash a well known marker horizon within late glacial sequences the horizon at ashik is dominated by basaltic shards and devitrified tephra shards giving the layer its characteristic black colour only rhyolitic shards have previously been reported from vedde ash horizons in the british isles this new evidence raises some important questions about the factors that govern the distribution and accumulation of basaltic tephra and about the methods used to detect ash shards in basins distal to centres of volcanic activity copyright 2001 john wiley sons ltd

holocene tephrostratigraphy of varved sediment records from lakes tiefer see ne germany and czechowskie n poland a detailed holocene tephrostratigraphic framework has been developed for two predominately varved lake sediment sequences from ne germany lake tiefer see and central n poland lake czechowskie a total of thirteen tephras and cryptotephras of icelandic provenance were detected and chemically fingerprinted in order to define correlatives and to integrate known tephra ages into the sediment chronologies out of these three cryptotephras askja ad1875 askja s and h asseldalen were identified in both records thus allowing a detailed synchronization of developing high resolution palaeoenvironmental proxy data the early holocene saksunarvatn ash layer and the middle holocene lairg b and hekla 4 cryptotephras in lake tiefer see are further important anchor points for the comparison with other high resolution palaeoclimate records in central and northern europe tentative correlations of cryptotephras have been made with a historical basaltic grimsv otn eruption ad890 e ad856 and three late holocene rhyolitic eruptions including the 2 1 ka glen garry and two unknown high silicic cryptotephras of probably icelandic provenance 1 9 cal ka bp

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

environmental changes in northern iceland since the younger dryas inferred from periglacial slope deposits the slopes in northern iceland show the widespread occurrence of solifluction features indicative of an active periglacial environment due to annual mean temperatures around 3 c at sea level and s

water mass properties and exchange between the nordic seas and the northern north atlantic during the period 23 6 ka benthic oxygen isotopic evidence 1 twenty benthic oxygen isotope records from different water depths in the nordic seas and the north atlantic are compared during the last glacial maximum brine formation on continental shelves produced brine shelf water bsw sinking below 1500 m in the nordic seas open ocean convection in the nordic seas produced glacial north atlantic intermediate water gnaiw gnaiw overflowed the greenland scotland ridge and entrained depths above and at least partly below 2000 m in the north atlantic during the early deglaciation bsw enriched intermediate water masses in the nordic seas were formed these overflowed the greenland scotland ridge and influenced the north atlantic intermediate and deepwater masses in the bolling allerod ba open ocean convection increased and produced intermediate water in the nordic seas with outflow to the north atlantic however deep water with modern characteristics did not entrain water below 2000 m in the north atlantic in similar amounts as during the holocene a new period of brine formation during the younger dryas transported bsw to intermediate water masses in the norwegian sea there was also open ocean convection and meridional overturning in the nordic seas but it was probably reduced compared to the ba in the early holocene and mid holocene meridional overturning appears similar to that of today potential locations for large scale formation of bsw might have been broad and shallow 200 m areas of the north sea northeast of greenland and north of east siberia these settings should be favorable for bsw formation during cold periods

high resolution study of icelandic tephras in the kangerlussuaq trough southeast greenland during the last deglaciation tephra abundance data and geochemistry in late glacial and holocene sediments on the east greenland shelf are presented two well known tephras were identified from electron microprobe analysis of tephra shards picked from ash peaks in the cores these are the vedde ash and saksunarvatn ash which probably were deposited on the shelf after transport on drifting ice the radiocarbon dates marine reservoir corrected by 550 yr that constrain the timing of deposition of the tephra layers compare well with the terrestrial and ice core ages of the tephras without requiring additional reservoir correction to align them with the known tephra ages several prominent tephra layers with a composition of ash zone 2 tephra punctuate the deglacial sediments these tephra peaks coincide with significant light stable isotope events signifying glacial meltwater and fine grained sediments poor in ice rafted detritus we interpret the ash zone 2 tephra peaks as sediment released from the greenland ice sheet during strong melting pulses of the deglaciation copyright 2002 john wiley sons ltd

consistently large marine reservoir ages in the norwegian sea during the last deglaciation with the exception of the gs 1 younger dryas coldperiodmarine reservoir ages for the last deglaciation in the north atlantic norwegian sea are generally assumed to have been around 400 500 radiocarbon years in magnitude earth planet sci lett 126 1994 275 radiocarbon 37 1995 53 quat res 52 1999 104 nature 412 2001 724 by comparing the climate records obtained from the grip ice core nature 359 1992 311 j quat sci 13 4 1998 283 andfrom north atlantic norwegian sea cores quat res 52 1999 104 geology 23 12 1995 1059 nature 356 1991 757 nature 356 1992 757 paleoceanography 3 1 1988 1 nature 343 1990 612 earth planet sci lett 126 1994 275 with radiocarbon dated european continental records we show that marine reservoir ages in the norwegian sea were of the order of 1000 14 c yr including large uncertainties this approach rests on the reasonable assumption that climate changes throughout the ne atlantic andeurope were more or less synchronous at the centennial scale fairly large variations in reservoir ages over time may have been causedby changing atmospheric 14 c content the results indicate that detailed land sea correlations for the north atlantic during the last deglaciation are not feasible using radiocarbon dating alone r 2003 elsevier science ltd all rights reserved

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

the impact of the laacher see tephra on terrestrial and aquatic ecosystems in the black forest southern germany late glacial lake sediments containing the laacher see tephra lst 11 000 yr bp have been analysed for pollen and diatoms at two sites hirschenmoor rotmeer in the montane belt of the black forest southern germany in order to detect the possible impact of this major volcanic eruption on terrestrial and aquatic biota the pollen assemblages at both sites show a minor increase in grasses and sedges following the tephra deposition whereas the pollen of aquatic macrophytes do not show any consistent pattern partial redundancy analysis and monte carlo permutation tests suggest however that the lst had no statistically significant effect either on the terrestrial or aquatic pollen assemblages at either site when the effects of time and climatic change are allowed for statistically the diatom assemblages at both sites changed after the deposition of the lst and diatom inferred ph estimates suggest a short but non significant excursion towards lower values multivariate analyses of the diatom data indicate a statistically significant impact of the deposition of the lst and associated changes in sediment lithology on the diatom assemblages when the effects of climatic change and time are allowed for statistically however owing to the interaction between tephra and lithology it is not possible to conclude if the diatom changes were caused by the deposition of the lst or by lithological changes

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

tephra horizons contemporary with short early holocene climate fluctuations new results from the faroe islands the climate of the north atlantic region was relatively unstable after the last termination at least three cold events superimposed upon a general warming took place during the earliest part of the

tephrostratigraphy of an loch mor inis oirr western ireland implications for holocene tephrochronology in the northeastern atlantic region twelve definable cryptotephra layers younger than c 8600cal bp are reported from lacustrine core material taken from an loch mor inis oirr aran islands western ireland the geochemistry of these shard layers which represent more holocene tephras than previously geochemically characterized from any european site outside the proximal volcanic influence of italy or iceland is presented of these tephras four may correlate with known iceland derived tephra horizons vo 1477 hi lairg a and h5 one appears to have two possible named correlatives hoy lairg b at sluggan bog n ireland another has a plausible correlative ad 860a but two others represent icelandic tephras apparently not previously reported on iceland itself including a tephra that has geochemistry very similar to hl ad 1104 but which dates to c cal ad 840 four tephras that date from the period c ad 40 1400 have a distinct geochemical signature that relates to jan mayen 750km to the northeast of iceland and some 1800km distant from an loch mor the results contribute substantially to the chronology of the sediments from an loch mor and at the international level to the tephrostratigraphy of the northeast atlantic region the well attested icelandic h4 tephra from a hekla eruption of c 4260cal bp was not recorded it is suggested that an loch mor lies south of its recordable distribution in this part of the northeast atlantic region taken together with work at other sites the findings point to a wealth of potential tephra isochrons in holocene deposits of the northeast atlantic seaboard it is clear also that calcareous lake sediments can be as fruitful a source of tephras as peats potential problems relating to dating and geochemical fingerprinting of tephra layers in individual sites are highlighted with reference to the lairg tephras as recorded in scotland and northern ireland and to the hoy tephra that has been described from orkney

seven tephra isochrones in scotland this paper reports the presence and geochemical characteristics of seven separate tephras in scotland that fell in ad 1510 and about 450 bp 2100 bp 3600 bp 3830 bp 5600 bp and around 6000 bp the results come from 14 peat bogs spread throughout the highlands and islands where 26 tephra deposits have been characterized using over 400 grain discrete electron probe micro analysis firstly tephras are identified and defined by major element characteristics at a reference site secondly tephras are linked between sites on the basis of geochemistry and dated informal names based on british sites are suggested for tephras not yet linked to precise sources in iceland despite some apparent variation in colour all analysed grains in these seven deposits are silicic or intermediate in composition sio2 57 this phenomenon does not appear to be an artifact of preservation for two reasons first small 40 m basic glass shards in peat bogs in northern iceland are found to have undergone minimal alte

the chronology of the last termination a review of radiocarbon dated high resolution terrestrial stratigraphies abstract the last termination is traditionally subdivided into the oldest dryas bolling older dryas allerod younger dryas and preboreal chronozones this paper briefly summarizes the history of the late weichselian chronostratigraphic system and gives an overview of recent developments in radiocarbon dating terrestrial records between 15 000 and 10 000 14 c years bp problems inherent in the traditional chronostratigraphy are discussed in the light of new and more advanced dating possibilities including accelerator mass spectrometry ams measurements on terrestrial macrofossils new results obtained using ams 14 c dated varve sequences are compared with each other and with the marine u th coral record in addition the importance of time synchronous marker horizons as a tool for long distance correlation between different archives is illustrated

towards a holocene tephrochronology for sweden geochemistry and correlation with the north atlantic tephra stratigraphy northern europe has been affected by fallout of tephra from volcanic eruptions in iceland throughout at least the late glacial and holocene microscopic volcanic ash horizons found in the british isles northern germany and scandinavia e g hekla 4 now provide important regional isochrons over recent years analytical techniques such as electron probe microanalysis epma have helped identify these distal tephra layers by glass geochemistry early tephra work in sweden used refractive indices and bracketing radiocarbon dates for identification resulting in tentative correlation this paper presents geochemical data for icelandic holocene tephra in sweden several sites in central sweden have four distinct mid holocene tephra layers correlation with the icelandic record indicates that the following tephra layers are present hekla 4 ca 3830 yr bp kebister tephra ca 3600 yr bp hekla 3 ca 2880 yr bp and askja ad 1875 preliminary analyses suggest that more previously unidentified tephra layers are present in low concentrations in the region indicating potential for expanding the swedish tephrochronology for palaeoecological and palaeoenvironmental work in northern europe copyright 2004 john wiley sons ltd

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

early to middle holocene silicic tephra horizons from the katla volcanic system iceland new results from the faroe islands comparatively few icelandic tephra horizons dated to the early part of the holocene have so far been detected outside iceland here i present several tephra horizons that have been recorded in a holocene peat sequence on the faroe islands geochemical analyses show that at least two dacitic and one rhyolitic tephra layers were erupted from the katla volcanic system on southern iceland between ca 8000 and 5900 cal yr bp the upper two layers can be correlated with the silk tephras described from southern iceland whereas the third dated to ca 8000 cal yr bp has a geochemistry virtually identical to the rhyolitic component of the vedde ash the results suggest that the late weichselian and early holocene eruption history of the katla volcano was probably more complex than inferred from iceland a new early holocene rhyolitic tephra dated to ca 10 500 cal yr bp probably originates in the snaefellsnes volcanic centre in western iceland these new findings may play an important role in developing a holocene tephra framework for northwest europe copyright 2002 john wiley sons ltd

lateglacial and early holocene climates of the atlantic margins of europe stable isotope mollusc and pollen records from orkney scotland the margins of mainland europe and especially those areas coming under the influence of north atlantic weather systems are ideally placed to record changing palaeoclimates cores from an infilled lake basin at crudale meadow in mainland orkney revealed basal deposits of calcareous mud marl beneath sedge peat stable isotope palynological and molluscan analyses allowed the establishment of palaeoenvironmental changes through the devensian lateglacial and the early holocene the 18omarl record exhibited the existence of possibly four climatic oscillations in the lateglacial one of which within event cf gi 1c is not often commented upon as well as the preboreal oscillation and other holocene perturbations the cold episodes succeeding the preboreal oscillation were demarcated conservatively and one of these event c5 11 0 ka may have previously been unremarked while the putative 9 3 and 8 2 ka events seem not to produce corresponding palynologically visible floristic changes the events at crudale meadow are consistent with those recorded at other sites from britain ireland and elsewhere and can be correlated with isotopic changes shown by the greenland ice cores the multi proxy approach enriches the environmental reconstructions from the site although the synchronicity of the response of the various proxies is sometimes equivocal depending upon the time period concerned taphonomy and the nature of the deposits the site may contain the most northerly lateglacial isotope record from northwest europe and it has yielded one of the best archives for the demonstration of abrupt early holocene events within britain

thin tephra layers in peat revealed by x radiography x radiography has been found to provide a rapid economical non destructive method of locating very thin fine grained tephra of icelandic origin in scottish peats tephra layers form time parallel marker horizons or isochrones that are of great archaeological significance because they cover large areas offer precise chronological control for associated material and occur at times of significant cultural and environmental changes not all of the discrete deposits of recent volcanic fallout in scotland are sufficiently dense to show clearly on x radiographs but those which do provide particularly clear easily located marker horizons with many applications in palaeoenvironmental studies the tephra layer in caithness produced by fallout from a c 4000 by eruption of hekla provides a particularly good example of the use of x radiography to locate volcanic ash the method also reveals other structures of archaeological and palaeoenvironmental significance butler 1992 journal of archaeological science 19 151 161

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

holocene tephra from iceland and alaska in se greenland shelf sediments the record of icelandic volcanic events in holocene marine sediments off se greenland provides evidence for the frequency and timing of atmospheric tephra plume dispersal from iceland towards greenland geochemistry of tephra abundance peaks from two se greenland shelf cores md99 2322 and jm96 1215 2gc are compared with core md99 2269 north iceland shelf to evaluate the dispersal direction of icelandic eruptions glass shard counts 106 1000 m in md99 2322 revealed 16 distinct cryptotephra peaks geochemical analyses of eight cryptotephra peaks in md99 2322 and two in jm96 1215 indicate sources in the volcanic systems of iceland and alaska a tephra layer matching in geochemistry and stratigraphy to the c 3600 bp eruption of the aniakchak volcano in the aleutian islands was identified in jm96 1215 2gc the settlement tephra ad 871 2 and hekla b h b were identified in md99 2322 a new marker horizon katla eg 6 73 was found in both se greenland cores three basaltic peaks between 9 9 and 10 4 cal kyr bp exhibit major element geochemistry indistinguishable from the c 10 2 kyr saksunarvatn tephra these layers represent 3 out of seven westward and northward dispersed grimsvotn layers found on the se greenland shelf and the north iceland shelf between 9 9 and 10 4 cal kyr bp

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

volcanogenic sedimentation in the iceland basin influence of subaerial and subglacial eruptions abstract cores recovered from the iceland basin show evidence of transport and deposition of volcaniclastic sediment from the eastern volcanic zone of iceland during the holocene and last glacial period three types of deposits have been identified tephra fall sediment gravity flows and bottom current controlled deposits tephra fall layers contain basaltic glass of composition that suggests katla volcano as the major source a chronology of the volcano activity is reconstructed back to isotopic stage 5d 120 000 yr glass chemistry of tephra in sediment gravity flows deposited south of myrdalsjokull canyon indicates a source in the grimsvotn lakagigar volcanic system these volcaniclastic gravity flows were most likely derived from jokulhlaups or large glacial floods at a time of a more extensive ice cover over the volcanic zone deposition of the sediment gravity flows has created a deep sea fan south of the canyon basalt glass composition age and depositional environment suggest that one early holocene turbidite sequence was derived from a large jokulhlaup of the grimsvotn area the volcanogenic sediment gravity flows were influenced by a strong contour current moving across the katla sediment ridges the contour current has winnowed the silt fraction and transported it downstream as suspended load the recovery of numerous silty volcaniclastic layers enriched in detrital crystals indicates that they contributed to the sedimentation of contourite drifts

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

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

new findings regarding the saksunarvatn ash in germany the saksunarvatn ash is an important tephra layer for the correlation of early holocene environmental records in northern europe the north atlantic and greenland the saksunarvatn ash is believed to have been produced by eruptions of the grimsvotn volcanic system 10 3 ka bp which had two axes of dispersal one plume in a north west direction over northern iceland and into greenland and a second southerly plume covering the faroe isles shetland isles western norway and northern germany here we present data from potremser moor north east germany extending the easterly margin of the ash fallout zone we also present single grain trace element data from the type site at saksunarvatn as well as from potremser moor the saksunarvatn ash is indistinguishable between potremser moor and saksunarvatn suggesting the two tephras were produced by the same eruption trace element compositions from both sites are similar to data from the north atlantic marine core link 14 185 but different from the grip ice core grip 1528 61 m indicating that the south east and north west plumes may have arisen from separate eruption events copyright 2013 john wiley sons ltd

tephra geochemistry a discussion of some persistent analytical problems distal tephrochronological studies are reliant upon precise and accurate geochemical quantitation this quantitation can involve difficulties not often encountered in more conventional petrology solving these problems is of particular importance in the holocene and late quaternary of northwest europe where numerous tephra layers of icelandic origin have been detected in peat bogs and lake and marine sediments electron probe microanalysis epma has proved the most applicable analytical technique when insufficient quantities of tephra are available for bulk analysis standard epma techniques require fine tuning to the tephra problem as the geochemical instability of glass is a common feature in many previous studies geochemical data of avoidably low quality have been produced and little attention appears to have been directed to modification of epma methods it is suggested that the black box approach to geochemical analysis should be avoided by the consideration of several factors these include

the drangajokull ice cap northwest iceland persisted into the early mid holocene abstract most glaciers and ice caps in iceland experienced rapid deglaciation in the early holocene reaching a minimum extent during the holocene thermal maximum here we present evidence of the holocene glacial history from lake sediment cores retrieved from seven threshold lakes around the drangajokull ice cap in the vestfir ir peninsula nw iceland the sediment cores show on off signals of glacial meltwater activity as minerogenic material deposited from glacial meltwater alternates with organic rich material gyttja deposited without glacial meltwater we base the chronology of the sediment cores on 14c ages and geochemical identification of key tephra layers with known ages a 25 cm thick layer of the saksunarvatn tephra in lake skorarvatn indicates that the northern part of the ice cap had reached a similar size as today or was smaller already by 10 2 cal kyr bp however 14c ages of lake sediment cores from the highlands southeast of drangajokull suggest that this part of the ice cap was larger than today until 7 8 7 2 cal kyr bp even today the drangajokull ice cap has a different behavior than the main ice caps in iceland characterized by a very low glaciation limit because palaeoclimatic proxies show an early mid holocene temperature optimum in this part of iceland we suggest that the persistence of drangajokull into the early holocene and possibly also the entire holocene was due to high winter precipitation

freshwater forcing from the greenland ice sheet during the younger dryas evidence from southeastern greenland shelf cores abstract we present evidence for freshwater forcing from the greenland ice sheet during the last deglaciation explore its potential involvement in the younger dryas cooling and investigate the role of atlantic intermediate water in the retreat of the greenland ice sheet paleoceanographic conditions and ice sheet retreat history are interpreted from ird stable isotopes and foraminiferal assemblages in sediment cores retrieved along the length of the kangerlussuaq trough a cross shelf trough on the southeast greenland shelf the vedde ash 11 980 cal yr bp which is a marker bed within the younger dryas and the saksunarvatn tephra 10 180 cal yr bp an early holocene marker horizon have been located in these cores the tephra markers and calibrated 14c dates on foraminifers and molluscs provide the basis for the age models in the cores the stable isotope records indicate a 0 5 depletion of the 18o between 13 4 and 12 8 cal ka bp a pronounced light isotope event exceeding 1 5 on the inner shelf and 0 8 on the outer shelf occurs at the beginning of the younger dryas cold period 12 8 cal ka bp and ends by 12 cal ka bp immediately before deposition of the vedde ash the light isotope spikes are interpreted as glacial meltwater spikes associated with retreat of the adjacent greenland ice sheet associated with the light isotope events are episodic high percentages of the atlantic intermediate water benthic foraminiferal species cassidulina neoteretis which continue from the bolling allerod into the younger dryas high percentages of this species suggest that atlantic intermediate water entered the kangerlussuaq trough during the allerod and the younger dryas via the irminger current as it does today we conclude that advection of atlantic intermediate water into the kangerlussuaq trough south of the denmark strait promoted melting and retreat of the marine portions of the greenland ice sheet explaining the observed glacial meltwater spikes

glacial and climatic events in iceland reflecting regional north atlantic climatic shifts during the pleistocene holocene transition abstract this paper presents a summary of the evidence for glacial and climatic changes during the late pleistocene early holocene transition in iceland the deglaciation during the bolling allerod event was interrupted by a short lived older dryas glacial advance a biostratigraphical record from northern iceland shows significant climate warming in late allerod when mean july temperatures were at least as warm as those of today an abrupt cooling marked the beginning of the younger dryas event it was characterised by a cold and stable polar climate and an extensive glaciation before the postglacial warming of climate set in the icelandic paleoclimatic record is discussed in the light of climatic oscillations recorded from the grip ice core from the greenland inland ice and with reference to major shifts in the oceanic front systems recorded in the troll 8903 marine sediment core from the north sea the vedde ash gives a unique opportunity to address the chronological problems and correlate event stratigraphies of the different proxies it is concluded that the icelandic record of glacial and climatic changes during the late pleistocene early holocene transition largely reflects the climatic development in the north atlantic region

late quaternary stratigraphy of the northern rockall trough and faeroe shetland channel northeast atlantic ocean a late quaternary deep water stratigraphic framework has been established for the deep water areas 450m of the northern rockall trough and faeroe shetland channel four stratigraphic units 1 4 are identified these are primarily biostratigraphic units based on dinoflagellate cyst evidence unit 1 represents the late weichselian glacial pre 13 000 yr bp unit 2 the late glacial interstadial 11 000 13 000 yr bp unit 3 is of younger dryas age 10 000 11 000 yr bp and unit 4 represents the holocene interglacial post 10 000 yr bp this stratigraphy is supported by the discovery of the mixed vedde ash 10 600 yr bp and north atlantic ash zone 1 and the saksunarvatn ash 9000 9100 yr bp concentrated in units 3 and 4 respectively the sedimentology indicates that the oceanographic regime underwent a major change between the glacial and interglacial stages this is marked by the onset of strong bottom current activity allied to the restoration of overflow of the norwegian sea deep water into the north atlantic towards the end of the younger dryas stadial despite intense bioturbation and bottom current reworking the basic stratigraphic framework is maintained recognition of two volcanic ash markers enables correlation with established onshore and offshore sequences of marine and non marine environments

late devensian and flandrian palaeoenvironmental changes on the scottish continental shelf west of the outer hebrides examination of two radiocarbon dated vibrocores taken from south of st kilda at a water depth of about 155 m a short distance within the maximum position of the late devensian dimlington stadial ice sheet suggests that the st kilda basin became free of glacier ice after 15250 yr bp sedimentation in a shallow low energy high arctic muddy environment continued until after 13500 yr bp there followed a higher energy temperate episode during which water depths were roughly about 40 m this is correlated with the latter part of the windermere interstadial and with the warmer interval known in shallow scottish seas about or a little before 11 000 yr bp the loch lomond younger dryas stadial is marked in the vibrocores by the return of muddy sediments and a cold water fauna relatively shallow water conditions seem to have persisted into the earliest flandrian when the water depth was still roughly 60 m corresponding to a sea level in the area 90 100 m below present it is suggested that pack ice was widespread in the northeast atlantic before the windermere interstadial and also during the loch lomond stadial when it transported shards of icelandic volcanic ash into the st kilda basin estimates of sea surface temperature for the last part of the windermere interstadial are close to those derived from the deep sea record for the same period

volcanoes and climate the triggering of preboreal jokulhlaups in iceland the early holocene 12 8 2 cal ka deglaciation and pulsed warming was associated in iceland with two major generations of jokulhlaups around the vatna ice cap vatnajokull at ca 11 4 11 2 cal ka and ca 10 4 9 9 cal ka and major tephra emissions from the grimsvotn and bar arbunga subglacial volcanoes the earliest flood events were recorded inland during the middle younger dryas and their deposits were overlain by the early preboreal vedde ash 11 8 cal ka the first holocene flood events ca 11 4 11 2 cal ka are issued from a glacial advance the second and major set of floods was partly driven by the erdalen cold events and advances 10 1 9 7 10be ka initially issued from the bar arbunga 10 4 10 1 9 9 ka and grimsvotn volcanoes saksunarvatn tephra complex ca 10 2 9 9 cal ka these floods were also fed by the residual glacio isostatic depressions below the vatnajokull that enabled the storage of meltwaters in large subglacial lakes or aquifers until ca 9 3 cal ka this storage was enhanced by ice damming and permafrost especially during the twinned erdalen events due to the glacio isostatic rebound the general slope was nearly flat and the valley was partly filled with sediments until ca 10 8 cal ka temporary lacustrine deposits in this valley resulted from the very broad splay of waters as for the ca 11 2 cal ka and ca 10 1 9 9 cal ka flood due to regional permafrost these floods had a potential duration of several months as they were mostly fed by climate driven meltwater the maximal volume evacuated by these events did not greatly exceed 1 106 m3 s 1 from the flood affected transverse profile of the valleys that remain partly filled with sediments

a rapid non destructive scanning method for detecting distal tephra layers in peats rapid automatic scanning of reflectance variations along peat profiles from corlea central ireland known to contain prehistoric tephra layers dated to around 2300 cal bc has enabled the detection of these layers by non destructive means by using both light reflectance and luminescence properties it is believed that very thin and often discontinuous distal tephras characteristic of the late quaternary in northwest europe may be detected within peat profiles

a late holocene record of landscape degradation from heygsvatn the faroe islands abstract diatom magnetic susceptibility and loss on ignition loi analyses of a 9 metre sediment core from heygsvatn su uroy the faroe islands were used to investigate the response of lake and catchment to mid late holocene environmental change a 30 lake training set from faroese lakes was also used to explore the relationships between diatoms and environmental variables and assist in the interpretation of the diatom stratigraphy canonical correspondence analysis showed that lake depth light penetration total phosphorus tp ph and dissolved organic carbon doc were the most significant variables affecting diatom distribution in faroese lakes p

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

establishing chronologies for woodland small hollow and mor humus deposits using tephrochronology and radiocarbon dating chronological precision is a pre requisite for all palaeoecological analyses especially in more recent holocene deposits such as small hollow peat and mor humus in woodlands here tephrochronology was employed to improve the chronological control of such deposits to aid subsequent sub fossil insect analyses from three sites in western and southwestern ireland six tephra layers were detected from the three small hollows but only one from the mor humus sites four of the layers were matched to known tephra horizons regularly recorded in ireland while two new tephras of possible azores and grimsvotn origin were recorded the latter tephra may be the first definitive record of laki 1783 4 from ireland and is potentially an important new chronological marker for irish palaeoecological investigations of late holocene deposits results suggest that tephrochronology is a successful additional chronological tool for small hollow palaeoecological studies but is less helpful in mor humus deposits

high resolution analyses of an early holocene climate event may imply decreased solar forcing as an important climate trigger early holocene lacustrine tree ring ice core and marine records reveal that the northern hemisphere underwent a short cooling event at 10 300 calendar yr b p 9100 14 c yr b p the records were compared on a common high resolution time scale and show that the event lasted less than 200 yr with a cooling peak of 50 yr and the event coincides with a distinct holocene thermohaline disturbance recognized in the north atlantic ocean in spite of wellknown freshwater forcings at the time of the event the negligible difference between the modeled d 14 c record based on the gisp2 greenland ice sheet project 2 10 be data and the measured values does not allow for detectable d 14 c changes related to global ocean ventilation we can however show that the onset of the cooling coincides with the onset of one of the largest holocene 10 be flux peaks this finding may imply that the climate system is more

two new icelandic tephra markers the hekla o tephra layer 6060 cal yr bp and hekla dh tephra layer 6650 cal yr bp land sea correlation of mid holocene tephra markers a sedimentary basin within the tjornes fracture zone on the north icelandic shelf has been investigated with the purpose of locating tephra layers for dating and stratigraphical correlations of terrestrial and marine archives two new mid holocene tephra markers originating from the hekla volcano in iceland have been identified in the marine sediment core md99 2275 retrieved from the basin east of the island of grimsey these tephra layers have been correlated to their terrestrial counterparts the hekla o tephra and the hekla dh dark horse tephra the hekla o tephra has been dated to 6060 115 cal yr bp by four ams 14c dates from two terrestrial sites in iceland an age estimate of 6650 cal yr bp has been calculated sar soil accumulation rate for the hekla dh tephra from three soil sections in iceland preliminary volume estimates of the hekla o and hekla dh tephra layers are 1 km 3 and 0 8 km3 respectively these two tephra layers enhance the age control between the hekla 4 and hekla 5 tephra m

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

eastern north atlantic deep sea corals tracing upper intermediate water δ14c during the holocene abstract paired 230th u and 14c dating were performed on deep sea corals lophelia pertusa and madrepora oculata from the northeastern north atlantic at 730 m bsl to investigate past changes of the thermohaline circulation these were estimated using the 14c value of the upper intermediate waters based on the 14c ages of the top and base of each coral where possible and the 230th u dating the reliability of these estimates was checked by dating two very young corals of the species l pertusa one of these corals collected alive in 1999 ad gave a 230th u age of 1995 4 ad after correction for non radiogenic 230th another coral the top of which dated to 1969 6 ad recorded the atmospheric 14c 12c increase due to the nuclear tests in the early 1960s the calculated 14c values from these two corals agree with those measured at geosecs station 23 in 1972 1973 ostlund et al earth planet sci lett 23 1974 69 86 and 1991 1992 nydal and gisfelos radiocarbon 38 1996 389 406 this together with the 100 aragonite content and the 234u and 230th 232th values of all the dated corals indicates that none of the corals behaved as open systems with respect to their u series nuclides and that they closely represent the water mass properties in which they lived the pre anthropogenic 14c value of the north atlantic intermediate waters was estimated at 69 4 the reservoir age varies from 400 years to 600 years and this variation is due to atmospheric 14c 12c changes a reservoir age of 610 80 years close to the pre anthropogenic value was determined from one coral dated at 10 430 120 cal yr bp when the global sea level was approximately at 35 m bard et al nature 382 1996 241 244 this suggests a modern like pattern of the oceanic circulation prevailed in the northeast atlantic ocean at this time although the deglaciation was not completely achieved

was the 12 1 ka icelandic vedde ash one of a kind abstract the vedde ash is the most important volcanic event marker layer for the correlation of late quaternary palaeoenvironmental archives in europe and the north atlantic first defined from its type site localities near alesund western norway the vedde ash has now been traced across much of northern and central europe into northwest russia within north atlantic marine sediments and into the greenland ice cores the vedde ash is thought to derive from an eruption of the katla volcano in iceland that occurred midway through the younger dryas greenland stadial 1 gs 1 12 1 ka bp visible and cryptotephra deposits of the vedde ash have been found in numerous stratified sites with robust chronologies which allow its age to be constrained and its dispersal to be mapped the eruption must have been highly explosive however few proximal outcrops have been confirmed and this crucial ash layer remains almost exclusively distally described and characterised using major element glass compositions the widespread distribution stratigraphic associations and consistent major element glass chemistry have led the quaternary tephrochronological community to see the vedde ash as a robust and unique chronological marker layer for the last glacial to interglacial transition 10 18 ka bp here we present new glass analyses of the vedde ash from multiple sites around the dispersal area using a full suite of compositional analysis including for the first time single grain trace element data these data demonstrate the strong compositional coherence of vedde ash deposits however comparison with major minor and trace element compositional data from several other distally described icelandic tephras reveals that both before and after the younger dryas chronozone there were eruptions that generated widespread tephra layers that have comparable glass shard compositions to the vedde ash this implies that these numerous events not only hail from the same volcanic system but that the melts share similar crystallisation trends and mixing patterns prior to eruption it seems therefore that composition alone is insufficient for the correlation of some widespread tephra layers good stratigraphic information and or robust dating control are also essential

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

a late younger dryas early holocene tephrostratigraphy for fosen central norway a number of rapid climate oscillations occur during the lateglacial early holocene 15 8 ka bp period and a well developed tephrostratigraphy in association with these oscillations increases the po

three new distal tephras in sediments spanning the last glacial interglacial transition in scotland three new microtephras are reported from a number of lake sites from the inner hebrides and scottish mainland one occurs stratigrapically in the middle of greenland interstadial 1 gi 1 and has been named the penifiler tephra it is rhyolitic and possesses a geochemical signature that is very similar to that of the borrobol tephra which also occurs in three of the sequences reported here but which lies close to the lower boundary of gi 1 the second occurs stratigraphically in the early holocene below the saksunarvatn ash and is named the ashik tephra this tephra is geochemically bimodal with a rhyolitic component comparable to the an druim tephra that occurs later in the holocene and a basaltic component which is similar to the saksunarvatn ash a third tephra occurs stratigraphically above the saksunarvatn ash and is provisionally named the breakish tephra the consistent inter site correlation demonstrated for these new tephras at several sites enhances the regional tephrostratigraphic framework and increases the potential for correlating palaeoenvironmental events during gi 1 and the early holocene however the occurrence of multiple tephras with similar geochemistry in close stratigraphic and temporal proximity has implications for the rigour with which tephrostratigraphic investigations must be performed copyright 2006 john wiley sons ltd

late weichselian and holocene sediment fluxes of the northern north sea margin abstract an event chronology has been determined for temporal and lateral magnitudes of material fluxes across the northern north sea margin including the norwegian channel and the north sea fan this has allowed the governing factors for the sediment processes on the margin to be estimated the chronological model of selected cores is based on 14 c ams dates regional tephra layers and planktonic foraminiferal stratigraphy based on this chronological framework the core sediments across the north sea margin have been divided into four main climatostratigraphic intervals a oldest dryas 15 13 ka b bolling allerod 13 11 ka c younger dryas 11 10 ka and d holocene 10 0 ka further the holocene period has also been divided into two subperiods the preboreal 10 9 ka and the holocene interglacial 9 0 ka creating five well defined lithological units deposition phases in all of which the deglaciation units 15 9 ka usually constitute 90 of the sediment budget the recognition of an almost identical lithological succession both in the records on the fan and in the high resolution record of the channel suggests that sedimentation on the north sea margin must be governed dominantly by regional sedimentary processes for each time interval the sedimentation rate in the norwegian channel is on average an order of magnitude higher than on the north sea fan diminishing distally from the shelf edge sedimentation under the holocene interglacial period 9 0 ka contrasts totally from the deglaciation pattern controlled dominantly by pelagic productivity in the area close to 50 of the hemipelagic sediments on the north sea margin are of bolling allerod age 15 13 ka this extreme sedimentation resulted from a combination of a rapid sea level rise constantly exposing new areas for marine erosion winnowing and aggressive surface ocean current activity surface ocean currents and the associated bottom currents provide the dominant control on the pattern of deglacial sedimentation on the north sea margin 15 9 ka this is especially apparent during the oldest dryas and the bolling allerod periods where the distribution pattern across the margin is essentially hydrodynamically controlled only during the younger dryas period are the surface ocean processes overprinted by sedimentary processes from melting icebergs the high resolution records reveal that the shifts in the lithological style of sedimentation are directly linked to the rapid reorganisation of the surface ocean system frequently taking place during the deglacial and holocene time period suggesting a fairly regional type of sedimentation pattern as the shift between the different lithological styles of sediments is both abrupt and regional they should be detectable on the seismic high frequency records

towards a european tephrochronological framework for termination 1 and the early holocene the record of deposition of tephras in europe and the north atlantic during the period 18 5 8 0 14 c ka bp the last termination and early holocene is reviewed altogether 34 tephras originating from four main volcanic provinces iceland the eifel district the massif central and italy have been identi ed so far in geological sequences spanning this time interval most of the records have been based until very recently on observations of visible layers of tephras here we report on the potential for extending the areas over which some of the tephras can be traced by the search for layers of micro tephra which are not visible to the naked eye and on the use of geochemical methods to correlate them with known tephra horizons this approach has greatly extended the area in northern europe over which the vedde ash can be traced the same potential exists in southern europe which is demonstrated for the rst time by the discovery of a distinct layer of micro tephra of the neapolitan yellow tu in a site in the northern apennines in italy far to the north of the occurrences of visible records of this tephra the paper closes by considering the potential for developing a robust european tephrostratigraphy to underpin the chronology of records of the last termination and early holocene thereby promoting a better understanding of the nature timing and environmental e ects of the abrupt climatic changes that characterized this period

tephra in deglacial ocean sediments south of iceland stratigraphy geochemistry and oceanic reservoir ages icelandic tephra layers within deglacial ocean sediment cores from south of iceland have been detected and their timing with respect to the climate shifts of the last deglaciation constrained geochemical analysis of the tephra allowed the likely source volcanic systems to be identified the previously known saksunarvatn ash and vedde ash are recognised and described several other major tephra layers are examined basaltic eruption s of katla at 8 4 ka a basaltic eruption of katla at 12 6 ka a rhyolitic eruption of katla at 13 6 ka producing tephra similar in appearance and composition to the vedde ash a basaltic eruption of katla at 14 0 ka and two basaltic eruptions of grimsvotn at 14 6 ka and 15 0 ka abundant rhyolitic ash with a similar appearance and chemistry to the vedde ash is found throughout the deglacial interval predating the vedde ash by up to 3000 years supporting previous suggestions that there were pre vedde ash eruptions of rhyolite that may have contributed to north atlantic ash zone 1 this study expands the tephro stratigraphic framework of the north atlantic and provides a marine archive in which the timing of tephra layers useful as isochrons can be directly compared to major ocean and climate events of the last deglaciation furthermore by correlating tephra layers and abundance changes in the polar foraminifera neogloboquadrina pachyderma sinistral to equivalent tephra events and inferred abrupt cooling warming in greenland ice cores contemporaneous 14c dated planktonic foraminifera have been used to estimate changes in the surface radiocarbon reservoir age south of iceland consistent with previous studies larger surface reservoir ages are calculated during late heinrich stadial 1 and the younger dryas 2000 years and 800 1900 years respectively

holocene temperature history of northern iceland inferred from subfossil midges abstract the holocene temperature history of iceland is not well known despite iceland s climatically strategic location at the intersection of major surface currents in the high latitude north atlantic existing terrestrial records reveal spatially heterogeneous changes in iceland s glacier extent vegetation cover and climate over the holocene but these records are temporally discontinuous and mostly qualitative this paper presents the first quantitative estimates of temperatures throughout the entire holocene on iceland mean july temperatures are inferred based upon subfossil midge chironomidae assemblages from three coastal lakes in northern iceland midge data from each of the three lakes indicate broadly similar temperature trends and suggest that the north icelandic coast experienced relatively cool early holocene summers and gradual warming throughout the holocene until after 3 ka this contrasts with many sites on iceland and around the high latitude northern hemisphere that experienced an early to mid holocene thermal maximum in response to enhanced summer insolation forcing our results suggest a heightened temperature gradient across iceland in the early holocene with suppressed terrestrial temperatures along the northern coastal fringe possibly as a result of sea surface conditions on the north iceland shelf

distribution sediment magnetism and geochemistry of the saksunarvatn 10 180 60 cal yr bp tephra in marine lake and terrestrial sediments northwest iceland in 1997 seismic surveys in the troughs off northwest and north iceland indicated the presence of a major regional sub bottom reflector that can be traced over large areas of the shelf cores taken in 1997 and later in 1999 on the images v cruise penetrated through the reflector in core md99 2269 in hunafloaall this reflector is shown to be represented by a basaltic tephra with a geochemical signature and radiocarbon age correlative with the north atlantic wide saksunarvatn tephra we trace this tephra throughout northwest iceland in a series of marine and lake cores as well as in terrestrial sediments it forms a layer 1 to 25 cm thick of fine to medium grained basaltic volcanic shards the base of the tephra unit is always sharp but visual inspection and other measurements carbonate and total organic carbon weight indicate a more diffuse upper boundary associated with bioturbation and with sediment reworking off northwest iceland the saksunarvatn tephra has distinct sediment magnetic properties this is evident as a dramatic reduction in magnetic susceptibility an increase in the frequency dependant magnetic susceptibility and hard magnetisation in a 0 1t irm backfield geochemical analyses from 11 sites indicate a tholeiitic basalt composition similar to the geochemistry of a tephra found in the greenland ice core that dates to 10 180 60 cal yr bp and which was correlated with the 9000 14c yr bp saksunarvatn tephra we present accelerator mass spectrometry 14c dates from the marine sites which indicate that the ocean reservoir correction is close to ca 400 yr at 9000 14c yr bp off northwest iceland copyright 2002 john wiley sons ltd

discussion of a miocene collisional belt in north borneo uplift mechanism and isostatic adjustment quantified by thermochronology scientific editing by alex maltman john milsom robert holt write knowledge of the gravity field is vital to any study of isostasy this was acknowledged by hutchison et al 2000 when they noted that the work of holt 1998 placed constraints on their geological model for sabah however they went on to ignore these constraints arguing that the depth of the crustal root beneath the western cordillera might have been overestimated due to the model assumption of an excessively thick ophiolitic basement and that the presence of thick crust beneath sabah was in conflict with the outcropping geology the hutchison et al interpretations of the deep structure of sabah were illustrated in a series of cross sections in which some features notably the topography were amplified for the sake of clarity there was however no suggestion that any features would be underemphasized and the depth scales although described as only rough guides indicated normal 5 10 km thicknesses for oceanic crust therefore and in the light of the comments quoted above the thin crust shown throughout sabah and the generally somewhat greater thickness of the extended continental crust of the dangerous grounds must be regarded as essential elements of the model the late miocene cross section fig 1 showing the end of orogeny in sabah is a guide to the hutchison et al view of the present day situation crust is less than 30 km thick beneath the western cordillera and less than 20 km thick elsewhere we contend that these values are incompatible with the gravity field and that it is no more acceptable to present a geological interpretation that ignores geophysical data than a geophysical interpretation that ignores geology some way must be found of reconciling the two fig 1 sabah in the late miocene from hutchison et al 2000 fig 6b

marker tephra in haukadalsvatn lake sediment a key to the holocene tephra stratigraphy of northwest iceland abstract emerging lake sediment records are rapidly improving iceland s holocene tephra stratigraphy and chronology here we expand upon these recent developments with a securely dated tephrochronological record from the lake haukadalsvatn in west iceland we capitalize on the existing paleomagnetic secular variation psv age model which uses 54 ties points to synchronize haukadalsvatn s high resolution lake sediment record to a well dated psv master chronology from north iceland shelf marine core md99 2269 major element composition permits the identification of 38 tephra layers over the last 10500 years of these tephra 15 can be traced to tephra found on the vestfir ir peninsula and represent a series of well dated marker tephra for west and northwest iceland that feature precise geochemical fingerprints based on these premises and in contrast to recent assertations there is no firm evidence for the presence of the presumed middle holocene hekla o tephra in west or northwest iceland despite their close geographical locations comparison of haukadalsvatn s tephra layer frequency record to that of northwest iceland s reveals different trends this regional disparity is likely the result of predominately small eruptions that featured narrower ash plumes we argue that haukadalsvatn serves as an important template for the tephrochronology of west iceland and for future studies investigating the tephra records in more distal regions of the northwest north atlantic such as greenland

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

comparison of the historical record of earthquake hazard with seismic hazard models for new zealand and the continental united states we compare the historical record of earthquake hazard experienced at 78 towns and cities sites distributed across new zealand and the continental united states with the hazard estimated from the national probabilistic seismic hazard psh models for the two countries the two psh models are constructed with similar methodologies and data our comparisons show a tendency for the psh models to slightly exceed the historical hazard in new zealand and westernmost continental united states interplate regions but show lower hazard than that of the historical record in the continental united states intraplate region factors such as non poissonian behavior parameterization of active fault data in the psh calculations and uncertainties in estimation of ground motion levels from historical felt intensity data for the interplate regions may have led to the higher than historical levels of hazard at the interplate sites in contrast the less than historical hazard for the remaining continental united states intraplate sites may be largely due to site conditions not having been considered at the intraplate sites and uncertainties in correlating ground motion levels to historical felt intensities the study also highlights the importance of evaluating psh models at more than one region because the conclusions reached on the basis of a solely interplate or intraplate study would be very different

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

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

tephrochronology of last termination sequences in europe a protocol for improved analytical precision and robust correlation procedures a joint scotav intimate proposal the precise sequence of events during the last termination 18 000 9000 ka 14 cy r bp and the extent to which major environmental changes were synchronous are difficult to estab lish using the radiocarbon method alone because of serious distortions of the radiocarbon time scale as well as the influences of site specific errors that can affect the materials dated attention has there fore turned to other methods that can provide independent tests of the chronology and correlation of events during the last termination with emphasis on european sequences we summarise here the potential of tephrostratigraphy and tephrochronology to fulfil this role recent advances in the detection and analysis of hidden tephra layers cryptotephra indicate that some tephras of last termination age are much more widespread in europe than appreciated hitherto and a number of new tephra deposits have also been identified there is much potential for developing an integrated tephrochronological framework for europe which can help to underpin the overall chronology of events during the last termination for that potential to be realised however there needs to be a more systematic and robust analysis of tephra layers than has been the practice in the past we pro pose a protocol for improving analytical and reporting procedures as well as the establishment of a centralised data base of the results which will provide an important geochronological tool to support a diverse range of stratigraphical studies including opportunities to reassess volcanic hazards although aimed primarily at europe the protocol proposed here is of equal relevance to other regions and periods of interest copyright 2004 john wiley sons ltd

paleoceanographic reconstructions of surface ocean conditions in the greenland iceland and norwegian seas through the last 14 ka based on diatoms prior reconstructions of the last glacial maximum and the holocene did not include detailed paleoclimate data from the greenland iceland and norwegian gin seas which cover sensitive areas for oceanographic boundaries sea ice distribution and deep water formation in order to fill this gap we studied nine well dated sediment cores from this area and reconstructed the paleoceanographic conditions of the surface gin seas at 2000 year intervals since 13 400 bp based on the diatom record results show that a n s extending sea ice free corridor had opened along norway already at 13 400 bp indicating a northward flow of a branch of the north atlantic drift possibly caused by a change in the jet stream flow due to the decreased height of the north american ice sheet a major change of climatic conditions occurred over the gin seas as the insolation anomaly reached its maximum around 9000 bp when the sea ice cover and the oceanic fronts retreated to a northwesterly position along greenland and the ocean temperatures rose the first half of the holocene is recorded as the warmest period during the last 13 400 bp in the gin seas the duration of this climatic optimum decreased both toward the north and toward the margins of the area the second half of the holocene is characterized by a cooling trend in step with the decreasing insolation these results support the proposal of imbrie et al 1992 that the gin seas region acts as an initial responder to insolation changes