glacial extent and catastrophic meltwater events during the deglaciation of southern iceland abstract reconstruction of the paleoenvironment of south iceland based on lithofacies and chronological studies of the budi morainal complex lacustrine deposits at ofaerugil and a sediment core from lake hestvatn south iceland revealed evidence for repeated catastrophic flood jokulhlaup activities during the late younger dryas yd and the early preboreal pb chronozones during this time thin and lobate outlet glaciers from the retreating iceland ice cap extended from major valleys and calved into the paleobay of southern lowlands of iceland where relative sea level was at least 70 m higher than today a number of ice marginal lakes formed during the stepwise retreat of the south iceland ice sheet at the transition of the yd and pb primary geomorphic and sedimentologic impact of the jokulhlaups was erosion of multiple channels downstream from the most prominent moraines in south iceland and through the coastal sediment accompanied by net aggradation of chaotically stratified sand and silt lenses at the ice distal environment these floods accumulated in the form of recurrent turbidity currents volcanic eruptions supplemented by a catastrophic release of the ice marginal lakes are postulated as the main triggers for the jokulhlaup activity the jokulhlaup events evidenced in this study and subsequent break up of the partly marine based glacier may have contributed to the ice rafting events found in the north atlantic paleoenvironmental record

permafrost and climate in europe monitoring and modelling thermal geomorphological and geotechnical responses we present a review of the changing state of european permafrost within a spatial zone that includes the continuous high latitude arctic permafrost of svalbard and the discontinuous high altitude mountain permafrost of iceland fennoscandia and the alps the paper focuses on methodological developments and data collection over the last decade or so including research associated with the continent scale network of instrumented permafrost boreholes established between 1998 and 2001 under the european union pace project data indicate recent warming trends with greatest warming at higher latitudes equally important are the impacts of shorter term extreme climatic events most immediately reflected in changes in active layer thickness a large number of complex variables including altitude topography insolation and snow distribution determine permafrost temperatures the development of regionally calibrated empirical statistical models and physically based process oriented models is described and it is shown that though more complex and data dependent process oriented approaches are better suited to estimating transient effects of climate change in complex mountain topography mapping and characterisation of permafrost depth and distribution requires integrated multiple geophysical approaches and recent advances are discussed we report on recent research into ground ice formation including ice segregation within bedrock and vein ice formation within ice wedge systems the potential impacts of climate change on rock weathering permafrost creep landslides rock falls debris flows and slow mass movements are also discussed recent engineering responses to the potentially damaging effects of climate warming are outlined and risk assessment strategies to minimise geological hazards are described we conclude that forecasting changes in hazard occurrence magnitude and frequency is likely to depend on process based modelling demanding improved understanding of geomorphological process response systems and their impacts on human activity

the sediments of lake logurinn a unique proxy record of holocene glacial meltwater variability in eastern iceland the full holocene development of the large 8100 km 2 vatnajokull ice cap in iceland with its many outlet glaciers is poorly known the idea of an early deglaciation leading to a glacier free period in mid holocene followed by the neoglaciation is still the main concept for the glacial history in the north atlantic region including iceland we have examined a continuous sediment record from the glacier fed lake logurinn in eastern iceland to infer holocene meltwater variability of eyjabakkajokull which is a surge type outlet glacier of the vatnajokull ice cap we focus on the early and mid holocene and our data show that eyjabakkajokull receded rapidly during the final phase of the last deglaciation and did not deliver glacial meltwater to lake logurinn by 9000 years bp suggesting that eyjabakkajokull was significantly smaller than today at that time the return of glacial meltwater transport to lake logurinn and thus a return of eyjabakkajokull is dated to ca 4400 years bp suggesting an almost 5000 years long glacier free period during early and mid holocene during this time period we infer that the 8 2 ka cold event did not cause a significant expansion of eyjabakkajokull however we note a marked decrease in the aquatic productivity in lake logurinn which is suggested to be the result of shorter ice free seasons of lake logurinn the holocene thermal maximum is inferred by a period of maximum holocene aquatic productivity and dated to ca 7900 7000 years bp following the re formation of eyjabakkajokull ca 4400 years bp we suggest that the glacier reached stable conditions ca 1700 years bp and remained fairly stable until the later part of the little ice age when eyjabakkajokull reached its maximum holocene extent c 2012 elsevier ltd all rights reserved less

silicic volcanism at ljosufjoll iceland insights into evolution and eruptive history from ar ar dating abstract ljosufjoll volcano is the largest outcrop of silicic volcanic material in the volcanic snaefellsnes flank non rifting zone of iceland the silicic eruptives range from trachytes to alkaline and peralkaline comenditic rhyolites and show evidence for eruption in both subaerial and subglacial environments thirteen silicic eruptive units have been identified and mapped by a combination of field observations and geochemical correlation the trachytes probably formed by fractional crystallisation of a basaltic magma to form an alkali feldspar rich trachytic mush with continued fractionation of the interstitial melt producing low ba and sr rhyolite magma ar ar dating of feldspars and matrix glass or holocrystalline groundmass has been carried out on twelve of the units many units have a complex ar isotopic system with many samples showing evidence for inherited 40ar in the form of feldspar xenocrysts the deduced eruption ages span an age range from 650ka the eruptive history of ljosufjoll probably extends further back than this but the products of previous eruptions have since been removed by erosion or buried a syenite xenolith was dated at 1 1ma indicating that silicic alkaline magmatism has been occurring at ljosufjoll for over one million years eruptions of silicic material at ljosufjoll appear to be more common during times of rapid climate change and fluctuating ice volume

a review of the environmental history of iceland 13 000 9000 yr bp a synthesis of the main environmental changes that are interpreted to have occurred in iceland during the period 13 9 ka bp is presented most of the evidence available relates to variations in the position of ice margins although some limited information on vegetation history and soil stability is also referred to only qualitative and limited climatic inferences can be made for this period because of the lack of detailed evidence a summary curve of the relative extent of ice cover is presented

glacial marine or subglacial origin of diamicton units from the southwest and north iceland shelf implications for the glacial history of iceland abstract the extent and timing of ice advances onto the north and southwest iceland shelf is reconstructed by identifying the depositional environment of four diamicton units present in two marine cores from shelf troughs we analyze a combination of properties including sedimentological parameters microfabric analyses radiocarbon dates and foraminiferal assemblage data this multi proxy approach for understanding depositional environments of diamicton units is critical in areas where ice sheets extended into the marine environment the two cores studied contain a lower diamicton unit that is interpreted as subglacial till and an overlying diamicton unit that is interpreted as glacial marine sediment our analysis showed that in general till is classified by lower water content lower total organic carbon and coarser grain size than glacial marine sediment anisotropy of magnetic susceptibility shows that the till has a sheared fabric low inclination of the short k3 axis whereas the glacial marine sediment has a high inclination of the short k3 axis and a more random unsheared fabric grain counts on the 106 1000 m fraction in till contain a higher percentage of basalt whereas the glacial marine sediments contain a higher percentage of quartz volcanic glass and foraminifera foraminiferal assemblage data support the interpretations from the sedimentology and microfabric data radiocarbon dates on shells and or foraminifera in sediments directly above the diamicton units show that the ice retreated from these shelf areas by approximately 13 ka

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

late holocene paleoenvironments of northwest iceland from lake sediments abstract frozen sediment cores from two lakes in northwest iceland vatnsdalsvatn and thi riksvallavatn provide a nearly 1000 year decadal scale record of past environmental changes based on environmental magnetism inductively coupled plasma optical emission spectroscopy geochemistry carbon content and c n analyses accelerator mass spectrometry 14 c and 210 pb results provide chronologies for both sites covering the late 20th century to 960 bp at vatnsdalsvatn and to 480 bp at thi riksvallavatn these analyses reveal higher levels of sedimentary carbon during the little ice age between 600 and 50 bp at vatnsdalsvatn c n analyses suggest that some of this carbon enrichment came from terrestrial plants higher erosion rates during the little ice age may also have increased the influx of limiting nutrients enhancing algal productivity erosion is the dominant mechanism for sedimentary changes at both sites and seems to occur at predictable intervals geochemical indicators of erosion oscillate with a distinct 80 100 yr periodicity for nine centuries at vatnsdalsvatn and for four centuries at thi riksvallavatn these erosion cycles are consistent with long term stability in the positive mode of the north atlantic oscillation but may also be attributed to local climatic effects associated with great salinity anomalies

climatic changes in areas adjacent to the north atlantic during the last glacial interglacial transition 14 9 ka bp a contribution to igcp 253 this paper presents a summary of the evidence for climatic changes during the last glacial interglacial transition 14 9 ka bp in land areas adjacent to the north atlantic it is a synthesis of the results of the 12 regional summaries compiled by contributors to the north atlantic seaboard programme of igcp 253 that are published separately in this issue of journal of quaternary science eighteen palaeotemperature curves are compared and arranged in three transects one from southern europe to spitsbergen a second from ireland to poland and the third from southern new england to the labrador baffin shelf area ten maps are presented that summarise the synoptic climatic conditions of the region in 500 year time periods the purpose of the exercise is to examine the extent to which any emerging patterns support the ruddiman and mclntyre model of large scale shifts in the position of the oceanic polar front during the last glacial interglacial transition some broad agreement emerges although the influence of oceanic changes is diminished in areas that lay in close proximity to the laurentide and fennoscandian ice sheets attention is drawn to limitations in the compilations and to the potential for improved models in the future

variation in surface and deep water circulation in the denmark strait north atlantic during marine isotope stages 3 and 2 1 the paleoceanography in the denmark strait north atlantic is reconstructed based on down core analysis of planktonic foraminifera carbon and oxygen isotopes carbonate and ice rafted debris ird the stratigraphy spans 57 to 6 calibrated cal ka years and reveals sea surface temperatures that covary with greenland ice core temperatures throughout marine isotope stages mis 3 and 2 planktonic 18o minima interpreted as meltwater events follow sea surface warming ird from both the greenland and iceland ice sheets was delayed by 2 ka relative to the north atlantic heinrich events ventilation of bottom water was mostly sustained through open ocean convection associated with north atlantic deep water production or by convection of glacial north atlantic intermediate water except for two episodes at 54 cal ka mis 3 31 and 18 15 cal ka termination i during these two periods we suggest that deep water ventilation was accomplished mainly by brine formation

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

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

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

holocene climate history of geographical society o east greenland evidence from lake sediments abstract sediment cores from two lakes in the outer coastal region of east greenland were investigated for chronology lithology palynology and biogeochemistry a 10 m long sequence recovered in basaltso comprises the entire lake history following the last glaciation of the area probably during the preboreal oscillation this is indicated by a succession from glacial via glaciolimnic to limnic sediments deglaciation of the area was associated with a high sedimentation rate mirrored also in the basal part of a 2 6 m long core from a smaller lake b1 about 1 km south of basaltso limnic sedimentation without glacial influence commenced about 10 000 cal yr bp according to radiocarbon dated terrestrial plant remains biogeochemical and palynological data indicate an early holocene climatic optimum from 9000 to 6500 cal yr bp a climatic deterioration began at 6500 cal yr bp with an increase in snow accumulation documented by a change in the pollen assemblage and a coinciding change in the grain size distribution at least since 5000 cal yr bp a decrease in the biogeochemical parameters in both lake sediment successions indicates a temperature decline this deterioration culminated at about 3000 1000 cal yr bp when the climate was cold and dry a slight warming is indicated in the pollen assemblage between ca 1000 and 800 cal yr bp following a subsequent rise in precipitation cooling during the little ice age is mirrored in lowest dwarf shrub pollen percentages and in low contents of organic components

holocene high altitude vegetation dynamics in the pyrenees a pedoanthracology contribution to an interdisciplinary approach abstract using an interdisciplinary methodology based on pedoanthracology palynology and sedimentary charcoals landscape transformation in the pyrenees mountains during the holocene is analyzed with special attention to altitudinal variation in the treeline the data sources were eight soil profiles on a transect at 2000 2600 m a s l and a sedimentary record extracted from a very nearby peat bog at 2247 m a s l the combination of three different proxies permits a more viable and qualitatively complementary data set making it possible to better interpret the vegetation dynamic in this space through the holocene analysis of the data showed that the pyrenees landscape has undergone important changes during this period the changing treeline is a good example there is evidence of the decisive role of fire in the configuration of this landscape finally this study shows that herding and agricultural uses over thousands of years in the study area have had a determining influence on the current configuration of the territory equal to or more important than climatic factors

the configuration sensitivity and rapid retreat of the late weichselian icelandic ice sheet abstract the fragmentary glacial geological record across the icelandic continental shelf has hampered reconstruction of the volume extent and chronology of the late weichselian ice sheet particularly in key offshore zones marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf break position in all sectors during the last glacial maximum though its precise timing and configuration remains largely unknown within this context we review the available empirical evidence and use a well constrained three dimensional thermomechanical model to investigate the drivers of an extensive late weichselian icelandic ice sheet its sensitivity to environmental forcing and phases of deglaciation our reconstruction attains the continental shelf break across all sectors with a total ice volume of 5 96 105 km3 with high precipitation rates being critical to forcing extensive ice sheet flow offshore due to its location astride an active mantle plume a relatively fast and dynamic ice sheet with a low aspect ratio is maintained our results reveal that once initial ice sheet retreat was triggered through climate warming at 21 8 ka bp marine deglaciation was rapid and accomplished in all sectors within c 5 ka at a mean rate of 71 gt of mass loss per year this rate of ice wastage is comparable to contemporary rates observed for the west antarctic ice sheet the ice sheet subsequently stabilised on shallow pinning points across the near shelf for two millennia but abrupt atmospheric warming during the bolling interstadial forced a second dramatic collapse of the ice sheet onshore with a net wastage of 221 gt a 1 over 750 years analogous to contemporary greenland rates of mass loss geothermal conditions impart a significant control on the ice sheet s transient response particularly during phases of rapid retreat insights from this study suggests that large sectors of contemporary ice sheets overlying geothermally active regions such as siple coast antarctica and ne greenland have the potential to experience rapid phases of mass loss and deglaciation once initial retreat is initiated

fast and partitioned postglacial rebound of southwestern iceland located both on the mid atlantic ridge and above a mantle plume iceland is subject to horizontal and vertical motions many studies described these deformations in terms of rifting episodes that have combined both extensional tectonics and magmatism however few studies have described the glacio isostatic response induced by the retreat of the weichselian ice cap the melting of this ice cap induced a postglacial rebound for the whole of iceland that may be controlled by the geodynamic setting and the rheological layering of the lithosphere this study is devoted to 1 understanding the holocene rebound on the southwestern coast and 2 estimating the asthenosphere viscosity and depth beneath iceland two stages of holocene evolution were determined by means of gps profiles morphological observations and data compilation the first stage corresponds to a vertical uplift of 67 5 to 157 5 m it started at 10 000 years bp and ended at 8500 years bp implying uplift rates between 4 5 and 10 5 cm a it was a quick isostatic response to the fast ice retreat the second stage had vertical motion of tens of meters with a probable tectonic origin and started at 8500 years bp the uplift rate is 1 to 2 orders of magnitude slower than the one during the first stage uplift partitioning during the first stage was controlled by the thermal state of the lithosphere the highest geothermal flux inducing the maximum uplift rates the relaxation time for uplift provides a viscosity estimate of 5 4 5 8 1019 pa s for the asthenosphere this value is similar to those determined for glacial areas in different continental contexts however the flexural wavelength indicates a shallower asthenosphere than that occurring in continental domains therefore this study highlights a coupling between the thermal structure of the icelandic asthenosphere and the glacial rebound

surface sediment diatom distribution and holocene paleotemperature variations in the greenland iceland and norwegian sea one hundred and four surface sediment samples and two piston cores from the greenland iceland and the norwegian gin sea hopkins 1988 were analyzed diatoms were common to abundant in most surface sediment samples and throughout the holocene q mode factor analysis allowed the definition of six significantly different floral assemblages which explained 91 7 of the total variance mapping of the six factors showed their close affinity to hydrographic regimes these are the norwegian atlantic current assemblage thalassionema nitzschioides paralia sulcata proboscia alata arctic water assemblage thalassiosira gravidaspores sea ice assemblage nitzschia grunowii nitzschia cylindra thalassiosira hyalina arctic norwegian waters mixing assemblage rhizosolenia hebetata f semispina rhizosolenia borealis atlantic assemblage thalassiosira oestrupii and norwegian arctic waters mixing assemblage thalassiosira gravida vegetative cells transfer functions gint2 relating factor distributions to winter february and summer august surface water temperatures were generated the transfer functions have a standard error of estimate of 1 5 c august and 1 0 c february downcore studies of core 52 43 from the norwegian basin and core 57 5 from the iceland plateau revealed diatom abundance and sea surface paleotemperature trends in the area during the holocene the first appearance of diatoms in cores 52 43 and 57 5 occurs within the vedde ash layer 10 600 years b p and the saksunarvatn ash layer 9100 years b p respectively diatom abundances increase steadily throughout the pre boreal atlantic time to 25 and 35 million valves per gram dry sediment in the norwegian basin and iceland plateau cores respectively application of the temperature transfer functions gint2 to the two holocene records revealed higher than present sea surface temperatures during the boreal atlantic chronozones for the iceland plateau and during the middle younger dryas sub boreal chronozones for the norwegian basin core temperatures decreased steadily since then with a slight increase to the present values both the iceland and the norwegian seas experienced a strong influx of temperate atlantic surface waters in the beginning of the holocene sea surface temperatures dropped steadily in the latter part of the holocene as the influx of the atlantic surface waters diminished

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

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

biostratigraphic evidence of the allerod younger dryas preboreal oscillation in northern iceland basal sediments of lake torfadalsvatn northern iceland record changes in terrestrial and limnic environments in the period 11 300 9000 14c yr b p these changes were probably forced by climate and connected with displacements of the marine polar front and sea ice margin pollen spores green algae pediastrum saturation isothermal remanent magnetization and carbon content of the basal sediments provide the first detailed biostratigraphic record of the last glacial interglacial transition in iceland during the first pioneer phase beginning at ca 11 300 14c yr b p grasses and fell field herbs became established and lake productivity was very low at ca 10 900 14c yr b p climatic and soil conditions became favorable for shrubs and dwarf shrubs this change together with increased limnic productivity clearly indicates long seasons without ice cover in the sea immediately north of iceland a return to a colder climate younger dryas probably in connection with a southward displacement of the marine polar front occurred by 10 600 14c yr b p shrub and dwarf shrub vegetation disappeared and limnic productivity diminished a second pioneer vegetation phase dominated by oxyria rumex and grasses was initiated by a change to longer seasons without sea ice at ca 9900 14c yr b p this warming is also evident as a contemporaneous increase in lake productivity after ca 9400 14c yr b p the reestablishment of dwarf shrub heaths and very high limnic productivity indicate further warming

the dynamics of the antarctic circumpolar current abstract the dynamics of the antarctic circumpolar current acc in a near eddy resolving model of the southern ocean fram are investigated a streamwise coordinate system is used rather than a more conventional approach of considering zonally averaged quantities the motivation for this approach is the large deviation from a purely zonal flow made by the current comparisons are made with a zonal mean analysis of the same model it is found that the topographic form drag is the main sink of the momentum that is input by the wind however in contrast to a zonal mean analysis other terms namely horizontal mixing bottom friction and advection of momentum are no longer negligible the total effect of transient eddies is to produce a drag on the mean flow again in contrast to the zonally averaged case the vertical penetration of stress is considered a generalized formula is derived for the interfacial form stress averaged along a convoluted path and that includes nonquasigeostrophic effects the i

10be ages of late pleistocene deglaciation and neoglaciation in the north central brooks range arctic alaska we present a chronology of late pleistocene deglaciation and neoglaciation for two valleys in the north central brooks range alaska using cosmogenic 10be exposure dating the two valleys show evidence of ice retreat from the northern range front before 16 15 ka and into individual cirques by 14 ka there is no evidence for a standstill or re advance during the lateglacial period indicating that a glacier advance during the younger dryas if any was less extensive than during the neoglaciation the maximum glacier expansion during the neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4 6 0 5 and 2 7 0 2 cal ka bp both moraine ages agree with previously published lichen inferred ages and confirm that glaciers in the brooks range experienced multiple advances of similar magnitude throughout the late holocene the similar extent of glaciers during the middle holocene and the little ice age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as neoglaciation progressed copyright 2012 john wiley sons ltd

geomorphology and the little ice age extent of the drangajokull ice cap nw iceland with focus on its three surge type outlets abstract detailed geomorphological maps from the forefields of three surging outlets of the drangajokull ice cap northwest iceland are presented the maps are based on field studies in 2011 2013 high resolution orthorectified aerial photographs recorded in 2005 2006 and airborne lidar data from 2011 the maps cover an area of about 40 60 km2 each furthermore we present an overview map that covers the area surrounding the drangajokull ice cap landforms and sediments were manually registered in a geographic information system esri arcgis 10 we mapped glacial landforms such as flutes ice sculpted bedrock hummocky moraine kame terraces and moraines fluvial landforms include outwash plains sandur pitted sandur and eskers in addition raised beaches were mapped the little ice age lia maximum extent of drangajokull and its outlet glaciers are fingerprinted by surficial till deposits and freshly glacially scoured bedrock sediments distal to the lia deposits were recorded and consist mainly of late weichselian and early holocene sediments and locally weathered bedrock periglacial activity is demonstrated by patterned ground mainly occurring on the 500 700 m high plateaux and three rock glaciers at least 3 4 surge events are described from each of the outlet glaciers occurring over the last three centuries in contrast to most other surge type outlets from icelandic ice caps the drangajokull outlets are confined within valleys which affect the forefield geomorphology glaciofluvial landforms moraines and a thin sheet of till with numerous boulders are characteristic for the forefields of the drangajokull outlets

icelandic permafrost dynamics since the last glacial maximum model results and geomorphological implications abstract iceland s periglacial realm is one of the most dynamic on the planet with active geomorphological processes and high weathering rates of young bedrock resulting in high sediment yields and ongoing mass movement permafrost is discontinuous in iceland s highlands and mountains over c 800 m a s l and sporadic in palsa mires in the central highlands during the late pleistocene and holocene iceland s periglacial environment varied considerably in time and space dominated by glacial fluctuations and periglacial processes to evaluate the dynamics of permafrost in iceland since the last deglaciation we use the output of a coupled climate ice sheet model to force a transient permafrost model cryogrid 2 from the last glacial maximum lgm through to the present we find that permafrost was widespread across the deglaciated areas of western northern and eastern iceland after the lgm and that up to 20 of iceland s terrestrial area was underlain by permafrost throughout the late pleistocene this influenced geomorphological processes and landform generation the early collapse of the marine based ice sheet together with the aggradation of permafrost in these zones initiated the formation of abundant and now relict rock glaciers across coastal margins permafrost degraded rapidly after the younger dryas with a marked impact on slope stability permafrost that formed during the little ice age is again thawing rapidly and an escalation in slope failure and mass movement might be currently underway our study demonstrates that large regions of iceland have been underlain by permafrost for millennia facilitating landform development and influencing the stability of steep slopes

migration of crude oil from the smackover source rock to jurassic and cretaceous reservoirs of the northern gulf rim abstract migration of distinctive crude oils from the upper jurassic smackover source rock across the northern gulf rim began at various times during the cretaceous regional source rock differences resulted in two compositional subfamilies of smackover crude oils type i crude oils in upper smackover reservoirs of east texas arkansas louisiana and mississippi reflect an origin from algal derived kerogen deposited in an anoxic environment type ii crude oils in upper smackover reservoirs of alabama and florida reflected an origin from kerogen preserved in a less anoxic environment with a terrestrial component comparison of molecular and carbon isotopic compositions of crude oils suggests that vertical migration of type i smackover crude oils charged many overlying upper jurassic lower cretaceous and upper cretaceous reservoirs some lateral migration to cretaceous reservoirs north of the updip limit of the smackover formation also occurred both type i smackover crude oils and geochemically dissimilar cretaceous sourced oils are found in upper cretaceous tuscaloosa and woodbine reservoirs because of impermeable barriers to migration especially in alabama vertical migration of type ii crude oils was less significant

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

the n and w iceland shelf insights into last glacial maximum ice extent and deglaciation based on acoustic stratigraphy and basal radiocarbon ams dates abstract we present 32 ams radiocarbon dates collected from sediments obtained during cruises of css hudson 1993 rv jan mayen 1996 and bjarni saemundsson 1997 the radiocarbon dates were obtained on samples from the basal part of sediment cores collected across an area between 64 and 67 n and 18 29 w core sites were based on 3 5 khz acoustic subbottom surveys the 3 5 khz subbottom profiles indicate that several of the troughs contain 30 m of quaternary sediment at many sites the acoustic surveys suggest the presence of one or more strong reflectors which can be traced over extended areas 100 km of the seafloor these may represent large scale volcanic ash falls such as the vedde ash and its correlatives as well as other regionally significant tephras we report dates from seven areas 1 northern troughs eyjafjardarall hunafloadjup and reykjafjardarall 2 hunafloi area and inner shelf and fjords 3 djupall area 4 isafjardardjup area 5 kolluall 6 western shelf break and slope and 7 jokuldjup the dates range in age from marine isotope stages 3 1 five cores have basal dates 16 ka and thus provide information on the timing and environments during the deglaciation several dates of 12 ka indicate that the inner shelf may have been largely ice free by that time estimates of average sediment accumulation rates vary between 4 and 90 cm kyr with modal estimates of 30 40 cm kyr

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

a 300 year surge history of the drangajokull ice cap northwest iceland and its maximum during the little ice age over the last 300 years each of the three surge type outlet glaciers of the drangajokull ice cap in northwest iceland has surged 2 4 times there is valuable historical information available on the surge frequencies since the little ice age lia maximum because of the proximity of the surging outlets reykjarfjar arjokull leirufjar arjokull and kaldalonsjokull to farms and pastures and monitoring of these glaciers since 1931 we have reconstructed the surge history of the drangajokull ice cap based on geomorphological mapping sedimentological studies and review of historical records geomorphological mapping of the glacier forefields reveals twice as many end moraines as previously recognized this indicates a higher surge interval than earlier perceived a clear relationship between the surge interval and climate cannot be established surges were observed more frequently during the 19th century and the earliest 20th century compared with the relatively cool 18th century and the late 20th century

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

glacial isostatic adjustment and the viscosity structure underlying the vatnajokull ice cap iceland we examine the dependence of glacial isostatic adjustment gia due to changes in the vatnajokull ice cap iceland on the underlying viscosity structure iceland offers a unique case study for gia research with a thinner elastic lithosphere underlain by a low viscosity zone or asthenosphere as opposed to regions such as fennoscandia or north america described by a thicker lithosphere while not necessarily featuring an asthenosphere

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

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

isopycnal averaging and the residual mean circulation abstract the zonally averaged circulation in the atmosphere or ocean can be misleading if the averaging is performed at constant height in the ocean there is apparently anomalously large diapycnal motion forming the so called deacon cell the atmospheric equivalents are the ferrel cells there are two zonal averaging techniques commonly used to avoid these spurious cells one involves averaging at constant density and this technique has been used in both fluids the other technique which has so far been applied only in the atmosphere involves taking into account perturbation correlation terms to form the residual mean circulation using a taylor series expansion we show that these apparently dissimilar techniques are formally equivalent at leading order in perturbation amplitude the equivalence is demonstrated using output from the fram southern ocean numerical model

similarities of the deacon cell in the southern ocean and ferrel cells in the atmosphere the meridional circulation in the ocean and the atmosphere when averaged over longitude and time at constant height shows a number of cells most of these appear as direct circulations with ascent in response to forcing which reduces the density there are several indirect circulations particularly the deacon cell in the southern ocean and the ferrel cells in the mid latitude atmosphere which appear to act against the mean density gradient in regions of no apparent mean density forcing when the zonal mean circulation is calculated in density coordinates both the deacon cell and the ferrel cells disappear a transformation of the zonal mean circulation as a function of height is used to give the residual mean circulation which is remarkably similar to the zonal mean circulation in density coordinates in both the southern ocean and the atmosphere this shows that the existence of the deacon and ferrel cells is the result of correlations of zonal variations of density and meridional flow and not of zonal mean density forcing zonal variations associated with the time mean eddies in the southern ocean are the main contributors to the deacon cell while correlations in transient weather systems are the major factor leading to ferrel cells

geology of the heimaey volcanic centre south iceland early evolution of a central volcano in a propagating rift geology of the heimaey volcanic centre south iceland early evolution of a central volcano in a propagating rift

a review of the late pleistocene stratigraphy of reykjavik iceland abstract the research history and geological problems of the stratigraphy of late pleistocene rocks in reykjavik iceland are reviewed new data are presented on the stratigraphy and palaentology of the sedimentary record the reykjavik sequence rests unconformably on reversed polarity rocks of early pleistocene age and includes tillites as well as marine mudrocks and sandstones terrestrial diamictites conglometrates sandstones and lignites these rocks are exposed along the coasts of reykjavik and have also been penetrated by several boreholes the lithostratigraphy climatic indicators and available dates indicate that the weichselian glaciation of the area was preceded by an ice free interval with climate that was comparable to the present one in south iceland the so called fossvogur beds and deposits in seltjarnarnes indicate three glaciations of the area after the last interglacial

modelling the southern extent of the last icelandic ice sheet a three dimensional time dependent numerical ice sheet model is used to investigate the southern extent of the last icelandic ice sheet since the last glacial maximum lgm ca 20 000 14c yr bp ice development over southern iceland is forced using a linear relationship between mass balance and altitude based on observations over solheimajokull a southern outlet glacier of the m rdalsjokull ice cap a continentality factor is introduced that raises inland equilibrium line altitudes elas and also slackens the mass balance altitude gradient driving the model with this calibration the present day ice distribution can be reconstructed growth from ice free to total ice cover is assessed and the sensitivity of ice extent to ela change is shown to be non linear the model indicates that an ela lowering of 500 m consistent with a ca 5 c temperature depression for southern iceland at the lgm would enable glacier ice to cover the whole land surface within the modelled area and inundate any putative ecological refugia modelling with a 300 m ela depression consistent with previous reconstructions of younger dryas yd 10 000 11 000 14c yr bp ice extent indicates that the principal outcrops of the solheimar ignimbrite were glaciated at this time suggesting that an origin during this stadial and a correlation with north atlantic ash zone i vedde ash is problematic copyright 2003 john wiley sons ltd

coupled response of the late glacial climatic shifts of northwest europe reflected in greenland ice cores evidence from the northern north sea the climatic regimes of the land areas adjacent to the north sea are controlled by the influx of atlantic water north of the british isles and into the north sea a high resolution record from the norwegian channel off western norway covering the past 15 ka 14 c shows that prior to the younger dryas there were three periods of sea surface conditions there similar to those of the present interspersed with arctic conditions these changes corresponding to an increase of approx 5 c in summer sea surface temperatures took place on the scale of

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

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

the north atlantic atmosphere sea surface 14c gradient during the younger dryas climatic event abstract we attempt to quantify the 14c difference between the atmosphere and the north atlantic surface during a prominent climatic period of the last deglaciation the younger dryas event yd our working hypothesis is that the north atlantic may have experienced a measurable change in 14c reservoir age due to large changes of the polar front position and variations in the mode and rate of north atlantic deep water nadw production we dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere sea surface 14c gradient we selected terrestrial vegetal macrofossils and planktonic foraminifera neogloboquadrina pachyderma left coiling mixed with the same volcanic tephra the vedde ash bed which occurred during the yd and which can be recognized in north european lake sediments and north atlantic deep sea sediments based on ams ages from two norwegian sites we obtained about 10 300 yr bp for the atmospheric 14c age of the volcanic eruption foraminifera from four north atlantic deep sea cores selected for their high sedimentation rates 10 cm kyr 1 were dated by ams 21 samples for each core the raw 14c ages assigned to the ash layer peak is significantly older than the 14c age obtained on land part of this discrepancy is due to bioturbation which is shown by numerical modelling nevertheless after correction of a bioturbation bias the mean 14c age obtained on the planktonic foraminifera is still about 11 000 11 100 yr bp the atmosphere sea surface 14c difference was roughly 700 800 yr during the yd whereas today it is 400 500 yr a reduced advection of surface waters to the north atlantic and the presence of sea ice are identified as potential causes of the high 14c reservoir age during the yd

late quaternary glacial and deglacial history of eastern vestfirdir iceland using cosmogenic isotope 36cl exposure ages and marine cores the late glacial and deglacial history of vestfirdir nw iceland is interpreted from terrestrial field based evidence and compared with marine cores and seismic studies understanding the timing of deglaciation is complicated by a lack of dateable organic material on land uncertainties associated with interpretation of diamictons and ambiguities in radiocarbon dating new 36cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice free by approximately 20 ka deglaciation of the valleys followed boulders from the crest of an end moraine in the sela river valley have a mean 36cl age of 14 6 ka 0 8 ka n 4 and the outermost moraine in the valley adjacent to kaldalonjokull has a mean 36cl age of 11 7 ka 0 9 ka n 2 tephrochronology provides a link between the terrestrial and marine sequences around vestfirdir the vedde ash ca 12 k cal yr bp is present in some offshore cores but it is absent from terrestrial sites suggesting that its distribution provides a constraint on ice extent during the younger dryas the saksunarvatn ash 10 2 0 6 k cal yr bp confirmed by geochemical analyses and radiocarbon dating is present in at least three terrestrial locations on eastern vestfirdir and in many cores from the fjords and shelf which constrains early holocene ice extent copyright 2006 john wiley sons ltd

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

an ash fall within the loch lomond stadial cores recovered from the witch ground basin central north sea and the northern rockall trough near the wyville thomson ridge have been found to contain volcanic glass shards these have been correlated with the vedde ash bed of western norway which has an age of 10 600 f 60yr bp and with north atlantic ash zone 1 this is the first time that this important chrono stratigraphic marker has been identified on the uk continental shelf and it is suggested that it might also be present in northern scotland if so it would be a useful tool in the correlation of terrestrial lacustrine and marine sequences of the loch lomond stadial journal of quaternary science

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

holocene and latest pleistocene climate and glacier fluctuations in iceland abstract multiproxy climate records from iceland document complex changes in terrestrial climate and glacier fluctuations through the holocene revealing some coherent patterns of change as well as significant spatial variability most studies on the last glacial maximum and subsequent deglaciation reveal a dynamic iceland ice sheet iis that responded abruptly to changes in ocean currents and sea level the iis broke up catastrophically around 15 ka as the polar front migrated northward and sea level rose indications of regional advance or halt of the glaciers are seen in late allerod early younger dryas time and again in preboreal time due to the apparent rise of relative sea level in iceland during this time most sites contain evidence for fluctuating tidewater glacier termini occupying paleo fjords and bays the time between the end of the younger dryas and the preboreal was characterized by repeated jokulhlaups that eroded glacial deposits by 10 3 ka the main ice sheet was in rapid retreat across the highlands of iceland the holocene thermal maximum htm was reached after 8 ka with land temperatures estimated to be 3 c higher than the 1961 1990 reference and net precipitation similar to modern such temperatures imply largely ice free conditions across iceland in the early to mid holocene several marine and lacustrine sediment climate proxies record substantial summer temperature depression between 8 5 and 8 ka but no moraines have been detected from that time termination of the htm and onset of neoglacial cooling took place sometime after 6 ka with increased glacier activity between 4 5 and 4 0 ka intensifying between 3 0 and 2 5 ka although a distinct warming during the medieval warm period is not dramatically apparent in icelandic records the interval from ca ad 0 to 1200 is commonly characterized by relative stability with slow rates of change the literature most commonly describes little ice age moraines ca ad 1250 1900 as representing the most extensive ice margins since early holocene deglaciation with temperature depressions of 1 2 c compared to the ad 1961 1990 average steep north south and west east temperature gradients are reconstructed in the holocene records of iceland suggesting a strong maritime influence on the terrestrial climate of iceland

an event stratigraphy for the last termination in the north atlantic region based on the greenland ice core record a proposal by the intimate group it is suggested that the grip greenland ice core should constitute the stratotype for the last termination based on the oxygen isotope signal in that core a new event stratigraphy spanning the time interval from ca 22 0 to 11 5 k grip yr bp ca 19 0 10 0 k 14 c yr bp is proposed for the north atlantic region this covers the period from the last glacial maximum through termination 1 of the deep ocean record to the pleistocene holocene boundary and encompasses the last glacial late glacial of the traditional northwest european stratigraphy the isotopic record for this period is divided into two stadial episodes greenland stadials 1 gs 1 and 2 gs 2 and two interstadial events greenland interstadials 1 gi 1 and 2 gi 2 in addition gi 1 and gs 2 are further subdivided into shorter episodes the event stratigraphy is equally applicable to ice core marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon dated chronostratigraphy that has been used hitherto 1998 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

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation