dinoflagellate cyst assemblages as tracers of sea surface conditions in the northern north atlantic arctic and sub arctic seas the new n 677 data base and its application for quantitative palaeoceanographic reconstruction the distribution of dinoflagellate cyst dinocyst assemblages in surface sediment samples from 677 sites of the northern north atlantic arctic and sub arctic seas is discussed with emphasis on the relationships with sea surface parameters including sea ice cover salinity and temperature of the coldest and warmest months difficulties in developing a circum arctic data base include the morphological variation within taxa e g operculodinium centrocarpum islandinium cezare and polykrikos sp which probably relate to phenotypic adaptations to cold and or low salinity environments sparse hydrographical data together with large interannual variations of temperature and salinity in surface waters of arctic seas constitute additional limitations nevertheless the use of the best analogue technique with this new dinocyst data base including 677 samples permits quantitative reconstruction of sea surface conditions at the scale of the northern north atlantic and the arctic domain the error of prediction calculated from modern assemblages is 1 3 ca nd 1 8 c for the temperature of february and august respectively 1 8 for the salinity and 1 5 months yr 1 for the sea ice cover application to late quaternary sequences from the western and eastern subpolar north atlantic labrador sea and barents sea provide reconstructions compatible with those obtained using the previous dinocyst data base n 371 which mainly included modern data from the northern north atlantic copyright 2001 john wiley sons ltd journal of quaternary science

formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

accelerator mass spectrometer ages for the younger dryas event in atlantic canada abstract in atlantic canada bulk sediment dates for the onset of a late glacial cooling widely regarded as the younger dryas event are highly variable ranging from 14 300 270 to 10 800 100 yr b p we present the first accelerator mass spectrometer ams 14c dates from atlantic canada at or close to the boundaries of this event from six sites in new brunswick and nova scotia the mean of five dates places the onset of this cooling at ca 10 770 yr b p the inclusion of a sixth perhaps anomalously old date changes the mean to 10 880 yr b p the termination averages three dates ca 10 000 yr b p these dates place the timing of the younger dryas event in atlantic canada closer in line with the traditional chronozone boundaries of 11 000 and 10 000 yr b p in northwest europe

paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

why permafrost rocks become unstable a rock ice mechanical model in time and space in this paper we develop a mechanical model that relates the destabilisation of thawing permafrost rock slopes to temperature related effects on both rock and ice mechanics and laboratory testing of key assumptions is performed degrading permafrost is considered to be an important factor for rock slope failures in alpine and arctic environments but the mechanics are poorly understood the destabilisation is commonly attributed to changes in ice mechanical properties while bedrock friction and fracture propagation have not been considered yet however fracture toughness compressive and tensile strength decrease by up to 50 and more when intact water saturated rock thaws based on literature and experiments we develop a modified mohr coulomb failure criterion for ice filled rock fractures thatincorporates fracturing of rock bridges friction of rough fracture surfaces ductile creep of ice and detachment mechanisms along rock ice interfaces novel laboratory setups were developed to assess the temperature dependency of the friction of ice free rock rock interfaces and the shear detachment of rock ice interfaces indegrading permafrost rock mechanical properties may control early stages of destabilisation and become more important for higher normal stress i e higher magnitudes of rock slope failure ice mechanical properties outbalance the importance of rock mechanical components after the deformation accelerates and are more relevant for smaller magnitudes the model explains why all magnitudes of rock slope failures can be prepared and triggered by permafrost degradation and is capable of conditioning long paraglacial response times here we present a synoptic rock and ice mechanical model that explains the mechanical destabilisation processes operating in warming permafrost rocks

improved schmidt hammer exposure ages for active and relict pronival ramparts in southern norway and their palaeoenvironmental implications abstract eight pronival protalus ramparts from alpine southern norway were dated using schmidt hammer exposure age dating shd based on local high precision linear calibration equations shd ages were 1355 1240 to 815 1000 years for three active ramparts and 8730 1050 to 14 635 1060 years for five relict ramparts different parts of the same rampart yielded ages that were in generally good agreement r value frequency distributions enabled the identification single age and mixed age boulder populations and the differentiation of active and relict rampart surfaces the relict ramparts are located outside younger dryas glacier limits and probably formed over a period of 6000 years between deglaciation following the last glacial maximum of the late weichselian 18 000 years ago and the end of the younger dryas 11 700 years ago at that time glacial debuttressing and permafrost degradation apparently enhanced the release of rock debris from rock faces to the ramparts the active ramparts which are located in areas deglaciated after the younger dryas are relatively uncommon in the study area due to diminished paraglacial effects and limited debris supply associated with seasonally frozen ground during the holocene thus the legacy of glaciers glacier permafrost interaction and the specific type of periglacial environment must all be considered when assessing the palaeoenvironmental and palaeoclimatic significance of pronival ramparts

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

the subglacial thermal organisation sto of ice sheets abstract this paper examines ice sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid latitude ice sheets the laurentide cordilleran fennoscandian and british irish ice sheets we compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary antarctic ice sheet inferred from radarsat 1 antarctic mapping project ramp data the evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice dynamical components that collectively define the subglacial thermal organisation sto of ice sheets these ice dynamical components are frozen bed patches ice streams ice stream tributaries and lateral shear zones frozen bed patches appear at a wide range of spatial scales spanning four orders of magnitude in some areas frozen bed zones comprise large proportions of the bed e g near the ice divide in continental areas whilst in other areas they constitute isolated islands in areas dominated by thawed bed conditions ice streams narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow are also common features of quaternary ice sheets tributaries to ice streams flow at velocities intermediate between full ice stream and sheet flow and may divert ice drainage from one primary ice stream corridor to an adjacent one sharp lateral boundaries between landforms indicate sliding and non sliding conditions respectively these lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed bed ice streams and intervening frozen bed areas we use the landform evidence in the area around great bear lake canada to trace the evolution of an ice stream web through time demonstrating that frozen bed patches are integral components of this complex system we conclude that frozen bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams

multiple causes of the younger dryas cold period the last deglaciation was interrupted by a cool period known as the younger dryas numerical simulations suggest that the cold interval was the result of a combination of changes in ocean and atmospheric circulation and reduced radiative forcing

biological responses to rapid climate change at the younger dryas holocene transition at krakenes western norway a fine resolution pollen stratigraphical study supported by macrofossil analysis has been made at krakenes lake western norway through the younger dryas holocene transition and the early holocen

a midge based late glacial temperature reconstruction from southwestern nova scotia we present a quantitative reconstruction of the thermal regime spanning the late glacial period of nova scotia 14 700 to 11 600 bp as inferred by analyzing fossil midges from a small lake lac a magie in southwestern nova scotia the gs 1 event equivalent to the younger dryas dating from 12 700 to 11 600 bp in maritime canada was marked by a 5 c decline in inferred mean july surface water temperatures and a 15 drop in organic content previous pollen and plant macrofossil analyses of this site demonstrate a response of vegetation to gs 1 cooling these data coupled with a midge inferred temperature reconstruction from a nearby site suggest that late glacial climate change was less pronounced in southern nova scotia than in other sites in maritime canada and adjacent eastern north america

schmidt hammer exposure age dating shd of snow avalanche impact ramparts in southern norway approaches results and implications for landform age dynamics and development schmidt hammer exposure age dating shd was applied to the problem of dating the diachronous surfaces of five distal river bank boulder ramparts deposited by snow avalanches plunging into the jostedola and sprongdola rivers in the jostedalsbreen region of southern norway approaches to local high precision linear age calibration which controlled in different ways for boulder roundness were developed the mean age shdmean and the maximum age shdmax of surface boulders were estimated for whole ramparts crests and distal fringes interpretation was further assisted by reference to r value distributions shdmean ages with 95 confidence intervals ranged from 520 270 years to 5375 965 years whereas shdmax ages expected to be exceeded by 5 of surface boulders ranged from 675 to 9065 years shd ages from the jostedola ramparts tended to be older than those associated with the sprongdola rampart crests were younger than the respective distal fringes and use of relatively rounded boulders yielded more consistent shd ages than angular boulders the shdmean ages indicate differences in recent levels of snow avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and in smaller numbers on the distal fringes shdmax ages provide minimum age estimates of rampart age i e the time elapsed since the ramparts began to form and suggest that at least some of the ramparts have been developing since the early holocene copyright 2015 john wiley sons ltd

rapid and widespread vegetation responses to past climate change in the north atlantic region ongoing anthropogenic perturbations to the atmosphere and biosphere increase the risk of future abrupt changes in the climate system and generate concern about the ability of natural ecosystems to respond to rapid climate change study of past climatic events and biotic responses can inform us about potential future change qualitatively fast local responses of plant taxa to abrupt late glacial climate oscillations have been reported from individual records and attributed to short migration distances in areas of high topographic relief by using quantitative time series analyses we show that vegetation responses to late glacial climate change around the north atlantic were rapid and widespread and occurred in areas of differing relief cross correlation analysis of 11 high resolution lacustrine records in eastern north america and europe indicates vegetation response times consistently of 200 yr and often 100 yr despite regional differences in physiography and species composition vegetation lags of 200 yr confirm theoretical predictions and the apparently tight coupling between vegetation and atmosphere suggests that recent climatic trends may already have begun to affect plant population abundances and distributions

late quaternary paleohydrology of the gulf of st lawrence quebec canada based on diatom analysis abstract postglacial sediments from three cores raised from the gulf of st lawrence along the path of the laurentian channel were analyzed for diatoms a sequence of four distinct zones was defined from oldest to youngest 1 characterized by low diatom concentrations this zone is mainly represented by heavily silicified species delphineis surirella stephanopyxis turris coscinodiscus radiatus and paralia ornata that were probably deposited by glacial drift in a glaciomarine environment from about 18 000 to 14 000 years bp 2 this postglacial sedimentation zone deposited around 13 000 years bp is marked by high diatom concentrations with cold water marine species thalassiosira antarctica resting spores and porosira glacialis the upper part of the zone suggests a gradual warming with the appearance of temperate water species bacterosira bathyomphala and chaetoceros spp both resting spores and vegetative cells 3 an important cooling of surface temperatures is noticed by the resurgence of cold species porosira glacialis thalassiosira antarctica resting spores and thalassiosira hyalina this zone is associated with the younger dryas chronozone dated from 10 800 to 10 300 years bp this interval is also characterized by two marked freshwater pulses coming from the outflow of laurentide ice sheet meltwater on the surface layer of the goldthwait sea although well defined in the northwestern gulf area core 90 031 015 the influence of this meltwater decreases considerably or even disappears in cabot strait core 89 007 111 and offshore core 90 031 044 evidence of reduced postglacial glacial runoff on surface water supports the conclusion that it could not have generated the younger dryas cooling episode 4 the diatom assemblages from 10 000 years bp through recent correspond to the progressive establishment of modern like surface water conditions

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

rock control on microweathering of bedrock surfaces in a periglacial environment abstract microweathering of ice smoothed bedrock surfaces was investigated in the roldal area of hardanger plateau 60 southern norway postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces weathering processes are inferred from assessment of weathering rind formation surface hardness and the preservation of small scale glacial erosional features surface lowering rates for a range of metamorphic rocks vary from 0 05 to 2 20 mm ka 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments the mean rate of surface lowering at 0 55 mm ka 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution variations in bedrock microweathering can be explained by lithological variation amphibolite and mica rich bedrock surfaces experience greater denudation and weakening least weathering rind formation and abundant preservation of glacial striae despite greater surface lowering conversely quartz rich bedrock surfaces are most resistant to denudation and weakening but have greater weathering rind formation and fewer preserved striae postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity granular decomposition is manifest in the formation of weathering rinds analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion a conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages the model proposes that cyclic processes of in situ disintegration decomposition and erosion are at work the relative balance between these processes varies with lithology so that in more resistant quartz rich rocks the net effect is minimal surface lowering and accumulation of weathering rind in weaker amphibolitic and micaceous rocks the net effect is greater surface lowering and minimal accumulation of weathering rind the results of the research demonstrate the important influence of rock properties notably mineral composition in postglacial microweathering of crystalline bedrock in a periglacial environment

a review of multi proxy data for the younger dryas in atlantic canada abstract multi proxy data obtained from lake sediments and buried organic sequences is reviewed and discussed as evidence for the younger dryas cooling event in atlantic canada sedimentological studies indicate that lake basins were subject to increased erosion due to climate cooling while glacial and periglacial sediments overlying peats have been attributed to the effects of small younger dryas ice caps building up in highland areas of nova scotia pollen evidence from over 30 sites shows two broad patterns of lateglacial vegetation change in the region the younger dryas cooling caused the replacement of closed boreal forest by shrub tundra in southern new brunswick and central mainland nova scotia and the replacement of shrub tundra by herb tundra in central new brunswick northern nova scotia and newfoundland chironomid data indicate that the younger dryas was marked by a drop in summer lake surface water temperatures of ca 6 c while diatom data suggest that marked limnological changes also occurred based on ams 14c dates from terrestrial plant macrofossils of 8 sites the younger dryas event in atlantic canada lasted from ca 10 830 to 10 000 bp these dates match most of those from northwest and central europe suggesting that this climatic event affected the entire north atlantic region essentially simultaneously

cosmogenic nuclide exposure ages along a vertical transect in western norway implications for the height of the fennoscandian ice sheet 10 be and 26 al exposure ages for bedrock samples from a vertical transect at skala in western norway provide new constraints on the history of the fennoscandian ice sheet the weathered bedrock surface autochthonous block field mantling the summit of skala has an exposure age of 55 ka suggesting that this surface formed before the last glacial maximum 18 14 c ka or 21 calendar ka the block field is truncated by a glacial trimline at 1660 m above sea level glaciated bedrock below the trimline has an exposure age of 26 21 ka the range depends on assumptions about erosion rate ice therefore receded from this altitude at about the time of the last glacial maximum the 10 be age for bedrock immediately below a second lower trimline at skala suggests a glacial advance or stillstand at 18 13 ka consistent with previously documented readvances or stillstands at the western and southern margins of the ice sheet

the characteristics and significance of some lateglacial protalus ramparts in upland britain arcuate and linear protalus ramparts of inferred loch lomond stadial age are widespread in upland britain outside the limits of contemporaneous glaciers survey and analysis of the morphology of nine ramparts suggests that these may have formed at the foot of slowly thickening snowbeds with rockfall debris accumulating against their distal slopes and that snowbed melting at the end of the stadial was uninterrupted by prolonged periods of stability or renewed growth rampart sediments consist of poorly sorted assemblages of clasts with a variable infill of fines clast size and shape are strongly influenced by lithology but rampart clasts are characteristically more angular and slabbier than those of similar lithology in ice marginal moraines ramparts may also be distinguished from moraines by their location morphology lack of a true matrix of fines and absence of erratics and from talus foot rock glaciers in terms of their width and the absence of flow structures the mapped distribution of rampart altitudes across the scottish highlands displays a marked regional trend with the lowest features in the west and south and highest in the cairngorms this pattern mirrors that of reconstructed firn line altitudes of loch lomond stadial glaciers and is inferred to reflect a pronounced eastwards and northwards decline in snowfall during the stadial

exceptionally steep north south gradients in lake temperatures during the last deglaciation during the transition from the last glacial to the present interglacial climate late glacial period high summer insolation1 combined with the presence of the laurentide ice sheet is thought to have promoted the development of strong summer thermal gradients in north america south of the ice margin2 here we use palaeoecological methods to obtain quantitative evidence for the existence of these gradients our palaeoclimate reconstructions are based on water temperatures inferred from fossil assemblages of aquatic midge larvae in five lakes along a 240 km transect extending from central new brunswick canada to southeastern maine usa we show that the temperature gradient shifted during the killarney oscillation ko and younger dryas yd cooling events and that water temperature differences of 9 and 11 c existed over distances of 55 and 240 km respectively during parts of the late glacial period these gradients are much stronger than the current north south trends of lake summer surface water temperatures for these five lakes and for lakes across the northern tree line the rapid motion of such steep temperature gradients may have affected the progressive development of aquatic and terrestrial ecosystems in the region

rapid oceanic and atmospheric changes during the younger dryas cold period the younger dryas event which began approximately 12 900 years ago was a period of rapid cooling in the northern hemisphere driven by large scale reorganizations of patterns of atmospheric and oceanic circulation 1 3 environmental changes during this period have been documented by both proxy based reconstructions 3 and model simulations 4 but there is currently no consensus on the exact mechanisms of onset stabilization or termination of the younger dryas 5 8 here we present high resolution records from two sediment cores obtained from lake krakenes in western norway and the nordic seas multiple proxies from lake krakenes are indicative of rapid alternations between glacial growth and melting during the later younger dryas meanwhile reconstructed sea surface temperature and salinity from the nordic seas show an alternation between sea ice cover and the influx of warm salty north atlantic waters we suggest that the influx of warm water enabled the westerly wind systems to drift northward closer to their present day positions the winds thus brought relatively warm maritime air to northern europe resulting in rising temperatures and the melting of glaciers subsequent input of this fresh meltwater into the ocean spurred the formation of sea ice which forced the westerly winds back to the south cooling northern europe we conclude that rapid alternations between these two states immediately preceded the termination of the younger dryas and the permanent transition to an interglacial state the impact of freshwater pulses released from northern hemisphere ice sheets on the north atlantic meridional overturning circulation has been suggested as a likely mechanism for the younger dryas cooling 7 11 in addition a responsive sea ice cover has been proposed as a mechanism that could rapidly alter the heat exchange between the ocean and atmosphere during the last glacial period 12 13 the roles of the ocean and the atmosphere in triggering the climate shifts around the younger dryas are much discussed 9 these hypotheses are difficult to resolve partly because the temporal resolution of most palaeoclimate archives is too coarse to enable the anatomy of the younger dryas stadial to be adequately described 14 to address these questions we here present a lake sediment record at sub annual resolution together with new data on the sea surface conditions of the norwegian atlantic current nwac throughouttheyoungerdryasstadial fig 1

changes in north atlantic radiocarbon reservoir ages during the allerod and younger dryas estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late quaternary climate we radiocarbon dated marine shells and terrestrial plant remains deposited in two bays on norway s west coast between 11 000 and 14 000 years ago a time of large and abrupt climatic changes that included the younger dryas yd cold episode the radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early yd stabilized for 900 years and dropped by 300 years within a century across the yd holocene transition

a late glacial holocene palaeoecological record from pye lake on the eastern shore of nova scotia canadageological survey of canada contribution 20080395 pollen and chironomid analyses and radiocarbon dating at pye lake on the eastern shore of nova scotia are used to outline the vegetation and climatic history of the area the coast was deglaciated prior to 12 200 14c bp 14 300 cal bp and herbaceous tundra vegetation invaded the area midge inferred maximum summer surface water temperatures in the lake ranged between 9 and 11 c subsequent gradual warming to 18 c by 10 800 14c bp 12 725 cal bp favoured the migration of a variety of herbaceous and shrub taxa into the region rapid cooling to 10 c saw vegetation revert to herbaceous tundra communities this interval related to the younger dryas cold interval of the north atlantic and europe lasted until 10 000 14c bp 11 630 cal bp the climate then warmed again to conditions similar to those that prevailed immediately before onset of younger dryas cooling further warming saw successive tree species migrate into the area until by the mid holocene the forests contained most of the taxa preva

late quaternary paleoceanography of deep and intermediate water masses off gaspe peninsula gulf of st lawrence foraminiferal evidence radiocarbon dated benthonic foraminiferal zones in three cores provide new information on the evolution of the deep and intermediate water masses off gaspe peninsula the deglacial phase in the deep laurentian channel began before 14 000 bp and was characterized by low salinity 20 or alternating low salinity and saline 35 water this was followed by a cold saline phase which ended ca 13 500 bp and a salinity minimum 30 33 5 which began ca 12 100 bp between 8700 and 7900 bp the temperature and salinity of the deep water mass increased resulting in the modern deep water mass temperature 4 6 c salinity 34 5 34 9 at the end of the goldthwait sea episode the salinity of the deep water was apparently controlled by the meltwater flux from the ice front during the deglacial phase after the deglacial phase the characteristics of the deep water mass were determined by the composition of offshore water entering the laurentian channel runoff from the lake agassiz great lakes system does n

late glacial stratigraphy and history of the gulf of st lawrence reply the three dimensional configuration of the quaternary sediments in the gulf of st lawrence is described based on analysis of 8000 km of high resolution seismic reflection data complemented by anal

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

a multiproxy investigation of late glacial climate and vegetation change at pine ridge pond southwest new brunswick canada abstract pollen plant macrofossil chironomid and lithological analyses of late glacial sediment from pine ridge pond all indicate that the warming following deglaciation was punctuated on two separate occasions by a return to colder climes initially by a brief and moderate cold episode the killarney oscillation followed shortly by the younger dryas the killarney oscillation ams 14 c dated at between 11 290 and 10 960 yr b p is characterized by abrupt and simultaneous increases in betula birch pollen and betula glandulosa dwarf birch macrofossils and a decline in tree pollen the younger dryas is distinguished by the reversion of a short lived closed picea spruce forest to a prolonged forest tundra stage ca 10 820 to 9500 yr b p during which macrofossils of arctic alpine plants such as salix herbaces cassiope hypnoides armeria maritima and thalictrum alpinum make their sole late glacial appearance chironomid inferred summer surface water temperatures indicate a cooling of approximately 8 and 12 c during the killarney oscillation and younger dryas respectively and coarse sand analysis indicates increased erosion on the landscape during these same intervals

oxygen isotopes in fresh water biogenic opal northeastern us allerod younger dryas temperature shift the first oxygen isotope analysis of biogenic opal from lake sediments from the allerod younger dryas transition in a core from linsley pond connecticut gives an average estimate of a 6 c drop in temperature during the younger dryas this shift represents temperatures during the bloom season and may be less than the winter temperature drop the sharp transition itself with a duration of about 200 years suggests that the temperature decrease may have been as large as 12 c previous estimates of the allerod younger dryas temperature shifts are controversial and range from 3 20 c suggesting that further interdisciplinary research on the same samples is warranted

the younger dryas in palynological records from the northern northwest atlantic does the terrestrial record lag the marine and air records abstract major changes in both pollen and dinocyst assemblages are recorded during the younger dryas in bay of islands and are associated with large drops in air and sea surface temperatures and sea surface salinity the changes in vegetation are similar with those observed at other sites in newfoundland dinoflagellate cyst assemblages also show similar species succession as nearby sites from the gulf of st lawrence and laurentian channel the amplitude of changes in air temperature a 7 c drop is similar to those recorded in northeastern north america in the sea surface temperature dropped by 7 c salinity by 4 psu and the sea ice cover duration increased by 7 months sea surface and air temperatures started cooling 250 and 110 years before the start of the yd hence there is a 140 years delay between ocean and atmosphere a warming trend is seen in the marine record 310 years before the end of the yd while vegetation and air temperatures started recovering after the end of the event some 370 years later the major lithological and vegetation changes observed during the yd period in eastern north america might actually represent the full impacts of the cooling associated with the yd since the cooling trend actually started before the start of the yd period as defined by radiocarbon dates and pollen zones

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

a calendar age estimate of a very late younger dryas ice sheet maximum in western norway abstract we have established an accurate chronology in calendar years for the maximum phase of the younger dryas yd scandinavian ice sheet in western norway glaciomarine silt confidentially identified in shallow marine basins located was 1 2 km distal to a yd ice marginal delta due to the topography of this area the silt monitors faithfully the period when the ice sheet reached and remained at its maximum position in these basins the deposition of silt commenced 6 10 cm above the vedde ash bed ca 10 300 14 c yr bp or ca 12 000 cal yr bp according to calculated sedimentation rates of the deposits the deposition of silt started and thus the ice sheet reached its maximum 300 400 years after the vedde ash fall around 11 600 11 700 cal yr bp the ice sheet receded from its maximum position simultaneously with the increase of betula birch pollen at the yd holocene boundary ca 11 500 cal yr bp the duration of the yd glacial maximum of the scandinavian ice sheet in western norway was only about 100 200 years and is constrained within the 14 c plateau at 10 000 14 c yr bp the yd glacial maximum occurred extremely late in western norway later than elsewhere in scandinavia the result also demonstrates different response times for different glaciers small cirque glaciers farther north in western norway expanded to their maximum position very early in the yd whereas the ice cap at alfotbreen reached its maximum later but still before the vedde ash fall the ice sheet reached its maximum well after the vedde ash fall and only 100 200 years before the yd holocene boundary

the schmidt hammer as a relative age dating tool and its potential for calibrated age dating in holocene glaciated environments the schmidt hammer is a relatively cheap portable sturdy instrument with proven value over the last two decades or so in rapidly dating coarse inorganic deposits of diverse origins early views were that its dating role was limited to distinguishing recently exposed from much older typically either a few sites of possibly different ages or occasional older surfaces amongst many young sites were studied more recently calibration curves based on individual r value means from small numbers 2 4 of sites of known ages have been used to estimate the ages of undated sites we present schmidt hammer rebound r values from 28 little ice age and younger 23 preboreal and 7 younger dryas glaciated surfaces in southern norway in order first to test rigorously the robustness of the instrument as a relative age dating tool despite being obtained from different surfaces moraines glaciofluvial deposits and bedrock and varied metamorphic lithologies the r value overall means and 95 confidence intervals for the little ice age preboreal and younger dryas age categories respectively 60 0 1 6 41 6 1 4 and 34 2 2 0 are statistically significantly different only two outlying sites in the two younger age categories have overlapping confidence intervals demonstrating remarkable robustness in differentiating early and late holocene surfaces the distinction between preboreal and younger dryas sites with terminal dates 2000 years apart is less clear but still statistically significant though possibly partly because of enhanced weathering conditions at the predominantly well vegetated younger dryas sites second we examine the feasibility and desirability of controlling non age related factors including some previously considered critical instrument wear operator bias initial rock surface texture which emerge either as less important than previously argued or as relatively unimportant together with others previously unreported e g long term changes in lichen soil snow and vegetation covers third we investigate the potential for calibrated age dating by applying exploratory linear rates of r value decline to selected combinations of sites the results suggest that error limits of ca 700 to 1600 years should be achievable over the holocene timescale this improved dating capability however will require adequate numbers of site means not only for each age category used to define these curves but also for each set of test surfaces of the same ages recommendations are made for a suitable sampling protocol for developing further the schmidt hammer as a calibrated age dating tool

reduced meltwater outflow from the laurentide ice margin during the younger dryas the cause of the younger dryas cold event which interrupted the last deglaciation is still a matter of debate1 a prevalent hypothesis proposed by broecker et al 2 is that the abrupt climate change was driven by a decrease in the rate of north atlantic deep water production triggered by a sudden dilution of north atlantic surface water in response to the diversion of laurentide icesheet melt water from the mississippi drainage system to that of the st lawrence river here we investigate the feasibility of this triggering mechanism by reconstructing sea surface temperature salinity and sea ice cover records for the outlet of the gulf of st lawrence into the north atlantic ocean these reconstructions based on dinoflagellate cyst assemblages3 4 in sediment cores from the region show reduced meltwater runoff low temperatures and extensive sea ice cover during the younger dryas dated here between 10 800 and 10 300 bp meltwater pulses did occur before and after the younger dryas event as early as 11 700 bp during the development of the champlain sea in the st lawrence lowland and afterwards until 10 100 bp at the resolution of our salinity proxy 0 7 the meltwater pulses preceding the younger dryas did not affect sea surface salinity off the shelf break these constraint on the meltwater outflow through the st lawrence drainage system do not support the triggering mechanism of the broecker et al hypothesis2 unless the north atlantic thermohaline circulation is more sensitive to small salinity changes than most models suggest23

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

rapid climate change in the north atlantic during the younger dryas recorded by deep sea corals research on global climate change has increasingly focused on rapid century scale and decadal changes one such climate shift the younger dryas cooling event1 took place during the last deglaciation from 13 000 to 11 700 years bp climate records from greenland ice cores and north atlantic sediment cores show high frequency fluctuations implying significant 5 c shifts in temperature at this time taking place within 50 100 years ref 2 the origin of the younger dryas has recently been attributed to a reduction or cessation of deep water production in the north atlantic and a concurrent lessening of the heat flux from low latitudes3 4 the role of intermediate waters 1 000 2 000 m depth is less certain however because climate proxies for this ocean reservoir are rare and ambiguous here we report on the use of a new climate archive deep sea corals from orphan knoll 1 600m depth in the northwestern atlantic ocean the oxygen isotope ratios in the coral skeletons accurately dated by the 230th 234u chronometric method change markedly coincident with the initiation of the younger dryas suggesting that there were profound changes in intermediate water circulation at this time

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

the anatomy of a climatic oscillation vegetation change in eastern north america during the younger dryas chronozone century scale climate changes reshaped circulation patterns over the north atlantic and adjacent regions during the last glacialto interglacial transition here we show that vegetation across eastern north america shifted dramatically at the beginning and end of the younger dryas chronozone ydc 12 900 11 600 cal yr b p when changes in ocean circulation rapidly cooled and then warmed the north atlantic sea surface on both the site specific scale and the continental scale vegetation changed only gradually during the millennia before 15 000 13 000 cal yr b p and after 11 000 9000 cal yr b p the ydc but climate changes ca 12 900 and 11 600 cal yr b p altered the vegetation on both spatial scales within centuries plant associations changed and some taxa rapidly migrated hundreds of kilometers 300 km within b100 yr in limited regions near the north atlantic coast abrupt cooling ca 12 900 cal yr b p resulted in a return to earlier vegetation types elsewhere however the vegetation patterns during the ydc were distinct from those of both earlier and later intervals they indicate abrupt non reversing seasonal temperature changes that were probably related to atmospheric circulation changes during the ydc rather than to the direct influence of north atlantic sea surface temperatures atmospheric circulation patterns during the ydc were unique within the last 21 000 yr because of a unique combination of climate controls insolation ice sheet extent and atmospheric composition were significantly different from their full glacial states even when the north atlantic returned to near full glacial conditions the ydc vegetation patterns demonstrate 1 rapid ecological responsiveness to abrupt climate change and 2 spatially varied patterns of ydc climate change r 2002 elsevier science ltd all rights reserved

synchronized terrestrial atmospheric deglacial records around the north atlantic on the basis of synchronization of three carbon 14 c 14 dated lacustrine sequences from sweden with tree ring and ice core records the absolute age of the younger dryas preboreal climatic shift was determined to be 11 450 to 11 390 80 years before the present a 150 year long cooling in the early preboreal associated with rising delta 14 c values is evident in all records and indicates an ocean ventilation change this cooling is similar to earlier deglacial coolings and box model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the north atlantic heat conveyor although the younger dryas may have begun as an anomalous meltwater event

allerod younger dryas lake temperatures from midge fossils in atlantic canada remains of freshwater midges are abundant in lake sediments and their species distributions are closely related to the surface water temperature of lakes their distributions thus provide a powerful tool for paleoclimatology the distribution of species in a core from splan pond in atlantic canada indicates that there were abrupt transitions in late glacial temperatures between warm and cold states the transitions are correlative with the well known warm allerod and cold younger dryas events in europe these data thus confirm the inference from palynological data that these events affected regions on both sides of the atlantic

cooling in the gulf of st lawrence and estuary region at 9 7 to 7 2 14c ka 11 2 8 0 cal ka palynological response to the pbo and 8 2 cal ka cold events laurentide ice sheet air mass circulation and enhanced freshwater runoff abstract an examination of post younger dryas yd pollen stratigraphies in the gulf of st lawrence and st lawrence estuary region reveals features in the pollen records that represent breaks in the normal vegetation succession widespread vegetation suppression and a delay in migration of plant taxa between 9 7 and 7 2 14 c ka 11 2 and 8 0 cal ka the domination of alnus crispa at sites bordering the st lawrence estuary gulf region in gaspesie and northern new brunswick within this timeframe represents a diversion from the typical vegetation progression from picea and or populus or picea betula to pinus and or betula and signifies a shift to a cooler drier climate coinciding with the a crispa expansion and domination in that region was the contraction of picea populations in other areas in southwestern new brunswick and eastern and southeastern nova scotia picea was replaced by the first appearance of tree birch b papyrifera whereas in western and southwestern newfoundland picea gave way to a resurgence of shrub birch betula glandulosa the picea contraction and immediate resurgence of betula represents cooling and is reliably dated at 9720 110 14 c bp 10 800 11 240 cal bp in southwest newfoundland this first post yd episode of widespread cooling is correlated with the north atlantic preboreal oscillation pbo centered around 9650 14 c bp 10 900 11 180 cal bp in the adjacent great lakes region sites exposed to winds from the gulf of st lawrence in eastern new brunswick prince edward island and northern nova scotia show a lingering persistence of picea and delay in arrival of pinus to 8 0 and 7 7 14 c ka 9 0 and 8 4 cal ka yet pinus was dominant as early as 9 4 14 c ka 10 6 cal ka in southwestern new brunswick at the same time tundra vegetation persisted at high elevations in western and southwestern newfoundland only to be replaced by upslope migration of shrub birch heath by 8 14 c ka prolonged broad scale cooling to 8 14 c ka and to as late as 7 7 14 c ka extended up to 200 km inland in areas exposed to the st lawrence estuary and gulf region and was in response to strong cold dry anticyclonic winds coming off the retreating laurentide ice sheet in combination with enhanced freshwater runoff through the gulf of st lawrence the end of the period of prolonged cooling and onset of regional warming coincided with the diversion of western canada runoff and agassiz ojibway drainage to hudson bay and reduced effect or final break up of the laurentide ice sheet several sites document a subsequent cold shift that interrupted regional warming at 7650 to 7200 14 c bp 8400 to 8000 cal bp and which is variously represented by the suppression of pinus and resurgence of picea sometimes with a crispa quebec maritime region or by an abrupt decrease of picea and resurgence of betula western newfoundland this second post yd cool interval is equated with the 8200 cal bp cold event registered in the greenland ice isotopic record

a multi disciplinary study of deformation of the basaltic cover over fine grained valley fills a case study from eastern sardinia italy the pliocene to early pleistocene volcanic activity which generated the basaltic plateau of the orosei dorgali area in eastern sardinia led to the disruption of the local hydrographic network by damming some tracts of the fluvial valleys incised in the granite basement this resulted in the formation of lacustrine basins whose fine grained fills were partly interfingered and eventually covered by younger lava flows in the sw part of the plateau close to the galtelli village a number of unknown depressions locally named paules were formed in order to reconstruct their subsurface structure two electrical resistivity tomography surveys were carried out across these depressions the geophysical results which demonstrate the existence of a disrupted layered system were used to build a numerical geomechanical model that suggest the depressions originated by local collapses of the basaltic cover due to the compaction of the underlying fine grained valley fills

palynological records of red tide producing species in canada past trends and implications for the future abstract increases in red tides and other harmful algal blooms habs during the past 50 yr on both the atlantic and pacific coasts of canada suggest that global scale factors such as climate change and increased international shipping trade are the driving forces because the historical record is too short to understand the long term dynamics of habs the holocene history of harmful phytoplankton species was examined using ultra high resolution studies annual to decadal scale of dinoflagellate cysts as a proxy for red tide production paleoecological transfer functions were then applied to the cyst assemblage data to determine correlations with changes in sea surface temperature and salinity pacific records were obtained from varved marine sediments in saanich inlet british columbia and in the santa barbara basin off california comparison of annual cyst production and historical plankton data provides cyst theca ratios from which the magnitude of past bloom size can be evaluated the 10 500 yr pacific record clearly shows that the largest blooms correspond to cysts of protoceratium reticulatum and gonyaulax spinifera during the early holocene sporadic blooms of potentially toxic alexandrium spp lingulodinium polyedrum and gymnodinium spp also occurred from ca 7000 to 5000 yr bp and more frequently from ca 2000 to 3000 yr bp individual holocene blooms were up to 10 times larger than in the historical record but they almost always occurred sequentially without overlap of red tide species in pre historical times the bloom cycles started and stopped abruptly in 10 yr or less and they persisted for about 100 1000 yr in contrast the variability and near concurrence of species blooms in the modern past 60 yr record is unmatched in the past and suggests disequilibrium of the natural ecosystem structure atlantic records from la have and emerald basins on the scotian shelf are less precise because bioturbation limits time resolution to ca 25 yr however cyst abundances of cf alexandrium protoceratium reticulatum gonyaulax spinifera and lingulodinium polyedrum were also an order of magnitude larger in the early holocene where they correspond to a summer sea surface warming of 2 5 c lesser peaks also appear during the past 2000 yr where they apparently correspond to a slight increase in winter temperature there is no evidence of much lower salinity that would support stronger stratification the similarity of pre industrial age cyst records of red tide histories in the oceanographically different pacific and atlantic regions of canada indicates that climate change including surface temperature and storminess is the main driving force stimulating blooms this implies that habs will reoccur regardless of efforts to limit spreading however reduced pollution may decrease the hab diversity thereby stabilizing the population dynamics and increasing the predictability of bloom occurrences

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

wisconsinan late glacial environmental change in newfoundland a regional review the distribution of 75 lake and bog sites from which pollen stratigraphical evidence relevant to the late quaternary of newfoundland has been obtained is presented the detailed records of lithology pollen and diatoms supplemented by geochemical data are discussed for three of the sites southwest brook lake woody hill brook pond and leading tickles and interpretations made are based on vegetational history relative climatic changes and extent of ice cover radiocarbon data from 14 sites are summarised a summary chart of late glacial environmental changes including a qualitative palaeotemperature curve is provided

geochemical proxies of north american freshwater routing during the younger dryas cold event the younger dryas cold interval represents a time when much of the northern hemisphere cooled from 12 9 to 11 5 kiloyears b p the cause of this event which has long been viewed as the canonical example of abrupt climate change was initially attributed to the routing of freshwater to the st lawrence river with an attendant reduction in atlantic meridional overturning circulation however this mechanism has recently been questioned because current proxies and dating techniques have been unable to confirm that eastward routing with an increase in freshwater flux occurred during the younger dryas here we use new geochemical proxies mg ca u ca and 87sr 86sr measured in planktonic foraminifera at the mouth of the st lawrence estuary as tracers of freshwater sources to further evaluate this question our proxies combined with planktonic 18oseawater and 13c confirm that routing of runoff from western canada to the st lawrence river occurred at the start of the younger dryas with an attendant increase in freshwater flux of 0 06 0 02 sverdrup 1 sverdrup 106 m3 s 1 this base discharge increase is sufficient to have reduced atlantic meridional overturning circulation and caused the younger dryas cold interval in addition our data indicate subsequent fluctuations in the freshwater flux to the st lawrence river of 0 06 0 12 sverdrup thus explaining the variability in the overturning circulation and climate during the younger dryas

high resolution holocene palynological record from the scotian shelf abstract because of their location at the confluence of polar and subtropical airmasses and near a transition zone between the cold labrador current and the gulf stream the atlantic provinces experience some of the most dynamic climate conditions in canada major climate changes occurred during the holocene as shown by pollen records from lakes but previous paleoceanographic studies based on low resolution proxy data records do not show major changes during the past 8000 years therefore the holocene history of canada s atlantic region was examined using a high resolution palynological record from the scotian shelf la have basin sea surface conditions were reconstructed using proxy data from dinoflagellate cysts and paleobioclimatic transfer functions ocean atmosphere interactions are determined by onshore offshore correlation of marine and pollen records from nova scotia results show a succession of major paleoceanographic events sea surface temperatures sst february and august up to 5 c higher than today s average and slightly higher salinity are reconstructed between 10 5 and 8 5 ka the last pulse of meltwater from the residual ice sheet affected the shelf waters between 8 5 and 6 5 ka by lowering the sst in february and the salinity most previous studies failed to record this event since 6 5 ka august temperature generally remained around today s value while february temperature was generally 2 c above it except for recurring colder and lower salinity intervals these cold intervals have a recurrence of about 1000 years a slight cooling of summer sst is recorded in the last 500 years comparison with climatic reconstructions from nova scotia pollen records shows a difference in timing between ocean and atmosphere the onset of the climatic optimum hypsithermal in nova scotia lags by about 2000 years until 8 ka relative to the ocean but it lasted longer the neoglacial cooling in atlantic canada however started earlier 2 ka than the late holocene ocean cooling la have basin s holocene paleoceanography presents some differences from most other studies from the region 1 the hypsithermal started earlier 2 the last pulse of meltwater is recorded 3 the last 6500 years are punctuated by colder intervals increased productivity and blooms of toxic algae in the early holocene are probably due to a combination of factors increased nutrients and a greater stability of the water column because of meltwaters higher sst and increased upwelling or storm activity

beryllium 10 exposure ages of erratic boulders in southern norway and implications for the history of the fennoscandian ice sheet the margins of the fennoscandian ice sheet fis during the last glacial maximum lgm are fairly well constrained yet the thickness of the fis and its temporal evolution are poorly known here we use beryllium 10 be 10 exposure ages of glacially transported boulders along three vertical transects in southern norway to determine past ice sheet elevations the ice surface elevation during the lgm at our westernmost site skala was likely at approximately 1440 in coinciding with a previously mapped trimline at our central site blaho the ice surface elevation at the lgm was at least at similar to 1620m likely closer to 1800m at elgahogna our easternmost site lgm ice was above the summit elevation of 1460m rapid deglaciation began at skala and blaho at approximately 13 5 14 5 10 beka and at approximately 12 be 10 ka at elgdhogna by approximately 9 be 10 ka the fis had thinned to below our lowest sample at each location periods of rapid thinning correlate with an exposure dated ice margin history as well as the glaciation curve for western scandinavia our data when combined with previous bedrock and blockfield highly weathered bedrock on summits exposure ages resolve a long standing debate over the age and geomorphic interpretation of blockfields and weathering zones in southern norway frozen bed low erosive ice clearly covered the summit blockfields at blaho and especially at elgdhogna where we find a large and progressive divergence between boulder and bedrock exposure ages with elevation we conclude that the lower limit of blockfields in these areas should be interpreted as an englacial thermal boundary rather than the upper limit of the lgm fis and that blockfields have survived multiple glacial cycles we also compare our deglaciation record with several models of the fis models that predict how the fis changed during deglaciation either through inversion of crustal rebound or through climate dependent forward modeling generally match our exposure ages reasonably well during deglaciation but predict larger lgm surface elevations than our data indicate on the other hand the climap maximum model which provides lgm elevations only agrees with our results fairly well c 2007 elsevier ltd all rights reserved

degree of rock surface weathering as an indicator of ice sheet thickness along an east west transect across southern norway rock surface weathering as reflected by rock surface hardness and roughness was measured at six mountains along an east west transect across southern norway at most sites the results show significant differences in rock surface weathering across the autochthonous blockfield boundary suggesting that the areas above the boundary have been exposed to subaerial weathering for a considerably longer time span that the areas below the results are interpreted as reflecting the surface profile of an asymmetric west centred low gradient ice sheet

autochthonous block fields in southern norway implications for the geometry thickness and isostatic loading of the late weichselian scandinavian ice sheet the consistent geographical and altitudinal distribution of autochthonous block fields mantle of bedrock weathered in situ and trimlines in southern norway suggests a multi domed and asymmetric late weichselian ice sheet low gradient ice sheet profiles in the southern baltic region in the north sea and along the outer fjord areas of southern norway are best explained by movement of ice on a bed of deforming sediment although water lubricated sliding or a combination of the two may not be excluded the ice thickness distribution of the late weichselian scandinavian ice sheet is not in correspondence with the modern uplift pattern of fennoscandia early holocene crustal rebound was apparently determined by an exponential glacio isostatic rise later however crustal movements appear to have been dominated by large scale tectonic uplift of the fennoscandian shield centred on the gulf of bothnia the region of maximum lithosphere thickness

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

permafrost thaw and destabilization of alpine rock walls in the hot summer of 2003 1 exceptional rockfall occurred throughout the alps during the unusually hot summer of 2003 it is likely related to the fast thermal reaction of the subsurface of steep rock slopes and a corresponding destabilization of ice filled discontinuities this suggests that rockfall may be a direct and unexpectedly fast impact of climate change based upon our measurements in alpine rock faces we present model simulations illustrating the distribution and degradation of permafrost where the summer of 2003 has resulted in extreme thaw we argue that hotter summers predicted by climate models for the coming decades will result in reduced stability of many alpine rock walls

delayed hydrological response to greenland cooling at the onset of the younger dryas in western europe during the younger dryas cold event about 12 800 years ago environmental change in western europe seems to occur 170 years after cooling over greenland lake sediment analyses confirm this delay and suggest european hydrological and vegetation change occurred only after the build up of sea ice in the north atlantic pushed the westerly wind system south

suggested terminology for quaternary dating methods abstract classification of quaternary dating methods should be based on the level of quantitative information and the degree of confidence contained in the age estimates produced by the dating methods we recommend the use of the terms numerical age calibrated age relative age and correlated age to describe these levels we also classify dating methods by type into sideral isotopic radiogenic chemical and biological geomorphic and correlation methods the use of absolute is inappropriate for most dating methods and should be replaced by numerical the use of date should be minimized in favor of age or age estimate we recommend use of the abbreviations ka and ma for most ages calender dates can be used where appropriate and yr b p can be used for radiocarbon ages

the schmidt hammer as a holocene calibrated age dating technique testing the form of the r value age relationship and defining the predicted age errors most recent developments of schmidt hammer exposure age dating shd as a calibrated age dating tool have been limited by the use of locations at two age control points this has necessitated 1 making assumptions about a linear r value age relationship and 2 basing predictions of age errors only on r value variance at the two age control points this paper analyses 9900 r values obtained from multiple age control points on a sequence of glacio isostatically raised shorelines with well constrained ages skuleskogen high coast world heritage site and environs gulf of bothnia northern sweden ranging from modern to 10 5 ka in age the sampling design involved 30 measurements on granite beach boulders from 30 sites at 11 age control points the r value age relationship is best described by a linear function ordinary least squares ols with an r 2 of 0 89 p 0 0001 predicted age errors are calculated using two approaches 1 ols regression which takes account of the uncertainties associated with the regression line and the age control points and 2 weighted total least squares wtls regression which in addition takes account of possible shoreline age errors and the heteroscedasticity of r value residuals with increasing age with both approaches 95 predicted age errors are relatively modest 355 455 years and 300 515 years respectively with larger r value variance and hence uncertainty for older surfaces and the possibility of further improvement from a more selective field sampling scheme that differentiates between age related and non age related rock surface variability our results also indicate that for certain lithologies and weathering environments it is possible to construct reliable calibrated age curves from relatively few age control points

a global perspective on last glacial maximum to holocene climate change while the abrupt climate events of the last deglaciation are well defined in ice core records from the polar regions of both hemispheres their manifestation elsewhere is less well constrained here we compile 104 high resolution paleoclimate records to characterize the timing and spatial pattern of climate change during the last deglaciation this compilation indicates relatively concurrent timing of the last glacial maximum lgm peak glacial conditions and the altithermal peak interglacial conditions in the northern 22 1 4 3 ka and 8 0 3 2 ka and southern 22 3 3 6 ka and 7 4 3 7 ka hemispheres suggesting the hemispheres were synchronized by greenhouse gases local insolation and or northern hemisphere induced ocean circulation changes the magnitude of the glacialeinterglacial temperature change increases with latitude reflecting the polar amplification of climate change with a likely minimum global mean cooling of ww4 9 c during the lgm relative to the altithermal empirical orthogonal function eof analysis of 71 records spanning 19e11 ka indicates that two modes explain 72 of deglacial climate variability eof1 61 of variance shows a globally near uniform pattern with its principal component pc1 strongly correlated with changes in atmospheric co2 e of2 11 of variance exhibits a bipolar seesaw pattern between the hemispheres with its principal component pc2 resembling changes in atlantic meridional overturning circulation strength eof analysis of 90 records from 15 to 11 ka indicates that northern and southern modes of climate variability characterize the younger dryas bolling allerod interval these modes dominate at the higher latitudes of each hemisphere and exhibit a complex interaction in the tropics the magnitude of the younger dryas climate anomaly cooler drier increases with latitude in the northern hemisphere with an opposite pattern warmer wetter in the southern hemisphere reflecting a general bipolar seesaw climate response global mean temperature decreased by w0 6 c during the younger dryas therefore our analysis supports the paradigm that while the younger dryas was a period of global climate change it was not a major global cooling event but rather a manifestation of the bipolar seesaw driven by a reduction in atlantic meridional overturning circulation strength

large ice contact slope movements glacial buttressing deformation and erosion glaciers and slope movements may act simultaneously to erode and modify glaciated slopes undercutting by glaciers can destabilize slopes but the extent to which slope failure may progress prior to subsequent glacier withdrawal has not hitherto been considered the traditional view has been that the buttressing effect of ice prevents slope movement the problem with this view is that ice is one third the density of rock and flows under low applied stress consequently failed slopes may move into the glacier if they exert a stress in excess of the resistance provided by the glacier slope movement rate depends on ice rheology and other factors influencing driving and resisting stresses simple viscous equations are used to investigate these variables the equations predict that small 108 m3 rockslides to test these estimates field evidence is presented of slope movements in glaciated valleys of new zealand narrowing or squeezing of glaciers adjacent to unstable rock slopes is demonstrated and considered to be the result of slope movement for one site geomorphic mapping and slope movement monitoring data show that movement rates are of similar order of magnitude to those predicted by the viscous equations closer agreement could be achieved with the application of modelling techniques that can more realistically model the complex slope geometries and stability factors encountered or by obtaining additional empirical data to calibrate the models this research implies that while the concept of glacial debuttressing the reduction of slope support from withdrawal of glaciers is valid complete debuttressing is not a prerequisite for the movement of ice contact rock slopes these slope movements may contribute to the erosional processes of glaciers and the evolution of glaciated slopes in a previously unrecognized way copyright 2012 john wiley sons ltd

pollen transport through distributaries and depositional patterns in coastal waters abstract in this study we compare seasonal pollen and spore assemblages in river waters from the mississippi river at vicksburg mississippi to those downstream at belle chasse louisiana and in a distributary the atchafalaya river at morgan city louisiana assemblages of pollen in waters at vicksburg and belle chasse are similar to each other but distinctively different from those in the atchafalaya river local pollen inputs are more important in the anastomosing atchafalaya river channel as compared to the meandering main stem mississippi channel which discharges through the bird foot delta riverine pollen and spore assemblages are also compared to those of surface sediments from the louisiana continental shelf in the vicinity of the mississippi river plume in this area the primary source of marine pollen and spore assemblages appears to be the discharge from the main stem mississippi with limited input from the atchafalaya thus pollen deposited in these coastal waters provides a record of vegetation in the mississippi drainage basin rather than local coastal areas pollen assemblages on the continental shelf vary with distance from the river source but not in a systematic manner the pattern is explained by biological controls on fine particle deposition in marine waters i e deposition of pollen in copepod fecal pellets as copepod grazing is dependent upon phytoplankton production pollen deposition from the river plume will be limited by high turbidities proximal to the river mouth we hypothesize that in neritic environments pollen is preferentially deposited in areas corresponding to high phytoplankton production which are characterized by reduced turbidity and high nutrient availability

timing equilibrium line altitudes and climatic implications of two early holocene glacier readvances during the erdalen event at jostedalsbreen western norway following the younger dryas the e rst evidence of glacial activity in southern norway in response to climatic change occurred during the early holocene when terminal moraines from the erdalen event formed beyond the position of later little ice age moraines in front of present outlet glaciers on both sides of the jostedalsbreen ice cap sets of pre little ice age marginal moraines have been morphostratigraphicallycorre lated with the erdalen event the lithostratigraphyin a peat bog at hellemyrane in jostedalen western norway provides e rm evidence for a two phase erdalen event associated with two glacier readvances of nigardsbreen at the preboreal boreal transition radiocarbon dates from the peat bog give age estimates for the two phases the e rst erdalen event readvance took place between 10 100 and 10 050 cal bp while the second occurred close to 9700 cal bp the lowering of the equilibrium linealtitude ela during these readvances is estimated using the little ice age ratio lr approach to be about 230 m and 215 m respectively the e rst readvance is attributed to an increase in winter precipitation while the second readvance may have been primarily caused by a marked drop in summer temperature which reactivated already existing ice masses

an abrupt wind shift in western europe at the onset of the younger dryas cold period the younger dryas cold reversal during the last glacial termination is one of the most abrupt climate change events observed in the northern hemisphere analyses of varved lake sediments from western germany suggest that storminess in the north atlantic region increased within a single year at this time providing a mechanistic link between a decrease in the meridional overturning circulation and western european cooling the younger dryas cooling 12 700 years ago is one of the most abrupt climate changes observed in northern hemisphere palaeoclimate records1 2 3 4 annually laminated lake sediments are ideally suited to record the dynamics of such abrupt changes as the seasonal deposition responds immediately to climate and the varve counts provide an accurate estimate of the timing of the change here we present sub annual records of varve microfacies and geochemistry from lake meerfelder maar in western germany providing one of the best dated records of this climate transition5 our data indicate an abrupt increase in storminess during the autumn to spring seasons occurring from one year to the next at 12 679 yr bp broadly coincident with other changes in this region we suggest that this shift in wind strength represents an abrupt change in the north atlantic westerlies towards a stronger and more zonal jet changes in meridional overturning circulation alone cannot fully explain the changes in european climate6 7 we suggest the observed wind shift provides the mechanism for the strong temporal link between north atlantic ocean overturning circulation and european climate during deglaciation

glacial lake development and marine inundation deer lake area newfoundland canada topographically controlled deglaciation of an interior basin a large interior basin in west central newfoundland covering the area of modern deer lake grand lake sandy lake and birchy lake is connected to the sea by a narrow breach of a coastal mountain range during retreat of late wisconsinan glaciers this basin was occupied by a short lived glacial lake impounded by remnant ice in coastal fjords and drained by a spillway at the western end of the lake evidence for this lake is fragmentary and consists of strandline features that fall on a plane of elevation consistent with the post glacial isostatic tilt following collapse of the ice dams and subsequent lake drainage at some time prior to 12 220 yr bp the deer lake basin was inundated by the sea to an elevation of about 45 m a s l deltas were formed at the basin edges and thick successions of fine grained rhythmites blanketed the basin floor isostatic rebound resulted in falling relative sea levels and following a stillstand marked by a period of deltaic deposition at 33 m a s l isolation of the deer lake basin from marine influence in the early holocene this style of deglaciation differs from previously accepted models for this part of eastern canada which showed progressive retreat from the coast to remnant centres on topographic highs in the model proposed here a large low elevation basin was deglaciated early at a similar time to ice retreat to coastal positions from offshore this pattern of deglaciation may be found in other areas with similar topographic settings

comparison of electronic and mechanical schmidt hammers in the context of exposure age dating are q and r values interconvertible application of schmidt hammer exposure age dating shd to landforms has substantially increased in recent years the original mechanical schmidt hammer records r rebound values although the newly introduced electronic schmidt hammer silverschmidt facilitates greatly improved data processing it measures surface hardness differently recording q velocity values that are not a priori interconvertible with r values this study is the first to compare the performance of both instruments in the context of field based exposure age dating with a particular focus on the interconvertibility of r values and q values the study was conducted on glacially polished pyroxene granulite gneiss jotunheimen southern norway results indicate that mean q values are consistently 8 10 units higher than mean r values over the range of values normally encountered in the application of shd to glacial and periglacial landforms a convenient conversion factor of 10 units may therefore be appropriate for all but the softest rock types close to the technical resolution of the instruments the electronic schmidt hammer should therefore be regarded as a useful complement and potential replacement for the mechanical schmidt hammer conversion of published r values data to q values requires however careful control and documentation of instrument calibration copyright 2014 john wiley sons ltd

permafrost in steep bedrock slopes and its temperature related destabilization following climate change permafrost in steep bedrock is abundant in many cold mountain areas and its degradation can cause slope instability that is unexpected and unprecedented in location magnitude frequency and timing these phenomena bear consequences for the understanding of landscape evolution natural hazards and the safe and sustainable operation of high mountain infrastructure permafrost in steep bedrock is an emerging field of research knowledge of rock temperatures ice content mechanisms of degradation and the processes that link warming and destabilization is often fragmental in this article we provide a review and discussion of existing literature and pinpoint important questions ice filled joints are common in bedrock permafrost and possibly actively widened by ice segregation broad evidence of destabilization by warming permafrost exists despite problems of attributing individual events to this phenomenon with certainty convex topography such as ridges spurs and peaks is often subject to faster and deeper thaw than other areas permafrost degradation in steep bedrock can be strongly affected by percolating water in fractures this degradation by advection is difficult to predict and can lead to quick and deepdevelopment of thaw corridors along fractures in permafrost and potentially destabilize much greater volumes of rock than conduction would although most research on steep bedrock permafrost originates from the alps it will likely gain importance in other geographic regions with mountain permafrost

late quaternary sea surface conditions in the laurentian fan evidence from coccolith and dinocyst assemblages abstract the analyses of coccoliths and dinocysts from the images core md95 2033 collected on the laurentian fan 44 39 87n 55 37 21w water depth 1412 m in the northwest north atlantic provide a new dataset to assess the magnitude of climatic changes during the holocene with a millennial time resolution coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions in addition the dinocyst assemblages were used to reconstruct the sea surface temperature sst and salinity sss based on the modern analog technique the distribution of the coccolith and dinocyst assemblages suggests a succession of climatic events during the late quaternary and early holocene linked to change in the influence of the labrador current and or the st lawrence river discharge the dinocyst assemblages recorded a thermal optimum during the mid holocene in the late holocene coccolith concentrations show two peaks at 2 3 and 1 1 ky which coincide with the presence of species with different ecological properties likely due to the localized influence of the slope water jet swj current the presence of this current has played a role in the development of the coccolith and dinocyst assemblages and sst fluctuations especially in the last 2 ky overall the interaction between the st lawrence river the swj the lc and the nac has all controlled the sss ssts and the development of the coccolith and dinocyst assemblages confirming a significant regionalism of the entire area

large rock slope failures in the highlands of scotland characterisation causes and spatial distribution abstract a comprehensive database of larger rock slope failures rsfs has been compiled and characterised for a whole mountain range possibly for the first time apart from iceland most rsfs in the scottish highlands occurred soon after deglaciation a threshold size of 0 25 km 2 focuses on rsfs which contribute significantly to gross erosion in the glacial paraglacial cycle and on the spatial concentration of this poorly recognised process database verification indicates that at least 90 of the total extant population in the highlands is covered standard mass movement typologies are broadly applicable but require some refinement to characterise rsfs in a passive margin glaciated mountain range comprised mainly of ancient metasediments most larger rsfs here are complex and difficult to categorise a continuum from cataclasmic failures including rock avalanches through arrested translational slides to almost in situ slope deformations is identified the prevailing modes of large rsf are arrested short travel translational sliding and gravitational sagging cataclasmic failure is rare and sub cataclasmic outcomes are more evident a significant class of deformations exhibits compressional rather than extensional features and may be responding to localised glacio isostatic rebound stresses the large rsf population is widely but very unevenly distributed across the main mountain areas 65 are in seven main clusters with the rest non randomly scattered previous glaciological lithological and seismotectonic explanations are insufficient to explain this spatial pattern and overlook the basic engineering geology prerequisites for failure massifs of similar relief and lithology can display intense or sparse rsf incidence geomorphological appraisal suggests an association with recently active glacial breaches of main and secondary watersheds with rsf being scarce or absent in valleys inherited from tertiary uplift and in mountain groups away from the main watersheds valleys which adapted early to ice discharge are seen as stress hardened with their slopes unlikely to reach critical thresholds for failure after subsequent reoccupations by ice concentrated erosion in the last glaciations is most likely to be found close to where breaches are actively forming or enlarging such erosion in the slope foot and valley floor may have daylighted failure planes or generated rebound stresses augmenting those from other endemic sources sufficiently to provoke widespread paraglacial rsf slope stress models for deglaciated valleys and comparative studies in other glaciated mountain ranges are required to test this concept and may assist in geohazard assessments