environmental and morphologic controls on wave induced dune response abstract the pacific northwest of the united states exhibits complex spatial patterns of storm induced coastal foredune erosion using oceanographic and morphologic data from three field sites encompassing a range of subaqueous and subaerial coastal profile configurations a relationship is found between morphologic characteristics and dune volume changes during storm events producing high water levels the data suggest that dune erosion increases with increasing backshore beach slope and that under particular oceanographic forcing conditions wave driven processes can grow the lower portion of dunes on low sloping dissipative beaches these observations of environmental and morphologic controls on storm induced dune impacts are further explored using xbeach a state of the art numerical model capable of simulating interactions between hydrodynamics and morphology consistent with the field data model simulations indicate that wave driven dune growth may occur on low sloping beaches in cases where the dynamic still water level still water level plus wave setup is lower than the dune toe however these accretional processes are restricted to events where limited incident wave energy impacts the dune cases with steep backshore beach slopes or dynamic still water levels exceeding the dune toe instead typically result in dune erosion additionally the model simulations suggest that morphologic properties of the shelf nearshore and the dune itself influence storm induced dune volume change therefore morphologic features far from the dune face including shelf geometries shaped in part by the regional historical sediment budget may have important implications on the susceptibility of coastal foredunes systems to storm impacts

modelling vegetated dune landscapes this letter presents a self organising cellular automaton model capable of simulating the evolution of vegetated dunes with multiple types of plant response in the environment it can successfully replicate hairpin or long walled parabolic dunes with trailing ridges as well as nebkha dunes with distinctive deposition tails quantification of simulated landscapes with eco geomorphic state variables and subsequent cluster analysis and pca yields a phase diagram of different types of coastal dunes developing from blow outs as a function of vegetation vitality this diagram indicates the potential sensitivity of dormant dune fields to reactivation under declining vegetation vitality e g due to climatic changes nebkha simulations with different grid resolutions demonstrate that the interaction between the abiotic geomorphic processes and the biological vegetation component life introduces a characteristic length scale on the resultant landforms that breaks the typical self similar scaling of un vegetated bare sand dunes

holocene glaciation and climate evolution of baffin island arctic canada abstract lake sediment cores and cosmogenic exposure ce dates constrain the pattern of deglaciation and evolution of climate across baffin island since the last glacial maximum lgm ce dating of erratics demonstrates that the northeastern coastal lowlands became ice free ca 14 ka as the laurentide ice sheet lis receded from its lgm margin on the continental shelf coastal lakes in southeastern baffin island started to accumulate sediment at this time whereas initial lacustrine sedimentation was delayed by two millennia in the north reduced organic matter in lake sediment deposited during the younger dryas chron and the lack of a glacial readvance at that time suggest cold summers and reduced snowfall ice retreated rapidly after 11 ka but was interrupted by a widespread readvance of both the lis and local mountain glaciers 9 6 ka cockburn substage a second readvance occurred just before 8 ka during a period of unusually cold summers corresponding to the 8 2 ka cold event in the greenland ice sheet most local glaciers were behind their present margins before 7 ka and in some instances much earlier although the foxe dome of the lis continued to slowly retract toward the present day barnes ice cap throughout the holocene pollen in lake sediments is rare and dominated by exotic sources prior to 12 ka subsequently grass tundra became established followed by modern tundra vegetation ca 8 ka with subtle changes in pollen assemblages in the late holocene lake primary productivity peaked in the early holocene before terrestrial vegetation or marine surface waters reached their apparent thermal maxima lacustrine marine and glacial proxies all reflect significant late holocene cooling the onset of neoglaciation is well dated in lacustrine records at ca 6 ka with intensification after 2 5 ka the expansion of local glaciers during the little ice age represents the most extensive advance since 7 ka we suggest that the replacement of atlantic surface waters by cold low salinity arctic ocean water coupled with the steady reduction of summer insolation resulted in a significant positive sea ice feedback that produced a larger late holocene summer temperature depression over the baffin region than in the pacific sector of the arctic

a continuous holocene glacial record inferred from proglacial lake sediments in banff national park alberta canada abstract sediment cores from three proglacial lakes in northern banff national park alberta preserve a record of holocene glacial activity upvalley which is more continuous and better dated than available surficial records dating of the cores is based on tephrochronology and 16 ams14c ages of terrestrial macrofossils all cores contain a threefold sequence of lacustrine sediments overlying a late pleistocene diamicton basal lacustrine sediments 10 10014c yr old contain little organic matter sediment composition indicates a large glacigenic contribution a sharp increase in organic content marks the beginning of the altithermal interval at all three lakes this transition occurred abruptly at about 10 10014c yr b p at crowfoot lake and possibly more gradually at the other lakes altithermal sediments contain relatively little glacigenic material and during most of the altithermal glaciers may have been absent above crowfoot and bow lakes glaciers draining into hector lake appear to have persisted through the altithermal a subsequent decrease in organic content in each lake reflecting increased clastic sedimentation marks the end of the altithermal and the onset of neoglacial ice advances the transition took place between about 5800 and 400014c yr b p and may be time transgressive beginning earlier in hector lake than in crowfoot lake changing neoglacial clastic sedimentation rates through the neoglacial interval indicate two main periods of increased glacier extent between ca 3000 and 1800 varve yr ago ca 2900 190014c yr b p and during the last several hundred years during the intervening period glaciers were less extensive but much more extensive than during the recessions of the altithermal interval

anthropogenic controls on overwash deposition evidence and consequences accelerated sea level rise and the potential for an increase in frequency of the most intense hurricanes due to climate change threaten the vitality and habitability of barrier islands by lowering their relative elevation and altering frequency of overwash high density development may further increase island vulnerability by restricting delivery of overwash to the subaerial island we analyzed pre hurricane sandy and post hurricane sandy 2012 lidar surveys of the new jersey coast to assess human influence on barrier overwash comparing natural environments to two developed environments commercial and residential using shore perpendicular topographic profiles the volumes of overwash delivered to residential and commercial environments are reduced by 40 and 90 respectively of that delivered to natural environments we use this analysis and an exploratory barrier island evolution model to assess long term impacts of anthropogenic structures simulations suggest that natural barrier islands may persist under a range of likely future sea level rise scenarios 7 13 mm yr whereas developed barrier islands will have a long term tendency toward drowning

holocene environmental variability in southern greenland inferred from lake sediments abstract sediments from qipisarqo lake provide a continuous holocene paleoenvironmental record from southern greenland following deglaciation and glacio isostatic emergence of the basin from the sea 9100 cal yr b p proxies of lake paleoproductivity including biogenic silica and organic matter increased markedly until 6000 cal yr b p and thereafter remained stable over the ensuing warm three millennia subsequent decreases in these proxies most dramatically between 3000 and 2000 cal yr b p show the lake s responses to initial neoglacial cooling intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr b p briefly interrupting the decreasing trend in productivity that culminated in the little ice age increased lake productivity during the latter half of the 20th century which reflects the limnological response to circum arctic warming still has not reached peak holocene values the neoglacial climate of the last 2000 yr includes the most rapid high amplitude environmental changes of the past nine millennia the norse thus migrated around the north atlantic ocean region in the most environmentally unstable period since deglaciation lacustrine sediment records provide a context with which to consider future environmental changes in the labrador sea region in particular any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales

identification and significance of tephras encountered in a core from mary lake yoho national park british columbia mary lake is a small subalpine lake located proximal 3 km to the continental divide near lake o hara in yoho national park british columbia a 1 25 m core recovered from surficial bottom sediments was found to contain both bridge river tephra 2350 years bp and mazama tephra 6800 years bp identification of the tephras was initially based on distinctive colour texture phenocryst assemblages and glass shard habits and was confirmed by electron microprobe analysis of the constituent glass shards the microprobe technique employed backscattered and secondary electron imagery and both energy dispersive and wavelength dispersive analyses mean annual sedimentation rates calculated from tephra depths in the mary lake core were found to be of the order of 0 15 mm year for the post bridge river time period and 0 02 mm year for the mazama bridge river interval the preservation of mazama tephra in mary lake lacustrine sediments indicates that deglaciation had proceeded upvalley from the mary lake basin

geomorphologic characteristics and evolution of managed dunes on the south west coast of france abstract the calibrated foredunes of the aquitaine coast sw france constitute an example of secular extensive application of nature based solution being one of the longest and largest dune systems in europe this iconic landscape offers considerable services to coastal societies since the mid half of the 18th century human work on sediment flows has resulted in the emergence of large sets of foredunes currently constituting an almost 230 km long managed barrier against inland sand invasion coastline erosion coastal flooding and also a major reserve of biodiversity last massive mechanic shaping of the foredunes following a so called ideal profile date back to the 1970s 80s and aimed to limit erosion dynamics and sediment mobility since they have been facing multiples disruptions over the years which have considerably modified their morphology especially during the last decades calibrated foredunes are currently exhibiting impressive dimensions with a mean dune height of about 16 6 m peaking at 30 m in some locations and a dune width mean along the coast of 187 m today 55 5 of them meet the ideal profile shape standards or surpass the in terms of dimensions whereas 21 5 of the calibrated foredunes are considered narrowed and need specific attention this regional analysis based on extensive airborne lidar datasets from 2011 to 2018 includes i a dune morphology classification based on several basic geomorphological indicators dune width height crest position back dune elevation compared to a calibrated idealised shaped profile ii a quantification of marine beach dune and aeolian sediments flows in m year and m m2 year and forms on dunes scarps blowouts depositional lobes as an indicator of the recent dynamics affecting dune morphology and iii a study of management control of calibrated foredunes 4613 interventions including actions taken after the outstanding winter of 2013 2014 as expected intensive dune management are mainly focused where assets are directly threatened the study highlights the importance and the efficiency of human management on dune evolutions long term dune form stability control of gullies and incipient frontal blowout after marine erosion protection of human issues however today management actions wind fence branch cover planting and reshaping are not conditioned by foredune morphology or last decade s beach dune dynamic sediment availability chronic coastline erosion considering long term erosion projections and expected impact of climate change the analysis shows the need of more global and extensive strategies in order to preserve the protection role of foredunes in the coming decades

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

foredunes and blowouts initiation geomorphology and dynamics this paper reviews the initiation dynamics geomorphology and evolution of incipient foredunes established foredunes and blowouts incipient foredunes may be initiated in a variety of ways leading to the formation of ramps terraces or ridges depending on progradation rates vegetation type and cover sediment transport rates and scale of erosional processes vegetation cover morphology growth rates and types combine with aerodynamic processes to determine dune and swale morphology established foredunes are classified into five morpho ecological types and the flow behaviour over two types is detailed a new model of foredune evolutionary paths at various possible time scales is presented blowout initiation dynamics and sediment transport and evolution is examined throughout the review the gaps in present understanding of dune processes and a range of ideas for new research possibilities are provided

effects of beach raking and sand fences on dune dimensions and morphology abstract raking beaches to remove wrack natural and human litter to enhance recreational use and using sand fences to build and stabilize dunes are common practices on developed shores but their effects on the landscape are not well understood managers in avalon nj ceased using sand fences and raking in a portion of beach in 1991 providing the opportunity to evaluate evolution of natural and managed dune systems over a 19 year period topographic and vegetation characteristics were evaluated on 15 transects within 5 sites in a managed area where raking and sand fences are still used and at 15 transects within 5 sites in a naturally evolving unmanaged area raking and deploying fences in the managed area restricted the size of the cross shore zone in which aeolian accretion occurred but resulted in greater dune crest heights than in the unmanaged area crest heights of the foredune in the managed area ranged from 4 45 m to 5 27 m crest heights in the unmanaged area ranged from 3 02 m to 4 27 m dune volume and beach volume were greater on average in the unmanaged area and the dune was wider mean of 72 m versus 40 m and had an additional ridge the unmanaged area had 35 more species and contained a greater percentage of all species encountered in the study area than the managed area 88 compared to 65 more species occurred in the swales than any other of the cross shore habitats and most of these species were observed in the deeper wider swales in the unmanaged area removing wrack from the beach prevents incipient dunes from forming thus reducing the number of dune crests and size of swales that create topographic variability and increase the number and types of habitats for flora and fauna suspension of raking can allow the dunes to build seaward while producing a greater variety and number of habitats but seaward growth does not mean that the height of the dune will increase substantially and fences may be needed to build an initial dune ridge for flood protection thereafter a policy of not raking in specially designated zones would be a good compromise between the need to accommodate nature and beach recreation

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

holocene and latest pleistocene alpine glacier fluctuations a global perspective abstract alpine glacier fluctuations provide important paleoclimate proxies where other records such as ice cores tree rings and speleothems are not available about 20 years have passed since a special issue of quaternary science reviews was published to review the worldwide evidence for holocene glacier fluctuations since that time numerous sites have been discovered new dating techniques have been developed and refined climatic hypotheses have been proposed that contribute to a better understanding of earth s climate system this special volume includes 12 papers on holocene and latest pleistocene alpine glacier fluctuations that update the seven review papers from 1988 major findings of these 12 papers include the following many but certainly not all alpine areas record glacier advances during the younger dryas cold interval most areas in the northern hemisphere witnessed maximum glacier recession during the early holocene with some glaciers disappearing although a few sites yield possible evidence for advances during the 8 2 ka cooling event in contrast some alpine areas in the southern hemisphere saw glaciers reach their maximum post glacial extents during the early to middle holocene in many parts of the globe glaciers reformed and or advanced during neoglaciation beginning as early as 6 5 ka neoglacial advances commonly occurred with millennial scale oscillations with many alpine glaciers reaching their maximum holocene extents during the little ice age of the last few centuries although the pattern and rhythm of these glacier fluctuations remain uncertain improved spatial coverage coupled with tighter age control for many events will provide a means to assess forcing mechanisms for holocene and latest pleistocene glacial activity and perhaps predict glacier response to future impacts from human induced climate change

holocene glacier fluctuations in alaska abstract this review summarizes forefield and lacustrine records of glacier fluctuations in alaska during the holocene following retreat from latest pleistocene advances valley glaciers with land based termini were in retracted positions during the early to middle holocene neoglaciation began in some areas by 4 0 ka and major advances were underway by 3 0 ka with perhaps two distinct early neoglacial expansions centered respectively on 3 3 2 9 and 2 2 2 0 ka tree ring cross dates of glacially killed trees at two termini in southern alaska show a major advance in the ad 550s 720s the subsequent little ice age lia expansion was underway in the ad 1180s 1320s and culminated with two advance phases respectively in the 1540s 1710s and in the 1810s 1880s the lia advance was the largest holocene expansion in southern alaska although older late holocene moraines are preserved on many forefields in northern and interior alaska tidewater glaciers around the rim of the gulf of alaska have made major advances throughout the holocene expansions were often asynchronous with neighboring termini and spanned both warm and cool intervals suggesting that non climatic factors were important in forcing these advances however climatic warming appears to have initiated most rapid iceberg calving retreats large glaciers terminating on the forelands around the gulf of alaska may have had tidewater termini early in the holocene but have progressively become isolated from the adjacent ocean by the accumulation and subaerial exposure of their own sediments

what do glaciers tell us about climate variability and climate change glaciers respond to long term climate changes and also to the year to year fluctuations inherent in a constant climate differentiating between these factors is critical for the correct interpretation of past glacier fluctuations and for the correct attribution of current changes previous work has established that century scale kilometre scale fluctuations can occur in a constant climate this study asks two further questions of practical significance how likely is an excursion of a given magnitude in a given amount of time and how large a trend in length is statistically significant a linear model permits analytical answers wherein the dependencies on glacier geometry and climate setting can be clearly understood the expressions are validated with a flowline glacier model the likelihood of glacier excursions is well characterized by extreme value statistics although probabilities are acutely sensitive to some poorly known glacier properties conventional statistical tests can be used for establishing the significance of an observed glacier trend however it is important to determine the independent information in the observations which can be effectively estimated from the glacier geometry finally the retreat of glaciers around mount baker washington state usa is consistent with but not independent proof of the regional climate warming that is established from the instrumental record

annual push moraines as climate proxy 1 we reconstruct the terminus position of a mountain glacier in british columbia canada from annual push moraines formed between 1959 and 2007 our reconstruction represents the longest annually resolved record of length change for a north american glacier comparison of annual recession with climate records indicates that glacier recession is controlled by air temperatures during the ablation season and accumulation season precipitation during the previous decade analysis among records of glacier frontal variation and mass balance in western north america similarly reveals an immediate terminus reaction to summer and net balance and a delayed reaction to winter and net balance other mountain ranges may contain long series of push moraines that could be exploited as climate proxies and to improve understanding of glacier response to climate

high frequency sediment transport responses on a vegetated foredune wind flow and sand transport intensity were measured on the seaward slope of a vegetated foredune during a 16 h storm using an array of sonic anemometers and wenglor laser particle counters the foredune had a compound seaward slope with a wave cut scarp about 0 5 m high separating the upper vegetated portion from the lower dune ramp which was bare of vegetation wind direction veered from obliquely offshore at the start of the event to obliquely onshore during the storm peak and finally to directly onshore during the final 2 h as wind speed dropped to below threshold sand transport was initially inhibited by a brief period of rain at the start of the event but as the surface dried and wind speed increased sand transport was initiated over the entire seaward slope transport intensity was quite variable both temporally and spatially on the upper slope as a result of fluctuating wind speed and direction but overall magnitudes were similar over the whole length ten minute average transport intensity correlates strongly with mean wind speed measured at the dune crest and there is also strong correlation between instantaneous wind speed and transport intensity measured at the same locations when the data are smoothed with a 10 s running mean transport on the beach for onshore winds is decoupled from that on the seaward slope above the small scarp when the wind angle is highly oblique but for wind angles 45 from shore perpendicular some sand is transported onto the lower slope copyright 2012 john wiley sons ltd

new accelerator mass spectrometry radiocarbon ages for the mazama tephra layer from kootenay national park british columbia canada charcoal fragments recovered from the mazama air fall tephra layer in cores from dog and cobb lakes kootenay national park british columbia yielded accelerator mass spectrometry ages of 6720 70 and 6760 70 14c years bp respectively these two new ages together with other previously published radiocarbon ages on charcoal and twig fragments from mazama air fall deposits indicate that the climactic eruption of mount mazama occurred 6730 40 14c years bp

air flow over foredunes and implications for sand transport more than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed wind flow over the foredunes is studied by means of the relative wind speed the ratio between wind speed at a certain location and the reference wind speed at the same height relative wind speeds appear to be independent of general wind speed but dependent on wind direction for perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness accelerations dominate over decelerations on the seaward slope the pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes but the magnitudes differ an increase in foredune height from 6 to 10m leads to an increase in speed up near the top of the seaward slope from 110 to 150 per cent during onshore wind but further increase of foredune height from 10 to 23 m appears to have little effect due to increased roughness and deflection of flow topography also influences the direction of the flow between beach and top the flow deflects in the direction of the normal during onshore winds during offshore winds the flow is deflected to the parallel near the dunefoot deflection is always in the direction of the parallel and increases with steeper topography the maximum deflection near the dunefoot was 90 over a 23 m high dune observed during offshore winds patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations owing to speed up on the seaward front of the foredune sand transport capacity of the wind increases which results in erosion if vegetation is absent during strong onshore wind sand is lifted near the dunefoot and moves over the foredune in suspension during weaker winds vertical wind velocities do not exceed fall velocities of the sand grains and most of the sand is deposited near the dunefoot

transition of a regressive to a transgressive barrier island due to back barrier erosion increased storminess and low sediment supply bogue banks north carolina usa abstract although back barrier erosion is a prevalent process of island narrowing it is often overlooked in conceptual models of barrier island evolution in many wave dominated barrier island settings the absence of overwash precludes landward movement of the back barrier shoreline and hence the island as a whole from sustaining its width typically regressive barriers are wide and exhibit high elevations with the most seaward dune ridge possessing the highest elevation this morphology may prevent overwash and inlets from breaching the barrier and therefore the associated sediment from reaching the back barrier shoreline for millennia back barrier shoreline erosion from sea level rise and storms can be permanent in the absence of sediment supply from rivers overwash and inlet processes with continued narrowing and lowering of the island regressive barriers may reach a critical state making overwash and inlet formation imminent and transitioning the island to a transgressive barrier the modern day morphologic variability along the 40 km long island of bogue banks north carolina includes both regressive and transgressive segments making this setting ideal for examining whether the transition between these barrier island types is gradual or threshold driven bogue banks consists of two discrete segments characterized by high elevation beach ridges large island widths and stratigraphy consistent with regressive barrier islands these regressive island segments are separated by a broad narrow section of the island devoid of any washover fans flood tide deltas or other transgressive elements analyses of seismic data from the inner continental shelf reveal paleochannels intersecting the wide sections of the island while the narrow central part of the island occupies an inter fluvial area reworking of fluvial sediment from paleochannels was an important sediment source for the barrier during regression optically stimulated luminescence osl dates from the most landward beach ridges constrained initiation of island regression at 3000 cal yr bp close to when there was a significant decrease in the rate of relative sea level rise from 5 mm yr to 0 8 mm yr transects of cores seismic data ground penetrating radar data and radiocarbon and osl dates show that prior to 1500 cal yr bp the central narrow section of the island was wide and progradational similar to adjacent areas back barrier erosion of the central part of the barrier primarily caused island narrowing as a result of increased storminess which occurred around the medieval climate anomaly 1100 cal yr bp this part of the island was more vulnerable to erosion than adjacent areas due to increased bay ravinement bogue sound is widest there and its lower elevation farther away from paleochannel sediment source relict inlet channels exist along the central portion of the island formed within the last 250 yr and likely closed shortly after formation the presence of historical inlets along the narrow central section of the island indicates bogue banks may be nearing a critical width threshold and will subsequently transition to a transgressive barrier because the change in barrier morphology associated with back barrier erosion occurred over a period of time when the rate of sea level rise was relatively low low sediment supply and increased storm frequency are shown to be the main forcing mechanisms of island narrowing these impacts in addition to a predicted increase in sea level rise rates and human modifications e g maintenance of a high elevation foredune closing of inlets prevention of island overwash and associated sediment delivery to the back barrier shoreline will likely promote rapid transition of regressive barrier islands to those dominated by transgressive processes

anomalous early 20th century sedimentation in proglacial green lake british columbia canada annually laminated sediments were recovered from green lake a proglacial lake in the southern coast mountains in british columbia to examine their potential as a temperature proxy varve thickness is moderately correlated with temperature anomalies a d 1900 1994 and annual maximum mean daily discharge of lillooet river a d 1930 1999 but these relations are not stable through time following a d 1977 the relation between varve thickness and annual maximum mean daily discharge is stronger prior to a d 1977 varve thickness is correlated with march to october air temperature which controls the intensity and duration of glacier runoff varve thickness is weakly correlated with reconstructed air temperature records for north america and the northern hemisphere for the period a d 1600 1976 less extensive glacier cover may explain the lack of a clear temperature signal in the varved sediment record prior to a d 1600 and following a d 1977 the period of highest lake sedimentation from a d 1920 to 1945 coincides with rapid retreat of glaciers in the watershed the lack of a similar level of sedimentation in the varve chronology suggests that glacier recession during the period 1920 1945 was higher than at any time in the past 600 years

calendar dated early little ice age glacier advance at robson glacier british columbia canada dendrochronological studies at robson and bennington glaciers have provided the first calendar dating of an early little ice age glacier advance in north america dates derived from in situ stumps indicate that robson glacier began over riding forest between c ad 1142 and 1150 and continued until at least ad 1350 the highest rates of glacier advance c 3 8 m yr 1 occurred between ad 1214 and 1261 based on a series of kill dates from in situ stumps between c ad 1142 1214 and 1261 1350 rates were somewhat lower at c 2 2 5 m yr 1 this glacier advance terminated upvalley of the little ice age maximum position of robson glacier and there is no evidence at this site for glacial events between ad 1350 and 1783 however two smaller glaciers in the robson area and the main tongue of small river glacier have outermost little ice age moraines that date from the first decades of the ad 1700s all glaciers examined in the mount robson area have several well developed moraines dating from the period c

latest pleistocene and holocene glacier fluctuations on mount baker washington abstract glaciers on stratovolcanoes of the pacific northwest of north america offer opportunities for dating late pleistocene and holocene glacier advances because tephra and fossil wood are common in lateral moraines and in glacier forefields we capitalize on this opportunity by examining the holocene glacial record at mount baker an active stratovolcano in northwest washington earlier workers concluded that glaciers on mount baker during the early holocene were more extensive than during the little ice age and hypothesized that the explanation lay in unusual climatic or hypsometric effects peculiar to large volcanoes we show that the main argument for an early holocene glacier advance on mount baker namely the absence of ca 10 000 year old tephra on part of the south flank of the mountain is incorrect moreover a lake sediment core indicates that a small cirque moraine previously thought be of early holocene age is also likely older than the tephra and consequently of late pleistocene age lateral and end moraines and wood mats ca 2 km downvalley of the present snout of deming glacier indicate that an advance during the younger dryas interval was little more extensive than the climactic little ice age advance tephra and wood between tills in the left lateral moraine of easton glacier suggest that ice on mount baker was restricted in the early holocene and that neoglaciation began ca 6 ka a series of progressively more extensive neoglacial advances dated to about 2 2 1 6 0 9 and 0 4 ka are recorded by stacked tills in the right lateral moraine of deming glacier intervening retreats were long enough to allow establishment of forests on the moraine wood mats in moraines of coleman and easton glaciers indicate that little ice age expansion began before 0 7 ka and was followed by retreat and a readvance ca 0 5 ka tree ring and lichen data indicate glaciers on the south side of the mountain reached their maximum extents in the mid 1800s the similarity between glacier fluctuations at mount baker and those elsewhere in the cascades and in british columbia suggests a coherent history of holocene climate change over a broad area of the western cordillera we found no evidence that glaciers on stratovolcanoes behave differently than glaciers elsewhere

the effect of sand fencing on the morphology of natural dune systems abstract sand fences are a frequently used management tool on developed coastlines because they are inexpensive and easy to install while the geomorphic effect of sand fences has been investigated before previous studies have been limited in both temporal and spatial domains here we present the evolution of bogue banks a developed barrier island along the outer banks of north carolina over a 20 year period from 1997 to 2016 where sand fences were emplaced along parts of the island in 2010 we use lidar derived cross shore transects n 38 454 to measure beach and foredune features along the extent 40 km of bogue banks for every available year of lidar data as well as the locations of sand fences which we identify in 39 of the transects following fence construction first we found that vertical growth of the natural foredunes along bogue banks was slightly positive between 2010 and 2016 despite an increased amount of shoreline erosion this pattern was coincident with a combination of sand fence installation and beach nourishment efforts which were most heavily focused on the eastern end of the island second we found that natural foredunes located behind fenced dunes are typically shorter wider and smaller in volume than natural foredunes in non fenced and undeveloped areas although this may partly be due to a tendency for fences to be installed in front of more vulnerable dunes our results suggest that once emplaced sand fences prevent growth of the landward foredune behind fenced dunes these findings suggest that sand fences block sediment supply to landward dunes leading to a shorter and wider complex foredune than would otherwise naturally occur

late holocene glacier expansion in the cariboo and northern rocky mountains british columbia canada abstract castle creek glacier in the cariboo mountains of british columbia remained close to its little ice age limit for most of the past 1500 years without significant recession until the 20th century this conclusion is based on radiocarbon dated detrital and in situ plant material overrun by the glacier and the sedimentary record from informally named on off lake which received clastic sediments only when castle creek glacier crossed a hydrologic divide 330 m upvalley of the little ice age limit plant macrofossils recovered from the transition between basal inorganic silt and overlying organic silty clay in a sediment core from the lake indicate that the glacier first retreated behind the divide ca 10 92 9 70 ka ages of 8 97 8 61 and 5 58 5 53 ka on detrital wood from the glacier s forefield may record earlier advances but the first unequivocal evidence of glacier expansion is from an overridden stump with an age of 4 96 4 45 ka continuous accumulation of gyttja within on off lake however indicates that castle creek glacier did not cross the hydrologic divide at any time during the first half of the holocene glacigenic sediments began to accumulate in the lake between 2 73 and 2 49 ka indicating that castle creek glacier expanded beyond the hydrologic divide at that time a coincident advance is also recorded in the northern rocky mountains of british columbia at kwadacha glacier which overran a vegetated surface at 2 69 2 36 ka clastic sedimentation in on off lake ceased soon after the bridge river volcanic eruption 2 70 2 35 ka indicating that castle creek glacier retreat to a position upvalley of the divide at that time sedimentation resumed before 1 87 1 72 ka when the glacier advanced again past the hydrologic divide following a second retreat castle creek glacier advanced across the divide a final time at ca 1 54 1 42 ka the snout of the glacier remained less than 330 m upvalley of the little ice age moraine until the early twentieth century when annual moraines indicate rapid frontal recession to a position upvalley of the hydrologic divide these data collectively indicate that glaciers in the cariboo mountains of british columbia nearly achieved their all time holocene limits as early as 2 73 2 49 ka and climatic conditions in the early 20th century abruptly ended a 1500 year period favoring glacier expansion

a simple model for the spatially variable coastal response to hurricanes abstract the vulnerability of a beach to extreme coastal change during a hurricane can be estimated by comparing the relative elevations of storm induced water levels to those of the dune or berm a simple model that defines the coastal response based on these elevations was used to hindcast the potential impact regime along a 50 km stretch of the north carolina coast to the landfalls of hurricane bonnie on august 27 1998 and hurricane floyd on september 16 1999 maximum total water levels at the shoreline were calculated as the sum of modeled storm surge astronomical tide and wave runup estimated from offshore wave conditions and the local beach slope using an empirical parameterization storm surge and wave runup each accounted for 48 of the signal the remaining 4 is attributed to astronomical tides indicating that wave driven process are a significant contributor to hurricane induced water levels expected water levels and lidar derived measures of pre storm dune and berm elevation were used to predict the spatially varying storm impact regime swash collision or overwash predictions were compared to the observed response quantified using a lidar topography survey collected following hurricane landfall the storm averaged mean accuracy of the model in predicting the observed impact regime was 55 4 a significant improvement over the 33 3 accuracy associated with random chance model sensitivity varied between regimes and was highest within the overwash regime where the accuracies were 84 2 and 89 7 for hurricanes bonnie and floyd respectively the model not only allows for prediction of the general coastal response to storms but also provides a framework for examining the longshore variable magnitudes of observed coastal change for hurricane bonnie shoreline and beach volume changes within locations that experienced overwash or dune erosion were two times greater than locations where wave runup was confined to the foreshore swash regime during hurricane floyd this pattern became more pronounced as magnitudes of change were four times greater within the overwash regime than in the swash regime comparisons of pre storm topography to a calm weather survey collected one year after hurricane floyd s landfall show long term beach volume loss at overwash locations here the volume of sand eroded from the beach was balanced by the volume of overwash deposits indicating that the majority of the sand removed from the beach was transported landward across the island rather than being transported offshore in overwash locations sand was removed from the nearshore system and unavailable for later beach recovery resulting in a more permanent response than observed within the other regimes these results support the predictive capabilities of the storm scaling model and illustrate that the impact regimes provide a framework for explaining the longshore variable coastal response to hurricanes

neoglacial glacier fluctuations in the canadian rockies abstract the little ice age was the most extensive neoglacial glacier advance in the canadian rockies evidence of earlier less extensive neoglacial glacier advances is based on wood recovered from several glacier forefields wood flushed out of athabasca glacier 7550 8230 yr b p three dates and dome glacier 6120 6380 yr b p two dates indicates that forests occurred upvalley of present glacier termini during the hypsithermal detrital logs from peyto 14 dates saskatchewan 3 dates robson 3 dates and yoho 1 date glaciers plus in situ slumps at peyto and robson glaciers have yielded 14 c dates between 2490 and 3300 yr b p 12 dates between 2800 and 2990 this wood is derived from sources at or upvalley from present glacier termini and represents forests overridden by glaciers between ca 3100 and 2500 yr b p treeline was higher than present immediately prior to this advance this advance which did not extend beyond the little ice age maximum position is designated the peyto advance and correlated with the tiedemann advance in western british columbia earliest little ice age advances at peyto and robson glaciers are dated ca 800 600 yr b p at positions ca 500 m upvalley from little ice age limits

timescales and mechanisms of ree and hf uptake in fossil bones abstract rare earth element ree patterns of fossil bones and teeth are widely used as proxies for provenance taphonomy and palaeoenvironment in order to investigate if fossil bones behave as closed systems over geologic time ree profiles were analysed by la icpms along cross sections of 54 bones from various well characterised and well dated settings these include terrestrial and marine diagenetic environments covering early triassic to holocene ages in general all fossil bones exhibit the highest ree concentrations at the outer rim gradually decreasing by up to four orders of magnitude toward the inner bone cortex intra bone ree concentration gradients decrease significantly from quaternary via tertiary to mesozoic specimens suggesting long term ree uptake and open system behaviour of fossil bone this view is further corroborated by 176lu 176hf dating of selected samples all yielding significantly younger ages than the known chronostratigraphic ages hence there is clear evidence for long term open system behaviour of fossil bones with respect to ree which is in marked contrast to currently accepted models suggesting that ree uptake is only early diagenetic although unexpected statistically significant four to seven point isochrons are observed for four fossil dinosaur bone samples and one upper triassic mastodonsaurus tooth with mswds ranging from 0 083 to 4 5 notably mobility of lu alone cannot account for the observed age patterns assuming constant lu uptake rates over time the radiometric ages should only be as low as half of the chronostratigraphic age however a six point isochron defined by subsamples of a single upper triassic mastodonsaurus tooth yields an age of 65 2 1 1 ma mswd 0 68 much younger than half of the stratigraphic age ca 234 ma hence hf must also undergo late diagenetic exchange likely mechanisms to account for the presence of statistically meaningful isochrons as well as for the late diagenetic exchange of both ree and hf are diffusion adsorption and dissolution reprecipitation processes

late holocene glacial activity in manatee valley southern coast mountains british columbia canada the dendroglaciologic and lichenometric research methodologies employed in this study provide a perspective of glaciological conditions from 5 ka to present in a remote headwater area of the british columbia coast mountains since holocene ice fronts of four glaciers at this site periodically extended below treeline previous glacier advances overrode and buried forests beneath till deposits this study suggests that glaciers were expanding into standing forests at 4 76 and 3 78 ka following glacier expansion at 3 78 ka a period of recession ensued when glaciers withdrew upvalley long enough for the development of deep pedogenic surfaces and the growth of trees exceeding 300 years investigations at beluga and manatee glaciers benchmark a subsequent episode of significant glacial expansion at 2 42 ka referred to as the manatee advance this advance has regional correlatives and is distinguished from the tiedemann advance at manatee glacier by documentation of substantive ice front retreat between the

improved age estimates for the white river and bridge river tephras western canada new 14c ages date the eruptions that produced the white river and bridge river tephras two important holocene marker beds in western canada the 14c ages were obtained on trees in growth position buried in coarse tephra and a pyroclastic flow near the source vents the mean calendric age of the white river eruption based on four 14c ages is 1147 cal years bp calibrated years approximately equivalent to calendric years or ad 803 the 2 age range obtained from the two most precise 14c ages is 1014 1256 cal years bp or ad 694 936 the mean age of the bridge river eruption determined both from i the single most precise outer ring 14c age and ii the weighted mean of six outer ring 14c ages is 2360 cal years bp or 411 bc 2 age range 2349 2704 cal years bp or 755 400 bc

an automated approach for extracting barrier island morphology from digital elevation models abstract the response and recovery of a barrier island to extreme storms depends on the elevation of the dune base and crest both of which can vary considerably alongshore and through time quantifying the response to and recovery from storms requires that we can first identify and differentiate the dune s from the beach and back barrier which in turn depends on accurate identification and delineation of the dune toe crest and heel the purpose of this paper is to introduce a multi scale automated approach for extracting beach dune dune toe dune crest and dune heel and barrier island morphology the automated approach introduced here extracts the shoreline and back barrier shoreline based on elevation thresholds and extracts the dune toe dune crest and dune heel based on the average relative relief rr across multiple spatial scales of analysis the multi scale automated rr approach to extracting dune toe dune crest and dune heel based upon relative relief is more objective than traditional approaches because every pixel is analyzed across multiple computational scales and the identification of features is based on the calculated rr values the rr approach out performed contemporary approaches and represents a fast objective means to define important beach and dune features for predicting barrier island response to storms the rr method also does not require that the dune toe crest or heel are spatially continuous which is important because dune morphology is likely naturally variable alongshore