late pleistocene and holocene paleoenvironments of the north pacific coast abstract unlike the north atlantic the north pacific ocean probably remained free of sea ice during the last glacial maximum lgm 22 000 to 17 000 bp following a eustatic low in sea level of ca 120 m at 19 000 bp a marine transgression had flooded the bering and chukchi shelves by 10 000 bp post glacial sea level history varied widely in other parts of the north pacific coastline according to the magnitude and timing of local tectonism and glacio isostatic rebound glaciers covered much of the continental shelf between the alaska peninsula and british columbia during the lgm maximum glacier extent during the lgm was out of phase between southern alaska and southern british columbia with northern glaciers reaching their outer limits earlier between 23 000 and 16 000 bp compared to 15 000 14 000 bp in the south glacier retreat was also time transgressive with glaciers retreating from the continental shelf of southern alaska before 16 000 bp but not until 14 000 13 000 bp in southwestern british columbia major climatic transitions occurred in the north pacific at 24 000 22 000 15 000 13 000 and 11 000 9000 bp rapid climate changes occurred within these intervals including a possible younger dryas episode an interval of climate warmer and drier than today occurred in the early holocene cooler and wetter conditions accompanied widespread neoglaciation beginning in some mountain ranges as early as the middle holocene but reaching full development after 3000 bp

global change in earth history a personal point of view the global changes of the past took place during the progress of geological cycles and marked a drastic passage from an ancient pangaean regime of continental emergence to a new tethyan regime of submergence they occurred with a certain violence and rapidity and represented critical phases in the destabilization and subsequent reorganization of the geosphere and biosphere this process resulted in the destruction of certain assemblages e g biotic mass extinctions and the rise of new ones e g the emergence of new taxa these major phases of evolution and growth were probably connected to the upwelling of hot mantle material from great depths and a subsequent process of lateral spreading and outward migration of the mantle melt the ensuing marked increase in mantle activity degassing and explosive volcanicity produced catastrophic environmental perturbations with turning points in tectonics global climate sea level ocean and atmospheric chemistry palaeocirculation and palaeogeography

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

timing of terminal pleistocene deglaciation at high elevations in southern and central british columbia constrained by 10be exposure dating abstract the cordilleran ice sheet cis covered most of british columbia and southern yukon territory at the local last glacial maximum llgm during marine oxygen isotope stage 2 however its subsequent demise is not well understood particularly at high elevations east of its ocean terminating margin we present 10be exposure ages from two high elevation sites in southern and central british columbia that help constrain the time of initial deglaciation at these sites we sampled granodiorite erratics at elevations of 2126 2230 m a s l in the marble range and 1608 1785 m a s l in the telkwa range at the western margin of the interior plateau the erratics at both sites are near ice marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation the locations of the erratics and their relations to meltwater channels ensure that the resulting 10be ages date cis deglaciation and not the retreat of local montane glaciers our sample sites emerged above the surface of the cis as its divide migrated westward from the interior plateau to the axis of the coast mountains two of the four samples from the summit area of the marble range yielded apparent exposure ages of 14 0 0 7 and 15 2 0 8 ka these ages are 1 8 3 0 ka younger than the well established llgm age of ca 17 ka for the puget lobe of the cis in washington state they are 1 7 ka younger than the llgm age for the puget lobe if a snow shielding correction to their uncertainty weighted mean age is applied the other two samples yielded much older apparent exposure ages 20 6 1 4 and 33 0 1 5 ka indicating the presence of inherited isotopes four samples collected from the summit area of the telkwa range in the hazelton mountains yielded well clustered apparent exposure ages of 10 1 0 6 10 2 0 7 10 4 0 5 and 11 5 1 1 ka significant present day snow cover introduces a large uncertainty in the apparent exposure ages from this site a snow shielding correction based on present day snow cover data increases the uncertainty weighted mean exposure age of the telkwa range erratics to 12 4 0 7 ka consistent with deglacial 14c ages from areas near sea level to the west our exposure ages show a thinning of the southern portion of the cis shortly after the llgm and persistence of a remnant mountain ice cap in the central coast mountains into the younger dryas chronozone our data also show that the summit area of the marble range was ice covered during the llgm the presence of an ice body of considerable dimension in north central british columbia until or possibly even after the younger dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the skeena mountains in northwest british columbia and the need for better understanding of the response of the cis to lateglacial climate fluctuations

marine tephrochronology of the mt edgecumbe volcanic field southeast alaska usa abstract the mt edgecumbe volcanic field mevf located on kruzof island near sitka sound in southeast alaska experienced a large multiple stage eruption during the last glacial maximum lgm holocene transition that generated a regionally extensive series of compositionally similar rhyolite tephra horizons and a single well dated dacite med tephra marine sediment cores collected from adjacent basins to the mevf contain both tephra fall and pyroclastic flow deposits that consist primarily of rhyolitic tephra and a minor dacitic tephra unit the recovered dacite tephra correlates with the med tephra whereas many of the rhyolitic tephras correlate with published mevf rhyolites correlations were based on age constraints and major oxide compositions of glass shards in addition to lgm holocene macroscopic tephra units four marine cryptotephras were also identified three of these units appear to be derived from mid holocene mevf activity while the youngest cryptotephra corresponds well with the white river ash eruption at 1147 cal yr bp furthermore the sedimentology of the sitka sound marine core ew0408 40jc and high resolution swath bathymetry both suggest that extensive pyroclastic flow deposits associated with the activity that generated the med tephra underlie sitka sound and that any future mevf activity may pose significant risk to local population centers

possible refugia in the alexander archipelago of southeastern alaska during the late wisconsin glaciation the interpretation of the extent of late wisconsin glaciation in southeastern alaska has varied between geologists and biologists maps and reports of the region prepared by geologists commonly indicated that late wisconsin ice extended as a large uniform front west to the edge of the continental shelf however the distribution of plants and animals in the region has led many biologists to suggest that there may have been ice free areas that served as refugia during the late wisconsin based on analyses of aerial photographs topographic maps and bathymetric charts in conjunction with a review of previous literature and reconnaissance fieldwork throughout the region this study presents data supporting a limited ice extent in the alexander archipelago during the late wisconsin and identifies possible ice free areas that may have served as refugia these areas include 1 the fairweather ground 2 the herbert graves island area 3 the western coast of southern baranof island and adjacent continental

observations of mt etna volcanic ash plumes in 2006 an integrated approach from ground based and polar satellite noaa avhrr monitoring system abstract mt etna in sicily italy is one of the world s most frequent emitters of volcanic plumes during the last ten years etna has produced copious tephra emission and fallout that have damaged the inhabited and cultivated areas on its slopes and created serious hazards to air traffic recurrent closures of the catania international airport have often been necessary causing great losses to the local economy recently frequent episodes of ash emission lasting from a few hours to days occurred from july to december 2006 necessitating a look at additional monitoring techniques such as remote sensing the combination of a ground monitoring system with polar satellite data represents a novel approach to monitor etna s eruptive activity and makes etna one of the few volcanoes for which this surveillance combination is routinely available in this work ash emission information derived from an integrated approach based on comparing ground and noaa avhrr polar satellite observations is presented this approach permits us to define the utility of real time satellite monitoring systems for both sporadic and continuous ash emissions using field data visible observations collection of tephra samples and accounts by local inhabitants the duration and intensity of most of the tephra fallout events were evaluated in detail and in some cases the order of magnitude of the erupted volume was estimated the ground data vs satellite data comparison allowed us to define five different categories of etna volcanic plumes according to their dimensions and plume height taking into account wind intensity using frequent and good quality satellite data in real time this classification scheme could prove helpful for investigations into a possible correlation between eruptive intensity and the presence and concentration of ash in the volcanic plume the development and improvement of this approach may constitute a powerful warning system for civil protection thus preventing unnecessary airport closures

synchronization of north pacific and greenland climates preceded abrupt deglacial warming some proposed mechanisms for transmission of major climate change events between the north pacific and north atlantic predict opposing patterns of variations others suggest synchronization resolving this conflict has implications for regulation of poleward heat transport and global climate change new multidecadal resolution foraminiferal oxygen isotope records from the gulf of alaska goa reveal sudden shifts between intervals of synchroneity and asynchroneity with the north greenland ice core project ngrip 18 o record over the past 18 000 years synchronization of these regions occurred 15 500 to 11 000 years ago just prior to and throughout the most abrupt climate transitions of the last 20 000 years suggesting that dynamic coupling of north pacific and north atlantic climates may lead to critical transitions in earth s climate system

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

late quaternary glaciation and postglacial stratigraphy of the northern pacific margin of canada abstract areas of southeastern alaska and the queen charlotte islands of the northwestern pacific coast of north america were considered to be ice free during the late wisconsinan glaciation and glacial refugia existed however a glacier extended from mainland north america to the shelfbreak in dixon entrance separating alaska and the queen charlotte islands glacial retreat to the east began sometime after 15 000 to 16 000 14 c yr b p and ice had completely left dixon entrance by 13 500 to 13 000 14 c yr b p a rapid sea level regression occurred soon after deglaciation began due to isostatic rebound with relative sea level falling to approximately 150 m below present in central dixon entrance decreasing the size of the inlet by about 30 percent by 12 400 14 c yr b p the late quaternary glacial and postglacial stratigraphic sequence is more than 100 m thick overlying older pleistocene sediments and tertiary bedrock a late wisconsinan diamicton is overlain by glaciomarine muds formed between approximately 14 400 and 13 000 14 c yr b p contemporaneous with the deposition of the glaciomarine muds an extensive outwash deposit formed off the northern coast of the queen charlotte islands to a present depth of 150 m during the sea level lowstand and subsequent transgression a reworked sand unit was deposited over much of the seafloor to depths greater than 450 m the unit is exposed at the seafloor over much of the region suggesting that seabed hydrodynamic energy levels were high after 13 000 14 c yr b p and remain so today

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

postglacial vegetation history of mitkof island alexander archipelago southeastern alaska abstract an ams radiocarbon dated pollen record from a peat deposit on mitkof island southeastern alaska provides a vegetation history spanning 12 900 cal yr bp to the present late wisconsin glaciers covered the entire island deglaciation occurred 15 400 cal yr bp the earliest known vegetation to develop on the island 12 900 cal yr bp was pine woodland pinus contorta with alder alnus sedges cyperaceae and ferns polypodiaceae type by 12 240 cal yr bp sitka spruce picea sitchensis began to colonize the island while pine woodland declined by 11 200 cal yr bp mountain hemlock tsuga mertensiana began to spread across the island sitka spruce mountain hemlock forests dominated the lowland landscapes of the island until 10 180 cal yr bp when western hemlock tsuga heterophylla began to colonize and soon became the dominant tree species rising percentages of pine sedge and sphagnum after 7100 cal yr bp may reflect an expansion of peat bog habitats as regional climate began to shift to cooler wetter conditions a decline in alders at that time suggests that coastal forests had spread into the island s uplands replacing large areas of alder thickets cedars chamaecyparis nootkatensis thuja plicata appeared on mitkof island during the late holocene

glaciation and post glacial history of the continental shelf off southwestern vancouver island british columbia abstract bathymetry sediment distribution and seismic stratigraphy are used to interpret the pattern of glaciation of the continental shelf off southwestern vancouver island canada four seismostratigraphic units are distinguished and mapped in relation to sediments and sedimentary rocks present on the shelf they are 1 undivided tertiary bedrock 2 a unit composed mainly of pleistocene outwash 3 pleistocene morainal deposits and 4 holocene marine sediments a large piedmont glacier is envisaged formed by the coalescence of glaciers emanating from juan de fuca strait and barkley sound it cut a system of deep troughs into the tertiary bedrock built up a complex of morainal ridges and built out an extensive outwash plain on the unglaciated shelf to the northwest during glacial maxima the piedmont glacier extended right across the shelf particularly high discharge of debris from the seaward ends of the glacial troughs may have caused the erosion of adjacent submarine canyons during the final deglaciation the ice withdrew somewhat faster than the sea advanced although masses of downwasting ice may have persisted in many of the troughs the glacial topography including moraines and tertiary bedrock were levelled by the advancing sea but many of the troughs were preserved from burial perhaps because they were still ice filled or because the coastal system was sediment starved strong currents sweep the present shelf redistributing sand and mud winnowed from the tops of the truncated moraines into low lying areas and leaving concentrations of gravel behind

vulnerability of the cordilleran ice sheet to iceberg calving during late quaternary rapid climate change events 1 we present the first high resolution record of iceberg calving on the continental slope of vancouver island british columbia md02 2496 48 58n 127 02w 1243 m water depth through the last glacial from the cordilleran ice sheet cis these previously unknown ice rafted debris ird events representing significant retreat of the western margin of the cis out of marine waters show little correspondence with local climate change high resolution radiocarbon dating indicates that the younger ird events coincide with global radiocarbon age plateaus that allow direct correlation with distal climate records where the same plateaus have been identified the coincidence of episodic shedding of ird from the cis with north atlantic climate events i e north atlantic deep water shutdown and heinrich events begs the question what drove cis destabilization forcing appears to be external to cis dynamics perhaps resulting from either eustatic sea level rise or episodes of atmospheric warming over the north american continent

post glacial sea level change along the pacific coast of north america abstract sea level history since the last glacial maximum on the pacific margin of north america is complex and heterogeneous owing to regional differences in crustal deformation neotectonics changes in global ocean volumes eustasy and the depression and rebound of the earth s crust in response to ice sheets on land isostasy at the last glacial maximum the cordilleran ice sheet depressed the crust over which it formed and created a raised forebulge along peripheral areas offshore this combined with different tectonic settings along the coast resulted in divergent relative sea level responses during the holocene for example sea level was up to 200 m higher than present in the lower fraser valley region of southwest british columbia due largely to isostatic depression at the same time sea level was 150 m lower than present in haida gwaii on the northern coast of british columbia due to the combined effects of the forebulge raising the land and lower eustatic sea level a forebulge also developed in parts of southeast alaska resulting in post glacial sea levels at least 122 m lower than present and possibly as low as 165 m on the coasts of washington and oregon as well as south central alaska neotectonics and eustasy seem to have played larger roles than isostatic adjustments in controlling relative sea level changes

deglacial ocean warming and marine margin retreat of the cordilleran ice sheet in the north pacific ocean abstract a new high resolution planktonic foraminiferal mg ca based ocean temperature record has been generated for deep sea core md02 2496 sited offshore of vancouver island western canada during the last deglaciation 21 12 ka the relationship between cordilleran ice sheet cis retreat and changing regional ocean temperatures has been reconstructed through glaciomarine sediments in md02 2496 that capture tidewater glacier response to surface ocean thermal forcing at cis maximum extent the marine margin of the ice sheet advanced onto the continental shelf during this interval ocean temperatures recorded by surface dwelling globigerina bulloides remained a relatively constant 7 5 c while subsurface dwelling neogloboquadrina pachyderma s recorded temperatures of 5 c these ocean temperatures were sufficiently warm to induce significant melt along the tidewater ice terminus similar to modern alaskan tidewater glacial systems during the deglacial retreat of the cis the n pachyderma temperature record shows two distinct warming steps of 2 and 2 5 c between 17 2 16 and 15 5 14 ka respectively coincident with ice rafting events from the cis while g bulloides records an 3 c warming from 15 to 14 ka we hypothesize that submarine melting resulting from relatively warm ocean temperatures was an important process driving ice removal from cis tidewater glaciers during the initial stages of deglaciation

atmospheric scaling of cosmogenic nuclide production climate effect 1 absorption of cosmic rays by atmospheric mass varies temporally due to a redistribution of atmospheric pressure by ice sheets during glaciations the compression and expansion of the atmosphere due to cooling and warming and changes in katabatic winds near large ice masses these atmospheric processes can result in changes in production rates of cosmogenic nuclides which when integrated over long exposure durations may result in 0 to 5 adjustments in site production rates depending on location combining a ccm3 model with imbedded ice sheets for 20 ka we show that production rates changes relative to today are greatest at high elevations 6 7 at 5 km altitude due to atmospheric compression from decreased temperature production rates at specific times for sites near ice sheet margins can be reduced more than 10 due to a combination of katabatic winds draining off the ice sheet margins and atmospheric cooling nunatak settings may be significantly affected by the climate effect due to persistent glacial atmospheric conditions atmospheric variability may explain some of the disparities among cosmogenic nuclide production rate calibrations

time of maximum late wisconsin glaciation west coast of canada new data from a deep sea core in the eastern north pacific ocean indicate that the western margin of the late wisconsin cordilleran ice sheet began to retreat from its maximum position after 15 600 yr b p ice rafted detritus is present in the core below the 15 600 yr b p level and was deposited while lobes of the cordilleran ice sheet advanced across the continental shelf in queen charlotte sound hecate strait and dixon entrance the core data are complemented by stratigraphic evidence and radiocarbon ages from quaternary exposures bordering hecate strait and dixon entrance these indicate that piedmont lobes reached the east and north shores of graham island part of the queen charlotte islands between about 23 000 and 21 000 yr b p sometime thereafter but before 15 000 16 000 yr b p these glaciers achieved their greatest late wisconsin extent radiocarbon ages of late glacial and postglacial sediments from queen charlotte sound hecate strait and adjacent land areas show that deglaciation began in these areas before 15 000 yr b p and that the shelf was completely free of ice by 13 000 yr b p

extent and timing of the last glacial maximum in southwestern alaska a glacier complex composed of confluent alpine glaciers island ice caps and piedmont lobes covered much of the alaska peninsula and kodiak island during the last glacial maximum lgm because this glacier complex formed the southeastern border of beringia its dynamics may have been important in the timing and feasibility of the northwest coast route for human migration into lower latitude north america radiocarbon dates from stratigraphic sections on kodiak island and in the bristol bay lowlands bracket the lgm in southwestern alaska between 23 000 and 14 700 yr b p reconstruction of ice thickness based on glacier trimlines moraines and calculations of basal shear stress depict the alaska peninsula glacier complex flowing to the outer edge of the continental shelf in the gulf of alaska equilibrium line altitudes elas were 300 to 700 m lower than today and approached sea level on the southwestern alaska peninsula in northeastern areas where elas were higher bedrock topography largely controlled ice flow except where ice saddles bridged straits and inlets

late quaternary geology of eastern graham island queen charlotte islands british columbia a reconnaissance study of quaternary sediments exposed in coastal bluffs on eastern graham island has revealed the presence of two major till units each of which is underlain by glaciomarine stony mud outwash sand and gravel and laminated to massive silt and sand of undetermined origin sediment units below the surface drift are older than the radiocarbon dating limit sediments above this drift provide a nearly continuous record of geologic events from before 16 000 years bp until the present stratigraphic evidence and radiocarbon dates indicate that 1 late wisconsin glaciation of the coastal lowlands of graham island was weak and of short duration and 2 a period of low sea levels during late pleistocene time was followed by a transgression that culminated about 7500 8000 years ago when the sea was about 15 m higher relative to the land than at present marine regression during middle and late holocene time produced wave cut scarps wave cut benches overlain by littoral sediments bars spits and beach and dune ridges