investigating the glacial history of the northern sector of the cordilleran ice sheet with cosmogenic 10be concentrations in quartz exposure durations of glacial landforms in widely separated areas of central yukon territory affected by the northern sector of the cordilleran ice sheet cis and alpine glaciers have been determined using cosmogenic 10be in quartz the aim of our research is to test previous reconstructions of glacial history and to begin to address the paucity of chronological control for the lateral and vertical extent of the northern cis chronological evidence for cis expansion predating the last glacial maximum comes from minimum surface exposure durations of c 100 ka for two bedrock samples within the reid glacial limit indicating a possible marine oxygen isotope stage ois 6 age for this event and from minimum exposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatak within the mcconnell glacial limit ois 2 indicating a possible ois 4 age high elevation minimum surface exposure durations within the mcconnell limit indicate that some areas formerly mapped as nunataks were covered by cold based ice prior to 30 ka montane glaciation in the mackenzie mountains outside the mcconnell glacial limit was contemporaneous with nearby cis advance at 17 ka with cis retreat by 15 ka deglaciation of the tintina trench a major ice discharge route was completed by 12 ka at this time ice in an adjacent discharge route to the south was still entering higher elevation valleys in the pelly mountains a lateglacial readvance may have peaked at ca 10 ka in the ogilvie mountains considerable variation in ages from individual landforms and possible complex histories require additional cosmogenic nuclide measurements to confirm interpretations

late pleistocene colonization of north america from northeast asia new insights from large scale paleogeographic reconstructions advances in large scale paleogeographic reconstruction define physical and environmental constraints relevant to understanding the timing and character of the first colonization of the americas during the late pleistocene diachronic mapping shows continental glaciers coalesced in central canada during the last glacial maximum lgm 20 000 14 000 years ago while unglaciated refugia existed along the northwest coast the bering land bridge connected asia and north america until about 10 000 years ago when the two continents were separated by rising sea level this visual analysis from large scale synthesis of recent geological and environmental research establishes timelines for biotically viable colonization corridors connecting eastern beringia to southern north america and provides insights into probable paleoindian origins and subsistence strategies

pollen and lignin records of late quaternary vegetation lake washington analyses of lignin oxidation products and pollen for an 11 meter core from lake washington provide independent but similar reconstructions of the late quaternary vegetation in the puget lowland an exception is in sediments of the late pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region this dissimilarity appears to result from different major provenances eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the lake washington drainage basin

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

evidence for nonlinear climate change two stratospheric regimes and a regime shift two regimes are found in the interannual variability of the large scale stratospheric flow in the northern hemisphere cold season the regimes are identified by studying the probability distribution of the leading principal component of the geopotential height which explains approximately 50 of the variance the probability distribution has a bimodal structure with two clearly separated peaks corresponding to two circulation regimes the two regimes are characterized by a strong and a weak vortex respectively and they therefore resemble the two phases of the stratospheric part of the arctic oscillation while the upper troposphere and the lower stratosphere are colder in the strong vortex regime than in the weak vortex regime the lower troposphere is warmer in particular over the continents an abrupt regime shift took place in the last half of the 1970s in favor of the more zonal regime the shift is manifested by a substantial change in the frequencies of the two regimes strong statistical significance for the two separate regimes is obtained by a monte carlo approach the regimes and the regime shift are found in two different datasets reducing the possibility that the results are due to inhomogeneities in the data the results support the nonlinear dynamical perspective on climate change suggested by t n palmer according to this idea the response to a weak forcing would be seen mainly in a change of the frequencies of the climate regimes while the spatial structure of the regimes would be relatively insensitive to the forcing

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

seismic anisotropy in the uppermost mantle back arc region of the northeast japan arc petrophysical analyses of ichinomegata peridotite xenoliths 1 a dense network of seismic stations has been deployed across the northeast japan arc to investigate mantle wedge structures to attain independent petrophysical constraints we determined the seismic properties of ichinomegata mantle xenoliths from the back arc region that were brought to the surface from the mantle lithosphere by volcanic eruptions we calculated the seismic properties of the xenoliths from olivine and pyroxene crystal preferred orientations and single crystal elastic constants the small magnitude of measured s wave splitting delay time of 0 22 s in the area where the xenoliths were entrained can be explained by the average seismic properties of mantle xenoliths for an approximately 20 km thick horizontal anisotropic layer indicating that the mantle lithosphere could be one of the dominant sources of seismic anisotropy this layer is possibly related to deformation in the uppermost mantle lithosphere due to back arc spreading along the northeast japan arc

shear wave polarization anisotropy and subduction induced flow in the mantle wedge of northeastern japan abstract shear wave polarization anisotropy in the central part of northeastern ne japan was investigated we analyzed s phases of 293 intermediate depth earthquakes recorded at 77 stations and obtained 1286 splitting parameters the obtained results show the systematic variation in splitting parameters across the arc the leading shear wave polarization directions fast direction obtained at stations in the western side of the study area are oriented nearly e w which is sub parallel to the direction of relative plate motion between the pacific plate and the north american okhotsk plate in contrast fast directions obtained at stations in the eastern side of the study area are oriented approximately n s stations in the western side have a larger average delay time compared to those in the eastern side these variations suggest that the nature of anisotropy is quite different between the eastern and the western sides both experimental studies on the deformation of olivine and numerical simulations of plate driven flow predict that the lattice preferred orientation of olivine causes the fast direction sub parallel to the flow direction for the conditions in the mantle wedge of ne japan we thus infer that the lattice preferred orientation of olivine generated by flow induced strain is the most likely candidate for anisotropy that produces splitting with e w fast direction three possible causes of anisotropy in the eastern side are considered deformation of water rich olivine in the mantle wedge trench parallel flow in the mantle wedge due to along strike dip variations in the slab and anisotropy in the crust and the slab we could not however determine which causes are dominant further systematic study is required to reveal the cause of anisotropy in the eastern side

late pleistocene coastal paleogeography of the queen charlotte islands british columbia canada and its implications for terrestrial biogeography and early postglacial human occupation molluscs sediment lithology and published sub bottom profiles are used to deduce sea levels outline the influence of glacially induced crustal displacement and reconstruct the paleoenvironment of the northeast pacific late quaternary coastline geo spatial modelling shows subaerially exposed land that could have been inhabited by plants and animals and also coastally migrating early north american peoples ice free terrain present by at least 13 790 150 14 c years bp a land bridge and edible molluscs are identified queen charlotte islands qci late pleistocene coastal paleogeography may assist in explaining the biogeography of many terrestrial plant and animal species along the broader northeastern pacific margin and provide evidence for researchers seeking late pleistocene early holocene glacial refugia late pleistocene early holocene coastlines that are not drowned and that may harbour early archaeological sites are identified along the western qci where migrants probably first travelled and the westernmost british columbia mainland where the effects of glacial ice were reduced

contrasting seismic reflectivity of the lower crust and uppermost mantle between ne japan and sw japan as illustrated by petrophysical analyses of mafic and ultramafic xenoliths 1 petrophysical analyses of mafic and ultramafic xenoliths reveal large contrasts in acoustic impedance between the lower crustal rocks and uppermost mantle rocks both beneath ichinomegata crater in ne japan and beneath oki dogo island in sw japan in contrast to minor contrasts in acoustic impedance both among the lower crustal rocks and among the uppermost mantle rocks beneath ichinomegata crater relatively large contrasts in acoustic impedance are present beneath oki dogo island between granulite and olivine gabbro in the lower crustal rocks as well as between plagioclase bearing wehrlite and other cumulus peridotites in the uppermost mantle rocks based on the existing petrologic models of the lower crust and uppermost mantle beneath ichinomegata crater and oki dogo island we then constructed model structures of the lower crust and uppermost mantle beneath these two areas composed of units with randomly arranged 100 m thick foliation parallel horizontal layers of xenolith samples and used these model structures to examine the seismic reflectivity beneath these two areas the results suggest the presence of strong seismic reflectors between the lower crust and the uppermost mantle in both areas although no other recognizable seismic reflector is expected beneath ichinomegata crater many seismic reflectors due to the above contrasts in acoustic impedance are expected both in the lower crust and in the uppermost mantle beneath oki dogo island thus a remarkable contrast in seismic reflectivity in the lower crust and uppermost mantle is likely present between these two areas as well as between ne japan and sw japan

investigating absolute chronologies of glacial advances in the nw sector of the cordilleran ice sheet with terrestrial in situ cosmogenic nuclides abstract geologic mapping in yukon territory canada over the past 100 years has revealed a consistent pattern of diminishing cordilleran ice sheet cis extent during successively younger glaciations although this pattern is generally accepted there is still much uncertainty about the number of glaciations their ages and the dynamics of the different lobes that constituted the digitate ice sheet margin their subglacial thermal regimes and ice thicknesses we address uncertainties in the timing of glaciation using cosmogenic nuclide exposure dating at key localities that straddle several major lobes of the cis in west central yukon territory differences in exposure duration within what are thought to be the same map units are perhaps due to inheritance older than expected but more likely result from postglacial shielding younger than expected or surface erosion despite a significant spread in exposure durations on moraines and within map units and tending to rely on longest exposure durations on moraines due to postglacial degradation and shielding our results indicate that the mcconnell glacial advance occurred during marine oxygen isotope stage mis 2 judging from oldest minimum apparent exposure ages of 15 7 1 5 and 17 7 1 6 ka a gladstone glacial advance occurred before 51 8 4 7 ka mis 4 and reid glacial advances before 79 8 7 3 and 82 8 7 5 ka consistent with mis 6 traces of even older glacial advances predate 100 ka 107 5 9 9 154 3 14 2 ka

chronological constraints on cordilleran ice sheet glaciomarine sedimentation from core md02 2496 off vancouver island western canada chronology based on 46 radiocarbon dates has been generated for md02 2496 western vancouver island canada subsequent correlation between glaciomarine sedimentary sequences within the core and the terrestrial stratigraphy of the cordilleran ice sheet for the last 50 ka provide new insight into cordilleran ice sheet processes glaciomarine sedimentation associated with the most recent advance fraser glaciation of the cordilleran ice sheet began at 30 5 cal kyr bp 25 14 c kyr bp extremely high sedimentation rates indicate the ice sheet became proximal to the site at 19 5 cal kyr bp 16 14 c kyr bp deposition of ice rafted detritus ird began at 17 cal kyr bp 14 14 c kyr bp and abruptly terminated at 16 2 cal kyr bp 13 5 14 c kyr bp indicating rapid regional ice sheet retreat a minor ird event followed at 14 7 cal kyr bp 12 5 14 c kyr bp glaciomarine sediment deposition abruptly ended at 10 2 cal kyr bp 8 8 14 c kyr bp with the resumption of biogenic sedimentation the olympia interstade is represented by an interval of hemipelagic sedimentation between 43 and 31 5 ka prior to 45 ka sediment deposition is controlled by glaciomarine processes with evidence for a significant ird event at 47 cal kyr bp 44171 06 14 c kyr bp

constraints on subduction geodynamics from seismic anisotropy 1 much progress has been made over the past several decades in delineating the structure of subducting slabs but several key aspects of their dynamics remain poorly constrained major unsolved problems in subduction geodynamics include those related to mantle wedge viscosity and rheology slab hydration and dehydration mechanical coupling between slabs and the ambient mantle the geometry of mantle flow above and beneath slabs and the interactions between slabs and deep discontinuities such as the core mantle boundary observations of seismic anisotropy can provide relatively direct constraints on mantle dynamics because of the link between deformation and the resulting anisotropy when mantle rocks are deformed a preferred orientation of individual mineral crystals or materials such as partial melt often develops resulting in the directional dependence of seismic wave speeds measurements of seismic anisotropy thus represent a powerful tool for probing mantle dynamics in subduction systems here i review the observational constraints on seismic anisotropy in subduction zones and discuss how seismic data can place constraints on wedge slab and sub slab anisotropy i also discuss constraints from mineral physics investigations and geodynamical modeling studies and how they inform our interpretation of observations i evaluate different models in light of constraints from seismology geodynamics and mineral physics finally i discuss some of the major unsolved problems related to the dynamics of subduction systems and how ongoing and future work on the characterization and interpretation of seismic anisotropy can lead to progress particularly in frontier areas such as understanding slab dynamics in the deep mantle

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

using a physical reference frame to study global circulation variability abstract the 3d structures of the free oscillations of an adiabatic and hydrostatic atmosphere around a basic state at rest were used as a physical filtering for atmospheric data this filtering procedure allows for the consideration of the three primitive variables u over the whole atmosphere simultaneously accordingly the computed statistics do not simply rely on the information provided by a single variable of circulation such as the 500 hpa geopotential field using this method two classical patterns were isolated in the barotropic component of the circulation one resembling the pacific north america pna pattern the other similar to the north atlantic oscillation nao pattern in summer associating the barotropic and the second baroclinic components a coupling in variability was retrieved between the strength of the winter stratospheric polar vortex and the tropospheric circulation over the north atlantic until now these modes had only been recovered by means of statistical analysis

progressive deformation partitioning and recrystallization of olivine in the lithospheric mantle abstract intense serpentinization within the machinoyama ultramafic body eastern most part of the yakuno ophiolite in the paleozoic maizuru belt sw japan resulted in the development of block in matrix structure in the brittle regime possibly associated with exhumation along a fault various microstructures are heterogeneously distributed throughout peridotite blocks in a serpentinite matrix the microstructures are classified into four domains according to olivine grain size coarse 1 0 1 5 mm medium 0 5 1 0 mm small 0 2 0 5 mm and fine grained 0 01 mm even in a single peridotite block the medium small and fine grained domains occur at various scales in particular the fine grained domain occurs in thin zones that cut across the other domains these observations suggest that deformation in the peridotites before the serpentinization was partitioned into anastomosing zones during progressive inhomogeneous non coaxial shear resulting in the simultaneous development of a range of microstructures from the coarse grained domain to the small grained domain olivine crystal preferred orientations tend to be weaker with decreasing olivine grain size indicating a change in deformation mechanism from dislocation creep to grain size sensitive creep moreover the fine grained domains contain much more second phase than the small grained domain even in the same sample suggesting the role of the second phases on strain localization during dynamic recrystallization of olivine

inchworm like source evolution through a geometrically complex fault fueled persistent supershear rupture during the 2018 palu indonesia earthquake abstract how does fault slip follow an earthquake rupture front propagating faster than the local shear wave velocity i e at supershear speed how does a supershear rupture front pass through a geometrically complex fault system resolving the evolution of such complex earthquake ruptures is fundamental to our understanding of earthquake source physics but these events have not been well captured by conventional waveform inversions of observational data we applied a new framework of finite fault inversion to globally observed teleseismic waveforms and resolved both the spatiotemporal evolution of slip and the fault geometry of the 2018 palu earthquake moment magnitude 7 6 in sulawesi indonesia we show that supershear rupture propagation for this event was sustained by transient slip stagnation and advancement as the rupture front passed through the geometrically complex fault system this peculiar inchworm like slip evolution was caused by the rupture front encountering fault bends with favorable and unfavorable orientations for rupture propagation our analysis also identified the possible existence of a fault junction beneath palu bay connecting an unmapped primary fault in northern sulawesi with the palu koro fault in the south

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

early wisconsinan mis 4 glaciation on haida gwaii british columbia and implications for biological refugia sea cliffs at cape ball on graham island british columbia expose a thick sequence of pleistocene sediments deposited during at least two glaciations in sequence from the base of the section the units are 1 stony mud 2 till 3 silt sand and peat 4 stony mud 5 laminated sand and silt 6 cross bedded sand and 7 till of special interest is unit 4 a massive to weakly stratified mud containing scattered stones that was deposited during the penultimate pleistocene glaciation marine isotope stage mis 4 this unit contains wood and marine shell fragments that have yielded non finite radiocarbon ages sand and silt with thin stringers of peat unit 3 directly underlie this stony mud and returned an optical age of 57 3 5 7 ka the stony mud is unconformably overlain by ponded sediments unit 5 and advance outwash unit 6 and till unit 7 deposited during the fraser glaciation mis 2 the optically dated unit and a correlative peat and silty sand unit at a nearby exposure have p

rarely observed short period 5 10 s suboceanic rayleigh waves propagating across the tyrrhenian sea 1 shallow earthquakes occurring in the southern part of the tyrrhenian basin excite a long duration low frequency coda that propagates efficiently along paths crossing the tyrrhenian sea seismograms recorded at regional distances in the italian peninsula are analysed in the frequency time domain and compared with synthetics computed in simple vertically varying media based on results of our modeling we interpret the coda as short period 5 10 s suboceanic rayleigh waves their large amplitude and long duration that we emphasize here are explained as due to the influence of the tyrrhenian water layer over a fast seafloor with little s wave attenuation qs 300 a satisfactory fit of amplitude and duration of the observed waveforms is obtained assuming a young oceanic model with an average water column of 1 to 2 km and relatively high s wave velocity 2 5 km s in the shallow crust

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

shear wave anisotropy beneath nicaragua and costa rica implications for flow in the mantle wedge 1 we present new shear wave splitting data from local events in costa rica and nicaragua recorded by the temporary july 2004 to march 2006 48 station tucan broadband seismic array observed fast polarization directions in the fore arc arc and back arc range from arc parallel to arc normal over very short distances 5 km when plotted at raypath midpoints making the direct interpretation of individual splitting measurements in terms of flow tenuous even when considering variations in the relationship between lattice preferred orientation and deformation e g b type dislocation creep in olivine therefore we tomographically invert the splitting measurements to find a three dimensional model of crystallographic orientation in the wedge we assume the elastic constants of olivine and orthopyroxene with hexagonal symmetry and use a damped iterative least squares approach to account for the nonlinear behavior of splitting when considering three dimensional ray propagation and distributions of anisotropy the best fitting model contains roughly horizontal arc parallel olivine 100 axes in the mantle wedge down to at least 125 km beneath the back arc and arc which we interpret to indicate along arc flow in the mantle wedge pb and nd isotopic ratios in arc lavas provide additional evidence for arc parallel flow and also constrain the direction northwest from costa rica to nicaragua and minimum flow rate 63 190 mm a with only slightly oblique subduction at 85 mm a of the relatively planar cocos plate the most likely mechanism for driving along arc transport is toroidal flow around the edge of the slab in southern costa rica generated by greater slab rollback in nicaragua two important implications of this arc parallel flow are the progressive depletion of the mantle source for arc lavas from costa rica to nicaragua and the possible need for significant decoupling between the wedge and downgoing plate

port eliza cave north american west coast interstadial environment and implications for human migrations abstract the timing of late pleistocene glacial advance retreat relative sea level and environmental viability between 25 and 12 5 ka 14 c yrs bp remain a key issue in the feasibility of a coastal migration route for the first north americans this is discussed on the basis of stratigraphic radiometric and faunal data for port eliza cave a raised sea cave on the west coast of vancouver island british columbia ice cover is indicated by the occurrence of 2 m of laminated clay representing deposition in a subglacial lake from immediately below this clay a diverse vertebrate fauna of marmot vole marten cervid and various species of birds and fish was recovered yielding ages of 18 16 ka these dates and others from the region show that ice cover on the outer coast was brief from ca 15 5 14 ka the fish species indicate that relative sea level was close to the cave and that salmon runs were likely present the terrestrial vertebrate fauna is consistent with a cool open parkland environment with maximum summer temperatures cooler than present these conditions lasted until at least 16 ka with a diverse fauna and favorable climate humans could have survived here on a mixed marine terrestrial diet confirming the viability of the coastal migration hypothesis for this portion of the route

late pleistocene terrestrial deposits on the continental shelf of western canada evidence for rapid sea level change at the end of the last glaciation a paleosol with in situ rooted plant remains has been found in a core at a water depth of 95 m on the central continental shelf of british columbia fluvial sediments associated with the paleosol are sharply overlain by lagoonal or shallow pond sediments these in turn are overlain by shallow marine ediments radiocarbon dates on wood fragments and root recovered from the cored sediments indicate that relative sea level was at least 95 m lower 10 500 yr b p and that the core site was rapidly transgressed by the sea shortly thereafter this rapid transgression was contemporaneous with an equally rapid regression at the heads of fiords on the british columbia mainland to the east the two are probably genetically linked and a result of late pleistocene deglaciation and the migration and collapse of a glacial forebulge our evidence indicates that large areas of the british columbia continental shelf were subaerially exposed 11 10 ka this may have facilitated the southward migration of early humans from beringia into mid continental north america at the end of the pleistocene

delaciation of the prince rupert kitimat area british columbia late wisconsinan sediments in the prince rupert kitimat area of west central british columbia were deposited in an isostatically depressed marine environment affected by grounded tidewater glaciers the most common sediments are 1 massive bedded and laminated muds and 2 stratified sand and gravel the former are accumulations of clay and silt size detritus transported in suspension from the mouths of meltwater streams and possibly in turbidity flows generated by submarine slope failures the muds locally contain scattered ice rafted stones fossil marine molluscs and foraminifera the main sand and gravel deposits are elevated deltas including both small incised fan shaped forms at the margins of the main valleys and enormous ice contact delta sandur complexes on the floor of kitsumkalum kitimat trough the largest valley in the study area delaciation occurred by downwasting and complex frontal retreat between about 13 000 and 10 000 bp the open outer coast became ice free first in response

resolving three dimensional anisotropic structure with shear wave splitting tomography summary shear wave splitting observations are a commonly used tool for inferring anisotropy and flow within the earth s interior here we present the development and validation of a new technique for imaging anisotropy in the upper mantle using local events shear wave splitting tomography swst the mantle is parametrized as a 3 d block model of crystallographic orientations with the elastic properties of olivine and orthopyroxene and both orthorhombic and hexagonal symmetries are tested to efficiently forward calculate splitting the christoffel equation is used to progressively split the horizontal components of a synthetic wavelet in each block of the model and predicted shear wave splitting parameters are obtained with an eigenvalue minimization technique numerically calculated partial derivatives are utilized in a linearized damped least squares inversion to solve for a best fitting model of crystallographic orientations to account for the non linear properties of shear wave splitting the inversion is applied iteratively and partial derivatives are recalculated after each iteration a starting model that incorporates information from predicted splitting parameters is found by spatially averaging fast directions and the ratio of observed to predicted splitting times models from inversions utilizing this average starting model reach lower misfit levels than do inversions with a random or uniform starting model modelling results using synthetic data from several anisotropic structures i e sharp lateral and vertical variations in anisotropy both within an idealized and a real nicaragua costa rica subduction zone illustrate the capabilities and limitations of swst with a station spacing of 25 km in an idealized subduction zone containing uniformly spaced events down to 225 km both the azimuth and dip of crystallographic axes are resolvable to a depth of 100 150 km and lateral heterogeneities in anisotropy on a scale of 50 km at arc and forearc distances from the trench are retrieved spatial resolution of anisotropy at scales of 75 km is possible further into the backarc above 150 km depth the geometry of stations and observed seismicity in the nicaragua costa rica subduction zone yields partial to good resolution at scales of 50 75 km beneath the forearc arc and limited regions of the backarc down to 100 km and resolution at coarser scales is possible in wider regions beneath the backarc given the distributions of seismic sources within many subduction zones and the advances in broad band seismic array deployments this new method offers a powerful means with which to constrain the orientation of anisotropic fabric in the upper mantle

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

three dimensional structure of p wave anisotropy beneath the tohoku district northeast japan 1 we retrieve three dimensional structures of isotropic and anisotropic velocities of p waves of the tohoku district from first p arrival time data assuming azimuthal anisotropy to be caused by hexagonal symmetry axes distributed horizontally in the earth the results show that the high velocity pacific slab is clearly imaged in the isotropic velocity structure even though the azimuthal anisotropy is taken into account in addition small scale low velocity regions and prominent low velocity anomalies are found just below the active volcanoes and in the mantle wedge above the high velocity pacific slab respectively the fast propagation axis of p waves is in mostly e w direction in the upper crust nearly n s and e w directions in the lower crust e w direction in the mantle wedge and n s direction in the descending pacific slab these features of the p wave anisotropy structure are consistent with those of lateral variations of the fast polarization directions measured previously by shear wave splitting observations the plausible factor that causes the crust anisotropy is interpreted as being alignment or preferred orientation of microcracks and crust minerals the mantle wedge anisotropy is attributed to lattice preferred orientation of the mantle minerals arising from present day mantle process such as the mantle wedge convection and the plate motion however the fast propagation axis of p waves in the slab is almost perpendicular to the magnetic lineation of the oceanic plate under the northwest pacific and thus the slab preserves the original anisotropic property that the pacific plate gained when it formed

the statistical connection between tropospheric and stratospheric circulation of the northern hemisphere in winter abstract the associated anomaly patterns of the stratospheric geopotential height field and the tropospheric geopetential and temperature height fields of the northern hemisphere are determined applying the canonical correlation analysis with this linear multivariate technique the coupled modes of variability of lime series of two fields are isolated in the space of empirical orthogonal functions the one dataset is the 50 hpa geopotential height field the other set consists of different height fields of the tropospheric pressure levels 200 500 700 and 850 hpa and the temperature of the 850 hpa pressure level for the winter months december january february two natural coupled modes a barotropic and a baroclinic one of linear relationship between stratospheric and tropospheric circulation are found the baroclinic mode describes a connection between the strength of the stratospheric cyclonic winter vortex and the tropospheric circulation over the north atlantic the corresponding temperature

deglacial rapid sea level rises caused by ice sheet saddle collapses a simulation of ice sheet retreat reveals two meltwater pulses coinciding with mwp 1a and the 8 200 year event caused by saddle collapses between ice domes during the last deglaciation the retreating ice sheets occasionally released massive amounts of fresh water these meltwater pulses are often implicated as important influences on abrupt climate change but the underlying triggering mechanisms are not clear here lauren gregoire et al show that saddle zones that connect adjacent high domes on ice sheets can be lowered by ongoing warming to an elevation at which they rapidly degrade leading to separate domes and a meltwater pulse that is consistent with geological observations although the mechanism itself is not novel the authors establish that two important sudden cooling events meltwater pulse 1a and the 8 200 year event were probably caused by saddle separation the last deglaciation 21 to 7 thousand years ago was punctuated by several abrupt meltwater pulses which sometimes caused noticeable climate change1 2 around 14 thousand years ago meltwater pulse 1a mwp 1a the largest of these events produced a sea level rise of 14 18 metres over 350 years3 although this enormous surge of water certainly originated from retreating ice sheets there is no consensus on the geographical source or underlying physical mechanisms governing the rapid sea level rise4 5 6 here we present an ice sheet modelling simulation in which the separation of the laurentide and cordilleran ice sheets in north america produces a meltwater pulse corresponding to mwp 1a another meltwater pulse is produced when the labrador and baffin ice domes around hudson bay separate which could be associated with the 8 200 year event the most pronounced abrupt climate event of the past nine thousand years7 for both modelled pulses the saddle between the two ice domes becomes subject to surface melting because of a general surface lowering caused by climate warming the melting then rapidly accelerates as the saddle between the two domes gets lower producing nine metres of sea level rise over 500 years this mechanism of an ice saddle collapse probably explains mwp 1a and the 8 200 year event and sheds light on the consequences of these events on climate

distinct winter patterns of tropical pacific convection anomaly and the associated extratropical wave trains in the northern hemisphere in this paper distinct patterns of boreal winter convection anomalies over the tropical pacific and associated wave trains in the extratropics are addressed the first leading mode eof1 of convection anomalies as measured by outgoing longwave radiation demonstrates an east west oscillation of deep convection with centers over the equatorial central pacific cp and over the tropical western north pacific and the maritime continent the second leading mode eof2 is also a dipole pattern with opposite centers straddling 170 w possibly modifying eof1 to some extent combining the first two leading modes five major categories of tropical convection anomalies can be identified for the period 1979 80 2012 13 the comparison between these five categories and the corresponding sst anomaly patterns indicates a nonlinear relationship between convection and sst the combination of eof1 and eof2 with in phase pcs exhibits an east west dipole pattern with opposite signs over west of the dateline and the maritime continent the negative phase of the two pcs named la nina pattern induces a negative pacific north american positive north atlantic oscillation teleconnection in the extratropics approximately opposite responses can be detected in its positive phase named cp el nino pattern the negative pc2 superposing positive pc1 named ep el nino pattern shows the strongest convection anomalies with enhanced depressed convection over the eastern western pacific and leads to a tropical northern hemisphere like teleconnection pattern and an anomalous anticyclone extending from the north pacific to the north atlantic the positive pc2 with neutral pc1 named western cp pattern shows weakly enhanced convection to the west of the dateline as a response to local sst warming around the dateline this convection anomaly pattern although weak is important and excites a northeastward wave train from the tropics to greenland resulting in surface air temperature cooling covering the northeastern north america and warmer and wetter conditions over western europe

a strong phase reversal of the arctic oscillation in midwinter 2015 2016 role of the stratospheric polar vortex and tropospheric blocking in january 2016 asia and north america experienced unusual cold temperatures although the global average of surface air temperature broke the warmest record during a strong el nino event this was closely related to the remarkable phase transition of the arctic oscillation ao which can be explained by stratosphere troposphere interactions first the quasi biennial oscillation changed to its westerly phase in summer 2015 and the stratospheric polar vortex was stronger in early to midwinter 2015 2016 as blocking did not occur in december the associated downward propagation signal resulted in a strongly positive ao in late december 2015 second after late december the positive phase of pacific north america pattern became apparent in el nino event which strengthened the aleutian anticyclone in the stratosphere in addition an equivalent barotropic blocking anticyclone was established in the troposphere over asia the coexistence of blocking over asia and north america characterized the negative ao and a strong zonal wave number 2 pattern due to stronger zonal wave number 2 signals from the troposphere the stronger stratospheric polar vortex was elongated with two cyclonic centers over asia and the north atlantic in january the resultant southward displacement of polar vortices was followed by rare snowfall in the subtropical region of east asia and a heavy snowstorm on the east coast of the united states

polar vortex controls coupling of north atlantic ocean and atmosphere 1 the structure of the north atlantic leading atmospheric winter variability mode strongly depends on the state of the polar stratospheric vortex if the polar vortex is strong one teleconnection pattern emerges in the upper troposphere while two mostly independent ones appear when the vortex is weak the anomaly patterns associated with the different polarities of these modes show strong differences in the wind fields and in the correlation of atmospheric variability with the sea surface temperature of the north atlantic only when the polar vortex is strong does a basin wide tripole correlation pattern exist between tropospheric variability and sea surface temperature under weak vortex conditions one of the variability modes correlates with the subtropical the other with the subpolar gyre these results suggest that a nao index based on near surface pressure that fails to account for the state of the polar vortex is a suboptimal representation of the tropospheric circulation variability

the kaapvaal craton seismic anisotropy petrophysical analyses of upper mantle kimberlite nodules a dense network of seismic stations has been deployed on the kaapvaal craton south africa to investigate the upper mantle seismic structures in order to bring independent petrophysical constraints we analyze a direct sampling of the cratonic upper mantle and determine the seismic properties of 48 mantle nodules brought up to the earth s surface by kimberlite eruptions seismic properties of these nodules are calculated from the olivine and pyroxene crystal preferred orientations and the single crystal elastic constants despite variations in the nodules compositions microstructures and crystallographic preferred orientations seismic anisotropy is rather homogeneous throughout the craton mean s wave anisotropy is weak 2 64 which is compatible with the small measured sks wave splitting mean delay time of 0 62 s

interdecadal variations in north atlantic sea surface temperature and associated atmospheric conditions abstract evidence is presented for a distinct pattern of ocean atmosphere relationship associated with interdecadal variability in the north atlantic region using a century of surface marine observations it is shown that middle and high latitude sea surface temperature sst display a long term fluctuation with negative anomalies before 1920 and during the 1970s and 1980s positive sst conditions prevailed from about 1930 to 1960 the pattern of interdecadal sst variability is constructed by subtracting the average field during 15 cold years from that during a similar interval of warm years the early century warming and the more recent cooling display a similar spatial pattern in both cases the pattern is basin scale and largely of one polarity with maxima in the vicinity of iceland in the labrador sea and northeast of bermuda the corresponding differences in surface atmospheric conditions are determined by averaging and subtracting in the same manner fields of sea level pressure slp and surf

early retreat of the alaska peninsula glacier complex and the implications for coastal migrations of first americans abstract the debate over a coastal migration route for the first americans revolves around two major points seafaring technology and a viable landscape and resource base three lake cores from sanak island in the western gulf of alaska yield the first radiocarbon ages from the continental shelf of the northeast pacific and record deglaciation nearly 17 ka bp thousands of calendar years ago much earlier than previous estimates based on extrapolated data from other sites outside the coastal corridor in the gulf of alaska pollen data suggest an arid terrestrial ecosystem by 16 3 ka bp therefore glaciers would not have hindered the movement of humans along the southern edge of the bering land bridge for two millennia before the first well recognized new world archaeological sites were inhabited

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

rapid sea level change and coastal evolution on the pacific margin of canada a rapid regression occurred off the northern pacific margin of canada approximately between 14 600 and 12 500 14c years b p contemporary with the deglaciation of the continental shelf primarily due to the rapid isostatic rebound sea level had reached a maximum lowering of greater than 150 m and remained low until approximately 12 400 14c years b p after which a rapid transgression occurred at 12 500 14c years b p the shelf tilt across the northern pacific margin of canada ranged between 50 m of submergence at prince rupert on the british columbia mainland to greater than 150 m of emergence on the western edge of the queen charlotte islands this regressive transgressive cycle lasted only from 5200 to 5500 14c years a result of the development and collapse of a glacioisostatic forebulge sediment supply wave action and tidal current energy are the primary factors that controlled the coastal response to these late quaternary relative sea level changes plate tectonics on the other hand played a secondary role in coastal evolution during deglacial regression extensive glacial outwash and glaciomarine deposition occurred except on the outer coast where sediment was transferred to the shelf break during the transgression of the shelf the sediment supply was primarily restricted to the erosion of the previously deposited deglacial deposits resulting in the formation of drowned wave cut terraces spit platforms and modification of estuarine environments as the sea level rose in steps the present unconsolidated coastline is mostly erosional during the most recent enso event the sea level rise of up to 0 4 m resulted in as much as 12 m of coastal retreat

on the changing nature of the regional connection between the north atlantic oscillation and sea surface temperature 1 evidence is presented that the correlation between the north atlantic oscillation nao in terms of the nao index and the north atlantic sea surface temperature sst is not stationary this is inferred from both reanalysis data from the u s national centers for environmental prediction national center for atmospheric research ncep ncar and the kaplan sea surface temperature data set two phases of winterly north atlantic atmosphere ocean covariability are identified by means of linear regression and correlation analysis during the recent decades since the late 1960s early 1970s and during the first 3 decades of the twentieth century the north atlantic sst is strongly correlated to the regional atmospheric circulation in the north atlantic sector i e the north atlantic oscillation during these periods the nao index defined as the difference of normalized sea level pressures on the azores and iceland is characterized by pronounced decadal variability and by mainly positive values in contrast the nao index is only weakly correlated to the north atlantic sst from the 1930s to the early 1960s when the nao index is characterized by weak decadal variability remote influences in particular from the tropical pacific region become important especially for the sst in the western tropical north atlantic

shear wave anisotropy in the crust mantle wedge and subducting pacific slab under northeast japan to study the anisotropic structure beneath northeast ne japan we made 4366 shear wave splitting measurements using high quality seismograms of many earthquakes occurring in the crust and the subducting pacific slab our results provide important new information on the s wave anisotropy in the upper crust lower crust mantle wedge and subducting pacific slab in the upper crust the anisotropy is mainly caused by the stress aligned fluid saturated microcracks the measured delay times dts increase to 0 10 s at 10 11 km depth the fast velocity directions fvds are parallel to either the tectonic stress or the strike of active faults the maximum dts for the low frequency earthquakes near the moho are 0 15 0 17 s suggesting strong anisotropy at the base of the crust or in the uppermost mantle the measurements for the intermediate depth earthquakes in the pacific slab show dominant e w trench normal fvds in the back arc area and n s trench parallel fvds in the fore arc area the trench normal fvds in the back arc area are caused by the corner flow in the mantle wedge as a result of the subduction of the pacific plate the maximum dts for the slab earthquakes reach 0 30 0 32 s at 100 km depth but only half of the total dts are produced in the mantle wedge the small dts in the mantle wedge may result from an isotropic or weak anisotropic zone in the middle of the mantle wedge in the fore arc the dominant trench parallel fvds for the slab earthquakes are consistent with those for the upper crust earthquakes and 80 of the total dts can be accounted for by the anisotropy in the crust in the subducting pacific slab the trench parallel fvds may reflect either the original fossil anisotropy in the pacific plate when the plate was produced in the mid ocean ridge or the preferred orientations of the crystals and cracks in the upper part of the subducting slab

late glacial and early holocene sea level fluctuations in the central puget lowland washington inferred from lake sediments abstract analyses of sediments diatoms and pollen in a 12 65 m long sediment core taken from lake carpenter in the central puget lowland washington provide detailed information regarding the history of deglaciation and late glacial early holocene sea level changes the lake outlet now 8 2 m above sea level has been lowered 1 1 5 m by postglacial erosion the lithology and pollen record suggest that no lengthy hiatuses in sedimentation have occurred the basal sediments are glacialmarine and contain shell fragments and brackish marine diatoms freshwater sediments above the basal section are interrupted only by a short section containing few fossils most of which are brackish to marine indicators and by the mazama tephra at 9 5 m the pollen record in the basal 4 m reveals a pinus zone ca 13 850 11 000 yr b p with a brief peak of picea at ca 13 700 yr b p and an alnus pseudotsuga zone ca 11 000 6500 yr b p the chronology is based on nine radiocarbon ages a relative lowering of sea level below the 9 5 m threshold is recorded in the core at 12 41 m and dates 13 850 to 13 700 yr b p a marine episode occurred about 13 600 yr b p implying that relative sea level temporarily rose above 9 5 m no subsequent transgressions above the 9 5 m level have been recorded comparison of six radiocarbon dates 13 600 yr b p suggest that the marine reservoir correction of 760 yr currently used for this area may be too high for this time period

paleogeography glacially induced crustal displacement and late quaternary coastlines on the continental shelf of british columbia canada abstract subsequent to the last glacial maximum lgm complex isostatic adjustments resulted from deglaciation eustatic sea level change tectonic faulting and a relatively thin flexible lithosphere in the queen charlotte islands qci region a geostatistical interpolation model charts the sequence of evolving landscapes and displays temporal changes in the magnitudes and extent of crustal flexure that accompanied forebulge development on the late quaternary northeast pacific continental shelf between 14 2 and 8 7 ka bp wavelength and forebulge amplitude are consistent with thermal modeling implying low upper mantle viscosity and thin elastic lithospheric thickness beneath queen charlotte qc sound and hecate strait glacial ice 690 m thick began retreating from dixon entrance after 14 5 ka bp 14c years ago and prior to 12 6 ka bp permitting over 100 m of crustal uplift in northern hecate strait a forebulge persisted in hecate strait and qc sound from 13 2 until after 9 7 ka bp implying fixed glacial ice on the british columbia bc mainland until 10 ka bp paleogeographic reconstructions show two emergent ice free terrains one extending eastward from the qci and the other in qc sound by 11 7 ka bp a landbridge connected the bc mainland and the qci

late quaternary geology and geochronology of the central continental shelf of western canada piston cores and high resolution seismic profiles from queen charlotte sound have yielded new information on the late quaternary history of this part of the western canada continental shelf cores in three major troughs goose island mitchell s and moresby up to 130 km apart sample a similar sedimentary sequence this sequence comprises five units the lowest unit a which is up to 40 m thick is a laminated to massive mud containing coarse ice rafted debris deposited between pre 13 6 ka and 12 9 ka during deglaciation of queen charlotte sound this unit is overlain by a sequence of stratified sediments units b1 b3 up to 20 m thick deposited during the transition from the pleistocene to the holocene unit b1 directly overlies and is similar to unit a but lacks ice rafted detritus unit b2 is sandy mud locally gravelly deposited during a period of lagging and winnowing from about 12 9 to 10 2 ka when sea level in queen charlotte sound was lower relative to the land than it is today unit b3 is a laminated to massive mud similar to unit b1 deposited when water depths in queen charlotte sound rapidly increased at the end of the pleistocene due to the combined effect of eustatic sea level rise and forebulge collapse the sedimentary sequence is capped by up to 10 m of mud unit c which is more organic rich and contains more clay than any of the other units it was accumulating under present day conditions as early as 9 7 k y ago

variable microstructure of peridotite samples from the southern mariana trench evidence of a complex tectonic evolution abstract we retrieved samples of peridotite from a dredge haul kh92 1 d2 collected during cruise kh92 1 undertaken by the research vessel r v hakuho in 1992 at the landward trench slope of the southern mariana trench 11 41 16 n 143 29 62 e depth 6594 7431 m which is the deepest ocean in the world ten of 30 retrieved samples possessed both a foliation and lineation as assessed from 46 thin sections of various orientations and observations of hand samples the samples showed marked variation in microstructure ranging from coarse 5 mm equigranular and intensely elongated textures to finer

north pacific north atlantic relationships under stratospheric control 1 based on a linear regression correlation analysis of monthly mean atmospheric sea level pressure slp data from the national centers for environmental prediction ncep reanalysis 1948 2000 we find a significant anticorrelation between pressure in the northern north atlantic and north pacific only if the stratospheric circulation is in the strong polar vortex regime but not when the vortex is weak since some general circulation models gcms e g european center hamburg echam4 are biased toward the strong vortex regime svr they tend to reproduce this anticorrelation already in the mean the pattern of the arctic oscillation ao is shown to be consistent with the mean surface pressure differences between the two stratospheric regimes the typical sw ne tilt of the node line of the north atlantic oscillation nao found with linear analyses i e with such that do not take the regime character of the stratospheric circulation into account in northern hemisphere winter is due to a superposition of correlation patterns based on physical processes working in the troposphere a strictly meridional dipole and the pattern resulting from planetary wave refraction in the strong vortex regime and those produced by the rapid transition from one stratospheric regime to the other with subsequent downward propagation of the signal this result underlines the necessity of the application of nonlinear statistics or the restriction of linear statistics to variations in the stable quasi linear environment of natural regimes

the california current system as a transmitter of millennial scale climate change on the northeastern pacific margin from 10 to 50 ka a high resolution record of 18o and mg ca based temperatures spanning 10 50 ka has been reconstructed from the vancouver margin of the northeastern pacific ocean md02 2496 from two planktonic foraminiferal species neogloboquadrina pachyderma s and globigerina bulloides while 18ocalcite appears synchronous with dansgaard oeschger interstadials dois throughout the record millennial scale variability in sea surface temperatures ssts and reconstructed 18oseawater are frequently out of phase with greenland climate changes in water mass characteristics such as 18ocalcite and enriched 15n events apparently responded to millennial scale climate change during marine isotope stage 3 mis 3 such that negative 18ocalcite excursions coincided with heavier 15n these water mass characteristic shifts are suggestive of the presence of surface water advected from the eastern tropical north pacific etnp by relative strengthening of the california undercurrent cuc bringing warm salty tropical waters poleward the linkage between the strength of the cuc on the ne pacific margin and millennial scale climate change may be related to increased sea surface heights off central america as the intertropical convergence zone itcz shifted northward in response to changes in north atlantic ocean circulation poor correlations between proxies exist through late mis 3 into mis 2 ice sheet growth could have disrupted the linkage between cuc and the ne pacific margin as the laurentide ice sheet disrupted atmospheric circulation and the cordilleran ice sheet increasingly influenced regional paleoceanography

a post glacial sea level hinge on the central pacific coast of canada abstract post glacial sea level dynamics during the last 15 000 calendar years are highly variable along the pacific coast of canada during the last glacial maximum the earth s crust was depressed by ice loading along the mainland inner coast and relative sea levels were as much as 200 m higher than today in contrast some outer coastal areas experienced a glacial forebulge uplift effect that caused relative sea levels to drop to as much as 150 m below present levels between these inner and outer coasts we hypothesize that there would have been an area where sea level remained relatively stable despite regional and global trends in sea level change to address this hypothesis we use pond basin coring diatom analysis archaeological site testing sedimentary exposure sampling and radiocarbon dating to construct sea level histories for the hakai passage region our data include 106 newly reported radiocarbon ages from key coastal sites that together support the thesis that this area has experienced a relatively stable sea level over the last 15 000 calendar years these findings are significant in that they indicate a relatively stable coastal environment amenable to long term human occupation and settlement of the area our results will help inform future archaeological investigations in the region

3 d seismic velocity structure of the crust and the uppermost mantle in the northeastern japan arc 3 d seismic velocity structure of the crust and the uppermost mantle beneath the northeastern japan arc is investigated by using arrival time data from local earthquakes we use a velocity model composed of three layers corresponding to the upper crust the lower crust and the uppermost mantle respectively taking into account the observed regional variation of pn velocity the uppermost mantle is further divided into three parts by two pn velocity boundaries near the coasts of the japan sea and the pacific ocean the velocities within the upper crust the lower crust and the three parts of the uppermost mantle are assumed to be constant locations of two pn velocity boundaries and depth distributions of the conrad and the moho discontinuities are expressed by continuous functions of unknown parameters station corrections and hypocenters are also introduced to be unknowns these unknown parameters are determined by inverting arrival time data of p and s wave first arrivals and clear later arrivals of pg and p waves the pn velocity boundary between the land and the pacific ocean is located approximately along the pacific coastline and that between the land and the japan sea is nearly along the japan sea coastline the conrad and the moho discontinuities are at depths ranging from 14 to 20 km and from 27 to 36 km respectively the conrad and the moho depths have similar spatial distributions they are deep beneath the land and become shallower toward the western and the eastern coastlines beneath the land they are shallow in the central part of the tohoku district and become deeper toward both the north and the south directions in the north they become shallow again

life cycles of north atlantic teleconnections under strong and weak polar vortex conditions this paper investigates the role of the strength of the polar stratospheric winter vortex in the dynamics of the life cycles of north atlantic teleconnections a new set of teleconnection patterns was produced from low pass filtered daily 300 hpa height data of ncep national centers for environmental prediction reanalysis data 1958 1998 all teleconnections are meridional dipoles which to a certain degree resemble the north atlantic oscillation based on surface pressure data there are two distinct teleconnections one over the eastern and one over the western north atlantic during episodes of weak polar vortex and only one over the central north atlantic during strong polar vortex episodes the teleconnections have periods of about two weeks stream function tendency analysis of the life cycles shows that the relatively simple resulting teleconnections evolve from very complex structures during the growth phase of the teleconnection indices there are strong and systematic differences between the two polar vortex regimes while in the weak vortex regime the anomaly growth is mainly driven by transient eddy vorticity fluxes from the low frequency domain in the strong vortex regime there is also low frequency advection of relative vorticity resulting from the interaction of low frequency eddies with stationary eddies copyright 2006 royal meteorological society

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

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

radiocarbon age constraints on rates of advance and retreat of the puget lobe of the cordilleran ice sheet during the last glaciation abstract calibrated radiocarbon dates of organic matter below and above till of the last fraser glaciation provide limiting ages that constrain the chronology and duration of the last advance retreat cycle of the puget lobe in the central and southeastern puget lowland seven dates for wood near the top of a thick proglacial delta have a weighted mean age of 17 420 90 cal yr b p which is the closest limiting age for arrival of the glacier near the latitude of seattle a time distance curve constructed along a flowline extending south from southwestern british columbia to the central puget lowland implies an average glacier advance rate of ca 135 m yr the glacier terminus reached its southernmost limit ca 16 950 yr ago and likely remained there for ca 100 yr in the vicinity of seattle where the glacier reached a maximum thickness of 1000 m ice covered the landscape for ca 1020 yr postglacial dates constraining the timing of ice retreat in the central lowland are as old as 16 420 cal yr b p and show that the terminus had retreated to the northern limit of the lowland within three to four centuries after the glacial maximum the average rate of retreat was about twice the rate of advance and was enhanced by rapid calving recession along flowline sectors where the glacier front crossed deep proglacial lakes

pleistocene glacimarine sedimentation on the continental slope off vancouver island british columbia abstract cordilleran ice sheet activity has had a significant influence on glacimarine sediment transport and deposition on the western canadian continental slope resulting in distinct sediment facies here we present lithogenic sediment grain size distributions grains 250 m g 1 63 m 10 to 60 m and 2 to 4 m and mass accumulation rates mar from a marine core md02 2496 collected 50 km offshore of vancouver island british columbia the lithogenic fraction of sediment deposited on the slope increased as grain size decreased and sediment sorting increased at 30 ka when the cordilleran ice sheet grew into southern british columbia during the fraser glaciation as the ice sheet advanced onto the continental shelf near core md02 2496 between 19 and 17 ka the proximal ice margin dramatically increased lithogenic sediment mars glacimarine sedimentation at this time was associated with cyclic deposition of generally coarse poorly sorted sediment an 80 year cyclicity suggests the influence of 1 outburst floods 2 lunar or 3 solar cycles on tidewater outlet glacier discharge rapid ice sheet retreat at 17 ka is indicated by ice rafted debris ird deposition followed by the deposition of fine well sorted silt suggestive of iceberg discharge followed by rock flour in a meltwater plume lithogenic sediment mars decreased dramatically at the bolling with a brief return to coarse poorly sorted sediments during the younger dryas glacimarine sedimentation decreased by 10 ka as the cordilleran ice sheet extent diminished to the areal extent of modern ice fields

combined impacts of pdo and two types of la nina on climate anomalies in europe abstractcombined impacts of the pacific decadal oscillation pdo and two types of la nina on climate anomalies in europe are studied particularly the conjunction of the negative pdo phase and two different types of la nina events favors strong and significant north atlantic oscillation nao pattern anomalies with opposite polarity for the central pacific cp la nina a clear positive nao signal can be detected which is accompanied by positive surface air temperature sat anomaly and a dipolar structure of precipitation anomalies in europe in addition a typical negative pacific north america pna teleconnection pattern forms including a high pressure anomaly over the southeastern united states which may contribute to the development and maintenance of the nao anomaly by strengthening the baroclinicity and the local eddy mean flow interaction however for the eastern pacific ep la nina a zonal wave train in the high latitudes can be observed which is quite different from the typical pna st

laboratory earthquakes triggered during eclogitization of lawsonite bearing blueschist abstract the origin of intermediate depth seismicity has been debated for decades a substantial fraction of these events occurs within the upper plane of wadati benioff double seismic zones believed to represent subducting oceanic crust we deformed natural lawsonite rich blueschist samples under eclogite facies conditions 1 5 p 3 5 gpa 583 k t 1121 k using a d dia apparatus installed at a synchrotron beamline continuously monitoring stress strain phase changes and acoustic emissions aes two distinct paths were investigated i heating during deformation at pressures 2 5 gpa to maximum temperatures ranging from 762 to 1073 k during which lawsonite and glaucophane became gradually unstable while entering the stability field of lawsonite eclogite and the breakdown reaction of lawsonite was only crossed in case of the highest final temperature ii heating while deforming at a pressure

anisotropic structure under a back arc spreading region the taupo volcanic zone new zealand 1 we investigate anisotropy surrounding a continental back arc spreading region the central volcanic region cvr in the north island of new zealand and present a simple method for spatial averaging to examine heterogeneous anisotropy s phases from local earthquakes yield consistent trench parallel fast directions in the southern compressional region but varied directions in the northern extensional region in the forearc east of the cvr is nearly trench parallel suggesting shear in the mantle or trench parallel flow in the western cvr local phases from 50 to 80 km depth give parallel to extension 120 and phases from 150 to 220 km depth yield similar 150 these results suggest asthenospheric flow with olivine a axes oriented in the extension direction down to 100 150 km depth in the eastern cvr local phases show mixed suggesting that it is a transition between the western cvr and the forearc trench parallel for shallow local events within the cvr may be caused by fluid filled cracks trench parallel for deeper local events and for sks phases can be explained by standard olivine fabrics developed by lithospheric shearing by trench parallel flow and by fossil anisotropy in the subducting oceanic lithosphere alternatively in the cvr they could be caused in part by hydrous minerals at the slab mantle upper interface which could cause olivine a axes to orient parallel to the trench due to a maximum shear stress oriented perpendicular to the trench along the slab we suggest that trench perpendicular flow in the extensional region helps to drive fluids away from the slab while in the compressional region trench parallel flow fails to distribute the fluids explaining the location of changes in geophysical properties

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

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

paleoseismic signature in late holocene sediment cores from saanich inlet british columbia abstract this paper explores the paleoseismic record potentially preserved in the upper 40 m of hydraulic piston cores collected in 1996 at two sites in saanich inlet british columbia during ocean drilling program odp leg 169s the odp cores are missing 1 2 m of water rich sediment directly underlying the seafloor but this sediment is preserved in shorter piston cores collected in 1989 and 1991 the upper part of the odp cores consists of rhythmically laminated varved marine mud with intercalated massive beds interpreted to be debris flow deposits some of the debris flow deposits are linked to past earthquakes including the 1946 vancouver island earthquake m7 2 a great m8 9 plate boundary earthquake at the cascadia subduction zone in january 1700 and a large crustal or plate boundary earthquake about 1000 yr ago earthquakes may also be responsible for debris flows in about ad 1600 1500 1250 1150 850 450 350 180 and bc 200 220 500 900 and 1050 if so the average recurrence interval for moderate to large earthquakes which trigger debris flows in saanich inlet is about 150 yr this recurrence interval is broadly consistent with the frequency of moderate to large earthquakes in the region during the historical period debris flows however can also be triggered by non seismic processes making it difficult to assemble a complete earthquake record from the saanich inlet cores we propose that extensive debris flow deposits emplaced by single large failures or many smaller coincident failures probably have a seismic origin

cosmogenic 36cl dating of the maximum limit of the laurentide ice sheet in southwestern alberta cosmogenic 36cl ages were determined on 11 glacial erratics from the summits of porcupine hills and cloudy ridge waterton valley and the foothills south of cardston alberta these erratics were derived from the canadian shield and the rocky mountains of the waterton area they were laid down by 1 the most extensive advance of a canadian shield centred continental ice sheet into this region stratigraphically oldest glacial deposits 2 a montane glacial advance from the waterton valley stratigraphically intermediate glacial deposits and 3 an advance of continental glacial ice that overrode deposits of the intermediate age montane advance zero erosion rate 36cl ages of the erratics uncorrected for snow cover range between about 12 and 18 ka they support the hypothesis that the laurentide ice sheet reached farther into the southwestern foothills than did all the previous continental ice sheets

laurentide cordilleran ice sheet saddle collapse as a contribution to meltwater pulse 1a the source or sources of meltwater pulse 1a mwp 1a at 14 5 ka recorded at widely distributed sites as a sea level rise of 10 20 m in less than 500 years is uncertain a recent ice modeling study of north america and greenland gregoire et al 2012 has suggested that the collapse of an ice saddle between the laurentide and cordilleran ice sheets with a eustatic sea level equivalent esle of 10 m may have been the dominant contributor to mwp 1a to test this suggestion we predict gravitationally self consistent sea level changes from the last glacial maximum to the present day associated with the gregoire et al 2012 ice model we find that a combination of the saddle collapse scenario and melting outside north america and greenland with an esle of 3 m yields sea level changes across mwp 1a that are consistent with far field sea level records at barbados tahiti and sunda shelf

a record of past ocean atmosphere radiocarbon differences from the northeast pacific a record of the 14c age differences between atmosphere and the mixed layer of the northeast pacific ocean was obtained from 58 radiocarbon measurements on shells and associated wood from coastal sediments in british columbia this series of mixed layer reservoir ages spans the holocene and extends into the period of the younger dryas cold event in the north atlantic and surrounding regions the data reflect the extent of upwelling in the northeast pacific and thus constrain models of carbon cycling and ocean circulation most of the reservoir ages are only slightly less than than the present preindustrial value of about 800 years and may be identical when probable sampling errors are taken into account either the north pacific reached a state close to its present mode of circulation at or before the end of the younger dryas or a different circulation fortuitously produced a similar reservoir age our results support the hypothesis that slow changes in atmospheric radiocarbon concentrations over the holocene arose from 14c production rate changes data corresponding to a radiocarbon age of around 6400 years b p give a reservoir age of 1200 years if this result is confirmed it indicates a much greater variability for the holocene ocean circulation than was previously believed possible

late quaternary paleoenvironments of northwestern north america implications for inland versus coastal migration routes abstract although the long held normative view of new world colonization relies on entrance through an interior ice free corridor by terrestrially adapted big game hunters a recently demonstrated human presence in southern chile dating prior to the existence of the corridor route implies different colonization scenarios which must be seriously considered a renewed focus of archaeological and paleoecological research on early post glacial landscapes in northwestern north america has revitalized the ice free vs coastal corridor controversy geological findings from glacial geology and paleo sea levels support the possibility of coastal migration from beringia to the pacific northwest between about 14 000 and 10 000 bp and preliminary paleoecological data suggest that the coastal landscape was in part vegetated and probably able to support a terrestrial fauna including humans the same cannot be said about the ice free corridor

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

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

postglacial viability and colonization in north america s ice free corridor during the last glacial maximum continental ice sheets isolated beringia northeast siberia and northwest north america from unglaciated north america by around 15 to 14 thousand calibrated radiocarbon years before present cal kyr bp glacial retreat opened an approximately 1 500 km long corridor between the ice sheets it remains unclear when plants and animals colonized this corridor and it became biologically viable for human migration we obtained radiocarbon dates pollen macrofossils and metagenomic dna from lake sediment cores in a bottleneck portion of the corridor we find evidence of steppe vegetation bison and mammoth by approximately 12 6 cal kyr bp followed by open forest with evidence of moose and elk at about 11 5 cal kyr bp and boreal forest approximately 10 cal kyr bp our findings reveal that the first americans whether clovis or earlier groups in unglaciated north america before 12 6 cal kyr bp are unlikely to have travelled by this route into the americas however later groups may have used this north south passageway

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

equilibrium atmospheric response to north atlantic sst anomalies abstract the equilibrium general circulation model gcm response to sea surface temperature sst anomalies in the western north atlantic region is studied a coarse resolution gcm with realistic lower boundary conditions including topography and climatological sst distribution is integrated in perpetual january and perpetual october modes distinguished from one another by the strength of the midlatitude westerlies an sst anomaly with a maximum of 4 c is added to the climatological sst distribution of the model with both positive and negative polarity these anomaly runs are compared to one another and to a control integration to determine the atmospheric response in all cases warming cooling of the midlatitude ocean surface yields a warming cooling of the atmosphere over and to the east of the sst anomaly center the atmospheric temperature change is largest near the surface and decreases upward consistent with this simple thermal response the geopotential height field displays a baroclinic

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