terrigenous sediment supply in the scotia sea southern ocean response to late quaternary ice dynamics in patagonia and on the antarctic peninsula geochemical and mineralogical compositions of modern and late quaternary marine sediments from the scotia sea trace sources and transport paths of terrigenous sediment we discuss downcore variations of compositional data of two sediment cores from the northern and southern scotia sea that correlate with fluctuations in magnetic susceptibility sediments were derived from very different sources at both localities as revealed by contrasting clay mineral assemblages however a common feature is the input of more basic and undifferentiated crustal material with the potential of high magnetic susceptibility during glacial periods indicated by variable quartz feldspar ratios and major trace and rare earth elements terrigenous sediments mainly originate from nearby terrestrial sources or are introduced through interbasinal sediment transfer from adjacent seas the observed temporal compositional variations have to be attributed to changes in the relative detrital contributions from the diverse source areas ice mass extensions in southern patagonia on the antarctic peninsula and adjacent islands likely control the supply of glaciogenic detritus to the open ocean during times of glacial expansion diluting the sediment input of interbasinal origin current transport is mainly responsible for sediment dispersal to the pelagic scotia sea and may amplify the glaciological source signals during glacial climate periods because of a stronger wind forcing of the antarctic circumpolar current

history and isostatic effects of the last ice sheet in southern british columbia abstract the late wisconsinan cordilleran ice sheet covered british columbia southern yukon territory and parts of alaska washington idaho and montana its major source areas were the high mountain ranges of the canadian cordillera and flow was strongly controlled by topography the last ice sheet began to develop about 30 000 25 000 14c yr ago but it did not achieve its maximum extent until 15 000 14 000 14c yr bp ice sheet growth was interrupted locally by stillstands and retreat ice sheet decay was rapid and was characterized by complex frontal retreat at the periphery accompanied locally by brief readvances and by downwasting and stagnation by 10 000 14c yr bp

four pleistocene formations in southwest british columbia their implications for patterns of sedimentation of possible sangamonian to early wisconsinan age semiahmoo and dashwood drifts were deposited during the penultimate glaciation and highbury sediments and muir point formation during the last interglacial these sediments are defined and described and stratotypes are established for them based on arboreal pollen assemblages lithologic similarity and relative stratigraphic position semiahmoo drift of the fraser lowland is tentatively correlated with dashwood drift of vancouver island stone provenance till fabrics glaciotectonic structures cross bedding and stone imbrication indicate that regional ice and meltwater flowed out of major fiords in the coast mountains and into the ancestral strait of georgia during the penultimate glaciation ice flowed southeastward against the east coast of vancouver island and down the axis of the strait pollen and molluscs in semiahmoo and dashwood fossiliferous muds give evidence of transition from glaciomarine to marine conditions at the close of the penultimate glaciation highbury sediments of the fraser lo

marine derived 14c calibration and activity record for the past 50 000 years updated from the cariaco basin abstract an expanded cariaco basin 14c chronology is tied to 230th dated hulu cave speleothem records in order to provide detailed marine based 14c calibration for the past 50 000 years the revised high resolution cariaco 14c calibration record agrees well with data from 230th dated fossil corals back to 33 ka with continued agreement despite increased scatter back to 50 ka suggesting that the record provides accurate calibration back to the limits of radiocarbon dating the calibration data document highly elevated 14c during the glacial period carbon cycle box model simulations show that the majority of observed 14c change can be explained by increased 14c production however from 45 to 15 ka 14c remains anomalously high indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today additional observations of the magnitude spatial extent and timing of deep ocean 14c shifts are critical for a complete understanding of observed glacial 14c variability

coquitlam drift a pre vashon fraser glacial formation in the fraser lowland british columbia coquitlam drift is formally defined and stratotypes established for it in the coquitlam port moody area b c it is a pleistocene formation consisting of till glaciofluvial ice contact and glaciomarine sediments deposited between 21 700 and 18 700 years bp during the fraser glaciation late wisconsin and prior to the main vashon glacial maximum at about 14 500 years bp the drift was deposited in short pulses by valley and piedmont glaciers fluctuating into the fraser lowland from the coast mountains to the north and cascade mountains to the east

marine and limnic radiocarbon reservoir corrections for studies of late and postglacial environments in georgia basin and puget lowland british columbia canada and washington usa models of late glacial environmental change in coastal areas are commonly based on radiocarbon ages on marine shell and basal lake sediments both of which may be compromised by reservoir effects the magnitude of the oceanic reservoir age in the inland waters of the georgia basin and puget lowland of northwestern north america is inferred from radiocarbon ages on shell wood pairs in saanich inlet and previously published estimates the weighted mean oceanic reservoir correction in the early and mid holocene is 720 90 yr slightly smaller than but not significantly different from the modern value the correction in late glacial time is 950 50 yr valley head sites yield higher reservoir values 1200 130 yr immediately after deglaciation the magnitude of the gyttja reservoir effect is inferred from pairs of bulk gyttja and plant macrofossil ages from four lakes in the region incorporation of old carbon into basal gyttja yields ages from bulk samples that are initially about 600 yr too old the reservoir age declines to less than 100 yr after the first millennium of lake development when these corrections are accounted for dates of deglaciation and late glacial sea level change in the study area are pushed forward in time by more than 500 yr

atmospheric radiocarbon calibration to 45 000 yr b p late glacial fluctuations and cosmogenic isotope production more than 250 carbon 14 accelerator mass spectrometry dates of terrestrial macrofossils from annually laminated sediments from lake suigetsu japan provide a first atmospheric calibration for almost the total range of the radiocarbon method 45 000 years before the present the results confirm the recently revised floating german pine chronology and are consistent with data from european and marine varved sediments and combined uranium thorium and carbon 14 dating of corals up to the last glacial maximum the data during the glacial show large fluctuations in the atmospheric carbon 14 content related to changes in global environment and in cosmogenic isotope production

enhanced marine productivity off western north america during warm climate intervals of the past 52 k y studies of the santa barbara basin off the coast of california have linked changes in its bottom water oxygen content to millennial scale climate changes as recorded by the oxygen isotope composition of greenland ice through the use of detailed records from a sediment core collected off the magdalena margin of baja california mexico we demonstrate that this teleconnection predominantly arose from changes in marine productivity rather than changes in ventilation of the north pacific as was originally proposed

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

evidence for a younger dryas like cooling event on the british columbia coast two independent paleoclimatic records from the pacific coast of canada indicate that a late glacial warming trend was interrupted by a return to colder conditions between about 11 000 and 10 200 radiocarbon yr b p correlative with the classical younger dryas chronozone of the north atlantic region fossil benthic foramnifera from three cores from the continental shelf dated by accelerator mass spectrometry show peak abundances of the cold water indicator species cassidulina reniforme at this time fossil pollen spectra from two sites on the queen charlotte islands record a shift from forest to open herb rich vegetation after 11 100 yr b p probably in response to colder and wetter conditions identified by pollen climate transfer functions these preliminary data for a cold oscillation between ca 11000 and 10000 yr ago in the northeast pacific argue that this deglacial phenomenon was not restricted to the north atlantic but was a hemispheric and possibly global event

late pleistocene chronology and paleoclimate of vancouver island determined from cave deposits speleothems from four caves in south central vancouver island have been analysed by the 230th 234u method only speleothems from one cave cascade cave near port alberni contained sufficient uranium for them to be dated twenty seven ages determined for seven speleothems were found to cluster in two periods 67 28 ka corresponding to the olympia interstadial and 23 10 ka or 15 ka if corrected for detrital thorium contamination corresponding to the fraser late wisconsin deglaciation and holocene periods two speleothems were found to be deposited in isotopic equilibrium with their seepage waters profiles of variations in 18o of the calcite 18oc of each of the two deposits show a decrease of 1 3 over the growth period 64 28 ka at all times 18oc was less than 18o of modern calcite in the cave using modern cave temperature and the variation of 18o of seawater over the dated period the profiles of 18oc are interpreted in terms of a paleotemperature record for the olympia interstadial

crustal structure of the arabian plate new constraints from the analysis of teleseismic receiver functions an edited version of this paper was published by elsevier science copyright 2005 elsevier science see also http dx doi org 10 1016 j epsl 2004 12 020 http atlas geo cornell edu saudiarabia publications al damegh 202005 htm

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

late pleistocene glacimarine record in saanich inlet british columbia canada abstract late pleistocene deposits were cored at two sites in saanich inlet and provide a record of the sedimentary environment during deglaciation of this fjord at site 1033 at the southern end of the fjord 59 3 m of late pleistocene sediment was obtained in a hole drilled to 105 1 mbsf at site 1034 4 8 km to the north a hole was drilled to 118 2 mbsf recovering 49 8 m of late pleistocene sediment sediments were deposited in this deep 200 m fjord basin as a lobe of the cordilleran ice sheet retreated at the end of fraser glaciation this is the first recovery of basin fill sediments from the pleistocene retreat of the cordilleran ice sheet lithofacies analysis particle size measurements and 17 ams 14 c dates on marine shells or wood fragments are used to reconstruct the glacimarine sedimentary environment sediments are dense gray to olive gray terrigenous silty clay with thick graded sand beds and interlaminated fine sand and silt with mud scattered dropstones clusters of pebbles and pods of sand and granules are common bioturbation indicated by disruption of laminae and horizontal burrows or black mottles is minimal to moderate and decreases downcore a calving tidewater glacier retreated northward through saanich inlet however the ice contact sediments are beneath the depth cored at both sites the glacier retreated rapidly and the basin was open to marine exchange through satellite channel prior to 13 270 60 14 c yr bp the oldest date from the cores deposition of lithofacies association i occurred in an iceberg zone depositional environment dominated by turbid meltwater plumes and intense iceberg rafting within approximately 10 km of the glacier terminus after the glacier grounded at the head of cowichan bay lithofacies association ii was deposited in the ice distal depositional environment by turbidity currents that by passed the sill and turbid meltwater plumes lithofacies association iii was deposited under post glacial conditions at the end of the pleistocene

late wisconsinan glaciomarine deposition and isostatic rebound northern puget lowland washington the distribution and age of glaciomarine and marine sediment in the northern puget lowland washington demonstrate that rapidretreatofcontinentalice theeverson marineincursion andhighratesofisostatic reboundoccurredbetweenabout13 600and 11 300 14 c yr b p 11 3 ka glaciomarine and marine deposits are thickest in zones where retreating ice lobes grounded in the northeast puget lowland and near large drainages glaciomarine sediment was depositedmainlyfrom 1 submarineoutwash in ice proximal zones 2 turbid underflows dispersed melt water icebergs and resedimentation in transitional zones and 3 dispersedmeltwaterandcurrentsinicedistal zones marine estuarine and emergence intertidalandbeach faciesaccumulated in areas more than 10 km from ice margins particularly near major rivers molluscan and foraminiferal assemblages intheglaciomarineandmarinedepositsindicate that turbid cool brackish water covered much of the puget lowland during the everson interval water was generally shallower 30 m in the southern part of the area and deeper 15 60 m to the north mineralogy and geochemical properties such as boron or sodium content of the gravel free fraction do not clearly distinguish glaciomarine and marine deposits from terrestrial deposits isostatic rebound rapidly lifted the glaciomarine and marine deposits through sea level between about 13 5 and 11 3 ka the presentaltitudesofradiocarbon datedshell and the marine limit show that initial rates of isostatic rebound exceeded 10 cm yr 21 in thenorthernpugetlowland butdroppedto 2cmyr 21 before 11 ka the uplift gradient is about 0 6 m km 21 to the north and steepens locally to at least 1 3 m km 21 the pattern of emergence in the northern puget lowland is anomalous locally perhaps as a result of complex isostatic effects near the glacier margin rapid rise of sea level or tectonic deformation

regional patterns of pleistocene ice rafted debris flux in the north pacific ird mass accumulation rate mar records are presented for deep sea drilling project site 580 and ocean drilling program sites 882 and 887 and are combined with results from previous ird mar studies to provide a synthesis of north pacific pleistocene ice rafting important regional differences in the ice rafting histories of the nw and ne pacific are highlighted by this synthesis and include 1 significant variations in ird fluxes across the north pacific which identify two major ird sources coastal alaska and coastal siberia kamchatka peninsula and 2 significant variations in the timing of ird supply across the north pacific particularly in response to global scale climatic forcing these regional differences indicate that local and regional controls on iceberg input transport and melting exert a major influence on ice rafting throughout the north pacific this suggests that a single generalized ice rafting record for the north pacific does not adequately describe the complexity of this basin s pleistocene history data used to calculate lsrs and ird mars for sites 380 882 and 887 are available on diskette or via anonymous ftp from kosmos agu org directory apend usemame anonymous password guest diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 or by phone at 800 966 2481 15 00 payment must accompany order

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

14c activity and global carbon cycle changes over the past 50 000 years a series of 14c measurements in ocean drilling program cores from the tropical cariaco basin which have been correlated to the annual layer counted chronology for the greenland ice sheet project 2 gisp2 ice core provides a high resolution calibration of the radiocarbon time scale back to 50 000 years before the present independent radiometric dating of events correlated to gisp2 suggests that the calibration is accurate reconstructed 14c activities varied substantially during the last glacial period including sharp peaks synchronous with the laschamp and mono lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14c production rate together with plausible changes in deep ocean ventilation and the global carbon cycle during glaciation

intensification of the oxygen minimum zone in the northeast pacific off vancouver island during the last deglaciation ventilation and or export production 1 the oxygen minimum zone omz off vancouver island was more oxygen depleted relative to modern conditions during the allerod 13 5 to 12 6 calendar kyr and again from 11 to 10 kyr the timing of omz intensification is similar to that seen throughout the north pacific although the onset appears to have been delayed by 1500 years off vancouver island radiocarbon dating of coeval benthic and planktonic foraminifera shows that between 16 0 and 12 6 kyr the age contrast between surface and intermediate waters 920 m depth off vancouver island was similar to or slightly less than that today there is no evidence of an increased age difference i e decreased ventilation during the deglaciation particularly during the allerod however sedimentary marine organic carbon concentration and mass accumulation rate increased substantially in the allerod suggesting that increased organic matter export was the principal cause of late pleistocene omz intensification off vancouver island

timing and extent of allerod and younger dryas age ca 12 500 10 000 14c yr b p oscillations of the cordilleran ice sheet in the fraser lowland western north america the use of shaded digital topographic models to visualizes suites of topographic features stratigraphy and field mapping reveals newly recognized multiple moraines associated with oscillations of the remnants of the cordilleran ice sheet in the fraser lowland along the western washington british columbia border morphologic features show the extent of ice represented by sumas drift ca 11 600 10 000 14c yr b p following ca 3000 yr of retreat from the glacial maximum fraser glaciation positions 80 km south of seattle and in the strait of juan de fuca the paleogeography of the ice margin and timing of ice retreat during the sumas stade is reconstructed and bracketed by 70 radiocarbon dates 24 on marine shells 46 on wood and peat which are secured by morphologic and stratigraphic evidence four topographically distinct phases of the sumas deglaciation model are suggested phase si 11 600 11 400 14c yr b p outermost drift scattered remnants of ice contact deposits phase sii 11 600 11 400 14c yr b p glacier readvance building prominent moraine followed by glacier retreat phase siii 10 980 10 250 14c yr b p glacier readvance building of multiple moraines followed by glacier retreat phase siv 10 250 10 000 14c yr b p glacier readvance building of inner moraine followed by glacier retreat

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

variations of younger dryas atmospheric radiocarbon explicable without ocean circulation changes the concentration of radiocarbon 14c in the atmosphere depends on its production rate by cosmic rays and on the intensity of carbon exchange between the atmosphere and other reservoirs for example the deep oceans for the holocene the past 11 500 years it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field1 2 3 recent progress in extending the radiocarbon record backwards in time4 5 6 7 8 9 10 has indicated especially high atmospheric radiocarbon concentrations in the younger dryas cold period between 12 700 and 11 500 years before the present these high concentrations have been interpreted as a result of a reduced exchange with the deep ocean reservoir caused by a drastic weakening of the deep ocean ventilation7 8 9 11 12 here we present a high resolution reconstruction of atmospheric radiocarbon concentrations derived from annually laminated sediments of two polish lakes lake go ciaz and lake perespilno these records indicate that the maximum in atmospheric radiocarbon concentrations in the early younger dryas was smaller than previously believed and might have been caused by variations in solar activity if so there is no indication that the deep ocean ventilation in the younger dryas was significantly different from today s

organic carbon accumulation over the last 16 kyr off vancouver island canada evidence for increased marine productivity during the deglacial abstract the organic carbon content of marine sediments is commonly used as a proxy for export production however in continental margin sediments a large fraction of the organic matter may be of terrestrial origin and it is necessary to correct the total organic carbon data accordingly radiocarbon dating of bulk organic carbon organic geochemistry and isotope data 13c and 15n are used here to characterize the type of organic matter present in core jt96 09 collected at a water depth of 920 m on the slope off western canada the quantities of marine and terrestrial organic carbon are then estimated using the 13c data the 16 kyr record obtained from core jt96 09 suggests that accumulation of total organic carbon was highest during the late glacial and deglacial but geochemical data indicate that as much as 70 of this carbon is terrestrial in origin when the palaeo record is corrected for this terrigenous input it is observed that accumulation of marine organic matter and presumably marine export production increased at the end of the last glacial contemporaneous with the bolling and that it peaked during the allerod data from other palaeoproductivity proxies i e bio barium opal and alkenones also indicate relatively high productivity during the deglacial these results indicate a return to modern upwelling conditions and high marine export production at 14 3 calendar kyr bp and a period of enhanced upwelling relative to the present during the allerod

the sisters creek formation pleistocene sediments representing a nonglacial interval in southwestern british columbia at about 18 ka sisters creek formation is formally defined stratotypes are established for it and the time space chart is updated for the fraser lowland southwestern british columbia the sisters creek is a pleistocene formation comprising in situ and reworked organic rich sediments and nonorganic silt sand and gravel the formation was deposited during the port moody interstade within the late wisconsinan fraser glaciation 18o stage 2 between the coquitlam stade early fraser glaciation and the main vashon stadial maximum that occurred about 14 5 ka the sisters creek formation represents a glacial recession in southwestern british columbia that generally coincided with the timing of the last global glacial maximum the new time space chart implies that in fraser lowland the fraser glaciation represents the rapid advances and retreats of glacial lobes issuing from surrounding mountains which remained ice covered during interstades

late quaternary stratigraphy and seafloor geology of eastern juan de fuca strait british columbia and washington abstract a combination of shallow sediment cores and high resolution seismic reflection data were used to identify and map four main surficial geologic units in eastern juan de fuca strait these units comprise bedrock unit 1 till diamict unit 2 glacial marine unit 3 and post glacial sediments unit 4 bedrock crops out only in nearshore environments off vancouver island diamicton forms the numerous morainal and drumlin like banks in the region a series of banks including middle and hein banks and the offshore extension of dungeness spit divide the strait into two major areas based on the dominant surficial sedimentary units post glacial sediments are most common to the east and glacial marine sediments to the west glacial marine sediments are represented by several seismo lithologic subunits that suggest progression from ice proximal to ice distal depositional environments radiocarbon dates indicate these sediments are a product of the last phase of glacier retreat there is relatively little modern sediment input to eastern juan de fuca strait so most post glacial sediments are thought to consist of material reworked from glacial outwash or eroded from shallow bank deposits this conclusion is supported by radiocarbon ages from the post glacial sediments most of which are early holocene or younger also there are sandwave fields sediment drifts and barrier spits that appear to be actively maintained the source of sediment to these features is probably the pre existing deposits that occur in banks and extensive coastal exposures

optical dating studies of quaternary organic rich sediments from southwestern british columbia and northwestern washington state the suitability of optical dating using 1 4 ev infrared excitation for determining the time of deposition or compaction of organic rich sediments and peat is assessed with measurements on seven samples from six different lithostratigraphic units one is of zero age two have associated 14c ages three are known to have been deposited during an interglaciation and one is 1 ma old the samples yield satisfactory optical ages ranging from 0 to over 100 ka we conclude that the muir point formation southern vancouver island and the whidbey formation northwestern washington state were both deposited during 18o stage 5 as previously deduced from other evidence the age obtained from the 1 ma sample was significantly too low the optical dating method is simpler and more precise than thermoluminescence dating and is recommended for future work

paleodeviations of radiocarbon marine reservoir values for the northeast pacific differences in the radiocarbon ages of coeval marine shells and wood from emergent glaciomarine sediments in the fraser lowland of southwestern british columbia and northwest washington indicate that a total marine radiocarbon reservoir value of 1 1 1 k y is applicable in the region this is 40 greater 300 yr than the 800 yr value currently used to correct the ages of both modern and late pleistocene marine shells from this area the glaciomarine sediments were deposited rapidly between ca 12 5 and 11 5 1 4 c k y b p paleodeviations of the marine reservoir value may illustrate that rapid environmental changes occurred during the last glacial to interglacial transition these variations are thought to have been caused by changes in both deep and surface ocean circulation and by variations in the production of atmospheric radiocarbon 1 4 c these findings may indicate a rapid reordering of oceanic atmospheric circulation in the region

initiation and development of the laurentide and cordilleran ice sheets following the last interglaciation abstract fossil records from sites overridden by or adjacent to the laurentide ice sheet indicate that the climate of the last interglaciation oxygen isotope substage 5e ca 130 116 ka was warmer than today following the last interglaciation the laurentide ice sheet first developed during stage 5 over keewatin quebec and baffin island along its northern margin the ice sheet reached its maximum extent of the last glaciation during stage 5 the ice sheet advanced across baffin island onto the continental shelf early during stage 5 5d whereas the advance into the western canadian arctic occurred late during stage 5 5b the ice sheet also may have advanced into the st lawrence lowland during substage 5b although this event may be younger stage 4 the hudson bay lowland became ice free during substage 5a retreat of the ice sheet on baffin island occurred during late stage 5 probably substage 5a the exact timing of retreat from the western canadian arctic is unknown but it occurred before 48 ka the southern sector including the st lawrence lowland was ice free during late stage 5 the hudson bay lowland may have remained ice free through stage 4 and much of stage 3 because of conflicting chronologies however it is more likely that this area was glaciated throughout stage 3 and perhaps stage 4 nevertheless the data demonstrate that the lowland was ice free during part of the last glaciation an independent ice cap developed over the appalachian uplands and advanced across nova scotia during stage 4 perhaps as far as the edge of the continental shelf the ice cap remained active over nova scotia as a setellite to the laurentide ice sheet throughout the remainder of the last glaciation the ice sheet advanced into the st lawrence lowland during stage 4 and subsequently overwhelmed the local ice cap in the appalachian uplands advancing perhaps into northern new england but not farther south the lowland remained covered by the ice sheet until late stage 2 the ice sheet may also have advanced into the lake ontario basin during stage 4 the position of the northern margin of the laurentide ice sheet during stage 4 is not known but it remained an unknown distance behind its maximum position reached during stage 5 cores from baffin bay indicate a substantial decrease in high latitude glaciation during stage 4 following retreat the keewatin sector of the ice sheet may have remained over much of northwestern canada as a quasi stable ice mass until it readvanced during stage 2 similarly the baffin island sector of the ice sheet may have remained largely intact the southern margin of the ice sheet may have advanced into the lake ontario basin and upper mississippi valley during the middle of stage 3 ca 50 ka reaching its maximum extent of the last glaciation during stage 2 ca 18 21 ka advance of the northern margin was younger ca 8 13 ka than that of the southern margin this advance was less extensive than the penultimate advance stage 5 paleoenvironmental records indicate that the last interglaciation in areas covered by and near the cordilleran ice sheet was as warm as or warmer than present the cordilleran ice sheet appears to have developed during stage 5 or 4 at that time it advanced over southern british columbia and into the northern puget lowland there is no record of this event in northern areas that were later covered by the ice sheet the ice sheet disappeared before 59 ka at the beginning of a lengthy nonglacial interval paleoenvironmental records indicate that climate was similar to the present during part of this interval the ice sheet was absent and glaciers probably were confined to mountain areas throughout stage 3 climatic deterioration marking the end of this nonglacial interval may have begun as early as 29 ka by 14 15 ka the ice sheet had achieved its maximum extent of the last glaciation because there are few suitable dating methods capable of resolving events beyond the radiocarbon limit and because sites that preserve a record of events from the last glaciation are spatially restricted we consider this synthesis as tentative and subject to significant revision as dating methods improve nevertheless this perspective of the north american ice sheets through the last glaciation demonstrates their complex and dynamic behavior and attendant rapid fluctuations in ice volume

diffuse spectral reflectance as a proxy for percent carbonate content in north atlantic sediments diffuse reflectance records from fern drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the fern drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing abstract diffuse reflectance records from feni drift in the north atlantic faithfully record sediment percent carbonate a high resolu tion reflectance based age model for these sediments derived from an orbitally tuned age model for western equatorial atlantic ceara rise sediments was generated by spectral frequency mapping power spectra of the feni drift record indicate statistically significant sub milankovitch cyclicity at 7 6 8 4 and 4 8 6 1 kyr we infer that these 8 and 5 kyr cycles document a linkage between north and equa torial atlantic climate given our ability to correlate these records these climate cycles influence atlantic basin carbonate prior to the intensification of northern hemisphere glaciation and thus must arise from some portion of the climate system other than the dynamics of large ice sheets the presence of these peaks which could be related to equatorial clipped precession implies a possible non linear response to milankovitch forcing

paleoenvironments of the strait of georgia british columbia during the last deglaciation microfaunal and microfloral evidence the strait of georgia is situated between vancouver island and the western canadian mainland it was deglaciated quickly around 12 500 14c yr bp by in situ downwasting the subsequent marine invasion has left glacimarine sediments with foraminifers diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide the first paleoenvironment represents near ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers mostly elphidium excavatum just off the plume the second environment shows a peak of nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers mostly ice dwelling forms implying a long annual sea ice cover further away cassidulina reniforme increases n labradorica decreases while other calcareous foraminifer species colonize the area there are fewer ice diatoms more marine planktonic diatoms and dinocysts become more abundant finally after 12 000 14c yr bp calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low diversity arenaceous assemblage at the same time abundant planktonic diatoms and dinocysts indicate warmer surface temperature the succession of fossils and environments compares well with modern horizontal off glacier successions observed in fjords of the european arctic

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 aminostratigraphy of the georgia depression southwest british columbia amino acid ratios of certain taxa of molluscs and wood were determined for quaternary sediments in the georgia depression southwest british columbia the stratigraphy and proposed ages of established major units are confirmed in all but one case by the amino acid results aspartic acid ratios in clinocardium serripes nuculana mya macoma and hiatella averaged about 0 22 0 23 0 37 0 28 0 28 and 0 27 respectively in late wisconsinan capilano sediments and 0 37 0 35 0 44 0 44 0 56 and 0 44 respectively in early wisconsinan dashwood and semiahmoo sediments d l ratios of aspartic acid in abies averaged about 0 14 in late wisconsinan fraser drift 0 24 in the middle wisconsinan cowichan head formation and 0 37 in the early wisconsinan dashwood and semiahmoo drifts whereas d l ratios of aspartic acid from picea averaged about 0 13 in the cowichan head formation and 0 27 in the sangamonian muir point formation ratios for the muir point formation are judged to be much too low for the age

glacier surge after ice shelf collapse the possibility that the west antarctic ice sheet will collapse as a consequence of ice shelf disintegration has been debated for many years this matter is of concern because such an event would imply a sudden increase in sea level evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the larsen ice shelf on the antarctic peninsula before its collapse in 1995 satellite images and airborne surveys allowed unambiguous identification of active surging phases of boydell sjogren edgeworth bombardier and drygalski glaciers this discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves

ice cores as an index of global volcanism from 1850 to the present to evaluate an important cause of past climate change climate researchers need reliable estimates of volcanic aerosol loading in the atmosphere previous indices the dust veil index volcanic explosivity index and those by mitchell 1970 sato et al 1993 and khmelevtsov et al unpublished manuscript 1993 all have drawbacks ice core acidity and sulfate records because they contain physical evidence of atmospheric loading are a promising source of information on past volcanic aerosols but these records contain large nonvolcanic signals as well we have compared northern hemisphere nh and southern hemisphere sh annual average versions of five indices with eight nh and six sh ice core records for the period 1850 to the present in an attempt to identify the volcanic signal common to all records the indices are all highly correlated with each other for the nh although the individual ice core records are in general not well correlated with each other or with any of the indices a composite derived from averaging the cores the ice core volcano index ivi shows promise as a new index of volcanic aerosol loading this new index correlates well with the existing non ice core volcanic indices and with high frequency temperature records for the sh the individual ice cores and indices are better correlated the shivi is again highly correlated with all indices and individual ice cores but not with high frequency temperature records for both hemispheres the southern oscillation index shows no significant correlation with the volcanic indices ice cores or the ivi thus providing no evidence for the impact of volcanic eruptions on el nino southern oscillation events

humptulips revisited a revised interpretation of quaternary vegetation and climate of western washington usa abstract new pollen data from a 770 cm core of a mire at humptulips on the southwestern olympic peninsula 47 17 00 n 123 54 40 w and from a nearby deposit regarded as interglacial in age on the west fork of the humptulips river provide evidence for a reinterpretation of previous accounts of the quaternary vegetation and climate using a new age model the highly variable record at humptulips is here correlated with marine oxygen isotope stages ois 1 5a vegetation during ois 5a was pine dominated mixed woodland and tundra in ois 4 3 and 2 oscillations in pollen assemblages imply repeated intervals of mountain hemlock parkland and tundra pine as an indicator of openness is also abundant in these stages interstadial fluctuations in ois 3 reflect episodes of lowland western hemlock communities the earliest of the episodes is of infinite radiocarbon age and the latest dates to approximately 30 000 14 c yr b p parkland in ois 2 occurring after 24 600 until at least 18 440 14 c yr b p was replaced by transitional pine alder in ois 1 holocene which unlike any of the earlier stages conveys the development of modern lowland forest dominated by western hemlock pollen assemblages over the length of record imply that temperature and humidity at no time were as high as at present only in ois 3 do conditions approach those occurring in ois 1 during ois 2 3 and 4 when tree line apparently stood at the location of the site climate was colder and drier temperatures were depressed an estimated 5 c with precipitation close to 1000 mm compared with 2000 3000 mm at present atmospheric circulation during ois 2 appears to have been much controlled by the location of the laurentide ice sheet in the continental interior whereas under the current climatic regime beginning in the early holocene westerly air flow has dominated regulated by interplay between the north pacific high in summer and the wintertime aleutian low

late quaternary deglaciation and sea level history of eastern juan de fuca strait cascadia abstract eastern juan de fuca strait of southwestern british columbia northwestern washington state is near the western and southern terminus of late wisconsinan glaciation in north america seismic reflection profiles bathymetric data sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea level change in the eastern portion of the strait the retreating ice margin appears to have passed through the area between 14 460 200 and 13 595 145 14c yr glacial marine sediments date between 12 889 50 and 11 110 50 14c yr bp wave eroded unconformities drowned prograded deposits and a partially isolated low stand basin are evidence attributed to low stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features sea level change was rapid from 75 m immediately after deglaciation to possibly 60 4 m at 9920 60 14c yr bp after this time gradual sea level transgression took place relative sea level reached its approximate present position by 5470 115 14c yr bp since then relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift

olympia interstadial vegetation landscape history and paleoclimatic implications of a mid wisconsinan mis3 nonglacial sequence from southwest british columbia canada lithostratigraphic 14c and palynologic analyses of peat and silty peat at three nearby sites reveal a 25 000 year vegetation and climate history of the olympia interstade for the fraser lowland british columbia 300 km within the southern limit of the cordilleran ice sheet at lynn valley polypodiaceae fern spores and nonarboreal pollen dominate 47 8 14c ka bp reflecting unstable and cold landscapes a pinus poaceae zone follows representing pine parkland and cool dry climate fluctuating values of picea and tsuga mertensiana pollen at lynn and seymour valleys and port moody characterize most of the olympia interstade during local peat deposition in cyperaceae and myrica wetlands until about 26 7 14c ka bp under a cool and moist climate a brief pinus tsuga heterophylla zone at lynn valley 44 39 14c ka bp suggests a climatic optimum a poaceae artemisia assemblage and deposition of silty sand after 26 7 14c ka bp reflect cooling and drying after which a unique lycopodium assemblage at lynn valley

gcm evaluation of a mechanism for el nino triggering by the el chichon ash cloud the el chichon volcanic eruption in 1982 was immediately followed by the strongest el nino of the century in 1982 83 we investigate a possible mechanism proposed by hirono whereby volcanic eruptions might trigger or enhance el ninos three distributions of volcanic ash aerosol in the troposphere over the eastern pacific ocean were used to force simulations with a modified version of the ncar ccm1 atmospheric general circulation model for the month of april 1982 using observed sea surface temperatures only in the case of mid tropospheric heating is there a strong dynamical reaction in the atmosphere resulting in a weakening of the trade winds in the eastern pacific ocean north of the equator consistent with surface wind observations and with the first part of hirono s theory however the 1982 enso event had started before this wind anomaly and only trade wind collapses in the western equatorial pacific can initiate el ninos the results suggest that while tropospheric aerosols from volcanic eruptions can influence atmospheric circulation the timing and location of the el chichon eruption and the large enso event that followed was a coincidence and that hirono s mechanism was not responsible for the strength or timing of the el nino

possible association of stratospheric aerosols and el nino type events to determine whether the 1982 83 el nino event and the eruption of el chichon in april 1982 are related eleven similar eruptions at low latitudes 20 show just the opposite behavior they show significant cooling of the sea surface temperatures in this region especially in the fourth and fifth season after the eruption the association is found to be significant at the 95 level

sea surface temperatures in the subarctic northeast pacific reflect millennial scale climate oscillations during the last 16 kyrs changes of sea surface temperature sst in the subarctic ne pacific over the last 16 000 calendar years before present 16 kyr bp have been inferred from the study of c 37 alkenone unsaturation in a sediment core from the western canadian continental slope between 16 0 and 11 0 kyr three distinct cold phases 6 7 c interrupt two warmer periods 9 10 c within the 2 range of the radiocarbon based time control the observed sst oscillations correspond to the oldest dryas the bolling the older dryas the allerod and the younger dryas periods in the gisp2 18 o record these results represent the first high resolution marine paleotemperature estimates off the northern west coast of north america and imply that the climate of this region may be very strongly coupled to that of the north atlantic given the fast rates of sst change 1 c 40 80 yr such coupling must be controlled by atmospheric transmission of the climate signal

el chinchon eruption the dust cloud of the century on passe en revue les differentes methodes d observation du nuage de l eruption d el chichon satellite lidar observation aerienne

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

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

evidence for two intervals of enhanced 10 be deposition in antarctic ice during the last glacial period we have previously reported concentration profiles of cosmic ray produced cosmogenic 10be in deep ice cores from dome c and vostok antarctica1 2 in both these cores we found a concentration of 10be approximately two times larger in ice from the late glacial period than in the holocene ice we interpreted this as probably resulting from a lower precipitation rate on the antarctic plateau during glacial periods compared to interglacial periods in the vostok profile there was one sample corresponding to 60 000 yr bp which gave an unusually large 10be concentration not correlated with any obvious climatic event we suggested that this sample might be reflecting increased 10be production as for example during a period of reduced solar modulation2 we have now measured a much more detailed concentration profile for 10be in the vostok core the results confirm a 10be peak lasting 1 000 2 000 years at 60 000 yr bp and show another similar peak at 35 000 yr bp we have also observed the latter peak in the dome c core we discuss possible sources for these peaks and their potential as stratigraphic markers

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

radiocarbon profiles of the nw pacific from the lgm and deglaciation evaluating ventilation metrics and the effect of uncertain surface reservoir ages during the last deglaciation the ventilation of the subarctic pacific is hypothesized to have changed dramatically including the rejuvenation of a poorly ventilated abyssal water mass that filled the deep ocean and fluctuations in the strength of north pacific intermediate and deep water formation at millennial timescales foraminiferal radiocarbon reconstructions of past ventilation changes in the pacific are valuable but are hampered by poor carbonate preservation low sediment accumulation rates bias from bioturbation and poorly constrained past surface reservoir age in this study we present paired benthic planktonic radiocarbon measurements from the okhotsk sea and emperor seamounts we take advantage of large contemporaneous peaks in benthic abundances from the last glacial maximum bolling allerod ba and early holocene to produce time slices of radiocarbon from 1 to 4 km water depth we explore the impact of uncertain surface reservoir age and evaluate several approaches to quantifying past ocean radiocarbon distribution using our nw pacific data and a compilation of published data from the north pacific both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age but for a time slice from a small geographical area with radiocarbon independent stratigraphic correlation between cores the shape of a water column profile is independent of surface reservoir age the nw pacific profiles are similar in shape to the compilation profiles for the entire north pacific which suggests that deglacial surface reservoir age changes across the n pacific did not diverge dramatically across the areas sampled the last glacial maximum lgm profile 2 km spans a wide range of values ranging from values similar to today to lower than today however by the ba the profile has a similar shape to today ultimately local surface reservoir ages end member water mass composition and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

thermoluminescence dating tests for lacustrine glaciomarine and floodplain sediments from western washington and british columbia to help further develop reliable procedures for accurate thermoluminescence tl dating of quaternary waterlaid sediments we tested tl dating procedures on sediment types rarely examined six glaciolacustrine samples three samples of glaciomarine drift and eight samples of floodplain deposits we used the partial bleach r beta gamma technique applied to fine silt polymineral grains results from our younger known age glaciolacustrine sediments confirm earlier observations that only the clayey laminae are generally suitable for tl dating a clayey lamina older than ca 140 150 ka produced no age underestimation and this result ca 300 ka suggests that such older lake sediments are probably suitable for tl dating two proximal samples of glaciomarine drift produced large tl age overestimates whereas the single distal glaciomarine drift sample yielded an expected age 177 38 ka suggesting that follow up studies are warranted our results for eight flood plain samples confirm that zeroing of li

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

cyclic sedimentation produced by fluctuations in meltwater discharge tides and marine productivity in an alaskan fjord glacimarine sediment deposited in the fjord adjacent to muir glacier in south eastern alaska consists of rhythmically laminated muds stratified sandy mud sand and gravelly mud facies cyclicity is recorded by gravelly mud facies deposited during winter by ice rafting black mud laminae formed by spring plankton blooms and variations in tidal rhythmite thickness and texture produced by the interaction of meltwater discharges and tidal currents in the macrotidal fjord regular cyclicity in laminae thickness is tested statistically by fourier transform and can be attributed to a lunar tidal cycle control in the five cores collected up to 6 km from the sediment source cores close to the source can have additional laminae as a result of discharge fluctuations and distal cores may lack full cycles because of variability in the plume path and attenuation with distance cyclic variations in sediment texture are recorded in magnetic susceptibility ms profiles of the cores high ms values are produced by turbidite sand beds or by stratified sandy mud deposited by overflow plumes during peak summer meltwater discharge low values reflect muddy intervals deposited during periods of low meltwater discharge such as during autumn and winter sediment accumulation rates measured by 210pb dating range from 82 cm year 1 2 km from the sediment source at the head of the fjord to 16 cm year 1 6 km away these rates are within the same range as average sediment accumulation rates determined from cyclic seasonal markers within the cores these data show that with careful documentation annual cycles of glacimarine sediment accumulation can be detected within marine cores cores collected from the distal portion of the basin were deposited during the transition of muir glacier from a tidewater terminus ending in deep water to a terrestrial glacier with an ice contact delta deposited in front of the terminus this transition is recorded by a coarsening upward sedimentary sequence formed by turbidite sands originating from the prograding delta above fine grained laminated basin fill deposited by turbid overflow plumes

the magnetic susceptibility of continental shelf sediments west coast vancouver island canada abstract measurements of magnetic susceptibility of continental shelf sands off central vancouver island revealed two areas of anomalously high values 1 at the mouths of coastal inlets suggesting a reworking of glacial and glacio fluvial sediments and 2 the outer shelf downslope from outcropping deformed tertiary pleistocene strata resulting from the winnowing of these older sediments during periods of lowered sea level magnetic susceptibility was highest within the silt and fine sand fractions and lowest in the clay and coarse sand fractions though because of the grain size distributions the fine sand invariably contributed more to the overall sample susceptibility than the other size fractions although no apparent relationships were found between magnetic susceptibility and commonly measured grain size statistics the highest values were concentrated within a narrow range of size sorting skewness and kurtosis magnetic susceptibility is a readily determined parameter of marine sediments which can contribute to the interpretation of the depositional history of a region and which may have direct economic applications because of the association between magnetite and heavy mineral placers

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr