little ice age glacial activity in peter lougheed and elk lakes provincial parks canadian rocky mountains dendrochronological lichenometric and i4c studies at 14 glacier sites in peter lougheed and elk lakes provincial parks were used to develop a chronology of little ice age glacial events the earliest indications of glacial activity are represented by moraines deposited prior to the 16th century a major glacial expansion in the 17th century is recorded at three sites where i4c dates show glaciers reached their maximum down valley positions lichenometric dates and tree growth suppression records show a phase of glacial activity early in the 18th century for which there is only sparse morainic evidence most moraines in the area date from a glacial advance culminating in the mid 19th century and moraine formation was complete everywhere by the late 1800 s recessional moraines are rare in the study area and indicate that ice front retreat has been relatively continuous since the 19th century the glacial chronology developed in this work is comparable to that reconstructed for both the main ranges of the canadian rockies and the coast ranges of the southern cordillera resum6 les ctudes dendrochronologique 1ichcnomctrique et radiomktrique au i4c de 14 sites rcalisces dans les parcs provinciaux de peter lougheed et de elk lakes ont servi a ctablir une chronologie des cvbnements glaciaires survenus durant le petit bge glaciaire les plus anciens indices de l activitk glaciaire sont reprcsentcs par les moraines dcposces anttrieurement au xvie sibcle une expansion glaciaire majeure durant le xviie sibcle est enregistrke sur trois sites ou les dates au 14c rcvklent la prksence de glaciers avec leurs positions de progression maximale vers le bas de la vallce les datations fondces sur la 1ichcnomctrie et sur les registres de cessation de la croissance des arbres montrent la prcsence d une phase d activitk glaciaire au debut du xviiie sibcle qui a iaissc peu de dcp8ts morainiques dtcelables la plupart des moraines qui apparaissent dans la rcgion datent d une avancce glaciaire qui avait atteint son apogce d extension au milieu du xixe sikcle et leur construction fut complctce vers la fin des annces 1800 les moraines de rkcession sont rares dans la rcgion ctudik cependant elles indiquent que depuis le xixe sibcle il y a eu un retrait relativement continu du front glaciaire la chronologie glaciaire ktablie dans la prcsente ctude est analogue i celle reconstruite pour les chaines principales des rocheuses du canada et pour le domaine c8tier de la cordillbre mkridionale traduit par la raaction

8000 year old wood from the athabasca glacier alberta several wood fragments of pinus sp dated at 8230 80 and 8000 90 years bp and abies sp were recovered from the snout of the athabasca glacier this wood derived from an unknown source up valley indicates that the glacier was less extensive than at present during the hypsithermal and that an area up valley of the present snout was tree covered ca 8000 8300 years bp

minimum age of deglaciation of upper elk valley british columbia bog sediments at an elevation of 1582 m in the upper elk valley of british columbia were dated at three horizons the lowermost of these radiocarbon dated at 13 430 450 years bp provides a mini

holocene tephrostratigraphy and glacial fluctuations in waterton lakes and glacier national parks alberta and montana waterton lakes national park in alberta and glacier national park in montana lie along adjacent sections of the continental divide in the rocky mountains in cirques or near divides there is evidence for two ages of glacial deposits younger deposits are generally well preserved poorly vegetated and bear no tephra and no or very small lichens older deposits are more poorly preserved better vegetated bear rhizocarpon sp lichens at least up to 92 mm in diameter and bear tephra the tephra often occurs in two different coloured horizons but both are compositionally equivalent to mazama tephra the older advance has a minimum age of about 6800 14c years bp and a probable maximum age of about 12 000 14c years bp it is correlated with the pre mazama crowfoot advance of the canadian rockies deposits of the younger advance are probably not too much older than mid 19th century because some glaciers began retreating from the deposits about then the younger advance is correlated to the cavell advance of t

evolution of the global overturning circulation since the last glacial maximum based on marine authigenic neodymium isotopes abstract the global overturning circulation is linked to climate change on glacial interglacial and multi millennial timescales the understanding of past climate circulation links remains hindered by apparent conflicts among proxy measures of circulation here we reconstruct circulation changes since the last glacial maximum lgm based on a global synthesis of authigenic neodymium isotope records end we propose the bottom up framework of interpreting seawater and authigenic end considering not only conservative watermass mixing but also the preformed properties and the non conservative behavior of end both subject to sedimentary influences we extract the major spatial temporal modes of authigenic end using principal component analysis and make a first order circulation reconstruction with budget constrained box model simulations we show that during the lgm the source region of north atlantic overturning shifted southward which led to more radiogenic preformed end of glacial northern source water nsw considering this preformed effect we infer that glacial deep atlantic had a similar proportion of nsw as today although the overall strength of glacial circulation appears reduced from both north atlantic and southern ocean sources which increased the relative importance of non conservative behavior of end and may have facilitated accumulation of respired carbon in the deep ocean during the deglaciation we find that southern ocean overturning increased which offset suppressed north atlantic overturning and resulted in a net stronger global abyssal circulation faster global scale deglacial circulation reduced the relative importance of non conservative effects resulting in atlantic pacific convergence of abyssal end signatures variations of southern ocean overturning likely drove a significant fraction of deglacial changes in atmospheric co2 and oceanic heat budget

pattern and forcing of northern hemisphere glacier variations during the last millennium time series depicting mountain glacier fluctuations in the alps display generally similar patterns over the last two centuries as do chronologies of glacier variations for the same interval from elsewhere in the northern hemisphere episodes of glacier advance consistently are associated with intervals of high average volcanic aerosol production as inferred from acidity variations in a greenland ice core advances occur whenever acidity levels rise sharply from background values to reach concentrations 1 2 equiv h kg above background a phase lag of about 10 15 yr equivalent to reported response lags of alpine glacier termini separates the beginning of acidity increases from the beginning of subsequent ice advances a similar relationship but based on limited and less reliable historical data and on lichenometric ages is found for the preceding 2 centuries calibrated radiocarbon dates related to advances of non calving and non surging glaciers during the earlier part of the little ice age display a comparable consistent pattern an interval of reduced acidity values between about 1090 and 1230 a d correlates with a time of inferred glacier contraction during the medieval optimum the observed close relation between noothern hemisphere glacier fluctuations and variations in greenland ice core acidity suggests that sulfur rich aerosols generated by volcanic eruptions are a primary forcing mechanism of glacier fluctuations and therefore of climate on a decadal scale the amount of surface cooling attributable to individual large eruptions or to episodes of eruptions is simlar to the probable average temperature reduction during culminations of little ice age alacier advances ca 0 5 1 2 c as inferred from depression of equilibrium line altitudes

neoglaciation in the southern coast mountains of british columbia chronology prior to the late neoglacial maximum moraine stratigraphy and morphology radiocarbon dates from klinaklini franklin tiedemann gilbert and bridge glaciers and related information from elsewhere in the coast mountains are used to construct a chronology for glacier fluctuations the garibaldi phase of glacier expansion 6000 5000 14c years bp at the end of the early holocene xerothermic interval is indicated by overridden tree stumps the mid neoglacial tiedemann advance 3300 1900 14c years bp is represented by moraines till and meltwater sediments at three glaciers but only tiedemann glacier attained its greatest holocene extent at this time late neoglacial expansion commenced before 900 14c years bp and continued without notable interruption until glaciers achieved their maximum post pleistocene expansion during the eighteenth and nineteenth centuries evidence for the garibaldi and tiedemann events is scarce within the coast mountains because of the more extensive late neoglacial advance however correlative advances have been

submesoscale instability and generation of mesoscale anticyclones near a separation of the california undercurrent abstractthe california undercurrent cuc flows poleward mostly along the continental slope it develops a narrow strip of large negative vertical vorticity through the turbulent boundary layer and bottom stress in several downstream locations the current separates aided by topographic curvature and flow inertia in particular near point sur ridge south of monterey bay when this happens the high vorticity strip undergoes rapid instability that appears to be mesoscale in eddy resolving simulations but is substantially submesoscale with a finer computational grid the negative relative vorticity in the cuc is larger than the background rotation f and ertel potential vorticity is negative this instigates ageostrophic centrifugal instability the submesoscale turbulence is partly unbalanced has elevated local dissipation and mixing and leads to dilution of the extreme vorticity values farther downstream the submesoscale activity abates and the remaining eddy motions exhibit an upscale organizati

postglacial vegetational history of tonquin pass british columbia a pollen and macrofossil study of peat sediments in tonquin pass british columbia provides the oldest dated record of vegetational and climatic changes in the middle canadian rockies paleoecological interpretation of these events dated by tephrochronology and radiocarbon dating is facilitated by comparisons with other regional pollen profiles late wisconsin ice receded from tonquin pass prior to 10 000 years bp by 9700 years bp a pinus contorta forest with an understory dominated by ferns had colonized the area the climate of this period was cool and moist following this interval was a brief episode 9000 8040 years bp of haploxylon pine dominance during which the climate became colder a long warm period beginning by 8040 years bp was characterized by desiccation of local meadows and fens and invasions of these areas by trees principally picea dated fossil picea and abies logs from alpine bogs within jasper national park document that timberlines had advanced beyond present limits by 8770 years b

glacier change in western north america influences on hydrology geomorphic hazards and water quality the glaciers of western canada and the conterminous united states have dominantly retreated since the end of the little ice age lia in the nineteenth century although average rates of retreat varied from strong in the first half of the twentieth century with glaciers stabilizing or even advancing until 1980 and then resuming consistent recession this retreat has been accompanied by statistically detectable declines in late summer streamflow from glacier fed catchments over much of the study area although there is some geographical variation over recent decades glaciers in northwest bc and southwest yukon have lost mass dominantly by thinning with relatively low rates of terminal retreat and glacier fed streams in that region have experienced increasing flows in many valleys glacier retreat has produced geomorphic hazards including outburst floods from moraine dammed lakes mass failures from oversteepened valley walls and debris flows generated on moraines in addition to these hydrologic and geomorphic changes evidence is presented that glacier retreat will result in higher stream temperatures possibly transient increases in suspended sediment fluxes and concentrations and changes in water chemistry with climate projected to continue warming over the twenty first century current trends in hydrology geomorphology and water quality should continue with a range of implications for water resources availability and management and hydroecology particularly for cool and cold water species such as salmonids copyright 2008 john wiley sons ltd

contourite distribution and bottom currents in the nw mediterranean sea coupling seafloor geomorphology and hydrodynamic modelling abstract contourites are common morphological features along continental margins where currents encounter the seafloor they can provide long term archives of palaeoceanography may be prone to sediment instability and can have a great potential for hydrocarbon exploration despite their importance and increasingly recognised ubiquitous occurrence worldwide the link between oceanographic processes and contourite features is poorly constrained in particular it is unclear under which specific conditions sediments are mobilised modified and deposited by bottom currents here we aim to determine key bottom current characteristics velocity and bottom shear stress affecting contourite deposition by assuming that recent oceanographic regimes may be extended back in time over the past glacial interglacial cycles with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials we present an integrated study from the nw mediterranean sea that couples results of the mars3d hydrodynamic model with high resolution sedimentological and geophysical data piston cores multibeam bathymetry and high resolution seismic data near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity respectively model results match well with the extent of contourite depositional systems and their different localised morphologic elements we deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces the heterogeneous distribution of bottom current intensity on slopes explains the development of different types of contourite drifts plastered drifts form in zones of low bottom current velocities constrained upslope and downslope by higher current velocities separated elongated mounded drifts develop where fast bottom currents decelerate at foot of the slope in contrast no mounded contourite morphologies develop when the current velocity is homogeneous across the slope especially in margins prone to downslope sediment transport processes in confined basins gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin favouring the development of fine grained contourites in the latter our results provide new insights into how detailed bottom circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow regimes at least over time spans when the overall paleogeography and the distribution of contourite drifts is comparable to present day conditions the approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional erosional and mixed contourite features may be used to understand other areas affected by bottom currents and for a better conceptual understanding of bottom current processes and their interactions with the seafloor

neoglacial history of the stikine iskut area northern coast mountains british columbia information about neoglacial features was obtained from aerial photograph interpretation observations during low level flights ground checking and historical records terminal moraines at great flood and mud glaciers date from the late seventeenth to early eighteenth centuries and recessional moraines at these glaciers and terminal moraines at glaciers farther east date from the late nineteenth to early twentieth centuries these late neoglacial terminal moraines appear in general to mark the greatest post pleistocene extent of the glaciers radiocarbon dates from overridden trees and soil indicate that 500 600 14c years bp glaciers were considerably more extensive than they are at present and were advancing preservation of a 3800 14c year old caribou antler in a snowbank that is now rapidly shrinking suggests that climate has been relatively cool and moist for the past four millennia

radiocarbon dated evidence of worldwide early holocene climate change radiocarbon dated glacial deposits from several different areas of the world indicate that alpine glaciers and ice caps in parts of both the northern and southern hemispheres expanded in response to climate change in early holocene time these data suggest that a worldwide episode of cooler climate similar in scope to the more recent neoglaciation occurred ca 8 500 7 500 yr b p

holocene glacier fluctuations in the canadian cordillera alberta and british columbia abstract although the record of holocene glacier fluctuations in british columbia and alberta is still very fragmentary much recent progress has been made in their study dating of end moraines has been supplemented by studies of lateral moraine stratigraphy and dating of glacially overridden organic matter upstream of end moraines dates from sites close to contemporary glaciers indicate that ice had retreated to about its present limits before 10 ka bp prior to deposition of mazama tephra a minor pre hypsithermal readvance the crowfoot advance left deposits in the rockies and the interior of british columbia the earliest known neoglacial advances occurred 5 6 ka bp in the coast mountains and shortly after 4 ka bp in the rockies an advance culminating ca 4 3 ka bp has been reported from bugaboo glacier while evidence of another advance culminating in the period ca 2 5 1 8 ka bp the tiedemann advance is reported from more than one site following a recession the little ice age expansion the cavell advance began shortly after 900 bp this advance culminated in most cases in the 18th or 19th centuries the crowfoot tiedemann and little ice age advances were apparently of roughly the same magnitude the latter was most extensive in most cases but at several sites crowfoot moraines lie slightly farther downvalley than little ice age moraines during the present century ice fronts have generally retreated particularly rapidly in the period 1920 1950 a d although rates of retreat have decreased in the last three decades and some glaciers have readvanced slightly

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

evidence for a neoglacial advance of the boundary glacier banff national park alberta direct evidence for an early neoglacial advance in the canadian rocky mountains is presented radiocarbon dates from buried peat and tree remains at boundary glacier suggest limiting dates for this advance of between 3800 and 4200 years bp these data from boundary glacier are consistent with previously published dates for the onset of the neoglacial and an early neoglacial advance

boundary mixing in orkney passage outflow one of the most remarkable features of contemporary oceanic climate change is the warming and contraction of antarctic bottom water over much of global ocean abyss these signatures represent changes in ventilation mediated by mixing and entrainment processes that may be location specific here we use available data to document as best possible those mixing processes as weddell sea deep and bottom waters flow along the south orkney plateau exit the weddell sea via orkney passage and fill the abyssal scotia sea first we find that an abrupt transition in topography upstream of orkney passage delimits the extent of the coldest waters along the plateau s flanks and may indicate a region of especially intense mixing second we revisit a control volume budget by heywood et al nature 2002 for waters trapped within the scotia sea after entering through orkney passage this budget requires extremely vigorous water mass transformations with a diapycnal transfer coefficient of 39 10 10 4 m2 s 1 evidence for such intense diapycnal mixing is not found in the abyssal scotia sea interior and while we do find large rates of diapycnal mixing in conjunction with a downwelling ekman layer on the western side of orkney passage it is insufficient to close the budget this leads us to hypothesize that the heywood budget is closed by a boundary mixing process in which the ekman layer associated with the weddell sea deep water boundary current experiences relatively large vertical scale overturning associated with tidal forcing along the southern boundary of the scotia sea this article is protected by copyright all rights reserved

reconstruction of holocene changes in alpine vegetation and climate in the maligne range jasper national park alberta abstract pollen macrofossil logs and needles and oxygen isotope data from tree rings are presented for three alpine bog sites in the maligne range of the canadian rockies organic sedimentation at the watchtower site began prior to ca 9500 14 c yr b p and by 8770 yr b p timberlines were at least 100 m above present levels the two pollen records are dominated by pinus and subsequent changes in timberlines are inferred from pollen ratio data abies pinus and from macrofossils the recovered records indicate two periods of high hypsithermal timberlines ca 8800 7500 and 7200 5200 yr b p separated by a short interval ca 7300 7400 yr b p when timberline approached modern levels after ca 4500 yr b p timberlines have been similar to or lower than present reaching minimum values in the last 500 yr 18 o determinations from the cellulose of samples of 5 or 10 annual rings cut from contemporary picea englemannii at timberline show strong correlations with mean annual temperatures at jasper isotopic determinations from hypsithermal age logs recovered from sites above present timberline indicate mean annual temperatures were at least 0 5 c warmer ca 8060 and 8770 yr b p than at present at the watchtower site data from logs at the maligne pass site suggest that temperatures were about 1 2 and 1 6 c warmer ca 6000 and 5300 yr b p estimates of temperature from the pollen ratio data are more conservative and suggest maximum differences of ca 1 0 c in july temperatures over the last 8000 yr

minimum age of deglaciation of upper elk valley british columbia discussion ferguson and osborn have reported a radionants but does not alter the basic isotopic composition carbon date of 13430 450years bp gx 5599 of the shells established while the gastropods were on gastropod shells from clay at the base of weary living and thus will not correct for old carbon effects bog in upper elk valley british columbia the date some indication of the magnitude of potential error in site is 29 km south of the mount joffre ice fields at the freshwater and terrestrial shell dates from western crest of the rocky mountains and therefore ferguson canada is provided by multiple radiocarbon determinaand osborn suggest that much or all of elk valley was tions on sundry organic materials from 1 early deglaciated before 13 500 years bp 2 postglacial lacustrine sediments in columbia valley because the interior plateau of british columbia near fauquier british columbia approximately 230 km remained covered by glacier ice until about 10500west southwest of weary bog lowdon and blake 11 000 years ago fulton 1971 clague 1980 1981 the 1976 p 10 and 2 postglacial fluvial or eolian weary bog date if valid has important implications for sediments adjacent to castle river near pincher creek the style and pattern of late wisconsin deglaciation in alberta approximately 120 km southeast of weary bog the southern canadian cordillera however for reasons lowdon and blake 1968 pp 220 22 1 outlined below i feel that deglaciation of upper elk five dates on wood and plant detritus at a single site valley before 13 500 years bp has not been conclusively near fauquier range from 8910 150 to 10 100 150 demonstrated by ferguson and osborn and i appeal years bp gsc 1212 and gsc 1012 shells anodonta for caution in the acceptance of their conclusions on the cf nuttalliana lea collected 1 m stratigraphically other hand in view of independent evidence that lower above wood dated 9590 150 years bp gsc 1613 elk valley perhaps was ice free by about 12 200 years yielded a date of 12 000 200 years bp gsc 1596 bp harrison 1976 i do not deny the possibility of early other shells from the same stratigraphic position as deglaciation gsc 1613 were dated at 12 800 250 years bp gscfreshwater and terrestrial shells commonly yield 1718 the dates on wood and plant detritus at this site errant radiocarbon dates due to incorporation of old are thought to be reliable because plant material is less carbon by mollusks prior to their death therefore the susceptible than shell to old carbon effects e g possibility that the true age of the weary bog gastropods hillaire marcel 1977 also the dates on wood and is younger than 13 430 450 years old must be plant detritus are compatible with independent radiocarconsidered ferguson and osborn briefly mention the bon geomorphic and stratigraphic data obtained elseincorporation of old carbon as a potential source of error where in columbia valley thus the shell dates at the in their shell date but elsewhere accept the date on face fauquier site probably are 2000 3000 years too old value without reservation as for example on p 1636 at castle river terrestrial gastropod shells and the date reported here suggests there was no major charcoal from the same stratum the charcoal is perhaps advance down the kananaskis valley after 13 500 years slightly lower in the sequence yielded radiocarbon bp and the canmore advance was probably dates of 3380 170 and 2680 140 years bp gscin retreat by 13 500 years bp the authors state that 741 and gsc 743 respectively the 700 year differsome potential error may have been prevented because ence between the two dates may be a result of old carbon the shells were leached in dilute hc1 to remove surface having been incorporated by the gastropods prior to their carbonate this procedure removes surface contamideath in view of the foregoing it seems likely that the weary bog shells are anomalously old although this note by a ferguson and g osborn 1981 canadian jourcannot be proved with the limited data on hand nal of earth sciences 18 pp 1635 1636 limestone and dolomite possible sources of dead 11 dates and time periods in this note are in radiocarbon carbon are common in the elk river basin upstream of years the date site and waters rich in bicarbonate probably

holocene and latest pleistocene glacial chronology glacier national park montana moraines of two different age groups have been identified fronting the present day glaciers and snowfields in glacier national park montana the subdued vegetated moraines of the older group have been found at 25 sites mainly in the central part of the lewis range these older moraines are in places overlain by the mazama ash although the exact age of the moraines has not been determined by radiocarbon dating vegetative evidence and correlation with other pre altithermal age moraines in the rocky mountains suggest that these older moraines date from 10 000 bp or earlier whether these moraines are the product of a separate advance after the end of the wisconsin glaciation or are simply the product of the last advance or stillstand of wisconsin glaciers before final deglaciation is not known moraines of the younger group consisting of fresh bouldery rubble are common throughout glacier park tree ring analyses indicate that some of these younger moraines were deposited by advances that culminated du

routes to energy dissipation for geostrophic flows in the southern ocean wind power inputs at the surface ocean are dissipated through smaller scale processes in the ocean interior and turbulent boundary layer simulations suggest that seafloor topography enhances turbulent mixing and energy dissipation in the ocean interior

recent glacier advances in the premier range british columbia aerial photography 1948 1985 and field investigations are used to reconstruct recent ice front fluctuations for 27 glaciers size range 0 63 17 9 km2 in the premier range british columbia rapid rates of frontal recession between ca 1930 and the mid fifties were followed by glacier readvance at many sites culminating in the 1973 1976 period when 90 of the monitored ice fronts were either advancing 68 or stable maximum downvalley advance was about 0 5 km median 90 m and 14 glaciers formed new terminal or lateral moraine ridges between 1970 and 1985 nine of these postdate 1976 one is dated to the 1980 1981 winter using tree rings the glacial advance is attributed to significant mass balance changes inferred from periods of increased winter precipitation ca 1951 1976 and low summer temperatures 1954 1968 measured at valemount warmer summers and reduced winter precipitation after 1976 account for the slight recession of ice fronts from maximum downvalley positions in the last few years

evidence from north west canada for an early holocene milankovitch thermal maximum according to the milankovitch theory of global climatic change maximum summer solar radiation at high latitudes of the northern hemisphere occurred at 10 000 yr bp refs 1 2 in particular it predicts summer solstice radiation greater by 9 10 preliminary climate simulation experiments with these increased values of radiation confirm that high latitude land surfaces received maximal insolation at 10 000 yr refs 3 4 paradoxically however the large volume of fossil pollen and other evidence from north america indicates a maximum of holocene warmth at 7 000 6 000 yr ref 5 and a recent review of the evidence from new england suggests that the warming began at 9 000 and ended at 5 000 yr but also stresses the difficulties of interpretation in terms of climate change6 we summarize here data from sites in the north west corner of mainland canada fig 1 that directly support the milankovitch hypothesis

the moho of north america a brief review focused on recent studies abstract recent national programs in canada lithoprobe and the u s earthscope are providing vast quantities of data and many new scientific insights concerning crustal and lithospheric mantle structure and evolution more modest but significant results are also being produced in and about mexico this paper primarily focuses on results published since 2005 and presents an updated moho map of north america this overview of crustal structure does reveal a number of interesting observations for example two buried distinct crustal blocks have been discovered in the past 20 years one was caught in a precambrian suture zone in canada and the other is buried under the gulf coast region and is still of unknown origin the precambrian assembly of the continent has been documented by the mapping of numerous suture zones and shallow portions of subducted slabs have been preserved in several cases not surprisingly the internal structure of these suture zones is complex and highly variable isostatic adjustment has been shown to be a complex process involving the lithospheric mantle not just crustal structure variations specifically the correlation of crustal thickness with elevation is only approximate at best several crustal blocks that have been stable over very long periods of time possess unusually thick crust whose lower portion is usually fast vp 7 0 km s rifting has been shown to affect the crust in a variety of ways ranging from the massive magmatic modification that produced the mid continent rift system to the broad region of extension in the basin and range province crustal structure along the active modern western margin of north america is highly complex as would be expected as a result of transitions between subduction and transform faulting and variations in volcanism and intraplate magmatism we clearly still have a lot to learn about the structure and evolution of this continent

overturning the mediterranean thermohaline circulation for more than five decades the mediterranean sea has been identified as a region of so called thermohaline circulation namely of basin scale overturning driven by surface heat and freshwater exchanges the commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites however the connection between convection and sinking in the overturning circulation remains unclear here we use a multidecadal eddy permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking we find that most of the net sinking occurs within 50 km of the boundary away from open sea convection sites vorticity dynamics provides the physical rationale for this sinking near topography only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking which is hence prevented in the open ocean these findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings they challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean

turning ocean mixing upside down abstractit is generally understood that small scale mixing such as is caused by breaking internal waves drives upwelling of the densest ocean waters that sink to the ocean bottom at high latitudes however the observational evidence that the strong turbulent fluxes generated by small scale mixing in the stratified ocean interior are more vigorous close to the ocean bottom boundary than above implies that small scale mixing converts light waters into denser ones thus driving a net sinking of abyssal waters using a combination of theoretical ideas and numerical models it is argued that abyssal waters upwell along weakly stratified boundary layers where small scale mixing of density decreases to zero to satisfy the no density flux condition at the ocean bottom the abyssal ocean meridional overturning circulation is the small residual of a large net sinking of waters driven by small scale mixing in the stratified interior above the bottom boundary layers and a slightly larger net upwelling driven b

revised 14c age for st helens y tephra at tonquin pass british columbia the age of a mount st helens set y tephra at tonquin pass british columbia previously assumed to be 4300 years bp is revised to ca 3400 years bp based on bracketing 14c dates of 3140 70 beta 13558 and 3680 80 years bp beta 13559 the implications of this revision for tephrostratigraphy of this area are discussed

use of lacustrine sedimentary sequences as indicators of holocene glacial history banff national park alberta canada abstract bottom sediments from three lakes in the canadian rocky mountains were examined with the aim of evaluating the usefulness of downvalley sediment studies in reconstruction of holocene glacial histories analyses of organic carbon and carbonate contents of core sediments provide information on changing sedimentation rate and changing relative importance of glacial and non glacial sediment sources sedimentary histories of the three lakes are similar suggesting that they record regional glacial climatic forcing rather than localized events and thus that they may be useful in reconstructing holocene glacial history lacustrine sediments indicate a period of high sedimentation rates and relatively large glacial sediment contribution prior to 7500 7000 yr b p with much reduced rates and decreased glacial sediment contribution between about 6000 and 4000 yr b p possibly interrupted by a brief period of increased glacial sediment output shortly after 5000 yr b p sometime after 4000 yr b p sedimentation rates and glacial sediment output began to rise again reaching approximately present levels by 2750 2650 yr b p and have not since returned to low mid holocene levels in detail over the last 3000 yr there is some indication of a slight decrease in sedimentation rate for more than 1000 yr after about 2200 yr b p sedimentation rates and glacial sediment input into all three lakes rose between about 900 and 750 yr b p and have remained very high since if the lake sediments are interpreted as a proxy record of upvalley glacial activity they allow the development of a glacial chronology which is at once generally consistent with and more complete and easily datable than the surficial glacial record

a perspective on the future of physical oceanography the ocean flows because it is forced by winds tides and exchanges of heat and freshwater with the overlying atmosphere and cryosphere to achieve a state where the defining properties of the ocean such as its energy and momentum do not continuously increase some form of dissipation or damping is required to balance the forcing the ocean circulation is thought to be forced primarily at the large scales characteristic of ocean basins yet to be damped at much smaller scales down to those of centimetre sized turbulence for decades physical oceanographers have sought to comprehend the fundamentals of this fractal puzzle how the ocean circulation is driven how it is damped and how ocean dynamics connects the very different scales of forcing and dissipation while in the last two decades significant advances have taken place on all these three fronts the thrust of progress has been in understanding the driving mechanisms of ocean circulation and the ocean s ensuing dynamical response with issues surrounding dissipation receiving comparatively little attention this choice of research priorities stems not only from logistical and technological difficulties in observing and modelling the physical processes responsible for damping the circulation but also from the untested assumption that the evolution of the ocean s state over time scales of concern to humankind is largely independent of dissipative processes in this article i illustrate some of the key advances in our understanding of ocean circulation that have been achieved in the last 20 years and based on a range of evidence contend that the field will soon reach a stage in which uncertainties surrounding the arrest of ocean circulation will pose the main challenge to further progress it is argued that the role of the circulation in the coupled climate system will stand as a further focal point of major advances in understanding within the next two decades supported by the drive of physical oceanography towards a more operational enterprise by contextual factors the basic elements that a strategy for the future must have to foster progress in these two areas are discussed with an overarching emphasis on the promotion of curiosity driven fundamental research against opposing external pressures and on the importance of upholding fundamental research as the apex of education in the field

late holocene environmental change at treeline in the northern coast mountains british columbia canada an integrated stratigraphic paleoecological and geochronological study of lake and fen sediments just beyond the terminus of berendon glacier provides insights into late holocene climate vegetation and glacier change in the northern coast mountains of british columbia cores collected from two small lakes in the foreland of berendon glacier and pits dug in a nearby fen record little lee age and older glacier advances the first little ice age advance in this area began more than 500 years ago and peaked in the early 17th century an earlier neoglacial advance began about 2800 3000 cal yr ago and may have lasted for hundreds of years there is also evidence for an intervening advance of even smaller magnitude around 1200 1300 cal yr ago the advances are broadly synchronous with those in other parts of western north america indicating that they were caused by regional possibly global changes in climate plant communities within the study area did not change dramatically during the late holocene the ranges of some plants however likely retracted or extended near treeline in response to changes in mean temperatures of perhaps 1 2degreesc as a well as changes in summer snow cover the greatest changes in vegetation occurred within and just beyond the forefields of berendon frank mackie and other nearby glaciers the largest climate shifts of the last 3000 years took place during the late little ice age and the last century climate warmed about 1 2degreesc during the 20th century accompanied by a rise in treeline an increase in coniferous tree cover in the subalpine zone and an increase in the temperature and biological productivity of ponds these trends are likely to continue if climate as expected continues to warm c 2004 elsevier ltd all rights reserved less

lateral moraine stratigraphy and neoglacial history of bugaboo glacier british columbia abstract most studies of alpine glacial history have concentrated on terminal moraines but such moraines provide dates only for maximum extents of glaciers some lateral moraines have the potential for providing more complete glacial histories because deposition by distal flank accretion may result in sequences of stacked tills interpretation is aided by 1 the approximation that any continuous surface within the moraine parallel to the moraine s distal flank is isochronous 2 inset gulley fill deposits which provide information on ice margin history and 3 incorporated organic material which can be radiocarbon dated lateral moraine stratigraphy of bugaboo glacier in southeastern british columbia suggests that the glacier was fairly close to its maximum neoglacial extent about 2500 14c yr b p a slow general expansion punctuated by at least one minor retreat continued from that time and culminated probably in the last century