sandwave migration in monterey submarine canyon central california abstract repeated high resolution multibeam bathymetric surveys from 2002 through 2006 at the head of the monterey submarine canyon reveal a sandwave field along the canyon axis between 20 and 250 m water depth these sandwaves range in wavelength from 20 to 70 m and 1 to 3 m in height a quantitative measure was devised to determine the direction of sandwave migration based on the asymmetry of their profiles despite appreciable spatial variation the sandwaves were found to migrate in a predominantly down canyon direction regardless of season and tidal phases a yearlong adcp measurement at 250 m water depth showed that intermittent internal tidal oscillations dominated the high speed canyon currents 50 80 cm s which are not correlated with the spring neap tidal cycle observed currents of 50 cm s or higher were predominantly down canyon applying a simple empirical model flows of such magnitudes were shown to be able to generate sandwaves of a size similar to the observed ones

stratigraphic and sedimentological evidence for late wisconsinan sub glacial outburst floods to laurentian fan abstract sub glacial meltwater produces a distinctive stratigraphic and sedimentological response on the continental margin seismo stratigraphy of laurentian channel reveals thick till deposits at its seaward end that pass laterally into stratified sediment in deeper basins that may record periods of water build up beneath the ice two scales of meltwater discharge are recognised large scale that caused catastrophic erosion and transported large volumes of coarse sediment to the abyssal plain and smaller scale yielding principally muddy sediment sub glacial outburst floods from the laurentian channel ice stream delivered distinctive red sediment derived from permian carboniferous strata of the gulf of st lawrence directly to laurentian fan between ca 17 and 14 14 c ka separate from north atlantic heinrich events on levees of laurentian fan three major pulses of meltwater plume muds are separated by intervals dominated by hemipelagic sediments these meltwater intervals are recognised distally as periods of plume sedimentation on the scotian slope and ice rafting of hematite stained quartz to the north atlantic ocean in channels of laurentian fan at least one major sediment transport event is recognised that eroded the upper slope and the major fan valleys depositing a bed of gravel at least 3 m thick in the characteristically wide fan valleys and thick sand on the sohm abyssal plain the same event was probably responsible for giant flute like scours the age of the gravel bed is directly constrained only by the presence of local overlying holocene sediment much of the surface of the gravel bed was re worked by the 1929 grand banks turbidity current an erosional event on the upper slope likely correlative with the flood generated gravel bed has been dated at 16 5 14 c ka such large scale erosional flood events can be recognised back through several glacial cycles and have played an important role in the architectural evolution of laurentian fan

structural and stratigraphie features and ers 1 synthetic aperture radar backscatter characteristics of ice growing on shallow lakes in nw alaska winter 1991 1992 changes in ers 1 c band synthetic aperture radar sar backscatter intensity from ice growing on shallow tundra lakes at three locations in nw alaska are described ice core analysis shows that at all lakes on the coast at barrow the ice whether floating or frozen to the bottom includes an inclusion free layer overlying a layer of ice with tubular bubbles oriented parallel to the direction of growth the clear ice may also be overlain by a discontinuous layer of bubbly snow ice backscatter is low 16 to 22 db at the time of initial ice formation probably due to the specular nature of the upper and lower ice surfaces causing the radar pulse to be reflected away from the radar as the ice thickens during the autumn backscatter rises steadily once the ice freezes to the lake bottom regardless of the presence of forward scattering tubular bubbles low backscatter values of 17 to 18 db are caused by absorption of the radar signal in the lake bed for ice that remains afloat all winter the ice water interface and the tubular bubbles combine presumably via an incoherent double bounce mechanism to cause maximum backscatter values of the order of 6 to 7 db the saturates at 6 to 7 db before maximum ice thickness and tubular bubble content are attained a simple ice growth model suggests that the layer of ice with tubular bubbles need be only a few centimeters thick midway through the growth season to cause maximum backscatter from floating ice during the spring thaw a previously unreported backscatter reversal is observed on the floating and grounded portions of the coastal lakes but not on the lakes farther inland this reversal may be related to the ice surface topography and wetness plus the effects of a longer cooler melt period by the coast time series of backscatter variations from shallow tundra lakes are a record of 1 the development of tubular bubbles in the ice and by association changes in the gas content of the underlying water and 2 the freezing of ice to the bottoms of the lakes and therefore lake bathymetry and water availability sar is also able to detect the onset of lake ice growth in autumn and the initiation of the spring thaw and thus has potential for monitoring high latitude lake ice growth and decay processes in relation to climate variability

estimation of ice thickness on large northern lakes from amsr e brightness temperature measurements abstract an ice thickness retrieval algorithm utilizing data from the advanced microwave scanning radiometer earth observing system amsr e was developed and applied to great bear lake gbl and great slave lake gsl northwest territories canada for the period 2002 2009 the temporal evolution of vertically polarized amsr e brightness temperature t b at 18 7 ghz was explored to estimate ice thickness between the late freeze up ice on and early break up melt onset periods the sensitivity of amsr e t b at h and v polarizations to the seasonal evolution of ice thickness was examined statistically and with forward simulations of t b using the most recent version of the helsinki university of technology hut model which incorporates a freshwater ice layer the strong relation found between t b at 18 7 ghz v pol and ice thickness was exploited for the development of a regression based ice thickness retrieval algorithm simple linear regression equations allow for the estimation of ice thickness on a monthly basis from january to april one the global equation combines t b data for gbl and gsl and two others the regional equations use t b data for each lake alone estimated late winter ice thicknesses on gbl were determined to be on average 5 10 cm thicker than on gsl with the exception of ice season 2005 2006 when it was estimated to be 10 cm thicker on gsl for both lakes the 2004 2005 and 2008 2009 ice seasons experienced the thickest end of winter ice thicknesses ranging from 130 to 134 cm on gbl and gsl the thinnest end of winter ice thicknesses were on average 120 cm on gbl 2005 2006 and 123 cm on gsl 2007 2008 variability in air temperature snowfall and subsequent redistribution by wind and lake depth explain ice thickness variations within and between lakes over the seven winter seasons analyzed estimated ice thicknesses from amsr e compare well with coincident in situ measurements collected on gbl and gsl over a limited number of ice seasons and sites within the large passive microwave footprints mean bias error mbe 6 cm root mean square error rmse 19 cm

atlantic meridional overturning circulation during the last glacial maximum the circulation of the deep atlantic ocean during the height of the last ice age appears to have been quite different from today we review observations implying that atlantic meridional overturning circulation during the last glacial maximum was neither extremely sluggish nor an enhanced version of present day circulation the distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the atlantic only slightly greater than today however evidence from multiple water mass tracers supports a different distribution of deep water properties including density which is dynamically linked to circulation

melt ponds on sea ice in the canadian archipelago 2 on the use of radarsat 1 synthetic aperture radar for geophysical inversion microwave scattering from a first year sea ice fyi melt ponded surface is examined using radarsat 1 synthetic aperture radar sar data collected during the 1997 collaborative interdisciplinary cryospheric experiment c ice 97 near resolute bay nunavut this paper 1 investigates the utility of time series of microwave scattering to detect melt pond formation and 2 investigates approaches toward geophysically inverting information on the physical and radiative properties of this surface we found melt pond formation to coincide with a sharp rise in the temporal evolution of the microwave scattering coefficient over fyi radarsat 1 incidence angle and surface wind speed explained 90 of the variation in radarsat 1 was sensitive r2 0 80 to the fractional coverage of melt ponds during windy conditions 5 3 m s 1 spatial and temporal coincident measurements of radarsat 1 and the integrated shortwave albedo revealed a strong negative statistical correlation r2 0 91 during windy conditions 5 3 m s 1 a weaker but strong negative relationship r2 0 78 was observed for less windy conditions 3 2 m s 1 and a very weak positive relationship r2 0 19 was found for low wind speed conditions 1 5 m s 1 all relationships were observed for melt pond fractions between 13 and 34

integrated pan arctic melt onset detection from satellite active and passive microwave measurements 2000 2009 1 an integrated pan arctic melt onset data set is generated for the first time by combining estimates derived from active and passive microwave satellite data using algorithms developed for the northern high latitude land surface ice caps large lakes and sea ice the data set yields new insights into the spatial and temporal patterns of mean melt onset date mmod and the associated geographic and topographic controls for example in the terrestrial arctic tree fraction and latitude explain more than 60 of the variance in mmod with the former exerting a stronger influence on mmod than the latter elevation is also found to be an important factor controlling mmod with most of the arctic exhibiting significant positive relationships between mmod and elevation with a mean value of 24 5 m d 1 melt onset progresses fastest over land areas of uniform cover or elevation 40 80 km d 1 or both and slows down in mountainous areas on ice caps and in the forest tundra ecotones over sea ice melt onset advances very slowly in the marginal seas while in the central arctic the rate of advance can exceed 100 km d 1 comparison of the observed mmod with simulated values from the third version of the canadian coupled global climate model showed good agreement over land areas but weaker agreement over sea ice particularly in the central arctic where simulated mmod is about 2 3 weeks later than observed because of a cold bias in simulated surface air temperatures over sea ice

analysis of ers 1 synthetic aperture radar data of frozen lakes in northern montana and implications for climate studies lakes that freeze each winter are good indicators of regional climate change if key parameters such as freeze up and breakup date and maximum ice thickness are measured over a decade scale time frame synthetic aperture radar sar satellite data have proven to be especially useful for measurement of climatologically significant parameters characteristic of frozen lakes in this paper five lakes in glacier national park montana have been studied both in the field and using ers 1 sar data during the 1992 1993 winter the lakes are characterized by clear ice sometimes with tubular or rounded bubbles and often with a layer of snow ice on top of the clear ice they are also often snow covered freeze up is detected quite easily using ers 1 sar data as soon as a thin layer of ice forms the effect of snow ice on the backscatter is thought to be significant but is as yet undetermined on the five lakes studied relative backscatter was found to increase with ice thickness until a maximum was reached in february breakup an often ill defined occurrence is difficult to detect because surface water causes the sar signal to be absorbed thus masking the ice below comparison of the bubble structure of thaw lakes in northern alaska with lakes in northern montana has shown that the ice structure is quite different and this difference may contribute to differential sar signature evolution in the lakes of the two areas

latest pleistocene ice rafting events on the scotian margin eastern canada and their relationship to heinrich events piston cores from the continental margin off nova scotia show up to four discrete intervals of brick red sandy mud which are up to 20 cm thick the ages of these intervals are bracketed by several radiocarbon dates and three fall in the range 12 5 14 1 ka radiocarbon years with 0 4 kyr reservoir correction the youngest dates from 10 4 ka placing it within the younger dryas the distribution of the beds and their petrographic character indicate a source in the gulf of saint lawrence the grain size of these beds suggests that they comprise a coarse component transported by ice rafting that diminishes distally and a fine component that represents suspension fallout from a surface plume and resulting nepheloid layers graded brick red beds in some cores were probably redeposited from turbidity currents the lowermost bed on the laurentian fan and east scotian rise is immediately overlain by a carbonate rich interval that can be identified all around the margin of the grand banks this interval is correlated with detrital carbonate bed dc 1 in the labrador sea and heinrich event h1 in the north atlantic the sequential occurrence of the two beds suggests that they may be a response to the same trigger probably sea level rise but that the gulf of saint lawrence source was more easily destabilized

which triggers produce the most erosive frequent and longest runout turbidity currents on deltas subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet and it is important to understand how they are linked offshore from river mouths previously it was thought that slope failures or direct plunging of river flood water hyperpycnal flow dominated the triggering of turbidity currents on delta fronts here we re analyse the most detailed time lapse monitoring yet of a submerged delta comprising 93 surveys of the squamish delta in british columbia canada we show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes rather than landslides or hyperpycnal flows turbidity currents triggered by settling plumes occur frequently run out as far as landslide triggered events and cause the greatest changes to delta and lobe morphology for the first time we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes

a multiscale subpixel mixture analysis applied for melt detection using passive microwave and radar scatterometer image time series of the antarctic peninsula 1999 2009

post lgm upward shift of the mediterranean outflow water recorded in a contourite drift off nw spain abstract the nw iberian continental margin is characterised by a complex morphology and by a sedimentary system which was highly dynamic over glacial to interglacial times the sedimentary history of the continental slope was strongly influenced by the interaction of bottom currents with topographic highs of structural origin leading to the accumulation of several sediment drifts a combined analysis of gravity cores from different water depth with hydroacoustic data reveals the vertical behaviour of the upper mediterranean outflow water mow core after the last glacial maximum lgm a coarser grained interval during deglacial and early holocene times 17 2 to 9 9 cal ka bp points to an increase in bottom current strength this increase in velocity was probably related to oceanic density fronts which migrated through the 300 m thick transition zone between the underlying labrador sea water and the overlying mow radiocarbon dates timed the current strengthening to 17 2 cal ka bp and a following weakening of the bottom current to 13 3 cal ka bp at 1965 m water depth and to 9 9 cal ka bp at 1885 m water depth the depth dependent current weakening suggests an upward shifting of the transition zone by 80 m that was related either to an overall shallowing of mow or a vertical contraction of this water mass the upward movement happened over a time interval of approximately 3 4 thousand years in addition sediment core analysis reveals significant lateral heterogeneities within cm to dm thick sediment layers in the contourite drift these heterogeneities suggest a need of a detailed core coverage across current influenced deposits for palaeoceanographic studies to minimize misinterpretations

size sorting in marine muds processes pitfalls and prospects for paleoflow speed proxies the basis for and use of fine grain size parameters for inference of paleoflow speeds is reviewed here the basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field experimental data on suspended sediment transport and deposition and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed in the deep sea sorting events occur under resuspension deposition events in benthic storms at flow speeds below 10 15 cm s 1 size in the noncohesive sortable silt 10 63 m range is controlled by selective deposition whereas above that range removal of finer material by winnowing also plays a role the best particle size instruments to measure a flow speed related grain size employ the settling velocity method while laser diffraction sizers can yield misleading results because of particle shape effects potential problems including source effects downslope supply on continental margins spatial variability of flow over bedforms and influence of ice rafted detritus are examined a number of studies using the sortable silt flow speed proxy are reviewed and inverse modeling of grain size distributions is examined outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed

observations of lake baikal ice from satellite altimetry and radiometry we demonstrate the potential of combining satellite altimetry and radiometry for lake ice studies using the example of lake baikal in siberia we show the synergy using active and passive microwave observations available from the recent satellite altimetry missions topex poseidon jason 1 envisat and geosat follow on complemented by the ssm i passive data we assess the applicability of altimetric and radiometric data for ice water discrimination and discuss the drawbacks and benefits of each type of sensor an ice discrimination method based on the combined use of the data from the four altimetric missions and ssm i is proposed and validated using available in situ observations and modis imagery the method is applied to the entire satellite data set and used to define specific dates of ice events first appearance of ice formation of stable ice cover first appearance of open water complete disappearance of ice and associated uncertainties using these satellite derived estimates we can extend the existing time series of ice events in the southern baikal up to 2004 and provide new information on the middle and northern baikal regions where no recent in situ ice cover observations are available our data show that over the last 10 15 years trends towards earlier ice formation and later ice break up result in a tendency for longer fast ice duration over the whole lake baikal the methods proposed here have been tested for lake baikal but they are applicable for other lakes and water bodies with seasonal ice cover

late quaternary stratigraphy of laurentian fan a record of events off the eastern canadian continental margin during the last deglacial period abstract examination and correlation of 10 piston cores from laurentian fan off the eastern canadian continental margin revealed a high resolution stratigraphic record of events since the last glacial maximum lgm the five lithofacies identified in the cores are 1 bioturbated olive grey silty mud with varying amounts of biogenic carbonate 2 olive grey and reddish brown silt laminated mud with rare fine to very fine sand beds 3 poorly sorted light grey and brick red gravelly sandy mud 4 colour banded silty mud with colours alternating at a centimetre scale between olive grey and reddish brown and 5 brown silty mud commonly massive but occasionally silt laminated the dominant depositional processes include hemipelagic sedimentation turbidity currents and ice rafting in these sediments colour is diagnostic of the sediment source area with reddish sediment being delivered to the fan from the gulf of st lawrence and laurentian channel whereas greenish sediment arrives on the fan from st pierre bank through grand banks valley turbidites are the most volumetrically significant facies conversely ice rafted beds are volumetrically minor but they are the most chronostratigraphically significant facies and include heinrich layers h0 h1 and h2 the chronological control provided by radiocarbon dating and stable oxygen isotopes suggests that sedimentation rates for the reddish brown turbidites deposited between the lgm and 14 ka exceeded 10 m kyr 1 mapping of the units together with a simple sediment deposition model suggest that these beds resulted from deposition by turbidity currents over 1 km thick that lasted on the order of weeks less information can be ascertained from the olive grey turbidites that interbed with h2 and directly overlie h1 because of a lack of sampling except that they had a lower sedimentation rate and include sediment derived from newfoundland and the grand banks comparison of the stratigraphy on laurentian fan with that of other deep water areas further north southwest grand banks margin flemish pass and the labrador sea shows striking similarities over the late quaternary with the deglacial period characterized by rapid sediment accumulation however only on laurentian fan does sediment gravity flow deposition occur during the lgm reddish brown turbidites deposited on laurentian fan during the deglacial period have no equivalent facies further north these unique features suggest important glaciological differences between the ice stream occupying laurentian channel and ice streams farther north the onset of widespread hemipelagic deposition occurred after ca 12 ka on laurentian fan and in flemish pass but not until ca 8 2 ka in the labrador sea consistent with the earlier retreat of glacial ice out of laurentian channel as compared to hudson strait

palaeogeography of atlantic canada 13 0 kyr abstract we combine isobase maps with a digital terrain model of atlantic canada to map coastlines from 13 14c kyr bp to the present at 13 14c kyr bp there are ridges of high relative sea level rsl values over newfoundland and the maritime provinces and a re entrant of low values in the gulf of st lawrence this pattern persists well into the holocene and reflects crustal response to the slow wasting of ice caps that persisted in newfoundland and the maritime provinces for up to five millennia after the removal of ice from the gulf of st lawrence by a migrating calving embayment the palaeogeographic reconstructions reveal an archipelago on the outer shelf from grand bank to the continent that persisted from 13 14c kyr bp until ca 8 14c kyr bp much of the magdalen shelf was exposed but the magdalen islands were never connected to the mainland prince edward island was initially separated from the mainland became connected after 11 14c kyr bp and was separated again just before 6 14c kyr bp when northumberland strait formed the reconstructions are highly sensitive to relatively small changes in isobase values especially on the shallow banks on the continental shelf

variability in ice phenology on great bear lake and great slave lake northwest territories canada from seawinds quikscat 2000 2006 abstract the temporal evolution of the backscatter coefficient sigma nought from quikscat was evaluated for monitoring ice phenology on great bear lake 66 n 121 w and great slave lake 61 40 n 114 w northwest territories canada results indicated that from quikscat can be used to detect melt onset water clear of ice and freeze onset dates on both lakes an ice phenology algorithm was then developed to assess the spatiotemporal variability on both lakes from quikscat for the period 2000 2006 results showed that for great slave lake the average melt onset date occurred on year day yd 123 the average water clear of ice date was on yd164 and the average freeze onset date was on yd330 on great bear lake the average melt onset date occurred on yd139 the average water clear of ice date was yd191 and the average freeze onset date was yd321 ice cover remained present for at least five weeks longer on great bear lake than on great slave lake and most of the difference can be explained by earlier ice melt on great slave lake spatially on great bear lake melt onset took place first in the eastern arm water clear of ice occurred first in southeastern and western arms and freeze onset appeared first in the northern arm and along the shorelines on great slave lake melt onset began first in the central basin and then progressed to the northern and eastern arms later in the season the central basin of great slave lake cleared earlier than the periphery due to the discharge from the slave river freeze onset on great slave lake occurred first within the east arm closely followed by the north and west arms and then finally in the centre of the main basin

rapid fluctuations in the deep north atlantic heat budget during the last glacial period 1 our understanding of past ocean climate interactions has been hampered by a paucity of proxy reconstructions of physical ocean circulation parameters here we present the first detailed record of deepwater temperature variability that resolves dansgaard oeschger climate fluctuations during the last glaciation results indicate a positive coupling between abrupt temperature changes over greenland and in the deep north atlantic that was mediated by perturbations to the atlantic overturning circulation the occurrence of sharp warming events at the center of the heinrich stadials 4 and 5 further indicates that the response of the ocean interior was less static across these major climate events than has been previously apparent

impact of melting of the laurentide ice sheet on sediments from the upper continental slope off southeastern canada evidence from sm nd isotopesthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new sm nd isotope data for sediments from a core located on the continental slope of the st pierre bank of canada s east coast the nd analyses indicate that the sediments were derived from two principal sources the north american shield that yields an average early proterozoic isotopic signature and a younger proterozoic signature attributed to appalachian crustal sources the appalachian sourced sediments predominated during the last glacial maximum lgm and were associated with low sedimentation rates 30 cm ka with the exception of a strong north american shield signature present in a detrital carbonate layer that corresponds to heinrich layer 1 h1 the dominance of the appalachian signature decreased subsequent to h1 the appalachian signatures closely follow the distribution of sediments interpreted as locally derived glacial tills while the north american shield signatures follow the distribution of hemipelagic mud that was likely deposited by the labrador current the nd data a

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

spectrocolorimetric interpretation of sedimentary dynamics the new q7 4 diagram colour is a fundamental property of sediment and is often used for lithographic description to determine sedimentological structures facies etc however the sedimentary information contained in this parameter is difficult to extract because it is difficult to quantify colour can be quantified by spectrocolorimetry which provides very high resolution data quickly and non destructively when adapted to sedimentology spectrocolorimeters prove to be powerful tools due to their low purchase and maintenance costs and some are portable and easily used in the field several methods have been used to extract sedimentological data from colorimetric spectra first derivatives factorial analysis etc in the present study we first provide a review of the sedimentological application of spectrophotometers and after having described these methods their advantages and disadvantages we then describe a new tool called the q7 4 diagram abscissa l ordinates 700 400 ratio this new technique permits sedimentological units to be defined allows the identification of different sediment components and provides 5 distinct poles clayey deposits organic rich deposits chlorophyll a and by products altered organic matter deposits iron rich deposits carbonated deposits coupled with the analysis of first derivative spectra it is possible to distinguish different pigments linked to the degradation and or nature of the organic material chlorophyll a melanoidin etc the state of iron oxidation for example hematite and goethite like signatures and the nature of clays the q7 4 diagram permits rapid acquisition of high resolution data on changes of sediment dynamics in geosystems that have been subjected to highly varied climatic environmental conditions the instrument is non destructive easy to use and maintain portable for use in the field fast to implement is capable of high resolution and has a vast range of possible applications spectrocolorimetry appears to provide many advantages and could become an essential and robust tool for preliminary sedimentological studies

down canyon evolution of turbidity currents at a late glacial ice margin halibut canyon offshore southeastern canada abstract submarine canyons are the principal conduit for turbidity currents transporting sediment to the deep sea this study examines the interplay between ice margin conditions and the style of turbidity currents during deglaciation from 19 to 11 ka we investigated 7 cores from halibut canyon located seaward of a small ice stream draining the newfoundland ice dome cores were x radiographed for sedimentary structures sediment provenance was assessed from x ray fluorescence geochemistry and age was determined by ams c 14 dating high resolution seismic profiles and cores show three phases of canyon evolution 1 canyon erosion by plunging hyperpycnal meltwater from shelf edge ice at maximum ice extent 2 during deglaciation active deposition of an inner levee by turbidity currents adjacent to an erosional talweg system recorded in cores from the younger dryas 12 ka to before h1 16 5 ka 3 passive canyon fill during the holocene by the alongslope labrador current with only minor down canyon sediment supply in the active canyon depositional phase turbidity currents were of variable size reaching thicknesses 390 m at 40 km down canyon numbers of sand beds and mean grain size decrease down canyon which is inferred to result from rapid entrainment of ambient seawater on the steep gradient and a downflow thinning of the lower part of the current with fine sand in suspension silt becomes increasingly segregated from muds downcanyon as a result of floc break up and re formation the processes inferred from halibut canyon are representative of other canyons on formerly glaciated margins

qualitative and quantitative approaches in palaeohydrography a case study from core top parameters in the gulf of cadiz palaeoceanography relies on the assumption that parameters measureable in sediment cores correlate reliably to hydrographic parameters areas of dynamic watermass mixing which generally have steep hydrographic gradients therefore provide both a tempting target large spatial and temporal differences in temperature and salinity and a significant challenge high flow velocities and high noise for palaeoceanographers here we investigate the ability of parameters measured on core tops to be used as the basis for simulating regional hydrography within one globally important area of watermass mixing the gulf of cadiz using grainsize sediment composition benthic foraminiferal assemblage and benthic foraminiferal stable isotope analysis it is possible to build an effective framework for qualitative constraint of the position of the modern mediterranean outflow water mw plume we propose that the gulf of cadiz slope can be sub divided into 8 hydrographic zones reflecting these parameters proximal mw core mw1 steep slopes core mw1 gentle slopes distal mw1 distal mw2 lower limit of mw plume north atlantic deep water and ambient atlantic water we anticipate that compilation of time slice data will reveal hydrographic sub divisions of the slope for the past in a similar manner improving our understanding of past changes in the size and position of the mw plume but more work needs to be done before a secure protocol for quantitative reconstruction can be created stable isotope analysis alone is insufficient for the task with 13c behaving in a non conservative manner and 18ocalcite acting in an ambiguous way due to the competing influences of 18owater and temperature it is likely that if a single parameter that unambiguously determines the difference between mediterranean water and atlantic water can be identified combination with 18ocalcite will allow extension of our qualitative analysis into a quantitative means of palaeohydrographic reconstruction for this region similar complexity to that found in this study would be expected in any mixing region and in particular on the majority of sediment drifts we recommend that core top surveys similar to this study are performed on these sediment drift systems before any form of quantitative palaeohydrology is attempted

integration of space borne and air borne data in monitoring river ice processes in the slave river canada abstract river ice plays an important role in the physical biological and human systems in northern regions due to the large extent and poor accessibility of many river systems remote sensing techniques are a potential tool for collecting information and analyzing characteristics of river ice covers optical data with high temporal resolution e g modis products are suitable for monitoring river ice phenology and mapping river ice cover extent while radar data e g radarsat 2 imagery offer an optimal approach to characterizing river ice thickness ice types and seasonal changes of ice cover characteristics an integrated automated approach utilizing remotely sensed data from both active and passive sensors was developed and applied to characterize river ice processes along the slave river northwest territories canada the results show that the analysis of modis band 2 841 876 nm time series can detect the date of river ice freeze onset fo and water clear of ice wci with a deviation of up to 12 days and 3 days respectively the rate of river ice breakup is much faster than the rate of river freeze up the profiles of modis band 2 reflectance data along the river however showed insignificant differences between different breakup stages and ice types making it challenging to map breakup ice types in this case radarsat 2 imagery can be used successfully to characterize and map four classes of water and ice covers during the breakup period including intact ice smooth rubble ice rough rubble ice and open water in association with hydrometeorological parameters the thermal deterioration of the ice cover during breakup appears to be the primary breakup event in the slave river the results obtained from the analysis of modis and radarsat 2 data were compared with ground measurements of weather flow and ice conditions 2000 2015 time lapse photos and aerial surveys 2013 2015 along the slave river and show strong agreement

on the role of the azores current in the ventilation of the north atlantic ocean three high resolution ocean circulation models of the north atlantic differing chiefly in their description of the vertical coordinate are used to examine the ventilation of the north atlantic subtropical gyre all the models produce mode waters of realistic densities in the sargasso sea and the european basin but have azores currents of differing strengths which are categorised as strong of realistic transport intermediate and weak these differences have a critical impact upon the ventilation of the gyre most importantly the strong azores current forms an effective barrier to the southward ventilation of eastern north atlantic water from the northern european basin initially driving it southwestwards into the central gyre before turning it back eastwards again in a general cyclonic circulation north of the current the intermediate and weak azores currents instead allow the southward ventilation of this water mass near the european and african coasts the situation in nature appears to be intermediate between these two cases with the azores current acting as a partial block the study also raises the possibility of the azores current forming an advective connection between the sargasso sea mode waters in the western basin and modes of similar densities found in the eastern basin on the southern side of the current although there are high levels of variability in the extent of these lighter modes in the eastern basin in nature this postulate is supported by a number of observational studies in addition the present study also provides some support for the local production of madeira mode water in the eastern basin associated with retroflecting current branches on the southern side of the azores current overall the azores current is therefore likely to have a critical impact upon the ventilation of the subtropical gyre over a large area rather than just locally affecting the potential vorticity and density structure of the upper ocean between subtropical latitudes and the northern european basin the study also contributes to an ongoing community effort to assess the realism of our current generation of ocean models

simulation of ice phenology on great slave lake northwest territories canada a one dimensional thermodynamic lake ice model canadian lake ice model or climo is used to simulate ice phenology on great slave lake gsl in the mackenzie river basin northwest territories canada model simulations are validated against freeze up and break up dates as well as ice thickness and on ice snow depth measurements made in situ at three sites on gsl back bay near yellowknife 1960 91 hay river 1965 91 charlton bay near fort reliance 1977 90 freeze up and break up dates from the lake ice model are also compared with those derived from ssm i 85 ghz passive microwave imagery over the entire lake surface 1988 99 results show a very good agreement between observed and simulated ice thickness and freeze up break up dates over the 30 40 years of observations particularly for the back bay and hay river sites climo simulates the ice thickness and annual freeze up break dates with a mean error of 7 cm and 4 days respectively however some limitations have been identified regarding the rather simplistic approach used to characterize the temporal evolution of snow cover on ice future model improvements will therefore focus on this particular aspect through linkage or coupling to a snow model

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

circulation patterns and transport of the azores front current system in this paper different types of new data sets hydrography lagrangian and eulerian current measurements and quasi geostrophic model results obtained after altimetric data assimilation are used to study the structure and variability of the azores current and frontal system the azores current was observed to transport between 11 0 and 18 0 sv eastwards and the associated counter current some 2 0 10 0 sv to the west resulting in a net value of about 8 9 sv furthermore both data and model results revealed a meandering azores current where some freely rotating eddies were also identified these hydrographic and lagrangian results exhibit space and time scales that agree fairly well with the dynamics shaped by baroclinic instability current meters moored across the azores current system delineated a mean counter current flowing westwards with a maximum subsurface core of about 2 0 cm s at a mean depth of 800 dbar this is in excellent agreement with previous studies which explains this azores counter current as the rectification process of the geostrophic turbulence occurring north of the main azores current stream a new scheme is proposed for the formation mechanism of the freely rotating cyclonic eddies observed south of the azores it is shown that the north south contrast thickness of the 17 19 c water layer across the azores front decreases downstream this will create in turn a downstream increase of the most unstable wavelength in a non linear baroclinic instability context as a consequence both large cyclonic and anticyclonic features are able to form at the eastern side of the azores current around 19 w while at the western side around 35 w only large anticyclones will survive western generated cyclones will be small enough to be quickly dissipated this means that the eastern cyclones of the azores current may live longer than the shorter western ones however because longer lived cyclonic eddies propagate westwards with a mean speed of 2 5 km day they may be observed south of azores and of the main stream several months later although they were not formed there

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

evidence of early bottom water current flow after the messinian salinity crisis in the gulf of cadiz highlights stratigraphic framework over the miocene pliocene boundary at iodp site u1387 abrupt sedimentary changes over the miocene pliocene boundary clear hints for onset of mediterranean outflow after the messinian salinity crisis evidence of bottom water currents in contouritic sedimentation and elevated zr al quiet hemipelagic sediment deposition during the messinian in the gulf of cadiz abstract integrated ocean drilling program iodp expedition 339 cored multiple sites in the gulf of cadiz in order to study contourite deposition resulting from mediterranean outflow water mow one hole u1387c was cored to a depth of 865 6 meters below seafloor mbsf with the goal of recovering the latest miocene to pliocene transition in order to evaluate the history of mow immediately after the end of the messinian salinity crisis to understand this history an accurate age model for the succession is needed but is challenging to construct because the miocene pliocene boundary is not marked by a clear biostratigraphic event in the atlantic and coring gaps occur within the recovered stratigraphic record these limitations are overcome by combining a variety of chronostratigraphic datasets to construct an age model that fits the currently available age indicators and demonstrates that coring in hole u1387c did indeed recover the miocene pliocene boundary at around 826 mbsf this boundary is associated with a distinct and abrupt change in depositional environment during the latest messinian hemipelagic sediments exhibiting precession induced climate variability were deposited these are overlain by pliocene sediments deposited at a much higher sedimentation rate with much higher and more variable xrf scanning zr al ratios than the underlying sediment and that show evidence of winnowing particle sorting and increasing grain size which we interpret to be related to the increasing flow of mow pliocene sedimentary cyclicity is clearly visible in both the benthic 18o record and the zr al data and is probably also precessionally controlled two contouritic bigradational sandy beds are revealed above the third sedimentary cycle of the pliocene on the basis of these results we conclude that sedimentation associated with weak mediterranean atlantic exchange began in the gulf of cadiz virtually at or shortly after the miocene pliocene boundary

glacial mediterranean sea surface temperatures based on planktonic foraminiferal assemblages we present a new reconstruction of mediterranean sea surface temperatures sst during the last glacial maximum lgm a calibration data set based on census counts of 23 species of planktonic foraminifera in 129 north atlantic and 145 mediterranean core top samples was used to develop summer winter and annual average sst reconstructions using artificial neural networks anns and the revised analogue method ram prediction errors determined by cross validation of the calibration data set ranged between 0 5 and 1 1 c with both techniques being most successful in predicting winter ssts glacial reconstructions are based on a new expanded data set of 273 samples in 37 cores with consistent minimum level of age control the new lgm reconstructions suggest that the east west temperature gradient during the glacial summer was 9 c whereas during the glacial winter the gradient was 6 c both some 4 c higher than that existing today in contrast to earlier studies our results tend to suggest much cooler sst estimates throughout the glacial mediterranean particularly in the eastern basin where previous sst reconstructions indicated a decrease of only 1 c our new sst reconstructions will provide the modelling community with a detailed and updated portrayal of the mediterranean sea during the lgm setting new targets on which glacial simulations can be tested

oceanic density fronts steering bottom current induced sedimentation deduced from a 50 ka contourite drift record and numerical modeling off nw spain abstract how the various bottom near hydrographic and sedimentary processes control the formation of contourite drifts i e of bottom current related confined deep sea depocenters usually remains widely speculative this study uses a transect of six sediment cores and a sediment echosounder profile across a whole contourite system off nw spain to address the sediment dynamics responsible for the depositional pattern this mounded patch type contourite drift 18 km long 20 km wide with a 150 m deep channel moat has formed around an 800 m high structural obstacle deposition on the contourite drift in the past was characterized by alternating calm and high energy bottom flow conditions calm conditions last glacial period 27 17 cal ka bp late holocene times process based numerical modeling demonstrates that pulse like oceanic density fronts traveling within the transition zone of two water masses labrador sea water mediterranean outflow water provide a powerful mechanism for contouritic deposition rather than the core of a water mass itself these gravity driven density fronts lead to local re suspension of sands stored inside the drift s moat and to subsequent upward transport towards the drift s crest here the oceanic density fronts produce additional km scale eddies these migrating eddies provide an efficient mechanism for further widespread sediment re distribution in comparison with paleoceanographic reconstructions a downward migration or expansion of the mediterranean outflow water by about 300 m led most probably to such temporary contouritic sand deposition we finally propose a conceptual model to explain how seafloor obstacles redirect and perturbate bottom currents this model proposes not only a sharp contact between two water masses but also the transition zone between those as an important high energy regime offering oceanic density fronts a travel medium these fronts are strong enough to distribute fine sands across highly pronounced seabed topography on the respective time scale the moat itself seems to act as the main source for those sands making a remote source and a long distance sediment transport unnecessary

interaction of the western boundary undercurrent with the continental margin off newfoundland sedimentation on the newfoundland rise is strongly influenced by the western boundary undercurrent wbu the upper rise 2600 2800 m is swept by a rapid 8 5 cm sec 1 south flowing core of the wbu which has generated a sandy contourite facies characterized by coarse gravelly sandy sediments current induced bedforms such as scour moats lineations and lee drifts ferro manganese stained gravel clasts a high proportion of broken foraminiferal tests and a diagnostic benthic foraminiferal assemblage the overlying nepheloid layer when compared to adjacent waters is thickest 800 m most sediment laden 80 g 1 1 contains the highest proportion of terrigenous sediment and exhibits the best developed bottom mixed layer 15 m thick comparisons with earlier data from the same area imply the dimensions and sediment load of the nepheloid layer vary with time empirical considerations based on near bottom current meter records from labrador and newfoundland suggest the wbu is capable of transporting bedload with threshold friction velocities u of around 0 87 1 14 cm sec 1 for between 1 and 15 of the time the prevailing transport direction is southwards along the rise but this may be punctuated periodically by brief incursions to the north the erosional regime of the upper rise is bordered by a regime of fine grained deposition typified by muddy contourites both the lower slope and lower rise are mantled by bioturbated muds the former zone having terrigenous mud and the latter biogenic calcareous mud the accompanying nepheloid layer is thin biogenic rich and devoid of an identifiable mixed layer

greenland freshwater pathways in the sub arctic seas from model experiments with passive tracers accelerating since the early 1990s the greenland ice sheet mass loss exerts a significant impact on thermohaline processes in the sub arctic seas surplus freshwater discharge from greenland since the 1990s comparable in volume to the amount of freshwater present during the great salinity anomaly events could spread and accumulate in the sub arctic seas influencing convective processes there however hydrographic observations in the labrador sea and the nordic seas where the greenland freshening signal might be expected to propagate do not show a persistent freshening in the upper ocean during last two decades this raises the question of where the surplus greenland freshwater has propagated in order to investigate the fate pathways and propagation rate of greenland meltwater in the sub arctic seas several numerical experiments using a passive tracer to track the spreading of greenland freshwater have been conducted as a part of the forum for arctic ocean modeling and observational synthesis effort the models show that greenland freshwater propagates and accumulates in the sub arctic seas although the models disagree on the amount of tracer propagation into the convective regions results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies it is estimated that surplus greenland freshwater flux should have caused a salinity decrease by 0 06 0 08 in the sub arctic seas in contradiction with the recently observed salinification by 0 15 0 2 in the region it is surmised that the increasing salinity of atlantic water has obscured the freshening signal

how turbidity current frequency and character varies down a fjord delta system combining direct monitoring deposits and seismic data submarine turbidity currents are one of the most important processes for moving sediment across our planet they are hazardous to offshore infrastructure deposit petroleum reservoirs worldwide and may record tsunamigenic landslides however there are few studies that have monitored these submarine flows in action and even fewer studies that have combined direct monitoring with longer term records from core and seismic data of deposits this article provides one of the most complete studies yet of a turbidity current system the aim here is to understand what controls changes in flow frequency and character along the turbidite system the study area is a 12 km long delta fed fjord howe sound in british columbia canada over 100 often powerful up to 2 to 3 m sec 1 events occur each year in the highly active proximal channels which extend for 1 to 2 km from the delta lip about half of these events reach the lobes at the channel mouths however flow frequency decreases rapidly once these initially sand rich flows become unconfined and only one to five flows run out across the mid slope each year many of these sand rich channelized delta sourced flows therefore dissipated over a few hundred metres once unconfined rather than eroding and igniting upflow migrating bedforms indicate that supercritical flow dominated in the proximal channels and lobes and also across the unconfined mid slope these supercritical flows deposited thick sand beds in proximal channels and lobes but thinner and finer beds on the unconfined mid slope the distal flat basin records far larger volume and more hazardous events that have a recurrence interval of ca 100 years this study shows how sand rich delta fed flows dissipate rapidly once they become unconfined that supercritical flows dominate in both confined and unconfined settings and how a second type of more hazardous and much less frequent event is linked to a different scale of margin failure

accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation 1 abrupt decreases of the atlantic meridional overturning circulation moc during the late pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater triggering disruption of northward marine heat transport and causing global climate changes here we provide measurements of excess sedimentary 231 pa 230 th from a high accumulation sediment drift deposit in the ne atlantic that record a sequence of sudden variations in the rate of moc associated deep ocean ventilation and surface ocean climatology the data series reveal a sequential decrease in the moc rate at 18 0 ka bp ago that coincides with only transient and localized freshwater inputs this change represents a substantial though not total cessation in moc that predates the major heinrich h1 meltwater event by at least 1 200 years these results highlight the potential of targeted freshwater perturbations in promoting substantial moc changes without a direct linking with catastrophic freshwater surges citation hall i r s b moran r zahn p c knutz c c shen and r l edwards 2006 accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation geophys res lett 33 l16616 doi 10 1029 2006gl026239

river ice break up freeze up a review of climatic drivers historical trends and future predictions river ice plays a fundamental role in biological chemical and physical processes that control freshwater regimes of the cold regions moreover it can have enormous economic implications for river based developments all such activities and processes can be modified significantly by any changes to river ice thickness composition or event timing and severity this paper briefly reviews some of the major hydraulic mechanical and thermodynamic processes controlling river ice events and how these are influenced by variations in climate a regional and temporal synthesis is also made of the observed historical trends in river ice break up freeze up occurrence from the eurasian and north american cold regions this involves assessment of several hydroclimatic variables that have influenced past trends and variability in river ice break up freeze up dates including air temperature indicators e g seasonal temperature 0 c isotherm dates and various degree days and large scale atmospheric circulation patterns or teleconnections implications of future climate change on the timing and severity of river ice events are presented and discussed in relation to the historical trends attention is drawn to the increasing trends towards the occurrence of mid winter break up events that can produce especially severe flood conditions but prove to be the most difficult type of event to model and predict

historical trends in lake and river ice cover in the northern hemisphere freeze and breakup dates of ice on lakes and rivers provide consistent evidence of later freezing and earlier breakup around the northern hemisphere from 1846 to 1995 over these 150 years changes in freeze dates averaged 5 8 days per 100 years later and changes in breakup dates averaged 6 5 days per 100 years earlier these translate to increasing air temperatures of about 1 2 c per 100 years interannual variability in both freeze and breakup dates has increased since 1950 a few longer time series reveal reduced ice cover a warming trend beginning as early as the 16th century with increasing rates of change after about 1850

menu of coupled velocity and sediment discharge relations for rivers nonlinear multiple regression analysis is used to derive relations among the velocity sediment discharge bed form geometry and friction factor of alluvial rivers a data base comprising 339 river flows and 608 flume flows is used in the analysis a hierarchy of formulations involving progressively more interdependencies among velocity depth sediment discharge and bed form geometry is developed procedures for computing velocity and sediment rating curves are presented a simplified procedure for preparing depth discharge relations for streams with strongly discontinuous rating curves is also presented rating curves for four rivers and computed depths and velocities for two others are presented the accuracies of the different methods are evaluated in terms of the mean normalized errors of predicted friction factors depths velocities and sediment discharges it is concluded that these formulations yield velocity and sediment rating curves that are as reliable as is permitted by the accuracy

slope instability on a shallow contourite dominated continental margin southeastern grand banks eastern canada abstract submarine sediment failures and related mass transport deposits mtds are widespread on the eastern canadian continental slope settings and in general have been related to ice sheets crossing the outer shelf the southeastern grand banks margin was not glaciated in the last 10 5 years and has a deep shelf break as a result the upper continental slope consists principally of sediment transported from the north by the labrador current high resolution seismic profiles and 10 m long piston cores show widespread sediment failure and mtds in a plastered contourite drift from 500 to 1000 m water depth this study documents the stratigraphy of the past 48 000 years and the record of sediment failure events heinrich layers h1 to h5 have been recognized from distinctive petrology physical properties and bulk geochemistry and are constrained by numerous 14 c ams dates the geotechnical analysis shows that the latest quaternary sediment section is mildly underconsolidated perhaps related to high sedimentation rates up to 0 5 m ka enhanced by some leakage of deep fluids nevertheless factor of safety calculations using su p 0 and friction angles from triaxial testing suggest the slope is statically stable up to gradients of 9 atterberg limit measurements of silty contourite sediments indicate susceptibility to liquefaction under cyclic loading there is evidence that apparently synchronous failure occurred over many tens of kilometres of the slope probably as a result of rare passive margin earthquakes these shallow water contourite deposits have a higher sand and coarse silt content much less biogenic material and more rapid variations in sediment and geotechnical properties than those of the deep water equivalents all of which make them more susceptible to sediment failure

interannual variability of the mediterranean outflow observed in espartel sill western strait of gibraltar 1 four year time series of observations in espartel sill at the western part of the strait of gibraltar have been analyzed in order to investigate the variability of the mediterranean outflow it is assumed that the observed variability comes from the changing properties of the dense waters that are located at the maximum depth from where they can be uplifted in the upstream basin alboran sea inside the mediterranean sea and evacuated through the strait from this perspective the following three mechanisms are investigated 1 the replenishment of the deep basin by newly formed western mediterranean deep water that depending on its density can either uplift old resident waters or lay above them leaving in any case a cold signature in the temperature series 2 the presence absence of the energetic anticyclonic gyres in the alboran sea particularly the western one which can transfer momentum to the underlying mediterranean vein and provide it with additional energy to ascend over the sills of the strait and 3 the meteorologically enhanced flows that follow the rapid changes of atmospheric pressure over the western mediterranean basin which would be able to aspire deeper waters residing in the upstream basin the three mechanisms act on different timescales from annual in case 1 to monthly in case 2 to weekly in case 3 although these two latter are modulated annually by the seasonal prevalence of the western alboran gyre in summer and of the strong meteorologically driven fluctuations in winter the mechanisms overlap at annual timescales making it difficult to separate out the different contributions

regional synthesis of mediterranean atmospheric circulation during the last glacial maximum atmospheric circulation leaves few direct traces in the geological record making reconstructions of this crucial element of the climate system inherently difficult we produced a regional mediterranean synthesis of paleo proxy data from the sea surface to alpine altitudes this provides a detailed observational context for change in the three dimensional structure of atmospheric circulation between the last glacial maximum lgm 23 000 to 19 000 years ago and the present the synthesis reveals evidence for frequent cold polar air incursions topographically channeled into the northwestern mediterranean anomalously steep vertical temperature gradients in the central mediterranean imply local convective precipitation we find the lgm patterns to be analogous though amplified to previously reconstructed phases of enhanced meridional winter circulation during the maunder minimum the little ice age

an updated radiocarbon based ice margin chronology for the last deglaciation of the north american ice sheet complex abstract the north american ice sheet complex naisc consisting of the laurentide cordilleran and innuitian ice sheets was the largest ice mass to repeatedly grow and decay in the northern hemisphere during the quaternary understanding its pattern of retreat following the last glacial maximum is critical for studying many facets of the late quaternary including ice sheet behaviour the evolution of holocene landscapes sea level atmospheric circulation and the peopling of the americas currently the most up to date and authoritative margin chronology for the entire ice sheet complex is featured in two publications geological survey of canada open file 1574 dyke et al 2003 quaternary glaciations extent and chronology part ii dyke 2004 these often cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka all ages in uncalibrated radiocarbon years using a combination of geomorphology stratigraphy and radiocarbon dating however by virtue of being over 15 years old the ice margin chronology requires updating to reflect new work and important revisions this paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies we also update the original radiocarbon dataset from the 2003 2004 papers with 1541 new ages to reflect work up to and including 2018 a major revision is made to the 18 ka ice margin where banks and eglinton islands once considered to be glacial refugia are now shown to be fully glaciated our updated 18 ka ice sheet increased in areal extent from 17 81 to 18 37 million km2 which is an increase of 3 1 in spatial coverage of the naisc at that time elsewhere we also summarize region by region significant changes to the deglaciation sequence this paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of dyke et al 2003 and dyke 2004 where new information is lacking this is a pragmatic solution to satisfy the needs of a quaternary research community that requires up to date knowledge of the pattern of ice margin recession of what was once the world s largest ice mass the 36 updated isochrones are available in pdf and shapefile format together with a spreadsheet of the expanded radiocarbon dataset n 5195 ages and estimates of uncertainty for each interval

late quaternary glacial history and meltwater discharges along the northeastern newfoundland shelf the geomorphology of the eastern canadian margin has been shaped by glacial processes during the quaternary many studies have focused on the ice sediment pathway through hudson strait to reconstruct the dynamics of the laurentide ice sheet and as a consequence little is known on its marginal ice domes here we reconstruct the dynamics of two trough mouth fans tmfs offshore ne newfoundland using sediment cores and radiocarbon ages supported by very high resolution seismic reflection profiles these two tmfs namely notre dame and hawke are fed by two glacial troughs incised in the bedrock the tmfs show a complete sedimentary sequence from 30 ka bp to the beginning of the holocene the sampled sedimentary record on the upper slope extends back to a thick heinrich event 3 h3 deposit that corresponds to the end of the maximum extent of the newfoundland ice dome above h3 a thick succession of turbidite deposits 10 m observed in both tmfs is correlated with periods of major meltwater supply from 2

mediterranean outflow mixing and dynamics the mediterranean sea produces a salty dense outflow that is strongly modified by entrainment as it first begins to descend the continental slope in the eastern gulf of cadiz the current accelerates to 1 3 meters per second which raises the internal froude number above 1 and is intensely turbulent through its full thickness the outflow loses about half of its density anomaly and roughly doubles its volume transport as it entrains less saline north atlantic central water within 100 kilometers downstream the current is turned by the coriolis force until it flows nearly parallel to topography in a damped geostrophic balance the mixed mediterranean outflow continues westward slowly descending the continental slope until it becomes neutrally buoyant in the thermocline where it becomes an important water mass

mediterranean sea level and barotropic flow through the strait of gibraltar for the period 1958 2001 and reconstructed since 1659 sea level values from a two dimensional model of the mediterranean sea forced by atmospheric pressure and wind are used to estimate the barotropic flow through the strait of gibraltar for the period 1958 2001 the mediterranean mean sea level derived from the model ranges between 20 cm with a standard deviation of 5 5 cm and is correlated to the north atlantic oscillation nao index thus nao historical data and reconstructions are used to derive the mediterranean sea level variability from 1659 until 2001 the accuracy of the reconstruction is estimated in 2 7 cm for monthly mean values 0 41 cm for annual mean values and 0 22 cm for decadal mean values 0 48 cm for decadal winter mean sea level the barotropic flow through the strait is computed from the model output as the time derivative of the total volume of the basin during the period 1958 2001 the estimated daily flow ranges between 2 7 sv with a standard deviation of 0 56 sv the dominant periodicities are in between 1 and 2 weeks at these scales the model successfully reproduces previously published flow estimates based on current meter observations which confirms that atmospheric pressure and wind dominate the intraseasonal variability of the flow for the annual cycle the variability of the atmospherically induced flow is similar to the variability of the flow induced by the evaporation precipitation e p budget 0 025 sv though absolute values of the first are about a third of the latter at longer timescales the atmospheric contribution is much smaller than the e p induced flow

mediterranean outflow water dynamics across the middle pleistocene transition based on a 1 3 million year benthic foraminiferal record off the portuguese margin abstract reconstruction of the mediterranean outflow water mow dynamics in the geologic past contributes to exploring its influence on the north atlantic ocean circulation and global climate the middle pleistocene transition mpt is one of the most important characteristics of quaternary climate change but until now research on the mow variability during this time interval has been limited to decipher the mow variability over the last 1 3 myr this work presents the first continuous and high resolution 2 kyr foraminiferal stable oxygen and carbon isotopes and benthic foraminiferal records from integrated ocean drilling program iodp site u1391 which was drilled off the portuguese margin in the northeast atlantic ocean and is currently bathed by the lower mow core based on spectral analysis results of the foraminiferal 18o record the mpt peaked from 0 9 to 0 7 ma the epibenthos group was previously found attached to elevated substrates only within the mow current and more abundant at higher current velocities so the relative abundance of the elevated epibenthos group was adopted as an indicator of mow strength in this study the mow indicator suggests that the mow strengthened during mis 1 mis 5 mis 7 mis 9 mis 11 mis 13 mis 15 mis 17 early mis 18 to late mis 19 mis 21 miss 23 25 miss 28 30 early mis 34 to mis 35 early mis 36 to late mis 37 and mis 40 with a 100 kyr cycle superimposed on the long term variability of the mow current the 41 kyr and 20 kyr cyclic fluctuations are also evident whereby the 41 kyr cycle is more significant the results of cross spectral analyses indicate that the 20 kyr cyclic variation in the mow intensity was drived by the precession forcing the 41 kyr cyclic variation in the pre mpt mow dynamics and the 100 kyr cyclic variation in the post mpt mow dynamics were strongly controlled by the earth s obliquity the variation in the abundance of the elevated epibenthos group was dominated by the 41 kyr cycle prior to the mpt and by the 100 kyr cycle after the mpt which suggested there was a mpt related shift in the mow dynamics benthic 13c record of the last 0 56 myr shows precessional 23 kyr and glacial interglacial 100 kyr cycles indicating cyclic variations in bottom water ventilation enhanced ventilation coincides with precession maxima and reduced ventilation with precession minima bottom water was well ventilated by mow during the interglacial periods and by gnaiw during the glacial periods and pooly ventilated during the glaical terminations

radarsat backscatter characteristics of ice growing on shallow sub arctic lakes churchill manitoba canada results from an investigation on the evaluation of radarsat c hh imagery for monitoring ice growth and decay and related processes of shallow sub arctic tundra and forest lakes in northern manitoba canada are presented field observations on the structural and stratigraphic characteristics of snow and ice from four lake sites are used in support of the interpretation of changes in synthetic aperture radar backscatter intensity as a function of time and incidence angle 20 49 results show that bubble inclusions most of which are tubular and oriented in the direction of growth strongly influence backscatter intensity from floating ice in radarsat standard beam mode imagery it is shown that radar return can vary considerably as a function of incidence angle differences of as much as 6 5 db were observed for the same ice cover when observed at steeper 20 35 compared with shallower 35 49 incidence angles during the early stages of ice growth and or when the ice volume contains a small amount of tubular bubbles backscatter intensity from the floating ice measured at shallower incidence angles 35 49 is similar to that observed from the grounded ice at any incidence angle 17 to 11 db a strong decrease in backscatter was observed at all sites during spring thaw and was explained by the microwave signal being absorbed by the wet snow cover and by specular reflection from the standing water ponds on the lake ice surface with its multiple beam mode configurations radarsat offers an improved temporal coverage over ers 1 2 thus making it possible to determine more precisely freeze up and break up dates and timing of bottom freezing from shallow arctic and sub arctic lakes copyright 2002 john wiley sons ltd

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

vertical density gradient in the eastern north atlantic during the last 30 000 years past changes in the density and momentum structure of oceanic circulation are an important aspect of changes in the atlantic meridional overturning circulation and consequently climate however very little is known about past changes in the vertical density structure of the ocean even very extensively studied systems such as the north atlantic here we exploit the physical controls on the settling depth of the dense mediterranean water plume derived from the strait of gibraltar to obtain the first robust observations based probabilistic reconstruction of the vertical density gradient in the eastern north atlantic during the last 30 000 years we find that this gradient was weakened by more than 50 relative to the present during the last glacial maximum and that changes in general are associated with reductions in amoc intensity however we find only a small change during heinrich event 1 relative to the last glacial maximum despite strong evidence that overturning was substantially altered this implies that millennial scale changes may not be reflected in vertical density structure of the ocean which may be limited to responses on an ocean overturning timescale or longer regardless our novel reconstruction of atlantic density structure can be used as the basis for a dynamical measure for validation of model based amoc reconstructions in addition our general approach is transferrable to other marginal sea outflow plumes to provide estimates of oceanic vertical density gradients in other locations

another description of the mediterranean sea outflow abstract papers about the outflow in the strait of gibraltar assume that i it is composed of only two mediterranean waters mws the levantine intermediate water liw and the western mediterranean deep water wmdw from the eastern and western basins respectively ii both mws are mixed near 6 w hence producing a homogeneous outflow that is then split into veins due to its cascading along different paths and to different mixing conditions with the atlantic water aw a re analysis of 1985 1986 ctd profiles gibraltar experiment indicates two other mws the winter intermediate water wiw from the western basin and the tyrrhenian dense water tdw basically originated from the eastern basin in the central alboran subbasin these four mws are clearly differentiated roughly lying one above the other in proportions varying from north to south proportions also vary with time so that the outflow can be mostly of either eastern or western origin while progressing westward the mws can still be differentiated and associated isopycnals tilt up southward as much as being in the sill surroundings roughly parallel to the moroccan continental slope where the densest mws are the mws at the sill are thus juxtaposed and they all mix with aw leading to an outflow that is horizontally heterogeneous just after the sill 5 45 w before progressively becoming vertically heterogeneous as soon as 6 15 w there can be little liw and or no wmdw outflowing for a while an analysis of new 2003 2008 time series from two ctds moored ciesm hydro changes programme at the sill 270 m and on the moroccan shelf 80 m confirms the juxtaposition of the mws their individual and generally intense mixing with aw as well as the large temporal variability of the outflow composition only liw and tdw were indicated at the sill while on the shelf only liw tdw sometimes denser there than 200 m below and wmdw were indicated but none of the mws has been permanently outflowing at one or the other place the available data can be analyzed coherently intermediate and deep mws are formed in both basins in amounts that although variable from year to year allow their tracing up to the strait four major mws circulate alongslope counterclockwise as density currents and as long as they are not trapped within a basin which is necessarily the case for the deep mws in the alboran the intermediate mws wiw liw and upper tdw circulate in the north while the deep mws lower tdw and wmdw are uplifted hence relatively motionless and mainly pushed away in the south since both the intermediate and deep mws outflow at the sill they are considered as light and dense mws the light dense mws interface possibly intersecting the aw mws interface in the sill surroundings considering an outflow east of the sill composed of only two light dense homogeneous layers gives significant results across the whole strait the outflow has spatial and temporal variabilities much larger than previously assumed the mws are superposed in the sea and lead at the sill to juxtaposed and vertically stratified suboutflows that will cascade independently before forming superposed veins in the ocean these veins can have similar densities and hydrographic characteristics even if associated with different mws which accounts for the features permanency assumed up to now the outflow structure downstream of the sill depends on its composition upstream and more importantly on that of aw in the sill surroundings where fortnightly and seasonal signals are imposed on the whole outflow

paleocurrent reconstruction of the deep pacific inflow during the middle miocene reflections of east antarctic ice sheet growth today the deep western boundary current dwbc east of new zealand is the most important route for deep water entering the pacific ocean large scale changes in deep water circulation patterns are thought to have been associated with the development of the east antarctic ice sheet eais close to the main source of bottom water for the dwbc here we reconstruct the changing speed of the southwest pacific dwbc during the middle miocene from 15 5 12 5 ma a period of significant global ice accumulation associated with eais growth sortable silt mean grain sizes from ocean drilling program site 1123 reveal variability in the speed of the pacific inflow on the timescale of the 41 kyr orbital obliquity cycle similar orbital period flow changes have recently been demonstrated for the pleistocene epoch collectively these observations suggest that a strong coupling between changes in the speed of the deep pacific inflow and high latitude climate forcing may have been a persistent feature of the global thermohaline circulation system for at least the past 15 myr furthermore long term changes in flow speed suggest an intensification of the dwbc under an inferred increase in southern component water production this occurred at the same time as decreasing tethyan outflow and major eais growth between 15 5 and 13 5 ma these results provide evidence that a major component of the deep thermohaline circulation was associated with the middle miocene growth of the eais and support the view that this time interval represents an important step in the development of the neogene icehouse climate

retrievals of lake ice thickness from great slave lake and great bear lake using cryosat 2 satellite observations have revealed decreases in the duration of the seasonal snow and ice coverage of great slave lake gsl and great bear lake gbl large freshwater lakes in northern canada however limited information is available about ice thickness changes here we present and validate a method to retrieve lake ice thickness using the cryosat 2 cs2 radar altimeter these are the first satellite altimeter retrievals of lake ice thickness under optimal conditions the cs2 signal is scattered from both the snow ice and the ice water interfaces with returns from each interface being of sufficient power to be identified in the radar waveform the distance between the scattering horizons is used to determine the ice thickness similar to traditional ground penetrating radar measurements the seasonal evolution of ice thickness of gbl and gsl is compared with in situ measurements modeled ice thicknesses and previous studies the impact of ice and snow properties on signal penetration and the thickness retrieval are examined with synthetic aperture radar imagery the cs2 ice thickness retrievals are able to observe the seasonal thickening of the lake ice and closely match the in situ measurements over both lakes r 0 65 text rmse m thickness retrievals of thin ice are limited by a minimum waveform peak separation of 2 range bins approximately 0 26 m in ice although not designed for lake ice studies cs2 and future sar satellite altimeter missions offer new possibilities to monitor the ice and water levels of climatically sensitive and influential lakes

sedimentary processes and cold water coral mini mounds at the ferrol canyon head nw iberian margin abstract the western iberian margin has a complex morphology controlled by both geological and oceanographic processes compared to the submarine canyons in the southern part of this margin e g nazare and setubal the canyons in the northern part e g ferrol and a coruna have received little attention this study maps the geomorphological features around the ferrol canyon head and combines them with oceanographic observations to infer the sedimentary and oceanographic processes active in this area furthermore the occurrence of a cold water coral cwc mini mound province near the canyon head and the ortegal spur pockmark field is investigated with regard to seepage processes oceanographic conditions and anthropogenic impact the ferrol canyon head and outer ortegal spur are characterized by erosional erosional and abraded surfaces contourite channels and furrows depositional contourite drifts and sediment waves and mixed contourite terrace features indicating a dominant control of bottom currents on the sedimentary processes bottom currents are related to the interaction of the canyon head topography with both the mediterranean outflow water mow slope current and with m2 internal tides associated to the interface pycnocline between eastern north atlantic central water enacw and mow due to this interaction the ferrol canyon head is subject to active sediment resuspension and forms a potential source area for the intermediate nepheloid layers along the nw iberian upper slope the cwc mini mounds 1 9 2 7 m high and 75 141 m in diameter occur between 400 and 560 m depth seismic facies signatures indicative of fluid flow and morphometric analysis implies that larger cwc mini mounds adjacent to the pockmark field initiated by colonization of pre existing pockmarks while smaller more clustered mounds developed independently the observed mini mounds are relict features likely related to their position outside of the contemporary enacw mow interface which favours cwc growth through 1 increased bottom currents enhancing food supply and 2 the presence of a potential density envelope 27 35 27 65 kg m3 proposed to control coral larvae transport along the ne atlantic margin alternatively the lack of contemporary coral growth might be related to habitat destruction by bottom trawling however a preliminary age constraint reveals cwc growth occurred during the early holocene coeval to relict cwc mini mounds near canyon heads on the armorican margin their existence suggests a regional shift in the ne atlantic density profile where the enacw mow interface occurred up to 200 m above its contemporary position

melt season duration on canadian arctic ice caps 2000 2004 1 the extent and duration of summer melt on ice caps in the queen elizabeth islands qei nunavut canada in 2000 2004 were mapped using enhanced resolution quikscat qscat scatterometer images the mean melt duration depends mainly on surface elevation and distance from baffin bay over most ice caps inter annual variations in melt duration and the variation in melt duration with elevation are closely related to variations in the july 500 hpa height over the qei pressure related variability in the vertical gradient of near surface air temperature appears to be a major control on the inter annual variations in average melt duration

sedimentary evolution of the le danois contourite drift systems southern bay of biscay ne atlantic a reconstruction of the atlantic mediterranean water circulation since the pliocene abstract the evolution of the le danois contourite depositional systems cds during the pliocene and quaternary was investigated based on high resolution seismic reflection data from old to young six seismic units u1 u6 bounded by major discontinuities h1 h6 were identified regarding variations of the bottom current circulation four evolution stages of the le danois cds were identified including onset 5 3 to 3 5 3 0 ma initial 3 5 3 0 to 2 5 2 1 ma intermediate 2 5 2 1 to 0 9 0 7 ma and drift growth 0 9 0 7 ma to present day stages the cds associated with the atlantic mediterranean water amw along the middle continental slope initiated at 3 5 3 ma and was widely built after the mid pleistocene transition mpt 0 9 07 ma at a shallower water depth a second cds associated with the eastern north atlantic central water enacw started to develop from the late quaternary 0 47 ma onwards in the amw related drift system the le danois drift was generated both under glacial and interglacial climatic oscilations repeated internal structures in unit 5 that consist of acoustically transparent lower parts moderate amplitude upper parts and high amplitude erosional surfaces at the top are compared with interglacial glacial cycles since the middle pleistocene to the present day these cyclic features suggest coarsening upward sequences of the le danois drift and processes related to enhanced amw during glacial stages the estimated sedimentation rate of the le danois cds reached a maximum during the mpt at least 27 cm ky and then decreased until present day 5 cm ky variations of sedimentary stacking patterns and processes of the le danois cds imply full domination of the intermediate water mass along the central atlantic and southwest european continental slopes from the late pliocene 3 5 3 0 ma onwards

dynamics of sediments on a glacially influenced sediment starved current swept continental margin the se grand banks slope off newfoundland abstract the se grand banks slope is unusual on the glaciated eastern canadian margin in that it was remote from ice stream and glacial ice of the laurentide ice sheet lis it thus allows an analysis of the role of contour currents and landslides in sculpting the continental margin processes that are largely masked where downslope proglacial sediment supply dominated detailed oxygen isotope geotechnical pxrf and bulk sediment geochemical analyses were made on seven piston cores and were placed in context using multi beam bathymetry and high resolution seismic reflection profiles cores have a record of sedimentation back to mis6 preserved in autochthonous sediment and slide blocks contourites and mass transport deposits mtds detrital carbonate rich heinrich layers h are present throughout the succession but red mud layers of glacial meltwater origin from ice streams in the se sector of the lis are identified only during mis2 and late mis3 both layers allowed high resolution correlation between cores sediments on the upper slope above h2 are condensed and the section above h1 is five horizons with mtds with headscarps generally up to 25 m high are recognized in the upper 50 70 m thick mtds are blocky in cores and in their seismic and bathymetric expression resemble spreads with local thin mud clast conglomerates that ran out as debris flows over the contemporaneous seabed geotechnical data suggest that the seabed is stable under static conditions although there is geological evidence for fluid escape and geotechnical evidence for underconsolidation weak layers along which failure took place are found somewhere around h3 h4 and at or near the top of h5 and mis6 the low plasticity and liquid limit of the h layers make these layers susceptible to failure during cyclic loading episodic earthquakes are the most likely cause of failure

mediterranean outflow strengthening during northern hemisphere coolings a salt source for the glacial atlantic abstract high resolution grain size and magnetic susceptibility records from the eastern gulf of cadiz site md99 2339 1170 m water depth reveal contourites formed by the mediterranean outflow mow during the last 47 kyr bp oscillations in the mow s intensity occurred in phase with greenland temperature variations with a stronger outflow during northern hemisphere coolings such as dansgaard oeschger stadials heinrich events and the younger dryas benthic 13c data implies the western mediterranean deep water as one of the main sources feeding the outflow current while differential changes in the properties of the mediterranean source and entrained north atlantic central water largely control the mow s strength detailed studies for heinrich events 1 4 and 5 show that the flow strength peaked only when subtropical surface waters prevailed in the eastern gulf of cadiz while incursions of icebergs and subpolar surface water were not favorable for the mow s intensification as the mow was strong when the atlantic s thermohaline circulation thc was weakened the heat and salt injected by the mow into the intermediate north atlantic waters might have preconditioned the thc to switch from the stadial to the interstadial mode

physical oceanography of the azores front abstract there is a considerable body of evidence for the existence of a permanent front sw of the azores surveys in the summer of 1981 show the structure to penetrate to a depth of 2 000 m and suggest that its meandering is related to the alignment of the atlantis gt meteor seamount chain the total volume transport above 2 000 m is between 10 and 12 106 m3 s 1 towards the east the main water mass contrasts across the front are confined to the upper 400 m of the water column only a small change in mediterranean water strength was seen across the front satellite tracked drogued buoys seeded into the front showed surface speeds of up to 40 cm sec 1 and revealed the formation of a closed cold core eddy some 100 115 km in diameter which propagated westward at 2 2 km day 1 over a 200 day period sea surface temperature contrasts across the frontal boundary are small and together with frequent cloud cover prevent the detection of the front and associated eddies by satellite infra red imagery the front apparently marks the eastward extension of the southern branch of the gulf stream recirculation and the northern limit of the 18 c water mass eddies formed at the front could propagate westward into the interior of the sargasso sea but have not yet been observed to cross the mid atlantic ridge

late glacial to holocene history of the mediterranean outflow evidence from benthic foraminiferal assemblages and stable isotopes at the portuguese margin records of benthic foraminiferal assemblage variations and benthic 13c along 12 sediment cores from the western iberian margin between 36 and 42 n at water depths from 820 to 3580 m are used to monitor fluctuations of the mediterranean outflow water mow during the past 30 ka the chronostratigraphy of the cores is based on planktonic 18o records 14c ams dating and the recognition of heinrich events h1 through h4 increased abundances of suspension feeding benthic foraminifers denoted as epibenthos group closely match areas where the recent mow core layers impinge on the continental slope at 800 and 1300 m water depth and near bottom current velocities are enhanced elevated epibenthos group abundances increased benthic 13c and sedimentological evidence for winnowing and erosion are found in glacial sections up to the earliest termination i in cores at water depths between 1600 and 2200 m off southern portugal the combined evidence reveals enhanced current activity at these depths due to a deep glacial mow the mow advection at the portuguese margin during the last glacial was about 700 m deeper than today conceivably forced by increased mow density due to higher salinity and colder temperatures of mediterranean waters the deep mow current gradually decreased in strength and shoaled to 1300 m water depth during the termination and early holocene a shallow mow core layer became active with the onset of termination i at depths between 600 and 1000 m both the shallow and deep mow current culminated during the younger dryas period the present flow pattern with two mow core layers centred at 800 and 1300 m water depth was established between 7 5 and 5 5 ka

mixing and spreading of the mediterranean outflow abstract hydrographic and current profiler data taken during the 1988 gulf of cadiz expedition have been analyzed to diagnose the mixing spreading and descent of the mediterranean outflow the s properties and the thickness and width of the outflow were similar to that seen in earlier surveys the transport of pure mediterranean water i e water with s 38 4 psu was estimated to be about 0 4 106 m3 s 1 which is lower than historical estimates most of which were indirect but comparable to other recent estimates made from direct velocity observations the outflow transport estimated at the west end of the strait of gibraltar was about 0 7 106 m3 s 1 of mixed water and the transport increased to about 1 9 106 m3 s 1 within the eastern gulf of cadiz this increase in transport occurred by entrainment of fresher north atlantic central water and the salinity anomaly of the outflow was consequently reduced the velocity weighted salinity decreased to 36 7 psu within 60 km of the strait and decre

glacial to interglacial changes in the settling depth of the mediterranean outflow plume we present micropalaeontological and grain size records for a set of sediment cores from the gulf of cadiz southwest spain that reflect changes in the position and strength of the mediterranean outflow mo current the cores sample a sediment drift the gil eanes drift that is positioned lower on the slope in the gulf of cadiz than the position of the main current today the data indicate that the drift is of glacial age and that the glacial mo current was positioned lower on the slope than today but also that it was active over a considerably reduced area of the slope we argue that this observation is consistent with physical constraints on the gibraltar exchange and on the likely settling and spreading behavior of the mo plume along the iberian margin under glacial environmental and sea level conditions the deeper settling of the mo is likely to have influenced the formation of glacial north atlantic intermediate water and also may have exerted indirect influence on the formation of glacial north atlantic deep water

short term sediment dynamics on a meso scale contourite drift off nw iberia impacts of multi scale oceanographic processes deduced from the analysis of mooring data and numerical modelling abstract possible driving mechanisms of sediment dynamics in a contourite drift moat obstacle system on the continental slope off the nw iberian peninsula are investigated in this study based on a statistical analysis of an 18 month long mooring record in combination with a 3 dimensional process based numerical modelling analysis of the mooring data indicates that the modern hydrodynamic regime in the study area is non linear with a significant impact of internal tides and a non negligible influence by the earth s rotation a consistent counteraction between barotropic and baroclinic tidal currents mainly at m2 frequency results in a weak bottom flow that rarely exceeds the threshold velocity for resuspension of sandy silts in the system this observation explains a late holocene hemipelagic vertical settling deposition of a fine grained 8 10 m sediment surface layer over the entire drift as well as inside the moat in order to unravel possible driving forces for active sediment remobilization during the deglacial early holocene interval between 17 000 and 4000 cal yr bp that is consistent with the sedimentary record different oceanographic scenarios were designed for a numerical study simulation results demonstrate that pulse like oceanic density fronts and associated km scale eddies which originate from instability in the transition zone of two water masses labrador sea water mediterranean outflow water being aided by tidal and geostrophic currents and locally strengthened by topography are the most reasonable mechanisms inducing contouritic sediment transport and deposition that are observed in the sediment core transect these density fronts are of subordinate impact for the modern contourite drift which is bathed by labrador sea water nowadays however a vertical downward migration or expansion of the overlying mediterranean outflow water by 300 m between 17 000 and 4000 cal yr bp would facilitate a generation of significant density fronts at the depth of the contourite drift this mow migration is believed to leave imprints on other contourite systems located at similar depth in the region

promotion of meridional overturning by mediterranean derived salt during the last deglaciation we demonstrate that changes in the behavior of the mediterranean outflow water mow prior to and through the last deglaciation played an important role in promoting meridional overturning circulation moc estimation of past mow salt and heat fluxes indicates that they gradually increased through the last deglaciation between 17 5 and 14 6 thousand years ago ka b p where b p references year 1950 net evaporation from the mediterranean exported sufficient fresh water from the north atlantic catchment to cause an average salinity increase of 0 5 psu throughout the upper 2000 m of the entire north atlantic to the north of 25

a conceptual model of the deglaciation of atlantic canada abstract we present a conceptual model for the deglaciation of atlantic canada in which a role is played by ice streams the ice margin lay close to the edge of the continental shelf at the last glacial maximum ice streams occupying shelf troughs comprised 1 a major ice stream in the laurentian channel 2 secondary streams in the bay of fundy gulf of maine trinity trough and notre dame channel and 3 lesser ice streams elsewhere early retreat in the northeast notre dame bay and in the southwest bay of fundy gulf of maine was mainly by calving along embayments by 18 ka radiocarbon years a calving embayment had opened on emerald basin scotian shelf retreat along channels marooned ice on intervening banks a major calving episode beginning just before 14 ka removed ice from the gulf of st lawrence triggering re advances down secondary troughs isolation of a newfoundland ice cap produced radial drainage via fiords and more extensive flow into the st george s bay lowlands on the west coast by 13 ka most ice was on land and was ablating by melting rather than calving shelf ice caps persisted until 11 ka

the late pleistocene holocene sedimentary evolution of the sines contourite drift sw portuguese margin a multiproxy approach abstract the sines contourite drift scd located in the alentejo margin southwest iberian continental margin has been through many depositional phases in result of climatic variations and bottom current oscillations which determined a variable depositional pattern and an irregular sedimentary evolution since the late pleistocene the scd being in the main path of the mediterranean outflow water mow which greatly constrains the sedimentary building of this drift constitutes the distal part of the gulf of cadiz contourite depositional system and its sedimentary evolution therefore reflects the history of mow variations in order to investigate this we report on a multiproxy analysis of grain size carbon content and physical geochemical and environmental magnetic properties on the ams 14c dated 350 cm long gravity core co14 gc 07 retrieved in the scd at 1425 meters water depth mwd the main objective is to reconstruct the evolution of the sedimentary package of the scd from 43 cal kyr bp to present and bring new insights about the impact of bottom currents activity on the morphosedimentary evolution of the margin results show the existence of four distinct depositional phases in response to climate variations and bottom current oscillations during the late pleistocene holocene phase 1 350 322 cm 42 9 cal kyr bp occurred in marine isotope stage mis 3 and presents silty muddy sediments with presence of shell fragments and moderate bioturbation phase 2 322 176 cm 42 9 30 5 cal kyr bp which lasted from middle mis 3 to the onset of mis 2 reveals sediment coarsening towards the top limit suggesting climate cooling and strong bottom current winnowing phase 3 176 144 cm 30 5 17 1 cal kyr bp covers most of mis 2 prior to the last deglaciation and shows the sharpest variations on all sediment properties and the coarsest sediment facies with fe rich layers associated with the increase of terrigenous input and sea level regression that coincide with the enhancement of mow phase 4 144 0 cm

melt season duration and ice layer formation on the greenland ice sheet 2000 2004 1 time series of enhanced resolution quikscat images were used to map the extent and duration of surface melt and the distribution of ice layer formation on the greenland ice sheet in the period 2000 2004 apart from the bare ice and the mixed pixels 10 along the ice sheet margin where melt cannot be determined reliably annual melt duration and melt anomaly maps were produced across the ice sheet 90 for each summer over the 5 year period the mean melt duration for the ice sheet ranged from 14 3 to 20 5 d the proportion of the ice sheet that experienced melting in a given year ranged from 44 2 to 79 2 extensive melt in 2002 was caused by a single melt event of a few days duration this event was associated with the intrusion of a ridge of high pressure from the north atlantic ocean that brought warm air onto the ice sheet the change in biweekly averaged backscatter between the freeze up periods in the current and previous falls was used to identify changes in the distribution of ice layers in snow between successive melt seasons the year 2002 had the maximum melt extent and duration and ice layer formation extended to higher elevations than in other years interannual changes in the distribution of ice layer formation may be associated with changes in surface height that are not necessarily indicative of mass balance changes mapping of ice layer formation is thus potentially useful for interpreting both real and apparent height changes measured by altimetry

glaciogenic debris flow deposits of orphan basin offshore eastern canada sedimentological and rheological properties origin and relationship to meltwater discharge abstract glaciogenic debris flow deposits gdfs have been recognized in the last decade seaward of many shelf crossing ice streams the rheology of gdfs remains poorly understood ultra high resolution sparker seismic profiles and 25 long piston cores were used to define the architecture age and sediment properties of the gdf deposits in trinity trough mouth fan tmf offshore northeast newfoundland and hence understand their origin and emplacement the gdf deposits comprise poorly sorted gravelly mud individual gdf lenses are 5 30 m thick 2 10 km wide and up to 250 km long shear strength measurements and grain size analysis indicate that gdfs have a different more fluid rheology at their margins and tops exhibiting a surging flow behavior on the upper slope the transition from hard over consolidated till to thin proximal gdf deposits is exposed in a mid holocene landslide scar the transition between the two lithotypes appears gradual and no pre holocene failure scarps were detected a process involving the continuous release of subglacial flowing material with high pore pressure and low shear strength is invoked for the production of gdfs five stacked gdf units a e were deposited during the last glacial maximum 20 5 28 cal ka and can be correlated into a regional lithostratigraphy based on the presence of heinrich beds and 8 local meltwater events r1 8 represented by red plumite deposits south of the trinity tmf this correlation indicates that the timing of major gdf pulses corresponds to the early part of five meltwater discharge events 20 5 21 23 23 5 23 8 24 5 25 27 and 27 5 28 5 cal ka so that gdf deposits represent only a small period of time during a major glacial advance three meltwater events 19 2 20 23 23 5 and 25 27 cal ka produced hyperpycnal flows that resulted in the formation of channel systems and distal sand turbidites the presence of such erosional features in tmfs on the continental margins of the norwegian greenland sea suggests that this novel relationship between gdfs and hyperpycnal turbidites may be widespread and thus important for understanding the glaciological processes involved

radiocarbon variability in the western north atlantic during the last deglaciation we present a detailed history of glacial to holocene radiocarbon in the deep western north atlantic from deep sea corals and paired benthic planktonic foraminifera the deglaciation is marked by switches between radiocarbon enriched and depleted waters leading to large radiocarbon gradients in the water column these changes played an important role in modulating atmospheric radiocarbon the deep ocean record supports the notion of a bipolar seesaw with increased northern source deep water formation linked to northern hemisphere warming and the reverse in contrast the more frequent radiocarbon variations in the intermediate deep ocean are associated with roughly synchronous changes at the poles

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

a 1 ma record of sediment flux south of the grand banks used to infer the development of glaciation in southeastern canada abstract a 20 m long piston core from a basement ridge on the continental rise off southeastern canada provides a 0 9 ma record of distal continental margin sedimentation sediment sources are distinguished by sand and clay sized mineralogy and detrital palynomorphs they include detritus eroded from a northern canadian shield and lower paleozoic rocks transported southward through the labrador sea b the grand banks and c the gulf of st lawrence and newfoundland isotopic stratigraphy allows correlation of glacial and interglacial stages with changes in sources and flux rates via different transport processes nepheloid layer ice rafting and distal turbidity currents the glacial history of southeastern canada is interpreted from variation in the flux and type of detrital material and correlation with other data from the continental margin from stages 27 to 15 the grand banks formed a forested coastal plain limited local glaciation may have occurred in stages 18 and 16 tertiary regolith and cretaceous clays were stripped from land areas in stages 14 and 12 culminating in the excavation of the laurentian channel late in stage 12 extensive cold based ice sheets are inferred for glacial stages 10 8 and 6 with less severe glaciation in stages 4 and 2 extent of this local appalachian ice correlates poorly with global ice volumes

probable late wisconsinan ice margin on the upper continental slope off st pierre bank eastern canada seismic reflection profiles from the continental slope off st pierre bank show a distinctive acoustic facies characterized by incoherent reflections unit e overlain by 5 20 m of stratified sediments units d a cores from unit e include poorly sorted silty diamict locally overconsolidated and including in places some foraminifera stratified sediments also occur in places in this facies the overlying sediments of units d a except for the topmost metre of unit a have a foraminiferal fauna dominated by elphidium excavatum forma clavata and cassidulina reniforme which has been interpreted elsewhere as indicating ice margin sedimentation the sediments contain turbidites and rare ice rafted detritus and are bioturbated accelerometer mass spectrometer radiocarbon dating of shells from the stratified sediments yielded dates between 3 3 and 11 8 ka facies e the top of which has an extrapolated age of 11 5 12 0 ka is interpreted as slumped morainal diamict and proglacial sediment resulting from a lat

the flow of atlantic water through the strait of gibraltar abstract we describe and analyze observations of the water exchange through the strait of gibraltar the primary observations were taken in april 1986 and included data from moored recording instruments at four locations in the strait together with an intensive survey by ship these measurements included extensive ctd profiling acoustic doppler current profiling numerous profiles from expendable instruments and imaging using a high frequency echo sounder the analysis focuses on the internal hydraulics of the strait and in particular the presence of hydraulic controls and their influence on the exchange our observations during april 1986 show that the maximal exchange condition in which a subcritical flow is bounded by supercritical flow at both ends of the strait did occur although with various subtleties not explicitly incorporated in our previous theoretical developments the atlantic water moving east along the surface encounters a control at tarifa narrows in the eastern part of the strait the mediterranean water passes through controls both at camarinal sill and at spartel sill further west at our westernmost mooring at spartel the outflowing mediterranean water is continuously supercritical with little tidal variability the control at camarinal sill is periodically lost due to tidal action and reappears on a reverse flow during a falling spring tide tangier basin bounded by camarinal and spartel sills acts as an internal reservoir for the outflowing mediterranean water the interface rising and falling through each tidal cycle during spring tides the tangier basin interface rises high enough to flood the control at camarinl sill and produces a reverse flow of the lower layer when control is lost at camarinal sill a travelling bore is released this bore may modify the location of the control acting on the surface layer in tarifa narrows the atlantic water enters the alboran sea as a jet which may have a well defined northern boundary where it separates from the european coast this boundary may be identified by the presence of a slick although the internal jump west of camarinal sill is almost certainly an area of intense mixing frictional effects do not appear to be dominant in the subcritical portion of the flow

sediment transport processes at the head of halibut canyon eastern canada margin an interplay between internal tides and dense shelf water cascading abstract to investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin the bottom boundary layer quadrapod ralph was deployed at 276 m depth in the west halibut canyon off newfoundland during winter 2008 2009 two main sediment transport processes were identified throughout the deployment firstly periodic increases of near bottom suspended sediment concentrations ssc were recorded associated with the up canyon propagation of the semidiurnal internal tidal bore along the canyon axis carrying fine sediment particles resuspended from deeper canyon regions the recorded ssc peaks lasting less than 1 h were observed sporadically and were linked to bottom intensified up canyon flows 40 cm s 1 concomitant with sharp drops in temperature secondly sediment transport was also observed during events of intensified down canyon current velocities that occurred during periods of sustained heat loss from surface waters but were not associated with large storm waves high resolution velocity profiles throughout the water column during these events revealed that the highest current speeds 1 m s 1 were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow such flows had associated low ssc and cold water temperatures and are interpreted as dense shelf water cascading events channelized along the canyon axis sediment transport during these events was largely restricted to bedload and saltation producing winnowing of sands and fine sediments around larger gravel particles analysis of historical hydrographic data suggests that such gravity flows are not related to the formation of coastal dense waters advected towards the outer shelf that reached the canyon head rather the dense shelf waters appear to be generated around the outer shelf where convection during winter is able to reach the sea floor and generate a pool of near bottom dense water that cascades into the canyon during one or two tidal cycles a similar transport mechanism is likely to occur in other submarine canyons along the eastern canadian margin as well in other canyoned margins where winter convection can reach the shelf edge

resolution enhancement of spaceborne scatterometer data a method for generating enhanced resolution radar images of the earth s surface using spaceborne scatterometry is presented the technique is based on an image reconstruction technique that takes advantage of the spatial overlap in scatterometer measurements made at different times to provide enhanced imaging resolution the reconstruction algorithm is described and the technique is demonstrated using both simulated and actual seasat a scatterometer sass measurements the technique can also be used with ers 1 scatterometer data the sass derived images which have approximately 4 km resolution illustrate the resolution enhancement capability of the technique which permits utilization of both historic and contemporary scatterometer data for medium scale monitoring of vegetation and polar ice the tradeoff between imaging noise and resolution inherent in the technique is discussed