dense water formation beneath a time dependent coastal polynya abstract recent modeling studies of dense water formation beneath an idealized steady coastal polynya have provided simple analytical expressions for the maximum density anomaly achievable as a function of the polynya geometry and the imposed surface buoyancy flux these studies have assumed that the buoyancy flux and polynya geometry are both constant and independent parameters to relax these assumptions dense water formation is examined beneath a coastal polynya whose size and surface buoyancy flux are computed from atmospheric temperature and wind velocity according to a polynya model developed by pease though highly idealized the pease model produces polynyas that open and close on reasonably realistic timescales and it thermodynamically couples the polynya size and buoyancy flux results reveal several interesting and potentially useful features of the ocean response to time dependent polynya forcing first under reasonable atmospheric conditions both the maximum density anomaly achievable and

erosion of the laurentide region of north america by glacial and glaciofluvial processes collection of seismic reflection data from continental margins and ocean basins surrounding north america makes it possible to estimate the amount of material eroded from the area formerly covered by laurentide ice sheets since major glaciation began in north america a minimum estimate is made of 1 62 106 km3 or an average 120 m of rock physically eroded from the laurentide region this figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift cenozoic marine sediments and modern sediment loads of rivers most of the sediment produced during laurentide glaciation has already been transported to the oceans the importance of continental glaciation as a geomorphic agency in north america may have to be reevaluated evidence from sedimentation rates in ocean basins surrounding greenland and antarctica suggests that sediment production sediment transport and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps such as the laurentide low rates of sediment survival from the time of the permo carboniferous and precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust

11 000 yrs of environmental change in the northwest passage a multiproxy core record from central parry channel canadian high arctic article i nfo piston core 97022 004pc 74 48 0 n 97 05 9 w 267 m water depth represents a rare paleoenvironmental archive from the understudied west central canadian arctic archipelago lithological biogeochemical and microfossil dinoflagellate cysts non pollen palynomorphs benthic and planktonic foraminifera character istics in combination with a chronostratigraphy based on seventeen radiocarbon dates show seven promi nent paleoenvironmental episodes since the end of the last regional glaciation the basal diamict zone i records decoupling of previously grounded glacial ice followed by ice proximal conditions zone iia commencing at 10 8 cal ka bp age depth model extrapolation after an interval of pervasive sea ice zone iib ice distal conditions are established zone iic although sparse microfossils are present in glaciomarine sediments zone ii noticeable biological activity with heightened abundances and diversities across all groups begins in the postglacial zone iii 10 3 10 0 cal ka bp when planktonic foraminifera neogloboquadrina pachyderma appear as planktonics are excluded from the study area today due to shal low inter channel sills this likely signals the inflow of relatively warm and saline atlantic derived arctic intermediate water below 250 m presumably facilitated by glacio isostatically enhanced deglacial water depths the subsequent zone iv 10 0 7 0 cal ka bp characterized by heightened biological productivity in both plankton and benthos and reduced seasonal sea ice cover may correspond to a previously proposed holocene thermal maximum this apparent amelioration ends by the mid holocene zone v 7 0 5 7 cal ka bp when arctic intermediate water is excluded from the study area and water depths approach modern values high arctic conditions with seasonal sea ice cover a circulation dominated by arctic ocean surface water and microfossil assemblages similar to modern are found from 5 7 cal ka bp onwards zones vi vii as only minor environmental fluctuations are apparent during the late holocene shorter term climatic episodes e g little ice age are not recognized in this record

micromechanics of the velocity and normal stress dependence of rock friction among the second order effects on friction the most important are those of variable normal stress and of slip velocity velocity weakening which is usually considered the source of the stick slip instability in rock friction has been observed in velocity stepping experiments with westerly granite the friction change was 0 01 to 0 008 for a tenfold velocity increase using normal closure measurements we observed dilation upon each increase in sliding rate we also observed for the first time time dependent closure between surfaces during static loading the dilation that occurred during the velocity stepping experiment was found to be that expected from the static time dependent closure phenomenon this change in closure was used to predict friction change with an elastic contact model the calculated friction change which results from a change in contact area and asperity interlocking is in good agreement with the observed velocity dependence of steady state friction variable normal stress during sliding has two effects first in creating new partial slip contacts and locking some existing fully sliding contacts and second in increasing interlocking for instance when normal load is suddenly increased as a result a transient change in friction occurs upon a sudden change in normal load

friction properties of hornblende and implications for slow slip events in subduction zones abstract in order to understand the friction properties of amphibole as a primary constituent mineral in subduction zones we used hornblende as the simulated gouge material to conduct two series of shearing experiments at temperatures from 101 to 607 c under confining pressures of 136 mpa and 83 mpa a pore pressure of 30 mpa and loading rates of 0 0488 1 22 m s steady state friction coefficients in the high confining pressure series exhibited values between 0 70 and 0 72 with an average of 0 71 without showing a systematic temperature dependence the counterpart in the low confining pressure series ranged from 0 67 to 0 73 and exhibited a temperature dependent decline for temperatures above 400 c velocity weakening behaviors were observed at 303 505 and 607 c in the high confining pressure series and at 303 and 403 c in the low confining pressure series the a b parameter associated with velocity weakening of hornblende in our high and low confining pressure experiments are 0 0005 0 0014 and 0 0014 0 0015 respectively the b values which represent the evolution effect in friction were found to increase with increasing temperature suggesting a thermally activated process that produced creep at asperity ubiquitously precipitated particles in the deformed gouge suggest that dissolution precipitation creep may be the most likely mechanism associated with the evolution effect and therefore velocity weakening the very low velocity weakening observed for hornblende a b 0 0015 provides a favorable condition for nucleation of slow slip events to occur in subduction zones over a wider range of effective normal stress

transition between stable sliding and stick slip due to variation in slip rate under variable normal stress condition this paper discusses a new mechanism that may control the transition between stable sliding and cyclic stick slip under variable normal stress condition with a rate and state dependent friction law that embodies the effect of normal stress a single degree of freedom spring slider system inclined to the driving direction has a velocity dependent critical stiffness which separates stable sliding and cyclic stick slip with steady state log linear rate dependent friction the critical stiffness decreases with increasing velocity accordingly higher velocity stabilizes a system for a predetermined stiffness lower than the critical value and may change the motion from cyclic stick slip to stable sliding and vice versa our numerical simulations in full dynamic motion confirmed such transition and agreed well with the analytical calculation such transitions can also be found in experimental works

frictional properties of sedimentary rocks and natural fault gouge from the longmen shan fault zone sichuan china in this paper we report friction experiments performed on samples collected from the region hit by the 2008 wenchuan earthquake in the longmen shan fault zone lfz of sichuan southwestern china the materials tested consisted of simulated gouges prepared from intact clay rich mudstone and sandstone a calcite limestone plus a natural fault gouge from a trenched surface rupture cutting the mudstone and sandstone the clay rich samples including the natural gouge were dominated by illite and quartz in our experiments we sheared 1 mm thick gouge layers between saw cut driver blocks using a triaxial testing machine at conditions corresponding to 2 km depth in the lfz temperature was varied from 25 c to 150 c and to investigate the velocity dependence of friction we stepped the shear displacement rate between 1 22 and 0 122 m s our results show that the natural gouge was more illite rich and much weaker than the protolith mudstone and sandstone and showed a steady state friction coefficient of 0 4 compared with 0 6 for the latter the limestone gouge displayed values of 0 6 0 7 all samples except the limestone showed stable velocity strengthening slip the limestone showed velocity strengthening at 25 c 50 c but quasi static oscillations at 100 c 150 c along with velocity weakening behavior at 150 c we apply our results to discuss the role of the sedimentary rocks studied during events such as the wenchuan earthquake and argue that the clay rich sediments of the region may have a damping effect upon ruptures propagating from depth whereas the limestone may accelerate propagation producing significant stress drops

quaternary correlations in arctic canada in the hudson bay james bay lowlands along the coasts of banks island and along the eastern coast of baffin island are continuous and extensive sections in quaternary sediments these sections are rich in marine fossils buried peats and soils and contain a wide variety of glaciagenic sediments together with glacial marine units and littoral deposits lake muds are also fairly common all three areas possess very long records that may extend to the early quaternary and pliocene the events of the last glaciation wisconsinan foxe amundsen are interpreted in terms of lithostratigraphy biostratigraphy and aminostratigraphy relative and absolute dating control is provided by radiocarbon dating of events that span the last 50 ka and in particular the last 11 ka and some age control is also provided by several u series dates on marine molluscs regional correlations are based on comparisons of amino acid ratios from marine shells suggested correlations during the last glaciation wisconsinan foxe amundsen are ka banks island hudson bay lowland baffin island 8 tyrrell sea sediments inugsuin regression 10 russell stade upper tills baffinland stade 40 friday creek sediments iron stand event till 80 fawn river gravels quajon interstade m clure stade adam till ayr lakde stade 120 cape collinson interglaciation missinaibi formation kogalu cape broughton interglaciation

a note on the glacial geology and postglacial emergence of the lake harbour region baffin island n w t ice flow indicators in the lake harbour region of northern hudson strait define two flow directions affecting this area during the late wisconsinan glaciation a pronounced southward flow direction indicated by medium and large scale erosional and depositional features represents ice flow from an ice dome centered to the north perhaps foxe basin and or amadjuak lake carbonate rich till and striations represent eastward southeastward ice flow down the axis of hudson strait convergence of ice sheet flow with a rapidly moving ice stream has been observed and modelled for west antarctic ice streams and involves sharp bending of flow lines at the point of convergence a similar scenario is proposed for the lake harbour region to explain the two contrasting ice flow patterns impingement of an ice stream in hudson strait onto the southern coast of baffin island suggests the influence of northerly flowing ice perhaps from the ungava plateau radiocarbon dates on marine shells and archeological samples are

organic matter biomarker analysis as a potential chemostratigraphic tool for late pleistocene tills from the hudson bay lowlands canada abstract during the last glacial maximum approximately 22 000 years ago the hudson bay lowlands hbl lay at the center of the 3 km thick laurentide ice sheet during the course of the last glacial cycle hbl was crossed by ice from the west the keewatin sector and from the east labrador sector but the relative influence of the outflow centers is debateable because of continuing uncertainty surrounding the age and stratigraphic position of lithologically similar tills in different areas this study examines the use of organic matter om biomarkers to analyze om sources in hbl tills these tills are believed to be of late wisconsin age sachigo severn and an older possibly early wisconsin deposit rocksand till and biomarkers may provide insights into source materials and degree of diagenesis solvent extraction base hydrolysis and cupric oxide oxidation were performed to isolate and quantify free lipids bound lipids and lignin derived phenols respectively lipid biomarker patterns indicate higher sphagnum derived om to the severn and rocksand tills relative to the sachigo till consistent with subglacial reworking and incorporation of peat om within the severn till is dominated by om derived from non woody gymnosperms and non woody angiosperms whereas sachigo and rocksand tills have both woody and non woody gymnosperms and angiosperms derived om furthermore the severn till contained the most suberin derived om while the sachigo till had the least acid to aldehyde ratios of lignin derived phenols suggest that the severn till has undergone less diagenesis in comparison to sachigo and rocksand confirming that it is likely the youngest of the three tills this study highlights that biomarker analysis is an important chemostratigraphic tool that may distinguish till deposits and provides insight into paleovegetation and paleoclimate in the hbl prior to glacial incorporation of om into till this information facilitates paleoenvironmental analyses to be extended into preglacial and interstadial episodes where no stratigraphic record exists

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

late glacial flow patterns deglaciation and postglacial emergence of south central baffin island and the north central coast of hudson strait eastern canadian arctic new georaorphic sedimentologic and chronologic data are used to reconstruct late quaternary ice sheet flow patterns deglaciation and isostatic uplift along the largest marine trough connecting the laurentide ice sheet with the north atlantic ocean the lake harbour region was targeted for study given its potential to record flow from several ice dispersal centers striations and sediment provenance indicators define flow patterns thirty four radiocarbon dates constrain a chronology of events centuries or millennia before deglaciation a southeast flowing ice stream impinged on southernmost big island as recorded by a single striation site and delimited in extent by geomorphic evidence of cold based ice during the cockburn substagc 9000 8000 bp the region was scoured by southward to southwestward flow from an ice cap on meta incognita peninsula as recorded by 60 striation sites along 200 km of coastline carbonate erratics are uncommon in till above the marine limit where present they sugg

role of glacial arctic ocean ice sheets in pleistocene oxygen isotope and sea level records abstract a comparison of the oxygen isotope signal in deep sea benthic foraminifera with the record of glacio eustatic sea level for the last 160 000 years reveals that the amplitude of the benthic 18 o records predicts more continental ice volume than appears to be reflected in lowered sea level stands these differences between the benthic 18 o ice volume estimates and radiometrically dated records of eustatic sea level are consistent with the presence of a large floating arctic ocean ice mass during glacial intervals the presence of an arctic ocean ice sheet during glacial intervals may account for the two climatic modes observed in oxygen isotope records which span the entire pleistocene the early pleistocene 1 8 to 0 9 myr b p interval is characterized by low amplitude high frequency 18 o fluctuations between glacial and interglacial periods while the late pleistocene 0 9 myr b p to present is characterized by large amplitude low frequency 18 o changes these two climatic modes can be explained by the initiation of earth orbital conditions favoring the co occurrence of glacial period arctic ocean ice sheets and large continental ice sheets approximately 900 000 years before present

multiple deglaciations of the hudson bay lowlands canada since deposition of the missinaibi last integlacial formation abstract the stratigraphic record in the james and hudson bay lowlands indicates that the sequence of glacial events at the geographical center of the 12 6 10 6 km 2 laurentide ice sheet may have been more complex than hitherto imagined isoleucine epimerization ratios of in situ and transported shells recovered from till and associated marine and fluvial sediments cluster into at least 4 discrete groups two alternative explanations of the data are offered of which we strongly favor the first hypothesis 1 setting the age of the last interglacial marine incursion the bell sea at 130 000 yr b p results in a long term average diagenetic temperature for the lowlands of 0 6 c using this temperature enables us to predict the age of shells intermediate in age between the last interglaciation and the incursion of the tyrrell sea 8000 yr ago between these two interglacial marine inundations hudson bay is predicted to have been free of ice along its southern shore about 35 000 75 000 and 105 000 yr ago based on amino acid ratios from shells occurring as erratics in several superimposed tills and fluvial sediments these results suggest 1 that traditional concepts of ice sheet build up and decay must be reexamined 2 that high sea levels may have occurred during the wisconsin glaciation and 3 that a critical reappraisal is required of the open ocean 18 o record as a simple indicator of global ice volume an alternative hypothesis 2 is also examined it is based on the assumption that the 35 000 yr old deposits calculated on the basis of hypothesis 1 date from the last interglaciation this in effect indicates that the missinaibi formation commonly accepted as sediments of the last interglaciation are about 500 000 yr old and that the effective diagenetic temperature in the lowlands during approximately the last 130 000 yr has been close to 6 c we argue for rejection of this alternative hypothesis

variations in locking along the east kunlun fault tibetan plateau china using gps and leveling data the east kunlun fault ekf is one of the largest and most active sinistral strike slip faults in the qinghai tibet plateau since 1900 many earthquakes of magnitude 7 have occurred in this region the maqin maqu segment mms a seismic gap underlying a densely populated zone is particularly important while the area has been extensively researched to assess seismic risk refined asperity geodetic imaging is deficient we combined multiple sets of gps and leveling observations to obtain spatial temporal distributions of locking along the ekf we delineated the probable asperity ranges according to the fault plane locking and the distribution of small earthquakes long term observations on gps velocity 1999 2013 and leveling 1970 2013 indicate that the dulan maduo segment dms of the ekf has a 140 km long strong coupling section and both the mms and the eastern ruoergai segments have a 40 km long locking range the 2013 2015 gps velocity observations show that from maqu to maqin the locked dms and mms lengths increased to 200 km and 240 km respectively while the locked eastern ruoergai segment decreased and migrated 60 km to the west this change in locking over time implies that the post seismic effects of surrounding earthquakes have had significant impacts on the ekf the locking area derived from 2015 to 2017 gps velocity shows a growing trend and indicates the connectedness between the two speculative asperities combining the distribution of historical earthquakes and the precision positioning of small earthquakes we conclude that the geodetic imaging of the ekf indicates that the mms and dms are high risk zones for destructive earthquakes

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

radiocarbon dates from cornwallis island area arctic canada an interim report new radiocarbon dates from the university of washington s quaternary isotope laboratory are given for cornwallis island northwest territories canada and these and other radiocarbon dates for the area are assembled in a diagram including the envelope of a tentative emergence curve most of the new dates are derived from surface collections but appear to represent a consistent altitude age relationship confirming the pattern of previously published dates for the general region the oldest of the new holocene dates on marine shells indicate that the resolute bay area began emerging by at least 9700 years bp the highest well developed marine strandlines recognized to date are at an altitude of ca 105 m however the postglacial marine limit is probably some 10 m or more higher as in adjacent regions early postglacial emergence was initially rapid of the order of an average 8 3 m 100 years for the first recorded 75 m then slowed to an average 0 5 m 100 years for the last 40 m

frictional behavior of simulated biotite fault gouge under hydrothermal conditions abstract we investigated frictional properties of biotite under hydrothermal conditions by shearing simulated biotite gouge sandwiched between saw cut driving blocks using a testing system with argon as confining medium experiments were conducted under an effective normal stress of 200 mpa with pore pressure of 30 mpa temperatures were varied from room temperature to 600 c with shear displacement rate stepped at standard velocities 1 22 0 122 m s and slow velocities 0 244 0 0488 m s to acquire rate dependence of friction our results show that the friction coefficient of biotite ranges from 0 25 to 0 44 significantly lower than that of muscovite documented in previous studies the steady state rate dependence shows velocity strengthening at temperatures of 25 c to 200 c and transitions to velocity weakening at temperatures above 300 c the velocity weakening is quite minor with a b ranging from 4 10 4 to 9 10 4 and stick slip motions at temperatures from 400 c to 600 c are found to be related to submicron dc values corresponding to critical stiffness higher than the actual stiffness surrounding the fault thus leading to unstable slips microstructures of deformed samples show three types corresponding respectively to three different temperature ranges while brittle structures are dominantly associated with deformation at 100 c significant plastic deformation occurred at higher temperatures deformation at temperatures of 200 c to 400 c are characterized with shear fracture zones accompanied with plastic deformation mostly associated with basal glide intensively deformed zones are the characteristic structures for samples deformed at 500 c to 600 c accompanied with shear fracture zones and moderately deformed zones it is evident that biotite alone is not weak enough to explain a weak fault like the san andreas fault thus overpressured pore fluid or another weaker mineral is needed to produce a weak fault with apparent friction coefficient of 0 1 0 2 the around neutral velocity weakening found for biotite may be appropriate in modeling fault creep transients in the mid crust

shallow convection and buoyancy equilibration in an idealized coastal polynya abstract the recent theoretical approach of visbeck marshall and jones is used to examine shallow convection and offshore transport of dense water from an idealized coastal polynya a constant negative buoyancy flux is applied in a half elliptical region adjacent to a coastal boundary surrounded by a forcing decay region with uniform width w over which the imposed buoyancy flux decreases smoothly to zero initially the density beneath the forcing increases linearly with time a baroclinically unstable front forms at the edge of the forcing region the width of the front is imposed by the width of the forcing decay region provided this distance is larger than the baroclinic rossby radius baroclinic eddies whose velocities are inversely proportional to w develop along the front and exchange dense water from the forcing region with ambient water eventually reaching an equilibrium in which the lateral buoyancy flux by eddies balances the prescribed surface buoyancy flux the time to reach equilibrium

fault slip controlled by stress path and fluid pressurization rate the practice of injecting fluids into the crust is linked to regional increases in seismicity increasing fluid pressure along preexisting faults is believed to enhance seismicity rates by reducing the shear stress required for slip but the processes that cause faults to slip under conditions of fluid pressurization are poorly constrained we use experimental rock deformation to investigate the controls of fluid pressurization and pressurization rates on fault slip style we show that pore fluid pressurization is less effective that mechanical changes in fault normal stress at initiating accelerated slip events fluid pressurization enhances the total slip slip velocity and shear stress drop of events initiated by mechanical changes in normal stress and these parameters are correlated with pressurization rate but not the magnitude of fluid pressure this result is consistent with field scale observations and indicates that processes active at the pore network scale affect induced seismicity

the late quaternary environmental evolution of marine arctic canada barrow strait to lancaster sound abstract a marine sediment core from the east central canadian arctic archipelago core 86027 154 74 22 01 n 89 51 26 w 329 m water depth studied by a multiproxy approach lithostratigraphy biogeochemistry micropalaeontology dinoflagellate cysts other non pollen palynomorphs benthic and planktonic foraminifera ostracods and encompassing 14 ams 14 c dates provides valuable insights into regional deglacial to holocene palaeoenvironments six palaeoenvironmental zones are recognized based on prominent changes in the litho and biostratigraphy the waterlain diamicton of zone i records immediate deglaciation being derived from lift off and calving of previously grounded glacial ice though deglacial timing is complicated by the sparsity of dating materials and the portlandia effect age depth model extrapolation places deglaciation at 11 54 cal ka bp zone ii 11 5 11 0 cal ka bp represents a distinct progression from initially ice proximal to increasingly ice distal conditions interrupted by an interval of pervasive sea ice 11 4 11 2 cal ka bp noteworthy biological activity commences in zone iii 11 0 9 7 cal ka bp with a prominent signal of planktonic foraminifera neogloboquadrina pachyderma this likely signifies penetration of deeper atlantic derived water through the central canadian arctic archipelago upon deglaciation facilitated by the greater glacioisostatically induced water depths 80 m and implies separation of laurentide and innuitian ice sheets by 11 0 cal ka bp zone iv 9 7 7 2 cal ka bp records ameliorated biologically favourable conditions with reduced seasonal sea ice accompanied by high microfossil species diversity and the presence of subpolar taxa zone v 7 2 6 5 cal ka bp signals the exclusion of atlantic derived water concomitant with increasing sea ice simultaneously representing the termination of the dynamic deglacial to early holocene environments zones i iv conditions similar to modern typified by uniform sediment characteristics present day microfossil assemblage structures and sparse benthic foraminifera were established by 5 6 cal ka bp zone vi

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic discussion the authors j a stravers g h miller and d s kaufman have provided an important synthesis of ongoing research bordering outer hudson strait their reconstruction proposes that on two occasions during the early holocene labrador sector ice crossed hudson strait to override parts of southeast baffin island their conclusion proposes that by 9900 bp the activity of foxe basin ice and the local ice caps had become subordinate to that of labrador ungava ice p 1015 so too had the hudson strait ice stream farther to the west if correct this reconstruction has considerable paleoclimatic and glaciological implications for the northeast laurentide ice sheet given its importance this hypothesis warrants further scrutiny especially the consideration of several alternative interpretations that arise from the data

shelf erosion and glacial ice proximity in the labrador sea during and after heinrich events h 3 or 4 to h 0 as shown by foraminifera

frictional behavior of granite at low and high sliding velocities to study how the velocity dependence of steady state friction of granite varies as a function of sliding rate we slid initially bare surfaces of westerly granite at rates of from 0 001 m s 32 mm yr to over 3 mm s accumulating 376 mm of total displacement the normal stress was 50 mpa we find that the velocity dependence measured by a b changes from negative velocity weakening at 32 m s modeling of experimental data using a simple constitutive law shows that the magnitude of a the direct dependence of friction on velocity remains nearly constant at all rates up to at least 100 m s the increase in a b with velocity is due to a reduction in the magnitude of b our results are consistent with the view that a measures the deformation rate sensitivity of the fault zone material and that b measures the amount of change of some fault zone property

comparison of uranium series radiocarbon and amino acid data from marine molluscs baffin island arctic canada uranium series and sup 14 c dates and the extent of amino acid racemization are reported for 24 marine shell samples from three areas of baffin island arctic canada when the radiometric dates are plotted against the ratio of d alloisoleucene l isoleucene in the shells five broad age groups are recognized the uranium series data indicate that sup 231 pa is incompletely retained in most fossil shells and that sup 230 th is lost from some of the samples therefore their apparent ages are minimum however a few dated samples in each group have yielded useful age results and the minimum ages of the five groups of samples are estimated as 7 000 to 11 000 greater than or equal to70 000 greater than or equal to136 000 greater than or equal to190 000 and 300 000 yr calculated integrated thermal histories based on the epimerization reaction in the mollusc hiatella arctica linne give paleotemperature estimates of around 5 sup o c compared to the present mean annual air temperature of about 11 sup o c

rapid fluctuations of the laurentide ice sheet at the mouth of hudson strait new evidence for ocean ice sheet interactions as a control on the younger dryas ice directional features and erratic lithologies of the last glaciation demonstrate that a major outlet glacier of the laurentide ice sheet flowed nne across outer hudson strait rather than se down the strait as previously hypothesized ice advanced more than 600 km from a labradorean source crossing hudson strait and outer frobisher bay and advancing onto hall peninsula the highest summits on loks land circa 400 m asl a large island at the se tip of hall peninsula were inundated by labradorean ice three distinct late wisconsin advances have been recognized the earliest most extensive advance crossed frobisher about 11 5 kyr b p and was maintained for circa 1 kyr differences in the extent of amino acid racemization in shells from interstadial and deglacial sites on eastern loks land limit the duration of the most extensive late wisconsin advance s to a brief interval of no more than 2 kyr radiocarbon dates on in situ shells and on shells incorporated in till indicate that frobisher bay was ice free from at least 10 5 to 10 2 kyr b p after which a second labradorean advance the gold cove readvance attained nearly the same extent as the earlier advance the readvance was short lived and the bay was deglaciated before 9 5 kyr b p a final readvance occurred during the cockburn substage 9 to 8 kyr b p but ice failed to cross frobisher bay the maximum extent of the labradorean advance coincides with the onset of younger dryas cooling based on a minimum cross sectional area and reasonable estimates of ice velocity the iceberg flux to the north atlantic ocean at this time was between 300 to 2400 km year 1 about the same as the freshwater influx from the diversion of lake agassiz drainage to the st lawrence the input of a significant volume of ice into the north atlantic via the labrador sea would have cooled sea surface and air temperatures increased sea surface albedo and diminished the effectiveness of wind mixing of surface waters thereby reducing the volume of water required to effectively cap the north atlantic we suggest that a combination of a massive iceberg flux and increased st lawrence discharge may have been required to initiate younger dryas cooling when the outflow of lake agassiz was again routed down the st lawrence at 9 5 kyr b p a second younger dryas event failed to occur because by that time labradorean ice had retreated within hudson strait and was unable to generate a substantial climate altering volume of icebergs the possibility of an iceberg flood in the north atlantic could be tested by measuring the concentration of ice rafted detritus ird traditionally defined as quartz feldspar grains 125 m in deep sea cores however sediment entrained by the labradorean ice is dominated by detrital carbonate and only a small fraction of the noncarbonate component is 125 m hence a revised definition of ird is required to evaluate the iceberg flood hypothesis

quaternary climates and sea levels of the u s atlantic coastal plain uranium series dating of corals from marine deposits of the u s atlantic coastal plain coupled with paleoclimatic reconstructions based on ostracode marine and pollen continent data document at least five relatively warm intervals during the last 500 000 years on the basis of multiple paleoenvironmental criteria we determined relative sea level positions during the warm intervals relative to present mean sea level were 7 5 meters at 188 000 years ago 7 5 1 5 meters at 120 000 years ago 6 5 3 5 meters at 94 000 years ago and 7 3 meters at 72 000 years ago the composite sea level chronology for the atlantic coastal plain is inconsistent with independent estimates of eustatic sea level positions during interglacial intervals of the last 200 000 years hydroisostatic adjustment from glacial interglacial sea level fluctuations lithospheric flexure and isostatic uplift from sediment unloading due to erosion provide possible mechanisms to account for the discrepancies alternatively current eustatic sea level estimates for the middle and late quaternary may require revision

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic radiocarbon dates from marine piston cores and from onshore raised marine stratigraphic sections in the hudson strait region were used to reconstruct deglacial isochrons for 9900 9500 8800 8500 and 8000 bp at the culmination of the gold cove readvance 9900 bp labrador ungava ice flowed northeastward across hudson strait and outer frobisher bay and stood for the last time on the baffin island continental shelf subsequent retreat by calving was rapid and profound opening the entire hudson strait marine trough by 9500 bp at this time ice dispersal from foxe basin labrador ungava and local ice on meta incognita peninsula supported tidewater margins along much of the coastline with the exception of northernmost ungava peninsula where the ice margin stabilized onshore this onshore margin remained in place throughout the cockburn substage while a major northeastward readvance of ungava bay ice the noble inlet readvance from 8800 to 8500 bp crossed outer hudson strait grounding on the hudson st

velocity weakening behavior of plagioclase and pyroxene gouges and stabilizing effect of small amounts of quartz under hydrothermal conditions 1 we investigated properties of frictional sliding of plagioclase pyroxene and their mixture gouges with a small amount of hornblende biotite and quartz as accessory minerals under hydrothermal conditions with an effective normal stress of 200 mpa pore pressure of 30 mpa and temperatures from 100 c to 600 c axial loading rate was stepped between 0 001 and 0 0001 mm s to acquire the rate dependence both plagioclase and pyroxene gouges showed velocity weakening behavior in the whole temperature range except the velocity strengthening behavior of pyroxene at 200 c for temperatures above 400 c both plagioclase and pyroxene gouges showed oscillatory slips as a result of small dc values of 3 4 m which make the critical stiffness rise remarkably and approach the system stiffness above 300 c the direct effect of plagioclase shows an increasing trend with temperature indicating control of the deformation process by thermally activated mechanisms as the difference of a and b values here are only 20 at most this trend also applies to the evolution effect our analytical derivation based on the theory of pressure solution shows a log linear contact area growth with time that corresponds to an evolution effect and estimations based on this encompass the plagioclase data though the identification of actual mechanisms is not easy finally it is found that a little quartz 3 5 added to the plagioclase 60 62 pyroxene 35 mixture has a strong stabilizing effect leading to a transition from velocity weakening to velocity strengthening these results may help constrain the depth range of seismic slips on deep faults in the lower crust of gabbroic composition

cryostratigraphical studies of ground ice formation and distribution in a high arctic polar desert landscape resolute bay nunavut ground ice distribution and abundance have wide ranging effects on periglacial environments and possible impacts on climate change scenarios in contrast very few studies measure ground ice in th

ice sheet dynamics and glacial history of southeasternmost baffin island and outermost hudson strait southeasternmost baffin island is mantled by hudson strait drift it contains abundant limestone erratics and 20 to 50 carbonate in the matrix to the northwest it is replaced by drift dominated by locally derived rock of the canadian shield the sense and orientation of ice erosional features demonstrate that hudson strait drift is associated with northeasterly ice flow that crossed the tip of meta incognita peninsula local drift associated with ice flow s10 w along the hudson strait coast was derived from a dispersal center on the peninsula erratic lithologies contained in the hudson strait drift indicate a labradorean provenance large scale bedrock molding and the distribution of cirques indicate ne flowing ice has been dominant throughout the middle and late quaternary radiocarbon dates of in situ shells confirm that deglaciation began more than 11 000 yr ago with the frobisher bay coast becoming ice free by 9300 yr ago five dates from hudson strait suggest that the strait was deglaciated before 9000 yr bp however ice from the labradorean sector recrossed hudson strait during the cockburn substage about 8500 yr ago damming drainage from the west final retreat of labradorean ice from baffin island was complete by 8000 yr ago at which time the sea was able to penetrate hudson bay

dynamics of isolated convective regions in the ocean abstract an initially resting ocean of stratification n is considered subject to buoyancy loss at its surface of magnitude b0 over a circular region of radius r at a latitude where the coriolis parameter is f initially the buoyancy loss gives rise to upright convection as an ensemble of plumes penetrates the stratified ocean creating a vertically mixed layer however as deepening proceeds horizontal density gradients at the edge of the forcing region support a geostrophic rim current which develops growing meanders through baroclinic instability eventually finite amplitude baroclinic eddies sweep stratified water into the convective region at the surface and transport convected water outward and away below setting up a steady state in which lateral buoyancy flux offsets buoyancy loss at the surface in this final state quasi horizontal baroclinic eddy transfer dominates upright plume convection by using parcel theory to consider the energy transformations taking place it is shown that the de

forms response times and variability of relative sea level curves glaciated north america abstract relative sea level curves from glaciated north america reveal coherent spatial patterns of response times in the laurentide ice sheet area curve half lives range from 1 2 1 4 ka at the uplift centre to 1 7 2 ka in a ridge of high values inboard of the glacial limit half lives decline from this ridge to less than 1 ka along the margin in the innuitian ice sheet area half lives are about 2 ka at the uplift centre and decline to less than 1 ka at the margin the central laurentide response times are about half those of central fennoscandia this accords with the theoretical expectation that central response times are inversely proportional to ice sheet radius for ice loads large enough that rebound at the centre is insensitive to lithospheric thickness the innuitian central response time indicates that rebound at the centre of this ice sheet which is much smaller than the fennoscandian ice sheet remains sensitive to lithospheric thickness radial gradients in response times reflect the increasing influence of the lithosphere at sites increasingly closer to the margin along this gradient rebound progresses as though at the centres of smaller and smaller ice sheets that is the effective spatial scale of the ice load decreases toward the margin near the glacial limit postglacial isostatic adjustment is complicated by forebulge migration and collapse this is seen most strongly in the relative sea level record of atlantic canada which has subsided during the holocene more than 20 m more than the adjacent american seaboard the relative sea level history of some areas notably the st lawrence estuary is complicated by tectonic processes

rate and state dependent friction of intact rock and gouge the shear traction during frictional sliding depends on the instantaneous sliding strain rate e and on a state variable which represents the previous history of the sample a formulation of rate and state friction covers the continuum between gouge and intact rock as well as the behavior at high and low normal tractions a traditional formula for the instantaneous coefficient of friction is retained 0 a in e e 0 b in 0 where 0 is the steady state coefficient of friction at the reference strain rate e 0 and a and b are small constants the normalizing 0 for isothermal conditions is p n p 0 n where ap is the effective normal traction p 0 is a reference normal traction and n is an exponent the coefficient of friction of intact rock is approximately close bn in p p close where the coefficient of friction is close at the normal traction p close where essentially all the pore space is closed during steady state sliding the formulation provides an acceptable fit to the observed coefficient of friction of westerly granite at normal tractions up to 1500 mpa including steady sliding and intact rock failure

aminostratigraphy of quaternary marine and glaciomarine sediments qivitu peninsula baffin island a complex sequence of cyclical marine and glaciomarine lithofacies exposed along the coastal lowlands of the qivitu peninsula was deposited during the marine transgressions and regressions that affected this area during repeated glaciation of the region multivariate analysis of amino acid ratios measured on shell fragments of the pelecypods hiatella arctica and myatruncata in the lithostratigraphic units provides a basis for their chronocorrelation through the use of informal regional aminostratigraphic units termed aminozones all but the oldest aminozones correspond with particular lithostratigraphic units deposited during transgressive regressive periods when relative sea level was higher than present sea level discriminant analysis shows total amino acid fraction allo iso ratios from either species are the best overall criteria for assigning a shell sample to a particular aminozone but free fraction allo iso ratios are more useful in the younger zones the distribution of ratios in lithostratigraph