the muirkirk mammoth a late pleistocene woolly mammoth mammuthus primigenius skeleton from southern ontario canada abstract the muirkirk mammoth found in 1895 2 4 km northeast of the village of muirkirk in southern ontario is the most complete woolly mammoth mammuthus primigenius skeleton known from canada approximate tusk measurements and extreme wear on the sixth molars indicate it is best referred to an old male its geological age was controversial because the first two holocene bone collagen radiocarbon dates were derived evidently from contaminated samples three new radiocarbon dates on carefully selected bone and ivory are close averaging 12 190 bp and indicate that this mammoth died before the close of the wisconsinan glaciation and near the time of extinction of woolly mammoths in this part of north america its assignment to regional pollen subzone 1b suggests that like the rostock mammoth of similar age from southern ontario it lived in a tundra woodland environment the highgate mastodon mammut americanum and giant beaver castoroides ohioensis found 4 km away and also assigned to pollen subzone 1b suggests that some spruce wetlands characterised the tundra woodland environment and that perhaps woolly mammoths and american mastodons lived almost side by side in southern ontario about12 000 radiocarbon years or 14 000 calendar years ago the muirkirk mammoth is discussed in relation to the dispersal history of woolly mammoths

geology of a vigorous hydrothermal system on the endeavour segment juan de fuca ridge a high precision high resolution geologic map explicitly documents relationships between tectonic features and large steep sided sulfide sulfate silica deposits in the vigorously venting endeavour hydrothermal field near the northern end of the juan de fuca ridge water depth in the vent field varies from 2220 to 2200 m location of the most massive sulfide structures appears to be controlled by intersections of ridge parallel normal faults and other fracture fissure sets that trend oblique to and perpendicular to the overall structural fabric of the axial valley the fractured basaltic substrate is primarily composed of well weathered pillow and lobate flows as presently mapped the field is about 200 by 400 m on a side and contains at least 15 large 1000 m3 sulfide edifices and many tens of smaller commonly inactive sulfide structures the larger sulfide structures are also the most vigorously venting features in the field they are commonly more than 30 m in diameter and up to 20 m in height actively venting sulfide structures in the northern portion of the field stand higher and are more massive than active structures in the southern portion of the field which tend to be slightly to distinctly smaller maximum venting temperatures of 375 c are associated with the smaller structures in the southeastern portion of the field highest temperature venting fluids from the more massive structures in the northern portion of the field are consistently 20 30 c lower hydrothermal output from individual active sulfide features varies from no flow in the lower third of the edifice to vigorous output from fracture controlled black smoker activity near the top of the structures a different type of high temperature venting takes place from the upper sides of the structures in the form of overflow from fully exposed quiescent pools of buoyant 350 c vent water trapped beneath overhanging sulfide sulfate silica ledges or flanges these flanges are attached to the upper outer walls of the large sulfide edifices two types of diffuse venting in the endeavour field include a lower temperature 8 15 c output through colonies of large tubeworms and 25 50 c vent fluid that seems to percolate through the tops of overhanging flanges the large size and steep walled nature of the these structures evidently results from sustained venting in a mature hydrothermal system coupled with dual mineral depositional mechanisms involving vertical growth by accumulation of chimney sulfide debris and lateral growth by means of flange development

microearthquake characteristics and crustal vp vs structure at the mid atlantic ridge 35 n we report on the results of a microearthquake experiment conducted at the along axis bathymetric high of the slow spreading ridge segment near 35 n on the mid atlantic ridge mar of a total of 255 microearthquakes recorded during the 43 day experiment 31 were located near the oceanographer transform at the northern end of the segment 79 occurred at the nontransform offset at the southern end of the segment and 145 were at the segment center at the segment center earthquake epicenters lay within the median valley inner floor and formed a 12 km long trend paralleling a steep scarp bounding the western wall of the inner valley focal depths were 3 4 km below the seafloor most 80 of the focal mechanisms for 32 segment center earthquakes are consistent with normal faulting on faults approximately parallel to the axial trend from a joint inversion for hypocenters and p and s wave velocity structures we determined a horizontally averaged v p v s ratio that decreases from 2 9 in the shallowmost 300 m to 1 7 at 2 km depth and we interpret this decrease as indicating a decreasing contribution of thin cracks to fracture porosity with depth the maximum depth of seismicity 4 km is anomalously shallow compared with other mar segments at which microearthquake experiments have been carried out cross axis relief is also anomalously low for this segment s center and on the basis of this and other mar microearthquake experiments there appears to be a correlation between cross axis relief and maximum depth of seismicity from the correlation of cross axis relief and inferred crustal thickness we suggest a relationship between thick crust high crustal temperatures and low cross axis relief in qualitative agreement with thermomechanical models for the depth of the axial valley

paleoclimatic implications of a late wisconsinan insect assemblage from rostock southwestern ontario the rostock site is situated in a peat covered wetland where fragments of a mammoth mammuthus primigenius were unearthed in 1982 excavation showed a descending sequence of peat silty marl gravel clayey silt and till approximately 300 kg of sediment was taken from the section for pollen invertebrate and geochemical analyses the peat marl transition is believed to be approximately contemporaneous with the spruce pine transition in southern ontario ca 10 600 years bp a date of 10 790 150 years bp on collagen from mammoth tusk fragments recovered from the same level substantiates this inference insects especially coleoptera were common throughout the marl and represent at least 2000 individuals from 16 different families on the basis of beetle ecologies and modern distributions the marl was subdivided into lower and upper horizons the lower horizon contains many species that are today restricted to western and northern north america they are typical residents of the northern boreal fore

sub bottom temperature anomalies detected by long term temperature monitoring at the tag hydrothermal mound during aug 1994 feb 1995 geothermal measurements were carried out on the tag hydrothermal mound 26 0 n 44 49 w of mid atlantic ridge two geothermal probes made reliable measurements six transient anomalies in subbottom temperatures were detected 20 m south of the central black smoker complex cbc having durations 40 to 400 hours and magnitude 0 2 c to 30 c these anomalies are probably evidence for short period fluctuations in the fluid circulation beneath the mound the time variability in subbottom temperatures near cbc suggests that instantaneous heat flow measurements may not represent the time average of heat flow there although it is difficult to specify the origin of thermal anomalies during the drilling period by the ocean drilling program at least one of them seems to correlate with the drilling events because it was also accompanied by transient temperature anomalies at cbc and 50 m east of cbc observed by other instruments

tidal current effects on temperature in diffuse hydrothermal flow guaymas basin a twelve day record of temperature collected from the diffuse flow area of a guaymas basin hydrothermal site exhibits variations from a minimum of 3 05 c to a maximum of 4 87 c whose periodicity is correlated with tides measured at the nearby town of guaymas a simple model based on the hypothesis that temperature variations result as changes in tidal bottom currents induce changes in the height of the thermal boundary layer is in good quantitative agreement with observed temperatures for most of the record the success of this model illustrates that the effects of tidal currents can be strong enough to dominate the time variability of a temperature signal at a fixed point in hydrothermal flow therefore tidal currents must be taken into account when using temperature measurements to estimate time varying heat fluxes from hydrothermal diffuse flow regions

current perspectives on the pleistocene archaeology of eastern beringia abstract most recent summaries of eastern beringian alaska and yukon archaeology present the nenana complex beginning 11 500 12 000 14c yr b p as the beginning of the regional archaeological record either explicitly or tacitly these summaries dismiss or ignore a body of older putative evidence of human occupation that may span the late wisconsin stade and even extend into part of the mid wisconsin interstade this paper summarizes the interpretive problems surrounding the older findings bringing together data that have accumulated over a period of two decades in the hope that a coherent presentation will encourage more careful appraisals of the materials the paper concludes with a family of testable hypotheses concerning the beginnings of human occupation in eastern beringia the hypothesis that people were present during the mid wisconsin interstade has not yet been falsified

a comparative study of woolly mammoths from the gravettian site krakow spadzista poland based on estimated shoulder heights demography and life conditions this article interprets the life conditions of woolly mammoths mammuthus primigenius from the upper paleolithic archaeological site krakow spadzista in poland we propose that the mammoths irregular mortality profile also known as age profile was shaped over several decades by major death events which serially depleted the youngest cohorts taphonomic data and comparisons with other eurasian archaeological and nonarchaeological sites provide context for hypothesizing that the mammoth bone assemblage was accumulated at least partly through opportunistic human hunting of the most vulnerable animals in mixed herds humans exploited heightened mammoth vulnerability during climatic stress periods killing and butchering most of the animals although some mammoths in the assemblage may have died from natural causes the evidence for environmental stress affecting the mammoths includes paleoecological data about local climatic conditions the abundant signs of mammoth bone abnormalities in the assemblage the relatively smaller size of adult female mammoths compared with those from the similarly dated archaeological site milovice i czech republic and the unusually high proportion of juvenile mammoths in the assemblage

tide related variability of tag hydrothermal activity observed by deep sea monitoring system and obsh abstract hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone obsh and a composite measuring system manatee including ctd current meter transmission meter and cameras at a small depression on the tag hydrothermal mound in the mid atlantic ridge low frequency pressure pulses detected by the hydrophone with semi diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short lived smoker vent close to the observing site the peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting temporal variations in bottom water temperature also have semi diurnal periodicity but are more complicated than the pressure events temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide

observation of pressure change associated with hydrothermal upwelling at a seamount in the south mariana trough using an ocean bottom seismometer an obsh ocean bottom seismometer with hydrophone was deployed just 1 m from a hot thermal vent on the summit region of a seamount located 18 km east of the south mariana trough axis to record continuous data on hydrothermal activity although the seismicity beneath the seamount was very weak numerous pulse shape pressure events showing sudden pressure decrease were observed on the hydrophone channel the characteristic period of the pressure events varied from 20 seconds to 1 minute after the submersible shinkai 6500 relocated the obsh 10 m south of the vent where no thermal vents existed the number and amplitude of pressure events drastically decreased this suggests that pressure events were generated by the hot water upwelling from the thermal vent the pressure events appear to be related to the ocean tide this experiment indicates that observations using obshs are an effective means of monitoring hydrothermal activity

seismic constraints on shallow crustal emplacement processes at the fast spreading east pacific rise we present the results of nine on bottom seismic refraction experiments carried out over young east pacific rise crust the experiments are unusual in that both the source and receiver are located within a few meters of the seafloor allowing high resolution determinations of shallow crustal structure three experiments were located within the axial summit caldera asc over zero age crust the seismic structure at these three locations is fundamentally the same with a thin 60 m surficial low velocity 2 5 km s layer a 100 to 150 m thick transition zone with velocities increasing by 2 5 km s and a layer with velocities of 5 km s at a depth beneath the seafloor of 130 190 m the surficial low velocity layer and transition zone are defined as seismic layer 2a and the 5 km s layer is defined as the top of layer 2b both the surficial low velocity layer and the transition zone double in thickness within 1 km of the rise axis we model layer 2a as the extrusive sequence and transition zone and the 2a 2b boundary as the top of the sheeted dikes the primary implication of this interpretation is that the depth to the top of the sheeted dikes deepens from 150 m to 300 m within 1 km of the asc the thickening of the extrusive layer is interpreted to be due to lava that either overflows the asc walls is emplaced through eruptions outside of the asc or travels laterally from the asc through conduits the most probable cause for the thickening of the transition zone is sill emplacement outside of the asc either from magma that does not reach the surface in an off axis eruption or magma that is transported laterally during the drainage process creating the asc we suggest that the mechanism controlling the magnitude and rate of the dike subsidence is the mechanism that determines the thickness of the extrusive section and the total thickness of layer 2a

pulse of the seafloor tidal triggering of microearthquakes at 9 50 n east pacific rise 1 unequivocal evidence of tidal triggering is observed for microearthquakes 0 4 to 2 0 ml recorded between october 2003 to april 2004 near 9 50 n on the east pacific rise epr although semidiurnal tidal stress changes are small 99 9 nonrandom temporal distribution with events occurring preferentially near times of peak extension due to the proximity of this site to an ocean tidal node where changes in sea surface height are minimal periodic stress changes are dominated by the solid earth tide in contrast previous studies on the juan de fuca ridge have shown microearthquake triggering to be a response to seafloor unloading during times of low ocean tide the modulation of 9 50 n microearthquakes by small amplitude periodic stresses is consistent with earthquake nucleation within a high stressing rate environment that is maintained near a critical state of failure by on axis magmatic and hydrothermal processes

a poroelastic model for the tidal modulation of seafloor hydrothermal systems 1 time series measurements of the temperature and exit velocity of hydrothermal effluent suggest that seafloor hydrothermal systems are modulated by tidal processes here we apply the theory of poroelasticity to predict the magnitude and phase of tidally induced changes in the temperature and flow rate of hydrothermal effluent at the seafloor we construct a model in which the steady state upwelling of buoyant fluid in the crust is modulated by tidal loading of a one dimensional seafloor by the overlying water column the nature of the solution is controlled by the relative magnitudes of three length scales these are 1 the depth h of the heat source below the seafloor 2 the skin depth d over which pore pressure signals can diffuse during one tidal cycle and 3 the advective length scale a over which the upwelling flow advects thermal signals during one tidal cycle we consider the likely magnitude of the parameters in a real system as well as the limitations of a one dimensional representation of that system we then discuss how observational data on the magnitude and phase lag of temperature and flow rate could be used to constrain the subseafloor parameters that govern hydrothermal circulation within the seafloor

pleistocene mammals of the edmonton area alberta part i the carnivores late pleistocene fossils have been recovered sporadically in the edmonton area in central alberta for many years but there has been little work in determining their age fossils from quarries in north saskatchewan river terraces and buried valley gravels are recognized as late pleistocene mid wisconsinan and early holocene taxa and numerous 14c dates on mammalian remains now support the assessment the mammalian fauna consists of at least 16 taxa including mostly grazing herbivores but also three carnivores canis cf canis lupus gray wolf arctodus simus giant short faced bear and panthera leo atrox pleistocene lion the carnivores are first records for the region and arctodus is a first record for alberta

temperature variations at diffuse and focused flow hydrothermal vent sites along the northern east pacific rise in the decade following documented volcanic activity on the east pacific rise near 9 50 n we monitored hydrothermal vent fluid temperature variations in conjunction with approximately yearly vent fluid sampling to better understand the processes and physical conditions that govern the evolution of seafloor hydrothermal systems the temperature of both diffuse flow low temperature and focused flow high temperature vent fluids decreased significantly within several years of eruptions in 1991 and 1992 after mid 1994 focused flow vents generally exhibited periods of relatively stable slowly varying temperatures with occasional high and low temperature excursions lasting days to weeks one such positive temperature excursion was associated with a crustal cracking event another with both positive and negative excursions demonstrated a subsurface connection between adjacent focused flow and diffuse flow vents diffuse flow vents exhibit much greater temperature variability than adjacent higher temperature vents on timescales of a week or less temperatures at a given position within a diffuse flow field often varied by 5 10 c synchronous with near bottom currents dominated by tidal and inertial forcing on timescales of a week and longer diffuse flow temperatures varied slowly and incoherently among different vent fields at diffuse flow vent sites the conceptual model of a thermal boundary layer immediately above the seafloor explains many of the temporal and spatial temperature variations observed within a single vent field the thermal boundary layer is a lens of warm water injected from beneath the seafloor that is mixed and distended by lateral near bottom currents the volume of the boundary layer is delineated by the position of mature communities of sessile e g tubeworms and relatively slow moving organisms e g mussels vertical flow rates of hydrothermal fluids exiting the seafloor at diffuse vents are less than lateral flow rates of near bottom currents 5 10 cm s the presence of a subsurface shallow reservoir of warm hydrothermal fluids can explain differing temperature behaviors of adjacent diffuse flow and focused flow vents at 9 50 n different average temperatures and daily temperature ranges are explained by variable amounts of mixing of hydrothermal fluids with ambient seawater through subsurface conduits that have varying lateral permeability

modulus decomposition of compressional and shear velocities in sand bodies the advent of borehole shear slowness measurements in sonically slow formations has lead to breakthroughs in the subsurface profiling of geological bodies in sand bodies compressional and shear velocities depend predictably on porosity mineralogy grain contacts and fluid saturation an interpretation is best performed by decomposing the velocities into moduli that are intrinsic measures of the rock frame and pore fluid compressibilities careful experiments on pure materials i e pure quartz sandstones demonstrate two simplifying constitutive relationships first the bulk and shear frame moduli are simple functions of the porosity a comparison of the measured shear frame modulus to the prediction for the pure material distinguishes sand from shale second the ratio of the bulk and shear frame moduli is a constant 0 9 independent of the porosity the measured velocities are directly inverted to yield the bulk modulus of the pore fluid the fluid saturation effects are so dramatic at high porosit

systematic along axis tidal triggering of microearthquakes observed at 9 50 n east pacific rise 1 hydrothermal fluid circulation at mid ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid earth and supports chemosynthetic microbial and macro faunal communities the structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems however direct measurements of subsurface processes remain technologically challenging to obtain previous studies have shown that tidally induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times in this study we observe systematic along axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9 50 n east pacific rise we interpret this systematic triggering to result from pore pressure perturbations propagating laterally through the hydrothermal system based on our observations and a one dimensional pore pressure perturbation model we estimate bulk permeability at 10 13 to 10 12 m2 within layer 2b over a calculated diffusive lengthscale of 2 0 km

proboscideans and paleoenvironments of the pleistocene great lakes landscape vegetation and stable isotopes abstract in this study we review the history of proboscideans in the great lakes region ontario and western new york in the context of local glacial and vegetational histories further we investigate mammoth mammuthus and mastodon mammut environmental niche partitioning using stable isotope analysis of bone and dentin collagen 13 c col 15 n col and structural carbonate in tooth enamel bioapatite 13 c sc 18 o sc and demonstrate that stable isotopes can be used to identify non locals among museum specimens with no contextual records new radiocarbon dates suggest that ontario mastodons lived in tundra like environments as well as their more common spruce forest habitat local ontario new york mammoths and mastodons consumed 100 c 3 plant diets and drank low 18 o waters consistent with colder than modern climates and proximity to glacial meltwater sources mammoths and mastodons occupied distinct environmental niches characterized by different oxygen and nitrogen isotope compositions and geographical locations this suggests that direct competition for resources was not a major factor in their local extinction we suggest that both mammoths and mastodons obtained water from sources formed primarily from precipitation rather than glacial meltwater we describe how high 15 n values in mammoths could have been caused by a combination of preferences for dry environments consumption of low nutrient forage particularly stems and stalks coprophagy geophagy and dung fertilization we argue that low 15 n values in mastodons could have been caused by consumption of trees and shrubs including nitrogen fixing taxa and a preference for recently deglaciated landscapes and or spruce environments finally we raise the possibility that mastodons contributed to the spruce pine transition by browsing directly on spruce trees

u pb shrimp and 40 ar 39 ar ages constrain the deformation history of the karakoram fault zone kfz sw tibet abstract the 800 km long dextral karakoram fault zone kfz bounds sw tibet and despite a number of recent studies its spatial and temporal evolution and consequent role in continental deformation remains under debate in order to better constrain fault evolution we present u pb sensitive high resolution ion microprobe shrimp and 40ar 39ar analyses of granitic samples from the southern portion of the karakoram fault zircons from the ductile shear zone in the namru region of the ayilari granite batholith record a crystallization age compatible with gangdese magmatism belt also known as the trans himalayan magmatic belt thb followed by a medium temperature cooling event between about 12 8 11 5 ma and zircons from the ductile shear zone in the zhaxigang region of the ayilari granite batholith record a crystallization age of 18 7 ma the ayilari granite batholith near namru appears to have experienced neither the 32 ma nor 25 22 ma magmatic events reported by previous studies biotite 40ar 39ar ages provide evidence that the 12 8 11 5 ma cooling event coincides with the initiation of the kfz cutting through the ayilari granite both at namru and zhaxigang consequently we conclude that the previously reported 32 ma 25 22 ma and 22 14 ma events bear no relationship to the activity along the karakoram fault but resulted from either local metamorphic events caused by regional tectonics such as activity on the south kailas thrust fault or from magmatism around shiquanhe also known as gar this study supports the conclusion that the kfz at least in the zhaxigang namru region propagated along strike to the gar menshi area as a thin skinned structure at around 13 ma

distribution of magma beneath the east pacific rise between the clipperton transform and the 9 17 n deval from forward modeling of common depth point data we have reprocessed seven cross axis common depth point cdp profiles between the clipperton transform and the 9 17 n deval deviation in axial linearity on the east pacific rise epr to understand the relationship between axial magma chamber amc width and seafloor morphology forward modeling of cross axis cdp profiles suggests a segmented amc in which significant variations in width occur across minor rise axis discontinuities e g devals the modeled rise segment widths bounded by the 9 53 n 9 35 n devals the 9 35 n 9 17 n devals and south of the 9 17 n deval were 0 7 km 1 0 1 2 km and 4 15 km respectively transition in amc width across these discontinuities is unclear due to the sparseness of cross axis line spacing however a simple association of devals with decreased magma supply is doubtful the minimum 250 m and maximum 4150 m amc widths are found near the 9 35 n and 9 17 n devals respectively the reprocessing of cdp profiles included repicking stacking velocities to ensure a proper stack of the amc reflector and its associated diffractions imaging postcritical reflections from the base of layer 2a finite difference time migration ray theoretical depth migration and travel time modeling of amc diffraction patterns constraints on amc width were derived from forward modeling techniques based on analytic raytracing velocity models were constructed from seabeam bathymetry and modified expanding spread profile esp velocity depth functions esp velocity models were altered to compensate for off axis thickening of layer 2a as imaged in the cdp reflection data continuous two dimensional velocity models constructed from modified esp velocity depth functions and seabeam bathymetry should account for ray bending at the seafloor basalt interface and any lateral velocity gradients induced by a thickening layer 2a stacked data were time migrated using a finite difference algorithm and extrapolated to depth using ray theoretical depth migration reflector positions were input into our forward modeling scheme to produce a zero offset travel time response of our migrated solution the travel time response was then overlain on the stacked section to ensure an adequate match especially to diffractions generated at the amc edge forward modeling of amc diffraction patterns reveals that original amc width estimates were too large the under migration of the amc reflector resulted from the conversion of stacking to interval velocities without accounting for topographic effects on individual cmp gathers thus resulting in improperly collapsed diffraction hyperbolae ship wandering relative to the amc edge can account for variations in amc reflector amplitude and dropout on the along axis cdp line the continuity of the amc appears unbroken across several ridge axis discontinuities between the clipperton transform and the 9 17 n deval which suggests an amc whose along axis dimension exceeds 75 km reflectivity modeling of cmp gathers suggests that the available data are consistent with a magma chamber comprising only a thin layer of melt overlying a zone of partially solidified crystal mush such a thin layer of melt might inhibit along axis mixing of magmas and thereby account for variations in magma composition along the rise crest this melt lens model for the amc would also produce strong diffraction patterns as imaged in the cdp data

statistical analysis of the el nino southern oscillation and sea floor seismicity in the eastern tropical pacific we present statistical evidence for a temporal link between variations in the el nino southern oscillation enso and the occurrence of earthquakes on the east pacific rise epr we adopt a zero inflated poisson regression model to represent the relationship between the number of earthquakes in the easter microplate on the epr and enso expressed using the southern oscillation index soi for east pacific sea level pressure anomalies from february 1973 to february 2009 we also examine the relationship between the numbers of earthquakes and sea levels as retrieved by topex poseidon from october 1992 to july 2002 we observe a significant 95 confidence level positive influence of soi on seismicity positive soi values trigger more earthquakes over the following 2 to 6 months than negative soi values there is a significant negative influence of absolute sea levels on seismicity at 6 months lag we propose that increased seismicity is associated with enso driven sea surface gradients rising from east to west in the equatorial pacific leading to a reduction in ocean bottom pressure over the epr by a few kilopascal this relationship is opposite to reservoir triggered seismicity and suggests that epr fault activity may be triggered by plate flexure associated with the reduced pressure

a preliminary tidal analysis of topex poseidon altimetry approximately 12 months of data from the topex poseidon satellite altimeter mission are analyzed for the major short period oceanic tides a harmonic analysis is performed on data captured within bins defined on a deep ocean grid which owing to tidal aliasing considerations must have a relatively coarse spatial resolution our analysis is in terms of corrections to the schwiderski and cartwright ray models and it confirms many of the schwiderski differences previously reported by cartwright and ray our differences with respect to the geosat based cartwright and ray model form a sectorial pattern in m2 with high low differences separated roughly 180 in longitude we suggest that these sectorial errors were most likely induced by geosat s relatively large orbit error comparisons to independent data validate the improved topex poseidon solutions in situ ground truth shows m2 rms differences of 4 10cm schwiderski 3 86cm cartwright and ray 2 63cm this paper global rates of energy dissipation confirm earlier estimates for m2 and show improved agreement with satellite tracking studies for k1 and s2 these preliminary exercises confirm that topex poseidon should result in a new generation of improved global tidal models

limits of tidal energy dissipation by fluid flow in subsea formations summary tidal loading causes fluid flow through permeable seafloor and between regions of contrasting elastic properties or porosity within subsea formations we examine theoretically the dissipation of energy by these flows and its global significance as a mechanism for tidal energy dissipation expressions are given for energy dissipation rates in layered formations due to vertical flow caused by tidal loading but the results can be used to constrain dissipation by other flow patterns we consider flow near the seafloor in gas bearing sediments and in highly fractured permeable igneous crust energy dissipation by the first two mechanisms is negligibly small globally although it may be locally significant under extreme conditions under favourable conditions flow in fractured crust may have greater energy dissipation but the total amount is limited by the thickness of the permeable layer based on our current understanding of subsea hydrogeology tidally induced flow in subsea formations appears to make little contribution to the observed global tidal energy dissipation

influence of fortnightly tides on earthquake triggering at the east pacific rise at 9 50 n the study of tidal forcing provides an opportunity to view the response of the solid earth to known changes in stress earthquakes triggered by diurnal and semidiurnal tidal forces have been well documented for the deep ocean and some terrestrial environments however few studies examine the influence of fortnightly tides on earthquake triggering and only in terrestrial environments we assess triggering of microearthquakes related to true fortnightly tides and fortnightly tidal modulations along the east pacific rise at 9 50 n where strong diurnal and semidiurnal triggering of earthquakes has been observed an ocean bottom seismograph experiment collected microearthquake data between october 2003 and january 2007 a time period that included a well documented submarine eruption culminating in january 2006 we examine how triggering changed through the build up to and aftermath of this seafloor spreading event results show that earthquakes occur preferentially during times of increasing peak volumetric stress leading up to the eruption with strong statistical significance schuster test p values up to 2 22e 31 however the correlation loses its strength immediately prior to and during the eruptive period p value as high as 0 2837 when competing tectonic and magmatic stresses may occur post eruption triggering reappears p value 1 45e 26 but with opposite phase statistical significance is also explored using monte carlo method highlighting limitations of swarm dominated time series for the schuster test nevertheless the observations are consistent with a shift in the dominating stress triggering the earthquakes from extensional tectonics to magmatic processes followed by a post eruption period of cooling relaxation and possibly magma chamber refilling

tidally driven effluent detected by long term temperature monitoring at the tag hydrothermal mound mid atlantic ridge abstract during aug 13 21 1994 temperatures and current velocity were simultaneously monitored on the tag hydrothermal mound three giant kelps gks vertical thermistor arrays of 50 m height were moored on the periphery of the central black smoker complex cbc a manatee multi monitoring system including current velocity was deployed 50 m east of cbc four daibutsu geothermal probes penetrated the sediment south to west of cbc compilation of all data revealed semi diurnal variations in water temperatures and current velocity and allowed us to discuss the source of these anomalies temperature anomalies of gks correlate well with current velocity and are interpreted to be caused by the main plume from cbc that was bent over by the tidal current we identified two types of asymmetric periodic temperature variations at daibutsu probes 2 and 8 located 20 m to the south of cbc by comparing temperatures and current velocity they are attributed to non buoyant effluents laterally advected by the tidal current the source of one variation is located east to ese of the probes and the source of the other is located to the north on aug 31 a new periodic anomaly emerged on probe 2 with its amplitude up to 0 8 c the 6 h offset between the new anomaly and the previous one suggests that the source of the new anomaly lies to the west of probe 2 the heat flux of these non buoyant effluents is estimated to range from 30 to 100 kw m 2 which is of the same order as direct estimates of diffuse flow at the tag mound it suggests that a significant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor

the trans atlantic geotraverse hydrothermal field a hydrothermal system on an active detachment fault abstract over the last ten years geophysical studies have revealed that the trans atlantic geotraverse tag hydrothermal field 26 08 n on the mid atlantic ridge is located on the hanging wall of an active detachment fault this is particularly important in light of the recognition that detachment faulting accounts for crustal accretion extension along a significant portion of the mid atlantic ridge and that the majority of confirmed vent sites on this slow spreading ridge are hosted on detachment faults the tag hydrothermal field is one of the largest sites of high temperature hydrothermal activity and mineralization found to date on the seafloor and is comprised of active and relict deposits in different stages of evolution the episodic nature of hydrothermal activity over the last 140 ka provides strong evidence that the complex shape and geological structure of the active detachment fault system exerts first order but poorly understood influences on the hydrothermal circulation patterns fluid chemistry and mineral deposition while hydrothermal circulation extracts heat from a deep source region the location of the source region at tag is unknown hydrothermal upflow is likely focused along the relatively permeable detachment fault interface at depth and then the high temperature fluids leave the low angle portion of the detachment fault and rise vertically through the highly fissured hanging wall to the seafloor the presence of abundant anhydrite in the cone on the summit of the tag active mound and in veins in the crust beneath provides evidence for a fluid circulation system that entrains significant amounts of seawater into the shallow parts of the mound and stockwork given the importance of detachment faulting for crustal extension at slow spreading ridges the fundamental question that still needs to be addressed is how do detachment fault systems and the structure at depth associated with these systems e g presence of plutons and or high permeability zones influence the pattern of hydrothermal circulation mineral deposition and fluid chemistry both in space and time within slowly accreted ocean crust

vertebrate paleontology and the alleged ice free corridor the meat of the matter abstract the existence of a full glacial ice free corridor through western alberta has been argued for many years it has been assumed to have existed notwithstanding a near total lack of evidence by many in the north american archeological community as a means of explaining the occurrence of early man south of the ice in early postglacial time in the last 15 years much has been done to fill the knowledge gap including theories on alternate routes but there is still no consensus quaternary vertebrate fossils from alberta accompanied by numerous radiocarbon dates with a clear gap between 21 ka bp and at least 11 6 ka bp now suggest that alberta was overridden by ice during an extensive late wisconsinan glaciation therefore a full glacial ice free corridor could not have existed however much of the province could have served as a migration route northward and southward both before and after late wisconsinan glaciation the preglacial passage could not have been a corridor because numerous megafaunal remains and conifer wood from numerous localities with finite dates from ca 43 ka to 21 ka bp indicate extensive ice free conditions similarly a late pleistocene corridor critically appraised from the standpoints of vertebrate paleontology and archeology is irrelevant because by the time human migrants arrived in southern alberta less than 11 ka bp the ice had been in retreat for well over 1000 years relative to human influx the continuing use of the term corridor with its connotation of a narrow or restricted passage seems inappropriate

temporal variations in diffuse hydrothermal flow at tag we have obtained direct measurements of diffuse hydrothermal effluent temperature velocity and chemistry from the tag hydrothermal mound 26 08 n 44 49 w mid atlantic ridge we report on the time series physical measurements obtained from a location on the eastern flank of the main summit complex several features were observed including strong tidal variability in flow a conspicuous elevation of effluent temperatures during the period 11 october 17 october 1994 and a long term increase in temperature superimposed upon all other trends the six day long temperature excursion is coincident with increases in sediment and effluent temperatures observed by instruments left in place on the tag mound by other workers we have established through time lapse seafloor video observations and through drilling records that the mid october effluent temperature excursion is correlated closely with local drilling activity by the ocean drilling program

near field variability of the tag non buoyant plume 26 n mid atlantic ridge we report the initial results of a nine hour monitoring of the non buoyant plume above the tag hydrothermal vent field at 26 n on the mid atlantic ridge a ctd conductivity temperature and pressure and nephelometer particle sensor were continuously raised and lowered through the non buoyant plume for nine hours at a site situated 100 m south of the hydrothermal mound this method permits a detailed record of the variability of the non buoyant plume close to the vent field to be made our results show that the particulate maximum of the non buoyant plume appears 150 m lower in the water column at the start and end of the record compared with profiles recorded towards the middle of the record a corresponding structure also appears in the temperature and salinity records with the result that the plume particle maximum resides on the 27 8035 isopycnal throughout modelling of the rise height of an axisymmetric plume can only account for 95 m of the variability in the final level of neutral buoyancy plume bending due to currents is a likely explanation for the recorded temporal variability

poisson s ratio structure of young oceanic crust we have applied full waveform inversion to wide aperture seismic reflection data from the southern east pacific rise near 14 s the data contain clear compressional wave and doubly converted shear wave arrivals that provide good constraints on the p and s wave velocities vp vs and hence poisson s ratio and seismic attenuation qp qs structure of seismic layer 2 layer 2a is highly attenuating qp 18 30 and qs 8 15 and layer 2b is moderately attenuating qp 30 50 and qs 20 25 our results show high at the seafloor and in layer 2a 0 48 across the top of the 2a b transition the rapid increase in vp is accompanied by a sharp drop in to 0 25 within just 200 m of the seafloor we perform simple calculations to gain an insight into the porosity and crack distribution with depth these calculations suggest that porosity is in excess of 30 in layer 2a but reduces to 6 7 at the top of the 2a b transition and to about 5 at a depth of 600 m below seafloor within layer 2b our results suggest that there is an increase in the average aspect ratio with depth across the 2a b transition the most likely explanation is that numerous thin cracks either mechanically close or are infilled at depth our results show there to be an abrupt change in the pore structure across the 2a b transition which is consistent with a lithologic transition from extrusives to dykes but is equally consistent with a transition mechanical or hydrothermal within the extrusive pile

taphonomy of two last glacial maximum mammoth sites in the central great plains of north america a preliminary report on la sena and lovewell abstract two mammoth sites from the central great plains of north america each containing one adult columbian mammoth mammuthus columbi were excavated from last glacial maximum lgm loess and fine grained alluvial deposits respectively taphonomic data from both sites indicate that the mammoth skeletons exhibit numerous spirally fractured limb elements dynamic loading points are present on midshafts of large limb bones bone flakes produced from the partial thickness of thick cortical bone are also present hypotheses of carnivore activity mammoth trampling and human induced fracturing are evaluated as possible causes of the fractured limb bone testing the hypotheses using modern data from actualistic taphonomic studies of elephant skeletons paleontological data from two proboscidean natural death sites experimental data from elephant bone fracturing and archaeologically derived data concerning late pleistocene human modification of mammoth limb bone indicates that the first two hypotheses can be rejected while the third hypothesis is supported

along the ice margin the cultural taphonomy of late pleistocene mammoth in southeastern wisconsin usa abstract four localities fenske mud lake schaefer and hebior in southeastern wisconsin have been put forth as probable sites associated with early peoples based on purported cultural marks on bones and lithic artifacts only two of the localities schaefer and hebior have associated lithics radiocarbon dates provide a time period of ca 13 530 11 200 yr bp results of the taphonomic analysis regarding natural modifications are reported elsewhere and the potential cultural modification category was examined further using established criteria as well as additional features two mark types are identified as caused by human agency foot elements are most affected by marks followed by long bones the marks indicate two major activities occurring that of cutting actions in defleshing and prying or leverage actions in disarticulation the mud lake and fenske mammoth are found carcasses already stiffened when scavenged by people schaefer most likely represents a hunted animal while hebior being a hunted or found fresh carcasses could not be determined the resource procurement strategy whether the carcass is fresh or stiffened appears to be the same easily accessible legs and feet form the focal point and provide a sizeable amount of protein from muscle bundles and fat from foot pads based on the wisconsin localities both hunting and scavenging of mammoth by early peoples have a time depth in the late pleistocene beyond the clovis age

a mammoth mammuthus primigenius tooth from late wisconsin deposits near embden north dakota and comments on the distribution of woolly mammoths south of the wisconsin ice sheets a well preserved third molar of a woolly mammoth mammuthus primigenius was recovered from sand and gravel forming the highest herman prominent strandline of lake agassiz near embden in western cass county north dakota the herman strandline is estimated to have formed about 11 500 years bp and presumably the tooth is of similar age perhaps the animal lived in a tundra like area near the lake agassiz shoreline additional evidence suggests that woolly mammoths occupied a tundra like range south of the wisconsin ice sheets extending from southern british columbia to the atlantic continental shelf off virginia

tidal pumping of fluids within and from the oceanic crust new observations and opportunities for sampling the crustal hydrosphere abstract seven boreholes established by the ocean drilling program in sedimented ridge crest and ridge flank environments have been sealed to stop the exchange of formation water and seawater via the holes after drilling and instrumented to allow long term hydrologic monitoring records of seafloor and basement fluid pressures in these holes document tidal frequency formation pressure variations that are attenuated and phase shifted relative to variations at the seafloor spatial variations in the response to seafloor tidal loading create oscillatory pressure gradients which drive fluid flow within the crust and tidal pressure differentials between the crust and the water column modulate flow through the seafloor both may have significant geochemical and biological consequences the magnitude of the tidal pressure differential observed across sediment sections is in many instances larger than the average differential pressure created by hydrothermal buoyancy forces and this causes the pressure difference across fluid sampling ports incorporated in the borehole seals to reverse sign periodically this can create a problem for obtaining undiluted crustal fluid samples at the seafloor from moderately overpressured holes but it also provides an opportunity for fluids to be pumped passively from moderately underpressured holes through the use of uni directional valves potential production rates estimated using pre and post seal thermal fluid flow and pressure data indicate that significant fluid fluxes can be established of the order of 10 m 3 typically one hole volume per month

time series measurements of hydrothermal activity on northern juan de fuca ridge during august september 1984 the submersible alvin visited a large active hydrothermal system on the juan de fuca ridge a time lapse camera taking photographs every 42 minutes for six days was deployed at an active vent to characterize the dynamic nature of this system this report documents the growth rate of a low temperature measured at 56 c hydrothermal deposit and establishes that this growth is not constant periods of substantial erosion are superimposed upon the general growth pattern quantitative photographic interpretation of the suspended particulate load suggests a strong diurnal component to these fluctuations water flow manifest by the movement of attached worm tubes also shows strong variations but on a semi diurnal basis correlated to tidal motions