glaciations of the west coast range tasmania geomorphic stratigraphic palynologic and 14c evidence indicates that the west coast range tasmania was glaciated at least three times during the late cenozoic the last or margaret glaciation commenced after 30 000 yr b p culminated about 19 000 yr b p and ended by 10 000 yr b p during this period a small ice cap ca 250 m thick and cirque and valley glaciers covered 108 km2 the glacial deposits show little chemical weathering or erosional dissection the snow line ranged from 690 to 1000 m with an average of 830 m for the ice cap mean temperature was 6 5 c below the present temperature during the preceding henty glaciation a 300 to 400 m thick ice cap and outlet glaciers exceeded 1000 km2 the glacial deposits are beyond 14c assay they are more weathered chemically and more dissected than margaret age deposits and the degree suggests a pre last interglaciation age 130 000 yr b p the snow line of the ice cap lay at 740 m and annual temperature was reduced by 7 c ice of the earliest linda glaciation slightly exceeded that of the henty glaciation but had a similar distribution the glacial deposits are intensely weathered have reversed magnetization and overlie a paleosol containing pollen of tertiary type an early pleistocene or tertiary age is indicated

late pleistocene glaciation of the kosciuszko massif snowy mountains australia abstract late pleistocene glaciation of the australian mainland was restricted to a small area of the southeastern highlands geomorphic mapping of the area and exposure dating using the in situ produced cosmogenic isotope 10be provides evidence for at least two distinct glaciations the early kosciuszko glaciation consisted of a single glacier advance before 59 300 5400 years ago snowy river advance the late kosciuszko glaciation comprised three glacier advances 32 000 2500 headley tarn advance 19 100 1600 blue lake advance and 16 800 1400 years ago mt twynam advance the early kosciuszko glaciation was the most extensive and the late kosciuszko advances were progressively less extensive these periods of glaciation in the highlands correspond to episodes of periglacial activity and peaks in lake levels and river discharge at lower elevations in southeastern australia glacier advances on the kosciuszko massif correlate with advances in tasmania south america and new zealand and are broadly representative of hemispheric climate changes during the last glacial cycle

resuspension measured with sediment traps in a high energy environment the near bottom sedimentation rates were measured by placing cylindrical sediment traps 10 m above the sea floor on each of six moorings deployed between 4100 and 5100 m along a transect across an energetic deep sea current in the hebble area centered at 40 n 63 w on the nova scotian rise sedimentation rates above the sea floor were monitored with additional traps at 23 54 100 200 and 500 m above the bottom mab on the mooring at 4950 m the total flux at 500 mab for the two week period consisting mostly of primary particles from surface water was 166 mg m2 day and increased exponentially towards the bottom the total flux at 10 mab increased down slope from 1160 mg m2 day at 4158 m where the mean current speed was 8 cm s to a maximum of 77 300 mg m2 day at 5022 m where the mean current speed was 32 cm s then decreased to 59 400 mg m2 day at the mooring at 5076 m the size frequency distributions of large discrete particles such as foraminifera diatoms radiolarians and fecal pellets were quantified in all trap samples to examine whether the large variation in fluxes was due to artifacts such as current velocity or trap tilt based on the source persistence and distribution of these particles we conclude that the large variations in fluxes across the rise and with distance from the sea floor are due primarily to resuspension and resettling of bottom sediments with tilt and current effects on trapping having only a secondary effect the vertical gradients of large particle fluxes suggest effective vertical eddy diffusivities of 102 104 cm2 s using a two dimensional model horizontal advection and secondary circulation probably play a large role in moving large rapidly falling up to 1 cm s particles to a height of 50 100 m above the sea floor

slow regolith degradation without creep determined by cosmogenic nuclide measurements in arena valley antarctica abstract estimates of regolith degradation in the mcmurdo dry valleys of antarctica are currently based on indirect evidence and ancient ashes at or near the soil surface that suggest excellent preservation of surfaces on the other hand the existing cosmogenic nuclide surface exposure ages from many parts of the dry valleys are younger than the age of surface deposits inferred from stratigraphic relations this suggests some combination of surface erosion or past ice cover both of which would reduce the apparent exposure age this paper quantifies the regolith degradation and or past ice cover by measuring 10be and 26al from a landslide deposit that contains 11 3 ma volcanic ash the surface sample yields an apparent exposure age of only 0 4 ma however measurements of the subsurface nuclide concentrations show that the deposit has not been shielded by ice and that the age of the ash does not conflict with the apparent exposure age when slow degradation of the deposit 2 m ma 1 is taken into account soil creep which is a common degradational process in a wide variety of environments is non existent at this field site which likely reflects the persistent lack of bio and cryoturbation

nepheloid layer dynamics in the northern portuguese shelf abstract a general hydrographic and nephelometric survey of the nw portuguese continental shelf and upper slope was undertaken under winter and spring conditions the nepheloid layer dynamics along the shelf during three cruises were controlled principally by the following factors a the hydrography of the shelf slope waters i e the nepheloid layers followed isopycnals and water masses b prevalence of upwelling or downwelling circulation over the shelf c dispersion of material by river discharge mainly the douro river d resuspension of mid shelf fine deposits induced by swell e peculiar morphology with the presence of porto canyon and outer shelf rock outcrops the general circulation controls the seaward extension of the nepheloid layers in winter under dominant downwelling conditions an intense bottom nepheloid layer bnl was observed on the shelf due to river borne particle supply and remobilization of mid shelf muddy sediments depth 100 m in this period the bnl increased in thickness to the top of the slope following the isopycnals near the shelf break the bnl detached to form intermediate nepheloid layers inl small inls appear deeper in some areas of the slope a surface nepheloid layer snl appears in the surface water over the shelf and slope in spring biological particles mainly contribute to the snl which is separated from the bnl by a zone of clear water in winter the snl is restricted to the inner shelf where there are high inputs of fluvial particles downwelling circulation probably induces transport of shelf particles to deeper waters in the bnl in spring the predominant circulation was southward upwelling the water column was highly stratified and dispersion of particles in the snl was offshore

the timing of the last glacial maximum in australia abstract late pleistocene glaciation of australia was restricted to the snowy mountains and the tasmanian highlands glaciers were most extensive in tasmania where ice caps formed on the central plateau and west coast ranges and systems of valley and cirque glaciers formed on surrounding mountains to investigate the timing of maximum glacier advance during the last glacial maximum lgm we dated boulders on 18 moraines in 8 glaciated areas using cosmogenic 36cl and 10be we sampled moraines deposited by cirque and valley glaciers in a range of climate types and lithologies over a 7 latitudinal and a 1430 m altitudinal transect exposure ages for lgm moraine boulders group tightly in the range 17 20 ka boulders from the hamilton moraine often treated as the lgm type moraine range in age from 190 350 ka indicating that it was deposited well before the last glaciation collectively the exposure ages show that southeastern australia was glaciated briefly during and after the lgm and deglaciated well before the holocene ice retreated from the terminal moraines after the period of coldest sea surface temperatures in the southwest pacific ocean no evidence was found for readvance of glaciers during the antarctic cold reversal or the younger dryas period

early pleistocene stratigraphy and timing of the bulgobac glaciation western tasmania australia abstract the pieman river drainage basin northwest tasmania preserves the most complete record of cenozoic glacial advances from australia although precise age control is mostly lacking at least four pre last interglacial glaciations can be recognised magnetostratigraphic evidence demonstrates that the minimum age of the glacial diamictons bulgobac formation deposited during the most extensive glacial event the bulgobac glaciation is early pleistocene in age 0 783 m y based on reversed polarity recorded in associated glaciolacustrine sediments the maximum age of this glaciation is 0 89 m y to latest pliocene based on the palynology and magnetostratigraphy of silts marionoak formation underlying the bulgobac formation at a site on the huskisson marionoak river divide plant macrofossils spores and pollen suggest that climates at the time of deposition of the marionoak formation silts were drier than at present and cool but not stadial or glacial in severity

in situ cosmogenic 10be production rate at lago argentino patagonia implications for late glacial climate chronology abstract when calculated with the commonly accepted average northern hemisphere production rate 10 be dates of surface boulders on moraines in the lago argentino area of patagonia are younger than minimum limiting 14 c ages for the same landforms this disagreement could result from the lack of a regional 10 be production rate calibration site to assess this possibility we here present high precision measurements of 10 be in samples collected from surface boulders on the herminita and puerto bandera moraine complexes deposited alongside lago argentino on the eastern flank of the andes at 50 s in patagonia together with maximum and minimum limiting 14 c ages for the two moraine systems these measurements confine the local 10 be production rate to between 3 60 and 3 82 atoms g yr midpoint 3 71 0 11 atoms g yr when using a time dependent scaling method that incorporates a high resolution geomagnetic model this range includes upper and lower error bounds of acceptable production rates derived from both the herminita and the puerto bandera sites the upper limit of this range is more than 12 below the average northern hemisphere production rate as calculated using the same scaling method given in balco et al quat geochron 3 2008 174 195 other scaling models yield production rates with similarly large offsets from the balco et al 2008 rate on the other hand the range of acceptable production rate values determined from patagonia overlaps at 1 with and encompasses the production rate recently derived in macaulay valley in the southern alps of new zealand a putnam et al quat geochron 5 2010a 392 409 within uncertainties i e overlap at 1 sigma this patagonian production rate range also agrees with a recently determined production rate from low elevation sites in northeastern north america and northern norway when the macaulay production rate is used to calculate patagonian exposure dates 14 c and 10 be chronologies are mutually compatible for late glacial moraine systems both chronologies then indicate that outlet glaciers of the southern patagonian icefield achieved a late glacial maximum in the western reaches of lago argentino at 13 000 cal yr bp at the end of the antarctic cold reversal 14 500 12 900 cal yr bp outlet glaciers subsequently receded to near present day ice margins during the younger dryas stadial 12 900 11 700 cal yr bp this general retreat was interrupted about 12 200 cal yr bp when upsala glacier constructed an interlobate complex of moraine ridges on herminita peninsula mountain glaciers in patagonia and new zealand on both sides of the south pacific ocean exhibited a coherent pattern of late glacial ice margin fluctuations

vegetation and climate change during the last interglacial glacial cycle in western tasmania australia abstract cool temperate phyllocladus aspleniifolius nothofagus cunninghamii rainforest occurred in western tasmania during isotope substage 5e during most of the last glacial stage substage 5d to stage 2 the vegetation was subalpine woodland and shrubland or alpine grassland herbland and heathland montane and subalpine rainforest existed at mid altitude 516 m during substages 5a and 5c during stage 2 the late wisconsin glacial maximum most of western tasmania had alpine grassland and herbland vegetation with areas of sclerophyll woodland and rainforest taxa below 100 m on valley floors near the coast cool temperate rainforest developed again during late glacial times after 14 k 14 c yr bp with maximum development of nothofagus cunninghamii rainforest in the early holocene estimates of temperature depression based on depression of the altitudinally zoned vegetation communities a lapse rate of 0 65 c 100 m and comparison with marine core rc 11 120 from the southwestern sub polar indian ocean indicate that the early stadials substages 5b and 5d were cold and the early interstadials substages 5a and 5c were cool stage 4 was cold and probably fully glacial temperature increased early in stage 3 but then decreased with some fluctuations towards stage 2 the late wisconsin glacial maximum an abrupt increase in temperature of ca 6 c occurred after 14 k 14 c yr bp

cosmic ray produced 10be and 26al in antarctic rocks exposure and erosion history we have measured cosmic ray produced t1 2 1 5 million years 10be and t1 2 0 705 million years 26al in purified quartz fractions of selected rock samples from antarctic mountains from these data we calculate 1 mean erosion rates for the limiting case of steady state surface exposure to cosmic rays and 2 minimum exposure ages for the limiting case of no erosion calculated mean erosion rates are very low on the order of a few times 10 5 cm yr we believe the sampling to be sufficient to generalize this result to exposed bedrock in antarctica in favorable cases it is possible to distinguish between the limiting cases steady state erosion seems a better description in such cases most samples including some taken a few meters above the present ice level seem to have been exposed for millions of years without major episodes of burial or abrasion by ice

accuracy of cosmogenic ages for moraines analyses of all published cosmogenic exposure ages for moraine boulders show an average age range of 38 between the oldest and youngest boulders from each moraine this range conflicts with the common assumption that ages of surface boulders are the same as the age of the landform the wide spread in boulder ages is caused by erosion of the moraine surface and consequent exhumation of fresh boulders a diffusion model of surface degradation explains the age range and shows that a randomly sampled small set of boulders n 3 7 will always yield a lower age limit for the moraine the model indicates that for identical dating accuracy six to seven boulders are needed from old and tall moraines 40 000 100 000 yr 50 100 m initial height but only one to four boulders from small moraines 20 000 100 000 yr 10 20 m by following these guidelines the oldest obtained boulder age will be 90 of the moraine age 95 probability this result is only weakly sensitive to a broad range of soil erosion rates our analysis of published boulder ages indicates that 3 of all moraine boulders have prior exposure and 85 of these boulders predate the dated moraine

cosmogenic nuclide chronology of pre last glacial maximum moraines at lago buenos aires 46 s argentina at lago buenos aires argentina 10 be 26 al and 40 ar 39 ar ages range from 190 000 to 109 000 yr for two moraines deposited prior to the last glaciation 23 000 16 000 yr ago two approaches maximum boulder ages assuming no erosion and the average age of all boulders and an erosion rate of 1 4 mm 10 3 yr both yield a common estimate age of 150 000 140 000 yr for the two moraines the erosion rate estimate derives from 10 be and 26 al concentrations in old erratics deposited on moraines that are n760 000 yr old on the basis of interbedded 40 ar 39 ar dated lavas the new cosmogenic ages indicate that a major glaciation during marine oxygen isotope stage 6 occurred in the mid latitude andes the next five youngest moraines correspond to stage 2 there is no preserved record of a glacial advance during stage 4 the distribution of dated boulders and their ages suggest that at least one major glaciation occurred between 760 000 and n200 000 yr ago the mid latitude patagonian glacial record which is well preserved because of low erosion rates indicates that during the last two glacial cycles major glaciations in the southern andes have been in phase with growth and decay of northern hemisphere ice sheets especially at the 100 000 yr periodicity thus glacial maxima are global in nature and are ultimately paced by small changes in northern hemisphere insolation d 2005 university of washington all rights reserved

late pleistocene vegetation and climate history of lake selina western tasmania analysis of pollen nrm intensity of sediments and dating of a 397 cm core from lake selina in western tasmania provides a detailed record of vegetation and climate changes for the last interglacial last glacial cycle the vegetation record shows that cool temperate rainforest was present during isotope substage 5e and during the holocene wet montane forest and subalpine shrublands dominated the early last glacial interstades subalpine alpine heathlands and herbfield the stadials stages 4 2 mainly had grassland herbland and heath vegetation there is close correlation between phases of maximum magnetic intensity in the sediments with pollen zones indicating presence of herbaceous vegetation this suggests erosion of the catchment was greater in the absence of forest or woodland climate may have been slightly cooler than present during substage 5e but the evidence is not definitive climate was colder at all times during the last glacial stage until after ca 14 kyr bp maximum temperature depression from present during stage 2 was 3 5 c at lake selina but probably as much as 6 5 c in the west coast range holocene climate was cool and wet comparison of the lake selina record with others in western tasmania and victoria indicate that variations in vegetation during the last interglacial last glacial cycle were primarily responses to temperature changes in western tasmania and to precipitation changes particularly summer drought in western victoria

exposure dating and glacial reconstruction at mt field tasmania australia identifies mis 3 and mis 2 glacial advances and climatic variability tasmania is important for understanding quaternary climatic change because it is one of only three areas that experienced extensive mid latitude southern hemisphere glaciation and it lies in a dominantly oceanic environment at a great distance from northern hemisphere ice sheet feedbacks we applied exposure dating using 36cl to an extensive sequence of moraines from the last glacial at mt field tasmania glaciers advanced at 41 44 ka during marine oxygen isotope stage mis 3 and at 18 ka during mis 2 both advances occurred in response to an ela lowering greater than 1100 m below the present day mean summer freezing level and a possible temperature reduction of 7 8 c deglaciation was rapid and complete by ca 16 ka the overall story emerging from studies of former tasmanian glaciers is that the mis 2 glaciation was of limited extent and that some glaciers were more extensive during earlier parts of the last glacial cycle copyright 2006 john wiley sons ltd

re assessment of the mid to late quaternary glacial and environmental history of the boco plain western tasmania the glacial geomorphology and drill core based stratigraphy of the boco plain western tasmania reveal a complex sequence of quaternary glacial and non glacial episodes the upper part of the southern boco plain stratigraphy was previously dated by 14c and u series on interbedded organics of mis 1 to mis 5 affinity u series dating of ferricretes associated with glacial diamictons from boco plain cores suggested that there were glacial advances broadly correlative with mis 6 8 and 10 however terrestrial cosmogenic nuclide 10be and 26al exposure ages for the moraine sequence preserved on the wider boco plain area indicate that moraines previously attributed to mis 6 and 8 advances were deposited during mis 10 or earlier cold stages there is no evidence for mis 2 4 or 6 affinity glacial advances onto the boco plain with ice of this age restricted to the west coast range new palynological records from the boco plain core 6690 confirmed the late quaternary ages of the upper part of the sequence whilst extinct palynomorphs indicate a pre quaternary age for the glacial diamictons at the base of core boco 4 and 10 consequently the mid pleistocene glacial sequence preserved in the boco plain is significantly older than previously envisaged with the post mis 10 to 12 geomorphology of the plain dominated by fluvial deltaic swamp peat and lacustrine environments

particulate size spectra behavior and origin of nepheloid layers over the nova scotian continental rise 1 26 32 m measured by coulter counter on 10 cm 3 samples correlate linearly with light beam attenuation coefficient correlation between particle volume and weight concentration indicates lower apparent particle density for low concentration suspensions a feature that is attributed to aggregation during aging of the suspension particle size distributions show unimodal form with a peak at 4 m in high concentrations near the bed changing to a bimodal form with an additional mode at 16 m in low concentrations high above the bed 500 and 1000 m a b meters above bottom the presence of the coarse mode at 1000 m a b coupled with its increase in the lower 250 m of the water column suggests that it both settles from the surface and is resuspended from the bed ultrasonic disaggregation experiments show that much of the fine mode is of aggregates but the coarse mode is single solid particles distributions with a low volume concentration increase in volume when disaggregated and are interpreted as having a relatively large part of their total distribution in unmeasured sizes 32 m distributions with a high concentration decrease in counted volume on disaggregation inversions in the light attenuation profiles are taken to indicate the presence of former bottom mixed layers and their occurrence suggests thickening of the nepheloid layer by detachment and lateral injection of these turbid mixed layers they occur at levels sufficiently high as to provide a nepheloid layer over 1500 m thick over the adjacent sohm abyssal plain the coarse mode probably comprises solid particles with a calculated settling velocity of 12 m day its absolute concentration increases toward the bed but as a proportion of the distribution it increases upward it is thus thought to be particles of surface origin both settling to the bottom and in the lower 250 m of the water column resuspended from the bed the fine mode at 4 m has a spatially constant form thought to be controlled by physical coagulation mechanisms rates of coagulation estimated from shear mechanisms suggest that the postulated change of peaked into flat size distribution by particle aggregation and settling has a time scale of a few years rather than months which is probably long when compared with the lateral injection process lower in the nepheloid layer for that reason distribution with a fine mode peak are found well above the bottom mixed layer

analysis of suspended particle size distributions over the nova scotian continental rise abstract the relationships of particle size distributions to particle concentrations silicate content and process of bottom boundary layer formation on the nova scotian continental rise were examined to analyze the dynamics of the benthic nepheloid layer high particle concentrations 400 g 1 1 in the intense benthic nepheloid layers are nearly always associated with a coarse 8 m particle mode these coarse particles must be renewed on a time scale of weeks in order to be maintained in suspension no unique type of particle size distribution in the benthic nepheloid layer is associated with water masses distinguished on the basis of silicate content however the method of formation of the bottom boundary layer does influence the particle size distributions locally mixed bottom boundary layers are dominated by a coarse particle mode 8 m bottom boundary layers composed of hydrographically distinct filaments of bottom water mainly contain fine particles 2 3 m obtained upstream where the filament has extremely high particle concentrations 1 mg 1 1 the fine particle mode is masked by a locally resuspended coarse mode indicating that the filament must occasionally within 200 300 km be accelerated by some external energy to the point that the critical shear stress for erosion is exceeded

sedimentology of box cores from the cap ferret canyon area bay of biscay abstract sedimentological and geochemical investigations of 45 box cores collected in various morphological settings of the cap ferret canyon bay of biscay are presented to document accurately present day sedimentary processes on the eastern atlantic continental slope the magnitude and variations through time and space of the canyon s channelling or sinking effect on fine grained particles behaviour in comparison with sediment flux across the continental margin was particularly considered and discussed 1 all the parameters grain size carbonate and water content major and trace elements measured both in surface sediment and downcore demonstrate that the characteristics at the sediment interface vary with water depth and with the morphological setting 2 surface sediment is generally coarser grained more terrigenous and deposited at higher rate in the canyon than outside the terrigenous particle supply must be preferentially directed and trapped within the canyon s depression due to present day dynamic conditions 3 the downcore gradients reflected in grain size variations yield information on settling processes the coarse grained population has the characteristics of a winnowed sediment similar to those on the outer shelf while the fine grained population has grain size spectra very similar to the present day fine grained suspensions 4 the carbonate particles are partly derived from direct pelagic production distinct grain size distribution and like terrigenous grains are partly reworked similar downslope decrease in the coarse grained fraction the relatively low caco 3 content observed in the canyon and its downward increase up to values observed at shallower depths may result from a channelling of terrigenous suspensions within the canyon 5 at the present high sea level stand the canyon should become a trap for sediments without much gravity remobilisation as indicated by a lack of sedimentary structures in box cores however a simple increase in sediment trapping can hardly account for the downcore gradients observed in the box cores these trends which are observed on other continental margins monaco et al 1993 journees specialisees de la soc geol france geosciences marines 16 17 december 1994 abstract p 83 indicate a probable increase in terrigenous supplies and or in settling energy

advances in quaternary studies in tasmania the last 35 years have seen rapid advances in our knowledge of climate change during the quaternary period in tasmania extensive mapping and new dating studies particularly since the advent of exposure dating have revealed that maximum ice advance occurred 1 ma ago and later advances were less extensive ice advances occurred several times during the last 100 ka not only during the last glacial maximum deglaciation was rapid after 18 ka and complete by 14 ka ice strongly affected limestone and produced extensive glaciokarst with deranged surface drainage glacial sediment plugged conduits to underground passages partially filled with glaciofluvial gravels periglacial erosion and human impact since late oxygen isotope stage ois 3 enhanced sediment influxes new pollen records particularly from lake selina provide a 125 ka vegetation and climate record representative of the southern hemisphere finally stable isotope studies of speleothem growth have revealed wide swings in climate the climate was warm and moist during ois 5e and early in ois 1 climate was cold and dry during ois 5d and 4 and prevented speleothem growth during ois 3 and ois 2

excepftonally strong near bottom flows on the continental rise of nova scotia recent current velocity measurements across the lower continental rise of nova scotia show a deep equatorwardflow with speeds maximum 73 centimeters per second among the highest recorded for the deep sea silicate measurements indicate that this flow usually consists of southern source antarctic bottom water these measurements confirm the existence of a second and deeper western boundary flow that was earlier inferredfrom geological observations

cosmogenic 10be and 26al exposure ages of moraines in the rakaia valley new zealand and the nature of the last termination in new zealand glacial systems new zealand glaciers reached their last glacial maximum position at or before 25 ka and as early as 23 ka commenced a slow and continual retreat new cosmogenic exposure ages and field mapping from the rakaia valley in the south island suggest that extensive ice survived well into the latter half of the last glacial interglacial transition 18 11 ka with the post 15 ka period inferred to have near holocene climate conditions based on ecological proxy data by as late as 15 5 ka glacier termini had retreated as little as 5 10 km from glacial maximum positions numerous minor ice still stand positions and oscillations are recognized but the record specifically excludes evidence for either a major climatic amelioration at 15 16 ka or a significant glacial re advance during the antarctic cold reversal acr or the younger dryas yd we conclude that the currently widespread interpretation of an episodic new zealand glacial record since the lgm is an artifact of valley dependent retreat processes pro glacial lake formation and local site conditions combined to give an apparent but misleading picture of glacial retreat punctuated by major climatically driven re advances copyright 2010 elsevier b v all rights reserved

suspended particulate matter transport through the vema channel richardson m j biscaye p e gardner w d and hogg n g 1987 suspended particulate matter transport through the vema channel mar geol 77 171 184 sixteen month time series measurements of water velocity and light scattering were coupled with hydrographic and suspended particulate matter sections to determine the flux and the variability in flux of suspended particulate matter through the vema channel the northward flux of spm through the vema channel ranged from 3 to 10 5 104 g s 1 with a mean of 6 5 104 g s 1 the largest fluxes were measured in the deepest and eastern portions of the channel with maximum fluxes of suspended particulate matter at specific sites being roughly two to four times the mean flux some of the suspended particulate matter in the channel may be eroded from the channel itself by the swift currents or eddy like features however the known manganese encrustation and hard floor of the channel suggest that the deep channel floor is not a likely source of sediment a primary source of the suspended particulate matter in the channel may be the sediment drifts in the argentine basin with their associated high standing crops of resuspended particulate matter this resuspended material would then be transported by the antarctic bottom water into and through the vema channel into the brazil basin the northward flux of suspended particulate matter through the vema channel is presently a significant but not dominant influence on sedimentation in the brazil basin

dating the late cenozoic glacial sequence pieman river basin western tasmania australia abstract the pieman river basin western tasmania displays one of the most complete middle to early pleistocene glacial sequences from a southern hemisphere mid latitude site most of the glacial deposits exceed the 14 c limit although mapping of the depositional units using morphostratigraphic post depositional weathering criteria and magnetostratigraphy shows that the sediments of the boco and bobadil glaciation were deposited during the brunhes normal chron 275 kyr late last margaret glaciation advances in the pieman basin are much more restricted in extent and display evidence for multiple stillstand readvance phases during the decay of the system with most of the ice having disappeared by 14 kyr bp

mid pleistocene cosmogenic minimum age limits for pre wisconsinan glacial surfaces in southwestern minnesota and southern baffin island a multiple nuclide approach abstract paired 10 be and 26 al analyses n 14 indicate that pre wisconsinan glaciated bedrock surfaces near the northern baffin island and southern minnesota paleo margins of the laurentide ice sheet have long and complex histories of cosmic ray exposure including significant periods of partial or complete shielding from cosmic rays using the ratio 26 al 10 be we calculate that striated outcrops of sioux quartzite in southwestern minnesota southern margin were last overrun by ice at least 500 000 years ago weathered bedrock tors on the once glaciated uplands of baffin island northern margin are eroding no faster than 1 1 m myr 1 the equivalent of at least 450 000 years of surface and near surface exposure our data demonstrate that exposure ages and erosion rates calculated from single nuclides can underestimate surface stability dramatically because any intermittent burial and the resultant lowering of nuclide production rates and nuclide abundances will remain undetected

cosmogenic radionuclide chronology of pre last glacial cycle moraines in the western arthur range southwest tasmania cosmogenic 10be and 26al exposure ages of 12 boulders from two moraine complexes in the western arthur range of southwest tasmania which previously were considered to have been deposited during the last glacial maximum predate the last glacial cycle zero erosion minimum exposure ages range from 95 ka to 232 ka based on weighted mean 10be and 26al ages per boulder for a reasonable choice of erosion rates 10be boulder ages range from 105 to 326 ka respectively although a direct association of moraine construction to a specific marine isotope stage mis glaciation is not definitive erosion corrected exposure ages indicate glacial advances commensurate with mis 6 and 10 although the latter advance may be attributable to mis 8 if the erosion rate correction is an over estimate given the relatively close proximity of the dated moraines to their source cirques this new cosmogenic glacial chronology implies a very limited extent for any younger glacial advances that occurred in the western arthur range during the last glacial cycle post mis 5 including the global lgm

particle size distributions within hydrothermal plumes over the juan de fuca ridge abstract the particle size distributions of suspended particles in neutrally buoyant hydrothermal plumes from two vent sites on the juan de fuca ridge were measured with a coulter counter hydrothermal particle populations were characterized by high volume concentrations of particles with diameters of m particle populations dominated by larger particles were rare and observed only very near active vent sources because of rapid settling and dilution particle size distributions from particle plumes of hydrothermal origin can be readily distinguished from those of benthic nepheloid layers by the fine particle tail which is expressed on a cumulative number distribution by a slope much steeper than the oceanic norm of 3 the predominance of particles with diameters m within neutrally buoyant hydrothermal plumes demonstrates that the bulk of hydrothermal precipitates are capable of being dispersed over wide areas

uranium thorium dating of ferricretes from mid to late pleistocene glacial sediments western tasmania australia the uranium thorium u th dating method was applied to pedogenic diagenic ferricretes developed within glacial drifts from the northern west coast ranges of tasmania the dates derived from the method are by definition minima for the sediments with the ferricretes being secondary mineral deposits which appear in the form of bands horizons or nodules comprised of indurated masses of iron oxy hydr oxides developed post depositionally within the host sediment or soil the absence of such deposits in well identified drift sediments of the last glaciation suggests the development of ferricrete horizons in glacial drifts occurred during earlier interstadials and interglacials this has been confirmed by the uranium thorium dating of ferricrete bands within glacigenic sediments obtained from three drill cores from the boco valley the ages derived were found to be consistent with estimates for the timing of glaciation derived from palaeomagnetic analyses radiocarbon dating and relative dating techniques the results show that the uranium thorium method can be used to successfully date ferricretes obtained from within glacial sediments of ages 350000 yr and provides valuable information regarding the minimum age of the host sediment 1997 john wiley sons ltd

cosmogenic nuclide ages for last glacial maximum moraine at schnells ridge southwest tasmania abstract moraines on schnells ridge southwest tasmania have been dated using in situ 10be an age of 19 400 600 yr is indicated for the well preserved innermost moraine from consistent measurements on four large quartzite boulders this corresponds closely with exposure ages reported by t t barrows et al 2002 quaternary science reviews 21 159 173 for last glacial maximum glacial features farther north in tasmania and southeast australia in contrast ages between 39 000 and 141 000 yr were obtained from a series of boulders on a more extensive outer moraine indicating that this has had a more complex history

in situ measurements of particle settling velocity in the deep sea two instruments the remote optical settling tube and the benthic autonomous settling tube have been deployed on the nova scotian continental rise at a depth of 4820 m the few results obtained suggest that optical and gravimetric methods give comparable results assumptions about particle density little affect the settling velocity distribution but do scale the total magnitude by using a distribution of declining density with increasing size indicating increasing water content the total concentration inferred from the light attenuation by using mie theory is quite close to the total found from gravimetric data the coarser end of the size distribution changes more with overall change in concentration than the fine end the settling velocity distribution shows the presence of several modes the two principal ones can be matched with modal sizes of 3 3 m and 60 m in coulter counter data allowing inference of stokes density contrasts of 1 5 and 0 061 g cm 3 respectively at concentrations of about 200 mg m 3 more than 50 of the material has a settling velocity less than 2 10 4 cm s 1 probably 3 m in size but this percentage appears to decrease with an increase in total concentration

dating sediment burial with in situ produced cosmogenic nuclides theory techniques and limitations abstract dating sediment burial over million year time scales is crucial in many areas of the earth sciences and archeology but is often difficult using traditional techniques sediment burial can be dated by the radioactive decay of cosmogenic nuclides provided that the sediment was exposed to cosmic rays prior to burial dating calculations are straightforward if sediment is buried deeply and rapidly enough to prevent cosmogenic nuclide production after burial however the analysis can be complicated by postburial production if sediment is insufficiently shielded from secondary cosmic ray nucleons and muons this paper discusses how buried sediments can be dated over timescales up to 5 myr using 26 al and 10 be in quartz

rates of particle scavenging sediment reworking and longitudinal ripple formation at the hebble site based on measurements of 234th and 210pb between 1982 and 1986 seabed and water column samples were collected on five cruises to the hebble site two particle reactive radionuclides 234th and 210pb have been used to examine rates of particle scavenging in bottom waters sediment reworking in the surface seabed and formation of longitudinal ripples settling particles at the hebble site which have been resuspended by strong bottom currents and benthic storm activity scavenge approximately 60 of the 234th half life of 24 days produced in the bottom 100 m of the water column corresponding to removal of 15 dpm cm2 234th inventories from cores collected during a single cruise show substantial variability e g 1 18 dpm cm2 over the 8 km2 study area indicating that resuspended particles are not deposited uniformly across the seabed after storm events the activity of benthic fauna and non uniform deposition over a topographically variable seabed are important processes affecting boundary layer sedimentation and the development of radionuclide inventories in surface sediments the mean 234th seabed inventory from individual cruises to the hebble area varies to a greater extent 2 to 38 dpm cm2 than the mean 210pb inventory 47 to 82 dpm cm2 because 234th inventories are dominated by sedimentary processes associated with an individual storm event whereas 210pb inventories integrate these processes over several cycles of deposition and erosion sediments at the hebble site are biologically reworked very rapidly on a 100 day time scale with 234th mixing coefficients db 1 to 33 cm2 yr comparable to values observed in nearshore environments on time scales of months to years 210pb data indicate that strong currents and benthic storm activity have eroded and redeposited the upper 5 10 cm in 17 of the 20 cores examined reoccupying field sites during the 4 year field program provided the unique opportunity to evaluate steady state models commonly used to determine rates of sediment reworking 210pb profiles and inventories showed significant temporal variations at hebble sites occupied between 1982 and 1986 steady state models should not be used to evaluate profiles of 210pb or other tracers with comparable half life in a dynamic environment like the hebble area because steady state assumptions are not justified and rates of sediment reworking can be underestimated by nearly an order of magnitude 234th and 210pb analyses of core samples from two longitudinal ripples suggest that these sedimentary features form on a time scale of months and consist of a mixture of recently deposited material from the water column and older sediment from depth the absence of 234th activity in one of the ripples indicates that these bedforms may be stable for periods of months without significant growth

exposure dating outwash gravels to determine the age of the greatest patagonian glaciations the relict moraines in argentine patagonia archive major expansions of the patagonian ice sheet throughout the quaternary and are one of the few terrestrial climate proxies in the middle latitudes of the southern hemisphere that extends beyond the last glacial cycle determining their individual ages has proved challenging but has important implications for our understanding of terrestrial climate change in southern south america over the duration of the quaternary here for the first time we demonstrate that sediment on outwash terraces can be directly dated to determine the timing of early middle quaternary glacial advances in southern south america cosmogenic 10 be and 26 al surface exposure ages were obtained from outwash gravels associated with two of the oldest glacial sequences in the lago pueyrredon valley 47 5 s argentina the outermost gorra de poivre glacial sequence marks the greatest extent of the patagonian ice sheet a cobble from this surface gives 10 be and 26 al surface exposure ages of ca 1 2 ma consistent with bracketing 40 ar 39 ar age constraints obtained elsewhere in patagonia this is the first time early pleistocene glacial surfaces have been directly dated in patagonia cobbles on a younger canadon de caracoles outwash terrace give exposure ages of ca 600 ka while 4 of 5 boulders on an associated moraine give exposure ages that are significantly younger if the demonstrated stability of outwash terraces in the valley is common throughout the region it will be possible to extend patagonian glacial chronologies as far back as the early pleistocene

volcanic diapirs in the orange mountain flood basalt new jersey usa abstract diapir shaped structures 4 30 m high consisting of vesicular basalt have intruded into the interior of a 50 70 m thick subaerial orange mountain basalt flow exposed at several rock quarries in northern new jersey the basalt flowed onto a travertine encrusted mudflat saturated with alkali salts we propose that pressurized alkali vapors trapped under the lava created a vesicular and viscous flow bottom layer about 10 m thick vesicle coalescence within this layer increased its buoyancy where it locally accumulated into diapirs and displaced overlying lava large bubbles within the diapirs expanded upon intrusion into hot flow interiors where they explosively escaped leaving lenses of breccia some early diapirs reached the base of the upper lava crust these diapirs document vapor driven convection of large blobs of contaminated lava into the lava core of the orange mountain flow

topographic and microclimatic impacts on glaciation of the denison range southwest tasmania abstract morphostratigraphic relationships between landforms and sediments comparative boulder weathering status and paired 10 be and 26 al exposure ages indicate the occurrence of at least three separate glaciations that are interpreted as dating from mis 2 6 and possibly 8 the rhona glacier remained at or close to its greatest lgm extent until 17 6 ka due to a very favourable micro climate that resulted from local topography that these factors were sufficient to over power relatively subtle zonal temperature shifts that caused significant changes in more exposed tasmanian glaciers implies a need for caution in correlating between glacier systems in markedly different topographic settings when environmental conditions are only marginally supportive of glaciation no evidence was detected for any greater ice extent during mis 3 or mis 4 than during mis 2 but much more extensive glaciations occurred during earlier glacial climatic cycles reduced local precipitation in parallel with increasing aridity of the australian continent may account for the progressively diminishing maximum extent of glaciers during the latter part of the pleistocene and it would have emphasized the importance of local topography and microclimate for the glaciers of southwest tasmania

a study of the optical characteristics of the suspended particles in the benthic nepheloid layer of the scotian rise light transmission profiles have been used to study the optical properties of the suspended particles which are characteristic of the area of the scotian rise in the north atlantic ocean this area is typified by very strong bottom currents and a highly variable bedform morphology a good correlation r 0 96 has been found between the suspended volume and the light beam attenuation coefficient this correlation is consistent with the fact that the cumulative slope of the hyperbolic particle size distribution is nearly constant throughout the region slope 3 1 0 3 numerical analysis of the optical data in conjunction with particle size analysis yields values of the index of refraction of the suspended particles of 1 20 0 07 relative to water the conclusion drawn from these results is that the scotian rise benthic zone is characterized by suspended particles of high relative index of refraction and size distributions which do not vary much with altitude above bottom or over periods of time of more than a year in spite of the extensive fluctuations in activity of the region

in situ10be 26al exposure ages at meteor crater arizona a new method of dating the surface exposure of rocks from in situ production of 10be and 26al has been applied to determine the age of meteor crater arizona a lower bound on the crater age of 49 200 1 700 years has been obtained by this method