submillimeter scale zonation of δ18o in quartz and feldspar isle of skye scotland abstract laser probe analysis of oxygen isotope ratios in submillimeter domains of quartz and feldspar in hydrothermally altered granite reveals complex intragranular zonation that can be contoured within individual grains two samples collected within 10 m of each other in the maol na gainmhich epigranite mge isle of skye scotland are similar petrographically yet display very different 18o zonation patterns sk1 has isotopically zoned quartz 18 o 1 8 8 2 with intragranular gradients of 18o as great as 5 mm and individually homogeneous grains of k feldspar 0 2 which also display a large range of values 18 o 1 7 to 7 3 oxygen isotope gradients of more than 11 mm were measured in this sample in contrast sk4 has homogeneous quartz 18o 5 7 0 3 n 14 and a zoned k feldspar phenocryst 18 o 3 3 to 6 9 isotopic heterogeneity in quartz correlates with the degree of chlorite alteration in adjacent hornblende grains the isotopic heterogeneity revealed by the laser probe in single grains of quartz and feldspar is greater than the entire range of values displayed by bulk mineral analysis of samples collected throughout the mge pluton although the average values of 18o obtained by laser probe are identical to the average bulk values values in k feldspar suggest exchange at 400 c with infiltrating meteoric water 18 o 10 the marked differences in zonation profiles between samples on the outcrop scale suggest that permeability and isotope exchange during hydrothermal alteration was highly heterogeneous these microanalytical data for quartz and feldspar provide the first oxygen isotope evidence from pervasively altered granites that paleopermeability is caused at least in part by intracrystalline microfractures

the attenuation of seismic shear waves in quaternary alluvium in santa clara valley california we used shear waves generated by an air powered source at the ground surface and recorded in a borehole to estimate the shear wave quality factor at strong motion station gilroy no 2 we find similar values of q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths we find no evidence of a frequency dependence of q the mean value of q over the depth range 10 to 115 m is close to 10 the use of this value over the depth of the borehole and the observed travel time of 0 358 sec gives a cumulative attenuation factor t of 0 036 sec for the upper 180 m of the quaternary alluvium this is comparable to the differential decay between gilroy no 2 and a rock site 1 9 km away gilroy no 1 as measured from the decay of the high frequency spectra of accelerograms from large earthquakes plotted on a log linear scale t 0 05 0 04 and 0 03 sec for the 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes respectively the similarity between the attenuations measured from the low strain surface source and those from the larger amplitude earthquake sources suggests that increases of damping due to nonlinear wave propagation effects are limited

rock magnetic proxies of wind intensity and dust since 51 200 cal bp from lacustrine sediments of laguna potrok aike southeastern patagonia the sedimentary archive from laguna potrok aike is the only continuous record reaching back to the last glacial period in continental southeastern patagonia located in the path of the southern hemisphere westerly winds and in the source region of dust deposited in antarctica during glacial periods southern patagonia is a vantage point to reconstruct past changes in aeolian activity here we use high resolution rock magnetic and physical grain size data from site 2 of the international continental scientific drilling program icdp potrok aike maar lake sediment archive drilling project pasado in order to develop magnetic proxies of dust and wind intensity at 52 s since 51 200 cal bp rock magnetic analysis indicates the magnetic mineral assemblage is dominated by detrital magnetite based on the estimated flux of magnetite to the lake and comparison with distal dust records from the southern ocean and antarctica klf is interpreted as a dust indicator in the dust source of southern patagonia at the millennial time scale when ferrimagnetic grain size and coercivity influence are minimal comparison to physical grain size data indicates that the median destructive field of isothermal remanent magnetization mdfirm mostly reflects medium to coarse magnetite bearing silts typically transported by winds for short term suspension comparison with wind intensity proxies from the southern hemisphere during the last glacial period and with regional records from patagonia since the last deglaciation including marine lacustrine and peat bog sediments as well as speleothems reveals similar variability with mdfirm up to the centennial time scale mdfirm is interpreted as a wind intensity proxy independent of moisture changes for southeastern patagonia with stronger winds capable of transporting coarser magnetite bearing silts to the lake

ion microprobe evidence for the mechanisms of stable isotope retrogression in high grade metamorphic rocks retrograde interdiffusion is widely proposed as the dominant factor in producing the stable isotopic fractionation among minerals in slowly cooled igneous and metamorphic rocks mineral zonation consistent with interdiffusion of stable isotopes has never been directly observed however leaving doubt as to the mechanism responsible for the bulk mineral isotopic compositions commonly measured ion microprobe analyses of oxygen isotope ratios in magnetite were combined with conventional bulk mineral analyses and diffusion modeling to document the relationship between mineral zonation and the mechanism of retrogression inferred from bulk mineral data two samples of magnetitebearing quartzo feldspathic lyon mountain gneiss from the adirondack mountains n y were studied in detail conventional stable isotope analysis of both samples indicates that isotope thermometers are discordant and were reset by as much as 200 c from the estimated peak temperature of 750 c the relative order of apparent temperatures recorded by various thermometers differs between the two samples however with t qtz fsp t mt qtz and t mt fsp in one sample and t qtz fsp t mt qtz and t mt fsp in the other diffusion modeling using the fast grain boundary model shows that the former pattern of apparent temperatures is consistent with closed system interdiffusion during cooling whereas the latter is not the modeling predicts that 0 5 mm diameter magnetite grains common to this rock type will contain isotopic zonation of 1 rims lower in 18 o than cores and that the cores of smaller 0 1 mm grains will be similarly lower than to the cores of large 0 5 mm grains ion microprobe analysis reveals that the zoning patterns of magnetite grains from the first sample contain clear core to rim zonation in multiple grains core rim 1 1 0 4 and predicted grain size vs core composition variations consistent with diffusion controlled resetting of bulk mineral fractionations in contrast the second sample shows irregular inter and intra granular variations over an 8 range consistent with open system alteration these results provide direct documentation of the importance of interdiffusion in affecting stable isotope distributions in slowly cooled rocks the correlations of bulk mineral resetting with zonation show that bulk mineral data when interpreted with detailed modeling can be used to determinate what processes controlling retrogression

holocene dust in east antarctica provenance and variability in time and space in this paper we provide a comprehensive overview of the state of knowledge of dust flux and variability in time and space in different sectors of east antarctica during the holocene by integrati

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

dust transport from patagonia to antarctica a new stratigraphic approach from the scotia sea and its implications for the last glacial cycle abstract we studied two deep sea cores from the scotia sea to reconstruct past atmospheric circulation in the southern hemisphere and to resolve a long standing debate on the interpretation of magnetic susceptibility ms records in southern ocean so sediment high sedimentation sites md07 3134 0 2 1 2 m kyr and md07 3133 0 3 2 1 m kyr cover the last 92 5 kyr and 36 kyr respectively both exhibit a one to one coupling of the ms and ca2 signal to the non sea salt nss ca2 signal of the edml ice core clearly identifying atmospheric circulation as means of distribution comparison of additional proxies also excludes major influence by volcanic sources sea ice icebergs or oceanic current transport the close resemblance of the dust proxies over the last glacial cycle in turn allows for the establishment of an age model of unprecedented resolution and precision for so deep sea sediment because atmospheric transport involves no major leads or lags this is of particular importance because ms is routinely measured on deep sea cores in the so but the sediments usually lack biogenic carbonate and therefore had only limited stratigraphic control so far southern south america ssa is the likely source of eolian material because site md07 3133 located closer to the continent has slightly higher ms values than site md07 3134 and also the ms record of patagonian site salsa shows comparable variability patagonia was the dust source for both the scotia sea and east antarctica dust fluxes were several times higher during glacial times when atmospheric circulation was either stronger or shifted in latitude sea level was lowered shelf surfaces were exposed and environmental conditions in ssa were dominated by glaciers and extended outwash plains hence ms records of so deep sea sediment are reliable tracers of atmospheric circulation allowing for chronologically constrained reconstructions of the circum antarctic paleoclimate history

the glaciogenic origin of the pleistocene calcareous dust in argentina on the basis of field mineralogical textural and geochemical analyses calcareous dust occurs in argentina as layers and pockets closely associated with pleistocene deposits and periglacial features from southernmost patagonia to at least the mendoza precordillera and has been traditionally interpreted as a soil horizon resulting from postdepositional pedogenesis during interglacials detailed field and microscopic observations and sedimentological and geochemical analyses of more than 100 samples collected from lower to upper pleistocene deposits between 51 s and 33 s and from near sea level to 2800 m asl allow us to interpret the dust as synchronous with the host sediment all observations and analyses lead us to conclude that 1 the cryogenic morphology and the chemical signatures of the calcite component show that the dust is glaciogenic 2 the dust was carried by southeasterly antarctic winds and 3 it was deposited over most of southern and central argentina field observations geomorphic evidence and radiocarbon dates suggest that the dust was deposited during several pleistocene glacial episodes

ice magnetization in the epica dome c ice core implication for dust sources during glacial and interglacial periods 1 isothermal remanent magnetization and insoluble dust content of ice samples from epica dome c ice core were measured to characterize the magnetic properties of atmospheric dust despite the larger concentration of dust aerosol during glacial stages the magnetization of the dust fraction was found to be higher during interglacials and exhibits a larger variability changes in magnetic mineralogy of aerosol dust in ice from different climatic stages were also characterized using coercivity of remanence variations of magnetic properties of dust from glacial to interglacial stages indicate changes in dust provenance in agreement with previous results based on geochemical analysis however the extremely large magnetizations of some interglacial samples also suggest that episodical eolian deposition from highly magnetic deposits occurred during interglacial periods

near surface attenuation and site effects from comparison of surface and deep borehole recordings abstract near surface attenuation and site effects are investigated using the seismograms of 17 local earthquakes recorded at depths of 0 0 3 1 5 2 5 and 2 9 km in the cajon pass borehole southern california the borehole penetrates 500 m of miocene sandstone and then crystalline granitic basement rock previous estimates of site response have been limited to shallower holes where the surface reflection interferes with the upgoing direct wave and the deepest sensor is not below the severe near surface effects in bedrock spectral ratios of the direct p and s waves for each earthquake between the different recording levels are well modeled with frequency independent q and amplification at the borehole q p 27 8 and q s 21 7 in the upper 2 9 km increasing from q p 26 and q s 15 in the upper 300 m to q p 133 and q s 47 between 1 5 and 3 km one event was also recorded at a surface granite site less than 1 5 km from the wellhead comparison of the 2 9 km recording with that at this granite site gives q p 50 and q s 23 the similarity of these values with those of previous studies at a wide range of sites suggests that q is very low in the near surface independent of rock type near surface amplification appears considerably more site dependent at the wellhead the amplifications at 1 hz of the direct p and s waves are 12 7 and 13 7 respectively these values include the free surface effect and are in reasonable agreement with the impedance contrast from the borehole logs at the granite site amplification of both p and s waves is less than four direct wave amplification at the wellhead is therefore at least three times that of the granite site the spectra of the direct and coda waves of the one earthquake recorded at both the wellhead and granite sites are compared with the corresponding 2 9 km recording coda wave amplification is in good agreement with the direct wave at the rock site but at the borehole the coda wave amplification factor overestimates the direct wave amplification by a factor of 3

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

the role of seasonality of mineral dust concentration and size on glacial interglacial dust changes in the epica dronning maud land ice core we present a record of particulate dust concentration and size distribution in subannual resolution measured on the european project for ice coring in antarctica epica dronning maud land edml ice core drilled in the atlantic sector of the east antarctic plateau the record reaches from present day back to the penultimate glacial until 145 000 years b p with subannual resolution from 60 000 years b p to the present mean dust concentrations are a factor of 46 higher during the glacial 850 4600 ng ml compared to the holocene 16 112 ng ml with slightly smaller dust particles during the glacial compared to the holocene and with an absolute minimum in the dust size at 16 000 years b p the changes in dust concentration are mainly attributed to changes in source conditions in southern south america an increase in the modal value of the dust size suggests that at 16 000 years b p a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the edml drill site we find a clear in phase relation of the seasonal variation in dust mass concentration and dust size during the glacial r conc size 0 8 but no clear phase relationship during the holocene 0 r conc size 0 4 with a simple conceptual 1 d model describing the transport of the dust to the ice sheet using the size as an indicator for transport intensity we find that the effect of the changes in the seasonality of the source emission strength and the transport intensity on the dust decrease over transition 1 can significantly contribute to the large decrease of dust concentration from the glacial to the holocene

origin of calcareous dust in argentinean pleistocene periglacial deposits traced by sr c and o isotopic compositions and ree distribution abstract calcareous dust is often closely associated with periglacial features in the pleistocene deposits of extra andean argentina conventionally interpreted as resulting from continental pedogenic weathering and precipitation during interglacial episodes little has yet been demonstrated about its origin strontium oxygen and carbon isotopic compositions and ree distributions were determined for such calcareous dust from a wide geographic area including sites in patagonia the southern pampa and the mendoza pre cordillera the 13 c values between 1 9 and 7 2 v pdb and 18 o values between 2 6 and 6 0 v smow confirm a glaciogenic origin and not the generally advocated pedogenic genesis the narrow 87 sr 86 sr ratio from 0 706463 0 000008 to 0 707477 0 000006 2 and the constant ree distribution with a specific negative ce anomaly both require crystallization in a large and homogeneous reservoir with some seawater supply during successive glacial episodes the homogeneous sr isotopic and ree data suggest that the ca sr and rees released from andean basement rocks during glacial episodes 1 were transported by rivers to the eastern continental shelf of which up to 1 million of km 2 was probably emerged during the successive glacial episodes 2 were mixed there in a semi marine lacustrian meander rich environment with seawater supply where they dissolved and re precipitated before 3 being eroded and dispersed by southeasterly winds over most of argentina

estimates of shear wave q and κ0 for unconsolidated and semiconsolidated sediments in eastern north america measured and calculated values of the effective quality factor qef and the site attenuation parameter 0 for unconsolidated and semiconsolidated sediments in eastern north america ena indicate that the latter is strongly dependent on sediment thickness estimates of 0 for national earthquake hazard reduction program nehrp bc site profiles sediment plus hard rock in the mississippi embayment and the atlantic coastal plain were found to increase from about 9 to 31 msec for sedi ment thicknesses ranging from 116 to 600 m stochastic simulations using the 175 m thick hypothetical nehrp bc site profile used to estimate ena ground motions in the nationalseismichazardmapsbytheu s geologicalsurvey usgs indicatethat 0 20 msec provides a smaller estimate of amplification that agrees more closely with the low strain short period site coefficients in the nehrp recommended provisions for seismic regulations for new buildings and other structures nehrpprovisions than the10msecvalueusedbytheusgs alinearregressionofthe 0 estimatescompiledin this study indicates that 0 20 msec corresponds to a relatively thick bc sediment thickness of 460 116 m these same stochastic simulations indicate that the rela tivelyshallowusgssiteprofileprovidesestimatesofamplificationthataresmallerthan thelow strainlong periodsitecoefficientsinthenehrpprovisions thedependenceof bothsiteattenuationandsiteamplificationonsedimentthicknesssuggeststhattheuseof a single reference site condition for hazard mapping might not be appropriate instead theseresultsimplythateitheraregionalsetofreferencesiteprofilesshouldbedeveloped or that a more uniform site condition such as hard rock should be used to define a more stable reference site condition in ena

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

empirical distance attenuation and the local magnitude scale for the central united states seismic waveform data from the cooperative new madrid seismic network cnmsn the u s national seismograph network usnsn and stations operated by the u s geological survey and the incorporated research institutions for seismology iu are corrected to the theoretical wood anderson response and the peak amplitudes are used to determine a local magnitude scale for the central united states the distance correction function can be expressed as graphic 1 with amplitude a in millimeters and hypocentral distance r in kilometers showing a weak attenuation with distance synthetic seismograms are calculated based on a detailed crustal model obtained from local well log acoustic data in the mississippi embayment to examine the effect of structure on station factors the results show that the mississippi embayment sediment as a whole may amplify seismic waves at some specific frequencies such as 0 5 and 5 0 6 0 hz with a factor less than 4 0 and may not amplify seismic waves in the frequency band from 0 5 to 9 9 hz on average even though the amplification factors do increase with the source magnitude estimations for b values and magnitudes of earthquakes with a return period of 500 yr in the central united states are performed based on the original new madrid catalog m d or m blg and the newly created m l catalog results show that the b value is smaller for the m l catalog 0 790 yielding one m 7 5 event every 500 yr a result that converges with the paleoearthquake estimate for the region on average the relation between m l and m d or m blg for 1 5 m d 5 0 can be expressed as m l 1 008 m d 0 0714 1 embed inline graphic 1 gif

kinetics of diffusion controlled mineral growth in the christmas mountains texas contact aureole chert nodules in limestone in the aureole of the christmas mountains gabbro are rimmed by wollastonite in the interval 102 25 m from the intrusive contact and by tilleyite or spurrite and wollastonite within 25 m of gabbro wollastonite rims thicken from 4 5 mm at 102 m to 7 mm at 80 m to 30 mm at 49 m and diminish in thickness from 79 to 53 mm over the interval 13 2 m from the gabbro wollastonite has two textural components polygonal matrix wollastonite grains coarsen from 0 011 mm at 102 m to 0 053 mm at 46 m to 0 2 0 3 mm within 20 m of the contact whereas scattered wollastonite porphyroblasts appear at 30 m and coarsen to impingement with a diameter of 1 07 mm at 12 m kinetic models for normal grain growth and for layer thickening set a function of the square of the grain diameter or layer thickness equal to the product of a material constant and a temperature time integral that includes the arrhenius function for the diffusion coefficient the time index for non isothermal diffusion controlled mineral growth is the temperature time integral numerically evaluated along t t curves for the thermal history of the contact aureole the thermal history of the christmas mountains aureole is obtained using a numerical model for a cylindrical intrusion radius 823 m that matches maximum temperatures in the contact aureole of 600 940 1000 and 1030 c at 115 23 13 and 0 m by convection for 700 yr followed by crystallization and cooling the log of the t t integral varies linearly with distance from the gabbro with a slope proportional to activation energy and an intercept proportional to the material constant a plot of the log of the square of the grain diameter of matrix wollastonite against distance from the gabbro is linear and the normal grain growth model yields the following arrhenius function for the diffusion of oxygen in wollastonite grain boundaries d gb o 2 9 333 x 10 4 m s exp 185 rt kj mole where is grain boundary width the fixed ratio of tilleyite to wollastonite rim thickness on nodules from the inner aureole yields a molar ratio of tilleyite to wollastonite in c t w q structures of 1t 24w and requires consumption of calcite and quartz in the ratio 29c 26q truncation of fully coarsened impingement wollastonite by columnar tilleyite implies that the tilleyite layer grew at expense of wollastonite and that wollastonite coarsened at temperatures greater than 940 c solution of a system of mass balance conservation and flux ratio equations describing diffusion controlled growth of a c t w q nodule matches the net mass transfer and observed textural features for onsager diffusion coefficient ratios of l cao l sio 2 42 and l cao l co 2 grain diameter of impingement wollastonite varies linearly with the radius of spherical wollastonite nodules that ceased growth on consumption of the quartz core implying that coarsening coincided in time with wollastonite rim growth grain boundary cross section of wollastonite decreased by two orders of magnitude during layer growth coupling of the kinetics of coarsening of impingement wollastonite with diffusion controlled growth of the wollastonite layer yields the following arrhenius function for the onsager diffusion coefficient for diffusion of cao in wollastonite grain boundaries l gb cao 1 731 x 10 4 rt mole 2 j s exp 220 rt kj mole the pre exponential term for grain boundary diffusion of sio 2 in wollastonite is obtained from the relation l cao l sio 2 42 values of the diffusion coefficients derived from analysis of grain coarsening and layer growth in the christmas mountains contact aureole satisfy the diffusion compensation relations for grain boundary diffusion of oxygen and cations in oxides based on laboratory experiment the value of the coefficient for diffusion of cao in tilleyite grain boundaries at 1000 c based on a time integrated aver age temperature is essentially identical to that obtained for wollastonite using the full non isothermal analysis suggesting that the values of onsager coefficients for grain boundary diffusion of a given cation are not strongly dependent on identity of solid phase wollastonite rims grow to 82 to 95 of their ultimate thickness during the period of heating that coincides with magmatic convection because growth of the wollastonite and tilleyite layers does not begin until temperature rises to 600 and 940 c respectively rim growth is not synchronous across the aureole

evaluation of methods for estimating linear site response amplifications in the los angeles region we have evaluated two methods of estimating linear site response amplifications and the standard index for classifying sites by comparing the results of each technique to observed ground motions at 33 sites in the los angeles region using velocity and density profiles from 33 boreholes we evaluated the use of the average 30 m shear wave velocity and associated site classifications the quarter wavelength method and the haskell propagator matrix method we correlated the average 30 m shear wave velocity and nehrp site classification at the borehole sites colocated within 290 m of a site with observed ground motion the observed data follow the expected trend of higher ground motion amplifications for lower average shear wave velocities but there is a significant degree of variability also there is a great deal of scatter in the observed amplifications within each national earthquake hazards reduction program nehrp class we used the velocity and density information in the database to calculate the average frequency dependent site response in the frequency ranges 1 3 hz 3 5 hz and 5 7 hz for a one dimensional flat layered structure using the haskell propagator matrix method and the quarter wavelength method there is a general correlation with the ground motion data however once again there is a great degree of scatter although slightly less for the quarter wavelength method we note that both the observed and predicted amplifications can change dramatically over a distance as small as 1 km or less even though all techniques considered give results that follow the expected trend of higher amplifications for softer sediments the predicted site response at any particular site with the current level of information may not be representative of the shaking that will actually occur during an earthquake the disparity between observed and predicted amplifications appears to be a result of oversimplification inherent in the amplificationestimation methods such as the use of average or assumed values for the site conditions in the absence of measured values the smoothing effect of using an average velocity limiting the properties considered to the uppermost 30 m of material and complexities in the wave propagation that are not addressed by these methods

determination of oxygen diffusion rates in magnetite from natural isotopic variations the oxygen isotope compositions of magnetite grains hosted in a calcite marble from the bancroft terrane of the ontario grenville province vary systematically with grain size the 18 o values of magnetite and corresponding closure temperatures t c based on calcite magnetite range from 18 o 2 6 t c 505 c for a grain radius of 0 075 mm to 18 o 5 5 t c 660 c for a grain radius of 1 15 mm the 18 o of the calcite is constant within a scale of 100 m at a value of 12 3 the observed isotopic variations can be fit to the diffusion model of dodson by the method of least squares r 0 98 to yield an activation energy q 211 20 kj mole and a pre exponential factor d o 4 3 3 3 1 9 x 10 7 cm 2 s for a cooling rate of 4 c m y the activation energy estimate is independent of the assumed cooling rate but the calculated pre exponential factor varies as follows d o cm 2 s d t d t x 1 08 x 10 7 note d t d t is in c m y the activation energy is identical to an experimental determination by giletti and hess but the pre exponential factor is 100 times lower the difference is attributed to the water rich conditions in the experiments and the absence of fluid in the slowly cooled marbles investigated in this study the strong dependence of diffusion rate on water presence or f h 2 o may be used as a sensor for water rich fluids during cooling in natural systems

glacial interglacial changes of southern hemisphere wind circulation from the geochemistry of south american dust abstract the latitudinal displacement of the southern westerlies and associated climate systems is a key parameter for understanding the variations of southern hemisphere atmospheric circulation during the late quaternary period to increase understanding of past atmospheric circulation and of the paleo environmental conditions associated with continental dust sources we dig deeper into dust provenance in paleo archives of the southern hemisphere we present here a sr nd isotopic and rare earth element study of surface sediments collected along a 4000 km latitudinal band from arid and semi arid terrains in southern south america findings from terrains that served as paleo dust suppliers are compared with modern dust collected from monitoring stations along the same latitudinal band which affords a test on how actual present day aeolian compositions compare to those of the past potential source areas moreover the comparison between past and present day datasets is useful for understanding present day atmospheric circulation armed with a new comprehensive dataset we revise previous interpretations of the provenance of dust trapped in the antarctic ice and sediments deposited in the south atlantic sector of the southern ocean these comparisons support multiple source regions in southern south america that changed with climates the findings reveal that although patagonia plays an important role in contributing dust to the higher latitudes central western argentina and to a lesser extent the southern puna region also emerge as potentially important dust sources during glacial times the southern altiplano appears to be a major contributor during interglacial periods as well we rely in part on an understanding of modern wind dust activities to conclude that the possible presence of southern south america source regions other than patagonia in east antarctic ice is consistent with an overall equatorward displacement during glacial times of both the mid latitude westerlies and the subtropical jet stream

links between patagonian ice sheet fluctuations and antarctic dust variability during the last glacial period mis 4 2 abstract antarctic and greenland ice core records reveal large fluctuations of dust input on both orbital and millennial time scales with potential global climate implications at least during glacial periods the antarctic dust fluctuations appear to be largely controlled by environmental changes in southern south america we compare dust flux records from two antarctic ice cores to variations in the composition of the terrigenous supply at odp site 1233 located off southern chile and known to record fluctuations in the extent of the northern part of the patagonian ice sheet npis during the last glacial period marine isotope stage mis 4 to 2 within age uncertainties millennial scale glacial advances retreats of the npis correlate to antarctic dust maxima minima in turn npis fluctuations were closely related to offshore sea surface temperature sst changes this pattern suggests a causal link involving changes in temperature in rock flour availability in latitudinal extensions of the westerly winds and in foehn winds in the southern pampas and patagonia we further suggest that the long term trend of dust accumulation is partly linked to the sea level related changes in the size if the patagonian source area due to the particular morphology of the argentine shelf we suggest that sea level drops at the beginning of mis 4 and mis 2 were important for long term dust increases while changes in the patagonian dust source regions primarily control the early dust decrease during the mis 4 3 transition and termination 1

modern and holocene aeolian dust variability from talos dome northern victoria land to the interior of the antarctic ice sheet abstract high elevation sites from the inner part of the east antarctic plateau sample windborne dust representative of large portions of the southern hemisphere and are sensitive to long range atmospheric transport conditions to polar areas on the periphery of the ice sheet conversely the aeolian transport of particles from high elevation ice free areas can locally represent a relatively important additional input of dust to the atmosphere and the interplay of atmospheric dynamics dust transport and deposition is strictly related to the regional atmospheric circulation behaviour both at present day and in the past the understanding of the spatial extent where local sources can influence the mineral dust budget on the ice sheet is fundamental for understanding the atmospheric dust cycle in antarctica and for the interpretation of the dust history in marginal glaciological settings in this work we investigate the spatial variability of dust flux and provenance during modern pre industrial and holocene times along a transect connecting talos dome to the internal sites of the antarctic plateau and we extend the existing documentation of the isotopic sr nd fingerprint of dust sized sediments from victoria land source areas dust flux grain size and isotopic composition show a marked variability between talos dome mid point d4 and dome c vostok suggesting that local sources play an important role on the periphery of the ice sheet microscope observations reveal that background mineral aerosol in the taldice core is composed by a mixture of dust volcanic particles and micrometric sized fragments of diatoms these latter representing a small but pervasive component of antarctic sediments a set of samples from victoria land mostly consisting of regolith and glacial deposits from high elevation areas was collected specially for this work and the isotopic composition of the dust sized fraction of samples was analyzed results reveal a close relationship with the parent lithologies but direct comparison between source samples and firn ice core dust is problematical because of the ubiquitous volcanic contribution to the environmental particulate input in the talos dome area the frequency of events potentially suitable for peripheral dust transport to talos dome appears relatively high for present day conditions according to back trajectories calculations and the related air flow pattern well defined from a seasonal and spatial perspective also as expected from palaeo data these events appear extremely uncommon for internal sites

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

the oxygen isotope anatomy of a slowly cooled metamorphic rock the distribution of o isotope ratios in a slowly cooled metamorphic rock is investigated by a combination of ion microprobe and laser probe techniques the sample has unusually simple geometry centimeter size domains of feldspar and garnet separated by a one millimeter to one centimeter thick layer of millimeter size magnetite grains isotopic zonation at two different scales is documented a sharp decrease in 18 o in the outer 10 100 m of individual magnetite grains is in agreement with modeling of isotopic reequilibration during cooling by interdiffusion between feldspar and magnetite the presence of this zonation in the outer portions of magnetite grains that are adjacent to garnet indicates extensive transport along grain boundaries during diffusive exchange millimeter scale zonation in the polygranular layer of magnetite is caused by the interaction of volume diffusion and grain boundary transport the effects of which depend upon local textures grain boundaries enhance bulk diffusion in polygranular aggregates and allow exchange between nontouching grains the results document a complex textural control to millimeter scale o isotope zonation and geothermometry in slowly cooled rocks and document the importance of fast grain boundary transport in controlling diffusive exchange

distinguishing magmatic from subsolidus epidote laser probe oxygen isotope compositions epidote occurs in four textural varieties in the mount lowe intrusion of southern california euhedra anhedra intergrowths and cross cutting veins of these conspicuous elongate euhedra which range up to 3 cm in length meet most of the established textural criteria for magmatic epidote equant anhedral grains which are 5 mm in diameter are texturally ambiguous although rare allanite cores are suggestive of a magmatic origin epidote intergrowths with hornblende and biotite also meet certain textural criteria for crystallization from a magma notably euhedral faces against biotite finally late stage veins of epidote cross cut all phases in the rock and are likely subsolidus oxygen isotopic compositions of these four textural varieties of epidote determined using the laser probe indicate that the use of textural criteria alone in establishing epidote parageneses can be misleading intracrystalline 18o variations in the euhedra document both magmatic and subsolidus compositions oxygen isotope compositions are bimodal averaging 5 36 0 13 n 11 and 4 66 0 23 n 21 these data combined with plagioclase and zircon 18o values are interpreted to indicate that magmatic oxygen isotopic compositions have been preserved where epidote 18o is greater than 5 significant portions of each euhedral crystal have been affected by subsolidus exchange and are characterized by epidote 18o values less than 5 intracrystalline 18o values of epidote anhedra range from 4 50 to 6 08 and thus also document both magmatic and subsolidus compositions subsolidus exchange is volumetrically less significant in the anhedra than in the euhedra values of 18o for intergrowths and late stage cross cutting veins of epidote average 3 81 0 22 and document clearly subsolidus growth the data confirm that in the mount lowe intrusion large euhedra of epidote are magmatic in origin consistent with textural evidence the data also indicate that equant anhedra of epidote are also magmatic in origin and thus the absence of good crystal faces does not necessarily indicate subsolidus growth the subsolidus origin of intergrowths of epidote with euhedral faces against biotite indicates that well developed crystal faces do not require growth from a magma finally the subsolidus origin of the vein epidote is consistent with textural evidence the increased resolution available with laser based oxygen isotope measurements offers an important test for documenting whether epidote is of magmatic or subsolidus origin given the barometric significance of magmatic epidote oxygen isotope compositions can be used to aid in the interpretation of epidote bearing plutons

magnetization of polar ice a measurement of terrestrial dust and extraterrestrial fallout abstract laboratory induced remanent magnetization of polar ice constitutes a measurement of the magnetization carried by the ferromagnetic dust particles in the ice this non destructive technique provides a novel kind of information on the dust deposited on the surface of polar ice sheets measurements made on ice samples from greenland north grip ice core and antarctica vostok and epica dome c ice cores allowed the recognition of a fraction of magnetic minerals in ice whose concentration and magnetic properties are directly related to that of insoluble dust the source of this fraction of magnetic minerals thus appears closely related to terrestrial dust transport and deposition and its magnetic properties are informative of the dust provenance areas the rock magnetic properties of the dust may reflect distinct changes of dust source areas from glacial to interglacial periods in agreement with and adding further information to the isotopic 87 sr 86 sr and 143 nd 144 nd analyses a second magnetic fraction consists of particles of nanometric size which are superparamagnetic at freezer temperature and whose concentration is independent of the mass of aerosol dust found in the ice the source of these nanometric sized magnetic particles is ascribed to fallout of meteoric smoke and their concentration in ice was found to be compatible with the extraterrestrial fallout inferred from ir concentrations the diameter of the smoke particles as inferred from magnetic measurements is in the range of about 7 20 nm

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites diffusive exchange as a guide to cooling history ion microprobe analysis of magnetites from the adirondack mountains ny yields oxygen isotope ratios with spatial resolution of 2 8 m and precision in the range of 1 1 sigma these analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of 18o at this scale high precision micro analyses of this sort will permit wide ranging new applications in stable isotope geochemistry the analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite magnetites are near to fe3o4 in composition and optically and chemically homogeneous a combination of ion probe plus conventional brf5 analysis shows that individual grains are homogeneous with 18o 8 9 1 smow from the core to near the rim of 0 1 1 2 mm diameter grains depth profiling into crystal growth faces of magnetites shows that rims are 9 depleted in 18o these low 18o values increase in smooth gradients across the outer 10 m of magnetite rims in contact with calcite these are the sharpest intracrystalline gradients measured to date in geological materials this discovery is confirmed by bulk analysis of 150 350 m diameter magnetites which average 1 2 lower in 18o than coarse magnetites due to low 18o rims conventional analysis of coexisting calcite yields 18o 18 19 suggesting that bulk 18o cc mt 9 3 and yielding an apparent equilibration temperature of 525 c over 200 c below the temperature of regional metamorphism consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories the data for oxygen in calcite under hydrothermal conditions at high p h2o indicates that diffusion is faster in magnetite and modelling of the low 18o rims on magnetite would suggest that the adirondacks experienced slow cooling after grenville metamorphism followed by a brief period of rapid cooling possibly related to uplift conversely the data for calcite at low p h2o show slower oxygen diffusion than in magnetite modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals suggesting that the low 18o rims form by exchange with late low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets in either case the ion microprobe results indicate that two distinct events are recorded in the post metamorphic exchange history of these magnetites recognition of these events is only possible through microanalysis and has important implications for geothermometry

a new andean deep ice core from nevado illimani 6350 m bolivia abstract a new ice core record from the nevado illimani 16 s bolivia covers approximately the last 18 000 years bp a comparison with two published ice records from sajama 18 s bolivia thompson et al science 282 1998 1858 1864 and huascaran 9 s peru thompson et al science 269 1996 46 50 documents a regionally coherent transition from glacial to modern climate conditions in south america north of 20 s the strong resemblance between the illimani and huascaran water isotope records and their differences from the sajama record in particular during the period from 9000 years bp to 14 000 years bp suggest that local water recycling or local circulation changes played a major role for sajama we interpret the common illimani huascaran water isotope history in terms of a common change from wetter cooler conditions during glacial times to drier warmer conditions in the early holocene

diffusion in silicate minerals and glasses a data digest and guide to the literature the rates of diffusion of cations oxygen and hydrogen in silicates are of fundamental importance to a wide range of petrological and geochronological problems in order that the earth scientist may readily apply the available experimentally determined diffusion rates to such problems a compilation of data for diffusion in silicate minerals and glasses is presented along with a working guide for its use published data and experimental conditions are listed in tables and these are preceded by an outline of diffusion mechanisms terminology equations and units diffusion regimes factors controlling diffusion rates measurement techniques and diffusional behaviour

the 1997 1998 umbria marche sequence central italy source path and site effects estimated from strong motion data recorded in the epicentral area 1 we apply a nonparametric spectral inversion scheme to calculate source spectra s wave attenuation and site transfer functions from strong motion records in the epicentral region of the 1997 1998 umbria marche seismic sequence central italy we use records from moderate size earthquakes 4 6 ml 5 9 to parameterize the spectral amplitude decay in the distance range from 5 to 40 km we find that the average quality factor q can be approximated by q f 49 f0 9 between 0 5 and 8 hz and the geometrical spreading by r 0 9 at high frequencies f 8 hz the dependence of q on frequency weakens and it takes an approximate constant value of 318 we fit the source spectra to the square model and calculate an average stress drop of 2 1 mpa the average value is consistent with the previous estimates from the weak events 1 4 ml 4 5 of the umbria marche seismic sequence the most remarkable site effects are found in correspondence of large sedimentary basins filled by alternation of sandy clayey deposits the estimated spectral parameters are used to simulate acceleration spectra recorded during several earthquakes of the umbria marche sequence both point source and finite fault effects are considered furthermore attenuation relationships for peak ground velocity and ground acceleration are estimated using synthetic data and compared to existing relationships

accounting for site effects in probabilistic seismic hazard analyses of southern california overview of the scec phase iii report this article presents an overview of the southern california earthquake center scec phase iii effort to determine the extent to which probabilistic seismic hazard analysis psha can be improved by accounting for site effects the contri butions made in this endeavor are represented in the various articles that compose this special issue of bssa given the somewhat arbitrary nature of the site effect distinction it must be care fully defined in any given context with respect to psha we define the site effect as the response relative to an attenuation relationship averaged over all damaging earthquakes in the region a diligent effort has been made to identify any attributes that predispose a site to greater or lower levels of shaking the most detailed maps of quaternary geology are not found to be helpful either they are overly detailed in terms of distinguishing different amplification factors or present southern california strong motion observations are inadequate to reveal their superiority a map based on the average shear wave velocity in the upper 30 m however is found to delineate significantly different amplification factors a correlation of amplification with basin depth is also found to be significant implying up to a factor of two difference between the shallowest and deepest parts of the los angeles basin in fact for peak accel eration the basin depth correction is more influential than the 30 m shear wave ve locity questions remain however as to whether basin depth is a proxy for some other site attribute in spite of these significant and important site effects the standard deviation of an attenuation relationship the prediction error is not significantly reduced by making such corrections that is given the influence of basin edge induced waves subsur face focusing and scattering in general any model that attempts to predict ground motion with only a few parameters will have a substantial intrinsic variability our best hope for reducing such uncertainties is via waveform modeling based on first principals of physics finally questions remain with respect to the overall reliability of attenuation re lationships at large magnitudes and short distances current discrepancies between viable models produce up to a factor of 3 difference among predicted 10 in 50 yr exceedance levels part of which results from the uncertain influence of sediment nonlinearity

multiple sources supply eolian mineral dust to the atlantic sector of coastal antarctica evidence from recent snow layers at the top of berkner island ice sheet the sr and nd isotopic composition of dust extracted from recent snow layers at the top of berkner island ice sheet located within the filchner ronne ice shelf at the southern end of the weddell sea enables us for the first time to document dust provenance in antarctica outside the east antarctic plateau eap where all previous studies based on isotopic fingerprinting were carried out berkner dust displays an overall crust like isotopic signature characterized by more radiogenic 87sr 86sr and much less radiogenic 143nd 144nd compared to dust deposited on the eap during glacial periods differences with eap interglacial dust are not as marked but still significant indicating that present day berkner dust provenance is distinct at least to some extent from that of the dust reaching the eap the fourteen snow pit sub seasonal samples that were obtained span a two year period 2002 2003 and their dust sr and nd isotopic composition reveals that multiple sources are at play over a yearly time period southern south america patagonia in particular likely accounts for part of the observed spring summer dust deposition maxima when isotopic composition is shifted towards younger isotopic signatures in the spring possible additional inputs from australian sources would also be supported by the data most of the year however the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in east antarctica which carry old crust like isotopic fingerprints whether the restricted east antarctic ice free areas produce sufficient eolian material has yet to be substantiated however the fact that large 5 mu m particles represent a significant fraction of the samples throughout the entire time series supports scenarios that involve contributions from proximal sources either in patagonia and or antarctica possibly including snow free areas in the antarctic peninsula and other areas as well this also indicates that additional dust transport which does not reach the eap must occur at low tropospheric levels to this coastal sector of antarctica

site amplification and attenuation via downhole array seismogram inversion a comparative study of the 2003 miyagi oki aftershock sequence weak motion geotechnical array recordings at 38 stations of the japanese strong motion network kik net from the 2003 m w 7 0 miyagi oki aftershock sequence are used here to quantify the amplification and attenuation effects of near surface formations to incident seismic motion initially a seismic waveform optimization algorithm is implemented for the evaluation of high resolution low strain velocity v s attenuation q s and density profiles at the sites of interest based on the inversion results v s versus q s correlations are developed and scattering versus intrinsic attenuation effects are accounted for in their physical interpretation surface to downhole traditional spectral ratios ssr cross spectral ratios c ssr and horizontal to vertical h v site response estimates are next evaluated and compared while their effectiveness is assessed as a function of the site conditions classified on the basis of the weighted average vs of the upper 30 m v s30 of the formations single and reference station site response estimates are successively compared to surface to rock outcrop amplification spectra and are evaluated by deconvolution of the downhole records based on the inversion results comparison of the observed ssr and estimated surface to rock outcrop amplification spectra illustrates the effects of destructive interference of downgoing waves at the downhole instrument level as a function of the site class site amplification factors are successively computed in reference to the national earthquake hazards reduction program nehrp b c boundary site conditions v s30 760 m sec and results are compared to published values developed on the basis of strong motion data and site response analyses finally weak motion ssr estimates are compared to the mainshock spectra and conclusions are drawn for the implications of soil nonlinearity in the near surface results presented in this article suggest that currently employed site classification criteria need to be reevaluated to ensure intraclass consistency in the assessment of amplification potentials and nonlinearity susceptibility of near surficial soil formations

defining the geochemical composition of the epica dome c ice core dust during the last glacial interglacial cycle the major element composition of the insoluble windborne long range dust archived in the european project for ice coring in antarctica dome c ice core has been determined by particle induced x ray emission analyses the geochemistry of dust from the last glacial maximum lgm and from the holocene is discussed in terms of past environmental changes throughout the last climatic cycle antarctic dust from glacial and interglacial climate clearly reveals different geochemical compositions the weathered crustal like signature of lgm dust is characterized by a low compositional variability suggesting a dominant source under the glacial regime the close correspondence between the major element composition of antarctic glacial dust and the composition of southern south american sediments supports the hypothesis of a dominant role of this area as major dust supplier during cold conditions conversely the major element composition of holocene dust displays high variability and high al content on average this implies that an additional source could also play some role comparison with size selected sediments suggests that a contribution from australia is likely during warm times when a reduced glacial erosion decreases the primary dust production and a more intense hydrological cycle and larger vegetation cover inactivates dust mobility in a large part of southern south america weakening its contribution as a massive dust supplier to antarctica

dust provenance in antarctic ice during glacial periods from where in southern south america 1 the origin of dust deposited in east antarctica is not fully understood yet this study demonstrates that contrary to nd sr isotopes are strongly fractionated in the finest sized material representing potential dust sources in south america analysis of nd isotopes suggests that argentine loess southern ocean sediments and antarctic dust may all have a related origin or can represent comparable mechanisms of eolian sediment transport and deposition this analysis also concludes that the patagonian signature can explain a high proportion of the isotopic composition of dust trapped in antarctic ice during glacial periods the puna altiplano plateau emerges as the second possible important sediment contributor explaining the crustal like signature found in east antarctic dust and should be considered as a potential source area when quaternary paleoclimate is reconstructed from argentine loess antarctic dust and south atlantic sediment records

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

unexpected values of qs in the unconsolidated sediments of the mississippi embayment we studied the attenuation of shear waves at three sites in the mississippi embayment using data recorded in boreholes drilled to depths of up to 60 m the source was a highly repeatable compressed air driven hammer to estimate attenuation we used a spectral ratio technique for fixed depth and variable frequency the best fit line for each depth z gives a measure of the cumulative attenuation indicated by z then we fit a straight line to z for a range of values of z the slope of this line gives an estimate of the average attenuation per distance and was used to determine an average q s for one of the sites newport northeastern arkansas q s ranges between 34 1 5 m z 44 2 m and 44 1 5 m z 51 8 m these values are significantly higher than the more typical value of about 10 determined for unconsolidated sediments by other authors in addition these high values correspond to sediments with low average shear wave velocity about 300 m sec in contrast average q s and velocity for sediments in shelby forest near memphis tennessee are 22 and 348 m sec 22 6 m z 60 1 m respectively therefore these results go against the conventional wisdom that low velocity implies low q for the third site marked tree northeastern arkansas average q s and velocity are 18 and 251 m sec 9 8 m z 33 6 m respectively this site is about 75 km from newport and the differences in attenuation appear related to differences in lithology manuscript received 5 april 2001

bulk sediment qp and qs in the mississippi embayment central united states we have estimated p wave ands wave anelastic attenuation coefficients for the thick unconsolidated sediments of the mississippi embayment central united states using the spectral distance decay of explosion p and rayleigh waves the sediment trapped p wave psed is observed to ranges of 80 km at 10 hz and 1 hz rayleigh waves are observed out to 130 km from a 5000 lb borehole explosion in the northern part of the embayment rayleigh waves of 4 hz are seen to distances of 3 km from a smaller 50 lb explosion analysis of the group velocity and amplitude distance decay of both waves yields an average qs of 100 and qp of 200 for embay ment sediments that are independent of frequency scatter in the q estimates comes from interference of multiple p wave reverberations and rayleigh wave modes the attenuation model is self consistent in that it is the same as obtained by the analysis of synthetic seismograms using the inferred q values inferred qp and qs values are more than three times higher than previous estimates and imply that unconsolidated sediments of the embayment do not significantly attenuate small strain earthquake ground motions these estimates represent a lower bound to q of the sediments since significant scattering is observed in the waveform data that contributes to the distance decay of wave amplitude higher q values also imply that the unconsolidated sedi ments of the embayment will form an efficient wave guide for surface waves radiated from shallow earthquakes or large earthquakes that rupture into the sediments pro ducing high amplitude long duration wave trains that should be considered in earth quake hazard assessments

isotopic constraints on the source of argentinian loess with implications for atmospheric circulation and the provenance of antarctic dust during recent glacial maxima we present rare earth element ree and sr nd isotopic data for argentinian loess 28 38 s with two aims 1 to examine the source regions of argentinian loess and the constraints that these put on palaeo wind directions 2 to further investigate the source of antarctic ice core dust and to test the hypothesis that some of it could be derived from a region to the north of patagonia into which the dry dusty westerly dominated patagonian climate expanded during quaternary glacial maxima sr nd isotopic data for argentinian loess from north of 37 s are distinct from patagonian loess compositions in that they have more radiogenic sr 87sr 86sr 0 7059 0 7123 and less radiogenic nd nd 0 8 to 6 4 ree patterns and sr nd isotopic values are relatively homogeneous for multiple samples taken from single loess sections but show significant differences between sections in general there is a northward change from patagonia like ree patterns and isotopic values away from volcanogenic signatures and towards those that are more like the continental crust the latitudinal nd isotopic pattern is remarkably similar to that for andean volcanic rocks and suggests derivation of loess from the andes by more or less direct westerly transport for loess sections in the north the data imply a contribution from palaeozoic gneisses to the northwest in the chilean altiplano sr nd data for extra patagonian argentinian loess north of 37 s do not support a significant role for this source region in supplying dust to antarctica at the last glacial maximum this conclusion contrasts with previous studies that suggest a significant northward shift in the climatic belts and in particular the westerlies and the antarctic polar front during quaternary glacial maxima very systematic relations between the sr nd isotopic composition of loess and their andean source highlights shifts in the sr isotopic composition of loess to more radiogenic values and strongly suggests that the slight offset between patagonian loess and ice core dust identified by previous workers is due to grain size differentiation effects

a uniform isotopic and chemical signature of dust exported from patagonia rock sources and occurrence in southern environments patagonia is considered to be the most important source of dust from south america that is deposited in surrounding areas and we present here a systematic sr and nd isotopic study of sediment currently being exported eolian and suspended riverine sediments from patagonia have a homogeneous chemical and isotopic composition that results from the mixing of by products from explosive andean volcanism derived from the extensive jurassic silicic province of chon aike and pyroclastic materials from the basic to intermediate southern andean quaternary arc which are easily denudated and dispersed the main andean uplift and the glaciations that began in the late tertiary account for the extensive distribution of these sediments in the extra andean region the present geochemical signature of patagonian sediments was produced during the pleistocene along with the onset of the southern andean explosive arc volcanism previously published compositions of sediments from other southern south american source regions assumed to be representative of patagonia are distinct from our data considering the alleged importance of patagonia as a dust source for different depositional environments in southern latitudes it is surprising to verify that the chemical and isotopic signatures of patagonian sourced sediments are different from those of sediments from the southern ocean the pampean region or the antarctic ice sediments from these areas have a crustal like geochemical signature reflecting a mixed origin with sediment from other southern south american sources whereas patagonian sediments likely represent the basic to intermediate end member composition

antarctic dome c ice core dust at 18 k y b p isotopic constraints on origins we have determined the source area from which dusts from the last glacial maximum lgm section of the dome c ice core were derived by comparing their strontium and neodymium isotopic ratios with those of samples from potential source areas the87sr 86sr and143nd 144nd isotope ratios of the dusts deposited 18 k y b p at the east antarctic dome c site were compared with potential antarctic australian southern african and south american sources the isotope ratios clearly define the patagonian provenance of the dust with the other potential source areas being at most minor contributors contributions by volcanic ash and tephra to the dust sample were also determined to be minimal based on the patterns of rare earth elements knowing the source of the dusts places constraints on the aeolian trajectory by which it was transported to antarctica and this serves as a test of the simulation of southern hemispheric circulation by atmospheric global circulation models during the lgm

the nature distribution and formation of pans in arid zones abstract pans closed depressions are a widespread feature of many of the world s drylands by using literature survey air photographs topographic maps orbital photographs and imagery combined with field work it is possible to describe the major areas where these features occur their distribution is controlled to a great extent by the availability of susceptible surfaces they also develop in certain particular environmental settings palaeolacustrine basins palaeodrainages interdunes and on coastal plains many of the pans have a distinctive morphology while on their lee sides they may have lunette dunes many processes combine to create and maintain pans and these can be considered in a general model which has certain key elements the first of these is that the area should not be one where fluvial processes are fully integrated it should also not be one where aeolian accumulation is such as to infill any irregularities in the land s surface if these two predisposing conditions are fulfilled then under dryland conditions if susceptible surfaces are present there are various circumstances that may lead to hollow development and enlargement although in some cases such processes as solution suffosion and animal activities may play a role we believe that the predominant reason why pans have the characteristics that they do including their shapes lunettes alignments etc is that they result from the operation of the twin processes of salt weathering and aeolian deflation

generation of a crust mantle magma mixture magma sources and contamination at cerro panizos central andes cerro panizos a large caldera in the central andes mountains produced two large dacitic ignimbrites at 7 9 ma and 6 7 ma and many andesitic and dacitic lava flows and domes the older rhyodacitic cienago ignimbrite represents the most silicic magma erupted by the system the younger much larger volume dacitic cerro panizos ignimbrite is very crystal rich containing up to 50 biotite plagioclase and quartz crystals in the pumice it is weakly zoned with most of the zoning apparent between two main cooling units major and most trace elements show little variation through the cerro panizos ignimbrite but the small range of composition is consistent with typical fractionation trends sr nd and pb isotopic ratios are very crustal with initial 87sr 86sr values of 0 711 to 0 715 nd values of 7 5 to 10 2 and nearly invariant pb isotopic ratios 206pb 204pb 18 85 207pb 204pb 15 67 and 208pb 204pb 38 80 the limited zonation observed in the cerro panizos ignimbrite is explained by impeded crystal settling due to high crystal content the magma body was a crystal liquid mush before ascent to the pre eruption crustal levels crystals formed but did not separate easily from the magma limited fractionation of plagioclase and biotite may have occurred but the composition was largely controlled by lower crustal mash processes afc modeling shows that the cerro panizos magmas resulted from a mixture of roughly equal proportions of late miocene mantle derived basalts and melts from 1 0 ga grenville age lower crust this occurred in a mash zone in the lower crust and set the crustal isotopic ratios observed in the cerro panizos magmas the great thickening of the crust beneath the central andes mountains sent upper and middle crustal rock types to lower crustal and deeper depths and this explains the upper crustal isotopic signatures of the cerro panizos rocks minor upper crustal assimilation of early miocene volcanic or subvolcanic rocks produced much of the isotopic variation seen in the system the nearly invariant high pb isotopic values and high pb concentrations indicate that pb came almost entirely from the crustal source and was little altered by any subsequent upper crustal assimilation this pb signature is isotopically similar to that of the southern bolivian tin belt suggesting a widely distributed pb source the great difference between compositions of miocene and quaternary central andean volcanic rocks is explained by crustal thickening in early miocene time leading to abundant lower crustal water and associated fluxed melting during the time of the earlier eruptions the lower crust dried out considerably by quaternary time so less crustal component is present

thunder induced ground motions 2 site characterization 1 thunder induced ground motion near surface refraction and rayleigh wave dispersion measurements were used to constrain near surface velocity structure at an unconsolidated sediment site we employed near surface seismic refraction measurements to first define ranges for site structure parameters air coupled and hammer generated rayleigh wave dispersion curves were used to further constrain the site structure by a grid search technique the acoustic to seismic coupling is modeled as an incident plane p wave in a fluid half space impinging into a solid layered half space we found that the infrasound induced ground motions constrained substrate velocities and the average thickness and velocities of the near surface layer the addition of higher frequency near surface rayleigh waves produced tighter constraints on the near surface velocities this suggests that natural or controlled airborne pressure sources can be used to investigate the near surface site structures for earthquake shaking hazard studies

coherent composition of glacial dust on opposite sides of the east antarctic plateau inferred from the deep epica ice cores 1 the dust provenance identification through isotopic and geochemical tracers focused mostly on ice cores drilled in the pacific indian sector of antarctica where a common provenance of dust from southern south america during glacial ages was demonstrated conversely in other areas of the east antarctic plateau as dronning maud land provenance was deduced indirectly from back trajectory analyses and soluble chemistry records in this work we present the first comparison of major elemental composition of dust archived in two ice cores from opposite sides of antarctica in the framework of the epica project mineral particles extracted from the edc and edml cores date back to glacial mis 2 4 and 6 over the last 200 kyr results reveal a coherent geochemical dust composition at both locations providing experimental evidence of a common provenance over the wide area of east antarctica during glacials and key analytical constrains for atmospheric general circulation models

determination of shallow shear wave attenuation in the mississippi embayment using vertical seismic profiling data abstract we used vertical seismic profiling vsp data collected in four shallow boreholes about 40 to 60 m deep to study the shear wave attenuation in the mississippi embayment in southwestern tennessee the source was an air powered hammer that produces repeatable sh waves that were recorded by monitor geophones deployed on the surface very close to the source the spectral ratio method was used to estimate the shear wave quality factor q s the method assumes that the amplitudes of the seismic waves decay exponentially in the frequency domain the spectral ratio was computed using a vsp trace at a certain depth and the corresponding monitor trace using the source monitor trace as reference eliminates possible artifacts that may be introduced by changes in the source ground coupling the slope of a least square line fitted to the logarithm of the spectral ratio versus frequency gives the attenuation coefficient z for that depth then a straight line is fitted to z as a function of z and the slope of this line is used to estimate an average value of q s for the four sites shelby farms covington brownsville and jackson the q s values are 25 3 2 6 18 6 3 4 18 4 7 6 and 16 4 2 6 respectively to assess the reliability of these results synthetic vsp data were generated from the first cycles of the monitor traces recorded in the four sites and these q s values except for brownsville good matches with correlation coefficients equal to 96 99 were obtained between the synthetic vsps and the actual vsps indicating that the q s values we obtained are reliable in addition these values are also consistent with recent results obtained by others using seismic data generated by small earthquakes recorded by the japanese strong motion network kiban kyoshin kik net

patagonian origin of glacial dust deposited in east antarctica vostok and dome c during glacial stages 2 4 and 6 abstract the source area of continental dust deposited at both vostok and dome c sites east antarctica during the glacial stages stage 2 18 ka last glacial maximum stage 4 60 ka and stage 6 160 ka of the last two climatic cycles has remained constant the isotopic composition 87 sr 86 sr and 143 nd 144 nd of the ice core dust has been compared with the isotopic composition of the potential source areas antarctica new zealand southern africa australia and south america this comparison reveals the southern south american provenance of the dust for all three glacial periods as has already been shown for the lgm 1 we show that the patagonian loess and the marine shelf sediments from the argentine continental shelf which was variably emerged during glacial periods display different isotopic compositions and that the composition of the patagonian loess best matches the signature of the ice core dust the identification of the patagonian region as the source of the windblown dust deposited over east antarctica during all the latest glacial periods permits a better understanding of paleo atmospheric circulations of the last climatic cycles and a better constraint on the parametrization of dust sources for paleoatmospheric general circulation models

a new look at stable isotope thermometry interdiffusion between coexisting minerals affects all rocks and causes resetting and discordance of stable isotope geothermometers that is commonly observed in slowly cooled igneous and metamorphic rocks the fast grain boundary fgb model describes the stable isotope fractionations and intracrystalline zonation which result from closed system interdiffusion eiler et al 1991 1992 this model assumes that grain boundary diffusion is much faster than volume diffusion and it accounts for exchange among all minerals in a rock previous models of closure temperature violate mass balance restrictions and will be inaccurate in most rocks modeling results are described for amphibolites and hornblende granites and gneisses biotite granites schists and gneisses pelitic and semi pelitic rocks garnet peridotites anorthosites gabbros pyroxenites and related rocks and calc silicate rocks examples of mineral pairs and specific rock types that allow accurate stable isotope thermometry include plagioclase pyroxene in pyroxene bearing anorthosites and garnet quartz in garnetiferous quartzites in contrast the same mineral pairs in related rocks such as pyroxenites and pelitic schists will exhibit reset apparent temperatures closed system processes are capable of producing a variety of patterns of stable isotope resetting discordance mineral zonation and fractionation reversals examples include large reversals of quartz feldspar fractionations in micaceous rocks and oscillatory zonation in feldspar from some quartz rich rocks these results permit reinterpretation of many studies of stable isotope thermometry speedometry and retrograde alteration history fgb modeling of mineral zonation provides an important new guide to applying recently developed micro analytical tools to slowly cooled rocks application of the fgb model to quartzo feldspathic gneisses from the adirondack mountains new york demonstrates the usefulness of diffusion modeling in discriminating closed system diffusion controlled retrogression from open system retrogression and illustrates the possible importance of incorporating the effect of water activity on mineral diffusivity

dust size evidence for opposite regional atmospheric circulation changes over east antarctica during the last climatic transition three east antarctic ice cores dome b epica dome c and komsomolskaia give evidence for a uniform dust input to the polar plateau during the last glacial maximum lgm holocene transition 20 to 10 kyr bp and the 87sr 86sr versus 143nd 144nd isotopic signature of the mineral particles highlights a common provenance from southern south america at that time however the size distribution of dust from the three ice cores highlights important differences within the east antarctic during the lgm and shows clearly opposite regional trends during the climatic transition between dome b and dome c the timing of these changes is also different a geographical diversity also arises from the different phasing of the short term multi secular scale dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes we hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway either in terms of horizontal trajectory or in altitude of transport such mechanism is supported also by the dust size changes observed during a volcanic event recorded in vostok ice ice core dust size data suggest preferential upper air subsidence over the edc kms region and easier penetration of relatively lower air masses to the db area during the lgm at the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward the scenario proposed supported also by the lgm holocene regional changes of snow accumulation likely operates even at sub millennial time scale

loess of southern south america abstract loess and loessoid loess like reworked loess sediments extend across the chaco pampean plains and the nw mountain environments of argentina and in neighbouring countries paraguay brazil uruguay bolivia loessoid sediments are much more abundant than primary loess the beginning of the loessoid sedimentation cycle was related to a phase of late miocene orogeny in the andes the plio pleistocene record is mostly composed of loessoid sediments modified by pedogenesis which produced welded palaeosols the late pleistocene holocene loess record reveals a heterogeneous composition across the region coarse textures and an andean derived volcanic composition prevail in the southern pampas finer textures and material coming from the andes and the other two sources sierras pampeanas and the parana basin characterize the loess deposits of the northern pampas and the eastern chaco a southern patagonian source is also suggested for the mountain valley loess of tucuman although a western andean provenance has been proposed it is believed that the material in the western chaco was derived from the bolivian andes loess deposition was related to a multistage transport mechanism involving fluvial and aeolian processes inferred westerly and southwesterly wind directions as dominant carriers of the aeolian deposits are in agreement with westerly palaeowind simulations using climate models however the role played by westerly tropospheric winds and northerly winds remains to be established

micro investigation of epica dome c bottom ice evidence of long term in situ processes involving acid salt interactions mineral dust and organic matter abstract the epica dome c ice core edc reached a final depth of 3260 m at a maximum height of about 15 m above the ice bedrock interface in december 2004 we present here data gained from a detailed investigation of selected samples of the deeper part of the core located below 3200 m and referred to as bottom ice this part of the core has been poorly investigated so far mainly because there are significant challenges in interpreting paleo records that were very likely modified by long term in situ processes our study combines high resolution ion chromatography high resolution synchrotron x ray micro fluorescence micro xrf scanning and transmission electron microscopy our aim was to identify the long term physico chemical processes at work close to the bedrock to determine how they have altered the initial registers and ultimately to extract information on the very ancient antarctic environment the ubiquitous presence of nanometer iron oxide crystals at the surface of wind borne dust aggregates containing also large amount of organic matter raises the possibility that the consolidation of windborne dust clusters formed during ice recrystallization could be related to microbial iron reduction and thus to the progressive reactivation of dormant bacterial activity in warming ice inclusions of size and number density increasing with depth observed in the 12 last meters 3248 3260 m contain liquid and solid species among them marine biogenic acids numerous wind borne dust aggregates and clusters of large reversible calcium carbonate particles precipitated once the inclusion was formed and often covered by secondary gypsum the refreezing of slush lenses is discussed as a potential cause of the formation of such heterogeneous and complex mixtures in addition to the very fine micrometer size minerals windborne from extra antarctic continental sources and often accreted in large aggregates single medium size particles a few to ca 20 m and among them organic debris are commonly encountered their size surface shape and mineralogy suggest that aerosol transport from antarctic ice free areas played a significant role at the time edc bottom ice was formed concentrations and concentration ratios of biogenic sulfur species also advocate for the strengthening of peri antarctic meteorological patterns that favor the inland penetration of disturbed flow carrying local material very large well preserved mineral particles several tens of micrometers in diameter and biotope relics in deeper ice close to 3260 m likely come from the sub glacial environment

extended east antarctic ice core tephrostratigraphy three new tephra layers have been identified and analysed in the deeper sections of the epica dome c edc and vostok ice record east antarctic plateau one from edc 358 ka old originated from an antarctic volcano and two from vostok 406 and 414 ka old respectively which are related to antarctic volcanoes and to southern andes and or antarctic peninsula centres respectively these layers represent the oldest tephra bearing events so far detected in deep polar ice cores and extend the regional tephrostratigraphic framework back to the fourth climatic cycle although differences between the drill sites are observed new and previously published tephra data from deep ice cores broadly confirm that the clockwise circum antarctic atmospheric circulation played a major role in the dispersal of volcanic dust onto the plateau while the last 220 ka core sections contain about a dozen visible tephra fall layers the ice representing the time interval from 220 ka back to 800 ka i e the edc core bottom is almost devoid of observed tephras although it is possible that the reduced frequency is an observational artefact the observed pattern could alternatively reflect late quaternary activity fluctuations of sources for tephra in the east antarctic plateau particularly south sandwich islands with enhanced explosive activity in the last two glacial cycles with respect to previous periods

upper mississippi embayment shallow seismic velocities measured in situ abstract vertical seismic compressional and shear wave p and s wave profiles were collected from three shallow boreholes in sediment of the upper mississippi embayment the site of the 60 m hole at shelby forest tennessee is on bluffs forming the eastern edge of the mississippi alluvial plain the bluffs are composed of pleistocene loess pliocene pleistocene alluvial clay and sand deposits and tertiary deltaic marine sediment the 36 m hole at marked tree arkansas and the 27 m hole at risco missouri are in holocene mississippi river floodplain sand silt and gravel deposits at each site impulsive p and s waves were generated by man made sources at the surface while a three component geophone was locked downhole at 0 91 m intervals consistent with their very similar geology the two floodplain locations have nearly identical s wave velocity vs profiles the lowest vs values are about 130 m s 1 and the highest values are about 300 m s 1 at these sites the shear wave velocity profile at shelby forest is very similar within the pleistocene loess 12 m thick in deeper older material vs exceeds 400 m s 1 at marked tree and at risco the compressional wave velocity vp values above the water table are as low as about 230 m s 1 and rise to about 1 9 km s 1 below the water table at shelby forest vp values in the unsaturated loess are as low as 302 m s 1 vp values below the water table are about 1 8 km s 1 for the two floodplain sites the vp vs ratio increases rapidly across the water table depth for the shelby forest site the largest increase in the vp vs ratio occurs at 20 m depth the boundary between the pliocene pleistocene clay and sand deposits and the eocene shallow marine clay and silt deposits until recently seismic velocity data for the embayment basin came from eartquake studies crustal scale seismic refraction and reflection profiles sonic logs and from analysis of dispersed earthquake surface waves since 1991 seismic data for shallow sediment obtained from reflection refraction crosshole and downhole techniques have been obtained for sites at the northern end of the embayment basin the present borehole data however are measured from sites representative of large areas in the mississippi embayment therefore they fill a gap in information needed for modeling the response of the embayment to destructive seismic shaking

provenance of dust to antarctica a lead isotopic perspective antarctic ice preserves an 800 kyr record of dust activity in the southern hemisphere major efforts have been dedicated to elucidate the origin of this material in order to gain greater insight into the atmospheric dust cycle on the basis of pb isotopes in antarctic dust samples and potential sources this contribution demonstrates for the first time that patagonia is the main contributor of dust to antarctica during interglacial periods as well as glacials although the potential importance of tierra del fuego remains unclear because of its geochemical similarities to patagonia an important new finding is that the puna altiplano sector of the continent is a second important dust source to eastern antarctica during both glacials and interglacials being more prominent during interglacials the data indicate south america is the primary dust source to antarctica during both glacials and interglacials

a 70 ka record of explosive eruptions from the taldice ice core talos dome east antarctic plateau the new antarctic taldice ice core 72 49 s 159 11 e 1620 m depth containing abundant primary tephras provides the opportunity to elucidate the late quaternary volcanic history of the south polar region as well as to broaden the east antarctic tephrostratigraphic framework here grain size and glass compositional data for representative tephra layers from the last 70 ka core section are used for source identification results point to origin of layers from centres of the melbourne volcanic province mcmurdo volcanic group located 250 km from the coring site occurrence of tephra layers within the ice core record suggests that explosive activity in the identified source was not constant over the considered period with a minimum of activity between 20 and 35 ka and increased activity back to 65 ka in addition to palaeovolcanic implications the taldice tephra layers offer prospects for firm correlations between diverse widely separated palaeoarchives and for accurate dating of the antarctic climatic record

seismic wave attenuation in volcanic rocks from vsp experiments seismic wave attenuation in the columbia plateau basalts and snake river plain volcanics was analyzed using vertical seismic profiling vsp data the computation of attenuation coefficients is based on fitting a straight line to the logarithm of amplitude ratios computed for fixed values of frequency and variable depth this approach does not require any assumptions on the dependence of q on frequency for the columbia plateau basalts the attenuation coefficients obtained from the field data are smaller than those computed from the synthetic vsp generated using the sonic and density logs indicating that the observed attenuation is related to scattering effects and is substantially larger than the intrinsic attenuation of basalt therefore it is concluded that only a lower bound for q can be established in agreement with recent findings by other authors the effective attenuation of seismic energy in basalts about 1 1 10 4dbs m for the peak frequency is comparable to the effective attenuation observ

comparing the epica and vostok dust records during the last 220 000 years stratigraphical correlation and provenance in glacial periods a new aeolian dust record from the first 2200 m of the epica dome c ice core 75 06 s 123 21 e covering about 220 000 years of climatic history is compared to the vostok 78 28 s 106 48 e ice core nature 399 1999 429 the two dust profiles are very similar and several common dust events allow to establish stratigraphical links the late quaternary period is characterized at both sites and likely overall east antarctic plateau by high dust input during glacial periods in the epica dome c ice core the dust flux rises by a factor of 25 20 and 12 in glacial stages 2 4 and 6 with respect to interglacial periods holocene and stage 5 5 the magnitude and pattern of changes are comparable in the vostok ice core in this study the geographical origin of ice core dust icd in cold periods has been investigated at both sites through 87sr 86sr versus 143nd 144nd isotopic tracers following the previous studies of grousset et al earth planet sci lett 111 1992 175 and basile et al earth planet sci lett 146 1997 573 the new data and the existing ones allow to define the isotopic fields for dust at the two antarctic sites that are almost identical and restricted into the 0 708 87sr 86sr 0 711 and 5 end 0 5 ranges this suggests a common geographical provenance for dust at vostok and dome c and for all the glacial periods of the late pleistocene to decipher the icd provenance more than 50 samples of loess and aeolian deposits sands and fluvioglacial sediments from the potential source areas psas of the southern hemisphere have been collected however the methodology has been refined with respect to former studies first the isotopic fractionation that can occur in function of grain size has been taken into account and the psa s signature has been defined in the 5 m size range within which fine grained dust reaching antarctica is found moreover a possible contribution from carbonates on the samples from psas has also been also considered south africa and australia can be excluded as dominant sources but a partial overlap arises among southern south america new zealand and the antarctic dry valleys isotopic fields these latter two documented for the first time a possible contribution from all these three sources cannot be excluded but complementary arguments suggest the dominant contribution to east antarctic dust in glacial times deriving from the southern south american region of patagonia and the pampas this study shows a first order uniformity in the dust flux and geographical provenance to the east antarctica plateau during glacial periods

identification of multiple natural and anthropogenic sources of dust in snow from zhongshan station to dome a east antarctica the stable oxygen isotope composition major ions and isotopic compositions of strontium sr neodymium nd and lead pb in insoluble dust from recent surface snow samples along the transect from the zhongshan and progress stations located on the amery ice shelf east antarctica to dome a summit antarctica were analysed no previous isotopic fingerprinting studies have been conducted for this transect these data were used to document the dust provenances in antarctica along the transect up to the highest site dome a for the first time the insoluble dust in snow samples along the coast displays an overall crust line isotopic signature that is characterised by highly radiogenic 87 sr 86 sr values and less radiogenic 143 nd 144 nd values these signatures are comparable with those of samples collected near the ice free areas of the zhongshan and progress stations spatial differences are statistically significant along the transect and the sr nd and pb isotope components in insoluble dust from two continuous snow samples at dome a exhibit marked differences indicating that additional dust reaches the east antarctic plateau the isotopic characteristics of insoluble dust from this transect indicate that the long distance natural dust and anthropogenic pollutants in these samples primarily originate from australia

damping values derived from surface source downhole receiver measurements at 22 sites in the san francisco bay area of central california and the san fernando valley of southern california

continuous record of microparticle concentration and size distribution in the central greenland ngrip ice core during the last glacial period 1 a novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the ngrip ice core covering continuously the period approximately from 9 5 100 kyr before present measurements were at 1 65 m depth resolution corresponding to approximately 35 200 yr particle concentration increased by a factor of 100 in the last glacial maximum lgm compared to the preboreal and sharp variations of concentration occurred synchronously with rapid changes in the 18o temperature proxy the lognormal mode of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods we find 1 7 m diameter during lgm and 1 3 m during the preboreal on timescales below several 100 years and the particle concentration exhibit a certain degree of independence present especially during warm periods when generally is more variable using highly simplifying considerations for atmospheric transport and deposition of particles we infer that 1 the observed changes of in the ice largely reflect changes in the size of airborne particles above the ice sheet and 2 changes of are indicative of changes in long range atmospheric transport time from the observed size changes we estimate shorter transit times by roughly 25 during lgm compared to the preboreal the associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude

atmospheric decadal variability from high resolution dome c ice core records of aerosol constituents beyond the last interglacial along the epica dome c ice core we measured concentrations of different water soluble aerosol constituents and deduced total depositional flux records here we present high resolution sodium calcium ammonium and nitrate data covering the last 173 000 years the first three of these species are passive tracers and reveal source and long range transport changes whereas nitrate is deposited reversibly however it can be used to check isotope derived accumulation rate estimates a prerequisite to calculate total depositional fluxes during the last two transitions from glacial to interglacial periods changes in the total depositional flux differ strongly for different aerosol species the largest changes are observed in the terrestrial aerosol proxy non sea salt calcium only moderate changes occur in the marine sea salt indicator sodium while ammonium a proxy for marine bioproductivity remains rather constant in agreement with previous studies we find that only considerable glacial interglacial changes at both the terrestrial and the marine sea salt aerosol source can explain the observed pronounced changes the unprecedented high resolution of our data allows for the first time the examination of decadal variability back to the penultimate glacial period on the one hand we find occasional fast shifts occurring within a few years here we present such an event in the calcium record from the penultimate glacial period on the other hand we examine variation coefficients and pairwise correlation coefficients both determined in 200 year windows they generally reveal only moderate changes during glacial periods slightly lower variation coefficients are found concurrent with slightly higher correlation coefficients which points to a more uniform and stronger coupled atmospheric long range transport of the different aerosol species to the east antarctic plateau and less influence of cyclonic activities during cold periods the opposite is observed for interglacial periods with probably even reinforced importance of cyclonic influences during the last interglacial period the marine isotope stage 5 5 this period reveals no evidence for abrupt climatic changes in any of the species however the marine sea salt aerosol indicator sodium shows a distinct minimum followed by a pronounced increase this pattern is explained by significantly reduced sea ice production in the indian southern ocean sector which is believed to be the dominant source of sodium deposited in dome c during warm periods

determination of shallow shear wave velocity at mississippi embayment sites using vertical seismic profiling data we used vertical seismic profiling vsp data collected in shallow bore holes about 40 60 m deep to determine the shear wave velocity at four sites in the mississippi embayment in southwestern tennessee the source was an air powered hammer that produces repeatable sh waves which were recorded by source monitor geophones deployed on the surface very close to the source three approaches were used to determine interval velocities an approximate zero offset method a layer stripping method and a waveform matching method the first two methods use arrival time picks whereas the latter is based on the fit of synthetic vsp data to the first half cycle approximately of each trace the advantage of this method over the other two is that it uses a segment of the data rather than a single data point there fore the velocities determined using the waveform matching method are better con strained and are not affected by picking errors which may translate into significant spurious velocity variations the source wavelets recorded by one of the monitor geophones and the velocity model computed with the layer stripping method were used to generate synthetic vertical seismic profiling data for comparison with the actual data then the model velocities were modified interactively one layer at a time until a satisfactory match was achieved this required including attenuation in the computation of the synthetic data the four sites investigated in this study can be divided into two groups low velocity sites shelby farms and covington and high velocity sites brownsville and jackson these last two sites are at larger dis tances from the embayment axis than the other two which means that the difference in velocities probably corresponds to the presence of different geologic units good agreements between the lithology in the boreholes and the velocity profiles were obtained for all the four sites

aeolian dust in the talos dome ice core east antarctica pacific ross sea sector victoria land versus remote sources over the last two climate cycles a new ice core taldice drilled at talos dome east antarctica ross sea sector preserves a ca 250 ka long record of palaeoclimate and atmospheric history we investigate dust variability and provenance at the site during glacial periods and the holocene through the sr nd isotopic composition of ice core dust and potential source areas psa we provide new isotopic data on dust sources from victoria land such as regoliths glacial drifts aeolian sands and beach deposits some of these sources are located at high altitude and are known to have been ice free throughout the pleistocene the major features of the taldice dust record are very similar to those from central east antarctica during glacial times south america was the dominant dust supplier for talos dome as well as for the entire east antarctic plateau conversely during the holocene the principal input of mineral dust at talos dome probably derives from proximal sources which are the ice free areas of northern victoria land located at similar altitude with respect to the drilling site atmospheric mobilisation of dust from these neighbouring areas and transport inland to talos dome can be ultimately associated with advection of maritime air masses from the pacific ross sea region copyright 2010 john wiley sons ltd supporting information can be found in the online version of this article

ground satellite observations and atmospheric modeling of dust storms originating in the high puna altiplano deserts south america implications for the interpretation of paleo climatic archives 1 this study provides a detailed description of the sources transport dispersion and deposition of two major dust events originating from the high altitude subtropical puna altiplano plateau 15 26 s 65 69 w in south america a long and severe drought provided the right conditions for the onset of both events in july 2009 and 2010 dust was transported se and deposited over the pampas region and was observed to continue to the atlantic ocean dust monitoring stations located downwind recorded both events and samples were characterized through chemical and textural analysis through a combination of meteorological data and satellite observations calipso and modis detectors we estimate the emission flux for the 2010 event this estimate was used to constrain the hybrid single particle lagrangian integrated trajectory hysplit transport model and simulate the dust event both satellite imagery and model results agree in the location and extension of the dust cloud calipso detected dust between 6000 and 8500 m a s l which remained at this height during most of its trajectory the dust cloud mixed with a strong convective system in the region and the associated precipitation brought down significant amounts of dust to the ground dust particle size analysis for both events indicates that near the sources dust samples show median modes of 12 4 14 1 m similar to modes observed 1300 km away chemical composition of sediments from potential dust sources shows distinct signatures within the puna altiplano plateau the puna sector being clearly different from the altiplano area in addition both sources are markedly different from the patagonian chemical fingerprint these results have important implications to improve the interpretation of paleo environmental archives preserved on the argentine loess antarctic ice cores and southern ocean marine sediments

influence of patagonian glaciers on antarctic dust deposition during the last glacial period dust deposition over antarctica was much higher during the last glacial period but the causes of this flux remain unclear an analysis of the composition and age of glacial outwash sediments indicates that growth and decay of glaciers in patagonia may have influenced dust transport to antarctica at that time

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

vertical seismic profiling vertical seismic profiling is one of the rapidly developing areas of geophysical technology for exploring in mature basins the measurement basically involves recording the total upgoing and downgoing seismic wave fields propagating through a stratigraphic section by means of geophones clamped to the wall of a drilled well

geographic provenance of aeolian dust in east antarctica during pleistocene glaciations preliminary results from talos dome and comparison with east antarctic and new andean ice core data abstract the strontium and neodymium isotopic signature of aeolian mineral particles archived in polar ice cores provides constraints on the geographic provenance of dust and paleo atmospheric circulation patterns data from different ice cores drilled in the centre of the east antarctic plateau such as epica dome c edc 75 06 s 123 21 e and vostok 78 28 s 106 48 e suggested a uniform geographic provenance for dust during pleistocene glacial ages likely from southern south america ssa in this work the existing dust isotopic data from edc have been integrated with new data from marine isotopic stage mis 14 about 536 ka before 1950ad and in parallel some first results are shown for the new taldice ice core which was drilled on the edge of the east antarctic plateau talos dome 72 48 s 159 06 e on the opposite side with respect to ssa interestingly the isotopic composition of taldice glacial dust is remarkably similar to that obtained from glacial dust from sites located in the east antarctic interior overall the glacial dust isotopic field obtained from six east antarctic ice cores matches well south american data obtained from target areas in this respect it was recently suggested that dust exported long range from south america originates from patagonia and from the puna altiplano plateau to test this hypothesis we analysed the isotopic composition of dust from an ice core drilled on the illimani glacier bolivia 16 37 s 67 46 w 6350 m a s l in order to obtain information on the isotopic composition of regional mineral aerosol uplifted from the altiplano area and likely transported over a long distance altogether ice core and source data strongly suggest that the westerly circulation pattern allowed efficient transfer of dust from south america to the east antarctic plateau under cold quaternary climates isotopic data support the hypothesis of a possible mixing of dust from patagonia and from the puna altiplano plateau interestingly high glacial dust inputs to antarctica are characterized by less radiogenic nd values an issue suggesting that enhanced dust production in patagonia was associated with the activation of a secondary source still patagonia was the most important supplier for dust to central east antarctica during quaternary glaciations

u pb zircon geochronology of the adirondack mountains and implications for their geologic evolution u pb zircon studies of metamorphosed igneous rocks in the adirondack mountains have yielded preliminary ages within the range 1420 990 ma several geochronologically and geochemically distinct episodes of igneous intrusion and at least one pre granulite facies dynamothermal metamorphic event are documented this information is consistent with recent field and geochronological studies throughout the grenville province and suggests that a complex sequence of events occurred in the adirondack mountains prior to the widespread deformation and metamorphism commonly attributed to the approximately 1100 1000 ma ottawan phase of the grenvillian orogenic cycle