millennial scale fluctuations of the european ice sheet at the end of the last glacial and their potential impact on global climate abstract reconstructing northern hemisphere ice sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes to date research efforts have mainly focused on the north american laurentide ice sheets lis leaving the potential role of the european ice sheet eis and of the scandinavian ice sheet sis in particular largely unexplored using neodymium isotopes in detrital sediments deposited off the channel river we provide a continuous and well dated record for the evolution of the eis southern margin through the end of the last glacial period and during the deglaciation our results reveal that the evolution of eis margins was accompanied with substantial ice recession especially of the sis and simultaneous release of meltwater to the north atlantic these events occurred both in the course of the eis to its lgm position i e during heinrich stadial hs 3 and hs2 31 29 ka and 26 23 ka respectively and during the deglaciation i e at 22 ka 20 19 ka and from 18 2 0 2 to 16 7 0 2 ka that corresponds to the first part of hs1 the deglaciation was discontinuous in character and similar in timing to that of the southern lis margin with moderate ice sheet retreat from 22 5 0 2 ka in the baltic lowlands as soon as the northern summer insolation increase from 23 ka and an acceleration of the margin retreat thereafter from 20 ka importantly our results show that eis retreat events and release of meltwater to the north atlantic during the deglaciation coincide with amoc destabilisation and interhemispheric climate changes they thus suggest that the eis together with the lis could have played a critical role in the climatic reorganization that accompanied the last deglaciation finally our data suggest that meltwater discharges to the north atlantic produced by large scale recession of continental parts of northern hemisphere ice sheets during hs could have been a possible source for the oceanic perturbations i e amoc shutdown responsible for the marine based ice stream purge cycle or so called he s that punctuate the last glacial period

formation of large beaches in an area of rapid differential isostatic rebound the three outlet control of lake agassiz abstract shorelines in basins undergoing differential isostatic rebound do not remain geographically fixed for long periods and are either transgressive or regressive during regression a relatively uniform blanket of shoreface sediment may be deposited but unless regression is slow or punctuated by periods of lake level equilibrium large beaches do not form in contrast along transgressive shorelines which migrate upslope large morphostratigraphic features commonly are maintained along the lake s margin these may subsequently be stranded when lake level declines beaches around isostatically rebounding proglacial lakes are commonly considered to have formed during a period of lake regression punctuated by abrupt drops in lake level however in basins that are differentially rebounding large beaches cannot form this way and only periods of transgressing waters allow enough time for large beaches to form and define a continuous shoreline around the basin with this in mind some of the largest and most extensive beaches in the glacial lake agassiz basin the norcross tintah and upper campbell constructed between 10 4 and 9 4 ka 14 c yr bp are reinterpreted as strandlines that were formed by transgression each of these three transgressions followed lower lake phases and resulted from in sequence differential isostatic rebound of the eastern outlet rebound and ice damming of the northwestern outlet and rebound of the northwestern outlet each of these transgressions ended when lake level reached the southern outlet stranding the norcross tintah and upper campbell beaches about 10 2 9 9 and 9 4 ka 14 c yr bp respectively

spectral discrimination between nts explosions and western united states earthquakes at regional distances spectral ratio disciminants are applied to 72 western united states earthquakes and 64 nts explosions recorded at four broadband seismic stations surrounding nts the ratio of the energy in the 1 to 2 and 6 to 8 hz bands for pn pg and lg is calculated and a simple distance correction applied to the data the spectral ratio appears to have potential as a disciminant at relatively small magnitudes 3 0 4 5 to 5 0 this may be due to uncertainties in the apparent source time function for explosions these complications may be due to changes in the dynamic response of the material in the near source region as a function of overburden pressure effects of secondary sources or to variations in regional phase excitation with depth

source effects on regional seismic discriminant measurements source effects on high frequency regional seismic discriminant measurements involving p s type ratios pn lg pg lg are isolated for earthquakes in southern california and southern nevada the scatter in earthquake population discriminant measurements for fixed propagation paths is statistically analyzed to assess the spatial and frequency dependent contributions from source radiation pattern and source depth variations along with variable near source scattering this is useful because procedures for reducing the variance caused by propagation effects must be constrained by knowledge of the intrinsic scatter resulting from independent source effects for which corrections are not available without a priori knowledge of the source type and depth broadband waveforms for earthquakes near the nevada test site nts and in southern california recorded at stations of the livermore nts network lnn the caltech terrascope network and the berkeley digital seismic network bdsn are used to obtain pg lg and pn lg measurements and to assess source depth and mechanism contributions to measurement variance pn lg and pg lg spectral amplitude ratios for several frequency bands between 0 5 and 10 hz from vertical velocity waveforms are computed for a total of 18 tightly located clusters of earthquakes for each cluster we examine the correlations between observed pn lg and pg lg ratios and estimated source depths or predictions based on previously determined source mechanisms focal mechanism predictions do not match the observations well likely due to strong near source scattering and directivity effects that overwhelm the point source radiation pattern however the data do show significant scatter even for sources only a few kilometers apart source depth produces some coherent trends which can be emphasized by averaging results from multiple stations these trends vary from region to region presumably due to specific local crustal layering but most of the variance is not deterministically predictable and appears to arise from strong variations in near source scattering variance estimates for logarithmic amplitude ratios normalized by mean amplitude ratios vary from 0 01 to 0 05 for different phase pairs frequency dependent variations of the mean variance minimum and maximum amplitude ratio parameters show strong distance dependence out to about 300 km and then appear to become independent of event station distance these variance parameters appear to be suitable for use in spatial interpolations of observed p s type ratios for a specific unidentified event path as needed for nuclear test monitoring

improvements to regional explosion identification using attenuation models of the lithosphere 1 regional p s amplitudes have been recognized as an effective discriminant between earthquakes and explosions while closely spaced events generally discriminate easily the application of this technique to broad regions has been hampered by large variations in the amplitude of phases due to the attenuation of the crust and upper mantle making use of a recent p wave and s wave attenuation model of the lithosphere we have found that correcting the events using our amplitude methodology significantly reduces the scattering in the earthquake population we demonstrate an application of this technique to station nil using broad area earthquakes and the 1998 indian nuclear explosion using the pn lg discriminant in the 1 2 hz passband we find that the explosion which is lost in the scatter of the earthquakes in the uncorrected discriminant clearly separates by correcting for attenuation structure we see a similar reduction in scatter and separation for the pn sn and pg lg discriminants

proglacial lakes character behaviour and geological importance proglacial lakes are ubiquitous within the quaternary record and can provide exceptional breadth and depth of palaeoenvironmental information present deglaciation is increasing the number and size of proglacial lakes around the world this study provides a synthesis of knowledge on proglacial lake character and behaviour and critically evaluates the importance of proglacial lakes from a geological perspective we show how ice marginal or ice contact lakes and other distal proglacial lakes can be distinguished from each other by geomorphological sedimentological chemical and biological characteristics the key controls on proglacial lake geomorphology and sedimentology are outlined and discussed proglacial lakes can exacerbate mountain glacier and ice sheet margin ablation via mechanical and thermal stresses but very large lakes can moderate summer air temperatures and relatively retard summer ice ablation proglacial lakes interrupt meltwater flux and are very efficient sediment traps hydrological routing and consequent geomorphological activity can be radically modified by sudden drainage of proglacial lakes and resultant glacial lake outburst floods exceptionally large proglacial lake drainages affected global ocean circulation and global climate during the quaternary overall analyses of proglacial lakes can provide a valuable insight into i patterns character and behaviour of mountain glaciers ice sheets and glaciations and ii the impacts of past present and future deglaciation

late pleistocene evolution of the lower mississippi river valley southern missouri to arkansas the mississippi river served as the principal conduit for meltwaters discharging from the southern margins of north american ice sheets the northern half of the mississippi river alluvial valley in missouri and arkansas can be subdivided into two distinct channel courses the western and eastern lowlands which are separated by crowleys ridge the eastern lowlands contain two entry points the bell city oran and thebes gaps the latter is a narrow bedrock gorge that contains the modern river this paper summarizes a model for evolution of channel courses in the western and eastern lowlands during the illinoian and wisconsin glacial stages for the western lowlands stratigraphic relations between loess units and subjacent fluvial deposits show that major continuous terrace surfaces or valley trains are illinoian or late wisconsin in age investigations of tributary valley fills further show the western lowlands were deeply incised during the early to middle wisconsin stage then aggraded during the late wisconsin stage to such an extent that tributary valleys were backfilled with slackwater deposits moreover analysis of loess thinning and fining trends shows that early to middle wisconsin roxana silt and the late wisconsin peoria loess covers on western lowlands valley trains were derived from deflation of valley trains in the eastern lowlands we conclude that the western lowlands were the primary mississippi river course during illinoian deglaciation but were abandoned shortly thereafter then episodically reoccupied during the late wisconsin stage for the eastern lowlands course valley trains of early to middle wisconsin age are not preserved with the exception of a small remnant where the mississippi river broke through a gap in the southern margins of crowleys ridge and reentered the western lowlands all valley trains in the eastern lowlands are late wisconsin age a series of discontinuous terrace surfaces in the bell city oran gap represent dissected remnants of the primary late wisconsin full glacial and early late glacial course of the mississippi river or combined mississippi and ohio rivers whereas younger continuous braided stream surfaces in the bell city oran and thebes gap courses represent valley trains of latest wisconsin and earliest holocene age hence the bell city oran gap was the primary course during the entire wisconsin stage and the thebes gap was permanently occupied in earliest holocene time as much as 5 m difference in elevation between successive late wisconsin terrace surfaces of the eastern lowlands indicates that valley trains were rapidly constructed incised and abandoned in response to fluctuations in the delivery of meltwater and outwash from the former ice margin moreover a variety of data indicates that deglacial meltwater floods were commonly of sufficient magnitude to overflow from the primary course in the bell city oran gap throughout the late wisconsin substage floodwaters overflowed into the western lowlands constructed a series of secondary valley trains and filled tributary valleys with slackwater deposits during the latest wisconsin stage perhaps in association with the drainage of glacial lake agassiz floodwaters overflowed into the western lowlands and broke through the thebes gap the charleston fan represents the initial deposits of the thebes gap course following deposition of a large crevasse splay at the western lowlands entrance that course was no longer active but flow was routed through the thebes gap during periods of high magnitude flooding until the bell city oran gap was abandoned and the thebes gap course was permanently occupied during earliest holocene time

regional unconformities and the sedimentary architecture of the oak ridges moraine area southern ontario seismic stratigraphy geometry and sediment facies within the oak ridges moraine orm area of ontario record major structural elements and surfaces of the quaternary sedimentary sequence the derived stratigraphic architecture can be used to identify the key elements of a regional erosional surface represented by an unconformity in the subsurface and associated overlying channel sediments the erosional surface unconformity forms a distinct time datum in the quaternary sequence which provides an important aid to lithostratigraphic correlation the architecture also gives improved understanding of the effects of erosion on the late glacial landscape the surfaces of erosional drumlins and intervening troughs and the beds and banks of meltwater channels in the orm area define the regional unconformity highlighted by seismic profiles linked to continuously cored boreholes these features are attributed to regional scale subglacial meltwater flow events the sculpted surfaces which are analogous to water eroded forms the presence of boulder lags and coarse grained deposits on the regional erosional surface and the channels with undulating profiles provide the vital supporting evidence for a meltwater interpretation the inter regional extent of the unconformity is inferred from the coherence of regional paleoflows and the extent of drumlinized uplands tunnel channels and scoured bedrock terrain across 75 of the landscape from the orm area east and south to the finger lakes new york the implied magnitude of erosion suggests a pressing need for directed sedimentological study in those ocean basins that were probable depositional sites for flood deposits

analysis of high frequency pg lg ratios from nts explosions and western u s earthquakes the high frequency pg lg discriminant is studied between frequencies of 0 5 and 10 hz using 294 nts explosions and 114 western u s earthquakes recorded at four broadband seismic stations operated by lawrence livermore national laboratory the stations are located at distances of about 200 to 400 km from the nevada test site nts event magnitudes ranged from about 2 5 to 6 5 and propagation paths for the earthquakes range from approximately 175 to 1300 km the discriminant is shown to be very effective and displays improved separation between earthquakes and explosions as frequency is increased because of propagation effects it is important to apply distance corrections directly to the amplitude ratios or to the magnitude corrected amplitudes prior to computing the ratios multivariate discrimination analysis using both maximum likelihood gaussian classifiers and a backpropagation neural network show that approximately 95 of the events can be correctly identified both classification procedures were designed to handle missing data filled in using a nearest neighbor algorithm except for a few notable exceptions most of the earthquake misclassifications occur for mb 4 which is expected for events having reduced signal to noise ratios all of the explosion misclassifications occur for mb 4 suggesting a source or near source effect rather than an effect of poor signal to noise ratio the explosions that were misclassified were typically of magnitude large enough to be classified correctly by mb ms or love wave energy the main drawback of the pg lg discriminant is that because of signal to noise considerations and propagation effects the number of measurements are reduced considerably at higher frequencies it is expected that the problem will be amplified as magnitudes are reduced and event receiver distances are increased

landscape evolution alluvial architecture environmental history and the archaeological record of the upper mississippi river valley abstract the alluvial fill in the upper mississippi river valley umv is a palimpsest of past landscapes environments and physical evidence of human life ways the valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes including changes in channel pattern location of depocenters and sediment lithology remnants of late glacial braidplains that predate human presence in the upper midwest occur as sandy terraces and terrace fills a subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12 4 ka 10 500 14c yr b p a shift to net transport of sandy bedload and storage of fine grained overbank sediment on the floodplain accompanied the change to an island braided channel pattern at that time the holocene channel belt has been significantly narrower and the zone of sediment storage is reduced relative to that of the late glacial river major holocene depocenters include alluvial fans and colluvial slopes floodbasins natural levees and fluvial fans at the junction of large tributaries climate models and paleobotanical and isotopic studies indicate that shifts in large scale patterns of atmospheric circulation and moisture transport into the mid continent of north america induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude the delivery of sediment from tributary basins and the evolution of the umv landscape understanding the alluvial architecture of the valley and the temporal spatial distribution of biotic environments and processes that have buried mixed altered or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record

chronology of glacial lake agassiz meltwater routed to the gulf of mexico abstract sediment cores with new radiocarbon dates from the southern outlet of glacial lake agassiz indicate that meltwater delivery to the mississippi valley was disrupted at 10 800 14 c yr b p and the outlet was abandoned by 9400 14 c yr b p these findings confirm the timing of generally accepted terminations of the lockhart and emerson phases of lake agassiz additionally the radiocarbon chronology indicates that the spillway was fully formed by 10 800 14 c yr b p and that the occupancy in late emerson time was likely short lived with minimal spillway erosion

provenance of freshwater pulses in the gulf of mexico during the last deglaciation during the last deglaciation the decaying laurentide ice sheet lis delivered huge volumes of meltwater toward the gulf of mexico the present investigation of clay mineralogy and grain size characteristics of terrigenous sediments deposited in the orca basin gulf of mexico offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns five peculiar sedimentary levels characterized by high smectite content and low caco3 content were identified and occurred simultaneously with major meltwater floods according to recently published clay mineral distribution maps for north america these results help to pinpoint the southwestern margin of the lis as a main contributor to most of the meltwater discharges in addition the peculiar mineralogical composition illite and chlorite rich of the sediments characterizing the meltwater episode associated with heinrich event 1 suggests a provenance from the great lakes area supporting the interpretation of destabilization of the lis southeastern margin during this event decreased terrigenous contribution associated with changing provenance of sediments after 12 9 cal ka bp suggests strong modifications of the continental hydrography in relation to lake agassiz history and changes in the morphology of mississippi delta due to rising sea level

deglaciation and glacial erosion a joint control on magma productivity by continental unloading glacial interglacial cycles affect the processes through which water and rocks are redistributed across the earth s surface thereby linking the solid earth and climate dynamics regional and global scale studies suggest that continental lithospheric unloading due to ice melting during the transition to interglacials leads to increased continental magmatic volcanic and degassing activity such a climatic forcing on the melting of the earth s interior however has always been evaluated regardless of continental unloading by glacial erosion albeit the density of rock exceeds that of ice by approximately 3 times here we present and discuss numerical results involving synthetic but realistic topographies ice caps and glacial erosion rates suggesting that erosion may be as important as deglaciation in affecting continental unloading our study represents an additional step toward a more general understanding of the links between a changing climate glacial processes and the melting of the solid earth

discrimination of earthquakes and explosions in the eastern united states using regional high frequency data high frequency regional records from small earthquakes 1 3 magnitude 4 and comparable magnitude explosions are analyzed to find a reliable seismic discriminant in the eastern u s over 500 digital vertical component seismograms recorded by the new york state seismic network in the distance ranges 10 to 610 km are used mean p lg spectral ratios in the band 1 25 hz are about 0 5 and 1 25 for earthquakes and explosions respectively in the eastern united states we find that the high frequency p lg spectral amplitude ratio in the frequency band 5 25 hz is a reliable and robust discriminant for classifying these events a linear discriminant function analysis indicates that the p lg spectral amplitude ratio method provides discrimination power with a total misclassification probability of about 1 single hole instantaneous explosions and ripple fired quarry blasts have somewhat different p lg spectral ratios but as a group are distinctly different from earthquakes

using p s amplitude ratios for seismic discrimination at local distances we used a dense seismic network to test the p s amplitude ratio discriminant for earthquakes and explosions at distances from 20 to 200 km in a complex tectonic setting we used data from several hundred seismic stations in northern wyoming to observe 22 earthquakes 37 mining blasts and 24 borehole shots and compared their p s amplitude ratios frequencies of 6 8 hz and above achieved the best discrimination results for single shot borehole explosions whereas 6 8 and 8 10 hz passbands were best for mining blasts the p s method appears valid for 50 200 km but fails at distances 50 km geologic heterogeneities and path effects have a large effect on amplitude measurements even after magnitude and distance amplitude corrections are applied geologic boundaries between source and receiver that cause sharp lateral discontinuities in seismic velocity can alter the measured p s ratio to the point that an event could be misidentified the source geology is a factor as well with noticeable amplitude differences between shots in bedrock and shots in sediment we tested the discrimination performance of the average log p s values of a network of seismometers which should reduce the discrimination errors caused by these heterogeneities relative to a single station by bootstrapping the single station measurements over varying sample sizes we found that averaging three or four stations achieved significantly better discrimination than just one or two stations finally we corrected the signal amplitude to remove prephase noise to improve p s discrimination results this shows promise for improving event discrimination with only simple corrections online material table of event information and figure showing waveforms overlaid with amplitude windows

marine evidence for episodic holocene megafloods in north america and the northern gulf of mexico hemipelagic muds deposited during the past 5 3 cal kyr in the northern gulf of mexico orca basin contain seven intervals punctuated by relatively coarse siliciclastic grain size peaks planktonic faunal turnovers and negative 13c excursions we believe these episodes represent megaflood deposits reflecting historically unprecedented outfall of north american floodwater and terrigenous mud plumes into the gulf resulting in collapse of the open ocean pelagic ecosystem the deposits record multidecadal episodes of high continental precipitation and large mississippi river floods at 4 7 3 5 3 0 2 5 2 0 1 2 and 0 3 cal ka 500 1200 year recurrence interval variations in tropical plankton frequencies define submillenial warming intervals that culminate in these fluvial episodes strengthened tropical currents in the gulf at these times appear to have increased sea surface temperatures and associated flow of moist gulf air to the midwest terrestrial paleohydrologic records support the marine evidence for millennial scale changes in recurrence of large midwest flood episodes

magnitude based discrimination of man made seismic events from naturally occurring earthquakes in utah usa we investigate using the difference between local ml and coda duration mc magnitude to discriminate manmade seismic events from naturally occurring tectonic earthquakes in and around utah for 6 846 well located earthquakes in the utah region we find that ml mc is on average 0 44 magnitude units smaller for mining induced seismicity mis than for tectonic seismicity ts our interpretation of this observation is that mis occurs within near surface low velocity layers that act as a waveguide and preferentially increase coda duration relative to peak amplitude while the vast majority of ts occurs beneath the near surface waveguide a second dataset of 3 723 confirmed or probable explosions in the utah region also has significantly lower ml mc values than ts likely for the same reason as the mis these observations suggest that ml mc is useful as a depth indicator and could discriminate small explosions and mining induced earthquakes from deeper naturally occurring earthquakes at local to regional distances

sedimentary evidence of deglacial megafloods in the northern gulf of mexico pigmy basin abstract cored sediments from the pigmy basin northern gulf of mexico were analyzed in order to better constrain late deglacial and early holocene paleoenvironmental and sedimentary changes in response to north american climate evolution mineralogical and geochemical proxies indicate the succession of two sedimentary regimes dominantly detrital during the deglaciation 15 12 9 cal ka bp whereas biogenic contribution relatively increased later on during the younger dryas and early holocene 12 9 and 10 cal ka bp geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the mississippi river rather than modifications of redox conditions in the basin specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode meltwater spike described or modeled in previous marine or continental studies during this episode most parameters display stair step like pattern variations highlighting three successive steps within the main meltwater flow variations in grain size and clay mineral assemblage recorded in the pigmy basin indicate that the erosional regime was very strong on land during the first part of the meltwater spike and then milder inducing more subtle modifications in the sedimentary regime in this part of the gulf specific geochemical and mineralogical signatures notably clay minerals and trace metal geochemistry pinpoint a dominant origin from nw north america for detrital particles reflecting meltwater outflow from the south western laurentide ice sheet lis margin during the most intense freshwater discharge the observed decrease of the sedimentation rate from about 200 to 25 cm ka at ca 12 9 ka evidenced a drastic decrease of erosional processes during late phase of discharge consistently with the hypotheses of major reduction of meltwater flow the major modification at 12 9 cal ka bp is interpreted to result from both modifications of the main mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the younger dryas and the increase of sea surface temperature linked to insolation finally slight grain size modifications suggest that some freshwater discharges may have episodically reached the gulf of mexico after the younger dryas reflecting possible small adjustments of the postglacial hydrological regime

seismic discrimination of controlled explosions and earthquakes near mount st helens using p s ratios explosions and earthquakes are effectively discriminated by p s amplitude ratios for moderate magnitude events m 4 observed at regional to teleseismic distances 200 km it is less clear if p s

glacial to holocene terrigenous organic matter input to sediments from orca basin gulf of mexico a combined optical and biomarker approach in this study we assessed changes in the contribution of terrigenous organic matter om to the gulf of mexico over the course of the last deglaciation the last 25 kyr to this end we combined optical kerogen analyses with bulk sedimentary biomarker and compound specific carbon isotope analyses samples were obtained from core md02 2550 from orca basin 2249 m water depth at 26 56 77n 91 20 74w with temporal resolution ranging from multi decadal to millennial scale depending on the proxy all proxies confirmed larger terrigenous input during glacial times compared to the holocene in addition the kerogen analyses suggest that much of the glacial om is reworked at least 50 of spores and pollen grains and 40 of dinoflagellate cysts the holocene sediments in contrast contain mainly marine om which is exceptionally well preserved during the deglaciation terrigenous input was generally high due to large meltwater fluxes whereby discrepancies between different proxies call for additional influences such as the change in distance to the river mouth local productivity changes and hydrodynamic particle sorting it is possible that kerogen particles and the terrigenous biomarkers studied here represent distinct pools of land derived om with inputs varying independently

evidence for calcification depth change of globorotalia truncatulinoides between deglaciation and holocene in the western atlantic ocean abstract measurements of the 18o in tests of planktonic and benthic foraminifera in the florida straits are used to reconstruct the properties of the water column through time over the last 12 ka lynch stieglitz et al in press the isotopic composition of the foraminifera largely reflects the vertical density gradient we use this reconstruction and 18o measurements on globorotalia truncatulinoides in a nearby core to track the depth habitat of this species from the last deglaciation to 1 6 ka b p around 9 ka g truncatulinoides was calcifying in much shallower water than during the late holocene the downward migration toward its modern habitat is a regional phenomenon over the western tropical atlantic continental slope the cause is still unclear but we hypothesize that the shallower calcification depth may be a response to the presence of glacial melt water or to circulation changes this study points to the value of further study of the ecology life cycle and calcification depth for g truncatulinoides and other planktonic foraminifera that are used to reconstruct the history of the thermocline and upper water column structure

clay mineral distributions in and around the mississippi river watershed and northern gulf of mexico sources and transport patterns abstract maps of the distributions of the four major clay minerals smectite illite kaolinite and chlorite in and around the mississippi river drainage basin and in the northern gulf of mexico have been produced using newly acquired data from erodible alluvial terrestrial sediments and marine surface sediments as well as from previously published data east of the rockies north america can be divided into four large clay mineral provinces 1 the north western mississippi river watershed smectite rich 2 the great lakes area and eastern mississippi river watershed illite and chlorite rich 3 the south eastern united states kaolinite rich and 4 the brazos river and south western mississippi river watersheds illite and kaolinite rich the clay mineral distributions in surface sediments of the present day gulf of mexico are strongly influenced by three main factors 1 by relative fluvial contributions the mississippi river delivers the bulk of the clay input to the northern gulf of mexico whereas the apalachicola mobile brazos and rio grande rivers inputs have more local influences 2 by differential settling of various clay mineral species which is identified for the first time in northern gulf of mexico sediments and 3 by oceanic current transport the gulf of mexico surface and subsurface circulation distributes the clay rich sediments from river mouth sources throughout the northern gulf of mexico

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

megaflood erosion and meltwater plumbing changes during last north american deglaciation recorded in gulf of mexico sediments submicrometer variations in the median diameter of siliciclastic mud in orca basin northern gulf of mexico sensitively monitor laurentide ice sheet runoff to the gulf during early stages of the last deglaciation grain size data document a prominent pulse of very fine grained sediment to the northern gulf from 12 6 to 12 0 ka corresponding with the well known sea surface meltwater spike in 18 o records meltwater megafloods at this time eroded and transported large volumes of clay to the gulf via the mississippi river system the nonquartzose megaflood sediments appear to have been derived from clay rich midcontinental terrace deposits rather than from glacial outwash supplied by the laurentide ice margin sediment grain size data in combination with other terrigenous proxies clay minerals and reworked calcareous nannofossils indicate substantial variability in deglacial meltwater discharge and associated sediment load of meltwater runoff this variability reflects changes in continental plumbing consistent with terrestrial records of north american deglaciation

rapid and widespread response of the lower mississippi river to eustatic forcing during the last glacial interglacial cycle the lower mississippi valley provides an exceptional fi eld example for studying the response of a continental scale alluvial system to upstream and downstream forcing associated with the large orbitally controlled glacialinter glacial cycles of the late quaternary however the lack of a numerical chronology for the widespread pleistocene strata assemblage known as the prairie complex which borders the holocene fl oodplain of the lower mississippi river has so far precluded such an analysis here we apply optically stimulated luminescence osl dating mainly on silt sized quartz from prairie complex strata in total 27 osl ages indicate that the prairie complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7 5e and 5a thus the aggradation of the prairie complex is strongly correlated with the sea level highstands of the last two glacialinterglacial cycles fluvial incision during the sea level fall associated with the mis 5a mis 4 transition extended as far inland as 600 km from the present day shoreline testifying to the dominant downstream control of fl stratigraphic architecture in the lower mississippi valley in addition the short reaction time of the lower mississippi river suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

phase and spectral ratio discrimination between nts earthquakes and explosions part i empirical observations seismic discrimination of small magnitude mb 0 5 hz regional measurements in this study we evaluate the most promising short period discriminants p wave to s wave phase amplitude ratios and low to high frequency spectral amplitude ratios for a data set from the nevada test site the data consist of 130 underground nuclear explosions one very large chemical explosion and 50 earthquakes ranging from magnitude 2 to 6 recorded at two broadband digital seismic stations operated by lawrence livermore national laboratory in contrast with much previous discrimination work in the western united states the common stations and paths for all the events in this study allow the discriminants to be evaluated without applying propagation corrections and differences between events can be ascribed to very near source effects the source effects found to have the most influence on the discriminants in this study are depth for the earthquakes and the source medium properties of gas porosity density and velocity for the explosions the phase amplitude ratio discriminants tested are pn lg and pg lg both show little dependence on magnitude and work better at higher frequencies and when averaged over the two stations at 6 to 8 hz pn lg discriminates all except the shallowest earthquakes while pg lg discriminates all but the high gas porosity explosions low to high frequency spectral amplitude ratio discriminants were tested in each of the phases pn pg lg and lg coda the explosions show significant dependence on source material properties such as gas porosity all the spectral ratios show dependence on magnitude and for 1 2 hz 6 8 hz none performs well below magnitude 3 5 of the spectral ratios lg coda performs the best at least in part because of its extremely small interstation variability discriminating all but the low gasporosity explosions the best discriminant performance is given by combining phase and spectral ratios a sum of the logarithmic values of pn lg pg lg and the lg coda discriminates all but two of the shallowest earthquakes the source medium dependence of the discriminants suggests that discrimination performance differences between the western united states and other regions of the world may be due more to source property differences than differences in the regional path simply put western united states discriminant studies differ from those in the rest of the world because of the lack of explosions in very high gas porosity low velocity materials outside of the nevada test site

impact of glacial lake paleofloods on valley development since glacial termination ii a conundrum of hydrology and scale for the lowstand brahmaputra jamuna paleovalley system

a preliminary study of regional seismic discrimination in central asia with emphasis on western china abstract in support of a comprehensive test ban treaty we have started to evaluate regional seismic event discrimination capabilities for central asia emphasizing western china we have measured noise and signal levels of over 260 earthquakes and 26 underground nuclear explosions recorded at the broadband digital station wmq in western china and over 120 earthquakes and five nuclear explosions at station aak in kyrgyzstan the explosions are from the kazakh test site kts and lop nor china the earthquakes are mostly from northwest china event magnitudes measured as either m b or m l range between 2 5 and 6 5 and maximum event station distance is about 1700 km we formed phase spectral cross spectral short period long period and long period ratios to test many possible event discriminants all ratios were corrected for distance effects before forming ratio versus magnitude discrimination plots the most consistent discriminants for separating earthquakes from explosions are p s phase ratios for frequencies above 3 to 4 hz p wave f 1 hz to rayleigh wave 0 03 hz f p s ratios separation between earthquakes and explosions increases with frequency and for the p r ratios separation increases with increasing p frequency the p 3 to 6 hz s 0 75 to 1 5 hz cross spectral ratios also separate earthquakes and explosions these cross spectral ratios may prove quite useful because due to weak high frequency l g signals from explosions the high frequency p l g ratio sometimes cannot be evaluated but the p 3 to 6 hz l g 0 75 to 1 5 hz can be evaluated successfully p spectral ratios 3 to 6 hz 0 75 to 1 5 hz also separate earthquakes and explosions but not quite as consistently as the p s ratios however p spectral ratios may prove useful in cases where path effects block or highly attenuate s n and l g waves rendering the p s ratios unavailable in contrast to nevada test site nts events the l g 3 to 6 hz 0 75 to 1 5 hz spectral ratio does not separate earthquakes and nuclear explosions in central asia this observation may be a source effect as asian explosions are thought to be detonated in highly lithified rocks below the water table while most of the smaller m b for station aak the short period spectral and cross spectral ratios identify a few earthquakes not recorded at wmq from the north pamir region that plot with the lop nor explosions the waveforms from these earthquakes lack surface waves and a distinct l g phase these events which we interpret as having occurred in a subducted slab do separate from the explosions on high frequency f 4 hz p s discrimination plots for station wmq long period r l rayleigh wave love wave ratios separate kts explosions and asian earthquakes however r l ratios fail to identify the large lop nor explosions recorded at station aak because the love waves are as large as the rayleigh waves suggesting that strong tectonic release occurs with these explosions because we have examined only one path at a single station for these explosions source radiation pattern may be influencing this observation

testing event discrimination over broad regions using the historical borovoye observatory explosion dataset we test the performance of high frequency regional p s discriminants to differentiate between earthquakes and explosions at test sites and over broad regions using a historical dataset of explosions recorded at the borovoye observatory in kazakhstan we compare these explosions to modern recordings of earthquakes at the same location we then evaluate the separation of the two types of events using the raw measurements and those where the amplitudes are corrected for 1 d and 2 d attenuation structure we find that high frequency p s amplitudes can reliably identify earthquakes and explosions and that the discriminant is applicable over broad regions as long as propagation effects are properly accounted for lateral attenuation corrections provide the largest improvement in the 2 4 hz band the use of which may successfully enable the identification of smaller distant events that have lower signal to noise at higher frequencies we also find variations in p s ratios among the three main nuclear testing locations within the semipalatinsk test site which due to their nearly identical paths to brvk must be a function of differing geology and emplacement conditions

internal tide oceanic tomography a concept of internal tide oceanic tomography itot is proposed to monitor ocean warming on a global scale itot is similar to acoustic tomography but that work waves are internal tides itot detects ocean temperature changes by precisely measuring travel time changes of long range propagating internal tides the underlying principle is that upper ocean warming strengthens ocean stratification and thus increases the propagation speed of internal tides this concept is inspired by recent advances in observing internal tides by satellite altimetry in particular a plane wave fit method can separately resolve multiple internal tidal waves and thus accurately determines the phase of each wave two examples are presented to demonstrate the feasibility and usefulness of itot in the eastern tropical pacific the yearly time series of travel time changes of the m2 internal tide is closely correlated with the el nino southern oscillation index in the north atlantic significant interannual variations and bidecadal trends are observed and consistent with the changes in ocean heat content measured by argo floats itot offers a long term cost effective environmentally friendly technique for monitoring global ocean warming future work is needed to quantify the accuracy of this technique