three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

clay minerals as indicators of sources of terrigenous sediments their transportation and deposition bering basin russian alaskan arctic abstract cluster analysis of clay mineral abundances in surficial sediments from 52 stations revealed the presence of four station cluster groups within the bering basin and contiguous eastern aleutian trench forearc these results can be explained using two end members of terrigenous clay mineral sources and their admixtures the first end member cluster group i consists of the highest average concentration of illite 48 and chlorite plus kaolinite 40 and lowest of expandable minerals 12 in contrast the second end member cluster group iv has the highest concentration of expandable minerals 43 and lowest concentrations of illite 30 and chlorite plus kaolinite 27 the group i assemblages come from two regions the eastern aleutian trench forearc and the northwestern margin of the bering basin off koryak mountains east siberia clays in the former region are derived primarily from the meta sedimentary and meta volcanic rocks of the chugach mountains with infiltrations from alaska peninsula and are transported from the southeastern kodiak shelf of the gulf of alaska to the trench forearc by the alaska current alaskan stream similar clays are derived from the koryak mountains group iv clays located within the komandorsky and bowers basins and unmak plateau originated from the mio pliocene andesites and basalts of the eastern kamchatka peninsula and aleutian islands respectively it is postulated that group ii clays in the southcentral aleutian basin and bowers ridge basin area and group iii clays in the northern aleutian basin are mixtures obtained primarily from terrigenous sources of group i and iv the distribution patterns and boundaries of the cluster groups reflect the dispersal pathways of clays from the primary sources and the extent of their mixing by regional and local surface currents and mesoscale gyres eddies presumably the minor infiltration of anadyr river clays into group iii is a result of clay transport by episodic turbidity currents most of the clays derived from the alaska mainland and russia proper do not reach the bering basin as these clays are trapped within the bering sea shelf

measurement of density and wetness in snow using time domain reflectometry time domain reflectometry tdr is widely used in soil physics to determine water content existing equipment and methods ran be adapted to measurements of snow wetness the main advantages compared to other methods are flexibility in constructing sensors minimal influence on snow cover during measurements and sensors can be multiplexed we developed sensors suitable for continuous and non continuous measurements of snow wetness and density measured the apparent permittivity in different snow densities and snow types and compared the measurements to existing mixing formulas for mixtures of snow and air in dry snow density was measured from 110 to 470 kg m 3 the residual error is 14 kg m 3 and the 95 confidence interval of our model is 3 kg m 3 to measure snow density and wetness continuously suitable sensors have been constructed their small size and high surface area to weight ratio minimizes their movement in the snowpack except when they are exposed to intense solar radiation results show that changes in dry snow density of less than 5 kgm 3 can be detected infiltration of even small amounts of water clearly shows up in the permittivity at the surface of the snowpack problems occur due to the formation of air pockets around the sensors during long term measurements

isotope thermometry in melt affected ice cores 1 a statistically significant relationship is observed between stable water isotopes 18o and melt amounts in a melt affected firn core ssummit taken from the prince of wales icefield ellesmere island canada by contrast a low melt firn core taken from a higher elevation higher latitude location on the same icefield shows no relationship between these variables we interpret this as evidence for meltwater induced isotopic enrichment at ssummit a percent melt based correction slope is applied to isotopic values from ssummit uncorrected and corrected temperature records derived from the raw and corrected 18o values are compared to bias corrected temperature data from the ncep reanalysis improvements are observed in the isotopic reconstruction of ssummit annual precipitation weighted temperatures when we correct for meltwater enrichment with a reduction from 0 6 c to 0 0 c in the mean annual error and a decrease in root mean square error from 1 8 c to 1 6 c the correction factor appears to overcorrect isotopic modification during high melt years such as 1999 during which ssummit experienced nearly 70 more melt than the average from 1975 to 2000 excluding 1999 data from the correction analysis results in a slight reduction in mean absolute error from 1 4 c to 1 3 c these results suggest that melt induced isotopic modification cannot be corrected in very high melt years

210po and210pb distributions in the central and eastern indian ocean abstract disequilibrium between 210 po and 210 pb and between 210 pb and 226 ra has been mapped in the eastern and central indian ocean based on stations from legs 3 and 4 of the geosecs indian ocean expedition 210 po 210 pb activity ratios are less than 1 0 in the surface mixed layer and indicate a residence time for po of 0 6 years 210 po and 210 pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100 500 m where po may be returned to solution after removal from the surface water and in samples taken near the bottom at a few stations 210 pb excesses relative to 226 ra are observed in the surface water but these excesses are not as pronounced as in the north pacific and north atlantic the difference is attributable to a lower flux of 210 pb from the atmosphere to the indian ocean below the main thermocline 210 pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom departures from this pattern are especially evident at stations taken in the bay of bengal where 210 pb 226 ra activity ratios as low as 0 16 are observed and near the mid indian ridge the data suggest that removal of 210 pb at oceanic boundaries coupled with eddy diffusion along isopycnals can explain gradients in 210 pb near the boundary application of a simple model including isopycnal diffusion chemical removal production and radioactive decay produces fits the observed 210 pb 226 ra gradients for eddy diffusion coeffients of 10 7 cm 2 s high productivity in surface waters of the bay of bengal makes this region a sink for reactive nuclides in the northern indian ocean

210pb and226ra distributions in the circumpolar waters abstract 210 pb and 226 ra profiles have been measured at five geosecs stations in the circumpolar region these profiles show that 226 ra is quite uniformly distributed throughout the circumpolar region with slightly lower activities in surface waters while 210 pb varies with depth as well as location or area there is a subsurface 210 pb maximum which matches the oxygen minimum in depth and roughly correlates with the temperature and salinity maxima this 210 pb maximum has its highest concentrations in the atlantic sector and appears to originate near the south sandwich islands northeast of the weddell sea concentrations in this maximum decrease toward the indian ocean sector and then become fairly constant along the easterly circumpolar current relative to 226 ra the activity of 210 pb is deficient in the entire water column of the circumpolar waters the deficiency increases from the depth of the 210 pb maximum toward the bottom and the 210 pb 226 ra activity ratio is lowest in the antarctic bottom water indicating a rapid removal of pb by particulate scavenging in the bottom layer and or a short mean residence time of the antarctic bottom water in the circumpolar region 226 ra is essentially linearly correlated with silica and barium in the circumpolar waters however close examination of the vertical profiles reveals that ba and si are more variable than 226 ra in this region

positive degree day factors for ablation on the greenland ice sheet studied by energy balance modelling ice ablation is related to air temperature by the positive degree day factor variations of the positive degree day factor in west greenland are studied using an energy balance model to simulate ablation under different conditions degree day factors for simulated and measured ice ablation at nordbogletscher and qaman rssup sermia agree well with values around 8 mm d 1 c 1 degree day factors for snow are less than half those for ice energy balance modelling shows that degree day factors vary with summer mean temperature surface albedo and turbulence but there is only evidence of large positive degree day factors at lower temperatures and with low albedo 0 3 the greatest effect of albedo variations 0 3 0 7 is at lower temperatures while variations in turbulence have greater effect at higher temperatures current models may underestimate runoff from the greenland ice sheet by several tenths because they use a degree day factor for melting ice that is too small for the colder parts of the ice sheet i e the upper ablation area and the northerly margin

from accumulation to discharge modification of stable isotopes during glacial and post glacial processes the isotopes of the water molecule tritium deuterium and oxygen 18 are considered to be ideal tracers of the water cycle an isobalance of accumulation and discharge from glaciated areas is therefore challenging in this article we review data from the alps concerning both the isotopic information of accumulated snow and ice and the relevant information of glacial discharge on a local to regional scale in the alps the seasonal distribution of accumulated snow is governed by small scale meteorology and exposition and distribution of cold and temperate glaciers from comparison with direct precipitation measurements it follows that uncontrolled erosive loss of parts of the seasonal mainly winter snow cover is more important for input output considerations of glacial discharge reconstruction of mean accumulation rates and palaeotemperatures by means of isotopes than occasional melting or even rainfall events the order of magnitude of the latter is controlled by laboratory and field experiments sublimation and evaporation turn out to be of minor influence if only the absolute values and not the deuterium excess the relationship of both stable isotopes deuterium and oxygen 18 is considered nevertheless during warming periods a pronounced increase of deuterium excess caused by intensive melting and evaporation may be used as an additional climate indicator the different isotopic signature of the seasonal snow cover old glacier ice and groundwater stored in the glacier bed enables a quantitative separation of the individual water components discharging at a given time of the day or the season although several detailed isotope studies are reported a complete isobalance from glaciated areas based on an interdisciplinary approach including hydrology and glaciology is still missing the hydroclimatic imprint of the discharge from glaciated areas remains even on a regional scale snowmelt shifts the more negative isotope values from winter precipitation to the summer months interannual climatic variability and changes in seasonal distribution of precipitation for instance reduced winter precipitation during the late 1980s are recorded by the stable isotopes in precipitation and discharge as well indicating that the modification of the isotopic information during glacial and post glacial processes does not override climatic trends

importance of lateral transport processes to 210pb budget in the eastern chukchi sea during summer 2003 chinese ipy research program national natural science foundation of china 41125020 fujian natural science foundation 2009j06026 state oceanic administration of china 201105022 4 ministry of education of china

the potential effects of percolating snowmelt on palynological records from firn and glacier ice the effects of meltwater percolation on pollen in snow firn and glacial ice are not fully understood and currently hamper the use of pollen in ice core studies of paleoclimate several studies have suggested that due to grain size pollen is not mobilized by meltwater transport however these findings contradict many ice core pollen studies that show pollen concentrations in snow and firn are much higher than concentrations found in the ice layers they eventually form this study addresses one aspect of this question by investigating whether meltwater percolation can effectively transport pollen within a snowpack we used nine styrofoam coolers filled by natural snow accumulation the coolers were tested in three groups of three replicates each to simulate different glacier snowpack conditions and spiked at the surface with a known amount of lycopodium marker spores the snow was melted to two thirds the original volume sampled stratigraphically and tested for spore concentrations meltwater effluent was also collected and examined results show substantial vertical and horizontal spore transport during the experiment peak spore concentrations were found in the bottommost snow layer or in the meltwater effluent in eight of nine coolers indicating that the majority of surface spores were transported through the snowpack via meltwater percolation and or runoff

wetting front advance and freezing of meltwater within a snow cover 1 observations in the canadian arctic in a naturally stratified snow cover the movement of meltwater into dry snow is complicated by the interaction of the wetting front with stratigraphic horizons field observations showed that when the wetting front reached premelt stratigraphic horizons water ponded at the interface and then flow fingers developed and penetrated the lower stratum the flux in these fingers which was increased to about twice that of the surface flux was used to feed water to the impeding horizons where it froze to form ice layers these ice layers were the major source of latent heat released within the snow cover and they were responsible for the warming of the snow and the underlying soil these continuous ice layers grew only at stratigraphic boundaries because of this ice layer growth the wetting front advance was retarded and the arrival of meltwater at the snow cover base was significantly delayed owing to a cold substrate the strong heat flux from the snow into the soil delays the warming of the snow cover and limits runoff after the snow is isothermal at 0 c by the refreezing of soil infiltration and the development of a basal ice layer

226ra in the western indian ocean abstract 226 ra profiles have been measured in the western indian ocean as part of the 1977 1978 indian ocean geosecs program these profiles show a general increase in deep and bottom water ra concentration from the circumpolar region to the arabian sea a deep ra maximum which originates in the arabian sea and in the somali basin at about 3000 m depth spreads southward into the mascarene basin and remains discernible in the madagascar and crozet basins in the western indian ocean the cold antarctic bottom water spreads northward under the possibly southward flowing deep water forming a clear benthic front along the crozet basin across the southwest indian ridge into the madagascar and mascarene basins the antarctic bottom water continues to spread farther north to the somali basin through the amirante passage at 10 s as a western boundary current the benthic front and other characteristic features in the western indian ocean are quite similar to those observed in the western pacific where the benthic front as a distinctive feature was first described by craig et al 15 across the mid indian ridge toward the ceylon abyssal plain near the triple junction ra profiles display a layered structure reflecting the topographic effect of the mid ocean ridge system on the mixing and circulation of the deep and bottom waters both ra and si show a deep maximum north of the madagascar basin linear relationships between these two elements are observed in the deep and bottom water with slopes increasing northward this suggests a preferential input of ra over si from the bottom sediments of the arabian sea and also from the flank sediments of the somali basin

atmospheric warming threatens the untapped glacial archive of ortles mountain south tyrol ortles mountain 3905 m a s l south tyrol italy is the highest mountain of the eastern european alps and its upper glacier alto dell ortles presents a unique opportunity to obtain the first paleoenvironmental record from an ice core in this area to study the suitability of this glacier as a drilling site in 2009 we performed the first preliminary study of its glaciological characteristics at 3830 m a s l the maximum thickness is 75 m and lamination of the exposed ice layers is excellent down to bedrock firn and ice lenses were observed in a 10 m shallow core and the firn ice transition was below 24 m the seasonal chemical signal is clearly preserved only within the uppermost 2008 and 2009 snow firn a simple mass balance model the incipient smoothing of the chemical record and the observed ice lenses provide evidence that melting infiltration and refreezing cycles occurred within the firn layers formed before 2008 nevertheless the mass balance of the upper part of alto dell ortles was positive 800 mm a 1 during the last few years we suggest that an environmental history is likely to be well preserved only within the ice layers formed before 1980 when summer air temperature was 28c colder than today in this area clearly the continued warming trend predicted to occur over the next few decades and the consequent increase in frequency and or intensity of infiltration processes will endanger the preservation of the glacial archive conserved in the deep ice layers of ortles mountain

a spatial random field model to characterize complexity in earthquake slip 1 finite fault source inversions reveal the spatial complexity of earthquake slip over the fault plane we develop a stochastic characterization of earthquake slip complexity based on published finite source rupture models in which we model the distribution of slip as a spatial random field the model most consistent with the data follows a von karman autocorrelation function acf for which the correlation lengths a increase with source dimension for earthquakes with large fault aspect ratios we observe substantial differences of the correlation length in the along strike a x and downdip a z directions increasing correlation length with increasing magnitude can be understood using concepts of dynamic rupture propagation the power spectrum of the slip distribution can also be well described with a power law decay i e a fractal distribution in which the fractal dimension d remains scale invariant with a median value d 2 29 0 23 while the comer wave number k c which is inversely proportional to source size decreases with earthquake magnitude accounting for larger slip patches for large magnitude events our stochastic slip model can be used to generate realizations of scenario earthquakes for near source ground motion simulations

some comments on climatic reconstructions from ice cores drilled in areas of high melt poor consideration has been given in many arctic circum polar ice core studies to the effect of summer snow melt on chemistry stable isotope concentrations and time scales many of these corps are drilled close to the firn line where melt is intense some come from below the firn line where accumulation is solely in the form of super imposed ice in all cases seasonal signals are reduced or removed and in some time gaps develop during periods of excessive melting which situate the drill site in the ablation zone consequently cross correlations of assumed synchronous events among the cores are invalid so that time scales along the same cores differ between authors by factors of over 2 many so called climatic signals are imaginary rather than real by reference to published analyses of cores from the superimposed ice zone on devon ice cap koerner 1970 and meighen ice cap koerner and paterson 1974 it is shown how melt affects all the normally well established ice core proxies and leads to their misinterpretation despite these limitations the cores can give valuable low resolution records for all or part of the holocene they show that the thermal maximum in the circum polar arctic occurred in the early holocene this maximum effected negative balances on all the ice caps and removed the smaller ones cooler conditions in the second half of the holocene have caused the regrowth of these same ice caps

vertex manganese transport through oxygen minima abstract manganese transport through a well developed oxygen minimum was studied off central mexico 18 n 108 w in october november 1981 as part of the vertex vertical transport and exchange research program refractory leachable and dissolved mn fractions associated with particulates caught in traps set at eight depths 120 1950 m were analyzed particles entering the oxygen minimum had relatively large mn loads however as the particulates sank further into the minimum total mn fluxes steadily decreased from 190 nmol m 2 day 1 at 120 m to 36 nmol m 2 day 1 at 400 m manganese fluxes then steadily increased in the remaining 800 1950 m reaching rates of up to 230 nmol m 2 day 1 at 1950 m manganese concentrations were also measured in the water column dissolved mn levels 1 were consistently observed within the 150 600 m depth interval in contrast suspended particulate leachable mn amounts were especially low at those depths and never exceeded 0 04 nmol kg 1 the combined water column and particle trap data clearly indicate that mn is released from particles as they sink through the oxygen minimum rate of change estimates based on trap flux data yield regeneration rates of up to 0 44 nmol kg 1 yr 1 in the upper oxygen minimum 120 200 m however only 30 of the dissolved mn in the oxygen minimum appears to be from sinking particulate regeneration the other 70 probably results from continental slope release horizontal transport processes dissolved mn scavenges back onto particles as oxygen levels begin to increase with depth scavenging rates ranging from 0 03 to 0 09 nmol kg 1 yr 1 were observed at depths from 700 to 1950 m these scavenging rates result in mn residence times of 16 19 years and scavenging rate constants on the order of 0 057 yr 1 manganese removal via scavenging on sinking particles below the oxygen minimum is balanced by mn released along continental boundaries and transported horizontally via advective diffusive processes manganese appears to be very weakly associated with particulates nevertheless the amounts of mn involved with sinking biogenic particles are large and the resulting fluxes are on the same order of magnitude as those necessary to explain the excess mn accumulating on the sea floor the overall behavior of mn observed in this and other studies strongly suggests some type of equilibrium occurring between dissolved and particulate phases this equilibrium appears to shift in direct or indirect response to dissolved oxygen levels

an assessment of the effect of chemical scavenging within submarine hydrothermal plumes upon ocean geochemistry profiles of 210pb over the endeavour and north cleft segments of the juan de fuca ridge are used to model a time scale for the scavenging by hydrothermal plumes of reactive elements in seawater the hydrothermal plumes above these ridge segments are sites of intense scavenging removal of 210pb at endeavour the total 210pb activities within the plume are as low as 8 dpm 100 l and dissolved activities are as low as 3 dpm 100 l at the north cleft which is characterized by higher particulate fe concentrations the total 210pb activities are 4 5 dpm 100 l the dissolved activities are 1 2 dpm 100 l and the 210pb activities are deficient with respect to the activity of the 210po daughter these are perhaps the lowest 210pb activities ever measured in the deep sea the large gradient of 210pb between the plume and surrounding deep water suggests that scavenging is focused into the plumes through horizontal transport the implication therefore is that this process might impact the ocean on a scale larger than that local to the ridge crest by coupling published measurements of particle flux from endeavour with 210pb activities on particles trapped at that site the total volume of seawater stripped of 210pb per year for that site was calculated to be 7 4 1012 l y globally the extrapolated volume flux of seawater stripped of reactive constituents is 5 7 1015 l y such that the entire ocean is processed in this manner in 2 4 105 y the geochemical cycle of elements with ocean residence times much shorter than this e g pb and th will not be greatly affected by hydrothermal scavenging on the other hand this process holds significance for the geochemistry of other elements scavenged by hydrothermal plumes such as p and v whose ocean residence times are 104 y

residence times of surface water and particle reactive 210pb and 210po in the east china and yellow seas 228ra 226ra 210pb and 210po were measured in the surface waters of the east china and yellow seas using mass balance equations for the ra isotopes we estimated the total flux of diffusion from sediments and desorption from suspended particles to be 0 1 dpm 226ra cm 2 a 1 and 1 dpm 228ra cm 2 a 1 and residence times to be 2 3 years for the waters on the east china sea shelf and 5 6 years for yellow sea waters box model calculations yielded generally congruent scavenging residence times for 210pb and 210po in the waters of 2 months on the shelf and 7 months in the kuroshio current these suggest that reactive heavy metals and pollutants discharged through rivers from the continent to the east asian continental shelf are largely deposited on the bottom sediments prior to transport to the pelagic ocean by lateral mixing

the effect of refreezing on the isotopic composition of melting snowpack the isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack the slope of the d 18o line for the liquid phase is found to be lower than for the solid phase this is proved to be due to the isotopic fractionation occurring in the melt freeze mass exchange within the snowpack melting of the snowpack has no clear impact on the d 18o line for the solid phase but the slope of the d 18o line for the liquid shows an overall slight decrease in the melting period when the snowpack is refrozen the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases thus the slope of the solid would become lower and lower as the diurnal melt freeze episodes cycle throughout the melting season this effect is then demonstrated by looking into the isotopic composition changes of glacier firn the extent of the effect depends on the snowpack properties and environmental conditions the slope changes also result in a decreasing trend in deuterium excess copyright 2007 john wiley sons ltd

the geochemistry of manganese in the northeast pacific ocean off washington1 2 water collected along a transect normal to the coast of washington was analyzed for dissolved co 4 pm and total dissolvable manganese tdm the vertical profiles exhibit the same general features observed elsewhere in the pacific but a horizontal section of the transect shows that concentrations increase markedly toward the continental margin a surface maximum ranging from 0 57 nmol kg in offshore waters to 5 24 over the continental slope is probably due to fluvial inputs especially from the columbia river another possible source is the upwelling of manganeseenriched bottom water over the shelf horizontal gradients are also observed in the oxygen minimum as manganese concentrations decrease from 4 75 nmol kg l near the continental slope to 0 7 1 in open ocean water porewater and solid phase data suggest that manganese is being actively remobilized under reducing conditions in the slope sediments and is diffusing into the overlying seawater at a rate sufficient to balance losses by vertical mixing and particulate scavenging two stations on opposite sides of the juan de fuca ridge have deep concentration maxima that are almost certainly due to injections of hydrothermal vent fluid along the ridge

signal and noise in four ice core records from the agassiz ice cap ellesmere island canada details of the last millennium for stable isotopes melt and solid conductivity four ice cores and two deep pit auger sequences from the top of the agassiz ice cap have been variously analysed for o18 ecm solid conductivity and ice melt layer stratigraphy the high resolution data are presented on time scales covering about the last 1000 years the 8 time series are compared and the noise examined in terms of snow drifting and wind scouring of winter snow from the higher exposed parts of flow lines the highly scoured 8 records reflect a mixture of summer biased conditions and the amount of winter scoured snow sites away from the ridges and domes are not scoured the signal part of the scoured and unscoured sites is obtained by stacking averaging normalized series the stacked unscoured series of 8 and accumulation are compared to similar stacked series from central greenland for the last century of annual averages the comparison is surprisingly good suggesting that at these resolutions low noise 8 series have some coherence over fairly large distances the percentage melt

234th balance and implications for seasonal particle retention in the eastern bering sea th abstract as part of the bering ecosystem study bering sea integrated ecosystem research program best bsierp distributions of 234 th in the water column and sediments were measured at approximately 60 stations over the shelf and slope oceanic regions of the eastern bering sea during spring and summer of 2009 and 2010 during this study period the inventory of sediment excess 234 th 234 thxs on the shelf was determined to be 1 3 of the total 234 th deficit in the overlying water column the average focusing factor ffth sediment 234 thxs water column 234 th deficit was 0 3470 23 in addition the export flux of 234 th from the shelf to the slope oceanic region was determined to be on average 30 of the total production of 234 th throughout the shelf taken together these results indicate that 234 th and associated particles are largely retained on the shelf and that shelf sediments represent a sink for particles in contrast the ffth in the slope oceanic region was higher averaging 1 5271 34 the higher ffth at the slope is attributed primarily to enhanced scavenging removal and sediment deposition of 234 th associated with periods of high biogenic particle flux at the marginal ice zone during the spring sea ice retreat a more general conclusion is that the ocean margin of the eastern bering sea may serve as an accumulation area for particles and associated reactive chemicals

210 po and 210 pb distribution dissolved particulate exchange rates and particulate export along the north atlantic us geotraces ga03 section vertical profiles of 210po and 210pb in the water column were measured in the dissolved phase 51 m particles at seven stations along the us geotraces north atlantic zonal transect ga03 mass balance calculations were employed to assess nuclide exchange rates at the dissolved small particle interface and between small and large particles and to quantify export with settling large particles in the surface ocean 210po scavenging is linearly correlated with the concentration of particulate organic carbon poc in large particles supporting the role of biogenic particle in 210po bioaccumulation and export in stations near the coast this link is more complex due to the variable source of biogenic material and temporal changes in the surface biogeochemical and physical conditions at depth 210po exhibits significant widespread deficit with respect to 210pb that could in part be attributed to in situ 210po scavenging and may be related to surface biological productivity as previously reported the 210pb scavenging rates in the surface ocean were higher at ocean margins at depth 210pb scavenging increases with depth and eastward due to the increase of adsorption sites available in the benthic layers and to a regional contribution of benthic 210pb scavenging and or particle flux respectively the benthic nepheloid layer bnl and the hydrothermal tag plume distinctly enhance 210pb scavenging due to increased surface adsorption in association with resuspended or freshly formed particles in contrast 210po is not seen to be significantly scavenged in these environments due to its relatively short half life and the long residence time of particles

the impact of marginal ice zone processes on the distribution of 21opb 21opo and 234th and implications for new production in the bellingshausen sea antarctica abstract the vertical distributions of 21opb 210po and 234th in both dissolved and particulate phases of seawater were measured at five stations along the 85 w meridian in the bellingshausen sea antarctica sea ice conditions during the expedition ranged from fully ice covered fast ice to open water away from the marginal ice zone concurrent primary productivity and algal chlorophyll measurements revealed a band of high productivity at approximately 67 30 s which remained in a rather static location during ice melt back along the transect a progressive increase in removal scavenging and sinking of 210pb 210po and 234th occurred towards the north open water conditions application of a simple irreversible scavenging model and particulate organic carbon and organic nitrogen to radionuclide ratios measured on suspended particulate matter allows the calculation of export production for this region under fast ice conditions some removal of phytodetritus from the euphotic zone was observed 1 2 mgc m 2 day 1 representing a low proportion of the primary production f ratio of 0 02 near the antarctic continental margin upwelling of regenerated dissolved 210po was found at the open water site near the algal band new production had risen to 27 252 mgc m 2 day 1 but a greater proportion of the original primary production was removed by sinking detritus f ratio of 0 03 0 33 comparison of 210po and 234th as tracers of of export production indicates considerable differences with 210po yielding rather lower rates of export flux compared to 234th radionuclide estimates of new production are significantly greater than those obtained by traditional sediment trap methods this may be due to the dynamic nature short duration and spatial variability of algal growth in the southern ocean

disequilibria between226ra 210pb and 210po in the arctic ocean and the implications for chemical modification of the pacific water inflow abstract measurements have been made of226ra and both dissolved and particulate forms of210pb and210po in a vertical profile at 85 50 n 108 50 w in the arctic ocean in the upper water column226ra shows a concentration maximum that is coincident with one in the nutrients silicate phosphate and nitrate while at the same depth dissolved and particulate210pb and210po all show minimum concentrations it is suggested that the concentration maxima are partly due to sources of the respective elements in the continental shelf sediments the shelf waters being subsequently advected into the arctic ocean basins the210pb and210po minima have similarly been explained by interaction between the shelf sediments and overlying waters an estimate is made of the possible contributions of shelf sediments to the layer of silica rich water which covers the canada basin at a depth of 100 150 m residence times have been calculated for dissolved210pb and210po at various depths in the water column surface water residence times of dissolved and particulate forms of these radionuclides are longer than in surface atlantic waters probably due to lower biological activity in the surface waters of the canada basin an estimatee has been made of the average sinking velocity of particulate material

uncertainties in strong ground motion prediction with finite fault synthetic seismograms an application to the 1984 m 5 7 gubbio central italy earthquake abstract this study investigates the engineering applicability of two conceptually different finite fault simulation techniques we focus our attention on two important aspects first to quantify the capability of the methods to reproduce the observed ground motion parameters peaks and integral quantities second to quantify the dependence of the strong motion parameters on the variability in the large scale kinematic definition of the source i e position of the nucleation point value of the rupture velocity and distribution of the final slip on the fault we applied an approximated simulation technique the deterministic stochastic method and a broadband technique the hybrid integral composite method to model the 1984 m w 5 7 gubbio central italy earthquake at five accelerometric stations we first optimize the position of the nucleation point and the value of the rupture velocity for three different final slip distributions on the fault by minimizing an error function in terms of acceleration response spectra in the frequency band from 1 to 9 hz we found that the best model is given by a rupture propagating at about 2 65 km sec from a hypocenter located approximately at the center of the fault in the second part of the article we calculate more than 2400 scenarios varying the kinematic source parameters at the five sites we compute the residuals distributions for the various strong motion parameters and show that their standard deviations depend on the source parameterization adopted by the two techniques furthermore we show that arias intensity ai and significant duration are characterized by the largest and smallest standard deviation respectively housner intensity is better modeled and less affected by uncertainties in the source kinematic parameters than ai the fact that the uncertainties in the kinematic model affects the variability of different ground motion parameters in different ways has to be taken into account when performing hazard assessment and earthquake engineering studies for future events

a constant stress drop model for producing broadband synthetic seismograms comparison with the next generation attenuation relations broadband 0 1 20 hz synthetic seismograms for finite fault sources were produced for a model where stress drop is constant with seismic moment to see if they can match the magnitude dependence and distance decay of response spec tral amplitudes found in the next generation attenuation nga relations recently developed from strong motion data of crustal earthquakes in tectonically active re gions the broadband synthetics were constructed for earthquakes of m 5 5 6 5 and 7 5 by combining deterministic synthetics for plane layered models at low fre quencies with stochastic synthetics at high frequencies the stochastic portion used a source model where the brune stress drop of 100 bars is constant with seismic mo ment the deterministic synthetics were calculated using an average slip velocity and hence dynamic stress drop on the fault that is uniform with magnitude one novel aspect of this procedure is that the transition frequency between the deterministic and stochastic portions varied with magnitude so that the transition frequency is inversely related to the rise time of slip on the fault the spectral accelerations at 0 2 1 0 and 3 0 sec periods from the synthetics generally agreed with those from the set of nga relations for m 5 5 7 5 for distances of 2 100 km at distances of 100 200 km some of the nga relations for 0 2 sec spectral acceleration were substantially larger than the values of the synthetics for m 7 5 and m 6 5 earthquakes because these relations do not have a term accounting for q at 3 and 5 sec periods the synthetics for m 7 5 earth quakes generally had larger spectral accelerations than the nga relations although there was large scatter in the results from the synthetics the synthetics showed a sag in response spectra at close in distances for m 5 5 between 0 3 and 0 7 sec that is not predicted from the nga relations

determination of timing and location of water movement and ice layer formation by temperature measurements in sub freezing snow measurements of temperature in snow along a vertical profile during the onset of spring melting are used to calculate spatial and temporal temperature gradients and terms of the conduction equation with an internal energy production term are calculated heat transfer information is combined with stratigraphic observations made during melting and allow detailed determination of the timing and location of heterogeneous water movement and of refreezing internal energy production is interpreted as latent heat of refreezing of percolated meltwater times and locations of flow and refreezing of meltwater are calculated and compared to stratigraphic observations of layering and changes in density and liquid water content sequences of melt piping layering and refreezing seen in calculations and in stratigraphy demonstrate retarded flow at fine to coarse transitions flow along such transitions and refreezing at the transitions to form ice layers downslope flow is also observed in the absence of an impermeable horizon to redirect flow from the vertical

separation of melting and environmental signals in an ice core with seasonal melt we examine the impact of melt water percolation on the soluble ion chemical record from the lomonosovfonna ice core principle component analysis shows that melting produces only simple changes bet

the geochemical cycling of stable pb 210pb and 210po in seasonally anoxic lake sammamish washington usa abstract the geochemical processes controlling the behavior of stable pb 210 pb and 210 po in seasonally anoxic lake sammamish washington were identified from water column distributions and box model calculations total sum of dissolved and particulate inventories of stable pb 210 pb and 210 po increased in the whole lake during the latter part of the oxic stage of the lake and were attributed to diffusion from sediments large decreases in the total inventories of these elements occurred during the transition from oxic to anoxic conditions and the lowest inventories were observed during the sulfidic stage of stratification the cycling of stable pb and 210 pb during oxic periods appeared to be linked to fe cycling while 210 po cycling was more closely linked to the cycling of mn the behavior of stable and radioactive pb and possibly 210 po during anoxia was influenced by sulfur cycling thermodynamic calculations indicated that dissolved pb concentrations might be controlled by pbs precipitation during anoxia flux balance calculations during stratification indicated that atmospheric deposition was the major source of both 210 pb and 210 po to the lake and fluvial input was more important for 210 po than for 210 pb 210 pb and 210 po supplied by atmospheric deposition were scavenged and removed by sedimentation from the epilimnion residence times with respect to scavenging and sedimentation in the epilimnion were 1 3 and 617 days respectively for 210 pb and 9 22 and 9 26 days for 210 po model results in the hypolimnion indicated that at certain times the radionuclides diffused out of the sediments and at other times into the sediments residence times with respect to sedimentation of particulate nuclides in the hypolimnion were 2 124 days for 210 pb and 8 48 days for 210 po the behavior of 210 pb and 210 po in lake sammamish was compared to that in b kford reservoir massachusetts although the comparison indicated similarities e g links to fe and mn cycling larger scavenging rates for 210 pb than for 210 po the major differences between the systems were that atmospheric inputs were greater than fluvial inputs activities of the radionuclides were lower and the presence of sulfide in the hypolimnion during anoxia affected the cycling of stable pb 210 pb and 210 po in lake sammamish

region specific spatial cross correlation model for stochastic simulation of regionalized ground motion time histories stochastic simulation of spatially distributed ground motion time histor ies is important for performance based earthquake design of geographically distrib uted systems in this study we develop a novel technique to stochastically simulate regionalized ground motion time histories by taking account of the influence of regional site conditions for this purpose a transient acceleration time history is char acterized by wavelet packet parameters proposed by yamamoto and baker 2013 the wavelet packet parameters can fully characterize ground motion time histories in terms of energy content time frequency domain characteristics and time frequency nonstationarity this study further investigates the spatial cross correlations of wavelet packet parameters based on geostatistical analysis of 1500 regionalized ground motion data from eight well recorded earthquakes in california mexico japan and taiwan the linear model of coregionalization lmc is used to develop a permissible spatial cross correlation model for each parameter group the geostatistical analysis of ground motion data from different regions reveals significant dependence of the lmc structure on regional site conditions which can be characterized by the correlation range of vs30 in each region in general the spatial correlation and cross correlation of wavelet packet parameters are stronger if the site condition is more homogeneous the pro posed region specific correlation model improves stochastic simulation of spatially correlated ground motions as is demonstrated in illustrative examples in this article the developed method has great potential to be used in computationally based seismic analysis and loss estimation in a regional scale

an assessment of the regional distribution of the oxygen isotope ratio in northeastern canada a compilation of mean values of the oxygen isotope ratio relative to standard mean ocean water for 22 sites representative of conditions in north eastern canada is complemented with data on mean annual surface temperature latitude surface elevation and mean annual shortest distance to open ocean denoted by the 10 sea ice concentration boundary stepwise regression analysis is used to develop a multivariate model suitable to infer the distribution of 6 1 0 in an area of complex topography and possibly mixed source of advected water vapor the best model is produced by a run in the backward mode at the 95 confidence level in which only temperature latitude and distance to the open ocean remain in the model the correlation coefficient is 0 915 the adjusted coefficient of determination is 0 809 the root mean square residual is 1 62 this model is similar to the best 6180 predictive model derived elsewhere for greenland suggesting a common principal source of advected moisture

enhanced particle scavenging in deep water of the aleutian basin revealed by 210po 210pb disequilibria the high sedimentation rate but low primary production in surface ocean raised a question whether particles from local upper water column could support high deposition in the aleutian basin here we first present large 210po 210pb disequilibria in deep water of the aleutian basin dissolved 210po and 210pb were depleted relative to 210pb and 226ra respectively in deep water below 1000 m as well as decreased with depth suggesting enhanced particle scavenging in the deep water the 210po residence times 1 2 a in deep water were comparable to those in the upper water column indicating that 210po scavenging rates were high in deep water of the aleutian basin the export fluxes of 210po from the upper 100 m were estimated to be 0 2 0 8 bq m2 d much lower than those in the deep water 7 8 bq m2 d similarly poc export fluxes in deep water 24 80 mmolc m2 d were higher than those in the upper 100 m 1 mmolc m2 d such a large discrepancy between the upper and deep water suggested that particles from local upper water column could not totally meet the enhanced scavenging in the deep water based on mass balance calculations the extra fluxes of 210pb and poc imported to deep water were estimated to be 8 12 bq m2 d and 22 79 mmolc m2 d respectively the ratio of poc to particulate 210pb i e poc ppb in the extra source was estimated to be 6 5 mmol bq which was lower than that in the bering shelf with a mean poc ppb ratio of 10 9 mmol bq implying that particles in the bering shelf could be a potential source for the enhanced particle scavenging in deep water of the aleutian basin however quantitative and detailed role of ridges and manganese from sediments in particle scavenging in the deep water was unclear and further studies are necessary

from precipitation to runoff stable isotopic fractionation effect of glacier melting on a catchment scale stable isotope variability and fractionation associated with transformation of precipitation accumulation to firn to glacial river water is critical in a variety of climatic hydrological and paleoenvironmental studies this paper documents the modification of stable isotopes in water from precipitation to glacier runoff in an alpine catchment located in the central tibetan plateau isotopic changes are observed by sampling firnpack profiles glacier surface snow ice meltwater on the glacier surface and catchment river water at different times during a melt season results show the isotopic fractionation effects associated with glacier melt processes the slope of the d 18o regression line and the deuterium excess values decreased from the initial precipitation to the melt impacted firnpack slope from 9 3 to 8 5 and average d excess from 13 4 to 7 4 the slope of the d 18o line further decreased to 7 6 for the glacier runoff water the glacier surface snow ice from different locations which produces the main runoff had the same d 18o line slope but lower deuterium excess by 3 9 compared to values observed in the firnpack profile during the melt season the d 18o regression line for the river water exhibited a lower slope compared to the surface snow ice samples although they were closely located on the d 18o plot isotope values for the river and glacier surface meltwater showed little scatter around the d 18o regression line although the samples were from different glaciers and were collected on different days results indicate a high consistency of isotopic fractionation in the d 18o relationships as well as a general consistency and temporal covariation of meltwater isotope values at the catchment scale copyright 2013 john wiley sons ltd

enhanced scavenging of210pb and210po by processes associated with the east pacific rise near 8 45 n in 1977 and 1981 a hydrothermal plume was detected at the east pacific rise epr near 8 45 n and at manop site m 25 km east of the epr by anomalous222rn and mn concentrations in 1981 samples were also taken for210pb 210po and226ra analyses to determine if enhanced scavenging of these elements occurred in the plume at both the ridge crest and at site m the 210pb 226ra ratios range from 0 09 to 0 35 which are among the lowest values ever measured it appears that removal of the210pb is occurring by processes operating at or near the seafloor there is also significant 210po 210pb disequilibrium at both locations which appears to increase away from the seafloor towards the plume as indicated by elevated mn concentrations an in situ water column scavenging process is suggested by correlation of 210pb 210po and mn concentrations in the plume the residence time of the210po is only about 1 year which is close to its residence time in surface waters but quite short compared to typical deep sea values thus rapid scavenging of the polonium in the plume and relatively rapid settling of particles from the plume is suggested

circulation in the bering sea basin observed by satellite tracked drifters 1986 1993 abstract from 1986 through april 1993 86 satellite tracked buoys were deployed in the north pacific and bering sea most of the buoys were drogued at 40 m a composite current pattern is derived using these data the two principal currents the alaskan stream and kamchatka current are clearly evident eddy kinetic mean kinetic energy ratios are low in the stream and along the western bering sea basin an eastward flowing current occurred along the north flank of the aleutian islands this flow was modified by inflow at the passes westward flow occurred north of 56 n its source was the bering slope current the kamchatka current originated near 175 e along the russian coast numerous eddies and meanders were observed in the kamchatka current eddies were also present on the eastern side of the basin

an improved approach for nonstationary strong ground motion simulation a new stochastic ground motion model for generating a suite of ground motion time history with both temporal and frequency nonstationarities for specified earthquake and site characteristics is proposed based on the wavelet method this new model is defined in terms of 6 key parameters that characterize the duration evolving intensity predominant frequency bandwidth and frequency variation of the ground acceleration process all parameters except for peak ground acceleration pga are identified manually from a database of 2444 recorded horizontal accelerations the two stage regression analysis method is used to investigate the inter and intra event residuals for any given earthquake and site characteristics in terms of the fault mechanism moment magnitude joyner and boore distance and site shear wave velocity sets of the model parameters are generated and used in turn by the stochastic model to generate strong ground motion accelerograms which can capture and properly embody the primary features of real strong ground motions including the duration evolving intensity spectral content frequency variation and peak values in addition it is shown that the characteristics of the simulated and observed response spectra are similar and the amplitude of the simulated response spectra are in line with the predicted values from the published seismic ground motion prediction equations sgmpe after a systematic comparison the proposed method can be used to estimate the strong ground motions as inputs for structural seismic dynamic analysis in engineering practice in conjunction with or instead of recorded ground motions

high frequency observations of melt effects on snowpack stratigraphy kahiltna glacier central alaska range with an increased volume of melt on many of the world s glaciers study of how meltwater affects the properties of glacial snowpack becomes essential to our understanding of how glaciers will respond to climate change we address this problem by studying how snow properties changed on sub daily timescales on the kahiltna glacier alaska between may 26 and june 10 2010 during this period we dug 1 8 m deep snow pits twice daily to record the stratigraphy of melt layers snow hardness grain size and density and sampled for hydrogen isotopic composition d on four occasions from these data we show that 65 of the melted surface snow infiltrates and refreezes in the snowpack this leads to a densification of the snow a 729 increase in volume of melt layers and a homogenization of isotopic and physical snow properties from visual and stratigraphic observations we show that meltwater flow within the snowpack is conducted primarily along lenses and pipes where melt layers later form but that more homogeneous capillary based flow is also important finally we show using isotope ratios that post depositional alteration is exacerbated with increased melt extent using the d profile below a volcanic ash layer as a case study in the future similar studies would benefit from this high frequency monitoring approach to assessing snowpack evolution as it allows for a greater understanding of short duration processes new directions for study would include longer term monitoring efforts over a wider spatial snow pit network copyright 2012 john wiley sons ltd

attenuation relations of strong ground motion in japan using site classification based on predominant period a spectral acceleration attenuation model for japan is presented in the present study the data set includes a very large number of strong ground motion records up to the 2003 off tokach main and aftershocks site class terms instead of individual site correction terms are used the site classes of recording stations are from a recent study on site classification for strong motion recording stations in japan according to a classification scheme that has been used in japanese engineering design the use of site class terms enables tectonic source type effects to be identified and accounted for in the present model the effects of a faulting mechanism for crustal earthquakes also are accounted for for crustal and interface earthquakes a simple form of an attenuation model with respect to distance is able to capture the main strong motion characteristics and achieves unbiased estimates for subduction slab events a simple distance modification factor is employed to achieve plausible and unbiased predictions the effects of source depth tectonic source type and faulting mechanism of crustal earthquakes are significant the need for magnitude squared terms is evaluated and the use of magnitude squared terms reduces the interevent error further

210pb in the pacific the geosecs measurements of particulate and dissolved concentrations abstract we report here on particulate and dissolved 210 pb profiles at 16 stations and on total 210 pb profiles at 3 stations all occupied during the pacific geosecs expedition comparison with measurements at yale on geosecs library samples indicates that during separation of particulate lead from dissolved lead our filtered water samples suffered some loss of 210 pb in the filtration system this effect appears to have reduced the dissolved 210 pb activities by 20 in stations where the water was filtered however for these first pacific data on the 210 pb distribution between the two phases this effect does not significantly interfere with our recognition of the major features of both particulate and dissolved 210 pb distributions the dissolved 210 pb profiles in general vary geographically following the 226 ra profiles in deep water 226 ra increases northward and eastward from the southwest pacific from 22dpm 100kg to over 40 dpm 100 kg in the northeast pacific our dissolved 210 pb profiles show a similar increase in deep water varying from about 10 to 20 dpm 100 kg along this line and are commonly characterized by a mid depth maximum this 210 pb maximum reflects the mid depth 226 ra maximum of the pacific deep water observed along the western boundary current in surface water at low latitudes there is a significant 210 pb flux from the atmosphere which produces a 210 pb 226 ra activity ratio generally greater than unity this flux penetrates as deep as 600 m as indicated by an induced 210 pb minimum caused by the surface maximum the surface water 210 pb excess decreases toward high southern latitudes and vanishes in the circumpolar region the particulate 210 pb profiles show a general increase with depth from 0 3dpm 100kg in subsurface water to 1 5dpm 100kg in bottom water with or without a mid depth maximum that reflects the 226 ra or dissolved 210 pb maximum the particulate 210 pb normally comprises about 2 of the total 210 pb in subsurface water and this fraction increases to about 10 near the bottom as the filtration loss is not taken into account the fraction of particulate 210 pb quoted here is an upper limit since the particulate matter concentrations are quite uniform in the water column below a few hundred meters the 210 pb activity of the particulate matter also increases with depth the particulate matter has a 210 pb concentration of 100dpm g in subsurface water but the concentration increases to 500dpm g or more toward the bottom this indicates that there is a cumulative adsorption of pb onto the suspended particles as they are sinking through the water column

modeling finite fault radiation from the ωn spectrum the high frequency seismic field near the epicenter of a large earth quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point each element is treated as a point source with an o92 spectral shape where co is the angular frequency ground motion contributions from the subsources are calculated using a stochastic model attenuation is based on simple geometric spreading in a whole space coupled with regional anelastic atten uation q operator the form of the co n spectrum with natural n follows from point shear dislocation theory with an appropriately chosen slip time function the seismic moment and comer frequency are the two parameters defining the point source spectrum and must be linked to the subfanlt size to make the method complete two coefficients aa and k provide this link assigning a moment to a subfault of specified size introduces the stress parameter ao the relationship between comer frequency dislocation growth rate and fault size is established through the coefficient k which is inherently nonunique these two parameters control the number of subsources and the ampli tudes of high frequency radiation respectively derivation of the model from shear dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size this uncertainty can only be reduced through empirical vali dation the method is verified by simulating data recorded on rock sites near epicenters of the m8 0 1985 michoacan mexico the m8 0 1985 valparaiso chile and the m5 8 1988 saguenay qurbec earthquakes each of these events is among the largest for which strong motion records are available in their respective tectonic environ ments the simulations for the first two earthquakes are compared to the more de tailed modeling of somerville et al 1991 which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response both methods predict the observations accurately on average the precision of the methods is also approximately equal the predicted acceleration amplitudes in our model are generally within 15 of observations an unexpected result of this study is that a single value of a parameter k provides a good fit to the data at high frequencies for all three earthquakes despite their different tectonic environments this suggests a simplicity in the modeling of source processes that was unanticipated

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

210pb in the western indian ocean distribution disequilibrium and partitioning between dissolved and particulate phases dissolved210pb profiles are presented for 13 geosecs stations in the western indian ocean in surface water away from high southern latitudes 210pb is in excess over226ra due to the atmospheric fallout from decay of222rn except in the circumpolar region the dissolved210pb profiles display a gentle mid depth maximum similar to the corresponding226ra profiles the210pb 226ra activity ratio ranges from 1 6 in the surface water east of madagascar to 0 4 or less in the bottom water of all the basins the lowest ratio observed was 0 1 in the gulf of aden very close to the continental land mass a ratio of 0 6 divides the western indian ocean horizontally into two portions with the contour at shallower depth in the north than in the south the deep water disequilibrium is thus more extensive north of madagascar than south of it it appears that locality and bottom topography play a strong role in controlling the distributions of210pb and226ra as well as their extent of disequilibrium in the water column the mean residence time for pb with respect to particulate and boundary scavenging in the deep water ranges from about 15 to 75 years

ice core net snow accumulation and seasonal snow chemistry at a temperate glacier site mount waddington southwest british columbia canada a 141m ice core was recovered from combatant col 51 385 n 125 258 w 3000ma s l mount waddington coast mountains british columbia canada records of black carbon dust lead and water stable isotopes demonstrate that unambiguous seasonality is preserved throughout the core despite summer surface snowmelt and temperate ice high accumulation rates at the site 4 m ice eq a 1 limit modification of annual stratigraphy by percolation of surface meltwater the ice core record spans the period 1973 2010 an annually averaged time series of lead concentrations from the core correlates well with historical records of lead emission from north america and with ice core records of lead from the greenland ice sheet the depth age scale for the ice core provides sufficient constraint on the vertical strain to allow estimation of the age of the ice at bedrock total ice thickness at combatant col is 250 m an ice core to bedrock would likely contain ice in excess of 200 years in age accumulation at combatant col is significantly correlated with both regional precipitation and large scale geopotential height anomalies

ice layers as an indicator of summer warmth and atmospheric blocking in alaska samples were collected from a snow pit and shallow firn core near kahiltna pass 2970 m a s l denali national park alaska usa in may 2008 the record spans autumn 2003 to spring 2008 and reveals clusters of ice layers interpreted as summertime intervals of above freezing temperatures high correlation coefficients 0 75 1 00 between annual ice layer thickness and regional summertime station temperatures for 4 years n 4 indicate ice layer thickness is a good proxy for mean and extreme summertime temperatures across alaska at least over the short period of record a rex block aka high over low pattern a downstream trough over hudson bay canada and an upstream trough over eastern siberia occurred during the three melting events that lasted at least 2 weeks about half of all shorter melting events were associated with a cut off low traversing the gulf of alaska we hypothesize that a surface to bedrock core extracted from this location would provide a high quality record of summer temperature and atmospheric blocking variability for the last several hundred years

the effects of meltwater percolation on the seasonal isotopic signals in an arctic snowpack we investigate the evolution of snow temperature water content density and stable water isotopes of 18 o at four arctic snow pit sites during early season melt in order to understand the effects of melt on snowpack stratigraphies and seasonal isotopic signals we relate isotopic changes observed at these sites to temperature reconstructions derived from a 33 year firn core record drilled on the same icefield decreases in seasonal isotopic amplitudes observed at all but one snow pit site coincide with the percolation of more enriched meltwater into the snowpack suggesting that meltwater percolation is the dominant process causing isotopic redistribution in arctic snowpacks during the melt season the decrease in isotopic range was accompanied by increases in mean 18 o values at all snow pit sites positive degree day pdd calculations are used to relate the amount of melt observed at the low elevation snow pit sites to the firn core site results based on pdd values suggest an average overestimation of 1 1 c in average annual temperature reconstructions from the firn core site from 1967 to 2006 with the possibility of errors in excess of 3 c during high melt years

deuterium excess record in a southern tibetan ice core and its potential climatic implications a 55 m long ice core drilled close to bedrock from mt noijin kangsang on the southern tibetan plateau in summer 2007 was annually dated covering the period of 1864 2006 ad the stable isotope ratios 18o and d of the ice core were measured and thereby the deuterium excess d was calculated by d d 8 18o for the individual ice samples results show that the d values of the ice samples were predominantly controlled by the moisture sources the significant increasing trend of annual mean d values along the ice core is mainly related to the rapid warming of the tropical indian ocean although the tendency is subjected to the modulation by the western derived moisture the decreasing indian monsoon precipitation on the southern tibetan plateau physically linked with the increasing tropical indian ocean sst reduced the share of monsoon precipitation in the annual total accumulation making an additional contribution to the significant increase of annual mean d in the noijin kangsang ice core with high values during the past 143 years

a stochastic ground motion model for switzerland abstract we present a stochastic ground motion model for switzerland a model for the far field fourier amplitude spectra of earthquakes is first proposed constrained by ground motions observed from small local and regional earthquakes in addition to macroseismic intensities observed from large damaging events in switzerland we then use this model in a stochastic simulation technique to generate predictions of peak ground acceleration and velocity and 5 damped response pseudo spectral acceleration we facilitate the prediction of ground motions from finite fault sources through the use of the r eff distance metric and show that magnitude and distance scaling behavior of events up to m w 7 5 is broadly consistent with next generation attenuation and japanese models ground motion prediction uncertainty is described in terms of between and within event uncertainties through residual analysis of response spectra finally single station sigma is derived accounting for the prediction uncertainty at a given site without the ergodic assumption consistency of the model is emphasized through its compatibility with other seismic hazard products the model is referenced to a generic rock profile that was developed by utilizing velocity profiles of the sites of seismic stations and is calibrated at higher magnitudes to the swiss regional macroseismic intensity prediction model furthermore the model is based on moment magnitudes from the recently developed earthquake catalogue of switzerland 2009 ecos09 the well defined reference for the model means that it can easily be adapted for a site specific application for instance through the use of proxies such as quarter wavelength velocity and travel time average shear wave velocity in the upper 30 m v s 30

effect of periodic melting on geochemical and isotopic signals in an ice core from lomonosovfonna svalbard 1 we examine the quality of atmospherically deposited ion and isotope signals in an ice core taken from a periodically melting ice field lomonosovfonna in central spitsbergen svalbard the aim is to determine the degree to which the signals are altered by periodic melting of the ice we use three diagnostics 1 the relation between peak values in the ice chemical and isotopic record and ice facies type 2 the number of apparent annual cycles in these records compared with independently determined number of years represented in the ice core and 3 a statistical comparison of the isotopic record in the ice core and the isotope records from coastal stations from the same region we find that during warm summers as much as 50 of the annual accumulation may melt and percolate into the firn in a median year this decreases to similar to25 as a consequence of percolation the most mobile acids show up to 50 higher concentrations in bubble poor ice facies compared with facies that are less affected by melt most of the other chemical species are less affected than the strong acids and the stable water isotopes show little evidence of mobility annual or biannual cycles are detected in most parameters and the water isotope record has a comparable statistical distribution to isotopic records from coastal stations we conclude that ice cores from sites like lomonosovfonna contain a useful environmental record despite melt events and percolation and that most parameters preserve an annual or in the worst cases a biannual atmospheric signal

a statistical model for ground motion produced by earthquakes at local and regional distances to adapt random process theory techniques for statistical estimation of peak ground motion to more realistic earth models we constrain the parameters of duration geometrical spreading and spectral shape by modeling the main ground motion as being the result of major contributions by the direct s wave and supercritically reflected s waves the results of our modeling are constrained to be consistent with values from full wave synthetics for the test models the combination of estimation theory and theoretical amplitude spectrum of the main ground motion within the ergodic window successfully predicts the mean peak vertical ground displacements velocities and accelerations of the 1982 miramichi earthquakes in new brunswick canada in addition upon considering the effects of source depth and crustal structure for the november 25 1988 saguenay earthquake m 5 8 in quebec canada the predicted mean peak horizontal ground accelerations match the observed data very well the effects of source depth and crustal structure on the peak ground motion are complicated for different source sizes and at different epicentral distance ranges

chlorofluorocarbon evidence for recent ventilation of the deep bering sea the pattern of the global thermohaline circulation of today s oceans is controlled by deep water formation at the northern and southern limits of the atlantic the apparent lack of deep water formation in the north pacific on the other hand suggests that this ocean plays only a minor role in the global circulation but it is unclear whether this was also the case during periods of glaciation there is conflicting evidence in the sedimentary record for the existence of a deep water source in the north pacific during the last glacial maximum1 4 here we report the detection of anthropogenic chlorofluorocarbons in the bottom waters of the aleutian basin in the eastern bering sea which suggests that a small amount of bottom water has formed in this region during the past 40 years although the small volumes of water involved are unlikely to play a significant role in determining present day global circulation patterns the results lend credence to the possibility that this sea was an important source of deep water for the northwestern pacific ocean during the last glacial maximum