very long period volcanic tremor at stromboli italy we analyze a long time space series of stromboli volcanic tremors a very low frequency content in the range of 0 02 0 5 hz has been found by using spectral analysis and independent component analysis independent component analysis is an entropy based technique we observe the occurrence of a component having a period of 30 sec polarization analysis shows that the wave field comes mainly from the crater area well evidenced by seismometers located around the summit ring whereas the radiation becomes increasingly scattered at stations located around the base of this volcano based on its apparent velocity the 30 sec component appears to be a slow wave related to inhomogeneities of the source and or gas pressure fluctuations inside the shallow plumbing system

broadband recording of strombolian explosions and associated very long period seismic signals on mount erebus volcano ross island antarctica in december 1996 and january 1997 broadband seismometers were deployed on the summit plateau of mount erebus at radial distances of 0 7 1 4 and 1 9 km from the central crater and lava lake strombolian explosions at erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 hz new observations document significant energy with spectral peaks as grave as 20 s nearly identical very long period vlp signals begin 1 5 s prior to explosions have dilatational onsets and persist for up to 150 s similar vlp waveforms were recorded at all three stations indicating that the seismograms are essentially source dominated particle motions suggest an initial depth for the vlp source of up to several hundred meters migrating deeper in the course of 15 s such explosion associated vlp signals may indicate a nondestructive lossy resonance or nonlinear fluid flow excitation within the shallow magmatic system

long period 12 sec volcanic tremor observed at usu 2000 eruption seismological detection of a deep magma plumbing system 1 from a temporal deployment of a broadband seismic network at usu volcano japan we observed long period 12 sec volcanic tremors during the first few weeks of the eruptive activity which started in the end of march 2000 the source of these long period tremors are located relatively deep at a depth of 5 km and their amplitude variation well correlates with the uplift rate of the eruption area we thus attribute these long period tremors to the flow induced vibration of a magma chamber and its outlet located around the source region of the long period tremors this may be the first seismological detection of long period 10 sec vibrations of a deep magma plumbing system

very long period oscillations of mount erebus volcano as the signal decays vlp scalar moments up to 5 10 11 n m exceed sp moments by an order of magnitude or more suggesting distinct though genetically related sp and vlp source mechanisms we conclude that vlp signals arise from excitation of a quasi linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent eruption and magma recharge vlp signal stability across hundreds of eruptions spanning 5 years the persistence of the lava lake and the rapid posteruptive lava lake recovery indicate a stable near summit magma reservoir and vlp source process index terms 4544 oceanography physical internal and inertial waves 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms 8419 volcanology eruption monitoring 7280 keywords strombolian very long period volcano seismology

broadband measurements of the sources of explosions at stromboli volcano italy during september october 1997 21 three component broadband seismometers were deployed on stromboli volcano at radial distances of 0 3 2 2 km from the active crater to investigate the source mechanisms of strombolian explosions in the 2 50 s band the very long period vlp signals associated with explosions are consistent with two stationary sources repeatedly activated in time vlp particle motions are essentially linear and analyses of semblance and particle motions are consistent with a source centroid offset 300 m beneath and 300 m northwest of the active vents similar vlp waveforms are observed at all 21 stations indicating that the seismograms are source dominated the vlp ground displacement response to each explosion may be qualitatively interpreted as 1 pressurization of the conduit associated with the ascent of a slug of gas 2 depressurization of the conduit in response to mass withdrawal during the eruption and 3 repressurization of the conduit associated with the replenishment of the source with fluid

overland flow and infiltration modelling for small plots during unsteady rain numerical results versus observed values this paper reports the development and application of a two dimensional model based on an explicit finite difference scheme coupling overland flow and infiltration processes for natural hillslopes represented by topographic elevation and soil hydraulics parameters this model allows modelling of hortonian overland flow and infiltration during complex rainfall events original procedures have been developed in order to simulate complex rainfall events on natural slopes the accuracy of the results is tested by comparison with experimental field data on the basis of calibrated soil and surface friction parameters good agreement between the calculated result and the measured data was found the scheme proposed was found to be appropriate the results of tests presented illustrate the effect of microtopography on the distribution of the flow depths the magnitude and direction of flow velocities and infiltration depths

field examination of the oceanic carbonate ion effect on stable isotopes in planktonic foraminifera we determined the 18o and 13c of individual globigerinoides ruber and pulleniatina obliquiloculata from sediment traps located from 5 n to 12 s along 140 w in the pacific ocean to evaluate the effects of varying co3 on shell 18o and 13c variations in the offset between shell 13c and 13cdic 13cs dic are attributed to differences in co3 temperature and shell size between sample sites when 13cs dic of g ruber was corrected for variations in co3 using the experimental slope of bijma et al 1998 the residual 13cs dic was correlated with mixed layer temperature 0 10 0 04 c 1 the slope of this temperature effect is consistent with experimental results in p obliquiloculata 13cs dic and temperature were strongly anticorrelated 0 14 0 03 c 1 we are unable to separate the influences of co3 and temperature in this species without independent experimental data correcting for co3 variability on 18os of g ruber improves the accuracy of estimated sea surface temperatures

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

comparison of overland flow hydrograph models the diffusion equation is a simplification of the two dimensional continuity and momentum equations this simpler dynamic model of two dimensional hydraulics affords the hydrologist a means to quickly estimate floodflow effects for overland flow a numerical model using the diffusion approach dhm is applied to a set of idealized catchments in order to develop synthetic unit hydrograph s graph equivalents the model is based on an explicit integrated finite difference scheme and the catchment is represented by topographic elevation and geometric data synthetic unit hydrographs s graphs developed from use of the dhm are used to advance interesting relationships between the unit hydrograph lag factor and the constant effective rainfall intensity used to generate the s graphs sensitivity of the synthetic s graphs to variations in idealized catchment size slope shape friction parameters and effective rainfall intensity are examined comparisons between linear and nonlinear unit hydrograph models a

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

source mechanisms of explosions at stromboli volcano italy determined from moment tensor inversions of very long period data 1 seismic data recorded in the 2 30 s band at stromboli volcano italy are analyzed to quantify the source mechanisms of strombolian explosions during september 1997 to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous elastic medium that takes topography into account two source centroids are identified each representative of the distinct event types associated with explosive eruptions from two different vents the observed waveforms are well reproduced by our inversion and the two source centroids that best fit the data are offset 220 and 260 m beneath and 160 m northwest of the active vents the source mechanisms include both moment tensor and single force components the principal axes of the moment tensor have amplitude ratios 1 1 2 which can be interpreted as representative of a crack if one assumes the rock matrix at the source to have a poisson ratio n 1 3 a value appropriate for hot rock both imaged cracks dip 60 to the northwest and strike northeast southwest along a direction parallel to the elongation of the volcanic edifice and a prominent zone of structural weakness as expressed by lineaments dikes and brittle structures for our data set the volume changes estimated from the moments are 200 m 3 for the largest explosion from each vent together with the volumetric source is a dominantly vertical force with a magnitude of 10 8 n consistent with the inferred movement of the magma column perched above the source centroid in response to the piston like rise of a slug of gas in the conduit index terms 7215 seismology earthquake parameters 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms keywords very long period seismicity moment tensor inversions eruption mehanics

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

modeling runoff and runon in a desert shrubland ecosystem jornada basin new mexico abstract a new two dimensional 2d distributed parameter model is developed to simulate overland flow in two small semiarid shrubland watersheds in the jornada basin southern new mexico the model is event based and represents the watershed by an array of 1 m2 cells in which the cell size is approximately equal to the average area of the shrubs in the model flow directions and volumes are computed by a second order predictor corrector finite difference scheme which is employed to solve the 2d kinematic wave equation thus flow routing is computed implicitly and may vary in response to flow conditions the model uses only six parameters for which values are obtained from field surveys and rainfall simulation experiments the model underpredicts runoff from the watersheds because the measured values of saturated hydraulic conductivity ks for intershrub areas are too high the likely reason for this overestimation is that values of ks were obtained from runoff plot experiments conducted at the beginning of summer on surfaces with degraded seals whereas most summer storms occur on surfaces that have experienced recent rainfall and have well developed seals model performance is much improved when ks is treated as a calibration parameter the importance of runon infiltration in supplying water to shrubs is investigated for a range of rainfall and antecedent soil moisture conditions on average runon infiltration accounts for between 3 and 20 of the total infiltration under a shrub the most favorable conditions for runon infiltration are an initially wet soil and a low mean rainfall rate

transport potential vorticity and current temperature structure across northwest providence and santaren channels and the florida current off cay sal bank currents and temperatures were measured using pegasus current profilers across northwest providence and santaren channels and across the florida current off cay sal bank during four cruises from november 1990 to september 1991 on average northwest providence 1 2 sv and santaren 1 8 sv contribute about 3 sv to the total florida current transport farther north e g 27 n partitioning of transport into temperature layers shows that about one half of this transport is of 18 c water 17 c 19 5 c this can account for all of the excess 18 c water observed in previous experiments this excess is thought to be injected into the 18 c layer in its region of formation in the northwestern north atlantic ocean due to its large thickness potential vorticities in this layer in its area of formation are very low in our data lowest potential vorticities in this layer are found on the northern end of northwest providence channel and are comparable to those observed on the eastern side of the florida current at 27 n on average a low potential vorticity 18 c layer was not found in the florida current off cay sal bank

climate change on the yucatan peninsula during the little ice age we studied a 5 1 m sediment core from aguada x caamal 20 36 6 n 89 42 9 w a small sinkhole lake in northwest yucatan mexico between 1400 and 1500 a d oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2 2 and the benthic foraminifer ammonia beccarii parkinsoniana appeared in the sediment profile indicating a hydrologic change that included increased lake water salinity pollen from a core in nearby cenote san jose chulchaca showed a decrease in mesic forest taxa during the same period oxygen isotopes of shell carbonate in sediment cores from lakes chichancanab 19 53 0 n 88 46 0 w and salpeten 16 58 6 n 89 40 5 w to the south also increased in the mid 15th century but less so than in aguada x caamal climate change in the 15th century is also supported by historical accounts of cold and famine described in maya and aztec chronicles we conclude that climate became drier on the yucatan peninsula in the 15th century a d near the onset of the little ice age lia comparison of results from the yucatan peninsula with other circum caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the lia at that time sea surface temperatures cooled and aridity in the circum caribbean region increased

temperature trends over the past five centuries reconstructed from borehole temperatures for an accurate assessment of the relative roles of natural variability and anthropogenic influence in the earth s climate reconstructions of past temperatures from the pre industrial as well as the industrial period are essential but instrumental records are typically available for no more than the past 150 years therefore reconstructions of pre industrial climate rely principally on traditional climate proxy records each with particular strengths and limitations in representing climatic variability subsurface temperatures comprise an independent archive of past surface temperature changes that is complementary to both the instrumental record and the climate proxies here we use present day temperatures in 616 boreholes from all continents except antarctica to reconstruct century long trends in temperatures over the past 500 years at global hemispheric and continental scales the results confirm the unusual warming of the twentieth century revealed by the instrumental record but suggest that the cumulative change over the past five centuries amounts to about 1 k exceeding recent estimates from conventional climate proxies the strength of temperature reconstructions from boreholes lies in the detection of long term trends complementary to conventional climate proxies but to obtain a complete picture of past warming the differences between the approaches need to be investigated in detail

simple spatially distributed models for predicting flood inundation a review abstract in this paper we review recent progress in the use of reduced complexity models for predicting floodplain inundation we review the theoretical basis for modelling floodplain flow with simplified hydraulic treatments based on a dimensional analysis of the one dimensional shallow water equations we then review how such schemes can be applied in practice and consider issues of space discretization time discretization and model parameterisation before going on to consider model assessment procedures we show that a key advantage of reduced complexity codes is that they force modellers to think about the minimum process representation necessary to predict particular quantities and act as a check on any tendency to reductionism at the same time however the use compared to standard hydraulic codes of strong simplifying assumptions requires us to also address the question how simple can a model be and still be physically realistic we show that by making explicit this debate about acceptable levels of abstraction reduced complexity codes allow progress to be made in addressing a number of long standing debates in hydraulics

highlights from a seismic broadband array on stromboli volcano an array of nine three component broadband seismometers was deployed in two different configurations on stromboli volcano the analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano these new observations are restricted to the low frequency range below 1 hz and underline therefore the superiority of broadband recordings over conventional short period observations surprisingly simple wavelets indicate an initially contracting source mechanism gas jets that could not be seen in a short period seismic record at all generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism the analysis of particle motion and seismic array techniques permits a location of the seismic source we find low frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption related events a video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

a storm event watershed model for surface runoff based on 2d fully dynamic wave equations the main purpose of this work concerns the development and testing of an overland flow model based on the two dimensional fully dynamic shallow water equations three key aspects fundamental to get accurate efficient and robust computation of surface runoff at basin scale are discussed by transferring the main findings obtained by the recent research on the topic of dam break wave and flood propagation in the context of rainfall runoff modelling in particular attention is focused on the numerical flux and bottom slope source terms computation on a numerical treatment of friction slope terms and on an algorithm for dealing with wetting drying fronts the performances of the numerical model have been preliminarily evaluated using experimental or ideal tests characterized by very critical conditions for the stability of a numerical model then attention was focused on a real event occurred in a sub basin of reno river in italy to analyse the suitability of the model in simulating real flood situations the numerical results highlight the good performances of the model in all the simulations discussed in the paper copyright 2012 john wiley sons ltd

spatially averaged conservation equations for interacting rill interrill area overland flows the modeling of flows at hillslope scale over land surfaces that contain rills and interrill areas is presented the flow in rills is treated as one dimensional channel flow the flow at interrill areas is treated as two dimensional sheet flow sheet flow equations are averaged along the interrill area width local averaging to account for the interaction between interrill and rill sections the flow depth at the interrill area outlet section is derived by assuming that the flow profile of the interrill area section has the profile of a sine function to minimize computational efforts and economize on the number of model parameters locally averaged rill and sheet flow equations are then averaged over the transects of a hillsope large scale averaging the expectations of the terms containing more than one variable are obtained through the taylor series expansion around their mean values only the first two moments of the series expansion are considered the results of the model are in good agreemen

shallow water simulation of overland flows in idealised catchments this paper investigates the relationship between the rainfall and runoff in idealised catchments either with or without obstacle arrays using an extensively validated fully dynamic shallow water model this two dimensional hydrodynamic model allows a direct transformation of the spatially distributed rainfall into the flow hydrograph at the catchment outlet the model was first verified by reproducing the analytical and experimental results in both one dimensional and two dimensional situations then dimensional analyses were exploited in deriving the dimensionless s curve which is able to generically depict the relationship between the rainfall and runoff for a frictionless plane catchment with or without an obstacle array the dimensionless s curve seems to be insensitive to the rainfall intensity catchment area and slope especially in the early steep rising section of the curve finally the model was used to study the hydrological response of an idealised catchment covered with buildings which were represented as an obstacle array the influences of the building array size and layout on the catchment response were presented in terms of the dimensionless time at which the catchment outflow reaches 50 of the equilibrium value

very long period signals associated with vulcanian explosions at popocatepetl volcano mexico very long period vlp seismic signals associated with large summit eruptions of popocatepetl volcano in the last four years are investigated using data from a broadband seismometer 0 04 120 s deployed on the north flank of the volcano at a radial distance of 5 km from the active crater the vlp signals associated with individual eruptions share similar waveforms discrete vlp signals accompanying long period lp events also share similar signatures and have dominant periods that are nearly identical to those observed in the vlp waveforms of explosions the vlp particle motions for eruption onsets consistently point to a source located a few km beneath the crater the vlp ground displacement response to each explosion is marked by a compression followed by a dilatation and terminating with another compression suggesting a sequence of pressurization depressurization repressurization of the conduit the repetitive nature of the waveforms points to a non destructive source process which has remained active in the magmatic system of popocatepetl at least since april 1997

modeling the topography of the salar de uyuni bolivia as an equipotential surface of earth s gravity field the salar de uyuni is a massive dry salt lake that lies at the lowest point of an internal drainage basin in the bolivian altiplano a kinematic gps survey of the salar in september 2002 found a topographic range of only 80 cm over a 54 45 km area and subtle surface features that appeared to correlate with mapped gravity in order to confirm the correlation between topography and gravity geopotential we use local gravity measurements and the egm96 global geopotential model to construct a centimeter level equipotential surface corresponding to the elevation of the salar our comparison of gps survey elevations with the equipotential surface estimate shows that 63 of the variance of the gps elevations can be explained by equipotential surface undulations and long wavelength error in the egm96 model alone with an additional 30 explained by the shorter wavelength equipotential surface derived from local gravity in order to establish a physical connection between topography and the geopotential we also develop and test a simple surface process model that redistributes salt via the dissolution transport and redeposition of salt by precipitated water forcing within the model pushes the system to evolve toward constant water depth with the salt surface approximating the shape of the local equipotential surface since the model removes almost all topographic relief with respect to the equipotential surface within a matter of decades it appears that observed 5 cm amplitude 5 km wavelength residual topography is actively maintained by a process independent of gravity driven fluid flow

influence of a co2 aq dependent biological c isotope fractionation on glacial 13c 12c ratios in the ocean planktonic foraminiferal shells buried in deep ocean sediments record lower 13c values of surface water dissolved inorganic carbon during glacial times than during holocene in the southern ocean and at high northern latitudes a drop of between 0 3 and 0 9 is observed whereas the mean change in low and middle latitudes is only 0 15 however a stronger biological carbon pump sufficient to explain the 80 ppmv lower atmospheric pco2 values during glacial times would raise the surface ocean 13c values of dissolved inorganic carbon by about 1 0 here the results of a three dimensional ocean circulation model study are presented which demonstrate that the increase of 13c values in the sea surface due to a strengthening of the biological carbon pump is counteracted by processes which drive the 13c values in the opposite direction this was found by performing simulations employing the three dimensional hamburg model of the oceanic carbon cycle hamocc combined with a co2 aq dependent parameterization of the biological carbon isotope fractionation the difference in the biological carbon isotope fractionation between glacial and holocene is responsible for a lowering of 13c values in surface water dissolved inorganic carbon by about 0 3 the additional effects of the glacially elevated co32 concentration 0 25 0 50 combined with the 0 35 lowering of 13c values for the whole ocean due to a transfer of terrestrial organic carbon from the biosphere to the ocean atmosphere reservoir also contribute to a further 13c drop of 0 6 0 85 hence a small glacial decrease of the planktonic foraminifera 13c of the order of 0 25 instead of an increase is predicted

climatic solar oceanic and geomagnetic influences on late glacial and holocene atmospheric 14c 12c change late glacial and holocene 14c12c ratios of atmospheric co2 vary in magnitude from a few per mil for annual decadal pertubations to more than 10 for events lasting millennia a data set illuminating 10 to 104 yr variability refines our understanding of oceanic climatic versus geomagnetic or solar forcing of atmospheric 14c12c ratios most of the variance in the holocene atmospheric 14c12c record can be attributed to the geomagnetic millennia time scale and solar century time scale influence on the flux of primary cosmic rays entering the atmosphere attributing the observed atmospheric 14c12c changes to climate alone leads to ocean circulation and or global wind speed changes incompatible with proxy records climate ocean related 14c redistribution between carbon reservoirs while evidently playing a minor role during the holocene may have perturbed atmospheric 14c12c ratios measurably during the late glacial younger dryas event first order corrections to the radiocarbon time scale 12 000 30 000 14c yr b p are calculated from adjusted lake sediment and tree ring records and from geomagnetically defined model 14c histories paleosunspot numbers 100 9700 cal yr b p are derived from the relationship of model 14c production rates to sunspot observations the spectral interpretation of the 14c12c atmospheric record favors higher than average solar activity levels for the next century minimal evidence was found for a sun weather relationship

modeling rain driven overland flow empirical versus analytical friction terms in the shallow water approximation modeling and simulating overland flow fed by rainfall is a common issue in watershed surface hydrology modelers have to choose among various friction models when defining their simulation framework the purpose of this work is to compare the simulation quality for the manning darcy weisbach and poiseuille friction models on the simple case of a constant rain on a thin experimental flume results show that the usual friction law of manning is not suitable for this type of flow the poiseuille friction model gave the best results both on the flux at the outlet and the velocity and depth profile along the flume the darcy weisbach model shows good results for laminar flow additional testing should be carried out for turbulent cases

a geostrophic transport estimate for the florida current from the oxygen isotope composition of benthic foraminifera we present a new method for the quantitative reconstruction of upper ocean flows for during times in the past for the warm t 5 c surface ocean density can be accurately reconstructed from calcite precipitated in equilibrium with seawater as both of these properties increase with decreasing temperature and increasing salinity vertical density profiles can be reconstructed from the oxygen isotopic composition of benthic foraminifera the net volume transport between two vertical density profiles can be calculated using the geostrophic method using benthic foraminifera from surface sediment samples from either side of the florida straits florida keys and little bahama bank we reconstruct two vertical density profiles and calculate a volume transport of 32 sv using this method this agrees well with estimates from physical oceanographic methods of 30 32 sv for the mean annual volume transport we explore the sensitivity of this technique to various changes in the relationship between temperature and salinity as well as salinity and the oxygen isotopic composition of seawater

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

the polarization of volcanic seismic signals medium or source abstract with the proliferation of three component seismometers on volcanoes the temptation is great to use polarization analysis as we do in earthquake seismology to determine propagation direction and or wavetype in order to locate and characterize the wave s source in volcano seismology there are two impediments to such a procedure the complexity of the volcano s structure and the often long lasting volcanic seismic signals i develop a simple model of acoustic scattering and apply it to three simple theoretical source signals which represent the classes of signals encountered at volcanoes when the medium is strongly scattering the polarization at a receiver location for impulsive sinusoidal or square wave sources mimics the characteristics for volcanic shocks tornillos with a single frequency and multichromatic tremor or tornillos the polarization observed for the square wave source resembles that observed for multichromatic tremor at lascar volcano chile and multichromatic tornillos at galeras volcano colombia at low frequencies the particle motion is fairly linear and nearly constant but cannot necessarily be used directly to indicate the direction to the source at all frequencies the particle motion exhibits some characteristics of rayleigh waves namely ellipticity of varying degrees and an rz product that oscillates with twice the frequency of the mode if this model is correct the lack of change of fundamental wavefield parameters such as the polarization for low frequencies during any given tornillo and from one tornillo to the next implies that the location of the source is stable to within a resolution of about 200 m

hydrodynamic description for advective sediment transport processes and rill initiation a physically based model for advective sediment transport during rill initiation is developed based on 1 a short wavelength rescaling of the momentum balance equations for the surface water flux 2 a deforming coordinate system which characterizes local morphological changes of the surface during erosion and 3 a generalized transport function for the surface sediment flux which distinguishes the contributions of diffusive and advective transport a linear stability analysis of the coupled system indicates that an intrinsic minimum transverse length scale for rill initiation is forced by the cross slope pressure gradient in the surface water the wavelength of this initial rill spacing is dependent upon the relative significance of the advective component of sediment transport and the hydraulic efficiency of the surface water flux and is independent of the total length of the hillslope the hydrodynamic model presented can also be used to evaluate the nonlinear development of rills and rill networks subsequent to initiation

analytical model of surface flow on hillslopes based on the zero inertia equations abstractcoming from the zero inertia zi equations an analytical model to describe sheet flow phenomena with a special focus on rainfall runoff processes is developed a slight modification of the zi equations which draws upon the concept of a momentum representative cross section of the moving water body leads after comprehensive mathematical calculus to an analytical solution describing essentially one dimensional shallow overland flow in a test series the analytical zi model is applied together with three numerical models one based on the saint venant equations one on the kinematic wave equations and another one on diffusion wave equations the test application refers to a typical rainfall runoff situation i e rather shallow overland flow on a hillslope as a consequence of excess rainfall contrary to the analytical model the comparative analysis clearly shows the difficulties of the numerical solutions in terms of exactness and robustness when approaching typical shallow water depths th

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

modeling of two dimensional overland flow a two dimensional hydrodynamic and numerical model for overland flow is developed in this paper the model allows spatial variations in hillslope physical characteristics including surface roughness infiltration and microtopography the accuracy of the model is tested by comparison with characteristic based solutions and experimental data the results of these tests indicate that the model is accurate and has good stability and convergence properties the application of the model to two dimensional overland flow on hillslopes is demonstrated by applying it to surfaces with spatially variable roughness infiltration and microtopography these simulations show that microtopography is the dominant factor causing spatial variation in overland flow depth velocity and direction

a seepage face model for the interaction of shallow water tables with the ground surface application of the obstacle type method this paper presents a model to simulate overland flow genesis induced by shallow water table movements in hillslopes variably saturated subsurface flows are governed by the richards equation discretized by continuous finite elements on unstructured meshes an obstacle type formulation is used to determine where saturation conditions and thus seepage face conditions are met at the ground surface the impact of hillslope geometry boundary conditions and soil hydraulic parameters on model predictions is investigated on two dimensional test cases at the metric and hectometric scales the obstacle type formulation is also compared with a more detailed model coupling subsurface and overland flow the latter being described by the shallow water equations in the diffusive wave regime

cyclic fluid effusion accompanied by pressure change implication for volcanic eruptions and tremor magma effusion and tremor sometimes occur in quite regular intervals with periodic pressure changes as observed in volcanic eruptions at kilauea volcano lava dome growth at unzen volcano and tremor episodes at izu oshima volcano these events have more or less asymmetric pressure change of quasi sinusoidal to saw toothed shape with longer time elapsing in build up of the fluid pressure than in its relaxation such cyclic fluid effusion can be explained systematically by a simple model in which fluid is supplied at a constant rate accumulates in an elastic chamber and flows out in a cylindrical vent that may widen or narrow due to viscous deformation of the surrounding country rock

magmatic dike resonances inferred from very long period seismic signals very long period vlp signals showing simple decaying harmonic oscillations with periods near 10 seconds and lasting for about 300 seconds were observed in association with an earthquake swarm that occurred beneath hachijo island japan results from the source mechanism analysis and waveform simulation based on a fluid filled crack model consistently point to the resonance of a dike filled with a basaltic magma as the source of the vlp signals thus vlp signals can be used to probe the state of the fluid and dynamic processes within a volcanic system

psem_2d a physically based model of erosion processes at the plot scale 1 this paper presents the development and first applications of the plot soil erosion model 2d psem 2d infiltration is computed using a green and ampt model overland flow is computed using the depth averaged two dimensional unsteady flow equations saint venant equations and soil erosion is computed by combining the equation of mass conservation of sediment and a detachment transport coupling model for erosion by runoff a shear stress approach is used to determine the transport capacity the formation of a covering cohesionless layer as a result of depositing sediment and action of rainfall impact before runoff is considered the erosion processes involved are rainfall and runoff detachment of original soil rainfall redetachment and overland flow entrainment of sediment from the deposited layer and deposition the model uses a single representative particle size complex rainfall events on natural slopes can be simulated the accuracy of the predictions for erosion of planar surfaces is tested by comparison with observed data obtained from experiments and with an analytical solution good agreement between the calculated results and measured data was found a sensitivity analysis was also performed limitations related to the description of overland flow on plane soil surface are pointed out finally an application to a nonplanar natural surface of 75 m2 illustrated the distribution of erosion and sedimentation over the plot

lattice boltzmann method for rain induced overland flow abstract complex rainfall situations can generate overland flow with complex hydrodynamic characteristics affecting the surface configuration i e sheet erosion and environment to varying degrees reliable numerical simulations can provide a scientific method for the optimization of environmental management a mesoscopic numerical method the lattice boltzmann method was employed to simulate overland flows to deal with complex rainfall two schemes were introduced to improve the lattice boltzmann equation and the local equilibrium function respectively four typical cases with differences in rainfall bed roughness and slopes were selected to test the accuracy and applicability of the proposed schemes it was found that the simulated results were in good agreement with the experimental data analytical values and the results produced by other models

one and two dimensional modelling of overland flow in semiarid shrubland jornada basin new mexico two distributed parameter models a one dimensional 1d model and a two dimensional 2d model are developed to simulate overland flow in two small semiarid shrubland watersheds in the jornada basin southern new mexico the models are event based and represent each watershed by an array of 1 m2 cells in which the cell size is approximately equal to the average area of the shrubs each model uses only six parameters for which values are obtained from field surveys and rainfall simulation experiments in the 1d model flow volumes through a fixed network are computed by a simple finite difference solution to the 1d kinematic wave equation in the 2d model flow directions and volumes are computed by a second order predictor corrector finite difference solution to the 2d kinematic wave equation in which flow routing is implicit and may vary in response to flow conditions the models are compared in terms of the runoff hydrograph and the spatial distribution of runoff the simulation results suggest that both the 1d and the 2d models have much to offer as tools for the large scale study of overland flow because it is based on a fixed flow network the 1d model is better suited to the study of runoff due to individual rainfall events whereas the 2d model may with further development be used to study both runoff and erosion during multiple rainfall events in which the dynamic nature of the terrain becomes an important consideration copyright 2006 john wiley sons ltd

measurement and modelling of high resolution flow velocity data under simulated rainfall on a low slope sandy soil the study presented here is focussed on the question of the hydraulic nature of the threshold that allows a rill to start a rainfall simulation experiment was carried out to produce high resolution flow velocity data the experiment employed a 10 m 4 m experimental plot with a 1 slope which had been previously eroded and had a small rill formed in the middle the experiment consisted of a 2 h 15 long rainfall at a constant intensity of 69 mm h 1 surface elevation was measured before rainfall at a horizontal resolution of 2 5 cm across and 5 cm along the slope direction during rainfall flow velocities were measured at 68 locations on the plot with the salt velocity gauge technology an automated miniaturized device based on the inverse modelling of the propagation of a salt plume the experiment led to the collection of flow velocity measurements which are novel in three ways i the small size of the measured section which was only 10 cm long and 1 cm wide ii the wide range of measured flow velocities which ranged from 0 006 m s 1 to 0 27 m s 1 and iii the large number of measured locations the flow velocity field was simulated with three models psem 2d solves the saint venant equations in 2d mahleran uses a 1d kinematic wave in the slope direction coupled with a 2d flow routing algorithm and rillgrow2 which involves an empirical runoff algorithm that is close in principle to the diffusion wave equation in 2d the darcy weisbach friction factor ff and the infiltration parameters were calibrated in all cases to investigate the capabilities of the different models to reproduce flow hydraulics compatible with the onset of rilling in a first set of numerical experiments ff was set uniform and calibration used only the hydrograph the comparison of simulated and observed flow velocity field showed that psem 2d was the most satisfying model at the cost of longer computational time mahleran gave surprisingly good results with regards to the simplicity of the model and its low computational needs however all models largely underestimated the highest velocity values located in the rill furthermore none of the models was able to simulate the reynolds re and froude fr numbers the next numerical experiment was done with psem 2d non uniform ff values were calibrated by fitting the simulated flow velocity field to the observed one the latter simulation produced realistic simulations of re and fr the hydraulic conditions at the transition from interrill flow to rill flow are discussed the results support the theory that supercritical flows are a necessary condition for a rill to emerge from a smooth surface

last glacial maximum paleochemistry and deepwater circulation in the southern ocean evidence from foraminiferal cadmium south atlantic benthic foraminiferal cd ca shows no glacial interglacial variation suggesting that the glacial contribution of north atlantic deep water to the southern ocean was not much different than at present in contrast cd ca in southeast indian ridge cores show lower glacial bottom water cd comparable to levels in intermediate depths of the north atlantic and significantly lower than in the deep south atlantic low glacial cd ca was also recorded in planktonic foraminifera suggesting a substantial decrease in the nutrient concentration of subantarctic surface water during the glacial maximum which most likely was caused by increased biological productivity the cd data are inconsistent with low glacial benthic foraminiferal 13c which suggest higher nutrient concentration we propose that the low cd ca in the southeast indian ridge records reflects a local source of nutrient depleted deepwater formed during the last glacial maximum by open ocean convection near the antarctic polar front downstream of the kerguelene plateau if this source was limited to the southeast indian basin then its impact on the overall chemistry of glacial circumpolar deepwater was rather small however if during glaciations open ocean convection became the dominant mode of bottom water formation it might have had a greater impact on cpdw chemistry

evidence of vlp volcanic tremor in the band 0 2 0 5 hz at stromboli volcano italy 1 we analyze time series of strombolian volcanic tremor recorded with a network of broadband seismic stations we evidence the occurrence of a significant component of volcanic tremor in the range 0 2 0 5 hz by using linear and nonlinear methods the polarization and zlcc analysis show that the wave field is characterized by high apparent velocity 2 km s it comes mainly from the crater area with a clear amplitude decay towards the sea level the previous properties are loosed when the tremor level is higher suggesting that in this case the wave field is more affected by oceanic noise the waveform extracted by independent component analysis ica shows a behaviour like nonlinear beats as in the case of high frequency waveforms we conclude that this component displays a behaviour like the wave field at higher frequencies in spite of its low frequency and it is produced by the vibrations of the volcanic conduit

calibration of stable isotopic data an enriched δ18o standard used for source gas mixing detection and correction we present empirically based calibrations of our measurements made on a finnigan mat252 equipped with a kiel device to vienna pee dee belemnite using an enriched 18o standard calibrations include corrections for biases caused by the differences in isotopic composition of carbonate standards measured on the two parallel extraction lines of the kiel device and for decreases in the isotopic difference between the reference and sample gas caused by mixing in the source after correcting for these biases the precision of 2200 nbs19 analyses 10 300 g is 0 07 for 18o and 0 03 for 13c we have shared our standard enriched in 18o with 18 laboratories engaged in paleoceanographic research producing the first large scale interlaboratory calibrations for this community using correction procedures reported here water mass reconstructions using data produced on multiple mass spectrometers may now be possible with a precision approaching the level necessary to reconstruct temperature salinity and density variability in the deep ocean

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

current meter observations in the old bahama channel current meter observations were made at 50 250 and 435 m in 495 m of water at the center of the old bahama channel between november 1990 and november 1991 the mean speed at those depths was 2 6 50 and 26 cm s 1 toward the straits of florida a maximum speed of 193 cm s 1 was found at the 250 m level there was evidence of a speed maximum between 50 and 250 m large internal diurnal tidal currents were observed that produced high shears in the water column under some conditions transport calculated from the single mooring using simple assumptions varied from 2 4 to 6 6 sv with a mean of 1 9 sv toward the straits of florida these values while based on limited data are very significant compared to the mean flow in the straits of florida thus flow through the old bahama channel may be an important component of heat and salt transport in the straits

pressure coefficient in dam break flows of dry granular matter abstractthe propagation of dry granular flows such as rock and snow avalanches can be described by depth averaged models different from classical shallow water equations these models take into account the anisotropy of normal stresses inside the flowing pile through using an earth pressure coefficient in the pressure term a new regularization function for calculating the pressure coefficient in the savage hutter type models at the early stages of dam break flows and collapses is proposed in such circumstances the flow lines are significantly curved with respect to the basal surface and a special treatment of the earth pressure coefficient is required for obtaining a satisfactory agreement with experimental data the comparison between numerical simulations and laboratory experimental data shows an apparent improvement in describing the early stages of dam break waves over rough beds the comparison with experiments over smooth bed surface exhibits minor evidence of improvement nonetheless in this

florida current surface temperature and salinity variability during the last millennium surface water d 18 ow near dry tortugas increased 0 4 during the course of the little ice age lia 1200 1850 a d equivalent to a salinity increase of 0 8 1 5 on the great bahama bank where surface waters are influenced by the north atlantic subtropical gyre d 18 ow increased by 0 3 during the last 200 years although a portion 0 1 of this shift may be an artifact of anthropogenically driven changes in surface water sco2 the remaining d 18 ow signal implies a 0 4 1 increase in salinity after 200 years b p the simplest explanation of the d 18 ow data is southward migration of the atlantic hadley circulation during the lia scaling of the d 18 ow records to salinity using the modern low latitude d 18 ow s slope produces an unrealistic reversal in the salinity gradient between the two sites only if d 18 ow is scaled to salinity using a high latitude d 18 ow s slope can the records be reconciled variable atmospheric 14 c paralleled dry tortugas d 18 ow suggesting that solar irradiance paced centennial scale migration of the inter tropical convergence zone and changes in florida current salinity during the last millennium citation lund d c and w curry 2006 florida current surface temperature and salinity variability during the last millennium paleoceanography 21 pa2009 doi 10 1029 2005pa001218

experimental validation of a 2d overland flow model using high resolution water depth and velocity data summary this paper presents a validation of a two dimensional overland flow model using empirical laboratory data unlike previous publications in which model performance is evaluated as the ability to predict an outlet hydrograph we use high resolution 2d water depth and velocity data to analyze to what degree the model is able to reproduce the spatial distribution of these variables several overland flow conditions over two impervious surfaces of the order of one square meter with different micro and macro roughness characteristics are studied the first surface is a simplified representation of a sinusoidal terrain with three crests and furrows while the second one is a mould of a real agricultural seedbed terrain we analyze four different bed friction parameterizations and we show that the performance of formulations which consider the transition between laminar smooth turbulent and rough turbulent flow do not improve the results obtained with manning or keulegan formulas for rough turbulent flow the simulations performed show that using keulegan formula with a physically based definition of the bed roughness coefficient a two dimensional shallow water model is able to reproduce satisfactorily the flow hydrodynamics it is shown that even if the resolution of the topography data and numerical mesh are high enough to include all the small scale features of the bed surface the roughness coefficient must account for the macro roughness characteristics of the terrain in order to correctly reproduce the flow hydrodynamics

late holocene variability in florida current surface density patterns and possible causes 1 planktonic foraminiferal 18o time series from three well dated high sedimentation rate cores near the florida keys 24 4 n 83 3 w exhibit repeated centennial to millennial scale oscillations during the late holocene isotopic shifts of 0 2 0 3 over the past 5200 years represent changes in sea surface temperature sst of 1 0 1 5 c or salinity variability of 1 2 psu the largest significant isotopic events are centered at approximately 200 2000 3200 and prior to 4000 calendar years bp high florida current 18o during the little ice age lia correlates with published records of high 18o in the sargasso sea and low sst off the coast of west africa an interval of generally low 18o in the florida straits from 1800 to 500 years bp is synchronous with the medieval warm period off west africa but leads low 18o in the sargasso sea by several hundred years synchronous cooling across the subtropical gyre during the lia is difficult to explain using interannual north atlantic oscillation patterns but may be consistent with the simulated effects of reduced solar irradiance at frequencies between 1 1000 and 1 300 years during the late holocene florida current 18o is coherent with a published estimate of 14c production rate radiocarbon production seems to lead 18o at these frequencies but uncertainty in the phase calculation precludes a clear lead lag relationship at frequencies lower than 1 300 years florida current 18o is coherent and in phase with atmospheric 14c the coherence of 14c and 18o at periods 1000 years implies oceanic circulation may play a role in modulating atmospheric radiocarbon on millennial timescales

a numerical model for simulating hortonian overland flow on tropical hillslopes with vegetation elements this paper describes a two dimensional hydrodynamic model that characterizes surface runoff process resulting from a varying rainfall intensity event on an infiltrating soil surface the soil surface has spatially varied soil physical hydraulic and microtopographic characteristics infiltration process is modelled with the philip two term equation and the time before ponding approximated with the time compression algorithm vegetation is modelled as a dynamic component with the modified gash model the equation is solved with a modified second order leapfrog explicit finite difference scheme with centred time and space derivatives the model was validated with standard analytical solutions evaluation with results from field campaigns in the volta basin of west africa during the 2002 rainfall season indicates good agreement with r2 values ranging from 0 89 to 0 96 the developed method will be useful in studying the dynamics of surface runoff generation under complex microtopographic conditions spatially varying soil hydraulic characteristics and temporally dynamic rainfall intensity as found in many tropical catchments copyright 2007 john wiley sons ltd

carbon isotope records from extant caribbean and south pacific sponges evolution of δ13c in surface water dic stable isotope records of demosponges from the caribbean and coral sea are described for the purpose of studying the influence of fossil fuel co2 on the carbon isotopic composition of dissolved inorganic carbon dic in surface water the slow growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in 13cdic from pre industrial times early 19th century to the present we observed similar shapes and ranges in 13c curves measured on caribbean specimens collected from water depths of 25 84 and 91 m as well as a specimen collected in shallow waters off new caledonia the records reveal a highly significant correlation with atmospheric 13cco2 13cdic values for caribbean and coral sea surface waters were calculated using the 13c sponge records while 13c of atmospheric co2 decreased by about 1 4 from the early 19th century to 1990 13cdic of caribbean and coral sea surface waters decreased by 0 9 0 2 and 0 7 0 3 respectively no isotopic equilibrium between surface water dic and atmospheric co2 was observed either during the pre industrial steady state or during the last 100 years the lower amount of depletion in the surface water 13cdic with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water dic the lower 13c decrease in the coral sea points to a stronger influence of the subsurface water source compared to the caribbean

caribbean sea surface temperatures two to three degrees cooler than present during the little ice age we determined the seasonal environmental conditions during the little ice age lia by interpreting isotope proxies in the coral skeleton of montastrea faveolata from the northeast caribbean the oxygen isotope composition was determined for three time intervals during the lia 1700 1705 1780 1785 1810 1815 thought to correspond to the coldest intervals the period 1984 1989 was used to represent modern calibration conditions we determined that ssts from the lia intervals are nearly 2 3 c cooler than present lia cooling in the caribbean may have resulted from regional oceanic and atmospheric circulation differences especially in winter we propose that a trough of cold air from the north atlantic may have extended farther south than present into the northern caribbean although there are indications from pacific corals that seasonality was greater during the lia this does not seem to be the case for the caribbean

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

glacial interglacial changes in subantarctic sea surface temperature and δ18o water using foraminiferal mg laboratory culturing experiments with living globigerina bulloides indicate that mg ca is primarily a function of seawater temperature and suggest that mg ca of fossil specimens is an effective paleotemperature proxy using culturing results and a core top neogloboquadrina pachyderma calibration we have estimated glacial interglacial changes in sea surface temperature sst using planktonic mg ca records from core rc11 120 in the subantarctic indian ocean 43 s 80 e and core e11 2 in the subantarctic pacific ocean 56 s 115 w our results suggest that glacial sst was about 4 c cooler in the subantarctic indian ocean and 2 5 c cooler in the subantarctic pacific comparison of sst and planktonic 18o records indicates that changes in sst lead changes in 18o by on average 1 3 kyr the glacial interglacial temperature change indicated by the subantarctic mg ca records suggests that temperature accounts for 40 60 of the foraminiferal 18o change we have used the mg ca based sst estimates and 18o determinations to generate site specific seawater 18o records which suggest that seawater 18o was on average 1 more positive during glacial episodes compared with interglacial episodes