reduced atlantic storminess during last glacial maximum evidence from a coupled climate model the last glacial maximum lgm 21 000 yr before present was the time of maximum land ice extent during the last ice age a recent simulation of the lgm climate by a state of the art fully coupled global climate model is shown to exhibit strong steady atmospheric jets and weak transient eddy activity in the atlantic sector compared to today s climate in contrast previous work based on uncoupled atmospheric model simulations has shown that the lgm jets and eddy activity in the atlantic sector are similar to those observed today with the main difference being a northeastward extension of their maxima the coupled model simulation is shown to agree more with paleoclimate proxy records and thus is taken as the more reliable representation of lgm climate the existence of this altered atmospheric circulation state during lgm in the model has implications for understanding the stability of glacial climates for the possibility of multiple atmospheric circulation regimes and for the interpretation of paleoclimate proxy records

erratum to observation and prediction of dynamic ground strains tilts and torsions caused by the mw 6 0 2004 parkfield california earthquake and aftershocks derived from upsar array observations online material corrected figures and strain rotation and displacement gradient time series

effect of stone content on water flow velocity over loess slope non frozen soil abstract stony soils are commonly found worldwide and are considerably studied for their hydrological characteristics and effect on soil erosion water flow velocity is an important parameter in understanding the effect of stone content on hydrodynamics and soil erosion in this study laboratory experiments were used to measure rill flow velocity by using electrolyte tracer method under different hydraulic conditions flow rates of 1 2 4 and 8 l min slope gradients of 5 10 15 and 20 and stone mass contents amounting to 0 10 20 and 50 nine sensors which were 1 m apart along the 8 m long rill were used to measure flow velocity by tracing solute transport measured flow velocity increased with slope gradient and flow rate the highest increase in flow velocity was measured from 15 to 20 which were also affected by flow rate effects of discharge rate on flow velocity presented the largest difference when flow rate increased from 2 l min to 8 l min at slope gradients higher than 5 the effects of different factors were quantified by a regression model with high accuracy of 0 99 maximum flow velocity of water was predicted at 15 23 of stone content flow velocity increased with 0 15 23 of stone content but decreased at higher values this study aims at further understanding the hydrodynamics of soil erosion and sediment transport behaviors in hillslopes with different stone contents to obtain information for quantifying soil erosion on stony slopes

high latitude eruptions cast shadow over the african monsoon and the flow of the nile 1 nile river records indicate very low flow following the 1783 1784 laki volcanic eruption as well as after other high latitude volcanic eruptions as shown by climate model simulations of the laki eruption significant cooling 1 to 3 c of the northern hemisphere land masses during the boreal summer of 1783 resulted in a strong dynamical effect of weakening the african and indian monsoon circulations with precipitation anomalies of 1 to 3 mm day over the sahel of africa thus producing the low nile flow future high latitude eruptions would significantly impact the food and water supplies in these areas using observations of the flow of the nile river this new understanding is used to support a date of 939 for the beginning of the eruption of the eldgja volcano in iceland the largest high latitude eruption of the past 1500 years

green mountains and white plains the effect of northern hemisphere ice sheets on the global energy budget abstractthe changes in the global energy budget in response to imposing an ice sheet s topography albedo or topography and albedo combined are examined the albedo of the ice sheet here called a white plain causes an outgoing top of the atmosphere radiation anomaly over the ice sheet that is balanced by an incoming anomaly in the southern hemisphere this causes a northward transport of heat across the equator that is carried equally by the ocean and atmosphere the topography of the ice sheet green mountain causes an incoming radiation anomaly over the ice sheet that is balanced predominantly by an outgoing anomaly to the south of the ice sheet with a smaller outgoing flux in the southern hemisphere the heat is transported across the equator by the atmosphere alone the combined topography and albedo of the ice sheet white mountain cause an outgoing radiation anomaly over the ice sheet that is balanced equally by an incoming flux in the southern hemisphere and to the south of the ice shee

interhemispheric thermal gradient and tropical pacific climate 1 we explore the impact of interhemispheric thermal gradients forcing on the tropical pacific ocean atmosphere climate in an intermediate coupled model the equatorial zonal sea surface temperature sst gradient strengthens with an increased northward interhemispheric thermal gradient the increase arising from earlier onset and later retreat of the seasonal cold tongue and intensification during the peak cold season when the mean interhemispheric thermal gradient is reversed the central equatorial pacific sst annual cycle abruptly reverses in phase with its cold season in mar may rather than sep nov while startling this response is consistent with a prevailing hypothesis that ties the cold tongue sst annual cycle phase to the hemispheric mean asymmetry of the intertropical convergence zone el nino southern oscillation activity is also sensitive to the interhemispheric thermal gradient with peak activity occurring when the mean gradient is small reducing rapidly as the mean gradient increases in either direction

thermocline dynamics in the northwestern tropical pacific over the past 700 kyr abstract variations in thermoclinal conditions play an important role in the evolution of the western pacific warm pool wpwp and in connecting the tropical and extratropical regions of the pacific ocean however secular thermoclinal changes in the northwestern part of the wpwp and their forcing mechanisms are not yet well understood particularly on orbital timescales in this study we report thermoclinal variation at site md06 3047 b in the western philippine sea over the last 700 kyr our data show that variations in thermocline temperature and salinity in the study area were correlated with changes in earth s obliquity with warmer and saltier colder and fresher thermocline waters corresponding to high low earth axial obliquity at high obliquity increases in thermocline temperature and salinity may have been linked to advection of warm north pacific tropical water in the study area a lower higher vertical temperature gradient in the upper water column suggests a deeper shallower thermocline during glacials interglacials the main factor leading to thermoclinal deepening during glacials was strengthening of the east asian winter monsoon eawm and more la nina like conditions may have contributed to concurrent subsurface warming and thus thermoclinal deepening in phase thermoclinal deepening in the northern and peri equatorial southern wpwp during glacial stages may have been triggered by changes in glacial boundary conditions such as increased ice sheet thickness through intensification of the eawm and strengthening of the tropical trade winds

tropical pacific response to continental ice sheet topography the last glacial maximum was marked by maximum land ice extent and lowest greenhouse gases concentration during the last ice age we explore the impact of glacial continental ice sheet topography on the large scale tropical ocean atmosphere climate in particular the tropical pacific in an intermediate complexity coupled model increasing the thickness of continental ice sheets causes a southward displaced pacific intertropical convergence zone itcz and a strengthening weakening of northern southern hemisphere winter hadley cell the equatorial zonal sea surface temperature gradient weakened with an increased continental ice sheets thickness the reduction being caused by cooling in the western equatorial pacific and warming in the eastern equatorial pacific the evolution of the tropical climate with changing ice thickness has distinct quasi linear and nonlinear parts while the linear part is a direct response to the ice topographic changes the nonlinear part was a result of the tropical thermocline adjustment our analysis of a fully coupled transient deglacial simulation strongly indicates the dominant role of ice sheet topography in determining the deglacial evolution of the simulated pacific climate the thickness of continental ice sheet separate from ice albedo effect has significant impact on the tropical ocean atmosphere climate in particular with the meridional displacement in the pacific itcz the altered circulation states seen in the model may aid understanding of the relationship between tropical and high latitude climate records in glacial interglacial cycles

response of the amazon rainforest to late pleistocene climate variability abstract variations in amazonian hydrology and forest cover have major consequences for the global carbon and hydrological cycles as well as for biodiversity yet the climate and vegetation history of the lowland amazon basin and its effect on biogeography remain debated due to the scarcity of suitable high resolution paleoclimate records here we use the isotopic composition d and 13 c of plant waxes from a high resolution marine sediment core collected offshore the amazon river to reconstruct the climate and vegetation history of the integrated lowland amazon basin for the period from 50 000 to 12 800 yr before present our results show that d values from the last glacial maximum were more enriched than those from marine isotope stage mis 3 and the present day we interpret this trend to reflect long term changes in precipitation and atmospheric circulation with overall drier conditions during the last glacial maximum our results thus suggest a dominant glacial forcing of the climate in lowland amazonia in addition to previously suggested thermodynamic mechanisms of precipitation change which are directly related to temperature we conclude that changes in atmospheric circulation are crucial to explain the temporal evolution of amazonian rainfall variations as demonstrated in climate model experiments our vegetation reconstruction based on 13 c values shows that the amazon rainforest was affected by intrusions of savannah or more open vegetation types in its northern sector during heinrich stadials while it was resilient to glacial drying this suggests that biogeographic patterns in tropical south america were affected by heinrich stadials in addition to glacial interglacial climate variability

a one dimensional model for the interaction between continental scale ice sheets and atmospheric stationary waves the great continental ice sheets of the pleistocene represented a significant topographic obstacle to the westerly winds in northern midlatitudes this work explores how consequent changes in the atmospheric stationary wave pattern might have affected the shape and growth of the ice sheets themselves a one dimensional 1 d model is developed which permits an examination of the types and magnitudes of the feedbacks that might be expected when plausible temperature perturbations are introduced at the ice sheet margin which are proportional to the stationary wave amplitude the equilibrium shape of the ice sheet is significantly altered and depends on the sign of the perturbation the proposed feedback also affects the response of the ice sheet to time varying climate forcing the results suggest that the evolution of a continental scale ice sheet with a land based margin may be significantly determined by the changes it induces in the atmospheric circulation

effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion rock fragments can act as a controlling factor for erosional rates and patterns in the landscape thus the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix play in concentrated flow hydraulics and erosion laboratory flume experiments were conducted with soil material that was mixed with rock fragments rock fragment content ranged from 0 to 40 per cent by volume other treatments were slope 7 and 14 and flow discharge 5 7 and 11 4 l min 1 an increase in rock fragment content resulted in lower sediment yield and broader width of flow rock fragment cover at the soil surface i e surface armour increased with time in experiments with rock fragments flow energy was largely dissipated by rock fragment cover for more turbulent flow conditions when roughness elements were submerged in the flow hydraulic roughness was similar for different rock fragment contents in experiments with few or no rock fragments a narrow rill incised flow energy was dissipated by headcuts total sediment yield was much larger than for experiments with rock fragments in the soil adding just a small number of rock fragments in the soil matrix resulted in a significant reduction of sediment yield copyright 2007 john wiley sons ltd

effects of rock fragment size and cover on overland flow hydraulics local turbulence and sediment yield on an erodible soil surface the interactions between overland flow hydraulics and sediment yield were studied in flume experiments on erodible soil surfaces covered by rock fragments the high erodibility of a non cohesive fine sediment d50 0 09mm permitted the effects of local turbulence and scour on sediment yield to be examined overland flow hydraulics and sediment yield were compared for experiments with pebble d50 1 5cm and cobble d50 8 6cm rock fragment covers cover percentages range from 0 to 99 per cent rock fragment size strongly affects the relations between flow hydraulics and rock fragment cover for pebbles spatially averaged hydraulic parameters flow velocity flow depth effective flow width unit discharge total shear stress darcy weisbach friction factor percentage grain friction and grain shear stress vary most rapidly within cover percentages at low covers power functions in contrast for cobbles these parameters vary most rapidly within cover percentages at high covers exponential functions as the type of the function that describes the relation between flow hydraulics and cover percentage can be deduced from the ratio of rock fragment height to flow depth the continuity equation can be employed to determine the actual coefficients of the functions provided the regression of one hydraulic parameter e g flow velocity with cover percentage is known and a good estimate exists for two values of another hydraulic variable for a low and a high cover percentage the variation of sediment yield with cover percentage is also strongly dependent on rock fragment size but neither the convex upward relation for pebbles nor the positive relation for cobbles can be solely attributed to the spatially averaged hydraulics of sheet flow rock fragments induce local turbulence that leads to scour hole development on the stoss side of the rock fragments while deposition commonly occurs in the wake this local scour and deposition substantially affects sediment yield however scour dimensions cannot be predicted by spatially averaged flow hydraulics an adjustment of existing scour formulas that predict scour around bridge piers is suggested sediment yield from non cohesive soils might then be estimated by a combination of sediment transport and scour formulas

spatial distribution of surface rock fragments along catenas in semiarid arizona and nevada usa improved techniques for estimating soil erosion by water have shown that soil surface cover is a major component in the estimate of soil loss erosion prediction models require the user to input slope gradient and soil profile descriptions if equations expressing the relations between slope gradient soil profile rock fragment content and surface rock fragment cover were embedded in these models then direct user input could be reduced field measurements of slope gradient soil profile rock fragment content surface rock fragment cover and vegetation type and cover were made on 12 soil slope complexes on catenas in southeastern arizona usa correlation analysis showed that both slope gradient and soil profile rock fragment content were significantly p 0 01 correlated to surface rock fragment cover additional analysis indicated that the combined effects of slope gradient and soil profile rock content were better defined by a soil slope factor ssf two equations were developed to estimate surface rock fragment cover a logarithmic relation using slope gradient as the independent variable and a hyperbolic equation using the ssf as the independent variable these equations were used to estimate surface rock fragment cover from a soil slope complex in southern nevada the ssfrfc equation gave better estimates of the measured surface rock fragment cover these relations developed for catenas in southeastern arizona may be site specific but they do show that a relation exists for this semiarid area and suggest that similar relations may exist in areas with similar geology and climate such as parts of africa asia australia and south america development of simple relations describing important erosion processes will improve erosion estimates while simultaneously decreasing time and costs associated with using erosion prediction models

rotational motions observed during an earthquake swarm in april 1998 offshore ito japan abstract we observed six components of ground rotational and translational motions in a near field region during an earthquake swarm in april 1998 offshore ito izu peninsula japan to check the reliability of our observation using a motionpack sensor we installed an 8301f sensor which is an inertial angular displacement sensor with a higher sensitivity than motionpack the noise level of the motionpack is much higher than that of the 8301f but the waveforms of these signal components are quite similar to each other suggesting that the motionpack records rotational rate correctly but with higher noise our observation made known a linear correlation between the maximum rotational displacements around the vertical axis and the maximum translational velocities the waveforms of rotational motion around the vertical axis are analogous to those of translational horizontal velocities suggesting the linear correlation between maximum values these rotational motions are much larger than those calculated by array data at the san andreas fault this large discrepancy might be explained by one or more of the following effects the difference in the spatial scale of rotational motion by single gyro measurement and by array observation the effect of the precipitous topography at the station of the offshore ito swarm and the difference of the degree of maturation between the san andreas fault and the swarm regions of offshore ito

the response of the itcz to extratropical thermal forcing idealized slab ocean experiments with a gcm using a comprehensive atmospheric gcm coupled to a slab mixed layer ocean experiments are performed to study the mechanism by which displacements of the intertropical convergence zone itcz are forced from the extratropics the northern extratropics are cooled and the southern extratropics are warmed by an imposed cross equatorial flux beneath the mixed layer forcing a southward shift in the itcz the itcz displacement can be understood in terms of the degree of compensation between the imposed oceanic flux and the resulting response in the atmospheric energy transport in the tropics the magnitude of the itcz displacement is very sensitive to a parameter in the convection scheme that limits the entrainment into convective plumes the change in the convection scheme affects the extratropical tropical interactions in the model primarily by modifying the cloud response the results raise the possibility that the response of tropical precipitation to extratropical thermal forcing important for a variety of problems in climate dynamics such as the response of the tropics to the northern hemisphere ice sheets during glacial maxima or to variations in the atlantic meridional overturning circulation may be strongly dependent on cloud feedback the model configuration described here is suggested as a useful benchmark helping to quantify extratropical tropical interactions in atmospheric models

tropical pacific ocean thermocline depth reconstructions for the last glacial maximum we evaluate the relationship between ten surface ocean 0 300 m hydrographic parameters and the spatial distribution of factor analyzed core top planktonic foraminiferal abundances in the tropical pacific ocean 24 n 24 s for core tops 3800 m the spatial distribution of the first three faunal factor loadings 88 of the variance are most highly correlated to subsurface variability mixed layer depth thermocline depth and resistant species percent rsp however rsp is not related to dissolution but is related to thermocline depth factor i mixed layer species g glutinata g ruber and factor iii g ruber can be distinguished from each other by low abundances of g glutinata in factor iii both assemblages spatially comprise the deep mixed layer region of the western tropical and equatorial pacific ocean but are associated with distinct water mass properties a combination of factor i and iii loadings shows a higher correlation to thermocline depth r 0 70 factor ii loadings dominated by thermocline dwelling species n dutertrei are most significantly correlated with the thermocline depth r 0 73 most factors show only marginally significant correlation to sea surface temperatures ssts indicating that sst is not the primary forcing factor on the planktonic foraminiferal species distributions in the tropical pacific a new transfer function was calculated to predict tropical pacific thermocline depth from planktonic foraminifera abundances using the imbrie kipp method ikm standard deviation of residuals 22 m 1 an additional 5 m error is attributed to low species counts in the core top database the modern analog technique mat was also used to predict thermocline depth standard deviation of residuals 21 m while last glacial maximum lgm thermocline depth changes by ikm and mat were generally within error estimated changes were geographically uniform suggesting an oceanographic response to climate forcing we estimate that the thermocline depth of the lgm was shallower than present by 20 m south of 8 s possibly due to a shift in the south pacific anticyclone to the northeast both the ikm and mat estimate a steeper east west thermocline slope along the equator suggesting that zonal wind stress walker circulation was intensified during the lgm collectively the thermocline estimates for the lgm suggest an equatorward compression of the climate zones in both hemispheres

inversion of long period p waves from great earthquakes along subduction zones abstract long period p waves from subduction zone earthquakes in the moment range from 7 1027to 8 1029dyn cm are analyzed using an iterative deconvolution method in addition to discrete subevents which effectively contribute to the observed seismograms the long period component of the moment rate function is derived with the constraint that the total seismic moment is equal to the moment determined from long period surface waves it is shown that great earthquakes can be described by several subevents with a duration of about 10 s which changes little from earthquake to earthquake in the above moment range the long period component of the moment rate function becomes larger for a greater earthquake the greatest earthquakes of mw 9 additionally involve subevents with another duration scale much longer than 10 s it is also shown that the local stress drop is 1 order of magnitude larger than the stress drop averaged over the entire fault plane the constancy of the local stress drop as well as the average stress drop holds among various magnitudes of earthquakes these observations suggest an essential similarity in the mode of dislocation distribution

abrupt intensification of enso forced by deglacial ice sheet retreat in ccsm3 the influence of ice sheet retreat on the el nino southern oscillation enso variability is studied using a transient simulation in ncar ccsm3 forced only by variations in continental ice sheets during the last deglaciation the most striking feature is an abrupt strengthening of enso by 25 at 14 thousand years before present ka bp in response to a significant retreat an equivalent 25 m sea level rise of the laurentide ice sheet lis this abrupt intensification of enso is caused mainly by a sudden weakening of the equatorial annual cycle through the nonlinear mechanism of frequency entrainment rather than an increase in the coupled ocean atmosphere instability the weakened annual cycle corresponds to a reduced north south cross equatorial annual mean sst contrast in the eastern pacific this reduced interhemispheric sst gradient significant cooling north of the equator is forced predominantly by an anomalous easterly from an abrupt polarward shift of the jet stream in the northern hemisphere which extends to the northeastern tropical pacific ocean surface and is reinforced by the wind evaporation sst feedback then propagates equatorward it could also be contributed by a fast sea ice expansion and a consequent cooling in the north pacific and north atlantic that is induced by the retreat of the lis

strain tilt and rotation associated with strong ground motion in the vicinity of earthquake faults abstract in the absence of near field records of differential ground motion induced by earthquakes we simulate the time histories of strain tilt and rotation in the vicinity of earthquake faults embedded in layered media we consider the case of both strike slip and dip slip fault models and study the effect of different crustal structures the maximum rotational motion produced by a buried 30 km long strike slip fault with slip of 1 m is of the order of 3 10 4 rad while the corresponding rotational velocity is about 1 5 10 3 rad sec a simulation of the san fernando earthquake yields maximum longitudinal strain and tilt a few kilometers from the fault of the order of 8 10 4 and 7 10 4 rad these values being small compared to the amplitude of ground displacement the results suggest that most of the damage occurring in earthquakes is caused by translation motions we also show that strain and tilt are closely related to ground velocity and that the phase velocities associated with strong ground motions are controlled by the rupture velocity and the basement rock shearwave velocity

the rupture process of the 1989 offshore ito earthquakes preceding a submarine volcanic eruption an earthquake swarm at the eastern offshore region of ito the izu peninsula started on june 30 1989 and became more active on and after july 4 the largest earthquake among the swarm mjma 5 5 occurred at 1109 jst 0209 ut on july 9 1989 and a second significant event followed 45 s later a remarkable volcanic tremor started on july 11 and a submarine eruption occurred just above the source region of the largest earthquake on july 13 in this paper we present a new inversion method to derive the source time function of rupture process the source time function is divided into several sections following an automatic algorithm and is interpolated with a cubic spline function the parameters which are the values and first derivatives at knots of the spline function are determined by minimizing a squared error between the observed and synthetic seismograms to demonstrate the performance of this method some numerical experiments simulations are carried out on near field seismic records applying this method to analysis of the two large earthquakes the detailed rupture processes are obtained a heterogeneous crustal structure near the volcanic area affects the rupture processes of these earthquakes the large stress drop due to the largest earthquake just beneath the submarine eruption point would assist a magma ascending and may have triggered the eruption 4 days after these earthquakes

geomorphic controls on biological soil crust distribution a conceptual model from the mojave desert usa abstract biological soil crusts bscs are bio sedimentary features that play critical geomorphic and ecological roles in arid environments extensive mapping surface characterization gis overlays and statistical analyses explored relationships among bscs geomorphology and soil characteristics in a portion of the mojave desert usa these results were used to develop a conceptual model that explains the spatial distribution of bscs in this model geologic and geomorphic processes control the ratio of fine sand to rocks which constrains the development of three surface cover types and biogeomorphic feedbacks across intermontane basins 1 cyanobacteria crusts grow where abundant fine sand and negligible rocks form saltating sand sheets cyanobacteria facilitate moderate sand sheet activity that reduces growth potential of mosses and lichens 2 extensive tall moss lichen pinnacled crusts are favored on early to late holocene surfaces composed of mixed rock and fine sand moss lichen crusts induce a dust capture feedback mechanism that promotes further crust propagation and forms biologically mediated vesicular av horizons the presence of thick biogenic vesicular horizons supports the interpretation that bscs are long lived surface features 3 low to moderate density moss lichen crusts grow on early holocene and older geomorphic surfaces that display high rock cover and negligible surficial fine sand desert pavement processes and abiotic vesicular horizon formation dominate these surfaces and minimize bioturbation potential the biogeomorphic interactions that sustain these three surface cover trajectories support unique biological communities and soil conditions thereby sustaining ecological stability the proposed conceptual model helps predict bsc distribution within intermontane basins to identify biologically sensitive areas set reference conditions for ecological restoration and potentially enhance arid landscape models as scientists address impacts of climate change and anthropogenic disturbances

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

measurement of rill and ephemeral gully flow velocities and their model expression affected by flow rate and slope gradient abstract water flow velocities in rill and ephemeral gully are useful for estimating hydrodynamics in the study on soil erosion laboratory experiments were conducted to measure erosive rill and ephemeral gully flow velocities including nine unit width flow rates of 0 17 0 33 0 67 1 33 2 67 5 33 10 67 21 33 and 42 67 10 3 m2 s 1 and five slope gradients of 8 7 17 6 26 8 36 4 and 46 6 on sandpaper slope glued with silt loam soil materials to imitate fixed rill and ephemeral gully beds using an electrolyte tracer method the flow velocities measured in this research ranged from 0 31 to 3 34 m s 1 for sediment free water flow the flow velocity fitted well with unit width flow rate and slope gradient by a power function yielding an improved model with higher coefficient of determination than that related flow velocity to flow rate alone the improved model is applicable for flow velocity and soil erosion predictions

using single forcing gcm simulations to reconstruct and interpret quaternary climate change abstractthe long term climate variations of the quaternary were primarily influenced by concurrent changes in earth s orbit greenhouse gases and ice sheets however because climate changes over the coming century will largely be driven by changes in greenhouse gases alone it is important to better understand the separate contributions of each of these forcings in the past to investigate this idealized equilibrium simulations are conducted in which the climate is driven by separate changes in obliquity precession co2 and ice sheets to test the linearity of past climate change anomalies from these single forcing experiments are scaled and summed to compute linear reconstructions of past climate which are then compared to mid holocene and last glacial maximum lgm snapshot simulations where all forcings are applied together as well as proxy climate records this comparison shows that much of the climate response may be approximated as a linear response to forcings while some features such as

meridional shifts in the marine itcz and the tropical hydrologic cycle over the last three glacial cycles 1 paleoproxy studies show a strong correlation between tropical climate and high latitude temperature variability recorded in the greenland ice cores over the last glacial cycle in particular abrupt cooling events in the greenland ice sheet project ii 18o ice record appear synchronous with a southward migration of the intertropical convergence zone itcz in the atlantic a weakening of the indian and east asian monsoon systems and a strengthening of the south american monsoon system because this high to low latitude climate teleconnection significantly alters the tropical hydrologic cycle around the globe it plays a critical role in regulating global climate on glacial interglacial time scales we compare 18oseawater reconstructions a salinity proxy generated from previously published mg ca and oxygen isotope data on globigerinoides ruber white var obtained from western caribbean core odp 999a and western equatorial pacific core 806b across the last three glacial cycles to show that systematic variations in surface salinity at these sites suggest the tropical hadley cell hydrologic system undergoes systematic reorganizations that differ dramatically between warm interglacial and cold glacial periods furthermore cross spectral and phase angle analyses of the ice volume corrected caribbean and western pacific 18osw records reveal a 100 kyr frequency in both records that is almost 180 out of phase and a 23 kyr frequency that is nearly in phase this results in the development of a very large 18osw gradient between the caribbean and the western equatorial pacific on glacial interglacial time scales that is best explained by a southward shift in both the atlantic and pacific itcz during north atlantic cold phases

abrupt reorganization of north pacific and western north american climate during the last deglaciation dramatic hydroclimate shifts occurred in western north america during the last deglaciation but the timing and mechanisms driving these changes are uncertain and debated and previous modeling has largely relied on linear interpolations between equilibrium snapshot simulations using a published transient climate simulation and a range of proxy records we analyze the region s climate evolution in order to identify the mechanisms governing hydroclimate shifts a rapid loss of ice around 14 000 years ago causes an abrupt reorganization of the circulation which precipitates drying and moistening of southwestern and northwestern north america respectively the atmospheric circulation transitions between two states on a timescale of decades to centuries during which time the westerly jet shifts north by about seven degrees in contrast to previous studies we find that changes in the water budget of western north america prior to this event are not attributable to variations in the position of the jet but rather to the intensity of moisture transport into the continent

transient simulation of last deglaciation with a new mechanism for bolling allerod warming we conducted the first synchronously coupled atmosphere ocean general circulation model simulation from the last glacial maximum to the bolling allerod ba warming our model reproduces several major features of the deglacial climate evolution suggesting a good agreement in climate sensitivity between the model and observations in particular our model simulates the abrupt ba warming as a transient response of the atlantic meridional overturning circulation amoc to a sudden termination of freshwater discharge to the north atlantic before the ba in contrast to previous mechanisms that invoke amoc multiple equilibrium and southern hemisphere climate forcing we propose that the ba transition is caused by the superposition of climatic responses to the transient co 2 forcing the amoc recovery from heinrich event 1 and an amoc overshoot

hydrological and vegetation shifts in the wallacean region of central indonesia since the last glacial maximum abstract precipitation is the most important variable of indonesian climate yet there are substantial uncertainties about past and future hydroclimate dynamics over the region this study explores vegetation and rainfall and associated changes in atmospheric circulation during the past 26 000 years in wallacea a biogeographical area in central indonesia wedged between the sunda and sahul shelves and known for its exceptionally high rainforest biodiversity we use terrestrial plant biomarkers from sediment cores retrieved from mandar bay off west sulawesi to reconstruct changes in wallacean vegetation and climate since the last glacial maximum lgm enriched leaf wax carbon isotope 13cwax values recorded in mandar bay during the lgm together with other regional vegetation records document grassland expansion implying a regionally dry and possibly more seasonal glacial climate depleted leaf wax deuterium isotope dwax values in mandar bay during the lgm and low reconstructed precipitation isotope compositions from nearby sites reveal an intensified austral asian summer monsoon circulation and a southward shift of the mean position of the intertropical convergence zone likely due to strong southern hemisphere summer insolation and the presence of large northern hemisphere ice sheets mandar bay 13cwax was anti correlated with dwax during the lgm and the last deglaciation but was positively correlated during most of the holocene indicating time varying controls on the isotopic composition of rainfall in this region the inundation event of the sunda shelf and in particular the opening of the java sea and karimata strait between 9 4 and 11 1 thousand years ago might have provided new moisture sources for regional convection and or influenced moisture source trajectories providing the trigger for shifts in atmospheric circulation and the controls on precipitation isotope compositions from the lgm to the holocene

glacial interglacial dynamics of the eastern equatorial pacific cold tongue intertropical convergence zone system reconstructed from oxygen isotope records record mean late holocene lh last glacial maximum lgm d 18 o amplitudes ranging between 1 0 and 1 3 we estimate that mean sea surface temperatures sst in this region during the lgm were on average 1 5 0 5 c lower than the lh larger d 18 o amplitudes are observed in sites north of the equator indicating a spatial pattern of reduced meridional sst gradient across the equator during the lgm this result is supported by comparison of mg ca sst reconstructions from two sites straddling the equator we interpret the reduction of this gradient during the lgm as evidence for a less intense cold tongue intertropical convergence zone itcz frontal system a more southerly position of the itcz and weaker southeast equatorial trades in the eep indexterms 1620 global change climate dynamics 3309 3339 meteorology and atmospheric dynamics ocean atmosphere interactions 0312 4504 3344 meteorology and atmospheric dynamics paleoclimatology 4231 oceanography general equatorial oceanography 4267 oceanography general paleoceanography keywords cold tongue itcz oxygen isotopes tropical pacific

sea ice control of plio pleistocene tropical pacific climate evolution marine proxies of sea surface temperature sst indicate that the tropical pacific thermal gradient intensified through the plio pleistocene and peaked during pleistocene glaciations the cause of this variability which has been linked to the initiation of the walker circulation is uncertain here we hypothesize that plio pleistocene tropical climate variability was coupled to high latitude southern hemisphere climate change specifically sea ice extent we use a coupled ocean atmosphere general circulation model to investigate the influences of sea ice extent and atmospheric co2 on the tropical pacific thermal structure in the model co2 radiative forcing in the absence of any sea ice feedbacks has little influence on the tropical sst gradient a 180 ppm reduction in co2 causes the sst gradient to decrease by 0 4 c in comparison an expansion of southern hemisphere high latitude sea ice reduces tropical ssts and enhances the sst gradient in the tropical pacific by as much as 3 5 c tropical cooling is primarily due to the advection and upwelling of waters into the eastern equatorial pacific that were cooled by sensible heat loss at the sea ice margin in the southern pacific an energy balance analysis indicates that the ocean heat flux into the eastern equatorial pacific decreases by 44 this mechanism provides an intimate coupling between the tropical pacific and the high latitude southern hemisphere through the thermocline circulation

soil erosion by surface water flow on a stony semiarid hillslope soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows this study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment a field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface the method allowed for measurements in this study of flow erosion at a much wider range of slopes 2 6 to 30 1 per cent and unit discharge rates 0 0007 to 0 007 m2 s 1 than have been previously feasible flow velocities were correlated to discharge and hydraulic radius but not to slope the lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity the detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected flow detachment rates were better correlated to a power function of either shear stress r2 0 51 or stream power r2 0 59 published in 1999 by john wiley sons ltd

dynamic effect of last glacial maximum ice sheet topography on the east asian summer monsoon the effect of ice sheet topography on the east asian summer monsoon easm during the last glacial maximum is studied using ccsm3 in a hierarchy of model configurations it is found that receding ice sheets result in a weakened easm with the reduced ice sheet thickness playing a major role the lower ice sheet topography weakens the easm through shifting the position of the midlatitude jet and through altering northern hemisphere stationary waves in the jet shifting mechanism the lowering of ice sheets shifts the westerly jet northward and decreases the westerly jet over the subtropics in summer which reduces the advection of dry enthalpy and in turn precipitation over the easm region in the stationary wave mechanism the lowering of ice sheets induces an anomalous stationary wave train along the westerly waveguide that propagates into the easm region generating an equivalent barotropic low response this leads to reduced lower tropospheric southerlies which in turn reduces the dry enthalpy advection into east asia and hence the easm precipitation less

transient stresses at parkfield california produced by the m 7 4 landers earthquake of june 28 1992 observations from the upsar dense seismograph array the m 7 4 landers earthquake triggered widespread seismicity in the western united states because the transient dynamic stresses induced at regional distances by the landers surface waves are much larger than the expected static stresses the magnitude and the characteristics of the dynamic stresses may bear upon the earthquake triggering mechanism the landers earthquake was recorded on the upsar u s geological survey parkfield small aperture array array a group of 14 triaxial accelerometers located within a 1 square km region 10 km southwest of the town of parkfield california 412 km northwest of the landers epicenter no triggered earthquakes were observed at parkfield multiple filter analysis shows that the displacements obtained by double integration are dominated by the fundamental mode love and rayleigh modes with some higher mode contributions for periods shorter than 10 s most of the surface waves propagated along the great circle path from landers but a late arriving surface wave appears to have been scattered from the sierra nevada mountains we used a standard geodetic inversion procedure to determine the surface strain and stress tensors as functions of time from the observed displacements peak dynamic strains and stresses at earth s surface are about 7 strain and 0 035 mpa respectively and they have a flat amplitude spectrum between 2 s and 15 s period these stresses agree well with stresses predicted from a simple equation using the ground velocity spectrum observed at a single station peak stresses ranged from about 0 035 mpa at the surface to about 0 12 mpa between 2 and 14 km depth with the sharp increase of stress away from the surface resulting from the rapid increase of rigidity with depth and from the influence of mode shapes because of the free surface boundary conditions the horizontal components of the stress tensor tend to dominate in the top 5 6 km of the crust which might cause triggered seismicity to have strike slip or normal mechanisms comparison of dynamic stresses induced by the landers loma prieta and petrolia earthquakes at a variety of sites indicates that the landers stresses were not spectacularly larger than those induced by the other sources landers dynamic stresses were comparable to coalinga static stresses at parkfield the effective strain caused by landers at parkfield where no earthquakes were triggered are the same amplitude as those at some sites in nevada where earthquakes were triggered comparing various authors observations of dynamic stresses there is no obvious characteristic of these stresses that correlates with the triggered seismicity

compound specific carbon isotope records of vegetation and hydrologic change in central sulawesi indonesia since 53 000 yr bp lake matano 2 29 1 s 121 20 e in central sulawesi the deepest and one of the largest lakes in indonesia provides an excellent opportunity to reconstruct long term hydrological and vegetation changes at the heart of the maritime continent within the tropical western pacific warm pool we measured the carbon isotopic composition of terrestrial leaf waxes 13cwax in new sediment cores from lake matano to understand regional variations in vegetation and their interactions with local and high latitude climate forcings during the past 53 kyr variations in 13cwax record the expansion and contraction of c3 versus c4 vegetation as well as changes in plants carbon and water use efficiency and by inference regional hydroclimate during marine isotope stages 1 and 3 more negative 13cwax values indicate that closed canopy c3 rainforests predominated in sulawesi reflecting a wetter less seasonal climate in contrast more positive 13cwax values record a terrestrial ecosystem with more abundant open canopy vegetation and possible expansion of c4 grasses between 29 and 14 ka bp indicating that during marine isotope stage 2 including the last glacial maximum the climate was more arid likely with increased precipitation seasonality in central sulawesi comparison of our record with other paleovegetation and paleohydrological records from sulawesi and nearby islands suggests coherent long term hydrological changes in central indonesia that appear to be sensitive to high latitude climate across glacial interglacial boundaries however variations in the amplitude of the response of vegetation to these glacial interglacial forcings highlight the importance of regional topographic control on climate and vegetation and suggest an important role for higher elevations in maintaining rainforest refugia during regionally arid time intervals when c4 savannas and grasslands expanded at lower elevations

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

a coupled climate model simulation of the last glacial maximum part 2 approach to equilibrium the climate of the last glacial maximum lgm is simulated with a coupled climate model the simulated climate undergoes a rapid adjustment during the first several decades after imposition of lgm boundary conditions as described in part 1 and then evolves toward equilibrium over 900 model years the climate simulated by the coupled model at this period is compared with observationally based lgm reconstructions and with lgm results obtained with an atmosphere mixed layer slab ocean version of the model in order to investigate the role of ocean dynamics in the lgm climate global mean surface air temperature and sea surface temperature sst decrease by about 10 c and 5 6 c in the coupled model which includes ocean dynamics compared to decreases of 6 3 and 3 8 c in slab ocean case the coupled model simulates a cooling of about 6 5 c over the tropics which is larger than that of the climap reconstruction 1 7 c and larger than that of the slab ocean simulation 3 3 c but which is in reasonable agreement with some recent proxy estimates the ocean dynamics of the coupled model captures features found in the climap reconstructions such as a relative maximum of ocean cooling over the tropical pacific associated with a mean la nina like response and lead to a more realistic sst pattern than in the slab model case the reduction in global mean precipitation simulated in the coupled model is larger 15 than that simulated with the slab ocean model 10 in conjunction with the enhanced cooling some regions such as the usa and the mediterranean region experience increased precipitation in accord with proxy paleoclimate evidence the overall much drier climate over the ocean leads to higher sea surface salinity sss in most ocean basins except for the north atlantic where sss is considerably lower due to an increase in the supply of fresh water from the mississippi and amazon rivers and presumably a decrease in salt transport by the weakened north atlantic overturning circulation the north atlantic overturning stream function weakens to less than half of the control run value the overturning is limited to a shallower depth less than 1000 m and its outflow is confined to the northern hemisphere in the southern ocean convection is much stronger than in the control run leading to a stronger overturning stream function associated with enhanced antarctic bottom water formation as a result southern ocean water masses fill the entire deep ocean the antarctic circumpolar current acc transport through the drake passage increases by about 25 the acc transport despite weaker zonal winds is enhanced due to changes in bottom pressure torque the weakening of the overturning circulation in the north atlantic and the accompanying 30 decrease in the poleward ocean heat transport contrasts with the strengthening of the overturning circulation in the southern ocean and a 40 increase in heat transport as a result sea ice coverage and thickness are affected in opposite senses in the two hemispheres the lgm climate simulated by the coupled model is in reasonable agreement with paleoclimate proxy evidence the dynamical response of the ocean in the coupled model plays an important role in determining the simulated and undoubtedly the actual lgm climate

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

the amplitude and phasing of climate change during the last deglaciation in the sulu sea western equatorial pacific 1 variations in tropical sea surface temperature patterns and the phasing relative to climate change in higher latitudes provide insight into the mechanisms of climate change on both orbital and shorter time scales here we present well dated high resolution records of planktonic foraminiferal 18o and mg ca based sst spanning the last deglaciation from the sulu sea located in the western equatorial pacific the results indicate that the last glacial maximum was 2 3 0 5 c cooler than present in the sulu sea with a concomitant decrease in sea surface salinity the similarity between variations in surface salinity in the sulu sea the western and eastern equatorial pacific and the greenland ice core record suggests that the observed changes in salinity reflect large scale rearrangement of atmospheric patterns which were coherent and synchronous throughout the northern hemisphere the results suggest that the glacial equatorial pacific climate was strongly influenced by both tropical and extra tropical forcing although it is not clear whether interannual enso variability is a good analogue of glacial interglacial climate change

sensitivity of the atlantic intertropical convergence zone to last glacial maximum boundary conditions 1 recent paleoproxy records suggest that the mean latitude of the atlantic intertropical convergence zone itcz varied synchronously with north atlantic climate over a range of timescales throughout the holocene and last glacial maximum we show that the present day meridional mode of atmosphere ocean variability in the tropical atlantic is a potentially useful model for understanding these paleoclimate changes the tropical atlantic in a coupled atmospheric general circulation and slab ocean model responds to last glacial maximum conditions with a southward displacement of the itcz this response arises primarily through the land ice sheet that forces increased north atlantic trades analogous to the forcing on the present day meridional mode changes to sea ice coverage and to ocean heat transport associated with a weakened atlantic thermohaline circulation also cause a meridional mode response though through different mechanisms our results highlight the potential for tropical atlantic paleoclimate to be driven from the high latitude influences in particular land ice on glacial interglacial timescales

glacial reduction of the north american monsoon via surface cooling and atmospheric ventilation nsf ags 1204011 ocn 1304910 oce 1651034 david and lucile packard foundation fellowship in science and engineering

inverting ground motion from a seismometer array to obtain the vertical component of rotation a test using data from explosions to study factors that affect reliability of the derived vertical rotational ground motions about vertical axis from translational array waveforms we have conducted a field test using explosion the dataset was collected on march 4 2008 from an active source experiment of the taiwan geodynamics research project taiger 2008 in which 750 kg of explosives were set off about 500 m away from a specially designed seismic array in free field consisting of 8 tri axial rotational sensors 13 tri axial accelerometers and 12 six channel 24 bit dataloggers with gps receivers our results show that the waveform fits were greatly improved when the explosion induced crustal strains were less than 2 10 5 for our station configuration as a result our modeling for the large amplitude part of the mainshock was not entirely successful however we have successfully recovered the first order features of the later part of the vertical rotational ground motions using translational velocity waveforms in the 0 5 20 hz bandwidth using the spudich and fletcher s procedure 2009 moreover we used a modified jaeger s 1969 formula and derived similar rotational synthetics we found that the best rotational rate waveform fits were derived using a station configuration of a dense small aperture translational array combined with a few largeoffset stations a small aperture array is needed to fulfill the uniform rotation assumption however inverting data from an array of small spatial dimension requires waveforms of high signal to noise ratio and high sampling rates surprisingly large offset translation stations provided additional constraints in time and space helping to fit the low frequency waveforms using the inverted result we forward predicted the vertical translational waveforms not used in the inversion and got excellent fits this suggests that the inverted results are of good quality for predicting the complete translational ground motions even though only horizontal components were used in the inversion array derived or directly measured rotational ground motions can be used to predict translational ground motions in the near by region lessons learned from this study could be helpful for future studies using translational ground motions to derive dynamic ground strains tilts and torsions

the interconnected global climate system a review of tropical polar teleconnections abstractthis paper summarizes advances in research on tropical polar teleconnections made roughly over the last decade elucidating el nino southern oscillation enso impacts on high latitudes has remained an important focus along different lines of inquiry tropical to polar connections have also been discovered at the intra seasonal timescale associated with madden julian oscillations mjo on the timescale of decades changes in mjo phases can result in temperature and sea ice changes in the polar regions of both hemispheres moreover the long term changes in sst of the western tropical pacific tropical atlantic and north atlantic ocean have been linked to the rapid winter warming around the antarctic peninsula while sst changes in the central tropical pacific have been linked to the warming in west antarctica rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal timescales enso related tropical sst anomal

the relation between surface rock fragment cover and semiarid hillslope profile morphology abstract rock fragment covers veneer hillslopes in many parts of the world and influence the operation of hydrologic and geomorphic processes on those surfaces the purpose of this investigation was the examine the spatial variability of rock fragment cover on morphological units of hillslopes in southeastern arizona u s a simple statistical models based upon hillslope gradient as well as a soil slope factor ssf were developed and validated for the estimation of percent rock fragment covers rfc on these units although reasonably accurate estimates were made using either hillslope gradient or the ssf it appears more efficient to utilize hillslope gradient alone likewise reasonably accurate estimates of rfc can be made using either a composite model for the entire hillslope or unit specific models however it appears more efficient to utilize the gradient composite model

relationship between discharge velocity and flow area for rills eroding loose non layered materials a relationship between discharge flow velocity and flow area in rills is established using data from four field and laboratory studies the proposed relationship is shown to predict successfully flow velocities measured in six other studies although slopes range from 0 035 to 0 45 and soil materials range from stony sands over silt loams to vertisols mean flow velocity can be well predicted from discharge alone thus there is no important influence of slope and or soil material characteristics on flow velocities in rills the proposed relationship may be used to improve performance of deterministic flow routing models when applied to rilled catchments furthermore it allows the calculation of unit stream power which has been shown to be related to the transporting capacity of overland flow in terms of slope and discharge

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

rill hydraulics on a semiarid hillslope southern arizona seventy field experiments were conducted in seven rills located on a semiarid rangeland hillslope underlain by gravelly soils at walnut gulch arizona the rills which are characterized by wide shallow cross sections and gravel covered beds have mean at a station hydraulic geometry exponents of b 0 33 f 0 34 and m 0 33 although the differences between these values and typical values of b 0 30 f 0 40 and m 0 30 for cropland rills are not statistically significant they are thought to be real as cropland rills often have more rectangular cross sections and steeper sides than the rangeland rills under study for rills formed in silty loamy soils govers developed an empirical relation between mean flow velocity and discharge emphasizing the generality of this relation he suggested that it may be used as a simple means of routing runoff through rills he also noted that this relation appeared to be unaffected by either slope or soil materials the present data represent rills underlain by coarser and somewhat more varied gravel rich soils these data do not conform to govers relation and a multiple regression analysis reveals that slope and soil materials either directly or indirectly through bed roughness exert almost as much influence on flow velocity as does discharge three alternative methods are developed for predicting flow velocity in the rills under study all three methods give good results with the largest root mean square deviation being 3 115 cm s 1

modeling el nino and its tropical teleconnections during the last glacial interglacial cycle 1 simulations with the ncar climate system model csm a global coupled ocean atmosphere sea ice model for the last glacial interglacial cycle reproduce recent estimates based on alkenones and mg ca ratios of sea surface temperature sst changes and gradients in the tropical pacific and predict weaker el ninos la ninas compared to present for the holocene and stronger el ninos la ninas for the last glacial maximum lgm changes for the lgm holocene are traced to a weakening strengthening of the tropical pacific zonal sst gradient wind stresses and upwelling and a sharpening weakening of the tropical thermocline results suggest that proxy evidence of weaker precipitation variability in new guinea and ecuador are explained not only by changes in el nino la nina but also changes in the atmospheric circulation and hydrologic cycle index terms 3344 meteorology and atmospheric dynamics paleoclimatology 4267 oceanography general paleoceanography 4522 oceanography physical el nino 3337 meteorology and atmospheric dynamics numerical modeling and data assimilation 9604 information related to geologic time cenozoic citation otto bliesner b l e c brady s i shin z liu and c shields modeling el nino and its tropical teleconnections during the last glacial interglacial cycle geophys res lett 30 23 2198 doi 10 1029 2003gl018553 2003

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion this makes modeling soil erosion difficult systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments high local turbulence was caused by horseshoe vortex erosion around individual rock fragments for a given discharge and slope the dimension of the scour was affected by the space between the rock fragments for low cover percentages the scour can develop undisturbed and sediment yield increases with percent of rock fragment cover up to about 20 sediment yield then declines as percent cover increases above 20 beyond a cover threshold value of 20 the larger opportunity for scour hole development is counteracted by limited inter rock fragment space that does not allow scour holes to develop to their full extent as sediment yield varies nonmonotonically with rock fragment cover percent sediment yield cannot be predicted by spatially averaged flow hydraulics

what can be learned from rotational motions excited by earthquakes summary one answer to the question posed in the title is that we will have more accurate data for arrival times of sh waves because the rotational component around the vertical axis is sensitive to sh waves although not to p sv waves importantly there is another answer related to seismic sources which will be discussed in this paper generally not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves in particular rotational strains at earthquake sources directly generate rotational components in seismic waves employing the geometrical theory of defects we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects using this expression together with one for translational motion we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes these quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and or a formation of tensile fractures

the effect of ocean dynamics in a coupled gcm simulation of the last glacial maximum general circulation models gcms of the climate system are powerful tools for understanding and predicting climate and climate change the last glacial maximum lgm provides an extreme test of the model s ability to simulate a change of climate and allows us to increase our understanding of mechanisms of climate change we have used a coupled high resolution ocean atmosphere gcm hadcm3 to simulate the equilibrium climate at the lgm the effect of ocean dynamics is investigated by carrying out a parallel experiment replacing the dynamic three dimensional ocean gcm with a static thermodynamic mixed layer ocean model changes to the ocean circulation and feedbacks between the ocean atmosphere and sea ice have an important influence on the surface response and are discussed the coupled model produces an intensified thermohaline circulation and an increase in the amount of heat transported northward by the atlantic ocean equatorward of 55 n which is at odds with the interpretation of some proxy records such changes which the thermodynamic mixed layer ocean model cannot produce have a large impact around the north atlantic region and are discussed in the study

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

tropical pacific climate response to obliquity forcing in the pleistocene 1 marine proxy records of pleistocene seawater temperature and productivity in the tropical pacific ocean vary over a 41 000 year period that has been attributed to earth s obliquity cycle the proxy records are paradoxical both because obliquity has a small effect on low latitude insolation and because tropical seawater temperature and productivity were anticorrelated with obliquity insolation forcing in this study we investigate the response of the tropical pacific climate to obliquity forcing using a coupled ocean atmosphere model to reconcile the proxy records with climate theory two glacial and two modern simulations were completed with extreme high and low axial tilts of 24 5 and 22 2 in response to an increase in axial tilt tropical sea surface temperatures decrease by as much as 0 8 c because of the local reduction in insolation subsurface water temperatures in the eastern and central equatorial pacific increase by nearly 1 c anomalous heating through high obliquity forcing also generates dynamical responses that weaken mean annual midlatitude westerlies and subtropical trade winds contributing to a 20 reduction in the subtropical gyre circulation analyses using a lagrangian transport model indicate that low latitude subsurface warming is due to a reduction in heat export from the tropics and the advection and ventilation of anomalously warm south pacific extratropical waters through the thermocline circulation the model s response to obliquity is consistent with pleistocene proxy data that indicate the tropical walker circulation and thermocline slope were not strongly influenced by changes in axial tilt the model results also support the hypothesis that earth s obliquity influences climate through its control on meridional insolation gradients

deglacial temperature history of west antarctica the most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how earth s climate responds to various forcings including a rise in atmospheric co2 this transition has left a direct thermal remnant in the polar ice sheets where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings for antarctica the deglacial warming has previously been constrained only by the water isotopic composition in ice cores without an absolute thermometric assessment of the isotopes sensitivity to temperature to overcome this limitation we measured temperatures in a deep borehole and analyzed them together with ice core data to reconstruct the surface temperature history of west antarctica the deglacial warming was formula see text c approximately two to three times the global average in agreement with theoretical expectations for antarctic amplification of planetary temperature changes consistent with evidence from glacier retreat in southern hemisphere mountain ranges the antarctic warming was mostly completed by 15 kybp several millennia earlier than in the northern hemisphere these results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on antarctic temperature although climate models perform well on average in this context some recent syntheses of deglacial climate history have underestimated antarctic warming and the models with lowest sensitivity can be discounted

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

surface roughness evolution of soils containing rock fragments soil surface roughness is a dynamic property which determines to a large extent erosion and infiltration rates although soils containing rock fragments are widespread in the mediterranean region the effect of the latter on surface roughness evolution is yet poorly understood therefore laboratory experiments were conducted in order to investigate the effect of rock fragment content rock fragment size and initial moisture content of the fine earth on the evolution of interrill surface roughness during simulated rainfall surface elevations of simulated plough layers along transects of 50 cm length were measured before and after simulated rainfall totalling 192 5mm z 70mm h with a laser microreliefmeter the results were used to investigate whether systematic variations in interrill surface roughness along stony hillslopes in southeastern spain could be attributed to rock fragment cover and rock fragment size soil surface elevations were measured along the contour lines 50 cm long transects with a contact microreliefmeter roughness was expressed by two parameters related to the height and frequency of roughness elements respectively standard deviation of de trended surface elevations random roughness rr and correlation length l derived from exponential fits of the autocorrelation functions the frequently used assumption that surface roughness rr of cultivated topsoils decreases exponentially with cumulative rain is not valid for soil surfaces covered by rock fragments the rr of soils containing small rock fragments 1 72 7 cm increased with cumulative rainfall after an initial decrease during the first 17 5 mm of rainfall for soils containing large rock fragments 7 7 cm rr increased with rainfall above a threshold rock fragment content by mass of 52 per cent for a given rainfall application rr increased non linearly with rock fragment content the correlation length for soils containing small rock fragments decreases with rock fragment content and is significantly lower than for soils with large rock fragments soils covered with small rock fragments large rr and small l are thus well protected against raindrop impact by a water film in the depressions between the rock fragments on abandoned agricultural fields along hillslopes in southeastern spain rock fragments cover increases non linearly with slope owing to selective erosion of finer particles on steep slopes the increase of surface cover by large rock fragments 25 mm is even more pronounced the simultaneous increase of rock fragment cover and rock fragment size with slope explains the non linear increase of rr with slope these relationships differ for soils covered by platy misaschists and those covered with cubic andesites the variations in correlation length along the hillslopes are not clear probably owing to a simultaneous increase in rock fragment cover and rock fragment size these findings may provide a better prediction of soil surface roughness of interrill areas covered by rock fragments using slope angle and lithology

low latitude control of interhemispheric sea surface temperature contrast in the tropical atlantic over the past 21 kyears the possible role of se trade winds to stimulate a discussion on the role of tropical atmospheric circulation versus thermohaline circulation changes for tropical atlantic sea surface temperature sst variations we present a record of the sst contrast sst between the tropical northwest and southeast atlantic from the last glacial maximum to the late holocene the sst was calculated from two alkenone derived sst records one from the caribbean sea and the other from the angola basin changes in the cross equatorial sst were then compared with an abundance record of florisphaera profunda from the equatorial atlantic which is indicative of se trade wind induced variations in thermocline depth in the equatorial divergence zone this comparison implies that the last glacial maximum the younger dryas and the mid to late holocene were periods of strong se trade winds which led to an intense upwelling related cooling in the southeast atlantic and concurrently enhanced advection of warm tropical south atlantic waters into the western tropical atlantic accordingly a coupled ocean atmospheric process has probably created a dipole like sst distribution pattern in the tropical atlantic during these three distinct climatic periods in contrast heinrich event 1 the bolling allerod and the early holocene were intervals of weakened se trade winds causing a warming in the southeast atlantic however synchronous warming in both regions during heinrich event 1 can be partially attributed to a weakening of thermohaline overturning which caused a reduced northward heat transport from the low latitude to the high latitude north atlantic

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

ground rotational motions recorded in near source region of earthquakes large rotational motions excited by earthquakes are recorded during an earthquake swarm of march 1997 offshore ito in izu peninsula japan the largest rotational velocity recorded at kaw is 2 6 10 2 rad s around the north south axis during an earthquake of magnitude 5 2 at 14 09 gmt on march 3 the rotational motions around the vertical axis excited by the largest event is 3 3 10 3 rad s considering a spatial variation of slip velocity which directly relates to excitation of a rotational motion we apply a simple point source model to the largest event and succeed in explaining the observed rotational motion around the vertical axis

western pacific thermocline structure and the pacific marine intertropical convergence zone during the last glacial maximum paleoclimate proxy evidence suggests a southward shift of the intertropical convergence zone itcz during times of northern hemisphere cooling including the last glacial maximum 19 23 ka before present however evidence for movement over the pacific has mainly been limited to precipitation reconstructions near the continents and the position of the pacific marine itcz is less well constrained in this study we address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field we reconstruct changes in the upper ocean density structure during the lgm using oxygen isotope measurements on the planktonic foraminifera g ruber and g tumida in a transect of sediment cores from the western tropical pacific the data suggests a ridge in the thermocline just north of the present day itcz persists for at least part of the lgm and a structure in the southern hemisphere that differs from today the reconstructed structure is consistent with that produced in a general circulation model with both a northern and southern hemisphere itcz