transport in fractured porous solids laboratory measurements are made of the permeability and the resistivity of sintered porous media with disordered fractures over a wide range of matrix porosity we discuss the preparation and characterisation of the samples approximating the topology of a rough fracture by a single discrete fracture can introduce large errors in the prediction of the permeability we test the validity of empirical expressions relating permeability resistivity and porosity for fractured samples resistivity correlations with porosity are independent of the presence of fractures in contrast permeability correlations show a strong dependence attempts to decouple the permeability of the fractured sample as a parallel sum of matrix and fracture permeability leads to large errors the results indicate that transport in a medium with two distinct families of pathways cannot be described by a single valued transport coefficient

the effects of softening on nearshore erosion of a cohesive shoreline abstract a study designed to measure spatial and temporal variation in the shear strength of the surface of a till substrate in the nearshore was carried out on the south shore of lake ontario canada the primary goal was to determine whether softening or reduction in shear strength occurred during the study period and the significance of this as a control on the overall rate of vertical lowering of the cohesive profile characteristics of the nearshore environment and the substrate were determined through the collection of till shear strength measurements substrate cores and surficial sediment thickness along a 300 m long underwater profile changes in shear strength were monitored over a four month period in experimental plots in water depths of 1 6 3 5 and 4 75 m together with measurements of bed erosion softening of the till was evident from cores which showed a rapid increase in strength and corresponding decrease in moisture content to a depth of about 0 1 m below the till surface after which they became constant shear strength of the exposed till surface decreased during periods of low wave activity and similar results were found in laboratory experiments periods of high wave activity resulted in the removal of a layer of softened material thus exposing harder underlying till the results suggest that erosion during a storm is related to the thickness of the softened layer that develops during non storm periods because of the steep increase in strength with depth below the till surface maximum erosion during a storm is generally

tropical sea surface temperatures for the past four centuries reconstructed from coral archives most annually resolved climate reconstructions of the common era are based on terrestrial data making it a challenge to independently assess how recent climate changes have affected the oceans here as part of the past global changes ocean2k project we present four regionally calibrated and validated reconstructions of sea surface temperatures in the tropics based on 57 published and publicly archived marine paleoclimate data sets derived exclusively from tropical coral archives validation exercises suggest that our reconstructions are interpretable for much of the past 400 years depending on the availability of paleoclimate data within and the reconstruction validation statistics for each target region analysis of the trends in the data suggests that the indian western pacific and western atlantic ocean regions were cooling until modern warming began around the 1830s the early 1800s were an exceptionally cool period in the indo pacific region likely due to multiple large tropical volcanic eruptions occurring in the early nineteenth century decadal scale variability is a quasi persistent feature of all basins twentieth century warming associated with greenhouse gas emissions is apparent in the indian west pacific and western atlantic oceans but we find no evidence that either natural or anthropogenic forcings have altered el nino southern oscillation related variance in tropical sea surface temperatures our marine based regional paleoclimate reconstructions serve as benchmarks against which terrestrial reconstructions as well as climate model simulations can be compared and as a basis for studying the processes by which the tropical oceans mediate climate variability and change

modeling of coastal profile evolution on the abandoned delta of the huanghe river abstract this paper presents a quantitative dynamic model for simulating and predicting the evolution of the nearshore muddy profile on the abandoned huanghe delta which has been undergoing severe erosion since the shift of the huanghe river in 1855 the model computes the wave induced bed shear stresses on the muddy profile and therefore calculates the erosion rate the sea level fluctuation caused by the oceanic tide plays an important role in redistributing the wave force and hence the sediment transport this factor is introduced into the model the steady state nearshore muddy profile is simulated as a response to the average erosion rate of the local wave climate however at long time scales the averaged erosion rate is significantly influenced by the surface sand armouring and the vertical increase with depth of cohesive sediment consolidation during coastal erosion leading to an irreversible evolution of the muddy profile the effective scouring wave derived from local wave climate is proposed to quantitatively incorporate these time variant geological influences the evolution of the muddy profile is determined by the change in the effective scouring wave climate the eroding muddy coast exhibits a monotonic concave upward profile whose curvature increases as the coastal erosion continues the maximum curvature of the profile lies below the mean low tidal level as the erosion continues the maximum curvature moves down and shoreward the position of the maximum curvature of the nearshore muddy profile can be used to estimate the evolutionary stages of the muddy coast on the northern abandoned huanghe delta the muddy profile approaches an equilibrium configuration when the maximum curvature reaches down to a water depth of about 6 m below the mean sea level the model reveals a dynamic geomorphic system as a response to the abandonment on the huanghe delta similar patterns and evolutionary processes may be generalized to erosional muddy coasts in other settings

nearshore erosion on a cohesive shoreline abstract a study to measure vertical erosion of till in the inner nearshore was carried out along a stretch of shoreline just west of port dalhousie on the south shore of lake ontario canada in addition to measuring the rate of vertical erosion an attempt was made to determine the influence of thickness and mobility of the surficial sediment cover and of softening of the till on erosion bluffs at the site are 4 5 m in height and developed almost entirely in till beach width at the time of the study ranged from 0 3 m and the toe of the bluff was actively undercut during periods of high waves till outcrops in the nearshore close to the shoreline and again beyond 100 m but considerable quantities of sand and gravel exist in the zone between forming a distinct nearshore bar located 40 60 m offshore elevation surficial sediment thickness and size and characteristics of the till surface were determined along 7 lines spaced 20 m apart vertical erosion was measured with a micro erosion meter at stations spaced 10 m apart a total of 16 stations was established along 3 lines to a maximum distance offshore of 120 m some erosion was measured in each time period with cumulative erosion during the period may to october 1992 being on the order of 3 4 cm erosion in any time period increased with increasing cumulative wave energy softening of the till surface was observed in many localities and appears to be an important factor that increases the erosion potential particularly lakeward of the nearshore bar where the till is always exposed erosion appears to be reduced where there is protection by surficial sediments but it is necessary to determine that the cover is maintained during high wave conditions the annual rate of vertical lowering determined from these measurements is of the same order as predicted from longterm bluff recession rates assuming maintenance of an equilibrium profile

a new process response coastal recession model of soft rock cliffs abstract the development of cliff erosion predictive models is limited by the complex interactions between environmental processes and material properties over a range of temporal and spatial scales current models incorporate a stochastic representation of cliff behavior based on assumptions regarding the magnitude and frequency of events in a probabilistic framework the new model presented here has been developed to incorporate the behavioral and mechanical characteristics of coastal cliffs which are dominated geologically by overconsolidated clays tills and an associated protective colluvial wedge this model is capable of providing precise and stable responses to some of the inherent uncertainties in cliff recession processes including those caused by different failure mechanisms e g colluvium generation groundwater and erosive tidal cycles material strength is incorporated using the unconfined compressive strength of the material that composes the cliff unlike previous models a calibration parameter is restricted to account for uncertainties linked to marine processes the mechanisms of cliffline retreat have been identified as slump and topple landslides once cliff material has fallen colluvium formation at the cliff foot is incorporated into the model using three different procedures according to the geomechanical characteristics of the debris the model is validated through profile evolution assessment at various locations of coastline retreat on the holderness coast uk higher groundwater content also produces an increase in the number and size of the slope failures the results represent an important step forward in linking material properties to the processes of cliff recession

hydraulic characterization of a fault zone from fracture distribution abstract a quantitative assessment of how faults control the migration of geofluids is critical in many areas of geosciences we integrated geological fieldwork quantitative analysis of the fractures distribution and numerical modeling to build a geometrical representation of a fault zone and to characterize its hydraulic properties our target is a fault located in the majella mountain italy we collected 21 scan lines across the fault profile in order to characterize its architecture the numerical modeling of the fracture network of the damage zones and their hydraulic parameters was performed using both commercial move and open source software dfnworks and pflotran move was used to build a representative model of the fault zone using fracture spacing as a proxy and to model the hydraulic parameters of the different fault domains dfnworks and pflotran were employed to infer the hydraulic parameters of the damage zones of the fault and then upscale these properties to an equivalent continuum domain suitable for fluid flow simulations through the whole fault zone our findings show how even in a relatively small area it is possible to describe changes in terms of hydraulic properties of a fault zone and to build models capable to represent these variations

last millennium climate and its variability in ccsm4 abstractan overview of a simulation referred to as the last millennium lm simulation of the community climate system model version 4 ccsm4 is presented the ccsm4 lm simulation reproduces many large scale climate patterns suggested by historical and proxy data records with northern hemisphere nh and southern hemisphere sh surface temperatures cooling to the early 1800s common era by 0 5 c nh and 0 3 c sh followed by warming to the present high latitudes of both hemispheres show polar amplification of the cooling from the medieval climate anomaly mca to the little ice age lia associated with sea ice increases the lm simulation does not reproduce la nina like cooling in the eastern pacific ocean during the mca relative to the lia as has been suggested by proxy reconstructions still dry medieval conditions over the southwestern and central united states are simulated in agreement with proxy indicators for these regions strong global cooling is associated with large volcanic erup

modeling cyclic recession of cohesive clay coasts effects of wave erosion and bluff stability abstract a mathematical model combining the effects of wave erosion beach sediment and bluff slope stability has been developed to study the episodic cyclical recession of cohesive clay coasts the model was applied to the southern great lakes in north america which although non tidal experience seasonal fluctuations in lake level of about 0 5 m and long term fluctuations of up to 2 m model runs were designed to explore the interaction between various components of the system including profile shape bluff recession rates lake level variations beach morphodynamics the geomechanical characteristics of the material and the type slump topple and size of the slope failures model runs were made for the equivalent of 100 years quasi equilibrium conditions developed in the runs which had similar erosion rates to the field with parallel slope retreat in the upper portion of the profiles and slope decline in the lower portion temporal variations in the rate of recession of the crest of the bluff closely matched changes in lake level the model confirmed previous work that suggested that rates of bluff recession are strongly controlled by the rate of erosion below the water surface but it also provided support for a more recent proposal that rates of bluff recession also influence rates of erosion in shallow water it was found that positive and negative changes in the size of the beach can either promote or hinder bluff and profile erosion depending on local circumstances the model demonstrated that bluff height debris mobility wave undercutting and groundwater levels are key factors in determining the stability of coastal bluffs the model represents a promising new tool to forecast and thereby mitigate the effects of climate change on marine and lacustrine coasts

laboratory characterization of fluid flow parameters in a porous rock containing a discrete fracture a porous block of volcanic tuff with an embedded fracture was used to perform laboratory scale water and gas flow experiments for the purpose of obtaining unsaturated fractured rock characterization parameters rock matrix properties included porosity hydraulic diffusivity and the gas phase diffusion coefficient fracture properties included apertures transmissivity hydraulic conductivity and air entry pressure gas tracer experiments using argon and helium are presented for estimating fracture hydraulic conductivity fracture apertures and rock matrix porosities

laboratory measurement of nearshore velocities and erosion of cohesive sediment till shorelines abstract the evolution of shorelines composed of consolidated cohesive sediments is dominated by irreversible erosion in this note measurements under laboratory conditions of bottom velocities wave heights and breaking characteristics over an actively eroding consolidated cohesive sediment shore are reported erosion is enhanced under breaking conditions and plunging breakers are markedly more erosive than spilling breakers the turbulence at the outer edge of the breaking zone has the 5 3 power high frequency dependence indicative of the inertial subrange

updated streamflow reconstructions for the upper colorado river basin 1 updated proxy reconstructions of water year october september streamflow for four key gauges in the upper colorado river basin were generated using an expanded tree ring network and longer calibration records than in previous efforts reconstructed gauges include the green river at green river utah colorado near cisco utah san juan near bluff utah and colorado at lees ferry arizona the reconstructions explain 72 81 of the variance in the gauge records and results are robust across several reconstruction approaches time series plots as well as results of cross spectral analysis indicate strong spatial coherence in runoff variations across the subbasins the lees ferry reconstruction suggests a higher long term mean than previous reconstructions but strongly supports earlier findings that colorado river allocations were based on one of the wettest periods in the past 5 centuries and that droughts more severe than any 20th to 21st century event occurred in the past

measurement of historical cliff top changes and estimation of future trends using gis data between bridlington and hornsea holderness coast uk abstract a key requirement for effective coastal zone management is good knowledge of historical rates of change and the ability to predict future shoreline evolution especially for rapidly eroding areas historical shoreline recession analysis was used for the prediction of future cliff shoreline positions along a section of 9 km between bridlington and hornsea on the northern area of the holderness coast uk the analysis was based on historical maps and aerial photographs dating from 1852 to 2011 using the digital shoreline analysis system dsas 4 3 extension of esri s arcinfo 10 the prediction of future shorelines was performed for the next 40 years using a variety of techniques ranging from extrapolation from historical data geometric approaches like the historical trend analysis to a process response numerical model that incorporates physically based equations and geotechnical stability analysis with climate change and sea level rise implying that historical rates of change may not be a reliable guide for the future enhanced visualization of the evolving coastline has the potential to improve awareness of these changing conditions following the ipcc 2013 report two sea level rise rates 2 mm yr and 6 mm yr have been used to estimate future shoreline conditions this study illustrated that good predictive models once their limitations are estimated or at least defined are available for use by managers planners engineers scientists and the public to make better decisions regarding coastal management development and erosion control strategies

storm wave development of shore normal grooves gutters on a steep sandstone beach face abstract shore normal grooves gutters cut into the seabed have been reported widely from the marine geological record grooves commonly are spaced regularly across plane consolidated surfaces in the littoral and sub littoral zones and may be deeply incised despite their common occurrence in the rock record there are few detailed descriptions of examples from modern environments previously reported examples have been ascribed to erosion by wave induced currents especially storm driven near shore flows in particular examples from beach faces have been related to either wave swash or backwash however no conceptual model exists to explain the presence of grooves their morphology or their spacing alongshore herein quasi regularly spaced grooves on a soft sandstone beach face are described and interpreted to have formed due to wave breaking and swash zone processes consequent upon exceptional storms at sea the groove morphologies are quantified using terrestrial laser scanning numerical modelling of the translation from offshore waves to nearshore breaking waves provides estimates of the swash zone parameters a consideration of swash zone processes provides an explanation for formation of the grooves in particular the swash zone shear stress distribution and consequent bed erosion is a dome shaped function of distance across the beach face and this controls the cross shore variability in groove depths high speed sheet flows such as swash and backwash develop periodic shore normal high and low speed streaks alongshore consequent streaky erosion produces the quasi regular alongshore groove spacings however on any given beach face the specific spacing of grooves is likely a property not only of the local sheet flow attributes but also of larger scale morphological forcing this outcome suggests that spacing is an emergent property of the coupled sheet flow and larger scale forcing and thus specific spacings on any beach face remain unpredictable

toward forward modeling for paleoclimatic proxy signal calibration a case study with oxygen isotopic composition of tropical woods a forward model of the oxygen isotopic composition 18o of wood cellulose is parameterized for time series prediction in tropical environments and driven with meteorological data observed at la selva biological research station costa rica for 1985 2001 monthly resolution model results correlate modestly r 0 34 p 0 05 with observed isotopic data with higher correlation r 0 45 p 0 01 over the earliest 10 years of comparison and nonsignificant correlation over the most recent 6 years of record analysis of model output for la selva suggests that isotopic variations are strongly controlled by rainfall amount the model simulates an analogous but stronger than observed negative isotopic anomaly associated with positive july september rainfall anomalies during el nino southern oscillation enso warm phase event years simulated tree isotope data for the global tropics suggest that a network of well replicated data series from selected locations may resolve the large scale precipitation anomaly pattern associated with enso

estimating central equatorial pacific sst variability over the past millennium part i methodology and validation abstractconstraining the low frequency lf behavior of general circulation models gcms requires reliable observational estimates of lf variability this two part paper presents multiproxy reconstructions of nino 3 4 sea surface temperature over the last millennium applying two techniques composite plus scale cps and hybrid regularized expectation maximization regem truncated total least squares ttls to a network of tropical high resolution proxy records this first part presents the data and methodology before evaluating their predictive skill using frozen network analysis fna and pseudoproxy experiments the fna results suggest that about half of the nino 3 4 variance can be reconstructed back to a d 1000 but they show little lf skill during certain intervals more variance can be reconstructed in the interannual band where climate signals are strongest but this band is affected by dating uncertainties which are not formally addressed here the cps reliably estimates interannual varia

a predictive mesoscale model of the erosion and profile development of soft rock shores the development application and behaviour of a generic model of retreating soft rock e g clay shores is described this represents a broad system in coastal modelling terms comprising shore platform beach tidal range wave transformation cliff and talus the coast is divided into a series of representative cross shore profiles each of which is discretised into a column of elements erosion of a platform element at each timestep depends on its gradient material strength is dealt with as a calibration constant wave forces are averaged over durations of a tide or hour and sediment transport is represented in bulk terms attention has been focussed on interaction between system parts and the emergence of system properties in particular profile shape this is allowed to develop towards dynamic equilibrium and is the principal means of model validation the emergence of the profile shape is dominated by the distribution of wave scour by the tide and by interaction with a beach if present because the model is process based it may be used to model the effects of climate change and engineering intervention yet it is also computationally inexpensive so may be used to explore uncertainty through probabilistic application the breadth of the included system coupled with short run times enables predictions over timescales of decades which we refer to as the mesoscale the model is used to explore the dynamics of retreating soft rock shore profiles and to predict future behaviour of a study site

flume experiments on the erosion of till shores by waves abstract hydraulic tests of the erosion by waves of a laboratory flume profile made from intact samples of till a preconsolidated cohesive material are described over 1000 h of testing were successfully completed using random breaking waves varying conditions of sand cover and varying mean water levels vertical erosion of the cohesive profile was measured with an optical bedplotter device the sand layer covering cohesive shores can vary spatially and temporally so erosion rates have been investigated under four different conditions of sand supply and the results are summarized here in addition two sets of tests were replicated in order to demonstrate their repeatability erosion rates compare favourably with results from unidirectional flow tests with a similar till material during the tests the unconfined compressive strength of the till surface was measured in a simple manner at selected locations

a numerical procedure for unsaturated seepage analysis in rock mass containing fracture networks and drainage holes abstract it is computationally difficult to model unsaturated flow through a highly fractured rock system that contains porous rock matrix densely distributed fracture networks and narrowly spaced drainage holes we present an efficient numerical procedure that uses a three dimensional finite element model to solve richards equation with embedded zero thickness elements for fractures and line elements for drainage holes a mixed boundary condition is applied at potential seepage surfaces and a water retention relation with extremely narrow unsaturated zone is specified to precisely locate the phreatic surface the procedure compares favorably with results from other numerical solutions and experimental data a case study is developed to evaluate seepage through a densely fractured rock slope the simulated results demonstrate that fractures disorder the hydraulic potential distribution with fracture patterns acting as significant influential factors and drainage holes dramatically lower the phreatic surface due to the effects of drainage and depressurization the proposed numerical procedure shows to be capable of investigating the unsaturated flow in highly fractured rock mass

modeling the erosion of cohesive clay coasts a model was developed to study the erosion of cohesive clay coasts in macro to non tidal environments the model shares some of the characteristics of previous models including the erosion of bare clay surfaces by wave generated bottom shear stresses and of mobile sediment covered surfaces by abrasion it differs from previous models however in several important ways the morphodynamics of beaches with clay foundations under different wave conditions are based on a previously developed model for beaches on rocky shore platforms sediment thickness along a beach profile is calculated at regular intervals and compared with the maximum thickness that could be moved at that location under prevailing wave conditions wave friction factors are determined where necessary according to the occurrence and morphology of ripples on the bottom in addition to abrasion and the effect of wave induced shear stresses on the clay bottom erosion by stresses generated by wave impact at the bluff foot and on the intertidal platform is calculated using an expression derived from hard rock coastal models tides are represented by their computed tidal duration values the amount of time each year that the water level falls within each 0 1 m vertical interval water depths are modified by wave setup and set down conditions several preliminary model runs were made the profiles were concave in the submarine zone and roughly linear in the intertidal zone equilibrium profiles developed which were maintained as they migrated landwards

infiltration of a liquid front in an unsaturated fractured porous medium we consider liquid infiltrating by gravity flow into a system of parallel regularly spaced fractures in an unsaturated porous medium the position of the fracture liquid front as a function of time under some simplifying assumptions is shown to obey a nonlinear integrodifferential equation approximate analytic solutions are developed showing that the movement of the liquid front exhibits three major flow periods 1 at early time the frontal position is determined by the fracture inlet boundary condition and the gravity driven flow behavior of the fracture with negligible influence by the matrix 2 at intermediate time matrix imbibition retards the frontal advance against the pull of gravity 3 at late time the matrix approaches saturation and the frontal velocity approaches a limiting value a two dimensional numerical model is used to confirm the approximate solutions implications of the model for nuclear waste storage are discussed the analysis is applicable not only to fractured rock but also to lateral infiltration into coarse grained sediments lying between layers of fine grained soil

equilibrium responses of cliffed coasts to changes in the rate of sea level rise abstract basic formulae have long been used to predict the effects of sea level rise on coastal recession for instance the geometric bruun rule and its modifications has often been applied to sandy coasts both low lying and steep however the behavior of rocky coasts whether strongly or poorly lithified should be significantly different than that of sandy coasts given that rocky coast evolution depends upon the irreversible breakdown of rock whereas sandy and depositional systems are controlled by the transport and related transport gradients of mobile sediment here we investigate the basis of a modeled relationship which suggests with a number of caveats that the equilibrium soft rock cliff recession rate can be estimated by the square root of the relative change in sea level rise rate although this relationship was derived using the numerical model scape soft cliff and platform erosion which simulates a broad soft rock cliffed coastal system driven by stochastic environmental forces here we show that a simplified modeling approach also reproduces the relationship we then extend this approach to develop a general theoretical framework within which it is possible to consider the potential responses of the different types of cliffed coasts to changes in the rate of sea level rise although a wide variety of processes affect different coastal settings this framework demonstrates how the strength and the nature of feedbacks within cliffed system control their response to sea level rise this suggests that cliffed environments controlled by different processes can still respond in similar ways to changes in the rate of sea level rise most rocky coasts would be expected to respond as a damped or negative feedback system between the extremes of a no feedback system that is unresponsive to sea level rise rate and an instant response system characterized by a linear response similar to the bruun rule this framework suggests that a potential inverse feedback case could also exist in which increased rates of sea level rise reduce the rate of coastal recession in almost all cases it is apparent that cliffed coast response to sea level rise depends not only upon the total elevation change of sea level but on the rate of the sea level rise these theoretical investigations and the classifications presented provide a framework to understand the behavior of systems affected by a wide array of processes and provide expectations that can be tested using more complex models of cliffed coast evolution in a variety of environments whether sandy or rocky hard or soft

annually resolved ice core records of tropical climate variability over the past 1800 years ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics but they are difficult to recover and few exist here we report annually resolved ice core records from the quelccaya ice cap 5670 meters above sea level in peru that extend back 1800 years and provide a high resolution record of climate variability there oxygen isotopic ratios 18 o are linked to sea surface temperatures in the tropical eastern pacific whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the intertropical convergence zone in the region of the tropical andes quelccaya continues to retreat and thin radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia

modeling cohesive clay coast evolution and response to climate change a model was used to study the evolution of cohesive clay coasts under different environmental and geological conditions and the effect of future climate change the model considered wave impact on the bluff and in the intertidal zone and bottom generated shear stresses and the protective and abrasive action of beach sediment in the intertidal and subtidal zones quasi equilibrium conditions developed in model runs with parallel slope retreat in the upper portion of the profiles and slope decline in the lower portions profile gradient below the low tidal level increased with the threshold shear stress for bottom erosion therefore rates of wave attenuation were lower in resistant than in weak materials and the intertidal zones were wider and more gently sloping the widest and gentlest intertidal zones developed in runs that had no sediment the largest waves played little role in platform development in part because of low frequency but mainly because they expend most of their energy in crossing wide turbulent surf zones the model suggested that rising sea level will usually result in accelerated rates of bluff recession especially if the rise is rapid simultaneous increases in the frequency of moderately large waves as opposed to the largest waves may also generate marked increases in erosion on bluffs and in intertidal and supratidal zones although erosion may be reduced at some elevations where there is beach sediment positive or negative changes in beach volume can increase or decrease rates of bluff erosion

improved spectral comparisons of paleoclimate models and observations via proxy system modeling implications for multi decadal variability abstract the spectral characteristics of paleoclimate observations spanning the last millennium suggest the presence of significant low frequency multi decadal to centennial scale variability in the climate system since this low frequency climate variability is critical for climate predictions on societally relevant scales it is essential to establish whether general circulation models gcms are able to simulate it faithfully recent studies find large discrepancies between models and paleoclimate data at low frequencies prompting concerns surrounding the ability of gcms to predict long term high magnitude variability under greenhouse forcing laepple and huybers 2014a 2014b however efforts to ground climate model simulations directly in paleoclimate observations are impeded by fundamental differences between models and the proxy data proxy systems often record a multivariate and or nonlinear response to climate precluding a direct comparison to gcm output in this paper we bridge this gap via a forward proxy modeling approach coupled to an isotope enabled gcm this allows us to disentangle the various contributions to signals embedded in ice cores speleothem calcite coral aragonite tree ring width and tree ring cellulose the paper addresses the following questions 1 do forward modeled pseudoproxies exhibit variability comparable to proxy data 2 if not which processes alter the shape of the spectrum of simulated climate variability and are these processes broadly distinguishable from climate we apply our method to representative case studies and broaden these insights with an analysis of the pages2k database pages2k consortium 2013 we find that current proxy system models psms can help resolve model data discrepancies on interannual to decadal timescales but cannot account for the mismatch in variance on multi decadal to centennial timescales we conclude that specific to this set of psms and isotope enabled model the paleoclimate record may exhibit larger low frequency variability than gcms currently simulate indicative of incomplete physics and or forcings