u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

reconstructing biomes from palaeoecological data a general method and its application to european pollen data at 0 and 6 ka biome models allow the results of experiments with atmospheric general circulation models to be translated into global maps of potential natural vegetation the use of biome models as a diagnostic tool for palaeoclimate simulations can yield maps that are directly comparable with palaeoecological pollen and plant macrofossil records provided these records are biomized i e assigned to biomes in a consistent way this article describes a method for the objective biomization of pollen samples based on fuzzy logic pollen types taxa are assigned to one or more plant functional types pfts then affinity scores are calculated for each biome in turn based on its list of characteristic pfts the pollen sample is assigned to the biome to which it has the highest affinity subject to a tie breaking rule modern pollen data from surface samples reflecting present vegetation across europe are used to validate the method pollen data from dated sediment cores are then used to reconstruct european vegetation patterns for 6 ka the reconstruction shows systematic differences from present that are consistent with previous interpretations the method has proved robust with respect to human impacts on vegetation and provides a rational way to interpret combinations of pollen types that do not have present day analogs the method demands minimal prior information and is therefore equally suitable for use in other regions with richer floras and or lower densities of available modern and fossil pollen samples than europe

quasi real time fault model estimation for near field tsunami forecasting based on rtk gps analysis application to the 2011 tohoku oki earthquake mw 9 0 1 real time crustal deformation monitoring is extremely important for achieving rapid understanding of actual earthquake scales because the measured permanent displacement directly gives the true earthquake size seismic moment mw information which in turn provides tsunami forecasting we have developed an algorithm to detect estimate static ground displacements due to earthquake faulting from real time kinematic gps rtk gps time series the new algorithm identifies permanent displacements by monitoring the difference of a short term average sta to a long term average lta of the gps time series we assessed the noise property and precision of the rtk gps time series with various baseline length conditions and orbits and discerned that the real time ephemerides based on the international gnss service igs are sufficient for crustal deformation monitoring with long baselines up to 1 000 km we applied the algorithm to data obtained in the 2011 off the pacific coast of tohoku earthquake mw 9 0 to test the possibility of coseismic displacement detections and further we inverted the obtained displacement fields for a fault model the inversion estimated a fault model with mw 8 7 which is close to the actual mw of 9 0 within five minutes from the origin time once the fault model is estimated tsunami waveforms can be immediately synthesized using pre computed tsunami green s functions the calculated waveforms showed good agreement with the actual tsunami observations both in arrival times and wave heights suggesting that the rtk gps data by our algorithm can provide reliable rapid tsunami forecasting that can complement existing tsunami forecasting systems based on seismic observations

using hydroacoustic stations as water column seismometers 1 getting seismic data from the deep oceans usually involves ocean bottom seismometers but hydrophone arrays may provide a practical alternative means of obtaining vector data we here explore this possibility using hydrophone stations of the international monitoring system which have been used to study icebergs and t wave propagation among others these stations consist of three hydrophones at about the depth of the deep sound channel in a horizontal triangle array with 2 km sides we use data from these stations in the very low frequency regime 0 01 0 05 hz band to demonstrate that these stations can also be used as water column seismometers by differencing the acoustic pressure we obtain vector quantities analogous to what a seismometer would record comparing processed hydrophone station records of the 2004 great sumatra andaman earthquake with broadband seismograms from a nearby island station we find that the differenced hydrophones are indeed a practical surrogate for seismometers

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

a self consistent mechanism for slow dynamic deformation and tsunami generation for earthquakes in the shallow subduction zone 1 dynamic pore pressure changes in the overriding wedge above a shallow dipping plate interface significantly affect the rupture dynamics of shallow subduction zone earthquakes and their tsunamigenesis for a wedge on the verge of coulomb failure everywhere including the basal fault the dynamic pore pressure increase due to up dip rupture propagation leads to widespread yielding within the wedge which is greatly enhanced by the shallow dip of the fault the widespread yielding reduces the stress drop slip velocity slip and rupture velocity giving rise to prolonged rupture duration thus explaining many anomalous features of shallow subduction zone earthquakes significant inelastic seafloor uplift occurs in the case of a shallow fault dip with the largest uplift located landward from the trench integrating this physical mechanism with existing seismic geodetic and tsunami observations can provide new insights into earthquake dynamics and deformation processes in shallow subduction zones

quantifying regional vegetation changes in china during three contrasting temperature intervals since the last glacial maximum abstract the need to reduce the uncertainty of predictions of vegetation change under global warming highlights the importance of understanding the vegetation patterns and possible mechanisms of vegetation response during past warming intervals here we present quantitative regional vegetation reconstructions for china during the last glacial maximum lgm 18 2 14c kyr b p early holocene eh 8 5 0 5 14c kyr b p and mid holocene mh 6 0 5 14c kyr b p using the biomization method and based on 249 pollen records in addition we used an inverse vegetation modeling approach to investigate the effect of climate change and co2 concentration on the observed vegetation changes the results demonstrate that during the lgm steppe expanded southeastwards reaching the present day temperate deciduous forest tede zone in contrast the forest in eastern china underwent a substantial southward retreat and its percentage reached a minimum the warm mixed forest wamf and tede shifted southwards of 10 n relative to today and tropical seasonal rain forest tsfo was almost absent in addition the forest steppe boundary shifted southwards to near the middle and lower reaches of the yangtze river during the eh and mh the tsfo wamf and tede exhibited respective northward shifts of 2 4 and 5 relative to today in mh the percentage of forest sites increased and reached a maximum and the forest steppe boundary had shifted northwestwards to near the present day 300 mm isohyet our palaeovegetation reconstructions and model sensitivity experiments suggest that temperature was the dominant factor controlling the vegetation distribution during the lgm while precipitation became increasingly more important during the holocene throughout china we further show that precipitation was the primary factor controlling palaeovegetation distribution in northern china while temperature became increasingly more important in southern china our findings are potentially important for understanding the evolution of vegetation in china in response to ongoing global warming

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

antarctic climate during the middle pliocene model sensitivity to ice sheet variation significant controversy exists surrounding the nature of the antarctic ice sheet during the period of middle pliocene warmth this paper outlines the output from three sensitivity experiments for the middle pliocene using the ukmo gcm and the usgs prism2 data set different east antarctic ice sheet configurations were prescribed in each modelling experiment conforming to a dynamic sea level 35 m higher than at present intermediate pliocene control sea level 25 m higher than at present and stable sea level 12 15 in higher than at present scenario for the nature of the antarctic ice sheet during the middle pliocene all three scenarios would have provided middle pliocene sea levels across the spectrum of estimates provided by known geological data model outputs indicate that surface temperature increases are greatest in the pliocene dynamic experiment climatic conditions for the pliocene control and stable experiments remain harsh over antarctica with surface temperatures rising above freezing mean 4degreesc for a maximum of 2 months per year in contrast mean surface temperatures from the pliocene dynamic experiment rise above freezing mean 10degreesc for 4 months of the year climatic outputs from all of the pliocene experiments were used in a biome model biome 4 for the pliocene control and stable experiments biome 4 predicted the occurrence of exclusively tundra type vegetation on antarctica for the dynamic experiment climatic conditions ameliorated sufficiently to allow biome 4 to predict deciduous taiga montane forests on antarctica thus the results from the dynamic experiment are consistent with reported pliocene nothofagus occurrences on antarctica in the future more sophisticated palaeoclimate modelling studies need to employ atmospheric general circulation models gcms coupled to dynamic ocean and ice sheet models this will allow the gcm to predict rather than prescribe an antarctic ice sheet configuration in equilibrium with reconstructed middle pliocene sea surface temperatures such an approach may also shed light on how the antarctic ice sheet responded to climate variability during the middle pliocene c 2002 elsevier science b v all rights reserved

sediment effect on tsunami generation of the 1896 sanriku tsunami earthquake the 1896 sanriku earthquake was one of the most devastating tsunami earthquakes which generated an anomalously larger tsunami than expected from its seismic waves previous studies indicate that the earthquake occurred beneath the accretionary wedge near the trench axis it was pointed out recently that sediments near a toe of an inner trench slope with a large horizontal movement due to the earthquake might have caused an additional uplift in this paper the effect of the additional uplift to tsunami generation of the 1896 sanriku tsunami earthquake is quantified we estimate the slip of the earthquake by numerically computing tsunamis and comparing their waveforms with those recorded at three tide gauges the estimated slip for the model without the additional uplift is 10 4 m and those with the additional uplift are 5 9 6 7 m this indicates that the additional uplift of the sediments near the trench has a large effect on the tsunami generation

vegetation and environment in eastern north america during the last glacial maximum abstract knowledge of the vegetation and environment of eastern north america during the last glacial maximum lgm is important to understanding postglacial vegetational and biogeographic dynamics assessing climate sensitivity and constraining and evaluating earth system models our understanding of lgm conditions in the region has been hampered by low site density problems of data quality particularly dating and the possibility that lgm vegetation and climate lacked modern analogs in order to generate improved reconstructions of lgm vegetation and environment we assembled pollen and plant macrofossil data from 21 and 17 well dated lgm sites respectively all sites have assemblages within the lgm timespan of 21 000 1500 calendar yr bp based on these data we prepared maps of isopolls macrofossil presence absence pollen analogs biomes inferred mean january and july temperatures and mean annual precipitation for the lgm tundra and open picea dominated forest grew along the laurentide ice sheet with tundra predominantly in the west in the east pinus dominated vegetation mainly p banksiana with local p resinosa and p strobus occurred extensively to 34 n and possibly as far south as 30 n picea glauca and a now extinct species p critchfieldii occurred locally picea dominated forest grew in the continental interior with temperate hardwoods quercus carya juglans liriodendron fagus ulmus growing locally near the lower mississippi valley at least as far north as 35 n picea critchfieldii was the dominant species in this region the florida peninsula was occupied by open vegetation with warm temperate species of pinus eastern texas was occupied by open vegetation with at least local quercus and picea extensive areas of peninsular florida and the continental interior had vegetation unmatched by any modern pollen samples the paleovegetational data indicate more extensive cooling in eastern north america at the lgm than simulated by either the ncar ccm0 or ccm1 climate models the occurrence of cool temperate conifers and hardwoods as far north as 34 35 n however indicates less severe cooling than some previous reconstructions paleoclimate inferences for the lgm are complicated by lowered atmospheric co 2 concentrations which may be responsible for the open nature and dominance of conifers in lgm vegetation

shallow dynamic overshoot and energetic deep rupture in the 2011 mw 9 0 tohoku oki earthquake strong spatial variation of rupture characteristics in the moment magnitude mw 9 0 tohoku oki megathrust earthquake controlled both the strength of shaking and the size of the tsunami that followed finite source imaging reveals that the rupture consisted of a small initial phase deep rupture for up to 40 seconds extensive shallow rupture at 60 to 70 seconds and continuing deep rupture lasting more than 100 seconds a combination of a shallow dipping fault and a compliant hanging wall may have enabled large shallow slip near the trench normal faulting aftershocks in the area of high slip suggest dynamic overshoot on the fault despite prodigious total slip shallower parts of the rupture weakly radiated at high frequencies whereas deeper parts of the rupture radiated strongly at high frequencies

pollen based biome reconstructions for the past 450 000 yr from the funza 2 core colombia comparisons with model based vegetation reconstructions abstract the 586 m funza 2 sequence from the high plain of bogota colombia has provided one of the longest pollen based vegetation reconstructions in the world affinity scores to seven biomes are compared to the record of co2 fluctuation from the vostok ice core for the period spanning from approximately 25 000 to 450 000 yr before present bp results are compared to output from the biome 3 vegetation model run under different environmental scenarios at regional and local scales the model is run with temperature and precipitation reductions relative to the present values of up to 10 c and 700 mm yr 1 respectively for this particular investigation we are interested in the role of co2 as a forcer of vegetation change we run the model with concentrations of atmospheric co2 co2 atm within the range of 170 to 340 ppmv during glacial periods the cool grass shrubland biome is highly dominant less so during interglacial periods when the cool evergreen and cool mixed forest biomes become co dominant in addition to this climate driven altitudinal oscillation of the vegetation there is also a signal that indicates longer term evolution of the vegetation the cool grass shrubland and cool evergreen and cool mixed forest biomes become co dominant for the first time over the 450 000 yr record at approximately 170 000 yr bp become completely anti phase during a period of extreme low co2 atm and then become co dominant from approximately 120 000 yr bp until the core top just prior to the last glacial maximum the model results for the funza area indicate that changes in co2 atm temperature and precipitation are inter linked by the vegetation response a shift of 5 5 c is required to lower the cool grass shrubland biome to altitudes about the funza catchment where the andean forest biome dominant at low co2 atm concentrations particularly below 180 ppmv the composition of the high latitudinal tropical vegetation about the funza catchment changed it is suggested that this low co2 atm combined with a period when the climate was characterised by extreme cooling and drying caused a readjustment of the tropical high altitudinal vegetation zonation and the formation of plant communities that are presently recorded

the climate of north america and adjacent ocean waters ca 6 ka the climate of north america and the adjacent ocean at 6000 bp was estimated using five independent approaches using pollen data the terrestrial climate was estimated by the movement of ecozone boundaries and by the method of modern analogues both analyses indicate warmer temperatures in the western great lakes area and the northern great plains a model of sphagnum dominated peatland initiation when forced by canadian climate model 6 ka output projected a cooler and or wetter climate for continental western north america contrary to this a reconstruction of the distribution of sphagnum dominated peatlands in western canada indicates that they were located north of their modern distribution suggesting warmer and or drier conditions at 6000 bp this interpretation is strengthened by observations of lower lake levels at 6000 bp in western canada this drier climate may have been associated with warmer conditions as indicated by the quantitative climate reconstructions in general eastern north a

constraining shallow slip and tsunami excitation in megathrust ruptures using seismic and ocean acoustic waves recorded on ocean bottom sensor networks abstract great earthquakes along subduction zone plate boundaries like the 2011 magnitude 9 0 tohoku oki japan event deform the seafloor to generate massive tsunamis tsunami wave heights near shore are greatest when excitation occurs far offshore near the trench where water depths are greatest and fault slip is shallow the tohoku event featuring over 30 m of slip near the trench exemplifies this hazard unfortunately the rupture process that far offshore is poorly constrained with land based geodetic and even most seafloor deformation measurements and seismic inferences of shallow slip are often nonunique here we demonstrate through dynamic rupture simulations of the tohoku event that long period guided waves in the ocean specifically leaking oceanic p wave modes known as pl waves can resolve the shallow rupture process and tsunami excitation near the trench with predicted pressure changes of 0 1 1 mpa along most of the seafloor landward of the trench and periods of several seconds these pl waves should be observable with ocean bottom pressure sensors and or seismometers with cabled sensor networks like those being deployed offshore japan and in other subduction zones these waves could be used to rapidly quantify shallow slip and near trench seafloor uplift and improve local tsunami early warning systems

holocene paleoclimate data from the arctic testing models of global climate change to evaluate the spatial variability of arctic climate change during the present interglacial cape project members compiled well dated terrestrial marine and ice core paleoenvironmental records spanning the past 10 12 thousand years ka six tundra biomes of increasing summer temperature requirements were defined based on regionally coherent pollen assemblages using a rule based approach pollen spectra were converted to tundra forest tundra or forest biomes ranked by their average growing season requirements marine sea surface reconstructions were based on proxy data following a similar rule based approach from these data based reconstructions departures in summer temperatures from modern normals were calculated in 1 ka time slices through the holocene to test predictive models data based summer temperature reconstructions were compared with general circulation model gcm simulations for 10 ka and 6 ka ago paleodata and model results both show that warming occurred earlier across beringia and asia relative to lands adjacent to the north atlantic and that late holocene cooling was most apparent in the north atlantic region however the gcm over predicts the magnitude of mid holocene warming over northern asia and underestimates the intensification of the north atlantic drift in the early holocene strong spatial variability in environmental response during the holocene despite symmetric insolation forcing suggests that any future changes whether caused by anthropogenic or natural factors are unlikely to result in a uniform change across the arctic adding additional complexity to forecasts of global impacts

mapping eastern north american vegetation change of the past 18 ka no analogs and the future the method of modern analogs and an extensive data base of modern and fossil pollen data were used to generate a new series of paleovegetation maps for eastern north america spanning the past 18 ka the maps illustrate the continuous nature of climate induced vegetation change and the development after about 10 ka of modern regional vegetation patterns before the holocene vegetation biomes without modern analogs were widespread in response to climate conditions without modern analogs and to a lesser extent to the rapidity of climate change over the last glacial interglacial transition this geological perspective suggests that possible future climate changes could force similarly complex changes in natural vegetation including the development of biomes without modern analogs

paleoclimate simulations for north america over the past 21 000 years features of the simulated climate and comparisons with paleoenvironmental data maps of upper level and surface winds and of surface temperature and precipitation illustrate the results of a sequence of global paleoclimatic simulations spanning the past 21 000 years for north america we review a the large scale features of circulation temperature and precipitation that appear in the simulations from the ncar community climate model version 1 ccm 1 b the implications of the simulated climate for the past continental scale distributions of three plant taxa picea spp pseudotsuga menziesii and artemisia tridentata which are broadly representative of the vegetation across the continent and c the potential explanations in terms of atmospheric circulation or surface energy and water balance processes for mismatches between the simulations and observations most of the broad scale features of previous paleoclimatic simulations with the ncar ccm 0 for north america are present in the current simulations many of the elements of a conceptual model based on previous climate simulations that describes the controls of paleoclimatic variations across north america during the past 21 000 years are found in simulations reviewed here these include 1 displacement of the jet stream by the laurentide ice sheet to the south of its present position in both winter and summer 2 generation of a glacial anticyclone over the ice sheet at the lgm and the consequent induction of large scale sinking motions induced over eastern north america 3 changes in the strength of surface atmospheric circulation features through time including weakening of the aleutian low in winter and strengthening of the eastern pacific and bermuda high pressure systems in summer as the ice sheet decreased in size 4 development of a heat low at the surface and a strengthened ridge in the upper atmosphere over the continent at the time of the maximum summer insolation anomaly 5 increases in summer temperature earlier in regions remote from the ice sheet these increases appear earlier in the present ccm 1 simulations than in the previous ccm 0 ones however and 6 continuation of negative winter temperature anomalies into the middle holocene in general simulated surface conditions that are discordant with paleoenvironmental observations can be attributed to the simulation of particular atmospheric circulation patterns e g those that suppress precipitation or advect warm air into a region with these mismatches amplified in beringia and the southeastern united states by surface energy and water balance processes

a pollen based pseudobiomisation approach to anthropogenic land cover change the degree of anthropogenic modification of land cover through the mid to late holocene is of significant interest for archaeologists climate modellers and conservation ecologists amongst others spatially extensive pollen data provide an appropriate resource for the reconstruction of land cover change however traditional simple methods e g the ap nap ratio do not provide the degree of detail required for these user groups a range of more sophisticated methods have been developed e g mechanistic model based methods but they require a high degree of understanding of the pollen vegetation relationship which is resource and time consuming this paper proposes a method of intermediate complexity by which major land cover changes can be assessed for individual sites and regions a pseudobiomisation approach is used in which pollen taxa are assigned to different land cover classes lcc and the sum of adjusted pollen proportions for each class used to determine an lcc affinity score for individu

on the sensitivity of ocean circulation to arctic freshwater input during the paleocene eocene thermal maximum abstract the paleocene eocene thermal maximum petm 55 ma ago corresponds to a time characterized by extreme global warming caused by a massive carbon input into the ocean and atmosphere climate proxies from sedimentary records suggest that fresh water flow from an ice free arctic into the remainder of the global ocean increased due to tectonic changes enhanced runoff and thermal expansion in this study we use the community climate system model version 3 ccsm 3 including a carbon cycle model to examine the sensitivity of the ocean circulation to freshwater outflow from the arctic ocean during the petm and whether these changes may have contributed to an additional warming during the petm two experiments the first with freshwater exchange between the arctic and pacific oceans and the second between the arctic and atlantic oceans are compared with a reference experiment with exchange between the arctic and indian oceans and with independent stratigraphic and geochemical records from the ocean drilling program odp as freshwater is transported from the arctic into the north pacific ocean stratification is enhanced in the north pacific due to a significant reduction in surface salinity as a consequence intermediate to deep water sources shift from both hemispheres in the pacific ocean to a dominant source in the south pacific ocean and an additional source in the northern tethys ocean this simulated shift of deep water sources during the petm is in agreement with recent nd isotope measurements the circulation patterns in the pacific are similar to those inferred from stable isotope reconstructions but contradicting a strong north atlantic deep water source during the petm freshwater input into the pacific ocean results in a warming of intermediate water masses of 2 c in the north pacific when freshwater flow is routed from the arctic into the atlantic ocean surface density changes are too small to change vertical stratification substantially contrary to a previous study in summary based upon circulation patterns and temperature increases due to freshwater flux through the bering strait arctic freshwater input into the north pacific may have contributed to methane hydrate destabilization an event suggested to have accelerated warming during the petm

comparison of north american pollen based temperature and global lake status with cccma agcm2 output at 6 ka abstract we present new paleoclimate reconstructions for the time period of 6000 yr bp 6 ka that permit a quantitative comparison to corresponding mapped patterns of the newest version of the canadian cccma agcm2 climate model july temperature reconstructions were estimated using the modern analog technique employing fossil pollen records from the north american pollen database we present a new method of optimizing critical choices within the application of the mat through modern calibration the pattern of 6 ka temperature anomalies generated by the cccma agcm2 generally agree with those of the pollen based reconstruction particularly in the presence of a band of positive temperature anomalies across the continent from the yukon through the great lakes region and along the st lawrence this agreement suggests that both the model and data are reconstructing a contraction in the polar vortex over north america at 6 ka major areas of disagreement between the pollen based reconstruction and model simulation are also areas where the data are sparse and edge effects produce less reliable reconstructions the cccma agcm2 simulates drier conditions in a west east band stretching from alaska through the canadian prairies and midwest united states in agreement with low lake level observations at 6 ka simulated and reconstructed precipitation evaporation are also in agreement over the southwest united states with the exception of north central africa the cccma agcm2 fails to capture the northward and eastern extension of the afro asian monsoon belt at 6 ka general agreement between cccma agcm2 p e anomalies and lake status change is found throughout europe at 6 ka

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

rupture to the trench dynamic rupture simulations of the 11 march 2011 tohoku earthquake there is strong evidence that the 11 march 2011 tohoku earthquake rupture reached the seafloor this is surprising because the shallow portion of the plate interface in subduction zones is thought to be frictionally stable leading to the widely held view that coseismic rupture would stop several tens of kilometers downdip of the seafloor various explanations have been proposed to reconcile this seeming inconsistency including dynamic weakening e g thermal pressurization and extreme stress release around shallow subducted seamounts we offer a simpler explanation supported by 2d dynamic rupture simulations of the tohoku earthquake our models account for depth dependent material properties and the complex geometry of the fault seafloor and material interfaces based on seismic surveys of the japan trench the fault obeys rate and state friction with standard logarithmic dependence of shear strength on slip velocity in steady state in our preferred model the uppermost section of the fault is velocity strengthening rupture nucleates on a deeper velocity weakening section waves released by deep slip reflect off the seafloor transmitting large stress changes to the upper section of the fault driving the rupture through the velocity strengthening region to the trench we validate the model against seafloor deformation and 1 hz global positioning system gps data the seafloor displacements constrain the seismogenic depth and overall amount of slip particularly near the trench our simulations reproduce many features in the gps data thereby providing insight into the rupture process and seismic wave field sensitivity to parameters is explored through an extensive suite of simulations neither static seafloor deformation nor onshore 1 hz gps data can uniquely determine near trench frictional properties due to trade offs with average stress drop while conducted specifically for the japan trench region our simulations suggest that rupture to the trench in megathrust events is quite possible even if velocity strengthening properties extend tens of kilometers landward from the trench online material mp4 movies of particle velocities

applying plant functional types to construct biome maps from eastern north american pollen data comparisons with model results abstract global biome models like biome1 convert climate model simulations of past climates into biome distributions and thus facilitate comparison of both climate and biome model results with biomes estimate from paleoecological data we adapted a biomization method recently developed for european pollen data for use with pollen data in eastern north america and then compared its estimated biomes with those derived from applying biome1 to the climate simulations from the ncar ccm1 national center for atmospheric research community climate model version 1 for 6000 years ago 6 ka we first tested the biomization method by seeing how well the biomes inferred from modern pollen data match observed biomes we found that modifications to the method were necessary in part to account for physiological differences between north american and european taxa and in part to cope with our choice of using just 23 major pollen taxa our modifications significantly improved the match between observed modern biomes and pollen derived biomes as measured by the kappa statistic we tested our tuning of the biomization method by matching its inferred 6 ka biomes to biomes estimated from pollen data using the modern analog technique the degree of agreement at 6 ka is close to that for today showing that 1 the biomization method and modern analog technique when applied to the same pollen data produce consistent results and 2 the modifications made to the biomization method are robust back to 6 ka we then used the results of the biomization method to test the biome maps simulated by biome1 which derives biome distributions from observed climate values for today and from the climatic simulations of the ccm1 for 6 ka only a fair agreement is seen and significant offsets exist in the placement of biomes by biome1 for today biome1 simulates the boundary between the temperate deciduous and cool mixed forests to be too far south and the steppe forest boundary to be too far west these model biases are also evident in the simulations at 6 ka despite the fact that ccm1 simulates warmer than present temperatures in the central united states to the north however biome1 correctly simulates the cool mixed forest and taiga boundary at 6 ka as more northwestward than at present

cenozoic aridification in northwest china evidenced by paleovegetation evolution abstract although the cenozoic aridification of the asian interior was of global significance the timing of its evolution and the drivers remain controversial however knowledge of the spatiotemporal pattern of vegetation evolution can inform our understanding of the aridification process here we integrate 58 pollen records with well constrained chronologies from across asia and use the biomization method to quantitatively reconstruct the cenozoic evolution of the vegetation the results reveal the occurrence of desert in northwest china during 43 35 ma indicating a dry climate after 22 ma there was a further expansion of desert and steppe in northwest china indicating the existence of a permanent arid environment the aridity was intensified after 8 7 ma evidenced by the replacement of forest by steppe and desert we suggest that the permanent aridification since 22 ma was related to the uplift of the tibetan plateau and that the enhanced aridification since 8 7 ma was caused by ongoing global cooling

simulated climate and biomes of africa during the late quaternary comparison with pollen and lake status data new compilations of african pollen and lake data are compared with climate ccm1 ncar boulder and vegetation biome 1 2 gsg lund simulations for the last glacial maximum lgm and early to mid holocene emh the simulated lgm climate was ca 4 c colder and drier than present with maximum reduction in precipitation in semi arid regions biome simulations show lowering of montane vegetation belts and expansion of southern xerophytic associations but no change in the distribution of deserts and tropical rain forests the lakes show lgm conditions similar or drier than present throughout northern and tropical africa pollen data indicate lowering of montane vegetation belts the stability of the sahara and a reduction of rain forest the paleoenvironmental data are consistent with the simulated changes in temperature and moisture budgets although they suggest the climate model underestimates equatorial aridity emh simulations show temperatures slightly less than present and increased monsoonal precipitation in the eastern sahara and east africa biome simulations show an upward shift of montane vegetation belts fragmentation of xerophytic vegetation in southern africa and a major northward shift of the southern margin of the eastern sahara the lakes indicate conditions wetter than present across northern africa pollen data show an upward shift of the montane forests the northward shift of the southern margin of the sahara and a major extension of tropical rain forest the lake and pollen data confirm monsoon expansion in eastern africa but the climate model fails to simulate the wet conditions in western africa

global middle pliocene biome reconstruction a data model synthesis 1 the middle pliocene warm interval ca 3 ma bp has been extensively studied however our knowledge concerning the global distribution of middle pliocene biomes remains far from complete this paper presents the results from a first attempt at simulating the distribution of different mid pliocene biomes using an advanced numerical general circulation climate model hadley centre atmospheric model version 3 and the biome 4 vegetation model the modeling indicates that during the middle pliocene the geographical coverage of tundra type biomes may have been significantly reduced compared with the present day in the northern hemisphere high latitude forests expand in the place of tundra forms of vegetation total area covered by forest increases for the pliocene case compared with the present day arid deserts become less prevalent in the pliocene scenario and are replaced by tropical xerophytic shrublands and savanna type vegetation these results compare favorably with geological data in general and with the u s geological survey s prism2 middle pliocene vegetation reconstruction although data model inconsistencies are apparent although some of these inconsistencies relate to the weaknesses of the climate and biome model employed others identify deficiencies in the extant geological data set or the interpretation of this data this modeled biome reconstruction will serve as a useful vehicle for aiding in future comparisons between geological data on middle pliocene biomes and model predictions

how well can we simulate past climates evaluating the models using global palaeoenvironmental datasets abstract global syntheses of palaeoenvironmental data are required to test climate models under conditions different from the present data sets for this purpose contain data from spatially extensive networks of sites the data are either directly comparable to model output or readily interpretable in terms of modelled climate variables data sets must contain sufficient documentation to distinguish between raw primary and interpreted secondary tertiary data to evaluate the assumptions involved in interpretation of the data to exercise quality control and to select data appropriate for specific goals four data bases for the late quaternary documenting changes in lake levels since 30 14 c kyr bp the global lake status data base vegetation distribution at 18 14 c kyr and 6 14 c kyr bp biome 6000 aeolian accumulation rates during the last glacial interglacial cycle dirtmap and tropical terrestrial climates at the last glacial maximum the lgm tropical terrestrial data synthesis are summarised each has been used to evaluate simulations of last glacial maximum lgm 21 calendar kyr bp and or mid holocene 6 cal kyr bp environments comparisons have demonstrated that changes in radiative forcing and orography due to orbital and ice sheet variations explain the first order broad scale in space and time features of global climate change since the lgm however atmospheric models forced by 6 cal kyr bp orbital changes with unchanged surface conditions fail to capture quantitative aspects of the observed climate including the greatly increased magnitude and northward shift of the african monsoon during the early to mid holocene similarly comparisons with palaeoenvironmental datasets show that atmospheric models have underestimated the magnitude of cooling and drying of much of the land surface at the lgm the inclusion of feedbacks due to changes in ocean and land surface conditions at both times and atmospheric dust loading at the lgm appears to be required in order to produce a better simulation of these past climates the development of earth system models incorporating the dynamic interactions among ocean atmosphere and vegetation is therefore mandated by quaternary science results as well as climatological principles for greatest scientific benefit this development must be paralleled by continued advances in palaeodata analysis and synthesis which in turn will help to define questions that call for new focused data collection efforts

mapped plant macrofossil and pollen records of late quaternary vegetation change in eastern north america abstract macrofossil presence absence maps and isopoll maps in 3000 year intervals show how ranges and abundance maxima for 12 eastern north american tree and shrub taxa picea p glauca p mariana larix laricina abies balsamea tsuga canadensis pinus strobus p resinosa p banksiana betula papyrifera b alleghaniensis b series humiles have changed from the last glacial maximum to the present the macrofossil maps corroborate patterns shown by the isopoll maps and provide spatial detail and taxonomic resolution the macrofossils confirm the inference from pollen data that unglaciated southeastern north america was cooler during the last glacial maximum 18 and 15 ka than simulated by the cohmap experiments with the ncar ccm0 general circulation model the geographic distribution of macrofossil occurrences during the late glacial 12 and 9 ka indicate that migration lag of boreal species did not occur at regional to subcontinental scales and that pollen assemblages lacking modern analogs resulted from climate gradients lacking modern analogs early holocene 9 and 6 ka macrofossil maps show rapid northward expansion of tree species ranges into deglaciated regions the data also show modest contractions of northern range limits of temperate species and expansions of southern range limits of boreal species in response to cooling trends during the late holocene 3 and 0 ka comparison of modern macrofossil maps of nine of these taxa with corresponding range maps confirm that the macrofossils record the geographic ranges accurately comparison of the modern macrofossil maps with maps of tree growing stock volume shows that for some taxa abies tsuga macrofossil occurrences were most frequent in regions of maximum tree abundance comparison of modern isopoll maps with the modern range and growing stock volume maps indicate that in contrast to the macrofossil data the pollen data provide poorer resolution of range limits for most taxa but better indications of abundance maxima and minima within the ranges

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

along arc structural variation of the plate boundary at the japan trench margin implication of interplate coupling 1 at the japan trench convergent margin many large interplate earthquakes of greater than m7 5 frequently occur their epicenters have uneven distribution mostly located in the northern area to investigate the relationship between this distribution and tectonic structures we have conducted multichannel seismic surveys since 1996 our data show two kinds of interplate sedimentary units a wedge shaped unit and a channel like unit both units have a lower p wave velocity than the basal part of the overriding island arc crust the wedge shaped unit having a velocity of 2 3 km s is widely distributed over the forearc region in the northern area its thickness decreases with depth becoming several hundred meters at a depth of 12 km the channel like unit having a velocity of 3 4 km s is observed in the southern area extending in the downdip direction its thickness reaches 2 km at a depth of 12 km if the low velocity of these units results from the existence of fluid as many authors assume the units being thick implies higher fluid content assuming constant porosity considering that fluid reduces basal friction and with an assumption that fluid available at a specific interface is proportional to the total fluid content in the sediment the thickness variation of the units would cause different degrees of coupling at the plate boundary along the arc this may provide one explanation for the regional disparity in the interplate earthquake occurrence in the margin furthermore we attempt to call attention to the possibility that the channel like sediment works as a shear stress releaser

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

magnitude of climate variability during middle pliocene warmth a palaeoclimate modelling study abstract the nature and magnitude of climatic variability during the period of middle pliocene warmth ca 3 29 2 97 ma is poorly understood we present a suite of palaeoclimate modelling experiments incorporating an advanced atmospheric general circulation model gcm coupled to a q flux ocean model for 3 29 3 12 and 2 97 ma bp astronomical solutions for the periods in question were derived from the berger and loutre bl2 astronomical solution boundary conditions excluding sea surface temperatures ssts which were predicted by the slab ocean model were provided from the usgs prism2 2 2 digital data set the model results indicate that little annual variation 0 5 c in ssts relative to a control experiment occurred during the middle pliocene in response to the altered orbital configurations annual surface air temperatures also displayed little variation seasonally surface air temperatures displayed a trend of cooler temperatures during december january and february and warmer temperatures during june july and august this pattern is consistent with altered seasonality resulting from the prescribed orbital configurations precipitation changes follow the seasonal trend observed for surface air temperature compared to present day surface wind strength and wind stress over the north atlantic north pacific and southern ocean remained greater in each of the pliocene experiments this suggests that wind driven gyral circulation may have been consistently greater during the middle pliocene the trend of climatic variability predicted by the gcm for the middle pliocene accords with geological data however it is unclear if the model correctly simulates the magnitude of the variation this uncertainty is derived from a the relative insensitivity of the gcm to perturbation in the imposed boundary conditions b a lack of detailed time series data concerning changes to terrestrial ice cover and greenhouse gas concentrations for the middle pliocene and c difficulties in representing the effects of climatic history in snap shot gcm experiments

sphagnum peatland distribution in north america and eurasia during the past 21 000 years the distribution and abundance of sphagnum spores in north america and eurasia are mapped for the past 21 ka the present day distribution of abundant sphagnum spores corresponds closely to areas with peatland development with maximum sphagnum abundance between 630 and 1300 mm annual precipitation and between 2 and 6 c mean annual air temperature during the wisconsin glaciation there were apparently not large areas of peatland in north america except in alaska high sphagnum spore percentages were found in eastern north america during deglaciation major peatland development occurred in boreal north america after 9 ka and there was a southward movement of high sphagnum spore abundance after 5 ka in the western great lakes region major peatland development began after 9 ka in europe and asia on the basis of maps of the area supporting peatlands carbon accumulation in peatlands is estimated to be low prior to 11 ka increased slightly between 11 and 5 ka and greatly increased during the past 5 ka

trench normal variation in observed seafloor displacements associated with the 2011 tohoku oki earthquake 1 seafloor geodetic measurements using the gps acoustic technique just above the rupture area of the 2011 tohoku oki earthquake revealed strong trench normal variation in the horizontal crustal displacement associated with the earthquake one set of observations at a site only 50 km away from the trench yielded the most trench ward data ever reported with an accuracy better than 1 m it showed a coseismic displacement of up to 31 m whereas another set of observations 100 km away from the trench showed a 15 m displacement these horizontal data as well as vertical data from pressure gauges and tsunami observations strongly indicate that the seismic slip reached the trench they are also likely to contribute quantitatively to further investigations that reveal the coseismic behavior of the frontal wedge of the overriding plate in the source region along the japan trench

late quaternary vegetation and climate changes inferred from a pollen record of dongyuan lake in southern taiwan abstract a pollen record sampled from a valley basin in southern taiwan shows the environmental change specifically vegetation and climate that has occurred there since 22 000 cal yr bp in contrast to the subtropical evergreen forest found there today temperate broadleaved and conifer mixed forest occupied the basin between 22 000 and 16 000 cal yr bp which suggests that climate conditions were considerably cold during the last glacial maximum lgm and early deglacial period during the interval from 16 000 to 11 400 cal yr bp this basin was situated near an ecotone of two altitudinal vegetation zones i e a temperate conifer broadleaved mixed forest and a warm temperate evergreen forest which suggests the gradually warming climate conditions of the late glacial period the climate experienced further warming between 11 400 and 8200 cal yr bp as evidenced by the dominance of warm temperate evergreen forest elements subsequently the subtropical evergreen forest prevailed in the basin between 8200 and 4100 cal yr bp which reflects a considerably warmer mid holocene in addition tropical evergreen forest appeared in the area circa 6100 cal yr bp marking the holocene thermal optimum hto following that a warm temperate evergreen forest thrived between 4100 and 2100 cal yr bp finally a subtropical evergreen forest began its reemergence in the basin from 2100 cal yr bp and continues to grow there today from a comparison of these changes in vegetation we propose that 1 the annual mean temperature of the lgm was at least 7 c lower than today and 2 the hto was at least 2 c higher than present

displacement above the hypocenter of the 2011 tohoku oki earthquake the moment magnitude m w 9 0 2011 tohoku oki mega thrust earthquake occurred off the coast of northeastern japan combining global positioning system gps and acoustic data we detected very large sea floor movements associated with this event directly above the focal region an area with more than 20 meters of horizontal displacement that is four times larger than those detected on land stretches several tens of kilometers long along the trench the largest amount reaches about 24 meters toward east southeast just above the hypocenter furthermore nearly 3 meters of vertical uplift occurred contrary to observed terrestrial subsidence

a 12 000 year history of vegetation and climate for cape cod massachusetts abstract pollen and charcoal analysis of radiocarbon dated sediment cores from duck pond in the cape cod national seashore provide a continuous 12 000 yr vegetation and climate history of outer cape cod a picea hudsonia parkland and then a picea pinus banksiana alnus crispa boreal forest association grew near the site between 12 000 and 10 000 yr b p this vegetation was replaced by a northern conifer forest of pinus strobus p banksiana and subsequently by a more mesophytic forest pinus strobus tsuga quercus fagus acer ulmus fraxinus ostrya as the climate became warmer and wetter by 9500 yr b p by 9000 yr b p a pinus rigida quercus association dominated the landscape high charcoal frequencies from this and subsequent levels suggest that the pine barrens association developed during a warmer and drier climate that lasted from 9000 to about 5000 yr b p increased percentages of pinus strobus pollen indicate a return to moister and cooler conditions by about 3500 yr b p a doubled sedimentation rate increased charcoal and increased herb pollen suggest land disturbance near the pond before european settlement these results suggest a rapid warming in the northeast in the early holocene and support a hypothesis of a rapid sea level rise at that time comparison of the pollen results from duck pond with those from rogers lake connecticut illustrates the importance of edaphic factors in determining the disturbance frequency and vegetation history of an area

tsunami generation by horizontal displacement of ocean bottom tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting the effect of horizontal deformation is usually neglected however when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement the effect becomes significant we show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves in the case of the 1994 june 2 java indonesia earthquake the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope in the case of the 1994 nov 14 mindoro philippines earthquake strike slip faulting extended from ocean to land perpendicular to the coast line in both cases we found that the horizontal motion of slope had an important contribution to the tsunami generation

fdm simulation of an anomalous later phase from the japan trench subduction zone earthquakes we investigated the development of a distinct later phase observed at stations near the japan trench associated with shallow outer rise earthquakes off the coast of sanriku northern japan based on the analysis of three component broadband seismograms and fdm simulations of seismic wave propagation using a heterogeneous structural model of the japan trench subduction zone snapshots of seismic wave propagation obtained through these simulations clearly demonstrate the complicated seismic wavefield constructed by a coupling of the ocean acoustic waves and the rayleigh waves propagating within seawater and below the sea bottom by multiple reflections associated with shallow subduction zone earthquakes we demonstrated that the conversion to the rayleigh wave from the coupled ocean acoustic waves and the rayleigh wave as they propagate upward along the slope of seafloor near the coast is the primary cause of the arrival of the distinct later phase at the station near the coast through a sequence of simulations using different structural models of the japan trench subduction zone we determined that the thick layer of seawater along the trench and the suddenly rising sea bottom onshore of the japanese island are the major causes of the distinct later phase the results of the present study indicate that for realistic modeling of seismic wave propagation from the subduction zone earthquakes a high resolution bathymetry model is very crucial although most current simulations do not include a water column in their simulation models

modeling of the hydroacoustic signal and tsunami wave generated by seafloor motion including a porous seabed 1 within the framework of a 2 d compressible tsunami generation model with a flat porous seabed acoustic waves are generated and travel outward from the source area the effects of the porous seabed during tsunami generation and propagation processes include wave amplitude attenuation and low pass filtering of both the hydroacoustic signal and tsunami wave the period of the acoustic wave generated by the seafloor motion depends on water depth over the source area and is given by four times the period of time required for sound to travel from the seabed to the surface these waves carry information about seafloor motion the semianalytical solution of the 2 d compressible water layer model overlying a porous seabed is presented and discussed furthermore to include the effects generated by the coupling between compressible porous sedimentary and water layers a simplified two layer model with the sediment modeled as a compressible viscous fluid is presented

topography s crucial role in heinrich events heinrich events the abrupt changes in the laurentide ice sheet that cause the appearance of the well observed heinrich layers are thought to have a strong effect on the global climate the focus of most studies that have looked at the climate s response to these events has been the freshwater flux that results from melting icebergs however there is the possibility that the varying height of the ice sheet could force a change in the climate in this study we present results from a newly developed coupled climate ice sheet model to show what effect this topographic change has both on its own and in concert with the flux of freshwater from melting icebergs we show that the topographic forcing can explain a number of the climate changes that are observed during heinrich events such as the warming and wettening in florida and the warm sea surface temperatures in the central north atlantic which freshwater forcing alone cannot we also find regions for example the tropical atlantic where the response is a mixture of the two here observations may help disentangle the relative importance of each mechanism these results suggest that the simple paradigm of a heinrich event causing climate change via freshwater inputs into the north atlantic needs to be revised