neogene and quaternary history of vegetation climate and plant diversity in amazonia the neotropical amazonian and andean plant diversity developed mainly during the tertiary in amazonia miocene oral diversity seems considerably higher than today during the neogene tropical taxa entered newly created montane area and montane taxa entered the tropical lowlands the general decrease of temperature during the upper neogene and especially during the quaternary glacial periods may have caused considerable extinctions in the lowlands representation of pollen of apparently principally montane taxa podocarpus hedyosmum in miocene pliocene and quaternary sediments of amazonia and surroundings is still di cult to interpret in terms of temperature decrease at low elevation changes in precipitation may have profound impact on the composition of vegetation communities ilex and melastomataceae increase signi cantly in many glacial pollen records increase of weinmannia in amazonian pollen records seems the best indicator of downward migration of montane vegetation belts a temperature lowering at sea level of 4 5 13c during the last glacial maximum lgm seems reasonable it may have caused a downslope migration of some 700 m of the lower montane vegetation belt lower montane arboreal species may have been able to grow in higher elevation areas 500 m of amazonia increasing background pollen values of montane taxa in the area di erence between a cool and wet middle pleniglacial 60 28 ka bp and a cold and dry upper pleniglacial 28 14 ka bp thus including the lgm is evident in andean and amazonian records statements about environmental conditions of the ice age amazon should be speci ed chronologically the middle pleniglacial is a time of accumulation of uvial sediments the upper pleniglacial is a time of incision of the rivers in their sediments sedimentation started again in the lateglacial since ca 13 ka bp and the holocene when lake levels rose again based on simpli ed considerations of precipitation changes and evaporation we estimate that lgm rainfall may have been reduced by values of ca 45 10 amazonian and cordilleran lakes dried up dry rain forest was locally replaced by savanna savanna forest or cerrado type vegetation dry rain forest savanna forest and pure savanna was locally replaced by extensive semi desert dune formations lower rio branco area in present day central amazonia the present day centers of higher rainfall 2500 mm surrounded by areas of lower rainfall are refuge areas of the very wet rain forest and of the very high plant diversity 300 plant species per 0 1 ha and they should have been that equally or more during the dry climate intervals plant diversity of drier forests is in the order of 100 150 species per 0 1 ha both extinction and speciation in isolation under precipitation and temperature stress may have taken place in these refugia 2000 elsevier science ltd all rights reserved

searching for eustasy in deglacial sea level histories abstract perturbations to the earth s gravity field and solid surface associated with glacial isostatic adjustment gia cause the total observable sea level change to depart from the eustatic curve which is defined as a spatially uniform height shift of the ocean surface to accommodate any mass gained lost from grounded ice in this study we apply a state of the art model of gia induced sea level change to quantify the magnitude and spatial form of this departure at the global scale for a range of model parameters with an aim to identify regions that are well suited to obtain accurate and precise estimates of eustatic sea level and therefore past grounded ice volume in general our results indicate that eustatic sea level is not a directly measurable quantity and so must be estimated by subtracting a model derived estimate of non eustatic contributions from observations in this regard we use our results to isolate regions where this procedure can be applied with optimal accuracy and precision that is where 1 the gia predictions are relatively insensitive to plausible ranges in input parameters and 2 where the non eustatic contribution is small i e the predicted sea level closely approximates the eustatic value we present maps that can be employed by the field community to identify areas where sea level reconstructions would be well suited to arrive at robust estimates of eustatic sea level note that sea level changes associated with tectonic motion and changes in ocean water temperature salinity which also lead to departures from eustasy are not considered in this analysis

recent controversies in predicting post glacial sea level change abstract we compare recent developments in the numerical prediction of post glacial sea level changes and comment on the controversies associated with these developments we conclude that 1 the broad shelf effect discussed by peltier and drummond 2002 in the context of water load modelling at migrating shorelines is incorporated into the sea level algorithms of johnston 1993 and milne et al 1999 and 2 the procedure used by yokoyama et al 2000 to infer an ice equivalent post lgm sea level rise of 130 135 m is technically sound

modelling post glacial rebound with lateral viscosity variations summary observations of isostatic adjustment of the earth s surface due to glacial loading provide important constraints on mantle viscosity structure we solve the forward problem of glacial isostatic adjustment in two complementary ways a spectral method for strictly 1 d spherically symmetric earth models and a finite element method that can accommodate 3 d viscosity structure we discuss how each method may be augmented in three ways to accommodate motion of the centre of mass to implement a gravitationally self consistent ocean load via the sea level equation and to include the influence of polar wander with all these effects implemented the two methods are benchmarked against each other we also study the influence of lateral viscosity variations upon measurements of post glacial rebound pgr in two ways first by observing the effect of viscosity perturbations in an idealized model and second by developing a realistic 3 d viscosity model and comparing it with results of related 1 d spherically symmetric models the 3 d viscosity structure is derived starting from seismic tomography models we conclude from both approaches that pgr observations are sensitive to both the local viscosity structure and to the viscosity structure beneath the loaded region even if it is removed from where the observations are made in particular pgr measurements made at hudson bay tend to reflect the local viscosity structure beneath hudson bay pgr measurements made along the east coast of north america being sensitive to both the local east coast viscosity structure as well as the loaded continental viscosity structure are not reproducible with a 1 d viscosity model

tropical climates at the last glacial maximum a new synthesis of terrestrial palaeoclimate data i vegetation lake levels and geochemistry palaeodata in synthesis form are needed as benchmarks for the palaeoclimate modelling intercomparison project pmip advances since the last synthesis of terrestrial palaeodata from the last glacial maximum lgm call for a new evaluation especially of data from the tropics here pollen plant macrofossil lake level noble gas from groundwater and delta 18 o from speleothems data are compiled for 18 2 ka c 14 32 degrees n 33 degrees s the reliability of the data was evaluated using explicit criteria and some types of data were re analysed using consistent methods in order to derive a set of mutually consistent palaeoclimate estimates of mean temperature of the coldest month mtco mean annual temperature mat plant available moisture pam and runoff p e cold month temperature mat anomalies from plant data range from 1 to 2 k near sea level in indonesia and the s pacific through 6 to 8 k at many high elevation sites to 8 to 15k in s china and the se usa mat anomalies from groundwater or speleothems seem more uniform 4 to 6 k but the data are as yet sparse a clear divergence between mat and cold month estimates from the same region is seen only in the se usa where cold air advection is expected to have enhanced cooling in winter regression of all cold month anomalies against site elevation yielded an estimated average cooling of 2 5 to 3 k at modern sea level increasing to approximate to 6 k by 3000m how ever neotropical sites showed larger than the average sea level cooling 5 to 6 k and a non significant elevation effect whereas w and s pacific sites showed much less sea level cooling 1 k and a stronger elevation effect these findings support the inference that tropical sea surface temperatures ssts were lower than the climap estimates but they limit the plausible average tropical sea surface cooling and they support the existence of climap like geographic patterns in sst anomalies trends of pam and lake levels indicate wet lgm conditions in the w usa and at the highest elevations with generally dry conditions elsewhere these results suggest a colder than present ocean surface producing a weaker hydrological cycle more arid continents and arguably steeper than present terrestrial lapse rates such linkages are supported by recent observations on freezing level height and tropical ssts moreover simulations of greenhouse and lgm climates point to several possible feedback processes by which low level temperature anomalies might be amplified aloft

montane bias in lowland amazonian peatlands plant assembly on heterogeneous landscapes and potential significance to palynological inference abstract past temperature changes in tropical mountain regions are commonly inferred from vertical elevational shifts of montane indicator taxa in the palynological record however temperature is one of several abiotic factors driving the low elevational limits of species and many montane taxa can occur in warmer lowlands by tracking appropriate habitat types especially highly flooded wetlands in this paper we explore ways in which lowland habitat heterogeneity might introduce error into paleo temperature reconstructions based on field data of seven modern peatland vegetation communities in the southern peruvian amazon 200 masl peat rich substrates are common edaphic transitions in pollen cores and provide detailed records of past vegetation change the data show that indicators of modern peatlands include genera with montane as well as lowland distributions while indicators of surrounding forests on mineral substrates have predominantly lowland distributions based on family level analyses we find that modern peatland vegetation communities have taxonomic compositions appearing to be 389 m to 1557 m mean 1050 391 m above their actual elevations due to a high abundance and number of families with high elevation optima we interpret the relatively higher prevalence of montane elements in modern peatlands as habitat tracking of a conserved montane niche on heterogeneous lowland landscapes we suggest that both high moisture availability and stressful edaphic conditions of peatland habitat may explain the montane bias observed to the extent that fossilization provides a better record of past vegetation that occurred proximate to the site of deposition we suggest that habitat tracking of montane elements may introduce a cool bias in lowland paleo temperature reconstructions based on pollen proxies

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

glacial isostatic adjustment on 3 d earth models a finite volume formulation summary we describe and present results from a finite volume fv parallel computer code for forward modelling the maxwell viscoelastic response of a 3 d self gravitating elastically compressible earth to an arbitrary surface load we implement a conservative control volume discretization of the governing equations using a tetrahedral grid in cartesian geometry and a low order linear interpolation the basic starting grid honours all major radial discontinuities in the preliminary reference earth model prem and the models are permitted arbitrary spatial variations in viscosity and elastic parameters these variations may be either continuous or discontinuous at a set of grid nodes forming a 3 d surface within the regional or global modelling domain in the second part of the paper we adopt the fv methodology and a spherically symmetric earth model to generate a suite of predictions sampling a broad class of glacial isostatic adjustment gia data types 3 d crustal motions long wavelength gravity anomalies these calculations based on either a simple disc load history or a global late pleistocene ice load reconstruction ice 3g are benchmarked against predictions generated using the traditional normal mode approach to gia the detailed comparison provides a guide for future analyses e g what grid resolution is required to obtain a specific accuracy and it indicates that discrepancies in predictions of 3 d crustal velocities less than 0 1 mm yr 1 are generally obtainable for global grids with 3 106 nodes however grids of higher resolution are required to predict large amplitude 1 cm yr 1 radial velocities in zones of peak post glacial uplift e g james bay to the same level of absolute accuracy we conclude the paper with a first application of the new formulation to a 3 d problem specifically we consider the impact of mantle viscosity heterogeneity on predictions of present day 3 d crustal motions in north america in these tests the lateral viscosity variation is constructed with suitable scaling from tomographic images of seismic s wave heterogeneity and it is characterized by approximately 2 orders of magnitude peak to peak lateral variations within the lower mantle and 1 order of magnitude variations in the bulk of the upper mantle below the asthenosphere we find that the introduction of 3 d viscosity structure has a profound impact on horizontal velocities indeed the magnitude of the perturbation of order 1 mm yr 1 is as large as the prediction generated from the underlying 1 d radial reference model and it far exceeds observational uncertainties currently being obtained from space geodetic surveying the relative impact of lateral viscosity variations on predicted radial motions is significantly smaller

on post glacial sea level i general theory summary modern analyses of sea level changes due to glacial isostatic adjustment gia are based on the classic sea level equation derived by farrell clark 1976 geophys j r astr soc 46 647 667 the connection between global sea level variations and changes to ocean height that is assumed within this equation breaks down in the presence of a time varying shoreline geometry we present a generalized sea level equation that overcomes this difficulty we also derive analytic expressions for and present schematic illustrations of the error in the ocean height change over finite time intervals introduced in published efforts to incorporate shoreline evolution into the theory of gia induced sea level change this comparison includes studies of shoreline migration due to either local sea level changes or the growth and ablation of marine based ice we conclude that the theories applied by johnston 1993 geophys j int 114 615 634 milne 1998 phd thesis university of toronto toronto and co workers are more accurate than the procedure advocated by peltier 1994 science 265 195 201 1998a geophys res lett 25 3955 3958 1998b rev geophys 114 615 634 although an improvement in the latter has recently been reported peltier drummond 2002 geophys res lett 29 10 1029 2001gl014273 our generalized theory is valid for any earth model in a companion paper we derive the equations necessary to treat the special case of a spherically symmetric linear viscoelastic and rotating earth and we quantify errors associated with previous work

decontaminating tide gauge records for the influence of glacial isostatic adjustment the potential impact of 3 d earth structure 1 we investigate the potential impact of lateral variations in mantle viscosity and lithospheric thickness on predictions of present day relative sea level change due to glacial isostatic adjustment gia we consider three viscoelastic earth models the first is a 1 d model with a lithospheric thickness of 120 km and upper and lower mantle viscosities of 5 1020 pa s and 5 1021 pa s respectively the second model includes global lithospheric thickness variations and lateral heterogeneities in upper mantle viscosity ranging over three orders of magnitude while the third model includes lateral variations in lower mantle viscosity alone we find that the impact of 3 d structure is significant indeed the difference between the 3 d and 1 d model predictions at 300 sites with tide gauge records longer than 40 years duration is greater than 0 2 mm yr and 0 5 mm yr for 50 and 25 of the sites respectively the maximum difference exceeds several mm yr we conclude that efforts to decontaminate tide gauge records for ongoing gia to determine the rate and origin of global sea level rise should incorporate 3 d mantle structure into the gia modelling

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

on postglacial sea level iii incorporating sediment redistribution we derive a generalized theory for gravitationally self consistent static sea level variations on earth models of arbitrary complexity that takes into account the redistribution of sediments the theory is an extension of previous work that incorporated into the governing equations shoreline migration due to local sea level variations and changes in the geometry of grounded marine based ice in addition we use viscoelastic love number theory to present a version of the new theory valid for spherically symmetric earth models the love number theory accounts for the gravitational deformational and rotational effects of the sediment redistribution as a first illustrative application of the new theory we compute the perturbation in sea level driven by an idealized pulse of sediment transport into the gulf of mexico we demonstrate that incorporating a gravitationally self consistent water load in this case significantly improves the accuracy of sea level predictions relative to previous simplified treatments of the sediment redistribution

forest changes in the amazon basin during the last glacial maximum we report here the discovery of forest beds in the amazon basin radiocarbon dated to the wisconsin wurm glaciation these are the first dates from the last glaciation determined on amazonian samples the locality is in ecuador at 1 100 m elevation near the upper limit of the present amazonian rainforest both pollen spectra and podocarpus wood in the deposits suggest that vegetation comparable to the present andean forest grew at least 700 m lower than it does now suggesting a temperature depression of at least 4 5 c for the amazon lowlands

sea level history of the gulf of mexico since the last glacial maximum with implications for the melting history of the laurentide ice sheet abstract sea level records from the gulf of mexico at the last glacial maximum 20 ka are up to 35 m higher than time equivalent sea level records from equatorial regions the most popular hypothesis for explaining this disparity has been uplift due to the forebulge created by loading from mississippi river sediments using over 50 new radiocarbon dates as well as existing published data obtained from shallow marine deposits within the northern gulf of mexico and numerical models simulating the impact of loading due to the mississippi fan and glacio hydro isostasy we test several possible explanations for this sea level disparity we find that neither a large radiocarbon reservoir sedimentary loading due to the mississippi fan nor large scale regional uplift can explain this disparity we do find that with an appropriate model for the laurentide ice sheet the observations from the gulf of mexico can be explained by the process of glacio hydro isostasy our analysis suggests that in order to explain this disparity one must consider a laurentide ice sheet reconstruction with less ice from 15 ka to its disappearance 6 ka and more ice from the last glacial maximum to 15 ka than some earlier models have suggested this supports a laurentide contribution to meltwater pulse 1 a which could not have come entirely from its southern sector

glacial isostatic adjustment and the free air gravity anomaly as a constraint on deep mantle viscosity summary a gravitationally self consistent theory for relative sea level variations forced by pleistocene deglaciation events is employed to explore the extent to which rsl and free air gravity observations together constrain the viscosity of the mantle beneath the seismic discontinuity at 670 km depth a trade off is revealed between errors in the assumed deglaciation history and errors in the inferred value of the viscosity of the lower mantle taking full account of such uncertainty plausible values of the viscosity beneath the transition region are bounded above by 1023 poise cgs units the preferred value is at least a factor of 2 lower than this and is strongly constrained by the observed free air gravity anomaly over hudson bay the calculations described in detail here show for the first time that the relatively large gravity anomalies observed over sites of wurm wisconsin deglaciation do not require any pronounced increase of mantle viscosity with depth in order to explain them

holocene history of the choco rain forest from laguna piusbi southern pacific lowlands of colombia abstract a high resolution pollen record from a 5 m long sediment core from the closed lake basin laguna piusbi in the southern colombian pacific lowlands of choco dated by 11 ams14c dates that range from ca 7670 to 22014c yr b p represents the first holocene record from the choco rain forest area the interval between 7600 and 610014c yr b p 500 265 cm composed of sandy clays that accumulated during the initial phase of lake formation is almost barren of pollen fungal spores and the presence of herbs and disturbance taxa suggest the basin was at least temporarily inundated and the vegetation was open the closed lake basin might have formed during an earthquake probably about 440014c yr b p from the interval of about 600014c yr b p onwards 200 different pollen and spore types were identified in the core illustrating a diverse floristic composition of the local rain forest main taxa are moraceae urticaceae cecropia melastomataceae combretaceae acalypha alchornea fabaceae mimosa piper protium sloanea euterpe geonoma socratea andwettinia little change took place during that time interval compared to the pollen records from the rain forests of the colombian amazon basin and adjacent savannas the choco rain forest ecosystem has been very stable during the late holocene paleoindians probably lived there at least since 346014c yr b p evidence of agricultural activity shown by cultivation ofzea maissurrounding the lake spans the last 1710 yr past and present very moist climate and little human influence are important factors in maintaining the stable ecosystem and high biodiversity of the choco rain forest

vegetation development in an amazonian peatland recent investigations of wetlands in western amazonia have revealed the presence of extensive peat deposits up to 7 5 m thick developing under a variety of vegetation types we report the first attempt to establish the long term centennial to millennial scale vegetation history of one of these peatland sites quistococha a palm swamp close to iquitos in northern peru pollen and sedimentological analyses show that peat formation began at the core site under sedge fen or floating mat vegetation c 2200 calendar years before present cal yr bp a seasonally flooded woodland developed c 1880 cal yr bp the permanently waterlogged palm swamp which persists today began to form c 1000 cal yr bp with the present vegetation community established by c 400 years ago the vegetation at this site has undergone continuous change throughout the period of peat formation with several abrupt transitions and reversals and repetitions in the apparent trajectory of change the pollen data combined with sedimentary evidence suggest that the dominant control on ecosystem functioning and development is the flooding regime there appears to have been a decrease in fluvial influence over time there is no clear evidence of direct climatic or anthropogenic influence although we cannot rule out the possibility of climatically driven hydrological changes our results caution against adopting a simple model of peatland vegetation succession in this region

the response of vegetation on the andean flank in western amazonia to pleistocene climate change a reconstruction of past environmental change from ecuador reveals the response of lower montane forest on the andean flank in western amazonia to glacial interglacial global climate change radiometric dating of volcanic ash indicates that deposition occurred 324 000 to 193 000 years ago during parts of marine isotope stages 9 7 and 6 fossil pollen and wood preserved within organic sediments suggest that the composition of the forest altered radically in response to glacial interglacial climate change the presence of podocarpus macrofossils 1000 meters below the lower limit of their modern distribution indicates a relative cooling of at least 5 c during glacials and persistence of wet conditions interglacial deposits contain thermophilic palms suggesting warm and wet climates hence global temperature change can radically alter vegetation communities and biodiversity in this region

global geoid and sea level changes due to present day ice mass fluctuations we predict gravitationally self consistent global geoid and relative sea level rsl perturbations due to present day melting of ice complexes including the antarctic and greenland ice sheets and a suite of mountain glaciers and ice sheets classic analyses of sea level change indicate that these perturbations will depart significantly from eustatic i e geographically uniform trends e g woodward 1888 farrell and clark 1976 although this result has not always been appreciated in modern analyses mass flux of individual ice reservoirs will produce unique geometries of sea level change and this distinctiveness admits the possibility of using global geoid sea surface and rsl signatures of recent climate change to infer the ongoing mass balance of each reservoir rather than simply the net mass flux as an example we show that perturbations to the geoid arising from noneustatic water loads associated with each ice reservoir are sufficiently large at low degrees to be theoretically measurable within 5 years by the grace satellite mission we complete the study by reanalyzing tide gauge data at 23 sites selected by douglas 1997 in a recent analysis of global rsl rise traditionally estimates of global sea level rise are generated by taking the mean of a set of secular tide gauge trends that have been corrected for the influence of ongoing glacial isostatic adjustment gia related to the late pleistocene glacial cycles the common assumption in such studies is that the geographic scatter in the residual gia corrected trends is due to errors in the gia model or unmodeled processes e g tectonics we consider a large suite of gia model predictions and apply a least squares approach to the gia corrected tide gauge trends to estimate the weighting of various present day sea level signatures we find that the fit to the residual rsl trends is significantly improved and that the procedure is able to resolve a long standing observation of anomalously low sea level rates in europe this preliminary analysis which is relatively insensitive to changes in the assumed geometry of the present day mass balance assumes that ocean thermal expansion is globally uniform however the procedure can be easily extended to incorporate a realistic steric contribution once the geometry of the process is sufficiently well constrained

the effect of spatially non uniform water loads on prediction of sea level change summary numerical modelling of postglacial rebound predics a spatially variable pattern of sea level change yet many previous models predicting late pleistocene sea level change either neglect the load of water added to the oceans or assume a spatially uniform time dependent load over the whole ocean this is a poor approximation of the load near the former ice sheet since sea level change varies geographically in addition the coastline goemetry changes through time a spectral technique has been used to solve the sea level equation on an earth model with axisymmetric distribution of ice and oceans and also for a realistic ice ocean configuration the axisymmetric model is useful for demonstrating the fundamental physics involved in sea level changes caused by changes in surface loads in particular it can be seen that the elastic and gravitational response to the load is spread over a great distance whereas the viscous response is more localized a realistic ice ocean configuration has been used to demonstrate that neglect of the melt water load underestimates the amount of uplift in fennoscandia and other regions where rebound occurs in the ocean as previously noted by wu peltier 1983 in hudson bay and that movement of the coastlines and spatially varying water loads must both be included in calculations for the north sea and other near field regions with shallow seas sea level calculations including these effects and careful analysis of the sea level and ice melting record are required to determine modifications to the viscosity profile and ice model inferred by previous inaccurate models of the ocean load in the near field

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

postglacial sealevels on a spherical self gravitating viscoelastic earth effects of lateral viscosity variations in the upper mantle on the inference of viscosity contrasts in the lower mantle abstract previous studies of lateral viscosity variations on postglacial rebound often neglect the spherical shape of the earth and the self gravity of the solid earth and oceans in this paper the consistent sealevel equation is solved by the coupled laplace finite element method for a spherical self gravitating incompressible maxwell earth it confirms the importance of self gravity in the oceans on sealevel computation near the ice margin where the data are most sensitive to the existence of lateral variations in lithospheric thickness and asthenospheric viscosity the effects of lateral variations in lower mantle viscosity asthenospheric viscosity and lithospheric thickness are investigated this paper confirms the finding of earlier investigations the combined effect of lateral viscosity variations in the lower mantle with reverse viscosity contrasts in the upper mantle is also investigated for sealevel data near the center of rebound the effect of lateral viscosity contrast in the lower mantle can be masked by the existence of a reverse lateral viscosity contrasts in the upper mantle however this is not the case for sealevel data just outside the ice margin

the pan amazonian ucayali peneplain late neogene sedimentation in amazonia and the birth of the modern amazon river system abstract we review the neogene geologic history of lowland amazonia in an attempt to focus attention on areas of agreement as well as areas in dispute in this research arena we reinterpret pre existing hypotheses present new data and discuss new insights intended to support a unified synthesis of the amazon basin as a single sedimentary basin albeit on a vast scale during the late miocene to middle late pliocene we document the ucayali peneplain as an isochronous pan amazonian geologic feature that formed following the early to mid miocene quechua i orogenic phase of andean tectonism peneplanation began possibly as early as 15 ma and terminated abruptly near the beginning of the late miocene quechua ii orogenic event at 9 5 9 0 ma subsequently a thin cover of sediments comprising the madre de dios formation began blanketing most of lowland amazonia excepting only the eastern subandean fold and thrust belt and isolated highlands within the basin the buried peneplain is readily observed in river cutbanks throughout amazonia as the marked often angular ucayali unconformity that separates eroded older often folded faulted and weathered moderately to well consolidated tertiary formations from unconsolidated near horizontal upper neogene deposits the dates of formation of major unconformities and subsequent depositional events at widely separated areas within the andes of bolivia ecuador and peru are coincident with that of the ucayali unconformity and deposition of the madre de dios formation and suggest that the events are linked to a common cause which is interpreted to be the still on going collision between the south american and nazca tectonic plates the madre de dios formation has three members the oldest of which documents a short lived high energy depositional environment followed by a moderate energy depositional environment both occurring at a time when drainage from the basin was unobstructed the upper two members record fluctuations between moderate and low energy continental depositional environments during a period when drainage from the basin was obstructed disorganized and took place over long distances with extremely low gradients the sedimentology of the madre de dios formation particularly the thick massive beds of clay and the widespread presence of paleodeltas and associated geomorphic features on the amazonian planato are consistent with the hypothesis that much of the upper two members formed as lacustrine and deltaic deposits within a gigantic lake lago amazonas or more probably within a complex series of interconnected mega lakes that occasionally united to cover most or all of lowland amazonia to a shallow depth from the latest miocene until 2 5 ma the presence of the ucayali unconformity and the relatively uniform lithostratigraphy basin wide of the fluvial fluviolacustrine and lacustrine sediments of the upper neogene madre de dios formation are consistent with the hypothesis that the amazon basin acted as a single undivided sedimentary basin in the late neogene the biostratigraphic correlation across important modern drainage divides of both micro and macro sized late miocene fossil vertebrates recovered from basal conglomerates of the madre de dios formation and the absence therefrom of fossil vertebrates of any other age is also consistent with this hypothesis two 40ar 39ar dates on ash deposits within the madre de dios formation corroborate the upper miocene age of the basal horizons of that formation indicated by fossil vertebrates and support an upper pliocene age for the youngest sediments of the formation the modern amazon river drainage system was established in the late pliocene at 2 5 ma by the breaching of the eastern rim of the sedimentary basin as a result of the basin being overfilled or by headward erosion of the lower amazon river or both data on cenozoic mass accumulation rates and the chemistry of terrigenous sediments in the atlantic ocean obtained by ocean drilling project leg 154 ceara rise support the postulated timing of the establishment of the modern amazon river drainage system at 2 5 ma rather than the long held view that this event occurred in the late miocene we discuss the important role of ocean currents and sea level fluctuations on terrigenous mass accumulation rates on the ceara rise the postulated time of formation of the modern amazon river is nearly coincident with the onset of the plio pleistocene glacial climatic regime and the lowest sea level stands since the latest middle miocene this analysis indicates that modern amazonia is a product of terrain development within an erosional regime since 2 5 ma

late pleistocene temperature depression and vegetation change in ecuadorian amazonia abstract paleoecological pollen phytolith and wood analyses of sediments radiocarbon dated 33 000 to 26 000 yr b p from two sites in ecuadorian amazonia provide data that suggest a cooling of ca 7 5 c below present in equatorial lowlands from 33 000 to 30 000 yr b p a period of warning followed in which novel species assemblages a blend of montane and lowland floral components persisted for at least 4000 years these data of forest community change from sites lying within the postulated glacial rain forest napo refugium provide the strongest paleoecological refutation of the refugial hypothesis yet obtained the large temperature depression at ca 30 000 yr b p allows the possibility that if maximum cooling at the equator was synchronous with the last glacial maximum lgm of the northern hemisphere freezing temperatures would have been experienced in parts of lowland amazonia between 25 000 and 18 000 b p

pleistocene deglaciation and the global gravity field the present day global geoid and free air gravity anomaly signals induced by pleistocene deglaciation have been computed along with their secular variations a revised green function has been derived for the free air gravity anomaly and we find that an earth model with a lower mantle viscosity moderately larger than the upper mantle value satisfies observations of the anomaly over both hudson s bay and fennoscandia using this preferred earth model the predicted global geoid anomaly map is characterized by peak negative values of 36 7 9 4 and 21 9 m over hudson s bay northern europe and antarctica respectively and by a smooth small amplitude 2 5 m upwarping over the major ocean basins although the field has an order of magnitude less power than the observed there is a significant spatial correlation between the two inferences of mantle viscosity based upon comparisons between the observed geoid and the computed deglaciation induced anomaly are hampered by the large contribution from the convective circulation in the earth s mantle we have subtracted a predicted convection signal based on seismic tomography from the observed field however the residual geoid thus obtained is still too inaccurate to allow a useful comparison in contrast a filtered version of the observed geoid over canada which retains harmonic coefficients in the degree range 10 22 provides a relatively uncontaminated by convection datum that is indeed satisfied by the preferred earth model secular variations in the earth s gravitational field are naturally dominated by the signal from pleistocene deglaciation in this respect we compute zonal harmonics in the expansion of the present day rate of change of the geopotential and in particular we predict amplitudes comparable to that for the previously analysed j2 for j4 j5 j7 and j9 all of which reflect in large part the response due to the melting of the massive laurentide ice sheet this analysis suggests that measurement of these higher order secular variations of the zonal harmonics based upon analysis of long time series of lageos ranging data could provide very useful additional constraints on the radial variation of mantle viscosity these constraints along with all others described in this paper are shown to be relatively insensitive to assumptions concerning the deflection during the glacial isostatic adjustment process of the 400 and 670 km density discontinuities within the mantle

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

meta analysis of tropical surface temperatures during the last glacial maximum 1 the magnitude of tropical cooling during the last glacial maximum lgm has been the subject of uncertainty for over 25 years we use principles of metaanalysis as an objective approach to reconcile estimates from different proxies this approach treats each observation as a random estimate of the true mean and weights estimates by their reported precision we assigned global uncertainties to proxies and derived a new regional standard deviation for temperatures calculated from the sr ca ratio in tropical corals s 1 4 c using a bayesian spatial interpolation scheme we estimate a mean cooling of lgm tropical sea surface temperatures of 2 7 0 5c s and surface air temperatures of 5 4 0 3c s citation ballantyne a p m lavine t j crowley j liu and p b baker 2005 meta analysis of tropical surface temperatures during the last glacial maximum geophys res lett 32 l05712 doi 10 1029 2004gl021217

earthquake ground motion and structural response in alluvial valleys this paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes it focuses on a small valley in kirovakan for which 1d wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 armenia earthquake a more realistic 2d finite element analysis is performed herein in search of an explanation of the observed behavior using as input an inferred rock accelerogram the response of the valley is calculated for a vertically incident sh wave synthetic accelerograms of the surface ground motion are presented for different sites these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free field motion of the rock outcrop for different frequencies and for a continuous set of sites in addition response spectra are evaluated for simple oscillators representing structures located at various sites results of the 2d simulations show striking differences with respect to those from 1d analyses in particular 1 while the resonant frequencies exhibited by a 1d model for a given site also appear in the 2d model the peak ground response and structural response are almost twice as large for the 2d as for the 1d model 2 the 2d model exhibits in addition a new set of resonant frequencies and concomitant mode shapes across the valley which are directly related to its finite width and 3 due to these additional resonances the ground amplification ratio tends to oscillate very rapidly both spatially and with frequency leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces even if the underlying soils have very similar characteristics these results provide a meaningful explanation for the observed damage and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior

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