human resilience to holocene climate changes inferred from rodent middens in drylands of northwestern patagonia argentina abstract we reconstruct the holocene vegetation climate and archaeological history for drylands of northwestern patagonia argentina based on multiproxy analysis plant macrofossil pollen and parasites of rodent middens integrated with a database of 14c dates associated with human occupations the local scale corresponds to the huenul paleoecological and archaeological locality emplaced in north western patagonia neuquen province argentina the rodent midden record from the huenul series reflects subtle vegetation changes driven by climatic variability at millennial timescale drier than present environmental conditions prevailed during the early holocene 10 500 9400 cal yr bp peaking during the mid holocene 9200 5500 cal yr bp when wetter than present conditions established during the late holocene 4400 2500 cal yr bp these environmental and climatic dynamics agree with other paleoclimatic records from northern patagonia suggesting the winter precipitation dynamics related to the southern westerlies as a common driver the diachronic distribution of anthropogenic radiocarbon dates from the western area of the south american arid diagonal between 32 40 s conforms to a fitted exponential model of steady background population growth not suggesting significant demographic changes that may have been the result of the impact of climate change this record indicates that these human populations coped successfully with aridity particularly during the mid holocene these findings reinforce the need to integrate multi scalar interdisciplinary analyses to assess the impact of climate change in human societies

characterization of site specific gps errors using a short baseline network of braced monuments at yucca mountain southern nevada 1 we use a short baseline network of braced monuments to investigate site specific gps effects the network has baseline lengths of 10 100 and 1000 m baseline time series have root mean square rms residuals about a model for the seasonal cycle of 0 05 0 24 mm for the horizontal components and 0 20 0 72 mm for the radial seasonal cycles occur with amplitudes of 0 04 0 60 mm even for the horizontal components and even for the shortest baselines for many time series these lag seasonal cycles in local temperature measurements by 23 43 days this could suggest that they are related to bedrock thermal expansion both shorter period signals and seasonal cycles for shorter baselines to rep2 the one short braced monument in our network are correlated with temperature with no lag time differences between rep2 and the other stations which are deep braced should reflect processes occurring in the upper few meters of the ground these correlations may be related to thermal expansion of these upper ground layers and or thermal expansion of the monuments themselves even over these short distances we see a systematic increase in rms values with increasing baseline length this and the low rms levels suggests that site specific effects are unlikely to be the limiting factor in the use of similar gps sites for geophysical investigations

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

crustal deformation rates in central and eastern u s inferred from gps analysis of continuous gps observations between 1996 and 2000 at 62 stations distributed throughout the central and eastern united states suggests that the area is generally stable seven of the 62 stations show anomalous velocities but there is reason to suspect their monument stability assuming the remaining 55 stations are stable with respect to interior north america we have found the north america itrf97 euler vector 1 88 1 04 n 77 67 0 39 w 0 201 0 004 myr 1 that minimizes the rms station velocity referred to fixed north america all of these velocities are less than 3 2 mm yr 1 motion of several stations suggests the mississippi embayment may be moving southward away from the rest of the continent at a rate of 1 7 0 9 mm yr 1 the motion of the embayment produces a large gradient in velocity which in turn implies the highest seismic moment accumulation rate that we found although the highest rate is only marginally significant the fact that it occurs near new madrid where earthquake risk is thought to be high argues that the anomaly may be real nevertheless the identification of the anomaly remains tentative

a vegetation history from the arid prepuna of northern chile 22 23 s over the last 13 500 years the quaternary paleoclimate of the central andes is poorly understood due to numerous discrepancies among the diverse proxy records that span this geographically and climatically complex region the exact timing duration and magnitude of wet and dry phases are seldom duplicated from one proxy type to another and there have been few opportunities to compare climatic records from the same proxy along environmental gradients vegetation histories from fossil rodent middens provide one such opportunity on the pacific slope of the andes we previously reported a vegetation history from the upper margin 2400 3000 m of the absolute desert in the central atacama desert of northern chile that record identified a distinct wet phase that peaked between 11 8 and 10 5 ka when steppe grasses and other upland elements expanded as much as 1000 m downslope and a secondary wet period during the middle to late holocene 7 1 3 5 ka the latter wet phase remains controversial and is not as readily apparent in our lowelevation midden record we thus sought to replicate both phases in a midden record from the mid elevations 3100 3300 m of the arid prepuna where slight precipitation increases would be amplified midden records from these elevations identify conditions wetter than today at 13 5 9 6 7 6 6 3 4 4 3 2 and possibly 1 8 1 2 ka dry phases occurred at 9 4 8 4 ka and possibly at ca 5 1 ka present floras and modern hyperarid conditions were established after 3 2 ka the records from the two elevational bands generally match with some important differences these differences could reflect both the discontinuous aspect of the midden record and the episodic nature of precipitation and plant establishment in this hyperarid desert 2003 elsevier science b v all rights reserved

postglacial vegetation fire and climate dynamics at central chilean patagonia lake shaman 44 s a 19 cal ka bp pollen and charcoal record from lake shaman 44 s 71 w chile was analyzed to establish vegetation fire and climate dynamics of the forest steppe ecotone in central chilean patagonia lake shaman record indicates that the upper rio cisnes valley was free of ice at around 19 cal ka bp from this date and until 14 8 cal ka bp a grass steppe with high proportions of shrubs associated to colder and drier conditions than present developed in this area a continuous increase of nothofagus accompanied by a decline in the steppe shrubs and sudden dominance of paludal over aquatic plants from 11 cal ka bp was associated to effective moisture increase but still under modern values the replacement of the cold dry grass shrub steppe by a similar than present forest steppe ecotone suggests an increase in temperature indicating the onset of the holocene at the same time moderate fire activity suggested by the charcoal record could be related to major fuel availability as consequence of nothofagus forest expansion between 8 and 3 cal ka bp the record indicates the easternmost position of the forest steppe ecotone suggesting the highest effective moisture with the establishment of seasonality between 5 and 3 cal ka bp from 3 cal ka bp the record indicates a retraction of the forest steppe ecotone accompanied by a high pollen record variability and an increased fire activity these late changes suggest decreased effective moisture associated with a high climatic variability at regional and extra regional scale climatic changes at lake shaman s record are mostly associated to changes latitudinal shifts and or strengthening weakening of past southern westerlies that were previously recorded along patagonia from the lateglacial to the mid holocene during the late holocene a regional pattern characterized by high record variability emerges throughout central chilean patagonia this variability would be related to 1 low magnitude southern westerlies changes probably associated to enso and or sam or 2 the complex relationships between vegetation fire and human occupations during the last 3 cal ka

atmospheric circulation changes and neoglacial conditions in the southern hemisphere mid latitudes insights from pmip2 simulations at 6 kyr glacial geologic studies in the southern hemisphere sh mid latitudes 40 54 s indicate renewed glacial activity in southern south america patagonia and new zealand s nz south island starting at 7 kyr the so called neoglaciation available data indicate that neoglacial advances in these regions occurred during a rising trend in atmospheric co2 and ch4 concentrations lower than present but increasing summer insolation and seasonality contrasts in this paper we examine the climatological context in which neoglaciations occurred through analysis of the complete paleoclimate modelling inter comparison project pmip2 database of simulations at 6 kyr for the sh we observe that the amplitude of the annual insolation cycle in the sh did not change significantly at 6 kyr compared to the pre industrial values the largest difference occurring in autumn mam negative anomalies and spring son positive anomalies the simulated changes in temperatures over the sh respond to the insolation changes with a 1 2 month delay over the oceans this results in a reduced amplitude of the annual cycle of temperature and precipitation over most continental regions except over patagonia and nz that show a slight increase in contrast large scale circulation features such as the low and upper level winds and the subtropical anticyclones show an amplified annual cycle as a direct response to the increased decreased insolation during the transitional seasons son mam in the annual mean there is a small but consistent equatorward shift of the latitude of maximum wind speed of 1 3 over the entire sh which results in a small increase of wind speed over the south pacific and atlantic oceans north of 50 s and a widespread decline south of 50 s pmip2 simulations for 6 kyr indicate that in the annual mean the sh mid latitudes were colder wetter and with stronger winds north of about 50 s these conditions are consistent with the observed neoglacial advances in the region as well as with terrestrial paleoclimate records from patagonia that indicate cooling and a multi millennial rising trend in southern westerly wind intensity starting at 7 8 kyr

estimation of microbial respiration rates in groundwater by geochemical modeling constrained with stable isotopes changes in geochemistry and stable isotopes along a well established groundwater flow path were used to estimate in situ microbial respiration rates in the middendorf aquifer in the southeastern united states respiration rates were determined for individual terminal electron acceptors including o2 mno2 fe3 and so42 the extent of biotic reactions were constrained by the fractionation of stable isotopes of carbon and sulfur sulfur isotopes and the presence of sulfur oxidizing microorganisms indicated that sulfate is produced through the oxidation of reduced sulfur species in the aquifer and not by the dissolution of gypsum as previously reported the respiration rates varied along the flow path as the groundwater transitioned between primarily oxic to anoxic conditions iron reducing microorganisms were the largest contributors to the oxidation of organic matter along the portion of the groundwater flow path investigated in this study the transition zone between oxic and anoxic groundwater contained a wide range of terminal electron acceptors and showed the greatest diversity and numbers of culturable microorganisms and the highest respiration rates a comparison of respiration rates measured from core samples and pumped groundwater suggests that variability in respiration rates may often reflect the measurement scales both in the sample volume and the time frame over which the respiration measurement is averaged chemical heterogeneity may create a wide range of respiration rates when the scale of the observation is below the scale of the heterogeneity

geodesy using the swedish permanent gps network effects of snow accumulation on estimates of site positions we have observed variations at the several centimeter level in estimates of the vertical coordinate of site position the estimates are obtained from our analysis of data acquired from the swedish permanent global positioning system gps network the observed variations are strongly correlated with changes in the indirectly inferred accumulation of snow which we assume collects on the radomes and pillars the gps sites could not be observed directly due to their remoteness numerical simulations which assume a simple geometry for the snow cover are used to study the effects of snow accumulation on gps phase observables and hence on estimates of the vertical coordinate of site position obtained from these observables our results indicate that the variations in the vertical coordinate of site position can be fully explained by reasonable accumulations of snow which retard the gps signals and enhance signal scattering effects

holocene climate change in southernmost south africa rock hyrax middens record shifts in the southern westerlies abstract south africa s southern coastal margin is recognised as being a highly dynamic climatic region that plays a critical role in both regional and global atmospheric and oceanic circulation dynamics our understanding of the past dynamics of this system however has been limited by the number and nature of datasets available that can be used to infer changes in key climatic parameters in the region in this paper we present new high resolution 13c and 15n data from two independently dated rock hyrax procavia capensis middens from seweweekspoort in south africa s groot swartberg mountains these data provide information regarding both past vegetation and hydroclimatic change and allow a regional integration of available data that explore the long term dynamics of mid latitude circulation systems in the african sector of the southern hemisphere combined a negative relationship is apparent between temperature and humidity in this area of the southern cape and these changes can for the first time be clearly linked to variations in antarctic sea ice extent and shifts in the southern westerly storm track this dynamic is particularly evident between 5 and 7 cal kbp when a reduction in sea ice extent and a southward shift of the westerlies are manifested regionally by increased temperatures and a phase of marked aridity

mid holocene radiocarbon ages in the subtropical andes 29 35 s climatic change and implications for human space organization this article discusses the distribution of radiocarbon age signatures obtained from archeological sites between 29 and 35 s in central chile and midwest argentina the goal of this analysis is to establish bases from which to interpret regional trends in the distribution of the archaeological record that connect these areas which have been traditionally considered to be geographically decoupled we propose a standardized methodology for selecting ages that provide a reliable human signature variations in date frequencies in a regional scale are discussed with the use of summed probability distributions radiocarbon voids at the regional level previously identified in midwest argentina are explored regional chronological information is compared to the available paleoenvironmental records thereby emphasizing the possible role of climate pulses in the spatial organization of human populations significant arid conditions between 7800 and 5700 cal bp are coincidental with a focused occupation of the andes mountains an area which may have offered stable resources and thus was more effectively occupied than other environmental bands

the little ice age glacier advance in the central andes 35 s argentina abstract this paper documents the occurrence of the little ice age lia in the el azufre and el penon glaciers at 35 s and in the las choicas and las damas glaciers at 34 55 s in the headwaters of the rio grande basin in the central andes of argentina moraine morphology stratigraphic relationships radiocarbon ages obtained from peat on these glacial deposits and the proximity to the active glaciers enabled us to reconstruct the lia advance in this area the lia maximum advance occurred between cal yr 1550 and 1720 ad and a readvance occurred around cal yr 1830 ad in addition glacier fluctuations of the las vacas and gussfeltd glaciers 33 s and el penon and el azufre glaciers were documented from the end of the 19th century to the present based on historical and aerial photographs and satellite images the glaciers showed a marked retreat during 1894 2007 minor readvances occurred in the 1980s and 1990s which could be related with strong warm enso events during these decades our results are consistent with observations made by other authors in the region

large scale global surface mass variations inferred from gps measurements of load induced deformation 1 detrended crustal deformation measurements from a global network of up to 200 continuous global positioning system gps tracking sites are inverted for low degree and order n m 6 spherical harmonic series of surface mass variations an independent geophysical model of the atmosphere oceans and water and snow on land is also used to guide the spherical harmonic truncation and to evaluate aliasing errors in the results inversion uncertainties decrease significantly as spatial coverage and data quality improve with time especially in the last few years consequently gps inverted seasonal geocenter and low degree zonal harmonics converge to those determined by measurements from satellite laser ranging slr significant n 1 and non zonal variations have also been found

geochemical patterns of arsenic enriched ground water in fractured crystalline bedrock northport maine usa abstract high mean as concentrations of up to 26 6 mol l 1990 g l occur in ground water collected from a fractured bedrock system composed of sulfidic schist with granitic to dioritic intrusions sulfides in the bedrock are the primary source of the as in the ground water but the presence of arsenopyrite in rock core retrieved from a borehole with as concentrations in the ground water barely above the detection limit of 2 0 mol l shows that there are complicating factors chemical analyses of water from 35 bedrock wells throughout a small watershed reveal spatial clustering of wells with high as concentrations stiff diagrams and box plots distinguish three distinct types calcium bicarbonate dominated water with low as concentrations cahco 3 type sodium bicarbonate dominated water with moderately high as concentrations nahco 3 type and calcium bicarbonate dominated water with very high as concentrations high as type it is proposed that differences in recharge area and ground water evolution and possible bedrock composition difference are responsible for the chemical distinctions within the watershed lack of correlation of as concentrations with ph indicates that desorption of as is an insignificant control on as concentration correlations of as concentrations with fe and redox parameters indicates that reductive dissolution of fe iii oxyhydroxides may play a role in the occurrence of high as concentrations in the nahco 3 and high as type water the oxidation of sulfide minerals occurs within the ground water system and is ultimately responsible for the existence of as in the ground water but there is no correlation between as and so 4 concentrations probably due to precipitation of fe iii oxyhydroxides and adsorption of as under oxidizing conditions

climate driven deformation of the solid earth from grace and gps 1 grace data indicate large seasonal variations in gravity that are assumed to be related to climate driven fluxes of surface water seasonal redistribution of surface mass should deform the earth and our calculations using grace data suggest vertical deformations of 13 mm in the region of greatest flux the amazon river basin to test the grace gravity hydrology connection we analyzed gps data acquired from sites in this region after accounting for degree 1 variations not observable with grace we find that annual deformation measured with gps correlates highly with predictions calculated from grace measurements these results confirm the variations in surface water sensed by grace which are significantly larger than those predicted by some hydrology models the results also demonstrate that grace can be an important tool for monitoring deformation of the earth and suggest that combined analysis of grace and gps may be a useful approach for estimation of geocenter variations

deeper groundwater chemistry and geochemical modeling of the arsenic affected western bengal basin west bengal india abstract a regional scale hydrogeochemical study of a 21 000 km2 area in the western bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers spatial trends of solutes and geochemical modeling indicate that carbonate dissolution silicate weathering and cation exchange control the major ion chemistry of groundwater and river water the main aquifer water has also evolved by mixing with seawater from the bay of bengal and connate water the isolated aquifers contain diagenetically altered water of probable marine origin the postoxic main aquifer water exhibits overlapping redox zones metal reducing sulfidic and methanogenic indicative of partial redox equilibrium with the possibility of oxidation in micro scale environments the redox processes are depth dependent and hydrostratigraphically variable elevated dissolved as in the groundwater is possibly related to fe iii reduction but is strongly influenced by coupled fe s c redox cycles arsenic does not show good correlations with most solutes suggesting involvement of multiple processes in as mobilization the main river in the area the bhagirathi hoogly is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry arsenic in water of smaller streams jalangi and ichamati is probably introduced by groundwater discharge during the dry season

small mammal remains from cueva huenul 1 northern patagonia argentina taphonomy and paleoenvironments since the late pleistocene abstract small mammal samples from the archaeological sequence of cueva huenul 1 ch1 36 56 45 s 69 47 32 w neuquen province argentina are described and taphonomic and paleoenvironmental conditions assessed this site is located near the steppe monte ecotone in the northernmost patagonia small mammal remains nisp 1426 mne 1409 mni 87 were recovered from late pleistocene 13 800 11 800 14 c bp early holocene 9500 14 c bp and late holocene layers 1400 14 c bp taphonomic analysis indicates that the ch1 assemblage is an archaeofaunistic owl pellet accumulation it has a good post depositional preservation since it was rapidly incorporated in the sedimentary matrix although it previously experienced trampling action from latest pleistocene to late holocene the assemblages are mainly composed by the sigmodontines eligmodontia spp and phyllotis xanthopygus and the caviomorphs microcavia australis and ctenomys sp suggesting in overall terms a marked ecological stability chl is one of the few sites where the pleistocene holocene transition is represented by faunal evidence the latest pleistocene sample spanning 13 800 and 11 800 14 c bp indicate scrub steppe with substantial open ground and rocky exposition one early holocene sample 9500 14 c bp suggests a more heterogeneous environment as evidenced by the first occurrence of akodon iniscatus and euneomys chinchilloides in this context ch1 assemblages do not reflect the small mammal community reworking that putatively accompanied the pleistocene holocene transition

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

geodesy using the global positioning system the effects of signal scattering on estimates of site position analysis of global positioning system gps data from two sites separated by a horizontal distance of only 2 2 m yielded phase residuals exhibiting a systematic elevation angle dependence one of the two gps antennas was mounted on an 1 m high concrete pillar and the other was mounted on a standard wooden tripod we performed elevation angle cutoff tests with these data and established that the estimate of the vertical coordinate of site position was sensitive to the minimum elevation angle elevation cutoff of the data analyzed for example the estimate of the vertical coordinate of site position changed by 9 7 0 8 mm when the minimum elevation angle was increased from 10 to 25 we performed simulations based on a simple ray tracing multipath model with a single horizontal reflector which demonstrated that the results from the elevation angle cutoff tests and the pattern of the residuals versus elevation angle could be qualitatively reproduced if the reflector were located 0 1 0 2 m beneath the antenna phase center we therefore hypothesized that the elevation angle dependent error was caused by scattering from the horizontal surface of the pillar located a distance of 0 2 m beneath the antenna phase center we tested this hypothesis by placing microwave absorbing material between the antenna and the pillar in a number of configurations and by analyzing the changes in apparent position of the antenna the results indicate that 1 the horizontal surface of the pillar is indeed the main scatterer 2 both the concrete and the metal plate embedded in the pillar are significant sources of scattering and 3 the scattering can be reduced greatly by the use of microwave absorbing materials these results have significant implications for the accuracy of global gps geodetic tracking networks which use pillar antenna configurations identical or similar to the one used for this study at the westford wfrd gps site

slip rate increase at parkfield in 1993 detected by high precision edm and borehole tensor strainmeters on two of the instrument networks at parkfield california the two color electronic distance meter edm network and borehole tensor strainmeter btsm network we have detected a rate change starting in 1993 that has persisted at least 5 years these and other instruments capable of measuring crustal deformation were installed at parkfield in anticipation of a moderate m6 earthquake on the san andreas fault many of these instruments have been in operation since the mid 1980s and have established an excellent baseline to judge changes in rate of deformation and the coherence of such changes between instruments the onset of the observed rate change corresponds in time to two other changes at parkfield from late 1992 through late 1994 the parkfield region had an increase in number of m4 to m5 earthquakes relative to the preceding 6 years the deformation rate change also coincides with the end of a 7 year period of sub normal rainfall both the spatial coherence of the rate change and hydrological modeling suggest a tectonic explanation for the rate change from these observations we infer that the rate of slip increased over the period 1993 1998

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

changing fire regimes in the temperate rainforest region of southern chile over the last 16 000 yr abstract a high resolution macroscopic charcoal record from lago melli 42 46 s 73 33 w documents the occurrence of forest fires in the lowlands of isla grande de chiloe southern chile over the last 16 000 yr our data suggest that fire activity in this region was largely modulated by the position intensity of the southern westerlies at multi millennial time scales fire activity was infrequent or absent between 16 000 11 000 and 8500 7000 cal yr bp and was maximal between 11 000 8500 and 3000 0 cal yr bp a mosaic of valdivian north patagonian rainforest species started at 6000 cal yr bp along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr bp the modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability suggesting the onset of high frequency variability in summer precipitation regimes starting at 5500 cal yr bp because negative anomalies in summer precipitation in this region are teleconnected with modern el nino events we propose that the onset of el nino like variability at 5700 6200 cal yr bp led to a reshuffling of rainforest communities in the lowlands of isla grande de chiloe and an increase in fire activity

noise properties of continuous gps data from concrete pillar geodetic monuments in new zealand and comparison with data from u s deep drilled braced monuments 1 reducing noise levels in geodetic data is critical for the interpretation and modeling of geophysically interesting signals in this paper i estimate noise properties of continuous gps time series collected on concrete pillar monuments and compare them with similar data from deep drilled braced monuments that are considered the most stable three dimensional monuments available i show that the time series noise properties are very similar between the monument types at least for time series up to 4 5 years duration differences between the monument types are therefore not a dominant influence on these time series implying that the less expensive concrete pillar monuments are a valid choice for recording many signals of geophysical interest

crustal displacements due to continental water loading the effects of long wavelength 100 km seasonal variability in continental water storage on vertical crustal motions are assessed the modeled vertical displace ments arm have root mean square rms values for 1994 1998 as large as 8 mm with ranges up to 30 mm and are predominantly annual in character regional strains are on the order of 20 nanostrain for tilt and 5 nanostrain for hori zontal deformation we compare arm with observed global positioning system gps heights aro which include ad justments to remove estimated effects of atmospheric pres sure and annual tidal and non tidal ocean loading for 147 globally distributed sites when the aro time series are ad justed by arm their variances are reduced on average by an amount equal to the variance of the arm of the aro time series exhibiting a strong annual signal more than half

geochemistry of groundwater in cretaceous sediments of the southeastern coastal plain of eastern mississippi and western alabama geochemical samples of waters along two hydrologic flow paths in four upper cretaceous aquifers of northeastern mississippi and western alabama indicate similar geochemical evolution of their respective waters the waters of the coker gordo and eutaw mcshan aquifers noncalcareous sands increase downgradient in dissolved solids and ph and are dominated by sodium and bicarbonate ions which generally result from a calcite dissolution cation exchange process increases in dissolved iron from oxidation reduction reactions followed by decreases in total inorganic carbon from siderite precipitation occur along the flow paths as the total inorganic carbon increases carbon 13 13c generally is enriched in the moving waters indicating the addition of a predominantly heavy source of carbon most likely dissolving calcite in the coker aquifer 13c values in the waters become more negative downgradient resulting from lignite oxidation followed by 13c values becoming more positive resulting from dissolving calcite and perhaps some mixing with brines in northeastern mississippi the ripley aquifer a calcareous sand initially contains calcium bicarbonate dominated water that evolves to a sodium bicarbonate dominated water downgradient primarily from the calcite dissolution cation exchange process feldspar hydrolysis to kaolinite dominates aluminosilicate reactions in the upgradient parts of the aquifers authigenesis of smectite clay may be occurring in the deeper downgradient parts of the aquifers

improved stability of a deeply anchored geodetic monument for deformation monitoring a test of two different monument designs used in geodetic networks shows that monuments installed to depths of 5 to 10 meters and laterally braced exhibit less environmentally caused displacement than those installed to 2 meters depth at parkfield california we have been monitoring the lengths of 17 baselines over the past decade with a 2 to 3 day interval between measurements using a two color geodimeter with a nominal precision of 0 5 mm over 5 km long baselines significant variations are observed on many of these baselines which appear to be related to the seasonally occurring rainfall with the larger variations approaching 10 mm over the past decade to test whether we could improve upon the measurements on some of the more susceptible lines at two sites we installed new monuments within about 30 meters of the original monuments after 1 5 years of measurements it is evident that the new monuments significantly attenuate the seasonal displacements to less than 1 mm the use of deeply anchored monuments should improve the ability of fault scale geodetic monitoring arrays to detect small tectonic displacements

contributions of thermal expansion of monuments and nearby bedrock to observed gps height changes 1 long term continuous global positioning system gps observations have become an important tool for studying the various geodynamic processes to fully study the geodynamic processes at gps stations the temporal movements of gps monuments and nearby bedrock induced by thermal expansion need to be considered in this paper we extend a theoretical model to estimate the thermal expansions of gps monuments and nearby bedrock for 86 globally distributed gps stations based upon measurements of surface air temperatures the results show that annual temperature variations are the dominant contributors for the thermal expansion of gps monuments and nearby bedrock the contributions of thermal expansion to gps height changes display largely spatial variations and can reach to a few millimeters citation yan h w chen y zhu w zhang and m zhong 2009 contributions of thermal expansion of monuments and nearby bedrock to observed gps height changes geophys res lett 36 l13301 doi 10 1029 2009gl038152

human refugia in australia during the last glacial maximum and terminal pleistocene a geospatial analysis of the 25 12 ka australian archaeological record a number of models developed primarily in the 1980s propose that aboriginal australian populations contracted to refugia well watered ranges and major riverine systems in response to climatic instability most notably around the last glacial maximum lgm 23 18 ka we evaluate these models using a comprehensive continent wide dataset of archaeological radiocarbon ages and geospatial techniques calibrated median radiocarbon ages are allocated to over lapping time slices and then k means cluster analysis and cluster centroid and point dispersal pattern analysis are used to define minimum bounding rectangles mbr representing human demographic patterns exploring data between 25 and 12 ka we find a refugia type hunter gatherer response during the lgm 23 18 ka and again during the antarctic cold reversal acr 14 5 12 5 ka with expansion in the intervening period several refugia persist between 25 and 12 ka including by interim biogeographic regionalisation for australia areas gulf plains einasleigh uplands brigalow belt south murray darling depression and tasmanian central highlands others appear sporadically through the same period these include south eastern highlands nsw south western slopes sydney basin warren murchison gascoyne central and northern kimberley ord victoria plain arnhem plateau macdonnell ranges and central ranges the pilbara may also have been a refugium during the lgm but geospatial results are problematic for this region areas devoid of human activity barriers include the main desert regions especially in the south and west of the continent although some of these may be the result of an absence of archaeological fieldwork point dispersal pattern analysis indicates a reduction in occupied territory of nearly 80 during the lgm a reduction of close to 50 was also evident during the acr a large number of the refugia were in close proximity to glaciated areas during the lgm and probably benefitted from increased summer snowmelt along the major river systems the remaining refugia are likely the result of a range of local environmental and resource factors we identify areas for future research including a focus on regional studies to determine possible cryptic or idiosyncratic refugia emerging in phlyogeographic studies

geochemistry of dissolved inorganic carbon in a coastal plain aquifer 2 modeling carbon sources sinks and δ13c evolution abstract stable isotope data for dissolved inorganic carbon dic carbonate shell material and cements and microbial co2 were combined with organic and inorganic chemical data from aquifer and confining bed pore waters to construct geochemical reaction models along a flowpath in the black creek aquifer of south carolina carbon isotope fractionation between dic and precipitating cements was treated as a rayleigh distillation process organic matter oxidation was coupled to microbial fermentation and sulfate reduction all reaction models reproduced the observed chemical and isotopic compositions of final waters however model 1 in which all sources of carbon and electron acceptors were assumed to be internal to the aquifer was invalidated owing to the large ratio of fermentation co2 to respiration co2 predicted by the model 5 49 compared with measured ratios two or less in model 2 this ratio was reduced by assuming that confining beds adjacent to the aquifer act as sources of dissolved organic carbon and sulfate this assumption was based on measured high concentrations of dissolved organic acids and sulfate in confining bed pore waters 60 100 m and 100 380 m respectively relative to aquifer pore waters from less than 30 m and 2 80 m respectively sodium was chosen as the companion ion to organic acid and sulfate transport from confining beds because it is the predominant cation in confining bed pore waters as a result excessive amounts of na for ca ion exchange and calcite precipitation three to four times more cement than observed in the aquifer were required by model 2 to achieve mass and isotope balance of final water for this reason model 2 was invalidated agreement between model predicted and measured amounts of carbonate cement and ratios of fermentation co2 to respiration co2 were obtained in a reaction model that assumed confining beds act as sources of dic as well as organic acids and sulfate this assumption was supported by measured high concentrations of dic in confining beds 2 6 2 7 mm results from this study show that geochemical models of confined aquifer systems must incorporate the effects of adjacent confining beds to reproduce observed groundwater chemistry accurately

choice of optimal averaging radii for temporal grace gravity solutions a comparison with gps and satellite altimetry summary one of the initial challenges of the gravity recovery and climate experiment grace mission is to validate the accuracy of the time variable gravity fields these gravity fields contain both spatially correlated systematic and random noise and hence spatial averaging needs to be implemented before the fields may be interpreted optimum averaging radii need to be determined through comparison with independent data we compare time series of vertical solid earth deformations computed from 22 approximately monthly grace gravity fields covering 2002 3 until 2004 6 with vertical displacements measured using a global gps network of 63 sites about half of which are located on small islands the gps data were processed using a precise point positioning approach using fiducial free orbits and attempting to minimize propagated systematic errors the optimum mean correlations were obtained at 500 km averaging radii for continental sites r 0 55 2000 km for island sites r 0 3 subtracting the grace displacement time series from the gps ones revealed a mean variance reduction of 14 per cent to supplement the gps data at the island sites we also computed displacements based on topex poseidon t p sea surface height data between 2002 3 and 2004 corrected for steric effects correlations reached a maximum at 2000 km with a correlation of 0 38 increasing to 0 47 after the removal of six outlying sites overall we conclude that optimum averaging radii are 500 km for continental sites and 2000 km over the oceans but that the measurement precision of gps and t p may be inflating these values

mid holocene paleoenvironments and the archeological record of southern mendoza argentina the environmental heterogeneity of southern mendoza led to different environmental responses during the mid holocene more arid conditions and perhaps higher temperatures were dominant in the lowlands while the high andes experienced increased snowfalls and neoglacial readvances from ca 6000 to 4000 years bp the opposing climate pattern of the region in comparison with the western pacific foothills of the andes is apparently related to the different influences exerted by the westerlies on both sides of the cordillera the archeological record of this time period is represented by very few sites with a low density of material both the temporal distribution of the radiocarbon dates and the occupation index suggest a significant decrease of human occupations manifested by a chronological hiatus which varies in timing and duration according to the areal scale of analysis the coincidence of the occupational hiatus and the low amount of archeological evidences would point to abandonment and or a change related to a low intensity pattern of land use across the region these human responses seem to parallel the general arid climatic conditions of the mid holocene although more detailed information and particularly numerical dates are needed to test the hypothesis site formation processes including site disturbance produced by later human occupations are alternative explanations also evaluated to give account of the archeological record

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

paleoenvironmental changes at the northern limit of the subantarctic nothofagus forest lat 37 s argentina paleoenvironmental changes dating back to before 10 000 yr b p at the northernmost occurrences of nothofagus forests in argentina at about latitude 37 s permit the reconstruction of past changes in the intensity of the winter rains related to the southern westerlies that appear to determine the forest boundary the paleoenvironmental interpretation is based on changes in the proportions of different nothofagus species and changes in the ratio betwen forest and steppe taxa the relatively most diverse and dense nothofagus forest developed only during the last 4500 yr prior to human impact during the last 300 yr before the middle holocene climatic conditions must have been different from the modern ones with less overall precipitation judging from the overall lower amount of tree pollen and the reduction to primarily nothfagus pumilio an interval dated to older than 10 000 yr b p is characterized by co occurrence of prumnopitys andina nothofagus pumilio and shrub steppe taxa prumnopitys andina is known today only from scattered upper montane forest sites in chile between 36 and 43 s lat and its ecological requirements are essentially unknown the taxa combination however suggests that late glacial climate must have been drier and probably cooler than today this implies that the winter rains and consequently the seasonal shift of the westerly circulation was reduced during the late pleistocene and did not reach modern levels before 8500 yr b p

nature and origin of authigenic rhodochrosite and siderite from the paleozoic aquifer northeast mississippi u s a abstract botryoidal rhodochrosite siderite and pyrite are the principal authigenic phases in fractured chert comprising the paleozoic aquifer of northeast mississippi locally alternating bands of near end member composition rhodochrosite and siderite occur in veinlets up to 2 mm wide in the fractured chert carbon isotope data for the carbonates 13c values ranging from 9 6 to 11 3 pdb indicate that both inorganic and organic c were incorporated into the authigenic phases the paleozoic aquifer is hydraulically connected with the overlying upper cretaceous coastal plain strata groundwater in the coastal plain units is undersaturated with respect to calcite and has relatively high fe and mn contents the latter apparently caused by the dissolution of fe mn oxyhydroxides the natural downward recharge of these waters into the paleozoic aquifer causes calcite dissolution in limestone at the base of the chert which in turn leads to the precipitation of rhodochrosite and siderite additionally pyrite is precipitated as so4 reduction occurs in the same zone rhodochrosite has not been previously documented as an authigenic phase in a fresh water aquifer system suggesting that the geochemical environment necessary for its precipitation is not common the alternating bands of rhodochrosite and siderite observed in this study coupled with available thermodynamic data indicate that the groundwater a mn2 afe2 ratio must have fluctuated over time variations in the ratio are best explained by variable eh conditions at the site where fe mn oxyhydroxide dissolution occurs

aliased tidal signatures in continuous gps height time series 1 coordinate time series are often derived from continuous gps data processed as discrete 24 hour solutions under this regimen residual semi diurnal and diurnal crustal tide signatures are under sampled resulting in aliased periodic signals in the coordinate time series a secondary aliasing effect well known from satellite altimetry studies but generally ignored in gps analysis arises from the repeat period of the satellite orbits being longer than the nyquist period of the semi diurnal and diurnal tidal signatures this paper derives the theoretical periods for these two aliasing effects for the principal semi diurnal and diurnal tidal constituents the presence of both types of aliased signals in gps time series is then demonstrated using simulated gps data and also considered for time series derived from real gps data it is shown that the beating of the two aliased signals invariably results in spurious signatures in the time series with semi annual and annual periods

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

holocene glacier chronology of valenzuela valley mendoza andes argentina glacial geologic evidence and radiocarbon dated glacial deposits provide evidence of glacier fluctuations during the last 5 ka years in the andes radiocarbon dated moraines morphological and stratigraphical studies permit the reconstruction of glacier fluctuations during the holocene in the valenzuela area of the mendoza andes valley located at 35s in the upper rio grande basin the holocene record in this part of the andes is mostly unknown so this research is relevant for palaeoclimatic reconstructions in south america in the rio valenzuela glacier variations were dated in the el azufre and el pefion valleys the first neoglacial advance occurred at c 5700 yr bp and a very close re advance of similar magnitude occurred at 4700 4300 yr bp which formed well preserved lateral terminal moraines the first neoglacial advance occurred in the el pefion valley at c 4400 yr bp and a well preserved terminal moraine is observed a second neoglacial advance reached its maxima at c 2500 2200 yr bp in the el

gps height time series short period origins of spurious long period signals gps height time series used in geophysical studies are often formed from discrete continuous nonoverlapping 24 hour processing sessions with such a strategy unmodeled periodic ground displacements with approximately semidiurnal and diurnal periods have often been assumed to average close to zero by analyzing several years of continuous gps data from globally distributed sites at which controlled errors were not modeled this paper shows such an assumption to be erroneous it is shown that each unmodeled sub daily periodic displacement can propagate to several spurious long wavelength features in a gps height time series ranging in period from about 2 weeks to 1 year admittances ratio of amplitude of spurious long wavelength output signal in the gps height time series to amplitude of unmodeled periodic ground displacement depend on the coordinate component and the tidal constituent considered for example it is shown that an unmodeled s2 north component periodic ground displacement can propagate to a semiannual height signal with admittance of greater than 100 whereas the height admittance is around 5 10 since model errors in ocean tide loading atmospheric pressure loading and solid earth tide displacement amplitudes can be several millimeters long wavelength spurious signals of up to these amplitudes may be expected to appear in gps height time series this paper provides an indication of how such errors will propagate where such errors are greatest and hence how spurious fortnightly semiannual and in some cases annual effects may be present at some sites copyright 2007 by the american geophysical union

from proxy data to paleoclimate interpretation the mid holocene paradox of the atacama desert northern chile abstract the question whether the mid holocene climate between ca 9 and 4 cal kyr b p in the atacama desert and the central andes in general was humid or dry has wide implications with regard to the understanding of long term climate variability in south america paleosols regional groundwater tables abiotic proxy data and pollen of aquatic plants in lake sediments show a marked and rapid shift from very humid late glacial early holocene climatic conditions between ca 14 and 9 5 kyr b p to extremely dry mid holocene conditions more arid than today between ca 9 and 4 kyr b p an exception during this hyperarid period is a century scale more humid interval around ca 5 5 6 kyr b p that appears systematically in lake sediment archives in contrast pollen for most terrestrial plants preserved in lake sediments do not show major changes during the holocene whereas more humid mid holocene conditions compared with late holocene conditions were inferred from plant macrofossils in rodent middens is the reason for this disagreement to be attributed to misinterpretation of the paleoenvironments or of the proxy records themselves or to incomplete paleoclimatic interpretation of the paleoenvironments we argue that these different paleoclimate archives record different aspects and facets of climate while paleosols and groundwater in the atacama desert record low frequency climate variability at century to millennium scales lake sediments on the altiplano record decade to century scale variability terrestrial vegetation responds to shorter high frequency climate variability at seasonal to inter annual scales and preferably to humid years vegetation remains in hibernation or does not germinate during arid years thus information from these three types of archives is not a priori comparable and requires careful site specific archive specific and time scale specific evaluation what is natural in modern climatology is also true for paleoclimatology a comprehensive assessment must account for the complex daily and seasonal cycles for the range of climate variability and trends at different scales in space and time for impacts of short term extreme events and for specific often non linear responses of individual bio geo physical archives to any of the numerous aspects of climate

late pleistocene human occupation of the hyperarid core in the atacama desert northern chile abstract few archeological sites in south america contain uncontroversial evidence for when the first peopling of the continent occurred largely ignored in this debate extreme environments are assumed either as barriers to this early wave of migration or without potential for past habitability here we report on a rare 12 13 ka human occupation from quebrada mani site qm12 a plantless near rainless landscape 1240 m asl and 85 km from the pacific ocean located in the hyperarid core of the atacama desert this location harbored wetlands and riparian woodlands that were fed by increased rainfall further east in the central andes during the latest pleistocene excavations at qm12 yielded a diverse cultural assemblage of lithics burned and cut bones marine gastropods pigments plant fibers and wooden artifacts alongside a prepared fireplace sixteen radiocarbon dates from site qm12 on charcoal marine shells animal dung plant remains and wood reveal that the occupation took place between 12 8 and 11 7 ka these results demonstrate that the atacama desert was not a barrier to early american settlement and dispersal and provide new clues for understanding the cultural complexity and diversity of the peopling of south america during the last glacial interglacial transition

a thermodynamic model for water column precipitation of siderite in the plio pleistocene black sea it has been hypothesized that finely disseminated soft wheat like grains of siderite in the sideritic muds of the plio pleistocene section of the black sea are sub aqueous precipitates hsu and kelts 1978 in an attempt to quantify this hypothesis we 1 investigated the chemistry mineralogy and isotopic composition of the siderites and associated calcite and 2 developed a thermodynamic model of endogenic siderite precipitation that is directly precipitated from the water column driven by sequential evaporative concentration of acidic dissolved or anic carbon and iron rich waters considering the average com position of the present day satilla drainage of the southeastern umted states as approximating the composition of the waters that fed the neogene black sea and allowing this water to evaporate isothermally at 25 c in equilibrium with atinospheric c02 pc02 l 0 3 5 attn we calculated the aqueous concentrations at which various carbonate phase5 would precipitate out of the system it is shown that evaporation of this water to roughly one twelfth of its original volume can result in precipitation of the pure endmember siderite alone relating our geochemical and modeling results to the details of black sea climatostratigraphic and evolutionary history dur ing the times of deposition of the siderite units we corroborate the qualitative arguments of hsu and kelts 1978 we also conclude that climate was the chief forcing function in transforming episodically the calcite precipitating eutrophic water masses of the plio pleistocene basin to one of siderite ptecipitation based on our model calculations of the thickness of siderite precipitated per cm2 of basin area we further predict that the observed laminae interbeds of siderite could be a composite of several microlayers of siderite and clays

calibrating the pollen signal in modern rodent middens from northern chile to improve the interpretation of the late quaternary midden record abstract the use of rodent middens from northern chile as paleoecological archives has at times been questioned due to concerns about their biogenic origin and the degree to which their record represents vegetation composition rather than rodent habits to address such concerns we carried out a modern calibration study to assess the representation of vegetation by pollen records from rodent middens we compared vegetation censuses with soil surface and midden matrix and feces pollen samples from sites between 21 and 28 s the results show that 1 the pollen signal from the midden matrix provides a more realistic reflection of local vegetation than soil surface samples due to the pollen deposition processes that occur in middens and 2 in contrast to feces pollen assemblages which feature some biases rodent dietary habits do not seem to influence midden matrix pollen assemblages probably because midden agents are dietary generalists our finding that modern pollen data from rodent middens reflect vegetation patterns confirms the reliability of midden pollen records as paleoecological archives in northern chile

resilience and the population history of the kuril islands northwest pacific a study in complex human ecodynamics living in remote places can strain the adaptive capacities of human settlers it can also protect communities from external social political and economic forces in this paper we present an archaeological population history of the kuril islands this string of small volcanic islands on the margins of the northwest pacific was occupied by maritime hunting fishing and gathering communities from the mid holocene to recent centuries we bring together 1 380 new and previously published archaeological radiocarbon dates 2 a new paleodemographic model based on a radiocarbon timestamped temporal frequency distribution of archaeological deposits 3 recently published paleoclimate trends and 4 recently published archaeological proxy evidence for changes in the extent of social networks we demonstrate that over the last two millennia inhabitants of the kuril islands underwent dramatic demographic fluctuations explanations of these fluctuations are considered in the context of environmental hazards social networks and the emergence of an east asian world system elucidating the tension between local and external adaptive strategies to social and ecological uncertainty results suggest that population resilience to local climate and environmental variability was achieved by virtue of social networks that maintained non local support in times of crisis conversely the expansion of the east asian political economy into neighboring regions of the southern margin of the kuril islands perhaps in conjunction with exposure to epidemic diseases appears to have undermined the adaptive strategies resulting in an increase in the vulnerability of kuril populations to environmental fluctuations

geochemical and palaeohydrological controls on the composition of shallow groundwater in the netherlands with the exception of the south of the country the netherlands has a strong bipartite hydrogeology the holocene part with a coastal dune belt and confining top layer of clay and peat further inland and the pleistocene where thick phreatic aquifers dominate this research aimed to ascertain the geochemical and palaeohydrological controls on the composition of shallow groundwater in 27 regions close to 6000 groundwater analyses were grouped and interpreted in terms of 1 salinity 2 redox status 3 acid base and carbonate status and 4 natural nutrients nh4 and po4 the a priori classification into geographical regions and geological formations revealed many statistically significant differences in medians even for geologically or geographically related data groups the compound specific interpretation indicates that there are geogenically controlled systematic differences in groundwater composition at the regional scale the imprint of the geological sediments on the groundwater composition decreases in the order marine estuarine via limnological fluvial to aeolian the imprints with respect to ph and carbonate status natural nutrients and redox status are not necessarily interrelated the vertical stratification in groundwater composition turns out to be often limited at the regional scale due to mutual occurrence of infiltrating and exfiltrating groundwater in regions and either the presence of a highly reactive holocene confining top layer or temporal changes in contamination in the holocene part the salinity is controlled by the palaeoenvironmental conditions during the holocene and by the recharge origin the average cl concentration decreases from estuarine via lagoonal to the former zuider sea which was a bay the most reduced states and also the highest nutrient concentrations and highest co2 pressure are related to the presence of holocene marine sediments in the confining top layer degradation of marine derived organic matter as a nutrient source is likely more intense in the holocene deposits than that of peat and sedimentary remnants of terrestrial plants a broad range in ph carbonate status and redox status is encountered in the pleistocene part here the palaeohydrological evolution in terms of carbonate leaching together with the geological controls on the calcareous nature of the shallow sedimentary deposits cause regional differences in ph calcite saturation and silicate weathering one region with late pleistocene limnological deposits has deviating groundwater characteristics and appears more similar to the holocene part of the netherlands furthermore reactive fe is not abundant in all pleistocene fluvial sediments nor is it maximally mobilised as not all anoxic groundwater in these sediments is siderite saturated this leads to considerable intra and inter region variability 2013 elsevier ltd

late quaternary environmental dynamics in the atacama desert reconstructed from rodent midden pollen records in the past two decades much has been learned about the late quaternary climate history of the atacama desert with some details still unclear about the seasonality timing and extent of wet and dry phases modern climate studies reveal that far from exhibiting a unique pattern seasonal precipitation originates from many sources and mechanisms for the last 16 ka we attempt to sort out these complexities in pollen records from four fossil rodent midden series spanning 22 25 s in northern chile widespread wet conditions prevailed during the late pleistocene and early holocene particularly between 13 and 9 ka evidenced by 400 m lowering of pollen zones plant communities compared to today regional differences in the timing and magnitude of this displacement may be related to the prevailing source tropical extra tropical or mode nnw se of tropical precipitation through time wet conditions persisted well into the early holocene lasting 1 1 5 ka longer than previously suggested the pollen record suggests extreme drying 8 ka possibly associated with a northward shift of the inter tropical convergence zone tracking minimum insolation values at subtropical latitudes during the austral summer the establishment of conditions similar to today happened 4 ka copyright 2017 john wiley sons ltd

geochemical and microbiological zonation of the middendorf aquifer south carolina we consider the nature and origin of the chemical and microbiological zonation of the cretaceous middendorf aquifer in the coastal plain of south carolina in light of the chemical evolution of groundwater along a flow path there some types of microbial activity most notably aerobic respiration and iron reduction lead to a net generation of acid as co2 but reaction of groundwater with minerals in the aquifer consumes the acid driving up ph and controlling the evolution of the groundwater s major ion chemistry the thermodynamic energy available to the various functional groups of microbes except the autotrophic hydrogen oxidizing methanogens is everywhere along the flow path sufficient to drive microbial growth the concentrations of acetate formate and lactate do not vary systematically from zone to zone along the flow path as might be expected if each zone were dominated by a single functional group of microbes the overall rate of microbial respiration in the aquifer appears to be limited by the rate of the initial fermentation of organic matter we found no compelling evidence indicating that one functional group of microbes excludes others from any of the aquifer s zones sulfate reduction for example may be non existent in the high iron zone associated with iron reduction or may account for up to 90 of the respiration occurring there zonation of the groundwater into high iron and low iron facies may result from a minor change along the aquifer in the balance between the activities of iron and sulfate reducers

geochemistry of groundwater in tertiary and cretaceous sediments of the southeastern coastal plain in eastern georgia south carolina and southeastern north carolina geochemical samples of groundwater taken along hydrologic flow paths in eastern georgia south carolina and southeastern north carolina from noncalcareous sand aquifers largely of cretaceous age are dominated by sodium and bicarbonate ions calcareous sand aquifers largely of tertiary age contain water whose chemistry is dominated by calcium and bicarbonate ions but may evolve downgradient to sodium and bicarbonate dominance water chemistry in both types of aquifer evolves to sodium chloride dominance as a result of fresh water mixing with subsurface brines or seawater present in the deeper downgradient parts of the aquifers principal aqueous chemical reactions appear to occur in five reaction zones in the aquifers and include feldspar hydrolysis to kaolinite calcite dissolution calcium for sodium cation exchange and neoformation of sodium smectite in the downgradient parts of the aquifers redox reactions produce dissolved iron concentrations greater than 1 mg l near the recharge areas organic matter in the aquifers is oxidized to co2 by iron reduction and sulfate reduction processes production of co2 by a methanogenic process may also occur geochemical mass transfer models simulating the observed chemistry in western alabama and eastern mississippi have been extended to account for higher concentrations of sodium and bicarbonate observed in the south carolina part of the aquifers

palynological evidence for increased aridity on the central chilean coast during the holocene abstract the late quaternary vegetation of the semiarid coast of central chile is inferred from the palynological analysis of profiles from quereo 31 55 s and quintero 32 47 s prior to 11 400 yr b p wet conditions are suggested by the abundance of pollen indicators of swamp and aquatic taxa such as cyperaceae and myriophyllum and by the presence of traces of arboreal pollen since ca 10 000 yr b p a trend toward increasingly drier conditions is implied by the almost complete absence of arboreal and aquatic taxa and a general decrease in the diversity of the semiarid shrubland indicators from 3000 yr b p onward the pollen records show the reappearance of swamp and aquatic taxa presumably associated with wetter conditions which led to recolonization by forest taxa at 1720 yr b p in quintero the drier climate detected along the semiarid coast of central chile during most of the holocene extended inland to the andean foot hills within the present mediterranean type climate zone of chile and also affected the distribution of the winter deciduous nothofagus forests and the northern boundary of the temperate rain forests

apparent stability of gps monumentation from short baseline time series 1 long running short 1 km gps baselines offer an insight into the accuracy budget of geophysical estimates inferred from gps coordinate time series in this paper we report on analysis of 10 short baselines using data spanning several years and examine deviations from a constant baseline length annual signals with amplitude 0 5 mm are evident in various coordinate components at 6 of the 10 sites with amplitudes exceeding 2 5 mm on two baselines these signals are largely invariant to elevation cutoff angle multipath and phase center model errors are shown to probably have negligible effects at most sites at annual periods they are therefore likely real monument motions although linear thermal expansion is negligible at most sites linear trends 0 25 mm yr 1 are evident on four baselines in at least one coordinate component subdaily signals are present at all sites at k1 and its higher harmonics time correlated noise possibly in the form of flicker noise dominates despite many common signals being eliminated as a result of the small baseline lengths although it is around 1 order of magnitude smaller than for single site ppp solutions we constrain monument random walk motion to be no more than 0 5 mm yr 1 2 if these baseline motion results were representative of the 300 currently active igs sites 180 would have annual signals 0 5 mm in at least one coordinate component 120 would have linear rates 0 25 mm yr 1 and almost all sites would have subdaily k1 k2 signals of 0 1 mm each solely due to local site effects

a comparison of annual vertical crustal displacements from gps and gravity recovery and climate experiment grace over europe 1 we compare approximately 3 years of gps height residuals with respect to the international terrestrial reference frame with predictions of vertical surface displacements derived from the gravity recovery and climate experiment grace gravity fields for stations in europe an annual signal fit to the residual monthly heights corrected for atmospheric pressure and barotropic ocean loading effects should primarily represent surface displacements due to long wavelength variations in water storage a comparison of the annual height signal from gps and grace over europe indicates that at most sites the annual signals do not agree in amplitude or phase we find that unlike the annual signal predicted from grace the annual signal in the gps heights is not coherent over the region displaying significant variability from site to site confidence in the grace data and the unlikely possibility of large amplitude small scale features in the load field not captured by the grace data leads us to conclude that some of the discrepancy between the gps and grace observations is due to technique errors in the gps data processing this is evidenced by the fact that the disagreement between gps and grace is largest at coastal sites where mismodeling of the semidiurnal ocean tidal loading signal can result in spurious annual signals

vegetation invasions into absolute desert a 45 th000 yr rodent midden record from the calama salar de atacama basins northern chile lat 22 24 s plant macrofossils percentage abundance of grass taxa fecal pellet d13 c and plant cuticle contents from 49 fossil rodent middens dated by 14 c record changes in local vegetation and precipitation since 45 ka calibrated or measured to thousands of calendar years before present in the central atacama desert lat 228 248s of northern chile the midden sites are along the hyperarid upper margin 2400 3100 m of the absolute desert in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs conditions between 40 and 22 ka may have been at least intermittently dry and possibly cooler as implied by four middens with low species richness we infer a large increase in summer rainfall between 16 2 and 10 5 ka on the basis of the lowering of steppe grasses by as much as 1000 m prominence of c4 grasses and summer annuals high species richness and displacement of northern species at least 50 km south of their modern ranges the precipitation increase was greatest for a cluster of middens between 11 8 and 10 5 ka abrupt drying evident in a dramatic decrease in grass abundance occurred after 10 5 ka at all four midden localities increased percentages of

validation of ocean tide models around antarctica using onshore gps and gravity data 1 ocean tide models around antarctica are presently only sparsely tested against independent data ocean tide modeling errors along with subsequent ocean tide loading otl displacement modeling errors alias into altimetry and time variable gravity e g gravity recovery and climate experiment grace time series for example to validate various ocean tide models around antarctica gps data from 15 sites have been used to derive three dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies using hundreds of days of gps data harmonic parameters were estimated on a daily basis then combined these were then compared with otl displacement estimates derived from global and regional ocean tide models in east antarctica where the tides are well defined submillimeter differences are demonstrated in each coordinate component with the lunar n2 and q1 constituents in closest agreement as found in other studies k1 and especially k2 agree less well the spatial variation in the misfits for these two constituents indicates a site dependency with the k2 errors also suggesting an interaction with satellite dependent effects in west antarctica where sites are nearer the largest ice shelves agreement with the older models csr3 and tpxo 2 and nao 99b is poor for all constituents modeled tidal gravity variations were also compared with gravity measurements at the south pole overall the gps and gravity data agree best with newer tide models namely tpxo 6 cada00 10 fes99 and cats02 01 however validation data are lacking at the southern extents of the large ice shelves and hence some uncertainty still exists in all ocean tide models in these regions