late quaternary palaeoenvironment of northern guatemala evidence from deep drill cores and seismic stratigraphy of lake peten itza long sediment cores were collected in spring 2006 from lake peten itza northern guatemala in water depths ranging from 30 to 150 m as part of an international continental scientific drilling program project the sediment records from deep water consist mainly of alternating clay gypsum and carbonate units and in at least two drill sites extend back 200 kyr most of the lithostratigraphic units are traceable throughout the basin along seismic reflections that serve as seismic stratigraphic boundaries and suggest that the lithostratigraphy can be used to infer regional palaeoenvironmental changes a revised seismic stratigraphy was established on the basis of integrated lithological and seismic reflection data from the basin from ca 200 to ca 85 ka sediments are dominated by carbonate clay silt often interbedded with sandy turbidites indicating a sediment regime dominated by detrital sedimentation in a relatively humid climate at ca 85 ka an exposure horizon consisting of gravels coarse sand and terrestrial gastropods marks a lake lowstand or partial basin desiccation indicating dry climate conditions from ca 85 to ca 48 ka transgressive carbonate clay sediments overlain by deep water clays suggest a lake level rise and subsequent stabilization at high stage from ca 48 ka to present the lithology is characterized by alternating clay and gypsum units gypsum deposition correlates with heinrich events i e dry climate whereas clay units coincide with more humid interstadials

climate change in the lake valencia basin venezuela 12600 yr bp to present we present a palaeoclimate record for northern south america extending from the latest pleistocene 12600 14c yr bp to present climate reconstruction for the valencia basin venezuela was base

the linked stress release model for spatio temporal seismicity formulations procedures and applications summary the linked stress release model is based on the build up of stress through elastic rebound and its dissipation in the form of earthquakes in addition stress can be transferred between large scale geological or seismic features the model can be statistically fitted to both historical and synthetic seismicity catalogues and through simulation can be used to create probabilistic forecasts of earthquake risk we review the genesis of the model provide some observations on forecasting using the model and follow with a comprehensive review of applications to date a systematic procedure for identification of the best model is illustrated by data from the persian region we then consider the evaluation of fitted models using residual point processes and information gains implications of the use of benioff strain rather than seismic moment are discussed the sensitivity of the model to regionalization magnitude errors catalogue incompleteness catalogue size and declustering magnitude cut off is then considered in detail with reference to data from north china the latter data are also used to illustrate the model evaluation techniques introduced earlier some technical material on numerical fitting simulation and calculation of the information gain is given in an appendix

great blue hole lighthouse reef belize a continuous annually resolved record of common era sea surface temperature atlantic multidecadal oscillation and cyclone controlled run off abstract the holocene 1900 ce is more likely the result of the suess effect anthropogenic impact of the industrial revolution on carbon isotopes composition than another reflection of a tc peak activity interval

quantitative estimates of tropical temperature change in lowland central america during the last 42 ka determining the magnitude of tropical temperature change during the last glacial period is a fundamental problem in paleoclimate research large discrepancies exist in estimates of tropical cooling inferred from marine and terrestrial archives here we present a reconstruction of temperature for the last 42 ka from a lake sediment core from lake peten itza guatemala located at 17 n in lowland central america we compared three independent methods of glacial temperature reconstruction pollen based temperature estimates tandem measurements of 18o in biogenic carbonate and gypsum hydration water and clumped isotope thermometry pollen provides a near continuous record of temperature change for most of the glacial period but the occurrence of a no analog pollen assemblage during cold dry stadials renders temperature estimates unreliable for these intervals in contrast the gypsum hydration and clumped isotope methods are limited mainly to the stadial periods when gypsum and biogenic carbonate co occur the combination of palynological and geochemical methods leads to a continuous record of tropical temperature change in lowland central america over the last 42 ka furthermore the gypsum hydration water method and clumped isotope thermometry provide independent estimates of not only temperature but also the 18o of lake water that is dependent on the hydrologic balance between evaporation and precipitation over the lake surface and its catchment the results show that average glacial temperature was cooler in lowland central america by 5 10 c relative to the holocene the coldest and driest times occurred during north atlantic stadial events particularly heinrich stadials hss when temperature decreased by up to 6 to 10 c relative to today this magnitude of cooling is much greater than estimates derived from caribbean marine records and model simulations the extreme dry and cold conditions during hss in the lowland central america were associated with fresh water forcing in the north atlantic which led to reduced atlantic meridional overturning circulation cooling of the north atlantic southern advance of sea ice and southward shift of the intertropical convergence zone although some models correctly predict the sign of temperature and precipitation changes they consistently underestimate the degree of observed cooling and decreased precipitation over land in lowland central america

accelerating seismic release from a self correcting stochastic model 1 we investigate the conditions under which the stress release model a stochastic version of the elastic rebound model produces synthetic earthquake sequences characterized by accelerating seismic release asr in this model the level or stress of the process accumulates linearly with time through tectonic input and decreases as the result of earthquakes these stress drops correspond to some power of the energy released in the earthquakes either e0 5 benioff strain or e seismic moment earthquakes occur in a point process with rate controlled by the level of the process we hypothesize that the critical factor in the appearance of asr is the manner in which the event sizes depend on the level of the process this is modeled by the square root of energy released following either a tapered pareto or truncated gutenberg richter distribution with maximum earthquake size controlled by a tail off or truncation point as the tail off point becomes large so does the average size corresponding to an acceleration to criticality of the system we found that those cases where the underlying level of the process corresponded to accumulated seismic moment produced numerous asr sequences whereas those cases using accumulated benioff strain as the level did not these results suggest that the occurrence of asr is strongly dependent on how large earthquakes affect the dynamics of the fault system in which they are embedded and hopefully provide some insight into the mechanics of acceleration to criticality i e on the possible causes of occurrence nonoccurrence of asr

a 3400 year paleolimnological record of prehispanic human environment interactions in the holmul region of the southern maya lowlands abstract the timing magnitude and drivers of late holocene environmental change in the holmul region of the southern maya lowlands are examined by combining paleoenvironmental and archeological data environmental proxy analyses on a 3350 cal yr lacustrine sediment record include pollen charcoal loss on ignition magnetic susceptibility and elemental geochemistry archeological evidence is derived from extensive settlement surveys conducted near the study site results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr bp the fire history shows a dramatic increase in burning during the classic period possibly reflecting changing agricultural strategies a distinct band of carbonate deposited from 1270 to 1040 cal yr bp suggests decreased hydrologic input associated with drier conditions abrupt changes in proxy data around 940 cal yr bp indicate a cessation of human disturbance and local abandonment of the area

seismic moment distribution summary we review possible errors in determining the size of earthquakes we propose that the size distribution can be effectively defined only for earthquake sequences not for individual earthquakes as a result of the error analysis we question the validity of many reported correlations between the 6 value and spatio temporal characteristics of tectonics and seismicity the study of the distribution of earthquake seismic moment largely avoids the influence of these errors and biases and is therefore superior to the standard analysis of the magnitude frequency law the gamma distribution is applied to describe the distribution of seismic moments of earthquake sequences this distribution which generalizes the well known gutenberg richter g r relation is characterized by two parameters we use the maximum likelihood method to determine the parameters of the gamma distribution for worldwide earthquakes in different depth ranges the empirical distribution is derived from the moment tensor catalogue compiled by the harvard group the p value for scalar seismic moment of earthquake sequences an analogue of the 6 value in the g r magnitude frequency law is close to 1 2 for all earthquakes the value predicted by a critical branching model of seismicity this result which will be improved as more seismic moment data become available provides input for modelling of seismicity based on percolation or on self organized criticality models if 3 equals 1 2 then using the critical branching model we find that most small earthquakes in available catalogues are dependent shocks i e aftershocks even among earthquakes of intermediate magnitudes the number of dependent events may exceed that of independent events

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

links between salinity variation in the caribbean and north atlantic thermohaline circulation variations in the strength of the north atlantic ocean thermohaline circulation have been linked to rapid climate changes1 during the last glacial cycle through oscillations in north atlantic deep water formation and northward oceanic heat flux2 3 4 the strength of the thermohaline circulation depends on the supply of warm salty water to the north atlantic which after losing heat to the atmosphere produces the dense water masses that sink to great depths and circulate back south2 here we analyse two caribbean sea sediment cores combining mg ca palaeothermometry with measurements of oxygen isotopes in foraminiferal calcite in order to reconstruct tropical atlantic surface salinity5 6 during the last glacial cycle we find that caribbean salinity oscillated between saltier conditions during the cold oxygen isotope stages 2 4 and 6 and lower salinities during the warm stages 3 and 5 covarying with the strength of north atlantic deep water formation7 at the initiation of the bolling allerod warm interval caribbean surface salinity decreased abruptly suggesting that the advection of salty tropical waters into the north atlantic amplified thermohaline circulation and contributed to high latitude warming

the arid humid transition in the sahara and the sahel during the last deglaciation at the time of the last glacial maximum the sahara and sahel regions of north africa were extremely dry new records of rainfall show that during the subsequent deglaciation the transition from arid to humid conditions in these regions occurred synchronously in two main steps comparison with other records of palaeoclimate in europe and the north atlantic ocean shows that certain common factors controlled changes in ocean and atmosphere dynamics during the deglaciation

the preboreal climate reversal and a subsequent solar forced climate shift accurate chronologies are essential for linking palaeoclimate archives carbon 14 wiggle match dating was used to produce an accurate chronology for part of an early holocene peat sequence from the borchert the netherlands following the younger dryas preboreal transition two climatic shifts could be inferred around 11 400 cal yr bp the expansion of birch betula forest was interrupted by a dry continental phase with dominantly open grassland vegetation coeval with the pbo preboreal oscillation as observed in the grip ice core at 11 250 cal yr bp a sudden shift to a humid climate occurred this second change appears to be contemporaneous with i a sharp increase of atmospheric c 14 ii a temporary decline of atmospheric co2 and iii an increase in the grip be 10 flux the close correspondence with excursions of cosmogenic nuclides points to a decline in solar activity which may have forced the changes in climate and vegetation at around 11 250 cal yr bp copyright c 2004 john wiley sons ltd

the midsummer drought over mexico and central america abstract the annual cycle of precipitation over the southern part of mexico and central america exhibits a bimodal distribution with maxima during june and september october and a relative minimum during july and august known as the midsummer drought msd the msd is not associated with the meridional migration of the intertropical convergence zone itcz and its double crossing over central america but rather with fluctuations in the intensity and location of the eastern pacific itcz during the transition from intense to weak weak to intense convective activity the trade winds over the caribbean strengthen weaken such acceleration in the trade winds is part of the dynamic response of the low level atmosphere to the magnitude of the convective forcing in the itcz the intensification of the trade winds during july and august and the orographic forcing of the mountains over most of central america result in maximum precipitation along the caribbean coast and minimum precipitation along the pacific

ecosystem responses to climate and disturbances in western central mexico during the late pleistocene and holocene abstract central mexico is a complex area with late quaternary volcanic activity climatic diversity and a long history of human occupation pollen microcharcoal and magnetic susceptibility analyses of two sedimentary sequences from lake zirahuen in western central mexico spanning the last 17 000 years provide evidence of a highly dynamic environment during the late glacial pinus forest developed around the lake indicating cold and dry conditions during the last deglaciation climatic amelioration was recorded at 13 5 ka driving a strong and rapid change in vegetation composition and increase in lake levels from the latest pleistocene to early holocene a hiatus probably related to an erosive event is recognized in the northern sequence the central sequence spans the entire holocene and reveals three periods of important ecological changes during the early holocene a first episode between 9 5 and 9 0 ka with a decrease in pine forest seems to have been associated with summer insolation increases a second peak of forest change at 8 2 ka and was probably associated with the cold oscillation documented in the north atlantic a third abrupt change was evident from 7 5 to 7 1 ka with an anomalous plant community related to wetter holocene climates and possible to a volcanic event an episode of dry conditions was recorded from 4 5 to 4 2 ka which was related to an increase in enso activity human influence over the landscape was evident from 3 5 ka to the present the zirahuen records offer a complex history of a landscape characterized by short and long term vegetation changes associated with factors ranging from global climate to local disturbances

stochastic synthesis of earthquake catalogs a model of earthquake occurrence is proposed that is based on results of statistical studies of earthquake catalogs we assume that each earthquake generates additional a probability that depends on time as t 1 this assumption together with one regarding the independence of branching events on adjacent branches of the event tree is sufficient to permit the generation of complete catalogs of earthquakes that have the same time magnitude statistical properties as real earthquake catalogs if is about 0 5 the process generates sequences that have statistical properties similar to those for shallow earthquakes many well known relations are reproduced including the magnitude frequency law omori s law of the rate of aftershock and foreshock occurrence the duration of a recorded seismic event versus its magnitude the self similarity or lack of scale of rate of earthquake occurrence in different magnitude ranges etc a value of closer to 0 8 or 0 9 seems to simulate the statistical properties of intermediate and deep shocks a formula for seismic risk prediction is proposed and the implications of the model for risk evaluation are outlined the possibilities of the determination of long term risk from real or synthetic catalogs that have the property of self similarity are dim

trench curvature and deformation of the subducting lithosphere summary the subduction of oceanic lithosphere is generally accompanied by downdip and lateral deformation the downdip component of strain is associated with external forces that are applied to the slab during its sinking namely the gravitational force and the mantle resistance to penetration here we present theoretical arguments showing that a tectonic plate is also subject to a predictable amount of lateral deformation as a consequence of its bending along an arcuate trench zone independently from the long term physical processes that have determined the actual curvature of the subduction zone in particular we show that the state of lateral strain and the lateral strain rate of a subducting slab depend from geometric and kinematic parameters such as trench curvature dip function and subduction velocity we also demonstrate that the relationship between the state of lateral strain in a subducting slab and the geometry of bending at the corresponding active margin implies a small component of lateral shortening at shallow depths and may include large extensional lateral deformation at intermediate depths whereas a state of lateral mechanical equilibrium can only represent a localized exception our formulation overcomes the flaws of the classic ping pong ball model for the bending of the lithosphere at subduction zones which lead to severe discrepancies with the observed geometry and style of deformation of the modern subducting slabs a study of the geometry and seismicity of eight modern subduction zones is performed to assess the validity of the theoretical relationship between trench curvature slab dip function and lateral strain rate the strain pattern within the eight present day slabs which is reconstructed through an analysis of harvard cmt solutions shows that tectonic plates cannot be considered as flexible inextensible spherical caps whereas the lateral intraslab deformation which is accommodated through seismic slip can be explained in terms of deviations from the mechanical equilibrium

quantification of soil erosion rates related to ancient maya deforestation we used seismic and sediment core data to quantify soil erosion rates for the past 6000 yr in the closed catchment of lake salpeten in the tropical lowlands of northern guatemala the region was affected by ancient maya land use from before ca 1000 b c to a d 900 this period of human impact coincided with deposition in the lake of a detrital unit maya clay as much as 7 m thick that contrasts sharply with the relatively organic rich gyttja deposited both before and after maya occupation of the watershed the greatest soil loss with mean sustained values of 1000 t km2yr 1 occurred in the middle and late preclassic periods 700 b c to a d 250 associated with relatively low maya population densities soil erosion slowed during the period of maximum population density in the late classic period a d 550 830 indicating a decoupling between human population density and soil erosion rate the most rapid soil loss occurred early during initial land clearance suggesting that even low numbers of people can have profound impacts on lowland tropical karst landscapes

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

seismicity rate immediately before and after main shock rupture from high frequency waveforms in japan 1 we analyze seismicity rate immediately before and after 82 main shocks with the magnitudes ranging from 3 to 5 using waveforms recorded by the hi net borehole array in japan by scrutinizing high frequency signals we detect 5 times as many aftershocks in the first 200 s as in the japan meteorological agency catalogue after correcting for the changing completeness level immediately after the main shock the aftershock rate shows a crossover from a slower decay with an omori s law exponent p 0 58 0 08 between 20 and 900 s after the main shock to a faster decay with p 0 92 0 04 after 900 s the foreshock seismicity rate follows an inverse omori s law with p 0 73 0 08 from several tens of days up to several hundred seconds before the main shock the seismicity rate in the 200 s immediately before the main shock appears steady with p 0 35 0 50 these observations can be explained by the epidemic type aftershock sequence etas model and the rate and state model for a heterogeneous stress field on the main shock rupture plane alternatively nonseismic stress changes near the source region such as episodic aseismic slip or pore fluid pressure fluctuations may be invoked to explain the observation of small p values immediately before and after the main shock

stochastic model of earthquake fault geometry summary an earthquake fault pattern is assumed to consist of a system of infinitesimal elementary dislocation loops after an initial dislocation subsequent ruptures occur according to a critical branching process the position of each secondary dislocation loop is randomly shifted along the initial fault plane from the location of the main shock in addition the orientations of the fault plane and slip vector of the secondary dislocations are rotated according to a three dimensional cauchy distribution which has one intrinsic scaling parameter in their turn the secondary dislocations produce new dependent shocks according to the same law the process cascades indefinitely we simulate an earthquake fault system by the monte carlo method this fault pattern is both visually and statistically similar to real earthquake faults the model yields statistical spatial distributions that correspond to those of the analysis of the catalogue data of real earthquakes we incorporate in our scheme the time magnitude model of earthquake occurrence developed earlier by the monte carlo method we then simulate synthetic sequences that reproduce all known magnitude space time statistical properties of real earthquake catalogues the results of these simulations make us question the suitability of some terms that are commonly used in the theory of an earthquake source for example as a consequence of the validity of the stochastic model the concepts like an individual earthquake fault plane or fault surface crack tip or fault tip and friction do not have an unambiguous definition

fractal approach in modelling of earthquakes a model for an earthquake simulation is proposed with the use of a fractal approach multiple generation and coalescence of shear faults in stochastic brittle media modelled as a 2d lattice are considered to be a source of seismicity dynamics of local failure events are governed by accumulation of shear defects described in terms of continuum damage mechanics fractal tree structure is used as an analogue for a stress redistribution process energy release caused by the non uniform failure is studied for a non conservative case effect of various types of rocks properties stochasticity on energy release dynamics is analysed with a utilization of multifractal formalism the latter is shown to be an additional method for seismicity characterization

calcite raft geochemistry as a hydrological proxy for holocene aquifer conditions in hoyo negro and ich balam sac actun cave system quintana roo mexico abstract two cores from calcite rafts deposits located in cenote ich balam and hoyo negro were dated and analyzed for 87sr 86sr 18o 13c sr ca and cl ca the geochemical records show changing aquifer salinity spanning the last 8 5 cal kyrs bp and interrelationships with holocene climate trends wet and dry periods during the wet mid holocene the salinity of the meteoric water mass wm at 7 8 8 3 cal kyrs bp was relatively high at 1 5 2 7 ppt and then became less saline 1 0 1 5 ppt during the last 7000 yrs as climate became progressively drier high salinity of the meteoric wm during the wet mid holocene is attributed to increased turbulent mixing between the meteoric and underlying marine wm increased precipitation in terms of amount frequency and intensity e g hurricanes causes higher flow of meteoric water towards the coast and mixing at the halocline a phenomenon recorded with recent instrumental monitoring of the aquifer conversely during dry periods reduced precipitation and flow in the meteoric wm would result in lower salinity karst properties and holocene sea level rise also seem to have an effect on the aquifer when the regionally extensive network of shallow cave passages 10 12 m water depth are flooded at 8000 cal yrs bp there is a rapid shift in salinity this study demonstrates that calcite raft deposits can be used as paleo environmental recorders documenting the effects of sea level and climate change on aquifer condition

glacial meltwater cooling of the gulf of mexico gcm implications for holocene and present day climates an atmospheric general circulation model the ncar ccm has been used to investigate the possible effects that reduced gulf of mexico sea surface temperatures sst could have on regional and hemispheric climates 18o records and terrestrial evidence indicate at least two major glacial meltwater discharges into the gulf of mexico subsequent to the last glacial maximum it is probable that these discharges reduced gulf of mexico sst we have conducted three numerical experiments with imposed gulf wide sst coolings of 3 c 6 c and 12 c and find in all three experiments significant reductions in the north atlantic storm track intensity along with a strong decrease in transient eddy water vapor transport out of the gulf of mexico surface pressures are higher over the north atlantic indicating a reduction of the climatological icelandic low the region is generally cooler and drier with a reduction in precipitation that agrees well with evidence from greenland ice cores other statistically significant changes occur across the northern hemisphere but vary between the three experiments in particular warmer wetter conditions are found over europe for both the 6 c and 12 c sst reductions but cooler conditions are found for the 3 c reduction this indicates a dependence in both the sign and magnitude of the model response on the magnitude of the imposed sst anomaly the results suggest that the present day north atlantic storm track is dependent on warm gulf of mexico sst for much of its intensity they also suggest that meltwater induced coolings may help account in part for some of the climatic oscillations that occurred during the last glacial interglacial transition

causes and timing of the 8200 yr bp event inferred from the comparison of the grip be 10 and the tree ring delta c 14 record we analyse the 8200 yr bp cold event by comparing the high resolution be 10 record from the grip ice core from central greenland with the well known tree ring delta 14 c record by transferring the absolute dated tree ring chronology to the ice core time scale we show that the coldest phase in the grip record occurred around 8150 yr bp furthermore this method allows us to disentangle production and climate effects on be 10 and c 14 with important implications for the reconstruction of past solar activity and changes in the carbon cycle and be 10 transport we show that in principle it is possible to infer changes in ocean circulation by comparing be 10 and c 14 records however the duration of the 8200 yr bp event is too short to assign unambiguously a significant change in atmospheric c 14 concentration to changes in the global ocean circulation based on the comparison of be 10 with climate records one could argue that the 8200 yr bp cold event is triggered by a change towards lower solar activity however this link is questioned by the fact that around this period there are other similar and even stronger changes in solar activity that have no apparent connection to climate changes c 2004 elsevier ltd all rights reserved less

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

terminal classic drought in the northern maya lowlands inferred from multiple sediment cores in lake chichancanab mexico we present new density records from sediment cores taken along a depth transect in lake chichancanab mexico the data reveal in great detail the climatic events that comprised the terminal classic drought tcd and coincided with the demise of classic maya civilization between ca 750 and 1050 ad in shallow water cores the tcd is marked by a condensed gypsum horizon in deeper water sections it is expanded and represented by numerous interbedded gypsum and organic rich strata the tcd was not a single two century long megadrought but rather consisted of a series of dry events separated by intervening periods of relatively moister conditions we estimate the tcd occurred between ca 770 and 1100 ad and included an early phase ca 770 870 ad and late phase ca 920 1100 ad the intervening 50 year period ca 870 920 ad was relatively moister each dry phase is represented by multiple gypsum density bands interbedded with organic rich sediment that indicate alternating dry and wet conditions spectral analysis revealed significant periods around 213 50 and 27 years despite uncertainty regarding the ages of these events their pattern is robust and generally consistent with other proxy records under the same climate regime such as the marine cariaco basin off northern venezuela science 299 2003 1731

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

rate and processes of river network rearrangement during incipient faulting the case of the cahabon river guatemala deeply incised river networks are generally regarded as robust features that are not easily modified by erosion or tectonics although the reorganization of deeply incised drainage systems has been documented the corresponding importance with regard to the overall landscape evolution of mountain ranges and the factors that permit such reorganizations are poorly understood to address this problem we have explored the rapid drainage reorganization that affected the cahabon river in guatemala during the quaternary sediment provenance analysis field mapping and electrical resistivity tomography ert imaging are used to reconstruct the geometry of the valley before the river was captured dating of the abandoned valley sediments by the be 10 al 26 burial method and geomagnetic polarity analysis allow us to determine the age of the capture events and then to quantify several processes such as the rate of tectonic deformation of the paleovalley the rate of propagation of post capture drainage reversal and the rate at which canyons that formed at the capture sites have propagated along the paleovalley transtensional faulting started 1 to 3 million years ago produced ground tilting and ground faulting along the cahabon river and thus generated differential uplift rate of 0 3 0 1 up to 0 7 0 4 mm y 1 along the river s course the river responded to faulting by incising the areas of relative uplift and depositing a few tens of meters of sediment above the areas of relative subsidence then the river experienced two captures and one avulsion between 700 ky and 100 ky the captures breached high standing ridges that separate the cahabon river from its captors captures occurred at specific points where ridges are made permeable by fault damage zones and or soluble rocks groundwater flow from the cahabon river down to its captors likely increased the erosive power of the captors thus promoting focused erosion of the ridges valley fill formation and capture occurred in close temporal succession suggesting a genetic link between the two we suggest that the aquifers accumulated within the valley fills increased the head along the subterraneous system connecting the cahabon river to its captors and promoted their development upon capture the breached valley experienced widespread drainage reversal toward the capture sites we attribute the generalized reversal to combined effects of groundwater sapping in the valley fill axial drainage obstruction by lateral fans and tectonic tilting drainage reversal increased the size of the captured areas by a factor of 4 to 6 at the capture sites 500 m deep canyons have been incised into the bedrock and are propagating upstream at a rate of 3 to 11 mm y 1 deepening at a rate of 0 7 to 1 5 mm y 1 at this rate 1 to 2 million years will be necessary for headward erosion to completely erase the topographic expression of the paleovalley it is concluded that the rapid reorganization of this drainage system was made possible by the way the river adjusted to the new tectonic strain field which involved transient sedimentation along the river s course if the river had escaped its early reorganization and had been given the time necessary to reach a new dynamic equilibrium then the transient conditions that promoted capture would have vanished and its vulnerability to capture would have been strongly reduced

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

a late holocene paleoenvironmental reconstruction from agua caliente southern belize linked to regional climate variability and cultural change at the maya polity of uxbenka abstract we report high resolution macroscopic charcoal pollen and sedimentological data for agua caliente a freshwater lagoon located in southern belize and infer a late holocene record of human land use climate interactions for the nearby prehistoric maya center of uxbenka land use activities spanning the initial clearance of forests for agriculture through the drought linked maya collapse and continuing into the historic recolonization of the region are all reflected in the record human land alteration in association with swidden agriculture is evident early in the record during the middle preclassic starting ca 2600 cal yr bp fire slowly tapered off during the late and terminal classic consistent with the gradual political demise and depopulation of the uxbenka polity sometime between ca 1150 and 950 cal yr bp during a period of multiple droughts evident in a nearby speleothem record fire activity was at its lowest during the maya postclassic ca 950 430 cal yr bp but rose consistent with increasing recolonization of the region between ca 430 cal yr bp and present these data suggest that this environmental record provides both a proxy for 2800 years of cultural change including colonization growth decline and reorganization of regional populations and an independent confirmation of recent paleoclimate reconstructions from the same region

man made changes of seismicity rates seismicity catalogs contain important information about processes which occur in seismically active regions of the earth many authors have examined these catalogs for patterns and variations in patterns which might reflect changes in these processes we have found that these catalogs include a complex mixture of real and man made changes one must identify and account for the man made changes before the real ones can be identified and understood many man made changes in seismicity catalogs are manifested as changes in seismicity rates and can therefore be identified through careful examination of these rates obvious effects include increases or decreases in the detection and reporting of smaller events which accompany the installation or closure of seismic stations these types of changes can be recognized by examining the distribution of seismicity rate changes in the magnitude domain they are characterized by increases or decreases in the number of small events in the catalog at times when the number of larger events remains constant systematic changes in the magnitudes assigned to events can also be identified by examining seismicity rates because they cause apparent changes in rates of data sets with magnitude cutoffs the sign of the apparent rate change depends on the sign of the magnitude change and the type of cutoff used the effects of detection changes can be easily remedied by using a magnitude cutoff which eliminates the smaller events from consideration the techniques we have developed allow one to determine the optimum cutoff magnitude corrections are necessary for remedying the effects of systematic changes in magnitude estimates these corrections can be determined through modeling of observed rate changes caused by these shifts man made changes are present in all seismicity catalogs whether local regional or teleseismic they must be accounted for if these catalogs are to provide meaningful information on real process changes in the earth

millennial scale climate variability during the last 12 5 ka recorded in a caribbean speleothem abstract we present a speleothem stable oxygen isotope record for the last 12 5 ka based on two stalagmites from western cuba the 18o signal is interpreted to represent past precipitation variability both stalagmites show a pronounced transition from higher 18o values indicating drier conditions to more negative 18o values suggesting wetter conditions between 10 and 6 ka this transition is also visible in a planktonic 18o record off haiti on orbital timescales the 18o value of caribbean precipitation thus strongly resembles the oxygen isotope composition of caribbean surface water on millenial timescales the speleothem 18o record shows a high correlation to a north atlantic sea surface temperature sst record off west africa as well as a similarity with the bond events periods of lower north atlantic sst correspond to less precipitation in the caribbean and vice versa the potential teleconnection to the caribbean may reflect the position of the intertropical convergence zone because a further southward position of the itcz leads to reduced precipitation in the northern caribbean

dynamics and scaling characteristics of shear crack propagation a model for a description of a shear crack fault propagation is proposed on the basis of the unification of continuum damage and fracture mechanics with ideas of fracture models for random media energy release linked with local failures of elements as a result of evolution of fracture processes at lower scale levels stimulated by the stress concentration in the vicinity of the fault is treated as a seismicity source 2d simulations are performed for analysis of the effect of the size of pre existing fault on characteristic features of rupture evolution scaling including multifractal character of crack propagation and of respective energy release is shown

a 10 300 14c yr record of climate and vegetation change from haiti abstract pleistocene and holocene vegetation dynamics in the american tropics are inferred largely from pollen in continental lake sediments maritime influences may have moderated climate and vegetation changes on caribbean islands stable isotope 18 o study of a 7 6 m core from lake miragoane haiti provided a high resolution record of changing evaporation precipitation e p since 10 300 14 c yr b p the miragoane pollen record documents climate influences and human impacts on vegetation in hispaniola the 18 o and pollen data near the base of the core indicate cool dry conditions before 10 000 14 c yr b p lake miragoane filled with water in the early holocene as e p declined and the freshwater aquifer rose despite increasing early holocene moisture shrubby xeric vegetation persisted forest expanded 7000 14 c yr b p in response to greater effective moisture and warming the middle holocene 7000 3200 14 c yr b p was characterized by high lake levels and greatest relative abundance of pollen from moist forest taxa climatic drying that began 3200 14 c yr b p may have driven some mesophilic animal species to extinction the pollen record of the last millennium reflects pre columbian taino and european deforestation long term holocene vegetation trends in southern haiti are comparable to trends from continental lowland circum caribbean sites suggesting a common response to regional climate change

evidence of bias in estimations of earthquake size magnitudes of earthquakes determined using traditional methods show systematic deviations dependent on tectonic setting from accurate estimates of earthquake size magnitudes are overestimated for most of the continental earthquakes underestimated for mid oceanic ridges and differences of varying sign are obtained for subduction zones this is important in evaluating the seismic risk or consideration of effects such as the seismic versus aseismic strain release as seismic moments determined from magnitudes can be wrong by as much as a factor of four

climate change in lowland central america during the late deglacial and early holocene the transition from arid glacial to moist early holocene conditions represented a pro found change in northern lowland neotropical climate here we report a detailed record of changes in moisture availability during the latter part of this transition 11 250 to 7500 cal yr bp inferred from sediment cores retrieved in lake peten itza northern guatemala pollen assemblages demon strate that a mesic forest had been largely established by 11 250 cal yr bp but sediment properties indicate that lake level was more than 35 m below modern stage from 11 250 to 10 350 cal yr bp during the preboreal period lithologic changes in sediments from deep water cores 50 m below modern water level indicate several wet dry cycles that suggest distinct changes in effective moisture four dry events designated pbe1 4 occurred centred at 11 200 10 900 10 700 and 10 400 cal yr bp and correlate with similar variability observed in the cariaco basin titanium record and glacial meltwater pulses into the gulf of mexico after 10 350 cal yr bp multiple sediment proxies suggest a shift to a more persistently moist early holocene climate comparison of results from lake peten itzawith other records from the circum caribbean demonstrates a coherent climate response during the entire span of our record furthermore lowland neotropical climate during the late deglacial and early holocene period appears to be tightly linked to climate change in the high latitude north atlantic we speculate that the observed changes in lowland neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the intertropical convergence zone and azores bermuda high pressure system this mechanism operated on millennial to submillennial timescales and may have responded to changes in solar radiation glacial meltwater north atlantic sea ice and the atlantic meridional overturning circulation moc copyright 2005 john wiley sons ltd

a 2000 year record of caribbean and tropical north atlantic hydrographic variability 1 here we present near annually resolved oxygen isotope records from two species of planktic foraminifera from the cariaco basin that reflect sea surface temperature sst and intertropical convergence zone itcz precipitation related salinity variations over the caribbean and tropical north atlantic spanning the last 2000 years a strong broad spatial pattern of correlation exists between foraminiferal 18o and ssts over the period of instrumental overlap but the correlations weaken as they are extended back in time and instrumental sst records become discontinuous a long term trend in the globigerinoides ruber 18o record can be explained by two different but equally plausible scenarios first the increase in 18o may indicate that tropical summer fall ssts have cooled by as much as 2 c over the last 2000 years possibly as a result of a long term increase in upwelling intensity alternately comparisons to other studies of itcz and regional evaporation precipitation variability suggest that much of the 18o record is influenced by decadal to centennial scale variations in the mean annual position of the itcz and associated rainfall patterns similarities between the g bulloides 18o record and the 11 year sunspot cycle support prior studies that suggest solar variability plays a role in influencing the hydrologic balance of the circum caribbean

the preboreal oscillation around the nordic seas terrestrial and lacustrine responses the occurrence of an early preboreal climatic cooling oscillation pbo in lacustrine and glacial records from northwest europe iceland and greenland is reviewed and documented the often subtle response of the proxy records to this oscillation in combination with its short duration make it difficult to detect owing to its chronostratigraphic position between the 10 000 9900 and 9600 9500 14 c plateaux c 11 300 11 150 calendar yr bp it is also difficult to 14 c date with precision we find that the vegetation response to the pbo varies between sites and regions in contrast to the pioneer vegetation in iceland and southern sweden the expanding birch pine forest in germany denmark was more susceptible to deteriorating growing conditions the combined lacustrine tree ring and glacial records imply that the pbo was characterised by cool and humid conditions throughout northwestern and central europe this is documented by vegetation changes decreased aquatic production increased soil erosion increased 2 h and 13 c content in tree rings readvances or stillstands of the ice sheet in norway and finland and ingression of brackish water into the baltic icelandic proxy records from lake sediments and glacial moraines imply cooler conditions than during the previous preboreal period but not as extreme as during the younger dryas greenland records suggest that the early preboreal was characterised by ice readvances as an effect of cool climate and increased precipitation in relation to the younger dryas it was not until the end of the pbo that climate was warm enough to melt the land based ice sheet this preboreal oscillation found on both sides of the nordic seas is interpreted as an effect of increased freshwater forcing on the thermohaline circulation in the nordic seas which is implied by a simultaneous and distinct rise in the atmospheric 14 c 12 c ratio a slow down of the thermohaline circulation may tempor arily have pushed the polar front further south 1997 by john wiley sons ltd preboreal oscillation thermohaline circulation lacustrine records glacial records chronology

meltwater cooling of the gulf of mexico a gcm simulation of climatic conditions at 12 ka marine and terrestrial evidence indicate that at least two major glacial meltwater discharges into the gulf of mexico occurred during the last deglaciation based on radiocarbon dates the time interval between these two meltwater events appears to coincide with the younger dryas roughly 10 11 ka we have used an atmospheric general circulation model the national center for atmospheric research community climate model version 1 ncar ccm1 to investigate possible effects of reduced gulf of mexico sea surface temperatures sst assumed due to the meltwater discharges on regional and hemispheric climates we conducted six numerical experiments 1 perpetual january wintertime and 2 july summertime sensitivity experiments using present day boundary conditions except for an imposed gulfwide sst cooling of 6 c 3 perpetual january and 4 july control simulations using 12 ka boundary conditions for continental ice sea surface temperature no reduction due to meltwater cooling sea ice and radiative forcing and 5 perpetual january and 6 july 12 ka simulations with a 6 c sst cooling of the gulf of mexico in both of the january simulations with a cooled gulf of mexico a significant reduction in the north atlantic storm track intensity occurred with higher surface pressures over the north atlantic indicating a reduction of the icelandic low in the january 12 ka control there are large changes in surface pressure over the atlantic ocean and greenland relative to the present day control however these changes are almost completely offset when the gulf of mexico is cooled in the july simulations with a cool gulf of mexico the atlantic subtropical high is strengthened and expanded to the west this results in stronger trade winds across the caribbean and southwest atlantic there is also an enhanced monsoonal flow of moisture over northwest mexico and the american southwest and rocky mountain regions leading to increased precipitation unlike the winter situation in summer the gulf of mexico cooling serves to enhance the effects of the other 12 ka boundary conditions

a 43 ka record of paleoenvironmental change in the central american lowlands inferred from stable isotopes of lacustrine ostracods we present a continuous ostracod isotope 18o and 13c record from lake peten itza peten guatemala in the northern lowland neotropics that spans the last 43 cal ka bp variations in oxygen and carbon isotopes closely follow lithologic variations which consist of alternating gypsum and clay deposits that were deposited under relatively dry and wet climate respectively during the last glacial period the greatest 18o and 13c values coincide with gypsum deposited during lake lowstands under arid climate conditions that were correlated previously with north atlantic heinrich events in contrast interstadials and the entirety of the last glacial maximum 24 19 cal ka bp are marked by clay deposition and lower 18o and 13c values reflecting higher lake levels and relatively moister climate isotope results and pollen data along with independently inferred past water levels show the early deglacial period 19 15 cal ka bp was the time of greatest aridity and lowest lake stage of the past 43 ka this period occurred during heinrich stadial 1 hs 1 when an extensive tropical megadrought has been postulated stager et al 2011 heinrich stadial 1 is represented by two episodes of gypsum precipitation and high 18o and 13c values in peten itza interrupted by an intervening period of lower 18o and 13c and clay deposition centered on 17 cal ka bp the two periods of inferred maximum cold and or arid conditions at 17 5 and 16 1 cal ka bp coincide approximately with two pulses of ice rafted debris ird recorded off southern portugal bard et al 2000 at 15 cal ka bp coinciding with the start of the bolling allerod period 18o and 13c decrease and gypsum precipitation ceases indicating a transition to warmer and or wetter conditions gypsum precipitation resumed while 18o and 13c increased at the start of the younger dryas at 13 1 cal ka bp and continued until 10 4 cal ka bp near the onset of the holocene precipitation changes during the last glacial period in the northern hemisphere neotropics were closely linked with freshwater forcing to the high latitude north atlantic and sensitive to changes in the location of meltwater input climate was coldest driest when meltwater directly entered the high latitude north atlantic permitting sea ice expansion and weakening of atlantic meridional overturning circulation amoc which resulted in a more southerly position of the intertropical convergence zone itcz upon deglaciation when meltwater was directed to the gulf of mexico at 17 ka and during the bolling allerod period 15 13 ka precipitation increased in the northern hemisphere neotropics as north atlantic sea ice retreated and the itcz shifted northward results from lake peten itza offer some support for the meltwater routing hypothesis of clark et al 2001

some results of the experimental study of seismic anisotropy of sedimentary rocks using different types of waves summary the presence of anisotropy has been established and its parameters have been estimated by the combined use of compressional and shear sh and sv waves anisotropy has been studied in argillaceous and carbonate rocks to a depth of 2 km by combined surface and borehole observations along longitudinal and non longitudinal vertical lines with linear shot lines anisotropy in carbonate rocks has been found to be a function of their heterogeneity ordered fracturing and the amount of clay the highest anisotropy has been found in argillaceous rocks irrespective of their depth and degree of heterogeneity

stable isotope values δ18o δ13c of multiple ostracode species in a large neotropical lake as indicators of past changes in hydrology abstract modern lake hydrodynamics ostracode species autecology stable isotopes 18 o and 13 c of multiple ostracode species ostracode taphonomy and sediment geochemistry were studied to improve interpretation of the late pleistocene early holocene 24 10 ka stable isotope record of ostracodes in sediment core pi 6 from lago peten itza northern guatemala oxygen and carbon stable isotopes in modern and fossil species assemblages of lago peten itza were used as indicators of changes in the balance between evaporation and precipitation past lake level and carbon source ostracode taphonomy was used to detect past periods of strong currents high energy environments and possible partial or full mixing of the lake the modern lake water isotopic composition displays clear seasonal differences that are independent of lake level fluctuations modern benthic species displayed lower 18 o and 13 c values than nektobenthic species with differences of 3 0 and 5 3 respectively valves of nektobenthic species display higher values of 13 c because these ostracodes live in shallower environments among abundant algae and aquatic plants where productivity is high the benthic species limnocythere opesta brehm 1939 displayed the smallest average offset from 18 o water 0 3 and the largest offset from 13 c dic values 4 1 among studied ostracode species nektobenthic species heterocypris punctata keyser 1975 displayed the smallest difference relative to the 13 c dic values 0 1 late pleistocene early holocene climate conditions and water levels in lago peten itza can be summarized as follows 1 high lake levels and cold conditions last glacial maximum lgm 24 19 ka 2 fluctuating lake levels and cold conditions heinrich stadial 1 hs1 19 15 ka 3 high lake levels and warm and wetter conditions bolling allerod ba 15 13 ka 4 low lake levels and dry conditions younger dryas yd 13 11 5 ka and 5 high lake levels and warm and wetter conditions early holocene 11 5 10 0 ka average lake level fluctuation in lago peten itza during the late pleistocene early holocene was as much as 25 m ostracode analyses suggest that the lgm was characterized by relatively low 18 o 4 7 to 6 0 and 13 c values 7 1 to 6 4 in ostracode valves high inferred water depths and high percentages of broken adult and juvenile valves 66 suggesting a high energy environment strong currents partial to full mixing downslope transport colder water temperatures and wetter conditions an increase in the relative abundance of the benthic species l opesta and higher numbers of broken valves suggest heavy precipitation events during the lgm 23 7 21 7 20 8 and 20 1 ka hs1 was predominantly dry but we identified times when lake levels were slightly higher at the onset of the deglacial and a brief period 17 16 ka between hs1b and hs1a all studied climate proxies indicate wetter and warmer conditions and lake system stability during the ba lake levels dropped during the yd and gradually increased during the preboreal and early holocene we demonstrate that modern and fossil ostracode isotopic signatures species assemblages and taphonomy can be used together with physical and geochemical variables in lago peten itza sediments to make high resolution inferences about late pleistocene early holocene environmental changes in the lowland neotropics

recovery of the forest ecosystem in the tropical lowlands of northern guatemala after disintegration of classic maya polities we employed paleolimnological methods to investigate tropical forest recovery and soil stabilization that followed abandonment of agricultural systems associated with disintegration of classic maya polities ca a d 800 1000 we used lithological geochemical magnetic and palynological data from sediment cores of lake peten itza in the maya lowlands of northern guatemala sediment core chronology was developed using radiocarbon dates on terrestrial wood and charcoal fragments our results indicate that in the absence of large human populations and extensive farming activities peten forests recovered under humid climate conditions within a span of 80 260 yr soil stabilization postdates pollen evidence of forest regrowth stratigraphically and required between 120 and 280 yr we conclude that the tropical forest ecosystem in the watershed of lake peten itza had been reestablished by the early postclassic period a d 1000 1200

palaeomagnetic secular variation and rock magnetic studies of holocene sediments from a maar lake hoya de san nicolas in central mexico summary three up to 520 cm long sediment cores from hoya san nicolas in guanajuato mexico were analysed for various magnetic properties in order to better define a palaeomagnetic secular curve for central mexico the results magnetic susceptibility hysteresis cycles anhysteretic and isothermal remanent magnetization suggest that the remanent magnetization of the sediments is controlled by ferrimagnetic minerals pseudo single domain magnetite which are suitable recorders of the geomagnetic field the age depth model indicates average deposition rates of 0 32 interval 146 198 cm and 0 45 mm yr 1 interval 200 520 cm and a basal age of about 11 600 calibrated years bp cal yr bp we used magnetic susceptibility and natural remanent magnetization to correlate the three cores a composite palaeomagnetic secular variation sv record was obtained from the cores with a stretching and stacking process and a chronology established with accelerator mass spectrometer dates on microscopic charcoal and stratigraphic correlations with other well dated holocene records from mexico and guatemala the declination and inclination results show oscillatory behaviour varying in a narrow range although a distinctive directional swing is evident between 9060 and 9810 cal yr bp the san nicolas palaeomagnetic sv curve is similar to palaeomagnetic master curves from europe and north america in shape occurrence and synchronicity of directional features especially with respect to inclination

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

late quaternary climate induced lake level variations in lake peten itza guatemala inferred from seismic stratigraphic analysis abstract we used seismic images and sedimentary data from piston cores to conduct a sequence stratigraphic analysis of sediments in lake peten itza northern guatemala our results document lake level fluctuations in this lowland neotropical region that were related to glacial to interglacial climate change during the late pleistocene a bathymetric survey of lake peten itza area 100 km2 revealed a maximum water depth of 160 m and the existence of a deep cryptodepression that extends 50 m below modern sea level the great depth suggests that the basin held water even during arid conditions associated with full glacial periods lake peten itza may thus possess the only long continuous lacustrine sediment record of late pleistocene environmental and climate change in the lowland neotropics two seismic reflection campaigns imaged the subsurface basin sediments that overlie basement the sediment package was divided into four major seismic sequences t g r and b sequences are separated by unconformities that represent depositional cycles related to lake level fluctuations sediments of the uppermost sequence t were recovered and radiocarbon dated in kullenberg piston cores taken along a water depth transect seismic profiles reveal a basin wide paleoshoreline just below sequence t at 56 m below present lake level this constructional feature formed during a lowstand of the last glacial period when the lake was reduced to only 13 of its present volume in cores taken landward of the paleoshoreline late glacial age deposits consist of paleosols indicating subaerial exposure basinward of the shoreline sediments are composed of dense gypsum sands and interbedded silty clays reflecting authigenic gypsum formation under arid climate conditions the top of the soil horizon and cessation of gypsum precipitation are represented by a strong seismic reflection t it marks the base of the uppermost seismic sequence t and is dated in several cores between 11 1 and 10 2 cal kyr bp lake level rose quickly at this time in response to a shift from arid to humid climate conditions at the late glacial early holocene transition we infer a similar sediment response to climate variations in the older stratigraphic sequences g r and b related to earlier glacial to interglacial and stadial to interstadial cycles older sequences are also distinguished from one another by erosional unconformities that probably represent major lake level falls future recovery of the older stratigraphic record by drilling in lake peten itza will provide ages for these older units and enable us to test the depositional model inferred from seismic stratigraphy

climate change in the circum north atlantic region during the last deglaciation a survey of new and published palaeoclimate data indicates that both the high and low latitude north atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial to interglacial transi tion climate model results suggest that changes in the melting history of the laurentide ice sheet may explain much of this nonlinear response of the climate system to astronomical milankovitch forcing

environmental change in northern belize since the latest pleistocene cores from the new river lagoon in belize have been analysed using a range of palaeolimnological proxies to reconstruct change since the latest pleistocene the combination of diatom and stable isotope analyses supported by mineralogical and major element data indicate that the new river lagoon has been a freshwater system throughout the period of record for most of this time the lagoon has been hydrologically open but there are indications that it may have become closed in the latest pleistocene or very early holocene this may have been associated with a drier climate and lower sea level mid holocene records are consistent with those from elsewhere in the region indicating a stable and moist climate the late holocene was marked by greater variability but there is no clear evidence of any drying in the late classic coincident with the maya collapse ca ad 900 our results indicate that the continuity of occupation at the maya site of lamanai on the shores of the new river lagoon is consistent with continued access to freshwater during periods of regional climatic variability the importance of conditions at individual sites when considering both system response and human vulnerability to climate change is emphasised copyright 2009 john wiley sons ltd

earthquake size distribution power law with exponent beta 1 2 we propose that the widely observed and universal gutenberg richter relation is a mathematical consequence of the critical branching nature of earthquake process in a brittle fracture environment these arguments though preliminary are confirmed by recent investigations of the seismic moment distribution in global earthquake catalogs and by the results on the distribution in crystals of dislocation avalanche sizes we consider possible systematic and random errors in determining earthquake size especially its seismic moment these effects increase the estimate of the parameter beta of the power law distribution of earthquake sizes in particular we find that estimated beta values may be inflated by 1 3 because relative moment uncertainties decrease with increasing earthquake size moreover earthquake clustering greatly influences the beta parameter if clusters aftershock sequences are taken as the entity to be studied then the exponent value for their size distribution would decrease by 5 10 the complexity of any earthquake source also inflates the estimated beta value by at least 3 7 the centroid depth distribution also should influence the beta value an approximate calculation suggests that the exponent value may be increased by 2 6 taking all these effects into account we propose that the recently obtained beta value of 0 63 could be reduced to about 0 52 0 56 near the universal constant value 1 2 predicted by theoretical arguments we also consider possible consequences of the universal beta value and its relevance for theoretical and practical understanding of earthquake occurrence in various tectonic and earth structure environments using comparative crystal deformation results may help us understand the generation of seismic tremors and slow earthquakes and illuminate the transition from brittle fracture to plastic flow

recent kinematics of the tectonic plates surrounding the red sea and gulf of aden this work was funded by the miur prin prot 20125jkany the geodas ship track data used in this study can be found at ngdc http www ngdc noaa gov mgg geodas trackline html

an 8700 year paleoclimate reconstruction from the southern maya lowlands abstract analysis of a sediment core from lago puerto arturo a closed basin lake in northern peten guatemala has provided an 8700 cal year record of climate change and human activity in the southern maya lowlands stable isotope magnetic susceptibility and pollen analyses were used to reconstruct environmental change in the region results indicate a relatively wet early to middle holocene followed by a drier late holocene which we interpret as reflecting long term changes in insolation precession higher frequency variability is more likely attributable to changes in ocean atmosphere circulation in both the north atlantic and the pacific oceans pollen and isotope data show that most of the period of prehispanic agricultural settlement i e 5000 1000 cal yr bp was characterized by drier conditions than previous or subsequent periods the presence of zea corn pollen through peak aridity during the terminal classic period 1250 1130 cal yr bp suggests that drought may not have had as negative an impact as previously proposed a dramatic negative shift in isotope values indicates an increase in precipitation after 950 cal yr bp hereafter bp

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

holocene palaeohydrology and climate variability in northeastern spain the sedimentary record of lake estanya pre pyrenean range abstract this multi proxy study of sediment cores from karstic lake estanya pre pyrenean range ne spain provides the first complete continuous record of the hydrological evolution in the northeastern iberian peninsula over the last 9500 yr six sedimentary facies and four main sedimentary units have been defined after integration of sedimentological mineralogical and geochemical analyses the use of total sulphur content and sedimentary facies as paleohydrological proxies allows reconstruction of relative changes in lake level the estanya record shows a large increase in water availability after 9 2 ka fluctuating lake levels and salinity during the period 9 2 4 2 ka and generally higher lake levels after 1 7 ka periods of increased run off and sediment delivery and less saline conditions occurred at 8 5 8 2 6 7 5 9 and 4 9 4 2 ka dominant lower lake levels and concentrated waters during the period 4 2 0 8 ka were punctuated by a higher lake level higher clastic input episode ca 1 7 1 ka fluctuating but higher lake levels occurred during the last 800 years the main hydrological phases in lake estanya are coherent with western mediterranean and north atlantic holocene reconstructions but they also show similarities with northern african records

statistics of characteristic earthquakes statistical methods are used to test the characteristic earthquake hypothesis several distributions of earthquake size seismic moment frequency relations are described based on the results of other researchers as well as my own tests evidence of the characteristic earthquake hypothesis can be explained either by statistical bias or statistical artifact since other distributions of earthquake size provide a simpler explanation for available information the hypothesis cannot be regarded as proven

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

multistage 8 2 kyr event revealed through high resolution xrf core scanning of cuban sinkhole sediments we use sediments from a flooded sinkhole cenote jennifer in northern cuba to provide new well dated high resolution evidence for the 8 2 kyr event from 7600 to 8700 cal yr b p the sinkhole contained shallow low salinity water which supported a marsh dominated by cattail and grass peaks in cl and br occurring at 8150 8200 and 8250 cal yr b p are attributable to increased evaporation due to regional drying associated with the 8 2 kyr event the three peaks in these elements also closely correspond to the greyscale record from the cariaco basin indicative of increased upwelling in the southern caribbean sea at this time supporting the notion of a multistage 8 2 kyr event our work provides new data that help to clarify the initiation behavior and impacts of the 8 2 kyr event in the northern tropics

the nature of deep focus earthquakes wadati 1928 first proved convincingly that some earthquakes occur at depths well beneath the earth s crust he essentially proposed the nomenclature used today by the international seismological centre isc i e earthquakes with focal depths exceeding 300 km are deep earthquakes and those with depths between 70 and 300 km are intermediate earth quakes however when there is little reason to distinguish between the two groups both types are called simply deep earthquakes to avoid confusion in this paper we refer to those with focal depths exceeding 300 km as very deep earthquakes and those with focal depths between 70 and 300 km as intermediate earthquakes deep earthquakes are of interest for at least four reasons first they are exceedingly common between 1964 and 1986 they constituted no less than 22 of all earthquakes having mb greater than 5 0 in the isc catalog second they most often occur in association with deep ocean trenches and volcanic island arcs in subduction zones one of the great achievements of twentieth century geophysics was the recognition that their occurrence in inclined planar groups or wadati benioff zones apparently delineates the cold down going cores of convection cells in the uppermost mantle third seismologists use body waves of deep earthquakes dispro portionately more often than those of shallow earthquakes to inves tigate core mantle and crustal structure this is because a deep earth quakes often possess relatively more impulsive sources b their body phases traverse the heterogeneous uppermost mantle only once on the ray path from hypocenter to station and c surface waves do not contaminate these body phase arrivals on seismograms finally deep earthquakes are

an 85 ka record of climate change in lowland central america drill cores obtained from lake peten itza peten guatemala contain a 85 kyr record of terrestrial climate from lowland central america that was used to reconstruct hydrologic changes in the northern neotropics during the last glaciation sediments are composed of alternating clay and gypsum reflecting relatively wet and dry climate conditions respectively from 85 to 48 ka sediments were dominated by carbonate clay indicating moist conditions during marine isotope stages mis 5a 4 and early 3 the first gypsum layer was deposited at 48 ka signifying a shift toward drier hydrologic conditions and the onset of wet dry oscillations during the latter part of mis 3 peten climate varied between wetter conditions during interstadials and drier states during stadials the pattern of clay gypsum wet dry oscillations during the latter part of mis 3 48 23 ka closely resembles the temperature records from greenland ice cores and north atlantic marine sediment cores and precipitation proxies from the cariaco basin the most arid periods coincided with heinrich events when cold sea surface temperatures prevailed in the north atlantic meridional overturning circulation was reduced and the intertropical convergence zone itcz was displaced southward a thick clay unit was deposited from 23 to 18 ka suggesting deposition in a deep lake and pollen accumulated during the same period indicates vegetation consisted of a temperate pine oak forest this finding contradicts previous inferences that climate was arid during the last glacial maximum lgm chronozone 21 2 ka at 18 ka peten climate switched from moist to arid conditions and remained dry from 18 to 14 7 ka during the early deglaciation moister conditions prevailed during the warmer bolling allerod 14 7 12 8 ka with the exception of a brief return to dry conditions at 13 8 ka that coincides with the older dryas and meltwater pulse 1a the onset of the younger dryas at 12 8 ka marked the return of gypsum and hence dry conditions the lake continued to precipitate gypsum until 10 3 ka when rainfall increased markedly in the early holocene

microslips as precursors of large slip events in the stick slip dynamics of sheared granular layers a discrete element model analysis 1 we investigate the stick slip behavior of a granular system confined and sheared by deformable solid blocks using three dimensional discrete element method simulations our modeling results show that large slip events are preceded by a sequence of small slip events microslips whose occurrence accelerates exponentially before the large slip event onset microslips exhibit energy release several orders of magnitude smaller than the large slip events the microslip event rate is proposed as a measure of slip activity in the granular gouge layer a statistical analysis shows that microslip event rate correlates well with large slip event onset and that variations in it can be used to predict large slip events the emergence of microslips and their duration are found to be controlled by the value of the slipping contact ratio and are therefore related to the jamming unjamming transition of frictional granular packings citation ferdowsi b m griffa r a guyer p a johnson c marone and j carmeliet 2013 microslips as precursors of large slip events in the stick slip dynamics of sheared granular layers a discrete element model analysis geophys res lett 40 doi 10 1002 grl 50813

depth dependence of earthquake frequency magnitude distributions in california implications for rupture initiation statistics of earthquakes in california show linear frequency magnitude relationships in the range of m2 0 to m5 5 for various data sets assuming gutenberg richter distributions there is a systematic decrease in b value with increasing depth of earthquakes we find consistent results for various data sets from northern and southern california that both include and exclude the larger aftershock sequences we suggest that at shallow depth 0 to 6 km conditions with more heterogeneous material properties and lower lithospheric stress prevail rupture initiations are more likely to stop before growing into large earthquakes producing relatively more smaller earthquakes and consequently higher b values these ideas help to explain the depth dependent observations of foreshocks in the western united states the higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock at greater depth 9 15 km any rupture initiation is more likely to continue growing into a larger event so there are fewer foreshocks if one assumes that frequency magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake then a small m2 rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a m5 5 or larger event compared to the same small rupture initiation at 0 to 3 km

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

bayesian analysis of extreme earthquake occurrences part ii application to the san jacinto fault zone of southern california abstract the bayesian extreme value distribution of earthquake occurrences developed in the first part of this study is tested and applied to the estimation of seismic hazards for the san jacinto fault zone of southern california prior estimates of seismicity are developed from seismotectonic data based on standard seismological relationships among seismic moment slip rate earthquake recurrence rate and magnitude these estimates are then updated using bayes9 theorem and historical estimates of seismicity associated with the san jacinto fault zone bayesian extreme value distributions available from the literature are found either to overestimate exceedance probabilities of earthquake occurrences or require more complex computations as compared to the distribution proposed in this study on the other hand the conventional extremevalue distribution of earthquake occurrences first proposed by epstein and lomnitz 1966 was found to give results consistent with the bayesian distribution of this study if updated estimates of the seismicity parameters are used and the standard deviations of these parameters are restricted to be less than about 25 per cent of their mean values the bayesian analysis of extreme earthquake occurrences for the 300 km long san jacinto fault zone indicated a rather large sensitivity to the uncertainty associated with the prior seismotectonic estimate of seismicity using moderate estimates of this uncertainty magnitudes of 6 2 6 9 7 1 7 4 and 7 5 are found to be associated with return periods at 10 50 100 500 and 1000 yr for an upper bound magnitude of 7 5 m s on the fault zone these estimates lie approximately midway between those based on historical and seismotectonic estimates of seismicity estimated magnitudes are reduced significantly for return periods of 50 to 1000 yr if upper bound magnitude is restricted to a value of 7 0 m s closer to the largest historical earthquake observed on the zone in this case for example the 100 and 1000 yr earthquakes have magnitudes of 6 8 and 7 0 respectively

tropical response to the 8200 yr b p cold event speleothem isotopes indicate a weakened early holocene monsoon in costa rica a 1 8 o monsoon rainfall proxy record from a u th dated costa rican stalagmite 8840 4920 yr b p documents an early holocene dry period correlative with the high latitude 8200 yr b p cold event high 1 8 o values between ca 8300 and 8000 yr b p demonstrate reduced rainfall and a weaker monsoon in central america a relatively wetter and more stable monsoon was established ca 7600 yr b p the early holocene dry event suggests a tropical extratropical teleconnection to the 8200 yr b p cold event and a possible association of isthmian rainfall anomalies with high latitude climate changes the likely source of such a tropical anomaly is a decrease in atlantic thermohaline circulation and atmospheric perturbations associated with drainage of proglacial lakes and freshwater discharge into the north atlantic a weaker monsoon at 8200 yr b p may be linked to wetland contraction and a decrease in methane observed in greenland ice cores

frequency distribution and quantification of deep earthquakes the frequency distribution of deep earthquakes d 350 km is analyzed on a regional scale using magnitude data from 4660 events reported in the international seismological center bulletin 1964 1982 and 391 centroid moment tensor solutions 1977 1987 we use the moment magnitude mw to define b values comparable with studies of shallow seismicity scaling laws relating mw mb and mo are derived mw 1 6mb 3 2 mb log mo 4 3 2 4 which compare very favorably with published laws uncertainties and biases of the mb and mo data sets are considered the slope of the frequency distribution is evaluated over a restricted magnitude range the results are very robust and independent from the magnitude range used from the mb magnitude data we obtain regional b values in the range 0 4 b 1 22 with a worldwide average value b 0 87 these results are confirmed by the analysis of the seismic moment data the steepest frequency distribution is observed in the tonga islands region b 1 22 although 60 of the worldwide deep seismicity occurs here only few events since 1977 had seismic moment exceeding 1019 n m the high fractal dimension d 2 4 implies a volume partially filled with fault planes in agreement with the observations on the seismic morphology of the region at the other extreme south america is characterized by the largest recorded deep events and an almost complete absence of small ones b 0 4

freshwater forcing of abrupt climate change during the last glaciation large millennial scale fluctuations of the southern margin of the north american laurentide ice sheet occurred during the last deglaciation when the margin was located between about 43 and 49 n fluctuations of the ice margin triggered episodic increases in the flux of freshwater to the north atlantic by rerouting continental runoff from the mississippi river drainage to the hudson or st lawrence rivers we found that periods of increased freshwater flow to the north atlantic occurred at the same time as reductions in the formation of north atlantic deep water thus providing a mechanism for observed climate variability that may be generally characteristic of times of intermediate global ice volume

triggering basaltic volcanic eruptions by bubble melt separation understanding the processes by which volcanic eruptions are triggered is crucial for volcanic hazard prediction and assessment in intermediate and silicic magmas where water is the dominant volatile phase1 2 second boiling provides an effective eruption trigger1 as the magma cools and crystallizes volatiles are increasingly concentrated in the residual melt where they eventually become saturated and are exsolved thereby raising the magma pressure to the point of eruption1 2 in contrast in basaltic magma chambers in which carbon dioxide is the dominant volatile phase the effect of second boiling is to decrease the chamber pressure but basaltic magmas are also relatively inviscid so volatile bubbles can separate from the turbulently convecting melt to produce a foam layer at the chamber roof3 4 decompression of the rising bubbles can increase the chamber pressure and so trigger an eruption5 6 here we model the complex competition between the processes of magma cooling and bubble ascent we find that in basalt of very low viscosity 1 10pas bubble separation dominates and can increase the reservoir pressure by as much as 10 mpa sufficient to trigger an eruption7 on timescales of 1 10 years comparable to the duration of eruptive episodes at kilauea volcano hawaii4 8

likelihood analysis of earthquake catalogues summary we apply several classes of stochastic multidimensional models to statistical analysis of earthquake catalogues using likelihood methods we investigate the importance of including different earthquake parameters in the model epicentral coordinates hypocentral depth time limits for interearthquake interaction and especially spatial distribution of earthquakes as well as spatial aftershock patterns results of this study combined with other investigations suggest that most distributions controlling earthquake interaction have a fractal or scale invariant form developed models are used for statistical analysis of several earthquake catalogues to evaluate parameters of earthquake occurrence these parameters are shown to be similar for shallow earthquakes of different magnitude ranges and seismogenic regions confirming self similarity of the earthquake process whereas intermediate earthquakes seem to emulate the pattern of shallow earthquake occurrence albeit at a much smaller aftershock rate deep earthquakes differ significantly in their properties predictability of standard shallow earthquake catalogues has been analysed we present evidence that for the best availabfe catalogues the predictability is close to 10 bits per earthquake several synthetic earthquake catalogues have been created and processed through the likelihood inversion scheme the results from likelihood analysis of these catalogues confirm our approach

late glacial temperature and precipitation changes in the lowland neotropics by tandem measurement of δ18o in biogenic carbonate and gypsum hydration water we applied a new method to reconstruct paleotemperature in the tropics during the last deglaciation by measuring oxygen isotopes of co occurring gypsum hydration water and biogenic carbonate in sediment cores from two lakes on the yucatan peninsula oxygen and hydrogen isotope values of interstitial and gypsum hydration water indicate that the crystallization water preserves the isotopic signal of the lake water and has not undergone post depositional isotopic exchange with sediment pore water the estimated lake water 18o is combined with carbonate 18o to calculate paleotemperature three paired measurements of 1200 yr old gypsum and gastropod aragonite from lake chichancanab mexico yielded a mean temperature of 26 c range 23 29 5 c which is consistent with the mean and range of mean annual temperatures mat in the region today paired measurements of ostracods gastropods and gypsum hydration water samples were measured in cores from lake peten itza guatemala spanning the late glacial and early holocene period 18 5 10 4 ka the lowest recorded temperatures occurred at the start of heinrich stadial hs 1 at 18 5 ka inferred temperatures from benthic ostracods ranged from 16 to 20 c during hs 1 which is 6 10 c cooler than mat in the region today whereas temperatures derived from shallow water gastropods were generally warmer 20 25 c reflecting epilimnetic temperatures the derived temperatures support previous findings of greater tropical cooling on land in central america during the late glacial than indicated by nearby marine records temperature increased in two steps during the last deglaciation the first occurred during the bolling allerod b a from 14 7 to 13 ka when temperature rose to 20 24 c towards the end of this period the second step occurred at 10 4 ka near the beginning of the holocene when ostracod inferred temperature rose to 26 c reflecting modern hypolimnetic temperature set during winter whereas gastropod derived temperature attained 30 c reflecting modern summer epilimnetic temperature

a 400 ka tephrochronological framework for central america from lake peten itza guatemala sediments highlights dating 400 ka paleoclimate record of neotropics revision and new eruptive volumes for large central american eruptions age models for peten itza sediments linking lacustrine ash inventory to eruptions from central america and mexico abstract lake peten itza northern guatemala lies within a hydrologically closed basin in the south central area of the yucatan peninsula and was drilled under the auspices of the international continental scientific drilling program icdp in 2006 at 16 55 n latitude the lake is ideally located for study of past climate and environmental conditions in the neotropical lowlands because of its great depth 160 m lake peten itza has a record of continuous sediment accumulation that extends well into the late pleistocene a key obstacle to obtaining long climate records from the region is the difficulty of establishing a robust chronology beyond 40 ka the limit of 14c dating tephra layers within the lake peten itza sediments however enable development of age depth relations beyond 40 ka ash beds from large magnitude pleistocene to holocene silicic eruptions of caldera volcanoes along the central american volcanic arc cava were found throughout drill cores collected from lake peten itza these ash beds were used to establish a robust chronology extending back 400 ka we used major and trace element glass composition to establish 12 well constrained correlations between the lacustrine tephra layers in lake peten itza sediments and dated deposits at the cava source volcanoes and with their marine equivalents in eastern pacific ocean sediments the data also enabled revision of eight previous determinations of erupted volumes and masses and initial estimates for another four eruptions as well as the designation of source areas for 14 previously unknown eruptions the new and revised sedimentation rates for the older sediment successions identify the interglacial of mis5a between 84 and 72 ka followed by a stadial between 72 and 59 ka that corresponds to mis4 we modified the age models for the lake peten itza sediment sequences extended the paleoclimate and paleoecological record for this neotropical region to 400 ka and determined the magnitude and timing of cava eruptions

synchroneity of tropical and high latitude atlantic temperatures over the last glacial termination a high resolution western tropical atlantic sea surface temperature sst record from the cariaco basin on the northern venezuelan shelf based on mg ca values in surface dwelling planktonic foraminifera reveals that changes in sst over the last glacial termination are synchronous within 30 to 90 years with the greenland ice sheet project 2 air temperature proxy record and atmospheric methane record the most prominent deglacial event in the cariaco record occurred during the younger dryas time interval when ssts dropped by 3 to 4 c a rapid southward shift in the atmospheric intertropical convergence zone could account for the synchroneity of tropical temperature atmospheric methane and high latitude changes during the younger dryas