the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

changes in graminoid stomatal morphology over the last glacial interglacial transition evidence from mount kenya east africa abstract stomatal size and density were measured from graminoid cuticular fragments extracted from dated sediments in two tropical montane crater lakes on mount kenya the sediments had been dated in other studies and spanned 1500 37 000 calibrated years bp changes in the mean size and density of the graminoid stomata were found using a coarse signal analysis the two lakes gave fairly similar results although there was some divergence at the start and end of the time period analyzed there is some correspondence between the atmospheric co 2 concentration and graminoid stomatal density during the transition from the lgm to the start of the holocene where stomatal density decreased while co 2 concentrations increased all the changes observed may have been plastic responses within existing species at the site or competitive replacements of grass floras we argue that higher stomatal density may have been a response to falling co 2 levels during the last glaciation accompanying the replacement of a c 3 flora by c 4 species the stomatal size changes exhibited over this time period may have adapted plants to changes in soil water availability that stomatal morphology changes in a sample flora not a single taxon over millennia is a novel finding and one that may have implications for paleoecological interpretation and the prediction of grass behavior in the future

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

landslide movement in southwest colorado triggered by atmospheric tides the slumgullion landslide in the western united states has been moving almost continuously for over 100 years observations and numerical modelling show that air pressure changes from atmospheric tides trigger daily movement

atmospheric co2 fluctuations during the last millennium reconstructed by stomatal frequency analysis of tsuga heterophylla needles a stomatal frequency record based on buried tsuga hetero phylla needles reveals significant centennial scale atmospheric co2 fluctuations during the last millennium the record includes four co2 minima of 260 275 ppmv ca a d 860 and a d 1150 and less prominently ca a d 1600 and 1800 alternating co2 max ima of 300 320 ppmv are present at a d 1000 a d 1300 and ca a d 1700 these co2 fluctuations parallel global terrestrial air temperature changes as well as oceanic surface temperature fluc tuations in the north atlantic the results obtained in this study corroborate the notion of a continuous coupling of the preindus trial atmospheric co2 regime and climate

stomatal proxy record of co2 concentrations from the last termination suggests an important role for co2 at climate change transitions a new stomatal proxy based record of co2 concentrations co2 based on betula nana dwarf birch leaves from the hasseldala port sedimentary sequence in south eastern sweden is presented the record is of high chronological resolution and spans most of greenland interstadial 1 gi 1a to 1c allerod pollen zone greenland stadial 1 gs 1 younger dryas pollen zone and the very beginning of the holocene preboreal pollen zone the record clearly demonstrates that i co2 were significantly higher than usually reported for the last termination and ii the overall pattern of co2 evolution through the studied time period is fairly dynamic with significant abrupt fluctuations in co2 when the climate moved from interstadial to stadial state and vice versa a new loss on ignition chemical record used here as a proxy for temperature lends independent support to the hasseldala port co2 record the large amplitude fluctuations around the climate change transitions may indicate unstable climates and that tippingpoint situations were involved in last termination climate evolution the scenario presented here is in contrast to co2 records reconstructed from air bubbles trapped in ice which indicate lower concentrations and a gradual linear increase of co2 through time the prevalent explanation for the main climate forcer during the last termination being ocean circulation patterns needs to re examined and a larger role for atmospheric co2 considered

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

predicting the response of leaf stomatal frequency to a future co 2 enriched atmosphere constraints from historical observations the majority of the water flux from the earth s land surface to the atmosphere passes through the tiny pores stomata in the leaves of land plants the maximum conductance to diffusion of the leaves determined by the number and geometry of stomata has a profound effect on the terrestrial water and energy balance among tree species there is ever increasing evidence that anthropogenic increase in atmospheric co2 concentrations results in a decrease in stomatal frequency the rate of historical co2 responsiveness of individual tree species can be used to calibrate empirical models of non linear sigmoid stomatal frequency response to co2 increase modelled response curves for european tree birches betula pendula betula pubescens and durmast oak quercus petraea predict different response limits to co2 increase 350 and 400 ppmv respectively indicating that non linear stomatal frequency responses may vary from one tree species to another information on a wider selection of species is needed but the models suggest that the maximum effect of anthropogenic co2 increase on stomatal frequency has already been reached further research is required to establish the effect of rapidly declining response rates on future stomatal conductance of the ecologically contrasting trees of boreal temperate subtropical and tropical forests

quantitative uncertainty analyses of ancient atmospheric co2 estimates from fossil leaves the relationship between atmospheric co 2 and ancient climate is of fundamental importance for gauging the climate sensitivity of the earth system to a changing co 2 regime one of the most widely adopted paleobiological co 2 proxies for reconstructing earth s atmospheric co 2 history exploits the inverse relationship between leaf stomatal index the fraction of leaf epidermal cells that are stomatal structures and atmospheric co 2 however fossil leaf based co 2 reconstructions make a prioii assumptions about the form of the empirical relationship between si and co 2 required for transfer functions and have failed to correctly propagate error terms these effects can translate into erroneous interpretations that undermine the value of the proxy here we report the development and application of a rigorous generalized statistical framework overcoming these limitations that generates probability density functions for each atmospheric co 2 estimate the utility of our statistical tools is demonstrated by showing how they revise earlier atmospheric co 2 estimates from fossil cuticles of ginkgo and metasequoia trees during the early eocene and middle miocene warm periods upwards by 150 to 250 ppm to 450 to 700 ppm the revised co 2 reconstructions therefore help to resolve the paradox of warm paleogene and neogene greenhouse climates co existing with near present day levels of co 2 and support the emerging view from independent paleoclimate studies for a high climate sensitivity of the earth system the statistical tools presented are sufficiently versatile to permit their use in other investigations of paleoco 2 estimates from fossil leaves

the development of two oceanic microplates easter and juan fernandez microplates east pacific rise in this paper we synthesize and discuss the results of recent detailed geophysical surveys and reconstructions of two active mid ocean ridge microplates on the east pacific rise we quantify their development in terms of the principal dimensions of the microplates and their boundaries and the temporal changes in these dimensions the results are discussed in the framework of the roller bearing microplate model of schouten and others which postulates that microplates are driven by shear couples imposed on them by the motions of their bounding major plates we test the specific predictions of this model for the geometry of the pseudofaults traces of the propagating tips of the microplates spreading boundaries and the histories of rotation of the microplates both microplates are currently rotating at the rates predicted by the model on the assumption of complete coupling no slip or deformation between the microplates and the major plates at instantaneous points of contact near the propagating tips of the spreading boundaries juan fernandez microplate was also rotating at the predicted rate just before 2 ma when it was driven by the nazca pacific couple rather than the nazca antarctic couple that currently applies however earlier rotations were slower than predicted implying some degree of decoupling or deformation at earlier times the microplates appear to have grown from moderate sized c 100 km probably left stepping offsets of the east pacific rise since about 5 ma the nature of these offsets is currently uncertain but they may have been propagating rifts which changed from shearing by bookshelf faulting to rigid block microplate rotation on reaching a critical size once rigid block rotation began the microplates grew by seafloor spreading accompanied by propagation of their bounding spreading centres the effects of the neighbouring easter mantle plume and pacific nazca antarctic triple junction can be discerned in the bathymetry and ridge propagation rates but do not appear to have had a major influence on the microplates development

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

rapid atmospheric co2 changes associated with the 8 200 years b p cooling event by applying the inverse relation between numbers of leaf stomata and atmospheric co2 concentration stomatal frequency analysis of fossil birch leaves from lake deposits in denmark reveals a century scale co2 change during the prominent holocene cooling event that occurred in the north atlantic region between 8 400 and 8 100 years b p in contrast to conventional co2 reconstructions based on ice cores from antarctica quantification of the stomatal frequency signal corroborates a distinctive temperature co2 correlation results indicate a global co2 decline of 25 ppm by volume over 300 years this reduction is in harmony with observed and modeled lowering of north atlantic sea surface temperatures associated with a short term weakening of thermohaline circulation

climate independent paleoaltimetry using stomatal density in fossil leaves as a proxy for co2 partial pressure existing methods for determining paleoelevation are primarily limited by 1 large errors 450 m 2 a reliance on incorrect assumptions that lapse rates in terrestrial temperature decrease with altitude in a globally predictable manner and or 3 are inherently climate dependent here i present a novel paleoelevation tool based on a predictable globally conserved decrease in co 2 partial pressure p co 2 with altitude as indicated by increased stomatal frequency of plant leaves the approach was validated using historical populations of black oak quercus kelloggii these analyses demonstrate highly significant inverse relationships between stomatal frequency and p co 2 r 2 0 73 independent of ecological or local climatic variability as such this is the first paleobotanical method to be globally applicable and independent of long term cenozoic climate change further tests on modern leaves of known elevations indicate that species specific application to the fossil record of q kelloggii q pseudolyrata will yield paleoelevation estimates within average errors of 300 m representing a significant improvement in accuracy over the majority of existing methods

an inter comparison study of three stomatal proxy methods for co2 reconstruction applied to early jurassic ginkgoales plants abstract the inverse relationship between concentrations of co2 in the atmosphere pco2 and the stomatal index of vascular plant has been widely used to estimate ancient levels of atmospheric co2 however some atmospheric concentration of co2 in the geological past paleo co2 estimates show little congruence because they are derived using different correlative methods or from different fossil plant species with different calibration approaches here we apply three methods including 1 the empirical method of mcelwain 1998 2 the empirical method of barclay and wing 2016 and 3 the mechanistic method of franks et al 2014 to a single fossil ginkgo species ginkgoites marginatus to track and assess their consistency of pco2 estimates for the early jurassic by using an inter comparison of three methods a high degree of consistency in pco2 estimates and trends has been observed in two empirical proxy methods in addition the mechanistic method and both the empirical methods also show generally good consistent paleo co2 estimates at the bed level to test the congruence of paleo co2 estimates we also apply all three methods to one additional ginkgoalean fossil species sphenobaiera huangii all three methods show species dependent uncertainty in paleo co2 estimates when applied to different ginkgalean fossil species collected from the same fossiliferous bed moreover considering the potential effect of guard cell size to the mechanistic method the genome size of fossil and living ginkgo taxa was analyzed based on the significant positive relationship between genome size and guard cell size the result demonstrates that a likely occurrence of polyploidy in sphenobaiera huangii may result in underestimated paleo co2 when applying mechanistic method due to an increase in the size of the stomatal complex

changes in atmospheric co2 concentrations and climate from the late eocene to early miocene palaeobotanical reconstruction based on fossil floras from saxony germany abstract in the present study proxy data concerning changes in atmospheric co2 and climatic conditions from the late eocene to the early miocene were acquired by applying palaeobotanical methods fossil floras from 10 well documented locations in saxony germany were investigated with respect to 1 stomatal density index of fossil leaves from three different taxa eotrigonobalanus furcinervis laurophyllum pseudoprinceps and laurophyllum acutimontanum 2 the coexistence approach ca based on nearest living relatives nlr and 3 leaf margin analysis lma whereas the results of approach 1 indicate changes in atmospheric co2 concentration approaches 2 and 3 provide climate data the results of the analysis of stomatal parameters indicate that the atmospheric co2 concentration was higher during the late eocene than during the early oligocene and increased towards the late oligocene a lower atmospheric pco2 level after the late eocene is also suggested by an increase in marine palaeoproductivity at this time from the late oligocene onwards no changes in atmospheric co2 concentration can be detected with the present data for the considered sites the results of the coexistence approach and of the leaf margin analysis document a significant cooling event from the late eocene to the early oligocene the pco2 decrease from the late eocene to the early oligocene indicated by the stomatal data raised in this study was thus coupled to a temperature decrease which is reflected by the present datasets from the early oligocene onwards however no further fundamental climate change can be inferred for the considered locations the pco2 increase from the early oligocene to the late oligocene which is indicated by the present data is thus not accompanied by a climate change at the considered sites a warming event during the late oligocene is however recorded by marine climate archives according to the present data no change in pco2 occurred during the cooling event at the oligocene miocene boundary which is also indicated by marine data the quality and validity of stomatal parameters as sensors for atmospheric co2 concentration are discussed

a poroelastic model for the tidal modulation of seafloor hydrothermal systems 1 time series measurements of the temperature and exit velocity of hydrothermal effluent suggest that seafloor hydrothermal systems are modulated by tidal processes here we apply the theory of poroelasticity to predict the magnitude and phase of tidally induced changes in the temperature and flow rate of hydrothermal effluent at the seafloor we construct a model in which the steady state upwelling of buoyant fluid in the crust is modulated by tidal loading of a one dimensional seafloor by the overlying water column the nature of the solution is controlled by the relative magnitudes of three length scales these are 1 the depth h of the heat source below the seafloor 2 the skin depth d over which pore pressure signals can diffuse during one tidal cycle and 3 the advective length scale a over which the upwelling flow advects thermal signals during one tidal cycle we consider the likely magnitude of the parameters in a real system as well as the limitations of a one dimensional representation of that system we then discuss how observational data on the magnitude and phase lag of temperature and flow rate could be used to constrain the subseafloor parameters that govern hydrothermal circulation within the seafloor

abrupt plant physiological changes in southern new zealand at the termination of the mi 1 event reflect shifts in hydroclimate and pco2 abstract a rise in atmospheric co2 is believed to be necessary for the termination of large scale glaciations although the antarctic ice sheet is estimated to have melted from 125 to 50 its modern size there is thus far no evidence for an increase in atmospheric co2 associated with the mi 1 glacial termination in the earliest miocene here we present evidence from a high resolution terrestrial record of leaf physiological change in southern new zealand for an abrupt increase in atmospheric co2 coincident with the termination of the mi 1 glaciation and lasting approximately 20 kyr quantitative p co 2 estimates made using a leaf gas exchange model suggest that atmospheric co2 levels may have doubled during this period from 516 111 ppm to 1144 410 ppm and subsequently returned back to 425 53 ppm the 20 kyr interval with high p co 2 estimates is also associated with a period of increased moisture supply to southern new zealand inferred from carbon and hydrogen isotopes of terrestrial leaf waxes the results provide the first high resolution record of terrestrial environmental change at the oligocene miocene boundary document a 20 kyr interval of elevated p co 2 and increased local moisture availability and provide insight into ecosystem response to a major orbitally driven climatic transition

eruptions of pavlof volcano alaska and their possible modulation by ocean load and tectonic stresses re evaluation of the hypothesis based on new data from 1984 1998 thirteen of sixteen magmatic eruptions of pavlof volcano in nine of the years from 1973 to 1998 have occurred between september 9 and december 29 volumes of erupted material range from 0 3 to 16 10 6 m 3 dense rock equivalent a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 0 6 times eruption volumes and it is postulated that the volcano acts as a long period several months volume strainmeter with lava being preferentially erupted when strain beneath the volcano is compressive previous observations of a tilt reversal and new observations of tectonic activity and eruptions in the spring and summer of 1986 also suggest tectonic modulation of eruptions the volcano appears to be responsive to small slow changes in ambient stresses or strains and these changes may modify or trigger eruptions

late early cretaceous climate and pco2 estimates in the liupanshan basin northwest china abstract the extinct conifer family cheirolepidiaceae especially pseudofrenelopsis is commonly used to reconstruct the atmospheric palaeo co2 concentration pco2 during the cretaceous period in recent years many pseudofrenelopsis specimens have been collected from the uppermost stratum of the naijiahe formation in the liupanshan basin ningxia hui autonomous region northwest china the stomatal parameters such as stomatal density stomatal index stomatal pore length and stomatal pore depth and the stable carbon isotope composition of the present pseudofrenelopsis were analyzed the palaeo co2 levels of the liupanshan basin during the late early cretaceous late albian were reconstructed using stomatal ratio sr and mechanistic model approaches the sr method yielded a semi quantitative pco2 estimate of 620 ppmv on the basis of the recent standardization and 1030 ppmv on the basis of the carboniferous standardization which show similarities with other sr based and geochemical based reconstructions for the late early cretaceous the pco2 was about 670 ppmv on the basis of mechanistic model method similar to the estimated pco2 values recovered by the sr method corrected with the recent standardization based on comparative studies of previously published pco2 results of the early cretaceous pco2 levels varied during the early cretaceous and pco2 was relatively stable during the late early cretaceous furthermore environmental conditions of the liupanshan basin during the late early cretaceous were studied the stable carbon isotope composition of pseudofrenelopsis leaves ranged from 21 5 to 24 3 with an average of 22 8 indicating an arid semi arid and high evaporation climate during the late early cretaceous in the liupanshan basin these environmental conditions were also supported by palynological lithological and geochemical evidence

systematic along axis tidal triggering of microearthquakes observed at 9 50 n east pacific rise 1 hydrothermal fluid circulation at mid ocean ridges facilitates the exchange of heat and chemicals between the oceans and the solid earth and supports chemosynthetic microbial and macro faunal communities the structure and evolution of newly formed oceanic crust plays a dominant role in controlling the character and longevity of hydrothermal systems however direct measurements of subsurface processes remain technologically challenging to obtain previous studies have shown that tidally induced stresses within the subseafloor modulate both fluid flow and microearthquake origin times in this study we observe systematic along axis variations between peak microearthquake activity and maximum predicted tidal extension beneath the hydrothermal vent site at 9 50 n east pacific rise we interpret this systematic triggering to result from pore pressure perturbations propagating laterally through the hydrothermal system based on our observations and a one dimensional pore pressure perturbation model we estimate bulk permeability at 10 13 to 10 12 m2 within layer 2b over a calculated diffusive lengthscale of 2 0 km

large rotation of the easter microplate as evidenced by oriented paleomagnetic samples from the ocean floor one of the goals of the pito93 cruise along the perimeter of the easter microplate was to obtain oriented rock samples from the ocean floor for paleomagnetic study using a new orienting device the geocompass 14 oriented blocks were obtained during 6 dives conducted using the ifremer dsrv nautile paleomagnetic analysis shows that 13 of these 14 blocks give consistent results in thermal and af demagnetizations and reveals a mean characteristic remanent magnetization chrm direction within each block with both normal and reverse polarities after elimination of data from 5 blocks situated outside the microplate and one block which bears an anomalous direction we have computed a mean chrm direction at dm 49 0 im 39 0 k 10 2 95 19 8 n 7 although the mean inclination is in agreement with the inclination of the recent dipole magnetic field d 0 i 43 the average declination is significantly different from this direction which we interpret as due to a bulk clockwise rotation of 48 5 11 after the bivariate average of the easter microplate over the past 2 3 ma this value is in excellent agreement with previous estimates based on remote geophysical measurements and models

statistical analysis of the el nino southern oscillation and sea floor seismicity in the eastern tropical pacific we present statistical evidence for a temporal link between variations in the el nino southern oscillation enso and the occurrence of earthquakes on the east pacific rise epr we adopt a zero inflated poisson regression model to represent the relationship between the number of earthquakes in the easter microplate on the epr and enso expressed using the southern oscillation index soi for east pacific sea level pressure anomalies from february 1973 to february 2009 we also examine the relationship between the numbers of earthquakes and sea levels as retrieved by topex poseidon from october 1992 to july 2002 we observe a significant 95 confidence level positive influence of soi on seismicity positive soi values trigger more earthquakes over the following 2 to 6 months than negative soi values there is a significant negative influence of absolute sea levels on seismicity at 6 months lag we propose that increased seismicity is associated with enso driven sea surface gradients rising from east to west in the equatorial pacific leading to a reduction in ocean bottom pressure over the epr by a few kilopascal this relationship is opposite to reservoir triggered seismicity and suggests that epr fault activity may be triggered by plate flexure associated with the reduced pressure

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

seismic cycles and earthquake predictability on east pacific rise transform faults the concept of a seismic cycle where the stress on a fault repeatedly builds up over a long period of time and then is rapidly released in a large earthquake influences studies of both the basic physics of faulting and applied research aimed at estimating earthquake hazards this hypothesis suggests that large earthquakes might be quasi periodic and that the probability of a particular portion of a fault rupturing twice in quick succession should be low however this basic hypothesis has been difficult to verify owing to the long repeat times of the largest earthquakes on most faults east pacific rise epr transform faults are an advantageous location to evaluate the seismic cycle hypothesis owing to their fast slip rates and the moderate size m w 6 of their largest earthquakes using surface wave based determinations of the relative separations between earthquake centroids i document 16 pairs of m w 5 5 events that had overlapping ruptures the distribution of interevent times for these pairs is tightly clustered around 5 yr with a coefficient of variation 0 2 indicating that quasi periodicity may be prevalent for the largest events on these faults moreover i find no pairs of overlapping m w 5 5 6 2 earthquakes separated by less than 50 cm of elapsed plate motion indicating that the two basic features of the seismic cycle hypothesis are evident in the timing of large epr transform mainshocks i have also confirmed earlier results demonstrating a high degree of short term predictability of epr mainshocks by combining teleseismic and hydroacoustic earthquake catalogs thus there appears to be a high degree of both short and long term predictability on epr transforms

acceleration of jakobshavn isbrae triggered by warm subsurface ocean waters observations over past decades show a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning in 1997 this switch is associated with a doubling in glacier velocity hydrographic data show a concurrent sudden increase in subsurface ocean temperatures along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were triggered by the arrival of relatively warm water originating from the irminger sea observations over the past decades show a rapid acceleration of several outlet glaciers in greenland and antarctica1 one of the largest changes is a sudden switch of jakobshavn isbrae a large outlet glacier feeding a deep ocean fjord on greenland s west coast from slow thickening to rapid thinning2 in 1997 associated with a doubling in glacier velocity3 suggested explanations for the speed up of jakobshavn isbrae include increased lubrication of the ice bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers4 and weakening and break up of the floating ice tongue that buttressed the glacier5 here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of greenland suggesting that the changes in jakobshavn isbrae were instead triggered by the arrival of relatively warm water originating from the irminger sea near iceland we trace these oceanic changes back to changes in the atmospheric circulation in the north atlantic region we conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets

abrupt climatic changes and an unstable transition into a late holocene thermal decline a multiproxy lacustrine record from southern sweden the transition from a middle holocene relatively warm and stable climate to a cooler and unstable late holocene climate is reconstructed using sediments from lake igelsjon south central sweden this multiproxy study illustrates local regional and global scale responses to climatic change by focusing on a previously identified abrupt hydrological shift to cooler and or wetter conditions around 4000 cal yr bp the results suggest that between ca 4600 and ca 3400 cal yr bp the environment around and within the lake responded in two major well defined steps the first between 4450 and 4350 cal yr bp and the second between 4000 and 3800 cal yr bp a series of rapid fluctuations of short duration were superimposed on the general cooling trend with the most severe aquatic response peaking at ca 3800 cal yr bp pollen percentage and influx values show forest composition and pollen productivity changes and a distinct decline in total and corylus pollen influx in the period of 4000 3500 cal yr bp stomatal based reconstruction of atmospheric co2 concentration produced a tenuous decrease with a minimum between 3650 and 3500 cal yr bp copyright 2005 john wiley sons ltd

why is it hard to predict the future of ice sheets ice sheet retreat hypotheses of instability could be missing important processes that limit the rate or extent of retreat or conversely ice sheet behavior is strongly influenced by processes at its margin and base observations of rapid changes at these boundaries are helping modelers to improve predictions of future changes

eruptions of pavlof volcano and their possible modulation by ocean load and tectonic stresses all nine magmatic eruptions at pavlof volcano in six of the years from 1973 to 1984 have occurred between september 9 and november 20 volumes of erupted material range from 0 1 to 15 9 106 m3 dense rock equivalent at an average rate of 3 106 m3 yr 1 the volumes are estimated from eyewitness reports for two eruptions the others are estimated from a relationship that we derive between eruption volume and harmonic tremor duration and amplitude the volume of lava erupted is approximately time predictable a significant correlation exists between the eruptions and yearly nontidal variations in sea level and may result from ocean loading calculated volume changes beneath the volcano due to ocean loading are from 0 02 to 2 times eruption volumes and we postulate that the volcano acts as a long period several month volume strain meter with lava being preferentially erupted when strain beneath the volcano is compressive the volcano did not erupt during the period 1978 1980 when tilt seismic data and sea level data indicate that deep aseismic slip may have occurred models of this event predict a volume increase beneath the volcano that might have compensated strain from magma injection these observations indicate that pavlof volcano may be responsive to small slow changes in ambient stresses or strains and that these changes may modify or trigger eruptions