a new estimate for present day cocos caribbean plate motion implications for slip along the central american volcanic arc velocities from 153 continuously operatinggps sites on the caribbean north american and pacic plates arecombinedwith61newlyestimatedpacic cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present daycocos caribbean plate motion acomparisonofthepredictedcocos caribbean di rectiontoslipdirectionsofnumerousshallow thrustsubduc tion earthquakes from the middle america trench between costa rica and guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc tion supporting thehypothesisthatfrequentdextralstrike slip earthquakes along the central american volcanic arc result from partitioning of oblique cocos caribbean plate convergence linear velocity analysis for forearc locations in nicaragua and guatemala predicts 14 2m m yr 1 of northwestward trench parallel slip of the forearc relative to thecaribbean plate possibly decreasing inmagnitude inel salvador and guatemala where extension east of the vol canic arc complicates the tectonic setting

variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

role of deep sea temperature in the carbon cycle during the last glacial 1 to characterize the response of earth s climate system to increases in atmospheric co2 climate modelers define climate sensitivity as the change in global mean temperature in response to prescribed forcing here we turn this approach around and use estimates of ocean temperature change to investigate the mechanisms driving co2 variations over the last glacial new records provide evidence of a link between deep ocean temperature and atmospheric co2 over the last glacial cycle two mechanisms simultaneously couple pco2 and deep ocean temperature the temperature dependent solubility of co2 in seawater and the atmospheric co2 dependent radiative forcing of temperature each of these forcing mechanisms leaves a unique slope of covariation between co2 and deep ocean temperature which we estimate using numerical models of climate and the carbon cycle the pco2 t slopes derived from paleoclimate data differ between the deglaciation and shorter 5 kyr duration events in marine isotope stage 3 mis 3 revealing different mechanisms driving atmospheric co2 variability the amplitude of changes over the deglaciation coincides with estimates for co2 forcing of temperature however co2 changes during mis 3 can be explained solely by temperature dependent solubility driving variations in atmospheric pco2 the deep water temperature changes during mis 3 may reflect changes in the temperature or relative contribution of antarctic bottom water and play a role in the bipolar seesaw

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

complexities of plinian fall deposition at vent an example from the 1912 novarupta eruption alaska abstract an extremely proximal ejecta ring with exposures to within 100 m of vent was deposited during later stage plinian fall activity during the 1912 novarupta eruption in alaska one bed in the ejecta ring bed s contains predominantly andesitic clasts which serve to delineate the striking contrast in thinning rates along dispersal axis of the ejecta ring pyle bt values of 70 m bed s alone or 190 m whole ejecta ring and the coeval dacitic plinian fall deposits pyle bt values of 4 km proximal and 37 km medial distal the locally deposited andesitic and dacitic clasts of the ejecta ring are interpreted as products of an irregular collar of low fountaining ejecta partially sheathing the core of higher velocity dacitic ejecta that fed the stable converting 23 km high column the presence of such an extremely proximal accumulation of ejecta appears to be a feature common to several other historic eruptions that generated widespread fall deposits this feature in part accounts for conflicts between measured and calculated values for thickness maxima in plinian fall deposits and suggests that modifications may be required of existing models for plinian eruption columns

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

3d basin modelling of the hammerfest basin southwestern barents sea a quantitative assessment of petroleum generation migration and leakage abstract 3d basin modelling of the hammerfest basin southwestern barents sea was performed in order to address the masses of petroleum generated accumulated and lost during the evolution of the basin calibration of the model based on observed maturity vitrinite reflectance and present day temperatures took into account 1 two main erosion episodes an oligocene miocene event due to tectonic uplift and a plio pleistocene glacial erosion event and 2 variable heat flow from late palaeozoic to cenozoic the maturity levels of the main source rocks kobbe snadd and hekkingen formations were reconstructed and show that the highest maturities have been reached in the western and northwestern margin of the basin the beginning of petroleum generation in the kobbe snadd and hekkingen source rocks has been predicted to occur during late triassic early cretaceous and late cretaceous respectively our model reproduces satisfactorily the distribution of the main oil and gas fields and discoveries that have been found in the study area our results indicate that two events of hydrocarbons redistribution occurred in the basin the first event resulted in the main oil redistribution episode which took place during the oligocene miocene associated with tectonic uplift and gas expansion and the second was related to the main gas leakage events that occurred during the pliocene pleistocene glacialinterglacial cycles in general and the episodes of glacial retreat in particular glacial loading and unloading cycles resulted in overpressure fluctuations in the subsurface reservoirs modelling results indicate that during these episodes a portion at least 0 247 gt of thermogenic gas leaked from the main sto formation reservoirs reached the sediment interface and was released to the surface in the hammerfest basin

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

geochemical evidence for a large methane release during the last deglaciation from marmara sea sediments abstract recent methane inventories have revealed the potential impact of gas hydrates on the global carbon cycle and hence in climate change milkov 2004 however only a few studies have traced methane release in the geologic record here we show geochemical evidence for a large scale methane release at mid latitudes during the last deglaciation the sea of marmara an enclosed sea between the mediterranean and black seas is located in a tectonically active basin with gas hydrate expulsion and the formation of shallow gas hydrates since depths in the basin are shallower than 1100 m future global temperatures are expected to have a great influence in destabilizing methane clathrates among the suite of biomarkers we have focused on diplopterol and diploptene profiles in core md012430 retrieved from the central basin in the marmara sea our results indicate that during the last 15 000 years hopanoids showed important concentration variations with a pronounced peak during the deglaciation the lack of a relationship between diplopterol diploptene and phytoplanktonic biomarker concentrations as well as a depleted isotopic composition have linked the hopanoid maxima to methanotrophic activity suggesting that an intense methane release occurred at the onset of deglaciation in the marmara sea the vulnerability of the hydrate stability zone to changes in temperature and pressure under this range of shallow water depths as well as the relative timing of the hopanoid maxima and sea surface temperature rise points to thermal destabilization of hydrates as a trigger for methane release in the water column

application of benthic foraminiferal mg ca ratios to questions of cenozoic climate change abstract we investigate the evolution of cenozoic climate and ice volume as evidenced by the oxygen isotopic composition of seawater 18osw derived from benthic foraminiferal mg ca ratios to constrain the temperature effect contained in foraminiferal 18o values we have constructed two benthic foraminiferal mg ca records from intermediate water depth sites ocean drilling program sites 757 and 689 from the subtropical indian ocean and the weddell sea respectively together with the previously published composite record of lear et al science 287 2002 269 272 and the neogene record from the southern ocean of billups and schrag paleoceanography 17 2002 10 1029 2000pa000567 we obtain three almost complete representations of the 18osw for the past 52 myr we discuss the sensitivity of early cenozoic mg ca derived paleotemperatures and hence the 18osw to assumptions about seawater mg ca ratios we find that during the middle eocene 49 40 ma modern seawater ratios yield mg ca derived temperatures that are in good agreement with the oxygen isotope paleothermometer assuming ice free conditions intermediate waters cooled during the middle eocene reaching minimum temperatures by 40 ma the corresponding 18osw reconstructions support ice growth on antarctica beginning by at least 40 ma at the eocene oligocene boundary mg ca ratios and hence temperatures from weddell sea site 689 display a well defined maximum we caution against a paleoclimatic significance of this result and put forth that the partitioning coefficient of mg in benthic foraminifera may be sensitive to factors other than temperature throughout the remainder of the cenozoic the temporal variability among 18osw records is similar and similar to longer term trends in the benthic foraminiferal 18o record an exception occurs during the pliocene when 18osw minima in two of the three records suggest reductions in global ice volume that are not apparent in foraminiferal 18o records which provides a new perspective to the ongoing debate about the stability of the antarctic ice sheet maximum 18osw values recorded during the pleistocene at southern ocean site 747 agree well with values derived from the geochemistry of pore waters schrag et al science 272 1996 1930 1932 further highlighting the value of the new mg ca calibrations of martin et al earth planet sci lett 198 2002 193 209 and lear et al geochim cosmochim acta 66 2002 3375 3387 applied in this study we conclude that the application of foraminiferal mg ca ratios allows a refined view of cenozoic ice volume history despite uncertainties related to the geochemical cycling of mg and ca on long time scales

mechanisms of thermohaline mode switching with application to warm equable climates abstract a three box model of haline and thermal mode overturning is developed to study thermohaline oscillations found in a number of ocean general circulation models and that might have occurred in warm equable paleoclimates by including convective adjustment modified to represent the localized nature of deep convection the box model shows that a steady haline mode circulation is unstable for certain ranges of freshwater forcing vertical diffusivity a self sustained oscillatory circulation is found in which haline thermal mode switching occurs with a period of centuries to millennia it is found that mode switching is most likely to occur in warm periods of earth s history with relative to the present climate a reduced pole ndash uator temperature gradient an enhanced hydrological cycle and somewhat smaller values of oceanic diffusivities

pacific offshore record of plinian arc volcanism in central america 2 tephra volumes and erupted masses 1 sediment gravity cores collected from the pacific seafloor offshore central america contain numerous distal ash layers from plinian type eruptions at the central american volcanic arc dating back to more than 200 ka in part 1 of this contribution we have correlated many of those ash layers between cores and with 26 tephras on land the marine ash layers cover areas of up to 106 km2 in the pacific ocean and represent a major fraction 60 90 of the erupted tephra volumes because the pacific coast lies within a few tens of kilometers downwind from the volcanic arc combining our own mapping efforts on land and published mapping results with our marine data yields erupted volumes of all major tephras along the arc that range from 1 to 420 km3 recalculated to erupted magma mass the widespread tephras account for 65 of the total magma output at the arc complementing our tephra data with published volumes of the arc volcanic edifices and volcano ages we calculate the long term average magma eruption rates for each volcano moreover we use incompatible element variations to calculate the cumulate masses that were fractionated during variable degrees of differentiation this yields a minimum estimate of long term average magma production rate at each volcano because intrusives without surface expression and losses by erosion are not accounted for peak magma production rates increase from costa rica to guatemala but there is considerable scatter within each region and large differences even between neighboring volcanoes

the middle pleistocene transition characteristics mechanisms and implications for long term changes in atmospheric pco2 abstract the emergence of low frequency high amplitude quasi periodic 100 kyr glacial variability during the middle pleistocene in the absence of any significant change in orbital forcing indicates a fundamental change internal to the climate system this middle pleistocene transition mpt began 1250 ka and was complete by 700 ka its onset was accompanied by decreases in sea surface temperatures ssts in the north atlantic and tropical ocean upwelling regions and by an increase in african and asian aridity and monsoonal intensity during the mpt long term average ice volume gradually increased by 50 m sea level equivalent whereas low frequency ice volume variability experienced a 100 kyr lull centered on 1000 ka followed by its reappearance 900 ka although as a broad band of power rather than a narrow persistent 100 kyr cycle additional changes at 900 ka indicate this to be an important time during the mpt beginning with an 80 kyr event of extreme sst cooling followed by the partial recovery and subsequent stabilization of long term north atlantic and tropical ocean ssts increasing southern ocean sst variability primarily associated with warmer interglacials the loss of permanent subpolar sea ice cover and the emergence of low frequency variability in pacific ssts and global deep ocean circulation since 900 ka ice sheets have been the only component of the climate system to exhibit consistent low frequency variability with the exception of a near universal organization of low frequency power associated with marine isotope stages 11 and 12 all other components show an inconsistent distribution of power in frequency time space suggesting a highly nonlinear system response to orbital and ice sheet forcing most hypotheses for the origin of the mpt invoke a response to a long term cooling possibly induced by decreasing atmospheric pco2 none of these hypotheses however accounts for the geological constraint that the earliest northern hemisphere ice sheets covered a similar or larger area than those that followed the mpt given that the mpt was associated with an increase in ice volume this constraint requires that post mpt ice sheets were substantially thicker than pre mpt ice sheets indicating a change in subglacial conditions that influence ice dynamics we review evidence in support of the hypothesis that such an increase in ice thickness occurred as crystalline precambrian shield bedrock became exposed by glacial erosion of a thick mantle of regolith this exposure of a high friction substrate caused thicker ice sheets with an attendant change in their response to the orbital forcing marine carbon isotope data indicate a rapid transfer of organic carbon to inorganic carbon in the ocean system during the mpt if this carbon came from terrigenous sources an increase in atmospheric pco2 would be likely which is inconsistent with evidence for widespread cooling apparently rapid carbon transfer from terrestrial sources is difficult to reconcile with gradual erosion of regolith a more likely source of organic carbon and nutrients which would mitigate pco2 rise is from shelf and upper slope marine sediments which were fully exposed for the first time in millions of years in response to thickening ice sheets and falling sealevels during the mpt modeling indicates that regolith erosion and resulting exposure of crystalline bedrock would cause an increase in long term silicate weathering rates in good agreement with marine sr and os isotopic records we use a carbon cycle model to show that a post mpt increase in silicate weathering rates would lower atmospheric pco2 by 7 12 ppm suggesting that the attendant cooling may have been an important feedback in causing the mpt

quaternary deep sea temperature histories derived from benthic foraminiferal mg ca abstract we have generated benthic foraminiferal mg ca records from eastern tropical atlantic core m16772 3 9 km and eastern tropical pacific core tr163 31p 3 2 km to assess the potential for using benthic mg paleothermometry to reconstruct quaternary bottom water temperature histories variations in mg ca records from both the atlantic and pacific show a significant correlation with climatic oscillations of the last 330 kyr shell mg ca peaks during interglacial episodes with marine isotope stage mis 5e mg ca nearly matching holocene values in both cores lower mg ca values occur during glacial intervals to estimate temperatures from downcore mg ca we have augmented the published cibicidoides sp mg ca temperature dataset rosenthal et al geochim cosmochim acta 61 1997 3633 3643 with new data to include the temperature range of deep waters applying the 10 9 change in mg ca per c defined by the expanded calibration to the deep atlantic data implies glacial interglacial shifts in deep water temperature of 2 4 c over the last 300 kyr temperature estimates are comparable to deep atlantic temperature changes proposed by labeyrie et al nature 327 1987 477 482 there is greater uncertainty in deriving temperatures from the tropical pacific core due to a limited uvigerina spp core top calibration set however glacial interglacial temperature oscillations appear to be on the order of 2 3 c in addition core tr163 31p records clear millennial scale mg ca and 18 o oscillations in mis 3 corresponding to temperature fluctuations of 0 5 c additional calibration studies are needed to address potential secondary effects on mg ca

gps based monitoring of land subsidence in the po plain northern italy abstract we use regional and local networks of continuously operating gps stations cgps distributed in the northern central part of the italian peninsula to investigate the subsidence phenomenon of the po plain sedimentary basin and vertical movements of the surrounding areas the observations of 146 scientific and commercial stations are analyzed and compared adopting analytical techniques widely used to study gps coordinate time series the use of simple antenna supports in commercial installations instead of a more rigorous geodetic monument does not seem to induce significant differences in the noise characteristics and in the amplitudes of annual and semi annual periodic signals the vertical velocity field deduced from 129 sites with observation time spans greater than one year located in the central northern italian peninsula indicates the presence of two mainly subsidence areas the po plain and the arno plain while the sites located in the alps and apennine domains show relatively low uplift the areas of the po plain monitored by gps seem to indicate that the subsidence rate is constant or in some cases decreasing with respect to the values obtained from the last measurements performed up to 2006 by means of both sar and levelling techniques only the central part of the eastern po plain close to the apennine border modena city area is characterized by a peak in subsidence consisting in a velocity of about 15 mm yr

apennines subduction related subsidence of venice italy 1 the foreland regional monocline related to the northern apennines subduction can be followed from the po basin to the friuli region italy at least 240 km north eastward in seismic reflection profiles of the po basin and of the northern adriatic sea the dip of the regional monocline gradually decreases from about 22 to close to 0 pleistocene sediments onlap and pinchout to the northeast venice is located on a segment of the active monocline dipping about 1 8 to the southwest in sediments around the venice area the 1 43 ma limit is in the 960 1500 m depth range indicating a long term subsidence rate of about 0 7 1 0 mm yr therefore a significant part of the natural component of the town subsidence is related to the north eastward retreat of the adriatic subduction the subduction related downflexure affects the whole of the po plain basin and part of the southern alps where it opposes to the general uplift related to orogenesis

dynamics of fossil fuel co2 neutralization by marine caco3 a detailed model of the ocean circulation and carbon cycle was coupled to a mechanistic model of caco3 diagenesis in deep sea sediments to simulate the millennium scale response of the oceans to future fossil fuel co2 emissions to the atmosphere and deep sea simulations of deep sea injection of co2 show that caco3 dissolution is sensitive to passage of high co2 waters through the atlantic ocean but caco3 dissolution has a negligible impact on atmospheric pco2 or the atmospheric stabilization co2 emission in the coming centuries the ultimate fate of the fossil fuel co2 will be to react with caco3 on the seafloor and on land an initial caco3 dissolution spike reverses the net sedimentation rate in the ocean until it is attenuated by an enhanced vertical gradient of alkalinity after about 1000 years the magnitude of the initial spike is sensitive to assumptions about the kinetics for caco3 dissolution but subsequent behavior appears to be less model dependent neutralization by seafloor caco3 occurs on a timescale of 5 6 kyr and is limited to at most 60 70 of the fossil fuel release even if the fossil fuel release is smaller than the seafloor erodible inventory of caco3 additional neutralization by terrestrial caco3 restores a balance between caco3 weathering and seafloor accumulation on a timescale of 8 5 kyr while the deficit of seafloor caco3 the lysocline is replenished with an e folding timescale of approximately 18 kyr the final equilibrium with caco3 leaves 7 8 of the fossil fuel co2 remaining in the atmosphere to be neutralized by the silicate rock cycle on a time frame of hundreds of thousands of years

late pleistocene to holocene temporal succession and magnitudes of highly explosive volcanic eruptions in west central nicaragua the stratigraphic succession of widespread tephra layers in west central nicaragua was emplaced by highly explosive eruptions from mainly three volcanoes the chiltepe volcanic complex and the masaya and apoyo calderas stratigraphic correlations are based on distinct compositions of tephras the total tephras combine to a total on shore volume of about 37 km3 produced during the last 60 ka the total erupted magma mass including also distal volumes of 184 gt dre distributes to 84 into 9 dacitic to rhyolitic eruptions and to 16 into 4 basaltic to basaltic andesitic eruptions the widely dispersed tephra sheets have up to five times the mass of their parental volcanic edifices and thus represent a significant albeit less obvious component of the arc volcanism eruption magnitudes m log10 m 7 with m the mass in kg range from m 4 1 to m 6 3 most of the eruptions were dominantly plinian with eruption columns reaching variably high into the stratosphere but minor phreatomagmatic phases were also involved two phreatomagmatic eruptions one dacitic and one basaltic andesitic produced mostly pyroclastic surges but also fallout from high eruption columns comparison of fallout tephra dispersal patterns with present day seasonally changing height dependant wind directions suggests that 8 eruptions occurred during the rainy season while 5 took place during the dry season the tephra succession documents two major phases of erosion the first phase 17 ka ago appears to be related to tectonic activity whereas the second phase may have been caused by wet climatic conditions between 2 to 6 ka ago the apoyo caldera had two large plinian caldera forming eruptions in rapid succession about 24 ka ago and should be considered a silicic volcano with long repose times three highly explosive basaltic eruptions were generated at the masaya caldera within the last 6 ka since then frequent but small eruptions and lava effusion were largely limited to the caldera interior the dacitic chiltepe volcanic complex experienced six plinian eruptions during the last 17 ka and seems to be an accelerating system in which eruption magnitude increased while the degree of differentiation of erupted magma decreased at the same time we speculate that the chiltepe system might produce the next large magnitude silicic eruption in west central nicaragua

an improved age framework for late quaternary silicic eruptions in northern central america five new stepwise heating 40 ar 39 ar ages and one new high sensitivity 14 c date of ash fall and ash flow deposits from late quaternary silicic volcanoes in northern central america document the eruption rates and frequencies of five major rhyodacite and rhyolite calderas atitlan amatitlan ayarza coatepe que and ilopango located north of the basalt ande site and dacite stratovolcanoes of the central ameri can volcanic front these deposits form extensive time stratigraphic horizons that intercalate regionally and knowledge of dates and stratigraphy provides a valua ble framework for age determinations of more local ized volcanic and nonvolcanic events the new data es pecially when integrated with previous stratigraphic and dating work show that all five calderas erupted several times in the past 200 ka and despite a lack of historic activity should be considered as active centers that could produce highly explosive eruptions again because of their locations near the highly vulnerable economic hearts of guatemala and el salvador the risks of eruptions from these calderas should be care fully considered along with risks of major earthquakes and volcanic front volcanoes which are much more fre quent but inflict less severe and extensive damage this

two years of continuous measurements of tidal and nontidal variations of gravity in boulder colorado we report here on the results of an analysis of 2 years of data from noaa s superconducting gravimeter located at the table mountain gravity observatory in boulder colorado observed tidal parameters corrected for ocean loading effects are compared with theoretical tidal parameters predicted for a non hydrostatic inelastic earth model and demonstrate excellent agreement tidal residuals corrected for polar motion and a linear instrument drift are highly correlated with gravity changes measured by two absolute gravimeters over the same time period the admittance to local pressure is found to be 0 356 gal mbar however this admittance factor is found to be seasonally and frequency dependent correlations between rainfall events and gravity changes are observed attempts to model these gravity changes as exponential functions of time were unsuccessful

periodic mid cretaceous oceanic anoxic events linked by oscillations of the phosphorus and oxygen biogeochemical cycles 1 a series of oceanic anoxic events oaes occurred in the mid cretaceous warm period 120 80 ma that have been linked with high rates of organic carbon burial warm high and low latitude temperatures and sea level changes oaes have been studied individually but a causal mechanism that connects them has been lacking we show that peaks in phosphorus accumulation in marine sediments broadly coincide with oaes 1a 1b 1d 2 and 3 and exhibit a 5 6 myr periodicity which for reactive p is prominent over 100 80 ma oxic anoxic oscillations of this frequency are also found in a model of the coupled n p c and o2 biogeochemical cycles these oscillations are maintained by positive feedbacks between phosphate concentration biological productivity and anoxia in the global ocean and counteracting but slower negative feedbacks involving changes in atmospheric oxygen an increase in phosphorus weathering rate above a critical threshold can shift the system into self sustaining oscillation this could have been caused by tectonic and volcanic forcing increasing atmospheric co2 and global warmth 120 80 ma augmented by the rise of flowering plants around 100 ma with a plausible forcing scenario we are able to reproduce the approximate timing of oaes 1a 1b 1d 2 and 3 in the model

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

sources of methane for marine gas hydrate inferences from a comparison of observations and numerical models the supply of methane for marine gas hydrate is commonly attributed to local conversion of organic material within the zone of stability or to migration of methane bearing fluids from a deeper source area however the relative importance of these methane sources is not well known we use numerical models for the formation of gas hydrate to assess the influence of methane supply on observable features of hydrate occurrences model predictions for the pore fluid chlorinity and the volumes of hydrate and free gas are compared with observations from the blake ridge and cascadia margin we find that the observations from the blake ridge can be explained with a deep methane source if a saturated fluid rises with a velocity of 0 26 mm yr 1 an equally good fit to the observations is obtained by combining in situ production of methane with an upward fluid velocity of 0 08 mm yr 1 which is compatible with estimates of fluid velocity at site 997 observations from the cascadia margin can be explained with a deep methane source if the upward fluid velocity is 0 42 mm yr 1 the predicted volume of hydrate 2 of the pore space is much smaller than some previous estimates and a layer of free gas 1 of the pore space develops below the stability zone allowing for in situ production at the cascadia margin lowers the upward fluid velocity 0 35 mm yr 1 needed to explain the pore water chlorinity

a new global mode of earth deformation seasonal cycle detected we have detected a global mode of earth deformation that is predicted by theory precise positioning of global positioning system sites distributed worldwide reveals that during february to march the northern hemisphere compresses and the southern hemisphere expands such that sites near the north pole move downward by 3 0 millimeters and sites near the equator are pulled northward by 1 5 millimeters the opposite pattern of deformation occurs during august to september we identify this pattern as the degree one spherical harmonic response of an elastic earth to increased winter loading of soil moisture snow cover and atmosphere data inversion shows the load moment s trajectory as a great circle traversing the continents peaking at 6 9 1022 kilogram meters near the north pole in winter indicating interhemispheric mass exchange of 1 0 1016 0 2 1016 kilograms

changes in the hydrological cycle ocean circulation and carbon nutrient cycling during the last interglacial and glacial transition 1 a complex earth system model has been forced by insolation changes for the last interglacial lig for which geological records evidence a climate cooling that culminated in the last glacial inception during an early warm period 127 125 ka b p the arctic north atlantic drainage basin north of 30 n receives 27 000 m3 s more fresh water mainly imported across the watershed of north america compared to a cooler period centered around 115 ka b p together with a strong surface warming by up to 2 k this results in a weaker north atlantic overturning reduced by 20 sea ice cover is reduced by 3 106 km2 in the northern hemisphere stimulating a stronger productivity in the barents and kara seas in the north pacific a lowered salinity and a surface warming of more than 3 k increase the stratification the eastern pacific becomes nutrient poorer which leads to a reduction in the export production in areas with vigorous upwelling the climate cooling in the course of the lig induces a carbon release by the terrestrial biosphere of 308 gt which is counteracted by an oceanic sedimentary uptake of 290 gt the rest remains in the atmosphere increasing the pco2 by 9 ppm the large oceanic co2 uptake corresponds to a rise of the calcite lysocline of about 300 m in the midlatitude atlantic the chemically interactive carbonate sediment pool in the atlantic is reduced by 10 for nearly the entire north atlantic our results are contradictory to the common interpretation of carbonate preservation proxies as a reliable tool for monitoring changes in deep water circulation

displacements of the earth s surface due to atmospheric loading effects on gravity and baseline measurements atmospheric mass loads and deforms the earth s crust by performing a convolution sum between daily global barometric pressure data and mass loading green s functions we estimate the time dependent effects of atmospheric loading including those associated with short term synoptic storms on surface point positioning measurements and surface gravity observations we calculate the response for both an oceanless earth and an earth with an inverted barometer ocean load responses for near coastal stations are significantly affected by the inclusion of an inverted barometer ocean peak to peak vertical displacements are frequently 15 20 mm with accompanying gravity perturbations of 3 6 gal baseline changes can be as large as 20 mm or more the perturbations are largest at higher latitudes and during winter months these amplitudes are consistent with the results of rabbel and zschau 1985 who modeled synoptic pressure disturbances as gaussian functions of radius around a central point deformation can be adequately computed using real pressure data from points within about 1000 km of the station knowledge of local pressure alone is not sufficient rabbel and zschau s hypothesized corrections for these displacements which use local pressure and the regionally averaged pressure prove accurate at points well inland but are in general inadequate within a few hundred kilometers of the coast

the malpaisillo formation a sequence of explosive eruptions in the mid to late pleistocene nicaragua central america abstract the subduction related volcanic front in nicaragua consists of the tertiary coyol member in the eastern highlands and the quaternary to recent volcanic arc within the nicaraguan depression although the holocene to recent explosive volcanism has been studied extensively no detailed work has been done on the products of explosive volcanism from quaternary volcanic complexes comprising also the malpaisillo and monte galan calderas the focus of this study the 11 km wide malpaisillo caldera and 3 5 km wide monte galan caldera located 50 km northwest of managua are surrounded by tens of meters of rhyolitic tephras these pyroclastic flow and fall deposits extend proximally at least 11 km to the southeast and 23 km to the southwest with observed depositional thicknesses of 16 m for a single ignimbrite unit or 25 m for the entire section distal deposits are found as far as 350 km offshore in the pacific at least twelve highly explosive large volume eruptive phases with corresponding tephra deposits lpt la paz centro tephra ppt punta de plancha tephra lcbt lower chibola tephra gt guacucal tephra ucbt upper chibola tephra fet la fuente tephra st sabanettas tephra mgt miralago tephra tot tolapa tephra lmt mmt umt lower middle and upper maderas negras tephras are distinguished based on geochemical correlations and similar depositional characteristics radiometric 40ar 39ar ages indicate that most activity related to the large malpaisillo caldera occurred between 570 and 420 ka the large pleistocene malpaisillo and monte galan calderas are characterized by a long lived history and if evolved a distinctly alkaline k2o 2 3 3 8 wt na2o 4 0 4 9 wt geochemical signature compared to the other nicaraguan tephra deposits as a result the previously defined malpaisillo formation has been considerably extended and revised our findings contribute to fill a considerable gap in the long term eruptive history of nicaraguan volcanoes with prominent implications for volcanic hazard evaluation for nicaragua

could the late permian deep ocean have been anoxic models of ocean circulation and biogeochemical cycles are used to speculate about possible mechanisms of deep sea anoxia across the permo triassic boundary two modes of likely late permian ocean thermohaline circulation are identified a vigorous thermal mode driven by cooling in southern polar latitudes and a weaker haline mode driven by evaporation from the subtropics we find that the thermal mode typical of climates such as our own is unlikely to surpport deep sea anoxia the haline mode which might exist in warm climates with enhanced hydrological cycles can lead to significant but periodic depletion of oxygen in the panthalassic deep ocean however owing to the inherent instability of the haline mode a deep sea anoxia persisting for millions of years is not clearly supported by this study though mechanisms emerge which might be consistent with the observed record the enhanced hydrological cycle or reduced oceanic diapycnal mixing required to obtain the haline mode remain unconstrained for the late permian

role of naturally occurring gas hydrates in sediment transport naturally occurring gas hydrates have the potential to store enormous volumes of both gas and water in semi solid form in ocean bottom sediments and then to release that gas and water when the hydrate s equilibrium conditions are disturbed therefore hydrates provide a potential mechanism for transporting large volumes of sediments under the combined low bottom water temperatures and moderate hydrostatic pressures that exist over most of the continental slopes and all of the continental rises and abyssal plains hydrocarbon gases at or near saturation in the interstitial waters of the near bottom sediments will form hydrates the gas can either be autochthonous microbially produced gas or allochthonous catagenic gas from deeper sediments equilibrium conditions that stabilize hydrated sediments may be disturbed for example by continued sedimentation or by lowering of sea level in either case some of the solid gas water matrix decomposes released gas and water volume exceeds the volume occupied by the hydrate so the internal pressure rises drastically if large volumes of hydrate are decomposed part of the once rigid sediment is converted to a gas and water rich relatively low density mud when the internal pressure due to the presence of the compressed gas or to buoyancy is sufficiently high the overlying sediment may be lifted and or breached and the less dense gas cut mud may break through such hydrate related phenomena can cause mud diapirs mud volcanos mud slides or turbidite flows depending on s diment configuration and bottom topography

uranium series accessory crystal dating of magmatic processes complex and protracted crystallization histories over geologic timescales are recorded in accessory minerals e g zircon allanite although magmatic crystallization was traditionally assumed to occur essentially instantaneously for the purposes of interpreting mineral geochronometers with low absolute time resolution for ancient samples it emerged relatively recently that magmatic crystallization can occur over extended durations this discovery arose from applying high spatial resolution accessory mineral dating techniques for uranium series isotopes to young volcanic and cognate plutonic rocks the emerging pattern from these studies is that individual crystals and crystal populations record crystallization episodes lasting from 1 000 to many hundreds of thousands of years accessory mineral dating of volcanic rocks and cognate plutonic xenoliths opens new research avenues for crystal age fingerprinting that correlates pyroclastic deposits lavas and plutonic rocks by using characteristic age dis

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

paleotemperatures and ice volume of the past 27 myr revisited with paired mg ca and 18o 16o measurements on benthic foraminifera 1 we explore the applicability of paired mg ca and 18o 16o measurements on benthic foraminifera from southern ocean site 747 to paleoceanographic reconstructions on pre pleistocene timescales we focus on the late oligocene through pleistocene 27 0 ma history of paleotemperatures and the evolution of the 18o values of seawater 18osw at a temporal resolution of 100 200 kyr absolute paleotemperature estimates depend on assumptions of how mg ca ratios of seawater have changed over the past 27 myr but relative changes that occur on geologically brief timescales are robust results indicate that at the oligocene to miocene boundary 23 8 ma temperatures lag the increase in global ice volume deduced from benthic foraminiferal 18o values but the smaller scale miocene glaciations are accompanied by ocean cooling of 1 c during the mid miocene phase of antarctic ice sheet growth 15 13 ma water temperatures cool by 3 c unlike the benthic foraminiferal 18o values which remain relatively constant thereafter temperatures vary by 3 c and reach maxima at 12 and 8 5 ma the onset of significant northern hemisphere glaciation during the late pliocene is synchronous with an 4 c cooling at site 747 a comparison of our 18osw curve to the haq et al 1987 sea level curve yields excellent agreement between sequence boundaries and times of increasing seawater 18o 16o ratios at 12 11 ma in particular when benthic foraminiferal 18o values do not support a further increase in ice volume the 18osw curve comes to a maximum that corresponds to a major mid miocene sea level regression the agreement between the character of our mg ca based 18osw curve and sequence stratigraphy demonstrates that benthic foramaniferal mg ca ratios can be used to trace the 18osw on pre pleistocene timescales despite a number of uncertainties related to poorly constrained temperature calibrations and paleoseawater mg ca ratios the mg ca record also highlights that deep ocean temperatures can vary independently and unexpectedly from ice volume changes which can lead to misinterpretations of the 18o record

comparative carbon cycle dynamics of the present and last interglacial changes in temperature and carbon dioxide during glacial cycles recorded in antarctic ice cores are tightly coupled however this relationship does not hold for interglacials while climate cooled towards the end of both the last eemian and present holocene interglacials co2 remained stable during the eemian while rising in the holocene we identify and review twelve biogeochemical mechanisms of terrestrial vegetation dynamics and co2 fertilization land use wildfire accumulation of peat changes in permafrost carbon subaerial volcanic outgassing and marine origin changes in sea surface temperature carbonate compensation to deglaciation and terrestrial biosphere regrowth shallow water carbonate sedimentation changes in the soft tissue pump and methane hydrates which potentially may have contributed to the co2 dynamics during interglacials but which remain not well quantified we use three earth system models esms of intermediate complexity to compare effects of selected mechanisms on the interglacial co2 and 13co2 changes focusing on those with substantial potential impacts namely carbonate sedimentation in shallow waters peat growth and in the case of the holocene human land use a set of specified carbon cycle forcings could qualitatively explain atmospheric co2 dynamics from 8 ka bp to the pre industrial however when applied to eemian boundary conditions from 126 to 115 ka bp the same set of forcings led to disagreement with the observed direction of co2 changes after 122 ka bp this failure to simulate late eemian co2 dynamics could be a result of the imposed forcings such as prescribed caco3 accumulation and or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial these experiments also reveal that key natural processes of interglacial co2 dynamics shallow water caco3 accumulation peat and permafrost carbon dynamics are not well represented in the current esms global scale modeling of these long term carbon cycle components started only in the last decade and uncertainty in parameterization of these mechanisms is a main limitation in the successful modeling of interglacial co2 dynamics

regulation of atmospheric co2 by deep sea sediments in an earth system model 1 we have extended the genie 1 earth system model to include a representation of sedimentary stratigraphy and the preservation of biogenic carbonates delivered to the ocean floor this has enabled us to take a novel approach in diagnosing modern marine carbon cycling assimilating observation of the calcium carbonate caco3 content of deep sea sediments with an ensemble kalman filter the resulting calibrated model predicts a mean surface sediment content 32 5 wt close to the observed value 34 8 wt and a global burial rate of caco3 in deep sea sediments of 0 121 pgc yr 1 in line with recent budget estimates of 0 10 0 14 pgc yr 1 we employ the genie 1 model in quantifying the multimillennial scale fate of fossil fuel co2 emitted to the atmosphere in the absence of any interaction between ocean and sediments an equilibrium partitioning of co2 is reached within 1000 years of emissions ceasing with 34 645 ppm remaining in the atmosphere out of a total fossil fuel burn of 4173 pgc an additional 12 of co2 emissions 223 ppm are sequestered as bicarbonate ions hco3 by reaction with deep sea carbonates seafloor caco3 neutralization on a timescale of 1 7 ka excess of carbonate weathering on land over deep sea burial results in a further net transformation of 14 of co2 emissions 261 ppm into hco3 terrestrial caco3 neutralization on a timescale of 8 3 ka we have also assessed the importance of a changing climate in modulating the stabilization of atmospheric co2 through ocean sediment interaction increased ocean stratification suppresses particulate organic carbon export which in turn enhances seafloor caco3 preservation the resulting reduction in the sequestration of fossil fuel co2 represents a new positive feedback on millennial scale climate change

the potential volume of oceanic methane hydrates with variable external conditions gas hydrate abundance in marine sediment depends on gas concentration and the available pore space within certain stability limits potentially gas hydrates can occur between the seafloor and a locus of subbottom depths where geothermal gradients intersect gas gas hydrate pore water equilibrium curves perpendicular to a given continental margin the lens shaped area between these two bounding surfaces a sl varies according to seven basic parameters gas composition water activity a w bottom water temperature t b geothermal gradient g slope depth z slb slope gradient z and sea level relative to the shelf break z 0 assuming pure ch 4 gas 35 km 2 of sediment can host gas hydrate across an average continental margin at a pleistocene lowstand a w 0 981 t b 0 c g 0 c z slb 4000 m z 0 04 z 0 0 however this potential area would decrease with smaller a w higher t b greater g shallower z slb steeper z and lower z 0 and increase with opposite external conditions of the basic parameters temperature t b and g and bathymetry z slb and z can particularly influence the distribution of gas hydrate on continental slopes a hydrothermal gradient with e g surface temperatures t b will also decrease a sl although minimally especially if t b is warm the sum of parallel cross sectional areas along a margin combined with porosity o gives the potential volume of gas hydrate v assuming 200 000 km of continental margin with a o of 50 3 5 10 6 km 3 of pore space can contain gas hydrates at present day a volume that compares favorably with previous estimates 1 2 to 6 4 10 6 km 3 although underlying approaches differ fundamentally since the triassic v glob probably has increased significantly because t b has cooled while total margin length has grown this trend was likely punctuated by at least one major decrease nominally 1 5 to 0 7 10 6 km 3 when t b suddenly rose by 5 c during the latest paleocene thermal maximum lptm a prominent global negative 13 c excursion across the lptm may signify massive release of ch 4 associated with this theoretical drop in v glob

triggering of destructive earthquakes in el salvador we investigate the existence of a mechanism of static stress triggering driven by the interaction of normal faults in the middle american subduction zone and strike slip faults in the el salvador volcanic arc the local geology points to a large strike slip fault zone the el salvador fault zone as the source of several destructive earthquakes in el salvador along the volcanic arc we modeled the coulomb failure stress cfs change produced by the june 1982 and january 2001 subduction events on planes parallel to the el salvador fault zone the results have broad implications for future risk management in the region as they suggest a causative relationship between the position of the normal slip events in the subduction zone and the strike slip events in the volcanic arc after the february 2001 event an important area of the el salvador fault zone was loaded with a positive change in coulomb failure stress 0 15 mpa this scenario must be considered in the seismic hazard assessment studies that will be carried out in this area

tephrochronology of the western gulf of mexico for the last 185 000 years abstract tephra in 31 piston cores from the western gulf of mexico and 7 piston cores from the equatorial pacific were analyzed by electron microprobe six ash layers in the western gulf of mexico were easily distinguished by tio2 feo and cao contents and correlated by geochemistry in order to determine the distribution pattern for each ash layer correlation by geochemistry is an easier more accurate method than biostratigraphic correlation some of the tephras were miscorrelated by biostratigraphy the six tephras were dated by geochemical identification in a piston core with oxygen isotope stratigraphy and the ages are y5 30 000 yr b p y6 65 000 yr b p y8 84 000 yr b p x2 110 000 yr b p w1 136 000 yr b p and w2 185 000 yr b p data from this study corroborated correlations of the y8 tephra in the western gulf of mexico with the d layer in the eastern equatorial pacific ocean none of the other five layers in the gulf of mexico however were found in the pacific ocean the limited distribution of the y5 y6 x2 and w2 ash layers close to mexico indicates possible sources in mexico tephra from the late pleistocene la primavera pumice in mexico however does not correlate with the marine tephra

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

time dependent response of the global ocean clathrate reservoir to climatic and anthropogenic forcing 1 buffett and archer 2004 showed a model of the steady state global ocean clathrate reservoir that reproduces drill data and predicts a global methane inventory of about 5000 gton c the model inventory is very sensitive to ocean temperature with factor of two changes in methane inventory in response to temperature changes of 1 5 c here we explore the potential time dependent behavior of the clathrate reservoir assuming simple first order rate constants for methane accumulation and meltdown in response to changes in the predicted steady state reservoir for melting we divide the reservoir into two parts one melting catastrophically and the other slowly evolution of clathrates through geologic time is very sensitive to the choice of these rate constants a positive feedback exists during a transient meltdown event stronger if the catastrophic melting fraction is high and its melting timescale is fast a clathrate reservoir governed by such kinetics would melt down periodically on a multimillion year timescale determined by the rate constant for clathrate accumulation ideally we would like a model that predicts runaway melting in the paleocene and stability in the pleistocene however the model is most unstable when climate is cold rather than warm opting for stability in the pleistocene constrains the melting kinetic parameters leaving one degree of freedom the grow in timescale must be 5 myr or longer to get the deglacial 13c right but shorter than 10 myr in order for clathrates to have built up through geologically recent cooling the model thus constrained predicts methane fluxes of 200 gton c or less on deglaciations but eventual releases of 2000 4000 gton c in response to a 2000 gton c anthropogenic carbon release anthropogenic climate change differs from a deglaciation in that it warms the ocean to temperatures not seen in millions of years

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

the importance of ocean temperature to global biogeochemistry variations in the mean temperature of the ocean on time scales from millennial to millions of years in the past and projected for the future are large enough to impact the geochemistry of the carbon oxygen and methane geochemical systems in each system the time scale of the temperature perturbation is key on time frames of 1 100 ky atmospheric co2 is controlled by the ocean co2 temperature dependent solubility and greenhouse forcing combine to create an amplifying feedback with ocean temperature the caco3 cycle increases this effect somewhat on time scales longer than f5 10 ky the co2 t feedback can be seen in the climate record from vostok and a model including the temperature feedback predicts that 10 of the fossil fuel co2 will reside in the atmosphere for longer than 100 ky timing is important for oxygen as well the atmosphere controls the ocean on short time scales but ocean anoxia controls atmospheric po2 on million year time scales and longer warming the ocean to cretaceous temperatures might eventually increase po2 by approximately 25 in the absence of other perturbations the response of methane clathrate to climate change in the coming century will probably be small but on longer time scales of 1 10 ky there may be a positive feedback with ocean temperature amplifying the long term climate impact of anthropogenic co2 release d 2004 elsevier b v all rights reserved

the role of co2 decline for the onset of northern hemisphere glaciation the pliocene pleistocene transition ppt from around 3 2 to 2 5 million years ago ma represented a major shift in the climate system and was characterized by a gradual cooling trend and the appearance of large continental ice sheets over northern eurasia and north america paleo evidence indicates that the ppt was accompanied and possibly caused by a decrease in atmospheric co2 but the temporal resolution of co2 reconstructions is low for this period of time and uncertainties remain large therefore instead of applying existent co2 reconstructions we solved an inverse problem by finding a schematic co2 concentration scenario that allows us to simulate the temporal evolution of key climate characteristics in agreement with paleoclimate records to this end we performed an ensemble of transient simulations with an earth system model of intermediate complexity from which we derived a best guess transient co2 scenario for the interval from 3 2 to 2 4 ma that gives the best fit between the simulated and reconstructed benthic 18o and global sea surface temperature evolution our data constrained co2 scenarios are consistent with recent co2 reconstructions and suggest a gradual co2 decline from 375 425 to 275 300 ppm between 3 2 and 2 4 ma in addition to a gradual decline the best fit to paleoclimate data requires the existence of pronounced co2 variability coherent with the 41 kyr 1 kyr 1000 years obliquity cycle in our simulations the long term co2 decline is accompanied by a relatively abrupt intensification of northern hemisphere glaciation at around 2 7 ma this is the result of a threshold behaviour of the ice sheets response to gradual co2 decrease and orbital forcing the simulated northern hemisphere ice sheets during the early pleistocene glacial cycles reach a maximum volume equivalent to a sea level drop of about 40 m both ice volume and benthic 18o are dominated by 41 kyr cyclicity our simulations suggest that before 2 7 ma greenland was ice free during summer insolation maxima and only partly ice covered during periods of minimum summer insolation a fully glaciated greenland comparable to its present day ice volume is modelled only during glacial maxima after 2 7 ma and more continuously after 2 5 ma

space geodesy subsidence and flooding in new orleans a subsidence map of the city offers insight into the failure of the levees during hurricane katrina

miocene to holocene marine tephrostratigraphy offshore northern central america and southern mexico pulsed activity of known volcanic complexes we studied the tephra inventory of fourteen deep sea drill sites of three dsdp and odp legs drilled offshore guatemala and el salvador legs 67 84 138 and one leg offshore mexico leg 66 marine tephra layers reach back from the miocene to the holocene we identified 223 primary ash beds and correlated these between the drill sites with regions along the volcanic arcs and to specific eruptions known from land in total 24 correlations were established between marine tephra layers and to well known quaternary eruptions from el salvador and guatemala additional 25 tephra layers were correlated between marine sites another 108 single ash layers have been assigned to source areas on land resulting in a total of 157 single eruptive events tephra layer correlations to independently dated terrestrial deposits provide new time markers and help to improve or confirm age models of the respective drill sites applying the respective sedimentation rates derived from the age models we calculated ages for all marine ash beds hence we also obtained new age estimates for eight known but so far undated large terrestrial eruptions furthermore this enables us to study the temporal evolution of explosive eruptions along the arc and we discovered five pulses of increased activity 1 a pulse during the quaternary 2 a pliocene pulse between 6 and 3 ma 3 a late miocene pulse between 10 and 7 ma 4 a middle miocene pulse between 17 11 ma and 5 an early miocene pulse 21 ma

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

effects of oceanographic changes on controlling the stability of gas hydrates and the formation of authigenic carbonates at mud volcanoes and seepage sites on the iberian margin of the gulf of cadiz abstract the gulf of cadiz is characterized by extensive active and inactive fluid escape structures which manifest as mud volcanoes diapiric ridges pockmarks and cold seeps the high methane content and the presence of gas hydrates in the shallow sediments of the most active fluid escape structures indicate that these are areas of preferential migration and escape of fluids enriched in hydrocarbons and methane extensive fields of methane derived authigenic carbonates are found at fluid escape structures along the upper and mid continental slope where the mediterranean outflow water is in direct contact with the seafloor at water depths generally 1400 m parts of the basin the estimated u th ages of the authigenic carbonates suggest that they were probably formed during discrete episodes of gas hydrate activity that may have occurred as a result of rapid climatic changes such as the termination of the last glacial stage numerical modelling indicates that seafloor temperature variations associated with glacial interglacial cycles and the changes of the mediterranean outflow pathway could have restricted or eliminated the gas hydrate stability zone at the mud volcanoes shallower than 1400 m resulting in intense fluxes of methane rich fluids to the shallow sediments or even the seafloor this fluid flux was recorded by the microbially mediated precipitation of authigenic carbonates

dynamics of slow moving landslides from permanent scatterer analysis high resolution interferometric synthetic aperture radar insar permanent scatterer data allow us to resolve the rates and variations in the rates of slow moving landslides satellite to ground distances range changes on landslides increase at rates of 5 to 7 millimeters per year indicating average downslope sliding velocities from 27 to 38 millimeters per year time series analysis shows that displacement occurs mainly during the high precipitation season during the 1997 1998 el nino event rates of range change increased to as much as 11 millimeters per year the observed nonlinear relationship of creep and precipitation rates suggests that increased pore fluid pressures within the shallow subsurface may initiate and accelerate these features changes in the slope of a hill resulting from increases in the pore pressure and lithostatic stress gradients may then lead to landslides

a quasi elastic aquifer deformational behavior madrid aquifer case study summary the purpose of this paper is to analyze the quasi elastic deformational behavior that has been induced by groundwater withdrawal of the tertiary detrital aquifer of madrid spain the spatial and temporal evolution of ground surface displacement was estimated by processing two datasets of radar satellite images sar using persistent scatterer interferometry psi the first sar dataset was acquired between april 1992 and november 2000 by ers 1 and ers 2 satellites and the second one by the envisat satellite between august 2002 and september 2010 the spatial distribution of psi measurements reveals that the magnitude of the displacement increases gradually towards the center of the well field area where approximately 80 mm of maximum cumulated displacement is registered the correlation analysis made between displacement and piezometric time series provides a correlation coefficient greater than 85 for all the wells the elastic and inelastic components of measured displacements were separated observing that the elastic component is on average more than 4 times the inelastic component for the studied period moreover the hysteresis loops on the stress strain plots indicate that the response is in the elastic range these results demonstrate the quasi elastic behavior of the aquifer during the aquifer recovery phase ground surface uplift almost recovers from the subsidence experienced during the preceding extraction phase taking into account this unique aquifer system a one dimensional elastic model was calibrated in the period 1997 2000 subsequently the model was used to predict the ground surface movements during the period 1992 2010 modeled displacements were validated with psi displacement measurements exhibiting an error of 13 on average related with the inelastic component of deformation occurring as a long term trend in low permeability fine grained units this result further demonstrates the quasi elastic deformational behavior of this unique aquifer system

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

lowering of glacial atmospheric co2 in response to changes in oceanic circulation and marine biogeochemistry 1 we use an earth system model of intermediate complexity climber 2 to investigate what recent improvements in the representation of the physics and biology of the glacial ocean imply for the atmospheric concentration the coupled atmosphere ocean model under the glacial boundary conditions is able to reproduce the deep salty stagnant water mass inferred from antarctic deep pore water data and the changing temperature of the entire deep ocean when carbonate compensation is included in the model we find a co2 drawdown of 43 ppmv associated mainly with the shoaling of the atlantic thermohaline circulation and an increased fraction of water masses of southern origin in the deep atlantic fertilizing the atlantic and indian sectors of the southern ocean north of the polar front leads to a further drawdown of 37 ppmv other changes to the glacial carbon cycle include a decrease in the amount of carbon stored in the terrestrial biosphere 540 pg c which increases atmospheric co2 by 15 ppmv and a change in ocean salinity resulting from a drop in sea level which elevates co2 by another 12 ppmv a decrease in shallow water caco3 deposition draws down co2 by 12 ppmv in total the model is able to explain more than two thirds 65 ppmv of the glacial to interglacial co2 change based only on mechanisms that are clearly documented in the proxy data a good match between simulated and reconstructed distribution of 13c changes in the deep atlantic suggests that the model captures the mechanisms of reorganization of biogeochemistry in the atlantic ocean reasonably well additional poorly constrained mechanisms to explain the rest of the observed drawdown include changes in the organic carbon caco3 ratio of sediment rain reaching the seafloor iron fertilization in the subantarctic pacific ocean and changes in terrestrial weathering

the arce tephra two subsequent paroxysmal plinian eruptions from coatepeque caldera el salvador abstract the coatepeque volcanic complex in el salvador produced at least four plinian eruptions within the last 80 kyr the eruption of the 72 ka old arce tephra formed the coatepeque caldera and was one of the most powerful explosive eruptions in el salvador hitherto it was thought that the arce tephra had been emplaced only by one mostly plinian eruptive event that ended with the deposition of a thick ignimbrite however our stratigraphic geochemical and zircon data reveal a temporally closely spaced double eruption separated by a gap of only a couple of hundred years and we therefore distinguish lower and upper arce tephras both eruptions produced in the beginning a series of fallout units generated from fluctuating eruption columns and turning wind directions the final phase of the upper arce eruption produced surge deposits by several eruption column collapses before the terminal phase of catastrophic ignimbrite eruption and caldera collapse mapping of the individual tephra units including the occurrences of distal marine and lacustrine ash layers in the pacific ocean the guatemalan lowlands and the caribbean sea result in 25 6 km3 tephra volume areal distribution of 4 105 km2 and eruption column heights between 20 33 km for the lower arce eruption and 40 5 km3 tephra volume including 10 km3 for the ignimbrite distributed across 6 105 km2 and eruption column heights of 23 28 km for the upper arce eruption these values and the detailed eruptive sequence emphasize the great hazard potential of possible future highly explosive eruptions at coatepeque caldera especially for this kind of double eruption

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

a coupled model study of the last glacial maximum was part of the north atlantic relatively warm a coupled ocean atmosphere general circulation model is used to simulate the climates of today and the last glacial maximum lgm the model which does not require artificial flux adjustments produces a pattern of cooling at the lgm that is broadly consistent with the findings from simpler models and palaeoclimatic data however changes to the ocean circulation produce anomalously warm lgm surface conditions over parts of the north atlantic seemingly at odds with palaeoceanographic data the thermohaline circulation is intensified for several centuries as is the northward heat transport in the atlantic equatorward of 55 n but this may be a transient result mechanisms that lead to this response are discussed

observing and assessing nontidal ocean loading using ocean continuous gps and gravity data in the adriatic area 1 the effect of nontidal ocean loading ntol is observed in the height series of four permanent gps stations in the northern adriatic a validation of the ecco model is performed by comparing model estimates of sea level anomalies from tide gauges with topex poseidon data and ecco model estimates of bottom pressure with those derived from temperature and salinity observations theamplitudesoftheeccosea levelanomaly are found to be 1 4 times smaller than observations bottom pressure is 2 times smaller using a green s functions approach to determine elastic deformations the ecco ocean bottom pressure is used to estimate surface displacements at the gps sites model results were compared with the height series and with the observed ntol effect the height series and the predicted ntol are highly correlated at all four stations the analysis performed on superconducting gravimeter data at the medicina station also shows high correlation index terms 1208 geodesy and gravity crustal movements intraplate 8110 1223 geodesy and gravity ocean earth atmosphere interactions 3339 1243 geodesy and gravity space geodetic surveys 1299 geodesy and gravity general or miscellaneous 1829 hydrology groundwater hydrology citation zerbini s f matonti f raicich b richter and t van dam 2004 observing and assessing nontidal ocean loading using ocean continuous gps and gravity data in the adriatic area geophys res lett 31 l 23609 doi 10 1029 2004gl021185

effect of annual signals on geodetic velocity 1 our analysis of global positioning system gps site coordinates in a global reference frame shows annual variation with typical amplitudes of 2 mm for horizontal and 4 mm for vertical with some sites at twice these amplitudes power spectrum analysis confirms that gps time series also contain significant power at annual harmonic frequencies with spectral indices 1 2 which indicates the presence of repeating signals van dam et al 2001 showed that a major annual component is induced by hydrological and atmospheric loading unless accounted for we show that annual signals can significantly bias estimation of site velocities intended for high accuracy purposes such as plate tectonics and reference frames for such applications annual and semiannual sinusoidal signals should be estimated simultaneously with site velocity and initial position we have developed a model to calculate the level of bias in published velocities that do not account for annual signals simultaneous estimation might not be necessary beyond 4 5 years as the velocity bias rapidly becomes negligible minimum velocity bias is theoretically predicted at integer plus half years as confirmed by tests with real data below 2 5 years the velocity bias can become unacceptably large and simultaneous estimation does not necessarily improve velocity estimates which rapidly become unstable due to correlated parameters we recommend that 2 5 years be adopted as a standard minimum data span for velocity solutions intended for tectonic interpretation or reference frame production and that we be skeptical of geophysical interpretations of velocities derived using shorter data spans

global change and the biogeochemistry of the north sea the possible role of phytoplankton and phytoplankton grazing phytoplankton plays a dominant role in shelf biogeochemistry by producing the major part of organic matter part of the organic matter will reach the sediment where diagenetic processes like denitrification apatite formation or burial will remove nutrients from the biogeochemical cycle in this article current knowledge on the decadal plankton variability in the north sea is summarized and possible implications of these changes for the biogeochemistry of the north sea are discussed most of the observed interdecadal dynamics seem to be linked to large scale oceanographic and atmospheric processes prominent changes in the north sea ecosystem have taken place around 1979 and 1988 in general the phytoplankton color cprs indicator of phytoplankton biomass reached minimum values during the end of the 1970s and has increased especially since the mid 1980s changes with a similar timing have been identified in many time series from the north sea through the entire ecosystem and are sometimes referred to as regime shifts it is suggested that the impact of global change on the local biogeochemistry is largely driven by the phyto and zooplankton dynamics during spring and early summer at that time the extent of zooplankton phytoplankton interaction either allows that a large part of the new production is settling to the sediment or that a significant part of the new production including the fixed nutrients is kept within the pelagic system the origin of the extent of the phytoplankton zooplankton interaction in spring is probably set in the previous autumn and winter in coastal areas both large scale atmospheric and oceanographic changes as well as anthropogenic factors influence the long term dynamics due to eutrophication local primary production nowadays still is up to five times higher than during pre industrial conditions despite a decreasing trend recently introduced species have strengthened the filter feeder component of coastal ecosystems especially in shallow coastal seas like the wadden sea this will enhance particle retention shift organic matter degradation to the benthic compartment and enhance nutrient removal from the biogeochemical cycle by denitrification or apatite formation

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

sea level changes forced ice breakouts in the last glacial cycle new results from coral terraces abstract sea level cycles recorded by coral terraces at huon peninsula hp in papua new guinea match rapid climate changes that occurred between 30 000 and 65 000 years ago seen in greenland ice cores and marine sediments each cycle of 6000 7000 years ended with a sea level rise of 10 15 m lasting 1000 2000 years following a longer period of falling sea level precise dating shows that each rise corresponds to a heinrich episode of ice rafted detritus in north atlantic signalling massive ice outbreak from north america sea level may be the trigger that forced near synchronous breakouts of ice from north america and eastern greenland the hp sea level changes also correspond to similar cycles in benthic oxygen isotopes reported from the north atlantic which are too large to be explained entirely in terms of ice volumes jointly the sea level and isotope records suggest that the north atlantic deep ocean cooled as sea level fell and warmed as sea level rose in each 6000 year cycle

a movable trigger fossil fuel co2 and the onset of the next glaciation 1 the initiation of northern hemisphere ice sheets in the last 800 kyr appears to be closely controlled by minima in summer insolation forcing at 65 n beginning from an initial typical interglacial pco2 of 280 ppm the climber 2 model initiates an ice sheet in the northern hemisphere when insolation drops 0 7 standard deviation or 15 w m2 below the mean this same value is required to explain the history of climate using an orbitally driven conceptual model based on insolation and ice volume thresholds paillard 1998 when the initial baseline pco2 is raised in climber 2 a deeper minimum in summertime insolation is required to nucleate an ice sheet carbon cycle models indicate that 25 of co2 from fossil fuel combustion will remain in the atmosphere for thousands of years and 7 will remain beyond one hundred thousand years archer 2005 we predict that a carbon release from fossil fuels or methane hydrate deposits of 5000 gton c could prevent glaciation for the next 500 000 years until after not one but two 400 kyr cycle eccentricity minima the duration and intensity of the projected interglacial period are longer than have been seen in the last 2 6 million years

some remarks on the origin of foredeeps abstract geological observations show that there are two main types of foredeep basins on the base of their subsidence rate and their relationship with the associated orogen or accretionary wedge high rates of subsidence up to 1600 m myr and a ratio lower than 1 between the area of the elevated belt and the area of the basin characterize the foredeeps associated with w dipping subduction low rates of subsidence up to 300 m myr and a ratio higher than 1 between the area of the orogen and the area of the basin characterize the foredeeps associated with e or ne dipping subductions this observation enables us to interpret the slow filling of foredeeps of the first type and the much faster filling of foredeeps of the second type moreover w dipping subductions have a steeper and faster monocline bounding the base of the deep foredeep in contrast to e or ne dipping subductions which have a shallower monocline this differentiation supports the notion of the eastward mantle flow with respect to the lithosphere detected in the hot spot reference frame in this view the foredeep depth in w dipping subductions is mainly controlled by the roll back of the subduction hinge pushed by the relative eastward mantle flow while foredeep depth in e or ne dipping subductions is instead mainly generated by the load of the thrust sheets and by the roll back of the subduction hinge due to the advancing upper plate contrasting the upward push of the mantle the shape of the foredeeps is regularly arcuate in case of w dipping subduction while is linear or following the shape of the inherited continental margin in case of e or ne dipping subduction fold development in the two opposite foredeeps is significantly different in w dipping subduction the folds are transported down in subduction while they are forming and consequently they are poorly eroded syntectonic sediments drape a preserved fold in the e ne dipping subduction folds and thrust sheets are instead uplifted and deeply eroded this is also predicted by the envelope of the crests in the two distinct accretionary wedges in the w dipping case the envelope may dip toward the subduction while it is rising toward the hinterland in the other cases this approach may explain the differences in terms of geometries amount and rates of subsidence between the foredeeps around the adriatic plate for instance the foredeep of the southern alps back thrust belt foredeep is deformed in the western part by the later apenninic foredeep development associated with the sinistral oblique ramp of the w dipping adriatic plate subduction the relationship in the frontal parts of a thrust belt between accretion and eustacy has to be analyzed in terms of when where and how fast thrusts propagation took place with respect to the randomly distributed sea level third order fluctuations and by the type of subduction which is connected to the foredeep and thrust belt or accretionary wedge therefore the stratigraphic patterns in foredeep basins are peculiar and casual successions that record the combination of regional tectonic evolution with independent wider scale sea level changes

a combination of space and terrestrial geodetic techniques to monitor land subsidence case study the southeastern po plain italy 1 the southeastern po plain is affected by high natural and anthropogenic subsidence the area is well suited to test the application of an observational strategy which combines different techniques to extract information on the spatial and temporal variability of the subsidence the simultaneous availability at a few stations of several geodetic observation techniques such as global positioning system gps gravity and interferometric synthetic aperture radar insar allows for validation of the individual time series the combination takes advantage of the complementary strengths of each technique by overcoming the limitations inherent in each single technique alone the combination of velocities derived from the gps and gravity data further complemented by the results of the insar permanent scatterers technique allows us to monitor continuously in space and time vertical crustal movements this high density information is of major importance for understanding the processes responsible for the observed deformation here long term trends were derived enabling us to map the behavior of subsidence even exceeding 20 mm yr with high spatial resolution in the southeastern po plain the uplifting behavior of the apennines chain bordering the po plain is identified together with a narrow zone separating the contrasting vertical crustal movements

the respiratory health hazards of volcanic ash a review for volcanic risk mitigation studies of the respiratory health effects of different types of volcanic ash have been undertaken only in the last 40 years and mostly since the eruption of mt st helens in 1980 this review of all published clinical epidemiological and toxicological studies and other work known to the authors up to and including 2005 highlights the sparseness of studies on acute health effects after eruptions and the complexity of evaluating the long term health risk silicosis non specific pneumoconiosis and chronic obstructive pulmonary disease in populations from prolonged exposure to ash due to persistent eruptive activity the acute and chronic health effects of volcanic ash depend upon particle size particularly the proportion of respirable sized material mineralogical composition including the crystalline silica content and the physico chemical properties of the surfaces of the ash particles all of which vary between volcanoes and even eruptions of the same volcano but adequate information on these key characteristics is not reported for most eruptions the incidence of acute respiratory symptoms e g asthma bronchitis varies greatly after ashfalls from very few if any reported cases to population outbreaks of asthma the studies are inadequate for excluding increases in acute respiratory mortality after eruptions individuals with pre existing lung disease including asthma can be at increased risk of their symptoms being exacerbated after falls of fine ash a comprehensive risk assessment including toxicological studies to determine the long term risk of silicosis from chronic exposure to volcanic ash has been undertaken only in the eruptions of mt st helens 1980 usa and soufriere hills montserrat 1995 onwards in the soufriere hills eruption a long term silicosis hazard has been identified and sufficient exposure and toxicological information obtained to make a probabilistic risk assessment for the development of silicosis in outdoor workers and the general population a more systematic approach to multi disciplinary studies in future eruptions is recommended including establishing an archive of ash samples and a website containing health advice for the public together with scientific and medical study guidelines for volcanologists and health care workers

a global biogeochemical perturbation across the silurian devonian boundary ocean continent biosphere feedbacks abstract the large scale global biogeochemical perturbation across the silurian devonian s d boundary recorded in the major positive excursion of the 13c time curve klonk event of an amplitude of 2 5 to 3 0 max 4 0 in europe and up to 5 0 in north america reflects a unique combination of palaeogeographic biogeochemical and evolutionary processes in the late caledonian geodynamic setting the steady sulfur isotopic ratios show an overall stability of the s d oceanic geochemical system as a whole and do not indicate any synchronous changes in anoxic deep oceanic and sediment processes therefore this led us to a hypothesis that the crucial changes that contributed to the recorded carbon cycling turnover are related to rapidly evolving ocean continent biosphere feedback coastal zones of the latest silurian epicontinental seas accumulated considerable quantities of organic carbon from early vascular vegetation which explosively expanded to inhabit vast near coastal shallows and deltas large primary production of these early terrestrial plants and rapidly enhanced sedimentary burial of organic carbon were also responsible for co2 drawdown which have resulted in reversed greenhouse effect and a global climatic cooling tendency this feedback was blocked when the sea level gradually dropped and led to shrinking of the silurian epicontinental seas and the growing climatic deterioration during the s d transition limited primary production furthermore continued processes of regressive abrasion and erosion limited the storage of organic carbon as well as the efficiency of the carbonate factory during the following early devonian greenhouse interval marine regression and active latest caledonian tectonism promoted progressive weathering of the sedimentary organic matter the oxidation of c rich deposits caused the subsequent growth of co2 levels in the early devonian culminating in the warming of global climate

glacial interglacial changes in subantarctic sea surface temperature and δ18o water using foraminiferal mg laboratory culturing experiments with living globigerina bulloides indicate that mg ca is primarily a function of seawater temperature and suggest that mg ca of fossil specimens is an effective paleotemperature proxy using culturing results and a core top neogloboquadrina pachyderma calibration we have estimated glacial interglacial changes in sea surface temperature sst using planktonic mg ca records from core rc11 120 in the subantarctic indian ocean 43 s 80 e and core e11 2 in the subantarctic pacific ocean 56 s 115 w our results suggest that glacial sst was about 4 c cooler in the subantarctic indian ocean and 2 5 c cooler in the subantarctic pacific comparison of sst and planktonic 18o records indicates that changes in sst lead changes in 18o by on average 1 3 kyr the glacial interglacial temperature change indicated by the subantarctic mg ca records suggests that temperature accounts for 40 60 of the foraminiferal 18o change we have used the mg ca based sst estimates and 18o determinations to generate site specific seawater 18o records which suggest that seawater 18o was on average 1 more positive during glacial episodes compared with interglacial episodes

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

sar monitoring of progressive and seasonal ground deformation using the permanent scatterers technique spaceborne differential radar interferometry has proven a remarkable potential for mapping ground deformation phenomena e g urban subsidence volcano dynamics coseismic and postseismic displacements along faults as well as slope instability however a full operational capability has not been achieved yet due to atmospheric disturbances and phase decorrelation phenomena these drawbacks can often be at least partially overcome by carrying out measurements on a subset of image pixels corresponding to natural or artificial stable reflectors permanent scatterers ps and exploiting long temporal series of interferometric data this approach allows one to push the measurement precision very close to its theoretical limit in the order of spl sim 1 mm for c band european remote sensing ers like sensors in this paper the detection of both time uniform and seasonal deformation phenomena is addressed and a first assessment of the precision achievable by means of the ps technique is discussed results highlighting deformation phenomena occurring in two test sites in california are reported fremont in the southern bay area and san jose in the santa clara valley

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