comparison of water column co2aq with sedimentary alkenone based estimates a test of the alkenone co2 proxy 1 the stable carbon isotopic compositions of alkenones have been used to interpret the long term history of the partial pressure of atmospheric carbon dioxide pco2 although extensive water column and culture studies document the potential utility and limitations of this approach to date the accuracy of pco2 values derived from sedimentary alkenones remains untested for this study we establish holocene aged alkenone based co2aq estimates co2aq alk from 20 sites along a central pacific ocean transect and compare them against both observed modern water column co2aq and estimated preindustrial concentrations at the depth of alkenone production at each site although the co2aq alk track measured water column values they are conspicuously lower than modern values across the subtropics this offset likely reflects the contributions of anthropogenic co2 in modern surface waters relative to preindustrial concentrations at the time of alkenone production when a model based estimate of anthropogenic co2 is removed from the modern observed values a majority 84 of co2aq alk falls within 20 of modeled preindustrial values consistency between the modeled and alkenone based estimates of preindustrial co2 levels points to the relative accuracy of the alkenone co2 method across a wide range of ocean and biogeographic regimes provided that phosphate concentrations at the depth of haptophyte production are reasonably constrained it further suggests that light limited growth and or active carbon uptake if they occur have a negligible effect on reconstructed co2aq

changes in seismicity and stress loading on subduction faults in the kanto region japan 2011 2014 seismic activity has increased in the kanto region japan following the 2011 m9 0 tohoku earthquake we here reassess this increase up to june 2014 to show that normal omori like relaxation characterizes the activity on crustal faults as well as on the philippine sea plate but not on the deeper pacific plate there repeating earthquakes display a twofold rate of occurrence still ongoing in june 2014 as compared to the pre tohoku rate suggesting enhanced creep we compute the coulomb stress changes on the upper locked portion of the philippine sea plate which last ruptured in 1923 we find that this fault was little affected by either the coseismic the postseismic the accelerated creep or the 2011 boso silent slip event

an effect of dissolved nutrient concentrations on alkenone based temperature estimates the ratio of 37 carbon diunsaturated to diunsaturated and triunsaturated alkenones uk 37 produced by some haptophytes is widely used as a proxy for past sea surface temperatures however our isothermal culturing experiments with emiliania huxleyi clone ccmp372 show uk 37 values to also vary with nutrient availability and cell division rate these results provide a reasonable explanation for large isothermal variation in uk 37 values of single coccolithophorid strains grown in culture they also suggest that alkenone based estimates of past sea surface temperatures may have been influenced by dissolved nutrient concentrations as well as by temperature

stable carbon isotope patterns of marine biomarker lipids in the arctic ocean during eocene thermal maximum 2 the middle paleocene through early eocene long term gradual warming was superimposed by several transient warming events such as the paleocene eocene thermal maximum petm and eocene thermal maximum 2 etm2 both events show evidence for extreme global warming associated with a major injection of carbon into the ocean atmosphere system but the mechanisms of carbon injection and many aspects of the environmental response are still poorly understood in this study we analyzed the concentration and stable carbon isotopic delta c 13 composition of several sulfur bound biomarkers derived from marine photoautotrophs deposited in the arctic ocean at similar to 85 degrees n during etm2 the presence of sulfur bound biomarkers across this event points toward high primary productivity and anoxic bottom water conditions the previously reported presence of isorenieratene derivatives indicates euxinic conditions in the photic zone likely caused by a combination of enhanced primary productivity and salinity stratification the negative carbon isotope excursion measured at the onset of etm2 for several biomarkers ranges between 3 and 4 5 much larger than the similar to 1 4 recorded in marine carbonates elsewhere suggesting substantial enhanced isotopic fractionation by the primary producers likely due to a significant rise in pco 2 in the absence of biogenic carbonates in the etm2 section of our core we use coeval planktonic delta c 13 from elsewhere to estimate surface water delta c 13 in the arctic ocean and then apply the relation between isotopic fractionation and pco 2 originally calibrated for haptophyte alkenones to three selected organic biomarkers i e s bound phytane c 35 hopane and a c 25 highly branched isoprenoid this yields pco 2 values potentially in the range of four times preindustrial levels however these estimates are uncertain because of a lack of knowledge on the importance of pco 2 on photosynthetic isotopic fractionation

depth ranges of alkenone production in the central pacific ocean we report analytical results of long chain c 37 c 39 alkenones in the surface sediments taken along a latitudinal transect at 175 e from 48 n to 15 s unsaturation degree of c 37 alkenones u k 37 indicated that alkenone temperature is the highest about 28 3 c in the tropical pacific and decreases toward 48 n about 10 1 c although the latitudinal trend of the alkenone temperature is generally similar to that of the observed sea surface temperature of the surface mixed layer the former exhibits markedly lower values than the latter does in the midlatitude 35 19 n on the basis of the comparisons between water column temperatures and alkenone temperatures in the surface sediments we estimated that in the midlatitudes alkenones are produced in the thermocline waters whereas in the high 48 40 n and low 10 n 2 s latitudes they are produced in the surface mixed layer this result is supported by the depth distribution of emiliania huxleyi and gephyrocapsa oceanica along a 155 w transect in the central pacific the latitudinal distribution of the alkenone production layers estimated from u k 37 is found to be consistent with that of the nitrate suggesting that the depth of alkenone production is mainly controlled by the nutrient supply from deeper waters alkenones in the sediments exhibited relatively large abundances in 43 27 n with a maximum at 30 n which may be explained by high productivity of haptophyte algae in kuroshio extension

the role of carbon dioxide during the onset of antarctic glaciation earth s modern climate characterized by polar ice sheets and large equator to pole temperature gradients is rooted in environmental changes that promoted antarctic glaciation 33 7 million years ago onset of antarctic glaciation reflects a critical tipping point for earth s climate and provides a framework for investigating the role of atmospheric carbon dioxide co2 during major climatic change previously published records of alkenone based co2 from high and low latitude ocean localities suggested that co2 increased during glaciation in contradiction to theory here we further investigate alkenone records and demonstrate that antarctic and subantarctic data overestimate atmospheric co2 levels biasing long term trends our results show that co2 declined before and during antarctic glaciation and support a substantial co2 decrease as the primary agent forcing antarctic glaciation consistent with model derived co2 thresholds

diatom δ18o evidence for the development of the modern halocline system in the subarctic northwest pacific at the onset of major northern hemisphere glaciation establishing a time frame for the development of the modern halocline and stratified water column in the subarctic north pacific has significant paleoclimatic implications here we present a d18o diatom record consisting of only two species that represents autumn winter conditions in the region across the onset of major northern hemisphere glaciation boundary at circa 2 73 ma a decrease in d18o diatom of 4 6 occurs whereas previously published d18o foram results show a 2 6 increase the d18o diatom and uk37 sea surface reconstructions indicate both a significant freshening of 2 4 practical salinity units and an increase in surface temperatures in the summer to early winter period from circa 2 73 ma onward in contrast the concomitant increase in d18o foram is likely to be reflective of conditions beneath the mesothermal structure and or spring conditions when warmer sea surface temperatures are not present in the region these results are consistent with the development of the modern halocline system at 2 73 ma with year round stratification of the water column and a strengthened seasonal thermocline during the summer to early winter period resulting in one of the largest summer to winter temperature gradients in the open ocean the onset of stratification would also have led to a warm pool of surface water from circa 2 73 ma which may have provided a potential source of extra moisture needed to supply the growing north american ice sheets at this time

molecular carbon isotopic fractionation of algal lipids during decomposition in natural oxic and anoxic seawaters abstract to evaluate molecular carbon isotopic fractionation of algal lipids during oxic and anoxic degradation emiliania huxleyi a marine haptophyte was incubated in seawater collected from two depths 30 and 930 m in the cariaco basin three classes of algal lipids alkenones fatty acids and sterols showed a degradation pattern characterized by complete loss in oxic seawater within 2 3 months the only exception was 16 0 fatty acid but 10 40 of initial algal lipids remained in the anoxic seawater after 3 months incubation oxic degradation rate constants of alkenones and fatty acids were generally 2 3 times higher than those derived from anoxic incubations however two sterols had similar degradation rate constants in oxic and anoxic seawater there was little preferential degradation of 37 3 relative to 37 2 alkenone in oxic and anoxic seawater leading to insignificant changes for u 37 k paleotemperature indicator in spite of alkenone degradation during oxic and anoxic degradation the same three classes of algal lipids exhibited different patterns of molecular carbon isotopic fractionation depletion 4 to 6 relative to initial value in 13 c for alkenones enrichment 2 to 7 relative to initial value for fatty acids and no change for sterols we postulate that the contrasting molecular isotopic fractionation patterns which depend on the structure of the lipid compounds are likely caused by different degradation reactions at specific functional groups where the carbon atoms may have dissimilar isotopic ratios from other carbon atoms in the molecules due to the differences in original precursors and synthesis pathways laboratory observation of these patterns of lipid fractionations during decomposition of a single phytoplankton material suggests that diagenetic processes can alter the molecular isotopic signals of preserved organic matter in a variety of ways

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

refining the alkenone pco2 method i lessons from the quaternary glacial cycles abstract the alkenone pco2 method is one of the most widely used approaches to reconstruct atmospheric co2 in the cenozoic the method depends upon fractionation of stable carbon isotopes during algal photosynthesis expressed as ep37 2 and a physiological scaling parameter b that accounts for biological factors such as growth rate cell size and membrane permeability alkenone derived co2 records for the late pleistocene however are poorly correlated with ice core co2 challenging the classic model that considers most of the co2 used for coccolithophore photosynthesis to be acquired through simple diffusion in this study we investigate the nature of the b term and the underlying patterns of the sensitivity of ep37 2 to pco2 changes we generated two new ep37 2 records from the south china sea md01 2392 and tropical atlantic ocean odp 668b and compiled other published ep37 2 records over glacial interglacial cycles using the ep37 2 data ocean temperature estimates and ice core co2 we were able to back calculate the corresponding values of b at all locations b varies over glacial cycles the highest values of b correspond to peak interglacial stages indicating that the phytoplankton growth rate is faster or cell size is smaller during interglacials than during glacial periods we further show that the range of ep37 2 between glacial and interglacial conditions ep37 2 scales with growth conditions consistent with the predictions of the carbon isotope fractionation model based on co2 diffusion in other words the sensitivity of ep37 2 to pco2 changes increases where the modern b values are large contradicting the recommendations that oligotrophic sites are the best for alkenone co2 applications because of the presumed stability of b using the average back calculated b value for each site the composite pco2 estimates from md01 2392 and odp 668b the two sites with adequate ep37 2 sensitivity show broad agreement with the ice core co2 record

diazotrophic cyanobacteria as the major photoautotrophs during mid cretaceous oceanic anoxic events nitrogen and carbon isotopic evidence from sedimentary porphyrin abstract we determined both the nitrogen and carbon isotopic compositions of nickel chelated deoxophylloerythroetioporphyrin ni dpep a major sedimentary porphyrin extracted from the livello selli and livello bonarelli black shales deposited in the western tethys sea during mid cretaceous oceanic anoxic events oaes based on empirical isotopic relationships between the tetrapyrrole nuclei of chlorophylls and photoautotroph cells we estimate that the mean nitrogen isotopic composition of the entire photoautotrophic communities during these periods ranged from 2 to 1 this result strongly suggests that n2 fixation was an important primary process in photoautotrophic production during these oaes the estimated carbon isotopic composition of the photoautotrophs was elevated between 20 and 22 relative to typical cretaceous examples indicating as much as a 5 reduction in the magnitude of carbon isotopic fractionation associated with photosynthesis during oaes in the western tethys sea this anomaly can be well explained if cyanobacteria were the dominant producers because they commonly conduct carboxylation and or active transport of carbon substrates resulting in reduced carbon isotopic fractionation we therefore conclude that diazotrophic cyanobacteria were the dominant components of primary production during oae 1a and oae 2 in the western tethys sea

interplate quasi static slip off sanriku ne japan estimated from repeating earthquakes 1 space time distribution of quasi static slip on the plate boundary off sanriku northeastern ne japan was estimated by using small repeating earthquakes we found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area we regarded these repeating events as creepmeters embedded on the plate boundary the results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi static slips in the surrounding areas

distribution of aseismic slip rate on the hayward fault inferred from seismic and geodetic data 1 we solve for the slip rate distribution on the hayward fault by performing a least squares inversion of geodetic and seismic data sets our analysis focuses on the northern 60 km of the fault interferometric synthetic aperture radar insar data from 13 independent ers interferograms are stacked to obtain range change rates from 1992 to 2000 horizontal surface displacement rates at 141 bench marks are measured using gps from 1994 to 2003 surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion the fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface south of the city of hayward a steeply east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth the inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of 5 mm yr to a depth of 4 6 km the interferometric synthetic aperture radar insar data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath point pinole although the insar data might be complicated by a small dip slip component at this location a low slip rate patch of 1 mm yr is inferred beneath san leandro consistent with the source location of the 1868 earthquake we calculate that the entire fault is accumulating a slip rate deficit equivalent to a mw 6 77 0 05 per century however this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip

characteristic repeating earthquakes in an arc continent collision boundary zone the chihshang fault of eastern taiwan abstract creeping crustal faults often generate a large number of microearthquakes and less commonly they may also produce major earthquakes that rupture the brittle crust the chihshang fault in eastern taiwan is characterized by such behavior and has been known to undergo 2 3 cm yr surface creep making it one of the most active creeping thrust faults known in the world it gives an excellent opportunity to study how a creeping fault can generate large earthquakes however the understanding of fault behavior at depth in this area has been limited due to sparse sampling from seismic and geodetic stations in this study we determine and evaluate a population of repeating earthquakes to improve the understanding of deep fault deformation we propose a repeating sequence identification scheme in the region where the station coverage is sparse and one sided using this identification method we found 30 m 2 3 characteristic repeating sequences under the northern half of the chihshang fault at 7 23 km depth slip estimates from these sequences indicate an average slip rate of 3 cm yr which is consistent with the rate inferred from surface geodetic measurements we infer that the 30 km long chihshang fault is creeping along its northern half and locked in the south consistent with the occurrence of the 2003 ml 6 4 earthquake on the southern fault section

carbon isotopic fractionation ep of c37 alkenones in deep sea sediments its potential as a paleonutrient proxy 1 we compared ocean atlas values of surface water po43 and co2 aq against the carbon isotopic fractionation ep of alkenones obtained from surface sediments of the south atlantic and the central pacific pacific data are from pagani et al 2002 we observed a positive correlation between ep and 1 co2 aq which is opposite of what would be expected if the concentration of co2 aq were the major factor controlling the carbon isotopic fractionation of c37 2 alkenones instead we found inverse relationships between ep and po43 for the two ocean basins for the atlantic ep 4 6 po43 15 1 r 0 76 for the pacific ep 4 1 po43 13 7 r 0 64 suggesting that ep is predominantly controlled by growth rate which in turn is related to nutrient concentration the similarity of the slopes implies that a general relationship between both parameters may exist using the relationship obtained from the south atlantic we estimated surface water nutrient concentrations for the past 200 000 years from a deep sea sediment core recovered off angola low ep values indicating high nutrient concentrations coincide with high contents of total organic carbon and c37 alkenones low surface water temperatures and decreased bulk 15n values suggesting an increased upwelling of nutrient rich cool subsurface waters as the main cause for the observed ep decrease

interactions and triggering in a 3 d rate and state asperity model we present a 3 d continuous quasi dynamic rate and state model of multiple seismic asperities forced by surrounding aseismic creep and motivated by observations of coplanar multiplets our model allows to study the physics of interactions among a set of asperities first we show that the amount of interactions and clustering characterized by the omori law and interevent time distribution depends on how far the system is from a critical density of asperities which is related to the friction properties of the barriers separating the sources this threshold controls the ability of a population of asperities to destabilize the creeping barriers between them and therefore determines whether dynamic sequences including several asperities in the same event might occur in agreement with what is expected from observed magnitude frequency distributions therefore the concept of critical density of asperity provides a mechanical interpretation of statistical properties of seismicity as an illustration we used our numerical results in the specific case of parkfield in the period preceding the mw 6 2004 earthquake in order to infer the steady state friction parameter a b characterizing the creep of this part of the san andreas fault we estimate a value of a b that locally exceeds 0 001 which is in the upper range of what has already been proposed for the postseimic period of the mw 6 2004 parkfield earthquake

variability of repeating earthquake behavior along the longitudinal valley fault zone of eastern taiwan 1 two major clusters of repeating earthquake sequences res are found on two fault patches near the longitudinal valley fault lvf in eastern taiwan the chihshang segment to the south and the hualien segment to the north the 25 m 2 3 4 6 res on the hualien segment are widely distributed in a nne direction over a distance of 45 km whereas on the chihshang segment the 30 m 2 2 3 4 res have a shorter along strike extent of about 15 km the longer spatial extent of res on the hualien segment may indicate a wider distributed creeping zone at depth m 3 8 res are observed on the hualien segment and are characterized by quasiperiodic recurrence statistical analysis of the size and number of earthquakes adjacent to the res indicates that the smaller number of large earthquakes in the vicinity may explain the quasiperiodic recurrence of res we argue that on the hualien segment m 4 or larger earthquakes are isolated enough in space to facilitate the occurrence of repeated ruptures

quaternary fluctuations in the northern hemisphere trade winds and westerlies the mass accumulation rate and grain size of the total colian component isolated from pelagic sediment in two north pacific cores piston core kk75 02 under the prevailing westerlies and deep sea drilling project site 503 beneath the trade winds have been used to evaluate changes in the intensity of atmospheric circulation and source area aridity over the past 700 000 yr the eolian grain size a direct indicator of wind intensity fluctuates at periodicities similar to those calculated for the earth s orbital parameters of precession obliquity and eccentricity both sites display greater variability in wind intensity prior to 250 000 yr ago eolian accumulation rates an indicator of source area aridity fluctuate at periodicities similar to those of the glacial interglacial cycles lower eolian accumulation rates during colder glacial times most likely reflect increased glacial age humidity at central asian and central american source areas

the influence of air sea exchange on the isotopic composition of oceanic carbon observations and modeling although the carbon isotropic composition of ocean waters after they leave the surface ocean is determined by biological cycling air sea exchange affects the carbon isotopic composition of surface waters in two ways the equilibrium fractionation between oceanic and atmospheric carbon increases with decreasing temperature in southern ocean surface waters this isotopic equilibrium enriches delta sup 13 c relative to the delta sup 13 c expected from uptake and release of carbon by biological processes alone similarly surface waters in the subtropical gyres are depleted in delta sup 13 c due to extensive air sea exchange at warm temperatures countering the tendency toward isotopic equilibration with the atmosphere a relatively slow process are the effects of the equilibration of co sub 2 itself a much faster process in regions where there is a net transfer of isotopically light co sub 2 from the ocean to the atmosphere e g the equator surface waters become enriched in sup 13 c whereas in regions where isotopically light co sub 2 is entering the ocean e g the north atlantic surface waters become depleted in sup 13 c a compilation of high quality oceanic delta sup 13 c measurements along with experiments performed using a zonally averaged three basin dynamic ocean model are used to explore these processes 40 refs 14more figs 1 tab less

do earthquakes talk to each other triggering and interaction of repeating sequences at parkfield 1 knowledge of what governs the timing of earthquakes is essential to understanding the nature of the earthquake cycle and to determining earthquake hazard yet the variability and controls of earthquake recurrences are not well established the large population of small characteristically repeating earthquakes at parkfield provides a unique opportunity to study how the interaction of earthquakes affects their recurrence properties we analyze 112 m 0 4 3 0 repeating earthquake sequences ress to examine the triggering effect from nearby microseismicity we find that the repeating events with a smaller number of neighboring earthquakes in their immediate vicinity tend to recur in a more periodic manner i e the coefficient of variation in recurrence intervals is less than 0 3 the total static stress perturbation from close by earthquakes however does not seem to strongly influence res regularity the uneven distribution of stress changes in time has a modest but significant impact on recurrence intervals a significant reduction of recurrence intervals occurs in the case of very high stress changes from neighboring events close by events influence res timing in a matter of several days or less by short term triggering events that occurred within less than 1 day of an res often imposed or experienced high stress changes a static stress increment of 30 kpa can be enough to produce such short term triggering we find that the triggered repeating events are often near the end of their average earthquake cycle but some events occur following a substantially shortened interval when comparing the accelerated occurrence at the time of res events following neighboring events with varying magnitudes we find that the distance of short term triggering increases from 1 km to 4 km for m1 to m4 events

towards a universal rule on the recurrence interval scaling of repeating earthquakes 1 a recent analysis of recurrence properties of small repeating earthquakes on a creeping oblique thrust fault in eastern taiwan reveals a weak variation in recurrence interval tr with seismic moment mo compared to the scaling of tr with mo from repeating earthquake data near parkfield in california the repeating data from eastern taiwan has recurrence intervals that are 2 times shorter also in northeastern japan tr of repeating quakes are 4 times shorter than those expected from the parkfield scaling law when adjusted to account for differences in the geodetically derived slip rates for the three fault zones however the tr mo scaling is remarkably consistent among the three regions it suggests that the tectonic loading rate is likely the most important factor that controls the repeat time it also suggests that there seems to exist a universal rule on recurrence interval scaling of repeating earthquakes in diverse tectonic settings

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

reconstructing the oceanic 13c suess effect the anthropogenic 13c change for the time period 1968 to 1991 was determined based on calculations of the preformed 13c 12c of dissolved inorganic carbon dic distributions on isopycnal surfaces in the main thermocline of the pacific north atlantic and south indian oceans the time rate of change of preformed 13c the 13c suess effect along isopycnals was calculated using cfc derived water ages and yields a time history of the surface water 13c change at the isopycnal outcrop location the surface ocean suess effect recorded on isopycnals decreased with increasing outcrop latitude from approximately 0 2 decade 1 within the subtropics to around 0 1 decade 1 in the subpolar oceans in the pacific ocean these surface 13c change rate reconstructions agree both in magnitude and meridional trend with direct observations of surface ocean 13c changes reported from time series measurements and from comparisons of surface water 13c of dic measurements in 1970 and 1993 a global ocean average surface 13c rate of change of 0 15 0 04 decade 1 is determined which is slightly smaller than a previous time series data and model based estimate 0 171 decade 1 bacastow etal 1996 depth integrations of the 13c reconstructions in the pacific indian and atlantic oceans when combined with these previous individual depth profile comparisons and geochemical ocean sections study bomb 14c inventories quay et al 1992 imply a global depth integrated 13c change rate of 9 7 2 4 m yr 1 over the time period 1970 1990 these results imply a net oceanic co2 uptake rate of 1 9 0 9 gt c yr 1 over the time period 1970 1990 when applied to an atmospheric 13co2 and 12co2 budget

seasonal patterns of alkenone production in the subtropical oligotrophic north pacific 1 seasonal alkenone concentrations production rates and unsaturation patterns u37k were measured at station aloha in the oligotrophic subtropical north pacific highest alkenone concentration and production rates were found in winter and fall or just below summer the surface mixed layer lowest alkenone concentration and production rates were found within the deep chlorophyll maximum layer dcml in the dcml which occurs at 80 120 m throughout the year u37k temperatures overestimated water temperatures by 2 4 c this result probably reflected the effect of light limitation on the physiology of alkenone producing algae at the depth of maximum alkenone production u37k temperatures underestimated water temperature by 2 4 c in summer and fall but overestimated in situ temperatures by 1 2 c in winter the underestimate of measured water temperature in summer and fall most likely reflected a physiological response to limited nutrient availability the u37k temperature overestimate in winter was best explained by a change in the ecology of alkenone producing algae

photosynthetic fractionation of 13c and concentrations of dissolved co2 in the central equatorial pacific during the last 255 000 years carbon isotopically based estimates of co2 levels have been generated from a record of the photosynthetic fractionation of 13c is equivalent to epsilon p in a central equatorial pacific sediment core that spans the last approximately 255 ka contents of 13c in phytoplanktonic biomass were determined by analysis of c37 alkadienones these compounds are exclusive products of prymnesiophyte algae which at present grow most abundantly at depths of 70 90 m in the central equatorial pacific a record of the isotopic composition of dissolved co2 was constructed from isotopic analyses of the planktonic foraminifera neogloboquadrina dutertrei which calcifies at 70 90 m in the same region values of epsilon p derived by comparison of the organic and inorganic delta values were transformed to yield concentrations of dissolved co2 is equivalent to c e based on a new site specific calibration of the relationship between epsilon p and c e the calibration was based on reassessment of existing epsilon p versus c e data which support a physiologically based model in which epsilon p is inversely related to c e values of pco2 the partial pressure of co2 that would be in equilibrium with the estimated concentrations of dissolved co2 were calculated using henry s law and the temperature determined from the alkenone unsaturation index u k 37 uncertainties in these values arise mainly from uncertainties about the appropriateness particularly over time of the site specific relationship between epsilon p and 1 c e these are discussed in detail and it is concluded that the observed record of epsilon p most probably reflects significant variations in delta pco2 the ocean atmosphere disequilibrium which appears to have ranged from approximately 110 microatmospheres during glacial intervals ocean atmosphere to approximately 60 microatmospheres during interglacials fluxes of co2 to the atmosphere would thus have been significantly larger during glacial intervals if this were characteristic of large areas of the equatorial pacific then greater glacial sinks for the equatorially evaded co2 must have existed elsewhere statistical analysis of air sea pco2 differences and other parameters revealed significant p 0 01 inverse correlations of delta pco2 with sea surface temperature and with the mass accumulation rate of opal the former suggests response to the strength of upwelling the latter may indicate either drawdown of co2 by siliceous phytoplankton or variation of co2 si oh 4 ratios in upwelling waters

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

sensitivity of simulated cfc 11 distributions in a global ocean model to the treatment of salt rejected during sea ice formation we show that simulated oceanic absorption of an atmospheric gas is very sensitive to the representation of a process that occurs beneath sea ice as sea ice forms salt is rejected locally increasing surface sea water density this dense water can sink to the pycnocline at the base of the mixed layer previous studies have not considered the impact of this subgrid scale process on transient tracers in the ocean to assess the potential importance of this process to the oceanic absorption of atmospheric gases we performed two idealized simulations a control simulation in which salt rejected during sea ice formation is placed in the model s 25 m thick surface layer and a test simulation in which salt rejected during sea ice formation is distributed uniformly through the upper 160 m beneath the forming sea ice our treatment of rejected salt is highly idealized and is intended to demonstrate the need for a physically based parameterization of subgrid scale convection for use in ocean general circulation models that takes into account the subgrid scale heterogeneity of surface buoyancy forcing distributing rejected salt more deeply during periods of ice formation helps to maintain vertical density gradients inhibiting grid scale convection especially in the southern ocean this greatly diminishes simulated ocean uptake of cfc 11 and generally improves simulated cfc 11 and salinity fields the modeled global ocean inventory of cfc 11 for year 1990 is about 30 lower and modeled column inventories in the southern ocean are up to 90 lower in our test simulation relative to our control simulation we infer that a more detailed treatment of subgrid scale processes occurring beneath sea ice may diminish simulated oceanic absorption of anthropogenic co2 especially in the southern ocean

inferring fault mechanical conditions from the source parameters of a complex microseismic multiplet in the corinth rift greece we develop a mechanical model of tight clusters of coplanar seismic asperities to investigate a particular microearthquake swarm located at 8 km depth in the corinth rift in greece which was active between 2001 and 2007 although it is classified as a multiplet based on waveform similarity this seismic sequence is much more complex than a repeating earthquake sequence and cannot be interpreted as the regular failure of a single asperity forced by surrounding aseismic creep here we suggest that such complex sequences could be generated by the failure of a set of coplanar asperities interacting in a small region of a fault segment we show that in order to reproduce the dynamics of the observed sequence and the characteristics of the events the cluster of asperities has to be located very close to an aseismically slipping fault segment which could be an updip extension of the deep detachment zone in the rift creeping at 1 5 cm yr for more general cases of coplanar clustered asperities we show that the shape of the cumulative coseismic displacement pattern associated with the repeated failures of the asperities is strongly controlled by the behavior of the fault area surrounding the asperity cluster in particular if the cluster is part of a locked fault area the resulting long term cumulative displacement is maximum at the center of the cluster in contrast an asperity cluster surrounded by aseismic creep leads to a uniform cumulative coseismic slip pattern the ratio between cumulative slip at the center of the seismogenic patch and cumulative slip at its periphery could therefore be an indicator of the mechanical conditions prevailing on the fault a systematic study of the source parameters of complex microseismic sequences could therefore provide insights into the mechanical state of active faults continuously generating microseismicity

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction abstract the successful reconstruction of sea surface temperatures using alkenone paleothermometry u37k has relied on the premise that there is no significant differential degradation of alkenones with different states of unsaturation during diagenetic processes to test this assumption we conducted a comparative study of contemporary sediments in oxic and anoxic bottom waters from the santa monica basin offshore california long chain alkenones were quantified and sea surface temperature were calculated using the calibrated u37k t relationship of prahl et al 1988 our results show that temperature record from the oxic sediments is higher by as much as 4 c compared to those from time equivalent anoxic sediments as a result of differential degradation of long chain unsaturated alkenones and bioturbation mixing in the oxic sediments the differential degradation of c37 3 vs c37 2 alone could account for up to 2 5 c difference between these two records this finding has significant implication in the interpretation of paleo sea surface temperature data using alkenone paleothermometry

unusual c35 to c38 alkenones in mid holocene sediments from a restricted estuary charlotte harbor florida unusual c 35 to c 38 alkenones were identified in mid holocene 8 3 5 kyr bp sediments from a restricted estuary in southwest florida charlotte harbor the distribution was dominated by a c 36 diunsaturated omega 15 20 ethyl ketone identical to the one present in black sea unit 2 sediments other unusual alkenones were tentatively assigned as a c 35 2 omega 15 20 methyl ketone a c 37 2 omega 17 22 methyl ketone and a c 38 2 omega 17 22 ethyl ketone in late holocene sediments 3 5 kyr bp the common c 37 to c 39 alkenones were found compound specific c 14 c 13 and d isotope measurements were used to constrain the possible origin of the alkenones conventional radiocarbon ages of alkenones and higher plant derived long chain n alcohols indicated no significant difference in age between mid holocene alkenones and higher plant n alcohols both alcohols and alkenones were offset vs calibrated ages of shell fragments in the same sediment core which suggests they were pre aged by 500 800 yr implying resuspension and redistribution of the fine grained sedimentary particles with which they are associated the hydrogen isotopic delta d composition 190 parts per thousand to 200 parts per thousand of the c 37 and c 38 alkenones in the late holocene sediments is in line with values for coastal haptophytes in brackish water however the unusual c 36 and c 38 alkenones from the mid holocene sediments were enriched in d by ca 100 parts per thousand vs the late holocene alkenones also delta c 13 values of mid holocene alkenones were consistently offset compared with late holocene alkenones 21 parts per thousand to 22 parts per thousand and 22 parts per thousand to 23 parts per thousand respectively we suggest that the alkenones in charlotte harbor were produced by unknown alkenone producing haptophyte

the carbon isotopic record of the c37 2 alkenone in the south atlantic last glacial maximum lgm vs holocene the carbon isotopic fractionation ep of the c37 2 alkenone was analysed for 19 south atlantic sediment samples from the last glacial maximum lgm our study covers the equatorial and subtropical ocean including the coastal upwelling regions off south africa the equatorial upwelling and the oligotrophic western basins the results were compared to the holocene ep records from the respective core locations andersen n muller p j kirst g schneider r r 1999 alkenone 13c as a proxy for past pco2 in surface waters results from the late quaternary angola current in fischer g wefer g eds use of proxies in paleoceanography examples from the south atlantic springer berlin pp 469 488 benthien a andersen n schulte s muller p j schneider r r wefer g 2002 carbon isotopic composition of the c37 2 alkenone in core top sediments of the south atlantic ocean effects of co2 and nutrient concentrations glob biogeochem cycles 16 10 1029 2001gb001433 generally alkenone ep was lower during the lgm compared to the holocene higher glacial ep values were only found in sediments from the angola basin and in one sample from the eastern crest of the walvis ridge considering present understanding of lgm holocene changes in surface water conditions i e nutrient level primary productivity phytoplankton assemblages the observed glacial interglacial difference in ep indicates that multiple factors controlled the isotopic fractionation in alkenone producing algae depending on the regional setting in the oligotrophic areas of the south atlantic the lower than holocene glacial ep values can be partly explained with a decrease in surface water pco2 during the lgm in contrast the holocene to lgm decrease in ep values in the coastal upwelling areas as well as in the eastern tropical atlantic most probably reflects much higher glacial haptophyte growth rates induced by an increase in surface water nutrient concentrations the exceptional opposite trend of the ep differences in the angola basin can be explained by a shift in the phytoplankton community towards a greater dominance of diatoms under glacial conditions thus leaving less nutrients available for haptophytes in this way the isotopic record of alkenones indicate lower haptophyte growth rates during the lgm although other palaeoceanographic proxies point to enhanced productivity and higher nutrient levels

scaling of small repeating earthquakes explained by interaction of seismic and aseismic slip in a rate and state fault model because of short recurrence times and known locations small repeating earthquakes present a rare predictable opportunity for detailed field observations they are used to study fault creeping velocities earthquake nucleation stress drops and other aspects of tectonophysics earthquake mechanics and seismology an intriguing observation about repeating earthquakes is their scaling of recurrence time with seismic moment which is significantly different from the scaling based on a simple conceptual model of circular ruptures with stress drop independent of seismic moment and no aseismic slip here we show that a model of repeating earthquakes based on laboratory derived rate and state friction laws reproduces the observed scaling in the model a small fault patch governed by steady state velocity weakening friction is surrounded by a much larger velocity strengthening region long term slip behavior of the fault is simulated using a methodology that fully accounts for both aseismic slip and inertial effects of occasional seismic events the model results in repeating earthquakes with typical stress drops and sizes comparable with observations for a fixed set of friction parameters the observed scaling is reproduced by varying the size of the velocity weakening patch in simulations a significant part of slip on the velocity weakening patches is accumulated aseismically even though the patches also produce seismic events the proposed model supplies a laboratory based framework for interpreting the wealth of observations about repeating earthquakes provides indirect evidence that rate and state friction acts on natural faults and has important implications for possible scenarios of slip partition into seismic and aseismic parts

what controls interplate coupling evidence for abrupt change in coupling across a border between two overlying plates in the ne japan subduction zone article i nfo interplate coupling in the southernmost extent of the northeast japan subduction zone east off kanto japan is investigated in detail using a large data set of small repeating earthquakes in this region of the trench trench trench type triple junction the subducting pacific plate is in contact with two different overlying plates the north american and philippine sea plates the border between the two overlying plates extending northwestward from the triple junction is identified along the upper surface of the pacific plate based on the slip vectors of many interplate events including small repeating earthquakes the interplate coupling coefficient estimated from the cumulative slip of small repeating earthquakes for the period from 1993 to 2007 reveals a distinct change from south ca 0 3 to north ca 0 7 across the border this border also corresponds to the southern limit of the source areas of mn7 interplate earthquakes in the last 80 years along the japan trench again indicating the stronger coupling to the north we also investigate hypocenter distribution and seismic velocity structure along the plate boundary from a large number of travel time data obtained from the nationwide seismograph network the results reveal a distinct low velocity zone just above the pacific plate and low seismicity along the plate boundary in the region overlain by the philippine sea plate whereas there are no low velocity zones and the seismicity is high in the region overlain by the north american plate these observations imply that the geological difference of overlying plate controls large scale coupling at the plate interface

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

controls on the molecular distribution and carbon isotopic composition of alkenones in certain haptophyte algae 1 although the biochemical functions and biosynthetic pathways of alkenones are still largely unknown alkenone unsaturation ratios are now used extensively to infer ancient sea surface temperature and their isotopic compositions have been used to reconstruct ancient atmospheric co2 levels the inferred relationships between alkenone unsaturation ratios isotopic compositions and growth conditions are based on empirical laboratory and field studies and in the case of isotope fractionation on simple models of carbon acquisition and fixation significant uncertainty still exists concerning the physiological and ecological factors affecting cellular production of alkenones unsaturation ratios and isotopic composition phytoplankton culture conditions have been shown to affect alkenone unsaturation u37k cellular alkenone content intracellular isotopic compositions and changes in fractionation ep as a function of the quotient of algal growth rate and aqueous carbon dioxide concentration co2 such studies imply that plant physiology can affect the interpretation of environmental signals the factor s controlling cellular alkenone concentrations and unsaturation ratios are reviewed as well as the carbon isotopic composition of the alkenone producing algae a new technique is presented to determine growth rates of the alkenone containing algae in natural settings that will facilitate testing laboratory based hypotheses concerning the carbon isotopic fractionation and its relationship to growth rate growth status of alkenone producing algae in the field

fossil leaves effective bioindicators of ancient co2 levels 1 past variations in the concentration of the greenhouse gas co2 are thought to have played a major role in controlling earth s climate on prequaternary and quaternary timescales to identify the contribution of co2 to past climatic change requires accurate quantification of its content in the ancient atmosphere and a number of proxies have been developed for this purpose for a review see royer et al 2001a for the late quaternary there is the unique opportunity to measure directly the composition of fossil air samples trapped in bubbles preserved in the polar ice sheets results from antarctic ice cores reveal that the glacialinterglacial changes characterizing quaternary climate were accompanied by variations in the atmospheric concentration of co2 petit et al 1999 although detection of phase relations between isotope derived temperature estimates and trace gas concentration values is hampered by the difference in age of ice and air from the same ice sample it is believed that co2 lags glacial interglacial temperature change and has acted as an amplifier of orbitally forced changes in temperature petit et al 1999 shackleton 2000 mudelsee 2001

seimological studies at parkfield v characteristic microearthquake sequences as fault zone drilling targets studies at very high resolution of microearthquakes at parkfield california since 1987 reveal a systematic organization in space and time dominated by clustering of nearly identical regularly occurring microearthquakes characteristic events on 10 to 20 m wide patches within the fault zone more than half of the 4000 events in our 1987 to 1996 catalog exhibit this trait in general recurrence intervals 0 5 to 2 yr scale with the magnitude of the repeating events for the on scale range mw 0 2 to 1 3 in this study the similar waveforms superimposed locations quasi periodic recurrence and uniform size of these characteristic events permit relative hypocenter location accuracy of meters and predictable occurrence times within windows of a few months clustered characteristic events occur at depths as shallow as about 3 km and these are feasible targets for deep scientific drilling and observation at the focus of a subsequent small earthquake within an active plate boundary fault zone at parkfield the achievable location accuracy to which a hypocenter can be specified as well as the predictability of its occurrence time appear to be uniquely favorable for in situ fault zone measurements

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

coccolithophore export production species composition and coccolith caco3 fluxes in the ne atlantic and abstract coccolithophores were examined in two sediment traps deployed for one year april 1989 to april 1990 at approximately 1 km water depth in the subtropical ne atlantic at 34 n 21 w station nabe 34 and in the temperate ne atlantic 48 n 21 w station nabe 48 as part of the jgofs north atlantic bloom experiment nabe at both stations maximum coccolith and coccosphere fluxes were recorded during local spring bloom periods the average coccolith and coccosphere fluxes at nabe 34 were 1 12 10 9 m 2 d 1 and 4 90 10 6 m 2 d 1 respectively at this station coccoliths from 51 taxa were identified a marked seasonal change was noticed in relative abundances of emiliania huxleyi and deep photic zone species e huxleyi dominated during spring while in late autumn the coccolith assemblage was dominated by florisphaera profunda and the coccosphere assemblage by g flabellatus and algirosphaera spp emiliania huxleyi was the most abundant species in the overall coccolith and coccosphere assemblages with 69 and 64 respectively at nabe 48 the average daily fluxes were significantly lower with 3 88 10 8 coccoliths m 2 d 1 and 8 45 10 5 coccospheres m 2 d 1 and only 36 taxa were recorded in the trap samples emiliania huxleyi was the dominant species in the coccolith assemblage throughout the year with 72 and showed maximum fluxes during spring 1990 coccolithus pelagicus exhibited a distinct seasonal pattern with maximum fluxes in early june 1989 probably related to the development of a mesoscale cyclonic eddy in the vicinity of the trap site holococcolithophore fluxes were highest during maximum sea surface temperatures in summer the coccosphere assemblage was dominated by gephyrocapsa spp syracosphaera spp and e huxleyi estimated caco3 fluxes of coccoliths coccospheres and calcareous dinophytes were compared with the caco3 content in the fine m fraction the annual mass estimated caco3 flux of coccoliths and coccospheres was 5 1 g m 2 yr at nabe 34 and 2 7 g m 2 yr at nabe 48 and that of calcareous dinophytes 0 9 and 0 1 g m 2 yr respectively these summed mass estimated values contributed on average only 55 at nabe 34 and 60 at nabe 48 to the fine fraction caco3

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

inferring the coseismic and postseismic stress changes caused by the 2004 mw 6 parkfield earthquake from variations of recurrence times of microearthquakes 1 kinematic models of coseismic stress inverted from ground motion data do not usually find good correlation between the location of aftershocks and high stress patches in particular numerous earthquakes are recorded in areas of the fault where the stress decreases however most of coseismic slip distributions have limited spatial resolution typically not better than 1 km here we investigate the stress changes produced by the 2004 mw 6 parkfield earthquake on and near its rupture zone at the scale of magnitude 2 earthquake asperities approximately tens of meters after relocating earthquakes in this zone between 1984 and 2007 we form repeating highly similar earthquake sequences and study how the quasiperiodicity of occurrence at each sequence observed during the 20 years preceding the 2004 main shock is perturbed by this event we apply a simple model of the seismic cycle to infer the coseismic and postseismic stresses experienced by the repeatedly failing asperities despite being spatially sparse these stress distributions have resolutions only limited by the typical scale of an asperity we propose that the high spatial variability of the seismicity patterns following the mw 6 earthquake results from an heterogeneous coseismic stress field the emergence of the omori utsu law observed at large scale greater than kilometers at parkfield is simply the outcome of averaging such quasi deterministic patterns over many sequences the fact that the coseismic stress can significantly change over distances of the order of 100 m adds credence to the hypothesis that earthquake rupture is intrinsically very heterogeneous

miocene evolution of atmospheric carbon dioxide changes in pco2 or ocean circulation are generally invoked to explain warm early miocene climates and a rapid east antarctic ice sheet eais expansion in the middle miocene this study reconstructs late oligocene to late miocene pco2 from ep values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from deep sea drilling project sites 588 and 608 and ocean drilling program site 730 our results indicate that highest pco2 occurred during the latest oligocene 350 ppmv but decreased rapidly at 25 ma the early and middle miocene was characterized by low pco2 260 190 ppmv lower intervals of pco2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle miocene there is no evidence for either high pco2 during the late early miocene climatic optimum or a sharp pco2 decrease associated with eais growth paradoxically pco2 increased following eais growth and obtained preindustrial levels by 10 ma although we emphasize an oceanographic control on miocene climate low pco2 could have primed the climate system to respond sensitively to changes in heat and vapor transport

behavior of repeating earthquake sequences in central california and the implications for subsurface fault creep repeating earthquakes res are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth we investigate the occurrence of these res along faults in central california to determine which faults exhibit creep and the spatiotemporal distribution of this creep at the juncture of the san andreas and southern calaveras paicines faults both faults as well as a smaller secondary fault the quien sabe fault are observed to produce res over the observation period of march 1984 through may 2005 res in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time cumulative slip over the observation period at individual sequence locations is determined to range from 5 5 58 2 cm on the san andreas fault from 4 8 14 1 cm on the southern calaveras paicines fault and from 4 9 24 8 cm on the quien sabe fault creep at depth appears to mimic the behaviors seen for creep on the surface in that evidence of steady slip triggered slip and episodic slip phenomena are also observed in the re sequences for comparison we investigate the occurrence of res west of the san andreas fault within the southern coast range events within these re sequences occurred only minutes to weeks apart from each other and then did not repeat again over the observation period suggesting that res in this area are not produced by steady aseismic creep of the surrounding fault surface

redox controlled preservation of organic matter during oae 3 within the western interior seaway during the cretaceous widespread black shale deposition occurred during a series of oceanic anoxic events oaes multiple processes are known to control the deposition of marine black shales including changes in primary productivity organic matter preservation and dilution oaes offer an opportunity to evaluate the relative roles of these forcing factors the youngest of these events the coniacian to santonian oae 3 resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the western interior seaway new high resolution isotope organic and trace metal records from the latest turonian to early santonian niobrara formation are used to characterize the amount and composition of organic matter preserved as well as the geochemical conditions under which it accumulated redox sensitive metals mo mn and re indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon rich up to 8 deposition high hydrogen indices hi and organic carbon to total nitrogen ratios c n demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions local changes in 13c indicate that redox controlled early diagenesis can also significantly alter 13corg records these results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the niobrara formation sea level reconstructions 18o results and mo total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen increased nutrients from benthic regeneration and or continental runoff may have sustained primary productivity

bayesian inversion of seismic spectral ratio for source scaling application to a persistent multiplet in the western corinth rift we propose a method to precisely estimate earthquake source parameters as magnitude size of rupture stress drop and coseismic slip and their uncertainties this method that relies on a bayesian approach allows the determination of the scalar seismic moment corner frequency fc and their associated uncertainties by inverting ratios between seismic displacement spectra of nearby located earthquakes we apply this method to a large earthquake multiplet 56 events located under the northern coast of the corinth gulf at 8 km depth this multiplet is regularly active between 2001 and 2007 results show fcp fcs ratios globally between 1 0 and 1 5 which is compatible with the values predicted by madariagas circular rupture model in details 6 earthquakes however exhibit corner frequency variations as a function of the station azimuth compatible with linear rupture propagation magnitude ranges 1 08 and 2 80 with a b value of 1 04 source rupture length globally ranges between 40 and 170 m for stress drop between 1 and 100 mpa we show that the number of ruptures and the cumulated coseismic slip are maximal at the center of the multiplet this suggests that multiplet 866 could be seen as a weak seismogenic patch surrounded by a locked fault how ever the large value of the maximum coseismic slip cumulated over the period 2000 2008 10 cm rather suggests creep allowing rapid stress reloading and repeated earthquakes with short delays we therefore propose that multiplet 866 is surrounded by a heterogeneous fault surface with both locked and creeping areas

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters