random variability explains apparent global clustering of large earthquakes 1 the occurrence of 5 mw 8 5 earthquakes since 2004 has created a debate over whether or not we are in a global cluster of large earthquakes temporarily raising risks above long term levels i use three classes of statistical tests to determine if the record of m 7 earthquakes since 1900 can reject a null hypothesis of independent random events with a constant rate plus localized aftershock sequences the data cannot reject this null hypothesis thus the temporal distribution of large global earthquakes is well described by a random process plus localized aftershocks and apparent clustering is due to random variability therefore the risk of future events has not increased except within ongoing aftershock sequences and should be estimated from the longest possible record of events

delayed dynamic triggering of deep tremor along the parkfield cholame section of the san andreas fault following the 2014 m6 0 south napa earthquake large distant earthquakes are known to trigger deep tectonic tremor along the san andreas fault and in subduction zones however there are relatively few observations of triggering from regional distance earthquakes here we show that a small tremor episode about 12 18 km nw of parkfield was triggered during and immediately following the passage of surface waves from the 2014 mw 6 0 south napa main shock more notably a major tremor episode followed beginning about 12 h later and centered se of parkfield near cholame this major episode is one of the largest seen over the past several years containing intense activity for 3 days and taking more than 3 weeks to return to background levels this episode showed systematic along strike migration at 5 km d suggesting that it was driven by a slow slip event our results suggest that moderate size earthquakes are capable of triggering major tremor and deep slow slip at regional distances

dynamic triggering and earthquake swarms on east pacific rise transform faults while dynamic earthquake triggering has been reported in several continental settings offshore observations are rare oceanic transform faults share properties with continental geothermal areas known for dynamic triggering high geothermal gradients high seismicity rates and frequent swarms we study dynamic triggering along the east pacific rise by analyzing 1 year of seismicity recorded by ocean bottom seismographs by comparing the response to teleseismic waves from global earthquakes we find triggering to be most sensitive to changes in normal stress and to preferentially occur above 0 25 kpa the clearest example of triggering occurs on the quebrada and gofar faults after the mw8 0 wenchuan earthquake on gofar triggered seismicity occurs between the rupture areas of large earthquakes within a zone characterized by aseismic slip abundant microseismicity frequent swarms and low vp we infer that lithological properties inhibiting rupture propagation such as high porosity and fluid content also favor dynamic triggering

exploration of remote triggering a survey of multiple fault structures in haiti triggering studies provide an important tool for understanding the fundamental physics of how faults slip and interact and they also provide clues about the stress states of faults in this study we explore how seismic waves from the 27 february 2010 mw8 8 maule chile mainshock interact with the left lateral strike slip enriquillo plantain garden fault epgf and surrounding reverse faults in the southern haiti peninsula the chile mainshock occurred 6 000 km away and just 46 days after the 12 january 2010 mw7 0 haiti earthquake a tragic event which activated multiple faults in the southern haiti peninsula during the surface waves of the chile mainshock several tectonic tremor signals were observed originating from south of the epgf trace cross correlation of the triggered tremor and transient stresses resolved onto to the epgf indicates that the love wave of the chile mainshock was the primary driving mechanism of the triggered deep shear slip and tremor signals as opposed to dilatational stress changes generated by the rayleigh wave we also searched for any influence of transient stresses on haiti aftershock activity by applying the matched filter technique to multiple days of seismic data around the time of the chile mainshock while we identified a slight increase in haiti aftershock activity rate the rate changes were significant only when small magnitude events were included in the significance tests these observations are generally consistent with recent inferences that deep tectonic tremor is more sensitive than shallow earthquakes to external stress perturbations

isolated regions of remote triggering in south southeast asia following the 2012 mw 8 6 indian ocean earthquake large earthquakes are capable of triggering either shallow earthquakes or deep tectonic tremors at long range distances so far most of remotely triggered tremors were found along major plate boundary faults around the pacific rim here we conduct a systematic search for remotely triggered earthquakes and tremors in south southeast asia following the april 11 2012 mw 8 6 indian ocean earthquake we find additional evidence of triggered tectonic tremors beneath the java island and the molucca island in eastern indonesia and triggered earthquakes in vietnam tremors mostly occurred during the large amplitude rayleigh waves of the indian ocean mainshock and were also triggered by several other large distant earthquakes although we are unable to locate them they were recorded at stations close to major tectonic faults suggesting that they are likely of tectonic origin however we find no evidence of triggered tremor earthquakes along the sumatra subduction zone and eastern portion of himalaya frontal thrusts indicating that remote triggering was not as widespread as previously thought

post glacial microbialite formation in coral reefs of the pacific atlantic and indian oceans abstract the occurrence of microbialites in post glacial coral reefs has been interpreted to reflect an ecosystem response to environmental change the greater thickness of microbialites in reefs with a volcanic hinterland compared to thinner microbial crusts in reefs with a non volcanic hinterland led to the suggestion that fertilization of the reefal environment by chemical weathering of volcanic rocks stimulated primary productivity and microbialite formation using a molecular and isotopic approach on reef microbialites from tahiti pacific ocean it was recently shown that sulfate reducing bacteria favored the formation of microbial carbonates to test if similar mechanisms induced microbialite formation in other reefs as well the tahitian microbialites are compared with similar microbialites from coral reefs off vanuatu pacific ocean belize caribbean sea atlantic ocean and the maldives indian ocean in this study the selected study sites cover a wide range of geological settings reflecting variable input and composition of detritus the new lipid biomarker data and stable sulfur isotope results confirm that sulfate reducing bacteria played an intrinsic role in the precipitation of microbial carbonate at all study sites irrespective of the geological setting abundant biomarkers indicative of sulfate reducers include a variety of terminally branched and mid chain branched fatty acids as well as mono o alkyl glycerol ethers isotope evidence for bacterial sulfate reduction is represented by low 34s values of pyrite 43 to 42 enclosed in the microbialites and compared to seawater sulfate slightly elevated 34s and 18o values of carbonate associated sulfate 21 9 to 22 2 and 11 3 to 12 4 respectively microbialite formation took place in anoxic micro environments which presumably developed through the fertilization of the reef environment and the resultant accumulation of organic matter including bacterial extracellular polymeric substances eps coral mucus and marine snow in cavities within the coral framework tof sims analysis reveals that the dark layers of laminated microbialites are enriched in carbohydrates which are common constituents of eps and coral mucus these results support the hypothesis that bacterial degradation of eps and coral mucus within microbial mats favored carbonate precipitation because reefal microbialites formed by similar processes in very different geological settings this comparative study suggests that a volcanic hinterland is not required for microbialite growth yet detrital input derived from the weathering of volcanic rocks appears to be a natural fertilizer being conductive for the growth of microbial mats which fosters the development of particularly abundant and thick microbial crusts

complexity of the deep san andreas fault zone defined by cascading tremor seismic tremors can be used to distinguish plate boundaries analysis of tremors occurring deep beneath the san andreas fault may identify the boundary between the north american plate and the preserved remnant of a subducted slab

vegetation change in equatorial west africa time slices for the last 150 ka abstract drawing on marine and terrestrial palynological data vegetation maps of equatorial west africa are presented for eleven time slices over the last 150 000 years long marine records are used as a basis for the regional picture and provide a chronology for the last glacial cycle much shorter terrestrial records help fill in the picture for the most recent periods and facilitate interpretation of regional patterns for the longer timescale temporal and spatial variation is revealed in relation to global patterns of climate change rain forest was widespread during oxygen isotope stages 1 and 5 but strongly reduced during stages 3 and 4 and especially during stages 2 and 6 when open grass rich vegetation prevailed glacial rain forest refuges are found in the southwest of the guinean mountains and along the eastern coast of the gulf of guinea miombo woodland of the zambezian vegetation zone expanded during stage 5 especially during the first half podocarpus forest had its largest expansion during substages 5d 115 to 105 ka and 5b 95 to 85 ka the last occurrence of podocarpus in the guinean mountains is during stage 5a the distribution of mangrove swamps was extremely reduced during glacial times during stage 6 savanna and open dry forest covered large areas along the northern coast of the gulf of guinea the southern saharan desert reached far to the south and the namib desert far to the north the area of rain forest was restricted mangrove swamps were strongly reduced and the area of podocarpus forest fluctuated during stage 5 large changes in the area of afromontane forest rain forest dry open forest and savanna occurred rain forest was widespread and mangroves were extensive along the coast during the last interglacial substage 5e podocarpus forest area strongly extended during substages 5d and 5b in substages 5c and 5a rain forest reclaimed areas it had lost in the previous substages 5d and 5b respectively mangrove swamps were less widespread in the later substages of stage 5 than during substage 5e during stage 4 the rain forest area was again strongly reduced and recovered only slightly during the following stage 3 also the mangrove swamp area was reduced except along the ivory coast and along the northwestern coast of the gulf of guinea podocarpus forest only occurred in angola and may be in congo during stage 4 again forest was much reduced during stage 2 and open vegetation types covered large parts of equatorial west africa mangrove swamps must have been rare at the beginning of the holocene mangrove swamps had recovered and reached their largest extension also the rain forests area increased in the early holocene and guinean and congolian rain forests were probably not separated by a savanna corridor now existing in togo and benin

rapid analysis of 13c in plant wax n alkanes for reconstruction of terrestrial vegetation signals from aquatic sediments long chain odd carbon numbered c25 to c35 n alkanes are characteristic components of epicuticular waxes produced by terrestrial higher plants they are delivered to aquatic systems via eolian and fluvial transport and are preserved in underlying sediments the isotopic compositions of these products can serve as records of past vegetation we have developed a rapid method for stable carbon isotopic analyses of total plant wax n alkanes using a novel moving wire system coupled to an isotope ratio mass spectrometer mw irms the n alkane fractions are prepared from sediment samples by 1 saponification and extraction with organic solvents 2 chromatographic separation using silica gel 3 isolation of straight chain carbon skeletons using a zeolite molecular sieve and 4 oxidation and removal of unsaturated hydrocarbons with ruo4 short chain n alkanes of nonvascular plant origin c25 are removed by evaporation on the moving wire test samples processed using this procedure yielded n alkane fractions essentially free of interfering components the 13c values obtained by mw irms did not differ significantly from weighted averages of individual n alkane 13c values obtained by irmgc ms isotopic variations in compound class n alkane fractions from a latitudinal transect of core top sediments from the southwest african margin 3 n 28 s were congruent with those measured by compound specific isotopic analyses of plant wax n alkanes the amplitude of the variations was smaller indicating contributions from non plant wax hydrocarbons but the measurements revealed variations in carbon isotopic composition that are consistent with vegetation zones on the adjacent continent

mapping of c4 plant input from north west africa into north east atlantic sediments abstract mapping the abundance of 13c in leaf wax components in surface sediments recovered from the seafloor off northwest africa 0 35 n reveals a clear pattern of 13c distribution indicating systematic changes in the proportions of terrestrial c3 and c4 plant input at 20 n latitude we find that isotopically enriched products characteristic of c4 plants account for more than 50 of the terrigenous inputs this signal extends westward beneath the path of the dust laden sahara air layer sal high c4 contributions apparently carried by january trade winds also extend far into the gulf of guinea similar distributions are obtained if summed pollen counts for the chenopodiaceae amaranthaceae and the poaceae are used as an independent c4 proxy we conclude that the specificity of the latitudinal distribution of vegetation in north west africa and the pathways of the wind systems trade winds and sal are responsible for the observed isotopic patterns observed in the surface sediments molecular isotopic maps on the marine sedimentary time horizons e g during the last glacial maximum are thus a robust tool for assessing the phytogeographic changes on the tropical and sub tropical continents which have important implications for the changes in climatic and atmospheric conditions

large scale dynamic triggering of shallow slow slip enhanced by overlying sedimentary wedge seismic waves can trigger further fault slip analysis of seismic and geodetic data shows that seismic waves from the 2016 kaik ura new zealand earthquake were amplified by subduction zone sediments triggering slow fault slip up to 600 km away

distribution and stable isotopes of plant wax derived n alkanes in lacustrine fluvial and marine surface sediments along an eastern italian transect and their potential to reconstruct the hydrological cycle reconstructing terrestrial water budgets is of prime importance for understanding past climate and environment to shed more light on how plant wax derived n alkanes may be used for this purpose we investigated the distribution and stable isotopic compositions of hydrogen d and carbon 13c of plant wax derived n c29 and c31 alkanes in terrestrial coastal and offshore surface sediments in relation to hydrology along a nw se transect east of the italian apennines from the po river to the eastern gulf of taranto the plant wax average chain length increases southward and may relate to increasing temperature and or aridity the plant wax d of the terrestrial and coastal samples also increases southward and mainly reflects changes in the d of precipitation the 13c of plant waxes is primarily interpreted in terms of c3 vegetation changes rather than varying contributions by c4 plants the plant wax 13c d composition of the po river and apennine rivers differs considerably from that in southern italy and suggests a mainly southern source for plant waxes in marine sediments of the gulf of taranto this calibration provides a basis for the reconstruction of past changes in the italian water balance and n alkane source areas

dynamic triggering of microseismicity in southwest china following the 2004 sumatra and 2012 indian ocean earthquakes abstract we conduct a systematic detection of microseismicity around yunnan province southwest china following the 2004 mw9 1 sumatra and 2012 mw8 6 indian ocean earthquakes based on seismicity analysis on china earthquake network center cenc catalog and spectral analysis of continuous waveforms we find clear evidence of triggered seismicity in yunnan immediately after the 2004 mainshock including a magnitude 4 8 earthquake near tengchong volcanic region in comparison we do not find clear evidence of instantaneous triggering following the 2012 mainshock we further apply a matched filter technique to detect microearthquakes in tengchong volcanic region 15 days before and 15 days after the 2012 mainshock the seismicity rate remains stable immediately after the 2012 mainshock and increases in the next few days indicating a possible delayed triggering although similar changes can be seen at other times long before and after the mainshock in addition we find possible evidence of remote triggering near the city of yibin in southern sichuan province southwest china near the sites with ongoing shale gas development we also examine other magnitude 8 earthquakes from the sumatra region and do not find any additional evidence of dynamic triggering around yunnan we suggest that the absolute value of dynamic stress change is the most important factor to explain why the 2004 sumatra event triggered a widespread seismicity rate increase around yunnan while other great events around sumatra did not

mid pleistocene environmental change in tropical africa began as early as 1 05 ma palynological records from the congo fan reveal environmental change in equatorial africa occurring 1 05 ma ago 100 k y before the mid pleistocene climatic shift at 0 9 ma prior to 1 05 ma a glacial interglacial rhythm is not obvious in the african vegetation variation afterwards podocarpus spread in the mountains of central africa mainly during glacials and congo river discharge decreased the sequence of vegetation variation associated with the mid pleistocene glacials and interglacials differed from that observed during the late pleistocene between 0 9 and 0 6 ma interglacials were characterized by warm dry conditions and glacials were characterized by cool humid conditions while during the past 0 2 ma glacials were cold and dry and interglacials warm and humid our data indicate that before the northern hemisphere ice caps dramatically increased in size 0 9 0 6 ma low latitude climate forcing and response in the tropics played an important role in the initiation of 100 k y ice age cycles during the mid to late pleistocene however the climate conditions in the tropics were increasingly influenced by the glacialinterglacial variations of continental ice sheets

cryptic biostalactites in a submerged karst cave of the belize barrier reef revisited pendant bioconstructions cemented by microbial micrite abstract microbial carbonates are important components of postglacial tropical coral reef frameworks curious calcium carbonate protrusions in a submarine karst cave in the belize barrier reef platform were initially interpreted as being largely the product of physicochemical precipitation around a meshwork of serpulid tubes new petrographical mineralogical geochronological and inorganic and organic geochemical data suggest that sulfate reducing bacteria played a substantial role in carbonate formation just as in cryptic settings of other modern tropical coralgal reefs the bacterial involvement in carbonate authigenesis is indicated by the content and isotopic composition of carbonate associated sulfate the presence of non isoprenoidal sn 1 mono o alkyl glycerol monoethers mages and terminally branched fatty acids and the observation that the majority of molecular fossils assigned to sulfate reducing bacteria are tightly associated with the carbonate mineral lattice the carbonate protrusions that were formerly named pseudostalactites are termed biostalactites here to underline the significance of biological activity during carbonate formation the belize biostalactites are composed of four carbonate phases including serpulid tubes lithified sediment and microbial carbonate as well as unconsolidated sediment usually found in macroborings of bivalve molluscs lithified sediment and microbial carbonate are fine grained with clotted mottled and peloidal textures while serpulid tubes are aragonitic lithified sediment and microbial carbonates are mixtures of high magnesium calcite and aragonite magnesium calcite content increases with increasing consolidation lithified sediment and microbial carbonate are interpreted as fine biodetrital sediment that was subsequently cemented by authigenic micrite scalenohedral high magnesium calcite and acicular aragonite cements played a subordinate role in cementation carbon and oxygen stable isotope ratios of lithified sediment and microbial carbonate exhibit similar ranges as modern reefal microbialites our study exemplifies that heterotrophic bacteria can be a crucial agent that contributes to the formation of carbonate build ups by cementing skeletal frameworks in cryptic environments

climate and co2 effects on the vegetation of southern tropical africa over the last 37 000 years the savanna vegetation of southern tropical africa is characterized by co dominance of c 4 grasslands and c 3 woodlands long term variations in the tropical savanna vegetation in arid and semi arid climates are commonly considered to be primarily sensitive to precipitation and atmospheric co2 concentrations the sensitivity of tropical vegetation to temperature however is often considered as secondary or negligible particularly in paleostudies due to difficulties of reconstructing terrestrial temperature in the tropics in this study we use the terrestrial vegetation model biome4 which was forced by climate simulations from the kiel climate model kcm for the holocene and by climate reconstructions for the most recent glacial period to understand reconstructed vegetation changes in southern tropical africa of the past 37 000 yr we focus on these two periods because vegetation reconstructions from a marine sediment core near the zambezi river mouth cannot be explained by precipitation changes and changes of atmospheric co2 alone for the holocene we force biome4 simulations with reconstructed atmospheric co2 concentrations and spatial and seasonal climate patterns from the early and mid holocene 9 5 and 6 ka bp simulations with the kcm for the glacial period we analyze idealized experiments based upon reconstructed temperature precipitation and co2 at 31 28 and 21 ka bp our study shows that both holocene and glacial simulations of vegetation cover exhibit good agreement with reconstructed c 4 c 3 ratios when temperature changes are taken into account while both precipitation and temperature control the c 4 c 3 ratio during the holocene atmospheric co2 and temperature variations are major factors controlling vegetation changes during the glacial period in our simulations variations in temperature along with precipitation and atmospheric co2 reconcile the evolution of vegetation observed in the zambezi catchment during the last 37 000 yr in consequence the effect of temperature variations on tropical savanna vegetation should be taken into account with respect to modeling past or future climates c 2014 elsevier b v all rights reserved

reconstruction of se trade wind intensity based on sea surface temperature gradients in the southeast atlantic over the last 25 kyr 1 a prominent feature in the southeast atlantic is the angola benguela front abf the convergence between warm tropical and cold subtropical upwelled waters at present the sea surface temperature sst gradient across the abf and its position are influenced by the strength of southeasterly se trade winds here we present a record of changes in the abf sst gradient over the last 25 kyr variations in this sst contrast indicate that periods of strengthened se trade wind intensity occurred during the last glacial maximum the younger dryas and the mid to late holocene while heinrich event 1 the early part of the bolling allerod and the early holocene were periods of weakened se trade winds

molecular and isotopic records of c4 grassland expansion in the late miocene abstract siwalik paleosol and bengal fan sediment samples were analyzed for the abundance and isotopic composition ofn alkanes in order to test for molecular evidence of the expansion of c4 grasslands on the indian subcontinent the carbon isotopic compositions of high molecular weight alkanes in both the ancient soils and sediments record a shift from low 13c values ca 30 to higher values ca 22 prior to 6 ma this shift is similar in magnitude to that recorded by paleosol carbonate and fossil teeth and is consistent with a relatively rapid transition from dominantly c3 vegetation to an ecosystem dominated by c4 plants typical of semi arid grasslands the n alkane values from our paleosol samples indicate that the isotopic change began as early as 9 ma reflecting either a growing contribution of c4 plants to a dominantly c3 biomass or a decrease in water availability to c3 plants molecular and isotopic analyses of other compounds including n alcohols and low molecular weightn alkanes indicate paleosol organic matter contains contributions from a mixture of sources including vascular plants algae and or cyanobacteria and microorganisms a range of inputs is likewise reflected in the isotopic composition of the total organic carbon from these samples in addition then alkanes from two samples show little evidence for pedegenic inputs and we suggest the compounds were derived instead from the paleosol s parent materials we suggest the record of vegetation in ancient terrestrial ecosystems is better reconstructed using isotopic signatures of molecular markers rather than bulk organic carbon this approach provides a means of expanding the spatial and temporal records of c4 plant biomass which will help to resolve possible tectonic climatic or biological controls on the rise of this important component of the terrestrial biosphere

fossil hyrax dung and evidence of late pleistocene and holocene vegetation types in the namib desert abstract pollen was derived from fossil dung of herbivorous hyraxes deposited in a rock shelteron the highest mountain in namibia da ures or brandberg situated on the namib desert margin radiocarbon dating ranging in age between modern times and 30000yrbp showed it representsthe rst empirical pollen evidence of continental palaeovegetation during the late pleistocene alongthe western escarpment of southern africa the initial results indicate last glacial maximum vegeta tion differed totally from the current pattern as vegetation types were dominated by small asteraceaeshrubs in contrast to those of the holocene and modern times which show more succulents grassandwoody elements arboreal pollen the resultssuggest that cape oral communities didnot reachinto thetropics along thewestern escarpment ofafrica despite such pollentypes occurring inmarinecores copyright 2004 john wiley sons ltd keywords palynology namibia restionaceae late pleistocene last glacial maximum

glacial interglacial changes in southern africa compound specific δ13c land plant biomarker and pollen records from southeast atlantic continental margin sediments this is part 2 of a study examining southwest african continental margin sediments from nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s representing two glacial mis 2 and 6a and two interglacial stages mis 1 and 5e contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 as indicators of land plant vegetation of different biosynthetic types were correlated with concentrations and distributions of pollen taxa in sediments of the same time horizons selected single pollen type data reveal details of vegetation changes but the overall picture is best illustrated by summing pollen known to predominantly derive from c4 plants or c4 plus cam plants the c4 plant signals in the biomarkers are recorded in the 13c data and in the abundances of c31 and c33n alkanes and the c32n alkanol calculated clusters of wind trajectories for austral summer and winter situations for the holocene and the last glacial maximum afford information on the source areas for the lipids and pollen and their transport pathways to the ocean this multidisciplinary approach provides clear evidence of latitudinal differences in leaf wax lipid and pollen composition with the holocene sedimentary data paralleling the current major phytogeographic zonations the northern sites congo fan area and northern angola basin get most of their terrestrial material from the congo basin and the angolan highlands dominated by c3 plants airborne particulates derived from the western and central south african hinterland dominated by deserts semideserts and savannah regions are rich in organic matter from c4 plants as can be expected from the present and glacial positions of the phytogeographic zones the carbon isotopic signatures of n alkanes and n alkanols both become isotopically more enriched in 13c from north to south in the northern part of the transect the relative importance of c4 plant indicators is higher during the glacials than in the interglacials indicating a northward extension of arid zones favoring grass vegetation in the south where grass rich vegetation merges into semidesert and desert the difference in c4 plant indicators is small

precession driven changes in terrestrial organic matter input to the eastern mediterranean leading up to the messinian salinity crisis abstract eastern mediterranean sediments over the past 12 myr commonly show strongly developed precessional cyclicity thought to be a biogeochemical response to insolation driven freshwater input from run off the mediterranean s dominant freshwater source today and in the past is the nile which is fed by north african monsoon rain other smaller circum mediterranean rivers also contribute to mediterranean hydrology crucially run off through all of these systems appears to vary with precession but there is no direct evidence linking individual water sources to the biogeochemical response recorded in mediterranean sediments consequently it is not clear whether the north african monsoon is entirely responsible for the mediterranean s sedimentary cyclicity or whether other precessional signals such as atlantic storm precipitation drive it organic matter in sediments derives from both marine and terrestrial sources and biomarker analysis can be used to discriminate between the two thereby providing insight into sedimentary and ecological processes we analysed a wide range of lipids from the late miocene 6 6 5 9 ma pissouri section southern cyprus and reconstructed the vegetation supplied to this region by measuring the carbon isotopes of the terrestrial component to identify its geographic source bit branched isoprenoidal tetraether indices reflect changes in the relative abundance of marine vs terrestrial soil organic matter inputs and with the exception of records from the last deglaciation this work is the first application of the bit approach to the reconstruction of orbital impacts on sedimentological processes bit indices show that the organic matter supplied to cyprus changed over the course of each precession cycle and was dominantly terrestrial during insolation maxima when north african run off was enhanced the 13 c values from these intervals are compatible with tropical north african vegetation however the 13 c record indicates that during insolation minima organic material supplied to southern cyprus derives from a more arid source region this is likely to have been aeolian transported organic matter from the anatolian plateau demonstrating that even in mediterranean sedimentary systems influenced by nile run off there is more than one independent precessional organic matter contribution to the sedimentary cyclicity pissouri s organic geochemistry also illustrates a long term trend towards more saline mediterranean conditions during the 600 kyr leading up to the messinian salinity crisis

a north to south transect of holocene southeast atlantic continental margin sediments relationship between aerosol transport and compound specific δ13c land plant biomarker and pollen records 1 we examined near surface late holocene deep sea sediments at nine sites on a north south transect from the congo fan 4 s to the cape basin 30 s along the southwest african continental margin contents distribution patterns and molecular stable carbon isotope signatures of long chain n alkanes c27 c33 and n alkanols c22 c32 are indicators of land plant vegetation of different biosynthetic types which can be correlated with concentrations and distributions of pollen taxa in the same sediments calculated clusters of wind trajectories and satellite aerosol index imagery afford information on the source areas for the lipids and pollen on land and their transport pathways to the ocean sites this multidisciplinary approach on an almost continental scale provides clear evidence of latitudinal differences in lipid and pollen composition paralleling the major phytogeographic zonations on the adjacent continent dust and smoke aerosols are mainly derived from the western and central south african hinterland dominated by deserts semi deserts and savannah regions rich in c4 and cam plants the northern sites congo fan area and northern angola basin which get most of their terrestrial material from the congo basin and the angolan highlands may also receive some material from the chad region very little aerosol from the african continent is transported to the most southerly sites in the cape basin as can be expected from the present position of the phytogeographic zones the carbon isotopic signatures of the n alkanes and n alkanols both become isotopically more enriched in 13c from north to south the results of the study suggest that this combination of pollen data and compound specific isotope geochemical proxies can be effectively applied in the reconstruction of past continental phytogeographic developments

triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes the passage of radiating seismic waves generates transient stresses in the earth s crust that can trigger slip on faults far away from the original earthquake source the triggered fault slip is detectable in the form of earthquakes 1 3 and seismic tremor 4 7 however the significance of these triggered events remains controversial 8 9 in part because they often occur with some delay long after the triggering stress has passed here we scrutinize the location and timing of tremor on the san andreas fault between 2001 and 2010 in relation to distant earthquakes we observe tremor on the san andreas fault that is initiated by passing seismic waves yet migrates along the fault at a much slower velocity than the radiating seismic waves we suggest that the migrating tremor records triggered slow slip of the san andreas fault as a propagating creep event we find that the triggered tremor and fault creep can be initiated by distant earthquakes as small as magnitude 5 4 and can persist for several days after the seismic waves have passed our observations of prolonged tremor activity provide a clear example of the delayed dynamic triggering of seismic events fault creep has been shown to trigger earthquakes 10 12 and we therefore suggest that the dynamic

deep sea terrigenous organic carbon transfer and accumulation impact of sea level variations and sedimentation processes off the ogooue river gabon abstract sedimentary isotopic and bulk geochemical proxies measured in sediment samples of five gravity cores collected in the distal part of the ogooue turbidite system around 4000 m depth were used to develop a conceptual model to describe the accumulation of terrigenous organic matter om during the last 200 000 yrs bp in the eastern part of the gulf of guinea this model takes into account the influence of the different depositional processes turbiditic vs hemipelagic sedimentation geomorphological features and sea level variations total organic carbon toc and the stable organic carbon isotopes of the om 13 c variability follow the highstand lowstand interglacial glacial cyclicity with a very low accumulation rate of terrigenous om during periods of high sea level and higher accumulation rate during period of low sea level a sea level of 80 120 m below present day seems to favor the transfer of terrigenous sediments to the deep offshore environment through the turbidite system and thanks to the connection of the canyons heads with the river system presently located at the shelf edge at 120 m water depth in this system terrigenous om matter delivered by the river accumulate in the sediments via two main processes indeed a part of the terrigenous om settles in combination with the finest particles forming hemipelagites while another part formed of very well preserved land plant debris is transported and deposited far offshore with turbidity currents the proportion of terrigenous om accumulated due to turbidity currents is important as it can represent more than 70 of the carbon accumulated during sea level lowstand moreover terrigenous om seems to preferentially accumulate in the levees and the lobes of the system notably due to the higher frequency of organic rich turbidites this study demonstrates that gravity flows influenced by the sea level variations can significantly affect the terrigenous om budget of the deep offshore atlantic margins and that channel levee complexes as well as turbidite lobes can be regarded as good sink for terrestrial organic carbon these processes should be taken into consideration in the context of source rocks exploration but also for the estimation of the general carbon accumulation in ocean sediment

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

seismic wave triggering of nonvolcanic tremor episodic tremor and slip and earthquakes on vancouver island 1 we explore the physical conditions that enable triggering of nonvolcanic tremor and earthquakes by considering local seismic activity on vancouver island british columbia during and immediately after the arrival of large amplitude seismic waves from 30 teleseismic and 17 regional or local earthquakes we identify tremor triggered by four of the teleseismic earthquakes the close temporal and spatial proximity of triggered tremor to ambient tremor and aseismic slip indicates that when a fault is close to or undergoing failure it is particularly susceptible to triggering of further events the amplitude of the triggering waves also influences the likelihood of triggering both tremor and earthquakes such that large amplitude waves triggered tremor in the absence of detectable aseismic slip or ambient tremor tremor and energy radiated from regional local earthquakes share the same frequency passband so that tremor cannot be identified during these smaller more frequent events we confidently identify triggered local earthquakes following only one teleseism that with the largest amplitude and four regional or local events that generated vigorous aftershock sequences in their immediate vicinity earthquakes tend to be triggered in regions different from tremor and with high ambient seismicity rates we also note an interesting possible correlation between large teleseismic events and episodic tremor and slip ets episodes whereby ets events that are late and have built up more stress than normal are susceptible to triggering by the slight nudge of the shaking from a large distant event while ets events that are early or on time are not

late pleistocene stalagmite growth in wolkberg cave south africa little is known about the sequence of climate and environmental change in southern africa during the last glacial period in spite of the intimations from records such as antarctic ice cores and archaeological sites that very marked changes took place which would have had profound effects on vegetation and animal distributions across the sub continent high resolution semi continuous climate and environmental records can be extracted from suitable cave speleothems speleothems are reasonably abundant in southern africa but their occurrence is patchy in time and space and the records can be difficult to interpret here we report our assessment of the stalagmite w5 from wolkberg cave in the northeastern part of south africa as an archive for glacial period climatic and environmental shifts the cave is located at 1450 m asl in the dolomitic limestones of the transvaal system in an area currently dominated by c4 grass vegetation nine u th dates show growth from 58 to 46 ka and a second brief phase ca 40 ka indicating that the available moisture was sufficient to allow speleothems to form the 18o and 13c values along the growth axis show variability in the order of 2 for the former while variability in the latter is characterized by a shift from values near 2 in the older section to 2 or more in the younger part these high 13c values are probably the combined result of co2 degassing of the percolating soil water prior to the carbonate precipitation in the cave chamber the increasing dominance of c4 over c3 vegetation and the high percentage of aragonite towards the stalagmite s top the retrieved data point towards increasingly drier and colder conditions during the growth period of the stalagmite furthermore the high frequency variations of 18o values indicate the presence of short term climate oscillations that are probably linked to shifts of the intertropical convergence zone

characteristics of secondary slip fronts associated with slow earthquakes in cascadia we implement an algorithm to automatically detect migrations of low frequency earthquakes at time scales between 30 min and 32 h during the 2003 2004 and 2005 slow slip events in cascadia we interpret these migrations of seismicity as a passive manifestation of secondary slip fronts ssfs that propagate faster than the main front we identify the dominant features of 383 ssfs including time location duration area propagation velocity and estimate their moment stress drop slip and slip rate we apply the same algorithm to continuous tremor detection in cascadia between 2009 and 2015 and characterize 693 ssfs at time scales between 4 h and 32 h we identify to our knowledge for the first time numerous 11 22 5 h long ssfs that propagate at velocities intermediate between slow slip events and previously reported ssfs the systematic detection of ssfs fills a gap between seismically and geodetically detectable slow earthquake processes analysis of ssf basic features indicates a wide range of stress drops and slip rates with medians of 5 8 kpa and 1 1 mm h as well as an intriguing relationship between ssf direction and duration that was observed in other contexts and could potentially help discriminate between the different physical models proposed to explain slow slip phenomena

reconstructing pathways of aeolian pollen transport to the marine sediments along the coastline of sw africa the distribution of pollen in marine sediments is used to reconstruct pathways of terrigenous input to the oceans and provides a record of vegetation change on adjacent continents the wind transport routes of aeolian pollen is comprehensively illustrated by clusters of trajectories isobaric 4 day backward trajectories are calculated using the modelled wind field of echam3 and are clustered on a seasonal basis to estimate the main pathways of aeolian particles to sites of marine cores in the south eastern atlantic trajectories and clusters based on the modelled wind field of the last glacial maximum hardly differ from those of the present day trajectory clusters show three regional and two seasonal patterns determining the pathways of aeolian pollen transport into the south eastern atlantic ocean mainly transport out of the continent occurs during austral fall and winter when easterly and south easterly winds prevail south of 25 s winds blow mostly from the west and southwest and aeolian terrestrial input is very low generally a good latitudinal correspondence exists between the distribution patterns of pollen in marine surface sediments and the occurrence of the source plants on the adjacent continent the northern angola basin receives pollen and spores from the congolian and zambezian forests mainly through river discharge the zambezian vegetation zone is the main source area for wind blown pollen in sediments of the angola basin while the semi desert and desert areas are the main sources for pollen in sediments of the walvis basin and on the walvis ridge a transect of six marine pollen records along the south western african coast indicates considerable changes in the vegetation of southern africa between glacial and interglacial periods important changes in the vegetation are the decline of forests in equatorial africa and the north of southern africa and a northward shift of winter rain vegetation along the western escarpment

late quaternary changes in ecosystems and carbon cycling on mt kenya east africa a landscape ecological perspective based on multi proxy lake sediment influxes abstract the degree to which different lakes within a landscape respond coherently in unison to external drivers such as climate change and soil development is uncertain presentation of multi proxy geochemical and palaeoecological data from individual lakes in the form of fluxes minimizes distortions resulting from variable sedimentation rates and changes in sediment composition we use the accumulation rates of magnetic minerals total organic c and n terrestrial and aquatic biomarkers graminoid epidermis pollen green algae diatoms and diatom c in four small lakes situated between 2350 and 4595 m a s l on the ne flank of mt kenya east africa to reconstruct changes in c cycling over the last 38 ka the results conflict with earlier models of landscape and lake development showing 1 that glacial interglacial changes in vegetation cannot be interpreted as simple altitudinal shifts in the modern vegetation belts and 2 that limnological changes were not coherent rapid variations in climate water level erosion and nutrient input overwhelmed long term successional trends in lake sedimentation and c accumulation since the last glacial maximum the results also reveal previously unrecognized features of the palaeoenvironmental record such as the rapid degradation of organic matter in diatoms and the occurrence of a productive fire prone montane grassland during the highly seasonal monsoonal climate of the lateglacial and early holocene

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

rare dynamic triggering of remote m 5 5 earthquakes from global catalog analysis probing the effects of a transient stress on the timing of an earthquake occurrence is necessary for understanding the remote interaction of large magnitude events global catalog data containing 35 years of m 5 5 earthquakes allow us to explore for periods of enhanced or suppressed seismic activity we consider 113 m 7 5 main shocks between 1977 and 2012 and focus on seismic activity on time scales from seconds to days following these main shocks we search for evidence of dynamic triggering of large magnitude events similar to the previously observed global increase during the first few days following the 2012 m8 6 indian ocean main shock we restrict the analysis to regions of elevated strain during the passage of surface waves using a threshold of 0 1 microstrain 3 kpa and a temporal window of 1 year we stack daily seismicity rate curves using the exclusion zone declustered m 5 5 catalog events in order to resolve deviations from the background rate our results do not indicate a significant change in activity for at least 10 days when considering the collective set of 113 main shocks and subsets at m8 0 and m8 5 thresholds the results also do not indicate immediate triggering of m 5 5 events we do find two instances of increased seismicity in the elevated strain region within 10 days these increases are subsequent to two main shocks the 1977 m8 3 and 2012 m8 6 both located in the indian ocean we conclude that a global change in m 5 5 earthquake rates following a transient stress from distant earthquakes is a rare occurrence

variations in slow slip moment rate associated with rapid tremor reversals in cascadia during large slow slip events tremor sometimes propagates in the reverse along strike direction for a few hours at speeds 10 to 40 times faster than the forward propagation we examine the aseismic slip that underlies this rapidly propagating tremor we use pbo plate boundary observatory borehole strainmeter data to search for variations in the slow slip moment rate during 35 rapid tremor reversals rtrs that occurred beneath vancouver island the strain records reveal that on average the strain rate increases by about 100 30 during rtrs given the green s functions expected for slip in the rtr locations these strain rate increases imply 50 to 130 increases in the aseismic moment rate the median moment released per rtr is between 8 and 21 of the daily slow slip moment equivalent to that of a mw 5 0 to 5 1 earthquake by combining the rtr moments with the spatial extents suggested by tremor we estimate that a typical rtr has peak slip of roughly one sixth of the peak slip in the main slow slip event near front slip rate of a few to ten times the main front slip rate stress drop around half the main event stress drop and strain energy release rate around one tenth that of the main front our observations support a picture of rtrs as aseismic subevents with high slip rates but modest strain energy release rtrs appear to contribute to but not dominate the overall slow slip moment though they may accommodate most of the slip in certain locations

sources transport and deposition of terrestrial organic material a case study from southwestern africa abstract southwestern africa s coastal marine mudbelt a prominent holocene sediment package provides a valuable archive for reconstructing terrestrial palaeoclimates on the adjacent continent while the origin of terrestrial inorganic material has been intensively studied the sources of terrigenous organic material deposited in the mudbelt are yet unclear in this study plant wax derived n alkanes and their compound specific 13c in soils flood deposits and suspension loads from regional fluvial systems and marine sediments are analysed to characterize the origin of terrestrial organic material in the southwest african mudbelt soils from different biomes in the catchments of the orange river and small west coast rivers show on average distinct n alkane distributions and compound specific 13c values reflecting biome specific vegetation types most notably the winter rainfall associated fynbos biome of the southwestern cape in the fluvial sediment samples from the orange river changes in the n alkane distributions and compound specific 13c compositions reveal an overprint by local vegetation along the river s course the smaller west coast rivers show distinct signals reflecting their small catchment areas and particular vegetation communities marine surface sediments spanning a transect from the northern mudbelt 29 s to st helena bay 33 s reveal subtle but spatially coherent changes in n alkane distributions and compound specific 13c indicating the influence of orange river sediments in the northern mudbelt the increasing importance of terrigenous input from the adjacent western coastal biomes in the central mudbelt and contributions from the fynbos biome to the southern mudbelt these findings indicate the different sources of terrestrial organic material deposited in the mudbelt and highlight the potential the mudbelt has to preserve evidence of environmental change from the adjacent continent

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

a 15 year catalog of more than 1 million low frequency earthquakes tracking tremor and slip along the deep san andreas fault low frequency earthquakes lfes are small rapidly recurring slip events that occur on the deep extensions of some major faults their collective activation is often observed as a semicontinuous signal known as tectonic or nonvolcanic tremor this manuscript presents a catalog of more than 1 million lfes detected along the central san andreas fault from 2001 to 2016 these events have been detected via a multichannel matched filter search cross correlating waveform templates representing 88 different lfe families with continuous seismic data together these source locations span nearly 150 km along the central san andreas fault ranging in depth from 16 to 30 km this accumulating catalog has been the source for numerous studies examining the behavior of these lfe sources and the inferred slip behavior of the deep fault the relatively high temporal and spatial resolutions of the catalog have provided new insights into properties such as tremor migration recurrence and triggering by static and dynamic stress perturbations collectively these characteristics are inferred to reflect a very weak fault likely under near lithostatic fluid pressure yet the physical processes controlling the stuttering rupture observed as tremor and lfe signals remain poorly understood this paper aims to document the lfe catalog assembly process and associated caveats while also updating earlier observations and inferred physical constraints the catalog itself accompanies this manuscript as part of the electronic supplement with the goal of providing a useful resource for continued future investigations

high frequency identification of non volcanic tremor triggered by regional earthquakes 1 subsequent to the discovery of ambient non volcanic tremor activity along the parkfield cholame section of the san andreas fault in central california triggered tremors associated with the surface waves of large teleseismic earthquakes have been recognized however no evidence of triggered tremors from regional earthquakes has previously been found either here or in other tremor regions by systematically filtering seismograms to higher frequencies i e above 20 hz associated with 99 regional m5 earthquakes since 2001 we identify four regional earthquakes that have triggered tremors in central california significant high frequency energy is also observed in previously identified teleseismically triggered and ambient tremors suggesting a common mechanism we find that long period and large amplitude surface waves from both regional and teleseismic events have a greater potential of triggering tremor in the same region and that the inferred minimum triggering dynamic stress is 1 kpa

low latitude hydro climatic changes during the plio pleistocene evidence from high resolution alkane records in the southern south china sea abstract high resolution records of long chain n alkane biomarkers from the southern south china sea reveal tightly response of n alkane distribution to hydro climate changes over the past 5 ma with increasing longer chain n c31 alkanes indicating a correlation with drier conditions and increasing shorter chain n c27 alkanes with wetter conditions the variations of the c31 c27 ratio or the alkane chain length index imply humid conditions before 2 9 ma progressively reduced moisture since then and to bigger fluctuations between wet and dry conditions since 1 2 ma this long term hydro climate trend is superimposed by glacial dry and interglacial wet patterns over the plio pleistocene glacial cycles combined with other proxy records our results indicate that precipitation over the tropical asia pacific strengthened before the onset of the northern hemisphere glaciation and the mid pleistocene climate transition at about 1 2 ma these dramatic humidity changes over major climate transitions imply a crucial role of tropical hydrology dynamics on global climate change in the late cenozoic

synthetic reconstructions of southern african environments during the last glacial maximum 21 18kyr and the holocene altithermal 8 6kyr abstract the pash database has been assembling palaeoclimatic data from the southern hemisphere for a number of years the southern african sector now contains more than 100 records spanning the last 200 000 years a number of these relate to the last glacial maximum and holocene altithermal which represent the two most recent extremes in global temperatures syntheses of these records have permitted the preparation of preliminary palaeoenvironmental maps for the two intervals the results provide insights into probable changes in atmospheric circulation as temperatures across the subcontinent rose by 6 7 c these changes are in agreement with a present day model which has been developed to explain short term variations in southern african climate the results presented here should assist in calibrating models developed to predict future climate change

orbital scale vegetation change in africa abstract palynological records of middle and late pleistocene marine sediments off african shores is reviewed in order to reveal long term patterns of vegetation change during climate cycles whether the transport of pollen and spores from the source areas on the continent to the ocean floor is mainly by wind or predominantly by rivers depends on the region despite the differences in transportation accumulation rates in the marine sediments decline exponentially with distance to the shore the marine sediments provide well dated records presenting the vegetation history of the main biomes of western and southern africa the extent of different biomes varied with the climate changes of the glacial interglacial cycle the mediterranean forest area expanded during interglacials the northern saharan desert during glacials and the semi desert area in between during the transitions in the sub saharan mountains ericaceous scrubland spread mainly during glacials and the mountainous forest area often increased during intermediate periods savannahs extended or shifted to lower latitudes during glacials while the representation of the tropical rain forest fluctuated with summer insolation and precession that of the subtropical biomes showed more obliquity variability or followed the pattern of glacial and interglacials

middle to late pleistocene vegetation and climate change in subtropical southern east africa in this study we investigate pleistocene vegetation and climate change in southern east africa by examining plant leaf waxes in a marine sediment core that receives terrestrial runoff from the limpopo river the plant leaf wax records are compared to a multi proxy sea surface temperature sst record and pollen assemblage data from the same site we find that indian ocean sst variability driven by high latitude obliquity exerted a strong control on the vegetation of southern east africa during the past 800 000 yr interglacial periods were characterized by relatively wetter and warmer conditions increased contributions of c3 vegetation and higher sst whereas glacial periods were marked by cooler and arid conditions increased contributions of c4 vegetation and lower sst we find that marine isotope stages mis 5e 11c 15e and 7a 7c are strongly expressed in the plant leaf wax records but mis 7e is absent while mis 9 is rather weak our plant leaf wax records also record the climate transition associated with the mid brunhes event mbe suggesting that the pre mbe interval 430 800 ka was characterized by higher inputs from grasses in comparison to relatively higher inputs from trees in the post mbe interval 430 to 0 ka differences in vegetation and sst of southern east africa between the pre and post mbe intervals appear to be related to shifts in the location of the subtropical front comparison with vegetation records from tropical east africa indicates that the vegetation of southern east africa while exhibiting glacial interglacial variability and notable differences between the pre and post mbe portions of the record likely did not experience such dramatic extremes as occurred to the north at lake malawi

influence of late pleistocene and holocene climate on vegetation distributions in southwest africa elucidated from sedimentary n alkanes differences between 12 s and 20 s abstract global and local climatic forcing e g concentration of atmospheric co2 or insolation influence the distribution of c3 and c4 plants in southwest africa c4 plants dominate in more arid and warmer areas and are favoured by lower pco2 levels several studies have assessed past and present continental vegetation by the analysis of terrestrial n alkanes in near coastal deep sea sediments using single samples or a small number of samples from a given climatic stage the objectives of this study were to evaluate vegetation changes in southwest africa with regard to climatic changes during the late pleistocene and the holocene and to elucidate the potential of single sample simplifications we analysed two sediment cores at high resolution altogether ca 240 samples from the southeast atlantic ocean 20 s and 12 s covering the time spans of 18 to 1 ka and 56 to 2 ka respectively our results for 20 s showed marginally decreasing c4 plant domination of ca 5 during deglaciation based on average chain length acl27 33 values and carbon isotopic composition of the c31 and c33n alkanes values for single samples from 18 ka and the holocene overlap and thus are not significantly representative of the climatic stages they derive from in contrast at 12 s the n alkane parameters show a clear difference of plant type for the late pleistocene c4 plant domination 66 c4 on average and the holocene c3 plant domination 40 c4 on average during deglaciation vegetation change highly correlates with the increase in pco2 r 0 91 short term climatic events such as heinrich stadials or antarctic warming periods are not reflected by vegetation changes in the catchment area instead smaller vegetation fluctuations during the late pleistocene occur in accordance with local variations of insolation

diverse origins and pre depositional histories of organic matter in contemporary chinese marginal sea sediments abstract marginal seas are estimated to account for up to 90 of organic carbon oc burial in marine sediments and thus play an important role in global carbon cycle however comprehensive assessments of carbon budgets for marginal sea systems are challenging due to their inherent complexity with spatial and temporal variability in carbon inputs and dispersal processes we examine the bohai sea and yellow sea bs ys in order to further our understanding of sedimentary oc delivery translocation and accumulation in a shallow marginal sea system bulk properties and the content and isotopic compositions 14c 13c of source specific plant wax n alkyl lipid biomarkers were determined for a suite of surficial sediment samples variable 13c values 25 1 to 28 5 and contemporary radiocarbon ages of short chain n fatty acids fas c16 c18 reflect modern autochthonous marine and or fresh terrestrial plant input in contrast extremely depleted 14c values 932 to 979 of short chain n alkanes c16 c18 suggest a predominant input from sedimentary rocks petrogenic oc or petroleum abundance weighted average 13c and 14c values of long chain leaf wax lipids c26 28 30 n fas c24 26 28 n alkanols c27 29 31 n alkanes are 29 1 1 1 to 30 2 0 3 and 286 150 to 442 119 respectively illustrating that terrestrial oc delivery is dominated by pre aged 3000 5000 14c yrs c3 vegetation sources a coupled carbon isotopic mixing model based on the bulk and compound specific biomarker 13c and 14c values is used to partition the bs ys sedimentary oc into three components that reflect both origins and transport processes for all sampling sites 31 64 is modern contemporary oc 24 49 is pre aged terrestrial oc and 7 26 is fossil oc the latter likely derived from both physical erosion of ancient sedimentary rocks and fossil fuel sources pre aged soil oc is most prominent in front of the modern and old huanghe yellow river delta 48 and 49 and fossil oc is most significant north of the old huanghe mouth 26 significant pre aged soil contributions 33 are also evident for sites further offshore where transport and deposition of eolian dust supply may be important for the three major deposition areas of the bs ys system bohai basin sub aqueous huanghe delta and central south ys basin we estimate that about 3 02 mt yr of refractory plant derived pre aged soil oc and 0 98 mt yr of 14c depleted fossil oc accumulates in surface sediments corresponding to 35 and 11 of sediment toc respectively compared with estimates for fluxes from corresponding sources the burial efficiency is close to 100 for pre aged soil oc and 70 for fossil oc implying efficient oc burial in delta and shelf environments re burial of these two pools of terrigenous oc only affects carbon cycling on millennial and longer timescales respectively and exerts little influence on the modern carbon cycle

anomalous molybdenum isotope trends in upper pennsylvanian euxinic facies significance for use of δ98mo as a global marine redox proxy abstract the use of molybdenum isotope data 98mo from organic rich shales to draw inferences concerning marine paleoredox conditions at a global scale is predicated upon the assumptions of 1 a residence time of mo in seawater much greater than the ocean mixing time and 2 quantitative removal of mo from a strongly euxinic h2s aq 11 m water column to the sediment thus preserving the seawater 98mo signature in this study we analyze mo isotopic variation in the hushpuckney shale a 73 cm thick unit representing the late transgressive to early regressive stages of a glacio eustatic cyclothem swope formation deposited in the late pennsylvanian midcontinent sea lpms of north america the hushpuckney can be subdivided into four stratigraphic zones of distinctive geochemical character zones i and iii which accumulated under weakly euxinic conditions acquired relatively high 98mo values 0 9 to 1 1 whereas zone ii which accumulated under intensely euxinic conditions acquired lower 98mo values 0 6 zone iv which accumulated under suboxic conditions in the water column acquired the heaviest 98mo values 1 1 to 1 8 these results contrast with the pattern of redox 98mo covariation in modern marine environments in which the heaviest 98mo values are found in the most intensely euxinic facies we evaluate three different hypotheses to account for the mo isotopic patterns of the hushpuckney shale one hypothesis seawater freshwater mixing is rejected owing to isotopic mass balance considerations a second hypothesis is a local control on 98mo by water column redox cycling of mn with particulate mn oxyhydroxides adsorbing isotopically light mo and transferring it to the sediment a process that was most active during deposition of zone ii the significance of this scenario is that euxinic black shales may not reliably record global seawater 98mo in areas where a mn particulate shuttle is operative a third hypothesis is based on rapid secular variation of the mo isotope composition of late pennsylvanian global seawater in order to account for 98mo trends within the hushpuckney shale seawater 98mo must have varied by 1 2 at a 100 kyr timescale which would have been possible only if the residence time of mo in late pennsylvanian seawater was

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

relationship between antarctic sea ice and southwest african climate during the late quaternary here we compare late quaternary southwest african climate records from the west coast of southern africa published winter rainfall and trade wind intensity records from a core off the coast of namibia to records of antarctic sea ice extent this comparison reveals coherent changes between antarctic sea ice extent and the southwest african winter rain region since 45 k y b p with enhanced winter rainfall and trade wind vigor during periods of increased sea ice presence we propose an oceanic and atmospheric coupling between antarctic sea ice and the winter rainfall zone of southwest africa that may lead to increased desertification in the region if global warming persists

dynamics of the australian indonesian monsoon across termination ii implications of molecular biomarker reconstructions from the timor sea abstract molecular biomarker derived proxies in a marine sediment core from the eastern timor sea have been employed to track changes in the australian indonesian monsoon system over the time period from the penultimate glacial to the last interglacial the average chain length of n alkanes originating from terrestrial higher plants reveals an expansion of woody plants during both termination ii and the last interglacial with respect to the penultimate glacial this is consistent with previous reconstructions for the last glacial interglacial cycle indicating that water stress conditions during dry seasons of southern indonesia should have been relieved during interglacials and deglacials relative to glacials however in contrast to an only muted response during heinrich stadial 1 the vegetation composition showed a dramatic and prominent change during heinrich stadial 11 this was probably caused by a much more significant and longer duration iceberg discharge event to the northern north atlantic during heinrich stadial 11 relative to heinrich stadial 1 which exerted a significant influence on the tropical hydrological cycle and monsoon rainfall seasonality in addition marine algae derived biomarkers are used to reconstruct primary productivity variations which are in agreement with previous studies from the same area the precessional cyclicity of paleo productivity variations is possibly induced by changes in the australian indonesian winter monsoon intensity showing a correlation with boreal winter insolation however this phase relationship is in contrast to the inference based on other lines of evidence which suggests strong winter monsoon strength during boreal summer insolation maxima new winter monsoon proxies are therefore required to clarify this discrepancy

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

pendant bioconstructions cemented by microbial carbonate in submerged marine caves holocene se sicily abstract unusual pendant bioconstructions occur within two submerged caves in the plemmirio marine protected area south of syracuse se sicily these cm to dm sized bioconstructions project downward from the cave roofs the main framework builders are serpulids belonging to the genera protula semivermilia and josephella encrusting bryozoans corals hydrozoans and sponges are subordinately present whereas bivalves and brachiopods are overall rare these faunal associations are characteristic of the studied caves but only in some places they form small bioconstructions that are cemented by microbial carbonates made up by autochthonous peloidal to clotted peloidal and aphanitic micrite the autochthonous micrite stabilizes the pendant bioconstructions herein referred to as biostalactites the microbial carbonate reveals high contents of bacterial lipid biomarkers among the most abundant compounds are mono o alkyl glycerol ethers mages and branched fatty acids 10 me c16 0 iso and anteiso c15 0 and c17 0 interpreted as biomarkers of sulfate reducing bacteria other compounds preserved in the autochthonous carbonates include lipids derived from marine zoo and phytoplankton brassicasterol dinosterol and monounsaturated short chain fatty acids unspecified marine bacteria saturated and monounsaturated short chain fatty acids and land plants long chain fatty acids long chain alcohols stigmasterol sitosterol and campesterol the observed lipid biomarker signatures are remarkably similar to those of post glacial reefal microbialites where microbialite formation in cavities of the coral framework was also mediated by sulfate reducing bacteria in the submerged caves of plemmirio marine protected area serpulid colonies apparently occur preferentially where freshwater is seeping through crevices in the limestone the consequent nutrification is believed to favor serpulid aggregation and the growth of other skeletal i e bryozoans and corals and soft bodied organisms i e sponges and ascidiae the resultant accumulation of biomass and its taphonomy provide niches for sulfate reducing bacteria which induce carbonate precipitation cementing and stabilizing the biostalactites the finding of pendant cemented bioconstructions in the mazzere and granchi caves of the plemmirio marine protected area reveals that sulfate reducing bacteria are involved in microbialite formation in various cryptic environments the formation of such peloidal to clotted peloidal microcrystalline carbonates in cryptic ecosystems is a significant factor for the stabilization of different kinds of bioconstructions spanning from small biostalactites to large reefs

a δ13c and δ2h leaf wax record from the late quaternary loess paleosoil sequence el paraiso central spain abstract the mediterranean peninsula increasingly suffers from droughts and aridity the first consequences of global climate change in that region precise scenarios for the region s future climate predictions require knowledge about the processes of past climate changes but information about the western mediterranean climate and its history is controversial for this study we applied compound specific 13c and 2h analyses on long chain n alkanes in the 8 m el paraiso loess paleosoil sequence lps central spain to investigate climate and environmental changes during the late quaternary the 13c values are most enriched during marine isotope stage mis 3 indicating more arid conditions while lower values during mis 4 and 2 are interpreted to document more humid conditions low values are also recorded for the holocene colluvium which can at least partly be explained with higher concentrations in atmospheric co2 the 2h values are mostly enriched during the last glacial compared to the holocene we suggest that this is mainly controlled by isotopic effects related to the moisture source yet other possible effects like evapotranspirative enrichment and changes in atmospheric circulation patterns shouldn t be ruled out our results corroborate previous findings based on leaf wax patterns geomorphological records and climate models they all indicate relatively humid conditions during mis 2 compared to more arid phases during mis 3

stable isotope proxy records in tropical terrestrial environments abstract the tropics refers to an area that is loosely equatorial characterized by relatively high temperatures at low altitude comparatively low seasonal contrast in temperatures and generally high or highly seasonal rainfall the stable isotopes of carbon oxygen and hydrogen are increasingly important tools of relevance to understanding trajectories and mechanisms of past environmental change in the tropics in the case of carbon this is because at the broadest level the carbon isotope composition of organic and carbon containing inorganic proxy materials formed in the tropics can be read as being derived from the balance between c3 tree and c4 grass photosynthesis hence providing a relative measure of vegetation type and indirectly climate likewise changes in the oxygen and hydrogen isotope composition of many proxy materials again at the broadest level can be read as indicative of changes in hydrological conditions and or altitude in the past this review provides an entry point into the literature relating to the use of stable isotopes as terrestrial environmental proxies for past environmental change with a focus on the measurement and interpretation of stable isotope data from the wide range of proxy materials preserved in tropical environments

comparable hydrogen isotopic fractionation of plant leaf wax n alkanoic acids in arid and humid subtropical ecosystems 1 leaf wax hydrogen isotope proxies have been widely used to reconstruct past hydrological changes however published reconstructions have given little consideration for the potentially variable hydrogen isotopic fractionation relative to precipitation ewax p under different climate and environmental settings chief among various potential factors controlling fractionation is relative humidity which is known to strongly affect oxygen isotopic ratios of plant cellulose but its effect on hydrogen isotopic fractionation of leaf waxes is still ambiguous analyses of lake surface sediments and individual modern plants have provided valuable information on the variability of ewax p but both approaches have significant limitations here we present an alternative method to obtain the integrated time resolved ecosystem level ewax p values by analyzing modern aerosol samples collected weekly from arid arizona lowlands and humid subtropical atlanta georgia environments during the main growth season because aerosol samples mainly reflect regional leaf wax resources the extreme contrast in the hydroclimate and associated vegetation assemblages between our study sites allows us to rigorously assess the impact of relative humidity and associated vegetation assemblages on leaf wax hydrogen isotopic fractionation we show there is only minor difference mostly 10 in the mean ewax p values in the two end member environments one possible explanation is that the positive isotopic effects of low relative humidity are offset by progressive replacement of trees with grasses that have a more negative apparent fractionation our results represent an important step toward quantitative interpretation of leaf wax hydrogen isotopic records

a search in strainmeter data for slow slip associated with triggered and ambient tremor near parkfield california 1 we test the hypothesis that as in subduction zones slow slip facilitates triggered and ambient tremor in the transform boundary setting of california our study builds on the study of peng et al 2009 of triggered and ambient tremor near parkfield california during time intervals surrounding 31 potentially triggering m 7 5 teleseismic earthquakes waves from 10 of these triggered tremor and 29 occurred in periods of ambient tremor activity we look for transient slow slip during 3 month windows that include 11 of these triggering and nontriggering teleseisms using continuous strain data recorded on two borehole gladwin tensor strainmeters gtsm located within the distribution of tremor epicenters we model the gtsm data assuming only tidal and drift signals are present and find no detectable slow slip either ongoing when the teleseismic waves passed or triggered by them we infer a conservative detection threshold of about 5 nanostrain for abrupt changes and about twice this for slowly evolving signals this could be lowered slightly by adding analyses of other data types modeled slow slip signals and gtsm data calibration detection of slow slip also depends on the slipping fault s location and size which we describe in terms of equivalent earthquake moment magnitude m in the best case of the gtsm above a very shallow slipping fault detectable slip events must exceed m 2 and if the slow slip is beneath the seismogenic zone below 15 km depth even m 5 events are likely to remain hidden

nonvolcanic tremor evolution and the san simeon and parkfield california earthquakes nonvolcanic tremors occur adjacent to locked faults and may be closely related to the generation of earthquakes monitoring of the san andreas fault in the parkfield california region revealed that after two strong earthquakes tremor activity increased in a nearly dormant tremor zone increased and became periodic in a previously active zone and has remained elevated and periodic for over 4 years static shear and coulomb stress increases of 6 to 14 kilopascals from these two earthquakes are coincident with sudden increases in tremor rates the persistent changes in tremor suggest that stress is now accumulating more rapidly beneath this part of the san andreas fault which ruptured in the moment magnitude 7 8 ft tejon earthquake of 1857

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

a hydroclimate regime shift around 270 ka in the western tropical pacific inferred from a late quaternary n alkane chain length record abstract the inert leaf wax deposited in deep sea sediment preserves clues of the past climate change in particular the n alkane distribution patterns characterized by the n alkane average chain length index acl provide useful information on the hydrological changes as longer chain alkanes are more frequently biosynthesized under relatively arid condition to prevent water loss our data from the western south china sea reveal the superimposition of a systematic regime shift in the regional mean precipitation at ca 420 270 ka on the glacial interglacial changes in the quaternary the dominance of shorter n alkane chain length between 420 ka and 270 ka is interpreted as overall wetter conditions during this period compared to the older or younger intervals a similar timing of hydrological regime shifts has also been observed in other paleoclimate records including major changes in productivity in the eastern pacific and pollen records from the western pacific we suggest that the changes in the regional mean hydroclimate states near 420 ka and 270 ka are most likely related to a regime change in the frequency and or intensity of the el nino southern oscillation with the overall wetter hydroclimate prior to 270 ka resulting in a more prevalent la nina like condition in the pacific

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

triggered seismic events along the eastern denali fault in northwest canada following the 2012 mw 7 8 haida gwaii 2013 mw 7 5 craig and two mw 8 5 teleseismic earthquakes we conduct a systematic search for remotely triggered seismic activity along the eastern denali fault edf in northwest canada an intraplate strike slip region we examine 19 distant earthquakes recorded by nine broadband stations in the canadian national seismograph network and find that the 2012 m w 7 8 haida gwaii and 2013 m w 7 5 craig alaska earthquakes triggered long duration 10 s emergent tremor like signals near the southeastern portion of the edf in both cases tremor coincides with the peak transverse velocities consistent with love wave triggering on right lateral strike slip faults the 2011 m w 9 0 tohoku oki and 2012 m w 8 6 indian ocean earthquakes possibly triggered tremor signals although we were unable to locate those sources in addition we also identify many short duration 5 s bursts that were repeatedly triggered by the rayleigh waves of the 2012 m w 7 8 haida gwaii earthquake although we were unable to precisely locate the short duration 5 s events they appear to be radiating from the direction of the klutlan glacier and from a belt of shallow historical seismicity at the eastern flank of the wrangell st elias mountain range the fact that these events were triggered solely by the rayleigh waves suggests a different source mechanism as compared with triggered tremor observed along the edf and other plate boundary regions online material description of rayleigh wave polarization detection figures of spectograms s wave amplitudes polarization analysis and static stress changes tables of earthquake catalogs and velocity model and animations of tremors and bursts

shallow microearthquakes near chongqing china triggered by the rayleigh waves of the 2015 m7 8 gorkha nepal earthquake abstract we present a case of remotely triggered seismicity in southwest china by the 2015 04 25 m7 8 gorkha nepal earthquake a local magnitude m l 3 8 event occurred near the qijiang district south of chongqing city approximately 12 min after the gorkha mainshock within 30 km of this m l 3 8 event there are 62 earthquakes since 2009 and only 7 m l 3 events which corresponds to a likelihood of 0 3 for a m l 3 on any given day by a random chance this observation motivates us to investigate the relationship between the m l 3 8 event and the gorkha mainshock the m l 3 8 event was listed in the china earthquake national center cenc catalog and occurred at shallow depth 3 km by examining high frequency waveforms we identify a smaller local event m l 2 5 15 s before the m l 3 8 event both events occurred during the first two cycles of the rayleigh waves from the gorkha mainshock we perform seismic event detection based on envelope function and waveform matching by using the two events as templates both analyses found a statistically significant rate change during the mainshock suggesting that they were indeed dynamically triggered by the rayleigh waves both events occurred during the peak normal and dilatational stress changes 10 30 kpa consistent with observations of dynamic triggering in other geothermal volcanic regions although other recent events i e the 2011 m9 1 tohoku oki earthquake produced similar peak ground velocities the 2015 gorkha mainshock was the only event that produced clear dynamic triggering in this region the triggering site is close to hydraulic fracturing wells that began production in 2013 2014 hence we suspect that fluid injections may increase the region s susceptibility to remote dynamic triggering

a record of aerobic methane oxidation in tropical africa over the last 2 5 ma abstract methane and co 2 are climatically active greenhouse gases ghg and are powerful drivers of rapid global warming comparable to the arctic the tropics store large volumes of labile sedimentary carbon that is vulnerable to climate change however little is known about this labile carbon reservoir in particular the behaviour of high methane producing environments e g wetlands and their role in driving or responding to past periods of global climate change in this study we use a microbial biomarker approach that traces continental aerobic methane oxidation amo from sedimentary organic matter in deep sea fan sediments off the congo river to reconstruct the link between central african methane cycling and continental export during key periods of global pleistocene warmth we use 35 amino bacteriohopanepolyols bhps specifically aminobacteriohopane 31 32 33 34 tetrol aminotetrol and 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol as diagnostic molecular markers for amo ch 4 oxidation markers and the prevalence of continental wetland environments bhps were analysed in sediments from the congo fan odp 1075 dated to 2 5 ma high resolution studies of key warm marine isotope stages mis 5 11 and 13 are included to test the relationship between ch 4 oxidation markers in sediments at different levels of elevated global atmospheric ghg this study presents the oldest reported occurrence to date of 35 amino bhps up to 200 m below sea floor 2 5 ma with no strong degradation signature observed low concentrations of ch 4 oxidation markers identified between 1 7 ma and 1 ma suggest a reduction in wetland extent in tropical africa in response to more arid environmental conditions correlation of high resolution ch 4 oxidation marker signatures with global atmospheric ghg concentrations during mis 5 11 and 13 further emphasize periods of enhanced tropical c cycling however subsequent analysis would be required to further extrapolate the relative importance of tropical methane sources as a driver of global methane concentrations during the pleistocene

climatic variability in mfabeni peatlands south africa since the late pleistocene abstract it has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the northern and southern hemisphere climates since the late pleistocene a key test for this proposition would be to undertake palaeoenvironmental studies on terrestrial archives in climatically sensitive regions southern africa s contemporary c 3 and c 4 terrestrial plant distributions display a definitive geographical pattern dictated by different growing season rainfall and temperature zones however the region is generally archive poor due to its overall semi arid climate and high relief topography the mfabeni peatland with a basal age of c 47 k yrs calibrated before present kcal yr bp is one of the oldest continuous coastal peat deposits in southern africa molecular leaf wax isotopes 13 c wax were generated for a 810 cm long core and combined with previously published bulk geochemical 13 c bulk toc palynological and stratigraphic data to reconstruct the late pleistocene and holocene palaeoenvironments we interpreted environmental shifts associated with the heinrich 4 last glacial maximum deglacial and holocene periods which are consistent with adjacent indian ocean sea surface temperature records however the other shorter climate perturbations during the heinrich 5 3 2 1 antarctic cold reversal and younger dryas were muted most likely due to local hydrological overprinting on the mfabeni record a general anti phase sequence was observed between the mfabeni record and better established northern hemisphere events underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the late pleistocene

pre aged soil organic carbon as a major component of the yellow river suspended load regional significance and global relevance abstract large rivers connect the continents and the oceans and corresponding material fluxes have a global impact on marine biogeochemistry the yellow river transports vast quantities of suspended sediments to the ocean yet the nature of the particulate organic carbon poc carried by this system is not well known the focus of this study is to characterize the sources composition and age of suspended poc collected near the terminus of this river system focusing on the abundance and carbon isotopic composition 13c and 14c of specific biomarkers the concentrations of vascular plant wax lipids long chain c24 n alkanes n fatty acids and poc co varied with total suspended solid tss concentrations indicating that both were controlled by the overall terrestrial sediment flux poc exhibited relatively uniform 13c values 23 8 to 24 2 and old radiocarbon ages 4000 4640 yr however different biomarkers exhibited a wide range of 14c ages short chain c16 c18 fatty acid 14c ages were variable but generally the youngest organic components from 502 yr to modern suggesting they reflect recently biosynthesized material lignin phenol 14c ages were also variable and relatively young 1070 yr to modern suggesting rapid export of carbon from terrestrial primary production in contrast long chain plant wax lipids display relatively uniform and significantly older 14c ages 1500 1800 yr likely reflecting inputs of pre aged mineral associated soil oc from the yellow river drainage basin even carbon numbered n alkanes yielded the oldest 14c ages up to 26 000 yr revealing the presence of fossil petrogenic oc two isotopic mass balance approaches were explored to quantitively apportion different oc sources in yellow river suspended sediments results indicate that the dominant component of poc 53 57 is substantially pre aged 1510 1770 yr and likely sourced from the extensive loess paleosol deposits outcropping within the drainage basin of the remaining poc between 10 and 31 is fossil in origin 26 000 yr resulting from the physical erosion of ancient sedimentary rock and input of fossil fuel residues from anthropogenic activity and 16 33 is modern carbon derived from terrestrial and aquatic productivity these findings have implications both regarding the provenance and vintage of organic matter signatures emanating from the yellow river basin and similar catchments containing extensive paleosol sequences as well as for the reactivity and fate of this poc upon supply to adjacent marginal seas

provenance of surface sediments along the southeastern adriatic coast off italy an overview multi proxy studies are necessary to understand sediment composition and related provenance on continental shelfs here it is shown that the spatial distribution of geochemical composition and grain size for surface sediments along the southeastern italian coast is related to provenance and mechanisms influencing sediment pathways a northern adriatic italian provenance can be distinguished from a southern apennine river source this is done independent of grain size using the element ratios ce ni and zr cr furthermore the origin of organic matter is determined using bulk carbon isotopes and the c n ratio integrating these results with those from complementary studies on 18o and 13c of globigerinoides ruber white the bit index stable isotopes of plant waxes and dinoflagellate cyst distribution from the same set of samples reveals that sediments from the northwestern adriatic are transported as far southward as the gallipoli shelf eastern gulf of taranto by the western adriatic current wac along the wac there is a consistent southward decrease in po river northern apennines provenance and a concomitant decrease in terrestrial soil organic matter om whereas the percentage of marine om increases the provenance for gallipoli shelf sediments is for 80 attributed to po river northern apennines sources and for 20 to southern italian sources om in the eastern gulf of taranto contains more marine om than other areas within the wac whereas om and sediments from the western part of the gulf of taranto have a more local riverine provenanc

equatorial indian ocean productivity during the last 33kyr and possible linkage to westerly jet variability the top 1 m radiocarbon dated section of a 5 6 m long sediment core retrieved from the equatorial indian ocean is studied for productivity changes in response to climate variability that have taken place during the last 33 kyr the robust indicators of marine productivity such as phytol and brassicasterol exhibit distinctly higher contents av 5 8 ng g and 4 8 ng g respectively during the lgm 25 17 ky bp as compared to the succeeding period 16 5 ky bp av 1 9 ng g each and preceding period 33 25 ky bp av 1 8 and 0 8 ng g respectively suggest increased productivity during the cold and dry climate of the lgm the corg content is also relatively higher during this period than the warmer holocene however marginally higher c n ratios 7 8 and enrichment of 13 corg 19 8 during the lgm than the holocene c n 6 4 and 13 corg 21 5 and also the higher carbon preference index cpi of n alkanes and n alkanols together suggest the presence of terrestrial organic matter in the sediment the increased equatorial productivity and terrestrial organic matter input together during the lgm may indicate intensified inter monsoon equatorial westerly jets resulting in elevated productivity

climatic conditions in southern africa since the last glacial maximum inferred from pollen analysis abstract a review of late quaternary palaeoclimatic data derived from several pollen sequences between ca 22 and 34 s in southern africa shows a degree of similarity in temperature and moisture variations between the various site pollen data from sites such as wonderkrater and rietvlei transvaal tate vondo venda elim orange free state equus cave southern kalahari and boomplaas cape province suggest relative dryness during the last glacial maximum wet conditions during the late glacial and dry conditions during the early holocene ca 8000 yr b p followed by progressively moister conditions peaking soon after the development of a temperature optimum ca 6500 yr b p problems with radiocarbon dating of polleniferous spring deposits however prevent precise correlations of especially late pleistocene sequences different seasonal patterns in the late glacial and early holocene may explain palaeobotanical data and are partly compatible with simulations of past climates of kutzbach and guetter 1986

paleoenvironmental change in a precession paced succession across the onset of the messinian salinity crisis insight from element geochemistry and molecular fossils abstract in marginal mediterranean sub basins the early phase of the messinian salinity crisis msc is recorded by cyclic successions of gypsum and shales which in deeper parts of the sub basins make lateral transition into organic rich shales marls and carbonates the cyclic stacking pattern of the gypsum bearing sequences is assumed to reflect periodic paleoenvironmental change induced by precession driven climate perturbations with the assumption that shales reflect humid climate precession minima while gypsum reflects arid conditions precession maxima however this correlation has not been verified to date mostly because of the scarcity of microfossils the most commonly used tools for the reconstruction of precession driven paleoenvironmental change such change can instead be reconstructed through the study of the deeper water counterparts of gypsum marly and carbonate layers with geochemical indicators major and trace elements molecular fossils which provide insight on climate and aquatic productivity we used this approach to study a section from the piedmont basin nw italy where the onset of the msc is archived in a sequence of organic rich sediments this sequence displays distinct lithological cyclicity evidenced by the repetition of couplets of organic rich shales and marls either bioturbated in the pre msc part of the section or laminated during the msc the influence of orbitally driven precession climate oscillations is demonstrated by fluctuations of ti al si al mg al k al zr al and ba al ratios that are in phase with lithological cyclicity these fluctuations are interpreted to reflect alternation of humid shales deposited during precession minima and arid bioturbated and laminated marls deposited during precession maxima phases dominated by fluvial and aeolian transport of detrital material respectively the cyclicity of the element ratios is mirrored by changes in organic carbon content and molecular fossil inventory in particular the distribution of long chain n alkanes and their degree of preservation reveal that humid phases at times of precession minima were typified by the maximum input of degraded terrestrial organic matter driven by enhanced riverine runoff which promoted water column stratification coeval increase in ba content a common paleoproductivity proxy agrees with enhanced nutrient supply during humid periods promoting phases of eutrophication in the basin lithological and geochemical changes are observed in msc sediments deposited at times of precession maxima evidenced by the replacement of pre msc bioturbated marls by laminated marls rich in filamentous fossils corresponding to the remains of probable colorless sulfide oxidizing bacteria such changes reflect an intensification of water column stratification after the onset of the msc possibly related to the combined effect of persistent freshwater inflow and basin isolation preluding the advent of gypsum precipitation

molecular proxies for paleoclimatology we summarize the applications of molecular proxies in paleoclimatology marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments loess deposits and ice cores the fundamentals of this approach are the molecular parameters the compound abundances and carbon hydrogen nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts these afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation we discuss two types of proxy those of terrigenous and those of aquatic origin and exemplify their application in the study of marine sediments through the medium of ten case studies based in the atlantic mediterranean and pacific oceans and in antarctica the studies are mainly for periods in the present the holocene and particularly the last glacial interglacial but they also include one study from the cretaceous the terrigenous proxies which are measures of continental vegetation are based on higher plant leaf wax compounds i e long chain circa c30 hydrocarbons alcohols and acids they register the relative contributions of c3 vs c4 type plants to the vegetation in the source areas the two marine proxies are measures of sea surface temperatures sst the longer established one u37k is based on the relative abundances of c37 alkenones photosynthesized by unicellular algae members of the haptophyta the newest proxy tex86 is based on c86 glycerol tetraethers gdgts synthesized in the water column by some of the archaeal microbiota the crenarchaeota

oceanic atmospheric and ice sheet forcing of south east atlantic ocean productivity and south african monsoon intensity during mis 12 to 10 variations in the strength of coastal upwelling in the south east atlantic ocean and summer monsoonal rains over south africa are controlled by the regional atmospheric circulation regime although information about these parameters exists for the last glacial period little detailed information exists for older time periods new information from odp site 1085 for marine isotope stages mis 12 10 shows that glacial interglacial productivity trends linked to upwelling variability followed a pattern similar to the last glacial cycle with maximums shortly before glacial maxima and minimums shortly before glacial terminations during the mis 11 10 transition several periodic oscillations in productivity and monsoonal proxies are best explained by southwards shifts in the southern sub tropical high pressure cells followed by abrupt northwards shifts comparison to coeval sea surface temperature measurements suggests that these monsoonal cycles were tightly coupled to anti phased hemispheric climate change with an intensified summer monsoon during periods of northern southern hemisphere cooling warming the timing of these events suggests a pacing by insolation over precession periods a lack of similar regional circulation shifts during the mis 13 12 transition is likely due to the large equatorwards shift in the tropical convection zone that occurred during this extreme glaciation

tidal triggering of low frequency earthquakes near parkfield california implications for fault mechanics within the brittle ductile transition 1 studies of nonvolcanic tremor nvt have established the significant impact of small stress perturbations on nvt generation here we analyze the influence of the solid earth and ocean tides on a catalog of 550 000 low frequency earthquakes lfes distributed along a 150 km section of the san andreas fault centered at parkfield lfe families are identified in the nvt data on the basis of waveform similarity and are thought to represent small effectively co located earthquakes occurring on brittle asperities on an otherwise aseismic fault at depths of 16 to 30 km we calculate the sensitivity of each of these 88 lfe families to the tidally induced right lateral shear stress rlss fault normal stress fns and their time derivatives and use the hypocentral locations of each family to map the spatial variability of this sensitivity lfe occurrence is most strongly modulated by fluctuations in shear stress with the majority of families demonstrating a correlation with rlss at the 99 confidence level or above producing the observed lfe rate modulation in response to shear stress perturbations requires low effective stress in the lfe source region there are substantial lateral and vertical variations in tidal shear stress sensitivity which we interpret to reflect spatial variation in source region properties such as friction and pore fluid pressure additionally we find that highly episodic shallow lfe families are generally less correlated with tidal stresses than their deeper continuously active counterparts the majority of families have weaker or insignificant correlation with positive tensile fns two groups of families demonstrate a stronger correlation with fault normal tension to the north and with compression to the south of parkfield the families that correlate with fault normal clamping coincide with a releasing right bend in the surface fault trace and the lfe locations suggesting that the san andreas remains localized and contiguous down to near the base of the crust the deep families that have high sensitivity to both shear and tensile normal stress perturbations may be indicative of an increase in effective fault contact area with depth synthesizing our observations with those of other lfe hosting localities will help to develop a comprehensive understanding of transient fault slip below the seismogenic zone by providing constraints on parameters in physical models of slow slip and lfes

matched filter detection of the missing pre mainshock events and aftershocks in the 2015 gorkha nepal earthquake sequence abstract the 25 april 2015 mw 7 8 gorkha nepal earthquake occurred at the bottom edge of the locked portion of the main himalayan thrust where the indian plate underthrusts the himalayan wedge the earthquake was followed by a number of large aftershocks but not preceded by any foreshocks within 3 weeks according to the neic or isc catalog however due to the limited station coverage of the local seismic network a large portion of events may not be reported in routine catalogs here we employ the matched filter technique to recover the undocumented earthquakes for the period beginning 80 days before through 30 days after the 2015 gorkha earthquake we detect twice as many aftershocks as those listed in the isc catalog we observe an along strike aftershock expansion after the mainshock and before the largest mw 7 3 aftershock that occurred on 12 may 2015 repeating earthquakes are found to the ese of the mainshock rupture area suggesting that the expansion may be partially driven by afterslip in addition we observe a significant increase in seismicity rate 3 4 days prior to the mainshock initiating 6 h after a m 5 2 earthquake located 240 km to the nw of the mainshock the increase of seismic activities occurs in a wide region around the gorkha principal slip zone indicating the effect of delayed dynamic triggering may contribute to the large scale unloading process prior to the 2015 gorkha mainshock

tremor reveals stress shadowing deep postseismic creep and depth dependent slip recurrence on the lower crustal san andreas fault near parkfield 1 the 2003 magnitude 6 5 san simeon and the 2004 magnitude 6 0 parkfield earthquakes induced small but significant static stress changes in the lower crust on the central san andreas fault where recently detected tectonic tremor sources provide new constraints on deep fault creep processes we find that these earthquakes affect tremor rates very differently consistent with their differing transferred static shear stresses the san simeon event appears to have cast a stress shadow north of parkfield where tremor activity was stifled for 3 6 weeks in contrast the 2004 parkfield earthquake dramatically increased tremor activity rates both north and south of parkfield allowing us to track deep postseismic slip following this event rates initially increased by up to two orders of magnitude for the relatively shallow tremor sources closest to the rupture with activity in some sources persisting above background rates for more than a year we also observe strong depth dependence in tremor recurrence patterns with shallower sources generally exhibiting larger less frequent bursts possibly signaling a transition toward steady creep with increasing temperature and depth

far field triggering of foreshocks near the nucleation zone of the 5 september 2012 m w 7 6 nicoya peninsula costa rica earthquake abstract on 5 september 2012 a moment magnitude mw 7 6 earthquake occurred directly beneath the nicoya peninsula an area with dense seismic and geodetic network coverage the mainshock ruptured a portion of a previously identified locked patch that was recognized due to a decade long effort to delineate the megathrust seismic and aseismic processes in this area here we conduct a comprehensive study of the seismicity prior to this event utilizing a matched filter analysis that allows us to decrease the magnitude of catalog completeness by 1 unit we observe a statistically significant increase in seismicity rate below the nicoya peninsula following the 27 august 2012 mw 7 3 el salvador earthquake about 450 km to the northwest and 9 days prior to the nicoya earthquake additionally we identify a cluster of small magnitude

a 300 kyr record of aridity and wind strength in southwestern africa inferences from grain size distributions of sediments on walvis ridge se atlantic abstract the terrigenous fraction of sediments recovered from walvis ridge se atlantic ocean reveals a history of southwestern african climate of the last 300 kyr end member modelling of a data set of grain size distributions n 428 results in three end members the two coarsest end members are interpreted as eolian dust the third end member as hemipelagic mud the ratio of the two eolian end members reflects the eolian grain size and is attributed to the intensity of the se trade winds trade winds were intensified during glacials compared to interglacials changes in the ratio of the two eolian end members over the hemipelagic one are interpreted as variations in southwestern african aridity late quaternary southwestern african climate was relatively arid during the interglacial stages and relatively humid during the glacial stages owing to meridional shifts in the atmospheric circulation system during glacials the polar front shifted equatorward resulting in a northward displacement of the zone of westerlies causing increased rainfall in southwestern africa the equatorward shift of the polar front is coupled with an increase of the meridional pressure gradient leading to enhanced atmospheric circulation and increased trade wind intensity

increasing seismicity in southern tibet following the 2015 mw 7 8 gorkha nepal earthquake abstract we conducted a systematic detection of micro seismicity in southern tibet 1 6 days before and 4 4 days after the 2015 mw 7 8 gorkha nepal earthquake our study employs 368 template events listed in the china earthquake networks center cenc catalog with the waveform based matched filter technique we detected five times more earthquakes than listed in the cenc catalog during our study period the seismicity in southern tibet shows a significant increase immediately following the gorkha nepal earthquake including two normal faulting events the mw 5 8 tingri and mw 5 3 nyalam earthquakes about 3 and 11 h after the mainshock respectively although the static stress changes cfs showed a slightly better correlation with the seismicity rate changes than the peak dynamic stress changes cfs t the absolute value of the static stress change at the epicenter region of the mw 5 8 tingri earthquake is 10 kpa roughly two orders smaller than the peak dynamic stress change of 2 2 mpa although we are unable to identify the primary triggering mechanism it is evident that the 2015 nepal earthquake triggered widespread seismicity in southern tibet our results highlight the potential increase of seismic hazard in southern tibet due to the occurrence of major thrust earthquakes along the himalaya frontal thrust faults

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event