new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

quaternary palaeohydrological evolution of a playa lake salada mediana central ebro basin spain this research was partly funded by the national science foundation usa under the ear 941 8657 programme and by the eead csic project number z 5 96 this is limnological research center contribution number 527

well preserved palaeogene and cretaceous biomarkers from the kilwa area tanzania we have investigated the biomarker composition of sediments ranging in age from 30 to 70 ma from the kilwa area of tanzania they are dominated by material of terrestrial n alkanols n alkanoic acids n alkanes and triterpenoids and bacterial hopanoids and a dipentadecyl glycerol diether dgd origin with only a minor contribution of marine origin crenarchaeol and some algal steroids this indicates a marine setting dominated by higher plant input which most likely stimulated sedimentary microbial activity including sulfate reduction the lipid composition specifically the presence of bacteriohopanepolyols bhps and the stereochemistry of hopanoids suggests a low degree of thermal maturity many biomarkers have still retained functionality even after 30 70 million years this is in good agreement with the exceptional preservation of foraminifera and nannofossils and can probably be attributed to the very low sediment permeability and burial depth there is a clear distinction in the biomarker distributions between the oligocene age sediments collected at the end of the peninsula near kilwa masoko and the older sediments collected from elsewhere indicating differences in depositional environment sediments from the end of the peninsula have higher branched and isoprenoid tetraether index values indicating a relatively higher terrestrial input they also contain two tentatively assigned c28 hopenes 28 30 dinorneohop 13 18 ene and 28 30 dinorhop 17 21 ene aromatic des a triterpenes des e hopenes aromatic pentacyclic triterpenoids c33 dgd archaeol and bhps which are absent from or only present in small amounts in the other sediments these differences likely reflect an evolution of the depositional area from a relative open shelf environment with substantial water depth to a shallower setting during the early oligocene

lipid geochemistry of a post glacial lacustrine sediment abstract the post glacial environmental history of voua de la motte a small pond was studied by the lipid geochemistry of a 6 m long core palynological studies show that the deepest part of the core goes back to 10 000 yr bp corresponding to the time of formation of the lake following the retreat of the rhodanian glacier hydrocarbons aldehydes linear alcohols sterols monocarboxylic and monohydroxy fatty acids were determined throughout the core both in the free and bound lipid fractions as well as in the tightly bound fraction for the carboxylic acids there is no clear evidence of a transformation from the unbound to the bound form except perhaps for the hydroxy acids qualitative as well as quantitative fluctuations in the distributions of these lipid classes were observed upward in the core an attempt is made to correlate these fluctuations with the bioenvironmental and climatological evolution of the basin on the basis of information obtained from palynology

glacial interglacial variations in carbon cycling revealed by molecular and isotope stratigraphy of lake nkunga mt kenya east africa abstract the lipid content n alkanes n alkanols n alkanoic acids and the 13c values of these lipids were measured in nineteen sediment samples taken from a 21 18 m long core from lake nkunga a high altitude 1820 m a s l freshwater lake situated in the montane rain forest on mt kenya the record spans the early last glacial marine isotope stages 5a to 4 and the late holocene 1030 45 14c yr bp to the present day the intervening hiatus spans the last glacial maximum and the early to mid holocene the molecular biogeochemical results are interpreted in terms of past changes in climate vegetation and atmospheric co2 concentration three different sources of organic matter input were identified from the n alkyl lipids namely terrestrial plants aquatic plants and algae unusual distribution patterns of dominant mid chain length n alkanes c23 25 n alkanols c22 24 and n alkanoic acids c22 24 are attributed to aquatic macrophytes an 11 decrease in bulk carbon isotope values between the sediments of early glacial 17 and late holocene age 28 is also apparent in the individual homologues of the n alkyl lipids the observed isotopic shift in terrestrial higher plant biomarkers is similar to that observed in nearby sacred lake and is consistent with an expansion of c4 grasses or sedges during the early glacial the corresponding vegetation was a dry montane juniper olive forest with a grassy understorey representing cold dry conditions with lower co2

fulgurite morphology a classification scheme and clues to formation fulgurites are natural glasses formed by cloud to ground lightning several different morphologies of fulgurites have been reported in previous studies including sand fulgurites rock fulgurites and clay fulgurites herein we examine sand clay and caliche fulgurites and demonstrate that these differ systematically in their morphology we further use morphological features to constrain properties of fulgurite forming lightning strikes we classify fulgurites into four types of morphologies with an additional minor type type i fulgurites are sand fulgurites consisting of thin glass walls type ii fulgurites are clay fulgurites consisting of thick melt rich walls type iii fulgurites are caliche fulgurites consisting of thick glass poor walls and type iv fulgurites are rock fulgurites consisting of glasses with walls consisting of surrounding unmelted rock fulgurite morphology shows that the energy of fulgurite forming strikes is between 1 and 30 mj m of fulgurite formed suggests heating rates in the order of 1 000 k s and lightning channel thicknesses of about 1 mm diameter lightning generates mixtures of at least two components in most fulgurites an sio2 glass identified as lechatelierite and a groundmass of more varied composition in addition to these four primary types a fifth type droplet fulgurites is morphologically dissimilar from the other types but is compositionally related to the type ii or iv fulgurites additionally two fulgurites both from york county pennsylvania usa showed the reduction of iron to iron metal with an assortment of fe ti and si p compounds with stoichiometry that ranges from nearly pure fe metal to fesi these metal silicides include stoichiometric fe3si fe2si and fe5si3 and possibly fe8si3 and fe7si3 and provide a terrestrial source for these phases which are typically associated with extraterrestrial material

hydrothermal exploration of the fonualei rift and spreading center and the northeast lau spreading center we report evidence for active hydrothermal venting along two back arc spreading centers of the ne lau basin the fonualei rift and spreading center frsc and the northeast lau spreading center nelsc the ridge segments investigated here are of particular interest as the potential source of a mid water hydrothermal plume 1500 2000 m depth which extends more than 2000 km across the sw pacific ocean dispersing away from an apparent origin close to the most northeastern limits of the lau basin our results indicate the presence of at least four new hydrothermal plume sources three along the frsc and one on the nelsc the latter situated within 150 km of the maximum for the previously identified sw pacific regional scale plume however tdfe and tdmn concentrations in the southernmost frsc plume that we have identified only reach values of 19 and 13 nmol l and dissolved 3he anomalies in the same plume are also small both in relation to the sw pacific plume and to local background which shows evidence for extensive 3he enrichment throughout the entire lau basin water column our results reveal no evidence for a single major point hydrothermal source anywhere in the ne lau basin instead we conclude that the regional scale sw pacific hydrothermal plume most probably results from the cumulative hydrothermal output of the entire topographically restricted lau basin discharging via its ne most corner

crustal construction and magma chamber properties along the eastern lau spreading center abstract the l scan active source seismic tomography experiment maps the crustal structure and magmatic system along a 120 km long section of the back arc eastern lau spreading center elsc where the ridge undergoes abrupt changes in morphology and composition associated with increasing proximity to the tofua volcanic arc using this dataset we picked 197 000 p wave travel times from 57 seismic airgun lines recorded at 83 ocean bottom seismograph stations and inverted for a 3 d p wave velocity image the seismic images reveal a prominent but narrow seismic low velocity volume lvv located beneath all surveyed ridge segments consistent with the high temperatures and melt of a crustal magmatic system crustal magmatic systems thus underlie spreading axes even where previous seismic reflection surveys did not detect magma lens reflectors accounting for the heat source of high temperature hydrothermal vents in these areas the top of the lvv closely follows the ridge axis and steps across three overlapping spreading centers as the offset of the overlap increases the lvv becomes increasingly discontinuous across the ridge limbs surprisingly the lvv is as much as twice as wide but deeper in the northern part of the ridge system where the crust is thinner as compared to the lvv beneath the southern segments where the crust is relatively thicker the width of the lvv may be modulated by the degree of deep hydrothermal activity or temporal variations in melt supply and thus may not correlate directly with the average melt flux as indicated by crustal thickness over the past 4 myr the location of the ridge has swept across different mantle compositional domains and the crust produced at the ridge formed a zoned pattern the interpretation is that thick highly porous volcanic layers with felsic compositions cap regions of thick crust thinner volcanic layers of basaltic composition cap regions of thinner crust the zonal pattern indicates that the influence of slab derived water on crustal construction has substantially decreased over time

the evolution of the serie dei laghi strona ceneri and scisti dei laghi the upper component of the ivrea verbano crustal section southern alps north italy and ticino switzerland abstract the serie dei laghi is the upper intermediate component of the exposed crustal section of massiccio dei laghi in the southern alps the latter including also the ivrea verbano zone its oldest event is a sedimentary cycle at least of early paleozoic age it starts with a pelitic sequence scisti dei laghi that later suffered a tectono metamorphic event of rather high pressure this event is recorded by rare mineral and textural relics detected in the scisti dei laghi of the m gambarogno area later an arenaceous sequence strona ceneri was deposited it is now represented at the base by basaltic metatuffites resulting from the reworking of an ophiolite belt then followed by paragneisses with detrital phenoclasts ceneri gneiss and by fine grained gneisses gneiss minuti during the ordovician conspicuous tonalitic to granitic masses were emplaced the induced thermal disturbance and the circulation of pegmatitic stage magmatic residuals caused contact metamorphism and granitization in the sedimentary country rocks during the hercynian a main prograde event generated the regional foliation with isoclinal geometry and transposed character a syn kinematic stage produced medium grade parageneses of relatively high pressure static recrystallization and sillimanite growth then followed during the uplift due to the combined action of hydration and decompression margarite bearing coronitic textures grew around kyanite a retrograde metamorphism was then recorded by the appearance of greenschist facies parageneses at particular structural sites the formation of the cossato mergozzo brissago cmb and pogallo fault system against the ivrea verbano zone as well as the schlingen folds in the northeast is of late hercynian age along the cmb fault calc alkaline dykes and stocks appinites were intruded probably towards the end of the upheaval but deep enough to induce partial melting in their country rocks between val d ossola and valsesia the hercynian evolution is concluded by the early permian magmatic cycle that gave rise to both extrusive rhyolitic sheets and to granitic epiplutonic bodies accompanied by mafic dykes in mesozoic times the serie dei laghi was dissected by many extensional faults these partly reactivated the hercynian lineaments such as the cmb and pogallo lines during the alpine orogenic cycle the serie dei laghi was affected by s verging cataclastic overthrusts

structural geology of impact craters abstract the formation of impact craters is a highly dynamic and complex process that subjects the impacted target rocks to numerous types of deformation mechanisms understanding and interpreting these styles of micro meso and macroscale deformation has proved itself challenging for the field of structural geology in this paper we give an overview of the structural inventory found in craters of all size ranges on earth and look into the structures of craters on other planetary bodies structural features are discussed here that are caused by i extremely high pressures and temperatures that occur during the initial passage of the shock wave through the target rock and projectile ii the resulting flow field in the target that excavates and ejects rock materials and iii the gravitationally induced modification of the crater cavity into the final crater form a special focus is put on the effects that low angle impacting bodies have on crater formation we hope that this review will help both planetary scientists and structural geologists understand the deformation processes and resulting structures generated by meteorite impact

diagenesis of biomarkers in biwa lake sediments over 1 million years abstract lipid biomarker compounds n alkanoic acids n alkanols sterols n alkanes chlorophyll derivatives and total lipid carbon in a chloroform extractable fraction isolated from sedimentary deposits up to 2 ma old of a 1400 m core sample of lake biwa were analyzed by gas chromatography gas chromatography mass spectrometry and a thin layer chromatography flame ionization detection analyzer tlc fid to investigate their diagenesis and their utilities as biomarkers the samples are divided into two parts at a depth of 911 4 m the samples below 911 4 m are basement rock the upper core is composed of clay from the surface to 249 5 m in depth and alternated with slit clay and gravels from 249 5 to 911 4 m the organic compound carbon obtained by hydrolysis of the lipid fraction by alkali solution comprised from 11 to 35 of the total lipid carbon tlc fid analysis indicated that significant amounts about 70 80 of the total lipid carbon were present in the polar fraction and small proportions were simple lipids the amounts of n alkanols were comparable to those of n alkanoic acids and sterols while contemporary lacustrine sediments usually contain a larger amount of n alkanoic acids than of n alkanols normal alkanes maximizing in abundance at c 27 or c 29 were most abundant among the lipid compounds variation in the distributions of sterols and stanols seemed to preserve the information of input sources and the c 27 c 29 ratios were correlated to the c n of the sediments the composition of n alkanols maximizing at c 24 or c 18 appeared to indicate an aquatic paleoenvironment a paleowater depth at least in the upper 250 m ratios of shorter to longer chain n alkanoic acids which had been believed to be an indicator of autochthonous to allochthonous origins clearly increased with time a marked correlation between chlorophyll derivatives ratio of chlorophyll derivatives to total lipid carbon and paleotemperature was found

characterization of exogenic fulgurites from an archaeological site in tiedra valladolid spainp martin ramos et al exogenic fulgurites from tiedra valladolid spain studies on type v fulgurites are very sparse in the literature this work reports on the characterization of natural exogenic fulgurites found at the archaeological site of cerro de la ermita tiedra valladolid spain which was firstly a celtiberian and then a roman locum sacrum data from x ray powder diffraction x ray fluorescence spectroscopy fourier transform infrared spectroscopy and raman spectroscopy suggest that the fulgurites consist of naquite piroxenes iron oxides shocked quartz and neo formed cristobalite

late weichselian and holocene relative sea level history of broggerhalvoya spitsbergen abstract radiocarbon dated whalebones from raised beaches record a relative sea level history for broggerhalvoya western spitsbergen that suggest a two step deglaciation on svalbard at the end of the late weichselian glaciation the late weichselian marine limit was reached at about 13 000 yr b p and was followed by relatively slow emergence until about 10 000 yr b p either in response to ice unloading in the barents sea initial retreat of local fjord glaciers or some combination of the two rare whale skeletons dating between 13 000 and 10 000 yr b p indicate that the norwegian sea was at least seasonally ice free during that interval deglaciation of spitsbergen is recorded by the rapid emergence of broggerhalvoya after 10 000 yr b p this was followed by a transgression during the mid holocene here named the talavera transgression and another in modern times raised beach morphologies suggest striking differences in nearshore depositional processes before and after 10 000 yr b p that are probably related to changes in the rate of uplift and in sea ice conditions

structure and growth of the izu bonin mariana arc crust 1 seismic constraint on crust and mantle structure of the mariana arc back arc system 1 a high resolution seismic velocity model is presented for the crust and upper mantle of the mariana arc back arc system mabs based on active source seismic profiling the major characteristics are 1 slow mantle velocity of 8 km s 1 in the uppermost mantle especially and deep reflectors under the mariana arc ma and the west mariana ridge wmr 2 a deep reflector in the upper mantle beneath the relative thick crust of the mariana trough mt axis 3 distribution of lower velocity lower crusts 6 7 6 9 km s 1 beneath the volcanic front and adjacent to the mt and 4 high velocity lower crust 7 2 7 4 km s 1 beneath the boundary regions between the ma and mt and between the wmr and the parece vela basin pvb adding to structural characteristics of crust and upper mantle beneath the mabs of the characteristics described above characteristic 1 suggests that the origins of the slow mantle velocity and the deep reflectors be explained by transfer of the lower crustal residues to the upper mantle across the moho considering that the wmr is extinct arc currently on the other hand characteristic 2 suggests that the origin of deep reflectors beneath the mt axis might be lower velocity materials due to the diffractive signals with strong amplitudes characteristic 3 suggests that the lower velocity lower crust advanced crustal growth and characteristic 4 suggests that the high velocity lower crust beneath arc back arc transition zone is composed of mafic ultramafic materials created by extensive partial melting of mantle peridotites or last stage of the arc magmatism rather than serpentinized peridotite

production of hybrid granitic magma at the advancing front of basaltic underplating inferences from the sesia magmatic system south western alps italy abstract the permian sesia magmatic system of the southwestern alps displays the plumbing system beneath a permian caldera including a deep crustal gabbroic complex upper crustal granite plutons and a bimodal volcanic field dominated by rhyolitic tuff filling the caldera isotopic compositions of the deep crustal gabbro overlap those of coeval andesitic basalts whereas granites define a distinct more radiogenic cluster sri 0 708 and 0 710 respectively afc computations starting from the best mafic candidate for a starting melt show that nd and sr isotopic compositions and trace elements of andesitic basalts may be modeled by reactive bulk assimilation of 30 of partially depleted crust and 15 30 gabbro fractionation trace elements of the deep crustal gabbro cumulates require a further 60 fractionation of the andesitic basalt and loss of 40 of silica rich residual melt the composition of the granite plutons is consistent with a mixture of relatively constant proportions of residual melt delivered from the gabbro and anatectic melt chemical and field evidence leads to a conceptual model which links the production of the two granitic components to the evolution of the mafic complex during the growth of the mafic complex progressive incorporation of packages of crustal rocks resulted in a roughly steady state rate of assimilation anatectic granite originates in the hot zone of melting crust located above the advancing mafic intrusion upward segregation of anatectic melts facilitates the assimilation of the partially depleted restite by stoping at each cycle of mafic intrusion and incorporation residual and anatectic melts are produced in roughly constant proportions because the amount of anatectic melt produced at the roof is a function of volume and latent heat of crystallization of the underplated mafic melt which in turn produces proportional amounts of hybrid gabbro cumulates and residual melt such a process can explain the restricted range in isotopic compositions of most rhyolitic and granitic rocks of the permo carboniferous province of europe and elsewhere

euphotic zone bacterioplankton sources major sedimentary bacteriohopanepolyols in the holocene black sea abstract bacteriohopanepolyols bhps are lipid constituents of many bacterial groups geohopanoids the diagenetic products are therefore ubiquitous in organic matter of the geosphere to examine the potential of bhps as environmental markers in marine sediments we investigated a holocene sediment core from the black sea the concentrations of bhps mirror the environmental shift from a well mixed lake to a stratified marine environment by a strong and gradual increase from low values 30 g g 1 toc in the oldest sediments to 170 g g 1 toc in sediments representing the onset of a permanently anoxic water body at about 7500 years before present bp this increase in bhp concentrations was most likely caused by a strong increase in bacterioplanktonic paleoproductivity brought about by several ingressions of mediterranean sea waters at the end of the lacustrine stage 9500 years bp 15n values coevally decreasing with increasing bhp concentrations may indicate a shift from a phosphorus to a nitrogen limited setting supporting growth of n2 fixing bhp producing bacteria in sediments of the last 3000 years bhp concentrations have remained relatively stable at about 50 g g 1 toc the distributions of major bhps did not change significantly during the shift from lacustrine or oligohaline to marine conditions tetrafunctionalized bhps prevailed throughout the entire sediment core with the common bacteriohopanetetrol and 35 aminobacteriohopanetriol and the rare 35 aminobacteriohopenetriol so far only known from a purple non sulfur proteobacterium being the main components other bhps specific to cyanobacteria and pelagic methanotrophic bacteria were also found but only in much smaller amounts our results demonstrate that bhps from microorganisms living in deeper biogeochemical zones of marine water columns are underrepresented or even absent in the sediment compared to the bhps of bacteria present in the euphotic zone obviously the assemblage of molecular fossils in the sediments does not represent an integrated image of the entire community living in the water column remnants of organisms living in zones where effective transport mechanisms such as the fecal pellet express exist are accumulated while those of others are underrepresented our work shows a high stability of bhps over geological time scales largely uniform distributions and only minor changes in structures like an increasing prevalence of saturated over unsaturated bhps with time were observed consequently sedimentary bhp distributions are less suitable as markers for in situ living bacteria but are useful for paleoreconstructions of bacterioplanktonic communities and productivity changes

shallow seismicity and tectonics of the central and northern lau basin abstract the lau basin is an active backarc comprising several spreading centers and microplates rapidly evolving in time as such crustal earthquakes within the lau basin derive from intrabasin tectonic volcanic and hydrothermal sources because of high mantle attenuation small earthquakes from the basin are seldom recorded on land seismographs and it has been difficult to study the pattern of crustal seismicity however the 1994 labatts ocean bottom seismograph experiment in the lau basin recorded more than 100 000 local t and body phases allowing for a detailed examination of basin seismotectonics nearly 1000 events are located within the basin proper with another 2000 associated with the forearc and the aseismic front we identify two previously undocumented tectonic features a triple junction in the northwestern basin and a nanoplate in the central lau basin the single most seismically active feature within the lau basin is the lau extensional transform zone letz just north of the central lau spreading center significant seismicity also occurs near the northern extension of the eastern lau spreading center and along a southeast extension of the letz delineating the boundary of a previously unknown nanoplate swarm activity is common in the backarc basin and dominates regions associated with actively reorganizing tectonics we see no evidence of deformation along the southern boundary of the niuafo ou microplate where 4 5 cm yr of strain is predicted it is possible that the plate boundary extends eastward from the fonualei rift fr tip towards the trench creating a niuatoputapu tonga plate division rather than westward implied by the currently accepted niuafo ou tonga plate system but more data are necessary from the fr to test that hypothesis instead we suggest that the niuafo ou tonga pole is 1 5 further north than previously proposed reducing the predicted strain in this region to

paleoecology reconstruction from trapped gases in a fulgurite from the late pleistocene of the libyan desert when lightning strikes the ground it heats melts and fuses the sand in soils to form glass tubes known as fulgurites we report here the composition of co 2 co and no contained within the glassy bubbles of a fulgurite from the libyan desert the results show that the fulgurite formed when the ground contained 0 1 wt organic carbon with a c n ratio of 10 15 and a 13 c of 13 96 compositions similar to those found in the present day semiarid region of the sahel where the vegetation is dominated by c 4 plants thermoluminescence dating indicates that this fulgurite formed 15 k y ago these results imply that the semiarid sahel at 17 n reached at least to 24 n at this time and demonstrate that fulgurite gases and luminescence geochronology can be used in quantitative paleoecology

the seismic structure and dynamics of the mantle wedge seismic imaging provides an opportunity to constrain mantle wedge processes associated with subduction slab dehydration arc volcanism and backarc spreading the mantle wedge is characterized by a low attenuation forearc an inclined zone of low velocity and high attenuation underlying the volcanic front and a broad region of low velocity and high attenuation beneath the backarc spreading center when present seismic velocities bathymetry and basalt chemistry suggest mantle temperature variations of 100 c between different backarc regions rock physics experiments and geodynamic modeling are essential for interpreting seismic observations seismic anisotropy indicates a complex pattern of mantle flow that can be modeled with along strike flow in a low viscosity channel beneath the arc and backarc comparison of geodynamic models with seismic tomographic results using experimentally derived relations between velocity attenuation and temperature suggests the existence of small melt fractions in the

electrical properties of granite with implications for the lower crust the electrical properties of granite appear to be dominantly controlled by the amount of free water in the granite and by temperature minor contributions to the electrical properties are provided by hydrostatic and lithostatic pressure structurally bound water oxygen fugacity and other parameters the effect of sulfur fugacity may be important but is experimentally unconfirmed in addition to changing the magnitude of electrical properties the amount and chemistry of water in granite significantly changes the temperature dependence of the electrical properties with increasing temperature changes in water content retain large but lessened effects on electrical properties near room temperature a monolayer of water will decrease the electrical resistivity by an order of magnitude several weight percent water may decrease the electrical resistivity by as much as 9 orders of magnitude and decrease the thermal activation energy by a factor of 5 at elevated temperatures just below granitic melting a few weight percent water may still decrease the resistivity by as much as 3 orders of magnitude and the activation energy by a factor of 2 above the melting temperature 650 to 1100 c depending upon water pressure a few weight percent water will decrease the resistivity by less than an order of magnitude and will barely change the activation energy remarkably the few weight percent water must be present as free water experiments with hydrated hornblende schist with structural water indicate an electrical resistivity very similar to that for dry granite the implications of these results together with the findings of deep magnetic sounding and magnetotelluric surveys suggest much more free water than is commonly associated with the lower crust and possibly into the upper mantle

temperature dependency of long chain alkenone distributions in recent to fossil limnic sediments and in lake waters distribution patterns of c37 and c38 polyunsaturated long chain alkenones lcas serve as proxies for the determination of paleotemperatures for marine surface waters we studied recent subrecent and late glacial holocene sediments from germany austria russia and the u s to test for a correspondence between lca distribution and surface water temperature in limnic systems previously reports of lca occurrence were restricted to sediments of 6 wide distributed freshwater and alkaline lakes in this study 13 of 27 investigated lakes contained lcas in surface sediments with concentrations varying between 12 to 205 g g toc late glacial to holocene sediment sequences from lake steisslingen and lake wummsee germany lake pichozero russia and brush lake u s a contained abundant lcas with averaged concentrations of 33 to 7536 g g toc for the first time we observed the occurrence of lcas within in the water column of oligotrophic lake stechlin ne germany alkenones were restricted to the zone of maximum chlorophyll concentration within the water column indicating that lcas have a biosynthetic origin and can be attributed to phototrophic micro algae attempts to identify the producing organism however were not successful culture experiments allow various phytoplankton to be excluded as producers alkenone producing algae are evidently of small size hindering microscopical identification lcas commonly occur in high concentrations in late glacial sediments mainly during the cold period of the younger dryas whereas the holocene usually is devoid of polyunsaturated alkenones the episodic occurrence of lcas restricts their utility as proxies for continuous geological records furthermore lack of microscopical verification and the episodic distribution allow for different producers of unsaturated alkenones in recent and late glacial sediments an empirical relationship between lca distribution and temperature was observed in fossil sediments from lake steisslingen there is a good correspondence between uk37 and the temperature controlled 18o isotope ratio of lake chalk comparison of lca patterns obtained from the uppermost centimetres of lake sediments with averaged summer surface water temperatures of the lakes studied demonstrates a trend of covariance r2 uk 37 0 90 uk37 0 67 n 9 hence the same mechanism that causes temperature dependence of lca patterns in marine systems might be effective in limnic settings identification of alkenone producers and their culture under controlled temperature are still mandatory before lcas can be routinely applied as paleotemperature proxy in limnic systems

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

seismic constraints of the formation process on the back arc basin in the southeastern japan sea to clarify the formation process of the back arc basin in the japan sea which is located next to the northwestern pacific a seismic survey using ocean bottom seismographs and an air gun array was undertaken in areas from the northern yamato basin to the coast of the northeastern japan island arc off awa shima island the crust beneath the northern yamato basin off awa shima island is approximately 16 km thick the upper and lower crusts are respectively about 5 km thick with a steep velocity gradient and about 10 km thick with a gentle velocity gradient in the basin there are very few units with p wave velocity of 5 4 6 0 km s corresponding to the continental upper crust the crustal structure of the northern yamato basin has characteristics of thicker oceanic crust the high velocity lowermost crust in the northern yamato basin with 7 2 7 4 km s might show melt formed by a slightly high mantle temperature during the opening of the basin however the crust beneath the areas from the sado ridge to the coast which is approximately 25 26 km thick is slightly thinner than that of the continental crust and island arc crust the crustal structure beneath this area is inferred to be a rifted continental and or a rifted island arc crust

dating of thaw depths in permafrost terrain by the palaeomagnetic method experimental acquisition of a freezing remanent magnetization summary the acquisition of a freezing remanent magnetization frm has been studied in controlled magnetic and thermal environments by successive freezing and thawing 18 to 20 c of samples of natural sediments from a frost polygon near ny alesund spitsbergen successive freeze thaw cycles cause a significant decrease in the intensity of the initially induced shock remanent magnetization srm associated with directional trends towards the ambient magnetic field direction during the freezing phase a slow increase in intensity commences after seven to 10 freeze thaw cycles the acquisition of a frm in samples carrying an isothermal remanent magnetization shows a significantly smaller reduction in intensity and only minor directional variations this result indicates that only a fraction of the magnetic grains in a natural sediment contributes to the natural remanent magnetization insignificant changes in lengths and directions of the principal susceptibility ellipsoid axes also indicate that magnetic fabric and remanent magnetization are carried by partly different populations of magnetic grains the acquisition of a frm in nature has yet to be explored if such a process is confirmed however it has the potential for obtaining age estimates of ancient thaw depths and for providing insights into material transport processes in frost polygons

characterization of model evaporitic environments through the study of lipid components abstract a saline circuit has been studied as a model of coastal evaporite system the lipid composition of diverse salt ponds encompassing calcite gypsum and halite domains has been determined most of the lipid materials has been found in the carbonate samples and is related to algal cyanobacterial debris lipids in the gypsum domain are of heterotropic microbialorigin and extreme halophilic bacteria constitute the main lipid contribution in the halite samples n alkane distributions with high predominance of n docosane constitute a previously described feature of sedimentary evaporitic conditions that is charateristics of the intermediate calcite gypsum samples in the calcite domain the presence of c20 highly branched isoprenid olephines tetrahymanol and the large amounts of phytol constitute likely precursors of lipids usually found in evaporitic environments i e c20 highly branched isoprenoid alkanes gammacerane and high phytane pristane ratios their occurence point to dehydration and hydrogenations as two main diagenetic processes leading to the formation of evaporitic molecular markers

distribution of polar membrane lipids in permafrost soils and sediments of a small high arctic catchment the distribution of bacteriohopanepolyols bhps and intact polar membrane lipids ipls was studied in different soil profiles and in fluvial and marine sediments along the pathway of transport in a small catchment in the high arctic at ny alesund svalbard 79 n 12 e both groups of cellular membrane lipids have been used as biomarkers for determining major microbial groups and biogeochemical processes in natural environments little is known about their distribution and usefulness as environmental markers in the arctic in this study we show that both membrane lipid groups are variably distributed in the drainage area of the broggerbreen glacier with highest abundance and diversity in the organic mat overlying the mineral soils as well as in mossy surface soil the bhp and ipl composition and abundance both indicate a larger community of phototrophic bacteria in the organic mats and fluvial sediments the greater diversity and abundance of bhps relative to ipls in sub soils including probable markers for cyanobacteria suggest a greater resistance to degradation in contrast ipl concentration decreased strongly with soil depth pointing to their rapid degradation bacterial ipls are thus thought to reflect more reliably the biomass of viable phototrophic bacteria the high concentrations of proposed soil marker bhps adenosylhopane and related structures vs published results and their relative increase with soil depth suggest better preservation and more effective accumulation of the compounds at low temperature

long chain alkenones in qinghai lake sediments abstract long chain methyl and ethyl alkenones c 37 c 40 containing two to four double bonds have been detected in sediments from qinghai lake china this is the first report of the alkenones in lake sediments deposited under a variety of salinity conditions where the lake has not encountered any marine incursions the presence of the alkenones suggests the presence of prymnesiophyceae in the lake which may have reached the lake via eolian transportation or seabirds sediment samples from the more saline areas of the lake contained higher concentrations of the more highly unsaturated compounds widespread use of these compounds as paleotemperature indicators in marine sediments introduces the possibility of extrapolating this approach to lacustrine environments if appropriate calibrations can be undertaken

influence of shock propagation on lightning evidence in volcanic ashfall deposits abstract lightning induced textures in volcanic ashfall deposits can take several forms including lightning induced volcanic spherules livs spherule aggregates and pumiceous particles here two newly identified textures are described in the products of current impulse experiments conducted on ash samples spanning a range of bulk compositions from basic 49 wt sio2 to intermediate 53 58 wt sio2 to acidic 72 76 wt sio2 at peak currents of 7 ka 25 ka and 100 ka due to the location of subjected samples on a solid flat surface in the experimental apparatus both hair like particles 1 10 m in diameter and plate like particles 100 m in diameter are produced these textures result from not only the high temperatures generated by the discharge 1500 c but also by the expansion of a shock front with a radius twice the size of the discharge channel the pressure behind this shock front ranges from 0 41 mpa for the 7 ka impulse currents to 0 77 mpa for the 100 ka impulse currents and the velocity of the shock ranges from 617 m s to 846 m s the combined high temperatures and shock wave expansion simultaneously melts the volcanic ash particles fuses them together and stretches them out which alters the very small

the 6 8 aug 2019 eruption of volcano f in the tofua arc tonga abstract in august 2019 a large raft of pumice appeared in the territorial waters of tonga as in many other cases this pumice raft was the only surface expression of a major submarine volcanic eruption discolored water and reconstruction of the drift path of the pumice raft using satellite imagery points towards volcano f in the tofua arc nw of the island of vava u as the most likely volcanic source here we present imagery from esa s sentinel 2 satellite that captured the start of the submarine eruption on 6 august 2019 and the waning of the eruption on 8 august followed by observations of the drifting pumice raft until 14 august this start time is consistent with t phase records at the seismic stations on niue island and rarotonga and the signal delay time of 733 s between the two stations is consistent with an origin at or at least near volcano f on 8 august a 136 7 km2 large raft of pumice appears at the sea surface the modelled minimum raft volume is 8 2 41 0 106 m3 which is equivalent to 2 5 12 3 106 m3 dense rock the eruption thus corresponds to a volcanic explosivity index vei 2 3 eruption in the submarine environment prior to the volcanic eruption a series of earthquakes close to volcano f was recorded the series started on 5 august with a mb 4 7 event followed by at least six shallow earthquakes mb 3 9 on 6 august in december 2018 and january 2019 we surveyed the seafloor around volcano f with multibeam sonar combining our data with pre existing information we present the first comprehensive bathymetric map of the volcanic edifice and its geologic setting we show that volcano f represents a major arc volcanic complex that is situated in an extensional setting the basal diameter of the volcanic apron is 50 km with a large central 8 7 x 6 km caldera with a floor at 700 m water depth the top of the post caldera constructional cone complex had a summit depth of 35 m below sea level in 2004 the volcano shows geochemical differences to the adjacent arc volcanoes on fonualei and late islands the volcano s pristine volcanic morphology and two documented eruptions 2001 and 2019 indicate a highly active volcanic system that warrants further scientific attention

distributions of bacterial and archaeal membrane lipids in surface sediments reflect differences in input and loss of terrestrial organic carbon along a cross shelf arctic transect enhanced climate warming affecting the arctic region could have a dramatic impact on the terrigenous organic carbon terroc stored in the eurasian permafrost and could increase the amount of oc remobilized to the arctic shelves an improved understanding of the fate of this remobilized soil oc is essential for better understanding of the consequences for the arctic and global carbon cycle in this study glycerol dialkyl glycerol tetraethers gdgts and bacteriohopanepolyols bhps in surface sediments along a 500 km cross shelf transect from the mouth of the kolyma river to the middle of the vast east siberian sea were analysed to assess their potential and that of the associated branched and isoprenoid tetraether bit and r 0 soil indices for tracing terroc in arctic systems both bhp and gdgt contributions indicated the greatest contribution of terroc close to the river mouth while the associated indices showed declining trends in an offshore direction supporting an increasing marine oc input and or a decrease in terroc however while the bhps indicated a dominance of terroc at the start of the transect the gdgts suggested a much larger almost 50 marine oc input at this point in addition the bit index displayed an exponential decline controlled mainly by a substantial contribution of marine gdgts while

physical properties of crustal and upper mantle rocks with regards to lithosphere dynamics and high pressure mineralogy this paper focusses on the physical properties of rocks and property changes occurring during geodynamic processes it addresses a number of outstanding petrophysical problems in the framework of crustal and mantle deformation the major themes to be discussed will be the seismic signature of crustal and mantle shear zones the nature of crustal and mantle anisotropy and the contribution of anisotropic rocks to seismic reflectivity in particular seismic shear waves traversing anisotropic strata can reveal important information on the spatial orientation of deformed structures because the measured seismic anisotropy has a structural origin emphasis will be placed on the relations between shear wave splitting and fabric anisotropy fabric anisotropy and strain and strain and geologic tectonic processes the second part of this paper discusses the effect that metamorphic phase transitions in crustal and mantle rocks may have on rock physical properties velocity density specifically the possible role that the gabbro eclogite transition could have in crustal delamination and recycling of material into the mantle will be considered

hopane derived triterpenoids in soils the occurrence distribution and degradation pathways of hopanoid triterpenes have been studied in thirteen soil samples with varying degrees of biological activity hopanoids were shown to occur in all samples suggesting that they are not only ubiquitous in subaquatic sediments but also in soils hop 22 29 ene was generally predominant in the hydrocarbons whereas the 17 h 21 h bishomohopanoic acid c32 was the major component in the acids the concentrations of hopanes were usually rather low except in acidic peat the distribution in carbon number of hopanes and hopanoic acids showed great similarities with those of moderately oxic subaquatic sediments intact bacteriohopane tetrol widespread in microorganisms and the main precursor of geohopanoids was identified in substantial amounts in a peat exposed to groundwater oscillations

lightning induced shock lamellae in quartz using transmission electron microscopy we show that planar deformation lamellae occur within quartz in the substrate of a rock fulgurite i e a lightning derived glass these lamellae exist only in a narrow zone adjacent to the quartz fulgurite boundary and are comparable to planar deformation features shock lamellae caused by hypervelocity impacts of extra terrestrial objects our observations strongly suggest that the lamellae described here have been formed as a result of the fulgurite producing lightning strike this event must have generated a transient pressure pulse whose magnitude however is uncertain at this stage

contrasting crustal production and rapid mantle transitions beneath back arc ridges the eastern lau spreading centre located on the lau back arc basin hydrothermal vent system between fiji and tonga is a focus site of the ridge 2000 research programme of the us national science foundation the first large scale seismic study of the area reveals large and abrupt across and along strike changes in crustal properties implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes the authors conclude that stable broad triangular upwelling regions as inferred for mid ocean ridges cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which the material is rapidly released resulting in rapid changes in the character of the crust formed at the ridge this study shows that across strike and along strike changes in crustal properties at the eastern lau spreading centre are large and abrupt implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes it is concluded that stable broad triangular upwelling regions as inferred for mid ocean ridges cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which that material is rapidly released resulting in rapid changes in the character of the crust formed at the ridge the opening of back arc basins behind subduction zones progresses from initial rifting near the volcanic arc to seafloor spreading1 during this process the spreading ridge and the volcanic arc separate and lavas erupted at the ridge are predicted to evolve away from being heavily subduction influenced with high volatile contents derived from the subducting plate 2 3 4 5 current models4 6 7 8 predict gradational rather than abrupt changes in the crust formed along the ridge as the inferred broad melting region beneath it migrates away from heavily subduction influenced mantle in contrast here we show that across strike and along strike changes in crustal properties at the eastern lau spreading centre are large and abrupt implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes with incremental separation of the ridge axis from the volcanic front of as little as 5 km seafloor morphology changes from shallower complex volcanic landforms to deeper flat sea floor dominated by linear abyssal hills upper crustal seismic velocities abruptly increase by over 20 and gravity anomalies and isostasy indicate crustal thinning of more than 1 9 km we infer that the abrupt changes in crustal properties reflect rapid evolution of the mantle entrained by the ridge such that stable broad triangular upwelling regions as inferred for mid ocean ridges9 10 cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which that material is rapidly released from the upwelling zone resulting in rapid changes in the character of the crust formed at the ridge

structural diversity and fate of intact polar lipids in marine sediments abstract marine sediments harbor an enormous quantity of microorganisms including a multitude of novel species the habitable zone of the marine sediment column begins at the sediment water interface and probably extends to depths of several thousands of meters studies of the microbial diversity in this ecosystem have mostly relied on molecular biological techniques we used a complementary method analysis of intact polar membrane lipids to characterize the in situ microbial community in sediments covering a wide range of environmental conditions from peru margin equatorial pacific hydrate ridge and juan de fuca ridge bacterial and eukaryotic phospholipids were only detected in surface sediments from the peru margin in contrast deeply buried sediments independent of their geographic location were dominated by archaeal diether and tetraether lipids with various polar head groups and core lipids we compared ring distributions of archaeal tetraether lipids derived from polar glycosidic precursors with those that are present as core lipids the distributions of these related compound pools were distinct suggestive of different archaeal sources i e the polar compounds derive from sedimentary communities and the core lipids are fossil remnants from planktonic communities with possible admixtures of decayed sedimentary archaea this in situ production of distinct archaeal lipid populations potentially affects applications of the tex86 paleotemperature proxy as demonstrated by offsets in reconstructed temperatures between both pools we evaluated how varying cell and lipid stabilities will influence the sedimentary pool by using a box model the results are consistent with i a requirement of continuous inputs of freshly synthesized lipids in subsurface sediments for explaining the observed distribution of intact polar lipids and ii decreasing lipid inputs with increasing burial depth

effect of latent heat of freezing on crustal generation at low spreading rates lithospheric structure changes at low spreading rates 40 mm a 1 such that steady state molten rock cannot exist above the normal moho depth of 6 km dredge statistics of recovered lithologies indicate that the percentage of basalt is significantly decreased compared to faster ridges and that the mode of crust generation is variable one important effect on lithospheric structure is the latent heat released when basaltic magma freezes within the mantle instead of being transported all the way to the surface using thermal models we show that freezing of melt at mantle depths buffers temperature due to the latent heat of crystallization two quasi stable seafloor spreading patterns are imposed on the model 1 upwelling of magma along a narrow axial zone and 2 pure shear extension over a broad zone the variability in crustal structure predicted by these models explains variability observed in dredge lithology statistics at eight slow to ultraslow spreading ridge segments for example the gakkel eastern volcanic zone and sparsely magmatic zone are both spreading at 12 mm a 1 but the former is composed of 7 peridotite whereas the latter is 46 peridotite this difference can be explained by a change from a narrow axis regime with 2 km thick crust to a wide axis regime with a crust mantle mix overall dredge statistics and thermal models suggest that some but not all latent heat of ascending magmas is released at mantle depths and that various ridge axial morphologies can occur

generation of shock lamellae and melting in rocks by lightning induced shock waves and electrical heating the very rapid energy release from impact events such as those resulting from lightning strikes or meteorites can drive a variety of physical and chemical processes which alter rocks and result in the formation of natural glasses i e fulgurites and tektites fulgurite is the vitrified soil sand or rock resulting from lightning strikes a thunderbolt is associated with air temperatures of up to 105 k which can heat rocks to 2000 k within tens of microseconds the rapid fusing and subsequent quenching of the surface of the rock leaves a distinctive thin garbled coating composed of a glassy to fine grained porous material previous studies on rock fulgurites found planar deformation features in quartz crystals within the target rock substrate evidence of strong shock waves during fulgurite formation in this paper we simulated the shock pressure and temperature caused by an idealized lightning impact on rocks and compared the model results with observations on rock fulgurites from the literature our model results indicate that a lightning strike can cause 7 gpa pressure on the rock surface generate a layer of fulgurite of radius 9 cm and leave a burned region of radius 11 cm the fulgurites found on rock surfaces share many features with sand fulgurites but their spatial distribution is completely different as sand fulgurites are hollow tube structures our study on rock fulgurites provides an indirect constraint on the energy of a lightning event and also demonstrates that the presence of shock features in rocks cannot be taken as unequivocal evidence for impact events

characterisation of bacterial populations in arctic permafrost soils using bacteriohopanepolyols bacteriohopanepolyols bhps are biomarkers providing taxonomically and environmentally diagnostic information bhps may help to unravel the composition of bacterial communities residing in recent as well as ancient permafrost soils and sediments and also provide information on associated environmental conditions however detailed data on their distribution in the heterogeneous arctic environment are scarce the distribution and structural diversity of bhps were studied in the annually thawing active layer of three different sites in the polygonal tundra of the lena delta in the siberian arctic variations between permafrost structures and soil horizons caused by differences in the physical and chemical soil properties were observed c and n content is significantly correlated with the bhp composition so that the highest bhp concentrations and greatest structural diversity occur in the uppermost organic soil horizons which consist mainly of fresh or little degraded plant material furthermore statistical analyses reveal that higher abundances of adenosylhopane type soil marker bhps are linked to higher soil ph values small scale environmental controls on bhp distributions are reflected by amine functionalised bhps from methanotrophic bacteria only occurring in the water saturated oxygen depleted polygon centres and by soil marker bhps which are significantly more abundant in the well aerated polygon rims than in the centres in contrast c 2 methylated bhps putative indicators of plant bacterial interactions are present in all soil horizons and permafrost structures and their relative distribution is not systematically linked to soil properties overall lipid based results agree with published 16s rrna based community structure assessments highlighting the usefulness of bhps to represent bacterial populations in recent and ancient permafrost soils

bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions lorca basin murcia spain abstract free lipids sulphur bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a messinian sequence of lorca basin the high abundance of phytane 2 3 dimethyl 5 2 6 10 trimethylundecyl thiophene mid chain c 20 isoprenoid thiophenes and bithiophenes and bis o phytanyl and o phytanyl o sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions the isopranyl glycerol ethers are essentially found in the sulphur bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids however the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid shales and laminated carbonate and 3 7 11 15 19 pentamethyleicosanoic acid only in the laminated carbonate the bacterial inputs are represented by 2 hydroxytetracosanoic acid n octadec 11 enoic acid hopanoic acids and the distributions of iso and anteiso c 15 and c 17 homologues and minor amounts of iso c 16 and anteiso c 14 these branched fatty acids are characteristic of sulphate reducing bacteria the relative proportions of the iso and anteiso compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments

lipid biomarker δ13c and plant macrofossil stratigraphy of a scottish montane peat bog over the last two millennia abstract seven horizons of a peat core covering the last 2000 years from moine mhor a blanket bog in the cairngorm mountains scotland have been examined for the carbon number distributions of the long chain hydrocarbon alcohol and acid components using gas chromatography gc and gas chromatography mass spectrometry gc ms compound specific 13 c values for individual n alkanes were obtained using gas chromatography isotope ratio mass spectrometry gc irms the lipid biomarker distributions and the 13 c values have been compared with those of eleven species of living plant dominant at the contemporary surface of the bog the observed lipid stratigraphy shows only partial agreement with that calculated using macrofossil abundance data and the lipid distributions for the living taxa a result which reflects the inherent uncertainties in both the lipid biomarker and the macrofossil approaches to palaeoenvironmental stratigraphy the carbon isotope values for the individual n alkanes of the plants 27 6 to 36 6 and of the peat layers 29 to 31 7 are as expected for the c 3 photosynthetic pathway however the n alkanes from the surface samples were more depleted by 2 in 13 c than those from the rest of the core a negative shift which may in part reflect the shift 1 2 in 13 c estimated for co 2 in a pre industrialised to an industrialised atmosphere

lipid geochemistry of lake sediments from semi arid spain relationships with source inputs and environmental factors the lipid geochemistry of lake sediments can provide information on past environmental change detailed interpretation is however often hampered by a limited understanding of the provenance of many compounds and the multiple factors influencing their distributions in modern lake sediments we have quantified the solvent extractable lipid compositions of modern surface sediments from fifty four spanish lakes covering a range of hydrochemical fresh to hypersaline and hydrological shallow ephemeral to deep permanent conditions lipid compositions across the dataset are dominated by carboxylic acids up to 86 total solvent extractable lipids alkanols up to 63 and sterols up to 58 with smaller relative proportions of alkanes alkenes ketones including long chain alkenones and hopanols here we employ the distributions of these dominant compounds to explore relationships between lipid composition source inputs and lake type source input is the major factor influencing the lipid composition but there are also some indicators of early stages of lipid diagenesis in these surface sediments multivariate data analysis non metric multidimensional scaling ordination and cluster analysis of normalised lipid concentrations shows a distinction between compounds originating primarily from algal bacterial macrophyte or terrestrial plant sources this statistical technique enables sites to be grouped according to their dominant lipid compositional characteristics as well as enabling us to identify broad trends in groups of sites in terms of their environmental features e g shallow or deep lakes this modern training set study provides insight into patterns of contemporary lipid distributions and lipid source and site relationships across diverse lacustrine environments which can then be useful in environmental monitoring and palaeoenvironmental studies using sediment cores

crustal structure of the kermadec arc from mango seismic refraction profiles three active source seismic refraction profiles are integrated with morphological and potential field data to place the first regional constraints on the structure of the kermadec subduction zone these observations are used to test contrasting tectonic models for an along strike transition in margin structure previously known as the 32 s boundary we use residual bathymetry to constrain the geometry of this boundary and propose the name central kermadec discontinuity ckd north of the ckd the buried tonga ridge occupies the forearc with vp 6 5 7 3 km s 1 and residual free air gravity anomalies constrain its latitudinal extent north of 30 5 s width 110 20 km and strike 005 south of 25 s south of the ckd the forearc is structurally homogeneous down dip with vp 5 7 7 3 km s 1 in the havre trough backarc crustal thickness south of the ckd is 8 9 km which is up to 4 km thinner than the northern havre trough and at least 1 km thinner than the southern havre trough we suggest that the eocene arc did not extend along the current length of the tonga kermadec trench the eocene arc was originally connected to the three kings ridge and the ckd was likely formed during separation and easterly translation of an eocene arc substrate during the early oligocene we suggest that the first order crustal thickness variations along the kermadec arc were inherited from before the neogene and reflect mesozoic crustal structure the cenozoic evolution of the tonga kermadec hikurangi margin and along strike variations in the duration of arc volcanism

sea floor spreading in the lau back arc basin abstract we report the first 3 d magnetization inversion of bathymetry and magnetics data for the entire lau basin and confirm a history of southward propagating sea floor spreading during the past 4 myr magnetic lineations seafloor fabric and ridge segmentation patterns indicate that lithospheric accretion on discrete spreading centers in this back arc basin is fundamentally similar to that occurring on mid ocean ridges the brunhes chron spreading rates 65 100 mm yr are

microbial biomarkers support organic carbon transport from methane rich amazon wetlands to the shelf and deep sea fan during recent and glacial climate conditions abstract we have investigated the delivery of terrestrial organic carbon oc to the amazon shelf and deep sea fan based on soil marker bacteriohopanepolyols bhps adenosylhopane and related compounds and branched glycerol dialkyl glycerol tetraethers gdgts as well as on 14c dating of bulk organic matter the microbial biomarker records show persistent burial of terrestrial oc evidenced by almost constant and high bit values 0 6 and soil marker bhp concentration 80 230 g g toc total oc on the late holocene shelf and even higher bit values 0 8 0 9 but lower and more variable soil marker bhp concentration 40 100 g g toc on the past glacial deep sea fan radiocarbon data show that oc on the shelf is 3 4 kyr older than corresponding bivalve shells emphasizing the presence of old carbon in this setting we observe comparable and unexpectedly invariant bhp composition in both marine sediment records with a remarkably high relative abundance of c 35 amino bhps including compounds specific for aerobic methane oxidation on the shelf avg 50 of all bhps and the fan avg 40 notably these marine bhp signatures are strikingly similar to those of a methane producing floodplain area in one of the amazonian wetland varzea regions the observation indicates that bhps in the marine sediments may have initially been produced within wetland regions of the amazon basin and may therefore document persistent export from terrestrial wetland regions with subsequent re working in the marine environment both during recent and past glacial climate conditions

hematite in porous red clouded feldspars evidence of large scale crustal fluid rock interaction abstract transmission electron microscopy shows that red clouded alkali feldspars from granitic rocks contain numerous open pores up to several hundred nanometres in cross section and that almost every pore contains rosettes or needles of crystalline hematite in the samples described here the hematite forms at the reaction interfaces at which plagioclase feldspar is replaced by alkali feldspar these observations together with the fact that the origin of the porosity can be explained by the mechanism of sub solidus mineral fluid replacement processes indicate that hematite is a direct product of fluid rock interaction and is not a solid state exsolution product from the feldspar

body wave attenuation in the tonga subduction zone attenuation p and s waves of in the tonga subduction zone is estimated from locally recorded data using a spectral ratio method the data consist of three component digital seismograms of 77 earthquakes recorded at two stations in fiji and one in tonga the stations in the fiji islands lie above the deep earthquakes in the subduction zone while the tonga station is close to the top of the subducted slab variations in the high frequency spectral decay rate define four attenuation provinces paths from earthquakes deeper than 350 km to stations on viti levu fiji and the lau ridge traverse mantle with normal attenuation qp 570 qs 200 400 the subducting tonga slab has very low attenuation qp 2000 qs 1800 relative to the surrounding mantle the wedge of mantle above the slab at depths shallower than 350 km and east of the lau ridge is extremely attenuating for p waves qp 240 several paths from main thrust zone events to the station in tonga show intermediate attenuation qp 300 500 in the forearc region the observed spectra do not require q to be frequency dependent in the 1 0 hz to 7 6 hz band in this region

influence of pressure and mineralogy on seismic velocities in oceanic gabbros implications for the composition and state of the lower oceanic crust 1 we have analyzed the relationship between p wave velocities measured at pressures of 40 100 and 200 mpa and modal mineralogy in oceanic gabbro samples from ocean drilling program holes 735b 894g and 923a at all pressures increasing velocities correspond to increasing pyroxene contents and decreasing alteration phyllosilicate and amphibole content but indicate little or no variation of olivine content in part because the olivine compositions are in the range fo65 to fo73 a voigt reuss hill inverse model reveals that the effective bulk density and elastic moduli of olivine in the gabbros are low even relative to fo73 possibly because the olivine grains contain ubiquitous networks of cracks even if the cracks are not present in situ on average gabbros with velocities typical of seismic layer 3 6 7 7 0 km s 1 contain 5 15 alteration products including 5 15 amphibole and 0 5 phyllosilicates these results suggest that the lower crust is on average slightly to moderately altered

crustal structure of the niuafo ou microplate and fonualei rift and spreading center in the northeastern lau basin southwestern pacific the northeastern lau basin is one of the fastest opening and magmatically most active back arc regions on earth although the current pattern of plate boundaries and motions in this complex mosaic of microplates is reasonably understood the internal structure and evolution of the back arc crust are not we present new geophysical data from a 290 km long east west oriented transect crossing the niuafo ou microplate back arc the fonualei rift and spreading center frsc and the tofua volcanic arc at 17 20 s our p wave tomography model and density modeling suggest that past crustal accretion inside the southern frsc was accommodated by a combination of arc crustal extension and magmatic activity the absence of magnetic reversals inside the frsc supports this and suggests that focused seafloor spreading has until now not contributed to crustal accretion the back arc crust constituting the southern niuafo ou microplate reveals a heterogeneous structure comprising several crustal blocks some regions of the back arc show a crustal structure similar to typical oceanic crust suggesting they originate from seafloor spreading other crustal blocks resemble a structure that is similar to volcanic arc crust or a hydrous type of oceanic crust that has been created at a spreading center influenced by slab derived water at distances 50 km to the arc throughout the back arc region we observe a high velocity vp 7 2 7 5 km s 1 lower crust which is an indication for magmatic underplating which is likely sustained by elevated upper mantle temperatures in this region

a three plate kinematic model for lau basin opening 1 we present revised compilations of bathymetry magnetization acoustic imagery and seismicity data for the lau basin and surrounds we interpret these data to more precisely locate the plate boundaries in the region and to derive a three plate kinematic model for the opening of the lau basin during the brunhes chron our tectonic model includes the niuafo ou microplate which is separated from the australian plate along the peggy ridge lau extensional transform zone central lau spreading center and from the tongan plate along the newly discovered fonualei rift and spreading center our model shows that australia tonga plate motion between 15 5 s and 19 s is partitioned across the microplate and it resolves the former apparent conflict between geodetic versus seafloor spreading velocities regionally this implies that the angular rate of opening of the lau basin has been faster than that of the havre trough to the south and that the rapid current rates of pacific subduction at the tonga trench 240 mm yr at 16 s have been sustained for at least 0 78 m y

fulgurites in the southern central sahara republic of niger and their palaeoenvironmental significance the mineralogical and chemical characteristics of fulgurites natural glasses formed by lightning strikes to the ground from the southern central sahara niger are presented the fulgurites are indicators of thunderstorms the northernmost important fulgurite formation in the study area reached up to about 18 n with decreasing fulgurite concentration from south to north their distribution pattern and the relative dating of their formation in relation to landscape history from the late pleistocene onwards e g palaeolakes palaeosols and to neolithic settlement reveals their value as palaeoenvironmental indicators they indicate 1 local palaeoenvironmental conditions depending on the topographical situation in a complex dune relief 2 climatic change during the mid holocene from northerly rains to southerly rains and 3 the northernmost limit of important thunderstorms and rainfall activity since this time in the southern central sahara

p wave attenuation structure of the lau back arc basin and implications for mantle wedge processes abstract we image 3 d seismic p wave attenuation structure of the tonga subduction zone and the lau back arc basin using local earthquake waveforms recorded by land and ocean bottom seismographs of the 2009 2010 lau spreading center imaging project the amplitude spectra of p waves from local earthquakes are inverted for the path average attenuation operator t with a variety of frequency dependence exponent values analysis shows that the data are best fit by the assumption of a weak frequency dependence 0 3 consistent with laboratory results modeled as the effects of grain boundary sliding the t measurements are inverted for a 3 d tomographic q p 1 model the results show high p wave attenuation within the upper 100 km of the back arc mantle with a sharp boundary at the tofua arc between high attenuation sub arc mantle and the low attenuation fore arc perhaps the highest p wave attenuation q p 1 0 036 or q p 28 known in the mantle occurs at 20 60 km depth beneath the back arc spreading centers high attenuation anomalies form an inclined zone dipping from the spreading centers to the west away from the slab indicating abnormally high temperature and the existence of hydrous partial melt these observations suggest that hot materials supplied from the australian mantle upwell along with the mantle wedge flow pattern triggering extensive decompression melting near the back arc spreading centers the along strike variation of p wave attenuation is different from that of sv velocity possibly implying the different effects of partial melt on seismic attenuation and velocity

alkenone producers inferred from well preserved 18s rdna in greenland lake sediments 1 the 18s ribosomal dna rdna sequences of haptophyte algae were successfully amplified using the polymerase chain reaction pcr from water filtrate surface sediments and a late holocene sediment sample 1000 years old from a group of lakes in the sondre stromfjord region of west greenland the dna of the algal primary producer is extremely well preserved in the laminated lake sediments which have been deposited in cold 1 2c anoxic and sulphidic bottom water phylogenetic analyses of the greenland haptophyte rdna sequences suggest that alkenones in the greenland lake sediments are produced by haptophyte algae of the class prymnesiophyceae the 18s rdna sequences from the greenland samples cluster within a distinct phylotype differing from both marine haptophytes and from those reported previously from ace lake antarctica the similarity of haptophyte rdna sequences among all samples in this study suggests a single alkenone based temperature calibration may be applied to these lakes for at least the past 1000 years these sedimentary archives hold great promise for highresolution alkenone based paleotemperature reconstruction of southern west greenland a region sensitive to atmospheric oceanic climate phenomena such as the north atlantic oscillation nao

postglacial climate reconstruction based on compound specific d h ratios of fatty acids from blood pond new england we determined hydrogen isotope ratios of individual fatty acids in a sediment core from blood pond massachusetts usa in order to reconstruct climate changes during the past 15 kyr in addition to palmitic acid c16n acid which has been shown to record lake water d h ratios our surface sediments and down core data indicate that behenic acid c22n acid produced mainly by aquatic macrophytes is also effective for capturing past environmental change calibration using surface sediments from two transects across eastern north america indicates that behenic acid records d variation of lake water down core variations in d values of behenic acid and pollen taxa are consistent with the known climate change history of new england by evaluating the hypothesis that d h fractionations of long chain even numbered fatty acids c24 c32n acids relative to lake water provide independent estimates of relative humidity during the growing season we find that differences between lake level records and isotopically inferred humidity estimates may provide useful insight into seasonal aspects of the hydrologic cycle combined analyses of d h of short and long chain fatty acids from lake sediment cores thus allow reconstructions of both past temperature and growing season relative humidity comparison of d records from two lakes in new england provides critical information on regional climate variation and abrupt climate change such as the 8 2 ka event

geology and kinematics of the niuafo ou microplate in the northern lau basin we present a revised three plate kinematic model for the lau basin focusing on new interpretations of the geologic characteristics of the niuafo ou microplate boundaries it builds upon the three plate model by zellmer and taylor 2001 while resolving some geologic discrepancies in that model along the southern branch of the mangatolu triple junction and the fonualei rift and spreading center which together form the niuafo ou tonga plate boundary our model predicts slow to ultraslow opening rates 32 8 mm yr southward consistent with axial morphology and magnetic profile modeling our interpretation of the seafloor magnetization pattern and flank morphology along the central lau spreading center clsc indicates that opening rates along the australia niuafo ou boundary are higher than predicted in the previous model thus compensating for slower rates along the niuafo ou tonga boundary lastly we show geologic evidence that peggy ridge pr interpreted previously as an active transform fault and therefore a strong azimuthal constraint on niuafo ou plate motion is inactive and that the active plate boundary is the adjacent lau extensional transform zone extending from the clsc to its intersection with the northwest lau spreading center the removal of the pr azimuthal constraint allows us to determine an euler pole for australia niuafo ou opening that satisfies three plate closure criterion and develop a geologically consistent model of lau basin kinematics while the final model focuses on constraining current plate velocities assuming rigid plate eulerian rotations the geologic analyses presented herein also provide insight into long term basin evolution which appears to involve significant nonrigid plate kinematics

xeropreservation of functionalized lipid biomarkers in hyperarid soils in the atacama desert our understanding of long term organic matter preservation comes mostly from studies in aquatic systems in contrast taphonomic processes in extremely dry environments are relatively understudied and are poorly understood we investigated the accumulation and preservation of lipid biomarkers in hyperarid soils in the yungay region of the atacama desert lipids from seven soil horizons in a 2 5 m vertical profile were extracted and analyzed using gc ms and lc ms diagnostic functionalized lipids and geolipids were detected and increased in abundance and diversity with depth deeper clay units contain fossil organic matter radiocarbon dead that has been protected from rainwater since the onset of hyperaridity we show that these clay units contain lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains this indicates that minimal degradation of lipids has occurred in these soils since the time of their deposition between 40 000 and 2 million years ago the exceptional structural preservation of biomarkers is likely due to the long term hyperaridity that has minimized microbial and enzymatic activity a taphonomic process we term xeropreservation i e preservation by drying the degree of biomarker preservation allowed us to reconstruct major changes in ecology in the yungay region that reflect a shift in hydrological regime from wet to dry since the early quaternary our results suggest that hyperarid environments which comprise 7 5 of the continental landmass could represent a rich and relatively unexplored source of paleobiological information on earth

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

diverse biohopanoid compositions of non marine sediments abstract biohopanoid compositions were determined for modern sediments from 27 lacustrine environments and 1 near coastal lagoon gc ms analysis of existing hopanols and those produced by a side chain cleavage reaction periodic acid and sodium borohydride of the bacteriohopanepolyols provided quantitative data for bacteriohopanetetrol bht bacteriohopanepentol and composite tetra penta and hexafunctionalised biohopanoids additional analysis of acetylated total extracts by hplc apci ms has allowed us to identify up to seven intact bacteriohopanepolyols in these environments including the first direct observation of 35 aminobacteriohopanepentol in environmental samples this method is complementary to the periodic acid approach in providing more specific compositional information the lacustrine environments exhibit a wide range of compositions many with high inputs of hexafunctionalised biohopanoids up to 60 of total tetra penta and hexafunctionalised biohopanoids indicative of major contributions to the sediment from type i methanotrophic bacteria several methylated biohopanoids were also detected in most of the samples with 2 as the dominant configuration of the methyl group 2 methylbacteriohopanetetrol was by far the most abundant and most commonly occurring compound of this type and comprised the most abundant bacteriohopanepolyol in one saline lake laguna grande spain such compounds are believed to be derived from cyanobacteria currently the only known quantitatively significant source of 2 methylated biohopanoids biohopanoids containing a methyl group at c 3 were also detected in a limited number of environments these data demonstrate the wide variability in bacteriohopanepolyol compositions among depositional environments and the potential of these compounds to preserve bacterial source information and thereby to record environmental change

tonga ridge and lau basin crustal structure from seismic refraction data 1 the crustal structure across the tonga lau arc back arc system from the lau ridge to the pacific plate 178 170 w 18 19 s is modeled using data from an 840 km long air gun refraction line over 19 ocean bottom seismometers and one land station the data reveal that the pacific plate crust is 5 5 km thick with a velocity structure similar to that found at the present day east pacific rise epr beneath tonga ridge an intermediate velocity layer 6 7 km s is up to 7 5 km thick and has a velocity depth distribution similar to andesitic rocks found in continental crust the crust is abnormally thin 4 km at the boundary between the tonga ridge and the lau basin at the east end of lau basin the crust is 5 5 6 5 km thick and resembles crust formed at the epr except for a thicker sheeted dike section 2 3 km and thinner lower crust 2 km the lau basin crust thickens to 7 8 km near the central lau spreading center clsc mostly through thickening of the lower crust the crust thickens again to 8 5 9 5 km at 50 km west of the clsc mostly through thickening of the midcrust in the thick westernmost section the crustal structure is uniform even though one part of this section formed through extension of arc type crust while the rest was created at an oceanic spreading center the relative homogeneity of these rocks suggests that their petrology may be dominated by postemplacement magmatic infilling from a mantle source west of the spreading center

diatom based transfer functions for inferring past hydrochemical characteristics of african lakes abstract a new dataset of 282 modern diatom samples and associated environmental information has been created by merging existing regional datasets from north and east africa and niger the relationships between diatom species distributions and hydrochemistry are examined using canonical correspondence analysis cca and partial cca variables reflecting water conductivity ph and cation and anion composition account for significant and independent components of the total variation in the diatom data predictive models transfer functions are developed using the method of weighted averaging for conductivity r 2 0 87 ph r 2 0 77 and ratios between alkali and alkaline earth metals r 2 0 81 and carbonate bicarbonate and sulphate chloride ions r 2 0 82 prediction errors are estimated using the computer intensive method of jackknifing these transfer functions enlarge the potential domain for reconstruction of past hydrochemistry from fossil diatoms preserved in lake sediments

bacteriohopanepolyols in tropical soils and sediments from the congo river catchment area the congo river basin drains the second largest area of tropical rainforest in the world including a large proportion of pristine wetlands we present the bacteriohopanepolyol bhp inventory of a suite of tropical soils and from comparison with published data propose some initial ideas on bhp distribution controls strong taxonomic controls on bhp production are evident in wetland sediments dominant within the suite were 35 aminobacteriohopane 31 32 33 34 tetrol aminotetrol and 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol indicating aerobic methanotrophy a narrow range and low mean relative abundance of 30 5 adenosyl hopane adenosylhopane and related compounds collectively termed soil marker bhps were observed in congo soils mean 17 range 7 9 36 of total bhps n 22 compared with literature data from temperate surface soils and arctic surface soils mean 36 range 0 66 of total bhps n 28 suggesting a greater rate of conversion of these bhp precursors to other structures

early evolution of a young back arc basin in the havre trough back arc basins are found at convergent plate boundaries nevertheless they are zones of significant crustal extension that show volcanic and hydrothermal processes somewhat similar to those of mid ocean ridges accepted models imply the initial rifting and thinning of a pre existing volcanic arc until seafloor spreading gradually develops over timescales of a few million years the havre trough northeast of new zealand is a unique place on earth where the early stages of back arc basin formation are well displayed in the recent geological record here we present evidence that in this region rifting of the original volcanic arc occurred in a very narrow area about 10 15 km wide which could only accommodate minimal stretching for a very short time before mass balance required oceanic crustal accretion an initial burst of seafloor spreading started around 5 5 5 0 million years ago and concluded abruptly about 3 0 2 5 million years ago after which arc magmatism dominated the crustal accretion the sudden transition between these different tectonomagmatic regimes is linked to trench rollback promoted by gradual sinking of the subducting lithosphere which could have diverted the arc flux outside the region of seafloor spreading and induced the vertical realignment of surface volcanism with the source of arc melts at depth the havre tough back arc basin new zealand formed rapidly and in two phases initial limited seafloor spreading was followed by a transition to arc magmatism as shown by geophysical data and modelling

spreading rate spreading obliquity and melt supply at the ultraslow spreading southwest indian ridge we use bathymetry gravimetry and basalt composition to examine the relationship between spreading rate spreading obliquity and the melt supply at the ultraslow spreading southwest indian ridge swir we find that at regional scales more than 200 km melt supply reflects variations in mantle melting that are primarily controlled by large scale heterogeneities in mantle temperature and or composition focusing on adjacent swir regions with contrasted obliquity we find that the effect of obliquity on melt production is significant about 1 5 km less melt produced for a decrease of 7 mm a to 4 mm a in effective spreading rates esr but not enough to produce near amagmatic spreading in the most oblique regions of the ridge unless associated with an anomalously cold and or depleted mantle source our observations lead us to support models in which mantle upwelling beneath slow and ultraslow ridges is somewhat focused and accelerated thereby reducing the effect of spreading rate and obliquity on upper mantle cooling and melt supply to explain why very oblique swir regions nonetheless have large outcrops of mantle derived ultramafic rocks and in many cases no evidence for axial volcanism cannat et al 2006 dick et al 2003 we develop a model which combines melt migration along axis to more volcanically robust areas melt trapping in the lithospheric mantle and melt transport in dikes that may only form where enough melt has gathered to build sufficient overpressure these dikes would open perpendicularly to the direction of the least compressive stress and favor the formation of orthogonal ridge sections the resulting segmentation pattern with prominent orthogonal volcanic centers and long intervening avolcanic or nearly avolcanic ridge sections is not specific to oblique ridge regions it is also observed along the swir and the arctic gakkel ridge in orthogonal regions underlain by cold and or depleted mantle

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

the origin of blue coloration in a fulgurite from marquette michigan abstract few rocks or minerals display a blue hue this is especially true for natural glasses as glasses are already uncommon compared to crystalline rocks due to their instability the rarity of blue glass makes a fulgurite found in marquette michigan worthy of further examination we study the morphology and the chemical and structural characteristics of the blue fulgurite using raman spectroscopy x ray fluorescence analysis election microprobe analysis and transmission election microscopy we use the experimental results to compare the fulgurite with another blue natural glass zhanmanshinite an impact glass named after an exposed impact crater in kazakhstan and to evaluate the support for several hypotheses of the origin of the blue color in the fulgurite

abundance and structural diversity of bacteriohopanepolyols in suspended particulate matter along a river to ocean transect abstract the concentration and structural diversity of a suite of bacteriohopanepolyols bhps was measured in suspended particulate matter spm from six stations along a river ocean transect off the pacific coast of panama riverine spm contained bhps diagnostic of soil input consistent with a terrigenous source the concentration of bhps was 10 times greater in riverine spm than marine spm demonstrating that terrigenous om exported to marine sediments could provide a significant contribution to the marine sedimentary hopanoid inventory given the rich structural diversity of bhps in terrigenous spm interpretations of the sedimentary record of hopanoids in coastal marine settings must resolve inputs from marine pelagic and terrigenous sources

soil organic matter transport along an sub arctic river sea transect bacteriohopanepolyols bhps and glycerol dialkyl glycerol tetraethers gdgts have potential as soil tracing biomarkers for the extensive shelves of the arctic ocean in this work these biomarkers

fossilization and degradation of intact polar lipids in deep subsurface sediments a theoretical approach intact polar membrane lipids ipls are frequently used as markers for living microbial cells in sedimentary environments the assumption with these studies is that ipls are rapidly degraded upon cell lysis and therefore ipls present in sediments are derived from in situ microbial production we used a theoretical approach to assess whether ipls in surface sediments can potentially represent fossilized ipls derived from the upper part of the water column and whether ipls can be preserved during sediment burial previous studies which examined the degradation kinetics of ipls show that phospholipids i e ester linked lipids with a phosphor containing head group degrade more rapidly than glycosidic ether lipids i e ether linked lipids with a glycosidically bound sugar moiety based on these studies we calculate that only a minor fraction of phospholipids but a major fraction of glycosidic ether lipids biosynthesized in the upper part of the water column can potentially reach deep sea surface sediments using a simple model and power law kinetic degradation parameters reported in the literature we also evaluated the degradation of ipls during sediment burial our model predicts a log log relationship between ipl concentrations and depth consistent with what has been observed in studies of ipls in subsurface sediments although our results do not exclude production of ipls in subsurface sediment they do suggest that ipls present in the deep biosphere may contain a substantial fossil component potentially masking in situ ipl production

tracking soil organic carbon transport to continental margin sediments using soil specific hopanoid biomarkers a case study from the congo fan odp site 1075 the transport and deposition of terrestrially derived organic matter tom into the ocean is an important but poorly constrained aspect of the modern global carbon cycle a preliminary study of late quaternary sediments from the congo deep sea fan odp leg 175 site 1075 2 km water depth and four surface samples from associated cores has confirmed the presence of proposed soil specific bacteriohopanepolyol biomarkers bhps including adenosylhopane in samples to a depth of 89 m concentrations of soil marker bhps are high in the upper sediment section to 49 m and the closest related surface sample 4913 supporting the case for these molecular markers as novel proxies for soil organic carbon soc supply via riverine transport and subsequent burial distinct peaks for the markers at about 21 34 and 60 m below surface level tentatively imply that the rate of tom discharge from tropical africa significantly increased at these times possibly associated with periods of reduced soil stability in the congo catchment

bacteriohopanepolyol distribution in yenisei river and kara sea suspended particulate matter and sediments traces terrigenous organic matter input abstract bacteriohopanepolyols bhps are ubiquitous bacterial membrane lipids encountered in soils river and marine suspended particulate matter spm and sediments their abundance and distribution provides a direct means to identify bacterial inputs and can be used to trace soil derived bacterial organic matter om and in some cases the presence of bacterial groups and their activities in aquatic systems we have studied the bhp distribution in the spm of a major siberian river yenisei river that crosses a large latitudinal gradient draining a large part of mongolia and siberian russia the yenisei river is the main river to flow into the kara sea a shelf sea of the arctic ocean we show that the bhp distribution and concentration of spm and surface sediments of the yenisei outflow in the kara sea allow to trace soil marker bhps and evaluate the performance of the r soil index a proxy developed to trace bacterial soil derived om soil marker bhps are present in the yenisei river and their concentration decreases from the yenisei river outflow into the offshore marine sediments the r soil correlates well with an independent proxy for bacterial om the bit index r2 0 82 and has a moderate correlation with the 13corg values a bulk om proxy for terrigenous input r2 0 44 consequently the r soil index performs well in the kara sea strengthening its application for tracing bacterial om in the arctic ocean both in modern and downcore sediments furthermore a suite of bhps that are characteristic for methanotrophic bacteria i e 35 aminobacteriohopane 30 31 32 33 34 pentol aminopentol and 35 aminobacteriohopane 31 32 33 34 tetrol aminotetrol is encountered in the yenisei outflow sediments these components are partly sourced from terrigenous sources but are likely also produced in situ in the marine sediments the distribution of the pentafunctionalized cyclitol ether bhp in the marine systems is noteworthy and indicates that it can possibly be applied as a marker for cyanobacterial biomass in marine sediments

occurrence and abundance of soil specific bacterial membrane lipid markers in the tet watershed southern france soil specific bhps and branched gdgts recently four bacteriohopanepolyols bhps adenosylhopane and structurally similar adenosylhopane type 1 2 methyl adenosylhopane and 2 methyl adenosylhopane type 1 have been suggested to be characteristic of soil microbial communities and therefore can serve as molecular markers for soil organic matter om supply in river lake and marine sediments in this study we analyzed bhps in peats and soils collected in the tet watershed southern france and compared them with branched glycerol dialkyl glycerol tetraethers gdgts a more established molecular tracer of soil om adenosylhopane type i is identified in all of the samples from the study area except one collected near the tet river mouth with up to three of the related compounds also frequently present particularly in the surface samples the concentrations of soil specific bhps in peat environments have been shown to increase with lower delta 15 n values providing evidence that n 2 fixing bacteria are probably a major source of soil specific bhps in acidic environments it seems likely that soil ph is a major factor controlling bhp occurrence based on statistical analysis of environmental parameters and bhp concentration data the comparison of the soil specific bhp concentrations with those of branched gdgts shows no clear relationship in the tet river system supporting the concept that these two groups of soil specific compounds are synthesized by different microbial organisms living in different niches in the soil profile e g oxic top versus anoxic deep

mineralogical and compositional features of rock fulgurites a record of lightning effects on granite fulgurites are a naturally occurring glass formed when sand rock or soil is struck by atmospheric electrical discharges lightning the aim of this paper is to provide insights into the conditions occurring in rocks during the lightning strike rock fulgurites collected from mt mottarone baveno piedmont italy have been investigated to assess the mineralogical and compositional changes occurring in granite due to a lightning strike x ray powder diffraction showed that the samples represent the dominant granitic rock type of the baveno massif the so called pink baveno fulgurite coats the surface of the granite as a brown black glassy to very fine grained porous layer powder diffraction data for the fulgurite reveal the presence of cristobalite and quartz crystals in a glass matrix suggesting that temperature exceeded 1700 c at near atmospheric conditions assuming thermodynamic equilibrium electron probe microanalysis of the glass revealed that it is mainly composed of sio 2 and al 2 o 3 and that it has a porosity of 5 7 area in the studied zones the presence of the amorphous phase indicates that the abrupt electrical joule heating of the rock surface yielded high temperatures producing a thin melt layer on the surface which then cooled adiabatically idealized physical model was developed to simulate the effects of joule heating and subsequent thermal conduction close to the rock surface during and after a lightning strike the quantity of organic matter in the glass obtained via elemental analyzer suggests that rapid quenching of the melt trapped no x and co x gases produced during heating raman spectroscopy revealed the presence of polyaromatic hydrocarbon molecules which combined with the elemental analyzer data suggest that organic matter was pyrolyzed at around 300 350 c and then trapped in the glass matrix of the studied rock fulgurites

seismological study of lau back arc crust mantle water magmatic differentiation and a compositionally zoned basin abstract on the basis of seismic tomography analyses a structural model of crust formed along the eastern lau spreading center elsc is presented as evidence for a transition from a hydrous type of oceanic crust to a more typical oceanic crust the seismic data indicate that as the spreading center moved away from the active arc the crust thinned from 8 9 km to 7 km the lower crust changed from high p wave velocity values 7 2 7 4 km s to typical values for oceanic crust 7 0 7 2 km s and the upper crustal volcanic layer changed from a thick low velocity layer to a thinner layer with more typical wave speeds the seismic results in combination with other geophysical and geochemical data suggest that crustal formation along the elsc is strongly controlled by the influence of slab water when a spreading center is near the active arc water from the downgoing slab is entrained in the melting zone beneath the ridges where it enhances melting thereafter the water enhances crustal differentiation within sub ridge magma chambers this creates an anomalous hydrous form of oceanic crust with a thick felsic volcanic layer and a mafic ultramafic lower crust features that are not typically observed in crust formed at mid ocean ridges the lau basin has a zoned structure with an abrupt transition from this type of oceanic crust to more typical oceanic crust which resulted from a rapid change in the influence of slab water as the ridge moved away from the arc the abundance and high rate of production of the hydrous crust suggests that such crust may make up a significant proportion of the arc like crust that forms continents

magmatic tectonic conditions for hydrothermal venting on an ultraslow spread oceanic core complex hydrothermal venting an important cooling mechanism of the earth supports a diverse array of seafloor and sub seafloor ecosystems that are sustained by large thermal and chemical fluxes vents have been found along even the slowest and coldest spreading centers calling into question the driving heat source for these vents the ultraslow spreading mid cayman spreading center in the caribbean sea which hosts the axial flank von damm vent field vdvf provides an opportunity to probe the mechanisms for venting at ultraslow spreading rates using active source seismic data from the 2015 cayseis cayman seismic experiment we determined the seismic velocities in the large massif beneath the vdvf we propose that this massif was produced by a pulse of on axis magmatism at ca 2 ma which was then followed by exhumation cooling and fracturing a low seismic velocity anomaly 5 km below the vdvf is evidence for either a cracking front mining lithospheric heat or intrusive magmatic sills both of which could drive ongoing deep hydrothermal fluid circulation we conclude that the transient magmatism and variable crustal thickness at ultraslow spreading centers create conditions for long lived hydrothermal venting that may be widespread and other vdvf like vents may be common in these areas

unusual distributions of long chain alkenones and tetrahymanol from the highly alkaline lake van turkey long chain c37 to c40 alkenones with di tri and tetra unsaturation are very abundant in sediment trap material and holocene to late pleistocene core samples from the earth s largest soda lake lake van turkey thus the known distribution range of these typical biomarkers for haptophyte microalgae is extended to highly alkaline environments the observed unsaturation patterns differ strikingly from those found in open marine haptophytes and sediments by an enhanced relative abundance of the tetra unsaturated compounds especially the c37 4 methyl ketone their preponderance is suggested to be a facies marker pattern for lacustrine and marginal marine areas of sedimentation using published u37k calibrations no reliable absolute temperatures were obtained for the lake van samples accordingly marine sea surface temperature determinations based on long chain alkenones should be applied with caution when a contribution of these compounds from coastal or nonmarine sources can not be excluded the presence of tetrahymanol and gammacer 3 one in the lake van materials is attributed to organic matter contributions of ciliates the relative abundance of long chain alkenones and of tetrahymanol gammacer 3 one is considered to reflect changes in the environmental conditions in particular in the hydrological setting we suggest that times of pronounced stagnation are recognised by very high tetrahymanol gammacer 3 one concentrations together with drastically increased stanol stenol ratios and intervals of enhanced convection or of high freshwater input are characterised by high alkenone contributions

impact geologists beware impact geologists have long assumed that shock metamorphic features such as planar fractures and planar deformation features pdfs in quartz are reliable indicators of an extraterrestrial impact a new paper by chen et al 2017 https doi org 10 1002 2017gl073843 now shows that such features might arise in terrestrial lightning strikes thus raising the bar for identification of impact sites