the amazon river plume during amasseds spatial characteristics and salinity variability the amazon river discharge forms a plume of low salinity water that extends offshore and northwestward over the north brazilian shelf observations acquired as part of a multidisciplinary amazon shelf sediment study amasseds are used to characterize the spatial structure and temporal variability of the amazon plume four shipboard conductivity temperature depth ctd surveys spanning the shelf from 1 s to 5 n during rising march 1990 maximum may 1990 falling august 1989 and minimum november 1991 discharge show the amazon plume is typically 3 to 10 m thick and 80 to over 200 km wide northwest of the river mouth the plume is often characterized by a wedge of low salinity water adjacent to the coast and a separate tongue of low salinity water extending offshore over the middle to outer shelf a bottom front separating the low salinity plume water from oceanic water is consistently located between the 10 and 20 m isobaths a moored array deployed about 300 km northwest of the river mouth from february to june 1990 included inner and midshelf moorings in 18 and 65 m of water on which temperature conductivity measurements were made the moored observations reveal salinity variations within the amazon plume of over 10 psu on timescales of days to weeks this variability includes intermittent events in which plume water pools up in the vicinity of the river mouth and the plume width can exceed 200 km these accumulation events are apparently due to wind events with a southeastward component which impede or block the normally northwestward freshwater transport the resulting bulges in the plume are then released northwestward when the wind reverses volume budgets indicate the amazon plume entrains roughly twice the river discharge between the river mouth at the equator and 3 n estimates of gradient richardson numbers from the moorings suggest entrainment due to the strong semidiurnal tidal currents occurs where the plume intersects the bottom and over the outer portion of the plume where salinities approach oceanic values

strong climate coupling of terrestrial and marine environments in the miocene of northwest europe a palynological and organic geochemical record from a shallow marine paleoenvironmental setting in se netherlands documents the coupled marine and terrestrial climate evolution from the late burdigalian 17 ma through the early zanclean 4 5 ma proxy climate records show several coeval variations in both relative sea surface deduced from percent cool dinocysts and terrestrial subtropical vs cool temperate pollen temperature indices the terrestrial climatic trend is confirmed by a quantitative reconstruction of annual mean air temperature based on the distribution of fossil branched glycerol dialkyl glycerol tetraethers showing a cooling from 27 c to 14 c between 17 and 5 ma punctuated by short term variations decreases in sea surface temperature broadly correlate to inferred third order sea level variations and correspond to isotope glacial events mi 3 through mi 7 an additional strong sst decrease occurs around 8 4 ma coincident with a strong reduction and regional disappearance of subtropical pollen types this cooling phase seems associated with lowered sea levels but it has not yet been described from the deep sea 18o record 2009 elsevier b v

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

eolian transport of glycerol dialkyl glycerol tetraethers gdgts off northwest africa branched glycerol dialkyl glycerol tetraethers brgdgts of purportedly terrestrial origin are frequently detected in marine sediments even in remote ocean sites where no direct impact from land erosion via rivers takes place at these places the most likely explanation for the presence of brgdgts is in situ production or eolian transport but neither possibility has been demonstrated for the open ocean here we report the presence of isoprenoid iso and brgdgts in eight dust samples collected off northwest africa based on previous studies prevailing wind patterns bulk chemistry n alkane composition and isotopic signatures we show that northwest africa is the likely principal origin of the gdgts in the dust the concentrations of plant wax n alkanes in the dust are several orders of magnitude higher than those of gdgts and based on the distributions of these two compound classes we infer that they tag different carbon pools and sources of organic matter our finding demonstrates that brgdgts and isogdgts in marine sediments and wind derived deposits can have an eolian source consequently climate reconstruction may be attempted from wind derived deposits of brgdgts even in remote oceanic areas

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

fluxes and distribution of tetraether lipids in an equatorial african lake constraints on the application of the tex86 palaeothermometer and bit index in lacustrine settings abstract the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in material from various sources in and around lake challa a crater lake on the southeastern slope of mt kilimanjaro tanzania to examine the provenance of gdgts in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies the study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle particles suspended in the stratified water column profundal surface sediments and soils surrounding the lake the sediment trap time series revealed that crenarchaeol and related isoprenoid gdgts were predominantly produced in january and february following the locally prominent short rain season november december the tex 86 inferred temperature derived from sedimenting particles corresponded well with lake surface water temperature at this time of largest crenarchaeol flux molecular ecological analysis showed that group 1 1a and 1 1b crenarchaeota are the most likely source organisms of these gdgts gdgt 0 in the lake sediments does not only originate from lake surface dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper anoxic part of the water column the main flux of branched gdgts to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run off however a contribution from in situ production of branched gdgts in the lake sediment or water or in groundwater cannot be fully excluded we conclude that palaeoclimatic reconstruction based on branched gdgt distributions in lake sediments should only be performed when the origin of those branched gdgts is well constrained

unusually low tex86 values in the transitional zone between pearl river estuary and coastal south china sea impact of changing archaeal community composition tex86 calculated based on the distribution of isoprenoid glycerol dialkyl glycerol tetraethers gdgts is used worldwide for paleotemperature reconstruction in marine and lacustrine environments recently however increasing evidence showed that tex86 could be affected by multiple environmental variables in this study tex86 was calculated for core and polar gdgts obtained from water column and surface sediments in the lower pearl river and its estuary together with previously published core gdgt data from the coastal and open south china sea scs a comparison was made between tex86 derived and satellite based surface water temperature which showed a tex86 temperature minimum that is considerably lower than winter satellite temperature in the transitional zone between the pearl river estuary and the coastal scs tex86 showed significantly positive correlation with gdgt 2 and gdgt 3 in this transitional zone indicating that they are the primary compounds for the tex86 bias toward cooler temperature lipid and molecular dna data both indicate that the variation in archaeal community composition rather than water depth or seasonality is likely the crucial factor causing the deviation of tex86 in the transitional area our study has implications for studies in ancient continental margins where unusually low tex86 temperatures may be observed in the geological record c 2015 elsevier b v all rights reserved

carbon isotopic compositions of prokaryotic lipids as tracers of carbon cycling in diverse settings recent work has highlighted the ubiquity of bacteria and archaea and continues to affirm their significance in diverse biogeochemical processes the 13c values and distributions of diagnostic lipids derived from such microorganisms can provide insights into prokaryotic processes in modern settings and are one of the few means by which past prokaryotic processes in depositional settings can be elucidated here we present a brief review of prokaryotic lipids commonly observed in sediments and the controls on their carbon isotopic compositions we then present two case studies one of mediterranean cold seeps at which anaerobic oxidation of methane occurs and one of a holocene peat deposit in which a variety of aerobic and anaerobic microorganisms govern the degradation of organic matter these two studies illustrate the potential utility of compound specific carbon isotope analyses to deconvolute pathways of carbon flow in microbial communities

spatial distributions of core and intact glycerol dialkyl glycerol tetraethers gdgts in the columbia river basin and willapa bay washington insights into origin and implications for the bit index abstract branched and isoprenoid glycerol dialkyl glycerol tetraethers brgdgts and isogdgts respectively are used to reconstruct carbon flow from terrestrial landscapes to the ocean in a proxy called the branched vs isoprenoid tetraether index or bit index the index is based on analysis of core gdgts c gdgts that are produced from intact gdgts i gdgts upon cell death gdgts are a component of the cell membranes of bacteria in soils br and archaea iso primarily in the marine environment however uncertainty as to the identity of the organisms that biosynthesize brgdgts the variation in the extent to which gdgts represent end member carbon pools and the suspected production of brgdgts and isogdgts in both marine and terrigenous environments hinders interpretation of the bit index since brgdgts remain our only tool for measuring the presence of unknown brgdgt producing organisms it is particularly important to use the intact form of brgdgts in living cells rather than c brgdgts in relict biomass to infer the distributions of the likely source organisms in situ production within riverine lacustrine and marine environments is currently thought to be possible yet few measures of i brgdgts are available in these environments to support these claims here we assess the spatial distribution of core and intact gdgts in the columbia river basin and nearby willapa bay washington and oregon in order to elucidate source environments and behavior of i gdgts vs c gdgts the presence of i brgdgts throughout the studied soils rivers and estuaries suggests in situ production across the continuum from soil to marine environments likewise intact crenarchaeol the marine end member isogdgt used in the bit index was present in all samples widespread production of each gdgt class along terrigenous carbon transport paths likely alters the bit index along this continuum core to intact ratios and the weak correlation between i gdgt derived bit values and carbon isotope signatures suggest a mixture of allochthonous and autochthonous sources of gdgts in riverine and marine environments our findings highlight the need for further work into the provenance and behavior of gdgts in order to improve interpretation of the bit index and other environmental proxies that rely on them

sources and distributions of tetraether lipids in surface sediments across a large river dominated continental margin glycerol dialkyl glycerol tetraether gdgt based proxies are increasingly used in modern carbon cycling and palaeoenvironmental investigations it is therefore crucial to examine the robustness sources transport and degradation of all gdgt based proxies in continental margins where sedimentation rates and extent of carbon cycling are high we have analyzed the distributions of gdgts in surface sediments from the lower yangtze river and east china sea ecs shelf the results revealed multiple sources and complex shelf processes that govern the distributions the isoprenoid gdgt inferred sea surface temperatures ssts are robust and reflect the satellite derived annual mean ssts on the shallow ecs shelf confirming an origin from surface water column dwelling crenarchaeota the input from methanogen sourced isoprenoid gdgts is significant in the river surface sediments but they are almost absent from the ecs shelf branched gdgts are also abundant in the river sediments but ca 95 are degraded in the yangtze estuary a much greater extent than observed for other terrigenous organic matter om proxies there is also evidence for production of branched gdgts in the oxic ecs shelf water column and the anoxic sediments waters of the lower yangtze river as a result branched gdgt based proxies in the lower river and ecs surface sediments do not reflect the catchment environmental conditions the effective degradation in the estuary and widespread aquatic contributions of branched gdgts improves our understanding of how to use branched gdgt based proxies in marginal seas

major changes in glacial and holocene terrestrial temperatures and sources of organic carbon recorded in the amazon fan by tetraether lipids the amazon basin is a major component of the global carbon and hydrological cycles a significant natural source of methane and home to remarkable biodiversity and endemism reconstructing past climate changes in the amazon basin is important for a better understanding of the effect of such changes on these critical functions of the basin using a novel biomarker proxy based on the membrane lipids of soil bacteria with a new regional calibration we present a reconstruction of changes in mean annual air temperatures for the amazon catchment during the last 37 kyr b p biomarkers were extracted from ocean drilling program sediment core odp942 recovered from the amazon fan the amazon fan is a major depository for terrestrial sediments with the advantage that the terrestrial material captured reflects a regional integration of the whole river catchment the reconstructed tropical amazonian temperatures were similar to 5 degrees c cooler at the last glacial maximum similar to 21 degrees c compared to modern values similar to 26 degrees c this is in agreement with previous estimates of tropical continental temperatures in the tropical amazon basin and tropical africa during the last glacial maximum moreover we also illustrate how the soil bacterial membrane lipid record reveals major changes in basin dynamics and sediment provenance during the glacial holocene transition impacting the biomarker reconstructions from similar to 11 kyr onward

a 30 ma history of the amazon river inferred from terrigenous sediments and organic matter on the ceara rise abstract the history of the amazon river is a much discussed subject and the timing of the development of a transcontinental system in particular is a matter of some controversy with estimations varying between the early miocene and the pliocene or even the pleistocene to shed further light on this we studied the sediment provenance of an oligocene to late pleistocene marine sedimentary section from the ceara rise odp site 925 a topographic high in the central atlantic ocean using major element concentrations and nd isotopic composition in 85 samples in addition the carbon isotopic composition of bulk organic matter and changes in the distribution of glycerol dialkyl glycerol tetraethers gdgts were used to identify periods of increased river outflow on the basis of these results we suggest that the history of the development of the amazon river is characterized by specific steps during the late oligocene early miocene 30 18 3 ma the terrigenous mass accumulation rates tars were high and sediment and gdgt compositions suggest that a large river system existed which at times received weathering products from a younger and probably andean sediment source a shift to a younger andean sediment provenance after 8 7 ma indicates that the amazon river became permanently connected with the andes between 18 3 and 4 5 ma tars were generally low and gdgts were derived for the most part from in situ production in marine waters around 4 5 ma the river expanded probably due to ongoing tectonic activity and uplift in the andes increased andean rock erosion this led to a strong increase in terrigenous sediment deposition and enhanced organic matter preservation on the ceara rise and the delivery of terrestrial both soil and riverine branched gdgts to the ceara rise

constraints on the application of the mbt cbt palaeothermometer at high latitude environments svalbard norway abstract branched glycerol dialkyl glycerol tetraethers gdgts are membrane lipids of unknown bacteria that are ubiquitous in soil and peat two indices based on the distribution of these lipids in soils the cyclization of branched tetraethers cbt and the methylation of branched tetraethers mbt indices have been shown to correlate with soil ph and mean annual air temperature mat and soil ph respectively and can be used to reconstruct mat in palaeoenvironments to verify the extent to which branched gdgts in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a mat of

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

strength evolution and the development of crystallographic preferred orientation during deformation of two phase marbles abstract we conducted conventional triaxial compression and confined torsion tests on calcite rocks at 1023 k and equivalent strain rates between 10 6 and 10 3 s 1 to investigate the influence of variations in volume fraction and geometry of a second phase on the evolution of strength and cpo nominally dense two phase marbles were made by hot isostatic pressing of mixtures of calcite and amorphous carbon the carbon grains were either spheres or splinters with known size distributions were chemically inert and are nearly rigid adding 1 vol spheres caused only small changes in strength or cpo strengths were consistent with the activation of slip on f 10 1 1 the hardest system in calcite adding 10 vol splinters increased the strength at low strains and strain rates but had smaller effects at high strains or rates the cpo of rocks containing splinters were similar to those in pure samples but with reduced intensity when 10 vol spheres were added the aggregate strength under confined torsion was less than that of the pure material distinct and intense cpos developed the reduced stresses were consistent with those necessary for slip on systems weaker than f viscoplastic self consistent calculations used to model the texture evolution required slip on f 10 1 1 and c 1 2 1 0 to match the cpo of pure samples results were consistent with the inclusion of slip on r 1 2 1 0 in samples containing 10 vol spheres deformed in torsion slip activity on the harder systems was decreased the exact cause of the strength reduction in these experiments is not understood but it is possible that adding smooth spheres enhanced grain boundary sliding thereby decreasing activity on f 10 1 1 thus shape and volume fraction of second phases may be important in determining cpo and strength and it is important to consider the loading geometry

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

glacial interglacial contrast in mbt cbt proxies in the south china sea implications for marine production of branched gdgts and continental teleconnection abstract two proxies derived from branched glycerol dialkyl glycerol tetraethers br gdgts the methylation index of branched tetraethers mbt and the cyclization ratio of branched tetraethers cbt are often used to reconstruct paleo mean annual air temperature maat and soil ph based on the premise that br gdgts in the marine environment are mainly of terrigenous origin however mounting evidence indicates that br gdgts can be produced in situ in oceanic settings which may affect maat reconstruction and the use of other related paleoenvironmental proxies we have determined br gdgt distributions in a sedimentary core md05 2896 7 from the southern south china sea which provided high resolution profiles of mbt and cbt indices as well as the branched and isoprenoid tetraether bit index bit varied systematically with glacial interglacial cycles reaching much lower

seismic anisotropy of the upper mantle 1 factors that affect mineral texture and effective elastic properties 1 flow induced mineral alignment in the earth s mantle affects the nature of seismic wave propagation since measurements of seismic travel time and shear wave splitting are a key means by which the structure of the upper mantle can be imaged it is important to understand the factors that contribute to variability in elastic properties seismic anisotropy associated with lattice preferred orientations of minerals in peridotite is the focus of this study one way to better understand anisotropy in a convecting upper mantle is to simulate texture evolution based on certain assumptions simulations of the development of olivine and orthopyroxene alignment along streamlines of a mantle flow field illustrate how continuously varying strain conditions affect the resulting orientation distribution there are various uncertainties in rock texture simulations and the aim here is to investigate how much model assumptions may influence the results a model of upper mantle flow in the vicinity of an oceanic spreading center is used to illustrate these points first we assess how sensitive results are on assumptions of different polycrystal plasticity models specifically lower bounds and viscoplastic self consistent approaches we also investigate how recrystallization during deformation might affect the texture that develops along a streamline the effects of grain growth and nucleation produce as expected textures that are different from the deformation only case however the basic p wave structure of the predicted anisotropy is similar between models for streamlines in a slow spreading passive flow model as is commonly used for simulating flow near this type of plate boundary shear wave splitting patterns are more complex and differ somewhat more between the models in the off axis region we also compare predictions for texture development of olivine only aggregates to that of mixed composition with 70 olivine and 30 orthopyroxene although we consider only one aspect of such polyphase deformation i e plastic deformation on specified crystal slip systems our results are consistent with field observations of the orientation distributions in ophiolitic peridotites finally we determine how simplifying assumptions about the symmetry of the elastic anisotropy can bias interpretations of seismic travel time and shear wave splitting whereas a hexagonal approximation can lead to underestimates of the degree of anisotropy an orthorhombic approximation is found to closely match the results predicted for a general elastic tensor corresponding to an orientation distribution whose symmetry is as low as monoclinic or triclinic

extended megadroughts in the southwestern united states during pleistocene interglacials the potential for increased drought frequency and severity linked to anthropogenic climate change in the semi arid regions of the southwestern united states us is a serious concern1 multi year droughts during the instrumental period2 and decadal length droughts of the past two millennia1 3 were shorter and climatically different from the future permanent dust bowl like megadrought conditions lasting decades to a century that are predicted as a consequence of warming4 so far it has been unclear whether or not such megadroughts occurred in the southwestern us and if so with what regularity and intensity here we show that periods of aridity lasting centuries to millennia occurred in the southwestern us during mid pleistocene interglacials using molecular palaeotemperature proxies5 to reconstruct the mean annual temperature mat in mid pleistocene lacustrine sediment from the valles caldera new mexico we found that the driest conditions occurred during the warmest phases of interglacials when the mat was comparable to or higher than the modern mat a collapse of drought tolerant c4 plant communities during these warm dry intervals indicates a significant reduction in summer precipitation possibly in response to a poleward migration of the subtropical dry zone three mat cycles 2 c in amplitude occurred within marine isotope stage mis 11 and seem to correspond to the muted precessional cycles within this interglacial in comparison with mis 11 mis 13 experienced higher precessional cycle amplitudes larger variations in mat 4 6 c and a longer period of extended warmth suggesting that local insolation variations were important to interglacial climatic variability in the southwestern us comparison of the early mis 11 climate record with the holocene record shows many similarities and implies that in the absence of anthropogenic forcing the region should be entering a cooler and wetter phase

flow laws of multiphase rocks calculated from experimental data on the constituent phases abstract an attempt has been made to develop expressions for the flow laws of polyphase rocks in terms of the volume fractions and flow laws of their constituent phases the flow strengths predicted by the proposed model for granite diorite diabase and lherzolite are in good agreement with previously determined experimental values the study allows one to calculate to the first approximation the flow laws of a large number of rocks at geologic conditions based on the experimentally determined flow laws of a relatively small number of monomineralic aggregates

spatial heterogeneity of sources of branched tetraethers in shelf systems the geochemistry of tetraethers in the berau river delta kalimantan indonesia abstract the bulk organic matter composition total organic carbon toc content and 13ctoc and composition of isoprenoid and branched glycerol dialkyl glycerol tetraethers gdgt in surface sediments from 43 stations in the berau river delta east kalimantan indonesia including two coast shelf transects and stations within the river mouth were examined to reveal the spatial heterogeneity in these parameters in order to assess the impact of a tropical river loaded with suspended matter on the sedimentary organic matter in the shelf system the high resolution study showed that despite the extensive transport of eroded soil material by the river to the sea terrestrial organic matter and brgdgts are only deposited on a relatively small part of the shelf the concentrations of brgdgts are highest up to 120 g g 1 toc in sediments deposited in and close to the mouth of the berau river and their distribution indicates that they represent a mixture of soil derived and river in situ produced brgdgts crenarchaeol concentrations reach 700 g g 1 toc in sediments deposited on the outer shelf due to thaumarchaeotal production in shelf waters this results in a strong gradient 0 93 0 03 in the bit index with high values in the river mouth and low values on the shelf the decline in the bit index is caused by both decreasing concentrations of the brgdgts and increasing concentrations of crenarchaeol the bit index shows a highly significant but non linear relationship with 13ctoc on the shelf in the area not under the direct influence of the berau river cyclic brgdgts become relatively dominant most probably due to in situ production in the alkaline pore waters of the surface sediments the spatial heterogeneity of sources of brgdgts on the berau shelf complicates the use of brgdgts as temperature proxies application of the global soil calibration to sedimentary mixtures of brgdgts in the river influenced area of the shelf results in a severe underestimation of mean annual air temperature mat by 6 c this is due to the mixed origin of the brgdgts which are not only derived from soil erosion but likely also from riverine production as has been observed for other river systems comparison of the berau shelf other shelf systems indicates that in situ production of brgdgts in shelf sediments is a widespread phenomenon that is especially pronounced at water depths of ca 50 300 m it is hypothesized that this is so because benthic in situ production of heterotrophic brgdgt producing bacteria is fueled by the higher delivery of fresh organic matter to these sediments as the consequence of higher primary productivity in shelf waters and a decreased mineralization due to the relatively short settling times of particles on the shelf for palaeoclimatic studies of marine shelf sediments the application of brgdgts as proxies is severely complicated by the heterogeneity of sources of brgdgts comparison of the brgdgt composition of soils with those of shelf sediments may assist in deciding if sedimentary brgdgts are predominantly derived from soil erosion several methods to do so are discussed

characteristics and implications of isoprenoid and hydroxy tetraether lipids in hadal sediments of mariana and yap trenches abstract as one of the least explored regions on earth the hadal zone remains poorly understood in terms of sedimentary organic geochemistry this study examined the composition of isoprenoid glycerol dialkyl glycerol tetraethers iso gdgts and hydroxy gdgts oh gdgts in sediment cores with water depths ranging from 5058 to 10 911 m from the mariana and yap trenches the results showed a higher proportion of gdgt 0 25 73 mean 49 in the trench iso gdgts pool than those from shallower ocean counterparts 5000 m revealed a significant negative linear correlation with water depth tex 86 h r2 0 89 p tex 86 l r2 0 89 p

vertical distribution of isoprenoid gdgts in suspended particles from the east china sea shelf and implications for sedimentary tex86h records abstract the t e x 86 h or tex86 paleothermometer has been widely applied for reconstructing water temperature in marine settings particularly in marginal seas which often archive paleoclimate records with high temporal resolution yet debate remains regarding the water depth at which the t e x 86 h signal is imparted in these settings in this study east china sea ecs surface sediments and suspended particulate matter spm from different water depths 0 60 m were analyzed for lipid biomarkers to better constrain the depth to which the sedimentary t e x 86 h signal corresponds our data showed divergent vertical distributions between archaeal lipids and phytoplankton lipids the maximum concentration of core lipid isoprenoid glycerol dialkyl glycerol tetraethers core igdgts appeared in bottom waters 2 5 m above the sea floor at all sites whereas phytoplankton lipids showed highest abundance in surface waters 0 m consistent with the maximum core igdgts concentration in bottom waters the best correlation was observed between spm t e x 86 h values and 2 4 weeks averaged water temperatures from the bottom waters moreover the spm core igdgts content was higher in bottom waters than in surface sediments implying that in situ production rather than sediment resuspension leads to the maximum concentration of core igdgts in bottom waters by compiling published surface sediment data from water depths t e x 86 h with bottom water temperature bwt exceeds that with sea surface temperature sst therefore it is proposed that sedimentary t e x 86 h is a bwt proxy in the shallow ecs

branched gdgt signals in fluvial sediments of the danube river basin method comparison and longitudinal evolution abundances and distributional changes of branched glycerol dialkyl glycerol tetraethers brgdgts in fluvially influenced sediments are used in various paleoclimate studies to reconstruct variations in soil export continental air temperature and soil ph in corresponding river basins for accurate interpretation of these records it is important to understand the provenance and the evolution of biomarker signals as they move through the river system here we investigate the brgdgt composition of modern river sediments of the danube river the second largest river in europe brgdgt based mean annual air temperature and soil ph parallel the actual values of air temperature and soil ph from the upper to the lower basin showing that signals predominantly reflect local as opposed to basin wide environmental conditions furthermore data generated using the recently developed method with improved chromatography separating the 6 methyl isomers from the 5 methyl isomers was compared with that resulting from the conventional method we show that the temperatures and ph values reconstructed using the data obtained by improved chromatography best resemble the local environmental conditions throughout the danube river basin our results highlight the importance of in depth studies within river systems to better understand the provenance of biomarker signals in fluvially derived sedimentary archives

archaeal and bacterial glycerol dialkyl glycerol tetraethers in sediments from the eastern lau spreading center south pacific ocean abstract the compositions of glycerol dialkyl glycerol tetraethers gdgts in surface sediments and sediment cores from the eastern lau spreading center elsc south pacific ocean were determined isoprenoid gdgts isogdgts and branched gdgts brgdgts are present in all the samples with archaea and bacteria respectively as the sources of these membrane lipids greater concentrations of isogdgts 0 08 38 0 ng g dry weight dw than brgdgts 0 05 27 4 ng g dw indicate that archaea made larger contributions to the gdgt pool in the elsc sediments than bacteria the relative abundance of brgdgts and bit index the branched vs isoprenoid tetraether values are higher in samples taken from the seafloor in the vicinity of or close to hydrothermal vents than in samples taken distant from hydrothermal activity suggesting that brgdgts are likely produced in the elsc hydrothermal vents temperature estimates based on tex 86 tetraether index of tetraethers consisting of 86 carbon atoms appear to reflect local surface water temperatures despite potential in situ hydrothermal input of gdgts to the elsc sediments

application of bacterial glycerol dialkyl glycerol tetraethers gdgts to develop modern and past temperature estimates from new zealand lakes abstract branched isoalkyl glycerol dialkyl glycerol tetraethers gdgts of bacterial origin have been found in high abundance in both modern and glacial sediments of new zealand south island freshwater lakes covering a wide range of altitude 101 2000 m like isoprenoid gdgts of archaeal origin they provide excellent potential for temperature assessment for this study their distribution patterns mbt methylation ratio and cbt cyclisation ratio of branched gdgts have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary palaeo environmental interpretations mbt data from modern lake sediments correlate well with measured annual air temperature r2 0 74 enabling a regional calibration for reconstructing palaeotemperatures for fossil samples mbt derived palaeotemperatures for alpine lake calibrated against mean annual temperature were determined for the last glacial during an early cold phase between 29 000 and 26 000 years bp and for later less cold phases between 23 000 and 18 000 years bp compared with the modern temperature regime the mbt data indicate a decrease of ca 5 6 and 2 8 c respectively during this time modern and past mbt derived temperatures correlate with chironomid based temperature reconstructions in the area archaeal gdgts commonly used for the tex86 index are abundant in fossil sediments alpine lake but scarce in modern sediments hindering a new local calibration for this palaeotemperature proxy

reply to comment on venus nightside ionospheric troughs implications for evidence of lightning and volcanism by h a taylor jr j m grebowsky and p a cloutier

applicability and calibration of the tex86 paleothermometer in lakes abstract we have conducted a global survey of archaeal glycerol dialkyl glycerol tetraether gdgt lipids in lake sediments in order to develop the tex86 paleotemperature proxy for application in continental systems surface sediments of 46 globally distributed lakes were analyzed for gdgt but isoprenoid gdgt derived from aquatic crenarchaeota were only unambiguously detected in 20 of the 46 lakes analyzed aquatic crenarchaeotal gdgt were detected mainly in sediments from large lakes 4000 km2 and hydrothermal or volcanic lakes suggesting that in some mostly smaller lakes either aquatic crenarchaeota are present at low abundance resulting in sedimentary lipids below levels of detection or they are absent branched gdgt thought to be derived primarily from soil bacteria were identified in all lake sediments analyzed correlation of the tex86 in those lakes with sufficient amounts of putative crenarchaeotal gdgt with annual mean lake temperature is reasonably good r2 0 68 n 20 in order to reduce the influence of soil derived isoprenoid gdgt on the tex86 lake temperatures we have applied a filter based on relative soil derived inputs as determined by the bit branched and isoprenoid tetraether index which results in a calibration relationship with r2 0 86 n 12 and an estimated temperature error of 3 6 c our results suggest that the tex86 should be applied only in lakes with sufficient production of gdgt by aquatic crenarchaeota relative to isoprenoid gdgt derived from soil in the watershed or other aquatic sources

origin transport and deposition of leaf wax biomarkers in the amazon basin and the adjacent atlantic paleoenvironmental studies based on terrigenous biomarker proxies from sediment cores collected close to the mouth of large river systems rely on a proper understanding of the processes controlling origin transport and deposition of biomarkers here we contribute to the understanding of these processes by analyzing long chain n alkanes from the amazon river system we use the dd composition of long chain n alkanes from river bed sediments from the amazon river and its major tributaries as well as marine core top samples collected off northeastern south america as tracers for different source areas the d13c composition of the same compounds is used to differentiate between long chain n alkanes from modern forest vegetation and petrogenic organic matter our d13c results show depleted d13c values 33 to 36 in most samples indicating a modern forest source for most of the samples enriched values 31 to 33 are only found in a few samples poor in organic carbon indicating minor contributions from a fossil petrogenic source long chain n alkane dd analyses show more depleted values for the western tributaries the madeira and solimoes rivers 152 to 168 while n alkanes from the lowland tributaries the negro xingu and tocantins rivers 142 to 154 yield more enriched values the n alkane dd values thus reflect the mean annual isotopic composition of precipitation which is most deuterium depleted in the western amazon basin and more enriched in the eastern sector of the basin samples from the amazon estuary show a mixed long chain n alkane dd signal from both eastern lowland and western tributaries marine core top samples underlying the amazon freshwater plume yield dd values similar to those from the amazon estuary while core top samples from outside the plume showed more enriched values although the variability in the river bed data precludes quantitative assessment of relative contributions our results indicate that long chain n alkanes from the amazon estuary and plume represent an integrated signal of different regions of the onshore basin our results also imply that n alkanes are not extensively remineralized during transport and that the signal at the amazon estuary and plume includes refractory compounds derived from the western sector of the basin these findings will aid in the interpretation of plant wax based records of marine sediment cores collected from the adjacent ocean

the c 32 alkane 1 15 diol as a tracer for riverine input in coastal seas long chain alkyl diols are lipids that occur ubiquitously in marine sediments and are used as a proxy for sea surface temperature sst using the long chain diol index ldi and for upwelling intensity high nutrient conditions the distribution of 1 13 and 1 15 diols has been documented in open marine and lacustrine sediments and suspended particulate matter but rarely in coastal seas receiving a significant riverine and thus continental organic matter input here we studied the distribution of diols in four shelf seas with major river outflows the gulf of lion the kara sea the amazon shelf and the berau delta covering a wide range of climate conditions the relative abundance of the c32 1 15 diol is consistently higher close to the river mouth and particularly in the suspended particulate matter of the rivers suggesting a terrigenous source this is supported by statistical analysis which points out a significant positive correlation between the c32 1 15 diol and the branched and isoprenoid tetraether index a proxy reflecting soil and riverine input in marine environments however the c32 1 15 diol was not detected in soils and is unlikely to be derived from vegetation suggesting that the c32 1 15 diol is mainly produced in rivers this agrees with the observation that it is a dominant diol in most cultivated freshwater eustigmatophyte algae we therefore suggest that the relative abundance of the c32 1 15 diol can potentially be used as a proxy for riverine organic matter input in shelf seas our results also show that long chain alkyl diols delivered by rivers can substantially affect ldi reconstructed ssts in coastal regions close to river mouths

change in provenance of branched glycerol dialkyl glycerol tetraethers over the holocene in the baltic sea and its impact on continental climate reconstruction abstract the baltic sea is an enclosed basin that experienced a number of different salinity phases during the holocene corresponding to the establishment of a connection with the north sea branched glycerol dialkyl glycerol tetraethers brgdgts in surface sediments and holocene sedimentary successions from the gotland and arkona basins were analyzed to examine their potential applicability as indicators for soil organic matter input as well as their suitability for paleoclimate reconstructions our results show a marked change in brgdgt distributions and the branched and isoprenoid tetraether bit index the transition of the ancylus lake fresh to the littorina sea brackish phase is revealed by a large drop in the bit index and an increase in the mbt 5me which reveals a large shift in provenance of the sedimentary brgdgts during the lake phase brgdgts are presumed to be primarily produced by in situ production in the water column during the brackish phase in situ brgdgt production in the alkaline pore waters of the surface sediments as revealed by their high degree of cyclization was predominant although there was evidence of occasional input of soil derived brgdgts the predominant aquatic autochthonous production of brgdgts does not allow the use of brgdgts for continental air temperature reconstructions but they can be used for bottom water and lake temperature reconstructions during some intervals the results from this study demonstrate that geological changes and concomittant salinity variations can be revealed by the provenance of brgdgts

characterization of transport and deposition of terrestrial organic matter in the southern north sea using the bit index we have applied a recently introduced proxy the bit branched and isoprenoid tetraether index to determine terrestrial organic matter tom transport from the rivers rhine and meuse and their tributaries to the southern north sea this index is based on crenarchaeol an isoprenoidal glycerol dialkyl glycerol tetraether gdgt predominantly derived from aquatic crenarchaeota and branched gdgts produced by soil bacteria up to 1 6 ng l 1 of branched gdgts were measured in seawater demonstrating the presence of tom in the southern north sea bit indices were inversely correlated with salinity indicating that this tom was recently supplied by rivers the substantial amount of branched gdgts 35 ng l 1 detected in river water and the high branched gdgt concentration measured in the water of a swiss peat bog 5 900 ng l 1 suggest fluvial transport of branched gdgts from peats and soils to the oceans the high crenarchaeol concentration measured in river water 4 4 ng l 1 was probably derived from crenarchaeota living in rivers and organic material from soil and peat the bit index 13c value and c n ratio of surface sediments deposited in the southern north sea were compared to determine tom deposition bit index 0 07 to 0 26 and d13c 220 6 to 222 9 both showed substantial small scale differences in tom deposition in the southern north sea but this pattern was not obvious from the c n ratios a good correlation was found between 13c and branched gdgt concentrations indicating that the absolute gdgt concentrations give additional information to the bit index

sources and distributions of branched and isoprenoid tetraether lipids on the amazon shelf and fan implications for the use of gdgt based proxies in marine sediments branched glycerol dialkyl glycerol tetraethers brgdgts in river fan sediments have been used successfully to reconstruct mean annual air temperature maat and soil ph of the congo river drainage basin however in a previous study of amazon deep sea fan sediments the reconstructed maats were ca 10 c colder than the actual maat of the amazon basin in this study we investigated this apparent offset by comparing the concentrations and distributions of brgdgts in amazon river suspended particulate matter spm and sediments to those in marine spm and surface sediments the riverine brgdgt input was evident from the elevated brgdgt concentrations in marine spm and surface sediments close to the river mouth the distributions of brgdgts in marine spm and sediments varied widely but generally showed a higher relative abundance of methylated and cyclic brgdgts than those in the river since this difference in brgdgt distribution was also found in intact polar lipid ipl derived brgdgts which were more recently produced the change in the marine brgdgt distribution was most likely due to marine in situ production consequently the maats calculated based on the methylation of branched tetraethers mbt and the cyclisation of branched tetraethers cbt were lower and the cbt derived ph values were higher than those of the amazon basin however spm and sediments from stations close to the river mouth still showed mbt cbt values that were similar to those of the river therefore we recommend caution when applying the mbt cbt proxy it should only be used in sediment cores that were under high river influence the influence of riverine derived isoprenoid gdgt isogdgt on the isogdgt based tex86 temperature proxy was also examined in marine spm and sediments an input of riverine isogdgts from the amazon river was apparent but its influence on the marine tex86 was minor since the tex86 of spm in the amazon river was similar to that in the marine spm and sediments

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

organic matter distribution in the modern sediments of the pearl river estuary we determined biomarker concentrations and distributions for surface sediments from 54 sites in the pearl river estuary china we focus on a suite of four biomarker based indicators for relative terrestrial to marine organic matter om source the branched isoprenoid tetraether bit index the ratio of high low molecular weight n alcohols c26 34 c16 18 c26 34 an analogous ratio for n fatty acids and the c29 steroids c29 steroids brassicasterol ratio all four exhibit the same terrestrial to marine transition seen in previous bulk 13c studies but with an abrupt decrease in the relative terrestrial contribution across the delta front to pro delta transition concentrations of terrestrially derived biomarkers show no systematic decrease across the transition instead the decrease in the proportion of terrestrial om is due to a decrease in the sedimentation rate and associated terrestrial om burial across the delta toe this suggests that diagenetic controls on the fate of terrestrial om such as increased biodegradation where sedimentation rate is low are subordinate to sedimentological processes biomarker derived temperature values are cooler than expected for the lower pearl river catchment suggesting that the dominant component of the terrestrial om is derived from the cooler upland regions of the catchment the dominance of input from more distal terrain with greater topographic relief is evidence for the importance of geomorphological control on terrigenous om transport collectively the results demonstrate the importance of sedimentological processes in the supply deposition and transport of terrestrial om

distribution of branched gdgts in surface sediments from the colville river alaska implications for the mbt cbt paleothermometer in arctic marine sediments significant climate fluctuations in the arctic over the recent past and additional predicted future temperature changes highlight the need for high resolution arctic paleoclimate records arctic coastal environments supplied with terrigenous sediment from arctic rivers have the potential to provide annual to subdecadal resolution records of climate variability over the last few millennia a potential tool for paleotemperature reconstructions in these marine sediments is the revised methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy based on branched glycerol dialkyl glycerol tetraethers brgdgts in this study we examine the source of brgdgts in the colville river alaska and the adjacent simpson lagoon and reconstruct temperatures from simpson lagoon sediments to evaluate the applicability of this proxy in arctic estuarine environments the colville catchment soils fluvial sediments and estuarine sediments contain statistically similar brgdgt distributions indicating that the brgdgts throughout the system are soil derived with little alteration from in situ brgdgt production in the river or coastal waters temperatures reconstructed from the mbt cbt indices for surface samples show good agreement with regional summer june through september temperatures suggesting a seasonal bias in arctic temperature reconstructions from the colville system in addition we reconstruct paleotemperatures from an estuarine sediment core that spans the last 75 years revealing an overall warming trend in the twentieth century that is consistent with trends observed in regional instrumental records these results support the application of this brgdgt based paleotemperature proxy for subdecadal scale summer temperature reconstructions in arctic estuaries containing organic material derived from sediment laden episodic rivers

tracing soil organic carbon in the lower amazon river and its tributaries using gdgt distributions and bulk organic matter properties abstract in order to trace the transport of soil organic carbon oc in the lower amazon basin we investigated the distributions of crenarchaeol and branched glycerol dialkyl glycerol tetraethers gdgts by analyzing riverbed sediments and river suspended particulate matter spm collected in the solimoes amazon river mainstem and its tributaries the branched and isoprenoid tetraether bit index a proxy for river transported soil oc into the ocean was determined from the distributions of these gdgts the gdgt derived parameters were compared with other bulk geochemical data i e c n ratio and stable carbon isotopic composition the gdgt derived and bulk geochemical data indicate that riverine spm and riverbed sediments in the lower amazon river and its tributaries are a mixture of c3 plant derived soil oc and aquatic derived oc the branched gdgts in the spm and riverbed sediments did not predominantly originate from the high andes soils 2500 m in altitude as was suggested previously however further constraint on the soil source area of branched gdgts was hampered due to the deficiency of soil data from the lower montane forest areas in the andes our study also revealed seasonal and interannual variation in gdgt composition as well as soil oc discharge which was closely related to the hydrological cycle by way of a simple binary mixing model using the flux weighted bit values at obidos the last gauging station in the amazon river we estimated that 70 80 of the poc pool in the river was derived of soil oc however care should be taken to use the bit index since it showed a non conservative behaviour along the river continuum due to the aquatic production of crenarchaeol further investigation using a continuous sampling strategy following the full hydrological cycle is required to fully understand how soil derived gdgt signals are transformed in large tropical river systems through their transport pathway to the ocean

drastic changes in the distribution of branched tetraether lipids in suspended matter and sediments from the yenisei river and kara sea siberia implications for the use of brgdgt based proxies in coastal marine sediments abstract the distribution of branched glycerol dialkyl glycerol tetraethers brgdgts in soils has been shown to correlate with ph and mean annual air temperature because of this dependence brgdgts have found an application as palaeoclimate proxies in coastal marine sediments based on the assumption that their distribution is not altered during the transport from soils to marine systems by rivers to study the processes acting on the brgdgt distributions we analysed the full suite of brgdgts including the recently described 6 me brgdgts in both the suspended particulate matter spm of the siberian yenisei river and the spm and sediments of its outflow in the kara sea the brgdgt distribution in the spm of the yenisei river was fairly constant and characterized by high abundances of the 6 me brgdgts reflecting their production at the neutral ph of the river water however the brgdgt distribution showed marked shifts in the marine system firstly in the yenisei river mouth the fractional abundance of the 6 me brgdgts decreases sharply the brgdgt signature in the yenisei river mouth possibly reflects brgdgts delivered during the spring floods that may carry a different distribution also coastal cliffs were shown to contain brgdgts and to influence especially those sites without major river inputs e g khalmyer bay further removed from the river mouth in situ production of brgdgts in the marine system influences the distribution however also the fractional abundance of the tetramethylated brgdgt ia increases resulting in a distribution that is distinct from in situ produced signals at similar latitudes svalbard we suggest that this shift may be caused by preferential degradation of labile riverine in situ produced brgdgts and the subsequent enrichment in less labile soil material the offshore distribution indeed agrees with the brgdgt distribution encountered in a lowland peat this implies that the offshore kara sea sediments possibly carry a soil dominated signal indicating potential for palaeoclimate reconstructions at this site both in the river system and coastal cliffs brgdgts were much more abundant than crenarchaeol an archaeal isoprenoid gdgt resulting in high 0 93 branched and isoprenoid tetraether bit index values moving downstream in the marine sediments a decrease in brgdgt concentrations coeval with an increase in crenarchaeol resulted in decreasing bit index values this decrease correlates with changes in bulk proxies for terrigenous input 13corg c n confirming the use of the bit index to trace the delivery of river transported and coastal cliff derived terrigenous organic matter

sediment production and delivery in the amazon river basin quantified by in situ produced cosmogenic nuclides and recent river loads we use cosmogenic nuclide derived denudation rates from in situ produced 10 be in river sediment to determine sediment production rates for the central amazon river and its major tributaries recent developments have shown that this method allows calculating denudation rates in large depositional basins despite intermediate sediment storage with the result that fluxes of the sediment producing hinterland can now be linked to those discharged at the basins outlet in rivers of the central amazonian plain sediment of finer grain sizes 125 500 m yields a weighted cosmogenic nuclide derived denudation rate of 0 24 0 02 mm yr that is comparable to the integrated rate of all main andean draining rivers 0 37 0 06 mm yr which are the beni napo mamore ucayali and maranon rivers coarser grained sediment 500 m of central amazonian rivers is indicative of a source from the tectonically stable cratonic headwaters of the guyana and brazilian shields for which the denudation rate is 0 01 0 02 mm yr respective sediment loads can be calculated by converting these cosmogenic nuclide derived rates using their sediment producing areas for the amazon river at obidos a sediment production rate of 610 mt yr results non andean source areas contribute only 45 mt yr a comparison with published modern sediment fluxes shows similarities within a factor of 2 with an average gauging derived sediment load of 1000 mt yr at obidos for example we attribute this similar trend in cosmogenic versus modern sediment loads first to the absence of long term deposition within the basin and second to the buffering capability of the large amazon floodplain the buffering capability dampens short term high amplitude fluctuations climatic variability in source areas and anthropogenic soil erosion by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin

microfabrics in carbonate mylonites along a large scale shear zone helvetic alps abstract carbonate mylonites with varying proportions of second phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the morcles nappe helvetic nappes switzerland variations of temperature stress and strain rate changes in chemistry of solid and fluid phases and differing degrees of strain localization and annealing were tracked by measuring the shapes mean sizes and size distributions of both matrix and second phase grains as well as crystal preferred orientation cpo of the matrix field structures suggest that strain rate was constant along the fault the mean and distribution of the calcite grain sizes were affected most profoundly by temperature increased temperature presumably accompanied by decreased stress correlated with larger mean sizes and wider size distributions at a given location the matrix grains in mylonites with more second phase particles are on average smaller have narrower size distributions and have more elongate shapes for example mylonites with 50 vol of second phases have matrix grain sizes half that of pure mylonites changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly temporal variations in conditions such as exhumation induced cooling apparently provoke changes in temperature stress and strain rate along the nappe these changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50 the matrix cpo strengthens with increasing temperature or strain but weakens and rotates with increasing second phase content these fabric changes suggest differing rates of grain growth grain size reduction and development of cpo owing to variations in the deformation conditions and perhaps mechanisms to interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric and in particular second phase minerals

microbial lipid records of highly alkaline deposits and enhanced aridity associated with significant uplift of the tibetan plateau in the late miocene saline alkaline sediments and soils are widespread in arid and semiarid regions but their occurrence in ancient dry periods remains unknown due to the lack of a suitable proxy on the basis of investigations of modern chinese soils with a wide ph range of 3 5 9 1 we suggest that the microbial lipid ratio r i b i e the abundance ratio of archaeal isoprenoid gdgts glycerol dialkyl glycerol tetraethers to bacterial branched gdgts indicates the presence of drought induced alkaline deposits in terrestrial settings the r i b is invariant in modern soils with ph 600 mm but it increases sharply at higher ph values and lower mean annual precipitation i b ratio in a fluviolacustrine section in the zhada basin of the southwestern tibetan plateau covering the time period 9 2 2 6 m y ago the r i b ratio remains relatively stable in most intervals but exhibits maxima in some horizons indicative of the occurrence of severe drought and alkaline deposits in the basin catchment these occur in fluvial sediments deposited 9 m y ago a critical time with respect to the intensification of the east asian and indian monsoons and the significant uplift of the plateau that has previously been associated with enhanced aridity in central asia

pronounced subsurface cooling of north atlantic waters off northwest africa during dansgaard oeschger interstadials millennial scale atlantic meridional overturning circulation amoc variability has often been invoked to explain the dansgaard oeschger do events however the underlying causes responsible for millennial scale amoc variability are still debated high resolution u37k and tex86h temperature records for the last 50 kyr obtained from the tropical northeast ne atlantic core geob7926 2 20 13 n 18 27 w 2500 m water depth show that distinctive do type subsurface i e below the mixed layer 20 m water depth temperature oscillations occurred with amplitudes of up to 8 c in the tropical ne atlantic during marine isotope stage 3 mis3 statistical analyses reveal a positive relationship between the reconstructed substantial cooling of subsurface waters and prominent surface warming over greenland during do interstadials general circulation model gcm simulations without external freshwater forcing the mechanism often invoked in explaining do events demonstrate similar anti phase correlations between amoc and pronounced ne atlantic subsurface temperatures under glacial climate conditions together with our paleoproxy dataset this suggests that the vertical temperature structure and associated changes in amoc were key elements governing do events during the last glacial

branched glycerol dialkyl glycerol tetraethers and crenarchaeol record post glacial sea level rise and shift in source of terrigenous brgdgts in the kara sea arctic ocean this study evaluates the glycerol dialkyl glycerol tetraether gdgt distribution and provenance in sediments spanning a minimum of 13 3 ka from the st anna trough northern kara sea the site has experienced extensive fluctuation in the delivery of river derived organic matter om caused by a eustatic change in sea level this is in line with the record of the concentration of the isoprenoid gdgt crenarchaeol produced by marine thaumarchaota which was low at the bottom of the core increasing gradually in the most shallow unit the concentration of branched br gdgts showed an opposite trend and a marked shift in distribution the deepest sediments 10 ka with a distribution currently encountered in surface sediments in front of the yenisei river are characterized by terrigenous brgdgts whereas the distribution in the shallowest unit 10 ka is strongly influenced by marine in situ brgdgts during the shift from terrigenous to marine sourced brgdgts there was one horizon where a pronounced shift in the brgdgt distribution was observed and the brgdgt concentration significantly decreased as the brgdgts delivered to the current kara sea system are derived from several sources we postulate that a temporary change in the relative importance of the brgdgt sources happened during this interval both in situ production and changing brgdgt provenance have implications for paleoclimate reconstruction using brgdgts in situ production of marine brgdgts results in a higher reconstructed ph however these in situ produced brgdgts did not influence the reconstructed mean annual air temperature mat when the matmrs calibration was used changes in the relative contribution of brgdgt sub pools were shown however to influence both soil ph reconstruction and mat reconstruction

disentangling marine soil and plant organic carbon contributions to continental margin sediments a multi proxy approach in a 20 000 year sediment record from the congo deep sea fan abstract a 20 kyr long sediment sequence from the congo deep sea fan core geob 6518 1 one of the world s largest deep sea river fans has been analysed for bulk and molecular proxies in order to reconstruct the marine soil and plant organic carbon oc contributions to these sediments since the last glacial maximum the bulk proxies applied c n ratio and 13 c org ranged from 10 to 12 5 and from 24 5 to 21 vpdb respectively as molecular proxies concentrations of marine derived alkenones and terrestrial derived odd numbered n alkanes were used which varied between 0 2 and 4 g g dry weight sediment in addition the branched vs isoprenoid tetraether bit index a proxy for soil organic matter input was used which varied from 0 3 to 0 5 in this core application of binary mixing models based on the different individual proxies showed estimates for terrestrial oc input varying by up to 50 due to the heterogeneous nature of the oc application of a three end member mixing model using the 13 c org content the c n ratio and the bit index enabled the distinction of soil and plant organic matter as separate contributors to the sedimentary oc pool the results show that marine oc accounts for 20 to 40 of the total oc present in the deep sea fan sediments over the last 20 kyr and that soil oc accounts for about half 45 on average of the oc present this suggests that soil oc represents the majority of the terrestrial oc delivered to the fan sediments accumulation rates of the plant and soil oc fractions over the last 20 kyr varied by a factor of up to 5 and are strongly related to sediment accumulation rates they showed an increase starting at ca 17 kyr bp a decline during the younger dryas peak values during the early holocene and lower values in the late holocene this pattern matches with reconstructions of past central african humidity and congo river discharge from the same core and revealed that central african precipitation patterns exert a dominant control on terrestrial oc deposition in the congo deep sea fan marine oc accumulation rates are only weakly related to sediment accumulation rates and vary only little over time compared to the terrigenous fractions these variations are likely a result of enhanced preservation during times of higher sedimentation rates and of relative small fluctuations in primary production due to wind driven upwelling

assessment of the sources of sedimentary organic matter in the bohai sea and the northern yellow sea using biomarker proxies abstract to evaluate the applicability of source proxies and to assess the sources of sedimentary organic matter in the bohai sea bs and the northern yellow sea nys we analyzed total organic carbon toc total nitrogen tn 13c of toc n alkanes phytoplankton biomarkers and glycerol dialkyl glycerol tetraethers gdgts including branched gdgts brgdgts in 60 surface sediment samples covering the bs and the nys spatial distribution comparison and principal component analysis indicate that with the exception of brgdgts terrestrial biomarkers have different spatial distribution pattern from marine biomarkers suggesting that the sources control the distributions of these biomarkers in spite of hydrodynamic forcing significantly positive correlation r2 0 5 between toc normalized brgdgts content and toc normalized crenarchaeol content suggested in situ production of brgdgts in the bs and the nys the 13c values tmbr terrestrial and marine biomarker ratio c27 c29 c31 n alkanes c27 c29 c31 n alkanes brassicasterol dinosterol alkenones and bit branched isoprenoid tetratether index proxy indicated high terrestrial organic matter tom input near the huanghe river estuary while toc ton did not reveal similar distribution pattern quantitative estimates of tom using a binary model revealed much higher tom percentage from 13c avg 58 and tmbr avg 31 than from bit avg 7 4 our results suggest that owing to significant in situ production of brgdgts the bit is not a good proxy for indicating soil om contribution in marine sediments from the bs and the nys

suspended sediments of the modern amazon and orinoco rivers abstract the amazon and orinoco rivers are massive transcontinental conveyance systems for suspended sediment they derive about 90 of their sediment from the andes that support their western headwaters transport it for thousands of kilometers across the breadth of the continent and deposit it in the coastal zones of the atlantic at their points of maximum suspended sediment discharge the amazon transports an average of 1100 1300 10 6 tons per year and the orinoco transports about 150 10 6 tons per year relations of sediment discharge to water discharge are complicated by unusual patterns of seasonal storage and remobilization increased storage and reduced transport of sediment in the middle orinoco during periods of peak water discharge and storage of suspended sediment in the lower amazon during rising discharge and resuspension during falling discharge spatial distributions of suspended sediment in cross sections of both rivers are typically heterogeneous not only in the vertical sense but also in the lateral the cross channel mixing of tributary inputs into the mainstem waters is a slow process that requires several hundred kilometers of downriver transport to complete considerable fine grained sediment is exchanged between rivers and floodplains by the combination of overbank deposition and bank erosion

effect of varying enstatite content on the deformation behavior of fine grained synthetic peridotite under wet conditions the effect of varying enstatite content on the deformation behavior of synthetic fine grained 1 to 2 m forsterite enstatite rock with 0 5 wt added water was investigated at temperatures of 900 to 1000 c strain rates between 10 7 and 10 5 s 1 and a confining pressure of 600 mpa the samples exhibited approached steady state flow at stresses 60 mpa the results show that at constant strain rate increasing enstatite content is associated with a sharp decrease in flow strength in the range 0 2 5 vol enstatite with little further change up to 20 vol the observed power law n value of 1 7 and microstructures are similar to those obtained in previous work on material with 2 5 wt enstatite and are consistent with a water enhanced grain boundary sliding gbs dominated deformation mechanism significantly a negative correlation was found between grain size and enstatite content indicating that enstatite content played a role in controlling the grain size of the starting materials moreover a high correlation between measured flow strength and grain size was found consistent with a grain size exponent of 3 in a conventional grain size sensitive flow equation a water enhanced deformation mechanism involving gbs accommodated probably by grain boundary diffusion and or dislocation activity is therefore implied with the effect of enstatite content on flow strength being an indirect physical effect caused by grain size control other effects of second phase content such as weakening caused by interphase boundary diffusion and or migration processes seem to be unimportant under the conditions investigated

distributional variations in marine crenarchaeotal membrane lipids a new tool for reconstructing ancient sea water temperatures it has recently been shown that membrane lipids of marine crenarchaeota a ubiquitous and abundant component of plankton occur in relatively high concentrations in recent and ancient sediments in this study we investigated the environmental controls on the relative distribution of these lipids in surface sediments we especially focussed on temperature as it is known from the thermophilic genetic relatives of marine crenarchaetoa that the composition of their membrane strongly depends on growth temperature indeed a significant linear correlation r2 0 92 is found between the number of cyclopentane rings in sedimentary membrane lipids derived from marine crenarchaeota and the annual mean sea surface temperatures this suggests that the mechanism of physical adaptation of their membrane compositions to temperature is identical to that of their thermophilic relatives in turn archaeal lipid distributions in sediments may thus allow the reconstruction of sea water temperatures of ancient marine environments

comparison of instrumental and gdgt based estimates of sea surface and air temperatures from the skagerrak sea surface temperatures ssts and annual mean air temperatures mats are estimated for the last 200 years from glycerol dialkyl glycerol tetraethers gdgts proxies in a marine sediment core from the skagerrak off southern norway the reconstructed values compare well with annual ssts and summer air temperatures obtained from composite regional instrumental records the results provide further confidence in the application of proxies based on gdgts to estimate past temperatures

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

currents on the shelf of north eastern south america from the continental shelf region extending 400 km north of the mouth of the amazon river current meter data data on salinity temperature and suspended material were analyzed to study mean and tidal currents based on a grid point system the mean circulation patterns along the shelf are shown and the temporal variations in the tidal currents are depicted for the region at 2 h intervals maximum and minimum current speeds were studied for information on the spatial structure of the flow and on the along shelf and across shelf components

signatures of tetraether lipids reveal anthropogenic overprinting of natural organic matter in sediments of the thames estuary uk intertidal foreshore sediments from a 110 km stretch of the thames estuary were analysed for glycerol dialkyl glycerol tetraethers gdgts to track soil organic matter om input and evaluate the impact of coastal urbanisation on their distribution concentration of branched br gdgts ranged from 1 to 15 g g organic carbon oc and crenarchaeol ranged from 0 6 to 19 g g oc an overall decrease in brgdgts was observed from the inner thames brentford to the outer thames isle of grain suggesting a drop in soil om input towards the sea in contrast crenarchaeol concentration was highest around east london rather than towards the open sea such elevated crenarchaeol concentration occurred in the section of the river most influenced by anthropogenic pollution such as discharge points for london s major sewage treatment plants docks and power plants the non systematic spatial distribution of crenarchaeol was also reflected in the branched isoprenoid tetraether bit index the highest bit values occurred upstream and in close proximity to salt marshes 0 8 1 whereas the lowest values 0 3 0 5 were towards the sea however unusually low values 0 4 were observed in the river section that had high crenarchaeol concentration in contrast bulk 13c values were insensitive to london s anthropogenic influence this suggests that the natural systematic decrease in bit index in the estuary is overprinted by london s anthropogenic activity between deptford creek and tilbury we therefore advise caution when interpreting the bit index for sediments in close proximity to megacities discharging industrial and municipal waste that can become incorporated into the near surface sedimentary record

significantly warmer arctic surface temperatures during the pliocene indicated by multiple independent proxies temperatures in the arctic have increased by an astounding 1 c in response to anthropogenic forcing over the past 20 years and are expected to rise further in the coming decades the pliocene 2 6 5 3 ma is of particular interest as an analog for future warming because global temperatures were signifi cantly warmer than today for a sustained period of time with continental confi gurations similar to present here we estimate mean annual temperature mat based upon three independent proxies from an early pliocene peat deposit in the canadian high arctic our proxies including oxygen isotopes and annual ring widths mat 0 5 1 9 c coexistence of paleovegetation mat 0 4 4 1 c and bacterial tetraether composition in paleosols mat 0 6 5 0 c yield estimates that are statistically indistinguishable the consensus among these proxies suggests that arctic temperatures were 19 c warmer during the pliocene than at present while atmospheric co 2 concentrations were 390 ppmv these elevated arctic pliocene temperatures result in a greatly reduced and asymmetrical latitudinal temperature gradient that is probably the result of increased poleward heat transport and decreased albedo these results indicate that arctic temperatures may be exceedingly sensitive to anthropogenic co 2 emissions

source settling and degradation of branched glycerol dialkyl glycerol tetraethers in the marine water column abstract branched glycerol dialkyl glycerol tetraethers branched gdgts are commonly found in distal marine sediments however their presence in the water column source and delivery process are not fully understood in this study we examined seasonal and depth variation in the flux of branched gdgts in sinking particles and underlying sediment at 39 n 147 e in the mid latitude nw pacific from november 1997 to august 1999 branched gdgts showed synchronous variation in their sinking flux at different depths and the variation was similar to that of lithogenic material of eolian dust origin their degrees of cyclization and methylation were nearly constant and bear some resemblance to those of alkaline soils this suggests that westerly winds transport branched gdgts to the study site via the atmosphere from continental asia the sinking flux of branched gdgts was higher in 1999 than in 1998 presumably reflecting changes in the migration path of asian dust in response to the el nino southern oscillation synchronous variation in branched gdgt concentrations at different depths implies rapid vertical transport of branched gdgts to deep water with a sinking velocity exceeding 260 m d 1 the sinking flux of the branched gdgts decreased with increasing depth but the rate of decrease was much smaller than those of other compounds the preservation efficiency of branched gdgts was 3 5 6 4 of surface inputs at the water sediment interface which is much higher than those of isoprenoid gdgts 1 0 1 3 and other compounds the branched and isoprenoid tetraether bit index values were extremely low i e