formal definition and dating of the gssp global stratotype section and point for the base of the holocene using the greenland ngrip ice core and selected auxiliary records the greenland ice core from northgrip ngrip contains a proxy climate record across the pleistocene holocene boundary of unprecedented clarity and resolution analysis of an array of physical and chemical parameters within the ice enables the base of the holocene as reflected in the first signs of climatic warming at the end of the younger dryas greenland stadial 1 cold phase to be located with a high degree of precision this climatic event is most clearly reflected in an abrupt shift in deuterium excess values accompanied by more gradual changes in d 18 o dust concentration a range of chemical species and annual layer thickness a timescale based on multi parameter annual layer counting provides an age of 11 700 calendar yr b2 k before ad 2000 for the base of the holocene with a maximum counting error of 99 yr a proposal that an archived core from this unique sequence should constitute the global stratotype section and point gssp for the base of the holocene series epoch quaternary system period has been ratified by the international union of geological sciences five auxiliary stratotypes for the pleistocene holocene boundary have also been recognised copyright 2008 john wiley sons ltd

multi proxy evidence of holocene climate variability in volhynia upland se poland recorded in spring fed fen deposits from the komarow site radiocarbon dated spring fed fen deposits from the komarow site volhynia upland se poland with its multi proxy data macrofossils molluscs geochemistry pollen stable isotopes of oxygen and c

sulfur record of rising and falling marine oxygen and sulfate levels during the lomagundi event carbonates from approximately 2 3 2 1 billion years ago show markedly positive 13c values commonly reaching and sometimes exceeding 10 traditional interpretation of these positive 13c values favors greatly enhanced organic carbon burial on a global scale although other researchers have invoked widespread methanogenesis within the sediments to resolve between these competing models and more generally among the mechanisms behind earth s most dramatic carbon isotope event we obtained coupled stable isotope data for carbonate carbon and carbonate associated sulfate cas cas from the lomagundi interval shows a narrow range of 34s values and concentrations much like those of phanerozoic and modern marine carbonate rocks the 34s values are a close match to those of coeval sulfate evaporites and likely reflect seawater composition these observations are inconsistent with the idea of diagenetic carbonate formation in the methanic zone toward the end of the carbon isotope excursion there is an increase in the 34s values of cas we propose that these trends in c and s isotope values track the isotopic evolution of seawater sulfate and reflect an increase in pyrite burial and a crash in the marine sulfate reservoir during ocean deoxygenation in the waning stages of the positive carbon isotope excursion

a study of oxygen isotopic fractionation during bio induced calcite precipitation in eutrophic baldeggersee switzerland in order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences we undertook an extensive one year study march 1995 to february 1996 of water column chemistry and daily sediment trap material from a small lake in central switzerland comparisons between calculated equilibrium isotope values using the fractionation equation of friedman and o neil 1977 and measured oxygen isotope ratios of calcite in the sediment traps reveal that oxygen isotopic values of autochthonous calcite 18o are in isotopic equilibrium with ambient water during most of the spring and summer when the majority of the calcite precipitates in contrast small amounts of calcite precipitated in early spring and again in late autumn are isotopically depleted in 18o relative to the calculated equilibrium values by as much as 0 8 this seasonally occurring apparent isotopic nonequilibrium is associated with times of high phosphorous concentrations elevated ph 8 6 and increased co32 50 mol l in the surface waters the resulting weighted average 18o value for the studied period is 9 6 compared with a calculated equilibrium 18o value of 9 4 these data convincingly demonstrate that 18o of calcite are for the most part a very reliable proxy for temperature and 18o of the water

calibration of the calcite water oxygen isotope geothermometer at devils hole nevada a natural laboratory abstract the 18 o of ground water 13 54 0 05 and inorganically precipitated holocene vein calcite 14 56 0 03 from devils hole cave 2 in southcentral nevada yield an oxygen isotopic fractionation factor between calcite and water at 33 7 c of 1 02849 0 00013 1000 ln calcite water 28 09 0 13 using the commonly accepted value of calcite water t of 0 00020 k 1 this corresponds to a 1000 ln calcite water value at 25 c of 29 80 which differs substantially from the current accepted value of 28 3 use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in devils hole that is 8 c lower than the measured ground water temperature alternatively previously published fractionation factors would yield a 18 o of water from which the calcite precipitated that is too negative by 1 5 using a temperature of 33 7 c several lines of evidence indicate that the geochemical environment of devils hole has been remarkably constant for at least 10 ka accordingly a re evaluation of calcite water oxygen isotopic fractionation factor may be in order assuming the devils hole oxygen isotopic value of calcite water represents thermodynamic equilibrium many marine carbonates are precipitated with a 18 o value that is too low apparently due to a kinetic isotopic fractionation that preferentially enriches 16 o in the solid carbonate over 18 o feigning oxygen isotopic equilibrium

recognition of 3850 ma water lain sediments in west greenland and their significance for the early archaean earth a layered body of amphibolite banded iron formation bif and ultramafic rocks from the island of akilia southern west greenland is cut by a quartz dioritic sheet from which shrimp zircon 206pb 207pb weighted mean ages of 3865 11 ma and 3840 8 ma 2 sigma can be calculated by different approaches three other methods of assessing the zircon data yield ages of 3830 ma the bifs are interpreted as water lain sediments which with a minimum age of approximately 3850 ma are the oldest sediments yet documented these rocks provide proof that by approximately 3850 ma 1 there was a hydrosphere supporting the chemical sedimentation of bif and that not all water was stored in hydrous minerals and 2 that conditions satisfying the stability of liquid water imply surface temperatures were similar to present carbon isotope data of graphitic microdomains in apatite from the akilia island bif are consistent with a bio organic origin mojzsis et al 1996 extending the record of life on earth to 3850 ma life and surface water by approximately 3850 ma provide constraints on either the energetics or termination of the late meteoritic bombardment event suggested from the lunar cratering record on earth

an ocean floor carbonaceous sedimentary sequence in the 3 2 ga dixon island formation coastal pilbara terrane western australia abstract the dixon island formation of the pilbara terrane western australia extends from cleaverville beach to the dixon island coast and is the only example worldwide of a coastal outcrop of a 3 2 3 1 ga low grade greenstone belt the dixon island formation was situated in an immature island arc setting and comprises siliceous carbonaceous deep water sediments that contain evidence for hydrothermal and microbial activity the extensive outcrop along the coastline makes it possible to examine in detail the characteristics of mesoarchean sedimentation in a hydrothermal environment this study focuses on a continuously exposed carbonaceous black chert succession in the central part of the northern coastline outcrop on dixon island at this site a 20 m thick carbonaceous black chert sequence conformably overlies basement rocks of highly altered komatiite rhyolite tuffs the black chert sequence formed well bedded black chert with carbonaceous peloidal matter and fragmented grains and the sequence is homogeneous and finely laminated in this sequence evidence of low temperature hydrothermal fluid sediments and alteration stractures are well preserved in the lowermost section indicating that high levels of hydrothermal activity occurred on the ocean floor during deposition in particular swarms of black chert veins provide evidence of post volcanic hydrothermal activity that released organic matter and silica to the ocean the carbonaceous peloidal textures and 13 c org values of sediments located just above the basement which hosts the vein swarms suggest that the veins were the conduits for hydrothermal fluid which contained organic rich silica material and that flowed onto the seafloor to form the homogeneous carbonaceous cherts along with hydrothermal related sediment the 13 c org values of organic matter in the black cherts range from 42 to 22 average 31 9 n 313 lighter 13 c values 35 to 42 characterize carbonaceous laminated black chert located 5 m above the basement where biogenic structures e g biomat bed microfossil structures are found the lighter 13 c values might be related to methanotrophic micro organic activity within the sediments during hydrothermal activity in summary we reconstructed the sedimentary environment upon a mesoarchean hydrothermal ocean floor that was a site of microbial activity and local methanogenesis

high resolution record of climate stability in france during the last interglacial period the last interglacial period 127 110 kyr ago has been considered to be an analogue to the present interglacial period the holocene which may help us to understand present climate evolution but whereas holocene climate has been essentially stable in europe variability in climate during the last interglacial period has remained unresolved because climate reconstructions from ice cores1 2 continental records3 4 and marine sediment cores5 6 give conflicting results for this period7 here we present a high resolution multi proxy lacustrine record of climate change during the last interglacial period based on oxygen isotopes in diatom silica diatom assemblages and pollen climate transfer functions from the ribains maar in france contrary to a previous study8 our data do not show a cold event interrupting the warm interglacial climate instead we find an early temperature maximum with a transition to a colder climate about halfway through the sequence the end of the interglacial period is clearly marked by an abrupt change in all proxy records our study confirms that in southwestern europe the last interglacial period was a time of climatic stability and is therefore still likely to represent a useful analogue for the present climate

sulfur and carbon isotopic evidence for metabolic pathway evolution and a four stepped earth system progression across the archean and paleoproterozoic abstract the earth s mantle has provided a ready redox gradient of sulfur compounds so2 h2s since the stabilization of the crust and formation of the ocean over 4 billion years ago and life has evolved a multitude of metabolic pathways to take advantage of this gradient these transitions are recorded in the sulfur and carbon isotope signals preserved in the rock record in the genomic records of extant microorganisms and in the changing mantle and crust structure composition and cycling here we have assembled approximately 20 000 sulfur 34s 33s 36s and carbon 13c isotope data points from scientific publications spanning over five decades of geochemical analyses on rocks deposited from 4 0 to 1 5 ga we place these data in the context of molecular clock and tectonic and surface redox indicators to identify overarching trends and integrate them into a holistic narrative on the transition of the earth s surface towards more oxidizing conditions the greatest extreme in 34s values of sulfide minerals 45 5 to 54 9 and sulfate minerals 13 6 to 46 6 as well as 13c values in carbonate minerals 16 8 to 29 6 occurred in the period following the great oxidation event goe while the greatest extremes in organic carbon 13c values 60 9 to 2 4 and sulfide and sulfate mineral 33s and 36s values 4 0 to 14 3 and 12 3 to 3 2 respectively occurred prior to the goe from our observations we divide transitions in earth s history into four periods period 1 4 00 to 2 80 ga during which geochemical cycles were initialized period 2 2 80 to 2 45 ga during which s and c isotope systems exhibit changes as conditions build up to the goe period 3 2 45 to 2 00 ga encompassing the goe and period 4 after 2 00 ga after which s and c isotopic systems remained relatively constant marking a time of earth system geochemical quiescence using these periods we link changes in s and c isotopes to molecular clock work to aid in interpreting emerging metabolic functions throughout earth s history while underscoring the need for better proxies for robust evolutionary analyses specifically results indicate 1 an early development of sulfide oxidation and dissimilatory sulfite reduction followed by disproportionation and then sulfate reduction to sulfite resulting in a fully biologically mediated sulfur cycle by 3 25 ga 2 support for the acetyl coenzyme a pathway as the most likely earliest form of biologically mediated carbon fixation following methanogenesis 3 an increasingly redox stratified ocean in the neoarchean with largely oxic surface water and euxinic bottom water during the first half of the paleoproterozoic and 4 that secular changes in earth system crustal cycling dynamics and continent formation likely played a key role in driving the timing of the goe finally based on geochemical data we suggest that the paleoproterozoic be divided into a new era of the eoproterozoic from 2 45 to 2 00 ga and the paleoproterozoic from 2 00 to 1 60 ga

palaeo seasonality of the last two millennia reconstructed from the oxygen isotope composition of carbonates and diatom silica from nar golu central turkey carbonates and diatoms are rarely deposited together in lake sediments in sufficient quantities for the oxygen isotope composition 18o to be investigated simultaneously from both hosts here 18ocarbonate are compared to 18odiatom data from the varved sediments of nar golu a closed lake in central turkey over the last 1710 years lake monitoring suggests carbonate is probably precipitated during may june and 18ocarbonate is a proxy for regional water balance diatom activity is mainly weighted towards the spring at times between 301 and 561 ad while 18ocarbonate values are the highest for the entire 1710 year period suggesting summer drought 18ocorrected diatom values are among the lowest 18olakewater values estimated for the times of diatom growth and carbonate precipitation show large differences we suggest this could be explained by increased snowmelt that formed a freshwater lid on the lake at the time of peak diatom growth increased snowmelt is also inferred 561 801 ad from 801 ad to the present precipitation is less winter dominated although increased snowmelt is inferred 921 1071 ad and in the latter part of the little ice age i e the mid to late 1800s ad by combining oxygen isotope data from hosts that form in lakes at different times of the year we show that such analyses can provide insights into palaeo seasonality

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

temperature dependence of the oxygen isotopic fractionation between diatom silica and water abstract we present a new paleotemperature scale based on the oxygen isotopic ratio of the non exchangeable fraction of the oxygen from diatom silica the equation t 17 2 2 4 18osilica 18owater 40 0 2 18osilica 18owater 40 2 was derived using recent sediment samples from different oceanic areas the temperature and isotopic composition of the local surface water comparison of our results with other relationships established for quartz water or amorphous silica water at higher temperature suggests no difference in isotopic fractionation between quartz water and biogenic silica water couples

hydrothermal flake graphite mineralisation in paleoproterozoic rocks of south east greenland flake graphite mineralisation is hosted in the kuummiut terrane of the paleoproterozoic nagssugtoqidian orogen south east greenland eclogite facies peak metamorphic assemblages record temperatures of 640 830 c and pressures of 22 25 kbar and are retrogressed in the high pressure amphibolite facies during ca 1870 1820 ma graphite occurs as lenses along cleavage planes in breccia and as garnet quartz graphite veins in various metamorphic host rocks in the tasiilaq area at auppaluttoq kangikajik and nuuk ilinnera graphite contents reach 30 vol in 0 2 4 20 m wide semi massive mineralisation auppaluttoq kangikajik supergene alteration formed 1 to 2 m thick and up to a 2 5 2 5 km wide loose limonitic gravel containing graphite flakes in places the flake size ranges from 1 to 6 mm in diameter with an average of 3 mm liberation efficiency is at minimum 60 hydrothermal fluids at 600 c transporting carbon as co2 and ch4 formed the mineralisation commonly hosted by shear zones which acted as pathways for the mineralising fluids the hydrothermal alteration assemblage is quartz biotite grunerite edenite pargasite k feldspar titanite the 13c values of graphite varying from 30 to 18 pdb indicate that the carbon was derived from organic matter most likely from metasedimentary sources devolatilisation of marble may have contributed a minor amount of carbon by fluid mixing precipitation of graphite involved retrograde hydration reactions depleting the fluid in h2o and causing graphite saturation although the high grade mineralisation is small it represents an excellent example of hydrothermal mineralisation in an eclogite facies terrane during retrograde exhumation

early life signatures in sulfur and carbon isotopes from isua barberton wabigoon steep rock and belingwe greenstone belts 3 8 to 2 7 ga

the origin of carbonaceous matter in pre 3 0 ga greenstone terrains a review and new evidence from the 3 42 ga buck reef chert abstract the geological record of carbonaceous matter from at least 3 5 ga to the end of the precambrian is fundamentally continuous in terms of carbonaceous matter structure composition environments of deposition preservation and abundance in host rocks no abiotic processes are currently known to be capable of producing continuity in all four of these properties although this broad view of the geological record does not prove that life had arisen by 3 5 ga the end of the early archean it suggests a working hypothesis most if not all carbonaceous matter present in rocks older than 3 0 ga was produced by living organisms this hypothesis must be tested by studies of specific early geological units designed to explore the form distribution and origin of enclosed carbonaceous matter the carbonaceous environmentally diverse 3416 ma buck reef chert brc of the barberton greenstone belt south africa provides an opportunity for such a study upward facies progressions in the brc reflect deposition in environments ranging from shallow marine evaporitic brine ponds to a storm and wave active shelf to a deep low energy basinal setting below storm wave base abundances and ratios of al2o3 zr tio2 and cr track inputs of various types of volcaniclastic and terrigenous clastic materials in particular zr al2o3 and zr serve as proxies for concentration of windblown dust and indirectly as proxies for sedimentation rate cu zn ni and feo were concentrated in the most slowly deposited transitional and basinal sediments inconsistent with a hydrothermal setting but consistent with a normal marine setting the distribution of microfacies defined by associations and layering of clastic ferruginous and carbonaceous grains correlates with facies transitions fine carbonaceous laminations which occur only in shallow platform settings represent photosynthetic microbial mats these were ripped up and the debris widely redistributed in shallow and deep water by waves and storms the isotopic composition of carbonaceous matter ranges from 35 to 30 in shallow water settings and to 20 in deep water units the heavier 13c in deep water carbonaceous matter is thought to reflect microbial processing possibly by fermentation and methanogenesis of organic matter originally produced in shallow water hydrothermal origins for brc carbonaceous matter are clearly excluded by the inferred depositional setting of the rocks as a whole an inference supported by field petrographic and geochemical analysis we suggest that the biological model proposed here for brc carbonaceous matter is the best currently available the hypothesis that at least some carbonaceous matter present in rocks older than 3 0 ga was produced by living organisms should be regarded as likely until extraordinary contradictory evidence is presented

middle and late holocene paleotemperatures reconstructed from oxygen isotopes and gdgts of sediments from lake pupuke new zealand abstract quantitative holocene temperature reconstructions for southern hemisphere terrestrial environments are still restricted to few records and multi proxy methods are rarely applied to the same system here we test the applicability and comparability of temperature reconstructions inferred from different methodological approaches we combined sedimentary cellulose and diatom oxygen isotope data from lake pupuke north island new zealand to derive a record of lake water temperatures this record is complemented with mean annual air temperatures derived from the branched gdgt index mbt measured on the same sedimentary record the datasets of both reconstructions show little temperature variation for the period 1320 7110 cal bp the exceptions are a warmer period culminating between 1700 and 1600 cal bp reflected in both proxies and centennial scale intervals with cooler water temperatures at 3380 and 2750 cal bp recorded in the oxygen isotope based temperature reconstruction but not in the mbt inferred air temperature estimates we suggest that variations in lake circulation are the likely reason for deviations between temperature reconstructed from different proxies

isotopic evolution of the biogeochemical carbon cycle during the proterozoic eon abstract time related changes in the proterozoic sedimentary isotopic record of organic carbon and carbonates are consistent with the following 1 an increase in the oxidation state of the environment 2 a transition towards microbial populations dominated by producers and utilizers of o 2 and so 4 2 and 3 a relatively minor increase in organic 13 c during postdepositional thermal alteration 13 c increased 3 as h c declined from 0 8 to 0 1 the progressive oxidation of the environment was episodic for example between 2 2 and 1 9 ga crustal and atmospheric reservoirs of o 2 fe 3 and so 4 2 increased relatively rapidly and this increase was too large to be attributed solely to the declining rate of oxidant consumption by volcanic and hydrothermal fluxes of reduced species additional fundamental changes seem to be required in the tectonic style of organic sedimentation and preservation episodic changes in both the biogeochemical c cycle and atmospheric o 2 levels during the proterozoic eon likely influenced the evolution of eukarya

a stable isotope study of microbial dolomite formation in the coorong region south australia abstract the coorong region of south australia is a classic location for the study of modern dolomite formation a number of ephemeral lakes here contain dolomite whilst other lakes in close proximity contain aragonite with minor magnesite our previous field and experimental work has revealed that sulphate reducing bacteria play a key role in overcoming kinetic inhibitors to dolomite formation in this area we here use a combination of oxygen carbon and sulphur isotopes to help to further constrain the processes leading to dolomite precipitation in modern hypersaline environments we report isotopic data from four dolomite and three aragonite containing lakes 34 s data for dissolved lake and porewater sulphates reveal 34 s enrichment of residual sulphate in all seven lakes consistent with bulk closed system microbial fractionation by sulphate reducing bacteria calculations using temperature dependent oxygen isotope fractionation factors between dolomite and the solution from which it precipitated are consistent with a strong microbial component to carbonate precipitation in these lakes a comparison of 18 o data from dolomite and aragonite sediment and from their associated lakewaters indicates seasonal mineral precipitation occurs late in the evaporative cycle of the lakes within a yoghurt like saturated mud horizon coincident with the zone of sulphate reduction surprisingly 13 c data from the carbonates do not show the characteristic wide range of values often associated with organogenic carbonates but instead show that these bacterially mediated precipitates incorporate carbon primarily from the inorganic lakewater reservoir partially diluted by an organic component a coorong type microbial model of dolomite formation may be particularly applicable to for example precambrian sedimentary dolomites where benthic microbial communities which are today restricted to extreme environments dominated the shallow marine ecosystem prior to the emergence of metazoa

middle archean volcano hydrothermal sequence bacterial microfossil bearing 3 2 ga dixon island formation coastal pilbara terrane australia the 3 2 ga dixon island formation in the cleaverville group of the coastal pilbara terrane australia is one of the most complete and best preserved examples of middle archean oceanic stratigraphy and contains possible microbial material field observations and geochemical evidence suggest that this formation contains a low temperature hydrothermal vent system with a biogenic microbial colony from the archean ocean the dixon island formation is 350 m thick and consists of the rhyolite tuff black chert and varicolored chert members in ascending order the rhyolite tuff member contains many vein swarms such as quartz and black chert veins and highly altered rhyolite tuff layers which are identified as an underground bypass zone for circulating hydrothermal fluid many black chert vein swarms in the rhyolite tuff member imply intensive low temperature hydrothermal activity during deposition of the black chert member which is 10 15 m thick the black chert member is composed of massive black chert laminated black chert dark greenish siliceous shale and tuffaceous laminated chert which are mainly composed of very fine quartz abundant pseudomorphs of silica after aragonite barite and gypsum and a distinctly continuous stromatolite like biomat layer 10 20 cm thick are preserved within the laminated black chert bed the stromatolite like biomat bed is formed of fine iron or iron coated quartz pisolite within fine grained silica the absence of detrital sediment of continental origin and the many vein injections imply that this sedimentary facies represents a pelagic hydrothermal environment at 500 2000 m paleodepth and may have been on the slope of an immature island arc microbial material has been preserved well in the lower part of black chert member the massive black chert has carbonaceous peloids 0 3 2 0 mm in diameter which are similar to those in the black chert veins the massive black chert contains spiral rod and dendrite shaped bacterial material the total organic carbon toc value of massive black chert in the lower part of the black chert member is higher toc 0 15 0 45 than that of the overlying laminated chert section toc 0 02 0 15 and the black chert vein toc 0 1 0 13 and the carbon isotope 13 c values of this lithology 33 to 27 are also lighter than for the black chert veins 29 to 26 and the laminated black chert in the upper part of the black chert member and the varicolored chert member 27 to 13 this evidence suggests that the carbonaceous grains and bacteria shaped material in the lower part of the black chert member are of bio genic origin and were formed close to a low temperature hydrothermal vent system the microbial colony may have been rapidly fossilized by silicification related to hydrothermal activity laminated black chert in the upper part of the black chert and the varicolored chert members may have formed by cyanobacterial sedimentation from the ocean surface

a widespread positive 13ccarbanomaly at around 2 33 2 06 ga on the fennoscandian shield a paradox carbon isotope measurements carried out on 201 carbonate samples from the early proterozoic of the kola peninsula n karelia and norway yield 13c pdb spanning 20 5 to 11 a general 13c secular trend shows that prior to 2 33 ga values are typically normal marine averaging around 3 0 between 2 33 and 2 06 ga in jatulian time there follows a rapid excursion to positive 13c of around 6 post jatulian time is characterized by 13c of sedimentary carbonates fluctuating between 5 and 3 also it is remarkable for the first pronounced development of diagenetic carbonates which have 13c between 14 and 6 the c 6 positive 13c shift with a duration of about 270 myr coincides with a maximum in the diversity and abundance of stromatolites and with widespread development of red beds but does not coincide with the maximum of buried corg mass the fennoscandian shield represents the largest isotoically anomalous carbonate province yet reported and the positive 13c excursion together with a series of major global palaeoenviromental changes seems to be more intense than the precambrian cambrian transition events however it is still not clear what kind of mechanism this phenomenon could be attributed to an increase of the ronov ratio and or broecker ratio and other possible models are discussed as the target for future investigations

penciling in details of the hadean some truly remarkable graphite is described by bell et al in pnas 1 graphite is of course the same material as found in pencil tips or in the anode of lithium ion batteries graphite is however also a very common material in earth science and is often the form of carbon found in very old fossils that have been subjected to substantial heat the graphite described in the bell et al article is remarkable because it is exceptionally old dating to the hadean eon officially the hadean is defined as the time period from the formation of the earth until 4 billion y ago until recently this has been a seemingly convenient definition leaving it as the geological eon without a rock record on earth over the past quarter century however the discovery and exploration of detrital zircon minerals from the jack hills conglomerates of western australia 2 have provided a new window into this early time jack hills zircons crystallized in magma chambers at various times as far back as 4 4 billion y ago 3 4 so far these zircons and their inclusions are currently our only tangible record of the first half a billion years of earth history based in part on the extreme age of some of these zircon minerals along with similarly old age dates for a martian meteorite 5 the planetary science and earth science communities now appreciate that planets form and cool rather quickly 6 no longer is the hadean just a placeholder on our timelines between the formation of the earth and the oldest known rocks the hadean earth is represented by tangible samples that appear to have formed in a continental crust setting likely above an active subduction zone 7 specifically bell et al 1 describe two sizable graphite inclusions within a 4 1 billion y old zircon from the jack hills this sample implies that a hadean chunk of organic material was transported by geological processes including subduction to a granitic magma chamber where it was incorporated into the crystalizing minerals the sheer existence of this new record of early carbon is exciting because it provides a new window into the seemingly accessible hadean earth

filamentous fossil bacteria from the archean of western australia abstract four morphotypes of structurally preserved filamentous fossil bacteria have been discovered in petrographic thin sections of laminated carbonaceous cherts from the 3500 ma old warrawoona group of northwestern australia these tubular and septate microfossils are interpreted here as being syngenetic with warrawoona sedimentation as such they are apparently the oldest such fossils now known in the geological record the diversity of this assemblage and the evident complexity of its individual components suggest that the beginnings of life on earth may have appreciably pre dated the deposition of the warrawoona sediments

a brachiopod calcite record of the oceanic carbon and oxygen isotope shifts at the permian triassic transition the permian triassic p t mass extinction was the most dramatic of all such events but its cause has thus far remained elusive1 3 carbon and oxygen isotope analyses may offer clues to this puzzle because their results identify major changes in the earth s exosystem4 5 several studies have already dealt with carbon and oxygen isotope records at the p t transition2 6 11 but we present here empirical data derived from the brachiopod shell calcite whose isotope composition generally corresponds to that of the sea water in which the animals lived originally12 15 these data allow us to assess quantitatively the magnitude of changes in the earth s exosystem during that critical time interval

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

ion microprobe analysis of graphite from ca 3 8 ga metasediments isua supracrustal belt west greenland relationship between metamorphism and carbon isotopic composition in situ ion microprobe measurements of carbon isotopic compositions of graphite were made in seven metasediments and two carbonate rocks from the ca 3 8 ga isua supracrustal belt west greenland the 13c values of micron scale graphite globules in the metasediments and the carbonate rocks vary from 18 to 2 and from 7 to 3 respectively the maximum 13c value of graphite globules in the metasediment rises from 14 to 5 as the metamorphic grade increases from epidote amphibolite to upper amphibolite facies in a single hand specimen the 13c values of graphite inclusions in garnet are 7 lower on average than those outside garnet similarly graphite armored by quartz apparently shows a few permil lower 13c values than those on grain boundaries between noncarbonate minerals the fact that early crystallized minerals include relatively 13c depleted graphite indicates that the regional metamorphism increased the 13c values of the isua graphite this is consistent with the regional trend of 13c enrichment accompanied by the increase of metamorphic grade the minimum fractionation between graphite and carbonate is consistent with the equilibrium fractionation at about 400 to 550 c these observations indicate that isotopic exchange with isotopically heavy carbonate caused 13c enrichment of isua graphite the 13c values of graphite reported here 13c 18 were produced either as a metamorphic modification of organic carbon with initially much lower 13c values or as an abiological reaction such as decomposition of carbonate if the isotopic exchange between carbonate and graphite during regional metamorphism controlled the 13c enrichment of isua graphite previously reported large 13c depletion of graphite especially armored by apatite mojzsis et al 1996 was probably premetamorphic in origin this supports the existence of life at isua time ca 3 8 ga

lakewater paleothermometry from deep lake minnesota during the deglacial holocene transition from combined δ18o analyses of authigenic carbonate and aquatic cellulose abstract carbonate cellulose and bulk organic isotope data from varved sediments of deep lake minnesota provide a record of paleohydrologic and paleoclimatic change during the deglacial holocene transition from 12 000 to 7500 cal bp deep lake became enriched in 18 o in response to increased influence of maritime tropical moisture from the gulf of mexico between 12 000 and 9500 cal bp culminating in regional expansion of pinus and quercus and then again as a result of increased aridity with the establishment of more zonal circulation and prairie vegetation by 8500 cal bp summer lake water temperatures simultaneously increased during the deglacial holocene transition as suggested by decoupling of carbonate 18 o and cellulose inferred lake water 18 o values between 11 000 and 9500 cal bp and then declined briefly around 8600 cal bp possibly in response to the cooling event associated with the final drainage of glacial lakes agassiz and ojibway into the labrador sea although the carbonate cellulose paleothermometer generated unrealistically high values these can readily be explained by imposing kinetic effects that occur during rapid carbonate precipitation and conservative estimates of a seasonal lag effect in the synthesis of cellulose with respect to carbonate these new results suggest that climatic variations during the deglacial holocene transition in northwestern minnesota were driven mainly by changes in large scale atmospheric circulation and that lake agassiz played a comparatively minor role except during its final drainage

isotopic evolution of glacial lake agassiz new insights from cellulose and porewater isotopic archives abstract significantly differing estimates of the oxygen isotope composition of lake agassiz have been obtained from two co existing isotopic archives within a sediment core originating from montcalm manitoba in the southern basin of the ancient proglacial lake oxygen isotope analysis of cellulose extracted from the sediments which originated during the lockhart phase 11 700 11 000 14 c yr bp suggests that phytoplankton lived in surface waters having 18 o around 18 1 vsmow substantially enriched relative to connate porewaters in the same core which indicate bottom waters had much lower values of around 24 5 0 5 vsmow this difference may be attributable to seasonal isotopic stratification of the upper part of the water column in the 250 m deep lake modern observations from analogous environments in northern canada suggest that inflow of evaporatively enriched runoff from the large area of deglaciated terrain contributing to lake agassiz possibly enhanced by evaporation from the surface of the lake itself could readily account for sufficient seasonal 18 o enrichment in the epilimnion sediment porewaters in contrast have preserved the isotopic signature of hypolimnion waters supplied by a mixture of glacial meltwater and precipitation derived runoff from the laurentide ice sheet and lack discernable isotopic alteration by evaporation these new estimates are combined with inferred lake water compositions from other isotopic archives to develop a speculative framework for the isotopic evolution of the lake providing improved constraints on the probable isotopic composition of lake agassiz outflow over time which has important implications for efforts to trace and model its changing discharge

a 3 800 million year isotopic record of life from carbon in sedimentary rocks an increased ratio of 12c to 13c an indicator of the principal carbon fixing reaction of photosynthesis is found in sedimentary organic matter dating back to almost four thousand million years ago a sign of prolific microbial life not long after the earth s formation partial biological control of the terrestrial carbon cycle must have been established very early and was in full operation when the oldest sediments were formed

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

earliest part of earth s stratigraphic record a reappraisal of the 3 7 ga isua greenland supracrustal sequence investigations of the isua supracrustal rocks in west greenland allow us to identify the protoliths and alteration history for most isua rocks the protoliths consisted of alternating basalt and banded iron formation this sequence was invaded by dunitic sills metamorphosed and later intruded by felsic gneisses pervasive carbonation and k metasomatism produced a sequence of lithologies mimicking those found in modern platform deposits however the protoliths could have originated in a purely oceanic environment with no sialic detrital components the isua sequence probably consists of several tectonic panels some of which are cut by 3810 ma felsic intrusive rocks

sediment isotope tracers from lake saarikko finland and implications for holocene hydroclimatology abstract multi component isotopic analyses on a sediment core from lake saarikko finland give insight into holocene climate changes in northern europe oxygen isotopic records from aquatic cellulose and authigenic carbonate reflect consistent similar trends in hydrological balance and are employed jointly to infer relative changes in lake water temperature other geochemical and isotopic tracers shed light on fluctuations in lake level and nutrient cycling facilitating the interpretation of the oxygen isotopic archives in the early holocene 10 000 9000 cal yr bp the lake level was low and dry conditions prevailed despite low temperatures higher lake levels and depleted oxygen isotopic values 9000 7500 cal yr bp were probably caused by several factors higher effective humidity an isotopically depleted precipitation source a cold event around 8300 cal yr bp and increased spring snowmelt in contrast higher summer temperatures lower effective humidity lower lake levels and enriched oxygen isotopic values were experienced during the mid holocene 7500 3300 cal yr bp the occurrence of the warmest inferred lake water and the most enriched cellulose oxygen isotope values 6000 5000 cal yr bp is consistent with a summer temperature maximum inferred from other proxy sources from the region the late holocene was characterized by higher effective humidity and higher lake levels increase in spring snowmelt and colder temperatures most likely related to the little ice age induced a drastic change in the lake hydrology and probably caused the formation of its present outlet 800 cal yr bp changes in the lake hydrological balance and climate variables inferred from oxygen isotopic records can be related to atmospheric circulation most clearly to changes in the dominance and strength of westerly air flow as well as summertime anticyclonic circulation

raman and ion microscopic imagery of graphitic inclusions in apatite from older than 3830 ma akilia supracrustal rocks west greenland three dimensional molecular structural images of apatite grains and associated minerals embedded in a banded quartz pyroxene magnetite supracrustal rock from akilia southern west greenland were constructed by using raman confocal spectroscopy the rock sample is the same as that from which apatite hosted isotopically light graphitic inclusions were reported by mojzsis and colleagues in 1996 the results were challenged in 2005 by lepland and colleagues who failed to find carbon bearing inclusions in this and other akilia samples here we demonstrate that inclusions of graphite wholly contained within apatite occur in this rock the carbon isotopic composition of one such inclusion its graphitic composition established by raman spectroscopy was measured by secondary ion mass spectrometry to be isotopically light 13 c 29 4 in agreement with earlier analyses our results are thus consistent with the hypothesis that graphite containing apatite grains of the older than 3830 ma akilia metasediments may represent chemical fossils of early life

understanding the transfer of contemporary temperature signals into lake sediments via paired oxygen isotope ratios in carbonates and diatom silica problems and potential abstract although the oxygen isotope composition 18o of calcite 18ocalcite and to a lesser extent diatom silica 18odiatom are widely used tracers of past hydroclimates especially temperature and surface water hydrology the degree to which these two hosts simultaneously acquire their isotope signals in modern lacustrine environments or how these are altered during initial sedimentation is poorly understood here we present a unique dataset from a natural limnological laboratory to explore these issues this study compares oxygen and hydrogen isotope data 18o 2h of contemporary lake water samples at 2 weekly intervals over a 2 year period 2010 12 with matching collections of diatoms 18odiatom and calcite 18ocalcite from sediment traps at 10 m and 25 m at rostherne mere maximum depth 30 m a well monitored eutrophic seasonally stratified monomictic lake in the uk the epilimnion shows a seasonal pattern of rising temperature and summer evaporative enrichment in 18o and while there is a temperature imprint in both 18odiatom and 18ocalcite there is significant inter annual variability in both of these signals the interpretation of 18odiatom and 18ocalcite values is complicated due to in lake processes e g non equilibrium calcite precipitation especially in spring leading to significant 18ocalcite depletion and for 18odiatom by post mortem depositional and possibly dissolution or diagenetic effects for 2010 and 2011 respectively there is a strong temperature dependence of 18ocalcite and 18odiatom in fresh trap material with the fractionation slope for 18odiatom of ca 0 2 c in agreement with several other studies the 18odiatom data indicate the initiation of rapid post mortem secondary alteration of fresh diatom silica within 6 months with some trap material undergoing partial maturation in situ diatom 18o of the trap material is also influenced by resuspension of diatom frustules from surface sediments notably in summer 2011 with the net effect seen as an enrichment of deep trap 18odiatom by about 0 7 relative to shallow trap values contact with anoxic water and anaerobic bacteria are potentially key to initiating this silica maturation process as deep trap samples that were removed prior to anoxia developing do not show enrichment dissolution perhaps enhanced by anaerobic bacterial communities may also be responsible for changes to 18odiatom that lead to increasing but potentially predictable error in inferred temperatures using this proxy high resolution multi year monitoring can shed light on the complex dynamics affecting 18odiatom and 18ocalcite and supports the careful use of sedimentary 18odiatom and 18ocalcite as containing valuable hydroclimatic signals especially at a multi annual resolution although there remain substantial challenges to developing a reliable geothermometer on paired 18odiatom and 18ocalcite in particular 18odiatom needs cautious interpretation where silica post mortem secondary alteration is incomplete and diatom preservation is not perfect and we recommend dissolution be routinely assessed on diatom samples used for isotopic analyses

carbon isotopes as biogeochemical recorders of life over 3 8 ga of earth history evolution of a concept ever since pioneering studies in the late 1930s had shown that the conversion of inorganic carbon into biogenic substances entails sizeable redistributions of the stable carbon isotopes biologically mediated 13c 12c fractionations have come to be recognized as a common corollary of biochemical reactions meanwhile it is firmly established that the universal bias in favour of 12c characterizing biological materials primarily derives from a kinetic isotope effect that is imposed on the first carbon fixing enzymatic carboxylation reaction in the primary metabolism of co2 fixing autotrophic organisms this preference for 12c has turned out to be one of the most enduring relics of the ordered state of the biological precursor substances that may be preserved in fossil organics over billions of years with the currently known sedimentary record at hand it can be stated with confidence that biological carbon isotope fractionations have persisted throughout 3 8 ga of recorded earth history indicating that microbial prokaryotic and archaeoprokaryotic ecosystems had been prolific already on the archean earth while for the time span 3 5 ga the isotopic evidence is unequivocal the information encoded in the preceding record is commonly blurred by a metamorphic overprint this holds particularly for the metasediments of the 3 8 ga old isua supracrustal belt of west greenland which apart from widespread metasomatism have suffered amphibolite grade metamorphism it is known that 13c 12c exchange occurs in organic kerogenous rock constituents during both amphibolite and granulite facies metamorphism if a second carbon partner is available as either fluids or carbonate with isotopic re equilibration often only partially achieved due to the sluggish kinetics of the exchange reaction thermodynamic equilibria predict however that 13c 12c ratios in kerogen and graphite increase during this process hence high t exchange equilibria are always bound to drive 13c values in positive direction the lowermost values encountered being consequently the least exchanged and most pristine with the lowest values of reduced graphitic carbon obtained in early isua studies falling into the range 22 to 28 pdb we had straightforward evidence since the late 1970s that carbon constituents with the isotopic composition of biogenic matter were indeed present in the pre metamorphic isua suite it was therefore by no means surprising that the results of recent isotope work performed on apatite hosted carbonaceous microdomains in isua banded iron formation utilizing advanced techniques of instrumental microanalysis had prompted similar conclusions hence the mainstream of the sedimentary carbon isotope record can be best interpreted as the geochemical manifestation of the isotope discriminating properties of the principal co2 fixing reactions s in biological carbon assimilation suggesting an extreme degree of evolutionary conservatism in the biochemistry of autotrophic carbon fixation as a consequence biological modulation of the geochemical carbon cycle had been established at least 3 8 ga ago having been fully operative by the time of formation of the earth s oldest sediments

variations of younger dryas atmospheric radiocarbon explicable without ocean circulation changes the concentration of radiocarbon 14c in the atmosphere depends on its production rate by cosmic rays and on the intensity of carbon exchange between the atmosphere and other reservoirs for example the deep oceans for the holocene the past 11 500 years it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field1 2 3 recent progress in extending the radiocarbon record backwards in time4 5 6 7 8 9 10 has indicated especially high atmospheric radiocarbon concentrations in the younger dryas cold period between 12 700 and 11 500 years before the present these high concentrations have been interpreted as a result of a reduced exchange with the deep ocean reservoir caused by a drastic weakening of the deep ocean ventilation7 8 9 11 12 here we present a high resolution reconstruction of atmospheric radiocarbon concentrations derived from annually laminated sediments of two polish lakes lake go ciaz and lake perespilno these records indicate that the maximum in atmospheric radiocarbon concentrations in the early younger dryas was smaller than previously believed and might have been caused by variations in solar activity if so there is no indication that the deep ocean ventilation in the younger dryas was significantly different from today s

abnormal positive δ13c values of carbonate in lake caohai southwest china and their possible relation to lower temperature abstract carbon source inputs co 2 exchange between atmosphere and lake water as well as lacustrine productivity are commonly served as the main controls on 13 c values of authigenic carbonates in lake sediments generally 13 c values of recent carbonates in most lakes are lower than 5 all values reported here with respect to the pdb standard and rather few reach up to 13 extreme positive 13 c values up to 23 10 are reported in authigenic carbonate in lake caohai southwest china and some 13 c values are the most positive values in the previously reported surface water carbonate 13 c values in lakes simultaneously there are two intervals of large carbonate 13 c enrichment during the past 500 years namely 1670 1714 ad and 1788 1881 ad on the basis of combination with the oxygen isotopic composition of carbonate and drought flood index proxies d f carbon source inputs co 2 exchange between atmosphere and lake water can not cause this extreme carbonate 13 c enrichment in addition the inconsistent between organic matter content and 13 c values of carbonate lower organic matter 13 c values as well as the weak negative correlation between 13 c values of organic matter and carbonate during these two intervals confirmed that lacustrine productivity is also not the dominant factor that controls abnormal positive carbonate 13 c values temperature variations in lake caohai during the past 500 years were reconstructed from co analysis of 18 o values of carbonate and organic matter cellulose and periods of abnormal positive 13 c values of carbonate correspond well with the lower temperature periods the 1670 1714 ad and 1788 1881 ad cold periods were synchronous with the coldest intervals of little ice age lia and also consistent with the maunder and dalton sunspot minimum respectively considering these geochemical data together although there is no direct effect between temperature and carbonate 13 c values the lower temperature restrains the degradation of organic matter and bacteria have the chance to participate the carbon isotopic fractionation of organic matter thus generating the methane ch 4 gas which has the extreme lower 13 c values up to 60 resulting in the extreme enrichment 13 c in carbonates due to the preferential synthesis of 12 ch 4 the important inputs of bacteria to sedimentary sequence during the periods of 1670 1714 ad and 1788 1881 ad have been further verified by the carbon isotopic fractionation between carbonate and organic matter therefore this mechanism may be responsible for abnormal positive 13 c values in lake caohai abnormal positive 13 c values of carbonate in lake caohai may be indirectly ascribed to the lower temperature and more attention should be paid to the carbon isotopic composition of carbonates in lake caohai in future research particular factors affecting carbonate carbon isotopic composition should be taken into account in order to avoid misinterpreting palaeoclimatic reconstructions

deglacial development of sub sea surface temperature and salinity in the subarctic northwest pacific implications for upper ocean stratification based on models and proxy data it has been proposed that salinity driven stratification weakened in the subarctic north pacific during the last deglaciation which potentially contributed to the deglacial rise in atmospheric carbon dioxide we present high resolution subsurface temperature tmg ca and subsurface salinity approximating 18oivc sw records across the last 20 000 years from the subarctic north pacific and its marginal seas derived from combined stable oxygen isotopes and mg ca ratios of the planktonic foraminiferal species neogloboquadrina pachyderma sin our results indicate regionally differing changes of subsurface conditions during the heinrich stadial 1 and the younger dryas cold phases our sites were subject to reduced thermal stratification brine rejection due to sea ice formation and increased advection of low salinity water from the alaskan stream in contrast the bolling allerod warm phase was characterized by strengthened thermal stratification stronger sea ice melting and influence of surface waters that were less diluted by the alaskan stream from direct comparison with alkenone based sea surface temperature estimates sstuk 37 we suggest deglacial thermocline changes that were closely related to changes in seasonal contrasts and stratification of the mixed layer the modern upper ocean conditions seem to have developed only since the early holocene

impacts of climate and river flooding on the hydro ecology of a floodplain basin peace athabasca delta canada since a d 1700 abstract multi proxy paleolimnological analyses on lake sediment cores from spruce island lake 58 50 82 n 111 28 84 w a perched basin in the northern peace sector of the peace athabasca delta pad canada give insights into the relative roles of flow regulation of the peace river and climatic variability on the basin hydro ecology results indicate substantial variability in basin hydro ecology over the past 300 years ranging from seasonal to periodic desiccation in the 1700s to markedly wetter conditions during the early 1800s to early 1900s the reconstruction is consistent with 1 dry climatic conditions that defined the peak of the little ice age and subsequent amelioration evident in conventional ring width and isotopic analyses of tree ring records located hydrologically and climatically upstream of the pad and 2 peace river flood history inferred from sub annual magnetic susceptibility measurements from another lake sediment record in the peace sector of the pad although regulation of the peace river for hydroelectric power generation since 1968 has long been considered a major stressor of the pad ecosystem leading to reduced frequency of ice jam and open water flooding and an extended period of drying our results show that current hydro ecological status is not unprecedented as both wetter and drier conditions have persisted for decades in the recent past under natural climatic variability furthermore paleolimnological evidence from spruce island lake indicates that recently observed dryness is part of a longer trend which began some 20 40 years prior to peace river regulation

pervasive aerobic nitrogen cycling in the surface ocean across the paleoproterozoic era abstract nitrogen isotope ratios in marine sedimentary rocks have become a widely used biogeochemical proxy that records information about nutrient cycling and redox conditions in earth s distant past while the past two decades have seen considerable progress in our understanding of the precambrian sedimentary nitrogen isotope record it is still compromised by substantial temporal gaps furthermore quantitative links between nitrogen isotope data marine redox conditions and nutrient availability are largely lacking in a precambrian context here we present new nitrogen isotope data from a suite of marine sedimentary rocks with ca 2 4 to 1 8 ga ages spanning the great oxidation event in the paleoproterozoic to better constrain the response of the nitrogen cycle to the first major redox transition in earth s history we further construct a simple box model to describe the major pathways that influenced the nitrogen isotope mass balance of the precambrian ocean and use this as a platform to evaluate the precambrian nitrogen isotope record within this framework we find that consistently positive nitrogen isotope values ranging from 1 1 to 7 7 across the early paleoproterozoic are strong evidence for an expansion of oxygenated surface waters since the isotopic signature of aerobic nitrogen cycling is recorded in the biomass of nitrate assimilating organisms this implicates widespread nitrate bioavailability in this time interval the decline in offshore nitrogen isotope ratios in the mesoproterozoic is consistent with the contraction of oxic waters which could have inhibited the expansion of nitrate fueled ecosystems to pelagic waters until the widespread oxygenation of the ocean in the latest neoproterozoic to early phanerozoic

application of stable carbon isotopes to early biochemical evolution on earth the emergence and early evolution of life on earth have long been intriguing subjects for scientific inquiry and a continuous source of intel lectual excitement current work at this frontier proceeds along a number of different avenues and comprises a variety of disciplinary approaches that together strongly suggest that the earth was inhabited by life as early as almost 4 gyr ago the present state of the field as inferred from the results of a broad interdisciplinary approach has recently been summarized by j w schopf and coworkers cf schopf 1 983 it is with the advantage of such a synoptic view that the present review addresses a single facet of the theme namely the potential isotopic infer ences of the presence of co2 fixing autotrophic organisms for the carbon cycle of the early earth with biologically derived organic carbon as well as carbonates limestone dolomite etc abundantly preserved in sediments relevant isotopic evidence should have been encoded in the geologic record from its onset about 3 8 gyr ago it has been known since the pioneering studies by nier gulbransen 1939 murphey nier 1941 and rankama 1948 that the trans formation of inorganic carbon into living matter entails a marked bias in favor of the light isotope c2c with the heavy species l3c retained in the inorganic reservoir subsequent work performed by many investigators e g craig 1953 park epstein 1960 has confirmed that all common

oxygen isotopes in fresh water biogenic opal northeastern us allerod younger dryas temperature shift the first oxygen isotope analysis of biogenic opal from lake sediments from the allerod younger dryas transition in a core from linsley pond connecticut gives an average estimate of a 6 c drop in temperature during the younger dryas this shift represents temperatures during the bloom season and may be less than the winter temperature drop the sharp transition itself with a duration of about 200 years suggests that the temperature decrease may have been as large as 12 c previous estimates of the allerod younger dryas temperature shifts are controversial and range from 3 20 c suggesting that further interdisciplinary research on the same samples is warranted

graphite and carbonates in the 3 8 ga old isua supracrustal belt southern west greenland we present a systematic study of abundance isotopic composition and petrographic associations of graphite in rocks from the ca 3 8 ga isua supracrustal belt isb in southern west greenland most of the graphite in the isb occurs in carbonate rich metasomatic rocks metacarbonates while sedimentary units including banded iron formations bifs and metacherts have exceedingly low graphite concentrations regardless of isotopic composition of graphite in metacarbonate rocks their secondary origin disqualifies them from providing evidence for traces of life stemming from 3 8 ga recognition of the secondary origin of isua metacarbonates thus calls for reevaluation of earlier interpretations that suggested the occurrence of 3 8 ga biogenic graphite in these rocks thermal decomposition of siderite 6feco3 2fe3o4 5co2 c is the process seemingly responsible for the graphite formation the cation composition fe mg mn and ca of the carbonate minerals carbon isotope ratios of carbonates and associated graphite and petrographic assemblages of a suite of metacarbonates support the conclusion that multiple pulses of metasomatism affected the isb causing the deposition of fe bearing carbonates and subsequent partial disproportionation to graphite and magnetite equilibrium isotope fractionation between carbonate and graphite in the rocks indicates peak metamorphic temperatures between 500 and 600 c in agreement with other estimates of metamorphic temperature for the isb

a search for molecular fossils in the kerogen of precambrian sedimentary rocks abstract hydrous pyrolysis of the kerogen in precambrian sedimentary rocks of a range of ages and thermal histories was used in an attempt to produce normal iso and anteiso isoprenoid sterane and triterpane hydrocarbons whose structures can be related to known biochemical precursors gas chromatography mass spectrometry was used in the selected ion monitoring mode to achieve a sensitivity of one part hydrocarbon in 10 9 of the rock small amounts of some of these hydrocarbon classes were found in certain lower cambrian and upper precambrian sediments with normal alkanes predominating the yields diminished with increasing age even for well preserved rocks where the minerals showed little effect of metamorphism samples with ages greater than 1 6 10 9 years yielded no detectable hydrocarbons spontaneous dehydrogenation of kerogen results in cross linking cyclization and aromatization of organic structures and extensive transformation of molecular fossils little information on the evolution of precambrian life is contained in the organic matter of the rocks studied in this work further advances along this line will depend critically on the discovery of sediments in which the kerogen is better preserved

evidence of archean life stromatolites and microfossils abstract fossil evidence of the existence of life during the archean eon of earth history 2500 ma is summarized data are outlined for 48 archean deposits reported to contain biogenic stromatolites and for 14 such units that contain a total of 40 morphotypes of described microfossils among the oldest of these putatively microfossiliferous units is a brecciated chert of the 3465 ma apex basalt of western australia the paleoenvironment carbonaceous composition mode of preservation and morphology of the apex microbe like filaments backed by new evidence of their cellular structure provided by two and three dimensional raman imagery support their biogenic interpretation such data together with the presence of stromatolites microfossils and carbon isotopic evidence of biological activity in similarly aged deposits indicate that the antiquity of life on earth extends to at least 3500 ma

multistage graphite precipitation through protracted fluid flow in sheared metagranitoid digana sri lanka evidence from stable isotopes abstract the digana metagranitoid situated within the digana shear zone a critical junction between the highland and wanni complexes of sri lanka hosts a variety of graphite types with structural evidence showing formation during different stages prior to and after deformational events affecting this terrain here we discuss their occurrence association and stable isotopes the carbon isotopes of graphite reported in this study from the sri lankan high grade metamorphic terrain differ significantly from the composition of graphite reported elsewhere in other precambrian terrains the stable isotope composition from random crystals depicts an enriched carbon isotopic composition in the range 1 6 to 8 suggesting precipitation by reduction from co2 rich fluids intracrystalline microscale traverses made on graphite crystals indicate the 13c composition of the rims becoming progressively lighter in 13c in metagranitoid hosted samples with the variation reaching up to 1 5 consistent with the changing fluid regimes induced by decreasing temperature during the graphite growth and shows the preservation of core at higher temperatures a highly enriched carbon isotopic composition 0 6 with a rimward enrichment of 13c observed in migmatites contrary to the values in metagranitoid indicates preferential enrichment of heavy isotopes as a result of the partial melting and dissolution reprecipitation of graphite the oxygen isotopic composition of a quartz calcite vein show values in the range 18 5 to 20 typical for recycled crustal source the tight constraint in the isotopic data from different graphite types studied indicates a homogeneous fluid source for the deposits prolonged fluid flow in this region is envisaged in this study which is related to the multistage deformation of the crustal scale shear zone

paleohydrology of a canadian shield lake inferred from 18o in sediment cellulose oxygen and carbon isotope analyses on cellulose in the postglacial sediment of weslemkoon lake southern ontario show that the cellulose came mainly from aquatic plants or algae rather than from terrestrial sources if a wholly aquatic source is assumed the oxygen isotope content permits inferences of lake water 18o values over the past 10 000 years by accounting for the isotopic fractionation that occurs during cellulose synthesis chronological control is provided by pollen analysis and six 14c dates our reconstruction shows lake water 18o fluctuated from about 5 lower than present in the early postglacial to 5 or more above present values during the mid postglacial these broad secular shifts reflect a combination of fluctuating mean annual 18o of local precipitation evaporative isotopic enrichment of surface waters and snowmelt bypass effects the first two factors reflect the changing paleotemperature and paleohydrology respectively whereas the third factor is a more speculative interp

multiple sulfur and carbon isotope composition of sediments from the belingwe greenstone belt zimbabwe a biogenic methane regulation on mass independent fractionation of sulfur during the neoarchean abstract to explore the linkage between mass independent sulfur isotope fractionation mif s and 13corg excursions during the neoarchean as well as the contemporary redox state and biogeochemical cycling of carbon and sulfur we report the results of a detailed carbon and multiple sulfur 34s 33s 36s isotopic study of the 2 7 ga manjeri and 2 65 ga cheshire formations of the ngezi group belingwe greenstone belt zimbabwe multiple sulfur isotope data show non zero 33s and 36s values for sediments older than 2 4 ga i e prior to the great oxidation event goe indicating mif s thought to be associated with low atmospheric oxygen concentration however in several 2 7 2 5 ga neoarchean localities small scale variations in mif s signal magnitude seem to correlate with negative excursion in 13corg possibly reflecting a global connection between the relative reaction rate of different mif s source reaction and sulfur exit channels and the biogenic flux of methane into the atmosphere during periods of localized microbiologically mediated shallow surface water oxygenation the manjeri formation black shales studied here display a wide range of 13corg between 35 4 and 16 2 average of 30 3 6 0 1 while the cheshire formation shales have 13corg between 47 7 and 35 1 average 41 3 3 1 the 34s values of sedimentary sulfides from manjeri formation vary between 15 15 and 2 37 average 1 71 4 76 1 showing very small and mostly negative 33s values varying from 0 58 to 0 87 average 0 02 0 43 1 cheshire formation black shale sulfide samples measured in this study have 34s values ranging from 2 11 to 2 39 average 0 25 1 08 1 and near zero and solely positive 33s anomalies between 0 14 and 1 17 average 0 56 0 29 1 moreover 36s 33s in the two formations are comparable with a slope of 1 38 manjeri formation and 1 67 cheshire formation respectively this differs from the archean reference line i e 0 9 the sulfur and carbon isotopic signatures recorded here likely reflect different environmental conditions and or ecosystems within the sampled cheshire and manjeri formations paleofacies the differences in carbon isotopes in different sedimentological facies are interpreted as recording different metabolic pathways including photosynthesis methanogenesis and methanotrophy low 13corg values in the cheshire formation black shales suggest a strong influence of methanotrophy likely preceded by bacterial methanogenesis while the large range of manjeri formation 34s may record bacterial sulfate reduction the c and multiple s isotopic variations recorded here may imply different patterns of c and s fractionation perhaps dependent on variations in the biogenic egress of methane to the atmosphere

late pleistocene oxygen isotope records of biogenic silica from the atlantic sector of the southern ocean we determined the isotopic composition of oxygen in marine diatoms in eight deep sea cores recovered from the atlantic sector of the southern ocean the analytical reproducibility and core to core consistency of the isotopic signal suggests that diatom 18o can be used as a new paleocenographic tool to reconstruct past variations in surface water characteristics and to generate 18o isotope based stratigraphy for the southern ocean the data indicate that diatom 18o reflects sea surface temperature and seawater isotopic composition and that diatoms retain their isotopic signal on timescales of a least 430 ka the 18o analyses of different diatom assemblages reveal that the isotopic signal is free of species effects and that the common antarctic species have the same water opal fractionation the transition from the last glacial maximum lgm to the holocene is fully recorded in high sedimentation rate cores an 18o enrichment during the lgm a post lgm meltwater spike and an input of meltwater during the late holocene are the main isotopic features observed in down core records the origin of this meltwater was very likely melting icebergs and or continental ice or by melting sea ice that had accumulated snow the most pronounced meltwater effects are recorded in cores that are associated with the weddel gyre our results provide the basis for extending isotope studies to oceanic regions devoid of carbonate further isotopic stratigraphies may be constructed for records and regions where they were previously not possible

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

microbial remains in some earliest earth rocks comparison with a potential modern analogue abstract carbonaceous matter cm from ca 3 5 ga hydrothermal black cherts of the pilbara craton of western australia and the barberton greenstone belt of south africa yielded transmission electron microscopy tem images that are suggestive of microbial remains and possible remnants of microbial cell walls these are compared to a potential modern analogue the hyperthermophilic methanocaldococcus jannaschii derived from an active seafloor hydrothermal environment and cultured under similar conditions a striking resemblance to the early archaean forms was evident in wall structure and thermal degradation mode cell disintegration of the cultures occurred at 100 c marking the limits of life complete disintegration deformation and shrinkage occurred at 132 c a multidisciplinary approach to the characterisation of the cm was undertaken using organic petrology tem coupled with electron dispersive spectral analysis eds high resolution tem hrtem to determine molecular ordering and elemental and carbon isotope geochemistry reflectance measurements of the cm to determine thermal stress yielded a range of values corresponding to several populations and pointing to different sources and processes the 13c values of dresser formation cm 36 5 to 32 1 are negatively correlated with toc 0 13 0 75 and positively correlated with c n ratio 134 569 which is interpreted to reflect the relative abundance of high ro oxidised recycled cm and preferential loss of 12c and n during thermal maturation tem observations inferred carbon isotopic heterogeneity and isotope fractionations of 27 to 32 are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the cm

lithifying microbial mats in lagoa vermelha brazil modern precambrian relics abstract bacterial populations microbial and mineral forming processes and their products were analyzed in lagoa vermelha brazil the microbial mat and underlying sediment were studied as a unique system to define the boundary conditions responsible for high mg calcite and dolomite formation in the uppermost layers of the microbial mat oxygenic photosynthesis and aerobic respiration resulted in calcite precipitation whereas in the underlying anoxic layers of the mat sulfide oxidation and sulfate reduction induced formation of a range of carbonate minerals with increasing mg concentrations the chemical mineralogical and biological conditions presently found in lagoa vermelha may have been more common in the precambrian the microorganisms performing the metabolic processes related to carbonate mineral formation within lagoa vermelha s hypersaline microbial mat may have already been present in the precambrian thus microbial carbonate as a biomineral could be a record of metabolism throughout geological time

carbon isotope thermometry in marbles of the adirondack mountains new york carbon isotope thermometry has been applied to coexisting calcite and graphite in marbles from throughout the adirondack mountains new york eighty nine calcite graphite pairs from the amphibolite grade nw adirondacks change systematically in temperature north westwards from 680 to 640 to 670 c over a 30 km distance reflecting transitions from amphibolite facies towards granulite facies to the north west and to the south east temperature contours based on calcite graphite thermometry in the nw adirondacks parallel mineral isograds with the orthopyroxene isograd falling above 675 c and indicate that regional metamorphic temperatures were up to 75 c higher than temperatures inferred from isotherms based on cation and solvus thermometry bohlen et al 1985 fifty five calcite graphite pairs from granulite grade marbles of the central adirondacks give regional metamorphic temperatures of 670 780 c in general agreement with cation and solvus thermometry data for amphibolite and granulite grade marbles show a 12 oo range in 13ccal and 13cgr a strong correlation between carbon isotopic composition and the abundance of graphite cgr crock indicates that the large spread in isotopic compositions results largely from exchange between calcite and graphite during closed system metamorphism the trends seen in 13c vs cgr crock and 13ccal vs 13cgr could not have been preserved if significant amounts of co2 rich fluid had pervasively infiltrated the adirondacks at any time the close fit between natural data and calculated trends of 13c vs cgr crock indicates a biogenic origin for adirondack graphites even though low 13c values are not preserved in marble delamination of 17 graphite flakes perpendicular to the c axis reveals isotopic zonation with higher 13c cores these isotopic gradients are consistent with new graphite growth or recrystallization during a period of decreasing temperature and could not have been produced by exchange with calcite on cooling due to the sluggish rate of diffusion in graphite samples located 2km from anorthosite show a decrease of 0 5 0 8 oo in the outer 100 of the grains while samples at distances over 8 km show smaller core to rim decreases of c 0 2 oo correlation between the degree of zonation and distance to anorthosite suggests that the isotopic profiles reflect partial overprinting of higher temperature contact metamorphism by later granulite facies metamorphism core graphite compositions indicate contact metamorphic temperatures were 860 890 c within 1 km of the marcy anorthosite massif if samples with a significant contact metamorphic effect cal gr 3 2 oo are not included then the remaining 38 granulite facies samples define the relation 13c cal gr 3 56 106t 2 k

carbon isotopic thermometry calibrated by dolomite calcite solvus temperatures abstract the temperature dependence of carbon isotopic fractionations between calcite and graphite and between dolomite and graphite are calibrated by the calcite dolomite solvus geothermometry using marbles collected from the contact metamorphic aureole in the kasuga area central japan the carbon isotopic fractionations 13ccc gr and 13cdo gr systematically decrease with increasing metamorphic temperature the concordant relationships between the fractionations and solvus temperatures are approximately linear with t 2 over the temperature range 400 to 680 c 13ccc gr 5 6 106 t 2 k 2 4 13cdo gr 5 9 106 t 2 k 1 9 these systematic relationships between fractionation and temperature suggest that carbon isotopic equilibria between carbonates and graphite were attained in many cases the equation for the calcite graphite system has a slope steeper than bottinga s 1969 results it is however in good agreement with that of valley and o neil 1981 in the temperature range from 600 to 800 c because of the relatively high sensitivity to temperature these isotopic geothermometers are useful for determining the temperatures in moderate to high grade metamorphosed carbonate rocks

a 200 year mid european air temperature record preserved in lake sediments an extension of the δ18op air temperature relation into the past abstract a detailed history of the water oxygen isotope ratios of lake ammersee southern germany was established for the last two centuries by analyzing oxygen isotope ratios of ostracod shells from a sediment core in a three to five year resolution empirical analysis and modelling of the isotope hydrology of the lake show that the oxygen isotopic composition of the lake water is mainly controlled by the isotopic composition of local precipitation for the last 200 years the lake isotope record is strongly correlated to the air temperature record from hohenpeisenberg situated within the lake s catchment area thus the mid european relation between 18 o in precipitation and air temperature documented for the last 20 years can be extended over a longer time and a larger temperature range the results provide further support for the validity of ostracod 18 o from ammersee sediments as a quantitative proxy for mean annual air temperature probably extending back to the last glaciation

graphite content and isotopic fractionation between calcite graphite pairs in metasediments from the mgama hills southern kenya abstract amphibolite grade metasediments from the mgama hills region kenya contain conspicuous quantities of graphite most probably derived from organic progenitor materials the highest graphite contents 5 1 20 4 are found in schists whereas calcite marbles intercalated in the sequence contain relatively low amounts 0 1 2 0 the graphitic constituents are consistently enriched in 13 c relative to common sedimentary organic material with the highest isotopic ratios in graphite from the marbles 13 c 7 3 5 0 n 10 carbon isotope fractionations between calcite and graphite mostly vary between 3 3 and 7 1 which comes close to both empirically recorded and thermodynamically calculated fractionations in the temperature range of the upper amphibolite facies 550 650 c however larger values occasionally encountered in the marbles suggest that complete isotopic equilibrium is not always attained in amphibolite facies metamorphism

recognizable primary volcanic and sedimentary features in a low strain domain of the highly deformed oldest known 3 7 3 8 gyr greenstone belt isua west greenland a low strain domain has been identified in the metamorphosed mostly highly deformed volcanic and sedimentary rocks of the early archaean isua supracrustal belt this domain contains well preserved volcanic and sedimentary features including basaltic pillow lavas pillow breccia heterogeneous volcanic breccia amygdules in metabasalt and polymict conglomerate dominated by recrystallized chert and volcanic clasts the low strain domain is bounded by highly deformed rocks mostly derived from basalt chert and banded iron formation these discoveries demonstrate that some primary features have escaped the pervasive metasomatism dominant in other parts of the belt and furthermore strengthen the characterization of the isua supracrustals as a typical greenstone belt

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

methanotrophs regulated atmospheric sulfur isotope anomalies during the mesoarchean tumbiana formation western australia abstract the 2 73 billion year old tumbiana formation of the fortescue group in the pilbara craton western australia preserves one of the best records of the fortescue negative carbon isotope excursion with organic 13 c values as low as 60 the prevailing environmental conditions at this biological excursion are not well understood here we present an integrated carbon 12 c 13 c and multiple sulfur 32 s 33 s 34 s 36 s isotopes study of a pristine diamond drill core through the tumbiana formation collected at meentheena by the pilbara drilling project our results show centimeter to meter scale heterogeneities in sulfur and carbon contents and isotope compositions organic 13 c values vary at the meter scale and display a bimodal distribution with peaks at about 44 and 34 this bimodal distribution is interpreted to reflect variations in the contribution of methanotrophic metabolism to the biomass the 34 s v cdt values of sedimentary pyrite vary from 5 73 to 2 75 sulfur isotopes sulfur contents and s c ratios are variable suggesting a complex local biotic sulfur cycling sedimentary pyrite preserves mass independent fractionation of sulfur mif s with 33 s v cdt ranging between 0 25 and 1 64 average 0 47 corresponding to the characteristic dampened mesoarchean anomalies positive correlation between sulfide mif s and a 13 c depletion of organic matter argues for a causal link between methanotrophs activity and the preservation of mif s anomalies in the rock record

the calcite graphite isotope thermometer data on graphite bearing marbles from naxos greece abstract graphite bearing marbles occur in the regional metamorphic complex of naxos over a continuous temperature range of 380 to 670 c the graphite is of biogenic origin and changed its original isotopic composition towards values in equilibrium with the calcite partial isotope exchange took place at temperatures as low as 380 c but near equilibrium values were generally not reached below 550 c the data agree better with the theoretically derived fractionation curve of bottinga 1969 than with the empirical curve proposed by valley and o neil 1981 we believe that the system will not provide a good thermometer

non biogenic graphite in 3 8 ga metamorphic rocks from the isua district greenland abstract a 3 8 ga old metamorphic rock that contains up to 5 5 wt reduced carbon as graphite was found in the isua district greenland this rock exhibits a strong schistosity comprises mostly talc contains high mgo 28 0 wt ni 553 ppm and cr 267 ppm and low al2o3 2 13 wt and bears a high fe 2 o 3 feo ratio 0 94 the original rock was probably a submarine ultramafic tuff the carbon content and the 13c value of the rock vary on a microscopic scale a few mm3 scale from 0 7 to 5 5 wt and from 15 to 12 respectively the second rock a quartzite contains 0 13 wt c as reduced carbon with a 13c value of 11 25 these 13c values fall within the range 27 to 10 reported by previous investigators for graphite from the isua district the 13c values of the isua graphite have been interpreted by previous investigators e g schidlowski and aharon 1992 as metamorphic modification of organic matter with initial 13c values of 30 an important implication of this model has been that the 3 8 ga ocean already supported some biological activity however an examination of the carbon content vs 13c relationship of the graphite bearing rocks from isua has revealed that the 13c value generally increases with increasing carbon contents the rocks with 13c values less than 20 contain extremely small amounts of carbon the mineralogical and elemental characteristics of the rocks of this study a thermodynamic consideration of the temperature and composition of metamorphic fluids and carbon isotope mass calculations suggest that the major component of graphite with 13c values around 12 was formed by an inorganic rather than by a biological process the graphite appeared to have formed at temperatures between 700 and 400 c by one or both of the following two processes 1 reactions between co2 and ch4 co2 ch4 2c 2h2o during cooling of fluids with a co 2 ch 4 molar ratio of 1 and or 2 reactions between the feo component in the ultramafic rock with co2 rich fluids 4 feo co2 2 fe2o3 c the 13c c values for the fluids for both i and 2 were probably between 12 and 5 suggesting that the carbon bearing fluids could have been derived from the mantle

multiple sulphur isotope records tracking basinal and global processes in the 1 98 ga zaonega formation nw russia abstract the exceptionally organic rich rocks of the 1 98 ga zaonega formation deposited in the onega basin nw russia have refined our understanding of earth system evolution during the paleoproterozoic rise in atmospheric oxygen these rocks were formed in vent or seep influenced settings contemporaneous with voluminous mafic volcanism and contain strongly 13c depleted organic matter here we report new isotopic 34s 33s 36s 13corg and mineralogical major element total sulphur and organic carbon data for the upper part of the zaonega formation which was deposited shortly after the termination of the lomagundi jatuli positive carbon isotope excursion the data were collected on a recently obtained 102 m drill core section and show a 13corg shift from 38 to 25 sedimentary sulphides have 34s values typically between 15 and 25 reflecting closed system sulphur isotope behaviour driven by high rates of microbial sulphate reduction high sulphate demand hydrothermal activity and hydrocarbon seepage four intervals record 34s values that exceed 30 we interpret these unusually 34s enriched sulphides to be a result of limited sulphate diffusion into pore waters due to changes in sedimentation and or periods of basinal restriction additionally there are four negative 34s excursions that are interpreted to reflect changes in the open closed system behaviour of sulphate reduction or availability of reactive iron our findings highlight the influence of basinal processes in regulating sulphur isotope records and the need for care before interpreting such signals as reflecting global conditions

a biogenic silica δ18o record of climatic change during the last glacial interglacial transition in southwestern alaska abstract despite growing evidence for environmental oscillations during the last glacial interglacial transition from high latitude terrestrial sites of the north pacific rim oxygen isotopic records of these oscillations remain sparse the lack of data is due partially to the paucity of lakes that contain carbonate sediment suitable for oxygen isotopic analysis we report here the first record of oxygen isotopic composition in diatom silica 18osi from a lake in that region 18osi increases gradually from 19 0 to 23 5 between 12 340 and 11 000 14c yr b p reflecting marked climatic warming at the end of the last glaciation around 11 000 14c yr b p 18osi decreases by 1 7 suggesting a temperature decrease of 3 5 8 9 c at the onset of the younger dryas yd in southwestern alaska climatic recovery began ca 10 740 14c yr b p as inferred from the increase of 18osi to a maximum of 23 9 near the end of the yd our data reveal that a yd climatic reversal in southwestern coastal areas of alaska occurred but the yd climate did not return to full glacial conditions

holocene changes in atmospheric circulation recorded in the oxygen isotope stratigraphy of lacustrine carbonates from northern sweden the oxygen isotope composition of local precipitation delta 18 o p is reconstructed from carbonate lake sediment components in a sediment core covering the last 10000 calendar years from lake tibetanus a small hydrologically open groundwater fed take in the abisko area northern sweden comparison of the delta 18 o p history with a pollen based palaeotemperature record from the same core clearly reveals pronounced deviations from the normally expected temporal delta 18 o p temperature relation so called dansgaard relation that may be a function of changing oceanicity the transition from relatively moist maritime conditions in the early holocene to a much drier climate after 6500 cal bp is reflected by major changes in forest extent and composition as recorded by pollen and plant macrofossil data at the time of maximum influence of westerly air mass circulation high zonal index c 9500 cal bp brought about by high summer insolation and enhanced meridional pressure gradients delta 18 o p at lake tibetanus was about 2 higher than would be predicted by the modem isotope temperature relation the occurrence of long term changes in delta 18 o p temperature relations which are more sensitive measures of palaeoclimate than either delta 18 o p or temperature alone needs to be taken into account when extracting palaeoclimatic information from continental oxygen isotope records less

a 220ka terrestrial δ18o and deuterium excess biomarker record from an eolian permafrost paleosol sequence ne siberia the natural abundances of stable oxygen 18o 16o and hydrogen isotopes 2h 1h are valuable proxies of climate changes in the past yet to date no continuous 18o and only few 2h records are available from loess paleosol sequences taking advantage of a recently developed method based on compound specific 18o analyses of hemicellulose sugar biomarkers in soils zech and glaser 2009 rcm 23 3522 3532 we here present a first terrestrial 18o biomarker record from an eolian permafrost paleosol sequence in ne siberia that covers the last 220 ka the 18o values of the hemicellulose biomarkers arabinose and xylose range from 22 5 to 32 8 and from 21 3 to 31 9 respectively and reveal systematic glacial interglacial shifts the modern topsoil and the interglacial paleosols exhibit more positive 18o values whereas the glacial paleosols are characterized by more negative 18o values this is in agreement with the 2h record obtained for sedimentary n alkane leaf wax biomarkers we present a conceptual model for interpreting the combined 18o and 2h biomarker record based on this model we suggest that both our 18o and the 2h records primarily reflect the temperature controlled isotopic composition of paleoprecipitation modified by evaporative isotope enrichment of leaf water during transpiration considering fractionation factors during sugar and n alkane biomarker biosynthesis allows reconstructing the leaf water isotopic composition and the deuterium excess of the leaf water the deuterium excess may serve as proxy for evaporative enrichment and allows calculating relative humidity using a craig gordon model accordingly relative humidity in ne siberia was higher during marine isotope stage mis 6 compared to mis 2 4 and 5d and thus could help explaining the much larger extent of the late saalian glaciation compared to the weichselian glaciations using the craig gordon model we also calculated 18o of the plant source water 18osource water which can be assumed to primarily reflect 18o of paleoprecipitation our 220 ka 18osource water record is well in agreement with the 18odiatom record from crater lake el gygytgyn in ne siberia and enables a regional paleoclimate reconstruction and interpretation accordingly summer temperature was periodically warmer than at present during the weichselian glacial period and there is a strong july insolation forcing of the summer temperature in the extremely continental study area overall our study highlights the great potential of the novel hemicellulose biomarker 18o method for paleoclimate reconstructions especially when combined with 2h analyses of n alkane lipid biomarkers

implications of in situ calcification for photosynthesis in a 3 3 ga old microbial biofilm from the barberton greenstone belt south africa timing the appearance of photosynthetic microorganisms is crucial to understanding the evolution of life on earth the ability of the biosphere to use sunlight as a source of energy photoautotrophy would have been essential for increasing biomass and for increasing the biogeochemical capacity of all prokaryotes across the range of redox reactions that support life typical proxies for photosynthesis in the rock record include features such as a mat like laminated morphology stratiform domical conical often associated with bulk geochemical signatures such as calcification and a fractionated carbon isotope signature however to date in situ calcification related to photosynthesis has not been demonstrated in the oldest known microbial mats we here use in situ nanometer scale techniques to investigate the structural and compositional architecture in a 3 3 billion year ga old microbial biofilm from the barberton greenstone belt thus documenting in situ calcification that was most likely related to anoxygenic photosynthesis the josefsdal chert microbial biofilm jcmb formed in a littoral photic environment it is characterised by a distinct vertical structural and compositional organisation the lower part is calcified in situ by aragonite progressing upwards into uncalcified kerogen characterised by up to 1 sulphur followed by an upper layer that contains intact filaments at the surface crystallites of pseudomorphed pyrite are also associated with the biofilm suggesting calcification related to the activity of heterotrophic sulphur reducing bacteria in this anoxygenic nutrient limited environment the carbon required by the sulphur reducing bacteria could only have been produced by photoautotrophy we conclude that the josfsdal chert microbial biofilm was formed by a consortium of anoxygenic microorganisms including photosynthesisers and sulphur reducing bacteria

oxygen isotope ratios of sedimentary biogenic silica reflect the european transcontinental climate gradient oxygen isotope ratios of biogenic silica offer considerable potential in tracing past climate change using both marine and lacustrine sediment records despite recent improvements and standardisation in preparatory and analytical methods evidence for a systematic relationship between climate parameters and the oxygen isotope composition of sedimentary diatom silica 18osilica is contradictory in particular observed differences between the 18osilica of living and sedimentary diatom silica in both lake and marine environments question the validity of applying isotope fractionation models derived from living diatoms to reconstructing climate from sediment records in order to address this issue oxygen isotope ratios of biogenic silica 18osilica are examined from a suite of lake surface sediment samples which span a large climatic gradient across western europe 18osilica values are strongly correlated with air temperature and the isotope composition of precipitation 18op when evaporation of lake waters is accounted for the time averaged surface sediment data suggest a fractionation of 35 between water and biogenic silica however the effect of temperature appears less marked than that observed between contemporary diatoms and lake water over short timescales suggesting that diagenetic processes may lead to a reduction in the temperature sensitivity of sediment 18osilica records comparison of 18osilica data with d analysed from n alkanes of aquatic origin n c17 n c21 and n c23 demonstrates that the slope of the regional 18o d water line is preserved within the sediment record offering exciting potential for palaeoclimate research

holocene paleohydrology and paleoclimate at treeline north central russia inferred from oxygen isotope records in lake sediment cellulose lake water oxygen isotope histories for three lakes in northern russia derived from the cellulose oxygen isotope stratigraphies of sediment cores provide the basis for preliminary reconstruction of holocene paleohydrology in two regions along the boreal treeline deconvolution of shifting precipitation 18o from secondary evaporative isotopic enrichment is aided by knowledge of the distribution of isotopes in modern precipitation the isotopic composition of paleo waters preserved in frozen peat deposits as well as other supporting paleoclimatic information these data indicate that during the early holocene when the boreal treeline advanced to the current arctic coastline conditions in the lower yenisey river region were moist compared to the present whereas greater aridity prevailed to the east near the lower lena river this longitudinal moisture gradient is consistent with the suggestion that oceanic forcing increased sea surface temperatures in the nordic seas and reduced sea ice cover was a major contributor to the development of a more maritime climate in western eurasia in addition to increased summer insolation east of the taimyr peninsula large tracts of the continental shelf exposed by glacial sea level drawdown may have suppressed maritime climatic influence in what are now coastal areas in contrast during the late holocene the two regions have apparently experienced coherent shifts in effective moisture the similarity of the records may primarily reflect reduced north atlantic influence in the nordic seas and southward retreat of coastline in eastern siberia coupled with declining summer insolation

microbial remains and other carbonaceous forms from the 3 24 ga sulphur springs black smoker deposit western australia well preserved carbonaceous materials including filamentous microbial remains have been isolated from an archaean sedimentary package overlying the sulphur springs volcanic hosted massive sulphide vhms deposit in the pilbara of western australia one of the oldest best preserved vhms deposits on earth the isotopically light carbonaceous material 13 c values of 26 8 to 34 0 v pdb occurs as finely striated lenticular to banded organic matter om within fine grained epiclastic sediments and silicified materials that overlie the deposit the predominant banded lenticular carbonaceous material occurs parallel to original sedimentary bedding planes and is distinctly visible in light microscopy transmission electron microscopy tem reveals this om as bundles of filamentous and tubular structure closely resembling both modern day and more ancient microbial forms documented from sea floor hydrothermal environments total organic carbon toc has a range of 1 0 to 2 3 while the thermal maturity of the filamentous microbial bundles indicated by reflectance ro points to maximum temperatures since deposition ca 3 24 ga of around 90 100 c a factor that has enabled the preservation of their morphology these results and the intimate association of sulphides with the om are suggestive of a well developed archaean sediment hosted microbial community situated within a basinal environment associated with an active centre of seafloor hydrothermal activity 2007 elsevier b v all rights reserved

very fast environmental changes at the pleistocene holocene boundary recorded in laminated sediments of lake gościz poland abstract this paper presents a reconstruction of the climatic changes at the pleistocene holocene transition recorded in the annually laminated sediments of lake go ci a z poland this reconstruction is based on pollen stable isotope mineralogical and chemical analyses of sediments made with a time resolution of 1 4 yr it reveals a sequence of abrupt climatic changes which preceded and followed the major warming around 11 500 cal bp our data show that the warming period was preceded by a 30 yr long phase of increased winter and decreased summer precipitation 11 550 11 520 cal bp about 11 520 cal bp a very brief period of wetter conditions occurred simultaneously with the beginning of the major warming however most of the first phase of the major warming 11 520 11 500 cal bp was characterised by a generally dry climate presumably due to lowered winter precipitation our records suggest that in this phase the warming concerned winter seasons mostly in the second phase 11 500 11 460 cal bp the warming also concerned summer seasons also a distinct increase of humidity is noted in this period which caused moistening of soils and despite enhanced evaporation and evapotranspiration inhibited the process of lake level drop the following 70 years 11 460 11 390 cal bp were rather dry which caused a distinct lowering of the lake and probably also of groundwater level in this period maximum biological productivity per unit area in the lake is noted the whole sequence of phases of rather different climates was completed within a time interval 160 years spanning two human lifes only one should stress that the transitions between the consecutive phases were rather abrupt lasting no longer than 10 years

isotope signature of the younger dryas and two minor oscillations at gerzensee switzerland palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates oxygen and carbon isotope ratios in the carbonate of benthic ostracodes pseudocandona marchica and molluscs pisidium ssp were measured across the transitions bordering the younger dryas chronozone in littoral lacustrine cores from gerzensee switzerland the specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk carbonate oxygen isotope record 18occ if corrected for their vital offsets oxygen isotope ratios of pisidium and juvenile p marchica both formed in summer are almost identical to 18occ this bulk carbonate is mainly composed of encrustations of benthic macrophythes chara ssp also mainly produced during summer adult p marchica which calcify in winter show consistently higher 18o larger shifts across both transitions and short positive excursions compared with the summer forms especially during early preboreal despite such complexity the 18o of adult p marchica probably reflects more accurately the variations of the 18o of former lake water because during winter calcification temperatures are less variable and the water column isotopically uniform the difference between normalised 18o of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures in general the results indicate warmer summers during the late allerod and early preboreal compared with the younger dryas altogether the isotopic composition of lake water 18ol and of the dissolved inorganic carbonate 13cdic reconstructed from adult pseudocandona marchica as well as the seasonal water temperature contrasts indicate that the major shifts in the 18o of local precipitation at gerzensee were augmented by changes of the lake s water balance with relatively higher evaporative loss occurring during the allerod compared with the younger dryas it is possible that during the early preboreal the lake might even have been hydrologically closed for a short period we speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts

oxygen isotope geothermometers in lacustrine sediments new insights through combined δ18o analyses of aquatic cellulose authigenic calcite and biogenic silica in lake gościąz central poland abstract two water based oxygen isotope geothermometers calcite cellulose and silica cellulose were tested using well dated intervals of laminated sediment retrieved from lake go ci z a small hardwater lake in central poland five sections spanning ca 90 200 years of deposition were selected and subsampled at approximately decadal resolution to characterize relatively stable climatic and hydrologic conditions during the middle of the younger dryas cold period the rapid environmental changes that occurred at the younger dryas preboreal yd pb boundary and three subsequent periods of relative stability during the early middle and late holocene the two geothermometers are based on the premise that aquatic cellulose 18 o serves as a direct proxy for lakewater 18 o thereby allowing resolution of temperature signals in 18 o records obtained from co existing authigenic calcite or diatom silica qualitatively consistent results from the calcite cellulose geothermometer were obtained for all five intervals clearly showing the expected low epilimnion water temperatures in the mid yd rapid warming during the yd bp transition and maximum temperatures during the early holocene followed by slightly lower temperatures during the middle and late holocene results from the silica cellulose geothermometer also showed lower temperatures during the yd than the late holocene although insufficient diatom silica for analysis was present in the intervening intervals the calcite cellulose geothermometer yielded consistently higher estimates of epilimnion temperatures than the silica cellulose thermometer in the yd and late holocene intervals and unrealistically high values throughout the holocene we speculate that the calcite cellulose geothermometer is influenced by kinetic effects during rapid carbonate precipitation which offsets temperature dependent fractionation and thus leads to high temperature estimates in contrast the silica cellulose geothermometer may be affected by the production of diatom silica early in the spring prior to seasonal warming and isotopic enrichment of the epilimnion thus generating low temperature estimates

stable isotope thermometry at high temperatures determination of accurate temperatures for geological events has been the grail of stable isotope geochemistry since the seminal 1947 paper by urey in theory this should be simple calibrated mineral pairs are common analysis is rapid and there is no significant pressure correction however in spite of widespread application the promise of reliable thermometry has been elusive stable isotope temperatures in metamorphic and igneous rocks are often controversial is the fractionation between two phases a thermometer speedometer rate dependant hygrometer p h2o dependant or chimera a number of factors have contributed to this uncertainty including incomplete and sometimes conflicting calibration of isotope fractionation factors limited understanding of the kinetics of mineral exchange and the lack of microanalytical techniques this situation has improved dramatically over the past decade permitting reliable and detailed thermal histories to be inferred in a landmark paper bottinga and javoy 1975 empirically calibrated the oxygen isotope fractionation factors among ten rock forming minerals at t 500 c their compilation shows that 84 of analyzed samples contain at least three minerals meeting a concordance test for equilibrium they concluded the great majority of igneous and metamorphic rocks has conserved a state of oxygen isotope exchange equilibrium if correct this bodes well for thermometry however this conclusion was contested by deines 1977 who critically examined the existing data and concluded that less than half of the rocks analyzed to date would yield concordant 18o derived temperatures while seeming irreconcilable both conclusions are based on fact all rocks contain some degree of disequilibrium but many also preserve a thermometric record it is the purpose of this review to discuss the new strategies for reliable isotope thermometry and to explore disequilibrium processes so they may be recognized and properly interpreted the organization of this paper will be to discuss the assumptions

climate and environment during the younger dryas gs 1 as reflected by composite stable isotope records of lacustrine carbonates at torreberga southern sweden climatic and environmental changes during the younger dryas stadial gs 1 and preceding and following transitions are inferred from stable carbon and oxygen isotope records obtained from the sediments of ancient lake torreberga southern sweden event gs 1 is represented in the sediment sequence by 3 5 m of clay containing lacustrine carbonates of various origins comparison of isotopic records obtained on mollusc shells ostracod valves and chara encrustations precipitated during specific seasons of the year supports estimates of relative changes in both lake water and mean annual air temperatures variations in soil erosion rates can also be estimated from a simple isotope mass balance model to separate allochthonous and autochthonous carbonate contributions to the bulk carbonate content of the sediments the well known rapid climatic shifts characterising the last termination in the north atlantic region are clearly reflected in the isotopic data as well as longer term changes within gs 1 following maximum cooling shortly after the allerod younger dryas gi 1 gs 1 transition a progressive warming and a slight increase in aquatic productivity is indicated at the younger dryas preboreal gs 1 pb transition mean annual air temperature rapidly increased by more than 5 c and summer lake water temperature increased by ca 12 c the subsequent preboreal oscillation is characterised by an increase in soil erosion and a slight decrease in mean annual air temperature these results are in harmony with recent findings about large scale climate dynamics during the last termination copyright 1999 john wiley sons ltd

protolith carbon isotope ratios in cordierite from metamorphic and igneous rocks cordierite commonly contains h 2 o and co 2 in the channels formed by its ring structure in many studies cordierite has been shown to have volatile contents and carbon isotope ratios consistent with high temperature equilibrium suggesting preservation of protolith carbon isotope ratios and motivating this survey of carbon isotopes in cordierite co 2 cordierite co 2 from pelitic country rocks in the etive aureole have 13 c values of 20 70 1 27 n 10 that are unaffected by a ca 150 c thermal gradient and fluid saturated and undersaturated regimes these 13 c values are consistent with expected carbon isotope ratios of organic carbon in protolith sediments similar lithologies from the cooma and huntly aureoles show more variable behavior in a more limited data set with some rocks preserving organic carbon 13 c values and others that may have been affected by externally derived fluids in cordierite gedrite gneisses carbon isotopes of cordierite crd are distinct from those of cordierite in pelites when excluding one outlier new data plus those from the literature average 13 c crd 12 51 2 45 n 17 these isotope ratios are higher than those of cordierite in typical metasedimentary protoliths and are similar to published carbon isotope ratios of trace carbonate in altered submarine volcanic rocks which are likely analogs for protoliths of many cordierite gedrite rocks igneous cordierite from granitic plutons have 13 c 23 61 2 08 n 13 which is interpreted as reflecting a magmatic carbon budget dominated by organic carbon from sedimentary source rocks in contrast small pegmatites reported in the literature have 13 c crd 10 20 3 06 n 6 which may indicate derivation from orthogneiss source materials these new data show that carbon isotopes in cordierite can be used to help understand the protolith of even carbon poor metamorphic rocks and can also shed light on carbon in the sources of magmatic rocks this latter approach has the potential for helping constrain the source rocks of peraluminous granitoids which is controversial determining the extent to which organic carbon 13 c is preserved in granitoids is important for understanding the deep carbon cycle and could serve as an important constraint in the search for low 13 c graphite inclusions in hadean detrital zircons which have been reported as a potential biosignature for the early earth