the meandering gulf stream as seen by the geosat altimeter surface transport position and velocity variance from 73 to 46 w the surface geostrophic velocity field for the gulf stream region was analyzed for the position structure and surface transport of the gulf stream for 2 5 years of the geosat altimeter exact repeat mission synthetic data using a gaussian velocity profile were generated and fit to the sea surface residual heights to create a synthetic mean sea surface height field and profiles of absolute geostrophic currents most of cross track velocity variance was due to the meandering of the gulf stream rather than to rings or complicated velocity profiles which suggested that the simple model parameters are an efficient description of the gulf stream fluctuations an analysis of the model parameters and the actual geostrophic velocity profiles revealed two different flow regimes for the gulf stream connected by a narrow transition region coincident with the new england seamount chain the upstream region was characterized by relatively straight gulf stream paths long eulerian time scales and eastward propagating meanders the downstream region had more large meanders no consistent propagation direction and shorter eulerian time scales a 25 reduction in surface transport occurred in the transition region with a corresponding reduction in current speed and no change in gulf stream width a significant anomaly in surface transport near 69 w suggested the existence of small scale recirculation gyres there the highest variance empirical orthogonal functions of position and surface transport were significantly correlated with larger surface transports leading more northerly positions by a month

variability in the location of the antarctic polar front 90 20 w from satellite sea surface temperature data the path of the antarctic polar front pf is mapped using satellite sea surface temperature data from the noaa nasa pathfinder program the mean path and variability of the pf are strongly influenced by bathymetry meandering intensity is weaker where the bathymetry is steeply sloped and increases in areas where the bottom is relatively flat there is an inverse relationship between meandering intensity and both the width of the front and the change in temperature across it there is a persistent large separation between the surface and subsurface expressions of the pf at ewing bank on the falkland plateau

some observations of the azores current and the north equatorial current the regions containing the two zonal currents of the subtropical gyre in the eastern north atlantic the azores current and the north equatorial current nec have quite different physical characteristics associated with the azores current are strong horizontal thermohaline gradients that can be located easily both at the surface and at depth with temperature data alone thus making satellite ir imagery and expendable bathythermograph profiles suitable for observing it during winter the surface expression of the azores current is often found to the north of the strongest subsurface gradients in contrast to the azores current and to the central water mass boundary just to the south the nec has relatively weak horizontal temperature and salinity gradients requiring density information in order to identify it there is no clear surface manifestation found with the nec common to both currents though is that each transports o 8 sv in the upper 800 m of the ocean near 27 w with the largest velocities being in the upper 400 m

stable isotopic evidence for climate and basin evolution of the late cretaceous songliao basin china abstract because of the need to understand the links and feedbacks of the carbon cycle during times of global greenhouse conditions numerous studies have focused on the cretaceous climate much of what we know about this warm period in earth s history comes from the study of ocean sediments recovered from both ocean drill cores and marine sediments exposed at the earth s surface in contrast there are few studies of cretaceous terrestrial sediments the songliao basin located in northeast china offers a unique opportunity to understand cretaceous paleoclimate of terrestrial settings because it contains a nearly complete record of lacustrine sediments deposited throughout the cretaceous and there is an active drilling program to recover core from this paleolake we present carbon oxygen and strontium isotopic data from ostracods collected from two drill cores sk 1 n and sk 1 s that cover a time interval that extends from the turonian through the maastrichtian these data record robust isotopic trends with numerous carbon and oxygen isotope shifts that are both rapid and long term we tentatively interpret this record to reflect changes in both global climate and regional basin evolution in the turonian and coniacian qingshankou formation we observe several carbon isotope shifts that appear to be correlative to marine isotopic records based upon timing and magnitude of the isotopic changes we suggest that the carbon isotope record in the songliao basin reflect the decrease in carbon isotope ratios following the strong positive excursion at the cenomanian turonian boundary a positive isotope excursion in the late turonian and the negative isotope shift that occurs at the turonian coniacian boundary upward in the section however the marine and songliao isotopic records diverge as sediment sources shift from the southwest east and north to more northerly strontium isotopes record the change in source region as they increase markedly between the coniacian santonian yaojia and santonian campanian nenjiang formations as this is the first isotopic record of the songliao basin we are cautious about many of our interpretations of these isotopic data yet it is clear that with tighter age constraints and focused sampling centered on many of the isotope excursions presented here will allow for a deeper understanding of the terrestrial response to changing climate and the hydrologic response to basin evolution

the importance of solar insolation on the temperature variations for the past 110 kyr on the chinese loess plateau abstract the late quaternary temperature history on the chinese loess plateau clp is little known due to the absence of suitable paleothermometers here we present a quantitative temperature record for the last 110 kyr from lantian county southern clp based on the distributions of bacterial tetraethers lantian loess temperature variations display significant correlation with the northern hemisphere insolation 35 n as well as the cave monsoon records at the precession band we attribute such correlation to both the latent heat release from the east asian summer monsoon and the direct influence of sun s sensible heat over the semi arid landscape the long term cooling during the marine isotope stage mis 3 and the modest temperature drop of 5 c from 79 to 65 ka are best explained by interactions among multiple climate forcings including insolation atmospheric co 2 concentration global ice volume and regional glacier activities the cold and modestly wet climate during mis 3 may have promoted maximum regional glacial advances whereas the minimal temperature during local lgm reduced moisture transfer and led to glacial recession the unusually early deglacial warming at 22 5 ka highlights the importance of regional climate records to decipher the complex continental climate dynamics

a statistical description of the mean circulation and eddy variability in the northwestern atlantic using sofar floats abstract velocity data obtained from trajectories of sofar floats launched as part of several experiments carried out in the northwest atlantic during the last two decades are used to give a statistical description of the mean gulf stream and its recirculation the distribution of eddy variability in the region is also presented a mean gulf stream which bifurcates between 55 and 45 w to feed the north atlantic current and a southern recirculation can be clearly identified a weak interior sverdrup flow is also suggested the spatial distribution of eddy variability is consistent with previous descriptions showing a maximum near the gulf stream

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

location and dynamics of the antarctic polar front from satellite sea surface temperature data the location of the antarctic polar front pf was mapped over a 7 year period 1987 1993 within images of satellite derived sea surface temperature the mean path of the pf is strongly steered by the topographic features of the southern ocean the topography places vorticity constraints on the dynamics of the pf that strongly affect spatial and temporal variability over the deep ocean basins the surface expression of the pf is weakened and the pf meanders over a wide latitudinal range near large topographic features width and temperature change across the front increase and large scale meandering is inhibited elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the pf encounters large topographic features the strong correlations between topography and pf dynamics can be understood in the context of the planetary potential vorticity ppv or f h field mean ppv at the pf varies by more than a factor of 2 along its circumpolar path however at the mesoscale the pf remains within a relatively narrow range of ppv values around the local mean away from large topographic features the pf returns to a preferred ppv value of 25 10 9 m 1 s 1 despite large latitudinal shifts the mean paths of the surface and subsurface expressions of the pf are closely coupled over much of the southern ocean

prediction of the gulf stream path from upstream parameters a linear wiener least squares optimal filter is used to predict the path of the gulf stream in the region between cape hatteras and 70 w using upstream inlet conditions as filter inputs although position angle curvature geostrophic velocity and curvature vorticity measured at 73 w were tested as multiple inlet parameters it was found that inlet position alone was the best predictor with inlet position as the predictor this filter is equivalent to propagating meanders downstream with a typical phase speed and growth rate forecasts of the downstream path position are produced more accurate than persistence 12 days in advance at 140 km from the inlet 24 days in advance at 240 km from the inlet and 28 days in advance at 340 km from the inlet

variations of the gulf stream s north wall east of cape hatteras abstract twelve years 1977 1988 of noaa infrared imagery data were used to study the variations of the north wall displacements of the gulf stream east of cape hatteras i e between 74 w and 65 w the variations of the north wall displacements were compared with the variations in the straits of florida transport which was estimated using a multifrequency model based on the sea level differences between siboney cuba and key west florida for the period 1977 1988 and with transport measurements based on the submarine cable between jupiter florida and settlement point in the bahamas for the period 1982 1988 the north wall reached a maximum northward position in 1985 when the cable data indicated that the straits of florida transport was a maximum the north wall reached a maximum southward position in 1981 cable data were not available before 1982 but the available data suggested that there may have been a minimum transport in 1981 a weak annual cycle of the north wall was found with a maximum northward position in the fall and a maximum southward position in the spring no relationship was found between the annual cycle of the gulf stream s north wall and the annual cycle of the straits of florida transport

the effect of the new england seamounts on gulf stream meandering as observed from satellite ir imagery abstract it is commonly held belief that meandering of the gulf stream increases dramatically downstream of the new england seamount chain in fact this appears not to be the case the envelope of gulf stream northern edges derived from 30 months of satellite data remains constant from 65 to 58 w only the mean of the integrated path length normalized by the mean path length appears to increase downstream of the seamounts but at very nearly the same rate as upstream of them

decoding a protracted zircon geochronological record in ultrahigh temperature granulite and persistence of partial melting in the crust rogaland norway this contribution evaluates the relation between protracted zircon geochronological signal and protracted crustal melting in the course of polyphase high to ultrahigh temperature uht t 900 c granulite facies metamorphism new u pb oxygen isotope trace element ion imaging and cathodoluminescence cl imaging data in zircon are reported from five samples from rogaland south norway the data reveal that the spread of apparent age captured by zircon between 1040 and 930 ma results both from open system growth and closed system post crystallization disturbance post crystallization disturbance is evidenced by inverse age zoning induced by solid state recrystallization of metamict cores that received an alpha dose above 35 1017 g 1 zircon neocrystallization is documented by cl dark domains displaying o isotope open system behaviour in uht samples o isotopic ratios are homogenous 18o 8 91 0 08 pointing to high temperature diffusion scanning ion imaging of these cl dark domains did not reveal unsupported radiogenic pb the continuous geochronological signal retrieved from the cl dark zircon in uht samples is similar to that of monazite for the two recognized metamorphic phases m1 1040 990 ma m2 940 930 ma a specific zircon forming event is identified in the orthopyroxene and uht zone with a probability peak at ca 975 ma lasting until ca 955 ma coupling u pb geochronology and ti in zircon thermometry provides firm evidence of protracted melting lasting up to 110 my 1040 930 ma in the uht zone 85 my ca 1040 955 ma in the orthopyroxene zone and some 40 my ca 1040 1000 ma in the regional basement these results demonstrate the persistence of melt over long timescales in the crust punctuated by two uht incursions

a biomarker study of depositional paleoenvironments and source inputs for the massive formation of upper cretaceous lacustrine source rocks in the songliao basin china abstract the abundance and composition of total organic carbon aliphatic and aromatic hydrocarbons including biomarkers and the 13c composition of total organic matter and individual compounds in core samples of the nenjiang formation from the sk 1 borehole of the songliao basin provide information on the paleoenvironmental conditions of lacustrine sediments formed during the upper cretaceous the distribution of n alkanes and their 13c composition and 4 methylsteranes and dinosteranes in the first member of the nenjiang formation k2n1 indicate that the organic matter largely originated from algal organisms and is dominated by types i and ii kerogen the occurrence of gammacerane aryl isoprenoids isorenieratane and low pristane phytane and diasterane sterane ratios further suggest a salinity stratified water column associated with anoxic bottom waters as well as possible photic zone oxygen depletion conditions during major source rock deposition of the k2n1 the organic geochemical data also indicate significantly different depositional environments for the second member of the nenjiang formation k2n2 sediments which are interpreted to have been deposited under a uniform salinity non stratified oxic water column consequently although the organic matter in the k2n2 sediments was largely derived from algal and bacterial sources the kerogen types are dominantly iib and iii due to the oxidative degradation of organic matter combined with a gradual increase in land plant input furthermore the occurrence and shift of two saw toothed distribution patterns of the 13c composition of c29 to c33 n alkanes with w and m patterns being isotopically heavy odd and even numbered alkanes respectively is suggestive of organic input shift or an unknown mechanism of carbon uptake or isotopic fractionation in particular the heavy even carbon numbered high molecular weight n alkanes is rare and needs further investigation

chronology of the terrestrial upper cretaceous in the songliao basin northeast asia the cretaceous was a period of great environmental biological and geodynamical change but a paucity of an accurate time frame for continental strata has prevented our understanding of the terrestrial processes and the integration of marine and terrestrial records here we present an integrated chronology for the terrestrial upper cretaceous in east asia based on new high resolution magnetostratigraphic results and previously published sims u pb zircon analyses of the cretaceous continental scientific drilling borehole sequence from the songliao basin in northeast china hereafter termed ccsd sk i which consists of a sedimentary sequence from the upper quantou formation k2q to the mingshui formation k2m correlation to the geomagnetic polarity timescale was achieved by combining magnetostratigraphic and sims u pb zircon geochronologic data and lithostratigraphy our correlation suggests that the ccsd sk i sedimentary sequence spans from the upper chron c34n to chron c29r the age of the sedimentary sequence from the upper quantou formation k2q to the mingshui formation k2m in the songliao basin can thus be constrained to an interval from the turonian to the maastrichtian ages in addition our correlation puts the cretaceous paleogene boundary in the upper part of member 2 of the mingshui formation k2m2 the constructed comprehensive chronology allows the precise correlation of the terrestrial upper cretaceous of the songliao basin to marine strata as well as other continental sequences

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

is there evidence for a substantial contribution of prokaryotic biomass to organic carbon in phanerozoic carbonaceous sediments the role of prokaryotes bacteria and archaea in producing biomass and reworking settling and buried organic matter is of paramount importance since it exerts a major impact on the composition of sedimentary organic matter and ultimately petroleum this key role of prokaryotes in combination with a biomarker fingerprint often dominated by prokaryotic molecular fossils e g hopanoids has led to the assumption that prokaryotic biomass is a substantial source for organic carbon in carbonaceous sediments however biosynthesising and reworking organic matter does not necessarily imply sourcing organic matter by the prokaryotes and the abundance of biomarkers does not always reflect relative contributions to sedimentary organic matter in this paper the existing evidence for a substantial prokaryotic biomass contribution to sedimentary organic carbon oc is critically evaluated this shows that despite the often prominent presence of prokaryotic biomarkers in sediments evidence for a substantial prokaryotic contribution to sedimentary oc is generally lacking this is demonstrated by i the application of the carbon isotopic mass balance principle in various sedimentary settings ii an alternative explanation for the proposed dominant role of heterotrophic reworking in the oxford clay iii a summary of the effects of bacterial oxidation in organic matter rich turbidites and iv recent data showing that the evidence for recalcitrant carbon in prokaryotes is scant although these observations do not rule out substantial contributions of prokaryotic carbon to oc in phanerozoic carbonaceous sediments this remains to be demonstrated and the final answer awaits the development of new technologies to full characterise sedimentary oc

western boundary currents and frontal air sea interaction gulf stream and kuroshio extension abstract in the northern hemisphere midlatitude western boundary current wbc systems there is a complex interaction between dynamics and thermodynamics and between atmosphere and ocean their potential contribution to the climate system motivated major parallel field programs in both the north pacific kuroshio extension system study kess and the north atlantic climate variability and predictability clivar mode water dynamics experiment climode and preliminary observations and analyses from these programs highlight that complexity the gulf stream gs in the north atlantic and the kuroshio extension ke in the north pacific have broad similarities as subtropical gyre wbcs but they also have significant differences which affect the regional air sea exchange processes and their larger scale interactions the 15 yr satellite altimeter data record which provides a rich source of information is combined here with the longer historical record from in situ data to describe and compare the curr

compound specific carbon isotope study on the hydrocarbon biomarkers in lacustrine source rocks from songliao basin abstract stable carbon isotopic composition of organic matter 13 c org and compound specific 13 c values of biomarkers from 15 lacustrine source rocks were analyzed to identify the original paleoenvironment and source organisms the 13 c values of hopanes 13 c hop ranged from 68 7 to 32 and exhibit strongly 13 c depleted values in the lower part of member 1 of the nenjiang formation k 2 n 1 up to 68 7 suggesting an origin from predominantly methanotrophic bacteria 13 c enriched 13 c ga values and significantly 13 c depleted 13 c hop in k 2 n 1 which coincide with water stratification and an intermittent anoxic photic zone represents a shallow chemocline the presence of an intermittent anoxic photic zone which means that the anoxia expanded into the euphotic zone is beneficial for om preservation and results in high values of toc and hi in this section however the absence of gammacerane and 13 c enrichment of 13 c hop in member 2 of nenjiang formation k 2 n 2 reflect a deeper chemocline corresponding to relatively oxidizing conditions and low values of toc and hi moreover the negative correlation of toc vs 13 c org and hi vs 13 c org reflects the control of om formation by sedimentary environments rather than productivity in the water column thus the depth of the chemocline not only controls the abundance of om but also affects the development of the microbial community such as chemoautotrophic bacteria in the deep chemocline and chemoautotrophic and methanotrophic bacteria in the shallow chemocline moreover 13 c ga and 13 c values for 4 methyl steranes are related to water salinity with a higher salinity accompanied by 13 c enrichment in gammacerane and 4 methyl steranes

hydrogen isotope ratios of palmitic acid in lacustrine sediments record late quaternary climate variations the rich paleoclimate information preserved in lacustrine sedimentary organic matter can be difficult to extract because of the mixed terrestrial and aquatic inputs herein we demonstrate that compound specific hydrogen isotope analysis of palmitic acid pa a ubiquitous compound in lacustrine sediments captures the d signals of lake water samples collected across a diverse range of 33 north american lakes show a strong correlation between water and dpa values at crooked pond massachusetts the dpa changes in a 14 k y sediment record parallel temperature trends inferred from fossil pollen downcore changes reveal differences between climatic trends in new england and in greenland that are consistent with important regional differences in climate controls

a rapid hydroclimate change and its influence on the songliao basin during the santonian campanian transition as recorded by compound specific isotopes abstract reconstruction of the paleoclimate and paleoenvironment of the songliao basin has important theoretical and practical significance to reveal the regional continental climate characteristics and continental organic matter accumulation under the cretaceous greenhouse climate conditions here we report the composition of biomarkers and the stable carbon and hydrogen isotope compositions of n alkanes from nenjiang formation sediments in the songliao basin which provide information on the source of organisms paleoenvironmental conditions and paleoclimate changes during the late cretaceous our hydrogen isotope records of n alkanes displayed a significantly negative shift indicating that a dramatically wet climate occurred during the santonian campanian transition a wet climate such as that during a prolonged rainfall event had a significant impact on the lake and resulted in the lake level increasing and the salinity decreasing in the surface water during this period however the freshwater input increased the salinity difference between the upper and lower water layers which caused stable water stratification to occur in the lake in addition the high total organic carbon toc content indicates high primary productivity because of increased precipitation carrying more terrigenous nutrients into the lake which resulted in eutrophication during this period notably the increased aryl isoprenoid ratios and the occurrence of isorenieratane indicates that photic zone euxinia pze was enhanced during the santonian campanian transition which was possibly due to the dramatic change in the hydroclimate we speculate that the large freshwater input promoted the formation of pze in the lake then pze restricted the habitat available for aerobic organisms which had fatal effects on the lake ecosystem

the climatology of the north atlantic abstract data from approximately 144 000 hydrographic stations in the north atlantic have been retrieved from the national oceanic data centre and analysed to produce maps of mean pressure temperature salinity and oxygen on selected potential density surfaces for the domain bounded by 0 85 w and 0 65 n the data span the period from 1904 to 1990 with the majority of the data from the last four decades the data set for this region is 60 larger than that used in the production of levitus climatological world atlas this increase in stations coupled with smoothing scales specific to the north atlantic rather than the global ocean considerably improves the resolution of the basin s features the mean property fields and their associated standard deviations are resolved on a one degree grid with little smoothing contrasting with the levitus atlas where properties although presented on a one degree grid have been smoothed on the order of 1000km another important feature of this database is the process by which irregularly spaced data are averaged onto a regular grid in a significant departure from the levitus analysis which averaged on depth surfaces these data were averaged on potential density surfaces thus eliminating an artificial mixing of water mass properties the database is used to describe the baroclinicity of well known features such as the gulf stream the north atlantic current and the deep western boundary current and to elucidate the recirculations associated with these currents it additionally resolves several new features in the intermediate and deep north atlantic these features include the signature of a large scale deep recirculation that extends southwestward from the eastward extension of the north atlantic current to the separation point of the gulf stream near cape hatteras this recirculation which spans approximately 2000m of the water column encompasses more local recirculations and potentially mixes subpolar and subtropical waters furthermore in the upper thermocline this database reveals a coherent azores current that stretches from the gulf stream system south of the tail of the grand banks to madeira this flow is marked by divergences to the south and convergences from the north such that its downstream transport is not much changed

δd values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha abstract a set of lake surface sediment samples and aquatic macrophytes from the eastern and central tibetan plateau and a sediment core from koucha lake northeastern tibetan plateau were analysed for hydrogen isotope signals of aliphatic lipid biomarkers the d values of n alkanes were correlated with those of meteoric water in the summer months and showed increasing pearson correlation coefficients with increasing n alkane chain length r 0 80 for n c 31 while in samples from the most humid regions southeastern tibetan plateau the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites e 135 for mid chain and 125 for long chain n alkanes they become smaller e 118 to 41 mean value 86 at sites with a negative moisture balance northeastern and central tibetan plateau and qaidam basin this might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration in the core from lake koucha decreasing d values of all n alkanes between 15 and 10 cal ka bp give evidence for an intensification of the asian summer monsoon at ca 9 cal ka bp a ca 15 shift towards higher d values of mid chain n alkanes suggests enhanced evaporation of the lake water which outweighs higher precipitation amounts because of a temperature increase during the early holocene monsoonal maximum only a few surface sediment samples show a significant offset between d values of mid chain n alkanes and n c 31 d mid n c31 and no systematic dependence between this offset and environmental parameters such as mean annual precipitation was found in the core available data for most samples also do not show a significant offset only a slight increase 15 of d mid n c31 at ca 10 0 cal ka bp and a decrease 17 at ca 6 8 cal ka bp might indicate wetter and drier conditions respectively however interpretation of d mid n c31 throughout the record is difficult because of a lack of reliable data for n c 31 in key sections of the core so more records are necessary to further test the potential applicability of d mid n c31 as a proxy for palaeo hydrological conditions

cretaceous paleogeography and paleoclimate and the setting of ski borehole sites in songliao basin northeast china article i nfo as a paradigm of greenhouse climate in earth s history the cretaceous provides significant rock records of global climate changes under conditions of greenhouse climate the songliao basin among the longest dura tion 85 90 m y of continental sedimentary basins provides an excellent opportunity to recover a nearly complete cretaceous terrestrial sedimentary record extensive lake deposits ten kilometers deep and cover ing an area of 260 000 km 2 of the songliao basin provide unique detailed records that can be tied to the glob al stratigraphic time scale thereby improving our understanding of the continental paleoclimate and ecological system the two coreholes at skis and skin sites were drilled into this basin and completed with a total length of 2485 89 m of recovered core that spanned the complete middle to upper cretaceous strata in the basin the unique geological setting of long term continuous subsidence within the largest cretaceous landmass in the world makes the cretaceous songliao basin of northeastern china an ideal place to study cretaceous climate change on the continent this paper reviews the literature on the paleogeography and paleoclimate of the northern east asia and the songliao basin during the cretaceous based on the climatolog ically sensitive deposits oxygen isotope studies and paleontology the climate during the cretaceous in the songliao basin was temperate and humid with relatively abundant rainfall during the period significant changes four cooling three warming and three semiarid events are generally consistent with the oxygen isotope data from east asia and the four cooling events in berriasian valanginian aptian albian early santonian and campanian maastrichtian may be related to potential glaciations in cretaceous

gulf stream surface transport and statistics at 69 w from the geosat altimeter geosat altimeter height measurements for the gulf stream for three subtracks from the exact repeat mission were processed to remove the geoid and mean gulf stream height a gaussian model for the gulf stream velocity profile was used to predict the form of the residual height profiles seen by geosat and the mean height profile using estimates of the width and position derived from the height residuals estimates of the maximum surface velocity and the surface transport were obtained by a least squares fit of the synthetic height profiles to the data location statistics from the geosat data were in good agreement with values obtained from infrared images of the gulf stream maximum surface velocities were typically between 1 2 and 2 0 m s 1 the time series showed that surface transport is correlated primarily with the magnitude of the surface velocities although an anomalously large increase in surface transport in the winter of 1987 1988 was caused by an increase in the width of the gulf stream an analysis of the average annual signal in transport showed maximum values in the late fall and minimum transport in the late spring maximum minimum surface transport generally occurred when the gulf stream was north south of its mean position

on the meridional surface profile of the gulf stream at 55 w nine month records from nine inverted echo sounders iess are analyzed to describe the mean baroclinic gulf stream at 55 w ies acoustic travel times are converted to thermocline depth which is optimally interpolated kinematic and dynamic parameters gulf stream meridional position velocity and vorticity are calculated primary gulf stream variability is attributed to meandering and changes in direction a mean stream coordinate relative to gulf stream instantaneous position and direction meridional profile is derived and compared with results presented by other investigators the mean velocity is estimated at 0 84 m s 1 directed 14 to the right of eastward and the thermocline 12 c drops 657 m north to south corresponding to a baroclinic rise of the surface of 0 87 m the effect of gulf stream curvature on temporal mean profiles is found to be unimportant and of minimal importance overall the derived downstream current profile is well represented by a gaussian function and is about 190 km wide where it crosses zero surface baroclinic transport is estimated to be 8 5 104 m2 s 1 and maximum shear flanking the maximum is 1 2 10 5 s 1 results compare well with other in situ observational results from the same time period on the other hand analyses by others of concurrent satellite altimetry geosat suggest a considerably narrower more intense mean gulf stream

cretaceous climatic oscillations in the bering area alaska and koryak upland isotopic and palaeontological evidence abstract new isotopic palaeotemperatures estimated from 18 o values of early albian latest campanian and early maastrichtian ammonoid shells of southern alaska as well as our previously published data on the cretaceous of the koryak upland have been used to reconstruct palaeonvironmental changes in the bering area significant seasonal contrast marked in alaska and the adjacent area during the early albian as well as the coniacian was partly connected apparently with the possible penetration of cooler waters from the polar area via the strait of alaska data suggest that the bering land bridge existed during the post aptian cretaceous with the exception of the early albian and coniacian both the stable isotope and the floral data on the post aptian cretaceous of the bering area suggest the existence of warm climatic conditions in the late albian latest cenomanian coniacian santonian to early campanian latest campanian and also late early maastrichtian recurrent terrestrial cooling in northern alaska reflected in the composition of corresponding floras took place possibly because of a barrier to poleward oceanic heat transport via the western interior seaway wis of north america during the turonian and santonian through early campanian then during the late maastrichtian through danian

on the recent destabilization of the gulf stream path downstream of cape hatteras mapped satellite altimetry reveals interannual variability in the position of initiation of gulf stream meanders downstream of cape hatteras the longitude where the gulf stream begins meandering varies by 1500 km there has been a general trend for the destabilization point to shift west and 5 of the last 6 years had a gulf stream destabilization point upstream of the new england seamounts independent in situ data suggest that this shift has increased both upper ocean deep ocean interaction events at line w and open ocean shelf interactions across the middle atlantic bight mab shelf break mooring data and along track altimetry indicate a recent increase in the number of deep cyclones that stir deep western boundary current waters from the mab slope into the deep interior temperature profiles from the oleander program suggest that recent enhanced warming of the mab shelf may be related to shifts in the gulf stream s destabilization point

the floating astronomical time scale for the terrestrial late cretaceous qingshankou formation from the songliao basin of northeast china and its stratigraphic and paleoclimate implications abstract the upper cretaceous qingshankou formation k 2 qn in the songliao basin slb of northeast china consists of up to 550 m thick lacustrine mudstone and shale that constitute one of the most important source rocks of the daqing oil field a high resolution cyclostratigraphic analysis of the natural gamma ray logging from 10 wells of the qingshankou formation k 2 qn reveals orbital cycles of precession 20 ka obliquity 40 ka and eccentricity 100 ka and 405 ka providing strong evidence for astronomically driven climate changes in the late cretaceous terrestrial environments floating astronomical time scales ats are established for all sections which demonstrate variable durations of k 2 qn across the basin 1 09 ma 5 20 ma and strong diachroneity of the lacustrine strata four periods of high depositional rates can be identified in the central parts of the basin possibly recording deposition during times of sustained wet climate and high chemical weathering an ats established from well m206 in the central depression zone of the basin where the most complete and stable milankovitch cycles are present suggests that the maximum duration of the k 2 qn is 5 20 ma from 94 27 ma to 89 07 ma late cenomanian to early coniacian the lacustrine anoxic event 1 lae1 at the cenomanian turonian boundary lasted 210 310 ka during which the most prolific petroleum source rocks in slb were deposited the onset 94 21 94 18 ma and duration 210 310 ka of lae1 in slb are comparable to those of the oceanic anoxic event 2 oae2 onset at 94 21 ma and duration of 320 900 ka suggesting that the same trigger mechanism such as increased atmospheric co 2 from large scale igneous activity may have initiated high primary productivity and organic carbon burial in both marine and terrestrial systems

gulf stream transport and mixing processes via coherent structure dynamics the gulf stream has been characterized as either a barrier or blender to fluid transfer a duality relevant to gyre scale climate adjustment however previous characterization depended on relatively sparse lagrangian in situ observations the finite time lyapunov exponent ftle is calculated from satellite altimetry to identify lagrangian coherent structures lcs in the gulf stream region these lcs provide dense sampling of flow and capture distinct regions associated with mixing independent observations of ocean color contain similar flow dependent structures providing verification of the method and highlighting transport and mixing processes that influence sea surface temperature and chlorophyll among other water properties diagnosed lcs support the existing bower kinematic model of the gulf stream but also highlight novel behavior of comparable importance these include vortex pinch off and formation of spiral eddies clearly identified by lcs and which may be explained by considering changes to flow topology and the dynamics of shear flow instability at both small and large rossby number such processes seen though lcs may further enable validation of climate models the spatial distribution of these intermittent processes is characterized in terms of the criticality of jet dynamics with respect to rossby wave propagation and whether the jet is in an unstable or wave maker regime the generation and connectivity of hyperbolic trajectories in the flow appears to play an important role in governing large scale transport and mixing across the gulf stream

visions of ice sheets in a greenhouse world abstract backstripped eustatic estimates from new jersey and the russian platform show large 25 m and rapid 18 o record highlights the enigma this was the warmest interval of the past 200 my yet it was bracketed by two inferred eustatic falls of 25 m that were associated with two large 0 75 deep sea 18 o increases 92 93 ma mid turonian and 96 ma mid cenomanian we reconcile records of warm high latitudes with glacioeustasy by proposing that late cretaceous early eocene ice sheets generally reached maximum volumes of 8 12 10 6 km 3 20 30 m glacioeustatic equivalent but did not reach the antarctic coast hence coastal antarctica hence deep water remained relatively warm even though there were significant changes in sea level as the result of glaciation unlike the oligocene and younger icehouse world these ice sheets only existed during short intervals of peak milankovitch insolation leaving antarctica ice free during much of the greenhouse late cretaceous to middle eocene these results highlight the need to re evaluate the paradigm that polar ice sheets did not exist during times of warm high latitude climates

five year climatological survey of the gulf stream system and its associated rings a 5 year climatological survey of the gulf stream system s landward surface edge defines the mean standard deviation extreme limits annual and interannual variabilities and frequency distributions along 0 5 longitudinal transects from 91 to 44 w the climatology covers the loop current in the gulf of mexico and the gulf stream in the northwest atlantic ocean autocorrelations and power spectra are derived for longitudinal transects between 79 5 and 57 5 w the study also investigates the observed warm core ring and cold core ring movements and their areal extent the observed data are compiled from the oceanographic analysis charts produced by the national oceanic and atmospheric administration which utilize infrared satellite imagery and in situ observations east of cape hatteras the gulf stream system landward surface edge exhibits both interannual and annual signals the interannual variability is equal to the annual variability the mean monthly gulf stream position for the longitudinal band 70 44 w shifts from farthest north in september to farthest south in february the magnitude of the annual shift is largest near the grand banks frequency distributions of the gulf stream system position are quasi normal nearly everywhere autocorrelation plots from the 5 year time series of gulf stream positions at longitudinal transects 79 5 57 5 w exhibit three well defined e folding time regimes with a maximum time of 10 weeks at 72 w power spectrums from 79 5 to 57 5 w are red spectrums having dominant peaks of 1 year period or greater the largest total spectra energies are found at 61 w the loop current sheds rings at two apparent spatial scales which are labeled major 307 km mean and minor 185 km mean warm core rings annually the loop current sheds about one major warm core ring which translates into the western basin of the gulf of mexico and one minor warm core ring which is usually reabsorbed by the loop current the major loop current warm core ring sheddings have no seasonal preference loop current warm core rings have a mean velocity of 2 4 km d west southwest an average of 22 gulf stream warm core rings are formed and absorbed annually between 75 and 44 w the largest frequency of warm core ring formations is seen near the new england seamounts while the largest frequency of warm core ring absorptions is found near cape hatteras gulf stream warm core rings can absorb each other as occurred in 14 of the absorption cases with the highest frequency just upstream of the new england seamounts the gulf stream warm core rings have a surface diameter decay rate of 0 026 per week loop current warm core rings are similar the gulf stream warm core rings have a mean velocity of 2 4 km d west southwest cold core rings have a mean cool core surface diameter of 105 km and a mean velocity of 1 km d southwest more definitive conclusions on cold core rings are not possible as ring identification and tracking by satellite infrared imagery is tentative

upper cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from sakhalin russian far east a proxy for the isotopic composition of paleoatmospheric co2 abstract time stratigraphic patterns of stable carbon isotopic ratios recorded in terrestrial organic matter from cenomanian maastrichtian successions for the russian far east can be correlated to those of carbonate carbon from well studied successions for other parts of the world age indicative biostratigraphy based on regional ammonoids and inoceramid bivalves are well established in japan and can be applied to the whole cretaceous succession except for the upper cenomanian lower turonian and the upper part of the maastrichtian zones lacking macrofossils globally correlative carbon isotopic events previously documented with carbonate carbon from europe and with carbonate carbon and marine organic matter from the u s western interior are recognized with similar magnitude through uppermost cenomanian lower campanian in ascending order these events are positive spike across the cenomanian turonian boundary step like leveled segment followed by negative shift lower middle turonian trough like negative excursion middle upper turonian positive rebound coupled with following broad peak coniacian and positive peak basal campanian followed by modest negative excursion the parallel fluctuation of the 13 c value between the terrestrial organic matter and carbonate suggests carbon isotopic equilibrium between surface seawater and atmospheric co 2 and demonstrates that the isotopic curve of terrestrial organic carbon can be used to monitor carbon isotopic fluctuations of co 2 in the ocean atmosphere system in the upper campanian and maastrichtian a negative 13 c excursion within chron 33r and a following rapid rebound can be correlated with the same distinctive carbon isotopic feature of carbonate observed in the deep sea cores from south and north atlantic the indian and the pacific oceans within this interval the 13 c value of terrestrial organic matter also reflects carbon isotopic fluctuation of the global co 2 reservoir with relatively minor regional local noise

observations on the long period variability of the gulf stream downstream of cape hatteras to examine the long period variability of the gulf stream sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 75 w and 60 w longitude are used residuals as derived from geosat altimetry between november 1986 and december 1988 were gridded in space and time at a temporal resolution of 10 days and spatial resolution of 1 4 complex empirical orthogonal function ceof analysis was applied to the data set to extract the spatially correlated signal with the original data sub sampled to 1 2 in addition to determining the space time scales and propagation characteristics of the different modes wavenumber frequency spectral techniques were used to separate the variability into propagating and stationary components the ceof technique applied to the data set indicated that the first four ceof modes accounted for 60 of the variability and were found to be above the noise level 99 of the time ceof 1 was associated with westward propagation at 5 km d at a wavelength of 2000 km and eastward propagation at 1 2 km d centered at a 500 km wavelength this first ceof is in good agreement with thin jet equivalent barotropic models which predict westward propagation for wavelengths greater than 1130 km a deflection of the wavelike pattern at 65 w also indicates a possible topographic effect a simple scaling of the effect of topography indicates that for length scales longer than the internal rossby radius of deformation the topographic term is at least of the same order of magnitude as the beta effect the second ceof was more broadbanded in wavenumber space with eastward propagation occurring in a wavenumber frequency band between 300 and 1400 km and 0 5 and 2 0 cycles yr the third ceof is similar in structure to the first but with less energy ceof 4 was clearly identifiable with higher frequencies than the first three with westward propagation at 4 km d the spatial location of this mode along with the westward propagation indicates possible influences from eddy stream interactions thus topography rossby wave dynamics and eddy stream interactions all appear to have a significant role in determining the space time scales and propagation properties of the long period response of sea level in the gulf stream

a comparison of surface eddy kinetic energy and reynolds stresses in the gulf stream and the kuroshio current systems from merged topex poseidon and ers 1 2 altimetric data analyses of surface eddy kinetic energy eke inferred from 5 years of merged topex poseidon and ers 1 2 altimetric data are presented in the gulf stream gs and the kuroshio ks current systems focusing on anisotropy and eke seasonal interannual and long term variations as well as reynolds stresses for both gs and ks a descriptive analysis of the eke field shows that it is anisotropic along the path of the currents and assesses the close relationship between the spatial distribution of eke high levels and bottom topography a striking ocean feature is found in the gs shaped as a zonal double blade structure in the eke field centered at 37 n 71 5 w that likely corresponds to a regular and permanent lateral displacement of the mean path of the current at this geographical location maps of eke seasonal means for years 1993 1996 and 1997 provide a detailed description of the surface variability meanders pinched off eddies etc and show strong interannual variations in the ks eke monthly mean changes in the ks reveal a well marked seasonal cycle during the first 3 years 1993 1995 with eke peaking in july august this is followed by a constant increase of its level from the beginning of year 1996 till the beginning of 1997 during this increase the zonal velocity variance u 2 is up to 30 higher than its meridional counterpart suggesting a zonal acceleration of the eastward flow eke seasonal changes are also found in the ks current 30 35 n 130 140 e and also show a regular annual cycle during the first 3 years which precedes by 2 months the eke seasonal cycle in the ks extension maximum in may june the maximum in eke in both regions precedes by 2 months the maximum surface transport found by qiu et al 1991 and zlotnicki 1991 occurring in july and late september respectively no such annual cycle is found in the gs region during the first 3 years year 1996 is anomalous in both current systems with mean eke level that increases by more than 20 compared to the other years also eke monthly mean changes in the ks reveal a well marked positive tendency in the eastern part of the current of more than 300 cm2 s 2 yr 1 and a negative tendency both in its eastern part and in the ks current this feature is absent from the gs at last eddy mean flow interaction is presented both the spatial averaging of turbulent quantities and the relative contribution of the different terms of the horizontal momentum fluxes are discussed a tentative explanation is given for the anomalously large u 2 at the end of 1996 in the ks extension

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

sea surface topographic variability near the new england seamounts an intercomparison among in situ observations numerical simulations and geosat altimetry from the regional energetics experiment intercomparisons are made among three sets of results for two regions of the gulf stream upstream and downstream of the new england seamount chain nesc observational records from 12 inverted echo sounders with pressure gauges ies pgs concurrent geosat altimeter crossover point differences and results from a primitive equation model of the region standard deviations of sea surface topography show generally good agreement for the three data sources no significant difference between the upstream and downstream regions is observed in the actual data ies pg records and geosat topographic variability have values of about 30 cm on both sides of the nesc although model results show a discrepancy in the eastern region barotropic fluctuations account for about 30 of the total surface topographic variability and are only partially correlated with baroclinic fluctuations

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

the stable hydrogen isotopic composition of sedimentary plant waxes as quantitative proxy for rainfall in the west african sahel various studies have demonstrated that the stable hydrogen isotopic composition d of terrestrial leaf waxes tracks that of precipitation d precip both spatially across climate gradients and over a range of different timescales yet reconstructed estimates of d precip and corresponding rainfall typically remain largely qualitative due mainly to uncertainties in plant ecosystem net fractionation relative humidity and the stability of the amount effect through time here we present d values of the c 31 n alkane d wax from a marine sediment core offshore the northwest nw african sahel covering the past 100 years and overlapping with the instrumental record of rainfall we use this record to investigate whether accurate quantitative estimates of past rainfall can be derived from our d wax time series we infer the composition of vegetation c 3 c 4 within the continental catchment area by analysis of the stable carbon isotopic composition of the same compounds 13 c wax calculated a net ecosystem fractionation factor and corrected the d wax time series accordingly to derive d precip using the present day relationship between d precip and the amount of precipitation in the tropics we derive quantitative estimates of past precipitation amounts our data show that a vegetation composition can be inferred from 13 c wax b the calculated net ecosystem fractionation represents a reasonable estimate and c estimated total amounts of rainfall based on d wax correspond to instrumental records of rainfall our study has important implications for future studies aiming to reconstruct rainfall based on d wax the combined data presented here demonstrate that it is feasible to infer absolute rainfall amounts from sedimentary d wax in tandem with 13 c wax in specific depositional settings

gulf stream path analysis near the new england seamounts as part of the naval ocean research and development activity s regional energetics experiment 12 inverted echo sounders iess were deployed from june 1985 to july 1986 in two arrays across the historical mean path of the gulf stream near 67 w and 58 w slightly upstream and downstream of the new england seamount chain gulf stream positions and directions were computed at half day intervals for adjacent ies pairs levels of variability at the two array locations were similar but the characteristics of the meanders in terms of propagation and current direction were quite different evidence was found for a quasi stationary meander near 58 w features deduced from ies measurements are compared with concurrent infrared air dropped expendable bathythermograph and geosat altimetry observations

assessment of the difference between mid and long chain compound specific δdn alkanes values in lacustrine sediments as a paleoclimatic indicator abstract previous studies have proposed that the difference between compound specific hydrogen isotopic composition of n alkanes d n alkanes of possible terrestrial origin and aquatic origin in lacustrine sediments is an indicator of hydroclimatic conditions for a lake environment e g terrestrial evapotranspiration of the lake drainage area or evaporation inflow ratio for the lake sachse d radke j gleixner g 2004 hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability geochimica et cosmochimca acta 68 4877 4889 sachse d radke j gleixner g 2006 d values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record organic geochemistry 37 469 483 mugler i sachse d werner m xu b q wu g j yao t d gleixner g 2008 effect of lake evaporation on d values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany organic geochemistry 39 711 729 and this proposed indicator has been applied to a paleoclimatic study of koucha lake kcl on the northeastern tibetan plateau netp however the application was not very successful due to an apparent discrepancy between the reconstructed possible hydroclimatic variation based on the proposed indicator and precipitation amount variation based on pollen in the same lake aichner b herzschuh u wilkes h vieth a bohner j 2010a d values of n alkanes in tibetan lake sediments and aquatic macrophytes a surface sediment study and application to a 16 ka record from lake koucha organic geochemistry 41 779 790 we report new compound specific d n alkanes data for sediments since the last glacial from hurleg lake klk and genggahai lake ggh both also on the netp ca 300 km apart together d n alkanes data from the three lakes were analyzed to assess the difference between mid chain and long chain compound specific d n alkanes values in the sediments as a paleoclimatic indicator our results indicate that mid chain n c 23 and n c 25 and long chain n c 27 n c 29 and n c 31 n alkanes as compounds representative of aquatic and terrestrial origins respectively were valid only for klk correspondingly the use of differences between mid chain and long chain compound specific d n alkanes as a possible paleoclimatic indicator was feasible only for this lake hence our results emphasize the complex relationship between the chain length of lacustrine n alkanes and their actual origins and suggest that the correlation analysis of d n alkanes data for different chain length could be part of the possible evaluation method for the application of lacustrine compound specific d n alkanes data in paleoclimatic studies

determination of sediment provenance at drift sites using hydrogen isotopes and unsaturation ratios in alkenones the large 20 hydrogen isotopic gradient in surface waters of the northwest atlantic ocean is exploited to track changes in the source of alkenones to the bermuda rise sediment drift cultures of the predominant alkenone producing coccolithophorid e huxleyi were grown in deuterium enriched seawater and shown to possess alkenones with a d h ratio that closely tracked the water d h ratio r 2 0 999 n 5 isotopic enrichments with a fractionation factor between 0 732 and 0 775 a hydrogen isotopic depletion of 193 3 n 9 was measured in alkenones from suspended particles relative to seawater in the subpolar and subtropical northwest atlantic ocean this value was used to calculate the water d values in which alkenones from bermuda rise sediment were synthesized and by extension the water mass in which they were produced applying this technique we find that 60 to 100 of the alkenones in late holocene bermuda rise sediment were produced in deuterium depleted subpolar water to the northwest of the drift to reconcile values of the alkenone unsaturation ratio u k 37 a widely used proxy for sea surface temperature with the d values of alkenones in late holocene sediments from the bermuda rise at least three sources of sediment must be invoked a cold very isotopically depleted source almost certain to be the scotian margin a warm moderately isotopically depleted source likely to be the northwestern edge of the subtropical gyre and a cold isotopically enriched source which we hypothesize to be the subpolar waters overlying the main branch of north atlantic deep water flowing southwest from the nordic seas copyright 2005 elsevier ltd paleoclimate records with sufficient length and temporal resolution to study the occurrence and causal mechanisms of abrupt climate change are exceedingly rare rapidly deposited ocean sediments provide the best archive for studying these events through geologic time but such sites in the open ocean are limited to sediment drift deposits such as the bermuda rise in the northwest atlantic using multiple climate proxies in a single core is becoming more common in high resolution pa leoclimate investigations but a major potential concern for this approach arises from the possibility that the fine fraction of sediment e g 63 m and the climate proxies within it may represent conditions far from the deposition site here we propose and test the hypothesis that hydrogen isotope ratios of alkenones a class of lipids from phytoplankton may provide insight into the source of fine grained sediment because of their restricted sources broad geographic distri bution and excellent preservation properties alkenones are of particular interest in the emerging field of compound specific hydrogen isotopic analysis the sedimentary abundances ex tents of unsaturations and isotopic compositions of alkenones provide quantitative and near continuous records we isolated alkenones from cultured unicellular algae haptophyte emil iania huxleyi surface ocean particulate material and open ocean sediments to determine the extent and variability of hydrogen isotopic fractionation in the di tri and tetraunsat urated c37 compounds we then compared the d values of the alkenones in surface sediments between the bermuda rise and the scotian margin above which a large 20 d gradient exists we determined the fractionation between alkenones from suspended particulate samples and the water in which the phytoplanton lived and examined the variability of alkenone d values during the medieval warm period little ice age climate transition cf keigwin 1996 at the bermuda rise

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

gulf stream path and thermocline structure near 74 w and 68 w the synoptic ocean prediction synop experiment had the goal of providing a physical understanding of energetic mesoscale eddy processes in the gulf stream in the synop inlet array off cape hatteras and in the central array near 68 w modred observations were collected from october 1987 through august 1990 the inlet array measured the surface path and bottom currents where the gulf stream leaves the continental margin to enter the deep water regime small amplitude propagating and growing meanders characterized the variability there the central array measured velocity and temperature as a proxy for density at four levels in the water column as well as the upper and deep level streamfunctions all with mesoscale resolution near 70 w the path envelope exhibited a relative node confined within a 40 km band 55 of the time near 68 w the path envelope was over 3 times as wide due to several elongated steep meander troughs and relatively steep meander crests the crests typically propagated downstream without much growth the troughs often stalled near 68 w steepened and persisted for one to several months two cases evolved into s shaped paths and subsequently formed rings even the time averaged fields showed a small trough in the mean path and thermocline structure whereas meanders of 20 to 60 day periods had similar spectral levels throughout 70 67 w meanders with long periods 85 day accounted for the local minimum in variance at 70 w bottom pressure and velocity observations revealed repeated periods of intense swirl speeds 0 30 m s 1 abyssal eddies the time averaged deep currents exhibited a mean cyclone centered 30 km offshore and downstream of the upper layer mean trough the cross stream slope of the thermocline steepened linearly with path curvature consistent with gradient wind balance structures are illustrated in the mapped fields consistent with baroclinic instability wherein troughs steepen and rings form

δd values of individual n alkanes from terrestrial plants along a climatic gradient implications for the sedimentary biomarker record abstract the compound specific hydrogen isotope composition d of sedimentary n alkanes is increasingly used as a palaeoclimate proxy to explore the origin of the hydrogen isotope signal of n alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n alkane composition and d values of 31 plant biomass samples birch betula beech fagus oak quercus alder alnus hornbeam carpinus and myrtle myrtus as well as non stomata containing sphagnum cladonia and moss from 14 sites along a climatic gradient from northern finland to southern italy eleven of the sites were previously investigated for the n alkane d values in adjacent lake sediments and are compared to the leaf wax n alkane d values the distribution of terrestrial n alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake evidently n alkane distributions within the same species at different sites were found to be variable these findings complicate the use of certain n alkane distributions in sediments as a palaeoenvironmental indicator d values of plant biomass n alkanes show a significant positive correlation with the precipitation d values biomass n alkane d values are in general less negative than the associated sedimentary n alkanes of terrestrial origin possibly due to the stronger evapotranspiration during the summer when sampling took place this suggests that n alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn when most leaves are incorporated into the sediment the variability of the d values from non stomata containing plants is much higher than for broadleaf trees since stomata can regulate water loss through evapotranspiration the average chain length acl of n alkanes from deciduous tree leaves increases from north to south with increasing acl the hydrogen isotopic fractionation e between source water and n alkanes also increases our results prove that terrestrial n alkane d values record the d value of precipitation modified by the amount of isotope enrichment in the leaf water due to plant anatomy stomata vs no stomata and site specific meteorological conditions such as evapotranspiration relative humidity and soil moisture therefore terrestrial n alkanes in lake sediments can deliver information on changes in these parameters over geological timescales in lake sediments where aquatic n alkanes such as n c 17 record the lake water d value the isotopic difference between terrestrial and aquatic n alkanes could therefore be used to reconstruct changes in evapotranspiration

high frequency variability of western boundary currents using ers 1 three day repeat altimeter data ers 1 three day repeat altimeter ocean products have been analyzed from september 3 to december 9 1991 in the high mesoscale energy areas of the world ocean the obtained height variability is comparable to that derived from 2 years of geosat altimeter data 17 day repeat while it is slightly lower elsewhere the data reveal some high frequency variability of western boundary currents but not the seasonal signals nor the low frequency mesoscale signal which dominates elsewhere isocorrelation maps show that the e folding time is around 10 to 15 days in strong currents the sea height variance integrated over all wavelengths in the frequency wavenumber spectrum corresponds to less than 5 of the total 3 month variance for periods shorter than 20 days up to 15 of this variance for periods shorter than 34 days which are respectively the nyquist frequencies of the topex poseidon and geosat data this signal covers a whole range of wavelengths that cannot be obtained from current meter data in the gulf stream area the total dynamic height signal is estimated by adding a climatological dynamic topography to the mesoscale variability near 60 w the height variations apparently correspond to meanders with periods of 30 to 40 days and latitudinal extension about 200 km they are consistent with westward propagation at about 10 cm s and their surface transport varies by about 50 on this timescale which is in agreement with in situ observations

late cretaceous stratigraphy songliao basin ne china sk1 cores abstract the songliao basin is the largest cretaceous oil and gas producing lacustrine basin in china with its greatest aerial extent in the middle cretaceous a coring program sk1 has to date yielded 2485 89 m of continuous core 96 46 recovery and provides significant material for cretaceous research the sequence of the core consists mainly of lacustrine sandstone dark grey mudstone shale and oil shale the upper cretaceous stratigraphic section has been subdivided into the quantou qingshankou yaojia nenjiang sifangtai and mingshui formations in ascending order late cretaceous microfossils are diverse and abundant a detailed biostratigraphic study has subdivided the sequence into high precision biozones 21 ostracode assemblages 10 phytoplankton assemblages 7 palynological zones and 4 charophyta assemblages respectively in addition marine foraminifera were first discovered from the basin three 206pb 238u ages and one 40ar 39ar age were analysed ten local magnetozones have been recognised in the sk1 north and two magnetozones have been indicated in the sk1 south based on biostratigraphy high resolution magnetostratigraphy and sims u pb zircon analyses the sk1 stratigraphy is correlated with upper cretaceous stages in the international geologic time scale the upper part of the quantou formation is the lower turonian the qingshankou formation is the upper turonian lower coniacian the yaojia formation is from the upper coniacian to middle santonian the nenjiang formation is the upper santonian to middle campanian the sifangtai formation is limited to the upper campanian and the mingshui formation is the uppermost campanian to maastrichtian it is likely that the upper part of the mingshui formation belongs to the paleocene and the k pg boundary is within the member 2 of the mingshui formation around the depth of 328 m by new micropalaeontologic and magnetostratigraphic data

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

effect of lake evaporation on δd values of lacustrine n alkanes a comparison of nam co tibetan plateau and holzmaar germany compound specific hydrogen isotope ratio values of lacustrine n alkanes from two contrasting ecosystems the semiarid to arid nam co central tibet and the humid holzmaar germany were compared in order to assess whether or not these environmental conditions are recorded in the isotopic signatures of biomarkers increased evaporation of lake water at nam co is recorded by the n alkanes of aquatic origin hence isotopic enrichment results in a di erence between terrestrial and aquatic n alkanes in the opposite direction 68 from that known for humid climate conditions 30 predominating at holzmaar based on this isotopic di erence between terrestrial and aquatic n alkanes evaporation to inflow ratio e i values were estimated and suggest that the isotopic di erence is indicative of the general hydroclimatic characteristics of a lake system moreover the comparison with e i values calculated with actual stable water isotope data showed that the dd values of aquatic and terrestrial lacustrine n alkanes serve as a proxy for the relative isotopic di erences between lake and inflow waters and can be used to assess the proportion of water undergoing evaporation relative to the inflow and thus to reconstruct the lake water balance in the past 2008 published by elsevier ltd

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

photic zone euxinia during the permian triassic superanoxic event carbon and sulfur isotopic data together with biomarker and iron speciation analyses of the hovea 3 core that was drilled in the perth basin western australia indicate that euxinic conditions prevailed in the paleowater column during the permian triassic superanoxic event biomarkers diagnostic for anoxygenic photosynthesis by chlorobiaceae are particularly abundant at the boundary and into the early triassic similar conditions prevailed in the contemporaneous seas off south china our evidence for widespread photiczone euxinic conditions suggests that sulfide toxicity was a driver of the extinction and a factor in the protracted recovery

chemical molecular and isotopic differentiation of organic facies in the tertiary lacustrine duaringa oil shale deposit queensland australia abstract total organic matter extractable organic matter bitumen and pyrolysates released on low temperature sealed tube pyrolysis of kerogen were analysed chemically and isotopically based on bulk bitumen and biomarker parameters the sediments are immature to a depth of approx 1300 m within the terrestrial and lacustrine depositional environments of the tertiary duaringa basin various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land plant and algal sources the latter derived mainly from pediastrum and with a varying botryococcus content the lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community relative contributions from allochthonous land plants and for the lower lamosite a slightly more saline and restricted lake environment the lower lamosite is associated with the highest concentrations of c 28 c 30 4 methylsteranes and 13 c depletion in toc in the upper lamosite there is a strong positive correlation between botryococcus content and 13 c enrichment the organically lean claystones have sources nearly identical to the lamosites but the organic matter is diluted due to rapid influx of siliciclastics the terrestrial facies the cannel coal and carbonaceous shales are mainly distinguished from the lacustrine facies by higher relative proportions of c 29 steranes c 30 4 methylsteranes and 13 c values for the pyrolysed hydrocarbons intermediate between the two lamosite facies the carbonaceous oil shale has a composite geochemical signature intermediate between the two end members lamosite and cannel coal oleanane and ring a degraded triterpanes derived from lupane arborane and oleanane skeletons are distributed throughout all organic facies representing both autochthonous and allochthonous higher plant inputs higher concentrations of oleanane and des a lupane are associated with the terrestrial facies hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies for the lamosites the aliphatic biopolymer algaenan is implicated as the dominant source for n alkanes from analysis of their yields homologue abundances and individual 13 c values in the terrestrial facies resinites are paraffinic and are a major source for the n alkanes released on pyrolysis compound specific analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen for the lamosites low molecular weight n alkanes in the bitumen are derived mainly from a pediastrum source while botryococcus is associated with waxy n alkanes however the situation is reversed in the kerogen pediastrum algeanan has a longer average alkyl chain length than botryococcus algaenan the magnitude of the isotopic differences between single n alkanes released at different temperatures is useful in determining multiplicity of sources

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

paleosalinity significance of occurrence and distribution of methyltrimethyltridecyl chromans in the upper cretaceous nenjiang formation songliao basin china abstract a group of methyltrimethyltridecyl chromans mttcs was found in core samples of member 1 k 2 n 1 and member 2 k 2 n 2 of the nenjiang formation upper cretaceous from the sk l southern borehole songliao basin china they are assigned for the first time in sediments older than the tertiary in china their composition and distribution are indicative mainly of the redox and salinity conditions in the depositional environment the mttc isomer is in relatively higher abundance in samples from enhanced salinity and reducing conditions but was not detected in samples from aerobic and low salinity environments while mttc appears to be present in samples from environments with a broad range of salinity and redox conditions the mttc mttc ratio has a similar indication as that of the ratio and could be used as a corroborative ratio of paleosalinity a combination of biomarker parameters suggests that the massive lacustrine petroleum prone source rocks associated with the k 2 n 1 interval were likely developed under a stratified water column with enhanced salinity and an anoxic bottom water layer associated with a much less saline fresh to brackish upper water layer

variability in the slope water and its relation to the gulf stream path 1 sea surface temperature sst and sea surface height ssh data for 1993 2007 for the north atlantic are combined with hydrographic data at 69w to investigate the relation between the gulf stream gs position and the slope water properties sst anomalies north of the gs are correlated with changes in its path the lag of this correlation is such that positive temperature anomalies precede northward shifts of the gs and suggests that sst anomalies move westward with speeds of several cm s eof analysis of the sst and ssh fields shows that cooling and strengthening of the sw flow are in phase over the slope water which is mirrored in the vertical structure of these fields at 69w indicating larger transports in the deep western boundary current lead to southward shifts of the mean gs path this relation between the slope water and the gs path provides some predictability for the latter

effects of an oceanic anoxic event on the stable carbon isotopic composition of early toarcian carbon the early toarcian transgression is marked by the occurrence of organic carbon rich shales in large parts of western europe and in other parts of the world as well based on the positive carbon isotope excursion of pelagic limestones in the middle to upper part of the falciferum zone in several of the tethyan sections the widespread occurrence of the early toarcian shales was explained by an oceanic anoxic event oae jenkyns 1988 jenkyns and clayton 1997 the rapid burial of large amounts of organic carbon which is rich in 12 c would have led to a relative enrichment in 13 c of the global carbon reservoir and hence to an increase in delta 13 c of the limestones in southwest germany and a number of other locations both organic and inorganic carbon display a negative isotope excursion in the upper part of the tenuicostatum zone and the lower part of the falciferum zone synchronous to black shale deposition and predating the positive isotopic excursion kuspert 1982 1983 it is presently unclear what the exact cause for this widespread negative isotopic excursion is jenkyns and clayton 1997 the objective of our study was to examine if the negative carbon isotope excursion of organic matter om in the southwest german toarcian shales can be attributed to compositional changes of the om or if the excursion is related to variations in delta 13 c sub co2 aq in the photic zone to this end we analyzed the molecular and stable carbon isotope composition of om in ten samples spanning the early toarcian toc 2 5 10 5 percent hi 350 700 biomarker distributions and kerogen pyrolysates differ only slightly among the samples and delta 13 c values of primary production markers follow closely those of associated carbonate and kerogen delta 13 c sub carb toc this strongly suggests that differences in delta 13 c toc are related to differences in delta 13 c of co 2 aq in the photic zone supporting kuspert9s model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters evidence for euxinic conditions extending into the photic zone was found by the presence of derivatives of carotenoids such as isorenieratane from anoxygenic phototrophic sulfur bacteria their concentrations are extremely low in black shales from the tenuicostatum zone but are significant in the falciferum and bifrons zone with a maximum in the exaratum subzone suggesting that photic zone euxinia pze was a common feature of the early toarcian sea in southwest germany our data therefore support the kuspert model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters to the upper part of the photic zone resulting in a negative isotope spike the enrichment in 13 c in the middle of the falciferum zone which followed the negative spike may be attributed to the burial of isotopically light organic matter through worldwide black shale deposition