early diagenesis in deep sea turbidites the imprint of paleo oxidation zones sediment cores up to 35 m long have been recovered from turbidite sequences in the madiera abyssal plain and the southern nares abyssal plain detailed geochemical analyses of these sediments si al fe mn ca organic and inorganic carbon and associate pore waters nitrate ammonia silicate fe2 mn2 and alkalinity provide representative profiles of both steady state and nonsteady state diagenetic reactions initiated by oxidation and reduction processes models demonstrate that chemical transport in the pore water system is diffusion dominated over periods of a few thousands of years to several hundreds of thousands of years mn and fe mobilized in the subsurface mildly reducing sediments are precipitated as easily reducible oxyhydroxides in the near surface oxidized sediments nonsteady state profiles show the influence of episodic and rapid turbidite deposition and the imprint of oxidation zones that developed as the result of oxygen diffusion into the upper portions of turbidites during intervals of slow pelagic deposition the time required for development of oxidation zones between turbidites ranges from 2 0 to 15 ka in the madeira abyssal plain and from 0 2 to 2 4 ka in the southern nares abyssal plain paleo oxidation zones can be recognized in old turbidites by distinct changes in color between lower and upper portions of the deposit in the basal unoxidized portion of the turbidite the sediments are characteristically dark green gray or brown in the paleo oxidized zone the sediments are pale green blue or yellowish brown these zones in both the madeira and southern nares abyssal plains contain distinctly less organic c and carbonate in the paleo oxidized zone as compared with the unoxidized sediments depletion of carbonate content in the oxidized zones in the southern nares abyssal plain is particularly significant in that as much as 80 of the initial carbonates have been lost also the relative amounts of weak acid soluble fe and mn are generally less in the paleo oxidized zones due to the initial oxidation of metal carbonate and metal hydroxide forms to easily reducible oxide forms which are then subsequently solubilized under the mildly reducing conditions at depth in the sediment column

ocean bottom profiling with ambient noise a model for the passive fathometer a model is presented for the complete passive fathometer response to ocean surface noise interfering discrete noise sources and locally uncorrelated noise in an ideal waveguide the leading order term of the ocean surface noise contribution produces the cross correlation of vertical multipaths and yields the depth of sub bottom reflectors discrete noise incident on the array via multipaths give multiple peaks in the fathometer response these peaks may obscure the sub bottom reflections but can be attenuated with use of minimum variance distortionless response mvdr steering vectors the seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response these peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle

influence of antarctic ice sheet lowering on the southern hemisphere climate modeling experiments mimicking the mid miocene a coupled global atmosphere ocean model is used to study the influence of the antarctica ice sheet in a configuration that mimics that of the early miocene on the atmospheric and oceanic circulations based on different climate simulations of the present day ctr and conducted with distinct antarctic ice sheet topography ais exp it is found that the reduction of the antarctic ice sheet topography ais induces warming of the southern hemisphere and reduces the meridional thermal gradient consequently the atmospheric transient low level eddy heat flux overline v prime t prime and the eddy momentum flux overline u prime v prime are reduced causing the reduced transport of heat from the mid latitudes to the pole the stationary flow and transient wave anomalies generate changes in the ssts which modify the rate of deep water formation strengthening the formation of the antarctic bottom water substantial changes are predicted to occur in the atmospheric and oceanic heat transport and a comparison between the total heat transport of the atmosphere ocean system as simulated by the ais exp and the ctr runs shows that the reduction of the ais height leads to reduced southern hemisphere poleward and increased equatorward heat transport these results are in agreement with reduced storm track activities and baroclinicity

improved constraints on open system processes in fossil reef corals by combined th u pa u and ra th dating a case study from aqaba jordan abstract here we present 230th u 231pa u as well as 226ra 230th isotope ratios from five fossil reef corals of last interglacial origin from the gulf of aqaba northern red sea the results show clear evidence for open system behaviour with strongly elevated 234u values and u concentrations indicating post depositional u addition the combined application of all isotope systems enables us to better constrain the nature and timing of the open system processes than only based on the 230th u data quantitative modelling of the diagenetic processes allowed us to reproduce the trends in the isotope ratios two of the five corals were probably affected by two separate phases of u addition with different 234u values the trends observed for two other corals can be explained by u addition followed by u loss the fifth coral shows signs of both u gain and loss at the same time in the more recent past the timing of the diagenetic processes is remarkably similar for the five corals and can be constrained to approx 1 and 6 thousand years ka and 100 and 102 ka after coral growth respectively based on the modelling results we suggest that conventional 231pa 230th ages provide the best estimate for the true age of four of the five corals which range from 109 1 to 114 1 ka this implies a late last interglacial time of deposition for the fifth coral the most reliable age estimate is the conventional 230th u age of one of the subsamples 117 3 ka based on a concordia diagram for all subsamples the timing of the modelled open system processes suggests that the early event of u addition was associated with interaction of the corals with 234u enriched seawater or saline groundwater the later open system event can be described as u redistribution within the coral reef since some corals apparently lost u while others gained u the timing of the second event is broadly consistent with the bolling allerod interstadial which was probably characterised by enhanced wetness in this typically hyper arid region

grain size variations in pelagic carbonate oozes from the walvis ridge se atlantic ocean odp site 1265 a low resolution miocene record of carbonate sedimentation and preservation abstract a record of variations in winnowing and dissolution was established for miocene 19 7 ma deep sea sediments at site 1265 from the walvis ridge south atlantic in this study we apply a new preservation index based on the abundance of coarse calcareous silt fraction 10 63 m the miocene record of this silt preservation index corresponds well with the conventional foraminiferal preservation index and variations in sand content preservation ranging from good to moderate during the miocene indicates that site 1265 is located above and close to the foraminiferal lysocline grain size mass accumulation rates of carbonate and organic carbon records indicate that changes in productivity and carbonate production play a minor role in variations of calcium carbonate concentration the miocene variation in carbonate content is caused mostly by a combination of winnowing and dissolution significant decreases of preservation at 17 3 16 3 13 8 13 0 11 6 and 10 4 ma coincide with miocene glacial events mi events suggesting that dissolution was caused by an increase of southern component water scw influence which occurred as a response to the intensification of antarctic ice sheet development the scw acts as the major deep water source during the global miocene cooling at 10 4 ma a change to overall better preservation points to a weakening of scw that occurred as a response to the initiation or strengthening of north atlantic deep water nadw

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

a case of post depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the madeira abyssal plain abstract a set of oxidized and unoxidized sediment intervals from the f turbidite identified in two piston cores from the madeira abyssal plain map was analyzed for calcium carbonate total organic carbon toc total nitrogen tn stable carbon composition of toc 13c toc total hydrolyzable amino acids thaa total neutral sugars tsug lignin phenols lig two different lipid biomarkers of marine phytoplankton origin and vascular plantwax n alkanes and n acids comparison shows changes for all properties depicting the effect of post depositional aerobic oxidation the oxidation process re mineralized approximately 80 of the toc and approximately 60 of the tn in the original deposit and left the residual organic matter depleted in 13c by 1 7 2 9 thaa and tsug account for 10 or less of the toc in all samples leaving approximately 90 of the toc chemically unidentified thaa tsug lig marine phytoplankton biomarkers and plantwax n acids were lost from the oxidized deposit to an extent as great as that for toc two non protein amino acids alanine and aminobutyric acid and plant wax n alkanes displayed much less degradation 9 37 and concentrated 3 3 4 8 times relative to toc by the oxidation process these observations show that both marine and terrestrial components contribute to the re mineralized toc fraction a binary mixing approach was used to model quantitatively the change in 13c toc and plantwax n alkane concentration results suggest that terrestrial organic carbon contributes approximately 15 to the toc content of the original turbidite its abundance increases approximately 2 4 times as a consequence of the oxidation process and approximately 40 and 90 of the terrestrial and marine component of toc in the original turbidite respectively was destroyed by the oxidation process although selective preservation of terrestrial relative to marine organic carbon is a well documented phenomenon in sedimentary processes this study represents the first attempt to assess the sensitivity of terrestrial organic matter to oxidative degradation in a sedimentary environment

early diagenesis of recently deposited organic matter a 9 yr time series study of a flood deposit abstract in fall 2000 the po river italy experienced a 100 yr return period flood that resulted in a 1 25 cm thick deposit in the adjacent prodelta 10 25 m water depth in the following years numerous post depositional perturbations occurred including bioturbation reworking by waves with heights exceeding 5 m as well as periods of extremely high and low sediment supply cores collected in the central prodelta after the fall 2000 flood and over the following 9 yr allowed characterization of the event strata in their initial state and documentation of their subsequent evolution sedimentological characteristics were investigated using x radiographs and sediment texture analyses whereas the composition of sedimentary organic matter om was studied via bulk and biomarker analyses including organic carbon oc total nitrogen tn carbon stable isotope composition 13c lignin phenols cutin products p hydroxy benzenes benzoic acids dicarboxylic acids and fatty acids the 9 yr time series analysis indicated that roughly the lower half of the original event bed was preserved in the sediment record conversely the upper half of the deposit experienced significant alterations including bioturbation addition of new material as well as coarsening comparison of the recently deposited material with 9 yr old preserved strata represented a unique natural laboratory to investigate the diagenesis of sedimentary om in a non steady system bulk data indicated that oc and tn were degraded at similar rates loss 17 whereas biomarkers exhibited a broad spectrum of reactivities loss from 6 to 60 indicating selective preservation during early diagenesis given the relevance of episodic sedimentation in several margins this study has demonstrated the utility of event response and time series sampling of the seabed for understanding the early diagenesis in non steady conditions

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

oligocene miocene relative geomagnetic paleointensity correlated from the equatorial pacific iodp site u1334 and odp site 1218 to the south atlantic odp site 1090 abstract late oligocene to early miocene relative paleointensity rpi proxies can be correlated from the equatorial pacific iodp site u1334 and odp site 1218 to the south atlantic odp site 1090 age models are constrained by magnetic polarity stratigraphy through correlation to a common geomagnetic polarity timescale the rpi records do not contain significant power at specific orbital frequencies and hence there is no significant coherency between rpi proxies and the normalizers used to construct the proxies although orbital power is present in some normalizers there is no obvious control on rpi proxies from mean sedimentation rate within polarity chrons magnetic grain size proxies or magnetic concentration parameters the salient test is whether the equatorial pacific records can be correlated one to another and to the records from the south atlantic all records are dominated by rpi minima at polarity reversals as expected although the comparison within polarity chrons is compelling enough to conclude that the intensity of the earth s axial dipole is being recorded this is supported by the fit of rpi data from sites u1334 and 1218 after correlation of the two sites using diverse core scanning data rather than polarity reversals alone we do not see a consistent relationship between polarity chron duration and mean rpi and no consistent skewness saw tooth pattern for rpi within polarity chrons stacks of rpi records for 17 5 26 5 ma include long term changes in rpi on myr timescales that are superimposed on rpi minima associated with polarity reversals and shorter term variations in rpi with an apparent pacing of 50 kyr the equatorial pacific to south atlantic correlations indicate that rpi can be used as a global stratigraphic tool in pre quaternary sediments with typical pelagic sedimentation rates of a few cm kyr

a passive fathometer technique for imaging seabed layering using ambient noise a passive acoustics method is presented that uses the ocean ambient noise field to determine water depth and seabed sub bottom layering correlating the noise field measured by two sensors one can recover a function that closely resembles the two point green s function representing the impulse response between the two sensors here a technique is described that is based on noise correlations and produces what is effectively a passive fathometer that can also be used to identify sub bottom layers in principle just one or two hydrophones are needed given enough averaging time however by combining the cross correlations of all hydrophone pairs in a vertical array a stronger signature can be obtained and this greatly reduces averaging time with a moving e g drifting vertical array the resulting algorithm yields both a map of the bottom depth passive fathometer and the locations of significant reflectors in the ocean sub bottom in this paper the technique is described and illustrated using numer

the first pacific record of the late aptian warming event carbonate platforms consisting of hermatypic coral rudists and larger foraminifers formed along the margin of the ne japanese islands during the mid late aptian the geographical northern limit of the carbonate platforms extended to c 36 n at that time which is the highest latitude for coral and or rudist formation in the north pacific region this geographical extension of the carbonate platform in the nw pacific indicates extreme climatic warmth in the mid latitudes and strong poleward heat transport systems contemporaneous warming has been detected in european and australian regions as represented by the migration of tethyan fauna toward the boreal realm and the positive excursion of 13 c and negative excursion of 18 o in deep sea carbonates our new constraint on the northern limit of reef growth reinforces the view that an interval of greenhouse like warmth punctuated the late aptian climate

sedimentary organic matter preservation a test for selective degradation under oxic conditions the authors report here a test of the hypothesis that the extent of organic matter preservation in continental margin sediments is controlled by the average period accumulating particles reside in oxic porewater immediately beneath the water sediment interface oxygen penetration depths organic element compositions and mineral surface areas were determined for 16 sediment cores collected along an offshore transect across the washington continental shelf slope and adjacent cascadia basin individual amino acid sugar and pollen distributions were analyzed for a 11 to 12 cm horizon from each core and sup 14 c based sediment accumulation rates and stable carbon isotope compositions were determined from depth profiles within a subset of six cores from representative sites sediment accumulation rates decreased and dissolved o sub 2 penetration depths increased offshore along the sampling transect as a result oxygen exposure times oet increased seaward from decades mid shelf and upper slope to more than a thousand years outer cascadia basin organic contents and compositions were essentially constant within individual sediment cores but varied consistently with location in particular organic carbon surface area ratios decreased progressively offshore and with increasing oet three independent compositional parameters demonstrated that the remnant organic matter in farther offshore sediments is more degraded both concentrationmore and compositional patterns indicated that sedimentary organic matter exhibits a distinct and reproducible oxic effect oet helps integrate and explain organic matter preservation in accumulating continental margin sediments and hence provides a useful tool for assessing transfer of organic matter from the biosphere to the geosphere less

effects of sea surface conditions on passive fathometry and bottom characterization recently a method has been developed that exploits the correlation properties of the ocean s ambient noise to measure water depth a passive fathometer and seabed layering m siderius et al j acoust soc am 120 1315 1323 2006 this processing is based on the cross correlation between the surface noise and the echo return from the seabed to quantitatively study the dependency between processing and environmental factors such as wind speed measurements were made using a fixed hydrophone array while simultaneously characterizing the environment the measurements were made in 2006 in the shallow waters 25 m approximately 75 km off the coast of savannah ga a navy tower about 100 m from the array was used to measure wind speed and to observe the sea surface using a video camera data were collected in various environmental conditions with wind speeds ranging from 5 to 21 m s and wave heights of 1 3 4 m the data are analyzed to quantify the dependency of passive fathometer results on wind speeds wave conditions and averaging times one result shows that the seabed reflection is detectable even in the lowest wind conditions further a technique is developed to remove the environmental dependency so that the returns estimate seabed impedance doi 10 1121 1 3216915

postdepositional oxic degradation of alkenones implications for the measurement of palaeo sea surface temperatures free and bound long chain alkenones c37 2 and c37 3 in oxidized and unoxidized sections of four organic matter rich pliocene and miocene madeira abyssal plain turbidites one from ocean drilling program site 951b and three from site 952a were analyzed to determine the effect of severe post depositional oxidation on the value of u37k the profiles of both alkenones across the redox boundary show a preferential degradation of the c37 3 compared to the c37 2 compound because of the high initial u37k values and the way of calculating the u37k this degradation hardly influences the u37k profiles however for lower u37k values measured selective degradation would increase u37k up to 0 17 units equivalent to 5 c for most of the u37k band width much smaller degradation already increases u37k beyond the analytical error 0 017 units consequently for interpreting the u37k record in terms of past sea surface temperatures selective degradation needs serious consideration

elemental and major biochemical changes across an oxidation front in a relict turbidite an oxygen effect abstract the elemental and major biochemical compositions of the relict f turbidite sampled in two cores from the madeira abyssal plain were determined this fine grained distal sequence occurs at ca 9 m core depth and includes a surficial oxidized horizon defined by a distinct color change oxygen diffused downward through sediments above this interface and in ca 10 kyr destroyed 80 of the organic substances that below the front had survived degradation in the presence of porewater sulfate for ca 140 kyr these deposits provide an opportunity to establish the extent and selectivity of oxic sedimentary degradation under natural conditions without the usual complications of bioturbation and varying sources or sedimentation rates in both cores a sample from the upper oxidized layer was compared to two samples from the underlying unoxidized layers the unoxidized sequences of both turbidities contained 0 93 1 02 wt organic carbon oc and 0 10 0 11 wt total nitrogen tn approximately 20 of the initial oc and 40 of the initial tn remained in the oxidized horizons with a consequent decrease in atomic c n ratio from ca 11 to ca 5 all samples gave very low yields of lignin phenols and comparable oc normalized yields of total aldoses and amino acids and indicated predominantly marine organic matter om and nonselective oxic degradation of these biochemical classes compositions of individual aldoses and amino acids generally were also similar in surface and deep sediments except that the oxidized horizons yielded markedly elevated 3 5x percentages of nonprotein amino acids this study clearly demonstrates that prolonged exposure to oz can lead to organic matter alteration which is far more extensive than that obtained with sulfate alone in comparison to early diagenesis however alteration of the measured biochemicals was largely nonselective such oxidation reactions could control the distribution and composition of organic matter in slowly accumulating continental rise and deep ocean environments

bottom profiling by correlating beam steered noise sequences it has already been established that by cross correlating ambient noise time series received on the upward and downward steered beams of a drifting vertical array one can obtain a subbottom layer profile strictly the time differential of the cross correlation is the impulse response of the seabed here it is shown theoretically and by simulation that completely uncorrelated surface noise results in a layer profile with predictable amplitudes proportional to those of an equivalent echo sounder at the same depth as the array the phenomenon is simulated by representing the sound sources as multiple random time sequences emitted from random locations in a horizontal plane above a vertical array and then accounting for the travel times of the direct and bottom reflected paths a well defined correlation spike is seen at the depth corresponding to the bottom reflection despite the fact that the sound sources contain no structure whatsoever the effects of using simultaneously steered upward and downward coni

modifications of the c37 alkenone and alkenoate composition in the water column and sediment possible implications for sea surface temperature estimates in paleoceanography 1 the literature pertaining to c37 alkenone and c37 and c38 alkenoate production and diagenesis has been reviewed and evaluated for issues that might jeopardize their usefulness in paleotemperature estimation we also examined the use of the c37 alkenones as paleoproductivity indicators the stability of their 13c isotopic compositions and their incorporation into the nonsolvent extractable organic matter fraction biological transformation of organic matter by bacteria and zooplankton does not appear to cause significant changes to the ratio of c37 2 and c37 3 alkenones but there are major alterations in the relative composition of alkenoates studies of water column processes and postdepositional sedimentary changes indicate overall stability in the c37 2 c37 2 c37 3 ratio leading to effective preservation of the paleotemperature signal this is not the case for alkenoates and there also appear to be some doubts about the dependence between sea surface temperature and the sedimentary abundance of the c37 4 alkenone c37 alkenones may provide useful qualitative estimates of marine paleoproductivity although these compounds are apparently only derived from haptophycea changes in their quantitative composition might reflect changes in nutrient availability that on sedimentary timescales should also be generally significant of other algal species one caveat is that in highly productive upwelling systems productivity may be expressed mostly in diatom growth and thus not measurable by the c37 alkenones no changes in 13c c37 alkenone composition are observed upon zooplankton ingestion although this is expected from a theoretical perspective further studies are encouraged in order to fully assess the stability of the isotopic signal during c37 alkenone diagenesis finally alkenones bound in the nonextractable fraction of sedimentary organics have not been adequately studied and further work is required to clarify any possible correspondence with a temperature signal

abrupt north atlantic circulation changes in response to gradual co2 forcing in a glacial climate state glacial climate is marked by abrupt millennial scale climate changes known as dansgaard oeschger cycles the most pronounced stadial coolings heinrich events are associated with massive iceberg discharges to the north atlantic these events have been linked to variations in the strength of the atlantic meridional overturning circulation however the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear here we show that in a fully coupled atmosphere ocean model gradual changes in atmospheric co2 concentrations can trigger abrupt climate changes associated with a regime of bi stability of the atlantic meridional overturning circulation under intermediate glacial conditions we find that changes in atmospheric co2 concentrations alter the transport of atmospheric moisture across central america which modulates the freshwater budget of the north atlantic and hence deep water formation in our simulations a change in atmospheric co2 levels of about 15 ppmv comparable to variations during dansgaard oeschger cycles containing heinrich events is sufficient to cause transitions between a weak stadial and a strong interstadial circulation mode because changes in the atlantic meridional overturning circulation are thought to alter atmospheric co2 levels we infer that atmospheric co2 may serve as a negative feedback to transitions between strong and weak circulation modes

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

preservation of the alkenone paleotemperature proxy in uplifted marine sequences a test from the vrica outcrop crotone italy the alkenone organic paleotemperature proxy has been used with great success to generate sea surface temperature sst records from diverse areas of the world ocean to date however this methodology has been applied almost exclusively to unconsolidated marine sediments the fidelity of alkenone preservation in lithified uplifted marine sequences exposed on land has not been explicitly investigated such sedimentary sequences have been buried at depths of hundreds of meters to kilometers before uplift and in addition have been exposed to oxic pore fluids and subaerial weathering upon ascent to the surface any of which may cause alteration of biomarker compounds in this study we compare alkenone sst estimates from the vrica land section in crotone italy with alkenone sst estimates derived from coeval marine sediments retrieved at ocean drilling program site 964 which is 300 km offshore of the vrica location we find that sst records from the land and marine sections are well correlated showing similar mean values cyclicity and amplitudes although results from different sedimentary sequences might depend on the lithologies burial depths and weathering histories of individual outcrops this study suggests that it will be possible to reconstruct quantitative sst histories from marine strata exposed on land

evolution of the sedimentary system beneath the deep pacific inflow off eastern new zealand results from ocean drilling program sites 1121 1124 show the eastern new zealand oceanic sedimentary system enzoss evolved in response to 1 the inception of the circum antarctic circulation 2 orbital and non orbital regulation of the global thermohaline flow and 3 development of the new zealand plate boundary enzoss began in the early oligocene following opening of the tasmanian gateway and inception of the ancestral antarctic circumpolar current acc and sw pacific deep western boundary current dwbc widespread erosion marked by the marshall paraconformity was followed by extensive drift formation in the late oligocene early miocene alternating nannofossil chalk and nannofossil rich mud deposited in response to 41 kyr orbital regulation of the abyssal circulation with the mudstones representing times of increased inflow of corrosive southern source waters drift deposition at the deepest sites was interrupted by bouts of erosion coincident with mi1 5 isotopic events signifying expansions of the east antarctic ice sheet and enhanced bottom water formation by late miocene times the basic enzoss was established south of bounty trough the energetic acc instigated an erosional low depositional regime to the north where the dwbc prevailed orbitally regulated drift deposition continued increased convergence at the new zealand plate boundary enhanced the terrigenous supply but little of this sediment reached the deep enzoss as the three main sediment conduits solander bounty and hikurangi channels had not fully developed the plio pleistocene heralded a change from a carbonate to terrigenous dominant supply caused by interception of the dwbc by the three channels 1 6 ma for bounty and hikurangi time of solander interception unknown the solander and bounty fans and hikurangi fan drift systems formed and drifts downstream of those systems received terrigenous detritus supply increased with accelerating uplift along the plate boundary but delivery to the dwbc was regulated by eustatic fluctuations of sea level times of maximum supply to all three channels was during glacial lowstands whereas the supply either ceased bounty solander or reduced hikurangi in highstands in glacial times sediment was entrained by a dwbc invigorated by an increased input of antarctic bottom water the acc also accelerated under strengthened glacial winds thus glacials were times of optimum sediment supply to enzoss depocentres where depositional rates were 2 3 times more than interglacial rates

quantitative reconstruction of temperature at a jōmon site in the incipient jōmon period in northern japan and its implications for the production of early pottery and stone arrowheads abstract the first emergence and development of pottery is an important archeological research topic climate change and associated ecological changes likely promoted the development of pottery however little is known about these environmental factors at the regional scale sedimentary core md01 2409 was collected off the coast of northern honshu japan and provided an excellent opportunity to quantitatively estimate temperature using an alkenone proxy this estimation is based upon the positive correlation between the sea surface temperature sst and the atmospheric temperature at near the core collection site the j mon began to produce the earliest pottery found in japan during this period this corresponds to a climatic anomaly that could be attributed to one of the global effects of the heinrich event i the event s origin in the northern north atlantic consequently weakened the asian monsoon because the two are linked via atmospheric circulation japan experienced its coldest summer sst of 8 7 c at of 5 2 c around 15 68 cal kyr bp these summer temperatures were approximately 7 11 c lower than they are currently 15 7 c and 16 7 c respectively the summer environment was a little colder than those experienced in the present day cities of nemuro and or nosappu in hokkaido subsistence in a terrestrial environment would have been difficult for the j mon people however marine products such as fish and shellfish would have been plentiful these conditions are consistent with the evidence that the earliest pottery was predominantly used for cooking marine and freshwater resources and increased diversification in the range of aquatic products used the bolling allerod and pre boreal warm episodes during deglaciation warmed climatic environments and enhanced marine biogenic production the maximum sst during this period is comparable to the modern sst despite its short duration of approximately a century or less even though the relationship between climate and the appearance of pottery in japan may not be direct the earliest pottery and projectile points stone arrows in the world are associated with the coldest period that homo sapiens experienced since arriving in the colder regions of the japanese archipelago

lipid biomarker fluxes in the arabian sea with a comparison to the equatorial pacific ocean abstract fluxes and distributions of organic carbon oc and lipid biomarkers were measured in the western arabian sea as a function of season depth and distance from the coast of oman during the us jgofs arabian sea process study in 1994 1995 a strong seasonal pattern in oc and lipid flux is related to the annual monsoon cycle in the western arabian sea with the highest fluxes measured during the southwest monsoon fluxes were greatly attenuated with depth in the water column and in surface sediments as remineralization effectively consumed particulate organic matter a comparison of water column fluxes with oc and lipid accumulation rates in sediments confirms that the water sediment interface is a hot spot for organic matter degradation biomarker compositions also varied seasonally and with distance offshore reflecting seasonal and spatial succession of their biological sources and their subsequent export through the water column degradation of oc and biomarkers was extremely efficient with only a tiny fraction

diploptene an indicator of terrigenous organic carbon in washington coastal sediments the pentacyclic triterpene 17 beta h 21 beta h hop 22 29 ene diploptene occurs in sediments throughout the columbia river drainage basin and off the southern coast of washington state in concentrations comparable to long chain plantwax n alkanes the same relationship is evident for diploptene and long chain n alkanes in soils from the willamette valley microorganisms indigenous to soils and soil erosion are indicated as the biological source and physical process respectively for diploptene in coastal sediments similarity between the stable carbon isotopic composition delta 13cpdb of diploptene isolated from soil in the willamette valley 31 2 0 3 and from sediments deposited throughout the washington coastal environment 31 2 0 5 supports this argument values of delta for diploptene in river sediments are variable and 8 17 lighter indicating that an additional biological source such as methane oxidizing bacteria makes a significant contribution to the diploptene record in river sediments selective biodegradation resulting from a difference in the physicochemical association within eroded particles can explain the absence of the more 13c depleted form of diploptene in washington coastal sediments but this mechanism remains unproven

the influence of oxic degradation on the sedimentary biomarker record i evidence from madeira abyssal plain turbidites free and ester bound lipid biomarkers were analysed in oxidised and unoxidised parts of four distinct turbidites from the madeira abyssal plain map which contained 1 to 2 organic carbon homogeneously distributed throughout the turbidites at the time they were deposited these turbidites are well suited to study the effects of oxic degradation on lipid biomarkers without the complicating influence of varying organic matter sources sedimentation rates or bioturbation one sample from the oxidised turbidite was compared with two samples from the unoxidised part of each turbidite postdepositional oxic degradation decreased concentrations of biomarkers by several orders of magnitude the ester bound lipids were degraded to a far lesser extent than their free counterparts were the extent of degradation of different compounds differed substantially within a specific class of biomarkers degradation also took place to a different extent altering their distributions this study shows that oxic degradation of the organic matter may have a profound effect on the biomarker fingerprint and may result in a severe bias in for example the interpretation of organic matter sources and the estimation of the palaeoproductivity of specific groups of phytoplankton

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

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

refined estimation of marine and terrigenous contributions to sedimentary organic carbon molecular carbon isotopic 13c 12c ratios of a selected marine organic biomarker compound a c37 alkadienone from the pigmy basin deep sea drilling program hole 619 in the northern gulf of mexico varied by 5 3 in sychrony with the last 100 ka glacial interglacial cycle this carbon isotopic 13c variation is likely due to the effect of climatically linked variations in concentrations of co2 aq on photosynthetic fractionation of carbon isotopes by phytoplankton measurement of the 13c of the alkadienone 37 2 to reconstruct the carbon isotopic composition of total marine organic carbon permits improved estimates of the time varying 13c of preserved marine organic carbon end members with the time series record of marine end members the concentrations and net accumulation rates of terrigenous corg and marine corg are calculated and their paleoceanographic significance is considered although this method may be improved by consideration of additional biomarkers representative of diverse marine and terrigenous inputs it is the first application of molecular isotopic analysis to quantifying marine and terrigenous corg concentrations further application of such techniques will be become valuable in reconstructing regional and global budgets of marine and terrigenous corg accumulation

composition and fate of terrigenous organic matter along the arctic land ocean continuum in east siberia insights from biomarkers and carbon isotopes abstract climate warming is predicted to translocate terrigenous organic carbon terroc to the arctic ocean and affect the marine biogeochemistry at high latitudes the magnitude of this translocation is currently unknown so is the climate response the fate of the remobilized terroc across the arctic shelves represents an unconstrained component of this feedback the present study investigated the fate of permafrost carbon along the land ocean continuum by characterizing the terroc composition in three different terrestrial carbon pools from siberian permafrost surface organic rich horizon mineral soil active layer and ice complex deposit and marine sediments collected on the extensive east siberian arctic shelf esas high levels of lignin phenols and cutin acids were measured in all terrestrial samples analyzed indicating that these compounds can be used to trace the heterogeneous terrigenous material entering the arctic ocean in esas sediments comparison of these terrigenous biomarkers with other terroc proxies bulk 13c 14c and hmw lipid biomarkers highlighted contrasting across shelf trends these differences could indicate that terroc in the esas is made up of several pools that exhibit contrasting reactivity toward oxidation during the transport in this reactive spectrum lignin is the most reactive decreasing up to three orders of magnitude from the inner to the outer shelf while the decrease of hmw wax lipid biomarkers was considerably less pronounced alternatively degradation might be negligible while sediment sorting during the across shelf transport could be the major physical forcing that redistributes different terroc pools characterized by different matrix association despite the marked decrease shown by lignin the fingerprint of lignin phenols such as the acid aldehyde ratio of vanillyl and syringyl phenols showed a lack of any across shelf trends and exhibited an extremely wide range of values in all terrestrial samples by contrast the 3 5 dihydroxybenzoic vanillyl phenols ratio exhibited a clear across shelf trend suggesting either increasing degradation with distance from the coast or terroc sorting along the sediment dispersal system the ratio of syringyl vanillyl phenols indicated that gymnosperm tissues are more important than angiosperm tissues in surface sediments in particular off the lena river mouth consistent with the vegetation in its watershed conversely the fingerprint of p hydroxybenzenes suggests lack of substantial input of moss derived material finally autochthonous lipid and protein derived cuo reaction products displayed a strong along shelf gradient likely reflecting the inflow of nutrient rich pacific waters from the bering strait that stimulate primary productivity in the eastern esas in particular short chain fatty acids showed a clear frontal transition zone between pacific influenced and river influenced waters approximately along the 160 e longitude considering the labile nature of phytoplankton priming and co metabolism processes might stimulate degradation of terroc in the easternmost region of the siberian shelf this study demonstrated the need to consider multiple terroc proxies at isotopic molecular levels to differentiate the fate for different allocthonous components in arctic sediments and the need to assess how these terroc pools are distributed in different density size and settling fractions to better discriminate between the extent of hydrodynamic sorting versus degradation

oligocene miocene magnetic stratigraphy carried by biogenic magnetite at sites u1334 and u1335 equatorial pacific ocean 1 sediments from the equatorial pacific ocean at the integrated ocean drilling program sites u1334 and u1335 record reliable magnetic polarity stratigraphies back to 26 5 ma late oligocene at sedimentation rates usually in the 5 20 m myr range putative polarity subchrons that do not appear in current polarity timescales occur within chrons c5acr c5adn and c5bn 1r at site u1335 and within chrons c6aar 2r c6br c7ar and c8n 1n at site u1334 subchron c5dr 1n 17 5 ma is recorded at both sites supporting its apparent recording in the south atlantic ocean and has an estimated duration of 40 kyr the oligocene miocene calcareous oozes have magnetizations carried by submicron magnetite as indicated by thermal demagnetization of magnetic remanences the anhysteretic remanence to susceptibility ratio and magnetic hysteresis parameters transmission electron microscopy of magnetic separates indicates the presence of low titanium iron oxide magnetite grains with size 50 100 nm and shape similar to modern and fossil bacterial magnetite supporting other evidence that biogenic submicron magnetite is the principal remanence carrier in these sediments in the equatorial pacific ocean low organic carbon burial arrests microbial pore water sulfate reduction thereby aiding preservation of bacterial magnetite

extracting coherent wave fronts from acoustic ambient noise in the ocean a method to obtain coherent acoustic wave fronts by measuring the space time correlation function of ocean noise between two hydrophones is experimentally demonstrated though the sources of ocean noise are uncorrelated the time averaged noise correlation function exhibits deterministic waveguide arrival structure embedded in the time domain green s function a theoretical approach is derived for both volume and surface noise sources shipping noise is also investigated and simulated results are presented in deep or shallow water configurations the data of opportunity used to demonstrate the extraction of wave fronts from ocean noise were taken from the synchronized vertical receive arrays used in the frame of the north pacific laboratory npal during time intervals when no source was transmitting

passive fathometer processing ocean acoustic noise can be processed efficiently to extract green s function information between two receivers by using noise array processing techniques it has been demonstrated that a passive array can be used as a fathometer siderius et al j acoust soc am 120 1315 1323 2006 here this approach is derived in both frequency and time domains and the output corresponds to the reflection sequence from this reflection sequence it is possible to extract seabed layering in the ocean waveguide most of the energy is horizontally propagating whereas the bottom information is contained in the vertically propagating noise extracting the seabed information requires a dense array since the resolution of the bottom layer is about half the array spacing if velocity sensors are used instead of pressure sensors the array spacing requirement can be relaxed and simulations show that just one vertical velocity sensor is sufficient

hemispherically asymmetric trade wind changes as signatures of past itcz shifts abstract the atmospheric hadley cells which meet at the intertropical convergence zone itcz play critical roles in transporting heat driving ocean circulation and supplying precipitation to the most heavily populated regions of the globe paleo reconstructions can provide concrete evidence of how these major features of the atmospheric circulation can change in response to climate perturbations while most such reconstructions have focused on itcz related rainfall here we show that trade wind proxies can document dynamical aspects of meridional itcz shifts theoretical expectations based on angular momentum constraints and results from freshwater hosing simulations with two different climate models predict that itcz shifts due to anomalous cooling of one hemisphere would be accompanied by a strengthening of the hadley cell and trade winds in the colder hemisphere with an opposite response in the warmer hemisphere this expectation of hemispherically asymmetric trade wind changes is confirmed by proxy data of coastal upwelling and windblown dust from the atlantic basin during heinrich stadials showing trade wind strengthening in the northern hemisphere and weakening in the southern hemisphere subtropics in concert with southward itcz shifts data from other basins show broadly similar patterns though improved constraints on past trade wind changes are needed outside the atlantic basin the asymmetric trade wind changes identified here suggest that itcz shifts are also marked by intensification of the ocean s wind driven subtropical cells in the cooler hemisphere and a weakening in the warmer hemisphere which induces cross equatorial oceanic heat transport into the colder hemisphere this response would be expected to prevent extreme meridional itcz shifts in response to asymmetric heating or cooling understanding trade wind changes and their coupling to cross equatorial ocean cells is key to better constraining itcz shifts and ocean and atmosphere dynamical changes in the past especially for regions and time periods for which few paleodata exist and also improves our understanding of what changes may occur in the future

effects of seafloor and laboratory dissolution on the mg ca composition of globigerinoides sacculifer and orbulina universa tests a laser ablation icpms microanalysis perspective article i nfo partial or selective dissolution of planktonic foraminiferal tests on the seafloor has been shown to alter original test mg ca compositions and thus may limit the accuracy of mg ca based thermometry for reconstructions of past sea surface temperatures we have employed laser ablation icpms to determine the extent of dissolution caused changes in mg ca distribution across individual chamber walls of the planktonic foraminifera globigerinoides sacculifer and orbulina universa g sacculifer samples collected from a core top depth transect in the ne indian ocean and laboratory dissolution experiments show little if any evidence of preferential removal of mg rich calcite layers by progressive dissolution of the tests we attribute the absence of selective dissolution to the banded distribution of mg across the chamber walls of these foraminiferal species and to the minimal presence of calcite crusts with relatively low mg composition on the outer surfaces of tests mg ca microanalyses of g sacculifer from core top samples further indicate that for samples collected above the calcite lysocline the effect of postdepositional dissolution on mg ca sample mean values is minimal and within the uncertainty of mg ca thermometry i e 0 4 mmol mol 0 8 c at 28 c comparison with previously published results for g sacculifer supports these observations simple modelling of g sacculifer test dissolution indicates that selective removal of calcite with high mg ca values from within the final chamber of g sacculifer test appears insufficient to cause the 10 decrease in mg ca values observed above calcite lysocline these changes in test composition might be related to development removal as a function of co3 2 of a thin diagenetic surface coating which has a relatively high mg ca

the plio pleistocene development of atlantic deep water circulation and its influence on climate trends abstract using benthic stable isotope records from 10 sites in the atlantic ocean including two new records from walvis ridge in the southeast atlantic sites 1264 and 1267 we review changes in atlantic deep water circulation in the context of plio pleistocene climate overall we find non linear responses of atlantic deep water circulation to a cooling climate with differently evolving glacial and interglacial states our main conclusion is that peak north atlantic deep water nadw production was reached between 2 0 and 1 5 ma most prominently seen by a maximum in ventilated high 13 c conditions in the mid depth southeast atlantic site 1264 we infer that a major source of nadw at this time was the export of dense overflow water from the nordic seas into the abyssal east atlantic sea surface temperature records from the north and south atlantic support this notion and indicate that the peak nadw production between 2 0 and 1 5 ma was compensated by a stronger warm surface water return flow i e atlantic meridional overturning circulation amoc was enhanced causing long term 10 5 year heat piracy from the south to the north atlantic in the wider picture of plio pleistocene climate evolution we find that a long term enhancement in the average state of amoc 2 4 1 3 ma coincides with the 41 kyr world hence we speculate that the transitory negative feedback response of enhanced amoc to a cooling climate supplied heat to key areas of ice sheet growth acting to limit their size and maintain the 41 kyr world once a threshold in global cooling was reached the strength of amoc lessened providing a positive feedback for the early middle pleistocene transition and the associated build up of northern hemisphere ice sheets

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

development of submarine canyons after the mid pleistocene transition on the ebro margin nw mediterranean the role of fluvial connections after the messinian salinity crisis msc the ebro margin like other mediterranean deltaic margins rebuilt through progradation and increasingly significant aggradation the plio quaternary transition from a ramp like system to a new margin with large clinoforms is an opportunity to understand the processes that govern canyon initiation and evolution we used a 3d seismic data set located at the outer shelf upper slope of the ebro margin we tied major bounding surfaces to chrono stratigraphic constraints from borehole data or for the most recent interval from averaged accumulation rates derived from borehole stratigraphy the major shelfal erosion surfaces are interpreted as sequence boundaries tied to major glacial maxima along these surfaces seismic attributes characterize the fluvial canyon connection viewed as one of the key factors in canyon development the first appearance of proto canyons dense networks of channels and gullies 50 100 m deep and 1 2 km wide occurs in the late zanclean their size increased progressively throughout the pliocene and early quaternary in relation to the increase in clinoform heights true canyons with distinct interfluves more than 200 m deep and 3 4 km wide appeared during the mid pleistocene transition mpt 1250 700 ka bp the first evidence of direct connection between canyon heads and fluvial systems is observed during marine isotope stage 22 one of the most pronounced glacial stages of the quaternary similar connections also existed at least during mis 16 and mis 12 which are also stages of pronounced low sea level the topography of fluvial channels in the outer shelf is not imaged in detail in the picked horizons at the resolution of our seismic data but sinuous fluvial systems are very well imaged through amplitude and coherency attributes direct connection of fluvial systems during and after mis 22 also favored headward erosion and the formation of shelf indenting canyons probably during early phases of sea level rise

a 28 ka history of sea surface temperature primary productivity and planktonic community variability in the western arabian sea 1 uranium series radionuclides and organic biomarkers which represent major groups of planktonic organisms were measured in western arabian sea sediments that span the past 28 ka variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity sea surface temperature sst and planktonic community structure were investigated the average alkenone derived sst for the last glacial period was 3 c lower than that measured for the holocene prior to the deglacial the lowest ssts coincide with the highest measured fluxes of organic biomarkers which represent primarily a planktonic suite of diatoms coccolithophorids dinoflagellates and zooplankton we propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing cold ssts and enhanced primary productivity in contrast postdeglacial 17 ka ssts are warmer during times in which biomarker fluxes are high associated with this transition is a planktonic community structure change in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and holocene than the average ratio during the last glacial period we suggest that this temporal transition represents a shift from a winter northeast monsoon dominated pre 17 ka to a summer southwest monsoon dominated post 17 ka wind system

paleoceanographic implications of nitrogen and organic carbon isotopic excursions in mid pleistocene sapropels from the tyrrhenian and levantine basins mediterranean sea abstract comparison of the total nitrogen and organic carbon isotopic compositions of sediment sequences from the tyrrhenian and levantine basins that contain three same age sapropels reveals evidence of both similarities and differences in mid pleistocene sapropel forming conditions in the western and eastern mediterranean sea total 15 n values systematically decrease at both locations from 5 in background sediments to 1 in the sapropels the lower 15 n values signify that nitrogen fixation was important to the increased marine productivity implied by the higher organic carbon concentrations which is consistent with widespread salinity stratification of surface waters when sapropels accumulated organic 13 c values systematically increase from 25 in the background sediments to 22 in the sapropels at the tyrrhenian site which confirms that increased marine productivity accompanied sapropel deposition in contrast 13 c values decrease in the sapropel layers in the levantine basin even though organic carbon concentrations are higher in these sapropels the different types of 13 c excursions associated with increased organic matter production at the two locations indicates a difference in the dissolved carbon pool from a combination of greater fluvial delivery of continental carbon and stronger recycling of organic matter in the levantine sea than in the tyrrhenian sea this difference implies that the shifts to wetter climate during times of sapropel deposition were stronger in the eastern than in the western mediterranean

geoacoustic inversion of ambient noise a simple method the vertical directionality of ambient noise is strongly influenced by seabed reflections therefore potentially geoacoustic parameters can be inferred by inversion of the noise in this approach using vertical array measurements the reflection loss is found directly by comparing the upward with the downward going noise theory suggests that this simple ratio is in fact the power reflection coefficient potentially a function of angle and frequency modeling and parameter searching are minimized and the method does not require a detailed knowledge of the noise source distribution the approach can handle stratified environments and is believed to tolerate range dependence experimental data from five sites four in the mediterranean one on the new jersey shelf are described most of the mediterranean sites had temporally varying noise directionality yet yielded the same reflection properties as one would hope one site was visited in conditions of very low surface noise this paper concentrates on an experimental demonstration of the feasibility of the method and data quality issues rather than automatic search techniques for geoacoustic parameters

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

distribution and sources of polycyclic aromatic hydrocarbons pahs in laminated santa barbara basin sediments abstract the santa barbara basin sbb preserves a high resolution sediment record that is varved down to ca 1700 ce and laminated for at least 2500 years the distributions of 25 polycyclic aromatic hydrocarbons pahs were investigated in a suite of samples from sediment cores representing different depositional scenarios varves laminae terrigenous flood layers and marine turbidites the concentrations of these pahs were determined using gas chromatography mass spectrometry in selected ion mode and evaluated in terms of their distributions diagnostic ratios and loadings recognized by principal component analysis pca two biogenic pahs perylene and retene provided the greatest variation in their downcore concentration values perylene concentrations increased downcore exhibiting markedly higher abundance in sediments older than 300 ce consistent with the interpretation that perylene is formed diagenetically in reducing sediments a modest increase in perylene concentrations in sediments from the late 1960s may be associated with flood derived transport of higher amounts of degraded terrestrial organic matter from fire denudated landscapes into the coastal environment the markedly higher concentrations of retene in flood layers and turbidites relative to varves laminae suggest that these lithologies are more effective in transporting pyrogenic pahs and can be interpreted as a proxy for wildfires in sbb changes in key diagnostic ratios reveal the shift from a dominance of petrogenic pahs in older sediments to a strong pyrogenic signal beginning in the latter half of the 20th century statistical analysis using pca of the pah distributions in the samples revealed that modern sediments showed a strong positive relationship with pc1 which represents the greatest variation among the samples whereas flood layers showed a strong relationship with the second major variable pc2 thus statistical approaches provide the capability to elucidate modern anthropogenic signatures within the complex pah distributions of sbb and also establish a pah profile that characterizes the lithological signature of flood layers

low frequency and high frequency changes in temperature and effective humidity during the holocene in south central sweden implications for atmospheric and oceanic forcings of climate an integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes here we report a 10 000 year quantitative record of annual mean temperature tann based on pollen climate transfer functions and pollen stratigraphical data from lake flarken south central sweden the pollen based temperature reconstruction is compared with a reconstruction of effective humidity as reflected by a 18o record obtained on stratigraphy of lacustrine carbonates from lake igelsjon c 10 km from lake flarken which gives evidence of pronounced changes in effective humidity the relatively low tann and high effective humidity as reflected by a low evaporation inflow ratio suggest a maritime early holocene climate 10 000 8 300 cal year bp seemingly incompatible with the highly seasonal solar insolation configuration we argue that the maritime climate was due to the stronger than present zonal flow enhanced by the high early holocene sea surface temperatures in the north atlantic the maritime climate mode was disrupted by the abrupt cold event at 8 200 cal year bp followed at 8 000 cal year bp by a stable holocene thermal maximum the latter was characterized by tann values about 2 5 c higher than at present and markedly dry conditions indicative of stable summer time anti cyclonic circulation possibly corresponding with modern blocking anticyclonic conditions the last 4 300 year period is characterized by an increasingly cold moist and unstable climate the results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability generality and interpretability of the palaeoclimatic results further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial scale climate dynamics

alkenone temperature anomalies in the brazil malvinas confluence area caused by lateral advection of suspended particulate material alkenone temperatures derived from suspended particulate organic material which was collected in austral summer 2001 from surface waters 5 m south of the brazil malvinas confluence deviate from measured temperatures by 4 to 7 c when uk 37 ratios are converted to temperature using the muller et al 1998 calibration and up to 3 c when using the calibration of conte et al 2006 in contrast alkenone temperatures determined from particulate material sampled north of the confluence reveal close correspondence to in situ temperatures or show slightly higher values we suggest that the southern samples are biased by suspended organic detritus originating from the cold subpolar waters of the northward flowing malvinas current whereas the northern samples carry an uk 37 signal of tropical subtropical origin transported southward with the brazil current on the basis of surface ocean transport pathways and velocities simulated with the large scale geostrophic lsg ocean general circulation model we identify areas of the world ocean where alkenone temperatures are potentially biased to higher or lower values due to long particle residence times and lateral advection by surface currents

the impact of oxic degradation on long chain alkyl diol distributions in arabian sea surface sediments oxygen exposure has a large impact on lipid biomarker preservation in surface sediments and may affect the application of organic proxies used for reconstructing past environmental conditions to determine its effect on long chain alkyl diol and keto ol based proxies the distributions of these lipids was studied in nine surface sediments from the murray ridge in the arabian sea obtained from varying water depths 900 3000 m but in close lateral proximity and therefore likely receiving a similar particle flux due to substantial differences in bottom water oxygen concentration 3 77 mol l and sedimentation rate substantial differences exist in the time the biomarker lipids are exposed to oxygen in the sediment long chain alkyl diol and keto ol concentrations in the surface sediments 0 0 5 cm decreased progressively with increasing oxygen exposure time suggesting increased oxic degradation the 1 15 keto ol diol ratio doxi increased slightly with oxygen exposure time as diols had apparently slightly higher degradation rates than keto ols the ratio of 1 14 vs 1 13 or 1 15 diols used as upwelling proxies did not show substantial changes however the c30 1 15 diol exhibited a slightly higher degradation rate than c28 and c30 1 13 diols and thus the long chain diol index ldi used as sea surface temperature proxy showed a negative correlation with the maximum residence time in the oxic zone of the sediment resulting in ca 2 3 5 c change when translated to temperature the uk 37 index did not show significant changes with increasing oxygen exposure this suggests that oxic degradation may affect temperature reconstructions using the ldi in oxic settings and where oxygen concentrations have varied substantially over time

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past

no evidence of extraterrestrial noble metal and helium anomalies at marinoan glacial termination abstract high concentrations of extraterrestrial iridium have been reported in terminal sturtian and marinoan glacial marine sediments and are used to argue for long likely 3 12 myr durations of these cryogenian glaciations reanalysis of the marinoan sedimentary rocks used in the original study supplemented by sedimentary rocks from additional terminal marinoan sections however does not confirm the initial report new platinum group element concentrations and 187os 188os and 3he 4he signatures are consistent with crustal origin and minimal extraterrestrial contributions the discrepancy is likely caused by different sample masses used in the two studies with this study being based on much larger samples that better capture the stochastic distribution of extraterrestrial particles in marine sediments strong enrichment of redox sensitive elements particularly rhenium up section in the basal postglacial cap carbonates may indicate a return to more fully oxygenated seawater in the aftermath of the marinoan snowball earth sections dominated by hydrogenous osmium indicate increasing submarine hydrothermal sources and or continental inputs that are increasingly dominated by young mantle derived rocks after deglaciation sedimentation rate estimates for the basal cap carbonates yield surprisingly slow rates of a few centimeters per thousand years this study highlights the importance of using sedimentary rock samples that represent sufficiently large area time products to properly sample extraterrestrial particles representatively and demonstrates the value of using multiple tracers of extraterrestrial matter

distribution of exchangeable fixed organic and total nitrogen in interbedded turbiditic pelagic sediments of the madeira abyssal plain eastern north atlantic abstract nitrogen compounds in the interbedded turbiditic pelagic sediments of the madeira abyssal plain from hereon map have been divided in separate extracted fractions such as exchangeable nitrogen nex fixed nitrogen nfix and organic nitrogen norg nex is found to be directly proportional to the amount of organic matter corg in the sediment and is not related to the amount of ammonium in the porewater only at a relatively low corg content is the nex determined by the mineralogy of the sediment the norg as determined from norg ntot nfix nex is strongly related with corg the nfix content and the n fix al ratio for organic rich sediments are high compared with other sediments and have not changed upon post depositional oxidation of the organic matter post depositional oxidation of organic matter through oxygen does lead to a decrease in the c n ratio of the remaining organic matter in the organic rich turbidites the c n ratio calculated for the organic matter that has been decomposed through oxygen is similar to that calculated through stoichiometric modelling for decomposition under reducing circumstances c n ratios of 17 and 18 respectively this implies that for the sediments of the map the c n ratio is identical for organic matter decomposed under oxygenated and under reducing conditions

imprints of high salinity water plumes originating from the red sea during termination ii abstract the investigation of a core collected in the socotran area western indian ocean provides new insights into water mass exchanges between the red sea and the gulf of aden through the strait of bab el mandeb during the penultimate deglaciation the benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea level rise plumes of warm and salty waters are recorded at the surface of the arabian sea and as far as the socotran coast for each increase in sea level these plumes disappeared whenever global sea level stopped rising or showed a brief lowering according to their high salinities these plumes can only originate in the red sea the sill of bab el mandeb becoming deeper and wider during the deglaciation allowed greater exchange between both seas and stronger flow out of the red sea at each episode of sea level rise isotopic and faunal evidence suggest a strengthening of coastal upwelling in the arabian sea during these periods this increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface moreover the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column the occurrence of at least high salinity salty water outflows during termination ii confirms the step wise non linear structure of the penultimate deglaciation providing a perfect example of the threshold concept in rapid climate changes

recognition of alkenones in a lower aptian porcellanite from the west central pacific odp leg 198 drilling on shatsky rise recovered a lower aptian porcellanite 120 5 ma deposited during oceanic anoxic event oae 1a that contains c36 c39 alkadienones c37 2 and c39 2 alkadien 2 ones and c36 2 and c38 2 alkadien 3 ones this alkenone distribution differs from that typical of contemporary sediments and haptophyte algae but resembles that of cretaceous sediments from the blake bahama basin the discovery of alkenones in the early aptian extends their sedimentary record by 15 m y to 120 5 m y and demonstrates the potential for long term survival of these diagnostic functional lipids under favorable depositional conditions and subsequent shallow burial it also contributes to the understanding and reconstruction of evolutionary developments in alkenone distributions and biosynthesis over geologic time 2003 elsevier ltd all rights reserved

selective aerobic and anaerobic degradation of lipids and palynomorphs in the eastern mediterranean since the onset of sapropel s1 deposition abstract selective degradation of organic matter in sediments is important for reconstructing past environments and understanding the carbon cycle here we report on compositional changes between and within lipid classes and kerogen types represented by palynomorph groups in relation to the organic matter flux to the sea floor and oxidation state of the sediments since the early holocene for central eastern mediterranean site abc26 this includes the initially oxic but nowadays anoxic presapropelic interval the still unoxidised lower part of the organic rich s1 sapropel its postdepositionally oxidised and nowadays organic poor upper part as well as the overlying postsapropelic sediments which have always been oxic a general 2 3 times increase in terrestrial and marine input during sapropel formation is estimated on the basis of the total organic carbon toc pollen spore dinoflagellate cyst n alkane n alkanol and n alkanoic acid concentration changes in the unoxidised part of the sapropel the long chain alkenones 1 15 diols and keto ols loliolides and sterols indicate that some plankton groups notably dinoflagellates may have increased much more apart from the terrestrial and surface water contributions to the sedimentary organic matter anomalous distributions and preservation of some c 23 c 27 alkanes alkanols and alkanoic acids have been observed which are interpreted as a contribution by organisms living in situ comparison of the unoxidised s1 sapropel with the overlying oxidised sapropel and the organic matter concentration profiles in the oxidised postsapropelic sediments demonstrates strong and highly selective aerobic degradation of lipids and palynomorphs there seems to be a fundamental difference in degradation kinetics between lipids and pollen which may be possibly related with the absence of sorptive preservation as a protective mechanism for palynomorph degradation the n alkanes impagidinium and nematosphaeropsis are clearly more resistant than toc the n alkanols and n carboxylic acids are about equally resistant whereas the pollen all other dinoflagellate cysts and other lipids appear to degrade considerably faster which questions the practice of normalising to toc without taking diagenesis into account selective degradation also modifies the relative distributions within lipid classes whereby the longer chain alkanes alcohols and fatty acids disappear faster than their shorter chain equivalents accordingly interpretation of lipid and palynomorph assemblages in terms of pre or syndepositional environmental change should be done carefully when proper knowledge of the postdepositional preservation history is absent two lipid based preservation proxies are tested the diol keto ol oxidation index based on the 1 15c 30 diol and keto ols doxi and the alcohol preservation index api whereby the former seems to be the most promising