a biomarker perspective on paleoproductivity variations in two late quaternary sediment sections from the southeast atlantic ocean abstract sedimentary inventories of selected molecular biomarkers in two sediment sections from the african continental margin below highly productive surface waters in the southeast atlantic ocean each spanning the last 76 kyr were investigated and compared to each other a principal component analysis of the stratigraphic data separated groups of biomarkers representing different assemblages of biological sources and or different diagenetic histories related to their chemical structures and their metabolic role in the food chain the concentrations of long chain n alkenones n diols the major n ketool and loliolide and its epimer isololiolide are correlated with paleoproductivity estimates that were calculated from organic carbon contents this group of relatively refractory compounds very likely represents those planktonic communities which contributed significantly to surface water productivity and subsequent burial of organic carbon during the considered time interval concentrations of dust transported terrigenous long chain fatty acids c24 to c28 are interpreted to be related to the intensity of upwelling driving winds and are also significantly correlated with high contents of organic matter concentrations of cholesterol and the major short chain fatty acids are not related to the marine paleoproductivity signal most likely as a consequence of their nonspecific origin and their metabolic role during heterotrophic feeding processes abundances of 24 ethylcholest 5 en 3 ol and its saturated counterpart 24 ethyl 5 cholestan 3 ol the major steroid alcohols in both sedimentary environments appear not to be related to any of the above mentioned components and probably represent the contribution of algal species adapted to nutrient conditions different from those of other major primary producers differences between both environments the angola dome and the benguela coastal upwelling are evident in the relative distribution of major components and the stratigraphic behavior of selected compounds relative to other variables these differences are discussed in relation to specific characteristics of both oceanographic environments 1999 elsevier science ltd all rights reserved

210pb derived sediment accumulation and mixing rates for the washington continental slope abstract total sediment accumulation rates g yr in four canyons indenting the washington continental shelf are about twice those on the nearby open slope even though canyons comprise less than 40 of the depositional area of the entire slope this is because 210 pb derived sediment accumulation rates g cm 2 yr for astoria and quinault canyons are 3 4 times greater than those for willapa and grays canyons and intermediate open slope areas supporting the hypothesis that columbia river derived solids are preferentially transported to these two canyons quinault canyon currently appears to be accumulating solids at rates much greater than its low long term accumulation rate which is attributed to turbidity currents transporting solids down this canyon roughly every 500 years the following four different approaches all show that mixing may cause 210 pb derived sediment accumulation rates for slope and canyon sediments to be 2 3 times higher than true accumulation rates 1 comparison between accumulation rates calculated from 210 pb profiles with and without surface zones in which mixing has obviously affected 210 pb distributions 2 comparison between 210 pb derived and independently determined long term accumulation rates 3 comparison between 210 pb derived accumulation and modern columbia river discharge rates 4 comparison between two and three layer steady state one dimensional diffusion advection decay models mixing coefficients for surface sediments calculated using a one dimensional two layer vertical eddy diffusion model show large differences within the region with most in the 3 30 cm 2 yr range mixing rates are several times larger in canyon sediments from 0 2 1 1 km water depth probably due to physical reworking processes erroneously neglected mixing at depth of no more than 5 of that calculated for the surface mixed layer can cause the 2 3 fold calculated overestimation of true sediment accumulation rates and 2 4 fold calculated underestimation of true mixing coefficients

palaeoenvironmental changes in the padul basin granada spain over the last 1 ma based on the biomarker content the n alkane components of sediments were measured in 530 samples taken from a 107 m long core in the padul basin andalusia spain covering from the lower pleistocene ca 1 ma to the mid holocene ca 4 5 ka b p we show that the relative percentages of the high molecular weight n alkanes c27 c29 and c31 are useful tools to reconstruct the ancient vegetation and palaeoclimatological evolution of this basin on the basis of these proxies we distinguished twelve long term climatic periods linked to alternating dry humid scenarios 6 dry episodes alternating with 5 humid episodes were interpreted in the pleistocene record together with a final episode covering the holocene dry scenarios produced the recession of forests and the development of grasses whereas the inverse pattern was interpreted during humid phases the good correlation with the guadix baza basin record showed that in most cases dry periods coexisted with warm conditions while humid ones were linked to temperate colder conditions only during the last long term dry episode of the pleistocene which coincided with the end of the last glacial period did low temperatures concur the relative percentages of the high molecular weight n alkanes also indicate rapid changes in vegetation produced by short scale arid cycles during the last glacial period 100 ka b p which are linked to the heinrich events and younger dryas this interpretation has been confirmed by previous pollen analysis performed in the padul basin likewise a correlation was observed with marine isotope stages mis these results show that vegetation responds to long term cycles orbital scale and millennial scale global cycles therefore climatic variations in the padul basin responded to global climatic changes although with local climatic effects good correspondence was also observed with elemental isotopic and other molecular organic proxies thereby amplifying the palaeoclimatological knowledge of the padul basin during the pleistocene especially in some spans that were previously unclear

distribution of terrigenous lipids in marine sediments off northeastern taiwan surface sediments on the continental margin off northeastern taiwan have been analyzed for terrigenous lipids including n alkanes n fatty alcohols and sterols marine input to the sediments is particularly low based on the average n c17 n c29 alkane and n c16 n c28 fatty alcohol ratios 0 15 0 13 and 0 13 0 06 respectively this may be due to the fact that marine lipids are more prone to degradation than terrestrial ones the study area has the highest plant wax n alkane contribution average carbon preference index 3 9 1 2 among the coastal marine areas surrounding taiwan lateral particle transport from the southern east china sea shelf and river runoff from the east taiwan coast are considered to be the major contributors the distributions of plant wax n alkane and n alkanol concentrations normalized to total organic carbon toc in the study area generally show maximum values on the upper slope of the southernmost okinawa trough but not for phytosterols linear regression of toc versus plant wax n alkane concentrations show a weak relationship r 0 64 p 0 001 and an even weaker relationship r 0 42 p 0 05 between toc and plant wax n fatty alcohol concentrations is found this could be attributed to several factors 1 a complex input not a point source of terrigenous organic matter to the study area 2 toc also including marine organic matter 3 temporal variations in river flow due to flooding and 4 different rates of degradation for toc and individual biomarkers however in spite of those factors toc and phytosterol concentrations are positively linearly correlated r 0 85 p 0 001 implying that the dilution of phytosterols in terrigenous organic carbon with marine organic carbon with or without the phytosterols follows a nearly constant ratio which is remarkable in addition the predominant source of diploptene in the sediments does not appear to be of higher plant origin

seabed bubble flux estimation by calibrated video survey for a large blowout seep in the north sea abstract a new approach to estimating seabed bubble emissions was applied to a rov video survey of the 22 4b blowout crater in the uk north sea video was analyzed to identify and classify bubble plumes and other seabed features plume occurrence then was gridded into quadrats and the total number of plumes in the crater s active portion estimated almost all of the seepage in the 40 45 m crater was localized within a 20 by 18 m ellipse all five major plumes in this ellipse were measured by direct capture with mean emission of 1 34 l s 1 at 12 bar range 0 54 3 5 l s 1 the primary source of variability 71 was temporal demonstrated by repeat measurements of a single vent overall temporal variability was consistent with highly fluid migration through a thick near seabed coarse grained sediment bed underlying the 22 4b crater seabed occurrence data were converted to flux based on direct capture measurements survey video and laboratory experiments where video was collected of bubble plumes of known flow for comparison with field video the derived best estimate total seabed emission flux was 90 l s 1 with an estimated uncertainty of 50 within a scenario uncertainty range of 50 142 l s 1 this is equivalent to 100 million l dy 1 at standard temperature and pressure or an annualized 25 kton however long term monitoring data showing large temporal variability suggests extrapolation to an annual basis is inappropriate

the use of radon 222 as a tracer of sediment irrigation and mixing on the washington continental shelf abstract observations of the natural radioisotope rn 222 were used in conjunction with radiochemical biological and sedimentological techniques to investigate the irrigation and mixing of sediment at three sites about 90 m water depth along the washington continental shelf the rn 222 deficit difference between observed and predicted concentrations within the seabed was greatest near the columbia river during the summer molecular diffusion at most locations and times could account for only a portion of the deficit irrigation and mixing of the seabed explain the remainder biological mixing bioturbation and physical irrigation wave and tidal pumping have relatively little effect on the rn 222 deficit physical mixing erosion and deposition has a significant effect soon after a major erosion event storm however no such event occurred prior to the observations the conclusion is that biological irrigation and molecular diffusion are the primary causes of the rn 222 deficit and that biological irrigation is responsible for the observed spatial and temporal variations in the deficit therefore biological irrigation is greatest near the columbia river during the summer the spatial increase of irrigation near the columbia is probably due to a relatively large population of tube dwelling filter feeding polychaetes the temporal increases of irrigation during the summer is probably due to annual growth cycles of the benthic community and is not due to water temperature changes

organic markers as source discriminants and sediment transport indicators in south san francisco bay california sediment samples from nearshore sites in south san francisco bay and from streams flowing into that section of the bay have been characterized in terms of their content of biogenic and anthropogenic molecular marker compounds the distributions input sources and applicability of these compounds in determining sediment movement are discussed by means of inspection and multivariate analysis the compounds were grouped according to probable input sources and the sampling stations according to the relative importance of source contributions a suite of polycyclic aromatic hydrocarbons pahs dominated by pyrene fluoranthene and phenanthrene typical of estuarine environments worldwide and suites of mature sterane and hopane biomarkers were found to be most suitable as background markers for the bay a homologous series of long chain n aldehydes c12 c32 with a strong even over odd carbon number dominance in the higher molecular weight range and the ubiquitous n alkanes n c24 c34 with a strong odd over even carbon number dominance were utilized as terrigenous markers several ratios of these terrigenous and bay markers were calculated for each station these ratios and the statistical indicators from the multivariate analysis point toward a strong terrigenous signal in the terminus of south bay and indicate net directional movement of recently introduced sediment where nontidal currents had been considered to be minimal or nonexistent and tidal currents had been assumed to be dominant

hydrocarbons in washington coastal sediments the sources and distributions of polycyclic aromatic hydrocarbons pah and aliphatic hydrocarbons are characterized in seventeen sediments from a highly river influenced sedimentary environment off the southwestern coast of washington the major hydrocarbons are land derived introduced as preformed compounds and display long term stability in sediment cores a series of pah of anthropogenic origin and two naturally derived compounds retene and perylene dominate the pah composition in these sediments plantwax n alkanes are the major aliphatic hydrocarbon constituents aliphatic hydrocarbons of marine origin pristane and a series of four acyclic multibranched c25 polyolefins are also observed in many sediments the concentrations of these marine derived hydrocarbons decrease to negligible levels rapidly with sediment depth from the sea sediment interface suggesting degradation in general the major land derived hydrocarbons are concentrated in the midshelf silt deposit which extends northwestward along the continental shelf from the columbia river mouth a quantitatively more minor natural series of phenanthrene homologs also of terrestrial origin is preferentially advected further offshore and deposited in continental slope sediments these distributions are consistent with recognized particle associations for these compounds and sediment dispersal processes in this coastal environment sediment core records suggest the present pattern of dispersal has persisted for at least the past century and possibly since the late pleistocene

sources and distributions of sedimentary organic matter in the columbia river drainage basin washington and oregon1 nonwoody angiosperm tissues and gymnosperm woods are the major types of vascular plant debris in bottom sediments from 16 sites within the columbia river and its tributaries in tributary sediments relative abundances of these types of tissue vary regionally and are consistent with drainage basin vegetation within the extensively dammed main river vascular plant debris mixtures are more uniform indicating downstream mixing of sedimentary material from reservoir to reserwoir vascular plant tissues account for an average of a third of the total sedimentary organic matter at the 16 river sites the remaining organic material has an atomic c n of 10 l 5 and a stable carbon isotope composition similar to average land plants organic matter in sediments of the columbia river system is generally enriched in nonwoody angiosperm tissues and ligninpoor organic matter in comparison to columbia river derived organic matter in modern marine sediments from the southern washington continental shelf

impacts of late quaternary fluctuations in water level on the accumulation of sedimentary organic matter in walker lake nevada meyers p a 1990 impacts of late quaternary fluctuations in water level on the accumulation of sedimentary organic matter in walker lake nevada palaeogeogr palaeoclimatol palaeoecol 78 229 240 walker lake a terminal saline lake in western nevada has experienced major fluctuations in its water level due to changes in regional climate and river diversions during the late quaternary change in the degree of preservation of sediment organic matter has accompanied the lake level fluctuations and changes in the biotic sources of organic matter to the lake sediments have occurred in response to the climate changes and water diversions the record of these events has been studied using organic matter c n ratios and carbon isotope contents and employing molecular compositions of geolipids extracted from the sediment modern sediments contain mostly lake derived organic matter which has been altered by microbial reworking decreasesin the degree of preservation of organic matter indicate lake lowstands increases in the proportion of land plant components in sediment organic matter also indicate lowstand conditions

hydrocarbon geochemistry of the puget sound region ii sedimentary diterpenoid steroid and triterpenoid hydrocarbons cyclic components of the aliphatic hydrocarbon mixtures extracted from puget sound sediment cores include a suite of c19 and c20 diterpenoid hydrocarbons of which fichtelite sandaracopimaradiene and isopimaradiene have been identified although apparently also derived from vascular plants these diterpenoid hydrocarbons have relative abundances distinctly different from the co existing plant wax n alkane suite five c27 c28 and c29 diasteranes and four c29 c30 and c31 17 h 21 h hopanes occur in relatively constant proportion as components of a highly weathered fossil hydrocarbon assemblage these chromatographically resolved cycloalkanes along with the strongly covarying unresolved complex mixture have been introduced to puget sound sediments from adjacent urban centres at increasing levels over the last 100 yr in the absence of any major oil spill naturally occurring triterpenoid hydrocarbons including hop 22 29 ene diploptene are also present a new group of c30 polyenes has been detected which contains compounds apparently structurally related to a co existing bicyclic c25 diene and to c20 and c25 acyclic multibranched hydrocarbons described in a previous paper barrick et al 1980

the palaeoenvironmental and palaeohydrological evolution of padul peat bog granada spain over one million years from elemental isotopic and molecular organic geochemical proxies abstract the elemental concentration of organic carbon atomic h c and c n ratios isotopic 13 c values of organic matter and molecular predominant n alkane chain length and carbon preference index cpi organic components were measured for 600 samples taken from a 107 m long core from the padul basin andalusia spain the record runs from the lower pleistocene ca 1 ma b p to the mid holocene ca 4 5 ka b p with in general little diagenesis removal of components two markedly different hydrogeological scenarios were interpreted 1 from ca 1 ma to ca 400 ka b p run off recharge was significant and water depths were greater lacustrine scenario from ca 400 to 4 5 ka b p the padul basin became a peat bog s s with the major water input coming from groundwater inflow from ca 400 to ca 180 ka b p alternating episodes with either predominant grasses trees or aquatic macrophytes which were linked to wet dry phases took place an important deglaciation episode has been interpreted to occur between ca 180 and 170 ka b p the global climatic changes occurring from ca 170 to 25 ka b p were not recorded in the proxies though they do show important variations linked to the last glacial maximum and the beginning of the holocene ca 25 10 ka b p 2 cold phases coexisting with dry periods produced the recession of forests and the development of grasses after these periods as both temperature and precipitation increased forests expanded and the water level linked to thaw rose especially at ca 20 ka b p few changes occurred during the holocene although there were short alternations between wet and dry episodes overall the techniques applied proved to be excellent palaeoenvironmental proxies for studying the basin s palaeoclimatological and palaeohydrological evolution

geochemistry of c25 and c30 biogenic alkenes in sediments of the narragansett bay estuary abstract the distributions of a series of structurally related c 25 and c 30 biogenic alkenes in sediments of the narragansett bay estuary have been determined the suite of alkenes detected differs both quantitatively and qualitatively from those previously reported in other estuanne and coastal regions four c 25 mono and dienes and one c 30 diene comprise 73 91 of the total alkenes in all surface upper 2 5 5 cm sediments analyzed however significant geographic variations exist in the relative abundance of these five compounds throughout the estuary a comparison of alkene concentrations with 13 c of the bulk sedimentary organic matter has shown that the geographic variations of some alkenes reflect the distribution of marine organic matter suggesting a marine source for these compounds the distributions of other alkenes are not similarly correlated in particular concentrations of the c 30 diene are relatively constant and exhibit no dependence on the origin of organic matter in these sediments this distribution implies an in situ production of this alkene throughout the estuary analysis of several sediment cores reveals that alkene concentrations are generally highest at the surface and decrease to low constant values within the upper 25 cm an exception is the subsurface concentration of one c 25 diene which exhibits an increase at the same depth in two separate upper bay cores

chemical evidence of differential particle dispersal in the southern washington coastal environment aliphatic hydrocarbons cupric oxide oxidation products of lignin and polycyclic aromatic hydrocarbons pah were analyzed by capillary gas chromatography in sediments from the southern washington continental shelf and slope the concentration of diploptene relative to plantwax n alkanes increased systematically in surface sediments with distance offshore along east west transects of the study area and remained constant in surface sediments along the midshelf silt deposit analogous trends were also observed for the concentration of cinnamyl phenols relative to vanillyl phenols and total methylphenanthrenes relative to phenanthrene these changes in sedimentary composition are evidence that diploptene from some terrestrial source lignin characteristic of non woody vascular plant tissue and a fossil organic material contained within weathered rock debris disperse across the washington continental shelf and slope in geographic patterns distinct from that for other river derived chemically related materials the compositional variations are explained by the particulate associations of the land derived chemicals and differential hydraulic dispersion of their respective carrier particles after discharge at the mouth of the columbia river

zinc and cadmium stable isotopes in the geological record a case study from the post snowball earth nuccaleena cap dolostone abstract zinc and cadmium are important biologically cycled nutrients in the modern ocean recent analytical advances and sampling efforts such as geotraces have led to measurements of the global distribution of zn and cd and their stable isotope ratios 66zn and 114cd providing an understanding of how biological processes cycle these elements and their isotopes in the modern ocean this opens the door to better application of 66zn and 114cd as tracers of biogeochemical processes archived in the geological record here we present new measurements of cd and 114cd on samples from the nuccaleena cap dolostone in south australia which was deposited during deglaciation of the ca 635 ma old marinoan snowball earth our new data are combined with previously measured 66zn data from the same samples the combined record of 114cd and 66zn is used to explore various hypotheses about the sources and sinks of cd and zn in the post marinoan ocean key features of this record are that zn and cd remain relatively similar throughout that 66zn and 114cd change at the same stratigraphic level and in the same direction and that 66zn changes are about four times larger than 114cd changes even though both quantities reflect a similar fractional mass difference we suggest that both zn and cd concentration and isotopic data are consistent with a change in the sink by which zn and cd are removed from the oceans we propose that no isotope fractionation is expressed during removal of zn and cd as sulfides while zn and cd removed with biological material are about 0 6 and 0 2 lighter than deep ocean 66zn and 114cd respectively many previous studies attribute the burial of isotopically light biological zn to preferential assimilation of isotopically lighter zn by phytoplankton in contrast we propose that lighter biological 66zn occurs mostly because isotopically heavy zn was scavenged by organic matter which causes dissolved 66zn in the surface ocean to be lighter than deep ocean 66zn the organic matter originated from primary producers that thrived in the surface ocean during deglaciation for cd whose isotope cycling in the modern ocean is dominated by preferential assimilation of isotopically lighter cd by phytoplankton much less biological fractionation is expressed the combined analyses of 66zn and 114cd provide insight into the biogeochemical processes which occurred after the marinoan snowball earth glaciation and may be a useful new tool to explore the history of life on earth in other geological records as well

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

factors affecting pore water hydrocarbon concentrations in puget sound sediments abstract polycyclic aromatic hydrocarbon pah and aliphatic hydrocarbon concentrations have been determined for sediments and associated pore waters collected at 2 sites 11 stations in puget sound washington northwest u s a these sediments have been contaminated to varying degrees by hydrocarbons from a creosote plant and from various combustion sources pah were not detected in pore waters of sediments whose pah were primarily derived from combustion and natural sources even though pore water concentrations predicted from sediment concentrations and two phase equilibrium partitioning models were above detection limits from most pah equilibrium partition coefficients calculated from field aqueous and solid phase data from an area contaminated with creosote agreed with laboratory derived coefficients to within a factor of 4 pore water concentrations of creosote derived aliphatic hydrocarbons increase with increasing concentration in bulk sediments however pore water concentrations of natural and contaminant aliphatic hydrocarbons are much higher than predicted by solubility data possibly due to association with nonfilterable dissolved organic matter and colloids other major factors controlling hydrocarbon pore water concentrations include differential hydrocarbon sources specific particle associations and solubility

anthropogenic influences on hydrocarbon contents of sediments deposited in eastern lake ontario since 1800 the amounts and types of extractable hydrocarbon components in sediment cores from the rochester basin of eastern lake ontario provide a record of environmental changes that have accompanied the settlement and population growth of the surrounding land areas sediments deposited prior to the mid 1800s contain low concentrations of hydrocarbons that are dominated by land plant wax components concentrations begin to rise in the late 1800s as erosion of soil and nutrients from watershed areas accelerated this pattern continues into modern times episodes of enhanced aquatic productivity are sometimes recorded in twentieth century sediments by the dominance of algal hydrocarbons but land plant components typically predominate petroleum residues begin to appear in sediments deposited in the late 1800 s but remain minor constituents of the hydrocarbon contents of modern sediments in the rochester basin

temporal trends of aliphatic and polyaromatic hydrocarbons in the bohai sea china evidence from the sedimentary record abstract this work reports the historical trends and sources of aliphatic hydrocarbons ahs and polycyclic aromatic hydrocarbons pahs in two 210 pb dated sediment cores extracted from the central mud areas of bohai sea bohai the toc tn ratio of the bulk organic matter om and the composition of the n alkanes suggest that the sedimentary organic matter was of mixed marine and terrigenous sources the coarser sediment grain size and decreasing c n ratios since 1976 could be attributed to the relocation of the yellow river mouth causing a decreased influence of yellow river derived sediments and associated om into the central bohai the concentration of total 16 pahs in the two cores ranged from 34 2 202 ng g mean 91 5 for bc1 and from 53 3 186 ng g mean 103 for bc2 with a high abundance of 2 3 ring pahs perylene in the two cores mainly originated from terrigenous sources via riverine discharge and thus could be potentially related to changes in the sediment load from the yellow river into the bohai over time petroleum inputs could be revealed by ratios of methylphenanthrenes to phenanthrene mp p and the patterns of more stable geochemical biomarkers hopanes and steranes along the two cores in addition to the presence of unresolved complex mixtures ucm in the surface layers source diagnostic ratios of pahs indicated a pyrogenic origin from biomass and coal combustion with a minor petroleum contribution downcore trends of compositional pahs profiles were in agreement with the socio economic development in china in the past decades this temporal variation of sedimentary pahs can also reflect a different evolution stage of energy structure in china as compared with those of the western developed countries

variability of early diagenesis in lake sediments evidence from the sedimentary geolipid record in an isolated tarn abstract a 0 5 m long core of sediment from coburn mountain pond maine u s a has provided a virtually undisturbed and continuous record of sediment deposition for the last 200 yr in this small essentially pristine tarn organic carbon concentrations c n ratios carbon isotopic compositions and extractable hydrocarbon molecular compositions indicate subtle differences in the sources of organic matter between sediments deposited before and after ca 1950 but are otherwise constant in contrast total concentrations and molecular distributions of n fatty acids and n alkanols vary considerably the fatty acid and alkanol geolipid fractions are both sensitive to early diagenetic alteration yet the two fractions react differently concentrations and compositional parameters such as long short even odd and branched unbranched ratios fluctuate with sediment depth and reflect amounts of microbial reworking which have varied repeatedly over the depositional history n alkane distributions are relatively unaffected by the short term changes and therefore better preserve the history of biolipid sources to the sediments

210pb activities in and fluxes to sediments of the washington continental slope and shelf abstract surface sediments of the washington coast have 210 pb activites which average 104 48dpm g for submarine canyon and slope regimes and 18 12dpm g for the continental shelf regime 210 pb sedimentary fluxes are also higher in canyons averaging 18 13dpm cm 2 per yr compared to 5 2 3 1 dpm cm 2 per yr for slope and 4 8 1 8dpm cm 2 per year for shelf regions these 210 pb activities and fluxes are 2 7 times greater than those reported for other coastal regions inputs from the atmosphere and the columbia river are not sufficient to supply the 210 pb but advection of seawater containing dissolved 210 pb produced in situ from 226 ra provides an input several times larger than the sedimentary fluxes the sedimentary 210 pb flux is limited by scavenging reactions rather than by supply of dissolved 210 pb calculations of maximum biological uptake and fluxes of 210 pb and selective chemical leaching experiments all show that the primary scavenging processes are due to hydrous mn and fe oxides rather than biological phases the pattern of higher 210 pb depositional fluxes in canyons than in nearby open slope areas of comparable water depth is most reasonably explained by enhanced scavenging of dissolved 210 pb near the sea floor rather than by processes operating throughout the water column relatively rapid removal of dissolved 210 pb from the near bottom nepheloid layer to slope and canyon sediments is shown by its mean residence time of less than two years in this layer

the importance of site selection sediment supply and hydrodynamics a case study of submarine paleoseismology on the northern cascadia margin washington usa abstract the washington continental margin presents both a classic test of submarine paleoseismology and an opportunity to explore advancement of the field through analysis of sediment dispersal in a heterogeneous system new and archive core bathymetric backscatter and seismic reflection data from the washington cascadia margin show that during high stand conditions the northernmost canyons barkley nitinat juan de fuca jdf and to some extent quillayute are relict systems with little holocene recharge the remaining canyons quinault grays guide and willapa are recharged to a varying degrees by northward transport of columbia river derived sediment all systems are nonetheless active conduits for turbidity currents during the holocene which are weaker and more restricted than their pleistocene counterparts sedimentologic and ct analysis supported by radiocarbon ages micropaleontology and the mazama ash datum show that the holocene sedimentary sequence consists of a series of sand to mud turbidites in the active portions of all systems interbedded with hemipelagic sediment however the pleistocene astoria and nitinat fans are largely inactive in the holocene with turbidity current activity limited to the proximal parts of the main channels within active systems the turbidite record is modulated by local landsliding and growth of active folds and faults in the relict systems the turbidite record begins in the middle canyon reaches as opposed to the actively recharged systems which have a turbidite record in the more proximal canyon reaches deposits in the relict systems increase in thickness and modal grain size downstream suggesting multiple sources and or entrainment of material along the canyon walls hydrodynamic models using monte carlo model searches for best fitting flow parameters show the most likely pathways by which holocene and pleistocene currents flowed through the complex accretionary wedge to the abyssal plain model results supported by heavy mineral distributions show that the northern canyon systems barkley nitinat jdf quillayute are independent of the southern systems quinault guide grays willapa during the holocene supporting the classic confluence test balancing of sediment volumes required suggests sediment supplied to the slope canyons and abyssal channels in turbidity current events is 2 5 times greater than that supplied by recharge to the canyon heads by external sources this implies a process that is independent of recharge that scavenges the plentiful relict and hemipelagic sediment supply on the continental slope lithostratigraphic correlation and age models suggest similar sequences were deposited in most systems independently and likely synchronously the correlated turbidite sequence suggests deposition of 23 holocene and 16 post mazama turbidites in most parts of the canyon systems with only modest variation mostly attributable to evidence of bypassing and erosion the best candidate for triggering of these sequences remains great earthquakes and the sequence correlates well to onshore and other offshore paleoseismologic evidence the new data including new cores in northern oregon suggest revisions to segmented rupture boundaries several partial ruptures segment b likely extended further north to juan de fuca canyon one event was resolved into two and one washington only event was added most segment c ruptures were found to extend further northward to the latitude of astoria canyon mean recurrence times are therefore revised to 434 years for the washington coast and 340 years for the central and northern oregon coast conditional probabilities in the next 50 years also are revised to 10 17 for the washington coast and 16 22 for the central and northern oregon coast in cascadia sumatra and other locales globally core siting spatial sample density high resolution analysis of core and regional geophysics and understanding of flow dynamics are critical to capturing a paleoseismic record sedimentary records vary across turbidity current systems of varying sediment supply physiography and sediment sources variations in the record will reflect these factors yet may still present a consistent paleoseismic history this analysis highlights the importance of a thorough understanding of flow paths hydrodynamics and the interplay of sedimentation and local tectonics when testing for evidence of earthquakes in the sedimentary record of active margins

a geochemical study of long chain n aldehydes in washington coastal sediments a series of n aldehydes c20 to c32 with strong even to odd carbon preference was identified in the mixture of solvent extractable lipids isolated from various washington coastal sediments a limited survey of the lipid composition of surface waxes of foliage and cuticular waxes of pollen from several major plant species indigenous to the pacific northwest revealed that similar series of n aldehydes are intrinsic to regional vegetation debris from such plants discharged at the mouth of the columbia river represents a preformed source of the n aldehyde series accumulating in sediments from the washington coastal region although the evidence suggests n aldehydes are largely introduced erosionally to this region as a chemical component of land derived debris and are not formed in situ in the coastal sediments further study is warranted to establish the postdepositional stability of this series of compounds relative to other lipids of higher plantwax origin despite but few literature reports of the occurrence of these geochemicals long chain n aldehydes are very likely common in many sediments from environments that receive an input of detrital organic matter from higher plants

reconstructing human landscape interactions in the ancient mediterranean harbour of cartagena spain here we sought to reconstruct the pleistocene and holocene evolution of cartagena bay therefore 16 borehole cores were analysed with the following aims 1 to define a chronological framework 2 to obtain data on the palaeoenvironment and 3 to establish the relationship with human activities especially focused on the reconstruction of the carthago nova also known as qart hadasht conquest a total of 147 samples were recovered for amino acid racemisation aar dating 32 for radiocarbon dating 14c and 159 for sedimentological palaeontological and biomarker determination these approaches allowed us to elucidate the evolutionary phases of the palaeolandscape in cartagena the simultaneous use of aar and 14c dating allowed the discrimination of spurious ages and the establishment of a chronological scale during the marine isotope stages mis 7 and 5 the sea level sl in cartagena bay was almost the same as today an alluvial plain developed in the northern area and a delta was formed by