sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

anomalous accumulation of acid volatile sulphides avs in a coastal marine sediment saguenay fjord canada sulpha te reduction usually leads to the formation and accumulation of authigenic pyrite fes2 in organic rich coastal marine sediments iron monosulphides fesx are most often found as a minor constituent of the reduced sulphur pool in these sediments and are believed to be precursor phases which convert to pyrite during early diagenesis abnormally high ratios of acid volatile sulphides avs to pyrite however are found in the sediments of the saguenay fjord canada the avs s fes2 s ratio observed throughout the anoxic zone in three sediment cores collected along the main axis of the fjord generally exceeds 1 and reaches values as high as 7 at the head of the fjord to document and explain this anomaly solid phase components avs fes2 s reactive iron feno coro and total n as well as porewater constituents so4 fe and mn were analyzed degree of pyritization dop values were low 0 1 11 and generally decreased toward the mouth of the fjord in contrast degree of sulphidization dos esti mates were high and reached values of up to 43 at the head of the fjord these latter values indicate that pyrite formation is not limited by iron availability but a large excess of reactive iron may in fact inhibit the build up of reduced sulphur zh2s in the porewaters as a result of avs s precipitation in the absence of a strong eh2s gradient slow diffusion to the redox boundary and limited formation of soluble inter mediate reduced sulphur species may hinder the conversion of avs to pyrite

importance of small scale paleo oceanographic conditions to interpret changes in size of california mussel mytilus californianus late holocene santa cruz island california abstract several authors have highlighted the difficulties in disentangling human from natural effects when studying shellfish foraging strategies and archeo malacogical records in coastal settings one of the reasons for this difficulty is the lack of understanding of small scale oceanographic conditions and their influence on coastal and marine species used by people in the past the present study evaluated the influence of environmental conditions on shellfish harvesting during the late holocene around santa cruz island southern california considering small scale nearshore oceanographic variability around the island and its effect on m californianus main shellfish species exploited through prehistory along the coast of california fluctuations in size and abundance of m californianus shells through time and local past sea surface temperature sst values from oxygen isotope analysis of mussel shells are correlated throughout the stratigraphy of two shell midden sites 2200 500 cal b p nearby coasts with different paleo oceanographic characteristics despite the fact that human harvesting seems to have been the main force shaping length and availability of m californianus no clear evidence of human pressure was found on archaeological mussel assemblages results also show that fluctuations in regional sst records santa barbara basin marine core do not represent local sst variations oxygen isotope analyses on mussel shells especially if the archaeological site is located on a coast exposed to strong and consistent upwelling activity by re evaluating human impact on mussel beds during the late holocene around santa cruz island the research presented here demonstrates the importance of considering small scale nearshore oceanography for understanding the archaeological evidence of prehistoric human foraging on important intertidal shellfish species

deposition and modification of a flood layer on the northern california shelf lessons from and about the fate of terrestrial particulate organic carbon the 1995 flood of the eel river in northern california provided an opportunity to follow the short term history of riverine particulate matter on a continental shelf particulate organic carbon including both vascular plant debris and soil carbon was utilized as a tracer of the distribution and modification of the shelf flood deposit these components were sorted during initial emplacement of the deposit both in the river plume and in the benthic boundary layer during the 8 months following the flood lateral transport shallow burial and bioturbation contributed to spatial changes in the amount and character of carbon in the flood deposit study of the deposit suggests that this and previous flood layers may be preserved in the shelf and upper slope stratigraphic record as clay rich beds with relatively high carbon to nitrogen ratios and more negative 13c values than background non flood sediment concentrations of vascular plant debris are locally characteristic of such layers and may serve as distinctive stratigraphic markers investigation of organic carbon in the 1995 flood layer on the eel river shelf provides insight into the fate of terrestrial particulate carbon on continental margins in general flooding of the eel river and of similar river systems draining mountainous terrains introduces large quantities of terrestrial carbon to the marine environment and may favor the preservation of both terrestrial and marine carbon the abundant woody vascular plant debris discharged during floods is especially likely to survive oxidation and sulfate reduction in the shallower zones of the seabed this study reveals the dominant role that physical and biological processes may play in attenuating the terrestrial organic carbon signal on shelves over monthly to yearly time scales

lignin geochemistry of a late quaternary sediment core from lake washington long term lignin stability and paleovegetation patterns were investigated using cuo oxidation products of sediments from an 11 m core of late quaternary sediment collected from the mid basin of lake washington washington state relatively constant yields of lignin derived phenols normalized to organic carbon from the entire core indicate minimal in situ lignin degradation over the last 13 000 years compositional patterns within the phenolic suite and increased corresponding yields from baseextracted sediments indicate that sedimentary lignins are present predominantly as well preserved plant tissue fragments abundance patterns of vanillyl syringyl and cinnamyl phenols record four distinct sequences within the core characterized by 1 a high concentrations of gymnosperm wood in a basal horizon of glacial flour 11 10 m 2 b an essentially pure mixture of nonwoody angiosperm tissues in late pleistocene sediments 10 8 m 3 c relatively high concentrations of angiosperm woods in the bottom half of a limnic peat sequence deposited approximately 10 000 7 000 years b p 8 4 m and 4 d a progressive enrichment in gymnosperm woods at the expense of angiosperm woods over the last 7 000 years in the upper limnic peat 4 0 m vascular plant tissues account for less than half the total sedimentary organic carbon throughout the core

human responses to middle holocene climate change on california s channel islands abstract high resolution archaeological and paleoenvironmental records from california s channel islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses available climate records in western north america 7 3 8 ka indicate a severe dry interval between 6 3 and 4 8 ka embedded within a generally warm and dry middle holocene very dry conditions in western north america between 6 3 and 4 8 ka correlate with cold to moderate sea surface temperatures sst along the southern california coast evident in ocean drilling program odp core 893a b santa barbara basin an episode of inferred high marine productivity between 6 3 and 5 8 ka corresponds with the coldest estimated ssts of the middle holocene otherwise marked by warm low productivity marine conditions 7 5 3 8 ka the impact of this severe aridity on humans was different between the northern and southern channel islands apparently related to degree of island isolation size and productivity of islands relative to population fresh water availability and on going social relationships between island and continental populations northern channel islanders seem to have been largely unaffected by this severe arid phase in contrast cultural changes on the southern channel islands were likely influenced by the climatically induced environmental changes we suggest that productive marine conditions coupled with a dry terrestrial climate between 6 3 and 5 8 ka stimulated early village development and intensified fishing on the more remote southern islands contact with people on the adjacent southern california coast increased during this time with increased participation in a down the line trade network extending into the western great basin and central oregon genetic similarities between middle holocene burial populations on the southern channel islands and modern california uto aztecan populations suggest middle holocene movement of people at this time from southern california desert environs westward to the southern islands a migration perhaps stimulated by increased continental aridity

tropopause folds and synoptic scale baroclinic wave life cycles abstract the linear stability of three midlatitude zonal mean states of varying baroclinicity and barotropy is examined using a primitive equation stability analysis under the anelastic approximation each of these basic states includes both tropospheric and stratospheric regions with realistic properties compared with those of the earth s atmosphere in midlatitudes in all three cases the fastest growing synoptic scale modes delivered by the linear stability analysis have wavelengths of approximately 4000 km the nonlinear evolution of these synoptic scale modes is explored using a three dimensional anelastic finite difference model whose zonal scale is chosen to be equal to the wavelength of the fastest growing mode of linear theory during the nonlinear evolution of the wave deep tropopause folds are shown to form generically and the depth to which the fold penetrates the troposphere is seen to increase with the baroclinicity of the mean state these folds descending along the sloping frontal zone

particulate manganese and iron in recent sediments of the gulf of lions continental margin north western mediterranean sea deposition and diagenetic process abstract this study aims at apprehending the major forcing factors which govern the spatial and vertical mn and fe distributions in ten cores from the gulf of lions speciation by chemical leaching experiments helps understanding their chemical behaviour during the early diagenetic processes in a marine environment under strong continental influence the distribution and chemical behaviour of mn and fe differ drastically the strong dependence of mn distribution on chemical conditions is expressed by a marked solid phase mn enrichment in the oxic layers of sediment deposits this enrichment increases with decreasing sedimentation rate increasing water depth it is illustrated by an enhanced portion of total mn in the reducible phase and the precipitation of todorokite on calcareous supports in the upper part of the deepest cores as a result 65 of the margin total particulate mn is thought to be stored in slope deposits in a relatively strongly held association conversely the low chemical mobility of iron in the sedimentary column is indicated by uniform depth profiles and an exclusive location in the residual chemical phase in all the studied sites the fe distribution is largely controlled by the dispersion of particulate material on the margin from the rhone river main source a budget of mn and fe accumulation based on the average amount of total mn and fe content of sediments deposited during the last 100 yr has been made taking into account diagenetic readjustments the total mn and fe amount stored on the margin during the last century is estimated to be 1 5 106 and 54 106 t respectively these values are seven times higher than the total secular external inputs calculated on the basis of present day riverine and atmospheric fluxes this large discrepancy is mainly explained by the sharp decrease of the rhone river discharge after dam buildings between 1950 and 1958 a residual discrepancy dating before 1950 is likely to be due to seafloor erosion and gravity induced mechanisms

ecogeochemical fate of coarse organic particles in sediments of the rhone river prodelta coarse particulate organic matter cpom represents a small portion of the inner shelf sediments but occurs across all river outlets to consider the ecogeochemical fate of cpom in such an environment we examined both the infauna community and secondary evidence of geochemical reactions preserved in the surface sediments of the rhone prodelta icp aes scanning electron microscopy and energy dispersive x ray spectrometry of the cpom showed that the fate of organic matter in this environment is driven by sulphate reduction and geochemical reactions resulting from the precipitation of sulfide due to the presence of large amounts of iron bearing minerals leaf litter debris contained such high quantities of iron that after dry ashing the remaining material is easily attracted by a magnet the observed geochemical trade off was proposed as a mechanism that helps to maintain a bioturbating animal community that in turn contributes to the mineralization of organic matter within this suboxic environment this study showed that the accumulation of refractory organic carbon in sediments was intimately associated with the sequestering of iron and sulphur by providing a nucleation point for mineral deposition and also that the extent of decomposition of the organic materials did not necessarily increase progressively from coarser to finer particles

on the antiquity of the single piece shell fishhook ams radiocarbon evidence from the southern california coast abstract during the late holocene a number of new technologies single piece fishhooks toggling harpoons plank canoes etc are thought to have significantly enhanced the fishing capabilities of california coastal peoples the single piece fishhook perhaps the most common of these artifacts appears to correlate with a regional intensification of marine fishing and a period of increased population growth determining the antiquity of the single piece fishhook has been complicated by a variety of taphonomic and methodological factors consequently age estimates for the initial appearance of these artifacts range from about 5500 to 2500 cal bp to help clarify the chronology of this important artifact type we had eight of the potentially oldest shell fishhooks in the region ams radiocarbon dated these dates indicate that the single piece shell fishhook appeared throughout the southern and central california coast by at least 2500 cal bp our data illustrate the utility of direct ams dating of individual artifacts as a method of documenting site disturbances bioturbation historical land use etc and refining artifact site and regional chronologies

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

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

a 7000 year sea surface temperature record from ca sri 147 santa rosa island california usa california mussels mytilus californianus excavated from archaeological site ca sri 147 on the southern side of santa rosa island california provided a discontinuous environmental record spanning about 7000 years an earlier report of the midden remains at this site found a weak inverse correlation between changes in mussel shell length and sea surface temperature sst but not productivity and a decline in mussel size from 5800 to 5100 calendar years before present during a period of low productivity and increasing sst this study uses oxygen isotopes from the site to directly compare environmental change to shifts in faunal assemblage four intervals of low temperatures are revealed in the nearshore environmental data each corresponding to a significant change in faunal assemblage at the site the first occurs c 6600 calendar years before present cal bp and coincides with the greatest amount of mussel shell mass and size in the site the second c 5500 cal bp occurs during an interval of variable mussel contribution and increasing red abalone haliotis rufescens contribution the third c 4800 cal bp occurs during a time when platform mussels septifer bifurcatus exceed california mussels in meat weight while the final interval c 3700 cal bp occurs prior to a period of probable site hiatus the overall pattern of decreasing shell contribution and size at the site is not found in the mollusk isotope data suggesting that environmental change had a profound impact on short term variability while human predation of key resources provided the long term primary stress on nearshore biota

diagnostic study of a narrow cold frontal rainband and severe winds associated with a stratospheric intrusion a diagnostic study of a severe wind event associated with a cold front is presented based on output from an operational numerical weather prediction model together with radar and satellite imagery and detailed surface observations an intrusion of stratospheric air initially with a potential vorticity of 2 pv units is shown as part of a backward tilted filament to have plunged down to the lower troposphere where it was associated with a narrow cold frontal rainband at its leading edge and produced severe wind gusts up to 70 knots a close correspondence in time and space is revealed between these surface events and the appearance in the model of a pocket of diluted stratospheric air with pv 1 at the 2 km level the stratospheric intrusion produced two distinguishable wind surges one behind the narrow cold frontal rainband and another mainly dry about 200 km farther behind the strength of the winds was attributable to the downward transport of momentum as part of the large scale dynamics local moist processes played only a minor role at coarse resolution the radar echo from the narrow cold frontal rainband resembled line convection but it is shown that there were significant differences between this event and the archetypal form of line convection often seen in the british isles

measurement of significant marine paleotemperature variation using black abalone shells from prehistoric middens abstract the archaeological record from the last millennium in southern california indicates that a period of significant cultural change was associated with a reported marine paleoenvironmental disruption ca 1150 1250 a d a lengthy warm water anomaly may have in part precipitated more complex sociopolitical and economic responses we develop independent verification of the perturbation originally deduced from sediment core data using archaeological data respiratory pore number allometry in the black abalone shell is known to vary clinally in modern populations in response to temperature induced variation in rate of growth we use developmental trajectories of abalone from dated stratified archaeological deposits to reconstruct prehistoric seawater temperatures

the origin and evolution of lunar high ti basalts periodic melting of a single source at mare tranquillitatis abstract five groups of basalts a b1 b2 b3 d with three principal ages exist at the apollo 11 site these range from the low k low rare earth element ree groups b1 b2 and b3 to the low k high ree group d basalts to the high k high ree group a basalts the group a basalts are the only high k 0 2 wt k2o basalts and youngest with an age of 3 59 02 ga groups b3 and b1 are 3 71 02 and 3 67 02 ga respectively group b2 basalts are the oldest at 3 85 02 ga group d basalts have not been dated fractionation modelling for major and trace elements indicates that the b1 basalts could have formed from a b3 like parent liquid the b2 and d basalts can also be related to liquids similar to the b3 b1 composition through the presence of varying amounts of modal whitlockite thus the entirety of low k high ti basalts at apollo 11 may have formed through melting of the same source region the group a basalt compositions are consistent with formation from a different parent liquid with the composition of apollo 11 orange glass modelling of major and trace elements in the apollo 11 orange glass indicate that the composition of the group a basalts is consistent with fractionation of this glass coupled with some assimilation 7 5 15 of an evolved kreep like material however this component is much younger than primitive kreep 4 4 ga this neukreep component similar to the composition of quartz monzodiorites described from the apollo 15 site probably represents evolved material formed during plutonism prior to the formation of the apollo 11 orange glass liquid

diagnosis of ageostrophic circulations in a two dimensional primitive equation model of frontogenesis abstract diagnoses are presented of the transverse ageostrophic circulation patterns for two cases from a two dimensional primitive equation model of frontogenesis forced by a combination of confluence and horizontal shear the cold advection case the specified alongfront potential temperature gradient results in differential cold advection by the upper level jet realistically simulates upper level frontogenesis in response to tilting by a cross front gradient of subsidence the warm advection case features a frontal system spanning the troposphere which develops in response to differential horizontal advection the diagnoses are performed by numerically solving three versions of the two dimensional sawyer eliassen equation for the streamfunction of the transverse ageostrophic circulation the quasi geostrophic qg and geostrophic momentum gm versions are based on the approximation of cross front geostrophic balance while the primitive equation pe version includes the possibility of an alongfront

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

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

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

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

time series measurements of macrobenthos abundance and sediment bioturbation intensity on a flood dominated shelf abstract four 70 m stations on the continental shelf offshore from the eel river northern california were occupied at roughly four month intervals between february 1995 and march 1998 and in august 1999 at each of the stations profiles of excess 234 th were used to quantify sediment bioturbation intensity in addition at two of the stations macrofaunal abundance species composition and functional groupings were quantified during the study period the eel river displayed a range of hydrological conditions with historically significant floods in january 1995 and january 1997 return periods of 15 and 40 y respectively relatively low flows during the winters of 1995 1996 and 1998 1999 and an el nino year characterized by moderate but frequent discharges in 1997 1998 the january 1995 and 1997 floods deposited 3 7 cm of fine grained high porosity sediment with high c n ratios and a terrestrial organic carbon signature at the study sites the following general questions are addressed herein 1 how do macrofaunal abundance species composition and functional groupings vary over time 2 does the sediment deposition following the january 1997 flood constitute a major disturbance to the eel shelf macrobenthos 3 how does sediment bioturbation intensity vary in time space and what are the main factors controlling this variation the eel shelf macrofauna is strongly dominated by subsurface deposit feeding polychaetes with anomalously low abundances of surface deposit feeders and virtually no suspension feeders among the community dominants the abundance data revealed a clear seasonal pattern with peak density 4 5 10 4 m 2 in the fall and a factor of two lower density in the late winter spring 2 10 4 m 2 within this seasonal context there was little evidence for extraordinary mortality caused by the january 1997 flood in that overall wintertime mortality and the mortality of most community dominants during a year 1995 1996 when there was no flood deposition were comparable to the mortality observed following the january 1997 flood in contrast the depth distribution of the macrofauna revealed a distinctive post flood pattern whereby a majority 55 70 of individuals were temporarily found at depths 4 cm this pattern suggests an active response by the resident fauna to sediment deposition and supports the idea that the floods did not cause a widespread disturbance although there may not be clear evidence for short term flood effects the overall species composition and functional groupings do imply that the sedimentary environment high sediment accumulation rates and abundant terrestrial organic matter has had a long term influence on the eel shelf macrofauna model fits to 75 profiles of excess 234 th show that in general the data are consistent with a steady state biodiffusive model the resultant mixing intensities ranged from 3 to 325 cm 2 y 1 with averages standard deviation of 35 33 24 19 37 35 and22 9 cm 2 y 1 at stations c70 i70 l70 and o70 respectively the average biodiffusivity for all stations and times was 29 25 cm 2 y 1 n 62 due to the large amount of variability which is consistent with other continental margin studies it was not possible to detect significant spatial or temporal variability although there is a hint of higher mixing intensities during the late summer early fall the period of maximal carbon flux to the seabed correlations between total macrofaunal abundance and mixing intensity are notably poor whereas a slightly better correlation r 2 0 22 was obtained between the abundance of large animals and bioturbation intensity by explicitly considering organic carbon flux or some measure of seabed food resources and the abundance of larger organisms it may be possible to predict bioturbation intensity better in future studies although the pervasive small scale variability detected on the eel river shelf warrants in depth theoretical and experimental consideration

terrestrial plant biopolymers in marine sediments the vascular land plant biopolymers lignin and cutin were surveyed in the surface sediments of coastal and open ocean waters by controlled alkaline cuo oxidation reaction two contrasting oceanic regimes were studied the northwest mediterranean nwm sea which receives significant particulate terrigenous debris through riverine discharge and the northeast atlantic nea ocean with poorly characterised terrestrial carbon inputs in the nwm products of lignin and cutin co occurred at all stations elevated levels ca 0 5 3 0 mg lignin phenols 100 mg organic carbon ca 0 01 0 09 mg cutin acids 100 mg organic carbon were observed for near shore deltaic and shelf sediments the influence of terrestrial land plant inputs extended across the shelf and through the slope to the abyssal plain providing molecular evidence for advective offshore transfer of terrestrial carbon mass balance estimates for the basin suggest riverine inputs account for the majority of surface sedimentary lignin cutin most of which 90 is deposited on the shelf products of cuo oxidation of lignin and cutin were also detected in nea surface sediments at levels comparable to those observed for the nwm continental slope and were detectable at low concentrations ca 0 5 gg 1 in the sediments of the abyssal plains 4 000 m depth while atmospheric deposition of lignin cutin derived material cannot be discounted in this open ocean system lateral advective transfer of enriched shelf sediments is inferred as a possible transport process a progressive enrichment in cutin derived material relative to lignin was observed offshore with evidence of an increase in the degree of oxidative alteration of lignin residues to account for these observations preferential offshore transport of finer and more degraded material is proposed nonspecific oxidation products dominated the gas chromatograms of nea sediments which appear to originate from marine sources of sedimentary organic carbon preliminary mass balance calculations applied to the global ocean margin suggest riverine sources of both particulate lignin and cutin are important and that most 95 deposition of recognisable land plant biopolymers occurs in shelf seas

glacial interglacial climatically forced δ 13 c variations in sedimentary organic matter sedimentary organic geochemical properties have long been used to characterize sedimentary organic matter sources1 8 but the characterizations are often not unique there are at least four plausible mechanisms to account for the large 3 6 glacial to interglacial climatic variations in the sedimentary organic carbon isotopic composition 13corg in the northern gulf of mexico they are temperature dependent c isotopic fractionation by phytoplankton mixing of c3 photosynthetic terrigenous and marine organic matter mixing of c3 and c4 photosynthetic organic matter and diagenetic alteration of the originally sedimented material in a 208 7 m deep sea drilling project hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico we find that paired analyses of 13corg and n c are consistent with the hypothesis that the sedimentary organic carbon in the pigmy basin is a glacial interglacial climati cally determined mixture of c3 photosynthetic terrigenous and marine organic matter9 confirming the model of sackett5

the relationship between sedimentary organic carbon isotopic composition and organic biomarker compound concentration abstract a study of organic biomarker compounds which could serve as tracers of terrigenous and marine sedimentary organic matter sources was performed on samples from a 208 7 m hydraulic piston core hole dsdp hole 619 from the hemipelagic pigmy basin in the northern gulf of mexico organic carbon normalized concentrations of total long chain c37 c39 alkenones and some individual c27 c29 desmethyl sterols were determined to be useful proportional indicators tracers of preserved marine and terrigenous organic carbon respectively the alkenones whose only known source is marine phytoplankton of the class prymnesiophyceae generally occurred in higher concentrations in interglacial isotope stages 1 and 5a b than in the intervening glacial stages sterols c27 c29 apparently of a dominantly terrigenous origin occurred in lower concentrations during interglacial stages than in glacial stages tracers of both terrigenous and marine organic matter appear to be affected by the differential diagenetic alteration of the biomarker corg ratios as indicated by a simple first order kinetic model the lack of any desmethylor 4a methylsterol which is linearly related to the proportion of marine sedimentary organic matter as scaled by 13corg indicates that either 1 1 sedimentary diagenesis has obscured the biomarker corg vs 13corg record 2 2 phytoplanktonic assemblage changes caused variations in the biomarker corg ratio of the primary input preferential preservation of terrigenous sterols may result in a biased sedimentary record of sterol input which could be misinterpreted as indicating solely terrigenous sterol sources a simple model which characterizes the effects of sedimentary diagenesis on the relationship between corg normalized biomarker ratios and 13corg demonstrates the potential problems of long term differential diagenetic skewing on those tracer records

atmospheric origin of the devastating coupled air sea event in the east adriatic enhanced sea level oscillations with devastating effects occurred on 26 27 june 2003 in the east adriatic the phenomenon was recognized as a resonantly coupled air sea interaction where the sea wave is forced by the propagating atmospheric pressure disturbance this study examines the dynamics and predictability of the atmospheric component of the coupled system first the initiation amplification and maintenance of the system are examined the source of the perturbation is traced back to the alpine region where the potentially unstable air in the westerly current lifts over the alps resulting in convection and wave development the wave and convective activity apparently couple in a wave cisk manner and propagate southeastward down the eastern adriatic coast due to the potentially unstable air above the adriatic the system additionally amplifies along its track the dissipation of the system occurs after the landfall second the performance of the numerical model at the resolution that is similar to operational nwp model resolution is examined this severe event is highly susceptible to the details of the model configuration presumably due to the sensitivity in coupling of the wave and mcs thus although the model is able to reproduce and forecast this kind of event at a fairly coarse resolution the details of the spatial structure as well as the time of onset are questionable in this case the greatest sensitivity is primarily in the treatment of moist and convective processes

macrofaunal density biomass and composition of estuarine sediments and their relationship to the river plume of the rhone river nw mediterranean this study investigates species community patterns and sediment relationships of benthic macrofauna off the rhone river delta along a we transect changes in diversity density biomass and trophic structure were coupled with the mean extension of the river dilution plume species number and diversity were at a minimum off the river mouth below the area of the minimum surface salinity density decreased by a factor 2 and biomass by a factor 5 from the fluvial to the marine system these features are due to high overload of terrestrial organic matter in the river prodelta as evidenced by the carbon isotopic signature of surface sediment and by pigment content on the basis of a non metric mds analysis and of dufrene and legendre method 1997 groups of stations and characteristic species associated were identified these species mainly small capitellids spionids lumbrinerids and sternaspids correspond to a successional dynamic in response to changes in sedimentation conditions mainly in organic matter quality of the surface sediment the succession observed in space was similar to described in macrotidal estuaries and off other deltaic systems all over the world and to that observed in time following the rhone river severe flood events results suggest that organic matter quality is an important factor with regard to benthic macrofauna successions and recovery mechanisms following disturbances the differences observed between the rhone deltaic system and the general model of relations between shelf processes and discharge of large rivers are attributed to a more regular supply of organic material from terrestrial origin on the rhone continental shelf

terrestrial organic carbon contributions to sediments on the washington margin elemental and stable carbon isotopic compositions and biomarker concentrations were determined in sediments from the columbia river basin and the washington margin in order to evaluate geochemical approaches for quantifying terrestrial organic matter in marine sediments the biomarkers include an homologous series of long chain n alkanes derived from the surface waxes of higher plants phenolic and hydroxyalkanoic compounds produced by cuo oxidation of two major vascular plant biopolymers lignin and cutin all marine sediments including samples collected from the most remote sites in cascadia basin showed organic geochemical evidence for the presence of terrestrial organic carbon using endmember values for the various biomarkers determined empirically by two independent means we estimate that the terrestrial contribution to the washington margin is 60 for shelf sediments 30 for slope sediments and decreases further to 15 in basin sediments results from the same geochemical measurements made with depth in gravity core 6705 7 from cascadia seachannel suggest that our approach to assess terrestrial organic carbon contributions to contemporary deposits on the washington margin can be applied to the study of sediments depositing in this region since the last glacial period

a general circulation model study of a tropopause folding event at middle latitudes the uk universities global atmospheric modelling programme general circulation model ugcm has been run at high horizontal resolution to investigate a tropopause folding event at middle latitudes geopotential height potential vorticity and specific humidity distributions were diagnosed from the model and showed a realistic representation of the synoptic development of the cut off low associated with the tropopause fold the model also successfully portrayed the frontogenesis associated with tropopause folding and represented both the upper level frontal region and the corresponding jet streaks as they progressed through the region of the developing trough a series of vertical cross sections at the ends of the jet streaks demonstrated that a fold could be captured by the ugcm using potential vorticity and specific humidity although more small scale features were evident in the specific humidity contours than in the corresponding potential vorticity fields the corresponding baroclinic zone was also resolved although both the slope and thickness were rather larger than sometimes observed both the spatial and temporal extent of the fold compared well with observations in addition the model simulated the ageostrophic winds in the entrance exit and middle streak regions a direct circulation was obtained at the entrance and an indirect circulation at the exit region of the jet streak in good agreement with theory and with observational data a combination of confluence cold advection and curvature was responsible for the forcing of the ageostrophic motion at the jet entrance whereas the forcing at the jet exit was attributed mainly to diffluence and curvature q vectors were employed to investigate the vertical motion in the vicinity of the fold and showed the precise positions of descent corresponding to the fold along the entire length of the jet streak finally a tropopause fold around a jet that was not subject to the development of strong baroclinic instabilities was reproduced by the model it was smaller in size than the fold of the cyclonic trough a q vector analysis confirmed the position of the small fold along the jet and revealed large scale ascending motion that may have been responsible for the small size of fold the possibility of using the model to yield a realistic estimate of the transfer of air from the stratosphere to the troposphere in a tropopause folding event at mid latitudes is discussed

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

reactive iron in marine sediments abstract a combined field laboratory study has been undertaken to explore the mineralogy concentrations and reactivity towards sulfide of iron in marine sediments also considered is the importance of bacterial fe liberation in regulating pore water chemistry two contrasting marine environments are included one is the relatively fe poor foam site and the other is the fe rich sediment of the subaqueous mississippi delta results show that oxide minerals are the most important fe phases in early diagenetic pyrite formation however viewed separately lepidocrocite and ferrihydrite are more reactive towards sulfide than goethite and hematite when fe oxides are present in relatively high concentrations dissolved sulfide is nearly absent from sediment pore waters with concomitant high concentrations of dissolved fe even in the presence of active sulfide production by sulfate reduction a combination of experimental results and diagenetic modelling shows that in some sediments pore water fe finds it origin in the bacterial reduction of iron oxides this seems the case even though greater amounts of fe are reduced by reaction of sulfide with iron oxides it appears that distinct microenvironments may exist in marine sediments where in one microenvironment sulfide reacts with fe oxides locally precipitating fe sulfide minerals in another fe reduced and solubilized by microorganisms migrates freely into solution

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

benthic remineralization at the land ocean interface a case study of the rhone river nw mediterranean sea abstract biogeochemical processes in sediments under the influence of the rhone river plume were studied using both in situ microelectrodes and ex situ sediment core incubations organic carbon oc and total nitrogen tn content as well as stable carbon isotopic composition of oc 13 c oc were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the rhone delta system large spatial variations were observed in both the total o 2 uptake 5 2 to 29 3 mmol m 2 d 1 and nh 4 release 0 1 to 3 5 mmol m 2 d 1 rates at the sediment water interface the highest fluxes were measured near the rhone river mouth where sedimentary oc and tn contents reached 1 81 and 0 23 respectively values of 13 c oc ranged from 26 83 to 23 88 with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf the amount of terrestrial derived oc reaches 85 in sediments close to the rhone mouth decreasing down to 25 in continental shelf sediments on the prodelta high terrestrial oc accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial oc is remineralized a particulate organic carbon poc mass balance indicates that only 3 of the deposited poc is remineralized in prodelta sediments while 96 is recycled on the continental shelf it was calculated that a large proportion of the rhone poc input is either buried 52 or remineralized 8 mostly on the prodelta area the remaining fraction 40 is either mineralized in the water or exported outside the rhone delta system in dissolved or particulate forms

a three dimensional view of the evolution of midlatitude stratospheric intrusions abstract three dimensional views of midlatitude stratospheric intrusions are presented the views are obtained by plotting a surface of constant potential vorticity pv where the pv is diagnosed from a 6 day run of the u k universities global atmospheric modelling project general circulation model the pv 1 10 6 k kg 1 m2 s 1 1 pvu isosurface is chosen as representative of the tropopause the evolution of this surface is examined during the development of baroclinic waves in the northern hemisphere during october 1990 the developments show a number of features expected during the evolution of upper level troughs such as vortex roll up and the generation of tropopause folds in which air from the stratosphere intrudes downward into the troposphere however it is shown that the combined effects of deformation and convergence lead to the rapid collapse of folded features to leave low level tubes of pv together with higher level filaments the result is that the air intruded in the vicinity of

comparative geochemistry of cadmium rhenium uranium and molybdenum in continental margin sediments the concentrations of authigenic phases of cd re u and mo increase with depth in four 45 cm long sediment box cores collected along the axis of the laurentian trough gulf of st lawrence average authigenic accumulation rates estimated from element inventories are similar to rates in other continental margin environments strong regional variations in sediment accumulation rate and sulfide concentration have little influence on the accumulation rates of cd and re this suggests that slow precipitation kinetics controls the accumulation of cd and re in these sediments the accumulation rate of authigenic u is more variable it may be tied to the kinetics of microbially mediated u reduction and be controlled by the availability of reactive organic matter authigenic mo is distinguished by a sharp subsurface concentration minimum above which mo cycles with manganese mo released to pore water upon reduction of mn oxides diffuses downward and enriches the subsurface sediment mo accumulates most rapidly in the sediment with the highest sulfide content slow conversion of molybdate to thiomolybdate may explain the much slower mo accumulation rate in the less sulfidic sediments a component of authigenic mo accumulates with pyrite in an approximately constant mo fe ratio the accumulation rate of pyrite and associated mo is insensitive to avs abundance pyrite formation may be limited by the reactivity of iron oxide minerals

the presidents day cyclone of 18 19 february 1979 influence of upstream trough amplification and associated tropopause folding on rapid cyclogenesis abstract a diagnostic analysis of an amplifying polar jet trough system and associated tropopause fold which preceded the 19 february 1979 presidents day cyclone is presented the analysis is based on conventional radiosonde data infrared and visible satellite imagery 6 7 m water vapor measurements from the temperature humidity infrared radiometer thir and ozone measurements from the total ozone mapping spectrometer toms the case study indicates that dynamically forced meso scale vertical circulations played an important role in the extrusion of stratospheric air along the axis of a polar jet and the subsequent development of the storm system specific findings include 1 tropopause folding accompanying an amplifying polar jet trough system occurred along the axis of the intensifying polar jet in response to subsidence forced by geostrophic deformation patterns associated with the jet streak 2 the folding process extruded dry stratosphere air marked by high values of potential vorticity dow

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir