glacial interglacial variablity in the benguela upwelling system spatial distribution and budgets of organic carbon accumulation 1 modern sedimentary total organic carbon toc content as a proxy for surface water export production was mapped on the shelf and on the upper continental slope of the benguela upwelling system using 137 core tops shelf maxima in toc can be correlated with maxima in surface water productivity on the slope high toc contents are observed offshore from sites of strong modern upwelling estimates of modern toc mass accumulation rates mar show that approximately 85 of the total is accumulating on the shelf toc mar were calculated mapped and budgeted for the holocene and for the last glacial maximum lgm using 19 sediment cores from the continental slope during the lgm centers of deposition and production have migrated offshore with respect to their holocene positions toc accumulation on the continental slope was approximately 84 higher during the lgm than during the holocene possibly reflecting enhanced productivity the toc distribution patterns and sediment echo sounding data suggest that undercurrents strongly influence the sedimentation off namibia winnowing and focusing result in great lateral heterogeneity of sedimentation rates and sediment properties individual cores therefore do not necessarily reflect general changes in export production these results highlight the need for detailed regional studies based on a large number of sediment cores for highly heterogeneous high productivity areas in order to derive general statements on total fluxes

seasonal variability of the long chain alkenone flux and the effect on the u37k index in the norwegian sea a seasonally varying sedimentation pattern was observed for the alkenone flux measured with sediment traps in the northern north atlantic in the norwegian sea traps were set at 500 1000 and 3000 m the alkenone flux varied between 0 1 and 7 1 g m 2 d 1 and followed the seasonal pattern of the bulk parameters maximum fluxes occurred from mid october until mid november and were also high in may a surprising result was that considerably higher particle fluxes were observed at 3000 m for the alkenone flux the highest additional input of 250 was observed during the period when sediment resuspension was greatest in summer at the barents sea continental margin traps at 1840 and 1950 m the alkenone fluxes follow the sedimentation pattern of the bulk parameters with a less visible signal of distinct seasonality observed in the 1950 m trap the sedimentation of total alkenones varied between 0 8 and 144 g m 2 d 1 at 1840 m and between 0 5 and 31 0 g m 2 d 1 at 1950 m resuspension and lateral advection contributed significantly to measured fluxes in the two near bottom traps alkenone concentrations were determined in faecal pellets of appendicularia ostracods and euphausids from selected samples at the barents sea site the alkenone flux in pellets 4 to 24 of total was 5 to 6 times higher at 1950 m depth than at 1840 m and the major part 77 78 of the total flux of c37 3 reaching the near bottom trap at 1950 m was associated with faecal pellets of the meso zooplankton spatial and temporal variations of the u37k signals were observed indicating that the imprint in the alkenone signal depends on the origin and transport pathway of the organic material strong deviations occur in areas where nepheloid layers contribute particles of long residence times to the primary flux

the transition of the monsoonal and the n atlantic climate system off nw africa during the holocene 1 the northward extent of the influence of the w african monsoon during humid periods of interglacials is subject to investigations highlighting feedback mechanisms such as vegetation to detect this regional variation and the climate system acting farther to the north will be the aim of this paper focussing on the holocene we present two very high resolution holocene sediment records off nw africa located at 31 n and 27 n the well known mid holocene climate change from the african humid period to present arid conditions is well reflected by the terrigenous input in the southern core in contrast in the northern core spectral and wavelet analyses indicate a periodic oscillation of about 900 years of the terrigenous input throughout the last 9000 years b p we conclude that the w african monsoonal influence characterized by the abrupt climatic change at 5000 years b p can be separated from the influence of the n atlantic climate system reflected by a periodic oscillation throughout the holocene

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

numerical modelling of tide induced beach water table fluctuations field studies have shown that the elevation of the beach groundwater table varies with the tide and such variations affect significantly beach erosion or accretion in this paper we present a bem boundary element method model for simulating the tidal fluctuation of the beach groundwater table the model solves the two dimensional flow equation subject to free and moving boundary conditions including the seepage dynamics at the beach face the simulated seepage faces were found to agree with the predictions of a simple model turner 1993 the advantage of the present model is however that it can be used with little modification to simulate more complicated cases e g surface recharge from rainfall and drainage in the aquifer may be included the latter is related to beach dewatering technique the model also simulated well the field data of nielsen 1990 in particular the model replicated three distinct features of local water table fluctuations steep rising phase versus flat falling phase amplitude attenuation and phase lagging

mediterranean moisture source for an early holocene humid period in the northern red sea paleosalinity and terrigenous sediment input changes reconstructed on two sediment cores from the northernmost red sea were used to infer hydrological changes at the southern margin of the mediterranean climate zone during the holocene between approximately 9 25 and 7 25 thousand years ago about 3 per thousand reduced surface water salinities and enhanced fluvial sediment input suggest substantially higher rainfall and freshwater runoff which thereafter decreased to modern values the northern red sea humid interval is best explained by enhancement and southward extension of rainfall from mediterranean sources possibly involving strengthened early holocene arctic oscillation patterns and a regional monsoon type circulation induced by increased land sea temperature contrasts we conclude that afro asian monsoonal rains did not cross the subtropical desert zone during the early to mid holocene

dansgaard oeschger and heinrich event imprints in alboran sea paleotemperatures past sea surface temperature sst evolution in the alboran sea western mediterranean during the last 50 000 years has been inferred from the study of c37 alkenones in international marine global change studies md952043 core this record has a time resolution of 200 years allowing the study of millennial scale and even shorter climatic changes the observed sst curve displays characteristic sequences of extremely rapid warming and cooling events along the glacial period comparison of this alboran record with 18o from greenland ice greenland ice sheet project 2 core shows a strong parallelism between these sst oscillations and the dansgaard oeschger events five prominent cooling episodes standing out in the sst profile are accompanied by an anomalous high abundance of neogloboquadrina pachyderma sinistral which is confined to the duration of these cold intervals these features and the isotopic record reflect drastic changes in the surface hydrography of the alboran sea in association with heinrich events hl 5

characterization of the lowland coastal aquifer of comacchio ferrara italy hydrology hydrochemistry and evolution of the system summary this study delineates the actual hydrogeochemistry and the geological evolution of an unconfined coastal aquifer located in a lowland setting in order to understand the drivers of the groundwater salinization physical aquifer parameterization highlights a vertical hydraulic gradient due to the presence of a heavy drainage system which controls the hydrodynamics of this coastal area forcing groundwater to flow from the bottom toward the top of the aquifer as a consequence relict seawater in stable density stratification preserved within low permeability sediments in the deepest portion of the aquifer has been drawn upward the hydrogeochemical investigations allow identifying the role of seepage and water sediment interactions in the aquifer salinization process and in the modification of groundwater chemistry mixing between freshwater and saltwater occurs however it is neither the only nor the dominant process driving groundwater hydrochemistry in the aquifer several concurring and competing water sediment interactions as nacl solution ion exchange calcite and dolomite dissolution precipitation oxidation of organic matter and sulfate bacterial reduction are triggered by or overlap freshwater saltwater mixing the hyper salinity found in the deepest portion of the aquifer cannot be associated with present seawater intrusion but suggests the presence of salt water of marine origin which was trapped in the inter basin during the holocene transgression the results of this study contribute to a better understanding of groundwater dynamics and salinization processes in this lowland coastal aquifer

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

radiocarbon age differences between coexisting foraminiferal species radiocarbon age measurements on single species of foraminifera from a core on the ceara rise demonstrate the importance of the joint effect of bioturbation and variable rain abundance of foraminifera the relatively high mixed layer ages for pulleniatina obliquiloculata reflect at least in part an early holocene peak in its abundance while the relatively young ages for globorotalia menardii reflect the delay until mid holocene of its reappearance in the atlantic ocean these results clearly demonstrate that core top sediment samples need not be representative foraminifera falling from today s surface ocean rather at least on the ceara rise such samples consist of a composite of changing species groupings these results also reconfirm the pitfalls associated with attempts to reconstruct the radiocarbon age of deep ocean water on the basis of benthic planktonic foraminiferal age differences

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

the internal seiches in gullmar fjord part i dynamics abstract internal seiche motions with period 1 3 days in gullmar fjord are investigated based on mooring data with high vertical and time resolution the period and structure of the internal seiches are well described by a simple analytical three layer model taking into account blocking of the basin water at the sill energy budgets for forcing and damping of the seiches are estimated the internal seiches are forced by direct wind stress on the surface and by internal coastal waves of frequency close to the seiches the latter contribution being a little larger the e folding timescale for the internal seiche damping is approximately equal to the seiche periods which means that the seiches are effectively damped but also that the forcing must be in near resonance in order to maintain the observed seiche motions in the basin water the seiches manifest themselves with large vertical motions and clear upward phase propagation the phase propagation is related with a continuous rather than strictly layer

terrigenous n alkane input in the south china sea high resolution records and surface sediments abstract molecular abundances of n nonacosane are reported for a suite of 44 surface sediments and four deep sea cores distributed throughout the south china sea scs covering the last 220 ky at different time resolutions the patterns of glacial to interglacial variability of the concentrations of this terrigenous marker are parallel for all cores taking values linearly inversely correlated to the u37k index sea surface temperatures sst with high concentrations during cold glacial intervals and low concentrations during warm interglacial periods the oscillations of this terrigenous marker likely result from the emergence and flooding of the shelves caused by sea level variations which together with scs ssts have a clear dependency on the northern hemisphere climate evolution calculation of accumulation rates for the northernmost core together with the modern distribution of n nonacosane concentrations in surface sediments evidences the complexity of sedimentation patterns in the northern scs in particular and in agreement with recent studies terrigenous materials deposited there might originate from areas different than the highly loaded pearl river for paleoceanographic purposes the noticeable general pattern of the n alkane concentration down core profiles for the four cores studied a parameter apparently unaffected by changes in sedimentation rates prompts its use as a tracer of variations in terrigenous input into this basin over glacial to interglacial times

a general analytical solution for groundwater fluctuations due to dual tide in long but narrow islands 1 this paper develops a general mathematical model for describing head fluctuations in an aquifer of long but narrow islands subject to a dual tide effect the upper boundary condition of the aquifer is represented by an equation combining the simplified free surface equation with a leakage term such an equation is considered as a general expression representing the upper boundary condition of a confined unconfined or leaky confined aquifer the closed form solution of the model represented by two series terms is developed by the direct fourier method and finite fourier sine transform one of the series can reduce to a closed form expression by means of contour integral and residue theorem if the width of the island is very large this solution gives the predicted head almost the same as that of the solution for an aquifer subject to a single tide effect it is found that the presence of an upper aquitard produces significant vertical flow in the lower leaky confined aquifer even if the aquitard permeability is low neglecting such vertical flow may result in an overestimate of hydraulic head in the leaky confined aquifer the attenuation factor and phase lag predicted from the present solution subject to the dual tide effect agree well with those estimated from 57 day head fluctuation data observed at garden island australia

freshwater seawater mixing experiments in sand columns summary a study was performed on vertical mixing between freshwater and seawater in controlled column experiments the aim was to quantify the variation in the thickness of the mixing zone caused by water table fluctuations in aeolian dune sandy sediments a series of column experiments were setup first a study on in well mixing was completed to understand the suitability of down hole logging in existing piezometers versus multi level sampling then an unsaturated saturated column experiment with sandy aeolian dune sediments of the target aquifer was performed to characterize the mixing zone thickness finally the third column experiment was conducted by imposing a groundwater fluctuation of 0 1 m to quantify the increase of the freshwater saltwater mixing zone due to vertical water table oscillations the freshwater saltwater mixing zone increase was very limited and did not exceed 0 1 m all experiments were modeled by means of the seawat numerical code and calibrated against saltwater concentrations the model fit was good for all experiments providing insights into the vertical dispersivity of sandy aeolian dune sediments and also into the reliability and precision of the freshwater saltwater interface monitoring methods the down hole logging technique in fact was demonstrated to be inefficient when horizontal flow velocity is negligible in this case only multi level sampling techniques provided reliable results

sedimentary response to late quaternary sea level changes in the romagna coastal plain northern italy data from 17 continuously cored boreholes 40 170 m deep reveal the subsurface stratigraphy of the romagna coastal plain sedimentological and microfaunal data allow the distinction of eight facies associations of late pleistocene holocene age including 18 lithofacies and 16 faunal associations ten 14c dates provide the basis to establish a sequence stratigraphic framework for the succession corresponding to the upper part 35 ky bp of the last glacio eustatic cycle the eight facies associations can be grouped into lowstand transgressive and highstand systems tracts the upper part of the lowstand systems tract consists of alluvial plain deposits these accumulated during the late pleistocene when the shoreline was 250 km south of its present day position a pronounced stratigraphic hiatus between 25 and 8 8 ky bp is invariably recorded at the upper boundary transgressive surface of these pleistocene indurated and locally pedogenized alluvial deposits the succeeding postglacial history is represented by a well developed transgressive regressive cycle transgressive deposits interpreted to reflect the rapid landward migration of a barrier lagoon system include two wedge shaped paralic and marine units these thicken in opposite directions and are separated by a ravinement surface above the transgressive deposits the maximum flooding surface mfs marks the change from a transgressive barrier lagoon complex to a prograding wave dominated delta system early po delta the mfs can be traced landwards where it constitutes the base of lagoonal deposits an aggradational to progradational stacking pattern of upper delta plain marsh lower delta plain lagoon bay and delta front beach ridge deposits reflects the progressive increase in the sediment supply accommodation ratio during the following highstand the alluvial deposits capping the sequence accumulated by the 13th century ad in response to an avulsion event that caused abandonment of the former po delta lobe and the northward migration of the po river towards its present position

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

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

sand composition and sedimentary evolution of a late quaternary depositional sequence northwestern adriatic coast italy abstract in order to detect temporal and spatial variations in detrital supply in the upper part of the last depositional sequence of late pleistocene holocene age we conducted a combined petrographic and stratigraphic study in the romagna coastal plain south of the po delta northern italy we analyzed heavy minerals and the bulk composition of sands from cores and surface samples by using petrographic and stratigraphic data on composition of modern beach and major river deposits new aspects of detrital dispersal mechanisms and the depositional history of the study area are documented the heavy mineral distribution coupled with the dolostone and volcanic rock fragment contents of bulk sands allow identification of three different petrofacies petrofacies a petrofacies b and petrofacies c which have been interpreted as of apenninic mixed eastern alps po river basin and po river catchment basin provenance respectively distribution of the three petrofacies changed through time in response to landward and seaward shifting of the coastline during the late pleistocene lowstand a pure apenninic provenance characterized the romagna coastal plain petrofacies a during the holocene transgression when the shoreline migrated tens of kilometers west of its present position eastern alpine sediment sources fed littoral facies petrofacies b probably as a result of southward transport by littoral drift this sediment supply continued during the early regressive phases and was cut off by a change in coastal morphology related to the development of the early po delta this led to the establishment of a sediment supply entirely related to the po river catchment basin petrofacies c changes in the compositional signature of sand in the youngest beach ridges mark the abandonment of the early po delta due to an avulsion event and testify to the establishment of a coastal system fed by rivers draining the apennines petrofacies a we emphasize sand petrography as an important tool in studying the internal architecture of sandy clastic depositional units on detailed spatial scales and its use in deciphering the depositional history of complex sedimentary successions fig 1 location of the study area end page 829

tidal water table fluctuations in a sandy ocean beach tidal water table fluctuations observed for 27 days in a gently sloped ocean beach are predicted well by numerical models based on the boussinesq equation driven with the observed 10 min averaged shoreline ocean beach intersection motion diurnal and semidiurnal water table fluctuations are almost completely damped 100 m landward of the mean shoreline location on this fine grained sand beach but fluctuations at spring neap periods 14 days are attenuated less comparison of the observations with the predictions suggests that the asymmetries in the water table level time series measured in this study result from nonlinearity owing to the large relative to the wavelength horizontal shoreline excursions rather than from nonlinearity owing to finite amplitude water table fluctuations cross shore variations of the aquifer depth are predicted to have a small effect on the landward decay rate of the water table fluctuations the seepage face width is predicted accurately and depends on the nonplanar beach profile in general the development of a seepage face is predicted to have little effect on the water table level landward of the intertidal region

barometric pressure influence on water table fluctuations in coastal aquifers of partially enclosed seas an example from the adriatic coast italy summary the water table level fluctuations in a coastal phreatic aquifer of the adriatic coast southern po plain italy were recorded to characterize groundwater level response to sea level fluctuations tide induced fluctuations atmospheric pressure loading and recharge from rainfall have all been recognized in the measured water table changes we also identified additional water table fluctuations that are not related to rain atmospheric pressure or tides we propose that these additional fluctuations are related to interaction of groundwater seiche events and inverted barometric effects their amplitude is important because at a distance of 70 m from the coast they have a magnitude of 0 07 m whereas the local tide has a 1 m amplitude seiches are standing waves that create sea water fluxes which affect groundwater below the first row of dunes in the study area we propose that this inverted barometric effect is an important process in creating water fluxes in the coastal zone that may strongly affect the position and width of the mixing zone between salt and fresh water

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

the plio quaternary ambon arc eastern indonesia abstract plio quaternary lavas and granites have been collected from ambon seram kelang haruku saparua ambelau and banda api islands eastern indonesia they include low k calc alkaline basalts andesites dacites and rhyolites and high k calc alkaline andesites dacites rhyolites and granites all these rocks present the usual chemical characteristics of island arc magmas the high k suite of ambon is mostly represented by cordierite bearing dacites known as ambonites and granites low k and high k magmas were emplaced in neighbouring islands or even in the same island ambon often concomitantly during two magmatic pulses at 5 3 2 ma and 2 3 1 ma respectively we propose that the low k suite results from the evolution of basaltic magmas derived from mantle melting above the western irian jaya plate which subducts along the seram trough intermediate and acidic rocks of the high k suite e g ambonites are thought to derive from low k mafic magmas through massive assimilation of the seram ambon continental crust as originally proposed by van bemmelen in 1949 the timing of magmatic events and the geochemical features of the studied lavas are clearly different from those of the southern part of the banda arc in which the low k suite is lacking in agreement with earlier seismic evidence for two different slabs subducting beneath the seram ambon continental block and beneath the southern banda arc from wetar to manuk respectively we propose to recognise a new plio quaternary island arc i e the ambon arc extending west east from ambelau to the banda archipelago active low k volcanoes through kelang southwestern seram ambon haruku and saparua

surface sediment distribution along the chilean continental slope related to upwelling and productivity abstract the coastal upwelling system of the peru chile current belongs to the most productive regions in the world oceans in spite of this remarkable fact only very little is known about the sediment distribution in its southern part off the coast of chile to increase the knowledge about this region a multiparameter study of the surface sediment distribution along the chilean continental slope between 27 and 42 s has been carried out detailed analyses of sedimentary data toc and carbonate contents 13corg 15n of the species composition of planktic foraminifera and of the stable isotope composition of the two planktic foraminifera species neogloboquadrina pachyderma dex and globigerina bulloides reveal a close relation to environmental conditions in the region the pattern of a southward increase of surface water productivity known from satellite data is closely reflected in the organic carbon and 15n data information about the water mass distribution especially about varying influences of upwelling waters and warmer subtropical surface waters can be derived from the species composition of the planktic foraminifera while the stable isotope data provide additional clues about water mass characteristics high productivity along the chilean margin north of 40 s is sustained by coastal upwelling while further to the south advection of nutrients with the antarctic circumpolar current and a significant riverine input fuel the highest productivity found in the study area this data set will provide the base for future paleoclimatic and paleoceanographic reconstructions of the southeast pacific region

influence of lateral particle advection and organic matter degradation on sediment accumulation and stable nitrogen isotope ratios along a productivity gradient in the canary islands region abstract we compare total and biogenic particle fluxes and stable nitrogen isotope ratios 15n at three mooring sites along a productivity gradient in the canary islands region with surface sediment accumulation rates and sedimentary 15n higher particle fluxes and sediment accumulation rates and lower 15n were observed in the upwelling influenced eastern boundary region ebc compared to the oligotrophic sites north of gran canaria european station for time series in the ocean canary islands estoc and north of la palma lp the impact of organic matter degradation and lateral particle advection on sediment accumulation was quantified with respect to the multi year flux record at the estoc remineralisation of organic matter in the water column and at the sediment surface resulted in an organic carbon preservation of about 0 8 and total nitrogen preservation of about 0 4 of the estimated export production higher total and carbonate fluxes and accumulation rates in the lower traps and surface sediment compared to the upper traps indicated that at least 50 of the particulate matter at the estoc was derived from allochthonous sources low 15n values in the lower traps of the estoc and lp point to a source region influenced by coastal upwelling we conclude from this study that the reconstruction of export production or nutrient regimes from sedimentary records in regions with strong productivity gradients might be biased due to the mixture of particles originating from autochthonous and allochthonous sources this could result in an imprint of high productivity signatures on sedimentation processes in oligotrophic regions

hemipelagic sediment accumulation rates in the south china sea related to late quaternary sea level changes sediments of 13 piston cores from opposite continental slopes of the south china sea off southern china and sabah northern borneo were analyzed by sedimentological methods and dated by oxygen isotope stratigraphy sediments mostly consist of hemipelagic clay with 20 carbonate off sabah and 40 off china we calculated terrigenous and carbonate accumulation rates for up to 11 time slices from the holocene to oxygen isotope stage 6 terrigenous accumulation rates generally increase with water depth and reach a maximum at the middle slope off sabah and at the lower continental slope off china during glacial and interglacial times this distribution pattern did not markedly change despite an increase of accumulation rates for glacial periods by a factor of 2 to 5 compared to interglacial periods rates are negatively correlated with positions of sea level which controls the partition of fluviatile terrigenous material for deposition on shelf slope and abyssal plain carbonate accumulation rates are higher off china by a factor of 2 compared to sabah probably indicating higher calcareous plankton productivity

early diagenetic remineralization of sedimentary organic c in the gulf of papua deltaic complex papua new guinea net loss of terrestrial c and diagenetic fractionation of c isotopes oceania supplies 40 of the global riverine flux of organic carbon approximately half of which is injected onto broad continental shelves and processed in shallow deltaic systems the gulf of papua on the south coast of the large island of new guinea is one such deltaic clinoform complex it receives 4 mt yr 1 particulate terrestrial organic carbon with initial particle corg loading 0 7 mg m 2 corg loading is reduced to 0 3 mg m 2 in the topset upper foreset zones of the delta despite additional inputs of mangrove and planktonic detritus and high net sediment accumulation rates of 1 4 cm yr 1 carbon isotopic analyses 13c 14c of co2 and corg demonstrate rapid 100 yr remineralization of both terrestrial 13c 28 6 and marine corg 13c 20 5 ranging in average age from modern bomb 14c 60 to 1000 yr 14c 140 efficient and rapid remineralization in the topset upper foreset zone is promoted by frequent physical reworking bioturbation exposure and reoxidation of deposits the seafloor in these regions particularly 20 m apparently functions as a periodically mixed suboxic batch reactor dominated by microbial biomass although terrestrial sources can be the primary metabolic substrates at inshore sites relatively young marine corg often preferentially dominates pore water co2 relative to bulk corg in the upper foreset thus a small quantity of young rapidly recycled marine organic material is often superimposed on a generally older less reactive terrestrial background whereas the pore water co2 reflects both rapidly cycled marine and terrestrial sources terrestrial material dominates the slower overall net loss of corg from particles in the topset upper foreset zone i e recycled marine corg leaves little residue preferential utilization of corg subpools and diagenetic fractionation of c isotopes supports the reactive continuum model as a conceptual basis for net decomposition kinetics early diagenetic fractionation of c isotopes relative to the bulk sedimentary corg composition can produce changes in 14c activity independent of radioactive decay in the gulf of papua topset upper foreset 14c of pore water co2 averaged 300 greater than corg sediment between 1 3 m depth in deposits diagenetic fractionation and decomposition aging of sedimentary corg compromises simple application of 14c for determination of sediment accumulation rates in diagenetically reactive deposits

tidal currents on the central oregon shelf models data and assimilation 1 measurements of tidal currents on the central oregon shelf are available from several sources including recent high frequency hf coastal radar and acoustic doppler profiler adp deployments and historical current moorings in this paper we use a generalized inverse gi approach to compare these data to and then assimilate them into numerical models for the barotropic tides harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the oregon shelf are highly variable in time and can contain significant baroclinic components data from the winter months when waters on the shelf are only weakly stratified are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model the various data sources are used in several different combinations for assimilation and validation forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent within estimated error limits with all available data in contrast diurnal currents on the shelf are very sensitive to details of the model configuration and are significantly improved by data assimilation very similar solutions result from assimilation of either the hf radar or adp data sets the high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves a short 85 km long section of shelf off the central oregon coast is wide enough to allow first mode barotropic shelf waves at the subinertial diurnal frequencies this results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing and hence quite variable in time

high and low latitude climate control on the position of the southern peru chile current during the holocene 1 we reconstructed changes of temperature salinity and productivity within the southern peru chile current during the last 8000 years from a high resolution sediment core recovered at 41 s using alkenones isotope ratios of planktic foraminifera biogenic opal and organic carbon paleotemperatures and paleosalinities reached maximum values at 5500 years ago and thereafter declined to modern values whereas paleoproductivity continuously increased throughout the last 8000 years we ascribe these long term holocene trends primarily to latitudinal shifts of the antarctic circumpolar current acc the concurrence with shifts in the position of the southern westerlies points to a common response of atmospheric and oceanographic circulation patterns off southern chile millennial to centennial scale fluctuations of paleotemperatures and paleosalinities on the other hand lag displacements in the position of the southern westerlies but reveal a significant correlation to short term temperature changes in antarctica indicating a high latitude control of the acc at these timescales

groundwater waves in a coastal aquifer a new governing equation including vertical effects and capillarity groundwater waves that is water table fluctuations are a natural phenomenon in coastal aquifers they represent an important part of the interaction between the ocean and aquifer and affect the mass exchange between them this paper presents a new groundwater wave equation because it includes the effects of vertical flows and capillarity the new equation is applicable to both intermediate depth aquifers and high frequency waves compared with the wave equation derived by nielsen et al 1997 the present equation provides a closer representation of groundwater waves in particular it predicts high frequency water table fluctuations as observed in the field a validation of the new equation has been carried out by comparing the analytical solutions to it with predictions from direct simulations using the numerical model sutra the effects of various physical parameters and their relative importance are also discussed

response of the water level in a well to earth tides and atmospheric loading under unconfined conditions the response of the water level in a well to earth tides and atmospheric loading under unconfined conditions can be explained if the water level is controlled by the aquifer response averaged over the saturated depth of the well because vertical averaging tends to diminish the influence of the water table the response is qualitatively similar to the response of a well under partially confined conditions when the influence of well bore storage can be ignored the response to earth tides is strongly governed by a dimensionless aquifer frequency q u the response to atmospheric loading is strongly governed by two dimensionless vertical fluid flow parameters a dimensionless unsaturated zone frequency r and a dimensionless aquifer frequency qu the differences between q u and qu are generally small for aquifers which are highly sensitive to earth tides when q u and qu are large the response of the well to earth tides and atmospheric loading approaches the static response of the aquifer under confined conditions at small values of q u and qu well response to earth tides and atmospheric loading is strongly influenced by water table drainage when r is large relative to qu the response to atmospheric loading is strongly influenced by attenuation and phase shift of the pneumatic pressure signal in the unsaturated zone the presence of partial penetration retards phase advance in well response to earth tides and atmospheric loading when the theoretical response of a phreatic well to earth tides and atmospheric loading is fit to the well response inferred from cross spectral estimation it is possible to obtain estimates of the pneumatic diffusivity of the unsaturated zone and the vertical hydraulic conductivity of the aquifer

an analytical solution of groundwater response to tidal fluctuation in a leaky confined aquifer an analytical solution is derived to investigate the influence of leakage on tidal response in a coastal leaky confined aquifer system the analytical solution developed here is more general than the traditional solution obtained by ferris 1951 which can be regarded as a special case of the solution presented in this paper this solution is based on a conceptual model under the assumption that the groundwater level in the confined aquifer fluctuates in response to sea tide while that of the overlying unconfined aquifer remains constant this conceptual model is supported by numerous field studies by previous researchers which have demonstrated that the tidal response in an unconfined aquifer may be negligible compared to that in a confined aquifer the leakage has a significant impact on the tidal behavior of the confined aquifer hypothetical studies indicate that both tidal amplitude of groundwater head in the aquifer and the distance over which the aquifer can be disturbed by the sea tide will be considerably reduced because of the existence of leakage this analytical solution is used to investigate the tidal and piezometer data at the chek lap kok airport hong kong special administrative region people s republic of china

asynchronous alkenone and foraminifera records from the benguela upwelling system abstract radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies including the investigation of temporal leads and lags the critical assumption is that temporal coupling between foraminifera and other sediment constituents including specific molecular organic compounds biomarkers of marine phytoplankton e g alkenones is maintained in the sediments to test this critical assumption in the benguela upwelling area we have determined radiocarbon ages of total c37 c39 alkenones in 20 samples from two gravity cores and three multicorer cores the cores were retrieved from the continental shelf and slope off namibia and samples were taken from holocene deglacial and last glacial maximum core sections the alkenone radiocarbon ages were compared to those of planktic foraminifera total organic carbon fatty acids and fine grained carbonates from the same samples interestingly the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples such age differences may be the result of different processes bioturbation associated with grain size effects lateral advection of recycled material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes based on the results of this study the age offsets between foraminifera and alkenones in sediments from the upper continental slope off namibia most probably do not result from particle selective bioturbation processes resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm s recorded near the core sites is the more likely explanation our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone based proxy data observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals i e the result of processes associated with particle settling and biological activity

collapse of the california current during glacial maxima linked to climate change on land time series of alkenone unsaturation indices gathered along the california margin reveal large 4 to 8 c glacial interglacial changes in sea surface temperature sst over the past 550 000 years interglacial times with ssts equal to or exceeding that of the holocene contain peak abundances in the pollen of redwood the distinctive component of the temperate rainforest of the northwest coast of california in the region now dominated by the california current ssts warmed 10 000 to 15 000 years in advance of deglaciation at each of the past five glacial maxima ssts did not rise in advance of deglaciation south of the modern california current front glacial warming along the california margin therefore is a regional signal of the weakening of the california current during times when large ice sheets reorganized wind systems over the north pacific both the timing and magnitude of the sst estimates suggest that the devils hole nevada calcite record represents regional but not global paleotemperatures and hence does not pose a fundamental challenge to the orbital milankovitch theory of the ice ages

coastal aquifer response to extreme storm events in emilia romagna italy with global warming and sea level rise many coastal systems will experience increased levels of inundation and storm flooding especially along sandy lowland coastal areas such as the northern adriatic coast italy understanding how extreme events may directly affect groundwater hydrology in shallow unconfined coastal aquifers is important to assess coastal vulnerability and quantifying freshwater resources this study investigates shallow coastal aquifer response to storm events the transitory and permanent effects of storm waves is evaluated through the real time monitoring of groundwater and soil parameters in order to characterize both the saturated and unsaturated portions of the coastal aquifer of ravenna and ferrara southern po delta italy results highlight a general increase in hydraulic head and soil moisture along with a decrease in groundwater salinity and pore water salinity due to rainfall infiltration during the 2 days storm event the only exceptions are represented by the observation wells in proximity to the coastline within 100 m which recorded a temporary increase in soil and water salinity caused by the exceptional high waves which persist on top of the dune crest during the storm event this generates a saline plume that infiltrates through the vadose zone down to the saturated portion of the aquifer causing a temporary disappearance of the freshwater lens generally present although limited in size below the coastal dunes despite the high hydraulic conductivity the aquifer system does not quickly recover the pre storm equilibrium and the storm effects are evident in groundwater and soil parameters after 10 days past the storm overwash recess

the flooding of sundaland during the last deglaciation imprints in hemipelagic sediments from the southern south china sea abstract during the last 30 ka the south china sea scs experienced pronounced palaeogeographic changes associated with the postglacial sea level rise which significantly modified the hydrography of this marginal sea the most crucial effects in the southern part of the basin were the submergence of sundaland and the opening of the southern channels connecting the scs to the tropical indo pacific isotopic sedimentological and organic geochemical parameters determined in two sediment cores from the southern scs one in the open sea and the other close to the continental shelf sites 17961 and 17964 respectively show that the main hydrographical changes during this period were related to critical thresholds in sea level rise the main changes occurred at about 15 13 5 ky bp coincident with meltwater pulse mwp ia when sea surface temperatures ssts at both sites experienced a rapid 1 5 c rise and the clay content and n nonacosane concentrations dropped significantly both trends reflect a rapid retreat of the coastline and an initial flooding of sundaland at that time a second important change starting with the beginning of mwp ib at about 11 5 ky bp and culminating at 10 ky bp involved the establishment of modern hydrographic conditions this is evident from the rapid convergence of the foraminiferal oxygen isotope records and the establishment of holocene sst values these results highlight the need to include the flooding emergence of sundaland as an important boundary condition in future modelling studies of asian palaeomonsoons

millennial scale dynamics of the east asian winter monsoon during the last 200 000 years the primary productivity dynamics of the last 200 000 years in the sulu sea was reconstructed using the abundance of the coccolithophore florisphaera profunda in the images md97 2141 core we find that primary productivity was enhanced during glacial periods which we suggest is due to a stronger east asian winter monsoon during the last 80 kyr eight significant increases in primary productivity pp in the sulu sea are similar to east asian winter monsoon changes recorded in chinese loess the pp maxima are not linked with heinrich events he in the north atlantic although four pp peaks are synchronous with he the pp oscillations have frequencies near those of the dansgaard oeschger cycles in northern hemisphere ice records and indicate a teleconnection of the east asian winter monsoon with greenland climate in this sulu sea record the east asian winter monsoon oscillates with periodicities of6 4 2 3 4 2 3 and 1 5 kyr in particular the 1 5 kyr cycle exhibits a strong and pervasive signal from stage 6 to the holocene without any ice volume modulation this stationarity suggests that the 1 5 kyr cycle is not driven by some high latitude forcing

on the significance of sea level variations and shelf paleo morphology in governing sedimentation in the southern south china sea during the last deglaciation abstract deglacial sedimentation on the outer sunda shelf the shelf margin and slope shows a close correlation with the stages of flooding of the emerged shelf it is mainly controlled by the relationship between shelf paleo physiography and changes in sea level and sediment supply based on the sedimentological and geochemical variability at five sites along a transect across the outer shelf and the continental slope covering the last 20 000 years four intervals of significant depositional changes are identified the first reorganization in the sedimentation regime which was established during sea level lowstand is associated with the drowning of the lower course of the north sunda river between 16 5 and 14 5 ka during and following the rapid rise in sea level at 14 5 14 ka sedimentation on the slope is characterized by an accelerated decrease in the supply of terrigenous material associated with the flooding of the middle part of the paleo valley this abrupt change in sedimentation is followed by a period of gradual decrease of terrigenous supply to the slope when the surrounding plains of the river valley were flooded 14 8 5 ka the final change occurred between ca 8 5 and 6 ka when the coastline reached its modern position and modern sedimentary patterns are established this change probably marks the end of reworking by transgression given the synchroneity of sedimentological changes along the transect across the sunda shelf and into the deep sea with the environmental shifts on the central shelf sedimentation on the margin and slope appears to be mainly controlled by the interrelationship of sea level shelf paleo physiography and sediment supply moreover the records display lateral changes through time associated with stages of the deglacial transgression which mask any potential sedimentological variability due to changes in precipitation vegetation or atmospheric circulation this fact cautions the interpretation of near shore sedimentary records as unequivocal recorders of local climate change e g se asian monsoon and highlights the need to include variations in shelf physiography and sea level in future paleoceanographic studies

tide induced groundwater fluctuation in a coastal leaky confined aquifer system extending under the sea this paper presents the analytical solution of groundwater response to tidal fluctuation in a coastal multilayer aquifer system consisting of a leaky confined aquifer a semipermeable layer and an unconfined aquifer the semipermeable layer or the roof of the leaky confined aquifer extends under the sea comparisons are made with solutions derived previously which considered only a single aquifer zero extension of the roof or infinite roof length and demonstrate that the previous solutions are special cases of the solution presented here a hypothetical example is used to discuss the impact of the dimensionless roof length dimensionless leakage and tidal efficiency on the groundwater level fluctuations in the inland part of the confined aquifer the fluctuation decreases significantly with the roof length when the roof length is small but is insensitive to the change of roof length when the roof length is greater than a threshold the impacts of leakage from the offshore and inland portions of the confining unit are different leakage from the offshore portion tends to increase the fluctuation of the groundwater level while leakage from the inland portion tends to decrease the fluctuation the fluctuation increases as the tidal efficiency increases this fact is significant only when the roof length is great and leakage is small

composition age and provenance of organic matter in nw african dust over the atlantic ocean 1 eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992 1993 in the northeast atlantic off northwest africa 18 n 22 w afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance the sample was subjected to microscopic examination and bulk elemental isotopic black carbon and molecular lignin lipid analyses the bulk elemental composition and organic carbon oc content 1 02 dry weight establishes the dust s origin as continental upper crust and is typical of dusts that emanate from west africa these data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the sahara and sahel regions e g nasa toms aerosol index microscopic examination reveals that charcoal like particles from vegetation fires black carbon bc are the most abundant morphologically distinct organic components accelerator mass spectrometry ams 14c analysis yields conventional 14c ages for bulk oc of 1260 40 years and bc of 2070 35 years taken together with corresponding stable carbon isotopic compositions 13c 18 9 and 15 1 respectively these results suggest the presence of biomass and burning residues derived from predominantly c4 vegetation that accumulated in soils over the late holocene molecular level measurements are also consistent with this scenario for example lignin derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass type tissue the altered nature of the lignin suggests storage as residues in soils solvent extractable lipid constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region the hydrocarbon fraction contained some diesel type contamination but the n alkanes c23 c33 retained a prominent odd even distribution with 13c ranging from 26 7 to 28 5 the suite of even carbon numbered n alkanols c22 c32 is 14c dated at 647 150 years with 13c values ranging from 23 9 to 30 4 the long chain n alkanoic acids c22 c32 exhibited 13c values ranging from 22 6 to 27 4 these waxes are evidently a mixed signal derived from contemporary c3 and c4 vegetation and from ablated soils and desiccated lake sediments of middle to late holocene age this molecular approach shows promise as a tool for continental paleoenvironmental assessment particularly with respect to past vegetation cover regional aridity and wind systems

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

synchronous tropical south china sea sst change and greenland warming during deglaciation the tropical ocean plays a major role in global climate it is therefore crucial to establish the precise phase between tropical and high latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change here we present alkenone sea surface temperature sst records from the tropical south china sea that show an abrupt temperature increase of at least 1 c at the end of the last glacial period within the recognized dating uncertainties this sst increase is synchronous with the bolling warming observed at 14 6 thousand years ago in the greenland ice sheet project 2 ice core

an organic tracer for surface ocean radiocarbon the 14c of surface water dissolved inorganic carbon dic in the southern california bight was compared to 14c as recorded by the sterols in santa monica and santa barbara basin sediments all of the c26 c27 c28 and c29 sterols as well as dinosterol had 14c concentrations equal to surface water dic indicating that all of the major sterols were derived from phytoplanktonic production there is no detectable terrestrial component their tracer capability was confirmed by comparing the bomb 14c derived change in surface water 14cdic with the change in 14csterol the prebomb 14cdic was 82 and prebomb sterols averaged 75 19 the 14c value in 1996 was 71 eighteen measurements representing eight different sterols from the sediment water interface of both santa monica and santa barbara basins averaged 62 23 when three of these values were eliminated because of suspected contamination the remaining data averaged 71 12 the entire compound class could serve as an excellent proxy for the 14c concentration of ocean surface waters

an evaluation of 14c age relationships between co occurring foraminifera alkenones and total organic carbon in continental margin sediments 1 radiocarbon age relationships between co occurring planktic foraminifera alkenones and total organic carbon in sediments from the continental margins of southern chile northwest africa and the south china sea were compared with published results from the namibian margin age relationships between the sediment components are site specific and relatively constant over time similar to the namibian slope where alkenones have been reported to be 1000 4500 years older than co occurring foraminifera alkenones were significantly similar to 1000 years older than co occurring foraminifera in the chilean margin sediments in contrast alkenones and foraminifera were of similar age within 2 sigma error or better in the nw african and south china sea sediments total organic matter and alkenone ages were similar off namibia age difference toc alkenones 200 700 years chile 100 450 years and nw africa 360 770 years suggesting minor contributions of preaged terrigenous material in the south china sea total organic carbon is significantly 2000 3000 years older owing to greater inputs of preaged terrigenous material age offsets between alkenones and planktic foraminifera are attributed to lateral advection of organic matter physical characteristics of the depositional setting such as seafloor morphology shelf width and sediment composition may control the age of co occurring sediment components in particular offsets between alkenones and foraminifera appear to be greatest in deposition centers in morphologic depressions aging of organic matter is promoted by transport age offsets are correlated with organic richness suggesting that formation of organic aggregates is a key process