monsoon related variations in zaire congo sediment load and influence of fluvial silicate supply on marine productivity in the east equatorial atlantic during the last 200 000 years two sediment cores from the zaire fan and the angola margin have been investigated for their composition of terrigenous and biogenic constituents respectively for the late quaternary kaolinite feldspar ratios and variations of terrigenous element ratios of zr ti k rb and al reveal that the composition of zaire river sediment load has fluctuated in tune with precessional variations of boreal summer insolation in particular the correspondence of high kaolinite feldspar and al k ratios with low latitude insolation maxima strongly corroborates the assumption that west african monsoonal precipitation and chemical weathering was enhanced during periods of increased central african heating the most striking feauture observed is that opal accumulation has been 2 to 10 times higher in zaire fan sediments than outside in continental margin sediments off angola although biogenic ba and corg fluctuations from both areas indicate that changes of total paleoproductivity were of the same magnitude in the zaire river plume and off angola from this we infer that the contribution of biogenic opal production to total paleoproductivity has been significantly higher within the zaire river plume than in the oceanic upwelling regime farther to the south off angola over the last 200 000 years the pattern of opal accumulation rates with respect to that of marine organic carbon implies that enhanced opal production off the zaire river to a great extent was the result of additional fluvial supply of dissolved silica during humid climates characterized by more intense chemical weathering on the continent while total paleoproductivity created by oceanic upwelling was high in periods of increased zonal trade wind intensity at precessional insolation minima and during cold more arid glacial climate conditions we presume that paleoproductivity off the zaire was controlled by the following two sources of nutrients 1 marine nutrients including nitrate and phosphate as well as the uptake of ba on particulate corg caused by upwelling and 2 silica mainly delivered by the zaire river dissolved silicate hence our results underline the importance of dissolved silicate in large rivers for marine silicate cycling in the tropical to subtropical atlantic at a millenial timescale

transience and persistence in the depositional record of continental margins 1 continental shelves and coastal plains are large persistent depositional landforms which are stationary nonmigrating at their proximal ends and characterized by relatively steady long term growth in detail however their surface form and stratigraphic record is built of transient freely migrating landscape elements we derive the timescales of crossover from transient to persistent topographic forms using empirical scaling relations for mean sediment accumulation as a function of averaging time based upon tens of thousands of empirical measurements a stochastic noisy diffusion model with drift predicts all the gross features of the empirical data it satisfies first order goals of describing both the surface morphology and stratigraphic completeness of depositional systems the model crossover from noise dominated to drift dominated behavior corresponds to the empirical crossover from transport dominated autogenic transient behavior to accommodation dominated subsidence persistent behavior which begins at timescales of 102 103 years and is complete by scales of 104 105 years because the same long term scaling behavior emerges for off shelf environments it is not entirely explicable by steady subsidence fluctuations in sediment supply and routing probably have significant influence at short term transient scales the exponents of the scaling relations vary with environment particularly the prevalence of channeled sediment transport at very small scales modeling sediment transport as a diffusive process is inappropriate our results indicate that some of the timescales of interest for climate interpretation may fall within the transitional interval where neither accommodation nor transport processes are negligible and deconvolution is most challenging

theory connecting nonlocal sediment transport earth surface roughness and the sadler effect earth surface evolution like many natural phenomena typified by fluctuations on a wide range of scales and deterministic smoothing results in a statistically rough surface we present theory demonstrating that scaling exponents of topographic and stratigraphic statistics arise from long time averaging of noisy surface evolution rather than specific landscape evolution processes this is demonstrated through use of elastic langevin equations that generically describe disturbance from a flat earth surface using a noise term that is smoothed deterministically via sediment transport when smoothing due to transport is a local process the geologic record self organizes such that a specific sadler effect and topographic power spectral density psd emerges variations in psd slope reflect the presence or absence and character of nonlocality of sediment transport the range of observed stratigraphic sadler slopes captures the same smoothing feature combined with the presence of long range spatial correlation in topographic disturbance

variability in upwelling intensity and nutrient regime in the coastal upwelling system offshore namibia results from sediment archives the coastal upwelling system offshore namibia is ideally suited to address a focal question of the integrated marine biogeochemistry and ecosystem research programme what are the mechanisms that drive long term changes in ecosystems considerable interannual variability in climatic forcing is indicated by long time series of meteorological and remote sensing observation these accompany considerable interannual to interdecadal changes in the upwelling intensity over the last 100 years as well as a centennial trend on longer time scales the only archives available are sediment records spanning the late holocene to decipher the sediment record we mapped surface sediment patterns of proxies for physical sea surface temperature sst from alkenone unsaturation indexes and nutrient 15n on bulk sedimentary n variables their present day surface sediment patterns outline the coastal upwelling cells and filaments and associated high productivity area analysed in an array of dated sediment cores the spatial patterns of sst suggest long term 100 years variability in the location and intensity of individual upwelling cells the patterns of 15n outline an area of intense denitrification near the coast and advection of water with low oxygen concentrations in the undercurrent from the north 15n exhibits considerable downcore variability in particular over the last 50 years the variability appears to be governed by differences in extent of denitrification and thus of the shelf oxygen balance which appears to have deteriorated in the last 50 years together the data suggest that sst and denitrification conditions have remained in the narrow bounds outlined by today s patterns in surface sediments but that spatially small variability in upwelling intensity and make up of upwelling feed waters induced considerable changes in the lower trophic levels of the coastal upwelling ecosystem over the last 6 000 years attempts to correlate proxy records from sediments with observational time series and regional climate reconstructions were not successful possibly because annual to interannual environmental signals are erased in the process of sediment formation

geostrophic transport in the benguela current region historical data from the region between the greenwich meridian and the african continental shelf are used to compute the offshore geostrophic transport of the benguela current at 32 s the benguela current is located near the african coast transporting about 21 sv 1 sv 106 m3 s 1 of surface water toward the north relative to a potential density surface lying between the upper branch of circumpolar deep water and the north atlantic deep watar two warm core eddies of probable agulhas current origin an observed west of the benguela current at 32 s near 30 s the benguela current turns toward the northwest and begins to separate from the eastern boundary it carries about 18 sv of surface water across 28 s the current then turns mainly toward the west to flow over a relatively deep segment of the walvis ridge south of the valdivia bank a surface current with northward surface of about 10 cm s 1 flows along the western side of the valdivia bank while another northward surface current flows at about 20 cm s 1 some 300 km west of the bank about 3 sv of surface now do not leave the cape basin south of the vaidivia bank but instead drift northward as a wide sluggish flow out of the northern end of the cape basin because of the more southerly seaward extensions of most of the benguela current there are no deep reaching interactions observed between this current and the cyclonic gyre in the angola basin east of the greenwich meridian beneath the surface layer about 4 5 sv of antarctic intermediate water are carried northward across 32 and 28 s by the benguela current essentially all of which turns westward to cross the greenwich meridian south of 24 s

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

real and apparent changes in sediment deposition rates through time 1 field measurements show that estimated sediment deposition rate decreases as a power law function of the measurement interval this apparent decrease in sediment deposition has been attributed to completeness of the sedimentary record the effect arises because of incorporation of longer hiatuses in deposition as averaging time is increased we demonstrate that a heavy tailed distribution of periods of nondeposition hiatuses produces this phenomenon and that observed accumulation rate decreases as t 1 over multiple orders of magnitude where 0 1 is the parameter describing the tail of the distribution of quiescent period length by using continuous time random walks and limit theory we can estimate the actual average deposition rate from observations of the surface location over time if geologic and geometric constraints place an upper limit on the length of hiatuses then average accumulation rates approach a constant value at very long times our model suggests an alternative explanation for the apparent increase in global sediment accumulation rates over the last 5 million years

late quaternary paleoproductivity and deep water circulation in the eastern south atlantic ocean evidence from benthic foraminifera abstract two late quaternary sediment cores from the northern cape basin in the eastern south atlantic ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition the locations of the cores were selected such that both of them presently are bathed by north atlantic deep water nadw and past changes in deep water circulation should be recorded simultaneously at both locations however the areas are different in terms of primary production one core was recovered from the nutrient depleted walvis ridge area whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high recent data served as the basis for the interpretation of the late quaternary faunal fluctuations and the paleoceanographic reconstruction during the last 450 000 years nadw flux into the eastern south atlantic ocean has been restricted to interglacial periods with the strongest dominance of a nadw driven deep water circulation during interglacial stages 1 9 and 11 at the continental margin high productivity faunas and very low epibenthic 13c values indicate enhanced fluxes of organic matter during glacial periods this can be attributed to a glacial increase and lateral extension of coastal upwelling the long term glacial interglacial paleoproductivity cycles are superimposed by high frequency variations with a period of about 23 000 yr enhanced productivity in surface waters above the walvis ridge far from the coast is indicated during glacial stages 8 10 and 12 during these periods cold nutrient rich filaments from the mixing area were probably driven as far as to the southeastern flank of the walvis ridge

spatial patterns of sediment accumulation on a holocene carbonate tidal flat northwest andros island bahamas abstract to characterize spatial patterns of sedimentation and analyze the morphology of part of the modern tidal flats of northwest andros island in the bahamas this study integrated remote sensing geographic information systems gis and carbonate sedimentology the fundamental data are a landsat tm image that has been classified to create a thematic map of eight subfacies interpreted to represent a distinct tidal flat subenvironment such as adjacent marine exposed levee beach ridge pond and algal marsh spatial statistics of the thematic map characterize the patterns of sediment accumulation quantitative analysis highlights several interesting results concerning subfacies character and distribution 1 of the eight mapped subfacies low algal marsh is most widespread representing 27 5 of the total area whereas exposed levee beach ridge is the least widespread accounting for 10 of the area 2 the patches of different subfacies have different shape complexities with low algal marsh high algal marsh and mangrove ponds being the least complex and exposed levee beach ridge being the most complex 3 markov chain analysis suggests that lateral transitions between different subfacies are highly ordered and 4 frequency distribution of subfacies patch area and lacunarity gap size distribution data exhibit power law relationships over several orders of magnitude consistent with fractal characteristics the fractal nature of patch size and gaps between facies illustrate that on this tidal flat neither the size nor the spatial distribution of subfacies has a characteristic scale this statistical behavior is consistent with the presence of self organization or emergence of pattern in the absence of a template or external forcing the statistical self organization on the tidal flat is the cumulative expression of local processes but it becomes apparent only through analysis of the whole system these results are inconsistent with models suggesting that tidal flats include a migrating complex of randomly distributed randomly sized subenvironments ancient successions that include random patterns may reflect the more pronounced influence of forces external to the sedimentary system instead of an absence of those forces

variability of sedimentary sequence numerical modeling of the deposition erosion process reinterpretation of field studies of bedload transport allowed some power law relations to be obtained between different quantities they were taken as a basis for the construction of a numerical model simulating bedload transport the deposition erosion process is presented as a sequence of individual events with intensities distributed according to a power law characteristic of the regime of self organized criticality the model output sedimentary cross sections with the model age of each of its elements is rich in features resulting from the non linearity of the underlying process analysis of the results of a series of numerical experiments provided an estimation of scale invariance of model sedimentary structures in space and time these data are tested against observed regularities of spaciotemporal variability of real sedimentary sequences good agreement of these data makes it possible to extrapolate the scaling relations obtained to larger scales

tectonic controls on the development of unconformities the north slope alaska the geology of northern alaska is defined by two complementary synchronous tectonic events opening of the canada basin breached the south facing ellesmerian passive margin in the late jurassic cutting off northerly derived sediment and initiating thermal subsidence of the north facing beaufort passive margin uplift of the brooks range on thrust faults loaded the lithosphere creating the colville trough a foreland basin more than 10 km deep and providing the bulk of the sediments that filled it the northerly advance of the brooks range caused the two independent loads to flexurally interfere the beaufort passive margin is separated from the foreland by the barrow arch which is in part the flexural bulge due to the interaction of these two loading events nunn et al 1987 a record of this interaction is preserved in the sediments north and south of the barrow arch we have used this stratigraphy coupled with simple basin modeling to consider the flexural and stratigraphic effects of the evolving thrust wedge and basin filling using a simple sedimentation model and loading on an elastic lithosphere we have produced two unconformity bounded sequences without sea level change the unconformities are produced as a consequence of sedimentation and two increments in the thrust load that cause the flexural bulge to translate laterally rise and fall the generation of unconformities over a flexural bulge by mass redistribution on a purely elastic lithosphere calls into question the use of these unconformities in other yoked systems to document viscoelastic lithospheric rheologies even if the lithospheric strength decays significantly on geologic time scales we may not observe this decay in stratigraphy if the basin filling time is a significant fraction of the relaxation time the beaufort passive margin and the thrust belt strike at an oblique angle to each other causing the independent bulges to constructively interfere in the west and destructively interfere in the east the advance of the thrust related bulge beyond the eastern beaufort shelf has by flattening the basal decollement exerted significant control on the thrust wedge of the brooks range allowing the thrust wedge tip to advance beyond the coastline

synthetic stratigraphy with a stochastic diffusion model of fluvial sedimentation abstract models of stratigraphic completeness and bed formation in fluvial depositional environments have most often assumed that successive depositional and erosional events deposit or erode amounts of sediment independently this results in a random walk model for the total amount of deposited sediment locally as a function of time we consider an extension of the random walk model of sedimentation in an alluvial plain in which deposition or erosion is concentrated in randomly avulsing channels and sediment transport is modeled by the diffusion equation culling s model in contrast to the random walk model this model results in an anticorrelated sequence locally as a function of time i e after an area has aggraded it has a higher elevation and a lower rate of future aggradation in a p evious paper we analyzed the topography generated by the model and argued that porosity variations could be associated with topographic variations the power spectrum s the square of the coefficients in a fourier series of one dimensional transects of topography and porosity horizontally and vertically in this model have a power law dependence on wave number k s k k s with values of s close to those observed in this paper we show that the model deposits sediment with a rate depending on time interval as a power law with exponent 3 4 more consistent with observations than the random walk model the model produces an exponential bed thickness distribution with a skew depen ent on the sedimentation rate of the basin in accordance with observations we also examine the persistence in the series of bed thicknesses as a function of depth for the stochastic diffusion model of sedimentation no persistence is observed if the model fully characterizes the autocyclic dynamics in fluvial sedimentary basins the lack of persistence in the synthetic bed sequences suggests that observed persistence and cyclicity in real bed thickness sequences must be the result of allocyclic processes

ordered hierarchy versus scale invariance in sequence stratigraphy sequence stratigraphy has been applied in a wide range of scales of time and space from decimeter thick layers formed within hours to kilometer thick basin fills formed during hundreds of millions of years the traditional approach to practice sequence stratigraphy in this wide range of scales is to subdivide the sediment piles into an ordered hierarchy of sequence cycles of different duration and different architecture an alternative are scale invariant models with fractal characteristics published data confirm two predictions of the ordered hierarchy model sequences of very short duration 200 106 years are symmetrical transgressive regressive cycles however the sequence record in the range of 1 104 200 106 years the principal domain of sequence stratigraphy shows a rather irregular succession of sequences with variable symmetry and bounded by flooding surfaces or exposure surfaces for these time scales scale invariant models are a good first approximation particularly because the evidence for scale invariance and randomness in the stratigraphic record is strong frequency spectra of sea level change as well as rates of sedimentation and rates of accommodation change plotted against length of observation span show basic trends indistinguishable from random walk these trends combined with scale invariant sequence models may be the most efficient tools for across the board predictions on sequences and for locating islands of order in the sequence record

the cantor dust model for discontinuity in geomorphic process rates abstract the temporal discontinuity in geomorphic processes that is responsible for time scale dependence in published process rates gardner et al 1987 is effectively modeled by a fractal construction the cantor dust points along the length of the dust represent geomorphic process events arrayed through time gaps in the dust are equally significant at all temporal scales resulting in a self similar clustering of events fractal dimension values estimated for processes of uplift 0 75 and denudation 0 81 suggest that uplift events are only slightly more clustered in time than are denudation events the results obtained from application of this model are unaffected by variability in magnitude of events

diagenetic dissolution of biogenic magnetite in surface sediments of the benguela upwelling system intense primary biologic productivity in the surface waters of the benguela upwelling system provides a high supply of organic matter to the sea floor at the continental slope off namibia and sustains extreme concentrations of magnetite producing bacteria in the top sediment layers biogenic magnetite is thus by far the dominant carrier of the magnetic signal in these deposits also because of a very minor input of terrigenous ferrimagnetic minerals reducing conditions in the sediment column cause a selective dissolution of the bacterial magnetite fraction just a few centimeters below the main mineralization horizon this diagenetic process is documented in detail by high resolution rock magnetic analyses and transmission electron microscopy concentration dependent and grain size sensitive magnetic parameters such as susceptibility laboratory imparted remanences and hysteresis data reveal a significant drop in ferrimagnetic mineral content within the upper 10 cm of the sediments accompanied by a gradual downward coarsening of the ferrimagnetic mineral assemblage from primarily magnetic single domain particles in the top centimeters to multi domain grains in deeper strata electron microscope observations enable both an unequivocal identification of bacterial magnetite on the basis of shape and grain size and to trace dissolution effects on the biogenic magnetic mineral component to depth

review stratigraphy meta stratigraphy and chaos an alternative approach to stratigraphic analysis is proposed it takes as its starting point the simple general characteristics of the stratigraphic record and the complex chaotic behaviours of the systems that combine to generate this record in this context smith s stratigraphy machine sm concept is developed the sm is a chaotic global system combining the operations of the atmosphere hydrosphere lithosphere and asthenosphere which everywhere tends to self organize towards a critical state in which continuous loading of the system with rock waste over time is balanced by the unloading that creates the record the outputs of the sm are simple and nonscale dependent in character with residence times in the record ranging from a second or less to 1 billion years however only those long lived in the human time frame are judged to be of stratigraphic significance and the range of residence times entails that the stratigraphic record embraces a similar range of hiatuses or gaps the value of the sm as developed here is that it can be regarded as a meta stratigraphic concept that transcends the usual frameworks of stratigraphic classification and interpretation and thus allows a reappraisal of significant features of the record such as its perceived cycles and sequences there are three outcomes of this meta stratigraphic analysis first the geometric units employed in sequence stratigraphy are components of a self similar series of essentially lenticular bodies with no fundamental characteristics to distinguish them from larger and smaller bodies in the generally self similar series secondly the interactions and feedbacks within the sm are so complex and its outputs so repetitive in general character that it is dangerous to assume that any perceived cyclicity provides an unambiguous chronicle of process cyclicity whether eustatic climatic or tectonic the classic coarsening upward cyclicity of shallow marine facies can for example be viewed solely as the outcome of the lack of phasing between the chaotic behaviours tending to unload the sm and those creating accommodation space finally the meta stratigraphic approach reinforces the view that in the absence of demonstrable stratal continuity chronostratigraphic correlation must continue to rely on sample based mainly biostratigraphical methods rather than sequence stratigraphy

reconstruction of past nutrient utilization in the eastern angola basin based on sedimentary 15n 14n ratios the 15n records of two sediment cores from the angola basin have been used to investigate past changes in nutrient utilization in the surface waters of this highly productive region low 15n 14n ratios in the cores from 3000 m water depth generally correspond to low sea surface temperatures and high sedimentary organic content demonstrating a link between upwelling productivity and the degree of nitrate depletion glacial 15n was lower by 0 5 0 7 and paleoproductivity was elevated by around 30 relative to interglacial periods indicating that although productivity was higher nitrate was less depleted during glacial than interglacial periods more pronounced than the glacial interglacial changes in 15n values of both cores are precession related 23 kyr fluctuations these cyclic 15n variations which are in phase with those of paleoproductivity and sea surface temperature indicate that changes in trade wind driven upwelling intensity and the advection of cold nutrient rich water from the south drive nutrient availability and productivity off the southwest coast of africa no strong evidence was found from sedimentary 15n values for denitrification in the water column in the angola basin during the past 180 kyr

the early matuyama diatom maximum off sw africa benguela current system odp leg 175 abstract several sites of ocean drilling program leg 175 between 20 and 30 s 1081 1082 1083 1084 and 1085 in the benguela current system show a distinct opal and diatom maximum within the late pliocene and early quaternary spanning the lower half of the matuyama reversed polarity chron mdm matuyama diatom maximum this maximum is centered around 2 0 2 6 ma and follows a rapid increase of diatom deposition near 3 1 ma within the mdm we recognized intervals dominated by the antarctic subantarctic species thalassiothrix antarctica which have the aspect of diatom mats the mdm and the mats developed during a time of sustained southern ocean influence 3 2 1 6 ma probably reflecting a period of seasonally pulsed continuous advection of subantarctic waters into the benguela oceanic current the onset and cessation of the mdm raises questions about modes in the operation of the silica cycle and the relation of these to major oceanographic events a depositional model for the late pliocene is proposed which involves positional changes in a longshore system of fronts substantial equatorward excursions of subantarctic waters during mdm time and subsurface waters greatly enriched in silicate

cantor set model of eolian dust deposits on desert alluvial fan terraces available data show that eolian dust accumulation rates on desert alluvial fan terraces are often inversely proportional to the square root of the terrace age for a given area this temporal scaling is similar to that observed in fluvial and marine stratigraphic sequences in which a fractal distribution of hiatuses occurs i e a cantor set eolian dust accumulation on alluvial fan terraces is controlled by regional climatic influences on dust deposition e g dessication of pluvial lakes in the early holocene and local surface characteristics e g vegetation and pavement coverage that control dust preservation in order to interpret the observed scaling in terms of these relative influences i consider two end member models 1 a deterministic model in which dust deposition is controlled by cyclical climatic changes i e glacial interglacial cycles and in which no erosion occurs and 2 a stochastic model in which erosion and deposition take place with equal probability and magnitude during each time step i e a bounded random walk the observed temporal scaling is most consistent with the bounded random walk model suggesting that long term eolian dust accumulation is predominantly controlled by episodic changes in vegetation and pavement coverage over time and that eolian dust deposits are strongly punctuated by episodes of erosional reworking at a wide range of temporal scales

accumulation rates of carbonate platforms the growth potential of carbonate platforms i e the maximum rate at which they can aggrade vertically is difficult to assess to estimate the growth potential from the conservative side and search for variations with time we have compiled published accumulation rates from the phanerozoic accumulation rates vary in a pattern with maximum rates up to 200 m ma or more not corrected for compaction in the late devonian permian late triassic late jurassic and mid cretaceous separated by intervals of reduced rates e g carboniferous early jurassic and late cretaceous the most dramatic drop occurs at the permo triassic boundary after which there is no documented platform growth this pattern resembles the evolutionary rhythm of bloom and demise of reefs and reef builders the observed maximum accumulation rate of 200 m ma over 10 6 10 7 yr is probably imposed by the maximum rate of long term relative sea level rise on passive margins the most favorable site for carbonate platform deve

a volume based approach to calculation of ancient carbonate accumulations abstract volumes of carbonate rocks are computed for mesozoic platforms over several orders of length scales reservoir to basin scale for millions of years time intervals the calculation is based on the restoration of depositional geometries by correlating genetic sequences and on the estimation of carbonate concentrations from core and well log data the interpolation yields the total amount of carbonate buried in a closed system and represents the net budget of production preservation of sedimentary carbonate for a given time interval over a defined area covering several depositional environments a three dimensional 3 d accumulation rate is obtained by dividing the total volume of carbonate rocks by the total surface over a time interval derived from biostratigraphic data estimates of such a carbonate accumulation rate for various jurassic and cretaceous platforms range from 8 to 67 m m yr errors in computing carbonate volumes are limited whereas an uncertainty is associated with the calculati

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

a fractal model for the distribution of stratigraphic hiatuses several recent studies have suggested that there is a negative log linear relationship between sedimentation rates and the time span over which they are measured i e measured sedimentation rates are slow when measured over long time spans and rapid when measured over short time spans this relationship may be due to the inclusion of more and longer hiatuses over long time spans this paper proposes a mathematical model consistent with this relationship that is based upon the fractal cantor bar this model allows the estimation of the relative number and durations of stratigraphic hiatuses within a given section

wavelet analysis of well logging data from oil source rock egret member offshore eastern canada wavelet analysis is a sensitive method for automatically detecting and distinguishing abrupt discontinuities i e faults unconformities cyclicity and gradual changes in sedimentation rate by transforming depth related sedimentary signals i e gamma rays into wavelengths at distinct depth intervals we used wavelet analysis for evaluation of the spatio temporal distribution of oil source rocks and for estimating accumulation rates in a sedimentary basin having high resolution the method was applied to 16 gamma ray logs from the jurassic egret member an oil source rock succession 55 m to 227 m in thickness offshore eastern canada dominant gamma ray cycles having wavelengths varying from 2 8 m western margin of the basin to 24 m eastern part of the basin have been detected by wavelet analysis the coincidence of the ratio of predominant gamma ray cycles with the ratio of milankovitch spectra about 400 100 40 20 k y suggests that climatic cycles are an important factor controlling sedimentary cyclicity in the egret member dominant wavelengths likely represent 100 k y eccentricity giving accumulation times of 1 9 m y for stratigraphically complete sections having 19 successive 2 8 m gamma ray cycles and giving accumulation times of 600 k y for incomplete successions having only 6 cycles up to four discontinuities occur in gamma ray log cyclicity and separate the egret member into subunits we interpret the discontinuities as unconformities or faults and as related to sediments having low petroleum potential the stratigraphic completeness of the egret member is correlated to total mass of organic carbon and decreasing thickness of non source rock intervals having correlation coefficients of r 0 8 and r 0 76 respectively

sedimentology floods of record research on two bolivian rivers provides explanations of how and when they flood it also gives pointers for interpreting earth s history as recorded by the sediments left behind by flood waters

precipitation as meteoric sediment and scaling laws of bedrock incision assessing the sadler effect abstractalthough it has been several decades since sadler 1981 first showed that sediment accumulation rates exhibit a negative power law dependence on measurement interval i e the sadler effect only recently has a manifestation of covariance in rate with duration become more widely appreciated in degradational settings because our collective understanding of rates of deposition and erosion are widely utilized to constrain the importance of active tectonism and climate forcing in shaping the surface of our planet cognizance of the dependence of rate on duration of observation is of critical importance relations between elevation change deposition erosion and rate scaling laws have often been examined by stochastic random walk simulations but this approach is generally confounded by insufficient data on amounts of land surface change on durations of land surface change and on hiatal durations separating time intervals of change deposition or erosion rates measured over short intervals suc

the late miocene onset of high productivity in the benguela current upwelling system as part of a global pattern abstract we have examined the history of the elevated primary productivity associated with the benguela current upwelling system off southwest africa using sediments from 7 5 to 4 8 ma at ocean drilling program site 1085 in the middle cape basin sedimentation rates are low until 6 9 ma low accumulation rates of benthic foraminifers and organic carbon indicate that biological productivity was also low paleoproductivity dramatically increased at 6 7 6 5 ma and was highly variable until 4 8 ma with productivity maxima during cooler periods the presence of radiolarian opal only between 5 8 and 5 2 ma suggests an interlude of silica rich intermediate water in the cape basin the onset of heightened productivity under the benguela current is mirrored by similar increases reported between 6 9 and 6 7 ma in the tropical eastern pacific the western and northern pacific and the indian ocean the similarity between the patterns at site 1085 and in the pacific and indian oceans suggests that the dramatic productivity increase off southwest africa is part of a global response to paleoceanographic changes

antarctic intermediate water circulation in the tropical and subtropical south atlantic recent hydrographic data from the south atlantic ventilation experiment cruises and others are combined with historical data and used to map the isopycnal properties corresponding to the antarctic intermediate water aaiw in the atlantic ocean the low salinity of the aaiw extends eastward across the south atlantic just south of the equator 3 4 s evidence of a weak eastward flow just north of the equator 1 2 n is also shown lateral and vertical homogenization of properties in the aaiw is found at the equator between 2 s and 2 n there is no clear zonal gradient in salinity just along the equator these observations suggest enhanced mixing within the equatorial baroclinic deformation radius the south atlantic tropical gyre is shown to consist of the following three cells one cyclonic cell centered at about 7 s another centered at about 19 s in the west and 23 s in the east and one anticyclonic cell centered at about 13 s these cells are associated with a westward extension at 10 s of high salinity and low oxygen which originates in the eastern tropical south atlantic and a front in these properties at about 15 s in the west and about 20 s in the east

discontinuity surfaces on a shallow marine carbonate platform berriasian valanginian france and switzerland discontinuities in sedimentation are commonly expressed as surfaces in outcrop sections and are due to rapid and substantial environmental changes on shallow marine carbonate platforms most such surfaces represent hiatuses below biostratigraphic resolution and detailed analysis is necessary to identify and evaluate the environmental change involved surfaces in nine sections of the lower cretaceous of the french and swiss jura platform are characterized on the basis of eight universally applicable criteria geometry lateral extent morphology biological activity mineralization facies contrast diagenetic contrast and biostratigraphy nine different surface types are distinguished by their common features and environment of formation all of them are related to environmental changes in the form of subaqueous erosion subaerial exposure subaqueous omission or changes in texture and facies the distribution of surface types in the studied sections shows that condensation and exposure related surfaces tend to occur repetitively in certain intervals calibrated by biostratigraphy these surface zones can be correlated across the platform from proximal to distal positions in comparison with the global sequence stratigraphic framework hardenbol et al 1997 most exposure zones correlate with third order sequence boundaries condensation zones fall in between in the studied sections third order eustatic sea level drops appear to be represented rather by zones of small scale discontinuities than by widespread and well marked single sequence boundaries this is explained by the superposition of high frequency low amplitude sea level fluctuations on a larger scale sea level trend under greenhouse conditions the lateral extent of the surface zones varies through time and indicates important changes in platform morphology changes in local subsidence rate indicated by variable thicknesses of the deposits in comparison with second and third order sea level trends suggest an evolution of the french jura platform from a ramp type morphology in the late middle berriasian to a flat topped platform in the late berriasian the early valanginian again is characterized by increased differential subsidence and well marked platform morphology this study demonstrates that 1 small scale and short lived discontinuities can reflect large scale variations of relative sea level 2 on shallow platforms characterized by small topographic variations and lateral facies changes third order sequence stratigraphic surfaces are not necessarily expressed by one widespread single surface but by zones of surfaces indicating repeated environmental changes surface zones can serve as an additional tool for correlation and interpretation of platform evolution and 3 small scale discontinuities form an integral part of the stratigraphic record and should receive the same attention as the sedimentary deposits they delimit

sediment deposits in the cape basin indications for shifting ocean currents the benguela current system running off southwest africa is one of the world s largest upwelling regions the current has strongly influenced sedimentary features on the continental margin to unravel its development seismic stratigraphy tied to drilling results from ocean drilling program leg 175 sites 10851087 was established four units southern cape basin scb 1 to scb 4 were defined for the cenozoic sediments the upper unit scb 1 1 5 ma characterized by continuous high amplitude reflectors represents global cooling and glacial interglacial cycles unit scb 2 14 ma distinguished by low amplitude reflections is associated with the onset of the upwelling system and establishment of the modern circulation pattern in the cape basin slump scarps are concentrated along the middle and upper shelf slope suggesting they are caused by a combination of mass movements triggered by bottom currents and slope instabilities because of increased deposition associated with the upwelling a westward extension and or movement of upwelling filaments is interpreted from the observed seaward shift of scarp locations with time erosion associated with stronger currents probably thinned unit scb 2 in the south the two lower units scb 3 and scb 4 56 ma probably represent material eroded from the shelf break and deposited during a major oligoceneearly miocene regression that is consistent with a significant uplift of southern africa the basal reflector scb d of unit scb 4 is associated with the prominent reflector d or l described in previous publications

an estimate of tidal energy lost to turbulence at the hawaiian ridge abstract an integrated analysis of turbulence observations from four unique instrument platforms obtained over the hawaiian ridge leads to an assessment of the vertical cross ridge and along ridge structure of turbulence dissipation rate and diffusivity the diffusivity near the seafloor was on average 15 times that in the midwater column at 1000 m depth the diffusivity atop the ridge was 30 times that 10 km off the ridge decreasing to background oceanic values by 60 km a weak factor of 2 spring neap variation in dissipation was observed the observations also suggest a kinematic relationship between the energy in the semidiurnal internal tide e and the depth integrated dissipation d such that d e1 0 5 at sites along the ridge this kinematic relationship is supported by combining a simple knife edge model to estimate internal tide generation with wave wave interaction time scales to estimate dissipation the along ridge kinematic relationship and the observed vertical and cross ridge st

advection and scavenging effects on 230th and 231pa distribution off southwest africa we investigated the controls of hydrography and of scavenging on the distribution of the particle reactive radionuclides 231pa and 230th in the water column and in surface sediments off southwest africa angola and cape basins based on a vertical section of total 230thex concentrations in the water column we show that small differences in the salinity between the north atlantic deep water nadw in the angola basin and the nadw in the cape basin as well as the advection of nadw associated with the namib col current are reflected in total 230thex concentrations these variable total concentrations are believed to reflect the flow path and mixing history of nadw with the nadw in the angola basin being relatively older and 230th enriched compared to the nadw in the cape basin in the area investigated we found high 231paex 230thex ratios 231paex 230thex 0 093 in surface sediments at the continental margin and lower ones 231paex 230thex 0 093 in the open ocean such a distribution is normally interpreted to result from high particle flux at ocean margins boundary scavenging however the lack of any significant depletion of dissolved 230th and 231pa in the water column does not indicate extensive scavenging at the continental margin high 231paex 230thex ratios are constrained to shallow waters depths 2000 m only and coincide with low fractionation between 231pa and 230th indicating that preferential scavenging of 231pa on opal may have caused high 231paex 230thex ratios in the sediments the observed close negative correlation r2 0 82 between 231paex 230thex ratios in sediments and water depths is believed to reflect changes in the particle composition i e a decrease in opal content with water depth in the angola and cape basins the total 231paex concentrations in nadw were the highest observed so far in the atlantic ocean and they are attributed to the meridional export of 231pa from the north atlantic this caused the average dissolved 231pa 230th in the southeast atlantic to be about a factor 2 higher when compared to the north atlantic labrador sea these differences in the dissolved 231pa 230th were not reflected in 231pa 230th ratios of surface sediments because the fractionation is lower in the labrador sea compared to the southeast atlantic i e fractionation counteracts changes in the dissolved 231pa 230th this suggests that fractionation is more important for the determination of 231paex 230thex ratios in sediments than the meridional export of 231pa from the north atlantic

sediments facies tracts and variations in sedimentation rates of holocene platform carbonate sediments and associated deposits northern belize implications for representative sedimentation rates full text is not available on soar publisher s website http jsedres geoscienceworld org cgi content abstract 74 4 498 doi 10 1306 012004740498

stratigraphic completeness and resolution in an ancient mudrock succession funded by nerc fellowship grant number ne i02089x 1 santander student project scholarship grant

characteristics of intermediate water flow in the benguela current as measured with rafos floats abstract seven floats not launched in rings crossed over the mid atlantic ridge in the benguela extension with a mean westward velocity of around 2 cm s between 22s and 35s two agulhas rings crossed over the mid atlantic ridge with a mean velocity of 5 7 cm s toward 285 this implies they translated at around 3 8 cm s through the background velocity field near 750 m the boundaries of the benguela current extension were clearly defined from the observations at 750 m the benguela extension was bounded on the south by 35s and the north by an eastward current located between 18s and 21s other recent float measurements suggest that this eastward current originates near the trindade ridge close to the western boundary and extends across most of the south atlantic limiting the benguela extension from flowing north of around 20s the westward transport of the benguela extension was estimated to be 15 sv by integrating the mean westward velocities from 22s to 35s and multiplying by the 500 m estimated thickness of intermediate water roughly 1 5 sv of this are transported by the 3 agulhas rings that cross the mid atlantic ridge each year as observed with altimetry this value of the benguela extension transport is the first one to have been obtained from long term two year observations and across the full width of the benguela extension

temporal distribution of diastems in deposits of an open coast tidal flat with high suspended sediment concentrations abstract based on field observations of the preservation potential and genesis of couplets and small sequences diastems occur within tidal flat deposits at scales of semi tidal daily monthly and yearly intervals thus tidal flat deposition is riddled with more diastems of different scales than previous assumptions units that are apparently complete when examined at longer time scales actually contain many diastems when examined at a shorter time scale diastems within tidal flat deposits are generated not only by high magnitude storm waves which occur during typhoon seasons but also by daily erosion produced by tides and weak waves during calm weather seasons the missing intervals in diastems generated by storm waves can be several days to several years preservation potential of storm generated small sequences is of the order of one third diastems generated by erosion by tides and weak waves can have spans from a semidiurnal cycle to several days they are easily overlooked because of the low magnitude destruction and lack of distinctive sedimentary features net erosion by tides and weak waves is unexpectedly increased by day to day processes alternations of sandy and muddy laminae are related to tidal rhythm but individual laminae can be separated by a significant diastem documentation of erosion by tides and weak waves under normal non typhoon conditions is the principal focus of this report

erosion and deposition from bottom currents during the givetian and frasnian response to intensified oceanic circulation between gondwana and laurussia abstract calcareous bottom current deposits in otherwise pelagic and hemipelagic successions of the harz mountains in germany herzyn limestone formation the eastern moroccan central massif ziar mrirt nappe and the carnic alps in austria italy valentin and pal limestone formation show strong evidence of bottom current reworking of carbonate ooze during givetian and early frasnian associated phosphates confirm that higher hydraulic energy temporarily prevailed the bottom current deposited facies builds up strongly condensed and reduced successions with stratigraphic gaps which also occur with similar features in other areas of central europe and northwest africa at the same stratigraphic interval the widespread current induced reworking of calcareous sediments and phosphate formation during the givetian and early frasnian as well as the associated erosional processes marked by pronounced hiatuses all signal a major circulation event the temporal and spatial positions of these fossil calcareous contourites in the devonian are discussed research concluded that thermohaline currents were intensified by the acceleration of flows constricted in the narrow oceanic passages between the approaching continental plates laurussia and gondwana areas affected were the southeastern rhenish sea shelf the disintegrated northern continental margin of gondwana and deep marginal plateaus of the noric terrane in the western part of the prototethys the disposition of the fossil calcareous contourites and faunal data corroborate palaeogeographic reconstructions that show an advanced convergence between gondwana and laurussia and the smaller continental plates such as the armorican and noric terranes during givetian and frasnian times

gssps global stratigraphy and correlation procedures used to define an international chronostratigraphic stage boundary and to locate and ratify a global boundary stratotype section and point gssp are outlined a majority of current gssps use biostratigraphic data as primary markers with no reference to any physico chemical markers despite the international subcommission on stratigraphic classification issc suggestion that such markers should be included if possible it is argued that such definitions will not produce the high precision phanerozoic time scale necessary to understand such phenomena as pre pleistocene ice ages and global climate change it is strongly recommended that all gssps should have physico chemical markers as an integral part of their guiding criteria and where such markers cannot be found the gssp should be relocated the methods and approach embodied in oceanic stratigraphy coring logging analysing and archiving of drill sites by numerous experts using a wide range of methods could usefully serve as a scientific model for the analysis and archiving of gssps all of which are on the present day continents the incorporation of many more stratigraphic sections into gssp studies the application of physico chemical methods and the replacement of old u pb dates by newer ca tims u pb dates together with the use of constrained optimization conop programs that produce a calendar of events from many sections should lead to much more precise timescales for pre cenozoic time than are currently available

estimation of completeness of stratigraphical sections using empirical data and theoretical models the completeness of a stratigraphical section is the fraction of time intervals of some specified length t that have left a record a record is left when some sediment is deposited during the interval and is not subsequently eroded a complete section contains no hiatuses longer than t the completeness of a section varies with t and its accumulation rate varies with the length of the time span over which it is measured plots of measured accumulation rate against time span are an empirical means of estimating completeness simple theoretical models help extrapolate meagre data and identify bias completeness at time scale t can depend upon three general properties of the accumulation history the age of the section the long term net accumulation rate drift and the unsteadiness of the sedimentation rate the way unsteadiness is measured depends upon the kinds of fluctuations that can be recognized in the accumulation rate to describe random fluctuations a standard deviation of rates is sufficient one dimensional brownian motion is a model of random fluctuations that explains many aspects of stratigraphical completeness regular periodic fluctuations in accumulation rate may be described in terms of wavelength and amplitude completeness is an increasing function of t drift and in the periodic case the wavelength of fluctuations it decreases with increasing standard deviation of accumulation rate and the amplitude of periodic fluctuations the completeness and thickness of stratigraphical sections are weakly positively associated

late quaternary paleoproductivity changes off the congo deduced from stable carbon isotopes of planktonic foraminifera a detailed record 2 kyr intervals of the difference in stable carbon isotopes 13c between globigerina bulloides and globigerinoides ruber pink is used to reconstruct changes in upwelling intensity off the congo river for the last 190 000 yr comparisons of the oxygen and carbon isotope data from this core with records from the niger fan and from pelagic cores in the eastern equatorial south atlantic indicate that the congo fan isotope records do not contain a strong freshwater signal as is described off other major rivers the temporal pattern of the 13c signal correlates with the marine organic carbon record from the congo fan thus the planktonic 13c record reflecting past changes in upwelling intensity and nutrient content corroborates the signal provided by sedimentary organic carbon which is presumed to indicate changes in the amount of biological productivity and export flux to the seafloor the planktonic 13c signal is characterized by a dominant 23 kyr periodicity which provides evidence for a strong response of upwelling fluctuations off the congo to precessional forcing minima in the 13c record are aligned with periods of minimum boreal summer insolation over central africa reflecting an increase of upwelling and biological productivity off the congo at periods of enhanced zonal intensity of southeast trades and corresponding weak southeast monsoon over the eastern south atlantic a strong response to changes in river discharge probably did not occur indicating that fertilization by river derived nutrients has played only a minor role with respect to late quaternary changes in the total amount of primary productivity off the congo

measured rates of sedimentation what exactly are we estimating and why abstract data on rates of sedimentation are essential in studies of sedimentation systems these data are obtained in three main study contexts 1 the study of sedimentation systems that are active today 2 the source to sink study of sedimentation systems that no longer are active and 3 the study of the relationship between accumulation rate and measurement timespan the aim of this paper is to question the meaning of measured rates of sedimentation and their interpretability particularly in these three contexts individual measurements of rate of sedimentation must always be interpreted with care firstly there are different definitions for instance with different statistical support or measurement dimension values that are defined differently cannot be compared directly secondly appropriate sampling schemes must have been used for the measurement this minimises sampling bias thirdly the inherent limitations of the data sources must be taken into account rates of sedimentation can usually be measured successfully in active sedimentation systems the same is not true for systems that are no longer active these can only be studied using the stratigraphic successions left behind rates of erosion can never be measured successfully in stratigraphic successions rate of sedimentation is essentially a ratio an amount of sedimentation per length of time therefore the obvious strategy to use in determining it is first to measure the amount and the time independently then to combine the values the amount can be measured in terms of thickness or volume or mass per unit area the duration of the time interval can be preset using quasi continuous measurement techniques or site reoccupation or it can be identified from interval specific sedimentary structures or it can be measured using dated horizons an alternative strategy is to use a surrogate measurement variable rates of erosion in ancient systems are usually measured in this way using cosmogenic radionuclide concentrations these two strategies are reviewed in this paper sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole this estimation is best carried out using geostatistical estimation techniques the alternative is simply to average the measured rate values this latter approach should not be used however because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries it says nothing at all about how the system is operating or about its spatial and temporal variability measurements of rates of sedimentation made for source to sink studies are necessarily made in stratigraphic successions the measurements are used to estimate quantities in the sediment mass budget equation the amount of decumulation is inherently incapable of being measured in stratigraphic successions therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere this means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non erosional for that entire time interval a highly unrealistic situation the consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale invariant this in turn is often taken as indicating that the stratigraphic record is fractal in nature there are nevertheless grounds for doubt all of which relate to the ways that the data are collected and used for estimation the relationship is in fact the natural mathematical result of last in first out lifo operation and is produced in any type of system in which addition and removal processes both operate it says nothing particular about sedimentation processes the future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a lifo model

planktonic foraminifers as tracers of ocean currents in the eastern south atlantic the standing stock of planktonic foraminifers collected at 16 stations by multinet plankton tow has been examined in five discrete depth intervals 0 25 m 25 50 m 50 100 m 100 150 m and 150 300 m the assemblages document the status of populations in the surface and subsurface waters of the southeast atlantic during february march 1988 standing crops document hydrographic conditions in the coastal and geostrophic branch of the benguela current the angola current the tropical cyclonic gyre and the south equatorial current standing stocks are highest when primary production is intermediate very high primary production reduces foraminiferal crops significantly eleven species occur abundantly average 10 of the total standing stock a few species g glutinata g quinqueloba g clarkei are abundant at each station whereas the occurrence of other species g ruber g sacculifer g scitula g menardii g crassaformis n incompta n dutertrei is spatially restricted g ruber g rubescens and g glutinata are abundant in high salinity surface water also g ruber is abundant within the equatorial undercurrent water when this water is brought to the surface high concentrations of n incompta and g bulloides are observed in the angola benguela front when nutrient concentration is moderately elevated in surface and subsurface water upper part of the thermocline g crassaformis becomes abundant in the subsurface water of the angola benguela front this species is restricted to lower oxygenated subsurface water and traces incursions of water transported by the angola current g menardii is considered as an indicator for the equatorial undercurrent below the mixed layer whereas g scitula most probably points to an admixture of water transported by the northward flowing benguela current high abundances of g quinqueloba g clarkei in the surface and subsurface waters reflect favorable nutrient conditions like those present in the geostrophic benguela current and in the equatorial divergence zone g falconensis n dutertrei and g siphonifera appear to trace the southern equatorial current

significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data how and where the ocean tides dissipate their energy are long standing questions1 that have consequences ranging from the history of the moon2 to the mixing of the oceans3 historically the principal sink of tidal energy has been thought to be bottom friction in shallow seas4 5 there has long been suggestive evidence6 7 however that tidal dissipation also occurs in the open ocean through the scattering by ocean bottom topography of surface tides into internal waves but estimates of the magnitude of this possible sink have varied widely3 8 9 10 11 here we use satellite altimeter data from topex poseidon to map empirically the tidal energy dissipation we show that approximately 1012 watts that is 1 tw representing 25 30 of the total dissipation occurs in the deep ocean generally near areas of rough topography of the estimated 2 tw of mixing energy required to maintain the large scale thermohaline circulation of the ocean12 one half could therefore be provided by the tides with the other half coming from action13 on the surface of the ocean

fractal characteristics of desert storm sequences and implications for geomorphic studies abstract daily precipitation sequences from desert climate stations located in southern california and nevada exhibit fractal characteristics at time bins less than 100 days and non fractal characteristics at time bins greater than 100 days the fractal behavior of these data is described as cantor dust with fractal dimensions ranging from 0 37 for bishop california down to 0 26 for the eagle mountain california due to its nature as a clustered event sequence computer modelers hoping to simulate geomorphic processes responding to precipitation events such as soil leaching paleoclimate lake levels and other processes linked to hydrologic budgets must use caution in devising time increments for their models significant water budget changes are possible without changing long term precipitation averages but rather by changing the precipitation delivery schedule over a period of time the cantor dust aptly quantifies these and other aspects of a precipitation sequence and can be used to more precisely characterize a climatic type because many geomorphic processes dependent on precipitation are a function of frequency magnitude and antecedent conditions the fractal characteristics of the precipitation sequence play an important role in understanding the limits of forward modeling

stochastic and deterministic controls on stratigraphic completeness and fidelity compilations of sedimentation rates determined across a large range of time spans and different sedimentary environments attest to the discontinuous nature of sedimentation and support the reasoning that hiatuses pervade sedimentary successions at multiple spatial and temporal scales the relationship between sedimentation rate and time span of observation also emphasises how stratigraphic completeness is a time span dependent concept the scaling of stratigraphic completeness with time span alludes to the likely stochastic and fractal nature of the stratigraphic record it also implies that the relationship between stratal thickness and time is inherently non linear and this has obvious implications for the way we should expect temporal processes to be recorded stratigraphically order within the stratigraphic record may arise from deterministic processes in stratigraphy most notably through astronomically influenced sedimentation intuitively a strongly ordered stratigraphic record due to the presence of cyclicity in sedimentation increases stratigraphic completeness at time spans equal to and longer than the time span of the cyclicity and minimises the non linearity between stratal thickness and time here geological data and simple modelling are used to support this supposition but these results also highlight how stochastic variability inherent in depositional processes may sensitise certain successions to missed cycles and incompleteness even in the presence of strong cyclicity this stochastic variability has the potential to mask evidence of astronomical forcing of sedimentation it is also shown how hiatuses affect the ability of a succession to faithfully record temporal processes and this is true regardless of whether hiatuses are deterministically controlled or random or indeed whether a succession is considered complete or not consequently stratigraphic completeness and stratigraphic fidelity are not synonymous terms

geometric interpretation of time scale dependent sedimentation rates abstract empirical rate data show that aggradation and progradation rates are negatively correlated with the duration they are averaged over this means that we cannot understand deep time sedimentation rates in terms of the abundant rate data we have from modern environments we are addressing this by investigating how growth of a sediment volume in multiple directions affects time averaged accumulation rates that do not necessarily measure all directions of growth we derive a mathematical model from mass balance considerations of a sedimentary deposit that grows without erosion we show that the non linear relationship between the lengths areas and volumes of growing objects require that time averaged sedimentation rates are time scale dependent when a deposit grows in multiple directions we generate rate compilations from simple synthetic stratigraphies which show that we can reproduce the empirical rate compilations by requiring only that deposition occur in a dynamic mosaic of sequential patches in which the areal extent of deposition increases with time scale as described by our mathematical model our model has two implications with application in stratigraphic analysis the first is that it provides a theoretical model of why we cannot expect high stratigraphic completeness if we measure a deposit in fewer directions than it has grown the second is that it provides a framework by which to attribute anomalies in the stratigraphic completeness of a one dimensional or two dimensional sample to scaling effects or erosional hiatuses

quantifying the stratigraphic completeness of delta shoreline trajectories understanding the incomplete nature of the stratigraphic record is fundamental for interpreting stratigraphic sequences methods for quantifying stratigraphic completeness for one dimensional stratigraphic columns defined as the proportion of time intervals of some length that contain stratigraphy are commonplace however quantitative assessments of completeness in higher dimensions are lacking here we present a metric for defining stratigraphic completeness of two dimensional shoreline trajectories using topset foreset rollover positions in dip parallel sections and describe the preservation potential of a shoreline trajectory derived from the geometry of the delta surface profile and the kinematics of the geomorphic shoreline trajectory two end member forward models are required to fully constrain the preservation potential of the shoreline dependent on whether or not a topset is eroded during base level fall a laboratory fan delta was constructed under nonsteady boundary conditions and one dimensional stratigraphic column and two dimensional shoreline completeness curves were calculated results are consistent with the hypothesis derived from conservation of sediment mass that completeness over all timescales should increase given increasing dimensions of analysis stratigraphic trajectories and completeness curves determined from forward models using experimental geomorphic trajectories compare well to values from transects when subsampled to the equivalent stratigraphic resolution as observed in the actual preserved sequence the concept of stratigraphic completeness applied to two dimensional trajectory analysis and the end member forward models presented here provide novel tools for a conceptual understanding of the nature of stratigraphic preservation at basin scales

upper ocean temperature and salinity sections in the south atlantic in 1911 hydrographic cruises conducted in july october 1911 by the fram the deutschland and the mowe and in january february 1911 by the stephan provide a survey of the upper south atlantic subtropical gyre during the cold season and of the equatorial atlantic the data accuracy is not as high as in more recent surveys in particular the depth of the measurement is not known precisely the fram temperature is only good to within 0 10 c accuracy and salinity to within 0 02 the south atlantic cold season stations often present a 100 m or thicker surface mixed layer overlaying a thermocline with maximum vertical gradient increasing from the southwest to the northeast a layer of minimum vertical temperature gradient of 0 01 c m 1 at a temperature close to 13 c is embedded in the upper thermocline between 40 w and 20 w on the southern section of the fram 30 s to 35 s this defines a mode water at a density 26 60 close to the surface density of deep mixed layers offshore of the brazil current found between 34 s and 39 21 s but which is warmer and saltier 14 9 c 35 70 the 1911 t s characteristics in the subtropical south atlantic thermocline present little zonal variations with the warmest saltiest water on isopycnal surfaces found in the southwestern portion of the survey and the coldest freshest waters near namibia the 1911 south atlantic surface waters are much colder than the average situation in recent decades average of 0 82 c and are a little fresher 0 04 than the hydrographic climatology for that season in the subtropical gyre the isopycnals were probably deeper in 1911 than in 1926 except in the southwestern corner and the slope of the t s relationship was larger in 1911 than in 1925 1926 with warmer and saltier waters in the upper thermocline above 26 6 26 4 and fresher and cooler waters in the lower thermocline on the other hand t s characteristics in the equatorial thermocline are comparable in 1911 and 1926 both surveys present water masses which are colder and fresher on isopycnal surfaces than the surveys in the 1960s

interannual variations in the atlantic meridional overturning circulation and its relationship with the net northward heat transport in the south atlantic 1 variability of the atlantic meridional overturning circulation amoc and its effect on the net northward heat transport nht in the south atlantic are examined using a trans basin expendable bathythermograph xbt high density line at 35s ax18 the time mean amoc is 17 9 2 2 sv during 2002 2007 although the geostrophic transport dominates the time mean amoc both geostrophic and ekman transports are important in explaining the amoc variability the contributions of geostrophic and ekman transports to the amoc show annual cycles but they are out ofphase resultinginweakseasonalvariabilityoftheamoc the nht variability is significantly correlated with the amoc where a 1 sv increase in the amoc would yield a 0 05 0 01 pw increase in the nht partition of transport into the western and eastern boundaries and interior suggests that to quantify changes in the amoc and nht it is critical to monitor all three regions citation dong s s garzoli m baringer c meinen andg goni 2009 interannualvariations intheatlanticmeridionaloverturningcirculationanditsrelationship with the net northward heat transport in the south atlantic geophys res lett 36 l20606 doi 10 1029 2009gl039356

internal tide radiation from mendocino escarpment abstract strong semidiurnal internal tides are observed near mendocino escarpment in full depth profile time series of velocity temperature and salinity velocity and density profiles are combined to estimate the internal tide energy flux divergence of this flux demonstrates that its source is the barotropic tide interacting with the escarpment a baroclinic energy flux of 7 kw m 1 radiates from the escarpment corresponding to 3 of the 220 kw m 1 fluxing poleward in the surface tide energy and energy flux are concentrated in packets that emanate from the flanks of the ridge surmounting the escarpment and one site 90 km north of the escarpment coherent beamlike structure along semidiurnal ray paths remains identifiable until the first surface reflection beyond the first surface reflection north of the escarpment the energy flux drops by 2 kw m 1 and beams are no longer discernible turbulence as inferred from finescale parameterizations is elevated by over two orders of magnitude relative to th