viable diatoms and chlorophylla in continental slope sediments off cape hatteras north carolina abstract continental slope sediments off cape hatteras north carolina were sampled by coring in late summer 1992 the chlorophylla concentrations measured in sediments from 16 sites at depths ranging from 530 to 2003 m averaged 19 9 mg chla m 2 a concentration much higher than observed elsewhere on the eastern u s continental slope indicating high depositional rates for microalgal material the variability in the chlorophylla values suggests strong environmental heterogeneity at both small and large spatial scales in this slope habitat probably a consequence of both topography and bioturbation viable diatoms were found in sediment samples across the range of depths sampled and up to 14 cm deep in sediments indicating high rates of deposition and bioturbation bulk sediment samples contained planktonic tychopelagic and benthic diatoms indicating that both phytoplankton and benthic microalgae from the continental shelf may be sources of organic matter for these slope sediments

hydrogeological constraints on the formation of palaeoproterozoic banded iron formations banded iron formations are critical to track changes in archaean to palaeoproterozoic ocean chemistry with deposition triggered by water column iron oxidation recently however it was suggested that reduced iron minerals were the primary precipitates and these were subsequently oxidized by oxygen bearing groundwater if true this would cast doubt on our understanding of how banded iron formations were deposited and their ability to record early ocean chemistry here we present a hydrogeological box model based on the approximately 2 5 billion year old hamersley basin of western australia developed to evaluate the plausibility of secondary iron oxidation the box model calculates the time required for groundwater to flux enough oxygen through the basin to oxidize a given amount of ferrous iron less than 9 of nearly four million model iterations returned oxidation times less than the age of the basin successful simulations required simultaneously steep hydraulic gradients high permeability and elevated oxygen concentrations our simulations show that the postdepositional oxidation of large banded iron formations is unlikely except on a limited scale that is during secondary ore formation and that oxidized iron phases were probably the precursor to large palaeoproterozoic banded iron formations banded iron formations could not have formed by postdepositional oxidation according to four million hydrogeological box model iterations that failed to reproduce secondary oxidation on reasonable timescales

the benguela current and associated upwelling on the southwest african margin a synthesis of the neogene quaternary sedimentary record at dsdp sites 362 and 532

oceanographic control of diatom abundances and species distributions in surface sediments of the tropical and southeast atlantic abstract this paper is a descriptive account of the diatomaceous component of pelagic sediments from the tropical and southeast atlantic ocean geographic patterns of diatom abundances whole and fragment forms per gram major species relative abundances and diatom assemblages resolved by q mode factor analysis are presented comparisons drawn to sea surface temperature salinity and productivity distributions suggest that i diatom abundances primarily reflect surface productivity with no apparent dissolution effects due to water depth ii relative abundances of major species vary in their ecologic dependence but do reflect major oceanographic features of the surface waters and iii of the five diatom assemblages resolved four finely delineate the complexity of the low latitude oceanography these assemblages in decreasing order of statistical importance are associated with 1 warm waters of moderate to high primary productivity 2 the oceanward margin of the benguela current a region of high primary production with a maximum in austral summer 3 low salinity waters off the mouths of the zaire and niger rivers and 4 subtropical to tropical waters of lower productivity mostly in the western equatorial atlantic the fifth factor represents the equatorward advection of subantarctic to antarctic diatoms by deep ocean currents

planktonic foraminiferal faunal and stable isotopic indices of upwelling a sediment trap study in the san pedro basin southern california bight

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

light dark cycles in opal rich sediments near the plio pleistocene boundary dsdp site 532 walvis ridge continental terrace diester haass l meyers p a and rothe p 1986 light dark cycles in opal rich sediments near the plio pleistocene boundary dsdp site 532 walvis ridge continental terrace mar geol 73 1 23 samples taken at 10 cm intervals from dsdp core 532b 17 contain variations in carbonate opal organic carbon and terrigenous components that correlate with light dark cycles in sediment color the core site at 1300 m water depth is well above the ccd yet the color variations appear to result largely from cyclical fluctuations in carbonate dissolution which was greater during glacial periods higher concentrations of organic carbon and of terrigenons sediment components correlate with enhanced carbonate dissolution but opal concentrations inversely correlate and suggest that biological productivity at this site diminished during glacial periods a complicated glacial interglacial picture emerges from the data in interglacial times upwelling associated with the benguela current produced abundant opaline material organic matter was fairly well preserved and carbonate was only moderately dissolved in glacial times the upwelling core shifted as sea level fell and winds intensified productivity in the waters over site 532 decreased but lateral supply of oxidizable organic matter enhanced carbonate dissolution giving rise to light dark cycles in these sediments

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

diatoms in southeast pacific surface sediments reflect environmental properties abstract diatom abundance and assemblage composition determined for 47 surface sediment samples from the southeast pacific 50 s 15 n combined with existing data for the peru and chile margins demonstrate responses to regional temperature upwelling and productivity high diatom abundances valves g mark the eastern equatorial pacific upwelling and the coastal upwelling areas in particular the upwelling centers off peru freshwater diatoms reflect the low salinity tongue off the chilean fjords diatom species composition distinguishes between coastal and eastern equatorial pacific upwelling conditions and records sea surface temperatures q mode factor analysis defines five floral assemblages factors 1 and 4 determined by the genus chaetoceros f1 and thalassionema f4 reflect coastal and equatorial upwelling conditions respectively factors 2 and 3 characterized by the genus thalassiosira and azpetia nodulifera can be associated with el nino conditions a 5th factor described by paralia sulcata records a near shore upwelling center off point concepcion central chile statistical transfer functions relate diatom species percentages to sea surface temperature and productivity with error estimates of 0 9 c and 23 gc m 2 yr respectively and provide new tools for estimating past temperature and productivity along the west coast of south america

late quaternary sedimentation on the eastern walvis ridge se atlantic hpc 532 and four piston cores five sediment cores from the eastern walvis ridge have been investigated by means of a quantitative coarse fraction analysis 40 m numerous biogenous terrigenous and authigenic particles have been distinguished the variations in composition suggest the following conclusions core walda ks 12 from the northern flank of the walvis ridge consists entirely of a slump which contains mainly glacconite sands and biogenous opal foraminiferal skeletons and terrigenous matter the sediments in the other four cores comprise the late quaternary oxygen isotope stages 1 6 there are several levels at the transition from warm to cold intervals where benthos plankton foraminiferal ratios increase from 10 up to 50 90 here imperforate benthonic foraminifera decrease strongly dissolution of planktonic foraminifera can only partly explain this finding lateral supply of benthos or the influence of reduced oxygen content in the bottom water might have played an additional role calcium carbonate dissolution as revealed by the fragmentation of planktonic foraminifera shows intermediate values in coldest and warmest periods dissolution maxima occur at warm cold stage boundaries dissolution minima have been found at the transition from cold to warm periods upwellinginfluence is reflected in varying amounts of biogenous opal in interglacial periods the influence of upwelling is strong in all cores with an increase in intensity to the east core v19 259 it is explained by eddies of upwelled water which drifted westward under the influence of the westward turning benguela current in glacial periods the influence of upwelling at the core sites was very reduced the benguela current problably was close to the continent and turned westward only at 17 s thus it did not affect the core sites climate in the near coastal area has been arid in the latitude of 20 s throughout the investigated time slice accumulation rates reflect the position of the cores hpc 532 and circe gb 211 are in the area of the sediment filled trough which forms the walvis ridge terrace here accumulation rates are 2 to 3 times higher in stages 2 4 and 5 than in v19 259 and walda ks 09 which are from the steeper flank of the terrace outside the trough mean values of calcium carbonate dissolution are similar in all cores lower caco3 content in v19 259 and lower sand fraction percentages are explained by lateral supply of fine grained terrigenous matter in the area of core v19 259 which probably received insoluble material from the kuene shelf area by the n s flowing countercurrent

distribution and paleoecology of molluscan skeletal remains along an upwelling tract benguela system namibian shelf abstract this study describes and categorizes the preservable and thus predominantly molluscan component of the macrofauna death assemblages of sub environments within the northern benguela upwelling system this is especially important for assembling actualistic data that can later serve for identifying similar settings in the geological record a total of 16 samples were examined contrary to stereotypes benthic communities are present but highly variable across the high productivity tract and are characterized by distinctive community structures benguela system document a decrease in body size of chemosymbiotic bivalves lucinids and percent of chemosymbionts and deposit feeders and an overall increase in species richness and epifaunal infaunal ratio this trend is in accordance with the upwelling facies gradient from diatomaceous ooze in areas of maximum upwelling intensity outward to the aerated but food abundant carbonate oozes and spatially coexisting phosphorite concentrations differences in seafloor oxygen concentration along with variable food availability played major roles in structuring the death assemblages under the benguela upwelling system the ecologic data provide ways to distinguish between facies of low and high shell production along an increasing oxygen gradient and also between assemblages with moderate and higher species richness associated with time averaging the data support the existence of a wider range of time averaging in the formation of molluscan sand and gravel samples in the northern benguela than previously appreciated given the scarcity of information on macrobenthic ecology from modern high productivity settings these death assemblages can represent a modern analog

a displaced neritic diatom delphineis karstenii in pelagic sediments of the southeast atlantic this paper documents the occurrence ofdelphineis karstenii a neritic diatom in pelagic sediments of the northern cape and southern angola basins southeast atlantic ocean maximum abundances are found in the southern angola basin although the source area appears to be the diatomaceous sediments which blanket much of the namibian continental shelf the observed pattern implies large scale displacement ofd karstenii valves first northward along the continental margin and then westward into deep waters transport evidently occurs in the surface waters of the benguela current which flow northward along the namibian coast and then turn westward away from the coast of angola and out into the angola basin these observations suggest thatdelphineis valves and perhaps other shallow water diatom valves may be displaced downslope on other continental margins failure to recognize such displacement could lead to incorrect ecological and paleoecological interpretations

diatom taphocoenoses in the coastal upwelling area off south west africa abstract the diatom floral composition of 124 sediment samples from the south east atlantic records the influence of coastal upwelling on sediment composition off south west africa inner shelf samples between 19 and 24 s are rich in diatom valves and the patterns of diatom species distribution in these samples are related to the coastal upwelling process comparison with recent phytoplankton data shows that the sediment assemblages preserve many of the important species of the diatom biocoenoses including chaetoceros resting spores delphineis karstenii thalassiosira eccentrica and thalassionema nitzschioides delphineis karstenii a pioneer species in enriched coastal water occurs nearshore and chaetoreros resting spores are widespread with highest relative abundance values in some more offshore samples the abundance of the thalassiosira eccentrica group and of thalassionema nitzschioides in sediment samples in and near walvis bay reflects the recurrence of intense upwelling off this part of the coast an abundance of large centric species has been reported in hydrological conditions characteristic of newly upwelled waters and correspondingly actinocyclus octonarius and some large coscinodiscus species occur in the sediments in nearshore patches or belts

a 220 000 year climatic record for the east equatorial atlantic ocean and equatorial africa evidence from diatoms and opal phytoliths in the zaire congo deep sea fan accumulation rates of microfossil associations are independent of each other and in addition to percentages give indispensable information about the significance of micropaleontological data marine diatoms reveal that coastal upwelling in the zaire fan region was strong during glacial stages and weaker during interglacial stages oceanic upwelling was intense in stages 6 and 2 and at the stage 5d 5c transition but not in stage 4 the benguela current did not penetrate into the gulf of guinea during the last 220 000 years the phfd index based on the contribution of freshwater diatoms and phytoliths is a measure of aridity in equatorial africa the production in the low salinity river plume was high in the most humid periods on land and low when the continent was arid on the long term nutrient supply of the zaire river to the ocean was probably larger in humid than in arid periods periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals except in the very humid interval with strong seasonal contrasts 35 000 20 000 years b p

the biogeography of major diatom taxa in southern ocean surface sediments 3 tropical subtropical species abstract this paper gives a modern circumscription of tropical subtropical diatoms regarding their relationship with sea surface temperatures sst and sea ice cover diatoms from 228 core top sediment samples collected from the southern ocean were studied to determine the geographic distribution of eight major diatom species taxa preserved in surface sediments generally located north of the subantarctic front the comparison of the relative contribution of diatom species with modern february sst and sea ice cover reveals species specific sedimentary distributions regulated both by water temperatures and sea ice conditions although selective preservation might have played some role their presence in surface and downcore sediments from the southern ocean are reliable indicators of high sst and poleward transport of waters from the tropical subtropical atlantic our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches

holocene variability in climate and oceanic conditions in the winter rainfall zone of south africa inferred from a high resolution diatom record from verlorenvlei

sediment supply and barrier dynamics as driving mechanisms of holocene coastal change for the southern north sea basin the combined effects of climate change and human impact lead to regional and local coastal responses that pose major challenges for the future resilience of coastal landscapes increasing the vulnerability of communities infrastructure and nature conservation interests using the suffolk coast southeast england as a case study we investigate the importance of sediment supply and barrier dynamics as driving mechanisms of coastal change throughout the holocene litho bio and chronostratigraphic methods are used to decipher the mechanisms of coastal change from the record preserved within coastal stratigraphy results suggest that local coastal configuration and sediment supply were the most influential in determining coastal change during the mid and late holocene against a background control of sea level rise the importance of sedimentological and morphological factors in shaping holocene coastal changes in the southern north sea basin must therefore be considered when using the database of evidence from this region as an analogue for future change under accelerated sea level rise

petrographic and isotope constraints on the origin of authigenic carbonate minerals and the associated fluid evolution in late permian coal measures bowen basin queensland australia authigenic carbonate minerals are ubiquitous throughout the late permian coal measures of the bowen basin queensland australia in the northern bowen basin carbonates include the following assemblages siderite i delta o 18 smow 11 4 to 17 delta c 13 pdb 5 3 to 120 fe mg calcite ankerite siderite ii mineral association delta o 18 smow 7 2 to 10 20 delta c 13 pdb 10 9 to 1 80 for ankerite and a later calcite delta o 18 smow 5 9 to 14 60 delta c 13 pdb 11 4 to 4 40 in the southern bowen basin the carbonate phase consists only of calcite delta o 18 smow 12 5 to 14 80 delta c 13 pdb 19 4 to 0 80 where it occurs extensively throughout all stratigraphic levels siderite i occurs in mudrocks and sandstones and predates all other carbonate minerals this carbonate phase is interpreted to have formed as an early diagenetic mineral from meteoric waters under cold climate and reducing conditions fe mg calcite ankerite siderite il occur in sandstones as replacement of volcanic rock fragments clay minerals illite smectite chlorite and kaolinite postdate ca fe mg carbonates and precipitation of the later calcite is associated with clay mineral formation the ca fe mg carbonates and later calcite of the northern bowen basin are regarded as having formed as a result of hydrothermal activity during the latest triassic extensional tectonic event which affected this part of the basin rather than deep burial diagenesis during the middle to late triassic as previously reported this hypothesis is based on the timing relationships of the authigenic mineral phases and the low delta o 18 values of ankerite and calcite together with radiometric dating of illitic clays and recently published regional geological evidence following the precipitation of the ca fe mg carbonates from strongly o 18 depleted meteoric hydrothermal fluids continuing fluid circulation and water rock interaction resulted in dissolution of these carbonate phases as well as labile fragments of volcaniclastic rocks subsequently the later calcite and day minerals precipitated from relatively evolved o 18 enriched fluids the nearly uniform delta o 18 values of the southern bowen basin calcite have been attributed to very low water rock ratio in the system where the fluid isotropic composition was buffered by the delta o 18 values of rocks c 2000 elsevier science b v all rights reserved