waxing and waning lyrical on hiatuses eocene quaternary indian ocean hiatuses as proxy indicators of water mass production the temporal distributions of cenozoic hiatuses in the indian ocean are reconsidered in the light of a new time framework developed by the paleoceanographic indian ocean synthesis on the basis of the temporal distribution of hiatus terminations eight 3 m y time slices were selected for plotting the paleogeographical distribution of hiatus terminations these distributions define areas of potential hiatus development which formed along flow paths of proto antarctic bottom water an analogue of modern antarctic bottom water and proto antarctic intermediate water an analogue of modern antarctic intermediate water expansion and contraction of these areas suggested changes in the volume of these water masses which modified the distibution patterns of erosive deepwater currents and corrosive bottom water consequently the spatial and bathymetric distribution of hiatus formation was altered age depth analysis of hiatuses from sites within post late eocene areas of potential hiatus development was used in conjunction with models of the behavior of unconformity boundaries within fluctuating water masses to construct waxing waning curves for proto antarctic bottom water and proto antarctic intermediate water these curves define volume changes in the production histories of these water masses which were related to the post late eocene glacial history of antarctica since the late oligocene the proto antarctic bottom water waned during intervals of increased glacial intensity whereas the proto antarctic intermediate water waxed during these intervals these relationships reversed during intervals of reduced glacial intensity including intervals where there is no evidence for antarctic glaciation this conflicts with interpretations made by other workers a comparison is made between the production histories of proto antarctric bottom water and northern component water an analogue of north atlantic deep water based on 13c for the miocene to pliocene

sedimentation at manop site h eastern equatorial pacific over the past 400 000 years climatically induced redox variations and their effects on transition metal cycling gravity cores recovered from manganese nodule project site h 6 33 n 92 49 w show marked downcore variations in the abundance of calcium carbonate organic carbon opal manganese and other components deposited over the past 400 000 years variations in the downcore abundance of organic carbon which ranges from 0 2 to 1 0 can be used to hindcast redox conditions in the surface sediments over this time the results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles downcore variations in solid phase mn ni and cu can be produced by such changes in redox conditions a model which predicts that solid phase mn can be trapped and buried when the mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and mn records and supports the reconstructed redox variations the history of redox variations at site h can be explained by changes with time in surface water productivity major productivity variations at the site occur over 100 kyr cycles with relatively higher productivity occurring during glacial stages thus quaternary climate changes influence surface water productivity redox conditions in sediments and the cycling of transition metals

slowdown of circumpolar deepwater flow during the late neogene evidence from a mudwave field at the argentine continental slope geochemical evidence from boreholes suggests enhanced transport of northern component water ncw to southern latitudes from about 6 ma onward however information on how this change in transport influenced the intensity and position of current systems is sparse here we use seismic reflection profiles interpreted together with bathymetric data to investigate current derived deposits at the central argentine margin upslope migrating mudwaves overlying a late miocene erosional unconformity provide evidence that circumpolar deepwater flow slowed down with the onset of ncw inflow during the last 3 ma changes in dimensions and migration rates of the waves are small indicating continuous bottom current flow conditions similar to today with only minor variations in flow speed suggesting that the deep western boundary current in the western south atlantic as observed today has been a pervasive feature of the global thermohaline circulation system during the plio pleistocene

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

kerguelen plateau quaternary late pliocene palaeoenvironments from diatom silicoflagellate and sedimentological data abstract gravity cores from the south kerguelen plateau contain sections representing two quaternary intervals 1

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

element accumulation rates in and growth histories of manganese nodules from the southwestern pacific basin abstract accretion rates and element accumulation rates of seven manganese nodules collected from the southwestern pacific basin during r v sonne cruise so 14 on a tahiti east pacific rise new zealand transect have been determined the accretion rates of the nodules lie in the range 3 5 6 0 mm 10 6 yr the highest rates correspond to areas with higher biogenic silica contents in the sediment suggesting a higher diagenetic contribution to the nodules in one nodule 143gb dated with 10 be nodule growth began at about 14 5 ma there is a change in structure of the nodule at 6 ma and concentric layers filled with detritus occur at 3 2 ma and 1 3 ma there is also a major change in the flux rates of the elements at the 6 ma time marker with the authigenic elements mn cu and ni showing greater accumulation rates in the outer zone and the detrital fraction al showing a greater accumulation rate in the inner zone the variations in the element accumulation rates probably reflect a change of abyssal circulation pattern at 6 2 ma however the precise nature of this change remains a matter for speculation

laboratory antarctica research contributions to global problems research in antarctica is becoming increasingly important in the large interdisciplinary studies of connections within the earth9s geosphere biosphere system four examples of broad research areas are discussed upper atmosphere research explores the sun earth interactions which are most intense in the polar regions the mass balance and dynamics of the large antarctic ice sheet and its paleoclimatic records recovered from deep ice cores are important indicators of past and present global changes antarctica and sediment cores from the southern ocean contain the history of inception and growth of the ice masses and their subsequent fluctuations and the long term history of paleoclimate the remarkable adaptations of antarctic biota to extreme cold and drought may allow through biotic monitoring the detection of changes in the ocean and climate of antarctica

temporal and spatial distributions of cold water corals in the drake passage insights from the last 35 000 years scleractinian corals have a global distribution ranging from shallow tropical seas to the depths of the southern ocean although this distribution is indicative of the corals having a tolerance to a wide spectrum of environmental conditions individual species seem to be restricted to a much narrower range of ecosystem variables one way to ascertain the tolerances of corals with particular focus on the potential impacts of changing climate is to reconstruct their growth history across a range of environmental regimes this study examines the spatial and temporal distribution of the solitary scleractinian corals desmophyllum dianthus gardineria antarctica balanophyllia malouinensis caryophyllia spp and flabellum spp from five sites in the drake passage which cross the major frontal zones a rapid reconnaissance radiocarbon method was used to date more than 850 individual corals coupled with u th dating an age range of present day back to more than 100 thousand years was established for corals in the region within this age range there are distinct changes in the temporal and spatial distributions of these corals both with depth and latitude and on millennial timescales two major patterns that emerge are 1 d dianthus populations show clear variability in their occurrence through time depending on the latitudinal position within the drake passage north of the subantarctic front d dianthus first appears in the late deglaciation 17 000 years ago and persists to today south of the polar front in contrast early deglacial periods with a few modern occurrences a seamount site between the two fronts exhibits characteristics similar to both the northern and southern sites this shift across the frontal zones within one species cannot yet be fully explained but it is likely to be linked to changes in surface productivity subsurface oxygen concentrations and carbonate saturation state 2 at locations where multiple genera were dated differences in age and depth distribution of the populations provide clear evidence that each genus has unique environmental requirements to sustain its population

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

thorium and uranium isotopes in a manganese nodule from the peru basin determined by alpha spectrometry and thermal ionization mass spectrometry tims are manganese supply and growth related to climate thorium and uranium isotopes were measured in a diagenetic manganese nodule from the peru basin applying alpha and thermal ionization mass spectrometry tims alpha counting of 62 samples was carried out with a depth resolution of 0 4 mm to gain a high resolution230thexcess profile in addition 17 samples were measured with tims to obtain precise isotope concentrations and isotope ratios we got values of 0 06 0 59 ppb 230th 0 43 1 40 ppm 232th 0 09 0 49 ppb 234u and 1 66 8 24 ppm 238u the uranium activity ratio in the uppermost samples 1 6 mm and in two further sections in the nodule at 12 5 1 0 mm and 27 3 33 5 mm comes close to the present ocean water value of 1 144 0 004 in two other sections of the nodule this ratio is significantly higher probably reflecting incorporation of diagenetic uranium the upper 25 mm section of the mn nodule shows a relatively smooth exponential decrease in the230thexcess concentration tims the slope of the best fit yields a growth rate of 110 mm ma up to 24 5 mm depth the section from 25 to 30 3 mm depth shows constant230thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule from 33 to 50 mm depth the growth rate is approximately 60 mm ma two layers in the nodule with distinct laminations 11 15 and 28 33 mm depth probably formed during the transition from isotopic stage 8 to 7 and in stage 5e respectively the mn fe ratio shows higher values during interglacials 5 and 7 and lower ones during glacials 4 and 6 a comparison of our data with data from adjacent sediment cores suggests a a variable supply of hydrothermal mn to sediments and mn nodules of the peru basin or b suboxic conditions at the water sediment interface during periods with lower mn fe ratios

the influence of suboxic diagenesis on the formation of manganese nodules in the clarion clipperton nodule belt of the pacific ocean abstract polymetallic nodules and a single fe mn crust from the clarion and clipperton zone ccz of the equatorial eastern pacific have been analyzed to determine their chemical and mineralogical compositions icp oes analyses of bulk nodules from the ccz indicate that the nodules formed under oxic diagenetic conditions with typical mn fe ratios of 4 6 ni cu values of 2 3 wt co contents of 0 12 0 17 wt however detail analyses of individual growth layers by electron microprobe analyses empa reveal much larger chemical heterogeneity of individual layers with mn fe ratios ranging from 800 two different genetic types of layers can be distinguished layer type 1 dense layer with average mn fe ratios of 1 80 average ni cu of 0 81 wt co contents of 0 30 wt hydrogenetic metal precipitation from oxic waters these layers consist of fe vernadite mno2 epitaxially intergrown with feroxyhyte feooh nanoparticles layer type 2 growth structures dendritic growth structures and dense layers with average mn fe ratios of 96 ni cu of 3 9 wt co contents of 0 08 wt and a distinct ni cu maximum of 6 51 wt at a mn fe ratio of 56 suboxic diagenetic metal precipitation from suboxic pore waters type 2 layers mainly consist of turbostratic phyllomanganates such as 10 a vernadite 7 a vernadite and todorokite are minor compounds mixed layer type 3 these layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm thin layers of low or high reflectivity the mn fe ratios of this material range between 3 and 11 ni cu of 1 4 6 wt and co contents are between 0 02 and 0 77 wt in most cases these growth structures represent a mixture of type 1 and 2 layers x ray photoelectron spectroscopy xps of the recent outermost nm layers of nodules top rim and bottom side indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water the mixed type ccz nodules are interpreted to consist of an oxic hydrogenetic and a suboxic diagenetic end member calculations of the proportions of the individual layer end members show that suboxic layers make up about 50 60 of the chemical inventory of the ccz nodules whereas oxic hydrogenetic layers comprise about 35 40 the remaining part 5 10 consists of incorporated sediment particles occurring along cracks and pores these results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern ccz this is probably due to fluctuating bioproductivity in the equatorial pacific surface waters during glacial interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments furthermore reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near surface sediments our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation

60 myr records of major elements and pb nd isotopes from hydrogenous ferromanganese crusts reconstruction of seawater paleochemistry we compare the time series of major element geochemical and pb and nd isotopic composition obtained for seven hydrogenous ferromanganese crusts from the atlantic indian and pacific oceans which cover the last 60 myr average crust growth rates and age depth relationships were determined directly for the last about 10 myr using be 10 be 9 profiles in the absence of other information these were extrapolated to the base of the crusts assuming constant growth rates and constant initial be 10 be 9 ratios due to the lack of additional information co contents have also been used previously to estimate growth rates in co rich pacific and atlantic seamount crusts puteanus and halbach 1988 a comparison of be 10 be 9 and co based dating of three co rich crusts supports the validity of this approach and confirms the earlier chronologies derived from extrapolated be 10 be 9 based growth rates back to 60 ma our data show that the flux of co into co poor crusts has been considerably lower the relationship between growth rate and co content for the co poor crusts developed from these data is in good agreement with a previous study of a wider range of marine deposits manheim 1986 the results suggest that the co content provides detailed information on the growth history of ferromanganese crusts particularly prior to 10 12 ma where the be 10 based method is not applicable the distributions of pb and nd isotopes in the deep oceans over the last 60 myr are expected to be controlled by two main factors a variations of oceanic mixing patterns and flow paths of water masses with distinct isotopic signatures related to major paleogeographic changes and b variability of supply rates or provenance of detrital material delivered to the ocean linked to climate change glaciations or major tectonic uplift the major element profiles of crusts in this study show neither systematic features which are common to crusts with similar isotope records nor do they generally show coherent relationships to the isotope records within a single crust consequently any interpretation of time series of major element concentrations of a single crust in terms of paleoceanograghic variations must be considered with caution this is because local processes appear to have dominated over more basin wide paleoceanographic effects in this study co is the only element which shows a relationship to pb and nd isotopes in pacific crusts a possible link to changes of pacific deep water properties associated with an enhanced northward advection of antarctic bottom water from about 14 ma is consistent with the pb but not with the nd isotopic results the self consistent profiles of the pb and nd isotopes suggest that postdepositional diagenetic processes in hydrogenous crusts including phosphatization events have been insignificant for particle reactive elements such as pb be and nd isotope time series of pb and nd show no systematic relationships with major element contents of the crusts which supports their use as tracers of paleo seawater isotopic composition

carbonate preservation history in the peru basin paleoceanographic implications we studied preservation dissolution cycles and paleoproductivity in eight sediment cores from the peru basin south of the highly productive surface waters of the eastern equatorial pacific stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy sediment cores which span the last 8 m y were retrieved during cruise 79 with rv sonne close to the carbonate compensation depth ccd in general sediments show pacific type carbonate cycles we interpret a pronounced carbonate peak between 6 and 7 ma as the result of a western and northern extension of the highly productive peru current decreased carbonate contents from the late miocene to the late pliocene might be associated with a slow contraction of the latitudinal extent of the high productivity belt north of the study areas during the pliocene carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets which should have been associated with pulsations of the antarctic ice cap an abrupt collapse of the carbonate system occurred at 2 4 ma higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation during the quaternary carbonate fluxes are high during glacials and low during interglacials large amplitude variations with long broad minima and maxima associated with small migrations of the lysocline and the ccd 200 m are indicative of the preservation dissolution history in the peru basin during the early pleistocene climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record during the last 800 kyr variability in the carbonate record was dominated by the 100 kyr eccentricity cycle fluxes of biogenic material calcium carbonate organic carbon opal and barium were greatest during glacials which imply higher productivity and export production of the peru current during cold climatic periods dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate after the mid brunhes event 400 ka we observe a plateaulike shift to enhanced dissolution and to intensified productivity

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

past hydrographic and climatic changes in the subantarctic zone of the south atlantic the pleistocene record from odp site 1090 abstract pleistocene summer sea surface temperatures ssst have been reconstructed on a composite core section recovered in the subantarctic zone of the southern ocean from planktonic foraminifers applying the modern analog technique the composite consists of core ps2489 2 and the sections recovered at odp site 1090 and documents the last 1 83 ma three distinct climatic periods can be identified that mirror the pleistocene development of the southern ocean hydrography cold climatic conditions prevailed at 43 s during glacial as well as during interglacial periods during the early pleistocene 1 83 0 87 ma indicating a northward shift of isotherms that characterize the present day polar front zone by about 7 of latitude evidence shows a strong linkage between southern ocean and low latitude climate during that interval time between the mid pleistocene revolution ca 0 9 ma and the mid brunhes event ca 0 4 ma we observe higher amplitude fluctuations in the ssst between glacial and interglacial periods corresponding to the temperature range between the present polar front and subantarctic front these climatic variations have been related to changes in the northern hemisphere ice sheets the past 0 4 ma are characterized by strong ssst variations of up to 8 c between glacials and interglacials only during the climatic optima stages 11 3 9 3 7 5 7 1 5 5 and the early holocene ssst exceeded present ssst at the core locality 10 2 c although the carbonate dissolution record exhibits high variability during the pleistocene it can be shown that ssst estimates were not significantly biased the mid brunhes dissolution cycle as well as the mid pleistocene enhanced carbonate preservation appear to belong to a global long term variability in carbonate preservation

scotia sea regional tectonic evolution implications for mantle flow and palaeocirculation abstract the scotia sea and surrounding scotia arc have evolved over the past 40 ma by extension behind an east migrating subduction zone at the boundary between the south american sam and antarctic ant plates the considerable data set now available regional geology and geophysics earthquake seismology satellite altimetry global plate analyses suggest why east migrating subduction began what has been the driving force that has sustained it and what other processes have controlled the mode of back arc extension in the scotia sea a suite of six reconstructions has been developed based on this data set the reconstruction to 40 ma creates a compact cuspate continental connection between south america and the antarctic peninsula at the subducting pacific margin with fragments now dispersed around the scotia arc occupying positions within it compatible with their known geology the driving force has been subduction of south american ocean floor which began as a result of southward migration of the pole of south american antarctic plate rotation and a key modulator of back arc extension has been collision of ridge crest sections of the south american antarctic plate boundary with the east advancing trench cenozoic regional tectonic evolution has two other likely consequences which greatly increase its importance firstly this region saw the tectonic disruption of the final barrier to complete circum antarctic deep water flow that may have had a profound effect on palaeoclimate secondly it is possible that the rapid roll back of the hinge of subduction is related to shallow eastward flow in the sub lithospheric mantle both of these consequences are explored the reconstructions show that rapid roll back of the subduction hinge averaging 50 mm a over the last 40 ma with respect to the south american plate has been a feature of all of scotia sea evolution and provide a history of motion of several oceanic microplates most of which are now welded together within the scotia sea this will guide the location of seismometers and or dredge hauls to test the hypothesis of shallow mantle flow and help interpret the results the reconstructions also allow an assessment of the creation of deep water pathways that would have permitted the development of the present day antarctic circumpolar current acc an early miocene onset within the period 22 17 ma seems likely for the acc depending on the structure and palaeo elevation of davis bank and aurora bank sections of the north scotia ridge however the study shows there was a delay of one or more million years between initial provision of a deep water pathway and the major mid miocene change in global climate involving the general level of antarctic glaciation that may have been related if these changes were related then the delay suggests that other factors possibly rough elevated ocean floor but also non tectonic factors such as atmospheric co2 were important in determining palaeoclimate

coarse grained terrigenous sediment deposition on continental rise drifts a record of plio pleistocene glaciation on the antarctic peninsula sediment drifts on the continental rise are located proximal to the western side of the antarctic peninsula and recorded changes in glacial volume and thermal regime over the last ca 15 m y at ocean drilling program odp site 1101 leg 178 which recovered sediments back to 3 1 ma glacial interglacial cyclicity was identified based on the biogenic component and sedimentary structures observed in x radiographs magnetic susceptibility and lithofacies descriptions glacial intervals are dominated by fine grained laminated mud and interglacial units consist of bioturbated muds enriched in biogenic components from 2 2 to 0 76 ma planktonic foraminifera and calcareous nannofossils dominate in the interglacials suggesting a shift of the antarctic polar front apf to the south near the drifts prior to 2 2 ma cyclicity cannot be identified and diatoms dominate the biogenic component and high percent opal suggests warmer conditions south of the apf and reduced sea ice over the drifts analyses of the coarse grained terrigenous fraction pebbles and coarse sand from sites 1096 and 1101 record glaciers at sea level releasing iceberg rafted debris ird throughout the last 3 1 m y analyses of quartz sand grains in ird with the scanning electron microscope sem show an abrupt change in the frequency of occurrence of microtextures at similar to 1 35 ma during the late pliocene to early pleistocene the population of quartz grains included completely weathered grains and a low frequency of crushing and abrasion suggesting that glaciers were small and did not inundate the topography debris shed from mountain peaks was transported supraglacially or englacially allowing weathered grains to pass through the glacier unmodified during glacial periods from 1 35 0 76 ma glaciers expanded in size the hid flux was very high and dropstones have diverse lithologies conditions resembling those at the last glacial maximum lgm have been episodically present on the antarctic peninsula since similar to 0 76 ma quartz sand grains show high relief fracture and abrasion common under thick ice and the ird flux is low with a more restricted range of dropstone lithologies

late mesozoic and cenozoic stratigraphy and geological history of the south atlantic high latitudes abstract the complex analysis of various organic remains in upper mesozoic and cenozoic deposits of the southwest atlantic legs 36 40 71 and piston cores has led to a reliable subdivision of the sedimentary cover in its high latitudinal part planktonic foraminifers and calcareous nannoplankton dominate the biostratigraphy of the cretaceous and paleogene from the oligocene the leading role in the subdivision of sediments gradually passed to siliceous microfossils that provided an extremely detailed stratigraphy in the late cenozoic the history of oceanic subsidence sedimentation hiatuses and ccd fluctuations within the falkland plateau have been reconstructed on the basis of the biostratigraphic scheme obtained an attempt to trace cretaceous and cenozoic relative climatic fluctuations according to the changing in planktonic foraminiferal assemblages has been made oceanic and continental data combined have specified some aspects in the geological evolution of the high latitude south atlantic basin from its opening to date this paper emphasizes the importance of the circum antarctic current in paleoclimatic and sedimentational changes as well as the onset of the antarctic cover glaciation

small scale mantle convection produces stratigraphic sequences in sedimentary basins cyclic sedimentary deposits link stratigraphic sequences that are now geographically distant but were once part of the same depositional environment some of these sequences occur at periods of 2 to 20 million years and eustatic sea level variations or regional tectonic events are likely causes of their formation using numerical modeling we demonstrate that small scale mantle convection can also cause the development of stratigraphic sequences through recurrent local and regional vertical surface movements small scale convection driven stratigraphic sequences occur at periods of 2 to 20 million years and correlate only at distances up to a few hundred kilometers these results suggest that previous sequence stratigraphic analyses may contain erroneous conclusions regarding eustatic sea level variations

tectono sedimentary analysis of a complex extensional neogene basin formed on thrust faulted northern apennines hinterland radicofani basin italy abstract large nw se oriented neogene quaternary structural depressions up to about 200 km long and 25 km wide have developed on the western side hinterland of the northern apennines over thrust substrate the depressions are now for the most part laterally bounded by normal faults and are longitudinally separated into basins by transfer zones a debate exists in the literature as to whether these basins have developed as half graben under a predominantly extensional regime since late miocene or as thrust top basins under a predominantly compressional regime that has continued until the pleistocene the radicofani basin is one of the best preserved basins it developed mainly during the late miocene early pliocene in the southern half of the siena radicofani structural depression and is now bounded on the east by normal faults that transect a thrust anticline nose in the substrate to the north by a substrate high or transfer zone and to the south and west by quaternary igneous volcanic edifices the basin experienced variable differential tectonic and associated sedimentation along linking normal boundary faults along its eastern margin it shows the development of thick 600 m alluvial fans that developed in relay areas between boundary faults and transverse faults and transfer zones well exposed sections generally show upward transitions from conglomeratic alluvial fans to shoreface sandstone to offshore mudstones locally the transition is marked by deltas primarily characterised by thick gravelly sandy stacked cross sets the thicker sandy gravel to gravelly sand cross sets 5 8 m thick are interpreted as gilbert type deltas interstratified thinner 0 5 1 m thick generally openwork gravelly strata are part of delta topset assemblages and probably represent prograding fluvial bars tectonic movements provided the accommodation space for the total 2700 m thick basin fill sea level fluctuations that led to the repeated development of the cross sets may also have been influenced by climatic or eustatic changes possibly related to the effects of early antarctic glaciations some features of the radicofani basin can be found in both extensional and compressional basins however the position of the basin in the mountain chain and the development of alluvial fans fandeltas and associated deposits along the main boundary fault combined with structural evidence from seismic lines show that during the early pliocene this basin best conforms to existing models of half graben

the late miocene to early pliocene climate transition in the southern ocean abstract we have constructed a relatively high resolution 5 10 kyr globigerina bulloides stable isotope record from ocean drilling program site 1088 south atlantic sector of the southern ocean together with the two published records from the high latitudes of the southern hemisphere that each span at least a portion of this interval of time we begin to assemble a spatial picture of sea surface hydrography during the late miocene early pliocene climate transition 8 3 ma we hypothesize that meridional movements in the frontal zones polar front and subtropical convergence with their impact on hydrographic gradients would be evident in temporal changes in the planktonic foraminiferal stable isotopic gradients among the sites our results indicate that there were no large changes in 18o gradients during the interval of study relatively small changes such as a gradual warming of about 3 4 c at site 1088 during the late miocene fall well within the realm of modern ocean seasonality in this region the early pliocene 18o records largely parallel the global decrease defined by benthic foraminifera in the deep pacific suggesting no amplified warming of surface waters in the southern ocean the planktic 13c records vary positively with the 18o records both in the long term trend as well as on the scale of individual data points we believe that this association reflects primarily reduced nutrient utilization during warmer intervals although a small component of the signal would also be consistent with reduced carbon isotope fractionation during air sea gas exchange during relatively warmer conditions if correct this argument would have implications for carbon cycling during the early pliocene and would support scenarios of elevated co2 levels

changes in mid depth north atlantic and mediterranean circulation during the late pliocene isotopic and sedimentological evidence abstract presently the intermediate depths of the north atlantic ocean are occupied by a great lens of warm saline water whose source is the mediterranean sea this water flows both westward and northward finally entering the norwegian sea where it may contribute to the formation of north atlantic deep water the late neogene history of mediterranean outflow in the atlantic can be monitored at dsdp ipod site 548 on the continental slope southwest of ireland using benthic foraminifera oxygen isotope values isotopic data from 154 samples indicate that mediterranean water was absent from the mid depth north atlantic from 3 4 to 3 2 ma ago however at about 2 9 ma ago the isotopic values at site 548 diverge from those recorded from the deep north atlantic and they can be interpreted to indicate the appearance of a new water mass possibly mediterranean water in the north atlantic water column this appearance may be related to climatic changes that occurred around the mediterranean basin at about 2 9 ma ago the analysis of 189 samples for grain size distributions shows that a significant increase in the silt size fraction occurs at the same level that isotopic analysis indicates a change in bottom waters at site 548 the grainsize data support the hypothesis that mid depth water mass changes occurred at about 2 9 ma ago

middle and late quaternary depositional sequences and cycles in the eastern mediterranean although most of the quaternary sediments of the eastern mediterranean appear reworked extensive areas of hemipelagic sediments occur mainly in the central part of the basin mediterranean ridge the most obvious character of these muddy sediments is the numerous changes in colour they result from the organic carbon content as well as from concentration and chemical form of metallic elements mn fe cu zn the succession of coloured layers is arranged into sequences developed between two sharp contacts a complete sequence involves five lithofacies from an oxidized layer at the base to a reduced sapropel at the top and displays progressive internal changes of colour from ochre beige greyish beige grey and black layers several sequence variants top truncated base truncated recurrent are identified these sequences are a consequence of changes in oceanographic conditions i e from oxidizing to reduced environments resulting in different organic and mineral contents based on detailed studies of quaternary sediments collected by coring a synthesized standard succession representative of the ordered sequences in the eastern mediterranean is proposed from about 650 000 yr as deduced from the calculated rate of sedimentation of 1 7 mm 1000yr 1 this succession appears modulated by cyclic events large scale periods 200 000 yr of reduced and oxidized sequences correlate with major alternate phases of flooding and reduced flow of the nile river during the quaternary subsequent sequences of shorter time scale 20 000 50 000 yr results from two factors heaviest monsoons leading to an increase of the influx of the nile river and global climatic changes eurasian ice sheet meltwater these two factors act synchronously or independently along the studied time span these interplaying factors result in periodic stages of increasingly restricted conditions in the basin and explain the complexity of the eastern mediterranean succession at least since 650 000 yr ago

seismic evidence for early tertlary bottom current controlled deposition in the charlie gibbs fracture zone abstract buried mounded and acoustically transparent sediment bodies banked up against a basement ridge at the eastern end of the charlie gibbs fracture zone are interpreted as a type of contourite drift as they are probably of eocene palaeocene age their origin has implications for the little known deep circulation pattern in the ne atlantic during this period possible sources for the bottom currents responsible for these drifts include labrador sea water norwegian sea overflow water antarctic bottom water or a gulf stream deep gyre system the preferred source is an early development of antarctic bottom water or an arm of a gulf stream gyre flowing eastwards through the fracture zone

latest miocene benthic δ 18 o changes global ice volume sea level and the messinian salinity crisis oxygen isotope evidence indicates high but variable 18o values in benthic foraminiferal calcite during the latest miocene and earliest pliocene these high values may represent increases in global ice volume and associated sea level fall the 18o record resembles glacial interglacial cycles but with only one third the amplitude of the late pleistocene signal this variability may reflect instability in the antarctic ice sheet and palaeomagnetic correlation points to an isotopic event coinciding with the isolation and desiccation of the mediterranean basin during the latest messinian

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

coupled productivity and carbon isotope records in the southwest pacific ocean during the late miocene early pliocene biogenic bloom biogenic components of sediment accumulated at high rates beneath frontal zones of the indian and pacific oceans during the late miocene and early pliocene the 13c of bulk and foraminiferal carbonate also decreased during this time interval although the two observations may be causally linked and signify a major perturbation in global biogeochemical cycling no site beneath a frontal zone has independent records of export production and 13c on multiple carbonate phases across the critical interval of interest deep sea drilling project dsdp site 590 lies beneath the tasman front tf an eddy generating jetstream in the southwest pacific ocean to complement previous 13c records of planktic and benthic foraminifera at this location late neogene records of caco3 mass accumulation rate mar ca ti ba ti al ti and of bulk carbonate and foraminiferal 13c were constructed at site 590 the 13c records include bulk sediment bulk sediment fractions 63 m and 5 25 m and the planktic foraminifera globigerina bulloides globigerinoides sacculifer with and without sac and orbulina universa using current time scales caco3 mars ca ti al ti and ba ti ratios are two to three times higher in upper miocene and lower pliocene sediment relative to overlying and underlying units a significant decrease also occurs in all 13c records all evidence indicates that enhanced export production the biogenic bloom extended to the southwest pacific ocean between ca 9 and 3 8 ma and this phenomenon is coupled with changes in 13c the chron c3ar carbon shift however caco3 mars peak ca 5 ma whereas elemental ratios are highest ca 6 5 ma foraminiferal 13c starts to decrease ca 8 ma whereas bulk carbonate 13c begins to drop ca 5 6 ma temporal discrepancies between the records can be explained by changes in the upwelling regime at the tf perhaps signifying a link between changes in ocean atmosphere circulation change and widespread primary productivity

pore water profiles and numerical modelling of biogeochemical processes in peru basin deep sea sediments abstract an extensive set of pore water profiles including o 2 no 3 no 2 nh 4 po 4 3 fe 2 mn 2 so 4 2 sio 4 4 ph and alkalinity as well as solid phase data on organic carbon content and porosity in 18 sediment cores obtained from five areas in the peru basin rv sonne 106 expedition in 1996 is presented the pore water profiles indicate that early diagenesis progresses through oxygen respiration denitrification and manganese iv reduction while the subsequent redox states iron iii reduction sulphate reduction and methanogenesis cannot be observed from the dissolved phase in these deep sea sediments a numerical diagenetic model was applied to the data in order to derive parameters such as the depositional flux of metabolizable organic matter or the bioturbation intensity that control the geochemical conditions in the deep sea floor and could not be obtained directly by measurements moreover the numerical simulations show that even those pore water no 3 profiles that decline non linearly to zero concentration are not compatible with a steady state assumption they can be explained only by transient downward progression of a nitrate front

climatic evolution of the southern ocean during the pliocene epoch from 4 8 to 2 6 million years ago abstract we studied the paleoclimatic history of the southern ocean during the pliocene before the intensification of northern hemisphere glaciation at 2 4 ma from isotopic and sedimentologic data from odp leg 114 sites subantarctic south atlantic relatively warm climatic conditions prevailed in the southern ocean during the early early pliocene between 4 6 and 4 2 ma as evidenced by benthic and planktonic 18 o values that were generally less than the holocene despite this warmth significant ice rafting episodes are recorded at several drill sites and piston core locations throughout the southern ocean this interval correlates with a eustatic highstand and represents a climatic optimum for the southern ocean when low and mid latitude species migrated into the antarctic and surface waters were warmer than at present although it is generally agreed that this interval was warm in the southern hemisphere divergent opinions exist as to whether this warming led to the partial decay or growth of the antarctic ice sheet a distinct mid pliocene cooling occurred between 3 5 and 3 2 ma as evidenced by an increase in 18 o values of planktonic and benthic foraminifers in hole 704a and by faunal changes indicative of progressive cooling of antarctic surface waters and development of biotic provinciality in the southern ocean during the late pliocene 3 25 2 6 ma planktonic and benthic 18 o values commonly exceeded those of the holocene and several distinct cooling and or ice volume events occurred during the late gauss chron most notably at 2 9 and 2 63 ma faunal studies suggest several northward advances of the polar front zone and expansion of sea ice in the antarctic during this period these events preceded the major climatic transition at 2 4 ma when the pfz moved to the north sea ice expanded in the antarctic and glaciation intensified in both hemispheres

late neogene paleoceanography and paleoclimatology of the gulf of aden region based on calcareous nannofossils quantitative study of climatically sensitive nannofossils in the sediments of the gulf of aden has provided a climatic and oceanographic scenario for the northwestern indian ocean during the late neogene the surface water temperature was relatively cold during the latest middle miocene to late miocene 10 7 to 6 32 ma with a probable warm interval in the early late miocene 9 82 to 8 49 ma this cooling is attributed to increased upwelling in the northwestern indian ocean the surface water was relatively warm from the latest late miocene to the middle of the late pliocene 6 32 to 2 59 ma the most intense cooling took place during the late pliocene to early pleistocene 2 59 to 1 69 ma intense upwelling during this interval coincides with worldwide climatic deterioration a probable short warm interval 1 69 to 1 59 ma followed this cold interval in the pleistocene the surface water was cold from 1 59 to 1 00 ma and from 0 61 to 0 24 ma and warm from 1 00 to 0 61 ma and after 0 24 ma

late miocene early pliocene stratigraphy and paleoceanography of the south atlantic and southwest pacific oceans a synthesis the stratigraphy and paleoceanography of the late miocene and early pliocene have been examined at six sites in the south atlantic and southwest pacific oceans deep sea drilling project dsdp sites 284 516a 519 588 and 590 and two piston cores from chain cruise 115 a consistent stratigraphy was developed among sites using graphic correlation which resulted in age models for all sites that are tied to the revised paleomagnetic time scale of berggren et al 1985 applying these chronologies we assessed latitudinal and interocean contrasts in the stratigraphic ranges of late miocene early pliocene planktonic foraminiferal and nanno fossil datums salient stratigraphic results include 1 the last appearance datum lad of globoquadrina dehiscens is a late miocene 6 4 ma event in the subtropics and is not useful for the placement of the miocene pliocene m p boundary in this biogeographic province 2 the first appearance datum fad of globorotalia crassaformis occurred at 5 1 ma in the south atlantic near the m p boundary suggesting that gr crassaformis may have first evolved in the south atlantic and later migrated to other regions 3 in the southwest pacific the fads of gr margaritae 5 97 ma gr puncticulata 5 09 ma and gr crassaformis 4 87 ma are significantly time transgressive between temperate and warm subtropical regions time lags of 1 0 m y were required for these species to adapt to physical and or biotic conditions peripheral to their endemic biogeographic provinces 4 between the subtropics of the south atlantic and southwest pacific many planktonic foraminiferal datums fad of dentogloboquadrina altispira gr cibaoensis gr conomiozea gr margaritae and gq dehiscens and lad of gr cibaoensis markedly depart from the correlation suggested by magnetostratigraphy indicating that these datum levels are unreliable for correlation between these ocean basins 5 in contrast available calcareous nannofossil datum levels fall on or near the paleomagnetic correlation line indicating synchroneity of events within the subtropics 6 biostratigraphic magnetic and 87sr 86sr correlation between sites 588 and 519 and the m p neostratotype at capo rossello sicily suggests that the base of the zanclean stratotype occurs at 5 1 5 0 ma in the lower reversed subchron of the gilbert about 2 3 105 years above the gilbert chron 5 boundary oxygen isotopic results from dsdp sites 284 519 and ch115 piston cores confirm a prolonged benthic 18o increase in the latest miocene between 5 6 and 5 0 ma as originally proposed by shackleton and kennett 1975 at dsdp site 588 the benthic 18o record in the latest miocene is marked by high frequency fluctuations with amplitude variations of 0 5 and a long period wavelength component of 400 000 years maximum 18o values however occurred during the late miocene kapitean stage between 5 5 and 5 1 ma the late miocene 18o changes resulted from mid and high latitude cooling and pulses of ice sheet expansion and contraction glacial events were most intense during the latest miocene kapitean stage and occurred at 5 50 5 35 ma and at 5 10 ma glacial events are estimated to have lowered sea level by 40 to 60 m and contributed to the isolation and desiccation of the mediterranean basin during the late messinian interglacial conditions prevailed at 5 2 ma and between 5 0 and 4 1 ma ihe early pliocene the beginning of the pliocene was marked by changes in many proxy climatic indicators at all sites suggesting a prolonged interval of warm interglacial conditions between 5 0 and 4 1 ma during the earliest pliocene supplementary tables are available with entire article onmicrofiche order from american geophysical union 2000florida avenue n w washington dc 20009 documentp86 001 2 50 payment must accompany order

messinian deep water turbidites and glacioeustatic sea level changes in the north atlantic linkage to the mediterranean salinity crisis our benthic foraminiferal data clearly indicate eight layers of deep water turbidites during the messinian mtl 1 8 and one in the early pliocene ptl 1 in ocean drilling program leg 105 site 646b these deep water tuibidite deposits are characterized by highly concentrated agglutinated marsh benthic foraminifera e g trochammina cf squamata ammotium sp a miliammina fusca rounded quartz polished thick walled benthic foraminifera wood fragments plant seeds plant fruit and highly concentrated mica and are interbedded with sediments containing deep water benthic faunas we suggest these turbidites deposited during sea level low stands 80 100 m below sea level and their ages are tentatively correlated to 6 59 6 22 6 01 5 89 5 75 5 7 5 65 5 60 and 5 55 ma respectively based on the messinian oxygen isotope enrichments at site 552a of deep sea drilling project leg 81 the turbidites layers during the late messinian coeval with frequent climate changes suggested by six oxygen enrichment excursions of site 552a may have been in part linked to the late messinian evaporite deposits in the mediterranean basin the most profound climate changes at 5 75 and 5 55 ma may have been related to the lower and upper evaporites in the mediterranean basin an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd apend typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 96pa00572 messinian deep water turbidites and glacioeustatic sea level changes inthe north atlantic linkage to the mediterranean salinity crisis jijunzhang and david b scott diskette may be ordered from americangeophysical union 2000 florida avenue n w washington d c 20009 15 00 payment must accompany order

paleo oceanography global ocean evolution paleoceanography one of the youngest branches of earth sciences is concerned with the development of oceanic circulation through geologic time this is a multifaceted and integrated endeavor since none of the subdisciplines is easily separated from the others the field is holistic in character and includes the history and effects of bottom intermediate and surface circulation patterns planktonic and benthonic biogeographic development and rates of organic evolution the history of biogenic productivity and dissolution and their effect on sediment distribution and the consequences of sea level change paleoceanography was largely born of the deep sea drilling project dsdp and continues to be nourished by it because problems are of global scope the appetite for new sediment core material is large and is being supplied by numerous expeditions of dsdp this article is a brief overview of a number of advances that have occurred in paleoceanography and related fields during the period from 1979 to 1982 because of page limitations all publications cannot be cited which is not meant to indicate any lack of importance

a geochemical model of the peru basin deep sea floor and the response of the system to technical impacts a geochemical model of the peru basin deep sea floor based on an extensive set of field data as well as on numerical simulations is presented the model takes into account the vertical oscillations of the redox zonation that occur in response to both long term glacial interglacial and short term el nino southern oscillation enso time scale variations in the depositional flux of organic matter field evidence of reaction between the pore water no3 and an oxidizable fraction of the structural fe ii in the clay mineral content of the deep sea sediments is provided the conditions of formation and destruction of reactive clay fe ii layers in the sea floor are defined whereby a new paleo redox proxy is established transitional no3 profile shapes are explained by periodic contractions and expansions of the oxic zone ocean bottom respiration on the enso time scale the near surface oscillations of the oxic suboxic boundary constitute a redox pump mechanism of major importance with respect to diagenetic trace metal enrichments and manganese nodule formation which may account for the particularly high nodule growth rates in this ocean basin these conditions are due to the similar depth ranges of both the o2 penetration in the sea floor and the bioturbated high reactivity surface layer hrsl all against the background of enso related large variations in depositional corg flux removal of the hrsl in the course of deep sea mining would result in a massive expansion of the oxic surface layer and thus the shut down of the near surface redox pump for centuries which is demonstrated by numerical modeling

tectonics and sedimentary environment of the north scotia ridge region revealed by side scan sonar the north scotia ridge is a series of islands and submarine ridges extending 2000 km from tierra del fuego to south georgia in the western south atlantic the ridge forms the elevated northern tectonic margin of the scotia sea and accommodates e w sinistral strike slip motion at the south american scotia plate boundary existing studies have shown that the northern flank of the north scotia ridge is a large and continuous accretionary prism formed during presumed mid late cenozoic n s convergence in this study we present long range side scan sonar gloria images and seismic reflection profiles which show the structural style of the accretionary prism for the first time the youngest accreted sediments show a uniform fabric of initial deformation symmetric gently asymmetric folds of 1 4 km wavelength which has been subsequently disrupted at shallower depths by additional shortening and uplift between 52 o 459w and 50 o 30 9 w the deformation front is exposed at the sea floor and the falkland trough retains the appearance of an active convergent margin elsewhere however the deformation front is buried beneath younger undeformed drift sediments indicating that convergence has ceased gloria sonographs also show geological features consistent with current control of sedimentation non deposition and erosion beneath the antarctic circumpolar current in particular this study describes current influenced sedimentation in the falkland trough and steep sided eroded depressions and diffuse slope parallel fabric on the elevated falkland plateau

transition from the cretaceous ocean to cenozoic circulation in the western south atlantic a twofold reconstruction abstract the cretaceous oceanic circulation has been quite different from the modern with a different distribution of the continents on the globe this has resulted in a much lower temperature gradient between poles and equator we have studied seismic reflection data and used numerical simulations of atmosphere and ocean dynamics to identify important steps in modifications of the oceanic circulation in the south atlantic from the cretaceous to the cenozoic and the major factors controlling them starting in the albian we could not identify any traces of an overturning circulation for the south atlantic although a weak proto antarctic circumpolar current acc was simulated no change in circulation was observed for the paleocene early eocene south atlantic which indicated that this period has witnessed a circulation similar to the albian and cenomanian turonian circulation the most drastic modifications were observed for the eocene oligocene boundary and the oligocene early miocene with the onset of an acc and atlantic meridional overturning circulation amoc and hence southern sourced deep and bottom water masses in the western south atlantic a modern amoc which intensified in strength after closure of the central american seaway cas and a strong acc have resulted in current controlled sedimentary features and wide spread hiatusses in the south atlantic since the middle miocene the opening of drake passage in early oligocene times and the closure of the cas at 6 ma i e tectonic processes have been identified as the key triggers for the observed most severe changes in oceanic circulation in the south atlantic

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

no evidence for extreme long term warming in early pliocene sediments of the southern ocean abstract during the past 10 years there has been considerable debate with respect to the response of the antarctic ice sheets to early pliocene warmth interpretations generally fall into one of three categories 1 there was a major drawdown of the east antarctic ice sheet eais 2 drawdown of eais was relatively small 3 eais was largely unaffected by early pliocene warmth here this question is approached by using biogenic opal and carbonate in deep sea sediments as proxy for paleoceanographic change during the present day these measures are largely dictated by the position of the antarctic polar front apf with biogenic carbonate exhibiting an increase north of the apf and biogenic opal increasing to the south that the carbonate opal transition zone is a reliable feature in deep sea sediments is evidenced by the fact that it is recorded north of its present position during the last glacial maximum lgm and to the south of it during oxygen isotope stage 11 a warmer than present interglacial when these proxies are applied to southern ocean sediments high frequency glacial interglacial changes are seen in the pliocene and early pleistocene what appears to be a major glacial is recorded at about 4 5 myrs b p three short duration carbonate highs up to 18 suggesting a southward movement of apf occur at discrete intervals between about 4 6 4 8 myrs b p however these disappear or become reduced in amplitude toward the continent such data do not support any appreciable warming of surface waters near the antarctic continent neither does it support any claims of high circa 20 c sea level air temperatures over the eais it is concluded that there is no evidence for significant drawdown of eais during early pliocene warmth

the record of late pleistocene biogenic sedimentation in the eastern tropical pacific ocean we have generated 300 kyr records of biogenic opal calcite and organic carbon corg for three cores in the eastern and central equatorial pacific ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region we find that corg has been deposited in common pulses throughout the area while opal has a much more local pattern of variation calcite varies regionally but the record is shaped by superimposed dissolution and productivity processes the most intense corg peak occurs at 18 ka and can have greater than 2 times the holocene corg content other major corg peaks occur 150 ka and perhaps at 280 ka we have compared the corg record in one of the cores v19 28 to a model deepwater oxygen record developed from 13c data in the nearby v19 30 to test whether the corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone we found no coherence between the two records implying that the corg record is primarily a measure of productivity by comparing the opal calcite and corg records in v19 28 a core which is at or above the lysocline we found that both increased calcite and opal deposition matches high corg accumulation we also found however that the calcite and opal records were uncorrelated so that episodes of high opal deposition do not necessarily accumulate calcite rapidly we hypothesize that at least two different plankton communities have been dominant in the waters above this site one rich in opal secreting plankton and one more dominated by calcite producers the opal rich plankton community was dominant during the intervals 10 15 ka and 35 60 ka supplement data table 2 is available with entire articleon microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p88001 2 50 payment must accompany order

were west antarctic ice sheet grounding events in the ross sea a consequence of east antarctic ice sheet expansion during the middle miocene abstract seismic correlation of glacial unconformities from the ross sea outer continental shelf to chronostratigraphic control at dsdp sites 272 and 273 indicates that at least two west antarctic ice sheet wais expansions occurred during the early part of the middle miocene i e well before completion of continental scale expansion of the east antarctic ice sheet eais inferred from 18o and eustatic shifts therefore if the volume of the eais was indeed relatively low and if the ross sea age model is valid then these wais expansions contractions were not a direct consequence of eais expansion over the transantarctic mountains onto west antarctica an in situ development of the wais during the middle miocene suggests that either west antarctic land elevations were above sea level and or that air and water temperatures were sufficiently cold to support a marine based ice sheet additional chronostratigraphic and lithologic data are needed from antarctic margins to test these speculations

the different diffusive transport behaviours of some metals in layers of peru basin surface sediment abstract diffusion experiments with a duration of 90 days were carried out with radio tracers in an oxic and a suboxic sediment layer from two deep sea sediment cores diffusion coefficients breakthrough and time lag values were determined and the results checked by modelling only small differences of diffusive transport were observed for na and cs during the four experiments na behaved as a perfect conservative tracer and the somewhat stronger uptake of cs in one sample was caused by preferential absorption by illite that was enriched in this sample the significant differences between the four experiments for the diffusion parameters of mn zn co and cd correlate with the differing chemical compositions of the sediment layers higher mn oxide concentrations in the sample led to slower diffusion through the sediment sample and to significant sorption of the diffusing heavy metals this result confirms the dominating role of mn oxide phases in controlling the diffusive exchange of heavy metals between deep sea sediment and bottom water sediment resuspension of the oxic surface layer such as during potential ferromanganese nodule mining in the deep sea would be followed by increased diffusive flux of dissolved heavy metals especially mn from suboxic sediment layers to the new disturbed sediment bottom water interface according to our modelling the mn flux from the oxic sediment surface of 0 3 mg m 2 yr 1 in the undisturbed state would increase to up to several mg m 2 yr 1 within the first few weeks after disturbance depending on the time necessary until a stable oxic and mn oxide rich layer is again re established a total mn2 release of 54 mg m 2 was calculated if the original state is reached within 100 yr in contrast to only 3 5 mg m 2 for 5 yr of re establishment the fluxes of the other heavy metals would be smaller corresponding to their lower pore water concentrations in the suboxic layer compared to mn

cretaceous ocean floor in the amirante passage tectonic and oceanographic implications abstract core v34 76 obtained near the summit of a basement ridge in the axis of the amirante passage recovered in situ pelagic chalk of latest cretaceous age abathomphalus mayaroensis zone ca 66 ma this minimal age for the nne trending basement ridges places important constraints on the crustal age of the amirante passage region in the western indian ocean and indicates that the passage has provided a deep water connection between the mascarene and somali basins throughout the entire cenozoic

mossbauer investigations to characterize fe lattice sites in sheet silicates and peru basin deep sea sediments abstract a procedure to classify different fe lattice sites i e oh group geometries in the clay mineral content of deep sea sediments was developed using mossbauer spectroscopy at low temperature 77 k this speciation is of interest with regard to the redox behavior reactivity and color of marine sediments since substantial iron redox transitions associated with sediment color change have been documented for the structural sheet silicate iron lattice site classification was achieved for the fe ii fraction all of which is structural clay fe ii in the sediments under investigation whereas the major part of the fe iii is structural clay iron as well there is a small fe iii fraction in oxide minerals therefore further elaboration of the procedure would be required to also achieve lattice site classification for the fe iii fraction analysis of the mossbauer spectra is based on computer fits the input parameters of which were derived from a separate study of fe ii rich pure chlorites the procedure of classification is qualified to investigate e g in laboratory experiments the site specific reaction rates and the effects on sediment color of iron redox transitions in the sheet silicate content of sediments the new skills were successfully applied in environmental impact studies on the mining of polymetallic nodules from the peru basin deep sea floor

diffusion and supply rates of 10be and 230th radioisotopes in two manganese encrustations from the south china sea ages of two mn encrustations estimated by their 230th and 10be distributions are compared with k ar ages and micropaleontological datings of their nuclei to discuss possible diffusion and supply effects of the radioisotope distribution and their influence on the reliability of age determinations based on comparable results obtained by the different methods the effective diffusion coefficient of 10be can be calculated as d 1 0 10 8cm2 y this coefficient is 3 8 times smaller than the best estimates available at present in both nodules we observe lower 10be concentrations in the uppermost 2 3 mm 1 3 m y which suggests that 10be uptake has been reduced since the middle pleistocene the 2 7 fold increase of the growth rate starting 3 2 m y ago coincides with the initiation of the northern hemisphere glaciation

timing of bottom water scour recorded by sedimentological parameters in the south australian basin abstract the south australian basin has been the site of extensive antarctic bottom water aabw scour during the late cenozoic the combination of detailed stratigraphy and sedimentological analyses of three piston cores allowed the identification of the major episodes of high bottom current paleovelocity the chronology of the cores was determined by magnetostratigraphy and biostratigraphy five parameters mean mode skewness coarsest 1 and sorting of the carbonate free silt particle size distribution were used to infer periods of high paleovelocity sorting was found to be an insensitive parameter within the inferred paleovelocity regimes the two major high velocity episodes during the last 3 3 m y occurred during the gauss chron and the upper matuyama chron several short episodes of high bottom water velocity occurred during the matuyama chron only one minor pulse was identified during the brunhes chron 0 0 73 m y b p the high velocity episode during the gauss chron produced a disconformity separating miocene and middle pliocene sediments while the upper matuyama episode may be responsible for the widespread disconformity at or near the seafloor which has been identified in many cores in the region

bottom current erosion along a traverse in the south atlantic sector of the southern ocean abstract the magnetostratigraphy and biostratigraphy of twenty five piston cores on a profile from antarctica to the cape basin south of africa reveal disconformities in the sedimentary record which are attributed to bottom current erosion increased antarctic bottom water production removed all sediment in the weddell and cape basins younger than middle pliocene 2 5 m y with miocene sediment exposed at or near the seafloor at some locations increases in the velocity of the circumpolar deep water eroded lower pliocene to upper pliocene 4 0 2 0 m y sediment on the crest and south flank of the atlantic indian ridge and maintains an active scour zone today with middle pleistocene 1 0 m y sediment exposed at the seafloor

eocene oligocene paleoceanography in the antarctic ocean atlantic sector maud rise odp leg 113 site 689b and 690b abstract middle eocene to late oligocene sediments from near the crest site 689b water depth 2080 m and flank water depth 2914 m of the maud rise 62 s have been investigated by coarse fraction analysis and have revealed the following 1 1 the middle eocene 50 40 ma was a period of pure carbonate sedimentation with good preservation of carbonate microfossils no opal 40 m is present 2 2 in the late eocene 40 36 5 ma opal fossils mainly radiolaria and some diatoms 40 m appeared for the first time three maxima in opal sedimentation eocene oligocene boundary middle early oligocene and early late oligocene boundary are separated by increases in carbonate sedimentation the dissolution of carbonate fossils is strong in the opal rich layers opal sedimentation is attributed to cooling and probably more vigorous atmospheric circulation and increased upwelling 3 3 carbonate dissolution increased with water depth in the oligocene whereas in the middle eocene excellent carbonate preservation in the deeper site 690b and stronger dissolution in the shallower site 689b is attributed to different bottom water characteristics the middle eocene bottom water probably was formed by strong evaporation at low latitudes whereas by the earliest oligocene formation of antarctic bottom water aabw had set in 4 4 current influence not on top but on the flank of the maud rise could be recorded by means of larger grain sizes of benthonic and planktonic microfossils 5 5 ice rafted debris was not found quartz and other minerals are very rare and not larger than 125 m and may have been supplied by ice as well as by wind or by deep currents mica contents were up to 10 times higher in the middle eocene on the flank compared to on the crest of the maud rise indicating deep current supply

change from atlantic type to pacific type carbonate stratigraphy in the middle pliocene equatorial pacific ocean a paleomagnetically dated piston core from the equatorial pacific ocean v28 179 contains levels of highest carbonate percentage in association with lower 18o values in early pliocene sediments this relationship is typical of the atlantic during the quaternary and is thus referred to as an atlantic type carbonate stratigraphy the change from an atlantic type to a pacific type stratigraphy high carbonate glacial episodes appears to have occurred during the earliest gauss magnetic chron 3 18 3 41 ma of middle pliocene age and may be related to the development of northern hemisphere glaciation samples deposited prior to the development of northern hemisphere glaciation in v28 179 have a significant proportion of low frequency 400 ka period variance in both the benthic o18 and carbonate spectra and an atlantic type correlation both the oxygen isotopic and the carbonate spectra of v28 179 have frequency specific correlation coherency with the calculated pliocene record of the eccentricity of earth s orbit thus orbital parameters may have affected equatorial pacific sedimentation in the pliocene the change from atlantic type to pacific type carbonate stratigraphy in the middle pliocene may have been related to a change in the dominant frequency of variance of carbonate oscillations related to orbital parameters and or to intensification of antarctic bottom water circulation during the middle pliocene near the base of the gauss chron

iron reduction through the tan green color transition in deep sea sediments mossbauer spectroscopic investigations of deep sea sediments from the peru basin revealed a prominent downcore increase of the bulk sediment fe ii fe iii ratio across the well known tan green color transition this increase occurs along a continuous gradient extending over a 3 cm zone at the two deep sea sites that we report remarkably constant values of the fe ii fe iii ratios above 11 2 89 2 and below 37 2 63 2 the iron redox transition zone delimit the gradient clearly a minor peak of diagenetic iron enrichment is manifest at the redox front this fe enrichment has accumulated in a redox cycle and amounts to 16 4 of the total fe at the peak maximum the data imply that 26 4 of the detrital iron has experienced in situ redox transition from fe iii to fe ii within the iron redox transition zone

environmental history of the south eastern south atlantic since the middle miocene evidence from the sedimentological records of odp sites 1088 and 1092 during leg 177 of the ocean drilling program odp well preserved middle miocene to pleistocene carbonate rich sediment records were recovered on a north south transect through the south eastern atlantic sector of the southern ocean at site 1088 on the agulhas ridge and site 1092 on meteor rise both sites were dominated by the deposition of calcareous nannofossil oozes through the miocene indicating low biological productivity in warm to temperate surface waters a continuous increase in the proportions of foraminifera since the latest miocene 6 5 ma points to enhanced nutrient supply possibly related to the global biogenic bloom event across the miocene pliocene boundary since the late pliocene different styles of biological productivity developed between the sites enhanced deposition of biosiliceous constituents at the southern site 1092 particularly in the early pleistocene is consistent with the formation of the circum antarctic opal belt since 2 5 ma in a setting near the polar front whereas carbonate deposition still prevailed at the northern site 1088 situated near the subtropical front clay mineral tracers of water mass advection together with the pattern of sedimentation rates and hiatuses reflect distinct pulses in the development of regional ocean circulation between 14 and 12 ma around 8 ma and since 2 8 ma these pulses can be related to antarctic ice sheet extension that mediates the production and flow of southern source water and stepwise increases in north atlantic deep water production that drives global conveyor circulation at site 1088 illite chemistry and silt clay ratios of the terrigenous sediment fraction reflect the history of terrestrial climate in southern africa with humid conditions prior to the early late miocene 9 7 ma followed by a dry episode until 7 7 ma the latest miocene and early pliocene were characterized by a humid episode until modern aridity was established in the late pliocene between 4 0 and 2 8 ma these climate changes were related to the latitudinal migration of climate belts in response to tectonically caused reorganizations in atmospheric and ocean circulation

development of sediment drifts approaching an active plate margin under the sw pacific deep western boundary current the abyssal pacific ocean is fed by a 1000 km wide deep western boundary current dwbc that flows northward along the continental margin east of new zealand between the passive margin of chatham rise and the subduction zone of kermadec trench a distance of 1200 km the dwbc has formed a suite of sediment drifts over a depth range of 2200 5700 m airgun and 3 5 khz profiles record a variety of drift types that reflect regional variations in bathymetry sediment supply and the tectonic volcanic framework on chatham rise the dwbc has deposited a sinuous linear body along the south flank 3000 m an extensive apronlike drift on the north flank 2200 4500 m and a ridgelike drift about the rise base 4500 5200 m the flow has also deposited a body of sediment over 400 km long within a moat at the base of the nearby louisville seamount chain further downcurrent the 250 km long rekohu drift 3600 4190 m has developed northward to 39 s south of this latitude drifts comprise mainly reworked pelagic hemipelagic material and sediment transported from distant southerly sources in contrast drifts north of 39 s have received a major injection of terrigenous sediment from hikurangi channel which runs 1400 km from new zealand eastward across the hikurangi plateau to disgorge on to the abyssal floor at the plateau edge en route turbidity current overspill from the channel has moved north under the influence of the shallow dwbc to contribute to a series of small ridge and patch drifts among the numerous seamounts on the plateau at 3500 4200 m off hikurangi channel mouth a large fan has accumulated the dwbc has extended the fan into a drift running over 250 km along the base of hikurangi plateau 5150 5770 m toward kermadec trench here drift sediment becomes increasingly disrupted by mass wasting associated with the active subduction in this area the seismic stratigraphy reveals the drifts to rest mainly on a widespread erosional surface that is interpreted to mark the inception of the dwbc in the region with the late oligocene opening of the australian antarctic seaway drift construction commenced during the miocene but was punctuated in the late miocene by another period of erosion that coincided with increased bottom water production in antarctica deposition resumed in plio pleistocene times when large quantities of sediment from the rapidly rising landmass of new zealand were injected into the boundary current the modern flow continues to affect drift deposition as manifest by an active boundary channel along the foot of hikurangi plateau and widespread scour zones and sediment wave fields

late miocene earliest pliocene glaciation in southern argentina implications for global ice sheet history abstract in south america at latitude 47 s till was deposited sometime between 7 m y and 4 6 m y ago at a time when the local climate was colder than today s during this same interval glaciers extended to sea level in southeast alaska and widespread cooling of the ocean surface in middle latitudes worldwide marine regression and change in the oxygen isotopic composition of ocean water occurred from the last three events major late miocene expansion of the antarctic ice sheet has been inferred on the assumption that the history of north atlantic ice rafting precludes the existence of northern hemisphere ice sheets until 3 m y ago this is disputed first because precipitation in antarctica would probably have decreased at temperatures below today s second because the antarctic ice sheet cannot expand appreciably until buildup of northern hemisphere ice sheets has lowered sea level third because virtually no late miocene sediments are present at the labrador sea dsdp sites that are critical to the reconstruction of north atlantic ice rafting history and fourth because the scale of late miocene glaciation in alaska is at least permissive for simultaneous buildup of ice at similar latitudes further east if global ice sheet volume at the end of the miocene was greater than it is today by an amount that would have lowered sea level by several tens of meters the excess ice did not accumulate in antarctica but in the northern hemisphere chiefly in north america away from the atlantic coast

repeated occurrences of methanogenic zones diagenetic dolomite formation and linked silicate alteration in southern bering sea sediments bowers ridge iodp exp 323 site u1341 abstract diagenetic precipitates such as dolomite and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments a 600 m thick sedimentary section recently drilled at integrated ocean drilling program iodp site u1341 on bowers ridge southern bering sea provides insight into such a 4 3 ma old paleo diagenetic archive hard lithified calcite dolomite layers and laminae of disseminated carbonate were recovered in diatom rich sediments over a depth range of 400 m carbon isotope values of the diagenetic carbonates between 16 6 and 14 4 vpdb and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon dic during elevated rates of organic carbon mineralization primarily via sulfate reduction at shallow sediment depth below the paleo seafloor diagenetic carbonates at 280 440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane aom at sulfate methane transition zones smtz these microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2 58 2 51 ma a minimum in sulfate concentrations in modern porewaters and low sedimentary ba al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone the minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations less radiogenic strontium and isotopically light calcium in the porewater it is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater the isotopic composition of porewater calcium was also influenced by ammonium calcium exchange on clay minerals and carbonate recrystallization our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites 2000 m water depth over prolonged timescales it shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization

mobility of metals over the redox boundary in peru basin sediments abstract downcore variations and phase distribution of metals in the quaternary sediments from six areas of the peru basin were investigated the sediments are characterised by a 5 20 cm thick oxic layer at the water sediment interface formed under the influence of dissolved oxygen in the bottom water in deeper sediment sections suboxic conditions are found due to the degradation of organic matter variations in the downcore abundance of metals e g fe mn co ni cu zn v mo cr were determined by bulk chemical methods a significant accumulation of manganese is observed at the depth of the manganese redox boundary caused by diagenetic remobilisation under suboxic conditions and reprecipitation under oxic conditions to investigate their phase distributions partitioning of elements in selected samples over the sediment column was carried out in sequential leaching experiments a comparison between the surface layer and deeper sediment layers shows a distinct change in the element distribution between operationally defined host phases carbonates oxy hydroxides detrital components above the redox boundary at the sediment surface transition metals are enriched in the reducible mn oxide fraction when the horizontal position of the mn redox boundary moves upward influenced by naturally occurring enhancement of surface water productivity these elements are mobilised and available to the manganese nodule accretion process if the redox boundary reaches the level of growth of the nodules in contrast to the naturally induced mobilisation of metals a technical impact e g mining of manganese nodules would be a rapid event occurring under completely different redox conditions metals would be released into the bottom water an oxic environment where scavenging of dissolved metals and resedimentation takes place in relatively short periods of time presumably a long distance transport of contaminants will not happen

post miocene disconformities and paleoceanography in the atlantic sector of the southern ocean abstract the magnetostratigraphy and biostratigraphy of 166 islas orcadas piston cores in the atlantic sector of the southern ocean reveal disconformities in the sedimentary record which are attributed to bottom current erosion the hiatus frequency as a function of water depth reveals both shallow erosion by circumpolar deep water cdw and deep erosion by antarctic bottom water aabw the post miocene history of erosion by both bottom currents is delineated by analysis of areal and temporal fluctuations of hiatus frequency erosion by cdw caused disconformities on the maud rise astrid ridge indian antarctic ridge scotia sea and islas orcadas rise the shallow disconformities increased in frequency and size from 4 0 to 1 0 ma with two periods of distinctly widespread disconformities from 5 5 to 4 5 ma and 2 5 to 1 5 ma after 1 0 ma the frequency and extent of the hiatuses decreased erosion by aabw caused disconformities in the weddell abyssal plain argentine basin and through a narrow conduit in the south sandwich basin downstream from the bullard fracture zone the deep disconformities increased in frequency and size from 4 5 to 5 0 ma 3 5 to 4 0 ma and from 1 0 to 2 5 ma after 1 5 ma the frequency and extent of hiatuses decreased fluctuations in hiatus frequency are consistent with results of a similar study in the southeast indian ocean and may be correlated with paleoceanographic events southern ocean cooling and possible re establishment of the west antarctic ice sheet and fringing ice shelves at 4 3 3 5 ma was accompanied by increased aabw and cdw activity the formation expansion of the northern hemisphere ice sheets at 2 5 3 0 ma resulted in a decrease in aabw velocity and was accompanied by increased cdw activity both deep and shallow bottom currents increased in velocity during the late matuyama chron 2 0 1 5 ma as a result of antarctic cooling after 1 0 ma however the frequency and extent of shallow and deep hiatuses was reduced and the modern extent of hiatuses is the lowest within the post miocene

for the deep biosphere the present is not always the key to the past what we can learn from the geological record microbial life below the earth s surface the deep biosphere has probably varied significantly since the archaean reconstructing changes in deep biosphere activity over geological timescales is necessary to understand its role in biogeochemical cycling even for the last few million years such changes are often not captured by studying the distribution of present activity however several studies using samples from scientific drilling have revealed mineralogical geochemical isotopic and fossil organic molecule imprints in the sedimentary record that document rather different past deep biosphere conditions changing deep biosphere conditions can also be simulated using geochemical models while some processes occurring in the past can be understood by comparing them with the present deep biosphere others lack any modern analogue they are defined as non actualistic a non actualistic consideration of the deep biosphere is therefore essential for a better understanding of how earth and life co evolved through time

geomorphology and shallow structure of a segment of the atlantic patagonian margin abstract we study an area little known of the atlantic patagonian margin from 44 30 s to 47 40 s and from 59 w to nearly 61 w the multi beam bathymetry coupled with high resolution seismic reflection profiles has provided details on the morphology and shallow acoustic structure on this area the main morphological characteristics of the seafloor features on the shelf and middle slope are described the atlantic patagonian continental shelf north of 45 40 s is located at a depth of 170 200 m south of this latitude the shelf edge is at 128 to 200 m the shelf surface is marred by circular depression and ridges oriented oblique to the shelf edge the upper slope and upper middle slope are plowing by icebergs from antarctica in pleistocene and local reefs of cold water coral further enhance the topography of the area in the middle slope there are two terraces the 20 to 60 km wide nagera and the 15 to 60 km wide perito moreno terraces showing moats hollows pot holes sediment drifts and sediment waves the terraces may have been formed in late miocene whereas the other forms are of pleistocene age other features are a sediment swell south of 47 s and seven submarine canyons on the middle slope these incipient canyons have been developed in the middle slope by retrogressive erosion some terminating on the upper middle slope and others on the upper slope and the canyon 6 breaching the shelf edge individual seafloor features existing on the atlantic patagonian margin have been classified into two main groups according to their origin along and across slope processes these primary agents were supplemented by endogenic processes such as expulsion of gas water diapirism of high pressure mud and folding faulting the results suggest that today down slope processes on the slope are practically non existent and that the morphology of the upper and middle slope is slowly being remolded by along slope bottom currents

taxonomic evolution of neogene planktonic foraminifera and paleoceanographic relations the taxonomic evolution of neogene 24 ma to present day planktonic foraminiferal species are described using four indices rate of speciation rate of extinction rate of diversification and rate of turnover the evolution of neogene planktonic foraminifera is marked by three principal stages 1 a diversification stage 24 to 16 ma early miocene 2 an equilibrium stage 16 to 5 ma middle and late miocene and 3 a declining stage 5 ma to recent pliocene and quaternary the early miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses during the middle and late miocene the assemblages remained close to their equilibria with relatively low diversification rates the decline in diversity during the pliocene and quaternary probably resulted from adverse effects imposed by both large scale paleoceanographic fluctuations that began about 6 ma and high frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2 5 ma bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes average evolutionary rates appear to be similar for tropical transitional and temperate assemblages although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution the observed evolutionary pattern supports the stationary model of stenseth and maynard smith 1984

the impact of the 1991 mount pinatubo tephra fallout on the geochemical environment of the deep sea sediments in the south china sea abstract seven years after the 1991 mount pinatubo eruption the current geochemical environment of ash covered deep sea sediments in the south china sea was investigated the depth distributions of o2 no3 mn2 corg and porosity at six representative sites covered with varying thicknesses of tephra are reported the shapes of the depth profiles reveal that o2 is totally exhausted within ash layers thicker than 3 cm while thinner layers are penetrated by oxygen followed by linear downcore profiles with depletion between 8 and 12 cm hence the zone between ash layer and total depletion of oxygen represents a zone of negligible oxygen consumption various multi layer models were developed to explain the observed oxygen concentration profiles these mathematical simulations also serve to assess both the development since the surface sediments were sealed by the ash fallout as well as the future evolution whereas thick tephra layers provoke a nearly stationary situation i e are capable of preventing oxygen from penetrating into the underlying sediments oxygenation of sediments below thin layers increases rapidly in these sediments the effect of oxygen diffusion velocity is drastically reduced by the reaction with dissolved manganese and therefore explains the linear profiles besides this study is suitable as a case study to assess the effects of human interventions in the deep sea ecosystem such as mining and waste dumping

cenozoic evolution of continental humidity and paleoenvironment deduced from the kaolinite content of oceanic sediments abstract the distribution of detrital kaolinite in cenozoic sediments of the atlantic and west pacific oceans has been used to reconstruct the variations of the continental humidity and associated paleoenvironmental factors five stages have been recognized 1 1 during the late oligocene chattian c 30 m y p21 and np24 increased kaolinite content at every site marked an increase of global humidity 2 2 during the early miocene aquitanian c 20 m y n5 n6 and nn2 nn3 increasing continental aridity is deduced from low kaolinite contents in the atlantic ocean and philippine sea 3 3 during the middle miocene langhian c 14 m y n10 n12 and nn5 nn6 increased kaolinite contents at most of the sites marked a further increase of global humidity which was especially important at low latitudes in africa 4 4 during the late miocene tortonian c 10 m y n16 and nn10 nn11 kaolinite content and inferred continental humidity increased toward high latitudes but decreased toward low latitudes especially off tropical africa where it marked the development of arid conditions 5 5 during the late pliocene piacenzian c 3 m y nn15 nn16 kaolinite content and humidity increased again toward high latitudes while these conditions decreased again toward low latitudes emphasizing the latitudinal climatic zonation periods of increasing humidity show good correlation with the development of polar ice locally volcanism tectonic activity oceanic circulation and migration of lithospheric obliterated the climatic significance of clay mineral associations which therefore express complementary aspects of the continental and marine paleoenvironments

benthic recycling of biogenic debris in the eastern tropical atlantic ocean abstract distributions of pore water o2 no 2 no 3 nh 4 si oh 4 po3 4 mn2 f and t a were determined at 15 stations in the eastern equatorial atlantic while overall profile characteristics are consistent with previous models of organic matter diagenesis profile shapes suggest that a deep reaction layer rich in organic c is also present at many sites while it is unlikely that the oxidation of organic c in this layer has had a major effect on the ocean c cycle pore water profile shapes are significantly altered despite exposure to seawater so2 4 concentrations for 1000 years decomposition of the organic matter in the layer appears to be restricted to oxic and suboxic processes these results suggest major differences in organic carbon decomposition and preservation under oxic suboxic and anoxic conditions present day benthic fluxes are largest adjacent to the eastern boundary coastal upwelling region and similar in magnitude to values reported for the eastern pacific preliminary estimates suggest that the benthic respiration in the eastern 1 3 of the north atlantic south of 20 n may alone account for 20 of the total deep north atlantic respiration combining these results with estimates of organic c burial and deep water column decomposition suggests that this region is a major location of organic c input into the deep sea

heavy metal distributions in peru basin surface sediments in relation to historic present and disturbed redox environments abstract heavy metal distributions in deep sea surface sediments and pore water profiles from five areas in the peru basin were investigated with respect to the redox environment and diagenetic processes in these areas the 10 20 cm thick mn oxide rich and minor metal rich top layer is underlain by an increase in dissolved mn and ni concentrations resulting from the reduction of the mno 2 phase below the oxic zone the mobilised associated metals like co zn and cu are partly immobilised by sorption on clay organic or fe compounds in the post oxic environment enrichment of dissolved cu zn ni co pb cd fe and v within the upper 1 5 cm of the oxic zone can be attributed to the degradation of organic matter in a core from one area at around 22 25 cm depth striking enrichments of these metals in dissolved and solid forms were observed offset distributions between oxygen penetration and mn reduction and the thickness of the mn oxide rich layer indicate fluctuations of the mn redox boundary on a short term time scale within the objectives of the german atesepp research programme the effect of an industrial impact such as manganese nodule mining on the heavy metal cycle in the surface sediment was considered if the oxic surface were to be removed or disturbed oxygen would penetrate deep into the formerly suboxic sediment and precipitate mn 2 and metals like ni and co which are preferably scavenged by mno 2 the solid enrichments of cd v and other metals formed in post oxic environments would move downward with the new redox boundary until a new equilibrium between oxygen diffusion and consumption is reached

geochemical and biological recovery of the disturbed seafloor in polymetallic nodule fields of the clipperton clarion fracture zone ccfz at 5 000 m depth environmental data were obtained on the nodule fields of the clipperton clarion fracture zone at 5 000 m depth in june 2004 during the nodinaut cruise the long term effects of physical disturbance made by a dredge 26 yr ago on the sediment were investigated we focused our study on its track which is still visible on the bottom the first major consequence of the passage of this equipment was to remove 4 cm 6 0 5 cm of superficial sediment the physical and chemical properties of this disturbed sediment sampled in the track did not change significantly over time and has not shown any recovery since the disturbance however an exception was observed for depth variations of manganese concentration in the sediment which were similar in the track to those in the surrounding undisturbed sediment and can be explained by the diffusion over time of oxygen from the sea water on the other hand the biological activity measured in the track with the respirometer rap2 carried by the submersible nautile did not differ from the unperturbed site which suggests that the benthic fauna has completely recovered as have nutrient fluxes at the water sediment interface

pliocene variations in the position of the antarctic convergence in the southwest atlantic middle to late pliocene 4 1 1 9 ma variations in the positions of surface water masses and migrations of the polar front in the southwest atlantic are inferred from a factor analysis of radiolarian assemblages from dsdp site 514 faunal results suggest that surface water masses underwent progressive cooling as the polar front zone pfz advanced northward during the latest gilbert to late gauss chron the late gilbert chron 4 12 3 86 ma was the waning phase of a mid gilbert warm interval northern subantarctic surface water prevailed between 4 12 and 3 97 ma indicative of surface water temperatures warmer than those during the succeeding pliocene a long term sea surface cooling trend began between 3 97 and 3 86 ma which moved the pfz northward and closer to site 514 bringing cooler southern subantarctic surface waters to the site this movement northward of cooler surface waters is inferred to be related to the initial growth of sea ice and ice shelves throughout regions of west antarctica which were deglaciated or unglaciated during the prior warming interval of the gilbert chron a major late gilbert early gauss chron increase in the production of antarctic bottom water aabw resulted in an erosional or nondepositional hiatus at site 514 spanning 3 86 to 3 18 ma increased aabw activity at this time is linked to continued growth of expansive ice shelves and sea ice in the west antarctic region in the east antarctic margin and possibly in the marine embayments of east antarctica decreased aabw production led to a 3 2 ma resumption of sedimentation at site 514 and elsewhere in the southern ocean antarctic surface water assemblages above the hiatus 3 18 3 16 ma suggest that the pfz first passed over site 514 during the 3 86 3 18 ma interval of the hiatus following this initial invasion of antarctic surface waters between 3 16 and 2 94 ma the pfz retreated to a position near or south of the site this slight retreat of the pfz with a corresponding decrease in aabw activity is possibly related to a significant reduction in the area of shelf and sea ice as grounded ice expanded in the west antarctic region we interpret the widespread global enrichment of 18o at approximately 3 2 ma to be partially related to a cooling of surface waters the production of cooler bottom waters and an expansion of west antarctic ice volume associated with its grounding phase between 3 5 and 2 7 ma based on surface water mass migrations at site 514 the west antarctic ice volume increased significantly slightly prior to or at approximately 3 2 ma decreased between 3 14 and 2 7 ma and then increased by 2 67 ma to a more stable configuration with a volume at least as great as that at 3 2 ma during the late gauss 2 94 2 47 ma four northward advances of the pfz led to the migration of antarctic surface waters over the site by 2 67 ma and continued dominance of antarctic surface water through the remainder of the pliocene we suggest that this permanent change from subantarctic to antarctic surface water mass dominance was linked indirectly to the initial growth of northern hemisphere ice and a reduction of sea level we propose a model of simultaneous northern and southern hemisphere ice volume growth induced by interhemisphere positive feedback which is responsible for the major late gauss advance of antarctic surface waters and the global enrichment of 18o at 2 5 ma

a magnetic signature of bottom current erosion abstract to characterize the magnetic signal associated with bottom current erosion we have conducted downcore measurements of magnetic texture and fabric in three cores containing known erosional hiatuses using biostratigraphic and magnetostratigraphic analysis erosional hiatuses were identified for three cores from two current dominated environments the northern bermuda rise and the south indian basin the cores were contiguously subsampled and the magnetic susceptibility k the anisotropy of magnetic susceptibility ams and the anhysteretic susceptibility k arm were measured the ams parameters h and q were used to describe the relative magnitude and the shape respectively of the representative susceptibility ellipsoid the concentration independent and dimensionless ratio k arm k was used to indicate relative changes in magnetic grain size hiatuses in the three cores were marked by unusually high values of h and q indicating a greater development of internal fabric with a more linear fabric representation depressed values of k arm k indicated a coarser mean magnetic grain size the magnitude of this signal however did not have a simple relationship with hiatus duration t test results statistically confirmed the existence of an erosional signature to enhance the applicability of this technique a quantitative discriminant model was constructed and calibrated using the magnetic characteristics of erosion since this model was constructed from samples of known erosional and non erosional character the discriminant functions could then be used as reference equations to identify erosion in other cores biostratigraphic and oxygen isotopic data from a 14 m core from the northern bermuda rise extending back to isotopic stage 8 250 ka bp indicate two short intervals of low accumulation rate which for this region are most probably attributable to bottom current erosion magnetic data for this core were entered into the reference discriminant model and the two zones of suspected erosion were classified by the functions as being highly crosional in character zones of probable erosion were identified at several other levels in the core the timing of these short term crosional events was found to coincide closely with glacial intervals suggesting that bottom currents active on the northern bermuda rise were invigorated periodically during glacial maxima at c 18 58 64 85 130 140 165 180 225 and 250 ka bp

compositional changes of surface sediments and variability of manganese nodules in the peru basin abstract two types of manganese nodules were observed in the peru basin large botryoidal nodules in basins and small ellipsoidal nodules on slope positions the sediment in areas with large botryoidal nodules contains a thinner and weaker oxidation zone than the sediment under small ellipsoidal nodules indicating that diagenetic processes in the sediment which supply manganese nodules with metals for their growth are stronger in sediments on which large botryoidal nodules grow organic matter which activates remobilization of metals occurs mostly in the form of refractory lipidic compounds in the inner capsule of radiolaria this material needs bacterial degradation to act as a reducing agent easily oxidizable organic components could not be found in the sediments other changes in sediment composition do not have a link to manganese nodule growth biogenous components radiolarians organogenic barite and apatite increase towards the equatorial high productivity zone authigenous clay minerals nontronite as well as montmorillonite with high fe 3 incorporation on positions of ochtaedral al increase with distance from the continent the assessment of environmental impacts will have to take into account the regional differences in sediment composition and the small scale variability of manganese nodules

miocene history of the benguela current and antarctic ice volumes evidence from rhythmic sedimentation and current growth across the walvis ridge deep sea drilling project sites 362 and 532 the history of the northward growth and of the fluctuations of the benguela current from the middle miocene ca 14 ma to the uppermost late miocene ca 5 ma has been reconstructed from analyses of the coarse and clay fractions and geochemical analyses of the organic matter in sediments from deep sea drilling project sites 362 and 532 in the middle miocene the benguela current had not yet reached the walvis ridge and consequently no local upwelling occurred carbonate preservation was good during this period of low productivity rhythmic changes related to antarctic ice volumes were weak leading to slightly higher organic matter concentrations and higher montmorillonite illite m i ratios in sediments deposited during times of greater continental ice montmorillonite was carried north from the orange river by the benguela current whereas illite originated from the nearby namib desert in the early late miocene the benguela current reached the walvis ridge in colder periods and led to well developed rhythmic increases in opal which was transported from near coastal upwelling areas organic matter concentration carbonate dissolution and m i ratios were also enhanced during periods of greater ice volume during the late miocene farther northward migration of the benguela current led to a change in the uppermost miocene sediments opal contents and m i ratios were high during times of low ice volume rather than in colder times during the cold periods local winds from the namib desert increased the illite supply to the walvis ridge and depressed the m i ratio in these periods the benguela current flowed farther to the north reaching the angola basin as it did in quaternary glacial periods throughout these changes sediment organic carbon content was always enhanced in high ice volume periods from near bottom downslope transport of organic matter from shelf regions during regressions and carbonate dissolution in the sediments was increased as a result of oxidation of this organic matter

post miocene fluctuations of antarctic bottom water paleospeed in the southwest atlantic ocean abstract a gap in the falkland escarpment serves as the primary channel through which antarctic bottom water aabw flows into the argentine basin from the georgia basin the particle size distributions of the biogenic free silt fraction in four cores near the falkland gap and the hiatus frequency at water depths greater than 4000 m throughout the southern ocean are used to infer post miocene aabw paleospeed analysis of aabw paleocirculation indicates episodes of increased bottom current speeds at 5 3 4 5 4 0 3 5 3 3 3 1 2 5 2 3 2 0 1 5 and 1 0 ma these fluctuations in inferred paleospeed are compared to both northern and southern hemisphere paleoceanographic and paleoclimatic events in order to examine the response of bottom water circulation to post miocene climates during the early gilbert middle matuyama 5 3 1 5 ma southern hemisphere climatic events provided the primary forcing mechanisms on aabw activity the model invoked involves increased salinity and overturn of weddell shelf water in response to increased sea ice formation during cold episodes from the late matuyama after 1 5 ma to present fluctuations in warm deep water resulting from northern hemisphere climatic evolution may have been the predominant factor influencing aabw paleospeed these episodes of increased bottom current activity may correlate to periods of mudwave migration in the argentine basin during the past 5 ma the mudwave fields consist of silty siliceous clays deposited in response to enhanced sediment supply and fast moving currents in the interior basin we speculate that the periods of enhanced bottom water activity may have been responsible for major episodes of mudwave growth that began since the late oligocene and have persisted into the holocene

plio pleistocene sedimentation on the walvis ridge southeast atlantic dsdp leg 75 site 532 influence of surface currents carbonate dissolution and climate an investigation of the quantitative composition of the coarse 40 m and clay 2 m fraction of hpc 532 dsdp leg 75 in 1300 m water depth on the eastern walvis ridge off southwest africa yielded the following results 1 1 the sediments reflect a complete latest miocene to recent depositional history sedimentation rates vary between 2 3 and 7 8 cm 10 3 years 2 2 preservation of calcium carbonate is subject to strong variations short term 100 000 years and long term about 1 m y cycles in carbonate dissolution have been observed with strongest dissolution occurring during periods of lowered sea level 3 3 upwelling influence from the near coastal upwelling centre has been detected by means of the opal content interglacial periods show high opal contents because the benguela current turned westward at about 20 s and carried opal laden upwelled water to the west sediments from glacial periods however show opal minima besides these short term cyclic variations in opal content long term cycles have been found with maximum upwelling influence in the latest pliocene early quaternary 4 4 each caco3 dissolution minimum maximum is correlated with an opal maximum minimum throughout the sediment sequence 5 5 the oceanographic system off southwest africa remained essentially unchanged since the latest miocene sea level rose and fell periodically on a small and on a large scale and the benguela current flowed southeast northwest and turned to the west at the latitude of site 532 during interglacial periods when sea level was high 6 6 the climate in the near coastal area of southwest africa in the latitude of site 532 has probably been arid throughout the investigated period

reactive fe ii layers in deep sea sediments the percentage of the structural fe ii in clay minerals that is readily oxidized to fe iii upon contact with atmospheric oxygen was determined across the downcore tan green color change in peru basin sediments this latent fraction of reactive fe ii was only found in the green strata where it proved to be large enough to constitute a deep reaction layer with respect to the pore water o2 and no3 large variations were detected in the proportion of the reactive fe ii concentration to the organic matter content along core profiles hence the commonly observed tan green color change in marine sediments marks the top of a reactive fe ii layer which may represent the major barrier to the movement of oxidation fronts in pelagic subsurface sediments this is also demonstrated by numerical model simulations the findings imply that geochemical barriers to pore water oxidation fronts form diagenetically in the sea floor wherever the stage of iron reduction is reached provided that the sediments contain a significant amount of structural iron in clay minerals

ventilation of the abyssal southern ocean during the late neogene a new perspective from the subantarctic pacific 1 benthic foraminiferal stable carbon isotope records from the south atlantic show significant declines toward more pacific like values at 7 and 2 7 ma and it has been posited that these shifts may mark steps toward increased co2 sequestration in the deep southern ocean as climate cooled over the late neogene we generated new stable isotope records from abyssal subantarctic pacific cores mv0502 4jc and elt 25 11 the record from mv0502 4jc suggests that the southern ocean remained well mixed and free of vertical or interbasinal 13c gradients following the late miocene carbon shift lmcs according to the records from mv0502 4jc and elt 25 11 however cold low 13c bottom waters developed in the southern ocean in the late pliocene and persisted until 1 7 ma these new data suggest that while conditions in the abyssal southern ocean following the lmcs were comparable to the present day sequestration of respired co2 may have increased in the deepest parts of the southern ocean during the late pliocene a critical period for the growth and establishment of the northern hemisphere ice sheets

regional late pliocene early pleistocene hiatuses of the southern ocean diatom evidence abstract the existence of regionally synchronous hiatuses in late neogene sediments of the southern ocean has been questioned on sedimentological grounds while their paleoclimatic interpretation has been questioned on theoretical grounds we evaluated the evidence used to identify these hiatuses in pliocene and lower pleistocene sediments by determining quantitatively the occurrence of diatom stratigraphic markers in eleven southern ocean piston cores three from the pacific sector and eight from the indian and atlantic sectors in the pacific sector some species have ranges similar to the published record but others show north south diachrony in the southeast indian sector some marker species have ranges at odds with the published magnetostratigraphy in the atlantic sector there is wide disparity between our data and published results in two of the cores our placement of the denticulopsis hustedtii datum differs with the published record by as much as 10 m a third core contained a number of barren intervals and could not be zoned while a fourth core previously zoned and dated with magneto and biostratigraphy contained too few diatoms for quantitative biostratigraphy we conclude that the question of regional hiatuses in southern ocean sediments while important cannot be addressed until a locally and regionally applicable biozonations are developed and b magnetostratigraphic data are properly evaluated resolution of these problems are essential before we can successfully use hiatus data to recover the paleoceanographic and paleoclimatic history of the southern ocean

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

palynological evidence for miocene climatic cooling in eastern iceland about 9 8 myr ago the processes which led to the pleistocene glaciations in the northern hemisphere are presently known only from fragmentary evidence of major tertiary climatic cooling events1 2 although there is good evidence3 for glacial intervals in alaska 10 9 myr most terrestrial records4 5 which suggest a corresponding high latitude climatic cooling in the north east atlantic are poorly dated and north atlantic palaeoceanographic records contain large erosional hiatuses2 6 we have obtained new palynological data from eastern iceland from clastic units between lava formations dated by k ar and palaeomagnetic methods7 8 we now report that these data record a floral succession which suggests that a temperature decrease of 10 c occurred in iceland between 10 and 9 5 myr

paleoceanographic implications of terrigenous deposits on the maurice ewing bank southwest atlantic ocean abstract grain size distributions of sediment samples from the maurice ewing bank meb were utilized to identify styles of sediment transport and to estimate current speeds within the benthic boundary layer these data allow for examination of the relationship between sedimentation on the bank and circumpolar currents causal relationships between glacial episodes current intensification and bottom current scour were previously postulated the intent of this study was to test the validity of these suggested relationships modern sediment distribution on the meb is controlled by water column winnowing bottom currents and variations in the flux of ice rafted detritus and biogenic material and is modified by mass flow processes indirect determinations of current speeds using well established curves relating current velocity to sediment transport suggest uniform near bottom current speeds of approximately 6 15 cm s 1 over the bank this velocity range is considered relative not absolute nonetheless these moderate velocities are supported by geostrophic velocity calculations grain size distributions of down core samples from plio pleistocene sandy units were examined in order to investigate the history of bottom current flow over the bank during this time the lack of significant variability of grain size distributions down core indicates that no major fluctuations in circumpolar current intensification have occurred since plio pleistocene time and therefore argue against a causal relationship between glacial conditions and deep sea geostrophic current intensification in addition mass movement mainly in the form of debris flows and turbidites has resulted in interruptions in the sedimentary record which in some cases could have been misinterpreted as unconformities our scenario for sedimentation over the bank differs from previous ones in that it calls for less dramatic variations in bottom current speeds during pliocene holocene time

evaluation of the environmental consequences of polymetallic nodule mining based on the results of the tusch research association abstract realising a need for increased general knowledge of the deep sea for environmental impact assessments related to the permanent storage of waste products and mining of metal resources the german bundesministerium fur bildung und forschung has funded targeted research in the deep sea for more than 10 years the research was carried out in an area in the southeast pacific ocean close to and within a german mining claim to match the interests of german deep sea polymetallic nodule mining enterprises and the developing mining code of the preparatory commission for the international seabed authority and the international tribunal for the law of the sea the tusch abbreviation for tiefsee umweltschutz deep sea environmental protection research association with members from various university and governmental institutions was part of the atesepp effects of technical interventions into the ecosystem of the deep sea in the southeast pacific ocean project between 1996 and 1998 geotechnical sedimentological geochemical hydrographic numerical modelling and ecological studies relevant to environmental impact assessment studies of polymetallic nodule mining were undertaken since general oceanographic knowledge of the deep sea is rather limited these various projects also have increased our general understanding of this region this paper describes the potential impacts of mining processes on the seafloor and the near bottom water layer as well as on bathyal and abyssal pelagic zones that will receive processed water sediment and abraded nodule fines tailings discharged after nodule transport to the mining vessel at the ocean surface the tusch research association defined various recommendations to keep the unavoidable impacts to a minimum such as limited penetration of the mining system into the sediment confining intensive resedimentation to the area behind the miner minimising transport of sediment to the ocean surface and discharging all tailings at great depths ideally close to the seafloor the recommendations are not new but the present studies have improved them from precautionary to scientifically based statements

the morpho tectonic setting of the southeast margin of iberia and the adjacent oceanic algero balearic basin abstract multi beam bathymetry and high resolution low penetration seismic reflection profiles of the offshore extensions of the betic internal zone off sierra de cartagena la union margin along its south side and the mar menor margin along its east side the mazarron escarpment forming its southern boundary and the adjacent oceanic algero balearic basin have provided images of the neo tectonic structures of the region equal to those provided by subaerial photography for the first time we mapped with unprecedented detail the mazarron escarpment and the southeast margin of iberia the first order structures of the region are due to the consequence of the collision of the african and eurasian plates during the alpine orogeny in late oligocene middle miocene the westward migration of the alboran plate in the middle miocene and the desiccation of the mediterranean in the messinian late miocene that led to the deposition of evaporites in the algero balearic basin and erosion of the mazarron escarpment the sierra de cartagena la union shelf the mar menor margin and the adjacent coast our data images second order tectonic features neo tectonic features superimposed on the larger structures these include the deformation of the strata in the algero balearic basin by the gliding of the plio quaternary sediments on messinian halite on the margins of the basin and sediment loading in its center the late miocene quaternary deformation of the area north of the mazarron escarpment resulting from the continuous oblique convergence of the african and eurasian plates in a nnw sse direction the miocene to pleistocene volcanic edifices and pinnacles dikes the pockmarks formed by the extrusion of gas water via faults and the massive gravitational failure of the mazarron escarpment triggered by this plate convergence the data also show in detail features formed on the mazarron escarpment during the messinian pliocene and pleistocene regressions and those on the shelf formed during the pleistocene glacially induced regressions transgression and sediment drifts generated by modern currents