distribution of arenaceous foraminifera in depth profiles of the southern ocean kerguelen plateau area abstract recent to subrecent benthonic arenaceous foraminifera from two areas of the southern ocean have been investigated with regard to their depth distribution and agglutination patterns strong differences exist between the arenaceous faunas from a diatomaceous sediments west of the kerguelen plateau and b glacial marine sediments from the slope of the antarctic continent major ecologic influences are seen in the effect of sedimentological factors especially the clay content of the sediment in the saturation level of calcium carbonate and in the nutrient condition of the biotope since these factors are a function of geographic position and related water masses the main differences of deep sea faunas are primarily induced by the overall situation of an oceanic area rather than by depth or oceanographic factors like temperature or salinity availability of colloidal iron compounds also seems to be a limiting factor for distinct arenaceous species

geochemistry of surface sediments from the arabian sea we report new geochemical data si al na k rb sr mn cu ni fe zn co and pb for 126 surficial sediments and base metal partition data for limited samples from the deep arabian sea and discuss the controls affecting these elemental concentrations the geochemical nature of and differences between sediments from three physiographically tectonically distinct regions have been identified the spatial resolution allows us to discern the various processes operative in the deep arabian sea during the holocene epoch r mode factor analysis on the geochemical data suggests that four dominant factors are responsible for the observed geochemical variations in the samples namely carlsberg ridge hydrothermal activity terrigenous contribution hydrogenous authigenic precipitates and biological contribution

oceanographic controls on benthic foraminifers from the bellingshausen margin of the antarctic peninsula abstract surface sediment samples collected from the bellingshausen sea continental margin of the antarctic peninsula were analyzed for benthic foraminifers a total fauna including live and dead specimen counts was used to statistically identify discrete benthic foraminifer assemblages two major assemblages were defined the bulimina aculeata and fursenkoina spp assemblages the distribution of the bulimina aculeata and fursenkoina spp assemblages are closely associated with the distribution of the two dominant bottom water masses on the continental margin the circumpolar warm deep water and weddell sea transitional water respectively their distributions cannot be related to organic carbon content or sediment texture of the surface sediments the faunal composition of the bellingshausen sea margin assemblages and their water mass associations are similar to faunal water mass relationships observed in the weddell sea and south atlantic ocean where bulimina aculeata is associated with circumpolar deep water and nonionella iridea n bradii and trifarina earlandi are associated with eastern shelf and modified weddell sea water

structural pattern of the galapagos microplate and evolution of the galapagos triple junctions a 13 000 km2 microplate intervenes to prevent the junction of the nazca cocos and pacific plates in the eastern equatorial pacific ocean west of the galapagos islands the microplate is rotating clockwise at 6 m y about an absolute pole 400 km southeast of its center so that although its northern margin has a similar motion to adjacent parts of the cocos plate its southern margin is 50 slower the perimeter of the galapagos microplate is best defined by bathymetry and has been surveyed with sea beam and examined by deep tow two of the three triple junctions on its margins are ridge ridge ridge rrr junctions 160 km apart on the crest of the east pacific rise epr the most like a classic rrr junction is the pacific nazca galapagos intersection at 1 10 n where the epr axis is joined by a narrow volcanic ridge 70 km long and 1 km high the cocos nazca galapagos junction at the west end of the cocos nazca spreading center is inferred to be of the rff type but the transform fault branches are represented by large nontransform offsets lack of stable transform faults is related to rapid westward migration of the junction caused by lengthening of the cocos nazca axis at 60 70 mm yr this rate which was once required to maintain a stable nazca cocos pacific rrr junction has persisted even after birth of the microplate about 1 ma continuing propagation of the cocos nazca axis has opened up the hess deep rift basin in the eastern epr flank in advance of the eruptive propagator tip this rift valley has a relief of more than 3 km from its uplifted rims to the floor where severe attenuation exposes basal layers of the epr crust the similar dietz deep rift basin at the southeastern margin of the microplate 70 km from hess deep was formed when a lengthening galapagos nazca spreading axis rifted through another part of the epr flank

benthic foraminiferal evidence and paleoenvironmental evolution of holocene coastal plains in the aegean sea greece abstract benthic foraminiferal composition of sedimentary successions during the last 7500 years was investigated from boreholes drilled in three rather tectonically stable coastal areas of the aegean sea alykes kitros lafrouda thrace and vravron attica the quantitative analysis of foraminiferal fauna enabled separation into two different groups that are supported by the analysis of modern benthic foraminiferal communities in the studied sites group a consists of ammonia tepida and haynesina germanica closed lagoon assemblage whereas the most common species of group b open lagoon assemblage are aubignyna perlucida miliolids elphidium spp and ammonia spp the foraminiferal composition integrated with radiometric dating provides information on holocene paleoenvironmental changes in the studied coastal plains related to sea land interaction alykes kitros and lafrouda thrace boreholes show a similar trend with an open lagoonal fauna in the lower part transitional upwards to closed lagoonal conditions this environmental change has taken place after 6500 cal bp in alykes kitros and around 3000 cal bp at lafrouda thrace the benthic communities of vravron attica borehole sediments seem to represent continuously an open lagoon shallow marine environment from 4700 to 400 cal bp

1 ma east pacific rise oceanic crust and uppermost mantle exposed by rifting in hess deep equatorial pacific ocean abstract a series of dives with the french submersible nautile has been conducted in the region of the galapagos triple junction at the tip of the cocos nazca propagator most of the dives were devoted to the study of hess deep a rift valley produced by rifting of oceanic crust created at the axis of the very fast spreading east pacific rise the dives have enabled the structures and lithologies to be assessed and confirmed earlier dredging evidence for abundant basal crust and mantle rocks on an intra rift ridge located to the north of the axis of hess deep this shows that this situation is not specific not slow spreading ridges a nearly complete and unique log of young 1 ma crust and uppermost mantle representative of very fast accretion can be reconstructed even though the section is discontinuous and highly dismembered we propose two models that can explain the exposure on the ocean floor of the deep foundation of the oceanic crust one model stresses symmetry and vertical tectonics through isostasy diapirism of serpentinized mantle another model requires a larger amount of extension and emphasizes asymmetry with denudation of the upper crust through low angle detachment faulting in both models which differ mainly in the structure at depth amagmatic extension of east pacific rise crust by the cocos nazca propagator tip results in uplift and denudation of lower crust and upper mantle

signature of the brazil malvinas confluence argentine basin in the isotopic composition of planktonic foraminifera from surface sediments we explored the potential to use the stable isotopic compositions of planktonic foraminifera as a proxy for the position of the brazil malvinas confluence bmc in the argentine basin for this purpose we measured the oxygen and carbon isotopic compositions of globigerinoides ruber pink and white varieties measured separately globigerinoides trilobus globigerina bulloides globorotalia inflata and globorotalia truncatulinoides left and right coiling forms measured separately from a latitudinal transect of 56 surface sediment samples from the continental slope off brazil uruguay and argentina between 20 and 48 s lowest oxygen isotopes values were found in g ruber pink followed by g ruber white and g trilobus reflecting the highly stratified near surface water conditions north of the bmc globigerina bulloides was present mainly south of the bmc and records subsurface conditions supporting earlier plankton tow studies globorotalia inflata and g truncatulinoides left and right were both available over the whole transect and calcify in the depth level with the steepest temperature change across the bmc accordingly the 18 o of these species depict a sharp gradient of 2 at the confluence with remarkably stable values north and south of the bmc our data show that the oxygen isotopic composition of g inflata and g truncatulinoides left and right are the most reliable indicators for the present position of the bmc and can therefore be used to define the past migration of the front if appropriate cores are available

natural variability of benthic foraminiferal assemblages and metal concentrations during the last 150 years in the ingoydjupet trough sw barents sea abstract while today the sw barents sea is a relatively un impacted and uncontaminated area industrial activities related to the petroleum industry are projected to increase in the coming decades this makes the area a valuable natural laboratory to establish pre impacted baselines as a precursor for future seabed monitoring programs here we present benthic foraminiferal assemblages and metal concentrations in four sediment cores from the ingoydjupet trough sw barents sea covering approximately the last 150 years this information supports the application of foraminiferal assemblages as a bio monitoring tool applicable in high latitudes at all stations metal concentrations in the sediment correspond to no effect concentrations the downcore metal concentrations are mainly attributed to natural variability of the clay fraction and total organic content of the sediments agglutinated foraminifera are poorly preserved down core patterns in the calcareous foraminiferal assemblages suggest an enhanced food supply as a result of increased atlantic water inflow through the region during the last 150 years at near shore stations the norwegian coastal current additionally influences assemblages decadal scale climatic oscillations are indicated by increased calcareous fluxes and are attributed to variability in the food rich atlantic water this study serves as an important baseline data set prior to increasing industrial activities in the sw barents sea and thereby contributes to a better understanding of natural environmental variability

benthic foraminiferal distribution and abundance changes in skagerrak surface sediments 1937 hoglund and 1992 1993 data compared both living stained and dead unstained foraminiferal assemblages from surface sediments 0 2 cm in the northwestern part of the skagerrak have been studied in order to 1 define and characterize the distribution of various modern benthic environments and 2 by comparing these findings with surface samples collected 40 60 years ago to document possible faunal changes that might have occurred the investigated area is physiographically divided into the norwegian slope the skagerrak basin and the danish slope the latter is under the influence of the jutland current while the basin and the investigated parts of the norwegian slope are bathed in atlantic water all areas have bottom waters with a high oxygen concentration three living stained and three dead unstained assemblages occupy the three physiographic areas only one assemblage on the norwegian slope is common to both the living and dead assemblages but the boundaries between them lie at comparable depths the higher standing crops are found on the fertile danish slope while the lower ones are in the deep basin where the diversity is at a maximum in the dead assemblages the relative abundance of agglutinated tests increases with depth comparison with data collected 40 to 60 years ago shows increases in absolute numbers of tests especially in the deep basin there are changes in assemblage compositions in all areas the dominant species found in 1937 are different from those of 1992 1993 there is a major change in the basin where one agglutinated species has changed its depth distribution downslope and two present day abundant species are new arrivals these faunal events are probably linked to environmental changes

environmental evolution of the paliouras coastal lagoon in the eastern thermaikos gulf greece during holocene the integration of lithology determination micropaleontological and molluscan analyses scanning electron microscopy magnetic susceptibility measurement and radiocarbon dating contributed to the interpretation of a sedimentary succession recovered from a 870 cm long borehole drilled at the paliouras coastal lagoon in the eastern thermaikos gulf greece in this way the reconstruction of the creation and evolution of the lagoon during the last 8000 years was accomplished four main evolutionary phases are identified 1 initially the pre holocene basement of the study area was inundated during the early holocene marine transgression 2 since 8000 7900 cal yr bp an inner lagoon had been formed in the paliouras coastal plain within a rather restricted environment characterized by a haynesina germanica cerastoderma glaucum and hydrobia sp assemblage relatively high sediment magnetic susceptibility and an intense presence of abnormal foraminiferal tests and lenticular gypsum crystals 3 during 7600 6900 cal yr bp the inner lagoon presented a transition to an open system clearly connected to the sea and characterized by an ammonia beccarii aubignyna perlucida and miliolids assemblage more diversified molluscan fauna minimum sediment magnetic susceptibility and the occurrence of lenticular gypsum aggregates and finally 4 since 5900 cal yr bp to the present time the lagoon water body appears isolated from the marine environment except of occasional seawater intrusions the proposed evolutionary scenario for the paliouras coastal lagoon is in accordance with the existing models of the sea level rise in the aegean coastal areas concerning the time span before 4000 yr bp and the mid late holocene climate events

factors influencing the distribution patterns of recent deep sea benthic foraminifera east of new zealand southwest pacific ocean abstract this study investigates which combination of environmental factors most strongly influences the distribution patterns of benthic foraminferal tests 0 63 m in a region bisected by the subtropical front east of new zealand seafloor sample sites extend from outer shelf 90 m to abyssal 4700 m depths across substrates ranging from biogenic terrigenous gravelly sand to hemipelagic mud and occur under the influence of antarctic intermediate water aaiw and circumpolar deep waters as well as receiving detritus from both subtropical and subantarctic surface water masses elevated values of the planktic foraminiferal fragmentation index and reworked small paleogene planktic foraminifera at outer shelf and bathyal depths coincide with areas of strong bottom currents q mode cluster analysis on the census counts of 398 benthic species clusters the 66 samples into three large groups shallow bathyal abyssal and at a lower level 10 mappable associations are recognised a combination of canonical correspondence analysis and a correlation coefficient matrix was used to relate the faunal data to a set of measured environmental proxies these analyses show that factors that have a relationship with depth are the most significant in determining foraminiferal distribution the principal environmental factors which appear to most strongly influence this benthic foraminiferal distribution are dissolved oxygen content in bottom waters sustainability of organic carbon flux rates seasonality of food supply lateral advection of water masses bottom water carbonate corrosiveness energetic state at the benthic boundary layer grain size composition of substrate salinity and temperature of the bottom waters shallow water associations 90 1250 m dominated by cassidulina carinata and trifarina angulosa occur within coarse substrates under well oxygenated high energy regimes and sustained food input the occurrence of the bathyal associations 230 2840 m dominated by c carinata alabaminella weddellensis and abditodentrix pseudothalmanni closely mirrors the distribution of aaiw within a region of variable food supply the sustainability of food supply combined with bottom water type and associated ventilation and dissolution strongly influence the composition of abyssal associations 1200 4700 m mostly dominated by epistominella exigua and a weddellensis

evidence for control of abyssal agglutinated foraminiferal community structure by substrate disturbance results from the hebble area abstract deep sea agglutinated foraminifera have been quantitatively examined from 28 coretop samples from seven box cores collected in june 1983 at the hebble high energy benthic boundary layer experiment site 40 27 n 62 20 w 4815 4825 m depth and hebble shallow site 40 53 n 63 44 w 4185 m depth on the nova scotian continental rise samples from the relatively tranquil hebble shallow site can be distinguished from the hebble site on the basis of their microfauna a q mode varimax factor analysis of species frequency data delineates three major faunal assemblages 1 1 a faunal assemblage from the hebble site dominated by ammobaculties sp cf a americanus this assemblage exhibits lowest species diversity suggesting a disturbed community and strongly associated with box cores containing fine grained laminated sediments 2 2 an assemblage associated with box cores from the hebble meadow dominated by saccammina tubulata psammosphaera sp cf p fusca a coarsely grained species of psammosphaera and reophax sp 1 3 3 a fauna occurring at the hebble shallow site dominated by hormosinella distans with reophax bacillaris and ammobaculites agglutinans unique to the assemblage this fauna displays a higher ratio of calcareous to agglutinated species significantly higher species diversity lower variability and a greater proportion of hormosinids and species utilizing finer grains than samples from the hebble site which is interpreted as reflecting environmental stability marked heterogeneity exists among agglutinated foraminiferal assemblages within box cores at the hebble meadow within box core faunal variability exceeds between box core variability suggesting that environmental factors influencing the distribution of species are patchy on a scale of approximately 40 cm

distribution and ecology of benthic foraminifera in mcmurdo sound antarctica abstract foraminifera from modern sediments in mcmurdo sound have been studied to provide a basis for interpreting fossil assemblages there the sound is 50 km across more than 900 m deep and ice covered for at least nine months of the year the salinity and temperature of the bottom water are nearly constant 33 96 34 99 and 1 95 c 1 4 c sea floor sediment is mainly fine sand and mud with a little ice rafted gravel nearly 40 000 specimens of foraminifers 2334 living and 36 875 dead were identified from 28 samples collected by gravity corer and grab from sites varying in depth between 79 and 856 m three present day assemblages can be recognised 1 1 shallow open water assemblage swa from 110 to 560 m found in shallower areas of the open sound dominated by calcareous species 2 2 deep open water assemblage dwa from 620 to 856 m found in deeper areas of central mcmurdo sound dominated by agglutinated species and 3 3 harbour assemblages ha from 79 to 796 m in the enclosed basins and harbours of the area dominated by agglutinates species the composition of the assemblages is controlled chiefly by the calcium carbonate compensaion depth ccd calcareous species are abundant and varied 84 calcareous species in the swa above 620 m but are almost absent from the dwa the dominance of agglutinated foraminifera in the ha indicates a shallower ccd about 230 m in restricted coastal settings comparison of mcmurdo sound assemblages to those from other areas of the antarctic the arctic and the deep ocean indicates that there are grpss similarities in the over all faunas but actual species in commin range from 6 to 41 of the mcmurdo sound total assemblage 124 species death assemblages have a similar species diversity to corresponding life assemblages from 620 the ccd to 420 m where death assembalges are representative of them except for open water assemblages from 620 the ccd to 420 m where death assemblages are depleted in calcareous taxa the diversity of the agglutinated component of each assemblage remains nearly constant in all habitats and at all water depths

metal variations in divergent plate boundary sediments from the pacific abstract one hundred and three deep sea sediments have been recovered on traverses along the east pacific rise epr between 3 and 20 s and the galapagos rift system grs between 86 and 102 w analyses of 23 elements by instrumental neutron activation revealed that co zn as and sb covary with fe suggesting probable adsorption of these metals from seawater onto fe oxyhydroxides as was found to be significantly higher in epr sediments probably due to hydrothermal as input sb and zn are especially enriched in the sediments of the easternmost traverse of the grs near the hydrothermal mounds area chemical gradients of some metals with depth in the sediments were found in particular u enrichment occurs in sediments from the epr at 13 s and zn and sb enrichment with depth is observed in the sediments near the hydrothermal mounds area rare earth elements ree contents of sediments are low compared to pelagic clay but epr sediments have slightly higher ree than grs sediments trivalent ree correlate with fe and the same is observed for ce grs sediments have however higher ce contents suggesting probably an additional biogenic input for ce in equatorial pacific regions a number of epr and grs sediments have significant au 10 20 ppb and some of the sediments have relatively high ag up to 13 ppm

impact of oil based drill mud disposal on benthic foraminiferal assemblages on the continental margin off angola abstract in order to assess the possible environmental impact of oily cuttings discharged during oil exploration activities we studied the benthic foraminiferal faunas in a five station 4 km long sampling transect around a cuttings disposal site at about 670 m depth offshore angola w africa where drilling activities started 1 5 years before sampling living rose bengal stained and dead foraminiferal faunas were sampled in march 2006 the faunal patterns mirror the spatial distribution of hydrocarbons which are dispersed into a southeastern direction four different areas can be distinguished on the basis of the investigated faunal parameters density diversity and species composition of the living fauna and comparison with subrecent dead faunas the fauna at station s31 300 m se of the oil cuttings disposal site appears to be clearly impacted the faunal density and diversity are maximal but evenness is minimal taxa sensitive to organic enrichment such as uvigerina peregrina cancris auriculus and cribrostomoides subglobosus have largely disappeared whereas the low oxygen resistant taxon chilostomella oolina and opportunistic buliminids and bolivinids attain relatively high densities at station s32 500 m se of the disposal site environmental impact is still perceptible the faunal density is slightly increased and u peregrina apparently the most sensitive species is still almost absent the faunas found at 1 and 1 8 km se of the disposal site are apparently no longer impacted by the drill mud disposal faunal density and diversity are low and the faunal composition is typical for a mesotrophic to eutrophic upper slope environment finally station s35 2 km nw of the disposal site contains an intermediate fauna where both the low oxygen resistant c oolina and the more sensitive taxa u peregrina c auriculus and c subglobosus are present all taxa live close to the sediment water interface here indicating a reduced oxygen penetration into the sediment since the hydrocarbon concentration is low at this station it appears that the faunal characteristics are the consequence of a slightly different environmental setting and not due to a contamination with drill cuttings our data underline the large potential of benthic foraminifera as bio indicators of anthropogenic enrichment in open marine settings such as caused by the disposal of oily drill cuttings the foraminiferal faunas react essentially by a density increase of a number of tolerant and or opportunistic taxa and a progressive disappearance of more sensitive taxa in the most impacted area rather surprisingly large sized taxa appear to be more sensitive than small sized foraminiferal taxa

benthic foraminiferal distribution at middle valley juan de fuca ridge a northeast pacific hydrothermal venting site fourteen benthic foraminiferal bearing surface samples collected from the area of active venting aav in middle valley at a depth of 2430 m at the northern end of juan de fuca ridge northeast pacific ocean yielded 156 identifiable taxa sample sites were selected near active or recently active vents where temperatures up to 274 c have been measured the sea floor beyond hydrothermal mounds is characterized by unaltered soft hemipelagic mud and is dominated by a calcareous foraminiferal assemblage which includes numerous allochthonous species derived from the shelf via turbidite flows into the valley within the aav agglutinated foraminifera dominate with proximity to hydrothermal vent activity species of the family hormosinidae subfamily reophacinae dominate in the hydrothermal habitat because of their success at colonization attached agglutinated foraminifera densely colonize the indurated sediment in close proximity to vent sites however like the macrofauna observed near hydrothermal vents foraminifera do not venture into the extreme habitats where temperatures are greater than 20 c where clam beds are found in association with active hydrogen sulphide venting benthic foraminifera occur rarely these beds occur in loose pyritic mud that is toxic to all but species e g the clam culyp ena that co exist symbiotically with sulphur oxidizing bacteria the sparse distribution of calcareous benthic foraminifera in the vent areas is caused by enhanced carbonate dissolution at ph values of 5 2 low foraminiferal abundance and species diversity at the immediate site of active venting is attributed to rapid changes in physical and chemical conditions caused by circulating hydrothermal vent waters

coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features the spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set from october 1978 through june 1986 enhanced pigment concentrations are observed between 35 s and 55 s throughout the year with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter north and south of the polar front phytoplankton blooms 1 mg m3 are not uniformly distributed around the circumpolar region instead blooms appear to be located in regions of ice retreat or high melt areas such as the scotia sea and the ross sea in relatively shallow areas e g the patagonian and the new zealand shelves in some regions of ekman upwelling like the tasman sea and near areas of high eddy kinetic energy such as the agulhas retroflection among all features examined by regression analysis bathymetry appears to be the one most consistently correlated with pigments correlation coefficient being about 0 3 for the entire region the cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the antarctic region it is also consistent with resuspension of phytoplankton cells by wind induced mixing especially in shallow waters on the other hand in the deep ocean especially at latitudes 30 in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters

petrology of the east pacific rise crust and upper mantle exposed in hess deep eastern equatorial pacific the hess deep a rifted oval shaped depression located east of the galapagos triple junction at the tip of the cocos nazca ridge about 101 w 2 n was explored in 1988 during 21 submersible dives a total of 11 dives were devoted to the exploration of the e w trending intrarift ridge 15 km in length 3000 5400 m in depth north of the hess deep depression the intrarift ridge represents an outcrop of recent 1 m y crustal and subcrustal material created at the axis of the east pacific rise epr and emplaced during the lithospheric extention responsible for the westward propagation of the cocos nazca rift francheteau et al 1990 the lithospheric block has undergone cataclastic deformation and was dislocated by tectonic activity as attested to by the mixed and erratic distribution of rock types and by the occurrence of polygenic breccias and gabbroic mylonites the samples are metamorphosed to varying degrees but their protolith textures are generally well preserved their relic mineralogy indicates that they consist of harzburgites dunites gabbroic cumulates gabbronorites and olivine gabbros isotropic gabbros dolerites and basalts some samples of refractory harzburgites and most dunitic cumulates with local accumulation of chromite have been impregnated by wehrlitic and gabbroic primitive melts similar to those described from the mantle crust transition zone of the samail ophiolite complex oman the mineral chemistry indicate that the ultramafics partly reequilibrated with the magmatic impregnations in the liquidus solidus temperature range of 980 1100 c the dolerites and basalts have been derived from mid ocean ridge basalt primary melts presenting a broad range of incompatible element composition which suggests intermittent cycles of magmatic processes involving a progressive melting of a composite source with discontinous extraction of liquids as proposed for the epr volcanics near 13 n hekinian et al 1989 most of the rocks underwent partial retrograde metamorphism and recorded several episodes of recrystallization from the upper greenschist facies ultramafics and gabbros to diagenetic alteration volcanics the cumulate gabbronorites the isotropic gabbros and some dolerites were partially albitized and amphibolitized during the penetration of seawater in the ocean crust prior to serpentinization several samples of unfoliated amphibolites are believed to be completely metamorphosed gabbroic rocks the gabbroic cumulates and the plagioclase rich melt impregnations were variably rodingitized presence of various ca silicates such as epidote prehnite hydrogarnet and zeolite in relation to the serpentinization of the peridotites one dive located on the scarps forming the northern wall of the hess deep to the east of the explored area revealed the presence of in situ outcrops of isotropic gabbros doleritic dikes and extrusives and permitted to observe the contact between the sheeted dike complex and the high level isotropic gabbros

chemical characteristics of metalliferous sediments from eight areas on the galapagos rift and east pacific rise between 2 n and 42 s abstract 594 sediment samples from eight areas situated along the crest of the east pacific rise epr and the galapagos rift system grs have been analyzed for 12 elements in order to evaluate the relative importance of the metalliferous component in each of the areas the data show marked differences in sediment composition between the two rifts the non carbonate fraction of the galapagos rift sediments consists of detrital alumosilicates biogenic opal and probably authigenic fe smectite surface sediments are diagenetically enriched in mn from east to west the detrital contribution decreases as the authigenic fe smectite increases authigenic fe smectite is most abundant at the tectonically active wall of the northern margin of the galapagos gore in the hess deep area hydrothermal input increases markedly along the epr from 2 n to 42 s the maximum input identified from high fe mn cu and zn values is at 20 s bottom currents have shifted the metalliferous sediments to the west of the rise at this location south of 10 s the sediments are basically undifferentiated fe mn hydroxides

factors influencing the distribution of subantarctic deep sea benthic foraminifera campbell and bounty plateaux new zealand abstract we investigate the combination of environmental factors that influence the distribution patterns of benthic foraminiferal tests 63 m in a topographically varied region crossed by both the subtropical and subantarctic fronts south east of new zealand seafloor sample sites extending from outer shelf 50 m to abyssal 5000 m depths are bathed by five different water masses and receive phytodetritus from subtropical subantarctic and circumpolar surface water masses eight mappable associations are recognised by q mode cluster analysis of the benthic foraminiferal census data similar associations are identified using cluster analysis based solely on the presence or absence of species canonical correspondence analysis and a correlation coefficient matrix were used to relate the faunal data to a set of environmental proxies these show that factors related to water depth especially decreasing food supply with increasing depth are the most significant in determining the overall foraminiferal distribution other contributing factors include surface water productivity and its seasonality bottom water ventilation energetic state of the benthic boundary layer and resulting substrate texture and bottom water carbonate corrosiveness three shallow water associations 50 700 m dominated by cassidulina carinata trifarina angulosa globocassidulina canalisuturata gavelinopsis praegeri and bolivina robusta occur in coarse substrates on the continental shelf and on the crests and upper slopes of four seamounts under well oxygenated high energy regimes and high food input three mid bathyal to upper abyssal associations 500 3300 m dominated by alabaminella weddellensis c carinata and epistominella exigua occur in biopelagic sandy mud beneath a region of strongly seasonal food supply with their composition influenced by total food flux ventilation oxygen minimum zone and bottom current strength an unusual lower bathyal association 1200 2100 m dominated by t angulosa and ehrenbergina glabra occurs in a belt of coarser sandy substrate that runs along the crest of the submarine plateaux slopes beneath the strongly flowing subantarctic front related currents a deep abyssal association 3500 5000 m dominated by nuttallides umbonifer and globocassidulina subglobosa occurs on the abyssal plain beneath oligotrophic lower circumpolar water south east of the subantarctic front and is strongly influenced by the cold carbonate corrosive conditions the faunal composition of this subantarctic region is most similar to adjacent southern new zealand but with the addition of a few significant antarctic elements e g e glabra globocassidulina crassa

recent benthic foraminiferal associations and ecology of the scotia sea and argentine basin abstract we investigated 88 surface sediment samples taken with a multiple corer from the southwestern south atlantic ocean for their live rose bengal stained and dead benthic foraminiferal content using q mode principal component analysis six live and six dead associations are differentiated live and dead association distributions correspond fairly well differences are mainly caused by downslope transport and selective test destruction in addition four potential fossil associations are calculated from the dead data set after removal of non fossilizable species these potential fossil associations are expected to be useful for paleoceanographic reconstructions environments are described in detail for the live and potential fossil associations and for selected species along the upper argentine continental slope strong bottom currents control the occurrence of live dead and potential fossil angulogerina angulosa associations here particles of a high organic carbon flux rate remain suspended below this high energy environment live dead and potential fossil uvigerina peregrina dominated associations correlate with enhanced sediment organic carbon content and still high organic carbon flux rates the live a angulosa and u peregrina associations correlate with high standing crops furthermore live and dead epistominella exigua nuttallides umbonifer associations were separated dominance of a nuttallides umbonifer potential fossil association relates to coverage by antarctic bottom water aabw and lower circumpolar deep water lcdw above the calcite compensation depth ccd three associations of mainly agglutinated foraminifera occur in sediments bathed mainly by aabw or cdw a reophax difflugiformis association was found in mud rich and diatomaceous sediments below the ccd a psammosphaera fusca association occurs in coarse sediments poor in organic carbon while a cribrostomoides subglobosus ammobaculites agglutinans association covers a more variable environmental range with mud contents exceeding 30 one single eggerella bradyi martinottiella communis association poor in both species and individuals remains from the agglutinated associations below the ccd if only preservable species are considered for calculation

deep sea pollen from the south china sea pleistocene indicators of east asian monsoon abstract a high resolution pollen record sampling interval averages 820 years has been obtained from odp site 1144 water depth 2037 m northern south china sea the 504 m sequence in composition length covers the last 1 03 million years according to micropaleontological and isotopic stratigraphy the pollen assemblages are characterized by high proportions of pinus and herb pollen and by their frequent alternations based on these alternations 29 pollen zones have been recognized that are closely correlated to the marine oxygen isotope stages mis 1 29 pinus dominant pollen zones correspond to interglacial periods with lighter 18o values while herb marked ones relate to the heavier 18o stages assigned to glacials judging from the pollen data the exposed northern continental shelf of the south china sea during the glacials was covered by grassland and the extensive northern shelf has formed only since mis 6 ca 150 ka probably as a result of tectonic subsidence tree pollen influx values are indicative of winter monsoon which began to intensify 600 ka ago the summer monsoon variations can be approximated by the fern percentage within the total pollen and spore abundance and the result shows high values in general occurring at interglacials with the maxima at mis 15 5e and 1 the relatively high fern percentage with smaller amplitude in variations before 600 ka might suggest more stable humid conditions before the intensification of winter monsoon

benthic foraminiferal assemblages from the eastern weddell sea between 68 and 73 s distribution ecology and fossilization potential surface sediment samples taken with a vented box corer from the eastern weddell sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content the live fauna was differentiated from empty tests comprising the foraminiferal death assemblage based on the dead assemblages potential fossil assemblages were calculated to facilitate the analogy with late neogene core material five distinct live assemblages inhabit the continental margin today six dead assemblages and five potential fossil assemblages respectively correspond to these biocoenoses a predominantly calcareous live fauna dominated by trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope below this on the upper slope down to 2000 m water depth the predominantly calcareous bulimina aculeata assemblage coincides with the core of warm 0 c weddell deep water and with fine and more organic rich sediments these calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment which depends largely on the grain size distribution of the sediment and the fluxes of organic matter therefore a still calcareous t angulosa dominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by martinottiella nodulosa the characteristic arenaceous fossil remnant of the former predominantly calcareous live b aculeata fauna on a continental terrace between 2500 and 3500 m water depth cribrostomoides subglobosus dominates the live fauna but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by oridorsalis umbonatus and epistominella exigua comprises the dead assemblage and the potential fossil assemblage respectively on the lower continental slope between the carbonate lysocline 3500 m and the carbonate compensation depth 4000 m tests of nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna which is associated with the lower part of the antarctic bottom water aabw this corroborates earlier investigations suggesting a relationship between the carbonate corrosiveness of water masses and the distribution of n umbonifer this is important for inferring paleo routes and estimates of paleo production rates of aabw during the neogene

live and dead benthic foraminiferal faunas from whittard canyon ne atlantic focus on taphonomic processes and paleo environmental applications abstract dead benthic foraminiferal assemblages were studied in the 150 m fraction of 4 5 cm deep sediment levels at 18 stations in the whittard canyon area in june 2007 this sediment layer is composed of fairly recent sediment in both canyon branches the population dynamics such as seasonal response to phytodetritus deposition certainly contribute to differences between live and dead faunas for instance bulimina marginata which is usually considered as an opportunistic species is over represented in the dead assemblage the fragility of the tests of some species can explain their total absence in the thanatocoenoses this concerns many organic cemented arenaceous tests miliolid tests sensitive to dissolution and perforate taxa with thin tests furthermore transport e g sediment gravity flows active in both canyon branches leads to an increasing relative contribution of allochthonous individuals originating from outer shelf and upper canyon sites towards the deeper canyon stations consequently the dead faunas do no reflect local environmental conditions the high abundance of transported dead foraminifera in both canyon branches leads to important biases in the foraminiferal assemblage composition but may also significantly bias the interpretation of 13 c 18 o trace elements and 14 c concentration in foraminiferal shells it may therefore strongly complicate the reconstruction of environmental parameters such as bottom water temperature or exported paleoproductivity and radiocarbon dating of the foraminiferal assemblages therefore in both canyon axes the use of dead foraminiferal faunas to reconstruct paleoenvironmental in situ conditions is precluded however the study of dead assemblages in the canyon branches in particular the quantity of allochthonous foraminifera can give important clues about the downslope sedimentary dynamics on both open slopes despite taphonomic test destruction and biological processes population dynamics the distribution and the composition of the live fauna resemble those of the dead assemblage in these areas dead foraminiferal faunas include much less material derived from downslope transport consequently on the open slope dead assemblages appear to better reflect local conditions therefore the ecological information obtained from fossil open slope samples can be more reliably used to reconstruct paleoenvironmental conditions

a benthic foraminiferal proxy of pulsed organic matter paleofluxes in the temperate open ocean of the modern northeast atlantic the spring bloom of phytoplankton leads to a seasonal pulse of detrital organic material phytodetritus to the ocean floor opportunistic benthic foraminifera rapidly colonise this food resource producing large numbers of individuals whose tests are ultimately added to the sediment one of these taxa epistominella exigua shows periodic peaks in abundance in the fossil record at many open ocean sites previously such peaks have been commonly interpreted to result from changes in physicochemical properties of bottom water mass and thus deep sea circulation the main purpose of this paper is to propose thate exigua may be used as a proxy of pulsed organic matter inputs to the deep ocean and therefore as an indicator of relative changes in productivity

hydrothermal serpentine in a hess deep sediment core abstract the mineralogy and chemistry of a sediment core from the hess deep is studied in detail the top 46 cm consists of a high charge smectite calcite and feldspar whereas serpentine dominates the lower portion of the core the serpentine was identified as 2m clinochrysotile microscopic and chemical studies suggest that the serpentine has been precipitated from hydrothermal solutions

planktic foraminifera from the mid cretaceous barremian early albian of the north sea basin palaeoecological and palaeoceanographic implications abstract a marine cretaceous succession barremian albian of a cored borehole bgs 81 40 located in the central north sea basin has been examined with respect to its planktic and benthic foraminiferal content as well as for calcareous nannofossils the distribution patterns of foraminifera and calcareous nannofossils allow for a two fold division of the investigated interval 1 the barremian earliest aptian interval which reflects a marine temporary restricted setting this is indicated by sporadic occurrences of planktic foraminifera with very rare planispiral forms suggesting short term connections of the boreal and tethyan realms the benthic foraminiferal assemblages indicate aerobic sometimes dysaerobic bottom water conditions high abundances of nannoconids in the barremian suggest enhanced stratification and or warm oligotrophic surface water 2 the late aptian early albian interval which was characterised by an open oceanic environment with cool and aerobic surface water conditions planktic foraminifera are more abundant and diverse than in the lower interval trochospiral hedbergellids dominate the foraminiferal assemblages the episodic occurrences of planispiral clavate and trochospiral flattened planktic morphotypes indicate the existence of a seaway between the boreal and the tethyan realms aerobic to dysaerobic bottom water conditions are suggested by the composition of the benthic foraminiferal assemblages high abundances of cool water taxa within the calcareous nannofossil assemblages indicate a cooling trend across the latest aptian and earliest albian

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

late quaternary changes in surface water and deep water masses of the nordic seas and north eastern north atlantic a review quantitative and semiquantitative proxy data based on more than 200 core top samples and 100 deep sea cores lead to important new insights about late quaternary changes in paleo oceanography climate and microfaunal habitats in the north eastern north atlantic and nordic seas insights resulting from a detailed investigation by the kiel research project sfb 313 132 summarized in this paper planktonic foraminifera species provide reliable tracers of past sea surface temperatures and currents the genus beella in particular was found to trace subtropical water masses up to the far north benthic foraminifera species served as sensors of bottom currents and local flux rates of organic matter new orders of time resolution are reached via stable isotope stratigraphy and accelerator mass spectrometry carbon 14 dating allowing the identification of meltwater events lasting a few hundred years and shorter a time range where however the yet unquantified role of bioturbation presents a growing problem based on this high resolution stratigraphy a number of time slices synoptic time intervals are defined to reconstruct the incursion of atlantic water masses to map paleocurrent patterns within the nordic seas and the north eastern north atlantic and to test alternative circulation models for example for the last glacial maximum lgm and various meltwater episodes these are clearly coeval with dansgaard oeschger events found in greenland ice cores with the actual cause of the flickering climate as yet unknown likewise there is ongoing controversy about the extent of past sea ice cover and about possible changes from the present anti estuarine to estuarine mode of deep water exchange between the north atlantic and the nordic seas during the lgm south of iceland however the history of deep water renewal over the last glacial cycle covering the last 30000 years was largely deciphered

ecology of deep sea benthic foraminifera in the north atlantic during the last glaciation food or temperature control abstract in this study we explore the paleoecology of nineteen species and two species groups of deep sea benthic foraminifera in relation to bottom water temperature and food supply in the central north atlantic during the last glaciation 60 000 28 000 years bp the study is based on core so82 02ggc taken from 1730 m water depth on the western flank of reykjanes ridge the climate of the investigated period was extremely unstable interrupted by thirteen warmings and coolings the so called dansgaard oeschger events at so82 02ggc surface and bottom water temperatures varied with up to 5 c between the warm interstadials and the cold stadials surface productivity as indicated by the flux of planktic foraminifera varied with a factor of up to ten the dansgaard oeschger events had a significant impact on the benthic foraminiferal faunas which experienced up to 70 replacement between the interstadials and stadials multivariate analysis reveals that the investigated species can be separated into two groups group 1 including bulimina costata brizalina subspinescens epistominella decorata and trifarina angulosa was attracted to higher temperatures and high food supply group 2 including pullenia bulloides valvulineria laevigata and melonis barleeanus was attracted to colder water and low food supply three species belonging to the cold group cibicidoides wuellerstorfi oridorsalis umbonatus and eponides tumidulus are almost exclusively confined to sediments rich in ice rafted detritus a few species including nonionella iridea and epistominella vitrea show opportunistic behaviour most species are epifaunal to shallow infaunal and live today in oligotrophic to mesotrophic habitats our investigations indicate that temperature was the primary factor responsible for the relative abundance and main grouping of species however four species show little influence by temperature and several perhaps most were clearly also affected by food supply

levantine intermediate water hydrodynamic and bottom water ventilation in the northern tyrrhenian sea over the past 56 000 years new insights from benthic foraminifera and ostracods abstract foraminifera and ostracods have been quantitatively studied in core md01 2472 from the upper continental slope at water depth of 501 m to evaluate their relationship with bottom water condition variability and decipher the control of the levantine intermediate water liw current on benthic faunas the occurrence of reworked ostracod species originating from the continental shelf and the presence of shallow water elphidium ammonia benthic foraminifera are used to estimate the degree of along slope transport at the core site this has revealed two intervals of along slope transport also associated with coarse grained contourite deposits deposited during the yd and hs2 episodes planktonic benthic foraminiferal and ostracod assemblages reflect climate oscillations peaks of the polar planktonic neogloboquadrina pachyderma left coiling s may be used to identify heinrich events interstadials are marked by abundant ostracod species such as paracypris sp argilloecia acuminata and cytheropteron alatum and the presence of benthic foraminifera like bulimina marginata bulimina costata and gyroidina altiformis the b a and holocene are characterized by abundant warm water species of planktonic foraminifera and by the ostracod species polycope sp we hypothesize that there is relationship between liw intensification during cold rapid climate events and benthic fauna assemblage variations due to changes in 1 bottom water ventilation and 2 the export of nutrients and or sediment particles by bottom currents

the taphonomy of deep sea benthic foraminifera comparisons of living and dead assemblages from and gravity cores taken in the sulu sea abstract comparisons between soutar core faunal data and gravity core top data from about 500 m to 4000 m in the sulu sea show that living stained benthic foraminiferal assemblages have similar faunal patterns to those observed in living dead assemblages for both assemblages faunal abundances and diversities decrease with increasing water depth to 4000 m and core samples and gravity core top sediments taken from the same water depth yield similar dominant taxa the similarity of living and living dead assemblage data indicates that at least most of these faunal patterns are independent of seasonal variations and that neither seasonality nor post depositional effects can account for the absence of significant numbers of bolivina bulimina globobulimina chilostomella and uvigerina below about 1500 m in the sulu sea the distribution of these taxa are similar in both cores and gravity core top sediments reconfirming the conclusion that the distributions of living representatives of these taxa are not due to bottom water oxygen concentrations differences which exist between living assemblages and combined living and dead assemblages of deep sea benthic foraminifera from about 500 m to 4000 m in the sulu sea result primarily from surficial material loss in gravity core samples mixing of older material from subsurface sediments and postdepositional destruction of some taxa based on the additional examination of the living dead assemblages found in 0 5 and 1 cm intervals of the top 10 cm in two cores 1980 m and 3000 m differences in abundance and percentage patterns for fauna found at 2000 and 3000 m in the sulu sea are not correlated with sedimentation rate but appear to be more strongly influenced by mixing from older material and postdepositional processes in the sediments increasing the interval of sediments examined does not necessarily improve the similarity between living assemblage faunal patterns and those of the dead or combined living and dead assemblage

benthic foraminiferal assemblages from the eastern south atlantic polar front region between 35 and 57 s distribution ecology and fossilization potential abstract surface sediment samples taken with a multiple corer from the polar front region along two profiles in the eastern south atlantic sector between 35 and 57 s have been investigated for their benthic foraminiferal content live fauna was differentiated from the death assemblage based on the dead assemblages potential fossil assemblages dead fauna reduced by non resistant agglutinants were calculated for comparison with upper neogene core material the distribution of the potential fossil assemblages defined byq mode principal component analysis mirrors the recent hydrographic as well as the trophic situation in the eastern south atlantic ocean circulation and productivity two southern component bottom water faunas reflect the northward flow of antarctic bottom water aabw and lower circum polar deep water lcdw an assemblage dominated by the arenaceousmultifidella nodulosa below the calcite compensation depth ccd and anuttallides umbonifer dominated assemblage above the ccd in the region of highest bio silicious primary productivity south of the polar front and north of the winter sea ice limit these faunas are overprinted by a southern high productivity fauna dominated by infaunal species such aspullenia bulloides melonis pompilioides andm zaandamae north atlantic deep water nadw meets the circum polar deep water cdw at intermediate depth as reflected in the distribution of the northern component deep water fauna dominated byepistominella exigua the high productivity assemblage overprinting this fauna the northern high productivity fauna is dominated by the shallow endobenthicbulimina aculeata a strong bottom current fauna dominated byangulogerina angulosa characterizes areas between 400 and 900 m water depth with sandy sediment independent from water mass characteristics and food supply

the subantarctic and polar fronts in relation to deep water masses through the southwestern atlantic the two principal fronts within the antarctic circumpolar current acc the subantarctic front saf and the polar front pf are investigated with respect to their spatial patterns and relations to deep water masses from the northern drake passage to the western and southern argentine basin observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters east of drake passage the width of the polar frontal zone pfz increases rapidly when the saf turns sharply northward as a part of the falkland malvinas current while the pf remains oriented mainly toward the northeast found within this region of the pfz are mesoscale eddies the upper layers of which consist of subantarctic mode water from the pacific the contrasts in upper layer water properties that identify the saf can be traced the entire length of the falkland current to the brazil falkland confluence zone and then southward to the southern argentine basin there the saf turns eastward and later but perhaps not always merges with the pf north of ewing bank to form a single intense current core strongly influenced by bottom topography at times this eastward current loops southward through a gap in the falkland ridge into the georgia basin thereby supplying relatively warm and salty subantarctic water to the antarctic zone east of the gap the two fronts become separated and are once again distinct features in the vicinity of the islas orcadas rise at depth within drake passage and the western scotia sea the saf and pf are not lateral boundaries between distinct water masses but are instead identified by enhanced vertical displacements of property isopleths with the northward turn of the saf east of drake passage a thick layer of circumpolar deep water cdw is advected over the falkland plateau into the argentine basin there it is joined by waters entering the argentine basin via a deep spreading route through the georgia basin denser cdw deep water from the weddell sea and episodically deep water from the southeastern pacific ocean together these waters form a northward flow off the patagonian shelf that extends from the sea surface to the bottom most of which turns back toward the south with the falkland current return also flowing south along the seaward side of the falkland current return well away from the western boundary is the main core of north atlantic deep water nadw detatched masses of nadw are observed within the cdw at the western boundary as well as within the acc south of the saf in the south central argentine basin

the vertical thermohaline structure in the argentine basin the vertical thermohaline structure in the central argentine basin is investigated on the basis of high resolution hydrographic data emphasis is placed on fronts their horizontal gradients vertical stability and associated fine structure horizontal thermohaline gradients vary strongly with depth regions of strong gradients alternating with those of weak gradients the strongest gradients occur often at depths below the upper mixed layer the salinity gradient maximum occurs above the temperature gradient maximum enhanced gradients are found where warm salty water moves over cooler fresher water such as between the subtropical water stw and antarctic intermediate water aaiw and between the north atlantic deep water nadw and the antarctic bottom water aabw temperature salinity and density fronts do not always coexist density compensating temperature and salinity fronts occur in the surface layer of the subantarctic and at abyssal depth below 3500 m vertical profiles of the vaisala frequency indicate much reduced hydrostatic stabilities in the brazil current and subantarctic frontal zones potential vorticity minima indicate the formation of subantarctic mode water just north of the subantarctic front and its subsequent northward and upward spread across isopycnals the thermohaline fine structure is vertically intermittent the amplitude variances between the enhanced and quiet regions vary by almost 2 orders of magnitude enhanced fine structure amplitudes are found near the stw aaiw and nadw aabw interfaces where large horizontal thermohaline gradients occur and the hydrostatic stability is low the temperature and salinity fine structures are largely density compensating the coherence between the temperature and salinity fine structure is strongly depth dependent and is highest in regions where warm salty water moves over cooler fresher water

the distribution of recent benthic foraminifera in the polar front region southwest atlantic abstract twenty five core top samples from the maurice ewing bank meb and islas orcadas rise ior were examined to determine the distribution of benthic foraminifera in the vicinity of the polar front in the southwest atlantic ocean the polar front has a subsurface expression that effects the areal and depth distribution of benthic foraminifera in this region three faunal assemblages were identified by q mode factor analysis the shallowest assemblage dominated by bulimina aculeata is present from 1500 to 2600 m on the maurice ewing bank and is associated with potential temperatures of 1 71 0 50 c salinities of 34 74 34 70 and potential density values of 45 84 46 04 sigma 4 a second assemblage dominated by uvigerina peregrina occurs in water depths from 2600 to 3100 m and is associated with potential temperatures of 0 40 0 26 c salinities of 34 70 34 69 and potential density values of 46 05 46 07 sigma 4 the third assemblage is dominated by nuttallides umbonifera ehrenbergina trigona and secondarily by oridorsalis umbonatus and pullenia bulloides the n umbonifera e trigona assemblage is present form 2770 to 3120 m on the islas orcadas rise this assemblage is associated with potential temperatures of 0 36 0 14 c salinities of 34 69 34 68 and potential density values of 46 06 46 09 sigma 4 although the u peregrina assemblage and the n umbonifera e trigona assemblage overlap bathymetrically they are present in waters of slightly different properties the bulimina aculeata assemblage is within the core of the lower circumpolar deep water lcdw while the other two assemblages occur within transition zones between the lcdw and weddell sea deep water wsdw the difference in the benthic foraminiferal assemblages at similar depths on the islas orcadas rise and the maurice ewing bank is the result of different water mass regimes separated by the polar front

seismotectonics of mid ocean ridge propagation in hess deep hydroacoustic data from the eastern equatorial pacific reveal low magnitude seismicity concentrated at the propagating tip of the galapagos rise in hess deep the patterns of seismicity and faulting are similar to those observed in the process zone of laboratory scale propagating tensile cracks because the fracture energy required for propagation scales with crack length and process zone size it follows that ridges can propagate stably in the brittle crust without exceptional resisting forces as proposed by previous models based on linear elastic fracture mechanics

living stained and dead foraminifera from the newly ice free larsen ice shelf weddell sea antarctica ecology and taphonomy within the past 7 years the northern larsen ice shelf has broken up so it is now possible to sample the sea floor that formerly lay beneath it box cores have yielded surface sediment samples 0 1 cm that give information on living and dead foraminiferal assemblages the living assemblages are of moderate diversity and four have 50 calcareous tests while five have 50 agglutinated tests this is an area of high primary production and the standing crops of the benthic foraminiferal assemblages are high all the dead assemblages are much enriched in agglutinated tests often 90 they give a time averaged record of the past 7 ice free years and several decades of ice cover the loss of permanent ice cover there is still seasonal ice cover may have caused some response from the fauna but it is likely that it was mainly changes in relative absolute abundance of the existing fauna the differences between the live and dead assemblages in the surface 1 cm are attributed mainly to taphonomic effects dissolution of calcareous tests and loss of fragile agglutinated tests subsurface samples down to 5 cm show that dissolution of calcareous tests is widespread and there may be some loss of fragile agglutinated forms such as reophax subdentaliniformis for these reasons in this area it may be best to make palaeoecological interpretations on the agglutinated component of the fossil assemblages