Grain size distribution of the lagoonal deposits within the South Malé Atoll, Maldives, Indian Ocean

Seismic and multibeam data, as well as sediment samples were acquired in the South Malé Atoll in the Maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits. Multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15-20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea-level lowstand. Such depocenters are located in current-protected areas flanking the reef rim of the atoll or in infillings of karst dolinas. Much of the 50 m deep sea floor in the lagoon interior is current swept, and has no or very minor sediment cover. Erosive current moats line drowned patch reefs, whereas other areas are characterized by nondeposition. Karst sink holes, blue holes and karst valleys occur throughout the lagoon, from its rim to its center. Lagoonal sediments are mostly carbonate rubble and coarse-grained carbonate sands with frequent large benthic foraminifers, Halimeda flakes, red algal nodules, mollusks, bioclasts, and intraclasts, some of them glauconitic, as well as very minor ooids. Finer-grained deposits locally are deposited in current-protected areas behind elongated faros, i.e., small atolls which are part of the rim of South Malé Atoll. The South Malé Atoll is a current-flushed atoll, where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim. With an elevated reef rim and tower-like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record.

Soil chemistry and particle size distribution of mountainous tundra soils in the Rai-Iz Massif

Gravelly clay loamy and clayey soils developed from the derivatives of ultramafic rocks of the dunite-harzburgite complex of the Rai-Iz massif in the Polar Urals have been studied. They are represented by raw-humus pelozems (weakly developed clayey soils) under conditions of perfect drainage on steep slopes and by the gleyzems (Gleysols) with vivid gley color patterns in the eluvial positions on leveled elements of the relief. The magnesium released from the silicates with the high content of this element (mainly from olivine) specifies the neutral-alkaline reaction in these soils. Cryoturbation, the accumulation of raw humus, the impregnation of the soil mass with humic substances, gleyzation, and the ferrugination of the gleyed horizons are also clearly pronounced in the studied soils. Despite the high pH values, the destruction of supergene smectites in the upper horizons and ferrugination (the accumulation of iron hydroxides) in the microfissures dissecting the grains of olivine, pyroxene, and serpentine, and in decomposing plant tissues take place. The development of these processes may be related to the local acidification (neutralization) of the soil medium under the impact of biota and carbonic acids. The specificity of gleyzation in the soils developing from ultra-mafic rocks is shown in the absence of iron depletion from the fine earth material against the background of the greenish blue gley color pattern.

Vertical distribution of suspended aggregates at time series station DYNAPROC

Day/night variations in the size distribution of the particulate matter >0.15 mm (PM) were studied in May 1995 during the DYNAPROC time-series cruise in the northwestern Mediterranean Sea. Data on vertical distributions of PM (>0.15 mm) and zooplankton were collected with the Underwater Video Profiler (UVP). The comparisons of the UVP data with plankton net data and POC data from water bottles indicated that more than 97% of the particles detected by the UVP were non-living particles (0.15 mm) and that the PM contributed 4-34% of the total dry weight measured on GF/F filters. Comparison of seven pairs of day and night vertical profiles performed during the cruise showed that in the upper 800 m, the mean size and the volume of particles was higher at night than during the day. During the night, the integrated volume of the PM increased on average by 32±20%. This increase corresponded to a shift of smaller size classes (<0.5 mm) towards the larger ones (>0.5 mm). During the day, the pattern was reversed, and the quantity of PM >0.5 mm decreased. During the study period, the standing stock of PM (60-800 m) decreased from 7.5 to less than 2 g m?2 but the diel variations persisted, except for two short periods in the superficial layer following a wind event. The cyclic feeding activity induced by the diel vertical migration of zooplankton could be the best candidate to explain the observed diel fluctuations in the size classes of PM in the water column. However, our results also suggest that in the upper layer additional driving forces such as the increase of the level of turbulence after a wind event or the modification of the zoo- and phytoplankton community can influence the PM temporal evolution.

Distribution of benthic and planktic foraminifera in surface sediments of the Indian and Pakistan continental margin, Arabian Sea

During the Indian Ocean Expedition of the German research vessel "Meteor" and the following cruise with the Pakistani fishing vessel "Machhera" in February and March 1965, sediments were sampled from the shelf, continental slope and the Arabian Basin off Pakistan and India. The biostratigraphic studies are based on sedimentary material from 24 sediment cores up to 480 cm long and 100 grab samples. The faunal residues of the > 160 µ fraction (chiefly foraminifera and pteropods) were determined and counted in order to get an idea of the climatic conditions during the Late Quaternary of this region. Biostratigraphic correlations of these Late Quaternary deposits are only possible if the thanatocoenosis of the surface sediments are well known. The analysis of the benthonic foraminiferal populations resulted in the definition of several foraminiferal facies. The following sequence of forarniniferal facies, named after their most characteristic members, can be distinguished from the shelf to the deep-sea: 1. Ammonia-Florilus facies ; 2. Ammonia-Cancris facies; 3. Cassidulina-Cibicides facies; 4. Uvigerina-Cassidulina facies ; 5. Buliminacea facies ; 6. deepwater facies, partly with Bulimina aculeata or with Nonionidae. On the upper continental slope there is a zone extremely poor in benthonic foraminifera. In this water depth the oxygen minimum layer (0.05-0.02 ml/l) of the water column reaches the slope. Almost no connection can be observed between the living and the dead foraminiferal population of the same sample. The regional distribution of the planktonic foraminifera from plankton tows as well as from the surface sediments shows marked differences in the species composition of faunas from different regions within the area of investigation. That depends on oceanographic conditions such as upwelling, dissolution of carbonate at great depths etc. Based on the results of faunal analysis of samples from the recent sea-floor, a biostratigraphic subdivision of the sediments in the cores was established. The following biostratigraphically defined sections could be distinguished from the top of the sediment cores downwards : 1. Relatively cool climatic conditions are reflected by the foraminifera of the uppermost core sections. 2. The next section is characterized by much warmer conditions (Holocene climatic optimum). The C-14 ages of this interval range from 4000 to 10 000 years B.P. according to different authors. C-14 dates on the material investigated do not give reliable clues. 3. Foraminiferal populations adapted to much colder conditions can be observed in the underlying core section. The boundary between the warm climate reflected by the foraminifera of section 2 and the cold climate (section 3) is relatively sharp. It can be correlated from core to core over the whole area investigated. The cold climate sediments of section 3 are underlain by different cool-, warm- and cold-climate sediments which can only be correlated over very short distances. Since it appears certain that the last really cold conditions ended earlier in the Arabian Sea and its vicinity than in Europe it is recommended not to use the European stratigraphic terms for the Quaternary. Because of the lack of reliable absolute sediment ages for the cores no exact sedimentation rates can be given. According to rough estimates, however, the rates are 1-2 cm/1000 years in the deep basin and up to 40 cm/1000 years on the upper continental slope. Sedimentation rates are always larger near the mouth of the Indus-River than off South India at stations of about the same water depth. Planktonic gastropods (mainly pteropods) cannot be used for biostratigraphic purposes in the region under consideration. All of them seem to be displaced from the shelf. Their distribution there is given in.

Vertical distribution of relative numbers of the main groups of sound-scattering fishes in the Central Indian Ocean

Findings made in 31 catches with an Isaacs-Kidd midwater trawl in the light (09.00-16.00) and dark (21.00-04.00) periods of a day within a survey area of about 100 sq. miles with approximate center coordinates of 13°S and 78°E have been used to investigate vertical distribution of the main groups of sound-scattering fishes (35 species of the family Myctophidae and 16 species of other families). It has been shown that during daylight hours all fishes sink to depths deeper than 400 m. Data are presented concerning the fish population of night-time sound-scattering layers at depths of 70-150 m and about 400 m and of the daytime ones at depths of about 450 m.

(Table 2) Distribution of alkenone unsaturation index UK37 of the eastern North Atlantic

This paper reports the concentrations and within-class distributions of long-chain alkenones and alkyl alkenoates in the surface waters (0-50 m) of the eastern North Atlantic, and correlates their abundance and distribution with those of source organisms and with water temperature and other environmental variables. We collected these samples of >0.8 µm particulate material from the euphotic zone along the JGOFS 20°W longitude transect, from 61°N to 24°N, during seven cruises of the UK-JGOFS Biogeochemical Ocean Flux Study (BOFS) in 1989-1991; the biogeographical range of our 53 samples extends from the cold (<10°C), nutrient-rich and highly productive subarctic waters of the Iceland Basin to the warm (>25°C) oligotrophic subtropical waters off Africa. Surface water concentrations of total alkenone and alkenoates ranged from <50 ng/l in oligotrophic waters below 40°N to 2000-4500 ng/l in high latitude E. huxleyi blooms, and were well correlated with E. huxleyi cell densities, supporting the assumption that E. huxleyi is the predominant source of these compounds in the present day North Atlantic. The within-class distribution of the C37 and C38 alkenones and C36 alkenoates varied strongly as a function of temperature, and was largely unaffected by nutrient concentration, bloom status and other surface water properties. The biosynthetic response of the source organisms to growth temperature differed between the cold (<16°C) waters above 47°N and the warmer waters to the south. In cold (<16°C) waters above 47°N, the relative amounts of alkenoates and C38 alkenones synthesized was a strong function of growth temperature, while the unsaturation ratio of the alkenones (C37 and C38) was uncorrelated with temperature. Conversely, in warm (>16°C) waters below 47°N, the relative proportions of alkenoates and alkenones synthesized remained constant with increasing temperature while the unsaturation ratios of the C37 and C38 methyl alkenones (Uk37 and Uk38Me, respectively) increased linearly. The fitted regressions of Uk37 and Uk38Me versus temperature for waters >16°C were both highly significant (r**2 > 0.96) and had identical slopes (0.057) that were 50% higher than the slope (0.034) of the temperature calibration of Uk37 reported by Prahl and Wakeham (1987; doi:10.1038/330367a0) over the same temperature range. These observations suggest either a physiological adjustment in biochemical response to growth temperature above a 16-17°C threshold and/or variation between different E. huxleyi strains and/or related species inhabiting the cold and warm water regions of the eastern North Atlantic. Using our North Atlantic data set, we have produced multivariate temperature calibrations incorporating all major features of the alkenone and alkenoate data set. Predicted temperatures using multivariate calibrations are largely unbiased, with a standard error of approximately ±1°C over the entire data range. In contrast, simpler calibration models cannot adequately incorporate regional diversity and nonlinear trends with temperature. Our results indicate that calibrations based upon single variables, such as Uk37, can be strongly biased by unknown systematic errors arising from natural variability in the biosynthetic response of the source organisms to growth temperature. Multivariate temperature calibration can be expected to give more precise estimates of Integrated Production Temperatures (IPT) in the sedimentary record over a wider range of paleoenvironmental conditions, when derived using a calibration data set incorporating a similar range of natural variability in biosynthetic response.

Sedimentology and geochemistry of the sand fraction in surface sediments off West Africa

Surface sediments from 5 profiles between 30 and 3000 m water depth off W Africa (12-19° N) have been studied for their sand fraction composition and their total calcium carbonate and organic matter contents to evaluate the effect of climatic and hydrographic factors on actual sedimentation. On the shelf and upper slope (< 500 m), currents prevent the deposition of significant amounts of fine-grained material. The sediments forming here are characterized by high sand contents (> 60 %; in most samples > 89 %), low organic carbon contents (in most samples < 0.8 %), high median diameters of the sand fraction (120-500 µm), and by a predominance of quartz and biogenic relict shells (most abundant: molluscs and bryozoans) in the sand fraction. Median diameters of total sand fraction and of major biogenic sand fraction components (biogenic relict material, benthonic molluscs, benthonic and planktonic foraminifers) co-vary to some extent and show maximum values in 100-300 m water depth, reflectingthe sorting effect of currents (perhaps the northward flowing undercurrent). In this water depth, biogenic relict material is considerably enriched relative to wuartz, the second dominating sand fraction component on the shelf and upper slope, resulting in distinct calcium carbonate maxima of the bulk sediments. The influence of the undercurrent is also reflected in a northward transport of fine grained river load and perhaps in the distribution of the red stained, coarse silt and sand-size clay aggregates, which show maxima in 300-500 m water depth. They probably originate from tropical soils. Abundant coarse red-stained quartz on the shelf off Cape Roxo (12-130° N) suggests a southward extension of last glacial dune fields to this latitude. Below about 500 m water depth, current influence becomes negligible - as indicated by a strong decrease in sand content, a concomitant increase in sedimentary organic carbon contents (up to 2.5-3.5 %), and the occurence of high mica/quartz ratios in the sand fraction. Downslope transport, presumably due to the bioturbation mechanism, is indicated by the presence of coarse shelf-borne particles (glauconite, relict shells) down to about 1000 m water depth. The fine/coarse ratio (clay + silt/sand) of the sediments from water deoth > 500 m never exceed a value of 11 in northern latitudes (19° - 26° N), but shows distinct maxima, ranging from 50 to 120, at latitudes 18°, 17° 15°30', and 14° N in about 2000 m water depth. This distribution is attributed to the deposition of fine-grained river load at the continental slope between 18° and 14° N, brought into the sea by the Senegal and souther rivers and transported northward ny the undercurrent. Strong calcium carbonate dissolution is indicated by the complete disappearance of pteropodes (aragonite) and high fragmentation of the planktoic foraminifers (calcite) in sediments from water depth > 300-600 m. Fragmentation ratios of planktonic foraminifers were found to depend on the organic carbon/carbonate ratios of the sediment suggesting that calcite dissolution at the sea bottom may also be significant in shelf and continental slope water depths if the organic matter/carbonate ratio of the surface sediment is high and the test remain long enough within the oxidizing layer on the top of the sulfate reduction zone. The fact that in the region under study intensity and anual duration of upwelling decrease from north to south is neither reflected in the composition on the sand fraction (i.e. radiolarian and fish debris contents, radiolarian/planktonic foraminiferal ratios, benthos/plankton ratios of foraminifers), nor in the sedimentary organic carbon distribution. On the contrary, these parameters even show in comparable water depths a tendency for highest values in the south, partly because primary production rates remain high in the whole region, particularly on the shelf, due to the nutrient input by rivers in the south. In addition, several hydrographic, sedimentological and climatic factors severely affect their distribution - for example currents, dissolution, grain size composition, deposition of river load, and bulk sedimentation rats.

Distribution of benthic abyssal gastropods in the Iberian Deep-Sea Basin (Table 2)

During the cruises 3 and 15 of R.V. "Meteor", representatives of 7 families of benthic abyssal gastropods were collected. The prevalent group was the Turridae; the Naticidae are represented by 2 species, the remaining families by a single species each. A survey of the frequency and distribution of the species within the study area is given. A systematic part deals with the individual species in detail, including notes on taxonomy, material and distribution. Concerning the composition of the abyssal gastropod fauna of the present material, Neogastropoda are 4 times as many as Archaeogastropoda and 6 times as many as Mesogastropoda and Opisthobranchia. 89 % of all specimens are Neogastropoda. Usually deep-sea organisms have a non-pelagic development, but many of the Iberian deep-sea Turrids have a planktotrophic protoconch, that means a long pelagic larval period. Among the 19 species, 2 are cosmopolitan, 9 show a transatlantic distribution and 8 are confined to East-Atlantic basins.

Vertical distribution of zooplankton biomass in the Sea of Japan

Vertical distribution of total zooplankton biomass and major taxonomic groups are investigated by layers to depths of 2500-3400 m on the basis of three series of net plankton collections. Zooplankton is most abundant above 1500-2000 m. Since true deep-water species do not occur in the Sea of Japan, biomass drops much more sharply at greater depths than it does in the ocean. Since few carnivores inhabit the deep layers, abundant remains of planktonic organisms fall to the bottom, and carnivorous detritovores feeding on these remains are dominant in deep water bottom fauna.

Distribution of Uvigerina proboscidea in Late Neogene sediments of DSDP Hole 22-214 in the northern Indian Ocean (Table 1)

This study attempts to understand the significance of Uvigerina proboscidea in paleoceanographic reconstructions at the northern (tropical) Indian Ocean DSDP Site 214 from the Late Miocene through the Pleistocene. In this interval at this site, U. proboscidea is the most abundant species of the benthic assemblage and shows abrupt frequency changes (about 1-74%). Based on relative percentages of U. proboscidea calibrated with oxygen and carbon isotope record and the sediment accumulation rates, the modern distribution of the species in the Indian Ocean, and other evidence, the peaks of abundance of U. proboscidea are inferred to represent times of high-surface productivity, This productivity is related to intensified trade winds during strong southwest (SW) Indian monsoons, causing widespread upwelling along equatorial divergemce in the Indian Ocean. The sudden increase of U. proboscidea abundance at approximately 8.5-7.5 Ma reflects significant upwelling at the equatorial divergence. This event corresponds to the permanent build-up of West Antarctic ice sheets, and a major increase in SW Indian monsoons related upwelling in the northwestern Indian Ocean. The Chron-6 carbon shift at approximately 6.2 Ma is marked by another peak of abundance, reflecting widespread ocean fertility. The highest abundances of U. proboscidea and highest sediment accumulation rates occur between 5.8 and 5.1 Ma, which coincidies with the greatest development of Antarctic ice sheets and strong southwest monsoons. The higher percentages at 3.2-3.1 Ma, approximately 2.4 Ma, and 1.6 Ma all represent phases of high productivity at the equatorial divergence.

Distribution of coccoliths in surface sediments of the south-eastern South Atlantic Ocean

Recent coccoliths from 52 surface sediment samples recovered from the south-eastern South Atlantic were examined qualitatively and quantitatively in order to assess the controlling mechanisms for their distribution patterns, such as ecological and preservational factors, and their role as carbonate producers. Total coccolith abundances range from 0.2 to 39.9 coccoliths*10**9/ g sediment. Four assemblages can be delineated by their coccolith content characterising the northern Benguela, the middle to southern Benguela, the Walvis Ridge and the deeper water. Distinctions are based on multivariate ordination techniques applied on the relative abundances of the most abundant taxa, Emiliania huxleyi, Calcidiscus leptoporus, Gephyrocapsa spp., Coccolithus pelagicus and subtropical to tropical species. The coccolith distribution seems to be temperature and nutrient controlled co-varying with the seaward extension of the upwelling filament zone in the Benguela. A preservation index (CEX') based on the differential dissolution behaviour of the delicate E. huxleyi and Gephyrocapsa ericsonii versus the robust C. leptoporus is applied in order to detect the position of the coccolith lysocline. Although some samples were recognised as dissolution-affected, the distribution of the coccoliths in the surface-sediments reflects the different oceanographic surface-water conditions. Mass estimations of the coccolith carbonate reveal coccoliths to be only minor contributors to the carbonate preserved in the surface sediments. The mean computed coccolith carbonate content is 17 wt.%, equivalent to a mean contribution of 23% to the bulk carbonate.