Radiolarian biogeography in surface sediments of the eastern Indian Ocean

We analyzed recurrent groups of Radiolaria in 74 core top samples from a transect through the eastern Indian Ocean in order to supplement our previous results from the western Indian Ocean (Johnson and Nigrini, 1980). We now identify six distinct recurrent groups and nine radiolarian assemblages in the combined data set of 120 samples; this extended sample coverage has led to several re-interpretations of the oceanographic significance of the radiolarian distribution patterns. Assemblage boundaries closely reflect the presence of major oceanographic fronts and surface currents including the South Equatorial Divergence, Subtropical Gyre, Subtropical Convergence, and Antarctic Convergence. At least four major aspects of the assemblages in the eastern transect are notably different from those in the western transect, leading to a marked east-west asymmetry in faunal distribution patterns across the Indian Ocean. The assemblage formerly associated with strong upwelling near the Arabian Peninsula is present throughout the Bay of Bengal as well, and is interpreted to reflect high salinity and low oxygen in the subsurface waters of the Indian Ocean north of the Equator. A new assemblage has been identified associated with the westward-flowing Pacific water into the eastern Indian Ocean in low latitudes, and may be a potential stratigraphic and paleoclimatic marker for times of low sea level when this westward near-surface flow was shut off (i.e., glacial maxima). An extensive region in the core of the subtropical gyre between 25°S and 35°S is relatively barren of Radiolaria, yet is marked by a characteristic assemblage distributed asymmetrically, perhaps reflecting the lack of a strong boundary current off the west coast of Australia. Assemblage boundaries in the vicinity of the eastward circumpolar flow are not strictly zonal, and may indicate significant deviations from the mean eastward flow as a necessary condition for conservation of potential vorticity when the flow encounters topographic irregularities.     

Distribution of recent planktonic foraminifera in surface sediments of the Mediterranean Sea

The Mediterranean Sea is a partillay isolated ocean where excess evaporation over precipitation results in large east to west gradients in temperature and salinity. Recent planktonic foraminiferal distributions have been examined in 66 surface sediment samples from the Mediterranean Sea. In addition to mapping the frequency distribution of 16 species, the faunal data has been subjected to cluster analysis, factor analysis and species diversity analysis. The clustering of species yields assemblages that are clearly temperature related. A warm assemblage contains both tropical and subtropical elements, while the cool assemblage can be subdivided into cool-subtropical, transitional and polar-subpolar groupings. Factor analysis is used to delineate the geographic distribution of four faunal assemblages. Factor 1 is a tropical-subtropical assemblage dominated by Globigerinoiden ruber. It has its highest values in the warmer eastern basin. Transitional species (Globorotalia inflata and Globigerina bulloides) dominate factor 2 with highest values occurring in the cooler western basin. Factor 3 reflects the distribution of Neogloboquadrina dutertrei and is considered to be salinity dependent. Subpolar species dominate factor 4 (Neoglobuquadrina pachyderma and G. bulloides), with highest values occurring in the northern part of the western basin where cold bottom water is presently being formed. The Shannon-Weiner index of species diversity shows that high diversity exists over much of the western basin and immediately east of the Strait of Sicily. This region is marked by equitable environmental conditions and relatively even distribution of individuals among the species. Conversely, in areas where temperature and salinity values are more extreme, diversity values are lower and the assemblages are dominated by one or two species.     

Planktonic foraminifera from the eastern Indian Ocean: distribution and ecology in relation to the Western Pacific Warm Pool (WPWP)

Faunal assemblages, principal component (PCA), canonical correspondence (CCA), and factor analysis are applied to planktonic foraminifera from 57 core-top samples from the eastern Indian Ocean. The foraminiferal lysocline occurs at 2400 m north of 15°S where carbonate dissolution is induced by the Java upwelling system, and occurs deeper south of 15°S where carbonate dissolution is characteristic of the oligotrophic regions in the Indian Ocean. Dissolution effects, the February standing stock at the time of collection of the plankton-tow material, and different production rates explain the different foraminiferal assemblages found between plankton-tow and core-top samples. Core-top samples are differentiated by PCA into four groups — Upwelling, Western Pacific Warm Pool (WPWP), Transitional, and Southern — that are related to environmental variables (temperature, salinity and nutrients); all environmental variables follow a strong latitudinal component as indicated by the CCA analysis. Similarly, three assemblages are recognized by factor analysis: Factor 1 (dominated by Globigerinoides sacculifer, G. ruber, Globigerinita glutinata and Globorotalia cultrata), factor 2 (dominated by Globigerina bulloides and Globorotalia inflata) and factor 3 (dominated by Neogloboquadrina dutertrei) explain more than 92% of the variance, and are related to sea-surface temperature, thermocline depth and nutrient levels. The seasonal influence of the Java upwelling system supplies nutrients, phyto- and zooplankton to the oligotrophic eastern Indian Ocean (factor 1). South of 24°S, a deep chlorophyll maximum, a deep euphotic zone, a deep thermocline, SSTs below 22°C, and brief upwelling pulses seem to explain factors 2 and 3. The ratio of G. sacculifer and N. dutertrei, two mutually excluding species, appears to indicate the southern boundary of the WPWP. This ratio is applied to core Fr10/95-11 to demonstrate past shifts of the southern boundary of the WPWP.     

Multivariate analysis and quantitative paleoecology of benthic foraminifera in surface and Late Quaternary shelf sediments,northern Canada

Benthic foraminifera in surface sediments from northeastern Canada and the Beaufort Shelf were studied to determine the quantitative relationship between recent assemblage distributions and modern water depth, temperature and salinity. Factor analysis shows that 7 factor assemblages account for 92% of the variance between samples. Multiple linear regression shows that different factors are significantly related to water depth, August bottom water temperature or salinity. Multiple correlation coefficients for depth, temperature and salinity are 0.94, 0.72 and 0.92, respectively. Labrador fjords contain arenaceous faunas dominated by eitherSaccammina atlantica andReophax fusiformis or byEggerella advena. Regression analysis shows that theSaccammina-Reophax factor is most strongly related to salinity. TheEggerella factor is related to depth and temperature. A fauna dominated byTrochammina nana andBuliminella elegantissima is correlated with warm, deep water in Davis Strait. Calcareous assemblages dominated byElphidium excavatum orCassidulina reniforme are found in Arctic bays and shelf areas. These factor assemblages are strongly related to temperature and depth;Cassidulina is also related to salinity. AnIslandiella helenae fauna on the inner Labrador Shelf is strongly correlated with depth and salinity. ANonionellina labradorica fauna in deep shelf basins is closely related to salinity.The multiple regression model for the sea-bed data estimates water depth, August bottom water temperature and salinity within confidence limits of ± 67 m, 1.3°C and 1.0‰. Paleoecological transfer functions were used to quantify environmental changes recorded by the foraminifera in two piston cores on a transect across the Labrador Shelf. Paleo-depth estimates obtained from the core data produce relative sea-level curves which are similar in shape to theoretical curves for this region. Paleo-salinity and -temperature estimates for offshore Core 12 show that the change from a postglacialNonionellina fauna to a late glacialE. excavatum fauna is accompanied by a decrease of about 2‰ in salinity and 4°C in temperature. Paleoecological estimates for fjord Core 111 show that the change from a modernSaccammina-Reophax fauna to a mid-HoloceneI. helenae fauna corresponds to a salinity increase of 3–5‰ and temperature increase of 1–2°C.     

Planktonic ciliates in the northwestern Indian Ocean: their abundance and biomass in waters of contrasting productivity

The abundance and biomass of planktonic ciliates in the northwesternIndian Ocean ranged from 31 l^–1 and 0.1 µg C l^–1in oligotrophic open-ocean waters to 823 l^–1 and 1.2 µgC l^–1 in more productive waters of the equator, northernArabian Sea and Gulf of Oman. ³Present address: British Antarctic Survey, High Cross, MadingleyRoad, Cambridge, CB3 OET, UK     

Distribution of myctophid resources in the Indian Ocean

Mesopelagics are one of the largest under-exploited marine resources with wide distribution in the world oceans. Lanternfishes are the key members of mesopelagic communities and the total resource in the world oceans is estimated at 600 million tons. Lanternfishes belong to the family Myctophidae which comprises of about 250 species in 35 genera. Myctophids account for about 75% of total global catch of small mesopelagic fishes. They are known to exhibit diel vertical migration, concentrating during the day time between 400 and 1,000 m, and between 5 and 100 m, during the night. In this paper, an attempt is made to review the existing information on the occurrence and distribution of myctophid resources in the Indian Ocean. 137 myctophid species have been reported from the entire Indian Ocean. Studies in the Arabian Sea have indicated that the area is rich in the midwater fish stocks dominated by myctophids with an estimated potential of 100 million tons.     

The surface ocean productivity response of deeper water benthic foraminifera in the Atlantic Ocean

We test the relationship of deep sea benthic foraminiferal assemblage composition to the surface ocean productivity gradient in the low latitude Atlantic Ocean using 81 surface sediment samples from a water depth range between 2800 and 3500 m. The samples are selected so that the surface ocean productivity gradient, controlling the flux of organic carbon to the seabed, will be the most important environmental variable. The first two principal components of the assemblage data account for 73% of data variance and are clearly linked to the productivity gradient across the Atlantic. These components show that under higher productivity the assemblages contain a higher abundance of Uvigerina peregrina, Melonis barleeanum, Globobulimina spp. and other taxa with probable infaunal microhabitats. Alabaminella weddellensis, a species linked to episodic phytoplankton debris falls, is also important in these assemblages. As productivity decreases there is a regular shift in assemblage composition so that low productivity assemblages are dominated by Globocassidulina subglobosa and several Cassidulina species along with Epistominella exigua. We hypothesize that these taxa are epifaunal to very shallow infaunal since nearly all organic carbon oxidation occurs near the sediment-water interface in low productivity settings. Discriminant function analysis of the foraminiferal assemblages, with groups selected on the basis of surface ocean productivity, shows clear separation among five productivity levels we used. This analysis demonstrates that productivity variations have a strong influence on assemblage composition. Finally, we used two groups of samples from the Rio-Grande Rise representing water depths from 2007 to 2340 m and 2739 to 3454 m to test for effects produced by changing water depth. All these samples are from a low productivity region and represent nearly identical environmental conditions. Although the low productivity nature of all the Rio-Grande Rise samples is obvious, there are assemblage differences between our depth groups. We cannot account for the assemblage differences with changes in organic carbon flux, dissolution effects or other physical/chemical properties of the ocean. Thus there are as yet unidentified factors related to water depth which cause some assemblage variation in the low productivity setting we investigated.     

Distribution of epiplanktonic Chaetognatha along a transect in the Indian Ocean

Chaetognaths were identified and counted in 23 samples collectedin the west Indian Ocean along a transect from the Gulf of Adento the Cape of Good Hope, in February–March 1967. Althoughthe hydrographic front located at 5°S does not seem to representa barrier for the distribution of the majority of the species,some of them are in a preferential area south or north of thefront. The principal component analysis indicates the locationswhere the more intense overlapping of species takes place. Itis important to mention the occurrence of S.pseudoserratodentatain the proximity of Madagascar Island.     

Distribution of arenaceous foraminifera in depth profiles of the Southern Ocean (kerguelen plateau area)

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.     

Coccolith distribution patterns in surface sediments of Equatorial and Southeastern Pacific Ocean

This study aims to contribute to a more detailed knowledge of the biogeography of coccolithophores in the Equatorial and Southeastern Pacific Ocean. Census data of fossil coccoliths are presented in a suite of core-top sediment samples from 15°N to 50.6°S and from 71°W to 93°W. Following standard preparation of smear slides, a total of 19 taxa are recognized in light microscopy and their relative abundances are determined for 134 surface sediment samples. Considering the multivariate character of oceanic conditions and their effects on phytoplankton, a Factor Analysis was performed and three factors were retained. Factor 1, dominated by Florisphaera profunda and Gephyrocapsa oceanica, includes samples located under warm water masses and indicates the occurrence of calcite dissolution in the water column in the area offshore Chile. Factor 2 is related to cold, low-salinity surface-water masses from the Chilean upwelling, and is dominated by Emiliania huxleyi, Gephyrocapsa sp. < 3 μm, Coccolithus pelagicus and Gephyrocapsa muellerae. Factor 3 is linked to more saline, coastal upwelling areas where Calcidiscus leptoporus and Helicosphaera carteri are the dominant species.     

Distribution of surface zooplankton and seabirds across the Southern Ocean

Surface zooplankton and seabird densities and community composition in the Atlantic (between Cape Town and Sanae) and Pacific (between New Zealand and the Ross Sea) sectors of the Southern Ocean are described and related to oceanographic features. Samples were collected during two return voyages aboard the MV Benjamin Bowring as part of the Transglobe Expedition (1979–1981). High abundances of surface zooplankton and seabirds were consistently observed within the main frontal systems of the Southern Ocean. Generally, on a mesoscale significant correlations between surface temperature and the distribution of zooplankton or seabirds were observed. On a macroscale, the geographical positions of the zooplankton and seabird communities coincided with specific water masses. The results of this study suggest that appropriate food availability rather than water temperature is important for the determination of seabird distribution. The ecological importance of the recently described frontal zone associated with the northern boundary of the maximum winter expansion of sea ice is confirmed by biological data obtained in this study.     

Distribution of living planktonic foraminifera in the Ross Sea and the Pacific sector of the Southern Ocean (Antarctica)

In order to determine the factors controlling the distribution of planktonic foraminifera as a proxy for reconstruction of paleoenvironments, we present data on live assemblages collected in the Southern Ocean. Plankton tows and hydrographic measurements were taken in the upper 400 m of the water column at different sites in the Ross Sea (site B) and at the Polar Front of the Pacific Ocean (site O) during austral summers from 1998 to 2003.Based on qualitative micropaleontological observations we discriminated between Neogloboquadrina pachyderma dextral (dex) and N. pachyderma sinistral (sin). In addition for N. pachyderma (sin) we distinguished four morphs: the first one (1) has a thickened test and depressed sutures; the second morph (2) is represented by specimens characterized by a subspheric and heavily encrusted test; the third morph (3) has a thin and lobate walled test; the fourth one (4) represent the juvenile stage of N. pachyderma (sin) and is characterized by a smaller average size.The microfauna collected in the Ross Sea (site B) is characterized by the dominance of N. pachyderma (sin) (morphs 1 and 2), whereas low occurrences of Turborotalia quinqueloba, N. pachyderma (dex) and Neogloboquadrina dutertrei were noted in the first 50 m of the water column. The water column at this station is characterized by a marked and shallow stratification and a marked thermocline during the sampling season.At the ocean station (site O), the assemblage shows increasing diversification: T. quinqueloba, G. bulloides, N. pachyderma (dex) and few specimens of Globigerinita uvula characterize the planktonic microfauna. There is a predominance of non-encrusted morphs and juvenile specimens (3 and 4). At this station the mixed surface layer is deeper than in the Ross Sea (60–70 m), the pycnocline and the thermocline less marked.The depth and the intensity of the Deep Chlorophyll Maximum (DCM) influence foraminiferal distribution: N. pachyderma (sin) shows abundance peaks at or just below the DCM while G. bulloides peaks above the DCM. Coiling direction of N. pachyderma seems to be not controlled exclusively by Sea Surface Temperature (SST): probably the two coiling types are genetically different.Results document that diversity of planktonic foraminifera, number of specimens and variations in test morphology are related to regional differences in water properties (temperature, salinity, and DCM depth).     

Diatoms from surface sediments of the northern part of Lake Tanganyika

227 Diatom taxa were observed in the surface sediments of the northern part of Lake Tanganyika, including 1 new to science: Amphora tanganyikae. The diatom community of these sediments is mainly composed of benthic organisms while planktonic diatoms are rather rare. Many brackish-water and a few marine organisms were observed. Cosmopolitan organisms (77.1%) dominate the diatom flora but tropical, tropical African and African taxa are also well represented (22.9%)Deceased.Deceased.     

Paleoceanographic interpretations of coccoliths and oxygen-isotopes from the sediment surface of the southwest Indian Ocean

The distribution of forty-four coccolithophore species in one hundred deep-sea core-tops from the southwest Indian Ocean is described. Three coccolith assemblages have been recognised (Maputo, Agulhas Current and deep water) by the relative abundances of four ecologically significant coccolithophore species (Gephyrocapsa oceanica, Emiliania huxleyi, Calcidiscus leptoporus and Umbilicosphaera sibogae). Their biogeographical distribution appears to be related to water temperature, nutrient concentration and dissolution.The degree of preservation of coccoliths and foraminifera indicates that the carbonate lysocline lies somewhere between 3500 and 4000 m, resulting in the concentration of dissolution-resistant microfossils below this depth.Stable oxygen isotope ratios of the planktonic foraminiferal species Globigerinoides sacculifer range between −1.5 to −1.0‰ PDB (equal to 22.8–25.1°C) and occur in a narrow band on the sea floor beneath the “A” route of the Agulhas Current.These values are about 0.5 per mil PDB lighter than samples analyzed on either side of this band and can be explained by the Agulhas Current's elevated temperature at the ocean surface of 2–3°C. Thus an oxygen isotope imprint of the Agulhas Current exists beneath it on the sea floor.The Agulhas Current is probably the major factor influencing sedimentation, sediment-distribution patterns and geological features in the study area. At present it is voluminous and fast flowing, possibly eroding sediments up to 2500 m below the surface.The oxygen-isotope ratios and nannoplankton counts obtained in this study indicate, however, that the majority of samples are most probably recent or at least not older than 85,000 years. This implies that sediments are accumulating on the ocean floor and that the Agulhas Current does not have a pronounced erosional influence, at least in areas from which cores were retrieved for this study.     

Fourier shape analysis of Globorotalia truncatulinoides from late Quaternary sediments in the southern Indian Ocean

Fourier shape analysis has been used to determine the morphological variation within the planktonic foraminifera,Globorotalia truncatulinoides from the southern Indian Ocean. Measured specimens are from 20 Recent core top samples distributed from 22°S (central gyre water mass) to 47°S (subantarctic water mass). Fourier analysis determined that the two most significant components of shape within this species are elongateness and conicalness which are characterized by harmonics 2 and 3, respectively. Mean harmonic 2 values are significantly correlated with the percentage of sinistral coiled individuals in each sample (r = +0.91). Mean values for harmonic 3 have a correlation coefficient with water temperature and salinity at 200 m of r = +0.85 and +0.88. Specimens become less elongate and more conical in a traverse from south to north.Fourier shape analysis of planktonic foraminifera was then shown to be useful in investigations of late Quaternary paleoceanographic problems. Four piston cores were examined from the southern Indian Ocean. Total faunal and oxygen isotope analyses provided the stratigraphic framework. The results indicated that the central gyre water mass remained relatively stable during glacial stages. The region of the Subtropical Convergence was strongly affected, however, by the northward migration of the Polar Front.     

Isolation and diversity analysis of arsenite-resistant bacteria in communities enriched from deep-sea sediments of the Southwest Indian Ocean Ridge

Microorganisms play an important role in the geobiocycling of arsenic element. However, little is known about the bacteria involved in this process in oceanic environments. In this report, arsenite-resistant bacteria were detected in deep-sea sediments on the Southwest Indian Ridge. From arsenite enriched cultures, 54 isolates were obtained, which showed varied tolerance to arsenite of 2–80 mM. Phylogenetic analysis based on 16S rRNA showed that they mainly belonged to Proteobacteria and Actinobacteria. Denaturing gradient gel electrophoresis revealed that Microbacterium esteraromaticum was the dominant member in the arsenite enriched communities, and this was reconfirmed by 16S rRNA gene library analyses. Thus, M. esteraromaticum showed highest resistant to arsenite among the detected bacteria. These results indicate that there are quite diverse bacteria of arsenite resistance inhabiting the deep sea sediment, which may play a role in the geobiocycling of arsenic element in marine environments.     

Distribution of the Bathypelagic family Arietellidae (Copepoda: Calanoida) in the upper 200 m in the Indian Ocean

The calanoid copepods of the family Arietellidae were studiedfrom the International Indian Ocean Expedition collections.The family is represented by three genera and the members usuallyinhabit deeper layers of the ocean. In the Indian Ocean fivespecies of Arietellus were encountered, mostly from southernlatitudes. Paraugaptilus is reported for the first time fromthe Indian Ocean. Three species of Phyllopus were encounteredin the IIOE collections. The members of the genus were concentratedmostly in the equatorial belt. ^*National Institute for Oceanography, Dona Paula-403004, Goa,India.     

Patchiness in the Distribution of Planktonic Heterotrophic Bacteria in Lakes

By using conventional dilution plating procedures, the heterotrophic planktonic bacteria in Lake Washington were found to be distributed in small-scale (<1.0 ml) and large-scale (>1 m in horizontal distance) patches. Recommendations are made on sampling and enumeration procedures to minimize the effect of patchiness on obtaining an accurate estimate of bacterial numbers.     

Plankton Biogeography of the Indian Ocean

Knowledge of plankton biogeography for the Indian and adjacent seas is necessary for an understanding of the regional characteristics and changes in the plankton composition. Some of the plankters will serve as good biogeographical indicator species. Some phytoplankters and tintinnids among zooplankton are promising for use as such labels for the presence of different waters in the Porto Novo (Coromandel coast, Bay of Bengal) region. A biogeographical classification of the local phytoplankton and peculiarities in the distribution of some rare tintinnids occurring there are discussed.     

Ocean basin and depth variability of oxygen isotopes in cenozoic benthic foraminifera

One of the longest, most detailed quantitative records of oceanographic change in the Cenozoic is that provided by oxygen isotope measurements made on the tests of foraminifera. As indicated by measurements on benthic foraminifera, the deep waters of the world ocean have undergone an overall cooling of about 10°C in the Cenozoic. This change has been neither monotonic nor gradual. Rather, it is evidenced by a few, relatively rapid increases in the ¹³O content of the benthic shells. These “steps” in the isotopic record have been associated with major evolutionary changes in the mean state of the deep ocean. The variance around this mean state has also changed through the Cenozoic. From relatively high variance in the Middle Eocene, the oceans showed low variance in the Late Eocene and Oligocene. In the Miocene the variance of the isotopic measurement again increased, reaching a maximum of short duration in the Middle Miocene. This maximum as well as that which occurred during the Late Pliocene and Quaternary, may be attributable to fluctuations in the isotopic composition of the oceans caused by growth and decay of large ice sheets.In the Late Miocene the benthic oxygen isotopes in Atlantic sites less than 3000 m deep have a higher variance than sites at similar depths in the Pacific and Indian Oceans. It is thought that this high variance results from long-term changes in the importance of the cool and salty North Atlantic Deep Water relative to that of the warmer and less saline Antarctic Intermediate Water at Atlantic sites between 1000 m and 3000 m water depth. Such significant differences in benthic isotopic variance between the ocean basins have been demonstrated only in post-Middle Miocene intervals.