Glacial-interglacial record of ODP Site 181-1119 in the Canterbury Bright, Southwest Pacific Ocean

Ocean Drilling Program (ODP) Site 1119 is located at water depth 395 m near the subtropical front (STF; here represented by the Southland Front), just downslope from the shelf edge of eastern South Island, New Zealand. The upper 86.19 metres composite depth (mcd) of Site 1119 sediment was deposited at an average sedimentation rate of 34 cm/kyr during Marine Isotope Stages (MIS) 1-8 (0-252 ka), and is underlain across a ~25 kyr intra-MIS 8 unconformity by MIS 8.5-11 (277-367 ka) and older sediment deposited at ~14 cm/kyr. A time scale is assigned to Site 1119 using radiocarbon dates for the period back to ~39 ka, and, prior to then, by matching its climatic record with that of the Vostok ice core, which it closely resembles. Four palaeoceanographic proxy measures for surface water masses vary together with the sandy-muddy, glacial-interglacial (G/I) cyclicity at the site. Interglacial intervals are characterised by heavy delta13C, high colour reflectance (a proxy for carbonate content), low Q-ray (a proxy for clay content) and light delta18O; conversely, glacial intervals exhibit light delta13C, low reflectance, high Q-ray and heavy delta18O signatures. Early interglacial intervals are represented by silty clays with 10-105-cm-thick beds of sharp-based (Chondrites-burrowed), shelly, graded, fine sand. The sands are rich in foraminifera, and were deposited distant from the shoreline under the influence of longitudinal flow in relatively deep water. Glacial intervals comprise mostly micaceous silty clay, though with some thin (2-10 cm thick) sands present also at peak cold periods, and contain the cold-water scallop Zygochlamys delicatula. Interglacial sandy intervals are characterised by relatively low sedimentation rates of 5-32 cm/kyr; cold climate intervals MIS 10, 6 and 2 have successively higher sedimentation rates of 45, 69 and 140 cm/kyr. Counter-intuitively,and forced by the bathymetric control of a laterally-moving shoreline during G/I and I/G transitions, the 1119 core records a southeasterly (seaward) movement of the STF during early glacial periods, accompanied by the incursion of subtropical water (STW) above the site, and northwesterly (landward) movement during late glacial and interglacial times, resulting in a dominant influence then of subantarctic surface water (SAW). The history of passage of these different water masses at the site is clearly delineated by their characteristic delta13C values. The intervals of thin, graded sands-muds which occur within MIS 2-3, 6, 7.4 and 10 indicate the onset at times of peak cold of intermittent bottom currents caused by strengthened and expanded frontal flows along the STF, which at such times lay near Site 1119 in close proximity to seaward-encroaching subantarctic waters within the Bounty gyre. In common with other nearby Southern Hemisphere records, the cold period which represents the last glacial maximum lasted between ~23-18 ka at Site 1119, during which time the STF and Subantarctic Front (SAF) probably merged into a single intense frontal zone around the head of the adjacent Bounty Trough.

Calcareous nannoplankton from the Southwest Pacific Ocean

The positions of all cores recovered during Leg 90 in the southwest Pacific are shown within the standard calcareous nannoplankton zonation. The stratigraphic and regional occurrences and preservation of Paleogene calcareous nannoplankton found at Sites 588, 592, and 593 are discussed, and fossil lists are given for selected samples. Data on the Eocene/Oligocene boundary found in Holes 592 and 593 and on the Oligocene/Miocene boundary in Hole 588C are presented. Regional unconformities are noted in Hole 588C, where the upper Eocene to middle Oligocene interval (Zones NP17 to NP23) is missing, and in Hole 592, in which the middle Oligocene to lowest Miocene interval (Zones NP23 to NN1) is not represented.

Composition of sediments from the north-west African continental margin

Entlang dreier Profile vom NW-afrikanischen Kontinentalrand wurden Oberflächensedimente aus Wassertiefen zwischen 39m und 1514m auf ihre Zusammensetzung der Sandfraktion, auf ihre Gehalte an Karbonat und organischer Substanzen sowie auf ihre mineralogische Zusammensetzung hin untersucht. 1) Die auf dem Schelf und dem oberen Hang abgelagerten Sedimente (<500m) zeichnen sich durch hohe Sandgehalte (>70%) und durch hohe Grob/Fein-Verhältnisse aus. Unterhalb dieses Bereiches nimmt der Einfluß von Strömungen, die die Ablagerung von wesentlichen Mengen an Feinmaterial oberhalb 500m verhindern, ab, wie die starke Abnahme des Sandgehaltes, des Quarz/Glimmer und des Grob/Fein-Verhältnisses zeigen. Die Sedimente aus diesen Wassertiefen werden zum großen Teil aus Partikeln der Siltfraktion aufgebaut. Mit zunehmender Tiefe ist auch eine Zunahme der Tonfraktion zu beobachten, wobei höhere Tonanteile (>10%) erst in Tiefen unterhalb von 1200m auftreten. 2) Die quantitative Komponentenanalyse der Sandfraktion zeigt, daß der karbonatische Anteil fast ausschließlich biogener Herkunft ist. Er besteht zum wesentlichen Teil aus planktonischen Komponenten, vorwiegend Foraminiferen und mengenmäßig nur sehr untergeordnet auftretenden Pteropoden. Das opalkieselige Plankton (Diatomeen, Radiolarien) ist nur in geringen Mengen in den untersuchten Proben vorhanden. Auch das Benthos stellt nur eine untergeordnete Komponente der Sandfraktion dar. Vor allem der Anteil von Foraminiferen und Mollusken nimmt mit zunehmender Wassertiefe relativ deutlich ab. Die übrigen benthonischen Komponenten sind im Sediment nur in geringen Anteilen vertreten. 3) Hauptsedimentbildner im Profil Nouakchott sind die nichtbiogenen, terrigen-detritischen Sandkomponenten. Sie bestehen vorwiegend aus Quarz und mit zunehmender Wassertiefe aus Kotpillen bzw. Kotpillenaggregaten. Je nach Tiefe treten vor allem Glimmer (>1000m) und Glaukonit (<800m) hinzu. Die restlichen Komponenten treten nur gelegentlich und in äußerst geringen Mengen im rezenten Oberflächensediment auf. 4) Quarz wird als Windstaub mit dem NE-Passat und vor allem durch den "Harmattan" aus der Sahara heraustransportiert und vorwiegend über dem Schelfbereich sedimentiert. Windstaubmaterial besteht primär weitgehend aus Siltkorngrößen, die vor Nouakchott über die Schelfkante hinaustransportiert werden und zu einer Grobsiltanreicherung am mittleren Hang führen. 5) Das Verhältnis zwischen den karbonatischen Biogenkomponenten und den nichtbiogenen Partikeln spiegelt sich deutlich in der Karbonatverteilung sowohl des Gesamtsedimentes als auch der Sandfraktion wider. Relativ hohe Karbonatgehalte vor Cap Leven im Norden stehen sehr geringen Anteilen von Nouakchott gegenüber. Mit zunehmender Wassertiefe ist eine deutliche Abnahme des Karbonatanteils zu verfolgen. 6) Die Tatsache, daß das Profil Cap Blanc im Bereich des ganzjährigen Auftriebs liegt, spiegelt sich nicht in der Zusammensetzung der Sandfraktion wider. Südlich der Zone des ganzjährigen Auftriebs weisen verschiedene Parameter (Radiolarien, Diatomeen, Verhältnis von Radiolarien zu planktonischen Foraminiferen, Benthos/Plankton-Verhältnis der Foraminiferen) trotz abnehmender Auftriebsintensität eher steigende Werte auf. Dies ist wesentlich auf eine infolge des Nährstoffeintrages durch Flußzufuhr bedingte Verschiebung der maximalen Primärproduktion weit in südliche Richtung zurückzuführen. 7) In den aufgeführten Parametern zeigen sich von Profil zu Profil sehr deutliche fazielle Unterschiede, obwohl der großklimatische Hintergrund im gesamten Untersuchungsgebiet etwa gleich ist. Vor Cap Leven bildet sich eine Fazies, die im wesentlichen aus planktonischen Foraminiferen besteht, während das Sediment vor Nouakchott zum überwiegenden Teil aus nichtbiogenen Komponenten aufgebaut wird. Im Übergangsbereich vor Cap Blanc bildet sich eine Mischfazies, die keinerlei Prägung durch das Auftriebsgeschehen erhält. Die Ursachen dieser faziellen Unterschiede werden auf fehlenden Terrigeneinfluß vor Cap Leven einerseits und hohe Terrigenanlieferung vor Nouakchott andererseits zurückgeführt. 8) Die Zusammensetzung und Verteilung der rezenten Grobfraktionssedimente am Kontinentalrand vor Nw-Afrika wird somit im wesentlichen als Ergebnis einer Überprägung der Biogenanlieferung durch nichtbiogene Komponenten angesehen. Wesentlicher steuernder Faktor ist demnach das hier vorherrschende Windsystem.

Slope stability analyses based on sediment cores of the Ligurian Margin, Southern France

Submarine slope failures of various types and sizes are common along the tectonic and seismically active Ligurian margin, northwestern Mediterranean Sea, primarily because of seismicity up to ~M6, rapid sediment deposition in the Var fluvial system, and steepness of the continental slope (average 11°). We present geophysical, sedimentological and geotechnical results of two distinct slides in water depth >1,500 m: one located on the flank of the Upper Var Valley called Western Slide (WS), another located at the base of continental slope called Eastern Slide (ES). WS is a superficial slide characterized by a slope angle of ~4.6° and shallow scar (~30 m) whereas ES is a deep-seated slide with a lower slope angle (~3°) and deep scar (~100 m). Both areas mainly comprise clayey silt with intermediate plasticity, low water content (30-75 %) and underconsolidation to strong overconsolidation. Upslope undeformed sediments have low undrained shear strength (0-20 kPa) increasing gradually with depth, whereas an abrupt increase in strength up to 200 kPa occurs at a depth of ~3.6 m in the headwall of WS and ~1.0 m in the headwall of ES. These boundaries are interpreted as earlier failure planes that have been covered by hemipelagite or talus from upslope after landslide emplacement. Infinite slope stability analyses indicate both sites are stable under static conditions; however, slope failure may occur in undrained earthquake condition. Peak earthquake acceleration from 0.09 g on WS and 0.12 g on ES, i.e. M5-5.3 earthquakes on the spot, would be required to induce slope instability. Different failure styles include rapid sedimentation on steep canyon flanks with undercutting causing superficial slides in the west and an earthquake on the adjacent Marcel fault to trigger a deep-seated slide in the east.

Age models of sediment cores from the continental margin of northwest Africa

Diatom abundance and species composition were quantitatively studied in two latest Quaternary (~130 ka to the Present) sequences from the continental margin of northwest Africa. Off this region, coastal upwelling is well developed under the influence of the NE trade winds. Variations in diatom abundance in these cores are inferred to represent changes caused by varying degrees of the upwelling fertility. Times of high productivity are marked by high relative frequencies of Chaetoceros, while low productivity is marked by the dominance of Aulacoseira granulata. Upwelling increased during glacial episodes (isotopic stages 2-4 and 6) relative to isotopic stages 1 and 5. During the late Holocene, primary productivity levels are similar to those for Stage 5, but in the early Holocene upwelling intensities seem to have been weaker than today. The paleoproductivity reconstruction based on the diatom record is supported by paleoproductivity estimations based on the organic carbon content of the sediments (Sarnthein et al., 1987).

Amino acid geochronology of foraminifera test from north Queensland margin

In this study, we demonstrate the utility of amino acid geochronology based on single-foraminiferal tests in Quaternary sediment cores from the Queensland margin, Australia. The large planktonic foraminifer Pulleniatina obliquiloculata is ubiquitous in shelf, slope, and basin sediments of north Queensland as well as pantropical oceans. Fossil tests are resistant to dissolution, and retain substantial concentrations of amino acids (2-4 nmol/mg of shell) over hundreds of thousands of years. Amino acid D and L isomers of aspartic acid (Asp) and glutamic acid (Glu) were separated using reverse phase chromatography, which is sensitive enough to analyze individual foraminifera tests. In all, 462 Pulleniatina tests from 80 horizons in 11 cores exhibit a systematic increase in D/L ratios down core. D/L ratios were determined in 32 samples whose ages are known from AMS 14C analyses. In all cases, the Asp and Glu D/L ratios are concordant with 14C age. D/L ratios of equal-age samples are slightly lower for cores taken from deeper water sites, reflecting the sensitivity of the rate of racemization to bottom water temperature. Beyond the range of 14C dating, previously identified marine oxygen-isotope stage boundaries provide approximate ages of the sediments up to about 500,000 years. For this longer time frame, D/L ratios also vary systematically with isotope-correlated ages. The rate of racemization for Glu and Asp was modeled using power functions. These equations can be used to estimate ages of samples from the Queensland margin extending back at least 500,000 years. This analytical approach provides new opportunities for geochronological control necessary to understand fundamental sedimentary processes affecting a wide range of marine environments.

The magnesium isotope composition of diagenetic dolomites from ODP Hole 112-685A and 201-1230A of the Peru Margin

The magnesium isotope composition of diagenetic dolomites and their adjacent pore fluids were studied in a 250 m thick sedimentary section drilled into the Peru Margin during Ocean Drilling Program (ODP) Leg 201 (Site 1230) and Leg 112 (Site 685). Previous studies revealed the presence of two types of dolomite: type I dolomite forms at ~ 6 m below seafloor (mbsf) due to an increase in alkalinity associated with anaerobic methane oxidation, and type II dolomite forms at focused sites below ~ 230 mbsf due to episodic inflow of deep-sourced fluids into an intense methanogenesis zone. The pore fluid delta 26Mg composition becomes progressively enriched in 26Mg with depth from values similar to seawater (i.e. -0.8 per mil, relative to DSM3 Mg reference material) in the top few meters below seafloor (mbsf) to 0.8 ± 0.2 per mil within the sediments located below 100 mbsf. Type I dolomites have a delta 26Mg of -3.5 per mil, and exhibit apparent dolomite-pore fluid fractionation factors of about -2.6 per mil consistent with previous studies of dolomite precipitation from seawater. In contrast, type II dolomites have delta 26Mg values ranging from -2.5 to -3.0 per mil and are up to -3.6 per mil lighter than the modern pore fluid Mg isotope composition. The enrichment of pore fluids in 26Mg and depletion in total Mg concentration below ~ 200 mbsf is likely the result of Mg isotope fractionation during dolomite formation, The 26Mg enrichment of pore fluids in the upper ~ 200 mbsf of the sediment sequence can be attributed to desorption of Mg from clay mineral surfaces. The obtained results indicate that Mg isotopes recorded in the diagenetic carbonate record can distinguish near surface versus deep formed dolomite demonstrating their usefulness as a paleo-diagenetic proxy.

Late Miocene palaeoflora and palaeoclimate of Lincang (China)

The Miocene Lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern Yunnan (SW China) and the evolution of monsoon intensity. Three quantitative methods were chosen for this reconstruction, i.e. Leaf Margin Analysis (LMA), Climate Leaf Analysis Multivariate Program (CLAMP), and the Coexistence Approach (CA). These methods, however, yield inconsistent results, particularly for the precipitation, as also shown in European and other East Asian Cenozoic floras. The wide range of the reconstructed climatic parameters includes the Mean Annual Temperature (MAT) of 18.5-24.7 °C and the Mean Annual Precipitation (MAP) of 1213-3711 mm. Compared with the modern Lincang climate (MAT, 17.3 °C; MAP, 1178.7 mm), the Miocene climate is slightly warmer, wetter and has a higher temperature seasonality. A detailed comparison on the palaeoclimatic variables with the coeval Late Miocene Xiaolongtan flora from the eastern part of Yunnan allows us to investigate the development and interactions of both South Asian and East Asian monsoons during the Late Miocene in southwest China, now under strong influence of these monsoon systems. Our results suggest that the monsoon climate has already been established in southwest Yunnan during the Late Miocene. Furthermore, our results support that both Southeast Asian and East Asian monsoons co-occurred in Yunnan during the Late Miocene.

(Table 1) Chlorophyll concentrations in the Southwest Indian Ocean

Results are examined of determinations of chlorophyll in seawater suspension by fluorescent and spectrophometric methods in the Southwest Indian Ocean near the African coast and in the Seychelles-Mauritius Plateau area in July-November 1977. During the study period near the African coast, the most productive regions, where the weighted average particulate chlorophyll concentration in the photic zone was greater than 0.5 µg/l, were off the Mozambique coast (near the mouth of the Zambezi River and in Delagoa Bay) and also off the coast of Tanzania, near the the Pemba and Zanzibar Islands. The most favorable conditions for growth of phytoplankton, i.e., a combination of distinct water stratification with intense upwelling, were observed in the equatorial divergence zone in the region of the Seychelles and Amirante Islands, where chlorophyll concentration in the layer of the maximum was as high as 3.4 µg/l. This region can be considered as one of the most productive regions of the Indian Ocean.

Composition of Fe-Mn nodules and crusts from the Southwest Pacific

A study of samples dredged within areas of tectonic arc-trench systems (Kermadec and New Hebrides) allows to distinguish three types of ferromanganese mineralization. Relationship between mineral and geochemical specialization is established. A conclusion is made that ferromanganese mineralization is a permanent genetic series of matter supply: from endogenic (hydrothermal solution is a dominant source at deposition of chemical elements from mixture seawater plus hydrothermal solutions) to hydrogenic (seawater is a dominant source at element deposition). This results in geochemical and mineralogical variety of ferromanganese mineralization within this part of the Pacific Ocean.

TOC and TIC concentration in sediments from Peru margin and eastern equatorial Pacific ODP sites

Organic matter deposited and buried under the seafloor is one of the major carbon sources for microbial life in the deep subsurface of the ocean. In this report, we present a compilation of all available total organic carbon (TOC) and total inorganic carbon (TIC) data for the sites drilled during Ocean Drilling Program (ODP) Leg 201. We include the TOC and TIC data from sites of Deep Sea Drilling (DSDP) Leg 34 and ODP Legs 112 and 138 (Yeats, Hart, et al., 1976, doi:10.2973/dsdp.proc.34.1976; Suess, von Huene, et al., 1988, doi:10.2973/odp.proc.ir.112.1988; Mayer, Pisias, Janecek, et al., 1992, doi:10.2973/odp.proc.ir.138.1992), which were reoccupied during ODP Leg 201. Additional data from Leg 201 shore-based analyses are also included in the compilation.