Lipid biomarkers in urface sediments of the Southeast Atlantic

Surface sediments from the eastern South Atlantic were investigated for their lipid biomarker contents and bulk organic geochemical characteristics to identify sources, transport pathways and preservation processes of organic components. The sediments cover a wide range of depositional settings with large differences in mass accumulation rates. The highest marine organic carbon (OC) contributions are detected along the coast, especially underlying the Benguela upwelling system. Terrigenous OC contributions are highest in the Congo deep-sea fan. Lipid biomarker fluxes are significantly correlated to the extent of oxygen exposure in the sediment. Normalization to total organic carbon (TOC) contents enabled the characterization of regional lipid biomarker production and transport mechanisms. Principal component analyses revealed five distinct groups of characteristic molecular and bulk organic geochemical parameters. Combined with information on lipid sources, the main controlling mechanisms of the spatial lipid distributions in the surface sediments are defined, indicating marine productivity related to river-induced mixing and oceanic upwelling, wind-driven deep upwelling, river-supply of terrigenous organic material, shallow coastal upwelling and eolian supply of plant-waxes.

Pliocene/Pleistocene benthic foraminiferal abundances from six drilling cores

Twenty percent (19 genera, 95 species) of cosmopolitan, deep-sea (500-4000 m), benthic foraminiferal species became extinct during the late Pliocene-Middle Pleistocene (3-0.12 Ma), with the peak of extinctions (76 species) occurring during the mid-Pleistocene Climate Transition (MPT, 1.2-0.55 Ma). One whole family (Stilostomellidae, 30 species) was wiped out, and a second (Pleurostomellidae, 29 species) was decimated with just one species possibly surviving through to the present. Our studies at 21 deep-sea core sites show widespread pulsed declines in abundance and diversity of the extinction group species during more extreme glacials, with partial interglacial recoveries. These declines started in the late Pliocene in southern sourced deep water masses (Antarctic Bottom Water, Circumpolar Deep Water) and extending into intermediate waters (Antarctic Intermediate Water, North Atlantic Deep Water) in the MPT, with the youngest declines in sites farthest downstream from high-latitude source areas for intermediate waters. We infer that the unusual apertural types that were targeted by this extinction period were adaptations for a specific kind of food source and that it was probably the demise of this microbial food that resulted in the foraminiferal extinctions. We hypothesize that it may have been increased cold and oxygenation of the southern sourced deep water masses that impacted on this deep water microbial food source during major late Pliocene and Early Pleistocene glacials when Antarctic ice was substantially expanded. The food source in intermediate water was not impacted until major glacials in the MPT when there were significant expansion of polar sea ice in both hemispheres and major changes in the source areas, temperature, and oxygenation of global intermediate waters.

Chemical analysis of ODP Hole 104-642E

During Ocean Drilling Program Leg 104 a 900-m-thick sequence of volcanic rocks was drilled at Hole 642E on the Vøring Plateau, Norwegian Sea. This sequence erupted in two series (upper and lower series) upon continental basement. The upper series corresponds to the seaward-dipping seismic reflectors and comprises a succession of about 122 flows of transitional oceanic tholeiite composition. They have been subdivided into several formations consisting of flows related to each other by crystal fractionation processes, magma mixing, or both. Major- and trace-element chemistry indicates affinities to Tertiary plateau lavas of northeast Greenland and to Holocene lavas from shallow transitional segments of the Mid-Atlantic Ridge, such as Reykjanes Ridge. The tholeiitic magmas have been derived from a slightly LREE-depleted mantle source. Two tholeiitic dikes that intruded the lower series derive from an extremely depleted mantle source. Interlayered volcaniclastic sediments are dominantly ferrobasaltic and more differentiated. They appear to come from a LREE-enriched mantle source, and may have been erupted in close vicinity of the Vøring Plateau during hydroclastic eruptions. The two tholeiitic dikes that intruded the lower series as well as some flows at the base of the upper series show evidence of assimilation of continental upper crustal material.

Eolian deposition on the Ontong Java Plateau

The record of eolian deposition on the Ontong Java Plateau (OJP) since the Oligocene (approximately 33 Ma) has been investigated using dust grain size, dust flux, and dust mineralogy, with the goal of interpreting the paleoclimatology and paleometeorology of the western equatorial Pacific. Studies of modern dust dispersal in the Pacific have indicated that the equatorial regions receive contributions from both the Northern Hemisphere westerly winds and the equatorial easterlies; limited meteorological data suggest that low-altitude westerlies could also transport dust to OJP from proximal sources in the western Pacific. Previous studies have established the characteristics of the grain-size, flux, and mineralogy records of dust deposited in the North Pacific by the mid-latitude westerlies and in the eastern equatorial Pacific by the low-latitude easterlies since the Oligocene. By comparing the OJP records with the well-defined records of the mid-latitude westerlies and the low-latitude easterlies, the importance of multiple sources of dust to OJP can be recognized. OJP dust is composed of quartz, illite, kaolinite/chlorite, plagioclase feldspar, smectite, and heulandite. Mineral abundance profiles and principal components analysis (PCA) of the mineral abundance data have been used to identify assemblages of minerals that covary through all or part of the OJP record. Abundances of quartz, illite, and kaolinite/chlorite covary throughout the interval studied, defining a mineralogical assemblage supplied from Asia. Some plagioclase and smectite were also supplied as part of this assemblage during the late Miocene and Pliocene/Pleistocene, but other source areas have supplied significant amounts of plagioclase, smectite, and heulandite to OJP since the Oligocene. OJP dust is generally coarser than dust deposited by the Northern Hemisphere westerlies or the equatorial easterlies, and it accumulates more rapidly by 1-2 orders of magnitude. These relationships indicate the importance of the local sources on dust deposition at OJP. The grain-size and flux records of OJP dust do not exhibit most of the events observed in the corresponding records of the Northern Hemisphere westerlies or the equatorial easterlies, because these features are masked by the mixing of dust from several sources at OJP. The abundance record of the Asian dust assemblage at OJP, however, does contain most of the features characteristic of dust flux by means of the Northern Hemisphere westerlies, indicating that the paleoclimatic and paleometeorologic signal of a particular source area and wind system can be preserved in areas well beyond the region dominated by that source and those winds. Identifying such a signal requires "unmixing" the various dust assemblages, which can be accomplished by combining grain-size, flux, and mineralogic data.

Lavas from the Elbrus volcano, Greater Caucasus

Comprehensive geochronological and isotope-geochemical studies showed that the Late Quaternary Elbrus Volcano (Greater Caucasus) experienced long (approximately 200 ka) discrete evolution with protracted periods of igneous quiescence (approximately 50 ka) between large-scale eruptions. Volcanic activity of Elbrus is subdivided into three phases: Middle Neopleistocene (225-170 ka), Late Neopleistocene (110-70 ka), and Late Neopleistocene - Holocene (earlier than 35 ka). Petrogeochemical and isotope (Sr-Nd-Pb) signatures of Elbrus lavas point to their mantle-crustal origin. It was shown that hybrid parental magmas of the volcano formed due to mixing and/or contamination of deep-seated mantle melts by Paleozoic upper crustal material of the Greater Caucasus. Mantle reservoir that participated in genesis of Elbrus lavas as well as most other Neogene-Quaternary magmatic rocks of Caucasus was represented by the lower mantle "Caucasus" source. Primary melts generated by this source in composition corresponded to K-Na subalkali basalts with the following isotopic characteristics: 87Sr/86Sr = 0.7041+/-0.0001, e-Nd = +4.1+/-0.2, 147Sm/144Nd = 0.105-0.114, 206Pb/204Pb = 18.72, 207Pb/204Pb = 15.62, and 208Pb/204Pb = 38.78. Temporal evolution of isotope characteristics for lavas of the Elbrus Volcano is well described by a Sr-Nd mixing hyperbole between "Caucasus" source and estimated average composition of the Paleozoic upper crust of the Greater Caucasus. It was shown that, with time, proportions of mantle material in parental magmas of Elbrus gently increased: from ~60% at the Middle-Neopleistocene phase of activity to ~80% at the Late Neopleistocene - Holocene phase, which indicates an increase of activity of a deep-seated source at decreasing input of crustal melts or contamination with time. Unraveled evolution of the volcano with discrete eruption events, lacking signs of cessation of the Late Neopleistocene - Holocene phase, increasing contribution of the deep-seated mantle source in genesis of Elbrus lavas with time as deduced from isotope-geochemical data, as well as numerous geophysical and geological evidence indicate that Elbrus is a potentially active volcano and its eruptions may be resumed. Possible scenarios were proposed for evolution of the volcano, if its eruptive activity continued.