Chemical composition of ferromanganese nodules from the Black Sea

Ferruginate shells and tubular worm burrows from the oxygenated zone of the Black Sea (Kalamit Bay and Danube River mouth) are studied by transmission and scanning electron microscopy combined with analyses of elemental composition. Iron and manganese oxyhydroxide nodules considered here are enriched in phosphorus. They contain variable amounts of terrigenous and biogenic material derived from host sediments. Oxyhydroxides are mainly characterized by colloform structure, whereas globular and crystalline structures are less common. The dominating iron phase is represented by ferroxyhite and protoferroxyhite, whereas the manganese phase is composed of Fe-free vernadite. Concentrations of Mn, As, and Mo are 12-18 times higher relative to sediments, while concentrations of Fe, P, Ni, and Co increase 5-7 times during nodule formation.

Distribution of pollen and spores in sediments of ODP Hole 175-1078C

The distribution of pollen in marine sediments is used to record vegetation change on the continent. Generally, a good latitudinal correspondence exists between the distribution patterns of pollen in the marine surface sediments and the occurrence of the source plants on the adjacent continent. To investigate land-sea interactions during deglaciation, we compare proxies for continental (pollen assemblages) and marine conditions (alkenone-derived sea surface temperatures) of two high-resolution, radiocarbon-dated sedimentary records from the tropical southeast Atlantic. The southern site is located West of the Cunene River mouth; the northern site is located West of the Angolan Huambe Mountains. It is inferred that the vegetation in Angola developed from Afroalpine and open savannah during the last Glacial maximum (LGM) via Afromontane Podocarpus forest during Heinrich Event 1 (H1), to an early increase of lowland forest after 14.5 ka. The vegetation record indicates dry and cold conditions during the LGM, cool and wet conditions during H1 and a gradual rise in temperature starting well before the Younger Dryas (YD) period. Terrestrial and oceanic climate developments seem largely running parallel, in contrast to the situation ca. 5° further South, where marine and terrestrial developments diverge during the YD. The cool and wet conditions in tropical West Africa, South of the equator, during H1 suggest that low-latitude insolation variation is more important than the slowdown of the thermohaline circulation for the climate in tropical Africa.

Strontium-90 and tritium concentrations in surface waters of the North Pacific

Results of determinations of 90Sr and tritium polluting surface water in different parts of the North Pacific are presented. The T/90Sr ratio lies within 90-600 over the referred water area and attains 2000 near the Columbia River mouth. Tritium concentration in sea water has been noted to be affected by river runoff and terrigenous sediments.

Climatic records of the late Holocene from sediment core GeoB9504-3 off Senegal

High-resolution climatic records of the late Holocene along the north-west African continental margin are scarce. Here we combine sediment grain size, elemental distribution and mineral assemblage data to trace dust and riverine sources at a shallow-marine sediment depocentre in the vicinity of the Senegal River mouth. The aim is to understand how these terrigenous components reflect climate variability during the late Holocene. Major element contents were measured and mineral identification was performed on three sub-fractions of our sediment core: (i) fluvial material <2 µm, (ii) aeolian material of 18-63 µm and (iii) a sub-fraction of dual-origin material of 2-18 µm. Results show that more than 80% of the total Al and Fe terrigenous bulk content is present in the fluviogenic fraction. In contrast, Ti, K and Si cannot be considered as proxies for one specific source off Senegal. The Al/Ca ratio, recording the continental river runoff, reveals two dry periods from 3010 to 2750 cal a BP and from 1900 to 1000 cal a BP, and two main humid periods from 2750 to 1900 cal a BP and from 1000 to 700 cal a BP. The match between (i) intervals of low river runoff inferred by low Al/Ca values, (ii) reduced river discharge inferred by integrated palynological data from offshore Senegal and (iii) periods of enhanced dune reactivation in Mali confirms this interpretation.

Pollen and organic-walled dinoflagellate cyst assemblages of sediment core GeoB9503-5

Pollen and organic-walled dinoflagellate cyst assemblages from core GeoB 9503-5 retrieved from the mud-belt ( 50 m water depth) off the Senegal River mouth have been analyzed to reconstruct short-term palaeoceanographic and palaeoenvironmental changes in subtropical NW Africa during the time interval from ca. 4200 to 1200 cal yr BP. Our study emphasizes significant coeval changes in continental and oceanic environments in and off Senegal and shows that initial dry conditions were followed by a strong and rapid increase in humidity between ca. 2900 and 2500 cal yr BP. After ca. 2500 cal yr BP, the environment slowly became drier again as indicated by slight increases in Sahelian savannah and desert elements in the pollen record. Around ca. 2200 cal yr BP, this relatively dry period ended with periodic pulses of high terrigenous contributions and strong fluctuations in fern spore and river plume dinoflagellate cyst percentages as well as in the fluxes of pollen, dinoflagellate cysts, fresh-water algae and plant cuticles, suggesting "episodic flash flood" events of the Senegal River. The driest phase developed after about 2100 cal yr BP.

Sea surface temperature reconstruction of sediment core GeoB6518-1

Past hydrological changes in Africa have been linked to various climatic processes, depending on region and timescale. Long-term precipitation changes in the regions of northern and southern Africa influenced by the monsoons are thought to have been governed by precessional variations in summer insolation (Kutzbach and Liu, 1997, doi:10.1126/science.278.5337.440; Partridge et al., 1997, doi:10.1016/S0277-3791(97)00005-X). Conversely, short-term precipitation changes in the northern African tropics have been linked to North Atlantic sea surface temperature anomalies, affecting the northward extension of the Intertropical Convergence Zone and its associated rainbelt (Hastenrath, 1990, doi:10.1002/joc.3370100504, Street-Perrott and Perrott, 1990, doi:10.1038/343607a0). Our knowledge of large-scale hydrological changes in equatorial Africa and their forcing factors is, however, limited (Gasse, 2000, doi:10.1016/S0277-3791(99)00061-X). Here we analyse the isotopic composition of terrigenous plant lipids, extracted from a marine sediment core close to the Congo River mouth, in order to reconstruct past central African rainfall variations and compare this record to sea surface temperature changes in the South Atlantic Ocean. We find that central African precipitation during the past 20,000 years was mainly controlled by the difference in sea surface temperatures between the tropics and subtropics of the South Atlantic Ocean, whereas we find no evidence that changes in the position of the Intertropical Convergence Zone had a significant influence on the overall moisture availability in central Africa. We conclude that changes in ocean circulation, and hence sea surface temperature patterns, were important in modulating atmospheric moisture transport onto the central African continent.

Geological, geochemical and biogeochemical data on boundary zones of the Atlantic Ocean

Results of studies in two biogeochemically active zones of the Atlantic Ocean (the Benguela upwelling waters and the region influenced by the Congo River run-off) are reported in the book. A multidisciplinary approach included studies of the major elements of the ocean ecosystem: sea water, plankton, suspended matter, bottom sediments, interstitial waters, aerosols, as well as a wide complex of oceanographic studies carried out under a common program. Such an approach, as well as a use of new methodical solutions led to obtaining principally new information on different aspects of oceanology.

Concentrations of As and other chemical elements in bottom sediments of the Baltic Sea

As is less toxic than Hg, Cd, Pb, Se, Zn, and Cu. The As clarke for clays and shales is 10 ppm. Our samples of bottom sediments from Kurshskii Bay were determined to contain from 15 to 26 ppm As and up to 34 ppm As in the vicinity of the Neman River mouth. Elevated As concentrations (50-114 ppm) were detected in four columns of subsurface bottom sediments (at depths of 10-65 cm) from the Vistula Lagoon. Elevated As concentrations (50-180 ppm) were also found in a few surface samples of sand from the Gdansk Deep near oil platform D-6. These sediments are either partly contaminated with anthropogenic As or contain Fe sulfides and glauconite, which can concentrate As and contain its elevated concentrations. The As concentration in columns of bottom sediments from the Gulf of Finland were at the natural background level (throughout the columns) typical of the area (9-34 ppm). We repeatedly detected very high As concentrations (up to 227 ppm As) in politic ooze from Bornholm Deep, in the vicinity of the sunken vessel with chemical weapons. The sources of elevated As concentrations in the Baltic Sea are the following: (1) chemical weapon (CW) material buried in the floor of the Baltic Sea; (2) As-bearing pesticides, agricultural mineral fertilizers, and burned coal and other fuels; (3) kerogen-bearing Ordovician rocks exposed on the bottom; and (4) As-rich Fe sulfides brought to the area together with construction sand and gravel. This mixture was used in paper production and for the construction of hydraulic engineering facilities in the Vistula Lagoon in the early 20th century and later caused the so-called lagoon disease.

Late Quaternary siliciclastic/carbonate sedimentation in the Cabricorn Channel

A model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial-interglacial cycle in the Capricorn Channel, southern Great Barrier Reef (GBR). Stable isotope ratios, grainsize, carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level (mbsl). Results show variations in the flux of terrigenous, neritic and pelagic sediments to the continental slope over the last sea level cycle. During the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl. The percentages of quartz and feldspar in the cores decreased with water depth, while the percentage of clay increased. X-ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the Fitzroy River, which debouched directly into the northwest sector of the Capricorn Channel at this time. The cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite (HMC) during the glacial. The influx of HMC and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial, and also from HMC ooids precipitated at the head of the Capricorn Channel at this time. Mass accumulation rates (MARs) are high (13.5 g/cm**/kyr) during the glacial and peak at ~20 g/cm** 3/kyr in the early transgression (16-14 ka BP). MARs then decline with further sea level rise as the Fitzroy River mouth retreats from the edge of the continental shelf after 13.5 ka BP. MARs remain low (4 g/cm**3/kyr) throughout the Holocene highstand. Data for the Holocene highstand indicate there is a reduction in siliciclastic influx to the Capricorn Channel with little quartz and feldspar below 350 mbsl. However, fine-grained fluvial sediments, presumably from the Fitzroy River, were still accumulating on the mid slope down to 2000 mbsl. The proportion of pelagic calcite in the core tops increases with water depth, while HMC decreases, and is present only in trace amounts in cores below 1500 mbsl. The difference in the percentage of HMC in the deeper cores between the glacial and Holocene may reflect differences in supply or deepening of the HMC lysocline during the glacial. Sediment accumulation rates also vary between cores in the Capricorn Channel and do not show the expected exponential decrease with depth. This may be due to intermediate or deep water currents reworking the sediments. It is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments. Comparison of the Capricorn Channel MARs with those for other mixed carbonate/siliciclastic provinces from the northeast margin of Australia indicates that peak MARs in the early transgression in the Capricorn Channel precede those from the central GBR and south of Fraser Island. The difference in the timing of the carbonate and siliciclastic MAR peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces. The only common trend in the MARs from the northeast margin of Australia is the near synchronicity of the carbonate and siliciclastic MAR peaks in individual sediment cores, which supports a coeval sedimentation model.

Accumulation and composition of terrigenous material on Ceara rise over the past 55 Ma

Ceara Rise, located east the Amazon River mouth, is covered with a thick blanket of pelagic carbonate and hemipelagic terrigenous sediment. The terrigenous component has been extracted from 57 bulk sediment samples at Ocean Drilling Program (ODP) Sites 925 and 929 on Ceara Rise to obtain a Cenozoic record of riverine discharge from northern South America. From the early Eocene to early Miocene (55-20 Ma), terrigenous accumulation was dominated by moderate amounts of generally large-grained, gray to green sediment especially depleted in elements that are enriched in post-Archaean shale (e.g. Cs, Th, Yb). However, pulsed inputs of relatively small-grained, gray to green terrigenous sediment less depleted in the above elements occurred in the late Eocene and Oligocene. The accumulation of terrigenous sediment decreased significantly until 16.5 Ma. In the middle Miocene (16.5-13 Ma), terrigenous accumulation was dominated by small amounts of small-grained, tan sediment notably depleted in Na and heavy rare earth elements. The accumulation rate of terrigenous sediment increased markedly from the latest Miocene (10 Ma) to the present day, a change characterized by deposition of gray-green sediment enriched in elements that are enriched in post-Archaean shale. Observed changes in terrigenous sediment at Ceara Rise record tectonism and erosion in northern South America. The Brazil and Guyana shields supplied sediment to the eastern South American margin until the middle Miocene (20-16.5 Ma) when a period of thrusting, shortening and uplift changed the source region, probably first to highly weathered and proximal Phanerozoic sediments. By the late Miocene (9 Ma), there was a transcontinental connection between the Andes and eastern South America. Weathering products derived from the Andes have increasingly dominated terrigenous deposition at Ceara Rise since the Late Miocene and especially since the late Pliocene.