Description: The usually high concentrations of Zn, Pb, Cd, and Cu in the most recently accreted portions of ferromanganese nodules from the western Baltic Sea are thought to reflect increased metal input due to anthropogenic mobilization. If so, the point of increase represents a time horizon within the structure of the nodule. Similar trace metal distributions of radiometrically dated sediments from the same area suggest that the ferromanganese nodules have grown in thickness between 0.02 and 0.16 mm yr−1. From this growth rate anthropogenic Zn flux to the nodule surface was calculated to be 80 mg m−2 yr−1.

Description: Microbial decomposition of organic matter in recent sediments of the Landsort Deep—an anoxic basin of the central Baltic Sea—resulted in the formation of a characteristic assemblage of authigenic mineral precipitates of carbonates, sulfides. phosphates and amorphous silica, The dominant crystalline phases are a mixed Mn-carbonate [(Mn0.85Ca0.10Mg0.05)CO3]. Mn-sulfide [MnS] and Fecarbonate [FeCO3]. Amorphous Fe-sulfide [FeS]. Mn-phosphate [Mn3(PO4)2] and a mixed Fe-Ca-phosphate [(Fe0.86Ca0.14)3(PO4)2] were identified by their chemical compositions only. The variability in composition of these solid phases and their mode of occurrence as a co-existing assemblage constrains the conditions and solution composition from which they precipitated. Estimates of activities for dissolved Fe. Mn. PO4, CO3 and S in equilibrium with such an assemblage are close to those found in recent anoxic interstitial water-sediment systems. It is important to have detailed knowledge of the composition and stability conditions of these solid precipitates in order to refine stoichiometric models of interstitial nutrient regeneration in anoxic sediments.

Description: Food production is affected by climate and by climate change. The indices for climate change may be recognized in long-term systematic observations of oceanic water columns at selected referential sites. The Mediterranean Sea, as part of the global oceanic circulation system, may be sensitive to climatic variation and may have an influence upon climate. The establishment of international referencestations for the Mediterranean area is suggested.

Description: A bathymetric map of the deep-sea floor off southeastern Africa shows the Agulhas Plateau to be separated from the continental margin of southeastern Africa by a narrow (50 km) elongate depression, the Agulhas Passage, which acts as a deep-water connection between the Agulhas and Transkei basins. Three regionally developed sediment layers occur in the deep (〉 4500 m) Transkei Basin/Agulhas Passage area. With the aid of a simple ocean crust sinking/carbonate compensation level (CCL) model these layers are related to the sedimentation history of the area. The model suggests that acoustic basement (Horizon X) represents Lower Cretaceous limestones draped over oceanic basement, and that this is overlain by an acoustically transparent sequence of pelagic/terrigenous material (Horizon A) that was deposited during a lengthy period (95 m.y.) beneath the carbonate compensation level. Post-Late Miocene sedimentation (Horizons B and C) has probably taken place above the CCL. Local sedimentation has always been influenced by strong sea-floor currents, but since middle Palaeogene times these currents have operated on a regional scale and have generated numerous large ridge and billow-like bed forms.

Description: Thick sediments (maximum of at least 4900 m) infill the Natal Valley, which lies between the coast of South Africa/Mozambique and the Mozambique Ridge. Eight physiographic provinces are recognised in the valley, and their boundaries can be related to well-defined sediment thickness or facies discontinuities within the basin infill. The acoustic stratigraphy of the area is established by reference to two regionally developed reflecting horizons, which, on the basis of previously published borehole and seismic data, are tentatively identified as mid-Cretaceous (McDuff) and mid-Cainozoic (Angus) hiatuses or important facies boundaries. Sedimentation began in the Natal Valley before mid-Cretaceous times and since then sediment dispersion has been strongly influenced by the disposition of large basement (? volcanic) highs: the approximately NE—SW Almirante Leite and Naudé ridges, and the larger N—S Mozambique Ridge. There is abundant evidence that sedimentation in the vicinity of these ridges has been current-controlled since at least mid-Cainozoic (Angus) times. The two main terrigenous sediment input points have been the Tugela and Limpopo rivers, which have large sediment cones adjacent to their mouths.

Description: Goban Spur lies on the continental margin of northwest Europe, southwest of Ireland. It is a marginal plateau underlain by Hercynian granites and Palaeozoic sediments, which form large horsts, grabens and tilted fault blocks with a trend that is approximately parallel to the main Celtic/Armorican Shelf edge. The spur is thought to be a westward continuation of the buoyant Cornubian Ridge, and is bounded to the north and south by large fault lines which probably represent reactivation of Hercynian structural trends. The continental basement is further divided longitudinally into a low-lying outer zone (Intermediate Zone) and a high inner region (Goban Spur proper). The ocean/continent boundary is thought to lie at the outer edge of the Intermediate Zone, Sea-floor spreading anomalies immediately west of the Intermediate Zone suggest that the adjacent ocean crust was created prior to anomaly 33 (say at ca. 90 m.y. B.P.). The sedimentary sequence on Goban Spur can be subdivided into four layers which can be tentatively correlated with the stratigraphic succession on the Meriadzek Terrace (IPOD sites). Such a correlation suggests that the lowermost sediment layer (?Jurassic-Albian) represents a tectono-sedimentary rift infill, and that Layers 2–4 (Upper Cretaceous to Quaternary) were deposited during slow epeirogenic downwarping of the plateau and that the sedimentary processes involved both draping and strong current moulding. The relatively buoyant nature of Inner Goban Spur has inhibited the accumulation of a thick post-rifting sedimentary sequence (700–1000 m), and has shielded the Intermediate Zone from downslope mass movements of material. This has resulted in the accumulation of an anomalously thin post-rift stage outer margin sediment prism (ca. 1000 m) compared to most continent rises (up to 10 km).

Description: Petrographic examination of amygdules and veins associated with moderately altered pillow basalts dredged from the Peru Trench has revealed that a consistent pattern of mineral crystallization has occurred. This sequence is: (1) green, weakly pleochroic clay (R.I. 〉 1.56); (2) dark yellowish brown, non-pleochroic clay (R.I. 〉 1.56); (3) light yellowish brown to colorless, fibrous, weakly pleochroic clay (R.I. 〈 1.56); and (4) calcite or celadonite. Chemical and X-ray diffraction analyses suggest that all clay mineral amygdule and vein fillings are dominated by intimate mixtures of an Fe-rich saponite and nontronite with very small admixtures of serpentine and illite. It is argued that sequential mineral fillings of fractures and vesicles may provide significant information about the chemistry of circulating interstitial fluids. For the pillow basalts studied the first-formed clays were enriched in nontronite, thereby suggesting Fe-rich fluids. These in turn were followed by saponite-rich clays and calcite. The change from Fe-and Mg-rich fluids to dominantly Ca-rich fluids is thought to correspond to a change from mafic mineral alteration to plagioclase alteration in the pillow basalts. An increase in the Fe3+/Fe2+ ratio of clays toward the centers of vesicles may indicate a change toward a more oxidizing environment of alteration.

Description: Five separate exposures of oceanic basalts were dredged in the vicinity of the Peru-Chile Trench between 9° and 27°S latitude. Each dredge is dominated by abundant pillow basalts. Approximately ten of the most unaltered, glassy and fine-grained samples were selected for detailed chemical and petrographic analyses from each dredge area. All basalts recovered in the Peru-Chile Trench are olivine and quartz-normative tholeiites that are believed to have formed at the now extinct Galapagos Rise 30–50 m.y. ago. Detailed chemical analyses of the basalts, including major and selected trace and rare earth elements, indicate that considerable compositional variability exists both within each of the dredged areas as well as between areas. Most of the inherent chemical variability observed within particular basement sections appears consistent with the concept of temporal evolution of magma bodies at a former spreading center by shallow-level fractional crystallization involving primarily plagioclase and olivine. In contrast, important chemical differences between the dredged areas suggest compositional heterogeneities in the mantle source regions. Our results indicate that although shallow-level fractionation has brought about large changes in composition of basalts in each area, compositional trends are distinct and appear to reflect original mantle-derived compositional differences.

Description: Thirty-four ash layers of Pleistocene and Pliocene age from DSDP Site 192, northwestern Pacific Ocean, have been subjected to detailed chemical and optical study to evaluate: (1) the chemical and optical variability in glass shards from deep-sea ash layers, and (2) secondary changes brought about by prolonged exposure to seawater. Glass shards from approximately half of the ash layers studied were found to have uniform compositions which approach the precision of the microprobe chemical analyses, whereas the remainder are compositionally diverse (e.g., SiO2, variations of 5–15% among shards from the same ash layer) and appear to be the eruptive products of compositionally zoned magma chambers. Optical studies of glass shards confirm the absence of devitrification or the formation of pervasive secondary alteration products. By contrast, chemical studies suggest that the glass shards have experienced progressive hydration with possible minor ion exchange of K, Mg, Ca and Si. The hydration occurs rapidly and leads to a rather uniform water content of 4.5–5% after several hundred thousands of years exposure to seawater. Step-wise heating dehydration experiments, optical effects, and published'oxygen isotope studies indicate that the water of hydration is incorporated uniformly within the glass. Systematic chemical differences between electron microprobe analyses of glass shard interiors and corresponding bulk chemical study by atomic absorption lead us to postulate that glass shard margins have undergone a minor chemical exchange with major cations in seawater. They have gained 0.10–0.20 wt. % K20, MgO, and CaO while losing a corresponding amount of Si2O. Although the glass shards from DSDP Site 192 are hydrated and may have experienced subtle, surficial ion exchange, we stress that they are the most chemically representative samples available of magmas that were explosively erupted from volcanic arcs.

Description: Several types of abyssal bedforms have been discovered during surveys with a deeply towed instrument package at water depths of 1.5–6 km in the Pacific and Atlantic Oceans. Cores and current-meter records obtained at the same sites provide data for interpreting their dynamics. Wave and current ripples are best portrayed in bottom photographs, but medium-scale bedforms, including sand waves, mud waves and erosional furrows, are described by interpreting high-resolution side-looking sonar records. The largest examples affect surface-ship echograms, though their shape and structure can seldom be resolved without near-bottom observations. Wave ripples are common on the slopes of seamounts and ridges, while current ripples and sand waves occur beneath some fast thermohaline currents whose beds are shallower than the foraminiferal compensation depth. Depositional and erosional bedforms in cohesive sediment have been found beneath the deepest thermohaline currents; they may be restricted to areas where the flow is unusually steady in direction.