Manganese contents and accumulation rates in reduced bottom sediments of the Sea of Okhotsk

Manganese contents in reduced sediments and accumulation rates were investigated. Their values in sediments of most of cores are background (0.03-0.07 %).Anomalous concentrations (up to 2.5 %) and accumulation rates (up to 60 mg/cm**2/ka) occur near the known region of hydrothermal barite mineralization in the Derugin Basin. High accumulation rates of Mn (>10 mg/cm**2/ka) also occur in Holocene sediments to south-east from the Derugin Basin. It can be assumed that high Mn contents and accumulation rates occur there due to transportation of Mn-rich water from the Derugin Basin in the near-bottom layer under the lower border of the Sea of Okhotsk Intermediate Water. Intensive Mn accumulation is also typical for the South Okhotsk Basin near the Bussol Strait. Mn accumulation rates of glacial sediments of the second oxygen isotope stage are less significant, which is presumed to be caused by paleoceanological reasons.

Geochemical and isotopic composition of pore fluids of ODP Hole 131-808C

At the Western Nankai Trough subduction zone at ODP Site 808, chemical concentration and isotopic ratio depth profiles of D, O, Sr, and He do not support fluid flow along the décollement nor at the frontal thrust. They do, however, support continuous or periodic lateral fluid flow: (1) at the base of the Shikoku Basin volcanic-rich sediment member, situated ~140 m above the décollement, and particularly (2) below the décollement. The latter must have been rather vigorous, as it was capable of transporting clay minerals over great distances. The fluid at ~140 m above the décollement is characterized by lower than seawater concentrations of Cl- (>=18% seawater dilution). It is 18O-rich and D-poor and has a non-radiogenic, oceanic, or volcanic arc Sr isotopic signature. It originates from "volcanic" clay diagenesis. The fluid below the décollement has also less Cl- than seawater (>20% dilution), is more enriched in 18O and depleted in D than fluid, but its Sr isotopic signature is radiogenic, continentalterrigenous. The source of this fluid is located arcward, is deep-seated, where illitization of the subducted clay minerals, a mixture of terrigenous and volcanic clays, occurs. The 3He/4He ratio below the décollement points to an ~25% mantle contribution. The nature of the physical and chemical discontinuities across the décollement suggests it is overpressured and is forming a leaky "dynamic seal" for fluid flow. In contrast with the situation at Barbados and Peru, where the major tectonic features are mineralized, here, although the complex is extremely fractured and faulted, mineralized macroscopic veins, fractures, and faults are absent. Instead, mineralized microstructures are widespread, indicating a diffuse mode of dewatering.

Geochemical analyses of chert nodules and beds from deep-sea sediments (Table 1)

Concentrations of Fe, Mg, Ca, Sr, Mn, Zn, and other heavy metals were analyzed by atomic absorption spectrometry in 27 chert samples from the Pacific deep sea, 17 chert samples from land, and 4 associated sediments from the Pacific Ocean. Among the elements, Fe and Mg concentrations are highly correlatable as are the relationships between Ca and Sr, or between Ca and CO2. The correlation between Fe and Mg is particularly high for Pacific deep-sea flints and cherts, and for cherts of deep-sea origin from outcrops on land. Enrichments in heavy metals were recognized in some deep-sea cherts; volcanogenic cherts are enriched in Fe, a chert nodule containing basaltic fragments is enriched in Zn and Cr, and biogenically enclosed carbonates in flint nodules are enriched in Mn. The correlation of Fe and Mg and their constant ratio [Mg(%)/Fe(%)] of around 0.33 might be characteristic features in the pelagic clays contained in deep-sea flints and cherts, and the concentrations of heavy metals in them would be controlled by the concentrations of Fe-Mg correlated clays. Although the mineralogical nature of the Fe-Mg clay in deep-sea cherts was not clarified by dissolution experiments on opaline minerals in chert, the high concentrations of Fe-montmorillonite and fine-grained olivine or other ferromagnesian silicate minerals in the clay may result in the high correlations between Fe and Mg.

Lignin, phenols, and some chemical elements in aerosols and bottom sediments from the Tropical North Atlantic

A study of composition of biomarkers (lignin and phenols) in aerosols and bottom sediments from the Tropical North Atlantic was carried out. It was shown that organic matter of aerosols was mostly composed of products of terrestrial plants (arboreal fibers, pollen, and spores). Biomarker composition in the aerosols and in the bottom sediments was practically similar, which proved delivery of terrigenous organic matter to the ocean via the atmosphere.

Composition of swamp waters from the lower Tom' River Basin

New data on chemical and trace component compositions of acidic and low acidic swamp waters and other types of low mineralized waters are reported in the paper. Special attention is paid to dissolved organic compounds: fulvic and humic acids, bitumen, and hydrocarbons. For the first time detailed data on organic trace components (alkanes, pentacyclic terpenoids, steranes, alkylbenzenes, naphthalenes, phenanthrenes, tetraarenes, etc.) in the swamp waters of the Western Siberia: are reported.

Chemical composition and accumulation rates of chemical elements in metalliferous sediments from axial zones of the East Pacific Rise and the Mid-Atlantic Ridge

In the monograph metalliferous sediments of the East Pacific Rise near 21°S are under consideration. Distribution trends of chemical, mineral and grain size compositions of metalliferous sediments accumulated near the axis of this ultrafast spreading segment of the EPR are shown. On the basis of lithological and geochemical investigations spatial and temporal variations of hydrothermal activity are estimated. Migration rates of hydrothermal fields along the spreading axis are calculated. The model of cyclic hydrothermal process is suggested as a result of tectono-magmatic development of the spreding centre.

Stable isotope and trace element geochemistry of carbonate sediments at DSDP Holes 87-577 and 6-47.2

Detailed analyses of well-preserved carbonate samples from across the Cretaceous/Tertiary boundary in Hole 577 have revealed a significant decline in the d13C values of calcareous nannoplankton from the Maestrichtian to the Danian Age accompanied by a substantial reduction in carbonate accumulation rates. Benthic foraminifers, however, do not exhibit a shift in carbon composition similar to that recorded by the calcareous nannoplankton, but actually increase slightly over the same time interval. These results are similar to the earlier findings at two North Pacific Deep Sea Drilling Project locations, Sites 47.2 and 465, and are considered to represent a dramatic decrease in oceanic phytoplankton production associated with the catastrophic Cretaceous/Tertiary boundary extinctions. In addition, the change in carbon composition of calcareous nannoplankton across the Cretaceous/Tertiary boundary at Hole 577 is accompanied by only minor changes in the oxygen isotope trends of both calcareous nannoplankton and benthic foraminifers, suggesting that temperature variations in the North Pacific from the late Maestrichtian to the early Danian Age were insignificant.

Composition of sediment pore water and isotopes in carbonate and benthic foraminifera at DSDP Holes 68-501, 69-505 and Site 69-504

Two sites on the southern flank of the Costa Rica Rift were drilled on DSDP Legs 68 and 69, one on crust 3.9 m.y. old and the other on crust 5.9 m.y. old. The basement of the younger site is effectively cooled by the circulation of seawater. The basement of the older site has been sealed by sediment, and an interval in the uppermost 560 meters of basement recently reheated to temperatures of 60 to 120°C. Although the thickness of the sediments at the two sites is similar (150-240 m versus 270 m), the much rougher basement topography at the younger Site 505 produces occasional basement outcrops, through which 80 to 90% of the total heat loss apparently occurs by advection of warm seawater. This seawater has been heated only slightly, however; the temperature at the base of the sediments is only 9°C. Changes in its composition due to reaction with the basement basalts are negligible, as indicated by profiles of sediment pore water chemistry. Bacterial sulfate reduction in the sediments produces a decrease in SO4 (and Ca) and an increase in alkalinity (and Sr and NH3) as depth increases to an intermediate level, but at deeper levels these trends reverse, and all of these species plus Mg, K, Na, and chlorinity approach seawater values near basement. Si, however, is higher, and Li may be lower. At the older site, Site 501/504, where heat loss is entirely by conduction, the temperature at the sediment/basement contact is 59°C. Sediment pore water chemistry is heavily affected by reaction with the basaltic basement, as indicated by large decreases in d18O, Mg, alkalinity, Na, and K and an increase in Ca with increasing depth. The size of the changes in d18O, Mg, alkalinity, Ca, Sr, and SO4 varies laterally over 500 meters, indicating lateral gradients in pore water chemistry that are nearly as large as the vertical gradients. The lateral gradients are believed to result from similar lateral gradients in the composition of the basement formation water, which propagate upward through the sediments by diffusion. A model of the d18O profile suggests that the basement at Site 501/504 was sealed off from advection about 1 m.y. ago, so that reaction rates began to dominate the basement pore water chemistry. A limestone-chert diagenetic front began to move upward through the lower sediments less than 200,000 yr. ago.

Composition of surface layer bottom sediments from the Kem' River estuary, White Sea

Based on grain-size, mineralogical and chemical analyses of samples collected in cruises of R/V Ekolog (Institute of Northern Water Problems, Karelian Research Centre of RAS, Petrozavodsk) in 2001 and 2003 regularities of chemical element distribution in surface layer bottom sediments of the Kem' River Estuary in the White Sea were studied. For some toxic elements labile and refractory forms were determined. Correlation analysis was carried out and ratios Me/Al were calculated as proxies of terrigenous contribution. Distribution of such elements as Fe, Mn, Zn, Cr, Ti was revealed to be influenced by natural factors, mainly by grain size composition of bottom sediments. These metals have a tendency for accumulation in fine-grained sediments with elevated organic carbon contents. Distribution of Ni is different from one of Fe, Mn, Zn, Cr, Ti. An assumption was made that these distinctions were caused by anthropogenic influence.