Tab. 3: Concentrations of selected chemical species at various depths in Ace Lake

This article reviews the history, chemical stratification, biology and biogeochemistry of Ace Lake, which is one of the many marine-derived meromictic (permanently stratified) lakes in the Vestfold Hills, Eastern Antarctica. The lake has an area of 18 ha, a maximum depth of 25 m, and a salinity range from 7 to 43 g l**-1. The lake mixes to a depth of 7 m in late winter as a result of brine freeze out during ice formation. Deeper mixing is precluded by a sharp halocline. The water beneath 12 m is permanently anoxic, The lake was formed approximately 10,800 yr BP as the polar ice cap melted. Sea level rise 7,800 yr BP resulted in invasion of seawater into the initially freshwater lake. Subsequently, sea level dropped, and the now saline lake became isolated from the ocean. The biota of the lake was derived from species trapped when the connection between the lake and the ocean was cut off. The oxic zone above 12 m supports a relatively simple community which includes microbial mats, four major species of phytoplankton (including a picocyanobacterium), two copepod species, and a variety of heterotrophic flagellates and ciliates. The anoxic zone contains populations of photosynthetic sulfur, sulfate reducing, fermentative and methanogenic bacteria, which combine to remineralise organic carbon which sediments from the upper waters. Research on the physics, biology and chemistry of Ace Lake has contributed significantly to knowledge of Antarctic meromictic lakes.

Geology, geochemistry, and mineralogy of sediments from the Trans Indian Ocean Geotraverse

The monograph is devoted to the main results of research on the Trans Indian Ocean Geotraverse from the Maskarene Basin to the north-western margin of Australia. These results were obtained by Russian specialists and together with Indian specialists during 15 years of cooperation in investigation of geological structure and mineral resources of the Indian Ocean. The monograph includes materials on information support of marine geological and geophysical studies, composition and structure of information resources on the Indian Ocean, bathymetry and geomorphology, structure and geological nature of the magnetic field, gravity field, plate tectonics, crustal structure and sedimentary cover, seismic stratigraphy, perspectives for detecting oil and gas, solid minerals, sediment composition, composition and properties of clay minerals, stratigraphy and sediment age, chemical composition of sediments, composition of and prospects for solid minerals.

Chemical composition of bottom sediments and rocks from DSDP Holes 3-14 through 64-477

Data on analyses of chemical composition of DSDP samples of bottom sediments and rocks carried out in P.P. Shirshov Institute of Oceanology are reported. Basal sediments and sedimentary rocks prevail in the sample set.

Microfossils and chemical elements in bottom sediments of the Ashadze-1 Hydrothermal Field (tropical Mid-Atlantic Ridge)

The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 Hydrothermal Field in the Mid-Atlantic Ridge sampled during Cruise 26 of R/V Professor Logachev in 2005 revealed substantial influence of hydrothermal processes on preservation of planktonic calcareous organisms as well as on preservation and composition of benthic foraminifera. From lateral and vertical distribution patterns and secondary alterations of microfossils it is inferred that the main phase of hydrothermal mineralization occurred in Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts. Distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to hydrothermal activity. There are three mineral-geochemical zones defined: sulfide zone, zone with elevated Mg content, and zone of Fe-Mn crusts.

Geochemistry of ODP Hole 121-752A

The present study involves the analysis and interpretation of geochemical data from a suite of sediment samples recovered at ODP Hole 752A. The samples encompass the time period that includes the lithospheric extension and uplift of Broken Ridge, and they record deposition below and above the mid-Eocene angular unconformity that denotes this uplift. A Q-mode factor analysis of the geochemical data indicates that the sediments in this section are composed of a mixture of three geochemical end members that collectively account for 94.2% of the total variance in the data. An examination of interelement ratios for each of these end members suggests that they represent the following sedimentary components: (1) a biogenic component, (2) a volcanogenic component, and (3) a hydrothermal component. The flux of the biogenic component decreases almost thirtyfold across the Eocene unconformity. This drastic reduction in the deposition of biogenic materials corresponds to the almost complete disappearance of chert layers, diatoms, and siliceous microfossils and is coincident with the uplift of Broken Ridge. The volcanogenic component is similar in composition to Santonian ash recovered at Hole 755A on Broken Ridge and is the apparent source of the Fe-stained sediment that immediately overlies the angular unconformity. This finding suggests that significant amounts of Santonian ash were subaerially exposed, weathered, and redeposited and is consistent with data that suggest that the vertical uplift of Broken Ridge was both rapid and extensive. The greatest flux of hydrothermal materials is recorded in the sediments immediately below the angular unconformity. This implies that the uplift of Broken Ridge was preceded by a significant amount of rifting, during which faulting and fracturing of the lithosphere led to enhanced hydrothermal circulation. This time sequence of events is consistent with (but not necessarily diagnostic of) the passive model of lithospheric extension and uplift.

Element and isotope compostion of basalts and sediments from the Japan Sea

Ocean Drilling Program Legs 127 and 128 in the Yamato Basin of the Japan Sea, a Miocene-age back-arc basin in the western Pacific Ocean, recovered incompatible-element-depleted and enriched tholeiitic dolerites and basalts from the basin floor, which provide evidence of a significant sedimentary component in their mantle source. Isotopically, the volcanic rocks cover a wide range of compositions (e.g., 87Sr/86Sr = 0.70369 - 0.70503, 206Pb/204Pb = 17.65 - 18.36) and define a mixing trend between a depleted mantle (DM) component and an enriched component with the composition of EM II. At Site 797, the combined isotope and trace element systematics support a model of two component mixing between depleted, MORB-like mantle and Pacific pelagic sediments. A best estimate of the composition of the sedimentary component has been determined by analyzing samples of differing lithology from DSDP Sites 579 and 581 in the western Pacific, east of the Japan arc. The sediments have large depletions in the high field strength elements and are relatively enriched in the large-ion-lithophile elements, including Pb. These characteristics are mirrored, with reduced amplitudes, in Japan Sea enriched tholeiites and northeast Japan arc lavas, which strengthens the link between source enrichment and subducted sediments. However, Site 579/581 sediments have higher LILE/REE and lower HFSE/REE than the enriched component inferred fiom mixing trends at Site 797. Sub-arc devolatilization of the sediments is a process that will lower LILE/REE and raise HFSE/REE in the residual sediment, and thus this residual sediment may serve as the enriched component in the back-arc basalt source. Samples from other potential sources of an enriched, EM II-like component beneath Japan, such as the subcontinental lithosphere or crust, have isotopic compositions which overlap those of the Japan Sea tholeiites and are not "enriched" enough to be the EM II end-member.

Geochemistry of Peru margin sediments

This data report tabulates results of chemical analyses of sediments from four sites (680, 682, 685, and 688) drilled during Leg 112 offshore Peru. These sediments were recovered from the forearc basins underlying the Peru upwelling area. They are equivalent in facies and age to the Pisco and Monterey formations, both of which are of considerable economic and geological interest as hydrocarbon source rocks deposited under conditions of coastal upwelling. Sediments recovered from the shelf (Site 680) and slope (Sites 682, 685, and 688) during Leg 112 are unconsolidated and are thermally immature. A lack of consolidation and thermal catagenesis makes these deposits ideal targets for chemical investigation into effects of early diagenesis in organic-carbon-rich siliceous muds.