Aerosols in the Arctic

In this monograph on the basis of materials obtained by the author and his colleagues in Arctic expeditions of 1991-2005 and of published data results of studies effect of aerosols on environmental conditions and marine sedimentation in the Arctic are summarizes. Processes of aeolian transport and transformation of sedimentary material from sources to places of its accumulation in bottom sediments are described. Results of this study can be used to assess current state of ecosystem of Arctic seas and as a background for evaluation of possible human impact on nature during exploration of mineral resources of the Arctic shelf. For oceanographers, geochemists, geoecologists.

Concentration and composition of aerosols in the near-water atmosphere layer above the Laptev Sea in July-September 1995

During the ARK-XI/1 expedition of R/V Polarstern in July-September 1995 12 samples of aerosols were collected in lower atmosphere layer over the Laptev Sea by filtration of air through AFA-HA filters. Element composition of the samples was determined by instrumental neutron activation analysis. Average atmospheric concentrations of Cr, Mn, Fe, Co, Zn and As are higher than in other regions of the Arctic. This can be explained by natural reasons: (1) by input of particles from the surface microlayer of sea water enriched by many chemical elements, (2) by atmospheric transfer of organic matter and lithogenic material from the land, and (3) by resuspension of particles from ice-rafted sediments. In some samples anthropogenic pollution was registered.

Mineral and chemical compositions of clay sediments from the Pacific Ocean, DSDP data

Mineral and chemical compositions, as well as conditions of formation of clay sediments in major structural elements of the Pacific Ocean floor with different ages are under consideration in the monograph. Depending on evolution of the region two ways of clay sediment formation are identified: terrigenous and authigenic. It is shown that terrigenous clay sediments predominate in marginal parts of the Pacific Ocean. Authigenic mineral formation occurring in the basal part of the sedimentary cover primarily results from removal of material from underlying basalts. This material is released during secondary alteration of the basalts due to their interaction with sea water, as well as with deep solutions.

(Table T1) Geochemical composition of xenoliths and host rocks from ODP Hole 193-1188A and dredge haul MD-138, PACMANUS field

A number of intensely altered, dark xenoliths with palimpsest quench textures were recorded within altered dacitic host rocks at Site 1189 (Roman Ruins, PACMANUS) during Ocean Drilling Program (ODP) Leg 193. Several of these displayed puzzling marginal fringes, apparently of altered plagioclase with variolitic texture, protruding into adjacent host rocks. Despite their alteration, the xenoliths were interpreted as fragments of rapidly chilled, possibly olivine-bearing basalts incorporated into the dacitic magmas either within the crustal plumbing system or during eruption at the seafloor (figures F15, F16, F17, F42, and F43 in Shipboard Scientific Party, 2002, doi:10.2973/odp.proc.ir.193.104.2002). An additional example of formerly spinifex-textured xenolith, the first from Site 1188 (Snowcap) and the first from the upper cristobalite-bearing zone of alteration, has been revealed by postcruise studies. Furthermore, a pristine sample of the parent lithology has been found within a dredge haul (MD-138, Binatang-2000 Cruise of Franklin; 3°43.60'S, 151°40.35'E, 1688 meters below sea level) from the Satanic Mills hydrothermal field at PACMANUS, near ODP Site 1191. The purpose of this report is to document these discoveries and thereby to confirm and build on shipboard interpretations. To my knowledge, similar xenoliths have never before been found in modern island arc or backarc volcanic sequences. Spinifex textures are most common in Archean komatiites, some of which are bimodally associated with calc-alkaline felsic volcanic rocks.

Composition of bottom sediments, rocks, and ores from the Tropical Atlantic

Geological features of some areas of the Tropical Atlantic (stratigraphy, tectonic structure, lithology, distribution of ore components in bottom sediments, petrography of bedrocks, etc.) are under consideration in the book. Regularities of concentration of trace elements in iron-manganese nodules, features of these nodules in bottom sediments, distribution of phosphorite nodules and other phosphorites have been studied. Much attention is paid to rocks of the ocean crust. A wide range of mineralization represented by magnetite, chromite, chalcopyrite, pyrite, pentlandite, and other minerals has been found.

Trace element contents in zircons from oceanic crust

We present newly acquired trace element compositions for more than 300 zircon grains in 36 gabbros formed at the slow-spreading Mid-Atlantic and Southwest Indian Ridges. Rare earth element patterns for zircon from modern oceanic crust completely overlap with those for zircon crystallized in continental granitoids. However, plots of U versus Yb and U/Yb versus Hf or Y discriminate zircons crystallized in oceanic crust from continental zircon, and provide a relatively robust method for distinguishing zircons from these environments. Approximately 80% of the modern ocean crust zircons are distinct from the field defined by more than 1700 continental zircons from Archean and Phanerozoic samples. These discrimination diagrams provide a new tool for fingerprinting ocean crust zircons derived from reservoirs like that of modern mid-ocean ridge basalt (MORB) in both modern and ancient detrital zircon populations. Hadean detrital zircons previously reported from the Acasta Gneiss, Canada, and the Narryer Gneiss terrane, Western Australia, plot in the continental granitoid field, supporting hypotheses that at least some Hadean detrital zircons crystallized in continental crust forming magmas and not from a reservoir like modern MORB.

Geochemistry, lithology, and bulk density of Cricket Flat paleosol samples

The high-resolution marine isotope climate record indicates pronounced global cooling during the Langhian (16-13.8 Ma), beginning with the warm middle Miocene climatic optimum and ending with significant Antarctic ice sheet expansion and the transition to "icehouse" conditions. Terrestrial paleoclimate data from this interval is sparse and sometimes conflicting. In particular, there are gaps in the terrestrial record in the Pacific Northwest during the late Langhian and early Serravallian between about 14.5 and 12.5 Ma. New terrestrial paleoclimate data from this time and region could reconcile these conflicting records. Paleosols are particularly useful for reconstructing paleoenvironment because the rate and style of pedogenesis is primarily a function of surface environmental conditions; however, complete and well-preserved paleosols are uncommon. Most soils form in erosive environments that are not preserved, or in environments such as floodplains that accumulate in small increments; the resulting cumulic soils are usually thin, weakly developed, and subject to diagenetic overprinting from subsequent soils. The paleosol at Cricket Flat in northeastern Oregon is an unusually complete and well-preserved paleosol from a middle Miocene volcanic sequence in the Powder River Volcanic Field. An olivine basalt flow buried the paleosol at approximately 13.8 ± 0.6 Ma, based on three 40Ar/39Ar dates on the basalt. We described the Cricket Flat paleosol and used its physical and chemical profile and micromorphology to assess pedogenesis. The Cricket Flat paleosol is an Ultisol-like paleosol, chemically consistent with a high degree of weathering. Temperature and rainfall proxies suggest that Cricket Flat received 1120 ± 180 mm precipitation y-1 and experienced a mean annual temperature of 14.5 ± 2.1 °C during the formation of the paleosol, significantly warmer and wetter than today. This suggests slower cooling after the middle Miocene climatic optimum than is seen in the existing paleosol record.