Carbonate mineralogical and isotopic analyses of TV-guided grab samples and TV-guided box corer samples from the Shumagin area

Methane seepage leads to Mg-calcite and aragonite precipitation at a depth of 4,850 m on the Aleutian accretionary margin. Stromatolitic and oncoid growth structures imply encrustation of microorganisms (microbial mats) in the host sediment with a unique growth direction downward into the sediment, forming crust-shaped lithologies. Biomarker investigations of the residue after carbonate dissolution show strong enrichments in crocetane and archaeol, which contain extremely low d13C values. This indicates the presence of methane-consuming archaea, and d13C values of -42 to -51 per mill PDB indicate that methane is the carbon source for the carbonate crusts. Thus, it appears that stromatolitic encrustations of methanotrophic anaerobic archaea probably occurs in a consortium with sulphate-reducing bacteria and that carbonate precipitation proceeds downward into the sediment, where ascending cold fluids provide a methane source. Strontium and oxygen isotope analyses as well as 14C ages of the carbonates suggest that the fluids come from deep within the sediment and that carbonate precipitation began about 3,000 years ago.

Hydrocarbons in particulate matter and bottom sediments from the north Caspian Sea shelf

Data are presented on content and composition of hydrocarbons (HC) (aliphatic AHC and polyaromatic PAH) in filtered particulate matter and in the surface layer of bottom sediments from the northern shelf of the Caspian Sea and related to data on their contents in the Volga River estuary. Because of transformation and precipitation of anthropogenic and natural compounds, HC composition in particulate matter and bottom sediments undergoes transformations caused by mixing of fresh and saline waters (in bottom sediments, within concentration ranges 70.4-4557.9 µg/g for AHC and 3.8-4800 ng/g for PAH). It was found that the greatest concentrating of HC proceeds in the region of the avalanche sedimentation, and their contents are independent of grain-size types of bottom sediments. Anthropogenic HC (oil and pyrogenous) do not get over the marginal filter of the Volga River and do not pass to the open part of the sea.

Chemical composition of Black Sea bottom sediments

Concentrations of major-, trace- and rare earth elements in recent and Old Black Sea bottom sediments are reported in the paper. Data presented suggest that accumulation of black shale deposits was not constrained to a certain time span but proceeds in certain modern basins and generates sediments with metal contents close to those in their ancients analogues in hydrogen sulfide contaminated environments. If REE are involved in the process, their composition can vary depending on such factors as variations in redox conditions and occurrence of phosphate and barite nodules, which can induce development of either positive or negative Eu anomalies.

Composition and crystal parameters of carbonate-apatites from animal teeth and bones and from phosphate rocks of the ocean bottom

Samples of recent to Miocene fish and marine mammal bones from the bottom of the Atlantic and Pacific Oceans and Miocene Maikop deposits (Transcaspian region) are studied by X-ray diffraction technique combined with chemical and energy-dispersive analyses. Changes of lattice parameters and chemical composition of bioapatite during fossilization and diagenesis suggest that development of skeletal apatite proceeds from dahllite-type hydroxyapatite to francolite-type carbonate-fluorapatite. It is assumed that jump-type transition from dahllite to francolite during initial fossilization reflects replacement of biogeochemical reactions in living organisms, which are subject to nonlinear laws of nonequilibrium thermodynamics, by physicochemical processes according to the linear equilibrium thermodynamics.

Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy. Wave-resistant algal rims, predominantly made up of the crustose coralline algae (CCA) Porolithon onkodes and P. pachydermum, are therefore critical structural elements for the survival of many shallow coral reefs. Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons. However, the recent discovery of dolomite (Mg0.5Ca0.5(CO3)), a stable carbonate, in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA. Here we show, using a dissolution experiment, that dried dolomite-rich CCA have 6-10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 (~ 700 ppm) and control (~ 380 ppm) environments, respectively. We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals. Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact. Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises.

Rates of sulfide formation and oxidation in the Black Sea waters in February-April 1991

Rate of hydrogen sulfide oxidation in the redox zone of the Black Sea and rate of hydrogen sulfide formation due to bacterial sulfate reduction in the upper layer of anaerobic waters were measured in February-April 1991. These measurements were made using sulfur radioisotope under conditions close to those in situ. It was established that hydrogen sulfide is oxidized in the layer of oxygen and hydrogen sulfide coexistence under the upper boundary of the hydrogen sulfide layer. Maximum rate of hydrogen sulfide oxidation was recorded within the limits of density values dT of 16.20-16.30, while varying in the layer from 2 to 4.5 µmol/day. The average rate of hydrogen sulfide oxidation was 1.5-3 times higher than that during the warm season. Sulfide formation was not observed at most of the stations in the examined lower portion of the pycnocline layer (140 to 400 m). Noticeable sulfate reduction was detected only at one station on the northwestern shelf. Intensified hydrodynamics in the upper layers of the water mass during the cold season can be a probable reason for such noticeable changes in sulfur dynamics in the water mass of the Black Sea. Data suggesting that hydrogen sulfide oxidation proceeds under the hydrogen sulfide boundary indicate absence of the so-called "suboxic zone" in this basin.

Limpets counteract ocean acidification induced shell corrosion by thickening of aragonitic shell layers

Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size-normalised aragonite area. Size-normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size-normalised thickness of the pHlow-shells, these data led us to conclude that low-pH-exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. This is different from normal elongation growth and proceeds through addition of aragonitic parts only, while the production of calcitic parts is confined to elongation growth. Therefore, aragonite cannot be regarded as a disadvantageous polymorph per se under ocean acidification conditions.

Reflection microscopy and geochemistry at DSDP Leg 55 Holes

Magnetic properties of volcanic rocks are controlled mainly by the physical and chemical state of their constituent ferromagnetic minerals. The most important parameters determining magnetic properties are concentration, composition, grain size, and oxidation state. In sea floor basalts, the main ferromagnetic minerals are titanomagnetites which are either unoxidized or, more commonly, have undergone various degrees of posteruptive low-temperature oxidation to become cationdeficient titanomagnetites, or titanomaghemites. The effects of this low-temperature alteration are seen in the increase of Curie temperature and decrease of saturation magnetization and lattice parameter of ferromagnetic minerals (Readman and O'Reilly, 1972). It is now believed that titanomaghemitization of newly formed mid-ocean ridge crust proceeds with a time constant of about 1 m.y., accompanying drastic decrease of the intensity of the natural remanent magnetization (NRM) (Johnson and Atwater, 1977).

Seed dispersal characteristics to polar regions by means of visitors

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Year's first season (2007-2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarctica's climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios Scenario A1B [Nakicenovic N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (~33,054) are higher than those of scientists (~7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides the means to mitigate this threat now and into the future as the continent's climate changes.

Modes of occurrence and geochemistry at DSDP Holes 69-505A and 69-505B

The compositions of chrome spinels of Costa Rica Rift basalts from Deep Sea Drilling Project Site 505 vary depending on their occurrences as (1) inclusions in olivine crystals, (2) inclusions in Plagioclase crystals, and (3) isolated crystals in variolitic or glassy samples. The variations are a consequence of (1) changes of melt compositions as crystallization proceeds, and (2) contrasting behavior of olivine and Plagioclase in competition with spinels for Al and Mg. Some spinels have skeletal rims compositionally less magnesian than mineral cores; however, the cores do not appear to be xenocrysts, unlike some texturally similar spinels in Mid-Atlantic Ridge basalts.

(Table 1) Chemical and isotopic composition of pore fluids in cores TGC-1 and TGC-6

The role of sediment diagenesis in the marine cycles of Li and B is poorly understood. Because Li and B are easily mobilized during burial and are consumed in authigenic clay mineral formation, their abundance in marine pore waters varies considerably. Exchange with the overlying ocean through diffusive fluxes should thus be common. Nevertheless, only a minor Li sink associated with the low-temperature alteration of volcanic ash has been observed. We describe a low-temperature diagenetic environment in the Black Sea dominated by the alteration of detrital plagioclase feldspars. Fluids expelled from the Odessa mud volcano in the Sorokin Trough originate from shallow (~100-400 m deep) sediments which are poor in volcanic materials but rich in anorthite. These fluids are depleted in Na+, K+, Li+, B, and 18O and enriched in Ca2+ and Sr2+, indicating that anorthite is dissolving and authigenic clays are forming. Using a simple chemical model, we calculate the pH and the partial pressure of CO2 (PCO2) in fluids associated with this alteration process. Our results show that the pH of these fluids is up to 1.5 pH units lower than in most deep marine sediments and that PCO2 levels are up to several hundred times higher than in the atmosphere. These conditions are similar to those which favor the weathering of silicate minerals in subaerial soil environments. We propose that in Black Sea sediments enhanced organic matter preservation favors CO2 production through methanogenesis and results in a low pore water pH, compared to most deep sea sediments. As a result, silicate mineral weathering, which is a sluggish process in most marine diagenetic environments, proceeds rapidly in Black Sea sediments. There is a potential for organic matter-rich continental shelf environments to host this type of diagenesis. Should such environments be widespread, this new Li and B sink could help balance the marine Li and Li isotope budgets but would imply an apparent imbalance in the B cycle.

Seawater carbonate chemistry and community metabolism during an experiment with a coral reef, 2003

The effect of elevated pCO2 on the metabolism of a coral reef community dominated by macroalgae has been investigated utilizing the large 2650 m3 coral reef mesocosm at the Biosphere-2 facility near Tucson, Arizona. The carbonate chemistry of the water was manipulated to simulate present-day and a doubled CO2 future condition. Each experiment consisted of a 1-2 month preconditioning period followed by a 7-9 day observational period. The pCO2 was 404 ± 63 ?atm during the present-day pCO2 experiment and 658 ± 59 ?atm during the elevated pCO2 experiment. Nutrient levels were low and typical of natural reefs waters (NO3? 0.5-0.9 ?M, NH4+ 0.4 ?M, PO43? 0.07-0.09 ?M). The temperature and salinity of the water were held constant at 26.5 ± 0.2°C and 34.4 ± 0.2 ppt. Photosynthetically available irradiance was 10 ± 2 during the present-day experiment and 7.4 ± 0.5 mol photons m?2 d?1 during the elevated pCO2 experiment. The primary producer biomass in the mesocosm was dominated by four species of macroalgae; Haptilon cubense, Amphiroa fragillisima, Gelidiopsis intricata and Chondria dasyphylla. Algal biomass was 10.4 mol C m?2 during the present-day and 8.7 mol C m?2 and during the elevated pCO2 experiments. As previously observed, the increase in pCO2 resulted in a decrease in calcification from 0.041 ± 0.007 to 0.006 ± 0.003 mol CaCO3 m?2 d?1. Net community production (NCP) and dark respiration did not change in response to elevated pCO2. Light respiration measured by a new radiocarbon isotope dilution method exceeded dark respiration by a factor of 1.2 ± 0.3 to 2.1 ± 0.4 on a daily basis and by 2.2 ± 0.6 to 3.9 ± 0.8 on an hourly basis. The 1.8-fold increase with increasing pCO2 indicates that the enhanced respiration in the light was not due to photorespiration. Gross production (GPP) computed as the sum of NCP plus daily respiration (light + dark) increased significantly (0.24 ± 0.03 vs. 0.32 ± 0.04 mol C m?2 d?1). However, the conventional calculation of GPP based on the assumption that respiration in the light proceeds at the same rate as the dark underestimated the true rate of GPP by 41-100% and completely missed the increased rate of carbon cycling due to elevated pCO2. We conclude that under natural, undisturbed, nutrient-limited conditions elevated CO2 depresses calcification, stimulates the rate of turnover of organic carbon, particularly in the light, but has no effect on net organic production. The hypothesis that an increase pCO2 would produce an increase in net production that would counterbalance the effect of decreasing saturation state on calcification is not supported by these data.