Hydrate abundances at the high-flux Batumi seep area in the southeastern Black Sea

Submarine gas hydrates are a major global reservoir of the potent greenhouse gas methane. Since current assessments of worldwide hydrate-bound carbon vary by one order of magnitude, new technical efforts are required for improved and accurate hydrate quantifications. Here we present hydrate abundances determined for surface sediments at the high-flux Batumi seep area in the southeastern Black Sea at 840 m water depth using state-of-the art autoclave technology. Pressure sediment cores of up to 2.65 m in length were recovered with an autoclave piston corer backed by conventional gravity cores. Quantitative core degassing yielded volumetric gas/bulk sediment ratios of up to 20.3 proving hydrate presence. The cores represented late glacial to Holocene hemipelagic sediments with the shallowest hydrates found at 90 cmbsf. Calculated methane concentrations in the different cores surpassed methane equilibrium concentrations in the two lowermost lithological Black Sea units sampled. The results indicated hydrate fractions of 5.2% of pore volume in the sapropelic Unit 2 and mean values of 21% pore volume in the lacustrine Unit 3. We calculate that the studied area of ~ 0.5 km**2 currently contains about 11.3 kt of methane bound in shallow hydrates. Episodic detachment and rafting of such hydrates is suggested by a rugged seafloor topography along with variable thicknesses in lithologies. We propose that sealing by hydrate precipitation in coarse-grained deposits and gas accumulation beneath induces detachment of hydrate/sediment chunks. Floating hydrates will rapidly transport methane into shallower waters and potentially to the sea-atmosphere boundary. In contrast, persistent in situ dissociation of shallow hydrates appears unlikely in the near future as deep water warming by about 1.6 °C and/or decrease in hydrostatic pressure corresponding to a sea level drop of about 130 m would be required. Because hydrate detachment should be primarily controlled by internal factors in this area and in similar hydrated settings, it serves as source of methane in shallow waters and the atmosphere which is mainly decoupled from external forcing.

Stable isotope record, and abundances of ice rafted debris and Neogloboquadrina pachyderma in sediments of the Iberian margin

This paper documents the migration of the Polar Front (PF) over the Iberian margin during some of the cold climatic extremes of the last 45 ka. It is based on a compilation of robust and coherent paleohydrological proxies obtained from eleven cores distributed between 36 and 42°N. Planktonic delta18O (Globigerina bulloides), ice-rafted detritus concentrations, and the relative abundance of the polar foraminifera Neogloboquadrina pachyderma sinistral were used to track the PF position. These three data sets, compared from core to core, show a consistent evolution of the sea surface paleohydrology along the Iberian margin over the last 45 ka. We focused on five time slices representative of cold periods under distinct paleoenvironmental forcings: the 8.2 ka event and the Younger Dryas (two recent cold events occurring within high values of summer insolation), Heinrich events 1 and 4 (reflecting major episodes of massive iceberg discharges into the North Atlantic), and the Last Glacial Maximum (typifying the highest ice volume accumulated in the Northern Hemisphere). For each event, we generated schematic maps mirroring past sea surface hydrological conditions. The maps revealed that the Polar Front presence along the Iberian margin was restricted to Heinrich events. The sea surface conditions during the Last Glacial Maximum were close to those at present day, except for the northern sites which briefly experienced subarctic conditions.

Platinum-group, major, and trace element abundances in ODP Leg 183 basalts

Seventeen basalts from Ocean Drilling Program (ODP) Leg 183 to the Kerguelen Plateau (KP) were analyzed for the platinum-group elements (PGEs: Ir, Ru, Rh, Pt, and Pd), and 15 were analyzed for trace elements. Relative concentrations of the PGEs ranged from ~0.1 (Ir, Ru) to ~5 (Pt) times primitive mantle. These relatively high PGE abundances and fractionated patterns are not accounted for by the presence of sulfide minerals; there are only trace sulfides present in thin-section. Sulfur saturation models applied to the KP basalts suggest that the parental magmas may have never reached sulfide saturation, despite large degrees of partial melting (~30%) and fractional crystallization (~45%). First order approximations of the fractionation required to produce the KP basalts from an ~30% partial melt of a spinel peridotite were determined using the PELE program. The model was adapted to better fit the physical and chemical observations from the KP basalts, and requires an initial crystal fractionation stage of at least 30% olivine plus Cr-spinel (49:1), followed by magma replenishment and fractional crystallization (RFC) that included clinopyroxene, plagioclase, and titanomagnetite (15:9:1). The low Pd values ([Pd/Pt]_pm < 1.7) for these samples are not predicted by currently available Kd values. These Pd values are lowest in samples with relatively higher degrees of alteration as indicated by petrographic observations. Positive anomalies are a function of the behavior of the PGEs; they can be reproduced by Cr-spinel, and titanomagnetite crystallization, followed by titanomagnetite resorption during the final stages of crystallization. Our modeling shows that it is difficult to reproduce the PGE abundances by either depleted upper or even primitive mantle sources. Crustal contamination, while indicated at certain sites by the isotopic compositions of the basalts, appears to have had a minimal affect on the PGEs. The PGE abundances measured in the Kerguelen Plateau basalts are best modeled by melting a primitive mantle source to which was added up to 1% of outer core material, followed by fractional crystallization of the melt produced. This reproduces both the abundances and patterns of the PGEs in the Kerguelen Plateau basalts. An alternative model for outer core PGE abundances requires only 0.3% of outer core material to be mixed into the primitive mantle source. While our results are clearly model dependent, they indicate that an outer core component may be present in the Kerguelen plume source.

Respiration rates and abundances of dominant copepods of the northern Benguela Current System

Respiration rates of 16 calanoid copepod species from the northern Benguela upwelling system were measured on board RRS Discovery in September/October 2010 to determine their energy requirements and assess their significance in the carbon cycle. Individual respiration rates were standardised to a mean copepod body mass and a temperature regime typical of the northern Benguela Current. These adjusted respiration rates revealed two different activity levels (active and resting) in copepodids C5 of Calanoides carinatus and females of Rhincalanus nasutus, which reduced their metabolism during dormancy by 82% and 62%, respectively. An allometric function (Imax) and an energy budget approach were performed to calculate ingestion rates. Imax generally overestimated the ingestion rates derived from the energy budget approach by >75%. We suggest that the energy budget approach is the more reliable approximation with a total calanoid copepod (mainly females) consumption of 78 mg C m-2 d-1 in neritic regions and 21 mg C m-2 d-1 in oceanic regions. The two primarily herbivorous copepods C. carinatus (neritic) and Nannocalanus minor (oceanic) contributed 83% and 5%, respectively, to total consumption by calanoid copepods. Locally, C. carinatus can remove up to 90% of the diatom biomass daily. In contrast, the maximum daily removal of dinoflagellate biomass by N. minor was 9%. These estimates imply that C. carinatus is an important primary consumers in the neritic province of the northern Benguela system, while N. minor has little grazing impact on phytoplankton populations further offshore. Data on energy requirements and total consumption rates of dominant calanoid copepods of this study are essential for the development of realistic carbon budgets and food-web models for the northern Benguela upwelling system.

Concentrations and accumulation rates of platinum-group elements and rhenium in Pacific and Atlantic sediments, DSDP and ODP data

The nature of Re-platinum-group element (PGE; Pt, Pd, Ir, Os, Ru) transport in the marine environment was investigated by means of marine sediments at and across the Cretaceous-Tertiary boundary (KTB) at two hemipelagic sites in Europe and two pelagic sites in the North and South Pacific. A traverse across the KTB in the South Pacific pelagic clay core found elevated levels of Re, Pt, Ir, Os, and Ru, each of which is approximately symmetrically distributed over a distance of ~1.8 m across the KTB. The Re-PGE abundance patterns are fractionated from chondritic relative abundances: Ru, Pt, Pd, and Re contents are slightly subchondritic relative to Ir, and Os is depleted by ~95% relative to chondritic Ir proportions. A similar depletion in Os (~90%) was found in a sample of the pelagic KTB in the North Pacific, but it is enriched in Ru, Pt, Pd, and Re relative to Ir. The two hemipelagic KTB clays have near-chondritic abundance patterns. The ~1.8-m-wide Re-PGE peak in the pelagic South Pacific section cannot be reconciled with the fallout of a single impactor, indicating that postdepositional redistribution has occurred. The elemental profiles appear to fit diffusion profiles, although bioturbation could have also played a role. If diffusion had occurred over ~65 Ma, the effective diffusivities are ~10**?13 cm**2/s, much smaller than that of soluble cations in pore waters (~10**?6 cm**2/s). The coupling of Re and the PGEs during redistribution indicates that postdepositional processes did not significantly fractionate their relative abundances. If redistribution was caused by diffusion, then the effective diffusivities are the same. Fractionation of Os from Ir during the KTB interval must therefore have occurred during aqueous transport in the marine environment. Distinctly subchondritic Os/Ir ratios throughout the Cenozoic in the South Pacific core further suggest that fractionation of Os from Ir in the marine environment is a general process throughout geologic time because most of the inputs of Os and Ir into the ocean have Os/Ir ratios >/=1. Mass balance calculations show that Os and Re burial fluxes in pelagic sediments account for only a small fraction of the riverine Os (<10%) and Re (<0.1%) inputs into the oceans. In contrast, burial of Ir in pelagic sediments is similar to the riverine Ir input, indicating that pelagic sediments are a much larger repository for Ir than for Os and Re. If all of the missing Os and Re is assumed to reside in anoxic sediments in oceanic margins, the calculated burial fluxes in anoxic sediments are similar to observed burial fluxes. However, putting all of the missing Os and Re into estuarine sediments would require high concentrations to balance the riverine input and would also fail to explain the depletion of Os at pelagic KTB sites, where at most ~25% of the K-T impactor's Os could have passed through estuaries. If Os is preferentially sequestered in anoxic marine environments, it follows that the Os/Ir ratio of pelagic sediments should be sensitive to changes in the rates of anoxic sediment deposition. There is thus a clear fractionation of Os and Re from Ir in precipitation out of sea water in pelagic sections. Accordingly, it is inferred here that Re and Os are removed from sea water in anoxic marine depositional regimes.

Elemental and isotopic compositions of metalliferous and pelagic sediments from the Galapagos mounds area, data of DSDP Leg 70

Nontronite, the main metalliferous phase of the Galapagos mounds, occurs at a subsurface depth of ~2-20 m; Mn-oxide material is limited to the upper 2 m of these mounds. The nontronite forms intervals of up to a few metres thickness, consisting essentially of 100% nontronite granules, which alternate with intervals of normal pelagic sediment. The metalliferous phases represent essentially authigenic precipitates, apparently formed in the presence of upwelling basement-derived hydrothermal solutions which dissolved pre-existent pelagic sediment. Electron microprobe analyses of nontronite granules from different core samples indicate that: (1) there is little difference in major-element composition between nontronitic material from varying locations within the mounds; and (2) adjacent granules from a given sample have very similar compositions and are internally homogeneous. This indicates that the granules are composed of a single mineral of essentially constant composition, consistent with relatively uniform conditions of solution Eh and composition during nontronite formation. The Pb-isotopic composition of the nontronite and Mn-oxide sediments indicates that they were formed from solutions which contained variable proportions of basaltic Pb, introduced into pore waters by basement-derived solutions, and of normal-seawater Pb. However, the Sr-isotopic composition of these sediments is essentially indistinguishable from the value for modern seawater. On the basis of 18O/16O ratios, formation temperatures of ~20-30°C have been estimated for the nontronites. By comparison, temperatures of up to 11.5°C at 9 m depth have been directly measured within the mounds and heat flow data suggest present basement-sediment interface temperatures of 15-25°C.

Composition of marine phosphorites and phosphate-bearing sediments

The book deals with behavior of phosphorus and its concentration in oceanic phosphorites. The major stages of marine geochemical cycle of phosphorus including its supply to sedimentary basins, precipitation from sea water, distribution and speciation in bottom sediments, diagenetic redistribution, and relation to other elements are under consideration. Formation of recent phosphorites as a culmination of phosphate accumulation in marine and oceanic sediments is examined. Distribution, structure, mineral and chemical compositions of major phosphorite deposits of various age on continental margins, as well as on submarine plateaus, uplifts and seamounts and some islands are described. A summary of trace element abundances in oceanic phosphorites is presented. Problems of phosphorite origin are discussed.

Geochemistry and mineralogy of coal samples from Dingji Mine, Huainan Coalfield, China

To investigate the geochemistry of trace elements in coals from the Dingji Mine of the Huainan Coalfield, Anhui province, China, 416 borehole samples of coal, one parting, two floor and two roof mudstones were collected from 9 minable coal seams in 24 boreholes drilled during exploration. The abundances of 47 elements in each sample were determined by various instruments. The boron concentration in the coals suggests that marine influence decreased from coal seam 1 to 13-1. The geometric means of the elements Sn, Bi, Sb, and B are higher than the average for the corresponding elements in the coals from China, the U.S., and world. The enrichment of certain elements in the Shanxi or Upper Shihezi Formations is related to their depositional environment. The roof, floor and parting samples have higher contents of some elements than coal seams. The mineral matters in the coals from the Dingji Mine were found to consist mainly of granular quartz, clay minerals, and carbonate minerals. The elements are classified into two groups based on their stratigraphic distribution from coal seam 1 to 13-1, and the characteristics of each group are discussed. Based on the correlation coefficients of elemental concentrations with ash yield, four groups of elements with different affinities were identified.

Relative abundances of stratigraphically useful planktonic foraminifers from ODP Leg 167 sites

Late Neogene biostratigraphy of planktonic foraminifers has been investigated from 13 sites cored during Ocean Drilling Program Leg 167 off the coast of California. The planktonic foraminiferal biostratigraphy of six of these sites is presented here at higher stratigraphic resolution for the interval that encompasses the late early Pliocene through the Quaternary (~3.5 Ma to present day). The sites form a transect along the California margin from 31°N to 41°N within the California Current system. A new planktonic foraminiferal zonation has been established largely on evolutionary changes within the Neogloboquadrina plexus, supported by other taxa. A total of eight zones are recognized, most of which are broadly applicable throughout the region, thus providing a biostratigraphic zonation of the sequence at ~0.5-m.y. intervals. The new zonation appears to be unique to the California Current system. The diversity of planktonic foraminiferal assemblages during the late Neogene appears to have remained relatively constant despite large-scale paleoclimatic change. The assemblages are consistently dominated by few taxa that almost always include the neogloboquadrinids and Globigerina bulloides. Low diversity and high dominance of the assemblages favored these and other taxa well adapted to upwelling systems exhibiting high seasonal surface ocean variability. Apparently the oceanographic conditions that favor such assemblages have persisted at least for the duration of the late Neogene (~3.5 Ma to present day). The biostratigraphically important forms have been illustrated with scanning electron micrographs.

Calcareous nannofossil abundances in Mesozoic sediments of ODP Leg 129 holes

Calcareous nannofossils were studied from Jurassic and Cretaceous sediments drilled in the western Pacific during Ocean Drilling Program Leg 129. Mesozoic sediments at Sites 800, 801, and 802 are dominated by volcaniclastic turbidites, claystones, porcellanites, and radiolarites. Pelagic limestones are limited to the middle Cretaceous, and a few calcareous claystones were recovered in the Upper Jurassic section at Site 801. We documented the distribution of nannofossils, their total abundance, preservation, and relative species abundance based on semiquantitative and qualitative studies. Preservation of the calcareous nannofloras is poor to moderate, and the total abundance fluctuates from rare to very abundant. Marker species proposed for the middle and Late Cretaceous were recognized, allowing the application of standard nannofossil biozonations. At Site 800 calcareous nannofloras are abundant and moderately preserved in the Aptian-Cenomanian, and nannofossil biostratigraphy constitutes the basic stratigraphic framework for this interval. Radiolarians are the most abundant and persistent group throughout the sequence drilled at Site 801. Long intervals are barren of nannofloras and assemblages are usually characterized by low abundance and poor preservation. Nannofossil biostratigraphy was applied to the upper Aptian-Cenomanian interval and a few marker species were recognized for the late Tithonian. At Site 802 Cretaceous biostratigraphy is mainly based on calcareous nannofossil biozones corroborated by radiolarian and palynomorph events in the late Aptian-Coniacian age interval. A hiatus was indicated between the Santonian and the late Campanian, and another is suspected in the interval between the Cenomanian and the Coniacian.