Fatty acids and intact polar lipids of laminated microbial sediments from St. Peter Ording, German Wadden Sea

Hidden for the untrained eye through a thin layer of sand, laminated microbial sediments occur in supratidal beaches along the North Sea coast. The inhabiting microbial communities organize themselves in response to vertical gradients of light, oxygen or sulfur compounds. We performed a fine-scale investigation on the vertical zonation of the microbial communities using a lipid biomarker approach, and assessed the biogeochemical processes using a combination of microsensor measurements and a 13C-labeling experiment. Lipid biomarker fingerprinting showed the overarching importance of cyanobacteria and diatoms in these systems, and heterocyst glycolipids revealed the presence of diazotrophic cyanobacteria even in 9 to 20 mm depth. High abundance of ornithine lipids (OL) throughout the system may derive from sulfate reducing bacteria, while a characteristic OL profile between 5 and 8 mm may indicate presence of purple non-sulfur bacteria. The fate of 13C-labeled bicarbonate was followed by experimentally investigating the uptake into microbial lipids, revealing an overarching importance of cyanobacteria for carbon fixation. However, in deeper layers, uptake into purple sulfur bacteria was evident, and a close microbial coupling could be shown by uptake of label into lipids of sulfate reducing bacteria in the deepest layer. Microsensor measurements in sediment cores collected at a later time point revealed the same general pattern as the biomarker analysis and the labeling experiments. Oxygen and pH-microsensor profiles showed active photosynthesis in the top layer. The sulfide that diffuses from deeper down and decreases just below the layer of active oxygenic photosynthesis indicates the presence of sulfur bacteria, like anoxygenic phototrophs that use sulfide instead of water for photosynthesis.

Granulometry, mineralogy and geochemistry of sediments from ODP Hole 169-1037B and Site 169-1038

Central Hill is in the northern part of the Escanaba Trough, which is a sediment-filled rift of southern Gorda Ridge. Central Hill is oriented north-south and is associated with extensive sulfide deposits. Hydrothermal alteration of sediment from Site 1038 was studied through analyses of mineralogy and the chemistry and oxygen isotopic compositions of one nearly pure clay sample. In addition, Site 1037 was drilled to establish the character of the unaltered sedimentary sequence away from the hydrothermal centers of the Northern Escanaba Trough Study Area (NESCA). Mineralogy of the clay-size fraction of turbiditic and hemipelagic sediments of Hole 1037B are predominantly quartz, feldspar, pyroxene, illite, chlorite, and smectite, representing continental-derived material. Cores from Hole 1038I, located within the area of Central Hill but away from known active vent areas, recovered minor amounts of chlorite/smectite mixed-layer clay in the fine fraction, indicating a low-temperature hydrothermal alteration. The 137.4-m-thick sediment section of Hole 1038G is located in an area of low-temperature venting. The uppermost sample is classified as chlorite/smectite mixed layer, which is underlain by chlorite as the dominant mineral. The lowermost deposits of Hole 1038G are also characterized by chlorite/smectite mixed-layer clay. In comparison to Hole 1038I, the mineralogic sequence of Hole 1038G reflects increased chloritization. Intensely altered sediment is almost completely replaced by hydrothermal chlorite in subsurface sediments of Hole 1038H. Alteration to chlorite is characterized by depletion in Na, K, Ti, Ca, Sr, Cs, and Tl and enrichment in Ba. Further, Eu depletion reflects a high-temperature plagioclase alteration. A chlorite 18O value of 2.6 indicates formation at a temperature of ~190°C. It is concluded that the authigenic chlorite in Hole 1038H formed by an active high-temperature fluid flow in the shallow subsurface.

Faecal pellet production of copepoda collected in water depth up to 30 meters in the eastern Mediterranean Sea in Oktober 2008 during SES_GR2

Mesozooplankton is collected by vertical tows within the Black sea water body mass layer in the NE Aegean, using a WP-2 200 µm net equipped with a large non-filtering cod-end (10 l). Macrozooplankton organisms are removed using a 2000 µm net. A few unsorted animals (approximately 100) are placed inside several glass beaker of 250 ml filled with GF/F or 0.2 µm Nucleopore filtered seawater and with a 100 µm net placed 1 cm above the beaker bottom. Beakers are then placed in an incubator at natural light and maintaining the in situ temperature. After 1 hour pellets are separated from animals and placed in separated flasks and preserved with formalin. Pellets are counted and measured using an inverted microscope. Animals are scanned and counted using an image analysis system. Carbon- Specific faecal pellet production is calculated from a) faecal pellet production, b) individual carbon: Animals are scanned and their body area is measured using an image analysis system. Body volume is then calculated as an ellipsoid using the major and minor axis of an ellipse of same area as the body. Individual carbon is calculated from a carbon- total body volume of organisms (relationship obtained for the Mediterranean Sea by Alcaraz et al. (2003) divided by the total number of individuals scanned and c) faecal pellet carbon: Faecal pellet length and width is measured using an inverted microscope. Faecal pellet volume is calculated from length and width assuming cylindrical shape. Conversion of faecal pellet volume to carbon is done using values obtained in the Mediterranean from: a) faecal pellet density 1,29 g cm**3 (or pg µm**3) from Komar et al. (1981); b) faecal pellet DW/WW=0,23 from Elder and Fowler (1977) and c) faecal pellet C%DW=25,5 Marty et al. (1994).

Chemistry of particles from the Toba ash layer

Two cores from the southern South China Sea contain discrete ash layers that mainly consist of rhyolithic glass shards. On the basis of the SPECMAP time scale, the ash layers were dated to ca. 74 ka, the age of the youngest Toba eruption in northern Sumatra. This link is supported by the chemical composition of the glass, which is distinct from volcanic glass supplied from the Philippines and the northern South China Sea, but is almost identical with the chemistry of the Toba ash. The youngest Toba ash layers in the South China Sea expand the previously known ash-fall zone over more than 1800 km to the east. The dispersal of ashes from Sumatra in both western and eastern directions indicates two contrasting wind directions and suggests that (1) the Toba eruption probably happened during the Southeast Asian summer monsoon season, and (2) the volume of erupted magma was larger than previously interpreted.

Major and minor elements in hydrothermal and pelagic sediments at DSDP Leg 70 Holes

Interaction between young basaltic crust and seawater near the oceanic speading centers is one of the important processes affecting the chemical composition of the oceanic layer. The formation of metalliferous hydrothermal sediments results from this interaction. The importance of the interaction between seawater and basalt in determining the chemical composition of pore waters from sediments is well known. The influence of mineral solutions derived from this interaction on ocean water composition and the significant flux of some elements (e.g., Mn) are reported by Lyle (1976), Bogdanov et al. (1979), and others. Metal-rich sediments found in active zones of the ocean basins illustrate the influence of seawater-basalt interaction and its effect on the sedimentary cover in such areas. The role of hydrothermal activity and seawater circulation in basalts with regard to global geochemistry cycles has recently been demonstrated by Edmond, Measures, McDuff, McDuff et al. (1979), and Edmond, Measures, Mangum (1979). In the area of the Galapagos Spreading Center the interaction of sediments and solutions derived from interaction of seawater and basalt has resulted in the formation of hydrothermal mounds. The mounds are composed of manganese crusts and green clay interbedded and mixed with pelagic nannofossil ooze. These mounds are observed only in areas characterized by high heat flow (Honnorez, et al., 1981) and high hydrothermal activity.

Carbon and oxygen isotope data for carbonates and benthic foraminifers from ODP Hole 113-689B

At Ocean Drilling Program Site 689 (Maud Rise, Southern Ocean), d18O records of fine-fraction bulk carbonate and benthic foraminifers indicate that accelerated climate cooling took place following at least two closely spaced early late Eocene extraterrestrial impact events. A simultaneous surface-water productivity increase, as interpreted from d13C data, is explained by enhanced water-column mixing due to increased latitudinal temperature gradients. These isotope data appear to be in concert with organic-walled dinoflagellate-cyst records across the same microkrystite-bearing impact-ejecta layer in the mid-latitude Massignano section (central Italy). In particular, the strong abundance increase of Thalassiphora pelagica is interpreted to indicate cooling or increased productivity at Massignano. Because impact-induced cooling processes are active on time scales of a few years at most, the estimated 100 k.y. duration of the cooling event appears to be too long to be explained by impact scenarios alone. This implies that a feedback mechanism, such as a global albedo increase due to extended snow and ice cover, may have sustained impact-induced cooling for a longer time after the impacts.

Acid-soluble sulfides in upper layer bottom sediments from the Tsemess and Gelendzhik bays and adjacent shelf area of the Black Sea

Contents of labile (acid-soluble) sulfides were determined in the upper layer of bottom sediments at 80 stations on the Caucasian shelf of the Black Sea. Maximum values of this parameter occurred in black mud accumulated in zones of intense pollution in the Gelendzhik and Tsemess bays and in shelf areas adjacent to large health resort objects and to seaports. Contents of acid-soluble sulfides in sediments varied from 400 to 900 mg S/dm**3 of wet mud. In zones of moderate pollution they varied from 200 to 400 mg S/dm**3. Rate of sulfate reduction was 10-40 mg S/dm**3 of wet sediment per day. Obtained data show that accumulation of labile sulfides in the upper layer of shelf bottom sediments is directly related to anthropogenic pollution and is one of the most hazardous environmental aftereffects.

Thorium and radiocarbon measurements on sediment cores from the Northseast Atlantic

Radiocarbon and 230Thexcess data from six NE Atlantic box cores are considered. The cores form a transect from the Porcupine Abyssal Plain over the East Thulean Rise to the southern end of Feni Drift. The chronology for the cores is established from bulk sediment carbonate radiocarbon data and reveals that sections exhibiting constant accumulation rates can be identified in all the cores, with rates of 3.0-3.5 cm/kyr on the plain through the Holocene and late Holocene rates of 4.3-6.6 cm/kyr elsewhere. Five out of the six cores show accumulations of more 230Thexcess than is produced in the overlying water column, with the greatest inventories (up to 225% of production) in the cores from the rise and drift. A size fraction comparison between two cores from the plain and rise reveals that the higher overall accumulation rates and 230Thexcess inventories in the off-plain cores are due to an increased fine (<5 µm) component fraction, whereas the flux of coarser material is similar to that received on the plain. This suggests that the higher fluxes of materials observed are physically (rather than biogeochemically) driven and also that drift formation has been continuously active in the late Holocene. Sections of all the cores where regular accumulation is defined by the radiocarbon data are modeled first by a linear radiocarbon age/depth model and second by a constant rain (230Thexcess)0 model prorated for the observed core inventories. These modeling approaches yield historical mass accumulation rate estimates which are generally in reasonable agreement (±30%), but the differences observed appear to be well organized in time rather than random.

Inorganic carbon and geochemistry measurements from landfast sea ice in Resolute Passage, Nunavut, Canada, as part of the Arctic-ICE project, May - June 2010

We conducted a six-week investigation of the sea ice inorganic carbon system during the winter-spring transition in the Canadian Arctic Archipelago. Samples for the determination of sea ice geochemistry were collected in conjunction with physical and biological parameters as part of the 2010 Arctic-ICE (Arctic - Ice-Covered Ecosystem in a Rapidly Changing Environment) program, a sea ice-based process study in Resolute Passage, Nunavut. The goal of Arctic-ICE was to determine the physical-biological processes controlling the timing of primary production in Arctic landfast sea ice and to better understand the influence of these processes on the drawdown and release of climatically active gases. The field study was conducted from 1 May to 21 June, 2010.

Oxygen and carbon isotope ratios of silicates and carbonates from exhumed peridotites in the Iberian Abyssal Plain

Legs 173 and 149 of the Ocean Drilling Program profiled a zone of exhumed mantle peridotite at the ocean-continent transition (OCT) beneath the Iberia Abyssal Plain. The zone of exhumed peridotite appears to be tens of kilometers wide and is situated between blocks of continental crust and the first products of ocean accretion. Exhumed peridotite is 95-100% serpentinised to probable depths of 2-3 km. Down core oxygen isotope profiles of serpentinised peridotite at Sites 1068 and 1070 (Leg 173) show evidence for two fluid infiltration events. The earlier event involved pervasive infiltration of comparatively warm (>175°C) sea water and accompanied serpentinisation. The later event involved structurally focused infiltration of comparatively cool (650-150°C) sea water and accompanied active mantle exhumation. We therefore conclude that the uppermost mantle was serpentinised before it was exhumed at the Iberian OCT. Implicit to this conclusion is that a sizeable region of serpentinised mantle existed directly beneath thinned but intact continental crust. Serpentinite has comparatively low density, low frictional strength and low permeability. The presence of such a "soft" layer may have localised deformation and consequently promoted detachment-style exhumation of the uppermost mantle. The low permeability of a serpentinite 'cap' layer might help to explain the lack of observed melt at the Iberian OCT.

Turbiditic trench deposits at the South-Chilean active margin

The active plate margin of South America is characterized by a frequent occurrence of large and devastating subduction earthquakes. Here we focus on marine sedimentary records off Southern Chile that are archiving the regional paleoseismic history over the Holocene and Late Pleistocene. The investigated records - Ocean Drilling Program (ODP) Site 1232 and SONNE core 50SL - are located at ~40°S and ~38°S, within the Perú-Chile trench, and are characterized by frequent interbedded strata of turbiditic and hemipelagic origin. On the basis of the sedimentological characteristics and the association with the active margin of Southern Chile, we assume that the turbidites are mainly seismically triggered, and may be considered as paleo-megaearthquake indicators. However, the long-term changes in turbidite recurrence times appear to be strongly influenced by climate and sea level changes as well. During sea level highstands in the Holocene and Marine Isotope Stage (MIS) 5, recurrence times of turbiditic layers are substantially higher, primarily reflecting a climate-induced reduction of sediment availability and enhanced slope stability. In addition, segmented tectonic uplift changes and related drainage inversions likely influenced the postglacial decrease in turbidite frequencies. Glacial turbidite recurrence times (including MIS 2, MIS 3, cold substages of MIS 5, and MIS 6), on the other hand, are within the same order of magnitude as earthquake recurrence times derived from the historical record and other terrestrial paleoseismic archives of the region. Only during these cold stages sediment availability and slope instability were high enough to enable recording of the complete sequence of large earthquakes in Southern Chile. Our data thus suggest that earthquake recurrence times on the order of 100 to 200 years are a persistent feature at least during the last glacial period.

Meiobenthos investigations in the Black Sea during Poseidon cruise POS317/3

Meiobenthos densities and higher taxon composition were studied in an active gas seepage area at depths from 182 to 252 m in the submarine Dnieper Canyon located in the northwestern part of the Black Sea. The meiobenthos was represented by Ciliata, Foraminifera, Nematoda, Polychaeta, Bivalvia, Gastropoda, Amphipoda, and Acarina. Also present in the sediment samples were juvenile stages of Copepoda and Cladocera which may be of planktonic origin. Nematoda and Foraminifera were the dominant groups. The abundance of the meiobenthos varied between 2397 and 52593 Ind./m**2. Maximum densities of Nematoda and Foraminifera were recorded in the upper sediment layer of a permanent H2S zone at depths from 220 to 250 m. This dense concentration of meiobenthos was found in an area where intense methane seeps were covered by methane-oxidizing microbial mats. Results suggest that methane and its microbial oxidation products are the factors responsible for the presence of a highly sulfidic and biologically productive zone characterized by specially adapted benthic groups. At the same time, an inverse correlation was found between meiofauna densities and methane concentrations in the uppermost sediment layers. The hypothesis is that the concentration of Nematoda and Foraminifera within the areas enriched with methane is an ecological compromise between the food requirements of these organisms and their adaptations to the toxic H2S.

Biomass of seston in the benthic layer of the Southwestern Indian Ocean

At stations to 1530 m depth in the Mozambique Channel and on the Saya-de-Malha and Walters banks seston biomass 2 m above the bottom was lower than at 30 m. Above the Walters shoal this difference was 13.2 mg/m**3 and was not equal to zero for P < 0.001. These results contradict previous ideas of biomass increase in benthic layers. The most likely cause of the observed impoverishment of plankton may be predominant consumption of living zooplankton component of seston by bottom and near-bottom predators. In the area of the Walters shoal this consumption is estimated as being about 300 mg/m**2 per day. Animals inhabiting this area live mainly on plankton brought in by horizontal advection, so that existence of faunal assemblages even on shallow-water submarine elevations is supported not mainly by local photosynthesis, but by primary production of surrounding waters.

Diatoms on the lower surface of Arctic sea ice and hydrochemical parameters in the water-ice layer

Morphology, ecology, range and species composition of diatom algae mass accumulations that are biotypically associated with the lower surface of Arctic sea ice are discussed. Materials were obtained by skindivers in the Central Arctic Basin at drift stations SP-23 in August 1977 and SP-22 in July 1980.