(Table 1) List of studied samples with vestimentiferan tubes

Vestimentiferan tube worms are prominent members of modern methane seep communities and are totally reliant as adults on symbiotic sulphide-oxidizing bacteria for their nutrition. The sulphide is produced in the sediment by a biochemical reaction called the anaerobic oxidation of methane (AOM). A well-studied species from the Gulf of Mexico shows that seep vestimentiferans 'mine' sulphide from the sediment using root-like, thin walled, permeable posterior tube extensions, which can also be used to pump sulphate and possibly hydrogen ions from the soft tissue back into the sediment to increase the local rate of AOM. The 'root-balls' of exhumed seep vestimentiferans are intimately associated with carbonate nodules, which are a result of AOM. We have studied vestimentiferan specimens and associated carbonates from seeps at the Kouilou pockmark field on the Congo deep-sea fan and find that some of the posterior 'root' tubes of living specimens are enclosed with carbonate indurated sediment and other, empty examples are partially or completely replaced by the carbonate mineral aragonite. This replacement occurs from the outside of the tube wall inwards and leaves fine-scale relict textures of the original organic tube wall. The process of mineralization is unknown, but is likely a result of post-mortem microbial decay of the tube wall proteins by microorganisms or the precipitation from locally high flux of AOM derived carbonate ions. The aragonite-replaced tubes from the Kouilou pockmarks show similar features to carbonate tubes in ancient seep deposits and make it more likely that many of these fossil tubes are those of vestimentiferans. These observations have implications for the supposed origination of this group, based on molecular divergence estimates.

Lipid biomarkers of shelf sediments from upwelling regions off Namibia, Peru, and Chile

Sediments of upwelling regions off Namibia, Peru, and Chile contain dense populations of large nitrate-storing sulfide-oxidizing bacteria, Thiomargarita, Beggiatoa, and Thioploca. Increased contents of monounsaturated C16 and C18 fatty acids have been found at all stations studied, especially when a high density of sulfide oxidizers in the sediments was observed. The distribution of lipid biomarkers attributed to sulfate reducers (10MeC16:0 fatty acid, ai-C15:0 fatty acid, and mono-O-alkyl glycerol ethers) compared to the distribution of sulfide oxidizers indicate a close association between these bacteria. As a consequence, the distributions of sulfate reducers in sediments of Namibia, Peru, and Chile are closely related to differences in the motility of the various sulfide oxidizers at the three study sites. Depth profiles of mono-O-alkyl glycerol ethers have been found to correlate best with the occurrence of large sulfide-oxidizing bacteria. This suggests a particularly close link between mono-O-alkyl glycerol ether-synthesizing sulfate reducers and sulfide oxidizers. The interaction between sulfide-oxidizing bacteria and sulfate-reducing bacteria reveals intense sulfur cycling and degradation of organic matter in different sediment depths.

Tab. 1: Mineralogical composition and chemical analyses of major and trace elements of Ameghino Formation rocks

As a result of a petrographical, mineralogical and geochemical characterization of the Ameghino Formation mudstones (Upper Jurassic- Lower Cretaceous, Antarctic Peninsula), "epiclastic" radiolaria-rich and mixed (radiolaria-rich + tuff) mudstone types were recognized. Contents of clastic material in the mudstones generally increase with younger paleontological age, but local exceptions to this trend have been found. The anoxic environment of the lower part of the sequence changes to more oxidizing conditions towards the top, in transition to the Hauterivian - Barrêmian conglomerates. Element to element correlations show good agreement with the normal differentiation trends of volcanic (andesite-rhyolite) rocks, suggesting that the overall sequence is mainly volcanic in origin with various grade of reworking. For example, the radiolaria-rich mudstone matrix could have been originated from very fine touffaceous suspensions deposited very slowly after the main fall of the tuffs. However, in the upper part of the sequence, some epiclastic supply is revealed by petrographic evidence and illite crystallinity index. The clay mineral association (illite, chlorite and illite-smectite mixed layers) is mainly of diagenetic origin in the stratigraphically lower sections. Low percentages of expandable layers in the illite-smectite mixed layers, as well as the general mineralogical association, suggest a late mesodiagenetic stage, and together with geological evidence, a relatively deep burial (> 1000 m - probably > 2500 m) and temperatures exceeding 100°C.

Oxygen isotope concentrations of minerals from the upper kilometer of the ocean crust, DSDP Hole 504B

DSDP Hole 504B is the deepest basement hole in the oceanic crust, penetrating through a 571.5 m pillow section, a 209 m lithologic transition zone, and 295 m into a sheeted dike complex. An oxygen isotopic profile through the upper crust at Site 504 is similar to that in many ophiolite complexes, where the extrusive section is enriched in 18O relative to unaltered basalts, and the dike section is variably depleted and enriched. Basalts in the pillow section at Site 504 have delta 18O values generally ranging from +6.1 to +8.5? SMOW (mean= +7.0?), although minor zeolite-rich samples range up to 12.7?. Rocks depleted in 18O appear abruptly at 624 m sub-basement in the lithologic transition from 100% pillows to 100% dikes, coinciding with the appearance of greenschist facies minerals in the rocks. Whole-rock values range to as low as +3.6?, but the mean values for the lithologic transition zone and dike section are +5.8 and +5.4?, respectively. Oxygen and carbon isotopic data for secondary vein minerals combined with the whole rock data provide evidence for the former presence of two distinct circulation systems separated by a relatively sharp boundary at the top of the lithologic transition zone. The pillow section reacted with seawater at low temperatures (near 0°C up to a maximum of around 150°C) and relatively high water/rock mass ratios (10-100); water/rock ratios were greater and conditions were more oxidizing during submarine weathering of the uppermost 320 m than deeper in the pillow section. The transition zone and dikes were altered at much higher temperatures (up to about 350°C) and generally low water/rock mass ratios (~1), and hydrothermal fluids probably contained mantle-derived CO2. Mixing of axial hydrothermal fluids upwelling through the dike section with cooler seawater circulating in the overlying pillow section resulted in a steep temperature gradient (~2.5°C/m) across a 70 m interval at the top of the lithologic transition zone. Progressive reaction during axial hydrothermal metamorphism and later off-axis alteration led to the formation of albite- and Ca-zeolite-rich alteration halos around fractures. This enhanced the effects of cooling and 18O enrichment of fluids, resulting in local increases in delta 18O of rocks which had been previously depleted in 18O during prior axial metamorphism.

Geochemistry of pore fluids from ODP Leg 134 sites

Depending on the temperature and the extent of diagenetic alteration of fluid chemistry, fluid flow at convergent margins may transfer important quantities of heat and mass between the crust and seawater, thereby influencing global mass, isotopic and heat budgets. In the North Aoba Basin, an intra-arc basin located at the New Hebrides Island Arc, alteration of volcanic ash to clay minerals and zeolites forms a CaCl2 brine, perhaps in less than 1 to 3 m.y. The brine results from an exchange of Ca for Na, K, and Mg, and an increase in Cl concentrations to a maximum of 1241 mM. The Cl increase is partly due to the transfer of H2O from the pore fluid into authigenic minerals, but water mass balances, d18O-Cl correlations, and Br/Cl ratios suggest that there is a source of Cl in the sediments. Concentration profiles indicate that Li is transferred from the fluid to solid phase at depths <300 meters below seafloor (mbsf), but at greater depths it is transferred from the solid to fluid phase, at temperatures possibly as low as 25°C. In the accretionary wedge extensive fluid flow appears to be confined to highly faulted regions. Although Cl concentrations less than seawater value are common at convergent margins, the New Hebrides margin contains little low-Cl fluid. Br/Cl ratios suggest the low-Cl fluid is from dilution, and d18O values indicate the water may be derived from mineral dehydration and mixing with meteoric water. The New Hebrides margin exhibits few surface manifestations of venting (e.g., sulfide-oxidizing benthic biological communities, carbonate crusts, mud volcanoes) and thus fluid fluxes may be smaller than at many other margins.

Gridded bathymetry from multibeam echosounder ELAC BottomChart MkII data of the cruise POS317/3 (2004)

Bathymetry based on data recorded during POS317-3 between 19.09.2004 and 13.10.2004 in the Black Sea. This cruise concentrated on bathymetric mapping and mapping of gas seeps by hydro-acoustic detection of gas flares in the water column and the quantification of microbial turnover of gassy sediments and microbial mats. The major objective during POS317-3 was the characterization and identification of microorganisms involved in the anaerobic methane oxidation in the sediment and in microbial mats. As part of these investigations characteristic organic molecules will be identified, which can be used as biomarkers for anaerobic methane oxidizing microorganisms.

Chemical composition of basalts from DSDP Hole 46-396B

Samples of crystalline basalt from Site 396 B are all more or less altered, usually in strongly zoned patterns. Evidence has been found for several related or independent alteration stages, including (1) minor localized deuteric (amphibole and mixed clay minerals in miarolitic voids); (2) minor widespread nonoxidizing (pyrite on walls of vugs and cracks); (3) localized diffusion-controlled rug filling ("glauconite" in black halos); (4) pervasive low level oxidizing (transformation of titanomagnetite to cation-deficient titanomaghemite); (5) localized diffusion-controlled strongly oxidizing (breakdown of olivine and titanomaghemite in brown zones). Plagioclase and pyroxene are essentially unaltered. Detailed analyses of gray and brown zones in pillow basalts show that low temperature oxidation has proceeded in a step-wise fashion, with the relative stabilities of the igneous minerals controlling the steps. Secondary minerals that crystallized from pore fluids on to the walls of vugs may or may not be related to local alteration of primary phases. During the most intense stage of alteration, brown oxidation zones grew into basalt fragments behind diffusion controlled fronts. The specific reactions and products of this stage differ among the lithologic units at the site. A model is proposed whereby efficient seawater circulation through the pillow units maintains the pH and the concentrations of Mg2+ and SiO2 dissolved at low levels in pore fluids, so that olivine is replaced by hydrous ferric oxides, and Mg and SiO2 are removed from the system. In the massive basalt unit, circulation is somewhat less effective and Mg and SiO2 are retained in smectites. Deposition of authigenic minerals in the sequence saponite/Fe-Mn oxides/phillipsite/calcite in vugs and cracks may reflect the gradual closing of the systems and probably signals the end of localized oxidation in parts of the core. Mineral compositions indicate that most of these deposits formed from seawater at very low temperature.

Chemistry of primary and secondary phases in intraplate basalts and volcaniclastic sediments at DSDP Leg 89 Holes

Electron microprobe data are presented for clinopyroxenes, plagioclases, palagonites, smectites, celadonites, and zeolites in Hole 462A sheet-flow basalts and Site 585 volcaniclastic sediments. Glomerocrystic clinopyroxenes in Hole 462A are predominantly Ti-poor augites with minor fractionation to ferroaugites in rim portions. Quenched plumose clinopyroxenes show considerable variation from Ca-rich to Ca-poor augites, although all are characterized by being Tirich and Cr-poor relative to the glomerocrysts. Two differentiated series of Site 585 pyroxene compositions, calcic augite and diopside-salite, demonstrate the coexistence, in the vitric and lithic clasts, of tholeiitic and alkali basalt types, respectively. Plagioclase compositions in all samples are mainly labradorites, although some zoned Hole 462A glomerocrysts range from An73 to An20 and are characterized by high Mg and Fe contents in the more calcic varieties. The K content of the plagioclases is highest in the more sodic crystals, although the overall higher orthoclase component of Site 585 plagioclases reflects the generally higher bulk-rock K content. The compositions of both secondary smectites and celadonites are similar irrespective of the alteration location (glass, matrix, vesicles, etc.), although brown smectites replacing interstitial glass have marginally higher total Fe contents than pale green and yellow smectites. Analyzed zeolites are mainly phillipsites with variable alkali content, and, together with associated celadonite, represent late-stage alteration repositories for K under mildly oxidizing conditions. The compositions of both early and late secondary minerals are typical of those formed by the submarine alteration of basaltic rocks at low temperatures.

Biogeochemistry and microbiology of groundwater during acetate and bicarbonate amendment to an alluvial aquifer

These data are from a field experiment conducted in a shallow alluvial aquifer along the Colorado River in Rifle, Colorado, USA. In this experiment, bicarbonate-promoted uranium desorption and acetate amendment were combined and compared to an acetate amendment-only experiment in the same experimental plot. Data include names and location data for boreholes, geochemical data for all the boreholes between June 1, 2010 and January 1, 2011, microarray data provided as signal to noise ratio (SNR) for individual microarray probes, microarray data provided as signal to noise ratio (SNR) by Genus.

Geochemistry of recent sediments of the East African continental margin, Arabian Sea

Chemical analyses have been carried out on 40 samples from the sediment surface and 210 samples from cores that were taken from the edge of the African continental block at the Arabian Sea (coasts of Somalia and Kenya, from Cape Guardafui to Mombasa) on the occasion of the Indian Ocean Expedition of the German research vessel "Meteor" during the years 1964/65. The carbonate content shows its maximum on the northern part of the continental shelf of Africa, where fossil reef debris furnish the detritic portion of carbonate. In the southern part of the continental shelf of Africa the portion of carbonate is low, as it is heavily diluted by the non-carbonatic detritus. It is also in the deep-sea that a lower carbonate content is encountered below the calcite compensation depth. Trace elements in the carbonates: On the shelf and in its vicinity Sr and Mg are enriched. The enrichment has been brought about by the portion of reef debris, as this latter contains aragonite (enrichment of Sr) as well as high-magnesium calcite. The greatest part of the slope contains carbonates that are poor in trace elements and mainly made up of foraminifera (and of coccoliths). Below the carbonate compensation depth another enrichment of Mg takes place in the carbonates, which is probably due to a selective dissolution of calcite in comparison to dolomite. The iron and manganese contents of the carbonates are high (iron higher in coast proximity, manganese higher in the depth), but not genuine, as they come about in the course of the extraction of the carbonates as a result of the dissolution of authigenic Mn-Fe-minerals. Non-carbonatic portion of the sediments: In coast proximity an enrichment of quartz comes about. Within the quartz-rich zone it is the elements V, Cr, Fe, Ti, and B that have been enriched in the non-carbonatic components. This enrichment must be attributed to an elevated content of heavy minerals. In the case of Ti and Fe the preliminary enrichment brought about by processes of lateritisation on the continent plays a certain role. Toward the deep-sea an enrichment of the elements Mn Ni, Cu, and Zn takes place; these enrichments must be explained by authigenic Mn-Fe-minerals. Within the Mn-rich zone a belt running parallel to the coast stands out that shows an increased Mn-enrichment. However, this increase in enrichment does not apply to the elements Ni, Cu, and Zn. It is probable that this latter increased enrichment comes about as a result of the migration of manganese to the sediment surface. (Within the sediments there prevail reductive conditions, in the presence of which Mn is capable of migration, whereas at the sediment surface its precipitation comes about under oxidizing conditions). The quantity of organic matter mainly is dependent on grain size and on the rate of sedimentation. On the shelf an impoverishment of organic matter is to be encountered, as the sediments are coarse-grained. In the depth the impoverishment must be explained on the strength of a small rate of sedimentation. Between those two ranges organic substance is enriched. P and N show an enrichment in comparison to Corg with this applying all the more the smaller the absolute quantity of Corg is. In this particular case one has to do with an enrichment coming about during the diagenetic processes of organic matter. A comparison with the sediments from the Indian and Pakistani continental border in Arabian Sea shows as follows: on the African continental border the coarse detrital material has been transported farther out to deep-sea, which has something to do with the greater inclination of the surface of sedimentation. Carbonate is found in greater abundance on the African side. Its chemical composition is influenced by reef-debris which is missing by Indian-Pakistani side. The content of organic matter is lower on the African side. Contrary to that, the enrichments of N and P compared to organic matter are of an equal order of magnitude on both sides of the Arabian Sea.

Geochemistry and petrogenesis of basalts from DSDP Leg 92 holes

Basalts recovered on DSDP Leg 92 include all the major basalt types so far recovered from the ocean crust of the eastern Pacific. Basalts from Holes 597, 597A, 597B, 597C, and 599B are tholeiites exhibiting all the mineralogical and geochemical characteristics of N-type mid-ocean ridge basalts (MORB). Fragments of ferrobasalts and alkali basalts were also obtained, however, from Holes 60IB and 602B, respectively. Hole 597C, which penetrated 91 m into basement and is the deepest hole so far drilled in fast-spreading crust, yielded basalts that can be divided into three major lithologic units. The lowest unit, Unit III, contains modal olivine and comprises basalts which, at about 8 to 10% MgO, are as basic as any sampled from fast-spreading crust. The middle unit, Unit II, is the most evolved; its basalts are olivine free and contain between 6 and 7.5% MgO. The upper unit, Unit I, is intermediate in composition between Units II and III; it is characterized by both modal olivine and glomerocrysts made up of plagioclase and rare olivine. Unit I is probably a massive flow, whereas Units II and III may be massive flows or sills. The basalts appear to have undergone three stages of alteration ("deuteric," "relatively reducing," and "oxidizing"), the intensity of alteration decreasing markedly downcore. Hole 597B, at 26.4 m of basement penetration the only other "deep" hole, contains just one lithologic unit, which closely resembles Unit I of Hole 597C. Petrogenetic modeling reveals that the three lithologic units in Hole 597C are cogenetic and that they were derived from a depleted mantle source similar to the source of the tholeiites and ferrobasalts sampled in other holes; the alkali basalts are the only rocks derived from enriched mantle. Lavas of Unit III probably lay on the olivine-plagioclase cotectic, whereas the other lavas lay on an olivine-plagioclase-clinopyroxene peritectic. Some 60% of closed-system crystallization is needed to generate the most-evolved from the last-fractionated tholeiite, and a further 50% crystallization (80% overall) is needed to generate the ferrobasalts. Xenocrysts of calcic plagioclase and pseudomorphosed olivine in tholeiites from Hole 597B and Unit I of Hole 597C, and in the ferrobasalts from Hole 601B, provide evidence, however, that some magma mixing may have taken place.

Glycerol dialkyl glycerol tetraethers (GDGT) abundance in suspended particulate matter from the South-west and Equatorial Atlantic Ocean

The TEX86 paleotemperature proxy is based on archaeal glycerol dibiphytanyl glycerol tetraether (GDGT) lipids preserved in marine sediments, yet both the influence of different physiological factors on the structural distribution of GDGTs, and the mechanism(s) by which GDGTs are exported to marine sediments remain unclear. In particular, TEX86 temperatures derived directly from suspended particulate matter (SPM) in the water column can diverge strongly from corresponding in situ temperatures. Here we investigated the abundance and structural distribution of GDGTs in the South-west and Equatorial Atlantic Ocean by examining SPM collected from four surface 1000 m depth profiles spanning 48 degrees of latitude. The depth distribution of GDGTs was consistent with our current understanding of marine archaeal ecology, and specifically of ammonia-oxidizing Thaumarchaeota. Maximum GDGT concentrations occurred at the base of the primary NO2- maximum. Core GDGTs dominated the structural distribution in surface waters, while intact polar GDGTs - thought to potentially indicate live cells - were more abundant at all depths below the maximum NO2- concentration. When integrated through the upper 1000 m of the water column, > 98% of GDGTs were present in waters at and below the depth of the primary NO2- maximum. TEX86-calculated temperatures showed local minima at the depth of the NO2- maximum, while the ratio of GDGT 2:GDGT 3 [2/3] increased with depth throughout the upper water column. These results were used to model the depth of origin for GDGTs exported to sediments. By comparing our SPM data to published TEX86 values and [2/3] ratios from sediments near our study sites, we conclude that most GDGTs are exported from the depth of maximum GDGT concentrations, near the subsurface NO2- maximum (~80-250 m). This indicates that local ammonia oxidation dynamics are important regional controls on the GDGT ratios preserved in sediments. Predicting the extent to which subsurface variations in archaeal activity may influence the sedimentary TEX86 record will require a better understanding of how site-specific productivity and particle dynamics in the upper water column influence the depth of origin for exported organic matter.