Brine Seeps Research Articles

Uptake of trace elements into authigenic carbonate at a brine seep in the northern Gulf of Mexico

Hypersaline seafloor environments formed by brine seepage represent role model examples of extreme marine ecosystems; they may for example help to identify potential habitats for life on other planets. Trace and rare earth elements (REEs) are crucial components enabling microbial life at brine and hydrocarbon seeps. However, the behavior of trace elements at brine seeps is currently poorly understood. Because authigenic carbonates forming at brine seeps archive information on the composition of seepage fluids, we have analyzed carbonates collected from a brine seep site (Mississippi Canyon 709, MC709 for short) of the northern Gulf of Mexico (GoM). The dominance of low-magnesium (Mg) calcite among the carbonate minerals, moderately low δ13Ccarb values (average: −26.1‰, VPDB), as well as the presence of oil in carbonates suggest concomitant seepage of brine fluids and crude oil at this site. High δ18Ocarb values (up to +4.5‰, VPDB) suggest the involvement of 18O-rich fluids during carbonate precipitation, likely resulting from mineral-water reactions in deeper sediments. Significant enrichments of barium (Ba), strontium (Sr), and lithium (Li) in the samples suggest that deep ascending brine fluids contributed to carbonate formation. Enrichments in molybdenum (Mo), arsenic (As), and antimony (Sb) and a correlation between Mo, As, and Sb enrichment factors (EF) and the authigenic iron fraction (Fe/Al ratios) suggest that iron particulate shuttle processes were involved in scavenging of dissolved Mo, As, and Sb from seawater. This notion is strengthened by the co-variation of MoEF and UEF and the shale-normalized REE patterns of the brine-seep carbonates. This study allows to constrain the enrichment mechanisms of trace and REE elements at brine seeps, providing the foundation for an improved understanding of the distribution and behavior of trace metals, as well as their role in microbial metabolisms in the local hypersaline environment.

The Geology and Biogeochemistry of Hydrocarbon Seeps

Hydrocarbon seeps, deep sea extreme environments where deeply sourced fluids discharge at the seabed, occur along continental margins across the globe. Energy-rich reduced substrates, namely hydrocarbons, support accelerated biogeochemical dynamics, creating unique geobiological habitats. Subseafloor geology dictates the surficial expression of seeps, generating hydrocarbon (gas and/or oil) seeps, brine seeps, and mud volcanoes. Biogeochemical processes across the redox spectrum are amplified at hydrocarbon seeps due to the abundance and diversity of reductant; anaerobic metabolism dominates within the sediment column since oxygen is consumed rapidly near the sediment surface. Microbial activity is constrained by electron acceptor availability, with rapid recycling required to support observed rates of hydrocarbon consumption. Geobiologic structures, from gas hydrate to solid asphalt to authigenic minerals, form as a result of hydrocarbon and associated fluid discharge. Animal-microbial associations and symbioses thrive at hydrocarbon seeps, generating diverse and dense deep sea oases that provide nutrition to mobile predators. ▪ Hydrocarbon seeps are abundant deep sea oases that support immense biodiversity and where specialization and adaptation create extraordinary lifestyles. ▪ Subseafloor geology shapes and defines the geochemical nature of fluid seepage and regulates the flux regime, which dictate the surface expression. ▪ High rates of anaerobic oxidation of methane require coupling to multiple processes and promote diversity in the anaerobic methanotroph microbial community. ▪ The recent discovery of novel phyla possessing hydrocarbon oxidation potential signals that aspects of seep biogeochemistry and geobiology remain to be discovered.

Porewater flow patterns in surficial cold seep sediments inferred from conservative tracer profiles and early diagenetic modeling

Porewater flow at cold seeps controls methane oxidation and carbonate precipitation rates, and also plays an important role in gas hydrate dynamics. We constrain the porewater flow rates in the upper sediment of Gulf of Mexico cold seeps by fitting measured 226Ra and Cl− profiles. The approach exploits their natural increase with depth through shallow sediments at non-brine (226Ra) and brine (Cl−) seeps. Vertical flow velocities at non-brine and brine seeps are found to be similar in magnitude, typically on the order of 0.1 m y−1. The accuracy of the flow estimates is assessed and shown to depend substantially on uncertainties in both concentrations and sediment tortuosity. Model simulations further reveal that the natural heterogeneity of sediment permeability can cause considerable lateral variability in vertical flow at the scale of a sediment core, which implies that the coring location and core size can have a substantial effect on the estimated porewater velocities. The formation of gas hydrates and calcium carbonates reduce sediment permeability, and decrease the spatial variability in flow over time, as the formation rates are higher along preferential flow paths. This analysis of the effect of spatiotemporal variability on chemical profiles improves the assessment of uncertainties in the estimated magnitude of flow, and is important for the evaluation of benthic-pelagic coupling at seeps.

New constraints on the formation of hydrocarbon-derived low magnesium calcite at brine seeps in the Gulf of Mexico

Hydrocarbon-rich brine seeps – representing extreme environments typified by halophilic and chemotrophic organisms – may provide insight into the ecology of microorganisms on an early Earth and possibly other planetary bodies. Authigenic low magnesium calcite (LMC) is common at brine seeps and represents an archive of fluid compositions, fluid origin, and the conditions under which this carbonate mineral formed. Here we present the analysis of authigenic LMC from three hydrocarbon-rich brine seeps (GB260, ~460 m; GB697, ~1280 m; AC601, ~2340 m) from the Gulf of Mexico. The formation of LMC was favored by brine fluids with extremely low Mg/Ca mole ratios (e.g. <2) relative to seawater (Mg/Ca mole ratio of ~5.2). Petrographic observations reveal that the studied LMC is of primary origin. Its δ13C values vary from −53.5‰ to 14.0‰, indicating variable carbon sources that include 13C-depleted methane, crude oil, seawater dissolved inorganic carbon, and 13C-enriched residual carbonate species reflecting methanogenesis. In contrast, LMC shows predominantly relatively high δ13Corg values (from −39.0‰ to −25.7‰), suggesting an unrecognized local source of nutrients fueling the local production of biomass. The δ18O values of LMC (as high as 6.0‰) are too high for precipitation in equilibrium with seawater, probably reflecting the involvement of deep formation fluids. The wide range of 87Sr/86Sr ratios and the enrichment of Sr and Ba in LMC is in accordance with pore fluids deriving from the dissolution of the Louann salt or alteration of silicates in deep sediments. Given the stability of LMC, its petrographic and geochemical characterization achieved in this study can be used to better constrain brine seep activities throughout the geological record.

Patterns and variability in geochemical signatures and microbial activity within and between diverse cold seep habitats along the lower continental slope, Northern Gulf of Mexico

We collected 69 sediment cores from distinct ecological and geological settings along the deep slope in the Northern Gulf of Mexico to evaluate whether specific geochemical- or habitat-related factors correlated with rates of microbial processes and geochemical signatures. By collecting replicate cores from distinct habitats across multiple sites, we illustrate and quantify the heterogeneity of cold seep geochemistry and microbial activity. These data also document the factors driving unique aspects of the geochemistry of deep slope gas, oil and brine seeps. Surprisingly little variation was observed between replicate (n=2–5) cores within sites for most analytes (except methane), implying that the common practice of collecting one core for geochemical analysis can capture the signature of a habitat in most cases. Depth-integrated concentrations of methane, dissolved inorganic carbon (DIC), and calcium were the predominant geochemical factors that correlated with a site׳s ecological or geological settings. Pore fluid methane concentration was related to the phosphate and DIC concentration, as well as to rates of sulfate reduction. While distinctions between seep habitats were identified from geochemical signatures, habitat specific geochemistry varied little across sites. The relative concentration of dissolved inorganic nitrogen versus phosphorus suggests that phosphorus availability limits biomass production at cold seeps. Correlations between calcium, chloride, and phosphate concentrations were indicative of brine-associated phosphate transport, suggesting that in addition to the co-migration of methane, dissolved organic carbon, and ammonium with brine, phosphate delivery is also associated with brine advection.

Barite encrustation of benthic sulfur‐oxidizing bacteria at a marine cold seep

Crusts and chimneys composed of authigenic barite are found at methane seeps and hydrothermal vents that expel fluids rich in barium. Microbial processes have not previously been associated with barite precipitation in marine cold seep settings. Here, we report on the precipitation of barite on filaments of sulfide-oxidizing bacteria at a brine seep in the Gulf of Mexico. Barite-mineralized bacterial filaments in the interiors of authigenic barite crusts resemble filamentous sulfide-oxidizing bacteria of the genus Beggiatoa. Clone library and iTag amplicon sequencing of the 16S rRNA gene show that the barite crusts that host these filaments also preserve DNA of Candidatus Maribeggiatoa, as well as sulfate-reducing bacteria. Isotopic analyses show that the sulfur and oxygen isotope compositions of barite have lower δ(34)S and δ(18)O values than many other marine barite crusts, which is consistent with barite precipitation in an environment in which sulfide oxidation was occurring. Laboratory experiments employing isolates of sulfide-oxidizing bacteria from Gulf of Mexico seep sediments showed that under low sulfate conditions, such as those encountered in brine fluids, sulfate generated by sulfide-oxidizing bacteria fosters rapid barite precipitation localized on cell biomass, leading to the encrustation of bacteria in a manner reminiscent of our observations of barite-mineralized Beggiatoa in the Gulf of Mexico. The precipitation of barite directly on filaments of sulfide-oxidizing bacteria, and not on other benthic substrates, suggests that sulfide oxidation plays a role in barite formation at certain marine brine seeps where sulfide is oxidized to sulfate in contact with barium-rich fluids, either prior to, or during, the mixing of those fluids with sulfate-containing seawater in the vicinity of the sediment/water interface. As with many other geochemical interfaces that foster mineral precipitation, both biological and abiological processes likely contribute to the precipitation of barite at marine brine seeps such as the one studied here.

Temperature and salinity tolerances of embryos and larvae of the deep-sea mytilid mussel “Bathymodiolus” childressi

We examined temperature and salinity tolerances of early embryonic and larval stages of the deep-sea, cold-seep mussel “Bathymodiolus” childressi to determine whether they may control the dispersal depth of larvae. Salinity and temperature tolerances increased with developmental stage, but tolerance ranges were not as wide for the larvae of “B.” childressi as for the larvae of the related shallow-water mussel Mytilus trossulus. Normal development occurred in “B.” childressi from 7 to 15°C and at salinities of 35 and 45. Greater tolerance of “B.” childressi embryos to high than low salinities may aid development of negatively buoyant early embryos at brine seeps. Although there was a decreasing trend in survival of “B.” childressi larvae with increasing temperature, survival of “B.” childressi trochophores was not significantly different at 20°C than at the adults’ ambient temperature. Since larvae tolerate increasing temperatures as they age and seawater temperatures at 100 m depth do not exceed 20°C in months following the mussels’ spawning season, we suggest that temperature would not limit vertical migration of the veliger larvae of “B.” childressi into even the uppermost layer of the water column above the cold seeps in the Gulf of Mexico.

Enumeration of viruses and prokaryotes in deep-sea sediments and cold seeps of the Gulf of Mexico

Little is known about the distribution and abundance of viruses in deep-sea cold-seep environments. Like hydrothermal vents, seeps support communities of macrofauna that are sustained by chemosynthetic bacteria. Sediments close to these communities are hypothesized to be more microbiologically active and therefore to host higher numbers of viruses than non-seep areas. Push cores were taken at five types of Gulf of Mexico habitats at water depths below 1000m using a remotely operated vehicle (ROV). The habitats included non-seep reference sediment, brine seeps, a microbial mat, an urchin field, and a pogonophoran worm community. Samples were processed immediately for enumeration of viruses and prokaryotes without the addition of a preservative. Prokaryote counts were an order of magnitude lower in sediments directly in contact with macrofauna (urchins, pogonophorans) compared to all other samples (107 vs. 108cellsg−1dry weight) and were highest in areas of elevated salinity (brine seeps). Viral-Like Particle (VLP) counts were lowest in the reference sediments and pogonophoran cores (108VLPg−1dry wt), higher in brine seeps (109VLPg−1dry wt), and highest in the microbial mats (1010VLPg−1dry wt). Virus-prokaryote ratios (VPR) ranged from <5 in the reference sediment to >30 in the microbial mats and >60 in the urchin field. VLP counts and VPR were all significantly greater than those reported from sediments in the deep Mediterranean Sea and in most cases were higher than recent data from a cold-seep site near Japan. The high VPR suggest that greater microbial activity in or near cold-seep environments results in greater viral production and therefore higher numbers of viruses.

Spatial variations in the salinity of pore waters in northern deep water Gulf of Mexico sediments: implications for pathways and mechanisms of solute transport

Geofluids (2010) 10, 83–93AbstractSpatial variations in the salinity of pore waters in sedimentary basins can provide important insight into basin‐scale hydrogeologic processes. Although there have been numerous studies of brine seeps in the deep water Gulf of Mexico, much less is known about porewater salinities in the vast areas between seeps. A study has been made of spatial variation in pore water salinities in sediments in an approximately 500 km by 200 km area of the northern deep water (water depth &gt;500 m) Gulf of Mexico sedimentary basin (GOM) to provide insight into pathways and mechanisms of solute transport in this portion of the basin. A second objective was to document salinities in the upper 500 m of the sedimentary section, the approximate depth to which methane hydrates, a potential future energy resource, may be stable. Elevated salinities would reduce the P–T stability range of hydrates. Salinities were calculated from borehole logs using a dual electrical conductivity model. Even though much of the northern GOM is underlain by allochthonous salt most of the undisturbed shallow sedimentary section has not been permeated by hypersaline waters. These waters are limited to areas near brine seeps. Hypersaline waters having salinities in excess of 100 g l−1 become more common at subseafloor depths of 2 km and greater. A field study at Green Canyon 65 and published numerical simulations of fluid flow above tabular salt bodies suggest that brines produced by salt dissolution migrate laterally and pond above salt and/or within minibasins and that the dominant mechanism of vertical solute transport is a combination of compaction‐driven advection and diffusion, not large‐scale thermohaline overturn. Superimposed on this diffuse upward flux of dissolved salt is the more focused and localized expulsion of saline fluids up faults.

Metabolic variability in seafloor brines revealed by carbon and sulphur dynamics

Brine fluids supply the sea floor with energy-rich substrates. Geochemical and genetic analyses indicate that the associated microbial communities—and their dominant metabolisms—vary between seep sites with different supplies of sulphate and organic matter. Brine fluids that upwell from deep, hot reservoirs below the sea bed supply the sea floor with energy-rich substrates and nutrients that are used by diverse microbial ecosystems. Contemporary hypersaline environments formed by brine seeps may provide insights into the metabolism and distribution of microorganisms on the early Earth1 or on extraterrestrial bodies2. Here we use geochemical and genetic analyses to characterize microbial community composition and metabolism in two seafloor brines in the Gulf of Mexico: an active mud volcano and a quiescent brine pool. Both brine environments are anoxic and hypersaline. However, rates of sulphate reduction and acetate production are much higher in the brine pool, whereas the mud volcano supports much higher rates of methane production. We find no evidence of anaerobic oxidation of methane, despite high methane fluxes at both sites. We conclude that the contrasting microbial community compositions and metabolisms are linked to differences in dissolved-organic-matter input from the deep subsurface and different fluid advection rates between the two sites.

Palaeontology and depositional environments of ancient brine seeps in the Middle Cambrian Burgess Shale at The Monarch, British Columbia, Canada

The Monarch, a mountain in southeastern British Columbia, exposes the Cathedral Escarpment, which abuts the basinal Burgess Shale and an underlying limestone, the upper Takakkaw Tongue. At one section, a dolomitized megabreccia, representing an intraformational collapsed cavern, forms the Cathedral Escarpment wall. The megabreccia is cross-cut by the subsequent megatruncation event marking the collapse of the Cathedral margin, which supports previous hypotheses that dolomitizing brines were active at the Cathedral margin, prior to and during deposition of the Burgess Shale. Epiphyton-rich carbonate megablocks within the basinal strata, previously interpreted as olistoliths spalled off the Escarpment, are unlike the peritidal strata comprising the Cathedral margin and are more likely deep-water carbonate mud mounds that grew in the basin near the Escarpment face. Evidence for early brines in basinal environments at this locality includes lenses of dark, magnesium-rich clinochlore (> 30 wt.% MgO vs ~ 2% in background shales) within the Burgess Shale at the Escarpment wall. These clinochlores are interpreted as precipitates from seafloor brine seeps analogous to ones currently found at the foot of the Florida Escarpment and on the distal shelf and slope of the northern Gulf of Mexico. Like the Gulf examples, the brines formed standing pools on the Cambrian seafloor and hosted abundant organisms in a narrow fringe around their peripheries but not within the pools. Sponges, priapulid worms, hyoliths, linguliform brachiopods and trilobites predominate. Shales only a few metres basinward from the pools are nearly barren of animal fossils. Increased biologic productivity localized at the seeps would account for the patchy distribution of fossils in the Burgess Shale in a narrow zone close to the Escarpment. The discovery of brine seep deposits and associated fringing communities at The Monarch shows that at least some assemblages in the Burgess Shale were preserved within their habitat and were supported by chemosynthesis.

A new, Middle Cambrian, Burgess Shale-type biota, Bolaspidella Zone, Chancellor Basin, southeastern British Columbia

A newly discovered Burgess Shale-type (BST) biota occurs in southeastern British Columbia on Haiduk and Tangle peaks. The fossiliferous rocks of the informally named Vermilion sub-unit and Duchesnay unit occur in the Bolaspidella Zone, one trilobite biozone younger than the Burgess Shale Formation. The younger rocks abut the Eldon Escarpment in a stratigraphic and depositional relationship that mirrors that of the Burgess Shale Formation and Cathedral Escarpment. The biota, concentrated at the Eldon Escarpment, is hosted predominantly in the Duchesnay unit, and includes Burgess Shale genera of sponges, worms, some arthropods and brachiopods. New taxa include an arborescent, benthic graptolite with preserved fuselli. Microbial fossils, including vendotaenid bacteria, are locally abundant and range up to 750 m basinward of the Escarpment in both the Vermilion sub-unit and Duchesnay unit, while concentrations of animal fossils are restricted to within 100 m. In the Vermilion sub-unit, large autochthonous carbonate mud mounds, previously interpreted as platform-derived olistoliths, originated at the base of the Escarpment, probably over fluid conduits, and then slid downslope, bulldozing and entraining sediments in their paths. Local magnesian- and barian-rich brine pool deposits occur up to 750 m distal of the Escarpment; fractionation of the fluids may explain the differing geochemistries. At least one MgO-rich brine pool deposit on Haiduk Peak is fringed by abundant animal fossils, including concentrations of priapulid worms. This assemblage, together with high-density, low-diversity assemblages on Tangle Peak likely represent “fringing fauna facies” around brine seeps, a model erected for similar fossil concentrations and distributions in the Burgess Shale. Intrabasinal comparison of the Vermilion sub-unit and Duchesnay unit with the Burgess Shale Formation reveals an identical stratigraphic ordering of carbonates and shales, brine pool deposits, major debris flow deposits, carbonate mud mound growth and fossiliferous deposits. The Eldon and Cathedral platform formations are known to share complimentary brine-derived characteristics as well. The stratigraphic patterns signify that the depositional processes producing the suite of older lithofacies recurred during deposition of the younger units. Interbasinal correlation with the Wheeler and Marjum formations, Utah, identifies the Duchesnay unit deposit as the youngest basinal Burgess Shale-type deposit in North America. Decreasing abundance of animal fossils away from the Eldon and Cathedral escarpments is generally attributed to increasing development of tectonic fabrics. However, on Haiduk Peak, rocks hundreds of metres basinward of the Escarpment contact are essentially undeformed and contain rare Planolites, brachiopods and trilobites as the only macrofauna; locally abundant vendotaenids and Morania are evidence that BST preservation occurred at these distances. The concentration of animal fossils at the Escarpment is therefore a primary ecological feature, not due to a preservational or rheological bias. Communities were clustered at the face of the Escarpment where brines were seeping.

Comparison of geochemical and distinctive mineralogical features associated with the Kinzers and Burgess Shale formations and their associated units

This paper compares two North American occurrences of fossils that exhibit Burgess Shale-type preservation (BST): the Middle Cambrian Burgess Shale Formation of southeastern British Columbia, and the Lower to Middle Cambrian Kinzers Fm of southeastern Pennsylvania. Redox-sensitive trace elements (Mo, Ni/Co, V/Sc) indicate that palaeo-oxygenation conditions varied with respect to faunal assemblage and location. Ogygopsis-bearing fauna in both the Burgess Shale and Kinzers formations are associated with a dysoxic metal signature. Burgess Shale-type preservation in the Kinzers Fm was deposited in a fluctuating oxycline, whereas the BST-fossil beds of Fossil Ridge and Mt Stephen (Burgess Shale Fm) yield a geochemical signature that consistently indicates oxic conditions. Thus, sustained low-oxygen conditions do not correlate with higher quality of fossil preservation at these sites. Ogygopsis is associated with dysoxic conditions in both localities, and may therefore be a faunal indicator of such environments in Middle Cambrian strata. Carbonate units associated with both the Burgess Shale and Kinzers formations contain large, generally concordant, near-surface cavities that contain herringbone calcite cements that show no significant enrichment in the potential calcite inhibitor ions such as reduced Fe, Sr, S, Pb, and Zn. The abundance of micro-inclusions of dolomite suggests that Mg may have been the calcite inhibitor ion responsible for herringbone cement in these Cambrian occurrences. Another distinctive mineralogical feature is the presence of doubly-terminated, euhedral, zoned, authigenic quartz as a conspicuous part of a carbonate host-rock replacement assemblage. The association of both herringbone calcite and zoned quartz crystals in units associated with the Burgess Shale and Kinzers formations suggest a common feature in the depositional and diagenetic environment of these two regions in which Burgess Shale-type fossil preservation occur; syn-depositional brine flow is the likely cause of these distinct mineralogical features. Brine seeps in the depositional environment may have provided nutrients for stable high-abundance faunal communities in a slope setting, thereby accounting for the abundance of fossil material. Furthermore, high-salinity brine in the pore waters of carcass-bearing Cambrian muds may have further limited shallow burrowing, scavenging, and decomposition rates, accounting for the exceptional preservation in these two localities.

Microbial methane oxidation and sulfate reduction at cold seeps of the deep Eastern Mediterranean Sea

The Eastern Mediterranean hosts a variety of active cold seep systems, such as gas chimneys, mud volcanoes and pockmarks, in water depths of 500 to 3200 m. As part of the NAUTINIL expedition in 2003, the sediments of cold seeps on the Nile Deep Sea Fan (NDSF) were sampled for the first time for biogeochemical and microbiological analyses. Here we compare rates of the anaerobic oxidation of methane (AOM) and sulfate reduction (SR) as well as the microbial community structure of a variety of cold seep systems including mud volcanoes, pockmarks and brine seeps. Our results revealed strong differences in microbial activity among the different seep systems of the Eastern, Central and Western provinces of the NDSF, as well as the Olimpi field (Central Mediterranean Ridge). Integrated over a sediment depth of 10 cm below the seafloor, SR rates ranged from 0.1–66 mmol m − 2 d − 1 and AOM rates from 0.1–3.6 mmol m − 2 d − 1 . SR was often considerably higher than methane oxidation, indicating that electron donors other than methane were utilized. In general, the lowest rates were associated with pockmarks and carbonate pavements, and highest rates with bacterial mats above the gassy sediments of mud volcano centers. 16S rRNA gene analysis and fluorescence in situ hybridization (FISH), revealed the presence of all known groups of marine methane oxidizing Archaea (i.e. ANME-1, -2, -3) and also of methane oxidizing Bacteria (i.e. Methylobacter sp. and relatives) in some seep sediments. Presumably syntrophic sulfate-reducing bacterial partners of ANMEs were also detected in association with the ANMEs. Several ANMEs formed consortia with unknown bacterial partners. The microbial community structure reflected the presence of typical seep microorganisms at all sites investigated, but differed to varying extents between the different types of seeps. Despite the high availability of methane and sulfate, methanotrophic microbial activity and biomass were lower at the seeps of the Eastern Mediterranean compared to those of other continental margins for unknown reasons.

Upward advection rates and methane fluxes, oxidation, and sources at two Gulf of Mexico brine seeps

Pore water chloride, sulfate, and methane profiles were measured at two Gulf of Mexico brine seeps to determine upward fluid advection rates and to quantify the advective methane flux from these sediments. We also measured δ 13C–CH 4 values to constrain the source of methane and determine whether anaerobic methane oxidation can occur at high chloride concentrations. Chloride concentrations were near seawater values at the sediment–water interface and reached as high as 4500 mM by 25 cm below seafloor (cmbsf). Advection rates were determined by a 1-D advection–diffusion model. Sulfate concentrations were near seawater values of 28 mM at the sediment–water interface and quickly decreased to ~ 1 mM by the bottom of the cores. The brine fluids were also charged with CH 4 enriched water, reaching up to 3 mM, compared to background cores and could be an important source of methane to the overlying water column. At one site, dissolved methane had an average δ 13C value of − 54 ± 0.2‰ and − 49 ± 6‰. Our main conclusions are: 1) advection rates are heterogeneous and range from 7 to 65 cm/year, 2) assuming brine fluids are devoid of sulfate, the sulfate depletion depth in these sediments is controlled by brine advection, 3) methane contained in the brine fluid has either a mixed biogenic/thermogenic source or a biogenic source that has been oxidized, and 4) the advective flux of methane from these brine seeps ranges from 2 to 58 mol m − 2 y − 1 .

Biomarker analysis of microbial diversity in sediments of a saline groundwater seep of Salt Basin, Nebraska

Lipids extracted from sediments in a saline seep in the Salt Basin of Lancaster County, Nebraska included alkanes, alkenes, alkanols, phytol, C 27–30 sterols, C 30–32 hopanoids, tetrahymanol, glycolipid and phospholipid fatty acids, and lipopolysaccharide hydroxyl fatty acids. Biomarker profiles suggest that the brine seeps of Salt Basin support a microbial ecosystem adapted to a relatively highly saline and sulfidic environment. The phospholipid fatty acid (PLFA) and lipopolysaccharide hydroxyl fatty acid profiles are consistent with the presence of large numbers of sulfate-reducing bacteria (SRB) in black, sulfidic muds surrounding the seeps. In the context of field and laboratory observations, the presence of large amounts of glycolipid fatty acids is attributed to large populations of photosynthetic microorganisms (cyanobacteria, phytoplankton, and purple sulfur bacteria) that likely play important roles in the local cycling of carbon and sulfur. The sterol profile and the detection of polyunsaturated alkenes (C 21:6, C 21:7, C 30:4, and C 30:5) implicates microalgae as important contributors of organic matter at the site. Comparatively high concentrations of phytol (58.2 μg g −1 dry wt sediment) record the activity of photosynthetic organisms in the system. The δ 13C of phytol (−37.1‰) is compatible with a dominance of microalgae, cyanobacteria, or higher plants and a lesser contribution from phototrophic sulfur bacteria. The presence of various intermediate degradation products of phytol (phytenes and phytadienes) indicates that SRB likely mediate the chemical reduction of phytol in the anaerobic zone. The presence of C 30–32 hopanols can be attributed to cyanobacteria and methanotrophs in oxic regions of the water column, whereas bacterivorous ciliates and phototrophic sulfur bacteria living at the chemocline are likely sources of tetrahymanol. The carbon isotopic composition of individual fatty acids and neutral lipids helps to identify source organisms. These microorganisms and others constitute a unique and integrated ecosystem prescribed by the geochemistry of the Salt Basin.

Population structure of the mussel “ Bathymodiolus” childressi from Gulf of Mexico hydrocarbon seeps

Hydrocarbon and brine seeps in the deep regions of the northern and western Gulf of Mexico often support populations of the bathymodiolin mussel, “ Bathymodiolus” childressi. In this study, we use two mitochondrial and six nuclear DNA markers to investigate relationships within the metapopulation of “ B.” childressi in the Gulf of Mexico from Mississippi Canyon to Alaminos Canyon over a range of 527–2222 m in depth and approximately 550 km in distance. Restriction fragment length polymorphism (RFLP) and size polymorphism analysis of the markers suggest that populations are not genetically differentiated. F ST values were not significantly different from zero. The presence of a panmictic population of “ B.” childressi over such a broad range of depth suggests that this species may be quite different from most members of the Gulf of Mexico seep chemosynthetic communities.

Middle Cambrian Brine Seeps on the Kicking Horse Rim and Their Relationship to Talc and Magnesite Mineralization and Associated Dolomitization, British Columbia, Canada

Middle Cambrian basinal strata along the Kicking Horse Rim, including the Burgess Shale Formation, contain lenses of black, thin-bedded, noncalcareous, geochemically anomalous chloritic rock. The lenses have extremely high MgO concentrations (up to 31 wt %), or less commonly are enriched in Ba (up to 1,680 ppm), which contrasts with surrounding strata where MgO and Ba content are low. Location in paleotopographic lows, proximity to ancient submarine Escarpments, association with syneresis cracks, distinct major element patterns, high fluorine contents, and geochemical signatures indicative of deposition in oxygen-deficient environments, are interpreted as evidence that the lenses formed by precipitation from dense brines that seeped onto the sea floor through the adjacent platform. The strata that precipitated from the magnesian brines have been metamorphosed to lower greenschist facies and currently consist of clinochlore and minor quartz. Based upon the bulk-rock composition, the protolith of these seep-related strata is inferred to have been composed of Mg smectite, with lesser kaolinite, and minor brucite. Middle Cambrian carbonates along the Kicking Horse Rim also host ore suites of magnesian minerals, including talc and magnesite, which are interpreted to have formed from similar Mg-rich brines, as suggested by their compositional and mineralogical similarities and their spatial and temporal association. The existence of Mg brines also may account for early dolomitization of the platform margin during the Middle Cambrian.

Formation and chemical evolution of magnesium chloride brines by evaporite dissolution processes—Implications for evaporite geochemistry

The evolution of magnesium chloride brines with high bromide contents via a multistage reaction and dissolution process has been studied in brine seeps of a German potash mine. The observed chemical trends and phase equilibria can be modeled and interpreted in terms of a NaCl solution (cap rock brine) infiltrating into a potash zone characterized by the metamorphic mineral assemblage kieserite + sylvite + halite + anhydrite. Establishment of a persistent, stable equilibrium assemblage and constant fluid composition in the invariant point IP1 of the six component (Na-K-Mg-Ca-Cl-SO 4-H 2O) system of oceanic salts is prevented by the perpetually renewed input of NaCl-brine and by the intermittent exposure of incompatible kieserite. Instead, the solutions develop towards the metastable invariant point IP1(gy), with the mineral assemblage carnallite + polyhalite + sylvite + halite + gypsum, where gypsum takes the place of anhydrite (stage I). The temporary exposure of kieserite and the ensuing formation of polyhalite effectively buffer the solutions along the metastable polyhalite phase boundary during stages II and III. Eventually, in stage IV, polyhalite becomes depleted and admixture of more NaCl brine leads to low sulfate solution compositions, which are now only constrained by carnallite + sylvite + halite, and the once hexary system degenerates to a quaternary one (Na-K-Mg-Cl-H 2O) in point E. Bromide in brines shows equilibrium partitioning with respect to the wall rock minerals. The pattern of evolving brine compositions may serve as a model for similar brine occurrences, which in some cases may have been misinterpreted as remains of fossil, highly concentrated and chemically modified seawater. Similar magnesium chloride brines of salt lakes (e.g., Dead Sea, Dabusun Lake) show subtle differences and are constrained by fewer mineral equilibria (more degrees of freedom), and their low sulfate contents are due to gypsum precipitation, driven by calcium chloride input from dolomitization reactions. Finally, the observed reaction sequence is generalized, and a model for the formation of magnesium sulfate depleted, chloride-type potash salts and bischofite deposits by leaching of sulfate-type evaporites is proposed.

05/00534 Preparation of solar grade silicon from optical fibers wastes with thermal plasmas: Ma, W. et al. Solar Energy Materials and Solar Cells, 2004, 81, (4), 477–483

The evolution of magnesium chloride brines with high bromide contents via a multistage reaction and dissolution process has been studied in brine seeps of a German potash mine. The observed chemical trends and phase equilibria can be modeled and interpreted in terms of a NaCl solution (cap rock brine) infiltrating into a potash zone characterized by the metamorphic mineral assemblage kieserite + sylvite + halite + anhydrite. Establishment of a persistent, stable equilibrium assemblage and constant fluid composition in the invariant point IP1 of the six component (Na-K-Mg-Ca-Cl-SO4-H2O) system of oceanic salts is prevented by the perpetually renewed input of NaCl-brine and by the intermittent exposure of incompatible kieserite. Instead, the solutions develop towards the metastable invariant point IP1(gy), with the mineral assemblage carnallite + polyhalite + sylvite + halite + gypsum, where gypsum takes the place of anhydrite (stage I). The temporary exposure of kieserite and the ensuing formation of polyhalite effectively buffer the solutions along the metastable polyhalite phase boundary during stages II and III. Eventually, in stage IV, polyhalite becomes depleted and admixture of more NaCl brine leads to low sulfate solution compositions, which are now only constrained by carnallite + sylvite + halite, and the once hexary system degenerates to a quaternary one (Na-K-Mg-Cl-H2O) in point E. Bromide in brines shows equilibrium partitioning with respect to the wall rock minerals. The pattern of evolving brine compositions may serve as a model for similar brine occurrences, which in some cases may have been misinterpreted as remains of fossil, highly concentrated and chemically modified seawater. Similar magnesium chloride brines of salt lakes (e.g., Dead Sea, Dabusun Lake) show subtle differences and are constrained by fewer mineral equilibria (more degrees of freedom), and their low sulfate contents are due to gypsum precipitation, driven by calcium chloride input from dolomitization reactions. Finally, the observed reaction sequence is generalized, and a model for the formation of magnesium sulfate depleted, chloride-type potash salts and bischofite deposits by leaching of sulfate-type evaporites is proposed.