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© 2016 International Society for Microbial Ecology All rights reserved. Although little is known regarding microbial life within our planet's rock-hosted deep subseafloor biosphere, boreholes drilled through deep ocean sediment and into the underlying basaltic crust provide invaluable windows of access that have been used previously to document the presence of microorganisms within fluids percolating through the deep ocean crust. In this study, the analysis of 1.7 million small subunit ribosomal RNA genes amplified and sequenced from marine sediment, bottom seawater and basalt-hosted deep subseafloor fluids that span multiple years and locations on the Juan de Fuca Ridge flank was used to quantitatively delineate a subseafloor microbiome comprised of distinct bacteria and archaea. Hot, anoxic crustal fluids tapped by newly installed seafloor sampling observatories at boreholes U1362A and U1362B contained abundant bacterial lineages of phylogenetically unique Nitrospirae, Aminicenantes, Calescamantes and Chloroflexi. Although less abundant, the domain Archaea was dominated by unique, uncultivated lineages of marine benthic group E, the Terrestrial Hot Spring Crenarchaeotic Group, the Bathyarchaeota and relatives of cultivated, sulfate-reducing Archaeoglobi. Consistent with recent geochemical measurements and bioenergetic predictions, the potential importance of methane cycling and sulfate reduction were imprinted within the basalt-hosted deep subseafloor crustal fluid microbial community. This unique window of access to the deep ocean subsurface basement reveals a microbial landscape that exhibits previously undetected spatial heterogeneity.

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The oceanic basaltic basement contains the largest aquifer on Earth and potentially plays an important role in the global carbon cycle as a net sink for dissolved organic carbon (DOC). However, few details of the organic matter cycling in the subsurface are known because great water depths and thick sediments typically hinder direct access to this environment. In an effort to examine the role of water–rock–microorganism interaction on organic matter cycling in the oceanic basaltic crust, basement fluid samples collected from three borehole observatories installed on the eastern flank of the Juan de Fuca Ridge were analyzed for dissolved amino acids. Our data show that dissolved free amino acids (1–13 nM) and dissolved hydrolyzable amino acids (43–89 nM) are present in the basement. The amino acid concentrations in the ridge-flank basement fluids are at the low end of all submarine hydrothermal fluids reported in the literature and are similar to those in deep seawater. Amino acids in recharging deep seawater, in situ amino acid production, and diffusional input from overlying sediments are potential sources of amino acids in the basement fluids. Thermodynamic modeling shows that amino acid synthesis in the basement can be sustained by energy supplied from inorganic substrates via chemolithotrophic metabolisms. Furthermore, an analysis of amino acid concentrations and compositions in basement fluids support the notion that heterotrophic activity is ongoing. Similarly, the enrichment of acidic amino acids and depletion of hydrophobic ones relative to sedimentary particulate organic matter suggests that surface sorption and desorption also alters amino acids in the basaltic basement. In summary, although the oceanic basement aquifer is a net sink for deep seawater DOC, similar amino acid concentrations in basement aquifer and deep seawater suggest that DOC is preferentially removed in the basement over dissolved amino acids. Our data also suggest that organic carbon cycling occurs in the oceanic basaltic basement, where an active subsurface biosphere is likely responsible for amino acid synthesis and degradation.

The oceanic basaltic crust is the largest aquifer on Earth and has the potential to harbor substantial subsurface microbial ecosystems, which hitherto remains largely uncharacterized and is analogous to extraterrestrial subsurface habitats. Within the sediment-buried 3.5 Myr old basaltic crust of the eastern Juan de Fuca Ridge flank, the circulating basement fluids have moderate temperature (∼65 °C) and low to undetectable dissolved oxygen and nitrate concentrations. Sulfate, present in high concentrations, is therefore expected to serve as the major electron acceptor in this subsurface environment. This study focused on the availability and potential sources of two important electron donors, methane (CH4) and hydrogen (H2), for the subseafloor biosphere. High integrity basement fluids were collected via fluid delivery lines associated with Integrated Ocean Drilling Program (IODP) Circulation Obviation Retrofit Kits (CORKs) that extend from basement depths to outlet ports at the seafloor. Two new CORKs installed during IODP 327 in 2010, 1362A and 1362B, were sampled in 2011 and 2013. The two CORKs are superior than earlier style CORKs in that they are equipped with coated casing and polytetrafluoroethylene fluid delivery lines, reducing the interaction between casing materials with the environment. Additional samples were collected from an earlier style CORK at Borehole 1301A. The basement fluids are enriched in H2 (0.05–1.8 μmol/kg), suggesting that the ocean basaltic aquifer can support H2-driven metabolism. The basement fluids also contain significant amount of CH4 (5–32 μmol/kg), revealing CH4 as an available substrate for subseafloor basaltic habitats. The δ13C values of CH4 from the three boreholes ranged from −22.5 to − 58 ‰ , while the δ2H values ranged from −316 to 57‰. The isotopic compositions of CH4 and the molecular compositions of hydrocarbons suggest that CH4 in the basement fluids is of both biogenic and abiotic origins, varying among sites and sampling times. The δ2H values of CH4 in CORK 1301A fluid samples are much more positive than found in all other marine environments investigated to date and are best explained by the partial microbial oxidation of biogenic CH4. In conclusion, our study shows that CH4 and H2 are persistently available to fuel the deep biosphere and that CH4 is both produced and potentially consumed by microorganisms in the oceanic basement.

The permeable rocks of the upper oceanic basement contain seawater-sourced fluids estimated to be ~ 2% of the global ocean volume. This represents a very large potential subsurface biosphere supported by chemosynthesis. Recent collection of high integrity samples of basement fluid from the sedimented young basaltic basement on the Juan de Fuca Ridge flanks, off the coasts of Vancouver Island (Canada) and Washington (USA), and subsequent chemical analyses permit numerical modeling of metabolic redox reaction energetics. Here, values of Gibbs free energy for potential chemolithotrophic net reactions were calculated in basement fluid and in zones where basement fluid and entrained seawater may mix; the energy yields are reported both on a per mole electrons transferred and on a per kg of basement fluid basis. In pure basement fluid, energy yields from the anaerobic respiration processes investigated are anemic, releasing

The rock-hosted, oceanic crustal aquifer is one of the largest ecosystems on Earth, yet little is known about its indigenous microorganisms. Here we provide the first phylogenetic and functional description of an active microbial community residing in the cold oxic crustal aquifer. Using subseafloor observatories, we recovered crustal fluids and found that the geochemical composition is similar to bottom seawater, as are cell abundances. However, based on relative abundances and functional potential of key bacterial groups, the crustal fluid microbial community is heterogeneous and markedly distinct from seawater. Potential rates of autotrophy and heterotrophy in the crust exceeded those of seawater, especially at elevated temperatures (25 °C) and deeper in the crust. Together, these results reveal an active, distinct, and diverse bacterial community engaged in both heterotrophy and autotrophy in the oxygenated crustal aquifer, providing key insight into the role of microbial communities in the ubiquitous cold dark subseafloor biosphere.

The permeable upper oceanic basement serves as a plausible habitat for a variety of microbial communities. There is growing evidence suggesting a substantial subseafloor biosphere. Here new time series data are presented on key inorganic species, methane, hydrogen and dissolved organic carbon (DOC) in ridge flank fluids obtained from subseafloor observatory CORKs (Circulation Obviation Retrofit Kits) at Integrated Ocean Drilling Program (IODP) boreholes 1301A and 1026B. These data show that the new sampling methods ( Cowen et al., 2012 ) employed at 1301A result in lower contamination than earlier studies. Furthermore, sample collection methods permitted most chemical analyses to be performed from aliquots of single large volume samples, thereby allowing more direct comparison of the data. The low phosphate concentrations (0.06–0.2 μM) suggest that relative to carbon and nitrogen, phosphorus could be a limiting nutrient in the basement biosphere. Coexisting sulfate (17–18 mM), hydrogen sulfide (∼0.1 μM), hydrogen (0.3–0.7 μM) and methane (1.5–2 μM) indicates that the basement aquifer at 1301A either draws fluids from multiple flow paths with different redox histories or is a complex environment that is not thermodynamically controlled and may allow co-occurring metabolic pathways including sulfate reduction and methanogenesis. The low DOC concentrations (11–18 μM) confirm that ridge flank basement is a net DOC sink and ultimately a net carbon sink. Based on the net amounts of DOC, oxygen, nitrate and sulfate removed (∼30 μM, ∼80 μM, ∼40 μM and ∼10 mM, respectively) from entrained bottom seawater, organic carbon may be aerobically or anaerobically oxidized in biotic and/or abiotic processes.

The East Pacific Rise from ~ 9–10°N is an archetype for a fast-spreading mid-ocean ridge. In particular, the segment near 9°50'N has been the focus of multidisciplinary research for over two decades, making it one of the best-studied areas of the global ridge system. It is also one of only two sites along the global ridge where two historical volcanic eruptions have been observed. This volcanically active segment has thus offered unparalleled opportunities to investigate a range of complex interactions among magmatic, volcanic, hydrothermal, and biological processes associated with crustal accretion over a full magmatic cycle. At this 9°50'N site, comprehensive physical oceanographic measurements and modeling have also shed light on linkages between hydrodynamic transport of larvae and other materials and biological dynamics influenced by magmatic processes. Integrated results of high-resolution mapping, and both in situ and laboratory-based geophysical, oceanographic, geochemical, and biological observations and sampling, reveal how magmatic events perturb the hydrothermal system and the biological communities it hosts.

A new media, iron coated pottery granules (ICPG) has been developed for As removal from drinking water. ICPG is a solid phase media that produces a stable Fe-Si surface complex for arsenic adsorption. Scanning electron microscopy (SEM) was used to document the physical attributes (grain size, pore size and distribution, surface roughness) of the ICPG media. Several advantages of the ICPG media such as (a) its granular structure, (b) its ability to absorb As via the F(0) coating on the granules' surface; (c) the inexpensive preparation process for the media from clay material make ICPG media a highly effective media for removing arsenic at normal pH. A column filtration test demonstrated that within the stability region (flow rate lower than 15L/h, EBCT >3 min), the concentration of As in the influent was always lower than 50 microg/L. The 2-week system ability test showed that the media consistently removed arsenic from test water to below the 5 microg/L level. The average removal efficiencies for total arsenic, As(III), and As(V) for a 2-week test period were 98%, 97%, and 99%, respectively, at an average flow rate of 4.1L/h and normal pH. Measurements of the Freundlich and Langmuir isotherms at normal pH show that the Freundlich constants of the ICPG are very close to those of ferric hydroxide, nanoscale zero-valent iron and much higher than those of nanocrystalline titanium dioxide. The parameter 1/n is smaller than 0.55 indicating a favorable adsorption process [K. Hristovski, A. Baumgardner, P. Westerhoff, Selecting metal oxide nanomaterials for arsenic removal in fixed bed columns: from nanopowders to aggregated nanoparticle media, J. Hazard. Mater. 147 (2007) 265-274]. The maximum adsorption capacity (q(e)) of the ICPG from the Langmuir isotherm is very close to that of nanoscale zero-valent indicating that zero-valent iron is involved in the process of the As removal from the water. The results of the toxicity characteristic leaching procedure (TCLP) analysis revealed that the media was non-hazardous, as shown by the ND (non-detectable) result for arsenic. The mechanism of As adsorption by ICPG has not been determined. Formation of Fe-Si complexes on the surface of the ICPG system may be responsible for the tight bonding of the As to the IGPC media.

The basaltic ocean crust is the largest aquifer system on Earth, yet the rates of biological activity in this environment are unknown. Low-temperature (100°C) fluid samples were investigated from two borehole observatories in the Juan de Fuca Ridge (JFR) flank, representing a range of upper oceanic basement thermal and geochemical properties. Microbial sulfate reduction rates (SRR) were measured in laboratory incubations with (35)S-sulfate over a range of temperatures and the identity of the corresponding sulfate-reducing microorganisms (SRM) was studied by analyzing the sequence diversity of the functional marker dissimilatory (bi)sulfite reductase (dsrAB) gene. We found that microbial sulfate reduction was limited by the decreasing availability of organic electron donors in higher temperature, more altered fluids. Thermodynamic calculations indicate energetic constraints for metabolism, which together with relatively higher cell-specific SRR reveal increased maintenance requirements, consistent with novel species-level dsrAB phylotypes of thermophilic SRM. Our estimates suggest that microbially-mediated sulfate reduction may account for the removal of organic matter in fluids within the upper oceanic crust and underscore the potential quantitative impact of microbial processes in deep subsurface marine crustal fluids on marine and global biogeochemical carbon cycling.

Transparent exopolymer particles (TEP) have recently been recognized as a class of sticky particles that often stimulate macroaggregate formation. Until now, TEP studies were focused on surface waters, particularly in association with diatom blooms. This is the first report of TEP concentrations in an open ocean deep-sea hydrothermal plume environment. The occurrence of TEP in deep water demonstrates its existence in an environment that is devoid of growing phytoplankton, the organisms generally regarded as TEP's primary source. The main objective of this study was to investigate the presence and potential abundance of TEP within hydrothermal plumes over the Juan de Fuca Ridge. Samples for TEP and bacteria were collected from CTD-rosette casts through hydrothermal plumes over the Juan de Fuca Ridge during the summers of 1999 and 2000. Concentrations of TEP and bacteria within the hydrothermal plumes were significantly greater than in background seawater. TEP number and volume concentrations reported here are low compared to reported values for shallow environments, but are substantially higher than published reports of TEP in other deep water environments. Ratios of TEP anomalies to temperature anomalies (a conservative hydrothermal tracer) increased with distance from the apparent plume source, suggesting that TEP are produced within the aging hydrothermal plumes. Potential TEP sources associated with hydrothermal plumes are discussed. TEP in hydrothermal plumes could stimulate in situ aggregate formation, support populations of attached bacteria, and serve as a potential food source to zooplankton.

Twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms (BAQCs; C14–C33 range) are present in the extractable organic matter of Cenomanian and Turonian black shales of Pasquia Hills (Saskatchewan, Canada). Five of these pseudohomologous series are also observed in a Holocene sample from the Russian Arctic. Three of the pseudohomologous series were identified by Kenig et al. [PNAS 100 (2003) 12554–12558] as 3,3- and 5,5-diethylalkanes (DEAs) and 2,2-dimethylalkanes (DMAs). The nine other pseudohomologous series of BAQCs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3,3-dimethylalkanes (DMAs), 3-ethyl-3-methyl- and 5-ethyl-5-methylalkanes, 9,9-, 7,7-, and 6,6-diethylalkanes (DEAs), 3,3,ω3,ω3- and 5,5,ω5,ω5-tetraethylalkanes, and 5-butyl-5-ethylalkanes. Pseudohomologous series of branched alkanes with tertiary carbon atoms, such as monomethyl- and monoethylalkanes are also present in the same carbon-number range. All these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers, clearly indicating a biosynthetic origin. BAQCs such as 5,5-DEAs, 3,3-DEAs and 3-ethyl-3-methylalkanes seem to be widespread in sediments and sedimentary rocks (ranging from modern to ∼2.1 billion years). A xenobiotic source for BAQCs can be excluded at this point. BAQCs seem to have a very low biodegradability, in part explaining their widespread occurrence in ancient sediments.

Direct evidence for autotrophic ammonia oxidation is documented for the first time in a deep-sea hydrothermal plume. Elevated NH(4) (+) concentrations of up to 341+/-136 nM were recorded in the plume core at Main Endeavour Field, Juan de Fuca Ridge. This fueled autotrophic ammonia oxidation rates as high as 91 nM day(-1), or 92% of the total net NH(4) (+) removal. High abundance of ammonia-oxidizing bacteria was detected using fluorescence in situ hybridization. Ammonia-oxidizing bacteria within the plume core (1.0-1.4x10(4) cells ml(-1)) accounted for 7.0-7.5% of the total microbial community, and were at least as abundant as methanotrophs. Ammonia-oxidizing bacteria were a substantial component of the particle-associated communities (up to 51%), with a predominance of the r-strategist Nitrosomonas-like cells. In situ chemolithoautotrophic organic carbon production via ammonia oxidation may yield 3.9-18 mg C m(-2) day(-1) within the plume directly over Main Endeavour Field. This rate was comparable to that determined for methane oxidation in a previous study, or at least four-fold greater than the flux of photosynthetic carbon reaching plume depths measured in another study. Hence, autotrophic ammonia oxidation in the neutrally buoyant hydrothermal plume is significant to both carbon and nitrogen cycling in the deep-sea water column at Endeavour, and represents another important link between seafloor hydrothermal systems and deep-sea biogeochemistry.

Particles are often regarded as microniches of enhanced microbial production and activities in the pelagic ocean and are vehicles of vertical material transport from the euphotic zone to the deep sea. Fluorescence in situ hybridization (FISH) can be a useful tool to study the microbial community structures associated with these particles, and thus their ecological significance, yet an appropriate protocol for processing deep-sea particle-rich water samples is lacking. Some sample processing considerations are discussed in the present study, and different combinations of existing procedures for preservation, size fractionation sequential filtration, and sonication were tested in conjunction with FISH. Results from this study show that water samples should be filtered and processed within no more than 10 to 12 h after collection, or else preservation is necessary. The commonly used prefiltration formaldehyde fixation was shown to be inadequate for the rRNA targeted by FISH. However, prefiltration formaldehyde fixation followed by immediate freezing and postfiltration paraformaldehyde fixation yielded highly consistent cell abundance estimates even after 96 days or potentially longer storage. Size fractionation sequential filtration and sonication together enhanced cell abundance estimates by severalfold. Size fractionation sequential filtration effectively separated particle-associated microbial communities from their free-living counterparts, while sonication detached cells from particles or aggregates for more-accurate cell counting using epifluorescence microscopy. Optimization in sonication time is recommended for different specific types of samples. These tested and optimized procedures can be incorporated into a FISH protocol for sampling in deep-sea particle-rich waters.

A pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom (BAQCs, specifically 2,2-dimethylalkanes and 3,3- and 5,5-diethylalkanes) were identified in warm (65°C) deep-sea hydrothermal waters and Late Cretaceous black shales. 5,5-Diethylalkanes were also observed in modern and Holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record. The carbon number distribution of BAQCs indicates a biological origin. These compounds were observed but not identified in previous studies of 2.0 billion- to 2.2 billion-year-old metasediments and were commonly misidentified in other sediment samples, indicating that BAQCs are widespread in the geological record. The source organisms of BAQCs are unknown, but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers.

Methane concentration and the stable carbon isotopic composition ( 13 C-CH4) were measured in aging hydrothermal plume waters originating at the Endeavour Segment, Juan de Fuca Ridge. CH4 concen- trations decreased systematically from 600 nM at on-axis stations to 11 nM at a distal station 15 km off axis; background CH4 concentrations are 2 nM. CH4 behaves nonconservatively in plume waters and does not correlate with conservative parameters such as temperature anomaly (), but is highly correlated with NH4 and total dissolvable Mn. 13 C-CH4 values for plume depth samples varies inversely and significantly (R 2 0.89) with methane concentrations normalized to . Some 13 C-CH4 values (1.8 and 10.9 ‰) measured at the 15 km off-axis station are among the heaviest yet reported from a natural marine environment. Less than 5% of original hydrothermal methane remains in the plume at this station. The data are consistent with extensive microbial methane oxidation. A narrow range of fractionation factors (rc 1.0072 to 1.0077) was calculated for the Endeavour samples. These fractionation factors are less than those reported by Coleman et al. (1981), but fall near the trend line of their rc versus temperature data when extrapolated to plume water temperature (2 °C). Copyright © 2002 Elsevier Science Ltd

Bio-acoustic surveys and associated zooplankton net tows have documented anomalously high concentrations of zooplankton within a 100 m layer above the hydrothermal plumes at Endeavour Segment, Juan de Fuca Ridge. These and other data suggest that congregating epi-plume zooplankton are exploiting a food substrate associated with the hydrothermal plume. Ascending, organic-rich particles could provide a connection. Consequently, two paired sequentially sampling ascending and descending particle flux traps and a current meter were deployed on each of three moorings from July 1994 to May 1995. Mooring sites included an on-axis site (OAS; 47°57.0′N, 129°05.7′W) near the main Endeavour vent field, a “down-current” site 3 km west of the main vent field (WS), and a third background station 43 km northeast of the vent field (ES). Significant ascending and descending particle fluxes were measured at all sites and depths. Lipid analyses indicated that ascending POC was derived from mid-depth and deep zooplankton whereas descending POC also contained a component of photosynthetically derived products from the sea surface. Highest ascending POC fluxes were found at the hydrothermal plume-swept sites (OAS and WS). The limited data available, however, precludes an unequivocal conclusion that hydrothermal processes contribute to the ascending flux of organic carbon at each site. Highest ascending to descending POC flux ratios were also found at WS. Observed trends in POC, PMn/PTi, and PFe/PTi clearly support a hydrothermal component to the descending flux at the plume-swept WS site (no descending data was recovered at OAS) but not at the background ES site. Alternative explanations for ascending particle data are discussed. First-order calculations for the organic carbon input (5–22 mg C m−2 d−1) required to sustain observed epi-plume zooplankton anomalies at Endeavour are comparable both to measured total POC flux to epi-plume depths (2–5 mg C m−2 d−1: combined hydrothermal and surface derived organic carbon) and to estimates of the total potential in situ organic carbon production (2–9 mg C m−2 d−1) from microbial oxidation of hydrothermal plume H2, CH4 and NH4+.

Samples of ascending and descending particulate matter from the hydrothermal plume at Endeavour Segment of the Juan de Fuca Ridge were analyzed for their lipid composition to investigate the biogeochemistry of particulate matter associated with oceanic hydrothermal processes. The ascending flux of lipid was up to ≈ six-fold greater than the descending flux, and ascending particles were significantly enriched up to ≈200-fold in lipid compared with descending particles. The dominant fatty acids in both ascending and descending particles were C16:1, C18:1ω9, C20:1, and C22:1, and the major neutral lipids were C20:1 and C22:1 fatty alcohols and cholesterol. C20:1 and C22:1 alcohols constituted up to >70% of neutral lipids in ascending particles at sites directly influenced by the plume, compared to 54% at the background site and 35 to 54% in descending particles. Comparison with zooplankton collected above the plume suggested that a large fraction of this lipid was derived from zooplankton that may be opportunistically feeding on organic matter associated with the plume. The high flux of lipid moving upward in the water column in the vicinity of the vent plume is roughly equivalent to downward fluxes at similar oceanic depths and suggests an important mechanism by which particulate lipids may be dispersed in the marine water column.

The Axial Response Team (ART-1) documented greatly intensified chronic-style hydrothermal plumes at Axial Volcano following a 1998 eruptive event. Significantly higher numbers of bacteria were found in the plume versus background stations and depths, due largely to 5 samples with high numbers (to 1.8×105 /ml) in far field stations. Highest ratios (0.20) of metal depositing capsuled bacteria to total bacteria were found in the near-field (over caldera) plume. An unusual capsule form (FeCap), that dominated the near field plume capsule populations, was present in all plume samples, but were absent in background samples. Multi-cell filaments, metal-encrusted sheathed clusters and matrix-enmeshed colonies, all uncommon in the water column, were also present in plume samples

In response to 12 days of seismic activity at Axial Volcano, Juan de Fuca Ridge in January–February 1998, the NSF/NOAA-sponsored Axial Response Team conducted three response cruises in February, August, and August/September to map and sample hydrothermal plumes over the region. Vertical profiles of particulate Fe and S over the eruption site show high concentrations from about 1400 m to the bottom. Chemical and scanning electron microscope analysis of the February plume samples revealed anhydrite, Fe-ferrihydrites, elemental sulfur, and angular glassy basalt shards up to 190 µm in the longest dimension. Many of these shards had halite coatings, which is consistent with subseafloor basalt seawater reactions at temperatures >450°C at 1500 m depth. In August and September cruises the basalt shards were no longer present in the hydrothermal plumes. Instead, the plumes were predominantly composed of Fe-ferrihydrites, elemental sulfur, and sulfur filaments. A unique feature of this data set is the high concentrations of elemental sulfur in the lower 60 m of the water column. The sulfur results are suggestive of a significant enrichment of the bacterial biomass in the water column over the eruption site with time. Within the Axial caldera, approximately 10–20% of the total sulfur is present as sulfur filaments. These post-eruption particle compositional changes have strong similarities to the results from the 1993 CoAxial eruption on the Juan de Fuca Ridge.

During the February response cruise to Axial Volcano, methane and hydrogen concentrations within the plume were significantly elevated above background. CH 4 / 3 He ratios were found to be 5-10 times greater than previously reported values for unsedimented ridges. An average δ 13 C value of -32.7±0.8‰ was determined for CH 4 concentrations > 10 nM and CH 4 /Mn ratios were determined to be 2.2. Hydrogen concentrations as high as 183 nM were measured; however most were < 10 nM. Microbial oxidation of methane was negligible (

A volcanic eruption at the summit of Axial Volcano on January 25, 1998, instantaneously created extensive and vigorous hydrothermal discharge. Moorings 2 km apart along the eruption fissure recorded temperature increases of ∼0.6°C up to 115 m above bottom within hours of initial seismic activity. Water temperatures at the mooring sites remained high for about 5 days, then declined steadily over the next 2 weeks. A response cruise 18 days after the eruption found hydrothermal temperature anomalies of ∼0.1°C over the eruption site, and a more intense and much thicker plume 20 km downstream of the eruption. We estimate the steady-state heat flux required to produce this distal plume, evidence of discharge conditions perhaps 1-13 days after the eruption, as 60-230 GW. The Axial eruption thus produced the largest vent field heat flux yet measured, but these high levels lasted less than 3 weeks.

Modern benthic foraminifera are important remineralizers of organic matter and a link between surface-ocean production and life in the deep sea. Assemblages of benthic foraminifera are preserved in the fossil record, providing clues to paleoceanographic conditions. These clues can be fully interpreted only when our knowledge of the biology and ecology of modern species is more complete. To study factors influencing foraminiferal colonization rates, artificial substrates were placed on Cross Seamount (18°40′N, 158°17′W) for 1 to 42 months between 1989 and 1994. The colonization rates of benthic foraminifera onto different substrates (five mineral types were used) at four water depths (800, 975, 1285 and 2000 m) were determined. Both calcareous and agglutinated foraminifera inhabited these artificial substrates at different rates. Many of the agglutinated forms colonized at a uniform rate through time. The colonization rates of other foraminifera, primarily calcareous forms, were not constant through time, nor could the variability be attributed to the controlled variables (water depth and substrate composition). Instead, these temporal variations in colonization rate corresponded with shifts in surface ocean conditions and export fluxes in the central Pacific. Other ecological observations are also presented, including size- and spatial-distributions.

Event plumes form as episodic discharges of large volumes of hydrothermal solutions in response to magmatic diking/eruptive events. In consequence, event plumes represent the sudden injection of exploitable reduced chemical substrates, as well as inhibitory constituents, and likely induce successional changes in the microbial community structure and activity within event plume waters. In response to a major seismic event detected beginning 28 February 1996 at the northern Gorda Ridge, a series of three rapid response and follow-up cruises (GREAT 1, 2 and 3) were mounted over a period of three months. This report focuses on time-series measurements of manganese geomicrobial parameters in the two event plumes found in association with this seismic event. Scanning transmission electron microscopy, elemental microanalysis, and radioisotope (54Mn) uptake experiments were employed on samples collected from vertical and tow-yo casts from the three cruises. Numbers of bacteria and ratios of metal precipitating capsuled bacteria to total bacteria were greatest in the youngest (days old) plume, EP96A, found during GREAT 1; however, when normalized to the hydrothermal temperature anomaly, the greatest values were found in a second event plume, EP96B, discovered during GREAT 2 (up to 1 month old). Early capsule bacteria and particulate Mn distributions may have been influenced by entrainment of resuspended sediment, while those of the oldest (2–3 months) plume sample may have been subjected to preferential aggregation and particle settling.

Anomalously high concentrations of NH+4 in hydrothermal vent discharge fluids were tracked in the resulting neutrally buoyant plume over the unsedimented Endeavour Segment, Juan de Fuca Ridge. Vertical profiles of NH+4 concentrations showed plume depth (∼2025 m) maxima of nearly 400 nM over the Endeavour Segment’s main vent field, on the same order as most subsurface NH+4 maxima. Plume NH+4 values decreased to just above background deep water values (50–70 nM) in older plume water at a station 15 km southwest of the vent field, although most of the plume NH+4 appears to be transported beyond the ridge axial valley. Preliminary net specific NH+4 removal rates determined within the plume maximum (0.04–0.13 d-1) and corresponding turnover times (8–28 d) are similar to values for CH4 oxidation rates. The data suggest that NH+4 may be a significant substrate for in situ chemolithotrophic production of organic matter in the Endeavour Segment hydrothermal plume.

The walls of many deep-sea foraminiferal tests contain abiogenic and biogenic, precip- itated and agglutinated, components. Both environmental and genetic factors can contribute to the great diversity in test form and composition in benthic foraminifera. Yet, small specimen size and the remoteness of the deep-sea environment have limited our ability to describe the relative influence of these biological and chemical factors. The use of fossilized foraminiferal tests as paleo-indicators requires that we understand the controls on test composition. Test wall morphology and composition were examined in foraminifera that colonized experimental substrates deployed on a seamount in the central North Pacific. Three types of agglutinated forms were identified. A triserial (Eggerella- like) and two-chambered (Hyperammina-like) form contained a Ca-rich (CaCO3) precipitate and the chamber walls of an encrusting two-chambered form was Ba-rich (BaSO4). We discuss the composi- tion of these biologically precipitated minerals in the context of the environmental conditions during the life of these foraminifera.

Two-thirds of Earth's surface is formed at mid-ocean ridges, yet sea-floor spreading events are poorly understood because they occur far beneath the ocean surface. At 9 degrees 50'N on the East Pacific Rise, ocean-bottom seismometers recently recorded the microearthquake character of a mid-ocean ridge eruption, including precursory activity. A gradual ramp-up in activity rates since seismic monitoring began at this site in October 2003 suggests that eruptions may be forecast in the fast-spreading environment. The pattern culminates in an intense but brief (approximately 6-hour) inferred diking event on 22 January 2006, followed by rapid tapering to markedly decreased levels of seismicity.

A technique was developed to image marine snow particles by scanning confocal laser microscopy (SCLM). This method allows structural and compositional characterization of fully hydrated marine snow particles with minimal disruption of the particle structure. High specificity fluorescent stains permitted sequential imaging of selected polysaccharides (concanavalin A: specific for mannose and glucose polymers), proteins [5-(4,6-dichlorotriazin-2-yl) aminofluorescein], and DNA (propidium iodide). Chl a autofluorescence can also be imaged. SCLM produced optical slices of marine snow particles that were suited for a number of image-processing applications. These applications include high-resolution fluorescently derived optical slices and composite images produced from combined optical slices. Initial observations suggest that marine snow particles found in the oligotrophic Pacific Ocean vary in composition and structure. Variations in polysaccharide and protein composition of marine snow particles may be related to particle morphology. When combined with other conventional analysis, such as epifluorescent and electron microscopy, LSCM can provide important contributions to characterizing composition and structure of marine snow.

Barite formation in the surface oceans is generally assumed to be dominated by abiotic precipitation. Acceptance of this pathway is largely the result of the absence of a pelagic marine organism known to precipitate the ovoid to rounded-rectangular barite crystals typically observed in marine waters and sediments. Barite crystals observed in net-tow particles and on substrates retrieved from the seafloor (both in the central North Pacific) were examined by scanning electron microscopy and energy dispersive X-ray spectrometry. Three distinct crystalline forms of bar&e were observed: ovoid and hexagonal crystals several microns in diameter, and aggregates of submicron-sized crystals. Ovoid and hexagonal-type crystals contained between 0 and 26 mole percent SrS04. The microcrystalline barite contained no detectable Sr (CO.05 percent). Hexagonal-type crystals were precipitated by an unusual benthic foraminifera. Comparison of the morphology and composition of the barite crystals observed in this study to crystals precipitated by a variety of biotic and abiotic processes suggests a biotic origin for the ovoid barite crystals, the most common form of barite observed in this region.

Despite its immense size, logistical and methodological constraints have largely limited microbiological investigations of the subseafloor basement biosphere. In this study, a unique sampling system was used to collect fluids from the subseafloor basaltic crust via a Circulation Obviation Retrofit Kit (CORK) observatory at Integrated Ocean Drilling Program borehole 1301A, located at a depth of 2667 m in the Pacific Ocean on the eastern flank of the Juan de Fuca Ridge. Here, a fluid delivery line directly accesses a 3.5 million years old basalt-hosted basement aquifer, overlaid by 262 m of sediment, which serves as a barrier to direct exchange with bottom seawater. At an average of 1.2 × 10(4) cells ml(-1), microorganisms in borehole fluids were nearly an order of magnitude less abundant than in surrounding bottom seawater. Ribosomal RNA genes were characterized from basement fluids, providing the first snapshots of microbial community structure using a high-integrity fluid delivery line. Interestingly, microbial communities retrieved from different CORKs (1026B and 1301A) nearly a decade apart shared major community members, consistent with hydrogeological connectivity. However, over three sampling years, the dominant gene clone lineage changed from relatives of Candidatus Desulforudis audaxviator within the bacterial phylum Firmicutes in 2008 to the Miscellaneous Crenarchaeotic Group in 2009 and a lineage within the JTB35 group of Gammaproteobacteria in 2010, and statistically significant variation in microbial community structure was observed. The enumeration of different phylogenetic groups of cells within borehole 1301A fluids supported our observation that the deep subsurface microbial community was temporally dynamic.

Vertical concentration profiles of the dissolved and suspended particulate phases were determined for a suite of reactive trace metals, Al, Fe, Mn, Zn, and Cd, during summertime at a station in the center of the North Pacific gyre. During summer the euphotic zone becomes stratified, forming a shallow (0–25 m), oligotrophic, mixed layer overlying a subsurface (25–140 m), strongly-stratified region. The physical, biological, and chemical structure within the euphotic zone during this period enhanced the effect of atmospheric inputs of Al, Fe, and Mn on mixed layer concentrations. For example, the concentration of dissolved Fe in the surface mixed layer was eighteen times that observed at a depth of 100 m. The observed aeolian signature of these metals matched that predicted from estimates of atmospheric input during the period between the onset of stratification and sampling. The distributions of suspended particulate Al, Fe, and Mn all exhibited minima in the euphotic zone and increased with depth into the main thermocline. Particulate Al and Fe were then uniform with depth below 1000 m before increasing in the near bottom nepheloid layer. Average particulate phase concentrations in intermediate and deep waters of the central North Pacific were 1.0, 0.31, and 0.055 nmol · kg −1 for Al, Fe, and Mn, respectively. The distribution of particulate Cd exhibited a maximum within the subsurface euphotic zone. Particulate zinc also exhibited a surface maximum, albeit a smaller one. Concentrations of particulate Zn and Cd in intermediate and deep waters were 17 and 0.2 pmol·kg −1 . Substantial interbasin differences in particulate trace metals occur. Concentrations of suspended particulate Al, Fe, and Mn were three to four times lower in the central North Pacific than recently reported for the central North Atlantic gyre, consistent with differences in atmospheric input to these two regions. Concentrations of suspended particulate Cd and Zn were enriched in the North Pacific relative to the North Atlantic, an observation consistent with their assimilation by plankton. Reactive trace metals exhibit a range of biogeochemical behaviors that can be characterized by two endmembers, nutrient-type and scavenged-type. Nutrient-type metals, best exemplified by Zn and Cd, are primarily removed from surface waters by biogenic particles and then remineralized at depth. Internal biogeochemical cycles together with physical mixing and circulation patterns control the distributions of nutrient-type metals. Scavenged-type metals, best exemplified by Al, continue to be removed onto particles in intermediate and deep waters as well as at the surface. External inputs, such as the deposition of aeolian dust, control the concentrations and distributions of scavenged-type metals. Other metals, such as Fe, exhibit a mixture of the characteristic behaviors of these two endmembers.

Subduction of oceanic crust and the formation of volcanic arcs above the subduction zone are important components in Earth’s geological and geochemical cycles. Subduction consumes and recycles material from the oceanic plates, releasing fluids and gases that enhance magmatic activity, feed hydrothermal systems, generate ore deposits and nurture chemosynthetic biological communities. Among the first lavas to erupt at the surface from a nascent subduction zone are a type classified as boninites. These lavas contain information about the early stages of subduction, yet because most subduction systems on Earth are old and well-established, boninite lavas have previously only been observed in the ancient geological record. Here we observe and sample an active boninite eruption occurring at 1,200 m depth at the West Mata submarine volcano in the northeast Lau Basin, southwest Pacific Ocean. We find that large volumes of H2O, CO2 and sulphur are emitted, which we suggest are derived from the subducting slab. These volatiles drive explosive eruptions that fragment rocks and generate abundant incandescent magma-skinned bubbles and pillow lavas. The eruption has been ongoing for at least 2.5 years and we conclude that this boninite eruption is a multi-year, low-mass-transfer-rate eruption. Thus the Lau Basin may provide an important site for the long-term study of submarine volcanic eruptions related to the early stages of subduction. Boninite lavas are erupted during the early stages of subduction, however they have previously been found only in the ancient geological record. Discovery of an active boninite eruption shows that abundant volatile gases derived from the subducting slab drive this violent eruptive activity, even in the deep sea.

Calcareous nannofossil biostratigraphy was employed to determine the age and growth rates of the different layers within ferromanganese crusts from Schumann Seamount, 200 miles north of the island of Kauai, Hawaii. This work is part of a study to reconstruct the paleoceanographic history of crusts using various geochemical indicators. The methods are based on the identification of coccolith imprints, not actual coccolith remains. Age constraints on the time span of a particular horizon are defined either (1) by the presence of a species which was extant for only a limited geological time interval or (2) by the presence of two organisms whose time ranges overlapped. Age resolution is optimized by short time ranges or narrow overlaps. In the crust studied there was considerable inter-horizon variability in the preservation of coccolith imprints, in imprint abundance and in species diversity. Some of the crust layers examined were narrowly constrained temporally (1–4 Myr), while others were less so (> 10 Myr). Our results indicate that the minimum age for the interval at 27 mm depth is at least Eocene. This is the maximum age many believe any crust can be. The position of this interval, however, is only about one half of the way through the crust. While the data support previous estimates of average crust growth rates (0.5 mm/Myr), the actual apparent growth rate appears to have varied by an order of magnitude (0.1 to 2 mm/Myr).

In September 1987 we collected samples for the determination of 222 Rn, 226 Ra, and dissolved and particulate manganese in “Megaplume 2” above the Juan de Fuca Ridge spreading center. The results of these analyses permit us to estimate the apparent age of the megaplume by two independent methods. The age estimate based on excess 222 Rn is 20±9 days. Based on the partitioning of manganese between the dissolved and particulate phases the age is estimated to be between 6 and 60 days. Both techniques confirm that Megaplume 2 was a separate hydrothermal event and that it was not Megaplume 1 sampled 1 year after it was first discovered.

[1] As part of a rapid response cruise in May 2006, we surveyed water column hydrothermal plumes and bottom conditions on the East Pacific Rise between 9°46.0′N and 9°57.6′N, where recent seafloor volcanic activity was suspected. Real-time measurements included temperature, light transmission, and salinity. Samples of the plume waters were analyzed for methane, manganese, helium concentrations, and the δ13C of methane. These data allow us to examine the effects of the 2005–2006 volcanic eruption(s) on plume chemistry. Methane and manganese are sensitive tracers of hydrothermal plumes, and both were present in high concentrations. Methane reached 347 nM in upper plume samples (250 m above seafloor) and exceeded 1085 nM in a near-bottom sample. Mn reached 54 nM in the upper plume and 98 nM in near-bottom samples. The concentrations of methane and Mn were higher than measurements made after a volcanic eruption in the same area in 1991, but the ratio of CH4/Mn, at 6.7, is slightly lower, though still well above the ratios measured in chronic plumes. High concentrations of methane in near-bottom samples were associated with areas of microbial mats and diffuse venting documented in seafloor imagery. The isotopic composition of the methane carbon shows evidence of active microbial oxidation; however, neither the fractionation factor nor the source of the eruption-associated methane can be determined with any certainty. Considerable scatter in the isotopic data is due to diverse sources for the methane as well as fractionation as methane is consumed. One sample at +21‰ versus Peedee belemnite standard is among the most enriched methane carbon values reported in a hydrothermal plume to date.

The biogeochemical scavenging of dissolved manganese (Mn) from hydrothermal plumes was investigated using radiotracer ( 54 Mn) techniques. The measured scavenging rate constant, k 1 , was lowest in the buoyant plume ( −1 ), increasing to ∼2 y −1 in the non-buoyant plume at distances of 20 km from the ridge valley axis. The direct biological contribution to the dissolved Mn scavenging rate (i.e the fraction suppressed by the addition of a metabolic poison) also increased over the same distances, being minor or absent at plume depths in the proximal plume, yet the major component at distal plume stations. These and other data suggest that the capacity for scavenging dissolved Mn onto particles evolves with increasing age of the plume, suggestive of a microbial response to changing conditions within the plume. Estimated maximum scavenging rates of dissolved Mn onto particles ( R DMn = k 1 [DMn])were noted at plume depths for all stations, a function of very high dissolved Mn concentrations in the case of the buoyant plume and proximal non-buoyant plume. R DMn values, integrated over plume depths, ranged from 3.4 to 1.7 mM m −2 y −1 for the non-buoyant plume at on-axis and off-axis stations, respectively. The application of the data to the dispersal of hydrothermal constituents and to plume aging is discussed.

Marine ferromanganese oxide crust fragments sampled from a massive equatorial Pacific Ocean crust deposit exhibit distinct micromorphological features and a microchemical distribution which have not been previous reported. Black, shiny upper layers of the crust display a prismoidal microstructure and a unique crystallite habit expressed by a mosaic-like design of hexagonal and pentagonal columns. This columnar arrangement, which has been previously reported on a scale of a few millimeters in other marine Fe-Mn deposits, extends vertically for several centimeters and is observed throughout the entire horizontal plane of growth of the crust, and is the largest scale of morphological regularity observed in marine Fe-Mn deposits to date. The polygonal columnar structures which constitute the crust are mainly composed of Mn, Fe, and Ti oxides. Aluminium- and Si-rich intercolumnar space (lamellae) surrounds individual columns and sharply defines each polyhedron. Additionally, the chemical composition of the crust fragments exhibits an unusual uniformity over several centimeters which, to our knowledge, has not been previously observed in marine Fe-Mn minerals.

The distributions of dissolved, particulate and sedimentary phosphorus were measured in the region of the Juan de Fuca Ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans. Significant negative dissolved phosphate anomalies, ranging from 0 to 60 nmol/l, were observed in the water column at depths between 1900 and 2300 db. The largest anomalies (

A protocol to enumerate particle-associated microbial indicator bacteria (heterotrophic plate count [HPC], enterococci [ENT] and Clostridium perfringens [CP]) by membrane filtration in a tropical stream is proposed that relies on high-speed homogenization and chemical treatment. Application of this protocol to stream samples suggest that ENT measurements are more biased by the presence of aggregates than HPC or CP. Whole sample treatment typically increased the colony forming units (CFU) count by 9–52%. Analysis of different settled fractions and examination of the number of indicators recoverable from particles retained on a 5 μm filter in relation to the number of particles containing target indicators both indicate that relatively more ENT form aggregates than HPC or CP. Although the bias is smallest for CP, this does not imply that CP is a better indicator as this depends on the unknown extent to which pathogens are themselves found associated with particles.

Low-temperature hydrothermal fluids, circulating within the vast volume of sediment-buried upper oceanic basement on the flanks of the global mid-ocean ridge system, represent a largely unexplored habitat that could potentially host a significant and unique microbial biosphere. The present state of knowledge and many remaining challenges are discussed.

Magmatic events are unpredictable dynamic processes that are integral to the evolution of mid-ocean ridges. Dikes and lava flows develop rapidly and instantly alter the local hydrothermal flow regime, initiating dramatic changes in hydrothermal discharge at the seafloor, and triggering geochemical and microbiological changes within the shallow crust, at the seafloor and within the overlying water column. Despite considerable logistical difficulties, real-time remote detection capabilities (SOSUS) along limited regions of the MOR system have allowed investigators to rapidly respond to significant seismic events. There have been more than 20 documented examples of seafloor volcanic/tectonic events, at both isolated volcanoes and mid-ocean ridges, but only a few of these have led to significant response efforts. The most rapid and thorough response efforts have been to the 1991 9° N EPR event and several events (1986, 1993, 1996, 1998, 2001) on the Juan de Fuca and Gorda Ridges. Together these 'SOSUS directed' responses plus the few serendipitous encounters have led to important discoveries (e.g., event plumes; 'snow-blower' vents) and provided basic new constraints on presently immature models of submarine magmatic-hydrothermal systems (e.g., intrusive/extrusive diking; event plume formation; subsurface hydrothermal communities). The event response community has gained valuable experience in learning how to exploit these opportunities for scientific observation and is currently poised to continue such studies with increased speed and efficiency. However, our understanding of these geophysical, chemical and biological processes is only in their infancy.

Little is known about the potential for life in the vast, low-temperature (

[1] Sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast Pacific Ocean between July 1994 and May 1995. One mooring was deployed near the Main Vent field on Endeavour Ridge (On-Axis site, 47°57.0′N, 129°05.7′W), a second, 3 km west of the Main vent site (West site), and the third, 43 km northeast of the Main vent site (East or background site). Ascending and descending particles were collected near 1600 and 2000 m depth, well above and within the top of laterally spreading hydrothermal plumes. The elemental composition of particles was used to evaluate their origins: biogenic fluxes were indicated by elevated Ca or Si, hydrothermal fluxes by elevated Fe, Mn, and Cu, and lithogenic fluxes by elevated Ti. We link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean. The relatively low hydrothermal Fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material. These results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below.

The migration and evolution of a deep ocean hydrothermal event plume were tracked with a neutrally buoyant RAFOS float. The float remained entrained in the plume for 60 days, and the plume vorticity was calculated directly from the anticyclonic motion of the float. Concentrations of suspended particles, particulate iron, and dissolved manganese in the plume did not decay significantly during the 60 days, which indicates that event plumes would be easily detectable a year after formation.