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Located 10° further north than any sponge ground yet reported, the population, primarily comprising Geodia parva, G. hentscheli and Stelletta rhaphidiophora individuals, covers the great majority of the Langseth Ridge from ∼1,000 m upward, to a shallowest peak of 580 m depth, at very high abundance1. Sizes of individual sponges varied, with a median diameter of 17 cm (± 0.10 cm SE, n = 10,839, and IQR 11–25 cm); the maximum diameter observed was 110 cm and the smallest were just over 1 cm. This size range equates to a median wet weight of 1.4 kg (± 0.12 kg SE, n = 10,839; IQR 0.4–5 kg; Figure S1). Sponges are opportunistic feeders; although they efficiently retain particulates by filter feeding, dissolved organic matter in seawater often represents the main food source2. The low productivity and nutrient fluxes that characterize this region — due to high latitude, permanent sea ice cover, and distance from land — raise the question of how this abundant biomass is maintained. We analyzed the many trails of interwoven spicules across the seamount peaks. Trails were observed to be several centimeters in height and up to meters in length, often connected directly to living sponges. These trails were particularly visible in areas of low sponge density, that is, where trails crossed bedrock in areas sparsely covered by sediments or organic debris (Figure 1A–E and Video S1). Spicule trails in areas of denser sponge aggregation exhibited a higher vertical thickness than observed elsewhere (Figures 1F and S1A, and Video S1). Our observations also suggest that the spicule trails correlated with the distribution of smaller juvenile sponges (Figure S1A).

High acoustic seafloor-backscatter signals characterize hundreds of patches of methane-derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the Nile Deep Sea Fan (NDSF) in the Eastern Mediterranean Sea. During a high-resolution ship-based multibeam survey covering a ~ 225 km2 large seafloor area in the Central Province of the NDSF we identified 163 high-backscatter patches at water depths between 1500 and 1800 m, and investigated the source, composition, turnover, flux and fate of emitted hydrocarbons. Systematic Parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies (flares), indicative of gas bubble streams, above 8% of the high-backscatter patches. In echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution. Visual inspection of three high-backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter. Volume estimates, considering results from high-resolution autonomous underwater vehicle (AUV)-based multibeam mapping, were used to calculate the amount of carbonate-bound carbon stored in these slabs. Additionally, the flux of methane bubbles emitted at one high-backscatter patch was estimated (0.23 to 2.3 × 106 mol a− 1) by combined AUV flare mapping with visual observations by remotely operated vehicle (ROV). Another high-backscatter patch characterized by single carbonate pieces, which were widely distributed and interspaced with sediments inhabited by thiotrophic, chemosynthetic organisms, was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption (0.1 to 1 × 106 mol a− 1) and dissolved methane flux (2 to 48 × 106 mol a− 1). Our comparison of dissolved and gaseous methane fluxes as well as methane-derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo-, bio-, and hydrosphere at cold seeps.

Tommeliten is a prominent methane seep area in the Central North Sea. Previous surveys revealed shallow gas-bearing sediments and methane gas ebullition into the water column. In this study, the in situ methane flux at Tommeliten is re-assessed and the potential methane transport to the atmosphere is discussed, with regards to the hydrographic setting and gas bubble modeling. We have compiled previous data, acquired new video and acoustic evidence of gas bubble release, and have measured the methane concentration, and its C-isotopic composition in the water column. Parametric subbottom sonar data reveal the three-dimensional extent of shallow gas and morphologic features relevant for gas migration. Five methane ebullition areas are identified and the main seepage area appears to be 21 times larger than previously estimated. Our video, hydroacoustic, subbottom, and chemical data suggest that similar to 1.5 x 10(6) mol CH(4)/yr (similar to 26 tons CH(4)/yr) of methane gas is being released from the seepage area of Tommeliten. Methane concentration profiles in the vicinity of the gas seeps show values of up to 268 nM (similar to 100 times background) close to the seafloor. A decrease in delta(13)C-CH(4) values at 40 m water depth indicates an unknown additional biogenic methane source within the well oxygenated thermocline between 30 and 40 m water depth. Numerical modeling of the methane bubbles due to their migration and dissolution was performed to estimate the bubble-derived vertical methane transport, the fate of this methane in the water column, and finally the flux to the atmosphere. Modeling indicates that less than similar to 4% of the gas initially released at the seafloor is transported via bubbles into the mixed layer and, ultimately, to the atmosphere. However, because of the strong seasonality of mixing in the North Sea, this flux is expected to increase as mixing increases, and almost all of the methane released at the seafloor could be transferred into the atmosphere in the stormy fall and winter time.

Gulf of Mexico cold seeps characterized by variable compositions and magnitudes of hydrocarbon seepage were sampled in order to investigate the effects of natural oils, methane, and non-methane hydrocarbons on microbial activity, diversity, and distribution in seafloor sediments. Though some sediments were characterized by relatively high quantities of oil, which may be toxic to some microorganisms, high rates of sulfate reduction (SR, 27.9714.7 mmol m

The Gulf of Cadiz is a tectonically active area of the European continental margin and characterised by a high abundance of mud volcanoes, diapirs, pockmarks and carbonate chimneys. During the R/V SONNE expedition ‘‘GAP–Gibraltar Arc Processes (SO-175)’’ in December 2003, several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover. Pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes Captain Arutyunov, Bonjardim, Ginsburg, Gemini and a newly discovered, mud volcano-like structure called ‘‘No Name’’ show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed. The presence of a distinct sulphate–methane transition zone (SMT) overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor. Anaerobic oxidation of methane (AOM) and sulphate reduction (SR) rates show maxima at the SMT, which was found between 20 and 200 cm below seafloor at the different mud volcanoes. In comparison to other methane seeps, AOM activity (

Microbial methanogenesis in the subsurface seafloor is responsible for the formation of large and dynamic gas reservoirs like the recently discovered gas hydrate deposits. Gas seepage occurs wherever methane builds up an overpressure outside the hydrate stability field, illustrating the potential importance of ocean margins for the global methane budget. However, a variety of bacteria and archaea are capable of methane consumption, and control the emission of methane to the hydrosphere. Unfortunately, much less is known about the microbial methane turnover in the ocean than about methane turnover in freshwater or terrestrial habitats. This investigation compares rates of methane production, anaerobic and aerobic methane oxidation at different marine sites, combining radiotracer (on-site) and in vitro measurements. Samples were obtained from gas hydrate bearing sediments, cold seeps, organic-rich and organic-poor subsurface sediments. All investigated subsurface sediments had the potential for methanogenesis as well as for methanotrophy. The anaerobic oxidation of methane (AOM) was highest in samples from gas hydrate areas and cold seeps. AOM was strongly influenced by methane partial pressure and temperature, indicating a substantial underestimation of in situ activity with current ex situ measuring techniques. A potential for aerobic methane oxidation was detected at all sites where the sediment had contact with oxic bottom water. A first comparison of methane turnover rates in diverse marine habitats showed that microbial methane oxidation provides a very effective barrier for methane emissions from the subsurface seafloor. D 2005 Elsevier B.V. All rights reserved.

The anaerobic oxidation of methane in aquatic environments is a globally significant sink for a potent greenhouse gas. Significant gaps remain in our understanding of the anaerobic oxidation of methane because data describing the distribution and abundance of putative anaerobic methanotrophs in relation to rates and patterns of anaerobic oxidation of methane activity are rare. An integrated biogeochemical, molecular ecological and organic geochemical approach was used to elucidate interactions between the anaerobic oxidation of methane, methanogenesis, and sulfate reduction in sediments from two cold seep habitats (one brine site, the other a gas hydrate site) along the continental slope in the Northern Gulf of Mexico. The results indicate decoupling of sulfate reduction from anaerobic oxidation of methane and the contemporaneous occurrence of methane production and consumption at both sites. Phylogenetic and organic geochemical evidence indicate that microbial groups previously suggested to be involved in anaerobic oxidation of methane coupled to sulfate reduction were present and active. The distribution and isotopic composition of lipid biomarkers correlated with microbial distributions, although concrete assignment of microbial function based on biomarker profiles was complicated given the observed overlap of competing microbial processes. Contemporaneous activity of anaerobic oxidation of methane and bicarbonate-based methanogenesis, the distribution of methane-oxidizing microorganisms, and lipid biomarker data suggest that the same microorganisms may be involved in both processes.

Anaerobic oxidation of methane (AOM) and sulfate reduction (SR) were investigated in sediments of the Chilean upwelling region at three stations between 800 and 3000 In water depth. Major goals of this study were to quantify and evaluate rates of AOM and SR in a coastal marine upwelling system with high organic input, to analyze the impact of AOM on the methane budget, and to determine the contribution of AOM to SR within the sulfate-methane transition zone (SMT). Furthermore, we investigated the formation of authigenic carbonates correlated with AOM. We determined the vertical distribution of AOM and SR activity, methane, sulfate, sulfide, pH, total chlorins, and a variety of other geochemical parameters. Depth-integrated rates of AOM within the SMT were between 7 and 1124 mmol m(-2) a(-1), effectively removing methane below the sediment-water interface. Single measurements revealed AOM peaks of 2 to 51 nmol cm(-3) d(-1), with highest rates at the shallowest station (800 m). The methane turnover was higher than in other diffusive systems of similar ocean depth. This higher turnover was most likely due to elevated organic matter input in this upwelling region offering significant amounts of substrates for methanogenesis. SR within the SMT was mostly fuelled by methane. AOM led to the formation of isotopically light DIC (delta(13)C: -24.6 parts per thousand VPDB) and of distinct layers of authigenic carbonates (delta(13)C: - 14.6 parts per thousand VPDB). Copyright (c) 2005 Elsevier Ltd.

The processes of methane oxidation and sulfate reduction were examined in subsamples of gas hydrate associated materials collected along the Gulf of Mexico continental slope. Standard radiotracer techniques were used to determine rates of microbial activity in different layers of the hydrate environment, including outer sediment (OS), interface sediment (IS), worm burrow sediment (WB), interior hydrate (IN) and a mixture of hydrate and sediment (MIX). The anaerobic oxidation of methane (AOM) and sulfate reduction (SR) were observed in all hydrate samples examined and the rates of these processes showed similar spatial trends between different hydrate layers. Highest rates of both AOM and SR were observed at interface between the sediment and hydrate. AOM rates were about 3–11 nmol cm � 3 day � 1 in worm burrow and interface sediments as compared to

Hydrate Ridge, Cascadia convergent margin, is characterized by abundant methane hydrates at and below the seafloor, active venting of fluids and gases, chemosynthetic communities composed of giant sulfide-oxidizing bacteria and clams, authigenic carbonates, and some of the highest methane oxidation rates ever found in the marine environment. Fluid flow rates vary over six orders of magnitude among closely spaced settings at the crest of Hydrate Ridge. The distribution of benthic communities is mainly related to the sulfide flux from the subsurface sediments produced by anaerobic oxidation of methane (AOM). Even at high flux rates, AOM removes most of the methane seeping from the subsurface. Less than 50% of the methane escapes from bacterial mats, from Calyptogena fields

Gravity driven mass-flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western Argentine Basin. In this study we present geochemical data from a total of 23 gravity cores. Pore-water SO 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane (AOM). The different shapes of SO 4 profiles (concave, kink- and s-type) can be consistently explained by sedimentary slides possibly in combination with changes in the CH 4 flux from below, thus, mostly representing transient pore-water conditions. Since slides may keep their original sedimentary signature, a combined analysis and numerical modeling of geochemical, physical properties, and hydro acoustic data could be applied in order to reconstruct the sedimentary history. We present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day. The results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep-sea, depositing high amounts of reactive compounds. The high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by AOM. For the total region we estimate a SO 4 (or CH 4 ) flux of 6.6 × 10 10 moles per year into the zone of AOM. Projected to the global continental slope and rise area, this may sum up to about 2.6 × 10 12 moles per year. Provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1.2 × 10 12 moles per year as previously estimated. Thus, AOM obviously contributes very significantly to the regulation of global sulfur reservoirs, which is hitherto not sufficiently recognized. This finding may have implications for global geochemical models, as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time.

Time-series measurements of particulate organic carbon (POC) and particulate nitrogen (PN) fluxes, sediment community composition, and sediment community oxygen consumption (SCOC) were made at the Hawaii Ocean Time-series station (Sta. ALOHA, 4730 m depth) between December 1997 and January 1999. POC and PN fluxes, estimated from sediment trap collections made at 4000 m depth (730 m above bottom), peaked in late August and early September 1998. SCOC was measured in situ using a free vehicle grab respirometer that also recovered sediments for chemical and biological analyses on six cruises during the 1-year study. Surface sediment organic carbon, total nitrogen and phaeopigments significantly increased in September, corresponding to the pulses in particulate matter fluxes. Bacterial abundance in the surface sediment was highest in September with a subsurface high in November. Sediment macrofauna were numerically dominated by agglutinating Foraminifera fragments with highest density in September. Metazoan abundance, dominated by nematodes was also highest in September. SCOC significantly increased from a low in February to a high in September. POC and PN fluxes at 730 m above bottom were significantly correlated with SCOC with a lag time of ⩽14 days, linking pelagic food supply with benthic processes in the oligotrophic North Pacific gyre. The annual supply of POC into the abyss compared to the estimated annual demand by the sediment community (POC:SCOC) indicates that only 65% of the food demand is met by the supply of organic carbon.

The distribution of suspended particulate matter as well as bacterial biomass and activity in near-bottom waters was investigated at six stations in the deep Arabian Sea (2000–4500 m water depth). Water samples were obtained from heights between 0.1–1000 m above bottom (m a.b.) with a bottom water sampler or with a CTD-rosette during two cruises in May 1997 and February 1998. The vertical variability in suspended particle concentrations as well as in bacterial activity was higher than the regional and temporal variability. Compared to the deep water column (250–1000 m a.b.; 0.1×108 cells l−1), an increase in bacterial numbers was observed from 40–100 m a.b. (0.24×108 cells l−1) towards the seafloor (0.1–0.6 m a.b.; 0.53×108 cells l−1). Suspended particulate matter ( 0.42 mg l −1 ) as well as bacterial leucine incorporation ( 1.81 pmol l −1 h −1 ) and the activity of different enzymes were highest in the near-bottom water ( 0.2 mg l −1 and 0.69 pmol l −1 h −1 , respectively). The suspended particles in the BNL had a high chlorophyll a to POC ratio and were of higher organic carbon concentrations than the sinking particles or the particulate matter at the sediment surface. The carbon demand of the bacterial community in the BNL ( 20 mg C m −2 d −1 ), which was estimated by leucine incorporation experiments, exceeded the vertical POC flux. Thus, we conclude that the enhanced microbial activity and biomass close to the seafloor is mainly supported by the resuspension of small phytodetrital particles and by the DOC flux.

Eight different sites from 2300 to 4420 m water depth in the Arabian Sea were sampled for a biochemical quantification of phospholipid concentrations in the sediments. This method serves as a measure of microbial biomass in marine sediments comprising all small-sized organisms, including bacteria, fungi, protozoa and metazoa. Phospholipid concentrations can be converted to carbon units as an estimate of total microbial biomass in the sediments. The average phospholipid concentrations in the surface sediments (0–1 cm) of the 4 abyssal sites ranged from 7 nmol cm−3 at the southern site (SAST, 10°N 65°E, 4425 m) to 29 nmol cm−3 at the western site (WAST, 16°N 60°E, 4045 m). The high values detected at the abyssal station WAST exceeded those in the literature for other abyssal sites and were comparable to values from the upper continental slope of the NE-Atlantic and the Arctic. At the four continental slope sites in the Arabian Sea, average phospholipid concentrations ranged from 9 to 53 nmol cm−3 with the maximum values at stations A (2314 m) and D (3142 m) close to the Omani coast. Records of particulate organic carbon flux to the deep sea are available for four of the investigated locations, allowing a test of the hypothesis that the standing stock of benthic microorganisms in the deep sea is controlled by substrate availability, i.e. particle sedimentation. Total microbial biomass in the surface sediments of the Arabian Sea was positively correlated with sedimentation rates, consistent with previous studies of other oceans. The use of the measurement of phospholipid concentrations as a proxy for input of particulate organic matter is discussed.

In the Arabian Sea, productivity in the surface waters and particle flux to the deep sea are controlled by monsoonal winds. The flux maxima during the South-West (June–September) and the North-East Monsoon (December–March) are some of the highest particle fluxes recorded with deep-sea sediment traps in the open ocean. Benthic microbial biomass and activities in surface sediments were measured for the first time in March 1995 subsequent to the NE-monsoon and in October 1995 subsequent to the SW-monsoon. These measurements were repeated in April/May 1997 and February/March 1998, at a total of six stations from 1920 to 4420 m water depth. This paper presents a summary on the regional and temporal variability of microbial biomass, production, enzyme activity, degradation of 14 C -labeled Synechococcus material as well as sulfate reduction in the northern, western, eastern, central and southern Arabian deep sea. We found a substantial regional variation in microbial biomass and activity, with highest values in the western Arabian Sea (station WAST), decreasing approximately threefold to the south (station SAST). Benthic microbial biomass and activity during the NE-monsoon was as high or higher than subsequent to the SW-monsoon, indicating a very rapid turnover of POC in the surface sediments. This variation in the biomass and activity of the microbial assemblages in the Arabian deep sea can largely be explained by the regional and temporal variation in POC flux. Compared to other abyssal regions, the substantially higher benthic microbial biomasses and activities in the Arabian Sea reflect the extremely high productivity of this tropical basin.

During cruise Meteor 33/1 in the northern Arabian Sea in September/October 1995, large numbers of the portunid crab Charybdis smithii were observed swimming in the open ocean. In a photographic survey at three abyssal stations in the northern Arabian Sea (NAST, WAST, CAST), even higher densities of Charybdis smithii – up to 1 crab m−2 – were found dead on the sea floor. Average sizes of the crabs were around 34–44 mm carapace width, indicating that the animals died prematurely, before returning to the breeding grounds presumable on the shelves of India or Oman. The average weight of the crabs was 10–14 g wet weight. From the photographic quantification it can be deduced that these large food falls represent a significant carbon input of at least 10–30% of the annual flux of POC as measured in sediment traps in this region. The exceptionally high microbial chitinase activity in the surface sediment layers detected at the same stations indicates that this energy is utilized and channelled into the deep-sea benthic food web of the deep Arabian Sea. There are frequent observations of dense Charybdis smithii swarms in the Arabian Sea from different years; however, it is not certain whether such large food falls as observed during M 33/1 are regular seasonal events that repeat each year.

The unparalleled accumulation of biological and contextual data is currently revolutionizing the way environmental microbiologists address ecological questions. Here, we briefly review the likely causes that may explain this remarkable scientific revolution and present a synthesized view about how to describe microbial communities in their complex environmental context.

In an extended deep-sea study the response of the benthic community to seasonally varying sedimentation rates of organic matter were investigated at a fixed abyssal site in the NE Atlantic (BIOTRANS station or JGOFS station L2 at 47°N–20°W, water depth >4500 m) on four legs of METEOR expedition 21 between March and August 1992. The vertical flux at 3500 m depth and temporal variations in the chloroplastic pigment concentration, a measure of phytodetritus deposition, and of total adenylates and total phospholipids, measures of benthic biomass, and of activity of hydrolytic enzymes were observed. The flux patterns in moored sediment traps of total chlorophyll, POC and total flux showed an early sedimentation peak in March/April 1992, followed by low fluxes in May and intermediate ones from June to August. Thus 1992 differed from other years, in which one large flux peak after the spring phytoplankton bloom was observed. Unusually high concentrations of chloroplastic pigments were consistently observed in March 1992, reflecting the early sedimentation input. At the same time biomass of small benthic organisms (bacteria to meiobenthos) and activity of hydrolytic enzymes were higher compared to values from March 1985 and from the following months in 1992. In May and August 1992 pigment concentrations and biomass and activity parameters in the sediment were lower than during previously observed depositions of phytodetrital matter in summer. The data imply that the deep ocean benthic community reacts to small sedimentation events with transient increases in metabolic activity and only small biomass production. The coupling between pelagic and benthic processes is so close that interannual variability in surface water production is “mirrored” by deep-sea benthic processes.

The relation of microbial biomass and extracellular enzymatic activities to substrate availability was investigated for the first time in deep-sea sediments of the Eastern Mediterranean basin, along a transect from the Gulf of Taranto (Italy) to the coasts of Egypt and Israel. Chloroplastic pigment equivalents (CPE), indicating the input of phytodetritus to the sediments, decreased from the shallow coastal stations around 200m water depth (4–6 μg cm−2) to the oligotrophic abyssal basins of the Ionian and Levantine Seas around 3000m water depth (0.1–1 μg cm−2). However, at two stations in the Hellenic Trench, at 4620 m and 3750 m, as well as in the Pliny Trench south of Crete at 4260 m, strikingly high accumulations of CPE above 10 μg cm−2 were recorded. The presence of relatively fresh detritus at these depths can only be explained by lateral flux of organic material down the steep slopes and its capture in the adjacent trenches. Consistently, microbial activity potentials in the trenches exceeded those at the abyssal plain by an order of magnitude. Microbial biomass was about 0.1 mg C cm −2 in the trenches and the coastal stations, compared to less than 0.05 mg C cm −2 at the abyssal plain stations. The increased availability of a potential food resource appears to have stimulated the deep-sea microbial assemblages to the same extent as those of shallower stations, suggesting that microbial activity in deep-sea sediments is mainly regulated by the level of food supply.