Publications

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2014
Marlow, JJ, Steele JA, Ziebis W, Thurber AR, Levin LA, Orphan VJ.  2014.  Carbonate-hosted methanotrophy represents an unrecognized methane sink in the deep sea. Nature Communications. 5   10.1038/ncomms6094   AbstractWebsite

The atmospheric flux of methane from the oceans is largely mitigated through microbially mediated sulphate-coupled methane oxidation, resulting in the precipitation of authigenic carbonates. Deep-sea carbonates are common around active and palaeo-methane seepage, and have primarily been viewed as passive recorders of methane oxidation; their role as active and unique microbial habitats capable of continued methane consumption has not been examined. Here we show that seep-associated carbonates harbour active microbial communities, serving as dynamic methane sinks. Microbial aggregate abundance within the carbonate interior exceeds that of seep sediments, and molecular diversity surveys reveal methanotrophic communities within protolithic nodules and well-lithified carbonate pavements. Aggregations of microbial cells within the carbonate matrix actively oxidize methane as indicated by stable isotope FISH-nanoSIMS experiments and (CH4)-C-14 radiotracer rate measurements. Carbonate-hosted methanotrophy extends the known ecological niche of these important methane consumers and represents a previously unrecognized methane sink that warrants consideration in global methane budgets.

2013
Thurber, AR, Levin LA, Rowden AA, Sommer S, Linke P, Kroger K.  2013.  Microbes, macrofauna, and methane: A novel seep community fueled by aerobic methanotrophy. Limnology and Oceanography. 58:1640-1656.   10.4319/lo.2013.58.5.1640   AbstractWebsite

During the discovery and description of seven New Zealand methane seep sites, an infaunal assemblage dominated by ampharetid polychaetes was found in association with high seabed methane emission. This ampharetid-bed assemblage had a mean density of 57,000 +/- 7800 macrofaunal individuals m(-2) and a maximum wet biomass of 274 g m(-2), both being among the greatest recorded from deep-sea methane seeps. We investigated these questions: Does the species assemblage present within these ampharetid beds form a distinct seep community on the New Zealand margin? and What type of chemoautotrophic microbes fuel this heterotrophic community? Unlike the other macro-infaunal assemblages, the ampharetid-bed assemblage composition was homogeneous, independent of location. Based on a mixing model of species-specific mass and isotopic composition, combined with published respiration measurements, we estimated that this community consumes 29-90 mmol C m(-2) d(-1) of methane-fueled biomass; this is > 290 times the carbon fixed by anaerobic methane oxidizers in these ampharetid beds. A fatty acid biomarker approach supported the finding that this community, unlike those previously known, consumes primarily aerobic methanotrophic bacteria. Due to the novel microbial fueling and high methane flux rates, New Zealand's ampharetid beds provide a model system to study the influence of metazoan grazing on microbially mediated biogeochemical cycles, including those that involve greenhouse gas emissions.

2010
Cordes, EE, Cunha MR, Galeron J, Mora C, Olu-Le Roy K, Sibuet M, Van Gaever S, Vanreusel A, Levin LA.  2010.  The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity. Marine Ecology-an Evolutionary Perspective. 31:51-65.   10.1111/j.1439-0485.2009.00334.x   AbstractWebsite

Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic Sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the 'species sorting' concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.

2002
Shankle, AM, Goericke R, Franks PJS, Levin LA.  2002.  Chlorin distribution and degradation in sediments within and below the Arabian Sea oxygen minimum zone. Deep-Sea Research Part I-Oceanographic Research Papers. 49:953-969.   10.1016/s0967-0637(01)00077-2   AbstractWebsite

The concentration of chlorophylla degradation products, i.e. chlorins, preserved in deep-sea sediments is a function of the amount of primary production input and the rate at which it is subsequently degraded. Sedimentary chlorins can be used as a proxy for paleoproductivity; however, our understanding of the factors controlling their preservation is limited. To study the effects of changes in export of primary production from the euphotic zone and of differences in depositional conditions on chlorin concentration in marine sediments, chlorins were analyzed by high pressure liquid chromatography from sediments taken within and below the oxygen minimum zone on the Oman margin in the Arabian Sea. Among five stations at water depths between 400 and 1250 m, variation in chlorin concentration in surface sediments (0-0.5 cm) was significantly related to water depth (used here as a proxy for chlorin fluxes to the sediments) and bottom-water oxygen concentration; the more important control on chlorin concentration of surficial sediments measured in this study is the amount of chlorins reaching the sediment. Chlorins decayed exponentially downcore (0-20 cm). The degradation of sedimentary chlorins was better described by a model in which chlorins decayed at different rates within and below the sediment mixed layer. The degradation rates within the mixed layer were 0.0280 +/- 0.0385 yr(-1) (t(1/2) = 73 yr). Below the mixed layer, degradation rates were one to two orders of magnitude less, ranging from 0.0022 +/- 0.0025 yr(-1) (t(1/2) = 680 yr). Many stations had subsurface chlorin concentration peaks between 6 and 10 cm depth. The most likely explanation for these peaks is a period of increased deposition of chlorins in the past. This could result from changes in local depositional environment or a more general increase in surface production resulting in an increased sedimentation of chlorins to the sediments 500-1000 years ago. Chlorins are a useful indicator of the magnitude of chlorin deposition; however their usage as indicators of paleoproductivity is more complicated. (C) 2002 Elsevier Science Ltd. All rights reserved.

2000
Smith, CR, Levin LA, Hoover DJ, McMurtry G, Gage JD.  2000.  Variations in bioturbation across the oxygen minimum zone in the northwest Arabian Sea. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 47:227-257.   10.1016/s0967-0645(99)00108-3   AbstractWebsite

Oxygen minimum zones are expected to alter substantially the nature, rates and depths of bioturbation along continental margins, yet these effects remain poorly studied. Using excess (210)Pb profiles, sediment X-radiography and box-core samples for macrofauna, we examined bioturbation processes at six stations (400, 700, 850, 1000, 1250 and 3400 m deep) along a transect across the oxygen minimum zone (OMZ) on the Oman margin. Bottom-water oxygen concentrations ranged from similar to 0.13 mi l(-1) at 400 m to similar to 2.99 mi l(-1) at 3400 m. (210)Pb mixed-layer depth and bioturbation intensity (D(b)) exhibited high within-station variance, and means did not differ significantly among stations. However, the mean mixed-layer depth (4.6 cm) for pooled OMZ stations (400-1000 m depths, 0.13-0.27 mi l(-1) bottom-water oxygen) was half that for stations from similar water depths along well-oxygenated Atlantic and Pacific slopes (11.1 cm), suggesting that oxygen stress reduced (210)Pb mixing depth on the Oman margin. Modal burrow diameter and the diversity of burrow types at a station were highly correlated with bottom-water oxygen concentration from the edge to the core of the Oman OMZ (Spearman's rho greater than or equal to 0.89, p less than or equal to 0.02), suggesting that these parameters are useful proxies for bottom-water oxygen concentrations under dysaerobic conditions. In contrast, neither the maximum diameter and nor the maximum penetration depth of open burrows exhibited oxygen-related patterns along the transect. Reduced (210)Pb mixing depth within the Oman-margin OMZ appeared to result from a predominance of surface-deposit feeders and tube builders within this zone, rather than from simple changes in horizontal or vertical distributions of macrofaunal abundance or biomass. The number of burrow types per station was highly correlated with macrofaunal species diversity, suggesting that burrow diversity may be a good proxy for species diversity in paleo-dysaerobic assemblages. We conclude that bottom-water oxygen concentrations of 0.13-0.27 mi l(-1) substantially alter a number of bioturbation parameters of importance to diagenetic and biofacies models for continental margins. (C) 1999 Elsevier Science Ltd. All rights reserved.