Permeable or sandy sediments cover the majority of the seafloor on continental shelves worldwide, but little is known about their role in the coastal nitrogen cycle. We investigated the rates and controls of nitrogen loss at a sand flat (Janssand) in the central German Wadden Sea using multiple experimental approaches, including the nitrogen isotope pairing technique in intact core incubations, slurry incubations, a flow-through stirred retention reactor and microsensor measurements. Results indicate that permeable Janssand sediments are characterized by some of the highest potential denitrification rates (X0.19 mmol N m À2 h À1 ) in the marine environment. Moreover, several lines of evidence showed that denitrification occurred under oxic conditions. In intact cores, microsensor measurements showed that the zones of nitrate/nitrite and O 2 consumption overlapped. In slurry incubations conducted with 15 NO 3 À enrichment in gas-impermeable bags, denitrification assays revealed that N 2 production occurred at initial O 2 concentrations of up to B90 lM. Initial denitrification rates were not substantially affected by O 2 in surficial (0-4 cm) sediments, whereas rates increased by twofold with O 2 depletion in the at 4-6 cm depth interval. In a well mixed, flow-through stirred retention reactor (FTSRR), 29 N 2 and 30 N 2 were produced and O 2 was consumed simultaneously, as measured online using membrane inlet mass spectrometry. We hypothesize that the observed high denitrification rates in the presence of O 2 may result from the adaptation of denitrifying bacteria to recurrent tidally induced redox oscillations in permeable sediments at Janssand.
Deep-sea hydrothermal vents are one of the most unique and fascinating ecosystems on Earth. Although phylogenetic diversity of vent communities has been extensively examined, their physiological diversity is poorly understood. In this study, a GeoChipbased, high-throughput metagenomics technology revealed dramatic differences in microbial metabolic functions in a newly grown protochimney (inner section, Proto-I; outer section, Proto-O) and the outer section of a mature chimney (4143-1) at the Juan de Fuca Ridge. Very limited numbers of functional genes were detected in Proto-I (113 genes), whereas much higher numbers of genes were detected in Proto-O (504 genes) and 4143-1 (5,414 genes). Microbial functional genes/populations in Proto-O and Proto-I were substantially different (around 1% common genes), suggesting a rapid change in the microbial community composition during the growth of the chimney. Previously retrieved cbbL and cbbM genes involved in the Calvin Benson Bassham (CBB) cycle from deep-sea hydrothermal vents were predominant in Proto-O and 4143-1, whereas photosynthetic green-like cbbL genes were the major components in Proto-I. In addition, genes involved in methanogenesis, aerobic and anaerobic methane oxidation (e.g., ANME1 and ANME2), nitrification, denitrification, sulfate reduction, degradation of complex carbon substrates, and metal resistance were also detected. Clone libraries supported the GeoChip results but were less effective than the microarray in delineating microbial populations of low biomass. Overall, these results suggest that the hydrothermal microbial communities are metabolically and physiologically highly diverse, and the communities appear to be undergoing rapid dynamic succession and adaptation in response to the steep temperature and chemical gradients across the chimney.metagenomics ͉ microarrays ͉ chimney ͉ deep sea ͉ dynamic
The global ridge system is dominated by oceanic rises reflecting large variations in axial depth associated with mantle hotspots. The little studied Marion Rise is as large as the Icelandic, considering length and depth, but has an axial rift rather than a high nearly its entire length. Uniquely, along the SW Indian Ridge systematic sampling allows direct examination of crustal architecture over its full length. Unlike Iceland, peridotites are extensively exposed high over the rise. This shows for the 1 st time that the crust is generally thin, and often missing over a rifted rise. Thus the rise must be largely an isostatic response to ancient melting events that created low-density depleted mantle beneath the ridge rather than thickened crust and/or a large thermal anomaly. The likely origin for the depleted mantle is that emplaced into the African asthenosphere during the Karoo and Madagascar flood basalt events. Following Morgan1 , common wisdom equates oceanic rises to a hot fertile mantle plume producing a flow of plume-derived mantle to the ridge and down the sub-axial asthenospheric channel, resulting in elevated mantle temperature, ridge topography, and thickened igneous crust (the mantle wedge hypothesis, e.g.:2 ). Studies of the Reykjanes Ridge support this, with seismic crust thickening from ~6 km near the Gibbs FZ for 1600 km to ~18 km at the Reykjanes Peninsula e.g.: 3 . The Icelandic Rise, also has a long axial high consistent with such robust magmatism 4 (Table 1). The current consensus is the igneous crust thickens from east to west up the Marion Rise, and indeed up all rises (e.g.: 5 6 ). Basalt sodium contents, like other rises, decrease systematically towards Marion, and are interpreted to represent higher degrees of mantle melting and thicker crust 7 . Dick et al. 8 , however, point out that such correlations can be due to variable mantle temperature, or an increasingly depleted mantle source composition, and do not require thicker crust. The Marion Rise, in particular, has numerous large-offset transforms that would block sub-axial asthenospheric flow (e.g.: 9 ), and its deep rift valley indicates anemic rather than robust magmatism 4 . Niu and O'Hara 10 , though assuming thick crust over rises, suggest the global correlation of basalt chemistry and ridge depth is best explained by mantle composition variations, with many rises supported by depleted chemically buoyant mantle as first proposed by O'hara 11 for the Iceland Rise and Presnall and Helsley 12 for the Azores.2 14 . c) Maximum and minimum elevations are measured from shallowest point on axis, or midpoint of Iceland plateau to the rift valley axis point where average depth stabilizes or blocking transform. d) The 200-km average represents average elevation about the highest or lowest point. e) Iceland average plateau height; crest of Azores Rise, SWIR @ 36°15Ed) MAR @ Charlie Gibbs FZ; axial valley floor, MAR @ 24°N, axial valley floor @61°45'E. e) Depth anomaly calculated for the 200-km averages to eliminate local topographic e...
48sulfide used by its symbionts. δ 15 N tissue values differed between the mussels, with B. 49 platifrons having a wider range of on average slightly lower values (mean = 50 3 +0.5±0.7‰, n=36) than B. aduloides (mean = +1.1±0.0‰). These values are 51 significantly lower than δ 15 N values of South China Sea deep-sea sediments (+5‰ to 52 +6‰), indicating that the organic nitrogen is of local origin, possibly resulting from the 53 activity of autotrophic bacteria and due to assimilation of isotopically light nitrate or 54 ammonium by the symbionts. 55 56
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.