A. Capone results 17
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This study explores the onset of thermal instability within a bidisperse porous medium saturated with a homogeneous, incompressible fluid, subjected to a non-uniform internal heat generation and constant temperature gradient due to heating from below. The fluid motion is modelled with the Darcy’s law in micropores, while the Brinkman’s law is employed in macropores to ensure a more accurate representation of momentum transfer...
The onset of thermal convection in an anisotropic horizontal porous layer heated from below and rotating about vertical axis, under local thermal non-equilibrium hypothesis is studied. Linear and nonlinear stability analysis of the conduction solution is performed. Coincidence between the linear instability and the global nonlinear stability thresholds with respect to the L 2 —norm is proved. Article Highlights A necessary and...
A chemosynthetic ecotone—“chemotone”—in the sediments surrounding deep‐sea methane seepsNARA Subscribed
Ecotones have been described as “biodiversity hotspots” from myriad environments, yet have not been studied extensively in the deep ocean. While physiologically challenging, deep‐water methane seeps host highly productive communities fueled predominantly by chemosynthetic pathways. We hypothesized that the biological and geochemical influence of methane seeps extends into background habitats, resulting in the formation of a “c...
Summary Results of recent modelling efforts imply denitrification‐influenced waters, such as those in the E astern T ropical S outh P acific ( ETSP ), may support high rates of biological nitrogen fixation ( BNF ), yet little is known about the N 2 ‐fixing microbial community in this region. Our characterization of the ETSP diazotrophic community along a gradient from upwelling‐influenced to oligotrophic waters did not detect...
Long‐term nitrogen and phosphorus fertilization effects on N 2 fixation rates and nifH gene community patterns in mangrove sedimentsNARA Subscribed
The bioavailability of nutrients is important in controlling ecological processes and nitrogen cycling in oligotrophic mangrove forests, yet the variation of diazotrophic community structure and activity with nutrient availability in sediments remains largely unexplored. To investigate for the first time how nutrients in sediments affect spatial and temporal patterns of diazotrophic community structure and activity, the sedime...
Vitamin B 12 excretion by cultures of the marine cyanobacteria Crocosphaera and SynechococcusNARA Subscribed
Axenic cultures of the N 2 ‐fixing marine cyanobacterium Crocosphaera watsonii exhibit very high B 12 excretion rates (up to 40 times higher per cell), compared to the smaller non‐N 2 ‐fixing strain of marine Synechococcus . The effect of N availability on vitamin synthesis is also evident in the non‐diazotrophic strain, as they release five times more B 12 under N‐replete conditions relative to N‐limiting conditions, although...
Trichodesmium spp. is a colonial diazotrophic cyanobacterium that occurs in the oligotrophic tropics and subtropics. Because of its ability to fix atmospheric N 2 , it is likely to be growth limited by P or Fe, and it has been hypothesized that limitation differs among different ocean basins. Two assays used as indices of P limitation or stress in Trichodesmium spp. are uptake of 33 PO 4 3‐ to determine maximal P uptake ( V ma...
The vertical and horizontal distributions of seven diazotrophic populations in the western tropical north Atlantic (WTNA) Ocean were examined using a nifH DNA quantitative polymerase chain reaction (QPCR) approach. The nifH phylotype abundances were highest near the surface and decreased with depth, with the exception of the cyanobacterial symbiont Calothrix , which was not detected at any station. Richelia associated with the...
We present the elemental composition (Al, Cd, Co, Cu, Fe, Mn, Mo, Ni, V, Zn, and P) of field‐collected Trichodesmium populations. To distinguish the effects of river discharges (Amazon and Niger Rivers) and Saharan dust deposition on metal concentrations in the colonies, samples were collected both in the western (February 2001, July‐August 2001, and April‐May 2003) and eastern (May‐June 2003) basins of the North Atlantic. Met...
We quantified the relationships among the specific growth rate, intracellular iron content, and steady state iron uptake rate for cultures of the marine diazotrophic cyanobacterium Trichodesmium (IMS 101) grown under differing conditions of Fe and N availability. The Fe quotas necessary to support a moderately Fe‐limited growth rate (70% mmax) of 0.1 d −1 under diazotrophy and ammonium were 38 and 8 µmol mol −1 , indicating a...
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