Evidence for enhanced mixing over rough topography in the abyssal ocean

The overturning circulation of the ocean plays an important role in modulating the Earth's climate. But whereas the mechanisms for the vertical transport of water into the deep ocean--deep water formation at high latitudes--and horizontal transport in ocean currents have been largely identified, it is not clear how the compensating vertical transport of water from the depths to the surface is accomplished. Turbulent mixing across surfaces of constant density is the only viable mechanism for reducing the density of the water and enabling it to rise. However, measurements of the internal wave field, the main source of energy for mixing, and of turbulent dissipation rates, have typically implied diffusivities across surfaces of equal density of only approximately 0.1 cm2 s(-1), too small to account for the return flow. Here we report measurements of tracer dispersion and turbulent energy dissipation in the Brazil basin that reveal diffusivities of 2-4 cm2 s(-1) at a depth of 500 m above abyssal hills on the flank of the Mid-Atlantic Ridge, and approximately 10 cm2 s(-1) nearer the bottom. This amount of mixing, probably driven by breaking internal waves that are generated by tidal currents flowing over the rough bathymetry, may be large enough to close the buoyancy budget for the Brazil basin and suggests a mechanism for closing the global overturning circulation.     

The effect of sea water on cytochrome oxidase and oxidative phosphorylation

Riassunto Piccole quantità di acqua di mare causano una forte inibizione della fosforilazione ossidativa, mentre l'effetto sulla attività citocromossidasica è piuttosto modesto. L'ione responsabile di questo effetto è il Calcio.

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This work has been supported in part by a grant of the National Institute of Health, U.S. Public Health Service (RG-6211) to the Laboratory of Comparative Anatomy.     

Distribution of radioactivity after administration of3H-5-hydroxytryptamine by three different routes to the musselMytilus edulis

Summary Intracardiac injection gives proportionately higher and earlier peak concentration in tissues that specifically accumulates it, i.m. injection gives slower but longer lasting accumulations, and topical application to a ganglia essentially localizes the drug in that structure.We wish to thank Drs Hiripi and Nemcsok for the demonstration of the intracardiac technique. We also wish to thank Drs Haley and Ledeen for the use of the scintillation counter.     

Deep sub-seafloor prokaryotes stimulated at interfaces over geological time

The sub-seafloor biosphere is the largest prokaryotic habitat on Earth but also a habitat with the lowest metabolic rates. Modelled activity rates are very low, indicating that most prokaryotes may be inactive or have extraordinarily slow metabolism. Here we present results from two Pacific Ocean sites, margin and open ocean, both of which have deep, subsurface stimulation of prokaryotic processes associated with geochemical and/or sedimentary interfaces. At 90 m depth in the margin site, stimulation was such that prokaryote numbers were higher (about 13-fold) and activity rates higher than or similar to near-surface values. Analysis of high-molecular-mass DNA confirmed the presence of viable prokaryotes and showed changes in biodiversity with depth that were coupled to geochemistry, including a marked community change at the 90-m interface. At the open ocean site, increases in numbers of prokaryotes at depth were more restricted but also corresponded to increased activity; however, this time they were associated with repeating layers of diatom-rich sediments (about 9 Myr old). These results show that deep sedimentary prokaryotes can have high activity, have changing diversity associated with interfaces and are active over geological timescales.     

2-Amino-6-[(1'R,2'S)-1',2'-dihydroxypropyl]-3-methyl-pterin-4-one,a biologically active metabolite from the anthozoanAstroides calycularis Pallas

Summary 2-Amino-6-[(1'R,2'S)-1',2'-dihydroxypropyl]-3-methyl-pterin-4-one (1) has been isolated from the marine anthozoanAstroides calycularis; its structure was illustrated by spectral analyses including 2D-NMR and by partial synthesis.1 appears to possess cell-growth inhibiting activity.29 December 1986Work supported by C.N.R. (Progetto Finalizzato Chimica Fine e Secondaria) and by Ministero Pubblica Istruzione Italy. — Acknowledgments. Mass spectral data were provided by Servizio di Spettrometria di massa del C.N.R. e dell'Università di Napoli. The assistance of the staff is gratefully appreciated. Finally we would like to thank Prof. C. Pietropaolo for supplying chick embryo fibroblasts.