Variations in Benthic Boundary Layer Phenomena: Nepheloid Layer in the North American Basin

  • Pierre E. Biscaye
  • Stephen L. Eittreim
Part of the Marine Science book series (MR, volume 4)


Observations of phenomena associated with a benthic boundary layer were made over a 19-day period in two different regimes in the western North American Basin. Repeated measurements of temperature, in situ and in vitro turbidity, suspended particulate concentrations and excess radon versus depth, as well as bottom photographs, were made as a function of time at two locations on the lower slope of the Blake-Bahama Outer Ridge (BBOR) and at one location on the Ratteras Abyssal Plain (HAP). At the BBOR sites the benthic boundary layer was manifest by high concentrations of suspended particulates, high turbidity, and intense vertical mixing indicated by excess radon. Vertical distributions of particulate matter and radon were related to the thermal structure of the water mass and, although the strongest manifestations of frictional interaction between the water and bottom were seen below 150–300 m, some influence was seen as high as 1500 m above bottom.

The 150–300-m particulate and radon boundary also coincided with the top of an adiabatic layer. Large, regular, temporal variations in these parameters with a period of about one week were in phase at the two stations, located 110 km apart. This benthic boundary layer regime was associated with current velocities from 10 to 30 cm/sec and with a current direction and temperature and salinity characteristics indicative of the Western Boundary Undercurrent (WBUC). At the RAP site, manifestations of the benthic boundary layer were less intense, less variable and restricted to a thinner layer. Turbidity and concentration of particulate matter were much lower than on the BBOR and vertical mixing measured by excess radon was an order of magnitude lower. Depth profiles of these parameters showed the strongest evidence of the benthic boundary layer to be restricted to 80–100 m above the bottom (cf. 150–300 m on the BBOR) but with some evidence of mixing of particulate matter and cold bottom waters to 900 m above the bottom (cf. 1500 m on the BBOR). Again, the top of the 80–100-m zone coincided with the top of the adiabatic bottom layer. Bottom photographs and water mass characteristics indicate that this benthic boundary layer regime is associated with the rather slowly northward moving Antarctic Bottom Water (AABW). An hypothesis to explain the variations observed on the BBOR is presented in which eddies of clear AABW are injected into the more turbid, rapidly southward flowing WBUC north of the study area. These are seen as temporal variations in the intensity of the nepheloid layer along the BBOR.


Vertical Distribution Particulate Concentration Suspended Particulate Matter Current Velocity Radon Concentration 
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  1. Amos, A., A. Gordon, and E. D. Schneider, Water masses and circulation patterns in the region of the Blake-Bahama Outer Ridge, Deep Sea Res., 18, 145–165, 1971.Google Scholar
  2. Broecker, W. S., An application of natural radon to problems in ocean circulation, in Symposium on Diffusion in Oceans and Fresh Waters, edited by T. Ichiye, pp. 116–144, 1965.Google Scholar
  3. Broecker, W. S., J. Cromwell, and Y. H. Li, Rates of vertical eddy diffusion near the ocean floor based on measurements of the distribution of excess 222Rn, Earth and Planet. Sci. Letters, vol. 5, pp. 101–105, 1968.CrossRefGoogle Scholar
  4. Broecker, W. S., Y. H. Li, and J. Cromwell, Radium-226 and Radon-222: Concentration in Atlantic and Pacific Oceans, Science, 158, 1307–1310, 1967.CrossRefGoogle Scholar
  5. Chung, Y., and H. Craig, Excess radon and temperature profiles from the Eastern Equatorial Pacific, Earth and Planetary Sci. Letters, vol. 14, pp. 55–64, 1972.CrossRefGoogle Scholar
  6. Connary, S. C., and M. Ewing, The nepheloid layer and bottom circulation in the Guinea and Angola Basins, in Studies in Physical Oceanography, edited by A. L. Gordon, Gordon and Breach, London, pp. 169–184, 1972.Google Scholar
  7. Eittreim, S., P. Bruchhausen, and M. Ewing,. Vertical distribution of turbidity in the South Indian and South Australian Basins, in Antarctic Oceanology II: The Australian-New Zealand Sector, edited by D. E. Hayes, Amer. Geophys. U., pp. 51–58, 1972a.CrossRefGoogle Scholar
  8. Eittreim, S., M. Ewing, and E. M. Thorndike, Suspended matter along the continental margin of the North American Basin, Deep Sea Res., 16, 613–624, 1969.Google Scholar
  9. Eittreim, S., and M. Ewing, Suspended particulate matter in the deep waters of the North American Basin, in Studies in Physical Oceanography, edited by A. L. Gordon, Gordon and Breach, London, pp. 123–167, 1972.Google Scholar
  10. Eittreim, S., A. L. Gordon, M. Ewing, E. M. Thorndike, and P. Bruchhausen, The nepheloid layer and obeerved bottom currents in the Indian-Pacific Antarctic Sea, in Studies in Physical Oceanography, edited by A. L. Gordon, Gordon and Breach, London, pp. 19–35, 1972b.Google Scholar
  11. Ewing, M., and S. Connary, Nepheloid layer in the North Pacific, in Geol. Soc. Am. Memoir l26, edited by J. D. Hays, pp. 41–82, 1970.Google Scholar
  12. Ewing, M., S. Eittreim, J. Ewing, and X. LePichon, Sediment transport and distribution in the Argentine Basin: Part 3, Nepheloid layer and processes of sedimentation, in Physics and Chemistry of the Earth, vol. 8, pp. 49–77, 1971.Google Scholar
  13. Ewing, M., and E. M. Thorndike, Suspended matter in deep ocean water, Science, 147, 1291–1294, 1965.CrossRefGoogle Scholar
  14. Fuglister, F. E., Atlantic Ocean Atlas of temperature and salinity profiles and data from the International Geophysical Year 1957–58, Atlas Ser. Woods Hole Oceanographic Inst., vol. 1., 1960.CrossRefGoogle Scholar
  15. Heezen, B. C., and C. D. Hollister, The Face of the Deep, Oxford University Press, New York, 659 pp., 1971.Google Scholar
  16. Heezen, B.C., and M. Tharp, Physiographic diagram of the North Atlantic Ocean (revised 1968 for The Floors of the Oceans), Geol. Soc. Amer. Spec. Paper 65, 1968.Google Scholar
  17. Hunkins, K., E. M. Thorndike, and G. Mathieu, Nepheloid layers and bottom currents in the Arctic Ocean, J. Geophys. Res., 74, 6995–7008, 1969.CrossRefGoogle Scholar
  18. Lee, A., and D. Ellet, On the water masses of the Northwest Atlantic Ocean, Deep Sea Res., 14, 183–190, 1967.Google Scholar
  19. Sternberg, R. W., Field measurements of the hydrodynamic roughness of the deep-sea boundary, Deep Sea Res., 17, 413–420, 1970.Google Scholar
  20. Swallow, J. C., and L. V. Worthington, An observation of a deep counter-current in the western North Atlantic, Deep Sea Res., 8, 1–9, 1961.CrossRefGoogle Scholar
  21. Thorndike, E. M., A deep sea photographic nephelometer; in preparation, 1974.Google Scholar
  22. Thorndike, E. M., and M. Ewing, Photographic nephelometers for the deep sea, in Deep-Sea Photography, edited by J. B. Hersey, Johns Hopkins Press, Baltimore, pp. 113–116, 1967.Google Scholar
  23. Wimbush, M., and W. Munk, The benthic boundary layer, in The Sea, vol. 4, part 1, edited by A. Maxwell, Wiley Interscience, New York, 731–758, 1970.Google Scholar
  24. Wüst, G., Das Bodenwasser und die Gliederung der Atlantischen Tiefsee, Wiss. Ergebn. dt. ablernt. Exped. Meteor 1925–27, vol. 6 (1) (1), 106 pp., 1933. (English translation No. 340 by M. Slessers, U.S. Naval Oceanographic Office, 1967)Google Scholar

Copyright information

© Plenum Press, New York 1974

Authors and Affiliations

  • Pierre E. Biscaye
    • 1
  • Stephen L. Eittreim
    • 1
  1. 1.Lamont-Doherty Geological ObservatoryUSA

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