Advertisement

Continuous Light-Scattering Profiles and Suspended Matter Over Nitinat Deep-Sea Fan

  • Edward T. Baker
  • Richard W. Sternberg
  • Dean A. McManus
Part of the Marine Science book series (MR, volume 4)

Abstract

During September 1971 and June 1972, a total of 65 light-scattering profiles were recorded in the waters over Nitinat Fan by means of a self-contained, continuously recording nephelometer. All profiles extend from the sea surface to a point 20 m above the sea floor (maximum depth 2400 m) and as many as 5 prominent scattering layers are observed within the water column at a given station. Some scattering layers can be traced over wide areas of the fan and appear on records from both cruises. The most persistent feature of the profiles, and the only one found on every record, is a bottom nepheloid layer (BNL) of steadily increasing light scattering immediately below a layer of relatively clearer water and immediately above the sea floor. Over short lateral distances the vertical extent and scattering intensity of the BNL (normalized to the scattering levels of the overlying clearer waters) change markedly in a manner apparently related to fan topography. In general, the BNL thickens to > 300 m and intensifies to > 2.5 times normal over the topographic lows, being most prominent above Cascadia Valley (the major valley crossing the fan) as well as above the steep non-channelled northern flank of the fan. Over the levees separating the smooth northern flank from Cascadia Valley to the south and over the foot of the continental slope which forms the eastern border of the fan, the BNL thins to < 50 m and the scattering intensity is < 1.5 times normal.

Twenty-four suspended sediment samples, collected by in situ filtration from within and just above the BNL, yielded inorganic particle concentrations of 20 to 80 µg/l. These concentrations correlate well (r = 0.73) with the simultaneously recorded scattering values, indicating that the nephelometer provides a fair estimate of suspended sediment concentrations in the bottom waters over Nitinat Fan.

By integrating the scattering profile within the BNL at each station and converting the average scattering value into particle mass by means of an empirical relationship derived from the measured concentration values, the average amount of inorganic suspended matter in the BNL can be calculated. In a 1-cm2 column of water, average particulate mass in the BNL was estimated at about 0.5 mg. Assuming that the bottom deposits are derived only from particles in the BNL, the measured sedimentation rate on the fan requires a mean residence time of about 1 month for these particles within the BNL.

Keywords

Suspended Sediment Continental Slope Suspended Sediment Concentration Turbidity Current Inorganic Sediment 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Ahlquist, N. C. and R. J. Charlson, Measurement of the vertical and horizontal profile of aerosol concentration in urban air with the integrating nephelometer, Env. Sci. Tech, 2, 363–366, 1968.CrossRefGoogle Scholar
  2. Ahlquist, N. C. and R. J. Charlson, Measurement of the wavelength dependence of atmospheric extinction due to scatter, Atm. Env., 3, 551–564, 1969.CrossRefGoogle Scholar
  3. Baker, E. T., Nephelometry and Mineralogy of Suspended Particulate Matter in the Waters Over the Washington Continental Slope and Nitinat Deep-Sea Fan, Ph.D. Thesis, Univ. Washington, Seattle, 1973.Google Scholar
  4. Barnard, W. D., Late Cenozic Sedimentation on the Washington Continental Slope, Ph.D. Thesis, Univ. Washington, Seattle, 1973.Google Scholar
  5. Beutell, R. G. and A. W. Brewer, Instruments for the measurement of the visual range, J. Sci. Inst., 26, 357–359, 1949.CrossRefGoogle Scholar
  6. Carson, B., Stratigraphy and Depositional History of Quaternary Sediments in Northern Cascadia Basin and Juan de Fuca Abyssal Plain, northeast Pacific Ocean, Ph.D. Thesis, Univ. Washington, Seattle, 249, 1971.Google Scholar
  7. Charlson, R. J., N. C. Ahlquist, H. Selvidge, and P. B. MacCready, Jr., Monitoring of atmospheric aerosol parameters with the integrating nephelometer, J. Air Poll. Control Assoc., 19, 937–942, 1969.CrossRefGoogle Scholar
  8. Eittreim, S. and M. Ewing, Suspended particulate matter in the deep waters of the North American Basin, in Studies in Physical Oceanography, vol. 2, edited by A. L. Gordon, pp. 123–167, Gordon and Breach, London, 1972.Google Scholar
  9. Eittreim, S., A. L. Gordon, M. Ewing, E. M. Thorndike, and P. Bruckhausen, The nepheloid layer and observed bottom currents in the Indian-Pacific Antarctic Sea, in Studies in Physical Oceanography, vol. 2, edited by A. L. Gordon, pp. 19–35, Gordon and Breach, London, 1972.Google Scholar
  10. Ewing, M., and S. D. Connary, Nepheloid layer in the North Pacific, in Geological Investigations of the North Pacific, Geol. Soc. Am. Mem. 126, p. 41–82, 1970.Google Scholar
  11. Ewing, M., S. L. Eittreim, J, I, Ewing, and X. LePichon, Sediment transport and distribution in the Argentine Basin, 3. Nepheloid layer and processes of sedimentation, in Physics and Chemistry of the Earth, vol. 8, pp. 49–77, Pergamon Press, New York, 1971.Google Scholar
  12. Griggs, G. B., and L. D. Kulm, Sedimentation in Cascadia Deep Sea Channel, Geol. Soc. Am. Bull., 81, 1361–1364, 1970.CrossRefGoogle Scholar
  13. Hunkins, K., E. M. Thorndike, and G. Mathieu, Nepheloid layers and bottom currents in the Arctic Ocean, Jour. Geophys. Bes., 74, p. 6995–7008, 1969.CrossRefGoogle Scholar
  14. Ingraham, Jr., W. J., The Geostrophic Circulation and Distribution of Mater Properties off the Coasts of Vancouver Island and Washington, Spring and Fall, 1963, Fishery Bull., 66, p. 223–250, 1967.Google Scholar
  15. Jerlov, N. G., Optical Oceanography, Elsevier, Amsterdam, 194 p., 1968. Sternberg, R. W., E. T. Baker, D. A. McManus, S. Smith, and D. R. Morrison, An integrating nephelometer for measuring suspended sediment concentrations in the deep sea, Deep Sea Res., in press, 1974.Google Scholar
  16. Thorndike, E. M. and M. Ewing, Photographic nephelometers for the deep sea, in Deep Sea Photography, edited by J. B. Hersey, Johns Hopkins University Press, Baltimore, Md., pp. 113–116, 1967.Google Scholar

Copyright information

© Plenum Press, New York 1974

Authors and Affiliations

  • Edward T. Baker
    • 1
  • Richard W. Sternberg
    • 1
  • Dean A. McManus
    • 1
  1. 1.University of WashingtonUSA

Personalised recommendations