Hein, J. R., Scholl, D. W., Barron, J. A., Jones, M. G., and Miller,
J. J., 1978. Diagenesis of Late Cenozoic diatomaceous deposits
and formation of the bottom simulating reflector in the southern
Bering Sea. Sedimentology, 25, 155–181.
Hesse, R., 1989. Silica diagenesis: origin of inorganic and replacement cherts. Earth-Science Reviews, 26, 253–284.
Holland, H. D., and Turekian, K. K., 2003. Treatise on Geochemistry. Elsevier Pergamon, Elsevier Ltd. The Boulevard, Langford
Lane, Kidlington, Oxford, QX5 IGB, UK, ISBN 978-0-08043751-4.
Hornbach, M. J., Holbrook, W. S., Gorman, A. R., Hackwith, K. L.,
Lizarralde, D., and Pecher, I., 2003. Direct seismic detection of
methane hydrate on the Blake Ridge. Geophysics, 68(1),
92–100.
Hurd, D. C., and Birdwhistell, S., 1983. On producing a more general model for biogenic silica dissolution. American Journal of
Science, 283, 1–28.
Hyndman, R. D., and Spence, G. D., 1992. A seismic study of methane hydrate marine bottom simulating reflectors. Journal of
Geophysical Research – Solid Earth, 97, 6683–6698.
Knauth, L. P., 1994. Petrogenesis of chert. Reviews of Mineralogy,
29, 233–258.
Kotelnikova, S., 2002. Microbial production and oxidation of methane in deep subsurface. Earth-Science Reviews, 58, 367–395.
Kvenvolden, K. A., 1993. Gas hydrates – geological perspective
and global change. Reviews of Geophysics, 31, 173–187.
Mienert, J., Vanneste, M., Bunz, S., Andreassen, K., Haflidason, H.,
and Sejrup, H. P., 2005. Ocean warming and gas hydrate stability
on the mid-Norwegian margin at the Storegga Slide. Marine and
Petroleum Geology, 22, 233–244.
Nouzé, H., Cosquer, E., Collot, J., Foucher, L. P., Klingelhoefer, F.,
Lafoy, Y., and Géli, L., 2009. Geophysical characterization of
bottom simulating reflectors in the Fairway Basin (off New Caledonia, Southwest Pacific), based on high resolution seismic
profiles and heat flow data. Marine Geology, 266(1–4), 80–90.
Phrampus, B. J., and Hornbach, M. J., 2012. Recent changes to the
Gulf Stream causing widespread gas hydrate destabilization.
Nature, 490(7421), 527–530.
Rajan, A., Bünz, S., Mienert, J., and Smith, A. J., 2013. Gas hydrate
in petroleum provinces of the SW-Barents Sea. Marine and
Petroleum Geology, 46, 92–106.
Rempel, A. W., and Buffett, B. A., 1997. Formation and accumulation of gas hydrate in porous media. Journal of Geophysical
Research, 102, 10151–10164.
Shipley, T. H., Houston, M. H., Buffler, R. T., Shaub, F. J.,
McMillen, K. J., Ladd, J. W., and Worzel, J. L., 1979.
Seismic reflection evidence for the widespread occurrence of
possible gas-hydrate horizons on continental slopes and rises.
American Association of Petroleum Geologists Bulletin, 63,
2204–2213.
Sloan, D. R., 2003. Fundamental principles and applications of natural gas hydrates. Nature, 426, 353–359.
Tribble, J. S., Mackenzie, F. T., Urmos, J., O’Brien, D. K., and
Manghnani, M. H., 1992. Effects of biogenic silica on acoustic
and physical properties of clay-rich marine sediments. American
Association of Petroleum Geologists Bulletin, 76, 792–804.
Vogt, P. R., and Jung, W. Y., 2002. Holocene mass wasting on upper
non-Polar continental slopes – due to post-Glacial ocean
warming and hydrate dissociation? Geophysical Research
Letters, 29, 55-1–55-4.
Wood, W. T., Gettrust, J. F., Chapman, N. R., Spence, G. D., and
Hyndman, R. D., 2002. Decreased stability of methane hydrates
in marine sediments owing to phase-boundary roughness.
Nature, 420, 656–660.
Zatsepina, O. Y., and Buffett, B. A., 1998. Thermodynamic conditions for the stability of gas hydrate in the seafloor. Journal of
Geophysical Research, 103, 24127–24139.
Cross-references
Cold Seeps
Deep-sea Sediments
Marine Gas Hydrates
Methane in Marine Sediments
Silica
BOTTOM-BOUNDARY LAYER
Wenyan Zhang
MARUM-Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Definition
In marine geosciences, the bottom boundary layer (BBL)
refers to a layer of flow in the immediate vicinity of the
solid sea bottom where the effects of viscosity are significant in determining the characteristics of the flow. The
BBL was first discovered by Prandtl (1905) in aerodynamics and subsequently applied to other fluids moving on the
surface of a solid body.
Starting upwards from the sea bed, the total thickness of
the BBL is defined as the distance above the bottom at which
the mean flow velocity equals to 0.99 U ? , where U ? is the
free-stream velocity of a layer that is in a geostrophic balance
overlying the BBL. On top of the geostrophically balanced
layer is a surface layer subjected to wind-wave mixing. When
both the bottom micro-topography is uniform and the overlying flow is steady, the BBL can be easily quantified from the
vertical flow structure. Various ways exist to estimate the
thickness d of the BBL under neutral conditions (e.g., Grant
and Madsen, 1986; Nielsen, 1992). In general, the BBL
thickness at continental margins is at the order of 5–50 m.
Theoretically the BBL can be classified into three different sub-layers:
(1) A thin inner layer just above the bottom where turbulence is inhibited by the presence of the solid boundary.
The flow is controlled by molecular viscosity and the
shear stress is consistent with the bottom shear stress.
(2) An outer layer where turbulence shear dominates and
viscous shear can be neglected.
(3) A transitional layer where both the viscous shear and
the turbulence shear are important.
As the shear stress is almost constant and fulfills Newton’s law of viscosity in the inner layer, flow velocity can
thus be approximated by a linear form. However, this only
applies to a hydraulically smooth bottom where bed
roughness is too small to affect the velocity distribution.
In hydraulically rough bottom, bed roughness is large
enough to produce eddies close to the bottom and the inner
layer may not be detectable. Upwards from the inner layer,
the importance of molecular viscous decreases and turbulence gradually dominates the flow. Mean flow velocity in
this transitional layer obeys the law of the wall and can be
BOTTOM-BOUNDARY LAYER
67
J. J., 1978. Diagenesis of Late Cenozoic diatomaceous deposits
and formation of the bottom simulating reflector in the southern
Bering Sea. Sedimentology, 25, 155–181.
Hesse, R., 1989. Silica diagenesis: origin of inorganic and replacement cherts. Earth-Science Reviews, 26, 253–284.
Holland, H. D., and Turekian, K. K., 2003. Treatise on Geochemistry. Elsevier Pergamon, Elsevier Ltd. The Boulevard, Langford
Lane, Kidlington, Oxford, QX5 IGB, UK, ISBN 978-0-08043751-4.
Hornbach, M. J., Holbrook, W. S., Gorman, A. R., Hackwith, K. L.,
Lizarralde, D., and Pecher, I., 2003. Direct seismic detection of
methane hydrate on the Blake Ridge. Geophysics, 68(1),
92–100.
Hurd, D. C., and Birdwhistell, S., 1983. On producing a more general model for biogenic silica dissolution. American Journal of
Science, 283, 1–28.
Hyndman, R. D., and Spence, G. D., 1992. A seismic study of methane hydrate marine bottom simulating reflectors. Journal of
Geophysical Research – Solid Earth, 97, 6683–6698.
Knauth, L. P., 1994. Petrogenesis of chert. Reviews of Mineralogy,
29, 233–258.
Kotelnikova, S., 2002. Microbial production and oxidation of methane in deep subsurface. Earth-Science Reviews, 58, 367–395.
Kvenvolden, K. A., 1993. Gas hydrates – geological perspective
and global change. Reviews of Geophysics, 31, 173–187.
Mienert, J., Vanneste, M., Bunz, S., Andreassen, K., Haflidason, H.,
and Sejrup, H. P., 2005. Ocean warming and gas hydrate stability
on the mid-Norwegian margin at the Storegga Slide. Marine and
Petroleum Geology, 22, 233–244.
Nouzé, H., Cosquer, E., Collot, J., Foucher, L. P., Klingelhoefer, F.,
Lafoy, Y., and Géli, L., 2009. Geophysical characterization of
bottom simulating reflectors in the Fairway Basin (off New Caledonia, Southwest Pacific), based on high resolution seismic
profiles and heat flow data. Marine Geology, 266(1–4), 80–90.
Phrampus, B. J., and Hornbach, M. J., 2012. Recent changes to the
Gulf Stream causing widespread gas hydrate destabilization.
Nature, 490(7421), 527–530.
Rajan, A., Bünz, S., Mienert, J., and Smith, A. J., 2013. Gas hydrate
in petroleum provinces of the SW-Barents Sea. Marine and
Petroleum Geology, 46, 92–106.
Rempel, A. W., and Buffett, B. A., 1997. Formation and accumulation of gas hydrate in porous media. Journal of Geophysical
Research, 102, 10151–10164.
Shipley, T. H., Houston, M. H., Buffler, R. T., Shaub, F. J.,
McMillen, K. J., Ladd, J. W., and Worzel, J. L., 1979.
Seismic reflection evidence for the widespread occurrence of
possible gas-hydrate horizons on continental slopes and rises.
American Association of Petroleum Geologists Bulletin, 63,
2204–2213.
Sloan, D. R., 2003. Fundamental principles and applications of natural gas hydrates. Nature, 426, 353–359.
Tribble, J. S., Mackenzie, F. T., Urmos, J., O’Brien, D. K., and
Manghnani, M. H., 1992. Effects of biogenic silica on acoustic
and physical properties of clay-rich marine sediments. American
Association of Petroleum Geologists Bulletin, 76, 792–804.
Vogt, P. R., and Jung, W. Y., 2002. Holocene mass wasting on upper
non-Polar continental slopes – due to post-Glacial ocean
warming and hydrate dissociation? Geophysical Research
Letters, 29, 55-1–55-4.
Wood, W. T., Gettrust, J. F., Chapman, N. R., Spence, G. D., and
Hyndman, R. D., 2002. Decreased stability of methane hydrates
in marine sediments owing to phase-boundary roughness.
Nature, 420, 656–660.
Zatsepina, O. Y., and Buffett, B. A., 1998. Thermodynamic conditions for the stability of gas hydrate in the seafloor. Journal of
Geophysical Research, 103, 24127–24139.
Cross-references
Cold Seeps
Deep-sea Sediments
Marine Gas Hydrates
Methane in Marine Sediments
Silica
BOTTOM-BOUNDARY LAYER
Wenyan Zhang
MARUM-Center for Marine Environmental Sciences,
University of Bremen, Bremen, Germany
Definition
In marine geosciences, the bottom boundary layer (BBL)
refers to a layer of flow in the immediate vicinity of the
solid sea bottom where the effects of viscosity are significant in determining the characteristics of the flow. The
BBL was first discovered by Prandtl (1905) in aerodynamics and subsequently applied to other fluids moving on the
surface of a solid body.
Starting upwards from the sea bed, the total thickness of
the BBL is defined as the distance above the bottom at which
the mean flow velocity equals to 0.99 U ? , where U ? is the
free-stream velocity of a layer that is in a geostrophic balance
overlying the BBL. On top of the geostrophically balanced
layer is a surface layer subjected to wind-wave mixing. When
both the bottom micro-topography is uniform and the overlying flow is steady, the BBL can be easily quantified from the
vertical flow structure. Various ways exist to estimate the
thickness d of the BBL under neutral conditions (e.g., Grant
and Madsen, 1986; Nielsen, 1992). In general, the BBL
thickness at continental margins is at the order of 5–50 m.
Theoretically the BBL can be classified into three different sub-layers:
(1) A thin inner layer just above the bottom where turbulence is inhibited by the presence of the solid boundary.
The flow is controlled by molecular viscosity and the
shear stress is consistent with the bottom shear stress.
(2) An outer layer where turbulence shear dominates and
viscous shear can be neglected.
(3) A transitional layer where both the viscous shear and
the turbulence shear are important.
As the shear stress is almost constant and fulfills Newton’s law of viscosity in the inner layer, flow velocity can
thus be approximated by a linear form. However, this only
applies to a hydraulically smooth bottom where bed
roughness is too small to affect the velocity distribution.
In hydraulically rough bottom, bed roughness is large
enough to produce eddies close to the bottom and the inner
layer may not be detectable. Upwards from the inner layer,
the importance of molecular viscous decreases and turbulence gradually dominates the flow. Mean flow velocity in
this transitional layer obeys the law of the wall and can be
BOTTOM-BOUNDARY LAYER
67