Chapter 7: APPLICATIONS
Aggregates collide and form larger aggregates. The large aggregates sink
until they reach neutral density. If this does not occur, then the thin layer will
never form because the aggregates will continue sinking and no
accumulation will occur. Attainment of neutral density is a requirement for
the persistence of any layer of passively sinking particles. Alldredge and
Crocker (1995) proposed that neutral buoyancy of an aggregate sinking from
a lower salinity surface layer into a halocline could be attained if some
proportion of the aggregate’s interstitial volume was occupied by lowerdensity mucus, which is resistant to the diffusion of salts and water.
Interstitial mucus would form from the gelatin and aggregation of
polysaccharides exuded by the diatoms in the lower-salinity layer (Alldredge
et al., 1993). The sharp salinity gradient in the fjord created the sharp density
interfaces that accumulated marine snow in the form of thin layers observed
in Figure 7-8.
The thin biologically active layers have mostly been observed in the
coastal zones of the ocean. Terrestrial runoff and river outflows provide
organic rich waters to the coastal ocean. In the open ocean, observations of
biological and chemical thin layers near the surface are nevertheless quite
rare. The importance and the frequency of occurrence of this phenomenon in
the open ocean are therefore largely unknown (which can in part be
explained by the absence of proper techniques for the measurement of
biochemical parameters near the air-sea interface).
Theoretical studies indicate that thin near-surface layers of biota can
change remote sensing reflectance R rs defined by (7.2) up to several percent
(Petrenko et al., 1998). The color imagery methods described in Section
7.1.6) are based on the assumption of a vertically homogeneous ocean.
Further development of remote sensing techniques may enable identification
of thin biological layers in the upper ocean.
7.4 Ocean Acoustics
The sea surface is an important element of the acoustic environment of
the ocean (Brekhovskich and Lysanov, 1978). However, in contrast to other
types of ocean boundaries such as the sea bottom or ice cover, the free sea
surface by itself does not absorb acoustical energy—it just scatters it. The
scattering of sound at the wave disturbed surface leads to space and time
fluctuations of the propagating sound; as a result, spectral and statistical
characteristics of the sound change. Sound scattered from the ocean surface
may represent a serious disturbance to the effectiveness of hydro-acoustical
systems.
In addition to scatter from the ocean surface, the acoustic signal may
scatter due to near-surface turbulence, microstructure, and fine structure.
Sound refraction due to internal waves in the near-surface thermocline or
459
Aggregates collide and form larger aggregates. The large aggregates sink
until they reach neutral density. If this does not occur, then the thin layer will
never form because the aggregates will continue sinking and no
accumulation will occur. Attainment of neutral density is a requirement for
the persistence of any layer of passively sinking particles. Alldredge and
Crocker (1995) proposed that neutral buoyancy of an aggregate sinking from
a lower salinity surface layer into a halocline could be attained if some
proportion of the aggregate’s interstitial volume was occupied by lowerdensity mucus, which is resistant to the diffusion of salts and water.
Interstitial mucus would form from the gelatin and aggregation of
polysaccharides exuded by the diatoms in the lower-salinity layer (Alldredge
et al., 1993). The sharp salinity gradient in the fjord created the sharp density
interfaces that accumulated marine snow in the form of thin layers observed
in Figure 7-8.
The thin biologically active layers have mostly been observed in the
coastal zones of the ocean. Terrestrial runoff and river outflows provide
organic rich waters to the coastal ocean. In the open ocean, observations of
biological and chemical thin layers near the surface are nevertheless quite
rare. The importance and the frequency of occurrence of this phenomenon in
the open ocean are therefore largely unknown (which can in part be
explained by the absence of proper techniques for the measurement of
biochemical parameters near the air-sea interface).
Theoretical studies indicate that thin near-surface layers of biota can
change remote sensing reflectance R rs defined by (7.2) up to several percent
(Petrenko et al., 1998). The color imagery methods described in Section
7.1.6) are based on the assumption of a vertically homogeneous ocean.
Further development of remote sensing techniques may enable identification
of thin biological layers in the upper ocean.
7.4 Ocean Acoustics
The sea surface is an important element of the acoustic environment of
the ocean (Brekhovskich and Lysanov, 1978). However, in contrast to other
types of ocean boundaries such as the sea bottom or ice cover, the free sea
surface by itself does not absorb acoustical energy—it just scatters it. The
scattering of sound at the wave disturbed surface leads to space and time
fluctuations of the propagating sound; as a result, spectral and statistical
characteristics of the sound change. Sound scattered from the ocean surface
may represent a serious disturbance to the effectiveness of hydro-acoustical
systems.
In addition to scatter from the ocean surface, the acoustic signal may
scatter due to near-surface turbulence, microstructure, and fine structure.
Sound refraction due to internal waves in the near-surface thermocline or
459