320
John D. GAGE
of 1000 to 2000 m they become unimportant (Turley,
1993). Probably, free-living bacteria are more active
in particle degradation, breaking them into fine nonsinking particles at the expense of fast-sinking ones
(Cho and Azam, 1988). Overall, such small particles
of intermediate size, whether representing macroaggregates or faecal pellets, constitute the majority
of the flux of organic material to the deep-sea floor
(McCave, 1975).
Very fine particles
There are, of course, smaller organic particles, (<1 micron to tens of microns) at the ocean surface, consisting
of fine organic detritus, nanoflagellates and free-living
bacteria, whose activity may be important in determining organic-carbon flux into deep water (Cho and
Azam, 1988). These fine particles stay in suspension
or sink very slowly and consist mainly of refractory
compounds. Stable isotope (d
13 C) and radiocarbon
(
14 C) ageing of deep particulate suspended carbon
(particulate organic carbon susp ) shows it to be older, as
well in far higher concentrations, near the margin than
in the adjacent oceanic gyres in the Atlantic and Pacific,
where it becomes diluted with particles of more recent
origin at the surface (Bauer and Druffel, 1998). Bauer
and Druffel show that, particularly in ocean margins,
the pool of particulate suspended carbon, like that
of dissolved organic carbon (DOM) (see p. 359), far
exceeds that constituted by sinking particulate carbon.
Faecal pellets
While marine-snow aggregates typically dominate
particle flux in some temperate areas such as the
Northeast Atlantic, at high latitudes faecal pellets
characteristically make up the dominant flux of fastsinking particles to the deep sea. The size and shape of
these pellets depend on the source organism (reviewed
by Fowler and Knauer, 1986). Copepod pellets may
sink at rates up to 153 m day
−1 (J.T. Turner, 1977).
Those produced by salps are like those of temperate
latitudes and are recorded as loose, amorphous aggregates resembling macroflocs, although Hamer and
Robison (1992) tracked the descent of faecal pellets
from doliolids, salps and pteropods, using an ROV,
at speeds of 2100 m per day. Such particles may be
quantitatively significant in many areas (e.g., Iseki,
1981; Bathmann et al., 1987; Pfannkuche et al., 1988).
The compact, streamlined, densely packed pellets
produced by small crustaceans such as copepods and
euphausiids should also sink very quickly, explaining
the response observed within days at 1430 m depth in
the Norwegian Sea (Graf, 1989). Many faecal pellets
are enclosed by a chitinous peritrophic membrane that
is important in determining their degradatory ‘half
life’ and whether they reach the deep-sea bed intact
(Lampitt et al., 1990). The composition of faecal
pellets is diverse. Most contain phytoplankton cells
along with gut bacteria that are claimed to be of
greater importance in their degradation than microbes
colonizing from the water (Gowing and Silver, 1983).
Inorganic components, mainly calcium carbonate and
silicate, ballast the particles, and increase rate of
sinking. Overall, the nutritive value of faecal pellets
on arrival is higher than that of fine particles because
their faster sinking means they are less degraded by
colonizing microbes. Particularly at high latitudes it
seems likely that such intermediate particles comprise
the dominant source of food for the deep-sea benthic
deposit-feeding community.
Moults and dead zooplankton
Crustacean moults and dead intact organisms may
comprise the dominant component in conditions of
large particle flux, such as during seasonal blooms of
zooplankton. The mass deposition to the seabed of
the bodies of macroplanktonic species such as salps,
larvaceans and jellyfish also has been noted by several
workers (e.g., Cacchione et al., 1978; Wiebe et al.,
1979; Stockton and DeLaca, 1982). Observations by
remote-operated vehicles show that these may sink
many hundreds of metres per day (Hamer and Robison,
1992). Although it is unlikely that these falls attract
specialized scavengers to the same extent as other
carcasses, they might form part of the diet of some
of the less specialized scavengers such as smaller
lysianassid amphipods and brittle stars. In the Southern
Ocean a ‘dead body rain’ composed of euphausiids
appears, from stomach contents of brittle stars, to make
up their main diet (Sokolova, 1994).
Pattern and quantification of particle flux
Measurements of particle flux from sediment traps
illustrate how small a proportion, roughly 1 to 14%,
of total organic-carbon production in the euphotic
zone sinks into the interior of the ocean. The bulk
composition of particles is far from uniform, the
John D. GAGE
of 1000 to 2000 m they become unimportant (Turley,
1993). Probably, free-living bacteria are more active
in particle degradation, breaking them into fine nonsinking particles at the expense of fast-sinking ones
(Cho and Azam, 1988). Overall, such small particles
of intermediate size, whether representing macroaggregates or faecal pellets, constitute the majority
of the flux of organic material to the deep-sea floor
(McCave, 1975).
Very fine particles
There are, of course, smaller organic particles, (<1 micron to tens of microns) at the ocean surface, consisting
of fine organic detritus, nanoflagellates and free-living
bacteria, whose activity may be important in determining organic-carbon flux into deep water (Cho and
Azam, 1988). These fine particles stay in suspension
or sink very slowly and consist mainly of refractory
compounds. Stable isotope (d
13 C) and radiocarbon
(
14 C) ageing of deep particulate suspended carbon
(particulate organic carbon susp ) shows it to be older, as
well in far higher concentrations, near the margin than
in the adjacent oceanic gyres in the Atlantic and Pacific,
where it becomes diluted with particles of more recent
origin at the surface (Bauer and Druffel, 1998). Bauer
and Druffel show that, particularly in ocean margins,
the pool of particulate suspended carbon, like that
of dissolved organic carbon (DOM) (see p. 359), far
exceeds that constituted by sinking particulate carbon.
Faecal pellets
While marine-snow aggregates typically dominate
particle flux in some temperate areas such as the
Northeast Atlantic, at high latitudes faecal pellets
characteristically make up the dominant flux of fastsinking particles to the deep sea. The size and shape of
these pellets depend on the source organism (reviewed
by Fowler and Knauer, 1986). Copepod pellets may
sink at rates up to 153 m day
−1 (J.T. Turner, 1977).
Those produced by salps are like those of temperate
latitudes and are recorded as loose, amorphous aggregates resembling macroflocs, although Hamer and
Robison (1992) tracked the descent of faecal pellets
from doliolids, salps and pteropods, using an ROV,
at speeds of 2100 m per day. Such particles may be
quantitatively significant in many areas (e.g., Iseki,
1981; Bathmann et al., 1987; Pfannkuche et al., 1988).
The compact, streamlined, densely packed pellets
produced by small crustaceans such as copepods and
euphausiids should also sink very quickly, explaining
the response observed within days at 1430 m depth in
the Norwegian Sea (Graf, 1989). Many faecal pellets
are enclosed by a chitinous peritrophic membrane that
is important in determining their degradatory ‘half
life’ and whether they reach the deep-sea bed intact
(Lampitt et al., 1990). The composition of faecal
pellets is diverse. Most contain phytoplankton cells
along with gut bacteria that are claimed to be of
greater importance in their degradation than microbes
colonizing from the water (Gowing and Silver, 1983).
Inorganic components, mainly calcium carbonate and
silicate, ballast the particles, and increase rate of
sinking. Overall, the nutritive value of faecal pellets
on arrival is higher than that of fine particles because
their faster sinking means they are less degraded by
colonizing microbes. Particularly at high latitudes it
seems likely that such intermediate particles comprise
the dominant source of food for the deep-sea benthic
deposit-feeding community.
Moults and dead zooplankton
Crustacean moults and dead intact organisms may
comprise the dominant component in conditions of
large particle flux, such as during seasonal blooms of
zooplankton. The mass deposition to the seabed of
the bodies of macroplanktonic species such as salps,
larvaceans and jellyfish also has been noted by several
workers (e.g., Cacchione et al., 1978; Wiebe et al.,
1979; Stockton and DeLaca, 1982). Observations by
remote-operated vehicles show that these may sink
many hundreds of metres per day (Hamer and Robison,
1992). Although it is unlikely that these falls attract
specialized scavengers to the same extent as other
carcasses, they might form part of the diet of some
of the less specialized scavengers such as smaller
lysianassid amphipods and brittle stars. In the Southern
Ocean a ‘dead body rain’ composed of euphausiids
appears, from stomach contents of brittle stars, to make
up their main diet (Sokolova, 1994).
Pattern and quantification of particle flux
Measurements of particle flux from sediment traps
illustrate how small a proportion, roughly 1 to 14%,
of total organic-carbon production in the euphotic
zone sinks into the interior of the ocean. The bulk
composition of particles is far from uniform, the