334
John D. GAGE
this community could have significant effects on
carbon dynamics in the deep ocean (Wishner and
Gowing, 1987). Although only a tiny fraction of
the biomass at the surface of the ocean, biomass
at 10 metres above the bottom, in response to the
relatively enriched conditions in the benthic boundary
layer, is nevertheless significantly greater than that at
and above 100 metres above the bottom in the deep
ocean interior (Wishner, 1980). Vereshchaka (1995) has
provided a useful classification of the benthopelagic
fauna in terms of their relationship with the bed.
Some organims, such as peracarid crustaceans, may be
regarded as benthopelagic by virtue of an ability to
swim up into the water above. These animals may be
an important part of the diet of larger benthopelagic
and motile megafauna such as decapod crustaceans
(Cartes, 1998). Studies of gut contents of benthopelagic
zooplankton indicate that they feed on detrital particles
and associated bacteria (Gowing and Wishner, 1986).
Studies of the rates of mineralization of organic
carbon, which have included the small benthopelagic
zooplankton (mainly copepods) along with bacterioplankton, have been conducted in the bathyal and
abyssal Pacific. These studies indicate that respiratory
demand by metazoan plankton and bacterioplankton
together, disregarding the amount utilized in growth
and reproduction, account in autumn for about 11%
of the total estimated input of organic carbon to the
benthic boundary layer (K.L. Smith et al., 1987).
This study indicated that bacterioplankton respiration
is more than an order of magnitude higher than that of
the benthopelagic zooplankton, and this was confirmed
in a more comprehensive study of all components of the
benthic boundary layer community in the central North
Pacific (K.L. Smith, 1992). As the most important
consumer group of the benthopelagic community, oxygen consumption by bacterioplankton is nevertheless
only about one-seventh that of the combined consumer
groups represented in the sediment community. But
nevertheless when compared to data for organic-carbon
flux estimated for various other consumer groups in
the benthic boundary layer (see K.L. Smith, 1992)
the benthopelagic plankton is sufficiently important to
merit inclusion in any attempt to model carbon and
energy flow in the deep sea.
Carbon utilization and remineralization by the
sediment community: measurement of oxygen
consumption
Measurements in situ of solute flux across the
sediment interface have provided the chief means of
estimating rates of seabed mineralization as a measure
of organic-carbon demand by the sediment, unenriched
by addition of any further organic material. Virtually
all of the organic input escaping burial is reduced by
oxygen, the secondary oxidants NO
−
3 , MnO 2 , Fe 2 O 3 ,
and SO
2−
4 occurring deep in the sediment and oxidizing
only a small fraction of particle rain to the sediment
(Bender and Heggie, 1984; Heggie et al., 1987). Some
of the alternative pathways may operate at certain sites,
such as upwelling zones on the continental slope. An
example of this was provided by Jorissen et al. (1998)
who found flourishing populations of foraminiferans
living deep in reducing conditions in the sediment in
the upwelling area on the upper continental slope off
Cap Blanc, Northwest Africa. These foraminiferans
were probably trophically dependent on anaerobic
and sulphate- and nitrate-reducing bacteria. But such
conditions are relatively exceptional, and never occur
to the same extent as in the coastal zone. Therefore
sediment community oxygen consumption (SCOC)
probably provides a good overall measure of organicmatter mineralization.
Methods for measuring sediment community oxygen
consumption (SCOC): Respiratory oxygen uptake
has been traditionally measured in a sealed, stirred
chamber, enclosing a small area of sediment. There
is a need to take into account pressure adaptation
and the effect of disturbance when measuring uptake
from a core of sediment retrieved from the bottom.
Sediment disturbance is important when a reactive
flocculent layer of fresh detrital material is present, in
which Pfannkuche (1993) found up to 80% of micobial
respiratory activity to be concentrated. It is best avoided
by a soft landing, with a controlled, slow emplacement
of the chamber, which prevents any ‘bow wave’ effect
that would blow superficial material sideways. If the
activity of such flocculent material is not included,
then artificially low values of sediment community
oxygen consumption may be measured. Ideally the
chamber is mounted on an autonomous vehicle, or
benthic lander, in order to measure rates in situ (e.g.,
K.L. Smith, 1978; Hall et al., 1989). (Measurements
of sediment community oxygen consumption from
cores recovered from the bottom and incubated on
shipboard tend to give higher values at greater depths
than those measured in situ; see Glud et al., 1994;
Duineveld et al., 1997). Details of the range of types
of benthic chambers and the delivery system, or
benthic lander, in present use are reviewed by Tengberg
John D. GAGE
this community could have significant effects on
carbon dynamics in the deep ocean (Wishner and
Gowing, 1987). Although only a tiny fraction of
the biomass at the surface of the ocean, biomass
at 10 metres above the bottom, in response to the
relatively enriched conditions in the benthic boundary
layer, is nevertheless significantly greater than that at
and above 100 metres above the bottom in the deep
ocean interior (Wishner, 1980). Vereshchaka (1995) has
provided a useful classification of the benthopelagic
fauna in terms of their relationship with the bed.
Some organims, such as peracarid crustaceans, may be
regarded as benthopelagic by virtue of an ability to
swim up into the water above. These animals may be
an important part of the diet of larger benthopelagic
and motile megafauna such as decapod crustaceans
(Cartes, 1998). Studies of gut contents of benthopelagic
zooplankton indicate that they feed on detrital particles
and associated bacteria (Gowing and Wishner, 1986).
Studies of the rates of mineralization of organic
carbon, which have included the small benthopelagic
zooplankton (mainly copepods) along with bacterioplankton, have been conducted in the bathyal and
abyssal Pacific. These studies indicate that respiratory
demand by metazoan plankton and bacterioplankton
together, disregarding the amount utilized in growth
and reproduction, account in autumn for about 11%
of the total estimated input of organic carbon to the
benthic boundary layer (K.L. Smith et al., 1987).
This study indicated that bacterioplankton respiration
is more than an order of magnitude higher than that of
the benthopelagic zooplankton, and this was confirmed
in a more comprehensive study of all components of the
benthic boundary layer community in the central North
Pacific (K.L. Smith, 1992). As the most important
consumer group of the benthopelagic community, oxygen consumption by bacterioplankton is nevertheless
only about one-seventh that of the combined consumer
groups represented in the sediment community. But
nevertheless when compared to data for organic-carbon
flux estimated for various other consumer groups in
the benthic boundary layer (see K.L. Smith, 1992)
the benthopelagic plankton is sufficiently important to
merit inclusion in any attempt to model carbon and
energy flow in the deep sea.
Carbon utilization and remineralization by the
sediment community: measurement of oxygen
consumption
Measurements in situ of solute flux across the
sediment interface have provided the chief means of
estimating rates of seabed mineralization as a measure
of organic-carbon demand by the sediment, unenriched
by addition of any further organic material. Virtually
all of the organic input escaping burial is reduced by
oxygen, the secondary oxidants NO
−
3 , MnO 2 , Fe 2 O 3 ,
and SO
2−
4 occurring deep in the sediment and oxidizing
only a small fraction of particle rain to the sediment
(Bender and Heggie, 1984; Heggie et al., 1987). Some
of the alternative pathways may operate at certain sites,
such as upwelling zones on the continental slope. An
example of this was provided by Jorissen et al. (1998)
who found flourishing populations of foraminiferans
living deep in reducing conditions in the sediment in
the upwelling area on the upper continental slope off
Cap Blanc, Northwest Africa. These foraminiferans
were probably trophically dependent on anaerobic
and sulphate- and nitrate-reducing bacteria. But such
conditions are relatively exceptional, and never occur
to the same extent as in the coastal zone. Therefore
sediment community oxygen consumption (SCOC)
probably provides a good overall measure of organicmatter mineralization.
Methods for measuring sediment community oxygen
consumption (SCOC): Respiratory oxygen uptake
has been traditionally measured in a sealed, stirred
chamber, enclosing a small area of sediment. There
is a need to take into account pressure adaptation
and the effect of disturbance when measuring uptake
from a core of sediment retrieved from the bottom.
Sediment disturbance is important when a reactive
flocculent layer of fresh detrital material is present, in
which Pfannkuche (1993) found up to 80% of micobial
respiratory activity to be concentrated. It is best avoided
by a soft landing, with a controlled, slow emplacement
of the chamber, which prevents any ‘bow wave’ effect
that would blow superficial material sideways. If the
activity of such flocculent material is not included,
then artificially low values of sediment community
oxygen consumption may be measured. Ideally the
chamber is mounted on an autonomous vehicle, or
benthic lander, in order to measure rates in situ (e.g.,
K.L. Smith, 1978; Hall et al., 1989). (Measurements
of sediment community oxygen consumption from
cores recovered from the bottom and incubated on
shipboard tend to give higher values at greater depths
than those measured in situ; see Glud et al., 1994;
Duineveld et al., 1997). Details of the range of types
of benthic chambers and the delivery system, or
benthic lander, in present use are reviewed by Tengberg