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Craig R. SMITH and Amanda W.J. DEMOPOULOS
remains); (3) the sinking carcasses of nekton (crustaceans, fish, whales, etc.); and (4) sinking parcels of
macroalgae such as kelp (e.g., Macrocystis pyrifera).
The rain of small particles is the best studied
pathway of carbon flux in the northeast Pacific. Based
on long-term sediment-trap measurements (K.L. Smith
et al., 1992; Thunell et al., 1994; Drazen et al., 1998),
the sinking flux of organic carbon in the form of small
particles to the California slope varies temporally, with
seasonal pulses apparently resulting from enhanced
phytoplankton production in the spring and summer
(K.L. Smith et al., 1992). These episodic inputs appear
to be important to the benthos because sedimentcommunity oxygen consumption, as measured with
in situ respirometers at 4100 m at the base of the
California slope (Station M, Fig. 6.1), tracks the
seasonal influx (K.L. Smith et al., 1992, 1994; Sayles
et al., 1994; Drazen et al., 1998). The time lag between
peaks in flux of small particulate organic carbon
and sediment-community oxygen consumption at this
site suggest that the mean half-life for the degrading
organic carbon is 25–50 days (Sayles et al., 1994) –
that is, it is similar in lability to fresh phytoplankton
detritus (C.R. Smith et al.,1993). Drazen et al. (1998)
also offer some tantalizing evidence that abundance of
the macrofaunal community at 4100 m may track the
seasonal pulse of particulate organic carbon, in this
case with an 8-month time lag; however, the temporal
coverage of their study (two years) was too small to be
conclusive.
As in the North Atlantic and equatorial Pacific,
centimeter-scale aggregates rich in phytoplankton remains (“phytodetritus”) also appear to arrive episodically on the deep seafloor along the California margin
(K.L. Smith et al., 1994; C.R. Smith, 1994). Off
California, as in the North Atlantic, the flux of
such phytodetritus appears be related to phytoplankton
blooms (Beaulieu and Smith, 1998). Whenever studied
in the deep sea, phytodetrital aggregates have proven
to be rich in fresh phytoplankton cells, chlorophyll a
and other labile organic compounds, and to sustain
high rates of microbial activity (Rice et al., 1986; Thiel
et al., 1988/89; C.R. Smith et al., 1996); thus, it is often
conjectured that phytodetritus provides a high-quality
food resource for the deep-sea fauna. At a site 4100 m
deep at the base of the California slope (Station M,
Fig. 6.1), K.L. Smith and co-workers have conducted
the most detailed study to date of the significance of
phytodetritus to a deep-sea ecosystem. At this station
beneath the California Current off central California,
phytodetrital aggregates arrive in pulses on the seafloor
between July and December (K.L. Smith et al., 1998).
Over a two-year period, mean aggregate size at
arrival varied roughly between 10 and 150 cm
2 , and
aggregates could cover up to 4.9% of the seafloor (K.L.
Smith et al., 1998). The composition of phytodetrital
aggregates was variable, but they included chainforming diatoms, phaeodarians and/or zooplankton mucus webs (Beaulieu and Smith, 1998); the aggregates
were substantially richer in organic carbon (4–5%
by weight), total nitrogen and phaeopigments than
underlying sediments (K.L. Smith et al., 1998). Based
on disappearance times of aggregates in time-lapse
photographs (~2 days), and direct measurements of
the organic-carbon content of aggregates recovered
in cores, the flux of organic carbon in the form
of phytodetritus was large, being equivalent to 43–
100% of the annual flux of small particulate organic
carbon into near-bottom sediments traps deployed at
the site. Nonetheless, sediment-community oxygen
consumption was only slightly elevated in tube cores
38 cm
2 in cross-section containing phytodetrital aggregates, and the total carbon mineralization in visible
aggregates, even during peak phytodetrital abundance,
was calculated to constitute only 0.34% of the oxygen
consumption of the sediment community (K.L. Smith
et al., 1998). Thus, much of the organic carbon in these
phytodetrital aggregates appeared to be metabolized
over much longer time scales than the two days or
so for which individual aggregates remained visible
on the seafloor. This is not surprising considering that
the mean half-life of metabolized particulate organic
carbon at this site appears to be 25–50 days (Sayles
et al., 1994). However, sediment protozoans (primarily
agglutinating Foraminifera) increased in abundance
and density within four weeks of phytodetrital input
(Drazen et al., 1998), and mobile epibenthic megafauna
appeared to increase their rates of locomotion when
phytodetritus was present. In conclusion, phytodetrital
aggregates provided a substantial flux of particulate
organic carbon to the seafloor, but during the short
period of time (~2 days) in which individual aggregates
remained coherent enough to be visible on the seafloor
they did not appear to be heavily utilized by the
benthic assemblage. However, following phytodetritus
disaggregation, labile organic matter derived from the
phytodetritus may have been preferentially utilized by
some components of the benthic community (e.g.,
Foraminifera, surface-deposit feeding megafauna).
Compared to the rain of fine particles, the flux of
Craig R. SMITH and Amanda W.J. DEMOPOULOS
remains); (3) the sinking carcasses of nekton (crustaceans, fish, whales, etc.); and (4) sinking parcels of
macroalgae such as kelp (e.g., Macrocystis pyrifera).
The rain of small particles is the best studied
pathway of carbon flux in the northeast Pacific. Based
on long-term sediment-trap measurements (K.L. Smith
et al., 1992; Thunell et al., 1994; Drazen et al., 1998),
the sinking flux of organic carbon in the form of small
particles to the California slope varies temporally, with
seasonal pulses apparently resulting from enhanced
phytoplankton production in the spring and summer
(K.L. Smith et al., 1992). These episodic inputs appear
to be important to the benthos because sedimentcommunity oxygen consumption, as measured with
in situ respirometers at 4100 m at the base of the
California slope (Station M, Fig. 6.1), tracks the
seasonal influx (K.L. Smith et al., 1992, 1994; Sayles
et al., 1994; Drazen et al., 1998). The time lag between
peaks in flux of small particulate organic carbon
and sediment-community oxygen consumption at this
site suggest that the mean half-life for the degrading
organic carbon is 25–50 days (Sayles et al., 1994) –
that is, it is similar in lability to fresh phytoplankton
detritus (C.R. Smith et al.,1993). Drazen et al. (1998)
also offer some tantalizing evidence that abundance of
the macrofaunal community at 4100 m may track the
seasonal pulse of particulate organic carbon, in this
case with an 8-month time lag; however, the temporal
coverage of their study (two years) was too small to be
conclusive.
As in the North Atlantic and equatorial Pacific,
centimeter-scale aggregates rich in phytoplankton remains (“phytodetritus”) also appear to arrive episodically on the deep seafloor along the California margin
(K.L. Smith et al., 1994; C.R. Smith, 1994). Off
California, as in the North Atlantic, the flux of
such phytodetritus appears be related to phytoplankton
blooms (Beaulieu and Smith, 1998). Whenever studied
in the deep sea, phytodetrital aggregates have proven
to be rich in fresh phytoplankton cells, chlorophyll a
and other labile organic compounds, and to sustain
high rates of microbial activity (Rice et al., 1986; Thiel
et al., 1988/89; C.R. Smith et al., 1996); thus, it is often
conjectured that phytodetritus provides a high-quality
food resource for the deep-sea fauna. At a site 4100 m
deep at the base of the California slope (Station M,
Fig. 6.1), K.L. Smith and co-workers have conducted
the most detailed study to date of the significance of
phytodetritus to a deep-sea ecosystem. At this station
beneath the California Current off central California,
phytodetrital aggregates arrive in pulses on the seafloor
between July and December (K.L. Smith et al., 1998).
Over a two-year period, mean aggregate size at
arrival varied roughly between 10 and 150 cm
2 , and
aggregates could cover up to 4.9% of the seafloor (K.L.
Smith et al., 1998). The composition of phytodetrital
aggregates was variable, but they included chainforming diatoms, phaeodarians and/or zooplankton mucus webs (Beaulieu and Smith, 1998); the aggregates
were substantially richer in organic carbon (4–5%
by weight), total nitrogen and phaeopigments than
underlying sediments (K.L. Smith et al., 1998). Based
on disappearance times of aggregates in time-lapse
photographs (~2 days), and direct measurements of
the organic-carbon content of aggregates recovered
in cores, the flux of organic carbon in the form
of phytodetritus was large, being equivalent to 43–
100% of the annual flux of small particulate organic
carbon into near-bottom sediments traps deployed at
the site. Nonetheless, sediment-community oxygen
consumption was only slightly elevated in tube cores
38 cm
2 in cross-section containing phytodetrital aggregates, and the total carbon mineralization in visible
aggregates, even during peak phytodetrital abundance,
was calculated to constitute only 0.34% of the oxygen
consumption of the sediment community (K.L. Smith
et al., 1998). Thus, much of the organic carbon in these
phytodetrital aggregates appeared to be metabolized
over much longer time scales than the two days or
so for which individual aggregates remained visible
on the seafloor. This is not surprising considering that
the mean half-life of metabolized particulate organic
carbon at this site appears to be 25–50 days (Sayles
et al., 1994). However, sediment protozoans (primarily
agglutinating Foraminifera) increased in abundance
and density within four weeks of phytodetrital input
(Drazen et al., 1998), and mobile epibenthic megafauna
appeared to increase their rates of locomotion when
phytodetritus was present. In conclusion, phytodetrital
aggregates provided a substantial flux of particulate
organic carbon to the seafloor, but during the short
period of time (~2 days) in which individual aggregates
remained coherent enough to be visible on the seafloor
they did not appear to be heavily utilized by the
benthic assemblage. However, following phytodetritus
disaggregation, labile organic matter derived from the
phytodetritus may have been preferentially utilized by
some components of the benthic community (e.g.,
Foraminifera, surface-deposit feeding megafauna).
Compared to the rain of fine particles, the flux of