THE DEEP ATLANTIC OCEAN
121
Deuser et al. (1981) and Deuser (1986) studied samples
collected between 1978 and 1984 by a trap moored
at 3200 m water depth (1000 m above the seafloor) in
the Sargasso Sea. The flux of particles of different
sizes and compositions fluctuated seasonally and there
was also considerable interannual variation in the
magnitude and timing of the flux. More recent studies
have been carried out in the Northeast Atlantic, a
more productive region than the Sargasso Sea, as
part of the Biochemical Ocean Flux Study (BOFS).
Traps were deployed by Honjo and Manganini (1993)
approximately 4000 m, 3200 m and 700 m above the
bottom at 48ºN, 21ºW (water depth 5261 m) and
34ºN, 21ºW (water depth 5083 m), and by Newton
et al. (1994) 1455 m and 90 m above the bottom at
47ºN, 20ºW (4555 m water depth). In all cases the
particulate flux through the water column was distinctly
seasonal.
The mass seasonal deposition of aggregated phytodetritus to the ocean floor was first revealed in studies
by the Institute of Oceanographic Sciences Deacon
Laboratory (IOSDL; now part of the Southampton
Oceanography Centre), conducted during the 1980s
in the Porcupine Seabight, an embayment of the
continental margin southwest of Ireland (50ºN, 13ºW)
(Rice et al., 1991). Phytodetritus was photographed
on the seabed down to 4000 m during phototransects
using the IOSDL epibenthic sledge and collected using
the Barnett-Watson multiple corer (Billett et al., 1983;
Rice et al., 1986). Subsequently, its arrival on the
seafloor during the late spring and early summer, and
its subsequent dispersal and disappearance from the
seafloor by late summer, were documented by means of
the BATHYSNAP time-lapse camera system (Lampitt
and Burnham, 1983; Lampitt, 1985). For example, the
BATHYSNAP record for 1984 shows a distinct peak
in late May (Lampitt et al., 1995), although the timing
of the peak and its intensity often varies between years
(Newton et al., 1994). Phytodetritus has been observed
at a variety of other continental margin sites in the
Northeast Atlantic including the Bay of Biscay (Sibuet,
1985), the Norwegian continental margin (Graf, 1989),
and at 20ºN off the Northwest African margin. Its
deposition is also well documented in more central
oceanic regions of the NE Atlantic, in particular the
BIOTRANS
5 area, which is centered around 19º40
W,
47º20
N in the foothills of the Mid-Atlantic Ridge
(Thiel et al., 1988/89; Pfannkuche, 1993), and on the
adjacent Porcupine Abyssal Plain (Rice et al., 1994).
On the western side of the North Atlantic, Hecker
(1990b) described the occurrence of phytodetritus
between 450 m and 2400 m on the continental slope
south of New England. Deposits were heaviest between
1000 m and 1500 m, and were observed to move
downslope over a five-day period. Phytodetritus was
also observed in the Lydonia canyon (2000 m) during
April 1996. The delivery of phytodetritus to the seafloor
appears to occur in areas of the North Atlantic where
the winter thermocline is relatively deep (>500 m on
the Porcupine Abyssal Plain), leading to a strong
spring bloom and an accumulation of phytoplankton
biomass (Rice et al., 1994). This corresponds broadly
to the North Atlantic Drift province of Longhurst
(1995) and Sathyendranath et al. (1995), and the
mid-latitude zone of Campbell and Aarup (1992).
There is no evidence for inputs of phytodetritus in
more oligotrophic regions such as the Sargasso Sea.
Phytodetritus was not observed in core samples or
in long-term BATHYSNAP sequences obtained at the
Madeira Abyssal Plain (4940 m; 31ºN, 21ºW) and Cape
Verde Abyssal Plain (4535 m; 21ºN, 31ºW) sites of the
Southampton Oceanography Centre (Rice et al., 1994).
Bottom photographs taken by Christiansen and Thiel
(1992) at 31º and 34ºN on the Madeira Plain, however,
suggest that some deposition may occur in this region.
North Atlantic phytodetritus has the following general characteristics. It is composed of the remains
of various organisms derived from the euphotic zone
(including Cyanobacteria, small chlorophyte algae,
diatoms, coccolithophorids, silicoflagellates, dinoflagellates, tintinnids, radiolarians and Foraminifera), crustacean moults, small fecal pellets (‘minipellets’), bound
together in a gelatinous matrix to form aggregates up
to about 1 cm in diameter (Billett et al., 1983; Thiel
et al., 1988/89). Phytodetritus contains rich populations
of bacteria, some of them barophilic
6 , as well as active
cyanobacteria which originate from surface waters
(Lochte and Turley, 1988) and may make good markers
for freshly deposited phytodetritus (Pfannkuche and
Lochte, 1993). The aggregates form an often extremely
patchy layer (from a few mm to several cm in thickness)
on the seafloor, and are typically concentrated in
5 BIOTRANS: BIOlogical vertical TRANSport and energetics in the benthic boundary layer of the deep sea. The BIOTRANS study area is
bounded by the following coordinates: 47º00 −47º30 N, 19º−20ºW.
6 Requiring high pressure for growth.
121
Deuser et al. (1981) and Deuser (1986) studied samples
collected between 1978 and 1984 by a trap moored
at 3200 m water depth (1000 m above the seafloor) in
the Sargasso Sea. The flux of particles of different
sizes and compositions fluctuated seasonally and there
was also considerable interannual variation in the
magnitude and timing of the flux. More recent studies
have been carried out in the Northeast Atlantic, a
more productive region than the Sargasso Sea, as
part of the Biochemical Ocean Flux Study (BOFS).
Traps were deployed by Honjo and Manganini (1993)
approximately 4000 m, 3200 m and 700 m above the
bottom at 48ºN, 21ºW (water depth 5261 m) and
34ºN, 21ºW (water depth 5083 m), and by Newton
et al. (1994) 1455 m and 90 m above the bottom at
47ºN, 20ºW (4555 m water depth). In all cases the
particulate flux through the water column was distinctly
seasonal.
The mass seasonal deposition of aggregated phytodetritus to the ocean floor was first revealed in studies
by the Institute of Oceanographic Sciences Deacon
Laboratory (IOSDL; now part of the Southampton
Oceanography Centre), conducted during the 1980s
in the Porcupine Seabight, an embayment of the
continental margin southwest of Ireland (50ºN, 13ºW)
(Rice et al., 1991). Phytodetritus was photographed
on the seabed down to 4000 m during phototransects
using the IOSDL epibenthic sledge and collected using
the Barnett-Watson multiple corer (Billett et al., 1983;
Rice et al., 1986). Subsequently, its arrival on the
seafloor during the late spring and early summer, and
its subsequent dispersal and disappearance from the
seafloor by late summer, were documented by means of
the BATHYSNAP time-lapse camera system (Lampitt
and Burnham, 1983; Lampitt, 1985). For example, the
BATHYSNAP record for 1984 shows a distinct peak
in late May (Lampitt et al., 1995), although the timing
of the peak and its intensity often varies between years
(Newton et al., 1994). Phytodetritus has been observed
at a variety of other continental margin sites in the
Northeast Atlantic including the Bay of Biscay (Sibuet,
1985), the Norwegian continental margin (Graf, 1989),
and at 20ºN off the Northwest African margin. Its
deposition is also well documented in more central
oceanic regions of the NE Atlantic, in particular the
BIOTRANS
5 area, which is centered around 19º40
W,
47º20
N in the foothills of the Mid-Atlantic Ridge
(Thiel et al., 1988/89; Pfannkuche, 1993), and on the
adjacent Porcupine Abyssal Plain (Rice et al., 1994).
On the western side of the North Atlantic, Hecker
(1990b) described the occurrence of phytodetritus
between 450 m and 2400 m on the continental slope
south of New England. Deposits were heaviest between
1000 m and 1500 m, and were observed to move
downslope over a five-day period. Phytodetritus was
also observed in the Lydonia canyon (2000 m) during
April 1996. The delivery of phytodetritus to the seafloor
appears to occur in areas of the North Atlantic where
the winter thermocline is relatively deep (>500 m on
the Porcupine Abyssal Plain), leading to a strong
spring bloom and an accumulation of phytoplankton
biomass (Rice et al., 1994). This corresponds broadly
to the North Atlantic Drift province of Longhurst
(1995) and Sathyendranath et al. (1995), and the
mid-latitude zone of Campbell and Aarup (1992).
There is no evidence for inputs of phytodetritus in
more oligotrophic regions such as the Sargasso Sea.
Phytodetritus was not observed in core samples or
in long-term BATHYSNAP sequences obtained at the
Madeira Abyssal Plain (4940 m; 31ºN, 21ºW) and Cape
Verde Abyssal Plain (4535 m; 21ºN, 31ºW) sites of the
Southampton Oceanography Centre (Rice et al., 1994).
Bottom photographs taken by Christiansen and Thiel
(1992) at 31º and 34ºN on the Madeira Plain, however,
suggest that some deposition may occur in this region.
North Atlantic phytodetritus has the following general characteristics. It is composed of the remains
of various organisms derived from the euphotic zone
(including Cyanobacteria, small chlorophyte algae,
diatoms, coccolithophorids, silicoflagellates, dinoflagellates, tintinnids, radiolarians and Foraminifera), crustacean moults, small fecal pellets (‘minipellets’), bound
together in a gelatinous matrix to form aggregates up
to about 1 cm in diameter (Billett et al., 1983; Thiel
et al., 1988/89). Phytodetritus contains rich populations
of bacteria, some of them barophilic
6 , as well as active
cyanobacteria which originate from surface waters
(Lochte and Turley, 1988) and may make good markers
for freshly deposited phytodetritus (Pfannkuche and
Lochte, 1993). The aggregates form an often extremely
patchy layer (from a few mm to several cm in thickness)
on the seafloor, and are typically concentrated in
5 BIOTRANS: BIOlogical vertical TRANSport and energetics in the benthic boundary layer of the deep sea. The BIOTRANS study area is
bounded by the following coordinates: 47º00 −47º30 N, 19º−20ºW.
6 Requiring high pressure for growth.