THE PERIPHERAL DEEP SEAS
265
round isolated hydrothermal vents, these represent the
warmest abyssal water in the world’s oceans. Minimum
oxygen levels are 3.5 ml °
−1 in the eastern basin, whilst
in the western basin values usually exceed 4.0 ml °
−1 .
There is recent evidence that shows there is seasonal
variation in oxygen content, at least in intermediate
waters (Souvermezoglou et al., 1999).
Deep water sediments
The sediments of the deeper parts of the Mediterranean are soft, consisting of firm red or blue clayish
muds (Emelyanov, 1972; Nairn et al., 1978; P´ er` es,
1985) resulting from river input, and aeolian dusts
blowing over the sea from North Africa. Riverine
input has increased as a result of deforestation of the
catchments feeding rivers entering the Mediterranean.
Exceptionally low surface productivity leads to a very
slow rate of accumulation of biogenous sediments,
particularly in the eastern Mediterranean. However,
biogenous sediments dominate eastwards, with an
increase in the calcium carbonate content. Oozes
are formed from Foraminifera, coccolithophorids and
pteropods. Terrigenous deposits arise from riverine
input, especially from the Rhˆ one, which gives rise
to a deep-sea fan (Bellaiche et al., 1983; Fredj and
Laubier, 1985). The calcium carbonate compensation
depth may vary from 1000 to 2500 m, which is much
shallower than in the major oceans because of the
high in situ temperature (see Chapter 3). The Nile
made a significant terrigenous contribution between
Cyprus and Syria, but this source has all but ceased
with the building of the High Aswan Dam. Values for
organic carbon in deep-water sediments range from
0.2 to 1.6% with typical values of 1.14% west of
Corsica and 0.9% off Monaco (Carpine, 1970). Hard
substrata are relatively rare, consisting of ahermatypic
corals; at bathyal depths these appear to be in decline.
The main areas of rock outcrop are near the coasts.
Lastly, there is evidence for mud volcanoes and
hypersaline lakes in the eastern Mediterranean (Corselli
and Basso, 1996). It should be noted, however, that
Fredj and Laubier (1985) doubted the importance of the
different sediment types in the soft-substratum deepwater ecology of the Mediterranean.
Surface production and vertical flux of organic
matter
Up to the 1980s relatively few data were available quantifying both total surface production and
vertical flux to depth (Table 9.2). Surface biomass
and productivity, for the western Mediterranean, has
been estimated from satellite imagery (Morel and
Andr´ e, 1991; Arnone, 1994). Surface productivity
over deep water varies seasonally, with maximum
production of ~400 mg C m
−2 d
−1 in May of each year
and a minimal production of <120 mg C m
−2 d
−1 in
November (Morel and Andr´ e, 1991). Phytoplankton
biomass decreases rapidly away from shore, with a
maximum biomass over the Alboran Sea and minimal
in the central western Mediterranean (Arnone, 1994).
Arnone also noted that subregions of the western
Mediterranean with energetic circulation have higher
chlorophyll concentrations. If one assumes that 1%
of surface production reaches a depth of 2000 m,
then the maximum vertical flux will be 4 mg C m
−2 d
−1
to the deep sea. Empirical data for vertical flux in
the Mediterranean are sparse and highly localized.
Off Corsica, sediment traps moored at a depth of
200 m collected a mass flux of material varying
from 8 to 335 mg m
−2 d
−1 of which between 8 and
15% was organic matter (Buat-M´ enard et al., 1989).
Much of the flux, particularly in late January and
early February, was in the form of faecal pellets.
Fowler et al. (1991) measured particle flux at 200 m
depth off Monaco. Maximum particle flux occurred
in late winter and early spring although the organiccarbon flux, equivalent to 42% of surface production,
followed the spring phytoplankton bloom. Fowler
et al. (1991) showed that organic-carbon flux varied
from 26.4 mg C m
−2 d
−1 in winter to 93.7 mg C m
−2 d
−1
during the spring phytoplankton bloom. Much of the
organic-carbon flux consisted of copepod faecal pellets,
although Andersen and Nival (1988) have suggested
that salps were the main producers of these pellets.
Sink rates in this region had been estimated at 29 m d
−1
(Fowler et al., 1987). In the Golfe du Lion and
the Catalan Sea vertical flux was highly seasonal
(Danovaro et al., 1999), although this seasonal variation
was damped in the Foix submarine canyon south of
Barcelona (41ºN, 2ºE) (Puig et al., 2000). Buscail et al.
(1990) recorded values of 92.7 mg C m
−2 d
−1 at a depth
of 645 m in the open sea of the Golfe du Lion. About
10% of surface production (~15 mg C m
−2 d
−1 in the
Golfe du Lion) reaches a depth of 1000 m. Monaco
et al. (1990a,b, 1999) have shown that there appears
to be preferential downward transport within canyons
in the Northwest Mediterranean.
Between Crete and the island of Antikythira in
the eastern Mediterannean the EU-funded PELAGOS
programme, using sediment traps to a maximum depth
of 1345 m, found that the total mass flux varied from
265
round isolated hydrothermal vents, these represent the
warmest abyssal water in the world’s oceans. Minimum
oxygen levels are 3.5 ml °
−1 in the eastern basin, whilst
in the western basin values usually exceed 4.0 ml °
−1 .
There is recent evidence that shows there is seasonal
variation in oxygen content, at least in intermediate
waters (Souvermezoglou et al., 1999).
Deep water sediments
The sediments of the deeper parts of the Mediterranean are soft, consisting of firm red or blue clayish
muds (Emelyanov, 1972; Nairn et al., 1978; P´ er` es,
1985) resulting from river input, and aeolian dusts
blowing over the sea from North Africa. Riverine
input has increased as a result of deforestation of the
catchments feeding rivers entering the Mediterranean.
Exceptionally low surface productivity leads to a very
slow rate of accumulation of biogenous sediments,
particularly in the eastern Mediterranean. However,
biogenous sediments dominate eastwards, with an
increase in the calcium carbonate content. Oozes
are formed from Foraminifera, coccolithophorids and
pteropods. Terrigenous deposits arise from riverine
input, especially from the Rhˆ one, which gives rise
to a deep-sea fan (Bellaiche et al., 1983; Fredj and
Laubier, 1985). The calcium carbonate compensation
depth may vary from 1000 to 2500 m, which is much
shallower than in the major oceans because of the
high in situ temperature (see Chapter 3). The Nile
made a significant terrigenous contribution between
Cyprus and Syria, but this source has all but ceased
with the building of the High Aswan Dam. Values for
organic carbon in deep-water sediments range from
0.2 to 1.6% with typical values of 1.14% west of
Corsica and 0.9% off Monaco (Carpine, 1970). Hard
substrata are relatively rare, consisting of ahermatypic
corals; at bathyal depths these appear to be in decline.
The main areas of rock outcrop are near the coasts.
Lastly, there is evidence for mud volcanoes and
hypersaline lakes in the eastern Mediterranean (Corselli
and Basso, 1996). It should be noted, however, that
Fredj and Laubier (1985) doubted the importance of the
different sediment types in the soft-substratum deepwater ecology of the Mediterranean.
Surface production and vertical flux of organic
matter
Up to the 1980s relatively few data were available quantifying both total surface production and
vertical flux to depth (Table 9.2). Surface biomass
and productivity, for the western Mediterranean, has
been estimated from satellite imagery (Morel and
Andr´ e, 1991; Arnone, 1994). Surface productivity
over deep water varies seasonally, with maximum
production of ~400 mg C m
−2 d
−1 in May of each year
and a minimal production of <120 mg C m
−2 d
−1 in
November (Morel and Andr´ e, 1991). Phytoplankton
biomass decreases rapidly away from shore, with a
maximum biomass over the Alboran Sea and minimal
in the central western Mediterranean (Arnone, 1994).
Arnone also noted that subregions of the western
Mediterranean with energetic circulation have higher
chlorophyll concentrations. If one assumes that 1%
of surface production reaches a depth of 2000 m,
then the maximum vertical flux will be 4 mg C m
−2 d
−1
to the deep sea. Empirical data for vertical flux in
the Mediterranean are sparse and highly localized.
Off Corsica, sediment traps moored at a depth of
200 m collected a mass flux of material varying
from 8 to 335 mg m
−2 d
−1 of which between 8 and
15% was organic matter (Buat-M´ enard et al., 1989).
Much of the flux, particularly in late January and
early February, was in the form of faecal pellets.
Fowler et al. (1991) measured particle flux at 200 m
depth off Monaco. Maximum particle flux occurred
in late winter and early spring although the organiccarbon flux, equivalent to 42% of surface production,
followed the spring phytoplankton bloom. Fowler
et al. (1991) showed that organic-carbon flux varied
from 26.4 mg C m
−2 d
−1 in winter to 93.7 mg C m
−2 d
−1
during the spring phytoplankton bloom. Much of the
organic-carbon flux consisted of copepod faecal pellets,
although Andersen and Nival (1988) have suggested
that salps were the main producers of these pellets.
Sink rates in this region had been estimated at 29 m d
−1
(Fowler et al., 1987). In the Golfe du Lion and
the Catalan Sea vertical flux was highly seasonal
(Danovaro et al., 1999), although this seasonal variation
was damped in the Foix submarine canyon south of
Barcelona (41ºN, 2ºE) (Puig et al., 2000). Buscail et al.
(1990) recorded values of 92.7 mg C m
−2 d
−1 at a depth
of 645 m in the open sea of the Golfe du Lion. About
10% of surface production (~15 mg C m
−2 d
−1 in the
Golfe du Lion) reaches a depth of 1000 m. Monaco
et al. (1990a,b, 1999) have shown that there appears
to be preferential downward transport within canyons
in the Northwest Mediterranean.
Between Crete and the island of Antikythira in
the eastern Mediterannean the EU-funded PELAGOS
programme, using sediment traps to a maximum depth
of 1345 m, found that the total mass flux varied from