THE PELAGIC ENVIRONMENT OF THE OPEN OCEAN
71
cycles and the pelagic community structure. Similarly
the differing seasonal patterns of input of organic
carbon to the bottom-living communities will influence
their structure and dynamics. There is initial evidence
of there being some coherence between Longhurst’s
provinces and the zoogeographical distributions of benthic abyssal species (Sokolova, 1990; Rex et al.,1993).
Merrett (1987) had already suggested that benthic
abyssal fishes show a clear faunal boundary in species
richness and dominance at around 40ºN in the Northeastern Atlantic – a boundary that is coincident with
the change from a domain in which there are markedlypulsed seasonal inputs to the subtropical/tropical domain in which the sedimentary inputs are far less
variable. At temperate latitudes, sediment trap records
show that the sedimentary fluxes vary by over two
orders of magnitude (Wefer, 1989; Fig. 3.13) and
there is heavy seasonal deposition of phytodetritus on
the sea-floor (Billett et al., 1983; Rice et al., 1994).
Deposition of phytodetritus has also been observed
beneath the high-productivity zone along the equator in
the Pacific (Smith et al., 1996). At lower latitudes, such
as the area off Bermuda (e.g., Deuser, 1987), the sediment trap fluxes vary by about an order of magnitude
throughout the year and there have been no reports of
deposition of phytodetritus. Lampitt and Antia (1997)
have recently analysed all the published data on fluxes
normalized to a depth of 2000 m from 67 long-term
sediment-trap records. Several of their conclusions
are unexpected. Organic carbon fluxes at depths of
2000 m ranged just over an order of magnitude, from
0.38 to 4.2 g C m
−2 y
−1 in most oceanic areas, but the
range was greater in polar seas (0.01–5.9 g C m
−2 y
−1 ).
Where fluxes were most variable throughout the
year, a greater proportion of primary production was
being exported. Where primary production less than
200 g C m
−2 y
−1 there is a positive correlation between
productivity and organic carbon fluxes at 2000 m.
But unexpectedly further increases in productivity did
not result in any further increases in fluxes. The
relationship between production and flux follows a
hyperbolic tangential curve, and reaches a maximum
flux of c. 3.5 g C m
−2 y
−1 . Once export production
attained this maximum, there was no evidence of the
deep fluxes being affected by further increases in
primary production. Thus, the ratio between export
production, as measured by sediment traps, and total
productivity declines as primary production increases
beyond 200 g C m
−2 y
−1 . In correlating flux patterns
Post bloom
1989
Bloom
Pre-bloom
1070m
1240 m
1990
Bloom
0
50
100
150
200
250
96
119 148 178 206 234 262 296 324 352
99
71
43
15
34°N 21°W
1203m
Pre-bloom
1990
Bloom
Post-bloom
1018m
1989
Bloom
250
200
150
100
50
96 119 148 178 206 234 262 296 324 352
15 43
71 99
0
48°N 21°W
Julian day
Julian day
Fig. 3.13. Seasonality of sedimentary fluxes measured in sediment
traps at Northeast Atlantic stations at depths of c. 1 km at 34ºN 21ºW
(upper) and 48ºN 21ºW (lower) in 1989–1990. Modified from Honjo
and Manganini (1993).
with Longhurst’s (1995) eight planktonic climatological
categories, Lampitt and Antia (1997) found that each
province has a characteristic level of flux variability
throughout the year; the greatest range of variation is
in the Antarctic and the lowest in the tropics. Only
fluxes of inorganic carbon showed any clear latitudinal
trend, with the inorganic fluxes reaching 2 g C m
−2 y
−1
in equatorial regions, four times the inorganic carbon
fluxes at high latitudes. None of the other fluxes
they analysed – dry mass, organic carbon and silicate
(opal) – showed any latitudinal trends. There was a
trend for an increase in depth to smooth the variability
of the fluxes.
It seems hard to reconcile some of these observations with other reports. For example the relationship between deep-living pelagic biomass and
primary productivity does not show a similar tangential
hyperbolic relationship; instead, deep biomass continues to increase with increasing primary productivity.
Lampitt and Antia (1997) pointed out that there are
clear differences between benthic environments with
71
cycles and the pelagic community structure. Similarly
the differing seasonal patterns of input of organic
carbon to the bottom-living communities will influence
their structure and dynamics. There is initial evidence
of there being some coherence between Longhurst’s
provinces and the zoogeographical distributions of benthic abyssal species (Sokolova, 1990; Rex et al.,1993).
Merrett (1987) had already suggested that benthic
abyssal fishes show a clear faunal boundary in species
richness and dominance at around 40ºN in the Northeastern Atlantic – a boundary that is coincident with
the change from a domain in which there are markedlypulsed seasonal inputs to the subtropical/tropical domain in which the sedimentary inputs are far less
variable. At temperate latitudes, sediment trap records
show that the sedimentary fluxes vary by over two
orders of magnitude (Wefer, 1989; Fig. 3.13) and
there is heavy seasonal deposition of phytodetritus on
the sea-floor (Billett et al., 1983; Rice et al., 1994).
Deposition of phytodetritus has also been observed
beneath the high-productivity zone along the equator in
the Pacific (Smith et al., 1996). At lower latitudes, such
as the area off Bermuda (e.g., Deuser, 1987), the sediment trap fluxes vary by about an order of magnitude
throughout the year and there have been no reports of
deposition of phytodetritus. Lampitt and Antia (1997)
have recently analysed all the published data on fluxes
normalized to a depth of 2000 m from 67 long-term
sediment-trap records. Several of their conclusions
are unexpected. Organic carbon fluxes at depths of
2000 m ranged just over an order of magnitude, from
0.38 to 4.2 g C m
−2 y
−1 in most oceanic areas, but the
range was greater in polar seas (0.01–5.9 g C m
−2 y
−1 ).
Where fluxes were most variable throughout the
year, a greater proportion of primary production was
being exported. Where primary production less than
200 g C m
−2 y
−1 there is a positive correlation between
productivity and organic carbon fluxes at 2000 m.
But unexpectedly further increases in productivity did
not result in any further increases in fluxes. The
relationship between production and flux follows a
hyperbolic tangential curve, and reaches a maximum
flux of c. 3.5 g C m
−2 y
−1 . Once export production
attained this maximum, there was no evidence of the
deep fluxes being affected by further increases in
primary production. Thus, the ratio between export
production, as measured by sediment traps, and total
productivity declines as primary production increases
beyond 200 g C m
−2 y
−1 . In correlating flux patterns
Post bloom
1989
Bloom
Pre-bloom
1070m
1240 m
1990
Bloom
0
50
100
150
200
250
96
119 148 178 206 234 262 296 324 352
99
71
43
15
34°N 21°W
1203m
Pre-bloom
1990
Bloom
Post-bloom
1018m
1989
Bloom
250
200
150
100
50
96 119 148 178 206 234 262 296 324 352
15 43
71 99
0
48°N 21°W
Julian day
Julian day
Fig. 3.13. Seasonality of sedimentary fluxes measured in sediment
traps at Northeast Atlantic stations at depths of c. 1 km at 34ºN 21ºW
(upper) and 48ºN 21ºW (lower) in 1989–1990. Modified from Honjo
and Manganini (1993).
with Longhurst’s (1995) eight planktonic climatological
categories, Lampitt and Antia (1997) found that each
province has a characteristic level of flux variability
throughout the year; the greatest range of variation is
in the Antarctic and the lowest in the tropics. Only
fluxes of inorganic carbon showed any clear latitudinal
trend, with the inorganic fluxes reaching 2 g C m
−2 y
−1
in equatorial regions, four times the inorganic carbon
fluxes at high latitudes. None of the other fluxes
they analysed – dry mass, organic carbon and silicate
(opal) – showed any latitudinal trends. There was a
trend for an increase in depth to smooth the variability
of the fluxes.
It seems hard to reconcile some of these observations with other reports. For example the relationship between deep-living pelagic biomass and
primary productivity does not show a similar tangential
hyperbolic relationship; instead, deep biomass continues to increase with increasing primary productivity.
Lampitt and Antia (1997) pointed out that there are
clear differences between benthic environments with