CHAPTER 5 . Particulate Organic Matter Composition and Fluxes in the Sea
127
lated flux at depth to euphotic zone export (or new production) rather than to primary production (Martin et al. 1987; Pace et al. 1987). However, due to the effects of
seasonality and complex food chains on flux, these models are not universally applicable.
Vertical fluxes of individual classes of biochemicals out of the surface ocean also
directly reflect local primary production (Lee and Cronin 1984; Ittekkot et al. 1984a,b;
Wakeham and Lee 1989, 1993). These relationships typically are much more variable
than for organic carbon alone, reflecting their greater sensitivity to food-web dynamics, source and other factors.
Relationships between primary production and the fluxes of various classes of organic compounds and primary production are illustrated in Fig. 5.2. This comparison
shows how different organic compound classes behave differently than total carbon.
This difference could have several explanations. The flux of material from the euphotic
zone reflects its production by phytoplankton; plankton growing in different areas
could have varying relative amounts of certain biochemicals, for example, higher storage lipid contents in colder waters (Sargent 1976). Export from the euphotic zone is
also dependent on the community of consumers present, because heterotrophs may
preferentially degrade certain compounds over others. For example, bacteria may selectively degrade certain compounds compared to zooplankton. These factors also
influence the variability of the flux-productivity relationship.
5.2.2
Temporal Relation
In addition to the spatial correlation of primary productivity with particle flux, there
exists a well-defined temporal relationship. Close temporal coupling between phytoplankton blooms and particle flux maxima in the underlying water column clearly
indicates rapid downward transport of biogenic debris (Deuser et al.1981, Ittekkot et al.
1984a,b, Deuser 1986). This close coupling can be seen in data showing carbon fluxes
to a 3 2oo-m sediment trap in the Sargasso Sea (Fig. 5.3). Fluxes peak each spring about
a month after the pigment maxima produced during the spring bloom, suggesting
particle sinking rates of about a hundred metres per day. This seven-year record illustrates the importance of long-term sampling for detecting changes that occur from
year to year. Clearly an unusual event in 1981 triggered higher fluxes than those normally observed. Observations at this site continue today (http://www.bbsr.edu/cintoo/
s202/s202_element/s2023Iement.html#flux) and have provided a wealth of data on
seasonal and interannual variability in the North Atlantic. More recent work during
the U.S. Global Ocean Flux Study (U.S. JGOFS) using time-series sediment traps has
shown a similar general relation between flux and productivity over time and space
in the Arabian Sea (Lee et al. 1998). However, temporal coupling between flux maxima
and productivity events in the Arabian Sea is most pronounced when productivity is
dominated by diatoms, indicating that biological community structure and/or composition strongly influence productivity-flux relations.
Specific organic compounds also show temporal productivity-flux relations. Amino
acid and carbohydrate fluxes in the Sargasso Sea (Fig. 5.4) show the same close coupling with the spring peak in pigment concentrations observed for total organic carbon seen in the satellite data in Fig. 5.3. These relationships again will be affected by
127
lated flux at depth to euphotic zone export (or new production) rather than to primary production (Martin et al. 1987; Pace et al. 1987). However, due to the effects of
seasonality and complex food chains on flux, these models are not universally applicable.
Vertical fluxes of individual classes of biochemicals out of the surface ocean also
directly reflect local primary production (Lee and Cronin 1984; Ittekkot et al. 1984a,b;
Wakeham and Lee 1989, 1993). These relationships typically are much more variable
than for organic carbon alone, reflecting their greater sensitivity to food-web dynamics, source and other factors.
Relationships between primary production and the fluxes of various classes of organic compounds and primary production are illustrated in Fig. 5.2. This comparison
shows how different organic compound classes behave differently than total carbon.
This difference could have several explanations. The flux of material from the euphotic
zone reflects its production by phytoplankton; plankton growing in different areas
could have varying relative amounts of certain biochemicals, for example, higher storage lipid contents in colder waters (Sargent 1976). Export from the euphotic zone is
also dependent on the community of consumers present, because heterotrophs may
preferentially degrade certain compounds over others. For example, bacteria may selectively degrade certain compounds compared to zooplankton. These factors also
influence the variability of the flux-productivity relationship.
5.2.2
Temporal Relation
In addition to the spatial correlation of primary productivity with particle flux, there
exists a well-defined temporal relationship. Close temporal coupling between phytoplankton blooms and particle flux maxima in the underlying water column clearly
indicates rapid downward transport of biogenic debris (Deuser et al.1981, Ittekkot et al.
1984a,b, Deuser 1986). This close coupling can be seen in data showing carbon fluxes
to a 3 2oo-m sediment trap in the Sargasso Sea (Fig. 5.3). Fluxes peak each spring about
a month after the pigment maxima produced during the spring bloom, suggesting
particle sinking rates of about a hundred metres per day. This seven-year record illustrates the importance of long-term sampling for detecting changes that occur from
year to year. Clearly an unusual event in 1981 triggered higher fluxes than those normally observed. Observations at this site continue today (http://www.bbsr.edu/cintoo/
s202/s202_element/s2023Iement.html#flux) and have provided a wealth of data on
seasonal and interannual variability in the North Atlantic. More recent work during
the U.S. Global Ocean Flux Study (U.S. JGOFS) using time-series sediment traps has
shown a similar general relation between flux and productivity over time and space
in the Arabian Sea (Lee et al. 1998). However, temporal coupling between flux maxima
and productivity events in the Arabian Sea is most pronounced when productivity is
dominated by diatoms, indicating that biological community structure and/or composition strongly influence productivity-flux relations.
Specific organic compounds also show temporal productivity-flux relations. Amino
acid and carbohydrate fluxes in the Sargasso Sea (Fig. 5.4) show the same close coupling with the spring peak in pigment concentrations observed for total organic carbon seen in the satellite data in Fig. 5.3. These relationships again will be affected by