273
1985; see also Holligan and Balch, this volume) as well as corals (Berger, 1982). On the other
hand, plankton organisms with calcareous tests generally sink faster than other organic
particles produced in surface waters (see above), thus reducing the amount of carbon respired
during their downward transit, and the adsorption of organic matter onto calcite particles
(Suess, 1973) may contribute to increase the burial of organic carbon in ocean sediments (see
Holligan and Balch, this volume). The production and export of biogenic carbon by calcareous
organisms may therefore lead to high sequestration of inorganic and organic carbon, but the
overall effect of calcite precipitation by organisms could, at least on some time scales, be an
increase in atmospheric CO 2 , The phenomenon is therefore of major significance for the
biogochemical flux of carbon, on both the short and long terms. As far as thecate
dinoflagellates are concerned, their production and export, although poorly documented in
terms of actual C/N ratios at sea, should favour high sequestration of carbon in the oceans.
LONG-LIVED DISSOLVED ORGANIC MATTER
It has been recently proposed that the concentrations of dissolved organic carbon (DOC) and
nitrogen (DON) in oceanic waters are much higher than previously thought (Sugimura and
Suzuki, 1988). Toggweiler (1989) has discussed the implication of these new values, and
reported results from a modelling exercise suggesting that about half the new production could
be exported to depth as long-lived DOM (with a characteristic lifetime of 200 years).
Legendre and Gosselin (1989) have shown that the partitioning of new production into POM
and DOM (Fig. 1), under the present conditions of global change, may effectively uncouple
the export of biogenic material to depth from the usually measured "f-ratio" (ratio of new to
total production). However, it must be realized that the long-lived DOC could chemically
retain (i.e. sequester) carbon in the surface layer, for periods of interest to global change (i.e.
100s years), before this carbon is transferred and released as CO 2 (respired) into the deep
waters. Toggweiler (1989) hypothesized that the long-lived organic compounds reported by
Sugimura and Suzuki (1988) may be formed by condensation reactions between carbon-rich
phytoplankton exudates and nitrogen-rich bacterial enzymes. Even if conditions leading to the
production and breakdown of the long-lived DOM are still poorly known, they obviously are
of major interest for the study of global carbon fluxes in the oceans.
1985; see also Holligan and Balch, this volume) as well as corals (Berger, 1982). On the other
hand, plankton organisms with calcareous tests generally sink faster than other organic
particles produced in surface waters (see above), thus reducing the amount of carbon respired
during their downward transit, and the adsorption of organic matter onto calcite particles
(Suess, 1973) may contribute to increase the burial of organic carbon in ocean sediments (see
Holligan and Balch, this volume). The production and export of biogenic carbon by calcareous
organisms may therefore lead to high sequestration of inorganic and organic carbon, but the
overall effect of calcite precipitation by organisms could, at least on some time scales, be an
increase in atmospheric CO 2 , The phenomenon is therefore of major significance for the
biogochemical flux of carbon, on both the short and long terms. As far as thecate
dinoflagellates are concerned, their production and export, although poorly documented in
terms of actual C/N ratios at sea, should favour high sequestration of carbon in the oceans.
LONG-LIVED DISSOLVED ORGANIC MATTER
It has been recently proposed that the concentrations of dissolved organic carbon (DOC) and
nitrogen (DON) in oceanic waters are much higher than previously thought (Sugimura and
Suzuki, 1988). Toggweiler (1989) has discussed the implication of these new values, and
reported results from a modelling exercise suggesting that about half the new production could
be exported to depth as long-lived DOM (with a characteristic lifetime of 200 years).
Legendre and Gosselin (1989) have shown that the partitioning of new production into POM
and DOM (Fig. 1), under the present conditions of global change, may effectively uncouple
the export of biogenic material to depth from the usually measured "f-ratio" (ratio of new to
total production). However, it must be realized that the long-lived DOC could chemically
retain (i.e. sequester) carbon in the surface layer, for periods of interest to global change (i.e.
100s years), before this carbon is transferred and released as CO 2 (respired) into the deep
waters. Toggweiler (1989) hypothesized that the long-lived organic compounds reported by
Sugimura and Suzuki (1988) may be formed by condensation reactions between carbon-rich
phytoplankton exudates and nitrogen-rich bacterial enzymes. Even if conditions leading to the
production and breakdown of the long-lived DOM are still poorly known, they obviously are
of major interest for the study of global carbon fluxes in the oceans.