300
C. Minero . E. Pelizzetti . M.R. Preston
should fall in the approximate range of 15-100 IlM C had been reached. Methods such
as that published by Collins and Williams (1977) or Mantoura and Woodward (1983)
had become the norm. However, there was still no real understanding of either the
vertical or seasonal variability in DOC other than the observation that concentrations
were highest in productive surface waters with featureless profiles in deeper waters
(Toggweiler 1988,1989; Williams and DruffeI1988). Nor was there any real insight into
the cycle of DOC where mass balance calculations into the fate of terrigenous organic
matter in the oceans revealed considerable discrepancies, leading to hypotheses about
unknown remineralisation processes (Hedges 1987).
Seasonal variability exists in the surface DOC concentrations: DOC accumulates due
to the spring bloom, it is partially consumed in summer and autumn, and it is transported under the euphotic layer by convection in winter. The DOC concentration in
deep water is almost constant from the North Atlantic to the Pacific (Martin and
Fitzwalter 1992), Above a depth of 400 m, DOM plays an important role in the biogeochemical cycles. DOM is carried by the Ekman transport from the equatorial to
the subtropical region. This transport reduces the nutrient trapping effect in the high
production areas and supplies nutrient to the low production areas. Geochemical
modelling suggests that above a depth of 400 m exists the so-called semilabile DOM,
with half-life of half a year, and that its vertical and horizontal transport plays an important role for the marine biogeochemical cycle. Below that depth only the inert refractory DOM exists, of minor importance for the biogeochemical cycle (Yamanaka
and Tajika 1997).
In the late 1980s and early 1990S a number of reports, deriving in considerable part
from Suzuki and co-workers (Sugimura and Suzuki 1988; Suzuki et al. 1990; Suzuki
and Tanoue 1991; Suzuki et al. 1992 but see also Martin and Fitzwalter 1992 and Kumar
et al. 1990), reported non-volatile DOC concentrations that were considerably higher
than previously accepted as the norm by a factor of between about 2 and 4. These measurements were conducted using a new high temperature catalytic oxidation method
(HTCO) and the data were given credence by an apparent link between measured DOC
values and an independent parameter of geochemical significance, the apparent oxygen utilization (AOU) parameter (Sugimura and Suzuki 1988).
The impact of these papers on the scientific community was considerable because
it necessitated an upward revision of the global ocean inventory of DOC up to around
800 Gt. The 600 Gt difference between this new value and the 200 Gt previously estimated is extremely large and equivalent to the entire pool of atmospheric carbon
(Hedges 1987). A major change in the accepted analytical procedures and historical
data had profound implications for the Joint Global Ocean Fluxes Study Programm
OGOFS) to examine carbon fluxes (Sharp et al. 1995) and on the modelling of biogeochemical general circulation (Yamanaka and Tajika 1997).
As can readily be imagined a considerable degree of controversy surrounded all of
these DOC determinations. Whilst some scientists accepted the new data and speculated about its significance, others recognised that the key issue lay not in the interpretation of the data but rather, the quality of the analytical method that produced it.
Recent data validating the utilization of several different techniques indicate that the
equatorial Pacific oceanic DOC values in near surface waters are on the order of
60-70 IlM C and deep water values on the order of 35-40 IlM C (Sharp et al. 1995).
Peltzer and Hayward (1996) reported that the total organic carbon concentration in
C. Minero . E. Pelizzetti . M.R. Preston
should fall in the approximate range of 15-100 IlM C had been reached. Methods such
as that published by Collins and Williams (1977) or Mantoura and Woodward (1983)
had become the norm. However, there was still no real understanding of either the
vertical or seasonal variability in DOC other than the observation that concentrations
were highest in productive surface waters with featureless profiles in deeper waters
(Toggweiler 1988,1989; Williams and DruffeI1988). Nor was there any real insight into
the cycle of DOC where mass balance calculations into the fate of terrigenous organic
matter in the oceans revealed considerable discrepancies, leading to hypotheses about
unknown remineralisation processes (Hedges 1987).
Seasonal variability exists in the surface DOC concentrations: DOC accumulates due
to the spring bloom, it is partially consumed in summer and autumn, and it is transported under the euphotic layer by convection in winter. The DOC concentration in
deep water is almost constant from the North Atlantic to the Pacific (Martin and
Fitzwalter 1992), Above a depth of 400 m, DOM plays an important role in the biogeochemical cycles. DOM is carried by the Ekman transport from the equatorial to
the subtropical region. This transport reduces the nutrient trapping effect in the high
production areas and supplies nutrient to the low production areas. Geochemical
modelling suggests that above a depth of 400 m exists the so-called semilabile DOM,
with half-life of half a year, and that its vertical and horizontal transport plays an important role for the marine biogeochemical cycle. Below that depth only the inert refractory DOM exists, of minor importance for the biogeochemical cycle (Yamanaka
and Tajika 1997).
In the late 1980s and early 1990S a number of reports, deriving in considerable part
from Suzuki and co-workers (Sugimura and Suzuki 1988; Suzuki et al. 1990; Suzuki
and Tanoue 1991; Suzuki et al. 1992 but see also Martin and Fitzwalter 1992 and Kumar
et al. 1990), reported non-volatile DOC concentrations that were considerably higher
than previously accepted as the norm by a factor of between about 2 and 4. These measurements were conducted using a new high temperature catalytic oxidation method
(HTCO) and the data were given credence by an apparent link between measured DOC
values and an independent parameter of geochemical significance, the apparent oxygen utilization (AOU) parameter (Sugimura and Suzuki 1988).
The impact of these papers on the scientific community was considerable because
it necessitated an upward revision of the global ocean inventory of DOC up to around
800 Gt. The 600 Gt difference between this new value and the 200 Gt previously estimated is extremely large and equivalent to the entire pool of atmospheric carbon
(Hedges 1987). A major change in the accepted analytical procedures and historical
data had profound implications for the Joint Global Ocean Fluxes Study Programm
OGOFS) to examine carbon fluxes (Sharp et al. 1995) and on the modelling of biogeochemical general circulation (Yamanaka and Tajika 1997).
As can readily be imagined a considerable degree of controversy surrounded all of
these DOC determinations. Whilst some scientists accepted the new data and speculated about its significance, others recognised that the key issue lay not in the interpretation of the data but rather, the quality of the analytical method that produced it.
Recent data validating the utilization of several different techniques indicate that the
equatorial Pacific oceanic DOC values in near surface waters are on the order of
60-70 IlM C and deep water values on the order of 35-40 IlM C (Sharp et al. 1995).
Peltzer and Hayward (1996) reported that the total organic carbon concentration in