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M. Fabiano et al.
of total suspended matter, protein, carbohydrate and total lipid concentrations. In
contrast, in Terra Nova Bay, most of the ATP content was collected in the picoparticulate fraction (84.5% of total ATP in the surface layer). Therefore, if we assume
that ATP represents a measure of the total amounts of living carbon [13], it is likely that most of the living biomass (as free-living bacteria and picophytoplankton)
was in the picoparticulate fraction whereas the microparticulate fraction contained a higher fraction of organic détritus. This interprétation is supported by a
sériés of pigment and microscopie analyses (SEM) carried out in the same area
during our sampling period by Innamorati et al. [16] and Fabiano et al. [11],
which indicated the dominance of detrital material (> 10 pm) with a phytoplankton senescence or in the early decompositon phase. Similar results concerning the
quantitative significance of bacteria and other picoplankton were reported by
Cota et al. [24] and Hewes et al. [25] in the Weddell Sea and Johnson and Sieburth
[26] in other océans.
Moreover, in Terra Nova Bay the picoparticulate ATP content was significantly
correlated (r=0.435, p<0.05) to the biopolymeric carbon of the picoparticulate
fraction (the sum of lipid, protein and carbohydrate carbon [3, 9, 27]) while no
significant corrélations were found for the microparticulate fraction. The intercept value of the y-axis (POM = 24.32 pg C) is équivalent to about 61% of the average picoparticulate carbon in the top 100 m of the water column (picoparticulate
matter concentration was on average 39.54 pg l’1). Therefore most of the picoparticulate matter was detrital (i.e. non-living), even though the pico-fraction contains most of the ATP content.
From the data it is possible to conclude that ail size classes of organic particles
at ail depths were mostly detrital, but détritus dominance was more pronounced in
the larger particles. Significant différences were found comparing the composition
of the two size classes of particles (Fig. 8). The microparticulate matter, in both the
photic and aphotic layers, was mostly composed of proteins, followed by carbohydrates and lipids. In contrast, the picoparticulate matter displayed an increase in
carbohydrate fraction that dominated in the aphotic layer, followed by proteins and
lipids. The different biochemical composition of the two size classes can be referred
to the different origin and évolution of the particles. As regards the microparticulate traction, during summer 1989-1990, high protein concentrations were reported in Terra Nova Bay where the freshly generated organic détritus was extensively
colonized by bacteria and other microheterotrophs [10]. In the southwestern
région of the Ross Sea (Stations 23 and 25) a typical marginal ice zone (MIZ) area
with high phytoplanktonic bloom (prevalently diatoms) was found associated with
grazing activity [9,28]. This situation may hâve determined a protein enrichment
compared to carbohydrates and lipids as reported by Fabiano et al. [9] and Smith
et al. [8]. In contrast, the dominance of carbohydrates in the picoparticles, particulary in lerra Nova Bay, would suggest a different origin. One possible explanation
was the high picophytoplankton density [10], but also protein déplétion from larger particles may hâve contributed to increase carbohydrate relative significance.
A change in particle composition with water depth was observed (Fig. 9). Total
carbohydrate concentrations did not show a strong decrease with depth and,
especially in the Coastal stations of Terra Nova Bay, their relative significance with
respect to proteins and lipids increased in the deeper water layers. These data are
M. Fabiano et al.
of total suspended matter, protein, carbohydrate and total lipid concentrations. In
contrast, in Terra Nova Bay, most of the ATP content was collected in the picoparticulate fraction (84.5% of total ATP in the surface layer). Therefore, if we assume
that ATP represents a measure of the total amounts of living carbon [13], it is likely that most of the living biomass (as free-living bacteria and picophytoplankton)
was in the picoparticulate fraction whereas the microparticulate fraction contained a higher fraction of organic détritus. This interprétation is supported by a
sériés of pigment and microscopie analyses (SEM) carried out in the same area
during our sampling period by Innamorati et al. [16] and Fabiano et al. [11],
which indicated the dominance of detrital material (> 10 pm) with a phytoplankton senescence or in the early decompositon phase. Similar results concerning the
quantitative significance of bacteria and other picoplankton were reported by
Cota et al. [24] and Hewes et al. [25] in the Weddell Sea and Johnson and Sieburth
[26] in other océans.
Moreover, in Terra Nova Bay the picoparticulate ATP content was significantly
correlated (r=0.435, p<0.05) to the biopolymeric carbon of the picoparticulate
fraction (the sum of lipid, protein and carbohydrate carbon [3, 9, 27]) while no
significant corrélations were found for the microparticulate fraction. The intercept value of the y-axis (POM = 24.32 pg C) is équivalent to about 61% of the average picoparticulate carbon in the top 100 m of the water column (picoparticulate
matter concentration was on average 39.54 pg l’1). Therefore most of the picoparticulate matter was detrital (i.e. non-living), even though the pico-fraction contains most of the ATP content.
From the data it is possible to conclude that ail size classes of organic particles
at ail depths were mostly detrital, but détritus dominance was more pronounced in
the larger particles. Significant différences were found comparing the composition
of the two size classes of particles (Fig. 8). The microparticulate matter, in both the
photic and aphotic layers, was mostly composed of proteins, followed by carbohydrates and lipids. In contrast, the picoparticulate matter displayed an increase in
carbohydrate fraction that dominated in the aphotic layer, followed by proteins and
lipids. The different biochemical composition of the two size classes can be referred
to the different origin and évolution of the particles. As regards the microparticulate traction, during summer 1989-1990, high protein concentrations were reported in Terra Nova Bay where the freshly generated organic détritus was extensively
colonized by bacteria and other microheterotrophs [10]. In the southwestern
région of the Ross Sea (Stations 23 and 25) a typical marginal ice zone (MIZ) area
with high phytoplanktonic bloom (prevalently diatoms) was found associated with
grazing activity [9,28]. This situation may hâve determined a protein enrichment
compared to carbohydrates and lipids as reported by Fabiano et al. [9] and Smith
et al. [8]. In contrast, the dominance of carbohydrates in the picoparticles, particulary in lerra Nova Bay, would suggest a different origin. One possible explanation
was the high picophytoplankton density [10], but also protein déplétion from larger particles may hâve contributed to increase carbohydrate relative significance.
A change in particle composition with water depth was observed (Fig. 9). Total
carbohydrate concentrations did not show a strong decrease with depth and,
especially in the Coastal stations of Terra Nova Bay, their relative significance with
respect to proteins and lipids increased in the deeper water layers. These data are