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M. Fabiano et al.
than surface concentrations. This may indicate that these compounds were readily available for heterotrophic metabolism and/or were converted into dissolved
macromolecular compounds [31].
The analysis of the vertical distribution and composition of the organic particles revealed also significant changes in terms of relative significance of the two
size fractions. Picoparticulate protein fractions, for instance, in the deeper water
layers increased in the Ross Sea area and decreased in Terra Nova Bay (from 20 to
35% and from 22 to 11% for the Ross Sea and Terra Nova Bay respectively). In
contrast, the relative significance of picoparticulate carbohydrates and lipids
(limited to Terra Nova Bay) increased with depth.
Significant différences were observed comparing the vertical patterns of the
picoparticulate fraction of ATP and the microparticulate fraction. In fact, while
the ATP content of the former fraction decreased strongly with depth (below the
mixed layer depth), the concentrations of the larger fraction slightly increased
(Fig. 7). Vertical decreases in ATP content hâve been reported by Karl et al. [32].
However, our results point to different patterns in the two size fractions, suggesting that changes in ATP content with depth may be the resuit of the balance
between rates of growth (e.g., of nanoflagellates) and consumption (by prédation
on bacteria or catabolism [33]). Large variations in the cellular ratios of ATP hâve
been observed [13] and this may represent another possible explanation of the
inverse pattern of the two size fractions.
TSM concentrations in Terra Nova Bay and in the southwestern région of the
Ross Sea were almost double those in the open Ross Sea. This may be related to
allochthonous, even though limited, input of terrigenous material [10, 12] for
Terra Nova Bay or to a phytoplankton bloom at stations 23 and 25 [9,28]. Despite
this, the characteristics of the particles in Coastal and open sea stations were quite
similar. In both areas the picoparticles accounted for < 38% of total seston.
Similar patterns were shown by proteins. Protein concentrations in Terra Nova
Bay were significantly higher than in the open Ross Sea, but again in both areas
microparticulate proteins accounted for 70 and 80% of the total protein concentration. Therefore, the two areas are quite different in terms of absolute concentrations of particulate matter but are not significantly different in terms of relative significance of the two size classes.
Other qualitative différences between Coastal and open sea stations may be
detected by comparing the ratio of proteins to carbohydrates (PRT:CHO ratio).
The PRT:CHO ratio varied spatially. Due to the dominance of proteins in the large
particles extensively colonized by bacteria and other microheterotrophs and fitoplankton, both in the Ross Sea and Terra Nova Bay, PRT:CHO ratios were higher in
the microparticulate than in the picoparticulate fraction. At the same time, the
average PRT:CHO ratio in Terra Nova Bay was much higher than in the Ross Sea.
This suggests that, during summer 1989-1990, in Terra Nova Bay the freshly generated organic détritus was extensively colonized by bacteria and other microheterotrophs. This may hâve determined a protein enrichment and an increase of
the PRT:CHO ratio. On the contrary, the particulate organic matter of the open
Ross Sea was extremely poor in proteins (especially in the picoparticulate fraction)
and appeared to be composed of older détritus scarcely colonized by bacteria.
Further investigations of particulate matter are required for a complété under-
M. Fabiano et al.
than surface concentrations. This may indicate that these compounds were readily available for heterotrophic metabolism and/or were converted into dissolved
macromolecular compounds [31].
The analysis of the vertical distribution and composition of the organic particles revealed also significant changes in terms of relative significance of the two
size fractions. Picoparticulate protein fractions, for instance, in the deeper water
layers increased in the Ross Sea area and decreased in Terra Nova Bay (from 20 to
35% and from 22 to 11% for the Ross Sea and Terra Nova Bay respectively). In
contrast, the relative significance of picoparticulate carbohydrates and lipids
(limited to Terra Nova Bay) increased with depth.
Significant différences were observed comparing the vertical patterns of the
picoparticulate fraction of ATP and the microparticulate fraction. In fact, while
the ATP content of the former fraction decreased strongly with depth (below the
mixed layer depth), the concentrations of the larger fraction slightly increased
(Fig. 7). Vertical decreases in ATP content hâve been reported by Karl et al. [32].
However, our results point to different patterns in the two size fractions, suggesting that changes in ATP content with depth may be the resuit of the balance
between rates of growth (e.g., of nanoflagellates) and consumption (by prédation
on bacteria or catabolism [33]). Large variations in the cellular ratios of ATP hâve
been observed [13] and this may represent another possible explanation of the
inverse pattern of the two size fractions.
TSM concentrations in Terra Nova Bay and in the southwestern région of the
Ross Sea were almost double those in the open Ross Sea. This may be related to
allochthonous, even though limited, input of terrigenous material [10, 12] for
Terra Nova Bay or to a phytoplankton bloom at stations 23 and 25 [9,28]. Despite
this, the characteristics of the particles in Coastal and open sea stations were quite
similar. In both areas the picoparticles accounted for < 38% of total seston.
Similar patterns were shown by proteins. Protein concentrations in Terra Nova
Bay were significantly higher than in the open Ross Sea, but again in both areas
microparticulate proteins accounted for 70 and 80% of the total protein concentration. Therefore, the two areas are quite different in terms of absolute concentrations of particulate matter but are not significantly different in terms of relative significance of the two size classes.
Other qualitative différences between Coastal and open sea stations may be
detected by comparing the ratio of proteins to carbohydrates (PRT:CHO ratio).
The PRT:CHO ratio varied spatially. Due to the dominance of proteins in the large
particles extensively colonized by bacteria and other microheterotrophs and fitoplankton, both in the Ross Sea and Terra Nova Bay, PRT:CHO ratios were higher in
the microparticulate than in the picoparticulate fraction. At the same time, the
average PRT:CHO ratio in Terra Nova Bay was much higher than in the Ross Sea.
This suggests that, during summer 1989-1990, in Terra Nova Bay the freshly generated organic détritus was extensively colonized by bacteria and other microheterotrophs. This may hâve determined a protein enrichment and an increase of
the PRT:CHO ratio. On the contrary, the particulate organic matter of the open
Ross Sea was extremely poor in proteins (especially in the picoparticulate fraction)
and appeared to be composed of older détritus scarcely colonized by bacteria.
Further investigations of particulate matter are required for a complété under-