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S. Tucci et al.
richest in particles (SRPI ) into three additional subgroups; the two groups of spectra poor in particles (SPP, and SPPs) are already distinct. The samples of each of
the clusters were then located by coordinates and depth to associate them with the
water masses that characterize the area under survey. In Table 1 we report the principal values calculated for each parameter in the five defined clusters.
We hâve used the représentative south-north section to indicate ail our results
in terms of concentration and sizes, and this has enabled us to hypothesize a characterization of the suspended matter (Fig. 8) that takes account of the water masses présent (the thermocline and the isotherm -1.95 °C, limit of DISW, are indicated in red in the figure).
Along the edge of the RIS, in the waters between the surface and the thermocline and up to the stations located at 77 °S, we find samples (Shallow Ice Shelf
Particulate, SISP) with higher values in terms of number of particles (25 00050000), with spectra with a médian of around 30 pm and high values of the main
mode (60 pm). In this cluster, 94% of the 64 samples were located in the Shallow
Ice Shelf Water (SISW).
In the Antarctic Surface Waters (located in the external part of the shelf), the suspended matter (AASP) is still rich in particles (12 000-25 000), with a higher médian, and main mode as above. The samples taken from this water mass account for
79% of the total in the cluster. The third group, 18 samples, is located on the bottom
and in the nearby waters, corresponding to the HSSW and the DISW, with a percentage of 77%. This group is distinguished from the other two groups by a lower number of particles (8000-18 000); range, main mode and médian values are also higher.
Spectral types SPPL and SPPs are rarely présent in surface waters (10% of the
total), while they characterize the intermediate water mass, which is therefore
poor in suspended matter (500-8000 particles). SPPL spectra with higher modal
characteristics and particle numbers in the range 2000-8000 are high in concentration (65%) offshore in the subsuperficial layer (10-100 m). The other samples
are diffused throughout the intermediate waters with no spécifie corrélation with
the water masses. The waters close to the RIS, that are not directly influenced by
the ice shelf, in general hâve few suspended particles of small size, particularly
between 200 and 500 m (65%). The same characteristics are encountered in the
intermediate water (70%) further out, the WMCO and the surrounding waters
modified by it (WMCOm).
Only suspended material in intermediate waters is not clearly characterized;
for this problem we examined the finest fraction and used only the data obtained
with a 30pm capillary. We adopted this solution to improve the séparation of the
samples with an abundant fine fraction. In particular, therefore, we examined the
SPPs class. The results confirmed that this type of spectra is correlated to the
WMCO, as 100% of the samples présent in this mass of water hâve the lowest values found in terms of particles, mode and médian.
4 Conclusions
From a sedimentological viewpoint, the effect of the barrier created by the
strong variations in the thermohaline characteristics of the waters has already
S. Tucci et al.
richest in particles (SRPI ) into three additional subgroups; the two groups of spectra poor in particles (SPP, and SPPs) are already distinct. The samples of each of
the clusters were then located by coordinates and depth to associate them with the
water masses that characterize the area under survey. In Table 1 we report the principal values calculated for each parameter in the five defined clusters.
We hâve used the représentative south-north section to indicate ail our results
in terms of concentration and sizes, and this has enabled us to hypothesize a characterization of the suspended matter (Fig. 8) that takes account of the water masses présent (the thermocline and the isotherm -1.95 °C, limit of DISW, are indicated in red in the figure).
Along the edge of the RIS, in the waters between the surface and the thermocline and up to the stations located at 77 °S, we find samples (Shallow Ice Shelf
Particulate, SISP) with higher values in terms of number of particles (25 00050000), with spectra with a médian of around 30 pm and high values of the main
mode (60 pm). In this cluster, 94% of the 64 samples were located in the Shallow
Ice Shelf Water (SISW).
In the Antarctic Surface Waters (located in the external part of the shelf), the suspended matter (AASP) is still rich in particles (12 000-25 000), with a higher médian, and main mode as above. The samples taken from this water mass account for
79% of the total in the cluster. The third group, 18 samples, is located on the bottom
and in the nearby waters, corresponding to the HSSW and the DISW, with a percentage of 77%. This group is distinguished from the other two groups by a lower number of particles (8000-18 000); range, main mode and médian values are also higher.
Spectral types SPPL and SPPs are rarely présent in surface waters (10% of the
total), while they characterize the intermediate water mass, which is therefore
poor in suspended matter (500-8000 particles). SPPL spectra with higher modal
characteristics and particle numbers in the range 2000-8000 are high in concentration (65%) offshore in the subsuperficial layer (10-100 m). The other samples
are diffused throughout the intermediate waters with no spécifie corrélation with
the water masses. The waters close to the RIS, that are not directly influenced by
the ice shelf, in general hâve few suspended particles of small size, particularly
between 200 and 500 m (65%). The same characteristics are encountered in the
intermediate water (70%) further out, the WMCO and the surrounding waters
modified by it (WMCOm).
Only suspended material in intermediate waters is not clearly characterized;
for this problem we examined the finest fraction and used only the data obtained
with a 30pm capillary. We adopted this solution to improve the séparation of the
samples with an abundant fine fraction. In particular, therefore, we examined the
SPPs class. The results confirmed that this type of spectra is correlated to the
WMCO, as 100% of the samples présent in this mass of water hâve the lowest values found in terms of particles, mode and médian.
4 Conclusions
From a sedimentological viewpoint, the effect of the barrier created by the
strong variations in the thermohaline characteristics of the waters has already