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M. Ravaioli et al.
flux. The différences between sites A and B, which show quite similar sédiment
features.can be due to the effect of water depth: it is known that faunal abundance
decreases strongly with depth, especially in soft sédiments.
The stratification pattern at these sites is consistent with the results of the
210Pbt.x profiles, which indicate the presence of a surface mixed layer in the upper
4-6 cm.
The living benthic community found at site C, mainly composed of epibenthic
filter feeders, confirms a high bottom dynamics, high level of sédiment instability
and flux of particles and food mainly advected laterally. These organisms do not
hâve a high potential of bioturbation, and they live mainly in the interstices of the
coarse organogenous component of the sédiment. Mixing at this site, confirmed
by the presence of an excess 2I0Pbex profile, is mainly physical in origin. The sessile forms settled on pebbles and other hard substrates probably are not able to
grow to the adult size because of the unpredictable and probably frequent catastrophe events (e.g., resuspension and winnowing). In view of this hypothesis, the
individuals probably never reach reproduction and the observed community may
be composed of pseudo-populations depending on recolonization from larvae
produced by adult populations of neighboring areas ("supply-side ecology" [28]).
6 Conclusions
From the discussion above the following conclusions can be drawn:
1. The three sites show different lithologies. A and B differ slightly, in that sédiment at A is a little coarser and contains more gravels, due to the proximity to
the ice shelf. B is a typical site for présent seasonally open marine sédimentation. Due to the action of strong bottom currents, C is not subject to présent
accumulation and is a residual glacial-marine sédiment with a high biodetritic calcareous component.
2. Both sites A and B are subject to processes of focusing, whereas sédiment at C
is resuspended and winnowed by bottom currents and shows 210Pbex profiles
due to the entrapment of fine particles
3. Apparent sédiment accumulation rates are similar at sites A and B (89 and 104
mg cm 2 year1, respectively), as well as apparent burial rates of biogenic
species. It was possible to establish that mass accumulation rates and burial
rates for site B are overestimated by a factor of 2.7, due to the influence of deep
mixing on the 21
deposit feeders, with reworking capability characterises sites A and B, whereas
at site C the community is mainly composed of epibenthic filter feeders and is
strongly influenced by sédiment instability. These différences are mainly due to
bottom water dynamics. Fluxes of biogenic particles do not seem to account
for the différences in faunal composition at sites A and B, which should be
ascribed to the influence of water depth. The slightly different lithologies,
which reflect the locations of the sites, and the different sources of coarse sedimentary materials may also play a rôle.
M. Ravaioli et al.
flux. The différences between sites A and B, which show quite similar sédiment
features.can be due to the effect of water depth: it is known that faunal abundance
decreases strongly with depth, especially in soft sédiments.
The stratification pattern at these sites is consistent with the results of the
210Pbt.x profiles, which indicate the presence of a surface mixed layer in the upper
4-6 cm.
The living benthic community found at site C, mainly composed of epibenthic
filter feeders, confirms a high bottom dynamics, high level of sédiment instability
and flux of particles and food mainly advected laterally. These organisms do not
hâve a high potential of bioturbation, and they live mainly in the interstices of the
coarse organogenous component of the sédiment. Mixing at this site, confirmed
by the presence of an excess 2I0Pbex profile, is mainly physical in origin. The sessile forms settled on pebbles and other hard substrates probably are not able to
grow to the adult size because of the unpredictable and probably frequent catastrophe events (e.g., resuspension and winnowing). In view of this hypothesis, the
individuals probably never reach reproduction and the observed community may
be composed of pseudo-populations depending on recolonization from larvae
produced by adult populations of neighboring areas ("supply-side ecology" [28]).
6 Conclusions
From the discussion above the following conclusions can be drawn:
1. The three sites show different lithologies. A and B differ slightly, in that sédiment at A is a little coarser and contains more gravels, due to the proximity to
the ice shelf. B is a typical site for présent seasonally open marine sédimentation. Due to the action of strong bottom currents, C is not subject to présent
accumulation and is a residual glacial-marine sédiment with a high biodetritic calcareous component.
2. Both sites A and B are subject to processes of focusing, whereas sédiment at C
is resuspended and winnowed by bottom currents and shows 210Pbex profiles
due to the entrapment of fine particles
3. Apparent sédiment accumulation rates are similar at sites A and B (89 and 104
mg cm 2 year1, respectively), as well as apparent burial rates of biogenic
species. It was possible to establish that mass accumulation rates and burial
rates for site B are overestimated by a factor of 2.7, due to the influence of deep
mixing on the 21
deposit feeders, with reworking capability characterises sites A and B, whereas
at site C the community is mainly composed of epibenthic filter feeders and is
strongly influenced by sédiment instability. These différences are mainly due to
bottom water dynamics. Fluxes of biogenic particles do not seem to account
for the différences in faunal composition at sites A and B, which should be
ascribed to the influence of water depth. The slightly different lithologies,
which reflect the locations of the sites, and the different sources of coarse sedimentary materials may also play a rôle.