Abstract
Continental slopes are important and complex regions that connect shallow shelf seas with the deep ocean. Since a large part of the global primary
productivity takes place on the continental margins, knowledge on sediment
resuspension and associated processes on the continental slope is crucial
to
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understand the fate of particles, including biogenic debris. The
objectives of the study described in this thesis were to better understand
the interactions between near-bottom currents and surface sediments of the
continental slope, and to assess the impact of sediment resuspension on the
cross-slope redistribution of biogenic and non-biogenic particles. While
most of the studies conducted on sediment resuspension on continental
margins have investigated the role of seasonal to inter-annual variations
of the near-bottom currents, this thesis particularly focuses on short-term
(tidal to sub-tidal) mechanisms. High-resolution studies have the potential
to provide valuable information on the short-term processes involved in
sediment resuspension, which, due to their difficulty to be resolved, have
not received much attention, yet. The novel aspect of this work lies in the
combination of fast sampling near-bottom sediment traps, turbidity sensors
and current meters moored on a high-energy continental slope.
Our data show that massive and abrupt sediment resuspension occurred at
mid-slope and is associated with sudden drop of the temperature and upslope
surge of the near-bottom currents. A more detailed study reveals that such
massive resuspension was facilitated by strong vertical velocities
generated at the leading edge of internal non-linear waves travelling up
the slope. This finding suggests the importance of the interaction of such
a phenomenon with the seabed can provide a potentially dominant mechanism
for upward transport of sediment over continental slopes that may
counteract downward avalanching of material by gravity.
The results presented in this thesis show the importance of the short-term
processes in the resuspension of sediment on the slope and in the transfer
of biogenic materials from the shelf to the deep ocean. This transfer may
have significant implications for organic matter recycling along the ocean
margins. This work represents the first step towards a better understanding
of these potentially very active processes. Clearly, further investigations
are needed, particularly for the highly productive ocean margins such as
areas with high continental input or coastal upwelling regions, which are
also receiving much attention in terms of their paleo-climatological
significance. Furthermore, high-energy processes (see Chapter 3) and the
associated massive sediment transport and organic matter recycling (see
Chapters 2, 4 and 5) may create major perturbations of the sedimentary
signal and lead to erroneous interpretation of proxy data.
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