General Characteristics of Density-Turbidity Currents
in the Ross Sea (Antarctica)
S. Gremes Cordero1 and E. Salusti2
'Dipartimento di Fisica, Université “La Sapienza”, Piazzale A. Moro 2,00185 Rome, Italy
2INFN, Dipartimento di Fisica, Université “La Sapienza”, Piazzale A. Moro 2,00185 Rome,
Italy
Abstract
To investigate thermodynamic currents in Antarctica, we here discuss quasisteady density currents flowing over a regular slope and their hydrodynamic stability, considering also bottom érosion phenomena: in other words, the current is
assumed to exchange sédiments with the bottom. To simplify this complex problem a model of sédiment évolution is assumed. As in recent work the excess mass
due to the bottom érosion and déposition is assumed to dépend only on the current stress on the bottom. A nonlinear équation considering both the time and
space variability of these “density-turbidity” currents for a two-layer model is
obtained and a novel criterion to identify the “ignition” point of these densityturbidity currents is discussed. In Polar Océans these interactions can play a fondamental rôle in the génération of new water masses, as a resuit of violent hydrodynamic instability concerning the downslope motion of dense shelf water along
submarine canyons.
1 The Problem
The rôle of dense water in deep polar basins is well established [ 1 ]. The paths that
the dense shelf water follows offshore from formation régions to the deep basins
nevertheless remain an open problem. Variable bottom topography has long been
recognized as an important mechanism for steering the flow of bottom water [2,
3]. This interaction was first emphasized by Nansen [4], who described the tendency of marine currents to follow the deepest channels of the sea bottom.
In general, density currents, whether related to a génération mechanism such
as quick storm waves or to long-lasting dense-water formation due to strong climatologie air-sea interaction, are interesting physical phenomena. They are
known to flow geostrophically along the isobaths over the shelf, entraining bottom sédiments, ultimately reaching the deepest layers [5-8]. However, if this
rather regular motion is interrupted by a cross-shelf submarine canyon, then the
dense water has to interrupt its geostrophic motion and sink along the canyon.
The resulting downslope turbulent flow can either be stable or subject to hydrodynamic instability processes [9]. In océans, violent mixing is to be expected, and
must generate an intermediate kind of oceanic water, a phenomenon of interest
in interpreting field observations.
in the Ross Sea (Antarctica)
S. Gremes Cordero1 and E. Salusti2
'Dipartimento di Fisica, Université “La Sapienza”, Piazzale A. Moro 2,00185 Rome, Italy
2INFN, Dipartimento di Fisica, Université “La Sapienza”, Piazzale A. Moro 2,00185 Rome,
Italy
Abstract
To investigate thermodynamic currents in Antarctica, we here discuss quasisteady density currents flowing over a regular slope and their hydrodynamic stability, considering also bottom érosion phenomena: in other words, the current is
assumed to exchange sédiments with the bottom. To simplify this complex problem a model of sédiment évolution is assumed. As in recent work the excess mass
due to the bottom érosion and déposition is assumed to dépend only on the current stress on the bottom. A nonlinear équation considering both the time and
space variability of these “density-turbidity” currents for a two-layer model is
obtained and a novel criterion to identify the “ignition” point of these densityturbidity currents is discussed. In Polar Océans these interactions can play a fondamental rôle in the génération of new water masses, as a resuit of violent hydrodynamic instability concerning the downslope motion of dense shelf water along
submarine canyons.
1 The Problem
The rôle of dense water in deep polar basins is well established [ 1 ]. The paths that
the dense shelf water follows offshore from formation régions to the deep basins
nevertheless remain an open problem. Variable bottom topography has long been
recognized as an important mechanism for steering the flow of bottom water [2,
3]. This interaction was first emphasized by Nansen [4], who described the tendency of marine currents to follow the deepest channels of the sea bottom.
In general, density currents, whether related to a génération mechanism such
as quick storm waves or to long-lasting dense-water formation due to strong climatologie air-sea interaction, are interesting physical phenomena. They are
known to flow geostrophically along the isobaths over the shelf, entraining bottom sédiments, ultimately reaching the deepest layers [5-8]. However, if this
rather regular motion is interrupted by a cross-shelf submarine canyon, then the
dense water has to interrupt its geostrophic motion and sink along the canyon.
The resulting downslope turbulent flow can either be stable or subject to hydrodynamic instability processes [9]. In océans, violent mixing is to be expected, and
must generate an intermediate kind of oceanic water, a phenomenon of interest
in interpreting field observations.