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Title: Seismic reflection along the path of the Mediterranean Undercurrent
Authors: Buffett, G. G.
Biescas, B.
Pelegrí Llopart,José Luis 
Machín, F. 
Sallarès, V.
Carbonell, R.
Klaeschen, D.
Hobbs, R.
UNESCO Clasification: 251007 Oceanografía física
Keywords: Seismic oceanography
Mediterranean Undercurrent
Thermohaline fine structure
Entrainment, et al
Issue Date: 2009
Publisher: 0278-4343
Journal: Continental Shelf Research 
Abstract: Seismic reflection profiling is applied to the study of large scale physical oceanographic processes in the Gulf of Cádiz and western Iberian coast, coinciding with the path of the Mediterranean Undercurrent. The multi-channel seismic reflection method provides clear images of thermohaline fine structure with a horizontal resolution approximately two orders of magnitude higher than CTD casting. The seismic data are compared with co-located historical oceanographic data. Three seismic reflectivity zones are identified: North Atlantic Central Water, Mediterranean Water and North Atlantic Deep Water. Seismic evidence for the path of the Mediterranean Undercurrent is found in the near-slope reflectivity patterns, with rising reflectors between about 500 and 1500 m. However, the core of the undercurrent is largely transparent. Seismic images show that central and, particularly, intermediate Mediterranean Waters have fine structure coherent over horizontal distances of several tens of kilometers. However, the intensity of the reflectors, and their horizontal coherence, decreases downstream. This change in seismic reflectivity is probably the result of diminished vertical thermohaline contrasts between adjacent water masses, so that double-diffusion processes become unable to sustain temperature and salinity staircases. Comparison of root-mean-square seismic amplitudes with temperature and salinity differences between the Mediterranean Undercurrent and the overlying central waters suggests a causal relationship between observed thermohaline fine structure and true seismic amplitudes. We estimate that, within this intermediate water stratum, impedance contrasts are mainly controlled by sound speed contrasts (a factor between 3.5 and 10 times larger than density contrasts), which are mainly controlled by temperature contrasts (a factor between 1.5 and 5 times larger than salinity contrasts).
ISSN: 0278-4343
DOI: 10.1016/j.csr.2009.05.017
Source: Continental Shelf Research [ISSN 0278-4343], v. 29, p. 1848-1860
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