The submerged chain of the Horseshoe (hereafter HS) seamounts in the north- eastern Atlantic is located along the eastern sector of the Acores- Gibraltar lineament, within a zone of convergence and strike-slip motion between Eurasia and Africa lithospheric plates. The Acores-Gibraltar belt is also characterized by present-day high seismicity and structural deformation. The HS seamounts raise until shallow depths (few hundreds to few tens metres) above Tagus, HS and Seine abyssal plains 4000 to 5000 m deep. They are all volcanic edifices apart from the Gorringe bank including Gettysburg and Ormonde seamounts where sub-oceanic mantle rocks crop out [Auzende et al.(1978)]. Despite the several geological and geophysical investigations carried out at the regional scale over the HS chain and the SW Iberian margin (see [Sartori et al.(1994),Banda et al.(1995),Hayward et al.(1999),Gracia et al.(2004)]) and apart from several direct observations and sampling (see next section) swath bathymetric exploration over the HS summit areas was initiated only very recently [de Alteriis et al.(2004)]. HS seamounts are also present-day natural laboratories for temperate-waters carbonate sedimentology and oceanography. Their peculiar physiography favours the production and accumulation of biogenic sands [Conti et al.(2004)] derived from the algal benthonic communities and from the associated invertebrated faunas. Upwelling currents, as well as interaction with Mediterranean waters eddies (Meddies) characterise their oceanographic regime [Bower (1994),Richardson et al.(2000)]. For these reasons some Atlantic seamounts have been chosen as protected ecosystems (see links to other projects).
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The expected results of the Horseshoe_2005 Cruise were:
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