Previous geological investigations of Ampere, Unicorn and Seine seamounts

The tops of the seamounts in the HS region are still relatively poorly known apart form large scale geophysical surveys, mostly regarding the SW Iberian margin (cited in the previous section). In the past 25 years Ampére  and Unicorn seamounts have been objects of several geophysical/geological expeditions including manned submersible dives, coring operations especially by Russian teams. The top of Seine seamount has been sampled mostly for biological purposes. The following are the most relevant expeditions:

• Cruise R/V Akademik Kurchatov n30, 1979-80. Institute of Oceanology- Soviet Academy of Sciences, Mosow, URSS. Single-beam bathymetry, dives with submersible Pisces. Area: Ampére.

• Cruise R/V Vityaz n7, 1984. Institute of Oceanology- Russian Academy of Sciences, Moscow. Russia. Single-beam bathymetry, dives with submersible. Area: Ampére .

• Cruise R/V Bavenit, 1991. Institut of Oceanology "P.P. Shirsovâ". Russian Academy of Sciences, Moscow. Russia. Geotechnical essays. Drilling cores. Zone: Gorringe, Ampére , Josephine.

• Cruise R/V Victor Hansenâ, 1997. Geomar, Kiel-Univeristat Tubingen. Bottom sampling (carbonate sediments and corals). Areas: Galicia Bank, Gorringe, Ampére , Unicorn, Coral Patch, Seine, Dacia.

• Cruise R/V Meteor n 51, September-October 2001. University of Hamburg (Germany) chief scientist: Prof. K Hoernle. Extensive dredging of NE Atlantic seamounts for study petrogenesis and volcanism; 5 dredge hauls from Unicorn and Seine seamounts.

• Cruise R/V Discovery n 282, June-August 2003. Southampton Oceanography Centre, UK. Chief scientist: B.J. Bett. Physical oceanography, biogeochemistry and ecology of seabed communities on and around Seine and Sedlo seamounts.

• On October 2005 just few weeks before our cruise the Coral Patch seamount, (east of the Ampére  seamount) was surveyed through MB bathymetry during the SWIM_2005 Cruise, R/V Explora (Italy), chief scientist: Nevio Zitellini, ISMAR-Istituto di Scienze Marine, CNR, Bologna (Italy) (see Zitellini et al., 2005 data report).

To date the official cartographic documents with bathymetry regarding the working area were the following:

• Bathymetry of northeast Atlantic, sheet 5 (Hunter, Sarle and Taughton eds., 1983, scale 1: 2.400.000); published by the Institute of Oceanographic Sciences, NERC, UK.
• Admiralty Chart n 3132 "Strait of Gibraltar to Arquipelago da Madeira", last update 1995, scale 1: 1.250.000, published by the Hydrographic Office, Taunton, UK.

It is worth noting that, according to these documents and to previous literature the minimum depths of both Ampére , Unicorn and Seine were controversial as shown below in Table 2.

Table 2: Literature Seamount depths.

Seamount	Ampere	Unicorn	Seine
Minimum depths (m)	59 (1)	246 (2)	89 (2)
	18 (2)	20 (3)	90 (3)
	60 (3)

1) [Litvin et al.(1982),Marova and Yevsyukov (1987),Matveyenkov et al.(1994)]
2) Bathymetry of northeast Atlantic, 1983
3) Admiralty Chart n 3132, 1995

As we will see in the following sections our survey has confirmed that most minimum soundings reported on (2) and (3) charts were affected by errors far from negligible (e.g. in the order of hundreds metres for Unicorn smt).