The OCEANAUT (an acronym for OCEAn and NAUTile) cruise was the first
diving cruise for which Daniel was fully in charge and I must say that he conducted it with great enthusiasm and passion. The Oceanaut program was designed
to observe the surface expression of ridge segments under different magmatic
regimes.
We embarked on the NO Nadir on August 23, and disembarked on September
20, 1995, in the port of Punta Delgada on the island of Sao Miguel (Azores). It
took several days to transit to the dive area on the Mid-Atlantic Ridge spreading
center near 34°50
0 N. The OCEANAUT cruise was intended to study two short
spreading ridge segments, which were previously recognized to be the sites of
contrasting geological processes. These two segments were called OH1 and OH3
(short for O = Oceanographer and H = Hays fracture zones respectively). These
segments separate the Oceanographer and Hayes Fracture zones.
The segment closest to the Oceanographer transform (called OH1) was the site
of a robust magmatic upwelling zone as defined by previous gravity measurements. Indeed, the presence of a strong ‘‘bull’s-eye’’ gravity-low suggested that
there is a deficit of mass, which was interpreted as being the presence of a magma
chamber underneath the spreading ridge. The other segment, closer to the Hayes
transform (called OH3), was considered as a quieter magmatic zone with a smaller
gravity-low interpreted as being due to a more fractured crust and a lack of
volcanism (Fig. 7.8a, b). In order to verify the ‘‘tectonic versus magmatic’’
Fig. 7.8 a Location map (inset) and bathymetric map of the Mid Atlantic Ridge segments
between the Oceanographer and the Hays Fracture zones obtained from the Simrad EM-12 swath
bathymetry data (Bideau et al. 1998). The contours are every 200 m. Sites of OH1
(Oceanographer-Hays fracture zone) and OH3. b The Mid Atlantic Ridge segment OH3 at
34°50
0 N, reproduced from bathymetry and dive observations during the ‘‘Oceanaut cruise’’ after
Bideau et al. (1998). The base map was obtained during the Sigma cruise (Courtesy of
H. D. Needham) with the N.O. L’Atalante equipped with a multichannel SIMRAD
The OCEANAUT Project: Mid Atlantic Ridge at 34°50
0 N
187
diving cruise for which Daniel was fully in charge and I must say that he conducted it with great enthusiasm and passion. The Oceanaut program was designed
to observe the surface expression of ridge segments under different magmatic
regimes.
We embarked on the NO Nadir on August 23, and disembarked on September
20, 1995, in the port of Punta Delgada on the island of Sao Miguel (Azores). It
took several days to transit to the dive area on the Mid-Atlantic Ridge spreading
center near 34°50
0 N. The OCEANAUT cruise was intended to study two short
spreading ridge segments, which were previously recognized to be the sites of
contrasting geological processes. These two segments were called OH1 and OH3
(short for O = Oceanographer and H = Hays fracture zones respectively). These
segments separate the Oceanographer and Hayes Fracture zones.
The segment closest to the Oceanographer transform (called OH1) was the site
of a robust magmatic upwelling zone as defined by previous gravity measurements. Indeed, the presence of a strong ‘‘bull’s-eye’’ gravity-low suggested that
there is a deficit of mass, which was interpreted as being the presence of a magma
chamber underneath the spreading ridge. The other segment, closer to the Hayes
transform (called OH3), was considered as a quieter magmatic zone with a smaller
gravity-low interpreted as being due to a more fractured crust and a lack of
volcanism (Fig. 7.8a, b). In order to verify the ‘‘tectonic versus magmatic’’
Fig. 7.8 a Location map (inset) and bathymetric map of the Mid Atlantic Ridge segments
between the Oceanographer and the Hays Fracture zones obtained from the Simrad EM-12 swath
bathymetry data (Bideau et al. 1998). The contours are every 200 m. Sites of OH1
(Oceanographer-Hays fracture zone) and OH3. b The Mid Atlantic Ridge segment OH3 at
34°50
0 N, reproduced from bathymetry and dive observations during the ‘‘Oceanaut cruise’’ after
Bideau et al. (1998). The base map was obtained during the Sigma cruise (Courtesy of
H. D. Needham) with the N.O. L’Atalante equipped with a multichannel SIMRAD
The OCEANAUT Project: Mid Atlantic Ridge at 34°50
0 N
187