Ocean Mapping

Short Sea-Beam survey cruises were conducted by the R.V. "Jean Charcot" in march 1980 along the Middle America Trench between Panama and Acapulco, with particular emphasis on the IPOD Legs 66 and 67 areas. These detailed mappings have revealed that the Cocos horst- and graben pattern, related to the bending of the oceanic plate, strikes generally 20°-30° oblique to the trench direction. This en-échelon pattern, closely parallel to the magnetic anomalies, is here proposed as being due to the reactivation of inherited fractures generated at the East Pacific Rise. Sea-Beam data, together with UTMSI multichannel seismic reflection profiles and IPOD drilling results, clearly show that at least two distinct geodynamic processes are presently working along the same trench: accretion and no accretion. They also show a relative structural homogeneity of the oceanic side of the trench in contrast to the dual aspect of the continental side.

To create maps of nearshore benthic habitats of Broward County, Florida, from 0 to 35 m depth, we combined laser bathymetry, acoustic ground discrimination, subbottom profiling, and aerial photography data in a geographic information system (GIS). A mosaic of interpolated, sun-shaded, laser bathymetry data served as the foundation upon which acoustic ground discrimination, limited subbottom profiling and aerial photography, and groundtruthing data
aided in interpretation of habitats. Mapping criteria similar to NOAA biogeographic Caribbean mapping were used to allow for a comparable output. Expert-driven visual interpretation outlined geomorphological features at a scale of 1 : 6000 with a minimum mapping unit of 1 acre. Acoustic data were then used to differentiate areas of similar geomorphology by their acoustic diversity into areas of high and low scatter, which could be equated to rugosity created by either the substratum or benthic fauna. Of the approximately 112 km2 mapped, 56.62 km2 were coral reef and
colonized hard bottom (50.42%), 54.78 km2 were unconsolidated sediments (46.80%), and 0.43 km2 were other categories
(2.78%). Three linear reef complexes exist. The outermost linear reef has a mature windward reef morphology including a drowned spur and groove system, which was absent on the other two reef lines. The acoustic ground discrimination and groundtruthing showed different benthic habitats on the outer vs. middle and inner reefs. Higher acoustic scatter could be related to taller benthos and more rugose substratum. A considerable amount of colonized
pavement (nearshore hard grounds) was found inshore. The map of Broward County yielded a high overall accuracy of 89.6%, only slightly less than the photo-interpreted NOAA Caribbean maps (overall accuracy of 91.1%). User and producer accuracies within each category were also similar. The combined technique approach was effective and accurate, and similar methodology can be used in other areas where photo interpretation is not feasible because of
turbidity or depth limitations.