HR: 1300h
AN: OS52C-06    [PDF]
TI: Acoustic Mapping and Sediment Composition of the Northernmost East Pacific Coral Reef at Cabo Pulmo, Mexico
AU: * Halfar, J
EM: jochen@pangea.stanford.edu
AF: IGP, Universitaet Stuttgart, Stuttgart, 70174 Germany
AU: Riegl, B
EM: rieglb@nova.edu
AF: National Coral Reef Institute, Nova Southeastern University, Dania, FL 33004 United States
AU: Godinez, L
EM: lorta@ipn.mx
AF: CICIMAR, IPN, La Paz, 23096 Mexico
AB: The bay of Cabo Pulmo in the Gulf of California, Mexico, is the location of the northernmost coral reef in the East Pacific developing at $23\deg$N latitude in a warm-temperate oligo-mesotrophic setting. In order to map the extent of the reef and associated sedimentary facies, quantitatively determine carbonate producers and evaluate the influence of siliciclastics on the coral system we employed a combined acoustic mapping and surface sediment sampling approach. Acoustic data was acquired along transect lines using a QTC View Series V hydrographic survey unit in order to classify seafloor facies based on the interpreted shape of echoes reflected off various substrates. Combining acoustic data with information from sediment samples allowed the distinction of the following bottom facies: a) coral reef facies; b) patch reef facies; c) mixed-carbonate siliciclastic molluskan facies, and d) foraminiferal facies. The coral reef facies is developed close to shore in less than 10m water depth and is surrounded by a patch reef facies (b), in which individual coral heads and coarse sand predominate. With increasing depth in the inner shelf a mixed carbonate-siliciclastic bivalve dominated facies (c) occupies the majority of the bay. Below 20m depth the foraminifera dominated facies (d) is apparent only in sediment samples. Even though the site is known as the northernmost coral reef of the East Pacific, significant framebuilding is absent and only 12\% (0.9km$^{2}$) of the area is occupied by corals overgrowing granitic rock ridges, 20\% (1.3km$^{2}$) by patch reefs made up by {\it Pocillopora} mega-colonies, and 60\% (4.2km$^{2}$) by molluskan rich mixed-carbonate siliciciclastic sediments. Most carbonate sediment is found in the southern part of the bay, whereas the rest of the bay is dominated by mixed-carbonate siliciclastics. This reflects the influence of an episodically active stream bed in the northern bay of Pulmo delivering coarse granite derived material to the system. Reasons for siliciclastics at Cabo Pulmo not being detrimental to coral reef development are their coarse grain size and only episodic delivery into the system.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3045 Seafloor morphology and bottom photography
DE: 3094 Instruments and techniques
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting