AUV and Multibeam Survey on the South Florida Escarpment
Authors: Sager William W. 
Published: October 2008

Florida Escarpment is the steep, rugged, western edge of the Florida carbonate platform. It is a poorly-surveyed but geologically complex feature. A small portion of the southern escarpment was surveyed as part of a project funded by the National Oceanic and Atmospheric Administration (NOAA) Office of Ocean Exploration to better understand the geology and habitats of the escarpment. The mapping was carried out by C&.C Technologies, Inc., using a surface multibeam echosounder and an Autonomous Underwater Vehicle (AUV), whose instrumentation included a multibeam echosounder, side-scan sonar, and chirp subbottom profiler. Surface multibeam bathymetry data cover 734 km2 and reveal three northeast-trending canyons incised into the southeast-trending escarpment, which is 750-1300 m in height. Multibeam backscatter data show strong returns from the canyon walls and from talus at the escarpment base. AUV data cover 66 km2 at the escarpment base and on the platform, the escarpment wall being too steep for the AUV to survey. AUV data show vastly higher resolution with features &lt;5 m in diameter visible in sonar backscatter images. These data indicate that the summit platform is mantled with sediment and contains numerous small mounds similar to carbonate biotherms imaged in other locations. The mounds are typically several tens of meters in diameter or less and can be up to tens of meters in height. Some are isolated, but many occur in clusters and mound fields. AUV data from the platform show a remnant ridge, blocky terrain, and headwall scarps at the platform edge adjacent to the canyons. At the escarpment base, side-scan sonar images show many rock outcrops protruding from sedimentary aprons. These outcrops have a large range in height and complexity, with some barely emergent. Many are linear and nearly perpendicular to the escarpment. Some appear to be piles of rock from masswasting of the escarpment face. On both the platform and at the escarpment base, AUV data show current scour or sediment sorting features trending northwest, indicative of strong currents from the southeast. Acoustic images suggest these currents are particularly strong and potentially erosive at the escarpment base.

Introduction

The Florida Escarpment is one of the outstanding bathymetric features of the Gulf of Mexico, a steep declivity standing in places more than a mile (1.6 km) high above the abyssal seafloor and stretching about 390 miles (622 km) from DeSoto Canyon at 29.5° N to the Straits of Florida at 24° N (Figure 1). Florida Escarpment is the western edge of the Florida carbonate platform, a thick accumulation of calcareous sediments deposited as a reef-bounded system mainly during the Cretaceous period1–3. Slopes on the escarpment are frequently greater than 40° and vertical or near vertical cliffs are not uncommon4. Outcropping platform interior sediments imply that erosion has cut into the platform edge by several kilometers5–6. South of approximately 27° N, the platform edge is incised by numerous canyons that appear to have an erosional origin, perhaps owing to corrosion by groundwater seeping out the platform edge7–9.