Zone 1 sediments are primarily terrigenous and are the products of river discharge into the coastal boundary current, Transport is from north to south and is accomplished by both the coastal boundary current and the strong longshore drift system, discussed below, within the zone of breaking waves. The distributions are skewed toward the fine sands, which probably reflects an interaction between carrying capacity of the coastal boundary current and winnowing processes by the coastal wave regime. In contrast to the smooth bottom areas of Zone 1, the interior shelf supports productive communities of sediment-producing calcareous green algae. This trend reflects the contribution of abundant flake-like grains of Halimeda. These and other coarse components are commonly found in a matrix of aragonitic mud, which also represents disintegration products of abundant calcareous green algae.
Sediments associated with the two zones of reef growth are very similar.
Particles in the range of 0.0 to -2.0f generally represent Halimeda, which is an important sediment producer in the reef as well as the open shelf areas of Zone 2. Coarser particles, about - 4.0f, primarily represent coral debris.