Continental margin sedimentation represents the terrestrial-marine geological transition. Coarser coastal sediments usually transition to fine-grained sediments across the shelf as the energy level decreases. As the distance from the continental source of terrigenous sediments increases, the mid-shelf mud belt transitions to a seaward organic/carbonatic sedimentation domain. However, this general pattern might change depending on the terrigenous sediment load. This is the case for the Amazon continental shelf, where the Amazon River empties and builds up the large Amazon River plume (ARP). The ARP promotes an inverse pattern with muddy nearshore prodelta sediments and siliciclastic sands offshore. This study investigates water and bottom characteristics to the east of the Amazon River mouth to understand the complex interplay that leads to simultaneous massive river plume spread and mesophotic reef development. Three cross-self profiles were performed, including physical-chemical water column measurements and bottom sample collection. The profiles were approximately 150 km apart, comprising a longitudinal gradient off of the ARP. The results reassure that there is enough light for mesophotic reefs to grow at the outer shelf and that at the mid-shelf, large-scale sand movement is likely to be the major limiting control on reef accretion. Also, mesophotic conditions (i.e., low light levels) occur in shallower waters, where a trend of reef expansion was identified, but high-energy levels and the lack of hard substrates hinder reef expansion.

Depth range
0- 120 m

Mesophotic “mentions”
12 x (total of 7259 words)

Classification
* Presents original data
* Focused on 'mesophotic' depth range
* Focused on 'mesophotic coral ecosystem'

Fields
Oceanography
Paleoecology

Focusgroups
Other invertebrates
Scleractinia (Hard Corals)

Locations
Brazil - Eastern Brazil

Platforms
Dredging / trawling
Surface-deployed sensors and samplers