Submerged reef and inter-reef morphology in the Western South Atlantic, Abrolhos Shelf (Brazil)

Abstract

Submarine geomorphology is a main environmental driver defining the seascape and associated benthic habitat. In this sense, eustatic sea-level fluctuations plays a major role in shaping the morphology of the seafloor. During the last deglaciation, changes in rates of sea-level rise led to moments of stillstand and rapid rise acceleration, forming and drowning distinct shelf geomorphological features. Here, we present and discuss the morphology and associated habitats related to submerged reefs and inter-reef areas along the southern Abrolhos inner shelf (western South Atlantic, Brazil). Our aim is to discuss the morphological evidence of reef drowning and related sea-level/climate events, and the formation of distinct habitats during the post-Last Glacial Maximum transgression. Multibeam echosounder data and sub-aquatic video footage are the basic datasets. Automatic seabed classification was carried out by combining morphometric analysis, acoustic backscatter and ground-truthing. Results show the presence of two clusters of submerged reefs (14-23 m and 24-35 m deep), associated with longitudinal and transverse bedforms, banks, and shelf-incised valleys. Rhodolith beds comprise the main inter-reef benthic habitat. Distinct reef clusters defined by reef top depths indicate that reef drowning occurred in two different moments. The shallower reefs are likely related to the rapid sea-level rise associated with MWP 1C, while deeper reefs are interpreted as remanent carbonate build-ups. Habitats are strongly influenced by the marine geodiversity forming a mosaic of reef, inter-reef and bedforms classes that seem to be associated with an antecedent paleo landscape marked by shelf-incised valleys and paleochannels. Submarine geomorphology is an environmental component that drives geodiversity and is driven by distinct seafloor processes acting in different time and spatial scales, as well as being able to quantify biogenic phenomena, for example, surrogacy and provide records of sea-level changes.