Recently acquired bathymetric and high-resolution seismic data from the upper slope of Santos Basin, southern Brazilian margin, reveal a major geomorphological feature in the SW Atlantic that is interpreted as a carbonate ridge - the Alpha Crucis Carbonate Ridge (ACCR). The ACCR is the first megastructure of this type described on the SW Atlantic margin. The ~17 × 11-km-wide ring-shaped ACCR features tens of >100-m-high steep-sided carbonate mounds protruding from the surrounding seabed and flanked by elongated depressions. Comet-like marks downstream of the mound structures indicate that the area is presently influenced by the northward flow of the Intermediate Western Boundary Current (IWBC), a branch of the Subtropical Gyre that transports Antarctic Intermediate Water. Abundant carbonate sands and gravels cover the mounds and are overlain by a biologically significant community of living and dead ramified corals and associated invertebrates. The IWBC acts as a hydrodynamic factor that is responsible for both shaping the bottom and transporting coral larvae. We contend that the ACCR was formed by upward fluid flow along active sub-surface faults and fractures that formed by lateral extension generated by the ascending movement of salt diapirs at depth. The ACCR provides an important modern and accessible analogue for a seabed carbonate build-up related to sub-surface hydrocarbon systems.
Whale carcasses create habitats in the deep sea which are colonized by organisms related to other chemosynthetic environments suggesting that whale falls may act as intermediate refugia for the dispersal and evolution of deep-sea organisms. Such evidence comes mainly from macrofaunal organisms whereas for the smaller meiofauna, data on whalebone assemblages is lacking. In this study, we investigated nematode colonization of whalebones experimentally deployed at 1500 and 3300 m depth and bones from a natural whale carcass found at 4204 m, in the Southwest Atlantic Ocean, off Brazil. By comparing whalebone assemblages to other deep-sea environments, we tested the hypothesis that whale fall nematode assemblages are more similar to those from other cognate chemosynthetic-based habitats, rather than those from sediments surrounding the carcass or other deep-sea habitats. Our results showed that whalebone nematode assemblages resemble those of hydrothermal vents and cold seeps and suggest that organic falls may act as intermediate refugia for meiofauna from chemosynthetic environments. It also showed that oceanographic conditions and the age of the carcasses on the ocean floor could influence nematode assemblage composition and richness. Such findings highlight the importance of organic falls for understanding the connectivity and phylogeny of benthic organisms, including representatives of the meiofauna.
Deep-sea coral distribution and composition are unknown in much of the global ocean, but repurposing ocean industry surveys can fill that gap. In Santos Basin, southeast Brazil, areas (241–963 m depth) were surveyed during seven Petrobras cruises, mapping bottom topography with multibeam sonar, then collecting video with remotely operated vehicles. Here, we defined deep-sea coral species distribution and richness, using these surveys, correlating them to physical oceanographic properties. Solenosmilia variabilis was the most prevalent colonial species in coral mounds. Overall, 67% of species were Octocorallia. Coral assemblage structure, abundance, and richness varied among sites both within and among depths, with higher density and richness in the northernmost Santos basin. Depth was the strongest predictor for scleractinian coral distribution, with depth ranges varying by species. Assemblage differences corresponded to changes in water mass. Desmophyllum pertusum was more abundant in South Atlantic Central Water and S. variabilis in Antarctic Intermediate Water influenced areas.
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