Deep-Sea Habitats and Megafauna on the Slopes of the São Paulo Ridge, SW Atlantic

Abstract

The São Paulo Ridge (SPR) is a 350 km-long linear geological feature located in the Continental Margin off Brazil (Latitude 28-29 • S, Longitude 40-45 • W). In 2013, the region was mapped during the SW Atlantic "Iata-Piuná" expedition and explored by a series of deep-sea dives of the manned submersible Shinkai 6500. A digital bathymetric model analyzed for seafloor morphology, delimited four major bathymetric sectors namely plateau, ridge crest, ridge escarpment and ridge foot. These sectors further enclosed 12 morphological features at smaller spatial scales (structural classes) including plains, valleys, peaks, terraces, and troughs. Video profiles across the depth gradient (4,219-2,644 m depths) revealed that the slopes of the SPR southern flank were gentle and terraced, mostly covered by biogenic sediments and interrupted by rocky cliffs/crests, dispersed outcrops and loose particles. The North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) overlaid at the escarpment along which they established colder (0.4-1.0 • C; 4,200-3,400 m) and warmer (2.0-3.0 • C; 3,400-2,600 m) habitats, respectively. Physical components were used to define seven seascape units in the ridge foot (2), escarpment (3), and plateau-ridge crest (2), where a total of 914 organisms of the epibenthic and benthopelagic megafauna were recorded. Over 70% of these records were sessile suspension feeders, including sponges (61.5%) and anthozoans (11.4%). Most taxonomic groups concentrated above 3,800 m, under the influence of NADW, where densities reached maximum values (mean 0.26 organisms.m −2 ; 0.024-0.027 organisms.m 2 95% CI). Also, nearly half of megafauna records concentrated in patches delimited by the 3,800-3,300 m and 2,900-2,700 m isobaths. The deepest patch (3800-3300 m) coincided with the interface zone between AABW and NADW, where mixing processes create a density gradient. Evidences suggested that topography-related deep-water flow dynamics, and not substrate availability, drives benthic megafauna distribution at meso-habitat scale.

Drivers of Biomass and Biodiversity of Non-Chemosynthetic Benthic Fauna of the Mid-Atlantic Ridge in the North Atlantic

“…Deep-sea animals generally have preferred depths resulting in restricted distributions within narrow depth ranges due to hydrostatic pressure tolerance (Macdonald, 2021) and hydrographic conditions, bottom substrate and interspecific competition (Rowe and Menzies, 1969;King et al, 2006). Perez et al (2020) show that on the São Paulo Ridge in the SW Atlantic topography-related deep-water flow dynamics and interfaces between water masses at different depths are the main drivers of benthic megafauna distribution. Living cold water corals occur within a narrow range seawater density found at particular depths in the NE Atlantic (Dullo et al, 2008) and aggregations of zooplankton and fish tend to occur over abrupt topographies (Genin, 2004).…”

Benthic habitat mapping: A review of three decades of mapping biological patterns on the seafloor

“…Box cores may provide both a large planar surficial sample -similar to that of a grab -and also a profile sample, making them highly useful for obtaining simultaneous representative biological and surficial geological samples (e.g., Leduc et al, 2015). Targeted sampling is used where feasible to obtain specific biological or geological samples (e.g., McRea et al, 1999;Perez et al, 2020). Benthic trawls are a method of sampling that may be targeted or indiscriminate, and are often deployed during scientific or fisheries surveys to sample benthic or demersal species (e.g., Montero et al, 2020;Murillo et al, 2020a).…”

Geomorphological imprint of opposing ocean bottom currents, a case study from the southeastern Brazilian Atlantic margin

“…It is embedded in the Cabo Frio Fault (Demercian et al, 1993;Szatmari et al, 1996). The ~4500-m deep São Paulo Channel is 15-20 km wide and 300 m deep and marks the passage with the São Paulo Plateau (Duarte and Viana, 2007;Perez et al, 2020), a deep marginal elevation underlain by oceanic crust and bounded by fracture zones (Butler, 1970;Kumar and Gambôa, 1979). Below 1500-1800 m deep, pervasive halokinesis formed a puzzling pattern of small basins, topographic highs, and salt diapir exhumations (Moreira et al, 2007;Caldas and Zalán, 2009).…”