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Abstract
Coral mounds formed by framework-forming cold-water corals pierce the seabed along most continental margins of the Atlantic Ocean and new sites are continuously being discovered. Here, we describe an extremely high accumulation of coral mounds at the NW Moroccan Atlantic margin between 35°N and 35.5°N. Within an area of only 1440 km2, >3400 mounds were found exposed at the seabed. The coral mounds are nowadays characterized by an almost complete lack of living cold-water corals. In addition, numerous buried mounds were identified in hydroacoustic sub-bottom profiles, and are estimated to be ~3.7 times more frequent than the exposed mounds. Consequently, a total of ~16,000 buried and exposed mounds is estimated for the entire study area. The exposed mounds are rather small with a mean height of 18 m and show a conspicuous arrangement in two slope-parallel belts that centre in water depths between 720 and 870 m and 890–980 m, respectively, putting them among the deepest mound occurrences discovered so far in the Atlantic. The mostly elongated mounds largely stretch downslope pointing to a significant influence of internal waves in the mound formation process. Moreover, based on their average dimensions, the entire coral mound volume can be estimated as 1.3 km3, which means the mounds store a considerable amount of coral carbonate highlighting their potentially important role as regional carbonate factories. In combination with further occurrences of coral mounds along the Moroccan margin, both in the Mediterranean and in the Atlantic Ocean, these new findings underline Morocco's role as a hotspot for the occurrence of cold-water coral mounds.
Highlights
Coral mounds, created by scleractinian framework-forming coldwater corals, are ubiquitous seabed features along the continental margins of the Atlantic Ocean and its adjacent marginal seas such as the Mediterranean Sea and the Gulf of Mexico (Hebbeln and Samankassou, 2015; Henriet et al, 2014; Wienberg and Titschack, 2017)
Geophysical data obtained from the area (1430 km of PARASOUND sub-bottom profiles shown in Fig. 2C) showed the presence of exposed and buried coral mounds (Vandorpe et al, 2017) indicated by their acoustic transparency (Fig. 3B)
The high number of mounds often found in individual coral mound provinces (e.g., Hebbeln et al, 2014; Muñoz et al, 2012; White and Dorschel, 2010) as well as the continuous discovery of new provinces – at least around the Atlantic – point to their role as common seabed features usually occurring in intermediate water depths that up to date have been largely neglected in any classification schemes describing submarine landscapes (e.g., Greene et al, 1999)
Summary
Coral mounds, created by scleractinian framework-forming coldwater corals, are ubiquitous seabed features along the continental margins of the Atlantic Ocean and its adjacent marginal seas such as the Mediterranean Sea and the Gulf of Mexico (Hebbeln and Samankassou, 2015; Henriet et al, 2014; Wienberg and Titschack, 2017). The appearance of coral mounds is highly variable (circular to oval, arcuate to Vshaped, elongated to ridge-like, irregular to multi-peaked), which is often related to the prevailing current regime shaping the mounds (e.g., Correa et al, 2012; Lüdmann et al, 2016) Their dimension varies considerably with heights from a few metres to impressive values of > 300 m in height and a lateral extension from a few 10 s to several 100 s of metres (e.g., Mienis et al, 2007; Wheeler et al, 2007)
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