Morphometry of Concepcion Bank: Evidence of Geological and Biological Processes on a Large Volcanic Seamount of the Canary Islands Seamount Province

Abstract

Concepcion Bank is the largest seamount in the Canary Islands Seamount Province (CISP), an oceanic area off NW Africa including 16 main seamounts, the Canaries archipelago and the Selvagens subarchipelago. The Bank is located 90 km northeast of Lanzarote Island and has been identified as a candidate Marine Protected Area (MPA) to be included in the Natura 2000 network. A compilation of complementary datasets consisting of multibeam bathymetry, TOPAS seismic reflection profiles, side scan sonar sonographs, Remotely Operated Vehicle video records and seafloor samples allowed describing in detail and ground truthing the submarine landforms and bioconstructions exhibited by the bank. The Concepcion Bank presently rises up to 2,433 m above the adjacent seafloor and exhibits two main domains: an extensive summit plateau and steep flanks. The sub-round summit plateau is 50km by 45 km and ranges from 158 to 1,485 m depth. The steep flanks that bound it descend to depths ranging between 1,700 and 2,500 m and define a seamount base that is 66km by 53 km. This morphology is the result of constructive and erosive processes involving different time scales, volumes of material and rates of change. The volcanic emplacement phase probably lasted 25–30 million years and was likely responsible for most of the 2,730 km3 of material that presently form the seamount. Subsequently, marine abrasion and, possibly, subaerial erosion modulated by global sea level oscillations, levelled the formerly emerging seamount summit plateau, in particular its shallower (<400 m), flatter (<0.5°) eastern half. Subsidence associated to the crustal cooling that followed the emplacement phase further contributed the current depth range of the seamount. The deeper and steeper (2.3°) western half of Concepcion Bank may result from tectonic tilting normal to a NNE-SSW fracture line. This fracture may still be expressed on the seafloor surface at some scarps detected on the seamount’s summit. Sediment waves and cold-water coral (CWC) mounds on the bank summit plateau are the youngest features contributing to its final shaping, and may be indicative of internal wave effects. Numerous submarine canyons generally less than 10 km in length are incised on the bank’s flanks. The most developed, hierarchized canyon system runs southwest of the bank, where it merges with other canyons coming from the southern bulges attached to some sections of the seamount flanks. These bulges are postulated as having an intrusive origin, as no major headwall landslide scars have been detected and their role as deposition areas for the submarine canyons seems to be minor. The results presented document how geological processes in the past and recent to subrecent oceanographic conditions and associated active processes determined the current physiography, morphology and sedimentary patterns of Concepcion Bank, including the development and decline of CWC mounds The setting of the seamount in the regional crustal structure is also discussed.

Seismicity and Noise Recorded by Passive Seismic Monitoring of Drilling Operations Offshore the Eastern Canary Islands

“…The crust in the easternmost islands of the Canary archipelago is 11-15 km thick (Banda et al, 1981). This area is located at the transition between continental and oceanic crust and is characterized by a 10-km-thick sediment layer east of the ridge (e.g., Rivera et al, 2016). The central seafloor surface of the Canary Channel extends between 1,240 m and 1,460 m water depth, and its most significant features are submarine hills of volcanic or diapiric origin (Acosta et al, 2005).…”

“…The central seafloor surface of the Canary Channel extends between 1,240 m and 1,460 m water depth, and its most significant features are submarine hills of volcanic or diapiric origin (Acosta et al, 2005). Along the Canary Channel, early Triassic evaporitic diapirs intrude Mesozoic sedimentary units and form mounds when they reach the seabed (Rivera et al, 2016). The diapir belt has gained the interest of oil companies for hydrocarbon exploration and it was the focus of the drilling activities monitored in this work.…”

Ocean Circulation Over North Atlantic Underwater Features in the Path of the Mediterranean Outflow Water: The Ormonde and Formigas Seamounts, and the Gazul Mud Volcano

“…This intense stratification is due to the density difference between the Atlantic and Mediterranean waters, which determines the stability of the water column. The associated high values of the Brunt-Väisälä frequency make the NACW-MOW interface an adequate area for the generation and propagation of internal waves, which after the interaction with the gentle slope of the seamounts, can end up breaking, and therefore enhancing the vertical mixing and producing upwelling (IUCN, 2013;Rivera et al, 2016).…”

Near-bottom zooplankton over three seamounts in the east Canary Islands: Influence of environmental variables on distribution and composition.

“…can act as mixing agents enhancing particle resuspension and availability. Rivera et al (2016) recently suggested that particle resuspension can be induced locally by internal waves generated at depths of the NACW-AAIW confluence. This is fully consistent with the local increase of zooplankton: total biomass and copepod, cnidarian, or chaetognath biomass in our results at the NACW-AAIW confluence near 700 m ( Figure 6).…”

“…This is fully consistent with the local increase of zooplankton: total biomass and copepod, cnidarian, or chaetognath biomass in our results at the NACW-AAIW confluence near 700 m ( Figure 6). Also, internal waves are mainly generated to the SW of the bank (Rivera et al, 2016), due to optimal inclination of the seamount flanks. This area coincided with the location of NACW-AAIW hauls at Concepción Bank (Figures 6 and 8).…”