Special Issue: Towards a new and integrated approach to submarine canyon research

Submarine canyons, steep-walled valleys that cut across virtu ally every continental margin around the world (Harris and Whiteway, 2011), are considered major sediment transport pathways between continental shelves and the deep sea (e.g., Shepard, 1963; Puig et al., 2014). Owing to their steep topography and high terrain heterogeneity, in addition to their unique current patterns and episodic down-canyon flushing events, which result in locally increased nutrient concentrations and food availability, submarine canyons are often considered as biodiversity hotspots (e.g., Tyler et al., 2009; De Leo et al., 2010). On the other hand, considerable differences have been observed between individual canyon systems, and between different faunal groups in terms of their response to the typical canyon environment (e.g., Cunha et al., 2011; Ingels et al., 2011; Schlacher et al., 2007). Unfortunately, in addition to transporting sediment, submarine canyons also tend to funnel our human litter and pollutants into the deep sea, extending the anthropogenic impact on the oceans far beyond our shores (e.g., de Jesus Mendes et al., 2011; Mordecai et al., 2011; Schlining et al., 2013). Submarine canyons have been the subject of research for a long time. Shepard (1972) refers to a study from as early as the late nineteenth century, carried out by Milne (1897), which looked at the instability of canyon floor sediments as a possible cause for the repeated breaking of submarine cables that had been laid across a canyon. However, as a result of the steep terrain, locally enhanced currents and occasional down-canyon flushing events, the initial submarine canyon investigations were extremely challenging, and the number of studies was limited. Acoustic methods had to deal with excessive scatter and noise, in-situ instruments were regularly washed away and the coarse canyon thalwegs and rocky walls proved difficult to sample (e.g., Paull et al., 2003; Shepard, 1972). Direct observations were limited to shallow waters, within reach of divers or early submarines. With the increasing availability of new sampling and surveying technologies (deep-towed acoustic instruments, drop-down video systems, and eventually robotic vehicles), submarine canyon research increased dramatically (Fig. 1). Particularly the advent of Remotely Operated Vehicles (ROVs) in many research institutes in the last 10 years opened up a new perspective on submarine canyons, allowing a wider community of researchers to access parts of the deep ocean that had been hidden until then (Tyler et al., 2009). As a result of this increased research effort, our understanding of submarine canyons is gradually growing. A number of individual canyon systems have received considerable attention (e.g. the Portuguese Canyons offshore Lisbon & Nazaré (Masson and Tyler, 2011 and references therein); Monterey Canyon (e.g., Hall and Carter, 2011; Paull et al., 2011; Robison et al., 2010) or the Cap de Creus Canyon and the other canyons in the Gulf of Lions (e.g., Canals et al., 2006; Lastras et al., 2007; Orejas et al., 2009; Palanques et al., 2008)) but most canyons around the world have not yet been studied, or only to a very limited extend. Furthermore, many of the studies carried out so far are focussing on one aspect (geology, geomorphology, sediment dynamics, hydrography, current patterns, mega-, macro-, meiofauna distribution, biogeochemistry.) of a single canyon or canyon system. The time seems right to start putting all those pieces of the jigsaw together, and to start looking at canyons in a more holistic way. To this end, the first International Symposium on Submarine Canyons was organised in Brest, France in July 2012. Canyon research from all over the world was presented, followed by cross-disciplinary discussions and networking. A good proportion of those studies are presented here, in this Special Issue. In addition, the meeting resulted in the formation of INCISE: the International Network for submarine Canyon Investigation and Scientific Exchange (www. incisenet.org). Further meetings and sessions at international conferences are planned, and an active forum has been set up, with the aim to stimulate cross-disciplinary discussions and research activities.