Whittard Canyon: a pathway and sink for organic carbon

Furu Mienis, Sofia Ledin, Marc Lavaleye and Gerard Duineveld, Royal Netherlands Institute for Sea Research, Den Burg, Netherlands
Submarine canyons provide effective connections between the productive shelf waters and the nutrient poor deep-sea, playing an important role in lateral transport of organic matter. This enrichment in organic matter and as well as the heterogeneity of canyons provides a multitude of habitats for deep-sea fauna. Pathways of organic matter transport were studied in the easternmost branch of the Whittard Canyon to determine which processes affect organic matter dispersal, remineralization and retention. Distinct nepheloid layers were observed between 1200 and 2500m water depth. Data collected with bottom observatories showed that these layers are related to internal waves that interact with the topography, resuspending (organic) matter. Over the year many large particle resuspension events were observed, which lasted from several days up to several weeks and which were observed up to 3000 m water depth. Some events were linked to major storms, like Ophelia, while others are still to be identified. Particle fluxes during these events were up to 5 times higher and transport was mainly focused along the canyon axis. Some events were characterized by peaks in fluorescence and high amounts of organic carbon, indicating the supply of relatively fresh organic matter. Analysis of surface sediments showed that the head of the canyon is characterized low organic matter contents, as are the slopes of the canyon. A depo center was found around 2000m water depth, showing high organic matter values and, while the deepest part of the canyon is dominated by marine derived material, containing high, but aged organic matter. Abovementioned patterns were corroborated by in situ respiration measurements, where a clear relation between respiration and the amount and freshness of organic matter was found. Our data shows that Whittard Canyon is an active system being a pathway as well as sink for organic matter and therefor plays an important role as hotspot for deep-sea fauna.