| From a (paleo)ecological point of view submarine canyons are not well studied, although they form essential elements in our global system. Through them huge amounts of erosional products, including nutrients and carbon, are transported to the deep sea, either directly from the riverine point source or indirectly after temporary deposition at the shelf. As such, canyons are important loci where already buried or degraded organic matter is oxidized or nutrients are re-mineralized. Consequently, the oxygen consumption in canyons is high but even under these circumstances a net burial of organic matter takes place in amounts possibly as high as on the total shelf. We have a rather poor understanding of the ecological functioning of canyons over time due to lack of adequate tools to unravel the fossil sequences in detail. Consequently, questions as whether canyons function more effectively in sediment discharge during glacial lowstands or under interglacial humid periods are still open. The biological and biogeochemical function of canyons as important sinks of organic carbon and sites of remineralization of nutrients is not well known at all. We assess the value of benthic foraminifers as proxies of canyon functioning using (experimental) knowledge on their microhabitat ecology. The ratio between infauna and epifauna is likely to be a good proxy of sedimentation rate and frequency of sedimentation events per time interval. Abundance of opportunistic taxa indicates the time span of non-sedimentation or non-disturbance. Selected taxa indicate the efficiency of the system as trap for organic matter or nutrients. We study the benthic foraminifera in three canyon systems that serve as modern analogues of canyon situations under glacial-interglacial humid-dry borderland conditions. The benthic foraminiferal patterns are cross-correlated with a host of physical and chemical variables (including current velocities, sediment load, degree of disturbance of the benthic environment, water/pore water/sediment geochemistry). The developed benthic foraminiferal proxies will be applied to well-dated (210Pb and 234Th) short cores. The combination of proxies and dating should lead to a better understanding of functioning of canyon systems with respect to the discharge and cycling of sediments and nutrients a) under different climate conditions, and b) compared to the surrounding shelves. |
