HR: 11:56h
AN: B22A-09    [Abstracts]
TI: Near Seabed Dynamics and Turbulence at Tisler Cold Water Coral Reef
AU: * Guihen, D
EM: damien.guihen@nuigalway.ie
AF: Dept. Earth and Ocean Sciences, NUI, Galway, Ireland, University Road, Galway, ie, Ireland
AU: Lundalv, T
EM: Tomas.Lundalv@tmbl.gu.se
AF: Tjarno Marine Biological Laboratory, Tjarno, Stromstad, SE-452 96, Sweden
AU: White, M
EM: martin.white@nuigalway.ie
AF: Dept. Earth and Ocean Sciences, NUI, Galway, Ireland, University Road, Galway, ie, Ireland
AB: The Tisler Reef, Norway, is a 2 km long cold-water coral reef, comprising principally of Lophelia pertusa, located at a sill in the north western Skagerrak at depths between 70 and 160 metres. The reef has been the subject of intensive multi-disciplinary observations as part of the EU wide project HERMES. Measurements have been made to asses the temporal and spatial variability in the environmental parameters that control organic matter and biogeochemical fluxes to the reef community. In general the reef is subject to small tidal currents, < 10 cm s^-1, with tidal excursions no more than the extent of the reef structure. Residual flow velocities may be larger and controlled by density forcing at the sill. Variability in the residual flow strength, therefore, determines residence times for water over the reef and consequently the biogeochemical fluxes. Significant modulation of the near seabed flow, associated with the coral reef structures, was measured, generating complex small scale flow patterns. Measurements with a Nortek Aquadopp high resolution ADCP and Vector Velocimeter have been used to characterise both the turbulence generated within and outside the reef structure. A number of different approaches to estimating the magnitude of the turbulence have been used and compared. Stresses of up to 1 Pa have been calculated at velocities of 40 cm s^-1. Results indicated that levels of turbulence are dependant not only on the presence of coral structures, or incident flow strength, but also on the incident flow direction relative to the reef itself. Acoustic backscatter data suggested that local re-suspension of material occurred at high turbulent stresses. In addition, higher turbidity observed downstream of the main reef at periods of high velocities, may have indicated a sweeping of material from the reef. This also implies that reefs may easily entrap material in low energy conditions. Implications for the distribution patterns and feeding behaviour, of the coral community will be highlighted.
DE: 4211 Benthic boundary layers
DE: 4220 Coral reef systems (4916)
DE: 4558 Sediment transport (1862)
DE: 4568 Turbulence, diffusion, and mixing processes (4490)
DE: 4594 Instruments and techniques
SC: Biogeosciences [B]
MN: 2007 Fall Meeting