Duncan J L Mercer

Monitoring environmental variability around cold-water coral reefs: the use of a benthic photolander and the potential of seafloor observatories

The environmental sensitivies of cold-water corals and their associated biota are likely to be determined by the natural variability of the cold-water coral reef environment. The sensitivity of reef biota to sedimentation and resuspension events is largely unknown and the influence of seasonal phytodetrital deposition is poorly understood. Here we describe the use of a benthic photolander to monitor this variability by the Sula Ridge reef complex on the mid-Norwegian continental shelf and from the Galway carbonate mound in the Porcupine Seabight. The photolander provides a platform for time-lapse digital and film cameras to image the seabed while recording the current regime and optical characteristics (light transmission, backscatter and fluorescence) of the seawater. In its first two deployments carried out in 2001 and 2002 by the Sula Ridge the lander recorded a dynamic environment around the reef site with a tidal current regime and periods of sediment resuspension. Current speeds by the Sula Ridge reef complex reached a maximum of 28 cm s−1 and 70 cm s−1 on the Galway carbonate mound, reinforcing much speculation about the dependence of these communities on current-swept conditions. Seabed photographs show intense feeding activity of echiuran worms (Bonellia viridis) near the Sula Ridge reef complex pointing to rapid bioturbation of the sediment. Fish were recorded sheltering near sponges that had colonised glacial dropstones. Longer term monitoring in situ is needed for study of seasonal change, to identify functional roles of associated fauna and to monitor potential coral spawning events. Benthic landers and seafloor observatories have great potential in these areas. Only with a better understanding of the natural variability of the cold-water coral environment can informed decisions about the environmental sensitivity of cold-water coral reefs and their management be made.

Wave measurements on sea ice: developments in instrumentation

Abstract Traditional methods of measuring the propagation of waves originating from ocean swell and other sources have relied on wire strain gauges, accelerometers or tiltmeters. All methods required constant attention to keep in range, while data recovery has demanded that the instrument site be revisited. In this paper, we describe the use of ultra-sensitive tiltmeters and novel re-zeroing techniques to autonomously gather wave data from both polar regions. A key feature of our deployments has been the use of the Iridium satellite communications system as a way of ensuring continuous data recovery and remote control of the instrumentation. Currently four instruments have been successfully reporting from the Arctic Ocean for over 18 months, with two further units deployed in 2005, one in the Weddell Sea, Antarctica, and one additional unit in the Arctic.

HOMER: early results from a novel seabed-resident water column profiler

The HOMER deep water vertical profiler (HOMing Environmental Recorder), originally devised at the Proudman Oceanographic Laboratory, has recently been further developed and tested at the Scottish Association for Marine Science (SAMS). The HOMER system comprises a seabed resident winch which repeatedly releases and recovers a buoyant, internally-recording, 0.25 m diameter spherical sensor module. The sensor sphere performs CTD (conductivity, temperature, depth) profiles of the water column from the seabed to a pre-programmed altitude. Other sensors will be added in due course, for example current meters and shear micro-structure sensors. In its present configuration the instrument is capable of a total of approximately 200 profiles to a height of 400 m above the bed in water depths of up to 4000 m. Deployments of up to 2 years duration are possible. Water column profiles are taken at pre-programmed time intervals, and winch control is performed through an embedded microcontroller. The pre-programmed microcontroller instructs a pair of oil filled brushless DC motors; one motor drives the main take-up spool and the other drives a capstan which controls the ascent and decent rate. Power is supplied through a bank of standard lithium D-cells. Sensor sphere and winch are connected via a non-conducting mono-filament line. An infra-red link transfers data from the sensor sphere to the sea-bed frame control sphere between profiles to minimise the risk of data loss. The entire instrument remains on the seabed between profiles, thus minimising problems associated with fishing damage and biofouling.

New developments in the remote measurement of currents and waves at the Scottish Association for Marine Science

In our last presentation to this conference in 1999, we outlined the incorporation of GPS and adaptive sampling techniques into a variety of Lagrangian drifters (the GPS-Argos Drifter, the Smart Buoy and the Mini-Drifter), each tailored to address a particular scientific question and optimised for given space and time scales. In this paper we will describe further developments which have led to the successful deployment of innovative ice buoys in both polar regions. These buoys have exploited the high resolution of post-processed GPS techniques, wave spectral data from on board accelerometers, and the enhanced bandwidth of new satellite communications systems to yield valuable new insights into the formation and deformation of young pack ice. At the other end of the scale, mini drifters are now routinely used to estimate diffusion parameters close to pollution sources as part of an ongoing modelling effort to quantify the fate of pollutants.