Monterey Bay is a dynamic oceanographic environment that offers scientists from around the world unlimited opportunities to study the interactions of marine organisms with their surroundings. The Monterey Bay Aquarium Research Institute (MBARI) coordinates and sponsors multi-institutional experiments in a project named CANON (Controlled, Agile, and Novel Observing Network). The main focus of CANON is to understand how microbial communities react to continuously changing physical and chemical conditions. CANON researchers use a wide variety of observations from satellite and airborne sensors, autonomous surface vessels, autonomous underwater vehicles, gliders, drifters, research ships, and moorings. For the most recent field campaign, the scientists were focused on remineralization of organic matter and its environmental controls. A technique valuable to this type of observational science is the use of a tracer, whose evolving distribution provides information about lateral and vertical mixing. This experiment employed fluorescent rhodamine dye as the tracer. In order to track the spatial distribution of the evolving dye patch, MBARI engineers integrated Turner Designs’ Cyclops rhodamine fluorometers into 3 of their vehicles, one ASV and two AUV’s. In the photos below you can see the Cyclops rhodamine fluorometers mounted on the nose of the Tethys AUV and another peeking through the shell of the Dorado AUV.
As the vehicles travel the bay, the response of the fluorometers indicates to the scientists the presence of the patch. If the response is high, the assumption is made that the patch has not dissipated. This situation would be indicative of a lack of mixing. As time after the tracer injection increases, one can expect the mixing to diffuse the patch. Following a dye patch and measuring the rhodamine concentration through time allows calculation of the mixing rates, which in turn are relevant to understanding microbial ecology. Further, if the dye marks a plankton patch of interest, the signal measured by the fluorometer can be used to autonomously target water sample acquisition. This was accomplished by the Dorado AUV.
The image below shows the Dorado trajectory during one of its surveys. From this image you can see the typical sampling pattern of an AUV, alternating between depths (yo-yo sampling). The color of the point represents the concentration of rhodamine (blue = none/low, yellow-red = high concentration; note the small areas of yellow-red). The small patch of rhodamine was detected by Dorado during a downward profile, and its intensity was recorded so that on the following upward profile, a sample was acquired by the AUV from within the patch. The interruptions in the cruise track of the Dorado are times when the vehicle was on the surface sending data.
Institution: Monterey Bay Aquarium Research Institute, Monterey Bay, CA, USA
CANON (Controlled, Agile, and Novel Observing Network)