Sea Glider Deployed in Oceanographic Study off Hawaii Island's Kona Coast

During the July 2011 cruise of the NOAA Ship Oscar Elton Sette, a sea glider was deployed to measure physical and biological oceanography off the Kona coast of the island of Hawaii. The expedition was undertaken in support of the Kona Integrated Ecosystem Assessment Program at the NOAA Pacific Islands Fisheries Science Center.

The glider performs dives to 900 m, taking measurements at regular intervals throughout its dive, and is propelled by shifting its buoyancy. Variables measured by the glider include temperature, salinity, fluorescence, and depth-averaged currents. The glider is also equipped with a hydrophone to record cetacean sounds. When the glider surfaces after each dive, all data collected during the dive, with the exception of the acoustic data, are downloaded from the glider via Iridium satellite telemetry. This allows for real-time data investigation and the opportunity to redirect the glider.

Path of sea glider off the Kona coast of the Island of Hawaii (red, black and white dots) in relation to mean sea level 
                 anomaly (color scale, from AVISO satellite altimeter data) defining a cyclonic eddy (white arrows).  Length and angle of 
                 black whiskers indicate strength and direction of ocean currents as measured by the glider.
Path of sea glider off the Kona coast of the Island of Hawaii (red, black and white dots) in relation to mean sea level anomaly (color scale, from AVISO satellite altimeter data) defining a cyclonic eddy (white arrows). Length and angle of black whiskers indicate strength and direction of ocean currents as measured by the glider.

For the remainder of its deployment, the glider will transit along three meridional transects. The data collected along these transects should provide a means for north-south, onshore-offshore, and onshelf–offshelf comparisons, corroborate CTD data collected during the Sette cruise, and provide information on mesoscale ocean features that develop in the area. The acoustic data collected can provide insight into how these features influence cetaceans and whether specific areas off Kona are preferred by cetaceans.

Two examples of features that can be examined with the glider are a cyclonic eddy that was present off Kona in late July and the environment over the Kohala Shelf that was surveyed by the Sette. As shown in the accompanying graphic, from late July and into August the glider moved from the center of an eddy (glider positions shown in red), through the edge of the eddy (glider positions shown in black) and to the Kohala Shelf (glider positions shown in white). High values of subsurface chlorophyll and a shoaling of the thermocline were seen during the dives when the glider was sampling in the interior of the eddy. As the glider traveled over the Kohala Shelf and into an area more strongly influenced by currents coming through the Alenuihaha Channel, the depth of the mixed layer decreased substantially and the thickness of the subsurface chlorophyll maximum increased. Once the glider is recovered, any recorded cetacean sounds can be examined in relation to these and other features.

The sea glider will remain off the coast of Kona until early October 2011. This glider mission is a collaboration between PIFSC and the Sea glider program at the School of Ocean and Earth Science and Technology (SOEST), University of Hawaii.