UH-PIFSC Seaglider launched off Kona!

A joint UH-PIFSC Seaglider was launched off Kona on Monday, 9 December 2013.  The glider will remain at sea for one month and gather data on habitat properties and cetacean presence.  This glider mission is a collaboration between the University of Hawaii’s SOEST Ocean Glider program (http://hahana.soest.hawaii.edu/seagliders/) and the Kona Integrated Ecosystem Assessment (Kona IEA; http://www.pifsc.noaa.gov/kona_iea/).

The Seaglider is a fully autonomous underwater glider that moves through the water by shifting its internal buoyancy.  Decreasing its buoyancy allows the glider to descend at a shallow angle to a maximum depth of 1000 meters.  Once it reaches this depth, the glider increases its buoyancy and glides back up towards the surface.  The glider will repeat these dives along predetermined transects for the duration of its deployment.

This Seaglider is equipped with a number of sensors, including ones to measure environmental variables such as temperature, salinity, and chlorophyll concentration.  It is also equipped with hydrophones that will record ambient sound, particularly those made by cetaceans.  By combining the recorded sound with the environmental data, we hope to learn more about preferred cetacean habitat.  Previous work off Kona suggests that cetaceans are found in distinct “hotspots” that result from variations in depth and circulation patterns.  The data gathered during this Seaglider mission should help PIFSC researchers gain a better understanding of the factors that influence the locations of these “hotspot” habitats. The Seaglider transects span nearly the full north-south extent of the Kona coast at three distances from shore.  This grid will give a full picture of the Kona ecosystem.

Each time the Seaglider surfaces following a dive, it transmits the environmental data it collected on that dive via Iridium satellite connection.  This allows scientists to monitor the Seaglider and its environment throughout its deployment.  For example, even though the glider has only been at sea for a few days, we can already get a sense of the currents it’s encountering.  We can also see the thermocline shoal and primary productivity increase as the Seaglider moves over the Kohala shelf.

In contrast to the environmental data, the acoustic data files recorded by the hydrophones are too large to be transmitted while the Seaglider is at sea, so we’ll have to wait until the Seaglider is recovered next month to learn where cetaceans are being detected.

In the meantime, you can track the Seaglider here: http://hahana.soest.hawaii.edu/seagliders/history500.html.

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Fig. 1: Seaglider track (black dots) and planned transects (thick black lines).  The green dot shows the deployment site and the red dot shows the most current Seaglider position.  Depth is contoured in 500m intervals from 500 – 2000m.  The Seaglider is currently moving south over the Kohala shelf, joining the easternmost transect.  Once it reaches the southern end of this transect, it will turn west and move north along the next transect.

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Fig. 2: Seaglider-measured currents.  Each barb shows the speed and direction of the depth-averaged current for one dive.  As the glider moves south away from the Alenuihaha Channel, the currents should become weaker.

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Fig. 3: Seaglider-measured temperature and chlorophyll concentration.  As the glider moves over the Kohala shelf, we see cooler temperatures closer to the surface, an increase in maximum chlorophyll concentration, and a narrower depth range with measureable chlorophyll concentrations.  The Seaglider’s early dives are shallow and get progressively deeper as the glider moves away from shore.

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