Taking a Closer Look at the North Pacific Chlorophyll Front!

(by guest blogger Lucas Moxey, scientist aboard Oscar Elton Sette SE-15-01)

Over the last few days, activity onboard the oceanographic research vessel NOAA Ship Oscar E. Sette has been fast-paced. Round-the-clock CTD sampling operations, acoustics transects, nighttime Cobb midwater trawls, and sorting & classification of micronekton have been just a few of the scientific activities routinely taking place during the SE-15-01 research cruise. In addition, occasional safety drills and even the celebration of a birthday at sea have also added to the list of recent events.

For the last week, our ship has been sailing north of the main Hawaiian Islands along the 159 W longitude line, conducting numerous transects along the way for collecting a variety of physical, chemical and biological data in an effort to identify and characterize the location and characteristics of the subtropical frontal region. This large oceanographic feature migrates north and south throughout the year in concert with the seasons, and is typically demarcated by two well-defined bio-physical indicators: a sea-surface temperature front (18 degrees Celsius) and an adjacent sea-surface bio-productive chlorophyll front (0.2 mg Chl /m^3). The data collected during this cruise will contribute valuable information to the historical time-series that NOAA ships have been collecting throughout the North Pacific over the last several decades.

During this research cruise, an additional tool is being used for getting a closer “in-situ” look at the unique and complex dynamics that are taking place at the chlorophyll front. Lucas Moxey, a scientist onboard the SE-15-01 cruise, designed and built a customized electronics package for an ocean drifter buoy as part of his graduate research at the University of Hawaii at Manoa – Electrical Engineering Department. Known as SVPs (“Surface Velocity Program”) buoys, these are comprised of a surface float, a tether line and a drogue. In the ocean, the drogue remains submerged at a depth of approximately 15 meters, and the drag that it generates ensures that the surface float remains coupled with the subsurface currents.

The electronics package included in this particular drifter was designed with the objective of collecting different types of information, including sea-surface temperature, salinity, geolocation (latitude & longitude), speed and direction of ocean currents, among other. In addition, the buoy was specifically configured to transmit data back to the scientists via satellite once an hour, in support of the subtropical frontal region research objectives of the SE-15-01 cruise.

During the chilly morning of April 9, upon reaching the chlorophyll front located at 30.5N 159W, the drifter was deployed from the Sette, therefore marking the start of its long journey throughout the Pacific Ocean. Within one hour of its deployment, the buoy was already transmitting real-time oceanographic data directly from within the transition zone chlorophyll front. The drifter is already providing valuable high-resolution information of the oceanic currents that exist in this region, which can be used for complementing and refining the synoptic perspectives provided by the available satellite observations.

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Photo Caption: Lucas Moxey, one of the scientists onboard the NOAA Ship Oscar Elton Sette, preparing the drifter buoy for its ocean deployment at 30.5N 159W (photo by Laura Lilly).

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Photo Caption: A view of the drifter buoy after deployment, showing the float (left) and the drogue (right). The drogue quickly sank to a depth of 15 meters as the paper-soluble tape disintegrated (photo by Laura Lilly).

 

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Photo Caption: Map from April 11 showing the latest geolocation information of the drifter since its release on April 9, 2015. Each data point represents hourly geolocation data.

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