Tuesday, June 3, 2014

Ready for the BIG ones!

Google Earth Image of Dongsha Atoll with approximate
location of DTS cable.
New and full phases of the moon bring "spring" tides - the largest amplitude tides.  Energetic tidal currents flowing over bumps in the ocean floor drive waves within the ocean, aka, "internal waves" (see Science section for a nice explanation).  Spring tides in the South China Sea produce some of the biggest internal waves that have been measured in the ocean… and they'll be heading toward the Dongsha atoll on June 12th (full moon)!
Fiberoptic cable deployed behind a small boat
on the reef flat.  The small dot on the horizon is
the scaffolding platform where the DTS
base station is located.

But, we're ready for them!

Yesterday, we completed the setup of the distributed temperature sensor (DTS), which includes 4 kilometers of fiberoptic cable laid from the lagoon, over the reef flat, and
down the fore reef slope to 50 m depth offshore - acting as an internal wave antenna (see blog post on May 27th for more detail on the DTS).  The DTS measures temperature and along with other instruments we have deployed on the reef, will allow us to better understand how much of the deep offshore water the internal waves bring onto the shallow reef and how it affects the corals that live there.

Aryan, Austin, and Kristen are very excited to have an
empty reel!  Note the yellow "lazy susan" that saved the day!
Deploying 4-km of cable on a reef is no small task.  It requires a lot of teamwork, good timing, and a little luck.  Our luck came in the form of good weather (small waves on the reef crest) and a useful reel mount that operates much like a "lazy susan" on the dining table that we borrowed from a nearby construction site!  We had planned some other methods for spooling out the cable, but the "lazy susan" turned out to be the best option.  Sometimes in field work, improvisation is key!

DTS cable over spur and groove formations
on the fore reef slope.
We still have a lot of work to do surveying the cable and ground-truthing our measurements with more traditional single-point ocean temperature sensors, but we're looking forward to capturing some internal waves in our DTS data!

- Kristen Davis
Coastal Dynamics Lab
University of California, Irvine

Kristen places a temperature sensor on the cable to
calibrate the DTS signal.


  1. Just Incredible! This is the first time ever for DTS deployment on a coral reef. Congratulations all of you!

  2. Can't wait to see that data visualized! You'll redefine bore-ing!

    1. Steven Davis - waves are constantly changing. You study ROCKS. And you think WAVES are boring????

    2. A bad pun: http://en.wikipedia.org/wiki/Tidal_bore

  3. Does the cable have to be periodically anchored down so that wave action doesn't move it?