Wednesday, May 28, 2014

Needle in a haystack

Finding something smaller than a soda can in the ocean is a bit like finding a needle in a haystack. But in this case, finding the needle means recovering very valuable information.
We found a temperature logger deployed on the forereef!
The logger was attached to a buoy to make it easier to find.
In this picture, Tom has just recovered the old loggers and
is about to attach new loggers to the buoy. Photo by Yalan,
National Sun Yat-Sen University.

During our expedition to Dongsha last year, we deployed about two dozen temperature loggers around the atoll. Every fifteen minutes over the past year, these loggers have recorded the temperature of seawater. These temperature records are incredibly important for understanding how internal waves affect corals living on the atoll, as well as identifying warm events that may have caused coral bleaching (see post below on bleaching at Dongsha).

The tricky part is finding our loggers. Dongsha Atoll is about 500 square kilometers, and our loggers are not much bigger than a pen. To make matters worse, after a year in the ocean the loggers will be completely covered with marine life, which acts as camouflage. The key is taking accurate GPS coordinates when we deploy the loggers, and a little bit of luck.
A temperature logger deployed in June 2013 that we just 
recovered. After a year in the ocean, the logger is
completely covered with fleshy and coralline algae, and
even a coral!

So far we have found all the loggers that we left on the reef flat, which is the relatively calm and shallow part of the reef. We haven't had quite the same luck (yet) with loggers on the deeper, rougher forereef - we found 2 out of 8 on our first attempt. Actually, finding any forereef loggers is a huge success because the only way to find them is by SCUBA, and at 70 feet depth we only have 10-15 minutes to search before we need to return to the surface. And of course there is always the possibility that our moorings broke free during storms - one of the largest typhoons of the year passed nearby Dongsha. Though very pleased with the valuable information we have already recovered from the loggers, we are holding out hope that we will still find the rest!

- Tom DeCarlo
Joint Program in Oceanography
Woods Hole Oceanographic Institution.

Tuesday, May 27, 2014

New technology

Austin and Pat load the DTS cable onto Atoll-1

Today we deployed the first 1 km section of fiber optic cable on the Dongsha reef between the lagoon and our scaffolding tower. Though it presented some challenges, we all made it through in one piece (especially the cable). The next step is to deploy another 3 km of cable to stretch from the lagoon all the way towards the open ocean to the forereef. During the next weeks the 4 km of cable that lies on the reef will collect accurate temperatures within 0.01°C every meter at 30 second intervals. These measurements will allow us to track the cold water brought to the reef by internal waves (see the "Science" section). All of this is accomplished using a technology known as DTS.

Tom swims behind Atoll-1, carefully laying cable across 
the reef. The scaffolding tower that will hold the solar panel
and electronics is in the background.
What is DTS? Distributed temperature sensing was developed for industrial use in the oil industry, but is more commonly being applied to hydrological and environmental applications. Instead of relying on data collected from individual sensors, the DTS records a continuous profile of temperatures along the fiber optic cable. It achieves this by measuring the light reflected back on sensor through a phenomenon known as Raman scattering. The signal consists of two wavelengths, Stokes and antiStokes. Because the antiStokes particle is strongly dependent on temperature, the ratio of the two can be translated into temperature. What does this all mean? Temperature can be cheaply and effectively measured over vast distances in time, using the same type of cable that plugs into your phone or television.

Ultimately, the scaffolding will hold the DTS, a small meteorological station, and solar panels to power the whole system. Stay tuned for progress on that in the coming days!

- Austin Hall
Water Resource Engineering
Oregon State University

Monday, May 26, 2014

Ghost reef

Diving into the water, it is as if we are surrounded by ghosts. Massive coral colonies surround us, but they are all bone-white. These are not actually ghost corals, they are "bleached" corals.

Tom inspects a recently bleached coral on Dongsha.
Coral reefs are typically found in the deserts of the ocean - regions where there are few sources of nutrients to the surface waters where the corals live. The reefs that corals build are like oases in the desert, but corals can only do this with the help of symbionts. Even though corals themselves are animals, within their cells they host photosynthetic algae. Everyone wins - the symbiotic algae provide energy to the coral from the products of their photosynthesis, and the algae receive shelter within the coral and benefit from coral waste products.

However, the symbiosis can go awry. Under certain conditions, typically when exposed to unusually warm temperatures, the symbiotic algae begin to produce chemicals that are toxic to the coral host. In response, the coral kicks out the symbionts. This is "coral bleaching" - the vibrant colors of coral colonies are actually caused by the symbiotic algae; once the algae are gone, the colony appears white because we are actually seeing the calcium carbonate skeleton through the translucent coral tissue. This is bad news for corals: without their symbionts, corals often starve and the colony dies. But bleaching is not always a death sentence - corals can acquire more symbionts from the seawater around them, and sometimes the coral colony fully recovers.

Sadly, we saw on Dongsha yesterday that most of the massive coral colonies are bleaching right now. They are still hanging on - with a close look at the colony surface, we could see that the coral animal is still alive. The question is whether they can hang on long enough to acquire new symbionts. With more than four weeks of our expedition remaining, we will continue to monitor these corals, and try to figure out why they bleached in the first place. Stay tuned for more - and cross your fingers that the corals here on Dongsha can recover!

- Tom DeCarlo
Joint Program in Oceanography
Woods Hole Oceanographic Institution

Saturday, May 24, 2014

2 fine days on the atoll

Pat and Austin happy to be on Dongsha!
Spirits were high as we arrived on Dongsha Atoll three days ago. Waiting for us as we got off the plane were three bicycles. The island is small enough to bike across in 3 minutes, but it sure beats walking!

Our first two days on Dongsha Atoll have gone remarkably well. Our first objective was to deploy a series of instruments across the reef to characterize water chemistry and the physics of water flowing over the reef (more on this later). We would have been pleased to accomplish this in the first week, but by the end of our first day all the instruments were in the water.

Some of our instruments ready to go in the ocean
The next step was to build a tower out on the reef. The reef itself all just barely below the surface of the ocean, but our distributed temperature sensor (DTS) needs a platform for an electronics box and a solar panel. Our solution? Build a scaffolding tower out on the reef. Assembling scaffolding underwater on SCUBA is not easy. Luckily, some researchers from the National Sun Yat-sen University and staff at the National Marine Park of Dongsha were interested in what we are doing and offered to help. A few hours later, we have a dry platform on the reef!

So far Tom, Pat, and Austin are on Dongsha. Kristen, Katie, and Aryan arrive on Thursday. We are accomplishing a lot now, but we will need everyone once we begin deploying our larger instruments: the DTS and our remote access sampler (RAS) - an automatic sampler that collects seawater samples for 4 days.

Instruments deployed on the reef measuring temperature
and salinity (left), pressure (right), and we are deploying an
instrument to measure pH (upper right).
Heading out shortly for another day of difficult (but very fun) research!

- Tom DeCarlo
Joint Program in Oceanography
Woods Hole Oceanographic Institution

Our scaffolding tower rising out of the water. Our research
vessel Atoll-2 is in the background.

Staff of the Marine National Park help us load scaffolding on Atoll-2

Monday, May 19, 2014

Beaufort Zero

Beaufort Zero during our 2013 expedition to Dongsha. The
ocean surface is like a mirror, the only ripple from the wake
of our boat. Dongsha Island is in the background.
Here we go. Our expedition to Dongsha is finally here. We are in Taipei for next two days meeting with our collaborators at Academia Sinica, and then on to Dongsha on Thursday. For the past few days (including a long plane ride), I have been working on a presentation for our collaborators - based on some of our initial data from our first expedition to Dongsha last year. Looking through pictures from last year reminded me how lucky we were to arrive in 2013 at a time perfect for fieldwork - Beaufort zero.

Stuck on-island under Beaufort five during
2013 expedition.
The Beaufort Scale describes the state of the sea in terms of wind and waves - twelve is a hurricane and zero is like a bathtub. When we arrived at Dongsha in June 2013, four days straight were Beaufort zero. That was a very rare treat indeed, and we got accomplished tons.

Of course, it couldn't last forever. On the fifth day, the tables turned and we hit Beaufort five. No going out in a small boat and conditions like that. The sixth day too. And the seventh. On the eleventh day, we finally got back out on the water.

So here's to a good start to our 2014 expedition, hoping for many days of Beaufort zero!

(from a hotel in the Tokyo airport - I missed my flight to Taipei!)
- Tom DeCarlo
Joint Program in Oceanography
Woods Hole Oceanographic Institution