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This week marked World Hydrography Day, an annual event started by the International Hydrographic Organization focused on increasing global awareness of the importance of hydrography to the safety of marine transportation and protection of the marine environment.
In recognition of the day, we have a special interview for you this week with the commander of the NOAA Ship Thomas Jefferson, currently in the Gulf of Mexico conducting research in support of the ongoing oil spill. Stay tuned.
It's Thursday, June 24, 2010, and this is Making Waves from NOAA's National Ocean Service.
(World Hydrography Day)
Today, we’re hear from Commander Shep Smith, commanding officer of the Thomas Jefferson, a 208-foot NOAA research and survey vessel that specializes in hydrography based out of Norfolk, Virginia. Cdr. Smith is part of the NOAA Corps, the nation’s smallest uniformed service. Smith serves as master of the vessel, the head of all ship operations, and as chief scientist and hydrographer for the Thomas Jefferson.
Cdr. Smith contacted us from the ship via satellite phone. When we spoke to him, he was about 20 miles south of Port Fouchon, Lousiania.
“Just west of the Mississippi Delta. We’re going to be working the coastal areas from here all the way to Tampa Bay, all the way along the coast. We came to the Gulf of Mexico in late April to conduct hydrographic surveys for the Office of Coast Survey in the Western Gulf of Mexico and around the Flower Gardens National Marine Sanctuary. The project we were working on was about half finished when we heard about the tragedy of the oil spill and the loss of life at the Deepwater Horizon oil rig, and a few weeks later we were engaged in some of the response efforts and have been working on that ever since.”
Now, the main mission of the Thomas Jefferson is to conduct hydrographic surveys to update nautical charts to keep ships safe as they move through our waterways. The two main things hydrographic surveys deal with are water depth and mapping what’s on the seafloor. Along with nautical charting, these surveys are important for many things ... port and harbor maintenance, coastal engineering, coastal management, offshore development, and even for managing fishery habitat.
To support the spill response, though, Cdr. Smith said that some of the tools of the Thomas Jefferson had to be adapted so they could be used to look for subsurface oil.
“We reconfigured one of our winches to be able to do water sampling at depth, spooled on around 1,400 meters of cable onto our winch that we usually use for sidescan operations. That allows us to conduct deep CTD casts with a rosette for water sampling and in situ measurements of water properties at depth.
The rosette Cdr. Smith mentioned is a round metal frame that holds bottles that can take water samples at different depths and a torpedo-shaped device called a CTD that measures conductivity, temperature, and depth. Conductivity is basically a measure of how salty the water is.
While the ship is stopped in one place, the rosette is lowered into the water with the cable from the winch. This instrument is a versatile tool that can be rigged with a variety of scientific sensors to measure different water properties. For this special mission, it’s equipped with two unique sensors to help find patches of oil deep under the surface of the ocean -- one of them is called a flourometer.
“Essentially, it sends out a little pulse of light -- think of it like a blacklight. And if you’ve ever seen a blacklight, there are certain types of materials, notably white things, that glow really brightly, where other things don’t glow. And so there’s a particular type of frequency combination that is indicative of crude oil in the water. So we have a flourometer that measures for concentrations of crude oil directly in the water column.”
The second special sensor measures dissolved oxygen levels -- how much oxygen is dissolved in the water.
“Oil itself in little droplets is a food source for particular kinds of microbes, and so as the microbes eat the oil they consume oxygen, and one of the signals we might see is lower dissolved oxygen in the water mass as a result of the microbial action on the oil.”
The crew of the Thomas Jefferson also reconfigured some of their multibeam sonars to help find where the oil is under the water. Cdr. Smith said that these high-frequency sonar systems are usually used for making highly-detailed maps of the seafloor in shallower waters and for fisheries research, but hydrographers are learning how to use them to map what’s going on in mid-water areas. What they’re looking for on the Thomas Jefferson are anomalous water masses -- places where oil may be potentially hiding.
“We’re not quite sure what the form of those mid-water water masses -- those anamolous water masses -- might look like, but these very highly sensitive transducers and transceiver systems allow us to make fine distinctions within the water column.”
What kind of distinctions? Well, sonar works by sending sound waves into the water. Those sound waves bounce off of objects in the water and return to the ship, and this paints a picture of what’s below the water. Cdr. Smith said that mid-water sonar readings received from the finely-tuned powerful sonar systems and digital processors aboard the Thomas Jefferson pick up all the little bits and pieces within the water column. A single fish would just send back a tiny acoustic return.
“Multiply that by thousands or millions of small creatures living in a particular layer and you would see a strong return within that layer from all those small creatures. Now different biological scatterers as they’re called have different types of returns, and so we can make some distinctions about what’s in the water column from those returns.”
It’s a tricky business. Not only do all of the small biological creatures in the water send back a sonar return, but Smith said so, too, can the water itself if there’s a very cold, salty layer of water beneath a less-salty warmer layer of ocean. That difference can be strong enough that the sound bounces back of the cold layer. Natural gas seeps are also really common in the Gulf of Mexico, sending up countless bubbles of gas into the sea that also get picked up by the ultra-sensitive sonar systems. But he added that what might be telling to help find pockets of oil under the water is what the sonar doesn’t see.
“The absence of a signal at a depth may actually be one of the more interesting things we’re looking for here. If, for instance, there’s a hypoxic layer or another layer that’s toxic for some reason -- if it has a high concentration of oil, for instance -- there may be no biological scatterers, there are no little critters living in that layer. And so where we would see continuos back scatter from all these little critters going down through some parts and then we see nothing, that may actually be one of the more interesting hints about wether we’re seeing one of these anomalous water masses.”
So far, Smith said they’ve had some interesting results, but since this type of sonar work is new, it’s too early to say for sure how well it’s working.
“We have some early indications that there’s a subtle signal that we may be able to recognize one of these anomalous water masses using the acoustics, but it’s really too early to be too sure of that, and we’re continuing to analyze our data and compare our findings to those of other ships to see if the types of observations we made are more widespread.”
The last tool the Thomas Jefferson is using to help locate subsurface pockets of oil is a system called a Moving Vessel Profiler that is towed behind the ship as it moves around from place to place. The Moving Vessel Profiler is a tool that’s used to measure the speed of sound underwater, which changes as water pressure, temperature, and salinity change. This data is used to correct the depth data the ship acquires. Without these corrections, maps of the seafloor wouldn’t be accurate. But it’s not the Profiler itself that’s being used for this mission, it’s another flourometer that’s been attached to it. If you recall, the flourometer seeks out frequencies of light in the water that match a profile for crude oil. What’s special about this flourometer is that it can be used while the ship is moving. It’s the first time this special tool has been used like this.
“That allows us to take underway casts all the way to 200 meters deep without stopping the ship. This will allow us to cover a large territory within the Gulf of Mexico looking for evidence of these anamolous water masses using the flourometer.”
This is particularly handy because the Gulf of Mexico is a vast body of water, and research ships in comparison are really tiny.
“The size of the plumes, even considering that they may contain lots and lots of oil, are still fairly small with respect to the scale of the Gulf of Mexico, and they’re very deep. And so trying to find evidence of these in water that deep is very difficult because of the size of the whole area.”
So that’s why Cdr. Smith’s team are using every tool they have -- it’s a large area, the water is deep, and the oil is hard to find. So, now that we’ve been introduced to the special tools being deployed by the Thomas Jefferson, let’s put it all together to get a big picture of the ships efforts to find subsurface oil. The ship runs the acoustics -- the sonar -- continuously while the ship is out, trying to find hints of where the oil may lie. At the same time, they also tow the Moving Vessel Profiler with the attached flourometer as the ship travels around to look for areas where there may be pockets of crude oil. If the flourometer that’s being towed behind the ship shows a promising reading, it’s used as a first signal that there’s something different going on in the water column.
“We would stop and take a CTD cast, and along with those measurements and sensors that I described earlier, the CTD casts have a rosette which allows it to take water samples. So we’ll drop this down to a certain depth, and we’ll see on the screen that there’s a layer of low dissolved oxygen or high flouresescence or something like that, and we can actually capture a sample of that water in a special bottle. And then when that comes back to the ship, we will take a sample of that water out of that bottle and send it to a laboratory for analysis. ”
And that’s where the mission stands today. The science crew of the Thomas Jefferson have taken many water samples, but they don’t have the equipment to test the samples on the ship. Smith said they are still awaiting those results.
“While I’ve talked about underwater clouds of oil and that sort of thing, the laboratory analysis for the samples we’ve taken have not come back yet, and so we cannot say for sure that what we’re seeing is oil, and we cannot say for sure that oil came from the well head until those laboratory analyses come back.”
We hope that gives you a better idea of some of the work going on in the field with one NOAA ship, the Thomas Jefferson. This current mission began on June 15th, and is scheduled to run for three weeks. NOAA ships Gordon Gunter and Pisces, one of NOAA’s newest research vessels, are also under way as part of an ongoing effort to collect valuable data about marine mammals, sea turtles, sea birds, fish and other marine life in the Gulf. In addition to providing baseline data, the information gathered during the missions will help researchers and resources managers better understand the spill’s impact on marine species and their habitat. And another NOAA ship, Oregon II, will depart Pascagoula, Miss., this week to conduct an annual shrimp stock assessment survey in the Gulf. Meanwhile, specialized NOAA aircraft operating out of Alabama, Florida and Louisiana continue to support the Deepwater Horizon response.
And a special thanks to Cdr. Shep Smith, commanding officer of the NOAA Ship Thomas Jefferson, for taking the time to speak with us from the Gulf of Mexico. If you’d like to see some video of what’s going on aboard the Thomas Jefferson, head to deepwaterhorizon.noaa.gov and look for the video link. And there, of course, you can also get the latest NOAA news, information, data, and maps related to the ongoing spill response effort.
That’s all for this episode. If you have any questions about this week’s podcast, about the National Ocean Service, or about our ocean, send us an email at email@example.com.
Let’s bring in the ocean....
This is Making Waves from NOAA’s National Ocean Service.