CDT – NOAA Teacher at Sea Blog

CDTs record conductivity, depth, and temperature

NOAA Teacher at Sea
Rita Salisbury
Aboard NOAA Ship Oscar Elton Sette
April 14–29, 2013

Mission: Hawaii Bottomfish Survey
Geographical Area of Cruise: Hawaiian Islands
Date: Tuesday, April 23, 2013

Science and Technology Log

CDT being lowered over the starboard side

A few days ago we dropped the CDT, an apparatus that collects data on the conductivity, the depth, and the temperature of the sea water in which the acoustic survey is taking place. All of these three things impact how quickly sound travels underwater. The scientists collect the information and then use it to figure out an accurate rate of speed for the sound waves. Once they have that information, they can determine how far a target is from the ship.I was able to ride along in a small boat to Maui to pick up parts for the AUV. While in the Maui harbor, I had the opportunity to visit the Huki Pono, a small boat working on this survey that is using BotCams to survey the fish population. The palu, or bait, that I help make every day is frozen and then transferred to the fishing boats. It is frozen in a shape that fits into a cage on the BotCam located near the camera. As the bait breaks up, fish are attracted to it and come close enough to the BotCam to be visually recorded. There is a lot of video to go through so Dr. Kobayashi says they won’t have the data from the BotCams for a while. But the other three fishing boats assigned to this project turn their survey information in every evening and I get to add it to a spreadsheet to help keep track of what section the boats were in and what they found while they were there.

Work continues with the ROV and AUV. The scientists are always working on them, trying to make them run as smoothly as possible. We worked on calibrating the acoustics again this morning for the same reason. The better the information you have when you start a project, the better chance you have of having a successful outcome.

As I mentioned before though, not everything we are doing is high tech. We fish off the side of the ship in the evenings, dropping our lines all the way to the bottom so they are on the sea floor. The scientists running the acoustics tell us if they see fish and then we do our best to catch a representative sample. Here are two of the fish I caught off the bottom: an opakapaka and a taape. The observers that ride in the small boats every day spend the night on the Sette. That way, they can turn their logs in and I can record the data. As a bonus, a few of them are expert fishermen and are a huge help to us as we fish from the ship.

Opakapaka and ta'ape — Opakapaka and ta’ape

Personal Log
I’m really enjoying my time on the Sette. In addition to learning new things that I can apply in my classroom, I’m making new friends. Everyone is exceptionally friendly and they go out of their way to explain things to me. Most of them call me “Teach” or “Taz” and almost all of them have sailed with a Teacher at Sea before.

Did You Know?
You can tell the age of a fish by their otoliths? The picture has the otoliths from an opakapaka, an ehu, and a hogo. Otoliths are a fish’s “ear bones” and they have growth lines in them much like a tree has growth rings.

Additional Section

Why are these bottom-dwelling fish red?

NOAA Teacher at Sea Rebecca Kimport
NOAA Ship Oscar Dyson
June 30, 2010 – July 19, 2010

Mission: Summer Pollock survey
Geograpical Area:Bering Sea, Alaska
Date: June 30, 2010

What’s in your water?

Now that we are at sea, I work a shift each day (as do all members of the crew and science team). I began my shift this morning at 0400 and reported to the Acoustics Lab to meet with chief scientist, Neal Williamson. In addition to Neal, my shift includes Abigail McCarthy, NOAA research fisheries biologist, Katie Wurtzell, awesome biologist and my fellow TAS, Michele Brustolon.We began the shift by observing our first CTD (Conductivity Temperature Depth) profiler which will be deployed at least 10 times throughout our trip. The CTD measures conductivity, temperature, and depth (used to calculate salinity) and gathers samples to measure dissolved oxygen. In other words, it measures many of the physical properties of the seawater mixture in a specific column of water. In addition, fluorescence is measured to monitor chlorophyll up to a 100 m from the surface.How it works: The CTD is lowered down to the ocean floor, collecting data on the way down. Then, on the way back up, the survey tech stops the CTD at specific depths to collect water for the samples. Upon its return, the water is collected and treated for future analysis.

Here is our CTD sensor before its launch

After our first CTD, we completed our first Methot trawl. A Methot trawl is named after the scientist who designed the net used. Here is a picture of the methot getting hauled back on deck (please note, it does actually get dark here. I woke up in the dead of night and had to wait two hours for sunrise. Sunrise is at the “normal” time of 6:30 am and I think that’s because we are on the western edge of the time zone)

A Methot net grabs the creatures and collects them into a codend (to make it easier for us to process) at 30-40 m below the surface – our Methot collected jellies and euphausiids (also known as krill). My first duty was to sort through the “catch” to pick out jellies. Next, we measured the weight of the krill before counting a small sample. We also preserved a couple samples for use in larger studies.

Following our Methot, I assisted with the completion of an XBT (eXpenable Bathymetric Thermograph). At left, you will see that I actually “launched” the XBT overboard. The XBT is used to collect quick temperature data from the surface to the sea floor. The data are graphed at depth vs. temperature to highlight the thermocline, that is where colder water meets water warmed by the sun. Here in the Bering Sea, the thermocline is not always noticeable as the water column is subject to mixing from heavy winds and shallow depths.

Lucky for us, it was a calm day on the water and we were able to see a distinct thermocline:

I think the CTDs and XBTs are really cool because they are pretty routine. Both processes are conducted all over the globe at consistent locations year after year. As you can see from the chart below, the CTDs and XBTs are marked out for the area the Oscar Dyson covers throughout the summer. (As I mentioned in my blog description, theOscar Dyson must travel the same route year after year for the pollock survey to ensure consistency in data collection).

Beyond the Oscar Dyson, these data are collected on every NOAA cruise that I read about and that data can be used to measure how a body of water is doing in general as well as how the water column of a specific location has changed over time. For example, longitudinal data are needed to note climate change within the Bering Sea. Pretty cool huh?

Vocabulary Note: I tried to define all the new terms I used in my entry. Did you notice a term I didn’t define? Ask me about it in the comments and I will make sure to provide you with a definition.

Thought Question: In the XBT data graph, why is the X axis labeled on the top rather than the bottom? (think about your coordinate plane)

Tag: CDT

Rita Salisbury: More on the Mission, April 23, 2013

Rebecca Kimport, JUNE 30, 2010 part2

What’s in your water?