Tonya Prentice: NOAA’s CTD and Carousel, August 20, 2024

NOAA Teacher at Sea

Tonya Prentice

Aboard NOAA Ship Henry B. Bigelow

August 8 – August 24, 2024

Mission: Northeast Ecosystem Monitoring Survey

Geographic Area of Cruise: Northwest Atlantic Ocean

Date: August 20, 2024

Weather Data from the Bridge
Latitude: 42.2212 º N
Longitude: 70.29659º W
Wind Speed: NW at 12 mph
Air Temperature: 19.8° Celsius (67.64° F)
Sea Temperature: 19.3 Celsius (66.74° F)

Science and Technology Log

Monitoring Ocean Parameters with NOAA’s CTD and Carousel Bottle Sampler

The CTD and Carousel Sampler are essential tools NOAA uses to monitor ocean conditions. “CTD” stands for Conductivity, Temperature, and Depth, the primary parameters this device measures. By running profiles of the water column from the surface to the bottom, the CTD helps us understand key ocean characteristics. The Carousel Sampler paired with the CTD allows collection of water samples at depth for laboratory analysis.

What Does the CTD Measure?

Conductivity: Helps determine the salinity of the water.
Temperature: Measures the thermal profile of the water column.
Depth: Tracks how deep the CTD is during data collection.

Together, these measurements give us a detailed profile of the water column, helping scientists monitor what we call “the Big Four” parameters.

Carousel: Collecting Water Samples

The CTD and Carousel is equipped with twelve Niskin bottles, which are used to collect discrete water samples from specific depths. The bottles are numbered 1-12, and are “fired” (closed) at different depths to capture water samples.

For example, bottle 1 might be fired near the bottom (a few meters above the seafloor), bottle 2 at 10 meters, bottle 3 at the determined chlorophyll maximum (C Max), and bottle 4 couple just below the surface. Multiple bottles are often fired at each depth to collect additional water. These samples provide critical data about the ocean’s chemical properties at various levels.

view of the carousel sampler resting on the deck of NOAA Ship Henry B Bigelow at night. A white cylindrical metal frame holds twelve gray cylindrical bottles in a round. The bottles have opened stoppers connected at the top and bottom. the CTD probe, at the center of the round, is not visible. Tonya has added yellow text boxes to label the following: carousel, Niskin bottles, top stopper, valves, bottom stopper. — CTD Carousel Bottle Sampler

Preparing the CTD Carousel Bottle Sampler

Before deployment, we ensure that all the stopper valves at the top and bottom of each Niskin bottle are closed. We also hook the wires at the top and bottom to prepare the bottles to open at the designated depths. Once the CTD is ready, it is carefully lowered into the water, beginning its descent through the water column.

Analyzing the Key Parameters

Once the water samples are retrieved, we focus on analyzing these key parameters:

Dissolved Inorganic Carbon (DIC)
pH
Total Alkalinity (TA)
Nutrients
Chlorophyll

view of a large scientific instrument, a cylindrical metal frame containing a round of tall dark gray sample bottles, suspended over the rail of a ship. The sky and the water are both a dark blue, fading into one another at the horizon. — Lowering the CTD into the water.

photo of a computer monitor displaying a graph; the graph itself is not really readable — Lowering the CTD into the water.

Storing the Samples

After processing, the nutrient and chlorophyll samples are stored in a freezer kept at -80°C (-112°F) to preserve them for further analysis. Mercuric chloride is added to the DIC, pH, and TA samples to preserve them until they are measured in the laboratory. These samples provide invaluable insights into ocean health. The DIC, TA and pH samples help us monitor the effects effects of ocean acidification— which occurs when carbon dioxide dissolves into the ocean. The chlorophyll samples measure the amount of phytoplankton living in the water. Like plants on land, microscopic phytoplankton carry out photosynthesis, produce oxygen, and are at the base of the marine food web.

Understanding these parameters allows us to monitor the ocean’s health and better predict how it may change in the future. For more information on ocean acidification, check out this resource: NOAA Ocean Acidification.

By closely monitoring DIC, TA and pH we can track important changes in our oceans, providing critical data for research and conservation efforts.

Personal Log

Life on a 12-Hour Work Shift at Sea

Working a 12-hour shift at sea might sound intense, but there’s often some downtime between stations and even a few hours after the work is done. The time you get can vary depending on how far apart each station is. Sometimes it’s just enough to process samples before heading to the next station, while other times you have several hours to relax and recharge.

So, how do you spend that free time on a ship? There’s no shortage of options. You could enjoy a movie in the lounge area, dive into a good book, play a board or card game with other crew members, or head to the flying deck to spot seabirds and marine life, or simply take in the stunning ocean views. Another interesting way to pass the time is visiting the bridge, where you can see how the ship is navigated, maneuvered, and commanded.

Let’s not forget “Activities and Crafts with Katy,” which can bring a whole new adventure to your day. Today, this included visiting the lab and looking at the different species of marine organisms that have been collected, such as stingray barbs, dogfish, and scallop shells. Katy then showed us how to make our own Acadian Redfish otolith (ear bone) earrings. “Scientists use the ear stones (bones) as a way to age the fish. Also called otoliths, they are bones found right behind the skulls of bony fishes.” (Smithsonian)

The balance of work and downtime can make those long shifts much more manageable and even enjoyable, offering moments to connect with colleagues and the environment around you in a way that few people get to experience.

view of two rows of large brown comfy-looking recliners facing a tv screen mounted on the wall above cabinets. there is a bookcase off to one side. — The Lounge area.

the flying deck - the uppermost deck on the ship - is bisected by the ship's yellow mast. a tall metal frame appears to be shade structure but may serve additional purposes. There are picnic benches and beach lounge chairs. — The Lounge area.

Did You Know?

“One atmosphere is equal to the weight of the earth’s atmosphere at sea level, about 14.6 pounds per square inch” (NOAA Water Pressures at Ocean Depths). Beneath the ocean’s surface, water pressure increases by approximately one atmosphere for every 10 meters of depth.

To illustrate just how intense this pressure can be, we conducted a simple yet fascinating experiment. We decorated 16 ounce styrofoam cups with artwork, then placed them in a mesh bag attached to the CTD Carousel Sampler. The CTD , along with the cups, was submerged to a depth of about 500 meters (1640.42 feet), where the pressure equals roughly 725 pounds per square inch (psi). We repeated this process by submerging the cups to 200 meters (656.17 feet), which equals about 291.18 psi.

As the cups descended into the depths, the increasing water pressure caused them to shrink dramatically because the air inside the cups was compressed. This simple experiment vividly demonstrates how powerful the forces at play beneath the ocean’s surface can be.

three styrofoam cups in a row on a table or desk surface. the leftmost cup is the standard size, undecorated. The middle cup is 30-40% smaller. It's colored with marker to be a flower scene, with "2024" written around the top rim. The rightmost cup is the smallest, probably less than half the size of the original. It says Go Wildcats, August 2024, Henry B Bigelow. — This is a normal size ounce styrofoam cup (left side). Here is the cup after it was submerged 200 m below the ocean surface (middle). The last cup was submerged 500 m and then again at 200 m (right side).