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If the ocean had vital signs, the CTD would be the instrument taking its pulse. With focused precision, this tool measures conductivity, temperature, and depth — the three critical clues that help scientists discover how the ocean works, from its chemistry to its creatures.
On the OceanXplorer, we call our CTD "Carl." Like all CTDs, Carl is the unsung hero of ocean science, a foundational component behind nearly every discovery we make.
Scientists call the CTD the workhorse of oceanography, and for good reason. Inside its sturdy metal frame, called the rosette, sensors and Niskin bottles capture seawater at different depths. Niskin bottles have triggered caps at both ends, which are connected to a cable on the vessel that tells the bottles to close. Carl has 24 Niskin bottles on his rosette, and each bottle can sample 10 liters of water. As the CTD descends thousands of meters beneath the waves, data from its sensors stream back to the ship in real time measuring temperature, salinity, and pressure — creating a dynamic profile of the ocean’s structure.
Once the CTD reaches the target depth, scientists trigger the bottles to close in an instant, sealing samples from precise layers. Those samples reveal the chemistry, biology, and physical forces shaping life below.
The ocean, spanning 70% of our planet, is the engine that drives the Earth’s climate. Small changes in ocean temperature can alter global currents, shift weather systems, and reshape ecosystems. Salinity tells us where freshwater from glaciers or rainfall enters the sea. Together, these readings form a detailed picture of how Earth’s interconnected systems are changing, and how these changes drastically impact life both below and above the surface.
"The CTD is such a fundamental part of oceanography, yet it rarely gets the attention it deserves. On my first research cruise, graduate students were woken at all hours of the day and night to help deploy and recover the CTD, squeezing in preparation for sampling during the brief windows in between. Though the deployment process could be demanding, it became one of the most formative experiences of my scientific journey." - Kailani Acosta, Science Program Associate at OceanX
The work of Carl, our CTD, is essential to daily life aboard the OceanXplorer. Each morning, the OceanXplorer’s crew casts the CTD to measure what’s happening in the water column, providing us with information that guides nearly every other research activity aboard the vessel. For example, submersible teams use CTD data to adjust submersible buoyancy, and mapping teams rely on it to calculate how sound travels through water to accurately map the seafloor.
"Watching the colorful lines trace the CTD's descent through the water column, I realized how each profile painted a portrait of the ocean’s physics, biology, and chemistry below the surface." - Kailani Acosta, Science Program Associate at OceanX
An exemplary moment of our CTD’s capabilities came during OceanX’s 2020 expedition in the Red Sea, when the team discovered a toxic, super-salty brine pool — a lake at the bottom of the ocean where nearly nothing can survive. These pools hold clues about Earth’s geology and even the potential for life beyond our planet, and are unusual to find, since there are only a few regions where these occur known to science.
To study the brine pool, the science team coordinated a daring maneuver: lowering both anthe ROV (Remotely Operated Vehicle) and the CTD nearly a mile beneath the ocean’s surface, side by side, to collect samples through the brine pool without damaging either instrument. Thanks to Carl’s precision, the team gathered data that revealed the chemical composition of the brine and the extremophile life forms thriving there, providing a rare glimpse into life under uninhabitable conditions for most organisms.
Carl may not grab the spotlight like some of our other tools, but without our CTD, none of OceanX’s exploration would be possible. His steady stream of data connects every link in the chain — from chemistry to climate, from microscopic plankton to massive mammals. The CTD turns invisible processes into measurable truths, helping OceanX unlock the ocean’s sustainable potential through science, education, and discovery.
See the OceanXplorer's CTD in action here.
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