Not that kind of cruise—a GEOTRACES glossary

As the Research Vessel Roger Revelle sails the Pacific Ocean on its mission to study ocean chemistry, certain normal sounding words and phrases take on altered meanings. What follows is a list of 10 common words and phrases one might hear during GP15 along with their definitions. They are not presented in alphabetical order.


These lines represent the many planned and completed GEOTRACES expeditions. Oceanographers typically call these scientific voyages cruises. Photo: GEOTRACES

In these blog posts, GP15 is mostly called an expedition, but when oceanographers talk to their colleagues GP15 is a cruise. Our outreach materials skip the word “cruise” because it makes it sound like we’re taking a vacation to Tahiti. GP15 is many things, but a vacation is not one of them.


GP15 cruise-track
This is GP15’s cruise track. Each dot is a different station. Red dots are Super Stations, blue and purple dots are “full” stations, white dots are “demi” stations, the three brown dots are shallow or shelf stations and the green dots are places the Revelle will stop in port. Photo: GEOTRACES

Each dot along this map of GP15’s path is a station—someplace we will stop to take measurements and collect samples of seawater. The different colors indicate how many depths we will study at each station. Ocean chemistry varies dramatically with depth, so the chemical oceanographers of GP15 are always looking to collect water from a carefully selected set of depths. The most intensive stations are called Super Stations, and take roughly 56 hours to complete.


things happening
Moments before the start of a cast, scientific equipment is airborne above the Pacific Ocean. Next, it will be lowered thousands of feet down by a cable to study ocean chemistry. Photo: Alex Fox

Whenever one of the instruments on board the Research Vessel Roger Revelle goes into the water, it’s called a cast—short for hydrocast. Like fishers casting their bait into the ocean with a rod a reel, the oceanographers of GP15 attach their devices to cables to study the ocean from top to bottom. Some casts are quick, others take more than five hours to complete.

For most of GP15, the bottom is more than 16,000 feet down, and a majority of our stations call for samples from near the seafloor. A round trip to 3,000 feet takes about an hour, and that’s more or less without stopping. Some instruments need to be lowered deeper than 16,000 feet and remain there for hours collecting data.

“The board of lies”

The whiteboard outside the main lab of the Roger Revelle shows the day’s schedule, but each day’s challenges result in frequent amendments and alterations. Photo: Alex Fox

Outside the main laboratory on the R/V Roger Revelle there is a whiteboard. This whiteboard is the subject of intense interest from the scientists of GP15 because it is where one of the chief scientists writes down the day’s schedule. The schedule tells everyone when they will be working and when they can sleep, eat or hang out.

However, there is a reason these schedules are written in dry erase marker and not etched in stone. They are subject to change. These changes can occur at any time, sometimes while the relevant parties are sleeping. The board strives to accurately represent the schedule, but its supreme authority combined with its unpredictability makes a certain amount of friction inevitable.

“CTD Rosette”

gtc drip
The trace metal CTD Rosette emerges from the ocean. Two tag lines are used to keep the CTD steady as it is reeled in. Photo: Alex Fox

CTD stands for conductivity, temperature, and depth. The measurement of electrical conductivity is used to determine the water’s salinity. Rosette refers to the ring of bottles attached to the cylindrical metal frame. The technology that measures conductivity, temperature and depth is nested in the center of the instrument’s metal frame, beneath the rows of bottles. Despite being composed of two separate systems it is often just called “the CTD.”

This key instrument is lowered into the ocean to collect seawater samples from various depths. On each cast the CTD’s rosette of bottles remain open on the way down, allowing water to pass through them freely. On the way back up, if the scientists of GP15 want a sample of seawater from a certain depth they can remotely trigger one of the bottles to snap shut—sealing the seawater inside.

odf ctd hang
GP15’s other CTD on its way down with its Rosette of bottles. Photo: Alex Fox

GP15 has two CTD Rosettes on board. One made specifically for studying trace metals without contaminating its samples, and the other is used to study less contamination prone elements of ocean chemistry.


artsy niskins
A row of bottles lines the wall of the ship’s hangar. Photo: Alex Fox

When oceanographers talk about popping bottles at sea they’re not planning a champagne-soaked celebration. The bottles of oceanography are devices that are used to bring samples of seawater back up to the surface. Their defining feature is the ability to be triggered from the surface to collect water from a particular depth. They can be used individually or they can be arranged in a ring as in a CTD Rosette.

everybody samples
After spending hours underwater, the CTD returns from the ocean. Once it’s inside the hangar, the scientists of GP15 flock to it to collect seawater for their research. Photo: Alex Fox

When arranged in a ring around a CTD the bottles can be “fired” remotely from the ship’s computer lab, but in the case of a single bottle the old school method is to send what’s called a “messenger.” The messenger is a puck with a hole in it that snaps onto the cable the bottle is attached to, slides down the cable and triggers the bottle’s spring loaded lid like a mousetrap. Depending on the system being used, GP15’s bottles may hold 10, 20 or 30 liters of water.


another pump
One of the in situ pumps of GP15 is raised out of the water after pumping seawater through its filters thousands of feet down. Photo: Alex Fox

Short for in situ pump, the pumps of GP15 use motors to push massive volumes of seawater through a set of filters designed to catch ocean particles for study. The in situ part of their full name means they do their pumping in the environment they’re studying, and in this case that means a specific depth at one of GP15’s stations in the Pacific Ocean.

Built around a metal frame, a pump’s main feature is a metal cylinder that can withstand the intense pressure 16,000 feet underwater. Inside the pressure case are a fleet of D-batteries that power the motor. Plastic tubes lead from the pump motor to the filters at the top of each pump that catch the particles the scientists are after. Each pump typically pumps for four hours at its chosen depth.


now that's a torpedo
GP15 scientists wrangle the fish’s torpedo. The fish’s plastic tube is attached to a rope that carries the load as it swims beneath the surface. Photo: Alex Fox

The fish is not some unfortunate sea creature that the scientists of GP15 pressed into oceanographic service. The fish swims alongside the Roger Revelle while it is in transit from one station to the next. At its most basic level, the fish is a tube that pumps seawater from the ocean’s surface back to the Revelle’s laboratory. It earns its piscine moniker by way of a torpedo that swims the tube below the surface and away from the moving ship.

once and future fish
The fish swims alongside the R/V Roger Revelle at a depth of around 15 feet. Photo: Alex Fox

The purpose of the fish is to deliver water samples from the ocean’s surface for trace metal analysis. The fish swims while the Revelle is underway to ensure the water it pumps is fresh and uncontaminated by the Revelle’s metal hull.


This van is responsible for processing samples from the trace metal CTD Rosette. These samples can easily become contaminated, which is why the van is a designated “clean room.” Photo: Alex Fox

On GP15, if someone invites you inside their van there’s no reason to get nervous. On GEOTRACES expeditions a van is a shipping container with a laboratory inside it. After a trip across the country to reach Seattle, WA where GP15 began, the crew of the Roger Revelle bolted the vans to the ship’s deck. GP15 has four vans, each specialized for a different type of oceanographic research. The vans provide crucial lab space to the 37 scientists of GP15 and also provide a little extra shade on deck.

“The bubble”

bubble pumps
Co-chief Scientist Phoebe Lam of the University of California Santa Cruz and her graduate students Vinicius Amaral and Yang Xiang work together inside the sterile confines of the bubble. Photo: Alex Fox

The bubble is a capsule of cleanliness for studying samples prone to contamination from the ship environment. Its walls are made out of sheets of plastic and a group of large air filters fill the bubble with clean air like a balloon. The bubble would pop, but, instead of doors that seal shut, it has flaps. The flaps allow clean air to slowly escape and, in the process, this slight outward pressure keeps contaminants from blowing in.

GP15 blog posts written by Alex Fox unless otherwise stated.

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GEOTRACES GP15 is supported by the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation.

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