Why Do Scientists Go On Research Cruises?

When we think about the ocean, most of us think of crashing waves and animals like whales and dolphins. The ocean covers 70% of our planet’s surface and is incredibly important to the Earth and human life. It helps determine our weather and climate, and it absorbs some of the gasses that cause climate change [1]. Fish from the ocean feed billions of people every day [2]. We rely on the ocean for so much that it is important to understand how it works and how humans are changing it. Scientists have lots of tools for studying the ocean. We can use satellites to look at the ocean from space, and we can study the ocean from the coast. These methods give us a good idea about the ocean’s edges, but we also need ways to study the deep ocean, far away from land. To do so, scientists go to sea on specially designed ships with science tools for collecting all kinds of information. These research expeditions can be days or even months long.

Come aboard our expedition! Here is a look into our voyage on board the Research Vessel Sally Ride in the North Pacific Ocean. You can learn what we did at sea and how we used four important tools to study the ocean: the CTD, the multicorer, the tow, and aerosol samplers (Figure 1).

The CTD: Diving Into the Deep Ocean

The CTD is named after three things it measures. “C” is for conductivity (how salty seawater is), “T” is for temperature (how hot or cold seawater is), and “D” is for depth (how deep the CTD has sunk). A CTD is shaped like a giant can with lots of smaller tubes inside it. It carries water samplers and electronic sensors [3]. We lower the CTD off the side of the ship, and as it sinks, it collects both samples and information (Figure 2A). We can also add more tools to the CTD to measure things like how much sunlight there is, how many living things there are, and how cloudy the water is. All this information is sent back up to the ship for the scientists to use.

The water samplers are bottles that can be opened and closed deep in the ocean using electronics on the ship. The water samples allow us to measure what makes up ocean water and what lives in it. By filtering the water, we can look at particles of dust, DNA and nutrients (Figure 2B). Just for fun, we decorated styrofoam and sent it down to the deep ocean on the CTD! The weight of the ocean above it squeezed all of the air out of the styrofoam and made it a lot smaller (Figures 3A,B).

We use information from the CTD to answer important questions about what happens in the ocean. On our cruise, Linqing used water from the CTD to explore how ocean water moves around. Tricia used the CTD to look at how food is recycled in the ocean (Figure 3C). Kaycie used the CTD to study how microbes, or tiny organisms, get energy from the food they eat. We sent the CTD down more than 4,500 m (14,764 feet) below the ocean’s surface.

Coring: Collecting Deep Ocean Mud

We have a time machine aboard. It does not carry us physically into the past, but we can use it to see what Earth was like long ago. Our time machine is a multicorer (Figure 2C). It collects mud from the seafloor that accumulated over the past centuries of ocean history [4]. The seafloor is constantly being rained on by mud carried into the sea by rivers, dust, pollen, and ash blown from land, and dead organisms that sink from the sea surface. All this stuff settles on the ocean bottom every hour of every day. As the centuries pass, the layers of mud thicken, preserving the history of fires, floods, and land life swept into the sea. The mud obtained by the multicorer tells the story of Earth’s past.

How does the multicorer work? It looks like a moon lander with four legs supporting a triangular structure attached to the ship with a cable. Heavy weights slowly shove eight plastic tubes into the seabed. The device is then hauled back to the ship with a cable. Each tube is sealed by spring-loaded doors to preserve the mud inside. The tubes of mud are called cores.

The layers in the cores capture information about how humans are changing the world. Looking back at what Earth was like long ago helps us predict how the Earth might change in the future. On our cruise, Cate is using cores to find out how much of the plastic that humans throw away ends up on the seafloor. She will compare the mud now to mud from decades ago, to see how it has changed. The cores are like a fat book of Earth’s history—a time machine to our past.

Tows: Catching Little Animals in Our Net

We do not care only about ocean mud and ocean water—we also care about ocean life! We use a net tow (Figure 2D) to catch zooplankton, which are small ocean animals that mostly drift along with ocean currents [5]. Most zooplankton are so tiny that you need a microscope to see them well (Figure 3D). Some zooplankton, like jellyfish, are bigger. Zooplankton are an important part of the ocean’s food web because they get eaten by fish and other animals. Lots of large animals like tuna, squid, and crabs start out as plankton before they get big, while others remain tiny their whole lives.

The tow looks like a net that you might use to catch fish in a stream, but ours is so big that it takes a full team of scientists to use. Its holes are much smaller than a fishing net’s holes, so zooplankton will not float through. We hang the tow off the side of the ship into the water. We then move the boat forward, so the tow catches the zooplankton swimming through the water. After a few minutes, we bring the net back to the ship to see what we caught. We have a microscope on the ship to see what the tiny zooplankton look like. We also store some of the zooplankton to study back on land.

We collect zooplankton to answer all sorts of questions: How do plankton change over time? Are large or small plankton more common? What do plankton eat and where does it come from? On our cruise, Annie collected zooplankton to help answer some of these questions. Some of the zooplankton also end up in the Scripps’ Collections, where they will sit on shelves like library books alongside samples over 100 years old!

Aerosol Sampling: Collecting Dust From Ocean Air

Did you know that plankton get food from the sky? Although you might not be able to see it, there are billions of tiny pieces of rock floating around in the air all around you [6]. These little particles are called dust. Around 500 million tons of dust fall into the ocean each year, bringing with it nutrients like iron that many organisms, like phytoplankton, need to live. This dust comes from all over the world, including the Sahara Desert in Africa and glaciers in Alaska. It floats with the wind until it eventually falls into the ocean, where it can be used by animals. The amount of dust that enters the ocean changes depending on what is happening on land. Dust helps determine how much life is in the ocean, which can affect global climate by adding or removing gasses from our atmosphere.

Onboard the ship, Emmet studied dust by sucking lots of air through a filter that catches the dust. To do this, he used a type of aerosol sampler called a Hi-Vol air sampler. Back on land in his lab, he can learn a lot about this dust. He hopes to learn more about the amazing ways that air transports nutrients around the world, even if we cannot see it with our eyes.

How Can I Go To Sea?

There are all sorts of ways to become a scientist who goes to sea. The scientists on our cruise are from five different countries. They studied various college subjects—chemistry, biology, physics, anthropology, and even art! Some of them have always wanted to study the ocean, and some did other things before becoming ocean scientists. We all worked really hard and prepared a lot so that we could deal with the challenges of being at sea. Some of the problems we overcame during our cruise were people getting sick, tools breaking, and experiments not working the way we expected. To get a taste of what it is like to be a scientist at sea, explore websites (like this one) about ocean science. You can also get out and explore near where you live, from a park to a stream to a city block. To become a scientist, you need a sense of wonder and you must pay attention to little details, write everything down, and notice changes that happen over time. Above all, have fun!

Glossary

Climate: ↑ The weather conditions of a place over a long period of time.

Aerosol: ↑ Small liquid or gas particles suspended in a gas. Here, this gas is air.

Conductivity: ↑ How easy it is for electricity to pass through a material. In the ocean, we use conductivity to measure how salty seawater is.

Microbes: ↑ Living things that are too small to see with just your eyes.

Zooplankton: ↑ A category of ocean animals that mostly drift along with ocean currents. Zooplankton include everything from big jellyfish to tiny larvae.

Phytoplankton: ↑ Microscopic organisms that live in water and get their energy from the sun, just like plants do on land.

Atmosphere: ↑ The layer of gases that surround our planet.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

The authors thank the science party and crew of SR2215 for their invaluable assistance and contributions. Funding for this research cruise was provided by the UC Ship Funds program. Additional funding supporting research completed on this research cruise was provided by the National Sciences Foundation, award number 2126668.

Author Contributions

TL, EN, DZ, RV, and RN conceptualized and planned this work. EN and DC created figures. All authors wrote and revised sections of the manuscript.