A multidisciplinary team of scientists, including a group from BIOS, spent six weeks this summer focused on the Pacific Ocean to study the lives and deaths of plankton, organisms that play a critical role in removing carbon dioxide from the atmosphere and in the ocean’s carbon cycle.
Beginning in early August, dozens of researchers worked from two vessels operating as floating laboratories about 1,000 miles (1,600 kilometers) northwest of Seattle. Researchers investigated plankton, as well as the chemical and physical properties of the ocean from the surface to half a mile (0.8 kilometer) below into the twilight zone, a region with little or no sunlight. In this region of the ocean, carbon from plankton can be sequestered, or kept out of the atmosphere, for periods ranging from decades to thousands of years.
The broad scope of the research required a full suite of modern scientific instrumentation, from space-based sensors to high-tech sampling nets and remotely operated underwater vehicles. Researchers combined these data with satellite imagery to better understand and predict what happens to atmospheric carbon dioxide once it enters the marine realm. The NASA-funded project—dubbed “EXPORTS” for EXport Processes in the Ocean from Remote Sensing—marks the first time that researchers have simultaneously studied all aspects of this complex planetary process.
“Basically we threw every type of modern science technology at this investigation,” said BIOS biologist Amy Maas, a co-principal investigator on the project. She said the project will continue in 2020 with a similar research focus in the Atlantic Ocean.
For Maas, who was based at BIOS during the six-week study, and biologist Andrea Miccoli and postdoctoral researcher Karen Stamieszkin, who worked from the research vessel Roger Revelle, it was a chance for a unique comprehensive look at plankton that live in the open ocean. Phytoplankton, the tiny, photosynthetic plant-like organisms that live in the sunlit upper ocean, use sunlight and dissolved carbon dioxide that enters the upper ocean from the atmosphere to grow, which is one way that ocean organisms cycle carbon. As primary producers, phytoplankton play an important role in removing atmospheric carbon dioxide and producing oxygen. When they die, these materials sink and some fraction of their carbon is exported to depth.
Zooplankton, or animal plankton, was the main focus of the BIOS team’s work. These organisms eat phytoplankton and are responsible for helping to quickly remove the carbon stored in phytoplankton from surface waters down to the ocean’s interior.
While the major export pathways of how carbon moves through the ocean are known, the magnitude of the carbon flows in the different oceanic pathways are poorly known. Scientists on the EXPORTS team are investigating how much carbon moves through the ocean within the upper sunlit layer and into the twilight zone, and how ocean ecological processes affect carbon fate and sequestration. This information is needed to predict how much carbon will cycle back into the atmosphere over various time scales, or how much carbon is exported to ocean depths.
Miccoli and Stamieszkin were members of the zooplankton team along with other researchers, including the expedition’s co-chief scientist Debbie Steinberg (also a BIOS Trustee). Their EXPORTS research had two goals. First, they wanted to understand the production and contribution of carbon in fecal pellets—plankton poop—and other plankton-related by-products, such as mucus, molts, and carcasses. They also wanted to quantify the transport of carbon from shallow and sunlit zones to ocean depths by plankton’s daily vertical migration.
During the night, plankton feed in the surface and near-surface waters. Then, when the sun comes up, they avoid predators by hiding in the lower, colder, and darker layers. At these depths they respire, breathing out part of the phytoplankton they have eaten in surface waters as carbon dioxide—an export pathway called “active transport,” as it relies on the active swimming of millions of tiny organisms from the surface to the deep.
Miccoli’s specific role was to carry out individual, 12-hour-long respiration experiments on live organisms in order to assess their metabolic rates. He also helped with colleagues’ sampling and experiments, as scientists at sea tend to work around the clock to maximize their ship time.
Miccoli, who completed his doctoral research in marine biology in 2017, was charged with what Maas described as the “somewhat stressful” responsibility of sending hundreds of delicate samples packed in dry ice back to BIOS for further study. Some of these samples are of individual zooplankton that will be photographed, measured, weighed, and identified by their genes to allow the results of the shipboard respiration experiments to be scaled up to community-level predictions of active transport. Others are “pooled” samples that will be used for measurements of the activity level of the electron transport system, an enzyme pathway that can be used to estimate the respiration of the entire community simultaneously.
Most days during the start of the cruise, Maas said she talked with Miccoli by WhatsApp. “He would send me data about the temperature or oxygen profiles, images of the respiration experiments he was running, and spreadsheets of how many experiments we had completed with what kinds of organisms,” Maas said. “We were a few time zones apart though, so he usually had to make the decisions alone and then get feedback from me later. He rocked it the whole time, and by the end he pretty much ran the show solo.”