Ocean winds and tides bring new data for climate models

To take measurements that nobody has taken before, Coty Jen's research group packed up nearly every instrument from their lab and traveled to the coast of Maine.

The Gulf of Maine is the fastest warming body of water on the planet. As the water temperature changes, so does its chemistry. Jen, associate professor of chemical engineering at Carnegie Mellon, received funding from the National Science Foundation to study emissions from the ocean and their impact on atmospheric chemistry.

"Understanding how emissions are changing in the Gulf of Maine will give insight into potential changes in other parts of the oceans," says Jen. She led the five-week field research campaign this fall in collaboration with Steve Archer, senior research scientist at Bigelow Laboratory for Ocean Sciences.

Marine phytoplankton and their microbial communities emit gases into the atmosphere. These gases react to form tiny seed particles, or aerosols, that are key to the formation of clouds. Water vapor condenses onto a seed particle, ultimately growing into a cloud droplet. Understanding how clouds form over land and ocean surfaces is critical to improving climate models.

If we want better climate model predictions, we have to go out and take more measurements.

Coty Jen, Associate Professor, Chemical Engineering

"If we want better climate model predictions, we have to go out and take more measurements," says Jen, a member of the Center for Atmospheric Particle Studies at Carnegie Mellon. Earth system models lack information about emissions along the coastline and over the open ocean because it is difficult and expensive to take atmospheric measurements. Jen is lowering some of those barriers by developing smaller, battery-operated instruments.

There have been very few field campaigns with as many instruments as the Jen Lab brought to Maine. Among the instruments made in the Jen Lab is a particle sizer and counter that can count aerosols as they form. They also took commercial instruments, such as the mass spectrometers that they use to determine what gases the aerosols are made from.

Christine Troller, a Ph.D. student in chemical engineering, led months of logistical planning for the field campaign. "There's a lot of tubing and wiring for our instruments. Working in small trailers right at the water's edge, we had to be cognizant of safety and leave room for me and the other students to reach and repair the instruments when something failed," she says. "It was fun problem-solving, and we made the limited space work quite well." Troller was joined by fellow Ph.D. students Joy Kiguru, Ziheng Zeng, and Malena Rybacki, and master's student Dallan Schoenberger.

"Field campaigns prepare students for high-intensity jobs," says Jen. "There is so much to keep track of: checking instruments, making sure the data looks reasonable, fixing instruments, and coordinating with collaborators."

Troller, who also participated in field research at the US Department of Energy's Atmospheric Radiation Measurement Southern Great Plains observatory last summer, notes how much she has learned from these experiences. "Working with teams outside of CMU has taught me about different scientific worlds, other perspectives on our research, and what is important for the general public," she says.

In Maine, scientists at Bigelow Laboratory's shoreside facility took water measurements from the Bigelow Laboratory dock that are complementary to the Jen Lab's atmosphere measurements. With only a small joint team, they collected a very comprehensive dataset, combining biological, chemical, and weather data. The collaboration enables researchers to study the feedback loops between particle formation, climate, and plankton.

The researchers found high amounts of iodine and dimethyl sulfide (DMS), which are key compounds for the nucleation of cloud droplets and not well known to come from local seaweed.

Jen and her group observed particles forming extremely quickly in the air above the Gulf of Maine. The speed continued at night, which is unusual because the process is typically driven by sunlight. This indicates that water, seaweed, and phytoplankton are very efficient at making particles.

"I have taken a lot of measurements in my life, across different parts of the country, and I was surprised by the emissions we measured. Even though it's a really clean environment, there is chemistry that I've never observed or read about before," says Jen.

The fastest particle formation seems to happen at low tide. When coastal seaweed is exposed to the air, it dehydrates and its emissions change.

"We saw a lot of interesting things happening during low tide, and we want to understand why," says Troller. She led experiments to take direct measurements from seawater and from rockweed, the dominant seaweed on the coast of Maine. Troller isolated water and seaweed samples in sealed tanks, then measured the direct emissions. By coupling this data with their measurements of outdoor air, the Jen Lab hopes to determine what happens to emissions in the atmosphere.

"I think there are a number of important stories that we're going to find as we analyze all of this data," says Troller. She and her fellow students in the Jen Lab are contrasting coastal emissions with emissions they measured in ocean wind.

They are also fine-tuning the prototype instruments that they tested in Maine. Jen's vision is to take the instruments off the coast and onto the open seas on Bigelow Laboratory's research vessel, the R/V Bowditch. She is planning a follow-up field campaign in a different season, when seaweed and phytoplankton will be at different stages in their growth cycles.

For media inquiries, please contact Lauren Smith at lsmith2@andrew.cmu.edu.