From Ash to Algae

Mount Shishaldin, a conical volcano covered in snow and ice in the Aleutian Islands of Alaska, erupted this July, spewing a large ash cloud miles into the air.

By chance, just a few weeks later, an international team of scientists set off to that remote corner of the North Pacific to collect data for a long-running oceanographic time series study. On board were a Bigelow Laboratory researcher and student with an interest in mountains like Shishaldin. They were there as part of an interdisciplinary project seeking to better understand the connection between the region’s volcanoes, which are some of the most active in the world, and its rich marine resources.

Phytoplankton form the base of the food web in this part of the ocean, supporting traditional subsistence livelihoods and a multi-billion-dollar fishing industry. Scientists have previously observed blooms of these microscopic algae after eruptions, suggesting that the minerals in volcanic ash provide critical nutrients, especially iron, that phytoplankton need to grow.

“It’s like a multivitamin for phytoplankton,” said Laura Sofen, a postdoctoral scientist at Bigelow Laboratory who was involved in the fieldwork this summer.

But much of the ash that erupts out of a volcano doesn’t land directly in the ocean. It lands on the volcano’s slopes, where it slowly erodes or is buried under mountains of snow, dirt, and peat. That “aged” ash can be remobilized later, picked up by the wind and blown out to sea years after it was originally deposited, potentially fertilizing a phytoplankton bloom. Yet, few studies have considered this significant source of nutrients.

The Volcanic Blooms project, a collaboration between Bigelow Laboratory and Colby College, is trying to better understand that process. Working at every scale — from satellites hundreds of miles up to individual cultures of phytoplankton — the team is trying to understand the impact of aged ash on marine productivity and how it compares to fresh ash and other sources of iron in this part of the world.

“We don’t have a good understanding broadly about the impacts of ash on phytoplankton communities, but there may also be a difference between the newly erupted ash versus this aged ash,” said Karen Stamieszkin, a Bigelow Laboratory research scientist who helped develop the project. “So, it’s the quality and quantity of ash that we’re asking about.”

From Space…

Stamieszkin and Senior Research Scientist Catherine Mitchell are focused on the macro scale, using satellite data to quantify the impact of dust plumes full of ash. Given how unusual — and difficult to predict — these wind-driven ash plumes are, this remote sensing approach is critical for detecting whether a plume produces a phytoplankton bloom and how long it lasts.

The assumption was that using satellite data might also be relatively easy. It’s not.

Researchers have developed algorithms that enable them to use satellite images of ocean color to measure the amount of chlorophyll in the water. Chlorophyll is the green pigment found in algae and plants that helps them absorb energy from light, and it can be used as a proxy for phytoplankton abundance. The problem is, when ash is floating around in the water, those calculations appear to be wrong.

“The standard methods we use for interpreting ocean color assume that phytoplankton is the only thing in the water,” Mitchell said. “So, because the ash may be mistaken for phytoplankton, those methods overestimate the amount of chlorophyll.”

Satellites also appear to be confused by ash in the air. Ocean color satellites sit at the top of the atmosphere, picking up everything between there and the sea surface. In fact, 90% of the signal they produce is coming from particles in the air, not in the ocean. The standard calculations for removing that atmospheric noise struggle when there’s a dust or ash plume, making it appear, again, like there’s more phytoplankton than there actually is.

Mitchell has been using lab experiments, adding ash into water and seeing how it affects the color, to create a more nuanced algorithm for translating ocean color into phytoplankton abundance. Stamieszkin, meanwhile, is trying to automate a process for identifying these plumes of ash-laden dust from satellite data. Together, they’ll be able to provide a more accurate method for detecting these ash clouds and accounting for their effects in satellite models, providing an important tool to help researchers understand the impact of atmospheric events on the ocean.

“Satellite data is incredibly useful, but we can’t use it off the shelf,” Mitchell said. “We need to understand what the limitations are, and learn to work around them as much as we can.”

…To a Ship

At the other end of the spectrum, several researchers, including Senior Research Scientist Ben Twining and Bess Koffman, an assistant professor of geology at Colby College, are exploring the relationship between ash and algae at the microscopic scale. With lab and field experiments, they’re aiming to understand the geochemistry of different kinds of ash and the biology of the phytoplankton communities that feed on it. Their results are also essential for validating the satellite models Mitchell and Stamieszkin are developing.

Last fall, Twining mentored a Colby College student, TJ Guercio, who participated in Bigelow Laboratory’s Sea Change Semester program. Guercio spent several weeks growing cultures of phytoplankton and observing how they responded to different iron-rich materials, including several sources of ash that Koffman obtained from the U.S. Geological Survey in Alaska.

This summer, the team took that work to the next level by running similar experiments in the field using samples of water and phytoplankton collected directly from the Northeast Pacific. Rather than growing algae in a lab, they incubated fresh water samples drawn from the ocean — full of phytoplankton and other microbes — and added ash to observe what grew in response. Laura Sofen, the Bigelow Laboratory postdoctoral scientist, and Guercio participated in the cruise, sailing for 14 days aboard a Canadian Coast Guard Vessel.

At 500 and 900 nautical miles out — far enough that the phytoplankton should be iron limited — Sofen and Guercio collected several samples of water. They then divided all that water into individual one-gallon sterile containers, adding unique amounts of ash of different ages from several Alaskan volcanoes to each before sealing them off and leaving them in a pool of seawater on the deck. After four or five days, they measured the amounts of chlorophyll and organic carbon particles inside each container, both proxies for phytoplankton growth, and took photos of the specific species that grew.

Going from the lab to the field was more complicated, though, than just handling larger samples. For example, Guercio and Sofen had to filter out larger organisms or risk a single hungry zooplankton eating all of the phytoplankton before the experiment could begin. Even timing how long they would let the samples incubate was a complex question.

“We were hoping four to five days was the sweet spot where you have enough time to actually see a response but don’t get ‘bottle effects’ because things are trapped in this artificial environment,” Sofen said. “That’s when the phytoplankton consume all the other nutrients in the seawater and become starved of those, rather than the nutrients you’ve added from the ash.”

The primary concern with research that involves trace amounts of metal such as iron, though, is that there’s a high risk for contamination. Not only did Sofen and Guercio have to work in a specialized shipping-container-turned-clean-room, they also had to modify the normal oceanographic sampling procedures. For example, they had to collect water further out from the deck to avoid rust coming off the ship, and they had to avoid any metal in their equipment.

Despite the challenges, Twining stressed that the ship-based work is an important expansion of the lab experiments and provides a more accurate reflection of the complex interactions in the ocean.

“There are a lot of things going on in the upper ocean that impact iron cycling, and it’s really hard to replicate those accurately in the lab,” Twining said. “So, taking a natural community in its natural water under natural ambient sunlight and adding our ash materials directly has a lot of benefits.”

A Unique Science Model

This interdisciplinary research project illuminates the advantages of Bigelow Laboratory’s approach to science.

An essential piece of that model is the involvement of students, who have been integrated into almost every step of the project. Stamieszkin hosted a student two summers ago from the University of Michigan who started the work using satellites to study these remobilized ash plumes. Mitchell worked with a student this summer from University of Virginia who undertook experiments looking at the impact of ash on the optical properties of water. And a student who both Twining and Stamieszkin taught in an introductory class at Colby College is now working with Twining and Koffman on X-ray analysis of volcanic ash to better understand its geological properties.

Guercio’s ongoing involvement in the project would also not have been possible without the institute’s long-term relationship with Colby College. He first met Twining his freshman year in a class on geoengineering during Colby’s “Jan Plan” term, and he began lab experiments during the Sea Change Semester program. This upcoming February, he also plans to attend the 2024 Ocean Sciences Meeting to present on this work.

“It’s a really nice example of a student who does a program and comes back for another opportunity,” Twining said. “That’s the model we like to follow in our education programs.”

Guercio is somewhat different from the other students who have been involved, though, because he is also majoring in anthropology. In fact, he got involved with the Volcanic Blooms project as a sophomore working with Koffman to examine the ethnohistory of the Indigenous Unangax̂ people and their relationship to the environment of the Aleutians.

In fact, one of the broader goals of the project is to tie the scientific findings to Indigenous knowledge of volcanoes and their impacts on the ocean. That effort highlights the interdisciplinary nature of the project and the advantages of having several research scientists, all with unique expertise, working together.

“I’m really excited about the science coming out of this project because it’s so multi-dimensional,” Stamieszkin said. “We can get at this question with a much greater depth of understanding.”

Twining described it as a Venn diagram, where each researcher has enough overlap to understand each other but also brings a unique niche to contribute to the project.

“There are very different aspects to this project, so having us all in the room has been really useful to help piece together the full story,” Mitchell said. “It’s a perfect example for me of why I like Bigelow Laboratory.”

Photo 1: Pavlof, one of the most active volcanoes in the U.S., is one of several Alaska volcanoes researchers are studying in connection to algal blooms. Chris Waythomas (Alaska Volcano Observatory/USGS)

Photos 2-3: Researchers from Colby College and partner institutions use ground-penetrating radar and collect sediment samples for geochemical analysis from the Kahiltna Glacier in Alaska for work related to the Volcanic Blooms project. Bess Koffman

Photos 4: A scanning electron microscope image shows a close-up of ash erupted from Pavlof Volcano in 2016. Pavel Izbekov (Alaska Volcano Observatory/UAF-GI)

Photos 5: A satellite image shows a plume of ash and dust, amid regular clouds, coming off of volcanoes in southwest Alaska and blowing toward Kodiak Island. NASA Modis/Catherine Mitchell

Photo 6: Colby College student TJ Guercio secures a water sample from the North Pacific for an experiment adding iron-laden ash to stimulate phytoplankton growth. Lynn Wharam

Photo 7: Postdoctoral Scientist Laura Sofen measures phytoplankton growth from water samples in a specialized lab designed to minimize metal contamination. Ian Tomkins

Photo 8: Kasatochi is one of the volcanos from which the team has collected ash. Burke Mees (Alaska Volcano Observatory/USGS)