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Beware of the Blob Ocean heatwaves could threaten microbes that counter global warming

Beware of the Blob Ocean heatwaves could threaten microbes that counter global warming

An photograph of microscopic ocean plants, or phytoplankton

An photograph of microscopic ocean plants, or phytoplanktonPhytoplankton plays a critical role in sequestering carbon from the ocean, which could be disrupted by ocean heatwaves such as the Blob. (Photo courtesy NOAA MESA Project)

The microbiologists didn’t set out to study the Blob. But the Blob came for them—and the climate—anyway.

Colleen Kellogg began sampling the oceanic microbial community at Ocean Station Papa in 2011. This buoy is located in the Pacific Ocean, 970 miles west from Vancouver, British Columbia. It is part of the longest-running oceanographic time series studies. Three times a year they collected samples of water from different layers of the ocean and sequenced a subset of the genetic material within to see “who’s there.” They wanted first to characterize the various bacteria and archaea at the site, and to see how those microbes behaved and changed from season to season, year to year.

Then, in late 2013, a mass of warm water formed, which came to be known as “the Blob.” The Blob was nearly 1,000 miles wide in all directions, some 300 feet deep, and up to 10 degrees Fahrenheit warmer than the average temperatures in the northeast Pacific Ocean. “Nothing like it has been seen in the climate record since climatologists have been recording data in this region,” according toThe National Park Service. “It is unprecedented in its magnitude (how warm and widespread) and its duration (to last multiple years).”

heatmap of a marine heatwave in the pacific ocean
A map showing the Blob in May 2015 (Courtesy NASA Physical Oceanography Distributed Active Archive Center).

Kellogg and her coworkers were able to compare their baseline with the Blob because they started their study before the anomaly. “We didn’t really know this was happening until we were in it,” Kellogg said. “If we hadn’t been sampling all along, we wouldn’t be able to detect change.”

Much to their surprise, the warm water anomaly—basically an ocean heatwave—profoundly changed the microbial community at Ocean Station Papa, and interrupted the mechanism by which the ocean sequesters carbon. Global warming may increase the likelihood of ocean heatwaves such as the Blob, but the Blob could also lead to more warming.

Kellogg said that she was skeptical about the Blob’s ability to make any significant changes in the microbe oceanscape. One of the most common hypotheses about microbes, is that they are resilient and flexible because they are diverse and many. Kellogg and coauthors noted in their recent paperIn Communications Biology: “Generally, prokaryotic communities are assumed functionally stable to incremental or episodic changes in their environments due to high diversity and large effective population sizes.”

Instead, they found that during the Blob, the types of prokaryotes—that is, single-celled organisms like bacteria—in the ocean shifted. “One of the most abundant sequences or microbes that we found in the ocean was something that really declined during the heatwave,” Kellogg said. “This type of microbe is really important for making vitamins for other organisms and stuff, and so if you don’t have that there, are they going to get the nutrition?”

Generally speaking, the number of larger phytoplankton, microscopic plant-like organisms, decreased during the ocean heatwave. These smaller phytoplankton were replaced. This is very important for the environment. Phytoplankton absorb carbon dioxide through photosynthesis and emit oxygen. The carbon they consumed is converted into biomass and taken to the ocean floor by phytoplankton that have died. Smaller phytoplankton don’t sink in the same way that larger phytoplankton sink, instead staying at the surface of the ocean where they might be consumed by bacteria. The ocean absorbs more carbon dioxide from the atmosphere when they are released into the water.

Kellogg explained how smaller phytoplankton means smaller zooplankton, microscopic animal-like organisms, which means that excretions from zooplankton are more likely float and ultimately be consumed by bacteria.

This change in the ocean’s ecosystem, sparked by the Blob, underscores the significance of the ocean’s microbial community. “You kind of get them out of whack and the whole system can kind of come out of whack,” Kellogg said. Indeed, the Blob eventually won. caused a massive die-off of Cassin’s Auklets, a seabird that eats zooplankton, because the zooplankton that were able to survive the warm-water heatwave were smaller and didn’t have enough fat to nourish the birds. The result was mass Auklet starvation, according to a group of researchers led by the University of Washington’s Timothy Jones.

Mariana Bif was, along with her colleagues, studying organic carbon production in Pacific Ocean when the Blob was formed. Bif is currently a researcher with the Monterey Bay Aquarium Research Institute. Bif studies carbon formation indirectly by measuring the density in the ocean. “We know that phytoplankton consume nutrients in a certain ratio to produce carbon in a certain ratio,” Bif explained. She can calculate how much organic carbon was produced by analyzing the water’s nutrients over time. These measurements are automatically taken every five to ten days by six floats in Pacific Ocean. They provide a high resolution picture of carbon production over time.

“I was looking at how much organic carbon that community was producing year by year, and I realized that in two specific years, we had a very high production in one year and a very low production in the other year, which seemed very odd,” Bif told the Bulletin. “Usually in the long term, the ocean kind of produces and consumes, there is a balance every year. And there was a very different dynamic going on in those two specific years.”

The first anomalous summer saw carbon production rise by 35 percent to a peak of 35 percent. However, production dropped to 15 percent in the following year. There was a modest rebound in autumn.

Both of these years were associated to the Blob. Bif explained that normal cooling of the surface water causes it to sink and displace some of the deeper, nutrient-rich water beneath. This water then moves to the surface, carrying the nutrients. However, the Blob was so warm that the exchange of surface water for deep ocean water never occurred—it increased ocean stratification. Bif’s conclusion was that in the first year, there were still enough nutrients near the surface for the phytoplankton to subsist on, and even thrive. The phytoplankton, which would normally be pulled to the bottom by ocean surface water cooling, were still present at the surface in higher than usual numbers, so carbon production spiked.

The ocean didn’t mix as it normally does when the warm water anomaly lasted for more than one year. So the following year, the phytoplankton didn’t have enough nutrients—Bif said iron is particularly important for the phytoplankton in this part of the Pacific—which resulted in a huge drop in carbon production. This had serious consequences for animals higher up the food chain. Bif also said that the researchers observed high levels of fish mortality in the whale population and low birth rates.

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Bif concludedAlthough the ocean is capable of handling a single year of warm water anomaly, it is not as resilient as the system to long-term ocean heat waves.

All this bodes poorly for the climate crisis.

“Global warming causes more marine heatwaves,” Bif said. “The warmer the world, the more these very extreme events are going to happen. It’s the same analogy that you make with a hurricane: the more the global warming, the more hurricanes that you have, the more extreme events you’re going to have, the more snow you’re going to have, the more heat waves you’re going to have. And this is also going to contribute to more warming, because you have these very high masses of warm waters.”

Two maps showing similar marine heatwaves in 2014 and 2019.
A warm water anomaly, similar to the Blob, was formed in the same region in late 2019. These anomalies are becoming more common due to climate change. (Courtesy NOAA Coral Reef Watch).

Is it possible that ocean heat waves such as the Blob will always result in lower carbon sequestration regardless of where they are formed? Bif said it’s hard to know for sure, because ocean microbial communities vary widely based on nutrient availability, location, seasons. We still have much to learn. We do know how vital the ocean is to life on Earth.

“As an ocean biologist, one of our favorite stats is every other breath you take comes from the ocean,” Kellogg said. “Phytoplankton in the ocean are producing 50 percent of the oxygen on Earth. Like, we wouldn’t have oxygen on Earth if it weren’t for cyanobacteria. You start to change little things in the ocean, then we’re changing how the Earth functions.”

To be clear, it’s not as if the ocean is about to become a source of carbon dioxide emissions—but the health and diversity of microbial communities at the surface of the ocean help determine how much carbon dioxide the ocean can sequester.

“If you’re relying on the ocean—the greatest carbon dioxide sink in the world is the ocean—if you’re relying on it to suck up this much every year, and it starts not doing quite that much,” Kellogg said, “then we need to do more on land.”

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