Beware the Blob! Ocean heat waves threaten microbes that help counter global warming

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

In 2011, Colleen Kellogg and her colleagues began sampling the microbial community at Ocean Station Papa, a research buoy in the Pacific Ocean about 970 miles west of Vancouver, British Columbia, which is part of one of the longest running oceanographic time series studies in the world. 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 to the National Park Service. “It is unprecedented in its magnitude (how warm and widespread) and its duration (to last multiple years).”

Having started their study before this anomaly occurred gave Kellogg and her colleagues a baseline to compare to the Blob. “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. So, while global warming increases the likelihood of ocean heatwaves like the Blob, the Blob could in turn could lead to more warming.

Kellogg said she was skeptical that the Blob would cause much of a change at all in the microbe seascape. One of the general hypotheses about microbes is that they are flexible and resilient because they are diverse and numerous. As Kellogg and her coauthors note in their recent paper in 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, during the ocean heatwave, the numbers of larger phytoplankton (microscopic plant-like organisms) declined and were replaced by smaller phytoplankton. This is environmentally significant: Like land-based plants, phytoplankton make their energy through photosynthesis, absorbing carbon dioxide and giving off oxygen in the process. When phytoplankton die and sink to the ocean floor, the carbon they consumed and converted into biomass sinks with them. 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. When that happens, the carbon they contain is released into the ocean, raising its carbon level and decreasing the amount of carbon dioxide that the ocean can absorb directly from the atmosphere.

Kellogg explained that smaller phytoplankton also means smaller zooplankton (microscopic animal-like organisms), which means smaller zooplankton excretions, which again, are more likely to float, ultimately being consumed by bacteria that respirate the carbon dioxide back into the ocean instead of sinking to the ocean floor.

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 ultimately 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.

Like Kellogg and her colleagues, Mariana Bif just happened to be studying organic carbon production in the Pacific Ocean when the Blob formed. Currently a researcher at the Monterey Bay Aquarium Research Institute, Bif studies carbon production indirectly by measuring the density of nutrients in the ocean. “We know that phytoplankton consume nutrients in a certain ratio to produce carbon in a certain ratio,” Bif explained. Based on the amounts of nutrients present in the water over time, she can estimate how much organic carbon was produced. These measurements are automatically taken every five or 10 days by six floats in the Pacific Ocean, which 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, carbon production was 35 percent greater than the usual peak; the following year, production plummeted to just 15 percent of an average summer, with a modest rebound in fall.

These anomalous years were both associated with the Blob. Normally, Bif explained, when the surface water cools, it sinks and displaces some of the deep, nutrient-rich water below, which moves to the surface bringing the nutrients along with it. 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. And phytoplankton that would normally get pulled to the bottom of the ocean as the surface water cooled were still at the surface in greater than usual numbers, so carbon production spiked.

However, when the warm water anomaly persisted for more than a year, the ocean did not mix in the way that it usually does. 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 also had ramifications for animals higher on the food chain. In addition to the seabird die-off, Bif said researchers saw high fish mortality and low birth rates in whale populations.

Bif concluded that, in terms of resiliency, the ocean is more than capable of handling a single-year warm water anomaly, but the system is less adapted to extended ocean heat waves.

All of this bodes ill 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.”

Will ocean heat waves like the Blob always result in reduced carbon sequestration, regardless of where they form? Bif said it’s hard to know for sure, because ocean microbial communities vary widely based on nutrient availability, location, seasons. We still have a lot to learn. But what we do know is how important the ocean is for 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.”