A circle of ocean 100 kilometers north of Oahu, Hawai’i, doesn’t look like much — just a buoy bobbing above an otherwise featureless patch of Pacific water. Still, for nearly three decades, scientists have sailed to this spot to look for something else that’s here, just below the water’s surface: billions of bacteria, algae and other microscopic organisms. These ocean microbes make the research site, called Station ALOHA, one of the most extraordinary expanses of water on Earth, one that holds clues about the ocean as a carbon dioxide sink. In fact, years of data from Station ALOHA have earned the site a Milestones in Microbiology award from the American Society for Microbiology, which recently recognized it for its “historic and visionary contributions” to understanding ocean microbes.
“These microbes matter,” says David Karl, an oceanographer at the University of Hawai’i at Manoa. “We are wholly dependent on them to breathe.” Scientists have long known that marine microbes, specifically plantlike ones called phytoplankton, play an important role in Earth’s ecosystem: They perform nearly half of the photosynthesis on Earth and, in turn, sequester about one-third of the world’s atmospheric carbon dioxide into the ocean. Yet the long-term responses of these microbes to a changing climate aren’t well understood.
Karl and his colleagues created Station ALOHA to gather baseline data on ocean microbes and search for signs suggesting that climate change was having an effect on them. The impetus came from geochemist Charles Keeling, who boldly proclaimed in the 1980s that the planet was changing right before our eyes and that we would never see those changes unless scientists took repeated measurements of the air and oceans over time. Keeling, then at the Scripps Institution of Oceanography in La Jolla, California, had collected decades of data on atmospheric carbon dioxide at a research station on Mauna Loa, a volcano on the island of Hawai’i. His analysis showed a steady upward trend in atmospheric carbon dioxide, which correlated with rising fossil fuel emissions. He also suggested that Earth’s oceans could absorb carbon dioxide from the atmosphere.
Station ALOHA is the marine version of the Mauna Loa station. The research site sits deep within the North Pacific Subtropical Gyre, a 20-million-square-kilometer system of swirling ocean currents. It is the largest ocean gyre and the largest ecosystem on Earth, home to billions of plants, animals and microbes. “We can’t study the whole gyre. It’s just too large,” Karl says. Instead, he and other scientists chose a 22-kilometer-wide circle well within the gyre because it was accessible in about 10 hours by boat. Station ALOHA was born.
The first cruise set sail to the site in October 1988, followed by trips out about once a month. Visiting the site regularly, scientists could monitor changes in ocean life far from shore. When they sail to the site, the scientists collect water and plankton samples, identify the kinds of microbes at the site and measure the amount of carbon dioxide there. “The ocean is like a sponge for carbon dioxide,” says Edward DeLong, a marine microbiologist and Karl’s colleague at the University of Hawai’i. “It absorbs carbon dioxide and turns it into carbonic acid, which makes the water more acidic.”
To understand the effects of increasing acidity and other changes to the ecosystem, scientists first had to determine which microbes were living at Station ALOHA. They initially believed life wouldn’t grow so well in the open ocean because waters so far from shore would lack nitrogen, phosphorus and other essential nutrients. It’s true that the waters of Station ALOHA lack nutrients. In fact, ALOHA is an acronym for A Long-Term Oligotrophic Habitat Assessment, with ‘oligotrophic’ referring to an environment that offers little to sustain life.
On the second cruise to the site, DeLong and his colleagues tried a new approach, called metagenomics, which sequences genomes directly from the environment rather than from cultivated samples in the lab. To the scientists’ surprise, the data revealed the existence of scores of previously unidentified microorganisms in the ocean and a remarkable amount of microbial diversity. “This was one of the first real-world applications of metagenomics,” DeLong says.
With time, the metagenomic data started to show that certain microorganisms made their home in this nutrient-poor place — through seemingly chaotic and intricate interactions, they thrived there. In turn, research activities at ALOHA expanded. In 1992, scientists added a sediment trap to the ocean bottom. Then moorings and more ocean-floor instruments were set up. One of the best additions, Karl says, was the ALOHA Cable Observatory, which came courtesy of AT&T. The company was transitioning from fiber optic cables running on the ocean bottom to satellite communications, so it gave one of its deep-sea cables to the University of Hawai’i. The university had the cable re-wired from Station ALOHA back to Oahu, enabling scientists there, and elsewhere, to have instant access to information about earthquakes, rainfall and other data from the site.
The new infrastructure, technology and continued monthly trips are beginning to provide a good picture of the ecosystem at Station ALOHA. DeLong’s metagenomic data have shown that assemblies of microbes cycle in and out of site’s waters depending on the season and currents, among other variables. “We’re still trying to understand how physical and chemical changes influence microbial processes and diversity over short timescales,” DeLong says. Those changes can influence how plankton grow. Still, he says, scientists have a lot to learn about which ocean-ecosystem changes represent natural variation and which are the result of human activities.
Data from the site do suggest that, in time, changes in climate may change the microbial makeup of Station ALOHA. Simulations recently showed that ocean acidification would change the composition of future phytoplankton populations in the area, with some species thriving while others would be completely wiped out. Because the tiny organisms are at the bottom of the food chain, a shift in species could have implications for animals that are a little higher up. That species shift could also change the amount of carbon dioxide the organisms are able to take out of the atmosphere.
To continue to investigate the intricate interactions of ocean microbes and their effect on Earth’s carbon dioxide, the Simons Foundation created SCOPE, the Simons Collaboration on Ocean Processes and Ecology, in 2014. Station ALOHA is the focal point of the collaboration, with Karl and DeLong co-directing the team. SCOPE investigators participate in the monthly cruises to the site and have also started to set sail for collaboration-specific missions. In the summer of 2015, SCOPE investigators used two ships to track the daily interactions of ocean microbes at Station ALOHA, an “unprecedented kind of cruise in ocean microbiology,” Karl says. Through continued expeditions, the site’s “historic and visionary reputation” seems destined to grow.