A team of Oregon State University biologists led by Dr. Luis Bolaños are taking part in a NASA-funded program called EXPORTS, making discoveries in the oceanic carbon cycle. The team studied the first-ever winter sampling of phytoplankton in the North Atlantic Ocean, and found smaller cells than they expected, which could mean more bad news for the future of our oceans.
Phytoplankton are mostly one-celled plants that are the foundation of the aquatic food web. Common types are cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated coccolithophores.
Marine biologists have long known that phytoplankton live in abundance in the surface layers of the oceans – where they use sunlight, nutrients in the water, and carbon dioxide from the air to grow and spread. Gradually, phytoplankton die and begin to sink toward the sea floor, miles below, where the dead plant life can remain for hundreds or even thousands of years, becoming some of the most sequestered carbon on Earth. Some have even suggested that phytoplankton blooms should be encouraged, to increase the decomposition of dead plankton on the sea floor.
Blooms can extend over hundreds of square kilometers in the ocean and last several weeks, however, phytoplankton generally only live for a few days. Massive blooms that sink to the ocean floor can create dead zones as the decomposing bacteria depletes oxygen and suffocates animal life.
Much dead phytoplankton never sinks all the way to the ocean floor. Upwellings of water can bring nutrients back to the surface, causing a sudden bloom of new phytoplankton. The question of how much carbon does reach the bottom is one of the main concerns of EXPORTS.
A Surprising Discovery
One of the biggest surprises the study found was that rather than being made up of mainly large plankton organisms called diatoms, the water was actually a complicated ecosystem of many different species, most of them far smaller than diatoms. These smaller organisms are less likely to sink as they die, and thus less carbon winds up on the sea floor, removed from the atmosphere for centuries.
Bolaños warns that “warming can create a feedback loop with unfortunate effects. As temperature increases… [diatoms will be replaced] by smaller organisms who can adapt to this shift (similar to those found in the tropics), diminishing the amount of carbon removed from the atmosphere to the deep ocean, therefore enhancing warming and setting the conditions for smaller organisms to keep thriving.”
“That’s why is important to keep funding these scientific studies,” he continues, “so we can keep tracking the evolution of these ecological systems and have more detailed data to predict the changes that a warming future could bring.”
By John M. Burt