Understanding the intricate carbon cycle processes that take place deep within Earth has been one of the most interesting frontiers for scientists and researchers. A key component of these deep earth processes is the oceans. On Earth, half of all the conversion of carbon to organic compounds—a process known as carbon fixation—occurs in the ocean.
In the same way that plants play a vital role in the reduction of carbon load by capturing carbon dioxide (CO2) for photosynthesis and storing carbon in plant biomass and woods, carbon fixation, or carbon assimilation, is the process in which living organisms convert inorganic carbon into organic compounds.
In the oceans, most of this work is done by microscopic plankton—but it has been difficult so far to study their behaviour at an individual level. Researchers at Stanford University have now designed a new tool—a vertical tracking microscope—that could make sampling, measuring these microorganisms and their molecular activities, much easier.
“Think of it as a treadmill for microscopic organisms, a hamster wheel, as one way of describing it,” says Manu Prakash, associate professor of bioengineering at Stanford. Prakash, along with the team of researchers at his lab, focuses on tools to study questions related to marine biology. The microscope—based on what they call a “hydrodynamic treadmill”—is one such creation.
An official statement explains how conventional approaches to sampling plankton are focused on large populations of the microorganisms and typically lack the resolution to measure individual plankton. “As a result, we know very little about microscale biological and molecular processes in the ocean, such as how plankton sense and regulate their depth or even how they can remain suspended in the water column despite having no appendages that aid in mobility,” the statement adds.
“Because microscopes are finite objects, you have to confine what you study. And hence it has not been possible before to study a microscopic object that’s unconfined,” adds Prakash, who is also a senior fellow at the Stanford Woods Institute for the Environment.
A key inspiration for this microscope came during a trip to Madagascar four years ago, when Prakash and one of his students, Deepak Krishnamurthy, were studying the parasite schistosomiasis. “It is a human parasite that infects people across Africa in many places, and India as well…. It swims to find humans. Deepak and I were travelling to Madagascar to build an instrument that would track these parasites across the depth of the lake and the big question was: How do we study it? The size of the microscope would have to fit the size of a suitcase or the side of a building, for example,” Prakash explains in a video call.
The tracking microscope has a simple design: a rotating, wheel-like structure that simulates an infinite column of water, like the ocean’s depth. “Organisms injected into this fluid-filled circular chamber move about freely as the device tracks them and rotates to accommodate their motion,” the statement explains. “A camera feeds full-resolution color images of the plankton and other microscopic marine critters into a computer for closed-loop feedback control.” The device also recreates different depth characteristics in the ocean, such as light intensity, creating what the researchers call a “virtual reality environment” for single cells.
“One of the mechanisms through which carbon is transported into deeper waters is on particles. All particles in the ocean tend to sink because they are slightly heavier than the surrounding water. It has been very hard to understand how heterogeneous these particles are…. This tool gives you a complementary view where you can actually understand how these particles are forming, how are they breaking up and what sets their sinking rate,” says Krishnamurthy during the call. “As Manu says, with larger marine organisms, there are methods to track them with radio tags, but when you get to things that are smaller than the width of a human hair, how do you do that, right? So, that’s the challenge,” he adds.
The tool allows Prakash, Krishnamurthy and the rest of the team to think about getting a “part of the ocean” to the lab—but the next phase of this research will see them taking “the lab to the ocean” to study the organisms in their native state. “We have lots of trips planned to spend more time in the ocean…. Most of these organisms cannot be grown or replicated in the lab. I think this is the other challenge of studying the ocean,” says Prakash, adding that it is crucial to learn more not only about marine biology but the ocean in general. “The ocean has been operating as a carbon sequestration technology for our planet for a long time. It’s a technology that we don’t understand… Carbon sequestration is not just a passive physical process; it is a biological process. That’s what we are trying to study.”