New research reveals that the ornate, glassy skeletons of diatoms, single-celled algae, play a much faster and more dynamic role in regulating ocean chemistry and climate than previously understood. Scientists have discovered that these microscopic skeletons can transform into clay minerals in as little as 40 days, a process called reverse weathering that was once thought to take hundreds or even thousands of years. This rapid transformation has significant implications for the ocean’s carbon cycle and its ability to sequester carbon, ultimately influencing global climate patterns.
Diatoms are already known for their crucial role in the marine food web and in pulling carbon dioxide from the atmosphere through photosynthesis. They are responsible for producing about a quarter of the oxygen we breathe and for a significant portion of the ocean’s carbon uptake. When they die, their silica-based skeletons sink to the seafloor, locking away carbon in deep-sea sediments. The recent findings, published in Science Advances, add a new layer of understanding to the posthumous impact of these tiny organisms, highlighting how their rapid chemical transformation on the seafloor can release carbon back into the environment and alter the chemical balance of the ocean.
A Faster Cycle of Transformation
The process of reverse weathering, where silica from diatom skeletons reacts with seawater to form new clay minerals, is a key component of the Earth’s long-term climate stability. For decades, scientists believed this process was incredibly slow, taking centuries or even millennia to occur. However, a team of researchers led by scientists from the Georgia Institute of Technology has overturned this long-held assumption. Their study demonstrates that this transformation can happen in a little over a month, a discovery that fundamentally changes our understanding of the ocean’s silicon and carbon cycles. “We’ve known that reverse weathering shapes ocean chemistry, but no one expected that it happens this fast,” said Yuanzhi Tang, a professor at the School of Earth and Atmospheric Sciences and senior author of the study. This accelerated timeline means that the impact of diatoms on ocean chemistry is far more immediate and dynamic than previously thought.
Methodology of the Discovery
To determine the rate of reverse weathering, Tang and her team developed a custom-built, two-chamber reactor to simulate the conditions of the seafloor. This allowed them to observe the transformation of diatom skeletons into clay minerals in a controlled laboratory setting. The experiment revealed the surprisingly rapid 40-day timescale for this process. The findings help to solve a long-standing puzzle in oceanography: the discrepancy between the amount of silica that enters the ocean and the amount that is buried in the seafloor. The new research suggests that a significant portion of this “missing” silica is rapidly converted into new minerals through reverse weathering, maintaining the ocean’s chemical equilibrium.
The Role of Diatoms in the Global Carbon Cycle
Diatoms are microscopic powerhouses when it comes to influencing the global carbon cycle. While they are alive, these single-celled algae act like the tropical rainforests of the ocean, absorbing vast amounts of carbon dioxide from the atmosphere through photosynthesis and releasing oxygen. They are responsible for an estimated 40% of the carbon fixation in the world’s oceans each year. This process forms the base of the marine food web, as diatoms are consumed by a wide range of organisms. When diatoms die, their journey is not over. Their heavy silica shells cause them to sink to the ocean floor, carrying with them the carbon they have absorbed. This process, known as the biological carbon pump, is a critical mechanism for sequestering carbon in the deep ocean, where it can remain for long periods.
A New Wrinkle in Carbon Cycling
Recent research from the University of California San Diego has added another layer of complexity to our understanding of how diatoms process carbon. A study published in Science Advances in July 2024 revealed that diatoms are not solely reliant on photosynthesis for their carbon intake. They are also capable of directly consuming organic carbon from their surroundings, a process known as mixotrophy. This finding could lead to a reassessment of the amount of carbon dioxide that diatoms remove from the atmosphere, potentially altering our understanding of the global carbon cycle. The study of the diatom species Cylindrotheca closterium found evidence of this dual feeding strategy in over 70% of ocean water samples analyzed from around the world.
Climate Change and the Future of Diatoms
The intricate relationship between diatoms and the climate is a two-way street. Just as diatoms influence the climate, changes in the global climate can have a profound impact on diatom populations. Diatoms generally thrive in colder, nutrient-rich waters. As global warming leads to rising ocean temperatures, there is concern that diatom populations could decline. This could have a cascading effect on the marine ecosystem and the ocean’s ability to absorb carbon dioxide. If other types of phytoplankton replace diatoms, they may not be as effective at sequestering carbon, potentially leading to a feedback loop that accelerates global warming.
Lessons from the Past
By studying the fossil record, scientists can gain insights into how diatoms have responded to past climate changes. Research led by scientists at the Museum für Naturkunde in Berlin has shown that diatom diversity was significantly lower during the middle Miocene, a period when atmospheric carbon dioxide levels were only moderately higher than today. This suggests that future warming could lead to the extinction of many diatom species, particularly those adapted to cold water environments, which are crucial for transporting carbon to the deep ocean. The loss of these key species would further diminish the ocean’s capacity to mitigate climate change.
Broader Implications for Ocean Science
The discovery of rapid reverse weathering and the confirmation of mixotrophy in diatoms have far-reaching implications for oceanography and climate science. These findings highlight the need to update our models of ocean chemistry and carbon cycling to account for these previously unknown or underestimated processes. The accelerated timeline of reverse weathering means that the ocean’s chemical balance may be more resilient than previously thought, but it also introduces new variables into our understanding of how the ocean will respond to future changes. “We already knew their importance to ocean processes while living,” Tang stated. “Now we know that even after they die, diatoms’ remains continue to shape ocean chemistry in ways that affect carbon and nutrient cycling. That’s a game-changer for how we think about these processes.”
Furthermore, the revelation that diatoms can directly consume organic carbon challenges the traditional view of these organisms as simple photosynthesizers. This new understanding of their metabolism could lead to more accurate assessments of their role in the marine food web and the global carbon cycle. As scientists continue to unravel the complex lives of these microscopic organisms, it becomes increasingly clear that even the smallest players in the ocean can have a significant impact on the health of our planet. These tiny, beautiful algae are more than just jewels of the sea; they are integral to the functioning of the Earth’s climate system.
