The Way Phytoplankton Die Determines Ocean Carbon Storage

Phytoplankton are microscopic photosynthetic organisms that thrive in our oceans, responsible for assimilating approximately 50% of the net carbon fixed annually by plants. They are the engine behind the 'biological carbon pump' (BCP), a vital mechanism that exports organic matter from the sunlit surface to the deep ocean, where carbon can be buried for millions of years. Currently, the BCP transports an estimated 5-12 Pg of carbon annually, playing a massive role in regulating Earth's climate.

However, humanity faces a significant challenge as rising atmospheric CO2 causes ocean acidification and warming. These environmental shifts affect phytoplankton dynamics, specifically the balance between growth and loss. While populations typically decline due to grazing by zooplankton or viral infections, stress-induced 'cell death'—both accidental and regulated—is becoming a critical factor. The specific manner in which phytoplankton die determines the structure of marine ecosystems and the efficiency of the carbon pump. As global change favours species adapted to these new stressors, the resulting shifts in cell death patterns could have profound consequences for the ocean’s capacity to store carbon.