Biochemical future of marine ecosystems
Phytoplankton are composed of proteins, carbohydrates, lipids, chlorophyll, and other macromolecules that are essential components of their cells.
In a new manuscript published in Nature Climate Change, we show that adaptation to different environmental conditions drives variation in their macromolecular composition at present and under projected climate change.
We suggest that these variations alter the energy availability at the base of the marine food web and alter global biogeochemical cycles.
The manuscript was highlighted in:
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Figure: Conceptual illustration of how climate change alters phytoplankton biochemical composition and its consequences for marine ecosystems and biogeochemistry. From Martiny 2026
The impact of phytoplankton chemical composition on ocean anoxia
There are many regions in the ocean where oxygen is too low to sustain aerobic life. These regions, called "oxygen minimum zones," are currently expanding and will continue to do so due to human-induced climate change.
A major source of uncertainty in predicting future ocean deoxygenation is how changes in phytoplankton chemical composition will alter respiration, the ocean's primary oxygen sink.
In a manuscript currently under review in Science Advances, we show that biochemical changes in phytoplankton macromolecular composition can alter global oxygen and organic carbon cycling.
Figure: Global map showing open ocean sites at 300 m of depth where oxygen levels are below 2 mg L-1. Adapted from Breitburg et al., 2018
Studying the co-evolution of phytoplankton and global biogeochemical cycles
The geological fossil record indicates major transitions in the dominance of phytoplankton groups. What was the trigger for these transitions? And how did they impact global biogeochemical cycles?
In a manuscript published in Nature Geoscience, we have shown that changes in the relative proportions of continental vs. seafloor weathering drove changes in phosphorus concentration, an essential nutrient that drives phytoplankton evolution.
In a PNAS manuscript, we have further shown that these changes in phosphorus concentration drove changes in the evolution of phytoplankton elemental composition.
We suggest that these changes alter global burial of oxygen and organic carbon over geological timescales.
Figure: Model scheme. The long-term cycling of phosphate, carbon, oxygen, calcium, and the sedimentary pools of organic matter and carbonate rocks. Black arrows represent fluxes between the pools, where the dashed lines are weathering fluxes.
The BioGeo model
During my PhD at the Weizmann Institute of Science, I developed the 'BioGeo' model. The BioGeo model simulates the evolution of carbon, oxygen, phosphorus, and alkalinity between the ocean, atmosphere, and Earth’s reservoirs.
Using this model, we found that the rate of seafloor weathering highly influenced geologic phosphate concentration, and we constrained the paleo Redfield ratio!
The model is written in MATLAB and is available here.