Plankton’s Ability To Sequester Carbon Is Influenced by Ocean Density, Study Shows

According to a study published in Royal Society Open Science on November 6, changes in ocean density significantly influence the ability of marine plankton to incorporate carbon into their shells. The findings, led by Dr Stergios Zarkogiannis from the Department of Earth Sciences at the University of Oxford, highlight the physical properties of the ocean, such as density and salinity, as major contributors to the carbon cycle. The study underscores the role of plankton in regulating atmospheric carbon dioxide levels, with implications for climate change.

Research Highlights Physical Drivers of Calcification

The research primarily focused on Trilobatus trilobus, a species of foraminifera, which are microscopic organisms known for their carbon-sequestering calcium carbonate shells. These shells sink to the ocean floor upon the organism's death, contributing to long-term carbon storage. The study indicates that changes in ocean density and salinity directly influence the calcification process in these organisms.

Dr Zarkogiannis found that decreased ocean density, often caused by melting ice sheets and the influx of freshwater, reduces calcification. This response prevents the organisms from sinking, maintaining their position in the water column. This adjustment not only ensures survival but also affects ocean alkalinity, enabling increased CO2 absorption.

Techniques and Key Findings

Modern fossil samples of T. trilobus from the Mid-Atlantic Ridge were analysed using advanced imaging methods like X-ray microcomputed tomography and trace element geochemistry. The results revealed regional differences in shell thickness, with thinner shells observed in equatorial regions and thicker ones in subtropical areas where ocean density is higher.

Broader Implications for Climate Research

The findings suggest that physical ocean changes are as critical as chemical factors in determining calcification. This interplay between marine life and ocean properties could influence climate models, particularly in regions affected by ice sheet melting. Dr Zarkogiannis emphasised the importance of understanding these dynamics, noting that marine organisms play an active role in the carbon cycle by regulating buoyancy and, consequently, CO2 absorption.