Sugars key to ancient and modern biogeochemistry

A new interdisciplinary study from researchers at Oxford University has shown how the biochemistry of ancient mineralising molecules has adapted to the changing environment over the last 100 million years.

Single celled microscopic algae called coccolithophores are some of the most prolific biomineralisers on the planet. They can produce over a trillion trillion of intricately sculpted calcified scales or liths each year in the surface ocean. Across the eons of geological history these liths accumulate to form chalk deposits of the geological record.

There is a secret to the ability of the coccolithophores to generate such vast quantities of the mineral- calcium carbonate. Lee et al., find that modern coccolithophores employ a sugar molecule, known as a coccolith associated acidic polysaccharide (CAP), to help transform the ingredients for calcite (calcium and carbon) into the mineral. Further, the cells are able to employ subtle biochemical differences in these CAPs to make the mineral even when there are very few ingredients around.

Lee et al., have perfected techniques to extract intact ancient CAPs from fossil cocccoliths. The adaptation of these prehistoric molecules from sediments of the last 120 million years chart an ever decreasing availability of carbon in the ocean to the modern day.

Since carbon in the ocean is dissolved from and at equilibrium with the atmosphere, the trend to a scarcity in availability of carbon from the past to the modern day suggests that a decline in atmospheric CO₂  helped transform the Earth from a past totally ice free world to our modern world with ice caps at both poles.

These new ancient molecules provide a unique biochemical window into past climates and their impact on life.

The paper was a joint project between Prof Rickaby, her postdoc Lee, and graduate student McClelland from Oxford Earth Sciences, as well as Despoina Mavridou and Grigorios Papdakos, researchers from Oxford’s Biochemistry Department. The research was funded by a European Research Council starting grant to Rickaby.

Paper

“The uronic acid content of coccolith-associated polysaccharides provides insight into coccolithogenesis and past climate” by Renee B. Y. Lee, Despoina A. I. Mavridou, Grigorios Papadakos, Harry L. O. McClelland & Rosalind E. M. Rickaby was published in Nature Communications. doi:10.1038/ncomms13144