Phytoplankton are new sediment evidence of ancient climate

[Global] Evidence of ancient climate patterns throughout the history of the Earth is recorded in tree rings, and bubbles in polar ice. For really ancient readings, scientists have looked at the oxygen isotopes within fossilized amoeba known as foraminifera, whose tiny shells act as a kind of historical thermometer in ocean sediments.

But now there is another reading which may be available to scientists investigating millions of years of temperature and atmosphere changes, according to a new paper in the journal Nature Communications.

The phytoplankton called coccolithophores, which thrive in the sunlight but die and descend to make up a huge proportion of the “calcareous ooze” on the ocean floor, could be a whole new gauge on how the Earth has changed, reports the team from the University of Oxford, Washington University in St. Louis, and the Plymouth Marine Laboratory.

The team grew different species of the coccolithophores, and then placed the algae in environments with an array of different levels of carbon, they report.

It was “not all that different from gardening,” said Harry McClelland, one of the authors, now of Washington University.

Based on light and heavy masses of isotopes of carbon and cross-referencing it with the fossils of their plates they produce, they were able to calculate the ratio of calcification to photosynthesis.

Senior author Rosalind Rickaby, a professor of biogeochemistry at Oxford, said the work could prove to be a whole new tool to assess ancient climate, and Earth’s temperature and atmosphere fluctuations.

“Our model allows scientists to understand algal signals of the past, like never before,” said Rickaby. “It unlocks the potential of fossilized coccolithophores to become a routine tool, used in studying ancient algal physiology and also ultimately as a recorder of past CO2 levels.”

Rickaby and some of the same personnel have published a series of coccolithophore studies over the last few months. A September paper in Scientific Reports outlined why the natural recordkeeping of the alage had eluded laboratory detection, and a follow-up in October that was also in the journal Nature Communications found that the uronic acid content of the species shows the adaptation to previous signatures of carbon dioxide in the ambient environment.

Photo: The famous White Cliffs of Dover consist of the crushed remains of numberless tiny plates of calcium carbonate formed by organisms called coccolithophores.

View original article at: Phytoplankton are new sediment evidence of ancient climate


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