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Fossil algae reveal 500 million years of climate change

For her research Witkowski collected seawater with fresh, modern algae to test potential indicators of the past. Credit: Caitlyn Witkowski    …



For her research Witkowski collected seawater with fresh, modern algae to test potential indicators of the past. Credit: Caitlyn Witkowski

Earth scientists are able to travel far back in time to reconstruct the geological past and paleoclimate to make better predictions about future climate conditions. Using the organic molecule phytane, a debris product or chlorophyll, scientists at the Netherlands Institute for Sea Research (NIOZ) and Utrecht University succeeded in developing a new indicator (proxy) or ancient CO 2 levels. This new organic proxy not only provides the most continuous record of CO 2 concentrations ever, it also covers a record-breaking half-billion years. The data confirms the idea that rises in CO 2 levels that used to take millions of years are now happening in a century. These findings are published in Science Advances on November 28th.

If CO 2 increases today, it’s vital to understand what impact these changes will have. To better predict the future, we must understand long-term changes in CO 2 on geological history. Direct measurements or fits CO 2 are available, for example, bubbles in ice cores containing ancient gases. However, ice cores have a limited time span of 1

million years. To go further back in time, earth scientists have developed various indirect measurements of CO 2 from proxies e.g.

Phytane, a new way to travel in time

A new proxy, using a degradation product of chlorophyll, allows geochemists to infer a continuous record of historical CO 2 levels in deep time. Scientists at NIOZ have recently developed phytane as a promising new organic proxy that reveals a half-billion years of CO 2 levels in the ocean, from the Cambrian until recent times.

Using the new proxy, they were able to make the most continuous record of ancient carbon dioxide levels ever. “We developed and validated a new way to travel further back in time and to more places,” says NIOZ scientist Caitlyn Witkowski. “With phytane, we now have the longest CO 2 -record with one single marine proxy. This new data is invaluable to modelers who can now more accurately make predictions of the future.”

Witkowski and colleagues Selected more than 300 samples of marine sediments from deep sea cores and oils from all over the globe, reflecting the majority of geological periods in the last 500 million years.

Fossil molecules

Past chemical reactions can be stored in fossil molecules, and so they may reflect various ancient environmental conditions. Geochemists can incorporate these conditions, such as seawater temperature, pH, salinity and CO 2 levels. Organic matter, such as phytane, reflects the pressure of CO 2 in ocean water or the atmosphere (pCO 2 ).

Although all organic matter has the potential to reflect CO 2 phytane is special. Phytane is the pigment responsible for our green world. Anything that uses photosynthesis to absorb sunlight, including plants, algae and some species of bacteria have chlorophyll, or which phytane is a constituent. Plants and algae take in CO 2 and produce oxygen.

Because chlorophyll is found all over the world, phytane is also everywhere, and is a major constituent of decayed and fossilized biomass. “Phytane does not chemically change over the course of time,” said Witkowski.

Carbon isotope fractionation

CO 2 of the past is estimated from organic matter, such as phytane, through the phenomenon of carbon isotope fractionation during photosynthesis. When taking CO 2 plants and algae prefer the light carbon isotope (12C) over the heavy carbon isotope (13C). They use only the heavy carbon isotope when CO 2 levels in the surrounding water or atmosphere are low.

This also explains why Witkowski did not use terrestrial plants as a source for her research, exclusively using phytane from (fossilized) marine sources. The plant world is divided into so-called C3 and C4 plants, each with their own unique ratio of light to heavy carbon. Phytoplankton all have very similar ratios compared to their plant counterparts. Witkowski: “In our data we see high levels of carbon dioxide, reaching 1000 ppm as opposed to today’s 410 ppm. In this data, we see high levels of carbon dioxide, we could limit the uncertainty of the phytane source in the dataset. respect, present day levels are not unique, but the speed of these changes has never been seen before. Changes that typically take millions of years are now happening in a century. This additional CO 2 data may help us understand the future of our planet. ” In toekomstige onderzoek kan Phytane gebruikt worden om verder te gaan in de tijd dan de Phanerozoic, het vroegst gevonden in twee miljard jaar oude samples.


Explore further:
Study advances understanding the stories of ancient climate told by tiny shells

More information:
“Molecular fossils from phytoplankton reveal secular PCO2 trend over the Phanerozoic” Science Advances (2018). advances.sciencemag.org/content/4/11/eaat4556

Journal reference:
Science Advances


Provided By:
Royal Netherlands Institute for Sea Research

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