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Algae fossils reveal 500 million years of climate change

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

Earth scientists can travel far into the past to reconstruct the geological and paleoclimate past to make better predictions about future climate conditions. Using phytane organic molecules, chlorophyll debris products, scientists at the Dutch Sea Research Institute (NIOZ) and Utrecht University succeeded in developing an old CO (new proxy) indicator.2 level. This new organic proxy not only provides the most sustainable CO records2 concentration that has ever existed, it also includes breaking a record half a billion years. Data confirms ideas that increase in CO2 the level used for millions of years now occurs in a century. This finding was published on Progress of Science on November 28.

Like CO2 increasing today, it is important to understand what the impact of this change is. To better predict the future, we must understand long-term change in CO2 over geological history. Direct measurement of past CO2 available, for example, bubbles in ancient gas-containing ice cores. However, ice cores have a limited time span of 1 million years. To go further into the past, earth scientists have developed various indirect measurements from CO2 from proxies for example from algae, leaves, ancient soil and chemicals stored in ancient sediments to reconstruct past environmental conditions.

Phytane, a new way to travel on time

The new proxy, using chlorophyll degradation products, allows geochemistry to deduce continuous records of the history of CO2 level in deep time. Scientists at NIOZ recently developed phytane as a promising new organic proxy that reveals half a billion years of CO2 level in the ocean, from the Cambrian to the present.

Using a new proxy, they are able to make the most continuous record of the levels of ancient carbon dioxide that have ever existed. "We develop and validate new ways for time travel – going further into the past and in many places," said scientist Niko-Caitlyn Witkowski. "With phytane, we now have the longest CO2records with one single sea proxy. This new data is very valuable for modelers who can now make predictions of the future more accurately. "

Witkowski and colleagues selected more than 300 samples of marine sediments from marine cores and oil from around the world, reflecting the majority of the geological period in the last 500 million years.

Fossil molecule

Past chemical reactions can be saved & # 39; in the fossil molecule, and therefore can reflect various ancient environmental conditions. Geochemists can deduce this condition, such as sea water temperature, pH, salinity and CO2 level. Organic matter, such as phytane, reflects CO pressure2 in the sea of ​​water or atmosphere (pCO2)

Although all organic materials have the potential to reflect CO2, special phytane. Phytane is a pigment that is responsible for our green world. Anything that uses photosynthesis to absorb sunlight, including plants, algae and some species of bacteria has chlorophyll, which phytane is the constituent of. Plants and algae take CO2 and produce oxygen.

Because chlorophyll is found throughout the world, phytane is also ubiquitous, and is a major constituent of decaying and petrified biomass. "Phytane doesn't chemically change over time, even if it's millions of years old," Witkowski said.

Fractionation of carbon isotopes

TOGETHER2 from the past it was estimated from organic materials, such as phytane, through the phenomenon of carbon isotope fractionation during photosynthesis. When taking CO2plants and algae prefer light carbon isotopes (12C) above heavy carbon isotopes (13C). They only use heavy carbon isotopes when CO2 the level around water or the atmosphere is low. The proportion between these two isotopes reflects the level of carbon dioxide in the environment at the time of growth.

This also explains why Witkowski did not use terrestrial plants as a source for his research, exclusively using phytane from (fossil) marine sources. The plant world is divided into so-called C3- and C4 plants, each with their unique ratio of light to heavy carbon. Phytoplankton have a very similar ratio compared to their plant counterparts. Witkowski: "By choosing only marine sources, we can limit the uncertainty of the phytane source in the dataset."

"In our data, we see high levels of carbon dioxide, reaching 1000 ppm compared to 410 ppm at present. In this case, today's level is not unique, but the speed of this change has never been seen before. Changes that usually occur millions of years now occur in a century, this additional CO2-data can help us understand the future of our planet. "In future research, phytane can be used to go further than the Phanerozoic, the earliest found in a sample of two billion years.

Explore more:
The progress of study understands ancient climate stories told by small shells

Further information:
"Molecular fossils of phytoplankton reveal secular PCO2 trends over the Phanerozoic" Progress of Science (2018). advances.sciencemag.org/content/4/11/eaat4556

Journal reference:
Progress of Science

Provided by:
Royal Netherlands Institute for Sea Research

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