There were no “syrupy oceans”: Israeli study undermines the myth that “in the past there was much more Carbon – so today is not unusual”

Iron “memory balls” show that the pool of dissolved organic matter in the oceans was small in the Neoproterozoic, and grew only with deep-sea oxygenation and the rise of complex food webs – an important correction for the public debate

Was it really the case that “in the past there was much more carbon in the ocean, so the present is not unusual”? A new study in Nature provides a different answer: for the first time, it constructs a continuous record of dissolved organic matter in seawater (DOC) spanning XNUMX billion years. The picture is clear: there were no ancient marine “super-reservoirs.” Throughout most of geological history, the reservoir was limited, and only with the oxygenation of the deep ocean and the emergence of complex ecosystems in the Phanerozoic did it reach levels comparable to modern ones.

The research was led by Prof. Nir Galili, an Israeli scientist at ETH Zurich and new faculty member in the Department of Earth and Planetary Sciences at the Weizmann Institute of Science. Collaborators included Prof. Alon Nissan (Hebrew University), Prof. Uriah Alcolumbri, Dr. Yifat Kaplan-Ashiri (Weizmann Institute), and others.

“The data-based record suggests three evolutionary stages, rather than a huge Neoproterozoic ‘leap,’” says Galili.

“Dissolved organic matter in seawater” is a collection of tiny biological molecules (sugars, amino acids, lipids, and more) that dissolve in water. It is a large carbon reservoir that influences ocean chemistry and gas exchange with the atmosphere, but it is not the same as the level of carbon dioxide in the air. For this reason, the marine reservoir must be measured on its own, without automatically extrapolating from one to the other. DOC consists of microscopic fragments of biological molecules created by the breakdown of marine organisms. They feed microbes, affect nitrogen and phosphorus cycles, and alter the exchange of gases between sea and atmosphere. The size of this reservoir is comparable to the total amount of carbon dioxide in the atmosphere—another reason why it must be measured accurately.

The innovation of Galili and his team is a direct “proxy”: they measured ancient organic carbon trapped inside ooids—tiny, layered marine iron grains formed in seawater. These can be thought of as mineral “memory balls,” preserving the signature of dissolved organic carbon present in seawater at the time of their formation. More than one hundred samples, ranging in age from hundreds of millions to billions of years, were compiled into a single curve: the long-term story of the marine reservoir.

Three states of the Earth system

1. Paleo-to Mesoproterozoic: Oxygen-poor oceans, a microbial world of small cells. Particles sank slowly; the “microbial loop” at the sea surface was strong, but in the deep ocean no massive reservoir accumulated. “The deep ocean did not build up the enormous DOC pools that had previously been proposed,” explains Prof. Galili. Not accumulated A huge reservoir. “The deep sea has not accumulated the huge DOC reservoirs that were previously proposed,” explains Prof. Galili.

2. Neoproterozoic: The Appearance of large cells and early multicellular colonies. Particles Sank more quickly“The deep ocean did not build up the enormous DOC pools that had previously been proposed,” explains Prof. Galili. More burial of particulate matter in sediments. The result: the DOC at the surface קטן Even more.
3. Phanerozoic: The Deep ocean become fully oxidized'(grazing, biomineralization, sponges). Under these conditions, particles dissolved on their way down, and microbes recycled carbon back into the dissolved pool. In this way, a significant reservoir was rebuilt—similar to today. again A significant reservoir—similar to modern.

The great increase came before land plants

The major increase in the dissolved reservoir occurred already in the ed already inOrdovician, Before the appearance of land plantsIt is therefore difficult to claim that it was mainly due to “organic-rich” terrestrial runoff from land. A better explaination lies in the internal marine processes : Internal marine processes: Deep oxidation, changes in particle size and sinking rate, and the suructure of food webs.

Some present the past as an “alibi”: if there were giant carbon reservoirs in the past that indicated high atmospheric CO₂, then perhaps the present is not unusual. The new findings weaken that claim: they show that the ocean was not an infinite carbon store through most of geological history, and that major changes took place under very different physical-chemical conditions and at rates far unlike those caused by humans today.

According to the researchers, the data also help refine models of the carbon cycle: instead of relying on rough guesses, we now have an independent benchmark for testing how a major marine reservoir responds to oxygenation, biological complexity, and particle dynamics. This is critical for the future—in an era of global warming, ocean acidification, and human disruption. “The moments when deep-sea oxygenation and ecosystem complexity shifted—those are the turning points for marine carbon reservoirs,” the researchers note.

conclusion

The history of the ocean is neither an ancient “thick soup” nor a straight line. It is dynamic, linked to ocean oxygenation and biological innovation. And most importantly—it does not provide an anchor for the argument that “in the past there was much more carbon, so today is not unusual.” The present is different in origin, in pace, and in feedbacks. History does not exempt us—it gives us homework.

For the scientific article in NATURE

More of the topic in Hayadan:

• The absorption of carbon dioxide in the oceans has slowed down
• breathe like a fish
• Discovery of archaea capable of producing elemental carbon
• A new material for absorbing a record amount of carbon dioxide
• "Red glow" in the ocean