Recommendation: “Cyclic advancement of phytoplankton forced by modifications in tropical seasonality” 1 December 2021, Nature.DOI: 10.1038/ s41586-021-04195-7.
Coccolithophores are microscopic algae that form tiny limestone plates, called coccoliths, around their single cells. The shape and size of coccoliths differs according to the species. After their death, coccolithophores sink to the bottom of the ocean and their coccoliths build up in sediments, which faithfully tape the detailed advancement of these organisms over geological time.
To attain this, no less than 9 million coccoliths, covering an interval of 2.8 million years and a number of places in the tropical ocean, were measured and classified utilizing automated microscope strategies and artificial intelligence.
Coccolithophores are microscopic algae that form tiny limestone plates, called coccoliths, around their single cells. The shape and size of coccoliths differs according to the species. After their death, coccolithophores sink to the bottom of the ocean and their coccoliths collect in sediments, which faithfully tape-record the in-depth advancement of these organisms over geological time.
To accomplish this, no less than 9 million coccoliths, spanning a period of 2.8 million years and a number of places in the tropical ocean, were measured and classified utilizing automated microscopic lense strategies and artificial intelligence.
Based at Centre Européen de Recherche et dEnseignement des Géosciences de lEnvironnement (CNRS/Aix-Marseille Université/ IRD/INRAE/Coll ège de France) and in collaboration with scientists from Rutgers University (USA).
Coccolithophores, a crucial constituent of the plankton, developed following the rhythm of Earths orbital eccentricity. Credit: Luc Beaufort/ CNRS/ CEREGE
The researchers observed that coccoliths went through cycles of higher and lower variety in size and shape, with rhythms of 100 and 400 thousand years. They also propose a cause: the basically circular shape of Earths orbit around the Sun, which differs at the very same rhythms. Therefore, when Earths orbit is more circular, as is the case today (this is referred to as low eccentricity), the equatorial regions reveal little seasonal variation, and types that are not very specialized dominate all the oceans.
On the other hand, as eccentricity increases and more noticable seasons appear near the equator, coccolithophores diversify into many specific species, however collectively produce less limestone. Most importantly, due to their abundance and global circulation, these organisms are accountable for half of the limestone (calcium carbonate, partly composed of carbon) produced in the oceans and for that reason play a major function in the carbon cycle and in identifying ocean chemistry.
The variety of coccolithophores and their collective limestome production progressed under the impact of Earths orbital eccentricity, which identifies the strength of seasonal variations near the equator. On the other hand, no link to global ice volume or temperature level was discovered. It was for that reason not worldwide climate change that determined micro-algae evolution but possibly the opposite throughout specific periods. Credit: Luc BEAUFORT/ CNRS/ CEREGE
It is therefore most likely that the cyclic abundance patterns of these limestone producers played a key role in ancient environments, and might discuss hitherto mysterious environment variations in previous warm periods. Simply put, in the lack of ice, the biological evolution of micro-algae might have set the tempo of climates. This hypothesis remains to be confirmed.
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