Discovery of ‘ghost’ fossils reveals plankton’s resilience to past global warming events

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Images show impressions of a collapsed cell wall lining (a coccosphere) on the surface of a fragment of ancient organic matter (left) with the individual plates (coccoliths) magnified to show the exquisite preservation of the structures inside. submicron scale (right). The blue image is inverted to give a virtual fossil cast, i.e. to show the original three-dimensional shape. The original plates were removed from the sediment by dissolution, leaving behind only the phantom footprints. Credit: SM Slater, P. Bown / Science log

An international team of scientists from UCL (University College London), the Swedish Museum of Natural History, the Museum of Natural History (London) and the University of Florence have discovered a remarkable type of fossilization which has remained almost completely ignored so far.

The fossils are microscopic imprints, or ‘ghosts’, of single-celled plankton, called coccolithophores, that lived in the seas millions of years ago, and their discovery changes our understanding of how plankton in the oceans are affected by climate change.

Coccolithophores are important in today’s oceans, providing much of the oxygen we breathe, supporting marine food webs, and trapping carbon in seafloor sediments. It is a type of microscopic plankton that surrounds its cells with hard calcareous plates, called coccoliths, which normally fossilize in rocks.

Declines in the abundance of these fossils have been documented from several past global warming events, suggesting that these planktons have been severely affected by climate change and ocean acidification. However, a study published today in the journal Science presents new global records of abundant ghost fossils from three Jurassic and Cretaceous warming events (94, 120 and 183 million years ago), suggesting that coccolithophores were more resilient to past climate change than previously thought thought so before.

Discovery of 'ghost' fossils reveals plankton's resilience to past global warming events

Ghost Nannofossil from the Jurassic Rocks of Yorkshire, UK. Credit: SM Slater et al

“The discovery of these magnificent ghost fossils was completely unexpected,” says Dr Sam Slater from the Swedish Museum of Natural History. “We first found them preserved on fossilized pollen surfaces, and it quickly became apparent that they were abundant during intervals when normal coccolithophore fossils were scarce or absent – this was a complete surprise!”

Despite their microscopic size, coccolithophores can be extremely abundant in today’s ocean, being visible from space as cloud-like flowers. After death, their calcareous exoskeletons sink to the bottom of the sea, accumulating in large numbers, forming rocks such as chalk.

“The preservation of these ghost nannofossils is truly remarkable,” says Professor Paul Bown (UCL). “Ghost fossils are extremely small – their length is about five thousandths of a millimetre, 15 times narrower than the width of a human hair! – but the detail of the original plates is still perfectly visible, pressed into the surfaces ancient organic matter, even though the plates themselves have dissolved”.

Discovery of 'ghost' fossils reveals plankton's resilience to past global warming events

The individual plates are coccoliths. Credit: Images from Nannotax mikrotax.org/Nannotax3/.

The ghost fossils were formed while the sediments of the sea floor were buried and turned into rock. As more mud settled on top, the resulting pressure crushed the plates of coccoliths and other organic remains together, and the hard coccoliths were pressed against the surfaces of pollen, spores and other matter. soft organics. Later, the acidic waters in the spaces of the rock dissolved the coccoliths, leaving behind only their impressions – the ghosts.

“Normally, paleontologists only look for the fossil coccoliths themselves, and if they don’t find any, they often assume that these ancient plankton communities have collapsed,” says Professor Vivi Vajda (Swedish Museum of Natural History). “These phantom fossils show us that sometimes the fossil record playing tricks on us and there are other ways to preserve this calcareous nannoplankton, which must be taken into account in order to understand the responses to past climate change”.

La découverte de fossiles «fantômes» révèle la résilience du plancton aux événements passés du réchauffement climatique

The fossils are about 5 µm long, 15 times narrower than the width of a human hair. Credit: SM Slater, P. Bown et al / Science log

Professor Silvia Danise (University of Florence) says: “Phantom nannofossils are probably common in the fossil record, but they have been overlooked due to their small size and cryptic mode of preservation. We believe this particular type of fossilization will be useful in the future, especially when studying geological intervals where the original coccoliths are missing from the fossil record.”

The study focused on the Toarcian Oceanic Anoxic Event (T-OAE), an interval of rapid global warming during the Early Jurassic (183 million years ago), caused by an increase in CO2-levels in the atmosphere of massive volcanism in the southern hemisphere. The researchers found ghost nannofossils associated with T-OAE from the UK, Germany, Japan and New Zealand, but also from two similar global warming events in the Cretaceous: Oceanic Anoxic Event 1a (there is 120 million years ago) from Sweden, and Oceanic Anoxic Event 2 (94 million years ago) from Italy.

La découverte de fossiles «fantômes» révèle la résilience du plancton aux événements passés du réchauffement climatique

Phantom nannofossils have been found in rocks from climate-warming intervals where normal coccolithophore fossils were rare or absent. Credit: SM Slater, P. Bown et al / Science log

“Shadow fossils show that nannoplankton were abundant, diverse and thriving during past Jurassic and Cretaceous warming events, where previous records assumed plankton collapsed due to ocean acidification,” explains the Professor Richard Twitchett (Natural History Museum, London). “These fossils rewrite our understanding of how calcareous nannoplankton respond to warming events.”

Discovery of 'ghost' fossils reveals plankton's resilience to past global warming events

Phantom nannofossils have been found around the world, in rocks from three rapid warming events in Earth’s history (T-OAE, OAE1a, and OAE2). Credit: SM Slater et al

Finally, Dr Sam Slater explains: “Our study shows that algal plankton were abundant during these past warming events and contributed to the expansion of marine dead zones, where seafloor oxygen levels were too low to that most species survive.These conditions, together with plankton blooms and dead zones, could become more prevalent in our globally warming oceans.”


A climate catastrophe has already happened and gives us information about the future


More information:
Sam M. Slater, Global “ghost” nannofossil record reveals plankton’s resilience to high CO2 and warming, Science (2022). DOI: 10.1126/science.abm7330. www.science.org/doi/10.1126/science.abm7330

Quote: Discovery of “ghost” fossils reveals plankton’s resilience to past global warming events (May 19, 2022) Retrieved May 19, 2022 from https://phys.org/news/2022-05-discovery-ghost-fossils -reveals-plankton. html

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