Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Secrets of the calcerous ooze revealed

28.02.2017

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

How can we know anything about the carbon dioxide levels in the atmosphere in earth's deep past? Tiny bubbles trapped in ice provide samples of ancient air but this record goes back only 800,000 years. To reach further back, scientists must depend on climate proxies, or measurable parameters that vary systematically with climate conditions.


Coccolithophores surround themselves with platelets of calcium carbonate, shown here greatly magnified. Because calcium carbonate is transparent, the platelet's don't compromise the organism's ability to photosynthesize. The scale bar represents a millionth of a meter.

Credit: Hermoso and McClelland

The standard proxy is the oxygen isotope ratios in tiny zooplankton called foraminifera. There are more than 50,000 different species of these bugs, 10,000 living and 40,000 extinct. Because the foraminifera shells fairly faithfully record the ratios of oxygen isotopes in seawater, they provide a signal that can be used to infer ancient temperatures.

But there's another potential proxy gathering dust in the sedimentary archive: tiny phytoplankton called coccolithophores. They are found in large numbers throughout the sunlight layer of the ocean. Their tiny, hub-cap-like plates, called coccoliths, are the main component of the Chalk, the Late Cretaceous formation that outcrops at the White Cliffs of Dover, and a major component of the "calcareous ooze" that covers much of the seafloor.

Because coccolithophores are primary producers that are important to ocean biogeochemistry they are well-studied organisms. They are less used for paleoceanographic reconstructions than foraminifera, however, because they create their plates inside their cells rather than precipitating them directly from seawater. This means there is a large biological overprint on the climate signal that makes it difficult to interpret.

But new findings, published in the Feb. 28 issue of the journal Nature Communications, could change that. Recreating the prehistoric environment in laboratory conditions, a team of scientists from the University of Oxford, including Harry McClelland, now a postdoctoral research associate at Washington University in St. Louis, and the Plymouth Marine Laboratory grew several different species of this algae, each with varying carbon levels.

With this experimental data, they created a mathematical model of carbon fluxes in the coccolithophore cell that accounts for previously unexplained variations in the isotopic composition of the platelets the algae produce and provides the framework for the development of a new set of proxies.

Properly understood, the "noise" may itself be a signal. Coccoliths provide a window on ancient biology as well as climate, McClelland said.

Heavy and light coccoliths

McClelland explains that the scientists began with a bit of a mystery. Coccoliths had been divided into two groups -- a light and a heavy group -- based on whether the platelets they precipitated was poorer or richer in the rarer heavy isotope of carbon compared to calcium carbonate formed by physical (abiotic) processes. The departures from abiotic norm were "both large and enigmatic," McClelland said.

Heavy isotopes undergo all of the same chemical reactions as light isotopes, but, simply because they have slightly different masses, they do so at slightly different rates. These tiny differences in reaction rates cause the products of reactions to have different isotope ratios than the source materials.

The coccolithophores undertake the relevant carbon chemistry in two different cellular compartments: the chloroplast, where photosynthesis takes place, and coccolith vesicles, where platelets are precipitated. The main problem with deciphering their isotopic record the algae leave is that these two processes drive the isotopic composition of the carbon pool in opposite directions.

In their chloroplasts, coccolithophores take inorganic carbon and build it into biological molecules. This process proceeds far more rapidly for the CO2 containing the light isotope of carbon, causing the isotopic composition to drift to the heavier variant. Platelets growing in coccolith vesicles, on the other hand, preferentially incorporate the heavier form of carbon from the substrate pool.

The team chose a number of coccolithophore species, both light and heavy, and grew them in the laboratory -- "it's not all that different from gardening, McClelland said" -- and then constructed a mathematical model of the cell that could predict the isotopic outcomes across all species for which data was available.

They were able to show that the ratio of calcification to photosynthesis determines whether the platelets are isotopically heavier or lighter than abiogenic calcium carbonate. They were able to explain the size of the departure as well its direction.

For McClelland, the most exciting part of the study is that it opens a window on the biology of ancient creatures. When people use foraminifera as a climate proxy, he said, they usually pick one species and assume a constant biological effect, or offset. But we can see the impact of varying biology in the chemical signatures of the coccolithophores.

With more research, said McClelland said, coccolith-based isotopic ratios could be developed into a paleobarometer that would help us to understand the climate system's sensitivity to atmospheric carbon dioxide.

"Our model allows scientists to understand algal signals of the past, like never before. It unlocks the potential of fossilized coccolithophores to become a routine tool, used in studying ancient algal physiology and also ultimately as a recorder of past CO2 levels," said senior author Rosalind Rickaby, professor of biogeochemistry at Oxford.

###

The study was funded by the National Environment Research Council and the European Research Council.

Media Contact

Diana Lutz
dlutz@wustl.edu
314-935-5272

 @WUSTLnews

http://www.wustl.edu 

Diana Lutz | EurekAlert!

More articles from Earth Sciences:

nachricht Tiny microenvironments in the ocean hold clues to global nitrogen cycle
23.04.2018 | University of Rochester

nachricht Clear as mud: Desiccation cracks help reveal the shape of water on Mars
20.04.2018 | Geological Society of America

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Molecules Brilliantly Illuminated

Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.

Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Structured light and nanomaterials open new ways to tailor light at the nanoscale

23.04.2018 | Physics and Astronomy

On the shape of the 'petal' for the dissipation curve

23.04.2018 | Physics and Astronomy

Clean and Efficient – Fraunhofer ISE Presents Hydrogen Technologies at the HANNOVER MESSE 2018

23.04.2018 | Trade Fair News

VideoLinks
Science & Research
Overview of more VideoLinks >>>