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Carbon cycle

Volcanic triggering of a biogeochemical cascade during Oceanic Anoxic Event 2

Two Northwestern University studies contribute new clues as to what drove large-scale changes to the carbon cycle nearly 100 million years ago. Both research teams conclude that a massive amount of volcanic activity introduced carbon dioxide and sulphur into the atmosphere, which in turn had a significant impact on the carbon cycle, oxygen levels in the oceans and marine plants and animals. Oxygen levels dropped so low that one-third of marine life died.

Title: Volcanic triggering of a biogeochemical cascade during Oceanic Anoxic Event 2
Authors: Derek D. Adams, Matthew T. Hurtgen & Bradley B. Sageman

During the Cretaceous period (~14565million years ago), there were several periods of global ocean anoxia, each lasting less than onemillion years. These events, known as ocean anoxic events, were marked by significant increases in organic carbon burial1, and are generally attributed to increased primary productivity in surface waters2. The details underpinning the initiation, maintenance and termination of these events, however, remain equivocal. Here we present sulphur isotope data spanning the Ocean Anoxic Event 2 (about 94.5million years ago) from sedimentary rocks in Colorado that were formed in the Western Interior Seaway; this seaway ran northsouth, splitting North America during the Cretaceous. Sulphate levels increased rapidly from relatively low background levels at the onset of the event, most likely from the release of sulphur by massive volcanism, and fell during the anoxic event. We infer that the input of sulphate facilitated increased carbon remineralisation, which enhanced nutrient recycling and increased global primary productivity, eventually resulting in widespread ocean anoxia. Our scenario indicates that Ocean Anoxic Event 2may have persisted until sulphate levels were stabilised by the formation and burial of the sulphur mineral pyrite, which returned primary productivity to background levels. We suggest that fluctuations in sulphate levels may have regulated the marine carbon cycle during past periods of low oceanic sulphate concentration.

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Cadmium's Role in Carbon Cycle

University of Saskatchewan Researchers Use Synchrotron to Shed Light on Cadmium's Role in the Carbon Cycle.
An international team that includes two University of Saskatchewan Canada Research Chairs has discovered that the element cadmium, well known for its toxicity to humans and other animals, may play an essential role in regulating atmospheric carbon.
The team includes U of S geological sciences professors Graham George and Ingrid Pickering and colleagues from Woods Hole Oceanographic Institute in Massachusetts, Sandia Laboratories in California, Exxon Mobil Research and Engineering, and Princeton University in New Jersey.
Working at the Stanford Synchrotron Radiation Laboratory in California, George and Pickering used synchrotron X-rays to partly determine the shape of an enzyme that regulates levels of carbon dioxide in single-celled plants called diatoms.
Colleagues on the team isolated the genes responsible for the cadmium enzyme, which also appear to be unique.
George and Pickering confirmed that the plant enzyme, cadmium carbonic anhydrase, does indeed use cadmium - the first known biological use of the element.
"Our research establishes a role for cadmium for the first time. No one has done this before."

The team found that the cadmium enzyme performs much the same role as zinc-based enzymes in land plants. The U of S researchers compared the two types of enzymes using data generated at the Stanford synchrotron.

"It turns out that cadmium may play a vital role in the global carbon cycle. The enzyme is used by diatoms in the first step of photosynthesis, which is responsible for uptake of carbon dioxide from the atmosphere."
Like all plants, diatoms use photosynthesis to take in carbon dioxide and release oxygen. Since they are present in the entire world's oceans, which cover about 70 per cent of the Earth's surface, diatoms have a huge collective impact.

The researchers speculate that the diatoms' capacity to use cadmium developed because ocean waters contain only trace amounts of certain essential metals. In fact, the diatoms prefer to produce a zinc-based enzyme rather than the cadmium version. But the ability to make a cadmium enzyme allows the microscopic plants to better survive in their environment because surface seawater contains almost no zinc.

Until now, cadmium was thought to be something solely to be avoided. While our bodies can get rid of the metal, excessive amounts can damage the kidneys, bones, nervous and cardiovascular systems.
Cadmium has many industrial uses such as nickel-cadmium rechargeable batteries, paint pigments, plating, alloys, and plastics. It is a naturally occurring element and can accumulate in crops, prompting efforts, for example, to develop low-cadmium varieties of durum wheat for Saskatchewan soils.

"What's interesting here is the changing face of cadmium from a bad guy to a good guy."

Press release

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